935 files changed, 63755 insertions, 33416 deletions

diff --git a/activerecord/.gitignore b/activerecord/.gitignore
new file mode 100644
index 0000000000..884ee009eb
--- /dev/null
+++ b/activerecord/.gitignore
@@ -0,0 +1,3 @@
+/sqlnet.log
+/test/config.yml
+/test/fixtures/*.sqlite*
diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index e4a6734009..2a237f86cf 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,996 +1,371 @@
-*   Fix through associations using scopes having the scope merged multiple
-    times.
-
-    Fixes #20721.
-    Fixes #20727.
-
-    *Sean Griffin*
-
-*   `ActiveRecord::Base.dump_schema_after_migration` applies migration tasks
-    other than `db:migrate`. (eg. `db:rollback`, `db:migrate:dup`, ...)
-
-    Fixes #20743.
-
-    *Yves Senn*
-
-*   Add alternate syntax to make `change_column_default` reversible.
-
-    User can pass in `:from` and `:to` to make `change_column_default` command
-    become reversible.
+*   Add an `:if_not_exists` option to `create_table`.
 
     Example:
 
-        change_column_default :posts, :status, from: nil, to: "draft"
-        change_column_default :users, :authorized, from: true, to: false
-
-    *Prem Sichanugrist*
-
-*   Prevent error when using `force_reload: true` on an unassigned polymorphic
-    belongs_to association.
-
-    Fixes #20426.
-
-    *James Dabbs*
+        create_table :posts, if_not_exists: true do |t|
+          t.string :title
+        end
 
-*   Correctly raise `ActiveRecord::AssociationTypeMismatch` when assigning
-    a wrong type to a namespaced association.
+    That would execute:
 
-    Fixes #20545.
+        CREATE TABLE IF NOT EXISTS posts (
+          ...
+        )
 
-    *Diego Carrion*
+    If the table already exists, `if_not_exists: false` (the default) raises an
+    exception whereas `if_not_exists: true` does nothing.
 
-*   `validates_absence_of` respects `marked_for_destruction?`.
+    *fatkodima*, *Stefan Kanev*
 
-    Fixes #20449.
+*   Defining an Enum as a Hash with blank key, or as an Array with a blank value, now raises an `ArgumentError`.
 
-    *Yves Senn*
+    *Christophe Maximin*
 
-*   Include the `Enumerable` module in `ActiveRecord::Relation`
+*   Adds support for multiple databases to `rails db:schema:cache:dump` and `rails db:schema:cache:clear`.
 
-    *Sean Griffin & bogdan*
+    *Gannon McGibbon*
 
-*   Use `Enumerable#sum` in `ActiveRecord::Relation` if a block is given.
+*   `update_columns` now correctly raises `ActiveModel::MissingAttributeError`
+    if the attribute does not exist.
 
     *Sean Griffin*
 
-*   Let `WITH` queries (Common Table Expressions) be explainable.
-
-    *Vladimir Kochnev*
-
-*   Make `remove_index :table, :column` reversible.
-
-    *Yves Senn*
-
-*   Fixed an error which would occur in dirty checking when calling
-    `update_attributes` from a getter.
-
-    Fixes #20531.
-
-    *Sean Griffin*
+*   Add support for hash and url configs in database hash of `ActiveRecord::Base.connected_to`.
 
-*   Make `remove_foreign_key` reversible. Any foreign key options must be
-    specified, similar to `remove_column`.
+    ````
+    User.connected_to(database: { writing: "postgres://foo" }) do
+      User.create!(name: "Gannon")
+    end
 
-    *Aster Ryan*
+    config = { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" }
+    User.connected_to(database: { reading: config }) do
+      User.count
+    end
+    ````
 
-*   Add `:enum_prefix`/`:enum_suffix` option to `enum` definition.
+    *Gannon McGibbon*
 
-    Fixes #17511, #17415.
+*   Support default expression for MySQL.
 
-    *Igor Kapkov*
+    MySQL 8.0.13 and higher supports default value to be a function or expression.
 
-*   Correctly handle decimal arrays with defaults in the schema dumper.
-
-    Fixes #20515.
-
-    *Sean Griffin & jmondo*
-
-*   Deprecate the PostgreSQL `:point` type in favor of a new one which will return
-    `Point` objects instead of an `Array`
-
-    *Sean Griffin*
-
-*   Ensure symbols passed to `ActiveRecord::Relation#select` are always treated
-    as columns.
-
-    Fixes #20360.
-
-    *Sean Griffin*
-
-*   Do not set `sql_mode` if `strict: :default` is specified.
-
-        ```
-        # database.yml
-        production:
-          adapter: mysql2
-          database: foo_prod
-          user: foo
-          strict: :default
-        ```
+    https://dev.mysql.com/doc/refman/8.0/en/create-table.html
 
     *Ryuta Kamizono*
 
-*   Allow proc defaults to be passed to the attributes API. See documentation
-    for examples.
-
-    *Sean Griffin*, *Kir Shatrov*
-
-*   SQLite: `:collation` support for string and text columns.
-
-    Example:
-
-        create_table :foo do |t|
-          t.string :string_nocase, collation: 'NOCASE'
-          t.text :text_rtrim, collation: 'RTRIM'
-        end
-
-        add_column :foo, :title, :string, collation: 'RTRIM'
-
-        change_column :foo, :title, :string, collation: 'NOCASE'
-
-    *Akshay Vishnoi*
+*   Support expression indexes for MySQL.
 
-*   Allow the use of symbols or strings to specify enum values in test
-    fixtures:
+    MySQL 8.0.13 and higher supports functional key parts that index
+    expression values rather than column or column prefix values.
 
-        awdr:
-          title: "Agile Web Development with Rails"
-          status: :proposed
-
-    *George Claghorn*
-
-*   Clear query cache when `ActiveRecord::Base#reload` is called.
-
-    *Shane Hender, Pierre Nespo*
-
-*   Include stored procedures and function on the MySQL structure dump.
-
-    *Jonathan Worek*
-
-*   Pass `:extend` option for `has_and_belongs_to_many` associations to the
-    underlying `has_many :through`.
-
-    *Jaehyun Shin*
-
-*   Deprecate `Relation#uniq` use `Relation#distinct` instead.
-
-    See #9683.
-
-    *Yves Senn*
-
-*   Allow single table inheritance instantiation to work when storing
-    demodulized class names.
-
-    *Alex Robbin*
-
-*   Correctly pass MySQL options when using `structure_dump` or
-    `structure_load`.
-
-    Specifically, it fixes an issue when using SSL authentication.
-
-    *Alex Coomans*
-
-*   Dump indexes in `create_table` instead of `add_index`.
-
-    If the adapter supports indexes in `create_table`, generated SQL is
-    slightly more efficient.
+    https://dev.mysql.com/doc/refman/8.0/en/create-index.html
 
     *Ryuta Kamizono*
 
-*   Correctly dump `:options` on `create_table` for MySQL.
+*   Fix collection cache key with limit and custom select to avoid ambiguous timestamp column error.
 
-    *Ryuta Kamizono*
+    Fixes #33056.
 
-*   PostgreSQL: `:collation` support for string and text columns.
+    *Federico Martinez*
 
-    Example:
+*   Add basic API for connection switching to support multiple databases.
 
-        create_table :foos do |t|
-          t.string :string_en, collation: 'en_US.UTF-8'
-          t.text   :text_ja,   collation: 'ja_JP.UTF-8'
-        end
+    1) Adds a `connects_to` method for models to connect to multiple databases. Example:
 
-    *Ryuta Kamizono*
+    ```
+    class AnimalsModel < ApplicationRecord
+      self.abstract_class = true
 
-*   Make `unscope` aware of "less than" and "greater than" conditions.
+      connects_to database: { writing: :animals_primary, reading: :animals_replica }
+    end
 
-    *TAKAHASHI Kazuaki*
+    class Dog < AnimalsModel
+      # connected to both the animals_primary db for writing and the animals_replica for reading
+    end
+    ```
 
-*   `find_by` and `find_by!` raise `ArgumentError` when called without
-    arguments.
+    2) Adds a `connected_to` block method for switching connection roles or connecting to
+    a database that the model didn't connect to. Connecting to the database in this block is
+    useful when you have another defined connection, for example `slow_replica` that you don't
+    want to connect to by default but need in the console, or a specific code block.
 
-    *Kohei Suzuki*
+    ```
+    ActiveRecord::Base.connected_to(role: :reading) do
+      Dog.first # finds dog from replica connected to AnimalsBase
+      Book.first # doesn't have a reading connection, will raise an error
+    end
+    ```
 
-*   Revert behavior of `db:schema:load` back to loading the full
-    environment. This ensures that initializers are run.
+    ```
+    ActiveRecord::Base.connected_to(database: :slow_replica) do
+      SlowReplicaModel.first # if the db config has a slow_replica configuration this will be used to do the lookup, otherwise this will throw an exception
+    end
+    ```
 
-    Fixes #19545.
+    *Eileen M. Uchitelle*
 
-    *Yves Senn*
+*   Enum raises on invalid definition values
 
-*   Fix missing index when using `timestamps` with the `index` option.
+    When defining a Hash enum it can be easy to use [] instead of {}. This
+    commit checks that only valid definition values are provided, those can
+    be a Hash, an array of Symbols or an array of Strings. Otherwise it
+    raises an ArgumentError.
 
-    The `index` option used with `timestamps` should be passed to both
-    `column` definitions for `created_at` and `updated_at` rather than just
-    the first.
+    Fixes #33961
 
-    *Paul Mucur*
+    *Alberto Almagro*
 
-*   Rename `:class` to `:anonymous_class` in association options.
+*   Reloading associations now clears the Query Cache like `Persistence#reload` does.
 
-    Fixes #19659.
+    ```
+    class Post < ActiveRecord::Base
+      has_one :category
+      belongs_to :author
+      has_many :comments
+    end
 
-    *Andrew White*
+    # Each of the following will now clear the query cache.
+    post.reload_category
+    post.reload_author
+    post.comments.reload
+    ```
 
-*   Autosave existing records on a has many through association when the parent
-    is new.
+    *Christophe Maximin*
 
-    Fixes #19782.
-
-    *Sean Griffin*
-
-*   Fixed a bug where uniqueness validations would error on out of range values,
-    even if an validation should have prevented it from hitting the database.
-
-    *Andrey Voronkov*
-
-*   MySQL: `:charset` and `:collation` support for string and text columns.
+*   Added `index` option for `change_table` migration helpers.
+    With this change you can create indexes while adding new
+    columns into the existing tables.
 
     Example:
 
-        create_table :foos do |t|
-          t.string :string_utf8_bin, charset: 'utf8', collation: 'utf8_bin'
-          t.text   :text_ascii,      charset: 'ascii'
+        change_table(:languages) do |t|
+          t.string :country_code, index: true
         end
 
-    *Ryuta Kamizono*
-
-*   Foreign key related methods in the migration DSL respect
-    `ActiveRecord::Base.pluralize_table_names = false`.
-
-    Fixes #19643.
-
     *Mehmet Emin İNAÇ*
 
-*   Reduce memory usage from loading types on PostgreSQL.
-
-    Fixes #19578.
-
-    *Sean Griffin*
-
-*   Add `config.active_record.warn_on_records_fetched_greater_than` option.
-
-    When set to an integer, a warning will be logged whenever a result set
-    larger than the specified size is returned by a query.
-
-    Fixes #16463.
-
-    *Jason Nochlin*
-
-*   Ignore `.psqlrc` when loading database structure.
-
-    *Jason Weathered*
-
-*   Fix referencing wrong table aliases while joining tables of has many through
-    association (only when calling calculation methods).
-
-    Fixes #19276.
+*   Fix `transaction` reverting for migrations.
 
-    *pinglamb*
+    Before: Commands inside a `transaction` in a reverted migration ran uninverted.
+    Now: This change fixes that by reverting commands inside `transaction` block.
 
-*   Correctly persist a serialized attribute that has been returned to
-    its default value by an in-place modification.
+    *fatkodima*, *David Verhasselt*
 
-    Fixes #19467.
+*   Raise an error instead of scanning the filesystem root when `fixture_path` is blank.
 
-    *Matthew Draper*
+    *Gannon McGibbon*, *Max Albrecht*
 
-*   Fix generating the schema file when using PostgreSQL `BigInt[]` data type.
-    Previously the `limit: 8` was not coming through, and this caused it to
-    become `Int[]` data type after rebuilding from the schema.
+*   Allow `ActiveRecord::Base.configurations=` to be set with a symbolized hash.
 
-    Fixes #19420.
+    *Gannon McGibbon*
 
-    *Jake Waller*
+*   Don't update counter cache unless the record is actually saved.
 
-*   Reuse the `CollectionAssociation#reader` cache when the foreign key is
-    available prior to save.
-
-    *Ben Woosley*
-
-*   Add `config.active_record.dump_schemas` to fix `db:structure:dump`
-    when using schema_search_path and PostgreSQL extensions.
-
-    Fixes #17157.
-
-    *Ryan Wallace*
-
-*   Renaming `use_transactional_fixtures` to `use_transactional_tests` for clarity.
-
-    Fixes #18864.
-
-    *Brandon Weiss*
-
-*   Increase pg gem version requirement to `~> 0.18`. Earlier versions of the
-    pg gem are known to have problems with Ruby 2.2.
-
-    *Matt Brictson*
-
-*   Correctly dump `serial` and `bigserial`.
-
-    *Ryuta Kamizono*
-
-*   Fix default `format` value in `ActiveRecord::Tasks::DatabaseTasks#schema_file`.
-
-    *James Cox*
-
-*   Don't enroll records in the transaction if they don't have commit callbacks.
-    This was causing a memory leak when creating many records inside a transaction.
-
-    Fixes #15549.
-
-    *Will Bryant*, *Aaron Patterson*
-
-*   Correctly create through records when created on a has many through
-    association when using `where`.
-
-    Fixes #19073.
-
-    *Sean Griffin*
-
-*   Add `SchemaMigration.create_table` support for any unicode charsets with MySQL.
-
-    *Ryuta Kamizono*
-
-*   PostgreSQL no longer disables user triggers if system triggers can't be
-    disabled. Disabling user triggers does not fulfill what the method promises.
-    Rails currently requires superuser privileges for this method.
-
-    If you absolutely rely on this behavior, consider patching
-    `disable_referential_integrity`.
-
-    *Yves Senn*
-
-*   Restore aborted transaction state when `disable_referential_integrity` fails
-    due to missing permissions.
-
-    *Toby Ovod-Everett*, *Yves Senn*
-
-*   In PostgreSQL, print a warning message if `disable_referential_integrity`
-    fails due to missing permissions.
-
-    *Andrey Nering*, *Yves Senn*
-
-*   Allow a `:limit` option for MySQL bigint primary key support.
-
-    Example:
-
-        create_table :foos, id: :primary_key, limit: 8 do |t|
-        end
-
-        # or
-
-        create_table :foos, id: false do |t|
-          t.primary_key :id, limit: 8
-        end
-
-    *Ryuta Kamizono*
-
-*   `belongs_to` will now trigger a validation error by default if the association is not present.
-    You can turn this off on a per-association basis with `optional: true`.
-    (Note this new default only applies to new Rails apps that will be generated with
-    `config.active_record.belongs_to_required_by_default = true` in initializer.)
-
-    *Josef Šimánek*
-
-*   Fixed `ActiveRecord::Relation#becomes!` and `changed_attributes` issues for type
-    columns.
-
-    Fixes #17139.
-
-    *Miklos Fazekas*
-
-*   Format the time string according to the precision of the time column.
+    Fixes #31493, #33113, #33117.
 
     *Ryuta Kamizono*
 
-*   Allow a `:precision` option for time type columns.
+*   Deprecate `ActiveRecord::Result#to_hash` in favor of `ActiveRecord::Result#to_a`.
 
-    *Ryuta Kamizono*
-
-*   Add `ActiveRecord::Base.suppress` to prevent the receiver from being saved
-    during the given block.
+    *Gannon McGibbon*, *Kevin Cheng*
 
-    For example, here's a pattern of creating notifications when new comments
-    are posted. (The notification may in turn trigger an email, a push
-    notification, or just appear in the UI somewhere):
+*   SQLite3 adapter supports expression indexes.
 
-        class Comment < ActiveRecord::Base
-          belongs_to :commentable, polymorphic: true
-          after_create -> { Notification.create! comment: self,
-            recipients: commentable.recipients }
-        end
-
-    That's what you want the bulk of the time. A new comment creates a new
-    Notification. There may be edge cases where you don't want that, like
-    when copying a commentable and its comments, in which case write a
-    concern with something like this:
-
-        module Copyable
-          def copy_to(destination)
-            Notification.suppress do
-              # Copy logic that creates new comments that we do not want triggering
-              # notifications.
-            end
-          end
-        end
+    ```
+    create_table :users do |t|
+      t.string :email
+    end
 
-    *Michael Ryan*
+    add_index :users, 'lower(email)', name: 'index_users_on_email', unique: true
+    ```
 
-*   `:time` option added for `#touch`.
+    *Gray Kemmey*
 
-    Fixes #18905.
+*   Allow subclasses to redefine autosave callbacks for associated records.
 
-    *Hyonjee Joo*
+    Fixes #33305.
 
-*   Deprecate passing of `start` value to `find_in_batches` and `find_each`
-    in favour of `begin_at` value.
+    *Andrey Subbota*
 
-    *Vipul A M*
+*   Bump minimum MySQL version to 5.5.8.
 
-*   Add `foreign_key_exists?` method.
+    *Yasuo Honda*
 
-    *Tõnis Simo*
+*   Use MySQL utf8mb4 character set by default.
 
-*   Use SQL COUNT and LIMIT 1 queries for `none?` and `one?` methods
-    if no block or limit is given, instead of loading the entire
-    collection into memory. This applies to relations (e.g. `User.all`)
-    as well as associations (e.g. `account.users`)
+    `utf8mb4` character set with 4-Byte encoding supports supplementary characters including emoji.
+    The previous default 3-Byte encoding character set `utf8` is not enough to support them.
 
-        # Before:
+    *Yasuo Honda*
 
-        users.none?
-        # SELECT "users".* FROM "users"
+*   Fix duplicated record creation when using nested attributes with `create_with`.
 
-        users.one?
-        # SELECT "users".* FROM "users"
+    *Darwin Wu*
 
-        # After:
+*   Configuration item `config.filter_parameters` could also filter out
+    sensitive values of database columns when call `#inspect`.
+    We also added `ActiveRecord::Base::filter_attributes`/`=` in order to
+    specify sensitive attributes to specific model.
 
-        users.none?
-        # SELECT 1 AS one FROM "users" LIMIT 1
+    ```
+    Rails.application.config.filter_parameters += [:credit_card_number, /phone/]
+    Account.last.inspect # => #<Account id: 123, name: "DHH", credit_card_number: [FILTERED], telephone_number: [FILTERED] ...>
+    SecureAccount.filter_attributes += [:name]
+    SecureAccount.last.inspect # => #<SecureAccount id: 42, name: [FILTERED], credit_card_number: [FILTERED] ...>
+    ```
 
-        users.one?
-        # SELECT COUNT(*) FROM "users"
-
-    *Eugene Gilburg*
-
-*   Have `enum` perform type casting consistently with the rest of Active
-    Record, such as `where`.
-
-    *Sean Griffin*
-
-*   `scoping` no longer pollutes the current scope of sibling classes when using
-    STI. e.x.
-
-        StiOne.none.scoping do
-          StiTwo.all
-        end
-
-    Fixes #18806.
-
-    *Sean Griffin*
+    *Zhang Kang*, *Yoshiyuki Kinjo*
 
-*   `remove_reference` with `foreign_key: true` removes the foreign key before
-    removing the column. This fixes a bug where it was not possible to remove
-    the column on MySQL.
-
-    Fixes #18664.
-
-    *Yves Senn*
-
-*   `find_in_batches` now accepts an `:end_at` parameter that complements the `:start`
-     parameter to specify where to stop batch processing.
-
-    *Vipul A M*
-
-*   Fix a rounding problem for PostgreSQL timestamp columns.
-
-    If a timestamp column has a precision specified, it needs to
-    format according to that.
-
-    *Ryuta Kamizono*
-
-*   Respect the database default charset for `schema_migrations` table.
-
-    The charset of `version` column in `schema_migrations` table depends
-    on the database default charset and collation rather than the encoding
-    of the connection.
+*   Deprecate `column_name_length`, `table_name_length`, `columns_per_table`,
+    `indexes_per_table`, `columns_per_multicolumn_index`, `sql_query_length`,
+    and `joins_per_query` methods in `DatabaseLimits`.
 
     *Ryuta Kamizono*
 
-*   Raise `ArgumentError` when passing `nil` or `false` to `Relation#merge`.
+*   `ActiveRecord::Base.configurations` now returns an object.
 
-    These are not valid values to merge in a relation, so it should warn users
-    early.
+    `ActiveRecord::Base.configurations` used to return a hash, but this
+    is an inflexible data model. In order to improve multiple-database
+    handling in Rails, we've changed this to return an object. Some methods
+    are provided to make the object behave hash-like in order to ease the
+    transition process. Since most applications don't manipulate the hash
+    we've decided to add backwards-compatible functionality that will throw
+    a deprecation warning if used, however calling `ActiveRecord::Base.configurations`
+    will use the new version internally and externally.
 
-    *Rafael Mendonça França*
+    For example, the following `database.yml`:
 
-*   Use `SCHEMA` instead of `DB_STRUCTURE` for specifying a structure file.
+    ```
+    development:
+      adapter: sqlite3
+      database: db/development.sqlite3
+    ```
 
-    This makes the db:structure tasks consistent with test:load_structure.
+    Used to become a hash:
 
-    *Dieter Komendera*
+    ```
+    { "development" => { "adapter" => "sqlite3", "database" => "db/development.sqlite3" } }
+    ```
 
-*   Respect custom primary keys for associations when calling `Relation#where`
+    Is now converted into the following object:
 
-    Fixes #18813.
+    ```
+    #<ActiveRecord::DatabaseConfigurations:0x00007fd1acbdf800 @configurations=[
+      #<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fd1acbded10 @env_name="development",
+        @spec_name="primary", @config={"adapter"=>"sqlite3", "database"=>"db/development.sqlite3"}>
+      ]
+    ```
 
-    *Sean Griffin*
-
-*   Fix several edge cases which could result in a counter cache updating
-    twice or not updating at all for `has_many` and `has_many :through`.
-
-    Fixes #10865.
-
-    *Sean Griffin*
+    Iterating over the database configurations has also changed. Instead of
+    calling hash methods on the `configurations` hash directly, a new method `configs_for` has
+    been provided that allows you to select the correct configuration. `env_name`, and
+    `spec_name` arguments are optional. For example these return an array of
+    database config objects for the requested environment and a single database config object
+    will be returned for the requested environment and specification name respectively.
 
-*   Foreign keys added by migrations were given random, generated names. This
-    meant a different `structure.sql` would be generated every time a developer
-    ran migrations on their machine.
+    ```
+    ActiveRecord::Base.configurations.configs_for(env_name: "development")
+    ActiveRecord::Base.configurations.configs_for(env_name: "development", spec_name: "primary")
+    ```
 
-    The generated part of foreign key names is now a hash of the table name and
-    column name, which is consistent every time you run the migration.
+    *Eileen M. Uchitelle*, *Aaron Patterson*
 
-    *Chris Sinjakli*
+*   Add database configuration to disable advisory locks.
 
-*   Validation errors would be raised for parent records when an association
-    was saved when the parent had `validate: false`. It should not be the
-    responsibility of the model to validate an associated object unless the
-    object was created or modified by the parent.
+    ```
+    production:
+      adapter: postgresql
+      advisory_locks: false
+    ```
 
-    This fixes the issue by skipping validations if the parent record is
-    persisted, not changed, and not marked for destruction.
+    *Guo Xiang*
 
-    Fixes #17621.
+*   SQLite3 adapter `alter_table` method restores foreign keys.
 
-    *Eileen M. Uchitelle, Aaron Patterson*
+    *Yasuo Honda*
 
-*   Fix n+1 query problem when eager loading nil associations (fixes #18312)
-
-    *Sammy Larbi*
-
-*   Change the default error message from `can't be blank` to `must exist` for
-    the presence validator of the `:required` option on `belongs_to`/`has_one`
-    associations.
-
-    *Henrik Nygren*
-
-*   Fixed `ActiveRecord::Relation#group` method when an argument is an SQL
-    reserved keyword:
+*   Allow `:to_table` option to `invert_remove_foreign_key`.
 
     Example:
 
-        SplitTest.group(:key).count
-        Property.group(:value).count
+       remove_foreign_key :accounts, to_table: :owners
 
-    *Bogdan Gusiev*
+    *Nikolay Epifanov*, *Rich Chen*
 
-*   Added the `#or` method on `ActiveRecord::Relation`, allowing use of the OR
-    operator to combine WHERE or HAVING clauses.
+*   Add environment & load_config dependency to `bin/rake db:seed` to enable
+    seed load in environments without Rails and custom DB configuration
 
-    Example:
-
-        Post.where('id = 1').or(Post.where('id = 2'))
-        # => SELECT * FROM posts WHERE (id = 1) OR (id = 2)
-
-    *Sean Griffin*, *Matthew Draper*, *Gael Muller*, *Olivier El Mekki*
-
-*   Don't define autosave association callbacks twice from
-    `accepts_nested_attributes_for`.
-
-    Fixes #18704.
-
-    *Sean Griffin*
-
-*   Integer types will no longer raise a `RangeError` when assigning an
-    attribute, but will instead raise when going to the database.
-
-    Fixes several vague issues which were never reported directly. See the
-    commit message from the commit which added this line for some examples.
-
-    *Sean Griffin*
-
-*   Values which would error while being sent to the database (such as an
-    ASCII-8BIT string with invalid UTF-8 bytes on SQLite3), no longer error on
-    assignment. They will still error when sent to the database, but you are
-    given the ability to re-assign it to a valid value.
-
-    Fixes #18580.
-
-    *Sean Griffin*
-
-*   Don't remove join dependencies in `Relation#exists?`
-
-    Fixes #18632.
-
-    *Sean Griffin*
-
-*   Invalid values assigned to a JSON column are assumed to be `nil`.
-
-    Fixes #18629.
-
-    *Sean Griffin*
-
-*   Add `ActiveRecord::Base#accessed_fields`, which can be used to quickly
-    discover which fields were read from a model when you are looking to only
-    select the data you need from the database.
-
-    *Sean Griffin*
-
-*   Introduce the `:if_exists` option for `drop_table`.
-
-    Example:
-
-        drop_table(:posts, if_exists: true)
-
-    That would execute:
-
-        DROP TABLE IF EXISTS posts
-
-    If the table doesn't exist, `if_exists: false` (the default) raises an
-    exception whereas `if_exists: true` does nothing.
-
-    *Cody Cutrer*, *Stefan Kanev*, *Ryuta Kamizono*
-
-*   Don't run SQL if attribute value is not changed for update_attribute method.
-
-    *Prathamesh Sonpatki*
-
-*   `time` columns can now get affected by `time_zone_aware_attributes`. If you have
-    set `config.time_zone` to a value other than `'UTC'`, they will be treated
-    as in that time zone by default in Rails 5.1. If this is not the desired
-    behavior, you can set
-
-        ActiveRecord::Base.time_zone_aware_types = [:datetime]
-
-    A deprecation warning will be emitted if you have a `:time` column, and have
-    not explicitly opted out.
-
-    Fixes #3145.
-
-    *Sean Griffin*
-
-*   Tests now run after_commit callbacks. You no longer have to declare
-    `uses_transaction ‘test name’` to test the results of an after_commit.
-
-    after_commit callbacks run after committing a transaction whose parent
-    is not `joinable?`: un-nested transactions, transactions within test cases,
-    and transactions in `console --sandbox`.
-
-    *arthurnn*, *Ravil Bayramgalin*, *Matthew Draper*
-
-*   `nil` as a value for a binary column in a query no longer logs as
-    "<NULL binary data>", and instead logs as just "nil".
-
-    *Sean Griffin*
-
-*   `attribute_will_change!` will no longer cause non-persistable attributes to
-    be sent to the database.
-
-    Fixes #18407.
-
-    *Sean Griffin*
-
-*   Remove support for the `protected_attributes` gem.
-
-    *Carlos Antonio da Silva*, *Roberto Miranda*
-
-*   Fix accessing of fixtures having non-string labels like Fixnum.
-
-    *Prathamesh Sonpatki*
-
-*   Remove deprecated support to preload instance-dependent associations.
-
-    *Yves Senn*
-
-*   Remove deprecated support for PostgreSQL ranges with exclusive lower bounds.
-
-    *Yves Senn*
-
-*   Remove deprecation when modifying a relation with cached Arel.
-    This raises an `ImmutableRelation` error instead.
-
-    *Yves Senn*
-
-*   Added `ActiveRecord::SecureToken` in order to encapsulate generation of
-    unique tokens for attributes in a model using `SecureRandom`.
-
-    *Roberto Miranda*
-
-*   Change the behavior of boolean columns to be closer to Ruby's semantics.
-
-    Before this change we had a small set of "truthy", and all others are "falsy".
-
-    Now, we have a small set of "falsy" values and all others are "truthy" matching
-    Ruby's semantics.
-
-    *Rafael Mendonça França*
-
-*   Deprecate `ActiveRecord::Base.errors_in_transactional_callbacks=`.
-
-    *Rafael Mendonça França*
-
-*   Change transaction callbacks to not swallow errors.
-
-    Before this change any errors raised inside a transaction callback
-    were getting rescued and printed in the logs.
-
-    Now these errors are not rescued anymore and just bubble up, as the other callbacks.
-
-    *Rafael Mendonça França*
-
-*   Remove deprecated `sanitize_sql_hash_for_conditions`.
-
-    *Rafael Mendonça França*
-
-*   Remove deprecated `Reflection#source_macro`.
-
-    *Rafael Mendonça França*
-
-*   Remove deprecated `symbolized_base_class` and `symbolized_sti_name`.
-
-    *Rafael Mendonça França*
-
-*   Remove deprecated `ActiveRecord::Base.disable_implicit_join_references=`.
+    *Tobias Bielohlawek*
 
-    *Rafael Mendonça França*
+*   Fix default value for mysql time types with specified precision.
 
-*   Remove deprecated access to connection specification using a string accessor.
+    *Nikolay Kondratyev*
 
-    Now all strings will be handled as a URL.
-
-    *Rafael Mendonça França*
-
-*   Change the default `null` value for `timestamps` to `false`.
-
-    *Rafael Mendonça França*
-
-*   Return an array of pools from `connection_pools`.
-
-    *Rafael Mendonça França*
-
-*   Return a null column from `column_for_attribute` when no column exists.
-
-    *Rafael Mendonça França*
-
-*   Remove deprecated `serialized_attributes`.
-
-    *Rafael Mendonça França*
-
-*   Remove deprecated automatic counter caches on `has_many :through`.
-
-    *Rafael Mendonça França*
-
-*   Change the way in which callback chains can be halted.
-
-    The preferred method to halt a callback chain from now on is to explicitly
-    `throw(:abort)`.
-    In the past, returning `false` in an Active Record `before_` callback had the
-    side effect of halting the callback chain.
-    This is not recommended anymore and, depending on the value of the
-    `config.active_support.halt_callback_chains_on_return_false` option, will
-    either not work at all or display a deprecation warning.
-
-    *claudiob*
-
-*   Clear query cache on rollback.
-
-    *Florian Weingarten*
-
-*   Fix setting of foreign_key for through associations when building a new record.
-
-    Fixes #12698.
-
-    *Ivan Antropov*
-
-*   Improve dumping of the primary key. If it is not a default primary key,
-    correctly dump the type and options.
-
-    Fixes #14169, #16599.
+*   Fix `touch` option to behave consistently with `Persistence#touch` method.
 
     *Ryuta Kamizono*
 
-*   Format the datetime string according to the precision of the datetime field.
-
-    Incompatible to rounding behavior between MySQL 5.6 and earlier.
-
-    In 5.5, when you insert `2014-08-17 12:30:00.999999` the fractional part
-    is ignored. In 5.6, it's rounded to `2014-08-17 12:30:01`:
-
-    http://bugs.mysql.com/bug.php?id=68760
-
-    *Ryuta Kamizono*
-
-*   Allow a precision option for MySQL datetimes.
-
-    *Ryuta Kamizono*
-
-*   Fixed automatic `inverse_of` for models nested in a module.
-
-    *Andrew McCloud*
-
-*   Change `ActiveRecord::Relation#update` behavior so that it can
-    be called without passing ids of the records to be updated.
-
-    This change allows updating multiple records returned by
-    `ActiveRecord::Relation` with callbacks and validations.
-
-        # Before
-        # ArgumentError: wrong number of arguments (1 for 2)
-        Comment.where(group: 'expert').update(body: "Group of Rails Experts")
-
-        # After
-        # Comments with group expert updated with body "Group of Rails Experts"
-        Comment.where(group: 'expert').update(body: "Group of Rails Experts")
-
-    *Prathamesh Sonpatki*
-
-*   Fix `reaping_frequency` option when the value is a string.
-
-    This usually happens when it is configured using `DATABASE_URL`.
-
-    *korbin*
-
-*   Fix error message when trying to create an associated record and the foreign
-    key is missing.
-
-    Before this fix the following exception was being raised:
+*   Migrations raise when duplicate column definition.
 
-        NoMethodError: undefined method `val' for #<Arel::Nodes::BindParam:0x007fc64d19c218>
+    Fixes #33024.
 
-    Now the message is:
+    *Federico Martinez*
 
-        ActiveRecord::UnknownAttributeError: unknown attribute 'foreign_key' for Model.
+*   Bump minimum SQLite version to 3.8
 
-    *Rafael Mendonça França*
+    *Yasuo Honda*
 
-*   Fix change detection problem for PostgreSQL bytea type and
-    `ArgumentError: string contains null byte` exception with pg-0.18.
+*   Fix parent record should not get saved with duplicate children records.
 
-    Fixes #17680.
+    Fixes #32940.
 
-    *Lars Kanis*
+    *Santosh Wadghule*
 
-*   When a table has a composite primary key, the `primary_key` method for
-    SQLite3 and PostgreSQL adapters was only returning the first field of the key.
-    Ensures that it will return nil instead, as Active Record doesn't support
-    composite primary keys.
+*   Fix logic on disabling commit callbacks so they are not called unexpectedly when errors occur.
 
-    Fixes #18070.
+    *Brian Durand*
 
-    *arthurnn*
+*   Ensure `Associations::CollectionAssociation#size` and `Associations::CollectionAssociation#empty?`
+    use loaded association ids if present.
 
-*   `validates_size_of` / `validates_length_of` do not count records
-    which are `marked_for_destruction?`.
+    *Graham Turner*
 
-    Fixes #7247.
+*   Add support to preload associations of polymorphic associations when not all the records have the requested associations.
 
-    *Yves Senn*
+    *Dana Sherson*
 
-*   Ensure `first!` and friends work on loaded associations.
-
-    Fixes #18237.
-
-    *Sean Griffin*
-
-*   `eager_load` preserves readonly flag for associations.
-
-    Closes #15853.
-
-    *Takashi Kokubun*
-
-*   Provide `:touch` option to `save()` to accommodate saving without updating
-    timestamps.
-
-    Fixes #18202.
-
-    *Dan Olson*
-
-*   Provide a more helpful error message when an unsupported class is passed to
-    `serialize`.
-
-    Fixes #18224.
-
-    *Sean Griffin*
-
-*   Add bigint primary key support for MySQL.
+*   Add `touch_all` method to `ActiveRecord::Relation`.
 
     Example:
 
-        create_table :foos, id: :bigint do |t|
-        end
-
-    *Ryuta Kamizono*
-
-*   Support for any type of primary key.
-
-    Fixes #14194.
-
-    *Ryuta Kamizono*
-
-*   Dump the default `nil` for PostgreSQL UUID primary key.
-
-    *Ryuta Kamizono*
-
-*   Add a `:foreign_key` option to `references` and associated migration
-    methods. The model and migration generators now use this option, rather than
-    the `add_foreign_key` form.
-
-    *Sean Griffin*
-
-*   Don't raise when writing an attribute with an out-of-range datetime passed
-    by the user.
-
-    *Grey Baker*
-
-*   Replace deprecated `ActiveRecord::Tasks::DatabaseTasks#load_schema` with
-    `ActiveRecord::Tasks::DatabaseTasks#load_schema_for`.
+        Person.where(name: "David").touch_all(time: Time.new(2020, 5, 16, 0, 0, 0))
 
-    *Yves Senn*
+    *fatkodima*, *duggiefresh*
 
-*   Fix bug with `ActiveRecord::Type::Numeric` that caused negative values to
-    be marked as having changed when set to the same negative value.
+*   Add `ActiveRecord::Base.base_class?` predicate.
 
-    Closes #18161.
-
-    *Daniel Fox*
-
-*   Introduce `force: :cascade` option for `create_table`. Using this option
-    will recreate tables even if they have dependent objects (like foreign keys).
-    `db/schema.rb` now uses `force: :cascade`. This makes it possible to
-    reload the schema when foreign keys are in place.
-
-    *Matthew Draper*, *Yves Senn*
-
-*   `db:schema:load` and `db:structure:load` no longer purge the database
-    before loading the schema. This is left for the user to do.
-    `db:test:prepare` will still purge the database.
-
-    Closes #17945.
-
-    *Yves Senn*
-
-*   Fix undesirable RangeError by `Type::Integer`. Add `Type::UnsignedInteger`.
-
-    *Ryuta Kamizono*
+    *Bogdan Gusiev*
 
-*   Add `foreign_type` option to `has_one` and `has_many` association macros.
+*   Add custom prefix/suffix options to `ActiveRecord::Store.store_accessor`.
 
-    This option enables to define the column name of associated object's type for polymorphic associations.
+    *Tan Huynh*, *Yukio Mizuta*
 
-    *Ulisses Almeida*, *Kassio Borges*
+*   Rails 6 requires Ruby 2.4.1 or newer.
 
-*   Remove deprecated behavior allowing nested arrays to be passed as query
-    values.
+    *Jeremy Daer*
 
-    *Melanie Gilman*
+*   Deprecate `update_attributes`/`!` in favor of `update`/`!`.
 
-*   Deprecate passing a class as a value in a query. Users should pass strings
-    instead.
+    *Eddie Lebow*
 
-    *Melanie Gilman*
+*   Add `ActiveRecord::Base.create_or_find_by`/`!` to deal with the SELECT/INSERT race condition in
+    `ActiveRecord::Base.find_or_create_by`/`!` by leaning on unique constraints in the database.
 
-*   `add_timestamps` and `remove_timestamps` now properly reversible with
-    options.
+    *DHH*
 
-    *Noam Gagliardi-Rabinovich*
+*   Add `Relation#pick` as short-hand for single-value plucks.
 
-*   `ActiveRecord::ConnectionAdapters::ColumnDumper#column_spec` and
-    `ActiveRecord::ConnectionAdapters::ColumnDumper#prepare_column_options` no
-    longer have a `types` argument. They should access
-    `connection#native_database_types` directly.
+    *DHH*
 
-    *Yves Senn*
 
-Please check [4-2-stable](https://github.com/rails/rails/blob/4-2-stable/activerecord/CHANGELOG.md) for previous changes.
+Please check [5-2-stable](https://github.com/rails/rails/blob/5-2-stable/activerecord/CHANGELOG.md) for previous changes.
diff --git a/activerecord/MIT-LICENSE b/activerecord/MIT-LICENSE
index 7c2197229d..04ba107c48 100644
--- a/activerecord/MIT-LICENSE
+++ b/activerecord/MIT-LICENSE
@@ -1,4 +1,6 @@
-Copyright (c) 2004-2015 David Heinemeier Hansson
+Copyright (c) 2004-2018 David Heinemeier Hansson
+
+Arel originally copyright (c) 2007-2016 Nick Kallen, Bryan Helmkamp, Emilio Tagua, Aaron Patterson
 
 Permission is hereby granted, free of charge, to any person obtaining
 a copy of this software and associated documentation files (the
@@ -17,4 +19,4 @@ MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
 LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
 OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
-WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
\ No newline at end of file
+WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
diff --git a/activerecord/README.rdoc b/activerecord/README.rdoc
index 049c5d2b3b..19650b82ae 100644
--- a/activerecord/README.rdoc
+++ b/activerecord/README.rdoc
@@ -26,7 +26,7 @@ The Product class is automatically mapped to the table named "products",
 which might look like this:
 
    CREATE TABLE products (
-     id int(11) NOT NULL auto_increment,
+     id bigint NOT NULL auto_increment,
      name varchar(255),
      PRIMARY KEY  (id)
    );
@@ -125,7 +125,7 @@ This would also define the following accessors: <tt>Product#name</tt> and
     )
 
   {Learn more}[link:classes/ActiveRecord/Base.html] and read about the built-in support for
-  MySQL[link:classes/ActiveRecord/ConnectionAdapters/MysqlAdapter.html],
+  MySQL[link:classes/ActiveRecord/ConnectionAdapters/Mysql2Adapter.html],
   PostgreSQL[link:classes/ActiveRecord/ConnectionAdapters/PostgreSQLAdapter.html], and
   SQLite3[link:classes/ActiveRecord/ConnectionAdapters/SQLite3Adapter.html].
 
@@ -138,7 +138,7 @@ This would also define the following accessors: <tt>Product#name</tt> and
 
 * Database agnostic schema management with Migrations.
 
-    class AddSystemSettings < ActiveRecord::Migration
+    class AddSystemSettings < ActiveRecord::Migration[5.0]
       def up
         create_table :system_settings do |t|
           t.string  :name
@@ -162,7 +162,7 @@ This would also define the following accessors: <tt>Product#name</tt> and
 == Philosophy
 
 Active Record is an implementation of the object-relational mapping (ORM)
-pattern[http://www.martinfowler.com/eaaCatalog/activeRecord.html] by the same
+pattern[https://www.martinfowler.com/eaaCatalog/activeRecord.html] by the same
 name described by Martin Fowler:
 
   "An object that wraps a row in a database table or view,
@@ -188,7 +188,7 @@ Admit the Database:
 
 The latest version of Active Record can be installed with RubyGems:
 
-  % gem install activerecord
+  $ gem install activerecord
 
 Source code can be downloaded as part of the Rails project on GitHub:
 
@@ -199,7 +199,7 @@ Source code can be downloaded as part of the Rails project on GitHub:
 
 Active Record is released under the MIT license:
 
-* http://www.opensource.org/licenses/MIT
+* https://opensource.org/licenses/MIT
 
 
 == Support
@@ -208,11 +208,10 @@ API documentation is at:
 
 * http://api.rubyonrails.org
 
-Bug reports can be filed for the Ruby on Rails project here:
+Bug reports for the Ruby on Rails project can be filed here:
 
 * https://github.com/rails/rails/issues
 
 Feature requests should be discussed on the rails-core mailing list here:
 
 * https://groups.google.com/forum/?fromgroups#!forum/rubyonrails-core
-
diff --git a/activerecord/RUNNING_UNIT_TESTS.rdoc b/activerecord/RUNNING_UNIT_TESTS.rdoc
index bae40604b1..60561e2c0f 100644
--- a/activerecord/RUNNING_UNIT_TESTS.rdoc
+++ b/activerecord/RUNNING_UNIT_TESTS.rdoc
@@ -7,11 +7,11 @@ http://edgeguides.rubyonrails.org/contributing_to_ruby_on_rails.html#setting-up-
 
 To run a specific test:
 
-  $ ruby -Itest test/cases/base_test.rb -n method_name
+  $ bundle exec ruby -Itest test/cases/base_test.rb -n method_name
 
 To run a set of tests:
 
-  $ ruby -Itest test/cases/base_test.rb
+  $ bundle exec ruby -Itest test/cases/base_test.rb
 
 You can also run tests that depend upon a specific database backend. For
 example:
@@ -20,7 +20,6 @@ example:
 
 Simply executing <tt>bundle exec rake test</tt> is equivalent to the following:
 
-  $ bundle exec rake test:mysql
   $ bundle exec rake test:mysql2
   $ bundle exec rake test:postgresql
   $ bundle exec rake test:sqlite3
@@ -42,7 +41,11 @@ parameters in +test/config.example.yml+ are.
 You can override the +connections:+ parameter in either file using the +ARCONN+
 (Active Record CONNection) environment variable:
 
-  $ ARCONN=postgresql ruby -Itest test/cases/base_test.rb
+  $ ARCONN=postgresql bundle exec ruby -Itest test/cases/base_test.rb
+
+Or
+
+  $ bundle exec rake test:postgresql TEST=test/cases/base_test.rb
 
 You can specify a custom location for the config file using the +ARCONFIG+
 environment variable.
diff --git a/activerecord/Rakefile b/activerecord/Rakefile
index a619204e6f..fae56a51bb 100644
--- a/activerecord/Rakefile
+++ b/activerecord/Rakefile
@@ -1,7 +1,9 @@
-require 'rake/testtask'
+# frozen_string_literal: true
 
-require File.expand_path(File.dirname(__FILE__)) + "/test/config"
-require File.expand_path(File.dirname(__FILE__)) + "/test/support/config"
+require "rake/testtask"
+
+require_relative "test/config"
+require_relative "test/support/config"
 
 def run_without_aborting(*tasks)
   errors = []
@@ -17,14 +19,16 @@ def run_without_aborting(*tasks)
   abort "Errors running #{errors.join(', ')}" if errors.any?
 end
 
-desc 'Run mysql, mysql2, sqlite, and postgresql tests by default'
-task :default => :test
+desc "Run mysql2, sqlite, and postgresql tests by default"
+task default: :test
+
+task :package
 
-desc 'Run mysql, mysql2, sqlite, and postgresql tests'
+desc "Run mysql2, sqlite, and postgresql tests"
 task :test do
   tasks = defined?(JRUBY_VERSION) ?
     %w(test_jdbcmysql test_jdbcsqlite3 test_jdbcpostgresql) :
-    %w(test_mysql test_mysql2 test_sqlite3 test_postgresql)
+    %w(test_mysql2 test_sqlite3 test_postgresql)
   run_without_aborting(*tasks)
 end
 
@@ -32,24 +36,26 @@ namespace :test do
   task :isolated do
     tasks = defined?(JRUBY_VERSION) ?
       %w(isolated_test_jdbcmysql isolated_test_jdbcsqlite3 isolated_test_jdbcpostgresql) :
-      %w(isolated_test_mysql isolated_test_mysql2 isolated_test_sqlite3 isolated_test_postgresql)
+      %w(isolated_test_mysql2 isolated_test_sqlite3 isolated_test_postgresql)
     run_without_aborting(*tasks)
   end
 end
 
-desc 'Build MySQL and PostgreSQL test databases'
 namespace :db do
-  task :create => ['db:mysql:build', 'db:postgresql:build']
-  task :drop => ['db:mysql:drop', 'db:postgresql:drop']
+  desc "Build MySQL and PostgreSQL test databases"
+  task create: ["db:mysql:build", "db:postgresql:build"]
+
+  desc "Drop MySQL and PostgreSQL test databases"
+  task drop: ["db:mysql:drop", "db:postgresql:drop"]
 end
 
-%w( mysql mysql2 postgresql sqlite3 sqlite3_mem db2 oracle jdbcmysql jdbcpostgresql jdbcsqlite3 jdbcderby jdbch2 jdbchsqldb ).each do |adapter|
+%w( mysql2 postgresql sqlite3 sqlite3_mem db2 oracle jdbcmysql jdbcpostgresql jdbcsqlite3 jdbcderby jdbch2 jdbchsqldb ).each do |adapter|
   namespace :test do
     Rake::TestTask.new(adapter => "#{adapter}:env") { |t|
-      adapter_short = adapter == 'db2' ? adapter : adapter[/^[a-z0-9]+/]
-      t.libs << 'test'
-      t.test_files = (Dir.glob( "test/cases/**/*_test.rb" ).reject {
-        |x| x =~ /\/adapters\//
+      adapter_short = adapter == "db2" ? adapter : adapter[/^[a-z0-9]+/]
+      t.libs << "test"
+      t.test_files = (Dir.glob("test/cases/**/*_test.rb").reject {
+        |x| x.include?("/adapters/")
       } + Dir.glob("test/cases/adapters/#{adapter_short}/**/*_test.rb"))
 
       t.warning = true
@@ -59,23 +65,23 @@ end
 
     namespace :isolated do
       task adapter => "#{adapter}:env" do
-        adapter_short = adapter == 'db2' ? adapter : adapter[/^[a-z0-9]+/]
+        adapter_short = adapter == "db2" ? adapter : adapter[/^[a-z0-9]+/]
         puts [adapter, adapter_short].inspect
         (Dir["test/cases/**/*_test.rb"].reject {
-          |x| x =~ /\/adapters\//
+          |x| x.include?("/adapters/")
         } + Dir["test/cases/adapters/#{adapter_short}/**/*_test.rb"]).all? do |file|
-          sh(Gem.ruby, '-w' ,"-Itest", file)
-        end or raise "Failures"
+          sh(Gem.ruby, "-w", "-Itest", file)
+        end || raise("Failures")
       end
     end
   end
 
   namespace adapter do
-    task :test => "test_#{adapter}"
-    task :isolated_test => "isolated_test_#{adapter}"
+    task test: "test_#{adapter}"
+    task isolated_test: "isolated_test_#{adapter}"
 
     # Set the connection environment for the adapter
-    task(:env) { ENV['ARCONN'] = adapter }
+    task(:env) { ENV["ARCONN"] = adapter }
   end
 
   # Make sure the adapter test evaluates the env setting task
@@ -83,70 +89,56 @@ end
   task "isolated_test_#{adapter}" => ["#{adapter}:env", "test:isolated:#{adapter}"]
 end
 
-rule '.sqlite3' do |t|
-  sh %Q{sqlite3 "#{t.name}" "create table a (a integer); drop table a;"}
-end
-
-task :test_sqlite3 => [
-  'test/fixtures/fixture_database.sqlite3',
-  'test/fixtures/fixture_database_2.sqlite3'
-]
-
 namespace :db do
   namespace :mysql do
-    desc 'Build the MySQL test databases'
+    desc "Build the MySQL test databases"
     task :build do
-      config = ARTest.config['connections']['mysql']
-      %x( mysql --user=#{config['arunit']['username']} -e "create DATABASE #{config['arunit']['database']} DEFAULT CHARACTER SET utf8 DEFAULT COLLATE utf8_unicode_ci ")
-      %x( mysql --user=#{config['arunit2']['username']} -e "create DATABASE #{config['arunit2']['database']} DEFAULT CHARACTER SET utf8 DEFAULT COLLATE utf8_unicode_ci ")
+      config = ARTest.config["connections"]["mysql2"]
+      %x( mysql --user=#{config["arunit"]["username"]} --password=#{config["arunit"]["password"]} -e "create DATABASE #{config["arunit"]["database"]} DEFAULT CHARACTER SET utf8mb4" )
+      %x( mysql --user=#{config["arunit2"]["username"]} --password=#{config["arunit2"]["password"]} -e "create DATABASE #{config["arunit2"]["database"]} DEFAULT CHARACTER SET utf8mb4" )
     end
 
-    desc 'Drop the MySQL test databases'
+    desc "Drop the MySQL test databases"
     task :drop do
-      config = ARTest.config['connections']['mysql']
-      %x( mysqladmin --user=#{config['arunit']['username']} -f drop #{config['arunit']['database']} )
-      %x( mysqladmin --user=#{config['arunit2']['username']} -f drop #{config['arunit2']['database']} )
+      config = ARTest.config["connections"]["mysql2"]
+      %x( mysqladmin --user=#{config["arunit"]["username"]} --password=#{config["arunit"]["password"]} -f drop #{config["arunit"]["database"]} )
+      %x( mysqladmin --user=#{config["arunit2"]["username"]} --password=#{config["arunit2"]["password"]} -f drop #{config["arunit2"]["database"]} )
     end
 
-    desc 'Rebuild the MySQL test databases'
-    task :rebuild => [:drop, :build]
+    desc "Rebuild the MySQL test databases"
+    task rebuild: [:drop, :build]
   end
 
   namespace :postgresql do
-    desc 'Build the PostgreSQL test databases'
+    desc "Build the PostgreSQL test databases"
     task :build do
-      config = ARTest.config['connections']['postgresql']
-      %x( createdb -E UTF8 -T template0 #{config['arunit']['database']} )
-      %x( createdb -E UTF8 -T template0 #{config['arunit2']['database']} )
-
-      # prepare hstore
-      if %x( createdb --version ).strip.gsub(/(.*)(\d\.\d\.\d)$/, "\\2") < "9.1.0"
-        puts "Please prepare hstore data type. See http://www.postgresql.org/docs/current/static/hstore.html"
-      end
+      config = ARTest.config["connections"]["postgresql"]
+      %x( createdb -E UTF8 -T template0 #{config["arunit"]["database"]} )
+      %x( createdb -E UTF8 -T template0 #{config["arunit2"]["database"]} )
     end
 
-    desc 'Drop the PostgreSQL test databases'
+    desc "Drop the PostgreSQL test databases"
     task :drop do
-      config = ARTest.config['connections']['postgresql']
-      %x( dropdb #{config['arunit']['database']} )
-      %x( dropdb #{config['arunit2']['database']} )
+      config = ARTest.config["connections"]["postgresql"]
+      %x( dropdb #{config["arunit"]["database"]} )
+      %x( dropdb #{config["arunit2"]["database"]} )
     end
 
-    desc 'Rebuild the PostgreSQL test databases'
-    task :rebuild => [:drop, :build]
+    desc "Rebuild the PostgreSQL test databases"
+    task rebuild: [:drop, :build]
   end
 end
 
-task :build_mysql_databases => 'db:mysql:build'
-task :drop_mysql_databases => 'db:mysql:drop'
-task :rebuild_mysql_databases => 'db:mysql:rebuild'
+task build_mysql_databases: "db:mysql:build"
+task drop_mysql_databases: "db:mysql:drop"
+task rebuild_mysql_databases: "db:mysql:rebuild"
 
-task :build_postgresql_databases => 'db:postgresql:build'
-task :drop_postgresql_databases => 'db:postgresql:drop'
-task :rebuild_postgresql_databases => 'db:postgresql:rebuild'
+task build_postgresql_databases: "db:postgresql:build"
+task drop_postgresql_databases: "db:postgresql:drop"
+task rebuild_postgresql_databases: "db:postgresql:rebuild"
 
 task :lines do
-  load File.expand_path('..', File.dirname(__FILE__)) + '/tools/line_statistics'
+  load File.expand_path("../tools/line_statistics", __dir__)
   files = FileList["lib/active_record/**/*.rb"]
   CodeTools::LineStatistics.new(files).print_loc
 end
diff --git a/activerecord/activerecord.gemspec b/activerecord/activerecord.gemspec
index bd95b57303..bcdd82052c 100644
--- a/activerecord/activerecord.gemspec
+++ b/activerecord/activerecord.gemspec
@@ -1,28 +1,36 @@
-version = File.read(File.expand_path('../../RAILS_VERSION', __FILE__)).strip
+# frozen_string_literal: true
+
+version = File.read(File.expand_path("../RAILS_VERSION", __dir__)).strip
 
 Gem::Specification.new do |s|
   s.platform    = Gem::Platform::RUBY
-  s.name        = 'activerecord'
+  s.name        = "activerecord"
   s.version     = version
-  s.summary     = 'Object-relational mapper framework (part of Rails).'
-  s.description = 'Databases on Rails. Build a persistent domain model by mapping database tables to Ruby classes. Strong conventions for associations, validations, aggregations, migrations, and testing come baked-in.'
+  s.summary     = "Object-relational mapper framework (part of Rails)."
+  s.description = "Databases on Rails. Build a persistent domain model by mapping database tables to Ruby classes. Strong conventions for associations, validations, aggregations, migrations, and testing come baked-in."
 
-  s.required_ruby_version = '>= 2.2.2'
+  s.required_ruby_version = ">= 2.4.1"
 
-  s.license = 'MIT'
+  s.license = "MIT"
 
-  s.author   = 'David Heinemeier Hansson'
-  s.email    = 'david@loudthinking.com'
-  s.homepage = 'http://www.rubyonrails.org'
+  s.author   = "David Heinemeier Hansson"
+  s.email    = "david@loudthinking.com"
+  s.homepage = "http://rubyonrails.org"
 
-  s.files        = Dir['CHANGELOG.md', 'MIT-LICENSE', 'README.rdoc', 'examples/**/*', 'lib/**/*']
-  s.require_path = 'lib'
+  s.files        = Dir["CHANGELOG.md", "MIT-LICENSE", "README.rdoc", "examples/**/*", "lib/**/*"]
+  s.require_path = "lib"
 
   s.extra_rdoc_files = %w(README.rdoc)
-  s.rdoc_options.concat ['--main',  'README.rdoc']
+  s.rdoc_options.concat ["--main",  "README.rdoc"]
+
+  s.metadata = {
+    "source_code_uri" => "https://github.com/rails/rails/tree/v#{version}/activerecord",
+    "changelog_uri"   => "https://github.com/rails/rails/blob/v#{version}/activerecord/CHANGELOG.md"
+  }
 
-  s.add_dependency 'activesupport', version
-  s.add_dependency 'activemodel',   version
+  # NOTE: Please read our dependency guidelines before updating versions:
+  # https://edgeguides.rubyonrails.org/security.html#dependency-management-and-cves
 
-  s.add_dependency 'arel', '7.0.0.alpha'
+  s.add_dependency "activesupport", version
+  s.add_dependency "activemodel",   version
 end
diff --git a/activerecord/bin/test b/activerecord/bin/test
index f8adf2aabc..9ecf27ce67 100755
--- a/activerecord/bin/test
+++ b/activerecord/bin/test
@@ -1,12 +1,21 @@
 #!/usr/bin/env ruby
-COMPONENT_ROOT = File.expand_path("../../", __FILE__)
-require File.expand_path("../tools/test", COMPONENT_ROOT)
+# frozen_string_literal: true
+
+adapter_index = ARGV.index("--adapter") || ARGV.index("-a")
+if adapter_index
+  ARGV.delete_at(adapter_index)
+  ENV["ARCONN"] = ARGV.delete_at(adapter_index).strip
+end
+
+COMPONENT_ROOT = File.expand_path("..", __dir__)
+require_relative "../../tools/test"
+
 module Minitest
   def self.plugin_active_record_options(opts, options)
     opts.separator ""
     opts.separator "Active Record options:"
     opts.on("-a", "--adapter [ADAPTER]",
-            "Run tests using a specific adapter (sqlite3, sqlite3_mem, mysql, mysql2, postgresql)") do |adapter|
+            "Run tests using a specific adapter (sqlite3, sqlite3_mem, mysql2, postgresql)") do |adapter|
       ENV["ARCONN"] = adapter.strip
     end
 
@@ -14,6 +23,5 @@ module Minitest
   end
 end
 
-Minitest.extensions.unshift 'active_record'
-
-exit Minitest.run(ARGV)
+Minitest.load_plugins
+Minitest.extensions.unshift "active_record"
diff --git a/activerecord/examples/.gitignore b/activerecord/examples/.gitignore
deleted file mode 100644
index 0dfc1cb7fb..0000000000
--- a/activerecord/examples/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-performance.sql
diff --git a/activerecord/examples/performance.rb b/activerecord/examples/performance.rb
index a5a1f284a0..024e503ec7 100644
--- a/activerecord/examples/performance.rb
+++ b/activerecord/examples/performance.rb
@@ -1,11 +1,12 @@
-require File.expand_path('../../../load_paths', __FILE__)
+# frozen_string_literal: true
+
 require "active_record"
-require 'benchmark/ips'
+require "benchmark/ips"
 
-TIME    = (ENV['BENCHMARK_TIME'] || 20).to_i
-RECORDS = (ENV['BENCHMARK_RECORDS'] || TIME*1000).to_i
+TIME    = (ENV["BENCHMARK_TIME"] || 20).to_i
+RECORDS = (ENV["BENCHMARK_RECORDS"] || TIME * 1000).to_i
 
-conn = { adapter: 'sqlite3', database: ':memory:' }
+conn = { adapter: "sqlite3", database: ":memory:" }
 
 ActiveRecord::Base.establish_connection(conn)
 
@@ -43,26 +44,26 @@ class Exhibit < ActiveRecord::Base
   def self.feel(exhibits) exhibits.each(&:feel) end
 end
 
-def progress_bar(int); print "." if (int%100).zero? ; end
+def progress_bar(int); print "." if (int % 100).zero? ; end
 
-puts 'Generating data...'
+puts "Generating data..."
 
 module ActiveRecord
   class Faker
-    LOREM = %Q{Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse non aliquet diam. Curabitur vel urna metus, quis malesuada elit.
+    LOREM = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Suspendisse non aliquet diam. Curabitur vel urna metus, quis malesuada elit.
      Integer consequat tincidunt felis. Etiam non erat dolor. Vivamus imperdiet nibh sit amet diam eleifend id posuere diam malesuada. Mauris at accumsan sem.
      Donec id lorem neque. Fusce erat lorem, ornare eu congue vitae, malesuada quis neque. Maecenas vel urna a velit pretium fermentum. Donec tortor enim,
      tempor venenatis egestas a, tempor sed ipsum. Ut arcu justo, faucibus non imperdiet ac, interdum at diam. Pellentesque ipsum enim, venenatis ut iaculis vitae,
      varius vitae sem. Sed rutrum quam ac elit euismod bibendum. Donec ultricies ultricies magna, at lacinia libero mollis aliquam. Sed ac arcu in tortor elementum
      tincidunt vel interdum sem. Curabitur eget erat arcu. Praesent eget eros leo. Nam magna enim, sollicitudin vehicula scelerisque in, vulputate ut libero.
-     Praesent varius tincidunt commodo}.split
+     Praesent varius tincidunt commodo".split
 
     def self.name
-      LOREM.grep(/^\w*$/).sort_by { rand }.first(2).join ' '
+      LOREM.grep(/^\w*$/).sort_by { rand }.first(2).join " "
     end
 
     def self.email
-      LOREM.grep(/^\w*$/).sort_by { rand }.first(2).join('@') + ".com"
+      LOREM.grep(/^\w*$/).sort_by { rand }.first(2).join("@") + ".com"
     end
   end
 end
@@ -73,7 +74,7 @@ end
 
 # Using the same paragraph for all exhibits because it is very slow
 # to generate unique paragraphs for all exhibits.
-notes = ActiveRecord::Faker::LOREM.join ' '
+notes = ActiveRecord::Faker::LOREM.join " "
 today = Date.today
 
 puts "Inserting #{RECORDS} users and exhibits..."
@@ -96,9 +97,9 @@ puts "Done!\n"
 
 Benchmark.ips(TIME) do |x|
   ar_obj       = Exhibit.find(1)
-  attrs        = { name: 'sam' }
-  attrs_first  = { name: 'sam' }
-  attrs_second = { name: 'tom' }
+  attrs        = { name: "sam" }
+  attrs_first  = { name: "sam" }
+  attrs_second = { name: "tom" }
   exhibit      = {
     name: ActiveRecord::Faker.name,
     notes: notes,
@@ -109,22 +110,22 @@ Benchmark.ips(TIME) do |x|
     ar_obj.id
   end
 
-  x.report 'Model.new (instantiation)' do
+  x.report "Model.new (instantiation)" do
     Exhibit.new
   end
 
-  x.report 'Model.new (setting attributes)' do
+  x.report "Model.new (setting attributes)" do
     Exhibit.new(attrs)
   end
 
-  x.report 'Model.first' do
+  x.report "Model.first" do
     Exhibit.first.look
   end
 
-  x.report 'Model.take' do 
+  x.report "Model.take" do
     Exhibit.take
   end
-  
+
   x.report("Model.all limit(100)") do
     Exhibit.look Exhibit.limit(100)
   end
@@ -141,41 +142,41 @@ Benchmark.ips(TIME) do |x|
     Exhibit.look Exhibit.limit(10000)
   end
 
-  x.report 'Model.named_scope' do
+  x.report "Model.named_scope" do
     Exhibit.limit(10).with_name.with_notes
   end
 
-  x.report 'Model.create' do
+  x.report "Model.create" do
     Exhibit.create(exhibit)
   end
 
-  x.report 'Resource#attributes=' do
+  x.report "Resource#attributes=" do
     e = Exhibit.new(attrs_first)
     e.attributes = attrs_second
   end
 
-  x.report 'Resource#update' do
-    Exhibit.first.update(name: 'bob')
+  x.report "Resource#update" do
+    Exhibit.first.update(name: "bob")
   end
 
-  x.report 'Resource#destroy' do
+  x.report "Resource#destroy" do
     Exhibit.first.destroy
   end
 
-  x.report 'Model.transaction' do
+  x.report "Model.transaction" do
     Exhibit.transaction { Exhibit.new }
   end
 
-  x.report 'Model.find(id)' do
+  x.report "Model.find(id)" do
     User.find(1)
   end
 
-  x.report 'Model.find_by_sql' do
+  x.report "Model.find_by_sql" do
     Exhibit.find_by_sql("SELECT * FROM exhibits WHERE id = #{(rand * 1000 + 1).to_i}").first
   end
 
   x.report "Model.log" do
-    Exhibit.connection.send(:log, "hello", "world") {}
+    Exhibit.connection.send(:log, "hello", "world") { }
   end
 
   x.report "AR.execute(query)" do
diff --git a/activerecord/examples/simple.rb b/activerecord/examples/simple.rb
index 4ed5d80eb2..280b786d73 100644
--- a/activerecord/examples/simple.rb
+++ b/activerecord/examples/simple.rb
@@ -1,14 +1,15 @@
-require File.expand_path('../../../load_paths', __FILE__)
-require 'active_record'
+# frozen_string_literal: true
+
+require "active_record"
 
 class Person < ActiveRecord::Base
-  establish_connection adapter: 'sqlite3', database: 'foobar.db'
+  establish_connection adapter: "sqlite3", database: "foobar.db"
   connection.create_table table_name, force: true do |t|
     t.string :name
   end
 end
 
-bob = Person.create!(name: 'bob')
+bob = Person.create!(name: "bob")
 puts Person.all.inspect
 bob.destroy
 puts Person.all.inspect
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index f5cf92db64..d43378c64f 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 #--
-# Copyright (c) 2004-2015 David Heinemeier Hansson
+# Copyright (c) 2004-2018 David Heinemeier Hansson
 #
 # Permission is hereby granted, free of charge, to any person obtaining
 # a copy of this software and associated documentation files (the
@@ -21,18 +23,18 @@
 # WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 #++
 
-require 'active_support'
-require 'active_support/rails'
-require 'active_model'
-require 'arel'
+require "active_support"
+require "active_support/rails"
+require "active_model"
+require "arel"
+require "yaml"
 
-require 'active_record/version'
-require 'active_record/attribute_set'
+require "active_record/version"
+require "active_model/attribute_set"
 
 module ActiveRecord
   extend ActiveSupport::Autoload
 
-  autoload :Attribute
   autoload :Base
   autoload :Callbacks
   autoload :Core
@@ -40,12 +42,12 @@ module ActiveRecord
   autoload :CounterCache
   autoload :DynamicMatchers
   autoload :Enum
+  autoload :InternalMetadata
   autoload :Explain
   autoload :Inheritance
   autoload :Integration
-  autoload :LegacyYamlAdapter
   autoload :Migration
-  autoload :Migrator, 'active_record/migration'
+  autoload :Migrator, "active_record/migration"
   autoload :ModelSchema
   autoload :NestedAttributes
   autoload :NoTouching
@@ -53,8 +55,9 @@ module ActiveRecord
   autoload :Persistence
   autoload :QueryCache
   autoload :Querying
+  autoload :CollectionCacheKey
   autoload :ReadonlyAttributes
-  autoload :RecordInvalid, 'active_record/validations'
+  autoload :RecordInvalid, "active_record/validations"
   autoload :Reflection
   autoload :RuntimeRegistry
   autoload :Sanitization
@@ -66,7 +69,6 @@ module ActiveRecord
   autoload :StatementCache
   autoload :Store
   autoload :Suppressor
-  autoload :TableMetadata
   autoload :Timestamp
   autoload :Transactions
   autoload :Translation
@@ -74,9 +76,9 @@ module ActiveRecord
   autoload :SecureToken
 
   eager_autoload do
-    autoload :ActiveRecordError, 'active_record/errors'
-    autoload :ConnectionNotEstablished, 'active_record/errors'
-    autoload :ConnectionAdapters, 'active_record/connection_adapters/abstract_adapter'
+    autoload :ActiveRecordError, "active_record/errors"
+    autoload :ConnectionNotEstablished, "active_record/errors"
+    autoload :ConnectionAdapters, "active_record/connection_adapters/abstract_adapter"
 
     autoload :Aggregations
     autoload :Associations
@@ -84,11 +86,13 @@ module ActiveRecord
     autoload :AttributeMethods
     autoload :AutosaveAssociation
 
+    autoload :LegacyYamlAdapter
+
     autoload :Relation
     autoload :AssociationRelation
     autoload :NullRelation
 
-    autoload_under 'relation' do
+    autoload_under "relation" do
       autoload :QueryMethods
       autoload :FinderMethods
       autoload :Calculations
@@ -99,11 +103,13 @@ module ActiveRecord
     end
 
     autoload :Result
+    autoload :TableMetadata
+    autoload :Type
   end
 
   module Coders
-    autoload :YAMLColumn, 'active_record/coders/yaml_column'
-    autoload :JSON, 'active_record/coders/json'
+    autoload :YAMLColumn, "active_record/coders/yaml_column"
+    autoload :JSON, "active_record/coders/json"
   end
 
   module AttributeMethods
@@ -135,7 +141,6 @@ module ActiveRecord
 
     eager_autoload do
       autoload :AbstractAdapter
-      autoload :ConnectionManagement, "active_record/connection_adapters/abstract/connection_pool"
     end
   end
 
@@ -152,13 +157,14 @@ module ActiveRecord
     extend ActiveSupport::Autoload
 
     autoload :DatabaseTasks
-    autoload :SQLiteDatabaseTasks, 'active_record/tasks/sqlite_database_tasks'
-    autoload :MySQLDatabaseTasks,  'active_record/tasks/mysql_database_tasks'
+    autoload :SQLiteDatabaseTasks, "active_record/tasks/sqlite_database_tasks"
+    autoload :MySQLDatabaseTasks,  "active_record/tasks/mysql_database_tasks"
     autoload :PostgreSQLDatabaseTasks,
-      'active_record/tasks/postgresql_database_tasks'
+      "active_record/tasks/postgresql_database_tasks"
   end
 
-  autoload :TestFixtures, 'active_record/fixtures'
+  autoload :TestDatabases, "active_record/test_databases"
+  autoload :TestFixtures, "active_record/fixtures"
 
   def self.eager_load!
     super
@@ -175,5 +181,9 @@ ActiveSupport.on_load(:active_record) do
 end
 
 ActiveSupport.on_load(:i18n) do
-  I18n.load_path << File.dirname(__FILE__) + '/active_record/locale/en.yml'
+  I18n.load_path << File.expand_path("active_record/locale/en.yml", __dir__)
 end
+
+YAML.load_tags["!ruby/object:ActiveRecord::AttributeSet"] = "ActiveModel::AttributeSet"
+YAML.load_tags["!ruby/object:ActiveRecord::Attribute::FromDatabase"] = "ActiveModel::Attribute::FromDatabase"
+YAML.load_tags["!ruby/object:ActiveRecord::LazyAttributeHash"] = "ActiveModel::LazyAttributeHash"
diff --git a/activerecord/lib/active_record/aggregations.rb b/activerecord/lib/active_record/aggregations.rb
index f7b50cd25a..3250e29b82 100644
--- a/activerecord/lib/active_record/aggregations.rb
+++ b/activerecord/lib/active_record/aggregations.rb
@@ -1,8 +1,8 @@
-module ActiveRecord
-  # = Active Record Aggregations
-  module Aggregations # :nodoc:
-    extend ActiveSupport::Concern
+# frozen_string_literal: true
 
+module ActiveRecord
+  # See ActiveRecord::Aggregations::ClassMethods for documentation
+  module Aggregations
     def initialize_dup(*) # :nodoc:
       @aggregation_cache = {}
       super
@@ -15,265 +15,271 @@ module ActiveRecord
 
     private
 
-      def clear_aggregation_cache # :nodoc:
+      def clear_aggregation_cache
         @aggregation_cache.clear if persisted?
       end
 
-      def init_internals # :nodoc:
+      def init_internals
         @aggregation_cache = {}
         super
       end
 
-    # Active Record implements aggregation through a macro-like class method called +composed_of+
-    # for representing attributes  as value objects. It expresses relationships like "Account [is]
-    # composed of Money [among other things]" or "Person [is] composed of [an] address". Each call
-    # to the macro adds a description of how the value objects are created from the attributes of
-    # the entity object (when the entity is initialized either as a new object or from finding an
-    # existing object) and how it can be turned back into attributes (when the entity is saved to
-    # the database).
-    #
-    #   class Customer < ActiveRecord::Base
-    #     composed_of :balance, class_name: "Money", mapping: %w(balance amount)
-    #     composed_of :address, mapping: [ %w(address_street street), %w(address_city city) ]
-    #   end
-    #
-    # The customer class now has the following methods to manipulate the value objects:
-    # * <tt>Customer#balance, Customer#balance=(money)</tt>
-    # * <tt>Customer#address, Customer#address=(address)</tt>
-    #
-    # These methods will operate with value objects like the ones described below:
-    #
-    #  class Money
-    #    include Comparable
-    #    attr_reader :amount, :currency
-    #    EXCHANGE_RATES = { "USD_TO_DKK" => 6 }
-    #
-    #    def initialize(amount, currency = "USD")
-    #      @amount, @currency = amount, currency
-    #    end
-    #
-    #    def exchange_to(other_currency)
-    #      exchanged_amount = (amount * EXCHANGE_RATES["#{currency}_TO_#{other_currency}"]).floor
-    #      Money.new(exchanged_amount, other_currency)
-    #    end
-    #
-    #    def ==(other_money)
-    #      amount == other_money.amount && currency == other_money.currency
-    #    end
-    #
-    #    def <=>(other_money)
-    #      if currency == other_money.currency
-    #        amount <=> other_money.amount
-    #      else
-    #        amount <=> other_money.exchange_to(currency).amount
-    #      end
-    #    end
-    #  end
-    #
-    #  class Address
-    #    attr_reader :street, :city
-    #    def initialize(street, city)
-    #      @street, @city = street, city
-    #    end
-    #
-    #    def close_to?(other_address)
-    #      city == other_address.city
-    #    end
-    #
-    #    def ==(other_address)
-    #      city == other_address.city && street == other_address.street
-    #    end
-    #  end
-    #
-    # Now it's possible to access attributes from the database through the value objects instead. If
-    # you choose to name the composition the same as the attribute's name, it will be the only way to
-    # access that attribute. That's the case with our +balance+ attribute. You interact with the value
-    # objects just like you would with any other attribute:
-    #
-    #   customer.balance = Money.new(20)     # sets the Money value object and the attribute
-    #   customer.balance                     # => Money value object
-    #   customer.balance.exchange_to("DKK")  # => Money.new(120, "DKK")
-    #   customer.balance > Money.new(10)     # => true
-    #   customer.balance == Money.new(20)    # => true
-    #   customer.balance < Money.new(5)      # => false
-    #
-    # Value objects can also be composed of multiple attributes, such as the case of Address. The order
-    # of the mappings will determine the order of the parameters.
-    #
-    #   customer.address_street = "Hyancintvej"
-    #   customer.address_city   = "Copenhagen"
-    #   customer.address        # => Address.new("Hyancintvej", "Copenhagen")
-    #
-    #   customer.address = Address.new("May Street", "Chicago")
-    #   customer.address_street # => "May Street"
-    #   customer.address_city   # => "Chicago"
-    #
-    # == Writing value objects
-    #
-    # Value objects are immutable and interchangeable objects that represent a given value, such as
-    # a Money object representing $5. Two Money objects both representing $5 should be equal (through
-    # methods such as <tt>==</tt> and <tt><=></tt> from Comparable if ranking makes sense). This is
-    # unlike entity objects where equality is determined by identity. An entity class such as Customer can
-    # easily have two different objects that both have an address on Hyancintvej. Entity identity is
-    # determined by object or relational unique identifiers (such as primary keys). Normal
-    # ActiveRecord::Base classes are entity objects.
-    #
-    # It's also important to treat the value objects as immutable. Don't allow the Money object to have
-    # its amount changed after creation. Create a new Money object with the new value instead. The
-    # Money#exchange_to method is an example of this. It returns a new value object instead of changing
-    # its own values. Active Record won't persist value objects that have been changed through means
-    # other than the writer method.
-    #
-    # The immutable requirement is enforced by Active Record by freezing any object assigned as a value
-    # object. Attempting to change it afterwards will result in a RuntimeError.
-    #
-    # Read more about value objects on http://c2.com/cgi/wiki?ValueObject and on the dangers of not
-    # keeping value objects immutable on http://c2.com/cgi/wiki?ValueObjectsShouldBeImmutable
-    #
-    # == Custom constructors and converters
-    #
-    # By default value objects are initialized by calling the <tt>new</tt> constructor of the value
-    # class passing each of the mapped attributes, in the order specified by the <tt>:mapping</tt>
-    # option, as arguments. If the value class doesn't support this convention then +composed_of+ allows
-    # a custom constructor to be specified.
-    #
-    # When a new value is assigned to the value object, the default assumption is that the new value
-    # is an instance of the value class. Specifying a custom converter allows the new value to be automatically
-    # converted to an instance of value class if necessary.
-    #
-    # For example, the NetworkResource model has +network_address+ and +cidr_range+ attributes that should be
-    # aggregated using the NetAddr::CIDR value class (http://www.rubydoc.info/gems/netaddr/1.5.0/NetAddr/CIDR).
-    # The constructor for the value class is called +create+ and it expects a CIDR address string as a parameter.
-    # New values can be assigned to the value object using either another NetAddr::CIDR object, a string
-    # or an array. The <tt>:constructor</tt> and <tt>:converter</tt> options can be used to meet
-    # these requirements:
-    #
-    #   class NetworkResource < ActiveRecord::Base
-    #     composed_of :cidr,
-    #                 class_name: 'NetAddr::CIDR',
-    #                 mapping: [ %w(network_address network), %w(cidr_range bits) ],
-    #                 allow_nil: true,
-    #                 constructor: Proc.new { |network_address, cidr_range| NetAddr::CIDR.create("#{network_address}/#{cidr_range}") },
-    #                 converter: Proc.new { |value| NetAddr::CIDR.create(value.is_a?(Array) ? value.join('/') : value) }
-    #   end
-    #
-    #   # This calls the :constructor
-    #   network_resource = NetworkResource.new(network_address: '192.168.0.1', cidr_range: 24)
-    #
-    #   # These assignments will both use the :converter
-    #   network_resource.cidr = [ '192.168.2.1', 8 ]
-    #   network_resource.cidr = '192.168.0.1/24'
-    #
-    #   # This assignment won't use the :converter as the value is already an instance of the value class
-    #   network_resource.cidr = NetAddr::CIDR.create('192.168.2.1/8')
-    #
-    #   # Saving and then reloading will use the :constructor on reload
-    #   network_resource.save
-    #   network_resource.reload
-    #
-    # == Finding records by a value object
-    #
-    # Once a +composed_of+ relationship is specified for a model, records can be loaded from the database
-    # by specifying an instance of the value object in the conditions hash. The following example
-    # finds all customers with +balance_amount+ equal to 20 and +balance_currency+ equal to "USD":
-    #
-    #   Customer.where(balance: Money.new(20, "USD"))
-    #
-    module ClassMethods
-      # Adds reader and writer methods for manipulating a value object:
-      # <tt>composed_of :address</tt> adds <tt>address</tt> and <tt>address=(new_address)</tt> methods.
-      #
-      # Options are:
-      # * <tt>:class_name</tt> - Specifies the class name of the association. Use it only if that name
-      #   can't be inferred from the part id. So <tt>composed_of :address</tt> will by default be linked
-      #   to the Address class, but if the real class name is CompanyAddress, you'll have to specify it
-      #   with this option.
-      # * <tt>:mapping</tt> - Specifies the mapping of entity attributes to attributes of the value
-      #   object. Each mapping is represented as an array where the first item is the name of the
-      #   entity attribute and the second item is the name of the attribute in the value object. The
-      #   order in which mappings are defined determines the order in which attributes are sent to the
-      #   value class constructor.
-      # * <tt>:allow_nil</tt> - Specifies that the value object will not be instantiated when all mapped
-      #   attributes are +nil+. Setting the value object to +nil+ has the effect of writing +nil+ to all
-      #   mapped attributes.
-      #   This defaults to +false+.
-      # * <tt>:constructor</tt> - A symbol specifying the name of the constructor method or a Proc that
-      #   is called to initialize the value object. The constructor is passed all of the mapped attributes,
-      #   in the order that they are defined in the <tt>:mapping option</tt>, as arguments and uses them
-      #   to instantiate a <tt>:class_name</tt> object.
-      #   The default is <tt>:new</tt>.
-      # * <tt>:converter</tt> - A symbol specifying the name of a class method of <tt>:class_name</tt>
-      #   or a Proc that is called when a new value is assigned to the value object. The converter is
-      #   passed the single value that is used in the assignment and is only called if the new value is
-      #   not an instance of <tt>:class_name</tt>. If <tt>:allow_nil</tt> is set to true, the converter
-      #   can return nil to skip the assignment.
-      #
-      # Option examples:
-      #   composed_of :temperature, mapping: %w(reading celsius)
-      #   composed_of :balance, class_name: "Money", mapping: %w(balance amount),
-      #                         converter: Proc.new { |balance| balance.to_money }
-      #   composed_of :address, mapping: [ %w(address_street street), %w(address_city city) ]
-      #   composed_of :gps_location
-      #   composed_of :gps_location, allow_nil: true
-      #   composed_of :ip_address,
-      #               class_name: 'IPAddr',
-      #               mapping: %w(ip to_i),
-      #               constructor: Proc.new { |ip| IPAddr.new(ip, Socket::AF_INET) },
-      #               converter: Proc.new { |ip| ip.is_a?(Integer) ? IPAddr.new(ip, Socket::AF_INET) : IPAddr.new(ip.to_s) }
-      #
-      def composed_of(part_id, options = {})
-        options.assert_valid_keys(:class_name, :mapping, :allow_nil, :constructor, :converter)
+      # Active Record implements aggregation through a macro-like class method called #composed_of
+      # for representing attributes as value objects. It expresses relationships like "Account [is]
+      # composed of Money [among other things]" or "Person [is] composed of [an] address". Each call
+      # to the macro adds a description of how the value objects are created from the attributes of
+      # the entity object (when the entity is initialized either as a new object or from finding an
+      # existing object) and how it can be turned back into attributes (when the entity is saved to
+      # the database).
+      #
+      #   class Customer < ActiveRecord::Base
+      #     composed_of :balance, class_name: "Money", mapping: %w(balance amount)
+      #     composed_of :address, mapping: [ %w(address_street street), %w(address_city city) ]
+      #   end
+      #
+      # The customer class now has the following methods to manipulate the value objects:
+      # * <tt>Customer#balance, Customer#balance=(money)</tt>
+      # * <tt>Customer#address, Customer#address=(address)</tt>
+      #
+      # These methods will operate with value objects like the ones described below:
+      #
+      #  class Money
+      #    include Comparable
+      #    attr_reader :amount, :currency
+      #    EXCHANGE_RATES = { "USD_TO_DKK" => 6 }
+      #
+      #    def initialize(amount, currency = "USD")
+      #      @amount, @currency = amount, currency
+      #    end
+      #
+      #    def exchange_to(other_currency)
+      #      exchanged_amount = (amount * EXCHANGE_RATES["#{currency}_TO_#{other_currency}"]).floor
+      #      Money.new(exchanged_amount, other_currency)
+      #    end
+      #
+      #    def ==(other_money)
+      #      amount == other_money.amount && currency == other_money.currency
+      #    end
+      #
+      #    def <=>(other_money)
+      #      if currency == other_money.currency
+      #        amount <=> other_money.amount
+      #      else
+      #        amount <=> other_money.exchange_to(currency).amount
+      #      end
+      #    end
+      #  end
+      #
+      #  class Address
+      #    attr_reader :street, :city
+      #    def initialize(street, city)
+      #      @street, @city = street, city
+      #    end
+      #
+      #    def close_to?(other_address)
+      #      city == other_address.city
+      #    end
+      #
+      #    def ==(other_address)
+      #      city == other_address.city && street == other_address.street
+      #    end
+      #  end
+      #
+      # Now it's possible to access attributes from the database through the value objects instead. If
+      # you choose to name the composition the same as the attribute's name, it will be the only way to
+      # access that attribute. That's the case with our +balance+ attribute. You interact with the value
+      # objects just like you would with any other attribute:
+      #
+      #   customer.balance = Money.new(20)     # sets the Money value object and the attribute
+      #   customer.balance                     # => Money value object
+      #   customer.balance.exchange_to("DKK")  # => Money.new(120, "DKK")
+      #   customer.balance > Money.new(10)     # => true
+      #   customer.balance == Money.new(20)    # => true
+      #   customer.balance < Money.new(5)      # => false
+      #
+      # Value objects can also be composed of multiple attributes, such as the case of Address. The order
+      # of the mappings will determine the order of the parameters.
+      #
+      #   customer.address_street = "Hyancintvej"
+      #   customer.address_city   = "Copenhagen"
+      #   customer.address        # => Address.new("Hyancintvej", "Copenhagen")
+      #
+      #   customer.address = Address.new("May Street", "Chicago")
+      #   customer.address_street # => "May Street"
+      #   customer.address_city   # => "Chicago"
+      #
+      # == Writing value objects
+      #
+      # Value objects are immutable and interchangeable objects that represent a given value, such as
+      # a Money object representing $5. Two Money objects both representing $5 should be equal (through
+      # methods such as <tt>==</tt> and <tt><=></tt> from Comparable if ranking makes sense). This is
+      # unlike entity objects where equality is determined by identity. An entity class such as Customer can
+      # easily have two different objects that both have an address on Hyancintvej. Entity identity is
+      # determined by object or relational unique identifiers (such as primary keys). Normal
+      # ActiveRecord::Base classes are entity objects.
+      #
+      # It's also important to treat the value objects as immutable. Don't allow the Money object to have
+      # its amount changed after creation. Create a new Money object with the new value instead. The
+      # <tt>Money#exchange_to</tt> method is an example of this. It returns a new value object instead of changing
+      # its own values. Active Record won't persist value objects that have been changed through means
+      # other than the writer method.
+      #
+      # The immutable requirement is enforced by Active Record by freezing any object assigned as a value
+      # object. Attempting to change it afterwards will result in a +RuntimeError+.
+      #
+      # Read more about value objects on http://c2.com/cgi/wiki?ValueObject and on the dangers of not
+      # keeping value objects immutable on http://c2.com/cgi/wiki?ValueObjectsShouldBeImmutable
+      #
+      # == Custom constructors and converters
+      #
+      # By default value objects are initialized by calling the <tt>new</tt> constructor of the value
+      # class passing each of the mapped attributes, in the order specified by the <tt>:mapping</tt>
+      # option, as arguments. If the value class doesn't support this convention then #composed_of allows
+      # a custom constructor to be specified.
+      #
+      # When a new value is assigned to the value object, the default assumption is that the new value
+      # is an instance of the value class. Specifying a custom converter allows the new value to be automatically
+      # converted to an instance of value class if necessary.
+      #
+      # For example, the +NetworkResource+ model has +network_address+ and +cidr_range+ attributes that should be
+      # aggregated using the +NetAddr::CIDR+ value class (http://www.rubydoc.info/gems/netaddr/1.5.0/NetAddr/CIDR).
+      # The constructor for the value class is called +create+ and it expects a CIDR address string as a parameter.
+      # New values can be assigned to the value object using either another +NetAddr::CIDR+ object, a string
+      # or an array. The <tt>:constructor</tt> and <tt>:converter</tt> options can be used to meet
+      # these requirements:
+      #
+      #   class NetworkResource < ActiveRecord::Base
+      #     composed_of :cidr,
+      #                 class_name: 'NetAddr::CIDR',
+      #                 mapping: [ %w(network_address network), %w(cidr_range bits) ],
+      #                 allow_nil: true,
+      #                 constructor: Proc.new { |network_address, cidr_range| NetAddr::CIDR.create("#{network_address}/#{cidr_range}") },
+      #                 converter: Proc.new { |value| NetAddr::CIDR.create(value.is_a?(Array) ? value.join('/') : value) }
+      #   end
+      #
+      #   # This calls the :constructor
+      #   network_resource = NetworkResource.new(network_address: '192.168.0.1', cidr_range: 24)
+      #
+      #   # These assignments will both use the :converter
+      #   network_resource.cidr = [ '192.168.2.1', 8 ]
+      #   network_resource.cidr = '192.168.0.1/24'
+      #
+      #   # This assignment won't use the :converter as the value is already an instance of the value class
+      #   network_resource.cidr = NetAddr::CIDR.create('192.168.2.1/8')
+      #
+      #   # Saving and then reloading will use the :constructor on reload
+      #   network_resource.save
+      #   network_resource.reload
+      #
+      # == Finding records by a value object
+      #
+      # Once a #composed_of relationship is specified for a model, records can be loaded from the database
+      # by specifying an instance of the value object in the conditions hash. The following example
+      # finds all customers with +address_street+ equal to "May Street" and +address_city+ equal to "Chicago":
+      #
+      #   Customer.where(address: Address.new("May Street", "Chicago"))
+      #
+      module ClassMethods
+        # Adds reader and writer methods for manipulating a value object:
+        # <tt>composed_of :address</tt> adds <tt>address</tt> and <tt>address=(new_address)</tt> methods.
+        #
+        # Options are:
+        # * <tt>:class_name</tt> - Specifies the class name of the association. Use it only if that name
+        #   can't be inferred from the part id. So <tt>composed_of :address</tt> will by default be linked
+        #   to the Address class, but if the real class name is +CompanyAddress+, you'll have to specify it
+        #   with this option.
+        # * <tt>:mapping</tt> - Specifies the mapping of entity attributes to attributes of the value
+        #   object. Each mapping is represented as an array where the first item is the name of the
+        #   entity attribute and the second item is the name of the attribute in the value object. The
+        #   order in which mappings are defined determines the order in which attributes are sent to the
+        #   value class constructor.
+        # * <tt>:allow_nil</tt> - Specifies that the value object will not be instantiated when all mapped
+        #   attributes are +nil+. Setting the value object to +nil+ has the effect of writing +nil+ to all
+        #   mapped attributes.
+        #   This defaults to +false+.
+        # * <tt>:constructor</tt> - A symbol specifying the name of the constructor method or a Proc that
+        #   is called to initialize the value object. The constructor is passed all of the mapped attributes,
+        #   in the order that they are defined in the <tt>:mapping option</tt>, as arguments and uses them
+        #   to instantiate a <tt>:class_name</tt> object.
+        #   The default is <tt>:new</tt>.
+        # * <tt>:converter</tt> - A symbol specifying the name of a class method of <tt>:class_name</tt>
+        #   or a Proc that is called when a new value is assigned to the value object. The converter is
+        #   passed the single value that is used in the assignment and is only called if the new value is
+        #   not an instance of <tt>:class_name</tt>. If <tt>:allow_nil</tt> is set to true, the converter
+        #   can return +nil+ to skip the assignment.
+        #
+        # Option examples:
+        #   composed_of :temperature, mapping: %w(reading celsius)
+        #   composed_of :balance, class_name: "Money", mapping: %w(balance amount)
+        #   composed_of :address, mapping: [ %w(address_street street), %w(address_city city) ]
+        #   composed_of :gps_location
+        #   composed_of :gps_location, allow_nil: true
+        #   composed_of :ip_address,
+        #               class_name: 'IPAddr',
+        #               mapping: %w(ip to_i),
+        #               constructor: Proc.new { |ip| IPAddr.new(ip, Socket::AF_INET) },
+        #               converter: Proc.new { |ip| ip.is_a?(Integer) ? IPAddr.new(ip, Socket::AF_INET) : IPAddr.new(ip.to_s) }
+        #
+        def composed_of(part_id, options = {})
+          options.assert_valid_keys(:class_name, :mapping, :allow_nil, :constructor, :converter)
 
-        name        = part_id.id2name
-        class_name  = options[:class_name]  || name.camelize
-        mapping     = options[:mapping]     || [ name, name ]
-        mapping     = [ mapping ] unless mapping.first.is_a?(Array)
-        allow_nil   = options[:allow_nil]   || false
-        constructor = options[:constructor] || :new
-        converter   = options[:converter]
+          unless self < Aggregations
+            include Aggregations
+          end
 
-        reader_method(name, class_name, mapping, allow_nil, constructor)
-        writer_method(name, class_name, mapping, allow_nil, converter)
+          name        = part_id.id2name
+          class_name  = options[:class_name]  || name.camelize
+          mapping     = options[:mapping]     || [ name, name ]
+          mapping     = [ mapping ] unless mapping.first.is_a?(Array)
+          allow_nil   = options[:allow_nil]   || false
+          constructor = options[:constructor] || :new
+          converter   = options[:converter]
 
-        reflection = ActiveRecord::Reflection.create(:composed_of, part_id, nil, options, self)
-        Reflection.add_aggregate_reflection self, part_id, reflection
-      end
+          reader_method(name, class_name, mapping, allow_nil, constructor)
+          writer_method(name, class_name, mapping, allow_nil, converter)
 
-      private
-        def reader_method(name, class_name, mapping, allow_nil, constructor)
-          define_method(name) do
-            if @aggregation_cache[name].nil? && (!allow_nil || mapping.any? {|key, _| !_read_attribute(key).nil? })
-              attrs = mapping.collect {|key, _| _read_attribute(key)}
-              object = constructor.respond_to?(:call) ?
-                constructor.call(*attrs) :
-                class_name.constantize.send(constructor, *attrs)
-              @aggregation_cache[name] = object
-            end
-            @aggregation_cache[name]
-          end
+          reflection = ActiveRecord::Reflection.create(:composed_of, part_id, nil, options, self)
+          Reflection.add_aggregate_reflection self, part_id, reflection
         end
 
-        def writer_method(name, class_name, mapping, allow_nil, converter)
-          define_method("#{name}=") do |part|
-            klass = class_name.constantize
-            if part.is_a?(Hash)
-              raise ArgumentError unless part.size == part.keys.max
-              part = klass.new(*part.sort.map(&:last))
+        private
+          def reader_method(name, class_name, mapping, allow_nil, constructor)
+            define_method(name) do
+              if @aggregation_cache[name].nil? && (!allow_nil || mapping.any? { |key, _| !_read_attribute(key).nil? })
+                attrs = mapping.collect { |key, _| _read_attribute(key) }
+                object = constructor.respond_to?(:call) ?
+                  constructor.call(*attrs) :
+                  class_name.constantize.send(constructor, *attrs)
+                @aggregation_cache[name] = object
+              end
+              @aggregation_cache[name]
             end
+          end
 
-            unless part.is_a?(klass) || converter.nil? || part.nil?
-              part = converter.respond_to?(:call) ? converter.call(part) : klass.send(converter, part)
-            end
+          def writer_method(name, class_name, mapping, allow_nil, converter)
+            define_method("#{name}=") do |part|
+              klass = class_name.constantize
 
-            if part.nil? && allow_nil
-              mapping.each { |key, _| self[key] = nil }
-              @aggregation_cache[name] = nil
-            else
-              mapping.each { |key, value| self[key] = part.send(value) }
-              @aggregation_cache[name] = part.freeze
+              unless part.is_a?(klass) || converter.nil? || part.nil?
+                part = converter.respond_to?(:call) ? converter.call(part) : klass.send(converter, part)
+              end
+
+              hash_from_multiparameter_assignment = part.is_a?(Hash) &&
+                part.each_key.all? { |k| k.is_a?(Integer) }
+              if hash_from_multiparameter_assignment
+                raise ArgumentError unless part.size == part.each_key.max
+                part = klass.new(*part.sort.map(&:last))
+              end
+
+              if part.nil? && allow_nil
+                mapping.each { |key, _| self[key] = nil }
+                @aggregation_cache[name] = nil
+              else
+                mapping.each { |key, value| self[key] = part.send(value) }
+                @aggregation_cache[name] = part.freeze
+              end
             end
           end
-        end
-    end
+      end
   end
 end
diff --git a/activerecord/lib/active_record/association_relation.rb b/activerecord/lib/active_record/association_relation.rb
index ee0bb8fafe..4c538ef2bd 100644
--- a/activerecord/lib/active_record/association_relation.rb
+++ b/activerecord/lib/active_record/association_relation.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class AssociationRelation < Relation
-    def initialize(klass, table, predicate_builder, association)
-      super(klass, table, predicate_builder)
+    def initialize(klass, association)
+      super(klass)
       @association = association
     end
 
@@ -10,7 +12,7 @@ module ActiveRecord
     end
 
     def ==(other)
-      other == to_a
+      other == records
     end
 
     def build(*args, &block)
@@ -28,8 +30,11 @@ module ActiveRecord
 
     private
 
-    def exec_queries
-      super.each { |r| @association.set_inverse_instance r }
-    end
+      def exec_queries
+        super do |record|
+          @association.set_inverse_instance_from_queries(record)
+          yield record if block_given?
+        end
+      end
   end
 end
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 82cb3fed59..fb1df00dc8 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1,99 +1,171 @@
-require 'active_support/core_ext/enumerable'
-require 'active_support/core_ext/string/conversions'
-require 'active_support/core_ext/module/remove_method'
-require 'active_record/errors'
+# frozen_string_literal: true
+
+require "active_support/core_ext/enumerable"
+require "active_support/core_ext/string/conversions"
+require "active_support/core_ext/module/remove_method"
+require "active_record/errors"
 
 module ActiveRecord
   class AssociationNotFoundError < ConfigurationError #:nodoc:
-    def initialize(record, association_name)
-      super("Association named '#{association_name}' was not found on #{record.class.name}; perhaps you misspelled it?")
+    def initialize(record = nil, association_name = nil)
+      if record && association_name
+        super("Association named '#{association_name}' was not found on #{record.class.name}; perhaps you misspelled it?")
+      else
+        super("Association was not found.")
+      end
     end
   end
 
   class InverseOfAssociationNotFoundError < ActiveRecordError #:nodoc:
-    def initialize(reflection, associated_class = nil)
-      super("Could not find the inverse association for #{reflection.name} (#{reflection.options[:inverse_of].inspect} in #{associated_class.nil? ? reflection.class_name : associated_class.name})")
+    def initialize(reflection = nil, associated_class = nil)
+      if reflection
+        super("Could not find the inverse association for #{reflection.name} (#{reflection.options[:inverse_of].inspect} in #{associated_class.nil? ? reflection.class_name : associated_class.name})")
+      else
+        super("Could not find the inverse association.")
+      end
     end
   end
 
   class HasManyThroughAssociationNotFoundError < ActiveRecordError #:nodoc:
-    def initialize(owner_class_name, reflection)
-      super("Could not find the association #{reflection.options[:through].inspect} in model #{owner_class_name}")
+    def initialize(owner_class_name = nil, reflection = nil)
+      if owner_class_name && reflection
+        super("Could not find the association #{reflection.options[:through].inspect} in model #{owner_class_name}")
+      else
+        super("Could not find the association.")
+      end
     end
   end
 
   class HasManyThroughAssociationPolymorphicSourceError < ActiveRecordError #:nodoc:
-    def initialize(owner_class_name, reflection, source_reflection)
-      super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' on the polymorphic object '#{source_reflection.class_name}##{source_reflection.name}' without 'source_type'. Try adding 'source_type: \"#{reflection.name.to_s.classify}\"' to 'has_many :through' definition.")
+    def initialize(owner_class_name = nil, reflection = nil, source_reflection = nil)
+      if owner_class_name && reflection && source_reflection
+        super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' on the polymorphic object '#{source_reflection.class_name}##{source_reflection.name}' without 'source_type'. Try adding 'source_type: \"#{reflection.name.to_s.classify}\"' to 'has_many :through' definition.")
+      else
+        super("Cannot have a has_many :through association.")
+      end
     end
   end
 
   class HasManyThroughAssociationPolymorphicThroughError < ActiveRecordError #:nodoc:
-    def initialize(owner_class_name, reflection)
-      super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.")
+    def initialize(owner_class_name = nil, reflection = nil)
+      if owner_class_name && reflection
+        super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.")
+      else
+        super("Cannot have a has_many :through association.")
+      end
     end
   end
 
   class HasManyThroughAssociationPointlessSourceTypeError < ActiveRecordError #:nodoc:
-    def initialize(owner_class_name, reflection, source_reflection)
-      super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' with a :source_type option if the '#{reflection.through_reflection.class_name}##{source_reflection.name}' is not polymorphic. Try removing :source_type on your association.")
+    def initialize(owner_class_name = nil, reflection = nil, source_reflection = nil)
+      if owner_class_name && reflection && source_reflection
+        super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' with a :source_type option if the '#{reflection.through_reflection.class_name}##{source_reflection.name}' is not polymorphic. Try removing :source_type on your association.")
+      else
+        super("Cannot have a has_many :through association.")
+      end
     end
   end
 
   class HasOneThroughCantAssociateThroughCollection < ActiveRecordError #:nodoc:
-    def initialize(owner_class_name, reflection, through_reflection)
-      super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' where the :through association '#{owner_class_name}##{through_reflection.name}' is a collection. Specify a has_one or belongs_to association in the :through option instead.")
+    def initialize(owner_class_name = nil, reflection = nil, through_reflection = nil)
+      if owner_class_name && reflection && through_reflection
+        super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' where the :through association '#{owner_class_name}##{through_reflection.name}' is a collection. Specify a has_one or belongs_to association in the :through option instead.")
+      else
+        super("Cannot have a has_one :through association.")
+      end
     end
   end
 
   class HasOneAssociationPolymorphicThroughError < ActiveRecordError #:nodoc:
-    def initialize(owner_class_name, reflection)
-      super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.")
+    def initialize(owner_class_name = nil, reflection = nil)
+      if owner_class_name && reflection
+        super("Cannot have a has_one :through association '#{owner_class_name}##{reflection.name}' which goes through the polymorphic association '#{owner_class_name}##{reflection.through_reflection.name}'.")
+      else
+        super("Cannot have a has_one :through association.")
+      end
     end
   end
 
   class HasManyThroughSourceAssociationNotFoundError < ActiveRecordError #:nodoc:
-    def initialize(reflection)
-      through_reflection      = reflection.through_reflection
-      source_reflection_names = reflection.source_reflection_names
-      source_associations     = reflection.through_reflection.klass._reflections.keys
-      super("Could not find the source association(s) #{source_reflection_names.collect(&:inspect).to_sentence(:two_words_connector => ' or ', :last_word_connector => ', or ', :locale => :en)} in model #{through_reflection.klass}. Try 'has_many #{reflection.name.inspect}, :through => #{through_reflection.name.inspect}, :source => <name>'. Is it one of #{source_associations.to_sentence(:two_words_connector => ' or ', :last_word_connector => ', or ', :locale => :en)}?")
+    def initialize(reflection = nil)
+      if reflection
+        through_reflection      = reflection.through_reflection
+        source_reflection_names = reflection.source_reflection_names
+        source_associations     = reflection.through_reflection.klass._reflections.keys
+        super("Could not find the source association(s) #{source_reflection_names.collect(&:inspect).to_sentence(two_words_connector: ' or ', last_word_connector: ', or ', locale: :en)} in model #{through_reflection.klass}. Try 'has_many #{reflection.name.inspect}, :through => #{through_reflection.name.inspect}, :source => <name>'. Is it one of #{source_associations.to_sentence(two_words_connector: ' or ', last_word_connector: ', or ', locale: :en)}?")
+      else
+        super("Could not find the source association(s).")
+      end
     end
   end
 
-  class HasManyThroughCantAssociateThroughHasOneOrManyReflection < ActiveRecordError #:nodoc:
-    def initialize(owner, reflection)
-      super("Cannot modify association '#{owner.class.name}##{reflection.name}' because the source reflection class '#{reflection.source_reflection.class_name}' is associated to '#{reflection.through_reflection.class_name}' via :#{reflection.source_reflection.macro}.")
+  class HasManyThroughOrderError < ActiveRecordError #:nodoc:
+    def initialize(owner_class_name = nil, reflection = nil, through_reflection = nil)
+      if owner_class_name && reflection && through_reflection
+        super("Cannot have a has_many :through association '#{owner_class_name}##{reflection.name}' which goes through '#{owner_class_name}##{through_reflection.name}' before the through association is defined.")
+      else
+        super("Cannot have a has_many :through association before the through association is defined.")
+      end
     end
   end
 
-  class HasManyThroughCantAssociateNewRecords < ActiveRecordError #:nodoc:
-    def initialize(owner, reflection)
-      super("Cannot associate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to create the has_many :through record associating them.")
+  class ThroughCantAssociateThroughHasOneOrManyReflection < ActiveRecordError #:nodoc:
+    def initialize(owner = nil, reflection = nil)
+      if owner && reflection
+        super("Cannot modify association '#{owner.class.name}##{reflection.name}' because the source reflection class '#{reflection.source_reflection.class_name}' is associated to '#{reflection.through_reflection.class_name}' via :#{reflection.source_reflection.macro}.")
+      else
+        super("Cannot modify association.")
+      end
     end
   end
 
-  class HasManyThroughCantDissociateNewRecords < ActiveRecordError #:nodoc:
-    def initialize(owner, reflection)
-      super("Cannot dissociate new records through '#{owner.class.name}##{reflection.name}' on '#{reflection.source_reflection.class_name rescue nil}##{reflection.source_reflection.name rescue nil}'. Both records must have an id in order to delete the has_many :through record associating them.")
+  class AmbiguousSourceReflectionForThroughAssociation < ActiveRecordError # :nodoc:
+    def initialize(klass, macro, association_name, options, possible_sources)
+      example_options = options.dup
+      example_options[:source] = possible_sources.first
+
+      super("Ambiguous source reflection for through association. Please " \
+            "specify a :source directive on your declaration like:\n" \
+            "\n" \
+            "  class #{klass} < ActiveRecord::Base\n" \
+            "    #{macro} :#{association_name}, #{example_options}\n" \
+            "  end"
+           )
     end
   end
 
-  class HasManyThroughNestedAssociationsAreReadonly < ActiveRecordError #:nodoc:
-    def initialize(owner, reflection)
-      super("Cannot modify association '#{owner.class.name}##{reflection.name}' because it goes through more than one other association.")
-    end
+  class HasManyThroughCantAssociateThroughHasOneOrManyReflection < ThroughCantAssociateThroughHasOneOrManyReflection #:nodoc:
+  end
+
+  class HasOneThroughCantAssociateThroughHasOneOrManyReflection < ThroughCantAssociateThroughHasOneOrManyReflection #:nodoc:
   end
 
-  class EagerLoadPolymorphicError < ActiveRecordError #:nodoc:
-    def initialize(reflection)
-      super("Cannot eagerly load the polymorphic association #{reflection.name.inspect}")
+  class ThroughNestedAssociationsAreReadonly < ActiveRecordError #:nodoc:
+    def initialize(owner = nil, reflection = nil)
+      if owner && reflection
+        super("Cannot modify association '#{owner.class.name}##{reflection.name}' because it goes through more than one other association.")
+      else
+        super("Through nested associations are read-only.")
+      end
     end
   end
 
-  class ReadOnlyAssociation < ActiveRecordError #:nodoc:
-    def initialize(reflection)
-      super("Cannot add to a has_many :through association. Try adding to #{reflection.through_reflection.name.inspect}.")
+  class HasManyThroughNestedAssociationsAreReadonly < ThroughNestedAssociationsAreReadonly #:nodoc:
+  end
+
+  class HasOneThroughNestedAssociationsAreReadonly < ThroughNestedAssociationsAreReadonly #:nodoc:
+  end
+
+  # This error is raised when trying to eager load a polymorphic association using a JOIN.
+  # Eager loading polymorphic associations is only possible with
+  # {ActiveRecord::Relation#preload}[rdoc-ref:QueryMethods#preload].
+  class EagerLoadPolymorphicError < ActiveRecordError
+    def initialize(reflection = nil)
+      if reflection
+        super("Cannot eagerly load the polymorphic association #{reflection.name.inspect}")
+      else
+        super("Eager load polymorphic error.")
+      end
     end
   end
 
@@ -101,8 +173,12 @@ module ActiveRecord
   # (has_many, has_one) when there is at least 1 child associated instance.
   # ex: if @project.tasks.size > 0, DeleteRestrictionError will be raised when trying to destroy @project
   class DeleteRestrictionError < ActiveRecordError #:nodoc:
-    def initialize(name)
-      super("Cannot delete record because of dependent #{name}")
+    def initialize(name = nil)
+      if name
+        super("Cannot delete record because of dependent #{name}")
+      else
+        super("Delete restriction error.")
+      end
     end
   end
 
@@ -118,33 +194,38 @@ module ActiveRecord
     autoload :CollectionAssociation
     autoload :ForeignAssociation
     autoload :CollectionProxy
-
-    autoload :BelongsToAssociation
-    autoload :BelongsToPolymorphicAssociation
-    autoload :HasManyAssociation
-    autoload :HasManyThroughAssociation
-    autoload :HasOneAssociation
-    autoload :HasOneThroughAssociation
     autoload :ThroughAssociation
 
     module Builder #:nodoc:
-      autoload :Association,           'active_record/associations/builder/association'
-      autoload :SingularAssociation,   'active_record/associations/builder/singular_association'
-      autoload :CollectionAssociation, 'active_record/associations/builder/collection_association'
+      autoload :Association,           "active_record/associations/builder/association"
+      autoload :SingularAssociation,   "active_record/associations/builder/singular_association"
+      autoload :CollectionAssociation, "active_record/associations/builder/collection_association"
 
-      autoload :BelongsTo,           'active_record/associations/builder/belongs_to'
-      autoload :HasOne,              'active_record/associations/builder/has_one'
-      autoload :HasMany,             'active_record/associations/builder/has_many'
-      autoload :HasAndBelongsToMany, 'active_record/associations/builder/has_and_belongs_to_many'
+      autoload :BelongsTo,           "active_record/associations/builder/belongs_to"
+      autoload :HasOne,              "active_record/associations/builder/has_one"
+      autoload :HasMany,             "active_record/associations/builder/has_many"
+      autoload :HasAndBelongsToMany, "active_record/associations/builder/has_and_belongs_to_many"
     end
 
     eager_autoload do
+      autoload :BelongsToAssociation
+      autoload :BelongsToPolymorphicAssociation
+      autoload :HasManyAssociation
+      autoload :HasManyThroughAssociation
+      autoload :HasOneAssociation
+      autoload :HasOneThroughAssociation
+
       autoload :Preloader
       autoload :JoinDependency
       autoload :AssociationScope
       autoload :AliasTracker
     end
 
+    def self.eager_load!
+      super
+      Preloader.eager_load!
+    end
+
     # Returns the association instance for the given name, instantiating it if it doesn't already exist
     def association(name) #:nodoc:
       association = association_instance_get(name)
@@ -160,7 +241,7 @@ module ActiveRecord
       association
     end
 
-    def association_cached?(name) # :nodoc
+    def association_cached?(name) # :nodoc:
       @association_cache.key?(name)
     end
 
@@ -176,16 +257,16 @@ module ActiveRecord
 
     private
       # Clears out the association cache.
-      def clear_association_cache # :nodoc:
+      def clear_association_cache
         @association_cache.clear if persisted?
       end
 
-      def init_internals # :nodoc:
+      def init_internals
         @association_cache = {}
         super
       end
 
-      # Returns the specified association instance if it exists, nil otherwise.
+      # Returns the specified association instance if it exists, +nil+ otherwise.
       def association_instance_get(name)
         @association_cache[name]
       end
@@ -195,1550 +276,1587 @@ module ActiveRecord
         @association_cache[name] = association
       end
 
-    # \Associations are a set of macro-like class methods for tying objects together through
-    # foreign keys. They express relationships like "Project has one Project Manager"
-    # or "Project belongs to a Portfolio". Each macro adds a number of methods to the
-    # class which are specialized according to the collection or association symbol and the
-    # options hash. It works much the same way as Ruby's own <tt>attr*</tt>
-    # methods.
-    #
-    #   class Project < ActiveRecord::Base
-    #     belongs_to              :portfolio
-    #     has_one                 :project_manager
-    #     has_many                :milestones
-    #     has_and_belongs_to_many :categories
-    #   end
-    #
-    # The project class now has the following methods (and more) to ease the traversal and
-    # manipulation of its relationships:
-    # * <tt>Project#portfolio, Project#portfolio=(portfolio), Project#portfolio.nil?</tt>
-    # * <tt>Project#project_manager, Project#project_manager=(project_manager), Project#project_manager.nil?,</tt>
-    # * <tt>Project#milestones.empty?, Project#milestones.size, Project#milestones, Project#milestones<<(milestone),</tt>
-    #   <tt>Project#milestones.delete(milestone), Project#milestones.destroy(milestone), Project#milestones.find(milestone_id),</tt>
-    #   <tt>Project#milestones.build, Project#milestones.create</tt>
-    # * <tt>Project#categories.empty?, Project#categories.size, Project#categories, Project#categories<<(category1),</tt>
-    #   <tt>Project#categories.delete(category1), Project#categories.destroy(category1)</tt>
-    #
-    # === A word of warning
-    #
-    # Don't create associations that have the same name as instance methods of
-    # <tt>ActiveRecord::Base</tt>. Since the association adds a method with that name to
-    # its model, it will override the inherited method and break things.
-    # For instance, +attributes+ and +connection+ would be bad choices for association names.
-    #
-    # == Auto-generated methods
-    # See also Instance Public methods below for more details.
-    #
-    # === Singular associations (one-to-one)
-    #                                     |            |  belongs_to  |
-    #   generated methods                 | belongs_to | :polymorphic | has_one
-    #   ----------------------------------+------------+--------------+---------
-    #   other(force_reload=false)         |     X      |      X       |    X
-    #   other=(other)                     |     X      |      X       |    X
-    #   build_other(attributes={})        |     X      |              |    X
-    #   create_other(attributes={})       |     X      |              |    X
-    #   create_other!(attributes={})      |     X      |              |    X
-    #
-    # ===Collection associations (one-to-many / many-to-many)
-    #                                     |       |          | has_many
-    #   generated methods                 | habtm | has_many | :through
-    #   ----------------------------------+-------+----------+----------
-    #   others(force_reload=false)        |   X   |    X     |    X
-    #   others=(other,other,...)          |   X   |    X     |    X
-    #   other_ids                         |   X   |    X     |    X
-    #   other_ids=(id,id,...)             |   X   |    X     |    X
-    #   others<<                          |   X   |    X     |    X
-    #   others.push                       |   X   |    X     |    X
-    #   others.concat                     |   X   |    X     |    X
-    #   others.build(attributes={})       |   X   |    X     |    X
-    #   others.create(attributes={})      |   X   |    X     |    X
-    #   others.create!(attributes={})     |   X   |    X     |    X
-    #   others.size                       |   X   |    X     |    X
-    #   others.length                     |   X   |    X     |    X
-    #   others.count                      |   X   |    X     |    X
-    #   others.sum(*args)                 |   X   |    X     |    X
-    #   others.empty?                     |   X   |    X     |    X
-    #   others.clear                      |   X   |    X     |    X
-    #   others.delete(other,other,...)    |   X   |    X     |    X
-    #   others.delete_all                 |   X   |    X     |    X
-    #   others.destroy(other,other,...)   |   X   |    X     |    X
-    #   others.destroy_all                |   X   |    X     |    X
-    #   others.find(*args)                |   X   |    X     |    X
-    #   others.exists?                    |   X   |    X     |    X
-    #   others.distinct                   |   X   |    X     |    X
-    #   others.reset                      |   X   |    X     |    X
-    #
-    # === Overriding generated methods
-    #
-    # Association methods are generated in a module that is included into the model class,
-    # which allows you to easily override with your own methods and call the original
-    # generated method with +super+. For example:
-    #
-    #   class Car < ActiveRecord::Base
-    #     belongs_to :owner
-    #     belongs_to :old_owner
-    #     def owner=(new_owner)
-    #       self.old_owner = self.owner
-    #       super
-    #     end
-    #   end
-    #
-    # If your model class is <tt>Project</tt>, the module is
-    # named <tt>Project::GeneratedAssociationMethods</tt>. The GeneratedAssociationMethods module is
-    # included in the model class immediately after the (anonymous) generated attributes methods
-    # module, meaning an association will override the methods for an attribute with the same name.
-    #
-    # == Cardinality and associations
-    #
-    # Active Record associations can be used to describe one-to-one, one-to-many and many-to-many
-    # relationships between models. Each model uses an association to describe its role in
-    # the relation. The +belongs_to+ association is always used in the model that has
-    # the foreign key.
-    #
-    # === One-to-one
-    #
-    # Use +has_one+ in the base, and +belongs_to+ in the associated model.
-    #
-    #   class Employee < ActiveRecord::Base
-    #     has_one :office
-    #   end
-    #   class Office < ActiveRecord::Base
-    #     belongs_to :employee    # foreign key - employee_id
-    #   end
-    #
-    # === One-to-many
-    #
-    # Use +has_many+ in the base, and +belongs_to+ in the associated model.
-    #
-    #   class Manager < ActiveRecord::Base
-    #     has_many :employees
-    #   end
-    #   class Employee < ActiveRecord::Base
-    #     belongs_to :manager     # foreign key - manager_id
-    #   end
-    #
-    # === Many-to-many
-    #
-    # There are two ways to build a many-to-many relationship.
-    #
-    # The first way uses a +has_many+ association with the <tt>:through</tt> option and a join model, so
-    # there are two stages of associations.
-    #
-    #   class Assignment < ActiveRecord::Base
-    #     belongs_to :programmer  # foreign key - programmer_id
-    #     belongs_to :project     # foreign key - project_id
-    #   end
-    #   class Programmer < ActiveRecord::Base
-    #     has_many :assignments
-    #     has_many :projects, through: :assignments
-    #   end
-    #   class Project < ActiveRecord::Base
-    #     has_many :assignments
-    #     has_many :programmers, through: :assignments
-    #   end
-    #
-    # For the second way, use +has_and_belongs_to_many+ in both models. This requires a join table
-    # that has no corresponding model or primary key.
-    #
-    #   class Programmer < ActiveRecord::Base
-    #     has_and_belongs_to_many :projects       # foreign keys in the join table
-    #   end
-    #   class Project < ActiveRecord::Base
-    #     has_and_belongs_to_many :programmers    # foreign keys in the join table
-    #   end
-    #
-    # Choosing which way to build a many-to-many relationship is not always simple.
-    # If you need to work with the relationship model as its own entity,
-    # use <tt>has_many :through</tt>. Use +has_and_belongs_to_many+ when working with legacy schemas or when
-    # you never work directly with the relationship itself.
-    #
-    # == Is it a +belongs_to+ or +has_one+ association?
-    #
-    # Both express a 1-1 relationship. The difference is mostly where to place the foreign
-    # key, which goes on the table for the class declaring the +belongs_to+ relationship.
-    #
-    #   class User < ActiveRecord::Base
-    #     # I reference an account.
-    #     belongs_to :account
-    #   end
-    #
-    #   class Account < ActiveRecord::Base
-    #     # One user references me.
-    #     has_one :user
-    #   end
-    #
-    # The tables for these classes could look something like:
-    #
-    #   CREATE TABLE users (
-    #     id int(11) NOT NULL auto_increment,
-    #     account_id int(11) default NULL,
-    #     name varchar default NULL,
-    #     PRIMARY KEY  (id)
-    #   )
-    #
-    #   CREATE TABLE accounts (
-    #     id int(11) NOT NULL auto_increment,
-    #     name varchar default NULL,
-    #     PRIMARY KEY  (id)
-    #   )
-    #
-    # == Unsaved objects and associations
-    #
-    # You can manipulate objects and associations before they are saved to the database, but
-    # there is some special behavior you should be aware of, mostly involving the saving of
-    # associated objects.
-    #
-    # You can set the <tt>:autosave</tt> option on a <tt>has_one</tt>, <tt>belongs_to</tt>,
-    # <tt>has_many</tt>, or <tt>has_and_belongs_to_many</tt> association. Setting it
-    # to +true+ will _always_ save the members, whereas setting it to +false+ will
-    # _never_ save the members. More details about <tt>:autosave</tt> option is available at
-    # AutosaveAssociation.
-    #
-    # === One-to-one associations
-    #
-    # * Assigning an object to a +has_one+ association automatically saves that object and
-    #   the object being replaced (if there is one), in order to update their foreign
-    #   keys - except if the parent object is unsaved (<tt>new_record? == true</tt>).
-    # * If either of these saves fail (due to one of the objects being invalid), an
-    #   <tt>ActiveRecord::RecordNotSaved</tt> exception is raised and the assignment is
-    #   cancelled.
-    # * If you wish to assign an object to a +has_one+ association without saving it,
-    #   use the <tt>build_association</tt> method (documented below). The object being
-    #   replaced will still be saved to update its foreign key.
-    # * Assigning an object to a +belongs_to+ association does not save the object, since
-    #   the foreign key field belongs on the parent. It does not save the parent either.
-    #
-    # === Collections
-    #
-    # * Adding an object to a collection (+has_many+ or +has_and_belongs_to_many+) automatically
-    #   saves that object, except if the parent object (the owner of the collection) is not yet
-    #   stored in the database.
-    # * If saving any of the objects being added to a collection (via <tt>push</tt> or similar)
-    #   fails, then <tt>push</tt> returns +false+.
-    # * If saving fails while replacing the collection (via <tt>association=</tt>), an
-    #   <tt>ActiveRecord::RecordNotSaved</tt> exception is raised and the assignment is
-    #   cancelled.
-    # * You can add an object to a collection without automatically saving it by using the
-    #   <tt>collection.build</tt> method (documented below).
-    # * All unsaved (<tt>new_record? == true</tt>) members of the collection are automatically
-    #   saved when the parent is saved.
-    #
-    # == Customizing the query
-    #
-    # \Associations are built from <tt>Relation</tt>s, and you can use the <tt>Relation</tt> syntax
-    # to customize them. For example, to add a condition:
-    #
-    #   class Blog < ActiveRecord::Base
-    #     has_many :published_posts, -> { where published: true }, class_name: 'Post'
-    #   end
-    #
-    # Inside the <tt>-> { ... }</tt> block you can use all of the usual <tt>Relation</tt> methods.
-    #
-    # === Accessing the owner object
-    #
-    # Sometimes it is useful to have access to the owner object when building the query. The owner
-    # is passed as a parameter to the block. For example, the following association would find all
-    # events that occur on the user's birthday:
-    #
-    #   class User < ActiveRecord::Base
-    #     has_many :birthday_events, ->(user) { where starts_on: user.birthday }, class_name: 'Event'
-    #   end
-    #
-    # Note: Joining, eager loading and preloading of these associations is not fully possible.
-    # These operations happen before instance creation and the scope will be called with a +nil+ argument.
-    # This can lead to unexpected behavior and is deprecated.
-    #
-    # == Association callbacks
-    #
-    # Similar to the normal callbacks that hook into the life cycle of an Active Record object,
-    # you can also define callbacks that get triggered when you add an object to or remove an
-    # object from an association collection.
-    #
-    #   class Project
-    #     has_and_belongs_to_many :developers, after_add: :evaluate_velocity
-    #
-    #     def evaluate_velocity(developer)
-    #       ...
-    #     end
-    #   end
-    #
-    # It's possible to stack callbacks by passing them as an array. Example:
-    #
-    #   class Project
-    #     has_and_belongs_to_many :developers,
-    #                             after_add: [:evaluate_velocity, Proc.new { |p, d| p.shipping_date = Time.now}]
-    #   end
-    #
-    # Possible callbacks are: +before_add+, +after_add+, +before_remove+ and +after_remove+.
-    #
-    # If any of the +before_add+ callbacks throw an exception, the object will not be
-    # added to the collection.
-    #
-    # Similarly, if any of the +before_remove+ callbacks throw an exception, the object
-    # will not be removed from the collection.
-    #
-    # == Association extensions
-    #
-    # The proxy objects that control the access to associations can be extended through anonymous
-    # modules. This is especially beneficial for adding new finders, creators, and other
-    # factory-type methods that are only used as part of this association.
-    #
-    #   class Account < ActiveRecord::Base
-    #     has_many :people do
-    #       def find_or_create_by_name(name)
-    #         first_name, last_name = name.split(" ", 2)
-    #         find_or_create_by(first_name: first_name, last_name: last_name)
-    #       end
-    #     end
-    #   end
-    #
-    #   person = Account.first.people.find_or_create_by_name("David Heinemeier Hansson")
-    #   person.first_name # => "David"
-    #   person.last_name  # => "Heinemeier Hansson"
-    #
-    # If you need to share the same extensions between many associations, you can use a named
-    # extension module.
-    #
-    #   module FindOrCreateByNameExtension
-    #     def find_or_create_by_name(name)
-    #       first_name, last_name = name.split(" ", 2)
-    #       find_or_create_by(first_name: first_name, last_name: last_name)
-    #     end
-    #   end
-    #
-    #   class Account < ActiveRecord::Base
-    #     has_many :people, -> { extending FindOrCreateByNameExtension }
-    #   end
-    #
-    #   class Company < ActiveRecord::Base
-    #     has_many :people, -> { extending FindOrCreateByNameExtension }
-    #   end
-    #
-    # Some extensions can only be made to work with knowledge of the association's internals.
-    # Extensions can access relevant state using the following methods (where +items+ is the
-    # name of the association):
-    #
-    # * <tt>record.association(:items).owner</tt> - Returns the object the association is part of.
-    # * <tt>record.association(:items).reflection</tt> - Returns the reflection object that describes the association.
-    # * <tt>record.association(:items).target</tt> - Returns the associated object for +belongs_to+ and +has_one+, or
-    #   the collection of associated objects for +has_many+ and +has_and_belongs_to_many+.
-    #
-    # However, inside the actual extension code, you will not have access to the <tt>record</tt> as
-    # above. In this case, you can access <tt>proxy_association</tt>. For example,
-    # <tt>record.association(:items)</tt> and <tt>record.items.proxy_association</tt> will return
-    # the same object, allowing you to make calls like <tt>proxy_association.owner</tt> inside
-    # association extensions.
-    #
-    # == Association Join Models
-    #
-    # Has Many associations can be configured with the <tt>:through</tt> option to use an
-    # explicit join model to retrieve the data. This operates similarly to a
-    # +has_and_belongs_to_many+ association. The advantage is that you're able to add validations,
-    # callbacks, and extra attributes on the join model. Consider the following schema:
-    #
-    #   class Author < ActiveRecord::Base
-    #     has_many :authorships
-    #     has_many :books, through: :authorships
-    #   end
-    #
-    #   class Authorship < ActiveRecord::Base
-    #     belongs_to :author
-    #     belongs_to :book
-    #   end
-    #
-    #   @author = Author.first
-    #   @author.authorships.collect { |a| a.book } # selects all books that the author's authorships belong to
-    #   @author.books                              # selects all books by using the Authorship join model
-    #
-    # You can also go through a +has_many+ association on the join model:
-    #
-    #   class Firm < ActiveRecord::Base
-    #     has_many   :clients
-    #     has_many   :invoices, through: :clients
-    #   end
-    #
-    #   class Client < ActiveRecord::Base
-    #     belongs_to :firm
-    #     has_many   :invoices
-    #   end
-    #
-    #   class Invoice < ActiveRecord::Base
-    #     belongs_to :client
-    #   end
-    #
-    #   @firm = Firm.first
-    #   @firm.clients.flat_map { |c| c.invoices } # select all invoices for all clients of the firm
-    #   @firm.invoices                            # selects all invoices by going through the Client join model
-    #
-    # Similarly you can go through a +has_one+ association on the join model:
-    #
-    #   class Group < ActiveRecord::Base
-    #     has_many   :users
-    #     has_many   :avatars, through: :users
-    #   end
-    #
-    #   class User < ActiveRecord::Base
-    #     belongs_to :group
-    #     has_one    :avatar
-    #   end
-    #
-    #   class Avatar < ActiveRecord::Base
-    #     belongs_to :user
-    #   end
-    #
-    #   @group = Group.first
-    #   @group.users.collect { |u| u.avatar }.compact # select all avatars for all users in the group
-    #   @group.avatars                                # selects all avatars by going through the User join model.
-    #
-    # An important caveat with going through +has_one+ or +has_many+ associations on the
-    # join model is that these associations are *read-only*. For example, the following
-    # would not work following the previous example:
-    #
-    #   @group.avatars << Avatar.new   # this would work if User belonged_to Avatar rather than the other way around
-    #   @group.avatars.delete(@group.avatars.last)  # so would this
-    #
-    # == Setting Inverses
-    #
-    # If you are using a +belongs_to+ on the join model, it is a good idea to set the
-    # <tt>:inverse_of</tt> option on the +belongs_to+, which will mean that the following example
-    # works correctly (where <tt>tags</tt> is a +has_many+ <tt>:through</tt> association):
-    #
-    #   @post = Post.first
-    #   @tag = @post.tags.build name: "ruby"
-    #   @tag.save
-    #
-    # The last line ought to save the through record (a <tt>Taggable</tt>). This will only work if the
-    # <tt>:inverse_of</tt> is set:
-    #
-    #   class Taggable < ActiveRecord::Base
-    #     belongs_to :post
-    #     belongs_to :tag, inverse_of: :taggings
-    #   end
-    #
-    # If you do not set the <tt>:inverse_of</tt> record, the association will
-    # do its best to match itself up with the correct inverse. Automatic
-    # inverse detection only works on <tt>has_many</tt>, <tt>has_one</tt>, and
-    # <tt>belongs_to</tt> associations.
-    #
-    # Extra options on the associations, as defined in the
-    # <tt>AssociationReflection::INVALID_AUTOMATIC_INVERSE_OPTIONS</tt> constant, will
-    # also prevent the association's inverse from being found automatically.
-    #
-    # The automatic guessing of the inverse association uses a heuristic based
-    # on the name of the class, so it may not work for all associations,
-    # especially the ones with non-standard names.
-    #
-    # You can turn off the automatic detection of inverse associations by setting
-    # the <tt>:inverse_of</tt> option to <tt>false</tt> like so:
-    #
-    #   class Taggable < ActiveRecord::Base
-    #     belongs_to :tag, inverse_of: false
-    #   end
-    #
-    # == Nested \Associations
-    #
-    # You can actually specify *any* association with the <tt>:through</tt> option, including an
-    # association which has a <tt>:through</tt> option itself. For example:
-    #
-    #   class Author < ActiveRecord::Base
-    #     has_many :posts
-    #     has_many :comments, through: :posts
-    #     has_many :commenters, through: :comments
-    #   end
-    #
-    #   class Post < ActiveRecord::Base
-    #     has_many :comments
-    #   end
-    #
-    #   class Comment < ActiveRecord::Base
-    #     belongs_to :commenter
-    #   end
-    #
-    #   @author = Author.first
-    #   @author.commenters # => People who commented on posts written by the author
-    #
-    # An equivalent way of setting up this association this would be:
-    #
-    #   class Author < ActiveRecord::Base
-    #     has_many :posts
-    #     has_many :commenters, through: :posts
-    #   end
-    #
-    #   class Post < ActiveRecord::Base
-    #     has_many :comments
-    #     has_many :commenters, through: :comments
-    #   end
-    #
-    #   class Comment < ActiveRecord::Base
-    #     belongs_to :commenter
-    #   end
-    #
-    # When using a nested association, you will not be able to modify the association because there
-    # is not enough information to know what modification to make. For example, if you tried to
-    # add a <tt>Commenter</tt> in the example above, there would be no way to tell how to set up the
-    # intermediate <tt>Post</tt> and <tt>Comment</tt> objects.
-    #
-    # == Polymorphic \Associations
-    #
-    # Polymorphic associations on models are not restricted on what types of models they
-    # can be associated with. Rather, they specify an interface that a +has_many+ association
-    # must adhere to.
-    #
-    #   class Asset < ActiveRecord::Base
-    #     belongs_to :attachable, polymorphic: true
-    #   end
-    #
-    #   class Post < ActiveRecord::Base
-    #     has_many :assets, as: :attachable         # The :as option specifies the polymorphic interface to use.
-    #   end
-    #
-    #   @asset.attachable = @post
-    #
-    # This works by using a type column in addition to a foreign key to specify the associated
-    # record. In the Asset example, you'd need an +attachable_id+ integer column and an
-    # +attachable_type+ string column.
-    #
-    # Using polymorphic associations in combination with single table inheritance (STI) is
-    # a little tricky. In order for the associations to work as expected, ensure that you
-    # store the base model for the STI models in the type column of the polymorphic
-    # association. To continue with the asset example above, suppose there are guest posts
-    # and member posts that use the posts table for STI. In this case, there must be a +type+
-    # column in the posts table.
-    #
-    # Note: The <tt>attachable_type=</tt> method is being called when assigning an +attachable+.
-    # The +class_name+ of the +attachable+ is passed as a String.
-    #
-    #   class Asset < ActiveRecord::Base
-    #     belongs_to :attachable, polymorphic: true
-    #
-    #     def attachable_type=(class_name)
-    #        super(class_name.constantize.base_class.to_s)
-    #     end
-    #   end
-    #
-    #   class Post < ActiveRecord::Base
-    #     # because we store "Post" in attachable_type now dependent: :destroy will work
-    #     has_many :assets, as: :attachable, dependent: :destroy
-    #   end
-    #
-    #   class GuestPost < Post
-    #   end
-    #
-    #   class MemberPost < Post
-    #   end
-    #
-    # == Caching
-    #
-    # All of the methods are built on a simple caching principle that will keep the result
-    # of the last query around unless specifically instructed not to. The cache is even
-    # shared across methods to make it even cheaper to use the macro-added methods without
-    # worrying too much about performance at the first go.
-    #
-    #   project.milestones             # fetches milestones from the database
-    #   project.milestones.size        # uses the milestone cache
-    #   project.milestones.empty?      # uses the milestone cache
-    #   project.milestones(true).size  # fetches milestones from the database
-    #   project.milestones             # uses the milestone cache
-    #
-    # == Eager loading of associations
-    #
-    # Eager loading is a way to find objects of a certain class and a number of named associations.
-    # It is one of the easiest ways to prevent the dreaded N+1 problem in which fetching 100
-    # posts that each need to display their author triggers 101 database queries. Through the
-    # use of eager loading, the number of queries will be reduced from 101 to 2.
-    #
-    #   class Post < ActiveRecord::Base
-    #     belongs_to :author
-    #     has_many   :comments
-    #   end
-    #
-    # Consider the following loop using the class above:
-    #
-    #   Post.all.each do |post|
-    #     puts "Post:            " + post.title
-    #     puts "Written by:      " + post.author.name
-    #     puts "Last comment on: " + post.comments.first.created_on
-    #   end
-    #
-    # To iterate over these one hundred posts, we'll generate 201 database queries. Let's
-    # first just optimize it for retrieving the author:
-    #
-    #   Post.includes(:author).each do |post|
-    #
-    # This references the name of the +belongs_to+ association that also used the <tt>:author</tt>
-    # symbol. After loading the posts, find will collect the +author_id+ from each one and load
-    # all the referenced authors with one query. Doing so will cut down the number of queries
-    # from 201 to 102.
-    #
-    # We can improve upon the situation further by referencing both associations in the finder with:
-    #
-    #   Post.includes(:author, :comments).each do |post|
-    #
-    # This will load all comments with a single query. This reduces the total number of queries
-    # to 3. In general, the number of queries will be 1 plus the number of associations
-    # named (except if some of the associations are polymorphic +belongs_to+ - see below).
-    #
-    # To include a deep hierarchy of associations, use a hash:
-    #
-    #   Post.includes(:author, { comments: { author: :gravatar } }).each do |post|
-    #
-    # The above code will load all the comments and all of their associated
-    # authors and gravatars. You can mix and match any combination of symbols,
-    # arrays, and hashes to retrieve the associations you want to load.
-    #
-    # All of this power shouldn't fool you into thinking that you can pull out huge amounts
-    # of data with no performance penalty just because you've reduced the number of queries.
-    # The database still needs to send all the data to Active Record and it still needs to
-    # be processed. So it's no catch-all for performance problems, but it's a great way to
-    # cut down on the number of queries in a situation as the one described above.
-    #
-    # Since only one table is loaded at a time, conditions or orders cannot reference tables
-    # other than the main one. If this is the case, Active Record falls back to the previously
-    # used LEFT OUTER JOIN based strategy. For example:
-    #
-    #   Post.includes([:author, :comments]).where(['comments.approved = ?', true])
-    #
-    # This will result in a single SQL query with joins along the lines of:
-    # <tt>LEFT OUTER JOIN comments ON comments.post_id = posts.id</tt> and
-    # <tt>LEFT OUTER JOIN authors ON authors.id = posts.author_id</tt>. Note that using conditions
-    # like this can have unintended consequences.
-    # In the above example posts with no approved comments are not returned at all, because
-    # the conditions apply to the SQL statement as a whole and not just to the association.
-    #
-    # You must disambiguate column references for this fallback to happen, for example
-    # <tt>order: "author.name DESC"</tt> will work but <tt>order: "name DESC"</tt> will not.
-    #
-    # If you want to load all posts (including posts with no approved comments) then write
-    # your own LEFT OUTER JOIN query using ON
-    #
-    #   Post.joins("LEFT OUTER JOIN comments ON comments.post_id = posts.id AND comments.approved = '1'")
-    #
-    # In this case it is usually more natural to include an association which has conditions defined on it:
-    #
-    #   class Post < ActiveRecord::Base
-    #     has_many :approved_comments, -> { where approved: true }, class_name: 'Comment'
-    #   end
-    #
-    #   Post.includes(:approved_comments)
-    #
-    # This will load posts and eager load the +approved_comments+ association, which contains
-    # only those comments that have been approved.
-    #
-    # If you eager load an association with a specified <tt>:limit</tt> option, it will be ignored,
-    # returning all the associated objects:
-    #
-    #   class Picture < ActiveRecord::Base
-    #     has_many :most_recent_comments, -> { order('id DESC').limit(10) }, class_name: 'Comment'
-    #   end
-    #
-    #   Picture.includes(:most_recent_comments).first.most_recent_comments # => returns all associated comments.
-    #
-    # Eager loading is supported with polymorphic associations.
-    #
-    #   class Address < ActiveRecord::Base
-    #     belongs_to :addressable, polymorphic: true
-    #   end
-    #
-    # A call that tries to eager load the addressable model
-    #
-    #   Address.includes(:addressable)
-    #
-    # This will execute one query to load the addresses and load the addressables with one
-    # query per addressable type.
-    # For example if all the addressables are either of class Person or Company then a total
-    # of 3 queries will be executed. The list of addressable types to load is determined on
-    # the back of the addresses loaded. This is not supported if Active Record has to fallback
-    # to the previous implementation of eager loading and will raise <tt>ActiveRecord::EagerLoadPolymorphicError</tt>.
-    # The reason is that the parent model's type is a column value so its corresponding table
-    # name cannot be put in the +FROM+/+JOIN+ clauses of that query.
-    #
-    # == Table Aliasing
-    #
-    # Active Record uses table aliasing in the case that a table is referenced multiple times
-    # in a join. If a table is referenced only once, the standard table name is used. The
-    # second time, the table is aliased as <tt>#{reflection_name}_#{parent_table_name}</tt>.
-    # Indexes are appended for any more successive uses of the table name.
-    #
-    #   Post.joins(:comments)
-    #   # => SELECT ... FROM posts INNER JOIN comments ON ...
-    #   Post.joins(:special_comments) # STI
-    #   # => SELECT ... FROM posts INNER JOIN comments ON ... AND comments.type = 'SpecialComment'
-    #   Post.joins(:comments, :special_comments) # special_comments is the reflection name, posts is the parent table name
-    #   # => SELECT ... FROM posts INNER JOIN comments ON ... INNER JOIN comments special_comments_posts
-    #
-    # Acts as tree example:
-    #
-    #   TreeMixin.joins(:children)
-    #   # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
-    #   TreeMixin.joins(children: :parent)
-    #   # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
-    #                               INNER JOIN parents_mixins ...
-    #   TreeMixin.joins(children: {parent: :children})
-    #   # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
-    #                               INNER JOIN parents_mixins ...
-    #                               INNER JOIN mixins childrens_mixins_2
-    #
-    # Has and Belongs to Many join tables use the same idea, but add a <tt>_join</tt> suffix:
-    #
-    #   Post.joins(:categories)
-    #   # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
-    #   Post.joins(categories: :posts)
-    #   # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
-    #                              INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories
-    #   Post.joins(categories: {posts: :categories})
-    #   # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
-    #                              INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories
-    #                              INNER JOIN categories_posts categories_posts_join INNER JOIN categories categories_posts_2
-    #
-    # If you wish to specify your own custom joins using <tt>joins</tt> method, those table
-    # names will take precedence over the eager associations:
-    #
-    #   Post.joins(:comments).joins("inner join comments ...")
-    #   # => SELECT ... FROM posts INNER JOIN comments_posts ON ... INNER JOIN comments ...
-    #   Post.joins(:comments, :special_comments).joins("inner join comments ...")
-    #   # => SELECT ... FROM posts INNER JOIN comments comments_posts ON ...
-    #                              INNER JOIN comments special_comments_posts ...
-    #                              INNER JOIN comments ...
-    #
-    # Table aliases are automatically truncated according to the maximum length of table identifiers
-    # according to the specific database.
-    #
-    # == Modules
-    #
-    # By default, associations will look for objects within the current module scope. Consider:
-    #
-    #   module MyApplication
-    #     module Business
-    #       class Firm < ActiveRecord::Base
-    #         has_many :clients
-    #       end
-    #
-    #       class Client < ActiveRecord::Base; end
-    #     end
-    #   end
-    #
-    # When <tt>Firm#clients</tt> is called, it will in turn call
-    # <tt>MyApplication::Business::Client.find_all_by_firm_id(firm.id)</tt>.
-    # If you want to associate with a class in another module scope, this can be done by
-    # specifying the complete class name.
-    #
-    #   module MyApplication
-    #     module Business
-    #       class Firm < ActiveRecord::Base; end
-    #     end
-    #
-    #     module Billing
-    #       class Account < ActiveRecord::Base
-    #         belongs_to :firm, class_name: "MyApplication::Business::Firm"
-    #       end
-    #     end
-    #   end
-    #
-    # == Bi-directional associations
-    #
-    # When you specify an association there is usually an association on the associated model
-    # that specifies the same relationship in reverse. For example, with the following models:
-    #
-    #    class Dungeon < ActiveRecord::Base
-    #      has_many :traps
-    #      has_one :evil_wizard
-    #    end
-    #
-    #    class Trap < ActiveRecord::Base
-    #      belongs_to :dungeon
-    #    end
-    #
-    #    class EvilWizard < ActiveRecord::Base
-    #      belongs_to :dungeon
-    #    end
-    #
-    # The +traps+ association on +Dungeon+ and the +dungeon+ association on +Trap+ are
-    # the inverse of each other and the inverse of the +dungeon+ association on +EvilWizard+
-    # is the +evil_wizard+ association on +Dungeon+ (and vice-versa). By default,
-    # Active Record can guess the inverse of the association based on the name
-    # of the class. The result is the following:
-    #
-    #    d = Dungeon.first
-    #    t = d.traps.first
-    #    d.object_id == t.dungeon.object_id # => true
-    #
-    # The +Dungeon+ instances +d+ and <tt>t.dungeon</tt> in the above example refer to
-    # the same in-memory instance since the association matches the name of the class.
-    # The result would be the same if we added +:inverse_of+ to our model definitions:
-    #
-    #    class Dungeon < ActiveRecord::Base
-    #      has_many :traps, inverse_of: :dungeon
-    #      has_one :evil_wizard, inverse_of: :dungeon
-    #    end
-    #
-    #    class Trap < ActiveRecord::Base
-    #      belongs_to :dungeon, inverse_of: :traps
-    #    end
-    #
-    #    class EvilWizard < ActiveRecord::Base
-    #      belongs_to :dungeon, inverse_of: :evil_wizard
-    #    end
-    #
-    # There are limitations to <tt>:inverse_of</tt> support:
-    #
-    # * does not work with <tt>:through</tt> associations.
-    # * does not work with <tt>:polymorphic</tt> associations.
-    # * for +belongs_to+ associations +has_many+ inverse associations are ignored.
-    #
-    # For more information, see the documentation for the +:inverse_of+ option.
-    #
-    # == Deleting from associations
-    #
-    # === Dependent associations
-    #
-    # +has_many+, +has_one+ and +belongs_to+ associations support the <tt>:dependent</tt> option.
-    # This allows you to specify that associated records should be deleted when the owner is
-    # deleted.
-    #
-    # For example:
-    #
-    #     class Author
-    #       has_many :posts, dependent: :destroy
-    #     end
-    #     Author.find(1).destroy # => Will destroy all of the author's posts, too
-    #
-    # The <tt>:dependent</tt> option can have different values which specify how the deletion
-    # is done. For more information, see the documentation for this option on the different
-    # specific association types. When no option is given, the behavior is to do nothing
-    # with the associated records when destroying a record.
-    #
-    # Note that <tt>:dependent</tt> is implemented using Rails' callback
-    # system, which works by processing callbacks in order. Therefore, other
-    # callbacks declared either before or after the <tt>:dependent</tt> option
-    # can affect what it does.
-    #
-    # Note that <tt>:dependent</tt> option is ignored for +has_one+ <tt>:through</tt> associations.
-    #
-    # === Delete or destroy?
-    #
-    # +has_many+ and +has_and_belongs_to_many+ associations have the methods <tt>destroy</tt>,
-    # <tt>delete</tt>, <tt>destroy_all</tt> and <tt>delete_all</tt>.
-    #
-    # For +has_and_belongs_to_many+, <tt>delete</tt> and <tt>destroy</tt> are the same: they
-    # cause the records in the join table to be removed.
-    #
-    # For +has_many+, <tt>destroy</tt> and <tt>destroy_all</tt> will always call the <tt>destroy</tt> method of the
-    # record(s) being removed so that callbacks are run. However <tt>delete</tt> and <tt>delete_all</tt> will either
-    # do the deletion according to the strategy specified by the <tt>:dependent</tt> option, or
-    # if no <tt>:dependent</tt> option is given, then it will follow the default strategy.
-    # The default strategy is to do nothing (leave the foreign keys with the parent ids set), except for
-    # +has_many+ <tt>:through</tt>, where the default strategy is <tt>delete_all</tt> (delete
-    # the join records, without running their callbacks).
-    #
-    # There is also a <tt>clear</tt> method which is the same as <tt>delete_all</tt>, except that
-    # it returns the association rather than the records which have been deleted.
-    #
-    # === What gets deleted?
-    #
-    # There is a potential pitfall here: +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt>
-    # associations have records in join tables, as well as the associated records. So when we
-    # call one of these deletion methods, what exactly should be deleted?
-    #
-    # The answer is that it is assumed that deletion on an association is about removing the
-    # <i>link</i> between the owner and the associated object(s), rather than necessarily the
-    # associated objects themselves. So with +has_and_belongs_to_many+ and +has_many+
-    # <tt>:through</tt>, the join records will be deleted, but the associated records won't.
-    #
-    # This makes sense if you think about it: if you were to call <tt>post.tags.delete(Tag.find_by(name: 'food'))</tt>
-    # you would want the 'food' tag to be unlinked from the post, rather than for the tag itself
-    # to be removed from the database.
-    #
-    # However, there are examples where this strategy doesn't make sense. For example, suppose
-    # a person has many projects, and each project has many tasks. If we deleted one of a person's
-    # tasks, we would probably not want the project to be deleted. In this scenario, the delete method
-    # won't actually work: it can only be used if the association on the join model is a
-    # +belongs_to+. In other situations you are expected to perform operations directly on
-    # either the associated records or the <tt>:through</tt> association.
-    #
-    # With a regular +has_many+ there is no distinction between the "associated records"
-    # and the "link", so there is only one choice for what gets deleted.
-    #
-    # With +has_and_belongs_to_many+ and +has_many+ <tt>:through</tt>, if you want to delete the
-    # associated records themselves, you can always do something along the lines of
-    # <tt>person.tasks.each(&:destroy)</tt>.
-    #
-    # == Type safety with <tt>ActiveRecord::AssociationTypeMismatch</tt>
-    #
-    # If you attempt to assign an object to an association that doesn't match the inferred
-    # or specified <tt>:class_name</tt>, you'll get an <tt>ActiveRecord::AssociationTypeMismatch</tt>.
-    #
-    # == Options
-    #
-    # All of the association macros can be specialized through options. This makes cases
-    # more complex than the simple and guessable ones possible.
-    module ClassMethods
-      # Specifies a one-to-many association. The following methods for retrieval and query of
-      # collections of associated objects will be added:
-      #
-      # +collection+ is a placeholder for the symbol passed as the +name+ argument, so
-      # <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.
-      #
-      # [collection(force_reload = false)]
-      #   Returns an array of all the associated objects.
-      #   An empty array is returned if none are found.
-      # [collection<<(object, ...)]
-      #   Adds one or more objects to the collection by setting their foreign keys to the collection's primary key.
-      #   Note that this operation instantly fires update SQL without waiting for the save or update call on the
-      #   parent object, unless the parent object is a new record.
-      # [collection.delete(object, ...)]
-      #   Removes one or more objects from the collection by setting their foreign keys to +NULL+.
-      #   Objects will be in addition destroyed if they're associated with <tt>dependent: :destroy</tt>,
-      #   and deleted if they're associated with <tt>dependent: :delete_all</tt>.
-      #
-      #   If the <tt>:through</tt> option is used, then the join records are deleted (rather than
-      #   nullified) by default, but you can specify <tt>dependent: :destroy</tt> or
-      #   <tt>dependent: :nullify</tt> to override this.
-      # [collection.destroy(object, ...)]
-      #   Removes one or more objects from the collection by running <tt>destroy</tt> on
-      #   each record, regardless of any dependent option, ensuring callbacks are run.
-      #
-      #   If the <tt>:through</tt> option is used, then the join records are destroyed
-      #   instead, not the objects themselves.
-      # [collection=objects]
-      #   Replaces the collections content by deleting and adding objects as appropriate. If the <tt>:through</tt>
-      #   option is true callbacks in the join models are triggered except destroy callbacks, since deletion is
-      #   direct.
-      # [collection_singular_ids]
-      #   Returns an array of the associated objects' ids
-      # [collection_singular_ids=ids]
-      #   Replace the collection with the objects identified by the primary keys in +ids+. This
-      #   method loads the models and calls <tt>collection=</tt>. See above.
-      # [collection.clear]
-      #   Removes every object from the collection. This destroys the associated objects if they
-      #   are associated with <tt>dependent: :destroy</tt>, deletes them directly from the
-      #   database if <tt>dependent: :delete_all</tt>, otherwise sets their foreign keys to +NULL+.
-      #   If the <tt>:through</tt> option is true no destroy callbacks are invoked on the join models.
-      #   Join models are directly deleted.
-      # [collection.empty?]
-      #   Returns +true+ if there are no associated objects.
-      # [collection.size]
-      #   Returns the number of associated objects.
-      # [collection.find(...)]
-      #   Finds an associated object according to the same rules as <tt>ActiveRecord::Base.find</tt>.
-      # [collection.exists?(...)]
-      #   Checks whether an associated object with the given conditions exists.
-      #   Uses the same rules as <tt>ActiveRecord::Base.exists?</tt>.
-      # [collection.build(attributes = {}, ...)]
-      #   Returns one or more new objects of the collection type that have been instantiated
-      #   with +attributes+ and linked to this object through a foreign key, but have not yet
-      #   been saved.
-      # [collection.create(attributes = {})]
-      #   Returns a new object of the collection type that has been instantiated
-      #   with +attributes+, linked to this object through a foreign key, and that has already
-      #   been saved (if it passed the validation). *Note*: This only works if the base model
-      #   already exists in the DB, not if it is a new (unsaved) record!
-      # [collection.create!(attributes = {})]
-      #   Does the same as <tt>collection.create</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt>
-      #   if the record is invalid.
-      #
-      # === Example
-      #
-      # A <tt>Firm</tt> class declares <tt>has_many :clients</tt>, which will add:
-      # * <tt>Firm#clients</tt> (similar to <tt>Client.where(firm_id: id)</tt>)
-      # * <tt>Firm#clients<<</tt>
-      # * <tt>Firm#clients.delete</tt>
-      # * <tt>Firm#clients.destroy</tt>
-      # * <tt>Firm#clients=</tt>
-      # * <tt>Firm#client_ids</tt>
-      # * <tt>Firm#client_ids=</tt>
-      # * <tt>Firm#clients.clear</tt>
-      # * <tt>Firm#clients.empty?</tt> (similar to <tt>firm.clients.size == 0</tt>)
-      # * <tt>Firm#clients.size</tt> (similar to <tt>Client.count "firm_id = #{id}"</tt>)
-      # * <tt>Firm#clients.find</tt> (similar to <tt>Client.where(firm_id: id).find(id)</tt>)
-      # * <tt>Firm#clients.exists?(name: 'ACME')</tt> (similar to <tt>Client.exists?(name: 'ACME', firm_id: firm.id)</tt>)
-      # * <tt>Firm#clients.build</tt> (similar to <tt>Client.new("firm_id" => id)</tt>)
-      # * <tt>Firm#clients.create</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save; c</tt>)
-      # * <tt>Firm#clients.create!</tt> (similar to <tt>c = Client.new("firm_id" => id); c.save!</tt>)
-      # The declaration can also include an +options+ hash to specialize the behavior of the association.
-      #
-      # === Scopes
-      #
-      # You can pass a second argument +scope+ as a callable (i.e. proc or
-      # lambda) to retrieve a specific set of records or customize the generated
-      # query when you access the associated collection.
-      #
-      # Scope examples:
-      #   has_many :comments, -> { where(author_id: 1) }
-      #   has_many :employees, -> { joins(:address) }
-      #   has_many :posts, ->(post) { where("max_post_length > ?", post.length) }
-      #
-      # === Extensions
-      #
-      # The +extension+ argument allows you to pass a block into a has_many
-      # association. This is useful for adding new finders, creators and other
-      # factory-type methods to be used as part of the association.
-      #
-      # Extension examples:
-      #   has_many :employees do
-      #     def find_or_create_by_name(name)
-      #       first_name, last_name = name.split(" ", 2)
-      #       find_or_create_by(first_name: first_name, last_name: last_name)
+      # \Associations are a set of macro-like class methods for tying objects together through
+      # foreign keys. They express relationships like "Project has one Project Manager"
+      # or "Project belongs to a Portfolio". Each macro adds a number of methods to the
+      # class which are specialized according to the collection or association symbol and the
+      # options hash. It works much the same way as Ruby's own <tt>attr*</tt>
+      # methods.
+      #
+      #   class Project < ActiveRecord::Base
+      #     belongs_to              :portfolio
+      #     has_one                 :project_manager
+      #     has_many                :milestones
+      #     has_and_belongs_to_many :categories
+      #   end
+      #
+      # The project class now has the following methods (and more) to ease the traversal and
+      # manipulation of its relationships:
+      # * <tt>Project#portfolio</tt>, <tt>Project#portfolio=(portfolio)</tt>, <tt>Project#reload_portfolio</tt>
+      # * <tt>Project#project_manager</tt>, <tt>Project#project_manager=(project_manager)</tt>, <tt>Project#reload_project_manager</tt>
+      # * <tt>Project#milestones.empty?</tt>, <tt>Project#milestones.size</tt>, <tt>Project#milestones</tt>, <tt>Project#milestones<<(milestone)</tt>,
+      #   <tt>Project#milestones.delete(milestone)</tt>, <tt>Project#milestones.destroy(milestone)</tt>, <tt>Project#milestones.find(milestone_id)</tt>,
+      #   <tt>Project#milestones.build</tt>, <tt>Project#milestones.create</tt>
+      # * <tt>Project#categories.empty?</tt>, <tt>Project#categories.size</tt>, <tt>Project#categories</tt>, <tt>Project#categories<<(category1)</tt>,
+      #   <tt>Project#categories.delete(category1)</tt>, <tt>Project#categories.destroy(category1)</tt>
+      #
+      # === A word of warning
+      #
+      # Don't create associations that have the same name as {instance methods}[rdoc-ref:ActiveRecord::Core] of
+      # <tt>ActiveRecord::Base</tt>. Since the association adds a method with that name to
+      # its model, using an association with the same name as one provided by <tt>ActiveRecord::Base</tt> will override the method inherited through <tt>ActiveRecord::Base</tt> and will break things.
+      # For instance, +attributes+ and +connection+ would be bad choices for association names, because those names already exist in the list of <tt>ActiveRecord::Base</tt> instance methods.
+      #
+      # == Auto-generated methods
+      # See also Instance Public methods below for more details.
+      #
+      # === Singular associations (one-to-one)
+      #                                     |            |  belongs_to  |
+      #   generated methods                 | belongs_to | :polymorphic | has_one
+      #   ----------------------------------+------------+--------------+---------
+      #   other                             |     X      |      X       |    X
+      #   other=(other)                     |     X      |      X       |    X
+      #   build_other(attributes={})        |     X      |              |    X
+      #   create_other(attributes={})       |     X      |              |    X
+      #   create_other!(attributes={})      |     X      |              |    X
+      #   reload_other                      |     X      |      X       |    X
+      #
+      # === Collection associations (one-to-many / many-to-many)
+      #                                     |       |          | has_many
+      #   generated methods                 | habtm | has_many | :through
+      #   ----------------------------------+-------+----------+----------
+      #   others                            |   X   |    X     |    X
+      #   others=(other,other,...)          |   X   |    X     |    X
+      #   other_ids                         |   X   |    X     |    X
+      #   other_ids=(id,id,...)             |   X   |    X     |    X
+      #   others<<                          |   X   |    X     |    X
+      #   others.push                       |   X   |    X     |    X
+      #   others.concat                     |   X   |    X     |    X
+      #   others.build(attributes={})       |   X   |    X     |    X
+      #   others.create(attributes={})      |   X   |    X     |    X
+      #   others.create!(attributes={})     |   X   |    X     |    X
+      #   others.size                       |   X   |    X     |    X
+      #   others.length                     |   X   |    X     |    X
+      #   others.count                      |   X   |    X     |    X
+      #   others.sum(*args)                 |   X   |    X     |    X
+      #   others.empty?                     |   X   |    X     |    X
+      #   others.clear                      |   X   |    X     |    X
+      #   others.delete(other,other,...)    |   X   |    X     |    X
+      #   others.delete_all                 |   X   |    X     |    X
+      #   others.destroy(other,other,...)   |   X   |    X     |    X
+      #   others.destroy_all                |   X   |    X     |    X
+      #   others.find(*args)                |   X   |    X     |    X
+      #   others.exists?                    |   X   |    X     |    X
+      #   others.distinct                   |   X   |    X     |    X
+      #   others.reset                      |   X   |    X     |    X
+      #   others.reload                     |   X   |    X     |    X
+      #
+      # === Overriding generated methods
+      #
+      # Association methods are generated in a module included into the model
+      # class, making overrides easy. The original generated method can thus be
+      # called with +super+:
+      #
+      #   class Car < ActiveRecord::Base
+      #     belongs_to :owner
+      #     belongs_to :old_owner
+      #
+      #     def owner=(new_owner)
+      #       self.old_owner = self.owner
+      #       super
       #     end
       #   end
       #
-      # === Options
-      # [:class_name]
-      #   Specify the class name of the association. Use it only if that name can't be inferred
-      #   from the association name. So <tt>has_many :products</tt> will by default be linked
-      #   to the Product class, but if the real class name is SpecialProduct, you'll have to
-      #   specify it with this option.
-      # [:foreign_key]
-      #   Specify the foreign key used for the association. By default this is guessed to be the name
-      #   of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_many+
-      #   association will use "person_id" as the default <tt>:foreign_key</tt>.
-      # [:foreign_type]
-      #   Specify the column used to store the associated object's type, if this is a polymorphic
-      #   association. By default this is guessed to be the name of the polymorphic association
-      #   specified on "as" option with a "_type" suffix. So a class that defines a
-      #   <tt>has_many :tags, as: :taggable</tt> association will use "taggable_type" as the
-      #   default <tt>:foreign_type</tt>.
-      # [:primary_key]
-      #   Specify the name of the column to use as the primary key for the association. By default this is +id+.
-      # [:dependent]
-      #   Controls what happens to the associated objects when
-      #   their owner is destroyed. Note that these are implemented as
-      #   callbacks, and Rails executes callbacks in order. Therefore, other
-      #   similar callbacks may affect the <tt>:dependent</tt> behavior, and the
-      #   <tt>:dependent</tt> behavior may affect other callbacks.
-      #
-      #   * <tt>:destroy</tt> causes all the associated objects to also be destroyed.
-      #   * <tt>:delete_all</tt> causes all the associated objects to be deleted directly from the database (so callbacks will not be executed).
-      #   * <tt>:nullify</tt> causes the foreign keys to be set to +NULL+. Callbacks are not executed.
-      #   * <tt>:restrict_with_exception</tt> causes an exception to be raised if there are any associated records.
-      #   * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there are any associated objects.
-      #
-      #   If using with the <tt>:through</tt> option, the association on the join model must be
-      #   a +belongs_to+, and the records which get deleted are the join records, rather than
-      #   the associated records.
-      # [:counter_cache]
-      #   This option can be used to configure a custom named <tt>:counter_cache.</tt> You only need this option,
-      #   when you customized the name of your <tt>:counter_cache</tt> on the <tt>belongs_to</tt> association.
-      # [:as]
-      #   Specifies a polymorphic interface (See <tt>belongs_to</tt>).
-      # [:through]
-      #   Specifies an association through which to perform the query. This can be any other type
-      #   of association, including other <tt>:through</tt> associations. Options for <tt>:class_name</tt>,
-      #   <tt>:primary_key</tt> and <tt>:foreign_key</tt> are ignored, as the association uses the
-      #   source reflection.
-      #
-      #   If the association on the join model is a +belongs_to+, the collection can be modified
-      #   and the records on the <tt>:through</tt> model will be automatically created and removed
-      #   as appropriate. Otherwise, the collection is read-only, so you should manipulate the
-      #   <tt>:through</tt> association directly.
-      #
-      #   If you are going to modify the association (rather than just read from it), then it is
-      #   a good idea to set the <tt>:inverse_of</tt> option on the source association on the
-      #   join model. This allows associated records to be built which will automatically create
-      #   the appropriate join model records when they are saved. (See the 'Association Join Models'
-      #   section above.)
-      # [:source]
-      #   Specifies the source association name used by <tt>has_many :through</tt> queries.
-      #   Only use it if the name cannot be inferred from the association.
-      #   <tt>has_many :subscribers, through: :subscriptions</tt> will look for either <tt>:subscribers</tt> or
-      #   <tt>:subscriber</tt> on Subscription, unless a <tt>:source</tt> is given.
-      # [:source_type]
-      #   Specifies type of the source association used by <tt>has_many :through</tt> queries where the source
-      #   association is a polymorphic +belongs_to+.
-      # [:validate]
-      #   If +false+, don't validate the associated objects when saving the parent object. true by default.
-      # [:autosave]
-      #   If true, always save the associated objects or destroy them if marked for destruction,
-      #   when saving the parent object. If false, never save or destroy the associated objects.
-      #   By default, only save associated objects that are new records. This option is implemented as a
-      #   +before_save+ callback. Because callbacks are run in the order they are defined, associated objects
-      #   may need to be explicitly saved in any user-defined +before_save+ callbacks.
-      #
-      #   Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>.
-      # [:inverse_of]
-      #   Specifies the name of the <tt>belongs_to</tt> association on the associated object
-      #   that is the inverse of this <tt>has_many</tt> association. Does not work in combination
-      #   with <tt>:through</tt> or <tt>:as</tt> options.
-      #   See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
-      # [:extend]
-      #   Specifies a module or array of modules that will be extended into the association object returned.
-      #   Useful for defining methods on associations, especially when they should be shared between multiple
-      #   association objects.
-      #
-      # Option examples:
-      #   has_many :comments, -> { order "posted_on" }
-      #   has_many :comments, -> { includes :author }
-      #   has_many :people, -> { where(deleted: false).order("name") }, class_name: "Person"
-      #   has_many :tracks, -> { order "position" }, dependent: :destroy
-      #   has_many :comments, dependent: :nullify
-      #   has_many :tags, as: :taggable
-      #   has_many :reports, -> { readonly }
-      #   has_many :subscribers, through: :subscriptions, source: :user
-      def has_many(name, scope = nil, options = {}, &extension)
-        reflection = Builder::HasMany.build(self, name, scope, options, &extension)
-        Reflection.add_reflection self, name, reflection
-      end
-
-      # Specifies a one-to-one association with another class. This method should only be used
-      # if the other class contains the foreign key. If the current class contains the foreign key,
-      # then you should use +belongs_to+ instead. See also ActiveRecord::Associations::ClassMethods's overview
-      # on when to use +has_one+ and when to use +belongs_to+.
-      #
-      # The following methods for retrieval and query of a single associated object will be added:
-      #
-      # +association+ is a placeholder for the symbol passed as the +name+ argument, so
-      # <tt>has_one :manager</tt> would add among others <tt>manager.nil?</tt>.
-      #
-      # [association(force_reload = false)]
-      #   Returns the associated object. +nil+ is returned if none is found.
-      # [association=(associate)]
-      #   Assigns the associate object, extracts the primary key, sets it as the foreign key,
-      #   and saves the associate object. To avoid database inconsistencies, permanently deletes an existing
-      #   associated object when assigning a new one, even if the new one isn't saved to database.
-      # [build_association(attributes = {})]
-      #   Returns a new object of the associated type that has been instantiated
-      #   with +attributes+ and linked to this object through a foreign key, but has not
-      #   yet been saved.
-      # [create_association(attributes = {})]
-      #   Returns a new object of the associated type that has been instantiated
-      #   with +attributes+, linked to this object through a foreign key, and that
-      #   has already been saved (if it passed the validation).
-      # [create_association!(attributes = {})]
-      #   Does the same as <tt>create_association</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt>
-      #   if the record is invalid.
-      #
-      # === Example
-      #
-      # An Account class declares <tt>has_one :beneficiary</tt>, which will add:
-      # * <tt>Account#beneficiary</tt> (similar to <tt>Beneficiary.where(account_id: id).first</tt>)
-      # * <tt>Account#beneficiary=(beneficiary)</tt> (similar to <tt>beneficiary.account_id = account.id; beneficiary.save</tt>)
-      # * <tt>Account#build_beneficiary</tt> (similar to <tt>Beneficiary.new("account_id" => id)</tt>)
-      # * <tt>Account#create_beneficiary</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save; b</tt>)
-      # * <tt>Account#create_beneficiary!</tt> (similar to <tt>b = Beneficiary.new("account_id" => id); b.save!; b</tt>)
-      #
-      # === Scopes
-      #
-      # You can pass a second argument +scope+ as a callable (i.e. proc or
-      # lambda) to retrieve a specific record or customize the generated query
-      # when you access the associated object.
-      #
-      # Scope examples:
-      #   has_one :author, -> { where(comment_id: 1) }
-      #   has_one :employer, -> { joins(:company) }
-      #   has_one :dob, ->(dob) { where("Date.new(2000, 01, 01) > ?", dob) }
-      #
-      # === Options
-      #
-      # The declaration can also include an +options+ hash to specialize the behavior of the association.
-      #
-      # Options are:
-      # [:class_name]
-      #   Specify the class name of the association. Use it only if that name can't be inferred
-      #   from the association name. So <tt>has_one :manager</tt> will by default be linked to the Manager class, but
-      #   if the real class name is Person, you'll have to specify it with this option.
-      # [:dependent]
-      #   Controls what happens to the associated object when
-      #   its owner is destroyed:
-      #
-      #   * <tt>:destroy</tt> causes the associated object to also be destroyed
-      #   * <tt>:delete</tt> causes the associated object to be deleted directly from the database (so callbacks will not execute)
-      #   * <tt>:nullify</tt> causes the foreign key to be set to +NULL+. Callbacks are not executed.
-      #   * <tt>:restrict_with_exception</tt> causes an exception to be raised if there is an associated record
-      #   * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there is an associated object
-      #
-      #   Note that <tt>:dependent</tt> option is ignored when using <tt>:through</tt> option.
-      # [:foreign_key]
-      #   Specify the foreign key used for the association. By default this is guessed to be the name
-      #   of this class in lower-case and "_id" suffixed. So a Person class that makes a +has_one+ association
-      #   will use "person_id" as the default <tt>:foreign_key</tt>.
-      # [:foreign_type]
-      #   Specify the column used to store the associated object's type, if this is a polymorphic
-      #   association. By default this is guessed to be the name of the polymorphic association
-      #   specified on "as" option with a "_type" suffix. So a class that defines a
-      #   <tt>has_one :tag, as: :taggable</tt> association will use "taggable_type" as the
-      #   default <tt>:foreign_type</tt>.
-      # [:primary_key]
-      #   Specify the method that returns the primary key used for the association. By default this is +id+.
-      # [:as]
-      #   Specifies a polymorphic interface (See <tt>belongs_to</tt>).
-      # [:through]
-      #   Specifies a Join Model through which to perform the query. Options for <tt>:class_name</tt>,
-      #   <tt>:primary_key</tt>, and <tt>:foreign_key</tt> are ignored, as the association uses the
-      #   source reflection. You can only use a <tt>:through</tt> query through a <tt>has_one</tt>
-      #   or <tt>belongs_to</tt> association on the join model.
-      # [:source]
-      #   Specifies the source association name used by <tt>has_one :through</tt> queries.
-      #   Only use it if the name cannot be inferred from the association.
-      #   <tt>has_one :favorite, through: :favorites</tt> will look for a
-      #   <tt>:favorite</tt> on Favorite, unless a <tt>:source</tt> is given.
-      # [:source_type]
-      #   Specifies type of the source association used by <tt>has_one :through</tt> queries where the source
-      #   association is a polymorphic +belongs_to+.
-      # [:validate]
-      #   If +false+, don't validate the associated object when saving the parent object. +false+ by default.
-      # [:autosave]
-      #   If true, always save the associated object or destroy it if marked for destruction,
-      #   when saving the parent object. If false, never save or destroy the associated object.
-      #   By default, only save the associated object if it's a new record.
-      #
-      #   Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>.
-      # [:inverse_of]
-      #   Specifies the name of the <tt>belongs_to</tt> association on the associated object
-      #   that is the inverse of this <tt>has_one</tt> association. Does not work in combination
-      #   with <tt>:through</tt> or <tt>:as</tt> options.
-      #   See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
-      # [:required]
-      #   When set to +true+, the association will also have its presence validated.
-      #   This will validate the association itself, not the id. You can use
-      #   +:inverse_of+ to avoid an extra query during validation.
-      #
-      # Option examples:
-      #   has_one :credit_card, dependent: :destroy  # destroys the associated credit card
-      #   has_one :credit_card, dependent: :nullify  # updates the associated records foreign
-      #                                                 # key value to NULL rather than destroying it
-      #   has_one :last_comment, -> { order 'posted_on' }, class_name: "Comment"
-      #   has_one :project_manager, -> { where role: 'project_manager' }, class_name: "Person"
-      #   has_one :attachment, as: :attachable
-      #   has_one :boss, -> { readonly }
-      #   has_one :club, through: :membership
-      #   has_one :primary_address, -> { where primary: true }, through: :addressables, source: :addressable
-      #   has_one :credit_card, required: true
-      def has_one(name, scope = nil, options = {})
-        reflection = Builder::HasOne.build(self, name, scope, options)
-        Reflection.add_reflection self, name, reflection
-      end
-
-      # Specifies a one-to-one association with another class. This method should only be used
-      # if this class contains the foreign key. If the other class contains the foreign key,
-      # then you should use +has_one+ instead. See also ActiveRecord::Associations::ClassMethods's overview
-      # on when to use +has_one+ and when to use +belongs_to+.
-      #
-      # Methods will be added for retrieval and query for a single associated object, for which
-      # this object holds an id:
-      #
-      # +association+ is a placeholder for the symbol passed as the +name+ argument, so
-      # <tt>belongs_to :author</tt> would add among others <tt>author.nil?</tt>.
-      #
-      # [association(force_reload = false)]
-      #   Returns the associated object. +nil+ is returned if none is found.
-      # [association=(associate)]
-      #   Assigns the associate object, extracts the primary key, and sets it as the foreign key.
-      # [build_association(attributes = {})]
-      #   Returns a new object of the associated type that has been instantiated
-      #   with +attributes+ and linked to this object through a foreign key, but has not yet been saved.
-      # [create_association(attributes = {})]
-      #   Returns a new object of the associated type that has been instantiated
-      #   with +attributes+, linked to this object through a foreign key, and that
-      #   has already been saved (if it passed the validation).
-      # [create_association!(attributes = {})]
-      #   Does the same as <tt>create_association</tt>, but raises <tt>ActiveRecord::RecordInvalid</tt>
-      #   if the record is invalid.
-      #
-      # === Example
-      #
-      # A Post class declares <tt>belongs_to :author</tt>, which will add:
-      # * <tt>Post#author</tt> (similar to <tt>Author.find(author_id)</tt>)
-      # * <tt>Post#author=(author)</tt> (similar to <tt>post.author_id = author.id</tt>)
-      # * <tt>Post#build_author</tt> (similar to <tt>post.author = Author.new</tt>)
-      # * <tt>Post#create_author</tt> (similar to <tt>post.author = Author.new; post.author.save; post.author</tt>)
-      # * <tt>Post#create_author!</tt> (similar to <tt>post.author = Author.new; post.author.save!; post.author</tt>)
-      # The declaration can also include an +options+ hash to specialize the behavior of the association.
-      #
-      # === Scopes
-      #
-      # You can pass a second argument +scope+ as a callable (i.e. proc or
-      # lambda) to retrieve a specific record or customize the generated query
-      # when you access the associated object.
-      #
-      # Scope examples:
-      #   belongs_to :firm, -> { where(id: 2) }
-      #   belongs_to :user, -> { joins(:friends) }
-      #   belongs_to :level, ->(level) { where("game_level > ?", level.current) }
-      #
-      # === Options
-      #
-      # [:class_name]
-      #   Specify the class name of the association. Use it only if that name can't be inferred
-      #   from the association name. So <tt>belongs_to :author</tt> will by default be linked to the Author class, but
-      #   if the real class name is Person, you'll have to specify it with this option.
-      # [:foreign_key]
-      #   Specify the foreign key used for the association. By default this is guessed to be the name
-      #   of the association with an "_id" suffix. So a class that defines a <tt>belongs_to :person</tt>
-      #   association will use "person_id" as the default <tt>:foreign_key</tt>. Similarly,
-      #   <tt>belongs_to :favorite_person, class_name: "Person"</tt> will use a foreign key
-      #   of "favorite_person_id".
-      # [:foreign_type]
-      #   Specify the column used to store the associated object's type, if this is a polymorphic
-      #   association. By default this is guessed to be the name of the association with a "_type"
-      #   suffix. So a class that defines a <tt>belongs_to :taggable, polymorphic: true</tt>
-      #   association will use "taggable_type" as the default <tt>:foreign_type</tt>.
-      # [:primary_key]
-      #   Specify the method that returns the primary key of associated object used for the association.
-      #   By default this is id.
-      # [:dependent]
-      #   If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
-      #   <tt>:delete</tt>, the associated object is deleted *without* calling its destroy method.
-      #   This option should not be specified when <tt>belongs_to</tt> is used in conjunction with
-      #   a <tt>has_many</tt> relationship on another class because of the potential to leave
-      #   orphaned records behind.
-      # [:counter_cache]
-      #   Caches the number of belonging objects on the associate class through the use of +increment_counter+
-      #   and +decrement_counter+. The counter cache is incremented when an object of this
-      #   class is created and decremented when it's destroyed. This requires that a column
-      #   named <tt>#{table_name}_count</tt> (such as +comments_count+ for a belonging Comment class)
-      #   is used on the associate class (such as a Post class) - that is the migration for
-      #   <tt>#{table_name}_count</tt> is created on the associate class (such that <tt>Post.comments_count</tt> will
-      #   return the count cached, see note below). You can also specify a custom counter
-      #   cache column by providing a column name instead of a +true+/+false+ value to this
-      #   option (e.g., <tt>counter_cache: :my_custom_counter</tt>.)
-      #   Note: Specifying a counter cache will add it to that model's list of readonly attributes
-      #   using +attr_readonly+.
-      # [:polymorphic]
-      #   Specify this association is a polymorphic association by passing +true+.
-      #   Note: If you've enabled the counter cache, then you may want to add the counter cache attribute
-      #   to the +attr_readonly+ list in the associated classes (e.g. <tt>class Post; attr_readonly :comments_count; end</tt>).
-      # [:validate]
-      #   If +false+, don't validate the associated objects when saving the parent object. +false+ by default.
-      # [:autosave]
-      #   If true, always save the associated object or destroy it if marked for destruction, when
-      #   saving the parent object.
-      #   If false, never save or destroy the associated object.
-      #   By default, only save the associated object if it's a new record.
-      #
-      #   Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>.
-      # [:touch]
-      #   If true, the associated object will be touched (the updated_at/on attributes set to current time)
-      #   when this record is either saved or destroyed. If you specify a symbol, that attribute
-      #   will be updated with the current time in addition to the updated_at/on attribute.
-      # [:inverse_of]
-      #   Specifies the name of the <tt>has_one</tt> or <tt>has_many</tt> association on the associated
-      #   object that is the inverse of this <tt>belongs_to</tt> association. Does not work in
-      #   combination with the <tt>:polymorphic</tt> options.
-      #   See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
-      # [:optional]
-      #   When set to +true+, the association will not have its presence validated.
-      # [:required]
-      #   When set to +true+, the association will also have its presence validated.
-      #   This will validate the association itself, not the id. You can use
-      #   +:inverse_of+ to avoid an extra query during validation.
-      #   NOTE: <tt>required</tt> is set to <tt>true</tt> by default and is deprecated. If
-      #   you don't want to have association presence validated, use <tt>optional: true</tt>.
-      #
-      # Option examples:
-      #   belongs_to :firm, foreign_key: "client_of"
-      #   belongs_to :person, primary_key: "name", foreign_key: "person_name"
-      #   belongs_to :author, class_name: "Person", foreign_key: "author_id"
-      #   belongs_to :valid_coupon, ->(o) { where "discounts > ?", o.payments_count },
-      #                             class_name: "Coupon", foreign_key: "coupon_id"
-      #   belongs_to :attachable, polymorphic: true
-      #   belongs_to :project, -> { readonly }
-      #   belongs_to :post, counter_cache: true
-      #   belongs_to :comment, touch: true
-      #   belongs_to :company, touch: :employees_last_updated_at
-      #   belongs_to :user, optional: true
-      def belongs_to(name, scope = nil, options = {})
-        reflection = Builder::BelongsTo.build(self, name, scope, options)
-        Reflection.add_reflection self, name, reflection
-      end
-
-      # Specifies a many-to-many relationship with another class. This associates two classes via an
-      # intermediate join table. Unless the join table is explicitly specified as an option, it is
-      # guessed using the lexical order of the class names. So a join between Developer and Project
-      # will give the default join table name of "developers_projects" because "D" precedes "P" alphabetically.
-      # Note that this precedence is calculated using the <tt><</tt> operator for String. This
-      # means that if the strings are of different lengths, and the strings are equal when compared
-      # up to the shortest length, then the longer string is considered of higher
-      # lexical precedence than the shorter one. For example, one would expect the tables "paper_boxes" and "papers"
-      # to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes",
-      # but it in fact generates a join table name of "paper_boxes_papers". Be aware of this caveat, and use the
-      # custom <tt>:join_table</tt> option if you need to.
-      # If your tables share a common prefix, it will only appear once at the beginning. For example,
-      # the tables "catalog_categories" and "catalog_products" generate a join table name of "catalog_categories_products".
-      #
-      # The join table should not have a primary key or a model associated with it. You must manually generate the
-      # join table with a migration such as this:
-      #
-      #   class CreateDevelopersProjectsJoinTable < ActiveRecord::Migration
-      #     def change
-      #       create_join_table :developers, :projects
+      # The association methods module is included immediately after the
+      # generated attributes methods module, meaning an association will
+      # override the methods for an attribute with the same name.
+      #
+      # == Cardinality and associations
+      #
+      # Active Record associations can be used to describe one-to-one, one-to-many and many-to-many
+      # relationships between models. Each model uses an association to describe its role in
+      # the relation. The #belongs_to association is always used in the model that has
+      # the foreign key.
+      #
+      # === One-to-one
+      #
+      # Use #has_one in the base, and #belongs_to in the associated model.
+      #
+      #   class Employee < ActiveRecord::Base
+      #     has_one :office
+      #   end
+      #   class Office < ActiveRecord::Base
+      #     belongs_to :employee    # foreign key - employee_id
+      #   end
+      #
+      # === One-to-many
+      #
+      # Use #has_many in the base, and #belongs_to in the associated model.
+      #
+      #   class Manager < ActiveRecord::Base
+      #     has_many :employees
+      #   end
+      #   class Employee < ActiveRecord::Base
+      #     belongs_to :manager     # foreign key - manager_id
+      #   end
+      #
+      # === Many-to-many
+      #
+      # There are two ways to build a many-to-many relationship.
+      #
+      # The first way uses a #has_many association with the <tt>:through</tt> option and a join model, so
+      # there are two stages of associations.
+      #
+      #   class Assignment < ActiveRecord::Base
+      #     belongs_to :programmer  # foreign key - programmer_id
+      #     belongs_to :project     # foreign key - project_id
+      #   end
+      #   class Programmer < ActiveRecord::Base
+      #     has_many :assignments
+      #     has_many :projects, through: :assignments
+      #   end
+      #   class Project < ActiveRecord::Base
+      #     has_many :assignments
+      #     has_many :programmers, through: :assignments
+      #   end
+      #
+      # For the second way, use #has_and_belongs_to_many in both models. This requires a join table
+      # that has no corresponding model or primary key.
+      #
+      #   class Programmer < ActiveRecord::Base
+      #     has_and_belongs_to_many :projects       # foreign keys in the join table
+      #   end
+      #   class Project < ActiveRecord::Base
+      #     has_and_belongs_to_many :programmers    # foreign keys in the join table
+      #   end
+      #
+      # Choosing which way to build a many-to-many relationship is not always simple.
+      # If you need to work with the relationship model as its own entity,
+      # use #has_many <tt>:through</tt>. Use #has_and_belongs_to_many when working with legacy schemas or when
+      # you never work directly with the relationship itself.
+      #
+      # == Is it a #belongs_to or #has_one association?
+      #
+      # Both express a 1-1 relationship. The difference is mostly where to place the foreign
+      # key, which goes on the table for the class declaring the #belongs_to relationship.
+      #
+      #   class User < ActiveRecord::Base
+      #     # I reference an account.
+      #     belongs_to :account
+      #   end
+      #
+      #   class Account < ActiveRecord::Base
+      #     # One user references me.
+      #     has_one :user
+      #   end
+      #
+      # The tables for these classes could look something like:
+      #
+      #   CREATE TABLE users (
+      #     id bigint NOT NULL auto_increment,
+      #     account_id bigint default NULL,
+      #     name varchar default NULL,
+      #     PRIMARY KEY  (id)
+      #   )
+      #
+      #   CREATE TABLE accounts (
+      #     id bigint NOT NULL auto_increment,
+      #     name varchar default NULL,
+      #     PRIMARY KEY  (id)
+      #   )
+      #
+      # == Unsaved objects and associations
+      #
+      # You can manipulate objects and associations before they are saved to the database, but
+      # there is some special behavior you should be aware of, mostly involving the saving of
+      # associated objects.
+      #
+      # You can set the <tt>:autosave</tt> option on a #has_one, #belongs_to,
+      # #has_many, or #has_and_belongs_to_many association. Setting it
+      # to +true+ will _always_ save the members, whereas setting it to +false+ will
+      # _never_ save the members. More details about <tt>:autosave</tt> option is available at
+      # AutosaveAssociation.
+      #
+      # === One-to-one associations
+      #
+      # * Assigning an object to a #has_one association automatically saves that object and
+      #   the object being replaced (if there is one), in order to update their foreign
+      #   keys - except if the parent object is unsaved (<tt>new_record? == true</tt>).
+      # * If either of these saves fail (due to one of the objects being invalid), an
+      #   ActiveRecord::RecordNotSaved exception is raised and the assignment is
+      #   cancelled.
+      # * If you wish to assign an object to a #has_one association without saving it,
+      #   use the <tt>#build_association</tt> method (documented below). The object being
+      #   replaced will still be saved to update its foreign key.
+      # * Assigning an object to a #belongs_to association does not save the object, since
+      #   the foreign key field belongs on the parent. It does not save the parent either.
+      #
+      # === Collections
+      #
+      # * Adding an object to a collection (#has_many or #has_and_belongs_to_many) automatically
+      #   saves that object, except if the parent object (the owner of the collection) is not yet
+      #   stored in the database.
+      # * If saving any of the objects being added to a collection (via <tt>push</tt> or similar)
+      #   fails, then <tt>push</tt> returns +false+.
+      # * If saving fails while replacing the collection (via <tt>association=</tt>), an
+      #   ActiveRecord::RecordNotSaved exception is raised and the assignment is
+      #   cancelled.
+      # * You can add an object to a collection without automatically saving it by using the
+      #   <tt>collection.build</tt> method (documented below).
+      # * All unsaved (<tt>new_record? == true</tt>) members of the collection are automatically
+      #   saved when the parent is saved.
+      #
+      # == Customizing the query
+      #
+      # \Associations are built from <tt>Relation</tt> objects, and you can use the Relation syntax
+      # to customize them. For example, to add a condition:
+      #
+      #   class Blog < ActiveRecord::Base
+      #     has_many :published_posts, -> { where(published: true) }, class_name: 'Post'
+      #   end
+      #
+      # Inside the <tt>-> { ... }</tt> block you can use all of the usual Relation methods.
+      #
+      # === Accessing the owner object
+      #
+      # Sometimes it is useful to have access to the owner object when building the query. The owner
+      # is passed as a parameter to the block. For example, the following association would find all
+      # events that occur on the user's birthday:
+      #
+      #   class User < ActiveRecord::Base
+      #     has_many :birthday_events, ->(user) { where(starts_on: user.birthday) }, class_name: 'Event'
+      #   end
+      #
+      # Note: Joining, eager loading and preloading of these associations is not possible.
+      # These operations happen before instance creation and the scope will be called with a +nil+ argument.
+      #
+      # == Association callbacks
+      #
+      # Similar to the normal callbacks that hook into the life cycle of an Active Record object,
+      # you can also define callbacks that get triggered when you add an object to or remove an
+      # object from an association collection.
+      #
+      #   class Project
+      #     has_and_belongs_to_many :developers, after_add: :evaluate_velocity
+      #
+      #     def evaluate_velocity(developer)
+      #       ...
       #     end
       #   end
       #
-      # It's also a good idea to add indexes to each of those columns to speed up the joins process.
-      # However, in MySQL it is advised to add a compound index for both of the columns as MySQL only
-      # uses one index per table during the lookup.
-      #
-      # Adds the following methods for retrieval and query:
-      #
-      # +collection+ is a placeholder for the symbol passed as the +name+ argument, so
-      # <tt>has_and_belongs_to_many :categories</tt> would add among others <tt>categories.empty?</tt>.
-      #
-      # [collection(force_reload = false)]
-      #   Returns an array of all the associated objects.
-      #   An empty array is returned if none are found.
-      # [collection<<(object, ...)]
-      #   Adds one or more objects to the collection by creating associations in the join table
-      #   (<tt>collection.push</tt> and <tt>collection.concat</tt> are aliases to this method).
-      #   Note that this operation instantly fires update SQL without waiting for the save or update call on the
-      #   parent object, unless the parent object is a new record.
-      # [collection.delete(object, ...)]
-      #   Removes one or more objects from the collection by removing their associations from the join table.
-      #   This does not destroy the objects.
-      # [collection.destroy(object, ...)]
-      #   Removes one or more objects from the collection by running destroy on each association in the join table, overriding any dependent option.
-      #   This does not destroy the objects.
-      # [collection=objects]
-      #   Replaces the collection's content by deleting and adding objects as appropriate.
-      # [collection_singular_ids]
-      #   Returns an array of the associated objects' ids.
-      # [collection_singular_ids=ids]
-      #   Replace the collection by the objects identified by the primary keys in +ids+.
-      # [collection.clear]
-      #   Removes every object from the collection. This does not destroy the objects.
-      # [collection.empty?]
-      #   Returns +true+ if there are no associated objects.
-      # [collection.size]
-      #   Returns the number of associated objects.
-      # [collection.find(id)]
-      #   Finds an associated object responding to the +id+ and that
-      #   meets the condition that it has to be associated with this object.
-      #   Uses the same rules as <tt>ActiveRecord::Base.find</tt>.
-      # [collection.exists?(...)]
-      #   Checks whether an associated object with the given conditions exists.
-      #   Uses the same rules as <tt>ActiveRecord::Base.exists?</tt>.
-      # [collection.build(attributes = {})]
-      #   Returns a new object of the collection type that has been instantiated
-      #   with +attributes+ and linked to this object through the join table, but has not yet been saved.
-      # [collection.create(attributes = {})]
-      #   Returns a new object of the collection type that has been instantiated
-      #   with +attributes+, linked to this object through the join table, and that has already been
-      #   saved (if it passed the validation).
-      #
-      # === Example
-      #
-      # A Developer class declares <tt>has_and_belongs_to_many :projects</tt>, which will add:
-      # * <tt>Developer#projects</tt>
-      # * <tt>Developer#projects<<</tt>
-      # * <tt>Developer#projects.delete</tt>
-      # * <tt>Developer#projects.destroy</tt>
-      # * <tt>Developer#projects=</tt>
-      # * <tt>Developer#project_ids</tt>
-      # * <tt>Developer#project_ids=</tt>
-      # * <tt>Developer#projects.clear</tt>
-      # * <tt>Developer#projects.empty?</tt>
-      # * <tt>Developer#projects.size</tt>
-      # * <tt>Developer#projects.find(id)</tt>
-      # * <tt>Developer#projects.exists?(...)</tt>
-      # * <tt>Developer#projects.build</tt> (similar to <tt>Project.new("developer_id" => id)</tt>)
-      # * <tt>Developer#projects.create</tt> (similar to <tt>c = Project.new("developer_id" => id); c.save; c</tt>)
-      # The declaration may include an +options+ hash to specialize the behavior of the association.
-      #
-      # === Scopes
-      #
-      # You can pass a second argument +scope+ as a callable (i.e. proc or
-      # lambda) to retrieve a specific set of records or customize the generated
-      # query when you access the associated collection.
-      #
-      # Scope examples:
-      #   has_and_belongs_to_many :projects, -> { includes :milestones, :manager }
-      #   has_and_belongs_to_many :categories, ->(category) {
-      #     where("default_category = ?", category.name)
-      #   }
-      #
-      # === Extensions
-      #
-      # The +extension+ argument allows you to pass a block into a
-      # has_and_belongs_to_many association. This is useful for adding new
-      # finders, creators and other factory-type methods to be used as part of
-      # the association.
-      #
-      # Extension examples:
-      #   has_and_belongs_to_many :contractors do
+      # It's possible to stack callbacks by passing them as an array. Example:
+      #
+      #   class Project
+      #     has_and_belongs_to_many :developers,
+      #                             after_add: [:evaluate_velocity, Proc.new { |p, d| p.shipping_date = Time.now}]
+      #   end
+      #
+      # Possible callbacks are: +before_add+, +after_add+, +before_remove+ and +after_remove+.
+      #
+      # If any of the +before_add+ callbacks throw an exception, the object will not be
+      # added to the collection.
+      #
+      # Similarly, if any of the +before_remove+ callbacks throw an exception, the object
+      # will not be removed from the collection.
+      #
+      # == Association extensions
+      #
+      # The proxy objects that control the access to associations can be extended through anonymous
+      # modules. This is especially beneficial for adding new finders, creators, and other
+      # factory-type methods that are only used as part of this association.
+      #
+      #   class Account < ActiveRecord::Base
+      #     has_many :people do
+      #       def find_or_create_by_name(name)
+      #         first_name, last_name = name.split(" ", 2)
+      #         find_or_create_by(first_name: first_name, last_name: last_name)
+      #       end
+      #     end
+      #   end
+      #
+      #   person = Account.first.people.find_or_create_by_name("David Heinemeier Hansson")
+      #   person.first_name # => "David"
+      #   person.last_name  # => "Heinemeier Hansson"
+      #
+      # If you need to share the same extensions between many associations, you can use a named
+      # extension module.
+      #
+      #   module FindOrCreateByNameExtension
       #     def find_or_create_by_name(name)
       #       first_name, last_name = name.split(" ", 2)
       #       find_or_create_by(first_name: first_name, last_name: last_name)
       #     end
       #   end
       #
-      # === Options
-      #
-      # [:class_name]
-      #   Specify the class name of the association. Use it only if that name can't be inferred
-      #   from the association name. So <tt>has_and_belongs_to_many :projects</tt> will by default be linked to the
-      #   Project class, but if the real class name is SuperProject, you'll have to specify it with this option.
-      # [:join_table]
-      #   Specify the name of the join table if the default based on lexical order isn't what you want.
-      #   <b>WARNING:</b> If you're overwriting the table name of either class, the +table_name+ method
-      #   MUST be declared underneath any +has_and_belongs_to_many+ declaration in order to work.
-      # [:foreign_key]
-      #   Specify the foreign key used for the association. By default this is guessed to be the name
-      #   of this class in lower-case and "_id" suffixed. So a Person class that makes
-      #   a +has_and_belongs_to_many+ association to Project will use "person_id" as the
-      #   default <tt>:foreign_key</tt>.
-      # [:association_foreign_key]
-      #   Specify the foreign key used for the association on the receiving side of the association.
-      #   By default this is guessed to be the name of the associated class in lower-case and "_id" suffixed.
-      #   So if a Person class makes a +has_and_belongs_to_many+ association to Project,
-      #   the association will use "project_id" as the default <tt>:association_foreign_key</tt>.
-      # [:readonly]
-      #   If true, all the associated objects are readonly through the association.
-      # [:validate]
-      #   If +false+, don't validate the associated objects when saving the parent object. +true+ by default.
-      # [:autosave]
-      #   If true, always save the associated objects or destroy them if marked for destruction, when
-      #   saving the parent object.
-      #   If false, never save or destroy the associated objects.
-      #   By default, only save associated objects that are new records.
-      #
-      #   Note that <tt>accepts_nested_attributes_for</tt> sets <tt>:autosave</tt> to <tt>true</tt>.
-      #
-      # Option examples:
-      #   has_and_belongs_to_many :projects
-      #   has_and_belongs_to_many :projects, -> { includes :milestones, :manager }
-      #   has_and_belongs_to_many :nations, class_name: "Country"
-      #   has_and_belongs_to_many :categories, join_table: "prods_cats"
-      #   has_and_belongs_to_many :categories, -> { readonly }
-      def has_and_belongs_to_many(name, scope = nil, options = {}, &extension)
-        if scope.is_a?(Hash)
-          options = scope
-          scope   = nil
+      #   class Account < ActiveRecord::Base
+      #     has_many :people, -> { extending FindOrCreateByNameExtension }
+      #   end
+      #
+      #   class Company < ActiveRecord::Base
+      #     has_many :people, -> { extending FindOrCreateByNameExtension }
+      #   end
+      #
+      # Some extensions can only be made to work with knowledge of the association's internals.
+      # Extensions can access relevant state using the following methods (where +items+ is the
+      # name of the association):
+      #
+      # * <tt>record.association(:items).owner</tt> - Returns the object the association is part of.
+      # * <tt>record.association(:items).reflection</tt> - Returns the reflection object that describes the association.
+      # * <tt>record.association(:items).target</tt> - Returns the associated object for #belongs_to and #has_one, or
+      #   the collection of associated objects for #has_many and #has_and_belongs_to_many.
+      #
+      # However, inside the actual extension code, you will not have access to the <tt>record</tt> as
+      # above. In this case, you can access <tt>proxy_association</tt>. For example,
+      # <tt>record.association(:items)</tt> and <tt>record.items.proxy_association</tt> will return
+      # the same object, allowing you to make calls like <tt>proxy_association.owner</tt> inside
+      # association extensions.
+      #
+      # == Association Join Models
+      #
+      # Has Many associations can be configured with the <tt>:through</tt> option to use an
+      # explicit join model to retrieve the data. This operates similarly to a
+      # #has_and_belongs_to_many association. The advantage is that you're able to add validations,
+      # callbacks, and extra attributes on the join model. Consider the following schema:
+      #
+      #   class Author < ActiveRecord::Base
+      #     has_many :authorships
+      #     has_many :books, through: :authorships
+      #   end
+      #
+      #   class Authorship < ActiveRecord::Base
+      #     belongs_to :author
+      #     belongs_to :book
+      #   end
+      #
+      #   @author = Author.first
+      #   @author.authorships.collect { |a| a.book } # selects all books that the author's authorships belong to
+      #   @author.books                              # selects all books by using the Authorship join model
+      #
+      # You can also go through a #has_many association on the join model:
+      #
+      #   class Firm < ActiveRecord::Base
+      #     has_many   :clients
+      #     has_many   :invoices, through: :clients
+      #   end
+      #
+      #   class Client < ActiveRecord::Base
+      #     belongs_to :firm
+      #     has_many   :invoices
+      #   end
+      #
+      #   class Invoice < ActiveRecord::Base
+      #     belongs_to :client
+      #   end
+      #
+      #   @firm = Firm.first
+      #   @firm.clients.flat_map { |c| c.invoices } # select all invoices for all clients of the firm
+      #   @firm.invoices                            # selects all invoices by going through the Client join model
+      #
+      # Similarly you can go through a #has_one association on the join model:
+      #
+      #   class Group < ActiveRecord::Base
+      #     has_many   :users
+      #     has_many   :avatars, through: :users
+      #   end
+      #
+      #   class User < ActiveRecord::Base
+      #     belongs_to :group
+      #     has_one    :avatar
+      #   end
+      #
+      #   class Avatar < ActiveRecord::Base
+      #     belongs_to :user
+      #   end
+      #
+      #   @group = Group.first
+      #   @group.users.collect { |u| u.avatar }.compact # select all avatars for all users in the group
+      #   @group.avatars                                # selects all avatars by going through the User join model.
+      #
+      # An important caveat with going through #has_one or #has_many associations on the
+      # join model is that these associations are *read-only*. For example, the following
+      # would not work following the previous example:
+      #
+      #   @group.avatars << Avatar.new   # this would work if User belonged_to Avatar rather than the other way around
+      #   @group.avatars.delete(@group.avatars.last)  # so would this
+      #
+      # == Setting Inverses
+      #
+      # If you are using a #belongs_to on the join model, it is a good idea to set the
+      # <tt>:inverse_of</tt> option on the #belongs_to, which will mean that the following example
+      # works correctly (where <tt>tags</tt> is a #has_many <tt>:through</tt> association):
+      #
+      #   @post = Post.first
+      #   @tag = @post.tags.build name: "ruby"
+      #   @tag.save
+      #
+      # The last line ought to save the through record (a <tt>Tagging</tt>). This will only work if the
+      # <tt>:inverse_of</tt> is set:
+      #
+      #   class Tagging < ActiveRecord::Base
+      #     belongs_to :post
+      #     belongs_to :tag, inverse_of: :taggings
+      #   end
+      #
+      # If you do not set the <tt>:inverse_of</tt> record, the association will
+      # do its best to match itself up with the correct inverse. Automatic
+      # inverse detection only works on #has_many, #has_one, and
+      # #belongs_to associations.
+      #
+      # Extra options on the associations, as defined in the
+      # <tt>AssociationReflection::INVALID_AUTOMATIC_INVERSE_OPTIONS</tt> constant, will
+      # also prevent the association's inverse from being found automatically.
+      #
+      # The automatic guessing of the inverse association uses a heuristic based
+      # on the name of the class, so it may not work for all associations,
+      # especially the ones with non-standard names.
+      #
+      # You can turn off the automatic detection of inverse associations by setting
+      # the <tt>:inverse_of</tt> option to <tt>false</tt> like so:
+      #
+      #   class Tagging < ActiveRecord::Base
+      #     belongs_to :tag, inverse_of: false
+      #   end
+      #
+      # == Nested \Associations
+      #
+      # You can actually specify *any* association with the <tt>:through</tt> option, including an
+      # association which has a <tt>:through</tt> option itself. For example:
+      #
+      #   class Author < ActiveRecord::Base
+      #     has_many :posts
+      #     has_many :comments, through: :posts
+      #     has_many :commenters, through: :comments
+      #   end
+      #
+      #   class Post < ActiveRecord::Base
+      #     has_many :comments
+      #   end
+      #
+      #   class Comment < ActiveRecord::Base
+      #     belongs_to :commenter
+      #   end
+      #
+      #   @author = Author.first
+      #   @author.commenters # => People who commented on posts written by the author
+      #
+      # An equivalent way of setting up this association this would be:
+      #
+      #   class Author < ActiveRecord::Base
+      #     has_many :posts
+      #     has_many :commenters, through: :posts
+      #   end
+      #
+      #   class Post < ActiveRecord::Base
+      #     has_many :comments
+      #     has_many :commenters, through: :comments
+      #   end
+      #
+      #   class Comment < ActiveRecord::Base
+      #     belongs_to :commenter
+      #   end
+      #
+      # When using a nested association, you will not be able to modify the association because there
+      # is not enough information to know what modification to make. For example, if you tried to
+      # add a <tt>Commenter</tt> in the example above, there would be no way to tell how to set up the
+      # intermediate <tt>Post</tt> and <tt>Comment</tt> objects.
+      #
+      # == Polymorphic \Associations
+      #
+      # Polymorphic associations on models are not restricted on what types of models they
+      # can be associated with. Rather, they specify an interface that a #has_many association
+      # must adhere to.
+      #
+      #   class Asset < ActiveRecord::Base
+      #     belongs_to :attachable, polymorphic: true
+      #   end
+      #
+      #   class Post < ActiveRecord::Base
+      #     has_many :assets, as: :attachable         # The :as option specifies the polymorphic interface to use.
+      #   end
+      #
+      #   @asset.attachable = @post
+      #
+      # This works by using a type column in addition to a foreign key to specify the associated
+      # record. In the Asset example, you'd need an +attachable_id+ integer column and an
+      # +attachable_type+ string column.
+      #
+      # Using polymorphic associations in combination with single table inheritance (STI) is
+      # a little tricky. In order for the associations to work as expected, ensure that you
+      # store the base model for the STI models in the type column of the polymorphic
+      # association. To continue with the asset example above, suppose there are guest posts
+      # and member posts that use the posts table for STI. In this case, there must be a +type+
+      # column in the posts table.
+      #
+      # Note: The <tt>attachable_type=</tt> method is being called when assigning an +attachable+.
+      # The +class_name+ of the +attachable+ is passed as a String.
+      #
+      #   class Asset < ActiveRecord::Base
+      #     belongs_to :attachable, polymorphic: true
+      #
+      #     def attachable_type=(class_name)
+      #        super(class_name.constantize.base_class.to_s)
+      #     end
+      #   end
+      #
+      #   class Post < ActiveRecord::Base
+      #     # because we store "Post" in attachable_type now dependent: :destroy will work
+      #     has_many :assets, as: :attachable, dependent: :destroy
+      #   end
+      #
+      #   class GuestPost < Post
+      #   end
+      #
+      #   class MemberPost < Post
+      #   end
+      #
+      # == Caching
+      #
+      # All of the methods are built on a simple caching principle that will keep the result
+      # of the last query around unless specifically instructed not to. The cache is even
+      # shared across methods to make it even cheaper to use the macro-added methods without
+      # worrying too much about performance at the first go.
+      #
+      #   project.milestones             # fetches milestones from the database
+      #   project.milestones.size        # uses the milestone cache
+      #   project.milestones.empty?      # uses the milestone cache
+      #   project.milestones.reload.size # fetches milestones from the database
+      #   project.milestones             # uses the milestone cache
+      #
+      # == Eager loading of associations
+      #
+      # Eager loading is a way to find objects of a certain class and a number of named associations.
+      # It is one of the easiest ways to prevent the dreaded N+1 problem in which fetching 100
+      # posts that each need to display their author triggers 101 database queries. Through the
+      # use of eager loading, the number of queries will be reduced from 101 to 2.
+      #
+      #   class Post < ActiveRecord::Base
+      #     belongs_to :author
+      #     has_many   :comments
+      #   end
+      #
+      # Consider the following loop using the class above:
+      #
+      #   Post.all.each do |post|
+      #     puts "Post:            " + post.title
+      #     puts "Written by:      " + post.author.name
+      #     puts "Last comment on: " + post.comments.first.created_on
+      #   end
+      #
+      # To iterate over these one hundred posts, we'll generate 201 database queries. Let's
+      # first just optimize it for retrieving the author:
+      #
+      #   Post.includes(:author).each do |post|
+      #
+      # This references the name of the #belongs_to association that also used the <tt>:author</tt>
+      # symbol. After loading the posts, +find+ will collect the +author_id+ from each one and load
+      # all of the referenced authors with one query. Doing so will cut down the number of queries
+      # from 201 to 102.
+      #
+      # We can improve upon the situation further by referencing both associations in the finder with:
+      #
+      #   Post.includes(:author, :comments).each do |post|
+      #
+      # This will load all comments with a single query. This reduces the total number of queries
+      # to 3. In general, the number of queries will be 1 plus the number of associations
+      # named (except if some of the associations are polymorphic #belongs_to - see below).
+      #
+      # To include a deep hierarchy of associations, use a hash:
+      #
+      #   Post.includes(:author, { comments: { author: :gravatar } }).each do |post|
+      #
+      # The above code will load all the comments and all of their associated
+      # authors and gravatars. You can mix and match any combination of symbols,
+      # arrays, and hashes to retrieve the associations you want to load.
+      #
+      # All of this power shouldn't fool you into thinking that you can pull out huge amounts
+      # of data with no performance penalty just because you've reduced the number of queries.
+      # The database still needs to send all the data to Active Record and it still needs to
+      # be processed. So it's no catch-all for performance problems, but it's a great way to
+      # cut down on the number of queries in a situation as the one described above.
+      #
+      # Since only one table is loaded at a time, conditions or orders cannot reference tables
+      # other than the main one. If this is the case, Active Record falls back to the previously
+      # used <tt>LEFT OUTER JOIN</tt> based strategy. For example:
+      #
+      #   Post.includes([:author, :comments]).where(['comments.approved = ?', true])
+      #
+      # This will result in a single SQL query with joins along the lines of:
+      # <tt>LEFT OUTER JOIN comments ON comments.post_id = posts.id</tt> and
+      # <tt>LEFT OUTER JOIN authors ON authors.id = posts.author_id</tt>. Note that using conditions
+      # like this can have unintended consequences.
+      # In the above example, posts with no approved comments are not returned at all because
+      # the conditions apply to the SQL statement as a whole and not just to the association.
+      #
+      # You must disambiguate column references for this fallback to happen, for example
+      # <tt>order: "author.name DESC"</tt> will work but <tt>order: "name DESC"</tt> will not.
+      #
+      # If you want to load all posts (including posts with no approved comments), then write
+      # your own <tt>LEFT OUTER JOIN</tt> query using <tt>ON</tt>:
+      #
+      #   Post.joins("LEFT OUTER JOIN comments ON comments.post_id = posts.id AND comments.approved = '1'")
+      #
+      # In this case, it is usually more natural to include an association which has conditions defined on it:
+      #
+      #   class Post < ActiveRecord::Base
+      #     has_many :approved_comments, -> { where(approved: true) }, class_name: 'Comment'
+      #   end
+      #
+      #   Post.includes(:approved_comments)
+      #
+      # This will load posts and eager load the +approved_comments+ association, which contains
+      # only those comments that have been approved.
+      #
+      # If you eager load an association with a specified <tt>:limit</tt> option, it will be ignored,
+      # returning all the associated objects:
+      #
+      #   class Picture < ActiveRecord::Base
+      #     has_many :most_recent_comments, -> { order('id DESC').limit(10) }, class_name: 'Comment'
+      #   end
+      #
+      #   Picture.includes(:most_recent_comments).first.most_recent_comments # => returns all associated comments.
+      #
+      # Eager loading is supported with polymorphic associations.
+      #
+      #   class Address < ActiveRecord::Base
+      #     belongs_to :addressable, polymorphic: true
+      #   end
+      #
+      # A call that tries to eager load the addressable model
+      #
+      #   Address.includes(:addressable)
+      #
+      # This will execute one query to load the addresses and load the addressables with one
+      # query per addressable type.
+      # For example, if all the addressables are either of class Person or Company, then a total
+      # of 3 queries will be executed. The list of addressable types to load is determined on
+      # the back of the addresses loaded. This is not supported if Active Record has to fallback
+      # to the previous implementation of eager loading and will raise ActiveRecord::EagerLoadPolymorphicError.
+      # The reason is that the parent model's type is a column value so its corresponding table
+      # name cannot be put in the +FROM+/+JOIN+ clauses of that query.
+      #
+      # == Table Aliasing
+      #
+      # Active Record uses table aliasing in the case that a table is referenced multiple times
+      # in a join. If a table is referenced only once, the standard table name is used. The
+      # second time, the table is aliased as <tt>#{reflection_name}_#{parent_table_name}</tt>.
+      # Indexes are appended for any more successive uses of the table name.
+      #
+      #   Post.joins(:comments)
+      #   # => SELECT ... FROM posts INNER JOIN comments ON ...
+      #   Post.joins(:special_comments) # STI
+      #   # => SELECT ... FROM posts INNER JOIN comments ON ... AND comments.type = 'SpecialComment'
+      #   Post.joins(:comments, :special_comments) # special_comments is the reflection name, posts is the parent table name
+      #   # => SELECT ... FROM posts INNER JOIN comments ON ... INNER JOIN comments special_comments_posts
+      #
+      # Acts as tree example:
+      #
+      #   TreeMixin.joins(:children)
+      #   # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
+      #   TreeMixin.joins(children: :parent)
+      #   # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
+      #                               INNER JOIN parents_mixins ...
+      #   TreeMixin.joins(children: {parent: :children})
+      #   # => SELECT ... FROM mixins INNER JOIN mixins childrens_mixins ...
+      #                               INNER JOIN parents_mixins ...
+      #                               INNER JOIN mixins childrens_mixins_2
+      #
+      # Has and Belongs to Many join tables use the same idea, but add a <tt>_join</tt> suffix:
+      #
+      #   Post.joins(:categories)
+      #   # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
+      #   Post.joins(categories: :posts)
+      #   # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
+      #                              INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories
+      #   Post.joins(categories: {posts: :categories})
+      #   # => SELECT ... FROM posts INNER JOIN categories_posts ... INNER JOIN categories ...
+      #                              INNER JOIN categories_posts posts_categories_join INNER JOIN posts posts_categories
+      #                              INNER JOIN categories_posts categories_posts_join INNER JOIN categories categories_posts_2
+      #
+      # If you wish to specify your own custom joins using ActiveRecord::QueryMethods#joins method, those table
+      # names will take precedence over the eager associations:
+      #
+      #   Post.joins(:comments).joins("inner join comments ...")
+      #   # => SELECT ... FROM posts INNER JOIN comments_posts ON ... INNER JOIN comments ...
+      #   Post.joins(:comments, :special_comments).joins("inner join comments ...")
+      #   # => SELECT ... FROM posts INNER JOIN comments comments_posts ON ...
+      #                              INNER JOIN comments special_comments_posts ...
+      #                              INNER JOIN comments ...
+      #
+      # Table aliases are automatically truncated according to the maximum length of table identifiers
+      # according to the specific database.
+      #
+      # == Modules
+      #
+      # By default, associations will look for objects within the current module scope. Consider:
+      #
+      #   module MyApplication
+      #     module Business
+      #       class Firm < ActiveRecord::Base
+      #         has_many :clients
+      #       end
+      #
+      #       class Client < ActiveRecord::Base; end
+      #     end
+      #   end
+      #
+      # When <tt>Firm#clients</tt> is called, it will in turn call
+      # <tt>MyApplication::Business::Client.find_all_by_firm_id(firm.id)</tt>.
+      # If you want to associate with a class in another module scope, this can be done by
+      # specifying the complete class name.
+      #
+      #   module MyApplication
+      #     module Business
+      #       class Firm < ActiveRecord::Base; end
+      #     end
+      #
+      #     module Billing
+      #       class Account < ActiveRecord::Base
+      #         belongs_to :firm, class_name: "MyApplication::Business::Firm"
+      #       end
+      #     end
+      #   end
+      #
+      # == Bi-directional associations
+      #
+      # When you specify an association, there is usually an association on the associated model
+      # that specifies the same relationship in reverse. For example, with the following models:
+      #
+      #    class Dungeon < ActiveRecord::Base
+      #      has_many :traps
+      #      has_one :evil_wizard
+      #    end
+      #
+      #    class Trap < ActiveRecord::Base
+      #      belongs_to :dungeon
+      #    end
+      #
+      #    class EvilWizard < ActiveRecord::Base
+      #      belongs_to :dungeon
+      #    end
+      #
+      # The +traps+ association on +Dungeon+ and the +dungeon+ association on +Trap+ are
+      # the inverse of each other, and the inverse of the +dungeon+ association on +EvilWizard+
+      # is the +evil_wizard+ association on +Dungeon+ (and vice-versa). By default,
+      # Active Record can guess the inverse of the association based on the name
+      # of the class. The result is the following:
+      #
+      #    d = Dungeon.first
+      #    t = d.traps.first
+      #    d.object_id == t.dungeon.object_id # => true
+      #
+      # The +Dungeon+ instances +d+ and <tt>t.dungeon</tt> in the above example refer to
+      # the same in-memory instance since the association matches the name of the class.
+      # The result would be the same if we added +:inverse_of+ to our model definitions:
+      #
+      #    class Dungeon < ActiveRecord::Base
+      #      has_many :traps, inverse_of: :dungeon
+      #      has_one :evil_wizard, inverse_of: :dungeon
+      #    end
+      #
+      #    class Trap < ActiveRecord::Base
+      #      belongs_to :dungeon, inverse_of: :traps
+      #    end
+      #
+      #    class EvilWizard < ActiveRecord::Base
+      #      belongs_to :dungeon, inverse_of: :evil_wizard
+      #    end
+      #
+      # For more information, see the documentation for the +:inverse_of+ option.
+      #
+      # == Deleting from associations
+      #
+      # === Dependent associations
+      #
+      # #has_many, #has_one, and #belongs_to associations support the <tt>:dependent</tt> option.
+      # This allows you to specify that associated records should be deleted when the owner is
+      # deleted.
+      #
+      # For example:
+      #
+      #     class Author
+      #       has_many :posts, dependent: :destroy
+      #     end
+      #     Author.find(1).destroy # => Will destroy all of the author's posts, too
+      #
+      # The <tt>:dependent</tt> option can have different values which specify how the deletion
+      # is done. For more information, see the documentation for this option on the different
+      # specific association types. When no option is given, the behavior is to do nothing
+      # with the associated records when destroying a record.
+      #
+      # Note that <tt>:dependent</tt> is implemented using Rails' callback
+      # system, which works by processing callbacks in order. Therefore, other
+      # callbacks declared either before or after the <tt>:dependent</tt> option
+      # can affect what it does.
+      #
+      # Note that <tt>:dependent</tt> option is ignored for #has_one <tt>:through</tt> associations.
+      #
+      # === Delete or destroy?
+      #
+      # #has_many and #has_and_belongs_to_many associations have the methods <tt>destroy</tt>,
+      # <tt>delete</tt>, <tt>destroy_all</tt> and <tt>delete_all</tt>.
+      #
+      # For #has_and_belongs_to_many, <tt>delete</tt> and <tt>destroy</tt> are the same: they
+      # cause the records in the join table to be removed.
+      #
+      # For #has_many, <tt>destroy</tt> and <tt>destroy_all</tt> will always call the <tt>destroy</tt> method of the
+      # record(s) being removed so that callbacks are run. However <tt>delete</tt> and <tt>delete_all</tt> will either
+      # do the deletion according to the strategy specified by the <tt>:dependent</tt> option, or
+      # if no <tt>:dependent</tt> option is given, then it will follow the default strategy.
+      # The default strategy is to do nothing (leave the foreign keys with the parent ids set), except for
+      # #has_many <tt>:through</tt>, where the default strategy is <tt>delete_all</tt> (delete
+      # the join records, without running their callbacks).
+      #
+      # There is also a <tt>clear</tt> method which is the same as <tt>delete_all</tt>, except that
+      # it returns the association rather than the records which have been deleted.
+      #
+      # === What gets deleted?
+      #
+      # There is a potential pitfall here: #has_and_belongs_to_many and #has_many <tt>:through</tt>
+      # associations have records in join tables, as well as the associated records. So when we
+      # call one of these deletion methods, what exactly should be deleted?
+      #
+      # The answer is that it is assumed that deletion on an association is about removing the
+      # <i>link</i> between the owner and the associated object(s), rather than necessarily the
+      # associated objects themselves. So with #has_and_belongs_to_many and #has_many
+      # <tt>:through</tt>, the join records will be deleted, but the associated records won't.
+      #
+      # This makes sense if you think about it: if you were to call <tt>post.tags.delete(Tag.find_by(name: 'food'))</tt>
+      # you would want the 'food' tag to be unlinked from the post, rather than for the tag itself
+      # to be removed from the database.
+      #
+      # However, there are examples where this strategy doesn't make sense. For example, suppose
+      # a person has many projects, and each project has many tasks. If we deleted one of a person's
+      # tasks, we would probably not want the project to be deleted. In this scenario, the delete method
+      # won't actually work: it can only be used if the association on the join model is a
+      # #belongs_to. In other situations you are expected to perform operations directly on
+      # either the associated records or the <tt>:through</tt> association.
+      #
+      # With a regular #has_many there is no distinction between the "associated records"
+      # and the "link", so there is only one choice for what gets deleted.
+      #
+      # With #has_and_belongs_to_many and #has_many <tt>:through</tt>, if you want to delete the
+      # associated records themselves, you can always do something along the lines of
+      # <tt>person.tasks.each(&:destroy)</tt>.
+      #
+      # == Type safety with ActiveRecord::AssociationTypeMismatch
+      #
+      # If you attempt to assign an object to an association that doesn't match the inferred
+      # or specified <tt>:class_name</tt>, you'll get an ActiveRecord::AssociationTypeMismatch.
+      #
+      # == Options
+      #
+      # All of the association macros can be specialized through options. This makes cases
+      # more complex than the simple and guessable ones possible.
+      module ClassMethods
+        # Specifies a one-to-many association. The following methods for retrieval and query of
+        # collections of associated objects will be added:
+        #
+        # +collection+ is a placeholder for the symbol passed as the +name+ argument, so
+        # <tt>has_many :clients</tt> would add among others <tt>clients.empty?</tt>.
+        #
+        # [collection]
+        #   Returns a Relation of all the associated objects.
+        #   An empty Relation is returned if none are found.
+        # [collection<<(object, ...)]
+        #   Adds one or more objects to the collection by setting their foreign keys to the collection's primary key.
+        #   Note that this operation instantly fires update SQL without waiting for the save or update call on the
+        #   parent object, unless the parent object is a new record.
+        #   This will also run validations and callbacks of associated object(s).
+        # [collection.delete(object, ...)]
+        #   Removes one or more objects from the collection by setting their foreign keys to +NULL+.
+        #   Objects will be in addition destroyed if they're associated with <tt>dependent: :destroy</tt>,
+        #   and deleted if they're associated with <tt>dependent: :delete_all</tt>.
+        #
+        #   If the <tt>:through</tt> option is used, then the join records are deleted (rather than
+        #   nullified) by default, but you can specify <tt>dependent: :destroy</tt> or
+        #   <tt>dependent: :nullify</tt> to override this.
+        # [collection.destroy(object, ...)]
+        #   Removes one or more objects from the collection by running <tt>destroy</tt> on
+        #   each record, regardless of any dependent option, ensuring callbacks are run.
+        #
+        #   If the <tt>:through</tt> option is used, then the join records are destroyed
+        #   instead, not the objects themselves.
+        # [collection=objects]
+        #   Replaces the collections content by deleting and adding objects as appropriate. If the <tt>:through</tt>
+        #   option is true callbacks in the join models are triggered except destroy callbacks, since deletion is
+        #   direct by default. You can specify <tt>dependent: :destroy</tt> or
+        #   <tt>dependent: :nullify</tt> to override this.
+        # [collection_singular_ids]
+        #   Returns an array of the associated objects' ids
+        # [collection_singular_ids=ids]
+        #   Replace the collection with the objects identified by the primary keys in +ids+. This
+        #   method loads the models and calls <tt>collection=</tt>. See above.
+        # [collection.clear]
+        #   Removes every object from the collection. This destroys the associated objects if they
+        #   are associated with <tt>dependent: :destroy</tt>, deletes them directly from the
+        #   database if <tt>dependent: :delete_all</tt>, otherwise sets their foreign keys to +NULL+.
+        #   If the <tt>:through</tt> option is true no destroy callbacks are invoked on the join models.
+        #   Join models are directly deleted.
+        # [collection.empty?]
+        #   Returns +true+ if there are no associated objects.
+        # [collection.size]
+        #   Returns the number of associated objects.
+        # [collection.find(...)]
+        #   Finds an associated object according to the same rules as ActiveRecord::FinderMethods#find.
+        # [collection.exists?(...)]
+        #   Checks whether an associated object with the given conditions exists.
+        #   Uses the same rules as ActiveRecord::FinderMethods#exists?.
+        # [collection.build(attributes = {}, ...)]
+        #   Returns one or more new objects of the collection type that have been instantiated
+        #   with +attributes+ and linked to this object through a foreign key, but have not yet
+        #   been saved.
+        # [collection.create(attributes = {})]
+        #   Returns a new object of the collection type that has been instantiated
+        #   with +attributes+, linked to this object through a foreign key, and that has already
+        #   been saved (if it passed the validation). *Note*: This only works if the base model
+        #   already exists in the DB, not if it is a new (unsaved) record!
+        # [collection.create!(attributes = {})]
+        #   Does the same as <tt>collection.create</tt>, but raises ActiveRecord::RecordInvalid
+        #   if the record is invalid.
+        # [collection.reload]
+        #   Returns a Relation of all of the associated objects, forcing a database read.
+        #   An empty Relation is returned if none are found.
+        #
+        # === Example
+        #
+        # A <tt>Firm</tt> class declares <tt>has_many :clients</tt>, which will add:
+        # * <tt>Firm#clients</tt> (similar to <tt>Client.where(firm_id: id)</tt>)
+        # * <tt>Firm#clients<<</tt>
+        # * <tt>Firm#clients.delete</tt>
+        # * <tt>Firm#clients.destroy</tt>
+        # * <tt>Firm#clients=</tt>
+        # * <tt>Firm#client_ids</tt>
+        # * <tt>Firm#client_ids=</tt>
+        # * <tt>Firm#clients.clear</tt>
+        # * <tt>Firm#clients.empty?</tt> (similar to <tt>firm.clients.size == 0</tt>)
+        # * <tt>Firm#clients.size</tt> (similar to <tt>Client.count "firm_id = #{id}"</tt>)
+        # * <tt>Firm#clients.find</tt> (similar to <tt>Client.where(firm_id: id).find(id)</tt>)
+        # * <tt>Firm#clients.exists?(name: 'ACME')</tt> (similar to <tt>Client.exists?(name: 'ACME', firm_id: firm.id)</tt>)
+        # * <tt>Firm#clients.build</tt> (similar to <tt>Client.new(firm_id: id)</tt>)
+        # * <tt>Firm#clients.create</tt> (similar to <tt>c = Client.new(firm_id: id); c.save; c</tt>)
+        # * <tt>Firm#clients.create!</tt> (similar to <tt>c = Client.new(firm_id: id); c.save!</tt>)
+        # * <tt>Firm#clients.reload</tt>
+        # The declaration can also include an +options+ hash to specialize the behavior of the association.
+        #
+        # === Scopes
+        #
+        # You can pass a second argument +scope+ as a callable (i.e. proc or
+        # lambda) to retrieve a specific set of records or customize the generated
+        # query when you access the associated collection.
+        #
+        # Scope examples:
+        #   has_many :comments, -> { where(author_id: 1) }
+        #   has_many :employees, -> { joins(:address) }
+        #   has_many :posts, ->(blog) { where("max_post_length > ?", blog.max_post_length) }
+        #
+        # === Extensions
+        #
+        # The +extension+ argument allows you to pass a block into a has_many
+        # association. This is useful for adding new finders, creators and other
+        # factory-type methods to be used as part of the association.
+        #
+        # Extension examples:
+        #   has_many :employees do
+        #     def find_or_create_by_name(name)
+        #       first_name, last_name = name.split(" ", 2)
+        #       find_or_create_by(first_name: first_name, last_name: last_name)
+        #     end
+        #   end
+        #
+        # === Options
+        # [:class_name]
+        #   Specify the class name of the association. Use it only if that name can't be inferred
+        #   from the association name. So <tt>has_many :products</tt> will by default be linked
+        #   to the +Product+ class, but if the real class name is +SpecialProduct+, you'll have to
+        #   specify it with this option.
+        # [:foreign_key]
+        #   Specify the foreign key used for the association. By default this is guessed to be the name
+        #   of this class in lower-case and "_id" suffixed. So a Person class that makes a #has_many
+        #   association will use "person_id" as the default <tt>:foreign_key</tt>.
+        #
+        #   If you are going to modify the association (rather than just read from it), then it is
+        #   a good idea to set the <tt>:inverse_of</tt> option.
+        # [:foreign_type]
+        #   Specify the column used to store the associated object's type, if this is a polymorphic
+        #   association. By default this is guessed to be the name of the polymorphic association
+        #   specified on "as" option with a "_type" suffix. So a class that defines a
+        #   <tt>has_many :tags, as: :taggable</tt> association will use "taggable_type" as the
+        #   default <tt>:foreign_type</tt>.
+        # [:primary_key]
+        #   Specify the name of the column to use as the primary key for the association. By default this is +id+.
+        # [:dependent]
+        #   Controls what happens to the associated objects when
+        #   their owner is destroyed. Note that these are implemented as
+        #   callbacks, and Rails executes callbacks in order. Therefore, other
+        #   similar callbacks may affect the <tt>:dependent</tt> behavior, and the
+        #   <tt>:dependent</tt> behavior may affect other callbacks.
+        #
+        #   * <tt>:destroy</tt> causes all the associated objects to also be destroyed.
+        #   * <tt>:delete_all</tt> causes all the associated objects to be deleted directly from the database (so callbacks will not be executed).
+        #   * <tt>:nullify</tt> causes the foreign keys to be set to +NULL+. Callbacks are not executed.
+        #   * <tt>:restrict_with_exception</tt> causes an <tt>ActiveRecord::DeleteRestrictionError</tt> exception to be raised if there are any associated records.
+        #   * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there are any associated objects.
+        #
+        #   If using with the <tt>:through</tt> option, the association on the join model must be
+        #   a #belongs_to, and the records which get deleted are the join records, rather than
+        #   the associated records.
+        #
+        #   If using <tt>dependent: :destroy</tt> on a scoped association, only the scoped objects are destroyed.
+        #   For example, if a Post model defines
+        #   <tt>has_many :comments, -> { where published: true }, dependent: :destroy</tt> and <tt>destroy</tt> is
+        #   called on a post, only published comments are destroyed. This means that any unpublished comments in the
+        #   database would still contain a foreign key pointing to the now deleted post.
+        # [:counter_cache]
+        #   This option can be used to configure a custom named <tt>:counter_cache.</tt> You only need this option,
+        #   when you customized the name of your <tt>:counter_cache</tt> on the #belongs_to association.
+        # [:as]
+        #   Specifies a polymorphic interface (See #belongs_to).
+        # [:through]
+        #   Specifies an association through which to perform the query. This can be any other type
+        #   of association, including other <tt>:through</tt> associations. Options for <tt>:class_name</tt>,
+        #   <tt>:primary_key</tt> and <tt>:foreign_key</tt> are ignored, as the association uses the
+        #   source reflection.
+        #
+        #   If the association on the join model is a #belongs_to, the collection can be modified
+        #   and the records on the <tt>:through</tt> model will be automatically created and removed
+        #   as appropriate. Otherwise, the collection is read-only, so you should manipulate the
+        #   <tt>:through</tt> association directly.
+        #
+        #   If you are going to modify the association (rather than just read from it), then it is
+        #   a good idea to set the <tt>:inverse_of</tt> option on the source association on the
+        #   join model. This allows associated records to be built which will automatically create
+        #   the appropriate join model records when they are saved. (See the 'Association Join Models'
+        #   section above.)
+        # [:source]
+        #   Specifies the source association name used by #has_many <tt>:through</tt> queries.
+        #   Only use it if the name cannot be inferred from the association.
+        #   <tt>has_many :subscribers, through: :subscriptions</tt> will look for either <tt>:subscribers</tt> or
+        #   <tt>:subscriber</tt> on Subscription, unless a <tt>:source</tt> is given.
+        # [:source_type]
+        #   Specifies type of the source association used by #has_many <tt>:through</tt> queries where the source
+        #   association is a polymorphic #belongs_to.
+        # [:validate]
+        #   When set to +true+, validates new objects added to association when saving the parent object. +true+ by default.
+        #   If you want to ensure associated objects are revalidated on every update, use +validates_associated+.
+        # [:autosave]
+        #   If true, always save the associated objects or destroy them if marked for destruction,
+        #   when saving the parent object. If false, never save or destroy the associated objects.
+        #   By default, only save associated objects that are new records. This option is implemented as a
+        #   +before_save+ callback. Because callbacks are run in the order they are defined, associated objects
+        #   may need to be explicitly saved in any user-defined +before_save+ callbacks.
+        #
+        #   Note that NestedAttributes::ClassMethods#accepts_nested_attributes_for sets
+        #   <tt>:autosave</tt> to <tt>true</tt>.
+        # [:inverse_of]
+        #   Specifies the name of the #belongs_to association on the associated object
+        #   that is the inverse of this #has_many association.
+        #   See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
+        # [:extend]
+        #   Specifies a module or array of modules that will be extended into the association object returned.
+        #   Useful for defining methods on associations, especially when they should be shared between multiple
+        #   association objects.
+        #
+        # Option examples:
+        #   has_many :comments, -> { order("posted_on") }
+        #   has_many :comments, -> { includes(:author) }
+        #   has_many :people, -> { where(deleted: false).order("name") }, class_name: "Person"
+        #   has_many :tracks, -> { order("position") }, dependent: :destroy
+        #   has_many :comments, dependent: :nullify
+        #   has_many :tags, as: :taggable
+        #   has_many :reports, -> { readonly }
+        #   has_many :subscribers, through: :subscriptions, source: :user
+        def has_many(name, scope = nil, **options, &extension)
+          reflection = Builder::HasMany.build(self, name, scope, options, &extension)
+          Reflection.add_reflection self, name, reflection
         end
 
-        habtm_reflection = ActiveRecord::Reflection::HasAndBelongsToManyReflection.new(name, scope, options, self)
+        # Specifies a one-to-one association with another class. This method should only be used
+        # if the other class contains the foreign key. If the current class contains the foreign key,
+        # then you should use #belongs_to instead. See also ActiveRecord::Associations::ClassMethods's overview
+        # on when to use #has_one and when to use #belongs_to.
+        #
+        # The following methods for retrieval and query of a single associated object will be added:
+        #
+        # +association+ is a placeholder for the symbol passed as the +name+ argument, so
+        # <tt>has_one :manager</tt> would add among others <tt>manager.nil?</tt>.
+        #
+        # [association]
+        #   Returns the associated object. +nil+ is returned if none is found.
+        # [association=(associate)]
+        #   Assigns the associate object, extracts the primary key, sets it as the foreign key,
+        #   and saves the associate object. To avoid database inconsistencies, permanently deletes an existing
+        #   associated object when assigning a new one, even if the new one isn't saved to database.
+        # [build_association(attributes = {})]
+        #   Returns a new object of the associated type that has been instantiated
+        #   with +attributes+ and linked to this object through a foreign key, but has not
+        #   yet been saved.
+        # [create_association(attributes = {})]
+        #   Returns a new object of the associated type that has been instantiated
+        #   with +attributes+, linked to this object through a foreign key, and that
+        #   has already been saved (if it passed the validation).
+        # [create_association!(attributes = {})]
+        #   Does the same as <tt>create_association</tt>, but raises ActiveRecord::RecordInvalid
+        #   if the record is invalid.
+        # [reload_association]
+        #   Returns the associated object, forcing a database read.
+        #
+        # === Example
+        #
+        # An Account class declares <tt>has_one :beneficiary</tt>, which will add:
+        # * <tt>Account#beneficiary</tt> (similar to <tt>Beneficiary.where(account_id: id).first</tt>)
+        # * <tt>Account#beneficiary=(beneficiary)</tt> (similar to <tt>beneficiary.account_id = account.id; beneficiary.save</tt>)
+        # * <tt>Account#build_beneficiary</tt> (similar to <tt>Beneficiary.new(account_id: id)</tt>)
+        # * <tt>Account#create_beneficiary</tt> (similar to <tt>b = Beneficiary.new(account_id: id); b.save; b</tt>)
+        # * <tt>Account#create_beneficiary!</tt> (similar to <tt>b = Beneficiary.new(account_id: id); b.save!; b</tt>)
+        # * <tt>Account#reload_beneficiary</tt>
+        #
+        # === Scopes
+        #
+        # You can pass a second argument +scope+ as a callable (i.e. proc or
+        # lambda) to retrieve a specific record or customize the generated query
+        # when you access the associated object.
+        #
+        # Scope examples:
+        #   has_one :author, -> { where(comment_id: 1) }
+        #   has_one :employer, -> { joins(:company) }
+        #   has_one :latest_post, ->(blog) { where("created_at > ?", blog.enabled_at) }
+        #
+        # === Options
+        #
+        # The declaration can also include an +options+ hash to specialize the behavior of the association.
+        #
+        # Options are:
+        # [:class_name]
+        #   Specify the class name of the association. Use it only if that name can't be inferred
+        #   from the association name. So <tt>has_one :manager</tt> will by default be linked to the Manager class, but
+        #   if the real class name is Person, you'll have to specify it with this option.
+        # [:dependent]
+        #   Controls what happens to the associated object when
+        #   its owner is destroyed:
+        #
+        #   * <tt>:destroy</tt> causes the associated object to also be destroyed
+        #   * <tt>:delete</tt> causes the associated object to be deleted directly from the database (so callbacks will not execute)
+        #   * <tt>:nullify</tt> causes the foreign key to be set to +NULL+. Callbacks are not executed.
+        #   * <tt>:restrict_with_exception</tt> causes an <tt>ActiveRecord::DeleteRestrictionError</tt> exception to be raised if there is an associated record
+        #   * <tt>:restrict_with_error</tt> causes an error to be added to the owner if there is an associated object
+        #
+        #   Note that <tt>:dependent</tt> option is ignored when using <tt>:through</tt> option.
+        # [:foreign_key]
+        #   Specify the foreign key used for the association. By default this is guessed to be the name
+        #   of this class in lower-case and "_id" suffixed. So a Person class that makes a #has_one association
+        #   will use "person_id" as the default <tt>:foreign_key</tt>.
+        #
+        #   If you are going to modify the association (rather than just read from it), then it is
+        #   a good idea to set the <tt>:inverse_of</tt> option.
+        # [:foreign_type]
+        #   Specify the column used to store the associated object's type, if this is a polymorphic
+        #   association. By default this is guessed to be the name of the polymorphic association
+        #   specified on "as" option with a "_type" suffix. So a class that defines a
+        #   <tt>has_one :tag, as: :taggable</tt> association will use "taggable_type" as the
+        #   default <tt>:foreign_type</tt>.
+        # [:primary_key]
+        #   Specify the method that returns the primary key used for the association. By default this is +id+.
+        # [:as]
+        #   Specifies a polymorphic interface (See #belongs_to).
+        # [:through]
+        #   Specifies a Join Model through which to perform the query. Options for <tt>:class_name</tt>,
+        #   <tt>:primary_key</tt>, and <tt>:foreign_key</tt> are ignored, as the association uses the
+        #   source reflection. You can only use a <tt>:through</tt> query through a #has_one
+        #   or #belongs_to association on the join model.
+        #
+        #   If you are going to modify the association (rather than just read from it), then it is
+        #   a good idea to set the <tt>:inverse_of</tt> option.
+        # [:source]
+        #   Specifies the source association name used by #has_one <tt>:through</tt> queries.
+        #   Only use it if the name cannot be inferred from the association.
+        #   <tt>has_one :favorite, through: :favorites</tt> will look for a
+        #   <tt>:favorite</tt> on Favorite, unless a <tt>:source</tt> is given.
+        # [:source_type]
+        #   Specifies type of the source association used by #has_one <tt>:through</tt> queries where the source
+        #   association is a polymorphic #belongs_to.
+        # [:validate]
+        #   When set to +true+, validates new objects added to association when saving the parent object. +false+ by default.
+        #   If you want to ensure associated objects are revalidated on every update, use +validates_associated+.
+        # [:autosave]
+        #   If true, always save the associated object or destroy it if marked for destruction,
+        #   when saving the parent object. If false, never save or destroy the associated object.
+        #   By default, only save the associated object if it's a new record.
+        #
+        #   Note that NestedAttributes::ClassMethods#accepts_nested_attributes_for sets
+        #   <tt>:autosave</tt> to <tt>true</tt>.
+        # [:inverse_of]
+        #   Specifies the name of the #belongs_to association on the associated object
+        #   that is the inverse of this #has_one association.
+        #   See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
+        # [:required]
+        #   When set to +true+, the association will also have its presence validated.
+        #   This will validate the association itself, not the id. You can use
+        #   +:inverse_of+ to avoid an extra query during validation.
+        #
+        # Option examples:
+        #   has_one :credit_card, dependent: :destroy  # destroys the associated credit card
+        #   has_one :credit_card, dependent: :nullify  # updates the associated records foreign
+        #                                                 # key value to NULL rather than destroying it
+        #   has_one :last_comment, -> { order('posted_on') }, class_name: "Comment"
+        #   has_one :project_manager, -> { where(role: 'project_manager') }, class_name: "Person"
+        #   has_one :attachment, as: :attachable
+        #   has_one :boss, -> { readonly }
+        #   has_one :club, through: :membership
+        #   has_one :primary_address, -> { where(primary: true) }, through: :addressables, source: :addressable
+        #   has_one :credit_card, required: true
+        def has_one(name, scope = nil, **options)
+          reflection = Builder::HasOne.build(self, name, scope, options)
+          Reflection.add_reflection self, name, reflection
+        end
 
-        builder = Builder::HasAndBelongsToMany.new name, self, options
+        # Specifies a one-to-one association with another class. This method should only be used
+        # if this class contains the foreign key. If the other class contains the foreign key,
+        # then you should use #has_one instead. See also ActiveRecord::Associations::ClassMethods's overview
+        # on when to use #has_one and when to use #belongs_to.
+        #
+        # Methods will be added for retrieval and query for a single associated object, for which
+        # this object holds an id:
+        #
+        # +association+ is a placeholder for the symbol passed as the +name+ argument, so
+        # <tt>belongs_to :author</tt> would add among others <tt>author.nil?</tt>.
+        #
+        # [association]
+        #   Returns the associated object. +nil+ is returned if none is found.
+        # [association=(associate)]
+        #   Assigns the associate object, extracts the primary key, and sets it as the foreign key.
+        #   No modification or deletion of existing records takes place.
+        # [build_association(attributes = {})]
+        #   Returns a new object of the associated type that has been instantiated
+        #   with +attributes+ and linked to this object through a foreign key, but has not yet been saved.
+        # [create_association(attributes = {})]
+        #   Returns a new object of the associated type that has been instantiated
+        #   with +attributes+, linked to this object through a foreign key, and that
+        #   has already been saved (if it passed the validation).
+        # [create_association!(attributes = {})]
+        #   Does the same as <tt>create_association</tt>, but raises ActiveRecord::RecordInvalid
+        #   if the record is invalid.
+        # [reload_association]
+        #   Returns the associated object, forcing a database read.
+        #
+        # === Example
+        #
+        # A Post class declares <tt>belongs_to :author</tt>, which will add:
+        # * <tt>Post#author</tt> (similar to <tt>Author.find(author_id)</tt>)
+        # * <tt>Post#author=(author)</tt> (similar to <tt>post.author_id = author.id</tt>)
+        # * <tt>Post#build_author</tt> (similar to <tt>post.author = Author.new</tt>)
+        # * <tt>Post#create_author</tt> (similar to <tt>post.author = Author.new; post.author.save; post.author</tt>)
+        # * <tt>Post#create_author!</tt> (similar to <tt>post.author = Author.new; post.author.save!; post.author</tt>)
+        # * <tt>Post#reload_author</tt>
+        # The declaration can also include an +options+ hash to specialize the behavior of the association.
+        #
+        # === Scopes
+        #
+        # You can pass a second argument +scope+ as a callable (i.e. proc or
+        # lambda) to retrieve a specific record or customize the generated query
+        # when you access the associated object.
+        #
+        # Scope examples:
+        #   belongs_to :firm, -> { where(id: 2) }
+        #   belongs_to :user, -> { joins(:friends) }
+        #   belongs_to :level, ->(game) { where("game_level > ?", game.current_level) }
+        #
+        # === Options
+        #
+        # [:class_name]
+        #   Specify the class name of the association. Use it only if that name can't be inferred
+        #   from the association name. So <tt>belongs_to :author</tt> will by default be linked to the Author class, but
+        #   if the real class name is Person, you'll have to specify it with this option.
+        # [:foreign_key]
+        #   Specify the foreign key used for the association. By default this is guessed to be the name
+        #   of the association with an "_id" suffix. So a class that defines a <tt>belongs_to :person</tt>
+        #   association will use "person_id" as the default <tt>:foreign_key</tt>. Similarly,
+        #   <tt>belongs_to :favorite_person, class_name: "Person"</tt> will use a foreign key
+        #   of "favorite_person_id".
+        #
+        #   If you are going to modify the association (rather than just read from it), then it is
+        #   a good idea to set the <tt>:inverse_of</tt> option.
+        # [:foreign_type]
+        #   Specify the column used to store the associated object's type, if this is a polymorphic
+        #   association. By default this is guessed to be the name of the association with a "_type"
+        #   suffix. So a class that defines a <tt>belongs_to :taggable, polymorphic: true</tt>
+        #   association will use "taggable_type" as the default <tt>:foreign_type</tt>.
+        # [:primary_key]
+        #   Specify the method that returns the primary key of associated object used for the association.
+        #   By default this is +id+.
+        # [:dependent]
+        #   If set to <tt>:destroy</tt>, the associated object is destroyed when this object is. If set to
+        #   <tt>:delete</tt>, the associated object is deleted *without* calling its destroy method.
+        #   This option should not be specified when #belongs_to is used in conjunction with
+        #   a #has_many relationship on another class because of the potential to leave
+        #   orphaned records behind.
+        # [:counter_cache]
+        #   Caches the number of belonging objects on the associate class through the use of CounterCache::ClassMethods#increment_counter
+        #   and CounterCache::ClassMethods#decrement_counter. The counter cache is incremented when an object of this
+        #   class is created and decremented when it's destroyed. This requires that a column
+        #   named <tt>#{table_name}_count</tt> (such as +comments_count+ for a belonging Comment class)
+        #   is used on the associate class (such as a Post class) - that is the migration for
+        #   <tt>#{table_name}_count</tt> is created on the associate class (such that <tt>Post.comments_count</tt> will
+        #   return the count cached, see note below). You can also specify a custom counter
+        #   cache column by providing a column name instead of a +true+/+false+ value to this
+        #   option (e.g., <tt>counter_cache: :my_custom_counter</tt>.)
+        #   Note: Specifying a counter cache will add it to that model's list of readonly attributes
+        #   using +attr_readonly+.
+        # [:polymorphic]
+        #   Specify this association is a polymorphic association by passing +true+.
+        #   Note: If you've enabled the counter cache, then you may want to add the counter cache attribute
+        #   to the +attr_readonly+ list in the associated classes (e.g. <tt>class Post; attr_readonly :comments_count; end</tt>).
+        # [:validate]
+        #   When set to +true+, validates new objects added to association when saving the parent object. +false+ by default.
+        #   If you want to ensure associated objects are revalidated on every update, use +validates_associated+.
+        # [:autosave]
+        #   If true, always save the associated object or destroy it if marked for destruction, when
+        #   saving the parent object.
+        #   If false, never save or destroy the associated object.
+        #   By default, only save the associated object if it's a new record.
+        #
+        #   Note that NestedAttributes::ClassMethods#accepts_nested_attributes_for
+        #   sets <tt>:autosave</tt> to <tt>true</tt>.
+        # [:touch]
+        #   If true, the associated object will be touched (the updated_at/on attributes set to current time)
+        #   when this record is either saved or destroyed. If you specify a symbol, that attribute
+        #   will be updated with the current time in addition to the updated_at/on attribute.
+        #   Please note that with touching no validation is performed and only the +after_touch+,
+        #   +after_commit+ and +after_rollback+ callbacks are executed.
+        # [:inverse_of]
+        #   Specifies the name of the #has_one or #has_many association on the associated
+        #   object that is the inverse of this #belongs_to association.
+        #   See ActiveRecord::Associations::ClassMethods's overview on Bi-directional associations for more detail.
+        # [:optional]
+        #   When set to +true+, the association will not have its presence validated.
+        # [:required]
+        #   When set to +true+, the association will also have its presence validated.
+        #   This will validate the association itself, not the id. You can use
+        #   +:inverse_of+ to avoid an extra query during validation.
+        #   NOTE: <tt>required</tt> is set to <tt>true</tt> by default and is deprecated. If
+        #   you don't want to have association presence validated, use <tt>optional: true</tt>.
+        # [:default]
+        #   Provide a callable (i.e. proc or lambda) to specify that the association should
+        #   be initialized with a particular record before validation.
+        #
+        # Option examples:
+        #   belongs_to :firm, foreign_key: "client_of"
+        #   belongs_to :person, primary_key: "name", foreign_key: "person_name"
+        #   belongs_to :author, class_name: "Person", foreign_key: "author_id"
+        #   belongs_to :valid_coupon, ->(o) { where "discounts > ?", o.payments_count },
+        #                             class_name: "Coupon", foreign_key: "coupon_id"
+        #   belongs_to :attachable, polymorphic: true
+        #   belongs_to :project, -> { readonly }
+        #   belongs_to :post, counter_cache: true
+        #   belongs_to :comment, touch: true
+        #   belongs_to :company, touch: :employees_last_updated_at
+        #   belongs_to :user, optional: true
+        #   belongs_to :account, default: -> { company.account }
+        def belongs_to(name, scope = nil, **options)
+          reflection = Builder::BelongsTo.build(self, name, scope, options)
+          Reflection.add_reflection self, name, reflection
+        end
 
-        join_model = builder.through_model
+        # Specifies a many-to-many relationship with another class. This associates two classes via an
+        # intermediate join table. Unless the join table is explicitly specified as an option, it is
+        # guessed using the lexical order of the class names. So a join between Developer and Project
+        # will give the default join table name of "developers_projects" because "D" precedes "P" alphabetically.
+        # Note that this precedence is calculated using the <tt><</tt> operator for String. This
+        # means that if the strings are of different lengths, and the strings are equal when compared
+        # up to the shortest length, then the longer string is considered of higher
+        # lexical precedence than the shorter one. For example, one would expect the tables "paper_boxes" and "papers"
+        # to generate a join table name of "papers_paper_boxes" because of the length of the name "paper_boxes",
+        # but it in fact generates a join table name of "paper_boxes_papers". Be aware of this caveat, and use the
+        # custom <tt>:join_table</tt> option if you need to.
+        # If your tables share a common prefix, it will only appear once at the beginning. For example,
+        # the tables "catalog_categories" and "catalog_products" generate a join table name of "catalog_categories_products".
+        #
+        # The join table should not have a primary key or a model associated with it. You must manually generate the
+        # join table with a migration such as this:
+        #
+        #   class CreateDevelopersProjectsJoinTable < ActiveRecord::Migration[5.0]
+        #     def change
+        #       create_join_table :developers, :projects
+        #     end
+        #   end
+        #
+        # It's also a good idea to add indexes to each of those columns to speed up the joins process.
+        # However, in MySQL it is advised to add a compound index for both of the columns as MySQL only
+        # uses one index per table during the lookup.
+        #
+        # Adds the following methods for retrieval and query:
+        #
+        # +collection+ is a placeholder for the symbol passed as the +name+ argument, so
+        # <tt>has_and_belongs_to_many :categories</tt> would add among others <tt>categories.empty?</tt>.
+        #
+        # [collection]
+        #   Returns a Relation of all the associated objects.
+        #   An empty Relation is returned if none are found.
+        # [collection<<(object, ...)]
+        #   Adds one or more objects to the collection by creating associations in the join table
+        #   (<tt>collection.push</tt> and <tt>collection.concat</tt> are aliases to this method).
+        #   Note that this operation instantly fires update SQL without waiting for the save or update call on the
+        #   parent object, unless the parent object is a new record.
+        # [collection.delete(object, ...)]
+        #   Removes one or more objects from the collection by removing their associations from the join table.
+        #   This does not destroy the objects.
+        # [collection.destroy(object, ...)]
+        #   Removes one or more objects from the collection by running destroy on each association in the join table, overriding any dependent option.
+        #   This does not destroy the objects.
+        # [collection=objects]
+        #   Replaces the collection's content by deleting and adding objects as appropriate.
+        # [collection_singular_ids]
+        #   Returns an array of the associated objects' ids.
+        # [collection_singular_ids=ids]
+        #   Replace the collection by the objects identified by the primary keys in +ids+.
+        # [collection.clear]
+        #   Removes every object from the collection. This does not destroy the objects.
+        # [collection.empty?]
+        #   Returns +true+ if there are no associated objects.
+        # [collection.size]
+        #   Returns the number of associated objects.
+        # [collection.find(id)]
+        #   Finds an associated object responding to the +id+ and that
+        #   meets the condition that it has to be associated with this object.
+        #   Uses the same rules as ActiveRecord::FinderMethods#find.
+        # [collection.exists?(...)]
+        #   Checks whether an associated object with the given conditions exists.
+        #   Uses the same rules as ActiveRecord::FinderMethods#exists?.
+        # [collection.build(attributes = {})]
+        #   Returns a new object of the collection type that has been instantiated
+        #   with +attributes+ and linked to this object through the join table, but has not yet been saved.
+        # [collection.create(attributes = {})]
+        #   Returns a new object of the collection type that has been instantiated
+        #   with +attributes+, linked to this object through the join table, and that has already been
+        #   saved (if it passed the validation).
+        # [collection.reload]
+        #   Returns a Relation of all of the associated objects, forcing a database read.
+        #   An empty Relation is returned if none are found.
+        #
+        # === Example
+        #
+        # A Developer class declares <tt>has_and_belongs_to_many :projects</tt>, which will add:
+        # * <tt>Developer#projects</tt>
+        # * <tt>Developer#projects<<</tt>
+        # * <tt>Developer#projects.delete</tt>
+        # * <tt>Developer#projects.destroy</tt>
+        # * <tt>Developer#projects=</tt>
+        # * <tt>Developer#project_ids</tt>
+        # * <tt>Developer#project_ids=</tt>
+        # * <tt>Developer#projects.clear</tt>
+        # * <tt>Developer#projects.empty?</tt>
+        # * <tt>Developer#projects.size</tt>
+        # * <tt>Developer#projects.find(id)</tt>
+        # * <tt>Developer#projects.exists?(...)</tt>
+        # * <tt>Developer#projects.build</tt> (similar to <tt>Project.new(developer_id: id)</tt>)
+        # * <tt>Developer#projects.create</tt> (similar to <tt>c = Project.new(developer_id: id); c.save; c</tt>)
+        # * <tt>Developer#projects.reload</tt>
+        # The declaration may include an +options+ hash to specialize the behavior of the association.
+        #
+        # === Scopes
+        #
+        # You can pass a second argument +scope+ as a callable (i.e. proc or
+        # lambda) to retrieve a specific set of records or customize the generated
+        # query when you access the associated collection.
+        #
+        # Scope examples:
+        #   has_and_belongs_to_many :projects, -> { includes(:milestones, :manager) }
+        #   has_and_belongs_to_many :categories, ->(post) {
+        #     where("default_category = ?", post.default_category)
+        #   }
+        #
+        # === Extensions
+        #
+        # The +extension+ argument allows you to pass a block into a
+        # has_and_belongs_to_many association. This is useful for adding new
+        # finders, creators and other factory-type methods to be used as part of
+        # the association.
+        #
+        # Extension examples:
+        #   has_and_belongs_to_many :contractors do
+        #     def find_or_create_by_name(name)
+        #       first_name, last_name = name.split(" ", 2)
+        #       find_or_create_by(first_name: first_name, last_name: last_name)
+        #     end
+        #   end
+        #
+        # === Options
+        #
+        # [:class_name]
+        #   Specify the class name of the association. Use it only if that name can't be inferred
+        #   from the association name. So <tt>has_and_belongs_to_many :projects</tt> will by default be linked to the
+        #   Project class, but if the real class name is SuperProject, you'll have to specify it with this option.
+        # [:join_table]
+        #   Specify the name of the join table if the default based on lexical order isn't what you want.
+        #   <b>WARNING:</b> If you're overwriting the table name of either class, the +table_name+ method
+        #   MUST be declared underneath any #has_and_belongs_to_many declaration in order to work.
+        # [:foreign_key]
+        #   Specify the foreign key used for the association. By default this is guessed to be the name
+        #   of this class in lower-case and "_id" suffixed. So a Person class that makes
+        #   a #has_and_belongs_to_many association to Project will use "person_id" as the
+        #   default <tt>:foreign_key</tt>.
+        #
+        #   If you are going to modify the association (rather than just read from it), then it is
+        #   a good idea to set the <tt>:inverse_of</tt> option.
+        # [:association_foreign_key]
+        #   Specify the foreign key used for the association on the receiving side of the association.
+        #   By default this is guessed to be the name of the associated class in lower-case and "_id" suffixed.
+        #   So if a Person class makes a #has_and_belongs_to_many association to Project,
+        #   the association will use "project_id" as the default <tt>:association_foreign_key</tt>.
+        # [:validate]
+        #   When set to +true+, validates new objects added to association when saving the parent object. +true+ by default.
+        #   If you want to ensure associated objects are revalidated on every update, use +validates_associated+.
+        # [:autosave]
+        #   If true, always save the associated objects or destroy them if marked for destruction, when
+        #   saving the parent object.
+        #   If false, never save or destroy the associated objects.
+        #   By default, only save associated objects that are new records.
+        #
+        #   Note that NestedAttributes::ClassMethods#accepts_nested_attributes_for sets
+        #   <tt>:autosave</tt> to <tt>true</tt>.
+        #
+        # Option examples:
+        #   has_and_belongs_to_many :projects
+        #   has_and_belongs_to_many :projects, -> { includes(:milestones, :manager) }
+        #   has_and_belongs_to_many :nations, class_name: "Country"
+        #   has_and_belongs_to_many :categories, join_table: "prods_cats"
+        #   has_and_belongs_to_many :categories, -> { readonly }
+        def has_and_belongs_to_many(name, scope = nil, **options, &extension)
+          habtm_reflection = ActiveRecord::Reflection::HasAndBelongsToManyReflection.new(name, scope, options, self)
 
-        const_set join_model.name, join_model
-        private_constant join_model.name
+          builder = Builder::HasAndBelongsToMany.new name, self, options
 
-        middle_reflection = builder.middle_reflection join_model
+          join_model = builder.through_model
 
-        Builder::HasMany.define_callbacks self, middle_reflection
-        Reflection.add_reflection self, middle_reflection.name, middle_reflection
-        middle_reflection.parent_reflection = habtm_reflection
+          const_set join_model.name, join_model
+          private_constant join_model.name
 
-        include Module.new {
-          class_eval <<-RUBY, __FILE__, __LINE__ + 1
-          def destroy_associations
-            association(:#{middle_reflection.name}).delete_all(:delete_all)
-            association(:#{name}).reset
-            super
-          end
-          RUBY
-        }
+          middle_reflection = builder.middle_reflection join_model
 
-        hm_options = {}
-        hm_options[:through] = middle_reflection.name
-        hm_options[:source] = join_model.right_reflection.name
+          Builder::HasMany.define_callbacks self, middle_reflection
+          Reflection.add_reflection self, middle_reflection.name, middle_reflection
+          middle_reflection.parent_reflection = habtm_reflection
 
-        [:before_add, :after_add, :before_remove, :after_remove, :autosave, :validate, :join_table, :class_name, :extend].each do |k|
-          hm_options[k] = options[k] if options.key? k
-        end
+          include Module.new {
+            class_eval <<-RUBY, __FILE__, __LINE__ + 1
+              def destroy_associations
+                association(:#{middle_reflection.name}).delete_all(:delete_all)
+                association(:#{name}).reset
+                super
+              end
+            RUBY
+          }
 
-        has_many name, scope, hm_options, &extension
-        self._reflections[name.to_s].parent_reflection = habtm_reflection
+          hm_options = {}
+          hm_options[:through] = middle_reflection.name
+          hm_options[:source] = join_model.right_reflection.name
+
+          [:before_add, :after_add, :before_remove, :after_remove, :autosave, :validate, :join_table, :class_name, :extend].each do |k|
+            hm_options[k] = options[k] if options.key? k
+          end
+
+          has_many name, scope, hm_options, &extension
+          _reflections[name.to_s].parent_reflection = habtm_reflection
+        end
       end
-    end
   end
 end
diff --git a/activerecord/lib/active_record/associations/alias_tracker.rb b/activerecord/lib/active_record/associations/alias_tracker.rb
index 2b7e4f28c5..272eede824 100644
--- a/activerecord/lib/active_record/associations/alias_tracker.rb
+++ b/activerecord/lib/active_record/associations/alias_tracker.rb
@@ -1,52 +1,41 @@
-require 'active_support/core_ext/string/conversions'
+# frozen_string_literal: true
+
+require "active_support/core_ext/string/conversions"
 
 module ActiveRecord
   module Associations
-    # Keeps track of table aliases for ActiveRecord::Associations::ClassMethods::JoinDependency and
-    # ActiveRecord::Associations::ThroughAssociationScope
+    # Keeps track of table aliases for ActiveRecord::Associations::JoinDependency
     class AliasTracker # :nodoc:
-      attr_reader :aliases
-
-      def self.create(connection, initial_table, type_caster)
-        aliases = Hash.new(0)
-        aliases[initial_table] = 1
-        new connection, aliases, type_caster
-      end
-
-      def self.create_with_joins(connection, initial_table, joins, type_caster)
+      def self.create(connection, initial_table, joins)
         if joins.empty?
-          create(connection, initial_table, type_caster)
+          aliases = Hash.new(0)
         else
           aliases = Hash.new { |h, k|
             h[k] = initial_count_for(connection, k, joins)
           }
-          aliases[initial_table] = 1
-          new connection, aliases, type_caster
         end
+        aliases[initial_table] = 1
+        new(connection, aliases)
       end
 
       def self.initial_count_for(connection, name, table_joins)
-        # quoted_name should be downcased as some database adapters (Oracle) return quoted name in uppercase
-        quoted_name = connection.quote_table_name(name).downcase
+        quoted_name = nil
 
         counts = table_joins.map do |join|
           if join.is_a?(Arel::Nodes::StringJoin)
+            # quoted_name should be case ignored as some database adapters (Oracle) return quoted name in uppercase
+            quoted_name ||= connection.quote_table_name(name)
+
             # Table names + table aliases
-            join.left.downcase.scan(
-              /join(?:\s+\w+)?\s+(\S+\s+)?#{quoted_name}\son/
+            join.left.scan(
+              /JOIN(?:\s+\w+)?\s+(?:\S+\s+)?(?:#{quoted_name}|#{name})\sON/i
             ).size
-          elsif join.respond_to? :left
-            join.left.table_name == name ? 1 : 0
+          elsif join.is_a?(Arel::Nodes::Join)
+            join.left.name == name ? 1 : 0
+          elsif join.is_a?(Hash)
+            join[name]
           else
-            # this branch is reached by two tests:
-            #
-            # activerecord/test/cases/associations/cascaded_eager_loading_test.rb:37
-            #   with :posts
-            #
-            # activerecord/test/cases/associations/eager_test.rb:1133
-            #   with :comments
-            #
-            0
+            raise ArgumentError, "joins list should be initialized by list of Arel::Nodes::Join"
           end
         end
 
@@ -54,17 +43,16 @@ module ActiveRecord
       end
 
       # table_joins is an array of arel joins which might conflict with the aliases we assign here
-      def initialize(connection, aliases, type_caster)
+      def initialize(connection, aliases)
         @aliases    = aliases
         @connection = connection
-        @type_caster = type_caster
       end
 
-      def aliased_table_for(table_name, aliased_name)
+      def aliased_table_for(table_name, aliased_name, type_caster)
         if aliases[table_name].zero?
           # If it's zero, we can have our table_name
           aliases[table_name] = 1
-          Arel::Table.new(table_name, type_caster: @type_caster)
+          Arel::Table.new(table_name, type_caster: type_caster)
         else
           # Otherwise, we need to use an alias
           aliased_name = @connection.table_alias_for(aliased_name)
@@ -77,10 +65,12 @@ module ActiveRecord
           else
             aliased_name
           end
-          Arel::Table.new(table_name, type_caster: @type_caster).alias(table_alias)
+          Arel::Table.new(table_name, type_caster: type_caster).alias(table_alias)
         end
       end
 
+      attr_reader :aliases
+
       private
 
         def truncate(name)
diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index 7c729676a7..bf4942aac8 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/array/wrap'
+# frozen_string_literal: true
+
+require "active_support/core_ext/array/wrap"
 
 module ActiveRecord
   module Associations
@@ -17,9 +19,8 @@ module ActiveRecord
     #         HasManyThroughAssociation + ThroughAssociation
     class Association #:nodoc:
       attr_reader :owner, :target, :reflection
-      attr_accessor :inversed
 
-      delegate :options, :to => :reflection
+      delegate :options, to: :reflection
 
       def initialize(owner, reflection)
         reflection.check_validity!
@@ -30,14 +31,6 @@ module ActiveRecord
         reset_scope
       end
 
-      # Returns the name of the table of the associated class:
-      #
-      #   post.comments.aliased_table_name # => "comments"
-      #
-      def aliased_table_name
-        klass.table_name
-      end
-
       # Resets the \loaded flag to +false+ and sets the \target to +nil+.
       def reset
         @loaded = false
@@ -47,7 +40,9 @@ module ActiveRecord
       end
 
       # Reloads the \target and returns +self+ on success.
-      def reload
+      # The QueryCache is cleared if +force+ is true.
+      def reload(force = false)
+        klass.connection.clear_query_cache if force && klass
         reset
         reset_scope
         load_target
@@ -73,7 +68,7 @@ module ActiveRecord
       #
       # Note that if the target has not been loaded, it is not considered stale.
       def stale_target?
-        !inversed && loaded? && @stale_state != stale_state
+        !@inversed && loaded? && @stale_state != stale_state
       end
 
       # Sets the target of this association to <tt>\target</tt>, and the \loaded flag to +true+.
@@ -83,19 +78,7 @@ module ActiveRecord
       end
 
       def scope
-        target_scope.merge(association_scope)
-      end
-
-      # The scope for this association.
-      #
-      # Note that the association_scope is merged into the target_scope only when the
-      # scope method is called. This is because at that point the call may be surrounded
-      # by scope.scoping { ... } or with_scope { ... } etc, which affects the scope which
-      # actually gets built.
-      def association_scope
-        if klass
-          @association_scope ||= AssociationScope.scope(self, klass.connection)
-        end
+        target_scope.merge!(association_scope)
       end
 
       def reset_scope
@@ -104,24 +87,46 @@ module ActiveRecord
 
       # Set the inverse association, if possible
       def set_inverse_instance(record)
-        if invertible_for?(record)
-          inverse = record.association(inverse_reflection_for(record).name)
-          inverse.target = owner
-          inverse.inversed = true
+        if inverse = inverse_association_for(record)
+          inverse.inversed_from(owner)
+        end
+        record
+      end
+
+      def set_inverse_instance_from_queries(record)
+        if inverse = inverse_association_for(record)
+          inverse.inversed_from_queries(owner)
         end
         record
       end
 
+      # Remove the inverse association, if possible
+      def remove_inverse_instance(record)
+        if inverse = inverse_association_for(record)
+          inverse.inversed_from(nil)
+        end
+      end
+
+      def inversed_from(record)
+        self.target = record
+        @inversed = !!record
+      end
+      alias :inversed_from_queries :inversed_from
+
       # Returns the class of the target. belongs_to polymorphic overrides this to look at the
       # polymorphic_type field on the owner.
       def klass
         reflection.klass
       end
 
-      # Can be overridden (i.e. in ThroughAssociation) to merge in other scopes (i.e. the
-      # through association's scope)
-      def target_scope
-        AssociationRelation.create(klass, klass.arel_table, klass.predicate_builder, self).merge!(klass.all)
+      def extensions
+        extensions = klass.default_extensions | reflection.extensions
+
+        if reflection.scope
+          extensions |= reflection.scope_for(klass.unscoped, owner).extensions
+        end
+
+        extensions
       end
 
       # Loads the \target if needed and returns it.
@@ -143,17 +148,9 @@ module ActiveRecord
         reset
       end
 
-      def interpolate(sql, record = nil)
-        if sql.respond_to?(:to_proc)
-          owner.instance_exec(record, &sql)
-        else
-          sql
-        end
-      end
-
-      # We can't dump @reflection since it contains the scope proc
+      # We can't dump @reflection and @through_reflection since it contains the scope proc
       def marshal_dump
-        ivars = (instance_variables - [:@reflection]).map { |name| [name, instance_variable_get(name)] }
+        ivars = (instance_variables - [:@reflection, :@through_reflection]).map { |name| [name, instance_variable_get(name)] }
         [@reflection.name, ivars]
       end
 
@@ -163,14 +160,46 @@ module ActiveRecord
         @reflection = @owner.class._reflect_on_association(reflection_name)
       end
 
-      def initialize_attributes(record) #:nodoc:
+      def initialize_attributes(record, except_from_scope_attributes = nil) #:nodoc:
+        except_from_scope_attributes ||= {}
         skip_assign = [reflection.foreign_key, reflection.type].compact
-        attributes = create_scope.except(*(record.changed - skip_assign))
-        record.assign_attributes(attributes)
+        assigned_keys = record.changed_attribute_names_to_save
+        assigned_keys += except_from_scope_attributes.keys.map(&:to_s)
+        attributes = scope_for_create.except!(*(assigned_keys - skip_assign))
+        record.send(:_assign_attributes, attributes) if attributes.any?
         set_inverse_instance(record)
       end
 
+      def create(attributes = {}, &block)
+        _create_record(attributes, &block)
+      end
+
+      def create!(attributes = {}, &block)
+        _create_record(attributes, true, &block)
+      end
+
       private
+        # The scope for this association.
+        #
+        # Note that the association_scope is merged into the target_scope only when the
+        # scope method is called. This is because at that point the call may be surrounded
+        # by scope.scoping { ... } or unscoped { ... } etc, which affects the scope which
+        # actually gets built.
+        def association_scope
+          if klass
+            @association_scope ||= AssociationScope.scope(self)
+          end
+        end
+
+        # Can be overridden (i.e. in ThroughAssociation) to merge in other scopes (i.e. the
+        # through association's scope)
+        def target_scope
+          AssociationRelation.create(klass, self).merge!(klass.all)
+        end
+
+        def scope_for_create
+          scope.scope_for_create
+        end
 
         def find_target?
           !loaded? && (!owner.new_record? || foreign_key_present?) && klass
@@ -182,8 +211,8 @@ module ActiveRecord
           if (reflection.has_one? || reflection.collection?) && !options[:through]
             attributes[reflection.foreign_key] = owner[reflection.active_record_primary_key]
 
-            if reflection.options[:as]
-              attributes[reflection.type] = owner.class.base_class.name
+            if reflection.type
+              attributes[reflection.type] = owner.class.polymorphic_name
             end
           end
 
@@ -214,12 +243,19 @@ module ActiveRecord
           unless record.is_a?(reflection.klass)
             fresh_class = reflection.class_name.safe_constantize
             unless fresh_class && record.is_a?(fresh_class)
-              message = "#{reflection.class_name}(##{reflection.klass.object_id}) expected, got #{record.class}(##{record.class.object_id})"
+              message = "#{reflection.class_name}(##{reflection.klass.object_id}) expected, "\
+                "got #{record.inspect} which is an instance of #{record.class}(##{record.class.object_id})"
               raise ActiveRecord::AssociationTypeMismatch, message
             end
           end
         end
 
+        def inverse_association_for(record)
+          if invertible_for?(record)
+            record.association(inverse_reflection_for(record).name)
+          end
+        end
+
         # Can be redefined by subclasses, notably polymorphic belongs_to
         # The record parameter is necessary to support polymorphic inverses as we must check for
         # the association in the specific class of the record.
@@ -242,15 +278,24 @@ module ActiveRecord
         # so that when stale_state is different from the value stored on the last find_target,
         # the target is stale.
         #
-        # This is only relevant to certain associations, which is why it returns nil by default.
+        # This is only relevant to certain associations, which is why it returns +nil+ by default.
         def stale_state
         end
 
         def build_record(attributes)
           reflection.build_association(attributes) do |record|
-            initialize_attributes(record)
+            initialize_attributes(record, attributes)
+            yield(record) if block_given?
           end
         end
+
+        # Returns true if statement cache should be skipped on the association reader.
+        def skip_statement_cache?(scope)
+          reflection.has_scope? ||
+            scope.eager_loading? ||
+            klass.scope_attributes? ||
+            reflection.source_reflection.active_record.default_scopes.any?
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/association_scope.rb b/activerecord/lib/active_record/associations/association_scope.rb
index a140dc239c..0a90a6104a 100644
--- a/activerecord/lib/active_record/associations/association_scope.rb
+++ b/activerecord/lib/active_record/associations/association_scope.rb
@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     class AssociationScope #:nodoc:
-      def self.scope(association, connection)
-        INSTANCE.scope(association, connection)
+      def self.scope(association)
+        INSTANCE.scope(association)
       end
 
       def self.create(&block)
@@ -16,20 +18,15 @@ module ActiveRecord
 
       INSTANCE = create
 
-      def scope(association, connection)
+      def scope(association)
         klass = association.klass
         reflection = association.reflection
         scope = klass.unscoped
         owner = association.owner
-        alias_tracker = AliasTracker.create connection, association.klass.table_name, klass.type_caster
-        chain_head, chain_tail = get_chain(reflection, association, alias_tracker)
-
-        scope.extending! Array(reflection.options[:extend])
-        add_constraints(scope, owner, klass, reflection, chain_head, chain_tail)
-      end
+        chain = get_chain(reflection, association, scope.alias_tracker)
 
-      def join_type
-        Arel::Nodes::InnerJoin
+        scope.extending! reflection.extensions
+        add_constraints(scope, owner, chain)
       end
 
       def self.get_bind_values(owner, chain)
@@ -38,129 +35,130 @@ module ActiveRecord
 
         binds << last_reflection.join_id_for(owner)
         if last_reflection.type
-          binds << owner.class.base_class.name
+          binds << owner.class.polymorphic_name
         end
 
         chain.each_cons(2).each do |reflection, next_reflection|
           if reflection.type
-            binds << next_reflection.klass.base_class.name
+            binds << next_reflection.klass.polymorphic_name
           end
         end
         binds
       end
 
-      protected
+      private
+        attr_reader :value_transformation
 
-      attr_reader :value_transformation
+        def join(table, constraint)
+          table.create_join(table, table.create_on(constraint))
+        end
 
-      private
-      def join(table, constraint)
-        table.create_join(table, table.create_on(constraint), join_type)
-      end
+        def last_chain_scope(scope, reflection, owner)
+          join_keys = reflection.join_keys
+          key = join_keys.key
+          foreign_key = join_keys.foreign_key
 
-      def last_chain_scope(scope, table, reflection, owner, association_klass)
-        join_keys = reflection.join_keys(association_klass)
-        key = join_keys.key
-        foreign_key = join_keys.foreign_key
+          table = reflection.aliased_table
+          value = transform_value(owner[foreign_key])
+          scope = apply_scope(scope, table, key, value)
 
-        value = transform_value(owner[foreign_key])
-        scope = scope.where(table.name => { key => value })
+          if reflection.type
+            polymorphic_type = transform_value(owner.class.polymorphic_name)
+            scope = apply_scope(scope, table, reflection.type, polymorphic_type)
+          end
 
-        if reflection.type
-          polymorphic_type = transform_value(owner.class.base_class.name)
-          scope = scope.where(table.name => { reflection.type => polymorphic_type })
+          scope
         end
 
-        scope
-      end
+        def transform_value(value)
+          value_transformation.call(value)
+        end
 
-      def transform_value(value)
-        value_transformation.call(value)
-      end
+        def next_chain_scope(scope, reflection, next_reflection)
+          join_keys = reflection.join_keys
+          key = join_keys.key
+          foreign_key = join_keys.foreign_key
 
-      def next_chain_scope(scope, table, reflection, association_klass, foreign_table, next_reflection)
-        join_keys = reflection.join_keys(association_klass)
-        key = join_keys.key
-        foreign_key = join_keys.foreign_key
+          table = reflection.aliased_table
+          foreign_table = next_reflection.aliased_table
+          constraint = table[key].eq(foreign_table[foreign_key])
 
-        constraint = table[key].eq(foreign_table[foreign_key])
+          if reflection.type
+            value = transform_value(next_reflection.klass.polymorphic_name)
+            scope = apply_scope(scope, table, reflection.type, value)
+          end
 
-        if reflection.type
-          value = transform_value(next_reflection.klass.base_class.name)
-          scope = scope.where(table.name => { reflection.type => value })
+          scope.joins!(join(foreign_table, constraint))
         end
 
-        scope = scope.joins(join(foreign_table, constraint))
-      end
+        class ReflectionProxy < SimpleDelegator # :nodoc:
+          attr_reader :aliased_table
 
-      class ReflectionProxy < SimpleDelegator # :nodoc:
-        attr_accessor :next
-        attr_reader :alias_name
+          def initialize(reflection, aliased_table)
+            super(reflection)
+            @aliased_table = aliased_table
+          end
 
-        def initialize(reflection, alias_name)
-          super(reflection)
-          @alias_name = alias_name
+          def all_includes; nil; end
         end
 
-        def all_includes; nil; end
-      end
-
-      def get_chain(reflection, association, tracker)
-        name = reflection.name
-        runtime_reflection = Reflection::RuntimeReflection.new(reflection, association)
-        previous_reflection = runtime_reflection
-        reflection.chain.drop(1).each do |refl|
-          alias_name = tracker.aliased_table_for(refl.table_name, refl.alias_candidate(name))
-          proxy = ReflectionProxy.new(refl, alias_name)
-          previous_reflection.next = proxy
-          previous_reflection = proxy
+        def get_chain(reflection, association, tracker)
+          name = reflection.name
+          chain = [Reflection::RuntimeReflection.new(reflection, association)]
+          reflection.chain.drop(1).each do |refl|
+            aliased_table = tracker.aliased_table_for(
+              refl.table_name,
+              refl.alias_candidate(name),
+              refl.klass.type_caster
+            )
+            chain << ReflectionProxy.new(refl, aliased_table)
+          end
+          chain
         end
-        [runtime_reflection, previous_reflection]
-      end
-
-      def add_constraints(scope, owner, association_klass, refl, chain_head, chain_tail)
-        owner_reflection = chain_tail
-        table = owner_reflection.alias_name
-        scope = last_chain_scope(scope, table, owner_reflection, owner, association_klass)
 
-        reflection = chain_head
-        loop do
-          break unless reflection
-          table = reflection.alias_name
+        def add_constraints(scope, owner, chain)
+          scope = last_chain_scope(scope, chain.last, owner)
 
-          unless reflection == chain_tail
-            next_reflection = reflection.next
-            foreign_table = next_reflection.alias_name
-            scope = next_chain_scope(scope, table, reflection, association_klass, foreign_table, next_reflection)
+          chain.each_cons(2) do |reflection, next_reflection|
+            scope = next_chain_scope(scope, reflection, next_reflection)
           end
 
-          # Exclude the scope of the association itself, because that
-          # was already merged in the #scope method.
-          reflection.constraints.each do |scope_chain_item|
-            item  = eval_scope(reflection.klass, scope_chain_item, owner)
+          chain_head = chain.first
+          chain.reverse_each do |reflection|
+            # Exclude the scope of the association itself, because that
+            # was already merged in the #scope method.
+            reflection.constraints.each do |scope_chain_item|
+              item = eval_scope(reflection, scope_chain_item, owner)
 
-            if scope_chain_item == refl.scope
-              scope.merge! item.except(:where, :includes)
-            end
+              if scope_chain_item == chain_head.scope
+                scope.merge! item.except(:where, :includes, :unscope, :order)
+              end
 
-            reflection.all_includes do
-              scope.includes! item.includes_values
-            end
+              reflection.all_includes do
+                scope.includes! item.includes_values
+              end
 
-            scope.where_clause += item.where_clause
-            scope.order_values |= item.order_values
-            scope.unscope!(*item.unscope_values)
+              scope.unscope!(*item.unscope_values)
+              scope.where_clause += item.where_clause
+              scope.order_values = item.order_values | scope.order_values
+            end
           end
 
-          reflection = reflection.next
+          scope
         end
 
-        scope
-      end
+        def apply_scope(scope, table, key, value)
+          if scope.table == table
+            scope.where!(key => value)
+          else
+            scope.where!(table.name => { key => value })
+          end
+        end
 
-      def eval_scope(klass, scope, owner)
-        klass.unscoped.instance_exec(owner, &scope)
-      end
+        def eval_scope(reflection, scope, owner)
+          relation = reflection.build_scope(reflection.aliased_table)
+          relation.instance_exec(owner, &scope) || relation
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/belongs_to_association.rb b/activerecord/lib/active_record/associations/belongs_to_association.rb
index 260a0c6a2d..3346725f2d 100644
--- a/activerecord/lib/active_record/associations/belongs_to_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_association.rb
@@ -1,25 +1,28 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Belongs To Association
   module Associations
+    # = Active Record Belongs To Association
     class BelongsToAssociation < SingularAssociation #:nodoc:
-
       def handle_dependency
-        target.send(options[:dependent]) if load_target
-      end
+        return unless load_target
 
-      def replace(record)
-        if record
-          raise_on_type_mismatch!(record)
-          update_counters(record)
-          replace_keys(record)
-          set_inverse_instance(record)
-          @updated = true
+        case options[:dependent]
+        when :destroy
+          target.destroy
+          raise ActiveRecord::Rollback unless target.destroyed?
         else
-          decrement_counters
-          remove_keys
+          target.send(options[:dependent])
         end
+      end
+
+      def inversed_from(record)
+        replace_keys(record)
+        super
+      end
 
-        self.target = record
+      def default(&block)
+        writer(owner.instance_exec(&block)) if reader.nil?
       end
 
       def reset
@@ -31,60 +34,74 @@ module ActiveRecord
         @updated
       end
 
-      def decrement_counters # :nodoc:
-        with_cache_name { |name| decrement_counter name }
+      def decrement_counters
+        update_counters(-1)
       end
 
-      def increment_counters # :nodoc:
-        with_cache_name { |name| increment_counter name }
+      def increment_counters
+        update_counters(1)
       end
 
-      private
-
-        def find_target?
-          !loaded? && foreign_key_present? && klass
+      def decrement_counters_before_last_save
+        if reflection.polymorphic?
+          model_was = owner.attribute_before_last_save(reflection.foreign_type).try(:constantize)
+        else
+          model_was = klass
         end
 
-        def with_cache_name
-          counter_cache_name = reflection.counter_cache_column
-          return unless counter_cache_name && owner.persisted?
-          yield counter_cache_name
-        end
+        foreign_key_was = owner.attribute_before_last_save(reflection.foreign_key)
 
-        def update_counters(record)
-          with_cache_name do |name|
-            return unless different_target? record
-            record.class.increment_counter(name, record.id)
-            decrement_counter name
-          end
+        if foreign_key_was && model_was < ActiveRecord::Base
+          update_counters_via_scope(model_was, foreign_key_was, -1)
         end
+      end
 
-        def decrement_counter(counter_cache_name)
-          if foreign_key_present?
-            klass.decrement_counter(counter_cache_name, target_id)
+      def target_changed?
+        owner.saved_change_to_attribute?(reflection.foreign_key)
+      end
+
+      private
+        def replace(record)
+          if record
+            raise_on_type_mismatch!(record)
+            set_inverse_instance(record)
+            @updated = true
           end
+
+          replace_keys(record)
+
+          self.target = record
         end
 
-        def increment_counter(counter_cache_name)
-          if foreign_key_present?
-            klass.increment_counter(counter_cache_name, target_id)
+        def update_counters(by)
+          if require_counter_update? && foreign_key_present?
             if target && !stale_target?
-              target.increment(counter_cache_name)
+              target.increment!(reflection.counter_cache_column, by, touch: reflection.options[:touch])
+            else
+              update_counters_via_scope(klass, owner._read_attribute(reflection.foreign_key), by)
             end
           end
         end
 
-        # Checks whether record is different to the current target, without loading it
-        def different_target?(record)
-          record.id != owner._read_attribute(reflection.foreign_key)
+        def update_counters_via_scope(klass, foreign_key, by)
+          scope = klass.unscoped.where!(primary_key(klass) => foreign_key)
+          scope.update_counters(reflection.counter_cache_column => by, touch: reflection.options[:touch])
+        end
+
+        def find_target?
+          !loaded? && foreign_key_present? && klass
+        end
+
+        def require_counter_update?
+          reflection.counter_cache_column && owner.persisted?
         end
 
         def replace_keys(record)
-          owner[reflection.foreign_key] = record._read_attribute(reflection.association_primary_key(record.class))
+          owner[reflection.foreign_key] = record ? record._read_attribute(primary_key(record.class)) : nil
         end
 
-        def remove_keys
-          owner[reflection.foreign_key] = nil
+        def primary_key(klass)
+          reflection.association_primary_key(klass)
         end
 
         def foreign_key_present?
@@ -98,14 +115,6 @@ module ActiveRecord
           inverse && inverse.has_one?
         end
 
-        def target_id
-          if options[:primary_key]
-            owner.send(reflection.name).try(:id)
-          else
-            owner._read_attribute(reflection.foreign_key)
-          end
-        end
-
         def stale_state
           result = owner._read_attribute(reflection.foreign_key) { |n| owner.send(:missing_attribute, n, caller) }
           result && result.to_s
diff --git a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
index b710cf6bdb..9ae452e7a1 100644
--- a/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
+++ b/activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb
@@ -1,26 +1,22 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Belongs To Polymorphic Association
   module Associations
+    # = Active Record Belongs To Polymorphic Association
     class BelongsToPolymorphicAssociation < BelongsToAssociation #:nodoc:
       def klass
         type = owner[reflection.foreign_type]
         type.presence && type.constantize
       end
 
-      private
+      def target_changed?
+        super || owner.saved_change_to_attribute?(reflection.foreign_type)
+      end
 
+      private
         def replace_keys(record)
           super
-          owner[reflection.foreign_type] = record.class.base_class.name
-        end
-
-        def remove_keys
-          super
-          owner[reflection.foreign_type] = nil
-        end
-
-        def different_target?(record)
-          super || record.class != klass
+          owner[reflection.foreign_type] = record ? record.class.polymorphic_name : nil
         end
 
         def inverse_reflection_for(record)
diff --git a/activerecord/lib/active_record/associations/builder/association.rb b/activerecord/lib/active_record/associations/builder/association.rb
index ba1b1814d1..7c69cd65ee 100644
--- a/activerecord/lib/active_record/associations/builder/association.rb
+++ b/activerecord/lib/active_record/associations/builder/association.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # This is the parent Association class which defines the variables
 # used by all associations.
 #
@@ -9,7 +11,7 @@
 #    - CollectionAssociation
 #      - HasManyAssociation
 
-module ActiveRecord::Associations::Builder
+module ActiveRecord::Associations::Builder # :nodoc:
   class Association #:nodoc:
     class << self
       attr_accessor :extensions
@@ -36,11 +38,6 @@ module ActiveRecord::Associations::Builder
     def self.create_reflection(model, name, scope, options, extension = nil)
       raise ArgumentError, "association names must be a Symbol" unless name.kind_of?(Symbol)
 
-      if scope.is_a?(Hash)
-        options = scope
-        scope   = nil
-      end
-
       validate_options(options)
 
       scope = build_scope(scope, extension)
@@ -107,8 +104,8 @@ module ActiveRecord::Associations::Builder
 
     def self.define_readers(mixin, name)
       mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}(*args)
-          association(:#{name}).reader(*args)
+        def #{name}
+          association(:#{name}).reader
         end
       CODE
     end
diff --git a/activerecord/lib/active_record/associations/builder/belongs_to.rb b/activerecord/lib/active_record/associations/builder/belongs_to.rb
index 97eb007f62..fc00f1e900 100644
--- a/activerecord/lib/active_record/associations/builder/belongs_to.rb
+++ b/activerecord/lib/active_record/associations/builder/belongs_to.rb
@@ -1,11 +1,13 @@
-module ActiveRecord::Associations::Builder
+# frozen_string_literal: true
+
+module ActiveRecord::Associations::Builder # :nodoc:
   class BelongsTo < SingularAssociation #:nodoc:
     def self.macro
       :belongs_to
     end
 
     def self.valid_options(options)
-      super + [:foreign_type, :polymorphic, :touch, :counter_cache, :optional]
+      super + [:polymorphic, :touch, :counter_cache, :optional, :default]
     end
 
     def self.valid_dependent_options
@@ -16,62 +18,40 @@ module ActiveRecord::Associations::Builder
       super
       add_counter_cache_callbacks(model, reflection) if reflection.options[:counter_cache]
       add_touch_callbacks(model, reflection)         if reflection.options[:touch]
-    end
-
-    def self.define_accessors(mixin, reflection)
-      super
-      add_counter_cache_methods mixin
-    end
-
-    def self.add_counter_cache_methods(mixin)
-      return if mixin.method_defined? :belongs_to_counter_cache_after_update
-
-      mixin.class_eval do
-        def belongs_to_counter_cache_after_update(reflection)
-          foreign_key  = reflection.foreign_key
-          cache_column = reflection.counter_cache_column
-
-          if (@_after_create_counter_called ||= false)
-            @_after_create_counter_called = false
-          elsif attribute_changed?(foreign_key) && !new_record? && reflection.constructable?
-            model           = reflection.klass
-            foreign_key_was = attribute_was foreign_key
-            foreign_key     = attribute foreign_key
-
-            if foreign_key && model.respond_to?(:increment_counter)
-              model.increment_counter(cache_column, foreign_key)
-            end
-            if foreign_key_was && model.respond_to?(:decrement_counter)
-              model.decrement_counter(cache_column, foreign_key_was)
-            end
-          end
-        end
-      end
+      add_default_callbacks(model, reflection)       if reflection.options[:default]
     end
 
     def self.add_counter_cache_callbacks(model, reflection)
       cache_column = reflection.counter_cache_column
 
       model.after_update lambda { |record|
-        record.belongs_to_counter_cache_after_update(reflection)
+        association = association(reflection.name)
+
+        if association.target_changed?
+          association.increment_counters
+          association.decrement_counters_before_last_save
+        end
       }
 
       klass = reflection.class_name.safe_constantize
       klass.attr_readonly cache_column if klass && klass.respond_to?(:attr_readonly)
     end
 
-    def self.touch_record(o, foreign_key, name, touch, touch_method) # :nodoc:
-      old_foreign_id = o.changed_attributes[foreign_key]
+    def self.touch_record(o, changes, foreign_key, name, touch, touch_method) # :nodoc:
+      old_foreign_id = changes[foreign_key] && changes[foreign_key].first
 
       if old_foreign_id
         association = o.association(name)
         reflection = association.reflection
         if reflection.polymorphic?
-          klass = o.public_send("#{reflection.foreign_type}_was").constantize
+          foreign_type = reflection.foreign_type
+          klass = changes[foreign_type] && changes[foreign_type].first || o.public_send(foreign_type)
+          klass = klass.constantize
         else
           klass = association.klass
         end
-        old_record = klass.find_by(klass.primary_key => old_foreign_id)
+        primary_key = reflection.association_primary_key(klass)
+        old_record = klass.find_by(primary_key => old_foreign_id)
 
         if old_record
           if touch != true
@@ -97,19 +77,33 @@ module ActiveRecord::Associations::Builder
       n           = reflection.name
       touch       = reflection.options[:touch]
 
-      callback = lambda { |record|
-        touch_method = touching_delayed_records? ? :touch : :touch_later
-        BelongsTo.touch_record(record, foreign_key, n, touch, touch_method)
-      }
+      callback = lambda { |changes_method| lambda { |record|
+        BelongsTo.touch_record(record, record.send(changes_method), foreign_key, n, touch, belongs_to_touch_method)
+      }}
 
-      model.after_save    callback, if: :changed?
-      model.after_touch   callback
-      model.after_destroy callback
+      if reflection.counter_cache_column
+        touch_callback = callback.(:saved_changes)
+        update_callback = lambda { |record|
+          instance_exec(record, &touch_callback) unless association(reflection.name).target_changed?
+        }
+        model.after_update update_callback, if: :saved_changes?
+      else
+        model.after_create callback.(:saved_changes), if: :saved_changes?
+        model.after_update callback.(:saved_changes), if: :saved_changes?
+        model.after_destroy callback.(:changes_to_save)
+      end
+
+      model.after_touch callback.(:changes_to_save)
+    end
+
+    def self.add_default_callbacks(model, reflection)
+      model.before_validation lambda { |o|
+        o.association(reflection.name).default(&reflection.options[:default])
+      }
     end
 
     def self.add_destroy_callbacks(model, reflection)
-      name = reflection.name
-      model.after_destroy lambda { |o| o.association(name).handle_dependency }
+      model.after_destroy lambda { |o| o.association(reflection.name).handle_dependency }
     end
 
     def self.define_validations(model, reflection)
diff --git a/activerecord/lib/active_record/associations/builder/collection_association.rb b/activerecord/lib/active_record/associations/builder/collection_association.rb
index 2ff67f904d..ff57c40121 100644
--- a/activerecord/lib/active_record/associations/builder/collection_association.rb
+++ b/activerecord/lib/active_record/associations/builder/collection_association.rb
@@ -1,10 +1,9 @@
-# This class is inherited by the has_many and has_many_and_belongs_to_many association classes
+# frozen_string_literal: true
 
-require 'active_record/associations'
+require "active_record/associations"
 
-module ActiveRecord::Associations::Builder
+module ActiveRecord::Associations::Builder # :nodoc:
   class CollectionAssociation < Association #:nodoc:
-
     CALLBACKS = [:before_add, :after_add, :before_remove, :after_remove]
 
     def self.valid_options(options)
@@ -25,7 +24,7 @@ module ActiveRecord::Associations::Builder
       if block_given?
         extension_module_name = "#{model.name.demodulize}#{name.to_s.camelize}AssociationExtension"
         extension = Module.new(&Proc.new)
-        model.parent.const_set(extension_module_name, extension)
+        model.module_parent.const_set(extension_module_name, extension)
       end
     end
 
@@ -70,7 +69,11 @@ module ActiveRecord::Associations::Builder
 
     def self.wrap_scope(scope, mod)
       if scope
-        proc { |owner| instance_exec(owner, &scope).extending(mod) }
+        if scope.arity > 0
+          proc { |owner| instance_exec(owner, &scope).extending(mod) }
+        else
+          proc { instance_exec(&scope).extending(mod) }
+        end
       else
         proc { extending(mod) }
       end
diff --git a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
index ffd9c9d6fc..0140aa15c8 100644
--- a/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
+++ b/activerecord/lib/active_record/associations/builder/has_and_belongs_to_many.rb
@@ -1,38 +1,7 @@
-module ActiveRecord::Associations::Builder
-  class HasAndBelongsToMany # :nodoc:
-    class JoinTableResolver
-      KnownTable = Struct.new :join_table
-
-      class KnownClass
-        def initialize(lhs_class, rhs_class_name)
-          @lhs_class      = lhs_class
-          @rhs_class_name = rhs_class_name
-          @join_table     = nil
-        end
-
-        def join_table
-          @join_table ||= [@lhs_class.table_name, klass.table_name].sort.join("\0").gsub(/^(.*[._])(.+)\0\1(.+)/, '\1\2_\3').tr("\0", "_")
-        end
-
-        private
-
-        def klass
-          @lhs_class.send(:compute_type, @rhs_class_name)
-        end
-      end
-
-      def self.build(lhs_class, name, options)
-        if options[:join_table]
-          KnownTable.new options[:join_table].to_s
-        else
-          class_name = options.fetch(:class_name) {
-            name.to_s.camelize.singularize
-          }
-          KnownClass.new lhs_class, class_name
-        end
-      end
-    end
+# frozen_string_literal: true
 
+module ActiveRecord::Associations::Builder # :nodoc:
+  class HasAndBelongsToMany # :nodoc:
     attr_reader :lhs_model, :association_name, :options
 
     def initialize(association_name, lhs_model, options)
@@ -42,11 +11,9 @@ module ActiveRecord::Associations::Builder
     end
 
     def through_model
-      habtm = JoinTableResolver.build lhs_model, association_name, options
-
       join_model = Class.new(ActiveRecord::Base) {
-        class << self;
-          attr_accessor :class_resolver
+        class << self
+          attr_accessor :left_model
           attr_accessor :name
           attr_accessor :table_name_resolver
           attr_accessor :left_reflection
@@ -54,29 +21,40 @@ module ActiveRecord::Associations::Builder
         end
 
         def self.table_name
-          table_name_resolver.join_table
+          # Table name needs to be resolved lazily
+          # because RHS class might not have been loaded
+          @table_name ||= table_name_resolver.call
         end
 
         def self.compute_type(class_name)
-          class_resolver.compute_type class_name
+          left_model.compute_type class_name
         end
 
         def self.add_left_association(name, options)
-          belongs_to name, options
+          belongs_to name, required: false, **options
           self.left_reflection = _reflect_on_association(name)
         end
 
         def self.add_right_association(name, options)
           rhs_name = name.to_s.singularize.to_sym
-          belongs_to rhs_name, options
+          belongs_to rhs_name, required: false, **options
           self.right_reflection = _reflect_on_association(rhs_name)
         end
 
+        def self.retrieve_connection
+          left_model.retrieve_connection
+        end
+
+        private
+
+          def self.suppress_composite_primary_key(pk)
+            pk unless pk.is_a?(Array)
+          end
       }
 
       join_model.name                = "HABTM_#{association_name.to_s.camelize}"
-      join_model.table_name_resolver = habtm
-      join_model.class_resolver      = lhs_model
+      join_model.table_name_resolver = -> { table_name }
+      join_model.left_model          = lhs_model
 
       join_model.add_left_association :left_side, anonymous_class: lhs_model
       join_model.add_right_association association_name, belongs_to_options(options)
@@ -85,7 +63,7 @@ module ActiveRecord::Associations::Builder
 
     def middle_reflection(join_model)
       middle_name = [lhs_model.name.downcase.pluralize,
-                     association_name].join('_'.freeze).gsub('::'.freeze, '_'.freeze).to_sym
+                     association_name].join("_").gsub("::", "_").to_sym
       middle_options = middle_options join_model
 
       HasMany.create_reflection(lhs_model,
@@ -96,29 +74,41 @@ module ActiveRecord::Associations::Builder
 
     private
 
-    def middle_options(join_model)
-      middle_options = {}
-      middle_options[:class_name] = "#{lhs_model.name}::#{join_model.name}"
-      middle_options[:source] = join_model.left_reflection.name
-      if options.key? :foreign_key
-        middle_options[:foreign_key] = options[:foreign_key]
+      def middle_options(join_model)
+        middle_options = {}
+        middle_options[:class_name] = "#{lhs_model.name}::#{join_model.name}"
+        middle_options[:source] = join_model.left_reflection.name
+        if options.key? :foreign_key
+          middle_options[:foreign_key] = options[:foreign_key]
+        end
+        middle_options
       end
-      middle_options
-    end
-
-    def belongs_to_options(options)
-      rhs_options = {}
 
-      if options.key? :class_name
-        rhs_options[:foreign_key] = options[:class_name].to_s.foreign_key
-        rhs_options[:class_name] = options[:class_name]
+      def table_name
+        if options[:join_table]
+          options[:join_table].to_s
+        else
+          class_name = options.fetch(:class_name) {
+            association_name.to_s.camelize.singularize
+          }
+          klass = lhs_model.send(:compute_type, class_name.to_s)
+          [lhs_model.table_name, klass.table_name].sort.join("\0").gsub(/^(.*[._])(.+)\0\1(.+)/, '\1\2_\3').tr("\0", "_")
+        end
       end
 
-      if options.key? :association_foreign_key
-        rhs_options[:foreign_key] = options[:association_foreign_key]
-      end
+      def belongs_to_options(options)
+        rhs_options = {}
 
-      rhs_options
-    end
+        if options.key? :class_name
+          rhs_options[:foreign_key] = options[:class_name].to_s.foreign_key
+          rhs_options[:class_name] = options[:class_name]
+        end
+
+        if options.key? :association_foreign_key
+          rhs_options[:foreign_key] = options[:association_foreign_key]
+        end
+
+        rhs_options
+      end
   end
 end
diff --git a/activerecord/lib/active_record/associations/builder/has_many.rb b/activerecord/lib/active_record/associations/builder/has_many.rb
index 1c1b47bd56..5b9617bc6d 100644
--- a/activerecord/lib/active_record/associations/builder/has_many.rb
+++ b/activerecord/lib/active_record/associations/builder/has_many.rb
@@ -1,11 +1,13 @@
-module ActiveRecord::Associations::Builder
+# frozen_string_literal: true
+
+module ActiveRecord::Associations::Builder # :nodoc:
   class HasMany < CollectionAssociation #:nodoc:
     def self.macro
       :has_many
     end
 
     def self.valid_options(options)
-      super + [:primary_key, :dependent, :as, :through, :source, :source_type, :inverse_of, :counter_cache, :join_table, :foreign_type]
+      super + [:primary_key, :dependent, :as, :through, :source, :source_type, :inverse_of, :counter_cache, :join_table, :foreign_type, :index_errors]
     end
 
     def self.valid_dependent_options
diff --git a/activerecord/lib/active_record/associations/builder/has_one.rb b/activerecord/lib/active_record/associations/builder/has_one.rb
index a272d3c781..bfb37d6eee 100644
--- a/activerecord/lib/active_record/associations/builder/has_one.rb
+++ b/activerecord/lib/active_record/associations/builder/has_one.rb
@@ -1,11 +1,13 @@
-module ActiveRecord::Associations::Builder
+# frozen_string_literal: true
+
+module ActiveRecord::Associations::Builder # :nodoc:
   class HasOne < SingularAssociation #:nodoc:
     def self.macro
       :has_one
     end
 
     def self.valid_options(options)
-      valid = super + [:as, :foreign_type]
+      valid = super + [:as]
       valid += [:through, :source, :source_type] if options[:through]
       valid
     end
diff --git a/activerecord/lib/active_record/associations/builder/singular_association.rb b/activerecord/lib/active_record/associations/builder/singular_association.rb
index 42542f188e..0a02ef4cc1 100644
--- a/activerecord/lib/active_record/associations/builder/singular_association.rb
+++ b/activerecord/lib/active_record/associations/builder/singular_association.rb
@@ -1,14 +1,25 @@
+# frozen_string_literal: true
+
 # This class is inherited by the has_one and belongs_to association classes
 
-module ActiveRecord::Associations::Builder
+module ActiveRecord::Associations::Builder # :nodoc:
   class SingularAssociation < Association #:nodoc:
     def self.valid_options(options)
-      super + [:dependent, :primary_key, :inverse_of, :required]
+      super + [:foreign_type, :dependent, :primary_key, :inverse_of, :required]
     end
 
     def self.define_accessors(model, reflection)
       super
-      define_constructors(model.generated_association_methods, reflection.name) if reflection.constructable?
+      mixin = model.generated_association_methods
+      name = reflection.name
+
+      define_constructors(mixin, name) if reflection.constructable?
+
+      mixin.class_eval <<-CODE, __FILE__, __LINE__ + 1
+        def reload_#{name}
+          association(:#{name}).force_reload_reader
+        end
+      CODE
     end
 
     # Defines the (build|create)_association methods for belongs_to or has_one association
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 6caadb4ce8..840d900bbc 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     # = Active Record Association Collection
@@ -10,9 +12,9 @@ module ActiveRecord
     #     HasManyAssociation => has_many
     #       HasManyThroughAssociation + ThroughAssociation => has_many :through
     #
-    # CollectionAssociation class provides common methods to the collections
+    # The CollectionAssociation class provides common methods to the collections
     # defined by +has_and_belongs_to_many+, +has_many+ or +has_many+ with
-    # +:through association+ option.
+    # the +:through association+ option.
     #
     # You need to be careful with assumptions regarding the target: The proxy
     # does not fetch records from the database until it needs them, but new
@@ -24,22 +26,14 @@ module ActiveRecord
     # If you need to work on all current children, new and existing records,
     # +load_target+ and the +loaded+ flag are your friends.
     class CollectionAssociation < Association #:nodoc:
-
       # Implements the reader method, e.g. foo.items for Foo.has_many :items
-      def reader(force_reload = false)
-        if force_reload
-          klass.uncached { reload }
-        elsif stale_target?
+      def reader
+        if stale_target?
           reload
         end
 
-        if null_scope?
-          # Cache the proxy separately before the owner has an id
-          # or else a post-save proxy will still lack the id
-          @null_proxy ||= CollectionProxy.create(klass, self)
-        else
-          @proxy ||= CollectionProxy.create(klass, self)
-        end
+        @proxy ||= CollectionProxy.create(klass, self)
+        @proxy.reset_scope
       end
 
       # Implements the writer method, e.g. foo.items= for Foo.has_many :items
@@ -50,92 +44,60 @@ module ActiveRecord
       # Implements the ids reader method, e.g. foo.item_ids for Foo.has_many :items
       def ids_reader
         if loaded?
-          load_target.map do |record|
-            record.send(reflection.association_primary_key)
-          end
+          target.pluck(reflection.association_primary_key)
+        elsif !target.empty?
+          load_target.pluck(reflection.association_primary_key)
         else
-          column  = "#{reflection.quoted_table_name}.#{reflection.association_primary_key}"
-          scope.pluck(column)
+          @association_ids ||= scope.pluck(reflection.association_primary_key)
         end
       end
 
       # Implements the ids writer method, e.g. foo.item_ids= for Foo.has_many :items
       def ids_writer(ids)
-        pk_type = reflection.primary_key_type
+        primary_key = reflection.association_primary_key
+        pk_type = klass.type_for_attribute(primary_key)
         ids = Array(ids).reject(&:blank?)
         ids.map! { |i| pk_type.cast(i) }
-        replace(klass.find(ids).index_by(&:id).values_at(*ids))
-      end
 
-      def reset
-        super
-        @target = []
-      end
+        records = klass.where(primary_key => ids).index_by do |r|
+          r.public_send(primary_key)
+        end.values_at(*ids).compact
 
-      def select(*fields)
-        if block_given?
-          load_target.select.each { |e| yield e }
+        if records.size != ids.size
+          found_ids = records.map { |record| record.public_send(primary_key) }
+          not_found_ids = ids - found_ids
+          klass.all.raise_record_not_found_exception!(ids, records.size, ids.size, primary_key, not_found_ids)
         else
-          scope.select(*fields)
+          replace(records)
         end
       end
 
-      def find(*args)
-        if block_given?
-          load_target.find(*args) { |*block_args| yield(*block_args) }
-        else
-          if options[:inverse_of] && loaded?
-            args_flatten = args.flatten
-            raise RecordNotFound, "Couldn't find #{scope.klass.name} without an ID" if args_flatten.blank?
-            result = find_by_scan(*args)
-
-            result_size = Array(result).size
-            if !result || result_size != args_flatten.size
-              scope.raise_record_not_found_exception!(args_flatten, result_size, args_flatten.size)
-            else
-              result
-            end
-          else
-            scope.find(*args)
-          end
-        end
-      end
-
-      def first(*args)
-        first_nth_or_last(:first, *args)
-      end
-
-      def second(*args)
-        first_nth_or_last(:second, *args)
-      end
-
-      def third(*args)
-        first_nth_or_last(:third, *args)
-      end
-
-      def fourth(*args)
-        first_nth_or_last(:fourth, *args)
+      def reset
+        super
+        @target = []
+        @association_ids = nil
       end
 
-      def fifth(*args)
-        first_nth_or_last(:fifth, *args)
-      end
+      def find(*args)
+        if options[:inverse_of] && loaded?
+          args_flatten = args.flatten
+          model = scope.klass
 
-      def forty_two(*args)
-        first_nth_or_last(:forty_two, *args)
-      end
+          if args_flatten.blank?
+            error_message = "Couldn't find #{model.name} without an ID"
+            raise RecordNotFound.new(error_message, model.name, model.primary_key, args)
+          end
 
-      def last(*args)
-        first_nth_or_last(:last, *args)
-      end
+          result = find_by_scan(*args)
 
-      def take(n = nil)
-        if loaded?
-          n ? target.take(n) : target.first
-        else
-          scope.take(n).tap do |record|
-            set_inverse_instance record if record.is_a? ActiveRecord::Base
+          result_size = Array(result).size
+          if !result || result_size != args_flatten.size
+            scope.raise_record_not_found_exception!(args_flatten, result_size, args_flatten.size)
+          else
+            result
           end
+        else
+          scope.find(*args)
         end
       end
 
@@ -143,20 +105,10 @@ module ActiveRecord
         if attributes.is_a?(Array)
           attributes.collect { |attr| build(attr, &block) }
         else
-          add_to_target(build_record(attributes)) do |record|
-            yield(record) if block_given?
-          end
+          add_to_target(build_record(attributes, &block))
         end
       end
 
-      def create(attributes = {}, &block)
-        _create_record(attributes, &block)
-      end
-
-      def create!(attributes = {}, &block)
-        _create_record(attributes, true, &block)
-      end
-
       # Add +records+ to this association. Returns +self+ so method calls may
       # be chained. Since << flattens its argument list and inserts each record,
       # +push+ and +concat+ behave identically.
@@ -204,12 +156,12 @@ module ActiveRecord
         end
 
         dependent = if dependent
-                      dependent
-                    elsif options[:dependent] == :destroy
-                      :delete_all
-                    else
-                      options[:dependent]
-                    end
+          dependent
+        elsif options[:dependent] == :destroy
+          :delete_all
+        else
+          options[:dependent]
+        end
 
         delete_or_nullify_all_records(dependent).tap do
           reset
@@ -227,28 +179,6 @@ module ActiveRecord
         end
       end
 
-      # Count all records using SQL.  Construct options and pass them with
-      # scope to the target class's +count+.
-      def count(column_name = nil)
-        relation = scope
-        if association_scope.distinct_value
-          # This is needed because 'SELECT count(DISTINCT *)..' is not valid SQL.
-          column_name ||= reflection.klass.primary_key
-          relation = relation.distinct
-        end
-
-        value = relation.count(column_name)
-
-        limit  = options[:limit]
-        offset = options[:offset]
-
-        if limit || offset
-          [ [value - offset.to_i, 0].max, limit.to_i ].min
-        else
-          value
-        end
-      end
-
       # Removes +records+ from this association calling +before_remove+ and
       # +after_remove+ callbacks.
       #
@@ -257,12 +187,7 @@ module ActiveRecord
       # are actually removed from the database, that depends precisely on
       # +delete_records+. They are in any case removed from the collection.
       def delete(*records)
-        return if records.empty?
-        _options = records.extract_options!
-        dependent = _options[:dependent] || options[:dependent]
-
-        records = find(records) if records.any? { |record| record.kind_of?(Fixnum) || record.kind_of?(String) }
-        delete_or_destroy(records, dependent)
+        delete_or_destroy(records, options[:dependent])
       end
 
       # Deletes the +records+ and removes them from this association calling
@@ -271,8 +196,6 @@ module ActiveRecord
       # Note that this method removes records from the database ignoring the
       # +:dependent+ option.
       def destroy(*records)
-        return if records.empty?
-        records = find(records) if records.any? { |record| record.kind_of?(Fixnum) || record.kind_of?(String) }
         delete_or_destroy(records, :destroy)
       end
 
@@ -288,14 +211,12 @@ module ActiveRecord
       # +count_records+, which is a method descendants have to provide.
       def size
         if !find_target? || loaded?
-          if association_scope.distinct_value
-            target.uniq.size
-          else
-            target.size
-          end
-        elsif !loaded? && !association_scope.group_values.empty?
+          target.size
+        elsif @association_ids
+          @association_ids.size
+        elsif !association_scope.group_values.empty?
           load_target.size
-        elsif !loaded? && !association_scope.distinct_value && target.is_a?(Array)
+        elsif !association_scope.distinct_value && !target.empty?
           unsaved_records = target.select(&:new_record?)
           unsaved_records.size + count_records
         else
@@ -303,15 +224,6 @@ module ActiveRecord
         end
       end
 
-      # Returns the size of the collection calling +size+ on the target.
-      #
-      # If the collection has been already loaded +length+ and +size+ are
-      # equivalent. If not and you are going to need the records anyway this
-      # method will take one less query. Otherwise +size+ is more efficient.
-      def length
-        load_target.size
-      end
-
       # Returns true if the collection is empty.
       #
       # If the collection has been loaded
@@ -321,43 +233,13 @@ module ActiveRecord
       # loaded and you are going to fetch the records anyway it is better to
       # check <tt>collection.length.zero?</tt>.
       def empty?
-        if loaded?
+        if loaded? || @association_ids
           size.zero?
         else
-          @target.blank? && !scope.exists?
-        end
-      end
-
-      # Returns true if the collections is not empty.
-      # If block given, loads all records and checks for one or more matches.
-      # Otherwise, equivalent to +!collection.empty?+.
-      def any?
-        if block_given?
-          load_target.any? { |*block_args| yield(*block_args) }
-        else
-          !empty?
+          target.empty? && !scope.exists?
         end
       end
 
-      # Returns true if the collection has more than 1 record.
-      # If block given, loads all records and checks for two or more matches.
-      # Otherwise, equivalent to +collection.size > 1+.
-      def many?
-        if block_given?
-          load_target.many? { |*block_args| yield(*block_args) }
-        else
-          size > 1
-        end
-      end
-
-      def distinct
-        seen = {}
-        load_target.find_all do |record|
-          seen[record.id] = true unless seen.key?(record.id)
-        end
-      end
-      alias uniq distinct
-
       # Replace this collection with +other_array+. This will perform a diff
       # and delete/add only records that have changed.
       def replace(other_array)
@@ -404,25 +286,9 @@ module ActiveRecord
         replace_on_target(record, index, skip_callbacks, &block)
       end
 
-      def replace_on_target(record, index, skip_callbacks)
-        callback(:before_add, record) unless skip_callbacks
-        yield(record) if block_given?
-
-        if index
-          @target[index] = record
-        else
-          @target << record
-        end
-
-        callback(:after_add, record) unless skip_callbacks
-        set_inverse_instance(record)
-
-        record
-      end
-
-      def scope(opts = {})
-        scope = super()
-        scope.none! if opts.fetch(:nullify, true) && null_scope?
+      def scope
+        scope = super
+        scope.none! if null_scope?
         scope
       end
 
@@ -430,31 +296,28 @@ module ActiveRecord
         owner.new_record? && !foreign_key_present?
       end
 
+      def find_from_target?
+        loaded? ||
+          owner.new_record? ||
+          target.any? { |record| record.new_record? || record.changed? }
+      end
+
       private
-      def get_records
-        if reflection.scope_chain.any?(&:any?) ||
-          scope.eager_loading? ||
-          klass.scope_attributes?
 
-          return scope.to_a
-        end
+        def find_target
+          scope = self.scope
+          return scope.to_a if skip_statement_cache?(scope)
 
-        conn = klass.connection
-        sc = reflection.association_scope_cache(conn, owner) do
-          StatementCache.create(conn) { |params|
+          conn = klass.connection
+          sc = reflection.association_scope_cache(conn, owner) do |params|
             as = AssociationScope.create { params.bind }
-            target_scope.merge as.scope(self, conn)
-          }
-        end
-
-        binds = AssociationScope.get_bind_values(owner, reflection.chain)
-        sc.execute binds, klass, klass.connection
-      end
+            target_scope.merge!(as.scope(self))
+          end
 
-        def find_target
-          records = get_records
-          records.each { |record| set_inverse_instance(record) }
-          records
+          binds = AssociationScope.get_bind_values(owner, reflection.chain)
+          sc.execute(binds, conn) do |record|
+            set_inverse_instance(record)
+          end
         end
 
         # We have some records loaded from the database (persisted) and some that are
@@ -474,7 +337,7 @@ module ActiveRecord
           persisted.map! do |record|
             if mem_record = memory.delete(record)
 
-              ((record.attribute_names & mem_record.attribute_names) - mem_record.changes.keys).each do |name|
+              ((record.attribute_names & mem_record.attribute_names) - mem_record.changed_attribute_names_to_save).each do |name|
                 mem_record[name] = record[name]
               end
 
@@ -495,25 +358,33 @@ module ActiveRecord
           if attributes.is_a?(Array)
             attributes.collect { |attr| _create_record(attr, raise, &block) }
           else
+            record = build_record(attributes, &block)
             transaction do
-              add_to_target(build_record(attributes)) do |record|
-                yield(record) if block_given?
-                insert_record(record, true, raise)
+              result = nil
+              add_to_target(record) do
+                result = insert_record(record, true, raise) {
+                  @_was_loaded = loaded?
+                  @association_ids = nil
+                }
               end
+              raise ActiveRecord::Rollback unless result
             end
+            record
           end
         end
 
         # Do the relevant stuff to insert the given record into the association collection.
-        def insert_record(record, validate = true, raise = false)
-          raise NotImplementedError
-        end
-
-        def create_scope
-          scope.scope_for_create.stringify_keys
+        def insert_record(record, validate = true, raise = false, &block)
+          if raise
+            record.save!(validate: validate, &block)
+          else
+            record.save(validate: validate, &block)
+          end
         end
 
         def delete_or_destroy(records, method)
+          return if records.empty?
+          records = find(records) if records.any? { |record| record.kind_of?(Integer) || record.kind_of?(String) }
           records = records.flatten
           records.each { |record| raise_on_type_mismatch!(record) }
           existing_records = records.reject(&:new_record?)
@@ -529,13 +400,14 @@ module ActiveRecord
           records.each { |record| callback(:before_remove, record) }
 
           delete_records(existing_records, method) if existing_records.any?
-          records.each { |record| target.delete(record) }
+          @target -= records
 
           records.each { |record| callback(:after_remove, record) }
         end
 
-        # Delete the given records from the association, using one of the methods :destroy,
-        # :delete_all or :nullify (or nil, in which case a default is used).
+        # Delete the given records from the association,
+        # using one of the methods +:destroy+, +:delete_all+
+        # or +:nullify+ (or +nil+, in which case a default is used).
         def delete_records(records, method)
           raise NotImplementedError
         end
@@ -560,17 +432,46 @@ module ActiveRecord
           end
         end
 
-        def concat_records(records, should_raise = false)
+        def concat_records(records, raise = false)
           result = true
 
           records.each do |record|
             raise_on_type_mismatch!(record)
-            add_to_target(record) do |rec|
-              result &&= insert_record(rec, true, should_raise) unless owner.new_record?
+            add_to_target(record) do
+              unless owner.new_record?
+                result &&= insert_record(record, true, raise) {
+                  @_was_loaded = loaded?
+                  @association_ids = nil
+                }
+              end
             end
           end
 
-          result && records
+          raise ActiveRecord::Rollback unless result
+
+          records
+        end
+
+        def replace_on_target(record, index, skip_callbacks)
+          callback(:before_add, record) unless skip_callbacks
+
+          set_inverse_instance(record)
+
+          @_was_loaded = true
+
+          yield(record) if block_given?
+
+          if index
+            target[index] = record
+          elsif @_was_loaded || !loaded?
+            target << record
+          end
+
+          callback(:after_add, record) unless skip_callbacks
+
+          record
+        ensure
+          @_was_loaded = nil
         end
 
         def callback(method, record)
@@ -584,25 +485,6 @@ module ActiveRecord
           owner.class.send(full_callback_name)
         end
 
-        # Should we deal with assoc.first or assoc.last by issuing an independent query to
-        # the database, or by getting the target, and then taking the first/last item from that?
-        #
-        # If the args is just a non-empty options hash, go to the database.
-        #
-        # Otherwise, go to the database only if none of the following are true:
-        #   * target already loaded
-        #   * owner is new record
-        #   * target contains new or changed record(s)
-        def fetch_first_nth_or_last_using_find?(args)
-          if args.first.is_a?(Hash)
-            true
-          else
-            !(loaded? ||
-              owner.new_record? ||
-              target.any? { |record| record.new_record? || record.changed? })
-          end
-        end
-
         def include_in_memory?(record)
           if reflection.is_a?(ActiveRecord::Reflection::ThroughReflection)
             assoc = owner.association(reflection.through_reflection.name)
@@ -629,16 +511,6 @@ module ActiveRecord
             load_target.select { |r| ids.include?(r.id.to_s) }
           end
         end
-
-        # Fetches the first/last using SQL if possible, otherwise from the target array.
-        def first_nth_or_last(type, *args)
-          args.shift if args.first.is_a?(Hash) && args.first.empty?
-
-          collection = fetch_first_nth_or_last_using_find?(args) ? scope : load_target
-          collection.send(type, *args).tap do |record|
-            set_inverse_instance record if record.is_a? ActiveRecord::Base
-          end
-        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index ddeafb40ea..811fbfd927 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     # Association proxies in Active Record are middlemen between the object that
@@ -28,13 +30,12 @@ module ActiveRecord
     # is computed directly through SQL and does not trigger by itself the
     # instantiation of the actual post records.
     class CollectionProxy < Relation
-      delegate(*(ActiveRecord::Calculations.public_instance_methods - [:count]), to: :scope)
-      delegate :find_nth, to: :scope
-
       def initialize(klass, association) #:nodoc:
         @association = association
-        super klass, klass.arel_table, klass.predicate_builder
-        merge! association.scope(nullify: false)
+        super klass
+
+        extensions = association.extensions
+        extend(*extensions) if extensions.any?
       end
 
       def target
@@ -54,6 +55,12 @@ module ActiveRecord
         @association.loaded?
       end
 
+      ##
+      # :method: select
+      #
+      # :call-seq:
+      #   select(*fields, &block)
+      #
       # Works in two ways.
       #
       # *First:* Specify a subset of fields to be selected from the result set.
@@ -76,7 +83,7 @@ module ActiveRecord
       #   #      #<Pet id: nil, name: "Choo-Choo">
       #   #    ]
       #
-      #   person.pets.select(:id, :name )
+      #   person.pets.select(:id, :name)
       #   # => [
       #   #      #<Pet id: 1, name: "Fancy-Fancy">,
       #   #      #<Pet id: 2, name: "Spook">,
@@ -101,18 +108,9 @@ module ActiveRecord
       #   #      #<Pet id: 2, name: "Spook", person_id: 1>,
       #   #      #<Pet id: 3, name: "Choo-Choo", person_id: 1>
       #   #    ]
-      #
-      #   person.pets.select(:name) { |pet| pet.name =~ /oo/ }
-      #   # => [
-      #   #      #<Pet id: 2, name: "Spook">,
-      #   #      #<Pet id: 3, name: "Choo-Choo">
-      #   #    ]
-      def select(*fields, &block)
-        @association.select(*fields, &block)
-      end
 
       # Finds an object in the collection responding to the +id+. Uses the same
-      # rules as <tt>ActiveRecord::Base.find</tt>. Returns <tt>ActiveRecord::RecordNotFound</tt>
+      # rules as ActiveRecord::Base.find. Returns ActiveRecord::RecordNotFound
       # error if the object cannot be found.
       #
       #   class Person < ActiveRecord::Base
@@ -127,7 +125,7 @@ module ActiveRecord
       #   #    ]
       #
       #   person.pets.find(1) # => #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>
-      #   person.pets.find(4) # => ActiveRecord::RecordNotFound: Couldn't find Pet with id=4
+      #   person.pets.find(4) # => ActiveRecord::RecordNotFound: Couldn't find Pet with 'id'=4
       #
       #   person.pets.find(2) { |pet| pet.name.downcase! }
       #   # => #<Pet id: 2, name: "fancy-fancy", person_id: 1>
@@ -137,10 +135,17 @@ module ActiveRecord
       #   #       #<Pet id: 2, name: "Spook", person_id: 1>,
       #   #       #<Pet id: 3, name: "Choo-Choo", person_id: 1>
       #   #    ]
-      def find(*args, &block)
-        @association.find(*args, &block)
+      def find(*args)
+        return super if block_given?
+        @association.find(*args)
       end
 
+      ##
+      # :method: first
+      #
+      # :call-seq:
+      #   first(limit = nil)
+      #
       # Returns the first record, or the first +n+ records, from the collection.
       # If the collection is empty, the first form returns +nil+, and the second
       # form returns an empty array.
@@ -167,35 +172,63 @@ module ActiveRecord
       #   another_person_without.pets          # => []
       #   another_person_without.pets.first    # => nil
       #   another_person_without.pets.first(3) # => []
-      def first(*args)
-        @association.first(*args)
-      end
 
-      # Same as +first+ except returns only the second record.
-      def second(*args)
-        @association.second(*args)
-      end
+      ##
+      # :method: second
+      #
+      # :call-seq:
+      #   second()
+      #
+      # Same as #first except returns only the second record.
 
-      # Same as +first+ except returns only the third record.
-      def third(*args)
-        @association.third(*args)
-      end
+      ##
+      # :method: third
+      #
+      # :call-seq:
+      #   third()
+      #
+      # Same as #first except returns only the third record.
 
-      # Same as +first+ except returns only the fourth record.
-      def fourth(*args)
-        @association.fourth(*args)
-      end
+      ##
+      # :method: fourth
+      #
+      # :call-seq:
+      #   fourth()
+      #
+      # Same as #first except returns only the fourth record.
 
-      # Same as +first+ except returns only the fifth record.
-      def fifth(*args)
-        @association.fifth(*args)
-      end
+      ##
+      # :method: fifth
+      #
+      # :call-seq:
+      #   fifth()
+      #
+      # Same as #first except returns only the fifth record.
 
-      # Same as +first+ except returns only the forty second record.
+      ##
+      # :method: forty_two
+      #
+      # :call-seq:
+      #   forty_two()
+      #
+      # Same as #first except returns only the forty second record.
       # Also known as accessing "the reddit".
-      def forty_two(*args)
-        @association.forty_two(*args)
-      end
+
+      ##
+      # :method: third_to_last
+      #
+      # :call-seq:
+      #   third_to_last()
+      #
+      # Same as #first except returns only the third-to-last record.
+
+      ##
+      # :method: second_to_last
+      #
+      # :call-seq:
+      #   second_to_last()
+      #
+      # Same as #first except returns only the second-to-last record.
 
       # Returns the last record, or the last +n+ records, from the collection.
       # If the collection is empty, the first form returns +nil+, and the second
@@ -223,12 +256,39 @@ module ActiveRecord
       #   another_person_without.pets         # => []
       #   another_person_without.pets.last    # => nil
       #   another_person_without.pets.last(3) # => []
-      def last(*args)
-        @association.last(*args)
+      def last(limit = nil)
+        load_target if find_from_target?
+        super
       end
 
-      def take(n = nil)
-        @association.take(n)
+      # Gives a record (or N records if a parameter is supplied) from the collection
+      # using the same rules as <tt>ActiveRecord::Base.take</tt>.
+      #
+      #   class Person < ActiveRecord::Base
+      #     has_many :pets
+      #   end
+      #
+      #   person.pets
+      #   # => [
+      #   #       #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>,
+      #   #       #<Pet id: 2, name: "Spook", person_id: 1>,
+      #   #       #<Pet id: 3, name: "Choo-Choo", person_id: 1>
+      #   #    ]
+      #
+      #   person.pets.take # => #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>
+      #
+      #   person.pets.take(2)
+      #   # => [
+      #   #      #<Pet id: 1, name: "Fancy-Fancy", person_id: 1>,
+      #   #      #<Pet id: 2, name: "Spook", person_id: 1>
+      #   #    ]
+      #
+      #   another_person_without.pets         # => []
+      #   another_person_without.pets.take    # => nil
+      #   another_person_without.pets.take(2) # => []
+      def take(limit = nil)
+        load_target if find_from_target?
+        super
       end
 
       # Returns a new object of the collection type that has been instantiated
@@ -290,7 +350,7 @@ module ActiveRecord
         @association.create(attributes, &block)
       end
 
-      # Like +create+, except that if the record is invalid, raises an exception.
+      # Like #create, except that if the record is invalid, raises an exception.
       #
       #   class Person
       #     has_many :pets
@@ -307,8 +367,8 @@ module ActiveRecord
       end
 
       # Add one or more records to the collection by setting their foreign keys
-      # to the association's primary key. Since << flattens its argument list and
-      # inserts each record, +push+ and +concat+ behave identically. Returns +self+
+      # to the association's primary key. Since #<< flattens its argument list and
+      # inserts each record, +push+ and #concat behave identically. Returns +self+
       # so method calls may be chained.
       #
       #   class Person < ActiveRecord::Base
@@ -364,7 +424,7 @@ module ActiveRecord
       # specified by the +:dependent+ option. If no +:dependent+ option is given,
       # then it will follow the default strategy.
       #
-      # For +has_many :through+ associations, the default deletion strategy is
+      # For <tt>has_many :through</tt> associations, the default deletion strategy is
       # +:delete_all+.
       #
       # For +has_many+ associations, the default deletion strategy is +:nullify+.
@@ -399,7 +459,7 @@ module ActiveRecord
       #   #       #<Pet id: 3, name: "Choo-Choo", person_id: nil>
       #   #    ]
       #
-      # Both +has_many+ and +has_many :through+ dependencies default to the
+      # Both +has_many+ and <tt>has_many :through</tt> dependencies default to the
       # +:delete_all+ strategy if the +:dependent+ option is set to +:destroy+.
       # Records are not instantiated and callbacks will not be fired.
       #
@@ -418,7 +478,7 @@ module ActiveRecord
       #   person.pets.delete_all
       #
       #   Pet.find(1, 2, 3)
-      #   # => ActiveRecord::RecordNotFound
+      #   # => ActiveRecord::RecordNotFound: Couldn't find all Pets with 'id': (1, 2, 3)
       #
       # If it is set to <tt>:delete_all</tt>, all the objects are deleted
       # *without* calling their +destroy+ method.
@@ -438,7 +498,7 @@ module ActiveRecord
       #   person.pets.delete_all
       #
       #   Pet.find(1, 2, 3)
-      #   # => ActiveRecord::RecordNotFound
+      #   # => ActiveRecord::RecordNotFound: Couldn't find all Pets with 'id': (1, 2, 3)
       def delete_all(dependent = nil)
         @association.delete_all(dependent)
       end
@@ -475,7 +535,7 @@ module ActiveRecord
       # then it will follow the default strategy. Returns an array with the
       # deleted records.
       #
-      # For +has_many :through+ associations, the default deletion strategy is
+      # For <tt>has_many :through</tt> associations, the default deletion strategy is
       # +:delete_all+.
       #
       # For +has_many+ associations, the default deletion strategy is +:nullify+.
@@ -532,7 +592,7 @@ module ActiveRecord
       #   # => [#<Pet id: 2, name: "Spook", person_id: 1>]
       #
       #   Pet.find(1, 3)
-      #   # => ActiveRecord::RecordNotFound: Couldn't find all Pets with IDs (1, 3)
+      #   # => ActiveRecord::RecordNotFound: Couldn't find all Pets with 'id': (1, 3)
       #
       # If it is set to <tt>:delete_all</tt>, all the +records+ are deleted
       # *without* calling their +destroy+ method.
@@ -560,9 +620,9 @@ module ActiveRecord
       #   #    ]
       #
       #   Pet.find(1)
-      #   # => ActiveRecord::RecordNotFound: Couldn't find Pet with id=1
+      #   # => ActiveRecord::RecordNotFound: Couldn't find Pet with 'id'=1
       #
-      # You can pass +Fixnum+ or +String+ values, it finds the records
+      # You can pass +Integer+ or +String+ values, it finds the records
       # responding to the +id+ and executes delete on them.
       #
       #   class Person < ActiveRecord::Base
@@ -624,9 +684,9 @@ module ActiveRecord
       #   person.pets.size  # => 0
       #   person.pets       # => []
       #
-      #   Pet.find(1, 2, 3) # => ActiveRecord::RecordNotFound: Couldn't find all Pets with IDs (1, 2, 3)
+      #   Pet.find(1, 2, 3) # => ActiveRecord::RecordNotFound: Couldn't find all Pets with 'id': (1, 2, 3)
       #
-      # You can pass +Fixnum+ or +String+ values, it finds the records
+      # You can pass +Integer+ or +String+ values, it finds the records
       # responding to the +id+ and then deletes them from the database.
       #
       #   person.pets.size # => 3
@@ -656,11 +716,17 @@ module ActiveRecord
       #   person.pets.size  # => 0
       #   person.pets       # => []
       #
-      #   Pet.find(4, 5, 6) # => ActiveRecord::RecordNotFound: Couldn't find all Pets with IDs (4, 5, 6)
+      #   Pet.find(4, 5, 6) # => ActiveRecord::RecordNotFound: Couldn't find all Pets with 'id': (4, 5, 6)
       def destroy(*records)
         @association.destroy(*records)
       end
 
+      ##
+      # :method: distinct
+      #
+      # :call-seq:
+      #   distinct(value = true)
+      #
       # Specifies whether the records should be unique or not.
       #
       #   class Person < ActiveRecord::Base
@@ -675,17 +741,35 @@ module ActiveRecord
       #
       #   person.pets.select(:name).distinct
       #   # => [#<Pet name: "Fancy-Fancy">]
-      def distinct
-        @association.distinct
+      #
+      #   person.pets.select(:name).distinct.distinct(false)
+      #   # => [
+      #   #      #<Pet name: "Fancy-Fancy">,
+      #   #      #<Pet name: "Fancy-Fancy">
+      #   #    ]
+
+      #--
+      def calculate(operation, column_name)
+        null_scope? ? scope.calculate(operation, column_name) : super
       end
-      alias uniq distinct
 
-      # Count all records using SQL.
+      def pluck(*column_names)
+        null_scope? ? scope.pluck(*column_names) : super
+      end
+
+      ##
+      # :method: count
+      #
+      # :call-seq:
+      #   count(column_name = nil, &block)
+      #
+      # Count all records.
       #
       #   class Person < ActiveRecord::Base
       #     has_many :pets
       #   end
       #
+      #   # This will perform the count using SQL.
       #   person.pets.count # => 3
       #   person.pets
       #   # => [
@@ -693,9 +777,11 @@ module ActiveRecord
       #   #       #<Pet id: 2, name: "Spook", person_id: 1>,
       #   #       #<Pet id: 3, name: "Choo-Choo", person_id: 1>
       #   #    ]
-      def count(column_name = nil)
-        @association.count(column_name)
-      end
+      #
+      # Passing a block will select all of a person's pets in SQL and then
+      # perform the count using Ruby.
+      #
+      #   person.pets.count { |pet| pet.name.include?('-') } # => 2
 
       # Returns the size of the collection. If the collection hasn't been loaded,
       # it executes a <tt>SELECT COUNT(*)</tt> query. Else it calls <tt>collection.size</tt>.
@@ -725,6 +811,12 @@ module ActiveRecord
         @association.size
       end
 
+      ##
+      # :method: length
+      #
+      # :call-seq:
+      #   length()
+      #
       # Returns the size of the collection calling +size+ on the target.
       # If the collection has been already loaded, +length+ and +size+ are
       # equivalent. If not and you are going to need the records anyway this
@@ -745,14 +837,11 @@ module ActiveRecord
       #   #       #<Pet id: 2, name: "Spook", person_id: 1>,
       #   #       #<Pet id: 3, name: "Choo-Choo", person_id: 1>
       #   #    ]
-      def length
-        @association.length
-      end
 
       # Returns +true+ if the collection is empty. If the collection has been
       # loaded it is equivalent
       # to <tt>collection.size.zero?</tt>. If the collection has not been loaded,
-      # it is equivalent to <tt>collection.exists?</tt>. If the collection has
+      # it is equivalent to <tt>!collection.exists?</tt>. If the collection has
       # not already been loaded and you are going to fetch the records anyway it
       # is better to check <tt>collection.length.zero?</tt>.
       #
@@ -771,6 +860,12 @@ module ActiveRecord
         @association.empty?
       end
 
+      ##
+      # :method: any?
+      #
+      # :call-seq:
+      #   any?()
+      #
       # Returns +true+ if the collection is not empty.
       #
       #   class Person < ActiveRecord::Base
@@ -781,7 +876,7 @@ module ActiveRecord
       #   person.pets.any?  # => false
       #
       #   person.pets << Pet.new(name: 'Snoop')
-      #   person.pets.count # => 0
+      #   person.pets.count # => 1
       #   person.pets.any?  # => true
       #
       # You can also pass a +block+ to define criteria. The behavior
@@ -800,10 +895,13 @@ module ActiveRecord
       #     pet.group == 'dogs'
       #   end
       #   # => true
-      def any?(&block)
-        @association.any?(&block)
-      end
 
+      ##
+      # :method: many?
+      #
+      # :call-seq:
+      #   many?()
+      #
       # Returns true if the collection has more than one record.
       # Equivalent to <tt>collection.size > 1</tt>.
       #
@@ -838,9 +936,6 @@ module ActiveRecord
       #     pet.group == 'cats'
       #   end
       #   # => true
-      def many?(&block)
-        @association.many?(&block)
-      end
 
       # Returns +true+ if the given +record+ is present in the collection.
       #
@@ -856,27 +951,14 @@ module ActiveRecord
         !!@association.include?(record)
       end
 
-      def arel
-        scope.arel
-      end
-
       def proxy_association
         @association
       end
 
-      # We don't want this object to be put on the scoping stack, because
-      # that could create an infinite loop where we call an @association
-      # method, which gets the current scope, which is this object, which
-      # delegates to @association, and so on.
-      def scoping
-        @association.scope.scoping { yield }
-      end
-
       # Returns a <tt>Relation</tt> object for the records in this association
       def scope
-        @association.scope
+        @scope ||= @association.scope
       end
-      alias spawn scope
 
       # Equivalent to <tt>Array#==</tt>. Returns +true+ if the two arrays
       # contain the same number of elements and if each element is equal
@@ -906,6 +988,12 @@ module ActiveRecord
         load_target == other
       end
 
+      ##
+      # :method: to_ary
+      #
+      # :call-seq:
+      #   to_ary()
+      #
       # Returns a new array of objects from the collection. If the collection
       # hasn't been loaded, it fetches the records from the database.
       #
@@ -939,10 +1027,10 @@ module ActiveRecord
       #   #       #<Pet id: 5, name: "Brain", person_id: 1>,
       #   #       #<Pet id: 6, name: "Boss",  person_id: 1>
       #   #    ]
-      def to_ary
-        load_target.dup
+
+      def records # :nodoc:
+        load_target
       end
-      alias_method :to_a, :to_ary
 
       # Adds one or more +records+ to the collection by setting their foreign keys
       # to the association's primary key. Returns +self+, so several appends may be
@@ -971,7 +1059,7 @@ module ActiveRecord
       alias_method :append, :<<
 
       def prepend(*args)
-        raise NoMethodError, "prepend on association is not defined. Please use << or append"
+        raise NoMethodError, "prepend on association is not defined. Please use <<, push or append"
       end
 
       # Equivalent to +delete_all+. The difference is that returns +self+, instead
@@ -986,7 +1074,6 @@ module ActiveRecord
       end
 
       # Reloads the collection from the database. Returns +self+.
-      # Equivalent to <tt>collection(true)</tt>.
       #
       #   class Person < ActiveRecord::Base
       #     has_many :pets
@@ -1000,12 +1087,9 @@ module ActiveRecord
       #
       #   person.pets.reload # fetches pets from the database
       #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
-      #
-      #   person.pets(true)  # fetches pets from the database
-      #   # => [#<Pet id: 1, name: "Snoop", group: "dogs", person_id: 1>]
       def reload
-        proxy_association.reload
-        self
+        proxy_association.reload(true)
+        reset_scope
       end
 
       # Unloads the association. Returns +self+.
@@ -1027,8 +1111,47 @@ module ActiveRecord
       def reset
         proxy_association.reset
         proxy_association.reset_scope
+        reset_scope
+      end
+
+      def reset_scope # :nodoc:
+        @offsets = {}
+        @scope = nil
         self
       end
+
+      delegate_methods = [
+        QueryMethods,
+        SpawnMethods,
+      ].flat_map { |klass|
+        klass.public_instance_methods(false)
+      } - self.public_instance_methods(false) - [:select] + [:scoping, :values]
+
+      delegate(*delegate_methods, to: :scope)
+
+      private
+
+        def find_nth_with_limit(index, limit)
+          load_target if find_from_target?
+          super
+        end
+
+        def find_nth_from_last(index)
+          load_target if find_from_target?
+          super
+        end
+
+        def null_scope?
+          @association.null_scope?
+        end
+
+        def find_from_target?
+          @association.find_from_target?
+        end
+
+        def exec_queries
+          load_target
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/foreign_association.rb b/activerecord/lib/active_record/associations/foreign_association.rb
index fe48ecec29..40010cde03 100644
--- a/activerecord/lib/active_record/associations/foreign_association.rb
+++ b/activerecord/lib/active_record/associations/foreign_association.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 module ActiveRecord::Associations
-  module ForeignAssociation
+  module ForeignAssociation # :nodoc:
     def foreign_key_present?
       if reflection.klass.primary_key
         owner.attribute_present?(reflection.active_record_primary_key)
diff --git a/activerecord/lib/active_record/associations/has_many_association.rb b/activerecord/lib/active_record/associations/has_many_association.rb
index ca27c9fdde..cf85a87fa7 100644
--- a/activerecord/lib/active_record/associations/has_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_association.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Has Many Association
   module Associations
+    # = Active Record Has Many Association
     # This is the proxy that handles a has many association.
     #
     # If the association has a <tt>:through</tt> option further specialization
@@ -15,35 +17,27 @@ module ActiveRecord
 
         when :restrict_with_error
           unless empty?
-            record = klass.human_attribute_name(reflection.name).downcase
-            owner.errors.add(:base, :"restrict_dependent_destroy.many", record: record)
+            record = owner.class.human_attribute_name(reflection.name).downcase
+            owner.errors.add(:base, :'restrict_dependent_destroy.has_many', record: record)
             throw(:abort)
           end
 
+        when :destroy
+          # No point in executing the counter update since we're going to destroy the parent anyway
+          load_target.each { |t| t.destroyed_by_association = reflection }
+          destroy_all
         else
-          if options[:dependent] == :destroy
-            # No point in executing the counter update since we're going to destroy the parent anyway
-            load_target.each { |t| t.destroyed_by_association = reflection }
-            destroy_all
-          else
-            delete_all
-          end
+          delete_all
         end
       end
 
       def insert_record(record, validate = true, raise = false)
         set_owner_attributes(record)
-        set_inverse_instance(record)
-
-        if raise
-          record.save!(:validate => validate)
-        else
-          record.save(:validate => validate)
-        end
+        super
       end
 
       def empty?
-        if has_cached_counter?
+        if reflection.has_cached_counter?
           size.zero?
         else
           super
@@ -66,84 +60,34 @@ module ActiveRecord
         # If the collection is empty the target is set to an empty array and
         # the loaded flag is set to true as well.
         def count_records
-          count = if has_cached_counter?
-            owner._read_attribute cached_counter_attribute_name
+          count = if reflection.has_cached_counter?
+            owner._read_attribute(reflection.counter_cache_column).to_i
           else
-            scope.count
+            scope.count(:all)
           end
 
           # If there's nothing in the database and @target has no new records
           # we are certain the current target is an empty array. This is a
           # documented side-effect of the method that may avoid an extra SELECT.
-          @target ||= [] and loaded! if count == 0
+          (@target ||= []) && loaded! if count == 0
 
           [association_scope.limit_value, count].compact.min
         end
 
-        def has_cached_counter?(reflection = reflection())
-          owner.attribute_present?(cached_counter_attribute_name(reflection))
-        end
-
-        def cached_counter_attribute_name(reflection = reflection())
-          if reflection.options[:counter_cache]
-            reflection.options[:counter_cache].to_s
-          else
-            "#{reflection.name}_count"
-          end
-        end
-
         def update_counter(difference, reflection = reflection())
-          update_counter_in_database(difference, reflection)
-          update_counter_in_memory(difference, reflection)
-        end
-
-        def update_counter_in_database(difference, reflection = reflection())
-          if has_cached_counter?(reflection)
-            counter = cached_counter_attribute_name(reflection)
-            owner.class.update_counters(owner.id, counter => difference)
+          if reflection.has_cached_counter?
+            owner.increment!(reflection.counter_cache_column, difference)
           end
         end
 
         def update_counter_in_memory(difference, reflection = reflection())
-          if counter_must_be_updated_by_has_many?(reflection)
-            counter = cached_counter_attribute_name(reflection)
-            owner[counter] += difference
-            owner.send(:clear_attribute_changes, counter) # eww
+          if reflection.counter_must_be_updated_by_has_many?
+            counter = reflection.counter_cache_column
+            owner.increment(counter, difference)
+            owner.send(:clear_attribute_change, counter) # eww
           end
         end
 
-        # This shit is nasty. We need to avoid the following situation:
-        #
-        #   * An associated record is deleted via record.destroy
-        #   * Hence the callbacks run, and they find a belongs_to on the record with a
-        #     :counter_cache options which points back at our owner. So they update the
-        #     counter cache.
-        #   * In which case, we must make sure to *not* update the counter cache, or else
-        #     it will be decremented twice.
-        #
-        # Hence this method.
-        def inverse_which_updates_counter_cache(reflection = reflection())
-          counter_name = cached_counter_attribute_name(reflection)
-          inverse_which_updates_counter_named(counter_name, reflection)
-        end
-        alias inverse_updates_counter_cache? inverse_which_updates_counter_cache
-
-        def inverse_which_updates_counter_named(counter_name, reflection)
-          reflection.klass._reflections.values.find { |inverse_reflection|
-            inverse_reflection.belongs_to? &&
-            inverse_reflection.counter_cache_column == counter_name
-          }
-        end
-
-        def inverse_updates_counter_in_memory?(reflection)
-          inverse = inverse_which_updates_counter_cache(reflection)
-          inverse && inverse == reflection.inverse_of
-        end
-
-        def counter_must_be_updated_by_has_many?(reflection)
-          !inverse_updates_counter_in_memory?(reflection) && has_cached_counter?(reflection)
-        end
-
         def delete_count(method, scope)
           if method == :delete_all
             scope.delete_all
@@ -153,7 +97,7 @@ module ActiveRecord
         end
 
         def delete_or_nullify_all_records(method)
-          count = delete_count(method, self.scope)
+          count = delete_count(method, scope)
           update_counter(-count)
         end
 
@@ -161,7 +105,7 @@ module ActiveRecord
         def delete_records(records, method)
           if method == :destroy
             records.each(&:destroy!)
-            update_counter(-records.length) unless inverse_updates_counter_cache?
+            update_counter(-records.length) unless reflection.inverse_updates_counter_cache?
           else
             scope = self.scope.where(reflection.klass.primary_key => records)
             update_counter(-delete_count(method, scope))
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index cd79266952..f84ac65fa2 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -1,14 +1,14 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Has Many Through Association
   module Associations
+    # = Active Record Has Many Through Association
     class HasManyThroughAssociation < HasManyAssociation #:nodoc:
       include ThroughAssociation
 
       def initialize(owner, reflection)
         super
-
-        @through_records     = {}
-        @through_association = nil
+        @through_records = {}
       end
 
       def concat(*records)
@@ -21,27 +21,11 @@ module ActiveRecord
         super
       end
 
-      def concat_records(records)
-        ensure_not_nested
-
-        records = super(records, true)
-
-        if owner.new_record? && records
-          records.flatten.each do |record|
-            build_through_record(record)
-          end
-        end
-
-        records
-      end
-
       def insert_record(record, validate = true, raise = false)
         ensure_not_nested
 
-        if raise
-          record.save!(:validate => validate)
-        else
-          return unless record.save(:validate => validate)
+        if record.new_record? || record.has_changes_to_save?
+          return unless super
         end
 
         save_through_record(record)
@@ -50,9 +34,18 @@ module ActiveRecord
       end
 
       private
+        def concat_records(records)
+          ensure_not_nested
+
+          records = super(records, true)
 
-        def through_association
-          @through_association ||= owner.association(through_reflection.name)
+          if owner.new_record? && records
+            records.flatten.each do |record|
+              build_through_record(record)
+            end
+          end
+
+          records
         end
 
         # The through record (built with build_record) is temporarily cached
@@ -66,6 +59,11 @@ module ActiveRecord
 
             through_record = through_association.build(*options_for_through_record)
             through_record.send("#{source_reflection.name}=", record)
+
+            if options[:source_type]
+              through_record.send("#{source_reflection.foreign_type}=", options[:source_type])
+            end
+
             through_record
           end
         end
@@ -81,7 +79,10 @@ module ActiveRecord
         end
 
         def save_through_record(record)
-          build_through_record(record).save!
+          association = build_through_record(record)
+          if association.changed?
+            association.save!
+          end
         ensure
           @through_records.delete(record.object_id)
         end
@@ -89,7 +90,7 @@ module ActiveRecord
         def build_record(attributes)
           ensure_not_nested
 
-          record = super(attributes)
+          record = super
 
           inverse = source_reflection.inverse_of
           if inverse
@@ -103,6 +104,11 @@ module ActiveRecord
           record
         end
 
+        def remove_records(existing_records, records, method)
+          super
+          delete_through_records(records)
+        end
+
         def target_reflection_has_associated_record?
           !(through_reflection.belongs_to? && owner[through_reflection.foreign_key].blank?)
         end
@@ -110,7 +116,7 @@ module ActiveRecord
         def update_through_counter?(method)
           case method
           when :destroy
-            !inverse_updates_counter_cache?(through_reflection)
+            !through_reflection.inverse_updates_counter_cache?
           when :nullify
             false
           else
@@ -127,21 +133,15 @@ module ActiveRecord
 
           scope = through_association.scope
           scope.where! construct_join_attributes(*records)
+          scope = scope.where(through_scope_attributes)
 
           case method
           when :destroy
             if scope.klass.primary_key
-              count = scope.destroy_all.length
+              count = scope.destroy_all.count(&:destroyed?)
             else
-              scope.each { |record| record.run_callbacks :destroy }
-
-              arel = scope.arel
-
-              stmt = Arel::DeleteManager.new
-              stmt.from scope.klass.arel_table
-              stmt.wheres = arel.constraints
-
-              count = scope.klass.connection.delete(stmt, 'SQL', scope.bound_attributes)
+              scope.each(&:_run_destroy_callbacks)
+              count = scope.delete_all
             end
           when :nullify
             count = scope.update_all(source_reflection.foreign_key => nil)
@@ -191,7 +191,7 @@ module ActiveRecord
 
         def find_target
           return [] unless target_reflection_has_associated_record?
-          get_records
+          super
         end
 
         # NOTE - not sure that we can actually cope with inverses here
diff --git a/activerecord/lib/active_record/associations/has_one_association.rb b/activerecord/lib/active_record/associations/has_one_association.rb
index 41a75b820e..390bfd8b08 100644
--- a/activerecord/lib/active_record/associations/has_one_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_association.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Belongs To Has One Association
   module Associations
+    # = Active Record Has One Association
     class HasOneAssociation < SingularAssociation #:nodoc:
       include ForeignAssociation
 
@@ -11,8 +13,8 @@ module ActiveRecord
 
         when :restrict_with_error
           if load_target
-            record = klass.human_attribute_name(reflection.name).downcase
-            owner.errors.add(:base, :"restrict_dependent_destroy.one", record: record)
+            record = owner.class.human_attribute_name(reflection.name).downcase
+            owner.errors.add(:base, :'restrict_dependent_destroy.has_one', record: record)
             throw(:abort)
           end
 
@@ -21,49 +23,49 @@ module ActiveRecord
         end
       end
 
-      def replace(record, save = true)
-        raise_on_type_mismatch!(record) if record
-        load_target
+      def delete(method = options[:dependent])
+        if load_target
+          case method
+          when :delete
+            target.delete
+          when :destroy
+            target.destroyed_by_association = reflection
+            target.destroy
+            throw(:abort) unless target.destroyed?
+          when :nullify
+            target.update_columns(reflection.foreign_key => nil) if target.persisted?
+          end
+        end
+      end
+
+      private
+        def replace(record, save = true)
+          raise_on_type_mismatch!(record) if record
 
-        return self.target if !(target || record)
+          return target unless load_target || record
 
-        assigning_another_record = target != record
-        if assigning_another_record || record.changed?
-          save &&= owner.persisted?
+          assigning_another_record = target != record
+          if assigning_another_record || record.has_changes_to_save?
+            save &&= owner.persisted?
 
-          transaction_if(save) do
-            remove_target!(options[:dependent]) if target && !target.destroyed? && assigning_another_record
+            transaction_if(save) do
+              remove_target!(options[:dependent]) if target && !target.destroyed? && assigning_another_record
 
-            if record
-              set_owner_attributes(record)
-              set_inverse_instance(record)
+              if record
+                set_owner_attributes(record)
+                set_inverse_instance(record)
 
-              if save && !record.save
-                nullify_owner_attributes(record)
-                set_owner_attributes(target) if target
-                raise RecordNotSaved, "Failed to save the new associated #{reflection.name}."
+                if save && !record.save
+                  nullify_owner_attributes(record)
+                  set_owner_attributes(target) if target
+                  raise RecordNotSaved, "Failed to save the new associated #{reflection.name}."
+                end
               end
             end
           end
-        end
 
-        self.target = record
-      end
-
-      def delete(method = options[:dependent])
-        if load_target
-          case method
-            when :delete
-              target.delete
-            when :destroy
-              target.destroy
-            when :nullify
-              target.update_columns(reflection.foreign_key => nil)
-          end
+          self.target = record
         end
-      end
-
-      private
 
         # The reason that the save param for replace is false, if for create (not just build),
         # is because the setting of the foreign keys is actually handled by the scoping when
@@ -75,18 +77,20 @@ module ActiveRecord
 
         def remove_target!(method)
           case method
-            when :delete
-              target.delete
-            when :destroy
-              target.destroy
-            else
-              nullify_owner_attributes(target)
-
-              if target.persisted? && owner.persisted? && !target.save
-                set_owner_attributes(target)
-                raise RecordNotSaved, "Failed to remove the existing associated #{reflection.name}. " +
-                                      "The record failed to save after its foreign key was set to nil."
-              end
+          when :delete
+            target.delete
+          when :destroy
+            target.destroyed_by_association = reflection
+            target.destroy
+          else
+            nullify_owner_attributes(target)
+            remove_inverse_instance(target)
+
+            if target.persisted? && owner.persisted? && !target.save
+              set_owner_attributes(target)
+              raise RecordNotSaved, "Failed to remove the existing associated #{reflection.name}. " \
+                                    "The record failed to save after its foreign key was set to nil."
+            end
           end
         end
 
@@ -101,6 +105,14 @@ module ActiveRecord
             yield
           end
         end
+
+        def _create_record(attributes, raise_error = false, &block)
+          unless owner.persisted?
+            raise ActiveRecord::RecordNotSaved, "You cannot call create unless the parent is saved"
+          end
+
+          super
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/has_one_through_association.rb b/activerecord/lib/active_record/associations/has_one_through_association.rb
index 08e0ec691f..10978b2d93 100644
--- a/activerecord/lib/active_record/associations/has_one_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_one_through_association.rb
@@ -1,30 +1,39 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Has One Through Association
   module Associations
+    # = Active Record Has One Through Association
     class HasOneThroughAssociation < HasOneAssociation #:nodoc:
       include ThroughAssociation
 
-      def replace(record)
-        create_through_record(record)
-        self.target = record
-      end
-
       private
+        def replace(record, save = true)
+          create_through_record(record, save)
+          self.target = record
+        end
 
-        def create_through_record(record)
+        def create_through_record(record, save)
           ensure_not_nested
 
-          through_proxy  = owner.association(through_reflection.name)
-          through_record = through_proxy.send(:load_target)
+          through_proxy  = through_association
+          through_record = through_proxy.load_target
 
           if through_record && !record
             through_record.destroy
           elsif record
             attributes = construct_join_attributes(record)
 
+            if through_record && through_record.destroyed?
+              through_record = through_proxy.tap(&:reload).target
+            end
+
             if through_record
-              through_record.update(attributes)
-            elsif owner.new_record?
+              if through_record.new_record?
+                through_record.assign_attributes(attributes)
+              else
+                through_record.update(attributes)
+              end
+            elsif owner.new_record? || !save
               through_proxy.build(attributes)
             else
               through_proxy.create(attributes)
diff --git a/activerecord/lib/active_record/associations/join_dependency.rb b/activerecord/lib/active_record/associations/join_dependency.rb
index 81eb5136a1..b76005b587 100644
--- a/activerecord/lib/active_record/associations/join_dependency.rb
+++ b/activerecord/lib/active_record/associations/join_dependency.rb
@@ -1,21 +1,21 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     class JoinDependency # :nodoc:
-      autoload :JoinBase,        'active_record/associations/join_dependency/join_base'
-      autoload :JoinAssociation, 'active_record/associations/join_dependency/join_association'
+      autoload :JoinBase,        "active_record/associations/join_dependency/join_base"
+      autoload :JoinAssociation, "active_record/associations/join_dependency/join_association"
 
       class Aliases # :nodoc:
         def initialize(tables)
           @tables = tables
-          @alias_cache = tables.each_with_object({}) { |table,h|
-            h[table.node] = table.columns.each_with_object({}) { |column,i|
+          @alias_cache = tables.each_with_object({}) { |table, h|
+            h[table.node] = table.columns.each_with_object({}) { |column, i|
               i[column.name] = column.alias
             }
           }
-          @name_and_alias_cache = tables.each_with_object({}) { |table,h|
-            h[table.node] = table.columns.map { |column|
-              [column.name, column.alias]
-            }
+          @columns_cache = tables.each_with_object({}) { |table, h|
+            h[table.node] = table.columns
           }
         end
 
@@ -23,30 +23,23 @@ module ActiveRecord
           @tables.flat_map(&:column_aliases)
         end
 
-        # An array of [column_name, alias] pairs for the table
         def column_aliases(node)
-          @name_and_alias_cache[node]
+          @columns_cache[node]
         end
 
         def column_alias(node, column)
           @alias_cache[node][column]
         end
 
-        class Table < Struct.new(:node, :columns)
-          def table
-            Arel::Nodes::TableAlias.new node.table, node.aliased_table_name
-          end
-
+        Table = Struct.new(:node, :columns) do # :nodoc:
           def column_aliases
-            t = table
+            t = node.table
             columns.map { |column| t[column.name].as Arel.sql column.alias }
           end
         end
         Column = Struct.new(:name, :alias)
       end
 
-      attr_reader :alias_tracker, :base_klass, :join_root
-
       def self.make_tree(associations)
         hash = {}
         walk_tree associations, hash
@@ -62,7 +55,7 @@ module ActiveRecord
             walk_tree assoc, hash
           end
         when Hash
-          associations.each do |k,v|
+          associations.each do |k, v|
             cache = hash[k] ||= {}
             walk_tree v, cache
           end
@@ -71,73 +64,41 @@ module ActiveRecord
         end
       end
 
-      # base is the base class on which operation is taking place.
-      # associations is the list of associations which are joined using hash, symbol or array.
-      # joins is the list of all string join commands and arel nodes.
-      #
-      #  Example :
-      #
-      #  class Physician < ActiveRecord::Base
-      #    has_many :appointments
-      #    has_many :patients, through: :appointments
-      #  end
-      #
-      #  If I execute `@physician.patients.to_a` then
-      #    base # => Physician
-      #    associations # => []
-      #    joins # =>  [#<Arel::Nodes::InnerJoin: ...]
-      #
-      #  However if I execute `Physician.joins(:appointments).to_a` then
-      #    base # => Physician
-      #    associations # => [:appointments]
-      #    joins # =>  []
-      #
-      def initialize(base, associations, joins)
-        @alias_tracker = AliasTracker.create_with_joins(base.connection, base.table_name, joins, base.type_caster)
+      def initialize(base, table, associations)
         tree = self.class.make_tree associations
-        @join_root = JoinBase.new base, build(tree, base)
-        @join_root.children.each { |child| construct_tables! @join_root, child }
+        @join_root = JoinBase.new(base, table, build(tree, base))
       end
 
       def reflections
         join_root.drop(1).map!(&:reflection)
       end
 
-      def join_constraints(outer_joins)
-        joins = join_root.children.flat_map { |child|
-          make_inner_joins join_root, child
-        }
+      def join_constraints(joins_to_add, join_type, alias_tracker)
+        @alias_tracker = alias_tracker
+
+        construct_tables!(join_root)
+        joins = make_join_constraints(join_root, join_type)
 
-        joins.concat outer_joins.flat_map { |oj|
+        joins.concat joins_to_add.flat_map { |oj|
+          construct_tables!(oj.join_root)
           if join_root.match? oj.join_root
             walk join_root, oj.join_root
           else
-            oj.join_root.children.flat_map { |child|
-              make_outer_joins oj.join_root, child
-            }
+            make_join_constraints(oj.join_root, join_type)
           end
         }
       end
 
-      def aliases
-        Aliases.new join_root.each_with_index.map { |join_part,i|
-          columns = join_part.column_names.each_with_index.map { |column_name,j|
-            Aliases::Column.new column_name, "t#{i}_r#{j}"
-          }
-          Aliases::Table.new(join_part, columns)
-        }
-      end
-
-      def instantiate(result_set, aliases)
+      def instantiate(result_set, &block)
         primary_key = aliases.column_alias(join_root, join_root.primary_key)
 
-        seen = Hash.new { |h,parent_klass|
-          h[parent_klass] = Hash.new { |i,parent_id|
-            i[parent_id] = Hash.new { |j,child_klass| j[child_klass] = {} }
+        seen = Hash.new { |i, object_id|
+          i[object_id] = Hash.new { |j, child_class|
+            j[child_class] = {}
           }
         }
 
-        model_cache = Hash.new { |h,klass| h[klass] = {} }
+        model_cache = Hash.new { |h, klass| h[klass] = {} }
         parents = model_cache[join_root]
         column_aliases = aliases.column_aliases join_root
 
@@ -148,138 +109,149 @@ module ActiveRecord
           class_name: join_root.base_klass.name
         }
 
-        message_bus.instrument('instantiation.active_record', payload) do
+        message_bus.instrument("instantiation.active_record", payload) do
           result_set.each { |row_hash|
-            parent = parents[row_hash[primary_key]] ||= join_root.instantiate(row_hash, column_aliases)
-            construct(parent, join_root, row_hash, result_set, seen, model_cache, aliases)
+            parent_key = primary_key ? row_hash[primary_key] : row_hash
+            parent = parents[parent_key] ||= join_root.instantiate(row_hash, column_aliases, &block)
+            construct(parent, join_root, row_hash, seen, model_cache)
           }
         end
 
         parents.values
       end
 
-      private
-
-      def make_constraints(parent, child, tables, join_type)
-        chain         = child.reflection.chain
-        foreign_table = parent.table
-        foreign_klass = parent.base_klass
-        child.join_constraints(foreign_table, foreign_klass, child, join_type, tables, child.reflection.scope_chain, chain)
-      end
-
-      def make_outer_joins(parent, child)
-        tables    = table_aliases_for(parent, child)
-        join_type = Arel::Nodes::OuterJoin
-        info      = make_constraints parent, child, tables, join_type
-
-        [info] + child.children.flat_map { |c| make_outer_joins(child, c) }
+      def apply_column_aliases(relation)
+        relation._select!(-> { aliases.columns })
       end
 
-      def make_inner_joins(parent, child)
-        tables    = child.tables
-        join_type = Arel::Nodes::InnerJoin
-        info      = make_constraints parent, child, tables, join_type
+      protected
+        attr_reader :join_root
 
-        [info] + child.children.flat_map { |c| make_inner_joins(child, c) }
-      end
+      private
+        attr_reader :alias_tracker
 
-      def table_aliases_for(parent, node)
-        node.reflection.chain.map { |reflection|
-          alias_tracker.aliased_table_for(
-            reflection.table_name,
-            table_alias_for(reflection, parent, reflection != node.reflection)
-          )
-        }
-      end
+        def aliases
+          @aliases ||= Aliases.new join_root.each_with_index.map { |join_part, i|
+            columns = join_part.column_names.each_with_index.map { |column_name, j|
+              Aliases::Column.new column_name, "t#{i}_r#{j}"
+            }
+            Aliases::Table.new(join_part, columns)
+          }
+        end
 
-      def construct_tables!(parent, node)
-        node.tables = table_aliases_for(parent, node)
-        node.children.each { |child| construct_tables! node, child }
-      end
+        def construct_tables!(join_root)
+          join_root.each_children do |parent, child|
+            child.tables = table_aliases_for(parent, child)
+          end
+        end
 
-      def table_alias_for(reflection, parent, join)
-        name = "#{reflection.plural_name}_#{parent.table_name}"
-        name << "_join" if join
-        name
-      end
+        def make_join_constraints(join_root, join_type)
+          join_root.children.flat_map do |child|
+            make_constraints(join_root, child, join_type)
+          end
+        end
 
-      def walk(left, right)
-        intersection, missing = right.children.map { |node1|
-          [left.children.find { |node2| node1.match? node2 }, node1]
-        }.partition(&:first)
+        def make_constraints(parent, child, join_type = Arel::Nodes::OuterJoin)
+          foreign_table = parent.table
+          foreign_klass = parent.base_klass
+          joins = child.join_constraints(foreign_table, foreign_klass, join_type, alias_tracker)
+          joins.concat child.children.flat_map { |c| make_constraints(child, c, join_type) }
+        end
 
-        ojs = missing.flat_map { |_,n| make_outer_joins left, n }
-        intersection.flat_map { |l,r| walk l, r }.concat ojs
-      end
+        def table_aliases_for(parent, node)
+          node.reflection.chain.map { |reflection|
+            alias_tracker.aliased_table_for(
+              reflection.table_name,
+              table_alias_for(reflection, parent, reflection != node.reflection),
+              reflection.klass.type_caster
+            )
+          }
+        end
 
-      def find_reflection(klass, name)
-        klass._reflect_on_association(name) or
-          raise ConfigurationError, "Association named '#{ name }' was not found on #{ klass.name }; perhaps you misspelled it?"
-      end
+        def table_alias_for(reflection, parent, join)
+          name = reflection.alias_candidate(parent.table_name)
+          join ? "#{name}_join" : name
+        end
 
-      def build(associations, base_klass)
-        associations.map do |name, right|
-          reflection = find_reflection base_klass, name
-          reflection.check_validity!
-          reflection.check_eager_loadable!
+        def walk(left, right)
+          intersection, missing = right.children.map { |node1|
+            [left.children.find { |node2| node1.match? node2 }, node1]
+          }.partition(&:first)
 
-          if reflection.polymorphic?
-            raise EagerLoadPolymorphicError.new(reflection)
-          end
+          joins = intersection.flat_map { |l, r| r.table = l.table; walk(l, r) }
+          joins.concat missing.flat_map { |_, n| make_constraints(left, n) }
+        end
 
-          JoinAssociation.new reflection, build(right, reflection.klass)
+        def find_reflection(klass, name)
+          klass._reflect_on_association(name) ||
+            raise(ConfigurationError, "Can't join '#{klass.name}' to association named '#{name}'; perhaps you misspelled it?")
         end
-      end
 
-      def construct(ar_parent, parent, row, rs, seen, model_cache, aliases)
-        return if ar_parent.nil?
-        primary_id  = ar_parent.id
+        def build(associations, base_klass)
+          associations.map do |name, right|
+            reflection = find_reflection base_klass, name
+            reflection.check_validity!
+            reflection.check_eager_loadable!
 
-        parent.children.each do |node|
-          if node.reflection.collection?
-            other = ar_parent.association(node.reflection.name)
-            other.loaded!
-          elsif ar_parent.association_cached?(node.reflection.name)
-            model = ar_parent.association(node.reflection.name).target
-            construct(model, node, row, rs, seen, model_cache, aliases)
-            next
+            if reflection.polymorphic?
+              raise EagerLoadPolymorphicError.new(reflection)
+            end
+
+            JoinAssociation.new(reflection, build(right, reflection.klass))
           end
+        end
 
-          key = aliases.column_alias(node, node.primary_key)
-          id = row[key]
-          if id.nil?
-            nil_association = ar_parent.association(node.reflection.name)
-            nil_association.loaded!
-            next
+        def construct(ar_parent, parent, row, seen, model_cache)
+          return if ar_parent.nil?
+
+          parent.children.each do |node|
+            if node.reflection.collection?
+              other = ar_parent.association(node.reflection.name)
+              other.loaded!
+            elsif ar_parent.association_cached?(node.reflection.name)
+              model = ar_parent.association(node.reflection.name).target
+              construct(model, node, row, seen, model_cache)
+              next
+            end
+
+            key = aliases.column_alias(node, node.primary_key)
+            id = row[key]
+            if id.nil?
+              nil_association = ar_parent.association(node.reflection.name)
+              nil_association.loaded!
+              next
+            end
+
+            model = seen[ar_parent.object_id][node][id]
+
+            if model
+              construct(model, node, row, seen, model_cache)
+            else
+              model = construct_model(ar_parent, node, row, model_cache, id)
+
+              seen[ar_parent.object_id][node][id] = model
+              construct(model, node, row, seen, model_cache)
+            end
           end
+        end
+
+        def construct_model(record, node, row, model_cache, id)
+          other = record.association(node.reflection.name)
 
-          model = seen[parent.base_klass][primary_id][node.base_klass][id]
+          model = model_cache[node][id] ||=
+            node.instantiate(row, aliases.column_aliases(node)) do |m|
+              other.set_inverse_instance(m)
+            end
 
-          if model
-            construct(model, node, row, rs, seen, model_cache, aliases)
+          if node.reflection.collection?
+            other.target.push(model)
           else
-            model = construct_model(ar_parent, node, row, model_cache, id, aliases)
-            model.readonly!
-            seen[parent.base_klass][primary_id][node.base_klass][id] = model
-            construct(model, node, row, rs, seen, model_cache, aliases)
+            other.target = model
           end
-        end
-      end
-
-      def construct_model(record, node, row, model_cache, id, aliases)
-        model = model_cache[node][id] ||= node.instantiate(row,
-                                                           aliases.column_aliases(node))
-        other = record.association(node.reflection.name)
 
-        if node.reflection.collection?
-          other.target.push(model)
-        else
-          other.target = model
+          model.readonly! if node.readonly?
+          model
         end
-
-        other.set_inverse_instance(model)
-        model
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_association.rb b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
index a6ad09a38a..4583d89cba 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_association.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -1,19 +1,19 @@
-require 'active_record/associations/join_dependency/join_part'
+# frozen_string_literal: true
+
+require "active_record/associations/join_dependency/join_part"
 
 module ActiveRecord
   module Associations
     class JoinDependency # :nodoc:
       class JoinAssociation < JoinPart # :nodoc:
-        # The reflection of the association represented
-        attr_reader :reflection
-
-        attr_accessor :tables
+        attr_reader :reflection, :tables
+        attr_accessor :table
 
         def initialize(reflection, children)
           super(reflection.klass, children)
 
-          @reflection      = reflection
-          @tables          = nil
+          @reflection = reflection
+          @tables     = nil
         end
 
         def match?(other)
@@ -21,107 +21,44 @@ module ActiveRecord
           super && reflection == other.reflection
         end
 
-        JoinInformation = Struct.new :joins, :binds
-
-        def join_constraints(foreign_table, foreign_klass, node, join_type, tables, scope_chain, chain)
-          joins         = []
-          binds         = []
-          tables        = tables.reverse
-
-          scope_chain_index = 0
-          scope_chain = scope_chain.reverse
+        def join_constraints(foreign_table, foreign_klass, join_type, alias_tracker)
+          joins = []
 
           # The chain starts with the target table, but we want to end with it here (makes
           # more sense in this context), so we reverse
-          chain.reverse_each do |reflection|
-            table = tables.shift
+          reflection.chain.reverse_each.with_index(1) do |reflection, i|
+            table = tables[-i]
             klass = reflection.klass
 
-            join_keys   = reflection.join_keys(klass)
-            key         = join_keys.key
-            foreign_key = join_keys.foreign_key
-
-            constraint = build_constraint(klass, table, key, foreign_table, foreign_key)
+            constraint = reflection.build_join_constraint(table, foreign_table)
 
-            predicate_builder = PredicateBuilder.new(TableMetadata.new(klass, table))
-            scope_chain_items = scope_chain[scope_chain_index].map do |item|
-              if item.is_a?(Relation)
-                item
-              else
-                ActiveRecord::Relation.create(klass, table, predicate_builder)
-                  .instance_exec(node, &item)
-              end
-            end
-            scope_chain_index += 1
-
-            relation = ActiveRecord::Relation.create(
-              klass,
-              table,
-              predicate_builder,
-            )
-            scope_chain_items.concat [klass.send(:build_default_scope, relation)].compact
-
-            rel = scope_chain_items.inject(scope_chain_items.shift) do |left, right|
-              left.merge right
-            end
-
-            if rel && !rel.arel.constraints.empty?
-              binds += rel.bound_attributes
-              constraint = constraint.and rel.arel.constraints
-            end
+            joins << table.create_join(table, table.create_on(constraint), join_type)
 
-            if reflection.type
-              value = foreign_klass.base_class.name
-              column = klass.columns_hash[reflection.type.to_s]
+            join_scope = reflection.join_scope(table, foreign_klass)
+            arel = join_scope.arel(alias_tracker.aliases)
 
-              substitute = klass.connection.substitute_at(column)
-              binds << Relation::QueryAttribute.new(column.name, value, klass.type_for_attribute(column.name))
-              constraint = constraint.and table[reflection.type].eq substitute
+            if arel.constraints.any?
+              joins.concat arel.join_sources
+              right = joins.last.right
+              right.expr = right.expr.and(arel.constraints)
             end
 
-            joins << table.create_join(table, table.create_on(constraint), join_type)
-
             # The current table in this iteration becomes the foreign table in the next
             foreign_table, foreign_klass = table, klass
           end
 
-          JoinInformation.new joins, binds
+          joins
         end
 
-        #  Builds equality condition.
-        #
-        #  Example:
-        #
-        #  class Physician < ActiveRecord::Base
-        #    has_many :appointments
-        #  end
-        #
-        #  If I execute `Physician.joins(:appointments).to_a` then
-        #    klass         # => Physician
-        #    table         # => #<Arel::Table @name="appointments" ...>
-        #    key           # =>  physician_id
-        #    foreign_table # => #<Arel::Table @name="physicians" ...>
-        #    foreign_key   # => id
-        #
-        def build_constraint(klass, table, key, foreign_table, foreign_key)
-          constraint = table[key].eq(foreign_table[foreign_key])
-
-          if klass.finder_needs_type_condition?
-            constraint = table.create_and([
-              constraint,
-              klass.send(:type_condition, table)
-            ])
-          end
-
-          constraint
+        def tables=(tables)
+          @tables = tables
+          @table  = tables.first
         end
 
-        def table
-          tables.first
-        end
+        def readonly?
+          return @readonly if defined?(@readonly)
 
-        def aliased_table_name
-          table.table_alias || table.name
+          @readonly = reflection.scope && reflection.scope_for(base_klass.unscoped).readonly_value
         end
       end
     end
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_base.rb b/activerecord/lib/active_record/associations/join_dependency/join_base.rb
index 3a26c25737..988b4e8fa2 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_base.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_base.rb
@@ -1,20 +1,21 @@
-require 'active_record/associations/join_dependency/join_part'
+# frozen_string_literal: true
+
+require "active_record/associations/join_dependency/join_part"
 
 module ActiveRecord
   module Associations
     class JoinDependency # :nodoc:
       class JoinBase < JoinPart # :nodoc:
-        def match?(other)
-          return true if self == other
-          super && base_klass == other.base_klass
-        end
+        attr_reader :table
 
-        def table
-          base_klass.arel_table
+        def initialize(base_klass, table, children)
+          super(base_klass, children)
+          @table = table
         end
 
-        def aliased_table_name
-          base_klass.table_name
+        def match?(other)
+          return true if self == other
+          super && base_klass == other.base_klass
         end
       end
     end
diff --git a/activerecord/lib/active_record/associations/join_dependency/join_part.rb b/activerecord/lib/active_record/associations/join_dependency/join_part.rb
index 9c6573f913..3ad72a3646 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_part.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_part.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     class JoinDependency # :nodoc:
@@ -15,17 +17,13 @@ module ActiveRecord
         # association.
         attr_reader :base_klass, :children
 
-        delegate :table_name, :column_names, :primary_key, :to => :base_klass
+        delegate :table_name, :column_names, :primary_key, to: :base_klass
 
         def initialize(base_klass, children)
           @base_klass = base_klass
           @children = children
         end
 
-        def name
-          reflection.name
-        end
-
         def match?(other)
           self.class == other.class
         end
@@ -35,13 +33,15 @@ module ActiveRecord
           children.each { |child| child.each(&block) }
         end
 
-        # An Arel::Table for the active_record
-        def table
-          raise NotImplementedError
+        def each_children(&block)
+          children.each do |child|
+            yield self, child
+            child.each_children(&block)
+          end
         end
 
-        # The alias for the active_record's table
-        def aliased_table_name
+        # An Arel::Table for the active_record
+        def table
           raise NotImplementedError
         end
 
@@ -54,16 +54,16 @@ module ActiveRecord
           length = column_names_with_alias.length
 
           while index < length
-            column_name, alias_name = column_names_with_alias[index]
-            hash[column_name] = row[alias_name]
+            column = column_names_with_alias[index]
+            hash[column.name] = row[column.alias]
             index += 1
           end
 
           hash
         end
 
-        def instantiate(row, aliases)
-          base_klass.instantiate(extract_record(row, aliases))
+        def instantiate(row, aliases, &block)
+          base_klass.instantiate(extract_record(row, aliases), &block)
         end
       end
     end
diff --git a/activerecord/lib/active_record/associations/preloader.rb b/activerecord/lib/active_record/associations/preloader.rb
index 6ecc741195..8997579527 100644
--- a/activerecord/lib/active_record/associations/preloader.rb
+++ b/activerecord/lib/active_record/associations/preloader.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     # Implements the details of eager loading of Active Record associations.
@@ -42,16 +44,8 @@ module ActiveRecord
       extend ActiveSupport::Autoload
 
       eager_autoload do
-        autoload :Association,           'active_record/associations/preloader/association'
-        autoload :SingularAssociation,   'active_record/associations/preloader/singular_association'
-        autoload :CollectionAssociation, 'active_record/associations/preloader/collection_association'
-        autoload :ThroughAssociation,    'active_record/associations/preloader/through_association'
-
-        autoload :HasMany,             'active_record/associations/preloader/has_many'
-        autoload :HasManyThrough,      'active_record/associations/preloader/has_many_through'
-        autoload :HasOne,              'active_record/associations/preloader/has_one'
-        autoload :HasOneThrough,       'active_record/associations/preloader/has_one_through'
-        autoload :BelongsTo,           'active_record/associations/preloader/belongs_to'
+        autoload :Association,        "active_record/associations/preloader/association"
+        autoload :ThroughAssociation, "active_record/associations/preloader/through_association"
       end
 
       # Eager loads the named associations for the given Active Record record(s).
@@ -88,18 +82,13 @@ module ActiveRecord
       #   [ :books, :author ]
       #   { author: :avatar }
       #   [ :books, { author: :avatar } ]
-
-      NULL_RELATION = Struct.new(:values, :where_clause, :joins_values).new({}, Relation::WhereClause.empty, [])
-
       def preload(records, associations, preload_scope = nil)
-        records       = Array.wrap(records).compact.uniq
-        associations  = Array.wrap(associations)
-        preload_scope = preload_scope || NULL_RELATION
+        records = Array.wrap(records).compact
 
         if records.empty?
           []
         else
-          associations.flat_map { |association|
+          Array.wrap(associations).flat_map { |association|
             preloaders_on association, records, preload_scope
           }
         end
@@ -107,97 +96,101 @@ module ActiveRecord
 
       private
 
-      def preloaders_on(association, records, scope)
-        case association
-        when Hash
-          preloaders_for_hash(association, records, scope)
-        when Symbol
-          preloaders_for_one(association, records, scope)
-        when String
-          preloaders_for_one(association.to_sym, records, scope)
-        else
-          raise ArgumentError, "#{association.inspect} was not recognised for preload"
+        # Loads all the given data into +records+ for the +association+.
+        def preloaders_on(association, records, scope, polymorphic_parent = false)
+          case association
+          when Hash
+            preloaders_for_hash(association, records, scope, polymorphic_parent)
+          when Symbol, String
+            preloaders_for_one(association, records, scope, polymorphic_parent)
+          else
+            raise ArgumentError, "#{association.inspect} was not recognized for preload"
+          end
         end
-      end
-
-      def preloaders_for_hash(association, records, scope)
-        association.flat_map { |parent, child|
-          loaders = preloaders_for_one parent, records, scope
 
-          recs = loaders.flat_map(&:preloaded_records).uniq
-          loaders.concat Array.wrap(child).flat_map { |assoc|
-            preloaders_on assoc, recs, scope
+        def preloaders_for_hash(association, records, scope, polymorphic_parent)
+          association.flat_map { |parent, child|
+            grouped_records(parent, records, polymorphic_parent).flat_map do |reflection, reflection_records|
+              loaders = preloaders_for_reflection(reflection, reflection_records, scope)
+              recs = loaders.flat_map(&:preloaded_records)
+              child_polymorphic_parent = reflection && reflection.options[:polymorphic]
+              loaders.concat Array.wrap(child).flat_map { |assoc|
+                preloaders_on assoc, recs, scope, child_polymorphic_parent
+              }
+              loaders
+            end
           }
-          loaders
-        }
-      end
+        end
 
-      # Not all records have the same class, so group then preload group on the reflection
-      # itself so that if various subclass share the same association then we do not split
-      # them unnecessarily
-      #
-      # Additionally, polymorphic belongs_to associations can have multiple associated
-      # classes, depending on the polymorphic_type field. So we group by the classes as
-      # well.
-      def preloaders_for_one(association, records, scope)
-        grouped_records(association, records).flat_map do |reflection, klasses|
-          klasses.map do |rhs_klass, rs|
-            loader = preloader_for(reflection, rs, rhs_klass).new(rhs_klass, rs, reflection, scope)
+        # Loads all the given data into +records+ for a singular +association+.
+        #
+        # Functions by instantiating a preloader class such as Preloader::Association and
+        # call the +run+ method for each passed in class in the +records+ argument.
+        #
+        # Not all records have the same class, so group then preload group on the reflection
+        # itself so that if various subclass share the same association then we do not split
+        # them unnecessarily
+        #
+        # Additionally, polymorphic belongs_to associations can have multiple associated
+        # classes, depending on the polymorphic_type field. So we group by the classes as
+        # well.
+        def preloaders_for_one(association, records, scope, polymorphic_parent)
+          grouped_records(association, records, polymorphic_parent)
+            .flat_map do |reflection, reflection_records|
+              preloaders_for_reflection reflection, reflection_records, scope
+            end
+        end
+
+        def preloaders_for_reflection(reflection, records, scope)
+          records.group_by { |record| record.association(reflection.name).klass }.map do |rhs_klass, rs|
+            loader = preloader_for(reflection, rs).new(rhs_klass, rs, reflection, scope)
             loader.run self
             loader
           end
         end
-      end
 
-      def grouped_records(association, records)
-        h = {}
-        records.each do |record|
-          next unless record
-          assoc = record.association(association)
-          klasses = h[assoc.reflection] ||= {}
-          (klasses[assoc.klass] ||= []) << record
+        def grouped_records(association, records, polymorphic_parent)
+          h = {}
+          records.each do |record|
+            next unless record
+            reflection = record.class._reflect_on_association(association)
+            next if polymorphic_parent && !reflection || !record.association(association).klass
+            (h[reflection] ||= []) << record
+          end
+          h
         end
-        h
-      end
 
-      class AlreadyLoaded # :nodoc:
-        attr_reader :owners, :reflection
+        class AlreadyLoaded # :nodoc:
+          def initialize(klass, owners, reflection, preload_scope)
+            @owners = owners
+            @reflection = reflection
+          end
 
-        def initialize(klass, owners, reflection, preload_scope)
-          @owners = owners
-          @reflection = reflection
-        end
+          def run(preloader); end
 
-        def run(preloader); end
+          def preloaded_records
+            owners.flat_map { |owner| owner.association(reflection.name).target }
+          end
 
-        def preloaded_records
-          owners.flat_map { |owner| owner.association(reflection.name).target }
+          private
+            attr_reader :owners, :reflection
         end
-      end
 
-      class NullPreloader # :nodoc:
-        def self.new(klass, owners, reflection, preload_scope); self; end
-        def self.run(preloader); end
-        def self.preloaded_records; []; end
-      end
-
-      def preloader_for(reflection, owners, rhs_klass)
-        return NullPreloader unless rhs_klass
+        # Returns a class containing the logic needed to load preload the data
+        # and attach it to a relation. The class returned implements a `run` method
+        # that accepts a preloader.
+        def preloader_for(reflection, owners)
+          if owners.first.association(reflection.name).loaded?
+            return AlreadyLoaded
+          end
+          reflection.check_preloadable!
 
-        if owners.first.association(reflection.name).loaded?
-          return AlreadyLoaded
-        end
-        reflection.check_preloadable!
-
-        case reflection.macro
-        when :has_many
-          reflection.options[:through] ? HasManyThrough : HasMany
-        when :has_one
-          reflection.options[:through] ? HasOneThrough : HasOne
-        when :belongs_to
-          BelongsTo
+          if reflection.options[:through]
+            ThroughAssociation
+          else
+            Association
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/associations/preloader/association.rb b/activerecord/lib/active_record/associations/preloader/association.rb
index 1dc8bff193..d6f7359055 100644
--- a/activerecord/lib/active_record/associations/preloader/association.rb
+++ b/activerecord/lib/active_record/associations/preloader/association.rb
@@ -1,8 +1,9 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     class Preloader
       class Association #:nodoc:
-        attr_reader :owners, :reflection, :preload_scope, :model, :klass
         attr_reader :preloaded_records
 
         def initialize(klass, owners, reflection, preload_scope)
@@ -11,152 +12,118 @@ module ActiveRecord
           @reflection    = reflection
           @preload_scope = preload_scope
           @model         = owners.first && owners.first.class
-          @scope         = nil
-          @owners_by_key = nil
           @preloaded_records = []
         end
 
         def run(preloader)
-          preload(preloader)
-        end
-
-        def preload(preloader)
-          raise NotImplementedError
-        end
+          records = load_records do |record|
+            owner = owners_by_key[convert_key(record[association_key_name])]
+            association = owner.association(reflection.name)
+            association.set_inverse_instance(record)
+          end
 
-        def scope
-          @scope ||= build_scope
+          owners.each do |owner|
+            associate_records_to_owner(owner, records[convert_key(owner[owner_key_name])] || [])
+          end
         end
 
-        def records_for(ids)
-          query_scope(ids)
-        end
+        private
+          attr_reader :owners, :reflection, :preload_scope, :model, :klass
 
-        def query_scope(ids)
-          scope.where(association_key_name => ids)
-        end
+          # The name of the key on the associated records
+          def association_key_name
+            reflection.join_primary_key(klass)
+          end
 
-        def table
-          klass.arel_table
-        end
+          # The name of the key on the model which declares the association
+          def owner_key_name
+            reflection.join_foreign_key
+          end
 
-        # The name of the key on the associated records
-        def association_key_name
-          raise NotImplementedError
-        end
+          def associate_records_to_owner(owner, records)
+            association = owner.association(reflection.name)
+            association.loaded!
+            if reflection.collection?
+              association.target.concat(records)
+            else
+              association.target = records.first unless records.empty?
+            end
+          end
 
-        # This is overridden by HABTM as the condition should be on the foreign_key column in
-        # the join table
-        def association_key
-          table[association_key_name]
-        end
+          def owner_keys
+            @owner_keys ||= owners_by_key.keys
+          end
 
-        # The name of the key on the model which declares the association
-        def owner_key_name
-          raise NotImplementedError
-        end
+          def owners_by_key
+            unless defined?(@owners_by_key)
+              @owners_by_key = owners.each_with_object({}) do |owner, h|
+                key = convert_key(owner[owner_key_name])
+                h[key] = owner if key
+              end
+            end
+            @owners_by_key
+          end
 
-        def owners_by_key
-          @owners_by_key ||= if key_conversion_required?
-                               owners.group_by do |owner|
-                                 owner[owner_key_name].to_s
-                               end
-                             else
-                               owners.group_by do |owner|
-                                 owner[owner_key_name]
-                               end
-                             end
-        end
+          def key_conversion_required?
+            unless defined?(@key_conversion_required)
+              @key_conversion_required = (association_key_type != owner_key_type)
+            end
 
-        def options
-          reflection.options
-        end
+            @key_conversion_required
+          end
 
-        private
+          def convert_key(key)
+            if key_conversion_required?
+              key.to_s
+            else
+              key
+            end
+          end
 
-        def associated_records_by_owner(preloader)
-          owners_map = owners_by_key
-          owner_keys = owners_map.keys.compact
+          def association_key_type
+            @klass.type_for_attribute(association_key_name).type
+          end
 
-          # Each record may have multiple owners, and vice-versa
-          records_by_owner = owners.each_with_object({}) do |owner,h|
-            h[owner] = []
+          def owner_key_type
+            @model.type_for_attribute(owner_key_name).type
           end
 
-          if owner_keys.any?
+          def load_records(&block)
+            return {} if owner_keys.empty?
             # Some databases impose a limit on the number of ids in a list (in Oracle it's 1000)
             # Make several smaller queries if necessary or make one query if the adapter supports it
-            sliced  = owner_keys.each_slice(klass.connection.in_clause_length || owner_keys.size)
-
-            records = load_slices sliced
-            records.each do |record, owner_key|
-              owners_map[owner_key].each do |owner|
-                records_by_owner[owner] << record
-              end
+            slices = owner_keys.each_slice(klass.connection.in_clause_length || owner_keys.size)
+            @preloaded_records = slices.flat_map do |slice|
+              records_for(slice, &block)
+            end
+            @preloaded_records.group_by do |record|
+              convert_key(record[association_key_name])
             end
           end
 
-          records_by_owner
-        end
-
-        def key_conversion_required?
-          association_key_type != owner_key_type
-        end
-
-        def association_key_type
-          @klass.type_for_attribute(association_key_name.to_s).type
-        end
-
-        def owner_key_type
-          @model.type_for_attribute(owner_key_name.to_s).type
-        end
-
-        def load_slices(slices)
-          @preloaded_records = slices.flat_map { |slice|
-            records_for(slice)
-          }
-
-          @preloaded_records.map { |record|
-            key = record[association_key_name]
-            key = key.to_s if key_conversion_required?
-
-            [record, key]
-          }
-        end
-
-        def reflection_scope
-          @reflection_scope ||= reflection.scope ? klass.unscoped.instance_exec(nil, &reflection.scope) : klass.unscoped
-        end
-
-        def build_scope
-          scope = klass.unscoped
-
-          values = reflection_scope.values
-          preload_values = preload_scope.values
-
-          scope.where_clause = reflection_scope.where_clause + preload_scope.where_clause
-          scope.references_values = Array(values[:references]) + Array(preload_values[:references])
-
-          scope._select! preload_values[:select] || values[:select] || table[Arel.star]
-          scope.includes! preload_values[:includes] || values[:includes]
-          if preload_scope.joins_values.any?
-            scope.joins!(preload_scope.joins_values)
-          else
-            scope.joins!(reflection_scope.joins_values)
+          def records_for(ids, &block)
+            scope.where(association_key_name => ids).load(&block)
           end
-          scope.order! preload_values[:order] || values[:order]
 
-          if preload_values[:readonly] || values[:readonly]
-            scope.readonly!
+          def scope
+            @scope ||= build_scope
           end
 
-          if options[:as]
-            scope.where!(klass.table_name => { reflection.type => model.base_class.sti_name })
+          def reflection_scope
+            @reflection_scope ||= reflection.scope ? reflection.scope_for(klass.unscoped) : klass.unscoped
           end
 
-          scope.unscope_values = Array(values[:unscope])
-          klass.default_scoped.merge(scope)
-        end
+          def build_scope
+            scope = klass.scope_for_association
+
+            if reflection.type
+              scope.where!(reflection.type => model.polymorphic_name)
+            end
+
+            scope.merge!(reflection_scope) if reflection.scope
+            scope.merge!(preload_scope) if preload_scope
+            scope
+          end
       end
     end
   end
diff --git a/activerecord/lib/active_record/associations/preloader/belongs_to.rb b/activerecord/lib/active_record/associations/preloader/belongs_to.rb
deleted file mode 100644
index 5091d4717a..0000000000
--- a/activerecord/lib/active_record/associations/preloader/belongs_to.rb
+++ /dev/null
@@ -1,17 +0,0 @@
-module ActiveRecord
-  module Associations
-    class Preloader
-      class BelongsTo < SingularAssociation #:nodoc:
-
-        def association_key_name
-          reflection.options[:primary_key] || klass && klass.primary_key
-        end
-
-        def owner_key_name
-          reflection.foreign_key
-        end
-
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/preloader/collection_association.rb b/activerecord/lib/active_record/associations/preloader/collection_association.rb
deleted file mode 100644
index 5adffcd831..0000000000
--- a/activerecord/lib/active_record/associations/preloader/collection_association.rb
+++ /dev/null
@@ -1,24 +0,0 @@
-module ActiveRecord
-  module Associations
-    class Preloader
-      class CollectionAssociation < Association #:nodoc:
-
-        private
-
-        def build_scope
-          super.order(preload_scope.values[:order] || reflection_scope.values[:order])
-        end
-
-        def preload(preloader)
-          associated_records_by_owner(preloader).each do |owner, records|
-            association = owner.association(reflection.name)
-            association.loaded!
-            association.target.concat(records)
-            records.each { |record| association.set_inverse_instance(record) }
-          end
-        end
-
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/preloader/has_many.rb b/activerecord/lib/active_record/associations/preloader/has_many.rb
deleted file mode 100644
index 3ea91a8c11..0000000000
--- a/activerecord/lib/active_record/associations/preloader/has_many.rb
+++ /dev/null
@@ -1,17 +0,0 @@
-module ActiveRecord
-  module Associations
-    class Preloader
-      class HasMany < CollectionAssociation #:nodoc:
-
-        def association_key_name
-          reflection.foreign_key
-        end
-
-        def owner_key_name
-          reflection.active_record_primary_key
-        end
-
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/preloader/has_many_through.rb b/activerecord/lib/active_record/associations/preloader/has_many_through.rb
deleted file mode 100644
index 2029871f39..0000000000
--- a/activerecord/lib/active_record/associations/preloader/has_many_through.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-module ActiveRecord
-  module Associations
-    class Preloader
-      class HasManyThrough < CollectionAssociation #:nodoc:
-        include ThroughAssociation
-
-        def associated_records_by_owner(preloader)
-          records_by_owner = super
-
-          if reflection_scope.distinct_value
-            records_by_owner.each_value(&:uniq!)
-          end
-
-          records_by_owner
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/preloader/has_one.rb b/activerecord/lib/active_record/associations/preloader/has_one.rb
deleted file mode 100644
index 24728e9f01..0000000000
--- a/activerecord/lib/active_record/associations/preloader/has_one.rb
+++ /dev/null
@@ -1,23 +0,0 @@
-module ActiveRecord
-  module Associations
-    class Preloader
-      class HasOne < SingularAssociation #:nodoc:
-
-        def association_key_name
-          reflection.foreign_key
-        end
-
-        def owner_key_name
-          reflection.active_record_primary_key
-        end
-
-        private
-
-        def build_scope
-          super.order(preload_scope.values[:order] || reflection_scope.values[:order])
-        end
-
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/preloader/has_one_through.rb b/activerecord/lib/active_record/associations/preloader/has_one_through.rb
deleted file mode 100644
index f063f85574..0000000000
--- a/activerecord/lib/active_record/associations/preloader/has_one_through.rb
+++ /dev/null
@@ -1,9 +0,0 @@
-module ActiveRecord
-  module Associations
-    class Preloader
-      class HasOneThrough < SingularAssociation #:nodoc:
-        include ThroughAssociation
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/preloader/singular_association.rb b/activerecord/lib/active_record/associations/preloader/singular_association.rb
deleted file mode 100644
index f60647a81e..0000000000
--- a/activerecord/lib/active_record/associations/preloader/singular_association.rb
+++ /dev/null
@@ -1,21 +0,0 @@
-module ActiveRecord
-  module Associations
-    class Preloader
-      class SingularAssociation < Association #:nodoc:
-
-        private
-
-        def preload(preloader)
-          associated_records_by_owner(preloader).each do |owner, associated_records|
-            record = associated_records.first
-
-            association = owner.association(reflection.name)
-            association.target = record
-            association.set_inverse_instance(record) if record
-          end
-        end
-
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/associations/preloader/through_association.rb b/activerecord/lib/active_record/associations/preloader/through_association.rb
index 56aa23b173..a6b7ab80a2 100644
--- a/activerecord/lib/active_record/associations/preloader/through_association.rb
+++ b/activerecord/lib/active_record/associations/preloader/through_association.rb
@@ -1,94 +1,106 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     class Preloader
-      module ThroughAssociation #:nodoc:
-        def through_reflection
-          reflection.through_reflection
-        end
-
-        def source_reflection
-          reflection.source_reflection
-        end
-
-        def associated_records_by_owner(preloader)
-          preloader.preload(owners,
-                            through_reflection.name,
-                            through_scope)
-
-          through_records = owners.map do |owner|
-            association = owner.association through_reflection.name
-
-            [owner, Array(association.reader)]
-          end
-
-          reset_association owners, through_reflection.name
-
-          middle_records = through_records.flat_map { |(_,rec)| rec }
-
-          preloaders = preloader.preload(middle_records,
-                                         source_reflection.name,
-                                         reflection_scope)
-
+      class ThroughAssociation < Association # :nodoc:
+        def run(preloader)
+          already_loaded     = owners.first.association(through_reflection.name).loaded?
+          through_scope      = through_scope()
+          reflection_scope   = target_reflection_scope
+          through_preloaders = preloader.preload(owners, through_reflection.name, through_scope)
+          middle_records     = through_preloaders.flat_map(&:preloaded_records)
+          preloaders         = preloader.preload(middle_records, source_reflection.name, reflection_scope)
           @preloaded_records = preloaders.flat_map(&:preloaded_records)
 
-          middle_to_pl = preloaders.each_with_object({}) do |pl,h|
-            pl.owners.each { |middle|
-              h[middle] = pl
-            }
-          end
-
-          record_offset = {}
-          @preloaded_records.each_with_index do |record,i|
-            record_offset[record] = i
-          end
-
-          through_records.each_with_object({}) { |(lhs,center),records_by_owner|
-            pl_to_middle = center.group_by { |record| middle_to_pl[record] }
-
-            records_by_owner[lhs] = pl_to_middle.flat_map do |pl, middles|
-              rhs_records = middles.flat_map { |r|
-                association = r.association source_reflection.name
-
-                association.reader
-              }.compact
-
-              rhs_records.sort_by { |rhs| record_offset[rhs] }
+          owners.each do |owner|
+            through_records = Array(owner.association(through_reflection.name).target)
+            if already_loaded
+              if source_type = reflection.options[:source_type]
+                through_records = through_records.select do |record|
+                  record[reflection.foreign_type] == source_type
+                end
+              end
+            else
+              owner.association(through_reflection.name).reset if through_scope
             end
-          }
+            result = through_records.flat_map do |record|
+              association = record.association(source_reflection.name)
+              target = association.target
+              association.reset if preload_scope
+              target
+            end
+            result.compact!
+            if reflection_scope
+              result.sort_by! { |rhs| preload_index[rhs] } if reflection_scope.order_values.any?
+              result.uniq! if reflection_scope.distinct_value
+            end
+            associate_records_to_owner(owner, result)
+          end
         end
 
         private
+          def through_reflection
+            reflection.through_reflection
+          end
 
-        def reset_association(owners, association_name)
-          should_reset = (through_scope != through_reflection.klass.unscoped) ||
-             (reflection.options[:source_type] && through_reflection.collection?)
-
-          # Don't cache the association - we would only be caching a subset
-          if should_reset
-            owners.each { |owner|
-              owner.association(association_name).reset
-            }
+          def source_reflection
+            reflection.source_reflection
           end
-        end
 
+          def preload_index
+            @preload_index ||= @preloaded_records.each_with_object({}).with_index do |(id, result), index|
+              result[id] = index
+            end
+          end
 
-        def through_scope
-          scope = through_reflection.klass.unscoped
+          def through_scope
+            scope = through_reflection.klass.unscoped
+            options = reflection.options
 
-          if options[:source_type]
-            scope.where! reflection.foreign_type => options[:source_type]
-          else
-            unless reflection_scope.where_clause.empty?
-              scope.includes_values = Array(reflection_scope.values[:includes] || options[:source])
+            if options[:source_type]
+              scope.where! reflection.foreign_type => options[:source_type]
+            elsif !reflection_scope.where_clause.empty?
               scope.where_clause = reflection_scope.where_clause
+              values = reflection_scope.values
+
+              if includes = values[:includes]
+                scope.includes!(source_reflection.name => includes)
+              else
+                scope.includes!(source_reflection.name)
+              end
+
+              if values[:references] && !values[:references].empty?
+                scope.references!(values[:references])
+              else
+                scope.references!(source_reflection.table_name)
+              end
+
+              if joins = values[:joins]
+                scope.joins!(source_reflection.name => joins)
+              end
+
+              if left_outer_joins = values[:left_outer_joins]
+                scope.left_outer_joins!(source_reflection.name => left_outer_joins)
+              end
+
+              if scope.eager_loading? && order_values = values[:order]
+                scope = scope.order(order_values)
+              end
             end
 
-            scope.references! reflection_scope.values[:references]
-            scope = scope.order reflection_scope.values[:order] if scope.eager_loading?
+            scope unless scope.empty_scope?
           end
 
-          scope
-        end
+          def target_reflection_scope
+            if preload_scope
+              reflection_scope.merge(preload_scope)
+            elsif reflection.scope
+              reflection_scope
+            else
+              nil
+            end
+          end
       end
     end
   end
diff --git a/activerecord/lib/active_record/associations/singular_association.rb b/activerecord/lib/active_record/associations/singular_association.rb
index bec9505bd2..8e50cce102 100644
--- a/activerecord/lib/active_record/associations/singular_association.rb
+++ b/activerecord/lib/active_record/associations/singular_association.rb
@@ -1,11 +1,11 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Associations
     class SingularAssociation < Association #:nodoc:
       # Implements the reader method, e.g. foo.bar for Foo.has_one :bar
-      def reader(force_reload = false)
-        if force_reload && klass
-          klass.uncached { reload }
-        elsif !loaded? || stale_target?
+      def reader
+        if !loaded? || stale_target?
           reload
         end
 
@@ -17,51 +17,40 @@ module ActiveRecord
         replace(record)
       end
 
-      def create(attributes = {}, &block)
-        _create_record(attributes, &block)
-      end
-
-      def create!(attributes = {}, &block)
-        _create_record(attributes, true, &block)
-      end
-
-      def build(attributes = {})
-        record = build_record(attributes)
-        yield(record) if block_given?
+      def build(attributes = {}, &block)
+        record = build_record(attributes, &block)
         set_new_record(record)
         record
       end
 
-      private
+      # Implements the reload reader method, e.g. foo.reload_bar for
+      # Foo.has_one :bar
+      def force_reload_reader
+        reload(true)
+        target
+      end
 
-        def create_scope
-          scope.scope_for_create.stringify_keys.except(klass.primary_key)
+      private
+        def scope_for_create
+          super.except!(klass.primary_key)
         end
 
-        def get_records
-          if reflection.scope_chain.any?(&:any?) ||
-              scope.eager_loading? ||
-              klass.scope_attributes?
-
-            return scope.limit(1).to_a
-          end
+        def find_target
+          scope = self.scope
+          return scope.take if skip_statement_cache?(scope)
 
           conn = klass.connection
-          sc = reflection.association_scope_cache(conn, owner) do
-            StatementCache.create(conn) { |params|
-              as = AssociationScope.create { params.bind }
-              target_scope.merge(as.scope(self, conn)).limit(1)
-            }
+          sc = reflection.association_scope_cache(conn, owner) do |params|
+            as = AssociationScope.create { params.bind }
+            target_scope.merge!(as.scope(self)).limit(1)
           end
 
           binds = AssociationScope.get_bind_values(owner, reflection.chain)
-          sc.execute binds, klass, klass.connection
-        end
-
-        def find_target
-          if record = get_records.first
+          sc.execute(binds, conn) do |record|
             set_inverse_instance record
-          end
+          end.first
+        rescue ::RangeError
+          nil
         end
 
         def replace(record)
@@ -72,9 +61,8 @@ module ActiveRecord
           replace(record)
         end
 
-        def _create_record(attributes, raise_error = false)
-          record = build_record(attributes)
-          yield(record) if block_given?
+        def _create_record(attributes, raise_error = false, &block)
+          record = build_record(attributes, &block)
           saved = record.save
           set_new_record(record)
           raise RecordInvalid.new(record) if !saved && raise_error
diff --git a/activerecord/lib/active_record/associations/through_association.rb b/activerecord/lib/active_record/associations/through_association.rb
index 55ee9f04e0..15e6565e69 100644
--- a/activerecord/lib/active_record/associations/through_association.rb
+++ b/activerecord/lib/active_record/associations/through_association.rb
@@ -1,11 +1,27 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Through Association
   module Associations
+    # = Active Record Through Association
     module ThroughAssociation #:nodoc:
+      delegate :source_reflection, to: :reflection
+
+      private
+        def through_reflection
+          @through_reflection ||= begin
+            refl = reflection.through_reflection
 
-      delegate :source_reflection, :through_reflection, :to => :reflection
+            while refl.through_reflection?
+              refl = refl.through_reflection
+            end
+
+            refl
+          end
+        end
 
-      protected
+        def through_association
+          @through_association ||= owner.association(through_reflection.name)
+        end
 
         # We merge in these scopes for two reasons:
         #
@@ -14,7 +30,7 @@ module ActiveRecord
         def target_scope
           scope = super
           reflection.chain.drop(1).each do |reflection|
-            relation = reflection.klass.all
+            relation = reflection.klass.scope_for_association
             scope.merge!(
               relation.except(:select, :create_with, :includes, :preload, :joins, :eager_load)
             )
@@ -22,8 +38,6 @@ module ActiveRecord
           scope
         end
 
-      private
-
         # Construct attributes for :through pointing to owner and associate. This is used by the
         # methods which create and delete records on the association.
         #
@@ -39,24 +53,22 @@ module ActiveRecord
         def construct_join_attributes(*records)
           ensure_mutable
 
-          if source_reflection.association_primary_key(reflection.klass) == reflection.klass.primary_key
+          association_primary_key = source_reflection.association_primary_key(reflection.klass)
+
+          if association_primary_key == reflection.klass.primary_key && !options[:source_type]
             join_attributes = { source_reflection.name => records }
           else
             join_attributes = {
-              source_reflection.foreign_key =>
-                records.map { |record|
-                  record.send(source_reflection.association_primary_key(reflection.klass))
-                }
+              source_reflection.foreign_key => records.map(&association_primary_key.to_sym)
             }
           end
 
           if options[:source_type]
-            join_attributes[source_reflection.foreign_type] =
-              records.map { |record| record.class.base_class.name }
+            join_attributes[source_reflection.foreign_type] = [ options[:source_type] ]
           end
 
           if records.count == 1
-            Hash[join_attributes.map { |k, v| [k, v.first] }]
+            join_attributes.transform_values!(&:first)
           else
             join_attributes
           end
@@ -76,13 +88,21 @@ module ActiveRecord
 
         def ensure_mutable
           unless source_reflection.belongs_to?
-            raise HasManyThroughCantAssociateThroughHasOneOrManyReflection.new(owner, reflection)
+            if reflection.has_one?
+              raise HasOneThroughCantAssociateThroughHasOneOrManyReflection.new(owner, reflection)
+            else
+              raise HasManyThroughCantAssociateThroughHasOneOrManyReflection.new(owner, reflection)
+            end
           end
         end
 
         def ensure_not_nested
           if reflection.nested?
-            raise HasManyThroughNestedAssociationsAreReadonly.new(owner, reflection)
+            if reflection.has_one?
+              raise HasOneThroughNestedAssociationsAreReadonly.new(owner, reflection)
+            else
+              raise HasManyThroughNestedAssociationsAreReadonly.new(owner, reflection)
+            end
           end
         end
 
@@ -94,7 +114,7 @@ module ActiveRecord
             attributes[inverse.foreign_key] = target.id
           end
 
-          super(attributes)
+          super
         end
     end
   end
diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb
deleted file mode 100644
index 73dd3fa041..0000000000
--- a/activerecord/lib/active_record/attribute.rb
+++ /dev/null
@@ -1,174 +0,0 @@
-module ActiveRecord
-  class Attribute # :nodoc:
-    class << self
-      def from_database(name, value, type)
-        FromDatabase.new(name, value, type)
-      end
-
-      def from_user(name, value, type)
-        FromUser.new(name, value, type)
-      end
-
-      def with_cast_value(name, value, type)
-        WithCastValue.new(name, value, type)
-      end
-
-      def null(name)
-        Null.new(name)
-      end
-
-      def uninitialized(name, type)
-        Uninitialized.new(name, type)
-      end
-    end
-
-    attr_reader :name, :value_before_type_cast, :type
-
-    # This method should not be called directly.
-    # Use #from_database or #from_user
-    def initialize(name, value_before_type_cast, type)
-      @name = name
-      @value_before_type_cast = value_before_type_cast
-      @type = type
-    end
-
-    def value
-      # `defined?` is cheaper than `||=` when we get back falsy values
-      @value = original_value unless defined?(@value)
-      @value
-    end
-
-    def original_value
-      type_cast(value_before_type_cast)
-    end
-
-    def value_for_database
-      type.serialize(value)
-    end
-
-    def changed_from?(old_value)
-      type.changed?(old_value, value, value_before_type_cast)
-    end
-
-    def changed_in_place_from?(old_value)
-      has_been_read? && type.changed_in_place?(old_value, value)
-    end
-
-    def with_value_from_user(value)
-      self.class.from_user(name, value, type)
-    end
-
-    def with_value_from_database(value)
-      self.class.from_database(name, value, type)
-    end
-
-    def with_cast_value(value)
-      self.class.with_cast_value(name, value, type)
-    end
-
-    def with_type(type)
-      self.class.new(name, value_before_type_cast, type)
-    end
-
-    def type_cast(*)
-      raise NotImplementedError
-    end
-
-    def initialized?
-      true
-    end
-
-    def came_from_user?
-      false
-    end
-
-    def has_been_read?
-      defined?(@value)
-    end
-
-    def ==(other)
-      self.class == other.class &&
-        name == other.name &&
-        value_before_type_cast == other.value_before_type_cast &&
-        type == other.type
-    end
-    alias eql? ==
-
-    def hash
-      [self.class, name, value_before_type_cast, type].hash
-    end
-
-    protected
-
-    def initialize_dup(other)
-      if defined?(@value) && @value.duplicable?
-        @value = @value.dup
-      end
-    end
-
-    class FromDatabase < Attribute # :nodoc:
-      def type_cast(value)
-        type.deserialize(value)
-      end
-    end
-
-    class FromUser < Attribute # :nodoc:
-      def type_cast(value)
-        type.cast(value)
-      end
-
-      def came_from_user?
-        true
-      end
-    end
-
-    class WithCastValue < Attribute # :nodoc:
-      def type_cast(value)
-        value
-      end
-
-      def changed_in_place_from?(old_value)
-        false
-      end
-    end
-
-    class Null < Attribute # :nodoc:
-      def initialize(name)
-        super(name, nil, Type::Value.new)
-      end
-
-      def value
-        nil
-      end
-
-      def with_type(type)
-        self.class.with_cast_value(name, nil, type)
-      end
-
-      def with_value_from_database(value)
-        raise ActiveModel::MissingAttributeError, "can't write unknown attribute `#{name}`"
-      end
-      alias_method :with_value_from_user, :with_value_from_database
-    end
-
-    class Uninitialized < Attribute # :nodoc:
-      def initialize(name, type)
-        super(name, nil, type)
-      end
-
-      def value
-        if block_given?
-          yield name
-        end
-      end
-
-      def value_for_database
-      end
-
-      def initialized?
-        false
-      end
-    end
-    private_constant :FromDatabase, :FromUser, :Null, :Uninitialized, :WithCastValue
-  end
-end
diff --git a/activerecord/lib/active_record/attribute/user_provided_default.rb b/activerecord/lib/active_record/attribute/user_provided_default.rb
deleted file mode 100644
index e0bee8c17e..0000000000
--- a/activerecord/lib/active_record/attribute/user_provided_default.rb
+++ /dev/null
@@ -1,32 +0,0 @@
-require 'active_record/attribute'
-
-module ActiveRecord
-  class Attribute # :nodoc:
-    class UserProvidedDefault < FromUser
-      def initialize(name, value, type, database_default)
-        super(name, value, type)
-        @database_default = database_default
-      end
-
-      def type_cast(value)
-        if value.is_a?(Proc)
-          super(value.call)
-        else
-          super
-        end
-      end
-
-      def changed_in_place_from?(old_value)
-        super || changed_from?(database_default.value)
-      end
-
-      def with_type(type)
-        self.class.new(name, value_before_type_cast, type, database_default)
-      end
-
-      protected
-
-      attr_reader :database_default
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/attribute_assignment.rb b/activerecord/lib/active_record/attribute_assignment.rb
index 45fdcaa1cd..b6f0e18764 100644
--- a/activerecord/lib/active_record/attribute_assignment.rb
+++ b/activerecord/lib/active_record/attribute_assignment.rb
@@ -1,99 +1,87 @@
-require 'active_model/forbidden_attributes_protection'
+# frozen_string_literal: true
+
+require "active_model/forbidden_attributes_protection"
 
 module ActiveRecord
   module AttributeAssignment
-    extend ActiveSupport::Concern
     include ActiveModel::AttributeAssignment
 
-    # Alias for `assign_attributes`. See +ActiveModel::AttributeAssignment+.
-    def attributes=(attributes)
-      assign_attributes(attributes)
-    end
-
     private
 
-    def _assign_attributes(attributes) # :nodoc:
-      multi_parameter_attributes  = {}
-      nested_parameter_attributes = {}
+      def _assign_attributes(attributes)
+        multi_parameter_attributes  = {}
+        nested_parameter_attributes = {}
 
-      attributes.each do |k, v|
-        if k.include?("(")
-          multi_parameter_attributes[k] = attributes.delete(k)
-        elsif v.is_a?(Hash)
-          nested_parameter_attributes[k] = attributes.delete(k)
+        attributes.each do |k, v|
+          if k.include?("(")
+            multi_parameter_attributes[k] = attributes.delete(k)
+          elsif v.is_a?(Hash)
+            nested_parameter_attributes[k] = attributes.delete(k)
+          end
         end
-      end
-      super(attributes)
+        super(attributes)
 
-      assign_nested_parameter_attributes(nested_parameter_attributes) unless nested_parameter_attributes.empty?
-      assign_multiparameter_attributes(multi_parameter_attributes) unless multi_parameter_attributes.empty?
-    end
-
-    # Tries to assign given value to given attribute.
-    # In case of an error, re-raises with the ActiveRecord constant.
-    def _assign_attribute(k, v) # :nodoc:
-      super
-    rescue ActiveModel::UnknownAttributeError
-      raise UnknownAttributeError.new(self, k)
-    end
+        assign_nested_parameter_attributes(nested_parameter_attributes) unless nested_parameter_attributes.empty?
+        assign_multiparameter_attributes(multi_parameter_attributes) unless multi_parameter_attributes.empty?
+      end
 
-    # Assign any deferred nested attributes after the base attributes have been set.
-    def assign_nested_parameter_attributes(pairs)
-      pairs.each { |k, v| _assign_attribute(k, v) }
-    end
+      # Assign any deferred nested attributes after the base attributes have been set.
+      def assign_nested_parameter_attributes(pairs)
+        pairs.each { |k, v| _assign_attribute(k, v) }
+      end
 
-    # Instantiates objects for all attribute classes that needs more than one constructor parameter. This is done
-    # by calling new on the column type or aggregation type (through composed_of) object with these parameters.
-    # So having the pairs written_on(1) = "2004", written_on(2) = "6", written_on(3) = "24", will instantiate
-    # written_on (a date type) with Date.new("2004", "6", "24"). You can also specify a typecast character in the
-    # parentheses to have the parameters typecasted before they're used in the constructor. Use i for Fixnum and
-    # f for Float. If all the values for a given attribute are empty, the attribute will be set to +nil+.
-    def assign_multiparameter_attributes(pairs)
-      execute_callstack_for_multiparameter_attributes(
-        extract_callstack_for_multiparameter_attributes(pairs)
-      )
-    end
+      # Instantiates objects for all attribute classes that needs more than one constructor parameter. This is done
+      # by calling new on the column type or aggregation type (through composed_of) object with these parameters.
+      # So having the pairs written_on(1) = "2004", written_on(2) = "6", written_on(3) = "24", will instantiate
+      # written_on (a date type) with Date.new("2004", "6", "24"). You can also specify a typecast character in the
+      # parentheses to have the parameters typecasted before they're used in the constructor. Use i for Integer and
+      # f for Float. If all the values for a given attribute are empty, the attribute will be set to +nil+.
+      def assign_multiparameter_attributes(pairs)
+        execute_callstack_for_multiparameter_attributes(
+          extract_callstack_for_multiparameter_attributes(pairs)
+        )
+      end
 
-    def execute_callstack_for_multiparameter_attributes(callstack)
-      errors = []
-      callstack.each do |name, values_with_empty_parameters|
-        begin
-          if values_with_empty_parameters.each_value.all?(&:nil?)
-            values = nil
-          else
-            values = values_with_empty_parameters
+      def execute_callstack_for_multiparameter_attributes(callstack)
+        errors = []
+        callstack.each do |name, values_with_empty_parameters|
+          begin
+            if values_with_empty_parameters.each_value.all?(&:nil?)
+              values = nil
+            else
+              values = values_with_empty_parameters
+            end
+            send("#{name}=", values)
+          rescue => ex
+            errors << AttributeAssignmentError.new("error on assignment #{values_with_empty_parameters.values.inspect} to #{name} (#{ex.message})", ex, name)
           end
-          send("#{name}=", values)
-        rescue => ex
-          errors << AttributeAssignmentError.new("error on assignment #{values_with_empty_parameters.values.inspect} to #{name} (#{ex.message})", ex, name)
+        end
+        unless errors.empty?
+          error_descriptions = errors.map(&:message).join(",")
+          raise MultiparameterAssignmentErrors.new(errors), "#{errors.size} error(s) on assignment of multiparameter attributes [#{error_descriptions}]"
         end
       end
-      unless errors.empty?
-        error_descriptions = errors.map(&:message).join(",")
-        raise MultiparameterAssignmentErrors.new(errors), "#{errors.size} error(s) on assignment of multiparameter attributes [#{error_descriptions}]"
-      end
-    end
 
-    def extract_callstack_for_multiparameter_attributes(pairs)
-      attributes = {}
+      def extract_callstack_for_multiparameter_attributes(pairs)
+        attributes = {}
 
-      pairs.each do |(multiparameter_name, value)|
-        attribute_name = multiparameter_name.split("(").first
-        attributes[attribute_name] ||= {}
+        pairs.each do |(multiparameter_name, value)|
+          attribute_name = multiparameter_name.split("(").first
+          attributes[attribute_name] ||= {}
 
-        parameter_value = value.empty? ? nil : type_cast_attribute_value(multiparameter_name, value)
-        attributes[attribute_name][find_parameter_position(multiparameter_name)] ||= parameter_value
-      end
+          parameter_value = value.empty? ? nil : type_cast_attribute_value(multiparameter_name, value)
+          attributes[attribute_name][find_parameter_position(multiparameter_name)] ||= parameter_value
+        end
 
-      attributes
-    end
+        attributes
+      end
 
-    def type_cast_attribute_value(multiparameter_name, value)
-      multiparameter_name =~ /\([0-9]*([if])\)/ ? value.send("to_" + $1) : value
-    end
+      def type_cast_attribute_value(multiparameter_name, value)
+        multiparameter_name =~ /\([0-9]*([if])\)/ ? value.send("to_" + $1) : value
+      end
 
-    def find_parameter_position(multiparameter_name)
-      multiparameter_name.scan(/\(([0-9]*).*\)/).first.first.to_i
-    end
+      def find_parameter_position(multiparameter_name)
+        multiparameter_name.scan(/\(([0-9]*).*\)/).first.first.to_i
+      end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_decorators.rb b/activerecord/lib/active_record/attribute_decorators.rb
index 7d0ae32411..98b7805c0a 100644
--- a/activerecord/lib/active_record/attribute_decorators.rb
+++ b/activerecord/lib/active_record/attribute_decorators.rb
@@ -1,19 +1,42 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module AttributeDecorators # :nodoc:
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :attribute_type_decorations, instance_accessor: false # :internal:
-      self.attribute_type_decorations = TypeDecorator.new
+      class_attribute :attribute_type_decorations, instance_accessor: false, default: TypeDecorator.new # :internal:
     end
 
     module ClassMethods # :nodoc:
+      # This method is an internal API used to create class macros such as
+      # +serialize+, and features like time zone aware attributes.
+      #
+      # Used to wrap the type of an attribute in a new type.
+      # When the schema for a model is loaded, attributes with the same name as
+      # +column_name+ will have their type yielded to the given block. The
+      # return value of that block will be used instead.
+      #
+      # Subsequent calls where +column_name+ and +decorator_name+ are the same
+      # will override the previous decorator, not decorate twice. This can be
+      # used to create idempotent class macros like +serialize+
       def decorate_attribute_type(column_name, decorator_name, &block)
         matcher = ->(name, _) { name == column_name.to_s }
         key = "_#{column_name}_#{decorator_name}"
         decorate_matching_attribute_types(matcher, key, &block)
       end
 
+      # This method is an internal API used to create higher level features like
+      # time zone aware attributes.
+      #
+      # When the schema for a model is loaded, +matcher+ will be called for each
+      # attribute with its name and type. If the matcher returns a truthy value,
+      # the type will then be yielded to the given block, and the return value
+      # of that block will replace the type.
+      #
+      # Subsequent calls to this method with the same value for +decorator_name+
+      # will replace the previous decorator, not decorate twice. This can be
+      # used to ensure that class macros are idempotent.
       def decorate_matching_attribute_types(matcher, decorator_name, &block)
         reload_schema_from_cache
         decorator_name = decorator_name.to_s
@@ -24,13 +47,13 @@ module ActiveRecord
 
       private
 
-      def load_schema!
-        super
-        attribute_types.each do |name, type|
-          decorated_type = attribute_type_decorations.apply(name, type)
-          define_attribute(name, decorated_type)
+        def load_schema!
+          super
+          attribute_types.each do |name, type|
+            decorated_type = attribute_type_decorations.apply(name, type)
+            define_attribute(name, decorated_type)
+          end
         end
-      end
     end
 
     class TypeDecorator # :nodoc:
@@ -53,15 +76,15 @@ module ActiveRecord
 
       private
 
-      def decorators_for(name, type)
-        matching(name, type).map(&:last)
-      end
+        def decorators_for(name, type)
+          matching(name, type).map(&:last)
+        end
 
-      def matching(name, type)
-        @decorations.values.select do |(matcher, _)|
-          matcher.call(name, type)
+        def matching(name, type)
+          @decorations.values.select do |(matcher, _)|
+            matcher.call(name, type)
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods.rb b/activerecord/lib/active_record/attribute_methods.rb
index 9d58a19304..fd8c1da842 100644
--- a/activerecord/lib/active_record/attribute_methods.rb
+++ b/activerecord/lib/active_record/attribute_methods.rb
@@ -1,7 +1,6 @@
-require 'active_support/core_ext/enumerable'
-require 'active_support/core_ext/string/filters'
-require 'mutex_m'
-require 'thread_safe'
+# frozen_string_literal: true
+
+require "mutex_m"
 
 module ActiveRecord
   # = Active Record Attribute Methods
@@ -23,43 +22,12 @@ module ActiveRecord
       delegate :column_for_attribute, to: :class
     end
 
-    AttrNames = Module.new {
-      def self.set_name_cache(name, value)
-        const_name = "ATTR_#{name}"
-        unless const_defined? const_name
-          const_set const_name, value.dup.freeze
-        end
-      end
-    }
-
-    BLACKLISTED_CLASS_METHODS = %w(private public protected allocate new name parent superclass)
+    RESTRICTED_CLASS_METHODS = %w(private public protected allocate new name parent superclass)
 
-    class AttributeMethodCache
-      def initialize
-        @module = Module.new
-        @method_cache = ThreadSafe::Cache.new
-      end
-
-      def [](name)
-        @method_cache.compute_if_absent(name) do
-          safe_name = name.unpack('h*').first
-          temp_method = "__temp__#{safe_name}"
-          ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
-          @module.module_eval method_body(temp_method, safe_name), __FILE__, __LINE__
-          @module.instance_method temp_method
-        end
-      end
-
-      private
-
-      # Override this method in the subclasses for method body.
-      def method_body(method_name, const_name)
-        raise NotImplementedError, "Subclasses must implement a method_body(method_name, const_name) method."
-      end
+    class GeneratedAttributeMethods < Module #:nodoc:
+      include Mutex_m
     end
 
-    class GeneratedAttributeMethods < Module; end # :nodoc:
-
     module ClassMethods
       def inherited(child_class) #:nodoc:
         child_class.initialize_generated_modules
@@ -67,7 +35,7 @@ module ActiveRecord
       end
 
       def initialize_generated_modules # :nodoc:
-        @generated_attribute_methods = GeneratedAttributeMethods.new { extend Mutex_m }
+        @generated_attribute_methods = GeneratedAttributeMethods.new
         @attribute_methods_generated = false
         include @generated_attribute_methods
 
@@ -82,11 +50,10 @@ module ActiveRecord
         # attribute methods.
         generated_attribute_methods.synchronize do
           return false if @attribute_methods_generated
-          superclass.define_attribute_methods unless self == base_class
+          superclass.define_attribute_methods unless base_class?
           super(attribute_names)
           @attribute_methods_generated = true
         end
-        true
       end
 
       def undefine_attribute_methods # :nodoc:
@@ -96,7 +63,7 @@ module ActiveRecord
         end
       end
 
-      # Raises a <tt>ActiveRecord::DangerousAttributeError</tt> exception when an
+      # Raises an ActiveRecord::DangerousAttributeError exception when an
       # \Active \Record method is defined in the model, otherwise +false+.
       #
       #   class Person < ActiveRecord::Base
@@ -106,7 +73,7 @@ module ActiveRecord
       #   end
       #
       #   Person.instance_method_already_implemented?(:save)
-      #   # => ActiveRecord::DangerousAttributeError: save is defined by ActiveRecord
+      #   # => ActiveRecord::DangerousAttributeError: save is defined by Active Record. Check to make sure that you don't have an attribute or method with the same name.
       #
       #   Person.instance_method_already_implemented?(:name)
       #   # => false
@@ -147,7 +114,7 @@ module ActiveRecord
       # A class method is 'dangerous' if it is already (re)defined by Active Record, but
       # not by any ancestors. (So 'puts' is not dangerous but 'new' is.)
       def dangerous_class_method?(method_name)
-        BLACKLISTED_CLASS_METHODS.include?(method_name.to_s) || class_method_defined_within?(method_name, Base)
+        RESTRICTED_CLASS_METHODS.include?(method_name.to_s) || class_method_defined_within?(method_name, Base)
       end
 
       def class_method_defined_within?(name, klass, superklass = klass.superclass) # :nodoc:
@@ -172,7 +139,7 @@ module ActiveRecord
       #   Person.attribute_method?(:age=)    # => true
       #   Person.attribute_method?(:nothing) # => false
       def attribute_method?(attribute)
-        super || (table_exists? && column_names.include?(attribute.to_s.sub(/=$/, '')))
+        super || (table_exists? && column_names.include?(attribute.to_s.sub(/=$/, "")))
       end
 
       # Returns an array of column names as strings if it's not an abstract class and
@@ -185,10 +152,73 @@ module ActiveRecord
       #   # => ["id", "created_at", "updated_at", "name", "age"]
       def attribute_names
         @attribute_names ||= if !abstract_class? && table_exists?
-            attribute_types.keys
-          else
-            []
-          end
+          attribute_types.keys
+        else
+          []
+        end
+      end
+
+      # Regexp for column names (with or without a table name prefix). Matches
+      # the following:
+      #   "#{table_name}.#{column_name}"
+      #   "#{column_name}"
+      COLUMN_NAME = /\A(?:\w+\.)?\w+\z/i
+
+      # Regexp for column names with order (with or without a table name
+      # prefix, with or without various order modifiers). Matches the following:
+      #   "#{table_name}.#{column_name}"
+      #   "#{table_name}.#{column_name} #{direction}"
+      #   "#{table_name}.#{column_name} #{direction} NULLS FIRST"
+      #   "#{table_name}.#{column_name} NULLS LAST"
+      #   "#{column_name}"
+      #   "#{column_name} #{direction}"
+      #   "#{column_name} #{direction} NULLS FIRST"
+      #   "#{column_name} NULLS LAST"
+      COLUMN_NAME_WITH_ORDER = /
+        \A
+        (?:\w+\.)?
+        \w+
+        (?:\s+asc|\s+desc)?
+        (?:\s+nulls\s+(?:first|last))?
+        \z
+      /ix
+
+      def disallow_raw_sql!(args, permit: COLUMN_NAME) # :nodoc:
+        unexpected = args.reject do |arg|
+          Arel.arel_node?(arg) ||
+            arg.to_s.split(/\s*,\s*/).all? { |part| permit.match?(part) }
+        end
+
+        return if unexpected.none?
+
+        if allow_unsafe_raw_sql == :deprecated
+          ActiveSupport::Deprecation.warn(
+            "Dangerous query method (method whose arguments are used as raw " \
+            "SQL) called with non-attribute argument(s): " \
+            "#{unexpected.map(&:inspect).join(", ")}. Non-attribute " \
+            "arguments will be disallowed in Rails 6.0. This method should " \
+            "not be called with user-provided values, such as request " \
+            "parameters or model attributes. Known-safe values can be passed " \
+            "by wrapping them in Arel.sql()."
+          )
+        else
+          raise(ActiveRecord::UnknownAttributeReference,
+            "Query method called with non-attribute argument(s): " +
+            unexpected.map(&:inspect).join(", ")
+          )
+        end
+      end
+
+      # Returns true if the given attribute exists, otherwise false.
+      #
+      #   class Person < ActiveRecord::Base
+      #   end
+      #
+      #   Person.has_attribute?('name')   # => true
+      #   Person.has_attribute?(:age)     # => true
+      #   Person.has_attribute?(:nothing) # => false
+      def has_attribute?(attr_name)
+        attribute_types.key?(attr_name.to_s)
       end
 
       # Returns the column object for the named attribute.
@@ -221,26 +251,27 @@ module ActiveRecord
     #   end
     #
     #   person = Person.new
-    #   person.respond_to(:name)    # => true
-    #   person.respond_to(:name=)   # => true
-    #   person.respond_to(:name?)   # => true
-    #   person.respond_to('age')    # => true
-    #   person.respond_to('age=')   # => true
-    #   person.respond_to('age?')   # => true
-    #   person.respond_to(:nothing) # => false
+    #   person.respond_to?(:name)    # => true
+    #   person.respond_to?(:name=)   # => true
+    #   person.respond_to?(:name?)   # => true
+    #   person.respond_to?('age')    # => true
+    #   person.respond_to?('age=')   # => true
+    #   person.respond_to?('age?')   # => true
+    #   person.respond_to?(:nothing) # => false
     def respond_to?(name, include_private = false)
       return false unless super
-      name = name.to_s
 
       # If the result is true then check for the select case.
       # For queries selecting a subset of columns, return false for unselected columns.
       # We check defined?(@attributes) not to issue warnings if called on objects that
       # have been allocated but not yet initialized.
-      if defined?(@attributes) && self.class.column_names.include?(name)
-        return has_attribute?(name)
+      if defined?(@attributes)
+        if name = self.class.symbol_column_to_string(name.to_sym)
+          return has_attribute?(name)
+        end
       end
 
-      return true
+      true
     end
 
     # Returns +true+ if the given attribute is in the attributes hash, otherwise +false+.
@@ -283,9 +314,8 @@ module ActiveRecord
     # Returns an <tt>#inspect</tt>-like string for the value of the
     # attribute +attr_name+. String attributes are truncated up to 50
     # characters, Date and Time attributes are returned in the
-    # <tt>:db</tt> format, Array attributes are truncated up to 10 values.
-    # Other attributes return the value of <tt>#inspect</tt> without
-    # modification.
+    # <tt>:db</tt> format. Other attributes return the value of
+    # <tt>#inspect</tt> without modification.
     #
     #   person = Person.create!(name: 'David Heinemeier Hansson ' * 3)
     #
@@ -296,20 +326,10 @@ module ActiveRecord
     #   # => "\"2012-10-22 00:15:07\""
     #
     #   person.attribute_for_inspect(:tag_ids)
-    #   # => "[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ...]"
+    #   # => "[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]"
     def attribute_for_inspect(attr_name)
-      value = read_attribute(attr_name)
-
-      if value.is_a?(String) && value.length > 50
-        "#{value[0, 50]}...".inspect
-      elsif value.is_a?(Date) || value.is_a?(Time)
-        %("#{value.to_s(:db)}")
-      elsif value.is_a?(Array) && value.size > 10
-        inspected = value.first(10).inspect
-        %(#{inspected[0...-1]}, ...])
-      else
-        value.inspect
-      end
+      value = _read_attribute(attr_name)
+      format_for_inspect(value)
     end
 
     # Returns +true+ if the specified +attribute+ has been set by the user or by a
@@ -338,8 +358,6 @@ module ActiveRecord
     #
     # Note: +:id+ is always present.
     #
-    # Alias for the <tt>read_attribute</tt> method.
-    #
     #   class Person < ActiveRecord::Base
     #     belongs_to :organization
     #   end
@@ -356,7 +374,7 @@ module ActiveRecord
     end
 
     # Updates the attribute identified by <tt>attr_name</tt> with the specified +value+.
-    # (Alias for the protected <tt>write_attribute</tt> method).
+    # (Alias for the protected #write_attribute method).
     #
     #   class Person < ActiveRecord::Base
     #   end
@@ -364,7 +382,7 @@ module ActiveRecord
     #   person = Person.new
     #   person[:age] = '22'
     #   person[:age] # => 22
-    #   person[:age] # => Fixnum
+    #   person[:age].class # => Integer
     def []=(attr_name, value)
       write_attribute(attr_name, value)
     end
@@ -377,92 +395,76 @@ module ActiveRecord
     #
     # For example:
     #
-    # class PostsController < ActionController::Base
-    #   after_action :print_accessed_fields, only: :index
+    #   class PostsController < ActionController::Base
+    #     after_action :print_accessed_fields, only: :index
     #
-    #   def index
-    #     @posts = Post.all
-    #   end
+    #     def index
+    #       @posts = Post.all
+    #     end
     #
-    #   private
+    #     private
     #
-    #   def print_accessed_fields
-    #     p @posts.first.accessed_fields
+    #     def print_accessed_fields
+    #       p @posts.first.accessed_fields
+    #     end
     #   end
-    # end
     #
     # Which allows you to quickly change your code to:
     #
-    # class PostsController < ActionController::Base
-    #   def index
-    #     @posts = Post.select(:id, :title, :author_id, :updated_at)
+    #   class PostsController < ActionController::Base
+    #     def index
+    #       @posts = Post.select(:id, :title, :author_id, :updated_at)
+    #     end
     #   end
-    # end
     def accessed_fields
       @attributes.accessed
     end
 
-    protected
-
-    def clone_attribute_value(reader_method, attribute_name) # :nodoc:
-      value = send(reader_method, attribute_name)
-      value.duplicable? ? value.clone : value
-    rescue TypeError, NoMethodError
-      value
-    end
-
-    def arel_attributes_with_values_for_create(attribute_names) # :nodoc:
-      arel_attributes_with_values(attributes_for_create(attribute_names))
-    end
-
-    def arel_attributes_with_values_for_update(attribute_names) # :nodoc:
-      arel_attributes_with_values(attributes_for_update(attribute_names))
-    end
-
-    def attribute_method?(attr_name) # :nodoc:
-      # We check defined? because Syck calls respond_to? before actually calling initialize.
-      defined?(@attributes) && @attributes.key?(attr_name)
-    end
-
     private
+      def attribute_method?(attr_name)
+        # We check defined? because Syck calls respond_to? before actually calling initialize.
+        defined?(@attributes) && @attributes.key?(attr_name)
+      end
 
-    # Returns a Hash of the Arel::Attributes and attribute values that have been
-    # typecasted for use in an Arel insert/update method.
-    def arel_attributes_with_values(attribute_names)
-      attrs = {}
-      arel_table = self.class.arel_table
-
-      attribute_names.each do |name|
-        attrs[arel_table[name]] = typecasted_attribute_value(name)
+      def attributes_with_values(attribute_names)
+        attribute_names.each_with_object({}) do |name, attrs|
+          attrs[name] = _read_attribute(name)
+        end
       end
-      attrs
-    end
 
-    # Filters the primary keys and readonly attributes from the attribute names.
-    def attributes_for_update(attribute_names)
-      attribute_names.reject do |name|
-        readonly_attribute?(name)
+      # Filters the primary keys and readonly attributes from the attribute names.
+      def attributes_for_update(attribute_names)
+        attribute_names &= self.class.column_names
+        attribute_names.delete_if do |name|
+          readonly_attribute?(name)
+        end
       end
-    end
 
-    # Filters out the primary keys, from the attribute names, when the primary
-    # key is to be generated (e.g. the id attribute has no value).
-    def attributes_for_create(attribute_names)
-      attribute_names.reject do |name|
-        pk_attribute?(name) && id.nil?
+      # Filters out the primary keys, from the attribute names, when the primary
+      # key is to be generated (e.g. the id attribute has no value).
+      def attributes_for_create(attribute_names)
+        attribute_names &= self.class.column_names
+        attribute_names.delete_if do |name|
+          pk_attribute?(name) && id.nil?
+        end
       end
-    end
 
-    def readonly_attribute?(name)
-      self.class.readonly_attributes.include?(name)
-    end
+      def format_for_inspect(value)
+        if value.is_a?(String) && value.length > 50
+          "#{value[0, 50]}...".inspect
+        elsif value.is_a?(Date) || value.is_a?(Time)
+          %("#{value.to_s(:db)}")
+        else
+          value.inspect
+        end
+      end
 
-    def pk_attribute?(name)
-      name == self.class.primary_key
-    end
+      def readonly_attribute?(name)
+        self.class.readonly_attributes.include?(name)
+      end
 
-    def typecasted_attribute_value(name)
-      _read_attribute(name)
-    end
+      def pk_attribute?(name)
+        name == self.class.primary_key
+      end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
index 56c1898551..5941f51a1a 100644
--- a/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
+++ b/activerecord/lib/active_record/attribute_methods/before_type_cast.rb
@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module AttributeMethods
     # = Active Record Attribute Methods Before Type Cast
     #
-    # <tt>ActiveRecord::AttributeMethods::BeforeTypeCast</tt> provides a way to
+    # ActiveRecord::AttributeMethods::BeforeTypeCast provides a way to
     # read the value of the attributes before typecasting and deserialization.
     #
     #   class Task < ActiveRecord::Base
@@ -63,14 +65,14 @@ module ActiveRecord
 
       private
 
-      # Handle *_before_type_cast for method_missing.
-      def attribute_before_type_cast(attribute_name)
-        read_attribute_before_type_cast(attribute_name)
-      end
+        # Handle *_before_type_cast for method_missing.
+        def attribute_before_type_cast(attribute_name)
+          read_attribute_before_type_cast(attribute_name)
+        end
 
-      def attribute_came_from_user?(attribute_name)
-        @attributes[attribute_name].came_from_user?
-      end
+        def attribute_came_from_user?(attribute_name)
+          @attributes[attribute_name].came_from_user?
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index 0171ef3bdf..ebc2252c50 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -1,8 +1,10 @@
-require 'active_support/core_ext/module/attribute_accessors'
+# frozen_string_literal: true
+
+require "active_support/core_ext/module/attribute_accessors"
 
 module ActiveRecord
   module AttributeMethods
-    module Dirty # :nodoc:
+    module Dirty
       extend ActiveSupport::Concern
 
       include ActiveModel::Dirty
@@ -12,177 +14,171 @@ module ActiveRecord
           raise "You cannot include Dirty after Timestamp"
         end
 
-        class_attribute :partial_writes, instance_writer: false
-        self.partial_writes = true
-      end
+        class_attribute :partial_writes, instance_writer: false, default: true
 
-      # Attempts to +save+ the record and clears changed attributes if successful.
-      def save(*)
-        if status = super
-          changes_applied
-        end
-        status
-      end
+        # Attribute methods for "changed in last call to save?"
+        attribute_method_affix(prefix: "saved_change_to_", suffix: "?")
+        attribute_method_prefix("saved_change_to_")
+        attribute_method_suffix("_before_last_save")
 
-      # Attempts to <tt>save!</tt> the record and clears changed attributes if successful.
-      def save!(*)
-        super.tap do
-          changes_applied
-        end
+        # Attribute methods for "will change if I call save?"
+        attribute_method_affix(prefix: "will_save_change_to_", suffix: "?")
+        attribute_method_suffix("_change_to_be_saved", "_in_database")
       end
 
       # <tt>reload</tt> the record and clears changed attributes.
       def reload(*)
         super.tap do
-          clear_changes_information
+          @previously_changed = ActiveSupport::HashWithIndifferentAccess.new
+          @mutations_before_last_save = nil
+          @attributes_changed_by_setter = ActiveSupport::HashWithIndifferentAccess.new
+          @mutations_from_database = nil
         end
       end
 
-      def initialize_dup(other) # :nodoc:
-        super
-        calculate_changes_from_defaults
-      end
-
-      def changes_applied
-        super
-        store_original_raw_attributes
-      end
-
-      def clear_changes_information
-        super
-        original_raw_attributes.clear
-      end
-
-      def changed_attributes
-        # This should only be set by methods which will call changed_attributes
-        # multiple times when it is known that the computed value cannot change.
-        if defined?(@cached_changed_attributes)
-          @cached_changed_attributes
-        else
-          super.reverse_merge(attributes_changed_in_place).freeze
-        end
-      end
-
-      def changes
-        cache_changed_attributes do
-          super
-        end
-      end
-
-      def attribute_changed_in_place?(attr_name)
-        old_value = original_raw_attribute(attr_name)
-        @attributes[attr_name].changed_in_place_from?(old_value)
+      # Did this attribute change when we last saved?
+      #
+      # This method is useful in after callbacks to determine if an attribute
+      # was changed during the save that triggered the callbacks to run. It can
+      # be invoked as +saved_change_to_name?+ instead of
+      # <tt>saved_change_to_attribute?("name")</tt>.
+      #
+      # ==== Options
+      #
+      # +from+ When passed, this method will return false unless the original
+      # value is equal to the given option
+      #
+      # +to+ When passed, this method will return false unless the value was
+      # changed to the given value
+      def saved_change_to_attribute?(attr_name, **options)
+        mutations_before_last_save.changed?(attr_name, **options)
+      end
+
+      # Returns the change to an attribute during the last save. If the
+      # attribute was changed, the result will be an array containing the
+      # original value and the saved value.
+      #
+      # This method is useful in after callbacks, to see the change in an
+      # attribute during the save that triggered the callbacks to run. It can be
+      # invoked as +saved_change_to_name+ instead of
+      # <tt>saved_change_to_attribute("name")</tt>.
+      def saved_change_to_attribute(attr_name)
+        mutations_before_last_save.change_to_attribute(attr_name)
+      end
+
+      # Returns the original value of an attribute before the last save.
+      #
+      # This method is useful in after callbacks to get the original value of an
+      # attribute before the save that triggered the callbacks to run. It can be
+      # invoked as +name_before_last_save+ instead of
+      # <tt>attribute_before_last_save("name")</tt>.
+      def attribute_before_last_save(attr_name)
+        mutations_before_last_save.original_value(attr_name)
+      end
+
+      # Did the last call to +save+ have any changes to change?
+      def saved_changes?
+        mutations_before_last_save.any_changes?
+      end
+
+      # Returns a hash containing all the changes that were just saved.
+      def saved_changes
+        mutations_before_last_save.changes
+      end
+
+      # Will this attribute change the next time we save?
+      #
+      # This method is useful in validations and before callbacks to determine
+      # if the next call to +save+ will change a particular attribute. It can be
+      # invoked as +will_save_change_to_name?+ instead of
+      # <tt>will_save_change_to_attribute("name")</tt>.
+      #
+      # ==== Options
+      #
+      # +from+ When passed, this method will return false unless the original
+      # value is equal to the given option
+      #
+      # +to+ When passed, this method will return false unless the value will be
+      # changed to the given value
+      def will_save_change_to_attribute?(attr_name, **options)
+        mutations_from_database.changed?(attr_name, **options)
+      end
+
+      # Returns the change to an attribute that will be persisted during the
+      # next save.
+      #
+      # This method is useful in validations and before callbacks, to see the
+      # change to an attribute that will occur when the record is saved. It can
+      # be invoked as +name_change_to_be_saved+ instead of
+      # <tt>attribute_change_to_be_saved("name")</tt>.
+      #
+      # If the attribute will change, the result will be an array containing the
+      # original value and the new value about to be saved.
+      def attribute_change_to_be_saved(attr_name)
+        mutations_from_database.change_to_attribute(attr_name)
+      end
+
+      # Returns the value of an attribute in the database, as opposed to the
+      # in-memory value that will be persisted the next time the record is
+      # saved.
+      #
+      # This method is useful in validations and before callbacks, to see the
+      # original value of an attribute prior to any changes about to be
+      # saved. It can be invoked as +name_in_database+ instead of
+      # <tt>attribute_in_database("name")</tt>.
+      def attribute_in_database(attr_name)
+        mutations_from_database.original_value(attr_name)
+      end
+
+      # Will the next call to +save+ have any changes to persist?
+      def has_changes_to_save?
+        mutations_from_database.any_changes?
+      end
+
+      # Returns a hash containing all the changes that will be persisted during
+      # the next save.
+      def changes_to_save
+        mutations_from_database.changes
+      end
+
+      # Returns an array of the names of any attributes that will change when
+      # the record is next saved.
+      def changed_attribute_names_to_save
+        mutations_from_database.changed_attribute_names
+      end
+
+      # Returns a hash of the attributes that will change when the record is
+      # next saved.
+      #
+      # The hash keys are the attribute names, and the hash values are the
+      # original attribute values in the database (as opposed to the in-memory
+      # values about to be saved).
+      def attributes_in_database
+        mutations_from_database.changed_values
       end
 
       private
-
-      def changes_include?(attr_name)
-        super || attribute_changed_in_place?(attr_name)
-      end
-
-      def calculate_changes_from_defaults
-        @changed_attributes = nil
-        self.class.column_defaults.each do |attr, orig_value|
-          set_attribute_was(attr, orig_value) if _field_changed?(attr, orig_value)
+        def write_attribute_without_type_cast(attr_name, _)
+          result = super
+          clear_attribute_change(attr_name)
+          result
         end
-      end
-
-      # Wrap write_attribute to remember original attribute value.
-      def write_attribute(attr, value)
-        attr = attr.to_s
-
-        old_value = old_attribute_value(attr)
-
-        result = super
-        store_original_raw_attribute(attr)
-        save_changed_attribute(attr, old_value)
-        result
-      end
-
-      def raw_write_attribute(attr, value)
-        attr = attr.to_s
-
-        result = super
-        original_raw_attributes[attr] = value
-        result
-      end
 
-      def save_changed_attribute(attr, old_value)
-        clear_changed_attributes_cache
-        if attribute_changed_by_setter?(attr)
-          clear_attribute_changes(attr) unless _field_changed?(attr, old_value)
-        else
-          set_attribute_was(attr, old_value) if _field_changed?(attr, old_value)
-        end
-      end
-
-      def old_attribute_value(attr)
-        if attribute_changed?(attr)
-          changed_attributes[attr]
-        else
-          clone_attribute_value(:_read_attribute, attr)
-        end
-      end
-
-      def _update_record(*)
-        partial_writes? ? super(keys_for_partial_write) : super
-      end
-
-      def _create_record(*)
-        partial_writes? ? super(keys_for_partial_write) : super
-      end
-
-      def keys_for_partial_write
-        changed & self.class.column_names
-      end
-
-      def _field_changed?(attr, old_value)
-        @attributes[attr].changed_from?(old_value)
-      end
-
-      def attributes_changed_in_place
-        changed_in_place.each_with_object({}) do |attr_name, h|
-          orig = @attributes[attr_name].original_value
-          h[attr_name] = orig
-        end
-      end
-
-      def changed_in_place
-        self.class.attribute_names.select do |attr_name|
-          attribute_changed_in_place?(attr_name)
+        def _update_record(attribute_names = attribute_names_for_partial_writes)
+          affected_rows = super
+          changes_applied
+          affected_rows
         end
-      end
 
-      def original_raw_attribute(attr_name)
-        original_raw_attributes.fetch(attr_name) do
-          read_attribute_before_type_cast(attr_name)
+        def _create_record(attribute_names = attribute_names_for_partial_writes)
+          id = super
+          changes_applied
+          id
         end
-      end
-
-      def original_raw_attributes
-        @original_raw_attributes ||= {}
-      end
 
-      def store_original_raw_attribute(attr_name)
-        original_raw_attributes[attr_name] = @attributes[attr_name].value_for_database rescue nil
-      end
-
-      def store_original_raw_attributes
-        attribute_names.each do |attr|
-          store_original_raw_attribute(attr)
+        def attribute_names_for_partial_writes
+          partial_writes? ? changed_attribute_names_to_save : attribute_names
         end
-      end
-
-      def cache_changed_attributes
-        @cached_changed_attributes = changed_attributes
-        yield
-      ensure
-        clear_changed_attributes_cache
-      end
-
-      def clear_changed_attributes_cache
-        remove_instance_variable(:@cached_changed_attributes) if defined?(@cached_changed_attributes)
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index c28374e4ab..9b267bb7c0 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -1,30 +1,31 @@
-require 'set'
+# frozen_string_literal: true
+
+require "set"
 
 module ActiveRecord
   module AttributeMethods
     module PrimaryKey
       extend ActiveSupport::Concern
 
-      # Returns this record's primary key value wrapped in an Array if one is
+      # Returns this record's primary key value wrapped in an array if one is
       # available.
       def to_key
-        sync_with_transaction_state
-        key = self.id
+        key = id
         [key] if key
       end
 
       # Returns the primary key value.
       def id
-        if pk = self.class.primary_key
-          sync_with_transaction_state
-          _read_attribute(pk)
-        end
+        sync_with_transaction_state
+        primary_key = self.class.primary_key
+        _read_attribute(primary_key) if primary_key
       end
 
       # Sets the primary key value.
       def id=(value)
         sync_with_transaction_state
-        write_attribute(self.class.primary_key, value) if self.class.primary_key
+        primary_key = self.class.primary_key
+        _write_attribute(primary_key, value) if primary_key
       end
 
       # Queries the primary key value.
@@ -45,84 +46,98 @@ module ActiveRecord
         attribute_was(self.class.primary_key)
       end
 
-      protected
-
-      def attribute_method?(attr_name)
-        attr_name == 'id' || super
+      def id_in_database
+        sync_with_transaction_state
+        attribute_in_database(self.class.primary_key)
       end
 
-      module ClassMethods
-        def define_method_attribute(attr_name)
-          super
+      private
 
-          if attr_name == primary_key && attr_name != 'id'
-            generated_attribute_methods.send(:alias_method, :id, primary_key)
-          end
+        def attribute_method?(attr_name)
+          attr_name == "id" || super
         end
 
-        ID_ATTRIBUTE_METHODS = %w(id id= id? id_before_type_cast id_was).to_set
+        module ClassMethods
+          ID_ATTRIBUTE_METHODS = %w(id id= id? id_before_type_cast id_was id_in_database).to_set
 
-        def dangerous_attribute_method?(method_name)
-          super && !ID_ATTRIBUTE_METHODS.include?(method_name)
-        end
+          def instance_method_already_implemented?(method_name)
+            super || primary_key && ID_ATTRIBUTE_METHODS.include?(method_name)
+          end
 
-        # Defines the primary key field -- can be overridden in subclasses.
-        # Overwriting will negate any effect of the +primary_key_prefix_type+
-        # setting, though.
-        def primary_key
-          @primary_key = reset_primary_key unless defined? @primary_key
-          @primary_key
-        end
+          def dangerous_attribute_method?(method_name)
+            super && !ID_ATTRIBUTE_METHODS.include?(method_name)
+          end
 
-        # Returns a quoted version of the primary key name, used to construct
-        # SQL statements.
-        def quoted_primary_key
-          @quoted_primary_key ||= connection.quote_column_name(primary_key)
-        end
+          # Defines the primary key field -- can be overridden in subclasses.
+          # Overwriting will negate any effect of the +primary_key_prefix_type+
+          # setting, though.
+          def primary_key
+            @primary_key = reset_primary_key unless defined? @primary_key
+            @primary_key
+          end
 
-        def reset_primary_key #:nodoc:
-          if self == base_class
-            self.primary_key = get_primary_key(base_class.name)
-          else
-            self.primary_key = base_class.primary_key
+          # Returns a quoted version of the primary key name, used to construct
+          # SQL statements.
+          def quoted_primary_key
+            @quoted_primary_key ||= connection.quote_column_name(primary_key)
           end
-        end
 
-        def get_primary_key(base_name) #:nodoc:
-          if base_name && primary_key_prefix_type == :table_name
-            base_name.foreign_key(false)
-          elsif base_name && primary_key_prefix_type == :table_name_with_underscore
-            base_name.foreign_key
-          else
-            if ActiveRecord::Base != self && table_exists?
-              connection.schema_cache.primary_keys(table_name)
+          def reset_primary_key #:nodoc:
+            if base_class?
+              self.primary_key = get_primary_key(base_class.name)
             else
-              'id'
+              self.primary_key = base_class.primary_key
             end
           end
-        end
 
-        # Sets the name of the primary key column.
-        #
-        #   class Project < ActiveRecord::Base
-        #     self.primary_key = 'sysid'
-        #   end
-        #
-        # You can also define the +primary_key+ method yourself:
-        #
-        #   class Project < ActiveRecord::Base
-        #     def self.primary_key
-        #       'foo_' + super
-        #     end
-        #   end
-        #
-        #   Project.primary_key # => "foo_id"
-        def primary_key=(value)
-          @primary_key        = value && value.to_s
-          @quoted_primary_key = nil
-          @attributes_builder = nil
+          def get_primary_key(base_name) #:nodoc:
+            if base_name && primary_key_prefix_type == :table_name
+              base_name.foreign_key(false)
+            elsif base_name && primary_key_prefix_type == :table_name_with_underscore
+              base_name.foreign_key
+            else
+              if ActiveRecord::Base != self && table_exists?
+                pk = connection.schema_cache.primary_keys(table_name)
+                suppress_composite_primary_key(pk)
+              else
+                "id"
+              end
+            end
+          end
+
+          # Sets the name of the primary key column.
+          #
+          #   class Project < ActiveRecord::Base
+          #     self.primary_key = 'sysid'
+          #   end
+          #
+          # You can also define the #primary_key method yourself:
+          #
+          #   class Project < ActiveRecord::Base
+          #     def self.primary_key
+          #       'foo_' + super
+          #     end
+          #   end
+          #
+          #   Project.primary_key # => "foo_id"
+          def primary_key=(value)
+            @primary_key        = value && value.to_s
+            @quoted_primary_key = nil
+            @attributes_builder = nil
+          end
+
+          private
+
+            def suppress_composite_primary_key(pk)
+              return pk unless pk.is_a?(Array)
+
+              warn <<~WARNING
+                WARNING: Active Record does not support composite primary key.
+
+                #{table_name} has composite primary key. Composite primary key is ignored.
+              WARNING
+            end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/query.rb b/activerecord/lib/active_record/attribute_methods/query.rb
index 553122a5fc..6757e9b66a 100644
--- a/activerecord/lib/active_record/attribute_methods/query.rb
+++ b/activerecord/lib/active_record/attribute_methods/query.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module AttributeMethods
     module Query
@@ -19,7 +21,7 @@ module ActiveRecord
             if Numeric === value || value !~ /[^0-9]/
               !value.to_i.zero?
             else
-              return false if ActiveRecord::ConnectionAdapters::Column::FALSE_VALUES.include?(value)
+              return false if ActiveModel::Type::Boolean::FALSE_VALUES.include?(value)
               !value.blank?
             end
           elsif value.respond_to?(:zero?)
diff --git a/activerecord/lib/active_record/attribute_methods/read.rb b/activerecord/lib/active_record/attribute_methods/read.rb
index 0d989c2eca..6e1275e990 100644
--- a/activerecord/lib/active_record/attribute_methods/read.rb
+++ b/activerecord/lib/active_record/attribute_methods/read.rb
@@ -1,69 +1,42 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module AttributeMethods
     module Read
-      ReaderMethodCache = Class.new(AttributeMethodCache) {
-        private
-        # We want to generate the methods via module_eval rather than
-        # define_method, because define_method is slower on dispatch.
-        # Evaluating many similar methods may use more memory as the instruction
-        # sequences are duplicated and cached (in MRI).  define_method may
-        # be slower on dispatch, but if you're careful about the closure
-        # created, then define_method will consume much less memory.
-        #
-        # But sometimes the database might return columns with
-        # characters that are not allowed in normal method names (like
-        # 'my_column(omg)'. So to work around this we first define with
-        # the __temp__ identifier, and then use alias method to rename
-        # it to what we want.
-        #
-        # We are also defining a constant to hold the frozen string of
-        # the attribute name. Using a constant means that we do not have
-        # to allocate an object on each call to the attribute method.
-        # Making it frozen means that it doesn't get duped when used to
-        # key the @attributes in read_attribute.
-        def method_body(method_name, const_name)
-          <<-EOMETHOD
-          def #{method_name}
-            name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{const_name}
-            _read_attribute(name) { |n| missing_attribute(n, caller) }
-          end
-          EOMETHOD
-        end
-      }.new
-
       extend ActiveSupport::Concern
 
-      module ClassMethods
-        protected
-
-        def define_method_attribute(name)
-          safe_name = name.unpack('h*').first
-          temp_method = "__temp__#{safe_name}"
-
-          ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
+      module ClassMethods # :nodoc:
+        private
 
-          generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
-            def #{temp_method}
-              name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
-              _read_attribute(name) { |n| missing_attribute(n, caller) }
+          def define_method_attribute(name)
+            sync_with_transaction_state = "sync_with_transaction_state" if name == primary_key
+
+            ActiveModel::AttributeMethods::AttrNames.define_attribute_accessor_method(
+              generated_attribute_methods, name
+            ) do |temp_method_name, attr_name_expr|
+              generated_attribute_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
+                def #{temp_method_name}
+                  #{sync_with_transaction_state}
+                  name = #{attr_name_expr}
+                  _read_attribute(name) { |n| missing_attribute(n, caller) }
+                end
+              RUBY
             end
-          STR
-
-          generated_attribute_methods.module_eval do
-            alias_method name, temp_method
-            undef_method temp_method
           end
-        end
       end
 
-      ID = 'id'.freeze
-
       # Returns the value of the attribute identified by <tt>attr_name</tt> after
       # it has been typecast (for example, "2004-12-12" in a date column is cast
       # to a date object, like Date.new(2004, 12, 12)).
       def read_attribute(attr_name, &block)
         name = attr_name.to_s
-        name = self.class.primary_key if name == ID
+        if self.class.attribute_alias?(name)
+          name = self.class.attribute_alias(name)
+        end
+
+        primary_key = self.class.primary_key
+        name = primary_key if name == "id" && primary_key
+        sync_with_transaction_state if name == primary_key
         _read_attribute(name, &block)
       end
 
@@ -72,7 +45,7 @@ module ActiveRecord
       if defined?(JRUBY_VERSION)
         # This form is significantly faster on JRuby, and this is one of our biggest hotspots.
         # https://github.com/jruby/jruby/pull/2562
-        def _read_attribute(attr_name, &block) # :nodoc
+        def _read_attribute(attr_name, &block) # :nodoc:
           @attributes.fetch_value(attr_name.to_s, &block)
         end
       else
@@ -83,7 +56,6 @@ module ActiveRecord
 
       alias :attribute :_read_attribute
       private :attribute
-
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_methods/serialization.rb b/activerecord/lib/active_record/attribute_methods/serialization.rb
index e03bf5945d..6e0e90f39c 100644
--- a/activerecord/lib/active_record/attribute_methods/serialization.rb
+++ b/activerecord/lib/active_record/attribute_methods/serialization.rb
@@ -1,23 +1,35 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module AttributeMethods
     module Serialization
       extend ActiveSupport::Concern
 
+      class ColumnNotSerializableError < StandardError
+        def initialize(name, type)
+          super <<~EOS
+            Column `#{name}` of type #{type.class} does not support `serialize` feature.
+            Usually it means that you are trying to use `serialize`
+            on a column that already implements serialization natively.
+          EOS
+        end
+      end
+
       module ClassMethods
         # If you have an attribute that needs to be saved to the database as an
         # object, and retrieved as the same object, then specify the name of that
         # attribute using this method and it will be handled automatically. The
         # serialization is done through YAML. If +class_name+ is specified, the
         # serialized object must be of that class on assignment and retrieval.
-        # Otherwise <tt>SerializationTypeMismatch</tt> will be raised.
+        # Otherwise SerializationTypeMismatch will be raised.
         #
-        # Empty objects as +{}+, in the case of +Hash+, or +[]+, in the case of
+        # Empty objects as <tt>{}</tt>, in the case of +Hash+, or <tt>[]</tt>, in the case of
         # +Array+, will always be persisted as null.
         #
         # Keep in mind that database adapters handle certain serialization tasks
         # for you. For instance: +json+ and +jsonb+ types in PostgreSQL will be
         # converted between JSON object/array syntax and Ruby +Hash+ or +Array+
-        # objects transparently. There is no need to use +serialize+ in this
+        # objects transparently. There is no need to use #serialize in this
         # case.
         #
         # For more complex cases, such as conversion to or from your application
@@ -26,7 +38,7 @@ module ActiveRecord
         # ==== Parameters
         #
         # * +attr_name+ - The field name that should be serialized.
-        # * +class_name_or_coder+ - Optional, a coder object, which responds to `.load` / `.dump`
+        # * +class_name_or_coder+ - Optional, a coder object, which responds to +.load+ and +.dump+
         #   or a class name that the object type should be equal to.
         #
         # ==== Example
@@ -50,17 +62,28 @@ module ActiveRecord
           # to ensure special objects (e.g. Active Record models) are dumped correctly
           # using the #as_json hook.
           coder = if class_name_or_coder == ::JSON
-                    Coders::JSON
-                  elsif [:load, :dump].all? { |x| class_name_or_coder.respond_to?(x) }
-                    class_name_or_coder
-                  else
-                    Coders::YAMLColumn.new(class_name_or_coder)
-                  end
+            Coders::JSON
+          elsif [:load, :dump].all? { |x| class_name_or_coder.respond_to?(x) }
+            class_name_or_coder
+          else
+            Coders::YAMLColumn.new(attr_name, class_name_or_coder)
+          end
 
           decorate_attribute_type(attr_name, :serialize) do |type|
+            if type_incompatible_with_serialize?(type, class_name_or_coder)
+              raise ColumnNotSerializableError.new(attr_name, type)
+            end
+
             Type::Serialized.new(type, coder)
           end
         end
+
+        private
+
+          def type_incompatible_with_serialize?(type, class_name)
+            type.is_a?(ActiveRecord::Type::Json) && class_name == ::JSON ||
+              type.respond_to?(:type_cast_array, true) && class_name == ::Array
+          end
       end
     end
   end
diff --git a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
index f9beb43e4b..294a3dc32c 100644
--- a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module AttributeMethods
     module TimeZoneConversion
@@ -7,93 +9,82 @@ module ActiveRecord
         end
 
         def cast(value)
-          if value.is_a?(Array)
-            value.map { |v| cast(v) }
-          elsif value.is_a?(Hash)
+          return if value.nil?
+
+          if value.is_a?(Hash)
             set_time_zone_without_conversion(super)
           elsif value.respond_to?(:in_time_zone)
             begin
-              user_input_in_time_zone(value) || super
+              super(user_input_in_time_zone(value)) || super
             rescue ArgumentError
               nil
             end
+          else
+            map_avoiding_infinite_recursion(super) { |v| cast(v) }
           end
         end
 
         private
 
-        def convert_time_to_time_zone(value)
-          if value.is_a?(Array)
-            value.map { |v| convert_time_to_time_zone(v) }
-          elsif value.acts_like?(:time)
-            value.in_time_zone
-          else
-            value
+          def convert_time_to_time_zone(value)
+            return if value.nil?
+
+            if value.acts_like?(:time)
+              value.in_time_zone
+            elsif value.is_a?(::Float)
+              value
+            else
+              map_avoiding_infinite_recursion(value) { |v| convert_time_to_time_zone(v) }
+            end
           end
-        end
 
-        def set_time_zone_without_conversion(value)
-          ::Time.zone.local_to_utc(value).in_time_zone
-        end
+          def set_time_zone_without_conversion(value)
+            ::Time.zone.local_to_utc(value).try(:in_time_zone) if value
+          end
+
+          def map_avoiding_infinite_recursion(value)
+            map(value) do |v|
+              if value.equal?(v)
+                nil
+              else
+                yield(v)
+              end
+            end
+          end
       end
 
       extend ActiveSupport::Concern
 
       included do
-        mattr_accessor :time_zone_aware_attributes, instance_writer: false
-        self.time_zone_aware_attributes = false
-
-        class_attribute :skip_time_zone_conversion_for_attributes, instance_writer: false
-        self.skip_time_zone_conversion_for_attributes = []
+        mattr_accessor :time_zone_aware_attributes, instance_writer: false, default: false
 
-        class_attribute :time_zone_aware_types, instance_writer: false
-        self.time_zone_aware_types = [:datetime, :not_explicitly_configured]
+        class_attribute :skip_time_zone_conversion_for_attributes, instance_writer: false, default: []
+        class_attribute :time_zone_aware_types, instance_writer: false, default: [ :datetime, :time ]
       end
 
-      module ClassMethods
+      module ClassMethods # :nodoc:
         private
 
-        def inherited(subclass)
-          # We need to apply this decorator here, rather than on module inclusion. The closure
-          # created by the matcher would otherwise evaluate for `ActiveRecord::Base`, not the
-          # sub class being decorated. As such, changes to `time_zone_aware_attributes`, or
-          # `skip_time_zone_conversion_for_attributes` would not be picked up.
-          subclass.class_eval do
-            matcher = ->(name, type) { create_time_zone_conversion_attribute?(name, type) }
-            decorate_matching_attribute_types(matcher, :_time_zone_conversion) do |type|
-              TimeZoneConverter.new(type)
+          def inherited(subclass)
+            super
+            # We need to apply this decorator here, rather than on module inclusion. The closure
+            # created by the matcher would otherwise evaluate for `ActiveRecord::Base`, not the
+            # sub class being decorated. As such, changes to `time_zone_aware_attributes`, or
+            # `skip_time_zone_conversion_for_attributes` would not be picked up.
+            subclass.class_eval do
+              matcher = ->(name, type) { create_time_zone_conversion_attribute?(name, type) }
+              decorate_matching_attribute_types(matcher, "_time_zone_conversion") do |type|
+                TimeZoneConverter.new(type)
+              end
             end
           end
-          super
-        end
-
-        def create_time_zone_conversion_attribute?(name, cast_type)
-          enabled_for_column = time_zone_aware_attributes &&
-            !self.skip_time_zone_conversion_for_attributes.include?(name.to_sym)
-          result = enabled_for_column &&
-            time_zone_aware_types.include?(cast_type.type)
 
-          if enabled_for_column &&
-            !result &&
-            cast_type.type == :time &&
-            time_zone_aware_types.include?(:not_explicitly_configured)
-            ActiveSupport::Deprecation.warn(<<-MESSAGE)
-              Time columns will become time zone aware in Rails 5.1. This
-              still causes `String`s to be parsed as if they were in `Time.zone`,
-              and `Time`s to be converted to `Time.zone`.
+          def create_time_zone_conversion_attribute?(name, cast_type)
+            enabled_for_column = time_zone_aware_attributes &&
+              !skip_time_zone_conversion_for_attributes.include?(name.to_sym)
 
-              To keep the old behavior, you must add the following to your initializer:
-
-                  config.active_record.time_zone_aware_types = [:datetime]
-
-              To silence this deprecation warning, add the following:
-
-                  config.active_record.time_zone_aware_types << :time
-            MESSAGE
+            enabled_for_column && time_zone_aware_types.include?(cast_type.type)
           end
-
-          result
-        end
       end
     end
   end
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index ab017c7b54..455e67e19b 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -1,72 +1,67 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module AttributeMethods
     module Write
-      WriterMethodCache = Class.new(AttributeMethodCache) {
-        private
-
-        def method_body(method_name, const_name)
-          <<-EOMETHOD
-          def #{method_name}(value)
-            name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{const_name}
-            write_attribute(name, value)
-          end
-          EOMETHOD
-        end
-      }.new
-
       extend ActiveSupport::Concern
 
       included do
         attribute_method_suffix "="
       end
 
-      module ClassMethods
-        protected
+      module ClassMethods # :nodoc:
+        private
 
-        def define_method_attribute=(name)
-          safe_name = name.unpack('h*').first
-          ActiveRecord::AttributeMethods::AttrNames.set_name_cache safe_name, name
+          def define_method_attribute=(name)
+            sync_with_transaction_state = "sync_with_transaction_state" if name == primary_key
 
-          generated_attribute_methods.module_eval <<-STR, __FILE__, __LINE__ + 1
-            def __temp__#{safe_name}=(value)
-              name = ::ActiveRecord::AttributeMethods::AttrNames::ATTR_#{safe_name}
-              write_attribute(name, value)
+            ActiveModel::AttributeMethods::AttrNames.define_attribute_accessor_method(
+              generated_attribute_methods, name, writer: true,
+            ) do |temp_method_name, attr_name_expr|
+              generated_attribute_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
+                def #{temp_method_name}(value)
+                  name = #{attr_name_expr}
+                  #{sync_with_transaction_state}
+                  _write_attribute(name, value)
+                end
+              RUBY
             end
-            alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
-            undef_method :__temp__#{safe_name}=
-          STR
-        end
+          end
       end
 
       # Updates the attribute identified by <tt>attr_name</tt> with the
-      # specified +value+. Empty strings for fixnum and float columns are
+      # specified +value+. Empty strings for Integer and Float columns are
       # turned into +nil+.
       def write_attribute(attr_name, value)
-        write_attribute_with_type_cast(attr_name, value, true)
-      end
+        name = attr_name.to_s
+        if self.class.attribute_alias?(name)
+          name = self.class.attribute_alias(name)
+        end
 
-      def raw_write_attribute(attr_name, value)
-        write_attribute_with_type_cast(attr_name, value, false)
+        primary_key = self.class.primary_key
+        name = primary_key if name == "id" && primary_key
+        sync_with_transaction_state if name == primary_key
+        _write_attribute(name, value)
       end
 
-      private
-      # Handle *= for method_missing.
-      def attribute=(attribute_name, value)
-        write_attribute(attribute_name, value)
+      # This method exists to avoid the expensive primary_key check internally, without
+      # breaking compatibility with the write_attribute API
+      def _write_attribute(attr_name, value) # :nodoc:
+        @attributes.write_from_user(attr_name.to_s, value)
+        value
       end
 
-      def write_attribute_with_type_cast(attr_name, value, should_type_cast)
-        attr_name = attr_name.to_s
-        attr_name = self.class.primary_key if attr_name == 'id' && self.class.primary_key
-
-        if should_type_cast
-          @attributes.write_from_user(attr_name, value)
-        else
-          @attributes.write_cast_value(attr_name, value)
+      private
+        def write_attribute_without_type_cast(attr_name, value)
+          name = attr_name.to_s
+          @attributes.write_cast_value(name, value)
+          value
         end
 
-        value
-      end
+        # Handle *= for method_missing.
+        def attribute=(attribute_name, value)
+          _write_attribute(attribute_name, value)
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/attribute_set.rb b/activerecord/lib/active_record/attribute_set.rb
deleted file mode 100644
index 013a7d0e01..0000000000
--- a/activerecord/lib/active_record/attribute_set.rb
+++ /dev/null
@@ -1,93 +0,0 @@
-require 'active_record/attribute_set/builder'
-
-module ActiveRecord
-  class AttributeSet # :nodoc:
-    def initialize(attributes)
-      @attributes = attributes
-    end
-
-    def [](name)
-      attributes[name] || Attribute.null(name)
-    end
-
-    def []=(name, value)
-      attributes[name] = value
-    end
-
-    def values_before_type_cast
-      attributes.transform_values(&:value_before_type_cast)
-    end
-
-    def to_hash
-      initialized_attributes.transform_values(&:value)
-    end
-    alias_method :to_h, :to_hash
-
-    def key?(name)
-      attributes.key?(name) && self[name].initialized?
-    end
-
-    def keys
-      attributes.each_key.select { |name| self[name].initialized? }
-    end
-
-    if defined?(JRUBY_VERSION)
-      # This form is significantly faster on JRuby, and this is one of our biggest hotspots.
-      # https://github.com/jruby/jruby/pull/2562
-      def fetch_value(name, &block)
-        self[name].value(&block)
-      end
-    else
-      def fetch_value(name)
-        self[name].value { |n| yield n if block_given? }
-      end
-    end
-
-    def write_from_database(name, value)
-      attributes[name] = self[name].with_value_from_database(value)
-    end
-
-    def write_from_user(name, value)
-      attributes[name] = self[name].with_value_from_user(value)
-    end
-
-    def write_cast_value(name, value)
-      attributes[name] = self[name].with_cast_value(value)
-    end
-
-    def freeze
-      @attributes.freeze
-      super
-    end
-
-    def initialize_dup(_)
-      @attributes = attributes.deep_dup
-      super
-    end
-
-    def initialize_clone(_)
-      @attributes = attributes.clone
-      super
-    end
-
-    def reset(key)
-      if key?(key)
-        write_from_database(key, nil)
-      end
-    end
-
-    def accessed
-      attributes.select { |_, attr| attr.has_been_read? }.keys
-    end
-
-    protected
-
-    attr_reader :attributes
-
-    private
-
-    def initialized_attributes
-      attributes.select { |_, attr| attr.initialized? }
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/attribute_set/builder.rb b/activerecord/lib/active_record/attribute_set/builder.rb
deleted file mode 100644
index e85777c335..0000000000
--- a/activerecord/lib/active_record/attribute_set/builder.rb
+++ /dev/null
@@ -1,92 +0,0 @@
-module ActiveRecord
-  class AttributeSet # :nodoc:
-    class Builder # :nodoc:
-      attr_reader :types, :always_initialized
-
-      def initialize(types, always_initialized = nil)
-        @types = types
-        @always_initialized = always_initialized
-      end
-
-      def build_from_database(values = {}, additional_types = {})
-        if always_initialized && !values.key?(always_initialized)
-          values[always_initialized] = nil
-        end
-
-        attributes = LazyAttributeHash.new(types, values, additional_types)
-        AttributeSet.new(attributes)
-      end
-    end
-  end
-
-  class LazyAttributeHash # :nodoc:
-    delegate :transform_values, :each_key, to: :materialize
-
-    def initialize(types, values, additional_types)
-      @types = types
-      @values = values
-      @additional_types = additional_types
-      @materialized = false
-      @delegate_hash = {}
-    end
-
-    def key?(key)
-      delegate_hash.key?(key) || values.key?(key) || types.key?(key)
-    end
-
-    def [](key)
-      delegate_hash[key] || assign_default_value(key)
-    end
-
-    def []=(key, value)
-      if frozen?
-        raise RuntimeError, "Can't modify frozen hash"
-      end
-      delegate_hash[key] = value
-    end
-
-    def initialize_dup(_)
-      @delegate_hash = delegate_hash.transform_values(&:dup)
-      super
-    end
-
-    def select
-      keys = types.keys | values.keys | delegate_hash.keys
-      keys.each_with_object({}) do |key, hash|
-        attribute = self[key]
-        if yield(key, attribute)
-          hash[key] = attribute
-        end
-      end
-    end
-
-    protected
-
-    attr_reader :types, :values, :additional_types, :delegate_hash
-
-    private
-
-    def assign_default_value(name)
-      type = additional_types.fetch(name, types[name])
-      value_present = true
-      value = values.fetch(name) { value_present = false }
-
-      if value_present
-        delegate_hash[name] = Attribute.from_database(name, value, type)
-      elsif types.key?(name)
-        delegate_hash[name] = Attribute.uninitialized(name, type)
-      end
-    end
-
-    def materialize
-      unless @materialized
-        values.each_key { |key| self[key] }
-        types.each_key { |key| self[key] }
-        unless frozen?
-          @materialized = true
-        end
-      end
-      delegate_hash
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/attributes.rb b/activerecord/lib/active_record/attributes.rb
index 8b2c4c7170..35150889d9 100644
--- a/activerecord/lib/active_record/attributes.rb
+++ b/activerecord/lib/active_record/attributes.rb
@@ -1,16 +1,14 @@
-require 'active_record/attribute/user_provided_default'
+# frozen_string_literal: true
+
+require "active_model/attribute/user_provided_default"
 
 module ActiveRecord
   # See ActiveRecord::Attributes::ClassMethods for documentation
   module Attributes
     extend ActiveSupport::Concern
 
-    # :nodoc:
-    Type = ActiveRecord::Type
-
     included do
-      class_attribute :attributes_to_define_after_schema_loads, instance_accessor: false # :internal:
-      self.attributes_to_define_after_schema_loads = {}
+      class_attribute :attributes_to_define_after_schema_loads, instance_accessor: false, default: {} # :internal:
     end
 
     module ClassMethods
@@ -18,7 +16,7 @@ module ActiveRecord
       # type of existing attributes if needed. This allows control over how
       # values are converted to and from SQL when assigned to a model. It also
       # changes the behavior of values passed to
-      # ActiveRecord::QueryMethods#where. This will let you use
+      # {ActiveRecord::Base.where}[rdoc-ref:QueryMethods#where]. This will let you use
       # your domain objects across much of Active Record, without having to
       # rely on implementation details or monkey patching.
       #
@@ -37,10 +35,10 @@ module ActiveRecord
       # is not passed, the previous default value (if any) will be used.
       # Otherwise, the default will be +nil+.
       #
-      # +array+ (PG only) specifies that the type should be an array (see the
+      # +array+ (PostgreSQL only) specifies that the type should be an array (see the
       # examples below).
       #
-      # +range+ (PG only) specifies that the type should be a range (see the
+      # +range+ (PostgreSQL only) specifies that the type should be a range (see the
       # examples below).
       #
       # ==== Examples
@@ -59,7 +57,7 @@ module ActiveRecord
       #   store_listing = StoreListing.new(price_in_cents: '10.1')
       #
       #   # before
-      #   store_listing.price_in_cents # => BigDecimal.new(10.1)
+      #   store_listing.price_in_cents # => BigDecimal(10.1)
       #
       #   class StoreListing < ActiveRecord::Base
       #     attribute :price_in_cents, :integer
@@ -70,12 +68,14 @@ module ActiveRecord
       #
       # A default can also be provided.
       #
+      #   # db/schema.rb
       #   create_table :store_listings, force: true do |t|
       #     t.string :my_string, default: "original default"
       #   end
       #
       #   StoreListing.new.my_string # => "original default"
       #
+      #   # app/models/store_listing.rb
       #   class StoreListing < ActiveRecord::Base
       #     attribute :my_string, :string, default: "new default"
       #   end
@@ -90,8 +90,9 @@ module ActiveRecord
       #   sleep 1
       #   Product.new.my_default_proc # => 2015-05-30 11:04:49 -0600
       #
-      # Attributes do not need to be backed by a database column.
+      # \Attributes do not need to be backed by a database column.
       #
+      #   # app/models/my_model.rb
       #   class MyModel < ActiveRecord::Base
       #     attribute :my_string, :string
       #     attribute :my_int_array, :integer, array: true
@@ -116,13 +117,13 @@ module ActiveRecord
       # Users may also define their own custom types, as long as they respond
       # to the methods defined on the value type. The method +deserialize+ or
       # +cast+ will be called on your type object, with raw input from the
-      # database or from your controllers. See ActiveRecord::Type::Value for the
+      # database or from your controllers. See ActiveModel::Type::Value for the
       # expected API. It is recommended that your type objects inherit from an
       # existing type, or from ActiveRecord::Type::Value
       #
       #   class MoneyType < ActiveRecord::Type::Integer
       #     def cast(value)
-      #       if value.include?('$')
+      #       if !value.kind_of?(Numeric) && value.include?('$')
       #         price_in_dollars = value.gsub(/\$/, '').to_f
       #         super(price_in_dollars * 100)
       #       else
@@ -134,7 +135,7 @@ module ActiveRecord
       #   # config/initializers/types.rb
       #   ActiveRecord::Type.register(:money, MoneyType)
       #
-      #   # /app/models/store_listing.rb
+      #   # app/models/store_listing.rb
       #   class StoreListing < ActiveRecord::Base
       #     attribute :price_in_cents, :money
       #   end
@@ -143,13 +144,13 @@ module ActiveRecord
       #   store_listing.price_in_cents # => 1000
       #
       # For more details on creating custom types, see the documentation for
-      # ActiveRecord::Type::Value. For more details on registering your types
+      # ActiveModel::Type::Value. For more details on registering your types
       # to be referenced by a symbol, see ActiveRecord::Type.register. You can
       # also pass a type object directly, in place of a symbol.
       #
-      # ==== Querying
+      # ==== \Querying
       #
-      # When ActiveRecord::QueryMethods#where is called, it will
+      # When {ActiveRecord::Base.where}[rdoc-ref:QueryMethods#where] is called, it will
       # use the type defined by the model class to convert the value to SQL,
       # calling +serialize+ on your type object. For example:
       #
@@ -157,7 +158,7 @@ module ActiveRecord
       #   end
       #
       #   class MoneyType < Type::Value
-      #     def initialize(currency_converter)
+      #     def initialize(currency_converter:)
       #       @currency_converter = currency_converter
       #     end
       #
@@ -170,11 +171,13 @@ module ActiveRecord
       #     end
       #   end
       #
+      #   # config/initializers/types.rb
       #   ActiveRecord::Type.register(:money, MoneyType)
       #
+      #   # app/models/product.rb
       #   class Product < ActiveRecord::Base
       #     currency_converter = ConversionRatesFromTheInternet.new
-      #     attribute :price_in_bitcoins, :money, currency_converter
+      #     attribute :price_in_bitcoins, :money, currency_converter: currency_converter
       #   end
       #
       #   Product.where(price_in_bitcoins: Money.new(5, "USD"))
@@ -188,8 +191,8 @@ module ActiveRecord
       # The type of an attribute is given the opportunity to change how dirty
       # tracking is performed. The methods +changed?+ and +changed_in_place?+
       # will be called from ActiveModel::Dirty. See the documentation for those
-      # methods in ActiveRecord::Type::Value for more details.
-      def attribute(name, cast_type, **options)
+      # methods in ActiveModel::Type::Value for more details.
+      def attribute(name, cast_type = Type::Value.new, **options)
         name = name.to_s
         reload_schema_from_cache
 
@@ -240,24 +243,24 @@ module ActiveRecord
 
       private
 
-      NO_DEFAULT_PROVIDED = Object.new # :nodoc:
-      private_constant :NO_DEFAULT_PROVIDED
+        NO_DEFAULT_PROVIDED = Object.new # :nodoc:
+        private_constant :NO_DEFAULT_PROVIDED
 
-      def define_default_attribute(name, value, type, from_user:)
-        if value == NO_DEFAULT_PROVIDED
-          default_attribute = _default_attributes[name].with_type(type)
-        elsif from_user
-          default_attribute = Attribute::UserProvidedDefault.new(
-            name,
-            value,
-            type,
-            _default_attributes[name],
-          )
-        else
-          default_attribute = Attribute.from_database(name, value, type)
+        def define_default_attribute(name, value, type, from_user:)
+          if value == NO_DEFAULT_PROVIDED
+            default_attribute = _default_attributes[name].with_type(type)
+          elsif from_user
+            default_attribute = ActiveModel::Attribute::UserProvidedDefault.new(
+              name,
+              value,
+              type,
+              _default_attributes.fetch(name.to_s) { nil },
+            )
+          else
+            default_attribute = ActiveModel::Attribute.from_database(name, value, type)
+          end
+          _default_attributes[name] = default_attribute
         end
-        _default_attributes[name] = default_attribute
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/autosave_association.rb b/activerecord/lib/active_record/autosave_association.rb
index 0792d19c3e..d77d76cb1e 100644
--- a/activerecord/lib/active_record/autosave_association.rb
+++ b/activerecord/lib/active_record/autosave_association.rb
@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # = Active Record Autosave Association
   #
-  # +AutosaveAssociation+ is a module that takes care of automatically saving
+  # AutosaveAssociation is a module that takes care of automatically saving
   # associated records when their parent is saved. In addition to saving, it
   # also destroys any associated records that were marked for destruction.
-  # (See +mark_for_destruction+ and <tt>marked_for_destruction?</tt>).
+  # (See #mark_for_destruction and #marked_for_destruction?).
   #
   # Saving of the parent, its associations, and the destruction of marked
   # associations, all happen inside a transaction. This should never leave the
@@ -22,7 +24,7 @@ module ActiveRecord
   #
   # == Validation
   #
-  # Children records are validated unless <tt>:validate</tt> is +false+.
+  # Child records are validated unless <tt>:validate</tt> is +false+.
   #
   # == Callbacks
   #
@@ -125,7 +127,6 @@ module ActiveRecord
   # Now it _is_ removed from the database:
   #
   #   Comment.find_by(id: id).nil? # => true
-
   module AutosaveAssociation
     extend ActiveSupport::Concern
 
@@ -141,22 +142,23 @@ module ActiveRecord
 
     included do
       Associations::Builder::Association.extensions << AssociationBuilderExtension
+      mattr_accessor :index_nested_attribute_errors, instance_writer: false, default: false
     end
 
-    module ClassMethods
+    module ClassMethods # :nodoc:
       private
 
         def define_non_cyclic_method(name, &block)
-          return if method_defined?(name)
+          return if instance_methods(false).include?(name)
           define_method(name) do |*args|
             result = true; @_already_called ||= {}
             # Loop prevention for validation of associations
             unless @_already_called[name]
               begin
-                @_already_called[name]=true
+                @_already_called[name] = true
                 result = instance_eval(&block)
               ensure
-                @_already_called[name]=false
+                @_already_called[name] = false
               end
             end
 
@@ -180,6 +182,7 @@ module ActiveRecord
 
           if reflection.collection?
             before_save :before_save_collection_association
+            after_save :after_save_collection_association
 
             define_non_cyclic_method(save_method) { save_collection_association(reflection) }
             # Doesn't use after_save as that would save associations added in after_create/after_update twice
@@ -214,14 +217,9 @@ module ActiveRecord
               method = :validate_single_association
             end
 
-            define_non_cyclic_method(validation_method) do
-              send(method, reflection)
-              # TODO: remove the following line as soon as the return value of
-              # callbacks is ignored, that is, returning `false` does not
-              # display a deprecation warning or halts the callback chain.
-              true
-            end
+            define_non_cyclic_method(validation_method) { send(method, reflection) }
             validate validation_method
+            after_validation :_ensure_no_duplicate_errors
           end
         end
     end
@@ -233,7 +231,7 @@ module ActiveRecord
       super
     end
 
-    # Marks this record to be destroyed as part of the parents save transaction.
+    # Marks this record to be destroyed as part of the parent's save transaction.
     # This does _not_ actually destroy the record instantly, rather child record will be destroyed
     # when <tt>parent.save</tt> is called.
     #
@@ -242,7 +240,7 @@ module ActiveRecord
       @marked_for_destruction = true
     end
 
-    # Returns whether or not this record will be destroyed as part of the parents save transaction.
+    # Returns whether or not this record will be destroyed as part of the parent's save transaction.
     #
     # Only useful if the <tt>:autosave</tt> option on the parent is enabled for this associated model.
     def marked_for_destruction?
@@ -265,7 +263,7 @@ module ActiveRecord
     # Returns whether or not this record has been changed in any way (including whether
     # any of its nested autosave associations are likewise changed)
     def changed_for_autosave?
-      new_record? || changed? || marked_for_destruction? || nested_records_changed_for_autosave?
+      new_record? || has_changes_to_save? || marked_for_destruction? || nested_records_changed_for_autosave?
     end
 
     private
@@ -315,7 +313,7 @@ module ActiveRecord
       def validate_collection_association(reflection)
         if association = association_instance_get(reflection.name)
           if records = associated_records_to_validate_or_save(association, new_record?, reflection.options[:autosave])
-            records.each { |record| association_valid?(reflection, record) }
+            records.each_with_index { |record, index| association_valid?(reflection, record, index) }
           end
         end
       end
@@ -323,17 +321,30 @@ module ActiveRecord
       # Returns whether or not the association is valid and applies any errors to
       # the parent, <tt>self</tt>, if it wasn't. Skips any <tt>:autosave</tt>
       # enabled records if they're marked_for_destruction? or destroyed.
-      def association_valid?(reflection, record)
-        return true if record.destroyed? || record.marked_for_destruction?
+      def association_valid?(reflection, record, index = nil)
+        return true if record.destroyed? || (reflection.options[:autosave] && record.marked_for_destruction?)
+
+        context = validation_context unless [:create, :update].include?(validation_context)
 
-        validation_context = self.validation_context unless [:create, :update].include?(self.validation_context)
-        unless valid = record.valid?(validation_context)
+        unless valid = record.valid?(context)
           if reflection.options[:autosave]
+            indexed_attribute = !index.nil? && (reflection.options[:index_errors] || ActiveRecord::Base.index_nested_attribute_errors)
+
             record.errors.each do |attribute, message|
-              attribute = "#{reflection.name}.#{attribute}"
+              attribute = normalize_reflection_attribute(indexed_attribute, reflection, index, attribute)
               errors[attribute] << message
               errors[attribute].uniq!
             end
+
+            record.errors.details.each_key do |attribute|
+              reflection_attribute =
+                normalize_reflection_attribute(indexed_attribute, reflection, index, attribute).to_sym
+
+              record.errors.details[attribute].each do |error|
+                errors.details[reflection_attribute] << error
+                errors.details[reflection_attribute].uniq!
+              end
+            end
           else
             errors.add(reflection.name)
           end
@@ -341,18 +352,29 @@ module ActiveRecord
         valid
       end
 
+      def normalize_reflection_attribute(indexed_attribute, reflection, index, attribute)
+        if indexed_attribute
+          "#{reflection.name}[#{index}].#{attribute}"
+        else
+          "#{reflection.name}.#{attribute}"
+        end
+      end
+
       # Is used as a before_save callback to check while saving a collection
       # association whether or not the parent was a new record before saving.
       def before_save_collection_association
         @new_record_before_save = new_record?
-        true
+      end
+
+      def after_save_collection_association
+        @new_record_before_save = false
       end
 
       # Saves any new associated records, or all loaded autosave associations if
       # <tt>:autosave</tt> is enabled on the association.
       #
       # In addition, it destroys all children that were marked for destruction
-      # with mark_for_destruction.
+      # with #mark_for_destruction.
       #
       # This all happens inside a transaction, _if_ the Transactions module is included into
       # ActiveRecord::Base after the AutosaveAssociation module, which it does by default.
@@ -360,6 +382,9 @@ module ActiveRecord
         if association = association_instance_get(reflection.name)
           autosave = reflection.options[:autosave]
 
+          # reconstruct the scope now that we know the owner's id
+          association.reset_scope
+
           if records = associated_records_to_validate_or_save(association, @new_record_before_save, autosave)
             if autosave
               records_to_destroy = records.select(&:marked_for_destruction?)
@@ -375,19 +400,21 @@ module ActiveRecord
               if autosave != false && (@new_record_before_save || record.new_record?)
                 if autosave
                   saved = association.insert_record(record, false)
-                else
-                  association.insert_record(record) unless reflection.nested?
+                elsif !reflection.nested?
+                  association_saved = association.insert_record(record)
+
+                  if reflection.validate?
+                    errors.add(reflection.name) unless association_saved
+                    saved = association_saved
+                  end
                 end
               elsif autosave
-                saved = record.save(:validate => false)
+                saved = record.save(validate: false)
               end
 
               raise ActiveRecord::Rollback unless saved
             end
           end
-
-          # reconstruct the scope now that we know the owner's id
-          association.reset_scope if association.respond_to?(:reset_scope)
         end
       end
 
@@ -395,7 +422,7 @@ module ActiveRecord
       # on the association.
       #
       # In addition, it will destroy the association if it was marked for
-      # destruction with mark_for_destruction.
+      # destruction with #mark_for_destruction.
       #
       # This all happens inside a transaction, _if_ the Transactions module is included into
       # ActiveRecord::Base after the AutosaveAssociation module, which it does by default.
@@ -414,9 +441,12 @@ module ActiveRecord
             if (autosave && record.changed_for_autosave?) || new_record? || record_changed?(reflection, record, key)
               unless reflection.through_reflection
                 record[reflection.foreign_key] = key
+                if inverse_reflection = reflection.inverse_of
+                  record.association(inverse_reflection.name).loaded!
+                end
               end
 
-              saved = record.save(:validate => !autosave)
+              saved = record.save(validate: !autosave)
               raise ActiveRecord::Rollback if !saved && autosave
               saved
             end
@@ -428,7 +458,7 @@ module ActiveRecord
       def record_changed?(reflection, record, key)
         record.new_record? ||
           (record.has_attribute?(reflection.foreign_key) && record[reflection.foreign_key] != key) ||
-          record.attribute_changed?(reflection.foreign_key)
+          record.will_save_change_to_attribute?(reflection.foreign_key)
       end
 
       # Saves the associated record if it's new or <tt>:autosave</tt> is enabled.
@@ -436,7 +466,9 @@ module ActiveRecord
       # In addition, it will destroy the association if it was marked for destruction.
       def save_belongs_to_association(reflection)
         association = association_instance_get(reflection.name)
-        record      = association && association.load_target
+        return unless association && association.loaded? && !association.stale_target?
+
+        record = association.load_target
         if record && !record.destroyed?
           autosave = reflection.options[:autosave]
 
@@ -444,7 +476,7 @@ module ActiveRecord
             self[reflection.foreign_key] = nil
             record.destroy
           elsif autosave != false
-            saved = record.save(:validate => !autosave) if record.new_record? || (autosave && record.changed_for_autosave?)
+            saved = record.save(validate: !autosave) if record.new_record? || (autosave && record.changed_for_autosave?)
 
             if association.updated?
               association_id = record.send(reflection.options[:primary_key] || :id)
@@ -456,5 +488,11 @@ module ActiveRecord
           end
         end
       end
+
+      def _ensure_no_duplicate_errors
+        errors.messages.each_key do |attribute|
+          errors[attribute].uniq!
+        end
+      end
   end
 end
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index c918e88590..db097cb930 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -1,27 +1,28 @@
-require 'yaml'
-require 'set'
-require 'active_support/benchmarkable'
-require 'active_support/dependencies'
-require 'active_support/descendants_tracker'
-require 'active_support/time'
-require 'active_support/core_ext/module/attribute_accessors'
-require 'active_support/core_ext/array/extract_options'
-require 'active_support/core_ext/hash/deep_merge'
-require 'active_support/core_ext/hash/slice'
-require 'active_support/core_ext/hash/transform_values'
-require 'active_support/core_ext/string/behavior'
-require 'active_support/core_ext/kernel/singleton_class'
-require 'active_support/core_ext/module/introspection'
-require 'active_support/core_ext/object/duplicable'
-require 'active_support/core_ext/class/subclasses'
-require 'arel'
-require 'active_record/attribute_decorators'
-require 'active_record/errors'
-require 'active_record/log_subscriber'
-require 'active_record/explain_subscriber'
-require 'active_record/relation/delegation'
-require 'active_record/attributes'
-require 'active_record/type_caster'
+# frozen_string_literal: true
+
+require "yaml"
+require "active_support/benchmarkable"
+require "active_support/dependencies"
+require "active_support/descendants_tracker"
+require "active_support/time"
+require "active_support/core_ext/module/attribute_accessors"
+require "active_support/core_ext/array/extract_options"
+require "active_support/core_ext/hash/deep_merge"
+require "active_support/core_ext/hash/slice"
+require "active_support/core_ext/string/behavior"
+require "active_support/core_ext/kernel/singleton_class"
+require "active_support/core_ext/module/introspection"
+require "active_support/core_ext/object/duplicable"
+require "active_support/core_ext/class/subclasses"
+require "active_record/attribute_decorators"
+require "active_record/define_callbacks"
+require "active_record/errors"
+require "active_record/log_subscriber"
+require "active_record/explain_subscriber"
+require "active_record/relation/delegation"
+require "active_record/attributes"
+require "active_record/type_caster"
+require "active_record/database_configurations"
 
 module ActiveRecord #:nodoc:
   # = Active Record
@@ -133,9 +134,6 @@ module ActiveRecord #:nodoc:
   #     end
   #   end
   #
-  # You can alternatively use <tt>self[:attribute]=(value)</tt> and <tt>self[:attribute]</tt>
-  # or <tt>write_attribute(:attribute, value)</tt> and <tt>read_attribute(:attribute)</tt>.
-  #
   # == Attribute query methods
   #
   # In addition to the basic accessors, query methods are also automatically available on the Active Record object.
@@ -171,10 +169,11 @@ module ActiveRecord #:nodoc:
   # <tt>Person.find_by_user_name(user_name)</tt>.
   #
   # It's possible to add an exclamation point (!) on the end of the dynamic finders to get them to raise an
-  # <tt>ActiveRecord::RecordNotFound</tt> error if they do not return any records,
+  # ActiveRecord::RecordNotFound error if they do not return any records,
   # like <tt>Person.find_by_last_name!</tt>.
   #
-  # It's also possible to use multiple attributes in the same find by separating them with "_and_".
+  # It's also possible to use multiple attributes in the same <tt>find_by_</tt> by separating them with
+  # "_and_".
   #
   #  Person.find_by(user_name: user_name, password: password)
   #  Person.find_by_user_name_and_password(user_name, password) # with dynamic finder
@@ -186,7 +185,8 @@ module ActiveRecord #:nodoc:
   # == Saving arrays, hashes, and other non-mappable objects in text columns
   #
   # Active Record can serialize any object in text columns using YAML. To do so, you must
-  # specify this with a call to the class method +serialize+.
+  # specify this with a call to the class method
+  # {serialize}[rdoc-ref:AttributeMethods::Serialization::ClassMethods#serialize].
   # This makes it possible to store arrays, hashes, and other non-mappable objects without doing
   # any additional work.
   #
@@ -226,39 +226,47 @@ module ActiveRecord #:nodoc:
   #
   # == Connection to multiple databases in different models
   #
-  # Connections are usually created through ActiveRecord::Base.establish_connection and retrieved
+  # Connections are usually created through
+  # {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection] and retrieved
   # by ActiveRecord::Base.connection. All classes inheriting from ActiveRecord::Base will use this
   # connection. But you can also set a class-specific connection. For example, if Course is an
   # ActiveRecord::Base, but resides in a different database, you can just say <tt>Course.establish_connection</tt>
   # and Course and all of its subclasses will use this connection instead.
   #
   # This feature is implemented by keeping a connection pool in ActiveRecord::Base that is
-  # a Hash indexed by the class. If a connection is requested, the retrieve_connection method
+  # a hash indexed by the class. If a connection is requested, the
+  # {ActiveRecord::Base.retrieve_connection}[rdoc-ref:ConnectionHandling#retrieve_connection] method
   # will go up the class-hierarchy until a connection is found in the connection pool.
   #
   # == Exceptions
   #
   # * ActiveRecordError - Generic error class and superclass of all other errors raised by Active Record.
-  # * AdapterNotSpecified - The configuration hash used in <tt>establish_connection</tt> didn't include an
-  #   <tt>:adapter</tt> key.
-  # * AdapterNotFound - The <tt>:adapter</tt> key used in <tt>establish_connection</tt> specified a
-  #   non-existent adapter
+  # * AdapterNotSpecified - The configuration hash used in
+  #   {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection]
+  #   didn't include an <tt>:adapter</tt> key.
+  # * AdapterNotFound - The <tt>:adapter</tt> key used in
+  #   {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection]
+  #   specified a non-existent adapter
   #   (or a bad spelling of an existing one).
   # * AssociationTypeMismatch - The object assigned to the association wasn't of the type
   #   specified in the association definition.
   # * AttributeAssignmentError - An error occurred while doing a mass assignment through the
-  #   <tt>attributes=</tt> method.
+  #   {ActiveRecord::Base#attributes=}[rdoc-ref:AttributeAssignment#attributes=] method.
   #   You can inspect the +attribute+ property of the exception object to determine which attribute
   #   triggered the error.
-  # * ConnectionNotEstablished - No connection has been established. Use <tt>establish_connection</tt>
-  #   before querying.
+  # * ConnectionNotEstablished - No connection has been established.
+  #   Use {ActiveRecord::Base.establish_connection}[rdoc-ref:ConnectionHandling#establish_connection] before querying.
   # * MultiparameterAssignmentErrors - Collection of errors that occurred during a mass assignment using the
-  #   <tt>attributes=</tt> method. The +errors+ property of this exception contains an array of
+  #   {ActiveRecord::Base#attributes=}[rdoc-ref:AttributeAssignment#attributes=] method.
+  #   The +errors+ property of this exception contains an array of
   #   AttributeAssignmentError
   #   objects that should be inspected to determine which attributes triggered the errors.
-  # * RecordInvalid - raised by <tt>save!</tt> and <tt>create!</tt> when the record is invalid.
-  # * RecordNotFound - No record responded to the +find+ method. Either the row with the given ID doesn't exist
-  #   or the row didn't meet the additional restrictions. Some +find+ calls do not raise this exception to signal
+  # * RecordInvalid - raised by {ActiveRecord::Base#save!}[rdoc-ref:Persistence#save!] and
+  #   {ActiveRecord::Base.create!}[rdoc-ref:Persistence::ClassMethods#create!]
+  #   when the record is invalid.
+  # * RecordNotFound - No record responded to the {ActiveRecord::Base.find}[rdoc-ref:FinderMethods#find] method.
+  #   Either the row with the given ID doesn't exist or the row didn't meet the additional restrictions.
+  #   Some {ActiveRecord::Base.find}[rdoc-ref:FinderMethods#find] calls do not raise this exception to signal
   #   nothing was found, please check its documentation for further details.
   # * SerializationTypeMismatch - The serialized object wasn't of the class specified as the second parameter.
   # * StatementInvalid - The database server rejected the SQL statement. The precise error is added in the message.
@@ -280,6 +288,8 @@ module ActiveRecord #:nodoc:
     extend Explain
     extend Enum
     extend Delegation::DelegateCache
+    extend CollectionCacheKey
+    extend Aggregations::ClassMethods
 
     include Core
     include Persistence
@@ -297,6 +307,7 @@ module ActiveRecord #:nodoc:
     include AttributeDecorators
     include Locking::Optimistic
     include Locking::Pessimistic
+    include DefineCallbacks
     include AttributeMethods
     include Callbacks
     include Timestamp
@@ -304,10 +315,9 @@ module ActiveRecord #:nodoc:
     include ActiveModel::SecurePassword
     include AutosaveAssociation
     include NestedAttributes
-    include Aggregations
     include Transactions
-    include NoTouching
     include TouchLater
+    include NoTouching
     include Reflection
     include Serialization
     include Store
diff --git a/activerecord/lib/active_record/callbacks.rb b/activerecord/lib/active_record/callbacks.rb
index 3027ce928e..5407af85ea 100644
--- a/activerecord/lib/active_record/callbacks.rb
+++ b/activerecord/lib/active_record/callbacks.rb
@@ -1,11 +1,13 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Callbacks
+  # = Active Record \Callbacks
   #
-  # Callbacks are hooks into the life cycle of an Active Record object that allow you to trigger logic
+  # \Callbacks are hooks into the life cycle of an Active Record object that allow you to trigger logic
   # before or after an alteration of the object state. This can be used to make sure that associated and
-  # dependent objects are deleted when +destroy+ is called (by overwriting +before_destroy+) or to massage attributes
-  # before they're validated (by overwriting +before_validation+). As an example of the callbacks initiated, consider
-  # the <tt>Base#save</tt> call for a new record:
+  # dependent objects are deleted when {ActiveRecord::Base#destroy}[rdoc-ref:Persistence#destroy] is called (by overwriting +before_destroy+) or
+  # to massage attributes before they're validated (by overwriting +before_validation+).
+  # As an example of the callbacks initiated, consider the {ActiveRecord::Base#save}[rdoc-ref:Persistence#save] call for a new record:
   #
   # * (-) <tt>save</tt>
   # * (-) <tt>valid</tt>
@@ -20,7 +22,7 @@ module ActiveRecord
   # * (7) <tt>after_commit</tt>
   #
   # Also, an <tt>after_rollback</tt> callback can be configured to be triggered whenever a rollback is issued.
-  # Check out <tt>ActiveRecord::Transactions</tt> for more details about <tt>after_commit</tt> and
+  # Check out ActiveRecord::Transactions for more details about <tt>after_commit</tt> and
   # <tt>after_rollback</tt>.
   #
   # Additionally, an <tt>after_touch</tt> callback is triggered whenever an
@@ -31,7 +33,7 @@ module ActiveRecord
   # are instantiated as well.
   #
   # There are nineteen callbacks in total, which give you immense power to react and prepare for each state in the
-  # Active Record life cycle. The sequence for calling <tt>Base#save</tt> for an existing record is similar,
+  # Active Record life cycle. The sequence for calling {ActiveRecord::Base#save}[rdoc-ref:Persistence#save] for an existing record is similar,
   # except that each <tt>_create</tt> callback is replaced by the corresponding <tt>_update</tt> callback.
   #
   # Examples:
@@ -53,9 +55,9 @@ module ActiveRecord
   #   end
   #
   #   class Firm < ActiveRecord::Base
-  #     # Destroys the associated clients and people when the firm is destroyed
-  #     before_destroy { |record| Person.destroy_all "firm_id = #{record.id}"   }
-  #     before_destroy { |record| Client.destroy_all "client_of = #{record.id}" }
+  #     # Disables access to the system, for associated clients and people when the firm is destroyed
+  #     before_destroy { |record| Person.where(firm_id: record.id).update_all(access: 'disabled')   }
+  #     before_destroy { |record| Client.where(client_of: record.id).update_all(access: 'disabled') }
   #   end
   #
   # == Inheritable callback queues
@@ -73,21 +75,7 @@ module ActiveRecord
   #   end
   #
   # Now, when <tt>Topic#destroy</tt> is run only +destroy_author+ is called. When <tt>Reply#destroy</tt> is
-  # run, both +destroy_author+ and +destroy_readers+ are called. Contrast this to the following situation
-  # where the +before_destroy+ method is overridden:
-  #
-  #   class Topic < ActiveRecord::Base
-  #     def before_destroy() destroy_author end
-  #   end
-  #
-  #   class Reply < Topic
-  #     def before_destroy() destroy_readers end
-  #   end
-  #
-  # In that case, <tt>Reply#destroy</tt> would only run +destroy_readers+ and _not_ +destroy_author+.
-  # So, use the callback macros when you want to ensure that a certain callback is called for the entire
-  # hierarchy, and use the regular overwritable methods when you want to leave it up to each descendant
-  # to decide whether they want to call +super+ and trigger the inherited callbacks.
+  # run, both +destroy_author+ and +destroy_readers+ are called.
   #
   # *IMPORTANT:* In order for inheritance to work for the callback queues, you must specify the
   # callbacks before specifying the associations. Otherwise, you might trigger the loading of a
@@ -96,9 +84,9 @@ module ActiveRecord
   # == Types of callbacks
   #
   # There are four types of callbacks accepted by the callback macros: Method references (symbol), callback objects,
-  # inline methods (using a proc), and inline eval methods (using a string). Method references and callback objects
+  # inline methods (using a proc). Method references and callback objects
   # are the recommended approaches, inline methods using a proc are sometimes appropriate (such as for
-  # creating mix-ins), and inline eval methods are deprecated.
+  # creating mix-ins).
   #
   # The method reference callbacks work by specifying a protected or private method available in the object, like this:
   #
@@ -107,7 +95,7 @@ module ActiveRecord
   #
   #     private
   #       def delete_parents
-  #         self.class.delete_all "parent_id = #{id}"
+  #         self.class.where(parent_id: id).delete_all
   #       end
   #   end
   #
@@ -140,7 +128,7 @@ module ActiveRecord
   #       end
   #   end
   #
-  # So you specify the object you want messaged on a given callback. When that callback is triggered, the object has
+  # So you specify the object you want to be messaged on a given callback. When that callback is triggered, the object has
   # a method by the name of the callback messaged. You can make these callbacks more flexible by passing in other
   # initialization data such as the name of the attribute to work with:
   #
@@ -175,26 +163,12 @@ module ActiveRecord
   #       end
   #   end
   #
-  # The callback macros usually accept a symbol for the method they're supposed to run, but you can also
-  # pass a "method string", which will then be evaluated within the binding of the callback. Example:
-  #
-  #   class Topic < ActiveRecord::Base
-  #     before_destroy 'self.class.delete_all "parent_id = #{id}"'
-  #   end
-  #
-  # Notice that single quotes (') are used so the <tt>#{id}</tt> part isn't evaluated until the callback
-  # is triggered. Also note that these inline callbacks can be stacked just like the regular ones:
-  #
-  #   class Topic < ActiveRecord::Base
-  #     before_destroy 'self.class.delete_all "parent_id = #{id}"',
-  #                    'puts "Evaluated after parents are destroyed"'
-  #   end
-  #
   # == <tt>before_validation*</tt> returning statements
   #
   # If the +before_validation+ callback throws +:abort+, the process will be
-  # aborted and <tt>Base#save</tt> will return +false+. If Base#save! is called it will raise a
-  # <tt>ActiveRecord::RecordInvalid</tt> exception. Nothing will be appended to the errors object.
+  # aborted and {ActiveRecord::Base#save}[rdoc-ref:Persistence#save] will return +false+.
+  # If {ActiveRecord::Base#save!}[rdoc-ref:Persistence#save!] is called it will raise an ActiveRecord::RecordInvalid exception.
+  # Nothing will be appended to the errors object.
   #
   # == Canceling callbacks
   #
@@ -206,12 +180,13 @@ module ActiveRecord
   # == Ordering callbacks
   #
   # Sometimes the code needs that the callbacks execute in a specific order. For example, a +before_destroy+
-  # callback (+log_children+ in this case) should be executed before the children get destroyed by the +dependent: destroy+ option.
+  # callback (+log_children+ in this case) should be executed before the children get destroyed by the
+  # <tt>dependent: :destroy</tt> option.
   #
   # Let's look at the code below:
   #
   #   class Topic < ActiveRecord::Base
-  #     has_many :children, dependent: destroy
+  #     has_many :children, dependent: :destroy
   #
   #     before_destroy :log_children
   #
@@ -222,10 +197,11 @@ module ActiveRecord
   #   end
   #
   # In this case, the problem is that when the +before_destroy+ callback is executed, the children are not available
-  # because the +destroy+ callback gets executed first. You can use the +prepend+ option on the +before_destroy+ callback to avoid this.
+  # because the {ActiveRecord::Base#destroy}[rdoc-ref:Persistence#destroy] callback gets executed first.
+  # You can use the +prepend+ option on the +before_destroy+ callback to avoid this.
   #
   #   class Topic < ActiveRecord::Base
-  #     has_many :children, dependent: destroy
+  #     has_many :children, dependent: :destroy
   #
   #     before_destroy :log_children, prepend: true
   #
@@ -235,23 +211,72 @@ module ActiveRecord
   #       end
   #   end
   #
-  # This way, the +before_destroy+ gets executed before the <tt>dependent: destroy</tt> is called, and the data is still available.
+  # This way, the +before_destroy+ gets executed before the <tt>dependent: :destroy</tt> is called, and the data is still available.
+  #
+  # Also, there are cases when you want several callbacks of the same type to
+  # be executed in order.
+  #
+  # For example:
+  #
+  #   class Topic < ActiveRecord::Base
+  #     has_many :children
+  #
+  #     after_save :log_children
+  #     after_save :do_something_else
+  #
+  #     private
+  #
+  #     def log_children
+  #       # Child processing
+  #     end
+  #
+  #     def do_something_else
+  #       # Something else
+  #     end
+  #   end
+  #
+  # In this case the +log_children+ gets executed before +do_something_else+.
+  # The same applies to all non-transactional callbacks.
   #
-  # == Transactions
+  # In case there are multiple transactional callbacks as seen below, the order
+  # is reversed.
+  #
+  # For example:
+  #
+  #   class Topic < ActiveRecord::Base
+  #     has_many :children
   #
-  # The entire callback chain of a +save+, <tt>save!</tt>, or +destroy+ call runs
-  # within a transaction. That includes <tt>after_*</tt> hooks. If everything
-  # goes fine a COMMIT is executed once the chain has been completed.
+  #     after_commit :log_children
+  #     after_commit :do_something_else
+  #
+  #     private
+  #
+  #     def log_children
+  #       # Child processing
+  #     end
+  #
+  #     def do_something_else
+  #       # Something else
+  #     end
+  #   end
+  #
+  # In this case the +do_something_else+ gets executed before +log_children+.
+  #
+  # == \Transactions
+  #
+  # The entire callback chain of a {#save}[rdoc-ref:Persistence#save], {#save!}[rdoc-ref:Persistence#save!],
+  # or {#destroy}[rdoc-ref:Persistence#destroy] call runs within a transaction. That includes <tt>after_*</tt> hooks.
+  # If everything goes fine a COMMIT is executed once the chain has been completed.
   #
   # If a <tt>before_*</tt> callback cancels the action a ROLLBACK is issued. You
   # can also trigger a ROLLBACK raising an exception in any of the callbacks,
   # including <tt>after_*</tt> hooks. Note, however, that in that case the client
-  # needs to be aware of it because an ordinary +save+ will raise such exception
+  # needs to be aware of it because an ordinary {#save}[rdoc-ref:Persistence#save] will raise such exception
   # instead of quietly returning +false+.
   #
   # == Debugging callbacks
   #
-  # The callback chain is accessible via the <tt>_*_callbacks</tt> method on an object. ActiveModel Callbacks support
+  # The callback chain is accessible via the <tt>_*_callbacks</tt> method on an object. Active Model \Callbacks support
   # <tt>:before</tt>, <tt>:after</tt> and <tt>:around</tt> as values for the <tt>kind</tt> property. The <tt>kind</tt> property
   # defines what part of the chain the callback runs in.
   #
@@ -277,36 +302,38 @@ module ActiveRecord
       :before_destroy, :around_destroy, :after_destroy, :after_commit, :after_rollback
     ]
 
-    module ClassMethods
-      include ActiveModel::Callbacks
-    end
-
-    included do
-      include ActiveModel::Validations::Callbacks
-
-      define_model_callbacks :initialize, :find, :touch, :only => :after
-      define_model_callbacks :save, :create, :update, :destroy
-    end
-
     def destroy #:nodoc:
-      run_callbacks(:destroy) { super }
+      @_destroy_callback_already_called ||= false
+      return if @_destroy_callback_already_called
+      @_destroy_callback_already_called = true
+      _run_destroy_callbacks { super }
+    rescue RecordNotDestroyed => e
+      @_association_destroy_exception = e
+      false
+    ensure
+      @_destroy_callback_already_called = false
     end
 
     def touch(*) #:nodoc:
-      run_callbacks(:touch) { super }
+      _run_touch_callbacks { super }
+    end
+
+    def increment!(attribute, by = 1, touch: nil) # :nodoc:
+      touch ? _run_touch_callbacks { super } : super
     end
 
   private
-    def create_or_update(*) #:nodoc:
-      run_callbacks(:save) { super }
+
+    def create_or_update(*)
+      _run_save_callbacks { super }
     end
 
-    def _create_record #:nodoc:
-      run_callbacks(:create) { super }
+    def _create_record
+      _run_create_callbacks { super }
     end
 
-    def _update_record(*) #:nodoc:
-      run_callbacks(:update) { super }
+    def _update_record(*)
+      _run_update_callbacks { super }
     end
   end
 end
diff --git a/activerecord/lib/active_record/coders/json.rb b/activerecord/lib/active_record/coders/json.rb
index 75d3bfe625..a69b38487e 100644
--- a/activerecord/lib/active_record/coders/json.rb
+++ b/activerecord/lib/active_record/coders/json.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Coders # :nodoc:
     class JSON # :nodoc:
@@ -6,7 +8,7 @@ module ActiveRecord
       end
 
       def self.load(json)
-        ActiveSupport::JSON.decode(json) unless json.nil?
+        ActiveSupport::JSON.decode(json) unless json.blank?
       end
     end
   end
diff --git a/activerecord/lib/active_record/coders/yaml_column.rb b/activerecord/lib/active_record/coders/yaml_column.rb
index 9ea22ed798..11559141c7 100644
--- a/activerecord/lib/active_record/coders/yaml_column.rb
+++ b/activerecord/lib/active_record/coders/yaml_column.rb
@@ -1,12 +1,14 @@
-require 'yaml'
+# frozen_string_literal: true
+
+require "yaml"
 
 module ActiveRecord
   module Coders # :nodoc:
     class YAMLColumn # :nodoc:
-
       attr_accessor :object_class
 
-      def initialize(object_class = Object)
+      def initialize(attr_name, object_class = Object)
+        @attr_name = attr_name
         @object_class = object_class
         check_arity_of_constructor
       end
@@ -14,36 +16,35 @@ module ActiveRecord
       def dump(obj)
         return if obj.nil?
 
-        unless obj.is_a?(object_class)
-          raise SerializationTypeMismatch,
-            "Attribute was supposed to be a #{object_class}, but was a #{obj.class}. -- #{obj.inspect}"
-        end
+        assert_valid_value(obj, action: "dump")
         YAML.dump obj
       end
 
       def load(yaml)
         return object_class.new if object_class != Object && yaml.nil?
-        return yaml unless yaml.is_a?(String) && yaml =~ /^---/
+        return yaml unless yaml.is_a?(String) && /^---/.match?(yaml)
         obj = YAML.load(yaml)
 
-        unless obj.is_a?(object_class) || obj.nil?
-          raise SerializationTypeMismatch,
-            "Attribute was supposed to be a #{object_class}, but was a #{obj.class}"
-        end
+        assert_valid_value(obj, action: "load")
         obj ||= object_class.new if object_class != Object
 
         obj
       end
 
+      def assert_valid_value(obj, action:)
+        unless obj.nil? || obj.is_a?(object_class)
+          raise SerializationTypeMismatch,
+            "can't #{action} `#{@attr_name}`: was supposed to be a #{object_class}, but was a #{obj.class}. -- #{obj.inspect}"
+        end
+      end
+
       private
 
-      def check_arity_of_constructor
-        begin
+        def check_arity_of_constructor
           load(nil)
         rescue ArgumentError
           raise ArgumentError, "Cannot serialize #{object_class}. Classes passed to `serialize` must have a 0 argument constructor."
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/collection_cache_key.rb b/activerecord/lib/active_record/collection_cache_key.rb
new file mode 100644
index 0000000000..4b6db8a96c
--- /dev/null
+++ b/activerecord/lib/active_record/collection_cache_key.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module CollectionCacheKey
+    def collection_cache_key(collection = all, timestamp_column = :updated_at) # :nodoc:
+      query_signature = ActiveSupport::Digest.hexdigest(collection.to_sql)
+      key = "#{collection.model_name.cache_key}/query-#{query_signature}"
+
+      if collection.loaded? || collection.distinct_value
+        size = collection.records.size
+        if size > 0
+          timestamp = collection.max_by(&timestamp_column)._read_attribute(timestamp_column)
+        end
+      else
+        if collection.eager_loading?
+          collection = collection.send(:apply_join_dependency)
+        end
+        column_type = type_for_attribute(timestamp_column)
+        column = connection.visitor.compile(collection.arel_attribute(timestamp_column))
+        select_values = "COUNT(*) AS #{connection.quote_column_name("size")}, MAX(%s) AS timestamp"
+
+        if collection.has_limit_or_offset?
+          query = collection.select("#{column} AS collection_cache_key_timestamp")
+          subquery_alias = "subquery_for_cache_key"
+          subquery_column = "#{subquery_alias}.collection_cache_key_timestamp"
+          subquery = query.arel.as(subquery_alias)
+          arel = Arel::SelectManager.new(subquery).project(select_values % subquery_column)
+        else
+          query = collection.unscope(:order)
+          query.select_values = [select_values % column]
+          arel = query.arel
+        end
+
+        result = connection.select_one(arel, nil)
+
+        if result.blank?
+          size = 0
+          timestamp = nil
+        else
+          size = result["size"]
+          timestamp = column_type.deserialize(result["timestamp"])
+        end
+
+      end
+
+      if timestamp
+        "#{key}-#{size}-#{timestamp.utc.to_s(cache_timestamp_format)}"
+      else
+        "#{key}-#{size}"
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
index 6535121075..99934a0e31 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -1,6 +1,8 @@
-require 'thread'
-require 'thread_safe'
-require 'monitor'
+# frozen_string_literal: true
+
+require "thread"
+require "concurrent/map"
+require "monitor"
 
 module ActiveRecord
   # Raised when a connection could not be obtained within the connection
@@ -10,8 +12,9 @@ module ActiveRecord
   end
 
   # Raised when a pool was unable to get ahold of all its connections
-  # to perform a "group" action such as +ConnectionPool#disconnect!+
-  # or +ConnectionPool#clear_reloadable_connections!+.
+  # to perform a "group" action such as
+  # {ActiveRecord::Base.connection_pool.disconnect!}[rdoc-ref:ConnectionAdapters::ConnectionPool#disconnect!]
+  # or {ActiveRecord::Base.clear_reloadable_connections!}[rdoc-ref:ConnectionAdapters::ConnectionHandler#clear_reloadable_connections!].
   class ExclusiveConnectionTimeoutError < ConnectionTimeoutError
   end
 
@@ -37,17 +40,18 @@ module ActiveRecord
     # Connections can be obtained and used from a connection pool in several
     # ways:
     #
-    # 1. Simply use ActiveRecord::Base.connection as with Active Record 2.1 and
+    # 1. Simply use {ActiveRecord::Base.connection}[rdoc-ref:ConnectionHandling.connection]
+    #    as with Active Record 2.1 and
     #    earlier (pre-connection-pooling). Eventually, when you're done with
     #    the connection(s) and wish it to be returned to the pool, you call
-    #    ActiveRecord::Base.clear_active_connections!. This will be the
-    #    default behavior for Active Record when used in conjunction with
+    #    {ActiveRecord::Base.clear_active_connections!}[rdoc-ref:ConnectionAdapters::ConnectionHandler#clear_active_connections!].
+    #    This will be the default behavior for Active Record when used in conjunction with
     #    Action Pack's request handling cycle.
     # 2. Manually check out a connection from the pool with
-    #    ActiveRecord::Base.connection_pool.checkout. You are responsible for
+    #    {ActiveRecord::Base.connection_pool.checkout}[rdoc-ref:#checkout]. You are responsible for
     #    returning this connection to the pool when finished by calling
-    #    ActiveRecord::Base.connection_pool.checkin(connection).
-    # 3. Use ActiveRecord::Base.connection_pool.with_connection(&block), which
+    #    {ActiveRecord::Base.connection_pool.checkin(connection)}[rdoc-ref:#checkin].
+    # 3. Use {ActiveRecord::Base.connection_pool.with_connection(&block)}[rdoc-ref:#with_connection], which
     #    obtains a connection, yields it as the sole argument to the block,
     #    and returns it to the pool after the block completes.
     #
@@ -59,30 +63,25 @@ module ActiveRecord
     # There are several connection-pooling-related options that you can add to
     # your database connection configuration:
     #
-    # * +pool+: number indicating size of connection pool (default 5)
-    # * +checkout_timeout+: number of seconds to block and wait for a connection
-    #   before giving up and raising a timeout error (default 5 seconds).
-    # * +reaping_frequency+: frequency in seconds to periodically run the
-    #   Reaper, which attempts to find and recover connections from dead
-    #   threads, which can occur if a programmer forgets to close a
-    #   connection at the end of a thread or a thread dies unexpectedly.
-    #   Regardless of this setting, the Reaper will be invoked before every
-    #   blocking wait. (Default nil, which means don't schedule the Reaper).
+    # * +pool+: maximum number of connections the pool may manage (default 5).
+    # * +idle_timeout+: number of seconds that a connection will be kept
+    #   unused in the pool before it is automatically disconnected (default
+    #   300 seconds). Set this to zero to keep connections forever.
+    # * +checkout_timeout+: number of seconds to wait for a connection to
+    #   become available before giving up and raising a timeout error (default
+    #   5 seconds).
     #
     #--
     # Synchronization policy:
     # * all public methods can be called outside +synchronize+
-    # * access to these i-vars needs to be in +synchronize+:
+    # * access to these instance variables needs to be in +synchronize+:
     #   * @connections
     #   * @now_connecting
     # * private methods that require being called in a +synchronize+ blocks
     #   are now explicitly documented
     class ConnectionPool
-      # Threadsafe, fair, FIFO queue.  Meant to be used by ConnectionPool
-      # with which it shares a Monitor.  But could be a generic Queue.
-      #
-      # The Queue in stdlib's 'thread' could replace this class except
-      # stdlib's doesn't support waiting with a timeout.
+      # Threadsafe, fair, LIFO queue.  Meant to be used by ConnectionPool
+      # with which it shares a Monitor.
       class Queue
         def initialize(lock = Monitor.new)
           @lock = lock
@@ -114,7 +113,7 @@ module ActiveRecord
           end
         end
 
-        # If +element+ is in the queue, remove and return it, or nil.
+        # If +element+ is in the queue, remove and return it, or +nil+.
         def delete(element)
           synchronize do
             @queue.delete(element)
@@ -133,14 +132,14 @@ module ActiveRecord
         # If +timeout+ is not given, remove and return the head the
         # queue if the number of available elements is strictly
         # greater than the number of threads currently waiting (that
-        # is, don't jump ahead in line).  Otherwise, return nil.
+        # is, don't jump ahead in line).  Otherwise, return +nil+.
         #
         # If +timeout+ is given, block if there is no element
         # available, waiting up to +timeout+ seconds for an element to
         # become available.
         #
         # Raises:
-        # - ConnectionTimeoutError if +timeout+ is given and no element
+        # - ActiveRecord::ConnectionTimeoutError if +timeout+ is given and no element
         # becomes available within +timeout+ seconds,
         def poll(timeout = nil)
           synchronize { internal_poll(timeout) }
@@ -148,61 +147,63 @@ module ActiveRecord
 
         private
 
-        def internal_poll(timeout)
-          no_wait_poll || (timeout && wait_poll(timeout))
-        end
+          def internal_poll(timeout)
+            no_wait_poll || (timeout && wait_poll(timeout))
+          end
 
-        def synchronize(&block)
-          @lock.synchronize(&block)
-        end
+          def synchronize(&block)
+            @lock.synchronize(&block)
+          end
 
-        # Test if the queue currently contains any elements.
-        def any?
-          !@queue.empty?
-        end
+          # Test if the queue currently contains any elements.
+          def any?
+            !@queue.empty?
+          end
 
-        # A thread can remove an element from the queue without
-        # waiting if and only if the number of currently available
-        # connections is strictly greater than the number of waiting
-        # threads.
-        def can_remove_no_wait?
-          @queue.size > @num_waiting
-        end
+          # A thread can remove an element from the queue without
+          # waiting if and only if the number of currently available
+          # connections is strictly greater than the number of waiting
+          # threads.
+          def can_remove_no_wait?
+            @queue.size > @num_waiting
+          end
 
-        # Removes and returns the head of the queue if possible, or nil.
-        def remove
-          @queue.shift
-        end
+          # Removes and returns the head of the queue if possible, or +nil+.
+          def remove
+            @queue.pop
+          end
 
-        # Remove and return the head the queue if the number of
-        # available elements is strictly greater than the number of
-        # threads currently waiting.  Otherwise, return nil.
-        def no_wait_poll
-          remove if can_remove_no_wait?
-        end
+          # Remove and return the head the queue if the number of
+          # available elements is strictly greater than the number of
+          # threads currently waiting.  Otherwise, return +nil+.
+          def no_wait_poll
+            remove if can_remove_no_wait?
+          end
 
-        # Waits on the queue up to +timeout+ seconds, then removes and
-        # returns the head of the queue.
-        def wait_poll(timeout)
-          @num_waiting += 1
+          # Waits on the queue up to +timeout+ seconds, then removes and
+          # returns the head of the queue.
+          def wait_poll(timeout)
+            @num_waiting += 1
 
-          t0 = Time.now
-          elapsed = 0
-          loop do
-            @cond.wait(timeout - elapsed)
+            t0 = Time.now
+            elapsed = 0
+            loop do
+              ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+                @cond.wait(timeout - elapsed)
+              end
 
-            return remove if any?
+              return remove if any?
 
-            elapsed = Time.now - t0
-            if elapsed >= timeout
-              msg = 'could not obtain a database connection within %0.3f seconds (waited %0.3f seconds)' %
-                [timeout, elapsed]
-              raise ConnectionTimeoutError, msg
+              elapsed = Time.now - t0
+              if elapsed >= timeout
+                msg = "could not obtain a connection from the pool within %0.3f seconds (waited %0.3f seconds); all pooled connections were in use" %
+                  [timeout, elapsed]
+                raise ConnectionTimeoutError, msg
+              end
             end
+          ensure
+            @num_waiting -= 1
           end
-        ensure
-          @num_waiting -= 1
-        end
       end
 
       # Adds the ability to turn a basic fair FIFO queue into one
@@ -266,25 +267,25 @@ module ActiveRecord
       # Connections must be leased while holding the main pool mutex. This is
       # an internal subclass that also +.leases+ returned connections while
       # still in queue's critical section (queue synchronizes with the same
-      # +@lock+ as the main pool) so that a returned connection is already
+      # <tt>@lock</tt> as the main pool) so that a returned connection is already
       # leased and there is no need to re-enter synchronized block.
       class ConnectionLeasingQueue < Queue # :nodoc:
         include BiasableQueue
 
         private
-        def internal_poll(timeout)
-          conn = super
-          conn.lease if conn
-          conn
-        end
+          def internal_poll(timeout)
+            conn = super
+            conn.lease if conn
+            conn
+          end
       end
 
-      # Every +frequency+ seconds, the reaper will call +reap+ on +pool+.
-      # A reaper instantiated with a nil frequency will never reap the
-      # connection pool.
+      # Every +frequency+ seconds, the reaper will call +reap+ and +flush+ on
+      # +pool+. A reaper instantiated with a zero frequency will never reap
+      # the connection pool.
       #
-      # Configure the frequency by setting "reaping_frequency" in your
-      # database yaml file.
+      # Configure the frequency by setting +reaping_frequency+ in your database
+      # yaml file (default 60 seconds).
       class Reaper
         attr_reader :pool, :frequency
 
@@ -294,17 +295,19 @@ module ActiveRecord
         end
 
         def run
-          return unless frequency
+          return unless frequency && frequency > 0
           Thread.new(frequency, pool) { |t, p|
-            while true
+            loop do
               sleep t
               p.reap
+              p.flush
             end
           }
         end
       end
 
       include MonitorMixin
+      include QueryCache::ConnectionPoolConfiguration
 
       attr_accessor :automatic_reconnect, :checkout_timeout, :schema_cache
       attr_reader :spec, :connections, :size, :reaper
@@ -321,36 +324,53 @@ module ActiveRecord
         @spec = spec
 
         @checkout_timeout = (spec.config[:checkout_timeout] && spec.config[:checkout_timeout].to_f) || 5
-        @reaper = Reaper.new(self, (spec.config[:reaping_frequency] && spec.config[:reaping_frequency].to_f))
-        @reaper.run
+        if @idle_timeout = spec.config.fetch(:idle_timeout, 300)
+          @idle_timeout = @idle_timeout.to_f
+          @idle_timeout = nil if @idle_timeout <= 0
+        end
 
         # default max pool size to 5
         @size = (spec.config[:pool] && spec.config[:pool].to_i) || 5
 
-        # The cache of threads mapped to reserved connections, the sole purpose
-        # of the cache is to speed-up +connection+ method, it is not the authoritative
-        # registry of which thread owns which connection, that is tracked by
-        # +connection.owner+ attr on each +connection+ instance.
-        # The invariant works like this: if there is mapping of +thread => conn+,
-        # then that +thread+ does indeed own that +conn+, however an absence of a such
-        # mapping does not mean that the +thread+ doesn't own the said connection, in
+        # This variable tracks the cache of threads mapped to reserved connections, with the
+        # sole purpose of speeding up the +connection+ method. It is not the authoritative
+        # registry of which thread owns which connection. Connection ownership is tracked by
+        # the +connection.owner+ attr on each +connection+ instance.
+        # The invariant works like this: if there is mapping of <tt>thread => conn</tt>,
+        # then that +thread+ does indeed own that +conn+. However, an absence of a such
+        # mapping does not mean that the +thread+ doesn't own the said connection. In
         # that case +conn.owner+ attr should be consulted.
-        # Access and modification of +@thread_cached_conns+ does not require
+        # Access and modification of <tt>@thread_cached_conns</tt> does not require
         # synchronization.
-        @thread_cached_conns = ThreadSafe::Cache.new(:initial_capacity => @size)
+        @thread_cached_conns = Concurrent::Map.new(initial_capacity: @size)
 
         @connections         = []
         @automatic_reconnect = true
 
-        # Connection pool allows for concurrent (outside the main `synchronize` section)
+        # Connection pool allows for concurrent (outside the main +synchronize+ section)
         # establishment of new connections. This variable tracks the number of threads
         # currently in the process of independently establishing connections to the DB.
         @now_connecting = 0
 
-        # A boolean toggle that allows/disallows new connections.
-        @new_cons_enabled = true
+        @threads_blocking_new_connections = 0
 
         @available = ConnectionLeasingQueue.new self
+
+        @lock_thread = false
+
+        # +reaping_frequency+ is configurable mostly for historical reasons, but it could
+        # also be useful if someone wants a very low +idle_timeout+.
+        reaping_frequency = spec.config.fetch(:reaping_frequency, 60)
+        @reaper = Reaper.new(self, reaping_frequency && reaping_frequency.to_f)
+        @reaper.run
+      end
+
+      def lock_thread=(lock_thread)
+        if lock_thread
+          @lock_thread = Thread.current
+        else
+          @lock_thread = nil
+        end
       end
 
       # Retrieve the connection associated with the current thread, or call
@@ -359,13 +379,13 @@ module ActiveRecord
       # #connection can be called any number of times; the connection is
       # held in a cache keyed by a thread.
       def connection
-        @thread_cached_conns[connection_cache_key(Thread.current)] ||= checkout
+        @thread_cached_conns[connection_cache_key(@lock_thread || Thread.current)] ||= checkout
       end
 
-      # Is there an open connection that is being used for the current thread?
+      # Returns true if there is an open connection being used for the current thread.
       #
-      # This method only works for connections that have been abtained through
-      # #connection or #with_connection methods, connections obtained through
+      # This method only works for connections that have been obtained through
+      # #connection or #with_connection methods. Connections obtained through
       # #checkout will not be detected by #active_connection?
       def active_connection?
         @thread_cached_conns[connection_cache_key(Thread.current)]
@@ -406,14 +426,17 @@ module ActiveRecord
       # Disconnects all connections in the pool, and clears the pool.
       #
       # Raises:
-      # - +ExclusiveConnectionTimeoutError+ if unable to gain ownership of all
+      # - ActiveRecord::ExclusiveConnectionTimeoutError if unable to gain ownership of all
       #   connections in the pool within a timeout interval (default duration is
-      #   +spec.config[:checkout_timeout] * 2+ seconds).
+      #   <tt>spec.config[:checkout_timeout] * 2</tt> seconds).
       def disconnect(raise_on_acquisition_timeout = true)
         with_exclusively_acquired_all_connections(raise_on_acquisition_timeout) do
           synchronize do
             @connections.each do |conn|
-              checkin conn
+              if conn.in_use?
+                conn.steal!
+                checkin conn
+              end
               conn.disconnect!
             end
             @connections = []
@@ -424,57 +447,58 @@ module ActiveRecord
 
       # Disconnects all connections in the pool, and clears the pool.
       #
-      # The pool first tries to gain ownership of all connections, if unable to
+      # The pool first tries to gain ownership of all connections. If unable to
       # do so within a timeout interval (default duration is
-      # +spec.config[:checkout_timeout] * 2+ seconds), the pool is forcefully
-      # disconneted wihout any regard for other connection owning threads.
+      # <tt>spec.config[:checkout_timeout] * 2</tt> seconds), then the pool is forcefully
+      # disconnected without any regard for other connection owning threads.
       def disconnect!
         disconnect(false)
       end
 
+      # Discards all connections in the pool (even if they're currently
+      # leased!), along with the pool itself. Any further interaction with the
+      # pool (except #spec and #schema_cache) is undefined.
+      #
+      # See AbstractAdapter#discard!
+      def discard! # :nodoc:
+        synchronize do
+          return if @connections.nil? # already discarded
+          @connections.each do |conn|
+            conn.discard!
+          end
+          @connections = @available = @thread_cached_conns = nil
+        end
+      end
+
       # Clears the cache which maps classes and re-connects connections that
       # require reloading.
       #
       # Raises:
-      # - +ExclusiveConnectionTimeoutError+ if unable to gain ownership of all
+      # - ActiveRecord::ExclusiveConnectionTimeoutError if unable to gain ownership of all
       #   connections in the pool within a timeout interval (default duration is
-      #   +spec.config[:checkout_timeout] * 2+ seconds).
+      #   <tt>spec.config[:checkout_timeout] * 2</tt> seconds).
       def clear_reloadable_connections(raise_on_acquisition_timeout = true)
-        num_new_conns_required = 0
-
         with_exclusively_acquired_all_connections(raise_on_acquisition_timeout) do
           synchronize do
             @connections.each do |conn|
-              checkin conn
+              if conn.in_use?
+                conn.steal!
+                checkin conn
+              end
               conn.disconnect! if conn.requires_reloading?
             end
             @connections.delete_if(&:requires_reloading?)
-
             @available.clear
-
-            if @connections.size < @size
-              # because of the pruning done by this method, we might be running
-              # low on connections, while threads stuck in queue are helpless
-              # (not being able to establish new connections for themselves),
-              # see also more detailed explanation in +remove+
-              num_new_conns_required = num_waiting_in_queue - @connections.size
-            end
-
-            @connections.each do |conn|
-              @available.add conn
-            end
           end
         end
-
-        bulk_make_new_connections(num_new_conns_required) if num_new_conns_required > 0
       end
 
       # Clears the cache which maps classes and re-connects connections that
       # require reloading.
       #
-      # The pool first tries to gain ownership of all connections, if unable to
+      # The pool first tries to gain ownership of all connections. If unable to
       # do so within a timeout interval (default duration is
-      # +spec.config[:checkout_timeout] * 2+ seconds), the pool forcefully
+      # <tt>spec.config[:checkout_timeout] * 2</tt> seconds), then the pool forcefully
       # clears the cache and reloads connections without any regard for other
       # connection owning threads.
       def clear_reloadable_connections!
@@ -494,7 +518,7 @@ module ActiveRecord
       # Returns: an AbstractAdapter object.
       #
       # Raises:
-      # - ConnectionTimeoutError: no connection can be obtained from the pool.
+      # - ActiveRecord::ConnectionTimeoutError no connection can be obtained from the pool.
       def checkout(checkout_timeout = @checkout_timeout)
         checkout_and_verify(acquire_connection(checkout_timeout))
       end
@@ -503,20 +527,22 @@ module ActiveRecord
       # no longer need this connection.
       #
       # +conn+: an AbstractAdapter object, which was obtained by earlier by
-      # calling +checkout+ on this pool.
+      # calling #checkout on this pool.
       def checkin(conn)
-        synchronize do
-          remove_connection_from_thread_cache conn
+        conn.lock.synchronize do
+          synchronize do
+            remove_connection_from_thread_cache conn
 
-          conn.run_callbacks :checkin do
-            conn.expire
-          end
+            conn._run_checkin_callbacks do
+              conn.expire
+            end
 
-          @available.add conn
+            @available.add conn
+          end
         end
       end
 
-      # Remove a connection from the connection pool.  The connection will
+      # Remove a connection from the connection pool. The connection will
       # remain open and active but will no longer be managed by this pool.
       def remove(conn)
         needs_new_connection = false
@@ -528,256 +554,321 @@ module ActiveRecord
           @available.delete conn
 
           # @available.any_waiting? => true means that prior to removing this
-          # conn, the pool was at its max size (@connections.size == @size)
-          # this would mean that any threads stuck waiting in the queue wouldn't
+          # conn, the pool was at its max size (@connections.size == @size).
+          # This would mean that any threads stuck waiting in the queue wouldn't
           # know they could checkout_new_connection, so let's do it for them.
           # Because condition-wait loop is encapsulated in the Queue class
           # (that in turn is oblivious to ConnectionPool implementation), threads
-          # that are "stuck" there are helpless, they have no way of creating
+          # that are "stuck" there are helpless. They have no way of creating
           # new connections and are completely reliant on us feeding available
           # connections into the Queue.
           needs_new_connection = @available.any_waiting?
         end
 
         # This is intentionally done outside of the synchronized section as we
-        # would like not to hold the main mutex while checking out new connections,
-        # thus there is some chance that needs_new_connection information is now
+        # would like not to hold the main mutex while checking out new connections.
+        # Thus there is some chance that needs_new_connection information is now
         # stale, we can live with that (bulk_make_new_connections will make
         # sure not to exceed the pool's @size limit).
         bulk_make_new_connections(1) if needs_new_connection
       end
 
-      # Recover lost connections for the pool.  A lost connection can occur if
+      # Recover lost connections for the pool. A lost connection can occur if
       # a programmer forgets to checkin a connection at the end of a thread
       # or a thread dies unexpectedly.
       def reap
         stale_connections = synchronize do
           @connections.select do |conn|
             conn.in_use? && !conn.owner.alive?
+          end.each do |conn|
+            conn.steal!
           end
         end
 
         stale_connections.each do |conn|
-          synchronize do
-            if conn.active?
-              conn.reset!
-              checkin conn
-            else
-              remove conn
-            end
+          if conn.active?
+            conn.reset!
+            checkin conn
+          else
+            remove conn
           end
         end
       end
 
+      # Disconnect all connections that have been idle for at least
+      # +minimum_idle+ seconds. Connections currently checked out, or that were
+      # checked in less than +minimum_idle+ seconds ago, are unaffected.
+      def flush(minimum_idle = @idle_timeout)
+        return if minimum_idle.nil?
+
+        idle_connections = synchronize do
+          @connections.select do |conn|
+            !conn.in_use? && conn.seconds_idle >= minimum_idle
+          end.each do |conn|
+            conn.lease
+
+            @available.delete conn
+            @connections.delete conn
+          end
+        end
+
+        idle_connections.each do |conn|
+          conn.disconnect!
+        end
+      end
+
+      # Disconnect all currently idle connections. Connections currently checked
+      # out are unaffected.
+      def flush!
+        reap
+        flush(-1)
+      end
+
       def num_waiting_in_queue # :nodoc:
         @available.num_waiting
       end
 
-      private
-      #--
-      # this is unfortunately not concurrent
-      def bulk_make_new_connections(num_new_conns_needed)
-        num_new_conns_needed.times do
-          # try_to_checkout_new_connection will not exceed pool's @size limit
-          if new_conn = try_to_checkout_new_connection
-            # make the new_conn available to the starving threads stuck @available Queue
-            checkin(new_conn)
-          end
-        end
-      end
-
-      #--
-      # From the discussion on Github:
-      #  https://github.com/rails/rails/pull/14938#commitcomment-6601951
-      # This hook-in method allows for easier monkey-patching fixes needed by
-      # JRuby users that use Fibers.
-      def connection_cache_key(thread)
-        thread
-      end
-
-      # Take control of all existing connections so a "group" action such as
-      # reload/disconnect can be performed safely. It is no longer enough to
-      # wrap it in +synchronize+ because some pool's actions are allowed
-      # to be performed outside of the main +synchronize+ block.
-      def with_exclusively_acquired_all_connections(raise_on_acquisition_timeout = true)
-        with_new_connections_blocked do
-          attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout)
-          yield
+      # Return connection pool's usage statistic
+      # Example:
+      #
+      #    ActiveRecord::Base.connection_pool.stat # => { size: 15, connections: 1, busy: 1, dead: 0, idle: 0, waiting: 0, checkout_timeout: 5 }
+      def stat
+        synchronize do
+          {
+            size: size,
+            connections: @connections.size,
+            busy: @connections.count { |c| c.in_use? && c.owner.alive? },
+            dead: @connections.count { |c| c.in_use? && !c.owner.alive? },
+            idle: @connections.count { |c| !c.in_use? },
+            waiting: num_waiting_in_queue,
+            checkout_timeout: checkout_timeout
+          }
         end
       end
 
-      def attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout = true)
-        collected_conns = synchronize do
-          # account for our own connections
-          @connections.select {|conn| conn.owner == Thread.current}
+      private
+        #--
+        # this is unfortunately not concurrent
+        def bulk_make_new_connections(num_new_conns_needed)
+          num_new_conns_needed.times do
+            # try_to_checkout_new_connection will not exceed pool's @size limit
+            if new_conn = try_to_checkout_new_connection
+              # make the new_conn available to the starving threads stuck @available Queue
+              checkin(new_conn)
+            end
+          end
         end
 
-        newly_checked_out = []
-        timeout_time      = Time.now + (@checkout_timeout * 2)
+        #--
+        # From the discussion on GitHub:
+        #  https://github.com/rails/rails/pull/14938#commitcomment-6601951
+        # This hook-in method allows for easier monkey-patching fixes needed by
+        # JRuby users that use Fibers.
+        def connection_cache_key(thread)
+          thread
+        end
 
-        @available.with_a_bias_for(Thread.current) do
-          while true
-            synchronize do
-              return if collected_conns.size == @connections.size && @now_connecting == 0
-              remaining_timeout = timeout_time - Time.now
-              remaining_timeout = 0 if remaining_timeout < 0
-              conn = checkout_for_exclusive_access(remaining_timeout)
-              collected_conns   << conn
-              newly_checked_out << conn
-            end
+        # Take control of all existing connections so a "group" action such as
+        # reload/disconnect can be performed safely. It is no longer enough to
+        # wrap it in +synchronize+ because some pool's actions are allowed
+        # to be performed outside of the main +synchronize+ block.
+        def with_exclusively_acquired_all_connections(raise_on_acquisition_timeout = true)
+          with_new_connections_blocked do
+            attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout)
+            yield
           end
         end
-      rescue ExclusiveConnectionTimeoutError
-        # `raise_on_acquisition_timeout == false` means we are directed to ignore any
-        # timeouts and are expected to just give up: we've obtained as many connections
-        # as possible, note that in a case like that we don't return any of the
-        # `newly_checked_out` connections.
 
-        if raise_on_acquisition_timeout
+        def attempt_to_checkout_all_existing_connections(raise_on_acquisition_timeout = true)
+          collected_conns = synchronize do
+            # account for our own connections
+            @connections.select { |conn| conn.owner == Thread.current }
+          end
+
+          newly_checked_out = []
+          timeout_time      = Time.now + (@checkout_timeout * 2)
+
+          @available.with_a_bias_for(Thread.current) do
+            loop do
+              synchronize do
+                return if collected_conns.size == @connections.size && @now_connecting == 0
+                remaining_timeout = timeout_time - Time.now
+                remaining_timeout = 0 if remaining_timeout < 0
+                conn = checkout_for_exclusive_access(remaining_timeout)
+                collected_conns   << conn
+                newly_checked_out << conn
+              end
+            end
+          end
+        rescue ExclusiveConnectionTimeoutError
+          # <tt>raise_on_acquisition_timeout == false</tt> means we are directed to ignore any
+          # timeouts and are expected to just give up: we've obtained as many connections
+          # as possible, note that in a case like that we don't return any of the
+          # +newly_checked_out+ connections.
+
+          if raise_on_acquisition_timeout
+            release_newly_checked_out = true
+            raise
+          end
+        rescue Exception # if something else went wrong
+          # this can't be a "naked" rescue, because we have should return conns
+          # even for non-StandardErrors
           release_newly_checked_out = true
           raise
+        ensure
+          if release_newly_checked_out && newly_checked_out
+            # releasing only those conns that were checked out in this method, conns
+            # checked outside this method (before it was called) are not for us to release
+            newly_checked_out.each { |conn| checkin(conn) }
+          end
         end
-      rescue Exception # if something else went wrong
-        # this can't be a "naked" rescue, because we have should return conns
-        # even for non-StandardErrors
-        release_newly_checked_out = true
-        raise
-      ensure
-        if release_newly_checked_out && newly_checked_out
-          # releasing only those conns that were checked out in this method, conns
-          # checked outside this method (before it was called) are not for us to release
-          newly_checked_out.each {|conn| checkin(conn)}
-        end
-      end
 
-      #--
-      # Must be called in a synchronize block.
-      def checkout_for_exclusive_access(checkout_timeout)
-        checkout(checkout_timeout)
-      rescue ConnectionTimeoutError
-        # this block can't be easily moved into attempt_to_checkout_all_existing_connections's
-        # rescue block, because doing so would put it outside of synchronize section, without
-        # being in a critical section thread_report might become inaccurate
-        msg = "could not obtain ownership of all database connections in #{checkout_timeout} seconds"
-
-        thread_report = []
-        @connections.each do |conn|
-          unless conn.owner == Thread.current
-            thread_report << "#{conn} is owned by #{conn.owner}"
+        #--
+        # Must be called in a synchronize block.
+        def checkout_for_exclusive_access(checkout_timeout)
+          checkout(checkout_timeout)
+        rescue ConnectionTimeoutError
+          # this block can't be easily moved into attempt_to_checkout_all_existing_connections's
+          # rescue block, because doing so would put it outside of synchronize section, without
+          # being in a critical section thread_report might become inaccurate
+          msg = +"could not obtain ownership of all database connections in #{checkout_timeout} seconds"
+
+          thread_report = []
+          @connections.each do |conn|
+            unless conn.owner == Thread.current
+              thread_report << "#{conn} is owned by #{conn.owner}"
+            end
           end
+
+          msg << " (#{thread_report.join(', ')})" if thread_report.any?
+
+          raise ExclusiveConnectionTimeoutError, msg
         end
 
-        msg << " (#{thread_report.join(', ')})" if thread_report.any?
+        def with_new_connections_blocked
+          synchronize do
+            @threads_blocking_new_connections += 1
+          end
 
-        raise ExclusiveConnectionTimeoutError, msg
-      end
+          yield
+        ensure
+          num_new_conns_required = 0
 
-      def with_new_connections_blocked
-        previous_value = nil
-        synchronize do
-          previous_value, @new_cons_enabled = @new_cons_enabled, false
-        end
-        yield
-      ensure
-        synchronize { @new_cons_enabled = previous_value }
-      end
+          synchronize do
+            @threads_blocking_new_connections -= 1
 
-      # Acquire a connection by one of 1) immediately removing one
-      # from the queue of available connections, 2) creating a new
-      # connection if the pool is not at capacity, 3) waiting on the
-      # queue for a connection to become available.
-      #
-      # Raises:
-      # - ConnectionTimeoutError if a connection could not be acquired
-      #
-      #--
-      # Implementation detail: the connection returned by +acquire_connection+
-      # will already be "+connection.lease+ -ed" to the current thread.
-      def acquire_connection(checkout_timeout)
-        # NOTE: we rely on `@available.poll` and `try_to_checkout_new_connection` to
-        # `conn.lease` the returned connection (and to do this in a `synchronized`
-        # section), this is not the cleanest implementation, as ideally we would
-        # `synchronize { conn.lease }` in this method, but by leaving it to `@available.poll`
-        # and `try_to_checkout_new_connection` we can piggyback on `synchronize` sections
-        # of the said methods and avoid an additional `synchronize` overhead.
-        if conn = @available.poll || try_to_checkout_new_connection
-          conn
-        else
-          reap
-          @available.poll(checkout_timeout)
+            if @threads_blocking_new_connections.zero?
+              @available.clear
+
+              num_new_conns_required = num_waiting_in_queue
+
+              @connections.each do |conn|
+                next if conn.in_use?
+
+                @available.add conn
+                num_new_conns_required -= 1
+              end
+            end
+          end
+
+          bulk_make_new_connections(num_new_conns_required) if num_new_conns_required > 0
         end
-      end
 
-      #--
-      # if owner_thread param is omitted, this must be called in synchronize block
-      def remove_connection_from_thread_cache(conn, owner_thread = conn.owner)
-        @thread_cached_conns.delete_pair(connection_cache_key(owner_thread), conn)
-      end
-      alias_method :release, :remove_connection_from_thread_cache
+        # Acquire a connection by one of 1) immediately removing one
+        # from the queue of available connections, 2) creating a new
+        # connection if the pool is not at capacity, 3) waiting on the
+        # queue for a connection to become available.
+        #
+        # Raises:
+        # - ActiveRecord::ConnectionTimeoutError if a connection could not be acquired
+        #
+        #--
+        # Implementation detail: the connection returned by +acquire_connection+
+        # will already be "+connection.lease+ -ed" to the current thread.
+        def acquire_connection(checkout_timeout)
+          # NOTE: we rely on <tt>@available.poll</tt> and +try_to_checkout_new_connection+ to
+          # +conn.lease+ the returned connection (and to do this in a +synchronized+
+          # section). This is not the cleanest implementation, as ideally we would
+          # <tt>synchronize { conn.lease }</tt> in this method, but by leaving it to <tt>@available.poll</tt>
+          # and +try_to_checkout_new_connection+ we can piggyback on +synchronize+ sections
+          # of the said methods and avoid an additional +synchronize+ overhead.
+          if conn = @available.poll || try_to_checkout_new_connection
+            conn
+          else
+            reap
+            @available.poll(checkout_timeout)
+          end
+        end
 
-      def new_connection
-        Base.send(spec.adapter_method, spec.config).tap do |conn|
-          conn.schema_cache = schema_cache.dup if schema_cache
+        #--
+        # if owner_thread param is omitted, this must be called in synchronize block
+        def remove_connection_from_thread_cache(conn, owner_thread = conn.owner)
+          @thread_cached_conns.delete_pair(connection_cache_key(owner_thread), conn)
         end
-      end
+        alias_method :release, :remove_connection_from_thread_cache
 
-      # If the pool is not at a +@size+ limit, establish new connection. Connecting
-      # to the DB is done outside main synchronized section.
-      #--
-      # Implementation constraint: a newly established connection returned by this
-      # method must be in the +.leased+ state.
-      def try_to_checkout_new_connection
-        # first in synchronized section check if establishing new conns is allowed
-        # and increment @now_connecting, to prevent overstepping this pool's @size
-        # constraint
-        do_checkout = synchronize do
-          if @new_cons_enabled && (@connections.size + @now_connecting) < @size
-            @now_connecting += 1
+        def new_connection
+          Base.send(spec.adapter_method, spec.config).tap do |conn|
+            conn.schema_cache = schema_cache.dup if schema_cache
           end
         end
-        if do_checkout
-          begin
-            # if successfully incremented @now_connecting establish new connection
-            # outside of synchronized section
-            conn = checkout_new_connection
-          ensure
-            synchronize do
-              if conn
-                adopt_connection(conn)
-                # returned conn needs to be already leased
-                conn.lease
+
+        # If the pool is not at a <tt>@size</tt> limit, establish new connection. Connecting
+        # to the DB is done outside main synchronized section.
+        #--
+        # Implementation constraint: a newly established connection returned by this
+        # method must be in the +.leased+ state.
+        def try_to_checkout_new_connection
+          # first in synchronized section check if establishing new conns is allowed
+          # and increment @now_connecting, to prevent overstepping this pool's @size
+          # constraint
+          do_checkout = synchronize do
+            if @threads_blocking_new_connections.zero? && (@connections.size + @now_connecting) < @size
+              @now_connecting += 1
+            end
+          end
+          if do_checkout
+            begin
+              # if successfully incremented @now_connecting establish new connection
+              # outside of synchronized section
+              conn = checkout_new_connection
+            ensure
+              synchronize do
+                if conn
+                  adopt_connection(conn)
+                  # returned conn needs to be already leased
+                  conn.lease
+                end
+                @now_connecting -= 1
               end
-              @now_connecting -= 1
             end
           end
         end
-      end
 
-      def adopt_connection(conn)
-        conn.pool = self
-        @connections << conn
-      end
+        def adopt_connection(conn)
+          conn.pool = self
+          @connections << conn
+        end
 
-      def checkout_new_connection
-        raise ConnectionNotEstablished unless @automatic_reconnect
-        new_connection
-      end
+        def checkout_new_connection
+          raise ConnectionNotEstablished unless @automatic_reconnect
+          new_connection
+        end
 
-      def checkout_and_verify(c)
-        c.run_callbacks :checkout do
-          c.verify!
+        def checkout_and_verify(c)
+          c._run_checkout_callbacks do
+            c.verify!
+          end
+          c
+        rescue
+          remove c
+          c.disconnect!
+          raise
         end
-        c
-      rescue
-        remove c
-        c.disconnect!
-        raise
-      end
     end
 
     # ConnectionHandler is a collection of ConnectionPool objects. It is used
-    # for keeping separate connection pools for Active Record models that connect
-    # to different databases.
+    # for keeping separate connection pools that connect to different databases.
     #
     # For example, suppose that you have 5 models, with the following hierarchy:
     #
@@ -788,7 +879,7 @@ module ActiveRecord
     #   end
     #
     #   class Book < ActiveRecord::Base
-    #     establish_connection "library_db"
+    #     establish_connection :library_db
     #   end
     #
     #   class ScaryBook < Book
@@ -819,28 +910,63 @@ module ActiveRecord
     # ConnectionHandler accessible via ActiveRecord::Base.connection_handler.
     # All Active Record models use this handler to determine the connection pool that they
     # should use.
+    #
+    # The ConnectionHandler class is not coupled with the Active models, as it has no knowledge
+    # about the model. The model needs to pass a specification name to the handler,
+    # in order to look up the correct connection pool.
     class ConnectionHandler
-      def initialize
-        # These caches are keyed by klass.name, NOT klass. Keying them by klass
-        # alone would lead to memory leaks in development mode as all previous
-        # instances of the class would stay in memory.
-        @owner_to_pool = ThreadSafe::Cache.new(:initial_capacity => 2) do |h,k|
-          h[k] = ThreadSafe::Cache.new(:initial_capacity => 2)
+      def self.unowned_pool_finalizer(pid_map) # :nodoc:
+        lambda do |_|
+          discard_unowned_pools(pid_map)
         end
-        @class_to_pool = ThreadSafe::Cache.new(:initial_capacity => 2) do |h,k|
-          h[k] = ThreadSafe::Cache.new
+      end
+
+      def self.discard_unowned_pools(pid_map) # :nodoc:
+        pid_map.each do |pid, pools|
+          pools.values.compact.each(&:discard!) unless pid == Process.pid
         end
       end
 
+      def initialize
+        # These caches are keyed by spec.name (ConnectionSpecification#name).
+        @owner_to_pool = Concurrent::Map.new(initial_capacity: 2) do |h, k|
+          # Discard the parent's connection pools immediately; we have no need
+          # of them
+          ConnectionHandler.discard_unowned_pools(h)
+
+          h[k] = Concurrent::Map.new(initial_capacity: 2)
+        end
+
+        # Backup finalizer: if the forked child never needed a pool, the above
+        # early discard has not occurred
+        ObjectSpace.define_finalizer self, ConnectionHandler.unowned_pool_finalizer(@owner_to_pool)
+      end
+
       def connection_pool_list
         owner_to_pool.values.compact
       end
       alias :connection_pools :connection_pool_list
 
-      def establish_connection(owner, spec)
-        @class_to_pool.clear
-        raise RuntimeError, "Anonymous class is not allowed." unless owner.name
-        owner_to_pool[owner.name] = ConnectionAdapters::ConnectionPool.new(spec)
+      def establish_connection(config)
+        resolver = ConnectionSpecification::Resolver.new(Base.configurations)
+        spec = resolver.spec(config)
+
+        remove_connection(spec.name)
+
+        message_bus = ActiveSupport::Notifications.instrumenter
+        payload = {
+          connection_id: object_id
+        }
+        if spec
+          payload[:spec_name] = spec.name
+          payload[:config] = spec.config
+        end
+
+        message_bus.instrument("!connection.active_record", payload) do
+          owner_to_pool[spec.name] = ConnectionAdapters::ConnectionPool.new(spec)
+        end
+
+        owner_to_pool[spec.name]
       end
 
       # Returns true if there are any active connections among the connection
@@ -857,6 +983,8 @@ module ActiveRecord
       end
 
       # Clears the cache which maps classes.
+      #
+      # See ConnectionPool#clear_reloadable_connections! for details.
       def clear_reloadable_connections!
         connection_pool_list.each(&:clear_reloadable_connections!)
       end
@@ -865,107 +993,72 @@ module ActiveRecord
         connection_pool_list.each(&:disconnect!)
       end
 
+      # Disconnects all currently idle connections.
+      #
+      # See ConnectionPool#flush! for details.
+      def flush_idle_connections!
+        connection_pool_list.each(&:flush!)
+      end
+
       # Locate the connection of the nearest super class. This can be an
       # active or defined connection: if it is the latter, it will be
       # opened and set as the active connection for the class it was defined
       # for (not necessarily the current class).
-      def retrieve_connection(klass) #:nodoc:
-        pool = retrieve_connection_pool(klass)
-        raise ConnectionNotEstablished, "No connection pool for #{klass}" unless pool
-        conn = pool.connection
-        raise ConnectionNotEstablished, "No connection for #{klass} in connection pool" unless conn
-        conn
+      def retrieve_connection(spec_name) #:nodoc:
+        pool = retrieve_connection_pool(spec_name)
+        raise ConnectionNotEstablished, "No connection pool with '#{spec_name}' found." unless pool
+        pool.connection
       end
 
       # Returns true if a connection that's accessible to this class has
       # already been opened.
-      def connected?(klass)
-        conn = retrieve_connection_pool(klass)
-        conn && conn.connected?
+      def connected?(spec_name)
+        pool = retrieve_connection_pool(spec_name)
+        pool && pool.connected?
       end
 
       # Remove the connection for this class. This will close the active
       # connection and the defined connection (if they exist). The result
-      # can be used as an argument for establish_connection, for easily
+      # can be used as an argument for #establish_connection, for easily
       # re-establishing the connection.
-      def remove_connection(owner)
-        if pool = owner_to_pool.delete(owner.name)
-          @class_to_pool.clear
+      def remove_connection(spec_name)
+        if pool = owner_to_pool.delete(spec_name)
           pool.automatic_reconnect = false
           pool.disconnect!
           pool.spec.config
         end
       end
 
-      # Retrieving the connection pool happens a lot so we cache it in @class_to_pool.
+      # Retrieving the connection pool happens a lot, so we cache it in @owner_to_pool.
       # This makes retrieving the connection pool O(1) once the process is warm.
       # When a connection is established or removed, we invalidate the cache.
-      #
-      # Ideally we would use #fetch here, as class_to_pool[klass] may sometimes be nil.
-      # However, benchmarking (https://gist.github.com/jonleighton/3552829) showed that
-      # #fetch is significantly slower than #[]. So in the nil case, no caching will
-      # take place, but that's ok since the nil case is not the common one that we wish
-      # to optimise for.
-      def retrieve_connection_pool(klass)
-        class_to_pool[klass.name] ||= begin
-          until pool = pool_for(klass)
-            klass = klass.superclass
-            break unless klass <= Base
-          end
-
-          class_to_pool[klass.name] = pool
-        end
-      end
-
-      private
-
-      def owner_to_pool
-        @owner_to_pool[Process.pid]
-      end
-
-      def class_to_pool
-        @class_to_pool[Process.pid]
-      end
-
-      def pool_for(owner)
-        owner_to_pool.fetch(owner.name) {
-          if ancestor_pool = pool_from_any_process_for(owner)
+      def retrieve_connection_pool(spec_name)
+        owner_to_pool.fetch(spec_name) do
+          # Check if a connection was previously established in an ancestor process,
+          # which may have been forked.
+          if ancestor_pool = pool_from_any_process_for(spec_name)
             # A connection was established in an ancestor process that must have
             # subsequently forked. We can't reuse the connection, but we can copy
             # the specification and establish a new connection with it.
-            establish_connection(owner, ancestor_pool.spec).tap do |pool|
+            establish_connection(ancestor_pool.spec.to_hash).tap do |pool|
               pool.schema_cache = ancestor_pool.schema_cache if ancestor_pool.schema_cache
             end
           else
-            owner_to_pool[owner.name] = nil
+            owner_to_pool[spec_name] = nil
           end
-        }
-      end
-
-      def pool_from_any_process_for(owner)
-        owner_to_pool = @owner_to_pool.values.find { |v| v[owner.name] }
-        owner_to_pool && owner_to_pool[owner.name]
-      end
-    end
-
-    class ConnectionManagement
-      def initialize(app)
-        @app = app
+        end
       end
 
-      def call(env)
-        testing = env['rack.test']
+      private
 
-        response = @app.call(env)
-        response[2] = ::Rack::BodyProxy.new(response[2]) do
-          ActiveRecord::Base.clear_active_connections! unless testing
+        def owner_to_pool
+          @owner_to_pool[Process.pid]
         end
 
-        response
-      rescue Exception
-        ActiveRecord::Base.clear_active_connections! unless testing
-        raise
-      end
+        def pool_from_any_process_for(spec_name)
+          owner_to_pool = @owner_to_pool.values.reverse.find { |v| v[spec_name] }
+          owner_to_pool && owner_to_pool[spec_name]
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
index 30b2fca2ca..1305216be2 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb
@@ -1,7 +1,10 @@
+# frozen_string_literal: true
+
+require "active_support/deprecation"
+
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
     module DatabaseLimits
-
       # Returns the maximum length of a table alias.
       def table_alias_length
         255
@@ -11,16 +14,18 @@ module ActiveRecord
       def column_name_length
         64
       end
+      deprecate :column_name_length
 
       # Returns the maximum length of a table name.
       def table_name_length
         64
       end
+      deprecate :table_name_length
 
       # Returns the maximum allowed length for an index name. This
       # limit is enforced by \Rails and is less than or equal to
-      # <tt>index_name_length</tt>. The gap between
-      # <tt>index_name_length</tt> is to allow internal \Rails
+      # #index_name_length. The gap between
+      # #index_name_length is to allow internal \Rails
       # operations to use prefixes in temporary operations.
       def allowed_index_name_length
         index_name_length
@@ -35,19 +40,22 @@ module ActiveRecord
       def columns_per_table
         1024
       end
+      deprecate :columns_per_table
 
       # Returns the maximum number of indexes per table.
       def indexes_per_table
         16
       end
+      deprecate :indexes_per_table
 
       # Returns the maximum number of columns in a multicolumn index.
       def columns_per_multicolumn_index
         16
       end
+      deprecate :columns_per_multicolumn_index
 
       # Returns the maximum number of elements in an IN (x,y,z) clause.
-      # nil means no limit.
+      # +nil+ means no limit.
       def in_clause_length
         nil
       end
@@ -56,12 +64,18 @@ module ActiveRecord
       def sql_query_length
         1048575
       end
+      deprecate :sql_query_length
 
       # Returns maximum number of joins in a single query.
       def joins_per_query
         256
       end
+      deprecate :joins_per_query
 
+      private
+        def bind_params_length
+          65535
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
index 38dd9578fe..0059f0b773 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
     module DatabaseStatements
@@ -7,29 +9,58 @@ module ActiveRecord
       end
 
       # Converts an arel AST to SQL
-      def to_sql(arel, binds = [])
-        if arel.respond_to?(:ast)
-          collected = visitor.accept(arel.ast, collector)
-          collected.compile(binds.dup, self)
+      def to_sql(arel_or_sql_string, binds = [])
+        sql, _ = to_sql_and_binds(arel_or_sql_string, binds)
+        sql
+      end
+
+      def to_sql_and_binds(arel_or_sql_string, binds = []) # :nodoc:
+        if arel_or_sql_string.respond_to?(:ast)
+          unless binds.empty?
+            raise "Passing bind parameters with an arel AST is forbidden. " \
+              "The values must be stored on the AST directly"
+          end
+          sql, binds = visitor.compile(arel_or_sql_string.ast, collector)
+          [sql.freeze, binds || []]
         else
-          arel
+          [arel_or_sql_string.dup.freeze, binds]
         end
       end
+      private :to_sql_and_binds
 
       # This is used in the StatementCache object. It returns an object that
       # can be used to query the database repeatedly.
-      def cacheable_query(arel) # :nodoc:
+      def cacheable_query(klass, arel) # :nodoc:
         if prepared_statements
-          ActiveRecord::StatementCache.query visitor, arel.ast
+          sql, binds = visitor.compile(arel.ast, collector)
+          query = klass.query(sql)
         else
-          ActiveRecord::StatementCache.partial_query visitor, arel.ast, collector
+          collector = klass.partial_query_collector
+          parts, binds = visitor.compile(arel.ast, collector)
+          query = klass.partial_query(parts)
         end
+        [query, binds]
       end
 
       # Returns an ActiveRecord::Result instance.
-      def select_all(arel, name = nil, binds = [])
-        arel, binds = binds_from_relation arel, binds
-        select(to_sql(arel, binds), name, binds)
+      def select_all(arel, name = nil, binds = [], preparable: nil)
+        arel = arel_from_relation(arel)
+        sql, binds = to_sql_and_binds(arel, binds)
+
+        if !prepared_statements || (arel.is_a?(String) && preparable.nil?)
+          preparable = false
+        elsif binds.length > bind_params_length
+          sql, binds = unprepared_statement { to_sql_and_binds(arel) }
+          preparable = false
+        else
+          preparable = visitor.preparable
+        end
+
+        if prepared_statements && preparable
+          select_prepared(sql, name, binds)
+        else
+          select(sql, name, binds)
+        end
       end
 
       # Returns a record hash with the column names as keys and column values
@@ -40,47 +71,61 @@ module ActiveRecord
 
       # Returns a single value from a record
       def select_value(arel, name = nil, binds = [])
-        arel, binds = binds_from_relation arel, binds
-        if result = select_rows(to_sql(arel, binds), name, binds).first
-          result.first
-        end
+        single_value_from_rows(select_rows(arel, name, binds))
       end
 
       # Returns an array of the values of the first column in a select:
       #   select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
-      def select_values(arel, name = nil)
-        arel, binds = binds_from_relation arel, []
-        select_rows(to_sql(arel, binds), name, binds).map(&:first)
+      def select_values(arel, name = nil, binds = [])
+        select_rows(arel, name, binds).map(&:first)
       end
 
       # Returns an array of arrays containing the field values.
       # Order is the same as that returned by +columns+.
-      def select_rows(sql, name = nil, binds = [])
+      def select_rows(arel, name = nil, binds = [])
+        select_all(arel, name, binds).rows
+      end
+
+      def query_value(sql, name = nil) # :nodoc:
+        single_value_from_rows(query(sql, name))
+      end
+
+      def query_values(sql, name = nil) # :nodoc:
+        query(sql, name).map(&:first)
       end
-      undef_method :select_rows
 
-      # Executes the SQL statement in the context of this connection.
+      def query(sql, name = nil) # :nodoc:
+        exec_query(sql, name).rows
+      end
+
+      # Executes the SQL statement in the context of this connection and returns
+      # the raw result from the connection adapter.
+      # Note: depending on your database connector, the result returned by this
+      # method may be manually memory managed. Consider using the exec_query
+      # wrapper instead.
       def execute(sql, name = nil)
+        raise NotImplementedError
       end
-      undef_method :execute
 
       # Executes +sql+ statement in the context of this connection using
       # +binds+ as the bind substitutes. +name+ is logged along with
       # the executed +sql+ statement.
-      def exec_query(sql, name = 'SQL', binds = [])
+      def exec_query(sql, name = "SQL", binds = [], prepare: false)
+        raise NotImplementedError
       end
 
       # Executes insert +sql+ statement in the context of this connection using
       # +binds+ as the bind substitutes. +name+ is logged along with
       # the executed +sql+ statement.
-      def exec_insert(sql, name, binds, pk = nil, sequence_name = nil)
+      def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil)
+        sql, binds = sql_for_insert(sql, pk, nil, sequence_name, binds)
         exec_query(sql, name, binds)
       end
 
       # Executes delete +sql+ statement in the context of this connection using
       # +binds+ as the bind substitutes. +name+ is logged along with
       # the executed +sql+ statement.
-      def exec_delete(sql, name, binds)
+      def exec_delete(sql, name = nil, binds = [])
         exec_query(sql, name, binds)
       end
 
@@ -92,39 +137,43 @@ module ActiveRecord
       # Executes update +sql+ statement in the context of this connection using
       # +binds+ as the bind substitutes. +name+ is logged along with
       # the executed +sql+ statement.
-      def exec_update(sql, name, binds)
+      def exec_update(sql, name = nil, binds = [])
         exec_query(sql, name, binds)
       end
 
-      # Returns the last auto-generated ID from the affected table.
+      # Executes an INSERT query and returns the new record's ID
       #
-      # +id_value+ will be returned unless the value is nil, in
+      # +id_value+ will be returned unless the value is +nil+, in
       # which case the database will attempt to calculate the last inserted
       # id and return that value.
       #
       # If the next id was calculated in advance (as in Oracle), it should be
       # passed in as +id_value+.
       def insert(arel, name = nil, pk = nil, id_value = nil, sequence_name = nil, binds = [])
-        sql, binds = sql_for_insert(to_sql(arel, binds), pk, id_value, sequence_name, binds)
-        value      = exec_insert(sql, name, binds, pk, sequence_name)
+        sql, binds = to_sql_and_binds(arel, binds)
+        value = exec_insert(sql, name, binds, pk, sequence_name)
         id_value || last_inserted_id(value)
       end
+      alias create insert
 
       # Executes the update statement and returns the number of rows affected.
       def update(arel, name = nil, binds = [])
-        exec_update(to_sql(arel, binds), name, binds)
+        sql, binds = to_sql_and_binds(arel, binds)
+        exec_update(sql, name, binds)
       end
 
       # Executes the delete statement and returns the number of rows affected.
       def delete(arel, name = nil, binds = [])
-        exec_delete(to_sql(arel, binds), name, binds)
+        sql, binds = to_sql_and_binds(arel, binds)
+        exec_delete(sql, name, binds)
       end
 
       # Returns +true+ when the connection adapter supports prepared statement
       # caching, otherwise returns +false+
-      def supports_statement_cache?
-        false
+      def supports_statement_cache? # :nodoc:
+        true
       end
+      deprecate :supports_statement_cache?
 
       # Runs the given block in a database transaction, and returns the result
       # of the block.
@@ -137,7 +186,7 @@ module ActiveRecord
       #
       # In order to get around this problem, #transaction will emulate the effect
       # of nested transactions, by using savepoints:
-      # http://dev.mysql.com/doc/refman/5.6/en/savepoint.html
+      # https://dev.mysql.com/doc/refman/5.7/en/savepoint.html
       # Savepoints are supported by MySQL and PostgreSQL. SQLite3 version >= '3.6.8'
       # supports savepoints.
       #
@@ -189,19 +238,17 @@ module ActiveRecord
       # You should consult the documentation for your database to understand the
       # semantics of these different levels:
       #
-      # * http://www.postgresql.org/docs/current/static/transaction-iso.html
-      # * https://dev.mysql.com/doc/refman/5.6/en/set-transaction.html
+      # * https://www.postgresql.org/docs/current/static/transaction-iso.html
+      # * https://dev.mysql.com/doc/refman/5.7/en/set-transaction.html
       #
-      # An <tt>ActiveRecord::TransactionIsolationError</tt> will be raised if:
+      # An ActiveRecord::TransactionIsolationError will be raised if:
       #
       # * The adapter does not support setting the isolation level
       # * You are joining an existing open transaction
       # * You are creating a nested (savepoint) transaction
       #
-      # The mysql, mysql2 and postgresql adapters support setting the transaction
-      # isolation level. However, support is disabled for MySQL versions below 5,
-      # because they are affected by a bug[http://bugs.mysql.com/bug.php?id=39170]
-      # which means the isolation level gets persisted outside the transaction.
+      # The mysql2 and postgresql adapters support setting the transaction
+      # isolation level.
       def transaction(requires_new: nil, isolation: nil, joinable: true)
         if !requires_new && current_transaction.joinable?
           if isolation
@@ -217,14 +264,16 @@ module ActiveRecord
 
       attr_reader :transaction_manager #:nodoc:
 
-      delegate :within_new_transaction, :open_transactions, :current_transaction, :begin_transaction, :commit_transaction, :rollback_transaction, to: :transaction_manager
+      delegate :within_new_transaction, :open_transactions, :current_transaction, :begin_transaction,
+               :commit_transaction, :rollback_transaction, :materialize_transactions,
+               :disable_lazy_transactions!, :enable_lazy_transactions!, to: :transaction_manager
 
       def transaction_open?
         current_transaction.open?
       end
 
       def reset_transaction #:nodoc:
-        @transaction_manager = TransactionManager.new(self)
+        @transaction_manager = ConnectionAdapters::TransactionManager.new(self)
       end
 
       # Register a record with the current transaction so that its after_commit and after_rollback callbacks
@@ -271,9 +320,6 @@ module ActiveRecord
         exec_rollback_to_savepoint(name)
       end
 
-      def exec_rollback_to_savepoint(name = nil) #:nodoc:
-      end
-
       def default_sequence_name(table, column)
         nil
       end
@@ -285,93 +331,132 @@ module ActiveRecord
 
       # Inserts the given fixture into the table. Overridden in adapters that require
       # something beyond a simple insert (eg. Oracle).
+      # Most of adapters should implement `insert_fixtures` that leverages bulk SQL insert.
+      # We keep this method to provide fallback
+      # for databases like sqlite that do not support bulk inserts.
       def insert_fixture(fixture, table_name)
-        columns = schema_cache.columns_hash(table_name)
+        fixture = fixture.stringify_keys
 
+        columns = schema_cache.columns_hash(table_name)
         binds = fixture.map do |name, value|
-          type = lookup_cast_type_from_column(columns[name])
-          Relation::QueryAttribute.new(name, value, type)
-        end
-        key_list = fixture.keys.map { |name| quote_column_name(name) }
-        value_list = prepare_binds_for_database(binds).map do |value|
-          begin
-            quote(value)
-          rescue TypeError
-            quote(YAML.dump(value))
+          if column = columns[name]
+            type = lookup_cast_type_from_column(column)
+            Relation::QueryAttribute.new(name, value, type)
+          else
+            raise Fixture::FixtureError, %(table "#{table_name}" has no column named #{name.inspect}.)
           end
         end
 
-        execute "INSERT INTO #{quote_table_name(table_name)} (#{key_list.join(', ')}) VALUES (#{value_list.join(', ')})", 'Fixture Insert'
+        table = Arel::Table.new(table_name)
+
+        values = binds.map do |bind|
+          value = with_yaml_fallback(bind.value_for_database)
+          [table[bind.name], value]
+        end
+
+        manager = Arel::InsertManager.new
+        manager.into(table)
+        manager.insert(values)
+        execute manager.to_sql, "Fixture Insert"
       end
 
-      def empty_insert_statement_value
+      # Inserts a set of fixtures into the table. Overridden in adapters that require
+      # something beyond a simple insert (eg. Oracle).
+      def insert_fixtures(fixtures, table_name)
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          `insert_fixtures` is deprecated and will be removed in the next version of Rails.
+          Consider using `insert_fixtures_set` for performance improvement.
+        MSG
+        return if fixtures.empty?
+
+        execute(build_fixture_sql(fixtures, table_name), "Fixtures Insert")
+      end
+
+      def insert_fixtures_set(fixture_set, tables_to_delete = [])
+        fixture_inserts = fixture_set.map do |table_name, fixtures|
+          next if fixtures.empty?
+
+          build_fixture_sql(fixtures, table_name)
+        end.compact
+
+        table_deletes = tables_to_delete.map { |table| +"DELETE FROM #{quote_table_name table}" }
+        total_sql = Array.wrap(combine_multi_statements(table_deletes + fixture_inserts))
+
+        disable_referential_integrity do
+          transaction(requires_new: true) do
+            total_sql.each do |sql|
+              execute sql, "Fixtures Load"
+              yield if block_given?
+            end
+          end
+        end
+      end
+
+      def empty_insert_statement_value(primary_key = nil)
         "DEFAULT VALUES"
       end
 
       # Sanitizes the given LIMIT parameter in order to prevent SQL injection.
       #
       # The +limit+ may be anything that can evaluate to a string via #to_s. It
-      # should look like an integer, or a comma-delimited list of integers, or
-      # an Arel SQL literal.
+      # should look like an integer, or an Arel SQL literal.
       #
       # Returns Integer and Arel::Nodes::SqlLiteral limits as is.
-      # Returns the sanitized limit parameter, either as an integer, or as a
-      # string which contains a comma-delimited list of integers.
       def sanitize_limit(limit)
         if limit.is_a?(Integer) || limit.is_a?(Arel::Nodes::SqlLiteral)
           limit
-        elsif limit.to_s.include?(',')
-          Arel.sql limit.to_s.split(',').map{ |i| Integer(i) }.join(',')
         else
           Integer(limit)
         end
       end
 
-      # The default strategy for an UPDATE with joins is to use a subquery. This doesn't work
-      # on MySQL (even when aliasing the tables), but MySQL allows using JOIN directly in
-      # an UPDATE statement, so in the MySQL adapters we redefine this to do that.
-      def join_to_update(update, select) #:nodoc:
-        key = update.key
-        subselect = subquery_for(key, select)
-
-        update.where key.in(subselect)
-      end
+      private
+        def default_insert_value(column)
+          Arel.sql("DEFAULT")
+        end
 
-      def join_to_delete(delete, select, key) #:nodoc:
-        subselect = subquery_for(key, select)
+        def build_fixture_sql(fixtures, table_name)
+          columns = schema_cache.columns_hash(table_name)
+
+          values = fixtures.map do |fixture|
+            fixture = fixture.stringify_keys
+
+            unknown_columns = fixture.keys - columns.keys
+            if unknown_columns.any?
+              raise Fixture::FixtureError, %(table "#{table_name}" has no columns named #{unknown_columns.map(&:inspect).join(', ')}.)
+            end
+
+            columns.map do |name, column|
+              if fixture.key?(name)
+                type = lookup_cast_type_from_column(column)
+                bind = Relation::QueryAttribute.new(name, fixture[name], type)
+                with_yaml_fallback(bind.value_for_database)
+              else
+                default_insert_value(column)
+              end
+            end
+          end
 
-        delete.where key.in(subselect)
-      end
+          table = Arel::Table.new(table_name)
+          manager = Arel::InsertManager.new
+          manager.into(table)
+          columns.each_key { |column| manager.columns << table[column] }
+          manager.values = manager.create_values_list(values)
 
-      protected
+          manager.to_sql
+        end
 
-        # Returns a subquery for the given key using the join information.
-        def subquery_for(key, select)
-          subselect = select.clone
-          subselect.projections = [key]
-          subselect
+        def combine_multi_statements(total_sql)
+          total_sql.join(";\n")
         end
 
         # Returns an ActiveRecord::Result instance.
         def select(sql, name = nil, binds = [])
-          exec_query(sql, name, binds)
+          exec_query(sql, name, binds, prepare: false)
         end
 
-
-        # Returns the last auto-generated ID from the affected table.
-        def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
-          execute(sql, name)
-          id_value
-        end
-
-        # Executes the update statement and returns the number of rows affected.
-        def update_sql(sql, name = nil)
-          execute(sql, name)
-        end
-
-        # Executes the delete statement and returns the number of rows affected.
-        def delete_sql(sql, name = nil)
-          update_sql(sql, name)
+        def select_prepared(sql, name = nil, binds = [])
+          exec_query(sql, name, binds, prepare: true)
         end
 
         def sql_for_insert(sql, pk, id_value, sequence_name, binds)
@@ -379,15 +464,31 @@ module ActiveRecord
         end
 
         def last_inserted_id(result)
-          row = result.rows.first
+          single_value_from_rows(result.rows)
+        end
+
+        def single_value_from_rows(rows)
+          row = rows.first
           row && row.first
         end
 
-        def binds_from_relation(relation, binds)
-          if relation.is_a?(Relation) && binds.empty?
-            relation, binds = relation.arel, relation.bound_attributes
+        def arel_from_relation(relation)
+          if relation.is_a?(Relation)
+            relation.arel
+          else
+            relation
+          end
+        end
+
+        # Fixture value is quoted by Arel, however scalar values
+        # are not quotable. In this case we want to convert
+        # the column value to YAML.
+        def with_yaml_fallback(value)
+          if value.is_a?(Hash) || value.is_a?(Array)
+            YAML.dump(value)
+          else
+            value
           end
-          [relation, binds]
         end
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb b/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
index 5e27cfe507..8aeb934ec2 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
@@ -1,9 +1,16 @@
+# frozen_string_literal: true
+
+require "concurrent/map"
+
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
     module QueryCache
       class << self
         def included(base) #:nodoc:
           dirties_query_cache base, :insert, :update, :delete, :rollback_to_savepoint, :rollback_db_transaction
+
+          base.set_callback :checkout, :after, :configure_query_cache!
+          base.set_callback :checkin, :after, :disable_query_cache!
         end
 
         def dirties_query_cache(base, *method_names)
@@ -18,11 +25,32 @@ module ActiveRecord
         end
       end
 
+      module ConnectionPoolConfiguration
+        def initialize(*)
+          super
+          @query_cache_enabled = Concurrent::Map.new { false }
+        end
+
+        def enable_query_cache!
+          @query_cache_enabled[connection_cache_key(Thread.current)] = true
+          connection.enable_query_cache! if active_connection?
+        end
+
+        def disable_query_cache!
+          @query_cache_enabled.delete connection_cache_key(Thread.current)
+          connection.disable_query_cache! if active_connection?
+        end
+
+        def query_cache_enabled
+          @query_cache_enabled[connection_cache_key(Thread.current)]
+        end
+      end
+
       attr_reader :query_cache, :query_cache_enabled
 
       def initialize(*)
         super
-        @query_cache         = Hash.new { |h,sql| h[sql] = {} }
+        @query_cache         = Hash.new { |h, sql| h[sql] = {} }
         @query_cache_enabled = false
       end
 
@@ -41,6 +69,7 @@ module ActiveRecord
 
       def disable_query_cache!
         @query_cache_enabled = false
+        clear_query_cache
       end
 
       # Disable the query cache within the block.
@@ -58,14 +87,16 @@ module ActiveRecord
       # the same SQL query and repeatedly return the same result each time, silently
       # undermining the randomness you were expecting.
       def clear_query_cache
-        @query_cache.clear
+        @lock.synchronize do
+          @query_cache.clear
+        end
       end
 
-      def select_all(arel, name = nil, binds = [])
+      def select_all(arel, name = nil, binds = [], preparable: nil)
         if @query_cache_enabled && !locked?(arel)
-          arel, binds = binds_from_relation arel, binds
-          sql = to_sql(arel, binds)
-          cache_sql(sql, binds) { super(sql, name, binds) }
+          arel = arel_from_relation(arel)
+          sql, binds = to_sql_and_binds(arel, binds)
+          cache_sql(sql, name, binds) { super(sql, name, binds, preparable: preparable) }
         else
           super
         end
@@ -73,23 +104,45 @@ module ActiveRecord
 
       private
 
-      def cache_sql(sql, binds)
-        result =
-          if @query_cache[sql].key?(binds)
-            ActiveSupport::Notifications.instrument("sql.active_record",
-              :sql => sql, :binds => binds, :name => "CACHE", :connection_id => object_id)
-            @query_cache[sql][binds]
-          else
-            @query_cache[sql][binds] = yield
+        def cache_sql(sql, name, binds)
+          @lock.synchronize do
+            result =
+              if @query_cache[sql].key?(binds)
+                ActiveSupport::Notifications.instrument(
+                  "sql.active_record",
+                  cache_notification_info(sql, name, binds)
+                )
+                @query_cache[sql][binds]
+              else
+                @query_cache[sql][binds] = yield
+              end
+            result.dup
           end
-        result.dup
-      end
+        end
 
-      # If arel is locked this is a SELECT ... FOR UPDATE or somesuch. Such
-      # queries should not be cached.
-      def locked?(arel)
-        arel.respond_to?(:locked) && arel.locked
-      end
+        # Database adapters can override this method to
+        # provide custom cache information.
+        def cache_notification_info(sql, name, binds)
+          {
+            sql: sql,
+            binds: binds,
+            type_casted_binds: -> { type_casted_binds(binds) },
+            name: name,
+            connection_id: object_id,
+            cached: true
+          }
+        end
+
+        # If arel is locked this is a SELECT ... FOR UPDATE or somesuch. Such
+        # queries should not be cached.
+        def locked?(arel)
+          arel = arel.arel if arel.is_a?(Relation)
+          arel.respond_to?(:locked) && arel.locked
+        end
+
+        def configure_query_cache!
+          enable_query_cache! if pool.query_cache_enabled
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb b/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
index 2c7409b2dc..07e86afe9a 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/quoting.rb
@@ -1,22 +1,18 @@
-require 'active_support/core_ext/big_decimal/conversions'
+# frozen_string_literal: true
+
+require "active_support/core_ext/big_decimal/conversions"
+require "active_support/multibyte/chars"
 
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
     module Quoting
       # Quotes the column value to help prevent
-      # {SQL injection attacks}[http://en.wikipedia.org/wiki/SQL_injection].
-      def quote(value, column = nil)
-        # records are quoted as their primary key
-        return value.quoted_id if value.respond_to?(:quoted_id)
+      # {SQL injection attacks}[https://en.wikipedia.org/wiki/SQL_injection].
+      def quote(value)
+        value = id_value_for_database(value) if value.is_a?(Base)
 
-        if column
-          ActiveSupport::Deprecation.warn(<<-MSG.squish)
-            Passing a column to `quote` has been deprecated. It is only used
-            for type casting, which should be handled elsewhere. See
-            https://github.com/rails/arel/commit/6160bfbda1d1781c3b08a33ec4955f170e95be11
-            for more information.
-          MSG
-          value = type_cast_from_column(column, value)
+        if value.respond_to?(:value_for_database)
+          value = value.value_for_database
         end
 
         _quote(value)
@@ -26,9 +22,7 @@ module ActiveRecord
       # SQLite does not understand dates, so this method will convert a Date
       # to a String.
       def type_cast(value, column = nil)
-        if value.respond_to?(:quoted_id) && value.respond_to?(:id)
-          return value.id
-        end
+        value = id_value_for_database(value) if value.is_a?(Base)
 
         if column
           value = type_cast_from_column(column, value)
@@ -43,9 +37,9 @@ module ActiveRecord
       # If you are having to call this function, you are likely doing something
       # wrong. The column does not have sufficient type information if the user
       # provided a custom type on the class level either explicitly (via
-      # `attribute`) or implicitly (via `serialize`,
-      # `time_zone_aware_attributes`). In almost all cases, the sql type should
-      # only be used to change quoting behavior, when the primitive to
+      # Attributes::ClassMethods#attribute) or implicitly (via
+      # AttributeMethods::Serialization::ClassMethods#serialize, +time_zone_aware_attributes+).
+      # In almost all cases, the sql type should only be used to change quoting behavior, when the primitive to
       # represent the type doesn't sufficiently reflect the differences
       # (varchar vs binary) for example. The type used to get this primitive
       # should have been provided before reaching the connection adapter.
@@ -58,31 +52,20 @@ module ActiveRecord
         end
       end
 
-      # See docs for +type_cast_from_column+
+      # See docs for #type_cast_from_column
       def lookup_cast_type_from_column(column) # :nodoc:
         lookup_cast_type(column.sql_type)
       end
 
-      def fetch_type_metadata(sql_type)
-        cast_type = lookup_cast_type(sql_type)
-        SqlTypeMetadata.new(
-          sql_type: sql_type,
-          type: cast_type.type,
-          limit: cast_type.limit,
-          precision: cast_type.precision,
-          scale: cast_type.scale,
-        )
-      end
-
       # Quotes a string, escaping any ' (single quote) and \ (backslash)
       # characters.
       def quote_string(s)
-        s.gsub('\\'.freeze, '\&\&'.freeze).gsub("'".freeze, "''".freeze) # ' (for ruby-mode)
+        s.gsub('\\', '\&\&').gsub("'", "''") # ' (for ruby-mode)
       end
 
       # Quotes the column name. Defaults to no quoting.
       def quote_column_name(column_name)
-        column_name
+        column_name.to_s
       end
 
       # Quotes the table name. Defaults to column name quoting.
@@ -93,7 +76,7 @@ module ActiveRecord
       # Override to return the quoted table name for assignment. Defaults to
       # table quoting.
       #
-      # This works for mysql and mysql2 where table.column can be used to
+      # This works for mysql2 where table.column can be used to
       # resolve ambiguity.
       #
       # We override this in the sqlite3 and postgresql adapters to use only
@@ -102,25 +85,29 @@ module ActiveRecord
         quote_table_name("#{table}.#{attr}")
       end
 
-      def quote_default_expression(value, column) #:nodoc:
-        value = lookup_cast_type(column.sql_type).serialize(value)
-        quote(value)
+      def quote_default_expression(value, column) # :nodoc:
+        if value.is_a?(Proc)
+          value.call
+        else
+          value = lookup_cast_type(column.sql_type).serialize(value)
+          quote(value)
+        end
       end
 
       def quoted_true
-        "'t'"
+        "TRUE"
       end
 
       def unquoted_true
-        't'
+        true
       end
 
       def quoted_false
-        "'f'"
+        "FALSE"
       end
 
       def unquoted_false
-        'f'
+        false
       end
 
       # Quote date/time values for use in SQL input. Includes microseconds
@@ -142,47 +129,72 @@ module ActiveRecord
         end
       end
 
-      def prepare_binds_for_database(binds) # :nodoc:
-        binds.map(&:value_for_database)
+      def quoted_time(value) # :nodoc:
+        value = value.change(year: 2000, month: 1, day: 1)
+        quoted_date(value).sub(/\A\d\d\d\d-\d\d-\d\d /, "")
       end
 
-      private
+      def quoted_binary(value) # :nodoc:
+        "'#{quote_string(value.to_s)}'"
+      end
 
-      def types_which_need_no_typecasting
-        [nil, Numeric, String]
-      end
-
-      def _quote(value)
-        case value
-        when String, ActiveSupport::Multibyte::Chars, Type::Binary::Data
-          "'#{quote_string(value.to_s)}'"
-        when true       then quoted_true
-        when false      then quoted_false
-        when nil        then "NULL"
-        # BigDecimals need to be put in a non-normalized form and quoted.
-        when BigDecimal then value.to_s('F')
-        when Numeric, ActiveSupport::Duration then value.to_s
-        when Date, Time then "'#{quoted_date(value)}'"
-        when Symbol     then "'#{quote_string(value.to_s)}'"
-        when Class      then "'#{value}'"
-        else raise TypeError, "can't quote #{value.class.name}"
+      def type_casted_binds(binds) # :nodoc:
+        if binds.first.is_a?(Array)
+          binds.map { |column, value| type_cast(value, column) }
+        else
+          binds.map { |attr| type_cast(attr.value_for_database) }
         end
       end
 
-      def _type_cast(value)
-        case value
-        when Symbol, ActiveSupport::Multibyte::Chars, Type::Binary::Data
-          value.to_s
-        when true       then unquoted_true
-        when false      then unquoted_false
-        # BigDecimals need to be put in a non-normalized form and quoted.
-        when BigDecimal then value.to_s('F')
-        when Date, Time then quoted_date(value)
-        when *types_which_need_no_typecasting
-          value
-        else raise TypeError
+      private
+        def lookup_cast_type(sql_type)
+          type_map.lookup(sql_type)
+        end
+
+        def id_value_for_database(value)
+          if primary_key = value.class.primary_key
+            value.instance_variable_get(:@attributes)[primary_key].value_for_database
+          end
+        end
+
+        def types_which_need_no_typecasting
+          [nil, Numeric, String]
+        end
+
+        def _quote(value)
+          case value
+          when String, ActiveSupport::Multibyte::Chars
+            "'#{quote_string(value.to_s)}'"
+          when true       then quoted_true
+          when false      then quoted_false
+          when nil        then "NULL"
+          # BigDecimals need to be put in a non-normalized form and quoted.
+          when BigDecimal then value.to_s("F")
+          when Numeric, ActiveSupport::Duration then value.to_s
+          when Type::Binary::Data then quoted_binary(value)
+          when Type::Time::Value then "'#{quoted_time(value)}'"
+          when Date, Time then "'#{quoted_date(value)}'"
+          when Symbol     then "'#{quote_string(value.to_s)}'"
+          when Class      then "'#{value}'"
+          else raise TypeError, "can't quote #{value.class.name}"
+          end
+        end
+
+        def _type_cast(value)
+          case value
+          when Symbol, ActiveSupport::Multibyte::Chars, Type::Binary::Data
+            value.to_s
+          when true       then unquoted_true
+          when false      then unquoted_false
+          # BigDecimals need to be put in a non-normalized form and quoted.
+          when BigDecimal then value.to_s("F")
+          when Type::Time::Value then quoted_time(value)
+          when Date, Time then quoted_date(value)
+          when *types_which_need_no_typecasting
+            value
+          else raise TypeError
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/savepoints.rb b/activerecord/lib/active_record/connection_adapters/abstract/savepoints.rb
index c0662f8473..52a796b926 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/savepoints.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/savepoints.rb
@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
-    module Savepoints #:nodoc:
-      def supports_savepoints?
-        true
+    module Savepoints
+      def current_savepoint_name
+        current_transaction.savepoint_name
       end
 
       def create_savepoint(name = current_savepoint_name)
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
index 18d943f452..2cb0a2a4df 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
@@ -1,4 +1,4 @@
-require 'active_support/core_ext/string/strip'
+# frozen_string_literal: true
 
 module ActiveRecord
   module ConnectionAdapters
@@ -14,41 +14,59 @@ module ActiveRecord
           send m, o
         end
 
-        delegate :quote_column_name, :quote_table_name, :quote_default_expression, :type_to_sql, to: :@conn
-        private :quote_column_name, :quote_table_name, :quote_default_expression, :type_to_sql
+        delegate :quote_column_name, :quote_table_name, :quote_default_expression, :type_to_sql,
+          :options_include_default?, :supports_indexes_in_create?, :supports_foreign_keys_in_create?, :foreign_key_options,
+          to: :@conn, private: true
 
         private
 
           def visit_AlterTable(o)
-            sql = "ALTER TABLE #{quote_table_name(o.name)} "
-            sql << o.adds.map { |col| accept col }.join(' ')
-            sql << o.foreign_key_adds.map { |fk| visit_AddForeignKey fk }.join(' ')
-            sql << o.foreign_key_drops.map { |fk| visit_DropForeignKey fk }.join(' ')
+            sql = +"ALTER TABLE #{quote_table_name(o.name)} "
+            sql << o.adds.map { |col| accept col }.join(" ")
+            sql << o.foreign_key_adds.map { |fk| visit_AddForeignKey fk }.join(" ")
+            sql << o.foreign_key_drops.map { |fk| visit_DropForeignKey fk }.join(" ")
           end
 
           def visit_ColumnDefinition(o)
-            o.sql_type ||= type_to_sql(o.type, o.limit, o.precision, o.scale)
-            column_sql = "#{quote_column_name(o.name)} #{o.sql_type}"
+            o.sql_type = type_to_sql(o.type, o.options)
+            column_sql = +"#{quote_column_name(o.name)} #{o.sql_type}"
             add_column_options!(column_sql, column_options(o)) unless o.type == :primary_key
             column_sql
           end
 
           def visit_AddColumnDefinition(o)
-            "ADD #{accept(o.column)}"
+            +"ADD #{accept(o.column)}"
           end
 
           def visit_TableDefinition(o)
-            create_sql = "CREATE#{' TEMPORARY' if o.temporary} TABLE "
+            create_sql = +"CREATE#{table_modifier_in_create(o)} TABLE "
+            create_sql << "IF NOT EXISTS " if o.if_not_exists
             create_sql << "#{quote_table_name(o.name)} "
-            create_sql << "(#{o.columns.map { |c| accept c }.join(', ')}) " unless o.as
-            create_sql << "#{o.options}"
-            create_sql << " AS #{@conn.to_sql(o.as)}" if o.as
+
+            statements = o.columns.map { |c| accept c }
+            statements << accept(o.primary_keys) if o.primary_keys
+
+            if supports_indexes_in_create?
+              statements.concat(o.indexes.map { |column_name, options| index_in_create(o.name, column_name, options) })
+            end
+
+            if supports_foreign_keys_in_create?
+              statements.concat(o.foreign_keys.map { |to_table, options| foreign_key_in_create(o.name, to_table, options) })
+            end
+
+            create_sql << "(#{statements.join(', ')})" if statements.present?
+            add_table_options!(create_sql, table_options(o))
+            create_sql << " AS #{to_sql(o.as)}" if o.as
             create_sql
           end
 
-          def visit_AddForeignKey(o)
-            sql = <<-SQL.strip_heredoc
-              ADD CONSTRAINT #{quote_column_name(o.name)}
+          def visit_PrimaryKeyDefinition(o)
+            "PRIMARY KEY (#{o.name.map { |name| quote_column_name(name) }.join(', ')})"
+          end
+
+          def visit_ForeignKeyDefinition(o)
+            sql = +<<~SQL
+              CONSTRAINT #{quote_column_name(o.name)}
               FOREIGN KEY (#{quote_column_name(o.column)})
                 REFERENCES #{quote_table_name(o.to_table)} (#{quote_column_name(o.primary_key)})
             SQL
@@ -57,21 +75,30 @@ module ActiveRecord
             sql
           end
 
+          def visit_AddForeignKey(o)
+            "ADD #{accept(o)}"
+          end
+
           def visit_DropForeignKey(name)
             "DROP CONSTRAINT #{quote_column_name(name)}"
           end
 
+          def table_options(o)
+            table_options = {}
+            table_options[:comment] = o.comment
+            table_options[:options] = o.options
+            table_options
+          end
+
+          def add_table_options!(create_sql, options)
+            if options_sql = options[:options]
+              create_sql << " #{options_sql}"
+            end
+            create_sql
+          end
+
           def column_options(o)
-            column_options = {}
-            column_options[:null] = o.null unless o.null.nil?
-            column_options[:default] = o.default unless o.default.nil?
-            column_options[:column] = o
-            column_options[:first] = o.first
-            column_options[:after] = o.after
-            column_options[:auto_increment] = o.auto_increment
-            column_options[:primary_key] = o.primary_key
-            column_options[:collation] = o.collation
-            column_options
+            o.options.merge(column: o)
           end
 
           def add_column_options!(sql, options)
@@ -89,8 +116,19 @@ module ActiveRecord
             sql
           end
 
-          def options_include_default?(options)
-            options.include?(:default) && !(options[:null] == false && options[:default].nil?)
+          def to_sql(sql)
+            sql = sql.to_sql if sql.respond_to?(:to_sql)
+            sql
+          end
+
+          # Returns any SQL string to go between CREATE and TABLE. May be nil.
+          def table_modifier_in_create(o)
+            " TEMPORARY" if o.temporary
+          end
+
+          def foreign_key_in_create(from_table, to_table, options)
+            options = foreign_key_options(from_table, to_table, options)
+            accept ForeignKeyDefinition.new(from_table, to_table, options)
           end
 
           def action_sql(action, dependency)
@@ -99,7 +137,7 @@ module ActiveRecord
             when :cascade  then "ON #{action} CASCADE"
             when :restrict then "ON #{action} RESTRICT"
             else
-              raise ArgumentError, <<-MSG.strip_heredoc
+              raise ArgumentError, <<~MSG
                 '#{dependency}' is not supported for :on_update or :on_delete.
                 Supported values are: :nullify, :cascade, :restrict
               MSG
@@ -107,5 +145,6 @@ module ActiveRecord
           end
       end
     end
+    SchemaCreation = AbstractAdapter::SchemaCreation # :nodoc:
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
index d17e272ed1..db489143af 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb
@@ -1,29 +1,79 @@
+# frozen_string_literal: true
+
+require "active_support/deprecation"
+
 module ActiveRecord
   module ConnectionAdapters #:nodoc:
     # Abstract representation of an index definition on a table. Instances of
     # this type are typically created and returned by methods in database
-    # adapters. e.g. ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter#indexes
-    class IndexDefinition < Struct.new(:table, :name, :unique, :columns, :lengths, :orders, :where, :type, :using) #:nodoc:
+    # adapters. e.g. ActiveRecord::ConnectionAdapters::MySQL::SchemaStatements#indexes
+    class IndexDefinition # :nodoc:
+      attr_reader :table, :name, :unique, :columns, :lengths, :orders, :opclasses, :where, :type, :using, :comment
+
+      def initialize(
+        table, name,
+        unique = false,
+        columns = [],
+        lengths: {},
+        orders: {},
+        opclasses: {},
+        where: nil,
+        type: nil,
+        using: nil,
+        comment: nil
+      )
+        @table = table
+        @name = name
+        @unique = unique
+        @columns = columns
+        @lengths = concise_options(lengths)
+        @orders = concise_options(orders)
+        @opclasses = concise_options(opclasses)
+        @where = where
+        @type = type
+        @using = using
+        @comment = comment
+      end
+
+      private
+        def concise_options(options)
+          if columns.size == options.size && options.values.uniq.size == 1
+            options.values.first
+          else
+            options
+          end
+        end
     end
 
     # Abstract representation of a column definition. Instances of this type
     # are typically created by methods in TableDefinition, and added to the
     # +columns+ attribute of said TableDefinition object, in order to be used
     # for generating a number of table creation or table changing SQL statements.
-    class ColumnDefinition < Struct.new(:name, :type, :limit, :precision, :scale, :default, :null, :first, :after, :auto_increment, :primary_key, :collation, :sql_type) #:nodoc:
-
+    ColumnDefinition = Struct.new(:name, :type, :options, :sql_type) do # :nodoc:
       def primary_key?
-        primary_key || type.to_sym == :primary_key
+        options[:primary_key]
       end
-    end
 
-    class AddColumnDefinition < Struct.new(:column) # :nodoc:
-    end
+      [:limit, :precision, :scale, :default, :null, :collation, :comment].each do |option_name|
+        module_eval <<-CODE, __FILE__, __LINE__ + 1
+          def #{option_name}
+            options[:#{option_name}]
+          end
 
-    class ChangeColumnDefinition < Struct.new(:column, :name) #:nodoc:
+          def #{option_name}=(value)
+            options[:#{option_name}] = value
+          end
+        CODE
+      end
     end
 
-    class ForeignKeyDefinition < Struct.new(:from_table, :to_table, :options) #:nodoc:
+    AddColumnDefinition = Struct.new(:column) # :nodoc:
+
+    ChangeColumnDefinition = Struct.new(:column, :name) #:nodoc:
+
+    PrimaryKeyDefinition = Struct.new(:name) # :nodoc:
+
+    ForeignKeyDefinition = Struct.new(:from_table, :to_table, :options) do #:nodoc:
       def name
         options[:name]
       end
@@ -48,27 +98,37 @@ module ActiveRecord
         options[:primary_key] != default_primary_key
       end
 
-      def defined_for?(options_or_to_table = {})
-        if options_or_to_table.is_a?(Hash)
-          options_or_to_table.all? {|key, value| options[key].to_s == value.to_s }
+      def validate?
+        options.fetch(:validate, true)
+      end
+      alias validated? validate?
+
+      def export_name_on_schema_dump?
+        name !~ ActiveRecord::SchemaDumper.fk_ignore_pattern
+      end
+
+      def defined_for?(to_table_ord = nil, to_table: nil, **options)
+        if to_table_ord
+          self.to_table == to_table_ord.to_s
         else
-          to_table == options_or_to_table.to_s
+          (to_table.nil? || to_table.to_s == self.to_table) &&
+            options.all? { |k, v| self.options[k].to_s == v.to_s }
         end
       end
 
       private
-      def default_primary_key
-        "id"
-      end
+        def default_primary_key
+          "id"
+        end
     end
 
     class ReferenceDefinition # :nodoc:
       def initialize(
         name,
         polymorphic: false,
-        index: false,
+        index: true,
         foreign_key: false,
-        type: :integer,
+        type: :bigint,
         **options
       )
         @name = name
@@ -97,47 +157,46 @@ module ActiveRecord
         end
       end
 
-      protected
-
-      attr_reader :name, :polymorphic, :index, :foreign_key, :type, :options
-
       private
+        attr_reader :name, :polymorphic, :index, :foreign_key, :type, :options
 
-      def as_options(value, default = {})
-        if value.is_a?(Hash)
-          value
-        else
-          default
+        def as_options(value)
+          value.is_a?(Hash) ? value : {}
         end
-      end
 
-      def polymorphic_options
-        as_options(polymorphic, options)
-      end
+        def polymorphic_options
+          as_options(polymorphic).merge(options.slice(:null, :first, :after))
+        end
 
-      def index_options
-        as_options(index)
-      end
+        def index_options
+          as_options(index)
+        end
 
-      def foreign_key_options
-        as_options(foreign_key)
-      end
+        def foreign_key_options
+          as_options(foreign_key).merge(column: column_name)
+        end
 
-      def columns
-        result = [["#{name}_id", type, options]]
-        if polymorphic
-          result.unshift(["#{name}_type", :string, polymorphic_options])
+        def columns
+          result = [[column_name, type, options]]
+          if polymorphic
+            result.unshift(["#{name}_type", :string, polymorphic_options])
+          end
+          result
         end
-        result
-      end
 
-      def column_names
-        columns.map(&:first)
-      end
+        def column_name
+          "#{name}_id"
+        end
 
-      def foreign_table_name
-        Base.pluralize_table_names ? name.to_s.pluralize : name
-      end
+        def column_names
+          columns.map(&:first)
+        end
+
+        def foreign_table_name
+          foreign_key_options.fetch(:to_table) do
+            Base.pluralize_table_names ? name.to_s.pluralize : name
+          end
+        end
     end
 
     module ColumnMethods
@@ -162,10 +221,12 @@ module ActiveRecord
         :decimal,
         :float,
         :integer,
+        :json,
         :string,
         :text,
         :time,
         :timestamp,
+        :virtual,
       ].each do |column_type|
         module_eval <<-CODE, __FILE__, __LINE__ + 1
           def #{column_type}(*args, **options)
@@ -173,15 +234,16 @@ module ActiveRecord
           end
         CODE
       end
+      alias_method :numeric, :decimal
     end
 
     # Represents the schema of an SQL table in an abstract way. This class
     # provides methods for manipulating the schema representation.
     #
-    # Inside migration files, the +t+ object in +create_table+
+    # Inside migration files, the +t+ object in {create_table}[rdoc-ref:SchemaStatements#create_table]
     # is actually of this type:
     #
-    #   class SomeMigration < ActiveRecord::Migration
+    #   class SomeMigration < ActiveRecord::Migration[5.0]
     #     def up
     #       create_table :foo do |t|
     #         puts t.class  # => "ActiveRecord::ConnectionAdapters::TableDefinition"
@@ -193,27 +255,40 @@ module ActiveRecord
     #     end
     #   end
     #
-    # The table definitions
-    # The Columns are stored as a ColumnDefinition in the +columns+ attribute.
     class TableDefinition
       include ColumnMethods
 
-      # An array of ColumnDefinition objects, representing the column changes
-      # that have been defined.
-      attr_accessor :indexes
-      attr_reader :name, :temporary, :options, :as, :foreign_keys
+      attr_reader :name, :temporary, :if_not_exists, :options, :as, :comment, :indexes, :foreign_keys
+      attr_writer :indexes
+      deprecate :indexes=
 
-      def initialize(types, name, temporary, options, as = nil)
+      def initialize(
+        name,
+        temporary: false,
+        if_not_exists: false,
+        options: nil,
+        as: nil,
+        comment: nil,
+        **
+      )
         @columns_hash = {}
-        @indexes = {}
-        @foreign_keys = {}
-        @native = types
+        @indexes = []
+        @foreign_keys = []
+        @primary_keys = nil
         @temporary = temporary
+        @if_not_exists = if_not_exists
         @options = options
         @as = as
         @name = name
+        @comment = comment
       end
 
+      def primary_keys(name = nil) # :nodoc:
+        @primary_keys = PrimaryKeyDefinition.new(name) if name
+        @primary_keys
+      end
+
+      # Returns an array of ColumnDefinition objects for the columns of the table.
       def columns; @columns_hash.values; end
 
       # Returns a ColumnDefinition for the column with name +name+.
@@ -222,90 +297,23 @@ module ActiveRecord
       end
 
       # Instantiates a new column for the table.
-      # The +type+ parameter is normally one of the migrations native types,
-      # which is one of the following:
-      # <tt>:primary_key</tt>, <tt>:string</tt>, <tt>:text</tt>,
-      # <tt>:integer</tt>, <tt>:bigint</tt>, <tt>:float</tt>, <tt>:decimal</tt>,
-      # <tt>:datetime</tt>, <tt>:time</tt>, <tt>:date</tt>,
-      # <tt>:binary</tt>, <tt>:boolean</tt>.
-      #
-      # You may use a type not in this list as long as it is supported by your
-      # database (for example, "polygon" in MySQL), but this will not be database
-      # agnostic and should usually be avoided.
-      #
-      # Available options are (none of these exists by default):
-      # * <tt>:limit</tt> -
-      #   Requests a maximum column length. This is number of characters for <tt>:string</tt> and
-      #   <tt>:text</tt> columns and number of bytes for <tt>:binary</tt> and <tt>:integer</tt> columns.
-      # * <tt>:default</tt> -
-      #   The column's default value. Use nil for NULL.
-      # * <tt>:null</tt> -
-      #   Allows or disallows +NULL+ values in the column. This option could
-      #   have been named <tt>:null_allowed</tt>.
-      # * <tt>:precision</tt> -
-      #   Specifies the precision for a <tt>:decimal</tt> column.
-      # * <tt>:scale</tt> -
-      #   Specifies the scale for a <tt>:decimal</tt> column.
+      # See {connection.add_column}[rdoc-ref:ConnectionAdapters::SchemaStatements#add_column]
+      # for available options.
+      #
+      # Additional options are:
       # * <tt>:index</tt> -
       #   Create an index for the column. Can be either <tt>true</tt> or an options hash.
       #
-      # Note: The precision is the total number of significant digits
-      # and the scale is the number of digits that can be stored following
-      # the decimal point. For example, the number 123.45 has a precision of 5
-      # and a scale of 2. A decimal with a precision of 5 and a scale of 2 can
-      # range from -999.99 to 999.99.
-      #
-      # Please be aware of different RDBMS implementations behavior with
-      # <tt>:decimal</tt> columns:
-      # * The SQL standard says the default scale should be 0, <tt>:scale</tt> <=
-      #   <tt>:precision</tt>, and makes no comments about the requirements of
-      #   <tt>:precision</tt>.
-      # * MySQL: <tt>:precision</tt> [1..63], <tt>:scale</tt> [0..30].
-      #   Default is (10,0).
-      # * PostgreSQL: <tt>:precision</tt> [1..infinity],
-      #   <tt>:scale</tt> [0..infinity]. No default.
-      # * SQLite2: Any <tt>:precision</tt> and <tt>:scale</tt> may be used.
-      #   Internal storage as strings. No default.
-      # * SQLite3: No restrictions on <tt>:precision</tt> and <tt>:scale</tt>,
-      #   but the maximum supported <tt>:precision</tt> is 16. No default.
-      # * Oracle: <tt>:precision</tt> [1..38], <tt>:scale</tt> [-84..127].
-      #   Default is (38,0).
-      # * DB2: <tt>:precision</tt> [1..63], <tt>:scale</tt> [0..62].
-      #   Default unknown.
-      # * SqlServer?: <tt>:precision</tt> [1..38], <tt>:scale</tt> [0..38].
-      #   Default (38,0).
-      #
       # This method returns <tt>self</tt>.
       #
       # == Examples
-      #  # Assuming +td+ is an instance of TableDefinition
-      #  td.column(:granted, :boolean)
-      #  # granted BOOLEAN
-      #
-      #  td.column(:picture, :binary, limit: 2.megabytes)
-      #  # => picture BLOB(2097152)
       #
-      #  td.column(:sales_stage, :string, limit: 20, default: 'new', null: false)
-      #  # => sales_stage VARCHAR(20) DEFAULT 'new' NOT NULL
-      #
-      #  td.column(:bill_gates_money, :decimal, precision: 15, scale: 2)
-      #  # => bill_gates_money DECIMAL(15,2)
-      #
-      #  td.column(:sensor_reading, :decimal, precision: 30, scale: 20)
-      #  # => sensor_reading DECIMAL(30,20)
-      #
-      #  # While <tt>:scale</tt> defaults to zero on most databases, it
-      #  # probably wouldn't hurt to include it.
-      #  td.column(:huge_integer, :decimal, precision: 30)
-      #  # => huge_integer DECIMAL(30)
-      #
-      #  # Defines a column with a database-specific type.
-      #  td.column(:foo, 'polygon')
-      #  # => foo polygon
+      #  # Assuming +td+ is an instance of TableDefinition
+      #  td.column(:granted, :boolean, index: true)
       #
       # == Short-hand examples
       #
-      # Instead of calling +column+ directly, you can also work with the short-hand definitions for the default types.
+      # Instead of calling #column directly, you can also work with the short-hand definitions for the default types.
       # They use the type as the method name instead of as a parameter and allow for multiple columns to be defined
       # in a single statement.
       #
@@ -337,7 +345,8 @@ module ActiveRecord
       # TableDefinition#references will add an appropriately-named _id column, plus a corresponding _type
       # column if the <tt>:polymorphic</tt> option is supplied. If <tt>:polymorphic</tt> is a hash of
       # options, these will be used when creating the <tt>_type</tt> column. The <tt>:index</tt> option
-      # will also create an index, similar to calling <tt>add_index</tt>. So what can be written like this:
+      # will also create an index, similar to calling {add_index}[rdoc-ref:ConnectionAdapters::SchemaStatements#add_index].
+      # So what can be written like this:
       #
       #   create_table :taggings do |t|
       #     t.integer :tag_id, :tagger_id, :taggable_id
@@ -351,16 +360,20 @@ module ActiveRecord
       #
       #   create_table :taggings do |t|
       #     t.references :tag, index: { name: 'index_taggings_on_tag_id' }
-      #     t.references :tagger, polymorphic: true, index: true
-      #     t.references :taggable, polymorphic: { default: 'Photo' }
+      #     t.references :tagger, polymorphic: true
+      #     t.references :taggable, polymorphic: { default: 'Photo' }, index: false
       #   end
       def column(name, type, options = {})
         name = name.to_s
-        type = type.to_sym
+        type = type.to_sym if type
         options = options.dup
 
-        if @columns_hash[name] && @columns_hash[name].primary_key?
-          raise ArgumentError, "you can't redefine the primary key column '#{name}'. To define a custom primary key, pass { id: false } to create_table."
+        if @columns_hash[name]
+          if @columns_hash[name].primary_key?
+            raise ArgumentError, "you can't redefine the primary key column '#{name}'. To define a custom primary key, pass { id: false } to create_table."
+          else
+            raise ArgumentError, "you can't define an already defined column '#{name}'."
+          end
         end
 
         index_options = options.delete(:index)
@@ -369,6 +382,8 @@ module ActiveRecord
         self
       end
 
+      # remove the column +name+ from the table.
+      #   remove_column(:account_id)
       def remove_column(name)
         @columns_hash.delete name.to_s
       end
@@ -378,20 +393,21 @@ module ActiveRecord
       #
       #   index(:account_id, name: 'index_projects_on_account_id')
       def index(column_name, options = {})
-        indexes[column_name] = options
+        indexes << [column_name, options]
       end
 
       def foreign_key(table_name, options = {}) # :nodoc:
-        foreign_keys[table_name] = options
+        table_name_prefix = ActiveRecord::Base.table_name_prefix
+        table_name_suffix = ActiveRecord::Base.table_name_suffix
+        table_name = "#{table_name_prefix}#{table_name}#{table_name_suffix}"
+        foreign_keys.push([table_name, options])
       end
 
       # Appends <tt>:datetime</tt> columns <tt>:created_at</tt> and
-      # <tt>:updated_at</tt> to the table. See SchemaStatements#add_timestamps
+      # <tt>:updated_at</tt> to the table. See {connection.add_timestamps}[rdoc-ref:SchemaStatements#add_timestamps]
       #
       #   t.timestamps null: false
-      def timestamps(*args)
-        options = args.extract_options!
-
+      def timestamps(**options)
         options[:null] = false if options[:null].nil?
 
         column(:created_at, :datetime, options)
@@ -403,46 +419,40 @@ module ActiveRecord
       #  t.references(:user)
       #  t.belongs_to(:supplier, foreign_key: true)
       #
-      # See SchemaStatements#add_reference for details of the options you can use.
+      # See {connection.add_reference}[rdoc-ref:SchemaStatements#add_reference] for details of the options you can use.
       def references(*args, **options)
-        args.each do |col|
-          ReferenceDefinition.new(col, **options).add_to(self)
+        args.each do |ref_name|
+          ReferenceDefinition.new(ref_name, options).add_to(self)
         end
       end
       alias :belongs_to :references
 
-      def new_column_definition(name, type, options) # :nodoc:
-        type = aliased_types(type.to_s, type)
-        column = create_column_definition name, type
-        limit = options.fetch(:limit) do
-          native[type][:limit] if native[type].is_a?(Hash)
+      def new_column_definition(name, type, **options) # :nodoc:
+        if integer_like_primary_key?(type, options)
+          type = integer_like_primary_key_type(type, options)
         end
-
-        column.limit       = limit
-        column.precision   = options[:precision]
-        column.scale       = options[:scale]
-        column.default     = options[:default]
-        column.null        = options[:null]
-        column.first       = options[:first]
-        column.after       = options[:after]
-        column.auto_increment = options[:auto_increment]
-        column.primary_key = type == :primary_key || options[:primary_key]
-        column.collation   = options[:collation]
-        column
+        type = aliased_types(type.to_s, type)
+        options[:primary_key] ||= type == :primary_key
+        options[:null] = false if options[:primary_key]
+        create_column_definition(name, type, options)
       end
 
       private
-      def create_column_definition(name, type)
-        ColumnDefinition.new name, type
-      end
+        def create_column_definition(name, type, options)
+          ColumnDefinition.new(name, type, options)
+        end
 
-      def native
-        @native
-      end
+        def aliased_types(name, fallback)
+          "timestamp" == name ? :datetime : fallback
+        end
 
-      def aliased_types(name, fallback)
-        'timestamp' == name ? :datetime : fallback
-      end
+        def integer_like_primary_key?(type, options)
+          options[:primary_key] && [:integer, :bigint].include?(type) && !options.key?(:default)
+        end
+
+        def integer_like_primary_key_type(type, options)
+          type
+        end
     end
 
     class AlterTable # :nodoc:
@@ -475,7 +485,7 @@ module ActiveRecord
     end
 
     # Represents an SQL table in an abstract way for updating a table.
-    # Also see TableDefinition and SchemaStatements#create_table
+    # Also see TableDefinition and {connection.create_table}[rdoc-ref:SchemaStatements#create_table]
     #
     # Available transformations are:
     #
@@ -496,12 +506,16 @@ module ActiveRecord
     #     t.bigint
     #     t.float
     #     t.decimal
+    #     t.numeric
     #     t.datetime
     #     t.timestamp
     #     t.time
     #     t.date
     #     t.binary
     #     t.boolean
+    #     t.foreign_key
+    #     t.json
+    #     t.virtual
     #     t.remove
     #     t.remove_references
     #     t.remove_belongs_to
@@ -525,14 +539,16 @@ module ActiveRecord
       #
       # See TableDefinition#column for details of the options you can use.
       def column(column_name, type, options = {})
+        index_options = options.delete(:index)
         @base.add_column(name, column_name, type, options)
+        index(column_name, index_options.is_a?(Hash) ? index_options : {}) if index_options
       end
 
       # Checks to see if a column exists.
       #
-      # t.string(:name) unless t.column_exists?(:name, :string)
+      #  t.string(:name) unless t.column_exists?(:name, :string)
       #
-      # See SchemaStatements#column_exists?
+      # See {connection.column_exists?}[rdoc-ref:SchemaStatements#column_exists?]
       def column_exists?(column_name, type = nil, options = {})
         @base.column_exists?(name, column_name, type, options)
       end
@@ -544,18 +560,18 @@ module ActiveRecord
       #  t.index([:branch_id, :party_id], unique: true)
       #  t.index([:branch_id, :party_id], unique: true, name: 'by_branch_party')
       #
-      # See SchemaStatements#add_index for details of the options you can use.
+      # See {connection.add_index}[rdoc-ref:SchemaStatements#add_index] for details of the options you can use.
       def index(column_name, options = {})
         @base.add_index(name, column_name, options)
       end
 
       # Checks to see if an index exists.
       #
-      # unless t.index_exists?(:branch_id)
-      #   t.index(:branch_id)
-      # end
+      #  unless t.index_exists?(:branch_id)
+      #    t.index(:branch_id)
+      #  end
       #
-      # See SchemaStatements#index_exists?
+      # See {connection.index_exists?}[rdoc-ref:SchemaStatements#index_exists?]
       def index_exists?(column_name, options = {})
         @base.index_exists?(name, column_name, options)
       end
@@ -564,7 +580,7 @@ module ActiveRecord
       #
       #  t.rename_index(:user_id, :account_id)
       #
-      # See SchemaStatements#rename_index
+      # See {connection.rename_index}[rdoc-ref:SchemaStatements#rename_index]
       def rename_index(index_name, new_index_name)
         @base.rename_index(name, index_name, new_index_name)
       end
@@ -573,7 +589,7 @@ module ActiveRecord
       #
       #  t.timestamps(null: false)
       #
-      # See SchemaStatements#add_timestamps
+      # See {connection.add_timestamps}[rdoc-ref:SchemaStatements#add_timestamps]
       def timestamps(options = {})
         @base.add_timestamps(name, options)
       end
@@ -594,7 +610,7 @@ module ActiveRecord
       #  t.change_default(:authorized, 1)
       #  t.change_default(:status, from: nil, to: "draft")
       #
-      # See SchemaStatements#change_column_default
+      # See {connection.change_column_default}[rdoc-ref:SchemaStatements#change_column_default]
       def change_default(column_name, default_or_changes)
         @base.change_column_default(name, column_name, default_or_changes)
       end
@@ -604,7 +620,7 @@ module ActiveRecord
       #  t.remove(:qualification)
       #  t.remove(:qualification, :experience)
       #
-      # See SchemaStatements#remove_columns
+      # See {connection.remove_columns}[rdoc-ref:SchemaStatements#remove_columns]
       def remove(*column_names)
         @base.remove_columns(name, *column_names)
       end
@@ -615,7 +631,7 @@ module ActiveRecord
       #   t.remove_index(column: [:branch_id, :party_id])
       #   t.remove_index(name: :by_branch_party)
       #
-      # See SchemaStatements#remove_index
+      # See {connection.remove_index}[rdoc-ref:SchemaStatements#remove_index]
       def remove_index(options = {})
         @base.remove_index(name, options)
       end
@@ -624,7 +640,7 @@ module ActiveRecord
       #
       #  t.remove_timestamps
       #
-      # See SchemaStatements#remove_timestamps
+      # See {connection.remove_timestamps}[rdoc-ref:SchemaStatements#remove_timestamps]
       def remove_timestamps(options = {})
         @base.remove_timestamps(name, options)
       end
@@ -633,7 +649,7 @@ module ActiveRecord
       #
       #  t.rename(:description, :name)
       #
-      # See SchemaStatements#rename_column
+      # See {connection.rename_column}[rdoc-ref:SchemaStatements#rename_column]
       def rename(column_name, new_column_name)
         @base.rename_column(name, column_name, new_column_name)
       end
@@ -643,9 +659,8 @@ module ActiveRecord
       #  t.references(:user)
       #  t.belongs_to(:supplier, foreign_key: true)
       #
-      # See SchemaStatements#add_reference for details of the options you can use.
-      def references(*args)
-        options = args.extract_options!
+      # See {connection.add_reference}[rdoc-ref:SchemaStatements#add_reference] for details of the options you can use.
+      def references(*args, **options)
         args.each do |ref_name|
           @base.add_reference(name, ref_name, options)
         end
@@ -657,9 +672,8 @@ module ActiveRecord
       #  t.remove_references(:user)
       #  t.remove_belongs_to(:supplier, polymorphic: true)
       #
-      # See SchemaStatements#remove_reference
-      def remove_references(*args)
-        options = args.extract_options!
+      # See {connection.remove_reference}[rdoc-ref:SchemaStatements#remove_reference]
+      def remove_references(*args, **options)
         args.each do |ref_name|
           @base.remove_reference(name, ref_name, options)
         end
@@ -668,26 +682,21 @@ module ActiveRecord
 
       # Adds a foreign key.
       #
-      # t.foreign_key(:authors)
+      #  t.foreign_key(:authors)
       #
-      # See SchemaStatements#add_foreign_key
-      def foreign_key(*args) # :nodoc:
+      # See {connection.add_foreign_key}[rdoc-ref:SchemaStatements#add_foreign_key]
+      def foreign_key(*args)
         @base.add_foreign_key(name, *args)
       end
 
       # Checks to see if a foreign key exists.
       #
-      # t.foreign_key(:authors) unless t.foreign_key_exists?(:authors)
+      #  t.foreign_key(:authors) unless t.foreign_key_exists?(:authors)
       #
-      # See SchemaStatements#foreign_key_exists?
-      def foreign_key_exists?(*args) # :nodoc:
+      # See {connection.foreign_key_exists?}[rdoc-ref:SchemaStatements#foreign_key_exists?]
+      def foreign_key_exists?(*args)
         @base.foreign_key_exists?(name, *args)
       end
-
-      private
-        def native
-          @base.native_database_types
-        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
index b944a8631c..622e00fffb 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb
@@ -1,89 +1,93 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
-    # The goal of this module is to move Adapter specific column
-    # definitions to the Adapter instead of having it in the schema
-    # dumper itself. This code represents the normal case.
-    # We can then redefine how certain data types may be handled in the schema dumper on the
-    # Adapter level by over-writing this code inside the database specific adapters
-    module ColumnDumper
-      def column_spec(column)
-        spec = prepare_column_options(column)
-        (spec.keys - [:name, :type]).each{ |k| spec[k].insert(0, "#{k}: ")}
-        spec
-      end
-
-      def column_spec_for_primary_key(column)
-        return if column.type == :integer
-        spec = { id: column.type.inspect }
-        spec.merge!(prepare_column_options(column).delete_if { |key, _| [:name, :type].include?(key) })
+    class SchemaDumper < SchemaDumper # :nodoc:
+      def self.create(connection, options)
+        new(connection, options)
       end
 
-      # This can be overridden on a Adapter level basis to support other
-      # extended datatypes (Example: Adding an array option in the
-      # PostgreSQLAdapter)
-      def prepare_column_options(column)
-        spec = {}
-        spec[:name]      = column.name.inspect
-        spec[:type]      = schema_type(column)
-        spec[:null]      = 'false' unless column.null
-
-        if limit = schema_limit(column)
-          spec[:limit] = limit
+      private
+        def column_spec(column)
+          [schema_type_with_virtual(column), prepare_column_options(column)]
         end
 
-        if precision = schema_precision(column)
-          spec[:precision] = precision
+        def column_spec_for_primary_key(column)
+          return {} if default_primary_key?(column)
+          spec = { id: schema_type(column).inspect }
+          spec.merge!(prepare_column_options(column).except!(:null))
+          spec[:default] ||= "nil" if explicit_primary_key_default?(column)
+          spec
         end
 
-        if scale = schema_scale(column)
-          spec[:scale] = scale
+        def prepare_column_options(column)
+          spec = {}
+          spec[:limit] = schema_limit(column)
+          spec[:precision] = schema_precision(column)
+          spec[:scale] = schema_scale(column)
+          spec[:default] = schema_default(column)
+          spec[:null] = "false" unless column.null
+          spec[:collation] = schema_collation(column)
+          spec[:comment] = column.comment.inspect if column.comment.present?
+          spec.compact!
+          spec
         end
 
-        default = schema_default(column) if column.has_default?
-        spec[:default]   = default unless default.nil?
-
-        if collation = schema_collation(column)
-          spec[:collation] = collation
+        def default_primary_key?(column)
+          schema_type(column) == :bigint
         end
 
-        spec
-      end
+        def explicit_primary_key_default?(column)
+          false
+        end
 
-      # Lists the valid migration options
-      def migration_keys
-        [:name, :limit, :precision, :scale, :default, :null, :collation]
-      end
+        def schema_type_with_virtual(column)
+          if @connection.supports_virtual_columns? && column.virtual?
+            :virtual
+          else
+            schema_type(column)
+          end
+        end
 
-      private
+        def schema_type(column)
+          if column.bigint?
+            :bigint
+          else
+            column.type
+          end
+        end
 
-      def schema_type(column)
-        column.type.to_s
-      end
+        def schema_limit(column)
+          limit = column.limit unless column.bigint?
+          limit.inspect if limit && limit != @connection.native_database_types[column.type][:limit]
+        end
 
-      def schema_limit(column)
-        limit = column.limit || native_database_types[column.type][:limit]
-        limit.inspect if limit
-      end
+        def schema_precision(column)
+          column.precision.inspect if column.precision
+        end
 
-      def schema_precision(column)
-        column.precision.inspect if column.precision
-      end
+        def schema_scale(column)
+          column.scale.inspect if column.scale
+        end
 
-      def schema_scale(column)
-        column.scale.inspect if column.scale
-      end
+        def schema_default(column)
+          return unless column.has_default?
+          type = @connection.lookup_cast_type_from_column(column)
+          default = type.deserialize(column.default)
+          if default.nil?
+            schema_expression(column)
+          else
+            type.type_cast_for_schema(default)
+          end
+        end
 
-      def schema_default(column)
-        type = lookup_cast_type_from_column(column)
-        default = type.deserialize(column.default)
-        unless default.nil?
-          type.type_cast_for_schema(default)
+        def schema_expression(column)
+          "-> { #{column.default_function.inspect} }" if column.default_function
         end
-      end
 
-      def schema_collation(column)
-        column.collation.inspect if column.collation
-      end
+        def schema_collation(column)
+          column.collation.inspect if column.collation
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index e3115abe66..38cfc3a241 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -1,6 +1,8 @@
-require 'active_record/migration/join_table'
-require 'active_support/core_ext/string/access'
-require 'digest'
+# frozen_string_literal: true
+
+require "active_record/migration/join_table"
+require "active_support/core_ext/string/access"
+require "digest/sha2"
 
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
@@ -18,9 +20,37 @@ module ActiveRecord
         nil
       end
 
+      # Returns the table comment that's stored in database metadata.
+      def table_comment(table_name)
+        nil
+      end
+
       # Truncates a table alias according to the limits of the current adapter.
       def table_alias_for(table_name)
-        table_name[0...table_alias_length].tr('.', '_')
+        table_name[0...table_alias_length].tr(".", "_")
+      end
+
+      # Returns the relation names useable to back Active Record models.
+      # For most adapters this means all #tables and #views.
+      def data_sources
+        query_values(data_source_sql, "SCHEMA")
+      rescue NotImplementedError
+        tables | views
+      end
+
+      # Checks to see if the data source +name+ exists on the database.
+      #
+      #   data_source_exists?(:ebooks)
+      #
+      def data_source_exists?(name)
+        query_values(data_source_sql(name), "SCHEMA").any? if name.present?
+      rescue NotImplementedError
+        data_sources.include?(name.to_s)
+      end
+
+      # Returns an array of table names defined in the database.
+      def tables
+        query_values(data_source_sql(type: "BASE TABLE"), "SCHEMA")
       end
 
       # Checks to see if the table +table_name+ exists on the database.
@@ -28,11 +58,30 @@ module ActiveRecord
       #   table_exists?(:developers)
       #
       def table_exists?(table_name)
+        query_values(data_source_sql(table_name, type: "BASE TABLE"), "SCHEMA").any? if table_name.present?
+      rescue NotImplementedError
         tables.include?(table_name.to_s)
       end
 
+      # Returns an array of view names defined in the database.
+      def views
+        query_values(data_source_sql(type: "VIEW"), "SCHEMA")
+      end
+
+      # Checks to see if the view +view_name+ exists on the database.
+      #
+      #   view_exists?(:ebooks)
+      #
+      def view_exists?(view_name)
+        query_values(data_source_sql(view_name, type: "VIEW"), "SCHEMA").any? if view_name.present?
+      rescue NotImplementedError
+        views.include?(view_name.to_s)
+      end
+
       # Returns an array of indexes for the given table.
-      # def indexes(table_name, name = nil) end
+      def indexes(table_name)
+        raise NotImplementedError, "#indexes is not implemented"
+      end
 
       # Checks to see if an index exists on a table for a given index definition.
       #
@@ -50,18 +99,21 @@ module ActiveRecord
       #
       def index_exists?(table_name, column_name, options = {})
         column_names = Array(column_name).map(&:to_s)
-        index_name = options.key?(:name) ? options[:name].to_s : index_name(table_name, column: column_names)
         checks = []
-        checks << lambda { |i| i.name == index_name }
         checks << lambda { |i| i.columns == column_names }
         checks << lambda { |i| i.unique } if options[:unique]
+        checks << lambda { |i| i.name == options[:name].to_s } if options[:name]
 
         indexes(table_name).any? { |i| checks.all? { |check| check[i] } }
       end
 
-      # Returns an array of Column objects for the table specified by +table_name+.
-      # See the concrete implementation for details on the expected parameter values.
-      def columns(table_name) end
+      # Returns an array of +Column+ objects for the table specified by +table_name+.
+      def columns(table_name)
+        table_name = table_name.to_s
+        column_definitions(table_name).map do |field|
+          new_column_from_field(table_name, field)
+        end
+      end
 
       # Checks to see if a column exists in a given table.
       #
@@ -79,19 +131,27 @@ module ActiveRecord
       #
       def column_exists?(table_name, column_name, type = nil, options = {})
         column_name = column_name.to_s
-        columns(table_name).any?{ |c| c.name == column_name &&
-                                      (!type                     || c.type == type) &&
-                                      (!options.key?(:limit)     || c.limit == options[:limit]) &&
-                                      (!options.key?(:precision) || c.precision == options[:precision]) &&
-                                      (!options.key?(:scale)     || c.scale == options[:scale]) &&
-                                      (!options.key?(:default)   || c.default == options[:default]) &&
-                                      (!options.key?(:null)      || c.null == options[:null]) }
+        checks = []
+        checks << lambda { |c| c.name == column_name }
+        checks << lambda { |c| c.type == type } if type
+        column_options_keys.each do |attr|
+          checks << lambda { |c| c.send(attr) == options[attr] } if options.key?(attr)
+        end
+
+        columns(table_name).any? { |c| checks.all? { |check| check[c] } }
+      end
+
+      # Returns just a table's primary key
+      def primary_key(table_name)
+        pk = primary_keys(table_name)
+        pk = pk.first unless pk.size > 1
+        pk
       end
 
       # Creates a new table with the name +table_name+. +table_name+ may either
       # be a String or a Symbol.
       #
-      # There are two ways to work with +create_table+. You can use the block
+      # There are two ways to work with #create_table. You can use the block
       # form or the regular form, like this:
       #
       # === Block form
@@ -123,15 +183,18 @@ module ActiveRecord
       # The +options+ hash can include the following keys:
       # [<tt>:id</tt>]
       #   Whether to automatically add a primary key column. Defaults to true.
-      #   Join tables for +has_and_belongs_to_many+ should set it to false.
+      #   Join tables for {ActiveRecord::Base.has_and_belongs_to_many}[rdoc-ref:Associations::ClassMethods#has_and_belongs_to_many] should set it to false.
       #
       #   A Symbol can be used to specify the type of the generated primary key column.
       # [<tt>:primary_key</tt>]
       #   The name of the primary key, if one is to be added automatically.
-      #   Defaults to +id+. If <tt>:id</tt> is false this option is ignored.
+      #   Defaults to +id+. If <tt>:id</tt> is false, then this option is ignored.
+      #
+      #   If an array is passed, a composite primary key will be created.
       #
       #   Note that Active Record models will automatically detect their
-      #   primary key. This can be avoided by using +self.primary_key=+ on the model
+      #   primary key. This can be avoided by using
+      #   {self.primary_key=}[rdoc-ref:AttributeMethods::PrimaryKey::ClassMethods#primary_key=] on the model
       #   to define the key explicitly.
       #
       # [<tt>:options</tt>]
@@ -142,19 +205,22 @@ module ActiveRecord
       #   Set to true to drop the table before creating it.
       #   Set to +:cascade+ to drop dependent objects as well.
       #   Defaults to false.
+      # [<tt>:if_not_exists</tt>]
+      #   Set to true to avoid raising an error when the table already exists.
+      #   Defaults to false.
       # [<tt>:as</tt>]
       #   SQL to use to generate the table. When this option is used, the block is
       #   ignored, as are the <tt>:id</tt> and <tt>:primary_key</tt> options.
       #
       # ====== Add a backend specific option to the generated SQL (MySQL)
       #
-      #   create_table(:suppliers, options: 'ENGINE=InnoDB DEFAULT CHARSET=utf8')
+      #   create_table(:suppliers, options: 'ENGINE=InnoDB DEFAULT CHARSET=utf8mb4')
       #
       # generates:
       #
       #   CREATE TABLE suppliers (
-      #     id int(11) DEFAULT NULL auto_increment PRIMARY KEY
-      #   ) ENGINE=InnoDB DEFAULT CHARSET=utf8
+      #     id bigint auto_increment PRIMARY KEY
+      #   ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4
       #
       # ====== Rename the primary key column
       #
@@ -165,7 +231,7 @@ module ActiveRecord
       # generates:
       #
       #   CREATE TABLE objects (
-      #     guid int(11) DEFAULT NULL auto_increment PRIMARY KEY,
+      #     guid bigint auto_increment PRIMARY KEY,
       #     name varchar(80)
       #   )
       #
@@ -182,18 +248,35 @@ module ActiveRecord
       #     label varchar
       #   )
       #
+      # ====== Create a composite primary key
+      #
+      #   create_table(:orders, primary_key: [:product_id, :client_id]) do |t|
+      #     t.belongs_to :product
+      #     t.belongs_to :client
+      #   end
+      #
+      # generates:
+      #
+      #   CREATE TABLE order (
+      #       product_id bigint NOT NULL,
+      #       client_id bigint NOT NULL
+      #   );
+      #
+      #   ALTER TABLE ONLY "orders"
+      #     ADD CONSTRAINT orders_pkey PRIMARY KEY (product_id, client_id);
+      #
       # ====== Do not add a primary key column
       #
       #   create_table(:categories_suppliers, id: false) do |t|
-      #     t.column :category_id, :integer
-      #     t.column :supplier_id, :integer
+      #     t.column :category_id, :bigint
+      #     t.column :supplier_id, :bigint
       #   end
       #
       # generates:
       #
       #   CREATE TABLE categories_suppliers (
-      #     category_id int,
-      #     supplier_id int
+      #     category_id bigint,
+      #     supplier_id bigint
       #   )
       #
       # ====== Create a temporary table based on a query
@@ -207,33 +290,43 @@ module ActiveRecord
       #     SELECT * FROM orders INNER JOIN line_items ON order_id=orders.id
       #
       # See also TableDefinition#column for details on how to create columns.
-      def create_table(table_name, options = {})
-        td = create_table_definition table_name, options[:temporary], options[:options], options[:as]
+      def create_table(table_name, **options)
+        td = create_table_definition(table_name, options)
 
         if options[:id] != false && !options[:as]
           pk = options.fetch(:primary_key) do
             Base.get_primary_key table_name.to_s.singularize
           end
 
-          td.primary_key pk, options.fetch(:id, :primary_key), options
+          if pk.is_a?(Array)
+            td.primary_keys pk
+          else
+            td.primary_key pk, options.fetch(:id, :primary_key), options
+          end
         end
 
         yield td if block_given?
 
-        if options[:force] && table_exists?(table_name)
-          drop_table(table_name, options)
+        if options[:force]
+          drop_table(table_name, options.merge(if_exists: true))
         end
 
         result = execute schema_creation.accept td
 
         unless supports_indexes_in_create?
-          td.indexes.each_pair do |column_name, index_options|
+          td.indexes.each do |column_name, index_options|
             add_index(table_name, column_name, index_options)
           end
         end
 
-        td.foreign_keys.each_pair do |other_table_name, foreign_key_options|
-          add_foreign_key(table_name, other_table_name, foreign_key_options)
+        if supports_comments? && !supports_comments_in_create?
+          if table_comment = options[:comment].presence
+            change_table_comment(table_name, table_comment)
+          end
+
+          td.columns.each do |column|
+            change_column_comment(table_name, column.name, column.comment) if column.comment.present?
+          end
         end
 
         result
@@ -245,9 +338,9 @@ module ActiveRecord
       #   # Creates a table called 'assemblies_parts' with no id.
       #   create_join_table(:assemblies, :parts)
       #
-      # You can pass a +options+ hash can include the following keys:
+      # You can pass an +options+ hash which can include the following keys:
       # [<tt>:table_name</tt>]
-      #   Sets the table name overriding the default
+      #   Sets the table name, overriding the default.
       # [<tt>:column_options</tt>]
       #   Any extra options you want appended to the columns definition.
       # [<tt>:options</tt>]
@@ -258,7 +351,7 @@ module ActiveRecord
       #   Set to true to drop the table before creating it.
       #   Defaults to false.
       #
-      # Note that +create_join_table+ does not create any indices by default; you can use
+      # Note that #create_join_table does not create any indices by default; you can use
       # its block form to do so yourself:
       #
       #   create_join_table :products, :categories do |t|
@@ -273,31 +366,30 @@ module ActiveRecord
       # generates:
       #
       #   CREATE TABLE assemblies_parts (
-      #     assembly_id int NOT NULL,
-      #     part_id int NOT NULL,
+      #     assembly_id bigint NOT NULL,
+      #     part_id bigint NOT NULL,
       #   ) ENGINE=InnoDB DEFAULT CHARSET=utf8
       #
-      def create_join_table(table_1, table_2, options = {})
+      def create_join_table(table_1, table_2, column_options: {}, **options)
         join_table_name = find_join_table_name(table_1, table_2, options)
 
-        column_options = options.delete(:column_options) || {}
-        column_options.reverse_merge!(null: false)
+        column_options.reverse_merge!(null: false, index: false)
 
-        t1_column, t2_column = [table_1, table_2].map{ |t| t.to_s.singularize.foreign_key }
+        t1_ref, t2_ref = [table_1, table_2].map { |t| t.to_s.singularize }
 
         create_table(join_table_name, options.merge!(id: false)) do |td|
-          td.integer t1_column, column_options
-          td.integer t2_column, column_options
+          td.references t1_ref, column_options
+          td.references t2_ref, column_options
           yield td if block_given?
         end
       end
 
       # Drops the join table specified by the given arguments.
-      # See +create_join_table+ for details.
+      # See #create_join_table for details.
       #
       # Although this command ignores the block if one is given, it can be helpful
       # to provide one in a migration's +change+ method so it can be reverted.
-      # In that case, the block will be used by create_join_table.
+      # In that case, the block will be used by #create_join_table.
       def drop_join_table(table_1, table_2, options = {})
         join_table_name = find_join_table_name(table_1, table_2, options)
         drop_table(join_table_name)
@@ -315,10 +407,12 @@ module ActiveRecord
       # [<tt>:bulk</tt>]
       #   Set this to true to make this a bulk alter query, such as
       #
-      #     ALTER TABLE `users` ADD COLUMN age INT(11), ADD COLUMN birthdate DATETIME ...
+      #     ALTER TABLE `users` ADD COLUMN age INT, ADD COLUMN birthdate DATETIME ...
       #
       #   Defaults to false.
       #
+      #   Only supported on the MySQL and PostgreSQL adapter, ignored elsewhere.
+      #
       # ====== Add a column
       #
       #   change_table(:suppliers) do |t|
@@ -343,7 +437,7 @@ module ActiveRecord
       #     t.references :company
       #   end
       #
-      # Creates a <tt>company_id(integer)</tt> column.
+      # Creates a <tt>company_id(bigint)</tt> column.
       #
       # ====== Add a polymorphic foreign key column
       #
@@ -351,7 +445,7 @@ module ActiveRecord
       #    t.belongs_to :company, polymorphic: true
       #  end
       #
-      # Creates <tt>company_type(varchar)</tt> and <tt>company_id(integer)</tt> columns.
+      # Creates <tt>company_type(varchar)</tt> and <tt>company_id(bigint)</tt> columns.
       #
       # ====== Remove a column
       #
@@ -372,7 +466,7 @@ module ActiveRecord
       #    t.remove_index :company_id
       #  end
       #
-      # See also Table for details on all of the various column transformation.
+      # See also Table for details on all of the various column transformations.
       def change_table(table_name, options = {})
         if supports_bulk_alter? && options[:bulk]
           recorder = ActiveRecord::Migration::CommandRecorder.new(self)
@@ -402,17 +496,93 @@ module ActiveRecord
       #
       # Although this command ignores most +options+ and the block if one is given,
       # it can be helpful to provide these in a migration's +change+ method so it can be reverted.
-      # In that case, +options+ and the block will be used by create_table.
+      # In that case, +options+ and the block will be used by #create_table.
       def drop_table(table_name, options = {})
         execute "DROP TABLE#{' IF EXISTS' if options[:if_exists]} #{quote_table_name(table_name)}"
       end
 
-      # Adds a new column to the named table.
-      # See TableDefinition#column for details of the options you can use.
-      #
-      # Note: Not all options will be available, generally this command should
-      # ignore most of them. In favor of doing a low-level call to simply
-      # create a column.
+      # Add a new +type+ column named +column_name+ to +table_name+.
+      #
+      # The +type+ parameter is normally one of the migrations native types,
+      # which is one of the following:
+      # <tt>:primary_key</tt>, <tt>:string</tt>, <tt>:text</tt>,
+      # <tt>:integer</tt>, <tt>:bigint</tt>, <tt>:float</tt>, <tt>:decimal</tt>, <tt>:numeric</tt>,
+      # <tt>:datetime</tt>, <tt>:time</tt>, <tt>:date</tt>,
+      # <tt>:binary</tt>, <tt>:boolean</tt>.
+      #
+      # You may use a type not in this list as long as it is supported by your
+      # database (for example, "polygon" in MySQL), but this will not be database
+      # agnostic and should usually be avoided.
+      #
+      # Available options are (none of these exists by default):
+      # * <tt>:limit</tt> -
+      #   Requests a maximum column length. This is the number of characters for a <tt>:string</tt> column
+      #   and number of bytes for <tt>:text</tt>, <tt>:binary</tt> and <tt>:integer</tt> columns.
+      #   This option is ignored by some backends.
+      # * <tt>:default</tt> -
+      #   The column's default value. Use +nil+ for +NULL+.
+      # * <tt>:null</tt> -
+      #   Allows or disallows +NULL+ values in the column.
+      # * <tt>:precision</tt> -
+      #   Specifies the precision for the <tt>:decimal</tt> and <tt>:numeric</tt> columns.
+      # * <tt>:scale</tt> -
+      #   Specifies the scale for the <tt>:decimal</tt> and <tt>:numeric</tt> columns.
+      # * <tt>:collation</tt> -
+      #   Specifies the collation for a <tt>:string</tt> or <tt>:text</tt> column. If not specified, the
+      #   column will have the same collation as the table.
+      # * <tt>:comment</tt> -
+      #   Specifies the comment for the column. This option is ignored by some backends.
+      #
+      # Note: The precision is the total number of significant digits,
+      # and the scale is the number of digits that can be stored following
+      # the decimal point. For example, the number 123.45 has a precision of 5
+      # and a scale of 2. A decimal with a precision of 5 and a scale of 2 can
+      # range from -999.99 to 999.99.
+      #
+      # Please be aware of different RDBMS implementations behavior with
+      # <tt>:decimal</tt> columns:
+      # * The SQL standard says the default scale should be 0, <tt>:scale</tt> <=
+      #   <tt>:precision</tt>, and makes no comments about the requirements of
+      #   <tt>:precision</tt>.
+      # * MySQL: <tt>:precision</tt> [1..63], <tt>:scale</tt> [0..30].
+      #   Default is (10,0).
+      # * PostgreSQL: <tt>:precision</tt> [1..infinity],
+      #   <tt>:scale</tt> [0..infinity]. No default.
+      # * SQLite3: No restrictions on <tt>:precision</tt> and <tt>:scale</tt>,
+      #   but the maximum supported <tt>:precision</tt> is 16. No default.
+      # * Oracle: <tt>:precision</tt> [1..38], <tt>:scale</tt> [-84..127].
+      #   Default is (38,0).
+      # * DB2: <tt>:precision</tt> [1..63], <tt>:scale</tt> [0..62].
+      #   Default unknown.
+      # * SqlServer: <tt>:precision</tt> [1..38], <tt>:scale</tt> [0..38].
+      #   Default (38,0).
+      #
+      # == Examples
+      #
+      #  add_column(:users, :picture, :binary, limit: 2.megabytes)
+      #  # ALTER TABLE "users" ADD "picture" blob(2097152)
+      #
+      #  add_column(:articles, :status, :string, limit: 20, default: 'draft', null: false)
+      #  # ALTER TABLE "articles" ADD "status" varchar(20) DEFAULT 'draft' NOT NULL
+      #
+      #  add_column(:answers, :bill_gates_money, :decimal, precision: 15, scale: 2)
+      #  # ALTER TABLE "answers" ADD "bill_gates_money" decimal(15,2)
+      #
+      #  add_column(:measurements, :sensor_reading, :decimal, precision: 30, scale: 20)
+      #  # ALTER TABLE "measurements" ADD "sensor_reading" decimal(30,20)
+      #
+      #  # While :scale defaults to zero on most databases, it
+      #  # probably wouldn't hurt to include it.
+      #  add_column(:measurements, :huge_integer, :decimal, precision: 30)
+      #  # ALTER TABLE "measurements" ADD "huge_integer" decimal(30)
+      #
+      #  # Defines a column that stores an array of a type.
+      #  add_column(:users, :skills, :text, array: true)
+      #  # ALTER TABLE "users" ADD "skills" text[]
+      #
+      #  # Defines a column with a database-specific type.
+      #  add_column(:shapes, :triangle, 'polygon')
+      #  # ALTER TABLE "shapes" ADD "triangle" polygon
       def add_column(table_name, column_name, type, options = {})
         at = create_alter_table table_name
         at.add_column(column_name, type, options)
@@ -436,9 +606,10 @@ module ActiveRecord
       #
       # The +type+ and +options+ parameters will be ignored if present. It can be helpful
       # to provide these in a migration's +change+ method so it can be reverted.
-      # In that case, +type+ and +options+ will be used by add_column.
+      # In that case, +type+ and +options+ will be used by #add_column.
+      # Indexes on the column are automatically removed.
       def remove_column(table_name, column_name, type = nil, options = {})
-        execute "ALTER TABLE #{quote_table_name(table_name)} DROP #{quote_column_name(column_name)}"
+        execute "ALTER TABLE #{quote_table_name(table_name)} #{remove_column_for_alter(table_name, column_name, type, options)}"
       end
 
       # Changes the column's definition according to the new options.
@@ -469,7 +640,7 @@ module ActiveRecord
         raise NotImplementedError, "change_column_default is not implemented"
       end
 
-      # Sets or removes a +NOT NULL+ constraint on a column. The +null+ flag
+      # Sets or removes a <tt>NOT NULL</tt> constraint on a column. The +null+ flag
       # indicates whether the value can be +NULL+. For example
       #
       #   change_column_null(:users, :nickname, false)
@@ -481,7 +652,7 @@ module ActiveRecord
       # allows them to be +NULL+ (drops the constraint).
       #
       # The method accepts an optional fourth argument to replace existing
-      # +NULL+s with some other value. Use that one when enabling the
+      # <tt>NULL</tt>s with some other value. Use that one when enabling the
       # constraint if needed, since otherwise those rows would not be valid.
       #
       # Please note the fourth argument does not set a column's default.
@@ -535,6 +706,8 @@ module ActiveRecord
       #
       #   CREATE INDEX by_name ON accounts(name(10))
       #
+      # ====== Creating an index with specific key lengths for multiple keys
+      #
       #   add_index(:accounts, [:name, :surname], name: 'by_name_surname', length: {name: 10, surname: 15})
       #
       # generates:
@@ -551,7 +724,7 @@ module ActiveRecord
       #
       #   CREATE INDEX by_branch_desc_party ON accounts(branch_id DESC, party_id ASC, surname)
       #
-      # Note: MySQL doesn't yet support index order (it accepts the syntax but ignores it).
+      # Note: MySQL only supports index order from 8.0.1 onwards (earlier versions accepted the syntax but ignored it).
       #
       # ====== Creating a partial index
       #
@@ -574,6 +747,19 @@ module ActiveRecord
       #
       # Note: only supported by PostgreSQL and MySQL
       #
+      # ====== Creating an index with a specific operator class
+      #
+      #   add_index(:developers, :name, using: 'gist', opclass: :gist_trgm_ops)
+      #   # CREATE INDEX developers_on_name ON developers USING gist (name gist_trgm_ops) -- PostgreSQL
+      #
+      #   add_index(:developers, [:name, :city], using: 'gist', opclass: { city: :gist_trgm_ops })
+      #   # CREATE INDEX developers_on_name_and_city ON developers USING gist (name, city gist_trgm_ops) -- PostgreSQL
+      #
+      #   add_index(:developers, [:name, :city], using: 'gist', opclass: :gist_trgm_ops)
+      #   # CREATE INDEX developers_on_name_and_city ON developers USING gist (name gist_trgm_ops, city gist_trgm_ops) -- PostgreSQL
+      #
+      # Note: only supported by PostgreSQL
+      #
       # ====== Creating an index with a specific type
       #
       #   add_index(:developers, :name, type: :fulltext)
@@ -582,7 +768,7 @@ module ActiveRecord
       #
       #   CREATE FULLTEXT INDEX index_developers_on_name ON developers (name) -- MySQL
       #
-      # Note: only supported by MySQL. Supported: <tt>:fulltext</tt> and <tt>:spatial</tt> on MyISAM tables.
+      # Note: only supported by MySQL.
       def add_index(table_name, column_name, options = {})
         index_name, index_type, index_columns, index_options = add_index_options(table_name, column_name, options)
         execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} (#{index_columns})#{index_options}"
@@ -590,15 +776,15 @@ module ActiveRecord
 
       # Removes the given index from the table.
       #
-      # Removes the +index_accounts_on_column+ in the +accounts+ table.
+      # Removes the index on +branch_id+ in the +accounts+ table if exactly one such index exists.
       #
       #   remove_index :accounts, :branch_id
       #
-      # Removes the index named +index_accounts_on_branch_id+ in the +accounts+ table.
+      # Removes the index on +branch_id+ in the +accounts+ table if exactly one such index exists.
       #
       #   remove_index :accounts, column: :branch_id
       #
-      # Removes the index named +index_accounts_on_branch_id_and_party_id+ in the +accounts+ table.
+      # Removes the index on +branch_id+ and +party_id+ in the +accounts+ table if exactly one such index exists.
       #
       #   remove_index :accounts, column: [:branch_id, :party_id]
       #
@@ -607,10 +793,7 @@ module ActiveRecord
       #   remove_index :accounts, name: :by_branch_party
       #
       def remove_index(table_name, options = {})
-        remove_index!(table_name, index_name_for_remove(table_name, options))
-      end
-
-      def remove_index!(table_name, index_name) #:nodoc:
+        index_name = index_name_for_remove(table_name, options)
         execute "DROP INDEX #{quote_column_name(index_name)} ON #{quote_table_name(table_name)}"
       end
 
@@ -623,7 +806,7 @@ module ActiveRecord
       def rename_index(table_name, old_name, new_name)
         validate_index_length!(table_name, new_name)
 
-        # this is a naive implementation; some DBs may support this more efficiently (Postgres, for instance)
+        # this is a naive implementation; some DBs may support this more efficiently (PostgreSQL, for instance)
         old_index_def = indexes(table_name).detect { |i| i.name == old_name }
         return unless old_index_def
         add_index(table_name, old_index_def.columns, name: new_name, unique: old_index_def.unique)
@@ -640,62 +823,73 @@ module ActiveRecord
             raise ArgumentError, "You must specify the index name"
           end
         else
-          index_name(table_name, :column => options)
+          index_name(table_name, index_name_options(options))
         end
       end
 
       # Verifies the existence of an index with a given name.
-      #
-      # The default argument is returned if the underlying implementation does not define the indexes method,
-      # as there's no way to determine the correct answer in that case.
-      def index_name_exists?(table_name, index_name, default)
-        return default unless respond_to?(:indexes)
+      def index_name_exists?(table_name, index_name)
         index_name = index_name.to_s
         indexes(table_name).detect { |i| i.name == index_name }
       end
 
-      # Adds a reference. The reference column is an integer by default,
+      # Adds a reference. The reference column is a bigint by default,
       # the <tt>:type</tt> option can be used to specify a different type.
       # Optionally adds a +_type+ column, if <tt>:polymorphic</tt> option is provided.
-      # <tt>add_reference</tt> and <tt>add_belongs_to</tt> are acceptable.
+      # #add_reference and #add_belongs_to are acceptable.
       #
       # The +options+ hash can include the following keys:
       # [<tt>:type</tt>]
-      #   The reference column type. Defaults to +:integer+.
+      #   The reference column type. Defaults to +:bigint+.
       # [<tt>:index</tt>]
-      #   Add an appropriate index. Defaults to false.
+      #   Add an appropriate index. Defaults to true.
+      #   See #add_index for usage of this option.
       # [<tt>:foreign_key</tt>]
-      #   Add an appropriate foreign key. Defaults to false.
+      #   Add an appropriate foreign key constraint. Defaults to false.
       # [<tt>:polymorphic</tt>]
       #   Whether an additional +_type+ column should be added. Defaults to false.
+      # [<tt>:null</tt>]
+      #   Whether the column allows nulls. Defaults to true.
       #
-      # ====== Create a user_id integer column
+      # ====== Create a user_id bigint column without a index
       #
-      #   add_reference(:products, :user)
+      #   add_reference(:products, :user, index: false)
       #
       # ====== Create a user_id string column
       #
       #   add_reference(:products, :user, type: :string)
       #
-      # ====== Create supplier_id, supplier_type columns and appropriate index
+      # ====== Create supplier_id, supplier_type columns
+      #
+      #   add_reference(:products, :supplier, polymorphic: true)
       #
-      #   add_reference(:products, :supplier, polymorphic: true, index: true)
+      # ====== Create a supplier_id column with a unique index
+      #
+      #   add_reference(:products, :supplier, index: { unique: true })
+      #
+      # ====== Create a supplier_id column with a named index
+      #
+      #   add_reference(:products, :supplier, index: { name: "my_supplier_index" })
       #
       # ====== Create a supplier_id column and appropriate foreign key
       #
       #   add_reference(:products, :supplier, foreign_key: true)
       #
-      def add_reference(table_name, *args)
-        ReferenceDefinition.new(*args).add_to(update_table_definition(table_name, self))
+      # ====== Create a supplier_id column and a foreign key to the firms table
+      #
+      #   add_reference(:products, :supplier, foreign_key: {to_table: :firms})
+      #
+      def add_reference(table_name, ref_name, **options)
+        ReferenceDefinition.new(ref_name, options).add_to(update_table_definition(table_name, self))
       end
       alias :add_belongs_to :add_reference
 
       # Removes the reference(s). Also removes a +type+ column if one exists.
-      # <tt>remove_reference</tt> and <tt>remove_belongs_to</tt> are acceptable.
+      # #remove_reference and #remove_belongs_to are acceptable.
       #
       # ====== Remove the reference
       #
-      #   remove_reference(:products, :user, index: true)
+      #   remove_reference(:products, :user, index: false)
       #
       # ====== Remove polymorphic reference
       #
@@ -703,21 +897,27 @@ module ActiveRecord
       #
       # ====== Remove the reference with a foreign key
       #
-      #   remove_reference(:products, :user, index: true, foreign_key: true)
+      #   remove_reference(:products, :user, foreign_key: true)
       #
-      def remove_reference(table_name, ref_name, options = {})
-        if options[:foreign_key]
+      def remove_reference(table_name, ref_name, foreign_key: false, polymorphic: false, **options)
+        if foreign_key
           reference_name = Base.pluralize_table_names ? ref_name.to_s.pluralize : ref_name
-          remove_foreign_key(table_name, reference_name)
+          if foreign_key.is_a?(Hash)
+            foreign_key_options = foreign_key
+          else
+            foreign_key_options = { to_table: reference_name }
+          end
+          foreign_key_options[:column] ||= "#{ref_name}_id"
+          remove_foreign_key(table_name, foreign_key_options)
         end
 
         remove_column(table_name, "#{ref_name}_id")
-        remove_column(table_name, "#{ref_name}_type") if options[:polymorphic]
+        remove_column(table_name, "#{ref_name}_type") if polymorphic
       end
       alias :remove_belongs_to :remove_reference
 
       # Returns an array of foreign keys for the given table.
-      # The foreign keys are represented as +ForeignKeyDefinition+ objects.
+      # The foreign keys are represented as ForeignKeyDefinition objects.
       def foreign_keys(table_name)
         raise NotImplementedError, "foreign_keys is not implemented"
       end
@@ -735,7 +935,7 @@ module ActiveRecord
       #
       # generates:
       #
-      #   ALTER TABLE "articles" ADD CONSTRAINT articles_author_id_fk FOREIGN KEY ("author_id") REFERENCES "authors" ("id")
+      #   ALTER TABLE "articles" ADD CONSTRAINT fk_rails_e74ce85cbc FOREIGN KEY ("author_id") REFERENCES "authors" ("id")
       #
       # ====== Creating a foreign key on a specific column
       #
@@ -751,7 +951,7 @@ module ActiveRecord
       #
       # generates:
       #
-      #   ALTER TABLE "articles" ADD CONSTRAINT articles_author_id_fk FOREIGN KEY ("author_id") REFERENCES "authors" ("id") ON DELETE CASCADE
+      #   ALTER TABLE "articles" ADD CONSTRAINT fk_rails_e74ce85cbc FOREIGN KEY ("author_id") REFERENCES "authors" ("id") ON DELETE CASCADE
       #
       # The +options+ hash can include the following keys:
       # [<tt>:column</tt>]
@@ -761,21 +961,15 @@ module ActiveRecord
       # [<tt>:name</tt>]
       #   The constraint name. Defaults to <tt>fk_rails_<identifier></tt>.
       # [<tt>:on_delete</tt>]
-      #   Action that happens <tt>ON DELETE</tt>. Valid values are +:nullify+, +:cascade:+ and +:restrict+
+      #   Action that happens <tt>ON DELETE</tt>. Valid values are +:nullify+, +:cascade+ and +:restrict+
       # [<tt>:on_update</tt>]
-      #   Action that happens <tt>ON UPDATE</tt>. Valid values are +:nullify+, +:cascade:+ and +:restrict+
+      #   Action that happens <tt>ON UPDATE</tt>. Valid values are +:nullify+, +:cascade+ and +:restrict+
+      # [<tt>:validate</tt>]
+      #   (Postgres only) Specify whether or not the constraint should be validated. Defaults to +true+.
       def add_foreign_key(from_table, to_table, options = {})
         return unless supports_foreign_keys?
 
-        options[:column] ||= foreign_key_column_for(to_table)
-
-        options = {
-          column: options[:column],
-          primary_key: options[:primary_key],
-          name: foreign_key_name(from_table, options),
-          on_delete: options[:on_delete],
-          on_update: options[:on_update]
-        }
+        options = foreign_key_options(from_table, to_table, options)
         at = create_alter_table from_table
         at.add_foreign_key to_table, options
 
@@ -795,11 +989,18 @@ module ActiveRecord
       #
       #   remove_foreign_key :accounts, column: :owner_id
       #
+      # Removes the foreign key on +accounts.owner_id+.
+      #
+      #   remove_foreign_key :accounts, to_table: :owners
+      #
       # Removes the foreign key named +special_fk_name+ on the +accounts+ table.
       #
       #   remove_foreign_key :accounts, name: :special_fk_name
       #
-      # The +options+ hash accepts the same keys as SchemaStatements#add_foreign_key.
+      # The +options+ hash accepts the same keys as SchemaStatements#add_foreign_key
+      # with an addition of
+      # [<tt>:to_table</tt>]
+      #   The name of the table that contains the referenced primary key.
       def remove_foreign_key(from_table, options_or_to_table = {})
         return unless supports_foreign_keys?
 
@@ -813,29 +1014,19 @@ module ActiveRecord
 
       # Checks to see if a foreign key exists on a table for a given foreign key definition.
       #
-      #   # Check a foreign key exists
+      #   # Checks to see if a foreign key exists.
       #   foreign_key_exists?(:accounts, :branches)
       #
-      #   # Check a foreign key on a specified column exists
+      #   # Checks to see if a foreign key on a specified column exists.
       #   foreign_key_exists?(:accounts, column: :owner_id)
       #
-      #   # Check a foreign key with a custom name exists
+      #   # Checks to see if a foreign key with a custom name exists.
       #   foreign_key_exists?(:accounts, name: "special_fk_name")
       #
       def foreign_key_exists?(from_table, options_or_to_table = {})
         foreign_key_for(from_table, options_or_to_table).present?
       end
 
-      def foreign_key_for(from_table, options_or_to_table = {}) # :nodoc:
-        return unless supports_foreign_keys?
-        foreign_keys(from_table).detect {|fk| fk.defined_for? options_or_to_table }
-      end
-
-      def foreign_key_for!(from_table, options_or_to_table = {}) # :nodoc:
-        foreign_key_for(from_table, options_or_to_table) or \
-          raise ArgumentError, "Table '#{from_table}' has no foreign key for #{options_or_to_table}"
-      end
-
       def foreign_key_column_for(table_name) # :nodoc:
         prefix = Base.table_name_prefix
         suffix = Base.table_name_suffix
@@ -843,48 +1034,48 @@ module ActiveRecord
         "#{name.singularize}_id"
       end
 
-      def dump_schema_information #:nodoc:
-        sm_table = ActiveRecord::Migrator.schema_migrations_table_name
+      def foreign_key_options(from_table, to_table, options) # :nodoc:
+        options = options.dup
+        options[:column] ||= foreign_key_column_for(to_table)
+        options[:name]   ||= foreign_key_name(from_table, options)
+        options
+      end
 
-        ActiveRecord::SchemaMigration.order('version').map { |sm|
-          "INSERT INTO #{sm_table} (version) VALUES ('#{sm.version}');"
-        }.join "\n\n"
+      def dump_schema_information #:nodoc:
+        versions = ActiveRecord::SchemaMigration.all_versions
+        insert_versions_sql(versions) if versions.any?
       end
 
-      # Should not be called normally, but this operation is non-destructive.
-      # The migrations module handles this automatically.
-      def initialize_schema_migrations_table
-        ActiveRecord::SchemaMigration.create_table
+      def internal_string_options_for_primary_key # :nodoc:
+        { primary_key: true }
       end
 
-      def assume_migrated_upto_version(version, migrations_paths = ActiveRecord::Migrator.migrations_paths)
+      def assume_migrated_upto_version(version, migrations_paths)
         migrations_paths = Array(migrations_paths)
         version = version.to_i
-        sm_table = quote_table_name(ActiveRecord::Migrator.schema_migrations_table_name)
+        sm_table = quote_table_name(ActiveRecord::SchemaMigration.table_name)
 
-        migrated = select_values("SELECT version FROM #{sm_table}").map(&:to_i)
-        paths = migrations_paths.map {|p| "#{p}/[0-9]*_*.rb" }
-        versions = Dir[*paths].map do |filename|
-          filename.split('/').last.split('_').first.to_i
+        migrated = ActiveRecord::SchemaMigration.all_versions.map(&:to_i)
+        versions = migration_context.migration_files.map do |file|
+          migration_context.parse_migration_filename(file).first.to_i
         end
 
         unless migrated.include?(version)
-          execute "INSERT INTO #{sm_table} (version) VALUES ('#{version}')"
+          execute "INSERT INTO #{sm_table} (version) VALUES (#{quote(version)})"
         end
 
-        inserted = Set.new
-        (versions - migrated).each do |v|
-          if inserted.include?(v)
-            raise "Duplicate migration #{v}. Please renumber your migrations to resolve the conflict."
-          elsif v < version
-            execute "INSERT INTO #{sm_table} (version) VALUES ('#{v}')"
-            inserted << v
+        inserting = (versions - migrated).select { |v| v < version }
+        if inserting.any?
+          if (duplicate = inserting.detect { |v| inserting.count(v) > 1 })
+            raise "Duplicate migration #{duplicate}. Please renumber your migrations to resolve the conflict."
           end
+          execute insert_versions_sql(inserting)
         end
       end
 
-      def type_to_sql(type, limit = nil, precision = nil, scale = nil) #:nodoc:
-        if native = native_database_types[type.to_sym]
+      def type_to_sql(type, limit: nil, precision: nil, scale: nil, **) # :nodoc:
+        type = type.to_sym if type
+        if native = native_database_types[type]
           column_type_sql = (native.is_a?(Hash) ? native[:name] : native).dup
 
           if type == :decimal # ignore limit, use precision and scale
@@ -900,7 +1091,7 @@ module ActiveRecord
               raise ArgumentError, "Error adding decimal column: precision cannot be empty if scale is specified"
             end
 
-          elsif [:datetime, :time].include?(type) && precision ||= native[:precision]
+          elsif [:datetime, :timestamp, :time, :interval].include?(type) && precision ||= native[:precision]
             if (0..6) === precision
               column_type_sql << "(#{precision})"
             else
@@ -917,18 +1108,19 @@ module ActiveRecord
       end
 
       # Given a set of columns and an ORDER BY clause, returns the columns for a SELECT DISTINCT.
-      # Both PostgreSQL and Oracle overrides this for custom DISTINCT syntax - they
+      # PostgreSQL, MySQL, and Oracle override this for custom DISTINCT syntax - they
       # require the order columns appear in the SELECT.
       #
       #   columns_for_distinct("posts.id", ["posts.created_at desc"])
-      def columns_for_distinct(columns, orders) #:nodoc:
+      #
+      def columns_for_distinct(columns, orders) # :nodoc:
         columns
       end
 
       # Adds timestamps (+created_at+ and +updated_at+) columns to +table_name+.
-      # Additional options (like <tt>null: false</tt>) are forwarded to #add_column.
+      # Additional options (like +:null+) are forwarded to #add_column.
       #
-      #   add_timestamps(:suppliers, null: false)
+      #   add_timestamps(:suppliers, null: true)
       #
       def add_timestamps(table_name, options = {})
         options[:null] = false if options[:null].nil?
@@ -950,16 +1142,15 @@ module ActiveRecord
         Table.new(table_name, base)
       end
 
-      def add_index_options(table_name, column_name, options = {}) #:nodoc:
-        column_names = Array(column_name)
+      def add_index_options(table_name, column_name, comment: nil, **options) # :nodoc:
+        column_names = index_column_names(column_name)
 
-        options.assert_valid_keys(:unique, :order, :name, :where, :length, :internal, :using, :algorithm, :type)
+        options.assert_valid_keys(:unique, :order, :name, :where, :length, :internal, :using, :algorithm, :type, :opclass)
 
         index_type = options[:type].to_s if options.key?(:type)
         index_type ||= options[:unique] ? "UNIQUE" : ""
         index_name = options[:name].to_s if options.key?(:name)
-        index_name ||= index_name(table_name, column: column_names)
-        max_index_length = options.fetch(:internal, false) ? index_name_length : allowed_index_name_length
+        index_name ||= index_name(table_name, column_names)
 
         if options.key?(:algorithm)
           algorithm = index_algorithms.fetch(options[:algorithm]) {
@@ -973,63 +1164,99 @@ module ActiveRecord
           index_options = options[:where] ? " WHERE #{options[:where]}" : ""
         end
 
-        if index_name.length > max_index_length
-          raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' is too long; the limit is #{max_index_length} characters"
-        end
-        if table_exists?(table_name) && index_name_exists?(table_name, index_name, false)
+        validate_index_length!(table_name, index_name, options.fetch(:internal, false))
+
+        if data_source_exists?(table_name) && index_name_exists?(table_name, index_name)
           raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' already exists"
         end
         index_columns = quoted_columns_for_index(column_names, options).join(", ")
 
-        [index_name, index_type, index_columns, index_options, algorithm, using]
+        [index_name, index_type, index_columns, index_options, algorithm, using, comment]
       end
 
-      protected
-        def add_index_sort_order(option_strings, column_names, options = {})
-          if options.is_a?(Hash) && order = options[:order]
-            case order
-            when Hash
-              column_names.each {|name| option_strings[name] += " #{order[name].upcase}" if order.has_key?(name)}
-            when String
-              column_names.each {|name| option_strings[name] += " #{order.upcase}"}
-            end
-          end
+      def options_include_default?(options)
+        options.include?(:default) && !(options[:null] == false && options[:default].nil?)
+      end
+
+      # Changes the comment for a table or removes it if +nil+.
+      def change_table_comment(table_name, comment)
+        raise NotImplementedError, "#{self.class} does not support changing table comments"
+      end
+
+      # Changes the comment for a column or removes it if +nil+.
+      def change_column_comment(table_name, column_name, comment)
+        raise NotImplementedError, "#{self.class} does not support changing column comments"
+      end
+
+      def create_schema_dumper(options) # :nodoc:
+        SchemaDumper.create(self, options)
+      end
 
-          return option_strings
+      private
+        def column_options_keys
+          [:limit, :precision, :scale, :default, :null, :collation, :comment]
         end
 
-        # Overridden by the MySQL adapter for supporting index lengths
-        def quoted_columns_for_index(column_names, options = {})
-          option_strings = Hash[column_names.map {|name| [name, '']}]
+        def add_index_sort_order(quoted_columns, **options)
+          orders = options_for_index_columns(options[:order])
+          quoted_columns.each do |name, column|
+            column << " #{orders[name].upcase}" if orders[name].present?
+          end
+        end
 
-          # add index sort order if supported
+        def options_for_index_columns(options)
+          if options.is_a?(Hash)
+            options.symbolize_keys
+          else
+            Hash.new { |hash, column| hash[column] = options }
+          end
+        end
+
+        # Overridden by the MySQL adapter for supporting index lengths and by
+        # the PostgreSQL adapter for supporting operator classes.
+        def add_options_for_index_columns(quoted_columns, **options)
           if supports_index_sort_order?
-            option_strings = add_index_sort_order(option_strings, column_names, options)
+            quoted_columns = add_index_sort_order(quoted_columns, options)
           end
 
-          column_names.map {|name| quote_column_name(name) + option_strings[name]}
+          quoted_columns
         end
 
-        def options_include_default?(options)
-          options.include?(:default) && !(options[:null] == false && options[:default].nil?)
+        def quoted_columns_for_index(column_names, **options)
+          return [column_names] if column_names.is_a?(String)
+
+          quoted_columns = Hash[column_names.map { |name| [name.to_sym, quote_column_name(name).dup] }]
+          add_options_for_index_columns(quoted_columns, options).values
         end
 
         def index_name_for_remove(table_name, options = {})
-          index_name = index_name(table_name, options)
+          return options[:name] if can_remove_index_by_name?(options)
 
-          unless index_name_exists?(table_name, index_name, true)
-            if options.is_a?(Hash) && options.has_key?(:name)
-              options_without_column = options.dup
-              options_without_column.delete :column
-              index_name_without_column = index_name(table_name, options_without_column)
+          checks = []
 
-              return index_name_without_column if index_name_exists?(table_name, index_name_without_column, false)
-            end
+          if options.is_a?(Hash)
+            checks << lambda { |i| i.name == options[:name].to_s } if options.key?(:name)
+            column_names = index_column_names(options[:column])
+          else
+            column_names = index_column_names(options)
+          end
 
-            raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' does not exist"
+          if column_names.present?
+            checks << lambda { |i| index_name(table_name, i.columns) == index_name(table_name, column_names) }
           end
 
-          index_name
+          raise ArgumentError, "No name or columns specified" if checks.none?
+
+          matching_indexes = indexes(table_name).select { |i| checks.all? { |check| check[i] } }
+
+          if matching_indexes.count > 1
+            raise ArgumentError, "Multiple indexes found on #{table_name} columns #{column_names}. " \
+                                 "Specify an index name from #{matching_indexes.map(&:name).join(', ')}"
+          elsif matching_indexes.none?
+            raise ArgumentError, "No indexes found on #{table_name} with the options provided."
+          else
+            matching_indexes.first.name
+          end
         end
 
         def rename_table_indexes(table_name, new_name)
@@ -1054,36 +1281,126 @@ module ActiveRecord
           end
         end
 
-      private
-      def create_table_definition(name, temporary = false, options = nil, as = nil)
-        TableDefinition.new native_database_types, name, temporary, options, as
-      end
+        def schema_creation
+          SchemaCreation.new(self)
+        end
 
-      def create_alter_table(name)
-        AlterTable.new create_table_definition(name)
-      end
+        def create_table_definition(*args)
+          TableDefinition.new(*args)
+        end
 
-      def foreign_key_name(table_name, options) # :nodoc:
-        identifier = "#{table_name}_#{options.fetch(:column)}_fk"
-        hashed_identifier = Digest::SHA256.hexdigest(identifier).first(10)
-        options.fetch(:name) do
-          "fk_rails_#{hashed_identifier}"
+        def create_alter_table(name)
+          AlterTable.new create_table_definition(name)
         end
-      end
 
-      def validate_index_length!(table_name, new_name) # :nodoc:
-        if new_name.length > allowed_index_name_length
-          raise ArgumentError, "Index name '#{new_name}' on table '#{table_name}' is too long; the limit is #{allowed_index_name_length} characters"
+        def fetch_type_metadata(sql_type)
+          cast_type = lookup_cast_type(sql_type)
+          SqlTypeMetadata.new(
+            sql_type: sql_type,
+            type: cast_type.type,
+            limit: cast_type.limit,
+            precision: cast_type.precision,
+            scale: cast_type.scale,
+          )
         end
-      end
 
-      def extract_new_default_value(default_or_changes)
-        if default_or_changes.is_a?(Hash) && default_or_changes.has_key?(:from) && default_or_changes.has_key?(:to)
-          default_or_changes[:to]
-        else
-          default_or_changes
+        def index_column_names(column_names)
+          if column_names.is_a?(String) && /\W/.match?(column_names)
+            column_names
+          else
+            Array(column_names)
+          end
+        end
+
+        def index_name_options(column_names)
+          if column_names.is_a?(String) && /\W/.match?(column_names)
+            column_names = column_names.scan(/\w+/).join("_")
+          end
+
+          { column: column_names }
+        end
+
+        def foreign_key_name(table_name, options)
+          options.fetch(:name) do
+            identifier = "#{table_name}_#{options.fetch(:column)}_fk"
+            hashed_identifier = Digest::SHA256.hexdigest(identifier).first(10)
+
+            "fk_rails_#{hashed_identifier}"
+          end
+        end
+
+        def foreign_key_for(from_table, options_or_to_table = {})
+          return unless supports_foreign_keys?
+          foreign_keys(from_table).detect { |fk| fk.defined_for? options_or_to_table }
+        end
+
+        def foreign_key_for!(from_table, options_or_to_table = {})
+          foreign_key_for(from_table, options_or_to_table) || \
+            raise(ArgumentError, "Table '#{from_table}' has no foreign key for #{options_or_to_table}")
+        end
+
+        def extract_foreign_key_action(specifier)
+          case specifier
+          when "CASCADE"; :cascade
+          when "SET NULL"; :nullify
+          when "RESTRICT"; :restrict
+          end
+        end
+
+        def validate_index_length!(table_name, new_name, internal = false)
+          max_index_length = internal ? index_name_length : allowed_index_name_length
+
+          if new_name.length > max_index_length
+            raise ArgumentError, "Index name '#{new_name}' on table '#{table_name}' is too long; the limit is #{allowed_index_name_length} characters"
+          end
+        end
+
+        def extract_new_default_value(default_or_changes)
+          if default_or_changes.is_a?(Hash) && default_or_changes.has_key?(:from) && default_or_changes.has_key?(:to)
+            default_or_changes[:to]
+          else
+            default_or_changes
+          end
+        end
+
+        def can_remove_index_by_name?(options)
+          options.is_a?(Hash) && options.key?(:name) && options.except(:name, :algorithm).empty?
+        end
+
+        def add_column_for_alter(table_name, column_name, type, options = {})
+          td = create_table_definition(table_name)
+          cd = td.new_column_definition(column_name, type, options)
+          schema_creation.accept(AddColumnDefinition.new(cd))
+        end
+
+        def remove_column_for_alter(table_name, column_name, type = nil, options = {})
+          "DROP COLUMN #{quote_column_name(column_name)}"
+        end
+
+        def remove_columns_for_alter(table_name, *column_names)
+          column_names.map { |column_name| remove_column_for_alter(table_name, column_name) }
+        end
+
+        def insert_versions_sql(versions)
+          sm_table = quote_table_name(ActiveRecord::SchemaMigration.table_name)
+
+          if versions.is_a?(Array)
+            sql = +"INSERT INTO #{sm_table} (version) VALUES\n"
+            sql << versions.map { |v| "(#{quote(v)})" }.join(",\n")
+            sql << ";\n\n"
+            sql
+          else
+            "INSERT INTO #{sm_table} (version) VALUES (#{quote(versions)});"
+          end
+        end
+
+        def data_source_sql(name = nil, type: nil)
+          raise NotImplementedError
+        end
+
+        def quoted_scope(name = nil, type: nil)
+          raise NotImplementedError
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
index 295a7bed87..0f2b1e85ff 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
@@ -1,10 +1,15 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     class TransactionState
-      VALID_STATES = Set.new([:committed, :rolledback, nil])
-
       def initialize(state = nil)
         @state = state
+        @children = []
+      end
+
+      def add_child(state)
+        @children << state
       end
 
       def finalized?
@@ -12,11 +17,23 @@ module ActiveRecord
       end
 
       def committed?
-        @state == :committed
+        @state == :committed || @state == :fully_committed
+      end
+
+      def fully_committed?
+        @state == :fully_committed
       end
 
       def rolledback?
-        @state == :rolledback
+        @state == :rolledback || @state == :fully_rolledback
+      end
+
+      def fully_rolledback?
+        @state == :fully_rolledback
+      end
+
+      def fully_completed?
+        completed?
       end
 
       def completed?
@@ -24,15 +41,49 @@ module ActiveRecord
       end
 
       def set_state(state)
-        unless VALID_STATES.include?(state)
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          The set_state method is deprecated and will be removed in
+          Rails 6.0. Please use rollback! or commit! to set transaction
+          state directly.
+        MSG
+        case state
+        when :rolledback
+          rollback!
+        when :committed
+          commit!
+        when nil
+          nullify!
+        else
           raise ArgumentError, "Invalid transaction state: #{state}"
         end
-        @state = state
+      end
+
+      def rollback!
+        @children.each { |c| c.rollback! }
+        @state = :rolledback
+      end
+
+      def full_rollback!
+        @children.each { |c| c.rollback! }
+        @state = :fully_rolledback
+      end
+
+      def commit!
+        @state = :committed
+      end
+
+      def full_commit!
+        @state = :fully_committed
+      end
+
+      def nullify!
+        @state = nil
       end
     end
 
     class NullTransaction #:nodoc:
       def initialize; end
+      def state; end
       def closed?; true; end
       def open?; false; end
       def joinable?; false; end
@@ -40,14 +91,14 @@ module ActiveRecord
     end
 
     class Transaction #:nodoc:
-
-      attr_reader :connection, :state, :records, :savepoint_name
-      attr_writer :joinable
+      attr_reader :connection, :state, :records, :savepoint_name, :isolation_level
 
       def initialize(connection, options, run_commit_callbacks: false)
         @connection = connection
         @state = TransactionState.new
         @records = []
+        @isolation_level = options[:isolation]
+        @materialized = false
         @joinable = options.fetch(:joinable, true)
         @run_commit_callbacks = run_commit_callbacks
       end
@@ -56,8 +107,12 @@ module ActiveRecord
         records << record
       end
 
-      def rollback
-        @state.set_state(:rolledback)
+      def materialize!
+        @materialized = true
+      end
+
+      def materialized?
+        @materialized
       end
 
       def rollback_records
@@ -71,10 +126,6 @@ module ActiveRecord
         end
       end
 
-      def commit
-        @state.set_state(:committed)
-      end
-
       def before_commit_records
         records.uniq.each(&:before_committed!) if @run_commit_callbacks
       end
@@ -86,7 +137,7 @@ module ActiveRecord
             record.committed!
           else
             # if not running callbacks, only adds the record to the parent transaction
-            record.add_to_transaction
+            connection.add_transaction_record(record)
           end
         end
       ensure
@@ -100,47 +151,55 @@ module ActiveRecord
     end
 
     class SavepointTransaction < Transaction
+      def initialize(connection, savepoint_name, parent_transaction, *args)
+        super(connection, *args)
+
+        parent_transaction.state.add_child(@state)
 
-      def initialize(connection, savepoint_name, options, *args)
-        super(connection, options, *args)
-        if options[:isolation]
+        if isolation_level
           raise ActiveRecord::TransactionIsolationError, "cannot set transaction isolation in a nested transaction"
         end
-        connection.create_savepoint(@savepoint_name = savepoint_name)
+
+        @savepoint_name = savepoint_name
       end
 
-      def rollback
-        connection.rollback_to_savepoint(savepoint_name)
+      def materialize!
+        connection.create_savepoint(savepoint_name)
         super
       end
 
+      def rollback
+        connection.rollback_to_savepoint(savepoint_name) if materialized?
+        @state.rollback!
+      end
+
       def commit
-        connection.release_savepoint(savepoint_name)
-        super
+        connection.release_savepoint(savepoint_name) if materialized?
+        @state.commit!
       end
 
       def full_rollback?; false; end
     end
 
     class RealTransaction < Transaction
-
-      def initialize(connection, options, *args)
-        super
-        if options[:isolation]
-          connection.begin_isolated_db_transaction(options[:isolation])
+      def materialize!
+        if isolation_level
+          connection.begin_isolated_db_transaction(isolation_level)
         else
           connection.begin_db_transaction
         end
+
+        super
       end
 
       def rollback
-        connection.rollback_db_transaction
-        super
+        connection.rollback_db_transaction if materialized?
+        @state.full_rollback!
       end
 
       def commit
-        connection.commit_db_transaction
-        super
+        connection.commit_db_transaction if materialized?
+        @state.full_commit!
       end
     end
 
@@ -148,52 +207,103 @@ module ActiveRecord
       def initialize(connection)
         @stack = []
         @connection = connection
+        @has_unmaterialized_transactions = false
+        @materializing_transactions = false
+        @lazy_transactions_enabled = true
       end
 
       def begin_transaction(options = {})
-        run_commit_callbacks = !current_transaction.joinable?
-        transaction =
-          if @stack.empty?
-            RealTransaction.new(@connection, options, run_commit_callbacks: run_commit_callbacks)
-          else
-            SavepointTransaction.new(@connection, "active_record_#{@stack.size}", options,
-                                     run_commit_callbacks: run_commit_callbacks)
-          end
+        @connection.lock.synchronize do
+          run_commit_callbacks = !current_transaction.joinable?
+          transaction =
+            if @stack.empty?
+              RealTransaction.new(@connection, options, run_commit_callbacks: run_commit_callbacks)
+            else
+              SavepointTransaction.new(@connection, "active_record_#{@stack.size}", @stack.last, options,
+                                       run_commit_callbacks: run_commit_callbacks)
+            end
+
+          transaction.materialize! unless @connection.supports_lazy_transactions? && lazy_transactions_enabled?
+          @stack.push(transaction)
+          @has_unmaterialized_transactions = true if @connection.supports_lazy_transactions?
+          transaction
+        end
+      end
+
+      def disable_lazy_transactions!
+        materialize_transactions
+        @lazy_transactions_enabled = false
+      end
+
+      def enable_lazy_transactions!
+        @lazy_transactions_enabled = true
+      end
 
-        @stack.push(transaction)
-        transaction
+      def lazy_transactions_enabled?
+        @lazy_transactions_enabled
+      end
+
+      def materialize_transactions
+        return if @materializing_transactions
+        return unless @has_unmaterialized_transactions
+
+        @connection.lock.synchronize do
+          begin
+            @materializing_transactions = true
+            @stack.each { |t| t.materialize! unless t.materialized? }
+          ensure
+            @materializing_transactions = false
+          end
+          @has_unmaterialized_transactions = false
+        end
       end
 
       def commit_transaction
-        transaction = @stack.last
-        transaction.before_commit_records
-        @stack.pop
-        transaction.commit
-        transaction.commit_records
+        @connection.lock.synchronize do
+          transaction = @stack.last
+
+          begin
+            transaction.before_commit_records
+          ensure
+            @stack.pop
+          end
+
+          transaction.commit
+          transaction.commit_records
+        end
       end
 
       def rollback_transaction(transaction = nil)
-        transaction ||= @stack.pop
-        transaction.rollback
-        transaction.rollback_records
+        @connection.lock.synchronize do
+          transaction ||= @stack.pop
+          transaction.rollback
+          transaction.rollback_records
+        end
       end
 
       def within_new_transaction(options = {})
-        transaction = begin_transaction options
-        yield
-      rescue Exception => error
-        rollback_transaction if transaction
-        raise
-      ensure
-        unless error
-          if Thread.current.status == 'aborting'
-            rollback_transaction if transaction
-          else
-            begin
-              commit_transaction
-            rescue Exception
-              rollback_transaction(transaction) unless transaction.state.completed?
-              raise
+        @connection.lock.synchronize do
+          begin
+            transaction = begin_transaction options
+            yield
+          rescue Exception => error
+            if transaction
+              rollback_transaction
+              after_failure_actions(transaction, error)
+            end
+            raise
+          ensure
+            unless error
+              if Thread.current.status == "aborting"
+                rollback_transaction if transaction
+              else
+                begin
+                  commit_transaction if transaction
+                rescue Exception
+                  rollback_transaction(transaction) unless transaction.state.completed?
+                  raise
+                end
+              end
             end
           end
         end
@@ -208,7 +318,15 @@ module ActiveRecord
       end
 
       private
+
         NULL_TRANSACTION = NullTransaction.new
+
+        # Deallocate invalidated prepared statements outside of the transaction
+        def after_failure_actions(transaction, error)
+          return unless transaction.is_a?(RealTransaction)
+          return unless error.is_a?(ActiveRecord::PreparedStatementCacheExpired)
+          @connection.clear_cache!
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 6d3a21a3dc..0fe868478c 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -1,11 +1,15 @@
-require 'active_record/type'
-require 'active_support/core_ext/benchmark'
-require 'active_record/connection_adapters/schema_cache'
-require 'active_record/connection_adapters/sql_type_metadata'
-require 'active_record/connection_adapters/abstract/schema_dumper'
-require 'active_record/connection_adapters/abstract/schema_creation'
-require 'arel/collectors/bind'
-require 'arel/collectors/sql_string'
+# frozen_string_literal: true
+
+require "active_record/connection_adapters/determine_if_preparable_visitor"
+require "active_record/connection_adapters/schema_cache"
+require "active_record/connection_adapters/sql_type_metadata"
+require "active_record/connection_adapters/abstract/schema_dumper"
+require "active_record/connection_adapters/abstract/schema_creation"
+require "active_support/concurrency/load_interlock_aware_monitor"
+require "arel/collectors/bind"
+require "arel/collectors/composite"
+require "arel/collectors/sql_string"
+require "arel/collectors/substitute_binds"
 
 module ActiveRecord
   module ConnectionAdapters # :nodoc:
@@ -14,7 +18,7 @@ module ActiveRecord
     autoload :Column
     autoload :ConnectionSpecification
 
-    autoload_at 'active_record/connection_adapters/abstract/schema_definitions' do
+    autoload_at "active_record/connection_adapters/abstract/schema_definitions" do
       autoload :IndexDefinition
       autoload :ColumnDefinition
       autoload :ChangeColumnDefinition
@@ -22,14 +26,14 @@ module ActiveRecord
       autoload :TableDefinition
       autoload :Table
       autoload :AlterTable
+      autoload :ReferenceDefinition
     end
 
-    autoload_at 'active_record/connection_adapters/abstract/connection_pool' do
+    autoload_at "active_record/connection_adapters/abstract/connection_pool" do
       autoload :ConnectionHandler
-      autoload :ConnectionManagement
     end
 
-    autoload_under 'abstract' do
+    autoload_under "abstract" do
       autoload :SchemaStatements
       autoload :DatabaseStatements
       autoload :DatabaseLimits
@@ -39,7 +43,7 @@ module ActiveRecord
       autoload :Savepoints
     end
 
-    autoload_at 'active_record/connection_adapters/abstract/transaction' do
+    autoload_at "active_record/connection_adapters/abstract/transaction" do
       autoload :TransactionManager
       autoload :NullTransaction
       autoload :RealTransaction
@@ -51,33 +55,37 @@ module ActiveRecord
     # related classes form the abstraction layer which makes this possible.
     # An AbstractAdapter represents a connection to a database, and provides an
     # abstract interface for database-specific functionality such as establishing
-    # a connection, escaping values, building the right SQL fragments for ':offset'
-    # and ':limit' options, etc.
+    # a connection, escaping values, building the right SQL fragments for +:offset+
+    # and +:limit+ options, etc.
     #
     # All the concrete database adapters follow the interface laid down in this class.
-    # ActiveRecord::Base.connection returns an AbstractAdapter object, which
+    # {ActiveRecord::Base.connection}[rdoc-ref:ConnectionHandling#connection] returns an AbstractAdapter object, which
     # you can use.
     #
     # Most of the methods in the adapter are useful during migrations. Most
-    # notably, the instance methods provided by SchemaStatement are very useful.
+    # notably, the instance methods provided by SchemaStatements are very useful.
     class AbstractAdapter
-      ADAPTER_NAME = 'Abstract'.freeze
+      ADAPTER_NAME = "Abstract"
+      include ActiveSupport::Callbacks
+      define_callbacks :checkout, :checkin
+
       include Quoting, DatabaseStatements, SchemaStatements
       include DatabaseLimits
       include QueryCache
-      include ActiveSupport::Callbacks
-      include ColumnDumper
+      include Savepoints
 
       SIMPLE_INT = /\A\d+\z/
 
-      define_callbacks :checkout, :checkin
-
       attr_accessor :visitor, :pool
-      attr_reader :schema_cache, :owner, :logger
+      attr_reader :schema_cache, :owner, :logger, :prepared_statements, :lock
       alias :in_use? :owner
 
+      set_callback :checkin, :after, :enable_lazy_transactions!
+
       def self.type_cast_config_to_integer(config)
-        if config =~ SIMPLE_INT
+        if config.is_a?(Integer)
+          config
+        elsif SIMPLE_INT.match?(config)
           config.to_i
         else
           config
@@ -92,58 +100,75 @@ module ActiveRecord
         end
       end
 
-      attr_reader :prepared_statements
-
-      def initialize(connection, logger = nil, pool = nil) #:nodoc:
+      def initialize(connection, logger = nil, config = {}) # :nodoc:
         super()
 
         @connection          = connection
         @owner               = nil
         @instrumenter        = ActiveSupport::Notifications.instrumenter
         @logger              = logger
-        @pool                = pool
+        @config              = config
+        @pool                = nil
+        @idle_since          = Concurrent.monotonic_time
         @schema_cache        = SchemaCache.new self
-        @visitor             = nil
-        @prepared_statements = false
-      end
+        @quoted_column_names, @quoted_table_names = {}, {}
+        @visitor = arel_visitor
+        @lock = ActiveSupport::Concurrency::LoadInterlockAwareMonitor.new
 
-      class BindCollector < Arel::Collectors::Bind
-        def compile(bvs, conn)
-          casted_binds = conn.prepare_binds_for_database(bvs)
-          super(casted_binds.map { |value| conn.quote(value) })
+        if self.class.type_cast_config_to_boolean(config.fetch(:prepared_statements) { true })
+          @prepared_statements = true
+          @visitor.extend(DetermineIfPreparableVisitor)
+        else
+          @prepared_statements = false
         end
+
+        @advisory_locks_enabled = self.class.type_cast_config_to_boolean(
+          config.fetch(:advisory_locks, true)
+        )
+
+        check_version
       end
 
-      class SQLString < Arel::Collectors::SQLString
-        def compile(bvs, conn)
-          super(bvs)
-        end
+      def replica?
+        @config[:replica] || false
       end
 
-      def collector
-        if prepared_statements
-          SQLString.new
-        else
-          BindCollector.new
-        end
+      def migrations_paths # :nodoc:
+        @config[:migrations_paths] || Migrator.migrations_paths
       end
 
-      def valid_type?(type)
-        true
+      def migration_context # :nodoc:
+        MigrationContext.new(migrations_paths)
       end
 
-      def schema_creation
-        SchemaCreation.new self
+      class Version
+        include Comparable
+
+        def initialize(version_string)
+          @version = version_string.split(".").map(&:to_i)
+        end
+
+        def <=>(version_string)
+          @version <=> version_string.split(".").map(&:to_i)
+        end
+
+        def to_s
+          @version.join(".")
+        end
+      end
+
+      def valid_type?(type) # :nodoc:
+        !native_database_types[type].nil?
       end
 
       # this method must only be called while holding connection pool's mutex
       def lease
         if in_use?
-          msg = 'Cannot lease connection, '
+          msg = +"Cannot lease connection, "
           if @owner == Thread.current
-            msg << 'it is already leased by the current thread.'
+            msg << "it is already leased by the current thread."
           else
-            msg << "it is already in use by a different thread: #{@owner}. " <<
+            msg << "it is already in use by a different thread: #{@owner}. " \
                    "Current thread: #{Thread.current}."
           end
           raise ActiveRecordError, msg
@@ -159,7 +184,37 @@ module ActiveRecord
 
       # this method must only be called while holding connection pool's mutex
       def expire
-        @owner = nil
+        if in_use?
+          if @owner != Thread.current
+            raise ActiveRecordError, "Cannot expire connection, " \
+              "it is owned by a different thread: #{@owner}. " \
+              "Current thread: #{Thread.current}."
+          end
+
+          @idle_since = Concurrent.monotonic_time
+          @owner = nil
+        else
+          raise ActiveRecordError, "Cannot expire connection, it is not currently leased."
+        end
+      end
+
+      # this method must only be called while holding connection pool's mutex (and a desire for segfaults)
+      def steal! # :nodoc:
+        if in_use?
+          if @owner != Thread.current
+            pool.send :remove_connection_from_thread_cache, self, @owner
+
+            @owner = Thread.current
+          end
+        else
+          raise ActiveRecordError, "Cannot steal connection, it is not currently leased."
+        end
+      end
+
+      # Seconds since this connection was returned to the pool
+      def seconds_idle # :nodoc:
+        return 0 if in_use?
+        Concurrent.monotonic_time - @idle_since
       end
 
       def unprepared_statement
@@ -175,17 +230,6 @@ module ActiveRecord
         self.class::ADAPTER_NAME
       end
 
-      # Does this adapter support migrations?
-      def supports_migrations?
-        false
-      end
-
-      # Can this adapter determine the primary key for tables not attached
-      # to an Active Record class, such as join tables?
-      def supports_primary_key?
-        false
-      end
-
       # Does this adapter support DDL rollbacks in transactions? That is, would
       # CREATE TABLE or ALTER TABLE get rolled back by a transaction?
       def supports_ddl_transactions?
@@ -201,6 +245,11 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support application-enforced advisory locking?
+      def supports_advisory_locks?
+        false
+      end
+
       # Should primary key values be selected from their corresponding
       # sequence before the insert statement? If true, next_sequence_value
       # is called before each insert to set the record's primary key.
@@ -218,6 +267,11 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support expression indices?
+      def supports_expression_index?
+        false
+      end
+
       # Does this adapter support explain?
       def supports_explain?
         false
@@ -244,6 +298,17 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support creating invalid constraints?
+      def supports_validate_constraints?
+        false
+      end
+
+      # Does this adapter support creating foreign key constraints
+      # in the same statement as creating the table?
+      def supports_foreign_keys_in_create?
+        supports_foreign_keys?
+      end
+
       # Does this adapter support views?
       def supports_views?
         false
@@ -254,6 +319,41 @@ module ActiveRecord
         false
       end
 
+      # Does this adapter support json data type?
+      def supports_json?
+        false
+      end
+
+      # Does this adapter support metadata comments on database objects (tables, columns, indexes)?
+      def supports_comments?
+        false
+      end
+
+      # Can comments for tables, columns, and indexes be specified in create/alter table statements?
+      def supports_comments_in_create?
+        false
+      end
+
+      # Does this adapter support multi-value insert?
+      def supports_multi_insert?
+        true
+      end
+      deprecate :supports_multi_insert?
+
+      # Does this adapter support virtual columns?
+      def supports_virtual_columns?
+        false
+      end
+
+      # Does this adapter support foreign/external tables?
+      def supports_foreign_tables?
+        false
+      end
+
+      def supports_lazy_transactions?
+        false
+      end
+
       # This is meant to be implemented by the adapters that support extensions
       def disable_extension(name)
       end
@@ -262,6 +362,24 @@ module ActiveRecord
       def enable_extension(name)
       end
 
+      def advisory_locks_enabled? # :nodoc:
+        supports_advisory_locks? && @advisory_locks_enabled
+      end
+
+      # This is meant to be implemented by the adapters that support advisory
+      # locks
+      #
+      # Return true if we got the lock, otherwise false
+      def get_advisory_lock(lock_id) # :nodoc:
+      end
+
+      # This is meant to be implemented by the adapters that support advisory
+      # locks.
+      #
+      # Return true if we released the lock, otherwise false
+      def release_advisory_lock(lock_id) # :nodoc:
+      end
+
       # A list of extensions, to be filled in by adapters that support them.
       def extensions
         []
@@ -272,12 +390,6 @@ module ActiveRecord
         {}
       end
 
-      # Returns a bind substitution value given a bind +column+
-      # NOTE: The column param is currently being used by the sqlserver-adapter
-      def substitute_at(column, _unused = 0)
-        Arel::Nodes::BindParam.new
-      end
-
       # REFERENTIAL INTEGRITY ====================================
 
       # Override to turn off referential integrity while executing <tt>&block</tt>.
@@ -308,6 +420,19 @@ module ActiveRecord
         reset_transaction
       end
 
+      # Immediately forget this connection ever existed. Unlike disconnect!,
+      # this will not communicate with the server.
+      #
+      # After calling this method, the behavior of all other methods becomes
+      # undefined. This is called internally just before a forked process gets
+      # rid of a connection that belonged to its parent.
+      def discard!
+        # This should be overridden by concrete adapters.
+        #
+        # Prevent @connection's finalizer from touching the socket, or
+        # otherwise communicating with its server, when it is collected.
+      end
+
       # Reset the state of this connection, directing the DBMS to clear
       # transactions and other connection-related server-side state. Usually a
       # database-dependent operation.
@@ -331,43 +456,32 @@ module ActiveRecord
       end
 
       # Checks whether the connection to the database is still active (i.e. not stale).
-      # This is done under the hood by calling <tt>active?</tt>. If the connection
+      # This is done under the hood by calling #active?. If the connection
       # is no longer active, then this method will reconnect to the database.
-      def verify!(*ignored)
+      def verify!
         reconnect! unless active?
       end
 
       # Provides access to the underlying database driver for this adapter. For
-      # example, this method returns a Mysql object in case of MysqlAdapter,
-      # and a PGconn object in case of PostgreSQLAdapter.
+      # example, this method returns a Mysql2::Client object in case of Mysql2Adapter,
+      # and a PG::Connection object in case of PostgreSQLAdapter.
       #
       # This is useful for when you need to call a proprietary method such as
       # PostgreSQL's lo_* methods.
       def raw_connection
+        disable_lazy_transactions!
         @connection
       end
 
-      def create_savepoint(name = nil)
-      end
-
-      def release_savepoint(name = nil)
-      end
-
-      def case_sensitive_modifier(node, table_attribute)
-        node
-      end
-
-      def case_sensitive_comparison(table, attribute, column, value)
-        table_attr = table[attribute]
-        value = case_sensitive_modifier(value, table_attr) unless value.nil?
-        table_attr.eq(value)
+      def case_sensitive_comparison(table, attribute, column, value) # :nodoc:
+        table[attribute].eq(value)
       end
 
-      def case_insensitive_comparison(table, attribute, column, value)
+      def case_insensitive_comparison(table, attribute, column, value) # :nodoc:
         if can_perform_case_insensitive_comparison_for?(column)
           table[attribute].lower.eq(table.lower(value))
         else
-          case_sensitive_comparison(table, attribute, column, value)
+          table[attribute].eq(value)
         end
       end
 
@@ -376,143 +490,164 @@ module ActiveRecord
       end
       private :can_perform_case_insensitive_comparison_for?
 
-      def current_savepoint_name
-        current_transaction.savepoint_name
-      end
-
       # Check the connection back in to the connection pool
       def close
         pool.checkin self
       end
 
-      def type_map # :nodoc:
-        @type_map ||= Type::TypeMap.new.tap do |mapping|
-          initialize_type_map(mapping)
-        end
+      def column_name_for_operation(operation, node) # :nodoc:
+        visitor.compile(node)
       end
 
-      def new_column(name, default, sql_type_metadata = nil, null = true, default_function = nil, collation = nil)
-        Column.new(name, default, sql_type_metadata, null, default_function, collation)
+      def default_index_type?(index) # :nodoc:
+        index.using.nil?
       end
 
-      def lookup_cast_type(sql_type) # :nodoc:
-        type_map.lookup(sql_type)
-      end
+      private
+        def check_version
+        end
 
-      def column_name_for_operation(operation, node) # :nodoc:
-        visitor.accept(node, collector).value
-      end
-
-      protected
-
-      def initialize_type_map(m) # :nodoc:
-        register_class_with_limit m, %r(boolean)i,       Type::Boolean
-        register_class_with_limit m, %r(char)i,          Type::String
-        register_class_with_limit m, %r(binary)i,        Type::Binary
-        register_class_with_limit m, %r(text)i,          Type::Text
-        register_class_with_precision m, %r(date)i,      Type::Date
-        register_class_with_precision m, %r(time)i,      Type::Time
-        register_class_with_precision m, %r(datetime)i,  Type::DateTime
-        register_class_with_limit m, %r(float)i,         Type::Float
-        register_class_with_limit m, %r(int)i,           Type::Integer
-
-        m.alias_type %r(blob)i,      'binary'
-        m.alias_type %r(clob)i,      'text'
-        m.alias_type %r(timestamp)i, 'datetime'
-        m.alias_type %r(numeric)i,   'decimal'
-        m.alias_type %r(number)i,    'decimal'
-        m.alias_type %r(double)i,    'float'
-
-        m.register_type(%r(decimal)i) do |sql_type|
-          scale = extract_scale(sql_type)
-          precision = extract_precision(sql_type)
-
-          if scale == 0
-            # FIXME: Remove this class as well
-            Type::DecimalWithoutScale.new(precision: precision)
-          else
-            Type::Decimal.new(precision: precision, scale: scale)
+        def type_map
+          @type_map ||= Type::TypeMap.new.tap do |mapping|
+            initialize_type_map(mapping)
           end
         end
-      end
 
-      def reload_type_map # :nodoc:
-        type_map.clear
-        initialize_type_map(type_map)
-      end
+        def initialize_type_map(m = type_map)
+          register_class_with_limit m, %r(boolean)i,       Type::Boolean
+          register_class_with_limit m, %r(char)i,          Type::String
+          register_class_with_limit m, %r(binary)i,        Type::Binary
+          register_class_with_limit m, %r(text)i,          Type::Text
+          register_class_with_precision m, %r(date)i,      Type::Date
+          register_class_with_precision m, %r(time)i,      Type::Time
+          register_class_with_precision m, %r(datetime)i,  Type::DateTime
+          register_class_with_limit m, %r(float)i,         Type::Float
+          register_class_with_limit m, %r(int)i,           Type::Integer
+
+          m.alias_type %r(blob)i,      "binary"
+          m.alias_type %r(clob)i,      "text"
+          m.alias_type %r(timestamp)i, "datetime"
+          m.alias_type %r(numeric)i,   "decimal"
+          m.alias_type %r(number)i,    "decimal"
+          m.alias_type %r(double)i,    "float"
+
+          m.register_type %r(^json)i, Type::Json.new
+
+          m.register_type(%r(decimal)i) do |sql_type|
+            scale = extract_scale(sql_type)
+            precision = extract_precision(sql_type)
+
+            if scale == 0
+              # FIXME: Remove this class as well
+              Type::DecimalWithoutScale.new(precision: precision)
+            else
+              Type::Decimal.new(precision: precision, scale: scale)
+            end
+          end
+        end
 
-      def register_class_with_limit(mapping, key, klass) # :nodoc:
-        mapping.register_type(key) do |*args|
-          limit = extract_limit(args.last)
-          klass.new(limit: limit)
+        def reload_type_map
+          type_map.clear
+          initialize_type_map
         end
-      end
 
-      def register_class_with_precision(mapping, key, klass) # :nodoc:
-        mapping.register_type(key) do |*args|
-          precision = extract_precision(args.last)
-          klass.new(precision: precision)
+        def register_class_with_limit(mapping, key, klass)
+          mapping.register_type(key) do |*args|
+            limit = extract_limit(args.last)
+            klass.new(limit: limit)
+          end
         end
-      end
 
-      def extract_scale(sql_type) # :nodoc:
-        case sql_type
+        def register_class_with_precision(mapping, key, klass)
+          mapping.register_type(key) do |*args|
+            precision = extract_precision(args.last)
+            klass.new(precision: precision)
+          end
+        end
+
+        def extract_scale(sql_type)
+          case sql_type
           when /\((\d+)\)/ then 0
           when /\((\d+)(,(\d+))\)/ then $3.to_i
+          end
         end
-      end
 
-      def extract_precision(sql_type) # :nodoc:
-        $1.to_i if sql_type =~ /\((\d+)(,\d+)?\)/
-      end
+        def extract_precision(sql_type)
+          $1.to_i if sql_type =~ /\((\d+)(,\d+)?\)/
+        end
 
-      def extract_limit(sql_type) # :nodoc:
-        case sql_type
-        when /^bigint/i
-          8
-        when /\((.*)\)/
-          $1.to_i
+        def extract_limit(sql_type)
+          $1.to_i if sql_type =~ /\((.*)\)/
         end
-      end
 
-      def translate_exception_class(e, sql)
-        begin
-          message = "#{e.class.name}: #{e.message}: #{sql}"
-        rescue Encoding::CompatibilityError
-          message = "#{e.class.name}: #{e.message.force_encoding sql.encoding}: #{sql}"
+        def translate_exception_class(e, sql)
+          begin
+            message = "#{e.class.name}: #{e.message}: #{sql}"
+          rescue Encoding::CompatibilityError
+            message = "#{e.class.name}: #{e.message.force_encoding sql.encoding}: #{sql}"
+          end
+
+          exception = translate_exception(e, message)
+          exception.set_backtrace e.backtrace
+          exception
         end
 
-        exception = translate_exception(e, message)
-        exception.set_backtrace e.backtrace
-        exception
-      end
+        def log(sql, name = "SQL", binds = [], type_casted_binds = [], statement_name = nil) # :doc:
+          @instrumenter.instrument(
+            "sql.active_record",
+            sql:               sql,
+            name:              name,
+            binds:             binds,
+            type_casted_binds: type_casted_binds,
+            statement_name:    statement_name,
+            connection_id:     object_id) do
+            begin
+              @lock.synchronize do
+                yield
+              end
+            rescue => e
+              raise translate_exception_class(e, sql)
+            end
+          end
+        end
 
-      def log(sql, name = "SQL", binds = [], statement_name = nil)
-        @instrumenter.instrument(
-          "sql.active_record",
-          :sql            => sql,
-          :name           => name,
-          :connection_id  => object_id,
-          :statement_name => statement_name,
-          :binds          => binds) { yield }
-      rescue => e
-        raise translate_exception_class(e, sql)
-      end
+        def translate_exception(exception, message)
+          # override in derived class
+          case exception
+          when RuntimeError
+            exception
+          else
+            ActiveRecord::StatementInvalid.new(message)
+          end
+        end
 
-      def translate_exception(exception, message)
-        # override in derived class
-        ActiveRecord::StatementInvalid.new(message, exception)
-      end
+        def without_prepared_statement?(binds)
+          !prepared_statements || binds.empty?
+        end
 
-      def without_prepared_statement?(binds)
-        !prepared_statements || binds.empty?
-      end
+        def column_for(table_name, column_name)
+          column_name = column_name.to_s
+          columns(table_name).detect { |c| c.name == column_name } ||
+            raise(ActiveRecordError, "No such column: #{table_name}.#{column_name}")
+        end
 
-      def column_for(table_name, column_name) # :nodoc:
-        column_name = column_name.to_s
-        columns(table_name).detect { |c| c.name == column_name } ||
-          raise(ActiveRecordError, "No such column: #{table_name}.#{column_name}")
-      end
+        def collector
+          if prepared_statements
+            Arel::Collectors::Composite.new(
+              Arel::Collectors::SQLString.new,
+              Arel::Collectors::Bind.new,
+            )
+          else
+            Arel::Collectors::SubstituteBinds.new(
+              self,
+              Arel::Collectors::SQLString.new,
+            )
+          end
+        end
+
+        def arel_visitor
+          Arel::Visitors::ToSql.new(self)
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 2027492f29..13c799b64a 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -1,329 +1,135 @@
-require 'active_support/core_ext/string/strip'
+# frozen_string_literal: true
+
+require "active_record/connection_adapters/abstract_adapter"
+require "active_record/connection_adapters/statement_pool"
+require "active_record/connection_adapters/mysql/column"
+require "active_record/connection_adapters/mysql/explain_pretty_printer"
+require "active_record/connection_adapters/mysql/quoting"
+require "active_record/connection_adapters/mysql/schema_creation"
+require "active_record/connection_adapters/mysql/schema_definitions"
+require "active_record/connection_adapters/mysql/schema_dumper"
+require "active_record/connection_adapters/mysql/schema_statements"
+require "active_record/connection_adapters/mysql/type_metadata"
 
 module ActiveRecord
   module ConnectionAdapters
     class AbstractMysqlAdapter < AbstractAdapter
-      include Savepoints
+      include MySQL::Quoting
+      include MySQL::SchemaStatements
 
-      module ColumnMethods
-        def primary_key(name, type = :primary_key, **options)
-          options[:auto_increment] = true if type == :bigint
-          super
-        end
-      end
-
-      class ColumnDefinition < ActiveRecord::ConnectionAdapters::ColumnDefinition
-        attr_accessor :charset
-      end
-
-      class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
-        include ColumnMethods
-
-        def new_column_definition(name, type, options) # :nodoc:
-          column = super
-          case column.type
-          when :primary_key
-            column.type = :integer
-            column.auto_increment = true
-          end
-          column.charset = options[:charset]
-          column
-        end
-
-        private
-
-        def create_column_definition(name, type)
-          ColumnDefinition.new(name, type)
-        end
-      end
+      ##
+      # :singleton-method:
+      # By default, the Mysql2Adapter will consider all columns of type <tt>tinyint(1)</tt>
+      # as boolean. If you wish to disable this emulation you can add the following line
+      # to your application.rb file:
+      #
+      #   ActiveRecord::ConnectionAdapters::Mysql2Adapter.emulate_booleans = false
+      class_attribute :emulate_booleans, default: true
 
-      class Table < ActiveRecord::ConnectionAdapters::Table
-        include ColumnMethods
-      end
+      NATIVE_DATABASE_TYPES = {
+        primary_key: "bigint auto_increment PRIMARY KEY",
+        string:      { name: "varchar", limit: 255 },
+        text:        { name: "text", limit: 65535 },
+        integer:     { name: "int", limit: 4 },
+        float:       { name: "float", limit: 24 },
+        decimal:     { name: "decimal" },
+        datetime:    { name: "datetime" },
+        timestamp:   { name: "timestamp" },
+        time:        { name: "time" },
+        date:        { name: "date" },
+        binary:      { name: "blob", limit: 65535 },
+        boolean:     { name: "tinyint", limit: 1 },
+        json:        { name: "json" },
+      }
 
-      class SchemaCreation < AbstractAdapter::SchemaCreation
+      class StatementPool < ConnectionAdapters::StatementPool # :nodoc:
         private
 
-        def visit_DropForeignKey(name)
-          "DROP FOREIGN KEY #{name}"
-        end
-
-        def visit_TableDefinition(o)
-          name = o.name
-          create_sql = "CREATE#{' TEMPORARY' if o.temporary} TABLE #{quote_table_name(name)} "
-
-          statements = o.columns.map { |c| accept c }
-          statements.concat(o.indexes.map { |column_name, options| index_in_create(name, column_name, options) })
-
-          create_sql << "(#{statements.join(', ')}) " if statements.present?
-          create_sql << "#{o.options}"
-          create_sql << " AS #{@conn.to_sql(o.as)}" if o.as
-          create_sql
-        end
-
-        def visit_AddColumnDefinition(o)
-          add_column_position!(super, column_options(o.column))
-        end
-
-        def visit_ChangeColumnDefinition(o)
-          change_column_sql = "CHANGE #{quote_column_name(o.name)} #{accept(o.column)}"
-          add_column_position!(change_column_sql, column_options(o.column))
-        end
-
-        def column_options(o)
-          column_options = super
-          column_options[:charset] = o.charset
-          column_options
-        end
-
-        def add_column_options!(sql, options)
-          if options[:charset]
-            sql << " CHARACTER SET #{options[:charset]}"
-          end
-          if options[:collation]
-            sql << " COLLATE #{options[:collation]}"
-          end
-          super
-        end
-
-        def add_column_position!(sql, options)
-          if options[:first]
-            sql << " FIRST"
-          elsif options[:after]
-            sql << " AFTER #{quote_column_name(options[:after])}"
+          def dealloc(stmt)
+            stmt.close
           end
-          sql
-        end
-
-        def index_in_create(table_name, column_name, options)
-          index_name, index_type, index_columns, _, _, index_using = @conn.add_index_options(table_name, column_name, options)
-          "#{index_type} INDEX #{quote_column_name(index_name)} #{index_using} (#{index_columns}) "
-        end
       end
 
-      def update_table_definition(table_name, base) # :nodoc:
-        Table.new(table_name, base)
-      end
+      def initialize(connection, logger, connection_options, config)
+        super(connection, logger, config)
 
-      def schema_creation
-        SchemaCreation.new self
+        @statements = StatementPool.new(self.class.type_cast_config_to_integer(config[:statement_limit]))
       end
 
-      def column_spec_for_primary_key(column)
-        spec = {}
-        if column.auto_increment?
-          spec[:id] = ':bigint' if column.bigint?
-          return if spec.empty?
-        else
-          spec[:id] = column.type.inspect
-          spec.merge!(prepare_column_options(column).delete_if { |key, _| [:name, :type, :null].include?(key) })
-        end
-        spec
+      def version #:nodoc:
+        @version ||= Version.new(version_string)
       end
 
-      private
-
-      def schema_limit(column)
-        super unless column.type == :boolean
+      def mariadb? # :nodoc:
+        /mariadb/i.match?(full_version)
       end
 
-      def schema_precision(column)
-        super unless /time/ === column.sql_type && column.precision == 0
-      end
-
-      def schema_collation(column)
-        if column.collation && table_name = column.instance_variable_get(:@table_name)
-          @collation_cache ||= {}
-          @collation_cache[table_name] ||= select_one("SHOW TABLE STATUS LIKE '#{table_name}'")["Collation"]
-          column.collation.inspect if column.collation != @collation_cache[table_name]
-        end
+      def supports_bulk_alter? #:nodoc:
+        true
       end
 
-      public
-
-      class Column < ConnectionAdapters::Column # :nodoc:
-        delegate :strict, :extra, to: :sql_type_metadata, allow_nil: true
-
-        def initialize(*)
-          super
-          assert_valid_default(default)
-          extract_default
-        end
-
-        def extract_default
-          if blob_or_text_column?
-            @default = null || strict ? nil : ''
-          elsif missing_default_forged_as_empty_string?(default)
-            @default = nil
-          end
-        end
-
-        def has_default?
-          return false if blob_or_text_column? # MySQL forbids defaults on blob and text columns
-          super
-        end
-
-        def blob_or_text_column?
-          sql_type =~ /blob/i || type == :text
-        end
-
-        def case_sensitive?
-          collation && !collation.match(/_ci$/)
-        end
-
-        def auto_increment?
-          extra == 'auto_increment'
-        end
-
-        private
-
-        # MySQL misreports NOT NULL column default when none is given.
-        # We can't detect this for columns which may have a legitimate ''
-        # default (string) but we can for others (integer, datetime, boolean,
-        # and the rest).
-        #
-        # Test whether the column has default '', is not null, and is not
-        # a type allowing default ''.
-        def missing_default_forged_as_empty_string?(default)
-          type != :string && !null && default == ''
-        end
-
-        def assert_valid_default(default)
-          if blob_or_text_column? && default.present?
-            raise ArgumentError, "#{type} columns cannot have a default value: #{default.inspect}"
-          end
-        end
+      def supports_index_sort_order?
+        !mariadb? && version >= "8.0.1"
       end
 
-      class MysqlTypeMetadata < DelegateClass(SqlTypeMetadata) # :nodoc:
-        attr_reader :extra, :strict
-
-        def initialize(type_metadata, extra: "", strict: false)
-          super(type_metadata)
-          @type_metadata = type_metadata
-          @extra = extra
-          @strict = strict
-        end
-
-        def ==(other)
-          other.is_a?(MysqlTypeMetadata) &&
-            attributes_for_hash == other.attributes_for_hash
-        end
-        alias eql? ==
-
-        def hash
-          attributes_for_hash.hash
-        end
-
-        protected
-
-        def attributes_for_hash
-          [self.class, @type_metadata, extra, strict]
-        end
+      def supports_expression_index?
+        !mariadb? && version >= "8.0.13"
       end
 
-      ##
-      # :singleton-method:
-      # By default, the MysqlAdapter will consider all columns of type <tt>tinyint(1)</tt>
-      # as boolean. If you wish to disable this emulation (which was the default
-      # behavior in versions 0.13.1 and earlier) you can add the following line
-      # to your application.rb file:
-      #
-      #   ActiveRecord::ConnectionAdapters::Mysql[2]Adapter.emulate_booleans = false
-      class_attribute :emulate_booleans
-      self.emulate_booleans = true
-
-      LOST_CONNECTION_ERROR_MESSAGES = [
-        "Server shutdown in progress",
-        "Broken pipe",
-        "Lost connection to MySQL server during query",
-        "MySQL server has gone away" ]
-
-      QUOTED_TRUE, QUOTED_FALSE = '1', '0'
-
-      NATIVE_DATABASE_TYPES = {
-        :primary_key => "int(11) auto_increment PRIMARY KEY",
-        :string      => { :name => "varchar", :limit => 255 },
-        :text        => { :name => "text" },
-        :integer     => { :name => "int", :limit => 4 },
-        :float       => { :name => "float" },
-        :decimal     => { :name => "decimal" },
-        :datetime    => { :name => "datetime" },
-        :time        => { :name => "time" },
-        :date        => { :name => "date" },
-        :binary      => { :name => "blob" },
-        :boolean     => { :name => "tinyint", :limit => 1 }
-      }
-
-      INDEX_TYPES  = [:fulltext, :spatial]
-      INDEX_USINGS = [:btree, :hash]
-
-      # FIXME: Make the first parameter more similar for the two adapters
-      def initialize(connection, logger, connection_options, config)
-        super(connection, logger)
-        @connection_options, @config = connection_options, config
-        @quoted_column_names, @quoted_table_names = {}, {}
-
-        @visitor = Arel::Visitors::MySQL.new self
-
-        if self.class.type_cast_config_to_boolean(config.fetch(:prepared_statements) { true })
-          @prepared_statements = true
-        else
-          @prepared_statements = false
-        end
+      def supports_transaction_isolation?
+        true
       end
 
-      MAX_INDEX_LENGTH_FOR_CHARSETS_OF_4BYTES_MAXLEN = 191
-      CHARSETS_OF_4BYTES_MAXLEN = ['utf8mb4', 'utf16', 'utf16le', 'utf32']
-      def initialize_schema_migrations_table
-        if CHARSETS_OF_4BYTES_MAXLEN.include?(charset)
-          ActiveRecord::SchemaMigration.create_table(MAX_INDEX_LENGTH_FOR_CHARSETS_OF_4BYTES_MAXLEN)
-        else
-          ActiveRecord::SchemaMigration.create_table
-        end
+      def supports_explain?
+        true
       end
 
-      # Returns true, since this connection adapter supports migrations.
-      def supports_migrations?
+      def supports_indexes_in_create?
         true
       end
 
-      def supports_primary_key?
+      def supports_foreign_keys?
         true
       end
 
-      def supports_bulk_alter? #:nodoc:
+      def supports_views?
         true
       end
 
-      # Technically MySQL allows to create indexes with the sort order syntax
-      # but at the moment (5.5) it doesn't yet implement them
-      def supports_index_sort_order?
-        true
+      def supports_datetime_with_precision?
+        if mariadb?
+          version >= "5.3.0"
+        else
+          version >= "5.6.4"
+        end
       end
 
-      # MySQL 4 technically support transaction isolation, but it is affected by a bug
-      # where the transaction level gets persisted for the whole session:
-      #
-      # http://bugs.mysql.com/bug.php?id=39170
-      def supports_transaction_isolation?
-        version[0] >= 5
+      def supports_virtual_columns?
+        if mariadb?
+          version >= "5.2.0"
+        else
+          version >= "5.7.5"
+        end
       end
 
-      def supports_indexes_in_create?
+      def supports_advisory_locks?
         true
       end
 
-      def supports_foreign_keys?
-        true
+      def supports_longer_index_key_prefix?
+        if mariadb?
+          version >= "10.2.2"
+        else
+          version >= "5.7.9"
+        end
       end
 
-      def supports_views?
-        version[0] >= 5
+      def get_advisory_lock(lock_name, timeout = 0) # :nodoc:
+        query_value("SELECT GET_LOCK(#{quote(lock_name.to_s)}, #{timeout})") == 1
       end
 
-      def supports_datetime_with_precision?
-        (version[0] == 5 && version[1] >= 6) || version[0] >= 6
+      def release_advisory_lock(lock_name) # :nodoc:
+        query_value("SELECT RELEASE_LOCK(#{quote(lock_name.to_s)})") == 1
       end
 
       def native_database_types
@@ -331,7 +137,7 @@ module ActiveRecord
       end
 
       def index_algorithms
-        { default: 'ALGORITHM = DEFAULT', copy: 'ALGORITHM = COPY', inplace: 'ALGORITHM = INPLACE' }
+        { default: +"ALGORITHM = DEFAULT", copy: +"ALGORITHM = COPY", inplace: +"ALGORITHM = INPLACE" }
       end
 
       # HELPER METHODS ===========================================
@@ -342,54 +148,16 @@ module ActiveRecord
         raise NotImplementedError
       end
 
-      def new_column(field, default, sql_type_metadata = nil, null = true, default_function = nil, collation = nil) # :nodoc:
-        Column.new(field, default, sql_type_metadata, null, default_function, collation)
-      end
-
       # Must return the MySQL error number from the exception, if the exception has an
       # error number.
       def error_number(exception) # :nodoc:
         raise NotImplementedError
       end
 
-      # QUOTING ==================================================
-
-      def _quote(value) # :nodoc:
-        if value.is_a?(Type::Binary::Data)
-          "x'#{value.hex}'"
-        else
-          super
-        end
-      end
-
-      def quote_column_name(name) #:nodoc:
-        @quoted_column_names[name] ||= "`#{name.to_s.gsub('`', '``')}`"
-      end
-
-      def quote_table_name(name) #:nodoc:
-        @quoted_table_names[name] ||= quote_column_name(name).gsub('.', '`.`')
-      end
-
-      def quoted_true
-        QUOTED_TRUE
-      end
-
-      def unquoted_true
-        1
-      end
-
-      def quoted_false
-        QUOTED_FALSE
-      end
-
-      def unquoted_false
-        0
-      end
-
       # REFERENTIAL INTEGRITY ====================================
 
       def disable_referential_integrity #:nodoc:
-        old = select_value("SELECT @@FOREIGN_KEY_CHECKS")
+        old = query_value("SELECT @@FOREIGN_KEY_CHECKS")
 
         begin
           update("SET FOREIGN_KEY_CHECKS = 0")
@@ -399,30 +167,43 @@ module ActiveRecord
         end
       end
 
+      # CONNECTION MANAGEMENT ====================================
+
+      # Clears the prepared statements cache.
+      def clear_cache!
+        reload_type_map
+        @statements.clear
+      end
+
       #--
       # DATABASE STATEMENTS ======================================
       #++
 
-      def clear_cache!
-        super
-        reload_type_map
+      def explain(arel, binds = [])
+        sql     = "EXPLAIN #{to_sql(arel, binds)}"
+        start   = Time.now
+        result  = exec_query(sql, "EXPLAIN", binds)
+        elapsed = Time.now - start
+
+        MySQL::ExplainPrettyPrinter.new.pp(result, elapsed)
       end
 
       # Executes the SQL statement in the context of this connection.
       def execute(sql, name = nil)
-        log(sql, name) { @connection.query(sql) }
-      end
+        materialize_transactions
 
-      # MysqlAdapter has to free a result after using it, so we use this method to write
-      # stuff in an abstract way without concerning ourselves about whether it needs to be
-      # explicitly freed or not.
-      def execute_and_free(sql, name = nil) #:nodoc:
-        yield execute(sql, name)
+        log(sql, name) do
+          ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+            @connection.query(sql)
+          end
+        end
       end
 
-      def update_sql(sql, name = nil) #:nodoc:
-        super
-        @connection.affected_rows
+      # Mysql2Adapter doesn't have to free a result after using it, but we use this method
+      # to write stuff in an abstract way without concerning ourselves about whether it
+      # needs to be explicitly freed or not.
+      def execute_and_free(sql, name = nil) # :nodoc:
+        yield execute(sql, name)
       end
 
       def begin_db_transaction
@@ -442,19 +223,7 @@ module ActiveRecord
         execute "ROLLBACK"
       end
 
-      # In the simple case, MySQL allows us to place JOINs directly into the UPDATE
-      # query. However, this does not allow for LIMIT, OFFSET and ORDER. To support
-      # these, we must use a subquery.
-      def join_to_update(update, select) #:nodoc:
-        if select.limit || select.offset || select.orders.any?
-          super
-        else
-          update.table select.source
-          update.wheres = select.constraints
-        end
-      end
-
-      def empty_insert_statement_value
+      def empty_insert_statement_value(primary_key = nil)
         "VALUES ()"
       end
 
@@ -470,7 +239,7 @@ module ActiveRecord
       end
 
       # Create a new MySQL database with optional <tt>:charset</tt> and <tt>:collation</tt>.
-      # Charset defaults to utf8.
+      # Charset defaults to utf8mb4.
       #
       # Example:
       #   create_database 'charset_test', charset: 'latin1', collation: 'latin1_bin'
@@ -478,9 +247,13 @@ module ActiveRecord
       #   create_database 'matt_development', charset: :big5
       def create_database(name, options = {})
         if options[:collation]
-          execute "CREATE DATABASE `#{name}` DEFAULT CHARACTER SET `#{options[:charset] || 'utf8'}` COLLATE `#{options[:collation]}`"
+          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT COLLATE #{quote_table_name(options[:collation])}"
+        elsif options[:charset]
+          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET #{quote_table_name(options[:charset])}"
+        elsif supports_longer_index_key_prefix?
+          execute "CREATE DATABASE #{quote_table_name(name)} DEFAULT CHARACTER SET `utf8mb4`"
         else
-          execute "CREATE DATABASE `#{name}` DEFAULT CHARACTER SET `#{options[:charset] || 'utf8'}`"
+          raise "Configure a supported :charset and ensure innodb_large_prefix is enabled to support indexes on varchar(255) string columns."
         end
       end
 
@@ -489,97 +262,42 @@ module ActiveRecord
       # Example:
       #   drop_database('sebastian_development')
       def drop_database(name) #:nodoc:
-        execute "DROP DATABASE IF EXISTS `#{name}`"
+        execute "DROP DATABASE IF EXISTS #{quote_table_name(name)}"
       end
 
       def current_database
-        select_value 'SELECT DATABASE() as db'
+        query_value("SELECT database()", "SCHEMA")
       end
 
       # Returns the database character set.
       def charset
-        show_variable 'character_set_database'
+        show_variable "character_set_database"
       end
 
       # Returns the database collation strategy.
       def collation
-        show_variable 'collation_database'
-      end
-
-      def tables(name = nil, database = nil, like = nil) #:nodoc:
-        sql = "SHOW TABLES "
-        sql << "IN #{quote_table_name(database)} " if database
-        sql << "LIKE #{quote(like)}" if like
-
-        execute_and_free(sql, 'SCHEMA') do |result|
-          result.collect(&:first)
-        end
+        show_variable "collation_database"
       end
 
       def truncate(table_name, name = nil)
         execute "TRUNCATE TABLE #{quote_table_name(table_name)}", name
       end
 
-      def table_exists?(name)
-        return false unless name.present?
-        return true if tables(nil, nil, name).any?
-
-        name          = name.to_s
-        schema, table = name.split('.', 2)
-
-        unless table # A table was provided without a schema
-          table  = schema
-          schema = nil
-        end
-
-        tables(nil, schema, table).any?
-      end
-
-      # Returns an array of indexes for the given table.
-      def indexes(table_name, name = nil) #:nodoc:
-        indexes = []
-        current_index = nil
-        execute_and_free("SHOW KEYS FROM #{quote_table_name(table_name)}", 'SCHEMA') do |result|
-          each_hash(result) do |row|
-            if current_index != row[:Key_name]
-              next if row[:Key_name] == 'PRIMARY' # skip the primary key
-              current_index = row[:Key_name]
-
-              mysql_index_type = row[:Index_type].downcase.to_sym
-              index_type  = INDEX_TYPES.include?(mysql_index_type)  ? mysql_index_type : nil
-              index_using = INDEX_USINGS.include?(mysql_index_type) ? mysql_index_type : nil
-              indexes << IndexDefinition.new(row[:Table], row[:Key_name], row[:Non_unique].to_i == 0, [], [], nil, nil, index_type, index_using)
-            end
+      def table_comment(table_name) # :nodoc:
+        scope = quoted_scope(table_name)
 
-            indexes.last.columns << row[:Column_name]
-            indexes.last.lengths << row[:Sub_part]
-          end
-        end
-
-        indexes
-      end
-
-      # Returns an array of +Column+ objects for the table specified by +table_name+.
-      def columns(table_name)#:nodoc:
-        sql = "SHOW FULL FIELDS FROM #{quote_table_name(table_name)}"
-        execute_and_free(sql, 'SCHEMA') do |result|
-          each_hash(result).map do |field|
-            field_name = set_field_encoding(field[:Field])
-            sql_type = field[:Type]
-            type_metadata = fetch_type_metadata(sql_type, field[:Extra])
-            new_column(field_name, field[:Default], type_metadata, field[:Null] == "YES", nil, field[:Collation])
-          end
-        end
-      end
-
-      def create_table(table_name, options = {}) #:nodoc:
-        super(table_name, options.reverse_merge(:options => "ENGINE=InnoDB"))
+        query_value(<<~SQL, "SCHEMA").presence
+          SELECT table_comment
+          FROM information_schema.tables
+          WHERE table_schema = #{scope[:schema]}
+            AND table_name = #{scope[:name]}
+        SQL
       end
 
       def bulk_change_table(table_name, operations) #:nodoc:
         sqls = operations.flat_map do |command, args|
           table, arguments = args.shift, args
-          method = :"#{command}_sql"
+          method = :"#{command}_for_alter"
 
           if respond_to?(method, true)
             send(method, table, *arguments)
@@ -591,6 +309,11 @@ module ActiveRecord
         execute("ALTER TABLE #{quote_table_name(table_name)} #{sqls}")
       end
 
+      def change_table_comment(table_name, comment) #:nodoc:
+        comment = "" if comment.nil?
+        execute("ALTER TABLE #{quote_table_name(table_name)} COMMENT #{quote(comment)}")
+      end
+
       # Renames a table.
       #
       # Example:
@@ -631,432 +354,521 @@ module ActiveRecord
 
       def change_column_default(table_name, column_name, default_or_changes) #:nodoc:
         default = extract_new_default_value(default_or_changes)
-        column = column_for(table_name, column_name)
-        change_column table_name, column_name, column.sql_type, :default => default
+        change_column table_name, column_name, nil, default: default
       end
 
       def change_column_null(table_name, column_name, null, default = nil) #:nodoc:
-        column = column_for(table_name, column_name)
-
         unless null || default.nil?
           execute("UPDATE #{quote_table_name(table_name)} SET #{quote_column_name(column_name)}=#{quote(default)} WHERE #{quote_column_name(column_name)} IS NULL")
         end
 
-        change_column table_name, column_name, column.sql_type, :null => null
+        change_column table_name, column_name, nil, null: null
+      end
+
+      def change_column_comment(table_name, column_name, comment) #:nodoc:
+        change_column table_name, column_name, nil, comment: comment
       end
 
       def change_column(table_name, column_name, type, options = {}) #:nodoc:
-        execute("ALTER TABLE #{quote_table_name(table_name)} #{change_column_sql(table_name, column_name, type, options)}")
+        execute("ALTER TABLE #{quote_table_name(table_name)} #{change_column_for_alter(table_name, column_name, type, options)}")
       end
 
       def rename_column(table_name, column_name, new_column_name) #:nodoc:
-        execute("ALTER TABLE #{quote_table_name(table_name)} #{rename_column_sql(table_name, column_name, new_column_name)}")
+        execute("ALTER TABLE #{quote_table_name(table_name)} #{rename_column_for_alter(table_name, column_name, new_column_name)}")
         rename_column_indexes(table_name, column_name, new_column_name)
       end
 
       def add_index(table_name, column_name, options = {}) #:nodoc:
-        index_name, index_type, index_columns, _, index_algorithm, index_using = add_index_options(table_name, column_name, options)
-        execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}"
+        index_name, index_type, index_columns, _, index_algorithm, index_using, comment = add_index_options(table_name, column_name, options)
+        sql = +"CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}"
+        execute add_sql_comment!(sql, comment)
+      end
+
+      def add_sql_comment!(sql, comment) # :nodoc:
+        sql << " COMMENT #{quote(comment)}" if comment.present?
+        sql
       end
 
       def foreign_keys(table_name)
-        fk_info = select_all <<-SQL.strip_heredoc
-          SELECT fk.referenced_table_name as 'to_table'
-                ,fk.referenced_column_name as 'primary_key'
-                ,fk.column_name as 'column'
-                ,fk.constraint_name as 'name'
-          FROM information_schema.key_column_usage fk
-          WHERE fk.referenced_column_name is not null
-            AND fk.table_schema = '#{@config[:database]}'
-            AND fk.table_name = '#{table_name}'
+        raise ArgumentError unless table_name.present?
+
+        scope = quoted_scope(table_name)
+
+        fk_info = exec_query(<<~SQL, "SCHEMA")
+          SELECT fk.referenced_table_name AS 'to_table',
+                 fk.referenced_column_name AS 'primary_key',
+                 fk.column_name AS 'column',
+                 fk.constraint_name AS 'name',
+                 rc.update_rule AS 'on_update',
+                 rc.delete_rule AS 'on_delete'
+          FROM information_schema.referential_constraints rc
+          JOIN information_schema.key_column_usage fk
+          USING (constraint_schema, constraint_name)
+          WHERE fk.referenced_column_name IS NOT NULL
+            AND fk.table_schema = #{scope[:schema]}
+            AND fk.table_name = #{scope[:name]}
+            AND rc.constraint_schema = #{scope[:schema]}
+            AND rc.table_name = #{scope[:name]}
         SQL
 
-        create_table_info = select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
-
         fk_info.map do |row|
           options = {
-            column: row['column'],
-            name: row['name'],
-            primary_key: row['primary_key']
+            column: row["column"],
+            name: row["name"],
+            primary_key: row["primary_key"]
           }
 
-          options[:on_update] = extract_foreign_key_action(create_table_info, row['name'], "UPDATE")
-          options[:on_delete] = extract_foreign_key_action(create_table_info, row['name'], "DELETE")
+          options[:on_update] = extract_foreign_key_action(row["on_update"])
+          options[:on_delete] = extract_foreign_key_action(row["on_delete"])
 
-          ForeignKeyDefinition.new(table_name, row['to_table'], options)
+          ForeignKeyDefinition.new(table_name, row["to_table"], options)
         end
       end
 
-      def table_options(table_name)
-        create_table_info = select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
+      def table_options(table_name) # :nodoc:
+        table_options = {}
+
+        create_table_info = create_table_info(table_name)
 
         # strip create_definitions and partition_options
-        raw_table_options = create_table_info.sub(/\A.*\n\) /m, '').sub(/\n\/\*!.*\*\/\n\z/m, '').strip
+        raw_table_options = create_table_info.sub(/\A.*\n\) /m, "").sub(/\n\/\*!.*\*\/\n\z/m, "").strip
 
         # strip AUTO_INCREMENT
-        raw_table_options.sub(/(ENGINE=\w+)(?: AUTO_INCREMENT=\d+)/, '\1')
-      end
+        raw_table_options.sub!(/(ENGINE=\w+)(?: AUTO_INCREMENT=\d+)/, '\1')
 
-      # Maps logical Rails types to MySQL-specific data types.
-      def type_to_sql(type, limit = nil, precision = nil, scale = nil)
-        case type.to_s
-        when 'binary'
-          binary_to_sql(limit)
-        when 'integer'
-          integer_to_sql(limit)
-        when 'text'
-          text_to_sql(limit)
-        else
-          super
+        table_options[:options] = raw_table_options
+
+        # strip COMMENT
+        if raw_table_options.sub!(/ COMMENT='.+'/, "")
+          table_options[:comment] = table_comment(table_name)
         end
-      end
 
-      # SHOW VARIABLES LIKE 'name'
-      def show_variable(name)
-        variables = select_all("SHOW VARIABLES LIKE '#{name}'", 'SCHEMA')
-        variables.first['Value'] unless variables.empty?
+        table_options
       end
 
-      # Returns a table's primary key and belonging sequence.
-      def pk_and_sequence_for(table)
-        execute_and_free("SHOW CREATE TABLE #{quote_table_name(table)}", 'SCHEMA') do |result|
-          create_table = each_hash(result).first[:"Create Table"]
-          if create_table.to_s =~ /PRIMARY KEY\s+(?:USING\s+\w+\s+)?\((.+)\)/
-            keys = $1.split(",").map { |key| key.delete('`"') }
-            keys.length == 1 ? [keys.first, nil] : nil
+      # Maps logical Rails types to MySQL-specific data types.
+      def type_to_sql(type, limit: nil, precision: nil, scale: nil, unsigned: nil, **) # :nodoc:
+        sql = \
+          case type.to_s
+          when "integer"
+            integer_to_sql(limit)
+          when "text"
+            text_to_sql(limit)
+          when "blob"
+            binary_to_sql(limit)
+          when "binary"
+            if (0..0xfff) === limit
+              "varbinary(#{limit})"
+            else
+              binary_to_sql(limit)
+            end
           else
-            nil
+            super
           end
-        end
+
+        sql = "#{sql} unsigned" if unsigned && type != :primary_key
+        sql
       end
 
-      # Returns just a table's primary key
-      def primary_key(table)
-        pk_and_sequence = pk_and_sequence_for(table)
-        pk_and_sequence && pk_and_sequence.first
+      # SHOW VARIABLES LIKE 'name'
+      def show_variable(name)
+        query_value("SELECT @@#{name}", "SCHEMA")
+      rescue ActiveRecord::StatementInvalid
+        nil
       end
 
-      def case_sensitive_modifier(node, table_attribute)
-        node = Arel::Nodes.build_quoted node, table_attribute
-        Arel::Nodes::Bin.new(node)
+      def primary_keys(table_name) # :nodoc:
+        raise ArgumentError unless table_name.present?
+
+        scope = quoted_scope(table_name)
+
+        query_values(<<~SQL, "SCHEMA")
+          SELECT column_name
+          FROM information_schema.key_column_usage
+          WHERE constraint_name = 'PRIMARY'
+            AND table_schema = #{scope[:schema]}
+            AND table_name = #{scope[:name]}
+          ORDER BY ordinal_position
+        SQL
       end
 
-      def case_sensitive_comparison(table, attribute, column, value)
-        if column.case_sensitive?
-          table[attribute].eq(value)
+      def case_sensitive_comparison(table, attribute, column, value) # :nodoc:
+        if column.collation && !column.case_sensitive?
+          table[attribute].eq(Arel::Nodes::Bin.new(value))
         else
           super
         end
       end
 
-      def case_insensitive_comparison(table, attribute, column, value)
-        if column.case_sensitive?
-          super
-        else
-          table[attribute].eq(value)
-        end
+      def can_perform_case_insensitive_comparison_for?(column)
+        column.case_sensitive?
+      end
+      private :can_perform_case_insensitive_comparison_for?
+
+      # In MySQL 5.7.5 and up, ONLY_FULL_GROUP_BY affects handling of queries that use
+      # DISTINCT and ORDER BY. It requires the ORDER BY columns in the select list for
+      # distinct queries, and requires that the ORDER BY include the distinct column.
+      # See https://dev.mysql.com/doc/refman/5.7/en/group-by-handling.html
+      def columns_for_distinct(columns, orders) # :nodoc:
+        order_columns = orders.reject(&:blank?).map { |s|
+          # Convert Arel node to string
+          s = s.to_sql unless s.is_a?(String)
+          # Remove any ASC/DESC modifiers
+          s.gsub(/\s+(?:ASC|DESC)\b/i, "")
+        }.reject(&:blank?).map.with_index { |column, i| "#{column} AS alias_#{i}" }
+
+        (order_columns << super).join(", ")
       end
 
       def strict_mode?
         self.class.type_cast_config_to_boolean(@config.fetch(:strict, true))
       end
 
-      def valid_type?(type)
-        !native_database_types[type].nil?
+      def default_index_type?(index) # :nodoc:
+        index.using == :btree || super
       end
 
-      protected
-
-      def initialize_type_map(m) # :nodoc:
-        super
-
-        register_class_with_limit m, %r(char)i, MysqlString
-
-        m.register_type %r(tinytext)i,   Type::Text.new(limit: 2**8 - 1)
-        m.register_type %r(tinyblob)i,   Type::Binary.new(limit: 2**8 - 1)
-        m.register_type %r(text)i,       Type::Text.new(limit: 2**16 - 1)
-        m.register_type %r(blob)i,       Type::Binary.new(limit: 2**16 - 1)
-        m.register_type %r(mediumtext)i, Type::Text.new(limit: 2**24 - 1)
-        m.register_type %r(mediumblob)i, Type::Binary.new(limit: 2**24 - 1)
-        m.register_type %r(longtext)i,   Type::Text.new(limit: 2**32 - 1)
-        m.register_type %r(longblob)i,   Type::Binary.new(limit: 2**32 - 1)
-        m.register_type %r(^float)i,     Type::Float.new(limit: 24)
-        m.register_type %r(^double)i,    Type::Float.new(limit: 53)
-
-        register_integer_type m, %r(^bigint)i,    limit: 8
-        register_integer_type m, %r(^int)i,       limit: 4
-        register_integer_type m, %r(^mediumint)i, limit: 3
-        register_integer_type m, %r(^smallint)i,  limit: 2
-        register_integer_type m, %r(^tinyint)i,   limit: 1
-
-        m.alias_type %r(tinyint\(1\))i,  'boolean' if emulate_booleans
-        m.alias_type %r(set)i,           'varchar'
-        m.alias_type %r(year)i,          'integer'
-        m.alias_type %r(bit)i,           'binary'
-
-        m.register_type(%r(enum)i) do |sql_type|
-          limit = sql_type[/^enum\((.+)\)/i, 1]
-            .split(',').map{|enum| enum.strip.length - 2}.max
-          MysqlString.new(limit: limit)
+      def insert_fixtures_set(fixture_set, tables_to_delete = [])
+        with_multi_statements do
+          super { discard_remaining_results }
         end
       end
 
-      def register_integer_type(mapping, key, options) # :nodoc:
-        mapping.register_type(key) do |sql_type|
-          if /unsigned/i =~ sql_type
-            Type::UnsignedInteger.new(options)
-          else
-            Type::Integer.new(options)
+      private
+        def check_version
+          if version < "5.5.8"
+            raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.5.8."
           end
         end
-      end
 
-      def extract_precision(sql_type)
-        if /time/ === sql_type
-          super || 0
-        else
-          super
+        def combine_multi_statements(total_sql)
+          total_sql.each_with_object([]) do |sql, total_sql_chunks|
+            previous_packet = total_sql_chunks.last
+            sql << ";\n"
+            if max_allowed_packet_reached?(sql, previous_packet) || total_sql_chunks.empty?
+              total_sql_chunks << sql
+            else
+              previous_packet << sql
+            end
+          end
         end
-      end
 
-      def fetch_type_metadata(sql_type, extra = "")
-        MysqlTypeMetadata.new(super(sql_type), extra: extra, strict: strict_mode?)
-      end
-
-      def add_index_length(option_strings, column_names, options = {})
-        if options.is_a?(Hash) && length = options[:length]
-          case length
-          when Hash
-            column_names.each {|name| option_strings[name] += "(#{length[name]})" if length.has_key?(name) && length[name].present?}
-          when Fixnum
-            column_names.each {|name| option_strings[name] += "(#{length})"}
+        def max_allowed_packet_reached?(current_packet, previous_packet)
+          if current_packet.bytesize > max_allowed_packet
+            raise ActiveRecordError, "Fixtures set is too large #{current_packet.bytesize}. Consider increasing the max_allowed_packet variable."
+          elsif previous_packet.nil?
+            false
+          else
+            (current_packet.bytesize + previous_packet.bytesize) > max_allowed_packet
           end
         end
 
-        return option_strings
-      end
-
-      def quoted_columns_for_index(column_names, options = {})
-        option_strings = Hash[column_names.map {|name| [name, '']}]
-
-        # add index length
-        option_strings = add_index_length(option_strings, column_names, options)
+        def max_allowed_packet
+          bytes_margin = 2
+          @max_allowed_packet ||= (show_variable("max_allowed_packet") - bytes_margin)
+        end
 
-        # add index sort order
-        option_strings = add_index_sort_order(option_strings, column_names, options)
+        def initialize_type_map(m = type_map)
+          super
 
-        column_names.map {|name| quote_column_name(name) + option_strings[name]}
-      end
+          register_class_with_limit m, %r(char)i, MysqlString
+
+          m.register_type %r(tinytext)i,   Type::Text.new(limit: 2**8 - 1)
+          m.register_type %r(tinyblob)i,   Type::Binary.new(limit: 2**8 - 1)
+          m.register_type %r(text)i,       Type::Text.new(limit: 2**16 - 1)
+          m.register_type %r(blob)i,       Type::Binary.new(limit: 2**16 - 1)
+          m.register_type %r(mediumtext)i, Type::Text.new(limit: 2**24 - 1)
+          m.register_type %r(mediumblob)i, Type::Binary.new(limit: 2**24 - 1)
+          m.register_type %r(longtext)i,   Type::Text.new(limit: 2**32 - 1)
+          m.register_type %r(longblob)i,   Type::Binary.new(limit: 2**32 - 1)
+          m.register_type %r(^float)i,     Type::Float.new(limit: 24)
+          m.register_type %r(^double)i,    Type::Float.new(limit: 53)
+
+          register_integer_type m, %r(^bigint)i,    limit: 8
+          register_integer_type m, %r(^int)i,       limit: 4
+          register_integer_type m, %r(^mediumint)i, limit: 3
+          register_integer_type m, %r(^smallint)i,  limit: 2
+          register_integer_type m, %r(^tinyint)i,   limit: 1
+
+          m.register_type %r(^tinyint\(1\))i, Type::Boolean.new if emulate_booleans
+          m.alias_type %r(year)i,          "integer"
+          m.alias_type %r(bit)i,           "binary"
+
+          m.register_type(%r(enum)i) do |sql_type|
+            limit = sql_type[/^enum\((.+)\)/i, 1]
+              .split(",").map { |enum| enum.strip.length - 2 }.max
+            MysqlString.new(limit: limit)
+          end
 
-      def translate_exception(exception, message)
-        case error_number(exception)
-        when 1062
-          RecordNotUnique.new(message, exception)
-        when 1452
-          InvalidForeignKey.new(message, exception)
-        else
-          super
+          m.register_type(%r(^set)i) do |sql_type|
+            limit = sql_type[/^set\((.+)\)/i, 1]
+              .split(",").map { |set| set.strip.length - 1 }.sum - 1
+            MysqlString.new(limit: limit)
+          end
         end
-      end
-
-      def add_column_sql(table_name, column_name, type, options = {})
-        td = create_table_definition(table_name)
-        cd = td.new_column_definition(column_name, type, options)
-        schema_creation.accept(AddColumnDefinition.new(cd))
-      end
 
-      def change_column_sql(table_name, column_name, type, options = {})
-        column = column_for(table_name, column_name)
+        def register_integer_type(mapping, key, options)
+          mapping.register_type(key) do |sql_type|
+            if /\bunsigned\b/.match?(sql_type)
+              Type::UnsignedInteger.new(options)
+            else
+              Type::Integer.new(options)
+            end
+          end
+        end
 
-        unless options_include_default?(options)
-          options[:default] = column.default
+        def extract_precision(sql_type)
+          if /\A(?:date)?time(?:stamp)?\b/.match?(sql_type)
+            super || 0
+          else
+            super
+          end
         end
 
-        unless options.has_key?(:null)
-          options[:null] = column.null
+        # See https://dev.mysql.com/doc/refman/5.7/en/error-messages-server.html
+        ER_DUP_ENTRY            = 1062
+        ER_NOT_NULL_VIOLATION   = 1048
+        ER_NO_REFERENCED_ROW    = 1216
+        ER_ROW_IS_REFERENCED    = 1217
+        ER_DO_NOT_HAVE_DEFAULT  = 1364
+        ER_ROW_IS_REFERENCED_2  = 1451
+        ER_NO_REFERENCED_ROW_2  = 1452
+        ER_DATA_TOO_LONG        = 1406
+        ER_OUT_OF_RANGE         = 1264
+        ER_LOCK_DEADLOCK        = 1213
+        ER_CANNOT_ADD_FOREIGN   = 1215
+        ER_CANNOT_CREATE_TABLE  = 1005
+        ER_LOCK_WAIT_TIMEOUT    = 1205
+        ER_QUERY_INTERRUPTED    = 1317
+        ER_QUERY_TIMEOUT        = 3024
+
+        def translate_exception(exception, message)
+          case error_number(exception)
+          when ER_DUP_ENTRY
+            RecordNotUnique.new(message)
+          when ER_NO_REFERENCED_ROW, ER_ROW_IS_REFERENCED, ER_ROW_IS_REFERENCED_2, ER_NO_REFERENCED_ROW_2
+            InvalidForeignKey.new(message)
+          when ER_CANNOT_ADD_FOREIGN
+            mismatched_foreign_key(message)
+          when ER_CANNOT_CREATE_TABLE
+            if message.include?("errno: 150")
+              mismatched_foreign_key(message)
+            else
+              super
+            end
+          when ER_DATA_TOO_LONG
+            ValueTooLong.new(message)
+          when ER_OUT_OF_RANGE
+            RangeError.new(message)
+          when ER_NOT_NULL_VIOLATION, ER_DO_NOT_HAVE_DEFAULT
+            NotNullViolation.new(message)
+          when ER_LOCK_DEADLOCK
+            Deadlocked.new(message)
+          when ER_LOCK_WAIT_TIMEOUT
+            LockWaitTimeout.new(message)
+          when ER_QUERY_TIMEOUT
+            StatementTimeout.new(message)
+          when ER_QUERY_INTERRUPTED
+            QueryCanceled.new(message)
+          else
+            super
+          end
         end
 
-        td = create_table_definition(table_name)
-        cd = td.new_column_definition(column.name, type, options)
-        schema_creation.accept(ChangeColumnDefinition.new(cd, column.name))
-      end
+        def change_column_for_alter(table_name, column_name, type, options = {})
+          column = column_for(table_name, column_name)
+          type ||= column.sql_type
 
-      def rename_column_sql(table_name, column_name, new_column_name)
-        column  = column_for(table_name, column_name)
-        options = {
-          default: column.default,
-          null: column.null,
-          auto_increment: column.auto_increment?
-        }
-
-        current_type = select_one("SHOW COLUMNS FROM #{quote_table_name(table_name)} LIKE '#{column_name}'", 'SCHEMA')["Type"]
-        td = create_table_definition(table_name)
-        cd = td.new_column_definition(new_column_name, current_type, options)
-        schema_creation.accept(ChangeColumnDefinition.new(cd, column.name))
-      end
+          unless options.key?(:default)
+            options[:default] = column.default
+          end
 
-      def remove_column_sql(table_name, column_name, type = nil, options = {})
-        "DROP #{quote_column_name(column_name)}"
-      end
+          unless options.key?(:null)
+            options[:null] = column.null
+          end
 
-      def remove_columns_sql(table_name, *column_names)
-        column_names.map {|column_name| remove_column_sql(table_name, column_name) }
-      end
+          unless options.key?(:comment)
+            options[:comment] = column.comment
+          end
 
-      def add_index_sql(table_name, column_name, options = {})
-        index_name, index_type, index_columns, _, index_algorithm, index_using = add_index_options(table_name, column_name, options)
-        index_algorithm[0, 0] = ", " if index_algorithm.present?
-        "ADD #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} (#{index_columns})#{index_algorithm}"
-      end
+          td = create_table_definition(table_name)
+          cd = td.new_column_definition(column.name, type, options)
+          schema_creation.accept(ChangeColumnDefinition.new(cd, column.name))
+        end
 
-      def remove_index_sql(table_name, options = {})
-        index_name = index_name_for_remove(table_name, options)
-        "DROP INDEX #{index_name}"
-      end
+        def rename_column_for_alter(table_name, column_name, new_column_name)
+          column  = column_for(table_name, column_name)
+          options = {
+            default: column.default,
+            null: column.null,
+            auto_increment: column.auto_increment?
+          }
 
-      def add_timestamps_sql(table_name, options = {})
-        [add_column_sql(table_name, :created_at, :datetime, options), add_column_sql(table_name, :updated_at, :datetime, options)]
-      end
+          current_type = exec_query("SHOW COLUMNS FROM #{quote_table_name(table_name)} LIKE #{quote(column_name)}", "SCHEMA").first["Type"]
+          td = create_table_definition(table_name)
+          cd = td.new_column_definition(new_column_name, current_type, options)
+          schema_creation.accept(ChangeColumnDefinition.new(cd, column.name))
+        end
 
-      def remove_timestamps_sql(table_name, options = {})
-        [remove_column_sql(table_name, :updated_at), remove_column_sql(table_name, :created_at)]
-      end
+        def add_index_for_alter(table_name, column_name, options = {})
+          index_name, index_type, index_columns, _, index_algorithm, index_using = add_index_options(table_name, column_name, options)
+          index_algorithm[0, 0] = ", " if index_algorithm.present?
+          "ADD #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} (#{index_columns})#{index_algorithm}"
+        end
 
-      private
+        def remove_index_for_alter(table_name, options = {})
+          index_name = index_name_for_remove(table_name, options)
+          "DROP INDEX #{quote_column_name(index_name)}"
+        end
 
-      # MySQL is too stupid to create a temporary table for use subquery, so we have
-      # to give it some prompting in the form of a subsubquery. Ugh!
-      def subquery_for(key, select)
-        subsubselect = select.clone
-        subsubselect.projections = [key]
-
-        subselect = Arel::SelectManager.new(select.engine)
-        subselect.project Arel.sql(key.name)
-        # Materialized subquery by adding distinct
-        # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
-        subselect.from subsubselect.distinct.as('__active_record_temp')
-      end
+        def add_timestamps_for_alter(table_name, options = {})
+          [add_column_for_alter(table_name, :created_at, :datetime, options), add_column_for_alter(table_name, :updated_at, :datetime, options)]
+        end
 
-      def version
-        @version ||= full_version.scan(/^(\d+)\.(\d+)\.(\d+)/).flatten.map(&:to_i)
-      end
+        def remove_timestamps_for_alter(table_name, options = {})
+          [remove_column_for_alter(table_name, :updated_at), remove_column_for_alter(table_name, :created_at)]
+        end
 
-      def mariadb?
-        full_version =~ /mariadb/i
-      end
+        def supports_rename_index?
+          mariadb? ? false : version >= "5.7.6"
+        end
 
-      def supports_rename_index?
-        mariadb? ? false : (version[0] == 5 && version[1] >= 7) || version[0] >= 6
-      end
+        def configure_connection
+          variables = @config.fetch(:variables, {}).stringify_keys
 
-      def configure_connection
-        variables = @config.fetch(:variables, {}).stringify_keys
+          # By default, MySQL 'where id is null' selects the last inserted id; Turn this off.
+          variables["sql_auto_is_null"] = 0
 
-        # By default, MySQL 'where id is null' selects the last inserted id; Turn this off.
-        variables['sql_auto_is_null'] = 0
+          # Increase timeout so the server doesn't disconnect us.
+          wait_timeout = self.class.type_cast_config_to_integer(@config[:wait_timeout])
+          wait_timeout = 2147483 unless wait_timeout.is_a?(Integer)
+          variables["wait_timeout"] = wait_timeout
 
-        # Increase timeout so the server doesn't disconnect us.
-        wait_timeout = @config[:wait_timeout]
-        wait_timeout = 2147483 unless wait_timeout.is_a?(Fixnum)
-        variables['wait_timeout'] = self.class.type_cast_config_to_integer(wait_timeout)
+          defaults = [":default", :default].to_set
 
-        defaults = [':default', :default].to_set
+          # Make MySQL reject illegal values rather than truncating or blanking them, see
+          # https://dev.mysql.com/doc/refman/5.7/en/sql-mode.html#sqlmode_strict_all_tables
+          # If the user has provided another value for sql_mode, don't replace it.
+          if sql_mode = variables.delete("sql_mode")
+            sql_mode = quote(sql_mode)
+          elsif !defaults.include?(strict_mode?)
+            if strict_mode?
+              sql_mode = "CONCAT(@@sql_mode, ',STRICT_ALL_TABLES')"
+            else
+              sql_mode = "REPLACE(@@sql_mode, 'STRICT_TRANS_TABLES', '')"
+              sql_mode = "REPLACE(#{sql_mode}, 'STRICT_ALL_TABLES', '')"
+              sql_mode = "REPLACE(#{sql_mode}, 'TRADITIONAL', '')"
+            end
+            sql_mode = "CONCAT(#{sql_mode}, ',NO_AUTO_VALUE_ON_ZERO')"
+          end
+          sql_mode_assignment = "@@SESSION.sql_mode = #{sql_mode}, " if sql_mode
+
+          # NAMES does not have an equals sign, see
+          # https://dev.mysql.com/doc/refman/5.7/en/set-names.html
+          # (trailing comma because variable_assignments will always have content)
+          if @config[:encoding]
+            encoding = +"NAMES #{@config[:encoding]}"
+            encoding << " COLLATE #{@config[:collation]}" if @config[:collation]
+            encoding << ", "
+          end
 
-        # Make MySQL reject illegal values rather than truncating or blanking them, see
-        # http://dev.mysql.com/doc/refman/5.6/en/sql-mode.html#sqlmode_strict_all_tables
-        # If the user has provided another value for sql_mode, don't replace it.
-        unless variables.has_key?('sql_mode') || defaults.include?(@config[:strict])
-          variables['sql_mode'] = strict_mode? ? 'STRICT_ALL_TABLES' : ''
-        end
+          # Gather up all of the SET variables...
+          variable_assignments = variables.map do |k, v|
+            if defaults.include?(v)
+              "@@SESSION.#{k} = DEFAULT" # Sets the value to the global or compile default
+            elsif !v.nil?
+              "@@SESSION.#{k} = #{quote(v)}"
+            end
+            # or else nil; compact to clear nils out
+          end.compact.join(", ")
 
-        # NAMES does not have an equals sign, see
-        # http://dev.mysql.com/doc/refman/5.6/en/set-statement.html#id944430
-        # (trailing comma because variable_assignments will always have content)
-        if @config[:encoding]
-          encoding = "NAMES #{@config[:encoding]}"
-          encoding << " COLLATE #{@config[:collation]}" if @config[:collation]
-          encoding << ", "
+          # ...and send them all in one query
+          execute "SET #{encoding} #{sql_mode_assignment} #{variable_assignments}"
         end
 
-        # Gather up all of the SET variables...
-        variable_assignments = variables.map do |k, v|
-          if defaults.include?(v)
-            "@@SESSION.#{k} = DEFAULT" # Sets the value to the global or compile default
-          elsif !v.nil?
-            "@@SESSION.#{k} = #{quote(v)}"
+        def column_definitions(table_name) # :nodoc:
+          execute_and_free("SHOW FULL FIELDS FROM #{quote_table_name(table_name)}", "SCHEMA") do |result|
+            each_hash(result)
           end
-          # or else nil; compact to clear nils out
-        end.compact.join(', ')
-
-        # ...and send them all in one query
-        @connection.query  "SET #{encoding} #{variable_assignments}"
-      end
+        end
 
-      def extract_foreign_key_action(structure, name, action) # :nodoc:
-        if structure =~ /CONSTRAINT #{quote_column_name(name)} FOREIGN KEY .* REFERENCES .* ON #{action} (CASCADE|SET NULL|RESTRICT)/
-          case $1
-          when 'CASCADE'; :cascade
-          when 'SET NULL'; :nullify
-          end
+        def create_table_info(table_name) # :nodoc:
+          exec_query("SHOW CREATE TABLE #{quote_table_name(table_name)}", "SCHEMA").first["Create Table"]
         end
-      end
 
-      def create_table_definition(name, temporary = false, options = nil, as = nil) # :nodoc:
-        TableDefinition.new(native_database_types, name, temporary, options, as)
-      end
+        def arel_visitor
+          Arel::Visitors::MySQL.new(self)
+        end
 
-      def binary_to_sql(limit) # :nodoc:
-        case limit
-        when 0..0xfff;           "varbinary(#{limit})"
-        when nil;                "blob"
-        when 0x1000..0xffffffff; "blob(#{limit})"
-        else raise(ActiveRecordError, "No binary type has character length #{limit}")
+        def mismatched_foreign_key(message)
+          parts = message.scan(/`(\w+)`[ $)]/).flatten
+          MismatchedForeignKey.new(
+            self,
+            message: message,
+            table: parts[0],
+            foreign_key: parts[1],
+            target_table: parts[2],
+            primary_key: parts[3],
+          )
         end
-      end
 
-      def integer_to_sql(limit) # :nodoc:
-        case limit
-        when 1; 'tinyint'
-        when 2; 'smallint'
-        when 3; 'mediumint'
-        when nil, 4, 11; 'int(11)'  # compatibility with MySQL default
-        when 5..8; 'bigint'
-        else raise(ActiveRecordError, "No integer type has byte size #{limit}")
+        def integer_to_sql(limit) # :nodoc:
+          case limit
+          when 1; "tinyint"
+          when 2; "smallint"
+          when 3; "mediumint"
+          when nil, 4; "int"
+          when 5..8; "bigint"
+          else raise(ActiveRecordError, "No integer type has byte size #{limit}. Use a decimal with scale 0 instead.")
+          end
         end
-      end
 
-      def text_to_sql(limit) # :nodoc:
-        case limit
-        when 0..0xff;               'tinytext'
-        when nil, 0x100..0xffff;    'text'
-        when 0x10000..0xffffff;     'mediumtext'
-        when 0x1000000..0xffffffff; 'longtext'
-        else raise(ActiveRecordError, "No text type has character length #{limit}")
+        def text_to_sql(limit) # :nodoc:
+          case limit
+          when 0..0xff;               "tinytext"
+          when nil, 0x100..0xffff;    "text"
+          when 0x10000..0xffffff;     "mediumtext"
+          when 0x1000000..0xffffffff; "longtext"
+          else raise(ActiveRecordError, "No text type has byte length #{limit}")
+          end
         end
-      end
 
-      class MysqlString < Type::String # :nodoc:
-        def serialize(value)
-          case value
-          when true then "1"
-          when false then "0"
-          else super
+        def binary_to_sql(limit) # :nodoc:
+          case limit
+          when 0..0xff;               "tinyblob"
+          when nil, 0x100..0xffff;    "blob"
+          when 0x10000..0xffffff;     "mediumblob"
+          when 0x1000000..0xffffffff; "longblob"
+          else raise(ActiveRecordError, "No binary type has byte length #{limit}")
           end
         end
 
-        private
+        def version_string
+          full_version.match(/^(?:5\.5\.5-)?(\d+\.\d+\.\d+)/)[1]
+        end
 
-        def cast_value(value)
-          case value
-          when true then "1"
-          when false then "0"
-          else super
+        class MysqlString < Type::String # :nodoc:
+          def serialize(value)
+            case value
+            when true then "1"
+            when false then "0"
+            else super
+            end
           end
+
+          private
+
+            def cast_value(value)
+              case value
+              when true then "1"
+              when false then "0"
+              else super
+              end
+            end
         end
-      end
 
-      ActiveRecord::Type.register(:string, MysqlString, adapter: :mysql)
-      ActiveRecord::Type.register(:string, MysqlString, adapter: :mysql2)
+        ActiveRecord::Type.register(:string, MysqlString, adapter: :mysql2)
+        ActiveRecord::Type.register(:unsigned_integer, Type::UnsignedInteger, adapter: :mysql2)
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/column.rb b/activerecord/lib/active_record/connection_adapters/column.rb
index 4b95b0681d..5d81de9fe1 100644
--- a/activerecord/lib/active_record/connection_adapters/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/column.rb
@@ -1,35 +1,29 @@
-require 'set'
+# frozen_string_literal: true
 
 module ActiveRecord
   # :stopdoc:
   module ConnectionAdapters
     # An abstract definition of a column in a table.
     class Column
-      FALSE_VALUES = [false, 0, '0', 'f', 'F', 'false', 'FALSE', 'off', 'OFF'].to_set
-
-      module Format
-        ISO_DATE = /\A(\d{4})-(\d\d)-(\d\d)\z/
-        ISO_DATETIME = /\A(\d{4})-(\d\d)-(\d\d) (\d\d):(\d\d):(\d\d)(\.\d+)?\z/
-      end
-
-      attr_reader :name, :null, :sql_type_metadata, :default, :default_function, :collation
+      attr_reader :name, :default, :sql_type_metadata, :null, :table_name, :default_function, :collation, :comment
 
       delegate :precision, :scale, :limit, :type, :sql_type, to: :sql_type_metadata, allow_nil: true
 
       # Instantiates a new column in the table.
       #
-      # +name+ is the column's name, such as <tt>supplier_id</tt> in <tt>supplier_id int(11)</tt>.
+      # +name+ is the column's name, such as <tt>supplier_id</tt> in <tt>supplier_id bigint</tt>.
       # +default+ is the type-casted default value, such as +new+ in <tt>sales_stage varchar(20) default 'new'</tt>.
       # +sql_type_metadata+ is various information about the type of the column
       # +null+ determines if this column allows +NULL+ values.
-      def initialize(name, default, sql_type_metadata = nil, null = true, default_function = nil, collation = nil)
-        @name = name
+      def initialize(name, default, sql_type_metadata = nil, null = true, table_name = nil, default_function = nil, collation = nil, comment: nil, **)
+        @name = name.freeze
+        @table_name = table_name
         @sql_type_metadata = sql_type_metadata
         @null = null
         @default = default
         @default_function = default_function
         @collation = collation
-        @table_name = nil
+        @comment = comment
       end
 
       def has_default?
@@ -37,7 +31,7 @@ module ActiveRecord
       end
 
       def bigint?
-        /bigint/ === sql_type
+        /\Abigint\b/.match?(sql_type)
       end
 
       # Returns the human name of the column name.
@@ -48,6 +42,28 @@ module ActiveRecord
         Base.human_attribute_name(@name)
       end
 
+      def init_with(coder)
+        @name = coder["name"]
+        @table_name = coder["table_name"]
+        @sql_type_metadata = coder["sql_type_metadata"]
+        @null = coder["null"]
+        @default = coder["default"]
+        @default_function = coder["default_function"]
+        @collation = coder["collation"]
+        @comment = coder["comment"]
+      end
+
+      def encode_with(coder)
+        coder["name"] = @name
+        coder["table_name"] = @table_name
+        coder["sql_type_metadata"] = @sql_type_metadata
+        coder["null"] = @null
+        coder["default"] = @default
+        coder["default_function"] = @default_function
+        coder["collation"] = @collation
+        coder["comment"] = @comment
+      end
+
       def ==(other)
         other.is_a?(Column) &&
           attributes_for_hash == other.attributes_for_hash
@@ -60,9 +76,9 @@ module ActiveRecord
 
       protected
 
-      def attributes_for_hash
-        [self.class, name, default, sql_type_metadata, null, default_function, collation]
-      end
+        def attributes_for_hash
+          [self.class, name, default, sql_type_metadata, null, table_name, default_function, collation]
+        end
     end
 
     class NullColumn < Column
diff --git a/activerecord/lib/active_record/connection_adapters/connection_specification.rb b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
index 08d46fca96..2e7a78215a 100644
--- a/activerecord/lib/active_record/connection_adapters/connection_specification.rb
+++ b/activerecord/lib/active_record/connection_adapters/connection_specification.rb
@@ -1,21 +1,26 @@
-require 'uri'
+# frozen_string_literal: true
+
+require "uri"
 
 module ActiveRecord
   module ConnectionAdapters
     class ConnectionSpecification #:nodoc:
-      attr_reader :config, :adapter_method
+      attr_reader :name, :config, :adapter_method
 
-      def initialize(config, adapter_method)
-        @config, @adapter_method = config, adapter_method
+      def initialize(name, config, adapter_method)
+        @name, @config, @adapter_method = name, config, adapter_method
       end
 
       def initialize_dup(original)
         @config = original.config.dup
       end
 
+      def to_hash
+        @config.merge(name: @name)
+      end
+
       # Expands a connection string into a hash.
       class ConnectionUrlResolver # :nodoc:
-
         # == Example
         #
         #   url = "postgresql://foo:bar@localhost:9000/foo_test?pool=5&timeout=3000"
@@ -33,11 +38,11 @@ module ActiveRecord
         def initialize(url)
           raise "Database URL cannot be empty" if url.blank?
           @uri     = uri_parser.parse(url)
-          @adapter = @uri.scheme.tr('-', '_')
+          @adapter = @uri.scheme && @uri.scheme.tr("-", "_")
           @adapter = "postgresql" if @adapter == "postgres"
 
           if @uri.opaque
-            @uri.opaque, @query = @uri.opaque.split('?', 2)
+            @uri.opaque, @query = @uri.opaque.split("?", 2)
           else
             @query = @uri.query
           end
@@ -45,65 +50,63 @@ module ActiveRecord
 
         # Converts the given URL to a full connection hash.
         def to_hash
-          config = raw_config.reject { |_,value| value.blank? }
-          config.map { |key,value| config[key] = uri_parser.unescape(value) if value.is_a? String }
+          config = raw_config.reject { |_, value| value.blank? }
+          config.map { |key, value| config[key] = uri_parser.unescape(value) if value.is_a? String }
           config
         end
 
         private
 
-        def uri
-          @uri
-        end
+          attr_reader :uri
 
-        def uri_parser
-          @uri_parser ||= URI::Parser.new
-        end
+          def uri_parser
+            @uri_parser ||= URI::Parser.new
+          end
 
-        # Converts the query parameters of the URI into a hash.
-        #
-        #   "localhost?pool=5&reaping_frequency=2"
-        #   # => { "pool" => "5", "reaping_frequency" => "2" }
-        #
-        # returns empty hash if no query present.
-        #
-        #   "localhost"
-        #   # => {}
-        def query_hash
-          Hash[(@query || '').split("&").map { |pair| pair.split("=") }]
-        end
+          # Converts the query parameters of the URI into a hash.
+          #
+          #   "localhost?pool=5&reaping_frequency=2"
+          #   # => { "pool" => "5", "reaping_frequency" => "2" }
+          #
+          # returns empty hash if no query present.
+          #
+          #   "localhost"
+          #   # => {}
+          def query_hash
+            Hash[(@query || "").split("&").map { |pair| pair.split("=") }]
+          end
 
-        def raw_config
-          if uri.opaque
-            query_hash.merge({
-              "adapter"  => @adapter,
-              "database" => uri.opaque })
-          else
-            query_hash.merge({
-              "adapter"  => @adapter,
-              "username" => uri.user,
-              "password" => uri.password,
-              "port"     => uri.port,
-              "database" => database_from_path,
-              "host"     => uri.hostname })
+          def raw_config
+            if uri.opaque
+              query_hash.merge(
+                "adapter"  => @adapter,
+                "database" => uri.opaque)
+            else
+              query_hash.merge(
+                "adapter"  => @adapter,
+                "username" => uri.user,
+                "password" => uri.password,
+                "port"     => uri.port,
+                "database" => database_from_path,
+                "host"     => uri.hostname)
+            end
           end
-        end
 
-        # Returns name of the database.
-        def database_from_path
-          if @adapter == 'sqlite3'
-            # 'sqlite3:/foo' is absolute, because that makes sense. The
-            # corresponding relative version, 'sqlite3:foo', is handled
-            # elsewhere, as an "opaque".
+          # Returns name of the database.
+          def database_from_path
+            if @adapter == "sqlite3"
+              # 'sqlite3:/foo' is absolute, because that makes sense. The
+              # corresponding relative version, 'sqlite3:foo', is handled
+              # elsewhere, as an "opaque".
 
-            uri.path
-          else
-            # Only SQLite uses a filename as the "database" name; for
-            # anything else, a leading slash would be silly.
+              uri.path
+            else
+              # Only SQLite uses a filename as the "database" name; for
+              # anything else, a leading slash would be silly.
 
-            uri.path.sub(%r{^/}, "")
+              uri.path.sub(%r{^/}, "")
+            end
           end
-        end
       end
 
       ##
@@ -111,8 +114,7 @@ module ActiveRecord
       class Resolver # :nodoc:
         attr_reader :configurations
 
-        # Accepts a hash two layers deep, keys on the first layer represent
-        # environments such as "production". Keys must be strings.
+        # Accepts a list of db config objects.
         def initialize(configurations)
           @configurations = configurations
         end
@@ -133,25 +135,14 @@ module ActiveRecord
         #   Resolver.new(configurations).resolve(:production)
         #   # => { "host" => "localhost", "database" => "foo", "adapter" => "postgresql" }
         #
-        def resolve(config)
-          if config
-            resolve_connection config
-          elsif env = ActiveRecord::ConnectionHandling::RAILS_ENV.call
-            resolve_symbol_connection env.to_sym
+        def resolve(config_or_env, pool_name = nil)
+          if config_or_env
+            resolve_connection config_or_env, pool_name
           else
             raise AdapterNotSpecified
           end
         end
 
-        # Expands each key in @configurations hash into fully resolved hash
-        def resolve_all
-          config = configurations.dup
-          config.each do |key, value|
-            config[key] = resolve(value) if value
-          end
-          config
-        end
-
         # Returns an instance of ConnectionSpecification for a given adapter.
         # Accepts a hash one layer deep that contains all connection information.
         #
@@ -165,91 +156,122 @@ module ActiveRecord
         #   # => { "host" => "localhost", "database" => "foo", "adapter" => "sqlite3" }
         #
         def spec(config)
-          spec = resolve(config).symbolize_keys
+          pool_name = config if config.is_a?(Symbol)
+
+          spec = resolve(config, pool_name).symbolize_keys
 
           raise(AdapterNotSpecified, "database configuration does not specify adapter") unless spec.key?(:adapter)
 
+          # Require the adapter itself and give useful feedback about
+          #   1. Missing adapter gems and
+          #   2. Adapter gems' missing dependencies.
           path_to_adapter = "active_record/connection_adapters/#{spec[:adapter]}_adapter"
           begin
             require path_to_adapter
-          rescue Gem::LoadError => e
-            raise Gem::LoadError, "Specified '#{spec[:adapter]}' for database adapter, but the gem is not loaded. Add `gem '#{e.name}'` to your Gemfile (and ensure its version is at the minimum required by ActiveRecord)."
           rescue LoadError => e
-            raise LoadError, "Could not load '#{path_to_adapter}'. Make sure that the adapter in config/database.yml is valid. If you use an adapter other than 'mysql', 'mysql2', 'postgresql' or 'sqlite3' add the necessary adapter gem to the Gemfile.", e.backtrace
+            # We couldn't require the adapter itself. Raise an exception that
+            # points out config typos and missing gems.
+            if e.path == path_to_adapter
+              # We can assume that a non-builtin adapter was specified, so it's
+              # either misspelled or missing from Gemfile.
+              raise e.class, "Could not load the '#{spec[:adapter]}' Active Record adapter. Ensure that the adapter is spelled correctly in config/database.yml and that you've added the necessary adapter gem to your Gemfile.", e.backtrace
+
+            # Bubbled up from the adapter require. Prefix the exception message
+            # with some guidance about how to address it and reraise.
+            else
+              raise e.class, "Error loading the '#{spec[:adapter]}' Active Record adapter. Missing a gem it depends on? #{e.message}", e.backtrace
+            end
           end
 
           adapter_method = "#{spec[:adapter]}_connection"
-          ConnectionSpecification.new(spec, adapter_method)
+
+          unless ActiveRecord::Base.respond_to?(adapter_method)
+            raise AdapterNotFound, "database configuration specifies nonexistent #{spec.config[:adapter]} adapter"
+          end
+
+          ConnectionSpecification.new(spec.delete(:name) || "primary", spec, adapter_method)
         end
 
         private
-
-        # Returns fully resolved connection, accepts hash, string or symbol.
-        # Always returns a hash.
-        #
-        # == Examples
-        #
-        # Symbol representing current environment.
-        #
-        #   Resolver.new("production" => {}).resolve_connection(:production)
-        #   # => {}
-        #
-        # One layer deep hash of connection values.
-        #
-        #   Resolver.new({}).resolve_connection("adapter" => "sqlite3")
-        #   # => { "adapter" => "sqlite3" }
-        #
-        # Connection URL.
-        #
-        #   Resolver.new({}).resolve_connection("postgresql://localhost/foo")
-        #   # => { "host" => "localhost", "database" => "foo", "adapter" => "postgresql" }
-        #
-        def resolve_connection(spec)
-          case spec
-          when Symbol
-            resolve_symbol_connection spec
-          when String
-            resolve_url_connection spec
-          when Hash
-            resolve_hash_connection spec
+          # Returns fully resolved connection, accepts hash, string or symbol.
+          # Always returns a hash.
+          #
+          # == Examples
+          #
+          # Symbol representing current environment.
+          #
+          #   Resolver.new("production" => {}).resolve_connection(:production)
+          #   # => {}
+          #
+          # One layer deep hash of connection values.
+          #
+          #   Resolver.new({}).resolve_connection("adapter" => "sqlite3")
+          #   # => { "adapter" => "sqlite3" }
+          #
+          # Connection URL.
+          #
+          #   Resolver.new({}).resolve_connection("postgresql://localhost/foo")
+          #   # => { "host" => "localhost", "database" => "foo", "adapter" => "postgresql" }
+          #
+          def resolve_connection(config_or_env, pool_name = nil)
+            case config_or_env
+            when Symbol
+              resolve_symbol_connection config_or_env, pool_name
+            when String
+              resolve_url_connection config_or_env
+            when Hash
+              resolve_hash_connection config_or_env
+            else
+              resolve_connection config_or_env
+            end
           end
-        end
 
-        # Takes the environment such as +:production+ or +:development+.
-        # This requires that the @configurations was initialized with a key that
-        # matches.
-        #
-        #   Resolver.new("production" => {}).resolve_symbol_connection(:production)
-        #   # => {}
-        #
-        def resolve_symbol_connection(spec)
-          if config = configurations[spec.to_s]
-            resolve_connection(config)
-          else
-            raise(AdapterNotSpecified, "'#{spec}' database is not configured. Available: #{configurations.keys.inspect}")
+          # Takes the environment such as +:production+ or +:development+ and a
+          # pool name the corresponds to the name given by the connection pool
+          # to the connection. That pool name is merged into the hash with the
+          # name key.
+          #
+          # This requires that the @configurations was initialized with a key that
+          # matches.
+          #
+          #   configurations = #<ActiveRecord::DatabaseConfigurations:0x00007fd9fdace3e0
+          #     @configurations=[
+          #       #<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fd9fdace250
+          #         @env_name="production", @spec_name="primary", @config={"database"=>"my_db"}>
+          #       ]>
+          #
+          #   Resolver.new(configurations).resolve_symbol_connection(:production, "primary")
+          #   # => { "database" => "my_db" }
+          def resolve_symbol_connection(env_name, pool_name)
+            db_config = configurations.find_db_config(env_name)
+
+            if db_config
+              resolve_connection(db_config.config).merge("name" => pool_name.to_s)
+            else
+              raise(AdapterNotSpecified, "'#{env_name}' database is not configured. Available: #{configurations.configurations.map(&:env_name).join(", ")}")
+            end
           end
-        end
 
-        # Accepts a hash. Expands the "url" key that contains a
-        # URL database connection to a full connection
-        # hash and merges with the rest of the hash.
-        # Connection details inside of the "url" key win any merge conflicts
-        def resolve_hash_connection(spec)
-          if spec["url"] && spec["url"] !~ /^jdbc:/
-            connection_hash = resolve_url_connection(spec.delete("url"))
-            spec.merge!(connection_hash)
+          # Accepts a hash. Expands the "url" key that contains a
+          # URL database connection to a full connection
+          # hash and merges with the rest of the hash.
+          # Connection details inside of the "url" key win any merge conflicts
+          def resolve_hash_connection(spec)
+            if spec["url"] && spec["url"] !~ /^jdbc:/
+              connection_hash = resolve_url_connection(spec.delete("url"))
+              spec.merge!(connection_hash)
+            end
+            spec
           end
-          spec
-        end
 
-        # Takes a connection URL.
-        #
-        #   Resolver.new({}).resolve_url_connection("postgresql://localhost/foo")
-        #   # => { "host" => "localhost", "database" => "foo", "adapter" => "postgresql" }
-        #
-        def resolve_url_connection(url)
-          ConnectionUrlResolver.new(url).to_hash
-        end
+          # Takes a connection URL.
+          #
+          #   Resolver.new({}).resolve_url_connection("postgresql://localhost/foo")
+          #   # => { "host" => "localhost", "database" => "foo", "adapter" => "postgresql" }
+          #
+          def resolve_url_connection(url)
+            ConnectionUrlResolver.new(url).to_hash
+          end
       end
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/determine_if_preparable_visitor.rb b/activerecord/lib/active_record/connection_adapters/determine_if_preparable_visitor.rb
new file mode 100644
index 0000000000..883747b84b
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/determine_if_preparable_visitor.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module DetermineIfPreparableVisitor
+      attr_reader :preparable
+
+      def accept(*)
+        @preparable = true
+        super
+      end
+
+      def visit_Arel_Nodes_In(o, collector)
+        @preparable = false
+        super
+      end
+
+      def visit_Arel_Nodes_NotIn(o, collector)
+        @preparable = false
+        super
+      end
+
+      def visit_Arel_Nodes_SqlLiteral(*)
+        @preparable = false
+        super
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/column.rb b/activerecord/lib/active_record/connection_adapters/mysql/column.rb
new file mode 100644
index 0000000000..fa1541019d
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/column.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      class Column < ConnectionAdapters::Column # :nodoc:
+        delegate :extra, to: :sql_type_metadata, allow_nil: true
+
+        def unsigned?
+          /\bunsigned(?: zerofill)?\z/.match?(sql_type)
+        end
+
+        def case_sensitive?
+          collation && !/_ci\z/.match?(collation)
+        end
+
+        def auto_increment?
+          extra == "auto_increment"
+        end
+
+        def virtual?
+          /\b(?:VIRTUAL|STORED|PERSISTENT)\b/.match?(extra)
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
new file mode 100644
index 0000000000..684c7042a7
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
@@ -0,0 +1,141 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      module DatabaseStatements
+        # Returns an ActiveRecord::Result instance.
+        def select_all(*) # :nodoc:
+          result = if ExplainRegistry.collect? && prepared_statements
+            unprepared_statement { super }
+          else
+            super
+          end
+          discard_remaining_results
+          result
+        end
+
+        def query(sql, name = nil) # :nodoc:
+          execute(sql, name).to_a
+        end
+
+        # Executes the SQL statement in the context of this connection.
+        def execute(sql, name = nil)
+          # make sure we carry over any changes to ActiveRecord::Base.default_timezone that have been
+          # made since we established the connection
+          @connection.query_options[:database_timezone] = ActiveRecord::Base.default_timezone
+
+          super
+        end
+
+        def exec_query(sql, name = "SQL", binds = [], prepare: false)
+          materialize_transactions
+
+          if without_prepared_statement?(binds)
+            execute_and_free(sql, name) do |result|
+              ActiveRecord::Result.new(result.fields, result.to_a) if result
+            end
+          else
+            exec_stmt_and_free(sql, name, binds, cache_stmt: prepare) do |_, result|
+              ActiveRecord::Result.new(result.fields, result.to_a) if result
+            end
+          end
+        end
+
+        def exec_delete(sql, name = nil, binds = [])
+          materialize_transactions
+
+          if without_prepared_statement?(binds)
+            execute_and_free(sql, name) { @connection.affected_rows }
+          else
+            exec_stmt_and_free(sql, name, binds) { |stmt| stmt.affected_rows }
+          end
+        end
+        alias :exec_update :exec_delete
+
+        private
+          def default_insert_value(column)
+            Arel.sql("DEFAULT") unless column.auto_increment?
+          end
+
+          def last_inserted_id(result)
+            @connection.last_id
+          end
+
+          def discard_remaining_results
+            @connection.abandon_results!
+          end
+
+          def supports_set_server_option?
+            @connection.respond_to?(:set_server_option)
+          end
+
+          def multi_statements_enabled?(flags)
+            if flags.is_a?(Array)
+              flags.include?("MULTI_STATEMENTS")
+            else
+              (flags & Mysql2::Client::MULTI_STATEMENTS) != 0
+            end
+          end
+
+          def with_multi_statements
+            previous_flags = @config[:flags]
+
+            unless multi_statements_enabled?(previous_flags)
+              if supports_set_server_option?
+                @connection.set_server_option(Mysql2::Client::OPTION_MULTI_STATEMENTS_ON)
+              else
+                @config[:flags] = Mysql2::Client::MULTI_STATEMENTS
+                reconnect!
+              end
+            end
+
+            yield
+          ensure
+            unless multi_statements_enabled?(previous_flags)
+              if supports_set_server_option?
+                @connection.set_server_option(Mysql2::Client::OPTION_MULTI_STATEMENTS_OFF)
+              else
+                @config[:flags] = previous_flags
+                reconnect!
+              end
+            end
+          end
+
+          def exec_stmt_and_free(sql, name, binds, cache_stmt: false)
+            # make sure we carry over any changes to ActiveRecord::Base.default_timezone that have been
+            # made since we established the connection
+            @connection.query_options[:database_timezone] = ActiveRecord::Base.default_timezone
+
+            type_casted_binds = type_casted_binds(binds)
+
+            log(sql, name, binds, type_casted_binds) do
+              if cache_stmt
+                stmt = @statements[sql] ||= @connection.prepare(sql)
+              else
+                stmt = @connection.prepare(sql)
+              end
+
+              begin
+                result = ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+                  stmt.execute(*type_casted_binds)
+                end
+              rescue Mysql2::Error => e
+                if cache_stmt
+                  @statements.delete(sql)
+                else
+                  stmt.close
+                end
+                raise e
+              end
+
+              ret = yield stmt, result
+              result.free if result
+              stmt.close unless cache_stmt
+              ret
+            end
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/explain_pretty_printer.rb b/activerecord/lib/active_record/connection_adapters/mysql/explain_pretty_printer.rb
new file mode 100644
index 0000000000..20c3c83664
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/explain_pretty_printer.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of an EXPLAIN in a way that resembles the output of the
+        # MySQL shell:
+        #
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   | id | select_type | table | type  | possible_keys | key     | key_len | ref   | rows | Extra       |
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   |  1 | SIMPLE      | users | const | PRIMARY       | PRIMARY | 4       | const |    1 |             |
+        #   |  1 | SIMPLE      | posts | ALL   | NULL          | NULL    | NULL    | NULL  |    1 | Using where |
+        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
+        #   2 rows in set (0.00 sec)
+        #
+        # This is an exercise in Ruby hyperrealism :).
+        def pp(result, elapsed)
+          widths    = compute_column_widths(result)
+          separator = build_separator(widths)
+
+          pp = []
+
+          pp << separator
+          pp << build_cells(result.columns, widths)
+          pp << separator
+
+          result.rows.each do |row|
+            pp << build_cells(row, widths)
+          end
+
+          pp << separator
+          pp << build_footer(result.rows.length, elapsed)
+
+          pp.join("\n") + "\n"
+        end
+
+        private
+
+          def compute_column_widths(result)
+            [].tap do |widths|
+              result.columns.each_with_index do |column, i|
+                cells_in_column = [column] + result.rows.map { |r| r[i].nil? ? "NULL" : r[i].to_s }
+                widths << cells_in_column.map(&:length).max
+              end
+            end
+          end
+
+          def build_separator(widths)
+            padding = 1
+            "+" + widths.map { |w| "-" * (w + (padding * 2)) }.join("+") + "+"
+          end
+
+          def build_cells(items, widths)
+            cells = []
+            items.each_with_index do |item, i|
+              item = "NULL" if item.nil?
+              justifier = item.is_a?(Numeric) ? "rjust" : "ljust"
+              cells << item.to_s.send(justifier, widths[i])
+            end
+            "| " + cells.join(" | ") + " |"
+          end
+
+          def build_footer(nrows, elapsed)
+            rows_label = nrows == 1 ? "row" : "rows"
+            "#{nrows} #{rows_label} in set (%.2f sec)" % elapsed
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/quoting.rb b/activerecord/lib/active_record/connection_adapters/mysql/quoting.rb
new file mode 100644
index 0000000000..75564a61d6
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/quoting.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      module Quoting # :nodoc:
+        def quote_column_name(name)
+          @quoted_column_names[name] ||= "`#{super.gsub('`', '``')}`"
+        end
+
+        def quote_table_name(name)
+          @quoted_table_names[name] ||= super.gsub(".", "`.`").freeze
+        end
+
+        def unquoted_true
+          1
+        end
+
+        def unquoted_false
+          0
+        end
+
+        def quoted_date(value)
+          if supports_datetime_with_precision?
+            super
+          else
+            super.sub(/\.\d{6}\z/, "")
+          end
+        end
+
+        def quoted_binary(value)
+          "x'#{value.hex}'"
+        end
+
+        def _type_cast(value)
+          case value
+          when Date, Time then value
+          else super
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb
new file mode 100644
index 0000000000..82ed320617
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      class SchemaCreation < AbstractAdapter::SchemaCreation # :nodoc:
+        delegate :add_sql_comment!, :mariadb?, to: :@conn, private: true
+
+        private
+
+          def visit_DropForeignKey(name)
+            "DROP FOREIGN KEY #{name}"
+          end
+
+          def visit_AddColumnDefinition(o)
+            add_column_position!(super, column_options(o.column))
+          end
+
+          def visit_ChangeColumnDefinition(o)
+            change_column_sql = +"CHANGE #{quote_column_name(o.name)} #{accept(o.column)}"
+            add_column_position!(change_column_sql, column_options(o.column))
+          end
+
+          def add_table_options!(create_sql, options)
+            add_sql_comment!(super, options[:comment])
+          end
+
+          def add_column_options!(sql, options)
+            # By default, TIMESTAMP columns are NOT NULL, cannot contain NULL values,
+            # and assigning NULL assigns the current timestamp. To permit a TIMESTAMP
+            # column to contain NULL, explicitly declare it with the NULL attribute.
+            # See https://dev.mysql.com/doc/refman/5.7/en/timestamp-initialization.html
+            if /\Atimestamp\b/.match?(options[:column].sql_type) && !options[:primary_key]
+              sql << " NULL" unless options[:null] == false || options_include_default?(options)
+            end
+
+            if charset = options[:charset]
+              sql << " CHARACTER SET #{charset}"
+            end
+
+            if collation = options[:collation]
+              sql << " COLLATE #{collation}"
+            end
+
+            if as = options[:as]
+              sql << " AS (#{as})"
+              if options[:stored]
+                sql << (mariadb? ? " PERSISTENT" : " STORED")
+              end
+            end
+
+            add_sql_comment!(super, options[:comment])
+          end
+
+          def add_column_position!(sql, options)
+            if options[:first]
+              sql << " FIRST"
+            elsif options[:after]
+              sql << " AFTER #{quote_column_name(options[:after])}"
+            end
+
+            sql
+          end
+
+          def index_in_create(table_name, column_name, options)
+            index_name, index_type, index_columns, _, _, index_using, comment = @conn.add_index_options(table_name, column_name, options)
+            add_sql_comment!((+"#{index_type} INDEX #{quote_column_name(index_name)} #{index_using} (#{index_columns})"), comment)
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb
new file mode 100644
index 0000000000..2ed4ad16ae
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb
@@ -0,0 +1,87 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      module ColumnMethods
+        def blob(*args, **options)
+          args.each { |name| column(name, :blob, options) }
+        end
+
+        def tinyblob(*args, **options)
+          args.each { |name| column(name, :tinyblob, options) }
+        end
+
+        def mediumblob(*args, **options)
+          args.each { |name| column(name, :mediumblob, options) }
+        end
+
+        def longblob(*args, **options)
+          args.each { |name| column(name, :longblob, options) }
+        end
+
+        def tinytext(*args, **options)
+          args.each { |name| column(name, :tinytext, options) }
+        end
+
+        def mediumtext(*args, **options)
+          args.each { |name| column(name, :mediumtext, options) }
+        end
+
+        def longtext(*args, **options)
+          args.each { |name| column(name, :longtext, options) }
+        end
+
+        def unsigned_integer(*args, **options)
+          args.each { |name| column(name, :unsigned_integer, options) }
+        end
+
+        def unsigned_bigint(*args, **options)
+          args.each { |name| column(name, :unsigned_bigint, options) }
+        end
+
+        def unsigned_float(*args, **options)
+          args.each { |name| column(name, :unsigned_float, options) }
+        end
+
+        def unsigned_decimal(*args, **options)
+          args.each { |name| column(name, :unsigned_decimal, options) }
+        end
+      end
+
+      class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
+        include ColumnMethods
+
+        def new_column_definition(name, type, **options) # :nodoc:
+          case type
+          when :virtual
+            type = options[:type]
+          when :primary_key
+            type = :integer
+            options[:limit] ||= 8
+            options[:primary_key] = true
+          when /\Aunsigned_(?<type>.+)\z/
+            type = $~[:type].to_sym
+            options[:unsigned] = true
+          end
+
+          super
+        end
+
+        private
+          def aliased_types(name, fallback)
+            fallback
+          end
+
+          def integer_like_primary_key_type(type, options)
+            options[:auto_increment] = true
+            type
+          end
+      end
+
+      class Table < ActiveRecord::ConnectionAdapters::Table
+        include ColumnMethods
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
new file mode 100644
index 0000000000..d23178e43c
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      class SchemaDumper < ConnectionAdapters::SchemaDumper # :nodoc:
+        private
+          def prepare_column_options(column)
+            spec = super
+            spec[:unsigned] = "true" if column.unsigned?
+            spec[:auto_increment] = "true" if column.auto_increment?
+
+            if @connection.supports_virtual_columns? && column.virtual?
+              spec[:as] = extract_expression_for_virtual_column(column)
+              spec[:stored] = "true" if /\b(?:STORED|PERSISTENT)\b/.match?(column.extra)
+              spec = { type: schema_type(column).inspect }.merge!(spec)
+            end
+
+            spec
+          end
+
+          def column_spec_for_primary_key(column)
+            spec = super
+            spec.delete(:auto_increment) if column.type == :integer && column.auto_increment?
+            spec
+          end
+
+          def default_primary_key?(column)
+            super && column.auto_increment? && !column.unsigned?
+          end
+
+          def explicit_primary_key_default?(column)
+            column.type == :integer && !column.auto_increment?
+          end
+
+          def schema_type(column)
+            case column.sql_type
+            when /\Atimestamp\b/
+              :timestamp
+            when "tinyblob"
+              :blob
+            else
+              super
+            end
+          end
+
+          def schema_precision(column)
+            super unless /\A(?:date)?time(?:stamp)?\b/.match?(column.sql_type) && column.precision == 0
+          end
+
+          def schema_collation(column)
+            if column.collation && table_name = column.table_name
+              @table_collation_cache ||= {}
+              @table_collation_cache[table_name] ||=
+                @connection.exec_query("SHOW TABLE STATUS LIKE #{@connection.quote(table_name)}", "SCHEMA").first["Collation"]
+              column.collation.inspect if column.collation != @table_collation_cache[table_name]
+            end
+          end
+
+          def extract_expression_for_virtual_column(column)
+            if @connection.mariadb? && @connection.version < "10.2.5"
+              create_table_info = @connection.send(:create_table_info, column.table_name)
+              column_name = @connection.quote_column_name(column.name)
+              if %r/#{column_name} #{Regexp.quote(column.sql_type)}(?: COLLATE \w+)? AS \((?<expression>.+?)\) #{column.extra}/ =~ create_table_info
+                $~[:expression].inspect
+              end
+            else
+              scope = @connection.send(:quoted_scope, column.table_name)
+              column_name = @connection.quote(column.name)
+              sql = "SELECT generation_expression FROM information_schema.columns" \
+                    " WHERE table_schema = #{scope[:schema]}" \
+                    "   AND table_name = #{scope[:name]}" \
+                    "   AND column_name = #{column_name}"
+              @connection.query_value(sql, "SCHEMA").inspect
+            end
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
new file mode 100644
index 0000000000..4894fd1c08
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
@@ -0,0 +1,177 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      module SchemaStatements # :nodoc:
+        # Returns an array of indexes for the given table.
+        def indexes(table_name)
+          indexes = []
+          current_index = nil
+          execute_and_free("SHOW KEYS FROM #{quote_table_name(table_name)}", "SCHEMA") do |result|
+            each_hash(result) do |row|
+              if current_index != row[:Key_name]
+                next if row[:Key_name] == "PRIMARY" # skip the primary key
+                current_index = row[:Key_name]
+
+                mysql_index_type = row[:Index_type].downcase.to_sym
+                case mysql_index_type
+                when :fulltext, :spatial
+                  index_type = mysql_index_type
+                when :btree, :hash
+                  index_using = mysql_index_type
+                end
+
+                indexes << [
+                  row[:Table],
+                  row[:Key_name],
+                  row[:Non_unique].to_i == 0,
+                  [],
+                  lengths: {},
+                  orders: {},
+                  type: index_type,
+                  using: index_using,
+                  comment: row[:Index_comment].presence
+                ]
+              end
+
+              if row[:Expression]
+                expression = row[:Expression]
+                expression = +"(#{expression})" unless expression.start_with?("(")
+                indexes.last[-2] << expression
+                indexes.last[-1][:expressions] ||= {}
+                indexes.last[-1][:expressions][expression] = expression
+                indexes.last[-1][:orders][expression] = :desc if row[:Collation] == "D"
+              else
+                indexes.last[-2] << row[:Column_name]
+                indexes.last[-1][:lengths][row[:Column_name]] = row[:Sub_part].to_i if row[:Sub_part]
+                indexes.last[-1][:orders][row[:Column_name]] = :desc if row[:Collation] == "D"
+              end
+            end
+          end
+
+          indexes.map do |index|
+            options = index.last
+
+            if expressions = options.delete(:expressions)
+              orders = options.delete(:orders)
+              lengths = options.delete(:lengths)
+
+              columns = index[-2].map { |name|
+                [ name.to_sym, expressions[name] || +quote_column_name(name) ]
+              }.to_h
+
+              index[-2] = add_options_for_index_columns(
+                columns, order: orders, length: lengths
+              ).values.join(", ")
+            end
+
+            IndexDefinition.new(*index)
+          end
+        end
+
+        def remove_column(table_name, column_name, type = nil, options = {})
+          if foreign_key_exists?(table_name, column: column_name)
+            remove_foreign_key(table_name, column: column_name)
+          end
+          super
+        end
+
+        def internal_string_options_for_primary_key
+          super.tap do |options|
+            if CHARSETS_OF_4BYTES_MAXLEN.include?(charset) && (mariadb? || version < "8.0.0")
+              options[:collation] = collation.sub(/\A[^_]+/, "utf8")
+            end
+          end
+        end
+
+        def update_table_definition(table_name, base)
+          MySQL::Table.new(table_name, base)
+        end
+
+        def create_schema_dumper(options)
+          MySQL::SchemaDumper.create(self, options)
+        end
+
+        private
+          CHARSETS_OF_4BYTES_MAXLEN = ["utf8mb4", "utf16", "utf16le", "utf32"]
+
+          def schema_creation
+            MySQL::SchemaCreation.new(self)
+          end
+
+          def create_table_definition(*args)
+            MySQL::TableDefinition.new(*args)
+          end
+
+          def new_column_from_field(table_name, field)
+            type_metadata = fetch_type_metadata(field[:Type], field[:Extra])
+            default, default_function = field[:Default], nil
+
+            if type_metadata.type == :datetime && /\ACURRENT_TIMESTAMP(?:\([0-6]?\))?\z/i.match?(default)
+              default, default_function = nil, default
+            elsif type_metadata.extra == "DEFAULT_GENERATED"
+              default = +"(#{default})" unless default.start_with?("(")
+              default, default_function = nil, default
+            end
+
+            MySQL::Column.new(
+              field[:Field],
+              default,
+              type_metadata,
+              field[:Null] == "YES",
+              table_name,
+              default_function,
+              field[:Collation],
+              comment: field[:Comment].presence
+            )
+          end
+
+          def fetch_type_metadata(sql_type, extra = "")
+            MySQL::TypeMetadata.new(super(sql_type), extra: extra)
+          end
+
+          def extract_foreign_key_action(specifier)
+            super unless specifier == "RESTRICT"
+          end
+
+          def add_index_length(quoted_columns, **options)
+            lengths = options_for_index_columns(options[:length])
+            quoted_columns.each do |name, column|
+              column << "(#{lengths[name]})" if lengths[name].present?
+            end
+          end
+
+          def add_options_for_index_columns(quoted_columns, **options)
+            quoted_columns = add_index_length(quoted_columns, options)
+            super
+          end
+
+          def data_source_sql(name = nil, type: nil)
+            scope = quoted_scope(name, type: type)
+
+            sql = +"SELECT table_name FROM information_schema.tables"
+            sql << " WHERE table_schema = #{scope[:schema]}"
+            sql << " AND table_name = #{scope[:name]}" if scope[:name]
+            sql << " AND table_type = #{scope[:type]}" if scope[:type]
+            sql
+          end
+
+          def quoted_scope(name = nil, type: nil)
+            schema, name = extract_schema_qualified_name(name)
+            scope = {}
+            scope[:schema] = schema ? quote(schema) : "database()"
+            scope[:name] = quote(name) if name
+            scope[:type] = quote(type) if type
+            scope
+          end
+
+          def extract_schema_qualified_name(string)
+            schema, name = string.to_s.scan(/[^`.\s]+|`[^`]*`/)
+            schema, name = nil, schema unless name
+            [schema, name]
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb b/activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb
new file mode 100644
index 0000000000..7ad0944d51
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module MySQL
+      class TypeMetadata < DelegateClass(SqlTypeMetadata) # :nodoc:
+        undef to_yaml if method_defined?(:to_yaml)
+
+        attr_reader :extra
+
+        def initialize(type_metadata, extra: "")
+          super(type_metadata)
+          @type_metadata = type_metadata
+          @extra = extra
+        end
+
+        def ==(other)
+          other.is_a?(MySQL::TypeMetadata) &&
+            attributes_for_hash == other.attributes_for_hash
+        end
+        alias eql? ==
+
+        def hash
+          attributes_for_hash.hash
+        end
+
+        protected
+
+          def attributes_for_hash
+            [self.class, @type_metadata, extra]
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index e97e82f056..9bdaa00336 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -1,26 +1,29 @@
-require 'active_record/connection_adapters/abstract_mysql_adapter'
+# frozen_string_literal: true
 
-gem 'mysql2', '~> 0.3.18'
-require 'mysql2'
+require "active_record/connection_adapters/abstract_mysql_adapter"
+require "active_record/connection_adapters/mysql/database_statements"
+
+gem "mysql2", ">= 0.4.4"
+require "mysql2"
 
 module ActiveRecord
   module ConnectionHandling # :nodoc:
     # Establishes a connection to the database that's used by all Active Record objects.
     def mysql2_connection(config)
       config = config.symbolize_keys
+      config[:flags] ||= 0
 
-      config[:username] = 'root' if config[:username].nil?
-
-      if Mysql2::Client.const_defined? :FOUND_ROWS
-        config[:flags] = Mysql2::Client::FOUND_ROWS
+      if config[:flags].kind_of? Array
+        config[:flags].push "FOUND_ROWS"
+      else
+        config[:flags] |= Mysql2::Client::FOUND_ROWS
       end
 
       client = Mysql2::Client.new(config)
-      options = [config[:host], config[:username], config[:password], config[:database], config[:port], config[:socket], 0]
-      ConnectionAdapters::Mysql2Adapter.new(client, logger, options, config)
+      ConnectionAdapters::Mysql2Adapter.new(client, logger, nil, config)
     rescue Mysql2::Error => error
       if error.message.include?("Unknown database")
-        raise ActiveRecord::NoDatabaseError.new(error.message, error)
+        raise ActiveRecord::NoDatabaseError
       else
         raise
       end
@@ -29,15 +32,33 @@ module ActiveRecord
 
   module ConnectionAdapters
     class Mysql2Adapter < AbstractMysqlAdapter
-      ADAPTER_NAME = 'Mysql2'.freeze
+      ADAPTER_NAME = "Mysql2"
+
+      include MySQL::DatabaseStatements
 
       def initialize(connection, logger, connection_options, config)
         super
-        @prepared_statements = false
+        @prepared_statements = false unless config.key?(:prepared_statements)
         configure_connection
       end
 
-      def supports_explain?
+      def supports_json?
+        !mariadb? && version >= "5.7.8"
+      end
+
+      def supports_comments?
+        true
+      end
+
+      def supports_comments_in_create?
+        true
+      end
+
+      def supports_savepoints?
+        true
+      end
+
+      def supports_lazy_transactions?
         true
       end
 
@@ -45,7 +66,7 @@ module ActiveRecord
 
       def each_hash(result) # :nodoc:
         if block_given?
-          result.each(:as => :hash, :symbolize_keys => true) do |row|
+          result.each(as: :hash, symbolize_keys: true) do |row|
             yield row
           end
         else
@@ -70,7 +91,6 @@ module ActiveRecord
       #++
 
       def active?
-        return false unless @connection
         @connection.ping
       end
 
@@ -85,181 +105,29 @@ module ActiveRecord
       # Otherwise, this method does nothing.
       def disconnect!
         super
-        unless @connection.nil?
-          @connection.close
-          @connection = nil
-        end
+        @connection.close
       end
 
-      #--
-      # DATABASE STATEMENTS ======================================
-      #++
-
-      def explain(arel, binds = [])
-        sql     = "EXPLAIN #{to_sql(arel, binds.dup)}"
-        start   = Time.now
-        result  = exec_query(sql, 'EXPLAIN', binds)
-        elapsed = Time.now - start
-
-        ExplainPrettyPrinter.new.pp(result, elapsed)
+      def discard! # :nodoc:
+        @connection.automatic_close = false
+        @connection = nil
       end
 
-      class ExplainPrettyPrinter # :nodoc:
-        # Pretty prints the result of a EXPLAIN in a way that resembles the output of the
-        # MySQL shell:
-        #
-        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
-        #   | id | select_type | table | type  | possible_keys | key     | key_len | ref   | rows | Extra       |
-        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
-        #   |  1 | SIMPLE      | users | const | PRIMARY       | PRIMARY | 4       | const |    1 |             |
-        #   |  1 | SIMPLE      | posts | ALL   | NULL          | NULL    | NULL    | NULL  |    1 | Using where |
-        #   +----+-------------+-------+-------+---------------+---------+---------+-------+------+-------------+
-        #   2 rows in set (0.00 sec)
-        #
-        # This is an exercise in Ruby hyperrealism :).
-        def pp(result, elapsed)
-          widths    = compute_column_widths(result)
-          separator = build_separator(widths)
-
-          pp = []
-
-          pp << separator
-          pp << build_cells(result.columns, widths)
-          pp << separator
-
-          result.rows.each do |row|
-            pp << build_cells(row, widths)
-          end
-
-          pp << separator
-          pp << build_footer(result.rows.length, elapsed)
-
-          pp.join("\n") + "\n"
-        end
-
-        private
-
-        def compute_column_widths(result)
-          [].tap do |widths|
-            result.columns.each_with_index do |column, i|
-              cells_in_column = [column] + result.rows.map {|r| r[i].nil? ? 'NULL' : r[i].to_s}
-              widths << cells_in_column.map(&:length).max
-            end
-          end
-        end
-
-        def build_separator(widths)
-          padding = 1
-          '+' + widths.map {|w| '-' * (w + (padding*2))}.join('+') + '+'
-        end
+      private
 
-        def build_cells(items, widths)
-          cells = []
-          items.each_with_index do |item, i|
-            item = 'NULL' if item.nil?
-            justifier = item.is_a?(Numeric) ? 'rjust' : 'ljust'
-            cells << item.to_s.send(justifier, widths[i])
-          end
-          '| ' + cells.join(' | ') + ' |'
+        def connect
+          @connection = Mysql2::Client.new(@config)
+          configure_connection
         end
 
-        def build_footer(nrows, elapsed)
-          rows_label = nrows == 1 ? 'row' : 'rows'
-          "#{nrows} #{rows_label} in set (%.2f sec)" % elapsed
+        def configure_connection
+          @connection.query_options[:as] = :array
+          super
         end
-      end
 
-      # FIXME: re-enable the following once a "better" query_cache solution is in core
-      #
-      # The overrides below perform much better than the originals in AbstractAdapter
-      # because we're able to take advantage of mysql2's lazy-loading capabilities
-      #
-      # # Returns a record hash with the column names as keys and column values
-      # # as values.
-      # def select_one(sql, name = nil)
-      #   result = execute(sql, name)
-      #   result.each(as: :hash) do |r|
-      #     return r
-      #   end
-      # end
-      #
-      # # Returns a single value from a record
-      # def select_value(sql, name = nil)
-      #   result = execute(sql, name)
-      #   if first = result.first
-      #     first.first
-      #   end
-      # end
-      #
-      # # Returns an array of the values of the first column in a select:
-      # #   select_values("SELECT id FROM companies LIMIT 3") => [1,2,3]
-      # def select_values(sql, name = nil)
-      #   execute(sql, name).map { |row| row.first }
-      # end
-
-      # Returns an array of arrays containing the field values.
-      # Order is the same as that returned by +columns+.
-      def select_rows(sql, name = nil, binds = [])
-        execute(sql, name).to_a
-      end
-
-      # Executes the SQL statement in the context of this connection.
-      def execute(sql, name = nil)
-        if @connection
-          # make sure we carry over any changes to ActiveRecord::Base.default_timezone that have been
-          # made since we established the connection
-          @connection.query_options[:database_timezone] = ActiveRecord::Base.default_timezone
+        def full_version
+          @full_version ||= @connection.server_info[:version]
         end
-
-        super
-      end
-
-      def exec_query(sql, name = 'SQL', binds = [])
-        result = execute(sql, name)
-        ActiveRecord::Result.new(result.fields, result.to_a)
-      end
-
-      alias exec_without_stmt exec_query
-
-      def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
-        super
-        id_value || @connection.last_id
-      end
-      alias :create :insert_sql
-
-      def exec_insert(sql, name, binds, pk = nil, sequence_name = nil)
-        execute to_sql(sql, binds), name
-      end
-
-      def exec_delete(sql, name, binds)
-        execute to_sql(sql, binds), name
-        @connection.affected_rows
-      end
-      alias :exec_update :exec_delete
-
-      def last_inserted_id(result)
-        @connection.last_id
-      end
-
-      private
-
-      def connect
-        @connection = Mysql2::Client.new(@config)
-        configure_connection
-      end
-
-      def configure_connection
-        @connection.query_options.merge!(:as => :array)
-        super
-      end
-
-      def full_version
-        @full_version ||= @connection.info[:version]
-      end
-
-      def set_field_encoding field_name
-        field_name
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
deleted file mode 100644
index 2ae462d773..0000000000
--- a/activerecord/lib/active_record/connection_adapters/mysql_adapter.rb
+++ /dev/null
@@ -1,468 +0,0 @@
-require 'active_record/connection_adapters/abstract_mysql_adapter'
-require 'active_record/connection_adapters/statement_pool'
-require 'active_support/core_ext/hash/keys'
-
-gem 'mysql', '~> 2.9'
-require 'mysql'
-
-class Mysql # :nodoc: all
-  class Time
-    # Used for casting DateTime fields to a MySQL friendly Time.
-    # This was documented in 48498da0dfed5239ea1eafb243ce47d7e3ce9e8e
-    def to_date
-      Date.new(year, month, day)
-    end
-  end
-  class Stmt; include Enumerable end
-  class Result; include Enumerable end
-end
-
-module ActiveRecord
-  module ConnectionHandling # :nodoc:
-    # Establishes a connection to the database that's used by all Active Record objects.
-    def mysql_connection(config)
-      config = config.symbolize_keys
-      host     = config[:host]
-      port     = config[:port]
-      socket   = config[:socket]
-      username = config[:username] ? config[:username].to_s : 'root'
-      password = config[:password].to_s
-      database = config[:database]
-
-      mysql = Mysql.init
-      mysql.ssl_set(config[:sslkey], config[:sslcert], config[:sslca], config[:sslcapath], config[:sslcipher]) if config[:sslca] || config[:sslkey]
-
-      default_flags = Mysql.const_defined?(:CLIENT_MULTI_RESULTS) ? Mysql::CLIENT_MULTI_RESULTS : 0
-      default_flags |= Mysql::CLIENT_FOUND_ROWS if Mysql.const_defined?(:CLIENT_FOUND_ROWS)
-      options = [host, username, password, database, port, socket, default_flags]
-      ConnectionAdapters::MysqlAdapter.new(mysql, logger, options, config)
-    rescue Mysql::Error => error
-      if error.message.include?("Unknown database")
-        raise ActiveRecord::NoDatabaseError.new(error.message, error)
-      else
-        raise
-      end
-    end
-  end
-
-  module ConnectionAdapters
-    # The MySQL adapter will work with both Ruby/MySQL, which is a Ruby-based MySQL adapter that comes bundled with Active Record, and with
-    # the faster C-based MySQL/Ruby adapter (available both as a gem and from http://www.tmtm.org/en/mysql/ruby/).
-    #
-    # Options:
-    #
-    # * <tt>:host</tt> - Defaults to "localhost".
-    # * <tt>:port</tt> - Defaults to 3306.
-    # * <tt>:socket</tt> - Defaults to "/tmp/mysql.sock".
-    # * <tt>:username</tt> - Defaults to "root"
-    # * <tt>:password</tt> - Defaults to nothing.
-    # * <tt>:database</tt> - The name of the database. No default, must be provided.
-    # * <tt>:encoding</tt> - (Optional) Sets the client encoding by executing "SET NAMES <encoding>" after connection.
-    # * <tt>:reconnect</tt> - Defaults to false (See MySQL documentation: http://dev.mysql.com/doc/refman/5.6/en/auto-reconnect.html).
-    # * <tt>:strict</tt> - Defaults to true. Enable STRICT_ALL_TABLES. (See MySQL documentation: http://dev.mysql.com/doc/refman/5.6/en/sql-mode.html)
-    # * <tt>:variables</tt> - (Optional) A hash session variables to send as <tt>SET @@SESSION.key = value</tt> on each database connection. Use the value +:default+ to set a variable to its DEFAULT value. (See MySQL documentation: http://dev.mysql.com/doc/refman/5.6/en/set-statement.html).
-    # * <tt>:sslca</tt> - Necessary to use MySQL with an SSL connection.
-    # * <tt>:sslkey</tt> - Necessary to use MySQL with an SSL connection.
-    # * <tt>:sslcert</tt> - Necessary to use MySQL with an SSL connection.
-    # * <tt>:sslcapath</tt> - Necessary to use MySQL with an SSL connection.
-    # * <tt>:sslcipher</tt> - Necessary to use MySQL with an SSL connection.
-    #
-    class MysqlAdapter < AbstractMysqlAdapter
-      ADAPTER_NAME = 'MySQL'.freeze
-
-      class StatementPool < ConnectionAdapters::StatementPool
-        private
-
-        def dealloc(stmt)
-          stmt[:stmt].close
-        end
-      end
-
-      def initialize(connection, logger, connection_options, config)
-        super
-        @statements = StatementPool.new(@connection,
-                                        self.class.type_cast_config_to_integer(config.fetch(:statement_limit) { 1000 }))
-        @client_encoding = nil
-        connect
-      end
-
-      # Returns true, since this connection adapter supports prepared statement
-      # caching.
-      def supports_statement_cache?
-        true
-      end
-
-      # HELPER METHODS ===========================================
-
-      def each_hash(result) # :nodoc:
-        if block_given?
-          result.each_hash do |row|
-            row.symbolize_keys!
-            yield row
-          end
-        else
-          to_enum(:each_hash, result)
-        end
-      end
-
-      def error_number(exception) # :nodoc:
-        exception.errno if exception.respond_to?(:errno)
-      end
-
-      # QUOTING ==================================================
-
-      def quote_string(string) #:nodoc:
-        @connection.quote(string)
-      end
-
-      #--
-      # CONNECTION MANAGEMENT ====================================
-      #++
-
-      def active?
-        if @connection.respond_to?(:stat)
-          @connection.stat
-        else
-          @connection.query 'select 1'
-        end
-
-        # mysql-ruby doesn't raise an exception when stat fails.
-        if @connection.respond_to?(:errno)
-          @connection.errno.zero?
-        else
-          true
-        end
-      rescue Mysql::Error
-        false
-      end
-
-      def reconnect!
-        super
-        disconnect!
-        connect
-      end
-
-      # Disconnects from the database if already connected. Otherwise, this
-      # method does nothing.
-      def disconnect!
-        super
-        @connection.close rescue nil
-      end
-
-      def reset!
-        if @connection.respond_to?(:change_user)
-          # See http://bugs.mysql.com/bug.php?id=33540 -- the workaround way to
-          # reset the connection is to change the user to the same user.
-          @connection.change_user(@config[:username], @config[:password], @config[:database])
-          configure_connection
-        end
-      end
-
-      #--
-      # DATABASE STATEMENTS ======================================
-      #++
-
-      def select_rows(sql, name = nil, binds = [])
-        @connection.query_with_result = true
-        rows = exec_query(sql, name, binds).rows
-        @connection.more_results && @connection.next_result    # invoking stored procedures with CLIENT_MULTI_RESULTS requires this to tidy up else connection will be dropped
-        rows
-      end
-
-      # Clears the prepared statements cache.
-      def clear_cache!
-        super
-        @statements.clear
-      end
-
-      # Taken from here:
-      #   https://github.com/tmtm/ruby-mysql/blob/master/lib/mysql/charset.rb
-      # Author: TOMITA Masahiro <tommy@tmtm.org>
-      ENCODINGS = {
-        "armscii8" => nil,
-        "ascii"    => Encoding::US_ASCII,
-        "big5"     => Encoding::Big5,
-        "binary"   => Encoding::ASCII_8BIT,
-        "cp1250"   => Encoding::Windows_1250,
-        "cp1251"   => Encoding::Windows_1251,
-        "cp1256"   => Encoding::Windows_1256,
-        "cp1257"   => Encoding::Windows_1257,
-        "cp850"    => Encoding::CP850,
-        "cp852"    => Encoding::CP852,
-        "cp866"    => Encoding::IBM866,
-        "cp932"    => Encoding::Windows_31J,
-        "dec8"     => nil,
-        "eucjpms"  => Encoding::EucJP_ms,
-        "euckr"    => Encoding::EUC_KR,
-        "gb2312"   => Encoding::EUC_CN,
-        "gbk"      => Encoding::GBK,
-        "geostd8"  => nil,
-        "greek"    => Encoding::ISO_8859_7,
-        "hebrew"   => Encoding::ISO_8859_8,
-        "hp8"      => nil,
-        "keybcs2"  => nil,
-        "koi8r"    => Encoding::KOI8_R,
-        "koi8u"    => Encoding::KOI8_U,
-        "latin1"   => Encoding::ISO_8859_1,
-        "latin2"   => Encoding::ISO_8859_2,
-        "latin5"   => Encoding::ISO_8859_9,
-        "latin7"   => Encoding::ISO_8859_13,
-        "macce"    => Encoding::MacCentEuro,
-        "macroman" => Encoding::MacRoman,
-        "sjis"     => Encoding::SHIFT_JIS,
-        "swe7"     => nil,
-        "tis620"   => Encoding::TIS_620,
-        "ucs2"     => Encoding::UTF_16BE,
-        "ujis"     => Encoding::EucJP_ms,
-        "utf8"     => Encoding::UTF_8,
-        "utf8mb4"  => Encoding::UTF_8,
-      }
-
-      # Get the client encoding for this database
-      def client_encoding
-        return @client_encoding if @client_encoding
-
-        result = exec_query(
-          "SHOW VARIABLES WHERE Variable_name = 'character_set_client'",
-          'SCHEMA')
-        @client_encoding = ENCODINGS[result.rows.last.last]
-      end
-
-      def exec_query(sql, name = 'SQL', binds = [])
-        if without_prepared_statement?(binds)
-          result_set, affected_rows = exec_without_stmt(sql, name)
-        else
-          result_set, affected_rows = exec_stmt(sql, name, binds)
-        end
-
-        yield affected_rows if block_given?
-
-        result_set
-      end
-
-      def last_inserted_id(result)
-        @connection.insert_id
-      end
-
-      module Fields # :nodoc:
-        class DateTime < Type::DateTime # :nodoc:
-          def cast_value(value)
-            if Mysql::Time === value
-              new_time(
-                value.year,
-                value.month,
-                value.day,
-                value.hour,
-                value.minute,
-                value.second,
-                value.second_part)
-            else
-              super
-            end
-          end
-        end
-
-        class Time < Type::Time # :nodoc:
-          def cast_value(value)
-            if Mysql::Time === value
-              new_time(
-                2000,
-                01,
-                01,
-                value.hour,
-                value.minute,
-                value.second,
-                value.second_part)
-            else
-              super
-            end
-          end
-        end
-
-        class << self
-          TYPES = Type::HashLookupTypeMap.new # :nodoc:
-
-          delegate :register_type, :alias_type, to: :TYPES
-
-          def find_type(field)
-            if field.type == Mysql::Field::TYPE_TINY && field.length > 1
-              TYPES.lookup(Mysql::Field::TYPE_LONG)
-            else
-              TYPES.lookup(field.type)
-            end
-          end
-        end
-
-        register_type Mysql::Field::TYPE_TINY,    Type::Boolean.new
-        register_type Mysql::Field::TYPE_LONG,    Type::Integer.new
-        alias_type Mysql::Field::TYPE_LONGLONG,   Mysql::Field::TYPE_LONG
-        alias_type Mysql::Field::TYPE_NEWDECIMAL, Mysql::Field::TYPE_LONG
-
-        register_type Mysql::Field::TYPE_DATE, Type::Date.new
-        register_type Mysql::Field::TYPE_DATETIME, Fields::DateTime.new
-        register_type Mysql::Field::TYPE_TIME, Fields::Time.new
-        register_type Mysql::Field::TYPE_FLOAT, Type::Float.new
-      end
-
-      def initialize_type_map(m) # :nodoc:
-        super
-        register_class_with_precision m, %r(datetime)i, Fields::DateTime
-        register_class_with_precision m, %r(time)i,     Fields::Time
-      end
-
-      def exec_without_stmt(sql, name = 'SQL') # :nodoc:
-        # Some queries, like SHOW CREATE TABLE don't work through the prepared
-        # statement API. For those queries, we need to use this method. :'(
-        log(sql, name) do
-          result = @connection.query(sql)
-          affected_rows = @connection.affected_rows
-
-          if result
-            types = {}
-            fields = []
-            result.fetch_fields.each { |field|
-              field_name = field.name
-              fields << field_name
-
-              if field.decimals > 0
-                types[field_name] = Type::Decimal.new
-              else
-                types[field_name] = Fields.find_type field
-              end
-            }
-
-            result_set = ActiveRecord::Result.new(fields, result.to_a, types)
-            result.free
-          else
-            result_set = ActiveRecord::Result.new([], [])
-          end
-
-          [result_set, affected_rows]
-        end
-      end
-
-      def execute_and_free(sql, name = nil) # :nodoc:
-        result = execute(sql, name)
-        ret = yield result
-        result.free
-        ret
-      end
-
-      def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil) #:nodoc:
-        super sql, name
-        id_value || @connection.insert_id
-      end
-      alias :create :insert_sql
-
-      def exec_delete(sql, name, binds) # :nodoc:
-        affected_rows = 0
-
-        exec_query(sql, name, binds) do |n|
-          affected_rows = n
-        end
-
-        affected_rows
-      end
-      alias :exec_update :exec_delete
-
-      def begin_db_transaction #:nodoc:
-        exec_query "BEGIN"
-      end
-
-      private
-
-      def exec_stmt(sql, name, binds)
-        cache = {}
-        type_casted_binds = binds.map { |attr| type_cast(attr.value_for_database) }
-
-        log(sql, name, binds) do
-          if binds.empty?
-            stmt = @connection.prepare(sql)
-          else
-            cache = @statements[sql] ||= {
-              :stmt => @connection.prepare(sql)
-            }
-            stmt = cache[:stmt]
-          end
-
-          begin
-            stmt.execute(*type_casted_binds)
-          rescue Mysql::Error => e
-            # Older versions of MySQL leave the prepared statement in a bad
-            # place when an error occurs. To support older MySQL versions, we
-            # need to close the statement and delete the statement from the
-            # cache.
-            if binds.empty?
-              stmt.close
-            else
-              @statements.delete sql
-            end
-            raise e
-          end
-
-          cols = nil
-          if metadata = stmt.result_metadata
-            cols = cache[:cols] ||= metadata.fetch_fields.map(&:name)
-            metadata.free
-          end
-
-          result_set = ActiveRecord::Result.new(cols, stmt.to_a) if cols
-          affected_rows = stmt.affected_rows
-
-          stmt.free_result
-          stmt.close if binds.empty?
-
-          [result_set, affected_rows]
-        end
-      end
-
-      def connect
-        encoding = @config[:encoding]
-        if encoding
-          @connection.options(Mysql::SET_CHARSET_NAME, encoding) rescue nil
-        end
-
-        if @config[:sslca] || @config[:sslkey]
-          @connection.ssl_set(@config[:sslkey], @config[:sslcert], @config[:sslca], @config[:sslcapath], @config[:sslcipher])
-        end
-
-        @connection.options(Mysql::OPT_CONNECT_TIMEOUT, @config[:connect_timeout]) if @config[:connect_timeout]
-        @connection.options(Mysql::OPT_READ_TIMEOUT, @config[:read_timeout]) if @config[:read_timeout]
-        @connection.options(Mysql::OPT_WRITE_TIMEOUT, @config[:write_timeout]) if @config[:write_timeout]
-
-        @connection.real_connect(*@connection_options)
-
-        # reconnect must be set after real_connect is called, because real_connect sets it to false internally
-        @connection.reconnect = !!@config[:reconnect] if @connection.respond_to?(:reconnect=)
-
-        configure_connection
-      end
-
-      # Many Rails applications monkey-patch a replacement of the configure_connection method
-      # and don't call 'super', so leave this here even though it looks superfluous.
-      def configure_connection
-        super
-      end
-
-      def select(sql, name = nil, binds = [])
-        @connection.query_with_result = true
-        rows = super
-        @connection.more_results && @connection.next_result    # invoking stored procedures with CLIENT_MULTI_RESULTS requires this to tidy up else connection will be dropped
-        rows
-      end
-
-      # Returns the full version of the connected MySQL server.
-      def full_version
-        @full_version ||= @connection.server_info
-      end
-
-      def set_field_encoding field_name
-        field_name.force_encoding(client_encoding)
-        if internal_enc = Encoding.default_internal
-          field_name = field_name.encode!(internal_enc)
-        end
-        field_name
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/column.rb b/activerecord/lib/active_record/connection_adapters/postgresql/column.rb
index bfa03fa136..3ccc7271ab 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/column.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/column.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     # PostgreSQL-specific extensions to column definitions in a table.
@@ -5,12 +7,37 @@ module ActiveRecord
       delegate :array, :oid, :fmod, to: :sql_type_metadata
       alias :array? :array
 
+      def initialize(*, max_identifier_length: 63, **)
+        super
+        @max_identifier_length = max_identifier_length
+      end
+
       def serial?
         return unless default_function
 
-        table_name = @table_name || '(?<table_name>.+)'
-        %r{\Anextval\('"?#{table_name}_#{name}_seq"?'::regclass\)\z} === default_function
+        if %r{\Anextval\('"?(?<sequence_name>.+_(?<suffix>seq\d*))"?'::regclass\)\z} =~ default_function
+          sequence_name_from_parts(table_name, name, suffix) == sequence_name
+        end
       end
+
+      private
+        attr_reader :max_identifier_length
+
+        def sequence_name_from_parts(table_name, column_name, suffix)
+          over_length = [table_name, column_name, suffix].map(&:length).sum + 2 - max_identifier_length
+
+          if over_length > 0
+            column_name_length = [(max_identifier_length - suffix.length - 2) / 2, column_name.length].min
+            over_length -= column_name.length - column_name_length
+            column_name = column_name[0, column_name_length - [over_length, 0].min]
+          end
+
+          if over_length > 0
+            table_name = table_name[0, table_name.length - over_length]
+          end
+
+          "#{table_name}_#{column_name}_#{suffix}"
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
index 11d3f5301a..6bd6b67165 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
@@ -1,97 +1,12 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module DatabaseStatements
         def explain(arel, binds = [])
           sql = "EXPLAIN #{to_sql(arel, binds)}"
-          ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN', binds))
-        end
-
-        class ExplainPrettyPrinter # :nodoc:
-          # Pretty prints the result of a EXPLAIN in a way that resembles the output of the
-          # PostgreSQL shell:
-          #
-          #                                     QUERY PLAN
-          #   ------------------------------------------------------------------------------
-          #    Nested Loop Left Join  (cost=0.00..37.24 rows=8 width=0)
-          #      Join Filter: (posts.user_id = users.id)
-          #      ->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=4)
-          #            Index Cond: (id = 1)
-          #      ->  Seq Scan on posts  (cost=0.00..28.88 rows=8 width=4)
-          #            Filter: (posts.user_id = 1)
-          #   (6 rows)
-          #
-          def pp(result)
-            header = result.columns.first
-            lines  = result.rows.map(&:first)
-
-            # We add 2 because there's one char of padding at both sides, note
-            # the extra hyphens in the example above.
-            width = [header, *lines].map(&:length).max + 2
-
-            pp = []
-
-            pp << header.center(width).rstrip
-            pp << '-' * width
-
-            pp += lines.map {|line| " #{line}"}
-
-            nrows = result.rows.length
-            rows_label = nrows == 1 ? 'row' : 'rows'
-            pp << "(#{nrows} #{rows_label})"
-
-            pp.join("\n") + "\n"
-          end
-        end
-
-        def select_value(arel, name = nil, binds = [])
-          arel, binds = binds_from_relation arel, binds
-          sql = to_sql(arel, binds)
-          execute_and_clear(sql, name, binds) do |result|
-            result.getvalue(0, 0) if result.ntuples > 0 && result.nfields > 0
-          end
-        end
-
-        def select_values(arel, name = nil)
-          arel, binds = binds_from_relation arel, []
-          sql = to_sql(arel, binds)
-          execute_and_clear(sql, name, binds) do |result|
-            if result.nfields > 0
-              result.column_values(0)
-            else
-              []
-            end
-          end
-        end
-
-        # Executes a SELECT query and returns an array of rows. Each row is an
-        # array of field values.
-        def select_rows(sql, name = nil, binds = [])
-          execute_and_clear(sql, name, binds) do |result|
-            result.values
-          end
-        end
-
-        # Executes an INSERT query and returns the new record's ID
-        def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil)
-          unless pk
-            # Extract the table from the insert sql. Yuck.
-            table_ref = extract_table_ref_from_insert_sql(sql)
-            pk = primary_key(table_ref) if table_ref
-          end
-
-          if pk && use_insert_returning?
-            select_value("#{sql} RETURNING #{quote_column_name(pk)}")
-          elsif pk
-            super
-            last_insert_id_value(sequence_name || default_sequence_name(table_ref, pk))
-          else
-            super
-          end
-        end
-
-        def create
-          super.insert
+          PostgreSQL::ExplainPrettyPrinter.new.pp(exec_query(sql, "EXPLAIN", binds))
         end
 
         # The internal PostgreSQL identifier of the money data type.
@@ -133,9 +48,9 @@ module ActiveRecord
               #  (2) $12.345.678,12
               case data
               when /^-?\D+[\d,]+\.\d{2}$/  # (1)
-                data.gsub!(/[^-\d.]/, '')
+                data.gsub!(/[^-\d.]/, "")
               when /^-?\D+[\d.]+,\d{2}$/  # (2)
-                data.gsub!(/[^-\d,]/, '').sub!(/,/, '.')
+                data.gsub!(/[^-\d,]/, "").sub!(/,/, ".")
               end
             end
           end
@@ -143,21 +58,31 @@ module ActiveRecord
 
         # Queries the database and returns the results in an Array-like object
         def query(sql, name = nil) #:nodoc:
+          materialize_transactions
+
           log(sql, name) do
-            result_as_array @connection.async_exec(sql)
+            ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+              result_as_array @connection.async_exec(sql)
+            end
           end
         end
 
-        # Executes an SQL statement, returning a PGresult object on success
-        # or raising a PGError exception otherwise.
+        # Executes an SQL statement, returning a PG::Result object on success
+        # or raising a PG::Error exception otherwise.
+        # Note: the PG::Result object is manually memory managed; if you don't
+        # need it specifically, you may want consider the <tt>exec_query</tt> wrapper.
         def execute(sql, name = nil)
+          materialize_transactions
+
           log(sql, name) do
-            @connection.async_exec(sql)
+            ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+              @connection.async_exec(sql)
+            end
           end
         end
 
-        def exec_query(sql, name = 'SQL', binds = [])
-          execute_and_clear(sql, name, binds) do |result|
+        def exec_query(sql, name = "SQL", binds = [], prepare: false)
+          execute_and_clear(sql, name, binds, prepare: prepare) do |result|
             types = {}
             fields = result.fields
             fields.each_with_index do |fname, i|
@@ -169,44 +94,44 @@ module ActiveRecord
           end
         end
 
-        def exec_delete(sql, name = 'SQL', binds = [])
-          execute_and_clear(sql, name, binds) {|result| result.cmd_tuples }
+        def exec_delete(sql, name = nil, binds = [])
+          execute_and_clear(sql, name, binds) { |result| result.cmd_tuples }
         end
         alias :exec_update :exec_delete
 
-        def sql_for_insert(sql, pk, id_value, sequence_name, binds)
-          unless pk
+        def sql_for_insert(sql, pk, id_value, sequence_name, binds) # :nodoc:
+          if pk.nil?
             # Extract the table from the insert sql. Yuck.
             table_ref = extract_table_ref_from_insert_sql(sql)
             pk = primary_key(table_ref) if table_ref
           end
 
-          if pk && use_insert_returning?
+          if pk = suppress_composite_primary_key(pk)
             sql = "#{sql} RETURNING #{quote_column_name(pk)}"
           end
 
-          [sql, binds]
+          super
         end
+        private :sql_for_insert
 
-        def exec_insert(sql, name, binds, pk = nil, sequence_name = nil)
-          val = exec_query(sql, name, binds)
-          if !use_insert_returning? && pk
+        def exec_insert(sql, name = nil, binds = [], pk = nil, sequence_name = nil)
+          if use_insert_returning? || pk == false
+            super
+          else
+            result = exec_query(sql, name, binds)
             unless sequence_name
               table_ref = extract_table_ref_from_insert_sql(sql)
-              sequence_name = default_sequence_name(table_ref, pk)
-              return val unless sequence_name
+              if table_ref
+                pk = primary_key(table_ref) if pk.nil?
+                pk = suppress_composite_primary_key(pk)
+                sequence_name = default_sequence_name(table_ref, pk)
+              end
+              return result unless sequence_name
             end
             last_insert_id_result(sequence_name)
-          else
-            val
           end
         end
 
-        # Executes an UPDATE query and returns the number of affected tuples.
-        def update_sql(sql, name = nil)
-          super.cmd_tuples
-        end
-
         # Begins a transaction.
         def begin_db_transaction
           execute "BEGIN"
@@ -226,6 +151,16 @@ module ActiveRecord
         def exec_rollback_db_transaction
           execute "ROLLBACK"
         end
+
+        private
+          # Returns the current ID of a table's sequence.
+          def last_insert_id_result(sequence_name)
+            exec_query("SELECT currval(#{quote(sequence_name)})", "SQL")
+          end
+
+          def suppress_composite_primary_key(pk)
+            pk unless pk.is_a?(Array)
+          end
       end
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb b/activerecord/lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb
new file mode 100644
index 0000000000..086a5dcc15
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module PostgreSQL
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of an EXPLAIN in a way that resembles the output of the
+        # PostgreSQL shell:
+        #
+        #                                     QUERY PLAN
+        #   ------------------------------------------------------------------------------
+        #    Nested Loop Left Join  (cost=0.00..37.24 rows=8 width=0)
+        #      Join Filter: (posts.user_id = users.id)
+        #      ->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=4)
+        #            Index Cond: (id = 1)
+        #      ->  Seq Scan on posts  (cost=0.00..28.88 rows=8 width=4)
+        #            Filter: (posts.user_id = 1)
+        #   (6 rows)
+        #
+        def pp(result)
+          header = result.columns.first
+          lines  = result.rows.map(&:first)
+
+          # We add 2 because there's one char of padding at both sides, note
+          # the extra hyphens in the example above.
+          width = [header, *lines].map(&:length).max + 2
+
+          pp = []
+
+          pp << header.center(width).rstrip
+          pp << "-" * width
+
+          pp += lines.map { |line| " #{line}" }
+
+          nrows = result.rows.length
+          rows_label = nrows == 1 ? "row" : "rows"
+          pp << "(#{nrows} #{rows_label})"
+
+          pp.join("\n") + "\n"
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid.rb
index 68752cdd80..247a25054e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid.rb
@@ -1,25 +1,28 @@
-require 'active_record/connection_adapters/postgresql/oid/array'
-require 'active_record/connection_adapters/postgresql/oid/bit'
-require 'active_record/connection_adapters/postgresql/oid/bit_varying'
-require 'active_record/connection_adapters/postgresql/oid/bytea'
-require 'active_record/connection_adapters/postgresql/oid/cidr'
-require 'active_record/connection_adapters/postgresql/oid/date_time'
-require 'active_record/connection_adapters/postgresql/oid/decimal'
-require 'active_record/connection_adapters/postgresql/oid/enum'
-require 'active_record/connection_adapters/postgresql/oid/hstore'
-require 'active_record/connection_adapters/postgresql/oid/inet'
-require 'active_record/connection_adapters/postgresql/oid/json'
-require 'active_record/connection_adapters/postgresql/oid/jsonb'
-require 'active_record/connection_adapters/postgresql/oid/money'
-require 'active_record/connection_adapters/postgresql/oid/point'
-require 'active_record/connection_adapters/postgresql/oid/rails_5_1_point'
-require 'active_record/connection_adapters/postgresql/oid/range'
-require 'active_record/connection_adapters/postgresql/oid/specialized_string'
-require 'active_record/connection_adapters/postgresql/oid/uuid'
-require 'active_record/connection_adapters/postgresql/oid/vector'
-require 'active_record/connection_adapters/postgresql/oid/xml'
+# frozen_string_literal: true
 
-require 'active_record/connection_adapters/postgresql/oid/type_map_initializer'
+require "active_record/connection_adapters/postgresql/oid/array"
+require "active_record/connection_adapters/postgresql/oid/bit"
+require "active_record/connection_adapters/postgresql/oid/bit_varying"
+require "active_record/connection_adapters/postgresql/oid/bytea"
+require "active_record/connection_adapters/postgresql/oid/cidr"
+require "active_record/connection_adapters/postgresql/oid/date"
+require "active_record/connection_adapters/postgresql/oid/date_time"
+require "active_record/connection_adapters/postgresql/oid/decimal"
+require "active_record/connection_adapters/postgresql/oid/enum"
+require "active_record/connection_adapters/postgresql/oid/hstore"
+require "active_record/connection_adapters/postgresql/oid/inet"
+require "active_record/connection_adapters/postgresql/oid/jsonb"
+require "active_record/connection_adapters/postgresql/oid/money"
+require "active_record/connection_adapters/postgresql/oid/oid"
+require "active_record/connection_adapters/postgresql/oid/point"
+require "active_record/connection_adapters/postgresql/oid/legacy_point"
+require "active_record/connection_adapters/postgresql/oid/range"
+require "active_record/connection_adapters/postgresql/oid/specialized_string"
+require "active_record/connection_adapters/postgresql/oid/uuid"
+require "active_record/connection_adapters/postgresql/oid/vector"
+require "active_record/connection_adapters/postgresql/oid/xml"
+
+require "active_record/connection_adapters/postgresql/oid/type_map_initializer"
 
 module ActiveRecord
   module ConnectionAdapters
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
index 25961a9869..6fbeaa2b9e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -5,10 +7,12 @@ module ActiveRecord
         class Array < Type::Value # :nodoc:
           include Type::Helpers::Mutable
 
+          Data = Struct.new(:encoder, :values) # :nodoc:
+
           attr_reader :subtype, :delimiter
-          delegate :type, :user_input_in_time_zone, :limit, to: :subtype
+          delegate :type, :user_input_in_time_zone, :limit, :precision, :scale, to: :subtype
 
-          def initialize(subtype, delimiter = ',')
+          def initialize(subtype, delimiter = ",")
             @subtype = subtype
             @delimiter = delimiter
 
@@ -17,8 +21,11 @@ module ActiveRecord
           end
 
           def deserialize(value)
-            if value.is_a?(::String)
+            case value
+            when ::String
               type_cast_array(@pg_decoder.decode(value), :deserialize)
+            when Data
+              type_cast_array(value.values, :deserialize)
             else
               super
             end
@@ -26,14 +33,21 @@ module ActiveRecord
 
           def cast(value)
             if value.is_a?(::String)
-              value = @pg_decoder.decode(value)
+              value = begin
+                @pg_decoder.decode(value)
+              rescue TypeError
+                # malformed array string is treated as [], will raise in PG 2.0 gem
+                # this keeps a consistent implementation
+                []
+              end
             end
             type_cast_array(value, :cast)
           end
 
           def serialize(value)
             if value.is_a?(::Array)
-              @pg_encoder.encode(type_cast_array(value, :serialize))
+              casted_values = type_cast_array(value, :serialize)
+              Data.new(@pg_encoder, casted_values)
             else
               super
             end
@@ -50,15 +64,27 @@ module ActiveRecord
             "[" + value.map { |v| subtype.type_cast_for_schema(v) }.join(", ") + "]"
           end
 
+          def map(value, &block)
+            value.map(&block)
+          end
+
+          def changed_in_place?(raw_old_value, new_value)
+            deserialize(raw_old_value) != new_value
+          end
+
+          def force_equality?(value)
+            value.is_a?(::Array)
+          end
+
           private
 
-          def type_cast_array(value, method)
-            if value.is_a?(::Array)
-              value.map { |item| type_cast_array(item, method) }
-            else
-              @subtype.public_send(method, value)
+            def type_cast_array(value, method)
+              if value.is_a?(::Array)
+                value.map { |item| type_cast_array(item, method) }
+              else
+                @subtype.public_send(method, value)
+              end
             end
-          end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb
index ea0fa2517f..e9a79526f9 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -7,7 +9,7 @@ module ActiveRecord
             :bit
           end
 
-          def cast(value)
+          def cast_value(value)
             if ::String === value
               case value
               when /^0x/i
@@ -16,7 +18,7 @@ module ActiveRecord
                 value                    # Bit-string notation
               end
             else
-              value
+              value.to_s
             end
           end
 
@@ -34,16 +36,15 @@ module ActiveRecord
             end
 
             def binary?
-              /\A[01]*\Z/ === value
+              /\A[01]*\Z/.match?(value)
             end
 
             def hex?
-              /\A[0-9A-F]*\Z/i === value
+              /\A[0-9A-F]*\Z/i.match?(value)
             end
 
-            protected
-
-            attr_reader :value
+            private
+              attr_reader :value
           end
         end
       end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit_varying.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit_varying.rb
index 4c21097d48..dc7079dda2 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit_varying.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/bit_varying.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/bytea.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/bytea.rb
index 8f9d6e7f9b..a3c60ecef6 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/bytea.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/bytea.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -6,7 +8,7 @@ module ActiveRecord
           def deserialize(value)
             return if value.nil?
             return value.to_s if value.is_a?(Type::Binary::Data)
-            PGconn.unescape_bytea(super)
+            PG::Connection.unescape_bytea(super)
           end
         end
       end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/cidr.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/cidr.rb
index eeccb09bdf..66e99d9404 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/cidr.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/cidr.rb
@@ -1,3 +1,7 @@
+# frozen_string_literal: true
+
+require "ipaddr"
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/date.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/date.rb
new file mode 100644
index 0000000000..24a1daa95a
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/date.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module PostgreSQL
+      module OID # :nodoc:
+        class Date < Type::Date # :nodoc:
+          def cast_value(value)
+            case value
+            when "infinity" then ::Float::INFINITY
+            when "-infinity" then -::Float::INFINITY
+            when / BC$/
+              astronomical_year = format("%04d", -value[/^\d+/].to_i + 1)
+              super(value.sub(/ BC$/, "").sub(/^\d+/, astronomical_year))
+            else
+              super
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/date_time.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/date_time.rb
index 2c04c46131..cd667422f5 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/date_time.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/date_time.rb
@@ -1,21 +1,19 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
         class DateTime < Type::DateTime # :nodoc:
           def cast_value(value)
-            if value.is_a?(::String)
-              case value
-              when 'infinity' then ::Float::INFINITY
-              when '-infinity' then -::Float::INFINITY
-              when / BC$/
-                astronomical_year = format("%04d", -value[/^\d+/].to_i + 1)
-                super(value.sub(/ BC$/, "").sub(/^\d+/, astronomical_year))
-              else
-                super
-              end
+            case value
+            when "infinity" then ::Float::INFINITY
+            when "-infinity" then -::Float::INFINITY
+            when / BC$/
+              astronomical_year = format("%04d", -value[/^\d+/].to_i + 1)
+              super(value.sub(/ BC$/, "").sub(/^\d+/, astronomical_year))
             else
-              value
+              super
             end
           end
         end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/decimal.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/decimal.rb
index 43d22c8daf..e7d33855c4 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/decimal.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/decimal.rb
@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
         class Decimal < Type::Decimal # :nodoc:
           def infinity(options = {})
-            BigDecimal.new("Infinity") * (options[:negative] ? -1 : 1)
+            BigDecimal("Infinity") * (options[:negative] ? -1 : 1)
           end
         end
       end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/enum.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/enum.rb
index 91d339f32c..f70f09ad95 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/enum.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/enum.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -9,9 +11,9 @@ module ActiveRecord
 
           private
 
-          def cast_value(value)
-            value.to_s
-          end
+            def cast_value(value)
+              value.to_s
+            end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb
index 9270fc9f21..aabe83b85d 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -12,8 +14,8 @@ module ActiveRecord
           def deserialize(value)
             if value.is_a?(::String)
               ::Hash[value.scan(HstorePair).map { |k, v|
-                v = v.upcase == 'NULL' ? nil : v.gsub(/\A"(.*)"\Z/m,'\1').gsub(/\\(.)/, '\1')
-                k = k.gsub(/\A"(.*)"\Z/m,'\1').gsub(/\\(.)/, '\1')
+                v = v.upcase == "NULL" ? nil : v.gsub(/\A"(.*)"\Z/m, '\1').gsub(/\\(.)/, '\1')
+                k = k.gsub(/\A"(.*)"\Z/m, '\1').gsub(/\\(.)/, '\1')
                 [k, v]
               }]
             else
@@ -23,7 +25,9 @@ module ActiveRecord
 
           def serialize(value)
             if value.is_a?(::Hash)
-              value.map { |k, v| "#{escape_hstore(k)}=>#{escape_hstore(v)}" }.join(', ')
+              value.map { |k, v| "#{escape_hstore(k)}=>#{escape_hstore(v)}" }.join(", ")
+            elsif value.respond_to?(:to_unsafe_h)
+              serialize(value.to_unsafe_h)
             else
               value
             end
@@ -33,25 +37,33 @@ module ActiveRecord
             ActiveRecord::Store::StringKeyedHashAccessor
           end
 
+          # Will compare the Hash equivalents of +raw_old_value+ and +new_value+.
+          # By comparing hashes, this avoids an edge case where the order of
+          # the keys change between the two hashes, and they would not be marked
+          # as equal.
+          def changed_in_place?(raw_old_value, new_value)
+            deserialize(raw_old_value) != new_value
+          end
+
           private
 
-          HstorePair = begin
-            quoted_string = /"[^"\\]*(?:\\.[^"\\]*)*"/
-            unquoted_string = /(?:\\.|[^\s,])[^\s=,\\]*(?:\\.[^\s=,\\]*|=[^,>])*/
-            /(#{quoted_string}|#{unquoted_string})\s*=>\s*(#{quoted_string}|#{unquoted_string})/
-          end
+            HstorePair = begin
+              quoted_string = /"[^"\\]*(?:\\.[^"\\]*)*"/
+              unquoted_string = /(?:\\.|[^\s,])[^\s=,\\]*(?:\\.[^\s=,\\]*|=[^,>])*/
+              /(#{quoted_string}|#{unquoted_string})\s*=>\s*(#{quoted_string}|#{unquoted_string})/
+            end
 
-          def escape_hstore(value)
-            if value.nil?
-              'NULL'
-            else
-              if value == ""
-                '""'
+            def escape_hstore(value)
+              if value.nil?
+                "NULL"
               else
-                '"%s"' % value.to_s.gsub(/(["\\])/, '\\\\\1')
+                if value == ""
+                  '""'
+                else
+                  '"%s"' % value.to_s.gsub(/(["\\])/, '\\\\\1')
+                end
               end
             end
-          end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/inet.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/inet.rb
index 96486fa65b..55be71fd26 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/inet.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/inet.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
deleted file mode 100644
index 8e1256baad..0000000000
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
+++ /dev/null
@@ -1,35 +0,0 @@
-module ActiveRecord
-  module ConnectionAdapters
-    module PostgreSQL
-      module OID # :nodoc:
-        class Json < Type::Value # :nodoc:
-          include Type::Helpers::Mutable
-
-          def type
-            :json
-          end
-
-          def deserialize(value)
-            if value.is_a?(::String)
-              ::ActiveSupport::JSON.decode(value) rescue nil
-            else
-              value
-            end
-          end
-
-          def serialize(value)
-            if value.is_a?(::Array) || value.is_a?(::Hash)
-              ::ActiveSupport::JSON.encode(value)
-            else
-              value
-            end
-          end
-
-          def accessor
-            ActiveRecord::Store::StringKeyedHashAccessor
-          end
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb
index 87391b5dc7..e0216f1089 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb
@@ -1,21 +1,13 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
-        class Jsonb < Json # :nodoc:
+        class Jsonb < Type::Json # :nodoc:
           def type
             :jsonb
           end
-
-          def changed_in_place?(raw_old_value, new_value)
-            # Postgres does not preserve insignificant whitespaces when
-            # round-tripping jsonb columns. This causes some false positives for
-            # the comparison here. Therefore, we need to parse and re-dump the
-            # raw value here to ensure the insignificant whitespaces are
-            # consistent with our encoder's output.
-            raw_old_value = serialize(deserialize(raw_old_value))
-            super(raw_old_value, new_value)
-          end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/rails_5_1_point.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/legacy_point.rb
index 7427a25ad5..7b057a8452 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/rails_5_1_point.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/legacy_point.rb
@@ -1,10 +1,10 @@
-module ActiveRecord
-  Point = Struct.new(:x, :y)
+# frozen_string_literal: true
 
+module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
-        class Rails51Point < Type::Value # :nodoc:
+        class LegacyPoint < Type::Value # :nodoc:
           include Type::Helpers::Mutable
 
           def type
@@ -14,21 +14,20 @@ module ActiveRecord
           def cast(value)
             case value
             when ::String
-              if value[0] == '(' && value[-1] == ')'
+              if value[0] == "(" && value[-1] == ")"
                 value = value[1...-1]
               end
-              x, y = value.split(",")
-              build_point(x, y)
+              cast(value.split(","))
             when ::Array
-              build_point(*value)
+              value.map { |v| Float(v) }
             else
               value
             end
           end
 
           def serialize(value)
-            if value.is_a?(ActiveRecord::Point)
-              "(#{number_for_point(value.x)},#{number_for_point(value.y)})"
+            if value.is_a?(::Array)
+              "(#{number_for_point(value[0])},#{number_for_point(value[1])})"
             else
               super
             end
@@ -36,13 +35,9 @@ module ActiveRecord
 
           private
 
-          def number_for_point(number)
-            number.to_s.gsub(/\.0$/, '')
-          end
-
-          def build_point(x, y)
-            ActiveRecord::Point.new(Float(x), Float(y))
-          end
+            def number_for_point(number)
+              number.to_s.gsub(/\.0$/, "")
+            end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb
index 2163674019..6434377b57 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb
@@ -1,10 +1,10 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
         class Money < Type::Decimal # :nodoc:
-          class_attribute :precision
-
           def type
             :money
           end
@@ -24,12 +24,12 @@ module ActiveRecord
             #  (3) -$2.55
             #  (4) ($2.55)
 
-            value.sub!(/^\((.+)\)$/, '-\1') # (4)
+            value = value.sub(/^\((.+)\)$/, '-\1') # (4)
             case value
             when /^-?\D+[\d,]+\.\d{2}$/  # (1)
-              value.gsub!(/[^-\d.]/, '')
+              value.gsub!(/[^-\d.]/, "")
             when /^-?\D+[\d.]+,\d{2}$/  # (2)
-              value.gsub!(/[^-\d,]/, '').sub!(/,/, '.')
+              value.gsub!(/[^-\d,]/, "").sub!(/,/, ".")
             end
 
             super(value)
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/oid.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/oid.rb
new file mode 100644
index 0000000000..d8c044320d
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/oid.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module PostgreSQL
+      module OID # :nodoc:
+        class Oid < Type::Integer # :nodoc:
+          def type
+            :oid
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/point.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/point.rb
index bf565bcf47..02a9c506f6 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/point.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/point.rb
@@ -1,4 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
+  Point = Struct.new(:x, :y)
+
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
@@ -12,20 +16,34 @@ module ActiveRecord
           def cast(value)
             case value
             when ::String
-              if value[0] == '(' && value[-1] == ')'
+              return if value.blank?
+
+              if value[0] == "(" && value[-1] == ")"
                 value = value[1...-1]
               end
-              cast(value.split(','))
+              x, y = value.split(",")
+              build_point(x, y)
             when ::Array
-              value.map { |v| Float(v) }
+              build_point(*value)
             else
               value
             end
           end
 
           def serialize(value)
-            if value.is_a?(::Array)
-              "(#{number_for_point(value[0])},#{number_for_point(value[1])})"
+            case value
+            when ActiveRecord::Point
+              "(#{number_for_point(value.x)},#{number_for_point(value.y)})"
+            when ::Array
+              serialize(build_point(*value))
+            else
+              super
+            end
+          end
+
+          def type_cast_for_schema(value)
+            if ActiveRecord::Point === value
+              [value.x, value.y]
             else
               super
             end
@@ -33,9 +51,13 @@ module ActiveRecord
 
           private
 
-          def number_for_point(number)
-            number.to_s.gsub(/\.0$/, '')
-          end
+            def number_for_point(number)
+              number.to_s.gsub(/\.0$/, "")
+            end
+
+            def build_point(x, y)
+              ActiveRecord::Point.new(Float(x), Float(y))
+            end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb
index fc201f8fb9..d85f9ab3ef 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb
@@ -1,4 +1,4 @@
-require 'active_support/core_ext/string/filters'
+# frozen_string_literal: true
 
 module ActiveRecord
   module ConnectionAdapters
@@ -6,6 +6,7 @@ module ActiveRecord
       module OID # :nodoc:
         class Range < Type::Value # :nodoc:
           attr_reader :subtype, :type
+          delegate :user_input_in_time_zone, to: :subtype
 
           def initialize(subtype, type = :range)
             @subtype = subtype
@@ -13,12 +14,12 @@ module ActiveRecord
           end
 
           def type_cast_for_schema(value)
-            value.inspect.gsub('Infinity', '::Float::INFINITY')
+            value.inspect.gsub("Infinity", "::Float::INFINITY")
           end
 
           def cast_value(value)
-            return if value == 'empty'
-            return value if value.is_a?(::Range)
+            return if value == "empty"
+            return value unless value.is_a?(::String)
 
             extracted = extract_bounds(value)
             from = type_cast_single extracted[:from]
@@ -34,7 +35,7 @@ module ActiveRecord
             if value.is_a?(::Range)
               from = type_cast_single_for_database(value.begin)
               to = type_cast_single_for_database(value.end)
-              "[#{from},#{to}#{value.exclude_end? ? ')' : ']'}"
+              ::Range.new(from, to, value.exclude_end?)
             else
               super
             end
@@ -46,39 +47,49 @@ module ActiveRecord
               other.type == type
           end
 
-          private
-
-          def type_cast_single(value)
-            infinity?(value) ? value : @subtype.deserialize(value)
+          def map(value) # :nodoc:
+            new_begin = yield(value.begin)
+            new_end = yield(value.end)
+            ::Range.new(new_begin, new_end, value.exclude_end?)
           end
 
-          def type_cast_single_for_database(value)
-            infinity?(value) ? '' : @subtype.serialize(value)
+          def force_equality?(value)
+            value.is_a?(::Range)
           end
 
-          def extract_bounds(value)
-            from, to = value[1..-2].split(',')
-            {
-              from:          (value[1] == ',' || from == '-infinity') ? infinity(negative: true) : from,
-              to:            (value[-2] == ',' || to == 'infinity') ? infinity : to,
-              exclude_start: (value[0] == '('),
-              exclude_end:   (value[-1] == ')')
-            }
-          end
+          private
 
-          def infinity(negative: false)
-            if subtype.respond_to?(:infinity)
-              subtype.infinity(negative: negative)
-            elsif negative
-              -::Float::INFINITY
-            else
-              ::Float::INFINITY
+            def type_cast_single(value)
+              infinity?(value) ? value : @subtype.deserialize(value)
             end
-          end
 
-          def infinity?(value)
-            value.respond_to?(:infinite?) && value.infinite?
-          end
+            def type_cast_single_for_database(value)
+              infinity?(value) ? value : @subtype.serialize(value)
+            end
+
+            def extract_bounds(value)
+              from, to = value[1..-2].split(",")
+              {
+                from:          (value[1] == "," || from == "-infinity") ? infinity(negative: true) : from,
+                to:            (value[-2] == "," || to == "infinity") ? infinity : to,
+                exclude_start: (value[0] == "("),
+                exclude_end:   (value[-1] == ")")
+              }
+            end
+
+            def infinity(negative: false)
+              if subtype.respond_to?(:infinity)
+                subtype.infinity(negative: negative)
+              elsif negative
+                -::Float::INFINITY
+              else
+                ::Float::INFINITY
+              end
+            end
+
+            def infinity?(value)
+              value.respond_to?(:infinite?) && value.infinite?
+            end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/specialized_string.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/specialized_string.rb
index 2d2fede4e8..4ad1344f05 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/specialized_string.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/specialized_string.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -5,8 +7,9 @@ module ActiveRecord
         class SpecializedString < Type::String # :nodoc:
           attr_reader :type
 
-          def initialize(type)
+          def initialize(type, **options)
             @type = type
+            super(options)
           end
         end
       end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/type_map_initializer.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/type_map_initializer.rb
index 191c828e60..83c21ba6ea 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/type_map_initializer.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/type_map_initializer.rb
@@ -1,3 +1,7 @@
+# frozen_string_literal: true
+
+require "active_support/core_ext/array/extract"
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -13,13 +17,13 @@ module ActiveRecord
           end
 
           def run(records)
-            nodes = records.reject { |row| @store.key? row['oid'].to_i }
-            mapped, nodes = nodes.partition { |row| @store.key? row['typname'] }
-            ranges, nodes = nodes.partition { |row| row['typtype'] == 'r'.freeze }
-            enums, nodes = nodes.partition { |row| row['typtype'] == 'e'.freeze }
-            domains, nodes = nodes.partition { |row| row['typtype'] == 'd'.freeze }
-            arrays, nodes = nodes.partition { |row| row['typinput'] == 'array_in'.freeze }
-            composites, nodes = nodes.partition { |row| row['typelem'].to_i != 0 }
+            nodes = records.reject { |row| @store.key? row["oid"].to_i }
+            mapped = nodes.extract! { |row| @store.key? row["typname"] }
+            ranges = nodes.extract! { |row| row["typtype"] == "r" }
+            enums = nodes.extract! { |row| row["typtype"] == "e" }
+            domains = nodes.extract! { |row| row["typtype"] == "d" }
+            arrays = nodes.extract! { |row| row["typinput"] == "array_in" }
+            composites = nodes.extract! { |row| row["typelem"].to_i != 0 }
 
             mapped.each     { |row| register_mapped_type(row)    }
             enums.each      { |row| register_enum_type(row)      }
@@ -29,79 +33,79 @@ module ActiveRecord
             composites.each { |row| register_composite_type(row) }
           end
 
-          def query_conditions_for_initial_load(type_map)
-            known_type_names = type_map.keys.map { |n| "'#{n}'" }
+          def query_conditions_for_initial_load
+            known_type_names = @store.keys.map { |n| "'#{n}'" }
             known_type_types = %w('r' 'e' 'd')
             <<-SQL % [known_type_names.join(", "), known_type_types.join(", ")]
               WHERE
                 t.typname IN (%s)
                 OR t.typtype IN (%s)
-                OR t.typinput::varchar = 'array_in'
+                OR t.typinput = 'array_in(cstring,oid,integer)'::regprocedure
                 OR t.typelem != 0
             SQL
           end
 
           private
-          def register_mapped_type(row)
-            alias_type row['oid'], row['typname']
-          end
+            def register_mapped_type(row)
+              alias_type row["oid"], row["typname"]
+            end
 
-          def register_enum_type(row)
-            register row['oid'], OID::Enum.new
-          end
+            def register_enum_type(row)
+              register row["oid"], OID::Enum.new
+            end
 
-          def register_array_type(row)
-            register_with_subtype(row['oid'], row['typelem'].to_i) do |subtype|
-              OID::Array.new(subtype, row['typdelim'])
+            def register_array_type(row)
+              register_with_subtype(row["oid"], row["typelem"].to_i) do |subtype|
+                OID::Array.new(subtype, row["typdelim"])
+              end
             end
-          end
 
-          def register_range_type(row)
-            register_with_subtype(row['oid'], row['rngsubtype'].to_i) do |subtype|
-              OID::Range.new(subtype, row['typname'].to_sym)
+            def register_range_type(row)
+              register_with_subtype(row["oid"], row["rngsubtype"].to_i) do |subtype|
+                OID::Range.new(subtype, row["typname"].to_sym)
+              end
             end
-          end
 
-          def register_domain_type(row)
-            if base_type = @store.lookup(row["typbasetype"].to_i)
-              register row['oid'], base_type
-            else
-              warn "unknown base type (OID: #{row["typbasetype"]}) for domain #{row["typname"]}."
+            def register_domain_type(row)
+              if base_type = @store.lookup(row["typbasetype"].to_i)
+                register row["oid"], base_type
+              else
+                warn "unknown base type (OID: #{row["typbasetype"]}) for domain #{row["typname"]}."
+              end
             end
-          end
 
-          def register_composite_type(row)
-            if subtype = @store.lookup(row['typelem'].to_i)
-              register row['oid'], OID::Vector.new(row['typdelim'], subtype)
+            def register_composite_type(row)
+              if subtype = @store.lookup(row["typelem"].to_i)
+                register row["oid"], OID::Vector.new(row["typdelim"], subtype)
+              end
             end
-          end
 
-          def register(oid, oid_type = nil, &block)
-            oid = assert_valid_registration(oid, oid_type || block)
-            if block_given?
-              @store.register_type(oid, &block)
-            else
-              @store.register_type(oid, oid_type)
+            def register(oid, oid_type = nil, &block)
+              oid = assert_valid_registration(oid, oid_type || block)
+              if block_given?
+                @store.register_type(oid, &block)
+              else
+                @store.register_type(oid, oid_type)
+              end
             end
-          end
 
-          def alias_type(oid, target)
-            oid = assert_valid_registration(oid, target)
-            @store.alias_type(oid, target)
-          end
+            def alias_type(oid, target)
+              oid = assert_valid_registration(oid, target)
+              @store.alias_type(oid, target)
+            end
 
-          def register_with_subtype(oid, target_oid)
-            if @store.key?(target_oid)
-              register(oid) do |_, *args|
-                yield @store.lookup(target_oid, *args)
+            def register_with_subtype(oid, target_oid)
+              if @store.key?(target_oid)
+                register(oid) do |_, *args|
+                  yield @store.lookup(target_oid, *args)
+                end
               end
             end
-          end
 
-          def assert_valid_registration(oid, oid_type)
-            raise ArgumentError, "can't register nil type for OID #{oid}" if oid_type.nil?
-            oid.to_i
-          end
+            def assert_valid_registration(oid, oid_type)
+              raise ArgumentError, "can't register nil type for OID #{oid}" if oid_type.nil?
+              oid.to_i
+            end
         end
       end
     end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb
index 5e839228e9..bc9b8dbfcf 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb
@@ -1,9 +1,11 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module OID # :nodoc:
         class Uuid < Type::Value # :nodoc:
-          ACCEPTABLE_UUID = %r{\A\{?([a-fA-F0-9]{4}-?){8}\}?\z}x
+          ACCEPTABLE_UUID = %r{\A(\{)?([a-fA-F0-9]{4}-?){8}(?(1)\}|)\z}
 
           alias_method :serialize, :deserialize
 
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/vector.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/vector.rb
index b26e876b54..88ef626a16 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/vector.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/vector.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/oid/xml.rb b/activerecord/lib/active_record/connection_adapters/postgresql/oid/xml.rb
index d40d837cee..042f32fdc3 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/xml.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/xml.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
index f175730551..0895d06356 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -27,8 +29,13 @@ module ActiveRecord
         # - schema_name."table.name"
         # - "schema.name".table_name
         # - "schema.name"."table.name"
-        def quote_table_name(name)
-          Utils.extract_schema_qualified_name(name.to_s).quoted
+        def quote_table_name(name) # :nodoc:
+          @quoted_table_names[name] ||= Utils.extract_schema_qualified_name(name.to_s).quoted.freeze
+        end
+
+        # Quotes schema names for use in SQL queries.
+        def quote_schema_name(name)
+          PG::Connection.quote_ident(name)
         end
 
         def quote_table_name_for_assignment(table, attr)
@@ -36,8 +43,8 @@ module ActiveRecord
         end
 
         # Quotes column names for use in SQL queries.
-        def quote_column_name(name) #:nodoc:
-          PGconn.quote_ident(name.to_s)
+        def quote_column_name(name) # :nodoc:
+          @quoted_column_names[name] ||= PG::Connection.quote_ident(super).freeze
         end
 
         # Quote date/time values for use in SQL input.
@@ -50,10 +57,15 @@ module ActiveRecord
           end
         end
 
-        # Does not quote function default values for UUID columns
-        def quote_default_expression(value, column) #:nodoc:
-          if column.type == :uuid && value =~ /\(\)/
-            value
+        def quoted_binary(value) # :nodoc:
+          "'#{escape_bytea(value.to_s)}'"
+        end
+
+        def quote_default_expression(value, column) # :nodoc:
+          if value.is_a?(Proc)
+            value.call
+          elsif column.type == :uuid && value.is_a?(String) && /\(\)/.match?(value)
+            value # Does not quote function default values for UUID columns
           elsif column.respond_to?(:array?)
             value = type_cast_from_column(column, value)
             quote(value)
@@ -67,43 +79,89 @@ module ActiveRecord
         end
 
         private
+          def lookup_cast_type(sql_type)
+            super(query_value("SELECT #{quote(sql_type)}::regtype::oid", "SCHEMA").to_i)
+          end
 
-        def _quote(value)
-          case value
-          when Type::Binary::Data
-            "'#{escape_bytea(value.to_s)}'"
-          when OID::Xml::Data
-            "xml '#{quote_string(value.to_s)}'"
-          when OID::Bit::Data
-            if value.binary?
-              "B'#{value}'"
-            elsif value.hex?
-              "X'#{value}'"
+          def _quote(value)
+            case value
+            when OID::Xml::Data
+              "xml '#{quote_string(value.to_s)}'"
+            when OID::Bit::Data
+              if value.binary?
+                "B'#{value}'"
+              elsif value.hex?
+                "X'#{value}'"
+              end
+            when Numeric
+              if value.finite?
+                super
+              else
+                "'#{value}'"
+              end
+            when OID::Array::Data
+              _quote(encode_array(value))
+            when Range
+              _quote(encode_range(value))
+            else
+              super
             end
-          when Float
-            if value.infinite? || value.nan?
-              "'#{value}'"
+          end
+
+          def _type_cast(value)
+            case value
+            when Type::Binary::Data
+              # Return a bind param hash with format as binary.
+              # See https://deveiate.org/code/pg/PG/Connection.html#method-i-exec_prepared-doc
+              # for more information
+              { value: value.to_s, format: 1 }
+            when OID::Xml::Data, OID::Bit::Data
+              value.to_s
+            when OID::Array::Data
+              encode_array(value)
+            when Range
+              encode_range(value)
             else
               super
             end
-          else
-            super
           end
-        end
 
-        def _type_cast(value)
-          case value
-          when Type::Binary::Data
-            # Return a bind param hash with format as binary.
-            # See http://deveiate.org/code/pg/PGconn.html#method-i-exec_prepared-doc
-            # for more information
-            { value: value.to_s, format: 1 }
-          when OID::Xml::Data, OID::Bit::Data
-            value.to_s
-          else
-            super
+          def encode_array(array_data)
+            encoder = array_data.encoder
+            values = type_cast_array(array_data.values)
+
+            result = encoder.encode(values)
+            if encoding = determine_encoding_of_strings_in_array(values)
+              result.force_encoding(encoding)
+            end
+            result
+          end
+
+          def encode_range(range)
+            "[#{type_cast_range_value(range.first)},#{type_cast_range_value(range.last)}#{range.exclude_end? ? ')' : ']'}"
+          end
+
+          def determine_encoding_of_strings_in_array(value)
+            case value
+            when ::Array then determine_encoding_of_strings_in_array(value.first)
+            when ::String then value.encoding
+            end
+          end
+
+          def type_cast_array(values)
+            case values
+            when ::Array then values.map { |item| type_cast_array(item) }
+            else _type_cast(values)
+            end
+          end
+
+          def type_cast_range_value(value)
+            infinity?(value) ? "" : type_cast(value)
+          end
+
+          def infinity?(value)
+            value.respond_to?(:infinite?) && value.infinite?
           end
-        end
       end
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/referential_integrity.rb b/activerecord/lib/active_record/connection_adapters/postgresql/referential_integrity.rb
index 44a7338bf5..8df91c988b 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/referential_integrity.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/referential_integrity.rb
@@ -1,27 +1,24 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
       module ReferentialIntegrity # :nodoc:
-        def supports_disable_referential_integrity? # :nodoc:
-          true
-        end
-
         def disable_referential_integrity # :nodoc:
-          if supports_disable_referential_integrity?
-            original_exception = nil
+          original_exception = nil
 
-            begin
-              transaction(requires_new: true) do
-                execute(tables.collect { |name| "ALTER TABLE #{quote_table_name(name)} DISABLE TRIGGER ALL" }.join(";"))
-              end
-            rescue ActiveRecord::ActiveRecordError => e
-              original_exception = e
+          begin
+            transaction(requires_new: true) do
+              execute(tables.collect { |name| "ALTER TABLE #{quote_table_name(name)} DISABLE TRIGGER ALL" }.join(";"))
             end
+          rescue ActiveRecord::ActiveRecordError => e
+            original_exception = e
+          end
 
-            begin
-              yield
-            rescue ActiveRecord::InvalidForeignKey => e
-              warn <<-WARNING
+          begin
+            yield
+          rescue ActiveRecord::InvalidForeignKey => e
+            warn <<-WARNING
 WARNING: Rails was not able to disable referential integrity.
 
 This is most likely caused due to missing permissions.
@@ -30,17 +27,14 @@ Rails needs superuser privileges to disable referential integrity.
     cause: #{original_exception.try(:message)}
 
               WARNING
-              raise e
-            end
+            raise e
+          end
 
-            begin
-              transaction(requires_new: true) do
-                execute(tables.collect { |name| "ALTER TABLE #{quote_table_name(name)} ENABLE TRIGGER ALL" }.join(";"))
-              end
-            rescue ActiveRecord::ActiveRecordError
+          begin
+            transaction(requires_new: true) do
+              execute(tables.collect { |name| "ALTER TABLE #{quote_table_name(name)} ENABLE TRIGGER ALL" }.join(";"))
             end
-          else
-            yield
+          rescue ActiveRecord::ActiveRecordError
           end
         end
       end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_creation.rb
new file mode 100644
index 0000000000..ceb8b40bd9
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_creation.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module PostgreSQL
+      class SchemaCreation < AbstractAdapter::SchemaCreation # :nodoc:
+        private
+          def visit_AlterTable(o)
+            super << o.constraint_validations.map { |fk| visit_ValidateConstraint fk }.join(" ")
+          end
+
+          def visit_AddForeignKey(o)
+            super.dup.tap { |sql| sql << " NOT VALID" unless o.validate? }
+          end
+
+          def visit_ValidateConstraint(name)
+            "VALIDATE CONSTRAINT #{quote_column_name(name)}"
+          end
+
+          def add_column_options!(sql, options)
+            if options[:collation]
+              sql << " COLLATE \"#{options[:collation]}\""
+            end
+            super
+          end
+
+          # Returns any SQL string to go between CREATE and TABLE. May be nil.
+          def table_modifier_in_create(o)
+            # A table cannot be both TEMPORARY and UNLOGGED, since all TEMPORARY
+            # tables are already UNLOGGED.
+            if o.temporary
+              " TEMPORARY"
+            elsif o.unlogged
+              " UNLOGGED"
+            end
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
index 022dbdfa27..dc4a0bb26e 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -11,11 +13,22 @@ module ActiveRecord
         #     t.timestamps
         #   end
         #
-        # By default, this will use the +uuid_generate_v4()+ function from the
-        # +uuid-ossp+ extension, which MUST be enabled on your database. To enable
-        # the +uuid-ossp+ extension, you can use the +enable_extension+ method in your
-        # migrations. To use a UUID primary key without +uuid-ossp+ enabled, you can
-        # set the +:default+ option to +nil+:
+        # By default, this will use the <tt>gen_random_uuid()</tt> function from the
+        # +pgcrypto+ extension. As that extension is only available in
+        # PostgreSQL 9.4+, for earlier versions an explicit default can be set
+        # to use <tt>uuid_generate_v4()</tt> from the +uuid-ossp+ extension instead:
+        #
+        #   create_table :stuffs, id: false do |t|
+        #     t.primary_key :id, :uuid, default: "uuid_generate_v4()"
+        #     t.uuid :foo_id
+        #     t.timestamps
+        #   end
+        #
+        # To enable the appropriate extension, which is a requirement, use
+        # the +enable_extension+ method in your migrations.
+        #
+        # To use a UUID primary key without any of the extensions, set the
+        # +:default+ option to +nil+:
         #
         #   create_table :stuffs, id: false do |t|
         #     t.primary_key :id, :uuid, default: nil
@@ -23,15 +36,18 @@ module ActiveRecord
         #     t.timestamps
         #   end
         #
-        # You may also pass a different UUID generation function from +uuid-ossp+
-        # or another library.
+        # You may also pass a custom stored procedure that returns a UUID or use a
+        # different UUID generation function from another library.
         #
         # Note that setting the UUID primary key default value to +nil+ will
         # require you to assure that you always provide a UUID value before saving
         # a record (as primary keys cannot be +nil+). This might be done via the
         # +SecureRandom.uuid+ method and a +before_save+ callback, for instance.
         def primary_key(name, type = :primary_key, **options)
-          options[:default] = options.fetch(:default, 'uuid_generate_v4()') if type == :uuid
+          if type == :uuid
+            options[:default] = options.fetch(:default, "gen_random_uuid()")
+          end
+
           super
         end
 
@@ -67,6 +83,10 @@ module ActiveRecord
           args.each { |name| column(name, :inet, options) }
         end
 
+        def interval(*args, **options)
+          args.each { |name| column(name, :interval, options) }
+        end
+
         def int4range(*args, **options)
           args.each { |name| column(name, :int4range, options) }
         end
@@ -75,10 +95,6 @@ module ActiveRecord
           args.each { |name| column(name, :int8range, options) }
         end
 
-        def json(*args, **options)
-          args.each { |name| column(name, :json, options) }
-        end
-
         def jsonb(*args, **options)
           args.each { |name| column(name, :jsonb, options) }
         end
@@ -99,10 +115,38 @@ module ActiveRecord
           args.each { |name| column(name, :numrange, options) }
         end
 
+        def oid(*args, **options)
+          args.each { |name| column(name, :oid, options) }
+        end
+
         def point(*args, **options)
           args.each { |name| column(name, :point, options) }
         end
 
+        def line(*args, **options)
+          args.each { |name| column(name, :line, options) }
+        end
+
+        def lseg(*args, **options)
+          args.each { |name| column(name, :lseg, options) }
+        end
+
+        def box(*args, **options)
+          args.each { |name| column(name, :box, options) }
+        end
+
+        def path(*args, **options)
+          args.each { |name| column(name, :path, options) }
+        end
+
+        def polygon(*args, **options)
+          args.each { |name| column(name, :polygon, options) }
+        end
+
+        def circle(*args, **options)
+          args.each { |name| column(name, :circle, options) }
+        end
+
         def serial(*args, **options)
           args.each { |name| column(name, :serial, options) }
         end
@@ -128,29 +172,42 @@ module ActiveRecord
         end
       end
 
-      class ColumnDefinition < ActiveRecord::ConnectionAdapters::ColumnDefinition
-        attr_accessor :array
-      end
-
       class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
         include ColumnMethods
 
-        def new_column_definition(name, type, options) # :nodoc:
-          column = super
-          column.array = options[:array]
-          column
+        attr_reader :unlogged
+
+        def initialize(*)
+          super
+          @unlogged = ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables
         end
 
         private
-
-          def create_column_definition(name, type)
-            PostgreSQL::ColumnDefinition.new name, type
+          def integer_like_primary_key_type(type, options)
+            if type == :bigint || options[:limit] == 8
+              :bigserial
+            else
+              :serial
+            end
           end
       end
 
       class Table < ActiveRecord::ConnectionAdapters::Table
         include ColumnMethods
       end
+
+      class AlterTable < ActiveRecord::ConnectionAdapters::AlterTable
+        attr_reader :constraint_validations
+
+        def initialize(td)
+          super
+          @constraint_validations = []
+        end
+
+        def validate_constraint(name)
+          @constraint_validations << name
+        end
+      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb
new file mode 100644
index 0000000000..84643d20da
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module PostgreSQL
+      class SchemaDumper < ConnectionAdapters::SchemaDumper # :nodoc:
+        private
+
+          def extensions(stream)
+            extensions = @connection.extensions
+            if extensions.any?
+              stream.puts "  # These are extensions that must be enabled in order to support this database"
+              extensions.sort.each do |extension|
+                stream.puts "  enable_extension #{extension.inspect}"
+              end
+              stream.puts
+            end
+          end
+
+          def prepare_column_options(column)
+            spec = super
+            spec[:array] = "true" if column.array?
+            spec
+          end
+
+          def default_primary_key?(column)
+            schema_type(column) == :bigserial
+          end
+
+          def explicit_primary_key_default?(column)
+            column.type == :uuid || (column.type == :integer && !column.serial?)
+          end
+
+          def schema_type(column)
+            return super unless column.serial?
+
+            if column.bigint?
+              :bigserial
+            else
+              :serial
+            end
+          end
+
+          def schema_expression(column)
+            super unless column.serial?
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index d114cad16b..fae3ddbad4 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -1,22 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
-      class SchemaCreation < AbstractAdapter::SchemaCreation
-        private
-
-        def visit_ColumnDefinition(o)
-          o.sql_type = type_to_sql(o.type, o.limit, o.precision, o.scale, o.array)
-          super
-        end
-
-        def add_column_options!(sql, options)
-          if options[:collation]
-            sql << " COLLATE \"#{options[:collation]}\""
-          end
-          super
-        end
-      end
-
       module SchemaStatements
         # Drops the database specified on the +name+ attribute
         # and creates it again using the provided +options+.
@@ -34,26 +20,26 @@ module ActiveRecord
         #   create_database config[:database], config
         #   create_database 'foo_development', encoding: 'unicode'
         def create_database(name, options = {})
-          options = { encoding: 'utf8' }.merge!(options.symbolize_keys)
+          options = { encoding: "utf8" }.merge!(options.symbolize_keys)
 
           option_string = options.inject("") do |memo, (key, value)|
             memo += case key
-            when :owner
-              " OWNER = \"#{value}\""
-            when :template
-              " TEMPLATE = \"#{value}\""
-            when :encoding
-              " ENCODING = '#{value}'"
-            when :collation
-              " LC_COLLATE = '#{value}'"
-            when :ctype
-              " LC_CTYPE = '#{value}'"
-            when :tablespace
-              " TABLESPACE = \"#{value}\""
-            when :connection_limit
-              " CONNECTION LIMIT = #{value}"
-            else
-              ""
+                    when :owner
+                      " OWNER = \"#{value}\""
+                    when :template
+                      " TEMPLATE = \"#{value}\""
+                    when :encoding
+                      " ENCODING = '#{value}'"
+                    when :collation
+                      " LC_COLLATE = '#{value}'"
+                    when :ctype
+                      " LC_CTYPE = '#{value}'"
+                    when :tablespace
+                      " TABLESPACE = \"#{value}\""
+                    when :connection_limit
+                      " CONNECTION LIMIT = #{value}"
+                    else
+                      ""
             end
           end
 
@@ -68,62 +54,48 @@ module ActiveRecord
           execute "DROP DATABASE IF EXISTS #{quote_table_name(name)}"
         end
 
-        # Returns the list of all tables in the schema search path or a specified schema.
-        def tables(name = nil)
-          select_values("SELECT tablename FROM pg_tables WHERE schemaname = ANY(current_schemas(false))", 'SCHEMA')
-        end
-
-        # Returns true if table exists.
-        # If the schema is not specified as part of +name+ then it will only find tables within
-        # the current schema search path (regardless of permissions to access tables in other schemas)
-        def table_exists?(name)
-          name = Utils.extract_schema_qualified_name(name.to_s)
-          return false unless name.identifier
-
-          select_value(<<-SQL, 'SCHEMA').to_i > 0
-              SELECT COUNT(*)
-              FROM pg_class c
-              LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
-              WHERE c.relkind IN ('r','v','m') -- (r)elation/table, (v)iew, (m)aterialized view
-              AND c.relname = '#{name.identifier}'
-              AND n.nspname = #{name.schema ? "'#{name.schema}'" : 'ANY (current_schemas(false))'}
-          SQL
-        end
-
         def drop_table(table_name, options = {}) # :nodoc:
           execute "DROP TABLE#{' IF EXISTS' if options[:if_exists]} #{quote_table_name(table_name)}#{' CASCADE' if options[:force] == :cascade}"
         end
 
         # Returns true if schema exists.
         def schema_exists?(name)
-          select_value("SELECT COUNT(*) FROM pg_namespace WHERE nspname = '#{name}'", 'SCHEMA').to_i > 0
+          query_value("SELECT COUNT(*) FROM pg_namespace WHERE nspname = #{quote(name)}", "SCHEMA").to_i > 0
         end
 
         # Verifies existence of an index with a given name.
-        def index_name_exists?(table_name, index_name, default)
-          select_value(<<-SQL, 'SCHEMA').to_i > 0
+        def index_name_exists?(table_name, index_name)
+          table = quoted_scope(table_name)
+          index = quoted_scope(index_name)
+
+          query_value(<<-SQL, "SCHEMA").to_i > 0
             SELECT COUNT(*)
             FROM pg_class t
             INNER JOIN pg_index d ON t.oid = d.indrelid
             INNER JOIN pg_class i ON d.indexrelid = i.oid
+            LEFT JOIN pg_namespace n ON n.oid = i.relnamespace
             WHERE i.relkind = 'i'
-              AND i.relname = '#{index_name}'
-              AND t.relname = '#{table_name}'
-              AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname = ANY (current_schemas(false)) )
+              AND i.relname = #{index[:name]}
+              AND t.relname = #{table[:name]}
+              AND n.nspname = #{index[:schema]}
           SQL
         end
 
         # Returns an array of indexes for the given table.
-        def indexes(table_name, name = nil)
-           result = query(<<-SQL, 'SCHEMA')
-             SELECT distinct i.relname, d.indisunique, d.indkey, pg_get_indexdef(d.indexrelid), t.oid
-             FROM pg_class t
-             INNER JOIN pg_index d ON t.oid = d.indrelid
-             INNER JOIN pg_class i ON d.indexrelid = i.oid
-             WHERE i.relkind = 'i'
-               AND d.indisprimary = 'f'
-               AND t.relname = '#{table_name}'
-               AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname = ANY (current_schemas(false)) )
+        def indexes(table_name) # :nodoc:
+          scope = quoted_scope(table_name)
+
+          result = query(<<-SQL, "SCHEMA")
+            SELECT distinct i.relname, d.indisunique, d.indkey, pg_get_indexdef(d.indexrelid), t.oid,
+                            pg_catalog.obj_description(i.oid, 'pg_class') AS comment
+            FROM pg_class t
+            INNER JOIN pg_index d ON t.oid = d.indrelid
+            INNER JOIN pg_class i ON d.indexrelid = i.oid
+            LEFT JOIN pg_namespace n ON n.oid = i.relnamespace
+            WHERE i.relkind = 'i'
+              AND d.indisprimary = 'f'
+              AND t.relname = #{scope[:name]}
+              AND n.nspname = #{scope[:schema]}
             ORDER BY i.relname
           SQL
 
@@ -133,73 +105,98 @@ module ActiveRecord
             indkey = row[2].split(" ").map(&:to_i)
             inddef = row[3]
             oid = row[4]
+            comment = row[5]
 
-            columns = Hash[query(<<-SQL, "SCHEMA")]
-            SELECT a.attnum, a.attname
-            FROM pg_attribute a
-            WHERE a.attrelid = #{oid}
-            AND a.attnum IN (#{indkey.join(",")})
-            SQL
-
-            column_names = columns.values_at(*indkey).compact
+            using, expressions, where = inddef.scan(/ USING (\w+?) \((.+?)\)(?: WHERE (.+))?\z/m).flatten
 
-            unless column_names.empty?
-              # add info on sort order for columns (only desc order is explicitly specified, asc is the default)
-              desc_order_columns = inddef.scan(/(\w+) DESC/).flatten
-              orders = desc_order_columns.any? ? Hash[desc_order_columns.map {|order_column| [order_column, :desc]}] : {}
-              where = inddef.scan(/WHERE (.+)$/).flatten[0]
-              using = inddef.scan(/USING (.+?) /).flatten[0].to_sym
+            orders = {}
+            opclasses = {}
 
-              IndexDefinition.new(table_name, index_name, unique, column_names, [], orders, where, nil, using)
+            if indkey.include?(0)
+              columns = expressions
+            else
+              columns = Hash[query(<<~SQL, "SCHEMA")].values_at(*indkey).compact
+                SELECT a.attnum, a.attname
+                FROM pg_attribute a
+                WHERE a.attrelid = #{oid}
+                AND a.attnum IN (#{indkey.join(",")})
+              SQL
+
+              # add info on sort order (only desc order is explicitly specified, asc is the default)
+              # and non-default opclasses
+              expressions.scan(/(?<column>\w+)\s?(?<opclass>\w+_ops)?\s?(?<desc>DESC)?\s?(?<nulls>NULLS (?:FIRST|LAST))?/).each do |column, opclass, desc, nulls|
+                opclasses[column] = opclass.to_sym if opclass
+                if nulls
+                  orders[column] = [desc, nulls].compact.join(" ")
+                else
+                  orders[column] = :desc if desc
+                end
+              end
             end
-          end.compact
+
+            IndexDefinition.new(
+              table_name,
+              index_name,
+              unique,
+              columns,
+              orders: orders,
+              opclasses: opclasses,
+              where: where,
+              using: using.to_sym,
+              comment: comment.presence
+            )
+          end
         end
 
-        # Returns the list of all column definitions for a table.
-        def columns(table_name)
-          # Limit, precision, and scale are all handled by the superclass.
-          column_definitions(table_name).map do |column_name, type, default, notnull, oid, fmod, collation|
-            oid = oid.to_i
-            fmod = fmod.to_i
-            type_metadata = fetch_type_metadata(column_name, type, oid, fmod)
-            default_value = extract_value_from_default(default)
-            default_function = extract_default_function(default_value, default)
-            new_column(column_name, default_value, type_metadata, !notnull, default_function, collation)
+        def table_options(table_name) # :nodoc:
+          if comment = table_comment(table_name)
+            { comment: comment }
           end
         end
 
-        def new_column(name, default, sql_type_metadata = nil, null = true, default_function = nil, collation = nil) # :nodoc:
-          PostgreSQLColumn.new(name, default, sql_type_metadata, null, default_function, collation)
+        # Returns a comment stored in database for given table
+        def table_comment(table_name) # :nodoc:
+          scope = quoted_scope(table_name, type: "BASE TABLE")
+          if scope[:name]
+            query_value(<<~SQL, "SCHEMA")
+              SELECT pg_catalog.obj_description(c.oid, 'pg_class')
+              FROM pg_catalog.pg_class c
+                LEFT JOIN pg_namespace n ON n.oid = c.relnamespace
+              WHERE c.relname = #{scope[:name]}
+                AND c.relkind IN (#{scope[:type]})
+                AND n.nspname = #{scope[:schema]}
+            SQL
+          end
         end
 
         # Returns the current database name.
         def current_database
-          select_value('select current_database()', 'SCHEMA')
+          query_value("SELECT current_database()", "SCHEMA")
         end
 
         # Returns the current schema name.
         def current_schema
-          select_value('SELECT current_schema', 'SCHEMA')
+          query_value("SELECT current_schema", "SCHEMA")
         end
 
         # Returns the current database encoding format.
         def encoding
-          select_value("SELECT pg_encoding_to_char(encoding) FROM pg_database WHERE datname LIKE '#{current_database}'", 'SCHEMA')
+          query_value("SELECT pg_encoding_to_char(encoding) FROM pg_database WHERE datname = current_database()", "SCHEMA")
         end
 
         # Returns the current database collation.
         def collation
-          select_value("SELECT datcollate FROM pg_database WHERE datname LIKE '#{current_database}'", 'SCHEMA')
+          query_value("SELECT datcollate FROM pg_database WHERE datname = current_database()", "SCHEMA")
         end
 
         # Returns the current database ctype.
         def ctype
-          select_value("SELECT datctype FROM pg_database WHERE datname LIKE '#{current_database}'", 'SCHEMA')
+          query_value("SELECT datctype FROM pg_database WHERE datname = current_database()", "SCHEMA")
         end
 
         # Returns an array of schema names.
         def schema_names
-          select_values(<<-SQL, 'SCHEMA')
+          query_values(<<-SQL, "SCHEMA")
             SELECT nspname
               FROM pg_namespace
              WHERE nspname !~ '^pg_.*'
@@ -209,53 +206,53 @@ module ActiveRecord
         end
 
         # Creates a schema for the given schema name.
-        def create_schema schema_name
-          execute "CREATE SCHEMA #{schema_name}"
+        def create_schema(schema_name)
+          execute "CREATE SCHEMA #{quote_schema_name(schema_name)}"
         end
 
         # Drops the schema for the given schema name.
-        def drop_schema schema_name
-          execute "DROP SCHEMA #{schema_name} CASCADE"
+        def drop_schema(schema_name, options = {})
+          execute "DROP SCHEMA#{' IF EXISTS' if options[:if_exists]} #{quote_schema_name(schema_name)} CASCADE"
         end
 
         # Sets the schema search path to a string of comma-separated schema names.
         # Names beginning with $ have to be quoted (e.g. $user => '$user').
-        # See: http://www.postgresql.org/docs/current/static/ddl-schemas.html
+        # See: https://www.postgresql.org/docs/current/static/ddl-schemas.html
         #
         # This should be not be called manually but set in database.yml.
         def schema_search_path=(schema_csv)
           if schema_csv
-            execute("SET search_path TO #{schema_csv}", 'SCHEMA')
+            execute("SET search_path TO #{schema_csv}", "SCHEMA")
             @schema_search_path = schema_csv
           end
         end
 
         # Returns the active schema search path.
         def schema_search_path
-          @schema_search_path ||= select_value('SHOW search_path', 'SCHEMA')
+          @schema_search_path ||= query_value("SHOW search_path", "SCHEMA")
         end
 
         # Returns the current client message level.
         def client_min_messages
-          select_value('SHOW client_min_messages', 'SCHEMA')
+          query_value("SHOW client_min_messages", "SCHEMA")
         end
 
         # Set the client message level.
         def client_min_messages=(level)
-          execute("SET client_min_messages TO '#{level}'", 'SCHEMA')
+          execute("SET client_min_messages TO '#{level}'", "SCHEMA")
         end
 
         # Returns the sequence name for a table's primary key or some other specified key.
-        def default_sequence_name(table_name, pk = nil) #:nodoc:
-          result = serial_sequence(table_name, pk || 'id')
+        def default_sequence_name(table_name, pk = "id") #:nodoc:
+          result = serial_sequence(table_name, pk)
           return nil unless result
           Utils.extract_schema_qualified_name(result).to_s
         rescue ActiveRecord::StatementInvalid
-          PostgreSQL::Name.new(nil, "#{table_name}_#{pk || 'id'}_seq").to_s
+          PostgreSQL::Name.new(nil, "#{table_name}_#{pk}_seq").to_s
         end
 
         def serial_sequence(table, column)
-          select_value("SELECT pg_get_serial_sequence('#{table}', '#{column}')", 'SCHEMA')
+          query_value("SELECT pg_get_serial_sequence(#{quote(table)}, #{quote(column)})", "SCHEMA")
         end
 
         # Sets the sequence of a table's primary key to the specified value.
@@ -266,16 +263,16 @@ module ActiveRecord
             if sequence
               quoted_sequence = quote_table_name(sequence)
 
-              select_value("SELECT setval('#{quoted_sequence}', #{value})", 'SCHEMA')
+              query_value("SELECT setval(#{quote(quoted_sequence)}, #{value})", "SCHEMA")
             else
-              @logger.warn "#{table} has primary key #{pk} with no default sequence" if @logger
+              @logger.warn "#{table} has primary key #{pk} with no default sequence." if @logger
             end
           end
         end
 
         # Resets the sequence of a table's primary key to the maximum value.
         def reset_pk_sequence!(table, pk = nil, sequence = nil) #:nodoc:
-          unless pk and sequence
+          unless pk && sequence
             default_pk, default_sequence = pk_and_sequence_for(table)
 
             pk ||= default_pk
@@ -283,15 +280,21 @@ module ActiveRecord
           end
 
           if @logger && pk && !sequence
-            @logger.warn "#{table} has primary key #{pk} with no default sequence"
+            @logger.warn "#{table} has primary key #{pk} with no default sequence."
           end
 
           if pk && sequence
             quoted_sequence = quote_table_name(sequence)
+            max_pk = query_value("SELECT MAX(#{quote_column_name pk}) FROM #{quote_table_name(table)}", "SCHEMA")
+            if max_pk.nil?
+              if postgresql_version >= 100000
+                minvalue = query_value("SELECT seqmin FROM pg_sequence WHERE seqrelid = #{quote(quoted_sequence)}::regclass", "SCHEMA")
+              else
+                minvalue = query_value("SELECT min_value FROM #{quoted_sequence}", "SCHEMA")
+              end
+            end
 
-            select_value(<<-end_sql, 'SCHEMA')
-              SELECT setval('#{quoted_sequence}', (SELECT COALESCE(MAX(#{quote_column_name pk})+(SELECT increment_by FROM #{quoted_sequence}), (SELECT min_value FROM #{quoted_sequence})) FROM #{quote_table_name(table)}), false)
-            end_sql
+            query_value("SELECT setval(#{quote(quoted_sequence)}, #{max_pk ? max_pk : minvalue}, #{max_pk ? true : false})", "SCHEMA")
           end
         end
 
@@ -299,7 +302,7 @@ module ActiveRecord
         def pk_and_sequence_for(table) #:nodoc:
           # First try looking for a sequence with a dependency on the
           # given table's primary key.
-          result = query(<<-end_sql, 'SCHEMA')[0]
+          result = query(<<-end_sql, "SCHEMA")[0]
             SELECT attr.attname, nsp.nspname, seq.relname
             FROM pg_class      seq,
                  pg_attribute  attr,
@@ -315,11 +318,11 @@ module ActiveRecord
               AND seq.relnamespace  = nsp.oid
               AND cons.contype      = 'p'
               AND dep.classid       = 'pg_class'::regclass
-              AND dep.refobjid      = '#{quote_table_name(table)}'::regclass
+              AND dep.refobjid      = #{quote(quote_table_name(table))}::regclass
           end_sql
 
-          if result.nil? or result.empty?
-            result = query(<<-end_sql, 'SCHEMA')[0]
+          if result.nil? || result.empty?
+            result = query(<<-end_sql, "SCHEMA")[0]
               SELECT attr.attname, nsp.nspname,
                 CASE
                   WHEN pg_get_expr(def.adbin, def.adrelid) !~* 'nextval' THEN NULL
@@ -333,7 +336,7 @@ module ActiveRecord
               JOIN pg_attrdef     def  ON (adrelid = attrelid AND adnum = attnum)
               JOIN pg_constraint  cons ON (conrelid = adrelid AND adnum = conkey[1])
               JOIN pg_namespace   nsp  ON (t.relnamespace = nsp.oid)
-              WHERE t.oid = '#{quote_table_name(table)}'::regclass
+              WHERE t.oid = #{quote(quote_table_name(table))}::regclass
                 AND cons.contype = 'p'
                 AND pg_get_expr(def.adbin, def.adrelid) ~* 'nextval|uuid_generate'
             end_sql
@@ -349,17 +352,45 @@ module ActiveRecord
           nil
         end
 
-        # Returns just a table's primary key
-        def primary_key(table)
-          pks = query(<<-end_sql, 'SCHEMA')
-            SELECT attr.attname
-            FROM pg_attribute attr
-            INNER JOIN pg_constraint cons ON attr.attrelid = cons.conrelid AND attr.attnum = any(cons.conkey)
-            WHERE cons.contype = 'p'
-              AND cons.conrelid = '#{quote_table_name(table)}'::regclass
-          end_sql
-          return nil unless pks.count == 1
-          pks[0][0]
+        def primary_keys(table_name) # :nodoc:
+          query_values(<<~SQL, "SCHEMA")
+            SELECT a.attname
+              FROM (
+                     SELECT indrelid, indkey, generate_subscripts(indkey, 1) idx
+                       FROM pg_index
+                      WHERE indrelid = #{quote(quote_table_name(table_name))}::regclass
+                        AND indisprimary
+                   ) i
+              JOIN pg_attribute a
+                ON a.attrelid = i.indrelid
+               AND a.attnum = i.indkey[i.idx]
+             ORDER BY i.idx
+          SQL
+        end
+
+        def bulk_change_table(table_name, operations)
+          sql_fragments = []
+          non_combinable_operations = []
+
+          operations.each do |command, args|
+            table, arguments = args.shift, args
+            method = :"#{command}_for_alter"
+
+            if respond_to?(method, true)
+              sqls, procs = Array(send(method, table, *arguments)).partition { |v| v.is_a?(String) }
+              sql_fragments << sqls
+              non_combinable_operations.concat(procs)
+            else
+              execute "ALTER TABLE #{quote_table_name(table_name)} #{sql_fragments.join(", ")}" unless sql_fragments.empty?
+              non_combinable_operations.each(&:call)
+              sql_fragments = []
+              non_combinable_operations = []
+              send(command, table, *arguments)
+            end
+          end
+
+          execute "ALTER TABLE #{quote_table_name(table_name)} #{sql_fragments.join(", ")}" unless sql_fragments.empty?
+          non_combinable_operations.each(&:call)
         end
 
         # Renames a table.
@@ -372,67 +403,55 @@ module ActiveRecord
           clear_cache!
           execute "ALTER TABLE #{quote_table_name(table_name)} RENAME TO #{quote_table_name(new_name)}"
           pk, seq = pk_and_sequence_for(new_name)
-          if seq && seq.identifier == "#{table_name}_#{pk}_seq"
-            new_seq = "#{new_name}_#{pk}_seq"
+          if pk
             idx = "#{table_name}_pkey"
             new_idx = "#{new_name}_pkey"
-            execute "ALTER TABLE #{quote_table_name(seq)} RENAME TO #{quote_table_name(new_seq)}"
             execute "ALTER INDEX #{quote_table_name(idx)} RENAME TO #{quote_table_name(new_idx)}"
+            if seq && seq.identifier == "#{table_name}_#{pk}_seq"
+              new_seq = "#{new_name}_#{pk}_seq"
+              execute "ALTER TABLE #{seq.quoted} RENAME TO #{quote_table_name(new_seq)}"
+            end
           end
-
           rename_table_indexes(table_name, new_name)
         end
 
         def add_column(table_name, column_name, type, options = {}) #:nodoc:
           clear_cache!
           super
+          change_column_comment(table_name, column_name, options[:comment]) if options.key?(:comment)
         end
 
         def change_column(table_name, column_name, type, options = {}) #:nodoc:
           clear_cache!
-          quoted_table_name = quote_table_name(table_name)
-          quoted_column_name = quote_column_name(column_name)
-          sql_type = type_to_sql(type, options[:limit], options[:precision], options[:scale], options[:array])
-          sql = "ALTER TABLE #{quoted_table_name} ALTER COLUMN #{quoted_column_name} TYPE #{sql_type}"
-          if options[:collation]
-            sql << " COLLATE \"#{options[:collation]}\""
-          end
-          if options[:using]
-            sql << " USING #{options[:using]}"
-          elsif options[:cast_as]
-            cast_as_type = type_to_sql(options[:cast_as], options[:limit], options[:precision], options[:scale], options[:array])
-            sql << " USING CAST(#{quoted_column_name} AS #{cast_as_type})"
-          end
-          execute sql
-
-          change_column_default(table_name, column_name, options[:default]) if options_include_default?(options)
-          change_column_null(table_name, column_name, options[:null], options[:default]) if options.key?(:null)
+          sqls, procs = Array(change_column_for_alter(table_name, column_name, type, options)).partition { |v| v.is_a?(String) }
+          execute "ALTER TABLE #{quote_table_name(table_name)} #{sqls.join(", ")}"
+          procs.each(&:call)
         end
 
         # Changes the default value of a table column.
         def change_column_default(table_name, column_name, default_or_changes) # :nodoc:
-          clear_cache!
-          column = column_for(table_name, column_name)
-          return unless column
-
-          default = extract_new_default_value(default_or_changes)
-          alter_column_query = "ALTER TABLE #{quote_table_name(table_name)} ALTER COLUMN #{quote_column_name(column_name)} %s"
-          if default.nil?
-            # <tt>DEFAULT NULL</tt> results in the same behavior as <tt>DROP DEFAULT</tt>. However, PostgreSQL will
-            # cast the default to the columns type, which leaves us with a default like "default NULL::character varying".
-            execute alter_column_query % "DROP DEFAULT"
-          else
-            execute alter_column_query % "SET DEFAULT #{quote_default_expression(default, column)}"
-          end
+          execute "ALTER TABLE #{quote_table_name(table_name)} #{change_column_default_for_alter(table_name, column_name, default_or_changes)}"
         end
 
         def change_column_null(table_name, column_name, null, default = nil) #:nodoc:
           clear_cache!
           unless null || default.nil?
             column = column_for(table_name, column_name)
-            execute("UPDATE #{quote_table_name(table_name)} SET #{quote_column_name(column_name)}=#{quote_default_expression(default, column)} WHERE #{quote_column_name(column_name)} IS NULL") if column
+            execute "UPDATE #{quote_table_name(table_name)} SET #{quote_column_name(column_name)}=#{quote_default_expression(default, column)} WHERE #{quote_column_name(column_name)} IS NULL" if column
           end
-          execute("ALTER TABLE #{quote_table_name(table_name)} ALTER #{quote_column_name(column_name)} #{null ? 'DROP' : 'SET'} NOT NULL")
+          execute "ALTER TABLE #{quote_table_name(table_name)} #{change_column_null_for_alter(table_name, column_name, null, default)}"
+        end
+
+        # Adds comment for given table column or drops it if +comment+ is a +nil+
+        def change_column_comment(table_name, column_name, comment) # :nodoc:
+          clear_cache!
+          execute "COMMENT ON COLUMN #{quote_table_name(table_name)}.#{quote_column_name(column_name)} IS #{quote(comment)}"
+        end
+
+        # Adds comment for given table or drops it if +comment+ is a +nil+
+        def change_table_comment(table_name, comment) # :nodoc:
+          clear_cache!
+          execute "COMMENT ON TABLE #{quote_table_name(table_name)} IS #{quote(comment)}"
         end
 
         # Renames a column in a table.
@@ -443,12 +462,34 @@ module ActiveRecord
         end
 
         def add_index(table_name, column_name, options = {}) #:nodoc:
-          index_name, index_type, index_columns, index_options, index_algorithm, index_using = add_index_options(table_name, column_name, options)
-          execute "CREATE #{index_type} INDEX #{index_algorithm} #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} #{index_using} (#{index_columns})#{index_options}"
+          index_name, index_type, index_columns_and_opclasses, index_options, index_algorithm, index_using, comment = add_index_options(table_name, column_name, options)
+          execute("CREATE #{index_type} INDEX #{index_algorithm} #{quote_column_name(index_name)} ON #{quote_table_name(table_name)} #{index_using} (#{index_columns_and_opclasses})#{index_options}").tap do
+            execute "COMMENT ON INDEX #{quote_column_name(index_name)} IS #{quote(comment)}" if comment
+          end
         end
 
-        def remove_index!(table_name, index_name) #:nodoc:
-          execute "DROP INDEX #{quote_table_name(index_name)}"
+        def remove_index(table_name, options = {}) #:nodoc:
+          table = Utils.extract_schema_qualified_name(table_name.to_s)
+
+          if options.is_a?(Hash) && options.key?(:name)
+            provided_index = Utils.extract_schema_qualified_name(options[:name].to_s)
+
+            options[:name] = provided_index.identifier
+            table = PostgreSQL::Name.new(provided_index.schema, table.identifier) unless table.schema.present?
+
+            if provided_index.schema.present? && table.schema != provided_index.schema
+              raise ArgumentError.new("Index schema '#{provided_index.schema}' does not match table schema '#{table.schema}'")
+            end
+          end
+
+          index_to_remove = PostgreSQL::Name.new(table.schema, index_name_for_remove(table.to_s, options))
+          algorithm =
+            if options.is_a?(Hash) && options.key?(:algorithm)
+              index_algorithms.fetch(options[:algorithm]) do
+                raise ArgumentError.new("Algorithm must be one of the following: #{index_algorithms.keys.map(&:inspect).join(', ')}")
+              end
+            end
+          execute "DROP INDEX #{algorithm} #{quote_table_name(index_to_remove)}"
         end
 
         # Renames an index of a table. Raises error if length of new
@@ -460,8 +501,9 @@ module ActiveRecord
         end
 
         def foreign_keys(table_name)
-          fk_info = select_all <<-SQL.strip_heredoc
-            SELECT t2.oid::regclass::text AS to_table, a1.attname AS column, a2.attname AS primary_key, c.conname AS name, c.confupdtype AS on_update, c.confdeltype AS on_delete
+          scope = quoted_scope(table_name)
+          fk_info = exec_query(<<~SQL, "SCHEMA")
+            SELECT t2.oid::regclass::text AS to_table, a1.attname AS column, a2.attname AS primary_key, c.conname AS name, c.confupdtype AS on_update, c.confdeltype AS on_delete, c.convalidated AS valid
             FROM pg_constraint c
             JOIN pg_class t1 ON c.conrelid = t1.oid
             JOIN pg_class t2 ON c.confrelid = t2.oid
@@ -469,94 +511,281 @@ module ActiveRecord
             JOIN pg_attribute a2 ON a2.attnum = c.confkey[1] AND a2.attrelid = t2.oid
             JOIN pg_namespace t3 ON c.connamespace = t3.oid
             WHERE c.contype = 'f'
-              AND t1.relname = #{quote(table_name)}
-              AND t3.nspname = ANY (current_schemas(false))
+              AND t1.relname = #{scope[:name]}
+              AND t3.nspname = #{scope[:schema]}
             ORDER BY c.conname
           SQL
 
           fk_info.map do |row|
             options = {
-              column: row['column'],
-              name: row['name'],
-              primary_key: row['primary_key']
+              column: row["column"],
+              name: row["name"],
+              primary_key: row["primary_key"]
             }
 
-            options[:on_delete] = extract_foreign_key_action(row['on_delete'])
-            options[:on_update] = extract_foreign_key_action(row['on_update'])
+            options[:on_delete] = extract_foreign_key_action(row["on_delete"])
+            options[:on_update] = extract_foreign_key_action(row["on_update"])
+            options[:validate] = row["valid"]
 
-            ForeignKeyDefinition.new(table_name, row['to_table'], options)
+            ForeignKeyDefinition.new(table_name, row["to_table"], options)
           end
         end
 
-        def extract_foreign_key_action(specifier) # :nodoc:
-          case specifier
-          when 'c'; :cascade
-          when 'n'; :nullify
-          when 'r'; :restrict
-          end
+        def foreign_tables
+          query_values(data_source_sql(type: "FOREIGN TABLE"), "SCHEMA")
         end
 
-        def index_name_length
-          63
+        def foreign_table_exists?(table_name)
+          query_values(data_source_sql(table_name, type: "FOREIGN TABLE"), "SCHEMA").any? if table_name.present?
         end
 
         # Maps logical Rails types to PostgreSQL-specific data types.
-        def type_to_sql(type, limit = nil, precision = nil, scale = nil, array = nil)
-          sql = case type.to_s
-          when 'binary'
-            # PostgreSQL doesn't support limits on binary (bytea) columns.
-            # The hard limit is 1GB, because of a 32-bit size field, and TOAST.
-            case limit
-            when nil, 0..0x3fffffff; super(type)
-            else raise(ActiveRecordError, "No binary type has byte size #{limit}.")
-            end
-          when 'text'
-            # PostgreSQL doesn't support limits on text columns.
-            # The hard limit is 1GB, according to section 8.3 in the manual.
-            case limit
-            when nil, 0..0x3fffffff; super(type)
-            else raise(ActiveRecordError, "The limit on text can be at most 1GB - 1byte.")
-            end
-          when 'integer'
-            case limit
-            when 1, 2; 'smallint'
-            when nil, 3, 4; 'integer'
-            when 5..8; 'bigint'
-            else raise(ActiveRecordError, "No integer type has byte size #{limit}. Use a numeric with precision 0 instead.")
+        def type_to_sql(type, limit: nil, precision: nil, scale: nil, array: nil, **) # :nodoc:
+          sql = \
+            case type.to_s
+            when "binary"
+              # PostgreSQL doesn't support limits on binary (bytea) columns.
+              # The hard limit is 1GB, because of a 32-bit size field, and TOAST.
+              case limit
+              when nil, 0..0x3fffffff; super(type)
+              else raise(ActiveRecordError, "No binary type has byte size #{limit}.")
+              end
+            when "text"
+              # PostgreSQL doesn't support limits on text columns.
+              # The hard limit is 1GB, according to section 8.3 in the manual.
+              case limit
+              when nil, 0..0x3fffffff; super(type)
+              else raise(ActiveRecordError, "The limit on text can be at most 1GB - 1byte.")
+              end
+            when "integer"
+              case limit
+              when 1, 2; "smallint"
+              when nil, 3, 4; "integer"
+              when 5..8; "bigint"
+              else raise(ActiveRecordError, "No integer type has byte size #{limit}. Use a numeric with scale 0 instead.")
+              end
+            else
+              super
             end
-          else
-            super(type, limit, precision, scale)
-          end
 
-          sql << '[]' if array && type != :primary_key
+          sql = "#{sql}[]" if array && type != :primary_key
           sql
         end
 
         # PostgreSQL requires the ORDER BY columns in the select list for distinct queries, and
         # requires that the ORDER BY include the distinct column.
         def columns_for_distinct(columns, orders) #:nodoc:
-          order_columns = orders.reject(&:blank?).map{ |s|
+          order_columns = orders.reject(&:blank?).map { |s|
               # Convert Arel node to string
               s = s.to_sql unless s.is_a?(String)
               # Remove any ASC/DESC modifiers
-              s.gsub(/\s+(?:ASC|DESC)\b/i, '')
-               .gsub(/\s+NULLS\s+(?:FIRST|LAST)\b/i, '')
+              s.gsub(/\s+(?:ASC|DESC)\b/i, "")
+               .gsub(/\s+NULLS\s+(?:FIRST|LAST)\b/i, "")
             }.reject(&:blank?).map.with_index { |column, i| "#{column} AS alias_#{i}" }
 
-          [super, *order_columns].join(', ')
+          (order_columns << super).join(", ")
+        end
+
+        def update_table_definition(table_name, base) # :nodoc:
+          PostgreSQL::Table.new(table_name, base)
+        end
+
+        def create_schema_dumper(options) # :nodoc:
+          PostgreSQL::SchemaDumper.create(self, options)
+        end
+
+        # Validates the given constraint.
+        #
+        # Validates the constraint named +constraint_name+ on +accounts+.
+        #
+        #   validate_constraint :accounts, :constraint_name
+        def validate_constraint(table_name, constraint_name)
+          return unless supports_validate_constraints?
+
+          at = create_alter_table table_name
+          at.validate_constraint constraint_name
+
+          execute schema_creation.accept(at)
         end
 
-        def fetch_type_metadata(column_name, sql_type, oid, fmod)
-          cast_type = get_oid_type(oid, fmod, column_name, sql_type)
-          simple_type = SqlTypeMetadata.new(
-            sql_type: sql_type,
-            type: cast_type.type,
-            limit: cast_type.limit,
-            precision: cast_type.precision,
-            scale: cast_type.scale,
-          )
-          PostgreSQLTypeMetadata.new(simple_type, oid: oid, fmod: fmod)
+        # Validates the given foreign key.
+        #
+        # Validates the foreign key on +accounts.branch_id+.
+        #
+        #   validate_foreign_key :accounts, :branches
+        #
+        # Validates the foreign key on +accounts.owner_id+.
+        #
+        #   validate_foreign_key :accounts, column: :owner_id
+        #
+        # Validates the foreign key named +special_fk_name+ on the +accounts+ table.
+        #
+        #   validate_foreign_key :accounts, name: :special_fk_name
+        #
+        # The +options+ hash accepts the same keys as SchemaStatements#add_foreign_key.
+        def validate_foreign_key(from_table, options_or_to_table = {})
+          return unless supports_validate_constraints?
+
+          fk_name_to_validate = foreign_key_for!(from_table, options_or_to_table).name
+
+          validate_constraint from_table, fk_name_to_validate
         end
+
+        private
+          def schema_creation
+            PostgreSQL::SchemaCreation.new(self)
+          end
+
+          def create_table_definition(*args)
+            PostgreSQL::TableDefinition.new(*args)
+          end
+
+          def create_alter_table(name)
+            PostgreSQL::AlterTable.new create_table_definition(name)
+          end
+
+          def new_column_from_field(table_name, field)
+            column_name, type, default, notnull, oid, fmod, collation, comment = field
+            type_metadata = fetch_type_metadata(column_name, type, oid.to_i, fmod.to_i)
+            default_value = extract_value_from_default(default)
+            default_function = extract_default_function(default_value, default)
+
+            PostgreSQLColumn.new(
+              column_name,
+              default_value,
+              type_metadata,
+              !notnull,
+              table_name,
+              default_function,
+              collation,
+              comment: comment.presence,
+              max_identifier_length: max_identifier_length
+            )
+          end
+
+          def fetch_type_metadata(column_name, sql_type, oid, fmod)
+            cast_type = get_oid_type(oid, fmod, column_name, sql_type)
+            simple_type = SqlTypeMetadata.new(
+              sql_type: sql_type,
+              type: cast_type.type,
+              limit: cast_type.limit,
+              precision: cast_type.precision,
+              scale: cast_type.scale,
+            )
+            PostgreSQLTypeMetadata.new(simple_type, oid: oid, fmod: fmod)
+          end
+
+          def extract_foreign_key_action(specifier)
+            case specifier
+            when "c"; :cascade
+            when "n"; :nullify
+            when "r"; :restrict
+            end
+          end
+
+          def change_column_sql(table_name, column_name, type, options = {})
+            quoted_column_name = quote_column_name(column_name)
+            sql_type = type_to_sql(type, options)
+            sql = +"ALTER COLUMN #{quoted_column_name} TYPE #{sql_type}"
+            if options[:collation]
+              sql << " COLLATE \"#{options[:collation]}\""
+            end
+            if options[:using]
+              sql << " USING #{options[:using]}"
+            elsif options[:cast_as]
+              cast_as_type = type_to_sql(options[:cast_as], options)
+              sql << " USING CAST(#{quoted_column_name} AS #{cast_as_type})"
+            end
+
+            sql
+          end
+
+          def add_column_for_alter(table_name, column_name, type, options = {})
+            return super unless options.key?(:comment)
+            [super, Proc.new { change_column_comment(table_name, column_name, options[:comment]) }]
+          end
+
+          def change_column_for_alter(table_name, column_name, type, options = {})
+            sqls = [change_column_sql(table_name, column_name, type, options)]
+            sqls << change_column_default_for_alter(table_name, column_name, options[:default]) if options.key?(:default)
+            sqls << change_column_null_for_alter(table_name, column_name, options[:null], options[:default]) if options.key?(:null)
+            sqls << Proc.new { change_column_comment(table_name, column_name, options[:comment]) } if options.key?(:comment)
+            sqls
+          end
+
+          # Changes the default value of a table column.
+          def change_column_default_for_alter(table_name, column_name, default_or_changes) # :nodoc:
+            column = column_for(table_name, column_name)
+            return unless column
+
+            default = extract_new_default_value(default_or_changes)
+            alter_column_query = "ALTER COLUMN #{quote_column_name(column_name)} %s"
+            if default.nil?
+              # <tt>DEFAULT NULL</tt> results in the same behavior as <tt>DROP DEFAULT</tt>. However, PostgreSQL will
+              # cast the default to the columns type, which leaves us with a default like "default NULL::character varying".
+              alter_column_query % "DROP DEFAULT"
+            else
+              alter_column_query % "SET DEFAULT #{quote_default_expression(default, column)}"
+            end
+          end
+
+          def change_column_null_for_alter(table_name, column_name, null, default = nil) #:nodoc:
+            "ALTER #{quote_column_name(column_name)} #{null ? 'DROP' : 'SET'} NOT NULL"
+          end
+
+          def add_timestamps_for_alter(table_name, options = {})
+            [add_column_for_alter(table_name, :created_at, :datetime, options), add_column_for_alter(table_name, :updated_at, :datetime, options)]
+          end
+
+          def remove_timestamps_for_alter(table_name, options = {})
+            [remove_column_for_alter(table_name, :updated_at), remove_column_for_alter(table_name, :created_at)]
+          end
+
+          def add_index_opclass(quoted_columns, **options)
+            opclasses = options_for_index_columns(options[:opclass])
+            quoted_columns.each do |name, column|
+              column << " #{opclasses[name]}" if opclasses[name].present?
+            end
+          end
+
+          def add_options_for_index_columns(quoted_columns, **options)
+            quoted_columns = add_index_opclass(quoted_columns, options)
+            super
+          end
+
+          def data_source_sql(name = nil, type: nil)
+            scope = quoted_scope(name, type: type)
+            scope[:type] ||= "'r','v','m','p','f'" # (r)elation/table, (v)iew, (m)aterialized view, (p)artitioned table, (f)oreign table
+
+            sql = +"SELECT c.relname FROM pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace"
+            sql << " WHERE n.nspname = #{scope[:schema]}"
+            sql << " AND c.relname = #{scope[:name]}" if scope[:name]
+            sql << " AND c.relkind IN (#{scope[:type]})"
+            sql
+          end
+
+          def quoted_scope(name = nil, type: nil)
+            schema, name = extract_schema_qualified_name(name)
+            type = \
+              case type
+              when "BASE TABLE"
+                "'r','p'"
+              when "VIEW"
+                "'v','m'"
+              when "FOREIGN TABLE"
+                "'f'"
+              end
+            scope = {}
+            scope[:schema] = schema ? quote(schema) : "ANY (current_schemas(false))"
+            scope[:name] = quote(name) if name
+            scope[:type] = type if type
+            scope
+          end
+
+          def extract_schema_qualified_name(string)
+            name = Utils.extract_schema_qualified_name(string.to_s)
+            [name.schema, name.identifier]
+          end
       end
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb b/activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb
index 58715978f7..cd69d28139 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb
@@ -1,6 +1,11 @@
+# frozen_string_literal: true
+
 module ActiveRecord
+  # :stopdoc:
   module ConnectionAdapters
     class PostgreSQLTypeMetadata < DelegateClass(SqlTypeMetadata)
+      undef to_yaml if method_defined?(:to_yaml)
+
       attr_reader :oid, :fmod, :array
 
       def initialize(type_metadata, oid: nil, fmod: nil)
@@ -8,7 +13,7 @@ module ActiveRecord
         @type_metadata = type_metadata
         @oid = oid
         @fmod = fmod
-        @array = /\[\]$/ === type_metadata.sql_type
+        @array = /\[\]$/.match?(type_metadata.sql_type)
       end
 
       def sql_type
@@ -27,9 +32,9 @@ module ActiveRecord
 
       protected
 
-      def attributes_for_hash
-        [self.class, @type_metadata, oid, fmod]
-      end
+        def attributes_for_hash
+          [self.class, @type_metadata, oid, fmod]
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/utils.rb b/activerecord/lib/active_record/connection_adapters/postgresql/utils.rb
index 9a0b80d7d3..bfd300723d 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/utils.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/utils.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -19,9 +21,9 @@ module ActiveRecord
 
         def quoted
           if schema
-            PGconn.quote_ident(schema) << SEPARATOR << PGconn.quote_ident(identifier)
+            PG::Connection.quote_ident(schema) << SEPARATOR << PG::Connection.quote_ident(identifier)
           else
-            PGconn.quote_ident(identifier)
+            PG::Connection.quote_ident(identifier)
           end
         end
 
@@ -35,6 +37,12 @@ module ActiveRecord
         end
 
         protected
+
+          def parts
+            @parts ||= [@schema, @identifier].compact
+          end
+
+        private
           def unquote(part)
             if part && part.start_with?('"')
               part[1..-2]
@@ -42,10 +50,6 @@ module ActiveRecord
               part
             end
           end
-
-          def parts
-            @parts ||= [@schema, @identifier].compact
-          end
       end
 
       module Utils # :nodoc:
@@ -53,7 +57,7 @@ module ActiveRecord
 
         # Returns an instance of <tt>ActiveRecord::ConnectionAdapters::PostgreSQL::Name</tt>
         # extracted from +string+.
-        # +schema+ is nil if not specified in +string+.
+        # +schema+ is +nil+ if not specified in +string+.
         # +schema+ and +identifier+ exclude surrounding quotes (regardless of whether provided in +string+)
         # +string+ supports the range of schema/table references understood by PostgreSQL, for example:
         #
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 2c43c46a3d..d2ed699ee2 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -1,29 +1,34 @@
+# frozen_string_literal: true
+
 # Make sure we're using pg high enough for type casts and Ruby 2.2+ compatibility
-gem 'pg', '~> 0.18'
-require 'pg'
+gem "pg", ">= 0.18", "< 2.0"
+require "pg"
+
+# Use async_exec instead of exec_params on pg versions before 1.1
+class ::PG::Connection # :nodoc:
+  unless self.public_method_defined?(:async_exec_params)
+    remove_method :exec_params
+    alias exec_params async_exec
+  end
+end
 
 require "active_record/connection_adapters/abstract_adapter"
+require "active_record/connection_adapters/statement_pool"
 require "active_record/connection_adapters/postgresql/column"
 require "active_record/connection_adapters/postgresql/database_statements"
+require "active_record/connection_adapters/postgresql/explain_pretty_printer"
 require "active_record/connection_adapters/postgresql/oid"
 require "active_record/connection_adapters/postgresql/quoting"
 require "active_record/connection_adapters/postgresql/referential_integrity"
+require "active_record/connection_adapters/postgresql/schema_creation"
 require "active_record/connection_adapters/postgresql/schema_definitions"
+require "active_record/connection_adapters/postgresql/schema_dumper"
 require "active_record/connection_adapters/postgresql/schema_statements"
 require "active_record/connection_adapters/postgresql/type_metadata"
 require "active_record/connection_adapters/postgresql/utils"
-require "active_record/connection_adapters/statement_pool"
-
-require 'ipaddr'
 
 module ActiveRecord
   module ConnectionHandling # :nodoc:
-    VALID_CONN_PARAMS = [:host, :hostaddr, :port, :dbname, :user, :password, :connect_timeout,
-                         :client_encoding, :options, :application_name, :fallback_application_name,
-                         :keepalives, :keepalives_idle, :keepalives_interval, :keepalives_count,
-                         :tty, :sslmode, :requiressl, :sslcompression, :sslcert, :sslkey,
-                         :sslrootcert, :sslcrl, :requirepeer, :krbsrvname, :gsslib, :service]
-
     # Establishes a connection to the database that's used by all Active Record objects
     def postgresql_connection(config)
       conn_params = config.symbolize_keys
@@ -34,12 +39,18 @@ module ActiveRecord
       conn_params[:user] = conn_params.delete(:username) if conn_params[:username]
       conn_params[:dbname] = conn_params.delete(:database) if conn_params[:database]
 
-      # Forward only valid config params to PGconn.connect.
-      conn_params.keep_if { |k, _| VALID_CONN_PARAMS.include?(k) }
+      # Forward only valid config params to PG::Connection.connect.
+      valid_conn_param_keys = PG::Connection.conndefaults_hash.keys + [:requiressl]
+      conn_params.slice!(*valid_conn_param_keys)
 
-      # The postgres drivers don't allow the creation of an unconnected PGconn object,
-      # so just pass a nil connection object for the time being.
-      ConnectionAdapters::PostgreSQLAdapter.new(nil, logger, conn_params, config)
+      conn = PG.connect(conn_params)
+      ConnectionAdapters::PostgreSQLAdapter.new(conn, logger, conn_params, config)
+    rescue ::PG::Error => error
+      if error.message.include?("does not exist")
+        raise ActiveRecord::NoDatabaseError
+      else
+        raise
+      end
     end
   end
 
@@ -66,20 +77,32 @@ module ActiveRecord
     #   defaults to true.
     #
     # Any further options are used as connection parameters to libpq. See
-    # http://www.postgresql.org/docs/current/static/libpq-connect.html for the
+    # https://www.postgresql.org/docs/current/static/libpq-connect.html for the
     # list of parameters.
     #
     # In addition, default connection parameters of libpq can be set per environment variables.
-    # See http://www.postgresql.org/docs/current/static/libpq-envars.html .
+    # See https://www.postgresql.org/docs/current/static/libpq-envars.html .
     class PostgreSQLAdapter < AbstractAdapter
-      ADAPTER_NAME = 'PostgreSQL'.freeze
+      ADAPTER_NAME = "PostgreSQL"
+
+      ##
+      # :singleton-method:
+      # PostgreSQL allows the creation of "unlogged" tables, which do not record
+      # data in the PostgreSQL Write-Ahead Log. This can make the tables faster,
+      # but significantly increases the risk of data loss if the database
+      # crashes. As a result, this should not be used in production
+      # environments. If you would like all created tables to be unlogged in
+      # the test environment you can add the following line to your test.rb
+      # file:
+      #
+      #   ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = true
+      class_attribute :create_unlogged_tables, default: false
 
       NATIVE_DATABASE_TYPES = {
-        primary_key: "serial primary key",
-        bigserial: "bigserial",
+        primary_key: "bigserial primary key",
         string:      { name: "character varying" },
         text:        { name: "text" },
-        integer:     { name: "integer" },
+        integer:     { name: "integer", limit: 4 },
         float:       { name: "float" },
         decimal:     { name: "decimal" },
         datetime:    { name: "timestamp" },
@@ -93,7 +116,6 @@ module ActiveRecord
         int8range:   { name: "int8range" },
         binary:      { name: "bytea" },
         boolean:     { name: "boolean" },
-        bigint:      { name: "bigint" },
         xml:         { name: "xml" },
         tsvector:    { name: "tsvector" },
         hstore:      { name: "hstore" },
@@ -106,9 +128,17 @@ module ActiveRecord
         ltree:       { name: "ltree" },
         citext:      { name: "citext" },
         point:       { name: "point" },
+        line:        { name: "line" },
+        lseg:        { name: "lseg" },
+        box:         { name: "box" },
+        path:        { name: "path" },
+        polygon:     { name: "polygon" },
+        circle:      { name: "circle" },
         bit:         { name: "bit" },
         bit_varying: { name: "bit varying" },
         money:       { name: "money" },
+        interval:    { name: "interval" },
+        oid:         { name: "oid" },
       }
 
       OID = PostgreSQL::OID #:nodoc:
@@ -117,97 +147,63 @@ module ActiveRecord
       include PostgreSQL::ReferentialIntegrity
       include PostgreSQL::SchemaStatements
       include PostgreSQL::DatabaseStatements
-      include Savepoints
-
-      def schema_creation # :nodoc:
-        PostgreSQL::SchemaCreation.new self
-      end
 
-      def column_spec_for_primary_key(column)
-        spec = {}
-        if column.serial?
-          return unless column.bigint?
-          spec[:id] = ':bigserial'
-        elsif column.type == :uuid
-          spec[:id] = ':uuid'
-          spec[:default] = column.default_function.inspect
-        else
-          spec[:id] = column.type.inspect
-          spec.merge!(prepare_column_options(column).delete_if { |key, _| [:name, :type, :null].include?(key) })
-        end
-        spec
+      def supports_bulk_alter?
+        true
       end
 
-      # Adds +:array+ option to the default set provided by the
-      # AbstractAdapter
-      def prepare_column_options(column) # :nodoc:
-        spec = super
-        spec[:array] = 'true' if column.array?
-        spec
+      def supports_index_sort_order?
+        true
       end
 
-      # Adds +:array+ as a valid migration key
-      def migration_keys
-        super + [:array]
+      def supports_partial_index?
+        true
       end
 
-      def schema_type(column)
-        return super unless column.serial?
-
-        if column.bigint?
-          'bigserial'
-        else
-          'serial'
-        end
+      def supports_expression_index?
+        true
       end
-      private :schema_type
 
-      def schema_default(column)
-        if column.default_function
-          column.default_function.inspect unless column.serial?
-        else
-          super
-        end
+      def supports_transaction_isolation?
+        true
       end
-      private :schema_default
 
-      # Returns +true+, since this connection adapter supports prepared statement
-      # caching.
-      def supports_statement_cache?
+      def supports_foreign_keys?
         true
       end
 
-      def supports_index_sort_order?
+      def supports_validate_constraints?
         true
       end
 
-      def supports_partial_index?
+      def supports_views?
         true
       end
 
-      def supports_transaction_isolation?
+      def supports_datetime_with_precision?
         true
       end
 
-      def supports_foreign_keys?
-        true
+      def supports_json?
+        postgresql_version >= 90200
       end
 
-      def supports_views?
+      def supports_comments?
         true
       end
 
-      def supports_datetime_with_precision?
+      def supports_savepoints?
         true
       end
 
       def index_algorithms
-        { concurrently: 'CONCURRENTLY' }
+        { concurrently: "CONCURRENTLY" }
       end
 
-      class StatementPool < ConnectionAdapters::StatementPool
+      class StatementPool < ConnectionAdapters::StatementPool # :nodoc:
         def initialize(connection, max)
-          super
+          super(max)
+          @connection = connection
           @counter = 0
         end
 
@@ -220,55 +216,46 @@ module ActiveRecord
         end
 
         private
-
           def dealloc(key)
             @connection.query "DEALLOCATE #{key}" if connection_active?
+          rescue PG::Error
           end
 
           def connection_active?
-            @connection.status == PGconn::CONNECTION_OK
-          rescue PGError
+            @connection.status == PG::CONNECTION_OK
+          rescue PG::Error
             false
           end
       end
 
       # Initializes and connects a PostgreSQL adapter.
       def initialize(connection, logger, connection_parameters, config)
-        super(connection, logger)
-
-        @visitor = Arel::Visitors::PostgreSQL.new self
-        if self.class.type_cast_config_to_boolean(config.fetch(:prepared_statements) { true })
-          @prepared_statements = true
-        else
-          @prepared_statements = false
-        end
+        super(connection, logger, config)
 
-        @connection_parameters, @config = connection_parameters, config
+        @connection_parameters = connection_parameters
 
         # @local_tz is initialized as nil to avoid warnings when connect tries to use it
         @local_tz = nil
-        @table_alias_length = nil
+        @max_identifier_length = nil
 
-        connect
+        configure_connection
         add_pg_encoders
         @statements = StatementPool.new @connection,
-                                        self.class.type_cast_config_to_integer(config.fetch(:statement_limit) { 1000 })
-
-        if postgresql_version < 80200
-          raise "Your version of PostgreSQL (#{postgresql_version}) is too old, please upgrade!"
-        end
+                                        self.class.type_cast_config_to_integer(config[:statement_limit])
 
         add_pg_decoders
 
         @type_map = Type::HashLookupTypeMap.new
-        initialize_type_map(type_map)
-        @local_tz = execute('SHOW TIME ZONE', 'SCHEMA').first["TimeZone"]
+        initialize_type_map
+        @local_tz = execute("SHOW TIME ZONE", "SCHEMA").first["TimeZone"]
         @use_insert_returning = @config.key?(:insert_returning) ? self.class.type_cast_config_to_boolean(@config[:insert_returning]) : true
       end
 
       # Clears the prepared statements cache.
       def clear_cache!
-        @statements.clear
+        @lock.synchronize do
+          @statements.clear
+        end
       end
 
       def truncate(table_name, name = nil)
@@ -277,59 +264,62 @@ module ActiveRecord
 
       # Is this connection alive and ready for queries?
       def active?
-        @connection.query 'SELECT 1'
+        @lock.synchronize do
+          @connection.query "SELECT 1"
+        end
         true
-      rescue PGError
+      rescue PG::Error
         false
       end
 
       # Close then reopen the connection.
       def reconnect!
-        super
-        @connection.reset
-        configure_connection
+        @lock.synchronize do
+          super
+          @connection.reset
+          configure_connection
+        end
       end
 
       def reset!
-        clear_cache!
-        reset_transaction
-        unless @connection.transaction_status == ::PG::PQTRANS_IDLE
-          @connection.query 'ROLLBACK'
+        @lock.synchronize do
+          clear_cache!
+          reset_transaction
+          unless @connection.transaction_status == ::PG::PQTRANS_IDLE
+            @connection.query "ROLLBACK"
+          end
+          @connection.query "DISCARD ALL"
+          configure_connection
         end
-        @connection.query 'DISCARD ALL'
-        configure_connection
       end
 
       # Disconnects from the database if already connected. Otherwise, this
       # method does nothing.
       def disconnect!
-        super
-        @connection.close rescue nil
+        @lock.synchronize do
+          super
+          @connection.close rescue nil
+        end
+      end
+
+      def discard! # :nodoc:
+        @connection.socket_io.reopen(IO::NULL) rescue nil
+        @connection = nil
       end
 
       def native_database_types #:nodoc:
         NATIVE_DATABASE_TYPES
       end
 
-      # Returns true, since this connection adapter supports migrations.
-      def supports_migrations?
-        true
+      def set_standard_conforming_strings
+        execute("SET standard_conforming_strings = on", "SCHEMA")
       end
 
-      # Does PostgreSQL support finding primary key on non-Active Record tables?
-      def supports_primary_key? #:nodoc:
+      def supports_ddl_transactions?
         true
       end
 
-      # Enable standard-conforming strings if available.
-      def set_standard_conforming_strings
-        old, self.client_min_messages = client_min_messages, 'panic'
-        execute('SET standard_conforming_strings = on', 'SCHEMA') rescue nil
-      ensure
-        self.client_min_messages = old
-      end
-
-      def supports_ddl_transactions?
+      def supports_advisory_locks?
         true
       end
 
@@ -337,13 +327,12 @@ module ActiveRecord
         true
       end
 
-      # Returns true if pg > 9.1
       def supports_extensions?
-        postgresql_version >= 90100
+        true
       end
 
-      # Range datatypes weren't introduced until PostgreSQL 9.2
       def supports_ranges?
+        # Range datatypes weren't introduced until PostgreSQL 9.2
         postgresql_version >= 90200
       end
 
@@ -351,6 +340,32 @@ module ActiveRecord
         postgresql_version >= 90300
       end
 
+      def supports_foreign_tables?
+        postgresql_version >= 90300
+      end
+
+      def supports_pgcrypto_uuid?
+        postgresql_version >= 90400
+      end
+
+      def supports_lazy_transactions?
+        true
+      end
+
+      def get_advisory_lock(lock_id) # :nodoc:
+        unless lock_id.is_a?(Integer) && lock_id.bit_length <= 63
+          raise(ArgumentError, "PostgreSQL requires advisory lock ids to be a signed 64 bit integer")
+        end
+        query_value("SELECT pg_try_advisory_lock(#{lock_id})")
+      end
+
+      def release_advisory_lock(lock_id) # :nodoc:
+        unless lock_id.is_a?(Integer) && lock_id.bit_length <= 63
+          raise(ArgumentError, "PostgreSQL requires advisory lock ids to be a signed 64 bit integer")
+        end
+        query_value("SELECT pg_advisory_unlock(#{lock_id})")
+      end
+
       def enable_extension(name)
         exec_query("CREATE EXTENSION IF NOT EXISTS \"#{name}\"").tap {
           reload_type_map
@@ -364,49 +379,31 @@ module ActiveRecord
       end
 
       def extension_enabled?(name)
-        if supports_extensions?
-          res = exec_query "SELECT EXISTS(SELECT * FROM pg_available_extensions WHERE name = '#{name}' AND installed_version IS NOT NULL) as enabled",
-            'SCHEMA'
-          res.cast_values.first
-        end
+        res = exec_query("SELECT EXISTS(SELECT * FROM pg_available_extensions WHERE name = '#{name}' AND installed_version IS NOT NULL) as enabled", "SCHEMA")
+        res.cast_values.first
       end
 
       def extensions
-        if supports_extensions?
-          exec_query("SELECT extname from pg_extension", "SCHEMA").cast_values
-        else
-          super
-        end
+        exec_query("SELECT extname FROM pg_extension", "SCHEMA").cast_values
       end
 
       # Returns the configured supported identifier length supported by PostgreSQL
-      def table_alias_length
-        @table_alias_length ||= query('SHOW max_identifier_length', 'SCHEMA')[0][0].to_i
+      def max_identifier_length
+        @max_identifier_length ||= query_value("SHOW max_identifier_length", "SCHEMA").to_i
       end
+      alias table_alias_length max_identifier_length
+      alias index_name_length max_identifier_length
 
       # Set the authorized user for this session
       def session_auth=(user)
         clear_cache!
-        exec_query "SET SESSION AUTHORIZATION #{user}"
+        execute("SET SESSION AUTHORIZATION #{user}")
       end
 
       def use_insert_returning?
         @use_insert_returning
       end
 
-      def valid_type?(type)
-        !native_database_types[type].nil?
-      end
-
-      def update_table_definition(table_name, base) #:nodoc:
-        PostgreSQL::Table.new(table_name, base)
-      end
-
-      def lookup_cast_type(sql_type) # :nodoc:
-        oid = execute("SELECT #{quote(sql_type)}::regtype::oid", "SCHEMA").first['oid'].to_i
-        super(oid)
-      end
-
       def column_name_for_operation(operation, node) # :nodoc:
         OPERATION_ALIASES.fetch(operation) { operation.downcase }
       end
@@ -417,91 +414,121 @@ module ActiveRecord
         "average" => "avg",
       }
 
-      protected
+      # Returns the version of the connected PostgreSQL server.
+      def postgresql_version
+        @connection.server_version
+      end
 
-        # Returns the version of the connected PostgreSQL server.
-        def postgresql_version
-          @connection.server_version
+      def default_index_type?(index) # :nodoc:
+        index.using == :btree || super
+      end
+
+      private
+        def check_version
+          if postgresql_version < 90100
+            raise "Your version of PostgreSQL (#{postgresql_version}) is too old. Active Record supports PostgreSQL >= 9.1."
+          end
         end
 
-        # See http://www.postgresql.org/docs/current/static/errcodes-appendix.html
+        # See https://www.postgresql.org/docs/current/static/errcodes-appendix.html
+        VALUE_LIMIT_VIOLATION = "22001"
+        NUMERIC_VALUE_OUT_OF_RANGE = "22003"
+        NOT_NULL_VIOLATION    = "23502"
         FOREIGN_KEY_VIOLATION = "23503"
         UNIQUE_VIOLATION      = "23505"
+        SERIALIZATION_FAILURE = "40001"
+        DEADLOCK_DETECTED     = "40P01"
+        LOCK_NOT_AVAILABLE    = "55P03"
+        QUERY_CANCELED        = "57014"
 
         def translate_exception(exception, message)
           return exception unless exception.respond_to?(:result)
 
-          case exception.result.try(:error_field, PGresult::PG_DIAG_SQLSTATE)
+          case exception.result.try(:error_field, PG::PG_DIAG_SQLSTATE)
           when UNIQUE_VIOLATION
-            RecordNotUnique.new(message, exception)
+            RecordNotUnique.new(message)
           when FOREIGN_KEY_VIOLATION
-            InvalidForeignKey.new(message, exception)
+            InvalidForeignKey.new(message)
+          when VALUE_LIMIT_VIOLATION
+            ValueTooLong.new(message)
+          when NUMERIC_VALUE_OUT_OF_RANGE
+            RangeError.new(message)
+          when NOT_NULL_VIOLATION
+            NotNullViolation.new(message)
+          when SERIALIZATION_FAILURE
+            SerializationFailure.new(message)
+          when DEADLOCK_DETECTED
+            Deadlocked.new(message)
+          when LOCK_NOT_AVAILABLE
+            LockWaitTimeout.new(message)
+          when QUERY_CANCELED
+            QueryCanceled.new(message)
           else
             super
           end
         end
 
-      private
-
-        def get_oid_type(oid, fmod, column_name, sql_type = '') # :nodoc:
+        def get_oid_type(oid, fmod, column_name, sql_type = "")
           if !type_map.key?(oid)
-            load_additional_types(type_map, [oid])
+            load_additional_types([oid])
           end
 
           type_map.fetch(oid, fmod, sql_type) {
             warn "unknown OID #{oid}: failed to recognize type of '#{column_name}'. It will be treated as String."
-            Type::Value.new.tap do |cast_type|
+            Type.default_value.tap do |cast_type|
               type_map.register_type(oid, cast_type)
             end
           }
         end
 
-        def initialize_type_map(m) # :nodoc:
-          register_class_with_limit m, 'int2', Type::Integer
-          register_class_with_limit m, 'int4', Type::Integer
-          register_class_with_limit m, 'int8', Type::Integer
-          m.alias_type 'oid', 'int2'
-          m.register_type 'float4', Type::Float.new
-          m.alias_type 'float8', 'float4'
-          m.register_type 'text', Type::Text.new
-          register_class_with_limit m, 'varchar', Type::String
-          m.alias_type 'char', 'varchar'
-          m.alias_type 'name', 'varchar'
-          m.alias_type 'bpchar', 'varchar'
-          m.register_type 'bool', Type::Boolean.new
-          register_class_with_limit m, 'bit', OID::Bit
-          register_class_with_limit m, 'varbit', OID::BitVarying
-          m.alias_type 'timestamptz', 'timestamp'
-          m.register_type 'date', Type::Date.new
-
-          m.register_type 'money', OID::Money.new
-          m.register_type 'bytea', OID::Bytea.new
-          m.register_type 'point', OID::Point.new
-          m.register_type 'hstore', OID::Hstore.new
-          m.register_type 'json', OID::Json.new
-          m.register_type 'jsonb', OID::Jsonb.new
-          m.register_type 'cidr', OID::Cidr.new
-          m.register_type 'inet', OID::Inet.new
-          m.register_type 'uuid', OID::Uuid.new
-          m.register_type 'xml', OID::Xml.new
-          m.register_type 'tsvector', OID::SpecializedString.new(:tsvector)
-          m.register_type 'macaddr', OID::SpecializedString.new(:macaddr)
-          m.register_type 'citext', OID::SpecializedString.new(:citext)
-          m.register_type 'ltree', OID::SpecializedString.new(:ltree)
-
-          # FIXME: why are we keeping these types as strings?
-          m.alias_type 'interval', 'varchar'
-          m.alias_type 'path', 'varchar'
-          m.alias_type 'line', 'varchar'
-          m.alias_type 'polygon', 'varchar'
-          m.alias_type 'circle', 'varchar'
-          m.alias_type 'lseg', 'varchar'
-          m.alias_type 'box', 'varchar'
-
-          register_class_with_precision m, 'time', Type::Time
-          register_class_with_precision m, 'timestamp', OID::DateTime
-
-          m.register_type 'numeric' do |_, fmod, sql_type|
+        def initialize_type_map(m = type_map)
+          m.register_type "int2", Type::Integer.new(limit: 2)
+          m.register_type "int4", Type::Integer.new(limit: 4)
+          m.register_type "int8", Type::Integer.new(limit: 8)
+          m.register_type "oid", OID::Oid.new
+          m.register_type "float4", Type::Float.new
+          m.alias_type "float8", "float4"
+          m.register_type "text", Type::Text.new
+          register_class_with_limit m, "varchar", Type::String
+          m.alias_type "char", "varchar"
+          m.alias_type "name", "varchar"
+          m.alias_type "bpchar", "varchar"
+          m.register_type "bool", Type::Boolean.new
+          register_class_with_limit m, "bit", OID::Bit
+          register_class_with_limit m, "varbit", OID::BitVarying
+          m.alias_type "timestamptz", "timestamp"
+          m.register_type "date", OID::Date.new
+
+          m.register_type "money", OID::Money.new
+          m.register_type "bytea", OID::Bytea.new
+          m.register_type "point", OID::Point.new
+          m.register_type "hstore", OID::Hstore.new
+          m.register_type "json", Type::Json.new
+          m.register_type "jsonb", OID::Jsonb.new
+          m.register_type "cidr", OID::Cidr.new
+          m.register_type "inet", OID::Inet.new
+          m.register_type "uuid", OID::Uuid.new
+          m.register_type "xml", OID::Xml.new
+          m.register_type "tsvector", OID::SpecializedString.new(:tsvector)
+          m.register_type "macaddr", OID::SpecializedString.new(:macaddr)
+          m.register_type "citext", OID::SpecializedString.new(:citext)
+          m.register_type "ltree", OID::SpecializedString.new(:ltree)
+          m.register_type "line", OID::SpecializedString.new(:line)
+          m.register_type "lseg", OID::SpecializedString.new(:lseg)
+          m.register_type "box", OID::SpecializedString.new(:box)
+          m.register_type "path", OID::SpecializedString.new(:path)
+          m.register_type "polygon", OID::SpecializedString.new(:polygon)
+          m.register_type "circle", OID::SpecializedString.new(:circle)
+
+          m.register_type "interval" do |_, _, sql_type|
+            precision = extract_precision(sql_type)
+            OID::SpecializedString.new(:interval, precision: precision)
+          end
+
+          register_class_with_precision m, "time", Type::Time
+          register_class_with_precision m, "timestamp", OID::DateTime
+
+          m.register_type "numeric" do |_, fmod, sql_type|
             precision = extract_precision(sql_type)
             scale = extract_scale(sql_type)
 
@@ -521,51 +548,45 @@ module ActiveRecord
             end
           end
 
-          load_additional_types(m)
-        end
-
-        def extract_limit(sql_type) # :nodoc:
-          case sql_type
-          when /^bigint/i, /^int8/i
-            8
-          when /^smallint/i
-            2
-          else
-            super
-          end
+          load_additional_types
         end
 
         # Extracts the value from a PostgreSQL column default definition.
-        def extract_value_from_default(default) # :nodoc:
+        def extract_value_from_default(default)
           case default
             # Quoted types
-            when /\A[\(B]?'(.*)'::/m
-              $1.gsub("''".freeze, "'".freeze)
+          when /\A[\(B]?'(.*)'.*::"?([\w. ]+)"?(?:\[\])?\z/m
+            # The default 'now'::date is CURRENT_DATE
+            if $1 == "now" && $2 == "date"
+              nil
+            else
+              $1.gsub("''", "'")
+            end
             # Boolean types
-            when 'true'.freeze, 'false'.freeze
-              default
+          when "true", "false"
+            default
             # Numeric types
-            when /\A\(?(-?\d+(\.\d*)?)\)?(::bigint)?\z/
-              $1
+          when /\A\(?(-?\d+(\.\d*)?)\)?(::bigint)?\z/
+            $1
             # Object identifier types
-            when /\A-?\d+\z/
-              $1
-            else
-              # Anything else is blank, some user type, or some function
-              # and we can't know the value of that, so return nil.
-              nil
+          when /\A-?\d+\z/
+            $1
+          else
+            # Anything else is blank, some user type, or some function
+            # and we can't know the value of that, so return nil.
+            nil
           end
         end
 
-        def extract_default_function(default_value, default) # :nodoc:
+        def extract_default_function(default_value, default)
           default if has_default_function?(default_value, default)
         end
 
-        def has_default_function?(default_value, default) # :nodoc:
-          !default_value && (%r{\w+\(.*\)} === default)
+        def has_default_function?(default_value, default)
+          !default_value && %r{\w+\(.*\)|\(.*\)::\w+|CURRENT_DATE|CURRENT_TIMESTAMP}.match?(default)
         end
 
-        def load_additional_types(type_map, oids = nil) # :nodoc:
+        def load_additional_types(oids = nil)
           initializer = OID::TypeMapInitializer.new(type_map)
 
           if supports_ranges?
@@ -584,55 +605,89 @@ module ActiveRecord
           if oids
             query += "WHERE t.oid::integer IN (%s)" % oids.join(", ")
           else
-            query += initializer.query_conditions_for_initial_load(type_map)
+            query += initializer.query_conditions_for_initial_load
           end
 
-          execute_and_clear(query, 'SCHEMA', []) do |records|
+          execute_and_clear(query, "SCHEMA", []) do |records|
             initializer.run(records)
           end
         end
 
         FEATURE_NOT_SUPPORTED = "0A000" #:nodoc:
 
-        def execute_and_clear(sql, name, binds)
-          result = without_prepared_statement?(binds) ? exec_no_cache(sql, name, binds) :
-                                                        exec_cache(sql, name, binds)
+        def execute_and_clear(sql, name, binds, prepare: false)
+          if without_prepared_statement?(binds)
+            result = exec_no_cache(sql, name, [])
+          elsif !prepare
+            result = exec_no_cache(sql, name, binds)
+          else
+            result = exec_cache(sql, name, binds)
+          end
           ret = yield result
           result.clear
           ret
         end
 
         def exec_no_cache(sql, name, binds)
-          log(sql, name, binds) { @connection.async_exec(sql, []) }
+          materialize_transactions
+
+          type_casted_binds = type_casted_binds(binds)
+          log(sql, name, binds, type_casted_binds) do
+            ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+              @connection.exec_params(sql, type_casted_binds)
+            end
+          end
         end
 
         def exec_cache(sql, name, binds)
+          materialize_transactions
+
           stmt_key = prepare_statement(sql)
-          type_casted_binds = binds.map { |attr| type_cast(attr.value_for_database) }
+          type_casted_binds = type_casted_binds(binds)
 
-          log(sql, name, binds, stmt_key) do
-            @connection.exec_prepared(stmt_key, type_casted_binds)
+          log(sql, name, binds, type_casted_binds, stmt_key) do
+            ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+              @connection.exec_prepared(stmt_key, type_casted_binds)
+            end
           end
         rescue ActiveRecord::StatementInvalid => e
-          pgerror = e.original_exception
-
-          # Get the PG code for the failure.  Annoyingly, the code for
-          # prepared statements whose return value may have changed is
-          # FEATURE_NOT_SUPPORTED.  Check here for more details:
-          # http://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/utils/cache/plancache.c#l573
-          begin
-            code = pgerror.result.result_error_field(PGresult::PG_DIAG_SQLSTATE)
-          rescue
-            raise e
-          end
-          if FEATURE_NOT_SUPPORTED == code
-            @statements.delete sql_key(sql)
-            retry
+          raise unless is_cached_plan_failure?(e)
+
+          # Nothing we can do if we are in a transaction because all commands
+          # will raise InFailedSQLTransaction
+          if in_transaction?
+            raise ActiveRecord::PreparedStatementCacheExpired.new(e.cause.message)
           else
-            raise e
+            @lock.synchronize do
+              # outside of transactions we can simply flush this query and retry
+              @statements.delete sql_key(sql)
+            end
+            retry
           end
         end
 
+        # Annoyingly, the code for prepared statements whose return value may
+        # have changed is FEATURE_NOT_SUPPORTED.
+        #
+        # This covers various different error types so we need to do additional
+        # work to classify the exception definitively as a
+        # ActiveRecord::PreparedStatementCacheExpired
+        #
+        # Check here for more details:
+        # https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/utils/cache/plancache.c#l573
+        CACHED_PLAN_HEURISTIC = "cached plan must not change result type"
+        def is_cached_plan_failure?(e)
+          pgerror = e.cause
+          code = pgerror.result.result_error_field(PG::PG_DIAG_SQLSTATE)
+          code == FEATURE_NOT_SUPPORTED && pgerror.message.include?(CACHED_PLAN_HEURISTIC)
+        rescue
+          false
+        end
+
+        def in_transaction?
+          open_transactions > 0
+        end
+
         # Returns the statement identifier for the client side cache
         # of statements
         def sql_key(sql)
@@ -642,38 +697,28 @@ module ActiveRecord
         # Prepare the statement if it hasn't been prepared, return
         # the statement key.
         def prepare_statement(sql)
-          sql_key = sql_key(sql)
-          unless @statements.key? sql_key
-            nextkey = @statements.next_key
-            begin
-              @connection.prepare nextkey, sql
-            rescue => e
-              raise translate_exception_class(e, sql)
+          @lock.synchronize do
+            sql_key = sql_key(sql)
+            unless @statements.key? sql_key
+              nextkey = @statements.next_key
+              begin
+                @connection.prepare nextkey, sql
+              rescue => e
+                raise translate_exception_class(e, sql)
+              end
+              # Clear the queue
+              @connection.get_last_result
+              @statements[sql_key] = nextkey
             end
-            # Clear the queue
-            @connection.get_last_result
-            @statements[sql_key] = nextkey
+            @statements[sql_key]
           end
-          @statements[sql_key]
         end
 
         # Connects to a PostgreSQL server and sets up the adapter depending on the
         # connected server's characteristics.
         def connect
-          @connection = PGconn.connect(@connection_parameters)
-
-          # Money type has a fixed precision of 10 in PostgreSQL 8.2 and below, and as of
-          # PostgreSQL 8.3 it has a fixed precision of 19. PostgreSQLColumn.extract_precision
-          # should know about this but can't detect it there, so deal with it here.
-          OID::Money.precision = (postgresql_version >= 80300) ? 19 : 10
-
+          @connection = PG.connect(@connection_parameters)
           configure_connection
-        rescue ::PG::Error => error
-          if error.message.include?("does not exist")
-            raise ActiveRecord::NoDatabaseError.new(error.message, error)
-          else
-            raise
-          end
         end
 
         # Configures the encoding, verbosity, schema search path, and time zone of the connection.
@@ -682,51 +727,40 @@ module ActiveRecord
           if @config[:encoding]
             @connection.set_client_encoding(@config[:encoding])
           end
-          self.client_min_messages = @config[:min_messages] || 'warning'
+          self.client_min_messages = @config[:min_messages] || "warning"
           self.schema_search_path = @config[:schema_search_path] || @config[:schema_order]
 
-          # Use standard-conforming strings if available so we don't have to do the E'...' dance.
+          # Use standard-conforming strings so we don't have to do the E'...' dance.
           set_standard_conforming_strings
 
+          variables = @config.fetch(:variables, {}).stringify_keys
+
           # If using Active Record's time zone support configure the connection to return
           # TIMESTAMP WITH ZONE types in UTC.
-          # (SET TIME ZONE does not use an equals sign like other SET variables)
-          if ActiveRecord::Base.default_timezone == :utc
-            execute("SET time zone 'UTC'", 'SCHEMA')
-          elsif @local_tz
-            execute("SET time zone '#{@local_tz}'", 'SCHEMA')
+          unless variables["timezone"]
+            if ActiveRecord::Base.default_timezone == :utc
+              variables["timezone"] = "UTC"
+            elsif @local_tz
+              variables["timezone"] = @local_tz
+            end
           end
 
           # SET statements from :variables config hash
-          # http://www.postgresql.org/docs/current/static/sql-set.html
-          variables = @config[:variables] || {}
+          # https://www.postgresql.org/docs/current/static/sql-set.html
           variables.map do |k, v|
-            if v == ':default' || v == :default
+            if v == ":default" || v == :default
               # Sets the value to the global or compile default
-              execute("SET SESSION #{k} TO DEFAULT", 'SCHEMA')
+              execute("SET SESSION #{k} TO DEFAULT", "SCHEMA")
             elsif !v.nil?
-              execute("SET SESSION #{k} TO #{quote(v)}", 'SCHEMA')
+              execute("SET SESSION #{k} TO #{quote(v)}", "SCHEMA")
             end
           end
         end
 
-        # Returns the current ID of a table's sequence.
-        def last_insert_id(sequence_name) #:nodoc:
-          Integer(last_insert_id_value(sequence_name))
-        end
-
-        def last_insert_id_value(sequence_name)
-          last_insert_id_result(sequence_name).rows.first.first
-        end
-
-        def last_insert_id_result(sequence_name) #:nodoc:
-          exec_query("SELECT currval('#{sequence_name}')", 'SQL')
-        end
-
         # Returns the list of a table's column names, data types, and default values.
         #
         # The underlying query is roughly:
-        #  SELECT column.name, column.type, default.value
+        #  SELECT column.name, column.type, default.value, column.comment
         #    FROM column LEFT JOIN default
         #      ON column.table_id = default.table_id
         #     AND column.num = default.column_num
@@ -741,27 +775,28 @@ module ActiveRecord
         # Query implementation notes:
         #  - format_type includes the column size constraint, e.g. varchar(50)
         #  - ::regclass is a function that gives the id for a table name
-        def column_definitions(table_name) # :nodoc:
-          query(<<-end_sql, 'SCHEMA')
+        def column_definitions(table_name)
+          query(<<-end_sql, "SCHEMA")
               SELECT a.attname, format_type(a.atttypid, a.atttypmod),
                      pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod,
-             (SELECT c.collname FROM pg_collation c, pg_type t
-               WHERE c.oid = a.attcollation AND t.oid = a.atttypid AND a.attcollation <> t.typcollation)
-                FROM pg_attribute a LEFT JOIN pg_attrdef d
-                  ON a.attrelid = d.adrelid AND a.attnum = d.adnum
-               WHERE a.attrelid = '#{quote_table_name(table_name)}'::regclass
+                     c.collname, col_description(a.attrelid, a.attnum) AS comment
+                FROM pg_attribute a
+                LEFT JOIN pg_attrdef d ON a.attrelid = d.adrelid AND a.attnum = d.adnum
+                LEFT JOIN pg_type t ON a.atttypid = t.oid
+                LEFT JOIN pg_collation c ON a.attcollation = c.oid AND a.attcollation <> t.typcollation
+               WHERE a.attrelid = #{quote(quote_table_name(table_name))}::regclass
                  AND a.attnum > 0 AND NOT a.attisdropped
                ORDER BY a.attnum
           end_sql
         end
 
-        def extract_table_ref_from_insert_sql(sql) # :nodoc:
-          sql[/into\s+([^\(]*).*values\s*\(/im]
+        def extract_table_ref_from_insert_sql(sql)
+          sql[/into\s("[A-Za-z0-9_."\[\]\s]+"|[A-Za-z0-9_."\[\]]+)\s*/im]
           $1.strip if $1
         end
 
-        def create_table_definition(name, temporary = false, options = nil, as = nil) # :nodoc:
-          PostgreSQL::TableDefinition.new native_database_types, name, temporary, options, as
+        def arel_visitor
+          Arel::Visitors::PostgreSQL.new(self)
         end
 
         def can_perform_case_insensitive_comparison_for?(column)
@@ -770,10 +805,14 @@ module ActiveRecord
             sql = <<-end_sql
               SELECT exists(
                 SELECT * FROM pg_proc
+                WHERE proname = 'lower'
+                  AND proargtypes = ARRAY[#{quote column.sql_type}::regtype]::oidvector
+              ) OR exists(
+                SELECT * FROM pg_proc
                 INNER JOIN pg_cast
-                  ON casttarget::text::oidvector = proargtypes
+                  ON ARRAY[casttarget]::oidvector = proargtypes
                 WHERE proname = 'lower'
-                  AND castsource = '#{column.sql_type}'::regtype::oid
+                  AND castsource = #{quote column.sql_type}::regtype
               )
             end_sql
             execute_and_clear(sql, "SCHEMA", []) do |result|
@@ -787,19 +826,18 @@ module ActiveRecord
           map[Integer] = PG::TextEncoder::Integer.new
           map[TrueClass] = PG::TextEncoder::Boolean.new
           map[FalseClass] = PG::TextEncoder::Boolean.new
-          map[Float] = PG::TextEncoder::Float.new
           @connection.type_map_for_queries = map
         end
 
         def add_pg_decoders
           coders_by_name = {
-            'int2' => PG::TextDecoder::Integer,
-            'int4' => PG::TextDecoder::Integer,
-            'int8' => PG::TextDecoder::Integer,
-            'oid' => PG::TextDecoder::Integer,
-            'float4' => PG::TextDecoder::Float,
-            'float8' => PG::TextDecoder::Float,
-            'bool' => PG::TextDecoder::Boolean,
+            "int2" => PG::TextDecoder::Integer,
+            "int4" => PG::TextDecoder::Integer,
+            "int8" => PG::TextDecoder::Integer,
+            "oid" => PG::TextDecoder::Integer,
+            "float4" => PG::TextDecoder::Float,
+            "float8" => PG::TextDecoder::Float,
+            "bool" => PG::TextDecoder::Boolean,
           }
           known_coder_types = coders_by_name.keys.map { |n| quote(n) }
           query = <<-SQL % known_coder_types.join(", ")
@@ -809,7 +847,7 @@ module ActiveRecord
           SQL
           coders = execute_and_clear(query, "SCHEMA", []) do |result|
             result
-              .map { |row| construct_coder(row, coders_by_name[row['typname']]) }
+              .map { |row| construct_coder(row, coders_by_name[row["typname"]]) }
               .compact
           end
 
@@ -820,7 +858,7 @@ module ActiveRecord
 
         def construct_coder(row, coder_class)
           return unless coder_class
-          coder_class.new(oid: row['oid'].to_i, name: row['typname'])
+          coder_class.new(oid: row["oid"].to_i, name: row["typname"])
         end
 
         ActiveRecord::Type.add_modifier({ array: true }, OID::Array, adapter: :postgresql)
@@ -829,17 +867,16 @@ module ActiveRecord
         ActiveRecord::Type.register(:bit_varying, OID::BitVarying, adapter: :postgresql)
         ActiveRecord::Type.register(:binary, OID::Bytea, adapter: :postgresql)
         ActiveRecord::Type.register(:cidr, OID::Cidr, adapter: :postgresql)
-        ActiveRecord::Type.register(:date_time, OID::DateTime, adapter: :postgresql)
+        ActiveRecord::Type.register(:date, OID::Date, adapter: :postgresql)
+        ActiveRecord::Type.register(:datetime, OID::DateTime, adapter: :postgresql)
         ActiveRecord::Type.register(:decimal, OID::Decimal, adapter: :postgresql)
         ActiveRecord::Type.register(:enum, OID::Enum, adapter: :postgresql)
         ActiveRecord::Type.register(:hstore, OID::Hstore, adapter: :postgresql)
         ActiveRecord::Type.register(:inet, OID::Inet, adapter: :postgresql)
-        ActiveRecord::Type.register(:json, OID::Json, adapter: :postgresql)
         ActiveRecord::Type.register(:jsonb, OID::Jsonb, adapter: :postgresql)
         ActiveRecord::Type.register(:money, OID::Money, adapter: :postgresql)
         ActiveRecord::Type.register(:point, OID::Point, adapter: :postgresql)
-        ActiveRecord::Type.register(:legacy_point, OID::Point, adapter: :postgresql)
-        ActiveRecord::Type.register(:rails_5_1_point, OID::Rails51Point, adapter: :postgresql)
+        ActiveRecord::Type.register(:legacy_point, OID::LegacyPoint, adapter: :postgresql)
         ActiveRecord::Type.register(:uuid, OID::Uuid, adapter: :postgresql)
         ActiveRecord::Type.register(:vector, OID::Vector, adapter: :postgresql)
         ActiveRecord::Type.register(:xml, OID::Xml, adapter: :postgresql)
diff --git a/activerecord/lib/active_record/connection_adapters/schema_cache.rb b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
index 981d5d7a3c..c29cf1f9a1 100644
--- a/activerecord/lib/active_record/connection_adapters/schema_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/schema_cache.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     class SchemaCache
@@ -10,7 +12,7 @@ module ActiveRecord
         @columns      = {}
         @columns_hash = {}
         @primary_keys = {}
-        @tables       = {}
+        @data_sources = {}
       end
 
       def initialize_dup(other)
@@ -18,32 +20,48 @@ module ActiveRecord
         @columns      = @columns.dup
         @columns_hash = @columns_hash.dup
         @primary_keys = @primary_keys.dup
-        @tables       = @tables.dup
+        @data_sources = @data_sources.dup
+      end
+
+      def encode_with(coder)
+        coder["columns"] = @columns
+        coder["columns_hash"] = @columns_hash
+        coder["primary_keys"] = @primary_keys
+        coder["data_sources"] = @data_sources
+        coder["version"] = connection.migration_context.current_version
+      end
+
+      def init_with(coder)
+        @columns = coder["columns"]
+        @columns_hash = coder["columns_hash"]
+        @primary_keys = coder["primary_keys"]
+        @data_sources = coder["data_sources"]
+        @version = coder["version"]
       end
 
       def primary_keys(table_name)
-        @primary_keys[table_name] ||= table_exists?(table_name) ? connection.primary_key(table_name) : nil
+        @primary_keys[table_name] ||= data_source_exists?(table_name) ? connection.primary_key(table_name) : nil
       end
 
       # A cached lookup for table existence.
-      def table_exists?(name)
-        prepare_tables if @tables.empty?
-        return @tables[name] if @tables.key? name
+      def data_source_exists?(name)
+        prepare_data_sources if @data_sources.empty?
+        return @data_sources[name] if @data_sources.key? name
 
-        @tables[name] = connection.table_exists?(name)
+        @data_sources[name] = connection.data_source_exists?(name)
       end
 
       # Add internal cache for table with +table_name+.
       def add(table_name)
-        if table_exists?(table_name)
+        if data_source_exists?(table_name)
           primary_keys(table_name)
           columns(table_name)
           columns_hash(table_name)
         end
       end
 
-      def tables(name)
-        @tables[name]
+      def data_sources(name)
+        @data_sources[name]
       end
 
       # Get the columns for a table
@@ -64,36 +82,36 @@ module ActiveRecord
         @columns.clear
         @columns_hash.clear
         @primary_keys.clear
-        @tables.clear
+        @data_sources.clear
         @version = nil
       end
 
       def size
-        [@columns, @columns_hash, @primary_keys, @tables].map(&:size).inject :+
+        [@columns, @columns_hash, @primary_keys, @data_sources].map(&:size).inject :+
       end
 
-      # Clear out internal caches for table with +table_name+.
-      def clear_table_cache!(table_name)
-        @columns.delete table_name
-        @columns_hash.delete table_name
-        @primary_keys.delete table_name
-        @tables.delete table_name
+      # Clear out internal caches for the data source +name+.
+      def clear_data_source_cache!(name)
+        @columns.delete name
+        @columns_hash.delete name
+        @primary_keys.delete name
+        @data_sources.delete name
       end
 
       def marshal_dump
         # if we get current version during initialization, it happens stack over flow.
-        @version = ActiveRecord::Migrator.current_version
-        [@version, @columns, @columns_hash, @primary_keys, @tables]
+        @version = connection.migration_context.current_version
+        [@version, @columns, @columns_hash, @primary_keys, @data_sources]
       end
 
       def marshal_load(array)
-        @version, @columns, @columns_hash, @primary_keys, @tables = array
+        @version, @columns, @columns_hash, @primary_keys, @data_sources = array
       end
 
       private
 
-        def prepare_tables
-          connection.tables.each { |table| @tables[table] = true }
+        def prepare_data_sources
+          connection.data_sources.each { |source| @data_sources[source] = true }
         end
     end
   end
diff --git a/activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb b/activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb
index ccb7e154ee..8489bcbf1d 100644
--- a/activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb
+++ b/activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # :stopdoc:
   module ConnectionAdapters
@@ -24,9 +26,9 @@ module ActiveRecord
 
       protected
 
-      def attributes_for_hash
-        [self.class, sql_type, type, limit, precision, scale]
-      end
+        def attributes_for_hash
+          [self.class, sql_type, type, limit, precision, scale]
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/explain_pretty_printer.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/explain_pretty_printer.rb
new file mode 100644
index 0000000000..832fdfe5c4
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/explain_pretty_printer.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      class ExplainPrettyPrinter # :nodoc:
+        # Pretty prints the result of an EXPLAIN QUERY PLAN in a way that resembles
+        # the output of the SQLite shell:
+        #
+        #   0|0|0|SEARCH TABLE users USING INTEGER PRIMARY KEY (rowid=?) (~1 rows)
+        #   0|1|1|SCAN TABLE posts (~100000 rows)
+        #
+        def pp(result)
+          result.rows.map do |row|
+            row.join("|")
+          end.join("\n") + "\n"
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/quoting.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/quoting.rb
new file mode 100644
index 0000000000..b2dcdb5373
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/quoting.rb
@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      module Quoting # :nodoc:
+        def quote_string(s)
+          @connection.class.quote(s)
+        end
+
+        def quote_table_name_for_assignment(table, attr)
+          quote_column_name(attr)
+        end
+
+        def quote_column_name(name)
+          @quoted_column_names[name] ||= %Q("#{super.gsub('"', '""')}")
+        end
+
+        def quoted_time(value)
+          value = value.change(year: 2000, month: 1, day: 1)
+          quoted_date(value).sub(/\A\d\d\d\d-\d\d-\d\d /, "2000-01-01 ")
+        end
+
+        def quoted_binary(value)
+          "x'#{value.hex}'"
+        end
+
+        def quoted_true
+          ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer ? "1" : "'t'"
+        end
+
+        def unquoted_true
+          ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer ? 1 : "t"
+        end
+
+        def quoted_false
+          ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer ? "0" : "'f'"
+        end
+
+        def unquoted_false
+          ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer ? 0 : "f"
+        end
+
+        private
+
+          def _type_cast(value)
+            case value
+            when BigDecimal
+              value.to_f
+            when String
+              if value.encoding == Encoding::ASCII_8BIT
+                super(value.encode(Encoding::UTF_8))
+              else
+                super
+              end
+            else
+              super
+            end
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_creation.rb
index fe1dcbd710..b842561317 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_creation.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_creation.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
     module SQLite3
-      class SchemaCreation < AbstractAdapter::SchemaCreation
+      class SchemaCreation < AbstractAdapter::SchemaCreation # :nodoc:
         private
           def add_column_options!(sql, options)
             if options[:collation]
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_definitions.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_definitions.rb
new file mode 100644
index 0000000000..c9855019c1
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_definitions.rb
@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      class TableDefinition < ActiveRecord::ConnectionAdapters::TableDefinition
+        def references(*args, **options)
+          super(*args, type: :integer, **options)
+        end
+        alias :belongs_to :references
+
+        private
+          def integer_like_primary_key_type(type, options)
+            :primary_key
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_dumper.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_dumper.rb
new file mode 100644
index 0000000000..621678ec65
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_dumper.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      class SchemaDumper < ConnectionAdapters::SchemaDumper # :nodoc:
+        private
+          def default_primary_key?(column)
+            schema_type(column) == :integer
+          end
+
+          def explicit_primary_key_default?(column)
+            column.bigint?
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb
new file mode 100644
index 0000000000..48277f0ae2
--- /dev/null
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb
@@ -0,0 +1,111 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module ConnectionAdapters
+    module SQLite3
+      module SchemaStatements # :nodoc:
+        # Returns an array of indexes for the given table.
+        def indexes(table_name)
+          exec_query("PRAGMA index_list(#{quote_table_name(table_name)})", "SCHEMA").map do |row|
+            # Indexes SQLite creates implicitly for internal use start with "sqlite_".
+            # See https://www.sqlite.org/fileformat2.html#intschema
+            next if row["name"].starts_with?("sqlite_")
+
+            index_sql = query_value(<<-SQL, "SCHEMA")
+              SELECT sql
+              FROM sqlite_master
+              WHERE name = #{quote(row['name'])} AND type = 'index'
+              UNION ALL
+              SELECT sql
+              FROM sqlite_temp_master
+              WHERE name = #{quote(row['name'])} AND type = 'index'
+            SQL
+
+            /\bON\b\s*"?(\w+?)"?\s*\((?<expressions>.+?)\)(?:\s*WHERE\b\s*(?<where>.+))?\z/i =~ index_sql
+
+            columns = exec_query("PRAGMA index_info(#{quote(row['name'])})", "SCHEMA").map do |col|
+              col["name"]
+            end
+
+            orders = {}
+
+            if columns.any?(&:nil?) # index created with an expression
+              columns = expressions
+            else
+              # Add info on sort order for columns (only desc order is explicitly specified,
+              # asc is the default)
+              if index_sql # index_sql can be null in case of primary key indexes
+                index_sql.scan(/"(\w+)" DESC/).flatten.each { |order_column|
+                  orders[order_column] = :desc
+                }
+              end
+            end
+
+            IndexDefinition.new(
+              table_name,
+              row["name"],
+              row["unique"] != 0,
+              columns,
+              where: where,
+              orders: orders
+            )
+          end.compact
+        end
+
+        def create_schema_dumper(options)
+          SQLite3::SchemaDumper.create(self, options)
+        end
+
+        private
+          def schema_creation
+            SQLite3::SchemaCreation.new(self)
+          end
+
+          def create_table_definition(*args)
+            SQLite3::TableDefinition.new(*args)
+          end
+
+          def new_column_from_field(table_name, field)
+            default = \
+              case field["dflt_value"]
+              when /^null$/i
+                nil
+              when /^'(.*)'$/m
+                $1.gsub("''", "'")
+              when /^"(.*)"$/m
+                $1.gsub('""', '"')
+              else
+                field["dflt_value"]
+              end
+
+            type_metadata = fetch_type_metadata(field["type"])
+            Column.new(field["name"], default, type_metadata, field["notnull"].to_i == 0, table_name, nil, field["collation"])
+          end
+
+          def data_source_sql(name = nil, type: nil)
+            scope = quoted_scope(name, type: type)
+            scope[:type] ||= "'table','view'"
+
+            sql = +"SELECT name FROM sqlite_master WHERE name <> 'sqlite_sequence'"
+            sql << " AND name = #{scope[:name]}" if scope[:name]
+            sql << " AND type IN (#{scope[:type]})"
+            sql
+          end
+
+          def quoted_scope(name = nil, type: nil)
+            type = \
+              case type
+              when "BASE TABLE"
+                "'table'"
+              when "VIEW"
+                "'view'"
+              end
+            scope = {}
+            scope[:name] = quote(name) if name
+            scope[:type] = type if type
+            scope
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 7c809b088c..3312c3de01 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -1,14 +1,22 @@
-require 'active_record/connection_adapters/abstract_adapter'
-require 'active_record/connection_adapters/statement_pool'
-require 'active_record/connection_adapters/sqlite3/schema_creation'
+# frozen_string_literal: true
 
-gem 'sqlite3', '~> 1.3.6'
-require 'sqlite3'
+require "active_record/connection_adapters/abstract_adapter"
+require "active_record/connection_adapters/statement_pool"
+require "active_record/connection_adapters/sqlite3/explain_pretty_printer"
+require "active_record/connection_adapters/sqlite3/quoting"
+require "active_record/connection_adapters/sqlite3/schema_creation"
+require "active_record/connection_adapters/sqlite3/schema_definitions"
+require "active_record/connection_adapters/sqlite3/schema_dumper"
+require "active_record/connection_adapters/sqlite3/schema_statements"
+
+gem "sqlite3", "~> 1.3.6"
+require "sqlite3"
 
 module ActiveRecord
   module ConnectionHandling # :nodoc:
-    # sqlite3 adapter reuses sqlite_connection.
     def sqlite3_connection(config)
+      config = config.symbolize_keys
+
       # Require database.
       unless config[:database]
         raise ArgumentError, "No database file specified. Missing argument: database"
@@ -17,7 +25,7 @@ module ActiveRecord
       # Allow database path relative to Rails.root, but only if the database
       # path is not the special path that tells sqlite to build a database only
       # in memory.
-      if ':memory:' != config[:database]
+      if ":memory:" != config[:database]
         config[:database] = File.expand_path(config[:database], Rails.root) if defined?(Rails.root)
         dirname = File.dirname(config[:database])
         Dir.mkdir(dirname) unless File.directory?(dirname)
@@ -25,7 +33,7 @@ module ActiveRecord
 
       db = SQLite3::Database.new(
         config[:database].to_s,
-        :results_as_hash => true
+        config.merge(results_as_hash: true)
       )
 
       db.busy_timeout(ConnectionAdapters::SQLite3Adapter.type_cast_config_to_integer(config[:timeout])) if config[:timeout]
@@ -33,7 +41,7 @@ module ActiveRecord
       ConnectionAdapters::SQLite3Adapter.new(db, logger, nil, config)
     rescue Errno::ENOENT => error
       if error.message.include?("No such file or directory")
-        raise ActiveRecord::NoDatabaseError.new(error.message, error)
+        raise ActiveRecord::NoDatabaseError
       else
         raise
       end
@@ -48,11 +56,13 @@ module ActiveRecord
     #
     # * <tt>:database</tt> - Path to the database file.
     class SQLite3Adapter < AbstractAdapter
-      ADAPTER_NAME = 'SQLite'.freeze
-      include Savepoints
+      ADAPTER_NAME = "SQLite"
+
+      include SQLite3::Quoting
+      include SQLite3::SchemaStatements
 
       NATIVE_DATABASE_TYPES = {
-        primary_key:  'INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL',
+        primary_key:  "integer PRIMARY KEY AUTOINCREMENT NOT NULL",
         string:       { name: "varchar" },
         text:         { name: "text" },
         integer:      { name: "integer" },
@@ -62,49 +72,40 @@ module ActiveRecord
         time:         { name: "time" },
         date:         { name: "date" },
         binary:       { name: "blob" },
-        boolean:      { name: "boolean" }
+        boolean:      { name: "boolean" },
+        json:         { name: "json" },
       }
 
-      class Version
-        include Comparable
-
-        def initialize(version_string)
-          @version = version_string.split('.').map(&:to_i)
-        end
-
-        def <=>(version_string)
-          @version <=> version_string.split('.').map(&:to_i)
-        end
-      end
+      ##
+      # :singleton-method:
+      # Indicates whether boolean values are stored in sqlite3 databases as 1
+      # and 0 or 't' and 'f'. Leaving <tt>ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer</tt>
+      # set to false is deprecated. SQLite databases have used 't' and 'f' to
+      # serialize boolean values and must have old data converted to 1 and 0
+      # (its native boolean serialization) before setting this flag to true.
+      # Conversion can be accomplished by setting up a rake task which runs
+      #
+      #   ExampleModel.where("boolean_column = 't'").update_all(boolean_column: 1)
+      #   ExampleModel.where("boolean_column = 'f'").update_all(boolean_column: 0)
+      # for all models and all boolean columns, after which the flag must be set
+      # to true by adding the following to your <tt>application.rb</tt> file:
+      #
+      #   Rails.application.config.active_record.sqlite3.represent_boolean_as_integer = true
+      class_attribute :represent_boolean_as_integer, default: false
 
-      class StatementPool < ConnectionAdapters::StatementPool
+      class StatementPool < ConnectionAdapters::StatementPool # :nodoc:
         private
-
-        def dealloc(stmt)
-          stmt[:stmt].close unless stmt[:stmt].closed?
-        end
-      end
-
-      def schema_creation # :nodoc:
-        SQLite3::SchemaCreation.new self
+          def dealloc(stmt)
+            stmt.close unless stmt.closed?
+          end
       end
 
       def initialize(connection, logger, connection_options, config)
-        super(connection, logger)
-
-        @active     = nil
-        @statements = StatementPool.new(@connection,
-                                        self.class.type_cast_config_to_integer(config.fetch(:statement_limit) { 1000 }))
-        @config = config
+        super(connection, logger, config)
 
-        @visitor = Arel::Visitors::SQLite.new self
-        @quoted_column_names = {}
-
-        if self.class.type_cast_config_to_boolean(config.fetch(:prepared_statements) { true })
-          @prepared_statements = true
-        else
-          @prepared_statements = false
-        end
+        @active     = true
+        @statements = StatementPool.new(self.class.type_cast_config_to_integer(config[:statement_limit]))
+        configure_connection
       end
 
       def supports_ddl_transactions?
@@ -116,34 +117,35 @@ module ActiveRecord
       end
 
       def supports_partial_index?
-        sqlite_version >= '3.8.0'
+        true
       end
 
-      # Returns true, since this connection adapter supports prepared statement
-      # caching.
-      def supports_statement_cache?
+      def supports_expression_index?
+        sqlite_version >= "3.9.0"
+      end
+
+      def requires_reloading?
         true
       end
 
-      # Returns true, since this connection adapter supports migrations.
-      def supports_migrations? #:nodoc:
+      def supports_foreign_keys_in_create?
         true
       end
 
-      def supports_primary_key? #:nodoc:
+      def supports_views?
         true
       end
 
-      def requires_reloading?
+      def supports_datetime_with_precision?
         true
       end
 
-      def supports_views?
+      def supports_json?
         true
       end
 
       def active?
-        @active != false
+        @active
       end
 
       # Disconnects from the database if already connected. Otherwise, this
@@ -164,7 +166,7 @@ module ActiveRecord
       end
 
       # Returns 62. SQLite supports index names up to 64
-      # characters. The rest is used by rails internally to perform
+      # characters. The rest is used by Rails internally to perform
       # temporary rename operations
       def allowed_index_name_length
         index_name_length - 2
@@ -183,42 +185,24 @@ module ActiveRecord
         true
       end
 
-      # QUOTING ==================================================
-
-      def _quote(value) # :nodoc:
-        case value
-        when Type::Binary::Data
-          "x'#{value.hex}'"
-        else
-          super
-        end
-      end
-
-      def _type_cast(value) # :nodoc:
-        case value
-        when BigDecimal
-          value.to_f
-        when String
-          if value.encoding == Encoding::ASCII_8BIT
-            super(value.encode(Encoding::UTF_8))
-          else
-            super
-          end
-        else
-          super
-        end
+      def supports_lazy_transactions?
+        true
       end
 
-      def quote_string(s) #:nodoc:
-        @connection.class.quote(s)
-      end
+      # REFERENTIAL INTEGRITY ====================================
 
-      def quote_table_name_for_assignment(table, attr)
-        quote_column_name(attr)
-      end
+      def disable_referential_integrity # :nodoc:
+        old_foreign_keys = query_value("PRAGMA foreign_keys")
+        old_defer_foreign_keys = query_value("PRAGMA defer_foreign_keys")
 
-      def quote_column_name(name) #:nodoc:
-        @quoted_column_names[name] ||= %Q("#{name.to_s.gsub('"', '""')}")
+        begin
+          execute("PRAGMA defer_foreign_keys = ON")
+          execute("PRAGMA foreign_keys = OFF")
+          yield
+        ensure
+          execute("PRAGMA defer_foreign_keys = #{old_defer_foreign_keys}")
+          execute("PRAGMA foreign_keys = #{old_foreign_keys}")
+        end
       end
 
       #--
@@ -227,52 +211,42 @@ module ActiveRecord
 
       def explain(arel, binds = [])
         sql = "EXPLAIN QUERY PLAN #{to_sql(arel, binds)}"
-        ExplainPrettyPrinter.new.pp(exec_query(sql, 'EXPLAIN', []))
-      end
-
-      class ExplainPrettyPrinter
-        # Pretty prints the result of a EXPLAIN QUERY PLAN in a way that resembles
-        # the output of the SQLite shell:
-        #
-        #   0|0|0|SEARCH TABLE users USING INTEGER PRIMARY KEY (rowid=?) (~1 rows)
-        #   0|1|1|SCAN TABLE posts (~100000 rows)
-        #
-        def pp(result) # :nodoc:
-          result.rows.map do |row|
-            row.join('|')
-          end.join("\n") + "\n"
-        end
-      end
-
-      def exec_query(sql, name = nil, binds = [])
-        type_casted_binds = binds.map { |attr| type_cast(attr.value_for_database) }
-
-        log(sql, name, binds) do
-          # Don't cache statements if they are not prepared
-          if without_prepared_statement?(binds)
-            stmt    = @connection.prepare(sql)
-            begin
-              cols    = stmt.columns
+        SQLite3::ExplainPrettyPrinter.new.pp(exec_query(sql, "EXPLAIN", []))
+      end
+
+      def exec_query(sql, name = nil, binds = [], prepare: false)
+        materialize_transactions
+
+        type_casted_binds = type_casted_binds(binds)
+
+        log(sql, name, binds, type_casted_binds) do
+          ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+            # Don't cache statements if they are not prepared
+            unless prepare
+              stmt = @connection.prepare(sql)
+              begin
+                cols = stmt.columns
+                unless without_prepared_statement?(binds)
+                  stmt.bind_params(type_casted_binds)
+                end
+                records = stmt.to_a
+              ensure
+                stmt.close
+              end
+            else
+              stmt = @statements[sql] ||= @connection.prepare(sql)
+              cols = stmt.columns
+              stmt.reset!
+              stmt.bind_params(type_casted_binds)
               records = stmt.to_a
-            ensure
-              stmt.close
             end
-            stmt = records
-          else
-            cache = @statements[sql] ||= {
-              :stmt => @connection.prepare(sql)
-            }
-            stmt = cache[:stmt]
-            cols = cache[:cols] ||= stmt.columns
-            stmt.reset!
-            stmt.bind_params type_casted_binds
-          end
 
-          ActiveRecord::Result.new(cols, stmt.to_a)
+            ActiveRecord::Result.new(cols, records)
+          end
         end
       end
 
-      def exec_delete(sql, name = 'SQL', binds = [])
+      def exec_delete(sql, name = "SQL", binds = [])
         exec_query(sql, name, binds)
         @connection.changes
       end
@@ -283,111 +257,36 @@ module ActiveRecord
       end
 
       def execute(sql, name = nil) #:nodoc:
-        log(sql, name) { @connection.execute(sql) }
-      end
-
-      def update_sql(sql, name = nil) #:nodoc:
-        super
-        @connection.changes
-      end
+        materialize_transactions
 
-      def delete_sql(sql, name = nil) #:nodoc:
-        sql += " WHERE 1=1" unless sql =~ /WHERE/i
-        super sql, name
-      end
-
-      def insert_sql(sql, name = nil, pk = nil, id_value = nil, sequence_name = nil) #:nodoc:
-        super
-        id_value || @connection.last_insert_row_id
-      end
-      alias :create :insert_sql
-
-      def select_rows(sql, name = nil, binds = [])
-        exec_query(sql, name, binds).rows
+        log(sql, name) do
+          ActiveSupport::Dependencies.interlock.permit_concurrent_loads do
+            @connection.execute(sql)
+          end
+        end
       end
 
       def begin_db_transaction #:nodoc:
-        log('begin transaction',nil) { @connection.transaction }
+        log("begin transaction", nil) { @connection.transaction }
       end
 
       def commit_db_transaction #:nodoc:
-        log('commit transaction',nil) { @connection.commit }
+        log("commit transaction", nil) { @connection.commit }
       end
 
       def exec_rollback_db_transaction #:nodoc:
-        log('rollback transaction',nil) { @connection.rollback }
+        log("rollback transaction", nil) { @connection.rollback }
       end
 
       # SCHEMA STATEMENTS ========================================
 
-      def tables(name = nil, table_name = nil) #:nodoc:
-        sql = <<-SQL
-          SELECT name
-          FROM sqlite_master
-          WHERE (type = 'table' OR type = 'view') AND NOT name = 'sqlite_sequence'
-        SQL
-        sql << " AND name = #{quote_table_name(table_name)}" if table_name
-
-        exec_query(sql, 'SCHEMA').map do |row|
-          row['name']
-        end
-      end
-
-      def table_exists?(table_name)
-        table_name && tables(nil, table_name).any?
-      end
-
-      # Returns an array of +Column+ objects for the table specified by +table_name+.
-      def columns(table_name) #:nodoc:
-        table_structure(table_name).map do |field|
-          case field["dflt_value"]
-          when /^null$/i
-            field["dflt_value"] = nil
-          when /^'(.*)'$/m
-            field["dflt_value"] = $1.gsub("''", "'")
-          when /^"(.*)"$/m
-            field["dflt_value"] = $1.gsub('""', '"')
-          end
-
-          collation = field['collation']
-          sql_type = field['type']
-          type_metadata = fetch_type_metadata(sql_type)
-          new_column(field['name'], field['dflt_value'], type_metadata, field['notnull'].to_i == 0, nil, collation)
-        end
-      end
-
-      # Returns an array of indexes for the given table.
-      def indexes(table_name, name = nil) #:nodoc:
-        exec_query("PRAGMA index_list(#{quote_table_name(table_name)})", 'SCHEMA').map do |row|
-          sql = <<-SQL
-            SELECT sql
-            FROM sqlite_master
-            WHERE name=#{quote(row['name'])} AND type='index'
-            UNION ALL
-            SELECT sql
-            FROM sqlite_temp_master
-            WHERE name=#{quote(row['name'])} AND type='index'
-          SQL
-          index_sql = exec_query(sql).first['sql']
-          match = /\sWHERE\s+(.+)$/i.match(index_sql)
-          where = match[1] if match
-          IndexDefinition.new(
-            table_name,
-            row['name'],
-            row['unique'] != 0,
-            exec_query("PRAGMA index_info('#{row['name']}')", "SCHEMA").map { |col|
-              col['name']
-            }, nil, nil, where)
-        end
-      end
-
-      def primary_key(table_name) #:nodoc:
-        pks = table_structure(table_name).select { |f| f['pk'] > 0 }
-        return nil unless pks.count == 1
-        pks[0]['name']
+      def primary_keys(table_name) # :nodoc:
+        pks = table_structure(table_name).select { |f| f["pk"] > 0 }
+        pks.sort_by { |f| f["pk"] }.map { |f| f["name"] }
       end
 
-      def remove_index!(table_name, index_name) #:nodoc:
+      def remove_index(table_name, options = {}) #:nodoc:
+        index_name = index_name_for_remove(table_name, options)
         exec_query "DROP INDEX #{quote_column_name(index_name)}"
       end
 
@@ -400,19 +299,18 @@ module ActiveRecord
         rename_table_indexes(table_name, new_name)
       end
 
-      # See: http://www.sqlite.org/lang_altertable.html
-      # SQLite has an additional restriction on the ALTER TABLE statement
-      def valid_alter_table_type?(type)
-        type.to_sym != :primary_key
+      def valid_alter_table_type?(type, options = {})
+        !invalid_alter_table_type?(type, options)
       end
+      deprecate :valid_alter_table_type?
 
       def add_column(table_name, column_name, type, options = {}) #:nodoc:
-        if valid_alter_table_type?(type)
-          super(table_name, column_name, type, options)
-        else
+        if invalid_alter_table_type?(type, options)
           alter_table(table_name) do |definition|
             definition.column(column_name, type, options)
           end
+        else
+          super
         end
       end
 
@@ -441,14 +339,13 @@ module ActiveRecord
 
       def change_column(table_name, column_name, type, options = {}) #:nodoc:
         alter_table(table_name) do |definition|
-          include_default = options_include_default?(options)
           definition[column_name].instance_eval do
             self.type    = type
             self.limit   = options[:limit] if options.include?(:limit)
-            self.default = options[:default] if include_default
+            self.default = options[:default] if options.include?(:default)
             self.null    = options[:null] if options.include?(:null)
             self.precision = options[:precision] if options.include?(:precision)
-            self.scale   = options[:scale] if options.include?(:scale)
+            self.scale = options[:scale] if options.include?(:scale)
             self.collation = options[:collation] if options.include?(:collation)
           end
         end
@@ -456,52 +353,130 @@ module ActiveRecord
 
       def rename_column(table_name, column_name, new_column_name) #:nodoc:
         column = column_for(table_name, column_name)
-        alter_table(table_name, rename: {column.name => new_column_name.to_s})
+        alter_table(table_name, rename: { column.name => new_column_name.to_s })
         rename_column_indexes(table_name, column.name, new_column_name)
       end
 
-      protected
+      def add_reference(table_name, ref_name, **options) # :nodoc:
+        super(table_name, ref_name, type: :integer, **options)
+      end
+      alias :add_belongs_to :add_reference
+
+      def foreign_keys(table_name)
+        fk_info = exec_query("PRAGMA foreign_key_list(#{quote(table_name)})", "SCHEMA")
+        fk_info.map do |row|
+          options = {
+            column: row["from"],
+            primary_key: row["to"],
+            on_delete: extract_foreign_key_action(row["on_delete"]),
+            on_update: extract_foreign_key_action(row["on_update"])
+          }
+          ForeignKeyDefinition.new(table_name, row["table"], options)
+        end
+      end
+
+      def insert_fixtures(rows, table_name)
+        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+          `insert_fixtures` is deprecated and will be removed in the next version of Rails.
+          Consider using `insert_fixtures_set` for performance improvement.
+        MSG
+        insert_fixtures_set(table_name => rows)
+      end
+
+      def insert_fixtures_set(fixture_set, tables_to_delete = [])
+        disable_referential_integrity do
+          transaction(requires_new: true) do
+            tables_to_delete.each { |table| delete "DELETE FROM #{quote_table_name(table)}", "Fixture Delete" }
+
+            fixture_set.each do |table_name, rows|
+              rows.each { |row| insert_fixture(row, table_name) }
+            end
+          end
+        end
+      end
+
+      private
+        # See https://www.sqlite.org/limits.html,
+        # the default value is 999 when not configured.
+        def bind_params_length
+          999
+        end
+
+        def check_version
+          if sqlite_version < "3.8.0"
+            raise "Your version of SQLite (#{sqlite_version}) is too old. Active Record supports SQLite >= 3.8."
+          end
+        end
+
+        def initialize_type_map(m = type_map)
+          super
+          register_class_with_limit m, %r(int)i, SQLite3Integer
+        end
 
         def table_structure(table_name)
-          structure = exec_query("PRAGMA table_info(#{quote_table_name(table_name)})", 'SCHEMA')
+          structure = exec_query("PRAGMA table_info(#{quote_table_name(table_name)})", "SCHEMA")
           raise(ActiveRecord::StatementInvalid, "Could not find table '#{table_name}'") if structure.empty?
           table_structure_with_collation(table_name, structure)
         end
+        alias column_definitions table_structure
+
+        # See: https://www.sqlite.org/lang_altertable.html
+        # SQLite has an additional restriction on the ALTER TABLE statement
+        def invalid_alter_table_type?(type, options)
+          type.to_sym == :primary_key || options[:primary_key]
+        end
 
-        def alter_table(table_name, options = {}) #:nodoc:
+        def alter_table(table_name, options = {})
           altered_table_name = "a#{table_name}"
-          caller = lambda {|definition| yield definition if block_given?}
+          foreign_keys = foreign_keys(table_name)
+
+          caller = lambda do |definition|
+            rename = options[:rename] || {}
+            foreign_keys.each do |fk|
+              if column = rename[fk.options[:column]]
+                fk.options[:column] = column
+              end
+              definition.foreign_key(fk.to_table, fk.options)
+            end
+
+            yield definition if block_given?
+          end
 
           transaction do
-            move_table(table_name, altered_table_name,
-              options.merge(:temporary => true))
-            move_table(altered_table_name, table_name, &caller)
+            disable_referential_integrity do
+              move_table(table_name, altered_table_name, options.merge(temporary: true))
+              move_table(altered_table_name, table_name, &caller)
+            end
           end
         end
 
-        def move_table(from, to, options = {}, &block) #:nodoc:
+        def move_table(from, to, options = {}, &block)
           copy_table(from, to, options, &block)
           drop_table(from)
         end
 
-        def copy_table(from, to, options = {}) #:nodoc:
+        def copy_table(from, to, options = {})
           from_primary_key = primary_key(from)
           options[:id] = false
           create_table(to, options) do |definition|
             @definition = definition
-            @definition.primary_key(from_primary_key) if from_primary_key.present?
+            if from_primary_key.is_a?(Array)
+              @definition.primary_keys from_primary_key
+            end
             columns(from).each do |column|
               column_name = options[:rename] ?
                 (options[:rename][column.name] ||
                  options[:rename][column.name.to_sym] ||
                  column.name) : column.name
-              next if column_name == from_primary_key
 
               @definition.column(column_name, column.type,
-                :limit => column.limit, :default => column.default,
-                :precision => column.precision, :scale => column.scale,
-                :null => column.null, collation: column.collation)
+                limit: column.limit, default: column.default,
+                precision: column.precision, scale: column.scale,
+                null: column.null, collation: column.collation,
+                primary_key: column_name == from_primary_key
+              )
             end
+
             yield @definition if block_given?
           end
           copy_table_indexes(from, to, options[:rename] || {})
@@ -510,7 +485,7 @@ module ActiveRecord
             options[:rename] || {})
         end
 
-        def copy_table_indexes(from, to, rename = {}) #:nodoc:
+        def copy_table_indexes(from, to, rename = {})
           indexes(from).each do |index|
             name = index.name
             if to == "a#{from}"
@@ -519,35 +494,39 @@ module ActiveRecord
               name = name[1..-1]
             end
 
-            to_column_names = columns(to).map(&:name)
-            columns = index.columns.map {|c| rename[c] || c }.select do |column|
-              to_column_names.include?(column)
+            columns = index.columns
+            if columns.is_a?(Array)
+              to_column_names = columns(to).map(&:name)
+              columns = columns.map { |c| rename[c] || c }.select do |column|
+                to_column_names.include?(column)
+              end
             end
 
             unless columns.empty?
               # index name can't be the same
               opts = { name: name.gsub(/(^|_)(#{from})_/, "\\1#{to}_"), internal: true }
               opts[:unique] = true if index.unique
+              opts[:where] = index.where if index.where
               add_index(to, columns, opts)
             end
           end
         end
 
-        def copy_table_contents(from, to, columns, rename = {}) #:nodoc:
-          column_mappings = Hash[columns.map {|name| [name, name]}]
+        def copy_table_contents(from, to, columns, rename = {})
+          column_mappings = Hash[columns.map { |name| [name, name] }]
           rename.each { |a| column_mappings[a.last] = a.first }
           from_columns = columns(from).collect(&:name)
-          columns = columns.find_all{|col| from_columns.include?(column_mappings[col])}
+          columns = columns.find_all { |col| from_columns.include?(column_mappings[col]) }
           from_columns_to_copy = columns.map { |col| column_mappings[col] }
-          quoted_columns = columns.map { |col| quote_column_name(col) } * ','
-          quoted_from_columns = from_columns_to_copy.map { |col| quote_column_name(col) } * ','
+          quoted_columns = columns.map { |col| quote_column_name(col) } * ","
+          quoted_from_columns = from_columns_to_copy.map { |col| quote_column_name(col) } * ","
 
           exec_query("INSERT INTO #{quote_table_name(to)} (#{quoted_columns})
                      SELECT #{quoted_from_columns} FROM #{quote_table_name(from)}")
         end
 
         def sqlite_version
-          @sqlite_version ||= SQLite3Adapter::Version.new(select_value('select sqlite_version(*)'))
+          @sqlite_version ||= SQLite3Adapter::Version.new(query_value("SELECT sqlite_version(*)"))
         end
 
         def translate_exception(exception, message)
@@ -557,51 +536,76 @@ module ActiveRecord
           # Older versions of SQLite return:
           #   column *column_name* is not unique
           when /column(s)? .* (is|are) not unique/, /UNIQUE constraint failed: .*/
-            RecordNotUnique.new(message, exception)
+            RecordNotUnique.new(message)
+          when /.* may not be NULL/, /NOT NULL constraint failed: .*/
+            NotNullViolation.new(message)
+          when /FOREIGN KEY constraint failed/i
+            InvalidForeignKey.new(message)
           else
             super
           end
         end
 
-      private
         COLLATE_REGEX = /.*\"(\w+)\".*collate\s+\"(\w+)\".*/i.freeze
 
         def table_structure_with_collation(table_name, basic_structure)
           collation_hash = {}
-          sql            = "SELECT sql FROM
-                              (SELECT * FROM sqlite_master UNION ALL
-                               SELECT * FROM sqlite_temp_master)
-                            WHERE type='table' and name='#{ table_name }' \;"
+          sql = <<-SQL
+            SELECT sql FROM
+              (SELECT * FROM sqlite_master UNION ALL
+               SELECT * FROM sqlite_temp_master)
+            WHERE type = 'table' AND name = #{quote(table_name)}
+          SQL
 
           # Result will have following sample string
           # CREATE TABLE "users" ("id" INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL,
           #                       "password_digest" varchar COLLATE "NOCASE");
-          result = exec_query(sql, 'SCHEMA').first
+          result = exec_query(sql, "SCHEMA").first
 
           if result
-            # Splitting with left parantheses and picking up last will return all
+            # Splitting with left parentheses and picking up last will return all
             # columns separated with comma(,).
-            columns_string = result["sql"].split('(').last
+            columns_string = result["sql"].split("(").last
 
-            columns_string.split(',').each do |column_string|
+            columns_string.split(",").each do |column_string|
               # This regex will match the column name and collation type and will save
               # the value in $1 and $2 respectively.
-              collation_hash[$1] = $2 if (COLLATE_REGEX =~ column_string)
+              collation_hash[$1] = $2 if COLLATE_REGEX =~ column_string
             end
 
             basic_structure.map! do |column|
-              column_name = column['name']
+              column_name = column["name"]
 
               if collation_hash.has_key? column_name
-                column['collation'] = collation_hash[column_name]
+                column["collation"] = collation_hash[column_name]
               end
 
               column
             end
           else
-            basic_structure.to_hash
+            basic_structure.to_a
           end
         end
+
+        def arel_visitor
+          Arel::Visitors::SQLite.new(self)
+        end
+
+        def configure_connection
+          execute("PRAGMA foreign_keys = ON", "SCHEMA")
+        end
+
+        class SQLite3Integer < Type::Integer # :nodoc:
+          private
+            def _limit
+              # INTEGER storage class can be stored 8 bytes value.
+              # See https://www.sqlite.org/datatype3.html#storage_classes_and_datatypes
+              limit || 8
+            end
+        end
+
+        ActiveRecord::Type.register(:integer, SQLite3Integer, adapter: :sqlite3)
     end
+    ActiveSupport.run_load_hooks(:active_record_sqlite3adapter, SQLite3Adapter)
   end
 end
diff --git a/activerecord/lib/active_record/connection_adapters/statement_pool.rb b/activerecord/lib/active_record/connection_adapters/statement_pool.rb
index 82e9ef3d3d..46bd831da7 100644
--- a/activerecord/lib/active_record/connection_adapters/statement_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/statement_pool.rb
@@ -1,12 +1,15 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionAdapters
-    class StatementPool
+    class StatementPool # :nodoc:
       include Enumerable
 
-      def initialize(connection, max = 1000)
-        @cache = Hash.new { |h,pid| h[pid] = {} }
-        @connection = connection
-        @max        = max
+      DEFAULT_STATEMENT_LIMIT = 1000
+
+      def initialize(statement_limit = nil)
+        @cache = Hash.new { |h, pid| h[pid] = {} }
+        @statement_limit = statement_limit || DEFAULT_STATEMENT_LIMIT
       end
 
       def each(&block)
@@ -26,7 +29,7 @@ module ActiveRecord
       end
 
       def []=(sql, stmt)
-        while @max <= cache.size
+        while @statement_limit <= cache.size
           dealloc(cache.shift.last)
         end
         cache[sql] = stmt
@@ -46,13 +49,13 @@ module ActiveRecord
 
       private
 
-      def cache
-        @cache[Process.pid]
-      end
+        def cache
+          @cache[Process.pid]
+        end
 
-      def dealloc(stmt)
-        raise NotImplementedError
-      end
+        def dealloc(stmt)
+          raise NotImplementedError
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/connection_handling.rb b/activerecord/lib/active_record/connection_handling.rb
index d6b661ff76..3ce9aad5fc 100644
--- a/activerecord/lib/active_record/connection_handling.rb
+++ b/activerecord/lib/active_record/connection_handling.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionHandling
-    RAILS_ENV   = -> { (Rails.env if defined?(Rails.env)) || ENV["RAILS_ENV"] || ENV["RACK_ENV"] }
+    RAILS_ENV   = -> { (Rails.env if defined?(Rails.env)) || ENV["RAILS_ENV"].presence || ENV["RACK_ENV"].presence }
     DEFAULT_ENV = -> { RAILS_ENV.call || "default_env" }
 
     # Establishes the connection to the database. Accepts a hash as input where
@@ -8,7 +10,7 @@ module ActiveRecord
     # example for regular databases (MySQL, PostgreSQL, etc):
     #
     #   ActiveRecord::Base.establish_connection(
-    #     adapter:  "mysql",
+    #     adapter:  "mysql2",
     #     host:     "localhost",
     #     username: "myuser",
     #     password: "mypass",
@@ -35,49 +37,120 @@ module ActiveRecord
     #     "postgres://myuser:mypass@localhost/somedatabase"
     #   )
     #
-    # In case <tt>ActiveRecord::Base.configurations</tt> is set (Rails
-    # automatically loads the contents of config/database.yml into it),
+    # In case {ActiveRecord::Base.configurations}[rdoc-ref:Core.configurations]
+    # is set (Rails automatically loads the contents of config/database.yml into it),
     # a symbol can also be given as argument, representing a key in the
     # configuration hash:
     #
     #   ActiveRecord::Base.establish_connection(:production)
     #
-    # The exceptions AdapterNotSpecified, AdapterNotFound and ArgumentError
+    # The exceptions AdapterNotSpecified, AdapterNotFound and +ArgumentError+
     # may be returned on an error.
-    def establish_connection(spec = nil)
-      spec     ||= DEFAULT_ENV.call.to_sym
-      resolver =   ConnectionAdapters::ConnectionSpecification::Resolver.new configurations
-      spec     =   resolver.spec(spec)
+    def establish_connection(config_or_env = nil)
+      config_hash = resolve_config_for_connection(config_or_env)
+      connection_handler.establish_connection(config_hash)
+    end
 
-      unless respond_to?(spec.adapter_method)
-        raise AdapterNotFound, "database configuration specifies nonexistent #{spec.config[:adapter]} adapter"
+    # Connects a model to the databases specified. The +database+ keyword
+    # takes a hash consisting of a +role+ and a +database_key+.
+    #
+    # This will create a connection handler for switching between connections,
+    # look up the config hash using the +database_key+ and finally
+    # establishes a connection to that config.
+    #
+    #   class AnimalsModel < ApplicationRecord
+    #     self.abstract_class = true
+    #
+    #     connects_to database: { writing: :primary, reading: :primary_replica }
+    #   end
+    #
+    # Returns an array of established connections.
+    def connects_to(database: {})
+      connections = []
+
+      database.each do |role, database_key|
+        config_hash = resolve_config_for_connection(database_key)
+        handler = lookup_connection_handler(role.to_sym)
+
+        connections << handler.establish_connection(config_hash)
       end
 
-      remove_connection
-      connection_handler.establish_connection self, spec
+      connections
     end
 
-    class MergeAndResolveDefaultUrlConfig # :nodoc:
-      def initialize(raw_configurations)
-        @raw_config = raw_configurations.dup
-        @env = DEFAULT_ENV.call.to_s
-      end
+    # Connects to a database or role (ex writing, reading, or another
+    # custom role) for the duration of the block.
+    #
+    # If a role is passed, Active Record will look up the connection
+    # based on the requested role:
+    #
+    #   ActiveRecord::Base.connected_to(role: :writing) do
+    #     Dog.create! # creates dog using dog connection
+    #   end
+    #
+    #   ActiveRecord::Base.connected_to(role: :reading) do
+    #     Dog.create! # throws exception because we're on a replica
+    #   end
+    #
+    #   ActiveRecord::Base.connected_to(role: :unknown_ode) do
+    #     # raises exception due to non-existent role
+    #   end
+    #
+    # For cases where you may want to connect to a database outside of the model,
+    # you can use +connected_to+ with a +database+ argument. The +database+ argument
+    # expects a symbol that corresponds to the database key in your config.
+    #
+    # This will connect to a new database for the queries inside the block.
+    #
+    #   ActiveRecord::Base.connected_to(database: :animals_slow_replica) do
+    #     Dog.run_a_long_query # runs a long query while connected to the +animals_slow_replica+
+    #   end
+    def connected_to(database: nil, role: nil, &blk)
+      if database && role
+        raise ArgumentError, "connected_to can only accept a `database` or a `role` argument, but not both arguments."
+      elsif database
+        if database.is_a?(Hash)
+          role, database = database.first
+          role = role.to_sym
+        else
+          role = database.to_sym
+        end
 
-      # Returns fully resolved connection hashes.
-      # Merges connection information from `ENV['DATABASE_URL']` if available.
-      def resolve
-        ConnectionAdapters::ConnectionSpecification::Resolver.new(config).resolve_all
-      end
+        config_hash = resolve_config_for_connection(database)
+        handler = lookup_connection_handler(role)
 
-      private
-        def config
-          @raw_config.dup.tap do |cfg|
-            if url = ENV['DATABASE_URL']
-              cfg[@env] ||= {}
-              cfg[@env]["url"] ||= url
-            end
-          end
+        with_handler(role) do
+          handler.establish_connection(config_hash)
+          yield
         end
+      elsif role
+        with_handler(role.to_sym, &blk)
+      else
+        raise ArgumentError, "must provide a `database` or a `role`."
+      end
+    end
+
+    def lookup_connection_handler(handler_key) # :nodoc:
+      connection_handlers[handler_key] ||= ActiveRecord::ConnectionAdapters::ConnectionHandler.new
+    end
+
+    def with_handler(handler_key, &blk) # :nodoc:
+      handler = lookup_connection_handler(handler_key)
+      swap_connection_handler(handler, &blk)
+    end
+
+    def resolve_config_for_connection(config_or_env) # :nodoc:
+      raise "Anonymous class is not allowed." unless name
+
+      config_or_env ||= DEFAULT_ENV.call.to_sym
+      pool_name = self == Base ? "primary" : name
+      self.connection_specification_name = pool_name
+
+      resolver = ConnectionAdapters::ConnectionSpecification::Resolver.new(Base.configurations)
+      config_hash = resolver.resolve(config_or_env, pool_name).symbolize_keys
+      config_hash[:name] = pool_name
+
+      config_hash
     end
 
     # Returns the connection currently associated with the class. This can
@@ -87,12 +160,14 @@ module ActiveRecord
       retrieve_connection
     end
 
-    def connection_id
-      ActiveRecord::RuntimeRegistry.connection_id ||= Thread.current.object_id
-    end
+    attr_writer :connection_specification_name
 
-    def connection_id=(connection_id)
-      ActiveRecord::RuntimeRegistry.connection_id = connection_id
+    # Return the specification name from the current class or its parent.
+    def connection_specification_name
+      if !defined?(@connection_specification_name) || @connection_specification_name.nil?
+        return self == Base ? "primary" : superclass.connection_specification_name
+      end
+      @connection_specification_name
     end
 
     # Returns the configuration of the associated connection as a hash:
@@ -106,20 +181,28 @@ module ActiveRecord
     end
 
     def connection_pool
-      connection_handler.retrieve_connection_pool(self) or raise ConnectionNotEstablished
+      connection_handler.retrieve_connection_pool(connection_specification_name) || raise(ConnectionNotEstablished)
     end
 
     def retrieve_connection
-      connection_handler.retrieve_connection(self)
+      connection_handler.retrieve_connection(connection_specification_name)
     end
 
     # Returns +true+ if Active Record is connected.
     def connected?
-      connection_handler.connected?(self)
+      connection_handler.connected?(connection_specification_name)
     end
 
-    def remove_connection(klass = self)
-      connection_handler.remove_connection(klass)
+    def remove_connection(name = nil)
+      name ||= @connection_specification_name if defined?(@connection_specification_name)
+      # if removing a connection that has a pool, we reset the
+      # connection_specification_name so it will use the parent
+      # pool.
+      if connection_handler.retrieve_connection_pool(name)
+        self.connection_specification_name = nil
+      end
+
+      connection_handler.remove_connection(name)
     end
 
     def clear_cache! # :nodoc:
@@ -127,6 +210,15 @@ module ActiveRecord
     end
 
     delegate :clear_active_connections!, :clear_reloadable_connections!,
-      :clear_all_connections!, :to => :connection_handler
+      :clear_all_connections!, :flush_idle_connections!, to: :connection_handler
+
+    private
+
+      def swap_connection_handler(handler, &blk) # :nodoc:
+        old_handler, ActiveRecord::Base.connection_handler = ActiveRecord::Base.connection_handler, handler
+        yield
+      ensure
+        ActiveRecord::Base.connection_handler = old_handler
+      end
   end
 end
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 8a014e682e..50f3087c51 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -1,7 +1,9 @@
-require 'thread'
-require 'active_support/core_ext/hash/indifferent_access'
-require 'active_support/core_ext/object/duplicable'
-require 'active_support/core_ext/string/filters'
+# frozen_string_literal: true
+
+require "active_support/core_ext/hash/indifferent_access"
+require "active_support/core_ext/string/filters"
+require "active_support/parameter_filter"
+require "concurrent/map"
 
 module ActiveRecord
   module Core
@@ -17,8 +19,15 @@ module ActiveRecord
       mattr_accessor :logger, instance_writer: false
 
       ##
+      # :singleton-method:
+      #
+      # Specifies if the methods calling database queries should be logged below
+      # their relevant queries. Defaults to false.
+      mattr_accessor :verbose_query_logs, instance_writer: false, default: false
+
+      ##
       # Contains the database configuration - as is typically stored in config/database.yml -
-      # as a Hash.
+      # as an ActiveRecord::DatabaseConfigurations object.
       #
       # For example, the following database.yml...
       #
@@ -32,22 +41,18 @@ module ActiveRecord
       #
       # ...would result in ActiveRecord::Base.configurations to look like this:
       #
-      #   {
-      #      'development' => {
-      #         'adapter'  => 'sqlite3',
-      #         'database' => 'db/development.sqlite3'
-      #      },
-      #      'production' => {
-      #         'adapter'  => 'sqlite3',
-      #         'database' => 'db/production.sqlite3'
-      #      }
-      #   }
+      #   #<ActiveRecord::DatabaseConfigurations:0x00007fd1acbdf800 @configurations=[
+      #     #<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fd1acbded10 @env_name="development",
+      #       @spec_name="primary", @config={"adapter"=>"sqlite3", "database"=>"db/development.sqlite3"}>,
+      #     #<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fd1acbdea90 @env_name="production",
+      #       @spec_name="primary", @config={"adapter"=>"mysql2", "database"=>"db/production.sqlite3"}>
+      #   ]>
       def self.configurations=(config)
-        @@configurations = ActiveRecord::ConnectionHandling::MergeAndResolveDefaultUrlConfig.new(config).resolve
+        @@configurations = ActiveRecord::DatabaseConfigurations.new(config)
       end
       self.configurations = {}
 
-      # Returns fully resolved configurations hash
+      # Returns fully resolved ActiveRecord::DatabaseConfigurations object
       def self.configurations
         @@configurations
       end
@@ -56,8 +61,7 @@ module ActiveRecord
       # :singleton-method:
       # Determines whether to use Time.utc (using :utc) or Time.local (using :local) when pulling
       # dates and times from the database. This is set to :utc by default.
-      mattr_accessor :default_timezone, instance_writer: false
-      self.default_timezone = :utc
+      mattr_accessor :default_timezone, instance_writer: false, default: :utc
 
       ##
       # :singleton-method:
@@ -67,23 +71,35 @@ module ActiveRecord
       # ActiveRecord::Schema file which can be loaded into any database that
       # supports migrations. Use :ruby if you want to have different database
       # adapters for, e.g., your development and test environments.
-      mattr_accessor :schema_format, instance_writer: false
-      self.schema_format = :ruby
+      mattr_accessor :schema_format, instance_writer: false, default: :ruby
+
+      ##
+      # :singleton-method:
+      # Specifies if an error should be raised if the query has an order being
+      # ignored when doing batch queries. Useful in applications where the
+      # scope being ignored is error-worthy, rather than a warning.
+      mattr_accessor :error_on_ignored_order, instance_writer: false, default: false
+
+      # :singleton-method:
+      # Specify the behavior for unsafe raw query methods. Values are as follows
+      #   deprecated - Warnings are logged when unsafe raw SQL is passed to
+      #                query methods.
+      #   disabled   - Unsafe raw SQL passed to query methods results in
+      #                UnknownAttributeReference exception.
+      mattr_accessor :allow_unsafe_raw_sql, instance_writer: false, default: :deprecated
 
       ##
       # :singleton-method:
       # Specify whether or not to use timestamps for migration versions
-      mattr_accessor :timestamped_migrations, instance_writer: false
-      self.timestamped_migrations = true
+      mattr_accessor :timestamped_migrations, instance_writer: false, default: true
 
       ##
       # :singleton-method:
       # Specify whether schema dump should happen at the end of the
-      # db:migrate rake task. This is true by default, which is useful for the
+      # db:migrate rails command. This is true by default, which is useful for the
       # development environment. This should ideally be false in the production
       # environment where dumping schema is rarely needed.
-      mattr_accessor :dump_schema_after_migration, instance_writer: false
-      self.dump_schema_after_migration = true
+      mattr_accessor :dump_schema_after_migration, instance_writer: false, default: true
 
       ##
       # :singleton-method:
@@ -92,8 +108,7 @@ module ActiveRecord
       # schema_search_path are dumped. Use :all to dump all schemas regardless
       # of schema_search_path, or a string of comma separated schemas for a
       # custom list.
-      mattr_accessor :dump_schemas, instance_writer: false
-      self.dump_schemas = :schema_search_path
+      mattr_accessor :dump_schemas, instance_writer: false, default: :schema_search_path
 
       ##
       # :singleton-method:
@@ -102,14 +117,17 @@ module ActiveRecord
       # be used to identify queries which load thousands of records and
       # potentially cause memory bloat.
       mattr_accessor :warn_on_records_fetched_greater_than, instance_writer: false
-      self.warn_on_records_fetched_greater_than = nil
 
       mattr_accessor :maintain_test_schema, instance_accessor: false
 
       mattr_accessor :belongs_to_required_by_default, instance_accessor: false
 
+      mattr_accessor :connection_handlers, instance_accessor: false, default: {}
+
       class_attribute :default_connection_handler, instance_writer: false
 
+      self.filter_attributes = []
+
       def self.connection_handler
         ActiveRecord::RuntimeRegistry.connection_handler || default_connection_handler
       end
@@ -119,16 +137,12 @@ module ActiveRecord
       end
 
       self.default_connection_handler = ConnectionAdapters::ConnectionHandler.new
+      self.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
     end
 
     module ClassMethods
-      def allocate
-        define_attribute_methods
-        super
-      end
-
       def initialize_find_by_cache # :nodoc:
-        @find_by_statement_cache = {}.extend(Mutex_m)
+        @find_by_statement_cache = { true => Concurrent::Map.new, false => Concurrent::Map.new }
       end
 
       def inherited(child_class) # :nodoc:
@@ -143,39 +157,36 @@ module ActiveRecord
         return super if block_given? ||
                         primary_key.nil? ||
                         scope_attributes? ||
-                        columns_hash.include?(inheritance_column) ||
-                        ids.first.kind_of?(Array)
-
-        id  = ids.first
-        if ActiveRecord::Base === id
-          id = id.id
-          ActiveSupport::Deprecation.warn(<<-MSG.squish)
-            You are passing an instance of ActiveRecord::Base to `find`.
-            Please pass the id of the object by calling `.id`
-          MSG
-        end
+                        columns_hash.include?(inheritance_column)
+
+        id = ids.first
+
+        return super if StatementCache.unsupported_value?(id)
 
         key = primary_key
 
         statement = cached_find_by_statement(key) { |params|
           where(key => params.bind).limit(1)
         }
-        record = statement.execute([id], self, connection).first
+
+        record = statement.execute([id], connection).first
         unless record
-          raise RecordNotFound, "Couldn't find #{name} with '#{primary_key}'=#{id}"
+          raise RecordNotFound.new("Couldn't find #{name} with '#{primary_key}'=#{id}",
+                                   name, primary_key, id)
         end
         record
-      rescue RangeError
-        raise RecordNotFound, "Couldn't find #{name} with an out of range value for '#{primary_key}'"
+      rescue ::RangeError
+        raise RecordNotFound.new("Couldn't find #{name} with an out of range value for '#{primary_key}'",
+                                 name, primary_key)
       end
 
       def find_by(*args) # :nodoc:
-        return super if scope_attributes? || !(Hash === args.first) || reflect_on_all_aggregations.any?
+        return super if scope_attributes? || reflect_on_all_aggregations.any?
 
         hash = args.first
 
-        return super if hash.values.any? { |v|
-          v.nil? || Array === v || Hash === v
+        return super if !(Hash === hash) || hash.values.any? { |v|
+          StatementCache.unsupported_value?(v)
         }
 
         # We can't cache Post.find_by(author: david) ...yet
@@ -190,32 +201,46 @@ module ActiveRecord
           where(wheres).limit(1)
         }
         begin
-          statement.execute(hash.values, self, connection).first
-        rescue TypeError => e
-          raise ActiveRecord::StatementInvalid.new(e.message, e)
-        rescue RangeError
+          statement.execute(hash.values, connection).first
+        rescue TypeError
+          raise ActiveRecord::StatementInvalid
+        rescue ::RangeError
           nil
         end
       end
 
       def find_by!(*args) # :nodoc:
-        find_by(*args) or raise RecordNotFound.new("Couldn't find #{name}")
+        find_by(*args) || raise(RecordNotFound.new("Couldn't find #{name}", name))
       end
 
       def initialize_generated_modules # :nodoc:
         generated_association_methods
       end
 
-      def generated_association_methods
+      def generated_association_methods # :nodoc:
         @generated_association_methods ||= begin
           mod = const_set(:GeneratedAssociationMethods, Module.new)
+          private_constant :GeneratedAssociationMethods
           include mod
+
           mod
         end
       end
 
+      # Returns columns which shouldn't be exposed while calling +#inspect+.
+      def filter_attributes
+        if defined?(@filter_attributes)
+          @filter_attributes
+        else
+          superclass.filter_attributes
+        end
+      end
+
+      # Specifies columns which shouldn't be exposed while calling +#inspect+.
+      attr_writer :filter_attributes
+
       # Returns a string like 'Post(id:integer, title:string, body:text)'
-      def inspect
+      def inspect # :nodoc:
         if self == Base
           super
         elsif abstract_class?
@@ -223,35 +248,30 @@ module ActiveRecord
         elsif !connected?
           "#{super} (call '#{super}.connection' to establish a connection)"
         elsif table_exists?
-          attr_list = attribute_types.map { |name, type| "#{name}: #{type.type}" } * ', '
+          attr_list = attribute_types.map { |name, type| "#{name}: #{type.type}" } * ", "
           "#{super}(#{attr_list})"
         else
           "#{super}(Table doesn't exist)"
         end
       end
 
-      # Overwrite the default class equality method to provide support for association proxies.
-      def ===(object)
+      # Overwrite the default class equality method to provide support for decorated models.
+      def ===(object) # :nodoc:
         object.is_a?(self)
       end
 
       # Returns an instance of <tt>Arel::Table</tt> loaded with the current table name.
       #
       #   class Post < ActiveRecord::Base
-      #     scope :published_and_commented, -> { published.and(self.arel_table[:comments_count].gt(0)) }
+      #     scope :published_and_commented, -> { published.and(arel_table[:comments_count].gt(0)) }
       #   end
       def arel_table # :nodoc:
         @arel_table ||= Arel::Table.new(table_name, type_caster: type_caster)
       end
 
-      # Returns the Arel engine.
-      def arel_engine # :nodoc:
-        @arel_engine ||=
-          if Base == self || connection_handler.retrieve_connection_pool(self)
-            self
-          else
-            superclass.arel_engine
-          end
+      def arel_attribute(name, table = arel_table) # :nodoc:
+        name = attribute_alias(name) if attribute_alias?(name)
+        table[name]
       end
 
       def predicate_builder # :nodoc:
@@ -264,25 +284,25 @@ module ActiveRecord
 
       private
 
-      def cached_find_by_statement(key, &block) # :nodoc:
-        @find_by_statement_cache[key] || @find_by_statement_cache.synchronize {
-          @find_by_statement_cache[key] ||= StatementCache.create(connection, &block)
-        }
-      end
+        def cached_find_by_statement(key, &block)
+          cache = @find_by_statement_cache[connection.prepared_statements]
+          cache.compute_if_absent(key) { StatementCache.create(connection, &block) }
+        end
 
-      def relation # :nodoc:
-        relation = Relation.create(self, arel_table, predicate_builder)
+        def relation
+          relation = Relation.create(self)
 
-        if finder_needs_type_condition?
-          relation.where(type_condition).create_with(inheritance_column.to_sym => sti_name)
-        else
-          relation
+          if finder_needs_type_condition? && !ignore_default_scope?
+            relation.where!(type_condition)
+            relation.create_with!(inheritance_column.to_s => sti_name)
+          else
+            relation
+          end
         end
-      end
 
-      def table_metadata # :nodoc:
-        TableMetadata.new(self, arel_table)
-      end
+        def table_metadata
+          TableMetadata.new(self, arel_table)
+        end
     end
 
     # New objects can be instantiated as either empty (pass no construction parameter) or pre-set with
@@ -294,8 +314,8 @@ module ActiveRecord
     #   # Instantiates a single new object
     #   User.new(first_name: 'Jamie')
     def initialize(attributes = nil)
-      @attributes = self.class._default_attributes.dup
       self.class.define_attribute_methods
+      @attributes = self.class._default_attributes.deep_dup
 
       init_internals
       initialize_internals_callback
@@ -303,12 +323,12 @@ module ActiveRecord
       assign_attributes(attributes) if attributes
 
       yield self if block_given?
-      run_callbacks :initialize
+      _run_initialize_callbacks
     end
 
     # Initialize an empty model object from +coder+. +coder+ should be
     # the result of previously encoding an Active Record model, using
-    # `encode_with`
+    # #encode_with.
     #
     #   class Post < ActiveRecord::Base
     #   end
@@ -320,18 +340,30 @@ module ActiveRecord
     #   post = Post.allocate
     #   post.init_with(coder)
     #   post.title # => 'hello world'
-    def init_with(coder)
+    def init_with(coder, &block)
       coder = LegacyYamlAdapter.convert(self.class, coder)
-      @attributes = coder['attributes']
+      attributes = self.class.yaml_encoder.decode(coder)
+      init_with_attributes(attributes, coder["new_record"], &block)
+    end
 
+    ##
+    # Initialize an empty model object from +attributes+.
+    # +attributes+ should be an attributes object, and unlike the
+    # `initialize` method, no assignment calls are made per attribute.
+    #
+    # :nodoc:
+    def init_with_attributes(attributes, new_record = false)
       init_internals
 
-      @new_record = coder['new_record']
+      @new_record = new_record
+      @attributes = attributes
 
       self.class.define_attribute_methods
 
-      run_callbacks :find
-      run_callbacks :initialize
+      yield self if block_given?
+
+      _run_find_callbacks
+      _run_initialize_callbacks
 
       self
     end
@@ -364,20 +396,22 @@ module ActiveRecord
 
     ##
     def initialize_dup(other) # :nodoc:
-      @attributes = @attributes.dup
+      @attributes = @attributes.deep_dup
       @attributes.reset(self.class.primary_key)
 
-      run_callbacks(:initialize)
+      _run_initialize_callbacks
 
-      @new_record  = true
-      @destroyed   = false
+      @new_record               = true
+      @destroyed                = false
+      @_start_transaction_state = {}
+      @transaction_state        = nil
 
       super
     end
 
     # Populate +coder+ with attributes about this record that should be
     # serialized. The structure of +coder+ defined in this method is
-    # guaranteed to match the structure of +coder+ passed to the +init_with+
+    # guaranteed to match the structure of +coder+ passed to the #init_with
     # method.
     #
     # Example:
@@ -388,11 +422,9 @@ module ActiveRecord
     #   Post.new.encode_with(coder)
     #   coder # => {"attributes" => {"id" => nil, ... }}
     def encode_with(coder)
-      # FIXME: Remove this when we better serialize attributes
-      coder['raw_attributes'] = attributes_before_type_cast
-      coder['attributes'] = @attributes
-      coder['new_record'] = new_record?
-      coder['active_record_yaml_version'] = 1
+      self.class.yaml_encoder.encode(@attributes, coder)
+      coder["new_record"] = new_record?
+      coder["active_record_yaml_version"] = 2
     end
 
     # Returns true if +comparison_object+ is the same exact object, or +comparison_object+
@@ -416,7 +448,7 @@ module ActiveRecord
     #   [ Person.find(1), Person.find(2), Person.find(3) ] & [ Person.find(1), Person.find(4) ] # => [ Person.find(1) ]
     def hash
       if id
-        id.hash
+        self.class.hash ^ id.hash
       else
         super
       end
@@ -438,7 +470,7 @@ module ActiveRecord
     # Allows sort on objects
     def <=>(other_object)
       if other_object.is_a?(self.class)
-        self.to_key <=> other_object.to_key
+        to_key <=> other_object.to_key
       else
         super
       end
@@ -464,82 +496,100 @@ module ActiveRecord
       # We check defined?(@attributes) not to issue warnings if the object is
       # allocated but not initialized.
       inspection = if defined?(@attributes) && @attributes
-                     self.class.column_names.collect { |name|
-                       if has_attribute?(name)
-                         "#{name}: #{attribute_for_inspect(name)}"
-                       end
-                     }.compact.join(", ")
-                   else
-                     "not initialized"
-                   end
+        self.class.attribute_names.collect do |name|
+          if has_attribute?(name)
+            attr = _read_attribute(name)
+            value = if attr.nil?
+              attr.inspect
+            else
+              attr = format_for_inspect(attr)
+              inspection_filter.filter_param(name, attr)
+            end
+            "#{name}: #{value}"
+          end
+        end.compact.join(", ")
+      else
+        "not initialized"
+      end
+
       "#<#{self.class} #{inspection}>"
     end
 
-    # Takes a PP and prettily prints this record to it, allowing you to get a nice result from `pp record`
+    # Takes a PP and prettily prints this record to it, allowing you to get a nice result from <tt>pp record</tt>
     # when pp is required.
     def pretty_print(pp)
       return super if custom_inspect_method_defined?
       pp.object_address_group(self) do
         if defined?(@attributes) && @attributes
-          column_names = self.class.column_names.select { |name| has_attribute?(name) || new_record? }
-          pp.seplist(column_names, proc { pp.text ',' }) do |column_name|
-            column_value = read_attribute(column_name)
-            pp.breakable ' '
+          attr_names = self.class.attribute_names.select { |name| has_attribute?(name) }
+          pp.seplist(attr_names, proc { pp.text "," }) do |attr_name|
+            pp.breakable " "
             pp.group(1) do
-              pp.text column_name
-              pp.text ':'
+              pp.text attr_name
+              pp.text ":"
               pp.breakable
-              pp.pp column_value
+              value = _read_attribute(attr_name)
+              value = inspection_filter.filter_param(attr_name, value) unless value.nil?
+              pp.pp value
             end
           end
         else
-          pp.breakable ' '
-          pp.text 'not initialized'
+          pp.breakable " "
+          pp.text "not initialized"
         end
       end
     end
 
     # Returns a hash of the given methods with their names as keys and returned values as values.
     def slice(*methods)
-      Hash[methods.map! { |method| [method, public_send(method)] }].with_indifferent_access
+      Hash[methods.flatten.map! { |method| [method, public_send(method)] }].with_indifferent_access
     end
 
     private
 
-    # Under Ruby 1.9, Array#flatten will call #to_ary (recursively) on each of the elements
-    # of the array, and then rescues from the possible NoMethodError. If those elements are
-    # ActiveRecord::Base's, then this triggers the various method_missing's that we have,
-    # which significantly impacts upon performance.
-    #
-    # So we can avoid the method_missing hit by explicitly defining #to_ary as nil here.
-    #
-    # See also http://tenderlovemaking.com/2011/06/28/til-its-ok-to-return-nil-from-to_ary.html
-    def to_ary # :nodoc:
-      nil
-    end
+      # +Array#flatten+ will call +#to_ary+ (recursively) on each of the elements of
+      # the array, and then rescues from the possible +NoMethodError+. If those elements are
+      # +ActiveRecord::Base+'s, then this triggers the various +method_missing+'s that we have,
+      # which significantly impacts upon performance.
+      #
+      # So we can avoid the +method_missing+ hit by explicitly defining +#to_ary+ as +nil+ here.
+      #
+      # See also https://tenderlovemaking.com/2011/06/28/til-its-ok-to-return-nil-from-to_ary.html
+      def to_ary
+        nil
+      end
 
-    def init_internals
-      @readonly                 = false
-      @destroyed                = false
-      @marked_for_destruction   = false
-      @destroyed_by_association = nil
-      @new_record               = true
-      @txn                      = nil
-      @_start_transaction_state = {}
-      @transaction_state        = nil
-    end
+      def init_internals
+        @readonly                 = false
+        @destroyed                = false
+        @marked_for_destruction   = false
+        @destroyed_by_association = nil
+        @new_record               = true
+        @_start_transaction_state = {}
+        @transaction_state        = nil
+      end
 
-    def initialize_internals_callback
-    end
+      def initialize_internals_callback
+      end
 
-    def thaw
-      if frozen?
-        @attributes = @attributes.dup
+      def thaw
+        if frozen?
+          @attributes = @attributes.dup
+        end
       end
-    end
 
-    def custom_inspect_method_defined?
-      self.class.instance_method(:inspect).owner != ActiveRecord::Base.instance_method(:inspect).owner
-    end
+      def custom_inspect_method_defined?
+        self.class.instance_method(:inspect).owner != ActiveRecord::Base.instance_method(:inspect).owner
+      end
+
+      def inspection_filter
+        @inspection_filter ||= begin
+          mask = DelegateClass(::String).new(ActiveSupport::ParameterFilter::FILTERED)
+          def mask.pretty_print(pp)
+            pp.text __getobj__
+          end
+          ActiveSupport::ParameterFilter.new(self.class.filter_attributes, mask: mask)
+        end
+      end
   end
 end
diff --git a/activerecord/lib/active_record/counter_cache.rb b/activerecord/lib/active_record/counter_cache.rb
index 82596b63df..27c1b7a311 100644
--- a/activerecord/lib/active_record/counter_cache.rb
+++ b/activerecord/lib/active_record/counter_cache.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # = Active Record Counter Cache
   module CounterCache
@@ -12,13 +14,21 @@ module ActiveRecord
       #
       # * +id+ - The id of the object you wish to reset a counter on.
       # * +counters+ - One or more association counters to reset. Association name or counter name can be given.
+      # * <tt>:touch</tt> - Touch timestamp columns when updating.
+      #   Pass +true+ to touch +updated_at+ and/or +updated_on+. Pass a symbol to
+      #   touch that column or an array of symbols to touch just those ones.
       #
       # ==== Examples
       #
-      #   # For Post with id #1 records reset the comments_count
+      #   # For the Post with id #1, reset the comments_count
       #   Post.reset_counters(1, :comments)
-      def reset_counters(id, *counters)
+      #
+      #   # Like above, but also touch the +updated_at+ and/or +updated_on+
+      #   # attributes.
+      #   Post.reset_counters(1, :comments, touch: true)
+      def reset_counters(id, *counters, touch: nil)
         object = find(id)
+
         counters.each do |counter_association|
           has_many_association = _reflect_on_association(counter_association)
           unless has_many_association
@@ -26,7 +36,7 @@ module ActiveRecord
             has_many_association = has_many.find { |association| association.counter_cache_column && association.counter_cache_column.to_sym == counter_association.to_sym }
             counter_association = has_many_association.plural_name if has_many_association
           end
-          raise ArgumentError, "'#{self.name}' has no association called '#{counter_association}'" unless has_many_association
+          raise ArgumentError, "'#{name}' has no association called '#{counter_association}'" unless has_many_association
 
           if has_many_association.is_a? ActiveRecord::Reflection::ThroughReflection
             has_many_association = has_many_association.through_reflection
@@ -37,24 +47,33 @@ module ActiveRecord
           reflection   = child_class._reflections.values.find { |e| e.belongs_to? && e.foreign_key.to_s == foreign_key && e.options[:counter_cache].present? }
           counter_name = reflection.counter_cache_column
 
-          unscoped.where(primary_key => object.id).update_all(
-            counter_name => object.send(counter_association).count(:all)
-          )
+          updates = { counter_name => object.send(counter_association).count(:all) }
+
+          if touch
+            names = touch if touch != true
+            updates.merge!(touch_attributes_with_time(*names))
+          end
+
+          unscoped.where(primary_key => object.id).update_all(updates)
         end
-        return true
+
+        true
       end
 
       # A generic "counter updater" implementation, intended primarily to be
-      # used by increment_counter and decrement_counter, but which may also
+      # used by #increment_counter and #decrement_counter, but which may also
       # be useful on its own. It simply does a direct SQL update for the record
       # with the given ID, altering the given hash of counters by the amount
       # given by the corresponding value:
       #
       # ==== Parameters
       #
-      # * +id+ - The id of the object you wish to update a counter on or an Array of ids.
+      # * +id+ - The id of the object you wish to update a counter on or an array of ids.
       # * +counters+ - A Hash containing the names of the fields
       #   to update as keys and the amount to update the field by as values.
+      # * <tt>:touch</tt> option - Touch timestamp columns when updating.
+      #   If attribute names are passed, they are updated along with updated_at/on
+      #   attributes.
       #
       # ==== Examples
       #
@@ -73,65 +92,78 @@ module ActiveRecord
       #   # UPDATE posts
       #   #    SET comment_count = COALESCE(comment_count, 0) + 1
       #   #  WHERE id IN (10, 15)
+      #
+      #   # For the Posts with id of 10 and 15, increment the comment_count by 1
+      #   # and update the updated_at value for each counter.
+      #   Post.update_counters [10, 15], comment_count: 1, touch: true
+      #   # Executes the following SQL:
+      #   # UPDATE posts
+      #   #    SET comment_count = COALESCE(comment_count, 0) + 1,
+      #   #    `updated_at` = '2016-10-13T09:59:23-05:00'
+      #   #  WHERE id IN (10, 15)
       def update_counters(id, counters)
-        updates = counters.map do |counter_name, value|
-          operator = value < 0 ? '-' : '+'
-          quoted_column = connection.quote_column_name(counter_name)
-          "#{quoted_column} = COALESCE(#{quoted_column}, 0) #{operator} #{value.abs}"
-        end
-
-        unscoped.where(primary_key => id).update_all updates.join(', ')
+        unscoped.where!(primary_key => id).update_counters(counters)
       end
 
       # Increment a numeric field by one, via a direct SQL update.
       #
       # This method is used primarily for maintaining counter_cache columns that are
-      # used to store aggregate values. For example, a DiscussionBoard may cache
+      # used to store aggregate values. For example, a +DiscussionBoard+ may cache
       # posts_count and comments_count to avoid running an SQL query to calculate the
       # number of posts and comments there are, each time it is displayed.
       #
       # ==== Parameters
       #
       # * +counter_name+ - The name of the field that should be incremented.
-      # * +id+ - The id of the object that should be incremented or an Array of ids.
+      # * +id+ - The id of the object that should be incremented or an array of ids.
+      # * <tt>:touch</tt> - Touch timestamp columns when updating.
+      #   Pass +true+ to touch +updated_at+ and/or +updated_on+. Pass a symbol to
+      #   touch that column or an array of symbols to touch just those ones.
       #
       # ==== Examples
       #
-      #   # Increment the post_count column for the record with an id of 5
-      #   DiscussionBoard.increment_counter(:post_count, 5)
-      def increment_counter(counter_name, id)
-        update_counters(id, counter_name => 1)
+      #   # Increment the posts_count column for the record with an id of 5
+      #   DiscussionBoard.increment_counter(:posts_count, 5)
+      #
+      #   # Increment the posts_count column for the record with an id of 5
+      #   # and update the updated_at value.
+      #   DiscussionBoard.increment_counter(:posts_count, 5, touch: true)
+      def increment_counter(counter_name, id, touch: nil)
+        update_counters(id, counter_name => 1, touch: touch)
       end
 
       # Decrement a numeric field by one, via a direct SQL update.
       #
-      # This works the same as increment_counter but reduces the column value by
+      # This works the same as #increment_counter but reduces the column value by
       # 1 instead of increasing it.
       #
       # ==== Parameters
       #
       # * +counter_name+ - The name of the field that should be decremented.
-      # * +id+ - The id of the object that should be decremented or an Array of ids.
+      # * +id+ - The id of the object that should be decremented or an array of ids.
+      # * <tt>:touch</tt> - Touch timestamp columns when updating.
+      #   Pass +true+ to touch +updated_at+ and/or +updated_on+. Pass a symbol to
+      #   touch that column or an array of symbols to touch just those ones.
       #
       # ==== Examples
       #
-      #   # Decrement the post_count column for the record with an id of 5
-      #   DiscussionBoard.decrement_counter(:post_count, 5)
-      def decrement_counter(counter_name, id)
-        update_counters(id, counter_name => -1)
+      #   # Decrement the posts_count column for the record with an id of 5
+      #   DiscussionBoard.decrement_counter(:posts_count, 5)
+      #
+      #   # Decrement the posts_count column for the record with an id of 5
+      #   # and update the updated_at value.
+      #   DiscussionBoard.decrement_counter(:posts_count, 5, touch: true)
+      def decrement_counter(counter_name, id, touch: nil)
+        update_counters(id, counter_name => -1, touch: touch)
       end
     end
 
     private
-
-      def _create_record(*)
+      def _create_record(attribute_names = self.attribute_names)
         id = super
 
         each_counter_cached_associations do |association|
-          if send(association.reflection.name)
-            association.increment_counters
-            @_after_create_counter_called = true
-          end
+          association.increment_counters
         end
 
         id
@@ -144,9 +176,7 @@ module ActiveRecord
           each_counter_cached_associations do |association|
             foreign_key = association.reflection.foreign_key.to_sym
             unless destroyed_by_association && destroyed_by_association.foreign_key.to_sym == foreign_key
-              if send(association.reflection.name)
-                association.decrement_counters
-              end
+              association.decrement_counters
             end
           end
         end
@@ -159,6 +189,5 @@ module ActiveRecord
           yield association(name.to_sym) if reflection.belongs_to? && reflection.counter_cache_column
         end
       end
-
   end
 end
diff --git a/activerecord/lib/active_record/database_configurations.rb b/activerecord/lib/active_record/database_configurations.rb
new file mode 100644
index 0000000000..30cb0a27e7
--- /dev/null
+++ b/activerecord/lib/active_record/database_configurations.rb
@@ -0,0 +1,186 @@
+# frozen_string_literal: true
+
+require "active_record/database_configurations/database_config"
+require "active_record/database_configurations/hash_config"
+require "active_record/database_configurations/url_config"
+
+module ActiveRecord
+  # ActiveRecord::DatabaseConfigurations returns an array of DatabaseConfig
+  # objects (either a HashConfig or UrlConfig) that are constructed from the
+  # application's database configuration hash or url string.
+  class DatabaseConfigurations
+    attr_reader :configurations
+    delegate :any?, to: :configurations
+
+    def initialize(configurations = {})
+      @configurations = build_configs(configurations)
+    end
+
+    # Collects the configs for the environment and optionally the specification
+    # name passed in. To include replica configurations pass `include_replicas: true`.
+    #
+    # If a spec name is provided a single DatabaseConfig object will be
+    # returned, otherwise an array of DatabaseConfig objects will be
+    # returned that corresponds with the environment and type requested.
+    #
+    # Options:
+    #
+    # <tt>env_name:</tt> The environment name. Defaults to nil which will collect
+    # configs for all environments.
+    # <tt>spec_name:</tt> The specification name (ie primary, animals, etc.). Defaults
+    # to +nil+.
+    # <tt>include_replicas:</tt> Determines whether to include replicas in
+    # the returned list. Most of the time we're only iterating over the write
+    # connection (i.e. migrations don't need to run for the write and read connection).
+    # Defaults to +false+.
+    def configs_for(env_name: nil, spec_name: nil, include_replicas: false)
+      configs = env_with_configs(env_name)
+
+      unless include_replicas
+        configs = configs.select do |db_config|
+          !db_config.replica?
+        end
+      end
+
+      if spec_name
+        configs.find do |db_config|
+          db_config.spec_name == spec_name
+        end
+      else
+        configs
+      end
+    end
+
+    # Returns the config hash that corresponds with the environment
+    #
+    # If the application has multiple databases `default_hash` will
+    # return the first config hash for the environment.
+    #
+    #   { database: "my_db", adapter: "mysql2" }
+    def default_hash(env = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call.to_s)
+      default = find_db_config(env)
+      default.config if default
+    end
+    alias :[] :default_hash
+
+    # Returns a single DatabaseConfig object based on the requested environment.
+    #
+    # If the application has multiple databases `find_db_config` will return
+    # the first DatabaseConfig for the environment.
+    def find_db_config(env)
+      configurations.find do |db_config|
+        db_config.env_name == env.to_s ||
+          (db_config.for_current_env? && db_config.spec_name == env.to_s)
+      end
+    end
+
+    # Returns the DatabaseConfigurations object as a Hash.
+    def to_h
+      configs = configurations.reverse.inject({}) do |memo, db_config|
+        memo.merge(db_config.to_legacy_hash)
+      end
+
+      Hash[configs.to_a.reverse]
+    end
+
+    # Checks if the application's configurations are empty.
+    #
+    # Aliased to blank?
+    def empty?
+      configurations.empty?
+    end
+    alias :blank? :empty?
+
+    private
+      def env_with_configs(env = nil)
+        if env
+          configurations.select { |db_config| db_config.env_name == env }
+        else
+          configurations
+        end
+      end
+
+      def build_configs(configs)
+        return configs.configurations if configs.is_a?(DatabaseConfigurations)
+
+        build_db_config = configs.each_pair.flat_map do |env_name, config|
+          walk_configs(env_name.to_s, "primary", config)
+        end.compact
+
+        if url = ENV["DATABASE_URL"]
+          build_url_config(url, build_db_config)
+        else
+          build_db_config
+        end
+      end
+
+      def walk_configs(env_name, spec_name, config)
+        case config
+        when String
+          build_db_config_from_string(env_name, spec_name, config)
+        when Hash
+          build_db_config_from_hash(env_name, spec_name, config.stringify_keys)
+        end
+      end
+
+      def build_db_config_from_string(env_name, spec_name, config)
+        begin
+          url = config
+          uri = URI.parse(url)
+          if uri.try(:scheme)
+            ActiveRecord::DatabaseConfigurations::UrlConfig.new(env_name, spec_name, url)
+          end
+        rescue URI::InvalidURIError
+          ActiveRecord::DatabaseConfigurations::HashConfig.new(env_name, spec_name, config)
+        end
+      end
+
+      def build_db_config_from_hash(env_name, spec_name, config)
+        if url = config["url"]
+          config_without_url = config.dup
+          config_without_url.delete "url"
+          ActiveRecord::DatabaseConfigurations::UrlConfig.new(env_name, spec_name, url, config_without_url)
+        elsif config["database"] || (config.size == 1 && config.values.all? { |v| v.is_a? String })
+          ActiveRecord::DatabaseConfigurations::HashConfig.new(env_name, spec_name, config)
+        else
+          config.each_pair.map do |sub_spec_name, sub_config|
+            walk_configs(env_name, sub_spec_name, sub_config)
+          end
+        end
+      end
+
+      def build_url_config(url, configs)
+        env = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call.to_s
+
+        if original_config = configs.find(&:for_current_env?)
+          if original_config.url_config?
+            configs
+          else
+            configs.map do |config|
+              ActiveRecord::DatabaseConfigurations::UrlConfig.new(env, config.spec_name, url, config.config)
+            end
+          end
+        else
+          configs + [ActiveRecord::DatabaseConfigurations::UrlConfig.new(env, "primary", url)]
+        end
+      end
+
+      def method_missing(method, *args, &blk)
+        if Hash.method_defined?(method)
+          ActiveSupport::Deprecation.warn \
+            "Returning a hash from ActiveRecord::Base.configurations is deprecated. Therefore calling `#{method}` on the hash is also deprecated. Please switch to using the `configs_for` method instead to collect and iterate over database configurations."
+        end
+
+        case method
+        when :each, :first
+          configurations.send(method, *args, &blk)
+        when :fetch
+          configs_for(env_name: args.first)
+        when :values
+          configurations.map(&:config)
+        else
+          super
+        end
+      end
+  end
+end
diff --git a/activerecord/lib/active_record/database_configurations/database_config.rb b/activerecord/lib/active_record/database_configurations/database_config.rb
new file mode 100644
index 0000000000..adc37cc439
--- /dev/null
+++ b/activerecord/lib/active_record/database_configurations/database_config.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class DatabaseConfigurations
+    # ActiveRecord::Base.configurations will return either a HashConfig or
+    # UrlConfig respectively. It will never return a DatabaseConfig object,
+    # as this is the parent class for the types of database configuration objects.
+    class DatabaseConfig # :nodoc:
+      attr_reader :env_name, :spec_name
+
+      def initialize(env_name, spec_name)
+        @env_name = env_name
+        @spec_name = spec_name
+      end
+
+      def replica?
+        raise NotImplementedError
+      end
+
+      def migrations_paths
+        raise NotImplementedError
+      end
+
+      def url_config?
+        false
+      end
+
+      def to_legacy_hash
+        { env_name => config }
+      end
+
+      def for_current_env?
+        env_name == ActiveRecord::ConnectionHandling::DEFAULT_ENV.call
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/database_configurations/hash_config.rb b/activerecord/lib/active_record/database_configurations/hash_config.rb
new file mode 100644
index 0000000000..c176a62458
--- /dev/null
+++ b/activerecord/lib/active_record/database_configurations/hash_config.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class DatabaseConfigurations
+    # A HashConfig object is created for each database configuration entry that
+    # is created from a hash.
+    #
+    # A hash config:
+    #
+    #   { "development" => { "database" => "db_name" } }
+    #
+    # Becomes:
+    #
+    #   #<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fd1acbded10
+    #     @env_name="development", @spec_name="primary", @config={"database"=>"db_name"}>
+    #
+    # Options are:
+    #
+    # <tt>:env_name</tt> - The Rails environment, ie "development"
+    # <tt>:spec_name</tt> - The specification name. In a standard two-tier
+    # database configuration this will default to "primary". In a multiple
+    # database three-tier database configuration this corresponds to the name
+    # used in the second tier, for example "primary_readonly".
+    # <tt>:config</tt> - The config hash. This is the hash that contains the
+    # database adapter, name, and other important information for database
+    # connections.
+    class HashConfig < DatabaseConfig
+      attr_reader :config
+
+      def initialize(env_name, spec_name, config)
+        super(env_name, spec_name)
+        @config = config
+      end
+
+      # Determines whether a database configuration is for a replica / readonly
+      # connection. If the `replica` key is present in the config, `replica?` will
+      # return +true+.
+      def replica?
+        config["replica"]
+      end
+
+      # The migrations paths for a database configuration. If the
+      # `migrations_paths` key is present in the config, `migrations_paths`
+      # will return its value.
+      def migrations_paths
+        config["migrations_paths"]
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/database_configurations/url_config.rb b/activerecord/lib/active_record/database_configurations/url_config.rb
new file mode 100644
index 0000000000..81917fc4c1
--- /dev/null
+++ b/activerecord/lib/active_record/database_configurations/url_config.rb
@@ -0,0 +1,74 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class DatabaseConfigurations
+    # A UrlConfig object is created for each database configuration
+    # entry that is created from a URL. This can either be a URL string
+    # or a hash with a URL in place of the config hash.
+    #
+    # A URL config:
+    #
+    #   postgres://localhost/foo
+    #
+    # Becomes:
+    #
+    #   #<ActiveRecord::DatabaseConfigurations::UrlConfig:0x00007fdc3238f340
+    #     @env_name="default_env", @spec_name="primary",
+    #     @config={"adapter"=>"postgresql", "database"=>"foo", "host"=>"localhost"},
+    #     @url="postgres://localhost/foo">
+    #
+    # Options are:
+    #
+    # <tt>:env_name</tt> - The Rails environment, ie "development"
+    # <tt>:spec_name</tt> - The specification name. In a standard two-tier
+    # database configuration this will default to "primary". In a multiple
+    # database three-tier database configuration this corresponds to the name
+    # used in the second tier, for example "primary_readonly".
+    # <tt>:url</tt> - The database URL.
+    # <tt>:config</tt> - The config hash. This is the hash that contains the
+    # database adapter, name, and other important information for database
+    # connections.
+    class UrlConfig < DatabaseConfig
+      attr_reader :url, :config
+
+      def initialize(env_name, spec_name, url, config = {})
+        super(env_name, spec_name)
+        @config = build_config(config, url)
+        @url = url
+      end
+
+      def url_config? # :nodoc:
+        true
+      end
+
+      # Determines whether a database configuration is for a replica / readonly
+      # connection. If the `replica` key is present in the config, `replica?` will
+      # return +true+.
+      def replica?
+        config["replica"]
+      end
+
+      # The migrations paths for a database configuration. If the
+      # `migrations_paths` key is present in the config, `migrations_paths`
+      # will return its value.
+      def migrations_paths
+        config["migrations_paths"]
+      end
+
+      private
+        def build_config(original_config, url)
+          if /^jdbc:/.match?(url)
+            hash = { "url" => url }
+          else
+            hash = ActiveRecord::ConnectionAdapters::ConnectionSpecification::ConnectionUrlResolver.new(url).to_hash
+          end
+
+          if original_config[env_name]
+            original_config[env_name].merge(hash)
+          else
+            original_config.merge(hash)
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/define_callbacks.rb b/activerecord/lib/active_record/define_callbacks.rb
new file mode 100644
index 0000000000..87ecd7cec5
--- /dev/null
+++ b/activerecord/lib/active_record/define_callbacks.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  # This module exists because ActiveRecord::AttributeMethods::Dirty needs to
+  # define callbacks, but continue to have its version of +save+ be the super
+  # method of ActiveRecord::Callbacks. This will be removed when the removal
+  # of deprecated code removes this need.
+  module DefineCallbacks
+    extend ActiveSupport::Concern
+
+    module ClassMethods # :nodoc:
+      include ActiveModel::Callbacks
+    end
+
+    included do
+      include ActiveModel::Validations::Callbacks
+
+      define_model_callbacks :initialize, :find, :touch, only: :after
+      define_model_callbacks :save, :create, :update, :destroy
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/dynamic_matchers.rb b/activerecord/lib/active_record/dynamic_matchers.rb
index b6dd6814db..3bb8c6f4e3 100644
--- a/activerecord/lib/active_record/dynamic_matchers.rb
+++ b/activerecord/lib/active_record/dynamic_matchers.rb
@@ -1,121 +1,122 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module DynamicMatchers #:nodoc:
-    def respond_to?(name, include_private = false)
-      if self == Base
-        super
-      else
+    private
+      def respond_to_missing?(name, _)
+        if self == Base
+          super
+        else
+          match = Method.match(self, name)
+          match && match.valid? || super
+        end
+      end
+
+      def method_missing(name, *arguments, &block)
         match = Method.match(self, name)
-        match && match.valid? || super
+
+        if match && match.valid?
+          match.define
+          send(name, *arguments, &block)
+        else
+          super
+        end
       end
-    end
 
-    private
+      class Method
+        @matchers = []
 
-    def method_missing(name, *arguments, &block)
-      match = Method.match(self, name)
+        class << self
+          attr_reader :matchers
 
-      if match && match.valid?
-        match.define
-        send(name, *arguments, &block)
-      else
-        super
-      end
-    end
+          def match(model, name)
+            klass = matchers.find { |k| k.pattern.match?(name) }
+            klass.new(model, name) if klass
+          end
 
-    class Method
-      @matchers = []
+          def pattern
+            @pattern ||= /\A#{prefix}_([_a-zA-Z]\w*)#{suffix}\Z/
+          end
 
-      class << self
-        attr_reader :matchers
+          def prefix
+            raise NotImplementedError
+          end
 
-        def match(model, name)
-          klass = matchers.find { |k| name =~ k.pattern }
-          klass.new(model, name) if klass
+          def suffix
+            ""
+          end
         end
 
-        def pattern
-          @pattern ||= /\A#{prefix}_([_a-zA-Z]\w*)#{suffix}\Z/
-        end
+        attr_reader :model, :name, :attribute_names
 
-        def prefix
-          raise NotImplementedError
+        def initialize(model, name)
+          @model           = model
+          @name            = name.to_s
+          @attribute_names = @name.match(self.class.pattern)[1].split("_and_")
+          @attribute_names.map! { |n| @model.attribute_aliases[n] || n }
         end
 
-        def suffix
-          ''
+        def valid?
+          attribute_names.all? { |name| model.columns_hash[name] || model.reflect_on_aggregation(name.to_sym) }
         end
-      end
-
-      attr_reader :model, :name, :attribute_names
 
-      def initialize(model, name)
-        @model           = model
-        @name            = name.to_s
-        @attribute_names = @name.match(self.class.pattern)[1].split('_and_')
-        @attribute_names.map! { |n| @model.attribute_aliases[n] || n }
-      end
+        def define
+          model.class_eval <<-CODE, __FILE__, __LINE__ + 1
+            def self.#{name}(#{signature})
+              #{body}
+            end
+          CODE
+        end
 
-      def valid?
-        attribute_names.all? { |name| model.columns_hash[name] || model.reflect_on_aggregation(name.to_sym) }
-      end
+        private
 
-      def define
-        model.class_eval <<-CODE, __FILE__, __LINE__ + 1
-          def self.#{name}(#{signature})
-            #{body}
+          def body
+            "#{finder}(#{attributes_hash})"
           end
-        CODE
-      end
-
-      private
-
-      def body
-        "#{finder}(#{attributes_hash})"
-      end
 
-      # The parameters in the signature may have reserved Ruby words, in order
-      # to prevent errors, we start each param name with `_`.
-      def signature
-        attribute_names.map { |name| "_#{name}" }.join(', ')
-      end
+          # The parameters in the signature may have reserved Ruby words, in order
+          # to prevent errors, we start each param name with `_`.
+          def signature
+            attribute_names.map { |name| "_#{name}" }.join(", ")
+          end
 
-      # Given that the parameters starts with `_`, the finder needs to use the
-      # same parameter name.
-      def attributes_hash
-        "{" + attribute_names.map { |name| ":#{name} => _#{name}" }.join(',') + "}"
-      end
+          # Given that the parameters starts with `_`, the finder needs to use the
+          # same parameter name.
+          def attributes_hash
+            "{" + attribute_names.map { |name| ":#{name} => _#{name}" }.join(",") + "}"
+          end
 
-      def finder
-        raise NotImplementedError
+          def finder
+            raise NotImplementedError
+          end
       end
-    end
 
-    class FindBy < Method
-      Method.matchers << self
+      class FindBy < Method
+        Method.matchers << self
 
-      def self.prefix
-        "find_by"
-      end
+        def self.prefix
+          "find_by"
+        end
 
-      def finder
-        "find_by"
+        def finder
+          "find_by"
+        end
       end
-    end
 
-    class FindByBang < Method
-      Method.matchers << self
+      class FindByBang < Method
+        Method.matchers << self
 
-      def self.prefix
-        "find_by"
-      end
+        def self.prefix
+          "find_by"
+        end
 
-      def self.suffix
-        "!"
-      end
+        def self.suffix
+          "!"
+        end
 
-      def finder
-        "find_by!"
+        def finder
+          "find_by!"
+        end
       end
-    end
   end
 end
diff --git a/activerecord/lib/active_record/enum.rb b/activerecord/lib/active_record/enum.rb
index c0d9d9c1c8..3a600835e1 100644
--- a/activerecord/lib/active_record/enum.rb
+++ b/activerecord/lib/active_record/enum.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/object/deep_dup'
+# frozen_string_literal: true
+
+require "active_support/core_ext/object/deep_dup"
 
 module ActiveRecord
   # Declare an enum attribute where the values map to integers in the database,
@@ -18,10 +20,9 @@ module ActiveRecord
   #   conversation.archived? # => true
   #   conversation.status    # => "archived"
   #
-  #   # conversation.update! status: 1
+  #   # conversation.status = 1
   #   conversation.status = "archived"
   #
-  #   # conversation.update! status: nil
   #   conversation.status = nil
   #   conversation.status.nil? # => true
   #   conversation.status      # => nil
@@ -47,13 +48,13 @@ module ActiveRecord
   # Good practice is to let the first declared status be the default.
   #
   # Finally, it's also possible to explicitly map the relation between attribute and
-  # database integer with a +Hash+:
+  # database integer with a hash:
   #
   #   class Conversation < ActiveRecord::Base
   #     enum status: { active: 0, archived: 1 }
   #   end
   #
-  # Note that when an +Array+ is used, the implicit mapping from the values to database
+  # Note that when an array is used, the implicit mapping from the values to database
   # integers is derived from the order the values appear in the array. In the example,
   # <tt>:active</tt> is mapped to +0+ as it's the first element, and <tt>:archived</tt>
   # is mapped to +1+. In general, the +i+-th element is mapped to <tt>i-1</tt> in the
@@ -61,7 +62,7 @@ module ActiveRecord
   #
   # Therefore, once a value is added to the enum array, its position in the array must
   # be maintained, and new values should only be added to the end of the array. To
-  # remove unused values, the explicit +Hash+ syntax should be used.
+  # remove unused values, the explicit hash syntax should be used.
   #
   # In rare circumstances you might need to access the mapping directly.
   # The mappings are exposed through a class method with the pluralized attribute
@@ -75,27 +76,28 @@ module ActiveRecord
   #
   #   Conversation.where("status <> ?", Conversation.statuses[:archived])
   #
-  # You can use the +:enum_prefix+ or +:enum_suffix+ options when you need
-  # to define multiple enums with same values. If the passed value is +true+,
-  # the methods are prefixed/suffixed with the name of the enum.
+  # You can use the +:_prefix+ or +:_suffix+ options when you need to define
+  # multiple enums with same values. If the passed value is +true+, the methods
+  # are prefixed/suffixed with the name of the enum. It is also possible to
+  # supply a custom value:
   #
-  #   class Invoice < ActiveRecord::Base
-  #     enum verification: [:done, :fail], enum_prefix: true
+  #   class Conversation < ActiveRecord::Base
+  #     enum status: [:active, :archived], _suffix: true
+  #     enum comments_status: [:active, :inactive], _prefix: :comments
   #   end
   #
-  # It is also possible to supply a custom prefix.
+  # With the above example, the bang and predicate methods along with the
+  # associated scopes are now prefixed and/or suffixed accordingly:
   #
-  #   class Invoice < ActiveRecord::Base
-  #     enum verification: [:done, :fail], enum_prefix: :verification_status
-  #   end
+  #   conversation.active_status!
+  #   conversation.archived_status? # => false
   #
-  # Note that <tt>:enum_prefix</tt>/<tt>:enum_suffix</tt> are reserved keywords
-  # and can not be used as an enum name.
+  #   conversation.comments_inactive!
+  #   conversation.comments_active? # => false
 
   module Enum
     def self.extended(base) # :nodoc:
-      base.class_attribute(:defined_enums)
-      base.defined_enums = {}
+      base.class_attribute(:defined_enums, instance_writer: false, default: {})
     end
 
     def inherited(base) # :nodoc:
@@ -103,10 +105,13 @@ module ActiveRecord
       super
     end
 
-    class EnumType < Type::Value
-      def initialize(name, mapping)
+    class EnumType < Type::Value # :nodoc:
+      delegate :type, to: :subtype
+
+      def initialize(name, mapping, subtype)
         @name = name
         @mapping = mapping
+        @subtype = subtype
       end
 
       def cast(value)
@@ -117,45 +122,55 @@ module ActiveRecord
         elsif mapping.has_value?(value)
           mapping.key(value)
         else
-          raise ArgumentError, "'#{value}' is not a valid #{name}"
+          assert_valid_value(value)
         end
       end
 
       def deserialize(value)
         return if value.nil?
-        mapping.key(value.to_i)
+        mapping.key(subtype.deserialize(value))
       end
 
       def serialize(value)
         mapping.fetch(value, value)
       end
 
-      protected
+      def assert_valid_value(value)
+        unless value.blank? || mapping.has_key?(value) || mapping.has_value?(value)
+          raise ArgumentError, "'#{value}' is not a valid #{name}"
+        end
+      end
 
-      attr_reader :name, :mapping
+      private
+        attr_reader :name, :mapping, :subtype
     end
 
     def enum(definitions)
       klass = self
-      enum_prefix = definitions.delete(:enum_prefix)
-      enum_suffix = definitions.delete(:enum_suffix)
+      enum_prefix = definitions.delete(:_prefix)
+      enum_suffix = definitions.delete(:_suffix)
       definitions.each do |name, values|
+        assert_valid_enum_definition_values(values)
         # statuses = { }
         enum_values = ActiveSupport::HashWithIndifferentAccess.new
-        name        = name.to_sym
+        name = name.to_s
 
-        # def self.statuses statuses end
-        detect_enum_conflict!(name, name.to_s.pluralize, true)
-        klass.singleton_class.send(:define_method, name.to_s.pluralize) { enum_values }
+        # def self.statuses() statuses end
+        detect_enum_conflict!(name, name.pluralize, true)
+        singleton_class.send(:define_method, name.pluralize) { enum_values }
+        defined_enums[name] = enum_values
 
         detect_enum_conflict!(name, name)
         detect_enum_conflict!(name, "#{name}=")
 
-        attribute name, EnumType.new(name, enum_values)
+        attr = attribute_alias?(name) ? attribute_alias(name) : name
+        decorate_attribute_type(attr, :enum) do |subtype|
+          EnumType.new(attr, enum_values, subtype)
+        end
 
         _enum_methods_module.module_eval do
           pairs = values.respond_to?(:each_pair) ? values.each_pair : values.each_with_index
-          pairs.each do |value, i|
+          pairs.each do |label, value|
             if enum_prefix == true
               prefix = "#{name}_"
             elsif enum_prefix
@@ -167,23 +182,23 @@ module ActiveRecord
               suffix = "_#{enum_suffix}"
             end
 
-            value_method_name = "#{prefix}#{value}#{suffix}"
-            enum_values[value] = i
+            value_method_name = "#{prefix}#{label}#{suffix}"
+            enum_values[label] = value
+            label = label.to_s
 
-            # def active?() status == 0 end
+            # def active?() status == "active" end
             klass.send(:detect_enum_conflict!, name, "#{value_method_name}?")
-            define_method("#{value_method_name}?") { self[name] == value.to_s }
+            define_method("#{value_method_name}?") { self[attr] == label }
 
-            # def active!() update! status: :active end
+            # def active!() update!(status: 0) end
             klass.send(:detect_enum_conflict!, name, "#{value_method_name}!")
-            define_method("#{value_method_name}!") { update! name => value }
+            define_method("#{value_method_name}!") { update!(attr => value) }
 
-            # scope :active, -> { where status: 0 }
+            # scope :active, -> { where(status: 0) }
             klass.send(:detect_enum_conflict!, name, value_method_name, true)
-            klass.scope value_method_name, -> { klass.where name => value }
+            klass.scope value_method_name, -> { where(attr => value) }
           end
         end
-        defined_enums[name.to_s] = enum_values
       end
     end
 
@@ -196,37 +211,45 @@ module ActiveRecord
         end
       end
 
+      def assert_valid_enum_definition_values(values)
+        unless values.is_a?(Hash) || values.all? { |v| v.is_a?(Symbol) } || values.all? { |v| v.is_a?(String) }
+          error_message = <<~MSG
+            Enum values #{values} must be either a hash, an array of symbols, or an array of strings.
+          MSG
+          raise ArgumentError, error_message
+        end
+
+        if values.is_a?(Hash) && values.keys.any?(&:blank?) || values.is_a?(Array) && values.any?(&:blank?)
+          raise ArgumentError, "Enum label name must not be blank."
+        end
+      end
+
       ENUM_CONFLICT_MESSAGE = \
         "You tried to define an enum named \"%{enum}\" on the model \"%{klass}\", but " \
         "this will generate a %{type} method \"%{method}\", which is already defined " \
         "by %{source}."
+      private_constant :ENUM_CONFLICT_MESSAGE
 
       def detect_enum_conflict!(enum_name, method_name, klass_method = false)
         if klass_method && dangerous_class_method?(method_name)
-          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
-            enum: enum_name,
-            klass: self.name,
-            type: 'class',
-            method: method_name,
-            source: 'Active Record'
-          }
+          raise_conflict_error(enum_name, method_name, type: "class")
+        elsif klass_method && method_defined_within?(method_name, Relation)
+          raise_conflict_error(enum_name, method_name, type: "class", source: Relation.name)
         elsif !klass_method && dangerous_attribute_method?(method_name)
-          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
-            enum: enum_name,
-            klass: self.name,
-            type: 'instance',
-            method: method_name,
-            source: 'Active Record'
-          }
+          raise_conflict_error(enum_name, method_name)
         elsif !klass_method && method_defined_within?(method_name, _enum_methods_module, Module)
-          raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
-            enum: enum_name,
-            klass: self.name,
-            type: 'instance',
-            method: method_name,
-            source: 'another enum'
-          }
+          raise_conflict_error(enum_name, method_name, source: "another enum")
         end
       end
+
+      def raise_conflict_error(enum_name, method_name, type: "instance", source: "Active Record")
+        raise ArgumentError, ENUM_CONFLICT_MESSAGE % {
+          enum: enum_name,
+          klass: name,
+          type: type,
+          method: method_name,
+          source: source
+        }
+      end
   end
 end
diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
index 0f1759abaa..f61bc7b9e8 100644
--- a/activerecord/lib/active_record/errors.rb
+++ b/activerecord/lib/active_record/errors.rb
@@ -1,5 +1,6 @@
-module ActiveRecord
+# frozen_string_literal: true
 
+module ActiveRecord
   # = Active Record Errors
   #
   # Generic Active Record exception class.
@@ -7,8 +8,10 @@ module ActiveRecord
   end
 
   # Raised when the single-table inheritance mechanism fails to locate the subclass
-  # (for example due to improper usage of column that +inheritance_column+ points to).
-  class SubclassNotFound < ActiveRecordError #:nodoc:
+  # (for example due to improper usage of column that
+  # {ActiveRecord::Base.inheritance_column}[rdoc-ref:ModelSchema::ClassMethods#inheritance_column]
+  # points to).
+  class SubclassNotFound < ActiveRecordError
   end
 
   # Raised when an object assigned to an association has an incorrect type.
@@ -40,27 +43,40 @@ module ActiveRecord
   class AdapterNotFound < ActiveRecordError
   end
 
-  # Raised when connection to the database could not been established (for
-  # example when +connection=+ is given a nil object).
+  # Raised when connection to the database could not been established (for example when
+  # {ActiveRecord::Base.connection=}[rdoc-ref:ConnectionHandling#connection]
+  # is given a +nil+ object).
   class ConnectionNotEstablished < ActiveRecordError
   end
 
-  # Raised when Active Record cannot find record by given id or set of ids.
+  # Raised when Active Record cannot find a record by given id or set of ids.
   class RecordNotFound < ActiveRecordError
+    attr_reader :model, :primary_key, :id
+
+    def initialize(message = nil, model = nil, primary_key = nil, id = nil)
+      @primary_key = primary_key
+      @model = model
+      @id = id
+
+      super(message)
+    end
   end
 
-  # Raised by ActiveRecord::Base.save! and ActiveRecord::Base.create! methods when record cannot be
-  # saved because record is invalid.
+  # Raised by {ActiveRecord::Base#save!}[rdoc-ref:Persistence#save!] and
+  # {ActiveRecord::Base.create!}[rdoc-ref:Persistence::ClassMethods#create!]
+  # methods when a record is invalid and can not be saved.
   class RecordNotSaved < ActiveRecordError
     attr_reader :record
 
-    def initialize(message, record = nil)
+    def initialize(message = nil, record = nil)
       @record = record
       super(message)
     end
   end
 
-  # Raised by ActiveRecord::Base.destroy! when a call to destroy would return false.
+  # Raised by {ActiveRecord::Base#destroy!}[rdoc-ref:Persistence#destroy!]
+  # when a call to {#destroy}[rdoc-ref:Persistence#destroy!]
+  # would return false.
   #
   #   begin
   #     complex_operation_that_internally_calls_destroy!
@@ -71,7 +87,7 @@ module ActiveRecord
   class RecordNotDestroyed < ActiveRecordError
     attr_reader :record
 
-    def initialize(message, record = nil)
+    def initialize(message = nil, record = nil)
       @record = record
       super(message)
     end
@@ -79,32 +95,70 @@ module ActiveRecord
 
   # Superclass for all database execution errors.
   #
-  # Wraps the underlying database error as +original_exception+.
+  # Wraps the underlying database error as +cause+.
   class StatementInvalid < ActiveRecordError
-    attr_reader :original_exception
-
-    def initialize(message, original_exception = nil)
-      super(message)
-      @original_exception = original_exception
+    def initialize(message = nil)
+      super(message || $!.try(:message))
     end
   end
 
   # Defunct wrapper class kept for compatibility.
-  # +StatementInvalid+ wraps the original exception now.
+  # StatementInvalid wraps the original exception now.
   class WrappedDatabaseException < StatementInvalid
   end
 
-  # Raised when a record cannot be inserted because it would violate a uniqueness constraint.
+  # Raised when a record cannot be inserted or updated because it would violate a uniqueness constraint.
   class RecordNotUnique < WrappedDatabaseException
   end
 
-  # Raised when a record cannot be inserted or updated because it references a non-existent record.
+  # Raised when a record cannot be inserted or updated because it references a non-existent record,
+  # or when a record cannot be deleted because a parent record references it.
   class InvalidForeignKey < WrappedDatabaseException
   end
 
+  # Raised when a foreign key constraint cannot be added because the column type does not match the referenced column type.
+  class MismatchedForeignKey < StatementInvalid
+    def initialize(adapter = nil, message: nil, table: nil, foreign_key: nil, target_table: nil, primary_key: nil)
+      @adapter = adapter
+      if table
+        msg = +<<~EOM
+          Column `#{foreign_key}` on table `#{table}` has a type of `#{column_type(table, foreign_key)}`.
+          This does not match column `#{primary_key}` on `#{target_table}`, which has type `#{column_type(target_table, primary_key)}`.
+          To resolve this issue, change the type of the `#{foreign_key}` column on `#{table}` to be :integer. (For example `t.integer #{foreign_key}`).
+        EOM
+      else
+        msg = +<<~EOM
+          There is a mismatch between the foreign key and primary key column types.
+          Verify that the foreign key column type and the primary key of the associated table match types.
+        EOM
+      end
+      if message
+        msg << "\nOriginal message: #{message}"
+      end
+      super(msg)
+    end
+
+    private
+      def column_type(table, column)
+        @adapter.columns(table).detect { |c| c.name == column }.sql_type
+      end
+  end
+
+  # Raised when a record cannot be inserted or updated because it would violate a not null constraint.
+  class NotNullViolation < StatementInvalid
+  end
+
+  # Raised when a record cannot be inserted or updated because a value too long for a column type.
+  class ValueTooLong < StatementInvalid
+  end
+
+  # Raised when values that executed are out of range.
+  class RangeError < StatementInvalid
+  end
+
   # Raised when number of bind variables in statement given to +:condition+ key
-  # (for example, when using +find+ method) does not match number of expected
-  # values supplied.
+  # (for example, when using {ActiveRecord::Base.find}[rdoc-ref:FinderMethods#find] method)
+  # does not match number of expected values supplied.
   #
   # For example, when there are two placeholders with only one value supplied:
   #
@@ -116,6 +170,11 @@ module ActiveRecord
   class NoDatabaseError < StatementInvalid
   end
 
+  # Raised when PostgreSQL returns 'cached plan must not change result type' and
+  # we cannot retry gracefully (e.g. inside a transaction)
+  class PreparedStatementCacheExpired < StatementInvalid
+  end
+
   # Raised on attempt to save stale record. Record is stale when it's being saved in another query after
   # instantiation, for example, when two users edit the same wiki page and one starts editing and saves
   # the page before the other.
@@ -125,16 +184,21 @@ module ActiveRecord
   class StaleObjectError < ActiveRecordError
     attr_reader :record, :attempted_action
 
-    def initialize(record, attempted_action)
-      super("Attempted to #{attempted_action} a stale object: #{record.class.name}")
-      @record = record
-      @attempted_action = attempted_action
+    def initialize(record = nil, attempted_action = nil)
+      if record && attempted_action
+        @record = record
+        @attempted_action = attempted_action
+        super("Attempted to #{attempted_action} a stale object: #{record.class.name}.")
+      else
+        super("Stale object error.")
+      end
     end
-
   end
 
   # Raised when association is being configured improperly or user tries to use
-  # offset and limit together with +has_many+ or +has_and_belongs_to_many+
+  # offset and limit together with
+  # {ActiveRecord::Base.has_many}[rdoc-ref:Associations::ClassMethods#has_many] or
+  # {ActiveRecord::Base.has_and_belongs_to_many}[rdoc-ref:Associations::ClassMethods#has_and_belongs_to_many]
   # associations.
   class ConfigurationError < ActiveRecordError
   end
@@ -143,9 +207,10 @@ module ActiveRecord
   class ReadOnlyRecord < ActiveRecordError
   end
 
-  # ActiveRecord::Transactions::ClassMethods.transaction uses this exception
-  # to distinguish a deliberate rollback from other exceptional situations.
-  # Normally, raising an exception will cause the +transaction+ method to rollback
+  # {ActiveRecord::Base.transaction}[rdoc-ref:Transactions::ClassMethods#transaction]
+  # uses this exception to distinguish a deliberate rollback from other exceptional situations.
+  # Normally, raising an exception will cause the
+  # {.transaction}[rdoc-ref:Transactions::ClassMethods#transaction] method to rollback
   # the database transaction *and* pass on the exception. But if you raise an
   # ActiveRecord::Rollback exception, then the database transaction will be rolled back,
   # without passing on the exception.
@@ -182,25 +247,26 @@ module ActiveRecord
   UnknownAttributeError = ActiveModel::UnknownAttributeError
 
   # Raised when an error occurred while doing a mass assignment to an attribute through the
-  # +attributes=+ method. The exception has an +attribute+ property that is the name of the
-  # offending attribute.
+  # {ActiveRecord::Base#attributes=}[rdoc-ref:AttributeAssignment#attributes=] method.
+  # The exception has an +attribute+ property that is the name of the offending attribute.
   class AttributeAssignmentError < ActiveRecordError
     attr_reader :exception, :attribute
 
-    def initialize(message, exception, attribute)
+    def initialize(message = nil, exception = nil, attribute = nil)
       super(message)
       @exception = exception
       @attribute = attribute
     end
   end
 
-  # Raised when there are multiple errors while doing a mass assignment through the +attributes+
+  # Raised when there are multiple errors while doing a mass assignment through the
+  # {ActiveRecord::Base#attributes=}[rdoc-ref:AttributeAssignment#attributes=]
   # method. The exception has an +errors+ property that contains an array of AttributeAssignmentError
   # objects, each corresponding to the error while assigning to an attribute.
   class MultiparameterAssignmentErrors < ActiveRecordError
     attr_reader :errors
 
-    def initialize(errors)
+    def initialize(errors = nil)
       @errors = errors
     end
   end
@@ -209,11 +275,16 @@ module ActiveRecord
   class UnknownPrimaryKey < ActiveRecordError
     attr_reader :model
 
-    def initialize(model)
-      super("Unknown primary key for table #{model.table_name} in model #{model}.")
-      @model = model
+    def initialize(model = nil, description = nil)
+      if model
+        message = "Unknown primary key for table #{model.table_name} in model #{model}."
+        message += "\n#{description}" if description
+        @model = model
+        super(message)
+      else
+        super("Unknown primary key.")
+      end
     end
-
   end
 
   # Raised when a relation cannot be mutated because it's already loaded.
@@ -236,7 +307,69 @@ module ActiveRecord
   # * You are joining an existing open transaction
   # * You are creating a nested (savepoint) transaction
   #
-  # The mysql, mysql2 and postgresql adapters support setting the transaction isolation level.
+  # The mysql2 and postgresql adapters support setting the transaction isolation level.
   class TransactionIsolationError < ActiveRecordError
   end
+
+  # TransactionRollbackError will be raised when a transaction is rolled
+  # back by the database due to a serialization failure or a deadlock.
+  #
+  # See the following:
+  #
+  # * https://www.postgresql.org/docs/current/static/transaction-iso.html
+  # * https://dev.mysql.com/doc/refman/5.7/en/error-messages-server.html#error_er_lock_deadlock
+  class TransactionRollbackError < StatementInvalid
+  end
+
+  # SerializationFailure will be raised when a transaction is rolled
+  # back by the database due to a serialization failure.
+  class SerializationFailure < TransactionRollbackError
+  end
+
+  # Deadlocked will be raised when a transaction is rolled
+  # back by the database when a deadlock is encountered.
+  class Deadlocked < TransactionRollbackError
+  end
+
+  # IrreversibleOrderError is raised when a relation's order is too complex for
+  # +reverse_order+ to automatically reverse.
+  class IrreversibleOrderError < ActiveRecordError
+  end
+
+  # LockWaitTimeout will be raised when lock wait timeout exceeded.
+  class LockWaitTimeout < StatementInvalid
+  end
+
+  # StatementTimeout will be raised when statement timeout exceeded.
+  class StatementTimeout < StatementInvalid
+  end
+
+  # QueryCanceled will be raised when canceling statement due to user request.
+  class QueryCanceled < StatementInvalid
+  end
+
+  # UnknownAttributeReference is raised when an unknown and potentially unsafe
+  # value is passed to a query method when allow_unsafe_raw_sql is set to
+  # :disabled. For example, passing a non column name value to a relation's
+  # #order method might cause this exception.
+  #
+  # When working around this exception, caution should be taken to avoid SQL
+  # injection vulnerabilities when passing user-provided values to query
+  # methods. Known-safe values can be passed to query methods by wrapping them
+  # in Arel.sql.
+  #
+  # For example, with allow_unsafe_raw_sql set to :disabled, the following
+  # code would raise this exception:
+  #
+  #   Post.order("length(title)").first
+  #
+  # The desired result can be accomplished by wrapping the known-safe string
+  # in Arel.sql:
+  #
+  #   Post.order(Arel.sql("length(title)")).first
+  #
+  # Again, such a workaround should *not* be used when passing user-provided
+  # values, such as request parameters or model attributes to query methods.
+  class UnknownAttributeReference < ActiveRecordError
+  end
 end
diff --git a/activerecord/lib/active_record/explain.rb b/activerecord/lib/active_record/explain.rb
index 727a9befc1..919e96cd7a 100644
--- a/activerecord/lib/active_record/explain.rb
+++ b/activerecord/lib/active_record/explain.rb
@@ -1,5 +1,6 @@
-require 'active_support/lazy_load_hooks'
-require 'active_record/explain_registry'
+# frozen_string_literal: true
+
+require "active_record/explain_registry"
 
 module ActiveRecord
   module Explain
@@ -16,15 +17,14 @@ module ActiveRecord
     # Makes the adapter execute EXPLAIN for the tuples of queries and bindings.
     # Returns a formatted string ready to be logged.
     def exec_explain(queries) # :nodoc:
-      str = queries.map do |sql, bind|
-        [].tap do |msg|
-          msg << "EXPLAIN for: #{sql}"
-          unless bind.empty?
-            bind_msg = bind.map {|col, val| [col.name, val]}.inspect
-            msg.last << " #{bind_msg}"
-          end
-          msg << connection.explain(sql, bind)
-        end.join("\n")
+      str = queries.map do |sql, binds|
+        msg = +"EXPLAIN for: #{sql}"
+        unless binds.empty?
+          msg << " "
+          msg << binds.map { |attr| render_bind(attr) }.inspect
+        end
+        msg << "\n"
+        msg << connection.explain(sql, binds)
       end.join("\n")
 
       # Overriding inspect to be more human readable, especially in the console.
@@ -34,5 +34,17 @@ module ActiveRecord
 
       str
     end
+
+    private
+
+      def render_bind(attr)
+        value = if attr.type.binary? && attr.value
+          "<#{attr.value_for_database.to_s.bytesize} bytes of binary data>"
+        else
+          connection.type_cast(attr.value_for_database)
+        end
+
+        [attr.name, value]
+      end
   end
 end
diff --git a/activerecord/lib/active_record/explain_registry.rb b/activerecord/lib/active_record/explain_registry.rb
index f5cd57e075..7fd078941a 100644
--- a/activerecord/lib/active_record/explain_registry.rb
+++ b/activerecord/lib/active_record/explain_registry.rb
@@ -1,4 +1,6 @@
-require 'active_support/per_thread_registry'
+# frozen_string_literal: true
+
+require "active_support/per_thread_registry"
 
 module ActiveRecord
   # This is a thread locals registry for EXPLAIN. For example
@@ -7,7 +9,7 @@ module ActiveRecord
   #
   # returns the collected queries local to the current thread.
   #
-  # See the documentation of <tt>ActiveSupport::PerThreadRegistry</tt>
+  # See the documentation of ActiveSupport::PerThreadRegistry
   # for further details.
   class ExplainRegistry # :nodoc:
     extend ActiveSupport::PerThreadRegistry
diff --git a/activerecord/lib/active_record/explain_subscriber.rb b/activerecord/lib/active_record/explain_subscriber.rb
index 9adabd7819..a86217abc0 100644
--- a/activerecord/lib/active_record/explain_subscriber.rb
+++ b/activerecord/lib/active_record/explain_subscriber.rb
@@ -1,5 +1,7 @@
-require 'active_support/notifications'
-require 'active_record/explain_registry'
+# frozen_string_literal: true
+
+require "active_support/notifications"
+require "active_record/explain_registry"
 
 module ActiveRecord
   class ExplainSubscriber # :nodoc:
@@ -14,14 +16,17 @@ module ActiveRecord
     end
 
     # SCHEMA queries cannot be EXPLAINed, also we do not want to run EXPLAIN on
-    # our own EXPLAINs now matter how loopingly beautiful that would be.
+    # our own EXPLAINs no matter how loopingly beautiful that would be.
     #
     # On the other hand, we want to monitor the performance of our real database
     # queries, not the performance of the access to the query cache.
-    IGNORED_PAYLOADS = %w(SCHEMA EXPLAIN CACHE)
+    IGNORED_PAYLOADS = %w(SCHEMA EXPLAIN)
     EXPLAINED_SQLS = /\A\s*(with|select|update|delete|insert)\b/i
     def ignore_payload?(payload)
-      payload[:exception] || IGNORED_PAYLOADS.include?(payload[:name]) || payload[:sql] !~ EXPLAINED_SQLS
+      payload[:exception] ||
+        payload[:cached] ||
+        IGNORED_PAYLOADS.include?(payload[:name]) ||
+        payload[:sql] !~ EXPLAINED_SQLS
     end
 
     ActiveSupport::Notifications.subscribe("sql.active_record", new)
diff --git a/activerecord/lib/active_record/fixture_set/file.rb b/activerecord/lib/active_record/fixture_set/file.rb
index 8132310c91..f1ea0e022f 100644
--- a/activerecord/lib/active_record/fixture_set/file.rb
+++ b/activerecord/lib/active_record/fixture_set/file.rb
@@ -1,5 +1,7 @@
-require 'erb'
-require 'yaml'
+# frozen_string_literal: true
+
+require "erb"
+require "yaml"
 
 module ActiveRecord
   class FixtureSet
@@ -17,38 +19,62 @@ module ActiveRecord
 
       def initialize(file)
         @file = file
-        @rows = nil
       end
 
       def each(&block)
         rows.each(&block)
       end
 
+      def model_class
+        config_row["model_class"]
+      end
 
       private
         def rows
-          return @rows if @rows
+          @rows ||= raw_rows.reject { |fixture_name, _| fixture_name == "_fixture" }
+        end
 
-          begin
+        def config_row
+          @config_row ||= begin
+            row = raw_rows.find { |fixture_name, _| fixture_name == "_fixture" }
+            if row
+              row.last
+            else
+              { 'model_class': nil }
+            end
+          end
+        end
+
+        def raw_rows
+          @raw_rows ||= begin
             data = YAML.load(render(IO.read(@file)))
+            data ? validate(data).to_a : []
           rescue ArgumentError, Psych::SyntaxError => error
             raise Fixture::FormatError, "a YAML error occurred parsing #{@file}. Please note that YAML must be consistently indented using spaces. Tabs are not allowed. Please have a look at http://www.yaml.org/faq.html\nThe exact error was:\n  #{error.class}: #{error}", error.backtrace
           end
-          @rows = data ? validate(data).to_a : []
+        end
+
+        def prepare_erb(content)
+          erb = ERB.new(content)
+          erb.filename = @file
+          erb
         end
 
         def render(content)
           context = ActiveRecord::FixtureSet::RenderContext.create_subclass.new
-          ERB.new(content).result(context.get_binding)
+          prepare_erb(content).result(context.get_binding)
         end
 
         # Validate our unmarshalled data.
         def validate(data)
           unless Hash === data || YAML::Omap === data
-            raise Fixture::FormatError, 'fixture is not a hash'
+            raise Fixture::FormatError, "fixture is not a hash: #{@file}"
           end
 
-          raise Fixture::FormatError unless data.all? { |name, row| Hash === row }
+          invalid = data.reject { |_, row| Hash === row }
+          if invalid.any?
+            raise Fixture::FormatError, "fixture key is not a hash: #{@file}, keys: #{invalid.keys.inspect}"
+          end
           data
         end
     end
diff --git a/activerecord/lib/active_record/fixture_set/model_metadata.rb b/activerecord/lib/active_record/fixture_set/model_metadata.rb
new file mode 100644
index 0000000000..fb23df6f45
--- /dev/null
+++ b/activerecord/lib/active_record/fixture_set/model_metadata.rb
@@ -0,0 +1,33 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class FixtureSet
+    class ModelMetadata # :nodoc:
+      def initialize(model_class)
+        @model_class = model_class
+      end
+
+      def primary_key_name
+        @primary_key_name ||= @model_class && @model_class.primary_key
+      end
+
+      def primary_key_type
+        @primary_key_type ||= @model_class && @model_class.type_for_attribute(@model_class.primary_key).type
+      end
+
+      def has_primary_key_column?
+        @has_primary_key_column ||= primary_key_name &&
+          @model_class.columns.any? { |col| col.name == primary_key_name }
+      end
+
+      def timestamp_column_names
+        @timestamp_column_names ||=
+          %w(created_at created_on updated_at updated_on) & @model_class.column_names
+      end
+
+      def inheritance_column_name
+        @inheritance_column_name ||= @model_class && @model_class.inheritance_column
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/fixture_set/render_context.rb b/activerecord/lib/active_record/fixture_set/render_context.rb
new file mode 100644
index 0000000000..c90b5343dc
--- /dev/null
+++ b/activerecord/lib/active_record/fixture_set/render_context.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+# NOTE: This class has to be defined in compact style in
+# order for rendering context subclassing to work correctly.
+class ActiveRecord::FixtureSet::RenderContext # :nodoc:
+  def self.create_subclass
+    Class.new(ActiveRecord::FixtureSet.context_class) do
+      def get_binding
+        binding()
+      end
+
+      def binary(path)
+        %(!!binary "#{Base64.strict_encode64(File.read(path))}")
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/fixture_set/table_row.rb b/activerecord/lib/active_record/fixture_set/table_row.rb
new file mode 100644
index 0000000000..cb4726f1ee
--- /dev/null
+++ b/activerecord/lib/active_record/fixture_set/table_row.rb
@@ -0,0 +1,153 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class FixtureSet
+    class TableRow # :nodoc:
+      class ReflectionProxy # :nodoc:
+        def initialize(association)
+          @association = association
+        end
+
+        def join_table
+          @association.join_table
+        end
+
+        def name
+          @association.name
+        end
+
+        def primary_key_type
+          @association.klass.type_for_attribute(@association.klass.primary_key).type
+        end
+      end
+
+      class HasManyThroughProxy < ReflectionProxy # :nodoc:
+        def rhs_key
+          @association.foreign_key
+        end
+
+        def lhs_key
+          @association.through_reflection.foreign_key
+        end
+
+        def join_table
+          @association.through_reflection.table_name
+        end
+      end
+
+      def initialize(fixture, table_rows:, label:, now:)
+        @table_rows = table_rows
+        @label = label
+        @now = now
+        @row = fixture.to_hash
+        fill_row_model_attributes
+      end
+
+      def to_hash
+        @row
+      end
+
+      private
+
+        def model_metadata
+          @table_rows.model_metadata
+        end
+
+        def model_class
+          @table_rows.model_class
+        end
+
+        def fill_row_model_attributes
+          return unless model_class
+          fill_timestamps
+          interpolate_label
+          generate_primary_key
+          resolve_enums
+          resolve_sti_reflections
+        end
+
+        def reflection_class
+          @reflection_class ||= if @row.include?(model_metadata.inheritance_column_name)
+            @row[model_metadata.inheritance_column_name].constantize rescue model_class
+          else
+            model_class
+          end
+        end
+
+        def fill_timestamps
+          # fill in timestamp columns if they aren't specified and the model is set to record_timestamps
+          if model_class.record_timestamps
+            model_metadata.timestamp_column_names.each do |c_name|
+              @row[c_name] = @now unless @row.key?(c_name)
+            end
+          end
+        end
+
+        def interpolate_label
+          # interpolate the fixture label
+          @row.each do |key, value|
+            @row[key] = value.gsub("$LABEL", @label.to_s) if value.is_a?(String)
+          end
+        end
+
+        def generate_primary_key
+          # generate a primary key if necessary
+          if model_metadata.has_primary_key_column? && !@row.include?(model_metadata.primary_key_name)
+            @row[model_metadata.primary_key_name] = ActiveRecord::FixtureSet.identify(
+              @label, model_metadata.primary_key_type
+            )
+          end
+        end
+
+        def resolve_enums
+          model_class.defined_enums.each do |name, values|
+            if @row.include?(name)
+              @row[name] = values.fetch(@row[name], @row[name])
+            end
+          end
+        end
+
+        def resolve_sti_reflections
+          # If STI is used, find the correct subclass for association reflection
+          reflection_class._reflections.each_value do |association|
+            case association.macro
+            when :belongs_to
+              # Do not replace association name with association foreign key if they are named the same
+              fk_name = (association.options[:foreign_key] || "#{association.name}_id").to_s
+
+              if association.name.to_s != fk_name && value = @row.delete(association.name.to_s)
+                if association.polymorphic? && value.sub!(/\s*\(([^\)]*)\)\s*$/, "")
+                  # support polymorphic belongs_to as "label (Type)"
+                  @row[association.foreign_type] = $1
+                end
+
+                fk_type = reflection_class.type_for_attribute(fk_name).type
+                @row[fk_name] = ActiveRecord::FixtureSet.identify(value, fk_type)
+              end
+            when :has_many
+              if association.options[:through]
+                add_join_records(HasManyThroughProxy.new(association))
+              end
+            end
+          end
+        end
+
+        def add_join_records(association)
+          # This is the case when the join table has no fixtures file
+          if (targets = @row.delete(association.name.to_s))
+            table_name  = association.join_table
+            column_type = association.primary_key_type
+            lhs_key     = association.lhs_key
+            rhs_key     = association.rhs_key
+
+            targets = targets.is_a?(Array) ? targets : targets.split(/\s*,\s*/)
+            joins   = targets.map do |target|
+              { lhs_key => @row[model_metadata.primary_key_name],
+                rhs_key => ActiveRecord::FixtureSet.identify(target, column_type) }
+            end
+            @table_rows.tables[table_name].concat(joins)
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/fixture_set/table_rows.rb b/activerecord/lib/active_record/fixture_set/table_rows.rb
new file mode 100644
index 0000000000..23814b6cb5
--- /dev/null
+++ b/activerecord/lib/active_record/fixture_set/table_rows.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require "active_record/fixture_set/table_row"
+require "active_record/fixture_set/model_metadata"
+
+module ActiveRecord
+  class FixtureSet
+    class TableRows # :nodoc:
+      def initialize(table_name, model_class:, fixtures:, config:)
+        @model_class = model_class
+
+        # track any join tables we need to insert later
+        @tables = Hash.new { |h, table| h[table] = [] }
+
+        # ensure this table is loaded before any HABTM associations
+        @tables[table_name] = nil
+
+        build_table_rows_from(table_name, fixtures, config)
+      end
+
+      attr_reader :tables, :model_class
+
+      def to_hash
+        @tables.transform_values { |rows| rows.map(&:to_hash) }
+      end
+
+      def model_metadata
+        @model_metadata ||= ModelMetadata.new(model_class)
+      end
+
+      private
+
+        def build_table_rows_from(table_name, fixtures, config)
+          now = config.default_timezone == :utc ? Time.now.utc : Time.now
+
+          @tables[table_name] = fixtures.map do |label, fixture|
+            TableRow.new(
+              fixture,
+              table_rows: self,
+              label: label,
+              now: now,
+            )
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index d062dd9e34..1248ed00c5 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -1,11 +1,16 @@
-require 'erb'
-require 'yaml'
-require 'zlib'
-require 'set'
-require 'active_support/dependencies'
-require 'active_support/core_ext/digest/uuid'
-require 'active_record/fixture_set/file'
-require 'active_record/errors'
+# frozen_string_literal: true
+
+require "erb"
+require "yaml"
+require "zlib"
+require "set"
+require "active_support/dependencies"
+require "active_support/core_ext/digest/uuid"
+require "active_record/fixture_set/file"
+require "active_record/fixture_set/render_context"
+require "active_record/fixture_set/table_rows"
+require "active_record/test_fixtures"
+require "active_record/errors"
 
 module ActiveRecord
   class FixtureClassNotFound < ActiveRecord::ActiveRecordError #:nodoc:
@@ -66,17 +71,36 @@ module ActiveRecord
   # By default, +test_helper.rb+ will load all of your fixtures into your test
   # database, so this test will succeed.
   #
-  # The testing environment will automatically load the all fixtures into the database before each
+  # The testing environment will automatically load all the fixtures into the database before each
   # test. To ensure consistent data, the environment deletes the fixtures before running the load.
   #
   # In addition to being available in the database, the fixture's data may also be accessed by
-  # using a special dynamic method, which has the same name as the model, and accepts the
-  # name of the fixture to instantiate:
+  # using a special dynamic method, which has the same name as the model.
   #
-  #   test "find" do
+  # Passing in a fixture name to this dynamic method returns the fixture matching this name:
+  #
+  #   test "find one" do
   #     assert_equal "Ruby on Rails", web_sites(:rubyonrails).name
   #   end
   #
+  # Passing in multiple fixture names returns all fixtures matching these names:
+  #
+  #   test "find all by name" do
+  #     assert_equal 2, web_sites(:rubyonrails, :google).length
+  #   end
+  #
+  # Passing in no arguments returns all fixtures:
+  #
+  #   test "find all" do
+  #     assert_equal 2, web_sites.length
+  #   end
+  #
+  # Passing in any fixture name that does not exist will raise <tt>StandardError</tt>:
+  #
+  #   test "find by name that does not exist" do
+  #     assert_raise(StandardError) { web_sites(:reddit) }
+  #   end
+  #
   # Alternatively, you may enable auto-instantiation of the fixture data. For instance, take the
   # following tests:
   #
@@ -88,8 +112,8 @@ module ActiveRecord
   #     assert_equal "Ruby on Rails", @rubyonrails.name
   #   end
   #
-  # In order to use these methods to access fixtured data within your testcases, you must specify one of the
-  # following in your <tt>ActiveSupport::TestCase</tt>-derived class:
+  # In order to use these methods to access fixtured data within your test cases, you must specify one of the
+  # following in your ActiveSupport::TestCase-derived class:
   #
   # - to fully enable instantiated fixtures (enable alternate methods #1 and #2 above)
   #     self.use_instantiated_fixtures = true
@@ -103,7 +127,7 @@ module ActiveRecord
   #
   # = Dynamic fixtures with ERB
   #
-  # Some times you don't care about the content of the fixtures as much as you care about the volume.
+  # Sometimes you don't care about the content of the fixtures as much as you care about the volume.
   # In these cases, you can mix ERB in with your YAML fixtures to create a bunch of fixtures for load
   # testing, like:
   #
@@ -124,9 +148,9 @@ module ActiveRecord
   #
   # Helper methods defined in a fixture will not be available in other fixtures, to prevent against
   # unwanted inter-test dependencies. Methods used by multiple fixtures should be defined in a module
-  # that is included in <tt>ActiveRecord::FixtureSet.context_class</tt>.
+  # that is included in ActiveRecord::FixtureSet.context_class.
   #
-  # - define a helper method in `test_helper.rb`
+  # - define a helper method in <tt>test_helper.rb</tt>
   #     module FixtureFileHelpers
   #       def file_sha(path)
   #         Digest::SHA2.hexdigest(File.read(Rails.root.join('test/fixtures', path)))
@@ -148,18 +172,18 @@ module ActiveRecord
   #     self.use_transactional_tests = true
   #
   #     test "godzilla" do
-  #       assert !Foo.all.empty?
+  #       assert_not_empty Foo.all
   #       Foo.destroy_all
-  #       assert Foo.all.empty?
+  #       assert_empty Foo.all
   #     end
   #
   #     test "godzilla aftermath" do
-  #       assert !Foo.all.empty?
+  #       assert_not_empty Foo.all
   #     end
   #   end
   #
-  # If you preload your test database with all fixture data (probably in the rake task) and use
-  # transactional tests, then you may omit all fixtures declarations in your test cases since
+  # If you preload your test database with all fixture data (probably by running `rails db:fixtures:load`)
+  # and use transactional tests, then you may omit all fixtures declarations in your test cases since
   # all the data's already there and every case rolls back its changes.
   #
   # In order to use instantiated fixtures with preloaded data, set +self.pre_loaded_fixtures+ to
@@ -395,54 +419,105 @@ module ActiveRecord
   #     <<: *DEFAULTS
   #
   # Any fixture labeled "DEFAULTS" is safely ignored.
+  #
+  # == Configure the fixture model class
+  #
+  # It's possible to set the fixture's model class directly in the YAML file.
+  # This is helpful when fixtures are loaded outside tests and
+  # +set_fixture_class+ is not available (e.g.
+  # when running <tt>rails db:fixtures:load</tt>).
+  #
+  #   _fixture:
+  #     model_class: User
+  #   david:
+  #     name: David
+  #
+  # Any fixtures labeled "_fixture" are safely ignored.
   class FixtureSet
     #--
     # An instance of FixtureSet is normally stored in a single YAML file and
     # possibly in a folder with the same name.
     #++
 
-    MAX_ID = 2 ** 30 - 1
+    MAX_ID = 2**30 - 1
 
-    @@all_cached_fixtures = Hash.new { |h,k| h[k] = {} }
+    @@all_cached_fixtures = Hash.new { |h, k| h[k] = {} }
 
-    def self.default_fixture_model_name(fixture_set_name, config = ActiveRecord::Base) # :nodoc:
-      config.pluralize_table_names ?
-        fixture_set_name.singularize.camelize :
-        fixture_set_name.camelize
-    end
+    cattr_accessor :all_loaded_fixtures, default: {}
 
-    def self.default_fixture_table_name(fixture_set_name, config = ActiveRecord::Base) # :nodoc:
-       "#{ config.table_name_prefix }"\
-       "#{ fixture_set_name.tr('/', '_') }"\
-       "#{ config.table_name_suffix }".to_sym
-    end
+    class ClassCache
+      def initialize(class_names, config)
+        @class_names = class_names.stringify_keys
+        @config      = config
 
-    def self.reset_cache
-      @@all_cached_fixtures.clear
-    end
+        # Remove string values that aren't constants or subclasses of AR
+        @class_names.delete_if do |klass_name, klass|
+          !insert_class(@class_names, klass_name, klass)
+        end
+      end
 
-    def self.cache_for_connection(connection)
-      @@all_cached_fixtures[connection]
-    end
+      def [](fs_name)
+        @class_names.fetch(fs_name) do
+          klass = default_fixture_model(fs_name, @config).safe_constantize
+          insert_class(@class_names, fs_name, klass)
+        end
+      end
+
+      private
+
+        def insert_class(class_names, name, klass)
+          # We only want to deal with AR objects.
+          if klass && klass < ActiveRecord::Base
+            class_names[name] = klass
+          else
+            class_names[name] = nil
+          end
+        end
 
-    def self.fixture_is_cached?(connection, table_name)
-      cache_for_connection(connection)[table_name]
+        def default_fixture_model(fs_name, config)
+          ActiveRecord::FixtureSet.default_fixture_model_name(fs_name, config)
+        end
     end
 
-    def self.cached_fixtures(connection, keys_to_fetch = nil)
-      if keys_to_fetch
-        cache_for_connection(connection).values_at(*keys_to_fetch)
-      else
-        cache_for_connection(connection).values
+    class << self
+      def default_fixture_model_name(fixture_set_name, config = ActiveRecord::Base) # :nodoc:
+        config.pluralize_table_names ?
+          fixture_set_name.singularize.camelize :
+          fixture_set_name.camelize
       end
-    end
 
-    def self.cache_fixtures(connection, fixtures_map)
-      cache_for_connection(connection).update(fixtures_map)
-    end
+      def default_fixture_table_name(fixture_set_name, config = ActiveRecord::Base) # :nodoc:
+        "#{ config.table_name_prefix }"\
+        "#{ fixture_set_name.tr('/', '_') }"\
+        "#{ config.table_name_suffix }".to_sym
+      end
 
-    def self.instantiate_fixtures(object, fixture_set, load_instances = true)
-      if load_instances
+      def reset_cache
+        @@all_cached_fixtures.clear
+      end
+
+      def cache_for_connection(connection)
+        @@all_cached_fixtures[connection]
+      end
+
+      def fixture_is_cached?(connection, table_name)
+        cache_for_connection(connection)[table_name]
+      end
+
+      def cached_fixtures(connection, keys_to_fetch = nil)
+        if keys_to_fetch
+          cache_for_connection(connection).values_at(*keys_to_fetch)
+        else
+          cache_for_connection(connection).values
+        end
+      end
+
+      def cache_fixtures(connection, fixtures_map)
+        cache_for_connection(connection).update(fixtures_map)
+      end
+
+      def instantiate_fixtures(object, fixture_set, load_instances = true)
+        return unless load_instances
         fixture_set.each do |fixture_name, fixture|
           begin
             object.instance_variable_set "@#{fixture_name}", fixture.find
@@ -451,155 +526,117 @@ module ActiveRecord
           end
         end
       end
-    end
 
-    def self.instantiate_all_loaded_fixtures(object, load_instances = true)
-      all_loaded_fixtures.each_value do |fixture_set|
-        instantiate_fixtures(object, fixture_set, load_instances)
+      def instantiate_all_loaded_fixtures(object, load_instances = true)
+        all_loaded_fixtures.each_value do |fixture_set|
+          instantiate_fixtures(object, fixture_set, load_instances)
+        end
       end
-    end
 
-    cattr_accessor :all_loaded_fixtures
-    self.all_loaded_fixtures = {}
+      def create_fixtures(fixtures_directory, fixture_set_names, class_names = {}, config = ActiveRecord::Base)
+        fixture_set_names = Array(fixture_set_names).map(&:to_s)
+        class_names = ClassCache.new class_names, config
 
-    class ClassCache
-      def initialize(class_names, config)
-        @class_names = class_names.stringify_keys
-        @config      = config
+        # FIXME: Apparently JK uses this.
+        connection = block_given? ? yield : ActiveRecord::Base.connection
 
-        # Remove string values that aren't constants or subclasses of AR
-        @class_names.delete_if { |klass_name, klass| !insert_class(@class_names, klass_name, klass) }
-      end
+        fixture_files_to_read = fixture_set_names.reject do |fs_name|
+          fixture_is_cached?(connection, fs_name)
+        end
 
-      def [](fs_name)
-        @class_names.fetch(fs_name) {
-          klass = default_fixture_model(fs_name, @config).safe_constantize
-          insert_class(@class_names, fs_name, klass)
-        }
+        if fixture_files_to_read.any?
+          fixtures_map = read_and_insert(
+            fixtures_directory,
+            fixture_files_to_read,
+            class_names,
+            connection,
+          )
+          cache_fixtures(connection, fixtures_map)
+        end
+        cached_fixtures(connection, fixture_set_names)
       end
 
-      private
-
-      def insert_class(class_names, name, klass)
-        # We only want to deal with AR objects.
-        if klass && klass < ActiveRecord::Base
-          class_names[name] = klass
+      # Returns a consistent, platform-independent identifier for +label+.
+      # Integer identifiers are values less than 2^30. UUIDs are RFC 4122 version 5 SHA-1 hashes.
+      def identify(label, column_type = :integer)
+        if column_type == :uuid
+          Digest::UUID.uuid_v5(Digest::UUID::OID_NAMESPACE, label.to_s)
         else
-          class_names[name] = nil
+          Zlib.crc32(label.to_s) % MAX_ID
         end
       end
 
-      def default_fixture_model(fs_name, config)
-        ActiveRecord::FixtureSet.default_fixture_model_name(fs_name, config)
+      # Superclass for the evaluation contexts used by ERB fixtures.
+      def context_class
+        @context_class ||= Class.new
       end
-    end
-
-    def self.create_fixtures(fixtures_directory, fixture_set_names, class_names = {}, config = ActiveRecord::Base)
-      fixture_set_names = Array(fixture_set_names).map(&:to_s)
-      class_names = ClassCache.new class_names, config
-
-      # FIXME: Apparently JK uses this.
-      connection = block_given? ? yield : ActiveRecord::Base.connection
 
-      files_to_read = fixture_set_names.reject { |fs_name|
-        fixture_is_cached?(connection, fs_name)
-      }
-
-      unless files_to_read.empty?
-        connection.disable_referential_integrity do
-          fixtures_map = {}
+      private
 
-          fixture_sets = files_to_read.map do |fs_name|
-            klass = class_names[fs_name]
-            conn = klass ? klass.connection : connection
-            fixtures_map[fs_name] = new( # ActiveRecord::FixtureSet.new
-              conn,
-              fs_name,
-              klass,
-              ::File.join(fixtures_directory, fs_name))
-          end
+      def read_and_insert(fixtures_directory, fixture_files, class_names, connection) # :nodoc:
+        fixtures_map = {}
+        fixture_sets = fixture_files.map do |fixture_set_name|
+          klass = class_names[fixture_set_name]
+          fixtures_map[fixture_set_name] = new( # ActiveRecord::FixtureSet.new
+            nil,
+            fixture_set_name,
+            klass,
+            ::File.join(fixtures_directory, fixture_set_name)
+          )
+        end
+        update_all_loaded_fixtures(fixtures_map)
 
-          update_all_loaded_fixtures fixtures_map
+        insert(fixture_sets, connection)
 
-          connection.transaction(:requires_new => true) do
-            deleted_tables = Set.new
-            fixture_sets.each do |fs|
-              conn = fs.model_class.respond_to?(:connection) ? fs.model_class.connection : connection
-              table_rows = fs.table_rows
+        fixtures_map
+      end
 
-              table_rows.each_key do |table|
-                unless deleted_tables.include? table
-                  conn.delete "DELETE FROM #{conn.quote_table_name(table)}", 'Fixture Delete'
-                end
-                deleted_tables << table
-              end
+      def insert(fixture_sets, connection) # :nodoc:
+        fixture_sets_by_connection = fixture_sets.group_by do |fixture_set|
+          fixture_set.model_class&.connection || connection
+        end
 
-              table_rows.each do |fixture_set_name, rows|
-                rows.each do |row|
-                  conn.insert_fixture(row, fixture_set_name)
-                end
-              end
+        fixture_sets_by_connection.each do |conn, set|
+          table_rows_for_connection = Hash.new { |h, k| h[k] = [] }
 
-              # Cap primary key sequences to max(pk).
-              if conn.respond_to?(:reset_pk_sequence!)
-                conn.reset_pk_sequence!(fs.table_name)
-              end
+          set.each do |fixture_set|
+            fixture_set.table_rows.each do |table, rows|
+              table_rows_for_connection[table].unshift(*rows)
             end
           end
+          conn.insert_fixtures_set(table_rows_for_connection, table_rows_for_connection.keys)
 
-          cache_fixtures(connection, fixtures_map)
+          # Cap primary key sequences to max(pk).
+          if conn.respond_to?(:reset_pk_sequence!)
+            set.each { |fs| conn.reset_pk_sequence!(fs.table_name) }
+          end
         end
       end
-      cached_fixtures(connection, fixture_set_names)
-    end
 
-    # Returns a consistent, platform-independent identifier for +label+.
-    # Integer identifiers are values less than 2^30. UUIDs are RFC 4122 version 5 SHA-1 hashes.
-    def self.identify(label, column_type = :integer)
-      if column_type == :uuid
-        Digest::UUID.uuid_v5(Digest::UUID::OID_NAMESPACE, label.to_s)
-      else
-        Zlib.crc32(label.to_s) % MAX_ID
+      def update_all_loaded_fixtures(fixtures_map) # :nodoc:
+        all_loaded_fixtures.update(fixtures_map)
       end
     end
 
-    # Superclass for the evaluation contexts used by ERB fixtures.
-    def self.context_class
-      @context_class ||= Class.new
-    end
-
-    def self.update_all_loaded_fixtures(fixtures_map) # :nodoc:
-      all_loaded_fixtures.update(fixtures_map)
-    end
-
     attr_reader :table_name, :name, :fixtures, :model_class, :config
 
-    def initialize(connection, name, class_name, path, config = ActiveRecord::Base)
+    def initialize(_, name, class_name, path, config = ActiveRecord::Base)
       @name     = name
       @path     = path
       @config   = config
-      @model_class = nil
 
-      if class_name.is_a?(Class) # TODO: Should be an AR::Base type class, or any?
-        @model_class = class_name
-      else
-        @model_class = class_name.safe_constantize if class_name
-      end
-
-      @connection  = connection
+      self.model_class = class_name
 
-      @table_name = ( model_class.respond_to?(:table_name) ?
-                      model_class.table_name :
-                      self.class.default_fixture_table_name(name, config) )
+      @fixtures = read_fixture_files(path)
 
-      @fixtures = read_fixture_files path, @model_class
+      @table_name = model_class&.table_name || self.class.default_fixture_table_name(name, config)
     end
 
     def [](x)
       fixtures[x]
     end
 
-    def []=(k,v)
+    def []=(k, v)
       fixtures[k] = v
     end
 
@@ -614,160 +651,38 @@ module ActiveRecord
     # Returns a hash of rows to be inserted. The key is the table, the value is
     # a list of rows to insert to that table.
     def table_rows
-      now = config.default_timezone == :utc ? Time.now.utc : Time.now
-
       # allow a standard key to be used for doing defaults in YAML
-      fixtures.delete('DEFAULTS')
-
-      # track any join tables we need to insert later
-      rows = Hash.new { |h,table| h[table] = [] }
-
-      rows[table_name] = fixtures.map do |label, fixture|
-        row = fixture.to_hash
-
-        if model_class
-          # fill in timestamp columns if they aren't specified and the model is set to record_timestamps
-          if model_class.record_timestamps
-            timestamp_column_names.each do |c_name|
-              row[c_name] = now unless row.key?(c_name)
-            end
-          end
-
-          # interpolate the fixture label
-          row.each do |key, value|
-            row[key] = value.gsub("$LABEL", label.to_s) if value.is_a?(String)
-          end
-
-          # generate a primary key if necessary
-          if has_primary_key_column? && !row.include?(primary_key_name)
-            row[primary_key_name] = ActiveRecord::FixtureSet.identify(label, primary_key_type)
-          end
-
-          # Resolve enums
-          model_class.defined_enums.each do |name, values|
-            if row.include?(name)
-              row[name] = values.fetch(row[name], row[name])
-            end
-          end
-
-          # If STI is used, find the correct subclass for association reflection
-          reflection_class =
-            if row.include?(inheritance_column_name)
-              row[inheritance_column_name].constantize rescue model_class
-            else
-              model_class
-            end
-
-          reflection_class._reflections.each_value do |association|
-            case association.macro
-            when :belongs_to
-              # Do not replace association name with association foreign key if they are named the same
-              fk_name = (association.options[:foreign_key] || "#{association.name}_id").to_s
-
-              if association.name.to_s != fk_name && value = row.delete(association.name.to_s)
-                if association.polymorphic? && value.sub!(/\s*\(([^\)]*)\)\s*$/, "")
-                  # support polymorphic belongs_to as "label (Type)"
-                  row[association.foreign_type] = $1
-                end
-
-                fk_type = reflection_class.type_for_attribute(fk_name).type
-                row[fk_name] = ActiveRecord::FixtureSet.identify(value, fk_type)
-              end
-            when :has_many
-              if association.options[:through]
-                add_join_records(rows, row, HasManyThroughProxy.new(association))
-              end
-            end
-          end
-        end
+      fixtures.delete("DEFAULTS")
 
-        row
-      end
-      rows
-    end
-
-    class ReflectionProxy # :nodoc:
-      def initialize(association)
-        @association = association
-      end
-
-      def join_table
-        @association.join_table
-      end
-
-      def name
-        @association.name
-      end
-
-      def primary_key_type
-        @association.klass.type_for_attribute(@association.klass.primary_key).type
-      end
-    end
-
-    class HasManyThroughProxy < ReflectionProxy # :nodoc:
-      def rhs_key
-        @association.foreign_key
-      end
-
-      def lhs_key
-        @association.through_reflection.foreign_key
-      end
-
-      def join_table
-        @association.through_reflection.table_name
-      end
+      TableRows.new(
+        table_name,
+        model_class: model_class,
+        fixtures: fixtures,
+        config: config,
+      ).to_hash
     end
 
     private
-      def primary_key_name
-        @primary_key_name ||= model_class && model_class.primary_key
-      end
-
-      def primary_key_type
-        @primary_key_type ||= model_class && model_class.type_for_attribute(model_class.primary_key).type
-      end
-
-      def add_join_records(rows, row, association)
-        # This is the case when the join table has no fixtures file
-        if (targets = row.delete(association.name.to_s))
-          table_name  = association.join_table
-          column_type = association.primary_key_type
-          lhs_key     = association.lhs_key
-          rhs_key     = association.rhs_key
 
-          targets = targets.is_a?(Array) ? targets : targets.split(/\s*,\s*/)
-          rows[table_name].concat targets.map { |target|
-            { lhs_key => row[primary_key_name],
-              rhs_key => ActiveRecord::FixtureSet.identify(target, column_type) }
-          }
+      def model_class=(class_name)
+        if class_name.is_a?(Class) # TODO: Should be an AR::Base type class, or any?
+          @model_class = class_name
+        else
+          @model_class = class_name.safe_constantize if class_name
         end
       end
 
-      def has_primary_key_column?
-        @has_primary_key_column ||= primary_key_name &&
-          model_class.columns.any? { |c| c.name == primary_key_name }
-      end
-
-      def timestamp_column_names
-        @timestamp_column_names ||=
-          %w(created_at created_on updated_at updated_on) & column_names
-      end
-
-      def inheritance_column_name
-        @inheritance_column_name ||= model_class && model_class.inheritance_column
-      end
-
-      def column_names
-        @column_names ||= @connection.columns(@table_name).collect(&:name)
-      end
-
-      def read_fixture_files(path, model_class)
+      # Loads the fixtures from the YAML file at +path+.
+      # If the file sets the +model_class+ and current instance value is not set,
+      # it uses the file value.
+      def read_fixture_files(path)
         yaml_files = Dir["#{path}/{**,*}/*.yml"].select { |f|
           ::File.file?(f)
         } + [yaml_file_path(path)]
 
         yaml_files.each_with_object({}) do |file, fixtures|
           FixtureSet::File.open(file) do |fh|
+            self.model_class ||= fh.model_class if fh.model_class
             fh.each do |fixture_name, row|
               fixtures[fixture_name] = ActiveRecord::Fixture.new(row, model_class)
             end
@@ -778,7 +693,6 @@ module ActiveRecord
       def yaml_file_path(path)
         "#{path}.yml"
       end
-
   end
 
   class Fixture #:nodoc:
@@ -812,214 +726,9 @@ module ActiveRecord
     alias :to_hash :fixture
 
     def find
-      if model_class
-        model_class.unscoped do
-          model_class.find(fixture[model_class.primary_key])
-        end
-      else
-        raise FixtureClassNotFound, "No class attached to find."
-      end
-    end
-  end
-end
-
-module ActiveRecord
-  module TestFixtures
-    extend ActiveSupport::Concern
-
-    def before_setup
-      setup_fixtures
-      super
-    end
-
-    def after_teardown
-      super
-      teardown_fixtures
-    end
-
-    included do
-      class_attribute :fixture_path, :instance_writer => false
-      class_attribute :fixture_table_names
-      class_attribute :fixture_class_names
-      class_attribute :use_transactional_tests
-      class_attribute :use_transactional_fixtures
-      class_attribute :use_instantiated_fixtures # true, false, or :no_instances
-      class_attribute :pre_loaded_fixtures
-      class_attribute :config
-
-      singleton_class.deprecate 'use_transactional_fixtures=' => 'use use_transactional_tests= instead'
-
-      self.fixture_table_names = []
-      self.use_instantiated_fixtures = false
-      self.pre_loaded_fixtures = false
-      self.config = ActiveRecord::Base
-
-      self.fixture_class_names = Hash.new do |h, fixture_set_name|
-        h[fixture_set_name] = ActiveRecord::FixtureSet.default_fixture_model_name(fixture_set_name, self.config)
-      end
-
-      silence_warnings do
-        define_singleton_method :use_transactional_tests do
-          if use_transactional_fixtures.nil?
-            true
-          else
-            use_transactional_fixtures
-          end
-        end
-      end
-    end
-
-    module ClassMethods
-      # Sets the model class for a fixture when the class name cannot be inferred from the fixture name.
-      #
-      # Examples:
-      #
-      #   set_fixture_class some_fixture:        SomeModel,
-      #                     'namespaced/fixture' => Another::Model
-      #
-      # The keys must be the fixture names, that coincide with the short paths to the fixture files.
-      def set_fixture_class(class_names = {})
-        self.fixture_class_names = self.fixture_class_names.merge(class_names.stringify_keys)
-      end
-
-      def fixtures(*fixture_set_names)
-        if fixture_set_names.first == :all
-          fixture_set_names = Dir["#{fixture_path}/{**,*}/*.{yml}"]
-          fixture_set_names.map! { |f| f[(fixture_path.to_s.size + 1)..-5] }
-        else
-          fixture_set_names = fixture_set_names.flatten.map(&:to_s)
-        end
-
-        self.fixture_table_names |= fixture_set_names
-        setup_fixture_accessors(fixture_set_names)
-      end
-
-      def setup_fixture_accessors(fixture_set_names = nil)
-        fixture_set_names = Array(fixture_set_names || fixture_table_names)
-        methods = Module.new do
-          fixture_set_names.each do |fs_name|
-            fs_name = fs_name.to_s
-            accessor_name = fs_name.tr('/', '_').to_sym
-
-            define_method(accessor_name) do |*fixture_names|
-              force_reload = fixture_names.pop if fixture_names.last == true || fixture_names.last == :reload
-
-              @fixture_cache[fs_name] ||= {}
-
-              instances = fixture_names.map do |f_name|
-                f_name = f_name.to_s if f_name.is_a?(Symbol)
-                @fixture_cache[fs_name].delete(f_name) if force_reload
-
-                if @loaded_fixtures[fs_name][f_name]
-                  @fixture_cache[fs_name][f_name] ||= @loaded_fixtures[fs_name][f_name].find
-                else
-                  raise StandardError, "No fixture named '#{f_name}' found for fixture set '#{fs_name}'"
-                end
-              end
-
-              instances.size == 1 ? instances.first : instances
-            end
-            private accessor_name
-          end
-        end
-        include methods
-      end
-
-      def uses_transaction(*methods)
-        @uses_transaction = [] unless defined?(@uses_transaction)
-        @uses_transaction.concat methods.map(&:to_s)
-      end
-
-      def uses_transaction?(method)
-        @uses_transaction = [] unless defined?(@uses_transaction)
-        @uses_transaction.include?(method.to_s)
-      end
-    end
-
-    def run_in_transaction?
-      use_transactional_tests &&
-        !self.class.uses_transaction?(method_name)
-    end
-
-    def setup_fixtures(config = ActiveRecord::Base)
-      if pre_loaded_fixtures && !use_transactional_tests
-        raise RuntimeError, 'pre_loaded_fixtures requires use_transactional_tests'
-      end
-
-      @fixture_cache = {}
-      @fixture_connections = []
-      @@already_loaded_fixtures ||= {}
-
-      # Load fixtures once and begin transaction.
-      if run_in_transaction?
-        if @@already_loaded_fixtures[self.class]
-          @loaded_fixtures = @@already_loaded_fixtures[self.class]
-        else
-          @loaded_fixtures = load_fixtures(config)
-          @@already_loaded_fixtures[self.class] = @loaded_fixtures
-        end
-        @fixture_connections = enlist_fixture_connections
-        @fixture_connections.each do |connection|
-          connection.begin_transaction joinable: false
-        end
-      # Load fixtures for every test.
-      else
-        ActiveRecord::FixtureSet.reset_cache
-        @@already_loaded_fixtures[self.class] = nil
-        @loaded_fixtures = load_fixtures(config)
-      end
-
-      # Instantiate fixtures for every test if requested.
-      instantiate_fixtures if use_instantiated_fixtures
-    end
-
-    def teardown_fixtures
-      # Rollback changes if a transaction is active.
-      if run_in_transaction?
-        @fixture_connections.each do |connection|
-          connection.rollback_transaction if connection.transaction_open?
-        end
-        @fixture_connections.clear
-      else
-        ActiveRecord::FixtureSet.reset_cache
-      end
-
-      ActiveRecord::Base.clear_active_connections!
-    end
-
-    def enlist_fixture_connections
-      ActiveRecord::Base.connection_handler.connection_pool_list.map(&:connection)
-    end
-
-    private
-      def load_fixtures(config)
-        fixtures = ActiveRecord::FixtureSet.create_fixtures(fixture_path, fixture_table_names, fixture_class_names, config)
-        Hash[fixtures.map { |f| [f.name, f] }]
-      end
-
-      def instantiate_fixtures
-        if pre_loaded_fixtures
-          raise RuntimeError, 'Load fixtures before instantiating them.' if ActiveRecord::FixtureSet.all_loaded_fixtures.empty?
-          ActiveRecord::FixtureSet.instantiate_all_loaded_fixtures(self, load_instances?)
-        else
-          raise RuntimeError, 'Load fixtures before instantiating them.' if @loaded_fixtures.nil?
-          @loaded_fixtures.each_value do |fixture_set|
-            ActiveRecord::FixtureSet.instantiate_fixtures(self, fixture_set, load_instances?)
-          end
-        end
-      end
-
-      def load_instances?
-        use_instantiated_fixtures != :no_instances
-      end
-  end
-end
-
-class ActiveRecord::FixtureSet::RenderContext # :nodoc:
-  def self.create_subclass
-    Class.new ActiveRecord::FixtureSet.context_class do
-      def get_binding
-        binding()
+      raise FixtureClassNotFound, "No class attached to find." unless model_class
+      model_class.unscoped do
+        model_class.find(fixture[model_class.primary_key])
       end
     end
   end
diff --git a/activerecord/lib/active_record/gem_version.rb b/activerecord/lib/active_record/gem_version.rb
index a388b529c9..72035a986b 100644
--- a/activerecord/lib/active_record/gem_version.rb
+++ b/activerecord/lib/active_record/gem_version.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # Returns the version of the currently loaded Active Record as a <tt>Gem::Version</tt>
   def self.gem_version
@@ -5,7 +7,7 @@ module ActiveRecord
   end
 
   module VERSION
-    MAJOR = 5
+    MAJOR = 6
     MINOR = 0
     TINY  = 0
     PRE   = "alpha"
diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index e613d157aa..138fd1cf53 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/hash/indifferent_access'
+# frozen_string_literal: true
+
+require "active_support/core_ext/hash/indifferent_access"
 
 module ActiveRecord
   # == Single table inheritance
@@ -19,7 +21,7 @@ module ActiveRecord
   # Be aware that because the type column is an attribute on the record every new
   # subclass will instantly be marked as dirty and the type column will be included
   # in the list of changed attributes on the record. This is different from non
-  # STI classes:
+  # Single Table Inheritance(STI) classes:
   #
   #   Company.new.changed? # => false
   #   Firm.new.changed?    # => true
@@ -30,33 +32,40 @@ module ActiveRecord
   # for differentiating between them or reloading the right type with find.
   #
   # Note, all the attributes for all the cases are kept in the same table. Read more:
-  # http://www.martinfowler.com/eaaCatalog/singleTableInheritance.html
+  # https://www.martinfowler.com/eaaCatalog/singleTableInheritance.html
   #
   module Inheritance
     extend ActiveSupport::Concern
 
     included do
       # Determines whether to store the full constant name including namespace when using STI.
-      class_attribute :store_full_sti_class, instance_writer: false
-      self.store_full_sti_class = true
+      # This is true, by default.
+      class_attribute :store_full_sti_class, instance_writer: false, default: true
     end
 
     module ClassMethods
       # Determines if one of the attributes passed in is the inheritance column,
       # and if the inheritance column is attr accessible, it initializes an
       # instance of the given subclass instead of the base class.
-      def new(*args, &block)
+      def new(attributes = nil, &block)
         if abstract_class? || self == Base
           raise NotImplementedError, "#{self} is an abstract class and cannot be instantiated."
         end
 
-        attrs = args.first
-        if subclass_from_attributes?(attrs)
-          subclass = subclass_from_attributes(attrs)
+        if has_attribute?(inheritance_column)
+          subclass = subclass_from_attributes(attributes)
+
+          if subclass.nil? && scope_attributes = current_scope&.scope_for_create
+            subclass = subclass_from_attributes(scope_attributes)
+          end
+
+          if subclass.nil? && base_class?
+            subclass = subclass_from_attributes(column_defaults)
+          end
         end
 
-        if subclass
-          subclass.new(*args, &block)
+        if subclass && subclass != self
+          subclass.new(attributes, &block)
         else
           super
         end
@@ -82,7 +91,7 @@ module ActiveRecord
       # Returns the class descending directly from ActiveRecord::Base, or
       # an abstract class, if any, in the inheritance hierarchy.
       #
-      # If A extends AR::Base, A.base_class will return A. If B descends from A
+      # If A extends ActiveRecord::Base, A.base_class will return A. If B descends from A
       # through some arbitrarily deep hierarchy, B.base_class will return A.
       #
       # If B < A and C < B and if A is an abstract_class then both B.base_class
@@ -99,21 +108,53 @@ module ActiveRecord
         end
       end
 
-      # Set this to true if this is an abstract class (see <tt>abstract_class?</tt>).
-      # If you are using inheritance with ActiveRecord and don't want child classes
-      # to utilize the implied STI table name of the parent class, this will need to be true.
-      # For example, given the following:
+      # Returns whether the class is a base class.
+      # See #base_class for more information.
+      def base_class?
+        base_class == self
+      end
+
+      # Set this to +true+ if this is an abstract class (see
+      # <tt>abstract_class?</tt>).
+      # If you are using inheritance with Active Record and don't want a class
+      # to be considered as part of the STI hierarchy, you must set this to
+      # true.
+      # +ApplicationRecord+, for example, is generated as an abstract class.
       #
-      #   class SuperClass < ActiveRecord::Base
+      # Consider the following default behaviour:
+      #
+      #   Shape = Class.new(ActiveRecord::Base)
+      #   Polygon = Class.new(Shape)
+      #   Square = Class.new(Polygon)
+      #
+      #   Shape.table_name   # => "shapes"
+      #   Polygon.table_name # => "shapes"
+      #   Square.table_name  # => "shapes"
+      #   Shape.create!      # => #<Shape id: 1, type: nil>
+      #   Polygon.create!    # => #<Polygon id: 2, type: "Polygon">
+      #   Square.create!     # => #<Square id: 3, type: "Square">
+      #
+      # However, when using <tt>abstract_class</tt>, +Shape+ is omitted from
+      # the hierarchy:
+      #
+      #   class Shape < ActiveRecord::Base
       #     self.abstract_class = true
       #   end
-      #   class Child < SuperClass
-      #     self.table_name = 'the_table_i_really_want'
-      #   end
-      #
+      #   Polygon = Class.new(Shape)
+      #   Square = Class.new(Polygon)
       #
-      # <tt>self.abstract_class = true</tt> is required to make <tt>Child<.find,.create, or any Arel method></tt> use <tt>the_table_i_really_want</tt> instead of a table called <tt>super_classes</tt>
+      #   Shape.table_name   # => nil
+      #   Polygon.table_name # => "polygons"
+      #   Square.table_name  # => "polygons"
+      #   Shape.create!      # => NotImplementedError: Shape is an abstract class and cannot be instantiated.
+      #   Polygon.create!    # => #<Polygon id: 1, type: nil>
+      #   Square.create!     # => #<Square id: 2, type: "Square">
       #
+      # Note that in the above example, to disallow the creation of a plain
+      # +Polygon+, you should use <tt>validates :type, presence: true</tt>,
+      # instead of setting it as an abstract class. This way, +Polygon+ will
+      # stay in the hierarchy, and Active Record will continue to correctly
+      # derive the table name.
       attr_accessor :abstract_class
 
       # Returns whether this class is an abstract class or not.
@@ -125,91 +166,104 @@ module ActiveRecord
         store_full_sti_class ? name : name.demodulize
       end
 
+      def polymorphic_name
+        base_class.name
+      end
+
+      def inherited(subclass)
+        subclass.instance_variable_set(:@_type_candidates_cache, Concurrent::Map.new)
+        super
+      end
+
       protected
 
-      # Returns the class type of the record using the current module as a prefix. So descendants of
-      # MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.
-      def compute_type(type_name)
-        if type_name.match(/^::/)
-          # If the type is prefixed with a scope operator then we assume that
-          # the type_name is an absolute reference.
-          ActiveSupport::Dependencies.constantize(type_name)
-        else
-          # Build a list of candidates to search for
-          candidates = []
-          name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }
-          candidates << type_name
-
-          candidates.each do |candidate|
-            constant = ActiveSupport::Dependencies.safe_constantize(candidate)
-            return constant if candidate == constant.to_s
-          end
+        # Returns the class type of the record using the current module as a prefix. So descendants of
+        # MyApp::Business::Account would appear as MyApp::Business::AccountSubclass.
+        def compute_type(type_name)
+          if type_name.start_with?("::")
+            # If the type is prefixed with a scope operator then we assume that
+            # the type_name is an absolute reference.
+            ActiveSupport::Dependencies.constantize(type_name)
+          else
+            type_candidate = @_type_candidates_cache[type_name]
+            if type_candidate && type_constant = ActiveSupport::Dependencies.safe_constantize(type_candidate)
+              return type_constant
+            end
 
-          raise NameError.new("uninitialized constant #{candidates.first}", candidates.first)
-        end
-      end
+            # Build a list of candidates to search for
+            candidates = []
+            name.scan(/::|$/) { candidates.unshift "#{$`}::#{type_name}" }
+            candidates << type_name
 
-      private
+            candidates.each do |candidate|
+              constant = ActiveSupport::Dependencies.safe_constantize(candidate)
+              if candidate == constant.to_s
+                @_type_candidates_cache[type_name] = candidate
+                return constant
+              end
+            end
 
-      # Called by +instantiate+ to decide which class to use for a new
-      # record instance. For single-table inheritance, we check the record
-      # for a +type+ column and return the corresponding class.
-      def discriminate_class_for_record(record)
-        if using_single_table_inheritance?(record)
-          find_sti_class(record[inheritance_column])
-        else
-          super
+            raise NameError.new("uninitialized constant #{candidates.first}", candidates.first)
+          end
         end
-      end
 
-      def using_single_table_inheritance?(record)
-        record[inheritance_column].present? && columns_hash.include?(inheritance_column)
-      end
+      private
 
-      def find_sti_class(type_name)
-        if store_full_sti_class
-          ActiveSupport::Dependencies.constantize(type_name)
-        else
-          compute_type(type_name)
+        # Called by +instantiate+ to decide which class to use for a new
+        # record instance. For single-table inheritance, we check the record
+        # for a +type+ column and return the corresponding class.
+        def discriminate_class_for_record(record)
+          if using_single_table_inheritance?(record)
+            find_sti_class(record[inheritance_column])
+          else
+            super
+          end
         end
-      rescue NameError
-        raise SubclassNotFound,
-          "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " +
-          "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " +
-          "Please rename this column if you didn't intend it to be used for storing the inheritance class " +
-          "or overwrite #{name}.inheritance_column to use another column for that information."
-      end
 
-      def type_condition(table = arel_table)
-        sti_column = table[inheritance_column]
-        sti_names  = ([self] + descendants).map(&:sti_name)
+        def using_single_table_inheritance?(record)
+          record[inheritance_column].present? && has_attribute?(inheritance_column)
+        end
 
-        sti_column.in(sti_names)
-      end
+        def find_sti_class(type_name)
+          type_name = base_class.type_for_attribute(inheritance_column).cast(type_name)
+          subclass = begin
+            if store_full_sti_class
+              ActiveSupport::Dependencies.constantize(type_name)
+            else
+              compute_type(type_name)
+            end
+          rescue NameError
+            raise SubclassNotFound,
+              "The single-table inheritance mechanism failed to locate the subclass: '#{type_name}'. " \
+              "This error is raised because the column '#{inheritance_column}' is reserved for storing the class in case of inheritance. " \
+              "Please rename this column if you didn't intend it to be used for storing the inheritance class " \
+              "or overwrite #{name}.inheritance_column to use another column for that information."
+          end
+          unless subclass == self || descendants.include?(subclass)
+            raise SubclassNotFound, "Invalid single-table inheritance type: #{subclass.name} is not a subclass of #{name}"
+          end
+          subclass
+        end
 
-      # Detect the subclass from the inheritance column of attrs. If the inheritance column value
-      # is not self or a valid subclass, raises ActiveRecord::SubclassNotFound
-      # If this is a StrongParameters hash, and access to inheritance_column is not permitted,
-      # this will ignore the inheritance column and return nil
-      def subclass_from_attributes?(attrs)
-        attribute_names.include?(inheritance_column) && attrs.is_a?(Hash)
-      end
+        def type_condition(table = arel_table)
+          sti_column = arel_attribute(inheritance_column, table)
+          sti_names  = ([self] + descendants).map(&:sti_name)
 
-      def subclass_from_attributes(attrs)
-        subclass_name = attrs.with_indifferent_access[inheritance_column]
+          sti_column.in(sti_names)
+        end
 
-        if subclass_name.present?
-          subclass = find_sti_class(subclass_name)
+        # Detect the subclass from the inheritance column of attrs. If the inheritance column value
+        # is not self or a valid subclass, raises ActiveRecord::SubclassNotFound
+        def subclass_from_attributes(attrs)
+          attrs = attrs.to_h if attrs.respond_to?(:permitted?)
+          if attrs.is_a?(Hash)
+            subclass_name = attrs[inheritance_column] || attrs[inheritance_column.to_sym]
 
-          if subclass.name != self.name
-            unless descendants.include?(subclass)
-              raise ActiveRecord::SubclassNotFound.new("Invalid single-table inheritance type: #{subclass.name} is not a subclass of #{name}")
+            if subclass_name.present?
+              find_sti_class(subclass_name)
             end
-
-            subclass
           end
         end
-      end
     end
 
     def initialize_dup(other)
@@ -219,21 +273,21 @@ module ActiveRecord
 
     private
 
-    def initialize_internals_callback
-      super
-      ensure_proper_type
-    end
+      def initialize_internals_callback
+        super
+        ensure_proper_type
+      end
 
-    # Sets the attribute used for single table inheritance to this class name if this is not the
-    # ActiveRecord::Base descendant.
-    # Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to
-    # do Reply.new without having to set <tt>Reply[Reply.inheritance_column] = "Reply"</tt> yourself.
-    # No such attribute would be set for objects of the Message class in that example.
-    def ensure_proper_type
-      klass = self.class
-      if klass.finder_needs_type_condition?
-        write_attribute(klass.inheritance_column, klass.sti_name)
+      # Sets the attribute used for single table inheritance to this class name if this is not the
+      # ActiveRecord::Base descendant.
+      # Considering the hierarchy Reply < Message < ActiveRecord::Base, this makes it possible to
+      # do Reply.new without having to set <tt>Reply[Reply.inheritance_column] = "Reply"</tt> yourself.
+      # No such attribute would be set for objects of the Message class in that example.
+      def ensure_proper_type
+        klass = self.class
+        if klass.finder_needs_type_condition?
+          _write_attribute(klass.inheritance_column, klass.sti_name)
+        end
       end
-    end
   end
 end
diff --git a/activerecord/lib/active_record/integration.rb b/activerecord/lib/active_record/integration.rb
index 15b2f65dcb..33c4066b89 100644
--- a/activerecord/lib/active_record/integration.rb
+++ b/activerecord/lib/active_record/integration.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/string/filters'
+# frozen_string_literal: true
+
+require "active_support/core_ext/string/filters"
 
 module ActiveRecord
   module Integration
@@ -7,17 +9,24 @@ module ActiveRecord
     included do
       ##
       # :singleton-method:
-      # Indicates the format used to generate the timestamp in the cache key.
-      # Accepts any of the symbols in <tt>Time::DATE_FORMATS</tt>.
+      # Indicates the format used to generate the timestamp in the cache key, if
+      # versioning is off. Accepts any of the symbols in <tt>Time::DATE_FORMATS</tt>.
+      #
+      # This is +:usec+, by default.
+      class_attribute :cache_timestamp_format, instance_writer: false, default: :usec
+
+      ##
+      # :singleton-method:
+      # Indicates whether to use a stable #cache_key method that is accompanied
+      # by a changing version in the #cache_version method.
       #
-      # This is +:nsec+, by default.
-      class_attribute :cache_timestamp_format, :instance_writer => false
-      self.cache_timestamp_format = :nsec
+      # This is +true+, by default on Rails 5.2 and above.
+      class_attribute :cache_versioning, instance_writer: false, default: false
     end
 
-    # Returns a String, which Action Pack uses for constructing an URL to this
-    # object. The default implementation returns this record's id as a String,
-    # or nil if this record's unsaved.
+    # Returns a +String+, which Action Pack uses for constructing a URL to this
+    # object. The default implementation returns this record's id as a +String+,
+    # or +nil+ if this record's unsaved.
     #
     # For example, suppose that you have a User model, and that you have a
     # <tt>resources :users</tt> route. Normally, +user_path+ will
@@ -42,29 +51,62 @@ module ActiveRecord
       id && id.to_s # Be sure to stringify the id for routes
     end
 
-    # Returns a cache key that can be used to identify this record.
+    # Returns a stable cache key that can be used to identify this record.
     #
     #   Product.new.cache_key     # => "products/new"
-    #   Product.find(5).cache_key # => "products/5" (updated_at not available)
-    #   Person.find(5).cache_key  # => "people/5-20071224150000" (updated_at available)
+    #   Product.find(5).cache_key # => "products/5"
     #
-    # You can also pass a list of named timestamps, and the newest in the list will be
-    # used to generate the key:
+    # If ActiveRecord::Base.cache_versioning is turned off, as it was in Rails 5.1 and earlier,
+    # the cache key will also include a version.
     #
-    #   Person.find(5).cache_key(:updated_at, :last_reviewed_at)
+    #   Product.cache_versioning = false
+    #   Product.find(5).cache_key  # => "products/5-20071224150000" (updated_at available)
     def cache_key(*timestamp_names)
-      case
-      when new_record?
+      if new_record?
         "#{model_name.cache_key}/new"
-      when timestamp_names.any?
-        timestamp = max_updated_column_timestamp(timestamp_names)
-        timestamp = timestamp.utc.to_s(cache_timestamp_format)
-        "#{model_name.cache_key}/#{id}-#{timestamp}"
-      when timestamp = max_updated_column_timestamp
-        timestamp = timestamp.utc.to_s(cache_timestamp_format)
-        "#{model_name.cache_key}/#{id}-#{timestamp}"
       else
-        "#{model_name.cache_key}/#{id}"
+        if cache_version && timestamp_names.none?
+          "#{model_name.cache_key}/#{id}"
+        else
+          timestamp = if timestamp_names.any?
+            ActiveSupport::Deprecation.warn(<<-MSG.squish)
+              Specifying a timestamp name for #cache_key has been deprecated in favor of
+              the explicit #cache_version method that can be overwritten.
+            MSG
+
+            max_updated_column_timestamp(timestamp_names)
+          else
+            max_updated_column_timestamp
+          end
+
+          if timestamp
+            timestamp = timestamp.utc.to_s(cache_timestamp_format)
+            "#{model_name.cache_key}/#{id}-#{timestamp}"
+          else
+            "#{model_name.cache_key}/#{id}"
+          end
+        end
+      end
+    end
+
+    # Returns a cache version that can be used together with the cache key to form
+    # a recyclable caching scheme. By default, the #updated_at column is used for the
+    # cache_version, but this method can be overwritten to return something else.
+    #
+    # Note, this method will return nil if ActiveRecord::Base.cache_versioning is set to
+    # +false+ (which it is by default until Rails 6.0).
+    def cache_version
+      if cache_versioning && timestamp = try(:updated_at)
+        timestamp.utc.to_s(:usec)
+      end
+    end
+
+    # Returns a cache key along with the version.
+    def cache_key_with_version
+      if version = cache_version
+        "#{cache_key}-#{version}"
+      else
+        cache_key
       end
     end
 
@@ -84,9 +126,9 @@ module ActiveRecord
       # Values longer than 20 characters will be truncated. The value
       # is truncated word by word.
       #
-      #   user = User.find_by(name: 'David HeinemeierHansson')
+      #   user = User.find_by(name: 'David Heinemeier Hansson')
       #   user.id         # => 125
-      #   user_path(user) # => "/users/125-david"
+      #   user_path(user) # => "/users/125-david-heinemeier"
       #
       # Because the generated param begins with the record's +id+, it is
       # suitable for passing to +find+. In a controller, for example:
@@ -100,7 +142,7 @@ module ActiveRecord
           define_method :to_param do
             if (default = super()) &&
                  (result = send(method_name).to_s).present? &&
-                   (param = result.squish.truncate(20, separator: /\s/, omission: nil).parameterize).present?
+                   (param = result.squish.parameterize.truncate(20, separator: /-/, omission: "")).present?
               "#{default}-#{param}"
             else
               default
diff --git a/activerecord/lib/active_record/internal_metadata.rb b/activerecord/lib/active_record/internal_metadata.rb
new file mode 100644
index 0000000000..3626a13d7c
--- /dev/null
+++ b/activerecord/lib/active_record/internal_metadata.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require "active_record/scoping/default"
+require "active_record/scoping/named"
+
+module ActiveRecord
+  # This class is used to create a table that keeps track of values and keys such
+  # as which environment migrations were run in.
+  class InternalMetadata < ActiveRecord::Base # :nodoc:
+    class << self
+      def primary_key
+        "key"
+      end
+
+      def table_name
+        "#{table_name_prefix}#{ActiveRecord::Base.internal_metadata_table_name}#{table_name_suffix}"
+      end
+
+      def []=(key, value)
+        find_or_initialize_by(key: key).update!(value: value)
+      end
+
+      def [](key)
+        where(key: key).pluck(:value).first
+      end
+
+      def table_exists?
+        connection.table_exists?(table_name)
+      end
+
+      # Creates an internal metadata table with columns +key+ and +value+
+      def create_table
+        unless table_exists?
+          key_options = connection.internal_string_options_for_primary_key
+
+          connection.create_table(table_name, id: false) do |t|
+            t.string :key, key_options
+            t.string :value
+            t.timestamps
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/legacy_yaml_adapter.rb b/activerecord/lib/active_record/legacy_yaml_adapter.rb
index 89dee58423..ffa095dd94 100644
--- a/activerecord/lib/active_record/legacy_yaml_adapter.rb
+++ b/activerecord/lib/active_record/legacy_yaml_adapter.rb
@@ -1,12 +1,14 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module LegacyYamlAdapter
     def self.convert(klass, coder)
       return coder unless coder.is_a?(Psych::Coder)
 
       case coder["active_record_yaml_version"]
-      when 1 then coder
+      when 1, 2 then coder
       else
-        if coder["attributes"].is_a?(AttributeSet)
+        if coder["attributes"].is_a?(ActiveModel::AttributeSet)
           Rails420.convert(klass, coder)
         else
           Rails41.convert(klass, coder)
diff --git a/activerecord/lib/active_record/locale/en.yml b/activerecord/lib/active_record/locale/en.yml
index 8a3c27e6da..0b35027b2b 100644
--- a/activerecord/lib/active_record/locale/en.yml
+++ b/activerecord/lib/active_record/locale/en.yml
@@ -16,8 +16,8 @@ en:
       messages:
         record_invalid: "Validation failed: %{errors}"
         restrict_dependent_destroy:
-          one: "Cannot delete record because a dependent %{record} exists"
-          many: "Cannot delete record because dependent %{record} exist"
+          has_one: "Cannot delete record because a dependent %{record} exists"
+          has_many: "Cannot delete record because dependent %{record} exist"
         # Append your own errors here or at the model/attributes scope.
 
       # You can define own errors for models or model attributes.
diff --git a/activerecord/lib/active_record/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index a09437b4b0..4a3a31fc95 100644
--- a/activerecord/lib/active_record/locking/optimistic.rb
+++ b/activerecord/lib/active_record/locking/optimistic.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Locking
     # == What is Optimistic Locking
@@ -22,7 +24,7 @@ module ActiveRecord
     #   p1.save
     #
     #   p2.first_name = "should fail"
-    #   p2.save # Raises a ActiveRecord::StaleObjectError
+    #   p2.save # Raises an ActiveRecord::StaleObjectError
     #
     # Optimistic locking will also check for stale data when objects are destroyed. Example:
     #
@@ -32,7 +34,7 @@ module ActiveRecord
     #   p1.first_name = "Michael"
     #   p1.save
     #
-    #   p2.destroy # Raises a ActiveRecord::StaleObjectError
+    #   p2.destroy # Raises an ActiveRecord::StaleObjectError
     #
     # You're then responsible for dealing with the conflict by rescuing the exception and either rolling back, merging,
     # or otherwise apply the business logic needed to resolve the conflict.
@@ -51,8 +53,7 @@ module ActiveRecord
       extend ActiveSupport::Concern
 
       included do
-        class_attribute :lock_optimistically, instance_writer: false
-        self.lock_optimistically = true
+        class_attribute :lock_optimistically, instance_writer: false, default: true
       end
 
       def locking_enabled? #:nodoc:
@@ -60,13 +61,7 @@ module ActiveRecord
       end
 
       private
-        def increment_lock
-          lock_col = self.class.locking_column
-          previous_lock_value = send(lock_col).to_i
-          send(lock_col + '=', previous_lock_value + 1)
-        end
-
-        def _create_record(attribute_names = self.attribute_names, *) # :nodoc:
+        def _create_record(attribute_names = self.attribute_names)
           if locking_enabled?
             # We always want to persist the locking version, even if we don't detect
             # a change from the default, since the database might have no default
@@ -75,127 +70,128 @@ module ActiveRecord
           super
         end
 
-        def _update_record(attribute_names = self.attribute_names) #:nodoc:
+        def _touch_row(attribute_names, time)
+          super
+        ensure
+          clear_attribute_change(self.class.locking_column) if locking_enabled?
+        end
+
+        def _update_row(attribute_names, attempted_action = "update")
           return super unless locking_enabled?
-          return 0 if attribute_names.empty?
 
-          lock_col = self.class.locking_column
-          previous_lock_value = send(lock_col).to_i
-          increment_lock
+          begin
+            locking_column = self.class.locking_column
+            previous_lock_value = read_attribute_before_type_cast(locking_column)
+            attribute_names << locking_column
 
-          attribute_names += [lock_col]
-          attribute_names.uniq!
+            self[locking_column] += 1
 
-          begin
-            relation = self.class.unscoped
-
-            affected_rows = relation.where(
-              self.class.primary_key => id,
-              lock_col => previous_lock_value,
-            ).update_all(
-              attributes_for_update(attribute_names).map do |name|
-                [name, _read_attribute(name)]
-              end.to_h
+            affected_rows = self.class._update_record(
+              attributes_with_values(attribute_names),
+              self.class.primary_key => id_in_database,
+              locking_column => previous_lock_value
             )
 
-            unless affected_rows == 1
-              raise ActiveRecord::StaleObjectError.new(self, "update")
+            if affected_rows != 1
+              raise ActiveRecord::StaleObjectError.new(self, attempted_action)
             end
 
             affected_rows
 
-          # If something went wrong, revert the version.
+          # If something went wrong, revert the locking_column value.
           rescue Exception
-            send(lock_col + '=', previous_lock_value)
+            self[locking_column] = previous_lock_value.to_i
             raise
           end
         end
 
         def destroy_row
-          affected_rows = super
+          return super unless locking_enabled?
+
+          locking_column = self.class.locking_column
 
-          if locking_enabled? && affected_rows != 1
+          affected_rows = self.class._delete_record(
+            self.class.primary_key => id_in_database,
+            locking_column => read_attribute_before_type_cast(locking_column)
+          )
+
+          if affected_rows != 1
             raise ActiveRecord::StaleObjectError.new(self, "destroy")
           end
 
           affected_rows
         end
 
-        def relation_for_destroy
-          relation = super
+        module ClassMethods
+          DEFAULT_LOCKING_COLUMN = "lock_version"
 
-          if locking_enabled?
-            locking_column = self.class.locking_column
-            relation = relation.where(locking_column => _read_attribute(locking_column))
+          # Returns true if the +lock_optimistically+ flag is set to true
+          # (which it is, by default) and the table includes the
+          # +locking_column+ column (defaults to +lock_version+).
+          def locking_enabled?
+            lock_optimistically && columns_hash[locking_column]
           end
 
-          relation
-        end
-
-      module ClassMethods
-        DEFAULT_LOCKING_COLUMN = 'lock_version'
-
-        # Returns true if the +lock_optimistically+ flag is set to true
-        # (which it is, by default) and the table includes the
-        # +locking_column+ column (defaults to +lock_version+).
-        def locking_enabled?
-          lock_optimistically && columns_hash[locking_column]
-        end
-
-        # Set the column to use for optimistic locking. Defaults to +lock_version+.
-        def locking_column=(value)
-          reload_schema_from_cache
-          @locking_column = value.to_s
-        end
+          # Set the column to use for optimistic locking. Defaults to +lock_version+.
+          def locking_column=(value)
+            reload_schema_from_cache
+            @locking_column = value.to_s
+          end
 
-        # The version column used for optimistic locking. Defaults to +lock_version+.
-        def locking_column
-          reset_locking_column unless defined?(@locking_column)
-          @locking_column
-        end
+          # The version column used for optimistic locking. Defaults to +lock_version+.
+          def locking_column
+            @locking_column = DEFAULT_LOCKING_COLUMN unless defined?(@locking_column)
+            @locking_column
+          end
 
-        # Reset the column used for optimistic locking back to the +lock_version+ default.
-        def reset_locking_column
-          self.locking_column = DEFAULT_LOCKING_COLUMN
-        end
+          # Reset the column used for optimistic locking back to the +lock_version+ default.
+          def reset_locking_column
+            self.locking_column = DEFAULT_LOCKING_COLUMN
+          end
 
-        # Make sure the lock version column gets updated when counters are
-        # updated.
-        def update_counters(id, counters)
-          counters = counters.merge(locking_column => 1) if locking_enabled?
-          super
-        end
+          # Make sure the lock version column gets updated when counters are
+          # updated.
+          def update_counters(id, counters)
+            counters = counters.merge(locking_column => 1) if locking_enabled?
+            super
+          end
 
-        private
-
-        # We need to apply this decorator here, rather than on module inclusion. The closure
-        # created by the matcher would otherwise evaluate for `ActiveRecord::Base`, not the
-        # sub class being decorated. As such, changes to `lock_optimistically`, or
-        # `locking_column` would not be picked up.
-        def inherited(subclass)
-          subclass.class_eval do
-            is_lock_column = ->(name, _) { lock_optimistically && name == locking_column }
-            decorate_matching_attribute_types(is_lock_column, :_optimistic_locking) do |type|
-              LockingType.new(type)
+          private
+
+            # We need to apply this decorator here, rather than on module inclusion. The closure
+            # created by the matcher would otherwise evaluate for `ActiveRecord::Base`, not the
+            # sub class being decorated. As such, changes to `lock_optimistically`, or
+            # `locking_column` would not be picked up.
+            def inherited(subclass)
+              subclass.class_eval do
+                is_lock_column = ->(name, _) { lock_optimistically && name == locking_column }
+                decorate_matching_attribute_types(is_lock_column, "_optimistic_locking") do |type|
+                  LockingType.new(type)
+                end
+              end
+              super
             end
-          end
-          super
         end
-      end
     end
 
+    # In de/serialize we change `nil` to 0, so that we can allow passing
+    # `nil` values to `lock_version`, and not result in `ActiveRecord::StaleObjectError`
+    # during update record.
     class LockingType < DelegateClass(Type::Value) # :nodoc:
       def deserialize(value)
-        # `nil` *should* be changed to 0
+        super.to_i
+      end
+
+      def serialize(value)
         super.to_i
       end
 
       def init_with(coder)
-        __setobj__(coder['subtype'])
+        __setobj__(coder["subtype"])
       end
 
       def encode_with(coder)
-        coder['subtype'] = __getobj__
+        coder["subtype"] = __getobj__
       end
     end
   end
diff --git a/activerecord/lib/active_record/locking/pessimistic.rb b/activerecord/lib/active_record/locking/pessimistic.rb
index 3d95c54ef3..130ef8a330 100644
--- a/activerecord/lib/active_record/locking/pessimistic.rb
+++ b/activerecord/lib/active_record/locking/pessimistic.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Locking
     # Locking::Pessimistic provides support for row-level locking using
@@ -12,9 +14,9 @@ module ActiveRecord
     # of your own such as 'LOCK IN SHARE MODE' or 'FOR UPDATE NOWAIT'. Example:
     #
     #   Account.transaction do
-    #     # select * from accounts where name = 'shugo' limit 1 for update
-    #     shugo = Account.where("name = 'shugo'").lock(true).first
-    #     yuko = Account.where("name = 'yuko'").lock(true).first
+    #     # select * from accounts where name = 'shugo' limit 1 for update nowait
+    #     shugo = Account.lock("FOR UPDATE NOWAIT").find_by(name: "shugo")
+    #     yuko = Account.lock("FOR UPDATE NOWAIT").find_by(name: "yuko")
     #     shugo.balance -= 100
     #     shugo.save!
     #     yuko.balance += 100
@@ -51,15 +53,25 @@ module ActiveRecord
     #   end
     #
     # Database-specific information on row locking:
-    #   MySQL: http://dev.mysql.com/doc/refman/5.6/en/innodb-locking-reads.html
-    #   PostgreSQL: http://www.postgresql.org/docs/current/interactive/sql-select.html#SQL-FOR-UPDATE-SHARE
+    #   MySQL: https://dev.mysql.com/doc/refman/5.7/en/innodb-locking-reads.html
+    #   PostgreSQL: https://www.postgresql.org/docs/current/interactive/sql-select.html#SQL-FOR-UPDATE-SHARE
     module Pessimistic
       # Obtain a row lock on this record. Reloads the record to obtain the requested
       # lock. Pass an SQL locking clause to append the end of the SELECT statement
       # or pass true for "FOR UPDATE" (the default, an exclusive row lock). Returns
       # the locked record.
       def lock!(lock = true)
-        reload(:lock => lock) if persisted?
+        if persisted?
+          if has_changes_to_save?
+            raise(<<-MSG.squish)
+              Locking a record with unpersisted changes is not supported. Use
+              `save` to persist the changes, or `reload` to discard them
+              explicitly.
+            MSG
+          end
+
+          reload(lock: lock)
+        end
         self
       end
 
diff --git a/activerecord/lib/active_record/log_subscriber.rb b/activerecord/lib/active_record/log_subscriber.rb
index 4d597a0ab1..6b84431343 100644
--- a/activerecord/lib/active_record/log_subscriber.rb
+++ b/activerecord/lib/active_record/log_subscriber.rb
@@ -1,7 +1,11 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class LogSubscriber < ActiveSupport::LogSubscriber
     IGNORE_PAYLOAD_NAMES = ["SCHEMA", "EXPLAIN"]
 
+    class_attribute :backtrace_cleaner, default: ActiveSupport::BacktraceCleaner.new
+
     def self.runtime=(value)
       ActiveRecord::RuntimeRegistry.sql_runtime = value
     end
@@ -15,58 +19,99 @@ module ActiveRecord
       rt
     end
 
-    def initialize
-      super
-      @odd = false
-    end
-
-    def render_bind(attribute)
-      value = if attribute.type.binary? && attribute.value
-        "<#{attribute.value.bytesize} bytes of binary data>"
-      else
-        attribute.value_for_database
-      end
-
-      [attribute.name, value]
-    end
-
     def sql(event)
-      return unless logger.debug?
-
       self.class.runtime += event.duration
+      return unless logger.debug?
 
       payload = event.payload
 
       return if IGNORE_PAYLOAD_NAMES.include?(payload[:name])
 
       name  = "#{payload[:name]} (#{event.duration.round(1)}ms)"
+      name  = "CACHE #{name}" if payload[:cached]
       sql   = payload[:sql]
       binds = nil
 
       unless (payload[:binds] || []).empty?
-        binds = "  " + payload[:binds].map { |attr| render_bind(attr) }.inspect
+        casted_params = type_casted_binds(payload[:type_casted_binds])
+        binds = "  " + payload[:binds].zip(casted_params).map { |attr, value|
+          render_bind(attr, value)
+        }.inspect
       end
 
-      name = color(name, nil, true)
+      name = colorize_payload_name(name, payload[:name])
       sql  = color(sql, sql_color(sql), true)
 
       debug "  #{name}  #{sql}#{binds}"
     end
 
-    def sql_color(sql)
-      case sql
-        when /\s*\Ainsert/i      then GREEN
-        when /\s*\Aselect/i      then BLUE
-        when /\s*\Aupdate/i      then YELLOW
-        when /\s*\Adelete/i      then RED
-        when /transaction\s*\Z/i then CYAN
-        else MAGENTA
+    private
+      def type_casted_binds(casted_binds)
+        casted_binds.respond_to?(:call) ? casted_binds.call : casted_binds
       end
-    end
 
-    def logger
-      ActiveRecord::Base.logger
-    end
+      def render_bind(attr, value)
+        if attr.is_a?(Array)
+          attr = attr.first
+        elsif attr.type.binary? && attr.value
+          value = "<#{attr.value_for_database.to_s.bytesize} bytes of binary data>"
+        end
+
+        [attr && attr.name, value]
+      end
+
+      def colorize_payload_name(name, payload_name)
+        if payload_name.blank? || payload_name == "SQL" # SQL vs Model Load/Exists
+          color(name, MAGENTA, true)
+        else
+          color(name, CYAN, true)
+        end
+      end
+
+      def sql_color(sql)
+        case sql
+        when /\A\s*rollback/mi
+          RED
+        when /select .*for update/mi, /\A\s*lock/mi
+          WHITE
+        when /\A\s*select/i
+          BLUE
+        when /\A\s*insert/i
+          GREEN
+        when /\A\s*update/i
+          YELLOW
+        when /\A\s*delete/i
+          RED
+        when /transaction\s*\Z/i
+          CYAN
+        else
+          MAGENTA
+        end
+      end
+
+      def logger
+        ActiveRecord::Base.logger
+      end
+
+      def debug(progname = nil, &block)
+        return unless super
+
+        if ActiveRecord::Base.verbose_query_logs
+          log_query_source
+        end
+      end
+
+      def log_query_source
+        source = extract_query_source_location(caller)
+
+        if source
+          logger.debug("  ↳ #{source}")
+        end
+      end
+
+      def extract_query_source_location(locations)
+        backtrace_cleaner.clean(locations).first
+      end
   end
 end
 
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index 4cfda302ea..6e5a610642 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -1,5 +1,9 @@
+# frozen_string_literal: true
+
+require "benchmark"
+require "set"
+require "zlib"
 require "active_support/core_ext/module/attribute_accessors"
-require 'set'
 
 module ActiveRecord
   class MigrationError < ActiveRecordError#:nodoc:
@@ -9,40 +13,171 @@ module ActiveRecord
     end
   end
 
-  # Exception that can be raised to stop migrations from going backwards.
+  # Exception that can be raised to stop migrations from being rolled back.
+  # For example the following migration is not reversible.
+  # Rolling back this migration will raise an ActiveRecord::IrreversibleMigration error.
+  #
+  #   class IrreversibleMigrationExample < ActiveRecord::Migration[5.0]
+  #     def change
+  #       create_table :distributors do |t|
+  #         t.string :zipcode
+  #       end
+  #
+  #       execute <<-SQL
+  #         ALTER TABLE distributors
+  #           ADD CONSTRAINT zipchk
+  #             CHECK (char_length(zipcode) = 5) NO INHERIT;
+  #       SQL
+  #     end
+  #   end
+  #
+  # There are two ways to mitigate this problem.
+  #
+  # 1. Define <tt>#up</tt> and <tt>#down</tt> methods instead of <tt>#change</tt>:
+  #
+  #  class ReversibleMigrationExample < ActiveRecord::Migration[5.0]
+  #    def up
+  #      create_table :distributors do |t|
+  #        t.string :zipcode
+  #      end
+  #
+  #      execute <<-SQL
+  #        ALTER TABLE distributors
+  #          ADD CONSTRAINT zipchk
+  #            CHECK (char_length(zipcode) = 5) NO INHERIT;
+  #      SQL
+  #    end
+  #
+  #    def down
+  #      execute <<-SQL
+  #        ALTER TABLE distributors
+  #          DROP CONSTRAINT zipchk
+  #      SQL
+  #
+  #      drop_table :distributors
+  #    end
+  #  end
+  #
+  # 2. Use the #reversible method in <tt>#change</tt> method:
+  #
+  #   class ReversibleMigrationExample < ActiveRecord::Migration[5.0]
+  #     def change
+  #       create_table :distributors do |t|
+  #         t.string :zipcode
+  #       end
+  #
+  #       reversible do |dir|
+  #         dir.up do
+  #           execute <<-SQL
+  #             ALTER TABLE distributors
+  #               ADD CONSTRAINT zipchk
+  #                 CHECK (char_length(zipcode) = 5) NO INHERIT;
+  #           SQL
+  #         end
+  #
+  #         dir.down do
+  #           execute <<-SQL
+  #             ALTER TABLE distributors
+  #               DROP CONSTRAINT zipchk
+  #           SQL
+  #         end
+  #       end
+  #     end
+  #   end
   class IrreversibleMigration < MigrationError
   end
 
   class DuplicateMigrationVersionError < MigrationError#:nodoc:
-    def initialize(version)
-      super("Multiple migrations have the version number #{version}")
+    def initialize(version = nil)
+      if version
+        super("Multiple migrations have the version number #{version}.")
+      else
+        super("Duplicate migration version error.")
+      end
     end
   end
 
   class DuplicateMigrationNameError < MigrationError#:nodoc:
-    def initialize(name)
-      super("Multiple migrations have the name #{name}")
+    def initialize(name = nil)
+      if name
+        super("Multiple migrations have the name #{name}.")
+      else
+        super("Duplicate migration name.")
+      end
     end
   end
 
   class UnknownMigrationVersionError < MigrationError #:nodoc:
-    def initialize(version)
-      super("No migration with version number #{version}")
+    def initialize(version = nil)
+      if version
+        super("No migration with version number #{version}.")
+      else
+        super("Unknown migration version.")
+      end
     end
   end
 
   class IllegalMigrationNameError < MigrationError#:nodoc:
-    def initialize(name)
-      super("Illegal name for migration file: #{name}\n\t(only lower case letters, numbers, and '_' allowed)")
+    def initialize(name = nil)
+      if name
+        super("Illegal name for migration file: #{name}\n\t(only lower case letters, numbers, and '_' allowed).")
+      else
+        super("Illegal name for migration.")
+      end
     end
   end
 
   class PendingMigrationError < MigrationError#:nodoc:
+    def initialize(message = nil)
+      if !message && defined?(Rails.env)
+        super("Migrations are pending. To resolve this issue, run:\n\n        rails db:migrate RAILS_ENV=#{::Rails.env}")
+      elsif !message
+        super("Migrations are pending. To resolve this issue, run:\n\n        rails db:migrate")
+      else
+        super
+      end
+    end
+  end
+
+  class ConcurrentMigrationError < MigrationError #:nodoc:
+    DEFAULT_MESSAGE = "Cannot run migrations because another migration process is currently running."
+    RELEASE_LOCK_FAILED_MESSAGE = "Failed to release advisory lock"
+
+    def initialize(message = DEFAULT_MESSAGE)
+      super
+    end
+  end
+
+  class NoEnvironmentInSchemaError < MigrationError #:nodoc:
     def initialize
+      msg = "Environment data not found in the schema. To resolve this issue, run: \n\n        rails db:environment:set"
+      if defined?(Rails.env)
+        super("#{msg} RAILS_ENV=#{::Rails.env}")
+      else
+        super(msg)
+      end
+    end
+  end
+
+  class ProtectedEnvironmentError < ActiveRecordError #:nodoc:
+    def initialize(env = "production")
+      msg = +"You are attempting to run a destructive action against your '#{env}' database.\n"
+      msg << "If you are sure you want to continue, run the same command with the environment variable:\n"
+      msg << "DISABLE_DATABASE_ENVIRONMENT_CHECK=1"
+      super(msg)
+    end
+  end
+
+  class EnvironmentMismatchError < ActiveRecordError
+    def initialize(current: nil, stored: nil)
+      msg = +"You are attempting to modify a database that was last run in `#{ stored }` environment.\n"
+      msg << "You are running in `#{ current }` environment. "
+      msg << "If you are sure you want to continue, first set the environment using:\n\n"
+      msg << "        rails db:environment:set"
       if defined?(Rails.env)
-        super("Migrations are pending. To resolve this issue, run:\n\n\tbin/rake db:migrate RAILS_ENV=#{::Rails.env}")
+        super("#{msg} RAILS_ENV=#{::Rails.env}\n\n")
       else
-        super("Migrations are pending. To resolve this issue, run:\n\n\tbin/rake db:migrate")
+        super("#{msg}\n\n")
       end
     end
   end
@@ -59,7 +194,7 @@ module ActiveRecord
   #
   # Example of a simple migration:
   #
-  #   class AddSsl < ActiveRecord::Migration
+  #   class AddSsl < ActiveRecord::Migration[5.0]
   #     def up
   #       add_column :accounts, :ssl_enabled, :boolean, default: true
   #     end
@@ -79,7 +214,7 @@ module ActiveRecord
   #
   # Example of a more complex migration that also needs to initialize data:
   #
-  #   class AddSystemSettings < ActiveRecord::Migration
+  #   class AddSystemSettings < ActiveRecord::Migration[5.0]
   #     def up
   #       create_table :system_settings do |t|
   #         t.string  :name
@@ -106,17 +241,18 @@ module ActiveRecord
   #
   # == Available transformations
   #
+  # === Creation
+  #
+  # * <tt>create_join_table(table_1, table_2, options)</tt>: Creates a join
+  #   table having its name as the lexical order of the first two
+  #   arguments. See
+  #   ActiveRecord::ConnectionAdapters::SchemaStatements#create_join_table for
+  #   details.
   # * <tt>create_table(name, options)</tt>: Creates a table called +name+ and
   #   makes the table object available to a block that can then add columns to it,
   #   following the same format as +add_column+. See example above. The options hash
   #   is for fragments like "DEFAULT CHARSET=UTF-8" that are appended to the create
   #   table definition.
-  # * <tt>drop_table(name)</tt>: Drops the table called +name+.
-  # * <tt>change_table(name, options)</tt>: Allows to make column alterations to
-  #   the table called +name+. It makes the table object available to a block that
-  #   can then add/remove columns, indexes or foreign keys to it.
-  # * <tt>rename_table(old_name, new_name)</tt>: Renames the table called +old_name+
-  #   to +new_name+.
   # * <tt>add_column(table_name, column_name, type, options)</tt>: Adds a new column
   #   to the table called +table_name+
   #   named +column_name+ specified to be one of the following types:
@@ -127,24 +263,61 @@ module ActiveRecord
   #   Other options include <tt>:limit</tt> and <tt>:null</tt> (e.g.
   #   <tt>{ limit: 50, null: false }</tt>) -- see
   #   ActiveRecord::ConnectionAdapters::TableDefinition#column for details.
-  # * <tt>rename_column(table_name, column_name, new_column_name)</tt>: Renames
-  #   a column but keeps the type and content.
-  # * <tt>change_column(table_name, column_name, type, options)</tt>:  Changes
-  #   the column to a different type using the same parameters as add_column.
-  # * <tt>remove_column(table_name, column_name, type, options)</tt>: Removes the column
-  #   named +column_name+ from the table called +table_name+.
+  # * <tt>add_foreign_key(from_table, to_table, options)</tt>: Adds a new
+  #   foreign key. +from_table+ is the table with the key column, +to_table+ contains
+  #   the referenced primary key.
   # * <tt>add_index(table_name, column_names, options)</tt>: Adds a new index
   #   with the name of the column. Other options include
   #   <tt>:name</tt>, <tt>:unique</tt> (e.g.
   #   <tt>{ name: 'users_name_index', unique: true }</tt>) and <tt>:order</tt>
   #   (e.g. <tt>{ order: { name: :desc } }</tt>).
+  # * <tt>add_reference(:table_name, :reference_name)</tt>: Adds a new column
+  #   +reference_name_id+ by default an integer. See
+  #   ActiveRecord::ConnectionAdapters::SchemaStatements#add_reference for details.
+  # * <tt>add_timestamps(table_name, options)</tt>: Adds timestamps (+created_at+
+  #   and +updated_at+) columns to +table_name+.
+  #
+  # === Modification
+  #
+  # * <tt>change_column(table_name, column_name, type, options)</tt>:  Changes
+  #   the column to a different type using the same parameters as add_column.
+  # * <tt>change_column_default(table_name, column_name, default_or_changes)</tt>:
+  #   Sets a default value for +column_name+ defined by +default_or_changes+ on
+  #   +table_name+. Passing a hash containing <tt>:from</tt> and <tt>:to</tt>
+  #   as +default_or_changes+ will make this change reversible in the migration.
+  # * <tt>change_column_null(table_name, column_name, null, default = nil)</tt>:
+  #   Sets or removes a +NOT NULL+ constraint on +column_name+. The +null+ flag
+  #   indicates whether the value can be +NULL+. See
+  #   ActiveRecord::ConnectionAdapters::SchemaStatements#change_column_null for
+  #   details.
+  # * <tt>change_table(name, options)</tt>: Allows to make column alterations to
+  #   the table called +name+. It makes the table object available to a block that
+  #   can then add/remove columns, indexes or foreign keys to it.
+  # * <tt>rename_column(table_name, column_name, new_column_name)</tt>: Renames
+  #   a column but keeps the type and content.
+  # * <tt>rename_index(table_name, old_name, new_name)</tt>: Renames an index.
+  # * <tt>rename_table(old_name, new_name)</tt>: Renames the table called +old_name+
+  #   to +new_name+.
+  #
+  # === Deletion
+  #
+  # * <tt>drop_table(name)</tt>: Drops the table called +name+.
+  # * <tt>drop_join_table(table_1, table_2, options)</tt>: Drops the join table
+  #   specified by the given arguments.
+  # * <tt>remove_column(table_name, column_name, type, options)</tt>: Removes the column
+  #   named +column_name+ from the table called +table_name+.
+  # * <tt>remove_columns(table_name, *column_names)</tt>: Removes the given
+  #   columns from the table definition.
+  # * <tt>remove_foreign_key(from_table, options_or_to_table)</tt>: Removes the
+  #   given foreign key from the table called +table_name+.
   # * <tt>remove_index(table_name, column: column_names)</tt>: Removes the index
   #   specified by +column_names+.
   # * <tt>remove_index(table_name, name: index_name)</tt>: Removes the index
   #   specified by +index_name+.
-  # * <tt>add_reference(:table_name, :reference_name)</tt>: Adds a new column
-  #   +reference_name_id+ by default a integer. See
-  #   ActiveRecord::ConnectionAdapters::SchemaStatements#add_reference for details.
+  # * <tt>remove_reference(table_name, ref_name, options)</tt>: Removes the
+  #   reference(s) on +table_name+ specified by +ref_name+.
+  # * <tt>remove_timestamps(table_name, options)</tt>: Removes the timestamp
+  #   columns (+created_at+ and +updated_at+) from the table definition.
   #
   # == Irreversible transformations
   #
@@ -168,24 +341,24 @@ module ActiveRecord
   #
   #   rails generate migration add_fieldname_to_tablename fieldname:string
   #
-  # This will generate the file <tt>timestamp_add_fieldname_to_tablename</tt>, which will look like this:
-  #   class AddFieldnameToTablename < ActiveRecord::Migration
+  # This will generate the file <tt>timestamp_add_fieldname_to_tablename.rb</tt>, which will look like this:
+  #   class AddFieldnameToTablename < ActiveRecord::Migration[5.0]
   #     def change
   #       add_column :tablenames, :fieldname, :string
   #     end
   #   end
   #
   # To run migrations against the currently configured database, use
-  # <tt>rake db:migrate</tt>. This will update the database by running all of the
+  # <tt>rails db:migrate</tt>. This will update the database by running all of the
   # pending migrations, creating the <tt>schema_migrations</tt> table
   # (see "About the schema_migrations table" section below) if missing. It will also
-  # invoke the db:schema:dump task, which will update your db/schema.rb file
+  # invoke the db:schema:dump command, which will update your db/schema.rb file
   # to match the structure of your database.
   #
   # To roll the database back to a previous migration version, use
-  # <tt>rake db:migrate VERSION=X</tt> where <tt>X</tt> is the version to which
+  # <tt>rails db:rollback VERSION=X</tt> where <tt>X</tt> is the version to which
   # you wish to downgrade. Alternatively, you can also use the STEP option if you
-  # wish to rollback last few migrations. <tt>rake db:migrate STEP=2</tt> will rollback
+  # wish to rollback last few migrations. <tt>rails db:rollback STEP=2</tt> will rollback
   # the latest two migrations.
   #
   # If any of the migrations throw an <tt>ActiveRecord::IrreversibleMigration</tt> exception,
@@ -200,7 +373,7 @@ module ActiveRecord
   #
   # Not all migrations change the schema. Some just fix the data:
   #
-  #   class RemoveEmptyTags < ActiveRecord::Migration
+  #   class RemoveEmptyTags < ActiveRecord::Migration[5.0]
   #     def up
   #       Tag.all.each { |tag| tag.destroy if tag.pages.empty? }
   #     end
@@ -213,7 +386,7 @@ module ActiveRecord
   #
   # Others remove columns when they migrate up instead of down:
   #
-  #   class RemoveUnnecessaryItemAttributes < ActiveRecord::Migration
+  #   class RemoveUnnecessaryItemAttributes < ActiveRecord::Migration[5.0]
   #     def up
   #       remove_column :items, :incomplete_items_count
   #       remove_column :items, :completed_items_count
@@ -227,7 +400,7 @@ module ActiveRecord
   #
   # And sometimes you need to do something in SQL not abstracted directly by migrations:
   #
-  #   class MakeJoinUnique < ActiveRecord::Migration
+  #   class MakeJoinUnique < ActiveRecord::Migration[5.0]
   #     def up
   #       execute "ALTER TABLE `pages_linked_pages` ADD UNIQUE `page_id_linked_page_id` (`page_id`,`linked_page_id`)"
   #     end
@@ -244,7 +417,7 @@ module ActiveRecord
   # <tt>Base#reset_column_information</tt> in order to ensure that the model has the
   # latest column data from after the new column was added. Example:
   #
-  #   class AddPeopleSalary < ActiveRecord::Migration
+  #   class AddPeopleSalary < ActiveRecord::Migration[5.0]
   #     def up
   #       add_column :people, :salary, :integer
   #       Person.reset_column_information
@@ -302,7 +475,7 @@ module ActiveRecord
   # To define a reversible migration, define the +change+ method in your
   # migration like this:
   #
-  #   class TenderloveMigration < ActiveRecord::Migration
+  #   class TenderloveMigration < ActiveRecord::Migration[5.0]
   #     def change
   #       create_table(:horses) do |t|
   #         t.column :content, :text
@@ -332,7 +505,7 @@ module ActiveRecord
   # can't execute inside a transaction though, and for these situations
   # you can turn the automatic transactions off.
   #
-  #   class ChangeEnum < ActiveRecord::Migration
+  #   class ChangeEnum < ActiveRecord::Migration[5.0]
   #     disable_ddl_transaction!
   #
   #     def up
@@ -343,11 +516,35 @@ module ActiveRecord
   # Remember that you can still open your own transactions, even if you
   # are in a Migration with <tt>self.disable_ddl_transaction!</tt>.
   class Migration
-    autoload :CommandRecorder, 'active_record/migration/command_recorder'
+    autoload :CommandRecorder, "active_record/migration/command_recorder"
+    autoload :Compatibility, "active_record/migration/compatibility"
+
+    # This must be defined before the inherited hook, below
+    class Current < Migration # :nodoc:
+    end
+
+    def self.inherited(subclass) # :nodoc:
+      super
+      if subclass.superclass == Migration
+        raise StandardError, "Directly inheriting from ActiveRecord::Migration is not supported. " \
+          "Please specify the Rails release the migration was written for:\n" \
+          "\n" \
+          "  class #{subclass} < ActiveRecord::Migration[4.2]"
+      end
+    end
+
+    def self.[](version)
+      Compatibility.find(version)
+    end
 
+    def self.current_version
+      ActiveRecord::VERSION::STRING.to_f
+    end
+
+    MigrationFilenameRegexp = /\A([0-9]+)_([_a-z0-9]*)\.?([_a-z0-9]*)?\.rb\z/ # :nodoc:
 
     # This class is used to verify that all migrations have been run before
-    # loading a web page if config.active_record.migration_error is set to :page_load
+    # loading a web page if <tt>config.active_record.migration_error</tt> is set to :page_load
     class CheckPending
       def initialize(app)
         @app = app
@@ -355,38 +552,42 @@ module ActiveRecord
       end
 
       def call(env)
-        if connection.supports_migrations?
-          mtime = ActiveRecord::Migrator.last_migration.mtime.to_i
-          if @last_check < mtime
-            ActiveRecord::Migration.check_pending!(connection)
-            @last_check = mtime
-          end
+        mtime = ActiveRecord::Base.connection.migration_context.last_migration.mtime.to_i
+        if @last_check < mtime
+          ActiveRecord::Migration.check_pending!(connection)
+          @last_check = mtime
         end
         @app.call(env)
       end
 
       private
 
-      def connection
-        ActiveRecord::Base.connection
-      end
+        def connection
+          ActiveRecord::Base.connection
+        end
     end
 
     class << self
       attr_accessor :delegate # :nodoc:
       attr_accessor :disable_ddl_transaction # :nodoc:
 
+      def nearest_delegate # :nodoc:
+        delegate || superclass.nearest_delegate
+      end
+
+      # Raises <tt>ActiveRecord::PendingMigrationError</tt> error if any migrations are pending.
       def check_pending!(connection = Base.connection)
-        raise ActiveRecord::PendingMigrationError if ActiveRecord::Migrator.needs_migration?(connection)
+        raise ActiveRecord::PendingMigrationError if connection.migration_context.needs_migration?
       end
 
       def load_schema_if_pending!
-        if ActiveRecord::Migrator.needs_migration? || !ActiveRecord::Migrator.any_migrations?
+        if Base.connection.migration_context.needs_migration? || !Base.connection.migration_context.any_migrations?
           # Roundtrip to Rake to allow plugins to hook into database initialization.
-          FileUtils.cd Rails.root do
+          root = defined?(ENGINE_ROOT) ? ENGINE_ROOT : Rails.root
+          FileUtils.cd(root) do
             current_config = Base.connection_config
             Base.clear_all_connections!
-            system("bin/rake db:test:prepare")
+            system("bin/rails db:test:prepare")
             # Establish a new connection, the old database may be gone (db:test:prepare uses purge)
             Base.establish_connection(current_config)
           end
@@ -401,14 +602,17 @@ module ActiveRecord
       end
 
       def method_missing(name, *args, &block) # :nodoc:
-        (delegate || superclass.delegate).send(name, *args, &block)
+        nearest_delegate.send(name, *args, &block)
       end
 
       def migrate(direction)
         new.migrate direction
       end
 
-      # Disable DDL transactions for this migration.
+      # Disable the transaction wrapping this migration.
+      # You can still create your own transactions even after calling #disable_ddl_transaction!
+      #
+      # For more details read the {"Transactional Migrations" section above}[rdoc-ref:Migration].
       def disable_ddl_transaction!
         @disable_ddl_transaction = true
       end
@@ -438,7 +642,7 @@ module ActiveRecord
     # and create the table 'apples' on the way up, and the reverse
     # on the way down.
     #
-    #   class FixTLMigration < ActiveRecord::Migration
+    #   class FixTLMigration < ActiveRecord::Migration[5.0]
     #     def change
     #       revert do
     #         create_table(:horses) do |t|
@@ -455,9 +659,9 @@ module ActiveRecord
     # Or equivalently, if +TenderloveMigration+ is defined as in the
     # documentation for Migration:
     #
-    #   require_relative '2012121212_tenderlove_migration'
+    #   require_relative '20121212123456_tenderlove_migration'
     #
-    #   class FixupTLMigration < ActiveRecord::Migration
+    #   class FixupTLMigration < ActiveRecord::Migration[5.0]
     #     def change
     #       revert TenderloveMigration
     #
@@ -471,27 +675,25 @@ module ActiveRecord
     def revert(*migration_classes)
       run(*migration_classes.reverse, revert: true) unless migration_classes.empty?
       if block_given?
-        if @connection.respond_to? :revert
-          @connection.revert { yield }
+        if connection.respond_to? :revert
+          connection.revert { yield }
         else
-          recorder = CommandRecorder.new(@connection)
+          recorder = command_recorder
           @connection = recorder
           suppress_messages do
-            @connection.revert { yield }
+            connection.revert { yield }
           end
           @connection = recorder.delegate
-          recorder.commands.each do |cmd, args, block|
-            send(cmd, *args, &block)
-          end
+          recorder.replay(self)
         end
       end
     end
 
     def reverting?
-      @connection.respond_to?(:reverting) && @connection.reverting
+      connection.respond_to?(:reverting) && connection.reverting
     end
 
-    class ReversibleBlockHelper < Struct.new(:reverting) # :nodoc:
+    ReversibleBlockHelper = Struct.new(:reverting) do # :nodoc:
       def up
         yield unless reverting
       end
@@ -510,7 +712,7 @@ module ActiveRecord
     # when the three columns 'first_name', 'last_name' and 'full_name' exist,
     # even when migrating down:
     #
-    #    class SplitNameMigration < ActiveRecord::Migration
+    #    class SplitNameMigration < ActiveRecord::Migration[5.0]
     #      def change
     #        add_column :users, :first_name, :string
     #        add_column :users, :last_name, :string
@@ -529,7 +731,25 @@ module ActiveRecord
     #    end
     def reversible
       helper = ReversibleBlockHelper.new(reverting?)
-      execute_block{ yield helper }
+      execute_block { yield helper }
+    end
+
+    # Used to specify an operation that is only run when migrating up
+    # (for example, populating a new column with its initial values).
+    #
+    # In the following example, the new column +published+ will be given
+    # the value +true+ for all existing records.
+    #
+    #    class AddPublishedToPosts < ActiveRecord::Migration[5.2]
+    #      def change
+    #        add_column :posts, :published, :boolean, default: false
+    #        up_only do
+    #          execute "update posts set published = 'true'"
+    #        end
+    #      end
+    #    end
+    def up_only
+      execute_block { yield } unless reverting?
     end
 
     # Runs the given migration classes.
@@ -545,7 +765,7 @@ module ActiveRecord
         revert { run(*migration_classes, direction: dir, revert: true) }
       else
         migration_classes.each do |migration_class|
-          migration_class.new.exec_migration(@connection, dir)
+          migration_class.new.exec_migration(connection, dir)
         end
       end
     end
@@ -571,7 +791,7 @@ module ActiveRecord
       when :down then announce "reverting"
       end
 
-      time   = nil
+      time = nil
       ActiveRecord::Base.connection_pool.with_connection do |conn|
         time = Benchmark.measure do
           exec_migration(conn, direction)
@@ -599,7 +819,7 @@ module ActiveRecord
       @connection = nil
     end
 
-    def write(text="")
+    def write(text = "")
       puts(text) if verbose
     end
 
@@ -609,10 +829,14 @@ module ActiveRecord
       write "== %s %s" % [text, "=" * length]
     end
 
-    def say(message, subitem=false)
+    # Takes a message argument and outputs it as is.
+    # A second boolean argument can be passed to specify whether to indent or not.
+    def say(message, subitem = false)
       write "#{subitem ? "   ->" : "--"} #{message}"
     end
 
+    # Outputs text along with how long it took to run its block.
+    # If the block returns an integer it assumes it is the number of rows affected.
     def say_with_time(message)
       say(message)
       result = nil
@@ -622,6 +846,7 @@ module ActiveRecord
       result
     end
 
+    # Takes a block as an argument and suppresses any output generated by the block.
     def suppress_messages
       save, self.verbose = verbose, false
       yield
@@ -634,10 +859,10 @@ module ActiveRecord
     end
 
     def method_missing(method, *arguments, &block)
-      arg_list = arguments.map(&:inspect) * ', '
+      arg_list = arguments.map(&:inspect) * ", "
 
       say_with_time "#{method}(#{arg_list})" do
-        unless @connection.respond_to? :revert
+        unless connection.respond_to? :revert
           unless arguments.empty? || [:execute, :enable_extension, :disable_extension].include?(method)
             arguments[0] = proper_table_name(arguments.first, table_name_options)
             if [:rename_table, :add_foreign_key].include?(method) ||
@@ -656,23 +881,25 @@ module ActiveRecord
 
       FileUtils.mkdir_p(destination) unless File.exist?(destination)
 
-      destination_migrations = ActiveRecord::Migrator.migrations(destination)
+      destination_migrations = ActiveRecord::MigrationContext.new(destination).migrations
       last = destination_migrations.last
       sources.each do |scope, path|
-        source_migrations = ActiveRecord::Migrator.migrations(path)
+        source_migrations = ActiveRecord::MigrationContext.new(path).migrations
 
         source_migrations.each do |migration|
           source = File.binread(migration.filename)
           inserted_comment = "# This migration comes from #{scope} (originally #{migration.version})\n"
-          if /\A#.*\b(?:en)?coding:\s*\S+/ =~ source
+          magic_comments = +""
+          loop do
             # If we have a magic comment in the original migration,
             # insert our comment after the first newline(end of the magic comment line)
             # so the magic keep working.
             # Note that magic comments must be at the first line(except sh-bang).
-            source[/\n/] = "\n#{inserted_comment}"
-          else
-            source = "#{inserted_comment}#{source}"
+            source.sub!(/\A(?:#.*\b(?:en)?coding:\s*\S+|#\s*frozen_string_literal:\s*(?:true|false)).*\n/) do |magic_comment|
+              magic_comments << magic_comment; ""
+            end || break
           end
+          source = "#{magic_comments}#{inserted_comment}#{source}"
 
           if duplicate = destination_migrations.detect { |m| m.name == migration.name }
             if options[:on_skip] && duplicate.scope != scope.to_s
@@ -716,7 +943,9 @@ module ActiveRecord
       end
     end
 
-    def table_name_options(config = ActiveRecord::Base)
+    # Builds a hash for use in ActiveRecord::Migration#proper_table_name using
+    # the Active Record object's table_name prefix and suffix
+    def table_name_options(config = ActiveRecord::Base) #:nodoc:
       {
         table_name_prefix: config.table_name_prefix,
         table_name_suffix: config.table_name_suffix
@@ -724,19 +953,22 @@ module ActiveRecord
     end
 
     private
-    def execute_block
-      if connection.respond_to? :execute_block
-        super # use normal delegation to record the block
-      else
-        yield
+      def execute_block
+        if connection.respond_to? :execute_block
+          super # use normal delegation to record the block
+        else
+          yield
+        end
+      end
+
+      def command_recorder
+        CommandRecorder.new(connection)
       end
-    end
   end
 
   # MigrationProxy is used to defer loading of the actual migration classes
   # until they are needed
-  class MigrationProxy < Struct.new(:name, :version, :filename, :scope)
-
+  MigrationProxy = Struct.new(:name, :version, :filename, :scope) do
     def initialize(name, version, filename, scope)
       super
       @migration = nil
@@ -762,7 +994,6 @@ module ActiveRecord
         require(File.expand_path(filename))
         name.constantize.new(name, version)
       end
-
   end
 
   class NullMigration < MigrationProxy #:nodoc:
@@ -775,131 +1006,185 @@ module ActiveRecord
     end
   end
 
-  class Migrator#:nodoc:
-    class << self
-      attr_writer :migrations_paths
-      alias :migrations_path= :migrations_paths=
-
-      def migrate(migrations_paths, target_version = nil, &block)
-        case
-        when target_version.nil?
-          up(migrations_paths, target_version, &block)
-        when current_version == 0 && target_version == 0
-          []
-        when current_version > target_version
-          down(migrations_paths, target_version, &block)
-        else
-          up(migrations_paths, target_version, &block)
-        end
-      end
+  class MigrationContext # :nodoc:
+    attr_reader :migrations_paths
 
-      def rollback(migrations_paths, steps=1)
-        move(:down, migrations_paths, steps)
-      end
+    def initialize(migrations_paths)
+      @migrations_paths = migrations_paths
+    end
 
-      def forward(migrations_paths, steps=1)
-        move(:up, migrations_paths, steps)
+    def migrate(target_version = nil, &block)
+      case
+      when target_version.nil?
+        up(target_version, &block)
+      when current_version == 0 && target_version == 0
+        []
+      when current_version > target_version
+        down(target_version, &block)
+      else
+        up(target_version, &block)
       end
+    end
 
-      def up(migrations_paths, target_version = nil)
-        migrations = migrations(migrations_paths)
-        migrations.select! { |m| yield m } if block_given?
+    def rollback(steps = 1)
+      move(:down, steps)
+    end
+
+    def forward(steps = 1)
+      move(:up, steps)
+    end
 
-        new(:up, migrations, target_version).migrate
+    def up(target_version = nil)
+      selected_migrations = if block_given?
+        migrations.select { |m| yield m }
+      else
+        migrations
       end
 
-      def down(migrations_paths, target_version = nil, &block)
-        migrations = migrations(migrations_paths)
-        migrations.select! { |m| yield m } if block_given?
+      Migrator.new(:up, selected_migrations, target_version).migrate
+    end
 
-        new(:down, migrations, target_version).migrate
+    def down(target_version = nil)
+      selected_migrations = if block_given?
+        migrations.select { |m| yield m }
+      else
+        migrations
       end
 
-      def run(direction, migrations_paths, target_version)
-        new(direction, migrations(migrations_paths), target_version).run
-      end
+      Migrator.new(:down, selected_migrations, target_version).migrate
+    end
 
-      def open(migrations_paths)
-        new(:up, migrations(migrations_paths), nil)
-      end
+    def run(direction, target_version)
+      Migrator.new(direction, migrations, target_version).run
+    end
 
-      def schema_migrations_table_name
-        SchemaMigration.table_name
-      end
+    def open
+      Migrator.new(:up, migrations, nil)
+    end
 
-      def get_all_versions(connection = Base.connection)
-        if connection.table_exists?(schema_migrations_table_name)
-          SchemaMigration.all.map { |x| x.version.to_i }.sort
-        else
-          []
-        end
+    def get_all_versions
+      if SchemaMigration.table_exists?
+        SchemaMigration.all_versions.map(&:to_i)
+      else
+        []
       end
+    end
 
-      def current_version(connection = Base.connection)
-        get_all_versions(connection).max || 0
-      end
+    def current_version
+      get_all_versions.max || 0
+    rescue ActiveRecord::NoDatabaseError
+    end
 
-      def needs_migration?(connection = Base.connection)
-        (migrations(migrations_paths).collect(&:version) - get_all_versions(connection)).size > 0
-      end
+    def needs_migration?
+      (migrations.collect(&:version) - get_all_versions).size > 0
+    end
 
-      def any_migrations?
-        migrations(migrations_paths).any?
-      end
+    def any_migrations?
+      migrations.any?
+    end
 
-      def last_version
-        last_migration.version
-      end
+    def last_migration #:nodoc:
+      migrations.last || NullMigration.new
+    end
 
-      def last_migration #:nodoc:
-        migrations(migrations_paths).last || NullMigration.new
-      end
+    def parse_migration_filename(filename) # :nodoc:
+      File.basename(filename).scan(Migration::MigrationFilenameRegexp).first
+    end
+
+    def migrations
+      migrations = migration_files.map do |file|
+        version, name, scope = parse_migration_filename(file)
+        raise IllegalMigrationNameError.new(file) unless version
+        version = version.to_i
+        name = name.camelize
 
-      def migrations_paths
-        @migrations_paths ||= ['db/migrate']
-        # just to not break things if someone uses: migration_path = some_string
-        Array(@migrations_paths)
+        MigrationProxy.new(name, version, file, scope)
       end
 
-      def migrations_path
-        migrations_paths.first
+      migrations.sort_by(&:version)
+    end
+
+    def migrations_status
+      db_list = ActiveRecord::SchemaMigration.normalized_versions
+
+      file_list = migration_files.map do |file|
+        version, name, scope = parse_migration_filename(file)
+        raise IllegalMigrationNameError.new(file) unless version
+        version = ActiveRecord::SchemaMigration.normalize_migration_number(version)
+        status = db_list.delete(version) ? "up" : "down"
+        [status, version, (name + scope).humanize]
+      end.compact
+
+      db_list.map! do |version|
+        ["up", version, "********** NO FILE **********"]
       end
 
-      def migrations(paths)
-        paths = Array(paths)
+      (db_list + file_list).sort_by { |_, version, _| version }
+    end
 
-        files = Dir[*paths.map { |p| "#{p}/**/[0-9]*_*.rb" }]
+    def migration_files
+      paths = Array(migrations_paths)
+      Dir[*paths.flat_map { |path| "#{path}/**/[0-9]*_*.rb" }]
+    end
+
+    def current_environment
+      ActiveRecord::ConnectionHandling::DEFAULT_ENV.call
+    end
 
-        migrations = files.map do |file|
-          version, name, scope = file.scan(/([0-9]+)_([_a-z0-9]*)\.?([_a-z0-9]*)?\.rb\z/).first
+    def protected_environment?
+      ActiveRecord::Base.protected_environments.include?(last_stored_environment) if last_stored_environment
+    end
+
+    def last_stored_environment
+      return nil if current_version == 0
+      raise NoEnvironmentInSchemaError unless ActiveRecord::InternalMetadata.table_exists?
+
+      environment = ActiveRecord::InternalMetadata[:environment]
+      raise NoEnvironmentInSchemaError unless environment
+      environment
+    end
 
-          raise IllegalMigrationNameError.new(file) unless version
-          version = version.to_i
-          name = name.camelize
+    private
+      def move(direction, steps)
+        migrator = Migrator.new(direction, migrations)
 
-          MigrationProxy.new(name, version, file, scope)
+        if current_version != 0 && !migrator.current_migration
+          raise UnknownMigrationVersionError.new(current_version)
         end
 
-        migrations.sort_by(&:version)
+        start_index =
+          if current_version == 0
+            0
+          else
+            migrator.migrations.index(migrator.current_migration)
+          end
+
+        finish = migrator.migrations[start_index + steps]
+        version = finish ? finish.version : 0
+        send(direction, version)
       end
+  end
 
-      private
+  class Migrator # :nodoc:
+    class << self
+      attr_accessor :migrations_paths
 
-      def move(direction, migrations_paths, steps)
-        migrator = new(direction, migrations(migrations_paths))
-        start_index = migrator.migrations.index(migrator.current_migration)
+      def migrations_path=(path)
+        ActiveSupport::Deprecation.warn \
+          "`ActiveRecord::Migrator.migrations_path=` is now deprecated and will be removed in Rails 6.0. " \
+          "You can set the `migrations_paths` on the `connection` instead through the `database.yml`."
+        self.migrations_paths = [path]
+      end
 
-        if start_index
-          finish = migrator.migrations[start_index + steps]
-          version = finish ? finish.version : 0
-          send(direction, migrations_paths, version)
-        end
+      # For cases where a table doesn't exist like loading from schema cache
+      def current_version
+        MigrationContext.new(migrations_paths).current_version
       end
     end
 
-    def initialize(direction, migrations, target_version = nil)
-      raise StandardError.new("This database does not yet support migrations") unless Base.connection.supports_migrations?
+    self.migrations_paths = ["db/migrate"]
 
+    def initialize(direction, migrations, target_version = nil)
       @direction         = direction
       @target_version    = target_version
       @migrated_versions = nil
@@ -907,7 +1192,8 @@ module ActiveRecord
 
       validate(@migrations)
 
-      Base.connection.initialize_schema_migrations_table
+      ActiveRecord::SchemaMigration.create_table
+      ActiveRecord::InternalMetadata.create_table
     end
 
     def current_version
@@ -920,32 +1206,18 @@ module ActiveRecord
     alias :current :current_migration
 
     def run
-      migration = migrations.detect { |m| m.version == @target_version }
-      raise UnknownMigrationVersionError.new(@target_version) if migration.nil?
-      unless (up? && migrated.include?(migration.version.to_i)) || (down? && !migrated.include?(migration.version.to_i))
-        begin
-          execute_migration_in_transaction(migration, @direction)
-        rescue => e
-          canceled_msg = use_transaction?(migration) ? ", this migration was canceled" : ""
-          raise StandardError, "An error has occurred#{canceled_msg}:\n\n#{e}", e.backtrace
-        end
+      if use_advisory_lock?
+        with_advisory_lock { run_without_lock }
+      else
+        run_without_lock
       end
     end
 
     def migrate
-      if !target && @target_version && @target_version > 0
-        raise UnknownMigrationVersionError.new(@target_version)
-      end
-
-      runnable.each do |migration|
-        Base.logger.info "Migrating to #{migration.name} (#{migration.version})" if Base.logger
-
-        begin
-          execute_migration_in_transaction(migration, @direction)
-        rescue => e
-          canceled_msg = use_transaction?(migration) ? "this and " : ""
-          raise StandardError, "An error has occurred, #{canceled_msg}all later migrations canceled:\n\n#{e}", e.backtrace
-        end
+      if use_advisory_lock?
+        with_advisory_lock { migrate_without_lock }
+      else
+        migrate_without_lock
       end
     end
 
@@ -970,70 +1242,145 @@ module ActiveRecord
     end
 
     def migrated
-      @migrated_versions ||= Set.new(self.class.get_all_versions)
+      @migrated_versions || load_migrated
     end
 
-    private
-    def ran?(migration)
-      migrated.include?(migration.version.to_i)
+    def load_migrated
+      @migrated_versions = Set.new(Base.connection.migration_context.get_all_versions)
     end
 
-    def execute_migration_in_transaction(migration, direction)
-      ddl_transaction(migration) do
-        migration.migrate(direction)
-        record_version_state_after_migrating(migration.version)
+    private
+
+      # Used for running a specific migration.
+      def run_without_lock
+        migration = migrations.detect { |m| m.version == @target_version }
+        raise UnknownMigrationVersionError.new(@target_version) if migration.nil?
+        result = execute_migration_in_transaction(migration, @direction)
+
+        record_environment
+        result
       end
-    end
 
-    def target
-      migrations.detect { |m| m.version == @target_version }
-    end
+      # Used for running multiple migrations up to or down to a certain value.
+      def migrate_without_lock
+        if invalid_target?
+          raise UnknownMigrationVersionError.new(@target_version)
+        end
 
-    def finish
-      migrations.index(target) || migrations.size - 1
-    end
+        result = runnable.each do |migration|
+          execute_migration_in_transaction(migration, @direction)
+        end
 
-    def start
-      up? ? 0 : (migrations.index(current) || 0)
-    end
+        record_environment
+        result
+      end
 
-    def validate(migrations)
-      name ,= migrations.group_by(&:name).find { |_,v| v.length > 1 }
-      raise DuplicateMigrationNameError.new(name) if name
+      # Stores the current environment in the database.
+      def record_environment
+        return if down?
+        ActiveRecord::InternalMetadata[:environment] = ActiveRecord::Base.connection.migration_context.current_environment
+      end
 
-      version ,= migrations.group_by(&:version).find { |_,v| v.length > 1 }
-      raise DuplicateMigrationVersionError.new(version) if version
-    end
+      def ran?(migration)
+        migrated.include?(migration.version.to_i)
+      end
 
-    def record_version_state_after_migrating(version)
-      if down?
-        migrated.delete(version)
-        ActiveRecord::SchemaMigration.where(:version => version.to_s).delete_all
-      else
-        migrated << version
-        ActiveRecord::SchemaMigration.create!(:version => version.to_s)
+      # Return true if a valid version is not provided.
+      def invalid_target?
+        @target_version && @target_version != 0 && !target
       end
-    end
 
-    def up?
-      @direction == :up
-    end
+      def execute_migration_in_transaction(migration, direction)
+        return if down? && !migrated.include?(migration.version.to_i)
+        return if up?   &&  migrated.include?(migration.version.to_i)
 
-    def down?
-      @direction == :down
-    end
+        Base.logger.info "Migrating to #{migration.name} (#{migration.version})" if Base.logger
 
-    # Wrap the migration in a transaction only if supported by the adapter.
-    def ddl_transaction(migration)
-      if use_transaction?(migration)
-        Base.transaction { yield }
-      else
+        ddl_transaction(migration) do
+          migration.migrate(direction)
+          record_version_state_after_migrating(migration.version)
+        end
+      rescue => e
+        msg = +"An error has occurred, "
+        msg << "this and " if use_transaction?(migration)
+        msg << "all later migrations canceled:\n\n#{e}"
+        raise StandardError, msg, e.backtrace
+      end
+
+      def target
+        migrations.detect { |m| m.version == @target_version }
+      end
+
+      def finish
+        migrations.index(target) || migrations.size - 1
+      end
+
+      def start
+        up? ? 0 : (migrations.index(current) || 0)
+      end
+
+      def validate(migrations)
+        name, = migrations.group_by(&:name).find { |_, v| v.length > 1 }
+        raise DuplicateMigrationNameError.new(name) if name
+
+        version, = migrations.group_by(&:version).find { |_, v| v.length > 1 }
+        raise DuplicateMigrationVersionError.new(version) if version
+      end
+
+      def record_version_state_after_migrating(version)
+        if down?
+          migrated.delete(version)
+          ActiveRecord::SchemaMigration.where(version: version.to_s).delete_all
+        else
+          migrated << version
+          ActiveRecord::SchemaMigration.create!(version: version.to_s)
+        end
+      end
+
+      def up?
+        @direction == :up
+      end
+
+      def down?
+        @direction == :down
+      end
+
+      # Wrap the migration in a transaction only if supported by the adapter.
+      def ddl_transaction(migration)
+        if use_transaction?(migration)
+          Base.transaction { yield }
+        else
+          yield
+        end
+      end
+
+      def use_transaction?(migration)
+        !migration.disable_ddl_transaction && Base.connection.supports_ddl_transactions?
+      end
+
+      def use_advisory_lock?
+        Base.connection.advisory_locks_enabled?
+      end
+
+      def with_advisory_lock
+        lock_id = generate_migrator_advisory_lock_id
+        connection = Base.connection
+        got_lock = connection.get_advisory_lock(lock_id)
+        raise ConcurrentMigrationError unless got_lock
+        load_migrated # reload schema_migrations to be sure it wasn't changed by another process before we got the lock
         yield
+      ensure
+        if got_lock && !connection.release_advisory_lock(lock_id)
+          raise ConcurrentMigrationError.new(
+            ConcurrentMigrationError::RELEASE_LOCK_FAILED_MESSAGE
+          )
+        end
       end
-    end
 
-    def use_transaction?(migration)
-      !migration.disable_ddl_transaction && Base.connection.supports_ddl_transactions?
-    end
+      MIGRATOR_SALT = 2053462845
+      def generate_migrator_advisory_lock_id
+        db_name_hash = Zlib.crc32(Base.connection.current_database)
+        MIGRATOR_SALT * db_name_hash
+      end
   end
 end
diff --git a/activerecord/lib/active_record/migration/command_recorder.rb b/activerecord/lib/active_record/migration/command_recorder.rb
index dcc2362397..82f5121d94 100644
--- a/activerecord/lib/active_record/migration/command_recorder.rb
+++ b/activerecord/lib/active_record/migration/command_recorder.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class Migration
     # <tt>ActiveRecord::Migration::CommandRecorder</tt> records commands done during
@@ -5,15 +7,36 @@ module ActiveRecord
     # knows how to invert the following commands:
     #
     # * add_column
+    # * add_foreign_key
     # * add_index
+    # * add_reference
     # * add_timestamps
-    # * create_table
+    # * change_column
+    # * change_column_default (must supply a :from and :to option)
+    # * change_column_null
     # * create_join_table
+    # * create_table
+    # * disable_extension
+    # * drop_join_table
+    # * drop_table (must supply a block)
+    # * enable_extension
+    # * remove_column (must supply a type)
+    # * remove_columns (must specify at least one column name or more)
+    # * remove_foreign_key (must supply a second table)
+    # * remove_index
+    # * remove_reference
     # * remove_timestamps
     # * rename_column
     # * rename_index
     # * rename_table
     class CommandRecorder
+      ReversibleAndIrreversibleMethods = [:create_table, :create_join_table, :rename_table, :add_column, :remove_column,
+        :rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps,
+        :change_column_default, :add_reference, :remove_reference, :transaction,
+        :drop_join_table, :drop_table, :execute_block, :enable_extension, :disable_extension,
+        :change_column, :execute, :remove_columns, :change_column_null,
+        :add_foreign_key, :remove_foreign_key
+      ]
       include JoinTable
 
       attr_accessor :commands, :delegate, :reverting
@@ -41,7 +64,7 @@ module ActiveRecord
         @reverting = !@reverting
       end
 
-      # record +command+. +command+ should be a method name and arguments.
+      # Record +command+. +command+ should be a method name and arguments.
       # For example:
       #
       #   recorder.record(:method_name, [:arg1, :arg2])
@@ -62,22 +85,16 @@ module ActiveRecord
       # invert the +command+.
       def inverse_of(command, args, &block)
         method = :"invert_#{command}"
-        raise IrreversibleMigration unless respond_to?(method, true)
+        raise IrreversibleMigration, <<~MSG unless respond_to?(method, true)
+          This migration uses #{command}, which is not automatically reversible.
+          To make the migration reversible you can either:
+          1. Define #up and #down methods in place of the #change method.
+          2. Use the #reversible method to define reversible behavior.
+        MSG
         send(method, args, &block)
       end
 
-      def respond_to?(*args) # :nodoc:
-        super || delegate.respond_to?(*args)
-      end
-
-      [:create_table, :create_join_table, :rename_table, :add_column, :remove_column,
-        :rename_index, :rename_column, :add_index, :remove_index, :add_timestamps, :remove_timestamps,
-        :add_reference, :remove_reference, :transaction,
-        :drop_join_table, :drop_table, :execute_block, :enable_extension,
-        :change_column, :execute, :remove_columns, :change_column_null,
-        :add_foreign_key, :remove_foreign_key
-       # irreversible methods need to be here too
-      ].each do |method|
+      ReversibleAndIrreversibleMethods.each do |method|
         class_eval <<-EOV, __FILE__, __LINE__ + 1
           def #{method}(*args, &block)          # def create_table(*args, &block)
             record(:"#{method}", args, &block)  #   record(:create_table, args, &block)
@@ -91,129 +108,163 @@ module ActiveRecord
         yield delegate.update_table_definition(table_name, self)
       end
 
+      def replay(migration)
+        commands.each do |cmd, args, block|
+          migration.send(cmd, *args, &block)
+        end
+      end
+
       private
 
-      module StraightReversions
-        private
-        { transaction:       :transaction,
-          execute_block:     :execute_block,
-          create_table:      :drop_table,
-          create_join_table: :drop_join_table,
-          add_column:        :remove_column,
-          add_timestamps:    :remove_timestamps,
-          add_reference:     :remove_reference,
-          enable_extension:  :disable_extension
-        }.each do |cmd, inv|
-          [[inv, cmd], [cmd, inv]].uniq.each do |method, inverse|
-            class_eval <<-EOV, __FILE__, __LINE__ + 1
-              def invert_#{method}(args, &block)    # def invert_create_table(args, &block)
-                [:#{inverse}, args, block]          #   [:drop_table, args, block]
-              end                                   # end
-            EOV
-          end
+        module StraightReversions # :nodoc:
+          private
+            {
+              execute_block:     :execute_block,
+              create_table:      :drop_table,
+              create_join_table: :drop_join_table,
+              add_column:        :remove_column,
+              add_timestamps:    :remove_timestamps,
+              add_reference:     :remove_reference,
+              enable_extension:  :disable_extension
+            }.each do |cmd, inv|
+              [[inv, cmd], [cmd, inv]].uniq.each do |method, inverse|
+                class_eval <<-EOV, __FILE__, __LINE__ + 1
+                  def invert_#{method}(args, &block)    # def invert_create_table(args, &block)
+                    [:#{inverse}, args, block]          #   [:drop_table, args, block]
+                  end                                   # end
+                EOV
+              end
+            end
         end
-      end
 
-      include StraightReversions
+        include StraightReversions
+
+        def invert_transaction(args)
+          sub_recorder = CommandRecorder.new(delegate)
+          sub_recorder.revert { yield }
+
+          invertions_proc = proc {
+            sub_recorder.replay(self)
+          }
 
-      def invert_drop_table(args, &block)
-        if args.size == 1 && block == nil
-          raise ActiveRecord::IrreversibleMigration, "To avoid mistakes, drop_table is only reversible if given options or a block (can be empty)."
+          [:transaction, args, invertions_proc]
         end
-        super
-      end
 
-      def invert_rename_table(args)
-        [:rename_table, args.reverse]
-      end
+        def invert_drop_table(args, &block)
+          if args.size == 1 && block == nil
+            raise ActiveRecord::IrreversibleMigration, "To avoid mistakes, drop_table is only reversible if given options or a block (can be empty)."
+          end
+          super
+        end
 
-      def invert_remove_column(args)
-        raise ActiveRecord::IrreversibleMigration, "remove_column is only reversible if given a type." if args.size <= 2
-        super
-      end
+        def invert_rename_table(args)
+          [:rename_table, args.reverse]
+        end
 
-      def invert_rename_index(args)
-        [:rename_index, [args.first] + args.last(2).reverse]
-      end
+        def invert_remove_column(args)
+          raise ActiveRecord::IrreversibleMigration, "remove_column is only reversible if given a type." if args.size <= 2
+          super
+        end
 
-      def invert_rename_column(args)
-        [:rename_column, [args.first] + args.last(2).reverse]
-      end
+        def invert_rename_index(args)
+          [:rename_index, [args.first] + args.last(2).reverse]
+        end
 
-      def invert_add_index(args)
-        table, columns, options = *args
-        options ||= {}
+        def invert_rename_column(args)
+          [:rename_column, [args.first] + args.last(2).reverse]
+        end
 
-        index_name = options[:name]
-        options_hash = index_name ? { name: index_name } : { column: columns }
+        def invert_add_index(args)
+          table, columns, options = *args
+          options ||= {}
 
-        [:remove_index, [table, options_hash]]
-      end
+          options_hash = options.slice(:name, :algorithm)
+          options_hash[:column] = columns if !options_hash[:name]
 
-      def invert_remove_index(args)
-        table, options_or_column = *args
-        if (options = options_or_column).is_a?(Hash)
-          unless options[:column]
-            raise ActiveRecord::IrreversibleMigration, "remove_index is only reversible if given a :column option."
+          [:remove_index, [table, options_hash]]
+        end
+
+        def invert_remove_index(args)
+          table, options_or_column = *args
+          if (options = options_or_column).is_a?(Hash)
+            unless options[:column]
+              raise ActiveRecord::IrreversibleMigration, "remove_index is only reversible if given a :column option."
+            end
+            options = options.dup
+            [:add_index, [table, options.delete(:column), options]]
+          elsif (column = options_or_column).present?
+            [:add_index, [table, column]]
           end
-          options = options.dup
-          [:add_index, [table, options.delete(:column), options]]
-        elsif (column = options_or_column).present?
-          [:add_index, [table, column]]
         end
-      end
 
-      alias :invert_add_belongs_to :invert_add_reference
-      alias :invert_remove_belongs_to :invert_remove_reference
+        alias :invert_add_belongs_to :invert_add_reference
+        alias :invert_remove_belongs_to :invert_remove_reference
 
-      def invert_change_column_default(args)
-        table, column, options = *args
+        def invert_change_column_default(args)
+          table, column, options = *args
 
-        unless options && options.is_a?(Hash) && options.has_key?(:from) && options.has_key?(:to)
-          raise ActiveRecord::IrreversibleMigration, "change_column_default is only reversible if given a :from and :to option."
+          unless options && options.is_a?(Hash) && options.has_key?(:from) && options.has_key?(:to)
+            raise ActiveRecord::IrreversibleMigration, "change_column_default is only reversible if given a :from and :to option."
+          end
+
+          [:change_column_default, [table, column, from: options[:to], to: options[:from]]]
         end
 
-        [:change_column_default, [table, column, from: options[:to], to: options[:from]]]
-      end
+        def invert_change_column_null(args)
+          args[2] = !args[2]
+          [:change_column_null, args]
+        end
 
-      def invert_change_column_null(args)
-        args[2] = !args[2]
-        [:change_column_null, args]
-      end
+        def invert_add_foreign_key(args)
+          from_table, to_table, add_options = args
+          add_options ||= {}
 
-      def invert_add_foreign_key(args)
-        from_table, to_table, add_options = args
-        add_options ||= {}
+          if add_options[:name]
+            options = { name: add_options[:name] }
+          elsif add_options[:column]
+            options = { column: add_options[:column] }
+          else
+            options = to_table
+          end
 
-        if add_options[:name]
-          options = { name: add_options[:name] }
-        elsif add_options[:column]
-          options = { column: add_options[:column] }
-        else
-          options = to_table
+          [:remove_foreign_key, [from_table, options]]
         end
 
-        [:remove_foreign_key, [from_table, options]]
-      end
+        def invert_remove_foreign_key(args)
+          from_table, options_or_to_table, options_or_nil = args
 
-      def invert_remove_foreign_key(args)
-        from_table, to_table, remove_options = args
-        raise ActiveRecord::IrreversibleMigration, "remove_foreign_key is only reversible if given a second table" if to_table.nil? || to_table.is_a?(Hash)
+          to_table = if options_or_to_table.is_a?(Hash)
+            options_or_to_table[:to_table]
+          else
+            options_or_to_table
+          end
 
-        reversed_args = [from_table, to_table]
-        reversed_args << remove_options if remove_options
+          remove_options = if options_or_to_table.is_a?(Hash)
+            options_or_to_table.except(:to_table)
+          else
+            options_or_nil
+          end
 
-        [:add_foreign_key, reversed_args]
-      end
+          raise ActiveRecord::IrreversibleMigration, "remove_foreign_key is only reversible if given a second table" if to_table.nil?
 
-      # Forwards any missing method call to the \target.
-      def method_missing(method, *args, &block)
-        if @delegate.respond_to?(method)
-          @delegate.send(method, *args, &block)
-        else
-          super
+          reversed_args = [from_table, to_table]
+          reversed_args << remove_options if remove_options.present?
+
+          [:add_foreign_key, reversed_args]
+        end
+
+        def respond_to_missing?(method, _)
+          super || delegate.respond_to?(method)
+        end
+
+        # Forwards any missing method call to the \target.
+        def method_missing(method, *args, &block)
+          if delegate.respond_to?(method)
+            delegate.public_send(method, *args, &block)
+          else
+            super
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/migration/compatibility.rb b/activerecord/lib/active_record/migration/compatibility.rb
new file mode 100644
index 0000000000..8f6fcfcaea
--- /dev/null
+++ b/activerecord/lib/active_record/migration/compatibility.rb
@@ -0,0 +1,235 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class Migration
+    module Compatibility # :nodoc: all
+      def self.find(version)
+        version = version.to_s
+        name = "V#{version.tr('.', '_')}"
+        unless const_defined?(name)
+          versions = constants.grep(/\AV[0-9_]+\z/).map { |s| s.to_s.delete("V").tr("_", ".").inspect }
+          raise ArgumentError, "Unknown migration version #{version.inspect}; expected one of #{versions.sort.join(', ')}"
+        end
+        const_get(name)
+      end
+
+      V6_0 = Current
+
+      class V5_2 < V6_0
+        module CommandRecorder
+          def invert_transaction(args, &block)
+            [:transaction, args, block]
+          end
+        end
+
+        private
+
+          def command_recorder
+            recorder = super
+            class << recorder
+              prepend CommandRecorder
+            end
+            recorder
+          end
+      end
+
+      class V5_1 < V5_2
+        def change_column(table_name, column_name, type, options = {})
+          if adapter_name == "PostgreSQL"
+            clear_cache!
+            sql = connection.send(:change_column_sql, table_name, column_name, type, options)
+            execute "ALTER TABLE #{quote_table_name(table_name)} #{sql}"
+            change_column_default(table_name, column_name, options[:default]) if options.key?(:default)
+            change_column_null(table_name, column_name, options[:null], options[:default]) if options.key?(:null)
+            change_column_comment(table_name, column_name, options[:comment]) if options.key?(:comment)
+          else
+            super
+          end
+        end
+
+        def create_table(table_name, options = {})
+          if adapter_name == "Mysql2"
+            super(table_name, options: "ENGINE=InnoDB", **options)
+          else
+            super
+          end
+        end
+      end
+
+      class V5_0 < V5_1
+        module TableDefinition
+          def primary_key(name, type = :primary_key, **options)
+            type = :integer if type == :primary_key
+            super
+          end
+
+          def references(*args, **options)
+            super(*args, type: :integer, **options)
+          end
+          alias :belongs_to :references
+        end
+
+        def create_table(table_name, options = {})
+          if adapter_name == "PostgreSQL"
+            if options[:id] == :uuid && !options.key?(:default)
+              options[:default] = "uuid_generate_v4()"
+            end
+          end
+
+          unless adapter_name == "Mysql2" && options[:id] == :bigint
+            if [:integer, :bigint].include?(options[:id]) && !options.key?(:default)
+              options[:default] = nil
+            end
+          end
+
+          # Since 5.1 PostgreSQL adapter uses bigserial type for primary
+          # keys by default and MySQL uses bigint. This compat layer makes old migrations utilize
+          # serial/int type instead -- the way it used to work before 5.1.
+          unless options.key?(:id)
+            options[:id] = :integer
+          end
+
+          if block_given?
+            super do |t|
+              yield compatible_table_definition(t)
+            end
+          else
+            super
+          end
+        end
+
+        def change_table(table_name, options = {})
+          if block_given?
+            super do |t|
+              yield compatible_table_definition(t)
+            end
+          else
+            super
+          end
+        end
+
+        def create_join_table(table_1, table_2, column_options: {}, **options)
+          column_options.reverse_merge!(type: :integer)
+
+          if block_given?
+            super do |t|
+              yield compatible_table_definition(t)
+            end
+          else
+            super
+          end
+        end
+
+        def add_column(table_name, column_name, type, options = {})
+          if type == :primary_key
+            type = :integer
+            options[:primary_key] = true
+          end
+          super
+        end
+
+        def add_reference(table_name, ref_name, **options)
+          super(table_name, ref_name, type: :integer, **options)
+        end
+        alias :add_belongs_to :add_reference
+
+        private
+          def compatible_table_definition(t)
+            class << t
+              prepend TableDefinition
+            end
+            t
+          end
+      end
+
+      class V4_2 < V5_0
+        module TableDefinition
+          def references(*, **options)
+            options[:index] ||= false
+            super
+          end
+          alias :belongs_to :references
+
+          def timestamps(**options)
+            options[:null] = true if options[:null].nil?
+            super
+          end
+        end
+
+        def create_table(table_name, options = {})
+          if block_given?
+            super do |t|
+              yield compatible_table_definition(t)
+            end
+          else
+            super
+          end
+        end
+
+        def change_table(table_name, options = {})
+          if block_given?
+            super do |t|
+              yield compatible_table_definition(t)
+            end
+          else
+            super
+          end
+        end
+
+        def add_reference(*, **options)
+          options[:index] ||= false
+          super
+        end
+        alias :add_belongs_to :add_reference
+
+        def add_timestamps(_, **options)
+          options[:null] = true if options[:null].nil?
+          super
+        end
+
+        def index_exists?(table_name, column_name, options = {})
+          column_names = Array(column_name).map(&:to_s)
+          options[:name] =
+            if options[:name].present?
+              options[:name].to_s
+            else
+              index_name(table_name, column: column_names)
+            end
+          super
+        end
+
+        def remove_index(table_name, options = {})
+          options = { column: options } unless options.is_a?(Hash)
+          options[:name] = index_name_for_remove(table_name, options)
+          super(table_name, options)
+        end
+
+        private
+          def compatible_table_definition(t)
+            class << t
+              prepend TableDefinition
+            end
+            super
+          end
+
+          def index_name_for_remove(table_name, options = {})
+            index_name = index_name(table_name, options)
+
+            unless index_name_exists?(table_name, index_name)
+              if options.is_a?(Hash) && options.has_key?(:name)
+                options_without_column = options.dup
+                options_without_column.delete :column
+                index_name_without_column = index_name(table_name, options_without_column)
+
+                return index_name_without_column if index_name_exists?(table_name, index_name_without_column)
+              end
+
+              raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' does not exist"
+            end
+
+            index_name
+          end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/migration/join_table.rb b/activerecord/lib/active_record/migration/join_table.rb
index 05569fadbd..9abb289bb0 100644
--- a/activerecord/lib/active_record/migration/join_table.rb
+++ b/activerecord/lib/active_record/migration/join_table.rb
@@ -1,15 +1,17 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class Migration
     module JoinTable #:nodoc:
       private
 
-      def find_join_table_name(table_1, table_2, options = {})
-        options.delete(:table_name) || join_table_name(table_1, table_2)
-      end
+        def find_join_table_name(table_1, table_2, options = {})
+          options.delete(:table_name) || join_table_name(table_1, table_2)
+        end
 
-      def join_table_name(table_1, table_2)
-        ModelSchema.derive_join_table_name(table_1, table_2).to_sym
-      end
+        def join_table_name(table_1, table_2)
+          ModelSchema.derive_join_table_name(table_1, table_2).to_sym
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/model_schema.rb b/activerecord/lib/active_record/model_schema.rb
index 5a6f42ba09..c50a420432 100644
--- a/activerecord/lib/active_record/model_schema.rb
+++ b/activerecord/lib/active_record/model_schema.rb
@@ -1,58 +1,123 @@
+# frozen_string_literal: true
+
+require "monitor"
+
 module ActiveRecord
   module ModelSchema
     extend ActiveSupport::Concern
 
+    ##
+    # :singleton-method: primary_key_prefix_type
+    # :call-seq: primary_key_prefix_type
+    #
+    # The prefix type that will be prepended to every primary key column name.
+    # The options are +:table_name+ and +:table_name_with_underscore+. If the first is specified,
+    # the Product class will look for "productid" instead of "id" as the primary column. If the
+    # latter is specified, the Product class will look for "product_id" instead of "id". Remember
+    # that this is a global setting for all Active Records.
+
+    ##
+    # :singleton-method: primary_key_prefix_type=
+    # :call-seq: primary_key_prefix_type=(prefix_type)
+    #
+    # Sets the prefix type that will be prepended to every primary key column name.
+    # The options are +:table_name+ and +:table_name_with_underscore+. If the first is specified,
+    # the Product class will look for "productid" instead of "id" as the primary column. If the
+    # latter is specified, the Product class will look for "product_id" instead of "id". Remember
+    # that this is a global setting for all Active Records.
+
+    ##
+    # :singleton-method: table_name_prefix
+    # :call-seq: table_name_prefix
+    #
+    # The prefix string to prepend to every table name.
+
+    ##
+    # :singleton-method: table_name_prefix=
+    # :call-seq: table_name_prefix=(prefix)
+    #
+    # Sets the prefix string to prepend to every table name. So if set to "basecamp_", all table
+    # names will be named like "basecamp_projects", "basecamp_people", etc. This is a convenient
+    # way of creating a namespace for tables in a shared database. By default, the prefix is the
+    # empty string.
+    #
+    # If you are organising your models within modules you can add a prefix to the models within
+    # a namespace by defining a singleton method in the parent module called table_name_prefix which
+    # returns your chosen prefix.
+
+    ##
+    # :singleton-method: table_name_suffix
+    # :call-seq: table_name_suffix
+    #
+    # The suffix string to append to every table name.
+
+    ##
+    # :singleton-method: table_name_suffix=
+    # :call-seq: table_name_suffix=(suffix)
+    #
+    # Works like +table_name_prefix=+, but appends instead of prepends (set to "_basecamp" gives "projects_basecamp",
+    # "people_basecamp"). By default, the suffix is the empty string.
+    #
+    # If you are organising your models within modules, you can add a suffix to the models within
+    # a namespace by defining a singleton method in the parent module called table_name_suffix which
+    # returns your chosen suffix.
+
+    ##
+    # :singleton-method: schema_migrations_table_name
+    # :call-seq: schema_migrations_table_name
+    #
+    # The name of the schema migrations table. By default, the value is <tt>"schema_migrations"</tt>.
+
+    ##
+    # :singleton-method: schema_migrations_table_name=
+    # :call-seq: schema_migrations_table_name=(table_name)
+    #
+    # Sets the name of the schema migrations table.
+
+    ##
+    # :singleton-method: internal_metadata_table_name
+    # :call-seq: internal_metadata_table_name
+    #
+    # The name of the internal metadata table. By default, the value is <tt>"ar_internal_metadata"</tt>.
+
+    ##
+    # :singleton-method: internal_metadata_table_name=
+    # :call-seq: internal_metadata_table_name=(table_name)
+    #
+    # Sets the name of the internal metadata table.
+
+    ##
+    # :singleton-method: pluralize_table_names
+    # :call-seq: pluralize_table_names
+    #
+    # Indicates whether table names should be the pluralized versions of the corresponding class names.
+    # If true, the default table name for a Product class will be "products". If false, it would just be "product".
+    # See table_name for the full rules on table/class naming. This is true, by default.
+
+    ##
+    # :singleton-method: pluralize_table_names=
+    # :call-seq: pluralize_table_names=(value)
+    #
+    # Set whether table names should be the pluralized versions of the corresponding class names.
+    # If true, the default table name for a Product class will be "products". If false, it would just be "product".
+    # See table_name for the full rules on table/class naming. This is true, by default.
+
     included do
-      ##
-      # :singleton-method:
-      # Accessor for the prefix type that will be prepended to every primary key column name.
-      # The options are :table_name and :table_name_with_underscore. If the first is specified,
-      # the Product class will look for "productid" instead of "id" as the primary column. If the
-      # latter is specified, the Product class will look for "product_id" instead of "id". Remember
-      # that this is a global setting for all Active Records.
       mattr_accessor :primary_key_prefix_type, instance_writer: false
 
-      ##
-      # :singleton-method:
-      # Accessor for the name of the prefix string to prepend to every table name. So if set
-      # to "basecamp_", all table names will be named like "basecamp_projects", "basecamp_people",
-      # etc. This is a convenient way of creating a namespace for tables in a shared database.
-      # By default, the prefix is the empty string.
-      #
-      # If you are organising your models within modules you can add a prefix to the models within
-      # a namespace by defining a singleton method in the parent module called table_name_prefix which
-      # returns your chosen prefix.
-      class_attribute :table_name_prefix, instance_writer: false
-      self.table_name_prefix = ""
-
-      ##
-      # :singleton-method:
-      # Works like +table_name_prefix+, but appends instead of prepends (set to "_basecamp" gives "projects_basecamp",
-      # "people_basecamp"). By default, the suffix is the empty string.
-      #
-      # If you are organising your models within modules, you can add a suffix to the models within
-      # a namespace by defining a singleton method in the parent module called table_name_suffix which
-      # returns your chosen suffix.
-      class_attribute :table_name_suffix, instance_writer: false
-      self.table_name_suffix = ""
-
-      ##
-      # :singleton-method:
-      # Accessor for the name of the schema migrations table. By default, the value is "schema_migrations"
-      class_attribute :schema_migrations_table_name, instance_accessor: false
-      self.schema_migrations_table_name = "schema_migrations"
-
-      ##
-      # :singleton-method:
-      # Indicates whether table names should be the pluralized versions of the corresponding class names.
-      # If true, the default table name for a Product class will be +products+. If false, it would just be +product+.
-      # See table_name for the full rules on table/class naming. This is true, by default.
-      class_attribute :pluralize_table_names, instance_writer: false
-      self.pluralize_table_names = true
-
-      self.inheritance_column = 'type'
+      class_attribute :table_name_prefix, instance_writer: false, default: ""
+      class_attribute :table_name_suffix, instance_writer: false, default: ""
+      class_attribute :schema_migrations_table_name, instance_accessor: false, default: "schema_migrations"
+      class_attribute :internal_metadata_table_name, instance_accessor: false, default: "ar_internal_metadata"
+      class_attribute :pluralize_table_names, instance_writer: false, default: true
+
+      self.protected_environments = ["production"]
+      self.inheritance_column = "type"
+      self.ignored_columns = [].freeze
 
       delegate :type_for_attribute, to: :class
+
+      initialize_load_schema_monitor
     end
 
     # Derives the join table name for +first_table+ and +second_table+. The
@@ -153,11 +218,26 @@ module ActiveRecord
       end
 
       def full_table_name_prefix #:nodoc:
-        (parents.detect{ |p| p.respond_to?(:table_name_prefix) } || self).table_name_prefix
+        (module_parents.detect { |p| p.respond_to?(:table_name_prefix) } || self).table_name_prefix
       end
 
       def full_table_name_suffix #:nodoc:
-        (parents.detect {|p| p.respond_to?(:table_name_suffix) } || self).table_name_suffix
+        (module_parents.detect { |p| p.respond_to?(:table_name_suffix) } || self).table_name_suffix
+      end
+
+      # The array of names of environments where destructive actions should be prohibited. By default,
+      # the value is <tt>["production"]</tt>.
+      def protected_environments
+        if defined?(@protected_environments)
+          @protected_environments
+        else
+          superclass.protected_environments
+        end
+      end
+
+      # Sets an array of names of environments where destructive actions should be prohibited.
+      def protected_environments=(environments)
+        @protected_environments = environments.map(&:to_s)
       end
 
       # Defines the name of the table column which will store the class name on single-table
@@ -179,8 +259,24 @@ module ActiveRecord
         @explicit_inheritance_column = true
       end
 
+      # The list of columns names the model should ignore. Ignored columns won't have attribute
+      # accessors defined, and won't be referenced in SQL queries.
+      def ignored_columns
+        if defined?(@ignored_columns)
+          @ignored_columns
+        else
+          superclass.ignored_columns
+        end
+      end
+
+      # Sets the columns names the model should ignore. Ignored columns won't have attribute
+      # accessors defined, and won't be referenced in SQL queries.
+      def ignored_columns=(columns)
+        @ignored_columns = columns.map(&:to_s)
+      end
+
       def sequence_name
-        if base_class == self
+        if base_class?
           @sequence_name ||= reset_sequence_name
         else
           (@sequence_name ||= nil) || base_class.sequence_name
@@ -193,7 +289,7 @@ module ActiveRecord
       end
 
       # Sets the name of the sequence to use when generating ids to the given
-      # value, or (if the value is nil or false) to the value returned by the
+      # value, or (if the value is +nil+ or +false+) to the value returned by the
       # given block. This is required for Oracle and is useful for any
       # database which relies on sequences for primary key generation.
       #
@@ -211,13 +307,29 @@ module ActiveRecord
         @explicit_sequence_name = true
       end
 
+      # Determines if the primary key values should be selected from their
+      # corresponding sequence before the insert statement.
+      def prefetch_primary_key?
+        connection.prefetch_primary_key?(table_name)
+      end
+
+      # Returns the next value that will be used as the primary key on
+      # an insert statement.
+      def next_sequence_value
+        connection.next_sequence_value(sequence_name)
+      end
+
       # Indicates whether the table associated with this class exists
       def table_exists?
-        connection.schema_cache.table_exists?(table_name)
+        connection.schema_cache.data_source_exists?(table_name)
       end
 
       def attributes_builder # :nodoc:
-        @attributes_builder ||= AttributeSet::Builder.new(attribute_types, primary_key)
+        unless defined?(@attributes_builder) && @attributes_builder
+          defaults = _default_attributes.except(*(column_names - [primary_key]))
+          @attributes_builder = ActiveModel::AttributeSet::Builder.new(attribute_types, defaults)
+        end
+        @attributes_builder
       end
 
       def columns_hash # :nodoc:
@@ -232,22 +344,43 @@ module ActiveRecord
 
       def attribute_types # :nodoc:
         load_schema
-        @attribute_types ||= Hash.new(Type::Value.new)
+        @attribute_types ||= Hash.new(Type.default_value)
       end
 
-      def type_for_attribute(attr_name) # :nodoc:
-        attribute_types[attr_name]
+      def yaml_encoder # :nodoc:
+        @yaml_encoder ||= ActiveModel::AttributeSet::YAMLEncoder.new(attribute_types)
+      end
+
+      # Returns the type of the attribute with the given name, after applying
+      # all modifiers. This method is the only valid source of information for
+      # anything related to the types of a model's attributes. This method will
+      # access the database and load the model's schema if it is required.
+      #
+      # The return value of this method will implement the interface described
+      # by ActiveModel::Type::Value (though the object itself may not subclass
+      # it).
+      #
+      # +attr_name+ The name of the attribute to retrieve the type for. Must be
+      # a string or a symbol.
+      def type_for_attribute(attr_name, &block)
+        attr_name = attr_name.to_s
+        if block
+          attribute_types.fetch(attr_name, &block)
+        else
+          attribute_types[attr_name]
+        end
       end
 
       # Returns a hash where the keys are column names and the values are
-      # default values when instantiating the AR object for this table.
+      # default values when instantiating the Active Record object for this table.
       def column_defaults
         load_schema
-        _default_attributes.to_hash
+        @column_defaults ||= _default_attributes.deep_dup.to_hash
       end
 
       def _default_attributes # :nodoc:
-        @default_attributes ||= AttributeSet.new({})
+        load_schema
+        @default_attributes ||= ActiveModel::AttributeSet.new({})
       end
 
       # Returns an array of column names as strings.
@@ -255,10 +388,20 @@ module ActiveRecord
         @column_names ||= columns.map(&:name)
       end
 
+      def symbol_column_to_string(name_symbol) # :nodoc:
+        @symbol_column_to_string_name_hash ||= column_names.index_by(&:to_sym)
+        @symbol_column_to_string_name_hash[name_symbol]
+      end
+
       # Returns an array of column objects where the primary id, all columns ending in "_id" or "_count",
       # and columns used for single table inheritance have been removed.
       def content_columns
-        @content_columns ||= columns.reject { |c| c.name == primary_key || c.name =~ /(_id|_count)$/ || c.name == inheritance_column }
+        @content_columns ||= columns.reject do |c|
+          c.name == primary_key ||
+          c.name == inheritance_column ||
+          c.name.end_with?("_id") ||
+          c.name.end_with?("_count")
+        end
       end
 
       # Resets all the cached information about columns, which will cause them
@@ -268,7 +411,7 @@ module ActiveRecord
       # when just after creating a table you want to populate it with some default
       # values, eg:
       #
-      #  class CreateJobLevels < ActiveRecord::Migration
+      #  class CreateJobLevels < ActiveRecord::Migration[5.0]
       #    def up
       #      create_table :job_levels do |t|
       #        t.integer :id
@@ -289,96 +432,95 @@ module ActiveRecord
       #  end
       def reset_column_information
         connection.clear_cache!
-        undefine_attribute_methods
-        connection.schema_cache.clear_table_cache!(table_name)
+        ([self] + descendants).each(&:undefine_attribute_methods)
+        connection.schema_cache.clear_data_source_cache!(table_name)
 
         reload_schema_from_cache
+        initialize_find_by_cache
       end
 
-      private
+      protected
 
-      def schema_loaded?
-        defined?(@columns_hash) && @columns_hash
-      end
+        def initialize_load_schema_monitor
+          @load_schema_monitor = Monitor.new
+        end
 
-      def load_schema
-        unless schema_loaded?
-          load_schema!
+      private
+
+        def inherited(child_class)
+          super
+          child_class.initialize_load_schema_monitor
         end
-      end
 
-      def load_schema!
-        @columns_hash = connection.schema_cache.columns_hash(table_name)
-        @columns_hash.each do |name, column|
-          warn_if_deprecated_type(column)
-          define_attribute(
-            name,
-            connection.lookup_cast_type_from_column(column),
-            default: column.default,
-            user_provided_default: false
-          )
+        def schema_loaded?
+          defined?(@schema_loaded) && @schema_loaded
         end
-      end
 
-      def reload_schema_from_cache
-        @arel_engine = nil
-        @arel_table = nil
-        @column_names = nil
-        @attribute_types = nil
-        @content_columns = nil
-        @default_attributes = nil
-        @inheritance_column = nil unless defined?(@explicit_inheritance_column) && @explicit_inheritance_column
-        @attributes_builder = nil
-        @columns = nil
-        @columns_hash = nil
-        @attribute_names = nil
-      end
+        def load_schema
+          return if schema_loaded?
+          @load_schema_monitor.synchronize do
+            return if defined?(@columns_hash) && @columns_hash
 
-      # Guesses the table name, but does not decorate it with prefix and suffix information.
-      def undecorated_table_name(class_name = base_class.name)
-        table_name = class_name.to_s.demodulize.underscore
-        pluralize_table_names ? table_name.pluralize : table_name
-      end
+            load_schema!
 
-      # Computes and returns a table name according to default conventions.
-      def compute_table_name
-        base = base_class
-        if self == base
-          # Nested classes are prefixed with singular parent table name.
-          if parent < Base && !parent.abstract_class?
-            contained = parent.table_name
-            contained = contained.singularize if parent.pluralize_table_names
-            contained += '_'
+            @schema_loaded = true
           end
-
-          "#{full_table_name_prefix}#{contained}#{undecorated_table_name(name)}#{full_table_name_suffix}"
-        else
-          # STI subclasses always use their superclass' table.
-          base.table_name
         end
-      end
 
-      def warn_if_deprecated_type(column)
-        return if attributes_to_define_after_schema_loads.key?(column.name)
-        if column.respond_to?(:oid) && column.sql_type.start_with?("point")
-          if column.array?
-            array_arguments = ", array: true"
-          else
-            array_arguments = ""
+        def load_schema!
+          @columns_hash = connection.schema_cache.columns_hash(table_name).except(*ignored_columns)
+          @columns_hash.each do |name, column|
+            define_attribute(
+              name,
+              connection.lookup_cast_type_from_column(column),
+              default: column.default,
+              user_provided_default: false
+            )
           end
-          ActiveSupport::Deprecation.warn(<<-WARNING.strip_heredoc)
-            The behavior of the `:point` type will be changing in Rails 5.1 to
-            return a `Point` object, rather than an `Array`. If you'd like to
-            keep the old behavior, you can add this line to #{self.name}:
+        end
 
-              attribute :#{column.name}, :legacy_point#{array_arguments}
+        def reload_schema_from_cache
+          @arel_table = nil
+          @column_names = nil
+          @symbol_column_to_string_name_hash = nil
+          @attribute_types = nil
+          @content_columns = nil
+          @default_attributes = nil
+          @column_defaults = nil
+          @inheritance_column = nil unless defined?(@explicit_inheritance_column) && @explicit_inheritance_column
+          @attributes_builder = nil
+          @columns = nil
+          @columns_hash = nil
+          @schema_loaded = false
+          @attribute_names = nil
+          @yaml_encoder = nil
+          direct_descendants.each do |descendant|
+            descendant.send(:reload_schema_from_cache)
+          end
+        end
 
-            If you'd like the new behavior today, you can add this line:
+        # Guesses the table name, but does not decorate it with prefix and suffix information.
+        def undecorated_table_name(class_name = base_class.name)
+          table_name = class_name.to_s.demodulize.underscore
+          pluralize_table_names ? table_name.pluralize : table_name
+        end
 
-              attribute :#{column.name}, :rails_5_1_point#{array_arguments}
-          WARNING
+        # Computes and returns a table name according to default conventions.
+        def compute_table_name
+          if base_class?
+            # Nested classes are prefixed with singular parent table name.
+            if module_parent < Base && !module_parent.abstract_class?
+              contained = module_parent.table_name
+              contained = contained.singularize if module_parent.pluralize_table_names
+              contained += "_"
+            end
+
+            "#{full_table_name_prefix}#{contained}#{undecorated_table_name(name)}#{full_table_name_suffix}"
+          else
+            # STI subclasses always use their superclass' table.
+            base_class.table_name
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/nested_attributes.rb b/activerecord/lib/active_record/nested_attributes.rb
index c942d0e265..8b9098df6c 100644
--- a/activerecord/lib/active_record/nested_attributes.rb
+++ b/activerecord/lib/active_record/nested_attributes.rb
@@ -1,6 +1,9 @@
-require 'active_support/core_ext/hash/except'
-require 'active_support/core_ext/object/try'
-require 'active_support/core_ext/hash/indifferent_access'
+# frozen_string_literal: true
+
+require "active_support/core_ext/hash/except"
+require "active_support/core_ext/module/redefine_method"
+require "active_support/core_ext/object/try"
+require "active_support/core_ext/hash/indifferent_access"
 
 module ActiveRecord
   module NestedAttributes #:nodoc:
@@ -10,8 +13,7 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :nested_attributes_options, instance_writer: false
-      self.nested_attributes_options = {}
+      class_attribute :nested_attributes_options, instance_writer: false, default: {}
     end
 
     # = Active Record Nested Attributes
@@ -61,6 +63,18 @@ module ActiveRecord
     #   member.update params[:member]
     #   member.avatar.icon # => 'sad'
     #
+    # If you want to update the current avatar without providing the id, you must add <tt>:update_only</tt> option.
+    #
+    #   class Member < ActiveRecord::Base
+    #     has_one :avatar
+    #     accepts_nested_attributes_for :avatar, update_only: true
+    #   end
+    #
+    #   params = { member: { avatar_attributes: { icon: 'sad' } } }
+    #   member.update params[:member]
+    #   member.avatar.id # => 2
+    #   member.avatar.icon # => 'sad'
+    #
     # By default you will only be able to set and update attributes on the
     # associated model. If you want to destroy the associated model through the
     # attributes hash, you have to enable it first using the
@@ -195,19 +209,27 @@ module ActiveRecord
     # Nested attributes for an associated collection can also be passed in
     # the form of a hash of hashes instead of an array of hashes:
     #
-    #   Member.create(name:             'joe',
-    #                 posts_attributes: { first:  { title: 'Foo' },
-    #                                     second: { title: 'Bar' } })
+    #   Member.create(
+    #     name: 'joe',
+    #     posts_attributes: {
+    #       first:  { title: 'Foo' },
+    #       second: { title: 'Bar' }
+    #     }
+    #   )
     #
     # has the same effect as
     #
-    #   Member.create(name:             'joe',
-    #                 posts_attributes: [ { title: 'Foo' },
-    #                                     { title: 'Bar' } ])
+    #   Member.create(
+    #     name: 'joe',
+    #     posts_attributes: [
+    #       { title: 'Foo' },
+    #       { title: 'Bar' }
+    #     ]
+    #   )
     #
     # The keys of the hash which is the value for +:posts_attributes+ are
     # ignored in this case.
-    # However, it is not allowed to use +'id'+ or +:id+ for one of
+    # However, it is not allowed to use <tt>'id'</tt> or <tt>:id</tt> for one of
     # such keys, otherwise the hash will be wrapped in an array and
     # interpreted as an attribute hash for a single post.
     #
@@ -259,7 +281,7 @@ module ActiveRecord
     #   member.avatar_attributes = {icon: 'sad'}
     #   member.avatar.width # => 200
     module ClassMethods
-      REJECT_ALL_BLANK_PROC = proc { |attributes| attributes.all? { |key, value| key == '_destroy' || value.blank? } }
+      REJECT_ALL_BLANK_PROC = proc { |attributes| attributes.all? { |key, value| key == "_destroy" || value.blank? } }
 
       # Defines an attributes writer for the specified association(s).
       #
@@ -309,7 +331,7 @@ module ActiveRecord
       #   # creates avatar_attributes= and posts_attributes=
       #   accepts_nested_attributes_for :avatar, :posts, allow_destroy: true
       def accepts_nested_attributes_for(*attr_names)
-        options = { :allow_destroy => false, :update_only => false }
+        options = { allow_destroy: false, update_only: false }
         options.update(attr_names.extract_options!)
         options.assert_valid_keys(:allow_destroy, :reject_if, :limit, :update_only)
         options[:reject_if] = REJECT_ALL_BLANK_PROC if options[:reject_if] == :all_blank
@@ -333,27 +355,25 @@ module ActiveRecord
 
       private
 
-      # Generates a writer method for this association. Serves as a point for
-      # accessing the objects in the association. For example, this method
-      # could generate the following:
-      #
-      #   def pirate_attributes=(attributes)
-      #     assign_nested_attributes_for_one_to_one_association(:pirate, attributes)
-      #   end
-      #
-      # This redirects the attempts to write objects in an association through
-      # the helper methods defined below. Makes it seem like the nested
-      # associations are just regular associations.
-      def generate_association_writer(association_name, type)
-        generated_association_methods.module_eval <<-eoruby, __FILE__, __LINE__ + 1
-          if method_defined?(:#{association_name}_attributes=)
-            remove_method(:#{association_name}_attributes=)
-          end
-          def #{association_name}_attributes=(attributes)
-            assign_nested_attributes_for_#{type}_association(:#{association_name}, attributes)
-          end
-        eoruby
-      end
+        # Generates a writer method for this association. Serves as a point for
+        # accessing the objects in the association. For example, this method
+        # could generate the following:
+        #
+        #   def pirate_attributes=(attributes)
+        #     assign_nested_attributes_for_one_to_one_association(:pirate, attributes)
+        #   end
+        #
+        # This redirects the attempts to write objects in an association through
+        # the helper methods defined below. Makes it seem like the nested
+        # associations are just regular associations.
+        def generate_association_writer(association_name, type)
+          generated_association_methods.module_eval <<-eoruby, __FILE__, __LINE__ + 1
+            silence_redefinition_of_method :#{association_name}_attributes=
+            def #{association_name}_attributes=(attributes)
+              assign_nested_attributes_for_#{type}_association(:#{association_name}, attributes)
+            end
+          eoruby
+        end
     end
 
     # Returns ActiveRecord::AutosaveAssociation::marked_for_destruction? It's
@@ -367,192 +387,214 @@ module ActiveRecord
 
     private
 
-    # Attribute hash keys that should not be assigned as normal attributes.
-    # These hash keys are nested attributes implementation details.
-    UNASSIGNABLE_KEYS = %w( id _destroy )
-
-    # Assigns the given attributes to the association.
-    #
-    # If an associated record does not yet exist, one will be instantiated. If
-    # an associated record already exists, the method's behavior depends on
-    # the value of the update_only option. If update_only is +false+ and the
-    # given attributes include an <tt>:id</tt> that matches the existing record's
-    # id, then the existing record will be modified. If no <tt>:id</tt> is provided
-    # it will be replaced with a new record. If update_only is +true+ the existing
-    # record will be modified regardless of whether an <tt>:id</tt> is provided.
-    #
-    # If the given attributes include a matching <tt>:id</tt> attribute, or
-    # update_only is true, and a <tt>:_destroy</tt> key set to a truthy value,
-    # then the existing record will be marked for destruction.
-    def assign_nested_attributes_for_one_to_one_association(association_name, attributes)
-      options = self.nested_attributes_options[association_name]
-      attributes = attributes.with_indifferent_access
-      existing_record = send(association_name)
-
-      if (options[:update_only] || !attributes['id'].blank?) && existing_record &&
-          (options[:update_only] || existing_record.id.to_s == attributes['id'].to_s)
-        assign_to_or_mark_for_destruction(existing_record, attributes, options[:allow_destroy]) unless call_reject_if(association_name, attributes)
-
-      elsif attributes['id'].present?
-        raise_nested_attributes_record_not_found!(association_name, attributes['id'])
-
-      elsif !reject_new_record?(association_name, attributes)
-        assignable_attributes = attributes.except(*UNASSIGNABLE_KEYS)
-
-        if existing_record && existing_record.new_record?
-          existing_record.assign_attributes(assignable_attributes)
-          association(association_name).initialize_attributes(existing_record)
-        else
-          method = "build_#{association_name}"
-          if respond_to?(method)
-            send(method, assignable_attributes)
+      # Attribute hash keys that should not be assigned as normal attributes.
+      # These hash keys are nested attributes implementation details.
+      UNASSIGNABLE_KEYS = %w( id _destroy )
+
+      # Assigns the given attributes to the association.
+      #
+      # If an associated record does not yet exist, one will be instantiated. If
+      # an associated record already exists, the method's behavior depends on
+      # the value of the update_only option. If update_only is +false+ and the
+      # given attributes include an <tt>:id</tt> that matches the existing record's
+      # id, then the existing record will be modified. If no <tt>:id</tt> is provided
+      # it will be replaced with a new record. If update_only is +true+ the existing
+      # record will be modified regardless of whether an <tt>:id</tt> is provided.
+      #
+      # If the given attributes include a matching <tt>:id</tt> attribute, or
+      # update_only is true, and a <tt>:_destroy</tt> key set to a truthy value,
+      # then the existing record will be marked for destruction.
+      def assign_nested_attributes_for_one_to_one_association(association_name, attributes)
+        options = nested_attributes_options[association_name]
+        if attributes.respond_to?(:permitted?)
+          attributes = attributes.to_h
+        end
+        attributes = attributes.with_indifferent_access
+        existing_record = send(association_name)
+
+        if (options[:update_only] || !attributes["id"].blank?) && existing_record &&
+            (options[:update_only] || existing_record.id.to_s == attributes["id"].to_s)
+          assign_to_or_mark_for_destruction(existing_record, attributes, options[:allow_destroy]) unless call_reject_if(association_name, attributes)
+
+        elsif attributes["id"].present?
+          raise_nested_attributes_record_not_found!(association_name, attributes["id"])
+
+        elsif !reject_new_record?(association_name, attributes)
+          assignable_attributes = attributes.except(*UNASSIGNABLE_KEYS)
+
+          if existing_record && existing_record.new_record?
+            existing_record.assign_attributes(assignable_attributes)
+            association(association_name).initialize_attributes(existing_record)
           else
-            raise ArgumentError, "Cannot build association `#{association_name}'. Are you trying to build a polymorphic one-to-one association?"
+            method = :"build_#{association_name}"
+            if respond_to?(method)
+              send(method, assignable_attributes)
+            else
+              raise ArgumentError, "Cannot build association `#{association_name}'. Are you trying to build a polymorphic one-to-one association?"
+            end
           end
         end
       end
-    end
 
-    # Assigns the given attributes to the collection association.
-    #
-    # Hashes with an <tt>:id</tt> value matching an existing associated record
-    # will update that record. Hashes without an <tt>:id</tt> value will build
-    # a new record for the association. Hashes with a matching <tt>:id</tt>
-    # value and a <tt>:_destroy</tt> key set to a truthy value will mark the
-    # matched record for destruction.
-    #
-    # For example:
-    #
-    #   assign_nested_attributes_for_collection_association(:people, {
-    #     '1' => { id: '1', name: 'Peter' },
-    #     '2' => { name: 'John' },
-    #     '3' => { id: '2', _destroy: true }
-    #   })
-    #
-    # Will update the name of the Person with ID 1, build a new associated
-    # person with the name 'John', and mark the associated Person with ID 2
-    # for destruction.
-    #
-    # Also accepts an Array of attribute hashes:
-    #
-    #   assign_nested_attributes_for_collection_association(:people, [
-    #     { id: '1', name: 'Peter' },
-    #     { name: 'John' },
-    #     { id: '2', _destroy: true }
-    #   ])
-    def assign_nested_attributes_for_collection_association(association_name, attributes_collection)
-      options = self.nested_attributes_options[association_name]
+      # Assigns the given attributes to the collection association.
+      #
+      # Hashes with an <tt>:id</tt> value matching an existing associated record
+      # will update that record. Hashes without an <tt>:id</tt> value will build
+      # a new record for the association. Hashes with a matching <tt>:id</tt>
+      # value and a <tt>:_destroy</tt> key set to a truthy value will mark the
+      # matched record for destruction.
+      #
+      # For example:
+      #
+      #   assign_nested_attributes_for_collection_association(:people, {
+      #     '1' => { id: '1', name: 'Peter' },
+      #     '2' => { name: 'John' },
+      #     '3' => { id: '2', _destroy: true }
+      #   })
+      #
+      # Will update the name of the Person with ID 1, build a new associated
+      # person with the name 'John', and mark the associated Person with ID 2
+      # for destruction.
+      #
+      # Also accepts an Array of attribute hashes:
+      #
+      #   assign_nested_attributes_for_collection_association(:people, [
+      #     { id: '1', name: 'Peter' },
+      #     { name: 'John' },
+      #     { id: '2', _destroy: true }
+      #   ])
+      def assign_nested_attributes_for_collection_association(association_name, attributes_collection)
+        options = nested_attributes_options[association_name]
+        if attributes_collection.respond_to?(:permitted?)
+          attributes_collection = attributes_collection.to_h
+        end
 
-      unless attributes_collection.is_a?(Hash) || attributes_collection.is_a?(Array)
-        raise ArgumentError, "Hash or Array expected, got #{attributes_collection.class.name} (#{attributes_collection.inspect})"
-      end
+        unless attributes_collection.is_a?(Hash) || attributes_collection.is_a?(Array)
+          raise ArgumentError, "Hash or Array expected for attribute `#{association_name}`, got #{attributes_collection.class.name} (#{attributes_collection.inspect})"
+        end
 
-      check_record_limit!(options[:limit], attributes_collection)
+        check_record_limit!(options[:limit], attributes_collection)
 
-      if attributes_collection.is_a? Hash
-        keys = attributes_collection.keys
-        attributes_collection = if keys.include?('id') || keys.include?(:id)
-          [attributes_collection]
-        else
-          attributes_collection.values
+        if attributes_collection.is_a? Hash
+          keys = attributes_collection.keys
+          attributes_collection = if keys.include?("id") || keys.include?(:id)
+            [attributes_collection]
+          else
+            attributes_collection.values
+          end
         end
-      end
 
-      association = association(association_name)
+        association = association(association_name)
 
-      existing_records = if association.loaded?
-        association.target
-      else
-        attribute_ids = attributes_collection.map {|a| a['id'] || a[:id] }.compact
-        attribute_ids.empty? ? [] : association.scope.where(association.klass.primary_key => attribute_ids)
-      end
+        existing_records = if association.loaded?
+          association.target
+        else
+          attribute_ids = attributes_collection.map { |a| a["id"] || a[:id] }.compact
+          attribute_ids.empty? ? [] : association.scope.where(association.klass.primary_key => attribute_ids)
+        end
 
-      attributes_collection.each do |attributes|
-        attributes = attributes.with_indifferent_access
+        attributes_collection.each do |attributes|
+          if attributes.respond_to?(:permitted?)
+            attributes = attributes.to_h
+          end
+          attributes = attributes.with_indifferent_access
 
-        if attributes['id'].blank?
-          unless reject_new_record?(association_name, attributes)
-            association.build(attributes.except(*UNASSIGNABLE_KEYS))
+          if attributes["id"].blank?
+            unless reject_new_record?(association_name, attributes)
+              association.reader.build(attributes.except(*UNASSIGNABLE_KEYS))
+            end
+          elsif existing_record = existing_records.detect { |record| record.id.to_s == attributes["id"].to_s }
+            unless call_reject_if(association_name, attributes)
+              # Make sure we are operating on the actual object which is in the association's
+              # proxy_target array (either by finding it, or adding it if not found)
+              # Take into account that the proxy_target may have changed due to callbacks
+              target_record = association.target.detect { |record| record.id.to_s == attributes["id"].to_s }
+              if target_record
+                existing_record = target_record
+              else
+                association.add_to_target(existing_record, :skip_callbacks)
+              end
+
+              assign_to_or_mark_for_destruction(existing_record, attributes, options[:allow_destroy])
+            end
+          else
+            raise_nested_attributes_record_not_found!(association_name, attributes["id"])
           end
-        elsif existing_record = existing_records.detect { |record| record.id.to_s == attributes['id'].to_s }
-          unless call_reject_if(association_name, attributes)
-            # Make sure we are operating on the actual object which is in the association's
-            # proxy_target array (either by finding it, or adding it if not found)
-            # Take into account that the proxy_target may have changed due to callbacks
-            target_record = association.target.detect { |record| record.id.to_s == attributes['id'].to_s }
-            if target_record
-              existing_record = target_record
+        end
+      end
+
+      # Takes in a limit and checks if the attributes_collection has too many
+      # records. It accepts limit in the form of symbol, proc, or
+      # number-like object (anything that can be compared with an integer).
+      #
+      # Raises TooManyRecords error if the attributes_collection is
+      # larger than the limit.
+      def check_record_limit!(limit, attributes_collection)
+        if limit
+          limit = \
+            case limit
+            when Symbol
+              send(limit)
+            when Proc
+              limit.call
             else
-              association.add_to_target(existing_record, :skip_callbacks)
+              limit
             end
 
-            assign_to_or_mark_for_destruction(existing_record, attributes, options[:allow_destroy])
+          if limit && attributes_collection.size > limit
+            raise TooManyRecords, "Maximum #{limit} records are allowed. Got #{attributes_collection.size} records instead."
           end
-        else
-          raise_nested_attributes_record_not_found!(association_name, attributes['id'])
         end
       end
-    end
 
-    # Takes in a limit and checks if the attributes_collection has too many
-    # records. It accepts limit in the form of symbol, proc, or
-    # number-like object (anything that can be compared with an integer).
-    #
-    # Raises TooManyRecords error if the attributes_collection is
-    # larger than the limit.
-    def check_record_limit!(limit, attributes_collection)
-      if limit
-        limit = case limit
-        when Symbol
-          send(limit)
-        when Proc
-          limit.call
-        else
-          limit
-        end
+      # Updates a record with the +attributes+ or marks it for destruction if
+      # +allow_destroy+ is +true+ and has_destroy_flag? returns +true+.
+      def assign_to_or_mark_for_destruction(record, attributes, allow_destroy)
+        record.assign_attributes(attributes.except(*UNASSIGNABLE_KEYS))
+        record.mark_for_destruction if has_destroy_flag?(attributes) && allow_destroy
+      end
 
-        if limit && attributes_collection.size > limit
-          raise TooManyRecords, "Maximum #{limit} records are allowed. Got #{attributes_collection.size} records instead."
-        end
+      # Determines if a hash contains a truthy _destroy key.
+      def has_destroy_flag?(hash)
+        Type::Boolean.new.cast(hash["_destroy"])
       end
-    end
 
-    # Updates a record with the +attributes+ or marks it for destruction if
-    # +allow_destroy+ is +true+ and has_destroy_flag? returns +true+.
-    def assign_to_or_mark_for_destruction(record, attributes, allow_destroy)
-      record.assign_attributes(attributes.except(*UNASSIGNABLE_KEYS))
-      record.mark_for_destruction if has_destroy_flag?(attributes) && allow_destroy
-    end
+      # Determines if a new record should be rejected by checking
+      # has_destroy_flag? or if a <tt>:reject_if</tt> proc exists for this
+      # association and evaluates to +true+.
+      def reject_new_record?(association_name, attributes)
+        will_be_destroyed?(association_name, attributes) || call_reject_if(association_name, attributes)
+      end
 
-    # Determines if a hash contains a truthy _destroy key.
-    def has_destroy_flag?(hash)
-      Type::Boolean.new.cast(hash['_destroy'])
-    end
+      # Determines if a record with the particular +attributes+ should be
+      # rejected by calling the reject_if Symbol or Proc (if defined).
+      # The reject_if option is defined by +accepts_nested_attributes_for+.
+      #
+      # Returns false if there is a +destroy_flag+ on the attributes.
+      def call_reject_if(association_name, attributes)
+        return false if will_be_destroyed?(association_name, attributes)
 
-    # Determines if a new record should be rejected by checking
-    # has_destroy_flag? or if a <tt>:reject_if</tt> proc exists for this
-    # association and evaluates to +true+.
-    def reject_new_record?(association_name, attributes)
-      has_destroy_flag?(attributes) || call_reject_if(association_name, attributes)
-    end
+        case callback = nested_attributes_options[association_name][:reject_if]
+        when Symbol
+          method(callback).arity == 0 ? send(callback) : send(callback, attributes)
+        when Proc
+          callback.call(attributes)
+        end
+      end
 
-    # Determines if a record with the particular +attributes+ should be
-    # rejected by calling the reject_if Symbol or Proc (if defined).
-    # The reject_if option is defined by +accepts_nested_attributes_for+.
-    #
-    # Returns false if there is a +destroy_flag+ on the attributes.
-    def call_reject_if(association_name, attributes)
-      return false if has_destroy_flag?(attributes)
-      case callback = self.nested_attributes_options[association_name][:reject_if]
-      when Symbol
-        method(callback).arity == 0 ? send(callback) : send(callback, attributes)
-      when Proc
-        callback.call(attributes)
+      # Only take into account the destroy flag if <tt>:allow_destroy</tt> is true
+      def will_be_destroyed?(association_name, attributes)
+        allow_destroy?(association_name) && has_destroy_flag?(attributes)
       end
-    end
 
-    def raise_nested_attributes_record_not_found!(association_name, record_id)
-      raise RecordNotFound, "Couldn't find #{self.class._reflect_on_association(association_name).klass.name} with ID=#{record_id} for #{self.class.name} with ID=#{id}"
-    end
+      def allow_destroy?(association_name)
+        nested_attributes_options[association_name][:allow_destroy]
+      end
+
+      def raise_nested_attributes_record_not_found!(association_name, record_id)
+        model = self.class._reflect_on_association(association_name).klass.name
+        raise RecordNotFound.new("Couldn't find #{model} with ID=#{record_id} for #{self.class.name} with ID=#{id}",
+                                 model, "id", record_id)
+      end
   end
 end
diff --git a/activerecord/lib/active_record/no_touching.rb b/activerecord/lib/active_record/no_touching.rb
index edb5066fa0..697076bdae 100644
--- a/activerecord/lib/active_record/no_touching.rb
+++ b/activerecord/lib/active_record/no_touching.rb
@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # = Active Record No Touching
   module NoTouching
     extend ActiveSupport::Concern
 
     module ClassMethods
-      # Lets you selectively disable calls to `touch` for the
+      # Lets you selectively disable calls to +touch+ for the
       # duration of a block.
       #
       # ==== Examples
@@ -41,10 +43,21 @@ module ActiveRecord
         end
     end
 
+    # Returns +true+ if the class has +no_touching+ set, +false+ otherwise.
+    #
+    #   Project.no_touching do
+    #     Project.first.no_touching? # true
+    #     Message.first.no_touching? # false
+    #   end
+    #
     def no_touching?
       NoTouching.applied_to?(self.class)
     end
 
+    def touch_later(*) # :nodoc:
+      super unless no_touching?
+    end
+
     def touch(*) # :nodoc:
       super unless no_touching?
     end
diff --git a/activerecord/lib/active_record/null_relation.rb b/activerecord/lib/active_record/null_relation.rb
index 74894d0c37..cf0de0fdeb 100644
--- a/activerecord/lib/active_record/null_relation.rb
+++ b/activerecord/lib/active_record/null_relation.rb
@@ -1,16 +1,12 @@
-# -*- coding: utf-8 -*-
+# frozen_string_literal: true
 
 module ActiveRecord
   module NullRelation # :nodoc:
-    def exec_queries
-      @records = []
-    end
-
     def pluck(*column_names)
       []
     end
 
-    def delete_all(_conditions = nil)
+    def delete_all
       0
     end
 
@@ -22,10 +18,6 @@ module ActiveRecord
       0
     end
 
-    def size
-      calculate :size, nil
-    end
-
     def empty?
       true
     end
@@ -50,33 +42,12 @@ module ActiveRecord
       ""
     end
 
-    def count(*)
-      calculate :count, nil
-    end
-
-    def sum(*)
-      calculate :sum, nil
-    end
-
-    def average(*)
-      calculate :average, nil
-    end
-
-    def minimum(*)
-      calculate :minimum, nil
-    end
-
-    def maximum(*)
-      calculate :maximum, nil
-    end
-
     def calculate(operation, _column_name)
-      if [:count, :sum, :size].include? operation
+      case operation
+      when :count, :sum
         group_values.any? ? Hash.new : 0
-      elsif [:average, :minimum, :maximum].include?(operation) && group_values.any?
-        Hash.new
-      else
-        nil
+      when :average, :minimum, :maximum
+        group_values.any? ? Hash.new : nil
       end
     end
 
@@ -87,5 +58,11 @@ module ActiveRecord
     def or(other)
       other.spawn
     end
+
+    private
+
+      def exec_queries
+        @records = [].freeze
+      end
   end
 end
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 0a6e4ac0bd..7bf8d568df 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Persistence
+  # = Active Record \Persistence
   module Persistence
     extend ActiveSupport::Concern
 
@@ -61,15 +63,155 @@ module ActiveRecord
       # +instantiate+ instead of +new+, finder methods ensure they get new
       # instances of the appropriate class for each record.
       #
-      # See +ActiveRecord::Inheritance#discriminate_class_for_record+ to see
+      # See <tt>ActiveRecord::Inheritance#discriminate_class_for_record</tt> to see
       # how this "single-table" inheritance mapping is implemented.
-      def instantiate(attributes, column_types = {})
+      def instantiate(attributes, column_types = {}, &block)
         klass = discriminate_class_for_record(attributes)
-        attributes = klass.attributes_builder.build_from_database(attributes, column_types)
-        klass.allocate.init_with('attributes' => attributes, 'new_record' => false)
+        instantiate_instance_of(klass, attributes, column_types, &block)
+      end
+
+      # Updates an object (or multiple objects) and saves it to the database, if validations pass.
+      # The resulting object is returned whether the object was saved successfully to the database or not.
+      #
+      # ==== Parameters
+      #
+      # * +id+ - This should be the id or an array of ids to be updated.
+      # * +attributes+ - This should be a hash of attributes or an array of hashes.
+      #
+      # ==== Examples
+      #
+      #   # Updates one record
+      #   Person.update(15, user_name: "Samuel", group: "expert")
+      #
+      #   # Updates multiple records
+      #   people = { 1 => { "first_name" => "David" }, 2 => { "first_name" => "Jeremy" } }
+      #   Person.update(people.keys, people.values)
+      #
+      #   # Updates multiple records from the result of a relation
+      #   people = Person.where(group: "expert")
+      #   people.update(group: "masters")
+      #
+      # Note: Updating a large number of records will run an UPDATE
+      # query for each record, which may cause a performance issue.
+      # When running callbacks is not needed for each record update,
+      # it is preferred to use {update_all}[rdoc-ref:Relation#update_all]
+      # for updating all records in a single query.
+      def update(id, attributes)
+        if id.is_a?(Array)
+          id.map { |one_id| find(one_id) }.each_with_index { |object, idx|
+            object.update(attributes[idx])
+          }
+        else
+          if ActiveRecord::Base === id
+            raise ArgumentError,
+              "You are passing an instance of ActiveRecord::Base to `update`. " \
+              "Please pass the id of the object by calling `.id`."
+          end
+          object = find(id)
+          object.update(attributes)
+          object
+        end
+      end
+
+      # Destroy an object (or multiple objects) that has the given id. The object is instantiated first,
+      # therefore all callbacks and filters are fired off before the object is deleted. This method is
+      # less efficient than #delete but allows cleanup methods and other actions to be run.
+      #
+      # This essentially finds the object (or multiple objects) with the given id, creates a new object
+      # from the attributes, and then calls destroy on it.
+      #
+      # ==== Parameters
+      #
+      # * +id+ - This should be the id or an array of ids to be destroyed.
+      #
+      # ==== Examples
+      #
+      #   # Destroy a single object
+      #   Todo.destroy(1)
+      #
+      #   # Destroy multiple objects
+      #   todos = [1,2,3]
+      #   Todo.destroy(todos)
+      def destroy(id)
+        if id.is_a?(Array)
+          find(id).each(&:destroy)
+        else
+          find(id).destroy
+        end
+      end
+
+      # Deletes the row with a primary key matching the +id+ argument, using a
+      # SQL +DELETE+ statement, and returns the number of rows deleted. Active
+      # Record objects are not instantiated, so the object's callbacks are not
+      # executed, including any <tt>:dependent</tt> association options.
+      #
+      # You can delete multiple rows at once by passing an Array of <tt>id</tt>s.
+      #
+      # Note: Although it is often much faster than the alternative, #destroy,
+      # skipping callbacks might bypass business logic in your application
+      # that ensures referential integrity or performs other essential jobs.
+      #
+      # ==== Examples
+      #
+      #   # Delete a single row
+      #   Todo.delete(1)
+      #
+      #   # Delete multiple rows
+      #   Todo.delete([2,3,4])
+      def delete(id_or_array)
+        where(primary_key => id_or_array).delete_all
+      end
+
+      def _insert_record(values) # :nodoc:
+        primary_key_value = nil
+
+        if primary_key && Hash === values
+          primary_key_value = values[primary_key]
+
+          if !primary_key_value && prefetch_primary_key?
+            primary_key_value = next_sequence_value
+            values[primary_key] = primary_key_value
+          end
+        end
+
+        if values.empty?
+          im = arel_table.compile_insert(connection.empty_insert_statement_value(primary_key))
+          im.into arel_table
+        else
+          im = arel_table.compile_insert(_substitute_values(values))
+        end
+
+        connection.insert(im, "#{self} Create", primary_key || false, primary_key_value)
+      end
+
+      def _update_record(values, constraints) # :nodoc:
+        constraints = _substitute_values(constraints).map { |attr, bind| attr.eq(bind) }
+
+        um = arel_table.where(
+          constraints.reduce(&:and)
+        ).compile_update(_substitute_values(values), primary_key)
+
+        connection.update(um, "#{self} Update")
+      end
+
+      def _delete_record(constraints) # :nodoc:
+        constraints = _substitute_values(constraints).map { |attr, bind| attr.eq(bind) }
+
+        dm = Arel::DeleteManager.new
+        dm.from(arel_table)
+        dm.wheres = constraints
+
+        connection.delete(dm, "#{self} Destroy")
       end
 
       private
+        # Given a class, an attributes hash, +instantiate_instance_of+ returns a
+        # new instance of the class. Accepts only keys as strings.
+        def instantiate_instance_of(klass, attributes, column_types = {}, &block)
+          attributes = klass.attributes_builder.build_from_database(attributes, column_types)
+          klass.allocate.init_with_attributes(attributes, &block)
+        end
+
         # Called by +instantiate+ to decide which class to use for a new
         # record instance.
         #
@@ -78,6 +220,14 @@ module ActiveRecord
         def discriminate_class_for_record(record)
           self
         end
+
+        def _substitute_values(values)
+          values.map do |name, value|
+            attr = arel_attribute(name)
+            bind = predicate_builder.build_bind_attribute(name, value)
+            [attr, bind]
+          end
+        end
     end
 
     # Returns true if this object hasn't been saved yet -- that is, a record
@@ -100,14 +250,18 @@ module ActiveRecord
       !(@new_record || @destroyed)
     end
 
+    ##
+    # :call-seq:
+    #   save(*args)
+    #
     # Saves the model.
     #
-    # If the model is new a record gets created in the database, otherwise
+    # If the model is new, a record gets created in the database, otherwise
     # the existing record gets updated.
     #
-    # By default, save always run validations. If any of them fail the action
-    # is cancelled and +save+ returns +false+. However, if you supply
-    # validate: false, validations are bypassed altogether. See
+    # By default, save always runs validations. If any of them fail the action
+    # is cancelled and #save returns +false+, and the record won't be saved. However, if you supply
+    # <tt>validate: false</tt>, validations are bypassed altogether. See
     # ActiveRecord::Validations for more information.
     #
     # By default, #save also sets the +updated_at+/+updated_on+ attributes to
@@ -121,20 +275,25 @@ module ActiveRecord
     #
     # Attributes marked as readonly are silently ignored if the record is
     # being updated.
-    def save(*args)
-      create_or_update(*args)
+    def save(*args, &block)
+      create_or_update(*args, &block)
     rescue ActiveRecord::RecordInvalid
       false
     end
 
+    ##
+    # :call-seq:
+    #   save!(*args)
+    #
     # Saves the model.
     #
     # If the model is new, a record gets created in the database, otherwise
     # the existing record gets updated.
     #
-    # With <tt>save!</tt> validations always run. If any of them fail
-    # ActiveRecord::RecordInvalid gets raised. See ActiveRecord::Validations
-    # for more information.
+    # By default, #save! always runs validations. If any of them fail
+    # ActiveRecord::RecordInvalid gets raised, and the record won't be saved. However, if you supply
+    # <tt>validate: false</tt>, validations are bypassed altogether. See
+    # ActiveRecord::Validations for more information.
     #
     # By default, #save! also sets the +updated_at+/+updated_on+ attributes to
     # the current time. However, if you supply <tt>touch: false</tt>, these
@@ -147,8 +306,10 @@ module ActiveRecord
     #
     # Attributes marked as readonly are silently ignored if the record is
     # being updated.
-    def save!(*args)
-      create_or_update(*args) || raise(RecordNotSaved.new("Failed to save the record", self))
+    #
+    # Unless an error is raised, returns true.
+    def save!(*args, &block)
+      create_or_update(*args, &block) || raise(RecordNotSaved.new("Failed to save the record", self))
     end
 
     # Deletes the record in the database and freezes this instance to
@@ -158,13 +319,13 @@ module ActiveRecord
     # The row is simply removed with an SQL +DELETE+ statement on the
     # record's primary key, and no callbacks are executed.
     #
-    # Note that this will also delete records marked as <tt>readonly?</tt>.
+    # Note that this will also delete records marked as {#readonly?}[rdoc-ref:Core#readonly?].
     #
     # To enforce the object's +before_destroy+ and +after_destroy+
     # callbacks or any <tt>:dependent</tt> association
     # options, use <tt>#destroy</tt>.
     def delete
-      self.class.delete(id) if persisted?
+      _delete_row if persisted?
       @destroyed = true
       freeze
     end
@@ -177,10 +338,14 @@ module ActiveRecord
     # and #destroy returns +false+.
     # See ActiveRecord::Callbacks for further details.
     def destroy
-      raise ReadOnlyRecord, "#{self.class} is marked as readonly" if readonly?
+      _raise_readonly_record_error if readonly?
       destroy_associations
       self.class.connection.add_transaction_record(self)
-      destroy_row if persisted?
+      @_trigger_destroy_callback = if persisted?
+        destroy_row > 0
+      else
+        true
+      end
       @destroyed = true
       freeze
     end
@@ -193,7 +358,7 @@ module ActiveRecord
     # and #destroy! raises ActiveRecord::RecordNotDestroyed.
     # See ActiveRecord::Callbacks for further details.
     def destroy!
-      destroy || raise(RecordNotDestroyed.new("Failed to destroy the record", self))
+      destroy || _raise_record_not_destroyed
     end
 
     # Returns an instance of the specified +klass+ with the attributes of the
@@ -207,18 +372,20 @@ module ActiveRecord
     # Note: The new instance will share a link to the same attributes as the original class.
     # Therefore the sti column value will still be the same.
     # Any change to the attributes on either instance will affect both instances.
-    # If you want to change the sti column as well, use +becomes!+ instead.
+    # If you want to change the sti column as well, use #becomes! instead.
     def becomes(klass)
-      became = klass.new
+      became = klass.allocate
+      became.send(:initialize)
       became.instance_variable_set("@attributes", @attributes)
+      became.instance_variable_set("@mutations_from_database", @mutations_from_database ||= nil)
       became.instance_variable_set("@changed_attributes", attributes_changed_by_setter)
       became.instance_variable_set("@new_record", new_record?)
       became.instance_variable_set("@destroyed", destroyed?)
-      became.instance_variable_set("@errors", errors)
+      became.errors.copy!(errors)
       became
     end
 
-    # Wrapper around +becomes+ that also changes the instance's sti column value.
+    # Wrapper around #becomes that also changes the instance's sti column value.
     # This is especially useful if you want to persist the changed class in your
     # database.
     #
@@ -238,19 +405,20 @@ module ActiveRecord
     # This is especially useful for boolean flags on existing records. Also note that
     #
     # * Validation is skipped.
-    # * Callbacks are invoked.
+    # * \Callbacks are invoked.
     # * updated_at/updated_on column is updated if that column is available.
     # * Updates all the attributes that are dirty in this object.
     #
-    # This method raises an +ActiveRecord::ActiveRecordError+  if the
+    # This method raises an ActiveRecord::ActiveRecordError  if the
     # attribute is marked as readonly.
     #
-    # See also +update_column+.
+    # Also see #update_column.
     def update_attribute(name, value)
       name = name.to_s
       verify_readonly_attribute(name)
       public_send("#{name}=", value)
-      save(validate: false) if changed?
+
+      save(validate: false)
     end
 
     # Updates the attributes of the model from the passed-in hash and saves the
@@ -266,9 +434,10 @@ module ActiveRecord
     end
 
     alias update_attributes update
+    deprecate :update_attributes
 
-    # Updates its receiver just like +update+ but calls <tt>save!</tt> instead
-    # of +save+, so an exception is raised if the record is invalid.
+    # Updates its receiver just like #update but calls #save! instead
+    # of +save+, so an exception is raised if the record is invalid and saving will fail.
     def update!(attributes)
       # The following transaction covers any possible database side-effects of the
       # attributes assignment. For example, setting the IDs of a child collection.
@@ -279,6 +448,7 @@ module ActiveRecord
     end
 
     alias update_attributes! update!
+    deprecate :update_attributes!
 
     # Equivalent to <code>update_columns(name => value)</code>.
     def update_column(name, value)
@@ -294,11 +464,12 @@ module ActiveRecord
     # the database, but take into account that in consequence the regular update
     # procedures are totally bypassed. In particular:
     #
-    # * Validations are skipped.
-    # * Callbacks are skipped.
+    # * \Validations are skipped.
+    # * \Callbacks are skipped.
     # * +updated_at+/+updated_on+ are not updated.
+    # * However, attributes are serialized with the same rules as ActiveRecord::Relation#update_all
     #
-    # This method raises an +ActiveRecord::ActiveRecordError+ when called on new
+    # This method raises an ActiveRecord::ActiveRecordError when called on new
     # objects, or when at least one of the attributes is marked as readonly.
     def update_columns(attributes)
       raise ActiveRecordError, "cannot update a new record" if new_record?
@@ -308,13 +479,17 @@ module ActiveRecord
         verify_readonly_attribute(key.to_s)
       end
 
-      updated_count = self.class.unscoped.where(self.class.primary_key => id).update_all(attributes)
-
+      id_in_database = self.id_in_database
       attributes.each do |k, v|
-        raw_write_attribute(k, v)
+        write_attribute_without_type_cast(k, v)
       end
 
-      updated_count == 1
+      affected_rows = self.class._update_record(
+        attributes,
+        self.class.primary_key => id_in_database
+      )
+
+      affected_rows == 1
     end
 
     # Initializes +attribute+ to zero if +nil+ and adds the value passed as +by+ (default is 1).
@@ -326,42 +501,56 @@ module ActiveRecord
       self
     end
 
-    # Wrapper around +increment+ that saves the record. This method differs from
-    # its non-bang version in that it passes through the attribute setter.
-    # Saving is not subjected to validation checks. Returns +true+ if the
-    # record could be saved.
-    def increment!(attribute, by = 1)
-      increment(attribute, by).update_attribute(attribute, self[attribute])
+    # Wrapper around #increment that writes the update to the database.
+    # Only +attribute+ is updated; the record itself is not saved.
+    # This means that any other modified attributes will still be dirty.
+    # Validations and callbacks are skipped. Supports the +touch+ option from
+    # +update_counters+, see that for more.
+    # Returns +self+.
+    def increment!(attribute, by = 1, touch: nil)
+      increment(attribute, by)
+      change = public_send(attribute) - (attribute_in_database(attribute.to_s) || 0)
+      self.class.update_counters(id, attribute => change, touch: touch)
+      clear_attribute_change(attribute) # eww
+      self
     end
 
     # Initializes +attribute+ to zero if +nil+ and subtracts the value passed as +by+ (default is 1).
     # The decrement is performed directly on the underlying attribute, no setter is invoked.
     # Only makes sense for number-based attributes. Returns +self+.
     def decrement(attribute, by = 1)
-      self[attribute] ||= 0
-      self[attribute] -= by
-      self
+      increment(attribute, -by)
     end
 
-    # Wrapper around +decrement+ that saves the record. This method differs from
-    # its non-bang version in that it passes through the attribute setter.
-    # Saving is not subjected to validation checks. Returns +true+ if the
-    # record could be saved.
-    def decrement!(attribute, by = 1)
-      decrement(attribute, by).update_attribute(attribute, self[attribute])
+    # Wrapper around #decrement that writes the update to the database.
+    # Only +attribute+ is updated; the record itself is not saved.
+    # This means that any other modified attributes will still be dirty.
+    # Validations and callbacks are skipped. Supports the +touch+ option from
+    # +update_counters+, see that for more.
+    # Returns +self+.
+    def decrement!(attribute, by = 1, touch: nil)
+      increment!(attribute, -by, touch: touch)
     end
 
     # Assigns to +attribute+ the boolean opposite of <tt>attribute?</tt>. So
     # if the predicate returns +true+ the attribute will become +false+. This
     # method toggles directly the underlying value without calling any setter.
     # Returns +self+.
+    #
+    # Example:
+    #
+    #   user = User.first
+    #   user.banned? # => false
+    #   user.toggle(:banned)
+    #   user.banned? # => true
+    #
     def toggle(attribute)
       self[attribute] = !public_send("#{attribute}?")
       self
     end
 
-    # Wrapper around +toggle+ that saves the record. This method differs from
-    # its non-bang version in that it passes through the attribute setter.
+    # Wrapper around #toggle that saves the record. This method differs from
+    # its non-bang version in the sense that it passes through the attribute setter.
     # Saving is not subjected to validation checks. Returns +true+ if the
     # record could be saved.
     def toggle!(attribute)
@@ -370,8 +559,8 @@ module ActiveRecord
 
     # Reloads the record from the database.
     #
-    # This method finds record by its primary key (which could be assigned manually) and
-    # modifies the receiver in-place:
+    # This method finds the record by its primary key (which could be assigned
+    # manually) and modifies the receiver in-place:
     #
     #   account = Account.new
     #   # => #<Account id: nil, email: nil>
@@ -383,7 +572,7 @@ module ActiveRecord
     # Attributes are reloaded from the database, and caches busted, in
     # particular the associations cache and the QueryCache.
     #
-    # If the record no longer exists in the database <tt>ActiveRecord::RecordNotFound</tt>
+    # If the record no longer exists in the database ActiveRecord::RecordNotFound
     # is raised. Otherwise, in addition to the in-place modification the method
     # returns +self+ for convenience.
     #
@@ -426,7 +615,7 @@ module ActiveRecord
           self.class.unscoped { self.class.find(id) }
         end
 
-      @attributes = fresh_object.instance_variable_get('@attributes')
+      @attributes = fresh_object.instance_variable_get("@attributes")
       @new_record = false
       self
     end
@@ -445,8 +634,8 @@ module ActiveRecord
     #   product.touch(:designed_at)           # updates the designed_at attribute and updated_at/on
     #   product.touch(:started_at, :ended_at) # updates started_at, ended_at and updated_at/on attributes
     #
-    # If used along with +belongs_to+ then +touch+ will invoke +touch+ method on
-    # associated object.
+    # If used along with {belongs_to}[rdoc-ref:Associations::ClassMethods#belongs_to]
+    # then +touch+ will invoke +touch+ method on associated object.
     #
     #   class Brake < ActiveRecord::Base
     #     belongs_to :car, touch: true
@@ -466,37 +655,19 @@ module ActiveRecord
     #   ball.touch(:updated_at)   # => raises ActiveRecordError
     #
     def touch(*names, time: nil)
-      raise ActiveRecordError, "cannot touch on a new record object" unless persisted?
-
-      time ||= current_time_from_proper_timezone
-      attributes = timestamp_attributes_for_update_in_model
-      attributes.concat(names)
-
-      unless attributes.empty?
-        changes = {}
-
-        attributes.each do |column|
-          column = column.to_s
-          changes[column] = write_attribute(column, time)
-        end
-
-        clear_attribute_changes(changes.keys)
-        primary_key = self.class.primary_key
-        scope = self.class.unscoped.where(primary_key => _read_attribute(primary_key))
-
-        if locking_enabled?
-          locking_column = self.class.locking_column
-          scope = scope.where(locking_column => _read_attribute(locking_column))
-          changes[locking_column] = increment_lock
-        end
-
-        result = scope.update_all(changes) == 1
+      unless persisted?
+        raise ActiveRecordError, <<-MSG.squish
+          cannot touch on a new or destroyed record object. Consider using
+          persisted?, new_record?, or destroyed? before touching
+        MSG
+      end
 
-        if !result && locking_enabled?
-          raise ActiveRecord::StaleObjectError.new(self, "touch")
-        end
+      attribute_names = timestamp_attributes_for_update_in_model
+      attribute_names |= names.map(&:to_s)
 
-        result
+      unless attribute_names.empty?
+        affected_rows = _touch_row(attribute_names, time)
+        @_trigger_update_callback = affected_rows == 1
       else
         true
       end
@@ -509,44 +680,93 @@ module ActiveRecord
     end
 
     def destroy_row
-      relation_for_destroy.delete_all
+      _delete_row
     end
 
-    def relation_for_destroy
-      self.class.unscoped.where(self.class.primary_key => id)
+    def _delete_row
+      self.class._delete_record(self.class.primary_key => id_in_database)
     end
 
-    def create_or_update(*args)
-      raise ReadOnlyRecord, "#{self.class} is marked as readonly" if readonly?
-      result = new_record? ? _create_record : _update_record(*args)
+    def _touch_row(attribute_names, time)
+      time ||= current_time_from_proper_timezone
+
+      attribute_names.each do |attr_name|
+        write_attribute(attr_name, time)
+        clear_attribute_change(attr_name)
+      end
+
+      _update_row(attribute_names, "touch")
+    end
+
+    def _update_row(attribute_names, attempted_action = "update")
+      self.class._update_record(
+        attributes_with_values(attribute_names),
+        self.class.primary_key => id_in_database
+      )
+    end
+
+    def create_or_update(*args, &block)
+      _raise_readonly_record_error if readonly?
+      return false if destroyed?
+      result = new_record? ? _create_record(&block) : _update_record(*args, &block)
       result != false
     end
 
     # Updates the associated record with values matching those of the instance attributes.
     # Returns the number of affected rows.
     def _update_record(attribute_names = self.attribute_names)
-      attributes_values = arel_attributes_with_values_for_update(attribute_names)
-      if attributes_values.empty?
-        0
+      attribute_names = attributes_for_update(attribute_names)
+
+      if attribute_names.empty?
+        affected_rows = 0
+        @_trigger_update_callback = true
       else
-        self.class.unscoped._update_record attributes_values, id, id_was
+        affected_rows = _update_row(attribute_names)
+        @_trigger_update_callback = affected_rows == 1
       end
+
+      yield(self) if block_given?
+
+      affected_rows
     end
 
     # Creates a record with values matching those of the instance attributes
     # and returns its id.
     def _create_record(attribute_names = self.attribute_names)
-      attributes_values = arel_attributes_with_values_for_create(attribute_names)
+      attribute_names = attributes_for_create(attribute_names)
+
+      new_id = self.class._insert_record(
+        attributes_with_values(attribute_names)
+      )
 
-      new_id = self.class.unscoped.insert attributes_values
       self.id ||= new_id if self.class.primary_key
 
       @new_record = false
+
+      yield(self) if block_given?
+
       id
     end
 
     def verify_readonly_attribute(name)
       raise ActiveRecordError, "#{name} is marked as readonly" if self.class.readonly_attributes.include?(name)
     end
+
+    def _raise_record_not_destroyed
+      @_association_destroy_exception ||= nil
+      raise @_association_destroy_exception || RecordNotDestroyed.new("Failed to destroy the record", self)
+    ensure
+      @_association_destroy_exception = nil
+    end
+
+    # The name of the method used to touch a +belongs_to+ association when the
+    # +:touch+ option is used.
+    def belongs_to_touch_method
+      :touch
+    end
+
+    def _raise_readonly_record_error
+      raise ReadOnlyRecord, "#{self.class} is marked as readonly"
+    end
   end
 end
diff --git a/activerecord/lib/active_record/query_cache.rb b/activerecord/lib/active_record/query_cache.rb
index dcb2bd3d84..28194c7c46 100644
--- a/activerecord/lib/active_record/query_cache.rb
+++ b/activerecord/lib/active_record/query_cache.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # = Active Record Query Cache
   class QueryCache
@@ -5,7 +7,7 @@ module ActiveRecord
       # Enable the query cache within the block if Active Record is configured.
       # If it's not, it will execute the given block.
       def cache(&block)
-        if ActiveRecord::Base.connected?
+        if connected? || !configurations.empty?
           connection.cache(&block)
         else
           yield
@@ -15,7 +17,7 @@ module ActiveRecord
       # Disable the query cache within the block if Active Record is configured.
       # If it's not, it will execute the given block.
       def uncached(&block)
-        if ActiveRecord::Base.connected?
+        if connected? || !configurations.empty?
           connection.uncached(&block)
         else
           yield
@@ -23,34 +25,21 @@ module ActiveRecord
       end
     end
 
-    def initialize(app)
-      @app = app
+    def self.run
+      ActiveRecord::Base.connection_handler.connection_pool_list.
+        reject { |p| p.query_cache_enabled }.each { |p| p.enable_query_cache! }
     end
 
-    def call(env)
-      connection    = ActiveRecord::Base.connection
-      enabled       = connection.query_cache_enabled
-      connection_id = ActiveRecord::Base.connection_id
-      connection.enable_query_cache!
+    def self.complete(pools)
+      pools.each { |pool| pool.disable_query_cache! }
 
-      response = @app.call(env)
-      response[2] = Rack::BodyProxy.new(response[2]) do
-        restore_query_cache_settings(connection_id, enabled)
+      ActiveRecord::Base.connection_handler.connection_pool_list.each do |pool|
+        pool.release_connection if pool.active_connection? && !pool.connection.transaction_open?
       end
-
-      response
-    rescue Exception => e
-      restore_query_cache_settings(connection_id, enabled)
-      raise e
     end
 
-    private
-
-    def restore_query_cache_settings(connection_id, enabled)
-      ActiveRecord::Base.connection_id = connection_id
-      ActiveRecord::Base.connection.clear_query_cache
-      ActiveRecord::Base.connection.disable_query_cache! unless enabled
+    def self.install_executor_hooks(executor = ActiveSupport::Executor)
+      executor.register_hook(self)
     end
-
   end
 end
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index 4e597590e9..c84f3d0fbb 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -1,17 +1,19 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Querying
-    delegate :find, :take, :take!, :first, :first!, :last, :last!, :exists?, :any?, :many?, to: :all
-    delegate :second, :second!, :third, :third!, :fourth, :fourth!, :fifth, :fifth!, :forty_two, :forty_two!, to: :all
+    delegate :find, :take, :take!, :first, :first!, :last, :last!, :exists?, :any?, :many?, :none?, :one?, to: :all
+    delegate :second, :second!, :third, :third!, :fourth, :fourth!, :fifth, :fifth!, :forty_two, :forty_two!, :third_to_last, :third_to_last!, :second_to_last, :second_to_last!, to: :all
     delegate :first_or_create, :first_or_create!, :first_or_initialize, to: :all
-    delegate :find_or_create_by, :find_or_create_by!, :find_or_initialize_by, to: :all
+    delegate :find_or_create_by, :find_or_create_by!, :create_or_find_by, :create_or_find_by!, :find_or_initialize_by, to: :all
     delegate :find_by, :find_by!, to: :all
-    delegate :destroy, :destroy_all, :delete, :delete_all, :update, :update_all, to: :all
-    delegate :find_each, :find_in_batches, to: :all
-    delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins, :or,
-             :where, :rewhere, :preload, :eager_load, :includes, :from, :lock, :readonly,
-             :having, :create_with, :uniq, :distinct, :references, :none, :unscope, to: :all
+    delegate :destroy_all, :delete_all, :update_all, to: :all
+    delegate :find_each, :find_in_batches, :in_batches, to: :all
+    delegate :select, :group, :order, :except, :reorder, :limit, :offset, :joins, :left_joins, :left_outer_joins, :or,
+             :where, :rewhere, :preload, :eager_load, :includes, :from, :lock, :readonly, :extending,
+             :having, :create_with, :distinct, :references, :none, :unscope, :merge, to: :all
     delegate :count, :average, :minimum, :maximum, :sum, :calculate, to: :all
-    delegate :pluck, :ids, to: :all
+    delegate :pluck, :pick, :ids, to: :all
 
     # Executes a custom SQL query against your database and returns all the results. The results will
     # be returned as an array with columns requested encapsulated as attributes of the model you call
@@ -35,8 +37,8 @@ module ActiveRecord
     #
     #   Post.find_by_sql ["SELECT title FROM posts WHERE author = ? AND created > ?", author_id, start_date]
     #   Post.find_by_sql ["SELECT body FROM comments WHERE author = :user_id OR approved_by = :user_id", { :user_id => user_id }]
-    def find_by_sql(sql, binds = [])
-      result_set = connection.select_all(sanitize_sql(sql), "#{name} Load", binds)
+    def find_by_sql(sql, binds = [], preparable: nil, &block)
+      result_set = connection.select_all(sanitize_sql(sql), "#{name} Load", binds, preparable: preparable)
       column_types = result_set.column_types.dup
       columns_hash.each_key { |k| column_types.delete k }
       message_bus = ActiveSupport::Notifications.instrumenter
@@ -46,8 +48,13 @@ module ActiveRecord
         class_name: name
       }
 
-      message_bus.instrument('instantiation.active_record', payload) do
-        result_set.map { |record| instantiate(record, column_types) }
+      message_bus.instrument("instantiation.active_record", payload) do
+        if result_set.includes_column?(inheritance_column)
+          result_set.map { |record| instantiate(record, column_types, &block) }
+        else
+          # Instantiate a homogeneous set
+          result_set.map { |record| instantiate_instance_of(self, record, column_types, &block) }
+        end
       end
     end
 
@@ -62,8 +69,7 @@ module ActiveRecord
     #
     # * +sql+ - An SQL statement which should return a count query from the database, see the example above.
     def count_by_sql(sql)
-      sql = sanitize_conditions(sql)
-      connection.select_value(sql, "#{name} Count").to_i
+      connection.select_value(sanitize_sql(sql), "#{name} Count").to_i
     end
   end
 end
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index da6b8447d3..538659d6bd 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -1,9 +1,11 @@
+# frozen_string_literal: true
+
 require "active_record"
 require "rails"
 require "active_model/railtie"
 
 # For now, action_controller must always be present with
-# rails, so let's make sure that it gets required before
+# Rails, so let's make sure that it gets required before
 # here. This is needed for correctly setting up the middleware.
 # In the future, this might become an optional require.
 require "action_controller/railtie"
@@ -13,26 +15,22 @@ module ActiveRecord
   class Railtie < Rails::Railtie # :nodoc:
     config.active_record = ActiveSupport::OrderedOptions.new
 
-    config.app_generators.orm :active_record, :migration => true,
-                                              :timestamps => true
-
-    config.app_middleware.insert_after "::ActionDispatch::Callbacks",
-      "ActiveRecord::QueryCache"
-
-    config.app_middleware.insert_after "::ActionDispatch::Callbacks",
-      "ActiveRecord::ConnectionAdapters::ConnectionManagement"
+    config.app_generators.orm :active_record, migration: true,
+                                              timestamps: true
 
     config.action_dispatch.rescue_responses.merge!(
-      'ActiveRecord::RecordNotFound'   => :not_found,
-      'ActiveRecord::StaleObjectError' => :conflict,
-      'ActiveRecord::RecordInvalid'    => :unprocessable_entity,
-      'ActiveRecord::RecordNotSaved'   => :unprocessable_entity
+      "ActiveRecord::RecordNotFound"   => :not_found,
+      "ActiveRecord::StaleObjectError" => :conflict,
+      "ActiveRecord::RecordInvalid"    => :unprocessable_entity,
+      "ActiveRecord::RecordNotSaved"   => :unprocessable_entity
     )
 
-
     config.active_record.use_schema_cache_dump = true
     config.active_record.maintain_test_schema = true
 
+    config.active_record.sqlite3 = ActiveSupport::OrderedOptions.new
+    config.active_record.sqlite3.represent_boolean_as_integer = nil
+
     config.eager_load_namespaces << ActiveRecord
 
     rake_tasks do
@@ -40,9 +38,9 @@ module ActiveRecord
         task :load_config do
           ActiveRecord::Tasks::DatabaseTasks.database_configuration = Rails.application.config.database_configuration
 
-          if defined?(ENGINE_PATH) && engine = Rails::Engine.find(ENGINE_PATH)
-            if engine.paths['db/migrate'].existent
-              ActiveRecord::Tasks::DatabaseTasks.migrations_paths += engine.paths['db/migrate'].to_a
+          if defined?(ENGINE_ROOT) && engine = Rails::Engine.find(ENGINE_ROOT)
+            if engine.paths["db/migrate"].existent
+              ActiveRecord::Tasks::DatabaseTasks.migrations_paths += engine.paths["db/migrate"].to_a
             end
           end
         end
@@ -57,8 +55,11 @@ module ActiveRecord
     console do |app|
       require "active_record/railties/console_sandbox" if app.sandbox?
       require "active_record/base"
-      console = ActiveSupport::Logger.new(STDERR)
-      Rails.logger.extend ActiveSupport::Logger.broadcast console
+      unless ActiveSupport::Logger.logger_outputs_to?(Rails.logger, STDERR, STDOUT)
+        console = ActiveSupport::Logger.new(STDERR)
+        Rails.logger.extend ActiveSupport::Logger.broadcast console
+      end
+      ActiveRecord::Base.verbose_query_logs = false
     end
 
     runner do
@@ -76,10 +77,39 @@ module ActiveRecord
       ActiveSupport.on_load(:active_record) { self.logger ||= ::Rails.logger }
     end
 
+    initializer "active_record.backtrace_cleaner" do
+      ActiveSupport.on_load(:active_record) { LogSubscriber.backtrace_cleaner = ::Rails.backtrace_cleaner }
+    end
+
     initializer "active_record.migration_error" do
       if config.active_record.delete(:migration_error) == :page_load
-        config.app_middleware.insert_after "::ActionDispatch::Callbacks",
-          "ActiveRecord::Migration::CheckPending"
+        config.app_middleware.insert_after ::ActionDispatch::Callbacks,
+          ActiveRecord::Migration::CheckPending
+      end
+    end
+
+    initializer "Check for cache versioning support" do
+      config.after_initialize do |app|
+        ActiveSupport.on_load(:active_record) do
+          if app.config.active_record.cache_versioning && Rails.cache
+            unless Rails.cache.class.try(:supports_cache_versioning?)
+              raise <<-end_error
+
+You're using a cache store that doesn't support native cache versioning.
+Your best option is to upgrade to a newer version of #{Rails.cache.class}
+that supports cache versioning (#{Rails.cache.class}.supports_cache_versioning? #=> true).
+
+Next best, switch to a different cache store that does support cache versioning:
+https://guides.rubyonrails.org/caching_with_rails.html#cache-stores.
+
+To keep using the current cache store, you can turn off cache versioning entirely:
+
+    config.active_record.cache_versioning = false
+
+end_error
+            end
+          end
+        end
       end
     end
 
@@ -87,15 +117,19 @@ module ActiveRecord
       if config.active_record.delete(:use_schema_cache_dump)
         config.after_initialize do |app|
           ActiveSupport.on_load(:active_record) do
-            filename = File.join(app.config.paths["db"].first, "schema_cache.dump")
+            filename = File.join(app.config.paths["db"].first, "schema_cache.yml")
 
             if File.file?(filename)
-              cache = Marshal.load File.binread filename
-              if cache.version == ActiveRecord::Migrator.current_version
-                self.connection.schema_cache = cache
-                self.connection_pool.schema_cache = cache.dup
+              current_version = ActiveRecord::Migrator.current_version
+
+              next if current_version.nil?
+
+              cache = YAML.load(File.read(filename))
+              if cache.version == current_version
+                connection.schema_cache = cache
+                connection_pool.schema_cache = cache.dup
               else
-                warn "Ignoring db/schema_cache.dump because it has expired. The current schema version is #{ActiveRecord::Migrator.current_version}, but the one in the cache is #{cache.version}."
+                warn "Ignoring db/schema_cache.yml because it has expired. The current schema version is #{current_version}, but the one in the cache is #{cache.version}."
               end
             end
           end
@@ -103,17 +137,27 @@ module ActiveRecord
       end
     end
 
+    initializer "active_record.define_attribute_methods" do |app|
+      config.after_initialize do
+        ActiveSupport.on_load(:active_record) do
+          descendants.each(&:define_attribute_methods) if app.config.eager_load
+        end
+      end
+    end
+
     initializer "active_record.warn_on_records_fetched_greater_than" do
       if config.active_record.warn_on_records_fetched_greater_than
         ActiveSupport.on_load(:active_record) do
-          require 'active_record/relation/record_fetch_warning'
+          require "active_record/relation/record_fetch_warning"
         end
       end
     end
 
     initializer "active_record.set_configs" do |app|
       ActiveSupport.on_load(:active_record) do
-        app.config.active_record.each do |k,v|
+        configs = app.config.active_record.dup
+        configs.delete(:sqlite3)
+        configs.each do |k, v|
           send "#{k}=", v
         end
       end
@@ -121,24 +165,10 @@ module ActiveRecord
 
     # This sets the database configuration from Configuration#database_configuration
     # and then establishes the connection.
-    initializer "active_record.initialize_database" do |app|
+    initializer "active_record.initialize_database" do
       ActiveSupport.on_load(:active_record) do
         self.configurations = Rails.application.config.database_configuration
-
-        begin
-          establish_connection
-        rescue ActiveRecord::NoDatabaseError
-          warn <<-end_warning
-Oops - You have a database configured, but it doesn't exist yet!
-
-Here's how to get started:
-
-  1. Configure your database in config/database.yml.
-  2. Run `bin/rake db:create` to create the database.
-  3. Run `bin/rake db:setup` to load your database schema.
-end_warning
-          raise
-        end
+        establish_connection
       end
     end
 
@@ -150,11 +180,16 @@ end_warning
       end
     end
 
-    initializer "active_record.set_reloader_hooks" do |app|
-      hook = app.config.reload_classes_only_on_change ? :to_prepare : :to_cleanup
+    initializer "active_record.collection_cache_association_loading" do
+      require "active_record/railties/collection_cache_association_loading"
+      ActiveSupport.on_load(:action_view) do
+        ActionView::PartialRenderer.prepend(ActiveRecord::Railties::CollectionCacheAssociationLoading)
+      end
+    end
 
+    initializer "active_record.set_reloader_hooks" do
       ActiveSupport.on_load(:active_record) do
-        ActionDispatch::Reloader.send(hook) do
+        ActiveSupport::Reloader.before_class_unload do
           if ActiveRecord::Base.connected?
             ActiveRecord::Base.clear_cache!
             ActiveRecord::Base.clear_reloadable_connections!
@@ -163,9 +198,65 @@ end_warning
       end
     end
 
+    initializer "active_record.set_executor_hooks" do
+      ActiveRecord::QueryCache.install_executor_hooks
+    end
+
     initializer "active_record.add_watchable_files" do |app|
       path = app.paths["db"].first
       config.watchable_files.concat ["#{path}/schema.rb", "#{path}/structure.sql"]
     end
+
+    initializer "active_record.clear_active_connections" do
+      config.after_initialize do
+        ActiveSupport.on_load(:active_record) do
+          # Ideally the application doesn't connect to the database during boot,
+          # but sometimes it does. In case it did, we want to empty out the
+          # connection pools so that a non-database-using process (e.g. a master
+          # process in a forking server model) doesn't retain a needless
+          # connection. If it was needed, the incremental cost of reestablishing
+          # this connection is trivial: the rest of the pool would need to be
+          # populated anyway.
+
+          clear_active_connections!
+          flush_idle_connections!
+        end
+      end
+    end
+
+    initializer "active_record.check_represent_sqlite3_boolean_as_integer" do
+      config.after_initialize do
+        ActiveSupport.on_load(:active_record_sqlite3adapter) do
+          represent_boolean_as_integer = Rails.application.config.active_record.sqlite3.delete(:represent_boolean_as_integer)
+          unless represent_boolean_as_integer.nil?
+            ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer = represent_boolean_as_integer
+          end
+
+          unless ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer
+            ActiveSupport::Deprecation.warn <<-MSG
+Leaving `ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer`
+set to false is deprecated. SQLite databases have used 't' and 'f' to serialize
+boolean values and must have old data converted to 1 and 0 (its native boolean
+serialization) before setting this flag to true. Conversion can be accomplished
+by setting up a rake task which runs
+
+  ExampleModel.where("boolean_column = 't'").update_all(boolean_column: 1)
+  ExampleModel.where("boolean_column = 'f'").update_all(boolean_column: 0)
+
+for all models and all boolean columns, after which the flag must be set to
+true by adding the following to your application.rb file:
+
+  Rails.application.config.active_record.sqlite3.represent_boolean_as_integer = true
+MSG
+          end
+        end
+      end
+    end
+
+    initializer "active_record.set_filter_attributes" do
+      ActiveSupport.on_load(:active_record) do
+        self.filter_attributes += Rails.application.config.filter_parameters
+      end
+    end
   end
 end
diff --git a/activerecord/lib/active_record/railties/collection_cache_association_loading.rb b/activerecord/lib/active_record/railties/collection_cache_association_loading.rb
new file mode 100644
index 0000000000..b5129e4239
--- /dev/null
+++ b/activerecord/lib/active_record/railties/collection_cache_association_loading.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module Railties # :nodoc:
+    module CollectionCacheAssociationLoading #:nodoc:
+      def setup(context, options, block)
+        @relation = relation_from_options(options)
+
+        super
+      end
+
+      def relation_from_options(cached: nil, partial: nil, collection: nil, **_)
+        return unless cached
+
+        relation = partial if partial.is_a?(ActiveRecord::Relation)
+        relation ||= collection if collection.is_a?(ActiveRecord::Relation)
+
+        if relation && !relation.loaded?
+          relation.skip_preloading!
+        end
+      end
+
+      def collection_without_template
+        @relation.preload_associations(@collection) if @relation
+        super
+      end
+
+      def collection_with_template
+        @relation.preload_associations(@collection) if @relation
+        super
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/railties/console_sandbox.rb b/activerecord/lib/active_record/railties/console_sandbox.rb
index 604a220303..8917638a5d 100644
--- a/activerecord/lib/active_record/railties/console_sandbox.rb
+++ b/activerecord/lib/active_record/railties/console_sandbox.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 ActiveRecord::Base.connection.begin_transaction(joinable: false)
 
 at_exit do
diff --git a/activerecord/lib/active_record/railties/controller_runtime.rb b/activerecord/lib/active_record/railties/controller_runtime.rb
index 8727e46cb3..309441a057 100644
--- a/activerecord/lib/active_record/railties/controller_runtime.rb
+++ b/activerecord/lib/active_record/railties/controller_runtime.rb
@@ -1,50 +1,51 @@
-require 'active_support/core_ext/module/attr_internal'
-require 'active_record/log_subscriber'
+# frozen_string_literal: true
+
+require "active_support/core_ext/module/attr_internal"
+require "active_record/log_subscriber"
 
 module ActiveRecord
   module Railties # :nodoc:
     module ControllerRuntime #:nodoc:
       extend ActiveSupport::Concern
 
-    protected
-
-      attr_internal :db_runtime
-
-      def process_action(action, *args)
-        # We also need to reset the runtime before each action
-        # because of queries in middleware or in cases we are streaming
-        # and it won't be cleaned up by the method below.
-        ActiveRecord::LogSubscriber.reset_runtime
-        super
+      module ClassMethods # :nodoc:
+        def log_process_action(payload)
+          messages, db_runtime = super, payload[:db_runtime]
+          messages << ("ActiveRecord: %.1fms" % db_runtime.to_f) if db_runtime
+          messages
+        end
       end
 
-      def cleanup_view_runtime
-        if logger.info? && ActiveRecord::Base.connected?
-          db_rt_before_render = ActiveRecord::LogSubscriber.reset_runtime
-          self.db_runtime = (db_runtime || 0) + db_rt_before_render
-          runtime = super
-          db_rt_after_render = ActiveRecord::LogSubscriber.reset_runtime
-          self.db_runtime += db_rt_after_render
-          runtime - db_rt_after_render
-        else
+      private
+        attr_internal :db_runtime
+
+        def process_action(action, *args)
+          # We also need to reset the runtime before each action
+          # because of queries in middleware or in cases we are streaming
+          # and it won't be cleaned up by the method below.
+          ActiveRecord::LogSubscriber.reset_runtime
           super
         end
-      end
 
-      def append_info_to_payload(payload)
-        super
-        if ActiveRecord::Base.connected?
-          payload[:db_runtime] = (db_runtime || 0) + ActiveRecord::LogSubscriber.reset_runtime
+        def cleanup_view_runtime
+          if logger && logger.info? && ActiveRecord::Base.connected?
+            db_rt_before_render = ActiveRecord::LogSubscriber.reset_runtime
+            self.db_runtime = (db_runtime || 0) + db_rt_before_render
+            runtime = super
+            db_rt_after_render = ActiveRecord::LogSubscriber.reset_runtime
+            self.db_runtime += db_rt_after_render
+            runtime - db_rt_after_render
+          else
+            super
+          end
         end
-      end
 
-      module ClassMethods # :nodoc:
-        def log_process_action(payload)
-          messages, db_runtime = super, payload[:db_runtime]
-          messages << ("ActiveRecord: %.1fms" % db_runtime.to_f) if db_runtime
-          messages
+        def append_info_to_payload(payload)
+          super
+          if ActiveRecord::Base.connected?
+            payload[:db_runtime] = (db_runtime || 0) + ActiveRecord::LogSubscriber.reset_runtime
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index 6a72d528b4..475baa7559 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -1,48 +1,83 @@
-require 'active_record'
+# frozen_string_literal: true
+
+require "active_record"
 
 db_namespace = namespace :db do
-  task :load_config do
+  desc "Set the environment value for the database"
+  task "environment:set" => :load_config do
+    ActiveRecord::InternalMetadata.create_table
+    ActiveRecord::InternalMetadata[:environment] = ActiveRecord::Base.connection.migration_context.current_environment
+  end
+
+  task check_protected_environments: :load_config do
+    ActiveRecord::Tasks::DatabaseTasks.check_protected_environments!
+  end
+
+  task load_config: :environment do
     ActiveRecord::Base.configurations       = ActiveRecord::Tasks::DatabaseTasks.database_configuration || {}
     ActiveRecord::Migrator.migrations_paths = ActiveRecord::Tasks::DatabaseTasks.migrations_paths
   end
 
   namespace :create do
-    task :all => :load_config do
+    task all: :load_config do
       ActiveRecord::Tasks::DatabaseTasks.create_all
     end
+
+    ActiveRecord::Tasks::DatabaseTasks.for_each do |spec_name|
+      desc "Create #{spec_name} database for current environment"
+      task spec_name => :load_config do
+        db_config = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env, spec_name: spec_name)
+        ActiveRecord::Tasks::DatabaseTasks.create(db_config.config)
+      end
+    end
   end
 
-  desc 'Creates the database from DATABASE_URL or config/database.yml for the current RAILS_ENV (use db:create:all to create all databases in the config). Without RAILS_ENV, it defaults to creating the development and test databases.'
-  task :create => [:load_config] do
+  desc "Creates the database from DATABASE_URL or config/database.yml for the current RAILS_ENV (use db:create:all to create all databases in the config). Without RAILS_ENV or when RAILS_ENV is development, it defaults to creating the development and test databases."
+  task create: [:load_config] do
     ActiveRecord::Tasks::DatabaseTasks.create_current
   end
 
   namespace :drop do
-    task :all => :load_config do
+    task all: [:load_config, :check_protected_environments] do
       ActiveRecord::Tasks::DatabaseTasks.drop_all
     end
+
+    ActiveRecord::Tasks::DatabaseTasks.for_each do |spec_name|
+      desc "Drop #{spec_name} database for current environment"
+      task spec_name => [:load_config, :check_protected_environments] do
+        db_config = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env, spec_name: spec_name)
+        ActiveRecord::Tasks::DatabaseTasks.drop(db_config.config)
+      end
+    end
+  end
+
+  desc "Drops the database from DATABASE_URL or config/database.yml for the current RAILS_ENV (use db:drop:all to drop all databases in the config). Without RAILS_ENV or when RAILS_ENV is development, it defaults to dropping the development and test databases."
+  task drop: [:load_config, :check_protected_environments] do
+    db_namespace["drop:_unsafe"].invoke
   end
 
-  desc 'Drops the database from DATABASE_URL or config/database.yml for the current RAILS_ENV (use db:drop:all to drop all databases in the config). Without RAILS_ENV, it defaults to dropping the development and test databases.'
-  task :drop => [:load_config] do
+  task "drop:_unsafe" => [:load_config] do
     ActiveRecord::Tasks::DatabaseTasks.drop_current
   end
 
   namespace :purge do
-    task :all => :load_config do
+    task all: [:load_config, :check_protected_environments] do
       ActiveRecord::Tasks::DatabaseTasks.purge_all
     end
   end
 
-  # desc "Empty the database from DATABASE_URL or config/database.yml for the current RAILS_ENV (use db:drop:all to drop all databases in the config). Without RAILS_ENV it defaults to purging the development and test databases."
-  task :purge => [:load_config] do
+  # desc "Empty the database from DATABASE_URL or config/database.yml for the current RAILS_ENV (use db:purge:all to purge all databases in the config). Without RAILS_ENV it defaults to purging the development and test databases."
+  task purge: [:load_config, :check_protected_environments] do
     ActiveRecord::Tasks::DatabaseTasks.purge_current
   end
 
   desc "Migrate the database (options: VERSION=x, VERBOSE=false, SCOPE=blog)."
-  task :migrate => [:environment, :load_config] do
-    ActiveRecord::Tasks::DatabaseTasks.migrate
-    db_namespace['_dump'].invoke
+  task migrate: :load_config do
+    ActiveRecord::Base.configurations.configs_for(env_name: Rails.env).each do |db_config|
+      ActiveRecord::Base.establish_connection(db_config.config)
+      ActiveRecord::Tasks::DatabaseTasks.migrate
+    end
+    db_namespace["_dump"].invoke
   end
 
   # IMPORTANT: This task won't dump the schema if ActiveRecord::Base.dump_schema_after_migration is set to false
@@ -57,165 +92,175 @@ db_namespace = namespace :db do
     end
     # Allow this task to be called as many times as required. An example is the
     # migrate:redo task, which calls other two internally that depend on this one.
-    db_namespace['_dump'].reenable
+    db_namespace["_dump"].reenable
   end
 
   namespace :migrate do
+    ActiveRecord::Tasks::DatabaseTasks.for_each do |spec_name|
+      desc "Migrate #{spec_name} database for current environment"
+      task spec_name => :load_config do
+        db_config = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env, spec_name: spec_name)
+        ActiveRecord::Base.establish_connection(db_config.config)
+        ActiveRecord::Tasks::DatabaseTasks.migrate
+      end
+    end
+
     # desc  'Rollbacks the database one migration and re migrate up (options: STEP=x, VERSION=x).'
-    task :redo => [:environment, :load_config] do
-      if ENV['VERSION']
-        db_namespace['migrate:down'].invoke
-        db_namespace['migrate:up'].invoke
+    task redo: :load_config do
+      raise "Empty VERSION provided" if ENV["VERSION"] && ENV["VERSION"].empty?
+
+      if ENV["VERSION"]
+        db_namespace["migrate:down"].invoke
+        db_namespace["migrate:up"].invoke
       else
-        db_namespace['rollback'].invoke
-        db_namespace['migrate'].invoke
+        db_namespace["rollback"].invoke
+        db_namespace["migrate"].invoke
       end
     end
 
     # desc 'Resets your database using your migrations for the current environment'
-    task :reset => ['db:drop', 'db:create', 'db:migrate']
+    task reset: ["db:drop", "db:create", "db:migrate"]
 
     # desc 'Runs the "up" for a given migration VERSION.'
-    task :up => [:environment, :load_config] do
-      version = ENV['VERSION'] ? ENV['VERSION'].to_i : nil
-      raise 'VERSION is required' unless version
-      ActiveRecord::Migrator.run(:up, ActiveRecord::Migrator.migrations_paths, version)
-      db_namespace['_dump'].invoke
+    task up: :load_config do
+      raise "VERSION is required" if !ENV["VERSION"] || ENV["VERSION"].empty?
+
+      ActiveRecord::Tasks::DatabaseTasks.check_target_version
+
+      ActiveRecord::Base.connection.migration_context.run(
+        :up,
+        ActiveRecord::Tasks::DatabaseTasks.target_version
+      )
+      db_namespace["_dump"].invoke
     end
 
     # desc 'Runs the "down" for a given migration VERSION.'
-    task :down => [:environment, :load_config] do
-      version = ENV['VERSION'] ? ENV['VERSION'].to_i : nil
-      raise 'VERSION is required - To go down one migration, run db:rollback' unless version
-      ActiveRecord::Migrator.run(:down, ActiveRecord::Migrator.migrations_paths, version)
-      db_namespace['_dump'].invoke
+    task down: :load_config do
+      raise "VERSION is required - To go down one migration, use db:rollback" if !ENV["VERSION"] || ENV["VERSION"].empty?
+
+      ActiveRecord::Tasks::DatabaseTasks.check_target_version
+
+      ActiveRecord::Base.connection.migration_context.run(
+        :down,
+        ActiveRecord::Tasks::DatabaseTasks.target_version
+      )
+      db_namespace["_dump"].invoke
     end
 
-    desc 'Display status of migrations'
-    task :status => [:environment, :load_config] do
-      unless ActiveRecord::SchemaMigration.table_exists?
-        abort 'Schema migrations table does not exist yet.'
+    desc "Display status of migrations"
+    task status: :load_config do
+      ActiveRecord::Base.configurations.configs_for(env_name: Rails.env).each do |db_config|
+        ActiveRecord::Base.establish_connection(db_config.config)
+        ActiveRecord::Tasks::DatabaseTasks.migrate_status
       end
-      db_list = ActiveRecord::SchemaMigration.normalized_versions
-
-      file_list =
-          ActiveRecord::Migrator.migrations_paths.flat_map do |path|
-            # match "20091231235959_some_name.rb" and "001_some_name.rb" pattern
-            Dir.foreach(path).grep(/^(\d{3,})_(.+)\.rb$/) do
-              version = ActiveRecord::SchemaMigration.normalize_migration_number($1)
-              status = db_list.delete(version) ? 'up' : 'down'
-              [status, version, $2.humanize]
-            end
-          end
+    end
 
-      db_list.map! do |version|
-        ['up', version, '********** NO FILE **********']
-      end
-      # output
-      puts "\ndatabase: #{ActiveRecord::Base.connection_config[:database]}\n\n"
-      puts "#{'Status'.center(8)}  #{'Migration ID'.ljust(14)}  Migration Name"
-      puts "-" * 50
-      (db_list + file_list).sort_by { |_, version, _| version }.each do |status, version, name|
-        puts "#{status.center(8)}  #{version.ljust(14)}  #{name}"
+    namespace :status do
+      ActiveRecord::Tasks::DatabaseTasks.for_each do |spec_name|
+        desc "Display status of migrations for #{spec_name} database"
+        task spec_name => :load_config do
+          db_config = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env, spec_name: spec_name)
+          ActiveRecord::Base.establish_connection(db_config.config)
+          ActiveRecord::Tasks::DatabaseTasks.migrate_status
+        end
       end
-      puts
     end
   end
 
-  desc 'Rolls the schema back to the previous version (specify steps w/ STEP=n).'
-  task :rollback => [:environment, :load_config] do
-    step = ENV['STEP'] ? ENV['STEP'].to_i : 1
-    ActiveRecord::Migrator.rollback(ActiveRecord::Migrator.migrations_paths, step)
-    db_namespace['_dump'].invoke
+  desc "Rolls the schema back to the previous version (specify steps w/ STEP=n)."
+  task rollback: :load_config do
+    step = ENV["STEP"] ? ENV["STEP"].to_i : 1
+    ActiveRecord::Base.connection.migration_context.rollback(step)
+    db_namespace["_dump"].invoke
   end
 
   # desc 'Pushes the schema to the next version (specify steps w/ STEP=n).'
-  task :forward => [:environment, :load_config] do
-    step = ENV['STEP'] ? ENV['STEP'].to_i : 1
-    ActiveRecord::Migrator.forward(ActiveRecord::Migrator.migrations_paths, step)
-    db_namespace['_dump'].invoke
+  task forward: :load_config do
+    step = ENV["STEP"] ? ENV["STEP"].to_i : 1
+    ActiveRecord::Base.connection.migration_context.forward(step)
+    db_namespace["_dump"].invoke
   end
 
   # desc 'Drops and recreates the database from db/schema.rb for the current environment and loads the seeds.'
-  task :reset => [ 'db:drop', 'db:setup' ]
+  task reset: [ "db:drop", "db:setup" ]
 
   # desc "Retrieves the charset for the current environment's database"
-  task :charset => [:environment, :load_config] do
+  task charset: :load_config do
     puts ActiveRecord::Tasks::DatabaseTasks.charset_current
   end
 
   # desc "Retrieves the collation for the current environment's database"
-  task :collation => [:environment, :load_config] do
+  task collation: :load_config do
     begin
       puts ActiveRecord::Tasks::DatabaseTasks.collation_current
     rescue NoMethodError
-      $stderr.puts 'Sorry, your database adapter is not supported yet. Feel free to submit a patch.'
+      $stderr.puts "Sorry, your database adapter is not supported yet. Feel free to submit a patch."
     end
   end
 
-  desc 'Retrieves the current schema version number'
-  task :version => [:environment, :load_config] do
-    puts "Current version: #{ActiveRecord::Migrator.current_version}"
+  desc "Retrieves the current schema version number"
+  task version: :load_config do
+    puts "Current version: #{ActiveRecord::Base.connection.migration_context.current_version}"
   end
 
   # desc "Raises an error if there are pending migrations"
-  task :abort_if_pending_migrations => [:environment, :load_config] do
-    pending_migrations = ActiveRecord::Migrator.open(ActiveRecord::Migrator.migrations_paths).pending_migrations
+  task abort_if_pending_migrations: :load_config do
+    pending_migrations = ActiveRecord::Base.connection.migration_context.open.pending_migrations
 
     if pending_migrations.any?
       puts "You have #{pending_migrations.size} pending #{pending_migrations.size > 1 ? 'migrations:' : 'migration:'}"
       pending_migrations.each do |pending_migration|
-        puts '  %4d %s' % [pending_migration.version, pending_migration.name]
+        puts "  %4d %s" % [pending_migration.version, pending_migration.name]
       end
-      abort %{Run `rake db:migrate` to update your database then try again.}
+      abort %{Run `rails db:migrate` to update your database then try again.}
     end
   end
 
-  desc 'Creates the database, loads the schema, and initializes with the seed data (use db:reset to also drop the database first)'
-  task :setup => ['db:schema:load_if_ruby', 'db:structure:load_if_sql', :seed]
+  desc "Creates the database, loads the schema, and initializes with the seed data (use db:reset to also drop the database first)"
+  task setup: ["db:schema:load_if_ruby", "db:structure:load_if_sql", :seed]
 
-  desc 'Loads the seed data from db/seeds.rb'
-  task :seed do
-    db_namespace['abort_if_pending_migrations'].invoke
+  desc "Loads the seed data from db/seeds.rb"
+  task seed: :load_config do
+    db_namespace["abort_if_pending_migrations"].invoke
     ActiveRecord::Tasks::DatabaseTasks.load_seed
   end
 
   namespace :fixtures do
     desc "Loads fixtures into the current environment's database. Load specific fixtures using FIXTURES=x,y. Load from subdirectory in test/fixtures using FIXTURES_DIR=z. Specify an alternative path (eg. spec/fixtures) using FIXTURES_PATH=spec/fixtures."
-    task :load => [:environment, :load_config] do
-      require 'active_record/fixtures'
+    task load: :load_config do
+      require "active_record/fixtures"
 
       base_dir = ActiveRecord::Tasks::DatabaseTasks.fixtures_path
 
-      fixtures_dir = if ENV['FIXTURES_DIR']
-                       File.join base_dir, ENV['FIXTURES_DIR']
-                     else
-                       base_dir
-                     end
+      fixtures_dir = if ENV["FIXTURES_DIR"]
+        File.join base_dir, ENV["FIXTURES_DIR"]
+      else
+        base_dir
+      end
 
-      fixture_files = if ENV['FIXTURES']
-                        ENV['FIXTURES'].split(',')
-                      else
-                        # The use of String#[] here is to support namespaced fixtures
-                        Dir["#{fixtures_dir}/**/*.yml"].map {|f| f[(fixtures_dir.size + 1)..-5] }
-                      end
+      fixture_files = if ENV["FIXTURES"]
+        ENV["FIXTURES"].split(",")
+      else
+        # The use of String#[] here is to support namespaced fixtures.
+        Dir["#{fixtures_dir}/**/*.yml"].map { |f| f[(fixtures_dir.size + 1)..-5] }
+      end
 
       ActiveRecord::FixtureSet.create_fixtures(fixtures_dir, fixture_files)
     end
 
     # desc "Search for a fixture given a LABEL or ID. Specify an alternative path (eg. spec/fixtures) using FIXTURES_PATH=spec/fixtures."
-    task :identify => [:environment, :load_config] do
-      require 'active_record/fixtures'
+    task identify: :load_config do
+      require "active_record/fixtures"
 
-      label, id = ENV['LABEL'], ENV['ID']
-      raise 'LABEL or ID required' if label.blank? && id.blank?
+      label, id = ENV["LABEL"], ENV["ID"]
+      raise "LABEL or ID required" if label.blank? && id.blank?
 
       puts %Q(The fixture ID for "#{label}" is #{ActiveRecord::FixtureSet.identify(label)}.) if label
 
       base_dir = ActiveRecord::Tasks::DatabaseTasks.fixtures_path
 
       Dir["#{base_dir}/**/*.yml"].each do |file|
-        if data = YAML::load(ERB.new(IO.read(file)).result)
+        if data = YAML.load(ERB.new(IO.read(file)).result)
           data.each_key do |key|
             key_id = ActiveRecord::FixtureSet.identify(key)
 
@@ -229,134 +274,126 @@ db_namespace = namespace :db do
   end
 
   namespace :schema do
-    desc 'Creates a db/schema.rb file that is portable against any DB supported by AR'
-    task :dump => [:environment, :load_config] do
-      require 'active_record/schema_dumper'
-      filename = ENV['SCHEMA'] || File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, 'schema.rb')
-      File.open(filename, "w:utf-8") do |file|
-        ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
+    desc "Creates a db/schema.rb file that is portable against any DB supported by Active Record"
+    task dump: :load_config do
+      require "active_record/schema_dumper"
+      ActiveRecord::Base.configurations.configs_for(env_name: Rails.env).each do |db_config|
+        filename = ActiveRecord::Tasks::DatabaseTasks.dump_filename(db_config.spec_name, :ruby)
+        File.open(filename, "w:utf-8") do |file|
+          ActiveRecord::Base.establish_connection(db_config.config)
+          ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, file)
+        end
       end
-      db_namespace['schema:dump'].reenable
+
+      db_namespace["schema:dump"].reenable
     end
 
-    desc 'Loads a schema.rb file into the database'
-    task :load => [:environment, :load_config] do
-      ActiveRecord::Tasks::DatabaseTasks.load_schema_current(:ruby, ENV['SCHEMA'])
+    desc "Loads a schema.rb file into the database"
+    task load: [:load_config, :check_protected_environments] do
+      ActiveRecord::Tasks::DatabaseTasks.load_schema_current(:ruby, ENV["SCHEMA"])
     end
 
-    task :load_if_ruby => ['db:create', :environment] do
+    task load_if_ruby: ["db:create", :environment] do
       db_namespace["schema:load"].invoke if ActiveRecord::Base.schema_format == :ruby
     end
 
     namespace :cache do
-      desc 'Creates a db/schema_cache.dump file.'
-      task :dump => [:environment, :load_config] do
-        con = ActiveRecord::Base.connection
-        filename = File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, "schema_cache.dump")
-
-        con.schema_cache.clear!
-        con.tables.each { |table| con.schema_cache.add(table) }
-        open(filename, 'wb') { |f| f.write(Marshal.dump(con.schema_cache)) }
+      desc "Creates a db/schema_cache.yml file."
+      task dump: :load_config do
+        ActiveRecord::Base.configurations.configs_for(env_name: Rails.env).each do |db_config|
+          ActiveRecord::Base.establish_connection(db_config.config)
+          filename = ActiveRecord::Tasks::DatabaseTasks.cache_dump_filename(db_config.spec_name)
+          ActiveRecord::Tasks::DatabaseTasks.dump_schema_cache(
+            ActiveRecord::Base.connection,
+            filename,
+          )
+        end
       end
 
-      desc 'Clears a db/schema_cache.dump file.'
-      task :clear => [:environment, :load_config] do
-        filename = File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, "schema_cache.dump")
-        FileUtils.rm(filename) if File.exist?(filename)
+      desc "Clears a db/schema_cache.yml file."
+      task clear: :load_config do
+        ActiveRecord::Base.configurations.configs_for(env_name: Rails.env).each do |db_config|
+          filename = ActiveRecord::Tasks::DatabaseTasks.cache_dump_filename(db_config.spec_name)
+          rm_f filename, verbose: false
+        end
       end
     end
-
   end
 
   namespace :structure do
-    desc 'Dumps the database structure to db/structure.sql. Specify another file with SCHEMA=db/my_structure.sql'
-    task :dump => [:environment, :load_config] do
-      filename = ENV['SCHEMA'] || File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, "structure.sql")
-      current_config = ActiveRecord::Tasks::DatabaseTasks.current_config
-      ActiveRecord::Tasks::DatabaseTasks.structure_dump(current_config, filename)
-
-      if ActiveRecord::Base.connection.supports_migrations? &&
-          ActiveRecord::SchemaMigration.table_exists?
-        File.open(filename, "a") do |f|
-          f.puts ActiveRecord::Base.connection.dump_schema_information
-          f.print "\n"
+    desc "Dumps the database structure to db/structure.sql. Specify another file with SCHEMA=db/my_structure.sql"
+    task dump: :load_config do
+      ActiveRecord::Base.configurations.configs_for(env_name: Rails.env).each do |db_config|
+        ActiveRecord::Base.establish_connection(db_config.config)
+        filename = ActiveRecord::Tasks::DatabaseTasks.dump_filename(db_config.spec_name, :sql)
+        ActiveRecord::Tasks::DatabaseTasks.structure_dump(db_config.config, filename)
+        if ActiveRecord::SchemaMigration.table_exists?
+          File.open(filename, "a") do |f|
+            f.puts ActiveRecord::Base.connection.dump_schema_information
+            f.print "\n"
+          end
         end
       end
-      db_namespace['structure:dump'].reenable
+
+      db_namespace["structure:dump"].reenable
     end
 
     desc "Recreates the databases from the structure.sql file"
-    task :load => [:load_config] do
-      ActiveRecord::Tasks::DatabaseTasks.load_schema_current(:sql, ENV['SCHEMA'])
+    task load: [:load_config, :check_protected_environments] do
+      ActiveRecord::Tasks::DatabaseTasks.load_schema_current(:sql, ENV["SCHEMA"])
     end
 
-    task :load_if_sql => ['db:create', :environment] do
+    task load_if_sql: ["db:create", :environment] do
       db_namespace["structure:load"].invoke if ActiveRecord::Base.schema_format == :sql
     end
   end
 
   namespace :test do
-
-    task :deprecated do
-      Rake.application.top_level_tasks.grep(/^db:test:/).each do |task|
-        $stderr.puts "WARNING: #{task} is deprecated. The Rails test helper now maintains " \
-                     "your test schema automatically, see the release notes for details."
-      end
-    end
-
     # desc "Recreate the test database from the current schema"
-    task :load => %w(db:test:purge) do
+    task load: %w(db:test:purge) do
       case ActiveRecord::Base.schema_format
-        when :ruby
-          db_namespace["test:load_schema"].invoke
-        when :sql
-          db_namespace["test:load_structure"].invoke
+      when :ruby
+        db_namespace["test:load_schema"].invoke
+      when :sql
+        db_namespace["test:load_structure"].invoke
       end
     end
 
     # desc "Recreate the test database from an existent schema.rb file"
-    task :load_schema => %w(db:test:purge) do
+    task load_schema: %w(db:test:purge) do
       begin
         should_reconnect = ActiveRecord::Base.connection_pool.active_connection?
         ActiveRecord::Schema.verbose = false
-        ActiveRecord::Tasks::DatabaseTasks.load_schema ActiveRecord::Base.configurations['test'], :ruby, ENV['SCHEMA']
+        ActiveRecord::Base.configurations.configs_for(env_name: "test").each do |db_config|
+          filename = ActiveRecord::Tasks::DatabaseTasks.dump_filename(db_config.spec_name, :ruby)
+          ActiveRecord::Tasks::DatabaseTasks.load_schema(db_config.config, :ruby, filename, "test")
+        end
       ensure
         if should_reconnect
-          ActiveRecord::Base.establish_connection(ActiveRecord::Base.configurations[ActiveRecord::Tasks::DatabaseTasks.env])
+          ActiveRecord::Base.establish_connection(ActiveRecord::Base.configurations.default_hash(ActiveRecord::Tasks::DatabaseTasks.env))
         end
       end
     end
 
     # desc "Recreate the test database from an existent structure.sql file"
-    task :load_structure => %w(db:test:purge) do
-      ActiveRecord::Tasks::DatabaseTasks.load_schema ActiveRecord::Base.configurations['test'], :sql, ENV['SCHEMA']
-    end
-
-    # desc "Recreate the test database from a fresh schema"
-    task :clone => %w(db:test:deprecated environment) do
-      case ActiveRecord::Base.schema_format
-        when :ruby
-          db_namespace["test:clone_schema"].invoke
-        when :sql
-          db_namespace["test:clone_structure"].invoke
+    task load_structure: %w(db:test:purge) do
+      ActiveRecord::Base.configurations.configs_for(env_name: "test").each do |db_config|
+        filename = ActiveRecord::Tasks::DatabaseTasks.dump_filename(db_config.spec_name, :sql)
+        ActiveRecord::Tasks::DatabaseTasks.load_schema(db_config.config, :sql, filename, "test")
       end
     end
 
-    # desc "Recreate the test database from a fresh schema.rb file"
-    task :clone_schema => %w(db:test:deprecated db:schema:dump db:test:load_schema)
-
-    # desc "Recreate the test database from a fresh structure.sql file"
-    task :clone_structure => %w(db:test:deprecated db:structure:dump db:test:load_structure)
-
     # desc "Empty the test database"
-    task :purge => %w(environment load_config) do
-      ActiveRecord::Tasks::DatabaseTasks.purge ActiveRecord::Base.configurations['test']
+    task purge: %w(load_config check_protected_environments) do
+      ActiveRecord::Base.configurations.configs_for(env_name: "test").each do |db_config|
+        ActiveRecord::Tasks::DatabaseTasks.purge(db_config.config)
+      end
     end
 
-    # desc 'Check for pending migrations and load the test schema'
-    task :prepare => %w(environment load_config) do
+    # desc 'Load the test schema'
+    task prepare: :load_config do
       unless ActiveRecord::Base.configurations.blank?
-        db_namespace['test:load'].invoke
+        db_namespace["test:load"].invoke
       end
     end
   end
@@ -365,13 +402,13 @@ end
 namespace :railties do
   namespace :install do
     # desc "Copies missing migrations from Railties (e.g. engines). You can specify Railties to use with FROM=railtie1,railtie2"
-    task :migrations => :'db:load_config' do
-      to_load = ENV['FROM'].blank? ? :all : ENV['FROM'].split(",").map(&:strip)
+    task migrations: :'db:load_config' do
+      to_load = ENV["FROM"].blank? ? :all : ENV["FROM"].split(",").map(&:strip)
       railties = {}
       Rails.application.migration_railties.each do |railtie|
         next unless to_load == :all || to_load.include?(railtie.railtie_name)
 
-        if railtie.respond_to?(:paths) && (path = railtie.paths['db/migrate'].first)
+        if railtie.respond_to?(:paths) && (path = railtie.paths["db/migrate"].first)
           railties[railtie.railtie_name] = path
         end
       end
@@ -384,8 +421,8 @@ namespace :railties do
         puts "Copied migration #{migration.basename} from #{name}"
       end
 
-      ActiveRecord::Migration.copy(ActiveRecord::Migrator.migrations_paths.first, railties,
-                                    :on_skip => on_skip, :on_copy => on_copy)
+      ActiveRecord::Migration.copy(ActiveRecord::Tasks::DatabaseTasks.migrations_paths.first, railties,
+                                    on_skip: on_skip, on_copy: on_copy)
     end
   end
 end
diff --git a/activerecord/lib/active_record/railties/jdbcmysql_error.rb b/activerecord/lib/active_record/railties/jdbcmysql_error.rb
deleted file mode 100644
index 6a38211bff..0000000000
--- a/activerecord/lib/active_record/railties/jdbcmysql_error.rb
+++ /dev/null
@@ -1,16 +0,0 @@
-#FIXME Remove if ArJdbcMysql will give.
-module ArJdbcMySQL #:nodoc:
-  class Error < StandardError #:nodoc:
-    attr_accessor :error_number, :sql_state
-
-    def initialize msg
-      super
-      @error_number = nil
-      @sql_state    = nil
-    end
-
-    # Mysql gem compatibility
-    alias_method :errno, :error_number
-    alias_method :error, :message
-  end
-end
diff --git a/activerecord/lib/active_record/readonly_attributes.rb b/activerecord/lib/active_record/readonly_attributes.rb
index ce78f1756d..7bc26993d5 100644
--- a/activerecord/lib/active_record/readonly_attributes.rb
+++ b/activerecord/lib/active_record/readonly_attributes.rb
@@ -1,22 +1,23 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ReadonlyAttributes
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :_attr_readonly, instance_accessor: false
-      self._attr_readonly = []
+      class_attribute :_attr_readonly, instance_accessor: false, default: []
     end
 
     module ClassMethods
       # Attributes listed as readonly will be used to create a new record but update operations will
       # ignore these fields.
       def attr_readonly(*attributes)
-        self._attr_readonly = Set.new(attributes.map(&:to_s)) + (self._attr_readonly || [])
+        self._attr_readonly = Set.new(attributes.map(&:to_s)) + (_attr_readonly || [])
       end
 
       # Returns an array of all the attributes that have been specified as readonly.
       def readonly_attributes
-        self._attr_readonly
+        _attr_readonly
       end
     end
   end
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index 5360db6a19..b2110f727c 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -1,5 +1,7 @@
-require 'thread'
-require 'active_support/core_ext/string/filters'
+# frozen_string_literal: true
+
+require "active_support/core_ext/string/filters"
+require "concurrent/map"
 
 module ActiveRecord
   # = Active Record Reflection
@@ -7,36 +9,41 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :_reflections
-      class_attribute :aggregate_reflections
-      self._reflections = {}
-      self.aggregate_reflections = {}
+      class_attribute :_reflections, instance_writer: false, default: {}
+      class_attribute :aggregate_reflections, instance_writer: false, default: {}
     end
 
-    def self.create(macro, name, scope, options, ar)
-      klass = case macro
-              when :composed_of
-                AggregateReflection
-              when :has_many
-                HasManyReflection
-              when :has_one
-                HasOneReflection
-              when :belongs_to
-                BelongsToReflection
-              else
-                raise "Unsupported Macro: #{macro}"
-              end
-
-      reflection = klass.new(name, scope, options, ar)
-      options[:through] ? ThroughReflection.new(reflection) : reflection
-    end
+    class << self
+      def create(macro, name, scope, options, ar)
+        reflection = reflection_class_for(macro).new(name, scope, options, ar)
+        options[:through] ? ThroughReflection.new(reflection) : reflection
+      end
 
-    def self.add_reflection(ar, name, reflection)
-      ar._reflections = ar._reflections.merge(name.to_s => reflection)
-    end
+      def add_reflection(ar, name, reflection)
+        ar.clear_reflections_cache
+        name = name.to_s
+        ar._reflections = ar._reflections.except(name).merge!(name => reflection)
+      end
 
-    def self.add_aggregate_reflection(ar, name, reflection)
-      ar.aggregate_reflections = ar.aggregate_reflections.merge(name.to_s => reflection)
+      def add_aggregate_reflection(ar, name, reflection)
+        ar.aggregate_reflections = ar.aggregate_reflections.merge(name.to_s => reflection)
+      end
+
+      private
+        def reflection_class_for(macro)
+          case macro
+          when :composed_of
+            AggregateReflection
+          when :has_many
+            HasManyReflection
+          when :has_one
+            HasOneReflection
+          when :belongs_to
+            BelongsToReflection
+          else
+            raise "Unsupported Macro: #{macro}"
+          end
+        end
     end
 
     # \Reflection enables the ability to examine the associations and aggregations of
@@ -61,24 +68,27 @@ module ActiveRecord
         aggregate_reflections[aggregation.to_s]
       end
 
-      # Returns a Hash of name of the reflection as the key and a AssociationReflection as the value.
+      # Returns a Hash of name of the reflection as the key and an AssociationReflection as the value.
       #
       #   Account.reflections # => {"balance" => AggregateReflection}
       #
-      # @api public
       def reflections
-        ref = {}
-        _reflections.each do |name, reflection|
-          parent_reflection = reflection.parent_reflection
+        @__reflections ||= begin
+          ref = {}
 
-          if parent_reflection
-            parent_name = parent_reflection.name
-            ref[parent_name.to_s] = parent_reflection
-          else
-            ref[name] = reflection
+          _reflections.each do |name, reflection|
+            parent_reflection = reflection.parent_reflection
+
+            if parent_reflection
+              parent_name = parent_reflection.name
+              ref[parent_name.to_s] = parent_reflection
+            else
+              ref[name] = reflection
+            end
           end
+
+          ref
         end
-        ref
       end
 
       # Returns an array of AssociationReflection objects for all the
@@ -91,10 +101,10 @@ module ActiveRecord
       #   Account.reflect_on_all_associations             # returns an array of all associations
       #   Account.reflect_on_all_associations(:has_many)  # returns an array of all has_many associations
       #
-      #   @api public
       def reflect_on_all_associations(macro = nil)
         association_reflections = reflections.values
-        macro ? association_reflections.select { |reflection| reflection.macro == macro } : association_reflections
+        association_reflections.select! { |reflection| reflection.macro == macro } if macro
+        association_reflections
       end
 
       # Returns the AssociationReflection object for the +association+ (use the symbol).
@@ -102,27 +112,42 @@ module ActiveRecord
       #   Account.reflect_on_association(:owner)             # returns the owner AssociationReflection
       #   Invoice.reflect_on_association(:line_items).macro  # returns :has_many
       #
-      #   @api public
       def reflect_on_association(association)
         reflections[association.to_s]
       end
 
-      #   @api private
       def _reflect_on_association(association) #:nodoc:
         _reflections[association.to_s]
       end
 
       # Returns an array of AssociationReflection objects for all associations which have <tt>:autosave</tt> enabled.
-      #
-      #   @api public
       def reflect_on_all_autosave_associations
         reflections.values.select { |reflection| reflection.options[:autosave] }
       end
+
+      def clear_reflections_cache # :nodoc:
+        @__reflections = nil
+      end
     end
 
-    # Holds all the methods that are shared between MacroReflection, AssociationReflection
-    # and ThroughReflection
+    # Holds all the methods that are shared between MacroReflection and ThroughReflection.
+    #
+    #   AbstractReflection
+    #     MacroReflection
+    #       AggregateReflection
+    #       AssociationReflection
+    #         HasManyReflection
+    #         HasOneReflection
+    #         BelongsToReflection
+    #         HasAndBelongsToManyReflection
+    #     ThroughReflection
+    #     PolymorphicReflection
+    #     RuntimeReflection
     class AbstractReflection # :nodoc:
+      def through_reflection?
+        false
+      end
+
       def table_name
         klass.table_name
       end
@@ -133,14 +158,6 @@ module ActiveRecord
         klass.new(attributes, &block)
       end
 
-      def quoted_table_name
-        klass.quoted_table_name
-      end
-
-      def primary_key_type
-        klass.type_for_attribute(klass.primary_key)
-      end
-
       # Returns the class name for the macro.
       #
       # <tt>composed_of :balance, class_name: 'Money'</tt> returns <tt>'Money'</tt>
@@ -151,29 +168,165 @@ module ActiveRecord
 
       JoinKeys = Struct.new(:key, :foreign_key) # :nodoc:
 
-      def join_keys(association_klass)
-        JoinKeys.new(foreign_key, active_record_primary_key)
+      def join_keys
+        @join_keys ||= get_join_keys(klass)
+      end
+
+      # Returns a list of scopes that should be applied for this Reflection
+      # object when querying the database.
+      def scopes
+        scope ? [scope] : []
+      end
+
+      def build_join_constraint(table, foreign_table)
+        key         = join_keys.key
+        foreign_key = join_keys.foreign_key
+
+        constraint = table[key].eq(foreign_table[foreign_key])
+
+        if klass.finder_needs_type_condition?
+          table.create_and([constraint, klass.send(:type_condition, table)])
+        else
+          constraint
+        end
+      end
+
+      def join_scope(table, foreign_klass)
+        predicate_builder = predicate_builder(table)
+        scope_chain_items = join_scopes(table, predicate_builder)
+        klass_scope       = klass_join_scope(table, predicate_builder)
+
+        if type
+          klass_scope.where!(type => foreign_klass.polymorphic_name)
+        end
+
+        scope_chain_items.inject(klass_scope, &:merge!)
+      end
+
+      def join_scopes(table, predicate_builder) # :nodoc:
+        if scope
+          [scope_for(build_scope(table, predicate_builder))]
+        else
+          []
+        end
+      end
+
+      def klass_join_scope(table, predicate_builder) # :nodoc:
+        relation = build_scope(table, predicate_builder)
+        klass.scope_for_association(relation)
       end
 
       def constraints
-        scope_chain.flatten
+        chain.flat_map(&:scopes)
+      end
+
+      def counter_cache_column
+        if belongs_to?
+          if options[:counter_cache] == true
+            "#{active_record.name.demodulize.underscore.pluralize}_count"
+          elsif options[:counter_cache]
+            options[:counter_cache].to_s
+          end
+        else
+          options[:counter_cache] ? options[:counter_cache].to_s : "#{name}_count"
+        end
+      end
+
+      def inverse_of
+        return unless inverse_name
+
+        @inverse_of ||= klass._reflect_on_association inverse_name
+      end
+
+      def check_validity_of_inverse!
+        unless polymorphic?
+          if has_inverse? && inverse_of.nil?
+            raise InverseOfAssociationNotFoundError.new(self)
+          end
+        end
+      end
+
+      # This shit is nasty. We need to avoid the following situation:
+      #
+      #   * An associated record is deleted via record.destroy
+      #   * Hence the callbacks run, and they find a belongs_to on the record with a
+      #     :counter_cache options which points back at our owner. So they update the
+      #     counter cache.
+      #   * In which case, we must make sure to *not* update the counter cache, or else
+      #     it will be decremented twice.
+      #
+      # Hence this method.
+      def inverse_which_updates_counter_cache
+        return @inverse_which_updates_counter_cache if defined?(@inverse_which_updates_counter_cache)
+        @inverse_which_updates_counter_cache = klass.reflect_on_all_associations(:belongs_to).find do |inverse|
+          inverse.counter_cache_column == counter_cache_column
+        end
+      end
+      alias inverse_updates_counter_cache? inverse_which_updates_counter_cache
+
+      def inverse_updates_counter_in_memory?
+        inverse_of && inverse_which_updates_counter_cache == inverse_of
+      end
+
+      # Returns whether a counter cache should be used for this association.
+      #
+      # The counter_cache option must be given on either the owner or inverse
+      # association, and the column must be present on the owner.
+      def has_cached_counter?
+        options[:counter_cache] ||
+          inverse_which_updates_counter_cache && inverse_which_updates_counter_cache.options[:counter_cache] &&
+          !!active_record.columns_hash[counter_cache_column]
+      end
+
+      def counter_must_be_updated_by_has_many?
+        !inverse_updates_counter_in_memory? && has_cached_counter?
       end
 
       def alias_candidate(name)
         "#{plural_name}_#{name}"
       end
+
+      def chain
+        collect_join_chain
+      end
+
+      def get_join_keys(association_klass)
+        JoinKeys.new(join_primary_key(association_klass), join_foreign_key)
+      end
+
+      def build_scope(table, predicate_builder = predicate_builder(table))
+        Relation.create(
+          klass,
+          table: table,
+          predicate_builder: predicate_builder
+        )
+      end
+
+      def join_primary_key(*)
+        foreign_key
+      end
+
+      def join_foreign_key
+        active_record_primary_key
+      end
+
+      protected
+        def actual_source_reflection # FIXME: this is a horrible name
+          self
+        end
+
+      private
+        def predicate_builder(table)
+          PredicateBuilder.new(TableMetadata.new(klass, table))
+        end
+
+        def primary_key(klass)
+          klass.primary_key || raise(UnknownPrimaryKey.new(klass))
+        end
     end
 
     # Base class for AggregateReflection and AssociationReflection. Objects of
     # AggregateReflection and AssociationReflection are returned by the Reflection::ClassMethods.
-    #
-    #   MacroReflection
-    #     AggregateReflection
-    #     AssociationReflection
-    #       HasManyReflection
-    #       HasOneReflection
-    #       BelongsToReflection
-    #         ThroughReflection
     class MacroReflection < AbstractReflection
       # Returns the name of the macro.
       #
@@ -204,7 +357,6 @@ module ActiveRecord
       end
 
       def autosave=(autosave)
-        @automatic_inverse_of = false
         @options[:autosave] = autosave
         parent_reflection = self.parent_reflection
         if parent_reflection
@@ -216,6 +368,17 @@ module ActiveRecord
       #
       # <tt>composed_of :balance, class_name: 'Money'</tt> returns the Money class
       # <tt>has_many :clients</tt> returns the Client class
+      #
+      #   class Company < ActiveRecord::Base
+      #     has_many :clients
+      #   end
+      #
+      #   Company.reflect_on_association(:clients).klass
+      #   # => Client
+      #
+      # <b>Note:</b> Do not call +klass.new+ or +klass.create+ to instantiate
+      # a new association object. Use +build_association+ or +create_association+
+      # instead. This allows plugins to hook into association object creation.
       def klass
         @klass ||= compute_class(class_name)
       end
@@ -234,14 +397,17 @@ module ActiveRecord
           active_record == other_aggregation.active_record
       end
 
+      def scope_for(relation, owner = nil)
+        relation.instance_exec(owner, &scope) || relation
+      end
+
       private
         def derive_class_name
           name.to_s.camelize
         end
     end
 
-
-    # Holds all the meta-data about an aggregation as it was specified in the
+    # Holds all the metadata about an aggregation as it was specified in the
     # Active Record class.
     class AggregateReflection < MacroReflection #:nodoc:
       def mapping
@@ -250,26 +416,13 @@ module ActiveRecord
       end
     end
 
-    # Holds all the meta-data about an association as it was specified in the
+    # Holds all the metadata about an association as it was specified in the
     # Active Record class.
     class AssociationReflection < MacroReflection #:nodoc:
-      # Returns the target association's class.
-      #
-      #   class Author < ActiveRecord::Base
-      #     has_many :books
-      #   end
-      #
-      #   Author.reflect_on_association(:books).klass
-      #   # => Book
-      #
-      # <b>Note:</b> Do not call +klass.new+ or +klass.create+ to instantiate
-      # a new association object. Use +build_association+ or +create_association+
-      # instead. This allows plugins to hook into association object creation.
-      def klass
-        @klass ||= compute_class(class_name)
-      end
-
       def compute_class(name)
+        if polymorphic?
+          raise ArgumentError, "Polymorphic associations do not support computing the class."
+        end
         active_record.send(:compute_type, name)
       end
 
@@ -278,22 +431,22 @@ module ActiveRecord
 
       def initialize(name, scope, options, active_record)
         super
-        @automatic_inverse_of = nil
         @type         = options[:as] && (options[:foreign_type] || "#{options[:as]}_type")
-        @foreign_type = options[:foreign_type] || "#{name}_type"
+        @foreign_type = options[:polymorphic] && (options[:foreign_type] || "#{name}_type")
         @constructable = calculate_constructable(macro, options)
-        @association_scope_cache = {}
-        @scope_lock = Mutex.new
+        @association_scope_cache = Concurrent::Map.new
+
+        if options[:class_name] && options[:class_name].class == Class
+          raise ArgumentError, "A class was passed to `:class_name` but we are expecting a string."
+        end
       end
 
-      def association_scope_cache(conn, owner)
+      def association_scope_cache(conn, owner, &block)
         key = conn.prepared_statements
         if polymorphic?
           key = [key, owner._read_attribute(@foreign_type)]
         end
-        @association_scope_cache[key] ||= @scope_lock.synchronize {
-          @association_scope_cache[key] ||= yield
-        }
+        @association_scope_cache.compute_if_absent(key) { StatementCache.create(conn, &block) }
       end
 
       def constructable? # :nodoc:
@@ -305,7 +458,7 @@ module ActiveRecord
       end
 
       def foreign_key
-        @foreign_key ||= options[:foreign_key] || derive_foreign_key
+        @foreign_key ||= options[:foreign_key] || derive_foreign_key.freeze
       end
 
       def association_foreign_key
@@ -321,26 +474,10 @@ module ActiveRecord
         @active_record_primary_key ||= options[:primary_key] || primary_key(active_record)
       end
 
-      def counter_cache_column
-        if options[:counter_cache] == true
-          "#{active_record.name.demodulize.underscore.pluralize}_count"
-        elsif options[:counter_cache]
-          options[:counter_cache].to_s
-        end
-      end
-
       def check_validity!
         check_validity_of_inverse!
       end
 
-      def check_validity_of_inverse!
-        unless polymorphic?
-          if has_inverse? && inverse_of.nil?
-            raise InverseOfAssociationNotFoundError.new(self)
-          end
-        end
-      end
-
       def check_preloadable!
         return unless scope
 
@@ -355,7 +492,7 @@ module ActiveRecord
       alias :check_eager_loadable! :check_preloadable!
 
       def join_id_for(owner) # :nodoc:
-        owner[active_record_primary_key]
+        owner[join_foreign_key]
       end
 
       def through_reflection
@@ -368,7 +505,7 @@ module ActiveRecord
 
       # A chain of reflections from this one back to the owner. For more see the explanation in
       # ThroughReflection.
-      def chain
+      def collect_join_chain
         [self]
       end
 
@@ -382,22 +519,14 @@ module ActiveRecord
         false
       end
 
-      # An array of arrays of scopes. Each item in the outside array corresponds to a reflection
-      # in the #chain.
-      def scope_chain
-        scope ? [[scope]] : [[]]
+      def has_scope?
+        scope
       end
 
       def has_inverse?
         inverse_name
       end
 
-      def inverse_of
-        return unless inverse_name
-
-        @inverse_of ||= klass._reflect_on_association inverse_name
-      end
-
       def polymorphic_inverse_of(associated_class)
         if has_inverse?
           if inverse_relationship = associated_class._reflect_on_association(options[:inverse_of])
@@ -439,73 +568,65 @@ module ActiveRecord
       # Returns +true+ if +self+ is a +has_one+ reflection.
       def has_one?; false; end
 
-      def association_class
-        case macro
-        when :belongs_to
-          if polymorphic?
-            Associations::BelongsToPolymorphicAssociation
-          else
-            Associations::BelongsToAssociation
-          end
-        when :has_many
-          if options[:through]
-            Associations::HasManyThroughAssociation
-          else
-            Associations::HasManyAssociation
-          end
-        when :has_one
-          if options[:through]
-            Associations::HasOneThroughAssociation
-          else
-            Associations::HasOneAssociation
-          end
-        end
-      end
+      def association_class; raise NotImplementedError; end
 
       def polymorphic?
         options[:polymorphic]
       end
 
       VALID_AUTOMATIC_INVERSE_MACROS = [:has_many, :has_one, :belongs_to]
-      INVALID_AUTOMATIC_INVERSE_OPTIONS = [:conditions, :through, :polymorphic, :foreign_key]
+      INVALID_AUTOMATIC_INVERSE_OPTIONS = [:through, :foreign_key]
 
-      protected
+      def add_as_source(seed)
+        seed
+      end
 
-        def actual_source_reflection # FIXME: this is a horrible name
-          self
-        end
+      def add_as_polymorphic_through(reflection, seed)
+        seed + [PolymorphicReflection.new(self, reflection)]
+      end
+
+      def add_as_through(seed)
+        seed + [self]
+      end
+
+      def extensions
+        Array(options[:extend])
+      end
 
       private
 
         def calculate_constructable(macro, options)
-          case macro
-          when :belongs_to
-            !polymorphic?
-          when :has_one
-            !options[:through]
-          else
-            true
-          end
+          true
         end
 
         # Attempts to find the inverse association name automatically.
         # If it cannot find a suitable inverse association name, it returns
-        # nil.
+        # +nil+.
         def inverse_name
-          options.fetch(:inverse_of) do
-            if @automatic_inverse_of == false
-              nil
-            else
-              @automatic_inverse_of ||= automatic_inverse_of
-            end
+          unless defined?(@inverse_name)
+            @inverse_name = options.fetch(:inverse_of) { automatic_inverse_of }
           end
+
+          @inverse_name
         end
 
-        # returns either nil or the inverse association name that it finds.
+        # returns either +nil+ or the inverse association name that it finds.
         def automatic_inverse_of
-          if can_find_inverse_of_automatically?(self)
-            inverse_name = ActiveSupport::Inflector.underscore(options[:as] || active_record.name.demodulize).to_sym
+          return unless can_find_inverse_of_automatically?(self)
+
+          inverse_name_candidates =
+            if options[:as]
+              [options[:as]]
+            else
+              active_record_name = active_record.name.demodulize
+              [active_record_name, ActiveSupport::Inflector.pluralize(active_record_name)]
+            end
 
+          inverse_name_candidates.map! do |candidate|
+            ActiveSupport::Inflector.underscore(candidate).to_sym
+          end
+
+          inverse_name_candidates.detect do |inverse_name|
             begin
               reflection = klass._reflect_on_association(inverse_name)
             rescue NameError
@@ -514,24 +635,17 @@ module ActiveRecord
               reflection = false
             end
 
-            if valid_inverse_reflection?(reflection)
-              return inverse_name
-            end
+            valid_inverse_reflection?(reflection)
           end
-
-          false
         end
 
         # Checks if the inverse reflection that is returned from the
         # +automatic_inverse_of+ method is a valid reflection. We must
         # make sure that the reflection's active_record name matches up
         # with the current reflection's klass name.
-        #
-        # Note: klass will always be valid because when there's a NameError
-        # from calling +klass+, +reflection+ will already be set to false.
         def valid_inverse_reflection?(reflection)
           reflection &&
-            klass.name == reflection.active_record.name &&
+            klass <= reflection.active_record &&
             can_find_inverse_of_automatically?(reflection)
         end
 
@@ -539,9 +653,8 @@ module ActiveRecord
         # us from being able to guess the inverse automatically. First, the
         # <tt>inverse_of</tt> option cannot be set to false. Second, we must
         # have <tt>has_many</tt>, <tt>has_one</tt>, <tt>belongs_to</tt> associations.
-        # Third, we must not have options such as <tt>:polymorphic</tt> or
-        # <tt>:foreign_key</tt> which prevent us from correctly guessing the
-        # inverse association.
+        # Third, we must not have options such as <tt>:foreign_key</tt>
+        # which prevent us from correctly guessing the inverse association.
         #
         # Anything with a scope can additionally ruin our attempt at finding an
         # inverse, so we exclude reflections with scopes.
@@ -571,56 +684,78 @@ module ActiveRecord
         def derive_join_table
           ModelSchema.derive_join_table_name active_record.table_name, klass.table_name
         end
-
-        def primary_key(klass)
-          klass.primary_key || raise(UnknownPrimaryKey.new(klass))
-        end
     end
 
     class HasManyReflection < AssociationReflection # :nodoc:
-      def initialize(name, scope, options, active_record)
-        super(name, scope, options, active_record)
-      end
-
       def macro; :has_many; end
 
       def collection?; true; end
-    end
 
-    class HasOneReflection < AssociationReflection # :nodoc:
-      def initialize(name, scope, options, active_record)
-        super(name, scope, options, active_record)
+      def association_class
+        if options[:through]
+          Associations::HasManyThroughAssociation
+        else
+          Associations::HasManyAssociation
+        end
       end
 
+      def association_primary_key(klass = nil)
+        primary_key(klass || self.klass)
+      end
+    end
+
+    class HasOneReflection < AssociationReflection # :nodoc:
       def macro; :has_one; end
 
       def has_one?; true; end
-    end
 
-    class BelongsToReflection < AssociationReflection # :nodoc:
-      def initialize(name, scope, options, active_record)
-        super(name, scope, options, active_record)
+      def association_class
+        if options[:through]
+          Associations::HasOneThroughAssociation
+        else
+          Associations::HasOneAssociation
+        end
       end
 
+      private
+
+        def calculate_constructable(macro, options)
+          !options[:through]
+        end
+    end
+
+    class BelongsToReflection < AssociationReflection # :nodoc:
       def macro; :belongs_to; end
 
       def belongs_to?; true; end
 
-      def join_keys(association_klass)
-        key = polymorphic? ? association_primary_key(association_klass) : association_primary_key
-        JoinKeys.new(key, foreign_key)
+      def association_class
+        if polymorphic?
+          Associations::BelongsToPolymorphicAssociation
+        else
+          Associations::BelongsToAssociation
+        end
       end
 
-      def join_id_for(owner) # :nodoc:
-        owner[foreign_key]
+      def join_primary_key(klass = nil)
+        polymorphic? ? association_primary_key(klass) : association_primary_key
       end
-    end
 
-    class HasAndBelongsToManyReflection < AssociationReflection # :nodoc:
-      def initialize(name, scope, options, active_record)
-        super
+      def join_foreign_key
+        foreign_key
       end
 
+      private
+        def can_find_inverse_of_automatically?(_)
+          !polymorphic? && super
+        end
+
+        def calculate_constructable(macro, options)
+          !polymorphic?
+        end
+    end
+
+    class HasAndBelongsToManyReflection < AssociationReflection # :nodoc:
       def macro; :has_and_belongs_to_many; end
 
       def collection?
@@ -628,19 +763,22 @@ module ActiveRecord
       end
     end
 
-    # Holds all the meta-data about a :through association as it was specified
+    # Holds all the metadata about a :through association as it was specified
     # in the Active Record class.
     class ThroughReflection < AbstractReflection #:nodoc:
-      attr_reader :delegate_reflection
-      delegate :foreign_key, :foreign_type, :association_foreign_key,
-               :active_record_primary_key, :type, :to => :source_reflection
+      delegate :foreign_key, :foreign_type, :association_foreign_key, :join_id_for,
+               :active_record_primary_key, :type, :get_join_keys, to: :source_reflection
 
       def initialize(delegate_reflection)
         @delegate_reflection = delegate_reflection
-        @klass         = delegate_reflection.options[:anonymous_class]
+        @klass = delegate_reflection.options[:anonymous_class]
         @source_reflection_name = delegate_reflection.options[:source]
       end
 
+      def through_reflection?
+        true
+      end
+
       def klass
         @klass ||= delegate_reflection.compute_class(class_name)
       end
@@ -699,78 +837,35 @@ module ActiveRecord
       #   # => [<ActiveRecord::Reflection::ThroughReflection: @delegate_reflection=#<ActiveRecord::Reflection::HasManyReflection: @name=:tags...>,
       #         <ActiveRecord::Reflection::HasManyReflection: @name=:taggings, @options={}, @active_record=Post>]
       #
-      def chain
-        @chain ||= begin
-          a = source_reflection.chain
-          b = through_reflection.chain.map(&:dup)
-
-          if options[:source_type]
-            b[0] = PolymorphicReflection.new(b[0], self)
-          end
-
-          chain = a + b
-          chain[0] = self # Use self so we don't lose the information from :source_type
-          chain
-        end
+      def collect_join_chain
+        collect_join_reflections [self]
       end
 
       # This is for clearing cache on the reflection. Useful for tests that need to compare
       # SQL queries on associations.
       def clear_association_scope_cache # :nodoc:
-        @chain = nil
         delegate_reflection.clear_association_scope_cache
         source_reflection.clear_association_scope_cache
         through_reflection.clear_association_scope_cache
       end
 
-      # Consider the following example:
-      #
-      #   class Person
-      #     has_many :articles
-      #     has_many :comment_tags, through: :articles
-      #   end
-      #
-      #   class Article
-      #     has_many :comments
-      #     has_many :comment_tags, through: :comments, source: :tags
-      #   end
-      #
-      #   class Comment
-      #     has_many :tags
-      #   end
-      #
-      # There may be scopes on Person.comment_tags, Article.comment_tags and/or Comment.tags,
-      # but only Comment.tags will be represented in the #chain. So this method creates an array
-      # of scopes corresponding to the chain.
-      def scope_chain
-        @scope_chain ||= begin
-          scope_chain = source_reflection.scope_chain.map(&:dup)
-
-          # Add to it the scope from this reflection (if any)
-          scope_chain.first << scope if scope
-
-          through_scope_chain = through_reflection.scope_chain.map(&:dup)
-
-          if options[:source_type]
-            type = foreign_type
-            source_type = options[:source_type]
-            through_scope_chain.first << lambda { |object|
-              where(type => source_type)
-            }
-          end
+      def scopes
+        source_reflection.scopes + super
+      end
 
-          # Recursively fill out the rest of the array from the through reflection
-          scope_chain + through_scope_chain
-        end
+      def join_scopes(table, predicate_builder) # :nodoc:
+        source_reflection.join_scopes(table, predicate_builder) + super
       end
 
-      def join_keys(association_klass)
-        source_reflection.join_keys(association_klass)
+      def has_scope?
+        scope || options[:source_type] ||
+          source_reflection.has_scope? ||
+          through_reflection.has_scope?
       end
 
       # A through association is nested if there would be more than one join table
       def nested?
-        chain.length > 2
+        source_reflection.through_reflection? || through_reflection.through_reflection?
       end
 
       # We want to use the klass from this reflection, rather than just delegate straight to
@@ -806,15 +901,13 @@ module ActiveRecord
         }
 
         if names.length > 1
-          example_options = options.dup
-          example_options[:source] = source_reflection_names.first
-          ActiveSupport::Deprecation.warn \
-            "Ambiguous source reflection for through association.  Please " \
-            "specify a :source directive on your declaration like:\n" \
-            "\n" \
-            "  class #{active_record.name} < ActiveRecord::Base\n" \
-            "    #{macro} :#{name}, #{example_options}\n" \
-            "  end"
+          raise AmbiguousSourceReflectionForThroughAssociation.new(
+            active_record.name,
+            macro,
+            name,
+            options,
+            source_reflection_names
+          )
         end
 
         @source_reflection_name = names.first
@@ -828,10 +921,6 @@ module ActiveRecord
         through_reflection.options
       end
 
-      def join_id_for(owner) # :nodoc:
-        source_reflection.join_id_for(owner)
-      end
-
       def check_validity!
         if through_reflection.nil?
           raise HasManyThroughAssociationNotFoundError.new(active_record.name, self)
@@ -861,6 +950,14 @@ module ActiveRecord
           raise HasOneThroughCantAssociateThroughCollection.new(active_record.name, self, through_reflection)
         end
 
+        if parent_reflection.nil?
+          reflections = active_record.reflections.keys.map(&:to_sym)
+
+          if reflections.index(through_reflection.name) > reflections.index(name)
+            raise HasManyThroughOrderError.new(active_record.name, self, through_reflection)
+          end
+        end
+
         check_validity_of_inverse!
       end
 
@@ -870,17 +967,37 @@ module ActiveRecord
         scope_chain
       end
 
-      protected
+      def add_as_source(seed)
+        collect_join_reflections seed
+      end
+
+      def add_as_polymorphic_through(reflection, seed)
+        collect_join_reflections(seed + [PolymorphicReflection.new(self, reflection)])
+      end
 
+      def add_as_through(seed)
+        collect_join_reflections(seed + [self])
+      end
+
+      protected
         def actual_source_reflection # FIXME: this is a horrible name
-          source_reflection.send(:actual_source_reflection)
+          source_reflection.actual_source_reflection
         end
 
-        def primary_key(klass)
-          klass.primary_key || raise(UnknownPrimaryKey.new(klass))
+      private
+        attr_reader :delegate_reflection
+
+        def collect_join_reflections(seed)
+          a = source_reflection.add_as_source seed
+          if options[:source_type]
+            through_reflection.add_as_polymorphic_through self, a
+          else
+            through_reflection.add_as_through a
+          end
         end
 
-      private
+        def inverse_name; delegate_reflection.send(:inverse_name); end
+
         def derive_class_name
           # get the class_name of the belongs_to association of the through reflection
           options[:source_type] || source_reflection.class_name
@@ -890,52 +1007,35 @@ module ActiveRecord
           public_instance_methods
 
         delegate(*delegate_methods, to: :delegate_reflection)
-
     end
 
-    class PolymorphicReflection < ThroughReflection # :nodoc:
+    class PolymorphicReflection < AbstractReflection # :nodoc:
+      delegate :klass, :scope, :plural_name, :type, :get_join_keys, :scope_for, to: :@reflection
+
       def initialize(reflection, previous_reflection)
         @reflection = reflection
         @previous_reflection = previous_reflection
       end
 
-      def klass
-        @reflection.klass
-      end
-
-      def scope
-        @reflection.scope
-      end
-
-      def table_name
-        @reflection.table_name
-      end
-
-      def plural_name
-        @reflection.plural_name
-      end
-
-      def join_keys(association_klass)
-        @reflection.join_keys(association_klass)
-      end
-
-      def type
-        @reflection.type
+      def join_scopes(table, predicate_builder) # :nodoc:
+        scopes = @previous_reflection.join_scopes(table, predicate_builder) + super
+        scopes << build_scope(table, predicate_builder).instance_exec(nil, &source_type_scope)
       end
 
       def constraints
-        [source_type_info]
+        @reflection.constraints + [source_type_scope]
       end
 
-      def source_type_info
-        type = @previous_reflection.foreign_type
-        source_type = @previous_reflection.options[:source_type]
-        lambda { |object| where(type => source_type) }
-      end
+      private
+        def source_type_scope
+          type = @previous_reflection.foreign_type
+          source_type = @previous_reflection.options[:source_type]
+          lambda { |object| where(type => source_type) }
+        end
     end
 
-    class RuntimeReflection < PolymorphicReflection # :nodoc:
-      attr_accessor :next
+    class RuntimeReflection < AbstractReflection # :nodoc:
+      delegate :scope, :type, :constraints, :get_join_keys, to: :@reflection
 
       def initialize(reflection, association)
         @reflection = reflection
@@ -946,24 +1046,8 @@ module ActiveRecord
         @association.klass
       end
 
-      def table_name
-        klass.table_name
-      end
-
-      def constraints
-        @reflection.constraints
-      end
-
-      def source_type_info
-        @reflection.source_type_info
-      end
-
-      def alias_candidate(name)
-        "#{plural_name}_#{name}_join"
-      end
-
-      def alias_name
-        Arel::Table.new(table_name)
+      def aliased_table
+        @aliased_table ||= Arel::Table.new(table_name, type_caster: klass.type_caster)
       end
 
       def all_includes; yield; end
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index e4df122af6..d5b6082d13 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -1,17 +1,17 @@
-# -*- coding: utf-8 -*-
-require "arel/collectors/bind"
+# frozen_string_literal: true
 
 module ActiveRecord
-  # = Active Record Relation
+  # = Active Record \Relation
   class Relation
     MULTI_VALUE_METHODS  = [:includes, :eager_load, :preload, :select, :group,
-                            :order, :joins, :references,
+                            :order, :joins, :left_outer_joins, :references,
                             :extending, :unscope]
 
     SINGLE_VALUE_METHODS = [:limit, :offset, :lock, :readonly, :reordering,
-                            :reverse_order, :distinct, :create_with]
+                            :reverse_order, :distinct, :create_with, :skip_query_cache]
+
     CLAUSE_METHODS = [:where, :having, :from]
-    INVALID_METHODS_FOR_DELETE_ALL = [:limit, :distinct, :offset, :group, :having]
+    INVALID_METHODS_FOR_DELETE_ALL = [:distinct, :group, :having]
 
     VALUE_METHODS = MULTI_VALUE_METHODS + SINGLE_VALUE_METHODS + CLAUSE_METHODS
 
@@ -19,97 +19,40 @@ module ActiveRecord
     include FinderMethods, Calculations, SpawnMethods, QueryMethods, Batches, Explain, Delegation
 
     attr_reader :table, :klass, :loaded, :predicate_builder
+    attr_accessor :skip_preloading_value
     alias :model :klass
     alias :loaded? :loaded
+    alias :locked? :lock_value
 
-    def initialize(klass, table, predicate_builder, values = {})
+    def initialize(klass, table: klass.arel_table, predicate_builder: klass.predicate_builder, values: {})
       @klass  = klass
       @table  = table
       @values = values
       @offsets = {}
       @loaded = false
       @predicate_builder = predicate_builder
+      @delegate_to_klass = false
     end
 
     def initialize_copy(other)
-      # This method is a hot spot, so for now, use Hash[] to dup the hash.
-      #   https://bugs.ruby-lang.org/issues/7166
-      @values        = Hash[@values]
+      @values = @values.dup
       reset
     end
 
-    def insert(values) # :nodoc:
-      primary_key_value = nil
-
-      if primary_key && Hash === values
-        primary_key_value = values[values.keys.find { |k|
-          k.name == primary_key
-        }]
-
-        if !primary_key_value && connection.prefetch_primary_key?(klass.table_name)
-          primary_key_value = connection.next_sequence_value(klass.sequence_name)
-          values[klass.arel_table[klass.primary_key]] = primary_key_value
-        end
-      end
-
-      im = arel.create_insert
-      im.into @table
-
-      substitutes, binds = substitute_values values
-
-      if values.empty? # empty insert
-        im.values = Arel.sql(connection.empty_insert_statement_value)
-      else
-        im.insert substitutes
-      end
-
-      @klass.connection.insert(
-        im,
-        'SQL',
-        primary_key,
-        primary_key_value,
-        nil,
-        binds)
-    end
-
-    def _update_record(values, id, id_was) # :nodoc:
-      substitutes, binds = substitute_values values
-
-      scope = @klass.unscoped
-
-      if @klass.finder_needs_type_condition?
-        scope.unscope!(where: @klass.inheritance_column)
-      end
-
-      relation = scope.where(@klass.primary_key => (id_was || id))
-      bvs = binds + relation.bound_attributes
-      um = relation
-        .arel
-        .compile_update(substitutes, @klass.primary_key)
-
-      @klass.connection.update(
-        um,
-        'SQL',
-        bvs,
-      )
+    def arel_attribute(name) # :nodoc:
+      klass.arel_attribute(name, table)
     end
 
-    def substitute_values(values) # :nodoc:
-      binds = values.map do |arel_attr, value|
-        QueryAttribute.new(arel_attr.name, value, klass.type_for_attribute(arel_attr.name))
-      end
-
-      substitutes = values.map do |(arel_attr, _)|
-        [arel_attr, connection.substitute_at(klass.columns_hash[arel_attr.name])]
-      end
-
-      [substitutes, binds]
+    def bind_attribute(name, value) # :nodoc:
+      attr = arel_attribute(name)
+      bind = predicate_builder.build_bind_attribute(attr.name, value)
+      yield attr, bind
     end
 
     # Initializes new record from relation while maintaining the current
     # scope.
     #
-    # Expects arguments in the same format as +Base.new+.
+    # Expects arguments in the same format as {ActiveRecord::Base.new}[rdoc-ref:Core.new].
     #
     #   users = User.where(name: 'DHH')
     #   user = users.new # => #<User id: nil, name: "DHH", created_at: nil, updated_at: nil>
@@ -118,8 +61,8 @@ module ActiveRecord
     #
     #   user = users.new { |user| user.name = 'Oscar' }
     #   user.name # => Oscar
-    def new(*args, &block)
-      scoping { @klass.new(*args, &block) }
+    def new(attributes = nil, &block)
+      scoping { klass.new(attributes, &block) }
     end
 
     alias build new
@@ -127,30 +70,34 @@ module ActiveRecord
     # Tries to create a new record with the same scoped attributes
     # defined in the relation. Returns the initialized object if validation fails.
     #
-    # Expects arguments in the same format as +Base.create+.
+    # Expects arguments in the same format as
+    # {ActiveRecord::Base.create}[rdoc-ref:Persistence::ClassMethods#create].
     #
     # ==== Examples
+    #
     #   users = User.where(name: 'Oscar')
-    #   users.create # #<User id: 3, name: "oscar", ...>
+    #   users.create # => #<User id: 3, name: "Oscar", ...>
     #
     #   users.create(name: 'fxn')
-    #   users.create # #<User id: 4, name: "fxn", ...>
+    #   users.create # => #<User id: 4, name: "fxn", ...>
     #
     #   users.create { |user| user.name = 'tenderlove' }
-    #   # #<User id: 5, name: "tenderlove", ...>
+    #   # => #<User id: 5, name: "tenderlove", ...>
     #
     #   users.create(name: nil) # validation on name
-    #   # #<User id: nil, name: nil, ...>
-    def create(*args, &block)
-      scoping { @klass.create(*args, &block) }
+    #   # => #<User id: nil, name: nil, ...>
+    def create(attributes = nil, &block)
+      scoping { klass.create(attributes, &block) }
     end
 
-    # Similar to #create, but calls +create!+ on the base class. Raises
-    # an exception if a validation error occurs.
+    # Similar to #create, but calls
+    # {create!}[rdoc-ref:Persistence::ClassMethods#create!]
+    # on the base class. Raises an exception if a validation error occurs.
     #
-    # Expects arguments in the same format as <tt>Base.create!</tt>.
-    def create!(*args, &block)
-      scoping { @klass.create!(*args, &block) }
+    # Expects arguments in the same format as
+    # {ActiveRecord::Base.create!}[rdoc-ref:Persistence::ClassMethods#create!].
+    def create!(attributes = nil, &block)
+      scoping { klass.create!(attributes, &block) }
     end
 
     def first_or_create(attributes = nil, &block) # :nodoc:
@@ -182,7 +129,7 @@ module ActiveRecord
     #   User.create_with(last_name: 'Johansson').find_or_create_by(first_name: 'Scarlett')
     #   # => #<User id: 2, first_name: "Scarlett", last_name: "Johansson">
     #
-    # This method accepts a block, which is passed down to +create+. The last example
+    # This method accepts a block, which is passed down to #create. The last example
     # above can be alternatively written this way:
     #
     #   # Find the first user named "Scarlett" or create a new one with a
@@ -194,36 +141,68 @@ module ActiveRecord
     #
     # This method always returns a record, but if creation was attempted and
     # failed due to validation errors it won't be persisted, you get what
-    # +create+ returns in such situation.
+    # #create returns in such situation.
     #
-    # Please note *this method is not atomic*, it runs first a SELECT, and if
+    # Please note <b>this method is not atomic</b>, it runs first a SELECT, and if
     # there are no results an INSERT is attempted. If there are other threads
     # or processes there is a race condition between both calls and it could
     # be the case that you end up with two similar records.
     #
-    # Whether that is a problem or not depends on the logic of the
-    # application, but in the particular case in which rows have a UNIQUE
-    # constraint an exception may be raised, just retry:
-    #
-    #  begin
-    #    CreditAccount.transaction(requires_new: true) do
-    #      CreditAccount.find_or_create_by(user_id: user.id)
-    #    end
-    #  rescue ActiveRecord::RecordNotUnique
-    #    retry
-    #  end
-    #
+    # If this might be a problem for your application, please see #create_or_find_by.
     def find_or_create_by(attributes, &block)
       find_by(attributes) || create(attributes, &block)
     end
 
-    # Like <tt>find_or_create_by</tt>, but calls <tt>create!</tt> so an exception
+    # Like #find_or_create_by, but calls
+    # {create!}[rdoc-ref:Persistence::ClassMethods#create!] so an exception
     # is raised if the created record is invalid.
     def find_or_create_by!(attributes, &block)
       find_by(attributes) || create!(attributes, &block)
     end
 
-    # Like <tt>find_or_create_by</tt>, but calls <tt>new</tt> instead of <tt>create</tt>.
+    # Attempts to create a record with the given attributes in a table that has a unique constraint
+    # on one or several of its columns. If a row already exists with one or several of these
+    # unique constraints, the exception such an insertion would normally raise is caught,
+    # and the existing record with those attributes is found using #find_by.
+    #
+    # This is similar to #find_or_create_by, but avoids the problem of stale reads between the SELECT
+    # and the INSERT, as that method needs to first query the table, then attempt to insert a row
+    # if none is found.
+    #
+    # There are several drawbacks to #create_or_find_by, though:
+    #
+    # * The underlying table must have the relevant columns defined with unique constraints.
+    # * A unique constraint violation may be triggered by only one, or at least less than all,
+    #   of the given attributes. This means that the subsequent #find_by may fail to find a
+    #   matching record, which will then raise an <tt>ActiveRecord::RecordNotFound</tt> exception,
+    #   rather than a record with the given attributes.
+    # * While we avoid the race condition between SELECT -> INSERT from #find_or_create_by,
+    #   we actually have another race condition between INSERT -> SELECT, which can be triggered
+    #   if a DELETE between those two statements is run by another client. But for most applications,
+    #   that's a significantly less likely condition to hit.
+    # * It relies on exception handling to handle control flow, which may be marginally slower.
+    #
+    # This method will return a record if all given attributes are covered by unique constraints
+    # (unless the INSERT -> DELETE -> SELECT race condition is triggered), but if creation was attempted
+    # and failed due to validation errors it won't be persisted, you get what #create returns in
+    # such situation.
+    def create_or_find_by(attributes, &block)
+      transaction(requires_new: true) { create(attributes, &block) }
+    rescue ActiveRecord::RecordNotUnique
+      find_by!(attributes)
+    end
+
+    # Like #create_or_find_by, but calls
+    # {create!}[rdoc-ref:Persistence::ClassMethods#create!] so an exception
+    # is raised if the created record is invalid.
+    def create_or_find_by!(attributes, &block)
+      transaction(requires_new: true) { create!(attributes, &block) }
+    rescue ActiveRecord::RecordNotUnique
+      find_by!(attributes)
+    end
+
+    # Like #find_or_create_by, but calls {new}[rdoc-ref:Core#new]
+    # instead of {create}[rdoc-ref:Persistence::ClassMethods#create].
     def find_or_initialize_by(attributes, &block)
       find_by(attributes) || new(attributes, &block)
     end
@@ -236,25 +215,25 @@ module ActiveRecord
     # are needed by the next ones when eager loading is going on.
     #
     # Please see further details in the
-    # {Active Record Query Interface guide}[http://guides.rubyonrails.org/active_record_querying.html#running-explain].
+    # {Active Record Query Interface guide}[https://guides.rubyonrails.org/active_record_querying.html#running-explain].
     def explain
-      #TODO: Fix for binds.
       exec_explain(collecting_queries_for_explain { exec_queries })
     end
 
     # Converts relation objects to Array.
-    def to_a
+    def to_ary
+      records.dup
+    end
+    alias to_a to_ary
+
+    def records # :nodoc:
       load
       @records
     end
 
     # Serializes the relation objects Array.
     def encode_with(coder)
-      coder.represent_seq(nil, to_a)
-    end
-
-    def as_json(options = nil) #:nodoc:
-      to_a.as_json(options)
+      coder.represent_seq(nil, records)
     end
 
     # Returns size of the records.
@@ -265,13 +244,7 @@ module ActiveRecord
     # Returns true if there are no records.
     def empty?
       return @records.empty? if loaded?
-
-      if limit_value == 0
-        true
-      else
-        c = count(:all)
-        c.respond_to?(:zero?) ? c.zero? : c.empty?
-      end
+      !exists?
     end
 
     # Returns true if there are no records.
@@ -289,13 +262,39 @@ module ActiveRecord
     # Returns true if there is exactly one record.
     def one?
       return super if block_given?
-      limit_value ? to_a.one? : size == 1
+      limit_value ? records.one? : size == 1
     end
 
     # Returns true if there is more than one record.
     def many?
       return super if block_given?
-      limit_value ? to_a.many? : size > 1
+      limit_value ? records.many? : size > 1
+    end
+
+    # Returns a cache key that can be used to identify the records fetched by
+    # this query. The cache key is built with a fingerprint of the sql query,
+    # the number of records matched by the query and a timestamp of the last
+    # updated record. When a new record comes to match the query, or any of
+    # the existing records is updated or deleted, the cache key changes.
+    #
+    #   Product.where("name like ?", "%Cosmic Encounter%").cache_key
+    #   # => "products/query-1850ab3d302391b85b8693e941286659-1-20150714212553907087000"
+    #
+    # If the collection is loaded, the method will iterate through the records
+    # to generate the timestamp, otherwise it will trigger one SQL query like:
+    #
+    #    SELECT COUNT(*), MAX("products"."updated_at") FROM "products" WHERE (name like '%Cosmic Encounter%')
+    #
+    # You can also pass a custom timestamp column to fetch the timestamp of the
+    # last updated record.
+    #
+    #   Product.where("name like ?", "%Game%").cache_key(:last_reviewed_at)
+    #
+    # You can customize the strategy to generate the key on a per model basis
+    # overriding ActiveRecord::Base#collection_cache_key.
+    def cache_key(timestamp_column = :updated_at)
+      @cache_keys ||= {}
+      @cache_keys[timestamp_column] ||= @klass.collection_cache_key(self, timestamp_column)
     end
 
     # Scope all queries to the current scope.
@@ -308,17 +307,20 @@ module ActiveRecord
     # Please check unscoped if you want to remove all previous scopes (including
     # the default_scope) during the execution of a block.
     def scoping
-      previous, klass.current_scope = klass.current_scope, self
-      yield
+      @delegate_to_klass ? yield : klass._scoping(self) { yield }
+    end
+
+    def _exec_scope(*args, &block) # :nodoc:
+      @delegate_to_klass = true
+      instance_exec(*args, &block) || self
     ensure
-      klass.current_scope = previous
+      @delegate_to_klass = false
     end
 
     # Updates all records in the current relation with details given. This method constructs a single SQL UPDATE
     # statement and sends it straight to the database. It does not instantiate the involved models and it does not
-    # trigger Active Record callbacks or validations. Values passed to `update_all` will not go through
-    # ActiveRecord's type-casting behavior. It should receive only values that can be passed as-is to the SQL
-    # database.
+    # trigger Active Record callbacks or validations. However, values passed to #update_all will still go through
+    # Active Record's normal type casting and serialization.
     #
     # ==== Parameters
     #
@@ -334,68 +336,99 @@ module ActiveRecord
     #
     #   # Update all books that match conditions, but limit it to 5 ordered by date
     #   Book.where('title LIKE ?', '%Rails%').order(:created_at).limit(5).update_all(author: 'David')
+    #
+    #   # Update all invoices and set the number column to its id value.
+    #   Invoice.update_all('number = id')
     def update_all(updates)
       raise ArgumentError, "Empty list of attributes to change" if updates.blank?
 
+      if eager_loading?
+        relation = apply_join_dependency
+        return relation.update_all(updates)
+      end
+
       stmt = Arel::UpdateManager.new
+      stmt.table(arel.join_sources.empty? ? table : arel.source)
+      stmt.key = arel_attribute(primary_key)
+      stmt.take(arel.limit)
+      stmt.offset(arel.offset)
+      stmt.order(*arel.orders)
+      stmt.wheres = arel.constraints
+
+      if updates.is_a?(Hash)
+        stmt.set _substitute_values(updates)
+      else
+        stmt.set Arel.sql(klass.sanitize_sql_for_assignment(updates, table.name))
+      end
 
-      stmt.set Arel.sql(@klass.send(:sanitize_sql_for_assignment, updates))
-      stmt.table(table)
-      stmt.key = table[primary_key]
+      @klass.connection.update stmt, "#{@klass} Update All"
+    end
 
-      if joins_values.any?
-        @klass.connection.join_to_update(stmt, arel)
+    def update(id = :all, attributes) # :nodoc:
+      if id == :all
+        each { |record| record.update(attributes) }
       else
-        stmt.take(arel.limit)
-        stmt.order(*arel.orders)
-        stmt.wheres = arel.constraints
+        klass.update(id, attributes)
+      end
+    end
+
+    def update_counters(counters) # :nodoc:
+      touch = counters.delete(:touch)
+
+      updates = {}
+      counters.each do |counter_name, value|
+        attr = arel_attribute(counter_name)
+        bind = predicate_builder.build_bind_attribute(attr.name, value.abs)
+        expr = table.coalesce(Arel::Nodes::UnqualifiedColumn.new(attr), 0)
+        expr = value < 0 ? expr - bind : expr + bind
+        updates[counter_name] = expr.expr
+      end
+
+      if touch
+        names = touch if touch != true
+        touch_updates = klass.touch_attributes_with_time(*names)
+        updates.merge!(touch_updates) unless touch_updates.empty?
       end
 
-      @klass.connection.update stmt, 'SQL', bound_attributes
+      update_all updates
     end
 
-    # Updates an object (or multiple objects) and saves it to the database, if validations pass.
-    # The resulting object is returned whether the object was saved successfully to the database or not.
+    # Touches all records in the current relation without instantiating records first with the updated_at/on attributes
+    # set to the current time or the time specified.
+    # This method can be passed attribute names and an optional time argument.
+    # If attribute names are passed, they are updated along with updated_at/on attributes.
+    # If no time argument is passed, the current time is used as default.
     #
-    # ==== Parameters
+    # === Examples
     #
-    # * +id+ - This should be the id or an array of ids to be updated.
-    # * +attributes+ - This should be a hash of attributes or an array of hashes.
+    #   # Touch all records
+    #   Person.all.touch_all
+    #   # => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670'"
     #
-    # ==== Examples
+    #   # Touch multiple records with a custom attribute
+    #   Person.all.touch_all(:created_at)
+    #   # => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670', \"created_at\" = '2018-01-04 22:55:23.132670'"
+    #
+    #   # Touch multiple records with a specified time
+    #   Person.all.touch_all(time: Time.new(2020, 5, 16, 0, 0, 0))
+    #   # => "UPDATE \"people\" SET \"updated_at\" = '2020-05-16 00:00:00'"
     #
-    #   # Updates one record
-    #   Person.update(15, user_name: 'Samuel', group: 'expert')
-    #
-    #   # Updates multiple records
-    #   people = { 1 => { "first_name" => "David" }, 2 => { "first_name" => "Jeremy" } }
-    #   Person.update(people.keys, people.values)
-    #
-    #   # Updates multiple records from the result of a relation
-    #   people = Person.where(group: 'expert')
-    #   people.update(group: 'masters')
-    #
-    #   Note: Updating a large number of records will run a
-    #   UPDATE query for each record, which may cause a performance
-    #   issue. So if it is not needed to run callbacks for each update, it is
-    #   preferred to use <tt>update_all</tt> for updating all records using
-    #   a single query.
-    def update(id = :all, attributes)
-      if id.is_a?(Array)
-        id.map.with_index { |one_id, idx| update(one_id, attributes[idx]) }
-      elsif id == :all
-        to_a.each { |record| record.update(attributes) }
+    #   # Touch records with scope
+    #   Person.where(name: 'David').touch_all
+    #   # => "UPDATE \"people\" SET \"updated_at\" = '2018-01-04 22:55:23.132670' WHERE \"people\".\"name\" = 'David'"
+    def touch_all(*names, time: nil)
+      if klass.locking_enabled?
+        names << { time: time }
+        update_counters(klass.locking_column => 1, touch: names)
       else
-        object = find(id)
-        object.update(attributes)
-        object
+        update_all klass.touch_attributes_with_time(*names, time: time)
       end
     end
 
-    # Destroys the records matching +conditions+ by instantiating each
-    # record and calling its +destroy+ method. Each object's callbacks are
-    # executed (including <tt>:dependent</tt> association options). Returns the
-    # collection of objects that were destroyed; each will be frozen, to
+    # Destroys the records by instantiating each
+    # record and calling its {#destroy}[rdoc-ref:Persistence#destroy] method.
+    # Each object's callbacks are executed (including <tt>:dependent</tt> association options).
+    # Returns the collection of objects that were destroyed; each will be frozen, to
     # reflect that no changes should be made (since they can't be persisted).
     #
     # Note: Instantiation, callback execution, and deletion of each
@@ -403,128 +436,59 @@ module ActiveRecord
     # once. It generates at least one SQL +DELETE+ query per record (or
     # possibly more, to enforce your callbacks). If you want to delete many
     # rows quickly, without concern for their associations or callbacks, use
-    # +delete_all+ instead.
-    #
-    # ==== Parameters
-    #
-    # * +conditions+ - A string, array, or hash that specifies which records
-    #   to destroy. If omitted, all records are destroyed. See the
-    #   Conditions section in the introduction to ActiveRecord::Base for
-    #   more information.
+    # #delete_all instead.
     #
     # ==== Examples
     #
-    #   Person.destroy_all("last_login < '2004-04-04'")
-    #   Person.destroy_all(status: "inactive")
     #   Person.where(age: 0..18).destroy_all
-    def destroy_all(conditions = nil)
-      if conditions
-        where(conditions).destroy_all
-      else
-        to_a.each(&:destroy).tap { reset }
-      end
-    end
-
-    # Destroy an object (or multiple objects) that has the given id. The object is instantiated first,
-    # therefore all callbacks and filters are fired off before the object is deleted. This method is
-    # less efficient than ActiveRecord#delete but allows cleanup methods and other actions to be run.
-    #
-    # This essentially finds the object (or multiple objects) with the given id, creates a new object
-    # from the attributes, and then calls destroy on it.
-    #
-    # ==== Parameters
-    #
-    # * +id+ - Can be either an Integer or an Array of Integers.
-    #
-    # ==== Examples
-    #
-    #   # Destroy a single object
-    #   Todo.destroy(1)
-    #
-    #   # Destroy multiple objects
-    #   todos = [1,2,3]
-    #   Todo.destroy(todos)
-    def destroy(id)
-      if id.is_a?(Array)
-        id.map { |one_id| destroy(one_id) }
-      else
-        find(id).destroy
-      end
+    def destroy_all
+      records.each(&:destroy).tap { reset }
     end
 
-    # Deletes the records matching +conditions+ without instantiating the records
-    # first, and hence not calling the +destroy+ method nor invoking callbacks. This
-    # is a single SQL DELETE statement that goes straight to the database, much more
-    # efficient than +destroy_all+. Be careful with relations though, in particular
+    # Deletes the records without instantiating the records
+    # first, and hence not calling the {#destroy}[rdoc-ref:Persistence#destroy]
+    # method nor invoking callbacks.
+    # This is a single SQL DELETE statement that goes straight to the database, much more
+    # efficient than #destroy_all. Be careful with relations though, in particular
     # <tt>:dependent</tt> rules defined on associations are not honored. Returns the
     # number of rows affected.
     #
-    #   Post.delete_all("person_id = 5 AND (category = 'Something' OR category = 'Else')")
-    #   Post.delete_all(["person_id = ? AND (category = ? OR category = ?)", 5, 'Something', 'Else'])
     #   Post.where(person_id: 5).where(category: ['Something', 'Else']).delete_all
     #
     # Both calls delete the affected posts all at once with a single DELETE statement.
     # If you need to destroy dependent associations or call your <tt>before_*</tt> or
-    # +after_destroy+ callbacks, use the +destroy_all+ method instead.
-    #
-    # If an invalid method is supplied, +delete_all+ raises an ActiveRecord error:
-    #
-    #   Post.limit(100).delete_all
-    #   # => ActiveRecord::ActiveRecordError: delete_all doesn't support limit
-    def delete_all(conditions = nil)
-      invalid_methods = INVALID_METHODS_FOR_DELETE_ALL.select { |method|
-        if MULTI_VALUE_METHODS.include?(method)
-          send("#{method}_values").any?
-        elsif SINGLE_VALUE_METHODS.include?(method)
-          send("#{method}_value")
-        elsif CLAUSE_METHODS.include?(method)
-          send("#{method}_clause").any?
-        end
-      }
+    # +after_destroy+ callbacks, use the #destroy_all method instead.
+    #
+    # If an invalid method is supplied, #delete_all raises an ActiveRecordError:
+    #
+    #   Post.distinct.delete_all
+    #   # => ActiveRecord::ActiveRecordError: delete_all doesn't support distinct
+    def delete_all
+      invalid_methods = INVALID_METHODS_FOR_DELETE_ALL.select do |method|
+        value = get_value(method)
+        SINGLE_VALUE_METHODS.include?(method) ? value : value.any?
+      end
       if invalid_methods.any?
         raise ActiveRecordError.new("delete_all doesn't support #{invalid_methods.join(', ')}")
       end
 
-      if conditions
-        where(conditions).delete_all
-      else
-        stmt = Arel::DeleteManager.new
-        stmt.from(table)
-
-        if joins_values.any?
-          @klass.connection.join_to_delete(stmt, arel, table[primary_key])
-        else
-          stmt.wheres = arel.constraints
-        end
+      if eager_loading?
+        relation = apply_join_dependency
+        return relation.delete_all
+      end
 
-        affected = @klass.connection.delete(stmt, 'SQL', bound_attributes)
+      stmt = Arel::DeleteManager.new
+      stmt.from(arel.join_sources.empty? ? table : arel.source)
+      stmt.key = arel_attribute(primary_key)
+      stmt.take(arel.limit)
+      stmt.offset(arel.offset)
+      stmt.order(*arel.orders)
+      stmt.wheres = arel.constraints
 
-        reset
-        affected
-      end
-    end
+      affected = @klass.connection.delete(stmt, "#{@klass} Destroy")
 
-    # Deletes the row with a primary key matching the +id+ argument, using a
-    # SQL +DELETE+ statement, and returns the number of rows deleted. Active
-    # Record objects are not instantiated, so the object's callbacks are not
-    # executed, including any <tt>:dependent</tt> association options.
-    #
-    # You can delete multiple rows at once by passing an Array of <tt>id</tt>s.
-    #
-    # Note: Although it is often much faster than the alternative,
-    # <tt>#destroy</tt>, skipping callbacks might bypass business logic in
-    # your application that ensures referential integrity or performs other
-    # essential jobs.
-    #
-    # ==== Examples
-    #
-    #   # Delete a single row
-    #   Todo.delete(1)
-    #
-    #   # Delete multiple rows
-    #   Todo.delete([2,3,4])
-    def delete(id_or_array)
-      where(primary_key => id_or_array).delete_all
+      reset
+      affected
     end
 
     # Causes the records to be loaded from the database if they have not
@@ -533,8 +497,8 @@ module ActiveRecord
     # return value is the relation itself, not the records.
     #
     #   Post.where(published: true).load # => #<ActiveRecord::Relation>
-    def load
-      exec_queries unless loaded?
+    def load(&block)
+      exec_queries(&block) unless loaded?
 
       self
     end
@@ -546,9 +510,9 @@ module ActiveRecord
     end
 
     def reset
-      @last = @to_sql = @order_clause = @scope_for_create = @arel = @loaded = nil
-      @should_eager_load = @join_dependency = nil
-      @records = []
+      @delegate_to_klass = false
+      @to_sql = @arel = @loaded = @should_eager_load = nil
+      @records = [].freeze
       @offsets = {}
       self
     end
@@ -559,32 +523,28 @@ module ActiveRecord
     #   # => SELECT "users".* FROM "users"  WHERE "users"."name" = 'Oscar'
     def to_sql
       @to_sql ||= begin
-                    relation   = self
-                    connection = klass.connection
-                    visitor    = connection.visitor
-
-                    if eager_loading?
-                      find_with_associations { |rel| relation = rel }
-                    end
-
-                    binds = relation.bound_attributes
-                    binds = connection.prepare_binds_for_database(binds)
-                    binds.map! { |value| connection.quote(value) }
-                    collect = visitor.accept(relation.arel.ast, Arel::Collectors::Bind.new)
-                    collect.substitute_binds(binds).join
-                  end
+        if eager_loading?
+          apply_join_dependency do |relation, join_dependency|
+            relation = join_dependency.apply_column_aliases(relation)
+            relation.to_sql
+          end
+        else
+          conn = klass.connection
+          conn.unprepared_statement { conn.to_sql(arel) }
+        end
+      end
     end
 
     # Returns a hash of where conditions.
     #
     #   User.where(name: 'Oscar').where_values_hash
     #   # => {name: "Oscar"}
-    def where_values_hash(relation_table_name = table_name)
+    def where_values_hash(relation_table_name = klass.table_name)
       where_clause.to_h(relation_table_name)
     end
 
     def scope_for_create
-      @scope_for_create ||= where_values_hash.merge(create_with_value)
+      where_values_hash.merge!(create_with_value.stringify_keys)
     end
 
     # Returns true if relation needs eager loading.
@@ -602,89 +562,144 @@ module ActiveRecord
       includes_values & joins_values
     end
 
-    # +uniq+ and +uniq!+ are silently deprecated. +uniq_value+ delegates to +distinct_value+
-    # to maintain backwards compatibility. Use +distinct_value+ instead.
-    def uniq_value
-      distinct_value
-    end
-    deprecate uniq_value: :distinct_value
-
     # Compares two relations for equality.
     def ==(other)
       case other
       when Associations::CollectionProxy, AssociationRelation
-        self == other.to_a
+        self == other.records
       when Relation
         other.to_sql == to_sql
       when Array
-        to_a == other
+        records == other
       end
     end
 
     def pretty_print(q)
-      q.pp(self.to_a)
+      q.pp(records)
     end
 
     # Returns true if relation is blank.
     def blank?
-      to_a.blank?
+      records.blank?
     end
 
     def values
-      Hash[@values]
+      @values.dup
     end
 
     def inspect
-      entries = to_a.take([limit_value, 11].compact.min).map!(&:inspect)
-      entries[10] = '...' if entries.size == 11
+      subject = loaded? ? records : self
+      entries = subject.take([limit_value, 11].compact.min).map!(&:inspect)
+
+      entries[10] = "..." if entries.size == 11
 
       "#<#{self.class.name} [#{entries.join(', ')}]>"
     end
 
-    private
+    def empty_scope? # :nodoc:
+      @values == klass.unscoped.values
+    end
+
+    def has_limit_or_offset? # :nodoc:
+      limit_value || offset_value
+    end
 
-    def exec_queries
-      @records = eager_loading? ? find_with_associations : @klass.find_by_sql(arel, bound_attributes)
+    def alias_tracker(joins = [], aliases = nil) # :nodoc:
+      joins += [aliases] if aliases
+      ActiveRecord::Associations::AliasTracker.create(connection, table.name, joins)
+    end
 
+    def preload_associations(records) # :nodoc:
       preload = preload_values
-      preload +=  includes_values unless eager_loading?
-      preloader = build_preloader
+      preload += includes_values unless eager_loading?
+      preloader = nil
       preload.each do |associations|
-        preloader.preload @records, associations
+        preloader ||= build_preloader
+        preloader.preload records, associations
       end
+    end
 
-      @records.each(&:readonly!) if readonly_value
+    protected
 
-      @loaded = true
-      @records
-    end
+      def load_records(records)
+        @records = records.freeze
+        @loaded = true
+      end
 
-    def build_preloader
-      ActiveRecord::Associations::Preloader.new
-    end
+    private
+      def _substitute_values(values)
+        values.map do |name, value|
+          attr = arel_attribute(name)
+          unless Arel.arel_node?(value)
+            type = klass.type_for_attribute(attr.name)
+            value = predicate_builder.build_bind_attribute(attr.name, type.cast(value))
+          end
+          [attr, value]
+        end
+      end
 
-    def references_eager_loaded_tables?
-      joined_tables = arel.join_sources.map do |join|
-        if join.is_a?(Arel::Nodes::StringJoin)
-          tables_in_string(join.left)
+      def exec_queries(&block)
+        skip_query_cache_if_necessary do
+          @records =
+            if eager_loading?
+              apply_join_dependency do |relation, join_dependency|
+                if ActiveRecord::NullRelation === relation
+                  []
+                else
+                  relation = join_dependency.apply_column_aliases(relation)
+                  rows = connection.select_all(relation.arel, "SQL")
+                  join_dependency.instantiate(rows, &block)
+                end.freeze
+              end
+            else
+              klass.find_by_sql(arel, &block).freeze
+            end
+
+          preload_associations(@records) unless skip_preloading_value
+
+          @records.each(&:readonly!) if readonly_value
+
+          @loaded = true
+          @records
+        end
+      end
+
+      def skip_query_cache_if_necessary
+        if skip_query_cache_value
+          uncached do
+            yield
+          end
         else
-          [join.left.table_name, join.left.table_alias]
+          yield
         end
       end
 
-      joined_tables += [table.name, table.table_alias]
+      def build_preloader
+        ActiveRecord::Associations::Preloader.new
+      end
 
-      # always convert table names to downcase as in Oracle quoted table names are in uppercase
-      joined_tables = joined_tables.flatten.compact.map(&:downcase).uniq
+      def references_eager_loaded_tables?
+        joined_tables = arel.join_sources.map do |join|
+          if join.is_a?(Arel::Nodes::StringJoin)
+            tables_in_string(join.left)
+          else
+            [join.left.table_name, join.left.table_alias]
+          end
+        end
 
-      (references_values - joined_tables).any?
-    end
+        joined_tables += [table.name, table.table_alias]
 
-    def tables_in_string(string)
-      return [] if string.blank?
-      # always convert table names to downcase as in Oracle quoted table names are in uppercase
-      # ignore raw_sql_ that is used by Oracle adapter as alias for limit/offset subqueries
-      string.scan(/([a-zA-Z_][.\w]+).?\./).flatten.map(&:downcase).uniq - ['raw_sql_']
-    end
+        # always convert table names to downcase as in Oracle quoted table names are in uppercase
+        joined_tables = joined_tables.flatten.compact.map(&:downcase).uniq
+
+        (references_values - joined_tables).any?
+      end
+
+      def tables_in_string(string)
+        return [] if string.blank?
+        # always convert table names to downcase as in Oracle quoted table names are in uppercase
+        # ignore raw_sql_ that is used by Oracle adapter as alias for limit/offset subqueries
+        string.scan(/([a-zA-Z_][.\w]+).?\./).flatten.map(&:downcase).uniq - ["raw_sql_"]
+      end
   end
 end
diff --git a/activerecord/lib/active_record/relation/batches.rb b/activerecord/lib/active_record/relation/batches.rb
index e07580a563..9c579843b1 100644
--- a/activerecord/lib/active_record/relation/batches.rb
+++ b/activerecord/lib/active_record/relation/batches.rb
@@ -1,8 +1,14 @@
+# frozen_string_literal: true
+
+require "active_record/relation/batches/batch_enumerator"
+
 module ActiveRecord
   module Batches
+    ORDER_IGNORE_MESSAGE = "Scoped order is ignored, it's forced to be batch order."
+
     # Looping through a collection of records from the database
-    # (using the +all+ method, for example) is very inefficient
-    # since it will try to instantiate all the objects at once.
+    # (using the Scoping::Named::ClassMethods.all method, for example)
+    # is very inefficient since it will try to instantiate all the objects at once.
     #
     # In that case, batch processing methods allow you to work
     # with the records in batches, thereby greatly reducing memory consumption.
@@ -26,16 +32,28 @@ module ActiveRecord
     #   end
     #
     # ==== Options
-    # * <tt>:batch_size</tt> - Specifies the size of the batch. Default to 1000.
-    # * <tt>:begin_at</tt> - Specifies the primary key value to start from, inclusive of the value.
-    # * <tt>:end_at</tt> - Specifies the primary key value to end at, inclusive of the value.
-    # This is especially useful if you want multiple workers dealing with
-    # the same processing queue. You can make worker 1 handle all the records
-    # between id 0 and 10,000 and worker 2 handle from 10,000 and beyond
-    # (by setting the +:begin_at+ and +:end_at+ option on each worker).
-    #
-    #   # Let's process for a batch of 2000 records, skipping the first 2000 rows
-    #   Person.find_each(begin_at: 2000, batch_size: 2000) do |person|
+    # * <tt>:batch_size</tt> - Specifies the size of the batch. Defaults to 1000.
+    # * <tt>:start</tt> - Specifies the primary key value to start from, inclusive of the value.
+    # * <tt>:finish</tt> - Specifies the primary key value to end at, inclusive of the value.
+    # * <tt>:error_on_ignore</tt> - Overrides the application config to specify if an error should be raised when
+    #   an order is present in the relation.
+    #
+    # Limits are honored, and if present there is no requirement for the batch
+    # size: it can be less than, equal to, or greater than the limit.
+    #
+    # The options +start+ and +finish+ are especially useful if you want
+    # multiple workers dealing with the same processing queue. You can make
+    # worker 1 handle all the records between id 1 and 9999 and worker 2
+    # handle from 10000 and beyond by setting the +:start+ and +:finish+
+    # option on each worker.
+    #
+    #   # In worker 1, let's process until 9999 records.
+    #   Person.find_each(finish: 9_999) do |person|
+    #     person.party_all_night!
+    #   end
+    #
+    #   # In worker 2, let's process from record 10_000 and onwards.
+    #   Person.find_each(start: 10_000) do |person|
     #     person.party_all_night!
     #   end
     #
@@ -44,24 +62,17 @@ module ActiveRecord
     # work. This also means that this method only works when the primary key is
     # orderable (e.g. an integer or string).
     #
-    # NOTE: You can't set the limit either, that's used to control
-    # the batch sizes.
-    def find_each(begin_at: nil, end_at: nil, batch_size: 1000, start: nil)
-      if start
-        begin_at = start
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-            Passing `start` value to find_each is deprecated, and will be removed in Rails 5.1.
-            Please pass `begin_at` instead.
-        MSG
-      end
+    # NOTE: By its nature, batch processing is subject to race conditions if
+    # other processes are modifying the database.
+    def find_each(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil)
       if block_given?
-        find_in_batches(begin_at: begin_at, end_at: end_at, batch_size: batch_size) do |records|
+        find_in_batches(start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore) do |records|
           records.each { |record| yield record }
         end
       else
-        enum_for(:find_each, begin_at: begin_at, end_at: end_at, batch_size: batch_size) do
+        enum_for(:find_each, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore) do
           relation = self
-          apply_limits(relation, begin_at, end_at).size
+          apply_limits(relation, start, finish).size
         end
       end
     end
@@ -85,16 +96,23 @@ module ActiveRecord
     # To be yielded each record one by one, use #find_each instead.
     #
     # ==== Options
-    # * <tt>:batch_size</tt> - Specifies the size of the batch. Default to 1000.
-    # * <tt>:begin_at</tt> - Specifies the primary key value to start from, inclusive of the value.
-    # * <tt>:end_at</tt> - Specifies the primary key value to end at, inclusive of the value.
-    # This is especially useful if you want multiple workers dealing with
-    # the same processing queue. You can make worker 1 handle all the records
-    # between id 0 and 10,000 and worker 2 handle from 10,000 and beyond
-    # (by setting the +:begin_at+ and +:end_at+ option on each worker).
-    #
-    #   # Let's process the next 2000 records
-    #   Person.find_in_batches(begin_at: 2000, batch_size: 2000) do |group|
+    # * <tt>:batch_size</tt> - Specifies the size of the batch. Defaults to 1000.
+    # * <tt>:start</tt> - Specifies the primary key value to start from, inclusive of the value.
+    # * <tt>:finish</tt> - Specifies the primary key value to end at, inclusive of the value.
+    # * <tt>:error_on_ignore</tt> - Overrides the application config to specify if an error should be raised when
+    #   an order is present in the relation.
+    #
+    # Limits are honored, and if present there is no requirement for the batch
+    # size: it can be less than, equal to, or greater than the limit.
+    #
+    # The options +start+ and +finish+ are especially useful if you want
+    # multiple workers dealing with the same processing queue. You can make
+    # worker 1 handle all the records between id 1 and 9999 and worker 2
+    # handle from 10000 and beyond by setting the +:start+ and +:finish+
+    # option on each worker.
+    #
+    #   # Let's process from record 10_000 on.
+    #   Person.find_in_batches(start: 10_000) do |group|
     #     group.each { |person| person.party_all_night! }
     #   end
     #
@@ -103,56 +121,170 @@ module ActiveRecord
     # work. This also means that this method only works when the primary key is
     # orderable (e.g. an integer or string).
     #
-    # NOTE: You can't set the limit either, that's used to control
-    # the batch sizes.
-    def find_in_batches(begin_at: nil, end_at: nil, batch_size: 1000, start: nil)
-      if start
-        begin_at = start
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-            Passing `start` value to find_in_batches is deprecated, and will be removed in Rails 5.1.
-            Please pass `begin_at` instead.
-        MSG
-      end
-
+    # NOTE: By its nature, batch processing is subject to race conditions if
+    # other processes are modifying the database.
+    def find_in_batches(start: nil, finish: nil, batch_size: 1000, error_on_ignore: nil)
       relation = self
       unless block_given?
-        return to_enum(:find_in_batches, begin_at: begin_at, end_at: end_at, batch_size: batch_size) do
-          total = apply_limits(relation, begin_at, end_at).size
+        return to_enum(:find_in_batches, start: start, finish: finish, batch_size: batch_size, error_on_ignore: error_on_ignore) do
+          total = apply_limits(relation, start, finish).size
           (total - 1).div(batch_size) + 1
         end
       end
 
-      if logger && (arel.orders.present? || arel.taken.present?)
-        logger.warn("Scoped order and limit are ignored, it's forced to be batch order and batch size")
+      in_batches(of: batch_size, start: start, finish: finish, load: true, error_on_ignore: error_on_ignore) do |batch|
+        yield batch.to_a
       end
+    end
 
-      relation = relation.reorder(batch_order).limit(batch_size)
-      relation = apply_limits(relation, begin_at, end_at)
-      records = relation.to_a
+    # Yields ActiveRecord::Relation objects to work with a batch of records.
+    #
+    #   Person.where("age > 21").in_batches do |relation|
+    #     relation.delete_all
+    #     sleep(10) # Throttle the delete queries
+    #   end
+    #
+    # If you do not provide a block to #in_batches, it will return a
+    # BatchEnumerator which is enumerable.
+    #
+    #   Person.in_batches.each_with_index do |relation, batch_index|
+    #     puts "Processing relation ##{batch_index}"
+    #     relation.delete_all
+    #   end
+    #
+    # Examples of calling methods on the returned BatchEnumerator object:
+    #
+    #   Person.in_batches.delete_all
+    #   Person.in_batches.update_all(awesome: true)
+    #   Person.in_batches.each_record(&:party_all_night!)
+    #
+    # ==== Options
+    # * <tt>:of</tt> - Specifies the size of the batch. Defaults to 1000.
+    # * <tt>:load</tt> - Specifies if the relation should be loaded. Defaults to false.
+    # * <tt>:start</tt> - Specifies the primary key value to start from, inclusive of the value.
+    # * <tt>:finish</tt> - Specifies the primary key value to end at, inclusive of the value.
+    # * <tt>:error_on_ignore</tt> - Overrides the application config to specify if an error should be raised when
+    #   an order is present in the relation.
+    #
+    # Limits are honored, and if present there is no requirement for the batch
+    # size, it can be less than, equal, or greater than the limit.
+    #
+    # The options +start+ and +finish+ are especially useful if you want
+    # multiple workers dealing with the same processing queue. You can make
+    # worker 1 handle all the records between id 1 and 9999 and worker 2
+    # handle from 10000 and beyond by setting the +:start+ and +:finish+
+    # option on each worker.
+    #
+    #   # Let's process from record 10_000 on.
+    #   Person.in_batches(start: 10_000).update_all(awesome: true)
+    #
+    # An example of calling where query method on the relation:
+    #
+    #   Person.in_batches.each do |relation|
+    #     relation.update_all('age = age + 1')
+    #     relation.where('age > 21').update_all(should_party: true)
+    #     relation.where('age <= 21').delete_all
+    #   end
+    #
+    # NOTE: If you are going to iterate through each record, you should call
+    # #each_record on the yielded BatchEnumerator:
+    #
+    #   Person.in_batches.each_record(&:party_all_night!)
+    #
+    # NOTE: It's not possible to set the order. That is automatically set to
+    # ascending on the primary key ("id ASC") to make the batch ordering
+    # consistent. Therefore the primary key must be orderable, e.g. an integer
+    # or a string.
+    #
+    # NOTE: By its nature, batch processing is subject to race conditions if
+    # other processes are modifying the database.
+    def in_batches(of: 1000, start: nil, finish: nil, load: false, error_on_ignore: nil)
+      relation = self
+      unless block_given?
+        return BatchEnumerator.new(of: of, start: start, finish: finish, relation: self)
+      end
+
+      if arel.orders.present?
+        act_on_ignored_order(error_on_ignore)
+      end
+
+      batch_limit = of
+      if limit_value
+        remaining   = limit_value
+        batch_limit = remaining if remaining < batch_limit
+      end
+
+      relation = relation.reorder(batch_order).limit(batch_limit)
+      relation = apply_limits(relation, start, finish)
+      relation.skip_query_cache! # Retaining the results in the query cache would undermine the point of batching
+      batch_relation = relation
+
+      loop do
+        if load
+          records = batch_relation.records
+          ids = records.map(&:id)
+          yielded_relation = where(primary_key => ids)
+          yielded_relation.load_records(records)
+        else
+          ids = batch_relation.pluck(primary_key)
+          yielded_relation = where(primary_key => ids)
+        end
+
+        break if ids.empty?
 
-      while records.any?
-        records_size = records.size
-        primary_key_offset = records.last.id
-        raise "Primary key not included in the custom select clause" unless primary_key_offset
+        primary_key_offset = ids.last
+        raise ArgumentError.new("Primary key not included in the custom select clause") unless primary_key_offset
 
-        yield records
+        yield yielded_relation
 
-        break if records_size < batch_size
+        break if ids.length < batch_limit
 
-        records = relation.where(table[primary_key].gt(primary_key_offset)).to_a
+        if limit_value
+          remaining -= ids.length
+
+          if remaining == 0
+            # Saves a useless iteration when the limit is a multiple of the
+            # batch size.
+            break
+          elsif remaining < batch_limit
+            relation = relation.limit(remaining)
+          end
+        end
+
+        batch_relation = relation.where(
+          bind_attribute(primary_key, primary_key_offset) { |attr, bind| attr.gt(bind) }
+        )
       end
     end
 
     private
 
-    def apply_limits(relation, begin_at, end_at)
-      relation = relation.where(table[primary_key].gteq(begin_at)) if begin_at
-      relation = relation.where(table[primary_key].lteq(end_at)) if end_at
-      relation
-    end
+      def apply_limits(relation, start, finish)
+        relation = apply_start_limit(relation, start) if start
+        relation = apply_finish_limit(relation, finish) if finish
+        relation
+      end
 
-    def batch_order
-      "#{quoted_table_name}.#{quoted_primary_key} ASC"
-    end
+      def apply_start_limit(relation, start)
+        relation.where(bind_attribute(primary_key, start) { |attr, bind| attr.gteq(bind) })
+      end
+
+      def apply_finish_limit(relation, finish)
+        relation.where(bind_attribute(primary_key, finish) { |attr, bind| attr.lteq(bind) })
+      end
+
+      def batch_order
+        arel_attribute(primary_key).asc
+      end
+
+      def act_on_ignored_order(error_on_ignore)
+        raise_error = (error_on_ignore.nil? ? klass.error_on_ignored_order : error_on_ignore)
+
+        if raise_error
+          raise ArgumentError.new(ORDER_IGNORE_MESSAGE)
+        elsif logger
+          logger.warn(ORDER_IGNORE_MESSAGE)
+        end
+      end
   end
 end
diff --git a/activerecord/lib/active_record/relation/batches/batch_enumerator.rb b/activerecord/lib/active_record/relation/batches/batch_enumerator.rb
new file mode 100644
index 0000000000..49697da3bf
--- /dev/null
+++ b/activerecord/lib/active_record/relation/batches/batch_enumerator.rb
@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module Batches
+    class BatchEnumerator
+      include Enumerable
+
+      def initialize(of: 1000, start: nil, finish: nil, relation:) #:nodoc:
+        @of       = of
+        @relation = relation
+        @start = start
+        @finish = finish
+      end
+
+      # Looping through a collection of records from the database (using the
+      # +all+ method, for example) is very inefficient since it will try to
+      # instantiate all the objects at once.
+      #
+      # In that case, batch processing methods allow you to work with the
+      # records in batches, thereby greatly reducing memory consumption.
+      #
+      #   Person.in_batches.each_record do |person|
+      #     person.do_awesome_stuff
+      #   end
+      #
+      #   Person.where("age > 21").in_batches(of: 10).each_record do |person|
+      #     person.party_all_night!
+      #   end
+      #
+      # If you do not provide a block to #each_record, it will return an Enumerator
+      # for chaining with other methods:
+      #
+      #   Person.in_batches.each_record.with_index do |person, index|
+      #     person.award_trophy(index + 1)
+      #   end
+      def each_record
+        return to_enum(:each_record) unless block_given?
+
+        @relation.to_enum(:in_batches, of: @of, start: @start, finish: @finish, load: true).each do |relation|
+          relation.records.each { |record| yield record }
+        end
+      end
+
+      # Delegates #delete_all, #update_all, #destroy_all methods to each batch.
+      #
+      #   People.in_batches.delete_all
+      #   People.where('age < 10').in_batches.destroy_all
+      #   People.in_batches.update_all('age = age + 1')
+      [:delete_all, :update_all, :destroy_all].each do |method|
+        define_method(method) do |*args, &block|
+          @relation.to_enum(:in_batches, of: @of, start: @start, finish: @finish, load: false).each do |relation|
+            relation.send(method, *args, &block)
+          end
+        end
+      end
+
+      # Yields an ActiveRecord::Relation object for each batch of records.
+      #
+      #   Person.in_batches.each do |relation|
+      #     relation.update_all(awesome: true)
+      #   end
+      def each
+        enum = @relation.to_enum(:in_batches, of: @of, start: @start, finish: @finish, load: false)
+        return enum.each { |relation| yield relation } if block_given?
+        enum
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index 0f6015fa93..0fa5ba2e50 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Calculations
     # Count the records.
@@ -14,33 +16,44 @@ module ActiveRecord
     #   Person.distinct.count(:age)
     #   # => counts the number of different age values
     #
-    # If +count+ is used with +group+, it returns a Hash whose keys represent the aggregated column,
+    # If #count is used with {Relation#group}[rdoc-ref:QueryMethods#group],
+    # it returns a Hash whose keys represent the aggregated column,
     # and the values are the respective amounts:
     #
     #   Person.group(:city).count
     #   # => { 'Rome' => 5, 'Paris' => 3 }
     #
-    # If +count+ is used with +group+ for multiple columns, it returns a Hash whose
+    # If #count is used with {Relation#group}[rdoc-ref:QueryMethods#group] for multiple columns, it returns a Hash whose
     # keys are an array containing the individual values of each column and the value
-    # of each key would be the +count+.
+    # of each key would be the #count.
     #
     #   Article.group(:status, :category).count
     #   # =>  {["draft", "business"]=>10, ["draft", "technology"]=>4,
     #          ["published", "business"]=>0, ["published", "technology"]=>2}
     #
-    # If +count+ is used with +select+, it will count the selected columns:
+    # If #count is used with {Relation#select}[rdoc-ref:QueryMethods#select], it will count the selected columns:
     #
     #   Person.select(:age).count
     #   # => counts the number of different age values
     #
-    # Note: not all valid +select+ expressions are valid +count+ expressions. The specifics differ
+    # Note: not all valid {Relation#select}[rdoc-ref:QueryMethods#select] expressions are valid #count expressions. The specifics differ
     # between databases. In invalid cases, an error from the database is thrown.
     def count(column_name = nil)
+      if block_given?
+        unless column_name.nil?
+          ActiveSupport::Deprecation.warn \
+            "When `count' is called with a block, it ignores other arguments. " \
+            "This behavior is now deprecated and will result in an ArgumentError in Rails 6.0."
+        end
+
+        return super()
+      end
+
       calculate(:count, column_name)
     end
 
     # Calculates the average value on a given column. Returns +nil+ if there's
-    # no row. See +calculate+ for examples with options.
+    # no row. See #calculate for examples with options.
     #
     #   Person.average(:age) # => 35.8
     def average(column_name)
@@ -49,7 +62,7 @@ module ActiveRecord
 
     # Calculates the minimum value on a given column. The value is returned
     # with the same data type of the column, or +nil+ if there's no row. See
-    # +calculate+ for examples with options.
+    # #calculate for examples with options.
     #
     #   Person.minimum(:age) # => 7
     def minimum(column_name)
@@ -58,7 +71,7 @@ module ActiveRecord
 
     # Calculates the maximum value on a given column. The value is returned
     # with the same data type of the column, or +nil+ if there's no row. See
-    # +calculate+ for examples with options.
+    # #calculate for examples with options.
     #
     #   Person.maximum(:age) # => 93
     def maximum(column_name)
@@ -66,59 +79,74 @@ module ActiveRecord
     end
 
     # Calculates the sum of values on a given column. The value is returned
-    # with the same data type of the column, 0 if there's no row. See
-    # +calculate+ for examples with options.
+    # with the same data type of the column, +0+ if there's no row. See
+    # #calculate for examples with options.
     #
     #   Person.sum(:age) # => 4562
-    def sum(*args)
-      return super if block_given?
-      calculate(:sum, *args)
+    def sum(column_name = nil)
+      if block_given?
+        unless column_name.nil?
+          ActiveSupport::Deprecation.warn \
+            "When `sum' is called with a block, it ignores other arguments. " \
+            "This behavior is now deprecated and will result in an ArgumentError in Rails 6.0."
+        end
+
+        return super()
+      end
+
+      calculate(:sum, column_name)
     end
 
-    # This calculates aggregate values in the given column. Methods for count, sum, average,
-    # minimum, and maximum have been added as shortcuts.
+    # This calculates aggregate values in the given column. Methods for #count, #sum, #average,
+    # #minimum, and #maximum have been added as shortcuts.
     #
-    # There are two basic forms of output:
+    #   Person.calculate(:count, :all) # The same as Person.count
+    #   Person.average(:age) # SELECT AVG(age) FROM people...
     #
-    #   * Single aggregate value: The single value is type cast to Fixnum for COUNT, Float
-    #     for AVG, and the given column's type for everything else.
+    #   # Selects the minimum age for any family without any minors
+    #   Person.group(:last_name).having("min(age) > 17").minimum(:age)
     #
-    #   * Grouped values: This returns an ordered hash of the values and groups them. It
-    #     takes either a column name, or the name of a belongs_to association.
+    #   Person.sum("2 * age")
     #
-    #       values = Person.group('last_name').maximum(:age)
-    #       puts values["Drake"]
-    #       # => 43
+    # There are two basic forms of output:
     #
-    #       drake  = Family.find_by(last_name: 'Drake')
-    #       values = Person.group(:family).maximum(:age) # Person belongs_to :family
-    #       puts values[drake]
-    #       # => 43
+    # * Single aggregate value: The single value is type cast to Integer for COUNT, Float
+    #   for AVG, and the given column's type for everything else.
     #
-    #       values.each do |family, max_age|
-    #       ...
-    #       end
+    # * Grouped values: This returns an ordered hash of the values and groups them. It
+    #   takes either a column name, or the name of a belongs_to association.
     #
-    #   Person.calculate(:count, :all) # The same as Person.count
-    #   Person.average(:age) # SELECT AVG(age) FROM people...
+    #      values = Person.group('last_name').maximum(:age)
+    #      puts values["Drake"]
+    #      # => 43
     #
-    #   # Selects the minimum age for any family without any minors
-    #   Person.group(:last_name).having("min(age) > 17").minimum(:age)
+    #      drake  = Family.find_by(last_name: 'Drake')
+    #      values = Person.group(:family).maximum(:age) # Person belongs_to :family
+    #      puts values[drake]
+    #      # => 43
     #
-    #   Person.sum("2 * age")
+    #      values.each do |family, max_age|
+    #        ...
+    #      end
     def calculate(operation, column_name)
-      if column_name.is_a?(Symbol) && attribute_alias?(column_name)
-        column_name = attribute_alias(column_name)
-      end
-
       if has_include?(column_name)
-        construct_relation_for_association_calculations.calculate(operation, column_name)
+        relation = apply_join_dependency
+
+        if operation.to_s.downcase == "count"
+          relation.distinct!
+          # PostgreSQL: ORDER BY expressions must appear in SELECT list when using DISTINCT
+          if (column_name == :all || column_name.nil?) && select_values.empty?
+            relation.order_values = []
+          end
+        end
+
+        relation.calculate(operation, column_name)
       else
         perform_calculation(operation, column_name)
       end
     end
 
-    # Use <tt>pluck</tt> as a shortcut to select one or more attributes without
+    # Use #pluck as a shortcut to select one or more attributes without
     # loading a bunch of records just to grab the attributes you want.
     #
     #   Person.pluck(:name)
@@ -127,7 +155,7 @@ module ActiveRecord
     #
     #   Person.all.map(&:name)
     #
-    # Pluck returns an <tt>Array</tt> of attribute values type-casted to match
+    # Pluck returns an Array of attribute values type-casted to match
     # the plucked column names, if they can be deduced. Plucking an SQL fragment
     # returns String values by default.
     #
@@ -151,33 +179,45 @@ module ActiveRecord
     #   # SELECT DATEDIFF(updated_at, created_at) FROM people
     #   # => ['0', '27761', '173']
     #
-    # See also +ids+.
+    # See also #ids.
     #
     def pluck(*column_names)
-      column_names.map! do |column_name|
-        if column_name.is_a?(Symbol) && attribute_alias?(column_name)
-          attribute_alias(column_name)
-        else
-          column_name.to_s
-        end
-      end
-
-      if loaded? && (column_names - @klass.column_names).empty?
-        return @records.pluck(*column_names)
+      if loaded? && (column_names.map(&:to_s) - @klass.attribute_names - @klass.attribute_aliases.keys).empty?
+        return records.pluck(*column_names)
       end
 
       if has_include?(column_names.first)
-        construct_relation_for_association_calculations.pluck(*column_names)
+        relation = apply_join_dependency
+        relation.pluck(*column_names)
       else
+        disallow_raw_sql!(column_names)
         relation = spawn
         relation.select_values = column_names.map { |cn|
-          columns_hash.key?(cn) ? arel_table[cn] : cn
+          @klass.has_attribute?(cn) || @klass.attribute_alias?(cn) ? arel_attribute(cn) : cn
         }
-        result = klass.connection.select_all(relation.arel, nil, bound_attributes)
+        result = skip_query_cache_if_necessary { klass.connection.select_all(relation.arel, nil) }
         result.cast_values(klass.attribute_types)
       end
     end
 
+    # Pick the value(s) from the named column(s) in the current relation.
+    # This is short-hand for <tt>relation.limit(1).pluck(*column_names).first</tt>, and is primarily useful
+    # when you have a relation that's already narrowed down to a single row.
+    #
+    # Just like #pluck, #pick will only load the actual value, not the entire record object, so it's also
+    # more efficient. The value is, again like with pluck, typecast by the column type.
+    #
+    #   Person.where(id: 1).pick(:name)
+    #   # SELECT people.name FROM people WHERE id = 1 LIMIT 1
+    #   # => 'David'
+    #
+    #   Person.where(id: 1).pick(:name, :email_address)
+    #   # SELECT people.name, people.email_address FROM people WHERE id = 1 LIMIT 1
+    #   # => [ 'David', 'david@loudthinking.com' ]
+    def pick(*column_names)
+      limit(1).pluck(*column_names).first
+    end
+
     # Pluck all the ID's for the relation using the table's primary key
     #
     #   Person.ids # SELECT people.id FROM people
@@ -188,205 +228,205 @@ module ActiveRecord
 
     private
 
-    def has_include?(column_name)
-      eager_loading? || (includes_values.present? && column_name && column_name != :all)
-    end
+      def has_include?(column_name)
+        eager_loading? || (includes_values.present? && column_name && column_name != :all)
+      end
 
-    def perform_calculation(operation, column_name)
-      operation = operation.to_s.downcase
+      def perform_calculation(operation, column_name)
+        operation = operation.to_s.downcase
+
+        # If #count is used with #distinct (i.e. `relation.distinct.count`) it is
+        # considered distinct.
+        distinct = distinct_value
+
+        if operation == "count"
+          column_name ||= select_for_count
+          if column_name == :all
+            if distinct && (group_values.any? || select_values.empty? && order_values.empty?)
+              column_name = primary_key
+            end
+          elsif /\s*DISTINCT[\s(]+/i.match?(column_name.to_s)
+            distinct = nil
+          end
+        end
 
-      # If #count is used with #distinct (i.e. `relation.distinct.count`) it is
-      # considered distinct.
-      distinct = self.distinct_value
+        if group_values.any?
+          execute_grouped_calculation(operation, column_name, distinct)
+        else
+          execute_simple_calculation(operation, column_name, distinct)
+        end
+      end
 
-      if operation == "count"
-        column_name ||= select_for_count
+      def aggregate_column(column_name)
+        return column_name if Arel::Expressions === column_name
 
-        unless arel.ast.grep(Arel::Nodes::OuterJoin).empty?
-          distinct = true
+        if @klass.has_attribute?(column_name) || @klass.attribute_alias?(column_name)
+          @klass.arel_attribute(column_name)
+        else
+          Arel.sql(column_name == :all ? "*" : column_name.to_s)
         end
-
-        column_name = primary_key if column_name == :all && distinct
-        distinct = nil if column_name =~ /\s*DISTINCT[\s(]+/i
       end
 
-      if group_values.any?
-        execute_grouped_calculation(operation, column_name, distinct)
-      else
-        execute_simple_calculation(operation, column_name, distinct)
+      def operation_over_aggregate_column(column, operation, distinct)
+        operation == "count" ? column.count(distinct) : column.send(operation)
       end
-    end
 
-    def aggregate_column(column_name)
-      if @klass.column_names.include?(column_name.to_s)
-        Arel::Attribute.new(@klass.unscoped.table, column_name)
-      else
-        Arel.sql(column_name == :all ? "*" : column_name.to_s)
-      end
-    end
+      def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
+        column_alias = column_name
 
-    def operation_over_aggregate_column(column, operation, distinct)
-      operation == 'count' ? column.count(distinct) : column.send(operation)
-    end
+        if operation == "count" && (column_name == :all && distinct || has_limit_or_offset?)
+          # Shortcut when limit is zero.
+          return 0 if limit_value == 0
 
-    def execute_simple_calculation(operation, column_name, distinct) #:nodoc:
-      # PostgreSQL doesn't like ORDER BY when there are no GROUP BY
-      relation = unscope(:order)
+          query_builder = build_count_subquery(spawn, column_name, distinct)
+        else
+          # PostgreSQL doesn't like ORDER BY when there are no GROUP BY
+          relation = unscope(:order).distinct!(false)
 
-      column_alias = column_name
+          column = aggregate_column(column_name)
 
-      if operation == "count" && (relation.limit_value || relation.offset_value)
-        # Shortcut when limit is zero.
-        return 0 if relation.limit_value == 0
+          select_value = operation_over_aggregate_column(column, operation, distinct)
+          if operation == "sum" && distinct
+            select_value.distinct = true
+          end
 
-        query_builder = build_count_subquery(relation, column_name, distinct)
-      else
-        column = aggregate_column(column_name)
+          column_alias = select_value.alias
+          column_alias ||= @klass.connection.column_name_for_operation(operation, select_value)
+          relation.select_values = [select_value]
 
-        select_value = operation_over_aggregate_column(column, operation, distinct)
+          query_builder = relation.arel
+        end
 
-        column_alias = select_value.alias
-        column_alias ||= @klass.connection.column_name_for_operation(operation, select_value)
-        relation.select_values = [select_value]
+        result = skip_query_cache_if_necessary { @klass.connection.select_all(query_builder, nil) }
+        row    = result.first
+        value  = row && row.values.first
+        type   = result.column_types.fetch(column_alias) do
+          type_for(column_name)
+        end
 
-        query_builder = relation.arel
+        type_cast_calculated_value(value, type, operation)
       end
 
-      result = @klass.connection.select_all(query_builder, nil, bound_attributes)
-      row    = result.first
-      value  = row && row.values.first
-      column = result.column_types.fetch(column_alias) do
-        type_for(column_name)
-      end
+      def execute_grouped_calculation(operation, column_name, distinct) #:nodoc:
+        group_attrs = group_values
 
-      type_cast_calculated_value(value, column, operation)
-    end
+        if group_attrs.first.respond_to?(:to_sym)
+          association  = @klass._reflect_on_association(group_attrs.first)
+          associated   = group_attrs.size == 1 && association && association.belongs_to? # only count belongs_to associations
+          group_fields = Array(associated ? association.foreign_key : group_attrs)
+        else
+          group_fields = group_attrs
+        end
+        group_fields = arel_columns(group_fields)
 
-    def execute_grouped_calculation(operation, column_name, distinct) #:nodoc:
-      group_attrs = group_values
+        group_aliases = group_fields.map { |field| column_alias_for(field) }
+        group_columns = group_aliases.zip(group_fields)
 
-      if group_attrs.first.respond_to?(:to_sym)
-        association  = @klass._reflect_on_association(group_attrs.first)
-        associated   = group_attrs.size == 1 && association && association.belongs_to? # only count belongs_to associations
-        group_fields = Array(associated ? association.foreign_key : group_attrs)
-      else
-        group_fields = group_attrs
-      end
+        if operation == "count" && column_name == :all
+          aggregate_alias = "count_all"
+        else
+          aggregate_alias = column_alias_for([operation, column_name].join(" "))
+        end
 
-      group_aliases = group_fields.map { |field|
-        column_alias_for(field)
-      }
-      group_columns = group_aliases.zip(group_fields).map { |aliaz,field|
-        [aliaz, field]
-      }
+        select_values = [
+          operation_over_aggregate_column(
+            aggregate_column(column_name),
+            operation,
+            distinct).as(aggregate_alias)
+        ]
+        select_values += self.select_values unless having_clause.empty?
+
+        select_values.concat group_columns.map { |aliaz, field|
+          if field.respond_to?(:as)
+            field.as(aliaz)
+          else
+            "#{field} AS #{aliaz}"
+          end
+        }
 
-      group = group_fields
+        relation = except(:group).distinct!(false)
+        relation.group_values  = group_fields
+        relation.select_values = select_values
 
-      if operation == 'count' && column_name == :all
-        aggregate_alias = 'count_all'
-      else
-        aggregate_alias = column_alias_for([operation, column_name].join(' '))
-      end
+        calculated_data = skip_query_cache_if_necessary { @klass.connection.select_all(relation.arel, nil) }
 
-      select_values = [
-        operation_over_aggregate_column(
-          aggregate_column(column_name),
-          operation,
-          distinct).as(aggregate_alias)
-      ]
-      select_values += select_values unless having_clause.empty?
-
-      select_values.concat group_fields.zip(group_aliases).map { |field,aliaz|
-        if field.respond_to?(:as)
-          field.as(aliaz)
-        else
-          "#{field} AS #{aliaz}"
+        if association
+          key_ids     = calculated_data.collect { |row| row[group_aliases.first] }
+          key_records = association.klass.base_class.where(association.klass.base_class.primary_key => key_ids)
+          key_records = Hash[key_records.map { |r| [r.id, r] }]
         end
-      }
-
-      relation = except(:group)
-      relation.group_values  = group
-      relation.select_values = select_values
-
-      calculated_data = @klass.connection.select_all(relation, nil, relation.bound_attributes)
 
-      if association
-        key_ids     = calculated_data.collect { |row| row[group_aliases.first] }
-        key_records = association.klass.base_class.where(association.klass.base_class.primary_key => key_ids)
-        key_records = Hash[key_records.map { |r| [r.id, r] }]
+        Hash[calculated_data.map do |row|
+          key = group_columns.map { |aliaz, col_name|
+            type = type_for(col_name) do
+              calculated_data.column_types.fetch(aliaz, Type.default_value)
+            end
+            type_cast_calculated_value(row[aliaz], type)
+          }
+          key = key.first if key.size == 1
+          key = key_records[key] if associated
+
+          type = calculated_data.column_types.fetch(aggregate_alias) { type_for(column_name) }
+          [key, type_cast_calculated_value(row[aggregate_alias], type, operation)]
+        end]
       end
 
-      Hash[calculated_data.map do |row|
-        key = group_columns.map { |aliaz, col_name|
-          column = calculated_data.column_types.fetch(aliaz) do
-            type_for(col_name)
-          end
-          type_cast_calculated_value(row[aliaz], column)
-        }
-        key = key.first if key.size == 1
-        key = key_records[key] if associated
+      # Converts the given keys to the value that the database adapter returns as
+      # a usable column name:
+      #
+      #   column_alias_for("users.id")                 # => "users_id"
+      #   column_alias_for("sum(id)")                  # => "sum_id"
+      #   column_alias_for("count(distinct users.id)") # => "count_distinct_users_id"
+      #   column_alias_for("count(*)")                 # => "count_all"
+      def column_alias_for(keys)
+        if keys.respond_to? :name
+          keys = "#{keys.relation.name}.#{keys.name}"
+        end
 
-        column_type = calculated_data.column_types.fetch(aggregate_alias) { type_for(column_name) }
-        [key, type_cast_calculated_value(row[aggregate_alias], column_type, operation)]
-      end]
-    end
+        table_name = keys.to_s.downcase
+        table_name.gsub!(/\*/, "all")
+        table_name.gsub!(/\W+/, " ")
+        table_name.strip!
+        table_name.gsub!(/ +/, "_")
 
-    # Converts the given keys to the value that the database adapter returns as
-    # a usable column name:
-    #
-    #   column_alias_for("users.id")                 # => "users_id"
-    #   column_alias_for("sum(id)")                  # => "sum_id"
-    #   column_alias_for("count(distinct users.id)") # => "count_distinct_users_id"
-    #   column_alias_for("count(*)")                 # => "count_all"
-    #   column_alias_for("count", "id")              # => "count_id"
-    def column_alias_for(keys)
-      if keys.respond_to? :name
-        keys = "#{keys.relation.name}.#{keys.name}"
+        @klass.connection.table_alias_for(table_name)
       end
 
-      table_name = keys.to_s.downcase
-      table_name.gsub!(/\*/, 'all')
-      table_name.gsub!(/\W+/, ' ')
-      table_name.strip!
-      table_name.gsub!(/ +/, '_')
-
-      @klass.connection.table_alias_for(table_name)
-    end
-
-    def type_for(field)
-      field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split('.').last
-      @klass.type_for_attribute(field_name)
-    end
+      def type_for(field, &block)
+        field_name = field.respond_to?(:name) ? field.name.to_s : field.to_s.split(".").last
+        @klass.type_for_attribute(field_name, &block)
+      end
 
-    def type_cast_calculated_value(value, type, operation = nil)
-      case operation
-        when 'count'   then value.to_i
-        when 'sum'     then type.deserialize(value || 0)
-        when 'average' then value.respond_to?(:to_d) ? value.to_d : value
+      def type_cast_calculated_value(value, type, operation = nil)
+        case operation
+        when "count"   then value.to_i
+        when "sum"     then type.deserialize(value || 0)
+        when "average" then value.respond_to?(:to_d) ? value.to_d : value
         else type.deserialize(value)
+        end
       end
-    end
 
-    # TODO: refactor to allow non-string `select_values` (eg. Arel nodes).
-    def select_for_count
-      if select_values.present?
-        select_values.join(", ")
-      else
-        :all
+      def select_for_count
+        if select_values.present?
+          return select_values.first if select_values.one?
+          select_values.join(", ")
+        else
+          :all
+        end
       end
-    end
 
-    def build_count_subquery(relation, column_name, distinct)
-      column_alias = Arel.sql('count_column')
-      subquery_alias = Arel.sql('subquery_for_count')
+      def build_count_subquery(relation, column_name, distinct)
+        if column_name == :all
+          relation.select_values = [ Arel.sql(FinderMethods::ONE_AS_ONE) ] unless distinct
+        else
+          column_alias = Arel.sql("count_column")
+          relation.select_values = [ aggregate_column(column_name).as(column_alias) ]
+        end
 
-      aliased_column = aggregate_column(column_name == :all ? 1 : column_name).as(column_alias)
-      relation.select_values = [aliased_column]
-      subquery = relation.arel.as(subquery_alias)
+        subquery = relation.arel.as(Arel.sql("subquery_for_count"))
+        select_value = operation_over_aggregate_column(column_alias || Arel.star, "count", false)
 
-      sm = Arel::SelectManager.new relation.engine
-      select_value = operation_over_aggregate_column(column_alias, 'count', distinct)
-      sm.project(select_value).from(subquery)
-    end
+        Arel::SelectManager.new(subquery).project(select_value)
+      end
   end
 end
diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index 86f2c30168..383dc1bf4b 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -1,14 +1,13 @@
-require 'set'
-require 'active_support/concern'
+# frozen_string_literal: true
 
 module ActiveRecord
   module Delegation # :nodoc:
-    module DelegateCache
-      def relation_delegate_class(klass) # :nodoc:
+    module DelegateCache # :nodoc:
+      def relation_delegate_class(klass)
         @relation_delegate_cache[klass]
       end
 
-      def initialize_relation_delegate_cache # :nodoc:
+      def initialize_relation_delegate_cache
         @relation_delegate_cache = cache = {}
         [
           ActiveRecord::Relation,
@@ -18,7 +17,11 @@ module ActiveRecord
           delegate = Class.new(klass) {
             include ClassSpecificRelation
           }
-          const_set klass.name.gsub('::', '_'), delegate
+          include_relation_methods(delegate)
+          mangled_name = klass.name.gsub("::", "_")
+          const_set mangled_name, delegate
+          private_constant mangled_name
+
           cache[klass] = delegate
         end
       end
@@ -27,6 +30,35 @@ module ActiveRecord
         child_class.initialize_relation_delegate_cache
         super
       end
+
+      protected
+        def include_relation_methods(delegate)
+          superclass.include_relation_methods(delegate) unless base_class?
+          delegate.include generated_relation_methods
+        end
+
+      private
+        def generated_relation_methods
+          @generated_relation_methods ||= Module.new.tap do |mod|
+            mod_name = "GeneratedRelationMethods"
+            const_set mod_name, mod
+            private_constant mod_name
+          end
+        end
+
+        def generate_relation_method(method)
+          if /\A[a-zA-Z_]\w*[!?]?\z/.match?(method)
+            generated_relation_methods.module_eval <<-RUBY, __FILE__, __LINE__ + 1
+              def #{method}(*args, &block)
+                scoping { klass.#{method}(*args, &block) }
+              end
+            RUBY
+          else
+            generated_relation_methods.send(:define_method, method) do |*args, &block|
+              scoping { klass.public_send(method, *args, &block) }
+            end
+          end
+        end
     end
 
     extend ActiveSupport::Concern
@@ -36,16 +68,12 @@ module ActiveRecord
     # may vary depending on the klass of a relation, so we create a subclass of Relation
     # for each different klass, and the delegations are compiled into that subclass only.
 
-    BLACKLISTED_ARRAY_METHODS = [
-      :compact!, :flatten!, :reject!, :reverse!, :rotate!, :map!,
-      :shuffle!, :slice!, :sort!, :sort_by!, :delete_if,
-      :keep_if, :pop, :shift, :delete_at, :select!
-    ].to_set # :nodoc:
+    delegate :to_xml, :encode_with, :length, :each, :join,
+             :[], :&, :|, :+, :-, :sample, :reverse, :rotate, :compact, :in_groups, :in_groups_of,
+             :to_sentence, :to_formatted_s, :as_json,
+             :shuffle, :split, :slice, :index, :rindex, to: :records
 
-    delegate :to_xml, :to_yaml, :length, :collect, :map, :each, :all?, :include?, :to_ary, :join, to: :to_a
-
-    delegate :table_name, :quoted_table_name, :primary_key, :quoted_primary_key,
-             :connection, :columns_hash, :to => :klass
+    delegate :primary_key, :connection, to: :klass
 
     module ClassSpecificRelation # :nodoc:
       extend ActiveSupport::Concern
@@ -63,7 +91,7 @@ module ActiveRecord
           @delegation_mutex.synchronize do
             return if method_defined?(method)
 
-            if method.to_s =~ /\A[a-zA-Z_]\w*[!?]?\z/
+            if /\A[a-zA-Z_]\w*[!?]?\z/.match?(method)
               module_eval <<-RUBY, __FILE__, __LINE__ + 1
                 def #{method}(*args, &block)
                   scoping { @klass.#{method}(*args, &block) }
@@ -76,28 +104,27 @@ module ActiveRecord
             end
           end
         end
-
-        def delegate(method, opts = {})
-          @delegation_mutex.synchronize do
-            return if method_defined?(method)
-            super
-          end
-        end
       end
 
-      protected
+      private
 
-      def method_missing(method, *args, &block)
-        if @klass.respond_to?(method)
-          self.class.delegate_to_scoped_klass(method)
-          scoping { @klass.public_send(method, *args, &block) }
-        elsif arel.respond_to?(method)
-          self.class.delegate method, :to => :arel
-          arel.public_send(method, *args, &block)
-        else
-          super
+        def method_missing(method, *args, &block)
+          if @klass.respond_to?(method)
+            self.class.delegate_to_scoped_klass(method)
+            scoping { @klass.public_send(method, *args, &block) }
+          elsif @delegate_to_klass && @klass.respond_to?(method, true)
+            ActiveSupport::Deprecation.warn \
+              "Delegating missing #{method} method to #{@klass}. " \
+              "Accessibility of private/protected class methods in :scope is deprecated and will be removed in Rails 6.0."
+            @klass.send(method, *args, &block)
+          elsif arel.respond_to?(method)
+            ActiveSupport::Deprecation.warn \
+              "Delegating #{method} to arel is deprecated and will be removed in Rails 6.0."
+            arel.public_send(method, *args, &block)
+          else
+            super
+          end
         end
-      end
     end
 
     module ClassMethods # :nodoc:
@@ -107,33 +134,14 @@ module ActiveRecord
 
       private
 
-      def relation_class_for(klass)
-        klass.relation_delegate_class(self)
-      end
-    end
-
-    def respond_to?(method, include_private = false)
-      super || @klass.respond_to?(method, include_private) ||
-        array_delegable?(method) ||
-        arel.respond_to?(method, include_private)
-    end
-
-    protected
-
-    def array_delegable?(method)
-      Array.method_defined?(method) && BLACKLISTED_ARRAY_METHODS.exclude?(method)
+        def relation_class_for(klass)
+          klass.relation_delegate_class(self)
+        end
     end
 
-    def method_missing(method, *args, &block)
-      if @klass.respond_to?(method)
-        scoping { @klass.public_send(method, *args, &block) }
-      elsif array_delegable?(method)
-        to_a.public_send(method, *args, &block)
-      elsif arel.respond_to?(method)
-        arel.public_send(method, *args, &block)
-      else
-        super
+    private
+      def respond_to_missing?(method, _)
+        super || @klass.respond_to?(method) || arel.respond_to?(method)
       end
-    end
   end
 end
diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 9fef55adea..afaa900442 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -1,8 +1,10 @@
-require 'active_support/core_ext/string/filters'
+# frozen_string_literal: true
+
+require "active_support/core_ext/string/filters"
 
 module ActiveRecord
   module FinderMethods
-    ONE_AS_ONE = '1 AS one'
+    ONE_AS_ONE = "1 AS one"
 
     # Find by id - This can either be a specific id (1), a list of ids (1, 5, 6), or an array of ids ([5, 6, 10]).
     # If one or more records can not be found for the requested ids, then RecordNotFound will be raised. If the primary key
@@ -16,9 +18,10 @@ module ActiveRecord
     #   Person.find([1])        # returns an array for the object with ID = 1
     #   Person.where("administrator = 1").order("created_on DESC").find(1)
     #
-    # NOTE: The returned records may not be in the same order as the ids you
-    # provide since database rows are unordered. You'd need to provide an explicit <tt>order</tt>
-    # option if you want the results are sorted.
+    # NOTE: The returned records are in the same order as the ids you provide.
+    # If you want the results to be sorted by database, you can use ActiveRecord::QueryMethods#where
+    # method and provide an explicit ActiveRecord::QueryMethods#order option.
+    # But ActiveRecord::QueryMethods#where method doesn't raise ActiveRecord::RecordNotFound.
     #
     # ==== Find with lock
     #
@@ -34,7 +37,7 @@ module ActiveRecord
     #     person.save!
     #   end
     #
-    # ==== Variations of +find+
+    # ==== Variations of #find
     #
     #   Person.where(name: 'Spartacus', rating: 4)
     #   # returns a chainable list (which can be empty).
@@ -42,13 +45,13 @@ module ActiveRecord
     #   Person.find_by(name: 'Spartacus', rating: 4)
     #   # returns the first item or nil.
     #
-    #   Person.where(name: 'Spartacus', rating: 4).first_or_initialize
+    #   Person.find_or_initialize_by(name: 'Spartacus', rating: 4)
     #   # returns the first item or returns a new instance (requires you call .save to persist against the database).
     #
-    #   Person.where(name: 'Spartacus', rating: 4).first_or_create
+    #   Person.find_or_create_by(name: 'Spartacus', rating: 4)
     #   # returns the first item or creates it and returns it.
     #
-    # ==== Alternatives for +find+
+    # ==== Alternatives for #find
     #
     #   Person.where(name: 'Spartacus', rating: 4).exists?(conditions = :none)
     #   # returns a boolean indicating if any record with the given conditions exist.
@@ -76,16 +79,17 @@ module ActiveRecord
     #   Post.find_by "published_at < ?", 2.weeks.ago
     def find_by(arg, *args)
       where(arg, *args).take
-    rescue RangeError
+    rescue ::RangeError
       nil
     end
 
-    # Like <tt>find_by</tt>, except that if no record is found, raises
-    # an <tt>ActiveRecord::RecordNotFound</tt> error.
+    # Like #find_by, except that if no record is found, raises
+    # an ActiveRecord::RecordNotFound error.
     def find_by!(arg, *args)
       where(arg, *args).take!
-    rescue RangeError
-      raise RecordNotFound, "Couldn't find #{@klass.name} with an out of range value"
+    rescue ::RangeError
+      raise RecordNotFound.new("Couldn't find #{@klass.name} with an out of range value",
+                               @klass.name, @klass.primary_key)
     end
 
     # Gives a record (or N records if a parameter is supplied) without any implied
@@ -96,13 +100,13 @@ module ActiveRecord
     #   Person.take(5) # returns 5 objects fetched by SELECT * FROM people LIMIT 5
     #   Person.where(["name LIKE '%?'", name]).take
     def take(limit = nil)
-      limit ? limit(limit).to_a : find_take
+      limit ? find_take_with_limit(limit) : find_take
     end
 
-    # Same as +take+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
-    # is found. Note that <tt>take!</tt> accepts no arguments.
+    # Same as #take but raises ActiveRecord::RecordNotFound if no record
+    # is found. Note that #take! accepts no arguments.
     def take!
-      take or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
+      take || raise_record_not_found_exception!
     end
 
     # Find the first record (or first N records if a parameter is supplied).
@@ -116,16 +120,16 @@ module ActiveRecord
     #
     def first(limit = nil)
       if limit
-        find_nth_with_limit(offset_index, limit)
+        find_nth_with_limit(0, limit)
       else
-        find_nth(0, offset_index)
+        find_nth 0
       end
     end
 
-    # Same as +first+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
-    # is found. Note that <tt>first!</tt> accepts no arguments.
+    # Same as #first but raises ActiveRecord::RecordNotFound if no record
+    # is found. Note that #first! accepts no arguments.
     def first!
-      find_nth! 0
+      first || raise_record_not_found_exception!
     end
 
     # Find the last record (or last N records if a parameter is supplied).
@@ -144,21 +148,18 @@ module ActiveRecord
     #
     #   [#<Person id:4>, #<Person id:3>, #<Person id:2>]
     def last(limit = nil)
-      if limit
-        if order_values.empty? && primary_key
-          order(arel_table[primary_key].desc).limit(limit).reverse
-        else
-          to_a.last(limit)
-        end
-      else
-        find_last
-      end
+      return find_last(limit) if loaded? || has_limit_or_offset?
+
+      result = ordered_relation.limit(limit)
+      result = result.reverse_order!
+
+      limit ? result.reverse : result.first
     end
 
-    # Same as +last+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
-    # is found. Note that <tt>last!</tt> accepts no arguments.
+    # Same as #last but raises ActiveRecord::RecordNotFound if no record
+    # is found. Note that #last! accepts no arguments.
     def last!
-      last or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
+      last || raise_record_not_found_exception!
     end
 
     # Find the second record.
@@ -168,13 +169,13 @@ module ActiveRecord
     #   Person.offset(3).second # returns the second object from OFFSET 3 (which is OFFSET 4)
     #   Person.where(["user_name = :u", { u: user_name }]).second
     def second
-      find_nth(1, offset_index)
+      find_nth 1
     end
 
-    # Same as +second+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # Same as #second but raises ActiveRecord::RecordNotFound if no record
     # is found.
     def second!
-      find_nth! 1
+      second || raise_record_not_found_exception!
     end
 
     # Find the third record.
@@ -184,13 +185,13 @@ module ActiveRecord
     #   Person.offset(3).third # returns the third object from OFFSET 3 (which is OFFSET 5)
     #   Person.where(["user_name = :u", { u: user_name }]).third
     def third
-      find_nth(2, offset_index)
+      find_nth 2
     end
 
-    # Same as +third+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # Same as #third but raises ActiveRecord::RecordNotFound if no record
     # is found.
     def third!
-      find_nth! 2
+      third || raise_record_not_found_exception!
     end
 
     # Find the fourth record.
@@ -200,13 +201,13 @@ module ActiveRecord
     #   Person.offset(3).fourth # returns the fourth object from OFFSET 3 (which is OFFSET 6)
     #   Person.where(["user_name = :u", { u: user_name }]).fourth
     def fourth
-      find_nth(3, offset_index)
+      find_nth 3
     end
 
-    # Same as +fourth+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # Same as #fourth but raises ActiveRecord::RecordNotFound if no record
     # is found.
     def fourth!
-      find_nth! 3
+      fourth || raise_record_not_found_exception!
     end
 
     # Find the fifth record.
@@ -216,13 +217,13 @@ module ActiveRecord
     #   Person.offset(3).fifth # returns the fifth object from OFFSET 3 (which is OFFSET 7)
     #   Person.where(["user_name = :u", { u: user_name }]).fifth
     def fifth
-      find_nth(4, offset_index)
+      find_nth 4
     end
 
-    # Same as +fifth+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # Same as #fifth but raises ActiveRecord::RecordNotFound if no record
     # is found.
     def fifth!
-      find_nth! 4
+      fifth || raise_record_not_found_exception!
     end
 
     # Find the forty-second record. Also known as accessing "the reddit".
@@ -232,17 +233,49 @@ module ActiveRecord
     #   Person.offset(3).forty_two # returns the forty-second object from OFFSET 3 (which is OFFSET 44)
     #   Person.where(["user_name = :u", { u: user_name }]).forty_two
     def forty_two
-      find_nth(41, offset_index)
+      find_nth 41
     end
 
-    # Same as +forty_two+ but raises <tt>ActiveRecord::RecordNotFound</tt> if no record
+    # Same as #forty_two but raises ActiveRecord::RecordNotFound if no record
     # is found.
     def forty_two!
-      find_nth! 41
+      forty_two || raise_record_not_found_exception!
+    end
+
+    # Find the third-to-last record.
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.third_to_last # returns the third-to-last object fetched by SELECT * FROM people
+    #   Person.offset(3).third_to_last # returns the third-to-last object from OFFSET 3
+    #   Person.where(["user_name = :u", { u: user_name }]).third_to_last
+    def third_to_last
+      find_nth_from_last 3
     end
 
-    # Returns +true+ if a record exists in the table that matches the +id+ or
-    # conditions given, or +false+ otherwise. The argument can take six forms:
+    # Same as #third_to_last but raises ActiveRecord::RecordNotFound if no record
+    # is found.
+    def third_to_last!
+      third_to_last || raise_record_not_found_exception!
+    end
+
+    # Find the second-to-last record.
+    # If no order is defined it will order by primary key.
+    #
+    #   Person.second_to_last # returns the second-to-last object fetched by SELECT * FROM people
+    #   Person.offset(3).second_to_last # returns the second-to-last object from OFFSET 3
+    #   Person.where(["user_name = :u", { u: user_name }]).second_to_last
+    def second_to_last
+      find_nth_from_last 2
+    end
+
+    # Same as #second_to_last but raises ActiveRecord::RecordNotFound if no record
+    # is found.
+    def second_to_last!
+      second_to_last || raise_record_not_found_exception!
+    end
+
+    # Returns true if a record exists in the table that matches the +id+ or
+    # conditions given, or false otherwise. The argument can take six forms:
     #
     # * Integer - Finds the record with this primary key.
     # * String - Finds the record with a primary key corresponding to this
@@ -252,10 +285,10 @@ module ActiveRecord
     # * Hash - Finds the record that matches these +find+-style conditions
     #   (such as <tt>{name: 'David'}</tt>).
     # * +false+ - Returns always +false+.
-    # * No args - Returns +false+ if the table is empty, +true+ otherwise.
+    # * No args - Returns +false+ if the relation is empty, +true+ otherwise.
     #
     # For more information about specifying conditions as a hash or array,
-    # see the Conditions section in the introduction to <tt>ActiveRecord::Base</tt>.
+    # see the Conditions section in the introduction to ActiveRecord::Base.
     #
     # Note: You can't pass in a condition as a string (like <tt>name =
     # 'Jamie'</tt>), since it would be sanitized and then queried against
@@ -268,243 +301,260 @@ module ActiveRecord
     #   Person.exists?(name: 'David')
     #   Person.exists?(false)
     #   Person.exists?
+    #   Person.where(name: 'Spartacus', rating: 4).exists?
     def exists?(conditions = :none)
       if Base === conditions
-        conditions = conditions.id
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
+        raise ArgumentError, <<-MSG.squish
           You are passing an instance of ActiveRecord::Base to `exists?`.
-          Please pass the id of the object by calling `.id`
+          Please pass the id of the object by calling `.id`.
         MSG
       end
 
-      return false if !conditions
+      return false if !conditions || limit_value == 0
 
-      relation = apply_join_dependency(self, construct_join_dependency)
-      return false if ActiveRecord::NullRelation === relation
-
-      relation = relation.except(:select, :order).select(ONE_AS_ONE).limit(1)
-
-      case conditions
-      when Array, Hash
-        relation = relation.where(conditions)
-      else
-        unless conditions == :none
-          relation = relation.where(primary_key => conditions)
-        end
+      if eager_loading?
+        relation = apply_join_dependency(eager_loading: false)
+        return relation.exists?(conditions)
       end
 
-      connection.select_value(relation, "#{name} Exists", relation.bound_attributes) ? true : false
+      relation = construct_relation_for_exists(conditions)
+
+      skip_query_cache_if_necessary { connection.select_value(relation.arel, "#{name} Exists") } ? true : false
+    rescue ::RangeError
+      false
     end
 
     # This method is called whenever no records are found with either a single
-    # id or multiple ids and raises a +ActiveRecord::RecordNotFound+ exception.
+    # id or multiple ids and raises an ActiveRecord::RecordNotFound exception.
     #
     # The error message is different depending on whether a single id or
     # multiple ids are provided. If multiple ids are provided, then the number
     # of results obtained should be provided in the +result_size+ argument and
     # the expected number of results should be provided in the +expected_size+
     # argument.
-    def raise_record_not_found_exception!(ids, result_size, expected_size) #:nodoc:
-      conditions = arel.where_sql(@klass.arel_engine)
+    def raise_record_not_found_exception!(ids = nil, result_size = nil, expected_size = nil, key = primary_key, not_found_ids = nil) # :nodoc:
+      conditions = arel.where_sql(@klass)
       conditions = " [#{conditions}]" if conditions
-
-      if Array(ids).size == 1
-        error = "Couldn't find #{@klass.name} with '#{primary_key}'=#{ids}#{conditions}"
+      name = @klass.name
+
+      if ids.nil?
+        error = +"Couldn't find #{name}"
+        error << " with#{conditions}" if conditions
+        raise RecordNotFound.new(error, name, key)
+      elsif Array(ids).size == 1
+        error = "Couldn't find #{name} with '#{key}'=#{ids}#{conditions}"
+        raise RecordNotFound.new(error, name, key, ids)
       else
-        error = "Couldn't find all #{@klass.name.pluralize} with '#{primary_key}': "
-        error << "(#{ids.join(", ")})#{conditions} (found #{result_size} results, but was looking for #{expected_size})"
+        error = +"Couldn't find all #{name.pluralize} with '#{key}': "
+        error << "(#{ids.join(", ")})#{conditions} (found #{result_size} results, but was looking for #{expected_size})."
+        error << " Couldn't find #{name.pluralize(not_found_ids.size)} with #{key.to_s.pluralize(not_found_ids.size)} #{not_found_ids.join(', ')}." if not_found_ids
+        raise RecordNotFound.new(error, name, key, ids)
       end
-
-      raise RecordNotFound, error
     end
 
     private
 
-    def offset_index
-      offset_value || 0
-    end
+      def offset_index
+        offset_value || 0
+      end
 
-    def find_with_associations
-      # NOTE: the JoinDependency constructed here needs to know about
-      #       any joins already present in `self`, so pass them in
-      #
-      # failing to do so means that in cases like activerecord/test/cases/associations/inner_join_association_test.rb:136
-      # incorrect SQL is generated. In that case, the join dependency for
-      # SpecialCategorizations is constructed without knowledge of the
-      # preexisting join in joins_values to categorizations (by way of
-      # the `has_many :through` for categories).
-      #
-      join_dependency = construct_join_dependency(joins_values)
-
-      aliases  = join_dependency.aliases
-      relation = select aliases.columns
-      relation = apply_join_dependency(relation, join_dependency)
-
-      if block_given?
-        yield relation
-      else
-        if ActiveRecord::NullRelation === relation
-          []
+      def construct_relation_for_exists(conditions)
+        relation = except(:select, :distinct, :order)._select!(ONE_AS_ONE).limit!(1)
+
+        case conditions
+        when Array, Hash
+          relation.where!(conditions) unless conditions.empty?
         else
-          arel = relation.arel
-          rows = connection.select_all(arel, 'SQL', relation.bound_attributes)
-          join_dependency.instantiate(rows, aliases)
+          relation.where!(primary_key => conditions) unless conditions == :none
         end
-      end
-    end
 
-    def construct_join_dependency(joins = [])
-      including = eager_load_values + includes_values
-      ActiveRecord::Associations::JoinDependency.new(@klass, including, joins)
-    end
+        relation
+      end
 
-    def construct_relation_for_association_calculations
-      from = arel.froms.first
-      if Arel::Table === from
-        apply_join_dependency(self, construct_join_dependency(joins_values))
-      else
-        # FIXME: as far as I can tell, `from` will always be an Arel::Table.
-        # There are no tests that test this branch, but presumably it's
-        # possible for `from` to be a list?
-        apply_join_dependency(self, construct_join_dependency(from))
+      def construct_join_dependency(associations)
+        ActiveRecord::Associations::JoinDependency.new(
+          klass, table, associations
+        )
       end
-    end
 
-    def apply_join_dependency(relation, join_dependency)
-      relation = relation.except(:includes, :eager_load, :preload)
-      relation = relation.joins join_dependency
+      def apply_join_dependency(eager_loading: group_values.empty?)
+        join_dependency = construct_join_dependency(eager_load_values + includes_values)
+        relation = except(:includes, :eager_load, :preload).joins!(join_dependency)
 
-      if using_limitable_reflections?(join_dependency.reflections)
-        relation
-      else
-        if relation.limit_value
-          limited_ids = limited_ids_for(relation)
-          limited_ids.empty? ? relation.none! : relation.where!(primary_key => limited_ids)
+        if eager_loading && !using_limitable_reflections?(join_dependency.reflections)
+          if has_limit_or_offset?
+            limited_ids = limited_ids_for(relation)
+            limited_ids.empty? ? relation.none! : relation.where!(primary_key => limited_ids)
+          end
+          relation.limit_value = relation.offset_value = nil
+        end
+
+        if block_given?
+          yield relation, join_dependency
+        else
+          relation
         end
-        relation.except(:limit, :offset)
       end
-    end
 
-    def limited_ids_for(relation)
-      values = @klass.connection.columns_for_distinct(
-        "#{quoted_table_name}.#{quoted_primary_key}", relation.order_values)
+      def limited_ids_for(relation)
+        values = @klass.connection.columns_for_distinct(
+          connection.visitor.compile(arel_attribute(primary_key)),
+          relation.order_values
+        )
 
-      relation = relation.except(:select).select(values).distinct!
-      arel = relation.arel
+        relation = relation.except(:select).select(values).distinct!
 
-      id_rows = @klass.connection.select_all(arel, 'SQL', relation.bound_attributes)
-      id_rows.map {|row| row[primary_key]}
-    end
+        id_rows = skip_query_cache_if_necessary { @klass.connection.select_all(relation.arel, "SQL") }
+        id_rows.map { |row| row[primary_key] }
+      end
 
-    def using_limitable_reflections?(reflections)
-      reflections.none?(&:collection?)
-    end
+      def using_limitable_reflections?(reflections)
+        reflections.none?(&:collection?)
+      end
 
-    protected
+      def find_with_ids(*ids)
+        raise UnknownPrimaryKey.new(@klass) if primary_key.nil?
 
-    def find_with_ids(*ids)
-      raise UnknownPrimaryKey.new(@klass) if primary_key.nil?
+        expects_array = ids.first.kind_of?(Array)
+        return [] if expects_array && ids.first.empty?
 
-      expects_array = ids.first.kind_of?(Array)
-      return ids.first if expects_array && ids.first.empty?
+        ids = ids.flatten.compact.uniq
 
-      ids = ids.flatten.compact.uniq
+        model_name = @klass.name
 
-      case ids.size
-      when 0
-        raise RecordNotFound, "Couldn't find #{@klass.name} without an ID"
-      when 1
-        result = find_one(ids.first)
-        expects_array ? [ result ] : result
-      else
-        find_some(ids)
+        case ids.size
+        when 0
+          error_message = "Couldn't find #{model_name} without an ID"
+          raise RecordNotFound.new(error_message, model_name, primary_key)
+        when 1
+          result = find_one(ids.first)
+          expects_array ? [ result ] : result
+        else
+          find_some(ids)
+        end
+      rescue ::RangeError
+        error_message = "Couldn't find #{model_name} with an out of range ID"
+        raise RecordNotFound.new(error_message, model_name, primary_key, ids)
       end
-    rescue RangeError
-      raise RecordNotFound, "Couldn't find #{@klass.name} with an out of range ID"
-    end
 
-    def find_one(id)
-      if ActiveRecord::Base === id
-        id = id.id
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          You are passing an instance of ActiveRecord::Base to `find`.
-          Please pass the id of the object by calling `.id`
-        MSG
+      def find_one(id)
+        if ActiveRecord::Base === id
+          raise ArgumentError, <<-MSG.squish
+            You are passing an instance of ActiveRecord::Base to `find`.
+            Please pass the id of the object by calling `.id`.
+          MSG
+        end
+
+        relation = where(primary_key => id)
+        record = relation.take
+
+        raise_record_not_found_exception!(id, 0, 1) unless record
+
+        record
       end
 
-      relation = where(primary_key => id)
-      record = relation.take
+      def find_some(ids)
+        return find_some_ordered(ids) unless order_values.present?
 
-      raise_record_not_found_exception!(id, 0, 1) unless record
+        result = where(primary_key => ids).to_a
 
-      record
-    end
+        expected_size =
+          if limit_value && ids.size > limit_value
+            limit_value
+          else
+            ids.size
+          end
 
-    def find_some(ids)
-      result = where(primary_key => ids).to_a
+        # 11 ids with limit 3, offset 9 should give 2 results.
+        if offset_value && (ids.size - offset_value < expected_size)
+          expected_size = ids.size - offset_value
+        end
 
-      expected_size =
-        if limit_value && ids.size > limit_value
-          limit_value
+        if result.size == expected_size
+          result
         else
-          ids.size
+          raise_record_not_found_exception!(ids, result.size, expected_size)
         end
+      end
+
+      def find_some_ordered(ids)
+        ids = ids.slice(offset_value || 0, limit_value || ids.size) || []
+
+        result = except(:limit, :offset).where(primary_key => ids).records
+
+        if result.size == ids.size
+          pk_type = @klass.type_for_attribute(primary_key)
 
-      # 11 ids with limit 3, offset 9 should give 2 results.
-      if offset_value && (ids.size - offset_value < expected_size)
-        expected_size = ids.size - offset_value
+          records_by_id = result.index_by(&:id)
+          ids.map { |id| records_by_id.fetch(pk_type.cast(id)) }
+        else
+          raise_record_not_found_exception!(ids, result.size, ids.size)
+        end
       end
 
-      if result.size == expected_size
-        result
-      else
-        raise_record_not_found_exception!(ids, result.size, expected_size)
+      def find_take
+        if loaded?
+          records.first
+        else
+          @take ||= limit(1).records.first
+        end
       end
-    end
 
-    def find_take
-      if loaded?
-        @records.first
-      else
-        @take ||= limit(1).to_a.first
+      def find_take_with_limit(limit)
+        if loaded?
+          records.take(limit)
+        else
+          limit(limit).to_a
+        end
       end
-    end
 
-    def find_nth(index, offset)
-      if loaded?
-        @records[index]
-      else
-        offset += index
-        @offsets[offset] ||= find_nth_with_limit(offset, 1).first
+      def find_nth(index)
+        @offsets[offset_index + index] ||= find_nth_with_limit(index, 1).first
       end
-    end
 
-    def find_nth!(index)
-      find_nth(index, offset_index) or raise RecordNotFound.new("Couldn't find #{@klass.name} with [#{arel.where_sql(@klass.arel_engine)}]")
-    end
+      def find_nth_with_limit(index, limit)
+        if loaded?
+          records[index, limit] || []
+        else
+          relation = ordered_relation
 
-    def find_nth_with_limit(offset, limit)
-      relation = if order_values.empty? && primary_key
-                   order(arel_table[primary_key].asc)
-                 else
-                   self
-                 end
+          if limit_value
+            limit = [limit_value - index, limit].min
+          end
 
-      relation = relation.offset(offset) unless offset.zero?
-      relation.limit(limit).to_a
-    end
+          if limit > 0
+            relation = relation.offset(offset_index + index) unless index.zero?
+            relation.limit(limit).to_a
+          else
+            []
+          end
+        end
+      end
 
-    def find_last
-      if loaded?
-        @records.last
-      else
-        @last ||=
-          if limit_value
-            to_a.last
+      def find_nth_from_last(index)
+        if loaded?
+          records[-index]
+        else
+          relation = ordered_relation
+
+          if equal?(relation) || has_limit_or_offset?
+            relation.records[-index]
           else
-            reverse_order.limit(1).to_a.first
+            relation.last(index)[-index]
           end
+        end
+      end
+
+      def find_last(limit)
+        limit ? records.last(limit) : records.last
+      end
+
+      def ordered_relation
+        if order_values.empty? && primary_key
+          order(arel_attribute(primary_key).asc)
+        else
+          self
+        end
       end
-    end
   end
 end
diff --git a/activerecord/lib/active_record/relation/from_clause.rb b/activerecord/lib/active_record/relation/from_clause.rb
index a93952fa30..c53a682aee 100644
--- a/activerecord/lib/active_record/relation/from_clause.rb
+++ b/activerecord/lib/active_record/relation/from_clause.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class Relation
-    class FromClause
+    class FromClause # :nodoc:
       attr_reader :value, :name
 
       def initialize(value, name)
@@ -8,14 +10,6 @@ module ActiveRecord
         @name = name
       end
 
-      def binds
-        if value.is_a?(Relation)
-          value.bound_attributes
-        else
-          []
-        end
-      end
-
       def merge(other)
         self
       end
@@ -25,7 +19,7 @@ module ActiveRecord
       end
 
       def self.empty
-        new(nil, nil)
+        @empty ||= new(nil, nil)
       end
     end
   end
diff --git a/activerecord/lib/active_record/relation/merger.rb b/activerecord/lib/active_record/relation/merger.rb
index 0b38666ce9..4de7465128 100644
--- a/activerecord/lib/active_record/relation/merger.rb
+++ b/activerecord/lib/active_record/relation/merger.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/hash/keys'
+# frozen_string_literal: true
+
+require "active_support/core_ext/hash/keys"
 
 module ActiveRecord
   class Relation
@@ -21,7 +23,11 @@ module ActiveRecord
       # build a relation to merge in rather than directly merging
       # the values.
       def other
-        other = Relation.create(relation.klass, relation.table, relation.predicate_builder)
+        other = Relation.create(
+          relation.klass,
+          table: relation.table,
+          predicate_builder: relation.predicate_builder
+        )
         hash.each { |k, v|
           if k == :joins
             if Hash === v
@@ -50,7 +56,7 @@ module ActiveRecord
 
       NORMAL_VALUES = Relation::VALUE_METHODS -
                       Relation::CLAUSE_METHODS -
-                      [:includes, :preload, :joins, :order, :reverse_order, :lock, :create_with, :reordering] # :nodoc:
+                      [:includes, :preload, :joins, :left_outer_joins, :order, :reverse_order, :lock, :create_with, :reordering] # :nodoc:
 
       def normal_values
         NORMAL_VALUES
@@ -77,84 +83,107 @@ module ActiveRecord
         merge_clauses
         merge_preloads
         merge_joins
+        merge_outer_joins
 
         relation
       end
 
       private
 
-      def merge_preloads
-        return if other.preload_values.empty? && other.includes_values.empty?
+        def merge_preloads
+          return if other.preload_values.empty? && other.includes_values.empty?
+
+          if other.klass == relation.klass
+            relation.preload!(*other.preload_values) unless other.preload_values.empty?
+            relation.includes!(other.includes_values) unless other.includes_values.empty?
+          else
+            reflection = relation.klass.reflect_on_all_associations.find do |r|
+              r.class_name == other.klass.name
+            end || return
 
-        if other.klass == relation.klass
-          relation.preload!(*other.preload_values) unless other.preload_values.empty?
-          relation.includes!(other.includes_values) unless other.includes_values.empty?
-        else
-          reflection = relation.klass.reflect_on_all_associations.find do |r|
-            r.class_name == other.klass.name
-          end || return
+            unless other.preload_values.empty?
+              relation.preload! reflection.name => other.preload_values
+            end
 
-          unless other.preload_values.empty?
-            relation.preload! reflection.name => other.preload_values
+            unless other.includes_values.empty?
+              relation.includes! reflection.name => other.includes_values
+            end
           end
+        end
 
-          unless other.includes_values.empty?
-            relation.includes! reflection.name => other.includes_values
+        def merge_joins
+          return if other.joins_values.blank?
+
+          if other.klass == relation.klass
+            relation.joins!(*other.joins_values)
+          else
+            joins_dependency = other.joins_values.map do |join|
+              case join
+              when Hash, Symbol, Array
+                other.send(:construct_join_dependency, join)
+              else
+                join
+              end
+            end
+
+            relation.joins!(*joins_dependency)
           end
         end
-      end
 
-      def merge_joins
-        return if other.joins_values.blank?
+        def merge_outer_joins
+          return if other.left_outer_joins_values.blank?
 
-        if other.klass == relation.klass
-          relation.joins!(*other.joins_values)
-        else
-          joins_dependency, rest = other.joins_values.partition do |join|
-            case join
-            when Hash, Symbol, Array
-              true
-            else
-              false
+          if other.klass == relation.klass
+            relation.left_outer_joins!(*other.left_outer_joins_values)
+          else
+            joins_dependency = other.left_outer_joins_values.map do |join|
+              case join
+              when Hash, Symbol, Array
+                other.send(:construct_join_dependency, join)
+              else
+                join
+              end
             end
+
+            relation.left_outer_joins!(*joins_dependency)
           end
+        end
 
-          join_dependency = ActiveRecord::Associations::JoinDependency.new(other.klass,
-                                                                           joins_dependency,
-                                                                           [])
-          relation.joins! rest
+        def merge_multi_values
+          if other.reordering_value
+            # override any order specified in the original relation
+            relation.reorder!(*other.order_values)
+          elsif other.order_values.any?
+            # merge in order_values from relation
+            relation.order!(*other.order_values)
+          end
 
-          @relation = relation.joins join_dependency
+          extensions = other.extensions - relation.extensions
+          relation.extending!(*extensions) if extensions.any?
         end
-      end
 
-      def merge_multi_values
-        if other.reordering_value
-          # override any order specified in the original relation
-          relation.reorder! other.order_values
-        elsif other.order_values
-          # merge in order_values from relation
-          relation.order! other.order_values
+        def merge_single_values
+          relation.lock_value ||= other.lock_value if other.lock_value
+
+          unless other.create_with_value.blank?
+            relation.create_with_value = (relation.create_with_value || {}).merge(other.create_with_value)
+          end
         end
 
-        relation.extend(*other.extending_values) unless other.extending_values.blank?
-      end
+        def merge_clauses
+          relation.from_clause = other.from_clause if replace_from_clause?
 
-      def merge_single_values
-        relation.lock_value ||= other.lock_value
+          where_clause = relation.where_clause.merge(other.where_clause)
+          relation.where_clause = where_clause unless where_clause.empty?
 
-        unless other.create_with_value.blank?
-          relation.create_with_value = (relation.create_with_value || {}).merge(other.create_with_value)
+          having_clause = relation.having_clause.merge(other.having_clause)
+          relation.having_clause = having_clause unless having_clause.empty?
         end
-      end
 
-      def merge_clauses
-        CLAUSE_METHODS.each do |name|
-          clause = relation.send("#{name}_clause")
-          other_clause = other.send("#{name}_clause")
-          relation.send("#{name}_clause=", clause.merge(other_clause))
+        def replace_from_clause?
+          relation.from_clause.empty? && !other.from_clause.empty? &&
+            relation.klass.base_class == other.klass.base_class
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/relation/predicate_builder.rb b/activerecord/lib/active_record/relation/predicate_builder.rb
index 43e9afe853..b59ff912fe 100644
--- a/activerecord/lib/active_record/relation/predicate_builder.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder.rb
@@ -1,13 +1,7 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class PredicateBuilder # :nodoc:
-    require 'active_record/relation/predicate_builder/array_handler'
-    require 'active_record/relation/predicate_builder/association_query_handler'
-    require 'active_record/relation/predicate_builder/base_handler'
-    require 'active_record/relation/predicate_builder/basic_object_handler'
-    require 'active_record/relation/predicate_builder/class_handler'
-    require 'active_record/relation/predicate_builder/range_handler'
-    require 'active_record/relation/predicate_builder/relation_handler'
-
     delegate :resolve_column_aliases, to: :table
 
     def initialize(table)
@@ -15,44 +9,25 @@ module ActiveRecord
       @handlers = []
 
       register_handler(BasicObject, BasicObjectHandler.new(self))
-      register_handler(Class, ClassHandler.new(self))
       register_handler(Base, BaseHandler.new(self))
       register_handler(Range, RangeHandler.new(self))
       register_handler(Relation, RelationHandler.new)
       register_handler(Array, ArrayHandler.new(self))
-      register_handler(AssociationQueryValue, AssociationQueryHandler.new(self))
+      register_handler(Set, ArrayHandler.new(self))
     end
 
     def build_from_hash(attributes)
-      attributes = convert_dot_notation_to_hash(attributes.stringify_keys)
+      attributes = convert_dot_notation_to_hash(attributes)
       expand_from_hash(attributes)
     end
 
-    def create_binds(attributes)
-      attributes = convert_dot_notation_to_hash(attributes.stringify_keys)
-      create_binds_for_hash(attributes)
-    end
-
-    def expand(column, value)
-      # Find the foreign key when using queries such as:
-      # Post.where(author: author)
-      #
-      # For polymorphic relationships, find the foreign key and type:
-      # PriceEstimate.where(estimate_of: treasure)
-      if table.associated_with?(column)
-        value = AssociationQueryValue.new(table.associated_table(column), value)
-      end
-
-      build(table.arel_attribute(column), value)
-    end
-
     def self.references(attributes)
       attributes.map do |key, value|
         if value.is_a?(Hash)
           key
         else
           key = key.to_s
-          key.split('.').first if key.include?('.')
+          key.split(".").first if key.include?(".")
         end
       end.compact
     end
@@ -67,83 +42,104 @@ module ActiveRecord
     #         Arel::Nodes::And.new([range.start, range.end])
     #       )
     #     end
-    #     ActiveRecord::PredicateBuilder.register_handler(MyCustomDateRange, handler)
+    #     ActiveRecord::PredicateBuilder.new("users").register_handler(MyCustomDateRange, handler)
     def register_handler(klass, handler)
       @handlers.unshift([klass, handler])
     end
 
     def build(attribute, value)
-      handler_for(value).call(attribute, value)
-    end
-
-    protected
-
-    attr_reader :table
-
-    def expand_from_hash(attributes)
-      return ["1=0"] if attributes.empty?
-
-      attributes.flat_map do |key, value|
-        if value.is_a?(Hash)
-          associated_predicate_builder(key).expand_from_hash(value)
-        else
-          expand(key, value)
-        end
+      if table.type(attribute.name).force_equality?(value)
+        bind = build_bind_attribute(attribute.name, value)
+        attribute.eq(bind)
+      else
+        handler_for(value).call(attribute, value)
       end
     end
 
+    def build_bind_attribute(column_name, value)
+      attr = Relation::QueryAttribute.new(column_name.to_s, value, table.type(column_name))
+      Arel::Nodes::BindParam.new(attr)
+    end
 
-    def create_binds_for_hash(attributes)
-      result = attributes.dup
-      binds = []
-
-      attributes.each do |column_name, value|
-        case value
-        when Hash
-          attrs, bvs = associated_predicate_builder(column_name).create_binds_for_hash(value)
-          result[column_name] = attrs
-          binds += bvs
-        when Relation
-          binds += value.bound_attributes
-        else
-          if can_be_bound?(column_name, value)
-            result[column_name] = Arel::Nodes::BindParam.new
-            binds << Relation::QueryAttribute.new(column_name.to_s, value, table.type(column_name))
+    protected
+      def expand_from_hash(attributes)
+        return ["1=0"] if attributes.empty?
+
+        attributes.flat_map do |key, value|
+          if value.is_a?(Hash) && !table.has_column?(key)
+            associated_predicate_builder(key).expand_from_hash(value)
+          elsif table.associated_with?(key)
+            # Find the foreign key when using queries such as:
+            # Post.where(author: author)
+            #
+            # For polymorphic relationships, find the foreign key and type:
+            # PriceEstimate.where(estimate_of: treasure)
+            associated_table = table.associated_table(key)
+            if associated_table.polymorphic_association?
+              case value.is_a?(Array) ? value.first : value
+              when Base, Relation
+                value = [value] unless value.is_a?(Array)
+                klass = PolymorphicArrayValue
+              end
+            end
+
+            klass ||= AssociationQueryValue
+            queries = klass.new(associated_table, value).queries.map do |query|
+              expand_from_hash(query).reduce(&:and)
+            end
+            queries.reduce(&:or)
+          elsif table.aggregated_with?(key)
+            mapping = table.reflect_on_aggregation(key).mapping
+            queries = Array.wrap(value).map do |object|
+              mapping.map do |field_attr, aggregate_attr|
+                if mapping.size == 1 && !object.respond_to?(aggregate_attr)
+                  build(table.arel_attribute(field_attr), object)
+                else
+                  build(table.arel_attribute(field_attr), object.send(aggregate_attr))
+                end
+              end.reduce(&:and)
+            end
+            queries.reduce(&:or)
+          else
+            build(table.arel_attribute(key), value)
           end
         end
       end
 
-      [result, binds]
-    end
-
     private
+      attr_reader :table
 
-    def associated_predicate_builder(association_name)
-      self.class.new(table.associated_table(association_name))
-    end
-
-    def convert_dot_notation_to_hash(attributes)
-      dot_notation = attributes.keys.select { |s| s.include?(".") }
+      def associated_predicate_builder(association_name)
+        self.class.new(table.associated_table(association_name))
+      end
 
-      dot_notation.each do |key|
-        table_name, column_name = key.split(".")
-        value = attributes.delete(key)
-        attributes[table_name] ||= {}
+      def convert_dot_notation_to_hash(attributes)
+        dot_notation = attributes.select do |k, v|
+          k.include?(".") && !v.is_a?(Hash)
+        end
 
-        attributes[table_name] = attributes[table_name].merge(column_name => value)
-      end
+        dot_notation.each_key do |key|
+          table_name, column_name = key.split(".")
+          value = attributes.delete(key)
+          attributes[table_name] ||= {}
 
-      attributes
-    end
+          attributes[table_name] = attributes[table_name].merge(column_name => value)
+        end
 
-    def handler_for(object)
-      @handlers.detect { |klass, _| klass === object }.last
-    end
+        attributes
+      end
 
-    def can_be_bound?(column_name, value)
-      !value.nil? &&
-        handler_for(value).is_a?(BasicObjectHandler) &&
-        !table.associated_with?(column_name)
-    end
+      def handler_for(object)
+        @handlers.detect { |klass, _| klass === object }.last
+      end
   end
 end
+
+require "active_record/relation/predicate_builder/array_handler"
+require "active_record/relation/predicate_builder/base_handler"
+require "active_record/relation/predicate_builder/basic_object_handler"
+require "active_record/relation/predicate_builder/range_handler"
+require "active_record/relation/predicate_builder/relation_handler"
+
+require "active_record/relation/predicate_builder/association_query_value"
+require "active_record/relation/predicate_builder/polymorphic_array_value"
diff --git a/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
index 95dbd6a77f..ee2ece1560 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/array_handler.rb
@@ -1,3 +1,7 @@
+# frozen_string_literal: true
+
+require "active_support/core_ext/array/extract"
+
 module ActiveRecord
   class PredicateBuilder
     class ArrayHandler # :nodoc:
@@ -6,18 +10,21 @@ module ActiveRecord
       end
 
       def call(attribute, value)
-        values = value.map { |x| x.is_a?(Base) ? x.id : x }
-        nils, values = values.partition(&:nil?)
-
-        return attribute.in([]) if values.empty? && nils.empty?
+        return attribute.in([]) if value.empty?
 
-        ranges, values = values.partition { |v| v.is_a?(Range) }
+        values = value.map { |x| x.is_a?(Base) ? x.id : x }
+        nils = values.extract!(&:nil?)
+        ranges = values.extract! { |v| v.is_a?(Range) }
 
         values_predicate =
           case values.length
           when 0 then NullPredicate
           when 1 then predicate_builder.build(attribute, values.first)
-          else attribute.in(values)
+          else
+            values.map! do |v|
+              predicate_builder.build_bind_attribute(attribute.name, v)
+            end
+            values.empty? ? NullPredicate : attribute.in(values)
           end
 
         unless nils.empty?
@@ -26,18 +33,17 @@ module ActiveRecord
 
         array_predicates = ranges.map { |range| predicate_builder.build(attribute, range) }
         array_predicates.unshift(values_predicate)
-        array_predicates.inject { |composite, predicate| composite.or(predicate) }
+        array_predicates.inject(&:or)
       end
 
-      protected
-
-      attr_reader :predicate_builder
+      private
+        attr_reader :predicate_builder
 
-      module NullPredicate # :nodoc:
-        def self.or(other)
-          other
+        module NullPredicate # :nodoc:
+          def self.or(other)
+            other
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb
deleted file mode 100644
index 159889d3b8..0000000000
--- a/activerecord/lib/active_record/relation/predicate_builder/association_query_handler.rb
+++ /dev/null
@@ -1,78 +0,0 @@
-module ActiveRecord
-  class PredicateBuilder
-    class AssociationQueryHandler # :nodoc:
-      def initialize(predicate_builder)
-        @predicate_builder = predicate_builder
-      end
-
-      def call(attribute, value)
-        queries = {}
-
-        table = value.associated_table
-        if value.base_class
-          queries[table.association_foreign_type] = value.base_class.name
-        end
-
-        queries[table.association_foreign_key] = value.ids
-        predicate_builder.build_from_hash(queries)
-      end
-
-      protected
-
-      attr_reader :predicate_builder
-    end
-
-    class AssociationQueryValue # :nodoc:
-      attr_reader :associated_table, :value
-
-      def initialize(associated_table, value)
-        @associated_table = associated_table
-        @value = value
-      end
-
-      def ids
-        case value
-        when Relation
-          value.select(primary_key)
-        when Array
-          value.map { |v| convert_to_id(v) }
-        else
-          convert_to_id(value)
-        end
-      end
-
-      def base_class
-        if associated_table.polymorphic_association?
-          @base_class ||= polymorphic_base_class_from_value
-        end
-      end
-
-      private
-
-      def primary_key
-        associated_table.association_primary_key(base_class)
-      end
-
-      def polymorphic_base_class_from_value
-        case value
-        when Relation
-          value.klass.base_class
-        when Array
-          val = value.compact.first
-          val.class.base_class if val.is_a?(Base)
-        when Base
-          value.class.base_class
-        end
-      end
-
-      def convert_to_id(value)
-        case value
-        when Base
-          value._read_attribute(primary_key)
-        else
-          value
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/association_query_value.rb b/activerecord/lib/active_record/relation/predicate_builder/association_query_value.rb
new file mode 100644
index 0000000000..88cd71cf69
--- /dev/null
+++ b/activerecord/lib/active_record/relation/predicate_builder/association_query_value.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class PredicateBuilder
+    class AssociationQueryValue # :nodoc:
+      def initialize(associated_table, value)
+        @associated_table = associated_table
+        @value = value
+      end
+
+      def queries
+        [associated_table.association_join_foreign_key.to_s => ids]
+      end
+
+      private
+        attr_reader :associated_table, :value
+
+        def ids
+          case value
+          when Relation
+            value.select_values.empty? ? value.select(primary_key) : value
+          when Array
+            value.map { |v| convert_to_id(v) }
+          else
+            convert_to_id(value)
+          end
+        end
+
+        def primary_key
+          associated_table.association_join_primary_key
+        end
+
+        def convert_to_id(value)
+          case value
+          when Base
+            value._read_attribute(primary_key)
+          else
+            value
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/base_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/base_handler.rb
index 6fa5b16f73..10c5c1a66a 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/base_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/base_handler.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class PredicateBuilder
     class BaseHandler # :nodoc:
@@ -9,9 +11,8 @@ module ActiveRecord
         predicate_builder.build(attribute, value.id)
       end
 
-      protected
-
-      attr_reader :predicate_builder
+      private
+        attr_reader :predicate_builder
     end
   end
 end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/basic_object_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/basic_object_handler.rb
index 6cec75dc0a..e8c9f60860 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/basic_object_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/basic_object_handler.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class PredicateBuilder
     class BasicObjectHandler # :nodoc:
@@ -6,12 +8,12 @@ module ActiveRecord
       end
 
       def call(attribute, value)
-        attribute.eq(value)
+        bind = predicate_builder.build_bind_attribute(attribute.name, value)
+        attribute.eq(bind)
       end
 
-      protected
-
-      attr_reader :predicate_builder
+      private
+        attr_reader :predicate_builder
     end
   end
 end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/class_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/class_handler.rb
deleted file mode 100644
index ed313fc9d4..0000000000
--- a/activerecord/lib/active_record/relation/predicate_builder/class_handler.rb
+++ /dev/null
@@ -1,27 +0,0 @@
-module ActiveRecord
-  class PredicateBuilder
-    class ClassHandler # :nodoc:
-      def initialize(predicate_builder)
-        @predicate_builder = predicate_builder
-      end
-
-      def call(attribute, value)
-        print_deprecation_warning
-        predicate_builder.build(attribute, value.name)
-      end
-
-      protected
-
-      attr_reader :predicate_builder
-
-      private
-
-      def print_deprecation_warning
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          Passing a class as a value in an Active Record query is deprecated and
-          will be removed. Pass a string instead.
-        MSG
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_value.rb b/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_value.rb
new file mode 100644
index 0000000000..aae04d9348
--- /dev/null
+++ b/activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_value.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  class PredicateBuilder
+    class PolymorphicArrayValue # :nodoc:
+      def initialize(associated_table, values)
+        @associated_table = associated_table
+        @values = values
+      end
+
+      def queries
+        type_to_ids_mapping.map do |type, ids|
+          {
+            associated_table.association_foreign_type.to_s => type,
+            associated_table.association_foreign_key.to_s => ids
+          }
+        end
+      end
+
+      private
+        attr_reader :associated_table, :values
+
+        def type_to_ids_mapping
+          default_hash = Hash.new { |hsh, key| hsh[key] = [] }
+          values.each_with_object(default_hash) do |value, hash|
+            hash[klass(value).polymorphic_name] << convert_to_id(value)
+          end
+        end
+
+        def primary_key(value)
+          associated_table.association_join_primary_key(klass(value))
+        end
+
+        def klass(value)
+          case value
+          when Base
+            value.class
+          when Relation
+            value.klass
+          end
+        end
+
+        def convert_to_id(value)
+          case value
+          when Base
+            value._read_attribute(primary_key(value))
+          when Relation
+            value.select(primary_key(value))
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/range_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/range_handler.rb
index 1b3849e3ad..44bb2c7ab6 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/range_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/range_handler.rb
@@ -1,17 +1,41 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class PredicateBuilder
     class RangeHandler # :nodoc:
+      class RangeWithBinds < Struct.new(:begin, :end)
+        def exclude_end?
+          false
+        end
+      end
+
       def initialize(predicate_builder)
         @predicate_builder = predicate_builder
       end
 
       def call(attribute, value)
-        attribute.between(value)
-      end
+        begin_bind = predicate_builder.build_bind_attribute(attribute.name, value.begin)
+        end_bind = predicate_builder.build_bind_attribute(attribute.name, value.end)
 
-      protected
+        if begin_bind.value.infinity?
+          if end_bind.value.infinity?
+            attribute.not_in([])
+          elsif value.exclude_end?
+            attribute.lt(end_bind)
+          else
+            attribute.lteq(end_bind)
+          end
+        elsif end_bind.value.infinity?
+          attribute.gteq(begin_bind)
+        elsif value.exclude_end?
+          attribute.gteq(begin_bind).and(attribute.lt(end_bind))
+        else
+          attribute.between(RangeWithBinds.new(begin_bind, end_bind))
+        end
+      end
 
-      attr_reader :predicate_builder
+      private
+        attr_reader :predicate_builder
     end
   end
 end
diff --git a/activerecord/lib/active_record/relation/predicate_builder/relation_handler.rb b/activerecord/lib/active_record/relation/predicate_builder/relation_handler.rb
index 063150958a..c8bbfa5051 100644
--- a/activerecord/lib/active_record/relation/predicate_builder/relation_handler.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder/relation_handler.rb
@@ -1,9 +1,15 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class PredicateBuilder
     class RelationHandler # :nodoc:
       def call(attribute, value)
+        if value.eager_loading?
+          value = value.send(:apply_join_dependency)
+        end
+
         if value.select_values.empty?
-          value = value.select(value.klass.arel_table[value.klass.primary_key])
+          value = value.select(value.arel_attribute(value.klass.primary_key))
         end
 
         attribute.in(value.arel)
diff --git a/activerecord/lib/active_record/relation/query_attribute.rb b/activerecord/lib/active_record/relation/query_attribute.rb
index e69319b4de..f64bd30d38 100644
--- a/activerecord/lib/active_record/relation/query_attribute.rb
+++ b/activerecord/lib/active_record/relation/query_attribute.rb
@@ -1,8 +1,10 @@
-require 'active_record/attribute'
+# frozen_string_literal: true
+
+require "active_model/attribute"
 
 module ActiveRecord
   class Relation
-    class QueryAttribute < Attribute
+    class QueryAttribute < ActiveModel::Attribute # :nodoc:
       def type_cast(value)
         value
       end
@@ -14,6 +16,28 @@ module ActiveRecord
       def with_cast_value(value)
         QueryAttribute.new(name, value, type)
       end
+
+      def nil?
+        !value_before_type_cast.is_a?(StatementCache::Substitute) &&
+          (value_before_type_cast.nil? || value_for_database.nil?)
+      end
+
+      def boundable?
+        return @_boundable if defined?(@_boundable)
+        nil?
+        @_boundable = true
+      rescue ::RangeError
+        @_boundable = false
+      end
+
+      def infinity?
+        _infinity?(value_before_type_cast) || boundable? && _infinity?(value_for_database)
+      end
+
+      private
+        def _infinity?(value)
+          value.respond_to?(:infinite?) && value.infinite?
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 706c99c245..eb80aab701 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -1,9 +1,10 @@
+# frozen_string_literal: true
+
 require "active_record/relation/from_clause"
 require "active_record/relation/query_attribute"
 require "active_record/relation/where_clause"
 require "active_record/relation/where_clause_factory"
-require 'active_model/forbidden_attributes_protection'
-require 'active_support/core_ext/string/filters'
+require "active_model/forbidden_attributes_protection"
 
 module ActiveRecord
   module QueryMethods
@@ -14,6 +15,8 @@ module ActiveRecord
     # WhereChain objects act as placeholder for queries in which #where does not have any parameter.
     # In this case, #where must be chained with #not to return a new relation.
     class WhereChain
+      include ActiveModel::ForbiddenAttributesProtection
+
       def initialize(scope)
         @scope = scope
       end
@@ -21,7 +24,7 @@ module ActiveRecord
       # Returns a new relation expressing WHERE + NOT condition according to
       # the conditions in the arguments.
       #
-      # +not+ accepts conditions as a string, array, or hash. See #where for
+      # #not accepts conditions as a string, array, or hash. See QueryMethods#where for
       # more details on each format.
       #
       #    User.where.not("name = 'Jon'")
@@ -42,6 +45,8 @@ module ActiveRecord
       #    User.where.not(name: "Jon", role: "admin")
       #    # SELECT * FROM users WHERE name != 'Jon' AND role != 'admin'
       def not(opts, *rest)
+        opts = sanitize_forbidden_attributes(opts)
+
         where_clause = @scope.send(:where_clause_factory).build(opts, rest)
 
         @scope.references!(PredicateBuilder.references(opts)) if Hash === opts
@@ -50,57 +55,27 @@ module ActiveRecord
       end
     end
 
-    Relation::MULTI_VALUE_METHODS.each do |name|
-      class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}_values                    # def select_values
-          @values[:#{name}] || []             #   @values[:select] || []
-        end                                   # end
-                                              #
-        def #{name}_values=(values)           # def select_values=(values)
-          assert_mutability!                  #   assert_mutability!
-          @values[:#{name}] = values          #   @values[:select] = values
-        end                                   # end
-      CODE
-    end
+    FROZEN_EMPTY_ARRAY = [].freeze
+    FROZEN_EMPTY_HASH = {}.freeze
 
-    (Relation::SINGLE_VALUE_METHODS - [:create_with]).each do |name|
+    Relation::VALUE_METHODS.each do |name|
+      method_name = \
+        case name
+        when *Relation::MULTI_VALUE_METHODS then "#{name}_values"
+        when *Relation::SINGLE_VALUE_METHODS then "#{name}_value"
+        when *Relation::CLAUSE_METHODS then "#{name}_clause"
+        end
       class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}_value                    # def readonly_value
-          @values[:#{name}]                  #   @values[:readonly]
+        def #{method_name}                   # def includes_values
+          get_value(#{name.inspect})         #   get_value(:includes)
         end                                  # end
-      CODE
-    end
 
-    Relation::SINGLE_VALUE_METHODS.each do |name|
-      class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}_value=(value)            # def readonly_value=(value)
-          assert_mutability!                 #   assert_mutability!
-          @values[:#{name}] = value          #   @values[:readonly] = value
+        def #{method_name}=(value)           # def includes_values=(value)
+          set_value(#{name.inspect}, value)  #   set_value(:includes, value)
         end                                  # end
       CODE
     end
 
-    Relation::CLAUSE_METHODS.each do |name|
-      class_eval <<-CODE, __FILE__, __LINE__ + 1
-        def #{name}_clause                           # def where_clause
-          @values[:#{name}] || new_#{name}_clause    #   @values[:where] || new_where_clause
-        end                                          # end
-                                                     #
-        def #{name}_clause=(value)                   # def where_clause=(value)
-          assert_mutability!                         #   assert_mutability!
-          @values[:#{name}] = value                  #   @values[:where] = value
-        end                                          # end
-      CODE
-    end
-
-    def bound_attributes
-      from_clause.binds + arel.bind_values + where_clause.binds + having_clause.binds
-    end
-
-    def create_with_value # :nodoc:
-      @values[:create_with] || {}
-    end
-
     alias extensions extending_values
 
     # Specify relationships to be included in the result set. For
@@ -113,7 +88,7 @@ module ActiveRecord
     #
     # allows you to access the +address+ attribute of the +User+ model without
     # firing an additional query. This will often result in a
-    # performance improvement over a simple +join+.
+    # performance improvement over a simple join.
     #
     # You can also specify multiple relationships, like this:
     #
@@ -134,7 +109,7 @@ module ActiveRecord
     #
     #   User.includes(:posts).where('posts.name = ?', 'example').references(:posts)
     #
-    # Note that +includes+ works with association names while +references+ needs
+    # Note that #includes works with association names while #references needs
     # the actual table name.
     def includes(*args)
       check_if_method_has_arguments!(:includes, args)
@@ -152,9 +127,9 @@ module ActiveRecord
     # Forces eager loading by performing a LEFT OUTER JOIN on +args+:
     #
     #   User.eager_load(:posts)
-    #   => SELECT "users"."id" AS t0_r0, "users"."name" AS t0_r1, ...
-    #   FROM "users" LEFT OUTER JOIN "posts" ON "posts"."user_id" =
-    #   "users"."id"
+    #   # SELECT "users"."id" AS t0_r0, "users"."name" AS t0_r1, ...
+    #   # FROM "users" LEFT OUTER JOIN "posts" ON "posts"."user_id" =
+    #   # "users"."id"
     def eager_load(*args)
       check_if_method_has_arguments!(:eager_load, args)
       spawn.eager_load!(*args)
@@ -165,10 +140,10 @@ module ActiveRecord
       self
     end
 
-    # Allows preloading of +args+, in the same way that +includes+ does:
+    # Allows preloading of +args+, in the same way that #includes does:
     #
     #   User.preload(:posts)
-    #   => SELECT "posts".* FROM "posts" WHERE "posts"."user_id" IN (1, 2, 3)
+    #   # SELECT "posts".* FROM "posts" WHERE "posts"."user_id" IN (1, 2, 3)
     def preload(*args)
       check_if_method_has_arguments!(:preload, args)
       spawn.preload!(*args)
@@ -181,14 +156,14 @@ module ActiveRecord
 
     # Use to indicate that the given +table_names+ are referenced by an SQL string,
     # and should therefore be JOINed in any query rather than loaded separately.
-    # This method only works in conjunction with +includes+.
+    # This method only works in conjunction with #includes.
     # See #includes for more details.
     #
     #   User.includes(:posts).where("posts.name = 'foo'")
-    #   # => Doesn't JOIN the posts table, resulting in an error.
+    #   # Doesn't JOIN the posts table, resulting in an error.
     #
     #   User.includes(:posts).where("posts.name = 'foo'").references(:posts)
-    #   # => Query now knows the string references posts, so adds a JOIN
+    #   # Query now knows the string references posts, so adds a JOIN
     def references(*table_names)
       check_if_method_has_arguments!(:references, table_names)
       spawn.references!(*table_names)
@@ -204,12 +179,13 @@ module ActiveRecord
 
     # Works in two unique ways.
     #
-    # First: takes a block so it can be used just like Array#select.
+    # First: takes a block so it can be used just like <tt>Array#select</tt>.
     #
     #   Model.all.select { |m| m.field == value }
     #
     # This will build an array of objects from the database for the scope,
-    # converting them into an array and iterating through them using Array#select.
+    # converting them into an array and iterating through them using
+    # <tt>Array#select</tt>.
     #
     # Second: Modifies the SELECT statement for the query so that only certain
     # fields are retrieved:
@@ -237,20 +213,28 @@ module ActiveRecord
     #   # => "value"
     #
     # Accessing attributes of an object that do not have fields retrieved by a select
-    # except +id+ will throw <tt>ActiveModel::MissingAttributeError</tt>:
+    # except +id+ will throw ActiveModel::MissingAttributeError:
     #
     #   Model.select(:field).first.other_field
     #   # => ActiveModel::MissingAttributeError: missing attribute: other_field
     def select(*fields)
-      return super if block_given?
-      raise ArgumentError, 'Call this with at least one field' if fields.empty?
+      if block_given?
+        if fields.any?
+          raise ArgumentError, "`select' with block doesn't take arguments."
+        end
+
+        return super()
+      end
+
+      raise ArgumentError, "Call `select' with at least one field" if fields.empty?
       spawn._select!(*fields)
     end
 
     def _select!(*fields) # :nodoc:
+      fields.reject!(&:blank?)
       fields.flatten!
       fields.map! do |field|
-        klass.attribute_alias?(field) ? klass.attribute_alias(field) : field
+        klass.attribute_alias?(field) ? klass.attribute_alias(field).to_sym : field
       end
       self.select_values += fields
       self
@@ -259,22 +243,23 @@ module ActiveRecord
     # Allows to specify a group attribute:
     #
     #   User.group(:name)
-    #   => SELECT "users".* FROM "users" GROUP BY name
+    #   # SELECT "users".* FROM "users" GROUP BY name
     #
     # Returns an array with distinct records based on the +group+ attribute:
     #
     #   User.select([:id, :name])
-    #   => [#<User id: 1, name: "Oscar">, #<User id: 2, name: "Oscar">, #<User id: 3, name: "Foo">
+    #   # => [#<User id: 1, name: "Oscar">, #<User id: 2, name: "Oscar">, #<User id: 3, name: "Foo">]
     #
     #   User.group(:name)
-    #   => [#<User id: 3, name: "Foo", ...>, #<User id: 2, name: "Oscar", ...>]
+    #   # => [#<User id: 3, name: "Foo", ...>, #<User id: 2, name: "Oscar", ...>]
     #
     #   User.group('name AS grouped_name, age')
-    #   => [#<User id: 3, name: "Foo", age: 21, ...>, #<User id: 2, name: "Oscar", age: 21, ...>, #<User id: 5, name: "Foo", age: 23, ...>]
+    #   # => [#<User id: 3, name: "Foo", age: 21, ...>, #<User id: 2, name: "Oscar", age: 21, ...>, #<User id: 5, name: "Foo", age: 23, ...>]
     #
     # Passing in an array of attributes to group by is also supported.
+    #
     #   User.select([:id, :first_name]).group(:id, :first_name).first(3)
-    #   => [#<User id: 1, first_name: "Bill">, #<User id: 2, first_name: "Earl">, #<User id: 3, first_name: "Beto">]
+    #   # => [#<User id: 1, first_name: "Bill">, #<User id: 2, first_name: "Earl">, #<User id: 3, first_name: "Beto">]
     def group(*args)
       check_if_method_has_arguments!(:group, args)
       spawn.group!(*args)
@@ -290,27 +275,28 @@ module ActiveRecord
     # Allows to specify an order attribute:
     #
     #   User.order(:name)
-    #   => SELECT "users".* FROM "users" ORDER BY "users"."name" ASC
+    #   # SELECT "users".* FROM "users" ORDER BY "users"."name" ASC
     #
     #   User.order(email: :desc)
-    #   => SELECT "users".* FROM "users" ORDER BY "users"."email" DESC
+    #   # SELECT "users".* FROM "users" ORDER BY "users"."email" DESC
     #
     #   User.order(:name, email: :desc)
-    #   => SELECT "users".* FROM "users" ORDER BY "users"."name" ASC, "users"."email" DESC
+    #   # SELECT "users".* FROM "users" ORDER BY "users"."name" ASC, "users"."email" DESC
     #
     #   User.order('name')
-    #   => SELECT "users".* FROM "users" ORDER BY name
+    #   # SELECT "users".* FROM "users" ORDER BY name
     #
     #   User.order('name DESC')
-    #   => SELECT "users".* FROM "users" ORDER BY name DESC
+    #   # SELECT "users".* FROM "users" ORDER BY name DESC
     #
     #   User.order('name DESC, email')
-    #   => SELECT "users".* FROM "users" ORDER BY name DESC, email
+    #   # SELECT "users".* FROM "users" ORDER BY name DESC, email
     def order(*args)
       check_if_method_has_arguments!(:order, args)
       spawn.order!(*args)
     end
 
+    # Same as #order but operates on relation in-place instead of copying.
     def order!(*args) # :nodoc:
       preprocess_order_args(args)
 
@@ -332,6 +318,7 @@ module ActiveRecord
       spawn.reorder!(*args)
     end
 
+    # Same as #reorder but operates on relation in-place instead of copying.
     def reorder!(*args) # :nodoc:
       preprocess_order_args(args)
 
@@ -341,8 +328,8 @@ module ActiveRecord
     end
 
     VALID_UNSCOPING_VALUES = Set.new([:where, :select, :group, :order, :lock,
-                                     :limit, :offset, :joins, :includes, :from,
-                                     :readonly, :having])
+                                     :limit, :offset, :joins, :left_outer_joins,
+                                     :includes, :from, :readonly, :having])
 
     # Removes an unwanted relation that is already defined on a chain of relations.
     # This is useful when passing around chains of relations and would like to
@@ -357,15 +344,15 @@ module ActiveRecord
     #   User.order('email DESC').select('id').where(name: "John")
     #       .unscope(:order, :select, :where) == User.all
     #
-    # One can additionally pass a hash as an argument to unscope specific :where values.
+    # One can additionally pass a hash as an argument to unscope specific +:where+ values.
     # This is done by passing a hash with a single key-value pair. The key should be
-    # :where and the value should be the where value to unscope. For example:
+    # +:where+ and the value should be the where value to unscope. For example:
     #
     #   User.where(name: "John", active: true).unscope(where: :name)
     #       == User.where(active: true)
     #
-    # This method is similar to <tt>except</tt>, but unlike
-    # <tt>except</tt>, it persists across merges:
+    # This method is similar to #except, but unlike
+    # #except, it persists across merges:
     #
     #   User.order('email').merge(User.except(:order))
     #       == User.order('email')
@@ -375,7 +362,7 @@ module ActiveRecord
     #
     # This means it can be used in association definitions:
     #
-    #   has_many :comments, -> { unscope where: :trashed }
+    #   has_many :comments, -> { unscope(where: :trashed) }
     #
     def unscope(*args)
       check_if_method_has_arguments!(:unscope, args)
@@ -389,7 +376,11 @@ module ActiveRecord
       args.each do |scope|
         case scope
         when Symbol
-          symbol_unscoping(scope)
+          scope = :left_outer_joins if scope == :left_joins
+          if !VALID_UNSCOPING_VALUES.include?(scope)
+            raise ArgumentError, "Called unscope() with invalid unscoping argument ':#{scope}'. Valid arguments are :#{VALID_UNSCOPING_VALUES.to_a.join(", :")}."
+          end
+          set_value(scope, DEFAULT_VALUES[scope])
         when Hash
           scope.each do |key, target_value|
             if key != :where
@@ -407,15 +398,35 @@ module ActiveRecord
       self
     end
 
-    # Performs a joins on +args+:
+    # Performs a joins on +args+. The given symbol(s) should match the name of
+    # the association(s).
     #
     #   User.joins(:posts)
-    #   => SELECT "users".* FROM "users" INNER JOIN "posts" ON "posts"."user_id" = "users"."id"
+    #   # SELECT "users".*
+    #   # FROM "users"
+    #   # INNER JOIN "posts" ON "posts"."user_id" = "users"."id"
+    #
+    # Multiple joins:
+    #
+    #   User.joins(:posts, :account)
+    #   # SELECT "users".*
+    #   # FROM "users"
+    #   # INNER JOIN "posts" ON "posts"."user_id" = "users"."id"
+    #   # INNER JOIN "accounts" ON "accounts"."id" = "users"."account_id"
+    #
+    # Nested joins:
+    #
+    #   User.joins(posts: [:comments])
+    #   # SELECT "users".*
+    #   # FROM "users"
+    #   # INNER JOIN "posts" ON "posts"."user_id" = "users"."id"
+    #   # INNER JOIN "comments" "comments_posts"
+    #   #   ON "comments_posts"."post_id" = "posts"."id"
     #
     # You can use strings in order to customize your joins:
     #
     #   User.joins("LEFT JOIN bookmarks ON bookmarks.bookmarkable_type = 'Post' AND bookmarks.user_id = users.id")
-    #   => SELECT "users".* FROM "users" LEFT JOIN bookmarks ON bookmarks.bookmarkable_type = 'Post' AND bookmarks.user_id = users.id
+    #   # SELECT "users".* FROM "users" LEFT JOIN bookmarks ON bookmarks.bookmarkable_type = 'Post' AND bookmarks.user_id = users.id
     def joins(*args)
       check_if_method_has_arguments!(:joins, args)
       spawn.joins!(*args)
@@ -428,6 +439,24 @@ module ActiveRecord
       self
     end
 
+    # Performs a left outer joins on +args+:
+    #
+    #   User.left_outer_joins(:posts)
+    #   => SELECT "users".* FROM "users" LEFT OUTER JOIN "posts" ON "posts"."user_id" = "users"."id"
+    #
+    def left_outer_joins(*args)
+      check_if_method_has_arguments!(__callee__, args)
+      spawn.left_outer_joins!(*args)
+    end
+    alias :left_joins :left_outer_joins
+
+    def left_outer_joins!(*args) # :nodoc:
+      args.compact!
+      args.flatten!
+      self.left_outer_joins_values += args
+      self
+    end
+
     # Returns a new relation, which is the result of filtering the current relation
     # according to the conditions in the arguments.
     #
@@ -471,7 +500,7 @@ module ActiveRecord
     # than the previous methods; you are responsible for ensuring that the values in the template
     # are properly quoted. The values are passed to the connector for quoting, but the caller
     # is responsible for ensuring they are enclosed in quotes in the resulting SQL. After quoting,
-    # the values are inserted using the same escapes as the Ruby core method <tt>Kernel::sprintf</tt>.
+    # the values are inserted using the same escapes as the Ruby core method +Kernel::sprintf+.
     #
     #   User.where(["name = '%s' and email = '%s'", "Joe", "joe@example.com"])
     #   # SELECT * FROM users WHERE name = 'Joe' AND email = 'joe@example.com';
@@ -548,7 +577,7 @@ module ActiveRecord
     # If the condition is any blank-ish object, then #where is a no-op and returns
     # the current relation.
     def where(opts = :chain, *rest)
-      if opts == :chain
+      if :chain == opts
         WhereChain.new(spawn)
       elsif opts.blank?
         self
@@ -558,23 +587,25 @@ module ActiveRecord
     end
 
     def where!(opts, *rest) # :nodoc:
-      if Hash === opts
-        opts = sanitize_forbidden_attributes(opts)
-        references!(PredicateBuilder.references(opts))
-      end
-
+      opts = sanitize_forbidden_attributes(opts)
+      references!(PredicateBuilder.references(opts)) if Hash === opts
       self.where_clause += where_clause_factory.build(opts, rest)
       self
     end
 
     # Allows you to change a previously set where condition for a given attribute, instead of appending to that condition.
     #
-    #   Post.where(trashed: true).where(trashed: false)                       # => WHERE `trashed` = 1 AND `trashed` = 0
-    #   Post.where(trashed: true).rewhere(trashed: false)                     # => WHERE `trashed` = 0
-    #   Post.where(active: true).where(trashed: true).rewhere(trashed: false) # => WHERE `active` = 1 AND `trashed` = 0
+    #   Post.where(trashed: true).where(trashed: false)
+    #   # WHERE `trashed` = 1 AND `trashed` = 0
     #
-    # This is short-hand for unscope(where: conditions.keys).where(conditions). Note that unlike reorder, we're only unscoping
-    # the named conditions -- not the entire where statement.
+    #   Post.where(trashed: true).rewhere(trashed: false)
+    #   # WHERE `trashed` = 0
+    #
+    #   Post.where(active: true).where(trashed: true).rewhere(trashed: false)
+    #   # WHERE `active` = 1 AND `trashed` = 0
+    #
+    # This is short-hand for <tt>unscope(where: conditions.keys).where(conditions)</tt>.
+    # Note that unlike reorder, we're only unscoping the named conditions -- not the entire where statement.
     def rewhere(conditions)
       unscope(where: conditions.keys).where(conditions)
     end
@@ -583,33 +614,34 @@ module ActiveRecord
     # argument.
     #
     # The two relations must be structurally compatible: they must be scoping the same model, and
-    # they must differ only by +where+ (if no +group+ has been defined) or +having+ (if a +group+ is
-    # present). Neither relation may have a +limit+, +offset+, or +distinct+ set.
+    # they must differ only by #where (if no #group has been defined) or #having (if a #group is
+    # present). Neither relation may have a #limit, #offset, or #distinct set.
     #
-    #    Post.where("id = 1").or(Post.where("id = 2"))
-    #    # SELECT `posts`.* FROM `posts`  WHERE (('id = 1' OR 'id = 2'))
+    #    Post.where("id = 1").or(Post.where("author_id = 3"))
+    #    # SELECT `posts`.* FROM `posts` WHERE ((id = 1) OR (author_id = 3))
     #
     def or(other)
+      unless other.is_a? Relation
+        raise ArgumentError, "You have passed #{other.class.name} object to #or. Pass an ActiveRecord::Relation object instead."
+      end
+
       spawn.or!(other)
     end
 
     def or!(other) # :nodoc:
-      unless structurally_compatible_for_or?(other)
-        raise ArgumentError, 'Relation passed to #or must be structurally compatible'
+      incompatible_values = structurally_incompatible_values_for_or(other)
+
+      unless incompatible_values.empty?
+        raise ArgumentError, "Relation passed to #or must be structurally compatible. Incompatible values: #{incompatible_values}"
       end
 
       self.where_clause = self.where_clause.or(other.where_clause)
-      self.having_clause = self.having_clause.or(other.having_clause)
+      self.having_clause = having_clause.or(other.having_clause)
+      self.references_values += other.references_values
 
       self
     end
 
-    private def structurally_compatible_for_or?(other) # :nodoc:
-      Relation::SINGLE_VALUE_METHODS.all? { |m| send("#{m}_value") == other.send("#{m}_value") } &&
-        (Relation::MULTI_VALUE_METHODS - [:extending]).all? { |m| send("#{m}_values") == other.send("#{m}_values") } &&
-        (Relation::CLAUSE_METHODS - [:having, :where]).all? { |m| send("#{m}_clause") != other.send("#{m}_clause") }
-    end
-
     # Allows to specify a HAVING clause. Note that you can't use HAVING
     # without also specifying a GROUP clause.
     #
@@ -619,6 +651,7 @@ module ActiveRecord
     end
 
     def having!(opts, *rest) # :nodoc:
+      opts = sanitize_forbidden_attributes(opts)
       references!(PredicateBuilder.references(opts)) if Hash === opts
 
       self.having_clause += having_clause_factory.build(opts, rest)
@@ -656,7 +689,7 @@ module ActiveRecord
     end
 
     # Specifies locking settings (default to +true+). For more information
-    # on locking, please see +ActiveRecord::Locking+.
+    # on locking, please see ActiveRecord::Locking.
     def lock(locks = true)
       spawn.lock!(locks)
     end
@@ -687,7 +720,7 @@ module ActiveRecord
     # For example:
     #
     #   @posts = current_user.visible_posts.where(name: params[:name])
-    #   # => the visible_posts method is expected to return a chainable Relation
+    #   # the visible_posts method is expected to return a chainable Relation
     #
     #   def visible_posts
     #     case role
@@ -701,7 +734,7 @@ module ActiveRecord
     #   end
     #
     def none
-      where("1=0").extending!(NullRelation)
+      spawn.none!
     end
 
     def none! # :nodoc:
@@ -713,7 +746,7 @@ module ActiveRecord
     #
     #   users = User.readonly
     #   users.first.save
-    #   => ActiveRecord::ReadOnlyRecord: ActiveRecord::ReadOnlyRecord
+    #   => ActiveRecord::ReadOnlyRecord: User is marked as readonly
     def readonly(value = true)
       spawn.readonly!(value)
     end
@@ -732,7 +765,7 @@ module ActiveRecord
     #   users = users.create_with(name: 'DHH')
     #   users.new.name # => 'DHH'
     #
-    # You can pass +nil+ to +create_with+ to reset attributes:
+    # You can pass +nil+ to #create_with to reset attributes:
     #
     #   users = users.create_with(nil)
     #   users.new.name # => 'Oscar'
@@ -745,7 +778,7 @@ module ActiveRecord
         value = sanitize_forbidden_attributes(value)
         self.create_with_value = create_with_value.merge(value)
       else
-        self.create_with_value = {}
+        self.create_with_value = FROZEN_EMPTY_HASH
       end
 
       self
@@ -754,15 +787,15 @@ module ActiveRecord
     # Specifies table from which the records will be fetched. For example:
     #
     #   Topic.select('title').from('posts')
-    #   # => SELECT title FROM posts
+    #   # SELECT title FROM posts
     #
     # Can accept other relation objects. For example:
     #
     #   Topic.select('title').from(Topic.approved)
-    #   # => SELECT title FROM (SELECT * FROM topics WHERE approved = 't') subquery
+    #   # SELECT title FROM (SELECT * FROM topics WHERE approved = 't') subquery
     #
     #   Topic.select('a.title').from(Topic.approved, :a)
-    #   # => SELECT a.title FROM (SELECT * FROM topics WHERE approved = 't') a
+    #   # SELECT a.title FROM (SELECT * FROM topics WHERE approved = 't') a
     #
     def from(value, subquery_name = nil)
       spawn.from!(value, subquery_name)
@@ -776,26 +809,22 @@ module ActiveRecord
     # Specifies whether the records should be unique or not. For example:
     #
     #   User.select(:name)
-    #   # => Might return two records with the same name
+    #   # Might return two records with the same name
     #
     #   User.select(:name).distinct
-    #   # => Returns 1 record per distinct name
+    #   # Returns 1 record per distinct name
     #
     #   User.select(:name).distinct.distinct(false)
-    #   # => You can also remove the uniqueness
+    #   # You can also remove the uniqueness
     def distinct(value = true)
       spawn.distinct!(value)
     end
-    alias uniq distinct
-    deprecate uniq: :distinct
 
     # Like #distinct, but modifies relation in place.
     def distinct!(value = true) # :nodoc:
       self.distinct_value = value
       self
     end
-    alias uniq! distinct!
-    deprecate uniq!: :distinct!
 
     # Used to extend a scope with additional methods, either through
     # a module or through a block provided.
@@ -865,247 +894,317 @@ module ActiveRecord
       self
     end
 
-    # Returns the Arel object associated with the relation.
-    def arel # :nodoc:
-      @arel ||= build_arel
+    def skip_query_cache!(value = true) # :nodoc:
+      self.skip_query_cache_value = value
+      self
     end
 
-    private
-
-    def assert_mutability!
-      raise ImmutableRelation if @loaded
-      raise ImmutableRelation if defined?(@arel) && @arel
+    def skip_preloading! # :nodoc:
+      self.skip_preloading_value = true
+      self
     end
 
-    def build_arel
-      arel = Arel::SelectManager.new(table)
+    # Returns the Arel object associated with the relation.
+    def arel(aliases = nil) # :nodoc:
+      @arel ||= build_arel(aliases)
+    end
 
-      build_joins(arel, joins_values.flatten) unless joins_values.empty?
+    private
+      # Returns a relation value with a given name
+      def get_value(name)
+        @values.fetch(name, DEFAULT_VALUES[name])
+      end
 
-      arel.where(where_clause.ast) unless where_clause.empty?
-      arel.having(having_clause.ast) unless having_clause.empty?
-      arel.take(connection.sanitize_limit(limit_value)) if limit_value
-      arel.skip(offset_value.to_i) if offset_value
-      arel.group(*arel_columns(group_values.uniq.reject(&:blank?))) unless group_values.empty?
+      # Sets the relation value with the given name
+      def set_value(name, value)
+        assert_mutability!
+        @values[name] = value
+      end
 
-      build_order(arel)
+      def assert_mutability!
+        raise ImmutableRelation if @loaded
+        raise ImmutableRelation if defined?(@arel) && @arel
+      end
 
-      build_select(arel)
+      def build_arel(aliases)
+        arel = Arel::SelectManager.new(table)
+
+        aliases = build_joins(arel, joins_values.flatten, aliases) unless joins_values.empty?
+        build_left_outer_joins(arel, left_outer_joins_values.flatten, aliases) unless left_outer_joins_values.empty?
+
+        arel.where(where_clause.ast) unless where_clause.empty?
+        arel.having(having_clause.ast) unless having_clause.empty?
+        if limit_value
+          limit_attribute = ActiveModel::Attribute.with_cast_value(
+            "LIMIT",
+            connection.sanitize_limit(limit_value),
+            Type.default_value,
+          )
+          arel.take(Arel::Nodes::BindParam.new(limit_attribute))
+        end
+        if offset_value
+          offset_attribute = ActiveModel::Attribute.with_cast_value(
+            "OFFSET",
+            offset_value.to_i,
+            Type.default_value,
+          )
+          arel.skip(Arel::Nodes::BindParam.new(offset_attribute))
+        end
+        arel.group(*arel_columns(group_values.uniq.reject(&:blank?))) unless group_values.empty?
 
-      arel.distinct(distinct_value)
-      arel.from(build_from) unless from_clause.empty?
-      arel.lock(lock_value) if lock_value
+        build_order(arel)
 
-      arel
-    end
+        build_select(arel)
 
-    def symbol_unscoping(scope)
-      if !VALID_UNSCOPING_VALUES.include?(scope)
-        raise ArgumentError, "Called unscope() with invalid unscoping argument ':#{scope}'. Valid arguments are :#{VALID_UNSCOPING_VALUES.to_a.join(", :")}."
-      end
+        arel.distinct(distinct_value)
+        arel.from(build_from) unless from_clause.empty?
+        arel.lock(lock_value) if lock_value
 
-      clause_method = Relation::CLAUSE_METHODS.include?(scope)
-      multi_val_method = Relation::MULTI_VALUE_METHODS.include?(scope)
-      if clause_method
-        unscope_code = "#{scope}_clause="
-      else
-        unscope_code = "#{scope}_value#{'s' if multi_val_method}="
+        arel
       end
 
-      case scope
-      when :order
-        result = []
-      else
-        result = [] if multi_val_method
+      def build_from
+        opts = from_clause.value
+        name = from_clause.name
+        case opts
+        when Relation
+          if opts.eager_loading?
+            opts = opts.send(:apply_join_dependency)
+          end
+          name ||= "subquery"
+          opts.arel.as(name.to_s)
+        else
+          opts
+        end
       end
 
-      self.send(unscope_code, result)
-    end
-
-    def association_for_table(table_name)
-      table_name = table_name.to_s
-      @klass._reflect_on_association(table_name) ||
-        @klass._reflect_on_association(table_name.singularize)
-    end
+      def build_left_outer_joins(manager, outer_joins, aliases)
+        buckets = outer_joins.group_by do |join|
+          case join
+          when Hash, Symbol, Array
+            :association_join
+          when ActiveRecord::Associations::JoinDependency
+            :stashed_join
+          else
+            raise ArgumentError, "only Hash, Symbol and Array are allowed"
+          end
+        end
 
-    def build_from
-      opts = from_clause.value
-      name = from_clause.name
-      case opts
-      when Relation
-        name ||= 'subquery'
-        opts.arel.as(name.to_s)
-      else
-        opts
+        build_join_query(manager, buckets, Arel::Nodes::OuterJoin, aliases)
       end
-    end
 
-    def build_joins(manager, joins)
-      buckets = joins.group_by do |join|
-        case join
-        when String
-          :string_join
-        when Hash, Symbol, Array
-          :association_join
-        when ActiveRecord::Associations::JoinDependency
-          :stashed_join
-        when Arel::Nodes::Join
-          :join_node
-        else
-          raise 'unknown class: %s' % join.class.name
+      def build_joins(manager, joins, aliases)
+        buckets = joins.group_by do |join|
+          case join
+          when String
+            :string_join
+          when Hash, Symbol, Array
+            :association_join
+          when ActiveRecord::Associations::JoinDependency
+            :stashed_join
+          when Arel::Nodes::Join
+            :join_node
+          else
+            raise "unknown class: %s" % join.class.name
+          end
         end
-      end
-      buckets.default = []
 
-      association_joins         = buckets[:association_join]
-      stashed_association_joins = buckets[:stashed_join]
-      join_nodes                = buckets[:join_node].uniq
-      string_joins              = buckets[:string_join].map(&:strip).uniq
+        build_join_query(manager, buckets, Arel::Nodes::InnerJoin, aliases)
+      end
 
-      join_list = join_nodes + convert_join_strings_to_ast(manager, string_joins)
+      def build_join_query(manager, buckets, join_type, aliases)
+        buckets.default = []
 
-      join_dependency = ActiveRecord::Associations::JoinDependency.new(
-        @klass,
-        association_joins,
-        join_list
-      )
+        association_joins = buckets[:association_join]
+        stashed_joins     = buckets[:stashed_join]
+        join_nodes        = buckets[:join_node].uniq
+        string_joins      = buckets[:string_join].map(&:strip).uniq
 
-      join_infos = join_dependency.join_constraints stashed_association_joins
+        join_list = join_nodes + convert_join_strings_to_ast(string_joins)
+        alias_tracker = alias_tracker(join_list, aliases)
 
-      join_infos.each do |info|
-        info.joins.each { |join| manager.from(join) }
-        manager.bind_values.concat info.binds
-      end
+        join_dependency = construct_join_dependency(association_joins)
 
-      manager.join_sources.concat(join_list)
+        joins = join_dependency.join_constraints(stashed_joins, join_type, alias_tracker)
+        joins.each { |join| manager.from(join) }
 
-      manager
-    end
+        manager.join_sources.concat(join_list)
 
-    def convert_join_strings_to_ast(table, joins)
-      joins
-        .flatten
-        .reject(&:blank?)
-        .map { |join| table.create_string_join(Arel.sql(join)) }
-    end
+        alias_tracker.aliases
+      end
 
-    def build_select(arel)
-      if select_values.any?
-        arel.project(*arel_columns(select_values.uniq))
-      else
-        arel.project(@klass.arel_table[Arel.star])
+      def convert_join_strings_to_ast(joins)
+        joins
+          .flatten
+          .reject(&:blank?)
+          .map { |join| table.create_string_join(Arel.sql(join)) }
       end
-    end
 
-    def arel_columns(columns)
-      columns.map do |field|
-        if (Symbol === field || String === field) && columns_hash.key?(field.to_s) && !from_clause.value
-          arel_table[field]
-        elsif Symbol === field
-          connection.quote_table_name(field.to_s)
+      def build_select(arel)
+        if select_values.any?
+          arel.project(*arel_columns(select_values.uniq))
+        elsif klass.ignored_columns.any?
+          arel.project(*klass.column_names.map { |field| arel_attribute(field) })
         else
-          field
+          arel.project(table[Arel.star])
         end
       end
-    end
 
-    def reverse_sql_order(order_query)
-      order_query = ["#{quoted_table_name}.#{quoted_primary_key} ASC"] if order_query.empty?
-
-      order_query.flat_map do |o|
-        case o
-        when Arel::Nodes::Ordering
-          o.reverse
-        when String
-          o.to_s.split(',').map! do |s|
-            s.strip!
-            s.gsub!(/\sasc\Z/i, ' DESC') || s.gsub!(/\sdesc\Z/i, ' ASC') || s.concat(' DESC')
+      def arel_columns(columns)
+        columns.flat_map do |field|
+          if (Symbol === field || String === field) && (klass.has_attribute?(field) || klass.attribute_alias?(field)) && !from_clause.value
+            arel_attribute(field)
+          elsif Symbol === field
+            connection.quote_table_name(field.to_s)
+          elsif Proc === field
+            field.call
+          else
+            field
           end
-        else
-          o
         end
       end
-    end
 
-    def build_order(arel)
-      orders = order_values.uniq
-      orders.reject!(&:blank?)
+      def reverse_sql_order(order_query)
+        if order_query.empty?
+          return [arel_attribute(primary_key).desc] if primary_key
+          raise IrreversibleOrderError,
+            "Relation has no current order and table has no primary key to be used as default order"
+        end
 
-      arel.order(*orders) unless orders.empty?
-    end
+        order_query.flat_map do |o|
+          case o
+          when Arel::Attribute
+            o.desc
+          when Arel::Nodes::Ordering
+            o.reverse
+          when String
+            if does_not_support_reverse?(o)
+              raise IrreversibleOrderError, "Order #{o.inspect} can not be reversed automatically"
+            end
+            o.split(",").map! do |s|
+              s.strip!
+              s.gsub!(/\sasc\Z/i, " DESC") || s.gsub!(/\sdesc\Z/i, " ASC") || (s << " DESC")
+            end
+          else
+            o
+          end
+        end
+      end
 
-    VALID_DIRECTIONS = [:asc, :desc, :ASC, :DESC,
-                        'asc', 'desc', 'ASC', 'DESC'] # :nodoc:
+      def does_not_support_reverse?(order)
+        # Account for String subclasses like Arel::Nodes::SqlLiteral that
+        # override methods like #count.
+        order = String.new(order) unless order.instance_of?(String)
 
-    def validate_order_args(args)
-      args.each do |arg|
-        next unless arg.is_a?(Hash)
-        arg.each do |_key, value|
-          raise ArgumentError, "Direction \"#{value}\" is invalid. Valid " \
-                               "directions are: #{VALID_DIRECTIONS.inspect}" unless VALID_DIRECTIONS.include?(value)
-        end
+        # Uses SQL function with multiple arguments.
+        (order.include?(",") && order.split(",").find { |section| section.count("(") != section.count(")") }) ||
+          # Uses "nulls first" like construction.
+          /nulls (first|last)\Z/i.match?(order)
       end
-    end
 
-    def preprocess_order_args(order_args)
-      order_args.flatten!
-      validate_order_args(order_args)
+      def build_order(arel)
+        orders = order_values.uniq
+        orders.reject!(&:blank?)
 
-      references = order_args.grep(String)
-      references.map! { |arg| arg =~ /^([a-zA-Z]\w*)\.(\w+)/ && $1 }.compact!
-      references!(references) if references.any?
+        arel.order(*orders) unless orders.empty?
+      end
 
-      # if a symbol is given we prepend the quoted table name
-      order_args.map! do |arg|
-        case arg
-        when Symbol
-          arg = klass.attribute_alias(arg) if klass.attribute_alias?(arg)
-          table[arg].asc
-        when Hash
-          arg.map { |field, dir|
-            field = klass.attribute_alias(field) if klass.attribute_alias?(field)
-            table[field].send(dir.downcase)
-          }
-        else
-          arg
+      VALID_DIRECTIONS = [:asc, :desc, :ASC, :DESC,
+                          "asc", "desc", "ASC", "DESC"].to_set # :nodoc:
+
+      def validate_order_args(args)
+        args.each do |arg|
+          next unless arg.is_a?(Hash)
+          arg.each do |_key, value|
+            unless VALID_DIRECTIONS.include?(value)
+              raise ArgumentError,
+                "Direction \"#{value}\" is invalid. Valid directions are: #{VALID_DIRECTIONS.to_a.inspect}"
+            end
+          end
         end
-      end.flatten!
-    end
+      end
 
-    # Checks to make sure that the arguments are not blank. Note that if some
-    # blank-like object were initially passed into the query method, then this
-    # method will not raise an error.
-    #
-    # Example:
-    #
-    #    Post.references()   # => raises an error
-    #    Post.references([]) # => does not raise an error
-    #
-    # This particular method should be called with a method_name and the args
-    # passed into that method as an input. For example:
-    #
-    # def references(*args)
-    #   check_if_method_has_arguments!("references", args)
-    #   ...
-    # end
-    def check_if_method_has_arguments!(method_name, args)
-      if args.blank?
-        raise ArgumentError, "The method .#{method_name}() must contain arguments."
+      def preprocess_order_args(order_args)
+        order_args.map! do |arg|
+          klass.sanitize_sql_for_order(arg)
+        end
+        order_args.flatten!
+
+        @klass.disallow_raw_sql!(
+          order_args.flat_map { |a| a.is_a?(Hash) ? a.keys : a },
+          permit: AttributeMethods::ClassMethods::COLUMN_NAME_WITH_ORDER
+        )
+
+        validate_order_args(order_args)
+
+        references = order_args.grep(String)
+        references.map! { |arg| arg =~ /^\W?(\w+)\W?\./ && $1 }.compact!
+        references!(references) if references.any?
+
+        # if a symbol is given we prepend the quoted table name
+        order_args.map! do |arg|
+          case arg
+          when Symbol
+            arel_attribute(arg).asc
+          when Hash
+            arg.map { |field, dir|
+              case field
+              when Arel::Nodes::SqlLiteral
+                field.send(dir.downcase)
+              else
+                arel_attribute(field).send(dir.downcase)
+              end
+            }
+          else
+            arg
+          end
+        end.flatten!
       end
-    end
 
-    def new_where_clause
-      Relation::WhereClause.empty
-    end
-    alias new_having_clause new_where_clause
+      # Checks to make sure that the arguments are not blank. Note that if some
+      # blank-like object were initially passed into the query method, then this
+      # method will not raise an error.
+      #
+      # Example:
+      #
+      #    Post.references()   # raises an error
+      #    Post.references([]) # does not raise an error
+      #
+      # This particular method should be called with a method_name and the args
+      # passed into that method as an input. For example:
+      #
+      # def references(*args)
+      #   check_if_method_has_arguments!("references", args)
+      #   ...
+      # end
+      def check_if_method_has_arguments!(method_name, args)
+        if args.blank?
+          raise ArgumentError, "The method .#{method_name}() must contain arguments."
+        end
+      end
 
-    def where_clause_factory
-      @where_clause_factory ||= Relation::WhereClauseFactory.new(klass, predicate_builder)
-    end
-    alias having_clause_factory where_clause_factory
+      STRUCTURAL_OR_METHODS = Relation::VALUE_METHODS - [:extending, :where, :having, :unscope, :references]
+      def structurally_incompatible_values_for_or(other)
+        values = other.values
+        STRUCTURAL_OR_METHODS.reject do |method|
+          get_value(method) == values.fetch(method, DEFAULT_VALUES[method])
+        end
+      end
 
-    def new_from_clause
-      Relation::FromClause.empty
-    end
+      def where_clause_factory
+        @where_clause_factory ||= Relation::WhereClauseFactory.new(klass, predicate_builder)
+      end
+      alias having_clause_factory where_clause_factory
+
+      DEFAULT_VALUES = {
+        create_with: FROZEN_EMPTY_HASH,
+        where: Relation::WhereClause.empty,
+        having: Relation::WhereClause.empty,
+        from: Relation::FromClause.empty
+      }
+
+      Relation::MULTI_VALUE_METHODS.each do |value|
+        DEFAULT_VALUES[value] ||= FROZEN_EMPTY_ARRAY
+      end
   end
 end
diff --git a/activerecord/lib/active_record/relation/record_fetch_warning.rb b/activerecord/lib/active_record/relation/record_fetch_warning.rb
index 14e1bf89fa..a7d07d23e1 100644
--- a/activerecord/lib/active_record/relation/record_fetch_warning.rb
+++ b/activerecord/lib/active_record/relation/record_fetch_warning.rb
@@ -1,16 +1,18 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class Relation
     module RecordFetchWarning
       # When this module is prepended to ActiveRecord::Relation and
-      # `config.active_record.warn_on_records_fetched_greater_than` is
+      # +config.active_record.warn_on_records_fetched_greater_than+ is
       # set to an integer, if the number of records a query returns is
-      # greater than the value of `warn_on_records_fetched_greater_than`,
+      # greater than the value of +warn_on_records_fetched_greater_than+,
       # a warning is logged. This allows for the detection of queries that
       # return a large number of records, which could cause memory bloat.
       #
       # In most cases, fetching large number of records can be performed
       # efficiently using the ActiveRecord::Batches methods.
-      # See active_record/lib/relation/batches.rb for more information.
+      # See ActiveRecord::Batches for more information.
       def exec_queries
         QueryRegistry.reset
 
@@ -23,23 +25,23 @@ module ActiveRecord
         end
       end
 
-      ActiveSupport::Notifications.subscribe("sql.active_record") do |*args|
-        payload = args.last
-
+      # :stopdoc:
+      ActiveSupport::Notifications.subscribe("sql.active_record") do |*, payload|
         QueryRegistry.queries << payload[:sql]
       end
+      # :startdoc:
 
       class QueryRegistry # :nodoc:
         extend ActiveSupport::PerThreadRegistry
 
-        attr_accessor :queries
+        attr_reader :queries
 
         def initialize
-          reset
+          @queries = []
         end
 
         def reset
-          @queries = []
+          @queries.clear
         end
       end
     end
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index 70da37fa84..562e04194c 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -1,17 +1,19 @@
-require 'active_support/core_ext/hash/except'
-require 'active_support/core_ext/hash/slice'
-require 'active_record/relation/merger'
+# frozen_string_literal: true
+
+require "active_support/core_ext/hash/except"
+require "active_support/core_ext/hash/slice"
+require "active_record/relation/merger"
 
 module ActiveRecord
   module SpawnMethods
-
     # This is overridden by Associations::CollectionProxy
     def spawn #:nodoc:
       clone
     end
 
-    # Merges in the conditions from <tt>other</tt>, if <tt>other</tt> is an <tt>ActiveRecord::Relation</tt>.
+    # Merges in the conditions from <tt>other</tt>, if <tt>other</tt> is an ActiveRecord::Relation.
     # Returns an array representing the intersection of the resulting records with <tt>other</tt>, if <tt>other</tt> is an array.
+    #
     #   Post.where(published: true).joins(:comments).merge( Comment.where(spam: false) )
     #   # Performs a single join query with both where conditions.
     #
@@ -28,7 +30,7 @@ module ActiveRecord
     # This is mainly intended for sharing common conditions between multiple associations.
     def merge(other)
       if other.is_a?(Array)
-        to_a & other
+        records & other
       elsif other
         spawn.merge!(other)
       else
@@ -37,11 +39,14 @@ module ActiveRecord
     end
 
     def merge!(other) # :nodoc:
-      if !other.is_a?(Relation) && other.respond_to?(:to_proc)
+      if other.is_a?(Hash)
+        Relation::HashMerger.new(self, other).merge
+      elsif other.is_a?(Relation)
+        Relation::Merger.new(self, other).merge
+      elsif other.respond_to?(:to_proc)
         instance_exec(&other)
       else
-        klass = other.is_a?(Hash) ? Relation::HashMerger : Relation::Merger
-        klass.new(self, other).merge
+        raise ArgumentError, "#{other.inspect} is not an ActiveRecord::Relation"
       end
     end
 
@@ -63,8 +68,8 @@ module ActiveRecord
 
     private
 
-      def relation_with(values) # :nodoc:
-        result = Relation.create(klass, table, predicate_builder, values)
+      def relation_with(values)
+        result = Relation.create(klass, values: values)
         result.extend(*extending_values) if extending_values.any?
         result
       end
diff --git a/activerecord/lib/active_record/relation/where_clause.rb b/activerecord/lib/active_record/relation/where_clause.rb
index 1f000b3f0f..e225628bae 100644
--- a/activerecord/lib/active_record/relation/where_clause.rb
+++ b/activerecord/lib/active_record/relation/where_clause.rb
@@ -1,68 +1,63 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class Relation
     class WhereClause # :nodoc:
-      attr_reader :binds
-
       delegate :any?, :empty?, to: :predicates
 
-      def initialize(predicates, binds)
+      def initialize(predicates)
         @predicates = predicates
-        @binds = binds
       end
 
       def +(other)
         WhereClause.new(
           predicates + other.predicates,
-          binds + other.binds,
+        )
+      end
+
+      def -(other)
+        WhereClause.new(
+          predicates - other.predicates,
         )
       end
 
       def merge(other)
         WhereClause.new(
           predicates_unreferenced_by(other) + other.predicates,
-          non_conflicting_binds(other) + other.binds,
         )
       end
 
       def except(*columns)
-        WhereClause.new(
-          predicates_except(columns),
-          binds_except(columns),
-        )
+        WhereClause.new(except_predicates(columns))
       end
 
       def or(other)
-        if empty?
-          self
-        elsif other.empty?
-          other
+        left = self - other
+        common = self - left
+        right = other - common
+
+        if left.empty? || right.empty?
+          common
         else
-          WhereClause.new(
-            [ast.or(other.ast)],
-            binds + other.binds
+          or_clause = WhereClause.new(
+            [left.ast.or(right.ast)],
           )
+          common + or_clause
         end
       end
 
       def to_h(table_name = nil)
-        equalities = predicates.grep(Arel::Nodes::Equality)
+        equalities = equalities(predicates)
         if table_name
           equalities = equalities.select do |node|
             node.left.relation.name == table_name
           end
         end
 
-        binds = self.binds.map { |attr| [attr.name, attr.value] }.to_h
-
         equalities.map { |node|
-          name = node.left.name
-          [name, binds.fetch(name.to_s) {
-            case node.right
-            when Array then node.right.map(&:val)
-            when Arel::Nodes::Casted, Arel::Nodes::Quoted
-              node.right.val
-            end
-          }]
+          name = node.left.name.to_s
+          value = extract_node_value(node.right)
+          [name, value]
         }.to_h
       end
 
@@ -72,102 +67,124 @@ module ActiveRecord
 
       def ==(other)
         other.is_a?(WhereClause) &&
-          predicates == other.predicates &&
-          binds == other.binds
+          predicates == other.predicates
       end
 
       def invert
-        WhereClause.new(inverted_predicates, binds)
+        WhereClause.new(inverted_predicates)
       end
 
       def self.empty
-        new([], [])
+        @empty ||= new([])
       end
 
       protected
 
-      attr_reader :predicates
+        attr_reader :predicates
 
-      def referenced_columns
-        @referenced_columns ||= begin
-          equality_nodes = predicates.select { |n| equality_node?(n) }
-          Set.new(equality_nodes, &:left)
+        def referenced_columns
+          @referenced_columns ||= begin
+            equality_nodes = predicates.select { |n| equality_node?(n) }
+            Set.new(equality_nodes, &:left)
+          end
         end
-      end
 
       private
+        def equalities(predicates)
+          equalities = []
+
+          predicates.each do |node|
+            case node
+            when Arel::Nodes::Equality
+              equalities << node
+            when Arel::Nodes::And
+              equalities.concat equalities(node.children)
+            end
+          end
 
-      def predicates_unreferenced_by(other)
-        predicates.reject do |n|
-          equality_node?(n) && other.referenced_columns.include?(n.left)
+          equalities
         end
-      end
 
-      def equality_node?(node)
-        node.respond_to?(:operator) && node.operator == :==
-      end
-
-      def non_conflicting_binds(other)
-        conflicts = referenced_columns & other.referenced_columns
-        conflicts.map! { |node| node.name.to_s }
-        binds.reject { |attr| conflicts.include?(attr.name) }
-      end
+        def predicates_unreferenced_by(other)
+          predicates.reject do |n|
+            equality_node?(n) && other.referenced_columns.include?(n.left)
+          end
+        end
 
-      def inverted_predicates
-        predicates.map { |node| invert_predicate(node) }
-      end
+        def equality_node?(node)
+          node.respond_to?(:operator) && node.operator == :==
+        end
 
-      def invert_predicate(node)
-        case node
-        when NilClass
-          raise ArgumentError, 'Invalid argument for .where.not(), got nil.'
-        when Arel::Nodes::In
-          Arel::Nodes::NotIn.new(node.left, node.right)
-        when Arel::Nodes::Equality
-          Arel::Nodes::NotEqual.new(node.left, node.right)
-        when String
-          Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new(node))
-        else
-          Arel::Nodes::Not.new(node)
+        def inverted_predicates
+          predicates.map { |node| invert_predicate(node) }
         end
-      end
 
-      def predicates_except(columns)
-        predicates.reject do |node|
+        def invert_predicate(node)
           case node
-          when Arel::Nodes::Between, Arel::Nodes::In, Arel::Nodes::NotIn, Arel::Nodes::Equality, Arel::Nodes::NotEqual, Arel::Nodes::LessThan, Arel::Nodes::LessThanOrEqual, Arel::Nodes::GreaterThan, Arel::Nodes::GreaterThanOrEqual
-            subrelation = (node.left.kind_of?(Arel::Attributes::Attribute) ? node.left : node.right)
-            columns.include?(subrelation.name.to_s)
+          when NilClass
+            raise ArgumentError, "Invalid argument for .where.not(), got nil."
+          when Arel::Nodes::In
+            Arel::Nodes::NotIn.new(node.left, node.right)
+          when Arel::Nodes::IsNotDistinctFrom
+            Arel::Nodes::IsDistinctFrom.new(node.left, node.right)
+          when Arel::Nodes::IsDistinctFrom
+            Arel::Nodes::IsNotDistinctFrom.new(node.left, node.right)
+          when Arel::Nodes::Equality
+            Arel::Nodes::NotEqual.new(node.left, node.right)
+          when String
+            Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new(node))
+          else
+            Arel::Nodes::Not.new(node)
           end
         end
-      end
 
-      def binds_except(columns)
-        binds.reject do |attr|
-          columns.include?(attr.name)
+        def except_predicates(columns)
+          predicates.reject do |node|
+            case node
+            when Arel::Nodes::Between, Arel::Nodes::In, Arel::Nodes::NotIn, Arel::Nodes::Equality, Arel::Nodes::NotEqual, Arel::Nodes::LessThan, Arel::Nodes::LessThanOrEqual, Arel::Nodes::GreaterThan, Arel::Nodes::GreaterThanOrEqual
+              subrelation = (node.left.kind_of?(Arel::Attributes::Attribute) ? node.left : node.right)
+              columns.include?(subrelation.name.to_s)
+            end
+          end
         end
-      end
 
-      def predicates_with_wrapped_sql_literals
-        non_empty_predicates.map do |node|
-          if Arel::Nodes::Equality === node
-            node
-          else
-            wrap_sql_literal(node)
+        def predicates_with_wrapped_sql_literals
+          non_empty_predicates.map do |node|
+            case node
+            when Arel::Nodes::SqlLiteral, ::String
+              wrap_sql_literal(node)
+            else node
+            end
           end
         end
-      end
 
-      def non_empty_predicates
-        predicates - ['']
-      end
+        ARRAY_WITH_EMPTY_STRING = [""]
+        def non_empty_predicates
+          predicates - ARRAY_WITH_EMPTY_STRING
+        end
 
-      def wrap_sql_literal(node)
-        if ::String === node
-          node = Arel.sql(node)
+        def wrap_sql_literal(node)
+          if ::String === node
+            node = Arel.sql(node)
+          end
+          Arel::Nodes::Grouping.new(node)
+        end
+
+        def extract_node_value(node)
+          case node
+          when Array
+            node.map { |v| extract_node_value(v) }
+          when Arel::Nodes::Casted, Arel::Nodes::Quoted
+            node.val
+          when Arel::Nodes::BindParam
+            value = node.value
+            if value.respond_to?(:value_before_type_cast)
+              value.value_before_type_cast
+            else
+              value
+            end
+          end
         end
-        Arel::Nodes::Grouping.new(node)
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/relation/where_clause_factory.rb b/activerecord/lib/active_record/relation/where_clause_factory.rb
index 0430922be3..c1b3eea9df 100644
--- a/activerecord/lib/active_record/relation/where_clause_factory.rb
+++ b/activerecord/lib/active_record/relation/where_clause_factory.rb
@@ -1,34 +1,33 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class Relation
-    class WhereClauseFactory
+    class WhereClauseFactory # :nodoc:
       def initialize(klass, predicate_builder)
         @klass = klass
         @predicate_builder = predicate_builder
       end
 
       def build(opts, other)
-        binds = []
-
         case opts
         when String, Array
-          parts = [klass.send(:sanitize_sql, other.empty? ? opts : ([opts] + other))]
+          parts = [klass.sanitize_sql(other.empty? ? opts : ([opts] + other))]
         when Hash
           attributes = predicate_builder.resolve_column_aliases(opts)
-          attributes = klass.send(:expand_hash_conditions_for_aggregates, attributes)
-
-          attributes, binds = predicate_builder.create_binds(attributes)
+          attributes.stringify_keys!
 
           parts = predicate_builder.build_from_hash(attributes)
-        else
+        when Arel::Nodes::Node
           parts = [opts]
+        else
+          raise ArgumentError, "Unsupported argument type: #{opts} (#{opts.class})"
         end
 
-        WhereClause.new(parts, binds)
+        WhereClause.new(parts)
       end
 
-      protected
-
-      attr_reader :klass, :predicate_builder
+      private
+        attr_reader :klass, :predicate_builder
     end
   end
 end
diff --git a/activerecord/lib/active_record/result.rb b/activerecord/lib/active_record/result.rb
index 500c478e65..da6d10b6ec 100644
--- a/activerecord/lib/active_record/result.rb
+++ b/activerecord/lib/active_record/result.rb
@@ -1,7 +1,10 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   ###
-  # This class encapsulates a Result returned from calling +exec_query+ on any
-  # database connection adapter. For example:
+  # This class encapsulates a result returned from calling
+  # {#exec_query}[rdoc-ref:ConnectionAdapters::DatabaseStatements#exec_query]
+  # on any database connection adapter. For example:
   #
   #   result = ActiveRecord::Base.connection.exec_query('SELECT id, title, body FROM posts')
   #   result # => #<ActiveRecord::Result:0xdeadbeef>
@@ -18,7 +21,7 @@ module ActiveRecord
   #        ]
   #
   #   # Get an array of hashes representing the result (column => value):
-  #   result.to_hash
+  #   result.to_a
   #   # => [{"id" => 1, "title" => "title_1", "body" => "body_1"},
   #         {"id" => 2, "title" => "title_2", "body" => "body_2"},
   #         ...
@@ -31,8 +34,6 @@ module ActiveRecord
   class Result
     include Enumerable
 
-    IDENTITY_TYPE = Type::Value.new # :nodoc:
-
     attr_reader :columns, :rows, :column_types
 
     def initialize(columns, rows, column_types = {})
@@ -42,10 +43,20 @@ module ActiveRecord
       @column_types = column_types
     end
 
+    # Returns true if this result set includes the column named +name+
+    def includes_column?(name)
+      @columns.include? name
+    end
+
+    # Returns the number of elements in the rows array.
     def length
       @rows.length
     end
 
+    # Calls the given block once for each element in row collection, passing
+    # row as parameter.
+    #
+    # Returns an +Enumerator+ if no block is given.
     def each
       if block_given?
         hash_rows.each { |row| yield row }
@@ -55,36 +66,62 @@ module ActiveRecord
     end
 
     def to_hash
-      hash_rows
+      ActiveSupport::Deprecation.warn(<<-MSG.squish)
+        `ActiveRecord::Result#to_hash` has been renamed to `to_a`.
+        `to_hash` is deprecated and will be removed in Rails 6.1.
+      MSG
+      to_a
     end
 
     alias :map! :map
     alias :collect! :map
 
-    # Returns true if there are no records.
+    # Returns true if there are no records, otherwise false.
     def empty?
       rows.empty?
     end
 
+    # Returns an array of hashes representing each row record.
     def to_ary
       hash_rows
     end
 
+    alias :to_a :to_ary
+
     def [](idx)
       hash_rows[idx]
     end
 
+    # Returns the first record from the rows collection.
+    # If the rows collection is empty, returns +nil+.
+    def first
+      return nil if @rows.empty?
+      Hash[@columns.zip(@rows.first)]
+    end
+
+    # Returns the last record from the rows collection.
+    # If the rows collection is empty, returns +nil+.
     def last
-      hash_rows.last
+      return nil if @rows.empty?
+      Hash[@columns.zip(@rows.last)]
     end
 
     def cast_values(type_overrides = {}) # :nodoc:
-      types = columns.map { |name| column_type(name, type_overrides) }
-      result = rows.map do |values|
-        types.zip(values).map { |type, value| type.deserialize(value) }
-      end
+      if columns.one?
+        # Separated to avoid allocating an array per row
+
+        type = column_type(columns.first, type_overrides)
 
-      columns.one? ? result.map!(&:first) : result
+        rows.map do |(value)|
+          type.deserialize(value)
+        end
+      else
+        types = columns.map { |name| column_type(name, type_overrides) }
+
+        rows.map do |values|
+          Array.new(values.size) { |i| types[i].deserialize(values[i]) }
+        end
+      end
     end
 
     def initialize_copy(other)
@@ -96,36 +133,36 @@ module ActiveRecord
 
     private
 
-    def column_type(name, type_overrides = {})
-      type_overrides.fetch(name) do
-        column_types.fetch(name, IDENTITY_TYPE)
+      def column_type(name, type_overrides = {})
+        type_overrides.fetch(name) do
+          column_types.fetch(name, Type.default_value)
+        end
       end
-    end
 
-    def hash_rows
-      @hash_rows ||=
-        begin
-          # We freeze the strings to prevent them getting duped when
-          # used as keys in ActiveRecord::Base's @attributes hash
-          columns = @columns.map { |c| c.dup.freeze }
-          @rows.map { |row|
-            # In the past we used Hash[columns.zip(row)]
-            #  though elegant, the verbose way is much more efficient
-            #  both time and memory wise cause it avoids a big array allocation
-            #  this method is called a lot and needs to be micro optimised
-            hash = {}
-
-            index = 0
-            length = columns.length
-
-            while index < length
-              hash[columns[index]] = row[index]
-              index += 1
-            end
-
-            hash
-          }
-        end
-    end
+      def hash_rows
+        @hash_rows ||=
+          begin
+            # We freeze the strings to prevent them getting duped when
+            # used as keys in ActiveRecord::Base's @attributes hash
+            columns = @columns.map(&:-@)
+            length  = columns.length
+
+            @rows.map { |row|
+              # In the past we used Hash[columns.zip(row)]
+              #  though elegant, the verbose way is much more efficient
+              #  both time and memory wise cause it avoids a big array allocation
+              #  this method is called a lot and needs to be micro optimised
+              hash = {}
+
+              index = 0
+              while index < length
+                hash[columns[index]] = row[index]
+                index += 1
+              end
+
+              hash
+            }
+          end
+      end
   end
 end
diff --git a/activerecord/lib/active_record/runtime_registry.rb b/activerecord/lib/active_record/runtime_registry.rb
index 9d605b826a..4975cb8967 100644
--- a/activerecord/lib/active_record/runtime_registry.rb
+++ b/activerecord/lib/active_record/runtime_registry.rb
@@ -1,4 +1,6 @@
-require 'active_support/per_thread_registry'
+# frozen_string_literal: true
+
+require "active_support/per_thread_registry"
 
 module ActiveRecord
   # This is a thread locals registry for Active Record. For example:
@@ -7,14 +9,14 @@ module ActiveRecord
   #
   # returns the connection handler local to the current thread.
   #
-  # See the documentation of <tt>ActiveSupport::PerThreadRegistry</tt>
+  # See the documentation of ActiveSupport::PerThreadRegistry
   # for further details.
   class RuntimeRegistry # :nodoc:
     extend ActiveSupport::PerThreadRegistry
 
-    attr_accessor :connection_handler, :sql_runtime, :connection_id
+    attr_accessor :connection_handler, :sql_runtime
 
-    [:connection_handler, :sql_runtime, :connection_id].each do |val|
+    [:connection_handler, :sql_runtime].each do |val|
       class_eval %{ def self.#{val}; instance.#{val}; end }, __FILE__, __LINE__
       class_eval %{ def self.#{val}=(x); instance.#{val}=x; end }, __FILE__, __LINE__
     end
diff --git a/activerecord/lib/active_record/sanitization.rb b/activerecord/lib/active_record/sanitization.rb
index ba75ffa5a1..3485d9e557 100644
--- a/activerecord/lib/active_record/sanitization.rb
+++ b/activerecord/lib/active_record/sanitization.rb
@@ -1,21 +1,25 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Sanitization
     extend ActiveSupport::Concern
 
     module ClassMethods
-      # Used to sanitize objects before they're used in an SQL SELECT statement. Delegates to <tt>connection.quote</tt>.
-      def sanitize(object) #:nodoc:
-        connection.quote(object)
-      end
-      alias_method :quote_value, :sanitize
-
-      protected
-
       # Accepts an array or string of SQL conditions and sanitizes
       # them into a valid SQL fragment for a WHERE clause.
-      #   ["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"
-      #   "name='foo''bar' and group_id='4'" returns "name='foo''bar' and group_id='4'"
-      def sanitize_sql_for_conditions(condition, table_name = self.table_name)
+      #
+      #   sanitize_sql_for_conditions(["name=? and group_id=?", "foo'bar", 4])
+      #   # => "name='foo''bar' and group_id=4"
+      #
+      #   sanitize_sql_for_conditions(["name=:name and group_id=:group_id", name: "foo'bar", group_id: 4])
+      #   # => "name='foo''bar' and group_id='4'"
+      #
+      #   sanitize_sql_for_conditions(["name='%s' and group_id='%s'", "foo'bar", 4])
+      #   # => "name='foo''bar' and group_id='4'"
+      #
+      #   sanitize_sql_for_conditions("name='foo''bar' and group_id='4'")
+      #   # => "name='foo''bar' and group_id='4'"
+      def sanitize_sql_for_conditions(condition)
         return nil if condition.blank?
 
         case condition
@@ -23,13 +27,23 @@ module ActiveRecord
         else        condition
         end
       end
-      alias_method :sanitize_sql, :sanitize_sql_for_conditions
-      alias_method :sanitize_conditions, :sanitize_sql
+      alias :sanitize_sql :sanitize_sql_for_conditions
 
       # Accepts an array, hash, or string of SQL conditions and sanitizes
       # them into a valid SQL fragment for a SET clause.
-      #   { name: nil, group_id: 4 }  returns "name = NULL , group_id='4'"
-      def sanitize_sql_for_assignment(assignments, default_table_name = self.table_name)
+      #
+      #   sanitize_sql_for_assignment(["name=? and group_id=?", nil, 4])
+      #   # => "name=NULL and group_id=4"
+      #
+      #   sanitize_sql_for_assignment(["name=:name and group_id=:group_id", name: nil, group_id: 4])
+      #   # => "name=NULL and group_id=4"
+      #
+      #   Post.sanitize_sql_for_assignment({ name: nil, group_id: 4 })
+      #   # => "`posts`.`name` = NULL, `posts`.`group_id` = 4"
+      #
+      #   sanitize_sql_for_assignment("name=NULL and group_id='4'")
+      #   # => "name=NULL and group_id='4'"
+      def sanitize_sql_for_assignment(assignments, default_table_name = table_name)
         case assignments
         when Array; sanitize_sql_array(assignments)
         when Hash;  sanitize_sql_hash_for_assignment(assignments, default_table_name)
@@ -37,49 +51,59 @@ module ActiveRecord
         end
       end
 
-      # Accepts a hash of SQL conditions and replaces those attributes
-      # that correspond to a +composed_of+ relationship with their expanded
-      # aggregate attribute values.
-      # Given:
-      #     class Person < ActiveRecord::Base
-      #       composed_of :address, class_name: "Address",
-      #         mapping: [%w(address_street street), %w(address_city city)]
-      #     end
-      # Then:
-      #     { address: Address.new("813 abc st.", "chicago") }
-      #       # => { address_street: "813 abc st.", address_city: "chicago" }
-      def expand_hash_conditions_for_aggregates(attrs)
-        expanded_attrs = {}
-        attrs.each do |attr, value|
-          if aggregation = reflect_on_aggregation(attr.to_sym)
-            mapping = aggregation.mapping
-            mapping.each do |field_attr, aggregate_attr|
-              if mapping.size == 1 && !value.respond_to?(aggregate_attr)
-                expanded_attrs[field_attr] = value
-              else
-                expanded_attrs[field_attr] = value.send(aggregate_attr)
-              end
-            end
-          else
-            expanded_attrs[attr] = value
+      # Accepts an array, or string of SQL conditions and sanitizes
+      # them into a valid SQL fragment for an ORDER clause.
+      #
+      #   sanitize_sql_for_order(["field(id, ?)", [1,3,2]])
+      #   # => "field(id, 1,3,2)"
+      #
+      #   sanitize_sql_for_order("id ASC")
+      #   # => "id ASC"
+      def sanitize_sql_for_order(condition)
+        if condition.is_a?(Array) && condition.first.to_s.include?("?")
+          disallow_raw_sql!([condition.first],
+            permit: AttributeMethods::ClassMethods::COLUMN_NAME_WITH_ORDER
+          )
+
+          # Ensure we aren't dealing with a subclass of String that might
+          # override methods we use (eg. Arel::Nodes::SqlLiteral).
+          if condition.first.kind_of?(String) && !condition.first.instance_of?(String)
+            condition = [String.new(condition.first), *condition[1..-1]]
           end
+
+          Arel.sql(sanitize_sql_array(condition))
+        else
+          condition
         end
-        expanded_attrs
       end
 
       # Sanitizes a hash of attribute/value pairs into SQL conditions for a SET clause.
-      #   { status: nil, group_id: 1 }
-      #     # => "status = NULL , group_id = 1"
+      #
+      #   sanitize_sql_hash_for_assignment({ status: nil, group_id: 1 }, "posts")
+      #   # => "`posts`.`status` = NULL, `posts`.`group_id` = 1"
       def sanitize_sql_hash_for_assignment(attrs, table)
         c = connection
         attrs.map do |attr, value|
-          value = type_for_attribute(attr.to_s).serialize(value)
+          type = type_for_attribute(attr)
+          value = type.serialize(type.cast(value))
           "#{c.quote_table_name_for_assignment(table, attr)} = #{c.quote(value)}"
-        end.join(', ')
+        end.join(", ")
       end
 
       # Sanitizes a +string+ so that it is safe to use within an SQL
-      # LIKE statement. This method uses +escape_character+ to escape all occurrences of "\", "_" and "%"
+      # LIKE statement. This method uses +escape_character+ to escape all occurrences of "\", "_" and "%".
+      #
+      #   sanitize_sql_like("100%")
+      #   # => "100\\%"
+      #
+      #   sanitize_sql_like("snake_cased_string")
+      #   # => "snake\\_cased\\_string"
+      #
+      #   sanitize_sql_like("100%", "!")
+      #   # => "100!%"
+      #
+      #   sanitize_sql_like("snake_cased_string", "!")
+      #   # => "snake!_cased!_string"
       def sanitize_sql_like(string, escape_character = "\\")
         pattern = Regexp.union(escape_character, "%", "_")
         string.gsub(pattern) { |x| [escape_character, x].join }
@@ -87,12 +111,20 @@ module ActiveRecord
 
       # Accepts an array of conditions. The array has each value
       # sanitized and interpolated into the SQL statement.
-      #   ["name='%s' and group_id='%s'", "foo'bar", 4]  returns  "name='foo''bar' and group_id='4'"
+      #
+      #   sanitize_sql_array(["name=? and group_id=?", "foo'bar", 4])
+      #   # => "name='foo''bar' and group_id=4"
+      #
+      #   sanitize_sql_array(["name=:name and group_id=:group_id", name: "foo'bar", group_id: 4])
+      #   # => "name='foo''bar' and group_id=4"
+      #
+      #   sanitize_sql_array(["name='%s' and group_id='%s'", "foo'bar", 4])
+      #   # => "name='foo''bar' and group_id='4'"
       def sanitize_sql_array(ary)
         statement, *values = ary
-        if values.first.is_a?(Hash) && statement =~ /:\w+/
+        if values.first.is_a?(Hash) && /:\w+/.match?(statement)
           replace_named_bind_variables(statement, values.first)
-        elsif statement.include?('?')
+        elsif statement.include?("?")
           replace_bind_variables(statement, values)
         elsif statement.blank?
           statement
@@ -101,57 +133,90 @@ module ActiveRecord
         end
       end
 
-      def replace_bind_variables(statement, values) #:nodoc:
-        raise_if_bind_arity_mismatch(statement, statement.count('?'), values.size)
-        bound = values.dup
-        c = connection
-        statement.gsub(/\?/) do
-          replace_bind_variable(bound.shift, c)
+      private
+        # Accepts a hash of SQL conditions and replaces those attributes
+        # that correspond to a {#composed_of}[rdoc-ref:Aggregations::ClassMethods#composed_of]
+        # relationship with their expanded aggregate attribute values.
+        #
+        # Given:
+        #
+        #   class Person < ActiveRecord::Base
+        #     composed_of :address, class_name: "Address",
+        #       mapping: [%w(address_street street), %w(address_city city)]
+        #   end
+        #
+        # Then:
+        #
+        #   { address: Address.new("813 abc st.", "chicago") }
+        #   # => { address_street: "813 abc st.", address_city: "chicago" }
+        def expand_hash_conditions_for_aggregates(attrs) # :doc:
+          expanded_attrs = {}
+          attrs.each do |attr, value|
+            if aggregation = reflect_on_aggregation(attr.to_sym)
+              mapping = aggregation.mapping
+              mapping.each do |field_attr, aggregate_attr|
+                expanded_attrs[field_attr] = if value.is_a?(Array)
+                  value.map { |it| it.send(aggregate_attr) }
+                elsif mapping.size == 1 && !value.respond_to?(aggregate_attr)
+                  value
+                else
+                  value.send(aggregate_attr)
+                end
+              end
+            else
+              expanded_attrs[attr] = value
+            end
+          end
+          expanded_attrs
         end
-      end
+        deprecate :expand_hash_conditions_for_aggregates
 
-      def replace_bind_variable(value, c = connection) #:nodoc:
-        if ActiveRecord::Relation === value
-          value.to_sql
-        else
-          quote_bound_value(value, c)
+        def replace_bind_variables(statement, values)
+          raise_if_bind_arity_mismatch(statement, statement.count("?"), values.size)
+          bound = values.dup
+          c = connection
+          statement.gsub(/\?/) do
+            replace_bind_variable(bound.shift, c)
+          end
         end
-      end
 
-      def replace_named_bind_variables(statement, bind_vars) #:nodoc:
-        statement.gsub(/(:?):([a-zA-Z]\w*)/) do |match|
-          if $1 == ':' # skip postgresql casts
-            match # return the whole match
-          elsif bind_vars.include?(match = $2.to_sym)
-            replace_bind_variable(bind_vars[match])
+        def replace_bind_variable(value, c = connection)
+          if ActiveRecord::Relation === value
+            value.to_sql
           else
-            raise PreparedStatementInvalid, "missing value for :#{match} in #{statement}"
+            quote_bound_value(value, c)
           end
         end
-      end
 
-      def quote_bound_value(value, c = connection) #:nodoc:
-        if value.respond_to?(:map) && !value.acts_like?(:string)
-          if value.respond_to?(:empty?) && value.empty?
-            c.quote(nil)
-          else
-            value.map { |v| c.quote(v) }.join(',')
+        def replace_named_bind_variables(statement, bind_vars)
+          statement.gsub(/(:?):([a-zA-Z]\w*)/) do |match|
+            if $1 == ":" # skip postgresql casts
+              match # return the whole match
+            elsif bind_vars.include?(match = $2.to_sym)
+              replace_bind_variable(bind_vars[match])
+            else
+              raise PreparedStatementInvalid, "missing value for :#{match} in #{statement}"
+            end
           end
-        else
-          c.quote(value)
         end
-      end
 
-      def raise_if_bind_arity_mismatch(statement, expected, provided) #:nodoc:
-        unless expected == provided
-          raise PreparedStatementInvalid, "wrong number of bind variables (#{provided} for #{expected}) in: #{statement}"
+        def quote_bound_value(value, c = connection)
+          if value.respond_to?(:map) && !value.acts_like?(:string)
+            if value.respond_to?(:empty?) && value.empty?
+              c.quote(nil)
+            else
+              value.map { |v| c.quote(v) }.join(",")
+            end
+          else
+            c.quote(value)
+          end
         end
-      end
-    end
 
-    # TODO: Deprecate this
-    def quoted_id
-      self.class.quote_value(@attributes[self.class.primary_key].value_for_database)
+        def raise_if_bind_arity_mismatch(statement, expected, provided)
+          unless expected == provided
+            raise PreparedStatementInvalid, "wrong number of bind variables (#{provided} for #{expected}) in: #{statement}"
+          end
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/schema.rb b/activerecord/lib/active_record/schema.rb
index 0a5546a760..216359867c 100644
--- a/activerecord/lib/active_record/schema.rb
+++ b/activerecord/lib/active_record/schema.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Schema
+  # = Active Record \Schema
   #
   # Allows programmers to programmatically define a schema in a portable
   # DSL. This means you can define tables, indexes, etc. without using SQL
@@ -27,38 +29,42 @@ module ActiveRecord
   #
   # ActiveRecord::Schema is only supported by database adapters that also
   # support migrations, the two features being very similar.
-  class Schema < Migration
-
-    # Returns the migrations paths.
-    #
-    #   ActiveRecord::Schema.new.migrations_paths
-    #   # => ["db/migrate"] # Rails migration path by default.
-    def migrations_paths
-      ActiveRecord::Migrator.migrations_paths
-    end
-
-    def define(info, &block) # :nodoc:
-      instance_eval(&block)
-
-      unless info[:version].blank?
-        initialize_schema_migrations_table
-        connection.assume_migrated_upto_version(info[:version], migrations_paths)
-      end
-    end
-
+  class Schema < Migration::Current
     # Eval the given block. All methods available to the current connection
     # adapter are available within the block, so you can easily use the
-    # database definition DSL to build up your schema (+create_table+,
-    # +add_index+, etc.).
+    # database definition DSL to build up your schema (
+    # {create_table}[rdoc-ref:ConnectionAdapters::SchemaStatements#create_table],
+    # {add_index}[rdoc-ref:ConnectionAdapters::SchemaStatements#add_index], etc.).
     #
     # The +info+ hash is optional, and if given is used to define metadata
     # about the current schema (currently, only the schema's version):
     #
-    #   ActiveRecord::Schema.define(version: 20380119000001) do
+    #   ActiveRecord::Schema.define(version: 2038_01_19_000001) do
     #     ...
     #   end
-    def self.define(info={}, &block)
+    def self.define(info = {}, &block)
       new.define(info, &block)
     end
+
+    def define(info, &block) # :nodoc:
+      instance_eval(&block)
+
+      if info[:version].present?
+        ActiveRecord::SchemaMigration.create_table
+        connection.assume_migrated_upto_version(info[:version], migrations_paths)
+      end
+
+      ActiveRecord::InternalMetadata.create_table
+      ActiveRecord::InternalMetadata[:environment] = connection.migration_context.current_environment
+    end
+
+    private
+      # Returns the migrations paths.
+      #
+      #   ActiveRecord::Schema.new.migrations_paths
+      #   # => ["db/migrate"] # Rails migration path by default.
+      def migrations_paths
+        ActiveRecord::Migrator.migrations_paths
+      end
   end
 end
diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index c5910fa1ad..d475e77444 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -1,4 +1,6 @@
-require 'stringio'
+# frozen_string_literal: true
+
+require "stringio"
 
 module ActiveRecord
   # = Active Record Schema Dumper
@@ -11,14 +13,19 @@ module ActiveRecord
     ##
     # :singleton-method:
     # A list of tables which should not be dumped to the schema.
-    # Acceptable values are strings as well as regexp.
-    # This setting is only used if ActiveRecord::Base.schema_format == :ruby
-    cattr_accessor :ignore_tables
-    @@ignore_tables = []
+    # Acceptable values are strings as well as regexp if ActiveRecord::Base.schema_format == :ruby.
+    # Only strings are accepted if ActiveRecord::Base.schema_format == :sql.
+    cattr_accessor :ignore_tables, default: []
+
+    ##
+    # :singleton-method:
+    # Specify a custom regular expression matching foreign keys which name
+    # should not be dumped to db/schema.rb.
+    cattr_accessor :fk_ignore_pattern, default: /^fk_rails_[0-9a-f]{10}$/
 
     class << self
-      def dump(connection=ActiveRecord::Base.connection, stream=STDOUT, config = ActiveRecord::Base)
-        new(connection, generate_options(config)).dump(stream)
+      def dump(connection = ActiveRecord::Base.connection, stream = STDOUT, config = ActiveRecord::Base)
+        connection.create_schema_dumper(generate_options(config)).dump(stream)
         stream
       end
 
@@ -43,27 +50,32 @@ module ActiveRecord
 
       def initialize(connection, options = {})
         @connection = connection
-        @version = Migrator::current_version rescue nil
+        @version = connection.migration_context.current_version rescue nil
         @options = options
       end
 
-      def header(stream)
-        define_params = @version ? "version: #{@version}" : ""
+      # turns 20170404131909 into "2017_04_04_131909"
+      def formatted_version
+        stringified = @version.to_s
+        return stringified unless stringified.length == 14
+        stringified.insert(4, "_").insert(7, "_").insert(10, "_")
+      end
 
-        if stream.respond_to?(:external_encoding) && stream.external_encoding
-          stream.puts "# encoding: #{stream.external_encoding.name}"
-        end
+      def define_params
+        @version ? "version: #{formatted_version}" : ""
+      end
 
+      def header(stream)
         stream.puts <<HEADER
 # This file is auto-generated from the current state of the database. Instead
 # of editing this file, please use the migrations feature of Active Record to
 # incrementally modify your database, and then regenerate this schema definition.
 #
-# Note that this schema.rb definition is the authoritative source for your
-# database schema. If you need to create the application database on another
-# system, you should be using db:schema:load, not running all the migrations
-# from scratch. The latter is a flawed and unsustainable approach (the more migrations
-# you'll amass, the slower it'll run and the greater likelihood for issues).
+# This file is the source Rails uses to define your schema when running `rails
+# db:schema:load`. When creating a new database, `rails db:schema:load` tends to
+# be faster and is potentially less error prone than running all of your
+# migrations from scratch. Old migrations may fail to apply correctly if those
+# migrations use external dependencies or application code.
 #
 # It's strongly recommended that you check this file into your version control system.
 
@@ -76,16 +88,8 @@ HEADER
         stream.puts "end"
       end
 
+      # extensions are only supported by PostgreSQL
       def extensions(stream)
-        return unless @connection.supports_extensions?
-        extensions = @connection.extensions
-        if extensions.any?
-          stream.puts "  # These are extensions that must be enabled in order to support this database"
-          extensions.each do |extension|
-            stream.puts "  enable_extension #{extension.inspect}"
-          end
-          stream.puts
-        end
       end
 
       def tables(stream)
@@ -104,10 +108,7 @@ HEADER
       end
 
       def table(table, stream)
-        columns = @connection.columns(table).map do |column|
-          column.instance_variable_set(:@table_name, table)
-          column
-        end
+        columns = @connection.columns(table)
         begin
           tbl = StringIO.new
 
@@ -115,63 +116,39 @@ HEADER
           pk = @connection.primary_key(table)
 
           tbl.print "  create_table #{remove_prefix_and_suffix(table).inspect}"
-          pkcol = columns.detect { |c| c.name == pk }
-          if pkcol
-            if pk != 'id'
-              tbl.print %Q(, primary_key: "#{pk}")
-            end
-            pkcolspec = @connection.column_spec_for_primary_key(pkcol)
-            if pkcolspec
-              pkcolspec.each do |key, value|
-                tbl.print ", #{key}: #{value}"
-              end
+
+          case pk
+          when String
+            tbl.print ", primary_key: #{pk.inspect}" unless pk == "id"
+            pkcol = columns.detect { |c| c.name == pk }
+            pkcolspec = column_spec_for_primary_key(pkcol)
+            if pkcolspec.present?
+              tbl.print ", #{format_colspec(pkcolspec)}"
             end
+          when Array
+            tbl.print ", primary_key: #{pk.inspect}"
           else
             tbl.print ", id: false"
           end
-          tbl.print ", force: :cascade"
 
           table_options = @connection.table_options(table)
-          tbl.print ", options: #{table_options.inspect}" unless table_options.blank?
+          if table_options.present?
+            tbl.print ", #{format_options(table_options)}"
+          end
 
-          tbl.puts " do |t|"
+          tbl.puts ", force: :cascade do |t|"
 
           # then dump all non-primary key columns
-          column_specs = columns.map do |column|
+          columns.each do |column|
             raise StandardError, "Unknown type '#{column.sql_type}' for column '#{column.name}'" unless @connection.valid_type?(column.type)
             next if column.name == pk
-            @connection.column_spec(column)
-          end.compact
-
-          # find all migration keys used in this table
-          keys = @connection.migration_keys
-
-          # figure out the lengths for each column based on above keys
-          lengths = keys.map { |key|
-            column_specs.map { |spec|
-              spec[key] ? spec[key].length + 2 : 0
-            }.max
-          }
-
-          # the string we're going to sprintf our values against, with standardized column widths
-          format_string = lengths.map{ |len| "%-#{len}s" }
-
-          # find the max length for the 'type' column, which is special
-          type_length = column_specs.map{ |column| column[:type].length }.max
-
-          # add column type definition to our format string
-          format_string.unshift "    t.%-#{type_length}s "
-
-          format_string *= ''
-
-          column_specs.each do |colspec|
-            values = keys.zip(lengths).map{ |key, len| colspec.key?(key) ? colspec[key] + ", " : " " * len }
-            values.unshift colspec[:type]
-            tbl.print((format_string % values).gsub(/,\s*$/, ''))
+            type, colspec = column_spec(column)
+            tbl.print "    t.#{type} #{column.name.inspect}"
+            tbl.print ", #{format_colspec(colspec)}" if colspec.present?
             tbl.puts
           end
 
-          indexes(table, tbl)
+          indexes_in_create(table, tbl)
 
           tbl.puts "  end"
           tbl.puts
@@ -183,35 +160,46 @@ HEADER
           stream.puts "#   #{e.message}"
           stream.puts
         end
-
-        stream
       end
 
+      # Keep it for indexing materialized views
       def indexes(table, stream)
         if (indexes = @connection.indexes(table)).any?
           add_index_statements = indexes.map do |index|
-            statement_parts = [
-              "t.index #{index.columns.inspect}",
-              "name: #{index.name.inspect}",
-            ]
-            statement_parts << 'unique: true' if index.unique
-
-            index_lengths = (index.lengths || []).compact
-            statement_parts << "length: #{Hash[index.columns.zip(index.lengths)].inspect}" if index_lengths.any?
-
-            index_orders = index.orders || {}
-            statement_parts << "order: #{index.orders.inspect}" if index_orders.any?
-            statement_parts << "where: #{index.where.inspect}" if index.where
-            statement_parts << "using: #{index.using.inspect}" if index.using
-            statement_parts << "type: #{index.type.inspect}" if index.type
-
-            "    #{statement_parts.join(', ')}"
+            table_name = remove_prefix_and_suffix(index.table).inspect
+            "  add_index #{([table_name] + index_parts(index)).join(', ')}"
           end
 
           stream.puts add_index_statements.sort.join("\n")
+          stream.puts
+        end
+      end
+
+      def indexes_in_create(table, stream)
+        if (indexes = @connection.indexes(table)).any?
+          index_statements = indexes.map do |index|
+            "    t.index #{index_parts(index).join(', ')}"
+          end
+          stream.puts index_statements.sort.join("\n")
         end
       end
 
+      def index_parts(index)
+        index_parts = [
+          index.columns.inspect,
+          "name: #{index.name.inspect}",
+        ]
+        index_parts << "unique: true" if index.unique
+        index_parts << "length: #{format_index_parts(index.lengths)}" if index.lengths.present?
+        index_parts << "order: #{format_index_parts(index.orders)}" if index.orders.present?
+        index_parts << "opclass: #{format_index_parts(index.opclasses)}" if index.opclasses.present?
+        index_parts << "where: #{index.where.inspect}" if index.where
+        index_parts << "using: #{index.using.inspect}" if !@connection.default_index_type?(index)
+        index_parts << "type: #{index.type.inspect}" if index.type
+        index_parts << "comment: #{index.comment.inspect}" if index.comment
+        index_parts
+      end
+
       def foreign_keys(table, stream)
         if (foreign_keys = @connection.foreign_keys(table)).any?
           add_foreign_key_statements = foreign_keys.map do |foreign_key|
@@ -228,7 +216,7 @@ HEADER
               parts << "primary_key: #{foreign_key.primary_key.inspect}"
             end
 
-            if foreign_key.name !~ /^fk_rails_[0-9a-f]{10}$/
+            if foreign_key.export_name_on_schema_dump?
               parts << "name: #{foreign_key.name.inspect}"
             end
 
@@ -242,12 +230,30 @@ HEADER
         end
       end
 
+      def format_colspec(colspec)
+        colspec.map { |key, value| "#{key}: #{value}" }.join(", ")
+      end
+
+      def format_options(options)
+        options.map { |key, value| "#{key}: #{value.inspect}" }.join(", ")
+      end
+
+      def format_index_parts(options)
+        if options.is_a?(Hash)
+          "{ #{format_options(options)} }"
+        else
+          options.inspect
+        end
+      end
+
       def remove_prefix_and_suffix(table)
-        table.gsub(/^(#{@options[:table_name_prefix]})(.+)(#{@options[:table_name_suffix]})$/,  "\\2")
+        prefix = Regexp.escape(@options[:table_name_prefix].to_s)
+        suffix = Regexp.escape(@options[:table_name_suffix].to_s)
+        table.sub(/\A#{prefix}(.+)#{suffix}\z/, "\\1")
       end
 
       def ignored?(table_name)
-        ['schema_migrations', ignore_tables].flatten.any? do |ignored|
+        [ActiveRecord::Base.schema_migrations_table_name, ActiveRecord::Base.internal_metadata_table_name, ignore_tables].flatten.any? do |ignored|
           ignored === remove_prefix_and_suffix(table_name)
         end
       end
diff --git a/activerecord/lib/active_record/schema_migration.rb b/activerecord/lib/active_record/schema_migration.rb
index cb47bf23f7..f2d8b038fa 100644
--- a/activerecord/lib/active_record/schema_migration.rb
+++ b/activerecord/lib/active_record/schema_migration.rb
@@ -1,42 +1,39 @@
-require 'active_record/scoping/default'
-require 'active_record/scoping/named'
+# frozen_string_literal: true
+
+require "active_record/scoping/default"
+require "active_record/scoping/named"
 
 module ActiveRecord
-  class SchemaMigration < ActiveRecord::Base
+  # This class is used to create a table that keeps track of which migrations
+  # have been applied to a given database. When a migration is run, its schema
+  # number is inserted in to the `SchemaMigration.table_name` so it doesn't need
+  # to be executed the next time.
+  class SchemaMigration < ActiveRecord::Base # :nodoc:
     class << self
       def primary_key
-        nil
+        "version"
       end
 
       def table_name
         "#{table_name_prefix}#{ActiveRecord::Base.schema_migrations_table_name}#{table_name_suffix}"
       end
 
-      def index_name
-        "#{table_name_prefix}unique_#{ActiveRecord::Base.schema_migrations_table_name}#{table_name_suffix}"
-      end
-
       def table_exists?
         connection.table_exists?(table_name)
       end
 
-      def create_table(limit=nil)
+      def create_table
         unless table_exists?
-          version_options = {null: false}
-          version_options[:limit] = limit if limit
+          version_options = connection.internal_string_options_for_primary_key
 
           connection.create_table(table_name, id: false) do |t|
-            t.column :version, :string, version_options
+            t.string :version, version_options
           end
-          connection.add_index table_name, :version, unique: true, name: index_name
         end
       end
 
       def drop_table
-        if table_exists?
-          connection.remove_index table_name, name: index_name
-          connection.drop_table(table_name)
-        end
+        connection.drop_table table_name, if_exists: true
       end
 
       def normalize_migration_number(number)
@@ -44,7 +41,11 @@ module ActiveRecord
       end
 
       def normalized_versions
-        pluck(:version).map { |v| normalize_migration_number v }
+        all_versions.map { |v| normalize_migration_number v }
+      end
+
+      def all_versions
+        order(:version).pluck(:version)
       end
     end
 
diff --git a/activerecord/lib/active_record/scoping.rb b/activerecord/lib/active_record/scoping.rb
index f049b658c4..9eba1254a4 100644
--- a/activerecord/lib/active_record/scoping.rb
+++ b/activerecord/lib/active_record/scoping.rb
@@ -1,4 +1,6 @@
-require 'active_support/per_thread_registry'
+# frozen_string_literal: true
+
+require "active_support/per_thread_registry"
 
 module ActiveRecord
   module Scoping
@@ -9,36 +11,36 @@ module ActiveRecord
       include Named
     end
 
-    module ClassMethods
-      def current_scope #:nodoc:
-        ScopeRegistry.value_for(:current_scope, self.to_s)
-      end
-
-      def current_scope=(scope) #:nodoc:
-        ScopeRegistry.set_value_for(:current_scope, self.to_s, scope)
-      end
-
+    module ClassMethods # :nodoc:
       # Collects attributes from scopes that should be applied when creating
       # an AR instance for the particular class this is called on.
-      def scope_attributes # :nodoc:
+      def scope_attributes
         all.scope_for_create
       end
 
       # Are there attributes associated with this scope?
-      def scope_attributes? # :nodoc:
+      def scope_attributes?
         current_scope
       end
+
+      private
+        def current_scope(skip_inherited_scope = false)
+          ScopeRegistry.value_for(:current_scope, self, skip_inherited_scope)
+        end
+
+        def current_scope=(scope)
+          ScopeRegistry.set_value_for(:current_scope, self, scope)
+        end
     end
 
-    def populate_with_current_scope_attributes
+    def populate_with_current_scope_attributes # :nodoc:
       return unless self.class.scope_attributes?
 
-      self.class.scope_attributes.each do |att,value|
-        send("#{att}=", value) if respond_to?("#{att}=")
-      end
+      attributes = self.class.scope_attributes
+      _assign_attributes(attributes) if attributes.any?
     end
 
-    def initialize_internals_callback
+    def initialize_internals_callback # :nodoc:
       super
       populate_with_current_scope_attributes
     end
@@ -53,18 +55,18 @@ module ActiveRecord
     # following code:
     #
     #   registry = ActiveRecord::Scoping::ScopeRegistry
-    #   registry.set_value_for(:current_scope, "Board", some_new_scope)
+    #   registry.set_value_for(:current_scope, Board, some_new_scope)
     #
     # Now when you run:
     #
-    #   registry.value_for(:current_scope, "Board")
+    #   registry.value_for(:current_scope, Board)
     #
-    # You will obtain whatever was defined in +some_new_scope+. The +value_for+
-    # and +set_value_for+ methods are delegated to the current +ScopeRegistry+
+    # You will obtain whatever was defined in +some_new_scope+. The #value_for
+    # and #set_value_for methods are delegated to the current ScopeRegistry
     # object, so the above example code can also be called as:
     #
     #   ActiveRecord::Scoping::ScopeRegistry.set_value_for(:current_scope,
-    #       "Board", some_new_scope)
+    #       Board, some_new_scope)
     class ScopeRegistry # :nodoc:
       extend ActiveSupport::PerThreadRegistry
 
@@ -74,25 +76,32 @@ module ActiveRecord
         @registry = Hash.new { |hash, key| hash[key] = {} }
       end
 
-      # Obtains the value for a given +scope_name+ and +variable_name+.
-      def value_for(scope_type, variable_name)
+      # Obtains the value for a given +scope_type+ and +model+.
+      def value_for(scope_type, model, skip_inherited_scope = false)
         raise_invalid_scope_type!(scope_type)
-        @registry[scope_type][variable_name]
+        return @registry[scope_type][model.name] if skip_inherited_scope
+        klass = model
+        base = model.base_class
+        while klass <= base
+          value = @registry[scope_type][klass.name]
+          return value if value
+          klass = klass.superclass
+        end
       end
 
-      # Sets the +value+ for a given +scope_type+ and +variable_name+.
-      def set_value_for(scope_type, variable_name, value)
+      # Sets the +value+ for a given +scope_type+ and +model+.
+      def set_value_for(scope_type, model, value)
         raise_invalid_scope_type!(scope_type)
-        @registry[scope_type][variable_name] = value
+        @registry[scope_type][model.name] = value
       end
 
       private
 
-      def raise_invalid_scope_type!(scope_type)
-        if !VALID_SCOPE_TYPES.include?(scope_type)
-          raise ArgumentError, "Invalid scope type '#{scope_type}' sent to the registry. Scope types must be included in VALID_SCOPE_TYPES"
+        def raise_invalid_scope_type!(scope_type)
+          if !VALID_SCOPE_TYPES.include?(scope_type)
+            raise ArgumentError, "Invalid scope type '#{scope_type}' sent to the registry. Scope types must be included in VALID_SCOPE_TYPES"
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/scoping/default.rb b/activerecord/lib/active_record/scoping/default.rb
index 3590b8846e..6caf9b3251 100644
--- a/activerecord/lib/active_record/scoping/default.rb
+++ b/activerecord/lib/active_record/scoping/default.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Scoping
     module Default
@@ -5,9 +7,8 @@ module ActiveRecord
 
       included do
         # Stores the default scope for the class.
-        class_attribute :default_scopes, instance_writer: false, instance_predicate: false
-
-        self.default_scopes = []
+        class_attribute :default_scopes, instance_writer: false, instance_predicate: false, default: []
+        class_attribute :default_scope_override, instance_writer: false, instance_predicate: false, default: nil
       end
 
       module ClassMethods
@@ -15,7 +16,7 @@ module ActiveRecord
         #
         #   class Post < ActiveRecord::Base
         #     def self.default_scope
-        #       where published: true
+        #       where(published: true)
         #     end
         #   end
         #
@@ -30,7 +31,14 @@ module ActiveRecord
         #     Post.limit(10) # Fires "SELECT * FROM posts LIMIT 10"
         #   }
         def unscoped
-          block_given? ? relation.scoping { yield } : relation
+          block_given? ? _scoping(relation) { yield } : relation
+        end
+
+        def _scoping(relation) # :nodoc:
+          previous, self.current_scope = current_scope(true), relation
+          yield
+        ensure
+          self.current_scope = previous
         end
 
         # Are there attributes associated with this scope?
@@ -42,97 +50,109 @@ module ActiveRecord
           self.current_scope = nil
         end
 
-        protected
+        private
 
-        # Use this macro in your model to set a default scope for all operations on
-        # the model.
-        #
-        #   class Article < ActiveRecord::Base
-        #     default_scope { where(published: true) }
-        #   end
-        #
-        #   Article.all # => SELECT * FROM articles WHERE published = true
-        #
-        # The +default_scope+ is also applied while creating/building a record.
-        # It is not applied while updating a record.
-        #
-        #   Article.new.published    # => true
-        #   Article.create.published # => true
-        #
-        # (You can also pass any object which responds to +call+ to the
-        # +default_scope+ macro, and it will be called when building the
-        # default scope.)
-        #
-        # If you use multiple +default_scope+ declarations in your model then
-        # they will be merged together:
-        #
-        #   class Article < ActiveRecord::Base
-        #     default_scope { where(published: true) }
-        #     default_scope { where(rating: 'G') }
-        #   end
-        #
-        #   Article.all # => SELECT * FROM articles WHERE published = true AND rating = 'G'
-        #
-        # This is also the case with inheritance and module includes where the
-        # parent or module defines a +default_scope+ and the child or including
-        # class defines a second one.
-        #
-        # If you need to do more complex things with a default scope, you can
-        # alternatively define it as a class method:
-        #
-        #   class Article < ActiveRecord::Base
-        #     def self.default_scope
-        #       # Should return a scope, you can call 'super' here etc.
-        #     end
-        #   end
-        def default_scope(scope = nil)
-          scope = Proc.new if block_given?
-
-          if scope.is_a?(Relation) || !scope.respond_to?(:call)
-            raise ArgumentError,
-              "Support for calling #default_scope without a block is removed. For example instead " \
-              "of `default_scope where(color: 'red')`, please use " \
-              "`default_scope { where(color: 'red') }`. (Alternatively you can just redefine " \
-              "self.default_scope.)"
+          # Use this macro in your model to set a default scope for all operations on
+          # the model.
+          #
+          #   class Article < ActiveRecord::Base
+          #     default_scope { where(published: true) }
+          #   end
+          #
+          #   Article.all # => SELECT * FROM articles WHERE published = true
+          #
+          # The #default_scope is also applied while creating/building a record.
+          # It is not applied while updating a record.
+          #
+          #   Article.new.published    # => true
+          #   Article.create.published # => true
+          #
+          # (You can also pass any object which responds to +call+ to the
+          # +default_scope+ macro, and it will be called when building the
+          # default scope.)
+          #
+          # If you use multiple #default_scope declarations in your model then
+          # they will be merged together:
+          #
+          #   class Article < ActiveRecord::Base
+          #     default_scope { where(published: true) }
+          #     default_scope { where(rating: 'G') }
+          #   end
+          #
+          #   Article.all # => SELECT * FROM articles WHERE published = true AND rating = 'G'
+          #
+          # This is also the case with inheritance and module includes where the
+          # parent or module defines a #default_scope and the child or including
+          # class defines a second one.
+          #
+          # If you need to do more complex things with a default scope, you can
+          # alternatively define it as a class method:
+          #
+          #   class Article < ActiveRecord::Base
+          #     def self.default_scope
+          #       # Should return a scope, you can call 'super' here etc.
+          #     end
+          #   end
+          def default_scope(scope = nil) # :doc:
+            scope = Proc.new if block_given?
+
+            if scope.is_a?(Relation) || !scope.respond_to?(:call)
+              raise ArgumentError,
+                "Support for calling #default_scope without a block is removed. For example instead " \
+                "of `default_scope where(color: 'red')`, please use " \
+                "`default_scope { where(color: 'red') }`. (Alternatively you can just redefine " \
+                "self.default_scope.)"
+            end
+
+            self.default_scopes += [scope]
           end
 
-          self.default_scopes += [scope]
-        end
+          def build_default_scope(base_rel = nil)
+            return if abstract_class?
+
+            if default_scope_override.nil?
+              self.default_scope_override = !Base.is_a?(method(:default_scope).owner)
+            end
 
-        def build_default_scope(base_rel = relation) # :nodoc:
-          if !Base.is_a?(method(:default_scope).owner)
-            # The user has defined their own default scope method, so call that
-            evaluate_default_scope { default_scope }
-          elsif default_scopes.any?
-            evaluate_default_scope do
-              default_scopes.inject(base_rel) do |default_scope, scope|
-                default_scope.merge(base_rel.scoping { scope.call })
+            if default_scope_override
+              # The user has defined their own default scope method, so call that
+              evaluate_default_scope do
+                if scope = default_scope
+                  (base_rel ||= relation).merge!(scope)
+                end
+              end
+            elsif default_scopes.any?
+              base_rel ||= relation
+              evaluate_default_scope do
+                default_scopes.inject(base_rel) do |default_scope, scope|
+                  scope = scope.respond_to?(:to_proc) ? scope : scope.method(:call)
+                  default_scope.merge!(base_rel.instance_exec(&scope))
+                end
               end
             end
           end
-        end
 
-        def ignore_default_scope? # :nodoc:
-          ScopeRegistry.value_for(:ignore_default_scope, self)
-        end
+          def ignore_default_scope?
+            ScopeRegistry.value_for(:ignore_default_scope, base_class)
+          end
 
-        def ignore_default_scope=(ignore) # :nodoc:
-          ScopeRegistry.set_value_for(:ignore_default_scope, self, ignore)
-        end
+          def ignore_default_scope=(ignore)
+            ScopeRegistry.set_value_for(:ignore_default_scope, base_class, ignore)
+          end
+
+          # The ignore_default_scope flag is used to prevent an infinite recursion
+          # situation where a default scope references a scope which has a default
+          # scope which references a scope...
+          def evaluate_default_scope
+            return if ignore_default_scope?
 
-        # The ignore_default_scope flag is used to prevent an infinite recursion
-        # situation where a default scope references a scope which has a default
-        # scope which references a scope...
-        def evaluate_default_scope # :nodoc:
-          return if ignore_default_scope?
-
-          begin
-            self.ignore_default_scope = true
-            yield
-          ensure
-            self.ignore_default_scope = false
+            begin
+              self.ignore_default_scope = true
+              yield
+            ensure
+              self.ignore_default_scope = false
+            end
           end
-        end
       end
     end
   end
diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index 7b62626896..d5cc5db97e 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -1,6 +1,8 @@
-require 'active_support/core_ext/array'
-require 'active_support/core_ext/hash/except'
-require 'active_support/core_ext/kernel/singleton_class'
+# frozen_string_literal: true
+
+require "active_support/core_ext/array"
+require "active_support/core_ext/hash/except"
+require "active_support/core_ext/kernel/singleton_class"
 
 module ActiveRecord
   # = Active Record \Named \Scopes
@@ -9,7 +11,7 @@ module ActiveRecord
       extend ActiveSupport::Concern
 
       module ClassMethods
-        # Returns an <tt>ActiveRecord::Relation</tt> scope object.
+        # Returns an ActiveRecord::Relation scope object.
         #
         #   posts = Post.all
         #   posts.size # Fires "select count(*) from  posts" and returns the count
@@ -20,27 +22,48 @@ module ActiveRecord
         #   fruits = fruits.limit(10) if limited?
         #
         # You can define a scope that applies to all finders using
-        # <tt>ActiveRecord::Base.default_scope</tt>.
+        # {default_scope}[rdoc-ref:Scoping::Default::ClassMethods#default_scope].
         def all
-          if current_scope
-            current_scope.clone
+          scope = current_scope
+
+          if scope
+            if self == scope.klass
+              scope.clone
+            else
+              relation.merge!(scope)
+            end
           else
             default_scoped
           end
         end
 
-        def default_scoped # :nodoc:
-          scope = build_default_scope
+        def scope_for_association(scope = relation) # :nodoc:
+          if current_scope&.empty_scope?
+            scope
+          else
+            default_scoped(scope)
+          end
+        end
 
-          if scope
-            relation.spawn.merge!(scope)
+        def default_scoped(scope = relation) # :nodoc:
+          build_default_scope(scope) || scope
+        end
+
+        def default_extensions # :nodoc:
+          if scope = current_scope || build_default_scope
+            scope.extensions
           else
-            relation
+            []
           end
         end
 
-        # Adds a class method for retrieving and querying objects. A \scope
-        # represents a narrowing of a database query, such as
+        # Adds a class method for retrieving and querying objects.
+        # The method is intended to return an ActiveRecord::Relation
+        # object, which is composable with other scopes.
+        # If it returns +nil+ or +false+, an
+        # {all}[rdoc-ref:Scoping::Named::ClassMethods#all] scope is returned instead.
+        #
+        # A \scope represents a narrowing of a database query, such as
         # <tt>where(color: :red).select('shirts.*').includes(:washing_instructions)</tt>.
         #
         #   class Shirt < ActiveRecord::Base
@@ -48,12 +71,12 @@ module ActiveRecord
         #     scope :dry_clean_only, -> { joins(:washing_instructions).where('washing_instructions.dry_clean_only = ?', true) }
         #   end
         #
-        # The above calls to +scope+ define class methods <tt>Shirt.red</tt> and
+        # The above calls to #scope define class methods <tt>Shirt.red</tt> and
         # <tt>Shirt.dry_clean_only</tt>. <tt>Shirt.red</tt>, in effect,
         # represents the query <tt>Shirt.where(color: 'red')</tt>.
         #
         # You should always pass a callable object to the scopes defined
-        # with +scope+. This ensures that the scope is re-evaluated each
+        # with #scope. This ensures that the scope is re-evaluated each
         # time it is called.
         #
         # Note that this is simply 'syntactic sugar' for defining an actual
@@ -66,14 +89,15 @@ module ActiveRecord
         #   end
         #
         # Unlike <tt>Shirt.find(...)</tt>, however, the object returned by
-        # <tt>Shirt.red</tt> is not an Array; it resembles the association object
-        # constructed by a +has_many+ declaration. For instance, you can invoke
-        # <tt>Shirt.red.first</tt>, <tt>Shirt.red.count</tt>,
+        # <tt>Shirt.red</tt> is not an Array but an ActiveRecord::Relation,
+        # which is composable with other scopes; it resembles the association object
+        # constructed by a {has_many}[rdoc-ref:Associations::ClassMethods#has_many]
+        # declaration. For instance, you can invoke <tt>Shirt.red.first</tt>, <tt>Shirt.red.count</tt>,
         # <tt>Shirt.red.where(size: 'small')</tt>. Also, just as with the
         # association objects, named \scopes act like an Array, implementing
         # Enumerable; <tt>Shirt.red.each(&block)</tt>, <tt>Shirt.red.first</tt>,
         # and <tt>Shirt.red.inject(memo, &block)</tt> all behave as if
-        # <tt>Shirt.red</tt> really was an Array.
+        # <tt>Shirt.red</tt> really was an array.
         #
         # These named \scopes are composable. For instance,
         # <tt>Shirt.red.dry_clean_only</tt> will produce all shirts that are
@@ -84,7 +108,8 @@ module ActiveRecord
         #
         # All scopes are available as class methods on the ActiveRecord::Base
         # descendant upon which the \scopes were defined. But they are also
-        # available to +has_many+ associations. If,
+        # available to {has_many}[rdoc-ref:Associations::ClassMethods#has_many]
+        # associations. If,
         #
         #   class Person < ActiveRecord::Base
         #     has_many :shirts
@@ -93,8 +118,8 @@ module ActiveRecord
         # then <tt>elton.shirts.red.dry_clean_only</tt> will return all of
         # Elton's red, dry clean only shirts.
         #
-        # \Named scopes can also have extensions, just as with +has_many+
-        # declarations:
+        # \Named scopes can also have extensions, just as with
+        # {has_many}[rdoc-ref:Associations::ClassMethods#has_many] declarations:
         #
         #   class Shirt < ActiveRecord::Base
         #     scope :red, -> { where(color: 'red') } do
@@ -135,7 +160,7 @@ module ActiveRecord
         #   Article.featured.titles
         def scope(name, body, &block)
           unless body.respond_to?(:call)
-            raise ArgumentError, 'The scope body needs to be callable.'
+            raise ArgumentError, "The scope body needs to be callable."
           end
 
           if dangerous_class_method?(name)
@@ -144,24 +169,40 @@ module ActiveRecord
               "a class method with the same name."
           end
 
+          if method_defined_within?(name, Relation)
+            raise ArgumentError, "You tried to define a scope named \"#{name}\" " \
+              "on the model \"#{self.name}\", but ActiveRecord::Relation already defined " \
+              "an instance method with the same name."
+          end
+
+          valid_scope_name?(name)
           extension = Module.new(&block) if block
 
           if body.respond_to?(:to_proc)
             singleton_class.send(:define_method, name) do |*args|
-              scope = all.scoping { instance_exec(*args, &body) }
+              scope = all._exec_scope(*args, &body)
               scope = scope.extending(extension) if extension
-
-              scope || all
+              scope
             end
           else
             singleton_class.send(:define_method, name) do |*args|
-              scope = all.scoping { body.call(*args) }
+              scope = body.call(*args) || all
               scope = scope.extending(extension) if extension
-
-              scope || all
+              scope
             end
           end
+
+          generate_relation_method(name)
         end
+
+        private
+
+          def valid_scope_name?(name)
+            if respond_to?(name, true) && logger
+              logger.warn "Creating scope :#{name}. " \
+                "Overwriting existing method #{self.name}.#{name}."
+            end
+          end
       end
     end
   end
diff --git a/activerecord/lib/active_record/secure_token.rb b/activerecord/lib/active_record/secure_token.rb
index ca11853da7..bcdb33901b 100644
--- a/activerecord/lib/active_record/secure_token.rb
+++ b/activerecord/lib/active_record/secure_token.rb
@@ -1,9 +1,11 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module SecureToken
     extend ActiveSupport::Concern
 
     module ClassMethods
-      # Example using has_secure_token
+      # Example using #has_secure_token
       #
       #   # Schema: User(token:string, auth_token:string)
       #   class User < ActiveRecord::Base
@@ -18,16 +20,16 @@ module ActiveRecord
       #   user.regenerate_token # => true
       #   user.regenerate_auth_token # => true
       #
-      # SecureRandom::base58 is used to generate the 24-character unique token, so collisions are highly unlikely.
+      # <tt>SecureRandom::base58</tt> is used to generate the 24-character unique token, so collisions are highly unlikely.
       #
       # Note that it's still possible to generate a race condition in the database in the same way that
-      # <tt>validates_uniqueness_of</tt> can. You're encouraged to add a unique index in the database to deal
-      # with this even more unlikely scenario.
+      # {validates_uniqueness_of}[rdoc-ref:Validations::ClassMethods#validates_uniqueness_of] can.
+      # You're encouraged to add a unique index in the database to deal with this even more unlikely scenario.
       def has_secure_token(attribute = :token)
         # Load securerandom only when has_secure_token is used.
-        require 'active_support/core_ext/securerandom'
+        require "active_support/core_ext/securerandom"
         define_method("regenerate_#{attribute}") { update! attribute => self.class.generate_unique_secure_token }
-        before_create { self.send("#{attribute}=", self.class.generate_unique_secure_token) unless self.send("#{attribute}?")}
+        before_create { send("#{attribute}=", self.class.generate_unique_secure_token) unless send("#{attribute}?") }
       end
 
       def generate_unique_secure_token
diff --git a/activerecord/lib/active_record/serialization.rb b/activerecord/lib/active_record/serialization.rb
index 48c12dcf9f..741fea43ce 100644
--- a/activerecord/lib/active_record/serialization.rb
+++ b/activerecord/lib/active_record/serialization.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 module ActiveRecord #:nodoc:
-  # = Active Record Serialization
+  # = Active Record \Serialization
   module Serialization
     extend ActiveSupport::Concern
     include ActiveModel::Serializers::JSON
@@ -9,7 +11,7 @@ module ActiveRecord #:nodoc:
     end
 
     def serializable_hash(options = nil)
-      options = options.try(:clone) || {}
+      options = options.try(:dup) || {}
 
       options[:except] = Array(options[:except]).map(&:to_s)
       options[:except] |= Array(self.class.inheritance_column)
@@ -18,5 +20,3 @@ module ActiveRecord #:nodoc:
     end
   end
 end
-
-require 'active_record/serializers/xml_serializer'
diff --git a/activerecord/lib/active_record/serializers/xml_serializer.rb b/activerecord/lib/active_record/serializers/xml_serializer.rb
deleted file mode 100644
index 89b7e0be82..0000000000
--- a/activerecord/lib/active_record/serializers/xml_serializer.rb
+++ /dev/null
@@ -1,193 +0,0 @@
-require 'active_support/core_ext/hash/conversions'
-
-module ActiveRecord #:nodoc:
-  module Serialization
-    include ActiveModel::Serializers::Xml
-
-    # Builds an XML document to represent the model. Some configuration is
-    # available through +options+. However more complicated cases should
-    # override ActiveRecord::Base#to_xml.
-    #
-    # By default the generated XML document will include the processing
-    # instruction and all the object's attributes. For example:
-    #
-    #   <?xml version="1.0" encoding="UTF-8"?>
-    #   <topic>
-    #     <title>The First Topic</title>
-    #     <author-name>David</author-name>
-    #     <id type="integer">1</id>
-    #     <approved type="boolean">false</approved>
-    #     <replies-count type="integer">0</replies-count>
-    #     <bonus-time type="dateTime">2000-01-01T08:28:00+12:00</bonus-time>
-    #     <written-on type="dateTime">2003-07-16T09:28:00+1200</written-on>
-    #     <content>Have a nice day</content>
-    #     <author-email-address>david@loudthinking.com</author-email-address>
-    #     <parent-id></parent-id>
-    #     <last-read type="date">2004-04-15</last-read>
-    #   </topic>
-    #
-    # This behavior can be controlled with <tt>:only</tt>, <tt>:except</tt>,
-    # <tt>:skip_instruct</tt>, <tt>:skip_types</tt>, <tt>:dasherize</tt> and <tt>:camelize</tt> .
-    # The <tt>:only</tt> and <tt>:except</tt> options are the same as for the
-    # +attributes+ method. The default is to dasherize all column names, but you
-    # can disable this setting <tt>:dasherize</tt> to +false+. Setting <tt>:camelize</tt>
-    # to +true+ will camelize all column names - this also overrides <tt>:dasherize</tt>.
-    # To not have the column type included in the XML output set <tt>:skip_types</tt> to +true+.
-    #
-    # For instance:
-    #
-    #   topic.to_xml(skip_instruct: true, except: [ :id, :bonus_time, :written_on, :replies_count ])
-    #
-    #   <topic>
-    #     <title>The First Topic</title>
-    #     <author-name>David</author-name>
-    #     <approved type="boolean">false</approved>
-    #     <content>Have a nice day</content>
-    #     <author-email-address>david@loudthinking.com</author-email-address>
-    #     <parent-id></parent-id>
-    #     <last-read type="date">2004-04-15</last-read>
-    #   </topic>
-    #
-    # To include first level associations use <tt>:include</tt>:
-    #
-    #   firm.to_xml include: [ :account, :clients ]
-    #
-    #   <?xml version="1.0" encoding="UTF-8"?>
-    #   <firm>
-    #     <id type="integer">1</id>
-    #     <rating type="integer">1</rating>
-    #     <name>37signals</name>
-    #     <clients type="array">
-    #       <client>
-    #         <rating type="integer">1</rating>
-    #         <name>Summit</name>
-    #       </client>
-    #       <client>
-    #         <rating type="integer">1</rating>
-    #         <name>Microsoft</name>
-    #       </client>
-    #     </clients>
-    #     <account>
-    #       <id type="integer">1</id>
-    #       <credit-limit type="integer">50</credit-limit>
-    #     </account>
-    #   </firm>
-    #
-    # Additionally, the record being serialized will be passed to a Proc's second
-    # parameter. This allows for ad hoc additions to the resultant document that
-    # incorporate the context of the record being serialized. And by leveraging the
-    # closure created by a Proc, to_xml can be used to add elements that normally fall
-    # outside of the scope of the model -- for example, generating and appending URLs
-    # associated with models.
-    #
-    #   proc = Proc.new { |options, record| options[:builder].tag!('name-reverse', record.name.reverse) }
-    #   firm.to_xml procs: [ proc ]
-    #
-    #   <firm>
-    #     # ... normal attributes as shown above ...
-    #     <name-reverse>slangis73</name-reverse>
-    #   </firm>
-    #
-    # To include deeper levels of associations pass a hash like this:
-    #
-    #   firm.to_xml include: {account: {}, clients: {include: :address}}
-    #   <?xml version="1.0" encoding="UTF-8"?>
-    #   <firm>
-    #     <id type="integer">1</id>
-    #     <rating type="integer">1</rating>
-    #     <name>37signals</name>
-    #     <clients type="array">
-    #       <client>
-    #         <rating type="integer">1</rating>
-    #         <name>Summit</name>
-    #         <address>
-    #           ...
-    #         </address>
-    #       </client>
-    #       <client>
-    #         <rating type="integer">1</rating>
-    #         <name>Microsoft</name>
-    #         <address>
-    #           ...
-    #         </address>
-    #       </client>
-    #     </clients>
-    #     <account>
-    #       <id type="integer">1</id>
-    #       <credit-limit type="integer">50</credit-limit>
-    #     </account>
-    #   </firm>
-    #
-    # To include any methods on the model being called use <tt>:methods</tt>:
-    #
-    #   firm.to_xml methods: [ :calculated_earnings, :real_earnings ]
-    #
-    #   <firm>
-    #     # ... normal attributes as shown above ...
-    #     <calculated-earnings>100000000000000000</calculated-earnings>
-    #     <real-earnings>5</real-earnings>
-    #   </firm>
-    #
-    # To call any additional Procs use <tt>:procs</tt>. The Procs are passed a
-    # modified version of the options hash that was given to +to_xml+:
-    #
-    #   proc = Proc.new { |options| options[:builder].tag!('abc', 'def') }
-    #   firm.to_xml procs: [ proc ]
-    #
-    #   <firm>
-    #     # ... normal attributes as shown above ...
-    #     <abc>def</abc>
-    #   </firm>
-    #
-    # Alternatively, you can yield the builder object as part of the +to_xml+ call:
-    #
-    #   firm.to_xml do |xml|
-    #     xml.creator do
-    #       xml.first_name "David"
-    #       xml.last_name "Heinemeier Hansson"
-    #     end
-    #   end
-    #
-    #   <firm>
-    #     # ... normal attributes as shown above ...
-    #     <creator>
-    #       <first_name>David</first_name>
-    #       <last_name>Heinemeier Hansson</last_name>
-    #     </creator>
-    #   </firm>
-    #
-    # As noted above, you may override +to_xml+ in your ActiveRecord::Base
-    # subclasses to have complete control about what's generated. The general
-    # form of doing this is:
-    #
-    #   class IHaveMyOwnXML < ActiveRecord::Base
-    #     def to_xml(options = {})
-    #       require 'builder'
-    #       options[:indent] ||= 2
-    #       xml = options[:builder] ||= ::Builder::XmlMarkup.new(indent: options[:indent])
-    #       xml.instruct! unless options[:skip_instruct]
-    #       xml.level_one do
-    #         xml.tag!(:second_level, 'content')
-    #       end
-    #     end
-    #   end
-    def to_xml(options = {}, &block)
-      XmlSerializer.new(self, options).serialize(&block)
-    end
-  end
-
-  class XmlSerializer < ActiveModel::Serializers::Xml::Serializer #:nodoc:
-    class Attribute < ActiveModel::Serializers::Xml::Serializer::Attribute #:nodoc:
-      def compute_type
-        klass = @serializable.class
-        cast_type = klass.type_for_attribute(name)
-
-        type = ActiveSupport::XmlMini::TYPE_NAMES[value.class.name] || cast_type.type
-
-        { :text => :string,
-          :time => :datetime }[type] || type
-      end
-      protected :compute_type
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/statement_cache.rb b/activerecord/lib/active_record/statement_cache.rb
index 95986c820c..1b1736dcab 100644
--- a/activerecord/lib/active_record/statement_cache.rb
+++ b/activerecord/lib/active_record/statement_cache.rb
@@ -1,5 +1,6 @@
-module ActiveRecord
+# frozen_string_literal: true
 
+module ActiveRecord
   # Statement cache is used to cache a single statement in order to avoid creating the AST again.
   # Initializing the cache is done by passing the statement in the create block:
   #
@@ -7,12 +8,14 @@ module ActiveRecord
   #     Book.where(name: "my book").where("author_id > 3")
   #   end
   #
-  # The cached statement is executed by using the +execute+ method:
+  # The cached statement is executed by using the
+  # {connection.execute}[rdoc-ref:ConnectionAdapters::DatabaseStatements#execute] method:
   #
-  #   cache.execute([], Book, Book.connection)
+  #   cache.execute([], Book.connection)
   #
-  # The relation returned by the block is cached, and for each +execute+ call the cached relation gets duped.
-  # Database is queried when +to_a+ is called on the relation.
+  # The relation returned by the block is cached, and for each
+  # {execute}[rdoc-ref:ConnectionAdapters::DatabaseStatements#execute]
+  # call the cached relation gets duped. Database is queried when +to_a+ is called on the relation.
   #
   # If you want to cache the statement without the values you can use the +bind+ method of the
   # block parameter.
@@ -23,7 +26,7 @@ module ActiveRecord
   #
   # And pass the bind values as the first argument of +execute+ call.
   #
-  #   cache.execute(["my book"], Book, Book.connection)
+  #   cache.execute(["my book"], Book.connection)
   class StatementCache # :nodoc:
     class Substitute; end # :nodoc:
 
@@ -38,28 +41,53 @@ module ActiveRecord
     end
 
     class PartialQuery < Query # :nodoc:
-      def initialize values
+      def initialize(values)
         @values = values
-        @indexes = values.each_with_index.find_all { |thing,i|
-          Arel::Nodes::BindParam === thing
+        @indexes = values.each_with_index.find_all { |thing, i|
+          Substitute === thing
         }.map(&:last)
       end
 
       def sql_for(binds, connection)
         val = @values.dup
-        binds = connection.prepare_binds_for_database(binds)
-        @indexes.each { |i| val[i] = connection.quote(binds.shift) }
+        casted_binds = binds.map(&:value_for_database)
+        @indexes.each { |i| val[i] = connection.quote(casted_binds.shift) }
         val.join
       end
     end
 
-    def self.query(visitor, ast)
-      Query.new visitor.accept(ast, Arel::Collectors::SQLString.new).value
+    class PartialQueryCollector
+      def initialize
+        @parts = []
+        @binds = []
+      end
+
+      def <<(str)
+        @parts << str
+        self
+      end
+
+      def add_bind(obj)
+        @binds << obj
+        @parts << Substitute.new
+        self
+      end
+
+      def value
+        [@parts, @binds]
+      end
+    end
+
+    def self.query(sql)
+      Query.new(sql)
     end
 
-    def self.partial_query(visitor, ast, collector)
-      collected = visitor.accept(ast, collector).value
-      PartialQuery.new collected
+    def self.partial_query(values)
+      PartialQuery.new(values)
+    end
+
+    def self.partial_query_collector
+      PartialQueryCollector.new
     end
 
     class Params # :nodoc:
@@ -68,7 +96,7 @@ module ActiveRecord
 
     class BindMap # :nodoc:
       def initialize(bound_attributes)
-        @indexes   = []
+        @indexes = []
         @bound_attributes = bound_attributes
 
         bound_attributes.each_with_index do |attr, i|
@@ -80,32 +108,39 @@ module ActiveRecord
 
       def bind(values)
         bas = @bound_attributes.dup
-        @indexes.each_with_index { |offset,i| bas[offset] = bas[offset].with_cast_value(values[i]) }
+        @indexes.each_with_index { |offset, i| bas[offset] = bas[offset].with_cast_value(values[i]) }
         bas
       end
     end
 
-    attr_reader :bind_map, :query_builder
-
     def self.create(connection, block = Proc.new)
-      relation      = block.call Params.new
-      bind_map      = BindMap.new relation.bound_attributes
-      query_builder = connection.cacheable_query relation.arel
-      new query_builder, bind_map
+      relation = block.call Params.new
+      query_builder, binds = connection.cacheable_query(self, relation.arel)
+      bind_map = BindMap.new(binds)
+      new(query_builder, bind_map, relation.klass)
     end
 
-    def initialize(query_builder, bind_map)
+    def initialize(query_builder, bind_map, klass)
       @query_builder = query_builder
-      @bind_map      = bind_map
+      @bind_map = bind_map
+      @klass = klass
     end
 
-    def execute(params, klass, connection)
+    def execute(params, connection, &block)
       bind_values = bind_map.bind params
 
       sql = query_builder.sql_for bind_values, connection
 
-      klass.find_by_sql sql, bind_values
+      klass.find_by_sql(sql, bind_values, preparable: true, &block)
     end
-    alias :call :execute
+
+    def self.unsupported_value?(value)
+      case value
+      when NilClass, Array, Range, Hash, Relation, Base then true
+      end
+    end
+
+    private
+      attr_reader :query_builder, :bind_map, :klass
   end
 end
diff --git a/activerecord/lib/active_record/store.rb b/activerecord/lib/active_record/store.rb
index 919bc58ba5..3537e2d008 100644
--- a/activerecord/lib/active_record/store.rb
+++ b/activerecord/lib/active_record/store.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/hash/indifferent_access'
+# frozen_string_literal: true
+
+require "active_support/core_ext/hash/indifferent_access"
 
 module ActiveRecord
   # Store gives you a thin wrapper around serialize for the purpose of storing hashes in a single column.
@@ -15,8 +17,9 @@ module ActiveRecord
   # You can set custom coder to encode/decode your serialized attributes to/from different formats.
   # JSON, YAML, Marshal are supported out of the box. Generally it can be any wrapper that provides +load+ and +dump+.
   #
-  # NOTE: If you are using PostgreSQL specific columns like +hstore+ or +json+ there is no need for
-  # the serialization provided by +store+. Simply use +store_accessor+ instead to generate
+  # NOTE: If you are using structured database data types (eg. PostgreSQL +hstore+/+json+, or MySQL 5.7+
+  # +json+) there is no need for the serialization provided by {.store}[rdoc-ref:rdoc-ref:ClassMethods#store].
+  # Simply use {.store_accessor}[rdoc-ref:ClassMethods#store_accessor] instead to generate
   # the accessor methods. Be aware that these columns use a string keyed hash and do not allow access
   # using a symbol.
   #
@@ -28,10 +31,18 @@ module ActiveRecord
   #
   #   class User < ActiveRecord::Base
   #     store :settings, accessors: [ :color, :homepage ], coder: JSON
+  #     store :parent, accessors: [ :name ], coder: JSON, prefix: true
+  #     store :spouse, accessors: [ :name ], coder: JSON, prefix: :partner
+  #     store :settings, accessors: [ :two_factor_auth ], suffix: true
+  #     store :settings, accessors: [ :login_retry ], suffix: :config
   #   end
   #
-  #   u = User.new(color: 'black', homepage: '37signals.com')
+  #   u = User.new(color: 'black', homepage: '37signals.com', parent_name: 'Mary', partner_name: 'Lily')
   #   u.color                          # Accessor stored attribute
+  #   u.parent_name                    # Accessor stored attribute with prefix
+  #   u.partner_name                   # Accessor stored attribute with custom prefix
+  #   u.two_factor_auth_settings       # Accessor stored attribute with suffix
+  #   u.login_retry_config             # Accessor stored attribute with custom suffix
   #   u.settings[:country] = 'Denmark' # Any attribute, even if not specified with an accessor
   #
   #   # There is no difference between strings and symbols for accessing custom attributes
@@ -41,11 +52,13 @@ module ActiveRecord
   #   # Add additional accessors to an existing store through store_accessor
   #   class SuperUser < User
   #     store_accessor :settings, :privileges, :servants
+  #     store_accessor :parent, :birthday, prefix: true
+  #     store_accessor :settings, :secret_question, suffix: :config
   #   end
   #
-  # The stored attribute names can be retrieved using +stored_attributes+.
+  # The stored attribute names can be retrieved using {.stored_attributes}[rdoc-ref:rdoc-ref:ClassMethods#stored_attributes].
   #
-  #   User.stored_attributes[:settings] # [:color, :homepage]
+  #   User.stored_attributes[:settings] # [:color, :homepage, :two_factor_auth, :login_retry]
   #
   # == Overwriting default accessors
   #
@@ -77,20 +90,41 @@ module ActiveRecord
 
     module ClassMethods
       def store(store_attribute, options = {})
-        serialize store_attribute, IndifferentCoder.new(options[:coder])
-        store_accessor(store_attribute, options[:accessors]) if options.has_key? :accessors
+        serialize store_attribute, IndifferentCoder.new(store_attribute, options[:coder])
+        store_accessor(store_attribute, options[:accessors], options.slice(:prefix, :suffix)) if options.has_key? :accessors
       end
 
-      def store_accessor(store_attribute, *keys)
+      def store_accessor(store_attribute, *keys, prefix: nil, suffix: nil)
         keys = keys.flatten
 
+        accessor_prefix =
+          case prefix
+          when String, Symbol
+            "#{prefix}_"
+          when TrueClass
+            "#{store_attribute}_"
+          else
+            ""
+          end
+        accessor_suffix =
+          case suffix
+          when String, Symbol
+            "_#{suffix}"
+          when TrueClass
+            "_#{store_attribute}"
+          else
+            ""
+          end
+
         _store_accessors_module.module_eval do
           keys.each do |key|
-            define_method("#{key}=") do |value|
+            accessor_key = "#{accessor_prefix}#{key}#{accessor_suffix}"
+
+            define_method("#{accessor_key}=") do |value|
               write_store_attribute(store_attribute, key, value)
             end
 
-            define_method(key) do
+            define_method(accessor_key) do
               read_store_attribute(store_attribute, key)
             end
           end
@@ -113,27 +147,26 @@ module ActiveRecord
 
       def stored_attributes
         parent = superclass.respond_to?(:stored_attributes) ? superclass.stored_attributes : {}
-        if self.local_stored_attributes
-          parent.merge!(self.local_stored_attributes) { |k, a, b| a | b }
+        if local_stored_attributes
+          parent.merge!(local_stored_attributes) { |k, a, b| a | b }
         end
         parent
       end
     end
 
-    protected
-      def read_store_attribute(store_attribute, key)
+    private
+      def read_store_attribute(store_attribute, key) # :doc:
         accessor = store_accessor_for(store_attribute)
         accessor.read(self, store_attribute, key)
       end
 
-      def write_store_attribute(store_attribute, key, value)
+      def write_store_attribute(store_attribute, key, value) # :doc:
         accessor = store_accessor_for(store_attribute)
         accessor.write(self, store_attribute, key, value)
       end
 
-    private
       def store_accessor_for(store_attribute)
-        type_for_attribute(store_attribute.to_s).accessor
+        type_for_attribute(store_attribute).accessor
       end
 
       class HashAccessor # :nodoc:
@@ -176,34 +209,34 @@ module ActiveRecord
         end
       end
 
-    class IndifferentCoder # :nodoc:
-      def initialize(coder_or_class_name)
-        @coder =
-          if coder_or_class_name.respond_to?(:load) && coder_or_class_name.respond_to?(:dump)
-            coder_or_class_name
-          else
-            ActiveRecord::Coders::YAMLColumn.new(coder_or_class_name || Object)
-          end
-      end
+      class IndifferentCoder # :nodoc:
+        def initialize(attr_name, coder_or_class_name)
+          @coder =
+            if coder_or_class_name.respond_to?(:load) && coder_or_class_name.respond_to?(:dump)
+              coder_or_class_name
+            else
+              ActiveRecord::Coders::YAMLColumn.new(attr_name, coder_or_class_name || Object)
+            end
+        end
 
-      def dump(obj)
-        @coder.dump self.class.as_indifferent_hash(obj)
-      end
+        def dump(obj)
+          @coder.dump self.class.as_indifferent_hash(obj)
+        end
 
-      def load(yaml)
-        self.class.as_indifferent_hash(@coder.load(yaml || ''))
-      end
+        def load(yaml)
+          self.class.as_indifferent_hash(@coder.load(yaml || ""))
+        end
 
-      def self.as_indifferent_hash(obj)
-        case obj
-        when ActiveSupport::HashWithIndifferentAccess
-          obj
-        when Hash
-          obj.with_indifferent_access
-        else
-          ActiveSupport::HashWithIndifferentAccess.new
+        def self.as_indifferent_hash(obj)
+          case obj
+          when ActiveSupport::HashWithIndifferentAccess
+            obj
+          when Hash
+            obj.with_indifferent_access
+          else
+            ActiveSupport::HashWithIndifferentAccess.new
+          end
         end
       end
-    end
   end
 end
diff --git a/activerecord/lib/active_record/suppressor.rb b/activerecord/lib/active_record/suppressor.rb
index b3644bf569..8cdb8e0765 100644
--- a/activerecord/lib/active_record/suppressor.rb
+++ b/activerecord/lib/active_record/suppressor.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # ActiveRecord::Suppressor prevents the receiver from being saved during
   # a given block.
@@ -30,14 +32,19 @@ module ActiveRecord
 
     module ClassMethods
       def suppress(&block)
+        previous_state = SuppressorRegistry.suppressed[name]
         SuppressorRegistry.suppressed[name] = true
         yield
       ensure
-        SuppressorRegistry.suppressed[name] = false
+        SuppressorRegistry.suppressed[name] = previous_state
       end
     end
 
-    def create_or_update(*args) # :nodoc:
+    def save(*) # :nodoc:
+      SuppressorRegistry.suppressed[self.class.name] ? true : super
+    end
+
+    def save!(*) # :nodoc:
       SuppressorRegistry.suppressed[self.class.name] ? true : super
     end
   end
diff --git a/activerecord/lib/active_record/table_metadata.rb b/activerecord/lib/active_record/table_metadata.rb
index 41f1c55c3c..b67479fb6a 100644
--- a/activerecord/lib/active_record/table_metadata.rb
+++ b/activerecord/lib/active_record/table_metadata.rb
@@ -1,7 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   class TableMetadata # :nodoc:
-    delegate :foreign_type, :foreign_key, to: :association, prefix: true
-    delegate :association_primary_key, to: :association
+    delegate :foreign_type, :foreign_key, :join_primary_key, :join_foreign_key, to: :association, prefix: true
 
     def initialize(klass, arel_table, association = nil)
       @klass = klass
@@ -10,36 +11,45 @@ module ActiveRecord
     end
 
     def resolve_column_aliases(hash)
-      hash = hash.dup
-      hash.keys.grep(Symbol) do |key|
-        if klass.attribute_alias? key
-          hash[klass.attribute_alias(key)] = hash.delete key
+      new_hash = hash.dup
+      hash.each do |key, _|
+        if (key.is_a?(Symbol)) && klass.attribute_alias?(key)
+          new_hash[klass.attribute_alias(key)] = new_hash.delete(key)
         end
       end
-      hash
+      new_hash
     end
 
     def arel_attribute(column_name)
-      arel_table[column_name]
+      if klass
+        klass.arel_attribute(column_name, arel_table)
+      else
+        arel_table[column_name]
+      end
     end
 
     def type(column_name)
       if klass
-        klass.type_for_attribute(column_name.to_s)
+        klass.type_for_attribute(column_name)
       else
-        Type::Value.new
+        Type.default_value
       end
     end
 
+    def has_column?(column_name)
+      klass && klass.columns_hash.key?(column_name.to_s)
+    end
+
     def associated_with?(association_name)
       klass && klass._reflect_on_association(association_name)
     end
 
     def associated_table(table_name)
-      return self if table_name == arel_table.name
+      association = klass._reflect_on_association(table_name) || klass._reflect_on_association(table_name.to_s.singularize)
 
-      association = klass._reflect_on_association(table_name)
-      if association && !association.polymorphic?
+      if !association && table_name == arel_table.name
+        return self
+      elsif association && !association.polymorphic?
         association_klass = association.klass
         arel_table = association_klass.arel_table.alias(table_name)
       else
@@ -55,8 +65,15 @@ module ActiveRecord
       association && association.polymorphic?
     end
 
-    protected
+    def aggregated_with?(aggregation_name)
+      klass && reflect_on_aggregation(aggregation_name)
+    end
+
+    def reflect_on_aggregation(aggregation_name)
+      klass.reflect_on_aggregation(aggregation_name)
+    end
 
-    attr_reader :klass, :arel_table, :association
+    private
+      attr_reader :klass, :arel_table, :association
   end
 end
diff --git a/activerecord/lib/active_record/tasks/database_tasks.rb b/activerecord/lib/active_record/tasks/database_tasks.rb
index 683741768b..27e401a756 100644
--- a/activerecord/lib/active_record/tasks/database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/database_tasks.rb
@@ -1,14 +1,16 @@
-require 'active_support/core_ext/string/filters'
+# frozen_string_literal: true
+
+require "active_record/database_configurations"
 
 module ActiveRecord
   module Tasks # :nodoc:
     class DatabaseAlreadyExists < StandardError; end # :nodoc:
     class DatabaseNotSupported < StandardError; end # :nodoc:
 
-    # <tt>ActiveRecord::Tasks::DatabaseTasks</tt> is a utility class, which encapsulates
+    # ActiveRecord::Tasks::DatabaseTasks is a utility class, which encapsulates
     # logic behind common tasks used to manage database and migrations.
     #
-    # The tasks defined here are used with Rake tasks provided by Active Record.
+    # The tasks defined here are used with Rails commands provided by Active Record.
     #
     # In order to use DatabaseTasks, a few config values need to be set. All the needed
     # config values are set by Rails already, so it's necessary to do it only if you
@@ -18,15 +20,15 @@ module ActiveRecord
     #
     # The possible config values are:
     #
-    #   * +env+: current environment (like Rails.env).
-    #   * +database_configuration+: configuration of your databases (as in +config/database.yml+).
-    #   * +db_dir+: your +db+ directory.
-    #   * +fixtures_path+: a path to fixtures directory.
-    #   * +migrations_paths+: a list of paths to directories with migrations.
-    #   * +seed_loader+: an object which will load seeds, it needs to respond to the +load_seed+ method.
-    #   * +root+: a path to the root of the application.
+    # * +env+: current environment (like Rails.env).
+    # * +database_configuration+: configuration of your databases (as in +config/database.yml+).
+    # * +db_dir+: your +db+ directory.
+    # * +fixtures_path+: a path to fixtures directory.
+    # * +migrations_paths+: a list of paths to directories with migrations.
+    # * +seed_loader+: an object which will load seeds, it needs to respond to the +load_seed+ method.
+    # * +root+: a path to the root of the application.
     #
-    # Example usage of +DatabaseTasks+ outside Rails could look as such:
+    # Example usage of DatabaseTasks outside Rails could look as such:
     #
     #   include ActiveRecord::Tasks
     #   DatabaseTasks.database_configuration = YAML.load_file('my_database_config.yml')
@@ -35,36 +37,62 @@ module ActiveRecord
     #
     #   DatabaseTasks.create_current('production')
     module DatabaseTasks
+      ##
+      # :singleton-method:
+      # Extra flags passed to database CLI tool (mysqldump/pg_dump) when calling db:structure:dump
+      mattr_accessor :structure_dump_flags, instance_accessor: false
+
+      ##
+      # :singleton-method:
+      # Extra flags passed to database CLI tool when calling db:structure:load
+      mattr_accessor :structure_load_flags, instance_accessor: false
+
       extend self
 
       attr_writer :current_config, :db_dir, :migrations_paths, :fixtures_path, :root, :env, :seed_loader
       attr_accessor :database_configuration
 
-      LOCAL_HOSTS    = ['127.0.0.1', 'localhost']
+      LOCAL_HOSTS = ["127.0.0.1", "localhost"]
+
+      def check_protected_environments!
+        unless ENV["DISABLE_DATABASE_ENVIRONMENT_CHECK"]
+          current = ActiveRecord::Base.connection.migration_context.current_environment
+          stored  = ActiveRecord::Base.connection.migration_context.last_stored_environment
+
+          if ActiveRecord::Base.connection.migration_context.protected_environment?
+            raise ActiveRecord::ProtectedEnvironmentError.new(stored)
+          end
+
+          if stored && stored != current
+            raise ActiveRecord::EnvironmentMismatchError.new(current: current, stored: stored)
+          end
+        end
+      rescue ActiveRecord::NoDatabaseError
+      end
 
       def register_task(pattern, task)
         @tasks ||= {}
         @tasks[pattern] = task
       end
 
-      register_task(/mysql/,        ActiveRecord::Tasks::MySQLDatabaseTasks)
-      register_task(/postgresql/,   ActiveRecord::Tasks::PostgreSQLDatabaseTasks)
-      register_task(/sqlite/,       ActiveRecord::Tasks::SQLiteDatabaseTasks)
+      register_task(/mysql/,        "ActiveRecord::Tasks::MySQLDatabaseTasks")
+      register_task(/postgresql/,   "ActiveRecord::Tasks::PostgreSQLDatabaseTasks")
+      register_task(/sqlite/,       "ActiveRecord::Tasks::SQLiteDatabaseTasks")
 
       def db_dir
         @db_dir ||= Rails.application.config.paths["db"].first
       end
 
       def migrations_paths
-        @migrations_paths ||= Rails.application.paths['db/migrate'].to_a
+        @migrations_paths ||= Rails.application.paths["db/migrate"].to_a
       end
 
       def fixtures_path
-        @fixtures_path ||= if ENV['FIXTURES_PATH']
-                             File.join(root, ENV['FIXTURES_PATH'])
-                           else
-                             File.join(root, 'test', 'fixtures')
-                           end
+        @fixtures_path ||= if ENV["FIXTURES_PATH"]
+          File.join(root, ENV["FIXTURES_PATH"])
+        else
+          File.join(root, "test", "fixtures")
+        end
       end
 
       def root
@@ -75,31 +103,54 @@ module ActiveRecord
         @env ||= Rails.env
       end
 
+      def spec
+        @spec ||= "primary"
+      end
+
       def seed_loader
         @seed_loader ||= Rails.application
       end
 
       def current_config(options = {})
-        options.reverse_merge! :env => env
+        options.reverse_merge! env: env
+        options[:spec] ||= "primary"
         if options.has_key?(:config)
           @current_config = options[:config]
         else
-          @current_config ||= ActiveRecord::Base.configurations[options[:env]]
+          @current_config ||= ActiveRecord::Base.configurations.configs_for(env_name: options[:env], spec_name: options[:spec]).config
         end
       end
 
       def create(*arguments)
         configuration = arguments.first
-        class_for_adapter(configuration['adapter']).new(*arguments).create
+        class_for_adapter(configuration["adapter"]).new(*arguments).create
+        $stdout.puts "Created database '#{configuration['database']}'" if verbose?
       rescue DatabaseAlreadyExists
-        $stderr.puts "#{configuration['database']} already exists"
+        $stderr.puts "Database '#{configuration['database']}' already exists" if verbose?
       rescue Exception => error
-        $stderr.puts error, *(error.backtrace)
-        $stderr.puts "Couldn't create database for #{configuration.inspect}"
+        $stderr.puts error
+        $stderr.puts "Couldn't create '#{configuration['database']}' database. Please check your configuration."
+        raise
       end
 
       def create_all
+        old_pool = ActiveRecord::Base.connection_handler.retrieve_connection_pool(ActiveRecord::Base.connection_specification_name)
         each_local_configuration { |configuration| create configuration }
+        if old_pool
+          ActiveRecord::Base.connection_handler.establish_connection(old_pool.spec.to_hash)
+        end
+      end
+
+      def for_each
+        databases = Rails.application.config.database_configuration
+        database_configs = ActiveRecord::DatabaseConfigurations.new(databases).configs_for(env_name: Rails.env)
+
+        # if this is a single database application we don't want tasks for each primary database
+        return if database_configs.count == 1
+
+        database_configs.each do |db_config|
+          yield db_config.spec_name
+        end
       end
 
       def create_current(environment = env)
@@ -111,12 +162,14 @@ module ActiveRecord
 
       def drop(*arguments)
         configuration = arguments.first
-        class_for_adapter(configuration['adapter']).new(*arguments).drop
+        class_for_adapter(configuration["adapter"]).new(*arguments).drop
+        $stdout.puts "Dropped database '#{configuration['database']}'" if verbose?
       rescue ActiveRecord::NoDatabaseError
         $stderr.puts "Database '#{configuration['database']}' does not exist"
       rescue Exception => error
-        $stderr.puts error, *(error.backtrace)
-        $stderr.puts "Couldn't drop #{configuration['database']}"
+        $stderr.puts error
+        $stderr.puts "Couldn't drop database '#{configuration['database']}'"
+        raise
       end
 
       def drop_all
@@ -130,37 +183,65 @@ module ActiveRecord
       end
 
       def migrate
-        verbose = ENV["VERBOSE"] ? ENV["VERBOSE"] == "true" : true
-        version = ENV["VERSION"] ? ENV["VERSION"].to_i : nil
-        scope   = ENV['SCOPE']
-        verbose_was, Migration.verbose = Migration.verbose, verbose
-        Migrator.migrate(Migrator.migrations_paths, version) do |migration|
+        check_target_version
+
+        scope = ENV["SCOPE"]
+        verbose_was, Migration.verbose = Migration.verbose, verbose?
+
+        Base.connection.migration_context.migrate(target_version) do |migration|
           scope.blank? || scope == migration.scope
         end
+
+        ActiveRecord::Base.clear_cache!
       ensure
         Migration.verbose = verbose_was
       end
 
-      def charset_current(environment = env)
-        charset ActiveRecord::Base.configurations[environment]
+      def migrate_status
+        unless ActiveRecord::SchemaMigration.table_exists?
+          Kernel.abort "Schema migrations table does not exist yet."
+        end
+
+        # output
+        puts "\ndatabase: #{ActiveRecord::Base.connection_config[:database]}\n\n"
+        puts "#{'Status'.center(8)}  #{'Migration ID'.ljust(14)}  Migration Name"
+        puts "-" * 50
+        ActiveRecord::Base.connection.migration_context.migrations_status.each do |status, version, name|
+          puts "#{status.center(8)}  #{version.ljust(14)}  #{name}"
+        end
+        puts
+      end
+
+      def check_target_version
+        if target_version && !(Migration::MigrationFilenameRegexp.match?(ENV["VERSION"]) || /\A\d+\z/.match?(ENV["VERSION"]))
+          raise "Invalid format of target version: `VERSION=#{ENV['VERSION']}`"
+        end
+      end
+
+      def target_version
+        ENV["VERSION"].to_i if ENV["VERSION"] && !ENV["VERSION"].empty?
+      end
+
+      def charset_current(environment = env, specification_name = spec)
+        charset ActiveRecord::Base.configurations.configs_for(env_name: environment, spec_name: specification_name).config
       end
 
       def charset(*arguments)
         configuration = arguments.first
-        class_for_adapter(configuration['adapter']).new(*arguments).charset
+        class_for_adapter(configuration["adapter"]).new(*arguments).charset
       end
 
-      def collation_current(environment = env)
-        collation ActiveRecord::Base.configurations[environment]
+      def collation_current(environment = env, specification_name = spec)
+        collation ActiveRecord::Base.configurations.configs_for(env_name: environment, spec_name: specification_name).config
       end
 
       def collation(*arguments)
         configuration = arguments.first
-        class_for_adapter(configuration['adapter']).new(*arguments).collation
+        class_for_adapter(configuration["adapter"]).new(*arguments).collation
       end
 
       def purge(configuration)
-        class_for_adapter(configuration['adapter']).new(configuration).purge
+        class_for_adapter(configuration["adapter"]).new(configuration).purge
       end
 
       def purge_all
@@ -179,65 +260,80 @@ module ActiveRecord
       def structure_dump(*arguments)
         configuration = arguments.first
         filename = arguments.delete_at 1
-        class_for_adapter(configuration['adapter']).new(*arguments).structure_dump(filename)
+        class_for_adapter(configuration["adapter"]).new(*arguments).structure_dump(filename, structure_dump_flags)
       end
 
       def structure_load(*arguments)
         configuration = arguments.first
         filename = arguments.delete_at 1
-        class_for_adapter(configuration['adapter']).new(*arguments).structure_load(filename)
+        class_for_adapter(configuration["adapter"]).new(*arguments).structure_load(filename, structure_load_flags)
       end
 
-      def load_schema(configuration, format = ActiveRecord::Base.schema_format, file = nil) # :nodoc:
-        file ||= schema_file(format)
+      def load_schema(configuration, format = ActiveRecord::Base.schema_format, file = nil, environment = env, spec_name = "primary") # :nodoc:
+        file ||= dump_filename(spec_name, format)
+
+        verbose_was, Migration.verbose = Migration.verbose, verbose? && ENV["VERBOSE"]
+        check_schema_file(file)
+        ActiveRecord::Base.establish_connection(configuration)
 
         case format
         when :ruby
-          check_schema_file(file)
-          ActiveRecord::Base.establish_connection(configuration)
           load(file)
         when :sql
-          check_schema_file(file)
           structure_load(configuration, file)
         else
           raise ArgumentError, "unknown format #{format.inspect}"
         end
+        ActiveRecord::InternalMetadata.create_table
+        ActiveRecord::InternalMetadata[:environment] = environment
+      ensure
+        Migration.verbose = verbose_was
       end
 
-      def load_schema_for(*args)
-        ActiveSupport::Deprecation.warn(<<-MSG.squish)
-          This method was renamed to `#load_schema` and will be removed in the future.
-          Use `#load_schema` instead.
-        MSG
-        load_schema(*args)
+      def schema_file(format = ActiveRecord::Base.schema_format)
+        File.join(db_dir, schema_file_type(format))
       end
 
-      def schema_file(format = ActiveRecord::Base.schema_format)
+      def schema_file_type(format = ActiveRecord::Base.schema_format)
         case format
         when :ruby
-          File.join(db_dir, "schema.rb")
+          "schema.rb"
         when :sql
-          File.join(db_dir, "structure.sql")
+          "structure.sql"
+        end
+      end
+
+      def dump_filename(namespace, format = ActiveRecord::Base.schema_format)
+        filename = if namespace == "primary"
+          schema_file_type(format)
+        else
+          "#{namespace}_#{schema_file_type(format)}"
         end
+
+        ENV["SCHEMA"] || File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, filename)
       end
 
-      def load_schema_current_if_exists(format = ActiveRecord::Base.schema_format, file = nil, environment = env)
-        if File.exist?(file || schema_file(format))
-          load_schema_current(format, file, environment)
+      def cache_dump_filename(namespace)
+        filename = if namespace == "primary"
+          "schema_cache.yml"
+        else
+          "#{namespace}_schema_cache.yml"
         end
+
+        ENV["SCHEMA_CACHE"] || File.join(ActiveRecord::Tasks::DatabaseTasks.db_dir, filename)
       end
 
       def load_schema_current(format = ActiveRecord::Base.schema_format, file = nil, environment = env)
-        each_current_configuration(environment) { |configuration|
-          load_schema configuration, format, file
+        each_current_configuration(environment) { |configuration, spec_name, env|
+          load_schema(configuration, format, file, env, spec_name)
         }
         ActiveRecord::Base.establish_connection(environment.to_sym)
       end
 
       def check_schema_file(filename)
         unless File.exist?(filename)
-          message = %{#{filename} doesn't exist yet. Run `rake db:migrate` to create it, then try again.}
-          message << %{ If you do not intend to use a database, you should instead alter #{Rails.root}/config/application.rb to limit the frameworks that will be loaded.} if defined?(::Rails)
+          message = +%{#{filename} doesn't exist yet. Run `rails db:migrate` to create it, then try again.}
+          message << %{ If you do not intend to use a database, you should instead alter #{Rails.root}/config/application.rb to limit the frameworks that will be loaded.} if defined?(::Rails.root)
           Kernel.abort message
         end
       end
@@ -246,48 +342,62 @@ module ActiveRecord
         if seed_loader
           seed_loader.load_seed
         else
-          raise "You tried to load seed data, but no seed loader is specified. Please specify seed " +
-                "loader with ActiveRecord::Tasks::DatabaseTasks.seed_loader = your_seed_loader\n" +
+          raise "You tried to load seed data, but no seed loader is specified. Please specify seed " \
+                "loader with ActiveRecord::Tasks::DatabaseTasks.seed_loader = your_seed_loader\n" \
                 "Seed loader should respond to load_seed method"
         end
       end
 
+      # Dumps the schema cache in YAML format for the connection into the file
+      #
+      # ==== Examples:
+      #   ActiveRecord::Tasks::DatabaseTasks.dump_schema_cache(ActiveRecord::Base.connection, "tmp/schema_dump.yaml")
+      def dump_schema_cache(conn, filename)
+        conn.schema_cache.clear!
+        conn.data_sources.each { |table| conn.schema_cache.add(table) }
+        open(filename, "wb") { |f| f.write(YAML.dump(conn.schema_cache)) }
+      end
+
       private
+        def verbose?
+          ENV["VERBOSE"] ? ENV["VERBOSE"] != "false" : true
+        end
 
-      def class_for_adapter(adapter)
-        key = @tasks.keys.detect { |pattern| adapter[pattern] }
-        unless key
-          raise DatabaseNotSupported, "Rake tasks not supported by '#{adapter}' adapter"
+        def class_for_adapter(adapter)
+          _key, task = @tasks.each_pair.detect { |pattern, _task| adapter[pattern] }
+          unless task
+            raise DatabaseNotSupported, "Rake tasks not supported by '#{adapter}' adapter"
+          end
+          task.is_a?(String) ? task.constantize : task
         end
-        @tasks[key]
-      end
 
-      def each_current_configuration(environment)
-        environments = [environment]
-        # add test environment only if no RAILS_ENV was specified.
-        environments << 'test' if environment == 'development' && ENV['RAILS_ENV'].nil?
+        def each_current_configuration(environment)
+          environments = [environment]
+          environments << "test" if environment == "development"
 
-        configurations = ActiveRecord::Base.configurations.values_at(*environments)
-        configurations.compact.each do |configuration|
-          yield configuration unless configuration['database'].blank?
+          environments.each do |env|
+            ActiveRecord::Base.configurations.configs_for(env_name: env).each do |db_config|
+              yield db_config.config, db_config.spec_name, env
+            end
+          end
         end
-      end
 
-      def each_local_configuration
-        ActiveRecord::Base.configurations.each_value do |configuration|
-          next unless configuration['database']
+        def each_local_configuration
+          ActiveRecord::Base.configurations.configs_for.each do |db_config|
+            configuration = db_config.config
+            next unless configuration["database"]
 
-          if local_database?(configuration)
-            yield configuration
-          else
-            $stderr.puts "This task only modifies local databases. #{configuration['database']} is on a remote host."
+            if local_database?(configuration)
+              yield configuration
+            else
+              $stderr.puts "This task only modifies local databases. #{configuration['database']} is on a remote host."
+            end
           end
         end
-      end
 
-      def local_database?(configuration)
-        configuration['host'].blank? || LOCAL_HOSTS.include?(configuration['host'])
-      end
+        def local_database?(configuration)
+          configuration["host"].blank? || LOCAL_HOSTS.include?(configuration["host"])
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/tasks/mysql_database_tasks.rb b/activerecord/lib/active_record/tasks/mysql_database_tasks.rb
index 673386f0d9..1c1b29b5e1 100644
--- a/activerecord/lib/active_record/tasks/mysql_database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/mysql_database_tasks.rb
@@ -1,10 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Tasks # :nodoc:
     class MySQLDatabaseTasks # :nodoc:
-      DEFAULT_CHARSET     = ENV['CHARSET']   || 'utf8'
-      DEFAULT_COLLATION   = ENV['COLLATION'] || 'utf8_unicode_ci'
-      ACCESS_DENIED_ERROR = 1045
-
       delegate :connection, :establish_connection, to: ActiveRecord::Base
 
       def initialize(configuration)
@@ -13,38 +11,24 @@ module ActiveRecord
 
       def create
         establish_connection configuration_without_database
-        connection.create_database configuration['database'], creation_options
+        connection.create_database configuration["database"], creation_options
         establish_connection configuration
       rescue ActiveRecord::StatementInvalid => error
-        if /database exists/ === error.message
+        if error.message.include?("database exists")
           raise DatabaseAlreadyExists
         else
           raise
         end
-      rescue error_class => error
-        if error.respond_to?(:errno) && error.errno == ACCESS_DENIED_ERROR
-          $stdout.print error.error
-          establish_connection root_configuration_without_database
-          connection.create_database configuration['database'], creation_options
-          if configuration['username'] != 'root'
-            connection.execute grant_statement.gsub(/\s+/, ' ').strip
-          end
-          establish_connection configuration
-        else
-          $stderr.puts error.inspect
-          $stderr.puts "Couldn't create database for #{configuration.inspect}, #{creation_options.inspect}"
-          $stderr.puts "(If you set the charset manually, make sure you have a matching collation)" if configuration['encoding']
-        end
       end
 
       def drop
         establish_connection configuration
-        connection.drop_database configuration['database']
+        connection.drop_database configuration["database"]
       end
 
       def purge
         establish_connection configuration
-        connection.recreate_database configuration['database'], creation_options
+        connection.recreate_database configuration["database"], creation_options
       end
 
       def charset
@@ -55,98 +39,75 @@ module ActiveRecord
         connection.collation
       end
 
-      def structure_dump(filename)
-        args = prepare_command_options('mysqldump')
+      def structure_dump(filename, extra_flags)
+        args = prepare_command_options
         args.concat(["--result-file", "#{filename}"])
         args.concat(["--no-data"])
         args.concat(["--routines"])
-        args.concat(["#{configuration['database']}"])
-        unless Kernel.system(*args)
-          $stderr.puts "Could not dump the database structure. "\
-                       "Make sure `mysqldump` is in your PATH and check the command output for warnings."
-        end
-      end
+        args.concat(["--skip-comments"])
 
-      def structure_load(filename)
-        args = prepare_command_options('mysql')
-        args.concat(['--execute', %{SET FOREIGN_KEY_CHECKS = 0; SOURCE #{filename}; SET FOREIGN_KEY_CHECKS = 1}])
-        args.concat(["--database", "#{configuration['database']}"])
-        Kernel.system(*args)
-      end
+        ignore_tables = ActiveRecord::SchemaDumper.ignore_tables
+        if ignore_tables.any?
+          args += ignore_tables.map { |table| "--ignore-table=#{configuration['database']}.#{table}" }
+        end
 
-      private
+        args.concat(["#{configuration['database']}"])
+        args.unshift(*extra_flags) if extra_flags
 
-      def configuration
-        @configuration
+        run_cmd("mysqldump", args, "dumping")
       end
 
-      def configuration_without_database
-        configuration.merge('database' => nil)
+      def structure_load(filename, extra_flags)
+        args = prepare_command_options
+        args.concat(["--execute", %{SET FOREIGN_KEY_CHECKS = 0; SOURCE #{filename}; SET FOREIGN_KEY_CHECKS = 1}])
+        args.concat(["--database", "#{configuration['database']}"])
+        args.unshift(*extra_flags) if extra_flags
+
+        run_cmd("mysql", args, "loading")
       end
 
-      def creation_options
-        Hash.new.tap do |options|
-          options[:charset]     = configuration['encoding']   if configuration.include? 'encoding'
-          options[:collation]   = configuration['collation']  if configuration.include? 'collation'
+      private
 
-          # Set default charset only when collation isn't set.
-          options[:charset]   ||= DEFAULT_CHARSET unless options[:collation]
+        attr_reader :configuration
 
-          # Set default collation only when charset is also default.
-          options[:collation] ||= DEFAULT_COLLATION if options[:charset] == DEFAULT_CHARSET
+        def configuration_without_database
+          configuration.merge("database" => nil)
         end
-      end
 
-      def error_class
-        if configuration['adapter'] =~ /jdbc/
-          require 'active_record/railties/jdbcmysql_error'
-          ArJdbcMySQL::Error
-        elsif defined?(Mysql2)
-          Mysql2::Error
-        elsif defined?(Mysql)
-          Mysql::Error
-        else
-          StandardError
+        def creation_options
+          Hash.new.tap do |options|
+            options[:charset]     = configuration["encoding"]   if configuration.include? "encoding"
+            options[:collation]   = configuration["collation"]  if configuration.include? "collation"
+          end
         end
-      end
-
-      def grant_statement
-        <<-SQL
-GRANT ALL PRIVILEGES ON #{configuration['database']}.*
-  TO '#{configuration['username']}'@'localhost'
-IDENTIFIED BY '#{configuration['password']}' WITH GRANT OPTION;
-        SQL
-      end
 
-      def root_configuration_without_database
-        configuration_without_database.merge(
-          'username' => 'root',
-          'password' => root_password
-        )
-      end
+        def prepare_command_options
+          args = {
+            "host"      => "--host",
+            "port"      => "--port",
+            "socket"    => "--socket",
+            "username"  => "--user",
+            "password"  => "--password",
+            "encoding"  => "--default-character-set",
+            "sslca"     => "--ssl-ca",
+            "sslcert"   => "--ssl-cert",
+            "sslcapath" => "--ssl-capath",
+            "sslcipher" => "--ssl-cipher",
+            "sslkey"    => "--ssl-key"
+          }.map { |opt, arg| "#{arg}=#{configuration[opt]}" if configuration[opt] }.compact
+
+          args
+        end
 
-      def root_password
-        $stdout.print "Please provide the root password for your MySQL installation\n>"
-        $stdin.gets.strip
-      end
+        def run_cmd(cmd, args, action)
+          fail run_cmd_error(cmd, args, action) unless Kernel.system(cmd, *args)
+        end
 
-      def prepare_command_options(command)
-        args = {
-          'host'      => '--host',
-          'port'      => '--port',
-          'socket'    => '--socket',
-          'username'  => '--user',
-          'password'  => '--password',
-          'encoding'  => '--default-character-set',
-          'sslca'     => '--ssl-ca',
-          'sslcert'   => '--ssl-cert',
-          'sslcapath' => '--ssl-capath',
-          'sslcipher' => '--ssh-cipher',
-          'sslkey'    => '--ssl-key'
-        }.map { |opt, arg| "#{arg}=#{configuration[opt]}" if configuration[opt] }.compact
-
-        [command, *args]
-      end
+        def run_cmd_error(cmd, args, action)
+          msg = +"failed to execute: `#{cmd}`\n"
+          msg << "Please check the output above for any errors and make sure that `#{cmd}` is installed in your PATH and has proper permissions.\n\n"
+          msg
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/tasks/postgresql_database_tasks.rb b/activerecord/lib/active_record/tasks/postgresql_database_tasks.rb
index d7da95c8a9..8acb11f75f 100644
--- a/activerecord/lib/active_record/tasks/postgresql_database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/postgresql_database_tasks.rb
@@ -1,9 +1,13 @@
-require 'shellwords'
+# frozen_string_literal: true
+
+require "tempfile"
 
 module ActiveRecord
   module Tasks # :nodoc:
     class PostgreSQLDatabaseTasks # :nodoc:
-      DEFAULT_ENCODING = ENV['CHARSET'] || 'utf8'
+      DEFAULT_ENCODING = ENV["CHARSET"] || "utf8"
+      ON_ERROR_STOP_1 = "ON_ERROR_STOP=1"
+      SQL_COMMENT_BEGIN = "--"
 
       delegate :connection, :establish_connection, :clear_active_connections!,
         to: ActiveRecord::Base
@@ -14,11 +18,11 @@ module ActiveRecord
 
       def create(master_established = false)
         establish_master_connection unless master_established
-        connection.create_database configuration['database'],
-          configuration.merge('encoding' => encoding)
+        connection.create_database configuration["database"],
+          configuration.merge("encoding" => encoding)
         establish_connection configuration
       rescue ActiveRecord::StatementInvalid => error
-        if /database .* already exists/ === error.message
+        if error.cause.is_a?(PG::DuplicateDatabase)
           raise DatabaseAlreadyExists
         else
           raise
@@ -27,7 +31,7 @@ module ActiveRecord
 
       def drop
         establish_master_connection
-        connection.drop_database configuration['database']
+        connection.drop_database configuration["database"]
       end
 
       def charset
@@ -44,55 +48,94 @@ module ActiveRecord
         create true
       end
 
-      def structure_dump(filename)
+      def structure_dump(filename, extra_flags)
         set_psql_env
 
-        search_path = case ActiveRecord::Base.dump_schemas
-        when :schema_search_path
-          configuration['schema_search_path']
-        when :all
-          nil
-        when String
-          ActiveRecord::Base.dump_schemas
-        end
+        search_path = \
+          case ActiveRecord::Base.dump_schemas
+          when :schema_search_path
+            configuration["schema_search_path"]
+          when :all
+            nil
+          when String
+            ActiveRecord::Base.dump_schemas
+          end
+
+        args = ["-s", "-x", "-O", "-f", filename]
+        args.concat(Array(extra_flags)) if extra_flags
         unless search_path.blank?
-          search_path = search_path.split(",").map{|search_path_part| "--schema=#{Shellwords.escape(search_path_part.strip)}" }.join(" ")
+          args += search_path.split(",").map do |part|
+            "--schema=#{part.strip}"
+          end
         end
 
-        command = "pg_dump -i -s -x -O -f #{Shellwords.escape(filename)} #{search_path} #{Shellwords.escape(configuration['database'])}"
-        raise 'Error dumping database' unless Kernel.system(command)
+        ignore_tables = ActiveRecord::SchemaDumper.ignore_tables
+        if ignore_tables.any?
+          args += ignore_tables.flat_map { |table| ["-T", table] }
+        end
 
+        args << configuration["database"]
+        run_cmd("pg_dump", args, "dumping")
+        remove_sql_header_comments(filename)
         File.open(filename, "a") { |f| f << "SET search_path TO #{connection.schema_search_path};\n\n" }
       end
 
-      def structure_load(filename)
+      def structure_load(filename, extra_flags)
         set_psql_env
-        Kernel.system("psql -X -q -f #{Shellwords.escape(filename)} #{configuration['database']}")
+        args = ["-v", ON_ERROR_STOP_1, "-q", "-X", "-f", filename]
+        args.concat(Array(extra_flags)) if extra_flags
+        args << configuration["database"]
+        run_cmd("psql", args, "loading")
       end
 
       private
 
-      def configuration
-        @configuration
-      end
+        attr_reader :configuration
 
-      def encoding
-        configuration['encoding'] || DEFAULT_ENCODING
-      end
+        def encoding
+          configuration["encoding"] || DEFAULT_ENCODING
+        end
 
-      def establish_master_connection
-        establish_connection configuration.merge(
-          'database'           => 'postgres',
-          'schema_search_path' => 'public'
-        )
-      end
+        def establish_master_connection
+          establish_connection configuration.merge(
+            "database"           => "postgres",
+            "schema_search_path" => "public"
+          )
+        end
 
-      def set_psql_env
-        ENV['PGHOST']     = configuration['host']          if configuration['host']
-        ENV['PGPORT']     = configuration['port'].to_s     if configuration['port']
-        ENV['PGPASSWORD'] = configuration['password'].to_s if configuration['password']
-        ENV['PGUSER']     = configuration['username'].to_s if configuration['username']
-      end
+        def set_psql_env
+          ENV["PGHOST"]     = configuration["host"]          if configuration["host"]
+          ENV["PGPORT"]     = configuration["port"].to_s     if configuration["port"]
+          ENV["PGPASSWORD"] = configuration["password"].to_s if configuration["password"]
+          ENV["PGUSER"]     = configuration["username"].to_s if configuration["username"]
+        end
+
+        def run_cmd(cmd, args, action)
+          fail run_cmd_error(cmd, args, action) unless Kernel.system(cmd, *args)
+        end
+
+        def run_cmd_error(cmd, args, action)
+          msg = +"failed to execute:\n"
+          msg << "#{cmd} #{args.join(' ')}\n\n"
+          msg << "Please check the output above for any errors and make sure that `#{cmd}` is installed in your PATH and has proper permissions.\n\n"
+          msg
+        end
+
+        def remove_sql_header_comments(filename)
+          removing_comments = true
+          tempfile = Tempfile.open("uncommented_structure.sql")
+          begin
+            File.foreach(filename) do |line|
+              unless removing_comments && (line.start_with?(SQL_COMMENT_BEGIN) || line.blank?)
+                tempfile << line
+                removing_comments = false
+              end
+            end
+          ensure
+            tempfile.close
+          end
+          FileUtils.cp(tempfile.path, filename)
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/tasks/sqlite_database_tasks.rb b/activerecord/lib/active_record/tasks/sqlite_database_tasks.rb
index 9ab64d0325..a82cea80ca 100644
--- a/activerecord/lib/active_record/tasks/sqlite_database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/sqlite_database_tasks.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Tasks # :nodoc:
     class SQLiteDatabaseTasks # :nodoc:
@@ -8,22 +10,26 @@ module ActiveRecord
       end
 
       def create
-        raise DatabaseAlreadyExists if File.exist?(configuration['database'])
+        raise DatabaseAlreadyExists if File.exist?(configuration["database"])
 
         establish_connection configuration
         connection
       end
 
       def drop
-        require 'pathname'
-        path = Pathname.new configuration['database']
+        require "pathname"
+        path = Pathname.new configuration["database"]
         file = path.absolute? ? path.to_s : File.join(root, path)
 
-        FileUtils.rm(file) if File.exist?(file)
+        FileUtils.rm(file)
+      rescue Errno::ENOENT => error
+        raise NoDatabaseError.new(error.message)
       end
 
       def purge
         drop
+      rescue NoDatabaseError
+      ensure
         create
       end
 
@@ -31,25 +37,41 @@ module ActiveRecord
         connection.encoding
       end
 
-      def structure_dump(filename)
-        dbfile = configuration['database']
-        `sqlite3 #{dbfile} .schema > #{filename}`
+      def structure_dump(filename, extra_flags)
+        args = []
+        args.concat(Array(extra_flags)) if extra_flags
+        args << configuration["database"]
+
+        ignore_tables = ActiveRecord::SchemaDumper.ignore_tables
+        if ignore_tables.any?
+          condition = ignore_tables.map { |table| connection.quote(table) }.join(", ")
+          args << "SELECT sql FROM sqlite_master WHERE tbl_name NOT IN (#{condition}) ORDER BY tbl_name, type DESC, name"
+        else
+          args << ".schema"
+        end
+        run_cmd("sqlite3", args, filename)
       end
 
-      def structure_load(filename)
-        dbfile = configuration['database']
-        `sqlite3 #{dbfile} < "#{filename}"`
+      def structure_load(filename, extra_flags)
+        dbfile = configuration["database"]
+        flags = extra_flags.join(" ") if extra_flags
+        `sqlite3 #{flags} #{dbfile} < "#{filename}"`
       end
 
       private
 
-      def configuration
-        @configuration
-      end
+        attr_reader :configuration, :root
 
-      def root
-        @root
-      end
+        def run_cmd(cmd, args, out)
+          fail run_cmd_error(cmd, args) unless Kernel.system(cmd, *args, out: out)
+        end
+
+        def run_cmd_error(cmd, args)
+          msg = +"failed to execute:\n"
+          msg << "#{cmd} #{args.join(' ')}\n\n"
+          msg << "Please check the output above for any errors and make sure that `#{cmd}` is installed in your PATH and has proper permissions.\n\n"
+          msg
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/test_databases.rb b/activerecord/lib/active_record/test_databases.rb
new file mode 100644
index 0000000000..999830ba79
--- /dev/null
+++ b/activerecord/lib/active_record/test_databases.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require "active_support/testing/parallelization"
+
+module ActiveRecord
+  module TestDatabases # :nodoc:
+    ActiveSupport::Testing::Parallelization.after_fork_hook do |i|
+      create_and_load_schema(i, env_name: Rails.env)
+    end
+
+    ActiveSupport::Testing::Parallelization.run_cleanup_hook do
+      drop(env_name: Rails.env)
+    end
+
+    def self.create_and_load_schema(i, env_name:)
+      old, ENV["VERBOSE"] = ENV["VERBOSE"], "false"
+
+      ActiveRecord::Base.configurations.configs_for(env_name: env_name).each do |db_config|
+        db_config.config["database"] += "-#{i}"
+        ActiveRecord::Tasks::DatabaseTasks.create(db_config.config)
+        ActiveRecord::Tasks::DatabaseTasks.load_schema(db_config.config, ActiveRecord::Base.schema_format, nil, env_name, db_config.spec_name)
+      end
+    ensure
+      ActiveRecord::Base.establish_connection(Rails.env.to_sym)
+      ENV["VERBOSE"] = old
+    end
+
+    def self.drop(env_name:)
+      old, ENV["VERBOSE"] = ENV["VERBOSE"], "false"
+
+      ActiveRecord::Base.configurations.configs_for(env_name: env_name).each do |db_config|
+        ActiveRecord::Tasks::DatabaseTasks.drop(db_config.config)
+      end
+    ensure
+      ENV["VERBOSE"] = old
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/test_fixtures.rb b/activerecord/lib/active_record/test_fixtures.rb
new file mode 100644
index 0000000000..7b7b3f7112
--- /dev/null
+++ b/activerecord/lib/active_record/test_fixtures.rb
@@ -0,0 +1,201 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module TestFixtures
+    extend ActiveSupport::Concern
+
+    def before_setup # :nodoc:
+      setup_fixtures
+      super
+    end
+
+    def after_teardown # :nodoc:
+      super
+      teardown_fixtures
+    end
+
+    included do
+      class_attribute :fixture_path, instance_writer: false
+      class_attribute :fixture_table_names, default: []
+      class_attribute :fixture_class_names, default: {}
+      class_attribute :use_transactional_tests, default: true
+      class_attribute :use_instantiated_fixtures, default: false # true, false, or :no_instances
+      class_attribute :pre_loaded_fixtures, default: false
+      class_attribute :config, default: ActiveRecord::Base
+      class_attribute :lock_threads, default: true
+    end
+
+    module ClassMethods
+      # Sets the model class for a fixture when the class name cannot be inferred from the fixture name.
+      #
+      # Examples:
+      #
+      #   set_fixture_class some_fixture:        SomeModel,
+      #                     'namespaced/fixture' => Another::Model
+      #
+      # The keys must be the fixture names, that coincide with the short paths to the fixture files.
+      def set_fixture_class(class_names = {})
+        self.fixture_class_names = fixture_class_names.merge(class_names.stringify_keys)
+      end
+
+      def fixtures(*fixture_set_names)
+        if fixture_set_names.first == :all
+          raise StandardError, "No fixture path found. Please set `#{self}.fixture_path`." if fixture_path.blank?
+          fixture_set_names = Dir["#{fixture_path}/{**,*}/*.{yml}"].uniq
+          fixture_set_names.map! { |f| f[(fixture_path.to_s.size + 1)..-5] }
+        else
+          fixture_set_names = fixture_set_names.flatten.map(&:to_s)
+        end
+
+        self.fixture_table_names |= fixture_set_names
+        setup_fixture_accessors(fixture_set_names)
+      end
+
+      def setup_fixture_accessors(fixture_set_names = nil)
+        fixture_set_names = Array(fixture_set_names || fixture_table_names)
+        methods = Module.new do
+          fixture_set_names.each do |fs_name|
+            fs_name = fs_name.to_s
+            accessor_name = fs_name.tr("/", "_").to_sym
+
+            define_method(accessor_name) do |*fixture_names|
+              force_reload = fixture_names.pop if fixture_names.last == true || fixture_names.last == :reload
+              return_single_record = fixture_names.size == 1
+              fixture_names = @loaded_fixtures[fs_name].fixtures.keys if fixture_names.empty?
+
+              @fixture_cache[fs_name] ||= {}
+
+              instances = fixture_names.map do |f_name|
+                f_name = f_name.to_s if f_name.is_a?(Symbol)
+                @fixture_cache[fs_name].delete(f_name) if force_reload
+
+                if @loaded_fixtures[fs_name][f_name]
+                  @fixture_cache[fs_name][f_name] ||= @loaded_fixtures[fs_name][f_name].find
+                else
+                  raise StandardError, "No fixture named '#{f_name}' found for fixture set '#{fs_name}'"
+                end
+              end
+
+              return_single_record ? instances.first : instances
+            end
+            private accessor_name
+          end
+        end
+        include methods
+      end
+
+      def uses_transaction(*methods)
+        @uses_transaction = [] unless defined?(@uses_transaction)
+        @uses_transaction.concat methods.map(&:to_s)
+      end
+
+      def uses_transaction?(method)
+        @uses_transaction = [] unless defined?(@uses_transaction)
+        @uses_transaction.include?(method.to_s)
+      end
+    end
+
+    def run_in_transaction?
+      use_transactional_tests &&
+        !self.class.uses_transaction?(method_name)
+    end
+
+    def setup_fixtures(config = ActiveRecord::Base)
+      if pre_loaded_fixtures && !use_transactional_tests
+        raise RuntimeError, "pre_loaded_fixtures requires use_transactional_tests"
+      end
+
+      @fixture_cache = {}
+      @fixture_connections = []
+      @@already_loaded_fixtures ||= {}
+      @connection_subscriber = nil
+
+      # Load fixtures once and begin transaction.
+      if run_in_transaction?
+        if @@already_loaded_fixtures[self.class]
+          @loaded_fixtures = @@already_loaded_fixtures[self.class]
+        else
+          @loaded_fixtures = load_fixtures(config)
+          @@already_loaded_fixtures[self.class] = @loaded_fixtures
+        end
+
+        # Begin transactions for connections already established
+        @fixture_connections = enlist_fixture_connections
+        @fixture_connections.each do |connection|
+          connection.begin_transaction joinable: false
+          connection.pool.lock_thread = true if lock_threads
+        end
+
+        # When connections are established in the future, begin a transaction too
+        @connection_subscriber = ActiveSupport::Notifications.subscribe("!connection.active_record") do |_, _, _, _, payload|
+          spec_name = payload[:spec_name] if payload.key?(:spec_name)
+
+          if spec_name
+            begin
+              connection = ActiveRecord::Base.connection_handler.retrieve_connection(spec_name)
+            rescue ConnectionNotEstablished
+              connection = nil
+            end
+
+            if connection && !@fixture_connections.include?(connection)
+              connection.begin_transaction joinable: false
+              connection.pool.lock_thread = true if lock_threads
+              @fixture_connections << connection
+            end
+          end
+        end
+
+      # Load fixtures for every test.
+      else
+        ActiveRecord::FixtureSet.reset_cache
+        @@already_loaded_fixtures[self.class] = nil
+        @loaded_fixtures = load_fixtures(config)
+      end
+
+      # Instantiate fixtures for every test if requested.
+      instantiate_fixtures if use_instantiated_fixtures
+    end
+
+    def teardown_fixtures
+      # Rollback changes if a transaction is active.
+      if run_in_transaction?
+        ActiveSupport::Notifications.unsubscribe(@connection_subscriber) if @connection_subscriber
+        @fixture_connections.each do |connection|
+          connection.rollback_transaction if connection.transaction_open?
+          connection.pool.lock_thread = false
+        end
+        @fixture_connections.clear
+      else
+        ActiveRecord::FixtureSet.reset_cache
+      end
+
+      ActiveRecord::Base.clear_active_connections!
+    end
+
+    def enlist_fixture_connections
+      ActiveRecord::Base.connection_handler.connection_pool_list.map(&:connection)
+    end
+
+    private
+      def load_fixtures(config)
+        fixtures = ActiveRecord::FixtureSet.create_fixtures(fixture_path, fixture_table_names, fixture_class_names, config)
+        Hash[fixtures.map { |f| [f.name, f] }]
+      end
+
+      def instantiate_fixtures
+        if pre_loaded_fixtures
+          raise RuntimeError, "Load fixtures before instantiating them." if ActiveRecord::FixtureSet.all_loaded_fixtures.empty?
+          ActiveRecord::FixtureSet.instantiate_all_loaded_fixtures(self, load_instances?)
+        else
+          raise RuntimeError, "Load fixtures before instantiating them." if @loaded_fixtures.nil?
+          @loaded_fixtures.each_value do |fixture_set|
+            ActiveRecord::FixtureSet.instantiate_fixtures(self, fixture_set, load_instances?)
+          end
+        end
+      end
+
+      def load_instances?
+        use_instantiated_fixtures != :no_instances
+      end
+  end
+end
diff --git a/activerecord/lib/active_record/timestamp.rb b/activerecord/lib/active_record/timestamp.rb
index 20e4235788..d32f971ad1 100644
--- a/activerecord/lib/active_record/timestamp.rb
+++ b/activerecord/lib/active_record/timestamp.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record Timestamp
+  # = Active Record \Timestamp
   #
   # Active Record automatically timestamps create and update operations if the
   # table has fields named <tt>created_at/created_on</tt> or
@@ -15,14 +17,25 @@ module ActiveRecord
   #
   # == Time Zone aware attributes
   #
-  # By default, ActiveRecord::Base keeps all the datetime columns time zone aware by executing following code.
+  # Active Record keeps all the <tt>datetime</tt> and <tt>time</tt> columns
+  # timezone aware. By default, these values are stored in the database as UTC
+  # and converted back to the current <tt>Time.zone</tt> when pulled from the database.
+  #
+  # This feature can be turned off completely by setting:
+  #
+  #   config.active_record.time_zone_aware_attributes = false
+  #
+  # You can also specify that only <tt>datetime</tt> columns should be time-zone
+  # aware (while <tt>time</tt> should not) by setting:
   #
-  #   config.active_record.time_zone_aware_attributes = true
+  #   ActiveRecord::Base.time_zone_aware_types = [:datetime]
   #
-  # This feature can easily be turned off by assigning value <tt>false</tt> .
+  # You can also add database specific timezone aware types. For example, for PostgreSQL:
   #
-  # If your attributes are time zone aware and you desire to skip time zone conversion to the current Time.zone
-  # when reading certain attributes then you can do following:
+  #   ActiveRecord::Base.time_zone_aware_types += [:tsrange, :tstzrange]
+  #
+  # Finally, you can indicate specific attributes of a model for which time zone
+  # conversion should not applied, for instance by setting:
   #
   #   class Topic < ActiveRecord::Base
   #     self.skip_time_zone_conversion_for_attributes = [:written_on]
@@ -31,8 +44,7 @@ module ActiveRecord
     extend ActiveSupport::Concern
 
     included do
-      class_attribute :record_timestamps
-      self.record_timestamps = true
+      class_attribute :record_timestamps, default: true
     end
 
     def initialize_dup(other) # :nodoc:
@@ -40,16 +52,48 @@ module ActiveRecord
       clear_timestamp_attributes
     end
 
+    module ClassMethods # :nodoc:
+      def touch_attributes_with_time(*names, time: nil)
+        attribute_names = timestamp_attributes_for_update_in_model
+        attribute_names |= names.map(&:to_s)
+        attribute_names.index_with(time ||= current_time_from_proper_timezone)
+      end
+
+      private
+        def timestamp_attributes_for_create_in_model
+          timestamp_attributes_for_create.select { |c| column_names.include?(c) }
+        end
+
+        def timestamp_attributes_for_update_in_model
+          timestamp_attributes_for_update.select { |c| column_names.include?(c) }
+        end
+
+        def all_timestamp_attributes_in_model
+          timestamp_attributes_for_create_in_model + timestamp_attributes_for_update_in_model
+        end
+
+        def timestamp_attributes_for_create
+          ["created_at", "created_on"]
+        end
+
+        def timestamp_attributes_for_update
+          ["updated_at", "updated_on"]
+        end
+
+        def current_time_from_proper_timezone
+          default_timezone == :utc ? Time.now.utc : Time.now
+        end
+    end
+
   private
 
     def _create_record
-      if self.record_timestamps
+      if record_timestamps
         current_time = current_time_from_proper_timezone
 
-        all_timestamp_attributes.each do |column|
-          column = column.to_s
-          if has_attribute?(column) && !attribute_present?(column)
-            write_attribute(column, current_time)
+        all_timestamp_attributes_in_model.each do |column|
+          if !attribute_present?(column)
+            _write_attribute(column, current_time)
           end
         end
       end
@@ -62,43 +106,34 @@ module ActiveRecord
         current_time = current_time_from_proper_timezone
 
         timestamp_attributes_for_update_in_model.each do |column|
-          column = column.to_s
-          next if attribute_changed?(column)
-          write_attribute(column, current_time)
+          next if will_save_change_to_attribute?(column)
+          _write_attribute(column, current_time)
         end
       end
       super(*args)
     end
 
     def should_record_timestamps?
-      self.record_timestamps && (!partial_writes? || changed?)
+      record_timestamps && (!partial_writes? || has_changes_to_save?)
     end
 
     def timestamp_attributes_for_create_in_model
-      timestamp_attributes_for_create.select { |c| self.class.column_names.include?(c.to_s) }
+      self.class.send(:timestamp_attributes_for_create_in_model)
     end
 
     def timestamp_attributes_for_update_in_model
-      timestamp_attributes_for_update.select { |c| self.class.column_names.include?(c.to_s) }
+      self.class.send(:timestamp_attributes_for_update_in_model)
     end
 
     def all_timestamp_attributes_in_model
-      timestamp_attributes_for_create_in_model + timestamp_attributes_for_update_in_model
-    end
-
-    def timestamp_attributes_for_update
-      [:updated_at, :updated_on]
-    end
-
-    def timestamp_attributes_for_create
-      [:created_at, :created_on]
+      self.class.send(:all_timestamp_attributes_in_model)
     end
 
-    def all_timestamp_attributes
-      timestamp_attributes_for_create + timestamp_attributes_for_update
+    def current_time_from_proper_timezone
+      self.class.send(:current_time_from_proper_timezone)
     end
 
-    def max_updated_column_timestamp(timestamp_names = timestamp_attributes_for_update)
+    def max_updated_column_timestamp(timestamp_names = timestamp_attributes_for_update_in_model)
       timestamp_names
         .map { |attr| self[attr] }
         .compact
@@ -106,10 +141,6 @@ module ActiveRecord
         .max
     end
 
-    def current_time_from_proper_timezone
-      self.class.default_timezone == :utc ? Time.now.utc : Time.now
-    end
-
     # Clear attributes and changed_attributes
     def clear_timestamp_attributes
       all_timestamp_attributes_in_model.each do |attribute_name|
diff --git a/activerecord/lib/active_record/touch_later.rb b/activerecord/lib/active_record/touch_later.rb
index 4352a0ffea..f70b7c50a2 100644
--- a/activerecord/lib/active_record/touch_later.rb
+++ b/activerecord/lib/active_record/touch_later.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # = Active Record Touch Later
   module TouchLater
@@ -8,7 +10,12 @@ module ActiveRecord
     end
 
     def touch_later(*names) # :nodoc:
-      raise ActiveRecordError, "cannot touch on a new record object" unless persisted?
+      unless persisted?
+        raise ActiveRecordError, <<-MSG.squish
+          cannot touch on a new or destroyed record object. Consider using
+          persisted?, new_record?, or destroyed? before touching
+        MSG
+      end
 
       @_defer_touch_attrs ||= timestamp_attributes_for_update_in_model
       @_defer_touch_attrs |= names
@@ -16,6 +23,13 @@ module ActiveRecord
 
       surreptitiously_touch @_defer_touch_attrs
       self.class.connection.add_transaction_record self
+
+      # touch the parents as we are not calling the after_save callbacks
+      self.class.reflect_on_all_associations(:belongs_to).each do |r|
+        if touch = r.options[:touch]
+          ActiveRecord::Associations::Builder::BelongsTo.touch_record(self, changes_to_save, r.foreign_key, r.name, touch, :touch_later)
+        end
+      end
     end
 
     def touch(*names, time: nil) # :nodoc:
@@ -26,6 +40,7 @@ module ActiveRecord
     end
 
     private
+
       def surreptitiously_touch(attrs)
         attrs.each { |attr| write_attribute attr, @_touch_time }
         clear_attribute_changes attrs
@@ -33,9 +48,8 @@ module ActiveRecord
 
       def touch_deferred_attributes
         if has_defer_touch_attrs? && persisted?
-          @_touching_delayed_records = true
           touch(*@_defer_touch_attrs, time: @_touch_time)
-          @_touching_delayed_records, @_defer_touch_attrs, @_touch_time = nil, nil, nil
+          @_defer_touch_attrs, @_touch_time = nil, nil
         end
       end
 
@@ -43,8 +57,8 @@ module ActiveRecord
         defined?(@_defer_touch_attrs) && @_defer_touch_attrs.present?
       end
 
-      def touching_delayed_records?
-        defined?(@_touching_delayed_records) && @_touching_delayed_records
+      def belongs_to_touch_method
+        :touch_later
       end
   end
 end
diff --git a/activerecord/lib/active_record/transactions.rb b/activerecord/lib/active_record/transactions.rb
index 6f2def0df1..fe3842b905 100644
--- a/activerecord/lib/active_record/transactions.rb
+++ b/activerecord/lib/active_record/transactions.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   # See ActiveRecord::Transactions::ClassMethods for documentation.
   module Transactions
@@ -16,10 +18,10 @@ module ActiveRecord
 
     # = Active Record Transactions
     #
-    # Transactions are protective blocks where SQL statements are only permanent
+    # \Transactions are protective blocks where SQL statements are only permanent
     # if they can all succeed as one atomic action. The classic example is a
     # transfer between two accounts where you can only have a deposit if the
-    # withdrawal succeeded and vice versa. Transactions enforce the integrity of
+    # withdrawal succeeded and vice versa. \Transactions enforce the integrity of
     # the database and guard the data against program errors or database
     # break-downs. So basically you should use transaction blocks whenever you
     # have a number of statements that must be executed together or not at all.
@@ -39,20 +41,20 @@ module ActiveRecord
     #
     # == Different Active Record classes in a single transaction
     #
-    # Though the transaction class method is called on some Active Record class,
+    # Though the #transaction class method is called on some Active Record class,
     # the objects within the transaction block need not all be instances of
     # that class. This is because transactions are per-database connection, not
     # per-model.
     #
     # In this example a +balance+ record is transactionally saved even
-    # though +transaction+ is called on the +Account+ class:
+    # though #transaction is called on the +Account+ class:
     #
     #   Account.transaction do
     #     balance.save!
     #     account.save!
     #   end
     #
-    # The +transaction+ method is also available as a model instance method.
+    # The #transaction method is also available as a model instance method.
     # For example, you can also do this:
     #
     #   balance.transaction do
@@ -79,7 +81,8 @@ module ActiveRecord
     #
     # == +save+ and +destroy+ are automatically wrapped in a transaction
     #
-    # Both +save+ and +destroy+ come wrapped in a transaction that ensures
+    # Both {#save}[rdoc-ref:Persistence#save] and
+    # {#destroy}[rdoc-ref:Persistence#destroy] come wrapped in a transaction that ensures
     # that whatever you do in validations or callbacks will happen under its
     # protected cover. So you can use validations to check for values that
     # the transaction depends on or you can raise exceptions in the callbacks
@@ -88,7 +91,7 @@ module ActiveRecord
     # As a consequence changes to the database are not seen outside your connection
     # until the operation is complete. For example, if you try to update the index
     # of a search engine in +after_save+ the indexer won't see the updated record.
-    # The +after_commit+ callback is the only one that is triggered once the update
+    # The #after_commit callback is the only one that is triggered once the update
     # is committed. See below.
     #
     # == Exception handling and rolling back
@@ -97,11 +100,11 @@ module ActiveRecord
     # be propagated (after triggering the ROLLBACK), so you should be ready to
     # catch those in your application code.
     #
-    # One exception is the <tt>ActiveRecord::Rollback</tt> exception, which will trigger
+    # One exception is the ActiveRecord::Rollback exception, which will trigger
     # a ROLLBACK when raised, but not be re-raised by the transaction block.
     #
-    # *Warning*: one should not catch <tt>ActiveRecord::StatementInvalid</tt> exceptions
-    # inside a transaction block. <tt>ActiveRecord::StatementInvalid</tt> exceptions indicate that an
+    # *Warning*: one should not catch ActiveRecord::StatementInvalid exceptions
+    # inside a transaction block. ActiveRecord::StatementInvalid exceptions indicate that an
     # error occurred at the database level, for example when a unique constraint
     # is violated. On some database systems, such as PostgreSQL, database errors
     # inside a transaction cause the entire transaction to become unusable
@@ -122,16 +125,16 @@ module ActiveRecord
     #     # statement will cause a PostgreSQL error, even though the unique
     #     # constraint is no longer violated:
     #     Number.create(i: 1)
-    #     # => "PGError: ERROR:  current transaction is aborted, commands
+    #     # => "PG::Error: ERROR:  current transaction is aborted, commands
     #     #     ignored until end of transaction block"
     #   end
     #
     # One should restart the entire transaction if an
-    # <tt>ActiveRecord::StatementInvalid</tt> occurred.
+    # ActiveRecord::StatementInvalid occurred.
     #
     # == Nested transactions
     #
-    # +transaction+ calls can be nested. By default, this makes all database
+    # #transaction calls can be nested. By default, this makes all database
     # statements in the nested transaction block become part of the parent
     # transaction. For example, the following behavior may be surprising:
     #
@@ -143,7 +146,7 @@ module ActiveRecord
     #     end
     #   end
     #
-    # creates both "Kotori" and "Nemu". Reason is the <tt>ActiveRecord::Rollback</tt>
+    # creates both "Kotori" and "Nemu". Reason is the ActiveRecord::Rollback
     # exception in the nested block does not issue a ROLLBACK. Since these exceptions
     # are captured in transaction blocks, the parent block does not see it and the
     # real transaction is committed.
@@ -167,28 +170,28 @@ module ActiveRecord
     # writing, the only database that we're aware of that supports true nested
     # transactions, is MS-SQL. Because of this, Active Record emulates nested
     # transactions by using savepoints on MySQL and PostgreSQL. See
-    # http://dev.mysql.com/doc/refman/5.6/en/savepoint.html
+    # https://dev.mysql.com/doc/refman/5.7/en/savepoint.html
     # for more information about savepoints.
     #
-    # === Callbacks
+    # === \Callbacks
     #
     # There are two types of callbacks associated with committing and rolling back transactions:
-    # +after_commit+ and +after_rollback+.
+    # #after_commit and #after_rollback.
     #
-    # +after_commit+ callbacks are called on every record saved or destroyed within a
-    # transaction immediately after the transaction is committed. +after_rollback+ callbacks
+    # #after_commit callbacks are called on every record saved or destroyed within a
+    # transaction immediately after the transaction is committed. #after_rollback callbacks
     # are called on every record saved or destroyed within a transaction immediately after the
     # transaction or savepoint is rolled back.
     #
     # These callbacks are useful for interacting with other systems since you will be guaranteed
     # that the callback is only executed when the database is in a permanent state. For example,
-    # +after_commit+ is a good spot to put in a hook to clearing a cache since clearing it from
+    # #after_commit is a good spot to put in a hook to clearing a cache since clearing it from
     # within a transaction could trigger the cache to be regenerated before the database is updated.
     #
     # === Caveats
     #
-    # If you're on MySQL, then do not use DDL operations in nested transactions
-    # blocks that are emulated with savepoints. That is, do not execute statements
+    # If you're on MySQL, then do not use Data Definition Language (DDL) operations in nested
+    # transactions blocks that are emulated with savepoints. That is, do not execute statements
     # like 'CREATE TABLE' inside such blocks. This is because MySQL automatically
     # releases all savepoints upon executing a DDL operation. When +transaction+
     # is finished and tries to release the savepoint it created earlier, a
@@ -204,9 +207,8 @@ module ActiveRecord
     #
     # Note that "TRUNCATE" is also a MySQL DDL statement!
     module ClassMethods
-      # See ActiveRecord::Transactions::ClassMethods for detailed documentation.
+      # See the ConnectionAdapters::DatabaseStatements#transaction API docs.
       def transaction(options = {}, &block)
-        # See the ConnectionAdapters::DatabaseStatements#transaction API docs.
         connection.transaction(options, &block)
       end
 
@@ -232,9 +234,27 @@ module ActiveRecord
         set_callback(:commit, :after, *args, &block)
       end
 
+      # Shortcut for <tt>after_commit :hook, on: :create</tt>.
+      def after_create_commit(*args, &block)
+        set_options_for_callbacks!(args, on: :create)
+        set_callback(:commit, :after, *args, &block)
+      end
+
+      # Shortcut for <tt>after_commit :hook, on: :update</tt>.
+      def after_update_commit(*args, &block)
+        set_options_for_callbacks!(args, on: :update)
+        set_callback(:commit, :after, *args, &block)
+      end
+
+      # Shortcut for <tt>after_commit :hook, on: :destroy</tt>.
+      def after_destroy_commit(*args, &block)
+        set_options_for_callbacks!(args, on: :destroy)
+        set_callback(:commit, :after, *args, &block)
+      end
+
       # This callback is called after a create, update, or destroy are rolled back.
       #
-      # Please check the documentation of +after_commit+ for options.
+      # Please check the documentation of #after_commit for options.
       def after_rollback(*args, &block)
         set_options_for_callbacks!(args)
         set_callback(:rollback, :after, *args, &block)
@@ -255,33 +275,25 @@ module ActiveRecord
         set_callback(:rollback_without_transaction_enrollment, :after, *args, &block)
       end
 
-      def raise_in_transactional_callbacks
-        ActiveSupport::Deprecation.warn('ActiveRecord::Base.raise_in_transactional_callbacks is deprecated and will be removed without replacement.')
-        true
-      end
-
-      def raise_in_transactional_callbacks=(value)
-        ActiveSupport::Deprecation.warn('ActiveRecord::Base.raise_in_transactional_callbacks= is deprecated, has no effect and will be removed without replacement.')
-        value
-      end
-
       private
 
-      def set_options_for_callbacks!(args)
-        options = args.last
-        if options.is_a?(Hash) && options[:on]
-          fire_on = Array(options[:on])
-          assert_valid_transaction_action(fire_on)
-          options[:if] = Array(options[:if])
-          options[:if] << "transaction_include_any_action?(#{fire_on})"
+        def set_options_for_callbacks!(args, enforced_options = {})
+          options = args.extract_options!.merge!(enforced_options)
+          args << options
+
+          if options[:on]
+            fire_on = Array(options[:on])
+            assert_valid_transaction_action(fire_on)
+            options[:if] = Array(options[:if])
+            options[:if].unshift(-> { transaction_include_any_action?(fire_on) })
+          end
         end
-      end
 
-      def assert_valid_transaction_action(actions)
-        if (actions - ACTIONS).any?
-          raise ArgumentError, ":on conditions for after_commit and after_rollback callbacks have to be one of #{ACTIONS}"
+        def assert_valid_transaction_action(actions)
+          if (actions - ACTIONS).any?
+            raise ArgumentError, ":on conditions for after_commit and after_rollback callbacks have to be one of #{ACTIONS}"
+          end
         end
-      end
     end
 
     # See ActiveRecord::Transactions::ClassMethods for detailed documentation.
@@ -294,9 +306,7 @@ module ActiveRecord
     end
 
     def save(*) #:nodoc:
-      rollback_active_record_state! do
-        with_transaction_returning_status { super }
-      end
+      with_transaction_returning_status { super }
     end
 
     def save!(*) #:nodoc:
@@ -307,48 +317,39 @@ module ActiveRecord
       with_transaction_returning_status { super }
     end
 
-    # Reset id and @new_record if the transaction rolls back.
-    def rollback_active_record_state!
-      remember_transaction_record_state
-      yield
-    rescue Exception
-      restore_transaction_record_state
-      raise
-    ensure
-      clear_transaction_record_state
-    end
-
     def before_committed! # :nodoc:
-      run_callbacks :before_commit_without_transaction_enrollment
-      run_callbacks :before_commit
+      _run_before_commit_without_transaction_enrollment_callbacks
+      _run_before_commit_callbacks
     end
 
-    # Call the +after_commit+ callbacks.
+    # Call the #after_commit callbacks.
     #
     # Ensure that it is not called if the object was never persisted (failed create),
     # but call it after the commit of a destroyed object.
     def committed!(should_run_callbacks: true) #:nodoc:
-      if should_run_callbacks && destroyed? || persisted?
-        run_callbacks :commit_without_transaction_enrollment
-        run_callbacks :commit
+      if should_run_callbacks && (destroyed? || persisted?)
+        @_committed_already_called = true
+        _run_commit_without_transaction_enrollment_callbacks
+        _run_commit_callbacks
       end
     ensure
+      @_committed_already_called = false
       force_clear_transaction_record_state
     end
 
-    # Call the +after_rollback+ callbacks. The +force_restore_state+ argument indicates if the record
+    # Call the #after_rollback callbacks. The +force_restore_state+ argument indicates if the record
     # state should be rolled back to the beginning or just to the last savepoint.
     def rolledback!(force_restore_state: false, should_run_callbacks: true) #:nodoc:
       if should_run_callbacks
-        run_callbacks :rollback
-        run_callbacks :rollback_without_transaction_enrollment
+        _run_rollback_callbacks
+        _run_rollback_without_transaction_enrollment_callbacks
       end
     ensure
       restore_transaction_record_state(force_restore_state)
       clear_transaction_record_state
     end
 
-    # Add the record to the current transaction so that the +after_rollback+ and +after_commit+ callbacks
+    # Add the record to the current transaction so that the #after_rollback and #after_commit callbacks
     # can be called.
     def add_to_transaction
       if has_transactional_callbacks?
@@ -370,115 +371,113 @@ module ActiveRecord
       status = nil
       self.class.transaction do
         add_to_transaction
-        begin
-          status = yield
-        rescue ActiveRecord::Rollback
-          clear_transaction_record_state
-          status = nil
-        end
-
+        status = yield
         raise ActiveRecord::Rollback unless status
       end
       status
     end
 
-    protected
-
-    # Save the new record state and id of a record so it can be restored later if a transaction fails.
-    def remember_transaction_record_state #:nodoc:
-      @_start_transaction_state[:id] = id
-      @_start_transaction_state.reverse_merge!(
-        new_record: @new_record,
-        destroyed: @destroyed,
-        frozen?: frozen?,
-      )
-      @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) + 1
-    end
+    private
+      attr_reader :_committed_already_called, :_trigger_update_callback, :_trigger_destroy_callback
+
+      # Save the new record state and id of a record so it can be restored later if a transaction fails.
+      def remember_transaction_record_state
+        @_start_transaction_state.reverse_merge!(
+          id: id,
+          new_record: @new_record,
+          destroyed: @destroyed,
+          frozen?: frozen?,
+        )
+        @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) + 1
+        remember_new_record_before_last_commit
+      end
 
-    # Clear the new record state and id of a record.
-    def clear_transaction_record_state #:nodoc:
-      @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) - 1
-      force_clear_transaction_record_state if @_start_transaction_state[:level] < 1
-    end
+      def remember_new_record_before_last_commit
+        if _committed_already_called
+          @_new_record_before_last_commit = false
+        else
+          @_new_record_before_last_commit = @_start_transaction_state[:new_record]
+        end
+      end
 
-    # Force to clear the transaction record state.
-    def force_clear_transaction_record_state #:nodoc:
-      @_start_transaction_state.clear
-    end
+      # Clear the new record state and id of a record.
+      def clear_transaction_record_state
+        @_start_transaction_state[:level] = (@_start_transaction_state[:level] || 0) - 1
+        force_clear_transaction_record_state if @_start_transaction_state[:level] < 1
+      end
+
+      # Force to clear the transaction record state.
+      def force_clear_transaction_record_state
+        @_start_transaction_state.clear
+      end
 
-    # Restore the new record state and id of a record that was previously saved by a call to save_record_state.
-    def restore_transaction_record_state(force = false) #:nodoc:
-      unless @_start_transaction_state.empty?
-        transaction_level = (@_start_transaction_state[:level] || 0) - 1
-        if transaction_level < 1 || force
-          restore_state = @_start_transaction_state
-          thaw
-          @new_record = restore_state[:new_record]
-          @destroyed  = restore_state[:destroyed]
-          pk = self.class.primary_key
-          if pk && read_attribute(pk) != restore_state[:id]
-            write_attribute(pk, restore_state[:id])
+      # Restore the new record state and id of a record that was previously saved by a call to save_record_state.
+      def restore_transaction_record_state(force = false)
+        unless @_start_transaction_state.empty?
+          transaction_level = (@_start_transaction_state[:level] || 0) - 1
+          if transaction_level < 1 || force
+            restore_state = @_start_transaction_state
+            thaw
+            @new_record = restore_state[:new_record]
+            @destroyed  = restore_state[:destroyed]
+            pk = self.class.primary_key
+            if pk && _read_attribute(pk) != restore_state[:id]
+              _write_attribute(pk, restore_state[:id])
+            end
+            freeze if restore_state[:frozen?]
           end
-          freeze if restore_state[:frozen?]
         end
       end
-    end
 
-    # Determine if a record was created or destroyed in a transaction. State should be one of :new_record or :destroyed.
-    def transaction_record_state(state) #:nodoc:
-      @_start_transaction_state[state]
-    end
-
-    # Determine if a transaction included an action for :create, :update, or :destroy. Used in filtering callbacks.
-    def transaction_include_any_action?(actions) #:nodoc:
-      actions.any? do |action|
-        case action
-        when :create
-          transaction_record_state(:new_record)
-        when :destroy
-          destroyed?
-        when :update
-          !(transaction_record_state(:new_record) || destroyed?)
+      # Determine if a transaction included an action for :create, :update, or :destroy. Used in filtering callbacks.
+      def transaction_include_any_action?(actions)
+        actions.any? do |action|
+          case action
+          when :create
+            persisted? && @_new_record_before_last_commit
+          when :update
+            !(@_new_record_before_last_commit || destroyed?) && _trigger_update_callback
+          when :destroy
+            _trigger_destroy_callback
+          end
         end
       end
-    end
-
-    private
 
-    def set_transaction_state(state) # :nodoc:
-      @transaction_state = state
-    end
+      def set_transaction_state(state)
+        @transaction_state = state
+      end
 
-    def has_transactional_callbacks? # :nodoc:
-      !_rollback_callbacks.empty? || !_commit_callbacks.empty? || !_before_commit_callbacks.empty?
-    end
+      def has_transactional_callbacks?
+        !_rollback_callbacks.empty? || !_commit_callbacks.empty? || !_before_commit_callbacks.empty?
+      end
 
-    # Updates the attributes on this particular ActiveRecord object so that
-    # if it's associated with a transaction, then the state of the ActiveRecord
-    # object will be updated to reflect the current state of the transaction
-    #
-    # The @transaction_state variable stores the states of the associated
-    # transaction. This relies on the fact that a transaction can only be in
-    # one rollback or commit (otherwise a list of states would be required)
-    # Each ActiveRecord object inside of a transaction carries that transaction's
-    # TransactionState.
-    #
-    # This method checks to see if the ActiveRecord object's state reflects
-    # the TransactionState, and rolls back or commits the ActiveRecord object
-    # as appropriate.
-    #
-    # Since ActiveRecord objects can be inside multiple transactions, this
-    # method recursively goes through the parent of the TransactionState and
-    # checks if the ActiveRecord object reflects the state of the object.
-    def sync_with_transaction_state
-      update_attributes_from_transaction_state(@transaction_state)
-    end
+      # Updates the attributes on this particular Active Record object so that
+      # if it's associated with a transaction, then the state of the Active Record
+      # object will be updated to reflect the current state of the transaction.
+      #
+      # The <tt>@transaction_state</tt> variable stores the states of the associated
+      # transaction. This relies on the fact that a transaction can only be in
+      # one rollback or commit (otherwise a list of states would be required).
+      # Each Active Record object inside of a transaction carries that transaction's
+      # TransactionState.
+      #
+      # This method checks to see if the ActiveRecord object's state reflects
+      # the TransactionState, and rolls back or commits the Active Record object
+      # as appropriate.
+      #
+      # Since Active Record objects can be inside multiple transactions, this
+      # method recursively goes through the parent of the TransactionState and
+      # checks if the Active Record object reflects the state of the object.
+      def sync_with_transaction_state
+        update_attributes_from_transaction_state(@transaction_state)
+      end
 
-    def update_attributes_from_transaction_state(transaction_state)
-      if transaction_state && transaction_state.finalized?
-        restore_transaction_record_state if transaction_state.rolledback?
-        clear_transaction_record_state
+      def update_attributes_from_transaction_state(transaction_state)
+        if transaction_state && transaction_state.finalized?
+          restore_transaction_record_state(transaction_state.fully_rolledback?) if transaction_state.rolledback?
+          force_clear_transaction_record_state if transaction_state.fully_committed?
+          clear_transaction_record_state if transaction_state.fully_completed?
+        end
       end
-    end
   end
 end
diff --git a/activerecord/lib/active_record/translation.rb b/activerecord/lib/active_record/translation.rb
index ddcb5f2a7a..82661a328a 100644
--- a/activerecord/lib/active_record/translation.rb
+++ b/activerecord/lib/active_record/translation.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Translation
     include ActiveModel::Translation
@@ -8,7 +10,7 @@ module ActiveRecord
       classes = [klass]
       return classes if klass == ActiveRecord::Base
 
-      while klass != klass.base_class
+      while !klass.base_class?
         classes << klass = klass.superclass
       end
       classes
diff --git a/activerecord/lib/active_record/type.rb b/activerecord/lib/active_record/type.rb
index 2c0cda69d0..c303186ef2 100644
--- a/activerecord/lib/active_record/type.rb
+++ b/activerecord/lib/active_record/type.rb
@@ -1,24 +1,22 @@
-require 'active_record/type/helpers'
-require 'active_record/type/value'
+# frozen_string_literal: true
 
-require 'active_record/type/big_integer'
-require 'active_record/type/binary'
-require 'active_record/type/boolean'
-require 'active_record/type/date'
-require 'active_record/type/date_time'
-require 'active_record/type/decimal'
-require 'active_record/type/decimal_without_scale'
-require 'active_record/type/float'
-require 'active_record/type/integer'
-require 'active_record/type/serialized'
-require 'active_record/type/string'
-require 'active_record/type/text'
-require 'active_record/type/time'
-require 'active_record/type/unsigned_integer'
+require "active_model/type"
 
-require 'active_record/type/adapter_specific_registry'
-require 'active_record/type/type_map'
-require 'active_record/type/hash_lookup_type_map'
+require "active_record/type/internal/timezone"
+
+require "active_record/type/date"
+require "active_record/type/date_time"
+require "active_record/type/decimal_without_scale"
+require "active_record/type/json"
+require "active_record/type/time"
+require "active_record/type/text"
+require "active_record/type/unsigned_integer"
+
+require "active_record/type/serialized"
+require "active_record/type/adapter_specific_registry"
+
+require "active_record/type/type_map"
+require "active_record/type/hash_lookup_type_map"
 
 module ActiveRecord
   module Type
@@ -29,13 +27,13 @@ module ActiveRecord
       delegate :add_modifier, to: :registry
 
       # Add a new type to the registry, allowing it to be referenced as a
-      # symbol by ActiveRecord::Attributes::ClassMethods#attribute.  If your
-      # type is only meant to be used with a specific database adapter, you can
-      # do so by passing +adapter: :postgresql+. If your type has the same
+      # symbol by {ActiveRecord::Base.attribute}[rdoc-ref:Attributes::ClassMethods#attribute].
+      # If your type is only meant to be used with a specific database adapter, you can
+      # do so by passing <tt>adapter: :postgresql</tt>. If your type has the same
       # name as a native type for the current adapter, an exception will be
-      # raised unless you specify an +:override+ option. +override: true+ will
-      # cause your type to be used instead of the native type. +override:
-      # false+ will cause the native type to be used over yours if one exists.
+      # raised unless you specify an +:override+ option. <tt>override: true</tt> will
+      # cause your type to be used instead of the native type. <tt>override:
+      # false</tt> will cause the native type to be used over yours if one exists.
       def register(type_name, klass = nil, **options, &block)
         registry.register(type_name, klass, **options, &block)
       end
@@ -44,6 +42,10 @@ module ActiveRecord
         registry.lookup(*args, adapter: adapter, **kwargs)
       end
 
+      def default_value # :nodoc:
+        @default_value ||= Value.new
+      end
+
       private
 
       def current_adapter_name
@@ -51,14 +53,25 @@ module ActiveRecord
       end
     end
 
+    Helpers = ActiveModel::Type::Helpers
+    BigInteger = ActiveModel::Type::BigInteger
+    Binary = ActiveModel::Type::Binary
+    Boolean = ActiveModel::Type::Boolean
+    Decimal = ActiveModel::Type::Decimal
+    Float = ActiveModel::Type::Float
+    Integer = ActiveModel::Type::Integer
+    String = ActiveModel::Type::String
+    Value = ActiveModel::Type::Value
+
     register(:big_integer, Type::BigInteger, override: false)
     register(:binary, Type::Binary, override: false)
     register(:boolean, Type::Boolean, override: false)
     register(:date, Type::Date, override: false)
-    register(:date_time, Type::DateTime, override: false)
+    register(:datetime, Type::DateTime, override: false)
     register(:decimal, Type::Decimal, override: false)
     register(:float, Type::Float, override: false)
     register(:integer, Type::Integer, override: false)
+    register(:json, Type::Json, override: false)
     register(:string, Type::String, override: false)
     register(:text, Type::Text, override: false)
     register(:time, Type::Time, override: false)
diff --git a/activerecord/lib/active_record/type/adapter_specific_registry.rb b/activerecord/lib/active_record/type/adapter_specific_registry.rb
index 5f71b3cb94..b300fdfa05 100644
--- a/activerecord/lib/active_record/type/adapter_specific_registry.rb
+++ b/activerecord/lib/active_record/type/adapter_specific_registry.rb
@@ -1,35 +1,26 @@
+# frozen_string_literal: true
+
+require "active_model/type/registry"
+
 module ActiveRecord
   # :stopdoc:
   module Type
-    class AdapterSpecificRegistry
-      def initialize
-        @registrations = []
-      end
-
-      def register(type_name, klass = nil, **options, &block)
-        block ||= proc { |_, *args| klass.new(*args) }
-        registrations << Registration.new(type_name, block, **options)
-      end
-
-      def lookup(symbol, *args)
-        registration = registrations
-          .select { |r| r.matches?(symbol, *args) }
-          .max
-
-        if registration
-          registration.call(self, symbol, *args)
-        else
-          raise ArgumentError, "Unknown type #{symbol.inspect}"
-        end
-      end
-
+    class AdapterSpecificRegistry < ActiveModel::Type::Registry
       def add_modifier(options, klass, **args)
         registrations << DecorationRegistration.new(options, klass, **args)
       end
 
-      protected
+      private
 
-      attr_reader :registrations
+        def registration_klass
+          Registration
+        end
+
+        def find_registration(symbol, *args)
+          registrations
+            .select { |registration| registration.matches?(symbol, *args) }
+            .max
+        end
     end
 
     class Registration
@@ -63,42 +54,42 @@ module ActiveRecord
 
       protected
 
-      attr_reader :name, :block, :adapter, :override
-
-      def priority
-        result = 0
-        if adapter
-          result |= 1
+        attr_reader :name, :block, :adapter, :override
+
+        def priority
+          result = 0
+          if adapter
+            result |= 1
+          end
+          if override
+            result |= 2
+          end
+          result
         end
-        if override
-          result |= 2
-        end
-        result
-      end
 
-      def priority_except_adapter
-        priority & 0b111111100
-      end
+        def priority_except_adapter
+          priority & 0b111111100
+        end
 
       private
 
-      def matches_adapter?(adapter: nil, **)
-        (self.adapter.nil? || adapter == self.adapter)
-      end
+        def matches_adapter?(adapter: nil, **)
+          (self.adapter.nil? || adapter == self.adapter)
+        end
 
-      def conflicts_with?(other)
-        same_priority_except_adapter?(other) &&
-          has_adapter_conflict?(other)
-      end
+        def conflicts_with?(other)
+          same_priority_except_adapter?(other) &&
+            has_adapter_conflict?(other)
+        end
 
-      def same_priority_except_adapter?(other)
-        priority_except_adapter == other.priority_except_adapter
-      end
+        def same_priority_except_adapter?(other)
+          priority_except_adapter == other.priority_except_adapter
+        end
 
-      def has_adapter_conflict?(other)
-        (override.nil? && other.adapter) ||
-          (adapter && other.override.nil?)
-      end
+        def has_adapter_conflict?(other)
+          (override.nil? && other.adapter) ||
+            (adapter && other.override.nil?)
+        end
     end
 
     class DecorationRegistration < Registration
@@ -121,22 +112,18 @@ module ActiveRecord
         super | 4
       end
 
-      protected
-
-      attr_reader :options, :klass
-
       private
+        attr_reader :options, :klass
 
-      def matches_options?(**kwargs)
-        options.all? do |key, value|
-          kwargs[key] == value
+        def matches_options?(**kwargs)
+          options.all? do |key, value|
+            kwargs[key] == value
+          end
         end
-      end
     end
   end
 
   class TypeConflictError < StandardError
   end
-
   # :startdoc:
 end
diff --git a/activerecord/lib/active_record/type/big_integer.rb b/activerecord/lib/active_record/type/big_integer.rb
deleted file mode 100644
index 0c72d8914f..0000000000
--- a/activerecord/lib/active_record/type/big_integer.rb
+++ /dev/null
@@ -1,13 +0,0 @@
-require 'active_record/type/integer'
-
-module ActiveRecord
-  module Type
-    class BigInteger < Integer # :nodoc:
-      private
-
-      def max_value
-        ::Float::INFINITY
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/binary.rb b/activerecord/lib/active_record/type/binary.rb
deleted file mode 100644
index 0baf8c63ad..0000000000
--- a/activerecord/lib/active_record/type/binary.rb
+++ /dev/null
@@ -1,50 +0,0 @@
-module ActiveRecord
-  module Type
-    class Binary < Value # :nodoc:
-      def type
-        :binary
-      end
-
-      def binary?
-        true
-      end
-
-      def cast(value)
-        if value.is_a?(Data)
-          value.to_s
-        else
-          super
-        end
-      end
-
-      def serialize(value)
-        return if value.nil?
-        Data.new(super)
-      end
-
-      def changed_in_place?(raw_old_value, value)
-        old_value = deserialize(raw_old_value)
-        old_value != value
-      end
-
-      class Data # :nodoc:
-        def initialize(value)
-          @value = value.to_s
-        end
-
-        def to_s
-          @value
-        end
-        alias_method :to_str, :to_s
-
-        def hex
-          @value.unpack('H*')[0]
-        end
-
-        def ==(other)
-          other == to_s || super
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/boolean.rb b/activerecord/lib/active_record/type/boolean.rb
deleted file mode 100644
index f6a75512fd..0000000000
--- a/activerecord/lib/active_record/type/boolean.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-module ActiveRecord
-  module Type
-    class Boolean < Value # :nodoc:
-      def type
-        :boolean
-      end
-
-      private
-
-      def cast_value(value)
-        if value == ''
-          nil
-        else
-          !ConnectionAdapters::Column::FALSE_VALUES.include?(value)
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/date.rb b/activerecord/lib/active_record/type/date.rb
index 3ceab59ebb..8177074a20 100644
--- a/activerecord/lib/active_record/type/date.rb
+++ b/activerecord/lib/active_record/type/date.rb
@@ -1,49 +1,9 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Type
-    class Date < Value # :nodoc:
-      include Helpers::AcceptsMultiparameterTime.new
-
-      def type
-        :date
-      end
-
-      def type_cast_for_schema(value)
-        "'#{value.to_s(:db)}'"
-      end
-
-      private
-
-      def cast_value(value)
-        if value.is_a?(::String)
-          return if value.empty?
-          fast_string_to_date(value) || fallback_string_to_date(value)
-        elsif value.respond_to?(:to_date)
-          value.to_date
-        else
-          value
-        end
-      end
-
-      def fast_string_to_date(string)
-        if string =~ ConnectionAdapters::Column::Format::ISO_DATE
-          new_date $1.to_i, $2.to_i, $3.to_i
-        end
-      end
-
-      def fallback_string_to_date(string)
-        new_date(*::Date._parse(string, false).values_at(:year, :mon, :mday))
-      end
-
-      def new_date(year, mon, mday)
-        if year && year != 0
-          ::Date.new(year, mon, mday) rescue nil
-        end
-      end
-
-      def value_from_multiparameter_assignment(*)
-        time = super
-        time && time.to_date
-      end
+    class Date < ActiveModel::Type::Date
+      include Internal::Timezone
     end
   end
 end
diff --git a/activerecord/lib/active_record/type/date_time.rb b/activerecord/lib/active_record/type/date_time.rb
index a5199959b9..4acde6b9f8 100644
--- a/activerecord/lib/active_record/type/date_time.rb
+++ b/activerecord/lib/active_record/type/date_time.rb
@@ -1,44 +1,9 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Type
-    class DateTime < Value # :nodoc:
-      include Helpers::TimeValue
-      include Helpers::AcceptsMultiparameterTime.new(
-        defaults: { 4 => 0, 5 => 0 }
-      )
-
-      def type
-        :datetime
-      end
-
-      private
-
-      def cast_value(string)
-        return string unless string.is_a?(::String)
-        return if string.empty?
-
-        fast_string_to_time(string) || fallback_string_to_time(string)
-      end
-
-      # '0.123456' -> 123456
-      # '1.123456' -> 123456
-      def microseconds(time)
-        time[:sec_fraction] ? (time[:sec_fraction] * 1_000_000).to_i : 0
-      end
-
-      def fallback_string_to_time(string)
-        time_hash = ::Date._parse(string)
-        time_hash[:sec_fraction] = microseconds(time_hash)
-
-        new_time(*time_hash.values_at(:year, :mon, :mday, :hour, :min, :sec, :sec_fraction, :offset))
-      end
-
-      def value_from_multiparameter_assignment(values_hash)
-        missing_parameter = (1..3).detect { |key| !values_hash.key?(key) }
-        if missing_parameter
-          raise ArgumentError, missing_parameter
-        end
-        super
-      end
+    class DateTime < ActiveModel::Type::DateTime
+      include Internal::Timezone
     end
   end
 end
diff --git a/activerecord/lib/active_record/type/decimal.rb b/activerecord/lib/active_record/type/decimal.rb
deleted file mode 100644
index f200a92d10..0000000000
--- a/activerecord/lib/active_record/type/decimal.rb
+++ /dev/null
@@ -1,48 +0,0 @@
-module ActiveRecord
-  module Type
-    class Decimal < Value # :nodoc:
-      include Helpers::Numeric
-
-      def type
-        :decimal
-      end
-
-      def type_cast_for_schema(value)
-        value.to_s.inspect
-      end
-
-      private
-
-      def cast_value(value)
-        case value
-        when ::Float
-          convert_float_to_big_decimal(value)
-        when ::Numeric, ::String
-          BigDecimal(value, precision.to_i)
-        else
-          if value.respond_to?(:to_d)
-            value.to_d
-          else
-            cast_value(value.to_s)
-          end
-        end
-      end
-
-      def convert_float_to_big_decimal(value)
-        if precision
-          BigDecimal(value, float_precision)
-        else
-          value.to_d
-        end
-      end
-
-      def float_precision
-        if precision.to_i > ::Float::DIG + 1
-          ::Float::DIG + 1
-        else
-          precision.to_i
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/decimal_without_scale.rb b/activerecord/lib/active_record/type/decimal_without_scale.rb
index ff5559e300..a207940dc7 100644
--- a/activerecord/lib/active_record/type/decimal_without_scale.rb
+++ b/activerecord/lib/active_record/type/decimal_without_scale.rb
@@ -1,11 +1,15 @@
-require 'active_record/type/big_integer'
+# frozen_string_literal: true
 
 module ActiveRecord
   module Type
-    class DecimalWithoutScale < BigInteger # :nodoc:
+    class DecimalWithoutScale < ActiveModel::Type::BigInteger # :nodoc:
       def type
         :decimal
       end
+
+      def type_cast_for_schema(value)
+        value.to_s.inspect
+      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/type/float.rb b/activerecord/lib/active_record/type/float.rb
deleted file mode 100644
index d88482b85d..0000000000
--- a/activerecord/lib/active_record/type/float.rb
+++ /dev/null
@@ -1,25 +0,0 @@
-module ActiveRecord
-  module Type
-    class Float < Value # :nodoc:
-      include Helpers::Numeric
-
-      def type
-        :float
-      end
-
-      alias serialize cast
-
-      private
-
-      def cast_value(value)
-        case value
-        when ::Float then value
-        when "Infinity" then ::Float::INFINITY
-        when "-Infinity" then -::Float::INFINITY
-        when "NaN" then ::Float::NAN
-        else value.to_f
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/hash_lookup_type_map.rb b/activerecord/lib/active_record/type/hash_lookup_type_map.rb
index 3b01e3f8ca..db9853fbcc 100644
--- a/activerecord/lib/active_record/type/hash_lookup_type_map.rb
+++ b/activerecord/lib/active_record/type/hash_lookup_type_map.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Type
     class HashLookupTypeMap < TypeMap # :nodoc:
@@ -15,9 +17,9 @@ module ActiveRecord
 
       private
 
-      def perform_fetch(type, *args, &block)
-        @mapping.fetch(type, block).call(type, *args)
-      end
+        def perform_fetch(type, *args, &block)
+          @mapping.fetch(type, block).call(type, *args)
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/type/helpers.rb b/activerecord/lib/active_record/type/helpers.rb
deleted file mode 100644
index 634d417d13..0000000000
--- a/activerecord/lib/active_record/type/helpers.rb
+++ /dev/null
@@ -1,4 +0,0 @@
-require 'active_record/type/helpers/accepts_multiparameter_time'
-require 'active_record/type/helpers/numeric'
-require 'active_record/type/helpers/mutable'
-require 'active_record/type/helpers/time_value'
diff --git a/activerecord/lib/active_record/type/helpers/accepts_multiparameter_time.rb b/activerecord/lib/active_record/type/helpers/accepts_multiparameter_time.rb
deleted file mode 100644
index be571fc1c7..0000000000
--- a/activerecord/lib/active_record/type/helpers/accepts_multiparameter_time.rb
+++ /dev/null
@@ -1,30 +0,0 @@
-module ActiveRecord
-  module Type
-    module Helpers
-      class AcceptsMultiparameterTime < Module # :nodoc:
-        def initialize(defaults: {})
-          define_method(:cast) do |value|
-            if value.is_a?(Hash)
-              value_from_multiparameter_assignment(value)
-            else
-              super(value)
-            end
-          end
-
-          define_method(:value_from_multiparameter_assignment) do |values_hash|
-            defaults.each do |k, v|
-              values_hash[k] ||= v
-            end
-            return unless values_hash[1] && values_hash[2] && values_hash[3]
-            values = values_hash.sort.map(&:last)
-            ::Time.send(
-              ActiveRecord::Base.default_timezone,
-              *values
-            )
-          end
-          private :value_from_multiparameter_assignment
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/helpers/mutable.rb b/activerecord/lib/active_record/type/helpers/mutable.rb
deleted file mode 100644
index 88a9099277..0000000000
--- a/activerecord/lib/active_record/type/helpers/mutable.rb
+++ /dev/null
@@ -1,18 +0,0 @@
-module ActiveRecord
-  module Type
-    module Helpers
-      module Mutable # :nodoc:
-        def cast(value)
-          deserialize(serialize(value))
-        end
-
-        # +raw_old_value+ will be the `_before_type_cast` version of the
-        # value (likely a string). +new_value+ will be the current, type
-        # cast value.
-        def changed_in_place?(raw_old_value, new_value)
-          raw_old_value != serialize(new_value)
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/helpers/numeric.rb b/activerecord/lib/active_record/type/helpers/numeric.rb
deleted file mode 100644
index a755a02a59..0000000000
--- a/activerecord/lib/active_record/type/helpers/numeric.rb
+++ /dev/null
@@ -1,34 +0,0 @@
-module ActiveRecord
-  module Type
-    module Helpers
-      module Numeric # :nodoc:
-        def cast(value)
-          value = case value
-                  when true then 1
-                  when false then 0
-                  when ::String then value.presence
-                  else value
-                  end
-          super(value)
-        end
-
-        def changed?(old_value, _new_value, new_value_before_type_cast) # :nodoc:
-          super || number_to_non_number?(old_value, new_value_before_type_cast)
-        end
-
-        private
-
-        def number_to_non_number?(old_value, new_value_before_type_cast)
-          old_value != nil && non_numeric_string?(new_value_before_type_cast)
-        end
-
-        def non_numeric_string?(value)
-          # 'wibble'.to_i will give zero, we want to make sure
-          # that we aren't marking int zero to string zero as
-          # changed.
-          value.to_s !~ /\A-?\d+\.?\d*\z/
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/helpers/time_value.rb b/activerecord/lib/active_record/type/helpers/time_value.rb
deleted file mode 100644
index 7eb41557cb..0000000000
--- a/activerecord/lib/active_record/type/helpers/time_value.rb
+++ /dev/null
@@ -1,58 +0,0 @@
-module ActiveRecord
-  module Type
-    module Helpers
-      module TimeValue # :nodoc:
-        def serialize(value)
-          if precision && value.respond_to?(:usec)
-            number_of_insignificant_digits = 6 - precision
-            round_power = 10 ** number_of_insignificant_digits
-            value = value.change(usec: value.usec / round_power * round_power)
-          end
-
-          if value.acts_like?(:time)
-            zone_conversion_method = ActiveRecord::Base.default_timezone == :utc ? :getutc : :getlocal
-
-            if value.respond_to?(zone_conversion_method)
-              value = value.send(zone_conversion_method)
-            end
-          end
-
-          value
-        end
-
-        def type_cast_for_schema(value)
-          "'#{value.to_s(:db)}'"
-        end
-
-        def user_input_in_time_zone(value)
-          value.in_time_zone
-        end
-
-        private
-
-        def new_time(year, mon, mday, hour, min, sec, microsec, offset = nil)
-          # Treat 0000-00-00 00:00:00 as nil.
-          return if year.nil? || (year == 0 && mon == 0 && mday == 0)
-
-          if offset
-            time = ::Time.utc(year, mon, mday, hour, min, sec, microsec) rescue nil
-            return unless time
-
-            time -= offset
-            Base.default_timezone == :utc ? time : time.getlocal
-          else
-            ::Time.public_send(Base.default_timezone, year, mon, mday, hour, min, sec, microsec) rescue nil
-          end
-        end
-
-        # Doesn't handle time zones.
-        def fast_string_to_time(string)
-          if string =~ ConnectionAdapters::Column::Format::ISO_DATETIME
-            microsec = ($7.to_r * 1_000_000).to_i
-            new_time $1.to_i, $2.to_i, $3.to_i, $4.to_i, $5.to_i, $6.to_i, microsec
-          end
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/integer.rb b/activerecord/lib/active_record/type/integer.rb
deleted file mode 100644
index c5040c6d3b..0000000000
--- a/activerecord/lib/active_record/type/integer.rb
+++ /dev/null
@@ -1,66 +0,0 @@
-module ActiveRecord
-  module Type
-    class Integer < Value # :nodoc:
-      include Helpers::Numeric
-
-      # Column storage size in bytes.
-      # 4 bytes means a MySQL int or Postgres integer as opposed to smallint etc.
-      DEFAULT_LIMIT = 4
-
-      def initialize(*)
-        super
-        @range = min_value...max_value
-      end
-
-      def type
-        :integer
-      end
-
-      def deserialize(value)
-        return if value.nil?
-        value.to_i
-      end
-
-      def serialize(value)
-        result = cast(value)
-        if result
-          ensure_in_range(result)
-        end
-        result
-      end
-
-      protected
-
-      attr_reader :range
-
-      private
-
-      def cast_value(value)
-        case value
-        when true then 1
-        when false then 0
-        else
-          value.to_i rescue nil
-        end
-      end
-
-      def ensure_in_range(value)
-        unless range.cover?(value)
-          raise RangeError, "#{value} is out of range for #{self.class} with limit #{_limit}"
-        end
-      end
-
-      def max_value
-        1 << (_limit * 8 - 1) # 8 bits per byte with one bit for sign
-      end
-
-      def min_value
-        -max_value
-      end
-
-      def _limit
-        self.limit || DEFAULT_LIMIT
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/internal/timezone.rb b/activerecord/lib/active_record/type/internal/timezone.rb
new file mode 100644
index 0000000000..3059755752
--- /dev/null
+++ b/activerecord/lib/active_record/type/internal/timezone.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module Type
+    module Internal
+      module Timezone
+        def is_utc?
+          ActiveRecord::Base.default_timezone == :utc
+        end
+
+        def default_timezone
+          ActiveRecord::Base.default_timezone
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/type/json.rb b/activerecord/lib/active_record/type/json.rb
new file mode 100644
index 0000000000..3f9ff22796
--- /dev/null
+++ b/activerecord/lib/active_record/type/json.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+module ActiveRecord
+  module Type
+    class Json < ActiveModel::Type::Value
+      include ActiveModel::Type::Helpers::Mutable
+
+      def type
+        :json
+      end
+
+      def deserialize(value)
+        return value unless value.is_a?(::String)
+        ActiveSupport::JSON.decode(value) rescue nil
+      end
+
+      def serialize(value)
+        ActiveSupport::JSON.encode(value) unless value.nil?
+      end
+
+      def changed_in_place?(raw_old_value, new_value)
+        deserialize(raw_old_value) != new_value
+      end
+
+      def accessor
+        ActiveRecord::Store::StringKeyedHashAccessor
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/active_record/type/serialized.rb b/activerecord/lib/active_record/type/serialized.rb
index ea3e0d6a45..0a2f6cb9fb 100644
--- a/activerecord/lib/active_record/type/serialized.rb
+++ b/activerecord/lib/active_record/type/serialized.rb
@@ -1,7 +1,11 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Type
-    class Serialized < DelegateClass(Type::Value) # :nodoc:
-      include Helpers::Mutable
+    class Serialized < DelegateClass(ActiveModel::Type::Value) # :nodoc:
+      undef to_yaml if method_defined?(:to_yaml)
+
+      include ActiveModel::Type::Helpers::Mutable
 
       attr_reader :subtype, :coder
 
@@ -32,7 +36,7 @@ module ActiveRecord
 
       def changed_in_place?(raw_old_value, value)
         return false if value.nil?
-        raw_new_value = serialize(value)
+        raw_new_value = encoded(value)
         raw_old_value.nil? != raw_new_value.nil? ||
           subtype.changed_in_place?(raw_old_value, raw_new_value)
       end
@@ -41,11 +45,27 @@ module ActiveRecord
         ActiveRecord::Store::IndifferentHashAccessor
       end
 
-      private
+      def assert_valid_value(value)
+        if coder.respond_to?(:assert_valid_value)
+          coder.assert_valid_value(value, action: "serialize")
+        end
+      end
 
-      def default_value?(value)
-        value == coder.load(nil)
+      def force_equality?(value)
+        coder.respond_to?(:object_class) && value.is_a?(coder.object_class)
       end
+
+      private
+
+        def default_value?(value)
+          value == coder.load(nil)
+        end
+
+        def encoded(value)
+          unless default_value?(value)
+            coder.dump(value)
+          end
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/type/string.rb b/activerecord/lib/active_record/type/string.rb
deleted file mode 100644
index 2662b7e874..0000000000
--- a/activerecord/lib/active_record/type/string.rb
+++ /dev/null
@@ -1,36 +0,0 @@
-module ActiveRecord
-  module Type
-    class String < Value # :nodoc:
-      def type
-        :string
-      end
-
-      def changed_in_place?(raw_old_value, new_value)
-        if new_value.is_a?(::String)
-          raw_old_value != new_value
-        end
-      end
-
-      def serialize(value)
-        case value
-        when ::Numeric, ActiveSupport::Duration then value.to_s
-        when ::String then ::String.new(value)
-        when true then "t"
-        when false then "f"
-        else super
-        end
-      end
-
-      private
-
-      def cast_value(value)
-        case value
-        when true then "t"
-        when false then "f"
-        # String.new is slightly faster than dup
-        else ::String.new(value.to_s)
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type/text.rb b/activerecord/lib/active_record/type/text.rb
index 26f980f060..6d19696671 100644
--- a/activerecord/lib/active_record/type/text.rb
+++ b/activerecord/lib/active_record/type/text.rb
@@ -1,8 +1,8 @@
-require 'active_record/type/string'
+# frozen_string_literal: true
 
 module ActiveRecord
   module Type
-    class Text < String # :nodoc:
+    class Text < ActiveModel::Type::String # :nodoc:
       def type
         :text
       end
diff --git a/activerecord/lib/active_record/type/time.rb b/activerecord/lib/active_record/type/time.rb
index 19a10021bc..f4da1ecf2c 100644
--- a/activerecord/lib/active_record/type/time.rb
+++ b/activerecord/lib/active_record/type/time.rb
@@ -1,40 +1,19 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Type
-    class Time < Value # :nodoc:
-      include Helpers::TimeValue
-      include Helpers::AcceptsMultiparameterTime.new(
-        defaults: { 1 => 1970, 2 => 1, 3 => 1, 4 => 0, 5 => 0 }
-      )
+    class Time < ActiveModel::Type::Time
+      include Internal::Timezone
 
-      def type
-        :time
+      class Value < DelegateClass(::Time) # :nodoc:
       end
 
-      def user_input_in_time_zone(value)
-        return unless value.present?
-
-        case value
-        when ::String
-          value = "2000-01-01 #{value}"
+      def serialize(value)
+        case value = super
         when ::Time
-          value = value.change(year: 2000, day: 1, month: 1)
-        end
-
-        super(value)
-      end
-
-      private
-
-      def cast_value(value)
-        return value unless value.is_a?(::String)
-        return if value.empty?
-
-        dummy_time_value = "2000-01-01 #{value}"
-
-        fast_string_to_time(dummy_time_value) || begin
-          time_hash = ::Date._parse(dummy_time_value)
-          return if time_hash[:hour].nil?
-          new_time(*time_hash.values_at(:year, :mon, :mday, :hour, :min, :sec, :sec_fraction))
+          Value.new(value)
+        else
+          value
         end
       end
     end
diff --git a/activerecord/lib/active_record/type/type_map.rb b/activerecord/lib/active_record/type/type_map.rb
index 09f5ba6b74..fc40b460f0 100644
--- a/activerecord/lib/active_record/type/type_map.rb
+++ b/activerecord/lib/active_record/type/type_map.rb
@@ -1,17 +1,19 @@
-require 'thread_safe'
+# frozen_string_literal: true
+
+require "concurrent/map"
 
 module ActiveRecord
   module Type
     class TypeMap # :nodoc:
       def initialize
         @mapping = {}
-        @cache = ThreadSafe::Cache.new do |h, key|
-          h.fetch_or_store(key, ThreadSafe::Cache.new)
+        @cache = Concurrent::Map.new do |h, key|
+          h.fetch_or_store(key, Concurrent::Map.new)
         end
       end
 
       def lookup(lookup_key, *args)
-        fetch(lookup_key, *args) { default_value }
+        fetch(lookup_key, *args) { Type.default_value }
       end
 
       def fetch(lookup_key, *args, &block)
@@ -44,21 +46,17 @@ module ActiveRecord
 
       private
 
-      def perform_fetch(lookup_key, *args)
-        matching_pair = @mapping.reverse_each.detect do |key, _|
-          key === lookup_key
-        end
+        def perform_fetch(lookup_key, *args)
+          matching_pair = @mapping.reverse_each.detect do |key, _|
+            key === lookup_key
+          end
 
-        if matching_pair
-          matching_pair.last.call(lookup_key, *args)
-        else
-          yield lookup_key, *args
+          if matching_pair
+            matching_pair.last.call(lookup_key, *args)
+          else
+            yield lookup_key, *args
+          end
         end
-      end
-
-      def default_value
-        @default_value ||= Value.new
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/type/unsigned_integer.rb b/activerecord/lib/active_record/type/unsigned_integer.rb
index ed3e527483..4619528f81 100644
--- a/activerecord/lib/active_record/type/unsigned_integer.rb
+++ b/activerecord/lib/active_record/type/unsigned_integer.rb
@@ -1,15 +1,17 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Type
-    class UnsignedInteger < Integer # :nodoc:
+    class UnsignedInteger < ActiveModel::Type::Integer # :nodoc:
       private
 
-      def max_value
-        super * 2
-      end
+        def max_value
+          super * 2
+        end
 
-      def min_value
-        0
-      end
+        def min_value
+          0
+        end
     end
   end
 end
diff --git a/activerecord/lib/active_record/type/value.rb b/activerecord/lib/active_record/type/value.rb
deleted file mode 100644
index 6b9d147ecc..0000000000
--- a/activerecord/lib/active_record/type/value.rb
+++ /dev/null
@@ -1,104 +0,0 @@
-module ActiveRecord
-  module Type
-    class Value
-      attr_reader :precision, :scale, :limit
-
-      def initialize(precision: nil, limit: nil, scale: nil)
-        @precision = precision
-        @scale = scale
-        @limit = limit
-      end
-
-      def type # :nodoc:
-      end
-
-      # Converts a value from database input to the appropriate ruby type. The
-      # return value of this method will be returned from
-      # ActiveRecord::AttributeMethods::Read#read_attribute. The default
-      # implementation just calls Value#cast.
-      #
-      # +value+ The raw input, as provided from the database.
-      def deserialize(value)
-        cast(value)
-      end
-
-      # Type casts a value from user input (e.g. from a setter). This value may
-      # be a string from the form builder, or a ruby object passed to a setter.
-      # There is currently no way to differentiate between which source it came
-      # from.
-      #
-      # The return value of this method will be returned from
-      # ActiveRecord::AttributeMethods::Read#read_attribute. See also:
-      # Value#cast_value.
-      #
-      # +value+ The raw input, as provided to the attribute setter.
-      def cast(value)
-        cast_value(value) unless value.nil?
-      end
-
-      # Casts a value from the ruby type to a type that the database knows how
-      # to understand. The returned value from this method should be a
-      # +String+, +Numeric+, +Date+, +Time+, +Symbol+, +true+, +false+, or
-      # +nil+.
-      def serialize(value)
-        value
-      end
-
-      # Type casts a value for schema dumping. This method is private, as we are
-      # hoping to remove it entirely.
-      def type_cast_for_schema(value) # :nodoc:
-        value.inspect
-      end
-
-      # These predicates are not documented, as I need to look further into
-      # their use, and see if they can be removed entirely.
-      def binary? # :nodoc:
-        false
-      end
-
-      # Determines whether a value has changed for dirty checking. +old_value+
-      # and +new_value+ will always be type-cast. Types should not need to
-      # override this method.
-      def changed?(old_value, new_value, _new_value_before_type_cast)
-        old_value != new_value
-      end
-
-      # Determines whether the mutable value has been modified since it was
-      # read. Returns +false+ by default. If your type returns an object
-      # which could be mutated, you should override this method. You will need
-      # to either:
-      #
-      # - pass +new_value+ to Value#serialize and compare it to
-      #   +raw_old_value+
-      #
-      # or
-      #
-      # - pass +raw_old_value+ to Value#deserialize and compare it to
-      #   +new_value+
-      #
-      # +raw_old_value+ The original value, before being passed to
-      # +deserialize+.
-      #
-      # +new_value+ The current value, after type casting.
-      def changed_in_place?(raw_old_value, new_value)
-        false
-      end
-
-      def ==(other)
-        self.class == other.class &&
-          precision == other.precision &&
-          scale == other.scale &&
-          limit == other.limit
-      end
-
-      private
-
-      # Convenience method for types which do not need separate type casting
-      # behavior for user and database inputs. Called by Value#cast for
-      # values except +nil+.
-      def cast_value(value) # :doc:
-        value
-      end
-    end
-  end
-end
diff --git a/activerecord/lib/active_record/type_caster.rb b/activerecord/lib/active_record/type_caster.rb
index 63ba10c289..2e5f45fa3d 100644
--- a/activerecord/lib/active_record/type_caster.rb
+++ b/activerecord/lib/active_record/type_caster.rb
@@ -1,7 +1,9 @@
-require 'active_record/type_caster/map'
-require 'active_record/type_caster/connection'
+# frozen_string_literal: true
+
+require "active_record/type_caster/map"
+require "active_record/type_caster/connection"
 
 module ActiveRecord
-  module TypeCaster
+  module TypeCaster # :nodoc:
   end
 end
diff --git a/activerecord/lib/active_record/type_caster/connection.rb b/activerecord/lib/active_record/type_caster/connection.rb
index 3878270770..7cf8181d8e 100644
--- a/activerecord/lib/active_record/type_caster/connection.rb
+++ b/activerecord/lib/active_record/type_caster/connection.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module TypeCaster
-    class Connection
+    class Connection # :nodoc:
       def initialize(klass, table_name)
         @klass = klass
         @table_name = table_name
@@ -12,18 +14,15 @@ module ActiveRecord
         connection.type_cast_from_column(column, value)
       end
 
-      protected
-
-      attr_reader :table_name
-      delegate :connection, to: :@klass
-
       private
+        attr_reader :table_name
+        delegate :connection, to: :@klass
 
-      def column_for(attribute_name)
-        if connection.schema_cache.table_exists?(table_name)
-          connection.schema_cache.columns_hash(table_name)[attribute_name.to_s]
+        def column_for(attribute_name)
+          if connection.schema_cache.data_source_exists?(table_name)
+            connection.schema_cache.columns_hash(table_name)[attribute_name.to_s]
+          end
         end
-      end
     end
   end
 end
diff --git a/activerecord/lib/active_record/type_caster/map.rb b/activerecord/lib/active_record/type_caster/map.rb
index 4b1941351c..663cdadb03 100644
--- a/activerecord/lib/active_record/type_caster/map.rb
+++ b/activerecord/lib/active_record/type_caster/map.rb
@@ -1,19 +1,20 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module TypeCaster
-    class Map
+    class Map # :nodoc:
       def initialize(types)
         @types = types
       end
 
       def type_cast_for_database(attr_name, value)
         return value if value.is_a?(Arel::Nodes::BindParam)
-        type = types.type_for_attribute(attr_name.to_s)
+        type = types.type_for_attribute(attr_name)
         type.serialize(value)
       end
 
-      protected
-
-      attr_reader :types
+      private
+        attr_reader :types
     end
   end
 end
diff --git a/activerecord/lib/active_record/validations.rb b/activerecord/lib/active_record/validations.rb
index 34d96b19fe..ca27a3f0ab 100644
--- a/activerecord/lib/active_record/validations.rb
+++ b/activerecord/lib/active_record/validations.rb
@@ -1,8 +1,11 @@
+# frozen_string_literal: true
+
 module ActiveRecord
-  # = Active Record RecordInvalid
+  # = Active Record \RecordInvalid
   #
-  # Raised by <tt>save!</tt> and <tt>create!</tt> when the record is invalid. Use the
-  # +record+ method to retrieve the record which did not validate.
+  # Raised by {ActiveRecord::Base#save!}[rdoc-ref:Persistence#save!] and
+  # {ActiveRecord::Base#create!}[rdoc-ref:Persistence::ClassMethods#create!] when the record is invalid.
+  # Use the #record method to retrieve the record which did not validate.
   #
   #   begin
   #     complex_operation_that_internally_calls_save!
@@ -12,62 +15,72 @@ module ActiveRecord
   class RecordInvalid < ActiveRecordError
     attr_reader :record
 
-    def initialize(record)
-      @record = record
-      errors = @record.errors.full_messages.join(", ")
-      super(I18n.t(:"#{@record.class.i18n_scope}.errors.messages.record_invalid", :errors => errors, :default => :"errors.messages.record_invalid"))
+    def initialize(record = nil)
+      if record
+        @record = record
+        errors = @record.errors.full_messages.join(", ")
+        message = I18n.t(:"#{@record.class.i18n_scope}.errors.messages.record_invalid", errors: errors, default: :"errors.messages.record_invalid")
+      else
+        message = "Record invalid"
+      end
+
+      super(message)
     end
   end
 
-  # = Active Record Validations
+  # = Active Record \Validations
   #
-  # Active Record includes the majority of its validations from <tt>ActiveModel::Validations</tt>
+  # Active Record includes the majority of its validations from ActiveModel::Validations
   # all of which accept the <tt>:on</tt> argument to define the context where the
   # validations are active. Active Record will always supply either the context of
   # <tt>:create</tt> or <tt>:update</tt> dependent on whether the model is a
-  # <tt>new_record?</tt>.
+  # {new_record?}[rdoc-ref:Persistence#new_record?].
   module Validations
     extend ActiveSupport::Concern
     include ActiveModel::Validations
 
     # The validation process on save can be skipped by passing <tt>validate: false</tt>.
-    # The regular Base#save method is replaced with this when the validations
-    # module is mixed in, which it is by default.
-    def save(options={})
+    # The regular {ActiveRecord::Base#save}[rdoc-ref:Persistence#save] method is replaced
+    # with this when the validations module is mixed in, which it is by default.
+    def save(options = {})
       perform_validations(options) ? super : false
     end
 
-    # Attempts to save the record just like Base#save but will raise a +RecordInvalid+
-    # exception instead of returning +false+ if the record is not valid.
-    def save!(options={})
+    # Attempts to save the record just like {ActiveRecord::Base#save}[rdoc-ref:Base#save] but
+    # will raise an ActiveRecord::RecordInvalid exception instead of returning +false+ if the record is not valid.
+    def save!(options = {})
       perform_validations(options) ? super : raise_validation_error
     end
 
     # Runs all the validations within the specified context. Returns +true+ if
     # no errors are found, +false+ otherwise.
     #
-    # Aliased as validate.
+    # Aliased as #validate.
     #
     # If the argument is +false+ (default is +nil+), the context is set to <tt>:create</tt> if
-    # <tt>new_record?</tt> is +true+, and to <tt>:update</tt> if it is not.
+    # {new_record?}[rdoc-ref:Persistence#new_record?] is +true+, and to <tt>:update</tt> if it is not.
     #
-    # Validations with no <tt>:on</tt> option will run no matter the context. Validations with
+    # \Validations with no <tt>:on</tt> option will run no matter the context. \Validations with
     # some <tt>:on</tt> option will only run in the specified context.
     def valid?(context = nil)
-      context ||= (new_record? ? :create : :update)
+      context ||= default_validation_context
       output = super(context)
       errors.empty? && output
     end
 
     alias_method :validate, :valid?
 
-  protected
+  private
+
+    def default_validation_context
+      new_record? ? :create : :update
+    end
 
     def raise_validation_error
       raise(RecordInvalid.new(self))
     end
 
-    def perform_validations(options={}) # :nodoc:
+    def perform_validations(options = {})
       options[:validate] == false || valid?(options[:context])
     end
   end
diff --git a/activerecord/lib/active_record/validations/absence.rb b/activerecord/lib/active_record/validations/absence.rb
index 2e19e6dc5c..6afb9eabd2 100644
--- a/activerecord/lib/active_record/validations/absence.rb
+++ b/activerecord/lib/active_record/validations/absence.rb
@@ -1,8 +1,9 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Validations
     class AbsenceValidator < ActiveModel::Validations::AbsenceValidator # :nodoc:
       def validate_each(record, attribute, association_or_value)
-        return unless should_validate?(record)
         if record.class._reflect_on_association(attribute)
           association_or_value = Array.wrap(association_or_value).reject(&:marked_for_destruction?)
         end
diff --git a/activerecord/lib/active_record/validations/associated.rb b/activerecord/lib/active_record/validations/associated.rb
index 47ccef31a5..3538aeec22 100644
--- a/activerecord/lib/active_record/validations/associated.rb
+++ b/activerecord/lib/active_record/validations/associated.rb
@@ -1,11 +1,19 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Validations
     class AssociatedValidator < ActiveModel::EachValidator #:nodoc:
       def validate_each(record, attribute, value)
-        if Array.wrap(value).reject {|r| r.marked_for_destruction? || r.valid?}.any?
-          record.errors.add(attribute, :invalid, options.merge(:value => value))
+        if Array(value).reject { |r| valid_object?(r) }.any?
+          record.errors.add(attribute, :invalid, options.merge(value: value))
         end
       end
+
+      private
+
+        def valid_object?(record)
+          (record.respond_to?(:marked_for_destruction?) && record.marked_for_destruction?) || record.valid?
+        end
     end
 
     module ClassMethods
@@ -24,13 +32,14 @@ module ActiveRecord
       #
       # NOTE: This validation will not fail if the association hasn't been
       # assigned. If you want to ensure that the association is both present and
-      # guaranteed to be valid, you also need to use +validates_presence_of+.
+      # guaranteed to be valid, you also need to use
+      # {validates_presence_of}[rdoc-ref:Validations::ClassMethods#validates_presence_of].
       #
       # Configuration options:
       #
       # * <tt>:message</tt> - A custom error message (default is: "is invalid").
       # * <tt>:on</tt> - Specifies the contexts where this validation is active.
-      #   Runs in all validation contexts by default (nil). You can pass a symbol
+      #   Runs in all validation contexts by default +nil+. You can pass a symbol
       #   or an array of symbols. (e.g. <tt>on: :create</tt> or
       #   <tt>on: :custom_validation_context</tt> or
       #   <tt>on: [:create, :custom_validation_context]</tt>)
diff --git a/activerecord/lib/active_record/validations/length.rb b/activerecord/lib/active_record/validations/length.rb
index 69e048eef1..f47b14ae3a 100644
--- a/activerecord/lib/active_record/validations/length.rb
+++ b/activerecord/lib/active_record/validations/length.rb
@@ -1,24 +1,14 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Validations
     class LengthValidator < ActiveModel::Validations::LengthValidator # :nodoc:
       def validate_each(record, attribute, association_or_value)
-        return unless should_validate?(record) || associations_are_dirty?(record)
         if association_or_value.respond_to?(:loaded?) && association_or_value.loaded?
           association_or_value = association_or_value.target.reject(&:marked_for_destruction?)
         end
         super
       end
-
-      def associations_are_dirty?(record)
-        attributes.any? do |attribute|
-          value = record.read_attribute_for_validation(attribute)
-          if value.respond_to?(:loaded?) && value.loaded?
-            value.target.any?(&:marked_for_destruction?)
-          else
-            false
-          end
-        end
-      end
     end
 
     module ClassMethods
diff --git a/activerecord/lib/active_record/validations/presence.rb b/activerecord/lib/active_record/validations/presence.rb
index 23a3985d35..75e97e1997 100644
--- a/activerecord/lib/active_record/validations/presence.rb
+++ b/activerecord/lib/active_record/validations/presence.rb
@@ -1,8 +1,9 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Validations
     class PresenceValidator < ActiveModel::Validations::PresenceValidator # :nodoc:
       def validate_each(record, attribute, association_or_value)
-        return unless should_validate?(record)
         if record.class._reflect_on_association(attribute)
           association_or_value = Array.wrap(association_or_value).reject(&:marked_for_destruction?)
         end
@@ -31,7 +32,7 @@ module ActiveRecord
       # This is due to the way Object#blank? handles boolean values:
       # <tt>false.blank? # => true</tt>.
       #
-      # This validator defers to the ActiveModel validation for presence, adding the
+      # This validator defers to the Active Model validation for presence, adding the
       # check to see that an associated object is not marked for destruction. This
       # prevents the parent object from validating successfully and saving, which then
       # deletes the associated object, thus putting the parent object into an invalid
@@ -39,12 +40,13 @@ module ActiveRecord
       #
       # NOTE: This validation will not fail while using it with an association
       # if the latter was assigned but not valid. If you want to ensure that
-      # it is both present and valid, you also need to use +validates_associated+.
+      # it is both present and valid, you also need to use
+      # {validates_associated}[rdoc-ref:Validations::ClassMethods#validates_associated].
       #
       # Configuration options:
       # * <tt>:message</tt> - A custom error message (default is: "can't be blank").
       # * <tt>:on</tt> - Specifies the contexts where this validation is active.
-      #   Runs in all validation contexts by default (nil). You can pass a symbol
+      #   Runs in all validation contexts by default +nil+. You can pass a symbol
       #   or an array of symbols. (e.g. <tt>on: :create</tt> or
       #   <tt>on: :custom_validation_context</tt> or
       #   <tt>on: [:create, :custom_validation_context]</tt>)
@@ -57,7 +59,7 @@ module ActiveRecord
       #   or <tt>unless: Proc.new { |user| user.signup_step <= 2 }</tt>). The method,
       #   proc or string should return or evaluate to a +true+ or +false+ value.
       # * <tt>:strict</tt> - Specifies whether validation should be strict.
-      #   See <tt>ActiveModel::Validation#validates!</tt> for more information.
+      #   See ActiveModel::Validations#validates! for more information.
       def validates_presence_of(*attr_names)
         validates_with PresenceValidator, _merge_attributes(attr_names)
       end
diff --git a/activerecord/lib/active_record/validations/uniqueness.rb b/activerecord/lib/active_record/validations/uniqueness.rb
index 5106f4e127..5a1dbc8e53 100644
--- a/activerecord/lib/active_record/validations/uniqueness.rb
+++ b/activerecord/lib/active_record/validations/uniqueness.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module Validations
     class UniquenessValidator < ActiveModel::EachValidator # :nodoc:
@@ -6,19 +8,27 @@ module ActiveRecord
           raise ArgumentError, "#{options[:conditions]} was passed as :conditions but is not callable. " \
                                "Pass a callable instead: `conditions: -> { where(approved: true) }`"
         end
+        unless Array(options[:scope]).all? { |scope| scope.respond_to?(:to_sym) }
+          raise ArgumentError, "#{options[:scope]} is not supported format for :scope option. " \
+            "Pass a symbol or an array of symbols instead: `scope: :user_id`"
+        end
         super({ case_sensitive: true }.merge!(options))
         @klass = options[:class]
       end
 
       def validate_each(record, attribute, value)
-        return unless should_validate?(record)
         finder_class = find_finder_class_for(record)
-        table = finder_class.arel_table
         value = map_enum_attribute(finder_class, attribute, value)
 
-        relation = build_relation(finder_class, table, attribute, value)
-        relation = relation.where.not(finder_class.primary_key => record.id) if record.persisted?
-        relation = scope_relation(record, table, relation)
+        relation = build_relation(finder_class, attribute, value)
+        if record.persisted?
+          if finder_class.primary_key
+            relation = relation.where.not(finder_class.primary_key => record.id_in_database)
+          else
+            raise UnknownPrimaryKey.new(finder_class, "Can not validate uniqueness for persisted record without primary key.")
+          end
+        end
+        relation = scope_relation(record, relation)
         relation = relation.merge(options[:conditions]) if options[:conditions]
 
         if relation.exists?
@@ -29,13 +39,13 @@ module ActiveRecord
         end
       end
 
-    protected
+    private
       # The check for an existing value should be run from a class that
       # isn't abstract. This means working down from the current class
       # (self), to the first non-abstract class. Since classes don't know
       # their subclasses, we have to build the hierarchy between self and
       # the record's class.
-      def find_finder_class_for(record) #:nodoc:
+      def find_finder_class_for(record)
         class_hierarchy = [record.class]
 
         while class_hierarchy.first != @klass
@@ -45,48 +55,42 @@ module ActiveRecord
         class_hierarchy.detect { |klass| !klass.abstract_class? }
       end
 
-      def build_relation(klass, table, attribute, value) #:nodoc:
+      def build_relation(klass, attribute, value)
         if reflection = klass._reflect_on_association(attribute)
           attribute = reflection.foreign_key
           value = value.attributes[reflection.klass.primary_key] unless value.nil?
         end
 
-        attribute_name = attribute.to_s
+        if value.nil?
+          return klass.unscoped.where!(attribute => value)
+        end
 
         # the attribute may be an aliased attribute
-        if klass.attribute_aliases[attribute_name]
-          attribute = klass.attribute_aliases[attribute_name]
-          attribute_name = attribute.to_s
+        if klass.attribute_alias?(attribute)
+          attribute = klass.attribute_alias(attribute)
         end
 
-        column = klass.columns_hash[attribute_name]
-        cast_type = klass.type_for_attribute(attribute_name)
-        value = cast_type.serialize(value)
-        value = klass.connection.type_cast(value)
-        if value.is_a?(String) && column.limit
-          value = value.to_s[0, column.limit]
-        end
+        attribute_name = attribute.to_s
+        value = klass.predicate_builder.build_bind_attribute(attribute_name, value)
 
-        value = Arel::Nodes::Quoted.new(value)
+        table = klass.arel_table
+        column = klass.columns_hash[attribute_name]
 
-        comparison = if !options[:case_sensitive] && !value.nil?
+        comparison = if !options[:case_sensitive]
           # will use SQL LOWER function before comparison, unless it detects a case insensitive collation
           klass.connection.case_insensitive_comparison(table, attribute, column, value)
         else
           klass.connection.case_sensitive_comparison(table, attribute, column, value)
         end
-        klass.unscoped.where(comparison)
-      rescue RangeError
-        klass.none
+        klass.unscoped.where!(comparison)
       end
 
-      def scope_relation(record, table, relation)
+      def scope_relation(record, relation)
         Array(options[:scope]).each do |scope_item|
-          if reflection = record.class._reflect_on_association(scope_item)
-            scope_value = record.send(reflection.foreign_key)
-            scope_item  = reflection.foreign_key
+          scope_value = if record.class._reflect_on_association(scope_item)
+            record.association(scope_item).reader
           else
-            scope_value = record._read_attribute(scope_item)
+            record._read_attribute(scope_item)
           end
           relation = relation.where(scope_item => scope_value)
         end
@@ -166,7 +170,8 @@ module ActiveRecord
       #
       # === Concurrency and integrity
       #
-      # Using this validation method in conjunction with ActiveRecord::Base#save
+      # Using this validation method in conjunction with
+      # {ActiveRecord::Base#save}[rdoc-ref:Persistence#save]
       # does not guarantee the absence of duplicate record insertions, because
       # uniqueness checks on the application level are inherently prone to race
       # conditions. For example, suppose that two users try to post a Comment at
@@ -200,21 +205,19 @@ module ActiveRecord
       #                                      | # Boom! We now have a duplicate
       #                                      | # title!
       #
-      # This could even happen if you use transactions with the 'serializable'
-      # isolation level. The best way to work around this problem is to add a unique
-      # index to the database table using
-      # ActiveRecord::ConnectionAdapters::SchemaStatements#add_index. In the
-      # rare case that a race condition occurs, the database will guarantee
+      # The best way to work around this problem is to add a unique index to the database table using
+      # {connection.add_index}[rdoc-ref:ConnectionAdapters::SchemaStatements#add_index].
+      # In the rare case that a race condition occurs, the database will guarantee
       # the field's uniqueness.
       #
       # When the database catches such a duplicate insertion,
-      # ActiveRecord::Base#save will raise an ActiveRecord::StatementInvalid
+      # {ActiveRecord::Base#save}[rdoc-ref:Persistence#save] will raise an ActiveRecord::StatementInvalid
       # exception. You can either choose to let this error propagate (which
       # will result in the default Rails exception page being shown), or you
       # can catch it and restart the transaction (e.g. by telling the user
       # that the title already exists, and asking them to re-enter the title).
       # This technique is also known as
-      # {optimistic concurrency control}[http://en.wikipedia.org/wiki/Optimistic_concurrency_control].
+      # {optimistic concurrency control}[https://en.wikipedia.org/wiki/Optimistic_concurrency_control].
       #
       # The bundled ActiveRecord::ConnectionAdapters distinguish unique index
       # constraint errors from other types of database errors by throwing an
@@ -224,7 +227,6 @@ module ActiveRecord
       #
       # The following bundled adapters throw the ActiveRecord::RecordNotUnique exception:
       #
-      # * ActiveRecord::ConnectionAdapters::MysqlAdapter.
       # * ActiveRecord::ConnectionAdapters::Mysql2Adapter.
       # * ActiveRecord::ConnectionAdapters::SQLite3Adapter.
       # * ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.
diff --git a/activerecord/lib/active_record/version.rb b/activerecord/lib/active_record/version.rb
index cf76a13b44..6b0d82d8fc 100644
--- a/activerecord/lib/active_record/version.rb
+++ b/activerecord/lib/active_record/version.rb
@@ -1,4 +1,6 @@
-require_relative 'gem_version'
+# frozen_string_literal: true
+
+require_relative "gem_version"
 
 module ActiveRecord
   # Returns the version of the currently loaded ActiveRecord as a <tt>Gem::Version</tt>
diff --git a/activerecord/lib/arel.rb b/activerecord/lib/arel.rb
new file mode 100644
index 0000000000..dab785738e
--- /dev/null
+++ b/activerecord/lib/arel.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require "arel/errors"
+
+require "arel/crud"
+require "arel/factory_methods"
+
+require "arel/expressions"
+require "arel/predications"
+require "arel/window_predications"
+require "arel/math"
+require "arel/alias_predication"
+require "arel/order_predications"
+require "arel/table"
+require "arel/attributes"
+require "arel/compatibility/wheres"
+
+require "arel/visitors"
+require "arel/collectors/sql_string"
+
+require "arel/tree_manager"
+require "arel/insert_manager"
+require "arel/select_manager"
+require "arel/update_manager"
+require "arel/delete_manager"
+require "arel/nodes"
+
+module Arel # :nodoc: all
+  VERSION = "10.0.0"
+
+  def self.sql(raw_sql)
+    Arel::Nodes::SqlLiteral.new raw_sql
+  end
+
+  def self.star
+    sql "*"
+  end
+
+  def self.arel_node?(value)
+    value.is_a?(Arel::Node) || value.is_a?(Arel::Attribute) || value.is_a?(Arel::Nodes::SqlLiteral)
+  end
+
+  ## Convenience Alias
+  Node = Arel::Nodes::Node
+end
diff --git a/activerecord/lib/arel/alias_predication.rb b/activerecord/lib/arel/alias_predication.rb
new file mode 100644
index 0000000000..4abbbb7ef6
--- /dev/null
+++ b/activerecord/lib/arel/alias_predication.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module AliasPredication
+    def as(other)
+      Nodes::As.new self, Nodes::SqlLiteral.new(other)
+    end
+  end
+end
diff --git a/activerecord/lib/arel/attributes.rb b/activerecord/lib/arel/attributes.rb
new file mode 100644
index 0000000000..35d586c948
--- /dev/null
+++ b/activerecord/lib/arel/attributes.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require "arel/attributes/attribute"
+
+module Arel # :nodoc: all
+  module Attributes
+    ###
+    # Factory method to wrap a raw database +column+ to an Arel Attribute.
+    def self.for(column)
+      case column.type
+      when :string, :text, :binary             then String
+      when :integer                            then Integer
+      when :float                              then Float
+      when :decimal                            then Decimal
+      when :date, :datetime, :timestamp, :time then Time
+      when :boolean                            then Boolean
+      else
+        Undefined
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/attributes/attribute.rb b/activerecord/lib/arel/attributes/attribute.rb
new file mode 100644
index 0000000000..ecf499a23e
--- /dev/null
+++ b/activerecord/lib/arel/attributes/attribute.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Attributes
+    class Attribute < Struct.new :relation, :name
+      include Arel::Expressions
+      include Arel::Predications
+      include Arel::AliasPredication
+      include Arel::OrderPredications
+      include Arel::Math
+
+      ###
+      # Create a node for lowering this attribute
+      def lower
+        relation.lower self
+      end
+
+      def type_cast_for_database(value)
+        relation.type_cast_for_database(name, value)
+      end
+
+      def able_to_type_cast?
+        relation.able_to_type_cast?
+      end
+    end
+
+    class String    < Attribute; end
+    class Time      < Attribute; end
+    class Boolean   < Attribute; end
+    class Decimal   < Attribute; end
+    class Float     < Attribute; end
+    class Integer   < Attribute; end
+    class Undefined < Attribute; end
+  end
+
+  Attribute = Attributes::Attribute
+end
diff --git a/activerecord/lib/arel/collectors/bind.rb b/activerecord/lib/arel/collectors/bind.rb
new file mode 100644
index 0000000000..6f8912575d
--- /dev/null
+++ b/activerecord/lib/arel/collectors/bind.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Collectors
+    class Bind
+      def initialize
+        @binds = []
+      end
+
+      def <<(str)
+        self
+      end
+
+      def add_bind(bind)
+        @binds << bind
+        self
+      end
+
+      def value
+        @binds
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/collectors/composite.rb b/activerecord/lib/arel/collectors/composite.rb
new file mode 100644
index 0000000000..0533544993
--- /dev/null
+++ b/activerecord/lib/arel/collectors/composite.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Collectors
+    class Composite
+      def initialize(left, right)
+        @left = left
+        @right = right
+      end
+
+      def <<(str)
+        left << str
+        right << str
+        self
+      end
+
+      def add_bind(bind, &block)
+        left.add_bind bind, &block
+        right.add_bind bind, &block
+        self
+      end
+
+      def value
+        [left.value, right.value]
+      end
+
+      private
+        attr_reader :left, :right
+    end
+  end
+end
diff --git a/activerecord/lib/arel/collectors/plain_string.rb b/activerecord/lib/arel/collectors/plain_string.rb
new file mode 100644
index 0000000000..c0e9fff399
--- /dev/null
+++ b/activerecord/lib/arel/collectors/plain_string.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Collectors
+    class PlainString
+      def initialize
+        @str = +""
+      end
+
+      def value
+        @str
+      end
+
+      def <<(str)
+        @str << str
+        self
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/collectors/sql_string.rb b/activerecord/lib/arel/collectors/sql_string.rb
new file mode 100644
index 0000000000..54e1e562c2
--- /dev/null
+++ b/activerecord/lib/arel/collectors/sql_string.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "arel/collectors/plain_string"
+
+module Arel # :nodoc: all
+  module Collectors
+    class SQLString < PlainString
+      def initialize(*)
+        super
+        @bind_index = 1
+      end
+
+      def add_bind(bind)
+        self << yield(@bind_index)
+        @bind_index += 1
+        self
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/collectors/substitute_binds.rb b/activerecord/lib/arel/collectors/substitute_binds.rb
new file mode 100644
index 0000000000..4b894bc4b1
--- /dev/null
+++ b/activerecord/lib/arel/collectors/substitute_binds.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Collectors
+    class SubstituteBinds
+      def initialize(quoter, delegate_collector)
+        @quoter = quoter
+        @delegate = delegate_collector
+      end
+
+      def <<(str)
+        delegate << str
+        self
+      end
+
+      def add_bind(bind)
+        self << quoter.quote(bind)
+      end
+
+      def value
+        delegate.value
+      end
+
+      private
+        attr_reader :quoter, :delegate
+    end
+  end
+end
diff --git a/activerecord/lib/arel/compatibility/wheres.rb b/activerecord/lib/arel/compatibility/wheres.rb
new file mode 100644
index 0000000000..c8a73f0dae
--- /dev/null
+++ b/activerecord/lib/arel/compatibility/wheres.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Compatibility # :nodoc:
+    class Wheres # :nodoc:
+      include Enumerable
+
+      module Value # :nodoc:
+        attr_accessor :visitor
+        def value
+          visitor.accept self
+        end
+
+        def name
+          super.to_sym
+        end
+      end
+
+      def initialize(engine, collection)
+        @engine     = engine
+        @collection = collection
+      end
+
+      def each
+        to_sql = Visitors::ToSql.new @engine
+
+        @collection.each { |c|
+          c.extend(Value)
+          c.visitor = to_sql
+          yield c
+        }
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/crud.rb b/activerecord/lib/arel/crud.rb
new file mode 100644
index 0000000000..e8a563ca4a
--- /dev/null
+++ b/activerecord/lib/arel/crud.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  ###
+  # FIXME hopefully we can remove this
+  module Crud
+    def compile_update(values, pk)
+      um = UpdateManager.new
+
+      if Nodes::SqlLiteral === values
+        relation = @ctx.from
+      else
+        relation = values.first.first.relation
+      end
+      um.key = pk
+      um.table relation
+      um.set values
+      um.take @ast.limit.expr if @ast.limit
+      um.order(*@ast.orders)
+      um.wheres = @ctx.wheres
+      um
+    end
+
+    def compile_insert(values)
+      im = create_insert
+      im.insert values
+      im
+    end
+
+    def create_insert
+      InsertManager.new
+    end
+
+    def compile_delete
+      dm = DeleteManager.new
+      dm.take @ast.limit.expr if @ast.limit
+      dm.wheres = @ctx.wheres
+      dm.from @ctx.froms
+      dm
+    end
+  end
+end
diff --git a/activerecord/lib/arel/delete_manager.rb b/activerecord/lib/arel/delete_manager.rb
new file mode 100644
index 0000000000..fdba937d64
--- /dev/null
+++ b/activerecord/lib/arel/delete_manager.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  class DeleteManager < Arel::TreeManager
+    include TreeManager::StatementMethods
+
+    def initialize
+      super
+      @ast = Nodes::DeleteStatement.new
+      @ctx = @ast
+    end
+
+    def from(relation)
+      @ast.relation = relation
+      self
+    end
+  end
+end
diff --git a/activerecord/lib/arel/errors.rb b/activerecord/lib/arel/errors.rb
new file mode 100644
index 0000000000..2f8d5e3c02
--- /dev/null
+++ b/activerecord/lib/arel/errors.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  class ArelError < StandardError
+  end
+
+  class EmptyJoinError < ArelError
+  end
+end
diff --git a/activerecord/lib/arel/expressions.rb b/activerecord/lib/arel/expressions.rb
new file mode 100644
index 0000000000..da8afb338c
--- /dev/null
+++ b/activerecord/lib/arel/expressions.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Expressions
+    def count(distinct = false)
+      Nodes::Count.new [self], distinct
+    end
+
+    def sum
+      Nodes::Sum.new [self]
+    end
+
+    def maximum
+      Nodes::Max.new [self]
+    end
+
+    def minimum
+      Nodes::Min.new [self]
+    end
+
+    def average
+      Nodes::Avg.new [self]
+    end
+
+    def extract(field)
+      Nodes::Extract.new [self], field
+    end
+  end
+end
diff --git a/activerecord/lib/arel/factory_methods.rb b/activerecord/lib/arel/factory_methods.rb
new file mode 100644
index 0000000000..83ec23e403
--- /dev/null
+++ b/activerecord/lib/arel/factory_methods.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  ###
+  # Methods for creating various nodes
+  module FactoryMethods
+    def create_true
+      Arel::Nodes::True.new
+    end
+
+    def create_false
+      Arel::Nodes::False.new
+    end
+
+    def create_table_alias(relation, name)
+      Nodes::TableAlias.new(relation, name)
+    end
+
+    def create_join(to, constraint = nil, klass = Nodes::InnerJoin)
+      klass.new(to, constraint)
+    end
+
+    def create_string_join(to)
+      create_join to, nil, Nodes::StringJoin
+    end
+
+    def create_and(clauses)
+      Nodes::And.new clauses
+    end
+
+    def create_on(expr)
+      Nodes::On.new expr
+    end
+
+    def grouping(expr)
+      Nodes::Grouping.new expr
+    end
+
+    ###
+    # Create a LOWER() function
+    def lower(column)
+      Nodes::NamedFunction.new "LOWER", [Nodes.build_quoted(column)]
+    end
+
+    def coalesce(*exprs)
+      Nodes::NamedFunction.new "COALESCE", exprs
+    end
+  end
+end
diff --git a/activerecord/lib/arel/insert_manager.rb b/activerecord/lib/arel/insert_manager.rb
new file mode 100644
index 0000000000..c90fc33a48
--- /dev/null
+++ b/activerecord/lib/arel/insert_manager.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  class InsertManager < Arel::TreeManager
+    def initialize
+      super
+      @ast = Nodes::InsertStatement.new
+    end
+
+    def into(table)
+      @ast.relation = table
+      self
+    end
+
+    def columns; @ast.columns end
+    def values=(val); @ast.values = val; end
+
+    def select(select)
+      @ast.select = select
+    end
+
+    def insert(fields)
+      return if fields.empty?
+
+      if String === fields
+        @ast.values = Nodes::SqlLiteral.new(fields)
+      else
+        @ast.relation ||= fields.first.first.relation
+
+        values = []
+
+        fields.each do |column, value|
+          @ast.columns << column
+          values << value
+        end
+        @ast.values = create_values values, @ast.columns
+      end
+      self
+    end
+
+    def create_values(values, columns)
+      Nodes::Values.new values, columns
+    end
+
+    def create_values_list(rows)
+      Nodes::ValuesList.new(rows)
+    end
+  end
+end
diff --git a/activerecord/lib/arel/math.rb b/activerecord/lib/arel/math.rb
new file mode 100644
index 0000000000..2359f13148
--- /dev/null
+++ b/activerecord/lib/arel/math.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Math
+    def *(other)
+      Arel::Nodes::Multiplication.new(self, other)
+    end
+
+    def +(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::Addition.new(self, other))
+    end
+
+    def -(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::Subtraction.new(self, other))
+    end
+
+    def /(other)
+      Arel::Nodes::Division.new(self, other)
+    end
+
+    def &(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseAnd.new(self, other))
+    end
+
+    def |(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseOr.new(self, other))
+    end
+
+    def ^(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseXor.new(self, other))
+    end
+
+    def <<(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseShiftLeft.new(self, other))
+    end
+
+    def >>(other)
+      Arel::Nodes::Grouping.new(Arel::Nodes::BitwiseShiftRight.new(self, other))
+    end
+
+    def ~@
+      Arel::Nodes::BitwiseNot.new(self)
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes.rb b/activerecord/lib/arel/nodes.rb
new file mode 100644
index 0000000000..5af0e532e2
--- /dev/null
+++ b/activerecord/lib/arel/nodes.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+# node
+require "arel/nodes/node"
+require "arel/nodes/node_expression"
+require "arel/nodes/select_statement"
+require "arel/nodes/select_core"
+require "arel/nodes/insert_statement"
+require "arel/nodes/update_statement"
+require "arel/nodes/bind_param"
+
+# terminal
+
+require "arel/nodes/terminal"
+require "arel/nodes/true"
+require "arel/nodes/false"
+
+# unary
+require "arel/nodes/unary"
+require "arel/nodes/grouping"
+require "arel/nodes/ascending"
+require "arel/nodes/descending"
+require "arel/nodes/unqualified_column"
+require "arel/nodes/with"
+
+# binary
+require "arel/nodes/binary"
+require "arel/nodes/equality"
+require "arel/nodes/in" # Why is this subclassed from equality?
+require "arel/nodes/join_source"
+require "arel/nodes/delete_statement"
+require "arel/nodes/table_alias"
+require "arel/nodes/infix_operation"
+require "arel/nodes/unary_operation"
+require "arel/nodes/over"
+require "arel/nodes/matches"
+require "arel/nodes/regexp"
+
+# nary
+require "arel/nodes/and"
+
+# function
+# FIXME: Function + Alias can be rewritten as a Function and Alias node.
+# We should make Function a Unary node and deprecate the use of "aliaz"
+require "arel/nodes/function"
+require "arel/nodes/count"
+require "arel/nodes/extract"
+require "arel/nodes/values"
+require "arel/nodes/values_list"
+require "arel/nodes/named_function"
+
+# windows
+require "arel/nodes/window"
+
+# conditional expressions
+require "arel/nodes/case"
+
+# joins
+require "arel/nodes/full_outer_join"
+require "arel/nodes/inner_join"
+require "arel/nodes/outer_join"
+require "arel/nodes/right_outer_join"
+require "arel/nodes/string_join"
+
+require "arel/nodes/sql_literal"
+
+require "arel/nodes/casted"
diff --git a/activerecord/lib/arel/nodes/and.rb b/activerecord/lib/arel/nodes/and.rb
new file mode 100644
index 0000000000..c530a77bfb
--- /dev/null
+++ b/activerecord/lib/arel/nodes/and.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class And < Arel::Nodes::Node
+      attr_reader :children
+
+      def initialize(children)
+        super()
+        @children = children
+      end
+
+      def left
+        children.first
+      end
+
+      def right
+        children[1]
+      end
+
+      def hash
+        children.hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.children == other.children
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/ascending.rb b/activerecord/lib/arel/nodes/ascending.rb
new file mode 100644
index 0000000000..8b617f4df5
--- /dev/null
+++ b/activerecord/lib/arel/nodes/ascending.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Ascending < Ordering
+      def reverse
+        Descending.new(expr)
+      end
+
+      def direction
+        :asc
+      end
+
+      def ascending?
+        true
+      end
+
+      def descending?
+        false
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/binary.rb b/activerecord/lib/arel/nodes/binary.rb
new file mode 100644
index 0000000000..e184e99c73
--- /dev/null
+++ b/activerecord/lib/arel/nodes/binary.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Binary < Arel::Nodes::NodeExpression
+      attr_accessor :left, :right
+
+      def initialize(left, right)
+        super()
+        @left  = left
+        @right = right
+      end
+
+      def initialize_copy(other)
+        super
+        @left  = @left.clone if @left
+        @right = @right.clone if @right
+      end
+
+      def hash
+        [self.class, @left, @right].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.left == other.left &&
+          self.right == other.right
+      end
+      alias :== :eql?
+    end
+
+    %w{
+      As
+      Assignment
+      Between
+      GreaterThan
+      GreaterThanOrEqual
+      Join
+      LessThan
+      LessThanOrEqual
+      NotEqual
+      NotIn
+      Or
+      Union
+      UnionAll
+      Intersect
+      Except
+    }.each do |name|
+      const_set name, Class.new(Binary)
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/bind_param.rb b/activerecord/lib/arel/nodes/bind_param.rb
new file mode 100644
index 0000000000..ba8340558a
--- /dev/null
+++ b/activerecord/lib/arel/nodes/bind_param.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class BindParam < Node
+      attr_reader :value
+
+      def initialize(value)
+        @value = value
+        super()
+      end
+
+      def hash
+        [self.class, self.value].hash
+      end
+
+      def eql?(other)
+        other.is_a?(BindParam) &&
+          value == other.value
+      end
+      alias :== :eql?
+
+      def nil?
+        value.nil?
+      end
+
+      def boundable?
+        !value.respond_to?(:boundable?) || value.boundable?
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/case.rb b/activerecord/lib/arel/nodes/case.rb
new file mode 100644
index 0000000000..654a54825e
--- /dev/null
+++ b/activerecord/lib/arel/nodes/case.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Case < Arel::Nodes::Node
+      attr_accessor :case, :conditions, :default
+
+      def initialize(expression = nil, default = nil)
+        @case = expression
+        @conditions = []
+        @default = default
+      end
+
+      def when(condition, expression = nil)
+        @conditions << When.new(Nodes.build_quoted(condition), expression)
+        self
+      end
+
+      def then(expression)
+        @conditions.last.right = Nodes.build_quoted(expression)
+        self
+      end
+
+      def else(expression)
+        @default = Else.new Nodes.build_quoted(expression)
+        self
+      end
+
+      def initialize_copy(other)
+        super
+        @case = @case.clone if @case
+        @conditions = @conditions.map { |x| x.clone }
+        @default = @default.clone if @default
+      end
+
+      def hash
+        [@case, @conditions, @default].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.case == other.case &&
+          self.conditions == other.conditions &&
+          self.default == other.default
+      end
+      alias :== :eql?
+    end
+
+    class When < Binary # :nodoc:
+    end
+
+    class Else < Unary # :nodoc:
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/casted.rb b/activerecord/lib/arel/nodes/casted.rb
new file mode 100644
index 0000000000..c1e6e97d6d
--- /dev/null
+++ b/activerecord/lib/arel/nodes/casted.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Casted < Arel::Nodes::NodeExpression # :nodoc:
+      attr_reader :val, :attribute
+      def initialize(val, attribute)
+        @val       = val
+        @attribute = attribute
+        super()
+      end
+
+      def nil?; @val.nil?; end
+
+      def hash
+        [self.class, val, attribute].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+            self.val == other.val &&
+            self.attribute == other.attribute
+      end
+      alias :== :eql?
+    end
+
+    class Quoted < Arel::Nodes::Unary # :nodoc:
+      alias :val :value
+      def nil?; val.nil?; end
+    end
+
+    def self.build_quoted(other, attribute = nil)
+      case other
+      when Arel::Nodes::Node, Arel::Attributes::Attribute, Arel::Table, Arel::Nodes::BindParam, Arel::SelectManager, Arel::Nodes::Quoted, Arel::Nodes::SqlLiteral
+        other
+      else
+        case attribute
+        when Arel::Attributes::Attribute
+          Casted.new other, attribute
+        else
+          Quoted.new other
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/count.rb b/activerecord/lib/arel/nodes/count.rb
new file mode 100644
index 0000000000..880464639d
--- /dev/null
+++ b/activerecord/lib/arel/nodes/count.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Count < Arel::Nodes::Function
+      def initialize(expr, distinct = false, aliaz = nil)
+        super(expr, aliaz)
+        @distinct = distinct
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/delete_statement.rb b/activerecord/lib/arel/nodes/delete_statement.rb
new file mode 100644
index 0000000000..a419975335
--- /dev/null
+++ b/activerecord/lib/arel/nodes/delete_statement.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class DeleteStatement < Arel::Nodes::Node
+      attr_accessor :left, :right, :orders, :limit, :offset, :key
+
+      alias :relation :left
+      alias :relation= :left=
+      alias :wheres :right
+      alias :wheres= :right=
+
+      def initialize(relation = nil, wheres = [])
+        super()
+        @left = relation
+        @right = wheres
+        @orders = []
+        @limit = nil
+        @offset = nil
+        @key = nil
+      end
+
+      def initialize_copy(other)
+        super
+        @left  = @left.clone if @left
+        @right = @right.clone if @right
+      end
+
+      def hash
+        [self.class, @left, @right, @orders, @limit, @offset, @key].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.left == other.left &&
+          self.right == other.right &&
+          self.orders == other.orders &&
+          self.limit == other.limit &&
+          self.offset == other.offset &&
+          self.key == other.key
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/descending.rb b/activerecord/lib/arel/nodes/descending.rb
new file mode 100644
index 0000000000..f3f6992ca8
--- /dev/null
+++ b/activerecord/lib/arel/nodes/descending.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Descending < Ordering
+      def reverse
+        Ascending.new(expr)
+      end
+
+      def direction
+        :desc
+      end
+
+      def ascending?
+        false
+      end
+
+      def descending?
+        true
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/equality.rb b/activerecord/lib/arel/nodes/equality.rb
new file mode 100644
index 0000000000..551d56c2ff
--- /dev/null
+++ b/activerecord/lib/arel/nodes/equality.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Equality < Arel::Nodes::Binary
+      def operator; :== end
+      alias :operand1 :left
+      alias :operand2 :right
+    end
+
+    %w{
+      IsDistinctFrom
+      IsNotDistinctFrom
+    }.each do |name|
+      const_set name, Class.new(Equality)
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/extract.rb b/activerecord/lib/arel/nodes/extract.rb
new file mode 100644
index 0000000000..5799ee9b8f
--- /dev/null
+++ b/activerecord/lib/arel/nodes/extract.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Extract < Arel::Nodes::Unary
+      attr_accessor :field
+
+      def initialize(expr, field)
+        super(expr)
+        @field = field
+      end
+
+      def hash
+        super ^ @field.hash
+      end
+
+      def eql?(other)
+        super &&
+          self.field == other.field
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/false.rb b/activerecord/lib/arel/nodes/false.rb
new file mode 100644
index 0000000000..1e5bf04be5
--- /dev/null
+++ b/activerecord/lib/arel/nodes/false.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class False < Arel::Nodes::NodeExpression
+      def hash
+        self.class.hash
+      end
+
+      def eql?(other)
+        self.class == other.class
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/full_outer_join.rb b/activerecord/lib/arel/nodes/full_outer_join.rb
new file mode 100644
index 0000000000..91bb81f2e3
--- /dev/null
+++ b/activerecord/lib/arel/nodes/full_outer_join.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class FullOuterJoin < Arel::Nodes::Join
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/function.rb b/activerecord/lib/arel/nodes/function.rb
new file mode 100644
index 0000000000..0a439b39f5
--- /dev/null
+++ b/activerecord/lib/arel/nodes/function.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Function < Arel::Nodes::NodeExpression
+      include Arel::WindowPredications
+      attr_accessor :expressions, :alias, :distinct
+
+      def initialize(expr, aliaz = nil)
+        super()
+        @expressions = expr
+        @alias       = aliaz && SqlLiteral.new(aliaz)
+        @distinct    = false
+      end
+
+      def as(aliaz)
+        self.alias = SqlLiteral.new(aliaz)
+        self
+      end
+
+      def hash
+        [@expressions, @alias, @distinct].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.expressions == other.expressions &&
+          self.alias == other.alias &&
+          self.distinct == other.distinct
+      end
+      alias :== :eql?
+    end
+
+    %w{
+      Sum
+      Exists
+      Max
+      Min
+      Avg
+    }.each do |name|
+      const_set(name, Class.new(Function))
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/grouping.rb b/activerecord/lib/arel/nodes/grouping.rb
new file mode 100644
index 0000000000..4d0bd69d4d
--- /dev/null
+++ b/activerecord/lib/arel/nodes/grouping.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Grouping < Unary
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/in.rb b/activerecord/lib/arel/nodes/in.rb
new file mode 100644
index 0000000000..2be45d6f99
--- /dev/null
+++ b/activerecord/lib/arel/nodes/in.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class In < Equality
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/infix_operation.rb b/activerecord/lib/arel/nodes/infix_operation.rb
new file mode 100644
index 0000000000..bc7e20dcc6
--- /dev/null
+++ b/activerecord/lib/arel/nodes/infix_operation.rb
@@ -0,0 +1,80 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class InfixOperation < Binary
+      include Arel::Expressions
+      include Arel::Predications
+      include Arel::OrderPredications
+      include Arel::AliasPredication
+      include Arel::Math
+
+      attr_reader :operator
+
+      def initialize(operator, left, right)
+        super(left, right)
+        @operator = operator
+      end
+    end
+
+    class Multiplication < InfixOperation
+      def initialize(left, right)
+        super(:*, left, right)
+      end
+    end
+
+    class Division < InfixOperation
+      def initialize(left, right)
+        super(:/, left, right)
+      end
+    end
+
+    class Addition < InfixOperation
+      def initialize(left, right)
+        super(:+, left, right)
+      end
+    end
+
+    class Subtraction < InfixOperation
+      def initialize(left, right)
+        super(:-, left, right)
+      end
+    end
+
+    class Concat < InfixOperation
+      def initialize(left, right)
+        super("||", left, right)
+      end
+    end
+
+    class BitwiseAnd < InfixOperation
+      def initialize(left, right)
+        super(:&, left, right)
+      end
+    end
+
+    class BitwiseOr < InfixOperation
+      def initialize(left, right)
+        super(:|, left, right)
+      end
+    end
+
+    class BitwiseXor < InfixOperation
+      def initialize(left, right)
+        super(:^, left, right)
+      end
+    end
+
+    class BitwiseShiftLeft < InfixOperation
+      def initialize(left, right)
+        super(:<<, left, right)
+      end
+    end
+
+    class BitwiseShiftRight < InfixOperation
+      def initialize(left, right)
+        super(:>>, left, right)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/inner_join.rb b/activerecord/lib/arel/nodes/inner_join.rb
new file mode 100644
index 0000000000..519fafad09
--- /dev/null
+++ b/activerecord/lib/arel/nodes/inner_join.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class InnerJoin < Arel::Nodes::Join
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/insert_statement.rb b/activerecord/lib/arel/nodes/insert_statement.rb
new file mode 100644
index 0000000000..d28fd1f6c8
--- /dev/null
+++ b/activerecord/lib/arel/nodes/insert_statement.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class InsertStatement < Arel::Nodes::Node
+      attr_accessor :relation, :columns, :values, :select
+
+      def initialize
+        super()
+        @relation = nil
+        @columns  = []
+        @values   = nil
+        @select   = nil
+      end
+
+      def initialize_copy(other)
+        super
+        @columns = @columns.clone
+        @values =  @values.clone if @values
+        @select =  @select.clone if @select
+      end
+
+      def hash
+        [@relation, @columns, @values, @select].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.relation == other.relation &&
+          self.columns == other.columns &&
+          self.select == other.select &&
+          self.values == other.values
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/join_source.rb b/activerecord/lib/arel/nodes/join_source.rb
new file mode 100644
index 0000000000..abf0944623
--- /dev/null
+++ b/activerecord/lib/arel/nodes/join_source.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    ###
+    # Class that represents a join source
+    #
+    #   http://www.sqlite.org/syntaxdiagrams.html#join-source
+
+    class JoinSource < Arel::Nodes::Binary
+      def initialize(single_source, joinop = [])
+        super
+      end
+
+      def empty?
+        !left && right.empty?
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/matches.rb b/activerecord/lib/arel/nodes/matches.rb
new file mode 100644
index 0000000000..fd5734f4bd
--- /dev/null
+++ b/activerecord/lib/arel/nodes/matches.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Matches < Binary
+      attr_reader :escape
+      attr_accessor :case_sensitive
+
+      def initialize(left, right, escape = nil, case_sensitive = false)
+        super(left, right)
+        @escape = escape && Nodes.build_quoted(escape)
+        @case_sensitive = case_sensitive
+      end
+    end
+
+    class DoesNotMatch < Matches; end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/named_function.rb b/activerecord/lib/arel/nodes/named_function.rb
new file mode 100644
index 0000000000..126462d6d6
--- /dev/null
+++ b/activerecord/lib/arel/nodes/named_function.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class NamedFunction < Arel::Nodes::Function
+      attr_accessor :name
+
+      def initialize(name, expr, aliaz = nil)
+        super(expr, aliaz)
+        @name = name
+      end
+
+      def hash
+        super ^ @name.hash
+      end
+
+      def eql?(other)
+        super && self.name == other.name
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/node.rb b/activerecord/lib/arel/nodes/node.rb
new file mode 100644
index 0000000000..8086102bde
--- /dev/null
+++ b/activerecord/lib/arel/nodes/node.rb
@@ -0,0 +1,50 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    ###
+    # Abstract base class for all AST nodes
+    class Node
+      include Arel::FactoryMethods
+      include Enumerable
+
+      ###
+      # Factory method to create a Nodes::Not node that has the recipient of
+      # the caller as a child.
+      def not
+        Nodes::Not.new self
+      end
+
+      ###
+      # Factory method to create a Nodes::Grouping node that has an Nodes::Or
+      # node as a child.
+      def or(right)
+        Nodes::Grouping.new Nodes::Or.new(self, right)
+      end
+
+      ###
+      # Factory method to create an Nodes::And node.
+      def and(right)
+        Nodes::And.new [self, right]
+      end
+
+      # FIXME: this method should go away.  I don't like people calling
+      # to_sql on non-head nodes.  This forces us to walk the AST until we
+      # can find a node that has a "relation" member.
+      #
+      # Maybe we should just use `Table.engine`?  :'(
+      def to_sql(engine = Table.engine)
+        collector = Arel::Collectors::SQLString.new
+        collector = engine.connection.visitor.accept self, collector
+        collector.value
+      end
+
+      # Iterate through AST, nodes will be yielded depth-first
+      def each(&block)
+        return enum_for(:each) unless block_given?
+
+        ::Arel::Visitors::DepthFirst.new(block).accept self
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/node_expression.rb b/activerecord/lib/arel/nodes/node_expression.rb
new file mode 100644
index 0000000000..cbcfaba37c
--- /dev/null
+++ b/activerecord/lib/arel/nodes/node_expression.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class NodeExpression < Arel::Nodes::Node
+      include Arel::Expressions
+      include Arel::Predications
+      include Arel::AliasPredication
+      include Arel::OrderPredications
+      include Arel::Math
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/outer_join.rb b/activerecord/lib/arel/nodes/outer_join.rb
new file mode 100644
index 0000000000..0a3042be61
--- /dev/null
+++ b/activerecord/lib/arel/nodes/outer_join.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class OuterJoin < Arel::Nodes::Join
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/over.rb b/activerecord/lib/arel/nodes/over.rb
new file mode 100644
index 0000000000..91176764a9
--- /dev/null
+++ b/activerecord/lib/arel/nodes/over.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Over < Binary
+      include Arel::AliasPredication
+
+      def initialize(left, right = nil)
+        super(left, right)
+      end
+
+      def operator; "OVER" end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/regexp.rb b/activerecord/lib/arel/nodes/regexp.rb
new file mode 100644
index 0000000000..7c25095569
--- /dev/null
+++ b/activerecord/lib/arel/nodes/regexp.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Regexp < Binary
+      attr_accessor :case_sensitive
+
+      def initialize(left, right, case_sensitive = true)
+        super(left, right)
+        @case_sensitive = case_sensitive
+      end
+    end
+
+    class NotRegexp < Regexp; end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/right_outer_join.rb b/activerecord/lib/arel/nodes/right_outer_join.rb
new file mode 100644
index 0000000000..04ed4aaa78
--- /dev/null
+++ b/activerecord/lib/arel/nodes/right_outer_join.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class RightOuterJoin < Arel::Nodes::Join
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/select_core.rb b/activerecord/lib/arel/nodes/select_core.rb
new file mode 100644
index 0000000000..73461ff683
--- /dev/null
+++ b/activerecord/lib/arel/nodes/select_core.rb
@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class SelectCore < Arel::Nodes::Node
+      attr_accessor :projections, :wheres, :groups, :windows
+      attr_accessor :havings, :source, :set_quantifier
+
+      def initialize
+        super()
+        @source         = JoinSource.new nil
+
+        # https://ronsavage.github.io/SQL/sql-92.bnf.html#set%20quantifier
+        @set_quantifier = nil
+        @projections    = []
+        @wheres         = []
+        @groups         = []
+        @havings        = []
+        @windows        = []
+      end
+
+      def from
+        @source.left
+      end
+
+      def from=(value)
+        @source.left = value
+      end
+
+      alias :froms= :from=
+      alias :froms :from
+
+      def initialize_copy(other)
+        super
+        @source      = @source.clone if @source
+        @projections = @projections.clone
+        @wheres      = @wheres.clone
+        @groups      = @groups.clone
+        @havings     = @havings.clone
+        @windows     = @windows.clone
+      end
+
+      def hash
+        [
+          @source, @set_quantifier, @projections,
+          @wheres, @groups, @havings, @windows
+        ].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.source == other.source &&
+          self.set_quantifier == other.set_quantifier &&
+          self.projections == other.projections &&
+          self.wheres == other.wheres &&
+          self.groups == other.groups &&
+          self.havings == other.havings &&
+          self.windows == other.windows
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/select_statement.rb b/activerecord/lib/arel/nodes/select_statement.rb
new file mode 100644
index 0000000000..eff5dad939
--- /dev/null
+++ b/activerecord/lib/arel/nodes/select_statement.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class SelectStatement < Arel::Nodes::NodeExpression
+      attr_reader :cores
+      attr_accessor :limit, :orders, :lock, :offset, :with
+
+      def initialize(cores = [SelectCore.new])
+        super()
+        @cores          = cores
+        @orders         = []
+        @limit          = nil
+        @lock           = nil
+        @offset         = nil
+        @with           = nil
+      end
+
+      def initialize_copy(other)
+        super
+        @cores  = @cores.map { |x| x.clone }
+        @orders = @orders.map { |x| x.clone }
+      end
+
+      def hash
+        [@cores, @orders, @limit, @lock, @offset, @with].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.cores == other.cores &&
+          self.orders == other.orders &&
+          self.limit == other.limit &&
+          self.lock == other.lock &&
+          self.offset == other.offset &&
+          self.with == other.with
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/sql_literal.rb b/activerecord/lib/arel/nodes/sql_literal.rb
new file mode 100644
index 0000000000..d25a8521b7
--- /dev/null
+++ b/activerecord/lib/arel/nodes/sql_literal.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class SqlLiteral < String
+      include Arel::Expressions
+      include Arel::Predications
+      include Arel::AliasPredication
+      include Arel::OrderPredications
+
+      def encode_with(coder)
+        coder.scalar = self.to_s
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/string_join.rb b/activerecord/lib/arel/nodes/string_join.rb
new file mode 100644
index 0000000000..86027fcab7
--- /dev/null
+++ b/activerecord/lib/arel/nodes/string_join.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class StringJoin < Arel::Nodes::Join
+      def initialize(left, right = nil)
+        super
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/table_alias.rb b/activerecord/lib/arel/nodes/table_alias.rb
new file mode 100644
index 0000000000..f95ca16a3d
--- /dev/null
+++ b/activerecord/lib/arel/nodes/table_alias.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class TableAlias < Arel::Nodes::Binary
+      alias :name :right
+      alias :relation :left
+      alias :table_alias :name
+
+      def [](name)
+        Attribute.new(self, name)
+      end
+
+      def table_name
+        relation.respond_to?(:name) ? relation.name : name
+      end
+
+      def type_cast_for_database(*args)
+        relation.type_cast_for_database(*args)
+      end
+
+      def able_to_type_cast?
+        relation.respond_to?(:able_to_type_cast?) && relation.able_to_type_cast?
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/terminal.rb b/activerecord/lib/arel/nodes/terminal.rb
new file mode 100644
index 0000000000..d84c453f1a
--- /dev/null
+++ b/activerecord/lib/arel/nodes/terminal.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Distinct < Arel::Nodes::NodeExpression
+      def hash
+        self.class.hash
+      end
+
+      def eql?(other)
+        self.class == other.class
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/true.rb b/activerecord/lib/arel/nodes/true.rb
new file mode 100644
index 0000000000..c891012969
--- /dev/null
+++ b/activerecord/lib/arel/nodes/true.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class True < Arel::Nodes::NodeExpression
+      def hash
+        self.class.hash
+      end
+
+      def eql?(other)
+        self.class == other.class
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/unary.rb b/activerecord/lib/arel/nodes/unary.rb
new file mode 100644
index 0000000000..00639304e4
--- /dev/null
+++ b/activerecord/lib/arel/nodes/unary.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Unary < Arel::Nodes::NodeExpression
+      attr_accessor :expr
+      alias :value :expr
+
+      def initialize(expr)
+        super()
+        @expr = expr
+      end
+
+      def hash
+        @expr.hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.expr == other.expr
+      end
+      alias :== :eql?
+    end
+
+    %w{
+      Bin
+      Cube
+      DistinctOn
+      Group
+      GroupingElement
+      GroupingSet
+      Lateral
+      Limit
+      Lock
+      Not
+      Offset
+      On
+      Ordering
+      RollUp
+    }.each do |name|
+      const_set(name, Class.new(Unary))
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/unary_operation.rb b/activerecord/lib/arel/nodes/unary_operation.rb
new file mode 100644
index 0000000000..524282ac84
--- /dev/null
+++ b/activerecord/lib/arel/nodes/unary_operation.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class UnaryOperation < Unary
+      attr_reader :operator
+
+      def initialize(operator, operand)
+        super(operand)
+        @operator = operator
+      end
+    end
+
+    class BitwiseNot < UnaryOperation
+      def initialize(operand)
+        super(:~, operand)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/unqualified_column.rb b/activerecord/lib/arel/nodes/unqualified_column.rb
new file mode 100644
index 0000000000..7c3e0720d7
--- /dev/null
+++ b/activerecord/lib/arel/nodes/unqualified_column.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class UnqualifiedColumn < Arel::Nodes::Unary
+      alias :attribute :expr
+      alias :attribute= :expr=
+
+      def relation
+        @expr.relation
+      end
+
+      def column
+        @expr.column
+      end
+
+      def name
+        @expr.name
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/update_statement.rb b/activerecord/lib/arel/nodes/update_statement.rb
new file mode 100644
index 0000000000..cfaa19e392
--- /dev/null
+++ b/activerecord/lib/arel/nodes/update_statement.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class UpdateStatement < Arel::Nodes::Node
+      attr_accessor :relation, :wheres, :values, :orders, :limit, :offset, :key
+
+      def initialize
+        @relation = nil
+        @wheres   = []
+        @values   = []
+        @orders   = []
+        @limit    = nil
+        @offset   = nil
+        @key      = nil
+      end
+
+      def initialize_copy(other)
+        super
+        @wheres = @wheres.clone
+        @values = @values.clone
+      end
+
+      def hash
+        [@relation, @wheres, @values, @orders, @limit, @offset, @key].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.relation == other.relation &&
+          self.wheres == other.wheres &&
+          self.values == other.values &&
+          self.orders == other.orders &&
+          self.limit == other.limit &&
+          self.offset == other.offset &&
+          self.key == other.key
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/values.rb b/activerecord/lib/arel/nodes/values.rb
new file mode 100644
index 0000000000..650248dc04
--- /dev/null
+++ b/activerecord/lib/arel/nodes/values.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Values < Arel::Nodes::Binary
+      alias :expressions :left
+      alias :expressions= :left=
+      alias :columns :right
+      alias :columns= :right=
+
+      def initialize(exprs, columns = [])
+        super
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/values_list.rb b/activerecord/lib/arel/nodes/values_list.rb
new file mode 100644
index 0000000000..27109848e4
--- /dev/null
+++ b/activerecord/lib/arel/nodes/values_list.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class ValuesList < Node
+      attr_reader :rows
+
+      def initialize(rows)
+        @rows = rows
+        super()
+      end
+
+      def hash
+        @rows.hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.rows == other.rows
+      end
+      alias :== :eql?
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/window.rb b/activerecord/lib/arel/nodes/window.rb
new file mode 100644
index 0000000000..4916fc7fbe
--- /dev/null
+++ b/activerecord/lib/arel/nodes/window.rb
@@ -0,0 +1,126 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class Window < Arel::Nodes::Node
+      attr_accessor :orders, :framing, :partitions
+
+      def initialize
+        @orders = []
+        @partitions = []
+        @framing = nil
+      end
+
+      def order(*expr)
+        # FIXME: We SHOULD NOT be converting these to SqlLiteral automatically
+        @orders.concat expr.map { |x|
+          String === x || Symbol === x ? Nodes::SqlLiteral.new(x.to_s) : x
+        }
+        self
+      end
+
+      def partition(*expr)
+        # FIXME: We SHOULD NOT be converting these to SqlLiteral automatically
+        @partitions.concat expr.map { |x|
+          String === x || Symbol === x ? Nodes::SqlLiteral.new(x.to_s) : x
+        }
+        self
+      end
+
+      def frame(expr)
+        @framing = expr
+      end
+
+      def rows(expr = nil)
+        if @framing
+          Rows.new(expr)
+        else
+          frame(Rows.new(expr))
+        end
+      end
+
+      def range(expr = nil)
+        if @framing
+          Range.new(expr)
+        else
+          frame(Range.new(expr))
+        end
+      end
+
+      def initialize_copy(other)
+        super
+        @orders = @orders.map { |x| x.clone }
+      end
+
+      def hash
+        [@orders, @framing].hash
+      end
+
+      def eql?(other)
+        self.class == other.class &&
+          self.orders == other.orders &&
+          self.framing == other.framing &&
+          self.partitions == other.partitions
+      end
+      alias :== :eql?
+    end
+
+    class NamedWindow < Window
+      attr_accessor :name
+
+      def initialize(name)
+        super()
+        @name = name
+      end
+
+      def initialize_copy(other)
+        super
+        @name = other.name.clone
+      end
+
+      def hash
+        super ^ @name.hash
+      end
+
+      def eql?(other)
+        super && self.name == other.name
+      end
+      alias :== :eql?
+    end
+
+    class Rows < Unary
+      def initialize(expr = nil)
+        super(expr)
+      end
+    end
+
+    class Range < Unary
+      def initialize(expr = nil)
+        super(expr)
+      end
+    end
+
+    class CurrentRow < Node
+      def hash
+        self.class.hash
+      end
+
+      def eql?(other)
+        self.class == other.class
+      end
+      alias :== :eql?
+    end
+
+    class Preceding < Unary
+      def initialize(expr = nil)
+        super(expr)
+      end
+    end
+
+    class Following < Unary
+      def initialize(expr = nil)
+        super(expr)
+      end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/nodes/with.rb b/activerecord/lib/arel/nodes/with.rb
new file mode 100644
index 0000000000..157bdcaa08
--- /dev/null
+++ b/activerecord/lib/arel/nodes/with.rb
@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Nodes
+    class With < Arel::Nodes::Unary
+      alias children expr
+    end
+
+    class WithRecursive < With; end
+  end
+end
diff --git a/activerecord/lib/arel/order_predications.rb b/activerecord/lib/arel/order_predications.rb
new file mode 100644
index 0000000000..d785bbba92
--- /dev/null
+++ b/activerecord/lib/arel/order_predications.rb
@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module OrderPredications
+    def asc
+      Nodes::Ascending.new self
+    end
+
+    def desc
+      Nodes::Descending.new self
+    end
+  end
+end
diff --git a/activerecord/lib/arel/predications.rb b/activerecord/lib/arel/predications.rb
new file mode 100644
index 0000000000..77502dd199
--- /dev/null
+++ b/activerecord/lib/arel/predications.rb
@@ -0,0 +1,249 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Predications
+    def not_eq(other)
+      Nodes::NotEqual.new self, quoted_node(other)
+    end
+
+    def not_eq_any(others)
+      grouping_any :not_eq, others
+    end
+
+    def not_eq_all(others)
+      grouping_all :not_eq, others
+    end
+
+    def eq(other)
+      Nodes::Equality.new self, quoted_node(other)
+    end
+
+    def is_not_distinct_from(other)
+      Nodes::IsNotDistinctFrom.new self, quoted_node(other)
+    end
+
+    def is_distinct_from(other)
+      Nodes::IsDistinctFrom.new self, quoted_node(other)
+    end
+
+    def eq_any(others)
+      grouping_any :eq, others
+    end
+
+    def eq_all(others)
+      grouping_all :eq, quoted_array(others)
+    end
+
+    def between(other)
+      if equals_quoted?(other.begin, -Float::INFINITY)
+        if equals_quoted?(other.end, Float::INFINITY)
+          not_in([])
+        elsif other.exclude_end?
+          lt(other.end)
+        else
+          lteq(other.end)
+        end
+      elsif equals_quoted?(other.end, Float::INFINITY)
+        gteq(other.begin)
+      elsif other.exclude_end?
+        gteq(other.begin).and(lt(other.end))
+      else
+        left = quoted_node(other.begin)
+        right = quoted_node(other.end)
+        Nodes::Between.new(self, left.and(right))
+      end
+    end
+
+    def in(other)
+      case other
+      when Arel::SelectManager
+        Arel::Nodes::In.new(self, other.ast)
+      when Range
+        if $VERBOSE
+          warn <<-eowarn
+Passing a range to `#in` is deprecated. Call `#between`, instead.
+          eowarn
+        end
+        between(other)
+      when Enumerable
+        Nodes::In.new self, quoted_array(other)
+      else
+        Nodes::In.new self, quoted_node(other)
+      end
+    end
+
+    def in_any(others)
+      grouping_any :in, others
+    end
+
+    def in_all(others)
+      grouping_all :in, others
+    end
+
+    def not_between(other)
+      if equals_quoted?(other.begin, -Float::INFINITY)
+        if equals_quoted?(other.end, Float::INFINITY)
+          self.in([])
+        elsif other.exclude_end?
+          gteq(other.end)
+        else
+          gt(other.end)
+        end
+      elsif equals_quoted?(other.end, Float::INFINITY)
+        lt(other.begin)
+      else
+        left = lt(other.begin)
+        right = if other.exclude_end?
+          gteq(other.end)
+        else
+          gt(other.end)
+        end
+        left.or(right)
+      end
+    end
+
+    def not_in(other)
+      case other
+      when Arel::SelectManager
+        Arel::Nodes::NotIn.new(self, other.ast)
+      when Range
+        if $VERBOSE
+          warn <<-eowarn
+Passing a range to `#not_in` is deprecated. Call `#not_between`, instead.
+          eowarn
+        end
+        not_between(other)
+      when Enumerable
+        Nodes::NotIn.new self, quoted_array(other)
+      else
+        Nodes::NotIn.new self, quoted_node(other)
+      end
+    end
+
+    def not_in_any(others)
+      grouping_any :not_in, others
+    end
+
+    def not_in_all(others)
+      grouping_all :not_in, others
+    end
+
+    def matches(other, escape = nil, case_sensitive = false)
+      Nodes::Matches.new self, quoted_node(other), escape, case_sensitive
+    end
+
+    def matches_regexp(other, case_sensitive = true)
+      Nodes::Regexp.new self, quoted_node(other), case_sensitive
+    end
+
+    def matches_any(others, escape = nil, case_sensitive = false)
+      grouping_any :matches, others, escape, case_sensitive
+    end
+
+    def matches_all(others, escape = nil, case_sensitive = false)
+      grouping_all :matches, others, escape, case_sensitive
+    end
+
+    def does_not_match(other, escape = nil, case_sensitive = false)
+      Nodes::DoesNotMatch.new self, quoted_node(other), escape, case_sensitive
+    end
+
+    def does_not_match_regexp(other, case_sensitive = true)
+      Nodes::NotRegexp.new self, quoted_node(other), case_sensitive
+    end
+
+    def does_not_match_any(others, escape = nil)
+      grouping_any :does_not_match, others, escape
+    end
+
+    def does_not_match_all(others, escape = nil)
+      grouping_all :does_not_match, others, escape
+    end
+
+    def gteq(right)
+      Nodes::GreaterThanOrEqual.new self, quoted_node(right)
+    end
+
+    def gteq_any(others)
+      grouping_any :gteq, others
+    end
+
+    def gteq_all(others)
+      grouping_all :gteq, others
+    end
+
+    def gt(right)
+      Nodes::GreaterThan.new self, quoted_node(right)
+    end
+
+    def gt_any(others)
+      grouping_any :gt, others
+    end
+
+    def gt_all(others)
+      grouping_all :gt, others
+    end
+
+    def lt(right)
+      Nodes::LessThan.new self, quoted_node(right)
+    end
+
+    def lt_any(others)
+      grouping_any :lt, others
+    end
+
+    def lt_all(others)
+      grouping_all :lt, others
+    end
+
+    def lteq(right)
+      Nodes::LessThanOrEqual.new self, quoted_node(right)
+    end
+
+    def lteq_any(others)
+      grouping_any :lteq, others
+    end
+
+    def lteq_all(others)
+      grouping_all :lteq, others
+    end
+
+    def when(right)
+      Nodes::Case.new(self).when quoted_node(right)
+    end
+
+    def concat(other)
+      Nodes::Concat.new self, other
+    end
+
+    private
+
+      def grouping_any(method_id, others, *extras)
+        nodes = others.map { |expr| send(method_id, expr, *extras) }
+        Nodes::Grouping.new nodes.inject { |memo, node|
+          Nodes::Or.new(memo, node)
+        }
+      end
+
+      def grouping_all(method_id, others, *extras)
+        nodes = others.map { |expr| send(method_id, expr, *extras) }
+        Nodes::Grouping.new Nodes::And.new(nodes)
+      end
+
+      def quoted_node(other)
+        Nodes.build_quoted(other, self)
+      end
+
+      def quoted_array(others)
+        others.map { |v| quoted_node(v) }
+      end
+
+      def equals_quoted?(maybe_quoted, value)
+        if maybe_quoted.is_a?(Nodes::Quoted)
+          maybe_quoted.val == value
+        else
+          maybe_quoted == value
+        end
+      end
+  end
+end
diff --git a/activerecord/lib/arel/select_manager.rb b/activerecord/lib/arel/select_manager.rb
new file mode 100644
index 0000000000..a2b2838a3d
--- /dev/null
+++ b/activerecord/lib/arel/select_manager.rb
@@ -0,0 +1,271 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  class SelectManager < Arel::TreeManager
+    include Arel::Crud
+
+    STRING_OR_SYMBOL_CLASS = [Symbol, String]
+
+    def initialize(table = nil)
+      super()
+      @ast = Nodes::SelectStatement.new
+      @ctx = @ast.cores.last
+      from table
+    end
+
+    def initialize_copy(other)
+      super
+      @ctx = @ast.cores.last
+    end
+
+    def limit
+      @ast.limit && @ast.limit.expr
+    end
+    alias :taken :limit
+
+    def constraints
+      @ctx.wheres
+    end
+
+    def offset
+      @ast.offset && @ast.offset.expr
+    end
+
+    def skip(amount)
+      if amount
+        @ast.offset = Nodes::Offset.new(amount)
+      else
+        @ast.offset = nil
+      end
+      self
+    end
+    alias :offset= :skip
+
+    ###
+    # Produces an Arel::Nodes::Exists node
+    def exists
+      Arel::Nodes::Exists.new @ast
+    end
+
+    def as(other)
+      create_table_alias grouping(@ast), Nodes::SqlLiteral.new(other)
+    end
+
+    def lock(locking = Arel.sql("FOR UPDATE"))
+      case locking
+      when true
+        locking = Arel.sql("FOR UPDATE")
+      when Arel::Nodes::SqlLiteral
+      when String
+        locking = Arel.sql locking
+      end
+
+      @ast.lock = Nodes::Lock.new(locking)
+      self
+    end
+
+    def locked
+      @ast.lock
+    end
+
+    def on(*exprs)
+      @ctx.source.right.last.right = Nodes::On.new(collapse(exprs))
+      self
+    end
+
+    def group(*columns)
+      columns.each do |column|
+        # FIXME: backwards compat
+        column = Nodes::SqlLiteral.new(column) if String === column
+        column = Nodes::SqlLiteral.new(column.to_s) if Symbol === column
+
+        @ctx.groups.push Nodes::Group.new column
+      end
+      self
+    end
+
+    def from(table)
+      table = Nodes::SqlLiteral.new(table) if String === table
+
+      case table
+      when Nodes::Join
+        @ctx.source.right << table
+      else
+        @ctx.source.left = table
+      end
+
+      self
+    end
+
+    def froms
+      @ast.cores.map { |x| x.from }.compact
+    end
+
+    def join(relation, klass = Nodes::InnerJoin)
+      return self unless relation
+
+      case relation
+      when String, Nodes::SqlLiteral
+        raise EmptyJoinError if relation.empty?
+        klass = Nodes::StringJoin
+      end
+
+      @ctx.source.right << create_join(relation, nil, klass)
+      self
+    end
+
+    def outer_join(relation)
+      join(relation, Nodes::OuterJoin)
+    end
+
+    def having(expr)
+      @ctx.havings << expr
+      self
+    end
+
+    def window(name)
+      window = Nodes::NamedWindow.new(name)
+      @ctx.windows.push window
+      window
+    end
+
+    def project(*projections)
+      # FIXME: converting these to SQLLiterals is probably not good, but
+      # rails tests require it.
+      @ctx.projections.concat projections.map { |x|
+        STRING_OR_SYMBOL_CLASS.include?(x.class) ? Nodes::SqlLiteral.new(x.to_s) : x
+      }
+      self
+    end
+
+    def projections
+      @ctx.projections
+    end
+
+    def projections=(projections)
+      @ctx.projections = projections
+    end
+
+    def distinct(value = true)
+      if value
+        @ctx.set_quantifier = Arel::Nodes::Distinct.new
+      else
+        @ctx.set_quantifier = nil
+      end
+      self
+    end
+
+    def distinct_on(value)
+      if value
+        @ctx.set_quantifier = Arel::Nodes::DistinctOn.new(value)
+      else
+        @ctx.set_quantifier = nil
+      end
+      self
+    end
+
+    def order(*expr)
+      # FIXME: We SHOULD NOT be converting these to SqlLiteral automatically
+      @ast.orders.concat expr.map { |x|
+        STRING_OR_SYMBOL_CLASS.include?(x.class) ? Nodes::SqlLiteral.new(x.to_s) : x
+      }
+      self
+    end
+
+    def orders
+      @ast.orders
+    end
+
+    def where_sql(engine = Table.engine)
+      return if @ctx.wheres.empty?
+
+      viz = Visitors::WhereSql.new(engine.connection.visitor, engine.connection)
+      Nodes::SqlLiteral.new viz.accept(@ctx, Collectors::SQLString.new).value
+    end
+
+    def union(operation, other = nil)
+      if other
+        node_class = Nodes.const_get("Union#{operation.to_s.capitalize}")
+      else
+        other = operation
+        node_class = Nodes::Union
+      end
+
+      node_class.new self.ast, other.ast
+    end
+
+    def intersect(other)
+      Nodes::Intersect.new ast, other.ast
+    end
+
+    def except(other)
+      Nodes::Except.new ast, other.ast
+    end
+    alias :minus :except
+
+    def lateral(table_name = nil)
+      base = table_name.nil? ? ast : as(table_name)
+      Nodes::Lateral.new(base)
+    end
+
+    def with(*subqueries)
+      if subqueries.first.is_a? Symbol
+        node_class = Nodes.const_get("With#{subqueries.shift.to_s.capitalize}")
+      else
+        node_class = Nodes::With
+      end
+      @ast.with = node_class.new(subqueries.flatten)
+
+      self
+    end
+
+    def take(limit)
+      if limit
+        @ast.limit = Nodes::Limit.new(limit)
+      else
+        @ast.limit = nil
+      end
+      self
+    end
+    alias limit= take
+
+    def join_sources
+      @ctx.source.right
+    end
+
+    def source
+      @ctx.source
+    end
+
+    class Row < Struct.new(:data) # :nodoc:
+      def id
+        data["id"]
+      end
+
+      def method_missing(name, *args)
+        name = name.to_s
+        return data[name] if data.key?(name)
+        super
+      end
+    end
+
+    private
+      def collapse(exprs)
+        exprs = exprs.compact
+        exprs.map! { |expr|
+          if String === expr
+            # FIXME: Don't do this automatically
+            Arel.sql(expr)
+          else
+            expr
+          end
+        }
+
+        if exprs.length == 1
+          exprs.first
+        else
+          create_and exprs
+        end
+      end
+  end
+end
diff --git a/activerecord/lib/arel/table.rb b/activerecord/lib/arel/table.rb
new file mode 100644
index 0000000000..c40c68715a
--- /dev/null
+++ b/activerecord/lib/arel/table.rb
@@ -0,0 +1,110 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  class Table
+    include Arel::Crud
+    include Arel::FactoryMethods
+
+    @engine = nil
+    class << self; attr_accessor :engine; end
+
+    attr_accessor :name, :table_alias
+
+    # TableAlias and Table both have a #table_name which is the name of the underlying table
+    alias :table_name :name
+
+    def initialize(name, as: nil, type_caster: nil)
+      @name = name.to_s
+      @type_caster = type_caster
+
+      # Sometime AR sends an :as parameter to table, to let the table know
+      # that it is an Alias.  We may want to override new, and return a
+      # TableAlias node?
+      if as.to_s == @name
+        as = nil
+      end
+      @table_alias = as
+    end
+
+    def alias(name = "#{self.name}_2")
+      Nodes::TableAlias.new(self, name)
+    end
+
+    def from
+      SelectManager.new(self)
+    end
+
+    def join(relation, klass = Nodes::InnerJoin)
+      return from unless relation
+
+      case relation
+      when String, Nodes::SqlLiteral
+        raise EmptyJoinError if relation.empty?
+        klass = Nodes::StringJoin
+      end
+
+      from.join(relation, klass)
+    end
+
+    def outer_join(relation)
+      join(relation, Nodes::OuterJoin)
+    end
+
+    def group(*columns)
+      from.group(*columns)
+    end
+
+    def order(*expr)
+      from.order(*expr)
+    end
+
+    def where(condition)
+      from.where condition
+    end
+
+    def project(*things)
+      from.project(*things)
+    end
+
+    def take(amount)
+      from.take amount
+    end
+
+    def skip(amount)
+      from.skip amount
+    end
+
+    def having(expr)
+      from.having expr
+    end
+
+    def [](name)
+      ::Arel::Attribute.new self, name
+    end
+
+    def hash
+      # Perf note: aliases and table alias is excluded from the hash
+      #  aliases can have a loop back to this table breaking hashes in parent
+      #  relations, for the vast majority of cases @name is unique to a query
+      @name.hash
+    end
+
+    def eql?(other)
+      self.class == other.class &&
+        self.name == other.name &&
+        self.table_alias == other.table_alias
+    end
+    alias :== :eql?
+
+    def type_cast_for_database(attribute_name, value)
+      type_caster.type_cast_for_database(attribute_name, value)
+    end
+
+    def able_to_type_cast?
+      !type_caster.nil?
+    end
+
+    private
+      attr_reader :type_caster
+  end
+end
diff --git a/activerecord/lib/arel/tree_manager.rb b/activerecord/lib/arel/tree_manager.rb
new file mode 100644
index 0000000000..0476399618
--- /dev/null
+++ b/activerecord/lib/arel/tree_manager.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  class TreeManager
+    include Arel::FactoryMethods
+
+    module StatementMethods
+      def take(limit)
+        @ast.limit = Nodes::Limit.new(Nodes.build_quoted(limit)) if limit
+        self
+      end
+
+      def offset(offset)
+        @ast.offset = Nodes::Offset.new(Nodes.build_quoted(offset)) if offset
+        self
+      end
+
+      def order(*expr)
+        @ast.orders = expr
+        self
+      end
+
+      def key=(key)
+        @ast.key = Nodes.build_quoted(key)
+      end
+
+      def key
+        @ast.key
+      end
+
+      def wheres=(exprs)
+        @ast.wheres = exprs
+      end
+
+      def where(expr)
+        @ast.wheres << expr
+        self
+      end
+    end
+
+    attr_reader :ast
+
+    def initialize
+      @ctx = nil
+    end
+
+    def to_dot
+      collector = Arel::Collectors::PlainString.new
+      collector = Visitors::Dot.new.accept @ast, collector
+      collector.value
+    end
+
+    def to_sql(engine = Table.engine)
+      collector = Arel::Collectors::SQLString.new
+      collector = engine.connection.visitor.accept @ast, collector
+      collector.value
+    end
+
+    def initialize_copy(other)
+      super
+      @ast = @ast.clone
+    end
+
+    def where(expr)
+      if Arel::TreeManager === expr
+        expr = expr.ast
+      end
+      @ctx.wheres << expr
+      self
+    end
+  end
+end
diff --git a/activerecord/lib/arel/update_manager.rb b/activerecord/lib/arel/update_manager.rb
new file mode 100644
index 0000000000..a809dbb307
--- /dev/null
+++ b/activerecord/lib/arel/update_manager.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  class UpdateManager < Arel::TreeManager
+    include TreeManager::StatementMethods
+
+    def initialize
+      super
+      @ast = Nodes::UpdateStatement.new
+      @ctx = @ast
+    end
+
+    ###
+    # UPDATE +table+
+    def table(table)
+      @ast.relation = table
+      self
+    end
+
+    def set(values)
+      if String === values
+        @ast.values = [values]
+      else
+        @ast.values = values.map { |column, value|
+          Nodes::Assignment.new(
+            Nodes::UnqualifiedColumn.new(column),
+            value
+          )
+        }
+      end
+      self
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors.rb b/activerecord/lib/arel/visitors.rb
new file mode 100644
index 0000000000..e350f52e65
--- /dev/null
+++ b/activerecord/lib/arel/visitors.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "arel/visitors/visitor"
+require "arel/visitors/depth_first"
+require "arel/visitors/to_sql"
+require "arel/visitors/sqlite"
+require "arel/visitors/postgresql"
+require "arel/visitors/mysql"
+require "arel/visitors/mssql"
+require "arel/visitors/oracle"
+require "arel/visitors/oracle12"
+require "arel/visitors/where_sql"
+require "arel/visitors/dot"
+require "arel/visitors/ibm_db"
+require "arel/visitors/informix"
+
+module Arel # :nodoc: all
+  module Visitors
+  end
+end
diff --git a/activerecord/lib/arel/visitors/depth_first.rb b/activerecord/lib/arel/visitors/depth_first.rb
new file mode 100644
index 0000000000..92d309453c
--- /dev/null
+++ b/activerecord/lib/arel/visitors/depth_first.rb
@@ -0,0 +1,199 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class DepthFirst < Arel::Visitors::Visitor
+      def initialize(block = nil)
+        @block = block || Proc.new
+        super()
+      end
+
+      private
+
+        def visit(o)
+          super
+          @block.call o
+        end
+
+        def unary(o)
+          visit o.expr
+        end
+        alias :visit_Arel_Nodes_Else              :unary
+        alias :visit_Arel_Nodes_Group             :unary
+        alias :visit_Arel_Nodes_Cube              :unary
+        alias :visit_Arel_Nodes_RollUp            :unary
+        alias :visit_Arel_Nodes_GroupingSet       :unary
+        alias :visit_Arel_Nodes_GroupingElement   :unary
+        alias :visit_Arel_Nodes_Grouping          :unary
+        alias :visit_Arel_Nodes_Having            :unary
+        alias :visit_Arel_Nodes_Lateral           :unary
+        alias :visit_Arel_Nodes_Limit             :unary
+        alias :visit_Arel_Nodes_Not               :unary
+        alias :visit_Arel_Nodes_Offset            :unary
+        alias :visit_Arel_Nodes_On                :unary
+        alias :visit_Arel_Nodes_Ordering          :unary
+        alias :visit_Arel_Nodes_Ascending         :unary
+        alias :visit_Arel_Nodes_Descending        :unary
+        alias :visit_Arel_Nodes_UnqualifiedColumn :unary
+
+        def function(o)
+          visit o.expressions
+          visit o.alias
+          visit o.distinct
+        end
+        alias :visit_Arel_Nodes_Avg    :function
+        alias :visit_Arel_Nodes_Exists :function
+        alias :visit_Arel_Nodes_Max    :function
+        alias :visit_Arel_Nodes_Min    :function
+        alias :visit_Arel_Nodes_Sum    :function
+
+        def visit_Arel_Nodes_NamedFunction(o)
+          visit o.name
+          visit o.expressions
+          visit o.distinct
+          visit o.alias
+        end
+
+        def visit_Arel_Nodes_Count(o)
+          visit o.expressions
+          visit o.alias
+          visit o.distinct
+        end
+
+        def visit_Arel_Nodes_Case(o)
+          visit o.case
+          visit o.conditions
+          visit o.default
+        end
+
+        def nary(o)
+          o.children.each { |child| visit child }
+        end
+        alias :visit_Arel_Nodes_And :nary
+
+        def binary(o)
+          visit o.left
+          visit o.right
+        end
+        alias :visit_Arel_Nodes_As                 :binary
+        alias :visit_Arel_Nodes_Assignment         :binary
+        alias :visit_Arel_Nodes_Between            :binary
+        alias :visit_Arel_Nodes_Concat             :binary
+        alias :visit_Arel_Nodes_DeleteStatement    :binary
+        alias :visit_Arel_Nodes_DoesNotMatch       :binary
+        alias :visit_Arel_Nodes_Equality           :binary
+        alias :visit_Arel_Nodes_FullOuterJoin      :binary
+        alias :visit_Arel_Nodes_GreaterThan        :binary
+        alias :visit_Arel_Nodes_GreaterThanOrEqual :binary
+        alias :visit_Arel_Nodes_In                 :binary
+        alias :visit_Arel_Nodes_InfixOperation     :binary
+        alias :visit_Arel_Nodes_JoinSource         :binary
+        alias :visit_Arel_Nodes_InnerJoin          :binary
+        alias :visit_Arel_Nodes_LessThan           :binary
+        alias :visit_Arel_Nodes_LessThanOrEqual    :binary
+        alias :visit_Arel_Nodes_Matches            :binary
+        alias :visit_Arel_Nodes_NotEqual           :binary
+        alias :visit_Arel_Nodes_NotIn              :binary
+        alias :visit_Arel_Nodes_NotRegexp          :binary
+        alias :visit_Arel_Nodes_IsNotDistinctFrom  :binary
+        alias :visit_Arel_Nodes_IsDistinctFrom     :binary
+        alias :visit_Arel_Nodes_Or                 :binary
+        alias :visit_Arel_Nodes_OuterJoin          :binary
+        alias :visit_Arel_Nodes_Regexp             :binary
+        alias :visit_Arel_Nodes_RightOuterJoin     :binary
+        alias :visit_Arel_Nodes_TableAlias         :binary
+        alias :visit_Arel_Nodes_Values             :binary
+        alias :visit_Arel_Nodes_When               :binary
+
+        def visit_Arel_Nodes_StringJoin(o)
+          visit o.left
+        end
+
+        def visit_Arel_Attribute(o)
+          visit o.relation
+          visit o.name
+        end
+        alias :visit_Arel_Attributes_Integer :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Float :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_String :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Time :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Boolean :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Attribute :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Decimal :visit_Arel_Attribute
+
+        def visit_Arel_Table(o)
+          visit o.name
+        end
+
+        def terminal(o)
+        end
+        alias :visit_ActiveSupport_Multibyte_Chars :terminal
+        alias :visit_ActiveSupport_StringInquirer  :terminal
+        alias :visit_Arel_Nodes_Lock               :terminal
+        alias :visit_Arel_Nodes_Node               :terminal
+        alias :visit_Arel_Nodes_SqlLiteral         :terminal
+        alias :visit_Arel_Nodes_BindParam          :terminal
+        alias :visit_Arel_Nodes_Window             :terminal
+        alias :visit_Arel_Nodes_True               :terminal
+        alias :visit_Arel_Nodes_False              :terminal
+        alias :visit_BigDecimal                    :terminal
+        alias :visit_Class                         :terminal
+        alias :visit_Date                          :terminal
+        alias :visit_DateTime                      :terminal
+        alias :visit_FalseClass                    :terminal
+        alias :visit_Float                         :terminal
+        alias :visit_Integer                       :terminal
+        alias :visit_NilClass                      :terminal
+        alias :visit_String                        :terminal
+        alias :visit_Symbol                        :terminal
+        alias :visit_Time                          :terminal
+        alias :visit_TrueClass                     :terminal
+
+        def visit_Arel_Nodes_InsertStatement(o)
+          visit o.relation
+          visit o.columns
+          visit o.values
+        end
+
+        def visit_Arel_Nodes_SelectCore(o)
+          visit o.projections
+          visit o.source
+          visit o.wheres
+          visit o.groups
+          visit o.windows
+          visit o.havings
+        end
+
+        def visit_Arel_Nodes_SelectStatement(o)
+          visit o.cores
+          visit o.orders
+          visit o.limit
+          visit o.lock
+          visit o.offset
+        end
+
+        def visit_Arel_Nodes_UpdateStatement(o)
+          visit o.relation
+          visit o.values
+          visit o.wheres
+          visit o.orders
+          visit o.limit
+        end
+
+        def visit_Array(o)
+          o.each { |i| visit i }
+        end
+        alias :visit_Set :visit_Array
+
+        def visit_Hash(o)
+          o.each { |k, v| visit(k); visit(v) }
+        end
+
+        DISPATCH = dispatch_cache
+
+        def get_dispatch_cache
+          DISPATCH
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/dot.rb b/activerecord/lib/arel/visitors/dot.rb
new file mode 100644
index 0000000000..6389c875cb
--- /dev/null
+++ b/activerecord/lib/arel/visitors/dot.rb
@@ -0,0 +1,292 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class Dot < Arel::Visitors::Visitor
+      class Node # :nodoc:
+        attr_accessor :name, :id, :fields
+
+        def initialize(name, id, fields = [])
+          @name   = name
+          @id     = id
+          @fields = fields
+        end
+      end
+
+      class Edge < Struct.new :name, :from, :to # :nodoc:
+      end
+
+      def initialize
+        super()
+        @nodes      = []
+        @edges      = []
+        @node_stack = []
+        @edge_stack = []
+        @seen       = {}
+      end
+
+      def accept(object, collector)
+        visit object
+        collector << to_dot
+      end
+
+      private
+
+        def visit_Arel_Nodes_Ordering(o)
+          visit_edge o, "expr"
+        end
+
+        def visit_Arel_Nodes_TableAlias(o)
+          visit_edge o, "name"
+          visit_edge o, "relation"
+        end
+
+        def visit_Arel_Nodes_Count(o)
+          visit_edge o, "expressions"
+          visit_edge o, "distinct"
+        end
+
+        def visit_Arel_Nodes_Values(o)
+          visit_edge o, "expressions"
+        end
+
+        def visit_Arel_Nodes_StringJoin(o)
+          visit_edge o, "left"
+        end
+
+        def visit_Arel_Nodes_InnerJoin(o)
+          visit_edge o, "left"
+          visit_edge o, "right"
+        end
+        alias :visit_Arel_Nodes_FullOuterJoin  :visit_Arel_Nodes_InnerJoin
+        alias :visit_Arel_Nodes_OuterJoin      :visit_Arel_Nodes_InnerJoin
+        alias :visit_Arel_Nodes_RightOuterJoin :visit_Arel_Nodes_InnerJoin
+
+        def visit_Arel_Nodes_DeleteStatement(o)
+          visit_edge o, "relation"
+          visit_edge o, "wheres"
+        end
+
+        def unary(o)
+          visit_edge o, "expr"
+        end
+        alias :visit_Arel_Nodes_Group             :unary
+        alias :visit_Arel_Nodes_Cube              :unary
+        alias :visit_Arel_Nodes_RollUp            :unary
+        alias :visit_Arel_Nodes_GroupingSet       :unary
+        alias :visit_Arel_Nodes_GroupingElement   :unary
+        alias :visit_Arel_Nodes_Grouping          :unary
+        alias :visit_Arel_Nodes_Having            :unary
+        alias :visit_Arel_Nodes_Limit             :unary
+        alias :visit_Arel_Nodes_Not               :unary
+        alias :visit_Arel_Nodes_Offset            :unary
+        alias :visit_Arel_Nodes_On                :unary
+        alias :visit_Arel_Nodes_UnqualifiedColumn :unary
+        alias :visit_Arel_Nodes_Preceding         :unary
+        alias :visit_Arel_Nodes_Following         :unary
+        alias :visit_Arel_Nodes_Rows              :unary
+        alias :visit_Arel_Nodes_Range             :unary
+
+        def window(o)
+          visit_edge o, "partitions"
+          visit_edge o, "orders"
+          visit_edge o, "framing"
+        end
+        alias :visit_Arel_Nodes_Window            :window
+
+        def named_window(o)
+          visit_edge o, "partitions"
+          visit_edge o, "orders"
+          visit_edge o, "framing"
+          visit_edge o, "name"
+        end
+        alias :visit_Arel_Nodes_NamedWindow       :named_window
+
+        def function(o)
+          visit_edge o, "expressions"
+          visit_edge o, "distinct"
+          visit_edge o, "alias"
+        end
+        alias :visit_Arel_Nodes_Exists :function
+        alias :visit_Arel_Nodes_Min    :function
+        alias :visit_Arel_Nodes_Max    :function
+        alias :visit_Arel_Nodes_Avg    :function
+        alias :visit_Arel_Nodes_Sum    :function
+
+        def extract(o)
+          visit_edge o, "expressions"
+          visit_edge o, "alias"
+        end
+        alias :visit_Arel_Nodes_Extract :extract
+
+        def visit_Arel_Nodes_NamedFunction(o)
+          visit_edge o, "name"
+          visit_edge o, "expressions"
+          visit_edge o, "distinct"
+          visit_edge o, "alias"
+        end
+
+        def visit_Arel_Nodes_InsertStatement(o)
+          visit_edge o, "relation"
+          visit_edge o, "columns"
+          visit_edge o, "values"
+        end
+
+        def visit_Arel_Nodes_SelectCore(o)
+          visit_edge o, "source"
+          visit_edge o, "projections"
+          visit_edge o, "wheres"
+          visit_edge o,  "windows"
+        end
+
+        def visit_Arel_Nodes_SelectStatement(o)
+          visit_edge o, "cores"
+          visit_edge o, "limit"
+          visit_edge o, "orders"
+          visit_edge o, "offset"
+        end
+
+        def visit_Arel_Nodes_UpdateStatement(o)
+          visit_edge o, "relation"
+          visit_edge o, "wheres"
+          visit_edge o, "values"
+        end
+
+        def visit_Arel_Table(o)
+          visit_edge o, "name"
+        end
+
+        def visit_Arel_Nodes_Casted(o)
+          visit_edge o, "val"
+          visit_edge o, "attribute"
+        end
+
+        def visit_Arel_Attribute(o)
+          visit_edge o, "relation"
+          visit_edge o, "name"
+        end
+        alias :visit_Arel_Attributes_Integer :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Float :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_String :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Time :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Boolean :visit_Arel_Attribute
+        alias :visit_Arel_Attributes_Attribute :visit_Arel_Attribute
+
+        def nary(o)
+          o.children.each_with_index do |x, i|
+            edge(i) { visit x }
+          end
+        end
+        alias :visit_Arel_Nodes_And :nary
+
+        def binary(o)
+          visit_edge o, "left"
+          visit_edge o, "right"
+        end
+        alias :visit_Arel_Nodes_As                 :binary
+        alias :visit_Arel_Nodes_Assignment         :binary
+        alias :visit_Arel_Nodes_Between            :binary
+        alias :visit_Arel_Nodes_Concat             :binary
+        alias :visit_Arel_Nodes_DoesNotMatch       :binary
+        alias :visit_Arel_Nodes_Equality           :binary
+        alias :visit_Arel_Nodes_GreaterThan        :binary
+        alias :visit_Arel_Nodes_GreaterThanOrEqual :binary
+        alias :visit_Arel_Nodes_In                 :binary
+        alias :visit_Arel_Nodes_JoinSource         :binary
+        alias :visit_Arel_Nodes_LessThan           :binary
+        alias :visit_Arel_Nodes_LessThanOrEqual    :binary
+        alias :visit_Arel_Nodes_IsNotDistinctFrom  :binary
+        alias :visit_Arel_Nodes_IsDistinctFrom     :binary
+        alias :visit_Arel_Nodes_Matches            :binary
+        alias :visit_Arel_Nodes_NotEqual           :binary
+        alias :visit_Arel_Nodes_NotIn              :binary
+        alias :visit_Arel_Nodes_Or                 :binary
+        alias :visit_Arel_Nodes_Over               :binary
+
+        def visit_String(o)
+          @node_stack.last.fields << o
+        end
+        alias :visit_Time :visit_String
+        alias :visit_Date :visit_String
+        alias :visit_DateTime :visit_String
+        alias :visit_NilClass :visit_String
+        alias :visit_TrueClass :visit_String
+        alias :visit_FalseClass :visit_String
+        alias :visit_Integer :visit_String
+        alias :visit_BigDecimal :visit_String
+        alias :visit_Float :visit_String
+        alias :visit_Symbol :visit_String
+        alias :visit_Arel_Nodes_SqlLiteral :visit_String
+
+        def visit_Arel_Nodes_BindParam(o); end
+
+        def visit_Hash(o)
+          o.each_with_index do |pair, i|
+            edge("pair_#{i}")   { visit pair }
+          end
+        end
+
+        def visit_Array(o)
+          o.each_with_index do |x, i|
+            edge(i) { visit x }
+          end
+        end
+        alias :visit_Set :visit_Array
+
+        def visit_edge(o, method)
+          edge(method) { visit o.send(method) }
+        end
+
+        def visit(o)
+          if node = @seen[o.object_id]
+            @edge_stack.last.to = node
+            return
+          end
+
+          node = Node.new(o.class.name, o.object_id)
+          @seen[node.id] = node
+          @nodes << node
+          with_node node do
+            super
+          end
+        end
+
+        def edge(name)
+          edge = Edge.new(name, @node_stack.last)
+          @edge_stack.push edge
+          @edges << edge
+          yield
+          @edge_stack.pop
+        end
+
+        def with_node(node)
+          if edge = @edge_stack.last
+            edge.to = node
+          end
+
+          @node_stack.push node
+          yield
+          @node_stack.pop
+        end
+
+        def quote(string)
+          string.to_s.gsub('"', '\"')
+        end
+
+        def to_dot
+          "digraph \"Arel\" {\nnode [width=0.375,height=0.25,shape=record];\n" +
+            @nodes.map { |node|
+              label = "<f0>#{node.name}"
+
+              node.fields.each_with_index do |field, i|
+                label += "|<f#{i + 1}>#{quote field}"
+              end
+
+              "#{node.id} [label=\"#{label}\"];"
+            }.join("\n") + "\n" + @edges.map { |edge|
+              "#{edge.from.id} -> #{edge.to.id} [label=\"#{edge.name}\"];"
+            }.join("\n") + "\n}"
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/ibm_db.rb b/activerecord/lib/arel/visitors/ibm_db.rb
new file mode 100644
index 0000000000..73166054da
--- /dev/null
+++ b/activerecord/lib/arel/visitors/ibm_db.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class IBM_DB < Arel::Visitors::ToSql
+      private
+
+        def visit_Arel_Nodes_Limit(o, collector)
+          collector << "FETCH FIRST "
+          collector = visit o.expr, collector
+          collector << " ROWS ONLY"
+        end
+
+        def is_distinct_from(o, collector)
+          collector << "DECODE("
+          collector = visit [o.left, o.right, 0, 1], collector
+          collector << ")"
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/informix.rb b/activerecord/lib/arel/visitors/informix.rb
new file mode 100644
index 0000000000..0a9713794e
--- /dev/null
+++ b/activerecord/lib/arel/visitors/informix.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class Informix < Arel::Visitors::ToSql
+      private
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          collector << "SELECT "
+          collector = maybe_visit o.offset, collector
+          collector = maybe_visit o.limit, collector
+          collector = o.cores.inject(collector) { |c, x|
+            visit_Arel_Nodes_SelectCore x, c
+          }
+          if o.orders.any?
+            collector << "ORDER BY "
+            collector = inject_join o.orders, collector, ", "
+          end
+          collector = maybe_visit o.lock, collector
+        end
+        def visit_Arel_Nodes_SelectCore(o, collector)
+          collector = inject_join o.projections, collector, ", "
+          if o.source && !o.source.empty?
+            collector << " FROM "
+            collector = visit o.source, collector
+          end
+
+          if o.wheres.any?
+            collector << " WHERE "
+            collector = inject_join o.wheres, collector, " AND "
+          end
+
+          if o.groups.any?
+            collector << "GROUP BY "
+            collector = inject_join o.groups, collector, ", "
+          end
+
+          if o.havings.any?
+            collector << " HAVING "
+            collector = inject_join o.havings, collector, " AND "
+          end
+          collector
+        end
+
+        def visit_Arel_Nodes_Offset(o, collector)
+          collector << "SKIP "
+          visit o.expr, collector
+        end
+        def visit_Arel_Nodes_Limit(o, collector)
+          collector << "FIRST "
+          visit o.expr, collector
+          collector << " "
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/mssql.rb b/activerecord/lib/arel/visitors/mssql.rb
new file mode 100644
index 0000000000..fdd864b40d
--- /dev/null
+++ b/activerecord/lib/arel/visitors/mssql.rb
@@ -0,0 +1,143 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class MSSQL < Arel::Visitors::ToSql
+      RowNumber = Struct.new :children
+
+      def initialize(*)
+        @primary_keys = {}
+        super
+      end
+
+      private
+
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          right = o.right
+
+          if right.nil?
+            collector = visit o.left, collector
+            collector << " IS NULL"
+          else
+            collector << "EXISTS (VALUES ("
+            collector = visit o.left, collector
+            collector << ") INTERSECT VALUES ("
+            collector = visit right, collector
+            collector << "))"
+          end
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          if o.right.nil?
+            collector = visit o.left, collector
+            collector << " IS NOT NULL"
+          else
+            collector << "NOT "
+            visit_Arel_Nodes_IsNotDistinctFrom o, collector
+          end
+        end
+
+        def visit_Arel_Visitors_MSSQL_RowNumber(o, collector)
+          collector << "ROW_NUMBER() OVER (ORDER BY "
+          inject_join(o.children, collector, ", ") << ") as _row_num"
+        end
+
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          if !o.limit && !o.offset
+            return super
+          end
+
+          is_select_count = false
+          o.cores.each { |x|
+            core_order_by = row_num_literal determine_order_by(o.orders, x)
+            if select_count? x
+              x.projections = [core_order_by]
+              is_select_count = true
+            else
+              x.projections << core_order_by
+            end
+          }
+
+          if is_select_count
+            # fixme count distinct wouldn't work with limit or offset
+            collector << "SELECT COUNT(1) as count_id FROM ("
+          end
+
+          collector << "SELECT _t.* FROM ("
+          collector = o.cores.inject(collector) { |c, x|
+            visit_Arel_Nodes_SelectCore x, c
+          }
+          collector << ") as _t WHERE #{get_offset_limit_clause(o)}"
+
+          if is_select_count
+            collector << ") AS subquery"
+          else
+            collector
+          end
+        end
+
+        def get_offset_limit_clause(o)
+          first_row = o.offset ? o.offset.expr.to_i + 1 : 1
+          last_row  = o.limit ? o.limit.expr.to_i - 1 + first_row : nil
+          if last_row
+            " _row_num BETWEEN #{first_row} AND #{last_row}"
+          else
+            " _row_num >= #{first_row}"
+          end
+        end
+
+        def visit_Arel_Nodes_DeleteStatement(o, collector)
+          collector << "DELETE "
+          if o.limit
+            collector << "TOP ("
+            visit o.limit.expr, collector
+            collector << ") "
+          end
+          collector << "FROM "
+          collector = visit o.relation, collector
+          if o.wheres.any?
+            collector << " WHERE "
+            inject_join o.wheres, collector, AND
+          else
+            collector
+          end
+        end
+
+        def determine_order_by(orders, x)
+          if orders.any?
+            orders
+          elsif x.groups.any?
+            x.groups
+          else
+            pk = find_left_table_pk(x.froms)
+            pk ? [pk] : []
+          end
+        end
+
+        def row_num_literal(order_by)
+          RowNumber.new order_by
+        end
+
+        def select_count?(x)
+          x.projections.length == 1 && Arel::Nodes::Count === x.projections.first
+        end
+
+        # FIXME raise exception of there is no pk?
+        def find_left_table_pk(o)
+          if o.kind_of?(Arel::Nodes::Join)
+            find_left_table_pk(o.left)
+          elsif o.instance_of?(Arel::Table)
+            find_primary_key(o)
+          end
+        end
+
+        def find_primary_key(o)
+          @primary_keys[o.name] ||= begin
+            primary_key_name = @connection.primary_key(o.name)
+            # some tables might be without primary key
+            primary_key_name && o[primary_key_name]
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/mysql.rb b/activerecord/lib/arel/visitors/mysql.rb
new file mode 100644
index 0000000000..dd77cfdf66
--- /dev/null
+++ b/activerecord/lib/arel/visitors/mysql.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class MySQL < Arel::Visitors::ToSql
+      private
+        def visit_Arel_Nodes_Bin(o, collector)
+          collector << "BINARY "
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_UnqualifiedColumn(o, collector)
+          visit o.expr, collector
+        end
+
+        ###
+        # :'(
+        # http://dev.mysql.com/doc/refman/5.0/en/select.html#id3482214
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          if o.offset && !o.limit
+            o.limit = Arel::Nodes::Limit.new(18446744073709551615)
+          end
+          super
+        end
+
+        def visit_Arel_Nodes_SelectCore(o, collector)
+          o.froms ||= Arel.sql("DUAL")
+          super
+        end
+
+        def visit_Arel_Nodes_Concat(o, collector)
+          collector << " CONCAT("
+          visit o.left, collector
+          collector << ", "
+          visit o.right, collector
+          collector << ") "
+          collector
+        end
+
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " <=> "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          collector << "NOT "
+          visit_Arel_Nodes_IsNotDistinctFrom o, collector
+        end
+
+        # In the simple case, MySQL allows us to place JOINs directly into the UPDATE
+        # query. However, this does not allow for LIMIT, OFFSET and ORDER. To support
+        # these, we must use a subquery.
+        def prepare_update_statement(o)
+          if o.offset || has_join_sources?(o) && has_limit_or_offset_or_orders?(o)
+            super
+          else
+            o
+          end
+        end
+        alias :prepare_delete_statement :prepare_update_statement
+
+        # MySQL is too stupid to create a temporary table for use subquery, so we have
+        # to give it some prompting in the form of a subsubquery.
+        def build_subselect(key, o)
+          subselect = super
+
+          # Materialize subquery by adding distinct
+          # to work with MySQL 5.7.6 which sets optimizer_switch='derived_merge=on'
+          unless has_limit_or_offset_or_orders?(subselect)
+            core = subselect.cores.last
+            core.set_quantifier = Arel::Nodes::Distinct.new
+          end
+
+          Nodes::SelectStatement.new.tap do |stmt|
+            core = stmt.cores.last
+            core.froms = Nodes::Grouping.new(subselect).as("__active_record_temp")
+            core.projections = [Arel.sql(quote_column_name(key.name))]
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/oracle.rb b/activerecord/lib/arel/visitors/oracle.rb
new file mode 100644
index 0000000000..f96bf65ee5
--- /dev/null
+++ b/activerecord/lib/arel/visitors/oracle.rb
@@ -0,0 +1,159 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class Oracle < Arel::Visitors::ToSql
+      private
+
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          o = order_hacks(o)
+
+          # if need to select first records without ORDER BY and GROUP BY and without DISTINCT
+          # then can use simple ROWNUM in WHERE clause
+          if o.limit && o.orders.empty? && o.cores.first.groups.empty? && !o.offset && o.cores.first.set_quantifier.class.to_s !~ /Distinct/
+            o.cores.last.wheres.push Nodes::LessThanOrEqual.new(
+              Nodes::SqlLiteral.new("ROWNUM"), o.limit.expr
+            )
+            return super
+          end
+
+          if o.limit && o.offset
+            o        = o.dup
+            limit    = o.limit.expr
+            offset   = o.offset
+            o.offset = nil
+            collector << "
+                SELECT * FROM (
+                  SELECT raw_sql_.*, rownum raw_rnum_
+                  FROM ("
+
+            collector = super(o, collector)
+
+            if offset.expr.is_a? Nodes::BindParam
+              collector << ") raw_sql_ WHERE rownum <= ("
+              collector = visit offset.expr, collector
+              collector << " + "
+              collector = visit limit, collector
+              collector << ") ) WHERE raw_rnum_ > "
+              collector = visit offset.expr, collector
+              return collector
+            else
+              collector << ") raw_sql_
+                  WHERE rownum <= #{offset.expr.to_i + limit}
+                )
+                WHERE "
+              return visit(offset, collector)
+            end
+          end
+
+          if o.limit
+            o       = o.dup
+            limit   = o.limit.expr
+            collector << "SELECT * FROM ("
+            collector = super(o, collector)
+            collector << ") WHERE ROWNUM <= "
+            return visit limit, collector
+          end
+
+          if o.offset
+            o        = o.dup
+            offset   = o.offset
+            o.offset = nil
+            collector << "SELECT * FROM (
+                  SELECT raw_sql_.*, rownum raw_rnum_
+                  FROM ("
+            collector = super(o, collector)
+            collector << ") raw_sql_
+                )
+                WHERE "
+            return visit offset, collector
+          end
+
+          super
+        end
+
+        def visit_Arel_Nodes_Limit(o, collector)
+          collector
+        end
+
+        def visit_Arel_Nodes_Offset(o, collector)
+          collector << "raw_rnum_ > "
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_Except(o, collector)
+          collector << "( "
+          collector = infix_value o, collector, " MINUS "
+          collector << " )"
+        end
+
+        def visit_Arel_Nodes_UpdateStatement(o, collector)
+          # Oracle does not allow ORDER BY/LIMIT in UPDATEs.
+          if o.orders.any? && o.limit.nil?
+            # However, there is no harm in silently eating the ORDER BY clause if no LIMIT has been provided,
+            # otherwise let the user deal with the error
+            o = o.dup
+            o.orders = []
+          end
+
+          super
+        end
+
+        ###
+        # Hacks for the order clauses specific to Oracle
+        def order_hacks(o)
+          return o if o.orders.empty?
+          return o unless o.cores.any? do |core|
+            core.projections.any? do |projection|
+              /FIRST_VALUE/ === projection
+            end
+          end
+          # Previous version with join and split broke ORDER BY clause
+          # if it contained functions with several arguments (separated by ',').
+          #
+          # orders   = o.orders.map { |x| visit x }.join(', ').split(',')
+          orders   = o.orders.map do |x|
+            string = visit(x, Arel::Collectors::SQLString.new).value
+            if string.include?(",")
+              split_order_string(string)
+            else
+              string
+            end
+          end.flatten
+          o.orders = []
+          orders.each_with_index do |order, i|
+            o.orders <<
+              Nodes::SqlLiteral.new("alias_#{i}__#{' DESC' if /\bdesc$/i === order}")
+          end
+          o
+        end
+
+        # Split string by commas but count opening and closing brackets
+        # and ignore commas inside brackets.
+        def split_order_string(string)
+          array = []
+          i = 0
+          string.split(",").each do |part|
+            if array[i]
+              array[i] << "," << part
+            else
+              # to ensure that array[i] will be String and not Arel::Nodes::SqlLiteral
+              array[i] = part.to_s
+            end
+            i += 1 if array[i].count("(") == array[i].count(")")
+          end
+          array
+        end
+
+        def visit_Arel_Nodes_BindParam(o, collector)
+          collector.add_bind(o.value) { |i| ":a#{i}" }
+        end
+
+        def is_distinct_from(o, collector)
+          collector << "DECODE("
+          collector = visit [o.left, o.right, 0, 1], collector
+          collector << ")"
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/oracle12.rb b/activerecord/lib/arel/visitors/oracle12.rb
new file mode 100644
index 0000000000..b092aa95e0
--- /dev/null
+++ b/activerecord/lib/arel/visitors/oracle12.rb
@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class Oracle12 < Arel::Visitors::ToSql
+      private
+
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          # Oracle does not allow LIMIT clause with select for update
+          if o.limit && o.lock
+            raise ArgumentError, <<-MSG
+            'Combination of limit and lock is not supported.
+            because generated SQL statements
+            `SELECT FOR UPDATE and FETCH FIRST n ROWS` generates ORA-02014.`
+          MSG
+          end
+          super
+        end
+
+        def visit_Arel_Nodes_SelectOptions(o, collector)
+          collector = maybe_visit o.offset, collector
+          collector = maybe_visit o.limit, collector
+          collector = maybe_visit o.lock, collector
+        end
+
+        def visit_Arel_Nodes_Limit(o, collector)
+          collector << "FETCH FIRST "
+          collector = visit o.expr, collector
+          collector << " ROWS ONLY"
+        end
+
+        def visit_Arel_Nodes_Offset(o, collector)
+          collector << "OFFSET "
+          visit o.expr, collector
+          collector << " ROWS"
+        end
+
+        def visit_Arel_Nodes_Except(o, collector)
+          collector << "( "
+          collector = infix_value o, collector, " MINUS "
+          collector << " )"
+        end
+
+        def visit_Arel_Nodes_UpdateStatement(o, collector)
+          # Oracle does not allow ORDER BY/LIMIT in UPDATEs.
+          if o.orders.any? && o.limit.nil?
+            # However, there is no harm in silently eating the ORDER BY clause if no LIMIT has been provided,
+            # otherwise let the user deal with the error
+            o = o.dup
+            o.orders = []
+          end
+
+          super
+        end
+
+        def visit_Arel_Nodes_BindParam(o, collector)
+          collector.add_bind(o.value) { |i| ":a#{i}" }
+        end
+
+        def is_distinct_from(o, collector)
+          collector << "DECODE("
+          collector = visit [o.left, o.right, 0, 1], collector
+          collector << ")"
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/postgresql.rb b/activerecord/lib/arel/visitors/postgresql.rb
new file mode 100644
index 0000000000..920776b4dc
--- /dev/null
+++ b/activerecord/lib/arel/visitors/postgresql.rb
@@ -0,0 +1,116 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class PostgreSQL < Arel::Visitors::ToSql
+      CUBE = "CUBE"
+      ROLLUP = "ROLLUP"
+      GROUPING_SETS = "GROUPING SETS"
+      LATERAL = "LATERAL"
+
+      private
+
+        def visit_Arel_Nodes_Matches(o, collector)
+          op = o.case_sensitive ? " LIKE " : " ILIKE "
+          collector = infix_value o, collector, op
+          if o.escape
+            collector << " ESCAPE "
+            visit o.escape, collector
+          else
+            collector
+          end
+        end
+
+        def visit_Arel_Nodes_DoesNotMatch(o, collector)
+          op = o.case_sensitive ? " NOT LIKE " : " NOT ILIKE "
+          collector = infix_value o, collector, op
+          if o.escape
+            collector << " ESCAPE "
+            visit o.escape, collector
+          else
+            collector
+          end
+        end
+
+        def visit_Arel_Nodes_Regexp(o, collector)
+          op = o.case_sensitive ? " ~ " : " ~* "
+          infix_value o, collector, op
+        end
+
+        def visit_Arel_Nodes_NotRegexp(o, collector)
+          op = o.case_sensitive ? " !~ " : " !~* "
+          infix_value o, collector, op
+        end
+
+        def visit_Arel_Nodes_DistinctOn(o, collector)
+          collector << "DISTINCT ON ( "
+          visit(o.expr, collector) << " )"
+        end
+
+        def visit_Arel_Nodes_BindParam(o, collector)
+          collector.add_bind(o.value) { |i| "$#{i}" }
+        end
+
+        def visit_Arel_Nodes_GroupingElement(o, collector)
+          collector << "( "
+          visit(o.expr, collector) << " )"
+        end
+
+        def visit_Arel_Nodes_Cube(o, collector)
+          collector << CUBE
+          grouping_array_or_grouping_element o, collector
+        end
+
+        def visit_Arel_Nodes_RollUp(o, collector)
+          collector << ROLLUP
+          grouping_array_or_grouping_element o, collector
+        end
+
+        def visit_Arel_Nodes_GroupingSet(o, collector)
+          collector << GROUPING_SETS
+          grouping_array_or_grouping_element o, collector
+        end
+
+        def visit_Arel_Nodes_Lateral(o, collector)
+          collector << LATERAL
+          collector << SPACE
+          grouping_parentheses o, collector
+        end
+
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " IS NOT DISTINCT FROM "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " IS DISTINCT FROM "
+          visit o.right, collector
+        end
+
+        # Used by Lateral visitor to enclose select queries in parentheses
+        def grouping_parentheses(o, collector)
+          if o.expr.is_a? Nodes::SelectStatement
+            collector << "("
+            visit o.expr, collector
+            collector << ")"
+          else
+            visit o.expr, collector
+          end
+        end
+
+        # Utilized by GroupingSet, Cube & RollUp visitors to
+        # handle grouping aggregation semantics
+        def grouping_array_or_grouping_element(o, collector)
+          if o.expr.is_a? Array
+            collector << "( "
+            visit o.expr, collector
+            collector << " )"
+          else
+            visit o.expr, collector
+          end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/sqlite.rb b/activerecord/lib/arel/visitors/sqlite.rb
new file mode 100644
index 0000000000..af6f7e856a
--- /dev/null
+++ b/activerecord/lib/arel/visitors/sqlite.rb
@@ -0,0 +1,39 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class SQLite < Arel::Visitors::ToSql
+      private
+
+        # Locks are not supported in SQLite
+        def visit_Arel_Nodes_Lock(o, collector)
+          collector
+        end
+
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          o.limit = Arel::Nodes::Limit.new(-1) if o.offset && !o.limit
+          super
+        end
+
+        def visit_Arel_Nodes_True(o, collector)
+          collector << "1"
+        end
+
+        def visit_Arel_Nodes_False(o, collector)
+          collector << "0"
+        end
+
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " IS "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          collector = visit o.left, collector
+          collector << " IS NOT "
+          visit o.right, collector
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/to_sql.rb b/activerecord/lib/arel/visitors/to_sql.rb
new file mode 100644
index 0000000000..f9fe4404eb
--- /dev/null
+++ b/activerecord/lib/arel/visitors/to_sql.rb
@@ -0,0 +1,911 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class UnsupportedVisitError < StandardError
+      def initialize(object)
+        super "Unsupported argument type: #{object.class.name}. Construct an Arel node instead."
+      end
+    end
+
+    class ToSql < Arel::Visitors::Visitor
+      ##
+      # This is some roflscale crazy stuff.  I'm roflscaling this because
+      # building SQL queries is a hotspot.  I will explain the roflscale so that
+      # others will not rm this code.
+      #
+      # In YARV, string literals in a method body will get duped when the byte
+      # code is executed.  Let's take a look:
+      #
+      # > puts RubyVM::InstructionSequence.new('def foo; "bar"; end').disasm
+      #
+      #   == disasm: <RubyVM::InstructionSequence:foo@<compiled>>=====
+      #    0000 trace            8
+      #    0002 trace            1
+      #    0004 putstring        "bar"
+      #    0006 trace            16
+      #    0008 leave
+      #
+      # The `putstring` bytecode will dup the string and push it on the stack.
+      # In many cases in our SQL visitor, that string is never mutated, so there
+      # is no need to dup the literal.
+      #
+      # If we change to a constant lookup, the string will not be duped, and we
+      # can reduce the objects in our system:
+      #
+      # > puts RubyVM::InstructionSequence.new('BAR = "bar"; def foo; BAR; end').disasm
+      #
+      #  == disasm: <RubyVM::InstructionSequence:foo@<compiled>>========
+      #  0000 trace            8
+      #  0002 trace            1
+      #  0004 getinlinecache   11, <ic:0>
+      #  0007 getconstant      :BAR
+      #  0009 setinlinecache   <ic:0>
+      #  0011 trace            16
+      #  0013 leave
+      #
+      # `getconstant` should be a hash lookup, and no object is duped when the
+      # value of the constant is pushed on the stack.  Hence the crazy
+      # constants below.
+      #
+      # `matches` and `doesNotMatch` operate case-insensitively via Visitor subclasses
+      # specialized for specific databases when necessary.
+      #
+
+      WHERE    = " WHERE "    # :nodoc:
+      SPACE    = " "          # :nodoc:
+      COMMA    = ", "         # :nodoc:
+      GROUP_BY = " GROUP BY " # :nodoc:
+      ORDER_BY = " ORDER BY " # :nodoc:
+      WINDOW   = " WINDOW "   # :nodoc:
+      AND      = " AND "      # :nodoc:
+
+      DISTINCT = "DISTINCT"   # :nodoc:
+
+      def initialize(connection)
+        super()
+        @connection = connection
+      end
+
+      def compile(node, collector = Arel::Collectors::SQLString.new)
+        accept(node, collector).value
+      end
+
+      private
+
+        def visit_Arel_Nodes_DeleteStatement(o, collector)
+          o = prepare_delete_statement(o)
+
+          if has_join_sources?(o)
+            collector << "DELETE "
+            visit o.relation.left, collector
+            collector << " FROM "
+          else
+            collector << "DELETE FROM "
+          end
+          collector = visit o.relation, collector
+
+          collect_nodes_for o.wheres, collector, " WHERE ", " AND "
+          collect_nodes_for o.orders, collector, " ORDER BY "
+          maybe_visit o.limit, collector
+        end
+
+        def visit_Arel_Nodes_UpdateStatement(o, collector)
+          o = prepare_update_statement(o)
+
+          collector << "UPDATE "
+          collector = visit o.relation, collector
+          collect_nodes_for o.values, collector, " SET "
+
+          collect_nodes_for o.wheres, collector, " WHERE ", " AND "
+          collect_nodes_for o.orders, collector, " ORDER BY "
+          maybe_visit o.limit, collector
+        end
+
+        def visit_Arel_Nodes_InsertStatement(o, collector)
+          collector << "INSERT INTO "
+          collector = visit o.relation, collector
+          if o.columns.any?
+            collector << " (#{o.columns.map { |x|
+              quote_column_name x.name
+            }.join ', '})"
+          end
+
+          if o.values
+            maybe_visit o.values, collector
+          elsif o.select
+            maybe_visit o.select, collector
+          else
+            collector
+          end
+        end
+
+        def visit_Arel_Nodes_Exists(o, collector)
+          collector << "EXISTS ("
+          collector = visit(o.expressions, collector) << ")"
+          if o.alias
+            collector << " AS "
+            visit o.alias, collector
+          else
+            collector
+          end
+        end
+
+        def visit_Arel_Nodes_Casted(o, collector)
+          collector << quoted(o.val, o.attribute).to_s
+        end
+
+        def visit_Arel_Nodes_Quoted(o, collector)
+          collector << quoted(o.expr, nil).to_s
+        end
+
+        def visit_Arel_Nodes_True(o, collector)
+          collector << "TRUE"
+        end
+
+        def visit_Arel_Nodes_False(o, collector)
+          collector << "FALSE"
+        end
+
+        def visit_Arel_Nodes_ValuesList(o, collector)
+          collector << "VALUES "
+
+          len = o.rows.length - 1
+          o.rows.each_with_index { |row, i|
+            collector << "("
+            row_len = row.length - 1
+            row.each_with_index do |value, k|
+              case value
+              when Nodes::SqlLiteral, Nodes::BindParam
+                collector = visit(value, collector)
+              else
+                collector << quote(value)
+              end
+              collector << COMMA unless k == row_len
+            end
+            collector << ")"
+            collector << COMMA unless i == len
+          }
+          collector
+        end
+
+        def visit_Arel_Nodes_Values(o, collector)
+          collector << "VALUES ("
+
+          len = o.expressions.length - 1
+          o.expressions.each_with_index { |value, i|
+            case value
+            when Nodes::SqlLiteral, Nodes::BindParam
+              collector = visit value, collector
+            else
+              collector << quote(value).to_s
+            end
+            unless i == len
+              collector << COMMA
+            end
+          }
+
+          collector << ")"
+        end
+
+        def visit_Arel_Nodes_SelectStatement(o, collector)
+          if o.with
+            collector = visit o.with, collector
+            collector << SPACE
+          end
+
+          collector = o.cores.inject(collector) { |c, x|
+            visit_Arel_Nodes_SelectCore(x, c)
+          }
+
+          unless o.orders.empty?
+            collector << ORDER_BY
+            len = o.orders.length - 1
+            o.orders.each_with_index { |x, i|
+              collector = visit(x, collector)
+              collector << COMMA unless len == i
+            }
+          end
+
+          visit_Arel_Nodes_SelectOptions(o, collector)
+
+          collector
+        end
+
+        def visit_Arel_Nodes_SelectOptions(o, collector)
+          collector = maybe_visit o.limit, collector
+          collector = maybe_visit o.offset, collector
+          collector = maybe_visit o.lock, collector
+        end
+
+        def visit_Arel_Nodes_SelectCore(o, collector)
+          collector << "SELECT"
+
+          collector = maybe_visit o.set_quantifier, collector
+
+          collect_nodes_for o.projections, collector, SPACE
+
+          if o.source && !o.source.empty?
+            collector << " FROM "
+            collector = visit o.source, collector
+          end
+
+          collect_nodes_for o.wheres, collector, WHERE, AND
+          collect_nodes_for o.groups, collector, GROUP_BY
+          collect_nodes_for o.havings, collector, " HAVING ", AND
+          collect_nodes_for o.windows, collector, WINDOW
+
+          collector
+        end
+
+        def collect_nodes_for(nodes, collector, spacer, connector = COMMA)
+          unless nodes.empty?
+            collector << spacer
+            inject_join nodes, collector, connector
+          end
+        end
+
+        def visit_Arel_Nodes_Bin(o, collector)
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_Distinct(o, collector)
+          collector << DISTINCT
+        end
+
+        def visit_Arel_Nodes_DistinctOn(o, collector)
+          raise NotImplementedError, "DISTINCT ON not implemented for this db"
+        end
+
+        def visit_Arel_Nodes_With(o, collector)
+          collector << "WITH "
+          inject_join o.children, collector, COMMA
+        end
+
+        def visit_Arel_Nodes_WithRecursive(o, collector)
+          collector << "WITH RECURSIVE "
+          inject_join o.children, collector, COMMA
+        end
+
+        def visit_Arel_Nodes_Union(o, collector)
+          infix_value_with_paren(o, collector, " UNION ")
+        end
+
+        def visit_Arel_Nodes_UnionAll(o, collector)
+          infix_value_with_paren(o, collector, " UNION ALL ")
+        end
+
+        def visit_Arel_Nodes_Intersect(o, collector)
+          collector << "( "
+          infix_value(o, collector, " INTERSECT ") << " )"
+        end
+
+        def visit_Arel_Nodes_Except(o, collector)
+          collector << "( "
+          infix_value(o, collector, " EXCEPT ") << " )"
+        end
+
+        def visit_Arel_Nodes_NamedWindow(o, collector)
+          collector << quote_column_name(o.name)
+          collector << " AS "
+          visit_Arel_Nodes_Window o, collector
+        end
+
+        def visit_Arel_Nodes_Window(o, collector)
+          collector << "("
+
+          collect_nodes_for o.partitions, collector, "PARTITION BY "
+
+          if o.orders.any?
+            collector << SPACE if o.partitions.any?
+            collector << "ORDER BY "
+            collector = inject_join o.orders, collector, ", "
+          end
+
+          if o.framing
+            collector << SPACE if o.partitions.any? || o.orders.any?
+            collector = visit o.framing, collector
+          end
+
+          collector << ")"
+        end
+
+        def visit_Arel_Nodes_Rows(o, collector)
+          if o.expr
+            collector << "ROWS "
+            visit o.expr, collector
+          else
+            collector << "ROWS"
+          end
+        end
+
+        def visit_Arel_Nodes_Range(o, collector)
+          if o.expr
+            collector << "RANGE "
+            visit o.expr, collector
+          else
+            collector << "RANGE"
+          end
+        end
+
+        def visit_Arel_Nodes_Preceding(o, collector)
+          collector = if o.expr
+            visit o.expr, collector
+          else
+            collector << "UNBOUNDED"
+          end
+
+          collector << " PRECEDING"
+        end
+
+        def visit_Arel_Nodes_Following(o, collector)
+          collector = if o.expr
+            visit o.expr, collector
+          else
+            collector << "UNBOUNDED"
+          end
+
+          collector << " FOLLOWING"
+        end
+
+        def visit_Arel_Nodes_CurrentRow(o, collector)
+          collector << "CURRENT ROW"
+        end
+
+        def visit_Arel_Nodes_Over(o, collector)
+          case o.right
+          when nil
+            visit(o.left, collector) << " OVER ()"
+          when Arel::Nodes::SqlLiteral
+            infix_value o, collector, " OVER "
+          when String, Symbol
+            visit(o.left, collector) << " OVER #{quote_column_name o.right.to_s}"
+          else
+            infix_value o, collector, " OVER "
+          end
+        end
+
+        def visit_Arel_Nodes_Offset(o, collector)
+          collector << "OFFSET "
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_Limit(o, collector)
+          collector << "LIMIT "
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_Lock(o, collector)
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_Grouping(o, collector)
+          if o.expr.is_a? Nodes::Grouping
+            visit(o.expr, collector)
+          else
+            collector << "("
+            visit(o.expr, collector) << ")"
+          end
+        end
+
+        def visit_Arel_SelectManager(o, collector)
+          collector << "("
+          visit(o.ast, collector) << ")"
+        end
+
+        def visit_Arel_Nodes_Ascending(o, collector)
+          visit(o.expr, collector) << " ASC"
+        end
+
+        def visit_Arel_Nodes_Descending(o, collector)
+          visit(o.expr, collector) << " DESC"
+        end
+
+        def visit_Arel_Nodes_Group(o, collector)
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_NamedFunction(o, collector)
+          collector << o.name
+          collector << "("
+          collector << "DISTINCT " if o.distinct
+          collector = inject_join(o.expressions, collector, ", ") << ")"
+          if o.alias
+            collector << " AS "
+            visit o.alias, collector
+          else
+            collector
+          end
+        end
+
+        def visit_Arel_Nodes_Extract(o, collector)
+          collector << "EXTRACT(#{o.field.to_s.upcase} FROM "
+          visit(o.expr, collector) << ")"
+        end
+
+        def visit_Arel_Nodes_Count(o, collector)
+          aggregate "COUNT", o, collector
+        end
+
+        def visit_Arel_Nodes_Sum(o, collector)
+          aggregate "SUM", o, collector
+        end
+
+        def visit_Arel_Nodes_Max(o, collector)
+          aggregate "MAX", o, collector
+        end
+
+        def visit_Arel_Nodes_Min(o, collector)
+          aggregate "MIN", o, collector
+        end
+
+        def visit_Arel_Nodes_Avg(o, collector)
+          aggregate "AVG", o, collector
+        end
+
+        def visit_Arel_Nodes_TableAlias(o, collector)
+          collector = visit o.relation, collector
+          collector << " "
+          collector << quote_table_name(o.name)
+        end
+
+        def visit_Arel_Nodes_Between(o, collector)
+          collector = visit o.left, collector
+          collector << " BETWEEN "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_GreaterThanOrEqual(o, collector)
+          collector = visit o.left, collector
+          collector << " >= "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_GreaterThan(o, collector)
+          collector = visit o.left, collector
+          collector << " > "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_LessThanOrEqual(o, collector)
+          collector = visit o.left, collector
+          collector << " <= "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_LessThan(o, collector)
+          collector = visit o.left, collector
+          collector << " < "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_Matches(o, collector)
+          collector = visit o.left, collector
+          collector << " LIKE "
+          collector = visit o.right, collector
+          if o.escape
+            collector << " ESCAPE "
+            visit o.escape, collector
+          else
+            collector
+          end
+        end
+
+        def visit_Arel_Nodes_DoesNotMatch(o, collector)
+          collector = visit o.left, collector
+          collector << " NOT LIKE "
+          collector = visit o.right, collector
+          if o.escape
+            collector << " ESCAPE "
+            visit o.escape, collector
+          else
+            collector
+          end
+        end
+
+        def visit_Arel_Nodes_JoinSource(o, collector)
+          if o.left
+            collector = visit o.left, collector
+          end
+          if o.right.any?
+            collector << SPACE if o.left
+            collector = inject_join o.right, collector, SPACE
+          end
+          collector
+        end
+
+        def visit_Arel_Nodes_Regexp(o, collector)
+          raise NotImplementedError, "~ not implemented for this db"
+        end
+
+        def visit_Arel_Nodes_NotRegexp(o, collector)
+          raise NotImplementedError, "!~ not implemented for this db"
+        end
+
+        def visit_Arel_Nodes_StringJoin(o, collector)
+          visit o.left, collector
+        end
+
+        def visit_Arel_Nodes_FullOuterJoin(o, collector)
+          collector << "FULL OUTER JOIN "
+          collector = visit o.left, collector
+          collector << SPACE
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_OuterJoin(o, collector)
+          collector << "LEFT OUTER JOIN "
+          collector = visit o.left, collector
+          collector << " "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_RightOuterJoin(o, collector)
+          collector << "RIGHT OUTER JOIN "
+          collector = visit o.left, collector
+          collector << SPACE
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_InnerJoin(o, collector)
+          collector << "INNER JOIN "
+          collector = visit o.left, collector
+          if o.right
+            collector << SPACE
+            visit(o.right, collector)
+          else
+            collector
+          end
+        end
+
+        def visit_Arel_Nodes_On(o, collector)
+          collector << "ON "
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_Not(o, collector)
+          collector << "NOT ("
+          visit(o.expr, collector) << ")"
+        end
+
+        def visit_Arel_Table(o, collector)
+          if o.table_alias
+            collector << "#{quote_table_name o.name} #{quote_table_name o.table_alias}"
+          else
+            collector << quote_table_name(o.name)
+          end
+        end
+
+        def visit_Arel_Nodes_In(o, collector)
+          if Array === o.right && !o.right.empty?
+            o.right.keep_if { |value| boundable?(value) }
+          end
+
+          if Array === o.right && o.right.empty?
+            collector << "1=0"
+          else
+            collector = visit o.left, collector
+            collector << " IN ("
+            visit(o.right, collector) << ")"
+          end
+        end
+
+        def visit_Arel_Nodes_NotIn(o, collector)
+          if Array === o.right && !o.right.empty?
+            o.right.keep_if { |value| boundable?(value) }
+          end
+
+          if Array === o.right && o.right.empty?
+            collector << "1=1"
+          else
+            collector = visit o.left, collector
+            collector << " NOT IN ("
+            collector = visit o.right, collector
+            collector << ")"
+          end
+        end
+
+        def visit_Arel_Nodes_And(o, collector)
+          inject_join o.children, collector, " AND "
+        end
+
+        def visit_Arel_Nodes_Or(o, collector)
+          collector = visit o.left, collector
+          collector << " OR "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_Assignment(o, collector)
+          case o.right
+          when Arel::Nodes::Node, Arel::Attributes::Attribute
+            collector = visit o.left, collector
+            collector << " = "
+            visit o.right, collector
+          else
+            collector = visit o.left, collector
+            collector << " = "
+            collector << quote(o.right).to_s
+          end
+        end
+
+        def visit_Arel_Nodes_Equality(o, collector)
+          right = o.right
+
+          collector = visit o.left, collector
+
+          if right.nil?
+            collector << " IS NULL"
+          else
+            collector << " = "
+            visit right, collector
+          end
+        end
+
+        def visit_Arel_Nodes_IsNotDistinctFrom(o, collector)
+          if o.right.nil?
+            collector = visit o.left, collector
+            collector << " IS NULL"
+          else
+            collector = is_distinct_from(o, collector)
+            collector << " = 0"
+          end
+        end
+
+        def visit_Arel_Nodes_IsDistinctFrom(o, collector)
+          if o.right.nil?
+            collector = visit o.left, collector
+            collector << " IS NOT NULL"
+          else
+            collector = is_distinct_from(o, collector)
+            collector << " = 1"
+          end
+        end
+
+        def visit_Arel_Nodes_NotEqual(o, collector)
+          right = o.right
+
+          collector = visit o.left, collector
+
+          if right.nil?
+            collector << " IS NOT NULL"
+          else
+            collector << " != "
+            visit right, collector
+          end
+        end
+
+        def visit_Arel_Nodes_As(o, collector)
+          collector = visit o.left, collector
+          collector << " AS "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_Case(o, collector)
+          collector << "CASE "
+          if o.case
+            visit o.case, collector
+            collector << " "
+          end
+          o.conditions.each do |condition|
+            visit condition, collector
+            collector << " "
+          end
+          if o.default
+            visit o.default, collector
+            collector << " "
+          end
+          collector << "END"
+        end
+
+        def visit_Arel_Nodes_When(o, collector)
+          collector << "WHEN "
+          visit o.left, collector
+          collector << " THEN "
+          visit o.right, collector
+        end
+
+        def visit_Arel_Nodes_Else(o, collector)
+          collector << "ELSE "
+          visit o.expr, collector
+        end
+
+        def visit_Arel_Nodes_UnqualifiedColumn(o, collector)
+          collector << "#{quote_column_name o.name}"
+          collector
+        end
+
+        def visit_Arel_Attributes_Attribute(o, collector)
+          join_name = o.relation.table_alias || o.relation.name
+          collector << "#{quote_table_name join_name}.#{quote_column_name o.name}"
+        end
+        alias :visit_Arel_Attributes_Integer :visit_Arel_Attributes_Attribute
+        alias :visit_Arel_Attributes_Float :visit_Arel_Attributes_Attribute
+        alias :visit_Arel_Attributes_Decimal :visit_Arel_Attributes_Attribute
+        alias :visit_Arel_Attributes_String :visit_Arel_Attributes_Attribute
+        alias :visit_Arel_Attributes_Time :visit_Arel_Attributes_Attribute
+        alias :visit_Arel_Attributes_Boolean :visit_Arel_Attributes_Attribute
+
+        def literal(o, collector); collector << o.to_s; end
+
+        def visit_Arel_Nodes_BindParam(o, collector)
+          collector.add_bind(o.value) { "?" }
+        end
+
+        alias :visit_Arel_Nodes_SqlLiteral :literal
+        alias :visit_Integer               :literal
+
+        def quoted(o, a)
+          if a && a.able_to_type_cast?
+            quote(a.type_cast_for_database(o))
+          else
+            quote(o)
+          end
+        end
+
+        def unsupported(o, collector)
+          raise UnsupportedVisitError.new(o)
+        end
+
+        alias :visit_ActiveSupport_Multibyte_Chars :unsupported
+        alias :visit_ActiveSupport_StringInquirer  :unsupported
+        alias :visit_BigDecimal                    :unsupported
+        alias :visit_Class                         :unsupported
+        alias :visit_Date                          :unsupported
+        alias :visit_DateTime                      :unsupported
+        alias :visit_FalseClass                    :unsupported
+        alias :visit_Float                         :unsupported
+        alias :visit_Hash                          :unsupported
+        alias :visit_NilClass                      :unsupported
+        alias :visit_String                        :unsupported
+        alias :visit_Symbol                        :unsupported
+        alias :visit_Time                          :unsupported
+        alias :visit_TrueClass                     :unsupported
+
+        def visit_Arel_Nodes_InfixOperation(o, collector)
+          collector = visit o.left, collector
+          collector << " #{o.operator} "
+          visit o.right, collector
+        end
+
+        alias :visit_Arel_Nodes_Addition       :visit_Arel_Nodes_InfixOperation
+        alias :visit_Arel_Nodes_Subtraction    :visit_Arel_Nodes_InfixOperation
+        alias :visit_Arel_Nodes_Multiplication :visit_Arel_Nodes_InfixOperation
+        alias :visit_Arel_Nodes_Division       :visit_Arel_Nodes_InfixOperation
+
+        def visit_Arel_Nodes_UnaryOperation(o, collector)
+          collector << " #{o.operator} "
+          visit o.expr, collector
+        end
+
+        def visit_Array(o, collector)
+          inject_join o, collector, ", "
+        end
+        alias :visit_Set :visit_Array
+
+        def quote(value)
+          return value if Arel::Nodes::SqlLiteral === value
+          @connection.quote value
+        end
+
+        def quote_table_name(name)
+          return name if Arel::Nodes::SqlLiteral === name
+          @connection.quote_table_name(name)
+        end
+
+        def quote_column_name(name)
+          return name if Arel::Nodes::SqlLiteral === name
+          @connection.quote_column_name(name)
+        end
+
+        def maybe_visit(thing, collector)
+          return collector unless thing
+          collector << " "
+          visit thing, collector
+        end
+
+        def inject_join(list, collector, join_str)
+          len = list.length - 1
+          list.each_with_index.inject(collector) { |c, (x, i)|
+            if i == len
+              visit x, c
+            else
+              visit(x, c) << join_str
+            end
+          }
+        end
+
+        def boundable?(value)
+          !value.respond_to?(:boundable?) || value.boundable?
+        end
+
+        def has_join_sources?(o)
+          o.relation.is_a?(Nodes::JoinSource) && !o.relation.right.empty?
+        end
+
+        def has_limit_or_offset_or_orders?(o)
+          o.limit || o.offset || !o.orders.empty?
+        end
+
+        # The default strategy for an UPDATE with joins is to use a subquery. This doesn't work
+        # on MySQL (even when aliasing the tables), but MySQL allows using JOIN directly in
+        # an UPDATE statement, so in the MySQL visitor we redefine this to do that.
+        def prepare_update_statement(o)
+          if o.key && (has_limit_or_offset_or_orders?(o) || has_join_sources?(o))
+            stmt = o.clone
+            stmt.limit = nil
+            stmt.offset = nil
+            stmt.orders = []
+            stmt.wheres = [Nodes::In.new(o.key, [build_subselect(o.key, o)])]
+            stmt.relation = o.relation.left if has_join_sources?(o)
+            stmt
+          else
+            o
+          end
+        end
+        alias :prepare_delete_statement :prepare_update_statement
+
+        # FIXME: we should probably have a 2-pass visitor for this
+        def build_subselect(key, o)
+          stmt             = Nodes::SelectStatement.new
+          core             = stmt.cores.first
+          core.froms       = o.relation
+          core.wheres      = o.wheres
+          core.projections = [key]
+          stmt.limit       = o.limit
+          stmt.offset      = o.offset
+          stmt.orders      = o.orders
+          stmt
+        end
+
+        def infix_value(o, collector, value)
+          collector = visit o.left, collector
+          collector << value
+          visit o.right, collector
+        end
+
+        def infix_value_with_paren(o, collector, value, suppress_parens = false)
+          collector << "( " unless suppress_parens
+          collector = if o.left.class == o.class
+            infix_value_with_paren(o.left, collector, value, true)
+          else
+            visit o.left, collector
+          end
+          collector << value
+          collector = if o.right.class == o.class
+            infix_value_with_paren(o.right, collector, value, true)
+          else
+            visit o.right, collector
+          end
+          collector << " )" unless suppress_parens
+          collector
+        end
+
+        def aggregate(name, o, collector)
+          collector << "#{name}("
+          if o.distinct
+            collector << "DISTINCT "
+          end
+          collector = inject_join(o.expressions, collector, ", ") << ")"
+          if o.alias
+            collector << " AS "
+            visit o.alias, collector
+          else
+            collector
+          end
+        end
+
+        def is_distinct_from(o, collector)
+          collector << "CASE WHEN "
+          collector = visit o.left, collector
+          collector << " = "
+          collector = visit o.right, collector
+          collector << " OR ("
+          collector = visit o.left, collector
+          collector << " IS NULL AND "
+          collector = visit o.right, collector
+          collector << " IS NULL)"
+          collector << " THEN 0 ELSE 1 END"
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/visitor.rb b/activerecord/lib/arel/visitors/visitor.rb
new file mode 100644
index 0000000000..1c17184e86
--- /dev/null
+++ b/activerecord/lib/arel/visitors/visitor.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class Visitor
+      def initialize
+        @dispatch = get_dispatch_cache
+      end
+
+      def accept(object, *args)
+        visit object, *args
+      end
+
+      private
+
+        attr_reader :dispatch
+
+        def self.dispatch_cache
+          Hash.new do |hash, klass|
+            hash[klass] = "visit_#{(klass.name || '').gsub('::', '_')}"
+          end
+        end
+
+        def get_dispatch_cache
+          self.class.dispatch_cache
+        end
+
+        def visit(object, *args)
+          dispatch_method = dispatch[object.class]
+          send dispatch_method, object, *args
+        rescue NoMethodError => e
+          raise e if respond_to?(dispatch_method, true)
+          superklass = object.class.ancestors.find { |klass|
+            respond_to?(dispatch[klass], true)
+          }
+          raise(TypeError, "Cannot visit #{object.class}") unless superklass
+          dispatch[object.class] = dispatch[superklass]
+          retry
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/visitors/where_sql.rb b/activerecord/lib/arel/visitors/where_sql.rb
new file mode 100644
index 0000000000..c6caf5e7c9
--- /dev/null
+++ b/activerecord/lib/arel/visitors/where_sql.rb
@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module Visitors
+    class WhereSql < Arel::Visitors::ToSql
+      def initialize(inner_visitor, *args, &block)
+        @inner_visitor = inner_visitor
+        super(*args, &block)
+      end
+
+      private
+
+        def visit_Arel_Nodes_SelectCore(o, collector)
+          collector << "WHERE "
+          wheres = o.wheres.map do |where|
+            Nodes::SqlLiteral.new(@inner_visitor.accept(where, collector.class.new).value)
+          end
+
+          inject_join wheres, collector, " AND "
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/arel/window_predications.rb b/activerecord/lib/arel/window_predications.rb
new file mode 100644
index 0000000000..3a8ee41f8a
--- /dev/null
+++ b/activerecord/lib/arel/window_predications.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+module Arel # :nodoc: all
+  module WindowPredications
+    def over(expr = nil)
+      Nodes::Over.new(self, expr)
+    end
+  end
+end
diff --git a/activerecord/lib/rails/generators/active_record.rb b/activerecord/lib/rails/generators/active_record.rb
index dc29213235..a7e5e373a7 100644
--- a/activerecord/lib/rails/generators/active_record.rb
+++ b/activerecord/lib/rails/generators/active_record.rb
@@ -1,7 +1,9 @@
-require 'rails/generators/named_base'
-require 'rails/generators/active_model'
-require 'rails/generators/active_record/migration'
-require 'active_record'
+# frozen_string_literal: true
+
+require "rails/generators/named_base"
+require "rails/generators/active_model"
+require "rails/generators/active_record/migration"
+require "active_record"
 
 module ActiveRecord
   module Generators # :nodoc:
@@ -10,7 +12,7 @@ module ActiveRecord
 
       # Set the current directory as base for the inherited generators.
       def self.base_root
-        File.dirname(__FILE__)
+        __dir__
       end
     end
   end
diff --git a/activerecord/lib/rails/generators/active_record/application_record/application_record_generator.rb b/activerecord/lib/rails/generators/active_record/application_record/application_record_generator.rb
new file mode 100644
index 0000000000..35d5664400
--- /dev/null
+++ b/activerecord/lib/rails/generators/active_record/application_record/application_record_generator.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require "rails/generators/active_record"
+
+module ActiveRecord
+  module Generators # :nodoc:
+    class ApplicationRecordGenerator < ::Rails::Generators::Base # :nodoc:
+      source_root File.expand_path("templates", __dir__)
+
+      # FIXME: Change this file to a symlink once RubyGems 2.5.0 is required.
+      def create_application_record
+        template "application_record.rb", application_record_file_name
+      end
+
+      private
+
+        def application_record_file_name
+          @application_record_file_name ||=
+            if namespaced?
+              "app/models/#{namespaced_path}/application_record.rb"
+            else
+              "app/models/application_record.rb"
+            end
+        end
+    end
+  end
+end
diff --git a/activerecord/lib/rails/generators/active_record/application_record/templates/application_record.rb.tt b/activerecord/lib/rails/generators/active_record/application_record/templates/application_record.rb.tt
new file mode 100644
index 0000000000..60050e0bf8
--- /dev/null
+++ b/activerecord/lib/rails/generators/active_record/application_record/templates/application_record.rb.tt
@@ -0,0 +1,5 @@
+<% module_namespacing do -%>
+class ApplicationRecord < ActiveRecord::Base
+  self.abstract_class = true
+end
+<% end -%>
diff --git a/activerecord/lib/rails/generators/active_record/migration.rb b/activerecord/lib/rails/generators/active_record/migration.rb
index b7418cf42f..cbb88d571d 100644
--- a/activerecord/lib/rails/generators/active_record/migration.rb
+++ b/activerecord/lib/rails/generators/active_record/migration.rb
@@ -1,4 +1,6 @@
-require 'rails/generators/migration'
+# frozen_string_literal: true
+
+require "rails/generators/migration"
 
 module ActiveRecord
   module Generators # :nodoc:
@@ -13,6 +15,34 @@ module ActiveRecord
           ActiveRecord::Migration.next_migration_number(next_migration_number)
         end
       end
+
+      private
+
+        def primary_key_type
+          key_type = options[:primary_key_type]
+          ", id: :#{key_type}" if key_type
+        end
+
+        def db_migrate_path
+          if defined?(Rails.application) && Rails.application
+            configured_migrate_path || default_migrate_path
+          else
+            "db/migrate"
+          end
+        end
+
+        def default_migrate_path
+          Rails.application.config.paths["db/migrate"].to_ary.first
+        end
+
+        def configured_migrate_path
+          return unless database = options[:database]
+          config = ActiveRecord::Base.configurations.configs_for(
+            env_name: Rails.env,
+            spec_name: database,
+          )
+          config&.migrations_paths
+        end
     end
   end
 end
diff --git a/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb b/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb
index 0d57de4d65..dd79bcf542 100644
--- a/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb
+++ b/activerecord/lib/rails/generators/active_record/migration/migration_generator.rb
@@ -1,56 +1,60 @@
-require 'rails/generators/active_record'
+# frozen_string_literal: true
+
+require "rails/generators/active_record"
 
 module ActiveRecord
   module Generators # :nodoc:
     class MigrationGenerator < Base # :nodoc:
-      argument :attributes, :type => :array, :default => [], :banner => "field[:type][:index] field[:type][:index]"
+      argument :attributes, type: :array, default: [], banner: "field[:type][:index] field[:type][:index]"
+
+      class_option :primary_key_type, type: :string, desc: "The type for primary key"
+      class_option :database, type: :string, aliases: %i(db), desc: "The database for your migration. By default, the current environment's primary database is used."
 
       def create_migration_file
         set_local_assigns!
         validate_file_name!
-        migration_template @migration_template, "db/migrate/#{file_name}.rb"
+        migration_template @migration_template, File.join(db_migrate_path, "#{file_name}.rb")
       end
 
-      protected
-      attr_reader :migration_action, :join_tables
+      private
+        attr_reader :migration_action, :join_tables
 
-      # Sets the default migration template that is being used for the generation of the migration.
-      # Depending on command line arguments, the migration template and the table name instance
-      # variables are set up.
-      def set_local_assigns!
-        @migration_template = "migration.rb"
-        case file_name
-        when /^(add|remove)_.*_(?:to|from)_(.*)/
-          @migration_action = $1
-          @table_name       = normalize_table_name($2)
-        when /join_table/
-          if attributes.length == 2
-            @migration_action = 'join'
-            @join_tables      = pluralize_table_names? ? attributes.map(&:plural_name) : attributes.map(&:singular_name)
+        # Sets the default migration template that is being used for the generation of the migration.
+        # Depending on command line arguments, the migration template and the table name instance
+        # variables are set up.
+        def set_local_assigns!
+          @migration_template = "migration.rb"
+          case file_name
+          when /^(add)_.*_to_(.*)/, /^(remove)_.*?_from_(.*)/
+            @migration_action = $1
+            @table_name       = normalize_table_name($2)
+          when /join_table/
+            if attributes.length == 2
+              @migration_action = "join"
+              @join_tables      = pluralize_table_names? ? attributes.map(&:plural_name) : attributes.map(&:singular_name)
 
-            set_index_names
+              set_index_names
+            end
+          when /^create_(.+)/
+            @table_name = normalize_table_name($1)
+            @migration_template = "create_table_migration.rb"
           end
-        when /^create_(.+)/
-          @table_name = normalize_table_name($1)
-          @migration_template = "create_table_migration.rb"
         end
-      end
 
-      def set_index_names
-        attributes.each_with_index do |attr, i|
-          attr.index_name = [attr, attributes[i - 1]].map{ |a| index_name_for(a) }
+        def set_index_names
+          attributes.each_with_index do |attr, i|
+            attr.index_name = [attr, attributes[i - 1]].map { |a| index_name_for(a) }
+          end
         end
-      end
 
-      def index_name_for(attribute)
-        if attribute.foreign_key?
-          attribute.name
-        else
-          attribute.name.singularize.foreign_key
-        end.to_sym
-      end
+        def index_name_for(attribute)
+          if attribute.foreign_key?
+            attribute.name
+          else
+            attribute.name.singularize.foreign_key
+          end.to_sym
+        end
 
-      private
         def attributes_with_index
           attributes.select { |a| !a.reference? && a.has_index? }
         end
@@ -58,7 +62,7 @@ module ActiveRecord
         # A migration file name can only contain underscores (_), lowercase characters,
         # and numbers 0-9. Any other file name will raise an IllegalMigrationNameError.
         def validate_file_name!
-          unless file_name =~ /^[_a-z0-9]+$/
+          unless /^[_a-z0-9]+$/.match?(file_name)
             raise IllegalMigrationNameError.new(file_name)
           end
         end
diff --git a/activerecord/lib/rails/generators/active_record/migration/templates/create_table_migration.rb b/activerecord/lib/rails/generators/active_record/migration/templates/create_table_migration.rb.tt
index 5b3e57dcf6..5f7201cfe1 100644
--- a/activerecord/lib/rails/generators/active_record/migration/templates/create_table_migration.rb
+++ b/activerecord/lib/rails/generators/active_record/migration/templates/create_table_migration.rb.tt
@@ -1,6 +1,6 @@
-class <%= migration_class_name %> < ActiveRecord::Migration
+class <%= migration_class_name %> < ActiveRecord::Migration[<%= ActiveRecord::Migration.current_version %>]
   def change
-    create_table :<%= table_name %> do |t|
+    create_table :<%= table_name %><%= primary_key_type %> do |t|
 <% attributes.each do |attribute| -%>
 <% if attribute.password_digest? -%>
       t.string :password_digest<%= attribute.inject_options %>
diff --git a/activerecord/lib/rails/generators/active_record/migration/templates/migration.rb b/activerecord/lib/rails/generators/active_record/migration/templates/migration.rb.tt
index 23a377db6a..481c70201b 100644
--- a/activerecord/lib/rails/generators/active_record/migration/templates/migration.rb
+++ b/activerecord/lib/rails/generators/active_record/migration/templates/migration.rb.tt
@@ -1,4 +1,4 @@
-class <%= migration_class_name %> < ActiveRecord::Migration
+class <%= migration_class_name %> < ActiveRecord::Migration[<%= ActiveRecord::Migration.current_version %>]
 <%- if migration_action == 'add' -%>
   def change
 <% attributes.each do |attribute| -%>
@@ -19,7 +19,11 @@ class <%= migration_class_name %> < ActiveRecord::Migration
   def change
     create_join_table :<%= join_tables.first %>, :<%= join_tables.second %> do |t|
     <%- attributes.each do |attribute| -%>
+      <%- if attribute.reference? -%>
+      t.references :<%= attribute.name %><%= attribute.inject_options %>
+      <%- else -%>
       <%= '# ' unless attribute.has_index? -%>t.index <%= attribute.index_name %><%= attribute.inject_index_options %>
+      <%- end -%>
     <%- end -%>
     end
   end
diff --git a/activerecord/lib/rails/generators/active_record/model/model_generator.rb b/activerecord/lib/rails/generators/active_record/model/model_generator.rb
index 7e8d68ce69..eac504f9f1 100644
--- a/activerecord/lib/rails/generators/active_record/model/model_generator.rb
+++ b/activerecord/lib/rails/generators/active_record/model/model_generator.rb
@@ -1,52 +1,49 @@
-require 'rails/generators/active_record'
+# frozen_string_literal: true
+
+require "rails/generators/active_record"
 
 module ActiveRecord
   module Generators # :nodoc:
     class ModelGenerator < Base # :nodoc:
-      argument :attributes, :type => :array, :default => [], :banner => "field[:type][:index] field[:type][:index]"
+      argument :attributes, type: :array, default: [], banner: "field[:type][:index] field[:type][:index]"
 
       check_class_collision
 
-      class_option :migration,  :type => :boolean
-      class_option :timestamps, :type => :boolean
-      class_option :parent,     :type => :string, :desc => "The parent class for the generated model"
-      class_option :indexes,    :type => :boolean, :default => true, :desc => "Add indexes for references and belongs_to columns"
+      class_option :migration, type: :boolean
+      class_option :timestamps, type: :boolean
+      class_option :parent, type: :string, desc: "The parent class for the generated model"
+      class_option :indexes, type: :boolean, default: true, desc: "Add indexes for references and belongs_to columns"
+      class_option :primary_key_type, type: :string, desc: "The type for primary key"
+      class_option :database, type: :string, aliases: %i(db), desc: "The database for your model's migration. By default, the current environment's primary database is used."
 
-      
       # creates the migration file for the model.
-
       def create_migration_file
         return unless options[:migration] && options[:parent].nil?
         attributes.each { |a| a.attr_options.delete(:index) if a.reference? && !a.has_index? } if options[:indexes] == false
-        migration_template "../../migration/templates/create_table_migration.rb", "db/migrate/create_#{table_name}.rb"
+        migration_template "../../migration/templates/create_table_migration.rb", File.join(db_migrate_path, "create_#{table_name}.rb")
       end
 
       def create_model_file
-        template 'model.rb', File.join('app/models', class_path, "#{file_name}.rb")
+        template "model.rb", File.join("app/models", class_path, "#{file_name}.rb")
       end
 
       def create_module_file
         return if regular_class_path.empty?
-        template 'module.rb', File.join('app/models', "#{class_path.join('/')}.rb") if behavior == :invoke
-      end
-
-      def attributes_with_index
-        attributes.select { |a| !a.reference? && a.has_index? }
-      end
-
-      def accessible_attributes
-        attributes.reject(&:reference?)
+        template "module.rb", File.join("app/models", "#{class_path.join('/')}.rb") if behavior == :invoke
       end
 
       hook_for :test_framework
 
-      protected
+      private
+
+        def attributes_with_index
+          attributes.select { |a| !a.reference? && a.has_index? }
+        end
 
         # Used by the migration template to determine the parent name of the model
         def parent_class_name
-          options[:parent] || "ActiveRecord::Base"
+          options[:parent] || "ApplicationRecord"
         end
-
     end
   end
 end
diff --git a/activerecord/lib/rails/generators/active_record/model/templates/model.rb b/activerecord/lib/rails/generators/active_record/model/templates/model.rb.tt
index 55dc65c8ad..55dc65c8ad 100644
--- a/activerecord/lib/rails/generators/active_record/model/templates/model.rb
+++ b/activerecord/lib/rails/generators/active_record/model/templates/model.rb.tt
diff --git a/activerecord/lib/rails/generators/active_record/model/templates/module.rb b/activerecord/lib/rails/generators/active_record/model/templates/module.rb.tt
index a3bf1c37b6..a3bf1c37b6 100644
--- a/activerecord/lib/rails/generators/active_record/model/templates/module.rb
+++ b/activerecord/lib/rails/generators/active_record/model/templates/module.rb.tt
diff --git a/activerecord/test/.gitignore b/activerecord/test/.gitignore
deleted file mode 100644
index a0ec5967dd..0000000000
--- a/activerecord/test/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-/config.yml
diff --git a/activerecord/test/active_record/connection_adapters/fake_adapter.rb b/activerecord/test/active_record/connection_adapters/fake_adapter.rb
index 49a68fb94c..f977b2997b 100644
--- a/activerecord/test/active_record/connection_adapters/fake_adapter.rb
+++ b/activerecord/test/active_record/connection_adapters/fake_adapter.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ConnectionHandling
     def fake_connection(config)
@@ -7,16 +9,16 @@ module ActiveRecord
 
   module ConnectionAdapters
     class FakeAdapter < AbstractAdapter
-      attr_accessor :tables, :primary_keys
+      attr_accessor :data_sources, :primary_keys
 
-      @columns = Hash.new { |h,k| h[k] = [] }
+      @columns = Hash.new { |h, k| h[k] = [] }
       class << self
         attr_reader :columns
       end
 
       def initialize(connection, logger)
         super
-        @tables       = []
+        @data_sources = []
         @primary_keys = {}
         @columns      = self.class.columns
       end
@@ -37,7 +39,7 @@ module ActiveRecord
         @columns[table_name]
       end
 
-      def table_exists?(*)
+      def data_source_exists?(*)
         true
       end
 
diff --git a/activerecord/test/assets/schema_dump_5_1.yml b/activerecord/test/assets/schema_dump_5_1.yml
new file mode 100644
index 0000000000..f37977daf2
--- /dev/null
+++ b/activerecord/test/assets/schema_dump_5_1.yml
@@ -0,0 +1,345 @@
+--- !ruby/object:ActiveRecord::ConnectionAdapters::SchemaCache
+columns:
+  posts:
+  - &1 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: id
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: INTEGER
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': false
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &2 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: author_id
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &3 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: title
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: varchar
+      type: :string
+      limit: 
+      precision: 
+      scale: 
+    'null': false
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &4 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: body
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: text
+      type: :text
+      limit: 
+      precision: 
+      scale: 
+    'null': false
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &5 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: type
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: varchar
+      type: :string
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: 
+    default_function: 
+    collation: 
+    comment: 
+  - &6 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: comments_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &7 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: taggings_with_delete_all_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &8 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: taggings_with_destroy_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &9 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: tags_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &10 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: tags_with_destroy_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+  - &11 !ruby/object:ActiveRecord::ConnectionAdapters::Column
+    name: tags_with_nullify_count
+    table_name: posts
+    sql_type_metadata: !ruby/object:ActiveRecord::ConnectionAdapters::SqlTypeMetadata
+      sql_type: integer
+      type: :integer
+      limit: 
+      precision: 
+      scale: 
+    'null': true
+    default: '0'
+    default_function: 
+    collation: 
+    comment: 
+columns_hash:
+  posts:
+    id: *1
+    author_id: *2
+    title: *3
+    body: *4
+    type: *5
+    comments_count: *6
+    taggings_with_delete_all_count: *7
+    taggings_with_destroy_count: *8
+    tags_count: *9
+    tags_with_destroy_count: *10
+    tags_with_nullify_count: *11
+primary_keys:
+  posts: id
+data_sources:
+  ar_internal_metadata: true
+  table_with_autoincrement: true
+  accounts: true
+  admin_accounts: true
+  admin_users: true
+  aircraft: true
+  articles: true
+  articles_magazines: true
+  articles_tags: true
+  audit_logs: true
+  authors: true
+  author_addresses: true
+  author_favorites: true
+  auto_id_tests: true
+  binaries: true
+  birds: true
+  books: true
+  booleans: true
+  bulbs: true
+  CamelCase: true
+  cars: true
+  carriers: true
+  categories: true
+  categories_posts: true
+  categorizations: true
+  citations: true
+  clubs: true
+  collections: true
+  colnametests: true
+  columns: true
+  comments: true
+  companies: true
+  content: true
+  content_positions: true
+  vegetables: true
+  computers: true
+  computers_developers: true
+  contracts: true
+  customers: true
+  customer_carriers: true
+  dashboards: true
+  developers: true
+  developers_projects: true
+  dog_lovers: true
+  dogs: true
+  doubloons: true
+  edges: true
+  engines: true
+  entrants: true
+  essays: true
+  events: true
+  eyes: true
+  funny_jokes: true
+  cold_jokes: true
+  friendships: true
+  goofy_string_id: true
+  having: true
+  guids: true
+  guitars: true
+  inept_wizards: true
+  integer_limits: true
+  invoices: true
+  iris: true
+  items: true
+  jobs: true
+  jobs_pool: true
+  keyboards: true
+  legacy_things: true
+  lessons: true
+  lessons_students: true
+  students: true
+  lint_models: true
+  line_items: true
+  lions: true
+  lock_without_defaults: true
+  lock_without_defaults_cust: true
+  magazines: true
+  mateys: true
+  members: true
+  member_details: true
+  member_friends: true
+  memberships: true
+  member_types: true
+  mentors: true
+  minivans: true
+  minimalistics: true
+  mixed_case_monkeys: true
+  mixins: true
+  movies: true
+  notifications: true
+  numeric_data: true
+  orders: true
+  organizations: true
+  owners: true
+  paint_colors: true
+  paint_textures: true
+  parrots: true
+  parrots_pirates: true
+  parrots_treasures: true
+  people: true
+  peoples_treasures: true
+  personal_legacy_things: true
+  pets: true
+  pets_treasures: true
+  pirates: true
+  posts: true
+  serialized_posts: true
+  images: true
+  price_estimates: true
+  products: true
+  product_types: true
+  projects: true
+  randomly_named_table1: true
+  randomly_named_table2: true
+  randomly_named_table3: true
+  ratings: true
+  readers: true
+  references: true
+  shape_expressions: true
+  ships: true
+  ship_parts: true
+  prisoners: true
+  shop_accounts: true
+  speedometers: true
+  sponsors: true
+  string_key_objects: true
+  subscribers: true
+  subscriptions: true
+  tags: true
+  taggings: true
+  tasks: true
+  topics: true
+  toys: true
+  traffic_lights: true
+  treasures: true
+  tuning_pegs: true
+  tyres: true
+  variants: true
+  vertices: true
+  warehouse-things: true
+  circles: true
+  squares: true
+  triangles: true
+  non_poly_ones: true
+  non_poly_twos: true
+  men: true
+  faces: true
+  interests: true
+  zines: true
+  wheels: true
+  countries: true
+  treaties: true
+  countries_treaties: true
+  liquid: true
+  molecules: true
+  electrons: true
+  weirds: true
+  nodes: true
+  trees: true
+  hotels: true
+  departments: true
+  cake_designers: true
+  drink_designers: true
+  chefs: true
+  recipes: true
+  records: true
+  overloaded_types: true
+  users: true
+  test_with_keyword_column_name: true
+  fk_test_has_pk: true
+  fk_test_has_fk: true
+version: 0
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index 1712ff0ac6..64c2b51f83 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -1,89 +1,135 @@
+# frozen_string_literal: true
+
 require "cases/helper"
+require "support/connection_helper"
 require "models/book"
 require "models/post"
 require "models/author"
+require "models/event"
 
 module ActiveRecord
   class AdapterTest < ActiveRecord::TestCase
     def setup
       @connection = ActiveRecord::Base.connection
+      @connection.materialize_transactions
     end
 
     ##
     # PostgreSQL does not support null bytes in strings
-    unless current_adapter?(:PostgreSQLAdapter)
+    unless current_adapter?(:PostgreSQLAdapter) ||
+        (current_adapter?(:SQLite3Adapter) && !ActiveRecord::Base.connection.prepared_statements)
       def test_update_prepared_statement
         b = Book.create(name: "my \x00 book")
         b.reload
         assert_equal "my \x00 book", b.name
-        b.update_attributes(name: "my other \x00 book")
+        b.update(name: "my other \x00 book")
         b.reload
         assert_equal "my other \x00 book", b.name
       end
     end
 
+    def test_create_record_with_pk_as_zero
+      Book.create(id: 0)
+      assert_equal 0, Book.find(0).id
+      assert_nothing_raised { Book.destroy(0) }
+    end
+
+    def test_valid_column
+      @connection.native_database_types.each_key do |type|
+        assert @connection.valid_type?(type)
+      end
+    end
+
+    def test_invalid_column
+      assert_not @connection.valid_type?(:foobar)
+    end
+
     def test_tables
       tables = @connection.tables
-      assert tables.include?("accounts")
-      assert tables.include?("authors")
-      assert tables.include?("tasks")
-      assert tables.include?("topics")
+      assert_includes tables, "accounts"
+      assert_includes tables, "authors"
+      assert_includes tables, "tasks"
+      assert_includes tables, "topics"
     end
 
     def test_table_exists?
       assert @connection.table_exists?("accounts")
-      assert !@connection.table_exists?("nonexistingtable")
-      assert !@connection.table_exists?(nil)
+      assert @connection.table_exists?(:accounts)
+      assert_not @connection.table_exists?("nonexistingtable")
+      assert_not @connection.table_exists?("'")
+      assert_not @connection.table_exists?(nil)
+    end
+
+    def test_data_sources
+      data_sources = @connection.data_sources
+      assert_includes data_sources, "accounts"
+      assert_includes data_sources, "authors"
+      assert_includes data_sources, "tasks"
+      assert_includes data_sources, "topics"
+    end
+
+    def test_data_source_exists?
+      assert @connection.data_source_exists?("accounts")
+      assert @connection.data_source_exists?(:accounts)
+      assert_not @connection.data_source_exists?("nonexistingtable")
+      assert_not @connection.data_source_exists?("'")
+      assert_not @connection.data_source_exists?(nil)
     end
 
     def test_indexes
       idx_name = "accounts_idx"
 
-      if @connection.respond_to?(:indexes)
-        indexes = @connection.indexes("accounts")
-        assert indexes.empty?
-
-        @connection.add_index :accounts, :firm_id, :name => idx_name
-        indexes = @connection.indexes("accounts")
-        assert_equal "accounts", indexes.first.table
-        assert_equal idx_name, indexes.first.name
-        assert !indexes.first.unique
-        assert_equal ["firm_id"], indexes.first.columns
-      else
-        warn "#{@connection.class} does not respond to #indexes"
-      end
+      indexes = @connection.indexes("accounts")
+      assert_empty indexes
 
+      @connection.add_index :accounts, :firm_id, name: idx_name
+      indexes = @connection.indexes("accounts")
+      assert_equal "accounts", indexes.first.table
+      assert_equal idx_name, indexes.first.name
+      assert_not indexes.first.unique
+      assert_equal ["firm_id"], indexes.first.columns
     ensure
-      @connection.remove_index(:accounts, :name => idx_name) rescue nil
+      @connection.remove_index(:accounts, name: idx_name) rescue nil
+    end
+
+    def test_remove_index_when_name_and_wrong_column_name_specified
+      index_name = "accounts_idx"
+
+      @connection.add_index :accounts, :firm_id, name: index_name
+      assert_raises ArgumentError do
+        @connection.remove_index :accounts, name: index_name, column: :wrong_column_name
+      end
+    ensure
+      @connection.remove_index(:accounts, name: index_name)
     end
 
     def test_current_database
       if @connection.respond_to?(:current_database)
-        assert_equal ARTest.connection_config['arunit']['database'], @connection.current_database
+        assert_equal ARTest.connection_config["arunit"]["database"], @connection.current_database
       end
     end
 
-    if current_adapter?(:MysqlAdapter)
+    if current_adapter?(:Mysql2Adapter)
       def test_charset
         assert_not_nil @connection.charset
-        assert_not_equal 'character_set_database', @connection.charset
-        assert_equal @connection.show_variable('character_set_database'), @connection.charset
+        assert_not_equal "character_set_database", @connection.charset
+        assert_equal @connection.show_variable("character_set_database"), @connection.charset
       end
 
       def test_collation
         assert_not_nil @connection.collation
-        assert_not_equal 'collation_database', @connection.collation
-        assert_equal @connection.show_variable('collation_database'), @connection.collation
+        assert_not_equal "collation_database", @connection.collation
+        assert_equal @connection.show_variable("collation_database"), @connection.collation
       end
 
       def test_show_nonexistent_variable_returns_nil
-        assert_nil @connection.show_variable('foo_bar_baz')
+        assert_nil @connection.show_variable("foo_bar_baz")
       end
 
       def test_not_specifying_database_name_for_cross_database_selects
         begin
           assert_nothing_raised do
-            ActiveRecord::Base.establish_connection(ActiveRecord::Base.configurations['arunit'].except(:database))
+            ActiveRecord::Base.establish_connection(ActiveRecord::Base.configurations["arunit"].except(:database))
 
             config = ARTest.connection_config
             ActiveRecord::Base.connection.execute(
@@ -104,9 +150,9 @@ module ActiveRecord
         alias_method :table_alias_length,     :test_table_alias_length
       end
 
-      assert_equal 'posts',      @connection.table_alias_for('posts')
-      assert_equal 'posts_comm', @connection.table_alias_for('posts_comments')
-      assert_equal 'dbo_posts',  @connection.table_alias_for('dbo.posts')
+      assert_equal "posts",      @connection.table_alias_for("posts")
+      assert_equal "posts_comm", @connection.table_alias_for("posts_comments")
+      assert_equal "dbo_posts",  @connection.table_alias_for("dbo.posts")
 
       class << @connection
         remove_method :table_alias_length
@@ -114,74 +160,61 @@ module ActiveRecord
       end
     end
 
-    # test resetting sequences in odd tables in PostgreSQL
-    if ActiveRecord::Base.connection.respond_to?(:reset_pk_sequence!)
-      require 'models/movie'
-      require 'models/subscriber'
-
-      def test_reset_empty_table_with_custom_pk
-        Movie.delete_all
-        Movie.connection.reset_pk_sequence! 'movies'
-        assert_equal 1, Movie.create(:name => 'fight club').id
+    def test_uniqueness_violations_are_translated_to_specific_exception
+      @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
+      error = assert_raises(ActiveRecord::RecordNotUnique) do
+        @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
       end
 
-      def test_reset_table_with_non_integer_pk
-        Subscriber.delete_all
-        Subscriber.connection.reset_pk_sequence! 'subscribers'
-        sub = Subscriber.new(:name => 'robert drake')
-        sub.id = 'bob drake'
-        assert_nothing_raised { sub.save! }
-      end
+      assert_not_nil error.cause
     end
 
-    def test_uniqueness_violations_are_translated_to_specific_exception
-      @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
-      assert_raises(ActiveRecord::RecordNotUnique) do
-        @connection.execute "INSERT INTO subscribers(nick) VALUES('me')"
+    def test_not_null_violations_are_translated_to_specific_exception
+      error = assert_raises(ActiveRecord::NotNullViolation) do
+        Post.create
       end
+
+      assert_not_nil error.cause
     end
 
     unless current_adapter?(:SQLite3Adapter)
-      def test_foreign_key_violations_are_translated_to_specific_exception
-        assert_raises(ActiveRecord::InvalidForeignKey) do
-          # Oracle adapter uses prefetched primary key values from sequence and passes them to connection adapter insert method
-          if @connection.prefetch_primary_key?
-            id_value = @connection.next_sequence_value(@connection.default_sequence_name("fk_test_has_fk", "id"))
-            @connection.execute "INSERT INTO fk_test_has_fk (id, fk_id) VALUES (#{id_value},0)"
-          else
-            @connection.execute "INSERT INTO fk_test_has_fk (fk_id) VALUES (0)"
-          end
+      def test_value_limit_violations_are_translated_to_specific_exception
+        error = assert_raises(ActiveRecord::ValueTooLong) do
+          Event.create(title: "abcdefgh")
         end
+
+        assert_not_nil error.cause
       end
 
-      def test_foreign_key_violations_are_translated_to_specific_exception_with_validate_false
-        klass_has_fk = Class.new(ActiveRecord::Base) do
-          self.table_name = 'fk_test_has_fk'
+      def test_numeric_value_out_of_ranges_are_translated_to_specific_exception
+        error = assert_raises(ActiveRecord::RangeError) do
+          Book.connection.create("INSERT INTO books(author_id) VALUES (9223372036854775808)")
         end
 
-        assert_raises(ActiveRecord::InvalidForeignKey) do
-          has_fk = klass_has_fk.new
-          has_fk.fk_id = 1231231231
-          has_fk.save(validate: false)
-        end
+        assert_not_nil error.cause
       end
     end
 
-    def test_disable_referential_integrity
-      assert_nothing_raised do
-        @connection.disable_referential_integrity do
-          # Oracle adapter uses prefetched primary key values from sequence and passes them to connection adapter insert method
-          if @connection.prefetch_primary_key?
-            id_value = @connection.next_sequence_value(@connection.default_sequence_name("fk_test_has_fk", "id"))
-            @connection.execute "INSERT INTO fk_test_has_fk (id, fk_id) VALUES (#{id_value},0)"
-          else
-            @connection.execute "INSERT INTO fk_test_has_fk (fk_id) VALUES (0)"
-          end
-          # should delete created record as otherwise disable_referential_integrity will try to enable constraints after executed block
-          # and will fail (at least on Oracle)
-          @connection.execute "DELETE FROM fk_test_has_fk"
-        end
+    def test_exceptions_from_notifications_are_not_translated
+      original_error = StandardError.new("This StandardError shouldn't get translated")
+      subscriber = ActiveSupport::Notifications.subscribe("sql.active_record") { raise original_error }
+      actual_error = assert_raises(StandardError) do
+        @connection.execute("SELECT * FROM posts")
       end
+
+      assert_equal original_error, actual_error
+
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscriber) if subscriber
+    end
+
+    def test_database_related_exceptions_are_translated_to_statement_invalid
+      error = assert_raises(ActiveRecord::StatementInvalid) do
+        @connection.execute("This is a syntax error")
+      end
+
+      assert_instance_of ActiveRecord::StatementInvalid, error
+      assert_kind_of Exception, error.cause
     end
 
     def test_select_all_always_return_activerecord_result
@@ -189,22 +222,61 @@ module ActiveRecord
       assert result.is_a?(ActiveRecord::Result)
     end
 
+    if ActiveRecord::Base.connection.prepared_statements
+      def test_select_all_with_legacy_binds
+        post = Post.create!(title: "foo", body: "bar")
+        expected = @connection.select_all("SELECT * FROM posts WHERE id = #{post.id}")
+        result = @connection.select_all("SELECT * FROM posts WHERE id = #{Arel::Nodes::BindParam.new(nil).to_sql}", nil, [[nil, post.id]])
+        assert_equal expected.to_a, result.to_a
+      end
+
+      def test_insert_update_delete_with_legacy_binds
+        binds = [[nil, 1]]
+        bind_param = Arel::Nodes::BindParam.new(nil)
+
+        id = @connection.insert("INSERT INTO events(id) VALUES (#{bind_param.to_sql})", nil, nil, nil, nil, binds)
+        assert_equal 1, id
+
+        @connection.update("UPDATE events SET title = 'foo' WHERE id = #{bind_param.to_sql}", nil, binds)
+        result = @connection.select_all("SELECT * FROM events WHERE id = #{bind_param.to_sql}", nil, binds)
+        assert_equal({ "id" => 1, "title" => "foo" }, result.first)
+
+        @connection.delete("DELETE FROM events WHERE id = #{bind_param.to_sql}", nil, binds)
+        result = @connection.select_all("SELECT * FROM events WHERE id = #{bind_param.to_sql}", nil, binds)
+        assert_nil result.first
+      end
+
+      def test_insert_update_delete_with_binds
+        binds = [Relation::QueryAttribute.new("id", 1, Type.default_value)]
+        bind_param = Arel::Nodes::BindParam.new(nil)
+
+        id = @connection.insert("INSERT INTO events(id) VALUES (#{bind_param.to_sql})", nil, nil, nil, nil, binds)
+        assert_equal 1, id
+
+        @connection.update("UPDATE events SET title = 'foo' WHERE id = #{bind_param.to_sql}", nil, binds)
+        result = @connection.select_all("SELECT * FROM events WHERE id = #{bind_param.to_sql}", nil, binds)
+        assert_equal({ "id" => 1, "title" => "foo" }, result.first)
+
+        @connection.delete("DELETE FROM events WHERE id = #{bind_param.to_sql}", nil, binds)
+        result = @connection.select_all("SELECT * FROM events WHERE id = #{bind_param.to_sql}", nil, binds)
+        assert_nil result.first
+      end
+    end
+
     def test_select_methods_passing_a_association_relation
-      author = Author.create!(name: 'john')
-      Post.create!(author: author, title: 'foo', body: 'bar')
-      query = author.posts.where(title: 'foo').select(:title)
-      assert_equal({"title" => "foo"}, @connection.select_one(query.arel, nil, query.bound_attributes))
-      assert_equal({"title" => "foo"}, @connection.select_one(query))
+      author = Author.create!(name: "john")
+      Post.create!(author: author, title: "foo", body: "bar")
+      query = author.posts.where(title: "foo").select(:title)
+      assert_equal({ "title" => "foo" }, @connection.select_one(query))
       assert @connection.select_all(query).is_a?(ActiveRecord::Result)
       assert_equal "foo", @connection.select_value(query)
       assert_equal ["foo"], @connection.select_values(query)
     end
 
     def test_select_methods_passing_a_relation
-      Post.create!(title: 'foo', body: 'bar')
-      query = Post.where(title: 'foo').select(:title)
-      assert_equal({"title" => "foo"}, @connection.select_one(query.arel, nil, query.bound_attributes))
-      assert_equal({"title" => "foo"}, @connection.select_one(query))
+      Post.create!(title: "foo", body: "bar")
+      query = Post.where(title: "foo").select(:title)
+      assert_equal({ "title" => "foo" }, @connection.select_one(query))
       assert @connection.select_all(query).is_a?(ActiveRecord::Result)
       assert_equal "foo", @connection.select_value(query)
       assert_equal ["foo"], @connection.select_values(query)
@@ -216,13 +288,111 @@ module ActiveRecord
 
     unless current_adapter?(:PostgreSQLAdapter)
       def test_log_invalid_encoding
-        assert_raise ActiveRecord::StatementInvalid do
+        error = assert_raises RuntimeError do
           @connection.send :log, "SELECT 'ы' FROM DUAL" do
-            raise 'ы'.force_encoding(Encoding::ASCII_8BIT)
+            raise (+"ы").force_encoding(Encoding::ASCII_8BIT)
           end
         end
+
+        assert_equal "ы", error.message
+      end
+    end
+
+    def test_supports_multi_insert_is_deprecated
+      assert_deprecated { @connection.supports_multi_insert? }
+    end
+
+    def test_column_name_length_is_deprecated
+      assert_deprecated { @connection.column_name_length }
+    end
+
+    def test_table_name_length_is_deprecated
+      assert_deprecated { @connection.table_name_length }
+    end
+
+    def test_columns_per_table_is_deprecated
+      assert_deprecated { @connection.columns_per_table }
+    end
+
+    def test_indexes_per_table_is_deprecated
+      assert_deprecated { @connection.indexes_per_table }
+    end
+
+    def test_columns_per_multicolumn_index_is_deprecated
+      assert_deprecated { @connection.columns_per_multicolumn_index }
+    end
+
+    def test_sql_query_length_is_deprecated
+      assert_deprecated { @connection.sql_query_length }
+    end
+
+    def test_joins_per_query_is_deprecated
+      assert_deprecated { @connection.joins_per_query }
+    end
+  end
+
+  class AdapterForeignKeyTest < ActiveRecord::TestCase
+    self.use_transactional_tests = false
+
+    fixtures :fk_test_has_pk
+
+    def setup
+      @connection = ActiveRecord::Base.connection
+    end
+
+    def test_foreign_key_violations_are_translated_to_specific_exception_with_validate_false
+      klass_has_fk = Class.new(ActiveRecord::Base) do
+        self.table_name = "fk_test_has_fk"
+      end
+
+      error = assert_raises(ActiveRecord::InvalidForeignKey) do
+        has_fk = klass_has_fk.new
+        has_fk.fk_id = 1231231231
+        has_fk.save(validate: false)
+      end
+
+      assert_not_nil error.cause
+    end
+
+    def test_foreign_key_violations_on_insert_are_translated_to_specific_exception
+      error = assert_raises(ActiveRecord::InvalidForeignKey) do
+        insert_into_fk_test_has_fk
+      end
+
+      assert_not_nil error.cause
+    end
+
+    def test_foreign_key_violations_on_delete_are_translated_to_specific_exception
+      insert_into_fk_test_has_fk fk_id: 1
+
+      error = assert_raises(ActiveRecord::InvalidForeignKey) do
+        @connection.execute "DELETE FROM fk_test_has_pk WHERE pk_id = 1"
+      end
+
+      assert_not_nil error.cause
+    end
+
+    def test_disable_referential_integrity
+      assert_nothing_raised do
+        @connection.disable_referential_integrity do
+          insert_into_fk_test_has_fk
+          # should delete created record as otherwise disable_referential_integrity will try to enable constraints
+          # after executed block and will fail (at least on Oracle)
+          @connection.execute "DELETE FROM fk_test_has_fk"
+        end
       end
     end
+
+    private
+      def insert_into_fk_test_has_fk(fk_id: 0)
+        # Oracle adapter uses prefetched primary key values from sequence and passes them to connection adapter insert method
+        if @connection.prefetch_primary_key?
+          id_value = @connection.next_sequence_value(@connection.default_sequence_name("fk_test_has_fk", "id"))
+          @connection.execute "INSERT INTO fk_test_has_fk (id,fk_id) VALUES (#{id_value},#{fk_id})"
+        else
+          @connection.execute "INSERT INTO fk_test_has_fk (fk_id) VALUES (#{fk_id})"
+        end
+      end
   end
 
   class AdapterTestWithoutTransaction < ActiveRecord::TestCase
@@ -243,16 +413,60 @@ module ActiveRecord
     unless in_memory_db?
       test "transaction state is reset after a reconnect" do
         @connection.begin_transaction
-        assert @connection.transaction_open?
+        assert_predicate @connection, :transaction_open?
         @connection.reconnect!
-        assert !@connection.transaction_open?
+        assert_not_predicate @connection, :transaction_open?
       end
 
       test "transaction state is reset after a disconnect" do
         @connection.begin_transaction
-        assert @connection.transaction_open?
+        assert_predicate @connection, :transaction_open?
         @connection.disconnect!
-        assert !@connection.transaction_open?
+        assert_not_predicate @connection, :transaction_open?
+      end
+    end
+
+    # test resetting sequences in odd tables in PostgreSQL
+    if ActiveRecord::Base.connection.respond_to?(:reset_pk_sequence!)
+      require "models/movie"
+      require "models/subscriber"
+
+      def test_reset_empty_table_with_custom_pk
+        Movie.delete_all
+        Movie.connection.reset_pk_sequence! "movies"
+        assert_equal 1, Movie.create(name: "fight club").id
+      end
+
+      def test_reset_table_with_non_integer_pk
+        Subscriber.delete_all
+        Subscriber.connection.reset_pk_sequence! "subscribers"
+        sub = Subscriber.new(name: "robert drake")
+        sub.id = "bob drake"
+        assert_nothing_raised { sub.save! }
+      end
+    end
+  end
+end
+
+if ActiveRecord::Base.connection.supports_advisory_locks?
+  class AdvisoryLocksEnabledTest < ActiveRecord::TestCase
+    include ConnectionHelper
+
+    def test_advisory_locks_enabled?
+      assert ActiveRecord::Base.connection.advisory_locks_enabled?
+
+      run_without_connection do |orig_connection|
+        ActiveRecord::Base.establish_connection(
+          orig_connection.merge(advisory_locks: false)
+        )
+
+        assert_not ActiveRecord::Base.connection.advisory_locks_enabled?
+
+        ActiveRecord::Base.establish_connection(
+          orig_connection.merge(advisory_locks: true)
+        )
+
+        assert ActiveRecord::Base.connection.advisory_locks_enabled?
       end
     end
   end
diff --git a/activerecord/test/cases/adapters/mysql/active_schema_test.rb b/activerecord/test/cases/adapters/mysql/active_schema_test.rb
deleted file mode 100644
index f0fd95ac16..0000000000
--- a/activerecord/test/cases/adapters/mysql/active_schema_test.rb
+++ /dev/null
@@ -1,192 +0,0 @@
-require "cases/helper"
-require 'support/connection_helper'
-
-class MysqlActiveSchemaTest < ActiveRecord::MysqlTestCase
-  include ConnectionHelper
-
-  def setup
-    ActiveRecord::Base.connection.singleton_class.class_eval do
-      alias_method :execute_without_stub, :execute
-      def execute(sql, name = nil) return sql end
-    end
-  end
-
-  teardown do
-    reset_connection
-  end
-
-  def test_add_index
-    # add_index calls table_exists? and index_name_exists? which can't work since execute is stubbed
-    def (ActiveRecord::Base.connection).table_exists?(*); true; end
-    def (ActiveRecord::Base.connection).index_name_exists?(*); false; end
-
-    expected = "CREATE  INDEX `index_people_on_last_name`  ON `people` (`last_name`) "
-    assert_equal expected, add_index(:people, :last_name, :length => nil)
-
-    expected = "CREATE  INDEX `index_people_on_last_name`  ON `people` (`last_name`(10)) "
-    assert_equal expected, add_index(:people, :last_name, :length => 10)
-
-    expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`(15)) "
-    assert_equal expected, add_index(:people, [:last_name, :first_name], :length => 15)
-
-    expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`) "
-    assert_equal expected, add_index(:people, [:last_name, :first_name], :length => {:last_name => 15})
-
-    expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`(10)) "
-    assert_equal expected, add_index(:people, [:last_name, :first_name], :length => {:last_name => 15, :first_name => 10})
-
-    %w(SPATIAL FULLTEXT UNIQUE).each do |type|
-      expected = "CREATE #{type} INDEX `index_people_on_last_name`  ON `people` (`last_name`) "
-      assert_equal expected, add_index(:people, :last_name, :type => type)
-    end
-
-    %w(btree hash).each do |using|
-      expected = "CREATE  INDEX `index_people_on_last_name` USING #{using} ON `people` (`last_name`) "
-      assert_equal expected, add_index(:people, :last_name, :using => using)
-    end
-
-    expected = "CREATE  INDEX `index_people_on_last_name` USING btree ON `people` (`last_name`(10)) "
-    assert_equal expected, add_index(:people, :last_name, :length => 10, :using => :btree)
-
-    expected = "CREATE  INDEX `index_people_on_last_name` USING btree ON `people` (`last_name`(10)) ALGORITHM = COPY"
-    assert_equal expected, add_index(:people, :last_name, :length => 10, using: :btree, algorithm: :copy)
-
-    assert_raise ArgumentError do
-      add_index(:people, :last_name, algorithm: :coyp)
-    end
-
-    expected = "CREATE  INDEX `index_people_on_last_name_and_first_name` USING btree ON `people` (`last_name`(15), `first_name`(15)) "
-    assert_equal expected, add_index(:people, [:last_name, :first_name], :length => 15, :using => :btree)
-  end
-
-  def test_index_in_create
-    def (ActiveRecord::Base.connection).table_exists?(*); false; end
-
-    %w(SPATIAL FULLTEXT UNIQUE).each do |type|
-      expected = "CREATE TABLE `people` (#{type} INDEX `index_people_on_last_name`  (`last_name`) ) ENGINE=InnoDB"
-      actual = ActiveRecord::Base.connection.create_table(:people, id: false) do |t|
-        t.index :last_name, type: type
-      end
-      assert_equal expected, actual
-    end
-
-    expected = "CREATE TABLE `people` ( INDEX `index_people_on_last_name` USING btree (`last_name`(10)) ) ENGINE=InnoDB"
-    actual = ActiveRecord::Base.connection.create_table(:people, id: false) do |t|
-      t.index :last_name, length: 10, using: :btree
-    end
-    assert_equal expected, actual
-  end
-
-  def test_index_in_bulk_change
-    def (ActiveRecord::Base.connection).table_exists?(*); true; end
-    def (ActiveRecord::Base.connection).index_name_exists?(*); false; end
-
-    %w(SPATIAL FULLTEXT UNIQUE).each do |type|
-      expected = "ALTER TABLE `people` ADD #{type} INDEX `index_people_on_last_name`  (`last_name`)"
-      actual = ActiveRecord::Base.connection.change_table(:people, bulk: true) do |t|
-        t.index :last_name, type: type
-      end
-      assert_equal expected, actual
-    end
-
-    expected = "ALTER TABLE `peaple` ADD  INDEX `index_peaple_on_last_name` USING btree (`last_name`(10)), ALGORITHM = COPY"
-    actual = ActiveRecord::Base.connection.change_table(:peaple, bulk: true) do |t|
-      t.index :last_name, length: 10, using: :btree, algorithm: :copy
-    end
-    assert_equal expected, actual
-  end
-
-  def test_drop_table
-    assert_equal "DROP TABLE `people`", drop_table(:people)
-  end
-
-  if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-    def test_create_mysql_database_with_encoding
-      assert_equal "CREATE DATABASE `matt` DEFAULT CHARACTER SET `utf8`", create_database(:matt)
-      assert_equal "CREATE DATABASE `aimonetti` DEFAULT CHARACTER SET `latin1`", create_database(:aimonetti, {:charset => 'latin1'})
-      assert_equal "CREATE DATABASE `matt_aimonetti` DEFAULT CHARACTER SET `big5` COLLATE `big5_chinese_ci`", create_database(:matt_aimonetti, {:charset => :big5, :collation => :big5_chinese_ci})
-    end
-
-    def test_recreate_mysql_database_with_encoding
-      create_database(:luca, {:charset => 'latin1'})
-      assert_equal "CREATE DATABASE `luca` DEFAULT CHARACTER SET `latin1`", recreate_database(:luca, {:charset => 'latin1'})
-    end
-  end
-
-  def test_add_column
-    assert_equal "ALTER TABLE `people` ADD `last_name` varchar(255)", add_column(:people, :last_name, :string)
-  end
-
-  def test_add_column_with_limit
-    assert_equal "ALTER TABLE `people` ADD `key` varchar(32)", add_column(:people, :key, :string, :limit => 32)
-  end
-
-  def test_drop_table_with_specific_database
-    assert_equal "DROP TABLE `otherdb`.`people`", drop_table('otherdb.people')
-  end
-
-  def test_add_timestamps
-    with_real_execute do
-      begin
-        ActiveRecord::Base.connection.create_table :delete_me
-        ActiveRecord::Base.connection.add_timestamps :delete_me, null: true
-        assert column_present?('delete_me', 'updated_at', 'datetime')
-        assert column_present?('delete_me', 'created_at', 'datetime')
-      ensure
-        ActiveRecord::Base.connection.drop_table :delete_me rescue nil
-      end
-    end
-  end
-
-  def test_remove_timestamps
-    with_real_execute do
-      begin
-        ActiveRecord::Base.connection.create_table :delete_me do |t|
-          t.timestamps null: true
-        end
-        ActiveRecord::Base.connection.remove_timestamps :delete_me, { null: true }
-        assert !column_present?('delete_me', 'updated_at', 'datetime')
-        assert !column_present?('delete_me', 'created_at', 'datetime')
-      ensure
-        ActiveRecord::Base.connection.drop_table :delete_me rescue nil
-      end
-    end
-  end
-
-  def test_indexes_in_create
-    ActiveRecord::Base.connection.stubs(:table_exists?).with(:temp).returns(false)
-    ActiveRecord::Base.connection.stubs(:index_name_exists?).with(:index_temp_on_zip).returns(false)
-
-    expected = "CREATE TEMPORARY TABLE `temp` ( INDEX `index_temp_on_zip`  (`zip`) ) ENGINE=InnoDB AS SELECT id, name, zip FROM a_really_complicated_query"
-    actual = ActiveRecord::Base.connection.create_table(:temp, temporary: true, as: "SELECT id, name, zip FROM a_really_complicated_query") do |t|
-      t.index :zip
-    end
-
-    assert_equal expected, actual
-  end
-
-  private
-    def with_real_execute
-      ActiveRecord::Base.connection.singleton_class.class_eval do
-        alias_method :execute_with_stub, :execute
-        remove_method :execute
-        alias_method :execute, :execute_without_stub
-      end
-
-      yield
-    ensure
-      ActiveRecord::Base.connection.singleton_class.class_eval do
-        remove_method :execute
-        alias_method :execute, :execute_with_stub
-      end
-    end
-
-    def method_missing(method_symbol, *arguments)
-      ActiveRecord::Base.connection.send(method_symbol, *arguments)
-    end
-
-    def column_present?(table_name, column_name, type)
-      results = ActiveRecord::Base.connection.select_all("SHOW FIELDS FROM #{table_name} LIKE '#{column_name}'")
-      results.first && results.first['Type'] == type
-    end
-end
diff --git a/activerecord/test/cases/adapters/mysql/case_sensitivity_test.rb b/activerecord/test/cases/adapters/mysql/case_sensitivity_test.rb
deleted file mode 100644
index 98d44315dd..0000000000
--- a/activerecord/test/cases/adapters/mysql/case_sensitivity_test.rb
+++ /dev/null
@@ -1,54 +0,0 @@
-require "cases/helper"
-
-class MysqlCaseSensitivityTest < ActiveRecord::MysqlTestCase
-  class CollationTest < ActiveRecord::Base
-  end
-
-  repair_validations(CollationTest)
-
-  def test_columns_include_collation_different_from_table
-    assert_equal 'utf8_bin', CollationTest.columns_hash['string_cs_column'].collation
-    assert_equal 'utf8_general_ci', CollationTest.columns_hash['string_ci_column'].collation
-  end
-
-  def test_case_sensitive
-    assert !CollationTest.columns_hash['string_ci_column'].case_sensitive?
-    assert CollationTest.columns_hash['string_cs_column'].case_sensitive?
-  end
-
-  def test_case_insensitive_comparison_for_ci_column
-    CollationTest.validates_uniqueness_of(:string_ci_column, :case_sensitive => false)
-    CollationTest.create!(:string_ci_column => 'A')
-    invalid = CollationTest.new(:string_ci_column => 'a')
-    queries = assert_sql { invalid.save }
-    ci_uniqueness_query = queries.detect { |q| q.match(/string_ci_column/) }
-    assert_no_match(/lower/i, ci_uniqueness_query)
-  end
-
-  def test_case_insensitive_comparison_for_cs_column
-    CollationTest.validates_uniqueness_of(:string_cs_column, :case_sensitive => false)
-    CollationTest.create!(:string_cs_column => 'A')
-    invalid = CollationTest.new(:string_cs_column => 'a')
-    queries = assert_sql { invalid.save }
-    cs_uniqueness_query = queries.detect { |q| q.match(/string_cs_column/) }
-    assert_match(/lower/i, cs_uniqueness_query)
-  end
-
-  def test_case_sensitive_comparison_for_ci_column
-    CollationTest.validates_uniqueness_of(:string_ci_column, :case_sensitive => true)
-    CollationTest.create!(:string_ci_column => 'A')
-    invalid = CollationTest.new(:string_ci_column => 'A')
-    queries = assert_sql { invalid.save }
-    ci_uniqueness_query = queries.detect { |q| q.match(/string_ci_column/) }
-    assert_match(/binary/i, ci_uniqueness_query)
-  end
-
-  def test_case_sensitive_comparison_for_cs_column
-    CollationTest.validates_uniqueness_of(:string_cs_column, :case_sensitive => true)
-    CollationTest.create!(:string_cs_column => 'A')
-    invalid = CollationTest.new(:string_cs_column => 'A')
-    queries = assert_sql { invalid.save }
-    cs_uniqueness_query = queries.detect { |q| q.match(/string_cs_column/) }
-    assert_no_match(/binary/i, cs_uniqueness_query)
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/charset_collation_test.rb b/activerecord/test/cases/adapters/mysql/charset_collation_test.rb
deleted file mode 100644
index f2117a97e6..0000000000
--- a/activerecord/test/cases/adapters/mysql/charset_collation_test.rb
+++ /dev/null
@@ -1,54 +0,0 @@
-require "cases/helper"
-require 'support/schema_dumping_helper'
-
-class MysqlCharsetCollationTest < ActiveRecord::MysqlTestCase
-  include SchemaDumpingHelper
-  self.use_transactional_tests = false
-
-  setup do
-    @connection = ActiveRecord::Base.connection
-    @connection.create_table :charset_collations, force: true do |t|
-      t.string :string_ascii_bin, charset: 'ascii', collation: 'ascii_bin'
-      t.text :text_ucs2_unicode_ci, charset: 'ucs2', collation: 'ucs2_unicode_ci'
-    end
-  end
-
-  teardown do
-    @connection.drop_table :charset_collations, if_exists: true
-  end
-
-  test "string column with charset and collation" do
-    column = @connection.columns(:charset_collations).find { |c| c.name == 'string_ascii_bin' }
-    assert_equal :string, column.type
-    assert_equal 'ascii_bin', column.collation
-  end
-
-  test "text column with charset and collation" do
-    column = @connection.columns(:charset_collations).find { |c| c.name == 'text_ucs2_unicode_ci' }
-    assert_equal :text, column.type
-    assert_equal 'ucs2_unicode_ci', column.collation
-  end
-
-  test "add column with charset and collation" do
-    @connection.add_column :charset_collations, :title, :string, charset: 'utf8', collation: 'utf8_bin'
-
-    column = @connection.columns(:charset_collations).find { |c| c.name == 'title' }
-    assert_equal :string, column.type
-    assert_equal 'utf8_bin', column.collation
-  end
-
-  test "change column with charset and collation" do
-    @connection.add_column :charset_collations, :description, :string, charset: 'utf8', collation: 'utf8_unicode_ci'
-    @connection.change_column :charset_collations, :description, :text, charset: 'utf8', collation: 'utf8_general_ci'
-
-    column = @connection.columns(:charset_collations).find { |c| c.name == 'description' }
-    assert_equal :text, column.type
-    assert_equal 'utf8_general_ci', column.collation
-  end
-
-  test "schema dump includes collation" do
-    output = dump_table_schema("charset_collations")
-    assert_match %r{t.string\s+"string_ascii_bin",\s+limit: 255,\s+collation: "ascii_bin"$}, output
-    assert_match %r{t.text\s+"text_ucs2_unicode_ci",\s+limit: 65535,\s+collation: "ucs2_unicode_ci"$}, output
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/connection_test.rb b/activerecord/test/cases/adapters/mysql/connection_test.rb
deleted file mode 100644
index ddbc007b87..0000000000
--- a/activerecord/test/cases/adapters/mysql/connection_test.rb
+++ /dev/null
@@ -1,191 +0,0 @@
-require "cases/helper"
-require 'support/connection_helper'
-require 'support/ddl_helper'
-
-class MysqlConnectionTest < ActiveRecord::MysqlTestCase
-  include ConnectionHelper
-  include DdlHelper
-
-  class Klass < ActiveRecord::Base
-  end
-
-  def setup
-    super
-    @connection = ActiveRecord::Base.connection
-  end
-
-  def test_mysql_reconnect_attribute_after_connection_with_reconnect_true
-    run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.merge({:reconnect => true}))
-      assert ActiveRecord::Base.connection.raw_connection.reconnect
-    end
-  end
-
-  unless ARTest.connection_config['arunit']['socket']
-    def test_connect_with_url
-      run_without_connection do
-        ar_config = ARTest.connection_config['arunit']
-
-        url = "mysql://#{ar_config["username"]}@localhost/#{ar_config["database"]}"
-        Klass.establish_connection(url)
-        assert_equal ar_config['database'], Klass.connection.current_database
-      end
-    end
-  end
-
-  def test_mysql_reconnect_attribute_after_connection_with_reconnect_false
-    run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.merge({:reconnect => false}))
-      assert !ActiveRecord::Base.connection.raw_connection.reconnect
-    end
-  end
-
-  def test_no_automatic_reconnection_after_timeout
-    assert @connection.active?
-    @connection.update('set @@wait_timeout=1')
-    sleep 2
-    assert !@connection.active?
-
-    # Repair all fixture connections so other tests won't break.
-    @fixture_connections.each(&:verify!)
-  end
-
-  def test_successful_reconnection_after_timeout_with_manual_reconnect
-    assert @connection.active?
-    @connection.update('set @@wait_timeout=1')
-    sleep 2
-    @connection.reconnect!
-    assert @connection.active?
-  end
-
-  def test_successful_reconnection_after_timeout_with_verify
-    assert @connection.active?
-    @connection.update('set @@wait_timeout=1')
-    sleep 2
-    @connection.verify!
-    assert @connection.active?
-  end
-
-  def test_bind_value_substitute
-    bind_param = @connection.substitute_at('foo')
-    assert_equal Arel.sql('?'), bind_param.to_sql
-  end
-
-  def test_exec_no_binds
-    with_example_table do
-      result = @connection.exec_query('SELECT id, data FROM ex')
-      assert_equal 0, result.rows.length
-      assert_equal 2, result.columns.length
-      assert_equal %w{ id data }, result.columns
-
-      @connection.exec_query('INSERT INTO ex (id, data) VALUES (1, "foo")')
-
-      # if there are no bind parameters, it will return a string (due to
-      # the libmysql api)
-      result = @connection.exec_query('SELECT id, data FROM ex')
-      assert_equal 1, result.rows.length
-      assert_equal 2, result.columns.length
-
-      assert_equal [['1', 'foo']], result.rows
-    end
-  end
-
-  def test_exec_with_binds
-    with_example_table do
-      @connection.exec_query('INSERT INTO ex (id, data) VALUES (1, "foo")')
-      result = @connection.exec_query(
-        'SELECT id, data FROM ex WHERE id = ?', nil, [ActiveRecord::Relation::QueryAttribute.new("id", 1, ActiveRecord::Type::Value.new)])
-
-      assert_equal 1, result.rows.length
-      assert_equal 2, result.columns.length
-
-      assert_equal [[1, 'foo']], result.rows
-    end
-  end
-
-  def test_exec_typecasts_bind_vals
-    with_example_table do
-      @connection.exec_query('INSERT INTO ex (id, data) VALUES (1, "foo")')
-      bind = ActiveRecord::Relation::QueryAttribute.new("id", "1-fuu", ActiveRecord::Type::Integer.new)
-
-      result = @connection.exec_query(
-        'SELECT id, data FROM ex WHERE id = ?', nil, [bind])
-
-      assert_equal 1, result.rows.length
-      assert_equal 2, result.columns.length
-
-      assert_equal [[1, 'foo']], result.rows
-    end
-  end
-
-  # Test that MySQL allows multiple results for stored procedures
-  if defined?(Mysql) && Mysql.const_defined?(:CLIENT_MULTI_RESULTS)
-    def test_multi_results
-      rows = ActiveRecord::Base.connection.select_rows('CALL ten();')
-      assert_equal 10, rows[0][0].to_i, "ten() did not return 10 as expected: #{rows.inspect}"
-      assert @connection.active?, "Bad connection use by 'MysqlAdapter.select_rows'"
-    end
-  end
-
-  def test_mysql_connection_collation_is_configured
-    assert_equal 'utf8_unicode_ci', @connection.show_variable('collation_connection')
-    assert_equal 'utf8_general_ci', ARUnit2Model.connection.show_variable('collation_connection')
-  end
-
-  def test_mysql_default_in_strict_mode
-    result = @connection.exec_query "SELECT @@SESSION.sql_mode"
-    assert_equal [["STRICT_ALL_TABLES"]], result.rows
-  end
-
-  def test_mysql_strict_mode_disabled
-    run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.merge({:strict => false}))
-      result = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.sql_mode"
-      assert_equal [['']], result.rows
-    end
-  end
-
-  def test_mysql_strict_mode_specified_default
-    run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.merge({strict: :default}))
-      global_sql_mode = ActiveRecord::Base.connection.exec_query "SELECT @@GLOBAL.sql_mode"
-      session_sql_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.sql_mode"
-      assert_equal global_sql_mode.rows, session_sql_mode.rows
-    end
-  end
-
-  def test_mysql_set_session_variable
-    run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => 3}}))
-      session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
-      assert_equal 3, session_mode.rows.first.first.to_i
-    end
-  end
-
-  def test_mysql_sql_mode_variable_overrides_strict_mode
-    run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { 'sql_mode' => 'ansi' }))
-      result = ActiveRecord::Base.connection.exec_query 'SELECT @@SESSION.sql_mode'
-      assert_not_equal [['STRICT_ALL_TABLES']], result.rows
-    end
-  end
-
-  def test_mysql_set_session_variable_to_default
-    run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => :default}}))
-      global_mode = ActiveRecord::Base.connection.exec_query "SELECT @@GLOBAL.DEFAULT_WEEK_FORMAT"
-      session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
-      assert_equal global_mode.rows, session_mode.rows
-    end
-  end
-
-  private
-
-  def with_example_table(&block)
-    definition ||= <<-SQL
-      `id` int(11) auto_increment PRIMARY KEY,
-      `data` varchar(255)
-    SQL
-    super(@connection, 'ex', definition, &block)
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/consistency_test.rb b/activerecord/test/cases/adapters/mysql/consistency_test.rb
deleted file mode 100644
index 743f6436e4..0000000000
--- a/activerecord/test/cases/adapters/mysql/consistency_test.rb
+++ /dev/null
@@ -1,49 +0,0 @@
-require "cases/helper"
-
-class MysqlConsistencyTest < ActiveRecord::MysqlTestCase
-  self.use_transactional_tests = false
-
-  class Consistency < ActiveRecord::Base
-    self.table_name = "mysql_consistency"
-  end
-
-  setup do
-    @old_emulate_booleans = ActiveRecord::ConnectionAdapters::MysqlAdapter.emulate_booleans
-    ActiveRecord::ConnectionAdapters::MysqlAdapter.emulate_booleans = false
-
-    @connection = ActiveRecord::Base.connection
-    @connection.clear_cache!
-    @connection.create_table("mysql_consistency") do |t|
-      t.boolean "a_bool"
-      t.string "a_string"
-    end
-    Consistency.reset_column_information
-    Consistency.create!
-  end
-
-  teardown do
-    ActiveRecord::ConnectionAdapters::MysqlAdapter.emulate_booleans = @old_emulate_booleans
-    @connection.drop_table "mysql_consistency"
-  end
-
-  test "boolean columns with random value type cast to 0 when emulate_booleans is false" do
-    with_new = Consistency.new
-    with_last = Consistency.last
-    with_new.a_bool = 'wibble'
-    with_last.a_bool = 'wibble'
-
-    assert_equal 0, with_new.a_bool
-    assert_equal 0, with_last.a_bool
-  end
-
-  test "string columns call #to_s" do
-    with_new = Consistency.new
-    with_last = Consistency.last
-    thing = Object.new
-    with_new.a_string = thing
-    with_last.a_string = thing
-
-    assert_equal thing.to_s, with_new.a_string
-    assert_equal thing.to_s, with_last.a_string
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/enum_test.rb b/activerecord/test/cases/adapters/mysql/enum_test.rb
deleted file mode 100644
index ef8ee0a6e3..0000000000
--- a/activerecord/test/cases/adapters/mysql/enum_test.rb
+++ /dev/null
@@ -1,10 +0,0 @@
-require "cases/helper"
-
-class MysqlEnumTest < ActiveRecord::MysqlTestCase
-  class EnumTest < ActiveRecord::Base
-  end
-
-  def test_enum_limit
-    assert_equal 6, EnumTest.columns.first.limit
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb b/activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb
deleted file mode 100644
index b804cb45b9..0000000000
--- a/activerecord/test/cases/adapters/mysql/mysql_adapter_test.rb
+++ /dev/null
@@ -1,152 +0,0 @@
-
-require "cases/helper"
-require 'support/ddl_helper'
-
-module ActiveRecord
-  module ConnectionAdapters
-    class MysqlAdapterTest < ActiveRecord::MysqlTestCase
-      include DdlHelper
-
-      def setup
-        @conn = ActiveRecord::Base.connection
-      end
-
-      def test_bad_connection_mysql
-        assert_raise ActiveRecord::NoDatabaseError do
-          configuration = ActiveRecord::Base.configurations['arunit'].merge(database: 'inexistent_activerecord_unittest')
-          connection = ActiveRecord::Base.mysql_connection(configuration)
-          connection.drop_table 'ex', if_exists: true
-        end
-      end
-
-      def test_valid_column
-        with_example_table do
-          column = @conn.columns('ex').find { |col| col.name == 'id' }
-          assert @conn.valid_type?(column.type)
-        end
-      end
-
-      def test_invalid_column
-        assert_not @conn.valid_type?(:foobar)
-      end
-
-      def test_client_encoding
-        assert_equal Encoding::UTF_8, @conn.client_encoding
-      end
-
-      def test_exec_insert_number
-        with_example_table do
-          insert(@conn, 'number' => 10)
-
-          result = @conn.exec_query('SELECT number FROM ex WHERE number = 10')
-
-          assert_equal 1, result.rows.length
-          # if there are no bind parameters, it will return a string (due to
-          # the libmysql api)
-          assert_equal '10', result.rows.last.last
-        end
-      end
-
-      def test_exec_insert_string
-        with_example_table do
-          str = 'いただきます！'
-          insert(@conn, 'number' => 10, 'data' => str)
-
-          result = @conn.exec_query('SELECT number, data FROM ex WHERE number = 10')
-
-          value = result.rows.last.last
-
-          # FIXME: this should probably be inside the mysql AR adapter?
-          value.force_encoding(@conn.client_encoding)
-
-          # The strings in this file are utf-8, so transcode to utf-8
-          value.encode!(Encoding::UTF_8)
-
-          assert_equal str, value
-        end
-      end
-
-      def test_tables_quoting
-        @conn.tables(nil, "foo-bar", nil)
-        flunk
-      rescue => e
-        # assertion for *quoted* database properly
-        assert_match(/database 'foo-bar'/, e.inspect)
-      end
-
-      def test_pk_and_sequence_for
-        with_example_table do
-          pk, seq = @conn.pk_and_sequence_for('ex')
-          assert_equal 'id', pk
-          assert_equal @conn.default_sequence_name('ex', 'id'), seq
-        end
-      end
-
-      def test_pk_and_sequence_for_with_non_standard_primary_key
-        with_example_table '`code` INT(11) auto_increment, PRIMARY KEY (`code`)' do
-          pk, seq = @conn.pk_and_sequence_for('ex')
-          assert_equal 'code', pk
-          assert_equal @conn.default_sequence_name('ex', 'code'), seq
-        end
-      end
-
-      def test_pk_and_sequence_for_with_custom_index_type_pk
-        with_example_table '`id` INT(11) auto_increment, PRIMARY KEY USING BTREE (`id`)' do
-          pk, seq = @conn.pk_and_sequence_for('ex')
-          assert_equal 'id', pk
-          assert_equal @conn.default_sequence_name('ex', 'id'), seq
-        end
-      end
-
-      def test_composite_primary_key
-        with_example_table '`id` INT(11), `number` INT(11), foo INT(11), PRIMARY KEY (`id`, `number`)' do
-          assert_nil @conn.primary_key('ex')
-        end
-      end
-
-      def test_tinyint_integer_typecasting
-        with_example_table '`status` TINYINT(4)' do
-          insert(@conn, { 'status' => 2 }, 'ex')
-
-          result = @conn.exec_query('SELECT status FROM ex')
-
-          assert_equal 2, result.column_types['status'].deserialize(result.last['status'])
-        end
-      end
-
-      def test_supports_extensions
-        assert_not @conn.supports_extensions?, 'does not support extensions'
-      end
-
-      def test_respond_to_enable_extension
-        assert @conn.respond_to?(:enable_extension)
-      end
-
-      def test_respond_to_disable_extension
-        assert @conn.respond_to?(:disable_extension)
-      end
-
-      private
-      def insert(ctx, data, table='ex')
-        binds = data.map { |name, value|
-          Relation::QueryAttribute.new(name, value, Type::Value.new)
-        }
-        columns = binds.map(&:name)
-
-        sql = "INSERT INTO #{table} (#{columns.join(", ")})
-               VALUES (#{(['?'] * columns.length).join(', ')})"
-
-        ctx.exec_insert(sql, 'SQL', binds)
-      end
-
-      def with_example_table(definition = nil, &block)
-        definition ||= <<-SQL
-          `id` int(11) auto_increment PRIMARY KEY,
-          `number` integer,
-          `data` varchar(255)
-        SQL
-        super(@conn, 'ex', definition, &block)
-      end
-    end
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/quoting_test.rb b/activerecord/test/cases/adapters/mysql/quoting_test.rb
deleted file mode 100644
index a296cf9d31..0000000000
--- a/activerecord/test/cases/adapters/mysql/quoting_test.rb
+++ /dev/null
@@ -1,15 +0,0 @@
-require "cases/helper"
-
-class MysqlQuotingTest < ActiveRecord::MysqlTestCase
-  def setup
-    @conn = ActiveRecord::Base.connection
-  end
-
-  def test_type_cast_true
-    assert_equal 1, @conn.type_cast(true)
-  end
-
-  def test_type_cast_false
-    assert_equal 0, @conn.type_cast(false)
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/reserved_word_test.rb b/activerecord/test/cases/adapters/mysql/reserved_word_test.rb
deleted file mode 100644
index 4ea1d9ad36..0000000000
--- a/activerecord/test/cases/adapters/mysql/reserved_word_test.rb
+++ /dev/null
@@ -1,153 +0,0 @@
-require "cases/helper"
-
-# a suite of tests to ensure the ConnectionAdapters#MysqlAdapter can handle tables with
-# reserved word names (ie: group, order, values, etc...)
-class MysqlReservedWordTest < ActiveRecord::MysqlTestCase
-  class Group < ActiveRecord::Base
-    Group.table_name = 'group'
-    belongs_to :select
-    has_one :values
-  end
-
-  class Select < ActiveRecord::Base
-    Select.table_name = 'select'
-    has_many :groups
-  end
-
-  class Values < ActiveRecord::Base
-    Values.table_name = 'values'
-  end
-
-  class Distinct < ActiveRecord::Base
-    Distinct.table_name = 'distinct'
-    has_and_belongs_to_many :selects
-    has_many :values, :through => :groups
-  end
-
-  def setup
-    @connection = ActiveRecord::Base.connection
-
-    # we call execute directly here (and do similar below) because ActiveRecord::Base#create_table()
-    # will fail with these table names if these test cases fail
-
-    create_tables_directly 'group'=>'id int auto_increment primary key, `order` varchar(255), select_id int',
-      'select'=>'id int auto_increment primary key',
-      'values'=>'id int auto_increment primary key, group_id int',
-      'distinct'=>'id int auto_increment primary key',
-      'distinct_select'=>'distinct_id int, select_id int'
-  end
-
-  teardown do
-    drop_tables_directly ['group', 'select', 'values', 'distinct', 'distinct_select', 'order']
-  end
-
-  # create tables with reserved-word names and columns
-  def test_create_tables
-    assert_nothing_raised {
-      @connection.create_table :order do |t|
-        t.column :group, :string
-      end
-    }
-  end
-
-  # rename tables with reserved-word names
-  def test_rename_tables
-    assert_nothing_raised { @connection.rename_table(:group, :order) }
-  end
-
-  # alter column with a reserved-word name in a table with a reserved-word name
-  def test_change_columns
-    assert_nothing_raised { @connection.change_column_default(:group, :order, 'whatever') }
-    #the quoting here will reveal any double quoting issues in change_column's interaction with the column method in the adapter
-    assert_nothing_raised { @connection.change_column('group', 'order', :Int, :default => 0) }
-    assert_nothing_raised { @connection.rename_column(:group, :order, :values) }
-  end
-
-  # introspect table with reserved word name
-  def test_introspect
-    assert_nothing_raised { @connection.columns(:group) }
-    assert_nothing_raised { @connection.indexes(:group) }
-  end
-
-  #fixtures
-  self.use_instantiated_fixtures = true
-  self.use_transactional_tests = false
-
-  #activerecord model class with reserved-word table name
-  def test_activerecord_model
-    create_test_fixtures :select, :distinct, :group, :values, :distinct_select
-    x = nil
-    assert_nothing_raised { x = Group.new }
-    x.order = 'x'
-    assert_nothing_raised { x.save }
-    x.order = 'y'
-    assert_nothing_raised { x.save }
-    assert_nothing_raised { Group.find_by_order('y') }
-    assert_nothing_raised { Group.find(1) }
-    Group.find(1)
-  end
-
-  # has_one association with reserved-word table name
-  def test_has_one_associations
-    create_test_fixtures :select, :distinct, :group, :values, :distinct_select
-    v = nil
-    assert_nothing_raised { v = Group.find(1).values }
-    assert_equal 2, v.id
-  end
-
-  # belongs_to association with reserved-word table name
-  def test_belongs_to_associations
-    create_test_fixtures :select, :distinct, :group, :values, :distinct_select
-    gs = nil
-    assert_nothing_raised { gs = Select.find(2).groups }
-    assert_equal gs.length, 2
-    assert(gs.collect(&:id).sort == [2, 3])
-  end
-
-  # has_and_belongs_to_many with reserved-word table name
-  def test_has_and_belongs_to_many
-    create_test_fixtures :select, :distinct, :group, :values, :distinct_select
-    s = nil
-    assert_nothing_raised { s = Distinct.find(1).selects }
-    assert_equal s.length, 2
-    assert(s.collect(&:id).sort == [1, 2])
-  end
-
-  # activerecord model introspection with reserved-word table and column names
-  def test_activerecord_introspection
-    assert_nothing_raised { Group.table_exists? }
-    assert_nothing_raised { Group.columns }
-  end
-
-  # Calculations
-  def test_calculations_work_with_reserved_words
-    assert_nothing_raised { Group.count }
-  end
-
-  def test_associations_work_with_reserved_words
-    assert_nothing_raised { Select.all.merge!(:includes => [:groups]).to_a }
-  end
-
-  #the following functions were added to DRY test cases
-
-  private
-  # custom fixture loader, uses FixtureSet#create_fixtures and appends base_path to the current file's path
-  def create_test_fixtures(*fixture_names)
-    ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT + "/reserved_words", fixture_names)
-  end
-
-  # custom drop table, uses execute on connection to drop a table if it exists. note: escapes table_name
-  def drop_tables_directly(table_names, connection = @connection)
-    table_names.each do |name|
-      connection.drop_table name, if_exists: true
-    end
-  end
-
-  # custom create table, uses execute on connection to create a table, note: escapes table_name, does NOT escape columns
-  def create_tables_directly (tables, connection = @connection)
-    tables.each do |table_name, column_properties|
-      connection.execute("CREATE TABLE `#{table_name}` ( #{column_properties} )")
-    end
-  end
-
-end
diff --git a/activerecord/test/cases/adapters/mysql/schema_test.rb b/activerecord/test/cases/adapters/mysql/schema_test.rb
deleted file mode 100644
index 2e18f609fd..0000000000
--- a/activerecord/test/cases/adapters/mysql/schema_test.rb
+++ /dev/null
@@ -1,100 +0,0 @@
-require "cases/helper"
-require 'models/post'
-require 'models/comment'
-
-module ActiveRecord
-  module ConnectionAdapters
-    class MysqlSchemaTest < ActiveRecord::MysqlTestCase
-      fixtures :posts
-
-      def setup
-        @connection = ActiveRecord::Base.connection
-        db          = Post.connection_pool.spec.config[:database]
-        table       = Post.table_name
-        @db_name    = db
-
-        @omgpost = Class.new(ActiveRecord::Base) do
-          self.table_name = "#{db}.#{table}"
-          def self.name; 'Post'; end
-        end
-
-        @connection.create_table "mysql_doubles"
-      end
-
-      teardown do
-        @connection.drop_table "mysql_doubles", if_exists: true
-      end
-
-      class MysqlDouble < ActiveRecord::Base
-        self.table_name = "mysql_doubles"
-      end
-
-      def test_float_limits
-        @connection.add_column :mysql_doubles, :float_no_limit, :float
-        @connection.add_column :mysql_doubles, :float_short, :float, limit: 5
-        @connection.add_column :mysql_doubles, :float_long, :float, limit: 53
-
-        @connection.add_column :mysql_doubles, :float_23, :float, limit: 23
-        @connection.add_column :mysql_doubles, :float_24, :float, limit: 24
-        @connection.add_column :mysql_doubles, :float_25, :float, limit: 25
-        MysqlDouble.reset_column_information
-
-        column_no_limit = MysqlDouble.columns.find { |c| c.name == 'float_no_limit' }
-        column_short = MysqlDouble.columns.find { |c| c.name == 'float_short' }
-        column_long = MysqlDouble.columns.find { |c| c.name == 'float_long' }
-
-        column_23 = MysqlDouble.columns.find { |c| c.name == 'float_23' }
-        column_24 = MysqlDouble.columns.find { |c| c.name == 'float_24' }
-        column_25 = MysqlDouble.columns.find { |c| c.name == 'float_25' }
-
-        # Mysql floats are precision 0..24, Mysql doubles are precision 25..53
-        assert_equal 24, column_no_limit.limit
-        assert_equal 24, column_short.limit
-        assert_equal 53, column_long.limit
-
-        assert_equal 24, column_23.limit
-        assert_equal 24, column_24.limit
-        assert_equal 53, column_25.limit
-      end
-
-      def test_schema
-        assert @omgpost.first
-      end
-
-      def test_primary_key
-        assert_equal 'id', @omgpost.primary_key
-      end
-
-      def test_table_exists?
-        name = @omgpost.table_name
-        assert @connection.table_exists?(name), "#{name} table should exist"
-      end
-
-      def test_table_exists_wrong_schema
-        assert(!@connection.table_exists?("#{@db_name}.zomg"), "table should not exist")
-      end
-
-      def test_dump_indexes
-        index_a_name = 'index_key_tests_on_snack'
-        index_b_name = 'index_key_tests_on_pizza'
-        index_c_name = 'index_key_tests_on_awesome'
-
-        table = 'key_tests'
-
-        indexes = @connection.indexes(table).sort_by(&:name)
-        assert_equal 3,indexes.size
-
-        index_a = indexes.select{|i| i.name == index_a_name}[0]
-        index_b = indexes.select{|i| i.name == index_b_name}[0]
-        index_c = indexes.select{|i| i.name == index_c_name}[0]
-        assert_equal :btree, index_a.using
-        assert_nil index_a.type
-        assert_equal :btree, index_b.using
-        assert_nil index_b.type
-
-        assert_nil index_c.using
-        assert_equal :fulltext, index_c.type
-      end
-    end
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/sp_test.rb b/activerecord/test/cases/adapters/mysql/sp_test.rb
deleted file mode 100644
index a3d5110032..0000000000
--- a/activerecord/test/cases/adapters/mysql/sp_test.rb
+++ /dev/null
@@ -1,15 +0,0 @@
-require "cases/helper"
-require 'models/topic'
-
-class StoredProcedureTest < ActiveRecord::MysqlTestCase
-  fixtures :topics
-
-  # Test that MySQL allows multiple results for stored procedures
-  if defined?(Mysql) && Mysql.const_defined?(:CLIENT_MULTI_RESULTS)
-    def test_multi_results_from_find_by_sql
-      topics = Topic.find_by_sql 'CALL topics();'
-      assert_equal 1, topics.size
-      assert ActiveRecord::Base.connection.active?, "Bad connection use by 'MysqlAdapter.select'"
-    end
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/sql_types_test.rb b/activerecord/test/cases/adapters/mysql/sql_types_test.rb
deleted file mode 100644
index 25b28de7f0..0000000000
--- a/activerecord/test/cases/adapters/mysql/sql_types_test.rb
+++ /dev/null
@@ -1,14 +0,0 @@
-require "cases/helper"
-
-class MysqlSqlTypesTest < ActiveRecord::MysqlTestCase
-  def test_binary_types
-    assert_equal 'varbinary(64)', type_to_sql(:binary, 64)
-    assert_equal 'varbinary(4095)', type_to_sql(:binary, 4095)
-    assert_equal 'blob(4096)', type_to_sql(:binary, 4096)
-    assert_equal 'blob', type_to_sql(:binary)
-  end
-
-  def type_to_sql(*args)
-    ActiveRecord::Base.connection.type_to_sql(*args)
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/statement_pool_test.rb b/activerecord/test/cases/adapters/mysql/statement_pool_test.rb
deleted file mode 100644
index 6be36566de..0000000000
--- a/activerecord/test/cases/adapters/mysql/statement_pool_test.rb
+++ /dev/null
@@ -1,19 +0,0 @@
-require 'cases/helper'
-
-class MysqlStatementPoolTest < ActiveRecord::MysqlTestCase
-  if Process.respond_to?(:fork)
-    def test_cache_is_per_pid
-      cache = ActiveRecord::ConnectionAdapters::MysqlAdapter::StatementPool.new nil, 10
-      cache['foo'] = 'bar'
-      assert_equal 'bar', cache['foo']
-
-      pid = fork {
-        lookup = cache['foo'];
-        exit!(!lookup)
-      }
-
-      Process.waitpid pid
-      assert $?.success?, 'process should exit successfully'
-    end
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/table_options_test.rb b/activerecord/test/cases/adapters/mysql/table_options_test.rb
deleted file mode 100644
index 99df6d6cba..0000000000
--- a/activerecord/test/cases/adapters/mysql/table_options_test.rb
+++ /dev/null
@@ -1,42 +0,0 @@
-require "cases/helper"
-require 'support/schema_dumping_helper'
-
-class MysqlTableOptionsTest < ActiveRecord::MysqlTestCase
-  include SchemaDumpingHelper
-
-  def setup
-    @connection = ActiveRecord::Base.connection
-  end
-
-  def teardown
-    @connection.drop_table "mysql_table_options", if_exists: true
-  end
-
-  test "table options with ENGINE" do
-    @connection.create_table "mysql_table_options", force: true, options: "ENGINE=MyISAM"
-    output = dump_table_schema("mysql_table_options")
-    options = %r{create_table "mysql_table_options", force: :cascade, options: "(?<options>.*)"}.match(output)[:options]
-    assert_match %r{ENGINE=MyISAM}, options
-  end
-
-  test "table options with ROW_FORMAT" do
-    @connection.create_table "mysql_table_options", force: true, options: "ROW_FORMAT=REDUNDANT"
-    output = dump_table_schema("mysql_table_options")
-    options = %r{create_table "mysql_table_options", force: :cascade, options: "(?<options>.*)"}.match(output)[:options]
-    assert_match %r{ROW_FORMAT=REDUNDANT}, options
-  end
-
-  test "table options with CHARSET" do
-    @connection.create_table "mysql_table_options", force: true, options: "CHARSET=utf8mb4"
-    output = dump_table_schema("mysql_table_options")
-    options = %r{create_table "mysql_table_options", force: :cascade, options: "(?<options>.*)"}.match(output)[:options]
-    assert_match %r{CHARSET=utf8mb4}, options
-  end
-
-  test "table options with COLLATE" do
-    @connection.create_table "mysql_table_options", force: true, options: "COLLATE=utf8mb4_bin"
-    output = dump_table_schema("mysql_table_options")
-    options = %r{create_table "mysql_table_options", force: :cascade, options: "(?<options>.*)"}.match(output)[:options]
-    assert_match %r{COLLATE=utf8mb4_bin}, options
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql/unsigned_type_test.rb b/activerecord/test/cases/adapters/mysql/unsigned_type_test.rb
deleted file mode 100644
index ed9398a918..0000000000
--- a/activerecord/test/cases/adapters/mysql/unsigned_type_test.rb
+++ /dev/null
@@ -1,30 +0,0 @@
-require "cases/helper"
-
-class MysqlUnsignedTypeTest < ActiveRecord::MysqlTestCase
-  self.use_transactional_tests = false
-
-  class UnsignedType < ActiveRecord::Base
-  end
-
-  setup do
-    @connection = ActiveRecord::Base.connection
-    @connection.create_table("unsigned_types", force: true) do |t|
-      t.column :unsigned_integer, "int unsigned"
-    end
-  end
-
-  teardown do
-    @connection.drop_table "unsigned_types"
-  end
-
-  test "unsigned int max value is in range" do
-    assert expected = UnsignedType.create(unsigned_integer: 4294967295)
-    assert_equal expected, UnsignedType.find_by(unsigned_integer: 4294967295)
-  end
-
-  test "minus value is out of range" do
-    assert_raise(RangeError) do
-      UnsignedType.create(unsigned_integer: -10)
-    end
-  end
-end
diff --git a/activerecord/test/cases/adapters/mysql2/active_schema_test.rb b/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
index 6558d60aa1..261fee13eb 100644
--- a/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/active_schema_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
+require "support/connection_helper"
 
 class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
   include ConnectionHelper
@@ -7,7 +9,7 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
   def setup
     ActiveRecord::Base.connection.singleton_class.class_eval do
       alias_method :execute_without_stub, :execute
-      def execute(sql, name = nil) return sql end
+      def execute(sql, name = nil) sql end
     end
   end
 
@@ -16,61 +18,64 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_add_index
-    # add_index calls table_exists? and index_name_exists? which can't work since execute is stubbed
-    def (ActiveRecord::Base.connection).table_exists?(*); true; end
+    # add_index calls data_source_exists? and index_name_exists? which can't work since execute is stubbed
+    def (ActiveRecord::Base.connection).data_source_exists?(*); true; end
     def (ActiveRecord::Base.connection).index_name_exists?(*); false; end
 
     expected = "CREATE  INDEX `index_people_on_last_name`  ON `people` (`last_name`) "
-    assert_equal expected, add_index(:people, :last_name, :length => nil)
+    assert_equal expected, add_index(:people, :last_name, length: nil)
 
     expected = "CREATE  INDEX `index_people_on_last_name`  ON `people` (`last_name`(10)) "
-    assert_equal expected, add_index(:people, :last_name, :length => 10)
+    assert_equal expected, add_index(:people, :last_name, length: 10)
 
     expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`(15)) "
-    assert_equal expected, add_index(:people, [:last_name, :first_name], :length => 15)
+    assert_equal expected, add_index(:people, [:last_name, :first_name], length: 15)
+    assert_equal expected, add_index(:people, ["last_name", "first_name"], length: 15)
 
     expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`) "
-    assert_equal expected, add_index(:people, [:last_name, :first_name], :length => {:last_name => 15})
+    assert_equal expected, add_index(:people, [:last_name, :first_name], length: { last_name: 15 })
+    assert_equal expected, add_index(:people, ["last_name", "first_name"], length: { last_name: 15 })
 
     expected = "CREATE  INDEX `index_people_on_last_name_and_first_name`  ON `people` (`last_name`(15), `first_name`(10)) "
-    assert_equal expected, add_index(:people, [:last_name, :first_name], :length => {:last_name => 15, :first_name => 10})
+    assert_equal expected, add_index(:people, [:last_name, :first_name], length: { last_name: 15, first_name: 10 })
+    assert_equal expected, add_index(:people, ["last_name", :first_name], length: { last_name: 15, "first_name" => 10 })
 
     %w(SPATIAL FULLTEXT UNIQUE).each do |type|
       expected = "CREATE #{type} INDEX `index_people_on_last_name`  ON `people` (`last_name`) "
-      assert_equal expected, add_index(:people, :last_name, :type => type)
+      assert_equal expected, add_index(:people, :last_name, type: type)
     end
 
     %w(btree hash).each do |using|
       expected = "CREATE  INDEX `index_people_on_last_name` USING #{using} ON `people` (`last_name`) "
-      assert_equal expected, add_index(:people, :last_name, :using => using)
+      assert_equal expected, add_index(:people, :last_name, using: using)
     end
 
     expected = "CREATE  INDEX `index_people_on_last_name` USING btree ON `people` (`last_name`(10)) "
-    assert_equal expected, add_index(:people, :last_name, :length => 10, :using => :btree)
+    assert_equal expected, add_index(:people, :last_name, length: 10, using: :btree)
 
     expected = "CREATE  INDEX `index_people_on_last_name` USING btree ON `people` (`last_name`(10)) ALGORITHM = COPY"
-    assert_equal expected, add_index(:people, :last_name, :length => 10, using: :btree, algorithm: :copy)
+    assert_equal expected, add_index(:people, :last_name, length: 10, using: :btree, algorithm: :copy)
 
     assert_raise ArgumentError do
       add_index(:people, :last_name, algorithm: :coyp)
     end
 
     expected = "CREATE  INDEX `index_people_on_last_name_and_first_name` USING btree ON `people` (`last_name`(15), `first_name`(15)) "
-    assert_equal expected, add_index(:people, [:last_name, :first_name], :length => 15, :using => :btree)
+    assert_equal expected, add_index(:people, [:last_name, :first_name], length: 15, using: :btree)
   end
 
   def test_index_in_create
-    def (ActiveRecord::Base.connection).table_exists?(*); false; end
+    def (ActiveRecord::Base.connection).data_source_exists?(*); false; end
 
     %w(SPATIAL FULLTEXT UNIQUE).each do |type|
-      expected = "CREATE TABLE `people` (#{type} INDEX `index_people_on_last_name`  (`last_name`) ) ENGINE=InnoDB"
+      expected = "CREATE TABLE `people` (#{type} INDEX `index_people_on_last_name`  (`last_name`))"
       actual = ActiveRecord::Base.connection.create_table(:people, id: false) do |t|
         t.index :last_name, type: type
       end
       assert_equal expected, actual
     end
 
-    expected = "CREATE TABLE `people` ( INDEX `index_people_on_last_name` USING btree (`last_name`(10)) ) ENGINE=InnoDB"
+    expected = "CREATE TABLE `people` ( INDEX `index_people_on_last_name` USING btree (`last_name`(10)))"
     actual = ActiveRecord::Base.connection.create_table(:people, id: false) do |t|
       t.index :last_name, length: 10, using: :btree
     end
@@ -78,7 +83,7 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_index_in_bulk_change
-    def (ActiveRecord::Base.connection).table_exists?(*); true; end
+    def (ActiveRecord::Base.connection).data_source_exists?(*); true; end
     def (ActiveRecord::Base.connection).index_name_exists?(*); false; end
 
     %w(SPATIAL FULLTEXT UNIQUE).each do |type|
@@ -89,8 +94,8 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
       assert_equal expected, actual
     end
 
-    expected = "ALTER TABLE `peaple` ADD  INDEX `index_peaple_on_last_name` USING btree (`last_name`(10)), ALGORITHM = COPY"
-    actual = ActiveRecord::Base.connection.change_table(:peaple, bulk: true) do |t|
+    expected = "ALTER TABLE `people` ADD  INDEX `index_people_on_last_name` USING btree (`last_name`(10)), ALGORITHM = COPY"
+    actual = ActiveRecord::Base.connection.change_table(:people, bulk: true) do |t|
       t.index :last_name, length: 10, using: :btree, algorithm: :copy
     end
     assert_equal expected, actual
@@ -100,17 +105,15 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
     assert_equal "DROP TABLE `people`", drop_table(:people)
   end
 
-  if current_adapter?(:Mysql2Adapter)
-    def test_create_mysql_database_with_encoding
-      assert_equal "CREATE DATABASE `matt` DEFAULT CHARACTER SET `utf8`", create_database(:matt)
-      assert_equal "CREATE DATABASE `aimonetti` DEFAULT CHARACTER SET `latin1`", create_database(:aimonetti, {:charset => 'latin1'})
-      assert_equal "CREATE DATABASE `matt_aimonetti` DEFAULT CHARACTER SET `big5` COLLATE `big5_chinese_ci`", create_database(:matt_aimonetti, {:charset => :big5, :collation => :big5_chinese_ci})
-    end
+  def test_create_mysql_database_with_encoding
+    assert_equal "CREATE DATABASE `matt` DEFAULT CHARACTER SET `utf8mb4`", create_database(:matt)
+    assert_equal "CREATE DATABASE `aimonetti` DEFAULT CHARACTER SET `latin1`", create_database(:aimonetti, charset: "latin1")
+    assert_equal "CREATE DATABASE `matt_aimonetti` DEFAULT COLLATE `utf8mb4_bin`", create_database(:matt_aimonetti, collation: "utf8mb4_bin")
+  end
 
-    def test_recreate_mysql_database_with_encoding
-      create_database(:luca, {:charset => 'latin1'})
-      assert_equal "CREATE DATABASE `luca` DEFAULT CHARACTER SET `latin1`", recreate_database(:luca, {:charset => 'latin1'})
-    end
+  def test_recreate_mysql_database_with_encoding
+    create_database(:luca, charset: "latin1")
+    assert_equal "CREATE DATABASE `luca` DEFAULT CHARACTER SET `latin1`", recreate_database(:luca, charset: "latin1")
   end
 
   def test_add_column
@@ -118,11 +121,11 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_add_column_with_limit
-    assert_equal "ALTER TABLE `people` ADD `key` varchar(32)", add_column(:people, :key, :string, :limit => 32)
+    assert_equal "ALTER TABLE `people` ADD `key` varchar(32)", add_column(:people, :key, :string, limit: 32)
   end
 
   def test_drop_table_with_specific_database
-    assert_equal "DROP TABLE `otherdb`.`people`", drop_table('otherdb.people')
+    assert_equal "DROP TABLE `otherdb`.`people`", drop_table("otherdb.people")
   end
 
   def test_add_timestamps
@@ -130,8 +133,8 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
       begin
         ActiveRecord::Base.connection.create_table :delete_me
         ActiveRecord::Base.connection.add_timestamps :delete_me, null: true
-        assert column_present?('delete_me', 'updated_at', 'datetime')
-        assert column_present?('delete_me', 'created_at', 'datetime')
+        assert column_present?("delete_me", "updated_at", "datetime")
+        assert column_present?("delete_me", "created_at", "datetime")
       ensure
         ActiveRecord::Base.connection.drop_table :delete_me rescue nil
       end
@@ -144,9 +147,9 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
         ActiveRecord::Base.connection.create_table :delete_me do |t|
           t.timestamps null: true
         end
-        ActiveRecord::Base.connection.remove_timestamps :delete_me, { null: true }
-        assert !column_present?('delete_me', 'updated_at', 'datetime')
-        assert !column_present?('delete_me', 'created_at', 'datetime')
+        ActiveRecord::Base.connection.remove_timestamps :delete_me, null: true
+        assert_not column_present?("delete_me", "updated_at", "datetime")
+        assert_not column_present?("delete_me", "created_at", "datetime")
       ensure
         ActiveRecord::Base.connection.drop_table :delete_me rescue nil
       end
@@ -154,15 +157,19 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_indexes_in_create
-    ActiveRecord::Base.connection.stubs(:table_exists?).with(:temp).returns(false)
-    ActiveRecord::Base.connection.stubs(:index_name_exists?).with(:index_temp_on_zip).returns(false)
+    assert_called_with(
+      ActiveRecord::Base.connection,
+      :data_source_exists?,
+      [:temp],
+      returns: false
+    ) do
+      expected = "CREATE TEMPORARY TABLE `temp` ( INDEX `index_temp_on_zip`  (`zip`)) AS SELECT id, name, zip FROM a_really_complicated_query"
+      actual = ActiveRecord::Base.connection.create_table(:temp, temporary: true, as: "SELECT id, name, zip FROM a_really_complicated_query") do |t|
+        t.index :zip
+      end
 
-    expected = "CREATE TEMPORARY TABLE `temp` ( INDEX `index_temp_on_zip`  (`zip`) ) ENGINE=InnoDB AS SELECT id, name, zip FROM a_really_complicated_query"
-    actual = ActiveRecord::Base.connection.create_table(:temp, temporary: true, as: "SELECT id, name, zip FROM a_really_complicated_query") do |t|
-      t.index :zip
+      assert_equal expected, actual
     end
-
-    assert_equal expected, actual
   end
 
   private
@@ -187,6 +194,6 @@ class Mysql2ActiveSchemaTest < ActiveRecord::Mysql2TestCase
 
     def column_present?(table_name, column_name, type)
       results = ActiveRecord::Base.connection.select_all("SHOW FIELDS FROM #{table_name} LIKE '#{column_name}'")
-      results.first && results.first['Type'] == type
+      results.first && results.first["Type"] == type
     end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/auto_increment_test.rb b/activerecord/test/cases/adapters/mysql2/auto_increment_test.rb
new file mode 100644
index 0000000000..4c67633946
--- /dev/null
+++ b/activerecord/test/cases/adapters/mysql2/auto_increment_test.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/schema_dumping_helper"
+
+class Mysql2AutoIncrementTest < ActiveRecord::Mysql2TestCase
+  include SchemaDumpingHelper
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+  end
+
+  def teardown
+    @connection.drop_table :auto_increments, if_exists: true
+  end
+
+  def test_auto_increment_without_primary_key
+    @connection.create_table :auto_increments, id: false, force: true do |t|
+      t.integer :id, null: false, auto_increment: true
+      t.index :id
+    end
+    output = dump_table_schema("auto_increments")
+    assert_match(/t\.integer\s+"id",\s+null: false,\s+auto_increment: true$/, output)
+  end
+
+  def test_auto_increment_with_composite_primary_key
+    @connection.create_table :auto_increments, primary_key: [:id, :created_at], force: true do |t|
+      t.integer :id, null: false, auto_increment: true
+      t.datetime :created_at, null: false
+    end
+    output = dump_table_schema("auto_increments")
+    assert_match(/t\.integer\s+"id",\s+null: false,\s+auto_increment: true$/, output)
+  end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/bind_parameter_test.rb b/activerecord/test/cases/adapters/mysql2/bind_parameter_test.rb
index abdf3dbf5b..825bddfb73 100644
--- a/activerecord/test/cases/adapters/mysql2/bind_parameter_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/bind_parameter_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
+require "models/topic"
 
 module ActiveRecord
   module ConnectionAdapters
@@ -20,7 +22,7 @@ module ActiveRecord
 
         def test_create_question_marks
           str = "foo?bar"
-          x   = Topic.create!(:title => str, :content => str)
+          x   = Topic.create!(title: str, content: str)
           x.reload
           assert_equal str, x.title
           assert_equal str, x.content
@@ -39,7 +41,7 @@ module ActiveRecord
 
         def test_create_null_bytes
           str = "foo\0bar"
-          x   = Topic.create!(:title => str, :content => str)
+          x   = Topic.create!(title: str, content: str)
           x.reload
           assert_equal str, x.title
           assert_equal str, x.content
diff --git a/activerecord/test/cases/adapters/mysql2/boolean_test.rb b/activerecord/test/cases/adapters/mysql2/boolean_test.rb
index 8575df9e43..db09b30361 100644
--- a/activerecord/test/cases/adapters/mysql2/boolean_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/boolean_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class Mysql2BooleanTest < ActiveRecord::Mysql2TestCase
@@ -38,28 +40,38 @@ class Mysql2BooleanTest < ActiveRecord::Mysql2TestCase
     assert_equal :string, string_column.type
   end
 
-  test "test type casting with emulated booleans" do
+  test "type casting with emulated booleans" do
     emulate_booleans true
 
     boolean = BooleanType.create!(archived: true, published: true)
     attributes = boolean.reload.attributes_before_type_cast
-
     assert_equal 1, attributes["archived"]
     assert_equal "1", attributes["published"]
 
+    boolean = BooleanType.create!(archived: false, published: false)
+    attributes = boolean.reload.attributes_before_type_cast
+    assert_equal 0, attributes["archived"]
+    assert_equal "0", attributes["published"]
+
     assert_equal 1, @connection.type_cast(true)
+    assert_equal 0, @connection.type_cast(false)
   end
 
-  test "test type casting without emulated booleans" do
+  test "type casting without emulated booleans" do
     emulate_booleans false
 
     boolean = BooleanType.create!(archived: true, published: true)
     attributes = boolean.reload.attributes_before_type_cast
-
     assert_equal 1, attributes["archived"]
     assert_equal "1", attributes["published"]
 
+    boolean = BooleanType.create!(archived: false, published: false)
+    attributes = boolean.reload.attributes_before_type_cast
+    assert_equal 0, attributes["archived"]
+    assert_equal "0", attributes["published"]
+
     assert_equal 1, @connection.type_cast(true)
+    assert_equal 0, @connection.type_cast(false)
   end
 
   test "with booleans stored as 1 and 0" do
@@ -76,11 +88,11 @@ class Mysql2BooleanTest < ActiveRecord::Mysql2TestCase
   end
 
   def boolean_column
-    BooleanType.columns.find { |c| c.name == 'archived' }
+    BooleanType.columns.find { |c| c.name == "archived" }
   end
 
   def string_column
-    BooleanType.columns.find { |c| c.name == 'published' }
+    BooleanType.columns.find { |c| c.name == "published" }
   end
 
   def emulate_booleans(value)
diff --git a/activerecord/test/cases/adapters/mysql2/case_sensitivity_test.rb b/activerecord/test/cases/adapters/mysql2/case_sensitivity_test.rb
index 963116f08a..c32475c683 100644
--- a/activerecord/test/cases/adapters/mysql2/case_sensitivity_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/case_sensitivity_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class Mysql2CaseSensitivityTest < ActiveRecord::Mysql2TestCase
@@ -7,48 +9,57 @@ class Mysql2CaseSensitivityTest < ActiveRecord::Mysql2TestCase
   repair_validations(CollationTest)
 
   def test_columns_include_collation_different_from_table
-    assert_equal 'utf8_bin', CollationTest.columns_hash['string_cs_column'].collation
-    assert_equal 'utf8_general_ci', CollationTest.columns_hash['string_ci_column'].collation
+    assert_equal "utf8mb4_bin", CollationTest.columns_hash["string_cs_column"].collation
+    assert_equal "utf8mb4_general_ci", CollationTest.columns_hash["string_ci_column"].collation
   end
 
   def test_case_sensitive
-    assert !CollationTest.columns_hash['string_ci_column'].case_sensitive?
-    assert CollationTest.columns_hash['string_cs_column'].case_sensitive?
+    assert_not_predicate CollationTest.columns_hash["string_ci_column"], :case_sensitive?
+    assert_predicate CollationTest.columns_hash["string_cs_column"], :case_sensitive?
   end
 
   def test_case_insensitive_comparison_for_ci_column
-    CollationTest.validates_uniqueness_of(:string_ci_column, :case_sensitive => false)
-    CollationTest.create!(:string_ci_column => 'A')
-    invalid = CollationTest.new(:string_ci_column => 'a')
+    CollationTest.validates_uniqueness_of(:string_ci_column, case_sensitive: false)
+    CollationTest.create!(string_ci_column: "A")
+    invalid = CollationTest.new(string_ci_column: "a")
     queries = assert_sql { invalid.save }
     ci_uniqueness_query = queries.detect { |q| q.match(/string_ci_column/) }
     assert_no_match(/lower/i, ci_uniqueness_query)
   end
 
   def test_case_insensitive_comparison_for_cs_column
-    CollationTest.validates_uniqueness_of(:string_cs_column, :case_sensitive => false)
-    CollationTest.create!(:string_cs_column => 'A')
-    invalid = CollationTest.new(:string_cs_column => 'a')
+    CollationTest.validates_uniqueness_of(:string_cs_column, case_sensitive: false)
+    CollationTest.create!(string_cs_column: "A")
+    invalid = CollationTest.new(string_cs_column: "a")
     queries = assert_sql { invalid.save }
-    cs_uniqueness_query = queries.detect { |q| q.match(/string_cs_column/)}
+    cs_uniqueness_query = queries.detect { |q| q.match(/string_cs_column/) }
     assert_match(/lower/i, cs_uniqueness_query)
   end
 
   def test_case_sensitive_comparison_for_ci_column
-    CollationTest.validates_uniqueness_of(:string_ci_column, :case_sensitive => true)
-    CollationTest.create!(:string_ci_column => 'A')
-    invalid = CollationTest.new(:string_ci_column => 'A')
+    CollationTest.validates_uniqueness_of(:string_ci_column, case_sensitive: true)
+    CollationTest.create!(string_ci_column: "A")
+    invalid = CollationTest.new(string_ci_column: "A")
     queries = assert_sql { invalid.save }
     ci_uniqueness_query = queries.detect { |q| q.match(/string_ci_column/) }
     assert_match(/binary/i, ci_uniqueness_query)
   end
 
   def test_case_sensitive_comparison_for_cs_column
-    CollationTest.validates_uniqueness_of(:string_cs_column, :case_sensitive => true)
-    CollationTest.create!(:string_cs_column => 'A')
-    invalid = CollationTest.new(:string_cs_column => 'A')
+    CollationTest.validates_uniqueness_of(:string_cs_column, case_sensitive: true)
+    CollationTest.create!(string_cs_column: "A")
+    invalid = CollationTest.new(string_cs_column: "A")
     queries = assert_sql { invalid.save }
     cs_uniqueness_query = queries.detect { |q| q.match(/string_cs_column/) }
     assert_no_match(/binary/i, cs_uniqueness_query)
   end
+
+  def test_case_sensitive_comparison_for_binary_column
+    CollationTest.validates_uniqueness_of(:binary_column, case_sensitive: true)
+    CollationTest.create!(binary_column: "A")
+    invalid = CollationTest.new(binary_column: "A")
+    queries = assert_sql { invalid.save }
+    bin_uniqueness_query = queries.detect { |q| q.match(/binary_column/) }
+    assert_no_match(/\bBINARY\b/, bin_uniqueness_query)
+  end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/charset_collation_test.rb b/activerecord/test/cases/adapters/mysql2/charset_collation_test.rb
index 4fd34def15..0bdbefdfb9 100644
--- a/activerecord/test/cases/adapters/mysql2/charset_collation_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/charset_collation_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class Mysql2CharsetCollationTest < ActiveRecord::Mysql2TestCase
   include SchemaDumpingHelper
@@ -8,8 +10,8 @@ class Mysql2CharsetCollationTest < ActiveRecord::Mysql2TestCase
   setup do
     @connection = ActiveRecord::Base.connection
     @connection.create_table :charset_collations, force: true do |t|
-      t.string :string_ascii_bin, charset: 'ascii', collation: 'ascii_bin'
-      t.text :text_ucs2_unicode_ci, charset: 'ucs2', collation: 'ucs2_unicode_ci'
+      t.string :string_ascii_bin, charset: "ascii", collation: "ascii_bin"
+      t.text :text_ucs2_unicode_ci, charset: "ucs2", collation: "ucs2_unicode_ci"
     end
   end
 
@@ -18,37 +20,37 @@ class Mysql2CharsetCollationTest < ActiveRecord::Mysql2TestCase
   end
 
   test "string column with charset and collation" do
-    column = @connection.columns(:charset_collations).find { |c| c.name == 'string_ascii_bin' }
+    column = @connection.columns(:charset_collations).find { |c| c.name == "string_ascii_bin" }
     assert_equal :string, column.type
-    assert_equal 'ascii_bin', column.collation
+    assert_equal "ascii_bin", column.collation
   end
 
   test "text column with charset and collation" do
-    column = @connection.columns(:charset_collations).find { |c| c.name == 'text_ucs2_unicode_ci' }
+    column = @connection.columns(:charset_collations).find { |c| c.name == "text_ucs2_unicode_ci" }
     assert_equal :text, column.type
-    assert_equal 'ucs2_unicode_ci', column.collation
+    assert_equal "ucs2_unicode_ci", column.collation
   end
 
   test "add column with charset and collation" do
-    @connection.add_column :charset_collations, :title, :string, charset: 'utf8', collation: 'utf8_bin'
+    @connection.add_column :charset_collations, :title, :string, charset: "utf8mb4", collation: "utf8mb4_bin"
 
-    column = @connection.columns(:charset_collations).find { |c| c.name == 'title' }
+    column = @connection.columns(:charset_collations).find { |c| c.name == "title" }
     assert_equal :string, column.type
-    assert_equal 'utf8_bin', column.collation
+    assert_equal "utf8mb4_bin", column.collation
   end
 
   test "change column with charset and collation" do
-    @connection.add_column :charset_collations, :description, :string, charset: 'utf8', collation: 'utf8_unicode_ci'
-    @connection.change_column :charset_collations, :description, :text, charset: 'utf8', collation: 'utf8_general_ci'
+    @connection.add_column :charset_collations, :description, :string, charset: "utf8mb4", collation: "utf8mb4_unicode_ci"
+    @connection.change_column :charset_collations, :description, :text, charset: "utf8mb4", collation: "utf8mb4_general_ci"
 
-    column = @connection.columns(:charset_collations).find { |c| c.name == 'description' }
+    column = @connection.columns(:charset_collations).find { |c| c.name == "description" }
     assert_equal :text, column.type
-    assert_equal 'utf8_general_ci', column.collation
+    assert_equal "utf8mb4_general_ci", column.collation
   end
 
   test "schema dump includes collation" do
     output = dump_table_schema("charset_collations")
-    assert_match %r{t.string\s+"string_ascii_bin",\s+limit: 255,\s+collation: "ascii_bin"$}, output
-    assert_match %r{t.text\s+"text_ucs2_unicode_ci",\s+limit: 65535,\s+collation: "ucs2_unicode_ci"$}, output
+    assert_match %r{t\.string\s+"string_ascii_bin",\s+collation: "ascii_bin"$}, output
+    assert_match %r{t\.text\s+"text_ucs2_unicode_ci",\s+collation: "ucs2_unicode_ci"$}, output
   end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/connection_test.rb b/activerecord/test/cases/adapters/mysql2/connection_test.rb
index 000bcadebe..3103589186 100644
--- a/activerecord/test/cases/adapters/mysql2/connection_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/connection_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
+require "support/connection_helper"
 
 class Mysql2ConnectionTest < ActiveRecord::Mysql2TestCase
   include ConnectionHelper
@@ -9,7 +11,7 @@ class Mysql2ConnectionTest < ActiveRecord::Mysql2TestCase
   def setup
     super
     @subscriber = SQLSubscriber.new
-    @subscription = ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
+    @subscription = ActiveSupport::Notifications.subscribe("sql.active_record", @subscriber)
     @connection = ActiveRecord::Base.connection
   end
 
@@ -20,9 +22,9 @@ class Mysql2ConnectionTest < ActiveRecord::Mysql2TestCase
 
   def test_bad_connection
     assert_raise ActiveRecord::NoDatabaseError do
-      configuration = ActiveRecord::Base.configurations['arunit'].merge(database: 'inexistent_activerecord_unittest')
+      configuration = ActiveRecord::Base.configurations["arunit"].merge(database: "inexistent_activerecord_unittest")
       connection = ActiveRecord::Base.mysql2_connection(configuration)
-      connection.drop_table 'ex', if_exists: true
+      connection.drop_table "ex", if_exists: true
     end
   end
 
@@ -38,80 +40,129 @@ class Mysql2ConnectionTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_no_automatic_reconnection_after_timeout
-    assert @connection.active?
-    @connection.update('set @@wait_timeout=1')
+    assert_predicate @connection, :active?
+    @connection.update("set @@wait_timeout=1")
     sleep 2
-    assert !@connection.active?
-
+    assert_not_predicate @connection, :active?
+  ensure
     # Repair all fixture connections so other tests won't break.
     @fixture_connections.each(&:verify!)
   end
 
   def test_successful_reconnection_after_timeout_with_manual_reconnect
-    assert @connection.active?
-    @connection.update('set @@wait_timeout=1')
+    assert_predicate @connection, :active?
+    @connection.update("set @@wait_timeout=1")
     sleep 2
     @connection.reconnect!
-    assert @connection.active?
+    assert_predicate @connection, :active?
   end
 
   def test_successful_reconnection_after_timeout_with_verify
-    assert @connection.active?
-    @connection.update('set @@wait_timeout=1')
+    assert_predicate @connection, :active?
+    @connection.update("set @@wait_timeout=1")
     sleep 2
     @connection.verify!
-    assert @connection.active?
+    assert_predicate @connection, :active?
+  end
+
+  def test_execute_after_disconnect
+    @connection.disconnect!
+
+    error = assert_raise(ActiveRecord::StatementInvalid) do
+      @connection.execute("SELECT 1")
+    end
+    assert_kind_of Mysql2::Error, error.cause
+  end
+
+  def test_quote_after_disconnect
+    @connection.disconnect!
+
+    assert_raise(Mysql2::Error) do
+      @connection.quote("string")
+    end
+  end
+
+  def test_active_after_disconnect
+    @connection.disconnect!
+    assert_equal false, @connection.active?
+  end
+
+  def test_wait_timeout_as_string
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.merge(wait_timeout: "60"))
+      result = ActiveRecord::Base.connection.select_value("SELECT @@SESSION.wait_timeout")
+      assert_equal 60, result
+    end
+  end
+
+  def test_wait_timeout_as_url
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.merge("url" => "mysql2:///?wait_timeout=60"))
+      result = ActiveRecord::Base.connection.select_value("SELECT @@SESSION.wait_timeout")
+      assert_equal 60, result
+    end
   end
 
   def test_mysql_connection_collation_is_configured
-    assert_equal 'utf8_unicode_ci', @connection.show_variable('collation_connection')
-    assert_equal 'utf8_general_ci', ARUnit2Model.connection.show_variable('collation_connection')
+    assert_equal "utf8mb4_unicode_ci", @connection.show_variable("collation_connection")
+    assert_equal "utf8mb4_general_ci", ARUnit2Model.connection.show_variable("collation_connection")
   end
 
-  # TODO: Below is a straight up copy/paste from mysql/connection_test.rb
-  # I'm not sure what the correct way is to share these tests between
-  # adapters in minitest.
   def test_mysql_default_in_strict_mode
-    result = @connection.exec_query "SELECT @@SESSION.sql_mode"
-    assert_equal [["STRICT_ALL_TABLES"]], result.rows
+    result = @connection.select_value("SELECT @@SESSION.sql_mode")
+    assert_match %r(STRICT_ALL_TABLES), result
   end
 
   def test_mysql_strict_mode_disabled
     run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.merge({:strict => false}))
-      result = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.sql_mode"
-      assert_equal [['']], result.rows
+      ActiveRecord::Base.establish_connection(orig_connection.merge(strict: false))
+      result = ActiveRecord::Base.connection.select_value("SELECT @@SESSION.sql_mode")
+      assert_no_match %r(STRICT_ALL_TABLES), result
     end
   end
 
   def test_mysql_strict_mode_specified_default
     run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.merge({strict: :default}))
-      global_sql_mode = ActiveRecord::Base.connection.exec_query "SELECT @@GLOBAL.sql_mode"
-      session_sql_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.sql_mode"
-      assert_equal global_sql_mode.rows, session_sql_mode.rows
+      ActiveRecord::Base.establish_connection(orig_connection.merge(strict: :default))
+      global_sql_mode = ActiveRecord::Base.connection.select_value("SELECT @@GLOBAL.sql_mode")
+      session_sql_mode = ActiveRecord::Base.connection.select_value("SELECT @@SESSION.sql_mode")
+      assert_equal global_sql_mode, session_sql_mode
     end
   end
 
-  def test_mysql_set_session_variable
+  def test_mysql_sql_mode_variable_overrides_strict_mode
     run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => 3}}))
-      session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
-      assert_equal 3, session_mode.rows.first.first.to_i
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { "sql_mode" => "ansi" }))
+      result = ActiveRecord::Base.connection.select_value("SELECT @@SESSION.sql_mode")
+      assert_no_match %r(STRICT_ALL_TABLES), result
     end
   end
 
-  def test_mysql_sql_mode_variable_overrides_strict_mode
+  def test_passing_arbitrary_flags_to_adapter
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.merge(flags: Mysql2::Client::COMPRESS))
+      assert_equal (Mysql2::Client::COMPRESS | Mysql2::Client::FOUND_ROWS), ActiveRecord::Base.connection.raw_connection.query_options[:flags]
+    end
+  end
+
+  def test_passing_flags_by_array_to_adapter
+    run_without_connection do |orig_connection|
+      ActiveRecord::Base.establish_connection(orig_connection.merge(flags: ["COMPRESS"]))
+      assert_equal ["COMPRESS", "FOUND_ROWS"], ActiveRecord::Base.connection.raw_connection.query_options[:flags]
+    end
+  end
+
+  def test_mysql_set_session_variable
     run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { 'sql_mode' => 'ansi' }))
-      result = ActiveRecord::Base.connection.exec_query 'SELECT @@SESSION.sql_mode'
-      assert_not_equal [['STRICT_ALL_TABLES']], result.rows
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { default_week_format: 3 }))
+      session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
+      assert_equal 3, session_mode.rows.first.first.to_i
     end
   end
 
   def test_mysql_set_session_variable_to_default
     run_without_connection do |orig_connection|
-      ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:default_week_format => :default}}))
+      ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { default_week_format: :default }))
       global_mode = ActiveRecord::Base.connection.exec_query "SELECT @@GLOBAL.DEFAULT_WEEK_FORMAT"
       session_mode = ActiveRecord::Base.connection.exec_query "SELECT @@SESSION.DEFAULT_WEEK_FORMAT"
       assert_equal global_mode.rows, session_mode.rows
@@ -119,16 +170,46 @@ class Mysql2ConnectionTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_logs_name_show_variable
-    @connection.show_variable 'foo'
+    ActiveRecord::Base.connection.materialize_transactions
+    @subscriber.logged.clear
+    @connection.show_variable "foo"
     assert_equal "SCHEMA", @subscriber.logged[0][1]
   end
 
-  def test_logs_name_rename_column_sql
+  def test_logs_name_rename_column_for_alter
     @connection.execute "CREATE TABLE `bar_baz` (`foo` varchar(255))"
     @subscriber.logged.clear
-    @connection.send(:rename_column_sql, 'bar_baz', 'foo', 'foo2')
+    @connection.send(:rename_column_for_alter, "bar_baz", "foo", "foo2")
     assert_equal "SCHEMA", @subscriber.logged[0][1]
   ensure
     @connection.execute "DROP TABLE `bar_baz`"
   end
+
+  def test_get_and_release_advisory_lock
+    lock_name = "test lock'n'name"
+
+    got_lock = @connection.get_advisory_lock(lock_name)
+    assert got_lock, "get_advisory_lock should have returned true but it didn't"
+
+    assert_equal test_lock_free(lock_name), false,
+      "expected the test advisory lock to be held but it wasn't"
+
+    released_lock = @connection.release_advisory_lock(lock_name)
+    assert released_lock, "expected release_advisory_lock to return true but it didn't"
+
+    assert test_lock_free(lock_name), "expected the test lock to be available after releasing"
+  end
+
+  def test_release_non_existent_advisory_lock
+    lock_name = "fake lock'n'name"
+    released_non_existent_lock = @connection.release_advisory_lock(lock_name)
+    assert_equal released_non_existent_lock, false,
+      "expected release_advisory_lock to return false when there was no lock to release"
+  end
+
+  private
+
+    def test_lock_free(lock_name)
+      @connection.select_value("SELECT IS_FREE_LOCK(#{@connection.quote(lock_name)})") == 1
+    end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/datetime_precision_quoting_test.rb b/activerecord/test/cases/adapters/mysql2/datetime_precision_quoting_test.rb
new file mode 100644
index 0000000000..00a075e063
--- /dev/null
+++ b/activerecord/test/cases/adapters/mysql2/datetime_precision_quoting_test.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+class Mysql2DatetimePrecisionQuotingTest < ActiveRecord::Mysql2TestCase
+  setup do
+    @connection = ActiveRecord::Base.connection
+  end
+
+  test "microsecond precision for MySQL gte 5.6.4" do
+    stub_version "5.6.4" do
+      assert_microsecond_precision
+    end
+  end
+
+  test "no microsecond precision for MySQL lt 5.6.4" do
+    stub_version "5.6.3" do
+      assert_no_microsecond_precision
+    end
+  end
+
+  test "microsecond precision for MariaDB gte 5.3.0" do
+    stub_version "5.5.5-10.1.8-MariaDB-log" do
+      assert_microsecond_precision
+    end
+  end
+
+  test "no microsecond precision for MariaDB lt 5.3.0" do
+    stub_version "5.2.9-MariaDB" do
+      assert_no_microsecond_precision
+    end
+  end
+
+  private
+    def assert_microsecond_precision
+      assert_match_quoted_microsecond_datetime(/\.000001\z/)
+    end
+
+    def assert_no_microsecond_precision
+      assert_match_quoted_microsecond_datetime(/\d\z/)
+    end
+
+    def assert_match_quoted_microsecond_datetime(match)
+      assert_match match, @connection.quoted_date(Time.now.change(usec: 1))
+    end
+
+    def stub_version(full_version_string)
+      @connection.stub(:full_version, full_version_string) do
+        @connection.remove_instance_variable(:@version) if @connection.instance_variable_defined?(:@version)
+        yield
+      end
+    ensure
+      @connection.remove_instance_variable(:@version) if @connection.instance_variable_defined?(:@version)
+    end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/enum_test.rb b/activerecord/test/cases/adapters/mysql2/enum_test.rb
index bd732b5eca..832f5d61d1 100644
--- a/activerecord/test/cases/adapters/mysql2/enum_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/enum_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class Mysql2EnumTest < ActiveRecord::Mysql2TestCase
@@ -5,6 +7,17 @@ class Mysql2EnumTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_enum_limit
-    assert_equal 6, EnumTest.columns.first.limit
+    column = EnumTest.columns_hash["enum_column"]
+    assert_equal 8, column.limit
+  end
+
+  def test_should_not_be_unsigned
+    column = EnumTest.columns_hash["enum_column"]
+    assert_not_predicate column, :unsigned?
+  end
+
+  def test_should_not_be_bigint
+    column = EnumTest.columns_hash["enum_column"]
+    assert_not_predicate column, :bigint?
   end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/explain_test.rb b/activerecord/test/cases/adapters/mysql2/explain_test.rb
index 4fc7414b18..b8e778f0b0 100644
--- a/activerecord/test/cases/adapters/mysql2/explain_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/explain_test.rb
@@ -1,27 +1,23 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/developer'
-require 'models/computer'
+require "models/author"
+require "models/post"
 
-module ActiveRecord
-  module ConnectionAdapters
-    class Mysql2Adapter
-      class ExplainTest < ActiveRecord::Mysql2TestCase
-        fixtures :developers
+class Mysql2ExplainTest < ActiveRecord::Mysql2TestCase
+  fixtures :authors
 
-        def test_explain_for_one_query
-          explain = Developer.where(:id => 1).explain
-          assert_match %(EXPLAIN for: SELECT `developers`.* FROM `developers` WHERE `developers`.`id` = 1), explain
-          assert_match %r(developers |.* const), explain
-        end
+  def test_explain_for_one_query
+    explain = Author.where(id: 1).explain
+    assert_match %(EXPLAIN for: SELECT `authors`.* FROM `authors` WHERE `authors`.`id` = 1), explain
+    assert_match %r(authors |.* const), explain
+  end
 
-        def test_explain_with_eager_loading
-          explain = Developer.where(:id => 1).includes(:audit_logs).explain
-          assert_match %(EXPLAIN for: SELECT `developers`.* FROM `developers` WHERE `developers`.`id` = 1), explain
-          assert_match %r(developers |.* const), explain
-          assert_match %(EXPLAIN for: SELECT `audit_logs`.* FROM `audit_logs` WHERE `audit_logs`.`developer_id` = 1), explain
-          assert_match %r(audit_logs |.* ALL), explain
-        end
-      end
-    end
+  def test_explain_with_eager_loading
+    explain = Author.where(id: 1).includes(:posts).explain
+    assert_match %(EXPLAIN for: SELECT `authors`.* FROM `authors` WHERE `authors`.`id` = 1), explain
+    assert_match %r(authors |.* const), explain
+    assert_match %(EXPLAIN for: SELECT `posts`.* FROM `posts` WHERE `posts`.`author_id` = 1), explain
+    assert_match %r(posts |.* ALL), explain
   end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/json_test.rb b/activerecord/test/cases/adapters/mysql2/json_test.rb
new file mode 100644
index 0000000000..de78ba91f5
--- /dev/null
+++ b/activerecord/test/cases/adapters/mysql2/json_test.rb
@@ -0,0 +1,24 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "cases/json_shared_test_cases"
+
+if ActiveRecord::Base.connection.supports_json?
+  class Mysql2JSONTest < ActiveRecord::Mysql2TestCase
+    include JSONSharedTestCases
+    self.use_transactional_tests = false
+
+    def setup
+      super
+      @connection.create_table("json_data_type") do |t|
+        t.json "payload"
+        t.json "settings"
+      end
+    end
+
+    private
+      def column_type
+        :json
+      end
+  end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb b/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
new file mode 100644
index 0000000000..0719baaa23
--- /dev/null
+++ b/activerecord/test/cases/adapters/mysql2/mysql2_adapter_test.rb
@@ -0,0 +1,77 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/ddl_helper"
+
+class Mysql2AdapterTest < ActiveRecord::Mysql2TestCase
+  include DdlHelper
+
+  def setup
+    @conn = ActiveRecord::Base.connection
+  end
+
+  def test_exec_query_nothing_raises_with_no_result_queries
+    assert_nothing_raised do
+      with_example_table do
+        @conn.exec_query("INSERT INTO ex (number) VALUES (1)")
+        @conn.exec_query("DELETE FROM ex WHERE number = 1")
+      end
+    end
+  end
+
+  def test_columns_for_distinct_zero_orders
+    assert_equal "posts.id",
+      @conn.columns_for_distinct("posts.id", [])
+  end
+
+  def test_columns_for_distinct_one_order
+    assert_equal "posts.created_at AS alias_0, posts.id",
+      @conn.columns_for_distinct("posts.id", ["posts.created_at desc"])
+  end
+
+  def test_columns_for_distinct_few_orders
+    assert_equal "posts.created_at AS alias_0, posts.position AS alias_1, posts.id",
+      @conn.columns_for_distinct("posts.id", ["posts.created_at desc", "posts.position asc"])
+  end
+
+  def test_columns_for_distinct_with_case
+    assert_equal(
+      "CASE WHEN author.is_active THEN UPPER(author.name) ELSE UPPER(author.email) END AS alias_0, posts.id",
+      @conn.columns_for_distinct("posts.id",
+        ["CASE WHEN author.is_active THEN UPPER(author.name) ELSE UPPER(author.email) END"])
+    )
+  end
+
+  def test_columns_for_distinct_blank_not_nil_orders
+    assert_equal "posts.created_at AS alias_0, posts.id",
+      @conn.columns_for_distinct("posts.id", ["posts.created_at desc", "", "   "])
+  end
+
+  def test_columns_for_distinct_with_arel_order
+    order = Object.new
+    def order.to_sql
+      "posts.created_at desc"
+    end
+    assert_equal "posts.created_at AS alias_0, posts.id",
+      @conn.columns_for_distinct("posts.id", [order])
+  end
+
+  def test_errors_for_bigint_fks_on_integer_pk_table
+    # table old_cars has primary key of integer
+
+    error = assert_raises(ActiveRecord::MismatchedForeignKey) do
+      @conn.add_reference :engines, :old_car
+      @conn.add_foreign_key :engines, :old_cars
+    end
+
+    assert_match "Column `old_car_id` on table `engines` has a type of `bigint(20)`", error.message
+    assert_not_nil error.cause
+    @conn.exec_query("ALTER TABLE engines DROP COLUMN old_car_id")
+  end
+
+  private
+
+    def with_example_table(definition = "id int auto_increment primary key, number int, data varchar(255)", &block)
+      super(@conn, "ex", definition, &block)
+    end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/reserved_word_test.rb b/activerecord/test/cases/adapters/mysql2/reserved_word_test.rb
deleted file mode 100644
index ffb4e2c5cf..0000000000
--- a/activerecord/test/cases/adapters/mysql2/reserved_word_test.rb
+++ /dev/null
@@ -1,152 +0,0 @@
-require "cases/helper"
-
-# a suite of tests to ensure the ConnectionAdapters#MysqlAdapter can handle tables with
-# reserved word names (ie: group, order, values, etc...)
-class Mysql2ReservedWordTest < ActiveRecord::Mysql2TestCase
-  class Group < ActiveRecord::Base
-    Group.table_name = 'group'
-    belongs_to :select
-    has_one :values
-  end
-
-  class Select < ActiveRecord::Base
-    Select.table_name = 'select'
-    has_many :groups
-  end
-
-  class Values < ActiveRecord::Base
-    Values.table_name = 'values'
-  end
-
-  class Distinct < ActiveRecord::Base
-    Distinct.table_name = 'distinct'
-    has_and_belongs_to_many :selects
-    has_many :values, :through => :groups
-  end
-
-  def setup
-    @connection = ActiveRecord::Base.connection
-
-    # we call execute directly here (and do similar below) because ActiveRecord::Base#create_table()
-    # will fail with these table names if these test cases fail
-
-    create_tables_directly 'group'=>'id int auto_increment primary key, `order` varchar(255), select_id int',
-      'select'=>'id int auto_increment primary key',
-      'values'=>'id int auto_increment primary key, group_id int',
-      'distinct'=>'id int auto_increment primary key',
-      'distinct_select'=>'distinct_id int, select_id int'
-  end
-
-  teardown do
-    drop_tables_directly ['group', 'select', 'values', 'distinct', 'distinct_select', 'order']
-  end
-
-  # create tables with reserved-word names and columns
-  def test_create_tables
-    assert_nothing_raised {
-      @connection.create_table :order do |t|
-        t.column :group, :string
-      end
-    }
-  end
-
-  # rename tables with reserved-word names
-  def test_rename_tables
-    assert_nothing_raised { @connection.rename_table(:group, :order) }
-  end
-
-  # alter column with a reserved-word name in a table with a reserved-word name
-  def test_change_columns
-    assert_nothing_raised { @connection.change_column_default(:group, :order, 'whatever') }
-    #the quoting here will reveal any double quoting issues in change_column's interaction with the column method in the adapter
-    assert_nothing_raised { @connection.change_column('group', 'order', :Int, :default => 0) }
-    assert_nothing_raised { @connection.rename_column(:group, :order, :values) }
-  end
-
-  # introspect table with reserved word name
-  def test_introspect
-    assert_nothing_raised { @connection.columns(:group) }
-    assert_nothing_raised { @connection.indexes(:group) }
-  end
-
-  #fixtures
-  self.use_instantiated_fixtures = true
-  self.use_transactional_tests = false
-
-  #activerecord model class with reserved-word table name
-  def test_activerecord_model
-    create_test_fixtures :select, :distinct, :group, :values, :distinct_select
-    x = nil
-    assert_nothing_raised { x = Group.new }
-    x.order = 'x'
-    assert_nothing_raised { x.save }
-    x.order = 'y'
-    assert_nothing_raised { x.save }
-    assert_nothing_raised { Group.find_by_order('y') }
-    assert_nothing_raised { Group.find(1) }
-  end
-
-  # has_one association with reserved-word table name
-  def test_has_one_associations
-    create_test_fixtures :select, :distinct, :group, :values, :distinct_select
-    v = nil
-    assert_nothing_raised { v = Group.find(1).values }
-    assert_equal 2, v.id
-  end
-
-  # belongs_to association with reserved-word table name
-  def test_belongs_to_associations
-    create_test_fixtures :select, :distinct, :group, :values, :distinct_select
-    gs = nil
-    assert_nothing_raised { gs = Select.find(2).groups }
-    assert_equal gs.length, 2
-    assert(gs.collect(&:id).sort == [2, 3])
-  end
-
-  # has_and_belongs_to_many with reserved-word table name
-  def test_has_and_belongs_to_many
-    create_test_fixtures :select, :distinct, :group, :values, :distinct_select
-    s = nil
-    assert_nothing_raised { s = Distinct.find(1).selects }
-    assert_equal s.length, 2
-    assert(s.collect(&:id).sort == [1, 2])
-  end
-
-  # activerecord model introspection with reserved-word table and column names
-  def test_activerecord_introspection
-    assert_nothing_raised { Group.table_exists? }
-    assert_nothing_raised { Group.columns }
-  end
-
-  # Calculations
-  def test_calculations_work_with_reserved_words
-    assert_nothing_raised { Group.count }
-  end
-
-  def test_associations_work_with_reserved_words
-    assert_nothing_raised { Select.all.merge!(:includes => [:groups]).to_a }
-  end
-
-  #the following functions were added to DRY test cases
-
-  private
-  # custom fixture loader, uses FixtureSet#create_fixtures and appends base_path to the current file's path
-  def create_test_fixtures(*fixture_names)
-    ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT + "/reserved_words", fixture_names)
-  end
-
-  # custom drop table, uses execute on connection to drop a table if it exists. note: escapes table_name
-  def drop_tables_directly(table_names, connection = @connection)
-    table_names.each do |name|
-      connection.drop_table name, if_exists: true
-    end
-  end
-
-  # custom create table, uses execute on connection to create a table, note: escapes table_name, does NOT escape columns
-  def create_tables_directly (tables, connection = @connection)
-    tables.each do |table_name, column_properties|
-      connection.execute("CREATE TABLE `#{table_name}` ( #{column_properties} )")
-    end
-  end
-
-end
diff --git a/activerecord/test/cases/adapters/mysql2/schema_migrations_test.rb b/activerecord/test/cases/adapters/mysql2/schema_migrations_test.rb
index 396f235e77..d7d9a2d732 100644
--- a/activerecord/test/cases/adapters/mysql2/schema_migrations_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/schema_migrations_test.rb
@@ -1,6 +1,10 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class SchemaMigrationsTest < ActiveRecord::Mysql2TestCase
+  self.use_transactional_tests = false
+
   def test_renaming_index_on_foreign_key
     connection.add_index "engines", "car_id"
     connection.add_foreign_key :engines, :cars, name: "fk_engines_cars"
@@ -12,31 +16,50 @@ class SchemaMigrationsTest < ActiveRecord::Mysql2TestCase
   end
 
   def test_initializes_schema_migrations_for_encoding_utf8mb4
-    smtn = ActiveRecord::Migrator.schema_migrations_table_name
-    connection.drop_table smtn, if_exists: true
+    with_encoding_utf8mb4 do
+      table_name = ActiveRecord::SchemaMigration.table_name
+      connection.drop_table table_name, if_exists: true
 
-    database_name = connection.current_database
-    database_info = connection.select_one("SELECT * FROM information_schema.schemata WHERE schema_name = '#{database_name}'")
+      ActiveRecord::SchemaMigration.create_table
 
-    original_charset = database_info["DEFAULT_CHARACTER_SET_NAME"]
-    original_collation = database_info["DEFAULT_COLLATION_NAME"]
+      assert connection.column_exists?(table_name, :version, :string)
+    end
+  end
 
-    execute("ALTER DATABASE #{database_name} DEFAULT CHARACTER SET utf8mb4")
+  def test_initializes_internal_metadata_for_encoding_utf8mb4
+    with_encoding_utf8mb4 do
+      table_name = ActiveRecord::InternalMetadata.table_name
+      connection.drop_table table_name, if_exists: true
 
-    connection.initialize_schema_migrations_table
+      ActiveRecord::InternalMetadata.create_table
 
-    limit = ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::MAX_INDEX_LENGTH_FOR_CHARSETS_OF_4BYTES_MAXLEN
-    assert connection.column_exists?(smtn, :version, :string, limit: limit)
+      assert connection.column_exists?(table_name, :key, :string)
+    end
   ensure
-    execute("ALTER DATABASE #{database_name} DEFAULT CHARACTER SET #{original_charset} COLLATE #{original_collation}")
+    ActiveRecord::InternalMetadata[:environment] = connection.migration_context.current_environment
   end
 
   private
-  def connection
-    @connection ||= ActiveRecord::Base.connection
-  end
 
-  def execute(sql)
-    connection.execute(sql)
-  end
+    def with_encoding_utf8mb4
+      database_name = connection.current_database
+      database_info = connection.select_one("SELECT * FROM information_schema.schemata WHERE schema_name = '#{database_name}'")
+
+      original_charset = database_info["DEFAULT_CHARACTER_SET_NAME"]
+      original_collation = database_info["DEFAULT_COLLATION_NAME"]
+
+      execute("ALTER DATABASE #{database_name} DEFAULT CHARACTER SET utf8mb4")
+
+      yield
+    ensure
+      execute("ALTER DATABASE #{database_name} DEFAULT CHARACTER SET #{original_charset} COLLATE #{original_collation}")
+    end
+
+    def connection
+      @connection ||= ActiveRecord::Base.connection
+    end
+
+    def execute(sql)
+      connection.execute(sql)
+    end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/schema_test.rb b/activerecord/test/cases/adapters/mysql2/schema_test.rb
index 880a2123d2..1283b0642c 100644
--- a/activerecord/test/cases/adapters/mysql2/schema_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/schema_test.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/comment'
+require "models/post"
+require "models/comment"
 
 module ActiveRecord
   module ConnectionAdapters
@@ -14,9 +16,41 @@ module ActiveRecord
         @db_name    = db
 
         @omgpost = Class.new(ActiveRecord::Base) do
+          self.inheritance_column = :disabled
           self.table_name = "#{db}.#{table}"
-          def self.name; 'Post'; end
+          def self.name; "Post"; end
+        end
+      end
+
+      def test_float_limits
+        @connection.create_table :mysql_doubles do |t|
+          t.float :float_no_limit
+          t.float :float_short, limit: 5
+          t.float :float_long, limit: 53
+
+          t.float :float_23, limit: 23
+          t.float :float_24, limit: 24
+          t.float :float_25, limit: 25
         end
+
+        column_no_limit = @connection.columns(:mysql_doubles).find { |c| c.name == "float_no_limit" }
+        column_short = @connection.columns(:mysql_doubles).find { |c| c.name == "float_short" }
+        column_long = @connection.columns(:mysql_doubles).find { |c| c.name == "float_long" }
+
+        column_23 = @connection.columns(:mysql_doubles).find { |c| c.name == "float_23" }
+        column_24 = @connection.columns(:mysql_doubles).find { |c| c.name == "float_24" }
+        column_25 = @connection.columns(:mysql_doubles).find { |c| c.name == "float_25" }
+
+        # Mysql floats are precision 0..24, Mysql doubles are precision 25..53
+        assert_equal 24, column_no_limit.limit
+        assert_equal 24, column_short.limit
+        assert_equal 53, column_long.limit
+
+        assert_equal 24, column_23.limit
+        assert_equal 24, column_24.limit
+        assert_equal 53, column_25.limit
+      ensure
+        @connection.drop_table "mysql_doubles", if_exists: true
       end
 
       def test_schema
@@ -24,39 +58,31 @@ module ActiveRecord
       end
 
       def test_primary_key
-        assert_equal 'id', @omgpost.primary_key
+        assert_equal "id", @omgpost.primary_key
       end
 
-      def test_table_exists?
+      def test_data_source_exists?
         name = @omgpost.table_name
-        assert @connection.table_exists?(name), "#{name} table should exist"
-      end
-
-      def test_table_exists_wrong_schema
-        assert(!@connection.table_exists?("#{@db_name}.zomg"), "table should not exist")
+        assert @connection.data_source_exists?(name), "#{name} data_source should exist"
       end
 
-      def test_tables_quoting
-        @connection.tables(nil, "foo-bar", nil)
-        flunk
-      rescue => e
-        # assertion for *quoted* database properly
-        assert_match(/database 'foo-bar'/, e.inspect)
+      def test_data_source_exists_wrong_schema
+        assert_not(@connection.data_source_exists?("#{@db_name}.zomg"), "data_source should not exist")
       end
 
       def test_dump_indexes
-        index_a_name = 'index_key_tests_on_snack'
-        index_b_name = 'index_key_tests_on_pizza'
-        index_c_name = 'index_key_tests_on_awesome'
+        index_a_name = "index_key_tests_on_snack"
+        index_b_name = "index_key_tests_on_pizza"
+        index_c_name = "index_key_tests_on_awesome"
 
-        table = 'key_tests'
+        table = "key_tests"
 
         indexes = @connection.indexes(table).sort_by(&:name)
-        assert_equal 3,indexes.size
+        assert_equal 3, indexes.size
 
-        index_a = indexes.select{|i| i.name == index_a_name}[0]
-        index_b = indexes.select{|i| i.name == index_b_name}[0]
-        index_c = indexes.select{|i| i.name == index_c_name}[0]
+        index_a = indexes.select { |i| i.name == index_a_name }[0]
+        index_b = indexes.select { |i| i.name == index_b_name }[0]
+        index_c = indexes.select { |i| i.name == index_c_name }[0]
         assert_equal :btree, index_a.using
         assert_nil index_a.type
         assert_equal :btree, index_b.using
@@ -79,3 +105,24 @@ module ActiveRecord
     end
   end
 end
+
+class Mysql2AnsiQuotesTest < ActiveRecord::Mysql2TestCase
+  def setup
+    @connection = ActiveRecord::Base.connection
+    @connection.execute("SET SESSION sql_mode='ANSI_QUOTES'")
+  end
+
+  def teardown
+    @connection.reconnect!
+  end
+
+  def test_primary_key_method_with_ansi_quotes
+    assert_equal "id", @connection.primary_key("topics")
+  end
+
+  def test_foreign_keys_method_with_ansi_quotes
+    fks = @connection.foreign_keys("lessons_students")
+    assert_equal([["lessons_students", "students", :cascade]],
+                 fks.map { |fk| [fk.from_table, fk.to_table, fk.on_delete] })
+  end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/sp_test.rb b/activerecord/test/cases/adapters/mysql2/sp_test.rb
new file mode 100644
index 0000000000..7b6dce71e9
--- /dev/null
+++ b/activerecord/test/cases/adapters/mysql2/sp_test.rb
@@ -0,0 +1,38 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/topic"
+require "models/reply"
+
+class Mysql2StoredProcedureTest < ActiveRecord::Mysql2TestCase
+  fixtures :topics
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+    unless ActiveRecord::Base.connection.version >= "5.6.0"
+      skip("no stored procedure support")
+    end
+  end
+
+  # Test that MySQL allows multiple results for stored procedures
+  #
+  # In MySQL 5.6, CLIENT_MULTI_RESULTS is enabled by default.
+  # https://dev.mysql.com/doc/refman/5.6/en/call.html
+  def test_multi_results
+    rows = @connection.select_rows("CALL ten();")
+    assert_equal 10, rows[0][0].to_i, "ten() did not return 10 as expected: #{rows.inspect}"
+    assert @connection.active?, "Bad connection use by 'Mysql2Adapter.select_rows'"
+  end
+
+  def test_multi_results_from_select_one
+    row = @connection.select_one("CALL topics(1);")
+    assert_equal "David", row["author_name"]
+    assert @connection.active?, "Bad connection use by 'Mysql2Adapter.select_one'"
+  end
+
+  def test_multi_results_from_find_by_sql
+    topics = Topic.find_by_sql "CALL topics(3);"
+    assert_equal 3, topics.size
+    assert @connection.active?, "Bad connection use by 'Mysql2Adapter.select'"
+  end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/sql_types_test.rb b/activerecord/test/cases/adapters/mysql2/sql_types_test.rb
index ae505d29c9..e10642cbb4 100644
--- a/activerecord/test/cases/adapters/mysql2/sql_types_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/sql_types_test.rb
@@ -1,14 +1,16 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class Mysql2SqlTypesTest < ActiveRecord::Mysql2TestCase
   def test_binary_types
-    assert_equal 'varbinary(64)', type_to_sql(:binary, 64)
-    assert_equal 'varbinary(4095)', type_to_sql(:binary, 4095)
-    assert_equal 'blob(4096)', type_to_sql(:binary, 4096)
-    assert_equal 'blob', type_to_sql(:binary)
+    assert_equal "varbinary(64)", type_to_sql(:binary, 64)
+    assert_equal "varbinary(4095)", type_to_sql(:binary, 4095)
+    assert_equal "blob", type_to_sql(:binary, 4096)
+    assert_equal "blob", type_to_sql(:binary)
   end
 
-  def type_to_sql(*args)
-    ActiveRecord::Base.connection.type_to_sql(*args)
+  def type_to_sql(type, limit = nil)
+    ActiveRecord::Base.connection.type_to_sql(type, limit: limit)
   end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/table_options_test.rb b/activerecord/test/cases/adapters/mysql2/table_options_test.rb
index af121ee7d9..1c92df940f 100644
--- a/activerecord/test/cases/adapters/mysql2/table_options_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/table_options_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class Mysql2TableOptionsTest < ActiveRecord::Mysql2TestCase
   include SchemaDumpingHelper
@@ -15,28 +17,103 @@ class Mysql2TableOptionsTest < ActiveRecord::Mysql2TestCase
   test "table options with ENGINE" do
     @connection.create_table "mysql_table_options", force: true, options: "ENGINE=MyISAM"
     output = dump_table_schema("mysql_table_options")
-    options = %r{create_table "mysql_table_options", force: :cascade, options: "(?<options>.*)"}.match(output)[:options]
+    options = %r{create_table "mysql_table_options", options: "(?<options>.*)"}.match(output)[:options]
     assert_match %r{ENGINE=MyISAM}, options
   end
 
   test "table options with ROW_FORMAT" do
     @connection.create_table "mysql_table_options", force: true, options: "ROW_FORMAT=REDUNDANT"
     output = dump_table_schema("mysql_table_options")
-    options = %r{create_table "mysql_table_options", force: :cascade, options: "(?<options>.*)"}.match(output)[:options]
+    options = %r{create_table "mysql_table_options", options: "(?<options>.*)"}.match(output)[:options]
     assert_match %r{ROW_FORMAT=REDUNDANT}, options
   end
 
   test "table options with CHARSET" do
     @connection.create_table "mysql_table_options", force: true, options: "CHARSET=utf8mb4"
     output = dump_table_schema("mysql_table_options")
-    options = %r{create_table "mysql_table_options", force: :cascade, options: "(?<options>.*)"}.match(output)[:options]
+    options = %r{create_table "mysql_table_options", options: "(?<options>.*)"}.match(output)[:options]
     assert_match %r{CHARSET=utf8mb4}, options
   end
 
   test "table options with COLLATE" do
     @connection.create_table "mysql_table_options", force: true, options: "COLLATE=utf8mb4_bin"
     output = dump_table_schema("mysql_table_options")
-    options = %r{create_table "mysql_table_options", force: :cascade, options: "(?<options>.*)"}.match(output)[:options]
+    options = %r{create_table "mysql_table_options", options: "(?<options>.*)"}.match(output)[:options]
     assert_match %r{COLLATE=utf8mb4_bin}, options
   end
 end
+
+class Mysql2DefaultEngineOptionSchemaDumpTest < ActiveRecord::Mysql2TestCase
+  include SchemaDumpingHelper
+  self.use_transactional_tests = false
+
+  def setup
+    @verbose_was = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+  end
+
+  def teardown
+    ActiveRecord::Base.connection.drop_table "mysql_table_options", if_exists: true
+    ActiveRecord::Migration.verbose = @verbose_was
+    ActiveRecord::SchemaMigration.delete_all rescue nil
+  end
+
+  test "schema dump includes ENGINE=InnoDB if not provided" do
+    ActiveRecord::Base.connection.create_table "mysql_table_options", force: true
+
+    output  = dump_table_schema("mysql_table_options")
+    options = %r{create_table "mysql_table_options", options: "(?<options>.*)"}.match(output)[:options]
+    assert_match %r{ENGINE=InnoDB}, options
+  end
+
+  test "schema dump includes ENGINE=InnoDB in legacy migrations" do
+    migration = Class.new(ActiveRecord::Migration[5.1]) do
+      def migrate(x)
+        create_table "mysql_table_options", force: true
+      end
+    end.new
+
+    ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+    output  = dump_table_schema("mysql_table_options")
+    options = %r{create_table "mysql_table_options", options: "(?<options>.*)"}.match(output)[:options]
+    assert_match %r{ENGINE=InnoDB}, options
+  end
+end
+
+class Mysql2DefaultEngineOptionSqlOutputTest < ActiveRecord::Mysql2TestCase
+  self.use_transactional_tests = false
+
+  def setup
+    @logger_was  = ActiveRecord::Base.logger
+    @log         = StringIO.new
+    @verbose_was = ActiveRecord::Migration.verbose
+    ActiveRecord::Base.logger = ActiveSupport::Logger.new(@log)
+    ActiveRecord::Migration.verbose = false
+  end
+
+  def teardown
+    ActiveRecord::Base.logger       = @logger_was
+    ActiveRecord::Migration.verbose = @verbose_was
+    ActiveRecord::Base.connection.drop_table "mysql_table_options", if_exists: true
+    ActiveRecord::SchemaMigration.delete_all rescue nil
+  end
+
+  test "new migrations do not contain default ENGINE=InnoDB option" do
+    ActiveRecord::Base.connection.create_table "mysql_table_options", force: true
+
+    assert_no_match %r{ENGINE=InnoDB}, @log.string
+  end
+
+  test "legacy migrations contain default ENGINE=InnoDB option" do
+    migration = Class.new(ActiveRecord::Migration[5.1]) do
+      def migrate(x)
+        create_table "mysql_table_options", force: true
+      end
+    end.new
+
+    ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+    assert_match %r{ENGINE=InnoDB}, @log.string
+  end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/transaction_test.rb b/activerecord/test/cases/adapters/mysql2/transaction_test.rb
new file mode 100644
index 0000000000..52e283f247
--- /dev/null
+++ b/activerecord/test/cases/adapters/mysql2/transaction_test.rb
@@ -0,0 +1,149 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/connection_helper"
+
+module ActiveRecord
+  class Mysql2TransactionTest < ActiveRecord::Mysql2TestCase
+    self.use_transactional_tests = false
+
+    class Sample < ActiveRecord::Base
+      self.table_name = "samples"
+    end
+
+    setup do
+      @abort, Thread.abort_on_exception = Thread.abort_on_exception, false
+      Thread.report_on_exception, @original_report_on_exception = false, Thread.report_on_exception
+
+      @connection = ActiveRecord::Base.connection
+      @connection.clear_cache!
+
+      @connection.transaction do
+        @connection.drop_table "samples", if_exists: true
+        @connection.create_table("samples") do |t|
+          t.integer "value"
+        end
+      end
+
+      Sample.reset_column_information
+    end
+
+    teardown do
+      @connection.drop_table "samples", if_exists: true
+
+      Thread.abort_on_exception = @abort
+      Thread.report_on_exception = @original_report_on_exception
+    end
+
+    test "raises Deadlocked when a deadlock is encountered" do
+      assert_raises(ActiveRecord::Deadlocked) do
+        barrier = Concurrent::CyclicBarrier.new(2)
+
+        s1 = Sample.create value: 1
+        s2 = Sample.create value: 2
+
+        thread = Thread.new do
+          Sample.transaction do
+            s1.lock!
+            barrier.wait
+            s2.update value: 1
+          end
+        end
+
+        begin
+          Sample.transaction do
+            s2.lock!
+            barrier.wait
+            s1.update value: 2
+          end
+        ensure
+          thread.join
+        end
+      end
+    end
+
+    test "raises LockWaitTimeout when lock wait timeout exceeded" do
+      assert_raises(ActiveRecord::LockWaitTimeout) do
+        s = Sample.create!(value: 1)
+        latch1 = Concurrent::CountDownLatch.new
+        latch2 = Concurrent::CountDownLatch.new
+
+        thread = Thread.new do
+          Sample.transaction do
+            Sample.lock.find(s.id)
+            latch1.count_down
+            latch2.wait
+          end
+        end
+
+        begin
+          Sample.transaction do
+            latch1.wait
+            Sample.connection.execute("SET innodb_lock_wait_timeout = 1")
+            Sample.lock.find(s.id)
+          end
+        ensure
+          Sample.connection.execute("SET innodb_lock_wait_timeout = DEFAULT")
+          latch2.count_down
+          thread.join
+        end
+      end
+    end
+
+    test "raises StatementTimeout when statement timeout exceeded" do
+      skip unless ActiveRecord::Base.connection.show_variable("max_execution_time")
+      assert_raises(ActiveRecord::StatementTimeout) do
+        s = Sample.create!(value: 1)
+        latch1 = Concurrent::CountDownLatch.new
+        latch2 = Concurrent::CountDownLatch.new
+
+        thread = Thread.new do
+          Sample.transaction do
+            Sample.lock.find(s.id)
+            latch1.count_down
+            latch2.wait
+          end
+        end
+
+        begin
+          Sample.transaction do
+            latch1.wait
+            Sample.connection.execute("SET max_execution_time = 1")
+            Sample.lock.find(s.id)
+          end
+        ensure
+          Sample.connection.execute("SET max_execution_time = DEFAULT")
+          latch2.count_down
+          thread.join
+        end
+      end
+    end
+
+    test "raises QueryCanceled when canceling statement due to user request" do
+      assert_raises(ActiveRecord::QueryCanceled) do
+        s = Sample.create!(value: 1)
+        latch = Concurrent::CountDownLatch.new
+
+        thread = Thread.new do
+          Sample.transaction do
+            Sample.lock.find(s.id)
+            latch.count_down
+            sleep(0.5)
+            conn = Sample.connection
+            pid = conn.query_value("SELECT id FROM information_schema.processlist WHERE info LIKE '% FOR UPDATE'")
+            conn.execute("KILL QUERY #{pid}")
+          end
+        end
+
+        begin
+          Sample.transaction do
+            latch.wait
+            Sample.lock.find(s.id)
+          end
+        ensure
+          thread.join
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/adapters/mysql2/unsigned_type_test.rb b/activerecord/test/cases/adapters/mysql2/unsigned_type_test.rb
index 9e06db2519..97da96003d 100644
--- a/activerecord/test/cases/adapters/mysql2/unsigned_type_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/unsigned_type_test.rb
@@ -1,6 +1,10 @@
+# frozen_string_literal: true
+
 require "cases/helper"
+require "support/schema_dumping_helper"
 
 class Mysql2UnsignedTypeTest < ActiveRecord::Mysql2TestCase
+  include SchemaDumpingHelper
   self.use_transactional_tests = false
 
   class UnsignedType < ActiveRecord::Base
@@ -9,12 +13,16 @@ class Mysql2UnsignedTypeTest < ActiveRecord::Mysql2TestCase
   setup do
     @connection = ActiveRecord::Base.connection
     @connection.create_table("unsigned_types", force: true) do |t|
-      t.column :unsigned_integer, "int unsigned"
+      t.integer :unsigned_integer, unsigned: true
+      t.bigint  :unsigned_bigint,  unsigned: true
+      t.float   :unsigned_float,   unsigned: true
+      t.decimal :unsigned_decimal, unsigned: true, precision: 10, scale: 2
+      t.column  :unsigned_zerofill, "int unsigned zerofill"
     end
   end
 
   teardown do
-    @connection.drop_table "unsigned_types"
+    @connection.drop_table "unsigned_types", if_exists: true
   end
 
   test "unsigned int max value is in range" do
@@ -23,8 +31,38 @@ class Mysql2UnsignedTypeTest < ActiveRecord::Mysql2TestCase
   end
 
   test "minus value is out of range" do
-    assert_raise(RangeError) do
+    assert_raise(ActiveModel::RangeError) do
       UnsignedType.create(unsigned_integer: -10)
     end
+    assert_raise(ActiveModel::RangeError) do
+      UnsignedType.create(unsigned_bigint: -10)
+    end
+    assert_raise(ActiveRecord::RangeError) do
+      UnsignedType.create(unsigned_float: -10.0)
+    end
+    assert_raise(ActiveRecord::RangeError) do
+      UnsignedType.create(unsigned_decimal: -10.0)
+    end
+  end
+
+  test "schema definition can use unsigned as the type" do
+    @connection.change_table("unsigned_types") do |t|
+      t.unsigned_integer :unsigned_integer_t
+      t.unsigned_bigint  :unsigned_bigint_t
+      t.unsigned_float   :unsigned_float_t
+      t.unsigned_decimal :unsigned_decimal_t, precision: 10, scale: 2
+    end
+
+    @connection.columns("unsigned_types").select { |c| /^unsigned_/.match?(c.name) }.each do |column|
+      assert_predicate column, :unsigned?
+    end
+  end
+
+  test "schema dump includes unsigned option" do
+    schema = dump_table_schema "unsigned_types"
+    assert_match %r{t\.integer\s+"unsigned_integer",\s+unsigned: true$}, schema
+    assert_match %r{t\.bigint\s+"unsigned_bigint",\s+unsigned: true$}, schema
+    assert_match %r{t\.float\s+"unsigned_float",\s+unsigned: true$}, schema
+    assert_match %r{t\.decimal\s+"unsigned_decimal",\s+precision: 10,\s+scale: 2,\s+unsigned: true$}, schema
   end
 end
diff --git a/activerecord/test/cases/adapters/mysql2/virtual_column_test.rb b/activerecord/test/cases/adapters/mysql2/virtual_column_test.rb
new file mode 100644
index 0000000000..8494acee3b
--- /dev/null
+++ b/activerecord/test/cases/adapters/mysql2/virtual_column_test.rb
@@ -0,0 +1,63 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/schema_dumping_helper"
+
+if ActiveRecord::Base.connection.supports_virtual_columns?
+  class Mysql2VirtualColumnTest < ActiveRecord::Mysql2TestCase
+    include SchemaDumpingHelper
+
+    self.use_transactional_tests = false
+
+    class VirtualColumn < ActiveRecord::Base
+    end
+
+    def setup
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table :virtual_columns, force: true do |t|
+        t.string  :name
+        t.virtual :upper_name,  type: :string,  as: "UPPER(`name`)"
+        t.virtual :name_length, type: :integer, as: "LENGTH(`name`)", stored: true
+        t.virtual :name_octet_length, type: :integer, as: "OCTET_LENGTH(`name`)", stored: true
+      end
+      VirtualColumn.create(name: "Rails")
+    end
+
+    def teardown
+      @connection.drop_table :virtual_columns, if_exists: true
+      VirtualColumn.reset_column_information
+    end
+
+    def test_virtual_column
+      column = VirtualColumn.columns_hash["upper_name"]
+      assert_predicate column, :virtual?
+      assert_match %r{\bVIRTUAL\b}, column.extra
+      assert_equal "RAILS", VirtualColumn.take.upper_name
+    end
+
+    def test_stored_column
+      column = VirtualColumn.columns_hash["name_length"]
+      assert_predicate column, :virtual?
+      assert_match %r{\b(?:STORED|PERSISTENT)\b}, column.extra
+      assert_equal 5, VirtualColumn.take.name_length
+    end
+
+    def test_change_table
+      @connection.change_table :virtual_columns do |t|
+        t.virtual :lower_name, type: :string, as: "LOWER(name)"
+      end
+      VirtualColumn.reset_column_information
+      column = VirtualColumn.columns_hash["lower_name"]
+      assert_predicate column, :virtual?
+      assert_match %r{\bVIRTUAL\b}, column.extra
+      assert_equal "rails", VirtualColumn.take.lower_name
+    end
+
+    def test_schema_dumping
+      output = dump_table_schema("virtual_columns")
+      assert_match(/t\.virtual\s+"upper_name",\s+type: :string,\s+as: "(?:UPPER|UCASE)\(`name`\)"$/i, output)
+      assert_match(/t\.virtual\s+"name_length",\s+type: :integer,\s+as: "(?:octet_length|length)\(`name`\)",\s+stored: true$/i, output)
+      assert_match(/t\.virtual\s+"name_octet_length",\s+type: :integer,\s+as: "(?:octet_length|length)\(`name`\)",\s+stored: true$/i, output)
+    end
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/active_schema_test.rb b/activerecord/test/cases/adapters/postgresql/active_schema_test.rb
index dc7ba314c6..afd422881b 100644
--- a/activerecord/test/cases/adapters/postgresql/active_schema_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/active_schema_test.rb
@@ -1,7 +1,11 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 class PostgresqlActiveSchemaTest < ActiveRecord::PostgreSQLTestCase
   def setup
+    ActiveRecord::Base.connection.materialize_transactions
+
     ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.class_eval do
       def execute(sql, name = nil) sql end
     end
@@ -15,40 +19,89 @@ class PostgresqlActiveSchemaTest < ActiveRecord::PostgreSQLTestCase
 
   def test_create_database_with_encoding
     assert_equal %(CREATE DATABASE "matt" ENCODING = 'utf8'), create_database(:matt)
-    assert_equal %(CREATE DATABASE "aimonetti" ENCODING = 'latin1'), create_database(:aimonetti, :encoding => :latin1)
-    assert_equal %(CREATE DATABASE "aimonetti" ENCODING = 'latin1'), create_database(:aimonetti, 'encoding' => :latin1)
+    assert_equal %(CREATE DATABASE "aimonetti" ENCODING = 'latin1'), create_database(:aimonetti, encoding: :latin1)
+    assert_equal %(CREATE DATABASE "aimonetti" ENCODING = 'latin1'), create_database(:aimonetti, "encoding" => :latin1)
   end
 
   def test_create_database_with_collation_and_ctype
-    assert_equal %(CREATE DATABASE "aimonetti" ENCODING = 'UTF8' LC_COLLATE = 'ja_JP.UTF8' LC_CTYPE = 'ja_JP.UTF8'), create_database(:aimonetti, :encoding => :"UTF8", :collation => :"ja_JP.UTF8", :ctype => :"ja_JP.UTF8")
+    assert_equal %(CREATE DATABASE "aimonetti" ENCODING = 'UTF8' LC_COLLATE = 'ja_JP.UTF8' LC_CTYPE = 'ja_JP.UTF8'), create_database(:aimonetti, encoding: :"UTF8", collation: :"ja_JP.UTF8", ctype: :"ja_JP.UTF8")
   end
 
   def test_add_index
     # add_index calls index_name_exists? which can't work since execute is stubbed
-    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.stubs(:index_name_exists?).returns(false)
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.send(:define_method, :index_name_exists?) { |*| false }
 
     expected = %(CREATE UNIQUE INDEX  "index_people_on_last_name" ON "people"  ("last_name") WHERE state = 'active')
-    assert_equal expected, add_index(:people, :last_name, :unique => true, :where => "state = 'active'")
+    assert_equal expected, add_index(:people, :last_name, unique: true, where: "state = 'active'")
+
+    expected = %(CREATE UNIQUE INDEX  "index_people_on_lower_last_name" ON "people"  (lower(last_name)))
+    assert_equal expected, add_index(:people, "lower(last_name)", unique: true)
+
+    expected = %(CREATE UNIQUE INDEX  "index_people_on_last_name_varchar_pattern_ops" ON "people"  (last_name varchar_pattern_ops))
+    assert_equal expected, add_index(:people, "last_name varchar_pattern_ops", unique: true)
 
     expected = %(CREATE  INDEX CONCURRENTLY "index_people_on_last_name" ON "people"  ("last_name"))
     assert_equal expected, add_index(:people, :last_name, algorithm: :concurrently)
 
+    expected = %(CREATE  INDEX  "index_people_on_last_name_and_first_name" ON "people"  ("last_name" DESC, "first_name" ASC))
+    assert_equal expected, add_index(:people, [:last_name, :first_name], order: { last_name: :desc, first_name: :asc })
+    assert_equal expected, add_index(:people, ["last_name", :first_name], order: { last_name: :desc, "first_name" => :asc })
+
     %w(gin gist hash btree).each do |type|
       expected = %(CREATE  INDEX  "index_people_on_last_name" ON "people" USING #{type} ("last_name"))
       assert_equal expected, add_index(:people, :last_name, using: type)
 
       expected = %(CREATE  INDEX CONCURRENTLY "index_people_on_last_name" ON "people" USING #{type} ("last_name"))
       assert_equal expected, add_index(:people, :last_name, using: type, algorithm: :concurrently)
+
+      expected = %(CREATE UNIQUE INDEX  "index_people_on_last_name" ON "people" USING #{type} ("last_name") WHERE state = 'active')
+      assert_equal expected, add_index(:people, :last_name, using: type, unique: true, where: "state = 'active'")
+
+      expected = %(CREATE UNIQUE INDEX  "index_people_on_lower_last_name" ON "people" USING #{type} (lower(last_name)))
+      assert_equal expected, add_index(:people, "lower(last_name)", using: type, unique: true)
+    end
+
+    expected = %(CREATE  INDEX  "index_people_on_last_name" ON "people" USING gist ("last_name" bpchar_pattern_ops))
+    assert_equal expected, add_index(:people, :last_name, using: :gist, opclass: { last_name: :bpchar_pattern_ops })
+
+    expected = %(CREATE  INDEX  "index_people_on_last_name_and_first_name" ON "people"  ("last_name" DESC NULLS LAST, "first_name" ASC))
+    assert_equal expected, add_index(:people, [:last_name, :first_name], order: { last_name: "DESC NULLS LAST", first_name: :asc })
+
+    expected = %(CREATE  INDEX  "index_people_on_last_name" ON "people"  ("last_name" NULLS FIRST))
+    assert_equal expected, add_index(:people, :last_name, order: "NULLS FIRST")
+
+    assert_raise ArgumentError do
+      add_index(:people, :last_name, algorithm: :copy)
+    end
+
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.send :remove_method, :index_name_exists?
+  end
+
+  def test_remove_index
+    # remove_index calls index_name_for_remove which can't work since execute is stubbed
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.send(:define_method, :index_name_for_remove) do |*|
+      "index_people_on_last_name"
     end
 
+    expected = %(DROP INDEX CONCURRENTLY "index_people_on_last_name")
+    assert_equal expected, remove_index(:people, name: "index_people_on_last_name", algorithm: :concurrently)
+
     assert_raise ArgumentError do
       add_index(:people, :last_name, algorithm: :copy)
     end
-    expected = %(CREATE UNIQUE INDEX  "index_people_on_last_name" ON "people" USING gist ("last_name"))
-    assert_equal expected, add_index(:people, :last_name, :unique => true, :using => :gist)
 
-    expected = %(CREATE UNIQUE INDEX  "index_people_on_last_name" ON "people" USING gist ("last_name") WHERE state = 'active')
-    assert_equal expected, add_index(:people, :last_name, :unique => true, :where => "state = 'active'", :using => :gist)
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.send :remove_method, :index_name_for_remove
+  end
+
+  def test_remove_index_when_name_is_specified
+    expected = %(DROP INDEX CONCURRENTLY "index_people_on_last_name")
+    assert_equal expected, remove_index(:people, name: "index_people_on_last_name", algorithm: :concurrently)
+  end
+
+  def test_remove_index_with_wrong_option
+    assert_raises ArgumentError do
+      remove_index(:people, coulmn: :last_name)
+    end
   end
 
   private
diff --git a/activerecord/test/cases/adapters/postgresql/array_test.rb b/activerecord/test/cases/adapters/postgresql/array_test.rb
index 380a90d765..42618c2ec3 100644
--- a/activerecord/test/cases/adapters/postgresql/array_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/array_test.rb
@@ -1,63 +1,100 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
   include InTimeZone
 
   class PgArray < ActiveRecord::Base
-    self.table_name = 'pg_arrays'
+    self.table_name = "pg_arrays"
   end
 
   def setup
     @connection = ActiveRecord::Base.connection
 
-    enable_extension!('hstore', @connection)
+    enable_extension!("hstore", @connection)
 
     @connection.transaction do
-      @connection.create_table('pg_arrays') do |t|
-        t.string 'tags', array: true
-        t.integer 'ratings', array: true
+      @connection.create_table("pg_arrays") do |t|
+        t.string "tags", array: true, limit: 255
+        t.integer "ratings", array: true
         t.datetime :datetimes, array: true
         t.hstore :hstores, array: true
+        t.decimal :decimals, array: true, default: [], precision: 10, scale: 2
+        t.timestamp :timestamps, array: true, default: [], precision: 6
       end
     end
     PgArray.reset_column_information
-    @column = PgArray.columns_hash['tags']
+    @column = PgArray.columns_hash["tags"]
     @type = PgArray.type_for_attribute("tags")
   end
 
   teardown do
-    @connection.drop_table 'pg_arrays', if_exists: true
-    disable_extension!('hstore', @connection)
+    @connection.drop_table "pg_arrays", if_exists: true
+    disable_extension!("hstore", @connection)
   end
 
   def test_column
     assert_equal :string, @column.type
-    assert_equal "character varying", @column.sql_type
-    assert @column.array?
-    assert_not @type.binary?
+    assert_equal "character varying(255)", @column.sql_type
+    assert_predicate @column, :array?
+    assert_not_predicate @type, :binary?
 
-    ratings_column = PgArray.columns_hash['ratings']
+    ratings_column = PgArray.columns_hash["ratings"]
     assert_equal :integer, ratings_column.type
-    assert ratings_column.array?
+    assert_predicate ratings_column, :array?
+  end
+
+  def test_not_compatible_with_serialize_array
+    new_klass = Class.new(PgArray) do
+      serialize :tags, Array
+    end
+    assert_raises(ActiveRecord::AttributeMethods::Serialization::ColumnNotSerializableError) do
+      new_klass.new
+    end
+  end
+
+  class MyTags
+    def initialize(tags); @tags = tags end
+    def to_a; @tags end
+    def self.load(tags); new(tags) end
+    def self.dump(object); object.to_a end
+  end
+
+  def test_array_with_serialized_attributes
+    new_klass = Class.new(PgArray) do
+      serialize :tags, MyTags
+    end
+
+    new_klass.create!(tags: MyTags.new(["one", "two"]))
+    record = new_klass.first
+
+    assert_instance_of MyTags, record.tags
+    assert_equal ["one", "two"], record.tags.to_a
+
+    record.tags = MyTags.new(["three", "four"])
+    record.save!
+
+    assert_equal ["three", "four"], record.reload.tags.to_a
   end
 
   def test_default
-    @connection.add_column 'pg_arrays', 'score', :integer, array: true, default: [4, 4, 2]
+    @connection.add_column "pg_arrays", "score", :integer, array: true, default: [4, 4, 2]
     PgArray.reset_column_information
 
-    assert_equal([4, 4, 2], PgArray.column_defaults['score'])
+    assert_equal([4, 4, 2], PgArray.column_defaults["score"])
     assert_equal([4, 4, 2], PgArray.new.score)
   ensure
     PgArray.reset_column_information
   end
 
   def test_default_strings
-    @connection.add_column 'pg_arrays', 'names', :string, array: true, default: ["foo", "bar"]
+    @connection.add_column "pg_arrays", "names", :string, array: true, default: ["foo", "bar"]
     PgArray.reset_column_information
 
-    assert_equal(["foo", "bar"], PgArray.column_defaults['names'])
+    assert_equal(["foo", "bar"], PgArray.column_defaults["names"])
     assert_equal(["foo", "bar"], PgArray.new.names)
   ensure
     PgArray.reset_column_information
@@ -68,11 +105,11 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     @connection.change_column :pg_arrays, :snippets, :text, array: true, default: []
 
     PgArray.reset_column_information
-    column = PgArray.columns_hash['snippets']
+    column = PgArray.columns_hash["snippets"]
 
     assert_equal :text, column.type
-    assert_equal [], PgArray.column_defaults['snippets']
-    assert column.array?
+    assert_equal [], PgArray.column_defaults["snippets"]
+    assert_predicate column, :array?
   end
 
   def test_change_column_cant_make_non_array_column_to_array
@@ -88,17 +125,17 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     @connection.change_column_default :pg_arrays, :tags, []
 
     PgArray.reset_column_information
-    assert_equal [], PgArray.column_defaults['tags']
+    assert_equal [], PgArray.column_defaults["tags"]
   end
 
   def test_type_cast_array
-    assert_equal(['1', '2', '3'], @type.deserialize('{1,2,3}'))
-    assert_equal([], @type.deserialize('{}'))
-    assert_equal([nil], @type.deserialize('{NULL}'))
+    assert_equal(["1", "2", "3"], @type.deserialize("{1,2,3}"))
+    assert_equal([], @type.deserialize("{}"))
+    assert_equal([nil], @type.deserialize("{NULL}"))
   end
 
   def test_type_cast_integers
-    x = PgArray.new(ratings: ['1', '2'])
+    x = PgArray.new(ratings: ["1", "2"])
 
     assert_equal([1, 2], x.ratings)
 
@@ -110,22 +147,23 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
 
   def test_schema_dump_with_shorthand
     output = dump_table_schema "pg_arrays"
-    assert_match %r[t\.string\s+"tags",\s+array: true], output
+    assert_match %r[t\.string\s+"tags",\s+limit: 255,\s+array: true], output
     assert_match %r[t\.integer\s+"ratings",\s+array: true], output
+    assert_match %r[t\.decimal\s+"decimals",\s+precision: 10,\s+scale: 2,\s+default: \[\],\s+array: true], output
   end
 
   def test_select_with_strings
     @connection.execute "insert into pg_arrays (tags) VALUES ('{1,2,3}')"
     x = PgArray.first
-    assert_equal(['1','2','3'], x.tags)
+    assert_equal(["1", "2", "3"], x.tags)
   end
 
   def test_rewrite_with_strings
     @connection.execute "insert into pg_arrays (tags) VALUES ('{1,2,3}')"
     x = PgArray.first
-    x.tags = ['1','2','3','4']
+    x.tags = ["1", "2", "3", "4"]
     x.save!
-    assert_equal ['1','2','3','4'], x.reload.tags
+    assert_equal ["1", "2", "3", "4"], x.reload.tags
   end
 
   def test_select_with_integers
@@ -137,25 +175,25 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
   def test_rewrite_with_integers
     @connection.execute "insert into pg_arrays (ratings) VALUES ('{1,2,3}')"
     x = PgArray.first
-    x.ratings = [2, '3', 4]
+    x.ratings = [2, "3", 4]
     x.save!
     assert_equal [2, 3, 4], x.reload.ratings
   end
 
   def test_multi_dimensional_with_strings
-    assert_cycle(:tags, [[['1'], ['2']], [['2'], ['3']]])
+    assert_cycle(:tags, [[["1"], ["2"]], [["2"], ["3"]]])
   end
 
   def test_with_empty_strings
-    assert_cycle(:tags, [ '1', '2', '', '4', '', '5' ])
+    assert_cycle(:tags, [ "1", "2", "", "4", "", "5" ])
   end
 
   def test_with_multi_dimensional_empty_strings
-    assert_cycle(:tags, [[['1', '2'], ['', '4'], ['', '5']]])
+    assert_cycle(:tags, [[["1", "2"], ["", "4"], ["", "5"]]])
   end
 
   def test_with_arbitrary_whitespace
-    assert_cycle(:tags, [[['1', '2'], ['    ', '4'], ['    ', '5']]])
+    assert_cycle(:tags, [[["1", "2"], ["    ", "4"], ["    ", "5"]]])
   end
 
   def test_multi_dimensional_with_integers
@@ -163,34 +201,47 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_strings_with_quotes
-    assert_cycle(:tags, ['this has','some "s that need to be escaped"'])
+    assert_cycle(:tags, ["this has", 'some "s that need to be escaped"'])
   end
 
   def test_strings_with_commas
-    assert_cycle(:tags, ['this,has','many,values'])
+    assert_cycle(:tags, ["this,has", "many,values"])
   end
 
   def test_strings_with_array_delimiters
-    assert_cycle(:tags, ['{','}'])
+    assert_cycle(:tags, ["{", "}"])
   end
 
   def test_strings_with_null_strings
-    assert_cycle(:tags, ['NULL','NULL'])
+    assert_cycle(:tags, ["NULL", "NULL"])
   end
 
   def test_contains_nils
-    assert_cycle(:tags, ['1',nil,nil])
+    assert_cycle(:tags, ["1", nil, nil])
   end
 
   def test_insert_fixture
     tag_values = ["val1", "val2", "val3_with_'_multiple_quote_'_chars"]
-    @connection.insert_fixture({"tags" => tag_values}, "pg_arrays" )
+    @connection.insert_fixture({ "tags" => tag_values }, "pg_arrays")
+    assert_equal(PgArray.last.tags, tag_values)
+  end
+
+  def test_insert_fixtures
+    tag_values = ["val1", "val2", "val3_with_'_multiple_quote_'_chars"]
+    assert_deprecated do
+      @connection.insert_fixtures([{ "tags" => tag_values }], "pg_arrays")
+    end
     assert_equal(PgArray.last.tags, tag_values)
   end
 
   def test_attribute_for_inspect_for_array_field
+    record = PgArray.new { |a| a.ratings = (1..10).to_a }
+    assert_equal("[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]", record.attribute_for_inspect(:ratings))
+  end
+
+  def test_attribute_for_inspect_for_array_field_for_large_array
     record = PgArray.new { |a| a.ratings = (1..11).to_a }
-    assert_equal("[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, ...]", record.attribute_for_inspect(:ratings))
+    assert_equal("[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]", record.attribute_for_inspect(:ratings))
   end
 
   def test_escaping
@@ -206,17 +257,18 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     x = PgArray.create!(tags: tags)
     x.reload
 
-    assert_equal x.tags_before_type_cast, PgArray.type_for_attribute('tags').serialize(tags)
+    assert_not_predicate x, :changed?
   end
 
   def test_quoting_non_standard_delimiters
     strings = ["hello,", "world;"]
     oid = ActiveRecord::ConnectionAdapters::PostgreSQL::OID
-    comma_delim = oid::Array.new(ActiveRecord::Type::String.new, ',')
-    semicolon_delim = oid::Array.new(ActiveRecord::Type::String.new, ';')
+    comma_delim = oid::Array.new(ActiveRecord::Type::String.new, ",")
+    semicolon_delim = oid::Array.new(ActiveRecord::Type::String.new, ";")
+    conn = PgArray.connection
 
-    assert_equal %({"hello,",world;}), comma_delim.serialize(strings)
-    assert_equal %({hello,;"world;"}), semicolon_delim.serialize(strings)
+    assert_equal %({"hello,",world;}), conn.type_cast(comma_delim.serialize(strings))
+    assert_equal %({hello,;"world;"}), conn.type_cast(semicolon_delim.serialize(strings))
   end
 
   def test_mutate_array
@@ -227,18 +279,18 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     x.reload
 
     assert_equal %w(one two three), x.tags
-    assert_not x.changed?
+    assert_not_predicate x, :changed?
   end
 
   def test_mutate_value_in_array
-    x = PgArray.create!(hstores: [{ a: 'a' }, { b: 'b' }])
+    x = PgArray.create!(hstores: [{ a: "a" }, { b: "b" }])
 
-    x.hstores.first['a'] = 'c'
+    x.hstores.first["a"] = "c"
     x.save!
     x.reload
 
-    assert_equal [{ 'a' => 'c' }, { 'b' => 'b' }], x.hstores
-    assert_not x.changed?
+    assert_equal [{ "a" => "c" }, { "b" => "b" }], x.hstores
+    assert_not_predicate x, :changed?
   end
 
   def test_datetime_with_timezone_awareness
@@ -285,6 +337,12 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     assert_equal record.tags, record.reload.tags
   end
 
+  def test_where_by_attribute_with_array
+    tags = ["black", "blue"]
+    record = PgArray.create!(tags: tags)
+    assert_equal record, PgArray.where(tags: tags).take
+  end
+
   def test_uniqueness_validation
     klass = Class.new(PgArray) do
       validates_uniqueness_of :tags
@@ -295,23 +353,38 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     assert e1.persisted?, "Saving e1"
 
     e2 = klass.create("tags" => ["black", "blue"])
-    assert !e2.persisted?, "e2 shouldn't be valid"
+    assert_not e2.persisted?, "e2 shouldn't be valid"
     assert e2.errors[:tags].any?, "Should have errors for tags"
     assert_equal ["has already been taken"], e2.errors[:tags], "Should have uniqueness message for tags"
   end
 
-  private
-  def assert_cycle field, array
-    # test creation
-    x = PgArray.create!(field => array)
-    x.reload
-    assert_equal(array, x.public_send(field))
+  def test_encoding_arrays_of_utf8_strings
+    arrays_of_utf8_strings = %w(nový ファイル)
+    assert_equal arrays_of_utf8_strings, @type.deserialize(@type.serialize(arrays_of_utf8_strings))
+    assert_equal [arrays_of_utf8_strings], @type.deserialize(@type.serialize([arrays_of_utf8_strings]))
+  end
 
-    # test updating
-    x = PgArray.create!(field => [])
-    x.public_send("#{field}=", array)
-    x.save!
-    x.reload
-    assert_equal(array, x.public_send(field))
+  def test_precision_is_respected_on_timestamp_columns
+    time = Time.now.change(usec: 123)
+    record = PgArray.create!(timestamps: [time])
+
+    assert_equal 123, record.timestamps.first.usec
+    record.reload
+    assert_equal 123, record.timestamps.first.usec
   end
+
+  private
+    def assert_cycle(field, array)
+      # test creation
+      x = PgArray.create!(field => array)
+      x.reload
+      assert_equal(array, x.public_send(field))
+
+      # test updating
+      x = PgArray.create!(field => [])
+      x.public_send("#{field}=", array)
+      x.save!
+      x.reload
+      assert_equal(array, x.public_send(field))
+    end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/bit_string_test.rb b/activerecord/test/cases/adapters/postgresql/bit_string_test.rb
index 6f72fa6e0f..c8e728bbb6 100644
--- a/activerecord/test/cases/adapters/postgresql/bit_string_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/bit_string_test.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
-require 'support/schema_dumping_helper'
+require "support/connection_helper"
+require "support/schema_dumping_helper"
 
 class PostgresqlBitStringTest < ActiveRecord::PostgreSQLTestCase
   include ConnectionHelper
@@ -10,7 +12,7 @@ class PostgresqlBitStringTest < ActiveRecord::PostgreSQLTestCase
 
   def setup
     @connection = ActiveRecord::Base.connection
-    @connection.create_table('postgresql_bit_strings', :force => true) do |t|
+    @connection.create_table("postgresql_bit_strings", force: true) do |t|
       t.bit :a_bit, default: "00000011", limit: 8
       t.bit_varying :a_bit_varying, default: "0011", limit: 4
       t.bit :another_bit
@@ -20,34 +22,34 @@ class PostgresqlBitStringTest < ActiveRecord::PostgreSQLTestCase
 
   def teardown
     return unless @connection
-    @connection.drop_table 'postgresql_bit_strings', if_exists: true
+    @connection.drop_table "postgresql_bit_strings", if_exists: true
   end
 
   def test_bit_string_column
     column = PostgresqlBitString.columns_hash["a_bit"]
     assert_equal :bit, column.type
     assert_equal "bit(8)", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlBitString.type_for_attribute("a_bit")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_bit_string_varying_column
     column = PostgresqlBitString.columns_hash["a_bit_varying"]
     assert_equal :bit_varying, column.type
     assert_equal "bit varying(4)", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlBitString.type_for_attribute("a_bit_varying")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_default
-    assert_equal "00000011", PostgresqlBitString.column_defaults['a_bit']
+    assert_equal "00000011", PostgresqlBitString.column_defaults["a_bit"]
     assert_equal "00000011", PostgresqlBitString.new.a_bit
 
-    assert_equal "0011", PostgresqlBitString.column_defaults['a_bit_varying']
+    assert_equal "0011", PostgresqlBitString.column_defaults["a_bit_varying"]
     assert_equal "0011", PostgresqlBitString.new.a_bit_varying
   end
 
@@ -57,16 +59,19 @@ class PostgresqlBitStringTest < ActiveRecord::PostgreSQLTestCase
     assert_match %r{t\.bit_varying\s+"a_bit_varying",\s+limit: 4,\s+default: "0011"$}, output
   end
 
-  def test_assigning_invalid_hex_string_raises_exception
-    assert_raises(ActiveRecord::StatementInvalid) { PostgresqlBitString.create! a_bit: "FF" }
-    assert_raises(ActiveRecord::StatementInvalid) { PostgresqlBitString.create! a_bit_varying: "FF" }
+  if ActiveRecord::Base.connection.prepared_statements
+    def test_assigning_invalid_hex_string_raises_exception
+      assert_raises(ActiveRecord::StatementInvalid) { PostgresqlBitString.create! a_bit: "FF" }
+      assert_raises(ActiveRecord::StatementInvalid) { PostgresqlBitString.create! a_bit_varying: "F" }
+    end
   end
 
   def test_roundtrip
-    PostgresqlBitString.create! a_bit: "00001010", a_bit_varying: "0101"
-    record = PostgresqlBitString.first
+    record = PostgresqlBitString.create!(a_bit: "00001010", a_bit_varying: "0101")
     assert_equal "00001010", record.a_bit
     assert_equal "0101", record.a_bit_varying
+    assert_nil record.another_bit
+    assert_nil record.another_bit_varying
 
     record.a_bit = "11111111"
     record.a_bit_varying = "0xF"
diff --git a/activerecord/test/cases/adapters/postgresql/bytea_test.rb b/activerecord/test/cases/adapters/postgresql/bytea_test.rb
index b6bb1929e6..3988c2adca 100644
--- a/activerecord/test/cases/adapters/postgresql/bytea_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/bytea_test.rb
@@ -1,26 +1,31 @@
+# frozen_string_literal: true
+
 require "cases/helper"
+require "support/schema_dumping_helper"
 
 class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+
   class ByteaDataType < ActiveRecord::Base
-    self.table_name = 'bytea_data_type'
+    self.table_name = "bytea_data_type"
   end
 
   def setup
     @connection = ActiveRecord::Base.connection
     begin
       @connection.transaction do
-        @connection.create_table('bytea_data_type') do |t|
-          t.binary 'payload'
-          t.binary 'serialized'
+        @connection.create_table("bytea_data_type") do |t|
+          t.binary "payload"
+          t.binary "serialized"
         end
       end
     end
-    @column = ByteaDataType.columns_hash['payload']
+    @column = ByteaDataType.columns_hash["payload"]
     @type = ByteaDataType.type_for_attribute("payload")
   end
 
   teardown do
-    @connection.drop_table 'bytea_data_type', if_exists: true
+    @connection.drop_table "bytea_data_type", if_exists: true
   end
 
   def test_column
@@ -29,9 +34,9 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_binary_columns_are_limitless_the_upper_limit_is_one_GB
-    assert_equal 'bytea', @connection.type_to_sql(:binary, 100_000)
+    assert_equal "bytea", @connection.type_to_sql(:binary, limit: 100_000)
     assert_raise ActiveRecord::ActiveRecordError do
-      @connection.type_to_sql :binary, 4294967295
+      @connection.type_to_sql(:binary, limit: 4294967295)
     end
   end
 
@@ -39,17 +44,17 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
     assert @column
 
     data = "\u001F\x8B"
-    assert_equal('UTF-8', data.encoding.name)
-    assert_equal('ASCII-8BIT', @type.deserialize(data).encoding.name)
+    assert_equal("UTF-8", data.encoding.name)
+    assert_equal("ASCII-8BIT", @type.deserialize(data).encoding.name)
   end
 
   def test_type_cast_binary_value
-    data = "\u001F\x8B".force_encoding("BINARY")
+    data = (+"\u001F\x8B").force_encoding("BINARY")
     assert_equal(data, @type.deserialize(data))
   end
 
   def test_type_case_nil
-    assert_equal(nil, @type.deserialize(nil))
+    assert_nil(@type.deserialize(nil))
   end
 
   def test_read_value
@@ -63,14 +68,14 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
   def test_read_nil_value
     @connection.execute "insert into bytea_data_type (payload) VALUES (null)"
     record = ByteaDataType.first
-    assert_equal(nil, record.payload)
+    assert_nil(record.payload)
     record.delete
   end
 
   def test_write_value
     data = "\u001F"
     record = ByteaDataType.create(payload: data)
-    assert_not record.new_record?
+    assert_not_predicate record, :new_record?
     assert_equal(data, record.payload)
   end
 
@@ -85,26 +90,27 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
   def test_via_to_sql_with_complicating_connection
     Thread.new do
       other_conn = ActiveRecord::Base.connection
-      other_conn.execute('SET standard_conforming_strings = off')
+      other_conn.execute("SET standard_conforming_strings = off")
+      other_conn.execute("SET escape_string_warning = off")
     end.join
 
     test_via_to_sql
   end
 
   def test_write_binary
-    data = File.read(File.join(File.dirname(__FILE__), '..', '..', '..', 'assets', 'example.log'))
+    data = File.read(File.join(__dir__, "..", "..", "..", "assets", "example.log"))
     assert(data.size > 1)
     record = ByteaDataType.create(payload: data)
-    assert_not record.new_record?
+    assert_not_predicate record, :new_record?
     assert_equal(data, record.payload)
     assert_equal(data, ByteaDataType.where(id: record.id).first.payload)
   end
 
   def test_write_nil
     record = ByteaDataType.create(payload: nil)
-    assert_not record.new_record?
-    assert_equal(nil, record.payload)
-    assert_equal(nil, ByteaDataType.where(id: record.id).first.payload)
+    assert_not_predicate record, :new_record?
+    assert_nil(record.payload)
+    assert_nil(ByteaDataType.where(id: record.id).first.payload)
   end
 
   class Serializer
@@ -122,4 +128,10 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
     obj.reload
     assert_equal "hello world", obj.serialized
   end
+
+  def test_schema_dumping
+    output = dump_table_schema("bytea_data_type")
+    assert_match %r{t\.binary\s+"payload"$}, output
+    assert_match %r{t\.binary\s+"serialized"$}, output
+  end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/case_insensitive_test.rb b/activerecord/test/cases/adapters/postgresql/case_insensitive_test.rb
new file mode 100644
index 0000000000..305e033642
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/case_insensitive_test.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+class PostgresqlCaseInsensitiveTest < ActiveRecord::PostgreSQLTestCase
+  class Default < ActiveRecord::Base; end
+
+  def test_case_insensitiveness
+    connection = ActiveRecord::Base.connection
+    table = Default.arel_table
+
+    column = Default.columns_hash["char1"]
+    comparison = connection.case_insensitive_comparison table, :char1, column, nil
+    assert_match(/lower/i, comparison.to_sql)
+
+    column = Default.columns_hash["char2"]
+    comparison = connection.case_insensitive_comparison table, :char2, column, nil
+    assert_match(/lower/i, comparison.to_sql)
+
+    column = Default.columns_hash["char3"]
+    comparison = connection.case_insensitive_comparison table, :char3, column, nil
+    assert_match(/lower/i, comparison.to_sql)
+
+    column = Default.columns_hash["multiline_default"]
+    comparison = connection.case_insensitive_comparison table, :multiline_default, column, nil
+    assert_match(/lower/i, comparison.to_sql)
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/change_schema_test.rb b/activerecord/test/cases/adapters/postgresql/change_schema_test.rb
index bc12df668d..6dba4f3e14 100644
--- a/activerecord/test/cases/adapters/postgresql/change_schema_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/change_schema_test.rb
@@ -1,4 +1,6 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class Migration
@@ -19,19 +21,19 @@ module ActiveRecord
 
       def test_change_string_to_date
         connection.change_column :strings, :somedate, :timestamp, using: 'CAST("somedate" AS timestamp)'
-        assert_equal :datetime, connection.columns(:strings).find { |c| c.name == 'somedate' }.type
+        assert_equal :datetime, connection.columns(:strings).find { |c| c.name == "somedate" }.type
       end
 
       def test_change_type_with_symbol
         connection.change_column :strings, :somedate, :timestamp, cast_as: :timestamp
-        assert_equal :datetime, connection.columns(:strings).find { |c| c.name == 'somedate' }.type
+        assert_equal :datetime, connection.columns(:strings).find { |c| c.name == "somedate" }.type
       end
 
       def test_change_type_with_array
         connection.change_column :strings, :somedate, :timestamp, array: true, cast_as: :timestamp
-        column = connection.columns(:strings).find { |c| c.name == 'somedate' }
+        column = connection.columns(:strings).find { |c| c.name == "somedate" }
         assert_equal :datetime, column.type
-        assert column.array?
+        assert_predicate column, :array?
       end
     end
   end
diff --git a/activerecord/test/cases/adapters/postgresql/cidr_test.rb b/activerecord/test/cases/adapters/postgresql/cidr_test.rb
index 52f2a0096c..f20958fbd2 100644
--- a/activerecord/test/cases/adapters/postgresql/cidr_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/cidr_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "ipaddr"
 
diff --git a/activerecord/test/cases/adapters/postgresql/citext_test.rb b/activerecord/test/cases/adapters/postgresql/citext_test.rb
index bd62041e79..9eb0b7d99c 100644
--- a/activerecord/test/cases/adapters/postgresql/citext_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/citext_test.rb
@@ -1,78 +1,78 @@
-require 'cases/helper'
-require 'support/schema_dumping_helper'
-
-if ActiveRecord::Base.connection.supports_extensions?
-  class PostgresqlCitextTest < ActiveRecord::PostgreSQLTestCase
-    include SchemaDumpingHelper
-    class Citext < ActiveRecord::Base
-      self.table_name = 'citexts'
-    end
+# frozen_string_literal: true
 
-    def setup
-      @connection = ActiveRecord::Base.connection
+require "cases/helper"
+require "support/schema_dumping_helper"
 
-      enable_extension!('citext', @connection)
+class PostgresqlCitextTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+  class Citext < ActiveRecord::Base
+    self.table_name = "citexts"
+  end
 
-      @connection.create_table('citexts') do |t|
-        t.citext 'cival'
-      end
-    end
+  def setup
+    @connection = ActiveRecord::Base.connection
 
-    teardown do
-      @connection.drop_table 'citexts', if_exists: true
-      disable_extension!('citext', @connection)
-    end
+    enable_extension!("citext", @connection)
 
-    def test_citext_enabled
-      assert @connection.extension_enabled?('citext')
+    @connection.create_table("citexts") do |t|
+      t.citext "cival"
     end
+  end
 
-    def test_column
-      column = Citext.columns_hash['cival']
-      assert_equal :citext, column.type
-      assert_equal 'citext', column.sql_type
-      assert_not column.array?
+  teardown do
+    @connection.drop_table "citexts", if_exists: true
+    disable_extension!("citext", @connection)
+  end
 
-      type = Citext.type_for_attribute('cival')
-      assert_not type.binary?
-    end
+  def test_citext_enabled
+    assert @connection.extension_enabled?("citext")
+  end
 
-    def test_change_table_supports_json
-      @connection.transaction do
-        @connection.change_table('citexts') do |t|
-          t.citext 'username'
-        end
-        Citext.reset_column_information
-        column = Citext.columns_hash['username']
-        assert_equal :citext, column.type
+  def test_column
+    column = Citext.columns_hash["cival"]
+    assert_equal :citext, column.type
+    assert_equal "citext", column.sql_type
+    assert_not_predicate column, :array?
 
-        raise ActiveRecord::Rollback # reset the schema change
+    type = Citext.type_for_attribute("cival")
+    assert_not_predicate type, :binary?
+  end
+
+  def test_change_table_supports_json
+    @connection.transaction do
+      @connection.change_table("citexts") do |t|
+        t.citext "username"
       end
-    ensure
       Citext.reset_column_information
+      column = Citext.columns_hash["username"]
+      assert_equal :citext, column.type
+
+      raise ActiveRecord::Rollback # reset the schema change
     end
+  ensure
+    Citext.reset_column_information
+  end
 
-    def test_write
-      x = Citext.new(cival: 'Some CI Text')
-      x.save!
-      citext = Citext.first
-      assert_equal "Some CI Text", citext.cival
+  def test_write
+    x = Citext.new(cival: "Some CI Text")
+    x.save!
+    citext = Citext.first
+    assert_equal "Some CI Text", citext.cival
 
-      citext.cival = "Some NEW CI Text"
-      citext.save!
+    citext.cival = "Some NEW CI Text"
+    citext.save!
 
-      assert_equal "Some NEW CI Text", citext.reload.cival
-    end
+    assert_equal "Some NEW CI Text", citext.reload.cival
+  end
 
-    def test_select_case_insensitive
-      @connection.execute "insert into citexts (cival) values('Cased Text')"
-      x = Citext.where(cival: 'cased text').first
-      assert_equal 'Cased Text', x.cival
-    end
+  def test_select_case_insensitive
+    @connection.execute "insert into citexts (cival) values('Cased Text')"
+    x = Citext.where(cival: "cased text").first
+    assert_equal "Cased Text", x.cival
+  end
 
-    def test_schema_dump_with_shorthand
-      output = dump_table_schema("citexts")
-      assert_match %r[t\.citext "cival"], output
-    end
+  def test_schema_dump_with_shorthand
+    output = dump_table_schema("citexts")
+    assert_match %r[t\.citext "cival"], output
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/collation_test.rb b/activerecord/test/cases/adapters/postgresql/collation_test.rb
index 8470329c35..7468f4c4f8 100644
--- a/activerecord/test/cases/adapters/postgresql/collation_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/collation_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class PostgresqlCollationTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
@@ -7,8 +9,8 @@ class PostgresqlCollationTest < ActiveRecord::PostgreSQLTestCase
   def setup
     @connection = ActiveRecord::Base.connection
     @connection.create_table :postgresql_collations, force: true do |t|
-      t.string :string_c, collation: 'C'
-      t.text :text_posix, collation: 'POSIX'
+      t.string :string_c, collation: "C"
+      t.text :text_posix, collation: "POSIX"
     end
   end
 
@@ -17,37 +19,37 @@ class PostgresqlCollationTest < ActiveRecord::PostgreSQLTestCase
   end
 
   test "string column with collation" do
-    column = @connection.columns(:postgresql_collations).find { |c| c.name == 'string_c' }
+    column = @connection.columns(:postgresql_collations).find { |c| c.name == "string_c" }
     assert_equal :string, column.type
-    assert_equal 'C', column.collation
+    assert_equal "C", column.collation
   end
 
   test "text column with collation" do
-    column = @connection.columns(:postgresql_collations).find { |c| c.name == 'text_posix' }
+    column = @connection.columns(:postgresql_collations).find { |c| c.name == "text_posix" }
     assert_equal :text, column.type
-    assert_equal 'POSIX', column.collation
+    assert_equal "POSIX", column.collation
   end
 
   test "add column with collation" do
-    @connection.add_column :postgresql_collations, :title, :string, collation: 'C'
+    @connection.add_column :postgresql_collations, :title, :string, collation: "C"
 
-    column = @connection.columns(:postgresql_collations).find { |c| c.name == 'title' }
+    column = @connection.columns(:postgresql_collations).find { |c| c.name == "title" }
     assert_equal :string, column.type
-    assert_equal 'C', column.collation
+    assert_equal "C", column.collation
   end
 
   test "change column with collation" do
     @connection.add_column :postgresql_collations, :description, :string
-    @connection.change_column :postgresql_collations, :description, :text, collation: 'POSIX'
+    @connection.change_column :postgresql_collations, :description, :text, collation: "POSIX"
 
-    column = @connection.columns(:postgresql_collations).find { |c| c.name == 'description' }
+    column = @connection.columns(:postgresql_collations).find { |c| c.name == "description" }
     assert_equal :text, column.type
-    assert_equal 'POSIX', column.collation
+    assert_equal "POSIX", column.collation
   end
 
   test "schema dump includes collation" do
     output = dump_table_schema("postgresql_collations")
-    assert_match %r{t.string\s+"string_c",\s+collation: "C"$}, output
-    assert_match %r{t.text\s+"text_posix",\s+collation: "POSIX"$}, output
+    assert_match %r{t\.string\s+"string_c",\s+collation: "C"$}, output
+    assert_match %r{t\.text\s+"text_posix",\s+collation: "POSIX"$}, output
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/composite_test.rb b/activerecord/test/cases/adapters/postgresql/composite_test.rb
index 1de87e5f01..b0ce2694a3 100644
--- a/activerecord/test/cases/adapters/postgresql/composite_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/composite_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
+require "support/connection_helper"
 
 module PostgresqlCompositeBehavior
   include ConnectionHelper
@@ -20,7 +22,7 @@ module PostgresqlCompositeBehavior
              street VARCHAR(90)
          );
         SQL
-      @connection.create_table('postgresql_composites') do |t|
+      @connection.create_table("postgresql_composites") do |t|
         t.column :address, :full_address
       end
     end
@@ -29,8 +31,8 @@ module PostgresqlCompositeBehavior
   def teardown
     super
 
-    @connection.drop_table 'postgresql_composites', if_exists: true
-    @connection.execute 'DROP TYPE IF EXISTS full_address'
+    @connection.drop_table "postgresql_composites", if_exists: true
+    @connection.execute "DROP TYPE IF EXISTS full_address"
     reset_connection
     PostgresqlComposite.reset_column_information
   end
@@ -49,10 +51,10 @@ class PostgresqlCompositeTest < ActiveRecord::PostgreSQLTestCase
     column = PostgresqlComposite.columns_hash["address"]
     assert_nil column.type
     assert_equal "full_address", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlComposite.type_for_attribute("address")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_composite_mapping
@@ -69,12 +71,12 @@ class PostgresqlCompositeTest < ActiveRecord::PostgreSQLTestCase
   end
 
   private
-  def ensure_warning_is_issued
-    warning = capture(:stderr) do
-      PostgresqlComposite.columns_hash
+    def ensure_warning_is_issued
+      warning = capture(:stderr) do
+        PostgresqlComposite.columns_hash
+      end
+      assert_match(/unknown OID \d+: failed to recognize type of 'address'\. It will be treated as String\./, warning)
     end
-    assert_match(/unknown OID \d+: failed to recognize type of 'address'\. It will be treated as String\./, warning)
-  end
 end
 
 class PostgresqlCompositeWithCustomOIDTest < ActiveRecord::PostgreSQLTestCase
@@ -104,17 +106,17 @@ class PostgresqlCompositeWithCustomOIDTest < ActiveRecord::PostgreSQLTestCase
   def setup
     super
 
-    @connection.type_map.register_type "full_address", FullAddressType.new
+    @connection.send(:type_map).register_type "full_address", FullAddressType.new
   end
 
   def test_column
     column = PostgresqlComposite.columns_hash["address"]
     assert_equal :full_address, column.type
     assert_equal "full_address", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlComposite.type_for_attribute("address")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_composite_mapping
@@ -126,7 +128,7 @@ class PostgresqlCompositeWithCustomOIDTest < ActiveRecord::PostgreSQLTestCase
     composite.address = FullAddress.new("Paris", "Rue Basse")
     composite.save!
 
-    assert_equal 'Paris', composite.reload.address.city
-    assert_equal 'Rue Basse', composite.reload.address.street
+    assert_equal "Paris", composite.reload.address.city
+    assert_equal "Rue Basse", composite.reload.address.street
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/connection_test.rb b/activerecord/test/cases/adapters/postgresql/connection_test.rb
index 820d41e13b..70aa189893 100644
--- a/activerecord/test/cases/adapters/postgresql/connection_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/connection_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
+require "support/connection_helper"
 
 module ActiveRecord
   class PostgresqlConnectionTest < ActiveRecord::PostgreSQLTestCase
@@ -13,8 +15,9 @@ module ActiveRecord
     def setup
       super
       @subscriber = SQLSubscriber.new
-      @subscription = ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
       @connection = ActiveRecord::Base.connection
+      @connection.materialize_transactions
+      @subscription = ActiveSupport::Notifications.subscribe("sql.active_record", @subscriber)
     end
 
     def teardown
@@ -23,23 +26,29 @@ module ActiveRecord
     end
 
     def test_truncate
-      count = ActiveRecord::Base.connection.execute("select count(*) from comments").first['count'].to_i
+      count = ActiveRecord::Base.connection.execute("select count(*) from comments").first["count"].to_i
       assert_operator count, :>, 0
       ActiveRecord::Base.connection.truncate("comments")
-      count = ActiveRecord::Base.connection.execute("select count(*) from comments").first['count'].to_i
+      count = ActiveRecord::Base.connection.execute("select count(*) from comments").first["count"].to_i
       assert_equal 0, count
     end
 
     def test_encoding
-      assert_not_nil @connection.encoding
+      assert_queries(1) do
+        assert_not_nil @connection.encoding
+      end
     end
 
     def test_collation
-      assert_not_nil @connection.collation
+      assert_queries(1) do
+        assert_not_nil @connection.collation
+      end
     end
 
     def test_ctype
-      assert_not_nil @connection.ctype
+      assert_queries(1) do
+        assert_not_nil @connection.ctype
+      end
     end
 
     def test_default_client_min_messages
@@ -54,85 +63,87 @@ module ActiveRecord
       NonExistentTable.establish_connection(params)
 
       # Verify the connection param has been applied.
-      expect = NonExistentTable.connection.query('show geqo').first.first
-      assert_equal 'off', expect
+      expect = NonExistentTable.connection.query("show geqo").first.first
+      assert_equal "off", expect
     end
 
     def test_reset
-      @connection.query('ROLLBACK')
-      @connection.query('SET geqo TO off')
+      @connection.query("ROLLBACK")
+      @connection.query("SET geqo TO off")
 
       # Verify the setting has been applied.
-      expect = @connection.query('show geqo').first.first
-      assert_equal 'off', expect
+      expect = @connection.query("show geqo").first.first
+      assert_equal "off", expect
 
       @connection.reset!
 
       # Verify the setting has been cleared.
-      expect = @connection.query('show geqo').first.first
-      assert_equal 'on', expect
+      expect = @connection.query("show geqo").first.first
+      assert_equal "on", expect
     end
 
     def test_reset_with_transaction
-      @connection.query('ROLLBACK')
-      @connection.query('SET geqo TO off')
+      @connection.query("ROLLBACK")
+      @connection.query("SET geqo TO off")
 
       # Verify the setting has been applied.
-      expect = @connection.query('show geqo').first.first
-      assert_equal 'off', expect
+      expect = @connection.query("show geqo").first.first
+      assert_equal "off", expect
 
-      @connection.query('BEGIN')
+      @connection.query("BEGIN")
       @connection.reset!
 
       # Verify the setting has been cleared.
-      expect = @connection.query('show geqo').first.first
-      assert_equal 'on', expect
+      expect = @connection.query("show geqo").first.first
+      assert_equal "on", expect
     end
 
     def test_tables_logs_name
-      @connection.tables('hello')
-      assert_equal 'SCHEMA', @subscriber.logged[0][1]
+      @connection.tables
+      assert_equal "SCHEMA", @subscriber.logged[0][1]
     end
 
     def test_indexes_logs_name
-      @connection.indexes('items', 'hello')
-      assert_equal 'SCHEMA', @subscriber.logged[0][1]
+      @connection.indexes("items")
+      assert_equal "SCHEMA", @subscriber.logged[0][1]
     end
 
     def test_table_exists_logs_name
-      @connection.table_exists?('items')
-      assert_equal 'SCHEMA', @subscriber.logged[0][1]
+      @connection.table_exists?("items")
+      assert_equal "SCHEMA", @subscriber.logged[0][1]
     end
 
     def test_table_alias_length_logs_name
-      @connection.instance_variable_set("@table_alias_length", nil)
+      @connection.instance_variable_set("@max_identifier_length", nil)
       @connection.table_alias_length
-      assert_equal 'SCHEMA', @subscriber.logged[0][1]
+      assert_equal "SCHEMA", @subscriber.logged[0][1]
     end
 
     def test_current_database_logs_name
       @connection.current_database
-      assert_equal 'SCHEMA', @subscriber.logged[0][1]
+      assert_equal "SCHEMA", @subscriber.logged[0][1]
     end
 
     def test_encoding_logs_name
       @connection.encoding
-      assert_equal 'SCHEMA', @subscriber.logged[0][1]
+      assert_equal "SCHEMA", @subscriber.logged[0][1]
     end
 
     def test_schema_names_logs_name
       @connection.schema_names
-      assert_equal 'SCHEMA', @subscriber.logged[0][1]
+      assert_equal "SCHEMA", @subscriber.logged[0][1]
     end
 
-    def test_statement_key_is_logged
-      bind = Relation::QueryAttribute.new(nil, 1, Type::Value.new)
-      @connection.exec_query('SELECT $1::integer', 'SQL', [bind])
-      name = @subscriber.payloads.last[:statement_name]
-      assert name
-      res = @connection.exec_query("EXPLAIN (FORMAT JSON) EXECUTE #{name}(1)")
-      plan = res.column_types['QUERY PLAN'].deserialize res.rows.first.first
-      assert_operator plan.length, :>, 0
+    if ActiveRecord::Base.connection.prepared_statements
+      def test_statement_key_is_logged
+        bind = Relation::QueryAttribute.new(nil, 1, Type::Value.new)
+        @connection.exec_query("SELECT $1::integer", "SQL", [bind], prepare: true)
+        name = @subscriber.payloads.last[:statement_name]
+        assert name
+        res = @connection.exec_query("EXPLAIN (FORMAT JSON) EXECUTE #{name}(1)")
+        plan = res.column_types["QUERY PLAN"].deserialize res.rows.first.first
+        assert_operator plan.length, :>, 0
+      end
     end
 
     # Must have PostgreSQL >= 9.2, or with_manual_interventions set to
@@ -141,20 +152,20 @@ module ActiveRecord
     # When prompted, restart the PostgreSQL server with the
     # "-m fast" option or kill the individual connection assuming
     # you know the incantation to do that.
-    # To restart PostgreSQL 9.1 on OS X, installed via MacPorts, ...
+    # To restart PostgreSQL 9.1 on macOS, installed via MacPorts, ...
     # sudo su postgres -c "pg_ctl restart -D /opt/local/var/db/postgresql91/defaultdb/ -m fast"
     def test_reconnection_after_actual_disconnection_with_verify
-      original_connection_pid = @connection.query('select pg_backend_pid()')
+      original_connection_pid = @connection.query("select pg_backend_pid()")
 
       # Sanity check.
-      assert @connection.active?
+      assert_predicate @connection, :active?
 
       if @connection.send(:postgresql_version) >= 90200
         secondary_connection = ActiveRecord::Base.connection_pool.checkout
         secondary_connection.query("select pg_terminate_backend(#{original_connection_pid.first.first})")
         ActiveRecord::Base.connection_pool.checkin(secondary_connection)
-      elsif ARTest.config['with_manual_interventions']
-        puts 'Kill the connection now (e.g. by restarting the PostgreSQL ' +
+      elsif ARTest.config["with_manual_interventions"]
+        puts "Kill the connection now (e.g. by restarting the PostgreSQL " \
           'server with the "-m fast" option) and then press enter.'
         $stdin.gets
       else
@@ -166,23 +177,23 @@ module ActiveRecord
 
       @connection.verify!
 
-      assert @connection.active?
+      assert_predicate @connection, :active?
 
       # If we get no exception here, then either we re-connected successfully, or
       # we never actually got disconnected.
-      new_connection_pid = @connection.query('select pg_backend_pid()')
+      new_connection_pid = @connection.query("select pg_backend_pid()")
 
       assert_not_equal original_connection_pid, new_connection_pid,
-        "umm -- looks like you didn't break the connection, because we're still " +
+        "umm -- looks like you didn't break the connection, because we're still " \
         "successfully querying with the same connection pid."
-
+    ensure
       # Repair all fixture connections so other tests won't break.
       @fixture_connections.each(&:verify!)
     end
 
     def test_set_session_variable_true
       run_without_connection do |orig_connection|
-        ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:debug_print_plan => true}}))
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { debug_print_plan: true }))
         set_true = ActiveRecord::Base.connection.exec_query "SHOW DEBUG_PRINT_PLAN"
         assert_equal set_true.rows, [["on"]]
       end
@@ -190,7 +201,7 @@ module ActiveRecord
 
     def test_set_session_variable_false
       run_without_connection do |orig_connection|
-        ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:debug_print_plan => false}}))
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { debug_print_plan: false }))
         set_false = ActiveRecord::Base.connection.exec_query "SHOW DEBUG_PRINT_PLAN"
         assert_equal set_false.rows, [["off"]]
       end
@@ -199,15 +210,64 @@ module ActiveRecord
     def test_set_session_variable_nil
       run_without_connection do |orig_connection|
         # This should be a no-op that does not raise an error
-        ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:debug_print_plan => nil}}))
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { debug_print_plan: nil }))
       end
     end
 
     def test_set_session_variable_default
       run_without_connection do |orig_connection|
         # This should execute a query that does not raise an error
-        ActiveRecord::Base.establish_connection(orig_connection.deep_merge({:variables => {:debug_print_plan => :default}}))
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { debug_print_plan: :default }))
+      end
+    end
+
+    def test_set_session_timezone
+      run_without_connection do |orig_connection|
+        ActiveRecord::Base.establish_connection(orig_connection.deep_merge(variables: { timezone: "America/New_York" }))
+        assert_equal "America/New_York", ActiveRecord::Base.connection.query_value("SHOW TIME ZONE")
+      end
+    end
+
+    def test_get_and_release_advisory_lock
+      lock_id = 5295901941911233559
+      list_advisory_locks = <<-SQL
+        SELECT locktype,
+              (classid::bigint << 32) | objid::bigint AS lock_id
+        FROM pg_locks
+        WHERE locktype = 'advisory'
+      SQL
+
+      got_lock = @connection.get_advisory_lock(lock_id)
+      assert got_lock, "get_advisory_lock should have returned true but it didn't"
+
+      advisory_lock = @connection.query(list_advisory_locks).find { |l| l[1] == lock_id }
+      assert advisory_lock,
+        "expected to find an advisory lock with lock_id #{lock_id} but there wasn't one"
+
+      released_lock = @connection.release_advisory_lock(lock_id)
+      assert released_lock, "expected release_advisory_lock to return true but it didn't"
+
+      advisory_locks = @connection.query(list_advisory_locks).select { |l| l[1] == lock_id }
+      assert_empty advisory_locks,
+        "expected to have released advisory lock with lock_id #{lock_id} but it was still held"
+    end
+
+    def test_release_non_existent_advisory_lock
+      fake_lock_id = 2940075057017742022
+      with_warning_suppression do
+        released_non_existent_lock = @connection.release_advisory_lock(fake_lock_id)
+        assert_equal released_non_existent_lock, false,
+          "expected release_advisory_lock to return false when there was no lock to release"
       end
     end
+
+    private
+
+      def with_warning_suppression
+        log_level = @connection.client_min_messages
+        @connection.client_min_messages = "error"
+        yield
+        @connection.client_min_messages = log_level
+      end
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/create_unlogged_tables_test.rb b/activerecord/test/cases/adapters/postgresql/create_unlogged_tables_test.rb
new file mode 100644
index 0000000000..a02bae1453
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/create_unlogged_tables_test.rb
@@ -0,0 +1,74 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/schema_dumping_helper"
+
+class UnloggedTablesTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+
+  TABLE_NAME = "things"
+  LOGGED_FIELD = "relpersistence"
+  LOGGED_QUERY = "SELECT #{LOGGED_FIELD} FROM pg_class WHERE relname = '#{TABLE_NAME}'"
+  LOGGED = "p"
+  UNLOGGED = "u"
+  TEMPORARY = "t"
+
+  class Thing < ActiveRecord::Base
+    self.table_name = TABLE_NAME
+  end
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = false
+  end
+
+  teardown do
+    @connection.drop_table TABLE_NAME, if_exists: true
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = false
+  end
+
+  def test_logged_by_default
+    @connection.create_table(TABLE_NAME) do |t|
+    end
+    assert_equal @connection.execute(LOGGED_QUERY).first[LOGGED_FIELD], LOGGED
+  end
+
+  def test_unlogged_in_test_environment_when_unlogged_setting_enabled
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = true
+
+    @connection.create_table(TABLE_NAME) do |t|
+    end
+    assert_equal @connection.execute(LOGGED_QUERY).first[LOGGED_FIELD], UNLOGGED
+  end
+
+  def test_not_included_in_schema_dump
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = true
+
+    @connection.create_table(TABLE_NAME) do |t|
+    end
+    assert_no_match(/unlogged/i, dump_table_schema(TABLE_NAME))
+  end
+
+  def test_not_changed_in_change_table
+    @connection.create_table(TABLE_NAME) do |t|
+    end
+
+    ActiveRecord::ConnectionAdapters::PostgreSQLAdapter.create_unlogged_tables = true
+
+    @connection.change_table(TABLE_NAME) do |t|
+      t.column :name, :string
+    end
+    assert_equal @connection.execute(LOGGED_QUERY).first[LOGGED_FIELD], LOGGED
+  end
+
+  def test_gracefully_handles_temporary_tables
+    @connection.create_table(TABLE_NAME, temporary: true) do |t|
+    end
+
+    # Temporary tables are already unlogged, though this query results in a
+    # different result ("t" vs. "u"). This test is really just checking that we
+    # didn't try to run `CREATE TEMPORARY UNLOGGED TABLE`, which would result in
+    # a PostgreSQL error.
+    assert_equal @connection.execute(LOGGED_QUERY).first[LOGGED_FIELD], TEMPORARY
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/datatype_test.rb b/activerecord/test/cases/adapters/postgresql/datatype_test.rb
index 232c25cb3b..b7535d5c9a 100644
--- a/activerecord/test/cases/adapters/postgresql/datatype_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/datatype_test.rb
@@ -1,6 +1,7 @@
-require "cases/helper"
-require 'support/ddl_helper'
+# frozen_string_literal: true
 
+require "cases/helper"
+require "support/ddl_helper"
 
 class PostgresqlTime < ActiveRecord::Base
 end
@@ -29,17 +30,17 @@ class PostgresqlDataTypeTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_data_type_of_time_types
-    assert_equal :string, @first_time.column_for_attribute(:time_interval).type
-    assert_equal :string, @first_time.column_for_attribute(:scaled_time_interval).type
+    assert_equal :interval, @first_time.column_for_attribute(:time_interval).type
+    assert_equal :interval, @first_time.column_for_attribute(:scaled_time_interval).type
   end
 
   def test_data_type_of_oid_types
-    assert_equal :integer, @first_oid.column_for_attribute(:obj_id).type
+    assert_equal :oid, @first_oid.column_for_attribute(:obj_id).type
   end
 
   def test_time_values
-    assert_equal '-1 years -2 days', @first_time.time_interval
-    assert_equal '-21 days', @first_time.scaled_time_interval
+    assert_equal "-1 years -2 days", @first_time.time_interval
+    assert_equal "-21 days", @first_time.scaled_time_interval
   end
 
   def test_oid_values
@@ -47,10 +48,10 @@ class PostgresqlDataTypeTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_update_time
-    @first_time.time_interval = '2 years 3 minutes'
+    @first_time.time_interval = "2 years 3 minutes"
     assert @first_time.save
     assert @first_time.reload
-    assert_equal '2 years 00:03:00', @first_time.time_interval
+    assert_equal "2 years 00:03:00", @first_time.time_interval
   end
 
   def test_update_oid
@@ -62,9 +63,9 @@ class PostgresqlDataTypeTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_text_columns_are_limitless_the_upper_limit_is_one_GB
-    assert_equal 'text', @connection.type_to_sql(:text, 100_000)
+    assert_equal "text", @connection.type_to_sql(:text, limit: 100_000)
     assert_raise ActiveRecord::ActiveRecordError do
-      @connection.type_to_sql :text, 4294967295
+      @connection.type_to_sql(:text, limit: 4294967295)
     end
   end
 end
@@ -77,15 +78,15 @@ class PostgresqlInternalDataTypeTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_name_column_type
-    with_example_table @connection, 'ex', 'data name' do
-      column = @connection.columns('ex').find { |col| col.name == 'data' }
+    with_example_table @connection, "ex", "data name" do
+      column = @connection.columns("ex").find { |col| col.name == "data" }
       assert_equal :string, column.type
     end
   end
 
   def test_char_column_type
-    with_example_table @connection, 'ex', 'data "char"' do
-      column = @connection.columns('ex').find { |col| col.name == 'data' }
+    with_example_table @connection, "ex", 'data "char"' do
+      column = @connection.columns("ex").find { |col| col.name == "data" }
       assert_equal :string, column.type
     end
   end
diff --git a/activerecord/test/cases/adapters/postgresql/date_test.rb b/activerecord/test/cases/adapters/postgresql/date_test.rb
new file mode 100644
index 0000000000..a86abac2be
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/date_test.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/topic"
+
+class PostgresqlDateTest < ActiveRecord::PostgreSQLTestCase
+  def test_load_infinity_and_beyond
+    topic = Topic.find_by_sql("SELECT 'infinity'::date AS last_read").first
+    assert topic.last_read.infinite?, "timestamp should be infinite"
+    assert_operator topic.last_read, :>, 0
+
+    topic = Topic.find_by_sql("SELECT '-infinity'::date AS last_read").first
+    assert topic.last_read.infinite?, "timestamp should be infinite"
+    assert_operator topic.last_read, :<, 0
+  end
+
+  def test_save_infinity_and_beyond
+    topic = Topic.create!(last_read: 1.0 / 0.0)
+    assert_equal(1.0 / 0.0, topic.last_read)
+
+    topic = Topic.create!(last_read: -1.0 / 0.0)
+    assert_equal(-1.0 / 0.0, topic.last_read)
+  end
+
+  def test_bc_date
+    date = Date.new(0) - 1.week
+    topic = Topic.create!(last_read: date)
+    assert_equal date, Topic.find(topic.id).last_read
+  end
+
+  def test_bc_date_leap_year
+    date = Time.utc(-4, 2, 29).to_date
+    topic = Topic.create!(last_read: date)
+    assert_equal date, Topic.find(topic.id).last_read
+  end
+
+  def test_bc_date_year_zero
+    date = Time.utc(0, 4, 7).to_date
+    topic = Topic.create!(last_read: date)
+    assert_equal date, Topic.find(topic.id).last_read
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/domain_test.rb b/activerecord/test/cases/adapters/postgresql/domain_test.rb
index 6102ddacd1..eeaad94c27 100644
--- a/activerecord/test/cases/adapters/postgresql/domain_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/domain_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
+require "support/connection_helper"
 
 class PostgresqlDomainTest < ActiveRecord::PostgreSQLTestCase
   include ConnectionHelper
@@ -12,15 +14,15 @@ class PostgresqlDomainTest < ActiveRecord::PostgreSQLTestCase
     @connection = ActiveRecord::Base.connection
     @connection.transaction do
       @connection.execute "CREATE DOMAIN custom_money as numeric(8,2)"
-      @connection.create_table('postgresql_domains') do |t|
+      @connection.create_table("postgresql_domains") do |t|
         t.column :price, :custom_money
       end
     end
   end
 
   teardown do
-    @connection.drop_table 'postgresql_domains', if_exists: true
-    @connection.execute 'DROP DOMAIN IF EXISTS custom_money'
+    @connection.drop_table "postgresql_domains", if_exists: true
+    @connection.execute "DROP DOMAIN IF EXISTS custom_money"
     reset_connection
   end
 
@@ -28,10 +30,10 @@ class PostgresqlDomainTest < ActiveRecord::PostgreSQLTestCase
     column = PostgresqlDomain.columns_hash["price"]
     assert_equal :decimal, column.type
     assert_equal "custom_money", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlDomain.type_for_attribute("price")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_domain_acts_like_basetype
@@ -42,6 +44,6 @@ class PostgresqlDomainTest < ActiveRecord::PostgreSQLTestCase
     record.price = "34.15"
     record.save!
 
-    assert_equal BigDecimal.new("34.15"), record.reload.price
+    assert_equal BigDecimal("34.15"), record.reload.price
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/enum_test.rb b/activerecord/test/cases/adapters/postgresql/enum_test.rb
index 6816a6514b..6789ff63e7 100644
--- a/activerecord/test/cases/adapters/postgresql/enum_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/enum_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
+require "support/connection_helper"
 
 class PostgresqlEnumTest < ActiveRecord::PostgreSQLTestCase
   include ConnectionHelper
@@ -14,15 +16,15 @@ class PostgresqlEnumTest < ActiveRecord::PostgreSQLTestCase
       @connection.execute <<-SQL
         CREATE TYPE mood AS ENUM ('sad', 'ok', 'happy');
       SQL
-      @connection.create_table('postgresql_enums') do |t|
+      @connection.create_table("postgresql_enums") do |t|
         t.column :current_mood, :mood
       end
     end
   end
 
   teardown do
-    @connection.drop_table 'postgresql_enums', if_exists: true
-    @connection.execute 'DROP TYPE IF EXISTS mood'
+    @connection.drop_table "postgresql_enums", if_exists: true
+    @connection.execute "DROP TYPE IF EXISTS mood"
     reset_connection
   end
 
@@ -30,17 +32,17 @@ class PostgresqlEnumTest < ActiveRecord::PostgreSQLTestCase
     column = PostgresqlEnum.columns_hash["current_mood"]
     assert_equal :enum, column.type
     assert_equal "mood", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlEnum.type_for_attribute("current_mood")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_enum_defaults
-    @connection.add_column 'postgresql_enums', 'good_mood', :mood, default: 'happy'
+    @connection.add_column "postgresql_enums", "good_mood", :mood, default: "happy"
     PostgresqlEnum.reset_column_information
 
-    assert_equal "happy", PostgresqlEnum.column_defaults['good_mood']
+    assert_equal "happy", PostgresqlEnum.column_defaults["good_mood"]
     assert_equal "happy", PostgresqlEnum.new.good_mood
   ensure
     PostgresqlEnum.reset_column_information
@@ -71,7 +73,7 @@ class PostgresqlEnumTest < ActiveRecord::PostgreSQLTestCase
     @connection.execute "INSERT INTO postgresql_enums VALUES (1, 'sad');"
     stderr_output = capture(:stderr) { PostgresqlEnum.first }
 
-    assert stderr_output.blank?
+    assert_predicate stderr_output, :blank?
   end
 
   def test_enum_type_cast
diff --git a/activerecord/test/cases/adapters/postgresql/explain_test.rb b/activerecord/test/cases/adapters/postgresql/explain_test.rb
index 4d0fd640aa..be525383e9 100644
--- a/activerecord/test/cases/adapters/postgresql/explain_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/explain_test.rb
@@ -1,20 +1,22 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/developer'
-require 'models/computer'
+require "models/author"
+require "models/post"
 
 class PostgreSQLExplainTest < ActiveRecord::PostgreSQLTestCase
-  fixtures :developers
+  fixtures :authors
 
   def test_explain_for_one_query
-    explain = Developer.where(:id => 1).explain
-    assert_match %(EXPLAIN for: SELECT "developers".* FROM "developers" WHERE "developers"."id" = $1), explain
+    explain = Author.where(id: 1).explain
+    assert_match %r(EXPLAIN for: SELECT "authors"\.\* FROM "authors" WHERE "authors"\."id" = (?:\$1 \[\["id", 1\]\]|1)), explain
     assert_match %(QUERY PLAN), explain
   end
 
   def test_explain_with_eager_loading
-    explain = Developer.where(:id => 1).includes(:audit_logs).explain
+    explain = Author.where(id: 1).includes(:posts).explain
     assert_match %(QUERY PLAN), explain
-    assert_match %(EXPLAIN for: SELECT "developers".* FROM "developers" WHERE "developers"."id" = $1), explain
-    assert_match %(EXPLAIN for: SELECT "audit_logs".* FROM "audit_logs" WHERE "audit_logs"."developer_id" = 1), explain
+    assert_match %r(EXPLAIN for: SELECT "authors"\.\* FROM "authors" WHERE "authors"\."id" = (?:\$1 \[\["id", 1\]\]|1)), explain
+    assert_match %r(EXPLAIN for: SELECT "posts"\.\* FROM "posts" WHERE "posts"\."author_id" = (?:\$1 \[\["author_id", 1\]\]|1)), explain
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/extension_migration_test.rb b/activerecord/test/cases/adapters/postgresql/extension_migration_test.rb
index 9cfc133308..df97ab11e7 100644
--- a/activerecord/test/cases/adapters/postgresql/extension_migration_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/extension_migration_test.rb
@@ -1,15 +1,17 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class PostgresqlExtensionMigrationTest < ActiveRecord::PostgreSQLTestCase
   self.use_transactional_tests = false
 
-  class EnableHstore < ActiveRecord::Migration
+  class EnableHstore < ActiveRecord::Migration::Current
     def change
       enable_extension "hstore"
     end
   end
 
-  class DisableHstore < ActiveRecord::Migration
+  class DisableHstore < ActiveRecord::Migration::Current
     def change
       disable_extension "hstore"
     end
@@ -20,13 +22,9 @@ class PostgresqlExtensionMigrationTest < ActiveRecord::PostgreSQLTestCase
 
     @connection = ActiveRecord::Base.connection
 
-    unless @connection.supports_extensions?
-      return skip("no extension support")
-    end
-
-    @old_schema_migration_tabel_name = ActiveRecord::SchemaMigration.table_name
-    @old_tabel_name_prefix = ActiveRecord::Base.table_name_prefix
-    @old_tabel_name_suffix = ActiveRecord::Base.table_name_suffix
+    @old_schema_migration_table_name = ActiveRecord::SchemaMigration.table_name
+    @old_table_name_prefix = ActiveRecord::Base.table_name_prefix
+    @old_table_name_suffix = ActiveRecord::Base.table_name_suffix
 
     ActiveRecord::Base.table_name_prefix = "p_"
     ActiveRecord::Base.table_name_suffix = "_s"
@@ -36,11 +34,11 @@ class PostgresqlExtensionMigrationTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def teardown
-    ActiveRecord::Base.table_name_prefix = @old_tabel_name_prefix
-    ActiveRecord::Base.table_name_suffix = @old_tabel_name_suffix
+    ActiveRecord::Base.table_name_prefix = @old_table_name_prefix
+    ActiveRecord::Base.table_name_suffix = @old_table_name_suffix
     ActiveRecord::SchemaMigration.delete_all rescue nil
     ActiveRecord::Migration.verbose = true
-    ActiveRecord::SchemaMigration.table_name = @old_schema_migration_tabel_name
+    ActiveRecord::SchemaMigration.table_name = @old_schema_migration_table_name
 
     super
   end
diff --git a/activerecord/test/cases/adapters/postgresql/foreign_table_test.rb b/activerecord/test/cases/adapters/postgresql/foreign_table_test.rb
new file mode 100644
index 0000000000..4fa315ad23
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/foreign_table_test.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/professor"
+
+if ActiveRecord::Base.connection.supports_foreign_tables?
+  class ForeignTableTest < ActiveRecord::TestCase
+    self.use_transactional_tests = false
+
+    class ForeignProfessor < ActiveRecord::Base
+      self.table_name = "foreign_professors"
+    end
+
+    class ForeignProfessorWithPk < ForeignProfessor
+      self.primary_key = "id"
+    end
+
+    def setup
+      @professor = Professor.create(name: "Nicola")
+
+      @connection = ActiveRecord::Base.connection
+      enable_extension!("postgres_fdw", @connection)
+
+      foreign_db_config = ARTest.connection_config["arunit2"]
+      @connection.execute <<-SQL
+        CREATE SERVER foreign_server
+          FOREIGN DATA WRAPPER postgres_fdw
+          OPTIONS (dbname '#{foreign_db_config["database"]}')
+      SQL
+
+      @connection.execute <<-SQL
+        CREATE USER MAPPING FOR CURRENT_USER
+          SERVER foreign_server
+      SQL
+
+      @connection.execute <<-SQL
+        CREATE FOREIGN TABLE foreign_professors (
+          id    int,
+          name  character varying NOT NULL
+        ) SERVER foreign_server OPTIONS (
+          table_name 'professors'
+        )
+      SQL
+    end
+
+    def teardown
+      disable_extension!("postgres_fdw", @connection)
+      @connection.execute <<-SQL
+        DROP SERVER IF EXISTS foreign_server CASCADE
+      SQL
+    end
+
+    def test_table_exists
+      table_name = ForeignProfessor.table_name
+      assert_not ActiveRecord::Base.connection.table_exists?(table_name)
+    end
+
+    def test_foreign_tables_are_valid_data_sources
+      table_name = ForeignProfessor.table_name
+      assert @connection.data_source_exists?(table_name), "'#{table_name}' should be a data source"
+    end
+
+    def test_foreign_tables
+      assert_equal ["foreign_professors"], @connection.foreign_tables
+    end
+
+    def test_foreign_table_exists
+      assert @connection.foreign_table_exists?("foreign_professors")
+      assert @connection.foreign_table_exists?(:foreign_professors)
+      assert_not @connection.foreign_table_exists?("nonexistingtable")
+      assert_not @connection.foreign_table_exists?("'")
+      assert_not @connection.foreign_table_exists?(nil)
+    end
+
+    def test_attribute_names
+      assert_equal ["id", "name"], ForeignProfessor.attribute_names
+    end
+
+    def test_attributes
+      professor = ForeignProfessorWithPk.find(@professor.id)
+      assert_equal @professor.attributes, professor.attributes
+    end
+
+    def test_does_not_have_a_primary_key
+      assert_nil ForeignProfessor.primary_key
+    end
+
+    def test_insert_record
+      # Explicit `id` here to avoid complex configurations to implicitly work with remote table
+      ForeignProfessorWithPk.create!(id: 100, name: "Leonardo")
+
+      professor = ForeignProfessorWithPk.last
+      assert_equal "Leonardo", professor.name
+    end
+
+    def test_update_record
+      professor = ForeignProfessorWithPk.find(@professor.id)
+      professor.name = "Albert"
+      professor.save!
+      professor.reload
+      assert_equal "Albert", professor.name
+    end
+
+    def test_delete_record
+      professor = ForeignProfessorWithPk.find(@professor.id)
+      assert_difference("ForeignProfessor.count", -1) { professor.destroy }
+    end
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/full_text_test.rb b/activerecord/test/cases/adapters/postgresql/full_text_test.rb
index bde7513339..95dee3bf44 100644
--- a/activerecord/test/cases/adapters/postgresql/full_text_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/full_text_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class PostgresqlFullTextTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
@@ -7,23 +9,23 @@ class PostgresqlFullTextTest < ActiveRecord::PostgreSQLTestCase
 
   setup do
     @connection = ActiveRecord::Base.connection
-    @connection.create_table('tsvectors') do |t|
-      t.tsvector 'text_vector'
+    @connection.create_table("tsvectors") do |t|
+      t.tsvector "text_vector"
     end
   end
 
   teardown do
-    @connection.drop_table 'tsvectors', if_exists: true
+    @connection.drop_table "tsvectors", if_exists: true
   end
 
   def test_tsvector_column
     column = Tsvector.columns_hash["text_vector"]
     assert_equal :tsvector, column.type
     assert_equal "tsvector", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = Tsvector.type_for_attribute("text_vector")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_update_tsvector
diff --git a/activerecord/test/cases/adapters/postgresql/geometric_test.rb b/activerecord/test/cases/adapters/postgresql/geometric_test.rb
index 0baf985654..8c6f046553 100644
--- a/activerecord/test/cases/adapters/postgresql/geometric_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/geometric_test.rb
@@ -1,16 +1,18 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
-require 'support/schema_dumping_helper'
+require "support/connection_helper"
+require "support/schema_dumping_helper"
 
 class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
   include ConnectionHelper
   include SchemaDumpingHelper
 
   class PostgresqlPoint < ActiveRecord::Base
-    attribute :x, :rails_5_1_point
-    attribute :y, :rails_5_1_point
-    attribute :z, :rails_5_1_point
-    attribute :array_of_points, :rails_5_1_point, array: true
+    attribute :x, :point
+    attribute :y, :point
+    attribute :z, :point
+    attribute :array_of_points, :point, array: true
     attribute :legacy_x, :legacy_point
     attribute :legacy_y, :legacy_point
     attribute :legacy_z, :legacy_point
@@ -18,7 +20,7 @@ class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
 
   def setup
     @connection = ActiveRecord::Base.connection
-    @connection.create_table('postgresql_points') do |t|
+    @connection.create_table("postgresql_points") do |t|
       t.point :x
       t.point :y, default: [12.2, 13.3]
       t.point :z, default: "(14.4,15.5)"
@@ -27,39 +29,27 @@ class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
       t.point :legacy_y, default: [12.2, 13.3]
       t.point :legacy_z, default: "(14.4,15.5)"
     end
-    @connection.create_table('deprecated_points') do |t|
-      t.point :x
-    end
   end
 
   teardown do
-    @connection.drop_table 'postgresql_points', if_exists: true
-    @connection.drop_table 'deprecated_points', if_exists: true
-  end
-
-  class DeprecatedPoint < ActiveRecord::Base; end
-
-  def test_deprecated_legacy_type
-    assert_deprecated do
-      DeprecatedPoint.new
-    end
+    @connection.drop_table "postgresql_points", if_exists: true
   end
 
   def test_column
     column = PostgresqlPoint.columns_hash["x"]
     assert_equal :point, column.type
     assert_equal "point", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlPoint.type_for_attribute("x")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_default
-    assert_equal ActiveRecord::Point.new(12.2, 13.3), PostgresqlPoint.column_defaults['y']
+    assert_equal ActiveRecord::Point.new(12.2, 13.3), PostgresqlPoint.column_defaults["y"]
     assert_equal ActiveRecord::Point.new(12.2, 13.3), PostgresqlPoint.new.y
 
-    assert_equal ActiveRecord::Point.new(14.4, 15.5), PostgresqlPoint.column_defaults['z']
+    assert_equal ActiveRecord::Point.new(14.4, 15.5), PostgresqlPoint.column_defaults["z"]
     assert_equal ActiveRecord::Point.new(14.4, 15.5), PostgresqlPoint.new.z
   end
 
@@ -89,7 +79,7 @@ class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
     p.reload
 
     assert_equal ActiveRecord::Point.new(10.0, 25.0), p.x
-    assert_not p.changed?
+    assert_not_predicate p, :changed?
   end
 
   def test_array_assignment
@@ -104,6 +94,11 @@ class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
     assert_equal ActiveRecord::Point.new(1, 2), p.x
   end
 
+  def test_empty_string_assignment
+    p = PostgresqlPoint.new(x: "")
+    assert_nil p.x
+  end
+
   def test_array_of_points_round_trip
     expected_value = [
       ActiveRecord::Point.new(1, 2),
@@ -122,17 +117,17 @@ class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
     column = PostgresqlPoint.columns_hash["legacy_x"]
     assert_equal :point, column.type
     assert_equal "point", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlPoint.type_for_attribute("legacy_x")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_legacy_default
-    assert_equal [12.2, 13.3], PostgresqlPoint.column_defaults['legacy_y']
+    assert_equal [12.2, 13.3], PostgresqlPoint.column_defaults["legacy_y"]
     assert_equal [12.2, 13.3], PostgresqlPoint.new.legacy_y
 
-    assert_equal [14.4, 15.5], PostgresqlPoint.column_defaults['legacy_z']
+    assert_equal [14.4, 15.5], PostgresqlPoint.column_defaults["legacy_z"]
     assert_equal [14.4, 15.5], PostgresqlPoint.new.legacy_z
   end
 
@@ -162,70 +157,72 @@ class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
     p.reload
 
     assert_equal [10.0, 25.0], p.legacy_x
-    assert_not p.changed?
+    assert_not_predicate p, :changed?
   end
 end
 
 class PostgresqlGeometricTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+
   class PostgresqlGeometric < ActiveRecord::Base; end
 
   setup do
     @connection = ActiveRecord::Base.connection
     @connection.create_table("postgresql_geometrics") do |t|
-      t.column :a_line_segment, :lseg
-      t.column :a_box, :box
-      t.column :a_path, :path
-      t.column :a_polygon, :polygon
-      t.column :a_circle, :circle
+      t.lseg    :a_line_segment
+      t.box     :a_box
+      t.path    :a_path
+      t.polygon :a_polygon
+      t.circle  :a_circle
     end
   end
 
   teardown do
-    @connection.drop_table 'postgresql_geometrics', if_exists: true
+    @connection.drop_table "postgresql_geometrics", if_exists: true
   end
 
   def test_geometric_types
     g = PostgresqlGeometric.new(
-      :a_line_segment => '(2.0, 3), (5.5, 7.0)',
-      :a_box          => '2.0, 3, 5.5, 7.0',
-      :a_path         => '[(2.0, 3), (5.5, 7.0), (8.5, 11.0)]',
-      :a_polygon      => '((2.0, 3), (5.5, 7.0), (8.5, 11.0))',
-      :a_circle       => '<(5.3, 10.4), 2>'
+      a_line_segment: "(2.0, 3), (5.5, 7.0)",
+      a_box: "2.0, 3, 5.5, 7.0",
+      a_path: "[(2.0, 3), (5.5, 7.0), (8.5, 11.0)]",
+      a_polygon: "((2.0, 3), (5.5, 7.0), (8.5, 11.0))",
+      a_circle: "<(5.3, 10.4), 2>"
     )
 
     g.save!
 
     h = PostgresqlGeometric.find(g.id)
 
-    assert_equal '[(2,3),(5.5,7)]', h.a_line_segment
-    assert_equal '(5.5,7),(2,3)', h.a_box # reordered to store upper right corner then bottom left corner
-    assert_equal '[(2,3),(5.5,7),(8.5,11)]', h.a_path
-    assert_equal '((2,3),(5.5,7),(8.5,11))', h.a_polygon
-    assert_equal '<(5.3,10.4),2>', h.a_circle
+    assert_equal "[(2,3),(5.5,7)]", h.a_line_segment
+    assert_equal "(5.5,7),(2,3)", h.a_box # reordered to store upper right corner then bottom left corner
+    assert_equal "[(2,3),(5.5,7),(8.5,11)]", h.a_path
+    assert_equal "((2,3),(5.5,7),(8.5,11))", h.a_polygon
+    assert_equal "<(5.3,10.4),2>", h.a_circle
   end
 
   def test_alternative_format
     g = PostgresqlGeometric.new(
-      :a_line_segment => '((2.0, 3), (5.5, 7.0))',
-      :a_box          => '(2.0, 3), (5.5, 7.0)',
-      :a_path         => '((2.0, 3), (5.5, 7.0), (8.5, 11.0))',
-      :a_polygon      => '2.0, 3, 5.5, 7.0, 8.5, 11.0',
-      :a_circle       => '((5.3, 10.4), 2)'
+      a_line_segment: "((2.0, 3), (5.5, 7.0))",
+      a_box: "(2.0, 3), (5.5, 7.0)",
+      a_path: "((2.0, 3), (5.5, 7.0), (8.5, 11.0))",
+      a_polygon: "2.0, 3, 5.5, 7.0, 8.5, 11.0",
+      a_circle: "((5.3, 10.4), 2)"
     )
 
     g.save!
 
     h = PostgresqlGeometric.find(g.id)
-    assert_equal '[(2,3),(5.5,7)]', h.a_line_segment
-    assert_equal '(5.5,7),(2,3)', h.a_box   # reordered to store upper right corner then bottom left corner
-    assert_equal '((2,3),(5.5,7),(8.5,11))', h.a_path
-    assert_equal '((2,3),(5.5,7),(8.5,11))', h.a_polygon
-    assert_equal '<(5.3,10.4),2>', h.a_circle
+    assert_equal "[(2,3),(5.5,7)]", h.a_line_segment
+    assert_equal "(5.5,7),(2,3)", h.a_box   # reordered to store upper right corner then bottom left corner
+    assert_equal "((2,3),(5.5,7),(8.5,11))", h.a_path
+    assert_equal "((2,3),(5.5,7),(8.5,11))", h.a_polygon
+    assert_equal "<(5.3,10.4),2>", h.a_circle
   end
 
   def test_geometric_function
-    PostgresqlGeometric.create! a_path: '[(2.0, 3), (5.5, 7.0), (8.5, 11.0)]'  # [ ] is an open path
-    PostgresqlGeometric.create! a_path: '((2.0, 3), (5.5, 7.0), (8.5, 11.0))'  # ( ) is a closed path
+    PostgresqlGeometric.create! a_path: "[(2.0, 3), (5.5, 7.0), (8.5, 11.0)]"  # [ ] is an open path
+    PostgresqlGeometric.create! a_path: "((2.0, 3), (5.5, 7.0), (8.5, 11.0))"  # ( ) is a closed path
 
     objs = PostgresqlGeometric.find_by_sql "SELECT isopen(a_path) FROM postgresql_geometrics ORDER BY id ASC"
     assert_equal [true, false], objs.map(&:isopen)
@@ -233,4 +230,144 @@ class PostgresqlGeometricTest < ActiveRecord::PostgreSQLTestCase
     objs = PostgresqlGeometric.find_by_sql "SELECT isclosed(a_path) FROM postgresql_geometrics ORDER BY id ASC"
     assert_equal [false, true], objs.map(&:isclosed)
   end
+
+  def test_schema_dumping
+    output = dump_table_schema("postgresql_geometrics")
+    assert_match %r{t\.lseg\s+"a_line_segment"$}, output
+    assert_match %r{t\.box\s+"a_box"$}, output
+    assert_match %r{t\.path\s+"a_path"$}, output
+    assert_match %r{t\.polygon\s+"a_polygon"$}, output
+    assert_match %r{t\.circle\s+"a_circle"$}, output
+  end
+end
+
+class PostgreSQLGeometricLineTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+
+  class PostgresqlLine < ActiveRecord::Base; end
+
+  setup do
+    unless ActiveRecord::Base.connection.send(:postgresql_version) >= 90400
+      skip("line type is not fully implemented")
+    end
+    @connection = ActiveRecord::Base.connection
+    @connection.create_table("postgresql_lines") do |t|
+      t.line :a_line
+    end
+  end
+
+  teardown do
+    if defined?(@connection)
+      @connection.drop_table "postgresql_lines", if_exists: true
+    end
+  end
+
+  def test_geometric_line_type
+    g = PostgresqlLine.new(
+      a_line: "{2.0, 3, 5.5}"
+    )
+    g.save!
+
+    h = PostgresqlLine.find(g.id)
+    assert_equal "{2,3,5.5}", h.a_line
+  end
+
+  def test_alternative_format_line_type
+    g = PostgresqlLine.new(
+      a_line: "(2.0, 3), (4.0, 6.0)"
+    )
+    g.save!
+
+    h = PostgresqlLine.find(g.id)
+    assert_equal "{1.5,-1,0}", h.a_line
+  end
+
+  def test_schema_dumping_for_line_type
+    output = dump_table_schema("postgresql_lines")
+    assert_match %r{t\.line\s+"a_line"$}, output
+  end
+end
+
+class PostgreSQLGeometricTypesTest < ActiveRecord::PostgreSQLTestCase
+  attr_reader :connection, :table_name
+
+  def setup
+    super
+    @connection = ActiveRecord::Base.connection
+    @table_name = :testings
+  end
+
+  def test_creating_column_with_point_type
+    connection.create_table(table_name) do |t|
+      t.point :foo_point
+    end
+
+    assert_column_exists(:foo_point)
+    assert_type_correct(:foo_point, :point)
+  end
+
+  def test_creating_column_with_line_type
+    connection.create_table(table_name) do |t|
+      t.line :foo_line
+    end
+
+    assert_column_exists(:foo_line)
+    assert_type_correct(:foo_line, :line)
+  end
+
+  def test_creating_column_with_lseg_type
+    connection.create_table(table_name) do |t|
+      t.lseg :foo_lseg
+    end
+
+    assert_column_exists(:foo_lseg)
+    assert_type_correct(:foo_lseg, :lseg)
+  end
+
+  def test_creating_column_with_box_type
+    connection.create_table(table_name) do |t|
+      t.box :foo_box
+    end
+
+    assert_column_exists(:foo_box)
+    assert_type_correct(:foo_box, :box)
+  end
+
+  def test_creating_column_with_path_type
+    connection.create_table(table_name) do |t|
+      t.path :foo_path
+    end
+
+    assert_column_exists(:foo_path)
+    assert_type_correct(:foo_path, :path)
+  end
+
+  def test_creating_column_with_polygon_type
+    connection.create_table(table_name) do |t|
+      t.polygon :foo_polygon
+    end
+
+    assert_column_exists(:foo_polygon)
+    assert_type_correct(:foo_polygon, :polygon)
+  end
+
+  def test_creating_column_with_circle_type
+    connection.create_table(table_name) do |t|
+      t.circle :foo_circle
+    end
+
+    assert_column_exists(:foo_circle)
+    assert_type_correct(:foo_circle, :circle)
+  end
+
+  private
+
+    def assert_column_exists(column_name)
+      assert connection.column_exists?(table_name, column_name)
+    end
+
+    def assert_type_correct(column_name, type)
+      column = connection.columns(table_name).find { |c| c.name == column_name.to_s }
+      assert_equal type, column.type
+    end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/hstore_test.rb b/activerecord/test/cases/adapters/postgresql/hstore_test.rb
index 6a2d501646..4b061a9375 100644
--- a/activerecord/test/cases/adapters/postgresql/hstore_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/hstore_test.rb
@@ -1,327 +1,353 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
-if ActiveRecord::Base.connection.supports_extensions?
-  class PostgresqlHstoreTest < ActiveRecord::PostgreSQLTestCase
-    include SchemaDumpingHelper
-    class Hstore < ActiveRecord::Base
-      self.table_name = 'hstores'
+class PostgresqlHstoreTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+  class Hstore < ActiveRecord::Base
+    self.table_name = "hstores"
 
-      store_accessor :settings, :language, :timezone
-    end
+    store_accessor :settings, :language, :timezone
+  end
 
-    def setup
-      @connection = ActiveRecord::Base.connection
+  class FakeParameters
+    def to_unsafe_h
+      { "hi" => "hi" }
+    end
+  end
 
-      unless @connection.extension_enabled?('hstore')
-        @connection.enable_extension 'hstore'
-        @connection.commit_db_transaction
-      end
+  def setup
+    @connection = ActiveRecord::Base.connection
 
-      @connection.reconnect!
+    enable_extension!("hstore", @connection)
 
-      @connection.transaction do
-        @connection.create_table('hstores') do |t|
-          t.hstore 'tags', :default => ''
-          t.hstore 'payload', array: true
-          t.hstore 'settings'
-        end
+    @connection.transaction do
+      @connection.create_table("hstores") do |t|
+        t.hstore "tags", default: ""
+        t.hstore "payload", array: true
+        t.hstore "settings"
       end
-      Hstore.reset_column_information
-      @column = Hstore.columns_hash['tags']
-      @type = Hstore.type_for_attribute("tags")
-    end
-
-    teardown do
-      @connection.drop_table 'hstores', if_exists: true
     end
+    Hstore.reset_column_information
+    @column = Hstore.columns_hash["tags"]
+    @type = Hstore.type_for_attribute("tags")
+  end
 
-    def test_hstore_included_in_extensions
-      assert @connection.respond_to?(:extensions), "connection should have a list of extensions"
-      assert @connection.extensions.include?('hstore'), "extension list should include hstore"
-    end
+  teardown do
+    @connection.drop_table "hstores", if_exists: true
+    disable_extension!("hstore", @connection)
+  end
 
-    def test_disable_enable_hstore
-      assert @connection.extension_enabled?('hstore')
-      @connection.disable_extension 'hstore'
-      assert_not @connection.extension_enabled?('hstore')
-      @connection.enable_extension 'hstore'
-      assert @connection.extension_enabled?('hstore')
-    ensure
-      # Restore column(s) dropped by `drop extension hstore cascade;`
-      load_schema
-    end
+  def test_hstore_included_in_extensions
+    assert_respond_to @connection, :extensions
+    assert_includes @connection.extensions, "hstore", "extension list should include hstore"
+  end
 
-    def test_column
-      assert_equal :hstore, @column.type
-      assert_equal "hstore", @column.sql_type
-      assert_not @column.array?
+  def test_disable_enable_hstore
+    assert @connection.extension_enabled?("hstore")
+    @connection.disable_extension "hstore"
+    assert_not @connection.extension_enabled?("hstore")
+    @connection.enable_extension "hstore"
+    assert @connection.extension_enabled?("hstore")
+  ensure
+    # Restore column(s) dropped by `drop extension hstore cascade;`
+    load_schema
+  end
 
-      assert_not @type.binary?
-    end
+  def test_column
+    assert_equal :hstore, @column.type
+    assert_equal "hstore", @column.sql_type
+    assert_not_predicate @column, :array?
 
-    def test_default
-      @connection.add_column 'hstores', 'permissions', :hstore, default: '"users"=>"read", "articles"=>"write"'
-      Hstore.reset_column_information
+    assert_not_predicate @type, :binary?
+  end
 
-      assert_equal({"users"=>"read", "articles"=>"write"}, Hstore.column_defaults['permissions'])
-      assert_equal({"users"=>"read", "articles"=>"write"}, Hstore.new.permissions)
-    ensure
-      Hstore.reset_column_information
-    end
+  def test_default
+    @connection.add_column "hstores", "permissions", :hstore, default: '"users"=>"read", "articles"=>"write"'
+    Hstore.reset_column_information
 
-    def test_change_table_supports_hstore
-      @connection.transaction do
-        @connection.change_table('hstores') do |t|
-          t.hstore 'users', default: ''
-        end
-        Hstore.reset_column_information
-        column = Hstore.columns_hash['users']
-        assert_equal :hstore, column.type
+    assert_equal({ "users" => "read", "articles" => "write" }, Hstore.column_defaults["permissions"])
+    assert_equal({ "users" => "read", "articles" => "write" }, Hstore.new.permissions)
+  ensure
+    Hstore.reset_column_information
+  end
 
-        raise ActiveRecord::Rollback # reset the schema change
+  def test_change_table_supports_hstore
+    @connection.transaction do
+      @connection.change_table("hstores") do |t|
+        t.hstore "users", default: ""
       end
-    ensure
       Hstore.reset_column_information
+      column = Hstore.columns_hash["users"]
+      assert_equal :hstore, column.type
+
+      raise ActiveRecord::Rollback # reset the schema change
     end
+  ensure
+    Hstore.reset_column_information
+  end
 
-    def test_hstore_migration
-      hstore_migration = Class.new(ActiveRecord::Migration) do
-        def change
-          change_table("hstores") do |t|
-            t.hstore :keys
-          end
+  def test_hstore_migration
+    hstore_migration = Class.new(ActiveRecord::Migration::Current) do
+      def change
+        change_table("hstores") do |t|
+          t.hstore :keys
         end
       end
-
-      hstore_migration.new.suppress_messages do
-        hstore_migration.migrate(:up)
-        assert_includes @connection.columns(:hstores).map(&:name), "keys"
-        hstore_migration.migrate(:down)
-        assert_not_includes @connection.columns(:hstores).map(&:name), "keys"
-      end
     end
 
-    def test_cast_value_on_write
-      x = Hstore.new tags: {"bool" => true, "number" => 5}
-      assert_equal({"bool" => true, "number" => 5}, x.tags_before_type_cast)
-      assert_equal({"bool" => "true", "number" => "5"}, x.tags)
-      x.save
-      assert_equal({"bool" => "true", "number" => "5"}, x.reload.tags)
+    hstore_migration.new.suppress_messages do
+      hstore_migration.migrate(:up)
+      assert_includes @connection.columns(:hstores).map(&:name), "keys"
+      hstore_migration.migrate(:down)
+      assert_not_includes @connection.columns(:hstores).map(&:name), "keys"
     end
+  end
 
-    def test_type_cast_hstore
-      assert_equal({'1' => '2'}, @type.deserialize("\"1\"=>\"2\""))
-      assert_equal({}, @type.deserialize(""))
-      assert_equal({'key'=>nil}, @type.deserialize('key => NULL'))
-      assert_equal({'c'=>'}','"a"'=>'b "a b'}, @type.deserialize(%q(c=>"}", "\"a\""=>"b \"a b")))
-    end
+  def test_cast_value_on_write
+    x = Hstore.new tags: { "bool" => true, "number" => 5 }
+    assert_equal({ "bool" => true, "number" => 5 }, x.tags_before_type_cast)
+    assert_equal({ "bool" => "true", "number" => "5" }, x.tags)
+    x.save
+    assert_equal({ "bool" => "true", "number" => "5" }, x.reload.tags)
+  end
 
-    def test_with_store_accessors
-      x = Hstore.new(language: "fr", timezone: "GMT")
-      assert_equal "fr", x.language
-      assert_equal "GMT", x.timezone
+  def test_type_cast_hstore
+    assert_equal({ "1" => "2" }, @type.deserialize("\"1\"=>\"2\""))
+    assert_equal({}, @type.deserialize(""))
+    assert_equal({ "key" => nil }, @type.deserialize("key => NULL"))
+    assert_equal({ "c" => "}", '"a"' => 'b "a b' }, @type.deserialize(%q(c=>"}", "\"a\""=>"b \"a b")))
+  end
 
-      x.save!
-      x = Hstore.first
-      assert_equal "fr", x.language
-      assert_equal "GMT", x.timezone
+  def test_with_store_accessors
+    x = Hstore.new(language: "fr", timezone: "GMT")
+    assert_equal "fr", x.language
+    assert_equal "GMT", x.timezone
 
-      x.language = "de"
-      x.save!
+    x.save!
+    x = Hstore.first
+    assert_equal "fr", x.language
+    assert_equal "GMT", x.timezone
 
-      x = Hstore.first
-      assert_equal "de", x.language
-      assert_equal "GMT", x.timezone
-    end
+    x.language = "de"
+    x.save!
 
-    def test_duplication_with_store_accessors
-      x = Hstore.new(language: "fr", timezone: "GMT")
-      assert_equal "fr", x.language
-      assert_equal "GMT", x.timezone
+    x = Hstore.first
+    assert_equal "de", x.language
+    assert_equal "GMT", x.timezone
+  end
 
-      y = x.dup
-      assert_equal "fr", y.language
-      assert_equal "GMT", y.timezone
-    end
+  def test_duplication_with_store_accessors
+    x = Hstore.new(language: "fr", timezone: "GMT")
+    assert_equal "fr", x.language
+    assert_equal "GMT", x.timezone
 
-    def test_yaml_round_trip_with_store_accessors
-      x = Hstore.new(language: "fr", timezone: "GMT")
-      assert_equal "fr", x.language
-      assert_equal "GMT", x.timezone
+    y = x.dup
+    assert_equal "fr", y.language
+    assert_equal "GMT", y.timezone
+  end
 
-      y = YAML.load(YAML.dump(x))
-      assert_equal "fr", y.language
-      assert_equal "GMT", y.timezone
-    end
+  def test_yaml_round_trip_with_store_accessors
+    x = Hstore.new(language: "fr", timezone: "GMT")
+    assert_equal "fr", x.language
+    assert_equal "GMT", x.timezone
 
-    def test_changes_in_place
-      hstore = Hstore.create!(settings: { 'one' => 'two' })
-      hstore.settings['three'] = 'four'
-      hstore.save!
-      hstore.reload
+    y = YAML.load(YAML.dump(x))
+    assert_equal "fr", y.language
+    assert_equal "GMT", y.timezone
+  end
 
-      assert_equal 'four', hstore.settings['three']
-      assert_not hstore.changed?
-    end
+  def test_changes_in_place
+    hstore = Hstore.create!(settings: { "one" => "two" })
+    hstore.settings["three"] = "four"
+    hstore.save!
+    hstore.reload
 
-    def test_gen1
-      assert_equal(%q(" "=>""), @type.serialize({' '=>''}))
-    end
+    assert_equal "four", hstore.settings["three"]
+    assert_not_predicate hstore, :changed?
+  end
 
-    def test_gen2
-      assert_equal(%q(","=>""), @type.serialize({','=>''}))
-    end
+  def test_dirty_from_user_equal
+    settings = { "alongkey" => "anything", "key" => "value" }
+    hstore = Hstore.create!(settings: settings)
 
-    def test_gen3
-      assert_equal(%q("="=>""), @type.serialize({'='=>''}))
-    end
+    hstore.settings = { "key" => "value", "alongkey" => "anything" }
+    assert_equal settings, hstore.settings
+    assert_not_predicate hstore, :changed?
+  end
 
-    def test_gen4
-      assert_equal(%q(">"=>""), @type.serialize({'>'=>''}))
-    end
+  def test_hstore_dirty_from_database_equal
+    settings = { "alongkey" => "anything", "key" => "value" }
+    hstore = Hstore.create!(settings: settings)
+    hstore.reload
 
-    def test_parse1
-      assert_equal({'a'=>nil,'b'=>nil,'c'=>'NuLl','null'=>'c'}, @type.deserialize('a=>null,b=>NuLl,c=>"NuLl",null=>c'))
-    end
+    assert_equal settings, hstore.settings
+    hstore.settings = settings
+    assert_not_predicate hstore, :changed?
+  end
 
-    def test_parse2
-      assert_equal({" " => " "},  @type.deserialize("\\ =>\\ "))
-    end
+  def test_gen1
+    assert_equal('" "=>""', @type.serialize(" " => ""))
+  end
 
-    def test_parse3
-      assert_equal({"=" => ">"},  @type.deserialize("==>>"))
-    end
+  def test_gen2
+    assert_equal('","=>""', @type.serialize("," => ""))
+  end
 
-    def test_parse4
-      assert_equal({"=a"=>"q=w"},   @type.deserialize('\=a=>q=w'))
-    end
+  def test_gen3
+    assert_equal('"="=>""', @type.serialize("=" => ""))
+  end
 
-    def test_parse5
-      assert_equal({"=a"=>"q=w"},   @type.deserialize('"=a"=>q\=w'))
-    end
+  def test_gen4
+    assert_equal('">"=>""', @type.serialize(">" => ""))
+  end
 
-    def test_parse6
-      assert_equal({"\"a"=>"q>w"},  @type.deserialize('"\"a"=>q>w'))
-    end
+  def test_parse1
+    assert_equal({ "a" => nil, "b" => nil, "c" => "NuLl", "null" => "c" }, @type.deserialize('a=>null,b=>NuLl,c=>"NuLl",null=>c'))
+  end
 
-    def test_parse7
-      assert_equal({"\"a"=>"q\"w"}, @type.deserialize('\"a=>q"w'))
-    end
+  def test_parse2
+    assert_equal({ " " => " " },  @type.deserialize("\\ =>\\ "))
+  end
 
-    def test_rewrite
-      @connection.execute "insert into hstores (tags) VALUES ('1=>2')"
-      x = Hstore.first
-      x.tags = { '"a\'' => 'b' }
-      assert x.save!
-    end
+  def test_parse3
+    assert_equal({ "=" => ">" },  @type.deserialize("==>>"))
+  end
 
-    def test_select
-      @connection.execute "insert into hstores (tags) VALUES ('1=>2')"
-      x = Hstore.first
-      assert_equal({'1' => '2'}, x.tags)
-    end
+  def test_parse4
+    assert_equal({ "=a" => "q=w" },   @type.deserialize('\=a=>q=w'))
+  end
 
-    def test_array_cycle
-      assert_array_cycle([{"AA" => "BB", "CC" => "DD"}, {"AA" => nil}])
-    end
+  def test_parse5
+    assert_equal({ "=a" => "q=w" },   @type.deserialize('"=a"=>q\=w'))
+  end
 
-    def test_array_strings_with_quotes
-      assert_array_cycle([{'this has' => 'some "s that need to be escaped"'}])
-    end
+  def test_parse6
+    assert_equal({ "\"a" => "q>w" },  @type.deserialize('"\"a"=>q>w'))
+  end
 
-    def test_array_strings_with_commas
-      assert_array_cycle([{'this,has' => 'many,values'}])
-    end
+  def test_parse7
+    assert_equal({ "\"a" => "q\"w" }, @type.deserialize('\"a=>q"w'))
+  end
 
-    def test_array_strings_with_array_delimiters
-      assert_array_cycle(['{' => '}'])
-    end
+  def test_rewrite
+    @connection.execute "insert into hstores (tags) VALUES ('1=>2')"
+    x = Hstore.first
+    x.tags = { '"a\'' => "b" }
+    assert x.save!
+  end
 
-    def test_array_strings_with_null_strings
-      assert_array_cycle([{'NULL' => 'NULL'}])
-    end
+  def test_select
+    @connection.execute "insert into hstores (tags) VALUES ('1=>2')"
+    x = Hstore.first
+    assert_equal({ "1" => "2" }, x.tags)
+  end
 
-    def test_contains_nils
-      assert_array_cycle([{'NULL' => nil}])
-    end
+  def test_array_cycle
+    assert_array_cycle([{ "AA" => "BB", "CC" => "DD" }, { "AA" => nil }])
+  end
 
-    def test_select_multikey
-      @connection.execute "insert into hstores (tags) VALUES ('1=>2,2=>3')"
-      x = Hstore.first
-      assert_equal({'1' => '2', '2' => '3'}, x.tags)
-    end
+  def test_array_strings_with_quotes
+    assert_array_cycle([{ "this has" => 'some "s that need to be escaped"' }])
+  end
 
-    def test_create
-      assert_cycle('a' => 'b', '1' => '2')
-    end
+  def test_array_strings_with_commas
+    assert_array_cycle([{ "this,has" => "many,values" }])
+  end
 
-    def test_nil
-      assert_cycle('a' => nil)
-    end
+  def test_array_strings_with_array_delimiters
+    assert_array_cycle(["{" => "}"])
+  end
 
-    def test_quotes
-      assert_cycle('a' => 'b"ar', '1"foo' => '2')
-    end
+  def test_array_strings_with_null_strings
+    assert_array_cycle([{ "NULL" => "NULL" }])
+  end
 
-    def test_whitespace
-      assert_cycle('a b' => 'b ar', '1"foo' => '2')
-    end
+  def test_contains_nils
+    assert_array_cycle([{ "NULL" => nil }])
+  end
 
-    def test_backslash
-      assert_cycle('a\\b' => 'b\\ar', '1"foo' => '2')
-    end
+  def test_select_multikey
+    @connection.execute "insert into hstores (tags) VALUES ('1=>2,2=>3')"
+    x = Hstore.first
+    assert_equal({ "1" => "2", "2" => "3" }, x.tags)
+  end
 
-    def test_comma
-      assert_cycle('a, b' => 'bar', '1"foo' => '2')
-    end
+  def test_create
+    assert_cycle("a" => "b", "1" => "2")
+  end
 
-    def test_arrow
-      assert_cycle('a=>b' => 'bar', '1"foo' => '2')
-    end
+  def test_nil
+    assert_cycle("a" => nil)
+  end
 
-    def test_quoting_special_characters
-      assert_cycle('ca' => 'cà', 'ac' => 'àc')
-    end
+  def test_quotes
+    assert_cycle("a" => 'b"ar', '1"foo' => "2")
+  end
 
-    def test_multiline
-      assert_cycle("a\nb" => "c\nd")
-    end
+  def test_whitespace
+    assert_cycle("a b" => "b ar", '1"foo' => "2")
+  end
 
-    class TagCollection
-      def initialize(hash); @hash = hash end
-      def to_hash; @hash end
-      def self.load(hash); new(hash) end
-      def self.dump(object); object.to_hash end
-    end
+  def test_backslash
+    assert_cycle('a\\b' => 'b\\ar', '1"foo' => "2")
+  end
 
-    class HstoreWithSerialize < Hstore
-      serialize :tags, TagCollection
-    end
+  def test_comma
+    assert_cycle("a, b" => "bar", '1"foo' => "2")
+  end
 
-    def test_hstore_with_serialized_attributes
-      HstoreWithSerialize.create! tags: TagCollection.new({"one" => "two"})
-      record = HstoreWithSerialize.first
-      assert_instance_of TagCollection, record.tags
-      assert_equal({"one" => "two"}, record.tags.to_hash)
-      record.tags = TagCollection.new("three" => "four")
-      record.save!
-      assert_equal({"three" => "four"}, HstoreWithSerialize.first.tags.to_hash)
-    end
+  def test_arrow
+    assert_cycle("a=>b" => "bar", '1"foo' => "2")
+  end
 
-    def test_clone_hstore_with_serialized_attributes
-      HstoreWithSerialize.create! tags: TagCollection.new({"one" => "two"})
-      record = HstoreWithSerialize.first
-      dupe = record.dup
-      assert_equal({"one" => "two"}, dupe.tags.to_hash)
-    end
+  def test_quoting_special_characters
+    assert_cycle("ca" => "cà", "ac" => "àc")
+  end
 
-    def test_schema_dump_with_shorthand
-      output = dump_table_schema("hstores")
-      assert_match %r[t\.hstore "tags",\s+default: {}], output
-    end
+  def test_multiline
+    assert_cycle("a\nb" => "c\nd")
+  end
+
+  class TagCollection
+    def initialize(hash); @hash = hash end
+    def to_hash; @hash end
+    def self.load(hash); new(hash) end
+    def self.dump(object); object.to_hash end
+  end
+
+  class HstoreWithSerialize < Hstore
+    serialize :tags, TagCollection
+  end
+
+  def test_hstore_with_serialized_attributes
+    HstoreWithSerialize.create! tags: TagCollection.new("one" => "two")
+    record = HstoreWithSerialize.first
+    assert_instance_of TagCollection, record.tags
+    assert_equal({ "one" => "two" }, record.tags.to_hash)
+    record.tags = TagCollection.new("three" => "four")
+    record.save!
+    assert_equal({ "three" => "four" }, HstoreWithSerialize.first.tags.to_hash)
+  end
 
-    private
+  def test_clone_hstore_with_serialized_attributes
+    HstoreWithSerialize.create! tags: TagCollection.new("one" => "two")
+    record = HstoreWithSerialize.first
+    dupe = record.dup
+    assert_equal({ "one" => "two" }, dupe.tags.to_hash)
+  end
+
+  def test_schema_dump_with_shorthand
+    output = dump_table_schema("hstores")
+    assert_match %r[t\.hstore "tags",\s+default: {}], output
+  end
+
+  def test_supports_to_unsafe_h_values
+    assert_equal("\"hi\"=>\"hi\"", @type.serialize(FakeParameters.new))
+  end
+
+  private
     def assert_array_cycle(array)
       # test creation
       x = Hstore.create!(payload: array)
@@ -338,16 +364,15 @@ if ActiveRecord::Base.connection.supports_extensions?
 
     def assert_cycle(hash)
       # test creation
-      x = Hstore.create!(:tags => hash)
+      x = Hstore.create!(tags: hash)
       x.reload
       assert_equal(hash, x.tags)
 
       # test updating
-      x = Hstore.create!(:tags => {})
+      x = Hstore.create!(tags: {})
       x.tags = hash
       x.save!
       x.reload
       assert_equal(hash, x.tags)
     end
-  end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/infinity_test.rb b/activerecord/test/cases/adapters/postgresql/infinity_test.rb
index bfda933fa4..5e56ce8427 100644
--- a/activerecord/test/cases/adapters/postgresql/infinity_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/infinity_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class PostgresqlInfinityTest < ActiveRecord::PostgreSQLTestCase
@@ -11,11 +13,12 @@ class PostgresqlInfinityTest < ActiveRecord::PostgreSQLTestCase
     @connection.create_table(:postgresql_infinities) do |t|
       t.float :float
       t.datetime :datetime
+      t.date :date
     end
   end
 
   teardown do
-    @connection.drop_table 'postgresql_infinities', if_exists: true
+    @connection.drop_table "postgresql_infinities", if_exists: true
   end
 
   test "type casting infinity on a float column" do
@@ -25,12 +28,12 @@ class PostgresqlInfinityTest < ActiveRecord::PostgreSQLTestCase
   end
 
   test "type casting string on a float column" do
-    record = PostgresqlInfinity.new(float: 'Infinity')
+    record = PostgresqlInfinity.new(float: "Infinity")
     assert_equal Float::INFINITY, record.float
-    record = PostgresqlInfinity.new(float: '-Infinity')
+    record = PostgresqlInfinity.new(float: "-Infinity")
     assert_equal(-Float::INFINITY, record.float)
-    record = PostgresqlInfinity.new(float: 'NaN')
-    assert_send [record.float, :nan?]
+    record = PostgresqlInfinity.new(float: "NaN")
+    assert record.float.nan?, "Expected #{record.float} to be NaN"
   end
 
   test "update_all with infinity on a float column" do
@@ -41,11 +44,25 @@ class PostgresqlInfinityTest < ActiveRecord::PostgreSQLTestCase
   end
 
   test "type casting infinity on a datetime column" do
+    record = PostgresqlInfinity.create!(datetime: "infinity")
+    record.reload
+    assert_equal Float::INFINITY, record.datetime
+
     record = PostgresqlInfinity.create!(datetime: Float::INFINITY)
     record.reload
     assert_equal Float::INFINITY, record.datetime
   end
 
+  test "type casting infinity on a date column" do
+    record = PostgresqlInfinity.create!(date: "infinity")
+    record.reload
+    assert_equal Float::INFINITY, record.date
+
+    record = PostgresqlInfinity.create!(date: Float::INFINITY)
+    record.reload
+    assert_equal Float::INFINITY, record.date
+  end
+
   test "update_all with infinity on a datetime column" do
     record = PostgresqlInfinity.create!
     PostgresqlInfinity.update_all(datetime: Float::INFINITY)
@@ -66,4 +83,28 @@ class PostgresqlInfinityTest < ActiveRecord::PostgreSQLTestCase
       PostgresqlInfinity.reset_column_information
     end
   end
+
+  test "where clause with infinite range on a datetime column" do
+    record = PostgresqlInfinity.create!(datetime: Time.current)
+
+    string = PostgresqlInfinity.where(datetime: "-infinity".."infinity")
+    assert_equal record, string.take
+
+    infinity = PostgresqlInfinity.where(datetime: -::Float::INFINITY..::Float::INFINITY)
+    assert_equal record, infinity.take
+
+    assert_equal infinity.to_sql, string.to_sql
+  end
+
+  test "where clause with infinite range on a date column" do
+    record = PostgresqlInfinity.create!(date: Date.current)
+
+    string = PostgresqlInfinity.where(date: "-infinity".."infinity")
+    assert_equal record, string.take
+
+    infinity = PostgresqlInfinity.where(date: -::Float::INFINITY..::Float::INFINITY)
+    assert_equal record, infinity.take
+
+    assert_equal infinity.to_sql, string.to_sql
+  end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/integer_test.rb b/activerecord/test/cases/adapters/postgresql/integer_test.rb
index b4e55964b9..3e45b057ff 100644
--- a/activerecord/test/cases/adapters/postgresql/integer_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/integer_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "active_support/core_ext/numeric/bytes"
 
diff --git a/activerecord/test/cases/adapters/postgresql/json_test.rb b/activerecord/test/cases/adapters/postgresql/json_test.rb
index f242f32496..ee08841eb3 100644
--- a/activerecord/test/cases/adapters/postgresql/json_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/json_test.rb
@@ -1,190 +1,37 @@
-# -*- coding: utf-8 -*-
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "cases/json_shared_test_cases"
 
 module PostgresqlJSONSharedTestCases
-  include SchemaDumpingHelper
-
-  class JsonDataType < ActiveRecord::Base
-    self.table_name = 'json_data_type'
-
-    store_accessor :settings, :resolution
-  end
+  include JSONSharedTestCases
 
   def setup
-    @connection = ActiveRecord::Base.connection
-    begin
-      @connection.create_table('json_data_type') do |t|
-        t.public_send column_type, 'payload', default: {} # t.json 'payload', default: {}
-        t.public_send column_type, 'settings'             # t.json 'settings'
-      end
-    rescue ActiveRecord::StatementInvalid
-      skip "do not test on PostgreSQL without #{column_type} type."
+    super
+    @connection.create_table("json_data_type") do |t|
+      t.public_send column_type, "payload", default: {} # t.json 'payload', default: {}
+      t.public_send column_type, "settings"             # t.json 'settings'
+      t.public_send column_type, "objects", array: true # t.json 'objects', array: true
     end
-  end
-
-  def teardown
-    @connection.drop_table :json_data_type, if_exists: true
-    JsonDataType.reset_column_information
-  end
-
-  def test_column
-    column = JsonDataType.columns_hash["payload"]
-    assert_equal column_type, column.type
-    assert_equal column_type.to_s, column.sql_type
-    assert_not column.array?
-
-    type = JsonDataType.type_for_attribute("payload")
-    assert_not type.binary?
+  rescue ActiveRecord::StatementInvalid
+    skip "do not test on PostgreSQL without #{column_type} type."
   end
 
   def test_default
-    @connection.add_column 'json_data_type', 'permissions', column_type, default: '{"users": "read", "posts": ["read", "write"]}'
-    JsonDataType.reset_column_information
-
-    assert_equal({"users"=>"read", "posts"=>["read", "write"]}, JsonDataType.column_defaults['permissions'])
-    assert_equal({"users"=>"read", "posts"=>["read", "write"]}, JsonDataType.new.permissions)
-  ensure
-    JsonDataType.reset_column_information
-  end
-
-  def test_change_table_supports_json
-    @connection.transaction do
-      @connection.change_table('json_data_type') do |t|
-        t.public_send column_type, 'users', default: '{}' # t.json 'users', default: '{}'
-      end
-      JsonDataType.reset_column_information
-      column = JsonDataType.columns_hash['users']
-      assert_equal column_type, column.type
-
-      raise ActiveRecord::Rollback # reset the schema change
-    end
-  ensure
-    JsonDataType.reset_column_information
-  end
-
-  def test_schema_dumping
-    output = dump_table_schema("json_data_type")
-    assert_match(/t\.#{column_type.to_s}\s+"payload",\s+default: {}/, output)
-  end
-
-  def test_cast_value_on_write
-    x = JsonDataType.new payload: {"string" => "foo", :symbol => :bar}
-    assert_equal({"string" => "foo", :symbol => :bar}, x.payload_before_type_cast)
-    assert_equal({"string" => "foo", "symbol" => "bar"}, x.payload)
-    x.save
-    assert_equal({"string" => "foo", "symbol" => "bar"}, x.reload.payload)
-  end
-
-  def test_type_cast_json
-    type = JsonDataType.type_for_attribute("payload")
-
-    data = "{\"a_key\":\"a_value\"}"
-    hash = type.deserialize(data)
-    assert_equal({'a_key' => 'a_value'}, hash)
-    assert_equal({'a_key' => 'a_value'}, type.deserialize(data))
-
-    assert_equal({}, type.deserialize("{}"))
-    assert_equal({'key'=>nil}, type.deserialize('{"key": null}'))
-    assert_equal({'c'=>'}','"a"'=>'b "a b'}, type.deserialize(%q({"c":"}", "\"a\"":"b \"a b"})))
-  end
-
-  def test_rewrite
-    @connection.execute "insert into json_data_type (payload) VALUES ('{\"k\":\"v\"}')"
-    x = JsonDataType.first
-    x.payload = { '"a\'' => 'b' }
-    assert x.save!
-  end
-
-  def test_select
-    @connection.execute "insert into json_data_type (payload) VALUES ('{\"k\":\"v\"}')"
-    x = JsonDataType.first
-    assert_equal({'k' => 'v'}, x.payload)
-  end
+    @connection.add_column "json_data_type", "permissions", column_type, default: { "users": "read", "posts": ["read", "write"] }
+    klass.reset_column_information
 
-  def test_select_multikey
-    @connection.execute %q|insert into json_data_type (payload) VALUES ('{"k1":"v1", "k2":"v2", "k3":[1,2,3]}')|
-    x = JsonDataType.first
-    assert_equal({'k1' => 'v1', 'k2' => 'v2', 'k3' => [1,2,3]}, x.payload)
+    assert_equal({ "users" => "read", "posts" => ["read", "write"] }, klass.column_defaults["permissions"])
+    assert_equal({ "users" => "read", "posts" => ["read", "write"] }, klass.new.permissions)
   end
 
-  def test_null_json
-    @connection.execute %q|insert into json_data_type (payload) VALUES(null)|
-    x = JsonDataType.first
-    assert_equal(nil, x.payload)
-  end
-
-  def test_select_array_json_value
-    @connection.execute %q|insert into json_data_type (payload) VALUES ('["v0",{"k1":"v1"}]')|
-    x = JsonDataType.first
-    assert_equal(['v0', {'k1' => 'v1'}], x.payload)
-  end
-
-  def test_rewrite_array_json_value
-    @connection.execute %q|insert into json_data_type (payload) VALUES ('["v0",{"k1":"v1"}]')|
-    x = JsonDataType.first
-    x.payload = ['v1', {'k2' => 'v2'}, 'v3']
-    assert x.save!
-  end
-
-  def test_with_store_accessors
-    x = JsonDataType.new(resolution: "320×480")
-    assert_equal "320×480", x.resolution
-
+  def test_deserialize_with_array
+    x = klass.new(objects: ["foo" => "bar"])
+    assert_equal ["foo" => "bar"], x.objects
     x.save!
-    x = JsonDataType.first
-    assert_equal "320×480", x.resolution
-
-    x.resolution = "640×1136"
-    x.save!
-
-    x = JsonDataType.first
-    assert_equal "640×1136", x.resolution
-  end
-
-  def test_duplication_with_store_accessors
-    x = JsonDataType.new(resolution: "320×480")
-    assert_equal "320×480", x.resolution
-
-    y = x.dup
-    assert_equal "320×480", y.resolution
-  end
-
-  def test_yaml_round_trip_with_store_accessors
-    x = JsonDataType.new(resolution: "320×480")
-    assert_equal "320×480", x.resolution
-
-    y = YAML.load(YAML.dump(x))
-    assert_equal "320×480", y.resolution
-  end
-
-  def test_changes_in_place
-    json = JsonDataType.new
-    assert_not json.changed?
-
-    json.payload = { 'one' => 'two' }
-    assert json.changed?
-    assert json.payload_changed?
-
-    json.save!
-    assert_not json.changed?
-
-    json.payload['three'] = 'four'
-    assert json.payload_changed?
-
-    json.save!
-    json.reload
-
-    assert_equal({ 'one' => 'two', 'three' => 'four' }, json.payload)
-    assert_not json.changed?
-  end
-
-  def test_assigning_invalid_json
-    json = JsonDataType.new
-
-    json.payload = 'foo'
-
-    assert_nil json.payload
+    assert_equal ["foo" => "bar"], x.objects
+    x.reload
+    assert_equal ["foo" => "bar"], x.objects
   end
 end
 
diff --git a/activerecord/test/cases/adapters/postgresql/ltree_test.rb b/activerecord/test/cases/adapters/postgresql/ltree_test.rb
index 56516c82b4..8349ee6ee2 100644
--- a/activerecord/test/cases/adapters/postgresql/ltree_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/ltree_test.rb
@@ -1,20 +1,22 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class PostgresqlLtreeTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
   class Ltree < ActiveRecord::Base
-    self.table_name = 'ltrees'
+    self.table_name = "ltrees"
   end
 
   def setup
     @connection = ActiveRecord::Base.connection
 
-    enable_extension!('ltree', @connection)
+    enable_extension!("ltree", @connection)
 
     @connection.transaction do
-      @connection.create_table('ltrees') do |t|
-        t.ltree 'path'
+      @connection.create_table("ltrees") do |t|
+        t.ltree "path"
       end
     end
   rescue ActiveRecord::StatementInvalid
@@ -22,28 +24,28 @@ class PostgresqlLtreeTest < ActiveRecord::PostgreSQLTestCase
   end
 
   teardown do
-    @connection.drop_table 'ltrees', if_exists: true
+    @connection.drop_table "ltrees", if_exists: true
   end
 
   def test_column
-    column = Ltree.columns_hash['path']
+    column = Ltree.columns_hash["path"]
     assert_equal :ltree, column.type
     assert_equal "ltree", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
-    type = Ltree.type_for_attribute('path')
-    assert_not type.binary?
+    type = Ltree.type_for_attribute("path")
+    assert_not_predicate type, :binary?
   end
 
   def test_write
-    ltree = Ltree.new(path: '1.2.3.4')
+    ltree = Ltree.new(path: "1.2.3.4")
     assert ltree.save!
   end
 
   def test_select
     @connection.execute "insert into ltrees (path) VALUES ('1.2.3')"
     ltree = Ltree.first
-    assert_equal '1.2.3', ltree.path
+    assert_equal "1.2.3", ltree.path
   end
 
   def test_schema_dump_with_shorthand
diff --git a/activerecord/test/cases/adapters/postgresql/money_test.rb b/activerecord/test/cases/adapters/postgresql/money_test.rb
index c031178479..1aa0348879 100644
--- a/activerecord/test/cases/adapters/postgresql/money_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/money_test.rb
@@ -1,22 +1,26 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class PostgresqlMoneyTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
 
-  class PostgresqlMoney < ActiveRecord::Base; end
+  class PostgresqlMoney < ActiveRecord::Base
+    validates :depth, numericality: true
+  end
 
   setup do
     @connection = ActiveRecord::Base.connection
     @connection.execute("set lc_monetary = 'C'")
-    @connection.create_table('postgresql_moneys', force: true) do |t|
+    @connection.create_table("postgresql_moneys", force: true) do |t|
       t.money "wealth"
       t.money "depth", default: "150.55"
     end
   end
 
   teardown do
-    @connection.drop_table 'postgresql_moneys', if_exists: true
+    @connection.drop_table "postgresql_moneys", if_exists: true
   end
 
   def test_column
@@ -24,15 +28,16 @@ class PostgresqlMoneyTest < ActiveRecord::PostgreSQLTestCase
     assert_equal :money, column.type
     assert_equal "money", column.sql_type
     assert_equal 2, column.scale
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlMoney.type_for_attribute("wealth")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_default
-    assert_equal BigDecimal.new("150.55"), PostgresqlMoney.column_defaults['depth']
-    assert_equal BigDecimal.new("150.55"), PostgresqlMoney.new.depth
+    assert_equal BigDecimal("150.55"), PostgresqlMoney.column_defaults["depth"]
+    assert_equal BigDecimal("150.55"), PostgresqlMoney.new.depth
+    assert_equal "150.55", PostgresqlMoney.new.depth_before_type_cast
   end
 
   def test_money_values
@@ -46,11 +51,11 @@ class PostgresqlMoneyTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_money_type_cast
-    type = PostgresqlMoney.type_for_attribute('wealth')
-    assert_equal(12345678.12, type.cast("$12,345,678.12"))
-    assert_equal(12345678.12, type.cast("$12.345.678,12"))
-    assert_equal(-1.15, type.cast("-$1.15"))
-    assert_equal(-2.25, type.cast("($2.25)"))
+    type = PostgresqlMoney.type_for_attribute("wealth")
+    assert_equal(12345678.12, type.cast(+"$12,345,678.12"))
+    assert_equal(12345678.12, type.cast(+"$12.345.678,12"))
+    assert_equal(-1.15, type.cast(+"-$1.15"))
+    assert_equal(-2.25, type.cast(+"($2.25)"))
   end
 
   def test_schema_dumping
@@ -60,10 +65,10 @@ class PostgresqlMoneyTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_create_and_update_money
-    money = PostgresqlMoney.create(wealth: "987.65")
+    money = PostgresqlMoney.create(wealth: +"987.65")
     assert_equal 987.65, money.wealth
 
-    new_value = BigDecimal.new('123.45')
+    new_value = BigDecimal("123.45")
     money.wealth = new_value
     money.save!
     money.reload
@@ -80,7 +85,7 @@ class PostgresqlMoneyTest < ActiveRecord::PostgreSQLTestCase
 
   def test_update_all_with_money_big_decimal
     money = PostgresqlMoney.create!
-    PostgresqlMoney.update_all(wealth: '123.45'.to_d)
+    PostgresqlMoney.update_all(wealth: "123.45".to_d)
     money.reload
 
     assert_equal 123.45, money.wealth
diff --git a/activerecord/test/cases/adapters/postgresql/network_test.rb b/activerecord/test/cases/adapters/postgresql/network_test.rb
index fe6ee4e2d9..736570451b 100644
--- a/activerecord/test/cases/adapters/postgresql/network_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/network_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class PostgresqlNetworkTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
@@ -7,75 +9,75 @@ class PostgresqlNetworkTest < ActiveRecord::PostgreSQLTestCase
 
   setup do
     @connection = ActiveRecord::Base.connection
-    @connection.create_table('postgresql_network_addresses', force: true) do |t|
-      t.inet 'inet_address', default: "192.168.1.1"
-      t.cidr 'cidr_address', default: "192.168.1.0/24"
-      t.macaddr 'mac_address', default: "ff:ff:ff:ff:ff:ff"
+    @connection.create_table("postgresql_network_addresses", force: true) do |t|
+      t.inet "inet_address", default: "192.168.1.1"
+      t.cidr "cidr_address", default: "192.168.1.0/24"
+      t.macaddr "mac_address", default: "ff:ff:ff:ff:ff:ff"
     end
   end
 
   teardown do
-    @connection.drop_table 'postgresql_network_addresses', if_exists: true
+    @connection.drop_table "postgresql_network_addresses", if_exists: true
   end
 
   def test_cidr_column
     column = PostgresqlNetworkAddress.columns_hash["cidr_address"]
     assert_equal :cidr, column.type
     assert_equal "cidr", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlNetworkAddress.type_for_attribute("cidr_address")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_inet_column
     column = PostgresqlNetworkAddress.columns_hash["inet_address"]
     assert_equal :inet, column.type
     assert_equal "inet", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlNetworkAddress.type_for_attribute("inet_address")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_macaddr_column
     column = PostgresqlNetworkAddress.columns_hash["mac_address"]
     assert_equal :macaddr, column.type
     assert_equal "macaddr", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = PostgresqlNetworkAddress.type_for_attribute("mac_address")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_network_types
-    PostgresqlNetworkAddress.create(cidr_address: '192.168.0.0/24',
-                                    inet_address: '172.16.1.254/32',
-                                    mac_address: '01:23:45:67:89:0a')
+    PostgresqlNetworkAddress.create(cidr_address: "192.168.0.0/24",
+                                    inet_address: "172.16.1.254/32",
+                                    mac_address: "01:23:45:67:89:0a")
 
     address = PostgresqlNetworkAddress.first
-    assert_equal IPAddr.new('192.168.0.0/24'), address.cidr_address
-    assert_equal IPAddr.new('172.16.1.254'), address.inet_address
-    assert_equal '01:23:45:67:89:0a', address.mac_address
+    assert_equal IPAddr.new("192.168.0.0/24"), address.cidr_address
+    assert_equal IPAddr.new("172.16.1.254"), address.inet_address
+    assert_equal "01:23:45:67:89:0a", address.mac_address
 
-    address.cidr_address = '10.1.2.3/32'
-    address.inet_address = '10.0.0.0/8'
-    address.mac_address = 'bc:de:f0:12:34:56'
+    address.cidr_address = "10.1.2.3/32"
+    address.inet_address = "10.0.0.0/8"
+    address.mac_address = "bc:de:f0:12:34:56"
 
     address.save!
     assert address.reload
-    assert_equal IPAddr.new('10.1.2.3/32'), address.cidr_address
-    assert_equal IPAddr.new('10.0.0.0/8'), address.inet_address
-    assert_equal 'bc:de:f0:12:34:56', address.mac_address
+    assert_equal IPAddr.new("10.1.2.3/32"), address.cidr_address
+    assert_equal IPAddr.new("10.0.0.0/8"), address.inet_address
+    assert_equal "bc:de:f0:12:34:56", address.mac_address
   end
 
   def test_invalid_network_address
-    invalid_address = PostgresqlNetworkAddress.new(cidr_address: 'invalid addr',
-                                                   inet_address: 'invalid addr')
+    invalid_address = PostgresqlNetworkAddress.new(cidr_address: "invalid addr",
+                                                   inet_address: "invalid addr")
     assert_nil invalid_address.cidr_address
     assert_nil invalid_address.inet_address
-    assert_equal 'invalid addr', invalid_address.cidr_address_before_type_cast
-    assert_equal 'invalid addr', invalid_address.inet_address_before_type_cast
+    assert_equal "invalid addr", invalid_address.cidr_address_before_type_cast
+    assert_equal "invalid addr", invalid_address.inet_address_before_type_cast
     assert invalid_address.save
 
     invalid_address.reload
diff --git a/activerecord/test/cases/adapters/postgresql/numbers_test.rb b/activerecord/test/cases/adapters/postgresql/numbers_test.rb
index ba7e7dc9a3..b53a12254d 100644
--- a/activerecord/test/cases/adapters/postgresql/numbers_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/numbers_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class PostgresqlNumberTest < ActiveRecord::PostgreSQLTestCase
@@ -5,14 +7,14 @@ class PostgresqlNumberTest < ActiveRecord::PostgreSQLTestCase
 
   setup do
     @connection = ActiveRecord::Base.connection
-    @connection.create_table('postgresql_numbers', force: true) do |t|
-      t.column 'single', 'REAL'
-      t.column 'double', 'DOUBLE PRECISION'
+    @connection.create_table("postgresql_numbers", force: true) do |t|
+      t.column "single", "REAL"
+      t.column "double", "DOUBLE PRECISION"
     end
   end
 
   teardown do
-    @connection.drop_table 'postgresql_numbers', if_exists: true
+    @connection.drop_table "postgresql_numbers", if_exists: true
   end
 
   def test_data_type
@@ -31,7 +33,7 @@ class PostgresqlNumberTest < ActiveRecord::PostgreSQLTestCase
     assert_equal 123456.789, first.double
     assert_equal(-::Float::INFINITY, second.single)
     assert_equal ::Float::INFINITY, second.double
-    assert_send [third.double, :nan?]
+    assert third.double.nan?, "Expected #{third.double} to be NaN"
   end
 
   def test_update
diff --git a/activerecord/test/cases/adapters/postgresql/partitions_test.rb b/activerecord/test/cases/adapters/postgresql/partitions_test.rb
new file mode 100644
index 0000000000..0ac9ca1200
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/partitions_test.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+class PostgreSQLPartitionsTest < ActiveRecord::PostgreSQLTestCase
+  def setup
+    @connection = ActiveRecord::Base.connection
+  end
+
+  def teardown
+    @connection.drop_table "partitioned_events", if_exists: true
+  end
+
+  def test_partitions_table_exists
+    skip unless ActiveRecord::Base.connection.postgresql_version >= 100000
+    @connection.create_table :partitioned_events, force: true, id: false,
+      options: "partition by range (issued_at)" do |t|
+      t.timestamp :issued_at
+    end
+    assert @connection.table_exists?("partitioned_events")
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
index 6e6850c4a9..cbb6cd42b5 100644
--- a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
@@ -1,10 +1,13 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/ddl_helper'
-require 'support/connection_helper'
+require "support/ddl_helper"
+require "support/connection_helper"
 
 module ActiveRecord
   module ConnectionAdapters
     class PostgreSQLAdapterTest < ActiveRecord::PostgreSQLTestCase
+      self.use_transactional_tests = false
       include DdlHelper
       include ConnectionHelper
 
@@ -14,199 +17,140 @@ module ActiveRecord
 
       def test_bad_connection
         assert_raise ActiveRecord::NoDatabaseError do
-          configuration = ActiveRecord::Base.configurations['arunit'].merge(database: 'should_not_exist-cinco-dog-db')
+          configuration = ActiveRecord::Base.configurations["arunit"].merge(database: "should_not_exist-cinco-dog-db")
           connection = ActiveRecord::Base.postgresql_connection(configuration)
-          connection.exec_query('SELECT 1')
-        end
-      end
-
-      def test_valid_column
-        with_example_table do
-          column = @connection.columns('ex').find { |col| col.name == 'id' }
-          assert @connection.valid_type?(column.type)
+          connection.exec_query("SELECT 1")
         end
       end
 
-      def test_invalid_column
-        assert_not @connection.valid_type?(:foobar)
-      end
-
       def test_primary_key
         with_example_table do
-          assert_equal 'id', @connection.primary_key('ex')
+          assert_equal "id", @connection.primary_key("ex")
         end
       end
 
       def test_primary_key_works_tables_containing_capital_letters
-        assert_equal 'id', @connection.primary_key('CamelCase')
+        assert_equal "id", @connection.primary_key("CamelCase")
       end
 
       def test_non_standard_primary_key
-        with_example_table 'data character varying(255) primary key' do
-          assert_equal 'data', @connection.primary_key('ex')
+        with_example_table "data character varying(255) primary key" do
+          assert_equal "data", @connection.primary_key("ex")
         end
       end
 
       def test_primary_key_returns_nil_for_no_pk
-        with_example_table 'id integer' do
-          assert_nil @connection.primary_key('ex')
-        end
-      end
-
-      def test_composite_primary_key
-        with_example_table 'id serial, number serial, PRIMARY KEY (id, number)' do
-          assert_nil @connection.primary_key('ex')
-        end
-      end
-
-      def test_primary_key_raises_error_if_table_not_found
-        assert_raises(ActiveRecord::StatementInvalid) do
-          @connection.primary_key('unobtainium')
-        end
-      end
-
-      def test_insert_sql_with_proprietary_returning_clause
-        with_example_table do
-          id = @connection.insert_sql("insert into ex (number) values(5150)", nil, "number")
-          assert_equal 5150, id
-        end
-      end
-
-      def test_insert_sql_with_quoted_schema_and_table_name
-        with_example_table do
-          id = @connection.insert_sql('insert into "public"."ex" (number) values(5150)')
-          expect = @connection.query('select max(id) from ex').first.first
-          assert_equal expect, id
+        with_example_table "id integer" do
+          assert_nil @connection.primary_key("ex")
         end
       end
 
-      def test_insert_sql_with_no_space_after_table_name
-        with_example_table do
-          id = @connection.insert_sql("insert into ex(number) values(5150)")
-          expect = @connection.query('select max(id) from ex').first.first
-          assert_equal expect, id
-        end
-      end
-
-      def test_multiline_insert_sql
-        with_example_table do
-          id = @connection.insert_sql(<<-SQL)
-          insert into ex(
-                         number)
-          values(
-                 5152
-                 )
-          SQL
-          expect = @connection.query('select max(id) from ex').first.first
-          assert_equal expect, id
-        end
-      end
-
-      def test_insert_sql_with_returning_disabled
+      def test_exec_insert_with_returning_disabled
         connection = connection_without_insert_returning
-        id = connection.insert_sql("insert into postgresql_partitioned_table_parent (number) VALUES (1)")
-        expect = connection.query('select max(id) from postgresql_partitioned_table_parent').first.first
-        assert_equal expect.to_i, id
+        result = connection.exec_insert("insert into postgresql_partitioned_table_parent (number) VALUES (1)", nil, [], "id", "postgresql_partitioned_table_parent_id_seq")
+        expect = connection.query("select max(id) from postgresql_partitioned_table_parent").first.first
+        assert_equal expect.to_i, result.rows.first.first
       end
 
-      def test_exec_insert_with_returning_disabled
+      def test_exec_insert_with_returning_disabled_and_no_sequence_name_given
         connection = connection_without_insert_returning
-        result = connection.exec_insert("insert into postgresql_partitioned_table_parent (number) VALUES (1)", nil, [], 'id', 'postgresql_partitioned_table_parent_id_seq')
-        expect = connection.query('select max(id) from postgresql_partitioned_table_parent').first.first
+        result = connection.exec_insert("insert into postgresql_partitioned_table_parent (number) VALUES (1)", nil, [], "id")
+        expect = connection.query("select max(id) from postgresql_partitioned_table_parent").first.first
         assert_equal expect.to_i, result.rows.first.first
       end
 
-      def test_exec_insert_with_returning_disabled_and_no_sequence_name_given
+      def test_exec_insert_default_values_with_returning_disabled_and_no_sequence_name_given
         connection = connection_without_insert_returning
-        result = connection.exec_insert("insert into postgresql_partitioned_table_parent (number) VALUES (1)", nil, [], 'id')
-        expect = connection.query('select max(id) from postgresql_partitioned_table_parent').first.first
+        result = connection.exec_insert("insert into postgresql_partitioned_table_parent DEFAULT VALUES", nil, [], "id")
+        expect = connection.query("select max(id) from postgresql_partitioned_table_parent").first.first
         assert_equal expect.to_i, result.rows.first.first
       end
 
-      def test_sql_for_insert_with_returning_disabled
+      def test_exec_insert_default_values_quoted_schema_with_returning_disabled_and_no_sequence_name_given
         connection = connection_without_insert_returning
-        result = connection.sql_for_insert('sql', nil, nil, nil, 'binds')
-        assert_equal ['sql', 'binds'], result
+        result = connection.exec_insert('insert into "public"."postgresql_partitioned_table_parent" DEFAULT VALUES', nil, [], "id")
+        expect = connection.query("select max(id) from postgresql_partitioned_table_parent").first.first
+        assert_equal expect.to_i, result.rows.first.first
       end
 
       def test_serial_sequence
-        assert_equal 'public.accounts_id_seq',
-          @connection.serial_sequence('accounts', 'id')
+        assert_equal "public.accounts_id_seq",
+          @connection.serial_sequence("accounts", "id")
 
         assert_raises(ActiveRecord::StatementInvalid) do
-          @connection.serial_sequence('zomg', 'id')
+          @connection.serial_sequence("zomg", "id")
         end
       end
 
       def test_default_sequence_name
-        assert_equal 'public.accounts_id_seq',
-          @connection.default_sequence_name('accounts', 'id')
+        assert_equal "public.accounts_id_seq",
+          @connection.default_sequence_name("accounts", "id")
 
-        assert_equal 'public.accounts_id_seq',
-          @connection.default_sequence_name('accounts')
+        assert_equal "public.accounts_id_seq",
+          @connection.default_sequence_name("accounts")
       end
 
       def test_default_sequence_name_bad_table
-        assert_equal 'zomg_id_seq',
-          @connection.default_sequence_name('zomg', 'id')
+        assert_equal "zomg_id_seq",
+          @connection.default_sequence_name("zomg", "id")
 
-        assert_equal 'zomg_id_seq',
-          @connection.default_sequence_name('zomg')
+        assert_equal "zomg_id_seq",
+          @connection.default_sequence_name("zomg")
       end
 
       def test_pk_and_sequence_for
         with_example_table do
-          pk, seq = @connection.pk_and_sequence_for('ex')
-          assert_equal 'id', pk
-          assert_equal @connection.default_sequence_name('ex', 'id'), seq.to_s
+          pk, seq = @connection.pk_and_sequence_for("ex")
+          assert_equal "id", pk
+          assert_equal @connection.default_sequence_name("ex", "id"), seq.to_s
         end
       end
 
       def test_pk_and_sequence_for_with_non_standard_primary_key
-        with_example_table 'code serial primary key' do
-          pk, seq = @connection.pk_and_sequence_for('ex')
-          assert_equal 'code', pk
-          assert_equal @connection.default_sequence_name('ex', 'code'), seq.to_s
+        with_example_table "code serial primary key" do
+          pk, seq = @connection.pk_and_sequence_for("ex")
+          assert_equal "code", pk
+          assert_equal @connection.default_sequence_name("ex", "code"), seq.to_s
         end
       end
 
       def test_pk_and_sequence_for_returns_nil_if_no_seq
-        with_example_table 'id integer primary key' do
-          assert_nil @connection.pk_and_sequence_for('ex')
+        with_example_table "id integer primary key" do
+          assert_nil @connection.pk_and_sequence_for("ex")
         end
       end
 
       def test_pk_and_sequence_for_returns_nil_if_no_pk
-        with_example_table 'id integer' do
-          assert_nil @connection.pk_and_sequence_for('ex')
+        with_example_table "id integer" do
+          assert_nil @connection.pk_and_sequence_for("ex")
         end
       end
 
       def test_pk_and_sequence_for_returns_nil_if_table_not_found
-        assert_nil @connection.pk_and_sequence_for('unobtainium')
+        assert_nil @connection.pk_and_sequence_for("unobtainium")
       end
 
       def test_pk_and_sequence_for_with_collision_pg_class_oid
-        @connection.exec_query('create table ex(id serial primary key)')
-        @connection.exec_query('create table ex2(id serial primary key)')
+        @connection.exec_query("create table ex(id serial primary key)")
+        @connection.exec_query("create table ex2(id serial primary key)")
 
         correct_depend_record = [
           "'pg_class'::regclass",
           "'ex_id_seq'::regclass",
-          '0',
+          "0",
           "'pg_class'::regclass",
           "'ex'::regclass",
-          '1',
+          "1",
           "'a'"
         ]
 
         collision_depend_record = [
           "'pg_attrdef'::regclass",
           "'ex2_id_seq'::regclass",
-          '0',
+          "0",
           "'pg_class'::regclass",
           "'ex'::regclass",
-          '1',
+          "1",
           "'a'"
         ]
 
@@ -220,39 +164,15 @@ module ActiveRecord
           "INSERT INTO pg_depend VALUES(#{correct_depend_record.join(',')})"
         )
 
-        seq = @connection.pk_and_sequence_for('ex').last
+        seq = @connection.pk_and_sequence_for("ex").last
         assert_equal PostgreSQL::Name.new("public", "ex_id_seq"), seq
 
         @connection.exec_query(
           "DELETE FROM pg_depend WHERE objid = 'ex2_id_seq'::regclass AND refobjid = 'ex'::regclass AND deptype = 'a'"
         )
       ensure
-        @connection.drop_table 'ex', if_exists: true
-        @connection.drop_table 'ex2', if_exists: true
-      end
-
-      def test_exec_insert_number
-        with_example_table do
-          insert(@connection, 'number' => 10)
-
-          result = @connection.exec_query('SELECT number FROM ex WHERE number = 10')
-
-          assert_equal 1, result.rows.length
-          assert_equal 10, result.rows.last.last
-        end
-      end
-
-      def test_exec_insert_string
-        with_example_table do
-          str = 'いただきます！'
-          insert(@connection, 'number' => 10, 'data' => str)
-
-          result = @connection.exec_query('SELECT number, data FROM ex WHERE number = 10')
-
-          value = result.rows.last.last
-
-          assert_equal str, value
-        end
+        @connection.drop_table "ex", if_exists: true
+        @connection.drop_table "ex2", if_exists: true
       end
 
       def test_table_alias_length
@@ -263,89 +183,105 @@ module ActiveRecord
 
       def test_exec_no_binds
         with_example_table do
-          result = @connection.exec_query('SELECT id, data FROM ex')
+          result = @connection.exec_query("SELECT id, data FROM ex")
           assert_equal 0, result.rows.length
           assert_equal 2, result.columns.length
           assert_equal %w{ id data }, result.columns
 
-          string = @connection.quote('foo')
+          string = @connection.quote("foo")
           @connection.exec_query("INSERT INTO ex (id, data) VALUES (1, #{string})")
-          result = @connection.exec_query('SELECT id, data FROM ex')
+          result = @connection.exec_query("SELECT id, data FROM ex")
           assert_equal 1, result.rows.length
           assert_equal 2, result.columns.length
 
-          assert_equal [[1, 'foo']], result.rows
+          assert_equal [[1, "foo"]], result.rows
         end
       end
 
-      def test_exec_with_binds
-        with_example_table do
-          string = @connection.quote('foo')
-          @connection.exec_query("INSERT INTO ex (id, data) VALUES (1, #{string})")
-          result = @connection.exec_query(
-                                          'SELECT id, data FROM ex WHERE id = $1', nil, [bind_param(1)])
+      if ActiveRecord::Base.connection.prepared_statements
+        def test_exec_with_binds
+          with_example_table do
+            string = @connection.quote("foo")
+            @connection.exec_query("INSERT INTO ex (id, data) VALUES (1, #{string})")
 
-          assert_equal 1, result.rows.length
-          assert_equal 2, result.columns.length
+            bind = Relation::QueryAttribute.new("id", 1, Type::Value.new)
+            result = @connection.exec_query("SELECT id, data FROM ex WHERE id = $1", nil, [bind])
+
+            assert_equal 1, result.rows.length
+            assert_equal 2, result.columns.length
 
-          assert_equal [[1, 'foo']], result.rows
+            assert_equal [[1, "foo"]], result.rows
+          end
         end
-      end
 
-      def test_exec_typecasts_bind_vals
-        with_example_table do
-          string = @connection.quote('foo')
-          @connection.exec_query("INSERT INTO ex (id, data) VALUES (1, #{string})")
+        def test_exec_typecasts_bind_vals
+          with_example_table do
+            string = @connection.quote("foo")
+            @connection.exec_query("INSERT INTO ex (id, data) VALUES (1, #{string})")
 
-          bind = ActiveRecord::Relation::QueryAttribute.new("id", "1-fuu", ActiveRecord::Type::Integer.new)
-          result = @connection.exec_query(
-                                          'SELECT id, data FROM ex WHERE id = $1', nil, [bind])
+            bind = Relation::QueryAttribute.new("id", "1-fuu", Type::Integer.new)
+            result = @connection.exec_query("SELECT id, data FROM ex WHERE id = $1", nil, [bind])
 
-          assert_equal 1, result.rows.length
-          assert_equal 2, result.columns.length
+            assert_equal 1, result.rows.length
+            assert_equal 2, result.columns.length
 
-          assert_equal [[1, 'foo']], result.rows
+            assert_equal [[1, "foo"]], result.rows
+          end
         end
       end
 
-      def test_substitute_at
-        bind = @connection.substitute_at(nil)
-        assert_equal Arel.sql('$1'), bind.to_sql
-      end
-
       def test_partial_index
         with_example_table do
-          @connection.add_index 'ex', %w{ id number }, :name => 'partial', :where => "number > 100"
-          index = @connection.indexes('ex').find { |idx| idx.name == 'partial' }
+          @connection.add_index "ex", %w{ id number }, name: "partial", where: "number > 100"
+          index = @connection.indexes("ex").find { |idx| idx.name == "partial" }
           assert_equal "(number > 100)", index.where
         end
       end
 
+      def test_expression_index
+        with_example_table do
+          @connection.add_index "ex", "mod(id, 10), abs(number)", name: "expression"
+          index = @connection.indexes("ex").find { |idx| idx.name == "expression" }
+          assert_equal "mod(id, 10), abs(number)", index.columns
+        end
+      end
+
+      def test_index_with_opclass
+        with_example_table do
+          @connection.add_index "ex", "data", opclass: "varchar_pattern_ops"
+          index = @connection.indexes("ex").find { |idx| idx.name == "index_ex_on_data" }
+          assert_equal ["data"], index.columns
+
+          @connection.remove_index "ex", "data"
+          assert_not @connection.indexes("ex").find { |idx| idx.name == "index_ex_on_data" }
+        end
+      end
+
       def test_columns_for_distinct_zero_orders
         assert_equal "posts.id",
           @connection.columns_for_distinct("posts.id", [])
       end
 
       def test_columns_for_distinct_one_order
-        assert_equal "posts.id, posts.created_at AS alias_0",
+        assert_equal "posts.created_at AS alias_0, posts.id",
           @connection.columns_for_distinct("posts.id", ["posts.created_at desc"])
       end
 
       def test_columns_for_distinct_few_orders
-        assert_equal "posts.id, posts.created_at AS alias_0, posts.position AS alias_1",
+        assert_equal "posts.created_at AS alias_0, posts.position AS alias_1, posts.id",
           @connection.columns_for_distinct("posts.id", ["posts.created_at desc", "posts.position asc"])
       end
 
       def test_columns_for_distinct_with_case
         assert_equal(
-          'posts.id, CASE WHEN author.is_active THEN UPPER(author.name) ELSE UPPER(author.email) END AS alias_0',
-          @connection.columns_for_distinct('posts.id',
+          "CASE WHEN author.is_active THEN UPPER(author.name) ELSE UPPER(author.email) END AS alias_0, posts.id",
+          @connection.columns_for_distinct("posts.id",
             ["CASE WHEN author.is_active THEN UPPER(author.name) ELSE UPPER(author.email) END"])
         )
       end
 
       def test_columns_for_distinct_blank_not_nil_orders
-        assert_equal "posts.id, posts.created_at AS alias_0",
+        assert_equal "posts.created_at AS alias_0, posts.id",
           @connection.columns_for_distinct("posts.id", ["posts.created_at desc", "", "   "])
       end
 
@@ -354,23 +290,23 @@ module ActiveRecord
         def order.to_sql
           "posts.created_at desc"
         end
-        assert_equal "posts.id, posts.created_at AS alias_0",
+        assert_equal "posts.created_at AS alias_0, posts.id",
           @connection.columns_for_distinct("posts.id", [order])
       end
 
       def test_columns_for_distinct_with_nulls
-        assert_equal "posts.title, posts.updater_id AS alias_0", @connection.columns_for_distinct("posts.title", ["posts.updater_id desc nulls first"])
-        assert_equal "posts.title, posts.updater_id AS alias_0", @connection.columns_for_distinct("posts.title", ["posts.updater_id desc nulls last"])
+        assert_equal "posts.updater_id AS alias_0, posts.title", @connection.columns_for_distinct("posts.title", ["posts.updater_id desc nulls first"])
+        assert_equal "posts.updater_id AS alias_0, posts.title", @connection.columns_for_distinct("posts.title", ["posts.updater_id desc nulls last"])
       end
 
       def test_columns_for_distinct_without_order_specifiers
-        assert_equal "posts.title, posts.updater_id AS alias_0",
+        assert_equal "posts.updater_id AS alias_0, posts.title",
           @connection.columns_for_distinct("posts.title", ["posts.updater_id"])
 
-        assert_equal "posts.title, posts.updater_id AS alias_0",
+        assert_equal "posts.updater_id AS alias_0, posts.title",
           @connection.columns_for_distinct("posts.title", ["posts.updater_id nulls last"])
 
-        assert_equal "posts.title, posts.updater_id AS alias_0",
+        assert_equal "posts.updater_id AS alias_0, posts.title",
           @connection.columns_for_distinct("posts.title", ["posts.updater_id nulls first"])
       end
 
@@ -390,29 +326,35 @@ module ActiveRecord
         reset_connection
       end
 
-      def test_only_reload_type_map_once_for_every_unknown_type
+      def test_only_reload_type_map_once_for_every_unrecognized_type
+        reset_connection
+        connection = ActiveRecord::Base.connection
+
         silence_warnings do
           assert_queries 2, ignore_none: true do
-            @connection.select_all "SELECT NULL::anyelement"
+            connection.select_all "select 'pg_catalog.pg_class'::regclass"
           end
           assert_queries 1, ignore_none: true do
-            @connection.select_all "SELECT NULL::anyelement"
+            connection.select_all "select 'pg_catalog.pg_class'::regclass"
           end
           assert_queries 2, ignore_none: true do
-            @connection.select_all "SELECT NULL::anyarray"
+            connection.select_all "SELECT NULL::anyarray"
           end
         end
       ensure
         reset_connection
       end
 
-      def test_only_warn_on_first_encounter_of_unknown_oid
+      def test_only_warn_on_first_encounter_of_unrecognized_oid
+        reset_connection
+        connection = ActiveRecord::Base.connection
+
         warning = capture(:stderr) {
-          @connection.select_all "SELECT NULL::anyelement"
-          @connection.select_all "SELECT NULL::anyelement"
-          @connection.select_all "SELECT NULL::anyelement"
+          connection.select_all "select 'pg_catalog.pg_class'::regclass"
+          connection.select_all "select 'pg_catalog.pg_class'::regclass"
+          connection.select_all "select 'pg_catalog.pg_class'::regclass"
         }
-        assert_match(/\Aunknown OID \d+: failed to recognize type of 'anyelement'. It will be treated as String.\n\z/, warning)
+        assert_match(/\Aunknown OID \d+: failed to recognize type of 'regclass'\. It will be treated as String\.\n\z/, warning)
       ensure
         reset_connection
       end
@@ -420,7 +362,7 @@ module ActiveRecord
       def test_unparsed_defaults_are_at_least_set_when_saving
         with_example_table "id SERIAL PRIMARY KEY, number INTEGER NOT NULL DEFAULT (4 + 4) * 2 / 4" do
           number_klass = Class.new(ActiveRecord::Base) do
-            self.table_name = 'ex'
+            self.table_name = "ex"
           end
           column = number_klass.columns_hash["number"]
           assert_nil column.default
@@ -435,31 +377,14 @@ module ActiveRecord
       end
 
       private
-      def insert(ctx, data)
-        binds = data.map { |name, value|
-          bind_param(value, name)
-        }
-        columns = binds.map(&:name)
-
-        bind_subs = columns.length.times.map { |x| "$#{x + 1}" }
-
-        sql = "INSERT INTO ex (#{columns.join(", ")})
-               VALUES (#{bind_subs.join(', ')})"
 
-        ctx.exec_insert(sql, 'SQL', binds)
-      end
-
-      def with_example_table(definition = 'id serial primary key, number integer, data character varying(255)', &block)
-        super(@connection, 'ex', definition, &block)
-      end
-
-      def connection_without_insert_returning
-        ActiveRecord::Base.postgresql_connection(ActiveRecord::Base.configurations['arunit'].merge(:insert_returning => false))
-      end
+        def with_example_table(definition = "id serial primary key, number integer, data character varying(255)", &block)
+          super(@connection, "ex", definition, &block)
+        end
 
-      def bind_param(value, name = nil)
-        ActiveRecord::Relation::QueryAttribute.new(name, value, ActiveRecord::Type::Value.new)
-      end
+        def connection_without_insert_returning
+          ActiveRecord::Base.postgresql_connection(ActiveRecord::Base.configurations["arunit"].merge(insert_returning: false))
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/prepared_statements_disabled_test.rb b/activerecord/test/cases/adapters/postgresql/prepared_statements_disabled_test.rb
new file mode 100644
index 0000000000..f7478b50c3
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/prepared_statements_disabled_test.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/computer"
+require "models/developer"
+
+class PreparedStatementsDisabledTest < ActiveRecord::PostgreSQLTestCase
+  fixtures :developers
+
+  def setup
+    @conn = ActiveRecord::Base.establish_connection :arunit_without_prepared_statements
+  end
+
+  def teardown
+    @conn.release_connection
+    ActiveRecord::Base.establish_connection :arunit
+  end
+
+  def test_select_query_works_even_when_prepared_statements_are_disabled
+    assert_not Developer.connection.prepared_statements
+
+    david = developers(:david)
+
+    assert_equal david, Developer.where(name: "David").last # With Binds
+    assert_operator Developer.count, :>, 0 # Without Binds
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/quoting_test.rb b/activerecord/test/cases/adapters/postgresql/quoting_test.rb
index 5e6f4dbbb8..d50dc49276 100644
--- a/activerecord/test/cases/adapters/postgresql/quoting_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/quoting_test.rb
@@ -1,5 +1,6 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'ipaddr'
 
 module ActiveRecord
   module ConnectionAdapters
@@ -10,20 +11,20 @@ module ActiveRecord
         end
 
         def test_type_cast_true
-          assert_equal 't', @conn.type_cast(true)
+          assert_equal true, @conn.type_cast(true)
         end
 
         def test_type_cast_false
-          assert_equal 'f', @conn.type_cast(false)
+          assert_equal false, @conn.type_cast(false)
         end
 
         def test_quote_float_nan
-          nan = 0.0/0
+          nan = 0.0 / 0
           assert_equal "'NaN'", @conn.quote(nan)
         end
 
         def test_quote_float_infinity
-          infinity = 1.0/0
+          infinity = 1.0 / 0
           assert_equal "'Infinity'", @conn.quote(infinity)
         end
 
@@ -36,7 +37,7 @@ module ActiveRecord
         def test_quote_bit_string
           value = "'); SELECT * FROM users; /*\n01\n*/--"
           type = OID::Bit.new
-          assert_equal nil, @conn.quote(type.serialize(value))
+          assert_nil @conn.quote(type.serialize(value))
         end
       end
     end
diff --git a/activerecord/test/cases/adapters/postgresql/range_test.rb b/activerecord/test/cases/adapters/postgresql/range_test.rb
index 02b1083430..433598500d 100644
--- a/activerecord/test/cases/adapters/postgresql/range_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/range_test.rb
@@ -1,14 +1,18 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/connection_helper'
+require "support/connection_helper"
 
 if ActiveRecord::Base.connection.respond_to?(:supports_ranges?) && ActiveRecord::Base.connection.supports_ranges?
   class PostgresqlRange < ActiveRecord::Base
     self.table_name = "postgresql_ranges"
+    self.time_zone_aware_types += [:tsrange, :tstzrange]
   end
 
   class PostgresqlRangeTest < ActiveRecord::PostgreSQLTestCase
     self.use_transactional_tests = false
     include ConnectionHelper
+    include InTimeZone
 
     def setup
       @connection = PostgresqlRange.connection
@@ -21,7 +25,7 @@ if ActiveRecord::Base.connection.respond_to?(:supports_ranges?) && ActiveRecord:
             );
 _SQL
 
-          @connection.create_table('postgresql_ranges') do |t|
+          @connection.create_table("postgresql_ranges") do |t|
             t.daterange :date_range
             t.numrange :num_range
             t.tsrange :ts_range
@@ -30,7 +34,7 @@ _SQL
             t.int8range :int8_range
           end
 
-          @connection.add_column 'postgresql_ranges', 'float_range', 'floatrange'
+          @connection.add_column "postgresql_ranges", "float_range", "floatrange"
         end
         PostgresqlRange.reset_column_information
       rescue ActiveRecord::StatementInvalid
@@ -91,8 +95,8 @@ _SQL
     end
 
     teardown do
-      @connection.drop_table 'postgresql_ranges', if_exists: true
-      @connection.execute 'DROP TYPE IF EXISTS floatrange'
+      @connection.drop_table "postgresql_ranges", if_exists: true
+      @connection.execute "DROP TYPE IF EXISTS floatrange"
       reset_connection
     end
 
@@ -130,10 +134,10 @@ _SQL
     end
 
     def test_numrange_values
-      assert_equal BigDecimal.new('0.1')..BigDecimal.new('0.2'), @first_range.num_range
-      assert_equal BigDecimal.new('0.1')...BigDecimal.new('0.2'), @second_range.num_range
-      assert_equal BigDecimal.new('0.1')...BigDecimal.new('Infinity'), @third_range.num_range
-      assert_equal BigDecimal.new('-Infinity')...BigDecimal.new('Infinity'), @fourth_range.num_range
+      assert_equal BigDecimal("0.1")..BigDecimal("0.2"), @first_range.num_range
+      assert_equal BigDecimal("0.1")...BigDecimal("0.2"), @second_range.num_range
+      assert_equal BigDecimal("0.1")...BigDecimal("Infinity"), @third_range.num_range
+      assert_equal BigDecimal("-Infinity")...BigDecimal("Infinity"), @fourth_range.num_range
       assert_nil @empty_range.num_range
     end
 
@@ -146,8 +150,8 @@ _SQL
     end
 
     def test_tstzrange_values
-      assert_equal Time.parse('2010-01-01 09:30:00 UTC')..Time.parse('2011-01-01 17:30:00 UTC'), @first_range.tstz_range
-      assert_equal Time.parse('2010-01-01 09:30:00 UTC')...Time.parse('2011-01-01 17:30:00 UTC'), @second_range.tstz_range
+      assert_equal Time.parse("2010-01-01 09:30:00 UTC")..Time.parse("2011-01-01 17:30:00 UTC"), @first_range.tstz_range
+      assert_equal Time.parse("2010-01-01 09:30:00 UTC")...Time.parse("2011-01-01 17:30:00 UTC"), @second_range.tstz_range
       assert_equal(-Float::INFINITY...Float::INFINITY, @fourth_range.tstz_range)
       assert_nil @empty_range.tstz_range
     end
@@ -160,18 +164,38 @@ _SQL
       assert_nil @empty_range.float_range
     end
 
+    def test_timezone_awareness_tzrange
+      tz = "Pacific Time (US & Canada)"
+
+      in_time_zone tz do
+        PostgresqlRange.reset_column_information
+        time_string = Time.current.to_s
+        time = Time.zone.parse(time_string)
+
+        record = PostgresqlRange.new(tstz_range: time_string..time_string)
+        assert_equal time..time, record.tstz_range
+        assert_equal ActiveSupport::TimeZone[tz], record.tstz_range.begin.time_zone
+
+        record.save!
+        record.reload
+
+        assert_equal time..time, record.tstz_range
+        assert_equal ActiveSupport::TimeZone[tz], record.tstz_range.begin.time_zone
+      end
+    end
+
     def test_create_tstzrange
-      tstzrange = Time.parse('2010-01-01 14:30:00 +0100')...Time.parse('2011-02-02 14:30:00 CDT')
+      tstzrange = Time.parse("2010-01-01 14:30:00 +0100")...Time.parse("2011-02-02 14:30:00 CDT")
       round_trip(@new_range, :tstz_range, tstzrange)
       assert_equal @new_range.tstz_range, tstzrange
-      assert_equal @new_range.tstz_range, Time.parse('2010-01-01 13:30:00 UTC')...Time.parse('2011-02-02 19:30:00 UTC')
+      assert_equal @new_range.tstz_range, Time.parse("2010-01-01 13:30:00 UTC")...Time.parse("2011-02-02 19:30:00 UTC")
     end
 
     def test_update_tstzrange
       assert_equal_round_trip(@first_range, :tstz_range,
-                              Time.parse('2010-01-01 14:30:00 CDT')...Time.parse('2011-02-02 14:30:00 CET'))
+                              Time.parse("2010-01-01 14:30:00 CDT")...Time.parse("2011-02-02 14:30:00 CET"))
       assert_nil_round_trip(@first_range, :tstz_range,
-                            Time.parse('2010-01-01 14:30:00 +0100')...Time.parse('2010-01-01 13:30:00 +0000'))
+                            Time.parse("2010-01-01 14:30:00 +0100")...Time.parse("2010-01-01 13:30:00 +0000"))
     end
 
     def test_create_tsrange
@@ -188,16 +212,87 @@ _SQL
                             Time.send(tz, 2010, 1, 1, 14, 30, 0)...Time.send(tz, 2010, 1, 1, 14, 30, 0))
     end
 
+    def test_timezone_awareness_tsrange
+      tz = "Pacific Time (US & Canada)"
+
+      in_time_zone tz do
+        PostgresqlRange.reset_column_information
+        time_string = Time.current.to_s
+        time = Time.zone.parse(time_string)
+
+        record = PostgresqlRange.new(ts_range: time_string..time_string)
+        assert_equal time..time, record.ts_range
+        assert_equal ActiveSupport::TimeZone[tz], record.ts_range.begin.time_zone
+
+        record.save!
+        record.reload
+
+        assert_equal time..time, record.ts_range
+        assert_equal ActiveSupport::TimeZone[tz], record.ts_range.begin.time_zone
+      end
+    end
+
+    def test_create_tstzrange_preserve_usec
+      tstzrange = Time.parse("2010-01-01 14:30:00.670277 +0100")...Time.parse("2011-02-02 14:30:00.745125 CDT")
+      round_trip(@new_range, :tstz_range, tstzrange)
+      assert_equal @new_range.tstz_range, tstzrange
+      assert_equal @new_range.tstz_range, Time.parse("2010-01-01 13:30:00.670277 UTC")...Time.parse("2011-02-02 19:30:00.745125 UTC")
+    end
+
+    def test_update_tstzrange_preserve_usec
+      assert_equal_round_trip(@first_range, :tstz_range,
+                              Time.parse("2010-01-01 14:30:00.245124 CDT")...Time.parse("2011-02-02 14:30:00.451274 CET"))
+      assert_nil_round_trip(@first_range, :tstz_range,
+                            Time.parse("2010-01-01 14:30:00.245124 +0100")...Time.parse("2010-01-01 13:30:00.245124 +0000"))
+    end
+
+    def test_create_tsrange_preseve_usec
+      tz = ::ActiveRecord::Base.default_timezone
+      assert_equal_round_trip(@new_range, :ts_range,
+                              Time.send(tz, 2010, 1, 1, 14, 30, 0, 125435)...Time.send(tz, 2011, 2, 2, 14, 30, 0, 225435))
+    end
+
+    def test_update_tsrange_preserve_usec
+      tz = ::ActiveRecord::Base.default_timezone
+      assert_equal_round_trip(@first_range, :ts_range,
+                              Time.send(tz, 2010, 1, 1, 14, 30, 0, 142432)...Time.send(tz, 2011, 2, 2, 14, 30, 0, 224242))
+      assert_nil_round_trip(@first_range, :ts_range,
+                            Time.send(tz, 2010, 1, 1, 14, 30, 0, 142432)...Time.send(tz, 2010, 1, 1, 14, 30, 0, 142432))
+    end
+
+    def test_timezone_awareness_tsrange_preserve_usec
+      tz = "Pacific Time (US & Canada)"
+
+      in_time_zone tz do
+        PostgresqlRange.reset_column_information
+        time_string = "2017-09-26 07:30:59.132451 -0700"
+        time = Time.zone.parse(time_string)
+        assert time.usec > 0
+
+        record = PostgresqlRange.new(ts_range: time_string..time_string)
+        assert_equal time..time, record.ts_range
+        assert_equal ActiveSupport::TimeZone[tz], record.ts_range.begin.time_zone
+        assert_equal time.usec, record.ts_range.begin.usec
+
+        record.save!
+        record.reload
+
+        assert_equal time..time, record.ts_range
+        assert_equal ActiveSupport::TimeZone[tz], record.ts_range.begin.time_zone
+        assert_equal time.usec, record.ts_range.begin.usec
+      end
+    end
+
     def test_create_numrange
       assert_equal_round_trip(@new_range, :num_range,
-                              BigDecimal.new('0.5')...BigDecimal.new('1'))
+                              BigDecimal("0.5")...BigDecimal("1"))
     end
 
     def test_update_numrange
       assert_equal_round_trip(@first_range, :num_range,
-                              BigDecimal.new('0.5')...BigDecimal.new('1'))
+                              BigDecimal("0.5")...BigDecimal("1"))
       assert_nil_round_trip(@first_range, :num_range,
-                            BigDecimal.new('0.5')...BigDecimal.new('0.5'))
+                            BigDecimal("0.5")...BigDecimal("0.5"))
     end
 
     def test_create_daterange
@@ -240,6 +335,18 @@ _SQL
       assert_raises(ArgumentError) { PostgresqlRange.create!(tstz_range: "(''2010-01-01 14:30:00+05'', ''2011-01-01 14:30:00-03'']") }
     end
 
+    def test_where_by_attribute_with_range
+      range = 1..100
+      record = PostgresqlRange.create!(int4_range: range)
+      assert_equal record, PostgresqlRange.where(int4_range: range).take
+    end
+
+    def test_where_by_attribute_with_range_in_array
+      range = 1..100
+      record = PostgresqlRange.create!(int4_range: range)
+      assert_equal record, PostgresqlRange.where(int4_range: [range]).take
+    end
+
     def test_update_all_with_ranges
       PostgresqlRange.create!
 
@@ -257,6 +364,18 @@ _SQL
       end
     end
 
+    def test_infinity_values
+      PostgresqlRange.create!(int4_range: 1..Float::INFINITY,
+                              int8_range: -Float::INFINITY..0,
+                              float_range: -Float::INFINITY..Float::INFINITY)
+
+      record = PostgresqlRange.first
+
+      assert_equal(1...Float::INFINITY, record.int4_range)
+      assert_equal(-Float::INFINITY...1, record.int8_range)
+      assert_equal(-Float::INFINITY...Float::INFINITY, record.float_range)
+    end
+
     private
       def assert_equal_round_trip(range, attribute, value)
         round_trip(range, attribute, value)
diff --git a/activerecord/test/cases/adapters/postgresql/referential_integrity_test.rb b/activerecord/test/cases/adapters/postgresql/referential_integrity_test.rb
index c895ab9db5..ba477c63f4 100644
--- a/activerecord/test/cases/adapters/postgresql/referential_integrity_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/referential_integrity_test.rb
@@ -1,5 +1,7 @@
-require 'cases/helper'
-require 'support/connection_helper'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/connection_helper"
 
 class PostgreSQLReferentialIntegrityTest < ActiveRecord::PostgreSQLTestCase
   self.use_transactional_tests = false
@@ -14,7 +16,7 @@ class PostgreSQLReferentialIntegrityTest < ActiveRecord::PostgreSQLTestCase
     def execute(sql)
       if IS_REFERENTIAL_INTEGRITY_SQL.call(sql)
         super "BROKEN;" rescue nil # put transaction in broken state
-        raise ActiveRecord::StatementInvalid, 'PG::InsufficientPrivilege'
+        raise ActiveRecord::StatementInvalid, "PG::InsufficientPrivilege"
       else
         super
       end
@@ -24,7 +26,7 @@ class PostgreSQLReferentialIntegrityTest < ActiveRecord::PostgreSQLTestCase
   module ProgrammerMistake
     def execute(sql)
       if IS_REFERENTIAL_INTEGRITY_SQL.call(sql)
-        raise ArgumentError, 'something is not right.'
+        raise ArgumentError, "something is not right."
       else
         super
       end
@@ -48,10 +50,10 @@ class PostgreSQLReferentialIntegrityTest < ActiveRecord::PostgreSQLTestCase
     warning = capture(:stderr) do
       e = assert_raises(ActiveRecord::InvalidForeignKey) do
         @connection.disable_referential_integrity do
-          raise ActiveRecord::InvalidForeignKey, 'Should be re-raised'
+          raise ActiveRecord::InvalidForeignKey, "Should be re-raised"
         end
       end
-      assert_equal 'Should be re-raised', e.message
+      assert_equal "Should be re-raised", e.message
     end
     assert_match (/WARNING: Rails was not able to disable referential integrity/), warning
     assert_match (/cause: PG::InsufficientPrivilege/), warning
@@ -63,10 +65,10 @@ class PostgreSQLReferentialIntegrityTest < ActiveRecord::PostgreSQLTestCase
     warning = capture(:stderr) do
       e = assert_raises(ActiveRecord::StatementInvalid) do
         @connection.disable_referential_integrity do
-          raise ActiveRecord::StatementInvalid, 'Should be re-raised'
+          raise ActiveRecord::StatementInvalid, "Should be re-raised"
         end
       end
-      assert_equal 'Should be re-raised', e.message
+      assert_equal "Should be re-raised", e.message
     end
     assert warning.blank?, "expected no warnings but got:\n#{warning}"
   end
@@ -99,13 +101,13 @@ class PostgreSQLReferentialIntegrityTest < ActiveRecord::PostgreSQLTestCase
     @connection.extend ProgrammerMistake
 
     assert_raises ArgumentError do
-      @connection.disable_referential_integrity {}
+      @connection.disable_referential_integrity { }
     end
   end
 
   private
 
-  def assert_transaction_is_not_broken
-    assert_equal 1, @connection.select_value("SELECT 1")
-  end
+    def assert_transaction_is_not_broken
+      assert_equal 1, @connection.select_value("SELECT 1")
+    end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/rename_table_test.rb b/activerecord/test/cases/adapters/postgresql/rename_table_test.rb
index bd64bae308..100d247113 100644
--- a/activerecord/test/cases/adapters/postgresql/rename_table_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/rename_table_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class PostgresqlRenameTableTest < ActiveRecord::PostgreSQLTestCase
@@ -24,11 +26,11 @@ class PostgresqlRenameTableTest < ActiveRecord::PostgreSQLTestCase
 
   private
 
-  def num_indices_named(name)
-    @connection.execute(<<-SQL).values.length
-      SELECT 1 FROM "pg_index"
-        JOIN "pg_class" ON "pg_index"."indexrelid" = "pg_class"."oid"
-        WHERE "pg_class"."relname" = '#{name}'
-    SQL
-  end
+    def num_indices_named(name)
+      @connection.execute(<<-SQL).values.length
+        SELECT 1 FROM "pg_index"
+          JOIN "pg_class" ON "pg_index"."indexrelid" = "pg_class"."oid"
+          WHERE "pg_class"."relname" = '#{name}'
+      SQL
+    end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/schema_authorization_test.rb b/activerecord/test/cases/adapters/postgresql/schema_authorization_test.rb
index fa6584eae5..fcb0aec81b 100644
--- a/activerecord/test/cases/adapters/postgresql/schema_authorization_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/schema_authorization_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class SchemaThing < ActiveRecord::Base
@@ -6,12 +8,12 @@ end
 class SchemaAuthorizationTest < ActiveRecord::PostgreSQLTestCase
   self.use_transactional_tests = false
 
-  TABLE_NAME = 'schema_things'
+  TABLE_NAME = "schema_things"
   COLUMNS = [
-    'id serial primary key',
-    'name character varying(50)'
+    "id serial primary key",
+    "name character varying(50)"
   ]
-  USERS = ['rails_pg_schema_user1', 'rails_pg_schema_user2']
+  USERS = ["rails_pg_schema_user1", "rails_pg_schema_user2"]
 
   def setup
     @connection = ActiveRecord::Base.connection
@@ -31,7 +33,7 @@ class SchemaAuthorizationTest < ActiveRecord::PostgreSQLTestCase
     set_session_auth
     @connection.execute "RESET search_path"
     USERS.each do |u|
-      @connection.execute "DROP SCHEMA #{u} CASCADE"
+      @connection.drop_schema u
       @connection.execute "DROP USER #{u}"
     end
   end
@@ -45,7 +47,7 @@ class SchemaAuthorizationTest < ActiveRecord::PostgreSQLTestCase
 
   def test_session_auth=
     assert_raise(ActiveRecord::StatementInvalid) do
-      @connection.session_auth = 'DEFAULT'
+      @connection.session_auth = "DEFAULT"
       @connection.execute "SELECT * FROM #{TABLE_NAME}"
     end
   end
@@ -55,31 +57,22 @@ class SchemaAuthorizationTest < ActiveRecord::PostgreSQLTestCase
       set_session_auth
       USERS.each do |u|
         set_session_auth u
-        assert_equal u, @connection.exec_query("SELECT name FROM #{TABLE_NAME} WHERE id = $1", 'SQL', [bind_param(1)]).first['name']
-        set_session_auth
-      end
-    end
-  end
-
-  def test_auth_with_bind
-    assert_nothing_raised do
-      set_session_auth
-      USERS.each do |u|
-        @connection.clear_cache!
-        set_session_auth u
-        assert_equal u, @connection.exec_query("SELECT name FROM #{TABLE_NAME} WHERE id = $1", 'SQL', [bind_param(1)]).first['name']
+        assert_equal u, @connection.select_value("SELECT name FROM #{TABLE_NAME} WHERE id = 1")
         set_session_auth
       end
     end
   end
 
-  def test_schema_uniqueness
-    assert_nothing_raised do
-      set_session_auth
-      USERS.each do |u|
-        set_session_auth u
-        assert_equal u, @connection.select_value("SELECT name FROM #{TABLE_NAME} WHERE id = 1")
+  if ActiveRecord::Base.connection.prepared_statements
+    def test_auth_with_bind
+      assert_nothing_raised do
         set_session_auth
+        USERS.each do |u|
+          @connection.clear_cache!
+          set_session_auth u
+          assert_equal u, @connection.select_value("SELECT name FROM #{TABLE_NAME} WHERE id = $1", "SQL", [bind_param(1)])
+          set_session_auth
+        end
       end
     end
   end
@@ -88,9 +81,9 @@ class SchemaAuthorizationTest < ActiveRecord::PostgreSQLTestCase
     assert_nothing_raised do
       USERS.each do |u|
         set_session_auth u
-        st = SchemaThing.new :name => 'TEST1'
+        st = SchemaThing.new name: "TEST1"
         st.save!
-        st = SchemaThing.new :id => 5, :name => 'TEST2'
+        st = SchemaThing.new id: 5, name: "TEST2"
         st.save!
         set_session_auth
       end
@@ -98,17 +91,17 @@ class SchemaAuthorizationTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_tables_in_current_schemas
-    assert !@connection.tables.include?(TABLE_NAME)
+    assert_not_includes @connection.tables, TABLE_NAME
     USERS.each do |u|
       set_session_auth u
-      assert @connection.tables.include?(TABLE_NAME)
+      assert_includes @connection.tables, TABLE_NAME
       set_session_auth
     end
   end
 
   private
-    def set_session_auth auth = nil
-       @connection.session_auth =  auth || 'default'
+    def set_session_auth(auth = nil)
+      @connection.session_auth = auth || "default"
     end
 
     def bind_param(value)
diff --git a/activerecord/test/cases/adapters/postgresql/schema_test.rb b/activerecord/test/cases/adapters/postgresql/schema_test.rb
index 35d5581aa7..a36d066c80 100644
--- a/activerecord/test/cases/adapters/postgresql/schema_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/schema_test.rb
@@ -1,36 +1,50 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/default'
-require 'support/schema_dumping_helper'
+require "models/default"
+require "support/schema_dumping_helper"
+
+module PGSchemaHelper
+  def with_schema_search_path(schema_search_path)
+    @connection.schema_search_path = schema_search_path
+    @connection.schema_cache.clear!
+    yield if block_given?
+  ensure
+    @connection.schema_search_path = "'$user', public"
+    @connection.schema_cache.clear!
+  end
+end
 
 class SchemaTest < ActiveRecord::PostgreSQLTestCase
+  include PGSchemaHelper
   self.use_transactional_tests = false
 
-  SCHEMA_NAME = 'test_schema'
-  SCHEMA2_NAME = 'test_schema2'
-  TABLE_NAME = 'things'
-  CAPITALIZED_TABLE_NAME = 'Things'
-  INDEX_A_NAME = 'a_index_things_on_name'
-  INDEX_B_NAME = 'b_index_things_on_different_columns_in_each_schema'
-  INDEX_C_NAME = 'c_index_full_text_search'
-  INDEX_D_NAME = 'd_index_things_on_description_desc'
-  INDEX_E_NAME = 'e_index_things_on_name_vector'
-  INDEX_A_COLUMN = 'name'
-  INDEX_B_COLUMN_S1 = 'email'
-  INDEX_B_COLUMN_S2 = 'moment'
-  INDEX_C_COLUMN = %q{(to_tsvector('english', coalesce(things.name, '')))}
-  INDEX_D_COLUMN = 'description'
-  INDEX_E_COLUMN = 'name_vector'
+  SCHEMA_NAME = "test_schema"
+  SCHEMA2_NAME = "test_schema2"
+  TABLE_NAME = "things"
+  CAPITALIZED_TABLE_NAME = "Things"
+  INDEX_A_NAME = "a_index_things_on_name"
+  INDEX_B_NAME = "b_index_things_on_different_columns_in_each_schema"
+  INDEX_C_NAME = "c_index_full_text_search"
+  INDEX_D_NAME = "d_index_things_on_description_desc"
+  INDEX_E_NAME = "e_index_things_on_name_vector"
+  INDEX_A_COLUMN = "name"
+  INDEX_B_COLUMN_S1 = "email"
+  INDEX_B_COLUMN_S2 = "moment"
+  INDEX_C_COLUMN = "(to_tsvector('english', coalesce(things.name, '')))"
+  INDEX_D_COLUMN = "description"
+  INDEX_E_COLUMN = "name_vector"
   COLUMNS = [
-    'id integer',
-    'name character varying(50)',
-    'email character varying(50)',
-    'description character varying(100)',
-    'name_vector tsvector',
-    'moment timestamp without time zone default now()'
+    "id integer",
+    "name character varying(50)",
+    "email character varying(50)",
+    "description character varying(100)",
+    "name_vector tsvector",
+    "moment timestamp without time zone default now()"
   ]
-  PK_TABLE_NAME = 'table_with_pk'
-  UNMATCHED_SEQUENCE_NAME = 'unmatched_primary_key_default_value_seq'
-  UNMATCHED_PK_TABLE_NAME = 'table_with_unmatched_sequence_for_pk'
+  PK_TABLE_NAME = "table_with_pk"
+  UNMATCHED_SEQUENCE_NAME = "unmatched_primary_key_default_value_seq"
+  UNMATCHED_PK_TABLE_NAME = "table_with_unmatched_sequence_for_pk"
 
   class Thing1 < ActiveRecord::Base
     self.table_name = "test_schema.things"
@@ -49,7 +63,7 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
   end
 
   class Thing5 < ActiveRecord::Base
-    self.table_name = 'things'
+    self.table_name = "things"
   end
 
   class Song < ActiveRecord::Base
@@ -79,13 +93,14 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
     @connection.execute "CREATE INDEX #{INDEX_E_NAME} ON #{SCHEMA_NAME}.#{TABLE_NAME}  USING gin (#{INDEX_E_COLUMN});"
     @connection.execute "CREATE INDEX #{INDEX_E_NAME} ON #{SCHEMA2_NAME}.#{TABLE_NAME}  USING gin (#{INDEX_E_COLUMN});"
     @connection.execute "CREATE TABLE #{SCHEMA_NAME}.#{PK_TABLE_NAME} (id serial primary key)"
+    @connection.execute "CREATE TABLE #{SCHEMA2_NAME}.#{PK_TABLE_NAME} (id serial primary key)"
     @connection.execute "CREATE SEQUENCE #{SCHEMA_NAME}.#{UNMATCHED_SEQUENCE_NAME}"
     @connection.execute "CREATE TABLE #{SCHEMA_NAME}.#{UNMATCHED_PK_TABLE_NAME} (id integer NOT NULL DEFAULT nextval('#{SCHEMA_NAME}.#{UNMATCHED_SEQUENCE_NAME}'::regclass), CONSTRAINT unmatched_pkey PRIMARY KEY (id))"
   end
 
   teardown do
-    @connection.execute "DROP SCHEMA #{SCHEMA2_NAME} CASCADE"
-    @connection.execute "DROP SCHEMA #{SCHEMA_NAME} CASCADE"
+    @connection.drop_schema SCHEMA2_NAME, if_exists: true
+    @connection.drop_schema SCHEMA_NAME, if_exists: true
   end
 
   def test_schema_names
@@ -118,13 +133,20 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
     ensure
       @connection.drop_schema "test_schema3"
     end
-    assert !@connection.schema_names.include?("test_schema3")
+    assert_not_includes @connection.schema_names, "test_schema3"
+  end
+
+  def test_drop_schema_if_exists
+    @connection.create_schema "some_schema"
+    assert_includes @connection.schema_names, "some_schema"
+    @connection.drop_schema "some_schema", if_exists: true
+    assert_not_includes @connection.schema_names, "some_schema"
   end
 
   def test_habtm_table_name_with_schema
+    ActiveRecord::Base.connection.drop_schema "music", if_exists: true
+    ActiveRecord::Base.connection.create_schema "music"
     ActiveRecord::Base.connection.execute <<-SQL
-      DROP SCHEMA IF EXISTS music CASCADE;
-      CREATE SCHEMA music;
       CREATE TABLE music.albums (id serial primary key);
       CREATE TABLE music.songs (id serial primary key);
       CREATE TABLE music.albums_songs (album_id integer, song_id integer);
@@ -134,69 +156,75 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
     Album.create
     assert_equal song, Song.includes(:albums).references(:albums).first
   ensure
-    ActiveRecord::Base.connection.execute "DROP SCHEMA music CASCADE;"
+    ActiveRecord::Base.connection.drop_schema "music", if_exists: true
   end
 
-  def test_raise_drop_schema_with_nonexisting_schema
+  def test_drop_schema_with_nonexisting_schema
     assert_raises(ActiveRecord::StatementInvalid) do
-      @connection.drop_schema "test_schema3"
+      @connection.drop_schema "idontexist"
+    end
+
+    assert_nothing_raised do
+      @connection.drop_schema "idontexist", if_exists: true
     end
   end
 
-  def test_raise_wraped_exception_on_bad_prepare
+  def test_raise_wrapped_exception_on_bad_prepare
     assert_raises(ActiveRecord::StatementInvalid) do
-      @connection.exec_query "select * from developers where id = ?", 'sql', [[nil, 1]]
+      @connection.exec_query "select * from developers where id = ?", "sql", [bind_param(1)]
     end
   end
 
-  def test_schema_change_with_prepared_stmt
-    altered = false
-    @connection.exec_query "select * from developers where id = $1", 'sql', [bind_param(1)]
-    @connection.exec_query "alter table developers add column zomg int", 'sql', []
-    altered = true
-    @connection.exec_query "select * from developers where id = $1", 'sql', [bind_param(1)]
-  ensure
-    # We are not using DROP COLUMN IF EXISTS because that syntax is only
-    # supported by pg 9.X
-    @connection.exec_query("alter table developers drop column zomg", 'sql', []) if altered
+  if ActiveRecord::Base.connection.prepared_statements
+    def test_schema_change_with_prepared_stmt
+      altered = false
+      @connection.exec_query "select * from developers where id = $1", "sql", [bind_param(1)]
+      @connection.exec_query "alter table developers add column zomg int", "sql", []
+      altered = true
+      @connection.exec_query "select * from developers where id = $1", "sql", [bind_param(1)]
+    ensure
+      # We are not using DROP COLUMN IF EXISTS because that syntax is only
+      # supported by pg 9.X
+      @connection.exec_query("alter table developers drop column zomg", "sql", []) if altered
+    end
   end
 
-  def test_table_exists?
+  def test_data_source_exists?
     [Thing1, Thing2, Thing3, Thing4].each do |klass|
       name = klass.table_name
-      assert @connection.table_exists?(name), "'#{name}' table should exist"
+      assert @connection.data_source_exists?(name), "'#{name}' data_source should exist"
     end
   end
 
-  def test_table_exists_when_on_schema_search_path
+  def test_data_source_exists_when_on_schema_search_path
     with_schema_search_path(SCHEMA_NAME) do
-      assert(@connection.table_exists?(TABLE_NAME), "table should exist and be found")
+      assert(@connection.data_source_exists?(TABLE_NAME), "data_source should exist and be found")
     end
   end
 
-  def test_table_exists_when_not_on_schema_search_path
-    with_schema_search_path('PUBLIC') do
-      assert(!@connection.table_exists?(TABLE_NAME), "table exists but should not be found")
+  def test_data_source_exists_when_not_on_schema_search_path
+    with_schema_search_path("PUBLIC") do
+      assert_not(@connection.data_source_exists?(TABLE_NAME), "data_source exists but should not be found")
     end
   end
 
-  def test_table_exists_wrong_schema
-    assert(!@connection.table_exists?("foo.things"), "table should not exist")
+  def test_data_source_exists_wrong_schema
+    assert_not(@connection.data_source_exists?("foo.things"), "data_source should not exist")
   end
 
-  def test_table_exists_quoted_names
+  def test_data_source_exists_quoted_names
     [ %("#{SCHEMA_NAME}"."#{TABLE_NAME}"), %(#{SCHEMA_NAME}."#{TABLE_NAME}"), %(#{SCHEMA_NAME}."#{TABLE_NAME}")].each do |given|
-      assert(@connection.table_exists?(given), "table should exist when specified as #{given}")
+      assert(@connection.data_source_exists?(given), "data_source should exist when specified as #{given}")
     end
     with_schema_search_path(SCHEMA_NAME) do
       given = %("#{TABLE_NAME}")
-      assert(@connection.table_exists?(given), "table should exist when specified as #{given}")
+      assert(@connection.data_source_exists?(given), "data_source should exist when specified as #{given}")
     end
   end
 
-  def test_table_exists_quoted_table
+  def test_data_source_exists_quoted_table
     with_schema_search_path(SCHEMA_NAME) do
-        assert(@connection.table_exists?('"things.table"'), "table should exist")
+      assert(@connection.data_source_exists?('"things.table"'), "data_source should exist")
     end
   end
 
@@ -221,9 +249,9 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_proper_encoding_of_table_name
-    assert_equal '"table_name"', @connection.quote_table_name('table_name')
+    assert_equal '"table_name"', @connection.quote_table_name("table_name")
     assert_equal '"table.name"', @connection.quote_table_name('"table.name"')
-    assert_equal '"schema_name"."table_name"', @connection.quote_table_name('schema_name.table_name')
+    assert_equal '"schema_name"."table_name"', @connection.quote_table_name("schema_name.table_name")
     assert_equal '"schema_name"."table.name"', @connection.quote_table_name('schema_name."table.name"')
     assert_equal '"schema.name"."table_name"', @connection.quote_table_name('"schema.name".table_name')
     assert_equal '"schema.name"."table.name"', @connection.quote_table_name('"schema.name"."table.name"')
@@ -235,25 +263,25 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
     assert_equal 0, Thing3.count
     assert_equal 0, Thing4.count
 
-    Thing1.create(:id => 1, :name => "thing1", :email => "thing1@localhost", :moment => Time.now)
+    Thing1.create(id: 1, name: "thing1", email: "thing1@localhost", moment: Time.now)
     assert_equal 1, Thing1.count
     assert_equal 0, Thing2.count
     assert_equal 0, Thing3.count
     assert_equal 0, Thing4.count
 
-    Thing2.create(:id => 1, :name => "thing1", :email => "thing1@localhost", :moment => Time.now)
+    Thing2.create(id: 1, name: "thing1", email: "thing1@localhost", moment: Time.now)
     assert_equal 1, Thing1.count
     assert_equal 1, Thing2.count
     assert_equal 0, Thing3.count
     assert_equal 0, Thing4.count
 
-    Thing3.create(:id => 1, :name => "thing1", :email => "thing1@localhost", :moment => Time.now)
+    Thing3.create(id: 1, name: "thing1", email: "thing1@localhost", moment: Time.now)
     assert_equal 1, Thing1.count
     assert_equal 1, Thing2.count
     assert_equal 1, Thing3.count
     assert_equal 0, Thing4.count
 
-    Thing4.create(:id => 1, :name => "thing1", :email => "thing1@localhost", :moment => Time.now)
+    Thing4.create(id: 1, name: "thing1", email: "thing1@localhost", moment: Time.now)
     assert_equal 1, Thing1.count
     assert_equal 1, Thing2.count
     assert_equal 1, Thing3.count
@@ -262,7 +290,7 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
 
   def test_raise_on_unquoted_schema_name
     assert_raises(ActiveRecord::StatementInvalid) do
-      with_schema_search_path '$user,public'
+      with_schema_search_path "$user,public"
     end
   end
 
@@ -276,13 +304,13 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
 
   def test_index_name_exists
     with_schema_search_path(SCHEMA_NAME) do
-      assert @connection.index_name_exists?(TABLE_NAME, INDEX_A_NAME, true)
-      assert @connection.index_name_exists?(TABLE_NAME, INDEX_B_NAME, true)
-      assert @connection.index_name_exists?(TABLE_NAME, INDEX_C_NAME, true)
-      assert @connection.index_name_exists?(TABLE_NAME, INDEX_D_NAME, true)
-      assert @connection.index_name_exists?(TABLE_NAME, INDEX_E_NAME, true)
-      assert @connection.index_name_exists?(TABLE_NAME, INDEX_E_NAME, true)
-      assert_not @connection.index_name_exists?(TABLE_NAME, 'missing_index', true)
+      assert @connection.index_name_exists?(TABLE_NAME, INDEX_A_NAME)
+      assert @connection.index_name_exists?(TABLE_NAME, INDEX_B_NAME)
+      assert @connection.index_name_exists?(TABLE_NAME, INDEX_C_NAME)
+      assert @connection.index_name_exists?(TABLE_NAME, INDEX_D_NAME)
+      assert @connection.index_name_exists?(TABLE_NAME, INDEX_E_NAME)
+      assert @connection.index_name_exists?(TABLE_NAME, INDEX_E_NAME)
+      assert_not @connection.index_name_exists?(TABLE_NAME, "missing_index")
     end
   end
 
@@ -298,37 +326,46 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
     do_dump_index_tests_for_schema("public, #{SCHEMA_NAME}", INDEX_A_COLUMN, INDEX_B_COLUMN_S1, INDEX_D_COLUMN, INDEX_E_COLUMN)
   end
 
+  def test_dump_indexes_for_table_with_scheme_specified_in_name
+    indexes = @connection.indexes("#{SCHEMA_NAME}.#{TABLE_NAME}")
+    assert_equal 5, indexes.size
+  end
+
   def test_with_uppercase_index_name
     @connection.execute "CREATE INDEX \"things_Index\" ON #{SCHEMA_NAME}.things (name)"
-    assert_nothing_raised { @connection.remove_index! "things", "#{SCHEMA_NAME}.things_Index"}
-    @connection.execute "CREATE INDEX \"things_Index\" ON #{SCHEMA_NAME}.things (name)"
 
     with_schema_search_path SCHEMA_NAME do
-      assert_nothing_raised { @connection.remove_index! "things", "things_Index"}
+      assert_nothing_raised { @connection.remove_index "things", name: "things_Index" }
     end
   end
 
+  def test_remove_index_when_schema_specified
+    @connection.execute "CREATE INDEX \"things_Index\" ON #{SCHEMA_NAME}.things (name)"
+    assert_nothing_raised { @connection.remove_index "things", name: "#{SCHEMA_NAME}.things_Index" }
+
+    @connection.execute "CREATE INDEX \"things_Index\" ON #{SCHEMA_NAME}.things (name)"
+    assert_nothing_raised { @connection.remove_index "#{SCHEMA_NAME}.things", name: "things_Index" }
+
+    @connection.execute "CREATE INDEX \"things_Index\" ON #{SCHEMA_NAME}.things (name)"
+    assert_nothing_raised { @connection.remove_index "#{SCHEMA_NAME}.things", name: "#{SCHEMA_NAME}.things_Index" }
+
+    @connection.execute "CREATE INDEX \"things_Index\" ON #{SCHEMA_NAME}.things (name)"
+    assert_raises(ArgumentError) { @connection.remove_index "#{SCHEMA2_NAME}.things", name: "#{SCHEMA_NAME}.things_Index" }
+  end
+
   def test_primary_key_with_schema_specified
     [
       %("#{SCHEMA_NAME}"."#{PK_TABLE_NAME}"),
       %(#{SCHEMA_NAME}."#{PK_TABLE_NAME}"),
       %(#{SCHEMA_NAME}.#{PK_TABLE_NAME})
     ].each do |given|
-      assert_equal 'id', @connection.primary_key(given), "primary key should be found when table referenced as #{given}"
+      assert_equal "id", @connection.primary_key(given), "primary key should be found when table referenced as #{given}"
     end
   end
 
   def test_primary_key_assuming_schema_search_path
-    with_schema_search_path(SCHEMA_NAME) do
-      assert_equal 'id', @connection.primary_key(PK_TABLE_NAME), "primary key should be found"
-    end
-  end
-
-  def test_primary_key_raises_error_if_table_not_found_on_schema_search_path
-    with_schema_search_path(SCHEMA2_NAME) do
-      assert_raises(ActiveRecord::StatementInvalid) do
-        @connection.primary_key(PK_TABLE_NAME)
-      end
+    with_schema_search_path("#{SCHEMA_NAME}, #{SCHEMA2_NAME}") do
+      assert_equal "id", @connection.primary_key(PK_TABLE_NAME), "primary key should be found"
     end
   end
 
@@ -339,19 +376,19 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
       %("#{SCHEMA_NAME}"."#{UNMATCHED_PK_TABLE_NAME}")
     ].each do |given|
       pk, seq = @connection.pk_and_sequence_for(given)
-      assert_equal 'id', pk, "primary key should be found when table referenced as #{given}"
+      assert_equal "id", pk, "primary key should be found when table referenced as #{given}"
       assert_equal pg_name.new(SCHEMA_NAME, "#{PK_TABLE_NAME}_id_seq"), seq, "sequence name should be found when table referenced as #{given}" if given == %("#{SCHEMA_NAME}"."#{PK_TABLE_NAME}")
-      assert_equal pg_name.new(SCHEMA_NAME, UNMATCHED_SEQUENCE_NAME), seq, "sequence name should be found when table referenced as #{given}" if given ==  %("#{SCHEMA_NAME}"."#{UNMATCHED_PK_TABLE_NAME}")
+      assert_equal pg_name.new(SCHEMA_NAME, UNMATCHED_SEQUENCE_NAME), seq, "sequence name should be found when table referenced as #{given}" if given == %("#{SCHEMA_NAME}"."#{UNMATCHED_PK_TABLE_NAME}")
     end
   end
 
   def test_current_schema
     {
-      %('$user',public)                        => 'public',
+      %('$user',public)                        => "public",
       SCHEMA_NAME                              => SCHEMA_NAME,
       %(#{SCHEMA2_NAME},#{SCHEMA_NAME},public) => SCHEMA2_NAME,
-      %(public,#{SCHEMA2_NAME},#{SCHEMA_NAME}) => 'public'
-    }.each do |given,expect|
+      %(public,#{SCHEMA2_NAME},#{SCHEMA_NAME}) => "public"
+    }.each do |given, expect|
       with_schema_search_path(given) { assert_equal expect, @connection.current_schema }
     end
   end
@@ -359,7 +396,7 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
   def test_prepared_statements_with_multiple_schemas
     [SCHEMA_NAME, SCHEMA2_NAME].each do |schema_name|
       with_schema_search_path schema_name do
-        Thing5.create(:id => 1, :name => "thing inside #{SCHEMA_NAME}", :email => "thing1@localhost", :moment => Time.now)
+        Thing5.create(id: 1, name: "thing inside #{SCHEMA_NAME}", email: "thing1@localhost", moment: Time.now)
       end
     end
 
@@ -372,11 +409,11 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
 
   def test_schema_exists?
     {
-      'public'     => true,
+      "public"     => true,
       SCHEMA_NAME  => true,
       SCHEMA2_NAME => true,
-      'darkside'   => false
-    }.each do |given,expect|
+      "darkside"   => false
+    }.each do |given, expect|
       assert_equal expect, @connection.schema_exists?(given)
     end
   end
@@ -400,32 +437,29 @@ class SchemaTest < ActiveRecord::PostgreSQLTestCase
   private
     def columns(table_name)
       @connection.send(:column_definitions, table_name).map do |name, type, default|
-        "#{name} #{type}" + (default ? " default #{default}" : '')
+        "#{name} #{type}" + (default ? " default #{default}" : "")
       end
     end
 
-    def with_schema_search_path(schema_search_path)
-      @connection.schema_search_path = schema_search_path
-      yield if block_given?
-    ensure
-      @connection.schema_search_path = "'$user', public"
-    end
-
     def do_dump_index_tests_for_schema(this_schema_name, first_index_column_name, second_index_column_name, third_index_column_name, fourth_index_column_name)
       with_schema_search_path(this_schema_name) do
         indexes = @connection.indexes(TABLE_NAME).sort_by(&:name)
-        assert_equal 4,indexes.size
-
-        do_dump_index_assertions_for_one_index(indexes[0], INDEX_A_NAME, first_index_column_name)
-        do_dump_index_assertions_for_one_index(indexes[1], INDEX_B_NAME, second_index_column_name)
-        do_dump_index_assertions_for_one_index(indexes[2], INDEX_D_NAME, third_index_column_name)
-        do_dump_index_assertions_for_one_index(indexes[3], INDEX_E_NAME, fourth_index_column_name)
-
-        indexes.select{|i| i.name != INDEX_E_NAME}.each do |index|
-           assert_equal :btree, index.using
-        end
-        assert_equal :gin, indexes.select{|i| i.name == INDEX_E_NAME}[0].using
-        assert_equal :desc, indexes.select{|i| i.name == INDEX_D_NAME}[0].orders[INDEX_D_COLUMN]
+        assert_equal 5, indexes.size
+
+        index_a, index_b, index_c, index_d, index_e = indexes
+
+        do_dump_index_assertions_for_one_index(index_a, INDEX_A_NAME, first_index_column_name)
+        do_dump_index_assertions_for_one_index(index_b, INDEX_B_NAME, second_index_column_name)
+        do_dump_index_assertions_for_one_index(index_d, INDEX_D_NAME, third_index_column_name)
+        do_dump_index_assertions_for_one_index(index_e, INDEX_E_NAME, fourth_index_column_name)
+
+        assert_equal :btree, index_a.using
+        assert_equal :btree, index_b.using
+        assert_equal :gin,   index_c.using
+        assert_equal :btree, index_d.using
+        assert_equal :gin,   index_e.using
+
+        assert_equal :desc,  index_d.orders
       end
     end
 
@@ -462,14 +496,74 @@ class SchemaForeignKeyTest < ActiveRecord::PostgreSQLTestCase
   ensure
     @connection.drop_table "wagons", if_exists: true
     @connection.drop_table "my_schema.trains", if_exists: true
-    @connection.execute "DROP SCHEMA IF EXISTS my_schema"
+    @connection.drop_schema "my_schema", if_exists: true
+  end
+end
+
+class SchemaIndexOpclassTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+
+  setup do
+    @connection = ActiveRecord::Base.connection
+    @connection.create_table "trains" do |t|
+      t.string :name
+      t.text :description
+    end
+  end
+
+  teardown do
+    @connection.drop_table "trains", if_exists: true
+  end
+
+  def test_string_opclass_is_dumped
+    @connection.execute "CREATE INDEX trains_name_and_description ON trains USING btree(name text_pattern_ops, description text_pattern_ops)"
+
+    output = dump_table_schema "trains"
+
+    assert_match(/opclass: :text_pattern_ops/, output)
+  end
+
+  def test_non_default_opclass_is_dumped
+    @connection.execute "CREATE INDEX trains_name_and_description ON trains USING btree(name, description text_pattern_ops)"
+
+    output = dump_table_schema "trains"
+
+    assert_match(/opclass: \{ description: :text_pattern_ops \}/, output)
+  end
+end
+
+class SchemaIndexNullsOrderTest < ActiveRecord::PostgreSQLTestCase
+  include SchemaDumpingHelper
+
+  setup do
+    @connection = ActiveRecord::Base.connection
+    @connection.create_table "trains" do |t|
+      t.string :name
+      t.text :description
+    end
+  end
+
+  teardown do
+    @connection.drop_table "trains", if_exists: true
+  end
+
+  def test_nulls_order_is_dumped
+    @connection.execute "CREATE INDEX trains_name_and_description ON trains USING btree(name NULLS FIRST, description)"
+    output = dump_table_schema "trains"
+    assert_match(/order: \{ name: "NULLS FIRST" \}/, output)
+  end
+
+  def test_non_default_order_with_nulls_is_dumped
+    @connection.execute "CREATE INDEX trains_name_and_desc ON trains USING btree(name DESC NULLS LAST, description)"
+    output = dump_table_schema "trains"
+    assert_match(/order: \{ name: "DESC NULLS LAST" \}/, output)
   end
 end
 
 class DefaultsUsingMultipleSchemasAndDomainTest < ActiveRecord::PostgreSQLTestCase
   setup do
     @connection = ActiveRecord::Base.connection
-    @connection.execute "DROP SCHEMA IF EXISTS schema_1 CASCADE"
+    @connection.drop_schema "schema_1", if_exists: true
     @connection.execute "CREATE SCHEMA schema_1"
     @connection.execute "CREATE DOMAIN schema_1.text AS text"
     @connection.execute "CREATE DOMAIN schema_1.varchar AS varchar"
@@ -487,7 +581,7 @@ class DefaultsUsingMultipleSchemasAndDomainTest < ActiveRecord::PostgreSQLTestCa
 
   teardown do
     @connection.schema_search_path = @old_search_path
-    @connection.execute "DROP SCHEMA IF EXISTS schema_1 CASCADE"
+    @connection.drop_schema "schema_1", if_exists: true
     Default.reset_column_information
   end
 
@@ -500,7 +594,7 @@ class DefaultsUsingMultipleSchemasAndDomainTest < ActiveRecord::PostgreSQLTestCa
   end
 
   def test_decimal_defaults_in_new_schema_when_overriding_domain
-    assert_equal BigDecimal.new("3.14159265358979323846"), Default.new.decimal_col, "Default of decimal column was not correctly parsed"
+    assert_equal BigDecimal("3.14159265358979323846"), Default.new.decimal_col, "Default of decimal column was not correctly parsed"
   end
 
   def test_bpchar_defaults_in_new_schema_when_overriding_domain
@@ -519,3 +613,40 @@ class DefaultsUsingMultipleSchemasAndDomainTest < ActiveRecord::PostgreSQLTestCa
     assert_equal "foo'::bar", Default.new.string_col
   end
 end
+
+class SchemaWithDotsTest < ActiveRecord::PostgreSQLTestCase
+  include PGSchemaHelper
+  self.use_transactional_tests = false
+
+  setup do
+    @connection = ActiveRecord::Base.connection
+    @connection.create_schema "my.schema"
+  end
+
+  teardown do
+    @connection.drop_schema "my.schema", if_exists: true
+  end
+
+  test "rename_table" do
+    with_schema_search_path('"my.schema"') do
+      @connection.create_table :posts
+      @connection.rename_table :posts, :articles
+      assert_equal ["articles"], @connection.tables
+    end
+  end
+
+  test "Active Record basics" do
+    with_schema_search_path('"my.schema"') do
+      @connection.create_table :articles do |t|
+        t.string :title
+      end
+      article_class = Class.new(ActiveRecord::Base) do
+        self.table_name = '"my.schema".articles'
+      end
+
+      article_class.create!(title: "zOMG, welcome to my blorgh!")
+      welcome_article = article_class.last
+      assert_equal "zOMG, welcome to my blorgh!", welcome_article.title
+    end
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/serial_test.rb b/activerecord/test/cases/adapters/postgresql/serial_test.rb
index 7d30db247b..83ea86be6d 100644
--- a/activerecord/test/cases/adapters/postgresql/serial_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/serial_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class PostgresqlSerialTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
@@ -10,6 +12,7 @@ class PostgresqlSerialTest < ActiveRecord::PostgreSQLTestCase
     @connection = ActiveRecord::Base.connection
     @connection.create_table "postgresql_serials", force: true do |t|
       t.serial :seq
+      t.integer :serials_id, default: -> { "nextval('postgresql_serials_id_seq')" }
     end
   end
 
@@ -21,12 +24,24 @@ class PostgresqlSerialTest < ActiveRecord::PostgreSQLTestCase
     column = PostgresqlSerial.columns_hash["seq"]
     assert_equal :integer, column.type
     assert_equal "integer", column.sql_type
-    assert column.serial?
+    assert_predicate column, :serial?
+  end
+
+  def test_not_serial_column
+    column = PostgresqlSerial.columns_hash["serials_id"]
+    assert_equal :integer, column.type
+    assert_equal "integer", column.sql_type
+    assert_not_predicate column, :serial?
   end
 
   def test_schema_dump_with_shorthand
     output = dump_table_schema "postgresql_serials"
-    assert_match %r{t\.serial\s+"seq"}, output
+    assert_match %r{t\.serial\s+"seq",\s+null: false$}, output
+  end
+
+  def test_schema_dump_with_not_serial
+    output = dump_table_schema "postgresql_serials"
+    assert_match %r{t\.integer\s+"serials_id",\s+default: -> \{ "nextval\('postgresql_serials_id_seq'::regclass\)" \}$}, output
   end
 end
 
@@ -39,6 +54,7 @@ class PostgresqlBigSerialTest < ActiveRecord::PostgreSQLTestCase
     @connection = ActiveRecord::Base.connection
     @connection.create_table "postgresql_big_serials", force: true do |t|
       t.bigserial :seq
+      t.bigint :serials_id, default: -> { "nextval('postgresql_big_serials_id_seq')" }
     end
   end
 
@@ -50,11 +66,91 @@ class PostgresqlBigSerialTest < ActiveRecord::PostgreSQLTestCase
     column = PostgresqlBigSerial.columns_hash["seq"]
     assert_equal :integer, column.type
     assert_equal "bigint", column.sql_type
-    assert column.serial?
+    assert_predicate column, :serial?
+  end
+
+  def test_not_bigserial_column
+    column = PostgresqlBigSerial.columns_hash["serials_id"]
+    assert_equal :integer, column.type
+    assert_equal "bigint", column.sql_type
+    assert_not_predicate column, :serial?
   end
 
   def test_schema_dump_with_shorthand
     output = dump_table_schema "postgresql_big_serials"
-    assert_match %r{t\.bigserial\s+"seq"}, output
+    assert_match %r{t\.bigserial\s+"seq",\s+null: false$}, output
+  end
+
+  def test_schema_dump_with_not_bigserial
+    output = dump_table_schema "postgresql_big_serials"
+    assert_match %r{t\.bigint\s+"serials_id",\s+default: -> \{ "nextval\('postgresql_big_serials_id_seq'::regclass\)" \}$}, output
+  end
+end
+
+module SequenceNameDetectionTestCases
+  class CollidedSequenceNameTest < ActiveRecord::PostgreSQLTestCase
+    include SchemaDumpingHelper
+
+    def setup
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table :foo_bar, force: true do |t|
+        t.serial :baz_id
+      end
+      @connection.create_table :foo, force: true do |t|
+        t.serial :bar_id
+        t.bigserial :bar_baz_id
+      end
+    end
+
+    def teardown
+      @connection.drop_table :foo_bar, if_exists: true
+      @connection.drop_table :foo, if_exists: true
+    end
+
+    def test_serial_columns
+      columns = @connection.columns(:foo)
+      columns.each do |column|
+        assert_equal :integer, column.type
+        assert_predicate column, :serial?
+      end
+    end
+
+    def test_schema_dump_with_collided_sequence_name
+      output = dump_table_schema "foo"
+      assert_match %r{t\.serial\s+"bar_id",\s+null: false$}, output
+      assert_match %r{t\.bigserial\s+"bar_baz_id",\s+null: false$}, output
+    end
+  end
+
+  class LongerSequenceNameDetectionTest < ActiveRecord::PostgreSQLTestCase
+    include SchemaDumpingHelper
+
+    def setup
+      @table_name = "long_table_name_to_test_sequence_name_detection_for_serial_cols"
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table @table_name, force: true do |t|
+        t.serial :seq
+        t.bigserial :bigseq
+      end
+    end
+
+    def teardown
+      @connection.drop_table @table_name, if_exists: true
+    end
+
+    def test_serial_columns
+      columns = @connection.columns(@table_name)
+      columns.each do |column|
+        assert_equal :integer, column.type
+        assert_predicate column, :serial?
+      end
+    end
+
+    def test_schema_dump_with_long_table_name
+      output = dump_table_schema @table_name
+      assert_match %r{create_table "#{@table_name}", force: :cascade}, output
+      assert_match %r{t\.serial\s+"seq",\s+null: false$}, output
+      assert_match %r{t\.bigserial\s+"bigseq",\s+null: false$}, output
+    end
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb b/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
index 5aab246c99..fef4b02b04 100644
--- a/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/statement_pool_test.rb
@@ -1,15 +1,17 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   module ConnectionAdapters
     class PostgreSQLAdapter < AbstractAdapter
-      class InactivePGconn
+      class InactivePgConnection
         def query(*args)
-          raise PGError
+          raise PG::Error
         end
 
         def status
-          PGconn::CONNECTION_BAD
+          PG::CONNECTION_BAD
         end
       end
 
@@ -17,22 +19,22 @@ module ActiveRecord
         if Process.respond_to?(:fork)
           def test_cache_is_per_pid
             cache = StatementPool.new nil, 10
-            cache['foo'] = 'bar'
-            assert_equal 'bar', cache['foo']
+            cache["foo"] = "bar"
+            assert_equal "bar", cache["foo"]
 
             pid = fork {
-              lookup = cache['foo'];
+              lookup = cache["foo"]
               exit!(!lookup)
             }
 
             Process.waitpid pid
-            assert $?.success?, 'process should exit successfully'
+            assert $?.success?, "process should exit successfully"
           end
         end
 
         def test_dealloc_does_not_raise_on_inactive_connection
-          cache = StatementPool.new InactivePGconn.new, 10
-          cache['foo'] = 'bar'
+          cache = StatementPool.new InactivePgConnection.new, 10
+          cache["foo"] = "bar"
           assert_nothing_raised { cache.clear }
         end
       end
diff --git a/activerecord/test/cases/adapters/postgresql/timestamp_test.rb b/activerecord/test/cases/adapters/postgresql/timestamp_test.rb
index 4c4866b46b..b7f213efc8 100644
--- a/activerecord/test/cases/adapters/postgresql/timestamp_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/timestamp_test.rb
@@ -1,6 +1,8 @@
-require 'cases/helper'
-require 'models/developer'
-require 'models/topic'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/developer"
+require "models/topic"
 
 class PostgresqlTimestampTest < ActiveRecord::PostgreSQLTestCase
   class PostgresqlTimestampWithZone < ActiveRecord::Base; end
@@ -21,7 +23,7 @@ class PostgresqlTimestampTest < ActiveRecord::PostgreSQLTestCase
       @connection.reconnect!
 
       timestamp = PostgresqlTimestampWithZone.find(1)
-      assert_equal Time.utc(2010,1,1, 11,0,0), timestamp.time
+      assert_equal Time.utc(2010, 1, 1, 11, 0, 0), timestamp.time
       assert_instance_of Time, timestamp.time
     end
   ensure
@@ -32,10 +34,10 @@ class PostgresqlTimestampTest < ActiveRecord::PostgreSQLTestCase
     with_timezone_config default: :local, aware_attributes: false do
       @connection.reconnect!
       # make sure to use a non-UTC time zone
-      @connection.execute("SET time zone 'America/Jamaica'", 'SCHEMA')
+      @connection.execute("SET time zone 'America/Jamaica'", "SCHEMA")
 
       timestamp = PostgresqlTimestampWithZone.find(1)
-      assert_equal Time.utc(2010,1,1, 11,0,0), timestamp.time
+      assert_equal Time.utc(2010, 1, 1, 11, 0, 0), timestamp.time
       assert_instance_of Time, timestamp.time
     end
   ensure
@@ -54,37 +56,37 @@ class PostgresqlTimestampFixtureTest < ActiveRecord::PostgreSQLTestCase
 
   def test_load_infinity_and_beyond
     d = Developer.find_by_sql("select 'infinity'::timestamp as updated_at")
-    assert d.first.updated_at.infinite?, 'timestamp should be infinite'
+    assert d.first.updated_at.infinite?, "timestamp should be infinite"
 
     d = Developer.find_by_sql("select '-infinity'::timestamp as updated_at")
     time = d.first.updated_at
-    assert time.infinite?, 'timestamp should be infinite'
+    assert time.infinite?, "timestamp should be infinite"
     assert_operator time, :<, 0
   end
 
   def test_save_infinity_and_beyond
-    d = Developer.create!(:name => 'aaron', :updated_at => 1.0 / 0.0)
+    d = Developer.create!(name: "aaron", updated_at: 1.0 / 0.0)
     assert_equal(1.0 / 0.0, d.updated_at)
 
-    d = Developer.create!(:name => 'aaron', :updated_at => -1.0 / 0.0)
+    d = Developer.create!(name: "aaron", updated_at: -1.0 / 0.0)
     assert_equal(-1.0 / 0.0, d.updated_at)
   end
 
   def test_bc_timestamp
     date = Date.new(0) - 1.week
-    Developer.create!(:name => "aaron", :updated_at => date)
+    Developer.create!(name: "aaron", updated_at: date)
     assert_equal date, Developer.find_by_name("aaron").updated_at
   end
 
   def test_bc_timestamp_leap_year
     date = Time.utc(-4, 2, 29)
-    Developer.create!(:name => "taihou", :updated_at => date)
+    Developer.create!(name: "taihou", updated_at: date)
     assert_equal date, Developer.find_by_name("taihou").updated_at
   end
 
   def test_bc_timestamp_year_zero
     date = Time.utc(0, 4, 7)
-    Developer.create!(:name => "yahagi", :updated_at => date)
+    Developer.create!(name: "yahagi", updated_at: date)
     assert_equal date, Developer.find_by_name("yahagi").updated_at
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/transaction_test.rb b/activerecord/test/cases/adapters/postgresql/transaction_test.rb
new file mode 100644
index 0000000000..984b2f5ea4
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/transaction_test.rb
@@ -0,0 +1,190 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/connection_helper"
+require "concurrent/atomic/cyclic_barrier"
+
+module ActiveRecord
+  class PostgresqlTransactionTest < ActiveRecord::PostgreSQLTestCase
+    self.use_transactional_tests = false
+
+    class Sample < ActiveRecord::Base
+      self.table_name = "samples"
+    end
+
+    setup do
+      @abort, Thread.abort_on_exception = Thread.abort_on_exception, false
+      Thread.report_on_exception, @original_report_on_exception = false, Thread.report_on_exception
+
+      @connection = ActiveRecord::Base.connection
+
+      @connection.transaction do
+        @connection.drop_table "samples", if_exists: true
+        @connection.create_table("samples") do |t|
+          t.integer "value"
+        end
+      end
+
+      Sample.reset_column_information
+    end
+
+    teardown do
+      @connection.drop_table "samples", if_exists: true
+
+      Thread.abort_on_exception = @abort
+      Thread.report_on_exception = @original_report_on_exception
+    end
+
+    test "raises SerializationFailure when a serialization failure occurs" do
+      assert_raises(ActiveRecord::SerializationFailure) do
+        before = Concurrent::CyclicBarrier.new(2)
+        after = Concurrent::CyclicBarrier.new(2)
+
+        thread = Thread.new do
+          with_warning_suppression do
+            Sample.transaction isolation: :serializable do
+              before.wait
+              Sample.create value: Sample.sum(:value)
+              after.wait
+            end
+          end
+        end
+
+        begin
+          with_warning_suppression do
+            Sample.transaction isolation: :serializable do
+              before.wait
+              Sample.create value: Sample.sum(:value)
+              after.wait
+            end
+          end
+        ensure
+          thread.join
+        end
+      end
+    end
+
+    test "raises Deadlocked when a deadlock is encountered" do
+      with_warning_suppression do
+        assert_raises(ActiveRecord::Deadlocked) do
+          barrier = Concurrent::CyclicBarrier.new(2)
+
+          s1 = Sample.create value: 1
+          s2 = Sample.create value: 2
+
+          thread = Thread.new do
+            Sample.transaction do
+              s1.lock!
+              barrier.wait
+              s2.update value: 1
+            end
+          end
+
+          begin
+            Sample.transaction do
+              s2.lock!
+              barrier.wait
+              s1.update value: 2
+            end
+          ensure
+            thread.join
+          end
+        end
+      end
+    end
+
+    test "raises LockWaitTimeout when lock wait timeout exceeded" do
+      skip unless ActiveRecord::Base.connection.postgresql_version >= 90300
+      assert_raises(ActiveRecord::LockWaitTimeout) do
+        s = Sample.create!(value: 1)
+        latch1 = Concurrent::CountDownLatch.new
+        latch2 = Concurrent::CountDownLatch.new
+
+        thread = Thread.new do
+          Sample.transaction do
+            Sample.lock.find(s.id)
+            latch1.count_down
+            latch2.wait
+          end
+        end
+
+        begin
+          Sample.transaction do
+            latch1.wait
+            Sample.connection.execute("SET lock_timeout = 1")
+            Sample.lock.find(s.id)
+          end
+        ensure
+          Sample.connection.execute("SET lock_timeout = DEFAULT")
+          latch2.count_down
+          thread.join
+        end
+      end
+    end
+
+    test "raises QueryCanceled when statement timeout exceeded" do
+      assert_raises(ActiveRecord::QueryCanceled) do
+        s = Sample.create!(value: 1)
+        latch1 = Concurrent::CountDownLatch.new
+        latch2 = Concurrent::CountDownLatch.new
+
+        thread = Thread.new do
+          Sample.transaction do
+            Sample.lock.find(s.id)
+            latch1.count_down
+            latch2.wait
+          end
+        end
+
+        begin
+          Sample.transaction do
+            latch1.wait
+            Sample.connection.execute("SET statement_timeout = 1")
+            Sample.lock.find(s.id)
+          end
+        ensure
+          Sample.connection.execute("SET statement_timeout = DEFAULT")
+          latch2.count_down
+          thread.join
+        end
+      end
+    end
+
+    test "raises QueryCanceled when canceling statement due to user request" do
+      assert_raises(ActiveRecord::QueryCanceled) do
+        s = Sample.create!(value: 1)
+        latch = Concurrent::CountDownLatch.new
+
+        thread = Thread.new do
+          Sample.transaction do
+            Sample.lock.find(s.id)
+            latch.count_down
+            sleep(0.5)
+            conn = Sample.connection
+            pid = conn.query_value("SELECT pid FROM pg_stat_activity WHERE query LIKE '% FOR UPDATE'")
+            conn.execute("SELECT pg_cancel_backend(#{pid})")
+          end
+        end
+
+        begin
+          Sample.transaction do
+            latch.wait
+            Sample.lock.find(s.id)
+          end
+        ensure
+          thread.join
+        end
+      end
+    end
+
+    private
+
+      def with_warning_suppression
+        log_level = ActiveRecord::Base.connection.client_min_messages
+        ActiveRecord::Base.connection.client_min_messages = "error"
+        yield
+      ensure
+        ActiveRecord::Base.connection.client_min_messages = log_level
+      end
+  end
+end
diff --git a/activerecord/test/cases/adapters/postgresql/type_lookup_test.rb b/activerecord/test/cases/adapters/postgresql/type_lookup_test.rb
index 77a99ca778..8212ed4263 100644
--- a/activerecord/test/cases/adapters/postgresql/type_lookup_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/type_lookup_test.rb
@@ -1,4 +1,6 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 class PostgresqlTypeLookupTest < ActiveRecord::PostgreSQLTestCase
   setup do
@@ -6,28 +8,28 @@ class PostgresqlTypeLookupTest < ActiveRecord::PostgreSQLTestCase
   end
 
   test "array delimiters are looked up correctly" do
-    box_array = @connection.type_map.lookup(1020)
-    int_array = @connection.type_map.lookup(1007)
+    box_array = @connection.send(:type_map).lookup(1020)
+    int_array = @connection.send(:type_map).lookup(1007)
 
-    assert_equal ';', box_array.delimiter
-    assert_equal ',', int_array.delimiter
+    assert_equal ";", box_array.delimiter
+    assert_equal ",", int_array.delimiter
   end
 
   test "array types correctly respect registration of subtypes" do
-    int_array = @connection.type_map.lookup(1007, -1, "integer[]")
-    bigint_array = @connection.type_map.lookup(1016, -1, "bigint[]")
+    int_array = @connection.send(:type_map).lookup(1007, -1, "integer[]")
+    bigint_array = @connection.send(:type_map).lookup(1016, -1, "bigint[]")
     big_array = [123456789123456789]
 
-    assert_raises(RangeError) { int_array.serialize(big_array) }
-    assert_equal "{123456789123456789}", bigint_array.serialize(big_array)
+    assert_raises(ActiveModel::RangeError) { int_array.serialize(big_array) }
+    assert_equal "{123456789123456789}", @connection.type_cast(bigint_array.serialize(big_array))
   end
 
   test "range types correctly respect registration of subtypes" do
-    int_range = @connection.type_map.lookup(3904, -1, "int4range")
-    bigint_range = @connection.type_map.lookup(3926, -1, "int8range")
+    int_range = @connection.send(:type_map).lookup(3904, -1, "int4range")
+    bigint_range = @connection.send(:type_map).lookup(3926, -1, "int8range")
     big_range = 0..123456789123456789
 
-    assert_raises(RangeError) { int_range.serialize(big_range) }
-    assert_equal "[0,123456789123456789]", bigint_range.serialize(big_range)
+    assert_raises(ActiveModel::RangeError) { int_range.serialize(big_range) }
+    assert_equal "[0,123456789123456789]", @connection.type_cast(bigint_range.serialize(big_range))
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/utils_test.rb b/activerecord/test/cases/adapters/postgresql/utils_test.rb
index 095c1826e5..c91884f384 100644
--- a/activerecord/test/cases/adapters/postgresql/utils_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/utils_test.rb
@@ -1,5 +1,7 @@
-require 'cases/helper'
-require 'active_record/connection_adapters/postgresql/utils'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "active_record/connection_adapters/postgresql/utils"
 
 class PostgreSQLUtilsTest < ActiveRecord::PostgreSQLTestCase
   Name = ActiveRecord::ConnectionAdapters::PostgreSQL::Name
@@ -7,14 +9,14 @@ class PostgreSQLUtilsTest < ActiveRecord::PostgreSQLTestCase
 
   def test_extract_schema_qualified_name
     {
-      %(table_name)            => [nil,'table_name'],
-      %("table.name")          => [nil,'table.name'],
+      %(table_name)            => [nil, "table_name"],
+      %("table.name")          => [nil, "table.name"],
       %(schema.table_name)     => %w{schema table_name},
       %("schema".table_name)   => %w{schema table_name},
       %(schema."table_name")   => %w{schema table_name},
       %("schema"."table_name") => %w{schema table_name},
-      %("even spaces".table)   => ['even spaces','table'],
-      %(schema."table.name")   => ['schema', 'table.name']
+      %("even spaces".table)   => ["even spaces", "table"],
+      %(schema."table.name")   => ["schema", "table.name"]
     }.each do |given, expect|
       assert_equal Name.new(*expect), extract_schema_qualified_name(given)
     end
@@ -54,9 +56,9 @@ class PostgreSQLNameTest < ActiveRecord::PostgreSQLTestCase
   end
 
   test "can be used as hash key" do
-    hash = {Name.new("schema", "article_seq") => "success"}
+    hash = { Name.new("schema", "article_seq") => "success" }
     assert_equal "success", hash[Name.new("schema", "article_seq")]
-    assert_equal nil, hash[Name.new("schema", "articles")]
-    assert_equal nil, hash[Name.new("public", "article_seq")]
+    assert_nil hash[Name.new("schema", "articles")]
+    assert_nil hash[Name.new("public", "article_seq")]
   end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/uuid_test.rb b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
index 7127d69e9e..71d07e2f4c 100644
--- a/activerecord/test/cases/adapters/postgresql/uuid_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 module PostgresqlUUIDHelper
   def connection
@@ -9,6 +11,14 @@ module PostgresqlUUIDHelper
   def drop_table(name)
     connection.drop_table name, if_exists: true
   end
+
+  def uuid_function
+    connection.supports_pgcrypto_uuid? ? "gen_random_uuid()" : "uuid_generate_v4()"
+  end
+
+  def uuid_default
+    connection.supports_pgcrypto_uuid? ? {} : { default: uuid_function }
+  end
 end
 
 class PostgresqlUUIDTest < ActiveRecord::PostgreSQLTestCase
@@ -20,8 +30,11 @@ class PostgresqlUUIDTest < ActiveRecord::PostgreSQLTestCase
   end
 
   setup do
+    enable_extension!("uuid-ossp", connection)
+    enable_extension!("pgcrypto",  connection) if connection.supports_pgcrypto_uuid?
+
     connection.create_table "uuid_data_type" do |t|
-      t.uuid 'guid'
+      t.uuid "guid"
     end
   end
 
@@ -29,72 +42,106 @@ class PostgresqlUUIDTest < ActiveRecord::PostgreSQLTestCase
     drop_table "uuid_data_type"
   end
 
+  if ActiveRecord::Base.connection.respond_to?(:supports_pgcrypto_uuid?) &&
+      ActiveRecord::Base.connection.supports_pgcrypto_uuid?
+    def test_uuid_column_default
+      connection.add_column :uuid_data_type, :thingy, :uuid, null: false, default: "gen_random_uuid()"
+      UUIDType.reset_column_information
+      column = UUIDType.columns_hash["thingy"]
+      assert_equal "gen_random_uuid()", column.default_function
+    end
+  end
+
   def test_change_column_default
-    @connection.add_column :uuid_data_type, :thingy, :uuid, null: false, default: "uuid_generate_v1()"
+    connection.add_column :uuid_data_type, :thingy, :uuid, null: false, default: "uuid_generate_v1()"
     UUIDType.reset_column_information
-    column = UUIDType.columns_hash['thingy']
+    column = UUIDType.columns_hash["thingy"]
     assert_equal "uuid_generate_v1()", column.default_function
 
-    @connection.change_column :uuid_data_type, :thingy, :uuid, null: false, default: "uuid_generate_v4()"
-
+    connection.change_column :uuid_data_type, :thingy, :uuid, null: false, default: "uuid_generate_v4()"
     UUIDType.reset_column_information
-    column = UUIDType.columns_hash['thingy']
+    column = UUIDType.columns_hash["thingy"]
     assert_equal "uuid_generate_v4()", column.default_function
   ensure
     UUIDType.reset_column_information
   end
 
+  def test_add_column_with_null_true_and_default_nil
+    connection.add_column :uuid_data_type, :thingy, :uuid, null: true, default: nil
+
+    UUIDType.reset_column_information
+    column = UUIDType.columns_hash["thingy"]
+
+    assert column.null
+    assert_nil column.default
+  end
+
+  def test_add_column_with_default_array
+    connection.add_column :uuid_data_type, :thingy, :uuid, array: true, default: []
+
+    UUIDType.reset_column_information
+    column = UUIDType.columns_hash["thingy"]
+
+    assert_predicate column, :array?
+    assert_equal "{}", column.default
+
+    schema = dump_table_schema "uuid_data_type"
+    assert_match %r{t\.uuid "thingy", default: \[\], array: true$}, schema
+  end
+
   def test_data_type_of_uuid_types
     column = UUIDType.columns_hash["guid"]
     assert_equal :uuid, column.type
     assert_equal "uuid", column.sql_type
-    assert_not column.array?
+    assert_not_predicate column, :array?
 
     type = UUIDType.type_for_attribute("guid")
-    assert_not type.binary?
+    assert_not_predicate type, :binary?
   end
 
   def test_treat_blank_uuid_as_nil
-    UUIDType.create! guid: ''
-    assert_equal(nil, UUIDType.last.guid)
+    UUIDType.create! guid: ""
+    assert_nil(UUIDType.last.guid)
   end
 
   def test_treat_invalid_uuid_as_nil
-    uuid = UUIDType.create! guid: 'foobar'
-    assert_equal(nil, uuid.guid)
+    uuid = UUIDType.create! guid: "foobar"
+    assert_nil(uuid.guid)
   end
 
   def test_invalid_uuid_dont_modify_before_type_cast
-    uuid = UUIDType.new guid: 'foobar'
-    assert_equal 'foobar', uuid.guid_before_type_cast
+    uuid = UUIDType.new guid: "foobar"
+    assert_equal "foobar", uuid.guid_before_type_cast
   end
 
   def test_acceptable_uuid_regex
     # Valid uuids
-    ['A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11',
-     '{a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11}',
-     'a0eebc999c0b4ef8bb6d6bb9bd380a11',
-     'a0ee-bc99-9c0b-4ef8-bb6d-6bb9-bd38-0a11',
-     '{a0eebc99-9c0b4ef8-bb6d6bb9-bd380a11}',
+    ["A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11",
+     "{a0eebc99-9c0b-4ef8-bb6d-6bb9bd380a11}",
+     "a0eebc999c0b4ef8bb6d6bb9bd380a11",
+     "a0ee-bc99-9c0b-4ef8-bb6d-6bb9-bd38-0a11",
+     "{a0eebc99-9c0b4ef8-bb6d6bb9-bd380a11}",
      # The following is not a valid RFC 4122 UUID, but PG doesn't seem to care,
      # so we shouldn't block it either. (Pay attention to "fb6d" – the "f" here
      # is invalid – it must be one of 8, 9, A, B, a, b according to the spec.)
-     '{a0eebc99-9c0b-4ef8-fb6d-6bb9bd380a11}',
+     "{a0eebc99-9c0b-4ef8-fb6d-6bb9bd380a11}",
     ].each do |valid_uuid|
       uuid = UUIDType.new guid: valid_uuid
       assert_not_nil uuid.guid
     end
 
     # Invalid uuids
-    [['A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11'],
+    [["A0EEBC99-9C0B-4EF8-BB6D-6BB9BD380A11"],
      Hash.new,
      0,
      0.0,
      true,
-     'Z0000C99-9C0B-4EF8-BB6D-6BB9BD380A11',
-     'a0eebc999r0b4ef8ab6d6bb9bd380a11',
-     'a0ee-bc99------4ef8-bb6d-6bb9-bd38-0a11',
-     '{a0eebc99-bb6d6bb9-bd380a11}'].each do |invalid_uuid|
+     "Z0000C99-9C0B-4EF8-BB6D-6BB9BD380A11",
+     "a0eebc999r0b4ef8ab6d6bb9bd380a11",
+     "a0ee-bc99------4ef8-bb6d-6bb9-bd38-0a11",
+     "{a0eebc99-bb6d6bb9-bd380a11}",
+     "{a0eebc99-9c0b4ef8-bb6d6bb9-bd380a11",
+     "a0eebc99-9c0b4ef8-bb6d6bb9-bd380a11}"].each do |invalid_uuid|
       uuid = UUIDType.new guid: invalid_uuid
       assert_nil uuid.guid
     end
@@ -131,7 +178,7 @@ class PostgresqlUUIDTest < ActiveRecord::PostgreSQLTestCase
     duplicate = klass.new(guid: record.guid)
 
     assert record.guid.present? # Ensure we actually are testing a UUID
-    assert_not duplicate.valid?
+    assert_not_predicate duplicate, :valid?
   end
 end
 
@@ -140,74 +187,102 @@ class PostgresqlUUIDGenerationTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
 
   class UUID < ActiveRecord::Base
-    self.table_name = 'pg_uuids'
+    self.table_name = "pg_uuids"
   end
 
   setup do
-    enable_extension!('uuid-ossp', connection)
-
-    connection.create_table('pg_uuids', id: :uuid, default: 'uuid_generate_v1()') do |t|
-      t.string 'name'
-      t.uuid 'other_uuid', default: 'uuid_generate_v4()'
+    connection.create_table("pg_uuids", id: :uuid, default: "uuid_generate_v1()") do |t|
+      t.string "name"
+      t.uuid "other_uuid", default: "uuid_generate_v4()"
     end
 
     # Create custom PostgreSQL function to generate UUIDs
     # to test dumping tables which columns have defaults with custom functions
     connection.execute <<-SQL
     CREATE OR REPLACE FUNCTION my_uuid_generator() RETURNS uuid
-    AS $$ SELECT * FROM uuid_generate_v4() $$
+    AS $$ SELECT * FROM #{uuid_function} $$
     LANGUAGE SQL VOLATILE;
     SQL
 
     # Create such a table with custom function as default value generator
-    connection.create_table('pg_uuids_2', id: :uuid, default: 'my_uuid_generator()') do |t|
-      t.string 'name'
-      t.uuid 'other_uuid_2', default: 'my_uuid_generator()'
+    connection.create_table("pg_uuids_2", id: :uuid, default: "my_uuid_generator()") do |t|
+      t.string "name"
+      t.uuid "other_uuid_2", default: "my_uuid_generator()"
+    end
+
+    connection.create_table("pg_uuids_3", id: :uuid, **uuid_default) do |t|
+      t.string "name"
     end
   end
 
   teardown do
     drop_table "pg_uuids"
-    drop_table 'pg_uuids_2'
-    connection.execute 'DROP FUNCTION IF EXISTS my_uuid_generator();'
-    disable_extension!('uuid-ossp', connection)
+    drop_table "pg_uuids_2"
+    drop_table "pg_uuids_3"
+    connection.execute "DROP FUNCTION IF EXISTS my_uuid_generator();"
   end
 
-  if ActiveRecord::Base.connection.supports_extensions?
-    def test_id_is_uuid
-      assert_equal :uuid, UUID.columns_hash['id'].type
-      assert UUID.primary_key
-    end
+  def test_id_is_uuid
+    assert_equal :uuid, UUID.columns_hash["id"].type
+    assert UUID.primary_key
+  end
 
-    def test_id_has_a_default
-      u = UUID.create
-      assert_not_nil u.id
-    end
+  def test_id_has_a_default
+    u = UUID.create
+    assert_not_nil u.id
+  end
 
-    def test_auto_create_uuid
-      u = UUID.create
-      u.reload
-      assert_not_nil u.other_uuid
-    end
+  def test_auto_create_uuid
+    u = UUID.create
+    u.reload
+    assert_not_nil u.other_uuid
+  end
 
-    def test_pk_and_sequence_for_uuid_primary_key
-      pk, seq = connection.pk_and_sequence_for('pg_uuids')
-      assert_equal 'id', pk
-      assert_equal nil, seq
-    end
+  def test_pk_and_sequence_for_uuid_primary_key
+    pk, seq = connection.pk_and_sequence_for("pg_uuids")
+    assert_equal "id", pk
+    assert_nil seq
+  end
 
-    def test_schema_dumper_for_uuid_primary_key
-      schema = dump_table_schema "pg_uuids"
-      assert_match(/\bcreate_table "pg_uuids", id: :uuid, default: "uuid_generate_v1\(\)"/, schema)
-      assert_match(/t\.uuid   "other_uuid", default: "uuid_generate_v4\(\)"/, schema)
-    end
+  def test_schema_dumper_for_uuid_primary_key
+    schema = dump_table_schema "pg_uuids"
+    assert_match(/\bcreate_table "pg_uuids", id: :uuid, default: -> { "uuid_generate_v1\(\)" }/, schema)
+    assert_match(/t\.uuid "other_uuid", default: -> { "uuid_generate_v4\(\)" }/, schema)
+  end
+
+  def test_schema_dumper_for_uuid_primary_key_with_custom_default
+    schema = dump_table_schema "pg_uuids_2"
+    assert_match(/\bcreate_table "pg_uuids_2", id: :uuid, default: -> { "my_uuid_generator\(\)" }/, schema)
+    assert_match(/t\.uuid "other_uuid_2", default: -> { "my_uuid_generator\(\)" }/, schema)
+  end
 
-    def test_schema_dumper_for_uuid_primary_key_with_custom_default
-      schema = dump_table_schema "pg_uuids_2"
-      assert_match(/\bcreate_table "pg_uuids_2", id: :uuid, default: "my_uuid_generator\(\)"/, schema)
-      assert_match(/t\.uuid   "other_uuid_2", default: "my_uuid_generator\(\)"/, schema)
+  def test_schema_dumper_for_uuid_primary_key_default
+    schema = dump_table_schema "pg_uuids_3"
+    if connection.supports_pgcrypto_uuid?
+      assert_match(/\bcreate_table "pg_uuids_3", id: :uuid, default: -> { "gen_random_uuid\(\)" }/, schema)
+    else
+      assert_match(/\bcreate_table "pg_uuids_3", id: :uuid, default: -> { "uuid_generate_v4\(\)" }/, schema)
     end
   end
+
+  def test_schema_dumper_for_uuid_primary_key_default_in_legacy_migration
+    @verbose_was = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+
+    migration = Class.new(ActiveRecord::Migration[5.0]) do
+      def version; 101 end
+      def migrate(x)
+        create_table("pg_uuids_4", id: :uuid)
+      end
+    end.new
+    ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+    schema = dump_table_schema "pg_uuids_4"
+    assert_match(/\bcreate_table "pg_uuids_4", id: :uuid, default: -> { "uuid_generate_v4\(\)" }/, schema)
+  ensure
+    drop_table "pg_uuids_4"
+    ActiveRecord::Migration.verbose = @verbose_was
+  end
 end
 
 class PostgresqlUUIDTestNilDefault < ActiveRecord::PostgreSQLTestCase
@@ -215,32 +290,46 @@ class PostgresqlUUIDTestNilDefault < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
 
   setup do
-    enable_extension!('uuid-ossp', connection)
-
-    connection.create_table('pg_uuids', id: false) do |t|
+    connection.create_table("pg_uuids", id: false) do |t|
       t.primary_key :id, :uuid, default: nil
-      t.string 'name'
+      t.string "name"
     end
   end
 
   teardown do
     drop_table "pg_uuids"
-    disable_extension!('uuid-ossp', connection)
   end
 
-  if ActiveRecord::Base.connection.supports_extensions?
-    def test_id_allows_default_override_via_nil
-      col_desc = connection.execute("SELECT pg_get_expr(d.adbin, d.adrelid) as default
-                                    FROM pg_attribute a
-                                    LEFT JOIN pg_attrdef d ON a.attrelid = d.adrelid AND a.attnum = d.adnum
-                                    WHERE a.attname='id' AND a.attrelid = 'pg_uuids'::regclass").first
-      assert_nil col_desc["default"]
-    end
+  def test_id_allows_default_override_via_nil
+    col_desc = connection.execute("SELECT pg_get_expr(d.adbin, d.adrelid) as default
+                                  FROM pg_attribute a
+                                  LEFT JOIN pg_attrdef d ON a.attrelid = d.adrelid AND a.attnum = d.adnum
+                                  WHERE a.attname='id' AND a.attrelid = 'pg_uuids'::regclass").first
+    assert_nil col_desc["default"]
+  end
 
-    def test_schema_dumper_for_uuid_primary_key_with_default_override_via_nil
-      schema = dump_table_schema "pg_uuids"
-      assert_match(/\bcreate_table "pg_uuids", id: :uuid, default: nil/, schema)
-    end
+  def test_schema_dumper_for_uuid_primary_key_with_default_override_via_nil
+    schema = dump_table_schema "pg_uuids"
+    assert_match(/\bcreate_table "pg_uuids", id: :uuid, default: nil/, schema)
+  end
+
+  def test_schema_dumper_for_uuid_primary_key_with_default_nil_in_legacy_migration
+    @verbose_was = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+
+    migration = Class.new(ActiveRecord::Migration[5.0]) do
+      def version; 101 end
+      def migrate(x)
+        create_table("pg_uuids_4", id: :uuid, default: nil)
+      end
+    end.new
+    ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+    schema = dump_table_schema "pg_uuids_4"
+    assert_match(/\bcreate_table "pg_uuids_4", id: :uuid, default: nil/, schema)
+  ensure
+    drop_table "pg_uuids_4"
+    ActiveRecord::Migration.verbose = @verbose_was
   end
 end
 
@@ -248,54 +337,47 @@ class PostgresqlUUIDTestInverseOf < ActiveRecord::PostgreSQLTestCase
   include PostgresqlUUIDHelper
 
   class UuidPost < ActiveRecord::Base
-    self.table_name = 'pg_uuid_posts'
+    self.table_name = "pg_uuid_posts"
     has_many :uuid_comments, inverse_of: :uuid_post
   end
 
   class UuidComment < ActiveRecord::Base
-    self.table_name = 'pg_uuid_comments'
+    self.table_name = "pg_uuid_comments"
     belongs_to :uuid_post
   end
 
   setup do
-    enable_extension!('uuid-ossp', connection)
-
     connection.transaction do
-      connection.create_table('pg_uuid_posts', id: :uuid) do |t|
-        t.string 'title'
+      connection.create_table("pg_uuid_posts", id: :uuid, **uuid_default) do |t|
+        t.string "title"
       end
-      connection.create_table('pg_uuid_comments', id: :uuid) do |t|
+      connection.create_table("pg_uuid_comments", id: :uuid, **uuid_default) do |t|
         t.references :uuid_post, type: :uuid
-        t.string 'content'
+        t.string "content"
       end
     end
   end
 
   teardown do
-      drop_table "pg_uuid_comments"
-      drop_table "pg_uuid_posts"
-      disable_extension!('uuid-ossp', connection)
+    drop_table "pg_uuid_comments"
+    drop_table "pg_uuid_posts"
   end
 
-  if ActiveRecord::Base.connection.supports_extensions?
-    def test_collection_association_with_uuid
-      post    = UuidPost.create!
-      comment = post.uuid_comments.create!
-      assert post.uuid_comments.find(comment.id)
-    end
-
-    def test_find_with_uuid
-      UuidPost.create!
-      assert_raise ActiveRecord::RecordNotFound do
-        UuidPost.find(123456)
-      end
-
-    end
+  def test_collection_association_with_uuid
+    post    = UuidPost.create!
+    comment = post.uuid_comments.create!
+    assert post.uuid_comments.find(comment.id)
+  end
 
-    def test_find_by_with_uuid
-      UuidPost.create!
-      assert_nil UuidPost.find_by(id: 789)
+  def test_find_with_uuid
+    UuidPost.create!
+    assert_raise ActiveRecord::RecordNotFound do
+      UuidPost.find(123456)
     end
   end
 
+  def test_find_by_with_uuid
+    UuidPost.create!
+    assert_nil UuidPost.find_by(id: 789)
+  end
 end
diff --git a/activerecord/test/cases/adapters/postgresql/view_test.rb b/activerecord/test/cases/adapters/postgresql/view_test.rb
deleted file mode 100644
index 2dd6ec5fe6..0000000000
--- a/activerecord/test/cases/adapters/postgresql/view_test.rb
+++ /dev/null
@@ -1,64 +0,0 @@
-require "cases/helper"
-require "cases/view_test"
-
-class UpdateableViewTest < ActiveRecord::PostgreSQLTestCase
-  fixtures :books
-
-  class PrintedBook < ActiveRecord::Base
-    self.primary_key = "id"
-  end
-
-  setup do
-    @connection = ActiveRecord::Base.connection
-    @connection.execute <<-SQL
-      CREATE VIEW printed_books
-        AS SELECT id, name, status, format FROM books WHERE format = 'paperback'
-    SQL
-  end
-
-  teardown do
-    @connection.execute "DROP VIEW printed_books" if @connection.table_exists? "printed_books"
-  end
-
-  def test_update_record
-    book = PrintedBook.first
-    book.name = "AWDwR"
-    book.save!
-    book.reload
-    assert_equal "AWDwR", book.name
-  end
-
-  def test_insert_record
-    PrintedBook.create! name: "Rails in Action", status: 0, format: "paperback"
-
-    new_book = PrintedBook.last
-    assert_equal "Rails in Action", new_book.name
-  end
-
-  def test_update_record_to_fail_view_conditions
-    book = PrintedBook.first
-    book.format = "ebook"
-    book.save!
-
-    assert_raises ActiveRecord::RecordNotFound do
-      book.reload
-    end
-  end
-end
-
-if ActiveRecord::Base.connection.respond_to?(:supports_materialized_views?) &&
-    ActiveRecord::Base.connection.supports_materialized_views?
-class MaterializedViewTest < ActiveRecord::PostgreSQLTestCase
-  include ViewBehavior
-
-  private
-  def create_view(name, query)
-    @connection.execute "CREATE MATERIALIZED VIEW #{name} AS #{query}"
-  end
-
-  def drop_view(name)
-    @connection.execute "DROP MATERIALIZED VIEW #{name}" if @connection.table_exists? name
-
-  end
-end
-end
diff --git a/activerecord/test/cases/adapters/postgresql/xml_test.rb b/activerecord/test/cases/adapters/postgresql/xml_test.rb
index add32699fa..71ead6f7f3 100644
--- a/activerecord/test/cases/adapters/postgresql/xml_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/xml_test.rb
@@ -1,28 +1,30 @@
-require 'cases/helper'
-require 'support/schema_dumping_helper'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/schema_dumping_helper"
 
 class PostgresqlXMLTest < ActiveRecord::PostgreSQLTestCase
   include SchemaDumpingHelper
   class XmlDataType < ActiveRecord::Base
-    self.table_name = 'xml_data_type'
+    self.table_name = "xml_data_type"
   end
 
   def setup
     @connection = ActiveRecord::Base.connection
     begin
       @connection.transaction do
-        @connection.create_table('xml_data_type') do |t|
-          t.xml 'payload'
+        @connection.create_table("xml_data_type") do |t|
+          t.xml "payload"
         end
       end
     rescue ActiveRecord::StatementInvalid
       skip "do not test on PG without xml"
     end
-    @column = XmlDataType.columns_hash['payload']
+    @column = XmlDataType.columns_hash["payload"]
   end
 
   teardown do
-    @connection.drop_table 'xml_data_type', if_exists: true
+    @connection.drop_table "xml_data_type", if_exists: true
   end
 
   def test_column
@@ -30,7 +32,7 @@ class PostgresqlXMLTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_null_xml
-    @connection.execute %q|insert into xml_data_type (payload) VALUES(null)|
+    @connection.execute "insert into xml_data_type (payload) VALUES(null)"
     assert_nil XmlDataType.first.payload
   end
 
diff --git a/activerecord/test/cases/adapters/sqlite3/bind_parameter_test.rb b/activerecord/test/cases/adapters/sqlite3/bind_parameter_test.rb
new file mode 100644
index 0000000000..93a7dafebd
--- /dev/null
+++ b/activerecord/test/cases/adapters/sqlite3/bind_parameter_test.rb
@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/topic"
+
+module ActiveRecord
+  module ConnectionAdapters
+    class SQLite3Adapter
+      class BindParameterTest < ActiveRecord::SQLite3TestCase
+        def test_too_many_binds
+          topics = Topic.where(id: (1..999).to_a << 2**63)
+          assert_equal Topic.count, topics.count
+
+          topics = Topic.where.not(id: (1..999).to_a << 2**63)
+          assert_equal 0, topics.count
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/adapters/sqlite3/collation_test.rb b/activerecord/test/cases/adapters/sqlite3/collation_test.rb
index 58a9469ce5..76c8f7d8dd 100644
--- a/activerecord/test/cases/adapters/sqlite3/collation_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/collation_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class SQLite3CollationTest < ActiveRecord::SQLite3TestCase
   include SchemaDumpingHelper
@@ -7,8 +9,8 @@ class SQLite3CollationTest < ActiveRecord::SQLite3TestCase
   def setup
     @connection = ActiveRecord::Base.connection
     @connection.create_table :collation_table_sqlite3, force: true do |t|
-      t.string :string_nocase, collation: 'NOCASE'
-      t.text :text_rtrim, collation: 'RTRIM'
+      t.string :string_nocase, collation: "NOCASE"
+      t.text :text_rtrim, collation: "RTRIM"
     end
   end
 
@@ -17,37 +19,37 @@ class SQLite3CollationTest < ActiveRecord::SQLite3TestCase
   end
 
   test "string column with collation" do
-    column = @connection.columns(:collation_table_sqlite3).find { |c| c.name == 'string_nocase' }
+    column = @connection.columns(:collation_table_sqlite3).find { |c| c.name == "string_nocase" }
     assert_equal :string, column.type
-    assert_equal 'NOCASE', column.collation
+    assert_equal "NOCASE", column.collation
   end
 
   test "text column with collation" do
-    column = @connection.columns(:collation_table_sqlite3).find { |c| c.name == 'text_rtrim' }
+    column = @connection.columns(:collation_table_sqlite3).find { |c| c.name == "text_rtrim" }
     assert_equal :text, column.type
-    assert_equal 'RTRIM', column.collation
+    assert_equal "RTRIM", column.collation
   end
 
   test "add column with collation" do
-    @connection.add_column :collation_table_sqlite3, :title, :string, collation: 'RTRIM'
+    @connection.add_column :collation_table_sqlite3, :title, :string, collation: "RTRIM"
 
-    column = @connection.columns(:collation_table_sqlite3).find { |c| c.name == 'title' }
+    column = @connection.columns(:collation_table_sqlite3).find { |c| c.name == "title" }
     assert_equal :string, column.type
-    assert_equal 'RTRIM', column.collation
+    assert_equal "RTRIM", column.collation
   end
 
   test "change column with collation" do
     @connection.add_column :collation_table_sqlite3, :description, :string
-    @connection.change_column :collation_table_sqlite3, :description, :text, collation: 'RTRIM'
+    @connection.change_column :collation_table_sqlite3, :description, :text, collation: "RTRIM"
 
-    column = @connection.columns(:collation_table_sqlite3).find { |c| c.name == 'description' }
+    column = @connection.columns(:collation_table_sqlite3).find { |c| c.name == "description" }
     assert_equal :text, column.type
-    assert_equal 'RTRIM', column.collation
+    assert_equal "RTRIM", column.collation
   end
 
   test "schema dump includes collation" do
     output = dump_table_schema("collation_table_sqlite3")
-    assert_match %r{t.string\s+"string_nocase",\s+collation: "NOCASE"$}, output
-    assert_match %r{t.text\s+"text_rtrim",\s+collation: "RTRIM"$}, output
+    assert_match %r{t\.string\s+"string_nocase",\s+collation: "NOCASE"$}, output
+    assert_match %r{t\.text\s+"text_rtrim",\s+collation: "RTRIM"$}, output
   end
 end
diff --git a/activerecord/test/cases/adapters/sqlite3/copy_table_test.rb b/activerecord/test/cases/adapters/sqlite3/copy_table_test.rb
index 34e3b2e023..ffb1d6afce 100644
--- a/activerecord/test/cases/adapters/sqlite3/copy_table_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/copy_table_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class CopyTableTest < ActiveRecord::SQLite3TestCase
@@ -10,8 +12,8 @@ class CopyTableTest < ActiveRecord::SQLite3TestCase
     end
   end
 
-  def test_copy_table(from = 'customers', to = 'customers2', options = {})
-    assert_nothing_raised {copy_table(from, to, options)}
+  def test_copy_table(from = "customers", to = "customers2", options = {})
+    assert_nothing_raised { copy_table(from, to, options) }
     assert_equal row_count(from), row_count(to)
 
     if block_given?
@@ -24,68 +26,69 @@ class CopyTableTest < ActiveRecord::SQLite3TestCase
   end
 
   def test_copy_table_renaming_column
-    test_copy_table('customers', 'customers2',
-        :rename => {'name' => 'person_name'}) do |from, to, options|
-      expected = column_values(from, 'name')
-      assert_equal expected, column_values(to, 'person_name')
+    test_copy_table("customers", "customers2",
+        rename: { "name" => "person_name" }) do |from, to, options|
+      expected = column_values(from, "name")
+      assert_equal expected, column_values(to, "person_name")
       assert expected.any?, "No values in table: #{expected.inspect}"
     end
   end
 
   def test_copy_table_allows_to_pass_options_to_create_table
-    @connection.create_table('blocker_table')
-    test_copy_table('customers', 'blocker_table', force: true)
+    @connection.create_table("blocker_table")
+    test_copy_table("customers", "blocker_table", force: true)
   end
 
   def test_copy_table_with_index
-    test_copy_table('comments', 'comments_with_index') do
-      @connection.add_index('comments_with_index', ['post_id', 'type'])
-      test_copy_table('comments_with_index', 'comments_with_index2') do
-        assert_equal table_indexes_without_name('comments_with_index'),
-                     table_indexes_without_name('comments_with_index2')
+    test_copy_table("comments", "comments_with_index") do
+      @connection.add_index("comments_with_index", ["post_id", "type"])
+      test_copy_table("comments_with_index", "comments_with_index2") do
+        assert_nil table_indexes_without_name("comments_with_index")
+        assert_nil table_indexes_without_name("comments_with_index2")
       end
     end
   end
 
   def test_copy_table_without_primary_key
-    test_copy_table('developers_projects', 'programmers_projects') do
-      assert_nil @connection.primary_key('programmers_projects')
+    test_copy_table("developers_projects", "programmers_projects") do
+      assert_nil @connection.primary_key("programmers_projects")
     end
   end
 
   def test_copy_table_with_id_col_that_is_not_primary_key
-    test_copy_table('goofy_string_id', 'goofy_string_id2') do
-      original_id = @connection.columns('goofy_string_id').detect{|col| col.name == 'id' }
-      copied_id = @connection.columns('goofy_string_id2').detect{|col| col.name == 'id' }
+    test_copy_table("goofy_string_id", "goofy_string_id2") do
+      original_id = @connection.columns("goofy_string_id").detect { |col| col.name == "id" }
+      copied_id = @connection.columns("goofy_string_id2").detect { |col| col.name == "id" }
       assert_equal original_id.type, copied_id.type
       assert_equal original_id.sql_type, copied_id.sql_type
-      assert_equal original_id.limit, copied_id.limit
+      assert_nil original_id.limit
+      assert_nil copied_id.limit
     end
   end
 
   def test_copy_table_with_unconventional_primary_key
-    test_copy_table('owners', 'owners_unconventional') do
-      original_pk = @connection.primary_key('owners')
-      copied_pk = @connection.primary_key('owners_unconventional')
+    test_copy_table("owners", "owners_unconventional") do
+      original_pk = @connection.primary_key("owners")
+      copied_pk = @connection.primary_key("owners_unconventional")
       assert_equal original_pk, copied_pk
     end
   end
 
   def test_copy_table_with_binary_column
-    test_copy_table 'binaries', 'binaries2'
+    test_copy_table "binaries", "binaries2"
   end
 
-protected
+private
   def copy_table(from, to, options = {})
-    @connection.copy_table(from, to, {:temporary => true}.merge(options))
+    @connection.copy_table(from, to, { temporary: true }.merge(options))
   end
 
   def column_names(table)
-    @connection.table_structure(table).map {|column| column['name']}
+    @connection.table_structure(table).map { |column| column["name"] }
   end
 
   def column_values(table, column)
-    @connection.select_all("SELECT #{column} FROM #{table} ORDER BY id").map {|row| row[column]}
+    @connection.select_all("SELECT #{column} FROM #{table} ORDER BY id").map { |row| row[column] }
   end
 
   def table_indexes_without_name(table)
@@ -93,6 +96,6 @@ protected
   end
 
   def row_count(table)
-    @connection.select_one("SELECT COUNT(*) AS count FROM #{table}")['count']
+    @connection.select_one("SELECT COUNT(*) AS count FROM #{table}")["count"]
   end
 end
diff --git a/activerecord/test/cases/adapters/sqlite3/explain_test.rb b/activerecord/test/cases/adapters/sqlite3/explain_test.rb
index 2aec322582..b6d2ccdb53 100644
--- a/activerecord/test/cases/adapters/sqlite3/explain_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/explain_test.rb
@@ -1,27 +1,23 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/developer'
-require 'models/computer'
+require "models/author"
+require "models/post"
 
-module ActiveRecord
-  module ConnectionAdapters
-    class SQLite3Adapter
-      class ExplainTest < ActiveRecord::SQLite3TestCase
-        fixtures :developers
+class SQLite3ExplainTest < ActiveRecord::SQLite3TestCase
+  fixtures :authors
 
-        def test_explain_for_one_query
-          explain = Developer.where(:id => 1).explain
-          assert_match %(EXPLAIN for: SELECT "developers".* FROM "developers" WHERE "developers"."id" = ?), explain
-          assert_match(/(SEARCH )?TABLE developers USING (INTEGER )?PRIMARY KEY/, explain)
-        end
+  def test_explain_for_one_query
+    explain = Author.where(id: 1).explain
+    assert_match %r(EXPLAIN for: SELECT "authors"\.\* FROM "authors" WHERE "authors"\."id" = (?:\? \[\["id", 1\]\]|1)), explain
+    assert_match(/(SEARCH )?TABLE authors USING (INTEGER )?PRIMARY KEY/, explain)
+  end
 
-        def test_explain_with_eager_loading
-          explain = Developer.where(:id => 1).includes(:audit_logs).explain
-          assert_match %(EXPLAIN for: SELECT "developers".* FROM "developers" WHERE "developers"."id" = ?), explain
-          assert_match(/(SEARCH )?TABLE developers USING (INTEGER )?PRIMARY KEY/, explain)
-          assert_match %(EXPLAIN for: SELECT "audit_logs".* FROM "audit_logs" WHERE "audit_logs"."developer_id" = 1), explain
-          assert_match(/(SCAN )?TABLE audit_logs/, explain)
-        end
-      end
-    end
+  def test_explain_with_eager_loading
+    explain = Author.where(id: 1).includes(:posts).explain
+    assert_match %r(EXPLAIN for: SELECT "authors"\.\* FROM "authors" WHERE "authors"\."id" = (?:\? \[\["id", 1\]\]|1)), explain
+    assert_match(/(SEARCH )?TABLE authors USING (INTEGER )?PRIMARY KEY/, explain)
+    assert_match %r(EXPLAIN for: SELECT "posts"\.\* FROM "posts" WHERE "posts"\."author_id" = (?:\? \[\["author_id", 1\]\]|1)), explain
+    assert_match(/(SCAN )?TABLE posts/, explain)
   end
 end
diff --git a/activerecord/test/cases/adapters/sqlite3/json_test.rb b/activerecord/test/cases/adapters/sqlite3/json_test.rb
new file mode 100644
index 0000000000..6f247fcd22
--- /dev/null
+++ b/activerecord/test/cases/adapters/sqlite3/json_test.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "cases/json_shared_test_cases"
+
+class SQLite3JSONTest < ActiveRecord::SQLite3TestCase
+  include JSONSharedTestCases
+
+  def setup
+    super
+    @connection.create_table("json_data_type") do |t|
+      t.json "payload", default: {}
+      t.json "settings"
+    end
+  end
+
+  def test_default
+    @connection.add_column "json_data_type", "permissions", column_type, default: { "users": "read", "posts": ["read", "write"] }
+    klass.reset_column_information
+
+    assert_equal({ "users" => "read", "posts" => ["read", "write"] }, klass.column_defaults["permissions"])
+    assert_equal({ "users" => "read", "posts" => ["read", "write"] }, klass.new.permissions)
+  end
+
+  private
+    def column_type
+      :json
+    end
+end
diff --git a/activerecord/test/cases/adapters/sqlite3/quoting_test.rb b/activerecord/test/cases/adapters/sqlite3/quoting_test.rb
index 87a892db37..40b58e86bf 100644
--- a/activerecord/test/cases/adapters/sqlite3/quoting_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/quoting_test.rb
@@ -1,94 +1,90 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'bigdecimal'
-require 'yaml'
-require 'securerandom'
-
-module ActiveRecord
-  module ConnectionAdapters
-    class SQLite3Adapter
-      class QuotingTest < ActiveRecord::SQLite3TestCase
-        def setup
-          @conn = Base.sqlite3_connection :database => ':memory:',
-            :adapter => 'sqlite3',
-            :timeout => 100
-        end
-
-        def test_type_cast_binary_encoding_without_logger
-          @conn.extend(Module.new { def logger; end })
-          binary = SecureRandom.hex
-          expected = binary.dup.encode!(Encoding::UTF_8)
-          assert_equal expected, @conn.type_cast(binary)
-        end
-
-        def test_type_cast_symbol
-          assert_equal 'foo', @conn.type_cast(:foo)
-        end
-
-        def test_type_cast_date
-          date = Date.today
-          expected = @conn.quoted_date(date)
-          assert_equal expected, @conn.type_cast(date)
-        end
-
-        def test_type_cast_time
-          time = Time.now
-          expected = @conn.quoted_date(time)
-          assert_equal expected, @conn.type_cast(time)
-        end
-
-        def test_type_cast_numeric
-          assert_equal 10, @conn.type_cast(10)
-          assert_equal 2.2, @conn.type_cast(2.2)
-        end
-
-        def test_type_cast_nil
-          assert_equal nil, @conn.type_cast(nil)
-        end
-
-        def test_type_cast_true
-          assert_equal 't', @conn.type_cast(true)
-        end
-
-        def test_type_cast_false
-          assert_equal 'f', @conn.type_cast(false)
-        end
-
-        def test_type_cast_bigdecimal
-          bd = BigDecimal.new '10.0'
-          assert_equal bd.to_f, @conn.type_cast(bd)
-        end
-
-        def test_type_cast_unknown_should_raise_error
-          obj = Class.new.new
-          assert_raise(TypeError) { @conn.type_cast(obj) }
-        end
-
-        def test_type_cast_object_which_responds_to_quoted_id
-          quoted_id_obj = Class.new {
-            def quoted_id
-              "'zomg'"
-            end
-
-            def id
-              10
-            end
-          }.new
-          assert_equal 10, @conn.type_cast(quoted_id_obj)
-
-          quoted_id_obj = Class.new {
-            def quoted_id
-              "'zomg'"
-            end
-          }.new
-          assert_raise(TypeError) { @conn.type_cast(quoted_id_obj) }
-        end
-
-        def test_quoting_binary_strings
-          value = "hello".encode('ascii-8bit')
-          type = Type::String.new
-
-          assert_equal "'hello'", @conn.quote(type.serialize(value))
-        end
+require "bigdecimal"
+require "securerandom"
+
+class SQLite3QuotingTest < ActiveRecord::SQLite3TestCase
+  def setup
+    @conn = ActiveRecord::Base.connection
+    @initial_represent_boolean_as_integer = ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer
+  end
+
+  def teardown
+    ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer = @initial_represent_boolean_as_integer
+  end
+
+  def test_type_cast_binary_encoding_without_logger
+    @conn.extend(Module.new { def logger; end })
+    binary = SecureRandom.hex
+    expected = binary.dup.encode!(Encoding::UTF_8)
+    assert_equal expected, @conn.type_cast(binary)
+  end
+
+  def test_type_cast_true
+    ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer = false
+    assert_equal "t", @conn.type_cast(true)
+
+    ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer = true
+    assert_equal 1, @conn.type_cast(true)
+  end
+
+  def test_type_cast_false
+    ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer = false
+    assert_equal "f", @conn.type_cast(false)
+
+    ActiveRecord::ConnectionAdapters::SQLite3Adapter.represent_boolean_as_integer = true
+    assert_equal 0, @conn.type_cast(false)
+  end
+
+  def test_type_cast_bigdecimal
+    bd = BigDecimal "10.0"
+    assert_equal bd.to_f, @conn.type_cast(bd)
+  end
+
+  def test_quoting_binary_strings
+    value = "hello".encode("ascii-8bit")
+    type = ActiveRecord::Type::String.new
+
+    assert_equal "'hello'", @conn.quote(type.serialize(value))
+  end
+
+  def test_quoted_time_returns_date_qualified_time
+    value = ::Time.utc(2000, 1, 1, 12, 30, 0, 999999)
+    type = ActiveRecord::Type::Time.new
+
+    assert_equal "'2000-01-01 12:30:00.999999'", @conn.quote(type.serialize(value))
+  end
+
+  def test_quoted_time_normalizes_date_qualified_time
+    value = ::Time.utc(2018, 3, 11, 12, 30, 0, 999999)
+    type = ActiveRecord::Type::Time.new
+
+    assert_equal "'2000-01-01 12:30:00.999999'", @conn.quote(type.serialize(value))
+  end
+
+  def test_quoted_time_dst_utc
+    with_env_tz "America/New_York" do
+      with_timezone_config default: :utc do
+        t = Time.new(2000, 7, 1, 0, 0, 0, "+04:30")
+
+        expected = t.change(year: 2000, month: 1, day: 1)
+        expected = expected.getutc.to_s(:db).sub(/\A\d\d\d\d-\d\d-\d\d /, "2000-01-01 ")
+
+        assert_equal expected, @conn.quoted_time(t)
+      end
+    end
+  end
+
+  def test_quoted_time_dst_local
+    with_env_tz "America/New_York" do
+      with_timezone_config default: :local do
+        t = Time.new(2000, 7, 1, 0, 0, 0, "+04:30")
+
+        expected = t.change(year: 2000, month: 1, day: 1)
+        expected = expected.getlocal.to_s(:db).sub(/\A\d\d\d\d-\d\d-\d\d /, "2000-01-01 ")
+
+        assert_equal expected, @conn.quoted_time(t)
       end
     end
   end
diff --git a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
index 7996e7ad50..89052019f8 100644
--- a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/owner'
-require 'tempfile'
-require 'support/ddl_helper'
+require "models/owner"
+require "tempfile"
+require "support/ddl_helper"
 
 module ActiveRecord
   module ConnectionAdapters
@@ -14,22 +16,22 @@ module ActiveRecord
       end
 
       def setup
-        @conn = Base.sqlite3_connection database: ':memory:',
-                                        adapter: 'sqlite3',
+        @conn = Base.sqlite3_connection database: ":memory:",
+                                        adapter: "sqlite3",
                                         timeout: 100
       end
 
       def test_bad_connection
         assert_raise ActiveRecord::NoDatabaseError do
           connection = ActiveRecord::Base.sqlite3_connection(adapter: "sqlite3", database: "/tmp/should/_not/_exist/-cinco-dog.db")
-          connection.drop_table 'ex', if_exists: true
+          connection.drop_table "ex", if_exists: true
         end
       end
 
       unless in_memory_db?
         def test_connect_with_url
           original_connection = ActiveRecord::Base.remove_connection
-          tf = Tempfile.open 'whatever'
+          tf = Tempfile.open "whatever"
           url = "sqlite3:#{tf.path}"
           ActiveRecord::Base.establish_connection(url)
           assert ActiveRecord::Base.connection
@@ -49,33 +51,17 @@ module ActiveRecord
         end
       end
 
-      def test_valid_column
-        with_example_table do
-          column = @conn.columns('ex').find { |col| col.name == 'id' }
-          assert @conn.valid_type?(column.type)
-        end
-      end
-
-      # sqlite3 databases should be able to support any type and not just the
-      # ones mentioned in the native_database_types.
-      #
-      # Therefore test_invalid column should always return true even if the
-      # type is not valid.
-      def test_invalid_column
-        assert @conn.valid_type?(:foobar)
-      end
-
       def test_column_types
-        owner = Owner.create!(name: "hello".encode('ascii-8bit'))
+        owner = Owner.create!(name: "hello".encode("ascii-8bit"))
         owner.reload
-        select = Owner.columns.map { |c| "typeof(#{c.name})" }.join ', '
+        select = Owner.columns.map { |c| "typeof(#{c.name})" }.join ", "
         result = Owner.connection.exec_query <<-esql
           SELECT #{select}
           FROM   #{Owner.table_name}
           WHERE  #{Owner.primary_key} = #{owner.id}
         esql
 
-        assert(!result.rows.first.include?("blob"), "should not store blobs")
+        assert_not(result.rows.first.include?("blob"), "should not store blobs")
       ensure
         owner.delete
       end
@@ -83,10 +69,10 @@ module ActiveRecord
       def test_exec_insert
         with_example_table do
           vals = [Relation::QueryAttribute.new("number", 10, Type::Value.new)]
-          @conn.exec_insert('insert into ex (number) VALUES (?)', 'SQL', vals)
+          @conn.exec_insert("insert into ex (number) VALUES (?)", "SQL", vals)
 
           result = @conn.exec_query(
-            'select number from ex where number = ?', 'SQL', vals)
+            "select number from ex where number = ?", "SQL", vals)
 
           assert_equal 1, result.rows.length
           assert_equal 10, result.rows.first.first
@@ -94,87 +80,82 @@ module ActiveRecord
       end
 
       def test_primary_key_returns_nil_for_no_pk
-        with_example_table 'id int, data string' do
-          assert_nil @conn.primary_key('ex')
+        with_example_table "id int, data string" do
+          assert_nil @conn.primary_key("ex")
         end
       end
 
       def test_connection_no_db
         assert_raises(ArgumentError) do
-          Base.sqlite3_connection {}
+          Base.sqlite3_connection { }
         end
       end
 
       def test_bad_timeout
         assert_raises(TypeError) do
-          Base.sqlite3_connection database: ':memory:',
-                                  adapter: 'sqlite3',
-                                  timeout: 'usa'
+          Base.sqlite3_connection database: ":memory:",
+                                  adapter: "sqlite3",
+                                  timeout: "usa"
         end
       end
 
       # connection is OK with a nil timeout
       def test_nil_timeout
-        conn = Base.sqlite3_connection database: ':memory:',
-                                       adapter: 'sqlite3',
+        conn = Base.sqlite3_connection database: ":memory:",
+                                       adapter: "sqlite3",
                                        timeout: nil
-        assert conn, 'made a connection'
+        assert conn, "made a connection"
       end
 
       def test_connect
-        assert @conn, 'should have connection'
+        assert @conn, "should have connection"
       end
 
       # sqlite3 defaults to UTF-8 encoding
       def test_encoding
-        assert_equal 'UTF-8', @conn.encoding
-      end
-
-      def test_bind_value_substitute
-        bind_param = @conn.substitute_at('foo')
-        assert_equal Arel.sql('?'), bind_param.to_sql
+        assert_equal "UTF-8", @conn.encoding
       end
 
       def test_exec_no_binds
-        with_example_table 'id int, data string' do
-          result = @conn.exec_query('SELECT id, data FROM ex')
+        with_example_table "id int, data string" do
+          result = @conn.exec_query("SELECT id, data FROM ex")
           assert_equal 0, result.rows.length
           assert_equal 2, result.columns.length
           assert_equal %w{ id data }, result.columns
 
           @conn.exec_query('INSERT INTO ex (id, data) VALUES (1, "foo")')
-          result = @conn.exec_query('SELECT id, data FROM ex')
+          result = @conn.exec_query("SELECT id, data FROM ex")
           assert_equal 1, result.rows.length
           assert_equal 2, result.columns.length
 
-          assert_equal [[1, 'foo']], result.rows
+          assert_equal [[1, "foo"]], result.rows
         end
       end
 
       def test_exec_query_with_binds
-        with_example_table 'id int, data string' do
+        with_example_table "id int, data string" do
           @conn.exec_query('INSERT INTO ex (id, data) VALUES (1, "foo")')
           result = @conn.exec_query(
-            'SELECT id, data FROM ex WHERE id = ?', nil, [Relation::QueryAttribute.new(nil, 1, Type::Value.new)])
+            "SELECT id, data FROM ex WHERE id = ?", nil, [Relation::QueryAttribute.new(nil, 1, Type::Value.new)])
 
           assert_equal 1, result.rows.length
           assert_equal 2, result.columns.length
 
-          assert_equal [[1, 'foo']], result.rows
+          assert_equal [[1, "foo"]], result.rows
         end
       end
 
       def test_exec_query_typecasts_bind_vals
-        with_example_table 'id int, data string' do
+        with_example_table "id int, data string" do
           @conn.exec_query('INSERT INTO ex (id, data) VALUES (1, "foo")')
 
           result = @conn.exec_query(
-            'SELECT id, data FROM ex WHERE id = ?', nil, [Relation::QueryAttribute.new("id", "1-fuu", Type::Integer.new)])
+            "SELECT id, data FROM ex WHERE id = ?", nil, [Relation::QueryAttribute.new("id", "1-fuu", Type::Integer.new)])
 
           assert_equal 1, result.rows.length
           assert_equal 2, result.columns.length
 
-          assert_equal [[1, 'foo']], result.rows
+          assert_equal [[1, "foo"]], result.rows
         end
       end
 
@@ -186,16 +167,16 @@ module ActiveRecord
             data binary
           )
         eosql
-        str = "\x80".force_encoding("ASCII-8BIT")
-        binary = DualEncoding.new name: 'いただきます！', data: str
+        str = (+"\x80").force_encoding("ASCII-8BIT")
+        binary = DualEncoding.new name: "いただきます！", data: str
         binary.save!
         assert_equal str, binary.data
       ensure
-        DualEncoding.connection.drop_table 'dual_encodings', if_exists: true
+        DualEncoding.connection.drop_table "dual_encodings", if_exists: true
       end
 
       def test_type_cast_should_not_mutate_encoding
-        name  = 'hello'.force_encoding(Encoding::ASCII_8BIT)
+        name = (+"hello").force_encoding(Encoding::ASCII_8BIT)
         Owner.create(name: name)
         assert_equal Encoding::ASCII_8BIT, name.encoding
       ensure
@@ -209,8 +190,8 @@ module ActiveRecord
           assert_equal 1, records.length
 
           record = records.first
-          assert_equal 10, record['number']
-          assert_equal 1, record['id']
+          assert_equal 10, record["number"]
+          assert_equal 1, record["id"]
         end
       end
 
@@ -218,24 +199,12 @@ module ActiveRecord
         assert_equal "''", @conn.quote_string("'")
       end
 
-      def test_insert_sql
-        with_example_table do
-          2.times do |i|
-            rv = @conn.insert_sql "INSERT INTO ex (number) VALUES (#{i})"
-            assert_equal(i + 1, rv)
-          end
-
-          records = @conn.execute "SELECT * FROM ex"
-          assert_equal 2, records.length
-        end
-      end
-
-      def test_insert_sql_logged
+      def test_insert_logged
         with_example_table do
           sql = "INSERT INTO ex (number) VALUES (10)"
           name = "foo"
           assert_logged [[sql, name, []]] do
-            @conn.insert_sql sql, name
+            @conn.insert(sql, name)
           end
         end
       end
@@ -243,8 +212,8 @@ module ActiveRecord
       def test_insert_id_value_returned
         with_example_table do
           sql = "INSERT INTO ex (number) VALUES (10)"
-          idval = 'vuvuzela'
-          id = @conn.insert_sql sql, nil, nil, idval
+          idval = "vuvuzela"
+          id = @conn.insert(sql, nil, nil, idval)
           assert_equal idval, id
         end
       end
@@ -254,7 +223,7 @@ module ActiveRecord
           2.times do |i|
             @conn.create "INSERT INTO ex (number) VALUES (#{i})"
           end
-          rows = @conn.select_rows 'select number, id from ex'
+          rows = @conn.select_rows "select number, id from ex"
           assert_equal [[0, 1], [1, 2]], rows
         end
       end
@@ -271,7 +240,7 @@ module ActiveRecord
 
       def test_transaction
         with_example_table do
-          count_sql = 'select count(*) from ex'
+          count_sql = "select count(*) from ex"
 
           @conn.begin_db_transaction
           @conn.create "INSERT INTO ex (number) VALUES (10)"
@@ -285,7 +254,7 @@ module ActiveRecord
       def test_tables
         with_example_table do
           assert_equal %w{ ex }, @conn.tables
-          with_example_table 'id integer PRIMARY KEY AUTOINCREMENT, number integer', 'people' do
+          with_example_table "id integer PRIMARY KEY AUTOINCREMENT, number integer", "people" do
             assert_equal %w{ ex people }.sort, @conn.tables.sort
           end
         end
@@ -293,38 +262,27 @@ module ActiveRecord
 
       def test_tables_logs_name
         sql = <<-SQL
-          SELECT name FROM sqlite_master
-          WHERE (type = 'table' OR type = 'view') AND NOT name = 'sqlite_sequence'
+          SELECT name FROM sqlite_master WHERE name <> 'sqlite_sequence' AND type IN ('table')
         SQL
-        assert_logged [[sql.squish, 'SCHEMA', []]] do
-          @conn.tables('hello')
-        end
-      end
-
-      def test_indexes_logs_name
-        with_example_table do
-          assert_logged [["PRAGMA index_list(\"ex\")", 'SCHEMA', []]] do
-            @conn.indexes('ex', 'hello')
-          end
+        assert_logged [[sql.squish, "SCHEMA", []]] do
+          @conn.tables
         end
       end
 
       def test_table_exists_logs_name
         with_example_table do
           sql = <<-SQL
-            SELECT name FROM sqlite_master
-            WHERE (type = 'table' OR type = 'view')
-            AND NOT name = 'sqlite_sequence' AND name = \"ex\"
+            SELECT name FROM sqlite_master WHERE name <> 'sqlite_sequence' AND name = 'ex' AND type IN ('table')
           SQL
-          assert_logged [[sql.squish, 'SCHEMA', []]] do
-            assert @conn.table_exists?('ex')
+          assert_logged [[sql.squish, "SCHEMA", []]] do
+            assert @conn.table_exists?("ex")
           end
         end
       end
 
       def test_columns
         with_example_table do
-          columns = @conn.columns('ex').sort_by(&:name)
+          columns = @conn.columns("ex").sort_by(&:name)
           assert_equal 2, columns.length
           assert_equal %w{ id number }.sort, columns.map(&:name)
           assert_equal [nil, nil], columns.map(&:default)
@@ -333,17 +291,17 @@ module ActiveRecord
       end
 
       def test_columns_with_default
-        with_example_table 'id integer PRIMARY KEY AUTOINCREMENT, number integer default 10' do
-          column = @conn.columns('ex').find { |x|
-            x.name == 'number'
+        with_example_table "id integer PRIMARY KEY AUTOINCREMENT, number integer default 10" do
+          column = @conn.columns("ex").find { |x|
+            x.name == "number"
           }
-          assert_equal '10', column.default
+          assert_equal "10", column.default
         end
       end
 
       def test_columns_with_not_null
-        with_example_table 'id integer PRIMARY KEY AUTOINCREMENT, number integer not null' do
-          column = @conn.columns('ex').find { |x| x.name == 'number' }
+        with_example_table "id integer PRIMARY KEY AUTOINCREMENT, number integer not null" do
+          column = @conn.columns("ex").find { |x| x.name == "number" }
           assert_not column.null, "column should not be null"
         end
       end
@@ -351,108 +309,288 @@ module ActiveRecord
       def test_indexes_logs
         with_example_table do
           assert_logged [["PRAGMA index_list(\"ex\")", "SCHEMA", []]] do
-            @conn.indexes('ex')
+            @conn.indexes("ex")
           end
         end
       end
 
       def test_no_indexes
-        assert_equal [], @conn.indexes('items')
+        assert_equal [], @conn.indexes("items")
       end
 
       def test_index
         with_example_table do
-          @conn.add_index 'ex', 'id', unique: true, name: 'fun'
-          index = @conn.indexes('ex').find { |idx| idx.name == 'fun' }
+          @conn.add_index "ex", "id", unique: true, name: "fun"
+          index = @conn.indexes("ex").find { |idx| idx.name == "fun" }
 
-          assert_equal 'ex', index.table
-          assert index.unique, 'index is unique'
-          assert_equal ['id'], index.columns
+          assert_equal "ex", index.table
+          assert index.unique, "index is unique"
+          assert_equal ["id"], index.columns
         end
       end
 
       def test_non_unique_index
         with_example_table do
-          @conn.add_index 'ex', 'id', name: 'fun'
-          index = @conn.indexes('ex').find { |idx| idx.name == 'fun' }
-          assert_not index.unique, 'index is not unique'
+          @conn.add_index "ex", "id", name: "fun"
+          index = @conn.indexes("ex").find { |idx| idx.name == "fun" }
+          assert_not index.unique, "index is not unique"
         end
       end
 
       def test_compound_index
         with_example_table do
-          @conn.add_index 'ex', %w{ id number }, name: 'fun'
-          index = @conn.indexes('ex').find { |idx| idx.name == 'fun' }
+          @conn.add_index "ex", %w{ id number }, name: "fun"
+          index = @conn.indexes("ex").find { |idx| idx.name == "fun" }
           assert_equal %w{ id number }.sort, index.columns.sort
         end
       end
 
+      if ActiveRecord::Base.connection.supports_expression_index?
+        def test_expression_index
+          with_example_table do
+            @conn.add_index "ex", "max(id, number)", name: "expression"
+            index = @conn.indexes("ex").find { |idx| idx.name == "expression" }
+            assert_equal "max(id, number)", index.columns
+          end
+        end
+
+        def test_expression_index_with_where
+          with_example_table do
+            @conn.add_index "ex", "id % 10, max(id, number)", name: "expression", where: "id > 1000"
+            index = @conn.indexes("ex").find { |idx| idx.name == "expression" }
+            assert_equal "id % 10, max(id, number)", index.columns
+            assert_equal "id > 1000", index.where
+          end
+        end
+
+        def test_complicated_expression
+          with_example_table do
+            @conn.execute "CREATE INDEX expression ON ex (id % 10, (CASE WHEN number > 0 THEN max(id, number) END))WHERE(id > 1000)"
+            index = @conn.indexes("ex").find { |idx| idx.name == "expression" }
+            assert_equal "id % 10, (CASE WHEN number > 0 THEN max(id, number) END)", index.columns
+            assert_equal "(id > 1000)", index.where
+          end
+        end
+
+        def test_not_everything_an_expression
+          with_example_table do
+            @conn.add_index "ex", "id, max(id, number)", name: "expression"
+            index = @conn.indexes("ex").find { |idx| idx.name == "expression" }
+            assert_equal "id, max(id, number)", index.columns
+          end
+        end
+      end
+
       def test_primary_key
         with_example_table do
-          assert_equal 'id', @conn.primary_key('ex')
-          with_example_table 'internet integer PRIMARY KEY AUTOINCREMENT, number integer not null', 'foos' do
-            assert_equal 'internet', @conn.primary_key('foos')
+          assert_equal "id", @conn.primary_key("ex")
+          with_example_table "internet integer PRIMARY KEY AUTOINCREMENT, number integer not null", "foos" do
+            assert_equal "internet", @conn.primary_key("foos")
           end
         end
       end
 
       def test_no_primary_key
-        with_example_table 'number integer not null' do
-          assert_nil @conn.primary_key('ex')
+        with_example_table "number integer not null" do
+          assert_nil @conn.primary_key("ex")
         end
       end
 
-      def test_composite_primary_key
-        with_example_table 'id integer, number integer, foo integer, PRIMARY KEY (id, number)' do
-          assert_nil @conn.primary_key('ex')
+      class Barcode < ActiveRecord::Base
+        self.primary_key = "code"
+      end
+
+      def test_copy_table_with_existing_records_have_custom_primary_key
+        connection = Barcode.connection
+        connection.create_table(:barcodes, primary_key: "code", id: :string, limit: 42, force: true) do |t|
+          t.text :other_attr
         end
+        code = "214fe0c2-dd47-46df-b53b-66090b3c1d40"
+        Barcode.create!(code: code, other_attr: "xxx")
+
+        connection.remove_column("barcodes", "other_attr")
+
+        assert_equal code, Barcode.first.id
+      ensure
+        Barcode.reset_column_information
+      end
+
+      def test_copy_table_with_composite_primary_keys
+        connection = Barcode.connection
+        connection.create_table(:barcodes, primary_key: ["region", "code"], force: true) do |t|
+          t.string :region
+          t.string :code
+          t.text :other_attr
+        end
+        region = "US"
+        code = "214fe0c2-dd47-46df-b53b-66090b3c1d40"
+        Barcode.create!(region: region, code: code, other_attr: "xxx")
+
+        connection.remove_column("barcodes", "other_attr")
+
+        assert_equal ["region", "code"], connection.primary_keys("barcodes")
+
+        barcode = Barcode.first
+        assert_equal region, barcode.region
+        assert_equal code, barcode.code
+      ensure
+        Barcode.reset_column_information
+      end
+
+      def test_custom_primary_key_in_create_table
+        connection = Barcode.connection
+        connection.create_table :barcodes, id: false, force: true do |t|
+          t.primary_key :id, :string
+        end
+
+        assert_equal "id", connection.primary_key("barcodes")
+
+        custom_pk = Barcode.columns_hash["id"]
+
+        assert_equal :string, custom_pk.type
+        assert_not custom_pk.null
+      ensure
+        Barcode.reset_column_information
+      end
+
+      def test_custom_primary_key_in_change_table
+        connection = Barcode.connection
+        connection.create_table :barcodes, id: false, force: true do |t|
+          t.integer :dummy
+        end
+        connection.change_table :barcodes do |t|
+          t.primary_key :id, :string
+        end
+
+        assert_equal "id", connection.primary_key("barcodes")
+
+        custom_pk = Barcode.columns_hash["id"]
+
+        assert_equal :string, custom_pk.type
+        assert_not custom_pk.null
+      ensure
+        Barcode.reset_column_information
+      end
+
+      def test_add_column_with_custom_primary_key
+        connection = Barcode.connection
+        connection.create_table :barcodes, id: false, force: true do |t|
+          t.integer :dummy
+        end
+        connection.add_column :barcodes, :id, :string, primary_key: true
+
+        assert_equal "id", connection.primary_key("barcodes")
+
+        custom_pk = Barcode.columns_hash["id"]
+
+        assert_equal :string, custom_pk.type
+        assert_not custom_pk.null
+      ensure
+        Barcode.reset_column_information
+      end
+
+      def test_remove_column_preserves_partial_indexes
+        connection = Barcode.connection
+        connection.create_table :barcodes, force: true do |t|
+          t.string :code
+          t.string :region
+          t.boolean :bool_attr
+
+          t.index :code, unique: true, where: :bool_attr, name: "partial"
+        end
+        connection.remove_column :barcodes, :region
+
+        index = connection.indexes("barcodes").find { |idx| idx.name == "partial" }
+        assert_equal "bool_attr", index.where
+      ensure
+        Barcode.reset_column_information
       end
 
       def test_supports_extensions
-        assert_not @conn.supports_extensions?, 'does not support extensions'
+        assert_not @conn.supports_extensions?, "does not support extensions"
       end
 
       def test_respond_to_enable_extension
-        assert @conn.respond_to?(:enable_extension)
+        assert_respond_to @conn, :enable_extension
       end
 
       def test_respond_to_disable_extension
-        assert @conn.respond_to?(:disable_extension)
+        assert_respond_to @conn, :disable_extension
       end
 
       def test_statement_closed
         db = ::SQLite3::Database.new(ActiveRecord::Base.
-                                   configurations['arunit']['database'])
+                                   configurations["arunit"]["database"])
         statement = ::SQLite3::Statement.new(db,
-                                           'CREATE TABLE statement_test (number integer not null)')
-        statement.stubs(:step).raises(::SQLite3::BusyException, 'busy')
-        statement.stubs(:columns).once.returns([])
-        statement.expects(:close).once
-        ::SQLite3::Statement.stubs(:new).returns(statement)
-
-        assert_raises ActiveRecord::StatementInvalid do
-          @conn.exec_query 'select * from statement_test'
+                                           "CREATE TABLE statement_test (number integer not null)")
+        statement.stub(:step, -> { raise ::SQLite3::BusyException.new("busy") }) do
+          assert_called(statement, :columns, returns: []) do
+            assert_called(statement, :close) do
+              ::SQLite3::Statement.stub(:new, statement) do
+                assert_raises ActiveRecord::StatementInvalid do
+                  @conn.exec_query "select * from statement_test"
+                end
+              end
+            end
+          end
         end
       end
 
-      private
+      def test_deprecate_valid_alter_table_type
+        assert_deprecated { @conn.valid_alter_table_type?(:string) }
+      end
 
-      def assert_logged logs
-        subscriber = SQLSubscriber.new
-        subscription = ActiveSupport::Notifications.subscribe('sql.active_record', subscriber)
-        yield
-        assert_equal logs, subscriber.logged
-      ensure
-        ActiveSupport::Notifications.unsubscribe(subscription)
+      def test_db_is_not_readonly_when_readonly_option_is_false
+        conn = Base.sqlite3_connection database: ":memory:",
+                                       adapter: "sqlite3",
+                                       readonly: false
+
+        assert_not_predicate conn.raw_connection, :readonly?
       end
 
-      def with_example_table(definition = nil, table_name = 'ex', &block)
-        definition ||= <<-SQL
-          id integer PRIMARY KEY AUTOINCREMENT,
-          number integer
-        SQL
-        super(@conn, table_name, definition, &block)
+      def test_db_is_not_readonly_when_readonly_option_is_unspecified
+        conn = Base.sqlite3_connection database: ":memory:",
+                                       adapter: "sqlite3"
+
+        assert_not_predicate conn.raw_connection, :readonly?
+      end
+
+      def test_db_is_readonly_when_readonly_option_is_true
+        conn = Base.sqlite3_connection database: ":memory:",
+                                       adapter: "sqlite3",
+                                       readonly: true
+
+        assert_predicate conn.raw_connection, :readonly?
+      end
+
+      def test_writes_are_not_permitted_to_readonly_databases
+        conn = Base.sqlite3_connection database: ":memory:",
+                                       adapter: "sqlite3",
+                                       readonly: true
+
+        assert_raises(ActiveRecord::StatementInvalid, /SQLite3::ReadOnlyException/) do
+          conn.execute("CREATE TABLE test(id integer)")
+        end
       end
+
+      private
+
+        def assert_logged(logs)
+          subscriber = SQLSubscriber.new
+          subscription = ActiveSupport::Notifications.subscribe("sql.active_record", subscriber)
+          yield
+          assert_equal logs, subscriber.logged
+        ensure
+          ActiveSupport::Notifications.unsubscribe(subscription)
+        end
+
+        def with_example_table(definition = nil, table_name = "ex", &block)
+          definition ||= <<-SQL
+            id integer PRIMARY KEY AUTOINCREMENT,
+            number integer
+          SQL
+          super(@conn, table_name, definition, &block)
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/adapters/sqlite3/sqlite3_create_folder_test.rb b/activerecord/test/cases/adapters/sqlite3/sqlite3_create_folder_test.rb
index 887dcfc96c..d70486605f 100644
--- a/activerecord/test/cases/adapters/sqlite3/sqlite3_create_folder_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/sqlite3_create_folder_test.rb
@@ -1,18 +1,24 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/owner'
+require "models/owner"
 
 module ActiveRecord
   module ConnectionAdapters
     class SQLite3CreateFolder < ActiveRecord::SQLite3TestCase
       def test_sqlite_creates_directory
         Dir.mktmpdir do |dir|
-          dir = Pathname.new(dir)
-          @conn = Base.sqlite3_connection :database => dir.join("db/foo.sqlite3"),
-                               :adapter => 'sqlite3',
-                               :timeout => 100
+          begin
+            dir = Pathname.new(dir)
+            @conn = Base.sqlite3_connection database: dir.join("db/foo.sqlite3"),
+                                 adapter: "sqlite3",
+                                 timeout: 100
 
-          assert Dir.exist? dir.join('db')
-          assert File.exist? dir.join('db/foo.sqlite3')
+            assert Dir.exist? dir.join("db")
+            assert File.exist? dir.join("db/foo.sqlite3")
+          ensure
+            @conn.disconnect! if @conn
+          end
         end
       end
     end
diff --git a/activerecord/test/cases/adapters/sqlite3/statement_pool_test.rb b/activerecord/test/cases/adapters/sqlite3/statement_pool_test.rb
index ef324183a7..61002435a4 100644
--- a/activerecord/test/cases/adapters/sqlite3/statement_pool_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/statement_pool_test.rb
@@ -1,24 +1,21 @@
-require 'cases/helper'
+# frozen_string_literal: true
 
-module ActiveRecord::ConnectionAdapters
-  class SQLite3Adapter
-    class StatementPoolTest < ActiveRecord::SQLite3TestCase
-      if Process.respond_to?(:fork)
-        def test_cache_is_per_pid
+require "cases/helper"
 
-          cache = StatementPool.new nil, 10
-          cache['foo'] = 'bar'
-          assert_equal 'bar', cache['foo']
+class SQLite3StatementPoolTest < ActiveRecord::SQLite3TestCase
+  if Process.respond_to?(:fork)
+    def test_cache_is_per_pid
+      cache = ActiveRecord::ConnectionAdapters::SQLite3Adapter::StatementPool.new(10)
+      cache["foo"] = "bar"
+      assert_equal "bar", cache["foo"]
 
-          pid = fork {
-            lookup = cache['foo'];
-            exit!(!lookup)
-          }
+      pid = fork {
+        lookup = cache["foo"]
+        exit!(!lookup)
+      }
 
-          Process.waitpid pid
-          assert $?.success?, 'process should exit successfully'
-        end
-      end
+      Process.waitpid pid
+      assert $?.success?, "process should exit successfully"
     end
   end
 end
diff --git a/activerecord/test/cases/aggregations_test.rb b/activerecord/test/cases/aggregations_test.rb
index 5536702f58..fbdf2ada4b 100644
--- a/activerecord/test/cases/aggregations_test.rb
+++ b/activerecord/test/cases/aggregations_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/customer'
+require "models/customer"
 
 class AggregationsTest < ActiveRecord::TestCase
   fixtures :customers
@@ -25,7 +27,7 @@ class AggregationsTest < ActiveRecord::TestCase
 
   def test_immutable_value_objects
     customers(:david).balance = Money.new(100)
-    assert_raise(RuntimeError) { customers(:david).balance.instance_eval { @amount = 20 } }
+    assert_raise(frozen_error_class) { customers(:david).balance.instance_eval { @amount = 20 } }
   end
 
   def test_inferred_mapping
@@ -51,17 +53,17 @@ class AggregationsTest < ActiveRecord::TestCase
 
     Customer.update_all("gps_location = '24x113'")
     customers(:david).reload
-    assert_equal '24x113', customers(:david)['gps_location']
+    assert_equal "24x113", customers(:david)["gps_location"]
 
-    assert_equal GpsLocation.new('24x113'), customers(:david).gps_location
+    assert_equal GpsLocation.new("24x113"), customers(:david).gps_location
   end
 
   def test_gps_equality
-    assert_equal GpsLocation.new('39x110'), GpsLocation.new('39x110')
+    assert_equal GpsLocation.new("39x110"), GpsLocation.new("39x110")
   end
 
   def test_gps_inequality
-    assert_not_equal GpsLocation.new('39x110'), GpsLocation.new('39x111')
+    assert_not_equal GpsLocation.new("39x110"), GpsLocation.new("39x111")
   end
 
   def test_allow_nil_gps_is_nil
@@ -102,7 +104,7 @@ class AggregationsTest < ActiveRecord::TestCase
   end
 
   def test_nil_assignment_results_in_nil
-    customers(:david).gps_location = GpsLocation.new('39x111')
+    customers(:david).gps_location = GpsLocation.new("39x111")
     assert_not_nil customers(:david).gps_location
     customers(:david).gps_location = nil
     assert_nil customers(:david).gps_location
@@ -129,26 +131,36 @@ class AggregationsTest < ActiveRecord::TestCase
   end
 
   def test_custom_constructor
-    assert_equal 'Barney GUMBLE', customers(:barney).fullname.to_s
+    assert_equal "Barney GUMBLE", customers(:barney).fullname.to_s
     assert_kind_of Fullname, customers(:barney).fullname
   end
 
   def test_custom_converter
-    customers(:barney).fullname = 'Barnoit Gumbleau'
-    assert_equal 'Barnoit GUMBLEAU', customers(:barney).fullname.to_s
+    customers(:barney).fullname = "Barnoit Gumbleau"
+    assert_equal "Barnoit GUMBLEAU", customers(:barney).fullname.to_s
     assert_kind_of Fullname, customers(:barney).fullname
   end
+
+  def test_assigning_hash_to_custom_converter
+    customers(:barney).fullname = { first: "Barney", last: "Stinson" }
+    assert_equal "Barney STINSON", customers(:barney).name
+  end
+
+  def test_assigning_hash_without_custom_converter
+    customers(:barney).fullname_no_converter = { first: "Barney", last: "Stinson" }
+    assert_equal({ first: "Barney", last: "Stinson" }.to_s, customers(:barney).name)
+  end
 end
 
 class OverridingAggregationsTest < ActiveRecord::TestCase
   class DifferentName; end
 
   class Person < ActiveRecord::Base
-    composed_of :composed_of, :mapping => %w(person_first_name first_name)
+    composed_of :composed_of, mapping: %w(person_first_name first_name)
   end
 
   class DifferentPerson < Person
-    composed_of :composed_of, :class_name => 'DifferentName', :mapping => %w(different_person_first_name first_name)
+    composed_of :composed_of, class_name: "DifferentName", mapping: %w(different_person_first_name first_name)
   end
 
   def test_composed_of_aggregation_redefinition_reflections_should_differ_and_not_inherited
diff --git a/activerecord/test/cases/ar_schema_test.rb b/activerecord/test/cases/ar_schema_test.rb
index 9d5327bf35..f05dcac7dd 100644
--- a/activerecord/test/cases/ar_schema_test.rb
+++ b/activerecord/test/cases/ar_schema_test.rb
@@ -1,130 +1,145 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
-if ActiveRecord::Base.connection.supports_migrations?
+class ActiveRecordSchemaTest < ActiveRecord::TestCase
+  self.use_transactional_tests = false
 
-  class ActiveRecordSchemaTest < ActiveRecord::TestCase
-    self.use_transactional_tests = false
+  setup do
+    @original_verbose = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+    @connection = ActiveRecord::Base.connection
+    ActiveRecord::SchemaMigration.drop_table
+  end
 
-    setup do
-      @original_verbose = ActiveRecord::Migration.verbose
-      ActiveRecord::Migration.verbose = false
-      @connection = ActiveRecord::Base.connection
-      ActiveRecord::SchemaMigration.drop_table
-    end
+  teardown do
+    @connection.drop_table :fruits rescue nil
+    @connection.drop_table :nep_fruits rescue nil
+    @connection.drop_table :nep_schema_migrations rescue nil
+    @connection.drop_table :has_timestamps rescue nil
+    @connection.drop_table :multiple_indexes rescue nil
+    ActiveRecord::SchemaMigration.delete_all rescue nil
+    ActiveRecord::Migration.verbose = @original_verbose
+  end
 
-    teardown do
-      @connection.drop_table :fruits rescue nil
-      @connection.drop_table :nep_fruits rescue nil
-      @connection.drop_table :nep_schema_migrations rescue nil
-      @connection.drop_table :has_timestamps rescue nil
-      ActiveRecord::SchemaMigration.delete_all rescue nil
-      ActiveRecord::Migration.verbose = @original_verbose
-    end
+  def test_has_primary_key
+    old_primary_key_prefix_type = ActiveRecord::Base.primary_key_prefix_type
+    ActiveRecord::Base.primary_key_prefix_type = :table_name_with_underscore
+    assert_equal "version", ActiveRecord::SchemaMigration.primary_key
 
-    def test_has_no_primary_key
-      old_primary_key_prefix_type = ActiveRecord::Base.primary_key_prefix_type
-      ActiveRecord::Base.primary_key_prefix_type = :table_name_with_underscore
-      assert_nil ActiveRecord::SchemaMigration.primary_key
+    ActiveRecord::SchemaMigration.create_table
+    assert_difference "ActiveRecord::SchemaMigration.count", 1 do
+      ActiveRecord::SchemaMigration.create version: 12
+    end
+  ensure
+    ActiveRecord::SchemaMigration.drop_table
+    ActiveRecord::Base.primary_key_prefix_type = old_primary_key_prefix_type
+  end
 
-      ActiveRecord::SchemaMigration.create_table
-      assert_difference "ActiveRecord::SchemaMigration.count", 1 do
-        ActiveRecord::SchemaMigration.create version: 12
+  def test_schema_define
+    ActiveRecord::Schema.define(version: 7) do
+      create_table :fruits do |t|
+        t.column :color, :string
+        t.column :fruit_size, :string  # NOTE: "size" is reserved in Oracle
+        t.column :texture, :string
+        t.column :flavor, :string
       end
-    ensure
-      ActiveRecord::SchemaMigration.drop_table
-      ActiveRecord::Base.primary_key_prefix_type = old_primary_key_prefix_type
     end
 
-    def test_schema_define
-      ActiveRecord::Schema.define(:version => 7) do
-        create_table :fruits do |t|
-          t.column :color, :string
-          t.column :fruit_size, :string  # NOTE: "size" is reserved in Oracle
-          t.column :texture, :string
-          t.column :flavor, :string
-        end
-      end
+    assert_nothing_raised { @connection.select_all "SELECT * FROM fruits" }
+    assert_nothing_raised { @connection.select_all "SELECT * FROM schema_migrations" }
+    assert_equal 7, @connection.migration_context.current_version
+  end
 
-      assert_nothing_raised { @connection.select_all "SELECT * FROM fruits" }
-      assert_nothing_raised { @connection.select_all "SELECT * FROM schema_migrations" }
-      assert_equal 7, ActiveRecord::Migrator::current_version
+  def test_schema_define_w_table_name_prefix
+    table_name = ActiveRecord::SchemaMigration.table_name
+    old_table_name_prefix = ActiveRecord::Base.table_name_prefix
+    ActiveRecord::Base.table_name_prefix = "nep_"
+    ActiveRecord::SchemaMigration.table_name = "nep_#{table_name}"
+    ActiveRecord::Schema.define(version: 7) do
+      create_table :fruits do |t|
+        t.column :color, :string
+        t.column :fruit_size, :string  # NOTE: "size" is reserved in Oracle
+        t.column :texture, :string
+        t.column :flavor, :string
+      end
     end
+    assert_equal 7, @connection.migration_context.current_version
+  ensure
+    ActiveRecord::Base.table_name_prefix = old_table_name_prefix
+    ActiveRecord::SchemaMigration.table_name = table_name
+  end
 
-    def test_schema_define_w_table_name_prefix
-      table_name = ActiveRecord::SchemaMigration.table_name
-      old_table_name_prefix = ActiveRecord::Base.table_name_prefix
-      ActiveRecord::Base.table_name_prefix  = "nep_"
-      ActiveRecord::SchemaMigration.table_name = "nep_#{table_name}"
-      ActiveRecord::Schema.define(:version => 7) do
-        create_table :fruits do |t|
-          t.column :color, :string
-          t.column :fruit_size, :string  # NOTE: "size" is reserved in Oracle
-          t.column :texture, :string
-          t.column :flavor, :string
+  def test_schema_raises_an_error_for_invalid_column_type
+    assert_raise NoMethodError do
+      ActiveRecord::Schema.define(version: 8) do
+        create_table :vegetables do |t|
+          t.unknown :color
         end
       end
-      assert_equal 7, ActiveRecord::Migrator::current_version
-    ensure
-      ActiveRecord::Base.table_name_prefix  = old_table_name_prefix
-      ActiveRecord::SchemaMigration.table_name = table_name
     end
+  end
 
-    def test_schema_raises_an_error_for_invalid_column_type
-      assert_raise NoMethodError do
-        ActiveRecord::Schema.define(:version => 8) do
-          create_table :vegetables do |t|
-            t.unknown :color
-          end
-        end
-      end
+  def test_schema_subclass
+    Class.new(ActiveRecord::Schema).define(version: 9) do
+      create_table :fruits
     end
+    assert_nothing_raised { @connection.select_all "SELECT * FROM fruits" }
+  end
+
+  def test_normalize_version
+    assert_equal "118", ActiveRecord::SchemaMigration.normalize_migration_number("0000118")
+    assert_equal "002", ActiveRecord::SchemaMigration.normalize_migration_number("2")
+    assert_equal "017", ActiveRecord::SchemaMigration.normalize_migration_number("0017")
+    assert_equal "20131219224947", ActiveRecord::SchemaMigration.normalize_migration_number("20131219224947")
+  end
 
-    def test_schema_subclass
-      Class.new(ActiveRecord::Schema).define(:version => 9) do
-        create_table :fruits
+  def test_schema_load_with_multiple_indexes_for_column_of_different_names
+    ActiveRecord::Schema.define do
+      create_table :multiple_indexes do |t|
+        t.string "foo"
+        t.index ["foo"], name: "multiple_indexes_foo_1"
+        t.index ["foo"], name: "multiple_indexes_foo_2"
       end
-      assert_nothing_raised { @connection.select_all "SELECT * FROM fruits" }
     end
 
-    def test_normalize_version
-      assert_equal "118", ActiveRecord::SchemaMigration.normalize_migration_number("0000118")
-      assert_equal "002", ActiveRecord::SchemaMigration.normalize_migration_number("2")
-      assert_equal "017", ActiveRecord::SchemaMigration.normalize_migration_number("0017")
-      assert_equal "20131219224947", ActiveRecord::SchemaMigration.normalize_migration_number("20131219224947")
-    end
+    indexes = @connection.indexes("multiple_indexes")
 
-    def test_timestamps_without_null_set_null_to_false_on_create_table
-      ActiveRecord::Schema.define do
-        create_table :has_timestamps do |t|
-          t.timestamps
-        end
-      end
+    assert_equal 2, indexes.length
+    assert_equal ["multiple_indexes_foo_1", "multiple_indexes_foo_2"], indexes.collect(&:name).sort
+  end
 
-      assert !@connection.columns(:has_timestamps).find { |c| c.name == 'created_at' }.null
-      assert !@connection.columns(:has_timestamps).find { |c| c.name == 'updated_at' }.null
+  def test_timestamps_without_null_set_null_to_false_on_create_table
+    ActiveRecord::Schema.define do
+      create_table :has_timestamps do |t|
+        t.timestamps
+      end
     end
 
-    def test_timestamps_without_null_set_null_to_false_on_change_table
-      ActiveRecord::Schema.define do
-        create_table :has_timestamps
+    assert_not @connection.columns(:has_timestamps).find { |c| c.name == "created_at" }.null
+    assert_not @connection.columns(:has_timestamps).find { |c| c.name == "updated_at" }.null
+  end
 
-        change_table :has_timestamps do |t|
-          t.timestamps default: Time.now
-        end
-      end
+  def test_timestamps_without_null_set_null_to_false_on_change_table
+    ActiveRecord::Schema.define do
+      create_table :has_timestamps
 
-      assert !@connection.columns(:has_timestamps).find { |c| c.name == 'created_at' }.null
-      assert !@connection.columns(:has_timestamps).find { |c| c.name == 'updated_at' }.null
+      change_table :has_timestamps do |t|
+        t.timestamps default: Time.now
+      end
     end
 
-    def test_timestamps_without_null_set_null_to_false_on_add_timestamps
-      ActiveRecord::Schema.define do
-        create_table :has_timestamps
-        add_timestamps :has_timestamps, default: Time.now
-      end
+    assert_not @connection.columns(:has_timestamps).find { |c| c.name == "created_at" }.null
+    assert_not @connection.columns(:has_timestamps).find { |c| c.name == "updated_at" }.null
+  end
 
-      assert !@connection.columns(:has_timestamps).find { |c| c.name == 'created_at' }.null
-      assert !@connection.columns(:has_timestamps).find { |c| c.name == 'updated_at' }.null
+  def test_timestamps_without_null_set_null_to_false_on_add_timestamps
+    ActiveRecord::Schema.define do
+      create_table :has_timestamps
+      add_timestamps :has_timestamps, default: Time.now
     end
+
+    assert_not @connection.columns(:has_timestamps).find { |c| c.name == "created_at" }.null
+    assert_not @connection.columns(:has_timestamps).find { |c| c.name == "updated_at" }.null
   end
 end
diff --git a/activerecord/test/cases/arel/attributes/attribute_test.rb b/activerecord/test/cases/arel/attributes/attribute_test.rb
new file mode 100644
index 0000000000..671e273543
--- /dev/null
+++ b/activerecord/test/cases/arel/attributes/attribute_test.rb
@@ -0,0 +1,1015 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+require "ostruct"
+
+module Arel
+  module Attributes
+    class AttributeTest < Arel::Spec
+      describe "#not_eq" do
+        it "should create a NotEqual node" do
+          relation = Table.new(:users)
+          relation[:id].not_eq(10).must_be_kind_of Nodes::NotEqual
+        end
+
+        it "should generate != in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_eq(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" != 10
+          }
+        end
+
+        it "should handle nil" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_eq(nil)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" IS NOT NULL
+          }
+        end
+      end
+
+      describe "#not_eq_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].not_eq_any([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_eq_any([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" != 1 OR "users"."id" != 2)
+          }
+        end
+      end
+
+      describe "#not_eq_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].not_eq_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_eq_all([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" != 1 AND "users"."id" != 2)
+          }
+        end
+      end
+
+      describe "#gt" do
+        it "should create a GreaterThan node" do
+          relation = Table.new(:users)
+          relation[:id].gt(10).must_be_kind_of Nodes::GreaterThan
+        end
+
+        it "should generate > in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gt(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" > 10
+          }
+        end
+
+        it "should handle comparing with a subquery" do
+          users = Table.new(:users)
+
+          avg = users.project(users[:karma].average)
+          mgr = users.project(Arel.star).where(users[:karma].gt(avg))
+
+          mgr.to_sql.must_be_like %{
+            SELECT * FROM "users" WHERE "users"."karma" > (SELECT AVG("users"."karma") FROM "users")
+          }
+        end
+
+        it "should accept various data types." do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].gt("fake_name")
+          mgr.to_sql.must_match %{"users"."name" > 'fake_name'}
+
+          current_time = ::Time.now
+          mgr.where relation[:created_at].gt(current_time)
+          mgr.to_sql.must_match %{"users"."created_at" > '#{current_time}'}
+        end
+      end
+
+      describe "#gt_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].gt_any([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gt_any([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" > 1 OR "users"."id" > 2)
+          }
+        end
+      end
+
+      describe "#gt_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].gt_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gt_all([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" > 1 AND "users"."id" > 2)
+          }
+        end
+      end
+
+      describe "#gteq" do
+        it "should create a GreaterThanOrEqual node" do
+          relation = Table.new(:users)
+          relation[:id].gteq(10).must_be_kind_of Nodes::GreaterThanOrEqual
+        end
+
+        it "should generate >= in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gteq(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" >= 10
+          }
+        end
+
+        it "should accept various data types." do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].gteq("fake_name")
+          mgr.to_sql.must_match %{"users"."name" >= 'fake_name'}
+
+          current_time = ::Time.now
+          mgr.where relation[:created_at].gteq(current_time)
+          mgr.to_sql.must_match %{"users"."created_at" >= '#{current_time}'}
+        end
+      end
+
+      describe "#gteq_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].gteq_any([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gteq_any([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" >= 1 OR "users"."id" >= 2)
+          }
+        end
+      end
+
+      describe "#gteq_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].gteq_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].gteq_all([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" >= 1 AND "users"."id" >= 2)
+          }
+        end
+      end
+
+      describe "#lt" do
+        it "should create a LessThan node" do
+          relation = Table.new(:users)
+          relation[:id].lt(10).must_be_kind_of Nodes::LessThan
+        end
+
+        it "should generate < in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lt(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" < 10
+          }
+        end
+
+        it "should accept various data types." do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].lt("fake_name")
+          mgr.to_sql.must_match %{"users"."name" < 'fake_name'}
+
+          current_time = ::Time.now
+          mgr.where relation[:created_at].lt(current_time)
+          mgr.to_sql.must_match %{"users"."created_at" < '#{current_time}'}
+        end
+      end
+
+      describe "#lt_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].lt_any([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lt_any([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" < 1 OR "users"."id" < 2)
+          }
+        end
+      end
+
+      describe "#lt_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].lt_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lt_all([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" < 1 AND "users"."id" < 2)
+          }
+        end
+      end
+
+      describe "#lteq" do
+        it "should create a LessThanOrEqual node" do
+          relation = Table.new(:users)
+          relation[:id].lteq(10).must_be_kind_of Nodes::LessThanOrEqual
+        end
+
+        it "should generate <= in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lteq(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" <= 10
+          }
+        end
+
+        it "should accept various data types." do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].lteq("fake_name")
+          mgr.to_sql.must_match %{"users"."name" <= 'fake_name'}
+
+          current_time = ::Time.now
+          mgr.where relation[:created_at].lteq(current_time)
+          mgr.to_sql.must_match %{"users"."created_at" <= '#{current_time}'}
+        end
+      end
+
+      describe "#lteq_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].lteq_any([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lteq_any([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" <= 1 OR "users"."id" <= 2)
+          }
+        end
+      end
+
+      describe "#lteq_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].lteq_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].lteq_all([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" <= 1 AND "users"."id" <= 2)
+          }
+        end
+      end
+
+      describe "#average" do
+        it "should create a AVG node" do
+          relation = Table.new(:users)
+          relation[:id].average.must_be_kind_of Nodes::Avg
+        end
+
+        it "should generate the proper SQL" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].average
+          mgr.to_sql.must_be_like %{
+            SELECT AVG("users"."id")
+            FROM "users"
+          }
+        end
+      end
+
+      describe "#maximum" do
+        it "should create a MAX node" do
+          relation = Table.new(:users)
+          relation[:id].maximum.must_be_kind_of Nodes::Max
+        end
+
+        it "should generate proper SQL" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].maximum
+          mgr.to_sql.must_be_like %{
+            SELECT MAX("users"."id")
+            FROM "users"
+          }
+        end
+      end
+
+      describe "#minimum" do
+        it "should create a Min node" do
+          relation = Table.new(:users)
+          relation[:id].minimum.must_be_kind_of Nodes::Min
+        end
+
+        it "should generate proper SQL" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].minimum
+          mgr.to_sql.must_be_like %{
+            SELECT MIN("users"."id")
+            FROM "users"
+          }
+        end
+      end
+
+      describe "#sum" do
+        it "should create a SUM node" do
+          relation = Table.new(:users)
+          relation[:id].sum.must_be_kind_of Nodes::Sum
+        end
+
+        it "should generate the proper SQL" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id].sum
+          mgr.to_sql.must_be_like %{
+            SELECT SUM("users"."id")
+            FROM "users"
+          }
+        end
+      end
+
+      describe "#count" do
+        it "should return a count node" do
+          relation = Table.new(:users)
+          relation[:id].count.must_be_kind_of Nodes::Count
+        end
+
+        it "should take a distinct param" do
+          relation = Table.new(:users)
+          count = relation[:id].count(nil)
+          count.must_be_kind_of Nodes::Count
+          count.distinct.must_be_nil
+        end
+      end
+
+      describe "#eq" do
+        it "should return an equality node" do
+          attribute = Attribute.new nil, nil
+          equality = attribute.eq 1
+          equality.left.must_equal attribute
+          equality.right.val.must_equal 1
+          equality.must_be_kind_of Nodes::Equality
+        end
+
+        it "should generate = in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq(10)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" = 10
+          }
+        end
+
+        it "should handle nil" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq(nil)
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" IS NULL
+          }
+        end
+      end
+
+      describe "#eq_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].eq_any([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq_any([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" = 1 OR "users"."id" = 2)
+          }
+        end
+
+        it "should not eat input" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          values = [1, 2]
+          mgr.where relation[:id].eq_any(values)
+          values.must_equal [1, 2]
+        end
+      end
+
+      describe "#eq_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].eq_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq_all([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" = 1 AND "users"."id" = 2)
+          }
+        end
+
+        it "should not eat input" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          values = [1, 2]
+          mgr.where relation[:id].eq_all(values)
+          values.must_equal [1, 2]
+        end
+      end
+
+      describe "#matches" do
+        it "should create a Matches node" do
+          relation = Table.new(:users)
+          relation[:name].matches("%bacon%").must_be_kind_of Nodes::Matches
+        end
+
+        it "should generate LIKE in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].matches("%bacon%")
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."name" LIKE '%bacon%'
+          }
+        end
+      end
+
+      describe "#matches_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:name].matches_any(["%chunky%", "%bacon%"]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].matches_any(["%chunky%", "%bacon%"])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."name" LIKE '%chunky%' OR "users"."name" LIKE '%bacon%')
+          }
+        end
+      end
+
+      describe "#matches_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:name].matches_all(["%chunky%", "%bacon%"]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].matches_all(["%chunky%", "%bacon%"])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."name" LIKE '%chunky%' AND "users"."name" LIKE '%bacon%')
+          }
+        end
+      end
+
+      describe "#does_not_match" do
+        it "should create a DoesNotMatch node" do
+          relation = Table.new(:users)
+          relation[:name].does_not_match("%bacon%").must_be_kind_of Nodes::DoesNotMatch
+        end
+
+        it "should generate NOT LIKE in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match("%bacon%")
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."name" NOT LIKE '%bacon%'
+          }
+        end
+      end
+
+      describe "#does_not_match_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:name].does_not_match_any(["%chunky%", "%bacon%"]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match_any(["%chunky%", "%bacon%"])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."name" NOT LIKE '%chunky%' OR "users"."name" NOT LIKE '%bacon%')
+          }
+        end
+      end
+
+      describe "#does_not_match_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:name].does_not_match_all(["%chunky%", "%bacon%"]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match_all(["%chunky%", "%bacon%"])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."name" NOT LIKE '%chunky%' AND "users"."name" NOT LIKE '%bacon%')
+          }
+        end
+      end
+
+      describe "with a range" do
+        it "can be constructed with a standard range" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(1..3)
+
+          node.must_equal Nodes::Between.new(
+            attribute,
+            Nodes::And.new([
+              Nodes::Casted.new(1, attribute),
+              Nodes::Casted.new(3, attribute)
+            ])
+          )
+        end
+
+        it "can be constructed with a range starting from -Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(-::Float::INFINITY..3)
+
+          node.must_equal Nodes::LessThanOrEqual.new(
+            attribute,
+            Nodes::Casted.new(3, attribute)
+          )
+        end
+
+        it "can be constructed with a quoted range starting from -Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(quoted_range(-::Float::INFINITY, 3, false))
+
+          node.must_equal Nodes::LessThanOrEqual.new(
+            attribute,
+            Nodes::Quoted.new(3)
+          )
+        end
+
+        it "can be constructed with an exclusive range starting from -Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(-::Float::INFINITY...3)
+
+          node.must_equal Nodes::LessThan.new(
+            attribute,
+            Nodes::Casted.new(3, attribute)
+          )
+        end
+
+        it "can be constructed with a quoted exclusive range starting from -Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(quoted_range(-::Float::INFINITY, 3, true))
+
+          node.must_equal Nodes::LessThan.new(
+            attribute,
+            Nodes::Quoted.new(3)
+          )
+        end
+
+        it "can be constructed with an infinite range" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(-::Float::INFINITY..::Float::INFINITY)
+
+          node.must_equal Nodes::NotIn.new(attribute, [])
+        end
+
+        it "can be constructed with a quoted infinite range" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(quoted_range(-::Float::INFINITY, ::Float::INFINITY, false))
+
+          node.must_equal Nodes::NotIn.new(attribute, [])
+        end
+
+
+        it "can be constructed with a range ending at Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(0..::Float::INFINITY)
+
+          node.must_equal Nodes::GreaterThanOrEqual.new(
+            attribute,
+            Nodes::Casted.new(0, attribute)
+          )
+        end
+
+        it "can be constructed with a quoted range ending at Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(quoted_range(0, ::Float::INFINITY, false))
+
+          node.must_equal Nodes::GreaterThanOrEqual.new(
+            attribute,
+            Nodes::Quoted.new(0)
+          )
+        end
+
+        it "can be constructed with an exclusive range" do
+          attribute = Attribute.new nil, nil
+          node = attribute.between(0...3)
+
+          node.must_equal Nodes::And.new([
+            Nodes::GreaterThanOrEqual.new(
+              attribute,
+              Nodes::Casted.new(0, attribute)
+            ),
+            Nodes::LessThan.new(
+              attribute,
+              Nodes::Casted.new(3, attribute)
+            )
+          ])
+        end
+
+        def quoted_range(begin_val, end_val, exclude)
+          OpenStruct.new(
+            begin: Nodes::Quoted.new(begin_val),
+            end: Nodes::Quoted.new(end_val),
+            exclude_end?: exclude,
+          )
+        end
+      end
+
+      describe "#in" do
+        it "can be constructed with a subquery" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match_all(["%chunky%", "%bacon%"])
+          attribute = Attribute.new nil, nil
+
+          node = attribute.in(mgr)
+
+          node.must_equal Nodes::In.new(attribute, mgr.ast)
+        end
+
+        it "can be constructed with a list" do
+          attribute = Attribute.new nil, nil
+          node = attribute.in([1, 2, 3])
+
+          node.must_equal Nodes::In.new(
+            attribute,
+            [
+              Nodes::Casted.new(1, attribute),
+              Nodes::Casted.new(2, attribute),
+              Nodes::Casted.new(3, attribute),
+            ]
+          )
+        end
+
+        it "can be constructed with a random object" do
+          attribute = Attribute.new nil, nil
+          random_object = Object.new
+          node = attribute.in(random_object)
+
+          node.must_equal Nodes::In.new(
+            attribute,
+            Nodes::Casted.new(random_object, attribute)
+          )
+        end
+
+        it "should generate IN in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].in([1, 2, 3])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" IN (1, 2, 3)
+          }
+        end
+      end
+
+      describe "#in_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].in_any([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].in_any([[1, 2], [3, 4]])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" IN (1, 2) OR "users"."id" IN (3, 4))
+          }
+        end
+      end
+
+      describe "#in_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].in_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].in_all([[1, 2], [3, 4]])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" IN (1, 2) AND "users"."id" IN (3, 4))
+          }
+        end
+      end
+
+      describe "with a range" do
+        it "can be constructed with a standard range" do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(1..3)
+
+          node.must_equal Nodes::Grouping.new(Nodes::Or.new(
+                                                Nodes::LessThan.new(
+                                                  attribute,
+                                                  Nodes::Casted.new(1, attribute)
+                                                ),
+            Nodes::GreaterThan.new(
+              attribute,
+              Nodes::Casted.new(3, attribute)
+            )
+          ))
+        end
+
+        it "can be constructed with a range starting from -Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(-::Float::INFINITY..3)
+
+          node.must_equal Nodes::GreaterThan.new(
+            attribute,
+            Nodes::Casted.new(3, attribute)
+          )
+        end
+
+        it "can be constructed with an exclusive range starting from -Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(-::Float::INFINITY...3)
+
+          node.must_equal Nodes::GreaterThanOrEqual.new(
+            attribute,
+            Nodes::Casted.new(3, attribute)
+          )
+        end
+
+        it "can be constructed with an infinite range" do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(-::Float::INFINITY..::Float::INFINITY)
+
+          node.must_equal Nodes::In.new(attribute, [])
+        end
+
+        it "can be constructed with a range ending at Infinity" do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(0..::Float::INFINITY)
+
+          node.must_equal Nodes::LessThan.new(
+            attribute,
+            Nodes::Casted.new(0, attribute)
+          )
+        end
+
+        it "can be constructed with an exclusive range" do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_between(0...3)
+
+          node.must_equal Nodes::Grouping.new(Nodes::Or.new(
+                                                Nodes::LessThan.new(
+                                                  attribute,
+                                                  Nodes::Casted.new(0, attribute)
+                                                ),
+            Nodes::GreaterThanOrEqual.new(
+              attribute,
+              Nodes::Casted.new(3, attribute)
+            )
+          ))
+        end
+      end
+
+      describe "#not_in" do
+        it "can be constructed with a subquery" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:name].does_not_match_all(["%chunky%", "%bacon%"])
+          attribute = Attribute.new nil, nil
+
+          node = attribute.not_in(mgr)
+
+          node.must_equal Nodes::NotIn.new(attribute, mgr.ast)
+        end
+
+        it "can be constructed with a Union" do
+          relation = Table.new(:users)
+          mgr1 = relation.project(relation[:id])
+          mgr2 = relation.project(relation[:id])
+
+          union = mgr1.union(mgr2)
+          node = relation[:id].in(union)
+          node.to_sql.must_be_like %{
+            "users"."id" IN (( SELECT "users"."id" FROM "users" UNION SELECT "users"."id" FROM "users" ))
+          }
+        end
+
+        it "can be constructed with a list" do
+          attribute = Attribute.new nil, nil
+          node = attribute.not_in([1, 2, 3])
+
+          node.must_equal Nodes::NotIn.new(
+            attribute,
+            [
+              Nodes::Casted.new(1, attribute),
+              Nodes::Casted.new(2, attribute),
+              Nodes::Casted.new(3, attribute),
+            ]
+          )
+        end
+
+        it "can be constructed with a random object" do
+          attribute = Attribute.new nil, nil
+          random_object = Object.new
+          node = attribute.not_in(random_object)
+
+          node.must_equal Nodes::NotIn.new(
+            attribute,
+            Nodes::Casted.new(random_object, attribute)
+          )
+        end
+
+        it "should generate NOT IN in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_in([1, 2, 3])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE "users"."id" NOT IN (1, 2, 3)
+          }
+        end
+      end
+
+      describe "#not_in_any" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].not_in_any([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ORs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_in_any([[1, 2], [3, 4]])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" NOT IN (1, 2) OR "users"."id" NOT IN (3, 4))
+          }
+        end
+      end
+
+      describe "#not_in_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].not_in_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].not_in_all([[1, 2], [3, 4]])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" NOT IN (1, 2) AND "users"."id" NOT IN (3, 4))
+          }
+        end
+      end
+
+      describe "#eq_all" do
+        it "should create a Grouping node" do
+          relation = Table.new(:users)
+          relation[:id].eq_all([1, 2]).must_be_kind_of Nodes::Grouping
+        end
+
+        it "should generate ANDs in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.where relation[:id].eq_all([1, 2])
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" WHERE ("users"."id" = 1 AND "users"."id" = 2)
+          }
+        end
+      end
+
+      describe "#asc" do
+        it "should create an Ascending node" do
+          relation = Table.new(:users)
+          relation[:id].asc.must_be_kind_of Nodes::Ascending
+        end
+
+        it "should generate ASC in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.order relation[:id].asc
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" ORDER BY "users"."id" ASC
+          }
+        end
+      end
+
+      describe "#desc" do
+        it "should create a Descending node" do
+          relation = Table.new(:users)
+          relation[:id].desc.must_be_kind_of Nodes::Descending
+        end
+
+        it "should generate DESC in sql" do
+          relation = Table.new(:users)
+          mgr = relation.project relation[:id]
+          mgr.order relation[:id].desc
+          mgr.to_sql.must_be_like %{
+            SELECT "users"."id" FROM "users" ORDER BY "users"."id" DESC
+          }
+        end
+      end
+
+      describe "equality" do
+        describe "#to_sql" do
+          it "should produce sql" do
+            table = Table.new :users
+            condition = table["id"].eq 1
+            condition.to_sql.must_equal '"users"."id" = 1'
+          end
+        end
+      end
+
+      describe "type casting" do
+        it "does not type cast by default" do
+          table = Table.new(:foo)
+          condition = table["id"].eq("1")
+
+          assert_not table.able_to_type_cast?
+          condition.to_sql.must_equal %("foo"."id" = '1')
+        end
+
+        it "type casts when given an explicit caster" do
+          fake_caster = Object.new
+          def fake_caster.type_cast_for_database(attr_name, value)
+            if attr_name == "id"
+              value.to_i
+            else
+              value
+            end
+          end
+          table = Table.new(:foo, type_caster: fake_caster)
+          condition = table["id"].eq("1").and(table["other_id"].eq("2"))
+
+          assert table.able_to_type_cast?
+          condition.to_sql.must_equal %("foo"."id" = 1 AND "foo"."other_id" = '2')
+        end
+
+        it "does not type cast SqlLiteral nodes" do
+          fake_caster = Object.new
+          def fake_caster.type_cast_for_database(attr_name, value)
+            value.to_i
+          end
+          table = Table.new(:foo, type_caster: fake_caster)
+          condition = table["id"].eq(Arel.sql("(select 1)"))
+
+          assert table.able_to_type_cast?
+          condition.to_sql.must_equal %("foo"."id" = (select 1))
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/attributes/math_test.rb b/activerecord/test/cases/arel/attributes/math_test.rb
new file mode 100644
index 0000000000..41eea217c0
--- /dev/null
+++ b/activerecord/test/cases/arel/attributes/math_test.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Attributes
+    class MathTest < Arel::Spec
+      %i[* /].each do |math_operator|
+        it "average should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].average.public_send(math_operator, 2)).to_sql.must_be_like %{
+            AVG("users"."id") #{math_operator} 2
+          }
+        end
+
+        it "count should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].count.public_send(math_operator, 2)).to_sql.must_be_like %{
+            COUNT("users"."id") #{math_operator} 2
+          }
+        end
+
+        it "maximum should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].maximum.public_send(math_operator, 2)).to_sql.must_be_like %{
+            MAX("users"."id") #{math_operator} 2
+          }
+        end
+
+        it "minimum should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].minimum.public_send(math_operator, 2)).to_sql.must_be_like %{
+            MIN("users"."id") #{math_operator} 2
+          }
+        end
+
+        it "attribute node should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].public_send(math_operator, 2)).to_sql.must_be_like %{
+            "users"."id" #{math_operator} 2
+          }
+        end
+      end
+
+      %i[+ - & | ^ << >>].each do |math_operator|
+        it "average should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].average.public_send(math_operator, 2)).to_sql.must_be_like %{
+            (AVG("users"."id") #{math_operator} 2)
+          }
+        end
+
+        it "count should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].count.public_send(math_operator, 2)).to_sql.must_be_like %{
+            (COUNT("users"."id") #{math_operator} 2)
+          }
+        end
+
+        it "maximum should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].maximum.public_send(math_operator, 2)).to_sql.must_be_like %{
+            (MAX("users"."id") #{math_operator} 2)
+          }
+        end
+
+        it "minimum should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].minimum.public_send(math_operator, 2)).to_sql.must_be_like %{
+            (MIN("users"."id") #{math_operator} 2)
+          }
+        end
+
+        it "attribute node should be compatible with #{math_operator}" do
+          table = Arel::Table.new :users
+          (table[:id].public_send(math_operator, 2)).to_sql.must_be_like %{
+            ("users"."id" #{math_operator} 2)
+          }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/attributes_test.rb b/activerecord/test/cases/arel/attributes_test.rb
new file mode 100644
index 0000000000..b00af4bd29
--- /dev/null
+++ b/activerecord/test/cases/arel/attributes_test.rb
@@ -0,0 +1,68 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  describe "Attributes" do
+    it "responds to lower" do
+      relation  = Table.new(:users)
+      attribute = relation[:foo]
+      node      = attribute.lower
+      assert_equal "LOWER", node.name
+      assert_equal [attribute], node.expressions
+    end
+
+    describe "equality" do
+      it "is equal with equal ivars" do
+        array = [Attribute.new("foo", "bar"), Attribute.new("foo", "bar")]
+        assert_equal 1, array.uniq.size
+      end
+
+      it "is not equal with different ivars" do
+        array = [Attribute.new("foo", "bar"), Attribute.new("foo", "baz")]
+        assert_equal 2, array.uniq.size
+      end
+    end
+
+    describe "for" do
+      it "deals with unknown column types" do
+        column = Struct.new(:type).new :crazy
+        Attributes.for(column).must_equal Attributes::Undefined
+      end
+
+      it "returns the correct constant for strings" do
+        [:string, :text, :binary].each do |type|
+          column = Struct.new(:type).new type
+          Attributes.for(column).must_equal Attributes::String
+        end
+      end
+
+      it "returns the correct constant for ints" do
+        column = Struct.new(:type).new :integer
+        Attributes.for(column).must_equal Attributes::Integer
+      end
+
+      it "returns the correct constant for floats" do
+        column = Struct.new(:type).new :float
+        Attributes.for(column).must_equal Attributes::Float
+      end
+
+      it "returns the correct constant for decimals" do
+        column = Struct.new(:type).new :decimal
+        Attributes.for(column).must_equal Attributes::Decimal
+      end
+
+      it "returns the correct constant for boolean" do
+        column = Struct.new(:type).new :boolean
+        Attributes.for(column).must_equal Attributes::Boolean
+      end
+
+      it "returns the correct constant for time" do
+        [:date, :datetime, :timestamp, :time].each do |type|
+          column = Struct.new(:type).new type
+          Attributes.for(column).must_equal Attributes::Time
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/collectors/bind_test.rb b/activerecord/test/cases/arel/collectors/bind_test.rb
new file mode 100644
index 0000000000..ffa9b15f66
--- /dev/null
+++ b/activerecord/test/cases/arel/collectors/bind_test.rb
@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+require "arel/collectors/bind"
+
+module Arel
+  module Collectors
+    class TestBind < Arel::Test
+      def setup
+        @conn = FakeRecord::Base.new
+        @visitor = Visitors::ToSql.new @conn.connection
+        super
+      end
+
+      def collect(node)
+        @visitor.accept(node, Collectors::Bind.new)
+      end
+
+      def compile(node)
+        collect(node).value
+      end
+
+      def ast_with_binds(bvs)
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.where(table[:age].eq(Nodes::BindParam.new(bvs.shift)))
+        manager.where(table[:name].eq(Nodes::BindParam.new(bvs.shift)))
+        manager.ast
+      end
+
+      def test_compile_gathers_all_bind_params
+        binds = compile(ast_with_binds(["hello", "world"]))
+        assert_equal ["hello", "world"], binds
+
+        binds = compile(ast_with_binds(["hello2", "world3"]))
+        assert_equal ["hello2", "world3"], binds
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/collectors/composite_test.rb b/activerecord/test/cases/arel/collectors/composite_test.rb
new file mode 100644
index 0000000000..545637496f
--- /dev/null
+++ b/activerecord/test/cases/arel/collectors/composite_test.rb
@@ -0,0 +1,47 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+require "arel/collectors/bind"
+require "arel/collectors/composite"
+
+module Arel
+  module Collectors
+    class TestComposite < Arel::Test
+      def setup
+        @conn = FakeRecord::Base.new
+        @visitor = Visitors::ToSql.new @conn.connection
+        super
+      end
+
+      def collect(node)
+        sql_collector = Collectors::SQLString.new
+        bind_collector = Collectors::Bind.new
+        collector = Collectors::Composite.new(sql_collector, bind_collector)
+        @visitor.accept(node, collector)
+      end
+
+      def compile(node)
+        collect(node).value
+      end
+
+      def ast_with_binds(bvs)
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.where(table[:age].eq(Nodes::BindParam.new(bvs.shift)))
+        manager.where(table[:name].eq(Nodes::BindParam.new(bvs.shift)))
+        manager.ast
+      end
+
+      def test_composite_collector_performs_multiple_collections_at_once
+        sql, binds = compile(ast_with_binds(["hello", "world"]))
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = ? AND "users"."name" = ?', sql
+        assert_equal ["hello", "world"], binds
+
+        sql, binds = compile(ast_with_binds(["hello2", "world3"]))
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = ? AND "users"."name" = ?', sql
+        assert_equal ["hello2", "world3"], binds
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/collectors/sql_string_test.rb b/activerecord/test/cases/arel/collectors/sql_string_test.rb
new file mode 100644
index 0000000000..443c7eb54b
--- /dev/null
+++ b/activerecord/test/cases/arel/collectors/sql_string_test.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Collectors
+    class TestSqlString < Arel::Test
+      def setup
+        @conn = FakeRecord::Base.new
+        @visitor = Visitors::ToSql.new @conn.connection
+        super
+      end
+
+      def collect(node)
+        @visitor.accept(node, Collectors::SQLString.new)
+      end
+
+      def compile(node)
+        collect(node).value
+      end
+
+      def ast_with_binds
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.where(table[:age].eq(Nodes::BindParam.new("hello")))
+        manager.where(table[:name].eq(Nodes::BindParam.new("world")))
+        manager.ast
+      end
+
+      def test_compile
+        sql = compile(ast_with_binds)
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = ? AND "users"."name" = ?', sql
+      end
+
+      def test_returned_sql_uses_utf8_encoding
+        sql = compile(ast_with_binds)
+        assert_equal sql.encoding, Encoding::UTF_8
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/collectors/substitute_bind_collector_test.rb b/activerecord/test/cases/arel/collectors/substitute_bind_collector_test.rb
new file mode 100644
index 0000000000..255c8e79e9
--- /dev/null
+++ b/activerecord/test/cases/arel/collectors/substitute_bind_collector_test.rb
@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+require "arel/collectors/substitute_binds"
+require "arel/collectors/sql_string"
+
+module Arel
+  module Collectors
+    class TestSubstituteBindCollector < Arel::Test
+      def setup
+        @conn = FakeRecord::Base.new
+        @visitor = Visitors::ToSql.new @conn.connection
+        super
+      end
+
+      def ast_with_binds
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.where(table[:age].eq(Nodes::BindParam.new("hello")))
+        manager.where(table[:name].eq(Nodes::BindParam.new("world")))
+        manager.ast
+      end
+
+      def compile(node, quoter)
+        collector = Collectors::SubstituteBinds.new(quoter, Collectors::SQLString.new)
+        @visitor.accept(node, collector).value
+      end
+
+      def test_compile
+        quoter = Object.new
+        def quoter.quote(val)
+          val.to_s
+        end
+        sql = compile(ast_with_binds, quoter)
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = hello AND "users"."name" = world', sql
+      end
+
+      def test_quoting_is_delegated_to_quoter
+        quoter = Object.new
+        def quoter.quote(val)
+          val.inspect
+        end
+        sql = compile(ast_with_binds, quoter)
+        assert_equal 'SELECT FROM "users" WHERE "users"."age" = "hello" AND "users"."name" = "world"', sql
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/crud_test.rb b/activerecord/test/cases/arel/crud_test.rb
new file mode 100644
index 0000000000..f3cdd8927f
--- /dev/null
+++ b/activerecord/test/cases/arel/crud_test.rb
@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  class FakeCrudder < SelectManager
+    class FakeEngine
+      attr_reader :calls, :connection_pool, :spec, :config
+
+      def initialize
+        @calls = []
+        @connection_pool = self
+        @spec = self
+        @config = { adapter: "sqlite3" }
+      end
+
+      def connection; self end
+
+      def method_missing(name, *args)
+        @calls << [name, args]
+      end
+    end
+
+    include Crud
+
+    attr_reader :engine
+    attr_accessor :ctx
+
+    def initialize(engine = FakeEngine.new)
+      super
+    end
+  end
+
+  describe "crud" do
+    describe "insert" do
+      it "should call insert on the connection" do
+        table = Table.new :users
+        fc = FakeCrudder.new
+        fc.from table
+        im = fc.compile_insert [[table[:id], "foo"]]
+        assert_instance_of Arel::InsertManager, im
+      end
+    end
+
+    describe "update" do
+      it "should call update on the connection" do
+        table = Table.new :users
+        fc = FakeCrudder.new
+        fc.from table
+        stmt = fc.compile_update [[table[:id], "foo"]], Arel::Attributes::Attribute.new(table, "id")
+        assert_instance_of Arel::UpdateManager, stmt
+      end
+    end
+
+    describe "delete" do
+      it "should call delete on the connection" do
+        table = Table.new :users
+        fc = FakeCrudder.new
+        fc.from table
+        stmt = fc.compile_delete
+        assert_instance_of Arel::DeleteManager, stmt
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/delete_manager_test.rb b/activerecord/test/cases/arel/delete_manager_test.rb
new file mode 100644
index 0000000000..0bad02f4d2
--- /dev/null
+++ b/activerecord/test/cases/arel/delete_manager_test.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  class DeleteManagerTest < Arel::Spec
+    describe "new" do
+      it "takes an engine" do
+        Arel::DeleteManager.new
+      end
+    end
+
+    it "handles limit properly" do
+      table = Table.new(:users)
+      dm = Arel::DeleteManager.new
+      dm.take 10
+      dm.from table
+      dm.key = table[:id]
+      assert_match(/LIMIT 10/, dm.to_sql)
+    end
+
+    describe "from" do
+      it "uses from" do
+        table = Table.new(:users)
+        dm = Arel::DeleteManager.new
+        dm.from table
+        dm.to_sql.must_be_like %{ DELETE FROM "users" }
+      end
+
+      it "chains" do
+        table = Table.new(:users)
+        dm = Arel::DeleteManager.new
+        dm.from(table).must_equal dm
+      end
+    end
+
+    describe "where" do
+      it "uses where values" do
+        table = Table.new(:users)
+        dm = Arel::DeleteManager.new
+        dm.from table
+        dm.where table[:id].eq(10)
+        dm.to_sql.must_be_like %{ DELETE FROM "users" WHERE "users"."id" = 10}
+      end
+
+      it "chains" do
+        table = Table.new(:users)
+        dm = Arel::DeleteManager.new
+        dm.where(table[:id].eq(10)).must_equal dm
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/factory_methods_test.rb b/activerecord/test/cases/arel/factory_methods_test.rb
new file mode 100644
index 0000000000..26d2cdd08d
--- /dev/null
+++ b/activerecord/test/cases/arel/factory_methods_test.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  module FactoryMethods
+    class TestFactoryMethods < Arel::Test
+      class Factory
+        include Arel::FactoryMethods
+      end
+
+      def setup
+        @factory = Factory.new
+      end
+
+      def test_create_join
+        join = @factory.create_join :one, :two
+        assert_kind_of Nodes::Join, join
+        assert_equal :two, join.right
+      end
+
+      def test_create_on
+        on = @factory.create_on :one
+        assert_instance_of Nodes::On, on
+        assert_equal :one, on.expr
+      end
+
+      def test_create_true
+        true_node = @factory.create_true
+        assert_instance_of Nodes::True, true_node
+      end
+
+      def test_create_false
+        false_node = @factory.create_false
+        assert_instance_of Nodes::False, false_node
+      end
+
+      def test_lower
+        lower = @factory.lower :one
+        assert_instance_of Nodes::NamedFunction, lower
+        assert_equal "LOWER", lower.name
+        assert_equal [:one], lower.expressions.map(&:expr)
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/helper.rb b/activerecord/test/cases/arel/helper.rb
new file mode 100644
index 0000000000..f8ce658440
--- /dev/null
+++ b/activerecord/test/cases/arel/helper.rb
@@ -0,0 +1,45 @@
+# frozen_string_literal: true
+
+require "active_support"
+require "minitest/autorun"
+require "arel"
+
+require_relative "support/fake_record"
+
+class Object
+  def must_be_like(other)
+    gsub(/\s+/, " ").strip.must_equal other.gsub(/\s+/, " ").strip
+  end
+end
+
+module Arel
+  class Test < ActiveSupport::TestCase
+    def setup
+      super
+      @arel_engine = Arel::Table.engine
+      Arel::Table.engine = FakeRecord::Base.new
+    end
+
+    def teardown
+      Arel::Table.engine = @arel_engine if defined? @arel_engine
+      super
+    end
+  end
+
+  class Spec < Minitest::Spec
+    before do
+      @arel_engine = Arel::Table.engine
+      Arel::Table.engine = FakeRecord::Base.new
+    end
+
+    after do
+      Arel::Table.engine = @arel_engine if defined? @arel_engine
+    end
+    include ActiveSupport::Testing::Assertions
+
+    # test/unit backwards compatibility methods
+    alias :assert_no_match :refute_match
+    alias :assert_not_equal :refute_equal
+    alias :assert_not_same :refute_same
+  end
+end
diff --git a/activerecord/test/cases/arel/insert_manager_test.rb b/activerecord/test/cases/arel/insert_manager_test.rb
new file mode 100644
index 0000000000..2376ad8d37
--- /dev/null
+++ b/activerecord/test/cases/arel/insert_manager_test.rb
@@ -0,0 +1,242 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  class InsertManagerTest < Arel::Spec
+    describe "new" do
+      it "takes an engine" do
+        Arel::InsertManager.new
+      end
+    end
+
+    describe "insert" do
+      it "can create a Values node" do
+        manager = Arel::InsertManager.new
+        values  = manager.create_values %w{ a b }, %w{ c d }
+
+        assert_kind_of Arel::Nodes::Values, values
+        assert_equal %w{ a b }, values.left
+        assert_equal %w{ c d }, values.right
+      end
+
+      it "allows sql literals" do
+        manager = Arel::InsertManager.new
+        manager.into Table.new(:users)
+        manager.values = manager.create_values [Arel.sql("*")], %w{ a }
+        manager.to_sql.must_be_like %{
+          INSERT INTO \"users\" VALUES (*)
+        }
+      end
+
+      it "works with multiple values" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.columns << table[:id]
+        manager.columns << table[:name]
+
+        manager.values = manager.create_values_list([
+          %w{1 david},
+          %w{2 kir},
+          ["3", Arel.sql("DEFAULT")],
+        ])
+
+        manager.to_sql.must_be_like %{
+          INSERT INTO \"users\" (\"id\", \"name\") VALUES ('1', 'david'), ('2', 'kir'), ('3', DEFAULT)
+        }
+      end
+
+      it "literals in multiple values are not escaped" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.columns << table[:name]
+
+        manager.values = manager.create_values_list([
+          [Arel.sql("*")],
+          [Arel.sql("DEFAULT")],
+        ])
+
+        manager.to_sql.must_be_like %{
+          INSERT INTO \"users\" (\"name\") VALUES (*), (DEFAULT)
+        }
+      end
+
+      it "works with multiple single values" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.columns << table[:name]
+
+        manager.values = manager.create_values_list([
+          %w{david},
+          %w{kir},
+          [Arel.sql("DEFAULT")],
+        ])
+
+        manager.to_sql.must_be_like %{
+          INSERT INTO \"users\" (\"name\") VALUES ('david'), ('kir'), (DEFAULT)
+        }
+      end
+
+      it "inserts false" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+
+        manager.insert [[table[:bool], false]]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("bool") VALUES ('f')
+        }
+      end
+
+      it "inserts null" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.insert [[table[:id], nil]]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id") VALUES (NULL)
+        }
+      end
+
+      it "inserts time" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+
+        time = Time.now
+        attribute = table[:created_at]
+
+        manager.insert [[attribute, time]]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("created_at") VALUES (#{Table.engine.connection.quote time})
+        }
+      end
+
+      it "takes a list of lists" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.into table
+        manager.insert [[table[:id], 1], [table[:name], "aaron"]]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id", "name") VALUES (1, 'aaron')
+        }
+      end
+
+      it "defaults the table" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.insert [[table[:id], 1], [table[:name], "aaron"]]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id", "name") VALUES (1, 'aaron')
+        }
+      end
+
+      it "noop for empty list" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        manager.insert [[table[:id], 1]]
+        manager.insert []
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id") VALUES (1)
+        }
+      end
+
+      it "is chainable" do
+        table = Table.new(:users)
+        manager = Arel::InsertManager.new
+        insert_result = manager.insert [[table[:id], 1]]
+        assert_equal manager, insert_result
+      end
+    end
+
+    describe "into" do
+      it "takes a Table and chains" do
+        manager = Arel::InsertManager.new
+        manager.into(Table.new(:users)).must_equal manager
+      end
+
+      it "converts to sql" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users"
+        }
+      end
+    end
+
+    describe "columns" do
+      it "converts to sql" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+        manager.columns << table[:id]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id")
+        }
+      end
+    end
+
+    describe "values" do
+      it "converts to sql" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.values = Nodes::Values.new [1]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" VALUES (1)
+        }
+      end
+
+      it "accepts sql literals" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.values = Arel.sql("DEFAULT VALUES")
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" DEFAULT VALUES
+        }
+      end
+    end
+
+    describe "combo" do
+      it "combines columns and values list in order" do
+        table   = Table.new :users
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        manager.values = Nodes::Values.new [1, "aaron"]
+        manager.columns << table[:id]
+        manager.columns << table[:name]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id", "name") VALUES (1, 'aaron')
+        }
+      end
+    end
+
+    describe "select" do
+      it "accepts a select query in place of a VALUES clause" do
+        table   = Table.new :users
+
+        manager = Arel::InsertManager.new
+        manager.into table
+
+        select = Arel::SelectManager.new
+        select.project Arel.sql("1")
+        select.project Arel.sql('"aaron"')
+
+        manager.select select
+        manager.columns << table[:id]
+        manager.columns << table[:name]
+        manager.to_sql.must_be_like %{
+          INSERT INTO "users" ("id", "name") (SELECT 1, "aaron")
+        }
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/and_test.rb b/activerecord/test/cases/arel/nodes/and_test.rb
new file mode 100644
index 0000000000..eff54abd91
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/and_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "And" do
+      describe "equality" do
+        it "is equal with equal ivars" do
+          array = [And.new(["foo", "bar"]), And.new(["foo", "bar"])]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different ivars" do
+          array = [And.new(["foo", "bar"]), And.new(["foo", "baz"])]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/as_test.rb b/activerecord/test/cases/arel/nodes/as_test.rb
new file mode 100644
index 0000000000..1169ea11c9
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/as_test.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "As" do
+      describe "#as" do
+        it "makes an AS node" do
+          attr = Table.new(:users)[:id]
+          as = attr.as(Arel.sql("foo"))
+          assert_equal attr, as.left
+          assert_equal "foo", as.right
+        end
+
+        it "converts right to SqlLiteral if a string" do
+          attr = Table.new(:users)[:id]
+          as = attr.as("foo")
+          assert_kind_of Arel::Nodes::SqlLiteral, as.right
+        end
+      end
+
+      describe "equality" do
+        it "is equal with equal ivars" do
+          array = [As.new("foo", "bar"), As.new("foo", "bar")]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different ivars" do
+          array = [As.new("foo", "bar"), As.new("foo", "baz")]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/ascending_test.rb b/activerecord/test/cases/arel/nodes/ascending_test.rb
new file mode 100644
index 0000000000..4811e6ff5b
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/ascending_test.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class TestAscending < Arel::Test
+      def test_construct
+        ascending = Ascending.new "zomg"
+        assert_equal "zomg", ascending.expr
+      end
+
+      def test_reverse
+        ascending = Ascending.new "zomg"
+        descending = ascending.reverse
+        assert_kind_of Descending, descending
+        assert_equal ascending.expr, descending.expr
+      end
+
+      def test_direction
+        ascending = Ascending.new "zomg"
+        assert_equal :asc, ascending.direction
+      end
+
+      def test_ascending?
+        ascending = Ascending.new "zomg"
+        assert ascending.ascending?
+      end
+
+      def test_descending?
+        ascending = Ascending.new "zomg"
+        assert_not ascending.descending?
+      end
+
+      def test_equality_with_same_ivars
+        array = [Ascending.new("zomg"), Ascending.new("zomg")]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [Ascending.new("zomg"), Ascending.new("zomg!")]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/bin_test.rb b/activerecord/test/cases/arel/nodes/bin_test.rb
new file mode 100644
index 0000000000..ee2ec3cf2f
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/bin_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class TestBin < Arel::Test
+      def test_new
+        assert Arel::Nodes::Bin.new("zomg")
+      end
+
+      def test_default_to_sql
+        viz  = Arel::Visitors::ToSql.new Table.engine.connection_pool
+        node = Arel::Nodes::Bin.new(Arel.sql("zomg"))
+        assert_equal "zomg", viz.accept(node, Collectors::SQLString.new).value
+      end
+
+      def test_mysql_to_sql
+        viz  = Arel::Visitors::MySQL.new Table.engine.connection_pool
+        node = Arel::Nodes::Bin.new(Arel.sql("zomg"))
+        assert_equal "BINARY zomg", viz.accept(node, Collectors::SQLString.new).value
+      end
+
+      def test_equality_with_same_ivars
+        array = [Bin.new("zomg"), Bin.new("zomg")]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [Bin.new("zomg"), Bin.new("zomg!")]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/binary_test.rb b/activerecord/test/cases/arel/nodes/binary_test.rb
new file mode 100644
index 0000000000..d160e7cd9d
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/binary_test.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class NodesTest < Arel::Spec
+      describe "Binary" do
+        describe "#hash" do
+          it "generates a hash based on its value" do
+            eq = Equality.new("foo", "bar")
+            eq2 = Equality.new("foo", "bar")
+            eq3 = Equality.new("bar", "baz")
+
+            assert_equal eq.hash, eq2.hash
+            assert_not_equal eq.hash, eq3.hash
+          end
+
+          it "generates a hash specific to its class" do
+            eq = Equality.new("foo", "bar")
+            neq = NotEqual.new("foo", "bar")
+
+            assert_not_equal eq.hash, neq.hash
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/bind_param_test.rb b/activerecord/test/cases/arel/nodes/bind_param_test.rb
new file mode 100644
index 0000000000..37a362ece4
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/bind_param_test.rb
@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "BindParam" do
+      it "is equal to other bind params with the same value" do
+        BindParam.new(1).must_equal(BindParam.new(1))
+        BindParam.new("foo").must_equal(BindParam.new("foo"))
+      end
+
+      it "is not equal to other nodes" do
+        BindParam.new(nil).wont_equal(Node.new)
+      end
+
+      it "is not equal to bind params with different values" do
+        BindParam.new(1).wont_equal(BindParam.new(2))
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/case_test.rb b/activerecord/test/cases/arel/nodes/case_test.rb
new file mode 100644
index 0000000000..89861488df
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/case_test.rb
@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class NodesTest < Arel::Spec
+      describe "Case" do
+        describe "#initialize" do
+          it "sets case expression from first argument" do
+            node = Case.new "foo"
+
+            assert_equal "foo", node.case
+          end
+
+          it "sets default case from second argument" do
+            node = Case.new nil, "bar"
+
+            assert_equal "bar", node.default
+          end
+        end
+
+        describe "#clone" do
+          it "clones case, conditions and default" do
+            foo = Nodes.build_quoted "foo"
+
+            node = Case.new
+            node.case = foo
+            node.conditions = [When.new(foo, foo)]
+            node.default = foo
+
+            dolly = node.clone
+
+            assert_equal dolly.case, node.case
+            assert_not_same dolly.case, node.case
+
+            assert_equal dolly.conditions, node.conditions
+            assert_not_same dolly.conditions, node.conditions
+
+            assert_equal dolly.default, node.default
+            assert_not_same dolly.default, node.default
+          end
+        end
+
+        describe "equality" do
+          it "is equal with equal ivars" do
+            foo = Nodes.build_quoted "foo"
+            one = Nodes.build_quoted 1
+            zero = Nodes.build_quoted 0
+
+            case1 = Case.new foo
+            case1.conditions = [When.new(foo, one)]
+            case1.default = Else.new zero
+
+            case2 = Case.new foo
+            case2.conditions = [When.new(foo, one)]
+            case2.default = Else.new zero
+
+            array = [case1, case2]
+
+            assert_equal 1, array.uniq.size
+          end
+
+          it "is not equal with different ivars" do
+            foo = Nodes.build_quoted "foo"
+            bar = Nodes.build_quoted "bar"
+            one = Nodes.build_quoted 1
+            zero = Nodes.build_quoted 0
+
+            case1 = Case.new foo
+            case1.conditions = [When.new(foo, one)]
+            case1.default = Else.new zero
+
+            case2 = Case.new foo
+            case2.conditions = [When.new(bar, one)]
+            case2.default = Else.new zero
+
+            array = [case1, case2]
+
+            assert_equal 2, array.uniq.size
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/casted_test.rb b/activerecord/test/cases/arel/nodes/casted_test.rb
new file mode 100644
index 0000000000..e27f58a4e2
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/casted_test.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe Casted do
+      describe "#hash" do
+        it "is equal when eql? returns true" do
+          one = Casted.new 1, 2
+          also_one = Casted.new 1, 2
+
+          assert_equal one.hash, also_one.hash
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/count_test.rb b/activerecord/test/cases/arel/nodes/count_test.rb
new file mode 100644
index 0000000000..daabea6c4c
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/count_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+class Arel::Nodes::CountTest < Arel::Spec
+  describe "as" do
+    it "should alias the count" do
+      table = Arel::Table.new :users
+      table[:id].count.as("foo").to_sql.must_be_like %{
+        COUNT("users"."id") AS foo
+      }
+    end
+  end
+
+  describe "eq" do
+    it "should compare the count" do
+      table = Arel::Table.new :users
+      table[:id].count.eq(2).to_sql.must_be_like %{
+        COUNT("users"."id") = 2
+      }
+    end
+  end
+
+  describe "equality" do
+    it "is equal with equal ivars" do
+      array = [Arel::Nodes::Count.new("foo"), Arel::Nodes::Count.new("foo")]
+      assert_equal 1, array.uniq.size
+    end
+
+    it "is not equal with different ivars" do
+      array = [Arel::Nodes::Count.new("foo"), Arel::Nodes::Count.new("foo!")]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/delete_statement_test.rb b/activerecord/test/cases/arel/nodes/delete_statement_test.rb
new file mode 100644
index 0000000000..3f078063a4
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/delete_statement_test.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+describe Arel::Nodes::DeleteStatement do
+  describe "#clone" do
+    it "clones wheres" do
+      statement = Arel::Nodes::DeleteStatement.new
+      statement.wheres = %w[a b c]
+
+      dolly = statement.clone
+      dolly.wheres.must_equal statement.wheres
+      dolly.wheres.wont_be_same_as statement.wheres
+    end
+  end
+
+  describe "equality" do
+    it "is equal with equal ivars" do
+      statement1 = Arel::Nodes::DeleteStatement.new
+      statement1.wheres = %w[a b c]
+      statement2 = Arel::Nodes::DeleteStatement.new
+      statement2.wheres = %w[a b c]
+      array = [statement1, statement2]
+      assert_equal 1, array.uniq.size
+    end
+
+    it "is not equal with different ivars" do
+      statement1 = Arel::Nodes::DeleteStatement.new
+      statement1.wheres = %w[a b c]
+      statement2 = Arel::Nodes::DeleteStatement.new
+      statement2.wheres = %w[1 2 3]
+      array = [statement1, statement2]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/descending_test.rb b/activerecord/test/cases/arel/nodes/descending_test.rb
new file mode 100644
index 0000000000..5f1747e1da
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/descending_test.rb
@@ -0,0 +1,46 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class TestDescending < Arel::Test
+      def test_construct
+        descending = Descending.new "zomg"
+        assert_equal "zomg", descending.expr
+      end
+
+      def test_reverse
+        descending = Descending.new "zomg"
+        ascending = descending.reverse
+        assert_kind_of Ascending, ascending
+        assert_equal descending.expr, ascending.expr
+      end
+
+      def test_direction
+        descending = Descending.new "zomg"
+        assert_equal :desc, descending.direction
+      end
+
+      def test_ascending?
+        descending = Descending.new "zomg"
+        assert_not descending.ascending?
+      end
+
+      def test_descending?
+        descending = Descending.new "zomg"
+        assert descending.descending?
+      end
+
+      def test_equality_with_same_ivars
+        array = [Descending.new("zomg"), Descending.new("zomg")]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [Descending.new("zomg"), Descending.new("zomg!")]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/distinct_test.rb b/activerecord/test/cases/arel/nodes/distinct_test.rb
new file mode 100644
index 0000000000..de5f0ee588
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/distinct_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "Distinct" do
+      describe "equality" do
+        it "is equal to other distinct nodes" do
+          array = [Distinct.new, Distinct.new]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with other nodes" do
+          array = [Distinct.new, Node.new]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/equality_test.rb b/activerecord/test/cases/arel/nodes/equality_test.rb
new file mode 100644
index 0000000000..e173720e86
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/equality_test.rb
@@ -0,0 +1,86 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "equality" do
+      # FIXME: backwards compat
+      describe "backwards compat" do
+        describe "operator" do
+          it "returns :==" do
+            attr = Table.new(:users)[:id]
+            left = attr.eq(10)
+            left.operator.must_equal :==
+          end
+        end
+
+        describe "operand1" do
+          it "should equal left" do
+            attr = Table.new(:users)[:id]
+            left = attr.eq(10)
+            left.left.must_equal left.operand1
+          end
+        end
+
+        describe "operand2" do
+          it "should equal right" do
+            attr = Table.new(:users)[:id]
+            left = attr.eq(10)
+            left.right.must_equal left.operand2
+          end
+        end
+
+        describe "to_sql" do
+          it "takes an engine" do
+            engine = FakeRecord::Base.new
+            engine.connection.extend Module.new {
+              attr_accessor :quote_count
+              def quote(*args) @quote_count += 1; super; end
+              def quote_column_name(*args) @quote_count += 1; super; end
+              def quote_table_name(*args) @quote_count += 1; super; end
+            }
+            engine.connection.quote_count = 0
+
+            attr = Table.new(:users)[:id]
+            test = attr.eq(10)
+            test.to_sql engine
+            engine.connection.quote_count.must_equal 3
+          end
+        end
+      end
+
+      describe "or" do
+        it "makes an OR node" do
+          attr = Table.new(:users)[:id]
+          left  = attr.eq(10)
+          right = attr.eq(11)
+          node  = left.or right
+          node.expr.left.must_equal left
+          node.expr.right.must_equal right
+        end
+      end
+
+      describe "and" do
+        it "makes and AND node" do
+          attr = Table.new(:users)[:id]
+          left  = attr.eq(10)
+          right = attr.eq(11)
+          node  = left.and right
+          node.left.must_equal left
+          node.right.must_equal right
+        end
+      end
+
+      it "is equal with equal ivars" do
+        array = [Equality.new("foo", "bar"), Equality.new("foo", "bar")]
+        assert_equal 1, array.uniq.size
+      end
+
+      it "is not equal with different ivars" do
+        array = [Equality.new("foo", "bar"), Equality.new("foo", "baz")]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/extract_test.rb b/activerecord/test/cases/arel/nodes/extract_test.rb
new file mode 100644
index 0000000000..8fc1e04d67
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/extract_test.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+class Arel::Nodes::ExtractTest < Arel::Spec
+  it "should extract field" do
+    table = Arel::Table.new :users
+    table[:timestamp].extract("date").to_sql.must_be_like %{
+      EXTRACT(DATE FROM "users"."timestamp")
+    }
+  end
+
+  describe "as" do
+    it "should alias the extract" do
+      table = Arel::Table.new :users
+      table[:timestamp].extract("date").as("foo").to_sql.must_be_like %{
+        EXTRACT(DATE FROM "users"."timestamp") AS foo
+      }
+    end
+
+    it "should not mutate the extract" do
+      table = Arel::Table.new :users
+      extract = table[:timestamp].extract("date")
+      before = extract.dup
+      extract.as("foo")
+      assert_equal extract, before
+    end
+  end
+
+  describe "equality" do
+    it "is equal with equal ivars" do
+      table = Arel::Table.new :users
+      array = [table[:attr].extract("foo"), table[:attr].extract("foo")]
+      assert_equal 1, array.uniq.size
+    end
+
+    it "is not equal with different ivars" do
+      table = Arel::Table.new :users
+      array = [table[:attr].extract("foo"), table[:attr].extract("bar")]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/false_test.rb b/activerecord/test/cases/arel/nodes/false_test.rb
new file mode 100644
index 0000000000..4ecf8e332e
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/false_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "False" do
+      describe "equality" do
+        it "is equal to other false nodes" do
+          array = [False.new, False.new]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with other nodes" do
+          array = [False.new, Node.new]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/grouping_test.rb b/activerecord/test/cases/arel/nodes/grouping_test.rb
new file mode 100644
index 0000000000..03d5c142d5
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/grouping_test.rb
@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class GroupingTest < Arel::Spec
+      it "should create Equality nodes" do
+        grouping = Grouping.new(Nodes.build_quoted("foo"))
+        grouping.eq("foo").to_sql.must_be_like "('foo') = 'foo'"
+      end
+
+      describe "equality" do
+        it "is equal with equal ivars" do
+          array = [Grouping.new("foo"), Grouping.new("foo")]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different ivars" do
+          array = [Grouping.new("foo"), Grouping.new("bar")]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/infix_operation_test.rb b/activerecord/test/cases/arel/nodes/infix_operation_test.rb
new file mode 100644
index 0000000000..dcf2200c12
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/infix_operation_test.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class TestInfixOperation < Arel::Test
+      def test_construct
+        operation = InfixOperation.new :+, 1, 2
+        assert_equal :+, operation.operator
+        assert_equal 1, operation.left
+        assert_equal 2, operation.right
+      end
+
+      def test_operation_alias
+        operation = InfixOperation.new :+, 1, 2
+        aliaz = operation.as("zomg")
+        assert_kind_of As, aliaz
+        assert_equal operation, aliaz.left
+        assert_equal "zomg", aliaz.right
+      end
+
+      def test_operation_ordering
+        operation = InfixOperation.new :+, 1, 2
+        ordering = operation.desc
+        assert_kind_of Descending, ordering
+        assert_equal operation, ordering.expr
+        assert ordering.descending?
+      end
+
+      def test_equality_with_same_ivars
+        array = [InfixOperation.new(:+, 1, 2), InfixOperation.new(:+, 1, 2)]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [InfixOperation.new(:+, 1, 2), InfixOperation.new(:+, 1, 3)]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/insert_statement_test.rb b/activerecord/test/cases/arel/nodes/insert_statement_test.rb
new file mode 100644
index 0000000000..252a0d0d0b
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/insert_statement_test.rb
@@ -0,0 +1,44 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+describe Arel::Nodes::InsertStatement do
+  describe "#clone" do
+    it "clones columns and values" do
+      statement = Arel::Nodes::InsertStatement.new
+      statement.columns = %w[a b c]
+      statement.values  = %w[x y z]
+
+      dolly = statement.clone
+      dolly.columns.must_equal statement.columns
+      dolly.values.must_equal statement.values
+
+      dolly.columns.wont_be_same_as statement.columns
+      dolly.values.wont_be_same_as statement.values
+    end
+  end
+
+  describe "equality" do
+    it "is equal with equal ivars" do
+      statement1 = Arel::Nodes::InsertStatement.new
+      statement1.columns = %w[a b c]
+      statement1.values  = %w[x y z]
+      statement2 = Arel::Nodes::InsertStatement.new
+      statement2.columns = %w[a b c]
+      statement2.values  = %w[x y z]
+      array = [statement1, statement2]
+      assert_equal 1, array.uniq.size
+    end
+
+    it "is not equal with different ivars" do
+      statement1 = Arel::Nodes::InsertStatement.new
+      statement1.columns = %w[a b c]
+      statement1.values  = %w[x y z]
+      statement2 = Arel::Nodes::InsertStatement.new
+      statement2.columns = %w[a b c]
+      statement2.values  = %w[1 2 3]
+      array = [statement1, statement2]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/named_function_test.rb b/activerecord/test/cases/arel/nodes/named_function_test.rb
new file mode 100644
index 0000000000..dbd7ae43be
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/named_function_test.rb
@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class TestNamedFunction < Arel::Test
+      def test_construct
+        function = NamedFunction.new "omg", "zomg"
+        assert_equal "omg", function.name
+        assert_equal "zomg", function.expressions
+      end
+
+      def test_function_alias
+        function = NamedFunction.new "omg", "zomg"
+        function = function.as("wth")
+        assert_equal "omg", function.name
+        assert_equal "zomg", function.expressions
+        assert_kind_of SqlLiteral, function.alias
+        assert_equal "wth", function.alias
+      end
+
+      def test_construct_with_alias
+        function = NamedFunction.new "omg", "zomg", "wth"
+        assert_equal "omg", function.name
+        assert_equal "zomg", function.expressions
+        assert_kind_of SqlLiteral, function.alias
+        assert_equal "wth", function.alias
+      end
+
+      def test_equality_with_same_ivars
+        array = [
+          NamedFunction.new("omg", "zomg", "wth"),
+          NamedFunction.new("omg", "zomg", "wth")
+        ]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [
+          NamedFunction.new("omg", "zomg", "wth"),
+          NamedFunction.new("zomg", "zomg", "wth")
+        ]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/node_test.rb b/activerecord/test/cases/arel/nodes/node_test.rb
new file mode 100644
index 0000000000..f4f07ef2c5
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/node_test.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  class TestNode < Arel::Test
+    def test_includes_factory_methods
+      assert Node.new.respond_to?(:create_join)
+    end
+
+    def test_all_nodes_are_nodes
+      Nodes.constants.map { |k|
+        Nodes.const_get(k)
+      }.grep(Class).each do |klass|
+        next if Nodes::SqlLiteral == klass
+        next if Nodes::BindParam == klass
+        next if klass.name =~ /^Arel::Nodes::(?:Test|.*Test$)/
+        assert klass.ancestors.include?(Nodes::Node), klass.name
+      end
+    end
+
+    def test_each
+      list = []
+      node = Nodes::Node.new
+      node.each { |n| list << n }
+      assert_equal [node], list
+    end
+
+    def test_generator
+      list = []
+      node = Nodes::Node.new
+      node.each.each { |n| list << n }
+      assert_equal [node], list
+    end
+
+    def test_enumerable
+      node = Nodes::Node.new
+      assert_kind_of Enumerable, node
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/not_test.rb b/activerecord/test/cases/arel/nodes/not_test.rb
new file mode 100644
index 0000000000..481e678700
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/not_test.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "not" do
+      describe "#not" do
+        it "makes a NOT node" do
+          attr = Table.new(:users)[:id]
+          expr  = attr.eq(10)
+          node  = expr.not
+          node.must_be_kind_of Not
+          node.expr.must_equal expr
+        end
+      end
+
+      describe "equality" do
+        it "is equal with equal ivars" do
+          array = [Not.new("foo"), Not.new("foo")]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different ivars" do
+          array = [Not.new("foo"), Not.new("baz")]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/or_test.rb b/activerecord/test/cases/arel/nodes/or_test.rb
new file mode 100644
index 0000000000..93f826740d
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/or_test.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "or" do
+      describe "#or" do
+        it "makes an OR node" do
+          attr = Table.new(:users)[:id]
+          left  = attr.eq(10)
+          right = attr.eq(11)
+          node  = left.or right
+          node.expr.left.must_equal left
+          node.expr.right.must_equal right
+
+          oror = node.or(right)
+          oror.expr.left.must_equal node
+          oror.expr.right.must_equal right
+        end
+      end
+
+      describe "equality" do
+        it "is equal with equal ivars" do
+          array = [Or.new("foo", "bar"), Or.new("foo", "bar")]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different ivars" do
+          array = [Or.new("foo", "bar"), Or.new("foo", "baz")]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/over_test.rb b/activerecord/test/cases/arel/nodes/over_test.rb
new file mode 100644
index 0000000000..981ec2e34b
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/over_test.rb
@@ -0,0 +1,69 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+class Arel::Nodes::OverTest < Arel::Spec
+  describe "as" do
+    it "should alias the expression" do
+      table = Arel::Table.new :users
+      table[:id].count.over.as("foo").to_sql.must_be_like %{
+        COUNT("users"."id") OVER () AS foo
+      }
+    end
+  end
+
+  describe "with literal" do
+    it "should reference the window definition by name" do
+      table = Arel::Table.new :users
+      table[:id].count.over("foo").to_sql.must_be_like %{
+        COUNT("users"."id") OVER "foo"
+      }
+    end
+  end
+
+  describe "with SQL literal" do
+    it "should reference the window definition by name" do
+      table = Arel::Table.new :users
+      table[:id].count.over(Arel.sql("foo")).to_sql.must_be_like %{
+        COUNT("users"."id") OVER foo
+      }
+    end
+  end
+
+  describe "with no expression" do
+    it "should use empty definition" do
+      table = Arel::Table.new :users
+      table[:id].count.over.to_sql.must_be_like %{
+        COUNT("users"."id") OVER ()
+      }
+    end
+  end
+
+  describe "with expression" do
+    it "should use definition in sub-expression" do
+      table = Arel::Table.new :users
+      window = Arel::Nodes::Window.new.order(table["foo"])
+      table[:id].count.over(window).to_sql.must_be_like %{
+        COUNT("users"."id") OVER (ORDER BY \"users\".\"foo\")
+      }
+    end
+  end
+
+  describe "equality" do
+    it "is equal with equal ivars" do
+      array = [
+        Arel::Nodes::Over.new("foo", "bar"),
+        Arel::Nodes::Over.new("foo", "bar")
+      ]
+      assert_equal 1, array.uniq.size
+    end
+
+    it "is not equal with different ivars" do
+      array = [
+        Arel::Nodes::Over.new("foo", "bar"),
+        Arel::Nodes::Over.new("foo", "baz")
+      ]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/select_core_test.rb b/activerecord/test/cases/arel/nodes/select_core_test.rb
new file mode 100644
index 0000000000..0b698205ff
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/select_core_test.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class TestSelectCore < Arel::Test
+      def test_clone
+        core = Arel::Nodes::SelectCore.new
+        core.froms       = %w[a b c]
+        core.projections = %w[d e f]
+        core.wheres      = %w[g h i]
+
+        dolly = core.clone
+
+        assert_equal core.froms, dolly.froms
+        assert_equal core.projections, dolly.projections
+        assert_equal core.wheres, dolly.wheres
+
+        assert_not_same core.froms, dolly.froms
+        assert_not_same core.projections, dolly.projections
+        assert_not_same core.wheres, dolly.wheres
+      end
+
+      def test_set_quantifier
+        core = Arel::Nodes::SelectCore.new
+        core.set_quantifier = Arel::Nodes::Distinct.new
+        viz = Arel::Visitors::ToSql.new Table.engine.connection_pool
+        assert_match "DISTINCT", viz.accept(core, Collectors::SQLString.new).value
+      end
+
+      def test_equality_with_same_ivars
+        core1 = SelectCore.new
+        core1.froms       = %w[a b c]
+        core1.projections = %w[d e f]
+        core1.wheres      = %w[g h i]
+        core1.groups      = %w[j k l]
+        core1.windows     = %w[m n o]
+        core1.havings     = %w[p q r]
+        core2 = SelectCore.new
+        core2.froms       = %w[a b c]
+        core2.projections = %w[d e f]
+        core2.wheres      = %w[g h i]
+        core2.groups      = %w[j k l]
+        core2.windows     = %w[m n o]
+        core2.havings     = %w[p q r]
+        array = [core1, core2]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        core1 = SelectCore.new
+        core1.froms       = %w[a b c]
+        core1.projections = %w[d e f]
+        core1.wheres      = %w[g h i]
+        core1.groups      = %w[j k l]
+        core1.windows     = %w[m n o]
+        core1.havings     = %w[p q r]
+        core2 = SelectCore.new
+        core2.froms       = %w[a b c]
+        core2.projections = %w[d e f]
+        core2.wheres      = %w[g h i]
+        core2.groups      = %w[j k l]
+        core2.windows     = %w[m n o]
+        core2.havings     = %w[l o l]
+        array = [core1, core2]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/select_statement_test.rb b/activerecord/test/cases/arel/nodes/select_statement_test.rb
new file mode 100644
index 0000000000..a91605de3e
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/select_statement_test.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+describe Arel::Nodes::SelectStatement do
+  describe "#clone" do
+    it "clones cores" do
+      statement = Arel::Nodes::SelectStatement.new %w[a b c]
+
+      dolly = statement.clone
+      dolly.cores.must_equal      statement.cores
+      dolly.cores.wont_be_same_as statement.cores
+    end
+  end
+
+  describe "equality" do
+    it "is equal with equal ivars" do
+      statement1 = Arel::Nodes::SelectStatement.new %w[a b c]
+      statement1.offset = 1
+      statement1.limit  = 2
+      statement1.lock   = false
+      statement1.orders = %w[x y z]
+      statement1.with   = "zomg"
+      statement2 = Arel::Nodes::SelectStatement.new %w[a b c]
+      statement2.offset = 1
+      statement2.limit  = 2
+      statement2.lock   = false
+      statement2.orders = %w[x y z]
+      statement2.with   = "zomg"
+      array = [statement1, statement2]
+      assert_equal 1, array.uniq.size
+    end
+
+    it "is not equal with different ivars" do
+      statement1 = Arel::Nodes::SelectStatement.new %w[a b c]
+      statement1.offset = 1
+      statement1.limit  = 2
+      statement1.lock   = false
+      statement1.orders = %w[x y z]
+      statement1.with   = "zomg"
+      statement2 = Arel::Nodes::SelectStatement.new %w[a b c]
+      statement2.offset = 1
+      statement2.limit  = 2
+      statement2.lock   = false
+      statement2.orders = %w[x y z]
+      statement2.with   = "wth"
+      array = [statement1, statement2]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/sql_literal_test.rb b/activerecord/test/cases/arel/nodes/sql_literal_test.rb
new file mode 100644
index 0000000000..3b95fed1f4
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/sql_literal_test.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+require "yaml"
+
+module Arel
+  module Nodes
+    class SqlLiteralTest < Arel::Spec
+      before do
+        @visitor = Visitors::ToSql.new Table.engine.connection
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      describe "sql" do
+        it "makes a sql literal node" do
+          sql = Arel.sql "foo"
+          sql.must_be_kind_of Arel::Nodes::SqlLiteral
+        end
+      end
+
+      describe "count" do
+        it "makes a count node" do
+          node = SqlLiteral.new("*").count
+          compile(node).must_be_like %{ COUNT(*) }
+        end
+
+        it "makes a distinct node" do
+          node = SqlLiteral.new("*").count true
+          compile(node).must_be_like %{ COUNT(DISTINCT *) }
+        end
+      end
+
+      describe "equality" do
+        it "makes an equality node" do
+          node = SqlLiteral.new("foo").eq(1)
+          compile(node).must_be_like %{ foo = 1 }
+        end
+
+        it "is equal with equal contents" do
+          array = [SqlLiteral.new("foo"), SqlLiteral.new("foo")]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different contents" do
+          array = [SqlLiteral.new("foo"), SqlLiteral.new("bar")]
+          assert_equal 2, array.uniq.size
+        end
+      end
+
+      describe 'grouped "or" equality' do
+        it "makes a grouping node with an or node" do
+          node = SqlLiteral.new("foo").eq_any([1, 2])
+          compile(node).must_be_like %{ (foo = 1 OR foo = 2) }
+        end
+      end
+
+      describe 'grouped "and" equality' do
+        it "makes a grouping node with an and node" do
+          node = SqlLiteral.new("foo").eq_all([1, 2])
+          compile(node).must_be_like %{ (foo = 1 AND foo = 2) }
+        end
+      end
+
+      describe "serialization" do
+        it "serializes into YAML" do
+          yaml_literal = SqlLiteral.new("foo").to_yaml
+          assert_equal("foo", YAML.load(yaml_literal))
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/sum_test.rb b/activerecord/test/cases/arel/nodes/sum_test.rb
new file mode 100644
index 0000000000..5015964951
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/sum_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+class Arel::Nodes::SumTest < Arel::Spec
+  describe "as" do
+    it "should alias the sum" do
+      table = Arel::Table.new :users
+      table[:id].sum.as("foo").to_sql.must_be_like %{
+        SUM("users"."id") AS foo
+      }
+    end
+  end
+
+  describe "equality" do
+    it "is equal with equal ivars" do
+      array = [Arel::Nodes::Sum.new("foo"), Arel::Nodes::Sum.new("foo")]
+      assert_equal 1, array.uniq.size
+    end
+
+    it "is not equal with different ivars" do
+      array = [Arel::Nodes::Sum.new("foo"), Arel::Nodes::Sum.new("foo!")]
+      assert_equal 2, array.uniq.size
+    end
+  end
+
+  describe "order" do
+    it "should order the sum" do
+      table = Arel::Table.new :users
+      table[:id].sum.desc.to_sql.must_be_like %{
+        SUM("users"."id") DESC
+      }
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/table_alias_test.rb b/activerecord/test/cases/arel/nodes/table_alias_test.rb
new file mode 100644
index 0000000000..c661b6771e
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/table_alias_test.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "table alias" do
+      describe "equality" do
+        it "is equal with equal ivars" do
+          relation1 = Table.new(:users)
+          node1     = TableAlias.new relation1, :foo
+          relation2 = Table.new(:users)
+          node2     = TableAlias.new relation2, :foo
+          array = [node1, node2]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different ivars" do
+          relation1 = Table.new(:users)
+          node1     = TableAlias.new relation1, :foo
+          relation2 = Table.new(:users)
+          node2     = TableAlias.new relation2, :bar
+          array = [node1, node2]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/true_test.rb b/activerecord/test/cases/arel/nodes/true_test.rb
new file mode 100644
index 0000000000..1e85fe7d48
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/true_test.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "True" do
+      describe "equality" do
+        it "is equal to other true nodes" do
+          array = [True.new, True.new]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with other nodes" do
+          array = [True.new, Node.new]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/unary_operation_test.rb b/activerecord/test/cases/arel/nodes/unary_operation_test.rb
new file mode 100644
index 0000000000..f0dd0c625c
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/unary_operation_test.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    class TestUnaryOperation < Arel::Test
+      def test_construct
+        operation = UnaryOperation.new :-, 1
+        assert_equal :-, operation.operator
+        assert_equal 1, operation.expr
+      end
+
+      def test_operation_alias
+        operation = UnaryOperation.new :-, 1
+        aliaz = operation.as("zomg")
+        assert_kind_of As, aliaz
+        assert_equal operation, aliaz.left
+        assert_equal "zomg", aliaz.right
+      end
+
+      def test_operation_ordering
+        operation = UnaryOperation.new :-, 1
+        ordering = operation.desc
+        assert_kind_of Descending, ordering
+        assert_equal operation, ordering.expr
+        assert ordering.descending?
+      end
+
+      def test_equality_with_same_ivars
+        array = [UnaryOperation.new(:-, 1), UnaryOperation.new(:-, 1)]
+        assert_equal 1, array.uniq.size
+      end
+
+      def test_inequality_with_different_ivars
+        array = [UnaryOperation.new(:-, 1), UnaryOperation.new(:-, 2)]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/update_statement_test.rb b/activerecord/test/cases/arel/nodes/update_statement_test.rb
new file mode 100644
index 0000000000..a83ce32f68
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/update_statement_test.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+describe Arel::Nodes::UpdateStatement do
+  describe "#clone" do
+    it "clones wheres and values" do
+      statement = Arel::Nodes::UpdateStatement.new
+      statement.wheres = %w[a b c]
+      statement.values = %w[x y z]
+
+      dolly = statement.clone
+      dolly.wheres.must_equal statement.wheres
+      dolly.wheres.wont_be_same_as statement.wheres
+
+      dolly.values.must_equal statement.values
+      dolly.values.wont_be_same_as statement.values
+    end
+  end
+
+  describe "equality" do
+    it "is equal with equal ivars" do
+      statement1 = Arel::Nodes::UpdateStatement.new
+      statement1.relation = "zomg"
+      statement1.wheres   = 2
+      statement1.values   = false
+      statement1.orders   = %w[x y z]
+      statement1.limit    = 42
+      statement1.key      = "zomg"
+      statement2 = Arel::Nodes::UpdateStatement.new
+      statement2.relation = "zomg"
+      statement2.wheres   = 2
+      statement2.values   = false
+      statement2.orders   = %w[x y z]
+      statement2.limit    = 42
+      statement2.key      = "zomg"
+      array = [statement1, statement2]
+      assert_equal 1, array.uniq.size
+    end
+
+    it "is not equal with different ivars" do
+      statement1 = Arel::Nodes::UpdateStatement.new
+      statement1.relation = "zomg"
+      statement1.wheres   = 2
+      statement1.values   = false
+      statement1.orders   = %w[x y z]
+      statement1.limit    = 42
+      statement1.key      = "zomg"
+      statement2 = Arel::Nodes::UpdateStatement.new
+      statement2.relation = "zomg"
+      statement2.wheres   = 2
+      statement2.values   = false
+      statement2.orders   = %w[x y z]
+      statement2.limit    = 42
+      statement2.key      = "wth"
+      array = [statement1, statement2]
+      assert_equal 2, array.uniq.size
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes/window_test.rb b/activerecord/test/cases/arel/nodes/window_test.rb
new file mode 100644
index 0000000000..729b0556a4
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes/window_test.rb
@@ -0,0 +1,81 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Nodes
+    describe "Window" do
+      describe "equality" do
+        it "is equal with equal ivars" do
+          window1 = Window.new
+          window1.orders = [1, 2]
+          window1.partitions = [1]
+          window1.frame 3
+          window2 = Window.new
+          window2.orders = [1, 2]
+          window2.partitions = [1]
+          window2.frame 3
+          array = [window1, window2]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different ivars" do
+          window1 = Window.new
+          window1.orders = [1, 2]
+          window1.partitions = [1]
+          window1.frame 3
+          window2 = Window.new
+          window2.orders = [1, 2]
+          window1.partitions = [1]
+          window2.frame 4
+          array = [window1, window2]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+
+    describe "NamedWindow" do
+      describe "equality" do
+        it "is equal with equal ivars" do
+          window1 = NamedWindow.new "foo"
+          window1.orders = [1, 2]
+          window1.partitions = [1]
+          window1.frame 3
+          window2 = NamedWindow.new "foo"
+          window2.orders = [1, 2]
+          window2.partitions = [1]
+          window2.frame 3
+          array = [window1, window2]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with different ivars" do
+          window1 = NamedWindow.new "foo"
+          window1.orders = [1, 2]
+          window1.partitions = [1]
+          window1.frame 3
+          window2 = NamedWindow.new "bar"
+          window2.orders = [1, 2]
+          window2.partitions = [1]
+          window2.frame 3
+          array = [window1, window2]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+
+    describe "CurrentRow" do
+      describe "equality" do
+        it "is equal to other current row nodes" do
+          array = [CurrentRow.new, CurrentRow.new]
+          assert_equal 1, array.uniq.size
+        end
+
+        it "is not equal with other nodes" do
+          array = [CurrentRow.new, Node.new]
+          assert_equal 2, array.uniq.size
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/nodes_test.rb b/activerecord/test/cases/arel/nodes_test.rb
new file mode 100644
index 0000000000..9021de0d20
--- /dev/null
+++ b/activerecord/test/cases/arel/nodes_test.rb
@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  module Nodes
+    class TestNodes < Arel::Test
+      def test_every_arel_nodes_have_hash_eql_eqeq_from_same_class
+        # #descendants code from activesupport
+        node_descendants = []
+        ObjectSpace.each_object(Arel::Nodes::Node.singleton_class) do |k|
+          next if k.respond_to?(:singleton_class?) && k.singleton_class?
+          node_descendants.unshift k unless k == self
+        end
+        node_descendants.delete(Arel::Nodes::Node)
+        node_descendants.delete(Arel::Nodes::NodeExpression)
+
+        bad_node_descendants = node_descendants.reject do |subnode|
+          eqeq_owner = subnode.instance_method(:==).owner
+          eql_owner = subnode.instance_method(:eql?).owner
+          hash_owner = subnode.instance_method(:hash).owner
+
+          eqeq_owner < Arel::Nodes::Node &&
+              eqeq_owner == eql_owner &&
+              eqeq_owner == hash_owner
+        end
+
+        problem_msg = "Some subclasses of Arel::Nodes::Node do not have a" \
+            " #== or #eql? or #hash defined from the same class as the others"
+        assert_empty bad_node_descendants, problem_msg
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/select_manager_test.rb b/activerecord/test/cases/arel/select_manager_test.rb
new file mode 100644
index 0000000000..5220950905
--- /dev/null
+++ b/activerecord/test/cases/arel/select_manager_test.rb
@@ -0,0 +1,1225 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  class SelectManagerTest < Arel::Spec
+    def test_join_sources
+      manager = Arel::SelectManager.new
+      manager.join_sources << Arel::Nodes::StringJoin.new(Nodes.build_quoted("foo"))
+      assert_equal "SELECT FROM 'foo'", manager.to_sql
+    end
+
+    describe "backwards compatibility" do
+      describe "project" do
+        it "accepts symbols as sql literals" do
+          table   = Table.new :users
+          manager = Arel::SelectManager.new
+          manager.project :id
+          manager.from table
+          manager.to_sql.must_be_like %{
+            SELECT id FROM "users"
+          }
+        end
+      end
+
+      describe "order" do
+        it "accepts symbols" do
+          table   = Table.new :users
+          manager = Arel::SelectManager.new
+          manager.project Nodes::SqlLiteral.new "*"
+          manager.from table
+          manager.order :foo
+          manager.to_sql.must_be_like %{ SELECT * FROM "users" ORDER BY foo }
+        end
+      end
+
+      describe "group" do
+        it "takes a symbol" do
+          table   = Table.new :users
+          manager = Arel::SelectManager.new
+          manager.from table
+          manager.group :foo
+          manager.to_sql.must_be_like %{ SELECT FROM "users" GROUP BY foo }
+        end
+      end
+
+      describe "as" do
+        it "makes an AS node by grouping the AST" do
+          manager = Arel::SelectManager.new
+          as = manager.as(Arel.sql("foo"))
+          assert_kind_of Arel::Nodes::Grouping, as.left
+          assert_equal manager.ast, as.left.expr
+          assert_equal "foo", as.right
+        end
+
+        it "converts right to SqlLiteral if a string" do
+          manager = Arel::SelectManager.new
+          as = manager.as("foo")
+          assert_kind_of Arel::Nodes::SqlLiteral, as.right
+        end
+
+        it "can make a subselect" do
+          manager = Arel::SelectManager.new
+          manager.project Arel.star
+          manager.from Arel.sql("zomg")
+          as = manager.as(Arel.sql("foo"))
+
+          manager = Arel::SelectManager.new
+          manager.project Arel.sql("name")
+          manager.from as
+          manager.to_sql.must_be_like "SELECT name FROM (SELECT * FROM zomg) foo"
+        end
+      end
+
+      describe "from" do
+        it "ignores strings when table of same name exists" do
+          table   = Table.new :users
+          manager = Arel::SelectManager.new
+
+          manager.from table
+          manager.from "users"
+          manager.project table["id"]
+          manager.to_sql.must_be_like 'SELECT "users"."id" FROM users'
+        end
+
+        it "should support any ast" do
+          table = Table.new :users
+          manager1 = Arel::SelectManager.new
+
+          manager2 = Arel::SelectManager.new
+          manager2.project(Arel.sql("*"))
+          manager2.from table
+
+          manager1.project Arel.sql("lol")
+          as = manager2.as Arel.sql("omg")
+          manager1.from(as)
+
+          manager1.to_sql.must_be_like %{
+            SELECT lol FROM (SELECT * FROM "users") omg
+          }
+        end
+      end
+
+      describe "having" do
+        it "converts strings to SQLLiterals" do
+          table = Table.new :users
+          mgr = table.from
+          mgr.having Arel.sql("foo")
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" HAVING foo }
+        end
+
+        it "can have multiple items specified separately" do
+          table = Table.new :users
+          mgr = table.from
+          mgr.having Arel.sql("foo")
+          mgr.having Arel.sql("bar")
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" HAVING foo AND bar }
+        end
+
+        it "can receive any node" do
+          table = Table.new :users
+          mgr = table.from
+          mgr.having Arel::Nodes::And.new([Arel.sql("foo"), Arel.sql("bar")])
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" HAVING foo AND bar }
+        end
+      end
+
+      describe "on" do
+        it "converts to sqlliterals" do
+          table = Table.new :users
+          right = table.alias
+          mgr   = table.from
+          mgr.join(right).on("omg")
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" INNER JOIN "users" "users_2" ON omg }
+        end
+
+        it "converts to sqlliterals with multiple items" do
+          table = Table.new :users
+          right = table.alias
+          mgr   = table.from
+          mgr.join(right).on("omg", "123")
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" INNER JOIN "users" "users_2" ON omg AND 123 }
+        end
+      end
+    end
+
+    describe "clone" do
+      it "creates new cores" do
+        table = Table.new :users, as: "foo"
+        mgr = table.from
+        m2 = mgr.clone
+        m2.project "foo"
+        mgr.to_sql.wont_equal m2.to_sql
+      end
+
+      it "makes updates to the correct copy" do
+        table = Table.new :users, as: "foo"
+        mgr = table.from
+        m2 = mgr.clone
+        m3 = m2.clone
+        m2.project "foo"
+        mgr.to_sql.wont_equal m2.to_sql
+        m3.to_sql.must_equal mgr.to_sql
+      end
+    end
+
+    describe "initialize" do
+      it "uses alias in sql" do
+        table = Table.new :users, as: "foo"
+        mgr = table.from
+        mgr.skip 10
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" "foo" OFFSET 10 }
+      end
+    end
+
+    describe "skip" do
+      it "should add an offset" do
+        table = Table.new :users
+        mgr = table.from
+        mgr.skip 10
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" OFFSET 10 }
+      end
+
+      it "should chain" do
+        table = Table.new :users
+        mgr = table.from
+        mgr.skip(10).to_sql.must_be_like %{ SELECT FROM "users" OFFSET 10 }
+      end
+    end
+
+    describe "offset" do
+      it "should add an offset" do
+        table = Table.new :users
+        mgr = table.from
+        mgr.offset = 10
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" OFFSET 10 }
+      end
+
+      it "should remove an offset" do
+        table = Table.new :users
+        mgr = table.from
+        mgr.offset = 10
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" OFFSET 10 }
+
+        mgr.offset = nil
+        mgr.to_sql.must_be_like %{ SELECT FROM "users" }
+      end
+
+      it "should return the offset" do
+        table = Table.new :users
+        mgr = table.from
+        mgr.offset = 10
+        assert_equal 10, mgr.offset
+      end
+    end
+
+    describe "exists" do
+      it "should create an exists clause" do
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.project Nodes::SqlLiteral.new "*"
+        m2 = Arel::SelectManager.new
+        m2.project manager.exists
+        m2.to_sql.must_be_like %{ SELECT EXISTS (#{manager.to_sql}) }
+      end
+
+      it "can be aliased" do
+        table = Table.new(:users)
+        manager = Arel::SelectManager.new table
+        manager.project Nodes::SqlLiteral.new "*"
+        m2 = Arel::SelectManager.new
+        m2.project manager.exists.as("foo")
+        m2.to_sql.must_be_like %{ SELECT EXISTS (#{manager.to_sql}) AS foo }
+      end
+    end
+
+    describe "union" do
+      before do
+        table = Table.new :users
+        @m1 = Arel::SelectManager.new table
+        @m1.project Arel.star
+        @m1.where(table[:age].lt(18))
+
+        @m2 = Arel::SelectManager.new table
+        @m2.project Arel.star
+        @m2.where(table[:age].gt(99))
+      end
+
+      it "should union two managers" do
+        # FIXME should this union "managers" or "statements" ?
+        # FIXME this probably shouldn't return a node
+        node = @m1.union @m2
+
+        # maybe FIXME: decide when wrapper parens are needed
+        node.to_sql.must_be_like %{
+          ( SELECT * FROM "users"  WHERE "users"."age" < 18 UNION SELECT * FROM "users"  WHERE "users"."age" > 99 )
+        }
+      end
+
+      it "should union all" do
+        node = @m1.union :all, @m2
+
+        node.to_sql.must_be_like %{
+          ( SELECT * FROM "users"  WHERE "users"."age" < 18 UNION ALL SELECT * FROM "users"  WHERE "users"."age" > 99 )
+        }
+      end
+    end
+
+    describe "intersect" do
+      before do
+        table = Table.new :users
+        @m1 = Arel::SelectManager.new table
+        @m1.project Arel.star
+        @m1.where(table[:age].gt(18))
+
+        @m2 = Arel::SelectManager.new table
+        @m2.project Arel.star
+        @m2.where(table[:age].lt(99))
+      end
+
+      it "should intersect two managers" do
+        # FIXME should this intersect "managers" or "statements" ?
+        # FIXME this probably shouldn't return a node
+        node = @m1.intersect @m2
+
+        # maybe FIXME: decide when wrapper parens are needed
+        node.to_sql.must_be_like %{
+          ( SELECT * FROM "users"  WHERE "users"."age" > 18 INTERSECT SELECT * FROM "users"  WHERE "users"."age" < 99 )
+        }
+      end
+    end
+
+    describe "except" do
+      before do
+        table = Table.new :users
+        @m1 = Arel::SelectManager.new table
+        @m1.project Arel.star
+        @m1.where(table[:age].between(18..60))
+
+        @m2 = Arel::SelectManager.new table
+        @m2.project Arel.star
+        @m2.where(table[:age].between(40..99))
+      end
+
+      it "should except two managers" do
+        # FIXME should this except "managers" or "statements" ?
+        # FIXME this probably shouldn't return a node
+        node = @m1.except @m2
+
+        # maybe FIXME: decide when wrapper parens are needed
+        node.to_sql.must_be_like %{
+          ( SELECT * FROM "users"  WHERE "users"."age" BETWEEN 18 AND 60 EXCEPT SELECT * FROM "users"  WHERE "users"."age" BETWEEN 40 AND 99 )
+        }
+      end
+    end
+
+    describe "with" do
+      it "should support basic WITH" do
+        users          = Table.new(:users)
+        users_top      = Table.new(:users_top)
+        comments       = Table.new(:comments)
+
+        top            = users.project(users[:id]).where(users[:karma].gt(100))
+        users_as       = Arel::Nodes::As.new(users_top, top)
+        select_manager = comments.project(Arel.star).with(users_as)
+                          .where(comments[:author_id].in(users_top.project(users_top[:id])))
+
+        select_manager.to_sql.must_be_like %{
+          WITH "users_top" AS (SELECT "users"."id" FROM "users" WHERE "users"."karma" > 100) SELECT * FROM "comments" WHERE "comments"."author_id" IN (SELECT "users_top"."id" FROM "users_top")
+        }
+      end
+
+      it "should support WITH RECURSIVE" do
+        comments           = Table.new(:comments)
+        comments_id        = comments[:id]
+        comments_parent_id = comments[:parent_id]
+
+        replies            = Table.new(:replies)
+        replies_id         = replies[:id]
+
+        recursive_term = Arel::SelectManager.new
+        recursive_term.from(comments).project(comments_id, comments_parent_id).where(comments_id.eq 42)
+
+        non_recursive_term = Arel::SelectManager.new
+        non_recursive_term.from(comments).project(comments_id, comments_parent_id).join(replies).on(comments_parent_id.eq replies_id)
+
+        union = recursive_term.union(non_recursive_term)
+
+        as_statement = Arel::Nodes::As.new replies, union
+
+        manager = Arel::SelectManager.new
+        manager.with(:recursive, as_statement).from(replies).project(Arel.star)
+
+        sql = manager.to_sql
+        sql.must_be_like %{
+          WITH RECURSIVE "replies" AS (
+              SELECT "comments"."id", "comments"."parent_id" FROM "comments" WHERE "comments"."id" = 42
+            UNION
+              SELECT "comments"."id", "comments"."parent_id" FROM "comments" INNER JOIN "replies" ON "comments"."parent_id" = "replies"."id"
+          )
+          SELECT * FROM "replies"
+        }
+      end
+    end
+
+    describe "ast" do
+      it "should return the ast" do
+        table = Table.new :users
+        mgr = table.from
+        assert mgr.ast
+      end
+
+      it "should allow orders to work when the ast is grepped" do
+        table = Table.new :users
+        mgr = table.from
+        mgr.project Arel.sql "*"
+        mgr.from table
+        mgr.orders << Arel::Nodes::Ascending.new(Arel.sql("foo"))
+        mgr.ast.grep(Arel::Nodes::OuterJoin)
+        mgr.to_sql.must_be_like %{ SELECT * FROM "users" ORDER BY foo ASC }
+      end
+    end
+
+    describe "taken" do
+      it "should return limit" do
+        manager = Arel::SelectManager.new
+        manager.take 10
+        manager.taken.must_equal 10
+      end
+    end
+
+    describe "lock" do
+      # This should fail on other databases
+      it "adds a lock node" do
+        table = Table.new :users
+        mgr = table.from
+        mgr.lock.to_sql.must_be_like %{ SELECT FROM "users" FOR UPDATE }
+      end
+    end
+
+    describe "orders" do
+      it "returns order clauses" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        order = table[:id]
+        manager.order table[:id]
+        manager.orders.must_equal [order]
+      end
+    end
+
+    describe "order" do
+      it "generates order clauses" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new "*"
+        manager.from table
+        manager.order table[:id]
+        manager.to_sql.must_be_like %{
+          SELECT * FROM "users" ORDER BY "users"."id"
+        }
+      end
+
+      # FIXME: I would like to deprecate this
+      it "takes *args" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new "*"
+        manager.from table
+        manager.order table[:id], table[:name]
+        manager.to_sql.must_be_like %{
+          SELECT * FROM "users" ORDER BY "users"."id", "users"."name"
+        }
+      end
+
+      it "chains" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.order(table[:id]).must_equal manager
+      end
+
+      it "has order attributes" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new "*"
+        manager.from table
+        manager.order table[:id].desc
+        manager.to_sql.must_be_like %{
+          SELECT * FROM "users" ORDER BY "users"."id" DESC
+        }
+      end
+    end
+
+    describe "on" do
+      it "takes two params" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right).on(predicate, predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id" AND
+               "users"."id" = "users_2"."id"
+        }
+      end
+
+      it "takes three params" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right).on(
+          predicate,
+          predicate,
+          left[:name].eq(right[:name])
+        )
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id" AND
+               "users"."id" = "users_2"."id" AND
+               "users"."name" = "users_2"."name"
+        }
+      end
+    end
+
+    it "should hand back froms" do
+      relation = Arel::SelectManager.new
+      assert_equal [], relation.froms
+    end
+
+    it "should create and nodes" do
+      relation = Arel::SelectManager.new
+      children = ["foo", "bar", "baz"]
+      clause = relation.create_and children
+      assert_kind_of Arel::Nodes::And, clause
+      assert_equal children, clause.children
+    end
+
+    it "should create insert managers" do
+      relation = Arel::SelectManager.new
+      insert = relation.create_insert
+      assert_kind_of Arel::InsertManager, insert
+    end
+
+    it "should create join nodes" do
+      relation = Arel::SelectManager.new
+      join = relation.create_join "foo", "bar"
+      assert_kind_of Arel::Nodes::InnerJoin, join
+      assert_equal "foo", join.left
+      assert_equal "bar", join.right
+    end
+
+    it "should create join nodes with a full outer join klass" do
+      relation = Arel::SelectManager.new
+      join = relation.create_join "foo", "bar", Arel::Nodes::FullOuterJoin
+      assert_kind_of Arel::Nodes::FullOuterJoin, join
+      assert_equal "foo", join.left
+      assert_equal "bar", join.right
+    end
+
+    it "should create join nodes with a outer join klass" do
+      relation = Arel::SelectManager.new
+      join = relation.create_join "foo", "bar", Arel::Nodes::OuterJoin
+      assert_kind_of Arel::Nodes::OuterJoin, join
+      assert_equal "foo", join.left
+      assert_equal "bar", join.right
+    end
+
+    it "should create join nodes with a right outer join klass" do
+      relation = Arel::SelectManager.new
+      join = relation.create_join "foo", "bar", Arel::Nodes::RightOuterJoin
+      assert_kind_of Arel::Nodes::RightOuterJoin, join
+      assert_equal "foo", join.left
+      assert_equal "bar", join.right
+    end
+
+    describe "join" do
+      it "responds to join" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it "takes a class" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right, Nodes::OuterJoin).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             LEFT OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it "takes the full outer join class" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right, Nodes::FullOuterJoin).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             FULL OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it "takes the right outer join class" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.join(right, Nodes::RightOuterJoin).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             RIGHT OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it "noops on nil" do
+        manager = Arel::SelectManager.new
+        manager.join(nil).must_equal manager
+      end
+
+      it "raises EmptyJoinError on empty" do
+        left      = Table.new :users
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        assert_raises(EmptyJoinError) do
+          manager.join("")
+        end
+      end
+    end
+
+    describe "outer join" do
+      it "responds to join" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+        manager   = Arel::SelectManager.new
+
+        manager.from left
+        manager.outer_join(right).on(predicate)
+        manager.to_sql.must_be_like %{
+           SELECT FROM "users"
+             LEFT OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it "noops on nil" do
+        manager = Arel::SelectManager.new
+        manager.outer_join(nil).must_equal manager
+      end
+    end
+
+    describe "joins" do
+      it "returns inner join sql" do
+        table   = Table.new :users
+        aliaz   = table.alias
+        manager = Arel::SelectManager.new
+        manager.from Nodes::InnerJoin.new(aliaz, table[:id].eq(aliaz[:id]))
+        assert_match 'INNER JOIN "users" "users_2" "users"."id" = "users_2"."id"',
+                     manager.to_sql
+      end
+
+      it "returns outer join sql" do
+        table   = Table.new :users
+        aliaz   = table.alias
+        manager = Arel::SelectManager.new
+        manager.from Nodes::OuterJoin.new(aliaz, table[:id].eq(aliaz[:id]))
+        assert_match 'LEFT OUTER JOIN "users" "users_2" "users"."id" = "users_2"."id"',
+                     manager.to_sql
+      end
+
+      it "can have a non-table alias as relation name" do
+        users    = Table.new :users
+        comments = Table.new :comments
+
+        counts = comments.from.
+          group(comments[:user_id]).
+          project(
+            comments[:user_id].as("user_id"),
+            comments[:user_id].count.as("count")
+          ).as("counts")
+
+        joins = users.join(counts).on(counts[:user_id].eq(10))
+        joins.to_sql.must_be_like %{
+          SELECT FROM "users" INNER JOIN (SELECT "comments"."user_id" AS user_id, COUNT("comments"."user_id") AS count FROM "comments" GROUP BY "comments"."user_id") counts ON counts."user_id" = 10
+        }
+      end
+
+      it "joins itself" do
+        left      = Table.new :users
+        right     = left.alias
+        predicate = left[:id].eq(right[:id])
+
+        mgr = left.join(right)
+        mgr.project Nodes::SqlLiteral.new("*")
+        mgr.on(predicate).must_equal mgr
+
+        mgr.to_sql.must_be_like %{
+           SELECT * FROM "users"
+             INNER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+        }
+      end
+
+      it "returns string join sql" do
+        manager = Arel::SelectManager.new
+        manager.from Nodes::StringJoin.new(Nodes.build_quoted("hello"))
+        assert_match "'hello'", manager.to_sql
+      end
+    end
+
+    describe "group" do
+      it "takes an attribute" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.group table[:id]
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" GROUP BY "users"."id"
+        }
+      end
+
+      it "chains" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.group(table[:id]).must_equal manager
+      end
+
+      it "takes multiple args" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.group table[:id], table[:name]
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" GROUP BY "users"."id", "users"."name"
+        }
+      end
+
+      # FIXME: backwards compat
+      it "makes strings literals" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.group "foo"
+        manager.to_sql.must_be_like %{ SELECT FROM "users" GROUP BY foo }
+      end
+    end
+
+    describe "window definition" do
+      it "can be empty" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window")
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS ()
+        }
+      end
+
+      it "takes an order" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").order(table["foo"].asc)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ORDER BY "users"."foo" ASC)
+        }
+      end
+
+      it "takes an order with multiple columns" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").order(table["foo"].asc, table["bar"].desc)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ORDER BY "users"."foo" ASC, "users"."bar" DESC)
+        }
+      end
+
+      it "takes a partition" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").partition(table["bar"])
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (PARTITION BY "users"."bar")
+        }
+      end
+
+      it "takes a partition and an order" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").partition(table["foo"]).order(table["foo"].asc)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (PARTITION BY "users"."foo"
+            ORDER BY "users"."foo" ASC)
+        }
+      end
+
+      it "takes a partition with multiple columns" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").partition(table["bar"], table["baz"])
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (PARTITION BY "users"."bar", "users"."baz")
+        }
+      end
+
+      it "takes a rows frame, unbounded preceding" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").rows(Arel::Nodes::Preceding.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS UNBOUNDED PRECEDING)
+        }
+      end
+
+      it "takes a rows frame, bounded preceding" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").rows(Arel::Nodes::Preceding.new(5))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS 5 PRECEDING)
+        }
+      end
+
+      it "takes a rows frame, unbounded following" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").rows(Arel::Nodes::Following.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS UNBOUNDED FOLLOWING)
+        }
+      end
+
+      it "takes a rows frame, bounded following" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").rows(Arel::Nodes::Following.new(5))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS 5 FOLLOWING)
+        }
+      end
+
+      it "takes a rows frame, current row" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").rows(Arel::Nodes::CurrentRow.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS CURRENT ROW)
+        }
+      end
+
+      it "takes a rows frame, between two delimiters" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        window = manager.window("a_window")
+        window.frame(
+          Arel::Nodes::Between.new(
+            window.rows,
+            Nodes::And.new([
+              Arel::Nodes::Preceding.new,
+              Arel::Nodes::CurrentRow.new
+            ])))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
+        }
+      end
+
+      it "takes a range frame, unbounded preceding" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").range(Arel::Nodes::Preceding.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE UNBOUNDED PRECEDING)
+        }
+      end
+
+      it "takes a range frame, bounded preceding" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").range(Arel::Nodes::Preceding.new(5))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE 5 PRECEDING)
+        }
+      end
+
+      it "takes a range frame, unbounded following" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").range(Arel::Nodes::Following.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE UNBOUNDED FOLLOWING)
+        }
+      end
+
+      it "takes a range frame, bounded following" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").range(Arel::Nodes::Following.new(5))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE 5 FOLLOWING)
+        }
+      end
+
+      it "takes a range frame, current row" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.window("a_window").range(Arel::Nodes::CurrentRow.new)
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE CURRENT ROW)
+        }
+      end
+
+      it "takes a range frame, between two delimiters" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        window = manager.window("a_window")
+        window.frame(
+          Arel::Nodes::Between.new(
+            window.range,
+            Nodes::And.new([
+              Arel::Nodes::Preceding.new,
+              Arel::Nodes::CurrentRow.new
+            ])))
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" WINDOW "a_window" AS (RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)
+        }
+      end
+    end
+
+    describe "delete" do
+      it "copies from" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        stmt = manager.compile_delete
+
+        stmt.to_sql.must_be_like %{ DELETE FROM "users" }
+      end
+
+      it "copies where" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where table[:id].eq 10
+        stmt = manager.compile_delete
+
+        stmt.to_sql.must_be_like %{
+          DELETE FROM "users" WHERE "users"."id" = 10
+        }
+      end
+    end
+
+    describe "where_sql" do
+      it "gives me back the where sql" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where table[:id].eq 10
+        manager.where_sql.must_be_like %{ WHERE "users"."id" = 10 }
+      end
+
+      it "joins wheres with AND" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where table[:id].eq 10
+        manager.where table[:id].eq 11
+        manager.where_sql.must_be_like %{ WHERE "users"."id" = 10 AND "users"."id" = 11}
+      end
+
+      it "handles database specific statements" do
+        old_visitor = Table.engine.connection.visitor
+        Table.engine.connection.visitor = Visitors::PostgreSQL.new Table.engine.connection
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where table[:id].eq 10
+        manager.where table[:name].matches "foo%"
+        manager.where_sql.must_be_like %{ WHERE "users"."id" = 10 AND "users"."name" ILIKE 'foo%' }
+        Table.engine.connection.visitor = old_visitor
+      end
+
+      it "returns nil when there are no wheres" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.where_sql.must_be_nil
+      end
+    end
+
+    describe "update" do
+      it "creates an update statement" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        stmt = manager.compile_update({ table[:id] => 1 }, Arel::Attributes::Attribute.new(table, "id"))
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET "id" = 1
+        }
+      end
+
+      it "takes a string" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        stmt = manager.compile_update(Nodes::SqlLiteral.new("foo = bar"), Arel::Attributes::Attribute.new(table, "id"))
+
+        stmt.to_sql.must_be_like %{ UPDATE "users" SET foo = bar }
+      end
+
+      it "copies limits" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.take 1
+        stmt = manager.compile_update(Nodes::SqlLiteral.new("foo = bar"), Arel::Attributes::Attribute.new(table, "id"))
+        stmt.key = table["id"]
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET foo = bar
+          WHERE "users"."id" IN (SELECT "users"."id" FROM "users" LIMIT 1)
+        }
+      end
+
+      it "copies order" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from table
+        manager.order :foo
+        stmt = manager.compile_update(Nodes::SqlLiteral.new("foo = bar"), Arel::Attributes::Attribute.new(table, "id"))
+        stmt.key = table["id"]
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET foo = bar
+          WHERE "users"."id" IN (SELECT "users"."id" FROM "users" ORDER BY foo)
+        }
+      end
+
+      it "copies where clauses" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.where table[:id].eq 10
+        manager.from table
+        stmt = manager.compile_update({ table[:id] => 1 }, Arel::Attributes::Attribute.new(table, "id"))
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET "id" = 1 WHERE "users"."id" = 10
+        }
+      end
+
+      it "copies where clauses when nesting is triggered" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.where table[:foo].eq 10
+        manager.take 42
+        manager.from table
+        stmt = manager.compile_update({ table[:id] => 1 }, Arel::Attributes::Attribute.new(table, "id"))
+
+        stmt.to_sql.must_be_like %{
+          UPDATE "users" SET "id" = 1 WHERE "users"."id" IN (SELECT "users"."id" FROM "users" WHERE "users"."foo" = 10 LIMIT 42)
+        }
+      end
+    end
+
+    describe "project" do
+      it "takes sql literals" do
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new "*"
+        manager.to_sql.must_be_like %{ SELECT * }
+      end
+
+      it "takes multiple args" do
+        manager = Arel::SelectManager.new
+        manager.project Nodes::SqlLiteral.new("foo"),
+          Nodes::SqlLiteral.new("bar")
+        manager.to_sql.must_be_like %{ SELECT foo, bar }
+      end
+
+      it "takes strings" do
+        manager = Arel::SelectManager.new
+        manager.project "*"
+        manager.to_sql.must_be_like %{ SELECT * }
+      end
+    end
+
+    describe "projections" do
+      it "reads projections" do
+        manager = Arel::SelectManager.new
+        manager.project Arel.sql("foo"), Arel.sql("bar")
+        manager.projections.must_equal [Arel.sql("foo"), Arel.sql("bar")]
+      end
+    end
+
+    describe "projections=" do
+      it "overwrites projections" do
+        manager = Arel::SelectManager.new
+        manager.project Arel.sql("foo")
+        manager.projections = [Arel.sql("bar")]
+        manager.to_sql.must_be_like %{ SELECT bar }
+      end
+    end
+
+    describe "take" do
+      it "knows take" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from(table).project(table["id"])
+        manager.where(table["id"].eq(1))
+        manager.take 1
+
+        manager.to_sql.must_be_like %{
+          SELECT "users"."id"
+          FROM "users"
+          WHERE "users"."id" = 1
+          LIMIT 1
+        }
+      end
+
+      it "chains" do
+        manager = Arel::SelectManager.new
+        manager.take(1).must_equal manager
+      end
+
+      it "removes LIMIT when nil is passed" do
+        manager = Arel::SelectManager.new
+        manager.limit = 10
+        assert_match("LIMIT", manager.to_sql)
+
+        manager.limit = nil
+        assert_no_match("LIMIT", manager.to_sql)
+      end
+    end
+
+    describe "where" do
+      it "knows where" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from(table).project(table["id"])
+        manager.where(table["id"].eq(1))
+        manager.to_sql.must_be_like %{
+          SELECT "users"."id"
+          FROM "users"
+          WHERE "users"."id" = 1
+        }
+      end
+
+      it "chains" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from(table)
+        manager.project(table["id"]).where(table["id"].eq 1).must_equal manager
+      end
+    end
+
+    describe "from" do
+      it "makes sql" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+
+        manager.from table
+        manager.project table["id"]
+        manager.to_sql.must_be_like 'SELECT "users"."id" FROM "users"'
+      end
+
+      it "chains" do
+        table   = Table.new :users
+        manager = Arel::SelectManager.new
+        manager.from(table).project(table["id"]).must_equal manager
+        manager.to_sql.must_be_like 'SELECT "users"."id" FROM "users"'
+      end
+    end
+
+    describe "source" do
+      it "returns the join source of the select core" do
+        manager = Arel::SelectManager.new
+        manager.source.must_equal manager.ast.cores.last.source
+      end
+    end
+
+    describe "distinct" do
+      it "sets the quantifier" do
+        manager = Arel::SelectManager.new
+
+        manager.distinct
+        manager.ast.cores.last.set_quantifier.class.must_equal Arel::Nodes::Distinct
+
+        manager.distinct(false)
+        manager.ast.cores.last.set_quantifier.must_be_nil
+      end
+
+      it "chains" do
+        manager = Arel::SelectManager.new
+        manager.distinct.must_equal manager
+        manager.distinct(false).must_equal manager
+      end
+    end
+
+    describe "distinct_on" do
+      it "sets the quantifier" do
+        manager = Arel::SelectManager.new
+        table = Table.new :users
+
+        manager.distinct_on(table["id"])
+        manager.ast.cores.last.set_quantifier.must_equal Arel::Nodes::DistinctOn.new(table["id"])
+
+        manager.distinct_on(false)
+        manager.ast.cores.last.set_quantifier.must_be_nil
+      end
+
+      it "chains" do
+        manager = Arel::SelectManager.new
+        table = Table.new :users
+
+        manager.distinct_on(table["id"]).must_equal manager
+        manager.distinct_on(false).must_equal manager
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/support/fake_record.rb b/activerecord/test/cases/arel/support/fake_record.rb
new file mode 100644
index 0000000000..559ff5d4e6
--- /dev/null
+++ b/activerecord/test/cases/arel/support/fake_record.rb
@@ -0,0 +1,129 @@
+# frozen_string_literal: true
+
+require "date"
+module FakeRecord
+  class Column < Struct.new(:name, :type)
+  end
+
+  class Connection
+    attr_reader :tables
+    attr_accessor :visitor
+
+    def initialize(visitor = nil)
+      @tables = %w{ users photos developers products}
+      @columns = {
+        "users" => [
+          Column.new("id", :integer),
+          Column.new("name", :string),
+          Column.new("bool", :boolean),
+          Column.new("created_at", :date)
+        ],
+        "products" => [
+          Column.new("id", :integer),
+          Column.new("price", :decimal)
+        ]
+      }
+      @columns_hash = {
+        "users" => Hash[@columns["users"].map { |x| [x.name, x] }],
+        "products" => Hash[@columns["products"].map { |x| [x.name, x] }]
+      }
+      @primary_keys = {
+        "users" => "id",
+        "products" => "id"
+      }
+      @visitor = visitor
+    end
+
+    def columns_hash(table_name)
+      @columns_hash[table_name]
+    end
+
+    def primary_key(name)
+      @primary_keys[name.to_s]
+    end
+
+    def data_source_exists?(name)
+      @tables.include? name.to_s
+    end
+
+    def columns(name, message = nil)
+      @columns[name.to_s]
+    end
+
+    def quote_table_name(name)
+      "\"#{name}\""
+    end
+
+    def quote_column_name(name)
+      "\"#{name}\""
+    end
+
+    def schema_cache
+      self
+    end
+
+    def quote(thing)
+      case thing
+      when DateTime
+        "'#{thing.strftime("%Y-%m-%d %H:%M:%S")}'"
+      when Date
+        "'#{thing.strftime("%Y-%m-%d")}'"
+      when true
+        "'t'"
+      when false
+        "'f'"
+      when nil
+        "NULL"
+      when Numeric
+        thing
+      else
+        "'#{thing.to_s.gsub("'", "\\\\'")}'"
+      end
+    end
+  end
+
+  class ConnectionPool
+    class Spec < Struct.new(:config)
+    end
+
+    attr_reader :spec, :connection
+
+    def initialize
+      @spec = Spec.new(adapter: "america")
+      @connection = Connection.new
+      @connection.visitor = Arel::Visitors::ToSql.new(connection)
+    end
+
+    def with_connection
+      yield connection
+    end
+
+    def table_exists?(name)
+      connection.tables.include? name.to_s
+    end
+
+    def columns_hash
+      connection.columns_hash
+    end
+
+    def schema_cache
+      connection
+    end
+
+    def quote(thing)
+      connection.quote thing
+    end
+  end
+
+  class Base
+    attr_accessor :connection_pool
+
+    def initialize
+      @connection_pool = ConnectionPool.new
+    end
+
+    def connection
+      connection_pool.connection
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/table_test.rb b/activerecord/test/cases/arel/table_test.rb
new file mode 100644
index 0000000000..91b7a5a480
--- /dev/null
+++ b/activerecord/test/cases/arel/table_test.rb
@@ -0,0 +1,216 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  class TableTest < Arel::Spec
+    before do
+      @relation = Table.new(:users)
+    end
+
+    it "should create join nodes" do
+      join = @relation.create_string_join "foo"
+      assert_kind_of Arel::Nodes::StringJoin, join
+      assert_equal "foo", join.left
+    end
+
+    it "should create join nodes" do
+      join = @relation.create_join "foo", "bar"
+      assert_kind_of Arel::Nodes::InnerJoin, join
+      assert_equal "foo", join.left
+      assert_equal "bar", join.right
+    end
+
+    it "should create join nodes with a klass" do
+      join = @relation.create_join "foo", "bar", Arel::Nodes::FullOuterJoin
+      assert_kind_of Arel::Nodes::FullOuterJoin, join
+      assert_equal "foo", join.left
+      assert_equal "bar", join.right
+    end
+
+    it "should create join nodes with a klass" do
+      join = @relation.create_join "foo", "bar", Arel::Nodes::OuterJoin
+      assert_kind_of Arel::Nodes::OuterJoin, join
+      assert_equal "foo", join.left
+      assert_equal "bar", join.right
+    end
+
+    it "should create join nodes with a klass" do
+      join = @relation.create_join "foo", "bar", Arel::Nodes::RightOuterJoin
+      assert_kind_of Arel::Nodes::RightOuterJoin, join
+      assert_equal "foo", join.left
+      assert_equal "bar", join.right
+    end
+
+    it "should return an insert manager" do
+      im = @relation.compile_insert "VALUES(NULL)"
+      assert_kind_of Arel::InsertManager, im
+      im.into Table.new(:users)
+      assert_equal "INSERT INTO \"users\" VALUES(NULL)", im.to_sql
+    end
+
+    describe "skip" do
+      it "should add an offset" do
+        sm = @relation.skip 2
+        sm.to_sql.must_be_like "SELECT FROM \"users\" OFFSET 2"
+      end
+    end
+
+    describe "having" do
+      it "adds a having clause" do
+        mgr = @relation.having @relation[:id].eq(10)
+        mgr.to_sql.must_be_like %{
+         SELECT FROM "users" HAVING "users"."id" = 10
+        }
+      end
+    end
+
+    describe "backwards compat" do
+      describe "join" do
+        it "noops on nil" do
+          mgr = @relation.join nil
+
+          mgr.to_sql.must_be_like %{ SELECT FROM "users" }
+        end
+
+        it "raises EmptyJoinError on empty" do
+          assert_raises(EmptyJoinError) do
+            @relation.join ""
+          end
+        end
+
+        it "takes a second argument for join type" do
+          right     = @relation.alias
+          predicate = @relation[:id].eq(right[:id])
+          mgr = @relation.join(right, Nodes::OuterJoin).on(predicate)
+
+          mgr.to_sql.must_be_like %{
+           SELECT FROM "users"
+             LEFT OUTER JOIN "users" "users_2"
+               ON "users"."id" = "users_2"."id"
+          }
+        end
+      end
+
+      describe "join" do
+        it "creates an outer join" do
+          right     = @relation.alias
+          predicate = @relation[:id].eq(right[:id])
+          mgr = @relation.outer_join(right).on(predicate)
+
+          mgr.to_sql.must_be_like %{
+            SELECT FROM "users"
+              LEFT OUTER JOIN "users" "users_2"
+                ON "users"."id" = "users_2"."id"
+          }
+        end
+      end
+    end
+
+    describe "group" do
+      it "should create a group" do
+        manager = @relation.group @relation[:id]
+        manager.to_sql.must_be_like %{
+          SELECT FROM "users" GROUP BY "users"."id"
+        }
+      end
+    end
+
+    describe "alias" do
+      it "should create a node that proxies to a table" do
+        node = @relation.alias
+        node.name.must_equal "users_2"
+        node[:id].relation.must_equal node
+      end
+    end
+
+    describe "new" do
+      it "should accept a hash" do
+        rel = Table.new :users, as: "foo"
+        rel.table_alias.must_equal "foo"
+      end
+
+      it "ignores as if it equals name" do
+        rel = Table.new :users, as: "users"
+        rel.table_alias.must_be_nil
+      end
+    end
+
+    describe "order" do
+      it "should take an order" do
+        manager = @relation.order "foo"
+        manager.to_sql.must_be_like %{ SELECT FROM "users" ORDER BY foo }
+      end
+    end
+
+    describe "take" do
+      it "should add a limit" do
+        manager = @relation.take 1
+        manager.project Nodes::SqlLiteral.new "*"
+        manager.to_sql.must_be_like %{ SELECT * FROM "users" LIMIT 1 }
+      end
+    end
+
+    describe "project" do
+      it "can project" do
+        manager = @relation.project Nodes::SqlLiteral.new "*"
+        manager.to_sql.must_be_like %{ SELECT * FROM "users" }
+      end
+
+      it "takes multiple parameters" do
+        manager = @relation.project Nodes::SqlLiteral.new("*"), Nodes::SqlLiteral.new("*")
+        manager.to_sql.must_be_like %{ SELECT *, * FROM "users" }
+      end
+    end
+
+    describe "where" do
+      it "returns a tree manager" do
+        manager = @relation.where @relation[:id].eq 1
+        manager.project @relation[:id]
+        manager.must_be_kind_of TreeManager
+        manager.to_sql.must_be_like %{
+          SELECT "users"."id"
+          FROM "users"
+          WHERE "users"."id" = 1
+        }
+      end
+    end
+
+    it "should have a name" do
+      @relation.name.must_equal "users"
+    end
+
+    it "should have a table name" do
+      @relation.table_name.must_equal "users"
+    end
+
+    describe "[]" do
+      describe "when given a Symbol" do
+        it "manufactures an attribute if the symbol names an attribute within the relation" do
+          column = @relation[:id]
+          column.name.must_equal :id
+        end
+      end
+    end
+
+    describe "equality" do
+      it "is equal with equal ivars" do
+        relation1 = Table.new(:users)
+        relation1.table_alias = "zomg"
+        relation2 = Table.new(:users)
+        relation2.table_alias = "zomg"
+        array = [relation1, relation2]
+        assert_equal 1, array.uniq.size
+      end
+
+      it "is not equal with different ivars" do
+        relation1 = Table.new(:users)
+        relation1.table_alias = "zomg"
+        relation2 = Table.new(:users)
+        relation2.table_alias = "zomg2"
+        array = [relation1, relation2]
+        assert_equal 2, array.uniq.size
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/update_manager_test.rb b/activerecord/test/cases/arel/update_manager_test.rb
new file mode 100644
index 0000000000..cc1b9ac5b3
--- /dev/null
+++ b/activerecord/test/cases/arel/update_manager_test.rb
@@ -0,0 +1,126 @@
+# frozen_string_literal: true
+
+require_relative "helper"
+
+module Arel
+  class UpdateManagerTest < Arel::Spec
+    describe "new" do
+      it "takes an engine" do
+        Arel::UpdateManager.new
+      end
+    end
+
+    it "should not quote sql literals" do
+      table = Table.new(:users)
+      um = Arel::UpdateManager.new
+      um.table table
+      um.set [[table[:name], Arel::Nodes::BindParam.new(1)]]
+      um.to_sql.must_be_like %{ UPDATE "users" SET "name" =  ? }
+    end
+
+    it "handles limit properly" do
+      table = Table.new(:users)
+      um = Arel::UpdateManager.new
+      um.key = "id"
+      um.take 10
+      um.table table
+      um.set [[table[:name], nil]]
+      assert_match(/LIMIT 10/, um.to_sql)
+    end
+
+    describe "set" do
+      it "updates with null" do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new
+        um.table table
+        um.set [[table[:name], nil]]
+        um.to_sql.must_be_like %{ UPDATE "users" SET "name" =  NULL }
+      end
+
+      it "takes a string" do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new
+        um.table table
+        um.set Nodes::SqlLiteral.new "foo = bar"
+        um.to_sql.must_be_like %{ UPDATE "users" SET foo = bar }
+      end
+
+      it "takes a list of lists" do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new
+        um.table table
+        um.set [[table[:id], 1], [table[:name], "hello"]]
+        um.to_sql.must_be_like %{
+          UPDATE "users" SET "id" = 1, "name" =  'hello'
+        }
+      end
+
+      it "chains" do
+        table = Table.new(:users)
+        um = Arel::UpdateManager.new
+        um.set([[table[:id], 1], [table[:name], "hello"]]).must_equal um
+      end
+    end
+
+    describe "table" do
+      it "generates an update statement" do
+        um = Arel::UpdateManager.new
+        um.table Table.new(:users)
+        um.to_sql.must_be_like %{ UPDATE "users" }
+      end
+
+      it "chains" do
+        um = Arel::UpdateManager.new
+        um.table(Table.new(:users)).must_equal um
+      end
+
+      it "generates an update statement with joins" do
+        um = Arel::UpdateManager.new
+
+        table = Table.new(:users)
+        join_source = Arel::Nodes::JoinSource.new(
+          table,
+          [table.create_join(Table.new(:posts))]
+        )
+
+        um.table join_source
+        um.to_sql.must_be_like %{ UPDATE "users" INNER JOIN "posts" }
+      end
+    end
+
+    describe "where" do
+      it "generates a where clause" do
+        table = Table.new :users
+        um = Arel::UpdateManager.new
+        um.table table
+        um.where table[:id].eq(1)
+        um.to_sql.must_be_like %{
+          UPDATE "users" WHERE "users"."id" = 1
+        }
+      end
+
+      it "chains" do
+        table = Table.new :users
+        um = Arel::UpdateManager.new
+        um.table table
+        um.where(table[:id].eq(1)).must_equal um
+      end
+    end
+
+    describe "key" do
+      before do
+        @table = Table.new :users
+        @um = Arel::UpdateManager.new
+        @um.key = @table[:foo]
+      end
+
+      it "can be set" do
+        @um.ast.key.must_equal @table[:foo]
+      end
+
+      it "can be accessed" do
+        @um.key.must_equal @table[:foo]
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/depth_first_test.rb b/activerecord/test/cases/arel/visitors/depth_first_test.rb
new file mode 100644
index 0000000000..f94ad521d7
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/depth_first_test.rb
@@ -0,0 +1,270 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class TestDepthFirst < Arel::Test
+      Collector = Struct.new(:calls) do
+        def call(object)
+          calls << object
+        end
+      end
+
+      def setup
+        @collector = Collector.new []
+        @visitor = Visitors::DepthFirst.new @collector
+      end
+
+      def test_raises_with_object
+        assert_raises(TypeError) do
+          @visitor.accept(Object.new)
+        end
+      end
+
+
+      # unary ops
+      [
+        Arel::Nodes::Not,
+        Arel::Nodes::Group,
+        Arel::Nodes::On,
+        Arel::Nodes::Grouping,
+        Arel::Nodes::Offset,
+        Arel::Nodes::Ordering,
+        Arel::Nodes::StringJoin,
+        Arel::Nodes::UnqualifiedColumn,
+        Arel::Nodes::Limit,
+        Arel::Nodes::Else,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          op = klass.new(:a)
+          @visitor.accept op
+          assert_equal [:a, op], @collector.calls
+        end
+      end
+
+      # functions
+      [
+        Arel::Nodes::Exists,
+        Arel::Nodes::Avg,
+        Arel::Nodes::Min,
+        Arel::Nodes::Max,
+        Arel::Nodes::Sum,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          func = klass.new(:a, "b")
+          @visitor.accept func
+          assert_equal [:a, "b", false, func], @collector.calls
+        end
+      end
+
+      def test_named_function
+        func = Arel::Nodes::NamedFunction.new(:a, :b, "c")
+        @visitor.accept func
+        assert_equal [:a, :b, false, "c", func], @collector.calls
+      end
+
+      def test_lock
+        lock = Nodes::Lock.new true
+        @visitor.accept lock
+        assert_equal [lock], @collector.calls
+      end
+
+      def test_count
+        count = Nodes::Count.new :a, :b, "c"
+        @visitor.accept count
+        assert_equal [:a, "c", :b, count], @collector.calls
+      end
+
+      def test_inner_join
+        join = Nodes::InnerJoin.new :a, :b
+        @visitor.accept join
+        assert_equal [:a, :b, join], @collector.calls
+      end
+
+      def test_full_outer_join
+        join = Nodes::FullOuterJoin.new :a, :b
+        @visitor.accept join
+        assert_equal [:a, :b, join], @collector.calls
+      end
+
+      def test_outer_join
+        join = Nodes::OuterJoin.new :a, :b
+        @visitor.accept join
+        assert_equal [:a, :b, join], @collector.calls
+      end
+
+      def test_right_outer_join
+        join = Nodes::RightOuterJoin.new :a, :b
+        @visitor.accept join
+        assert_equal [:a, :b, join], @collector.calls
+      end
+
+      [
+        Arel::Nodes::Assignment,
+        Arel::Nodes::Between,
+        Arel::Nodes::Concat,
+        Arel::Nodes::DoesNotMatch,
+        Arel::Nodes::Equality,
+        Arel::Nodes::GreaterThan,
+        Arel::Nodes::GreaterThanOrEqual,
+        Arel::Nodes::In,
+        Arel::Nodes::LessThan,
+        Arel::Nodes::LessThanOrEqual,
+        Arel::Nodes::Matches,
+        Arel::Nodes::NotEqual,
+        Arel::Nodes::NotIn,
+        Arel::Nodes::Or,
+        Arel::Nodes::TableAlias,
+        Arel::Nodes::Values,
+        Arel::Nodes::As,
+        Arel::Nodes::DeleteStatement,
+        Arel::Nodes::JoinSource,
+        Arel::Nodes::When,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          binary = klass.new(:a, :b)
+          @visitor.accept binary
+          assert_equal [:a, :b, binary], @collector.calls
+        end
+      end
+
+      def test_Arel_Nodes_InfixOperation
+        binary = Arel::Nodes::InfixOperation.new(:o, :a, :b)
+        @visitor.accept binary
+        assert_equal [:a, :b, binary], @collector.calls
+      end
+
+      # N-ary
+      [
+        Arel::Nodes::And,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          binary = klass.new([:a, :b, :c])
+          @visitor.accept binary
+          assert_equal [:a, :b, :c, binary], @collector.calls
+        end
+      end
+
+      [
+        Arel::Attributes::Integer,
+        Arel::Attributes::Float,
+        Arel::Attributes::String,
+        Arel::Attributes::Time,
+        Arel::Attributes::Boolean,
+        Arel::Attributes::Attribute
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          binary = klass.new(:a, :b)
+          @visitor.accept binary
+          assert_equal [:a, :b, binary], @collector.calls
+        end
+      end
+
+      def test_table
+        relation = Arel::Table.new(:users)
+        @visitor.accept relation
+        assert_equal ["users", relation], @collector.calls
+      end
+
+      def test_array
+        node = Nodes::Or.new(:a, :b)
+        list = [node]
+        @visitor.accept list
+        assert_equal [:a, :b, node, list], @collector.calls
+      end
+
+      def test_set
+        node = Nodes::Or.new(:a, :b)
+        set  = Set.new([node])
+        @visitor.accept set
+        assert_equal [:a, :b, node, set], @collector.calls
+      end
+
+      def test_hash
+        node = Nodes::Or.new(:a, :b)
+        hash = { node => node }
+        @visitor.accept hash
+        assert_equal [:a, :b, node, :a, :b, node, hash], @collector.calls
+      end
+
+      def test_update_statement
+        stmt = Nodes::UpdateStatement.new
+        stmt.relation = :a
+        stmt.values << :b
+        stmt.wheres << :c
+        stmt.orders << :d
+        stmt.limit = :e
+
+        @visitor.accept stmt
+        assert_equal [:a, :b, stmt.values, :c, stmt.wheres, :d, stmt.orders,
+          :e, stmt], @collector.calls
+      end
+
+      def test_select_core
+        core = Nodes::SelectCore.new
+        core.projections << :a
+        core.froms = :b
+        core.wheres << :c
+        core.groups << :d
+        core.windows << :e
+        core.havings << :f
+
+        @visitor.accept core
+        assert_equal [
+          :a, core.projections,
+          :b, [],
+          core.source,
+          :c, core.wheres,
+          :d, core.groups,
+          :e, core.windows,
+          :f, core.havings,
+          core], @collector.calls
+      end
+
+      def test_select_statement
+        ss = Nodes::SelectStatement.new
+        ss.cores.replace [:a]
+        ss.orders << :b
+        ss.limit = :c
+        ss.lock = :d
+        ss.offset = :e
+
+        @visitor.accept ss
+        assert_equal [
+          :a, ss.cores,
+          :b, ss.orders,
+          :c,
+          :d,
+          :e,
+          ss], @collector.calls
+      end
+
+      def test_insert_statement
+        stmt = Nodes::InsertStatement.new
+        stmt.relation = :a
+        stmt.columns << :b
+        stmt.values = :c
+
+        @visitor.accept stmt
+        assert_equal [:a, :b, stmt.columns, :c, stmt], @collector.calls
+      end
+
+      def test_case
+        node = Arel::Nodes::Case.new
+        node.case = :a
+        node.conditions << :b
+        node.default = :c
+
+        @visitor.accept node
+        assert_equal [:a, :b, node.conditions, :c, node], @collector.calls
+      end
+
+      def test_node
+        node = Nodes::Node.new
+        @visitor.accept node
+        assert_equal [node], @collector.calls
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb b/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb
new file mode 100644
index 0000000000..a07a1a050a
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/dispatch_contamination_test.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+require "concurrent"
+
+module Arel
+  module Visitors
+    class DummyVisitor < Visitor
+      def initialize
+        super
+        @barrier = Concurrent::CyclicBarrier.new(2)
+      end
+
+      def visit_Arel_Visitors_DummySuperNode(node)
+        42
+      end
+
+      # This is terrible, but it's the only way to reliably reproduce
+      # the possible race where two threads attempt to correct the
+      # dispatch hash at the same time.
+      def send(*args)
+        super
+      rescue
+        # Both threads try (and fail) to dispatch to the subclass's name
+        @barrier.wait
+        raise
+      ensure
+        # Then one thread successfully completes (updating the dispatch
+        # table in the process) before the other finishes raising its
+        # exception.
+        Thread.current[:delay].wait if Thread.current[:delay]
+      end
+    end
+
+    class DummySuperNode
+    end
+
+    class DummySubNode < DummySuperNode
+    end
+
+    class DispatchContaminationTest < Arel::Spec
+      before do
+        @connection = Table.engine.connection
+        @table = Table.new(:users)
+      end
+
+      it "dispatches properly after failing upwards" do
+        node = Nodes::Union.new(Nodes::True.new, Nodes::False.new)
+        assert_equal "( TRUE UNION FALSE )", node.to_sql
+
+        node.first # from Nodes::Node's Enumerable mixin
+
+        assert_equal "( TRUE UNION FALSE )", node.to_sql
+      end
+
+      it "is threadsafe when implementing superclass fallback" do
+        visitor = DummyVisitor.new
+        main_thread_finished = Concurrent::Event.new
+
+        racing_thread = Thread.new do
+          Thread.current[:delay] = main_thread_finished
+          visitor.accept DummySubNode.new
+        end
+
+        assert_equal 42, visitor.accept(DummySubNode.new)
+        main_thread_finished.set
+
+        assert_equal 42, racing_thread.value
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/dot_test.rb b/activerecord/test/cases/arel/visitors/dot_test.rb
new file mode 100644
index 0000000000..6b3c132f83
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/dot_test.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class TestDot < Arel::Test
+      def setup
+        @visitor = Visitors::Dot.new
+      end
+
+      # functions
+      [
+        Nodes::Sum,
+        Nodes::Exists,
+        Nodes::Max,
+        Nodes::Min,
+        Nodes::Avg,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          op = klass.new(:a, "z")
+          @visitor.accept op, Collectors::PlainString.new
+        end
+      end
+
+      def test_named_function
+        func = Nodes::NamedFunction.new "omg", "omg"
+        @visitor.accept func, Collectors::PlainString.new
+      end
+
+      # unary ops
+      [
+        Arel::Nodes::Not,
+        Arel::Nodes::Group,
+        Arel::Nodes::On,
+        Arel::Nodes::Grouping,
+        Arel::Nodes::Offset,
+        Arel::Nodes::Ordering,
+        Arel::Nodes::UnqualifiedColumn,
+        Arel::Nodes::Limit,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          op = klass.new(:a)
+          @visitor.accept op, Collectors::PlainString.new
+        end
+      end
+
+      # binary ops
+      [
+        Arel::Nodes::Assignment,
+        Arel::Nodes::Between,
+        Arel::Nodes::DoesNotMatch,
+        Arel::Nodes::Equality,
+        Arel::Nodes::GreaterThan,
+        Arel::Nodes::GreaterThanOrEqual,
+        Arel::Nodes::In,
+        Arel::Nodes::LessThan,
+        Arel::Nodes::LessThanOrEqual,
+        Arel::Nodes::Matches,
+        Arel::Nodes::NotEqual,
+        Arel::Nodes::NotIn,
+        Arel::Nodes::Or,
+        Arel::Nodes::TableAlias,
+        Arel::Nodes::Values,
+        Arel::Nodes::As,
+        Arel::Nodes::DeleteStatement,
+        Arel::Nodes::JoinSource,
+        Arel::Nodes::Casted,
+      ].each do |klass|
+        define_method("test_#{klass.name.gsub('::', '_')}") do
+          binary = klass.new(:a, :b)
+          @visitor.accept binary, Collectors::PlainString.new
+        end
+      end
+
+      def test_Arel_Nodes_BindParam
+        node = Arel::Nodes::BindParam.new(1)
+        collector = Collectors::PlainString.new
+        assert_match '[label="<f0>Arel::Nodes::BindParam"]', @visitor.accept(node, collector).value
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/ibm_db_test.rb b/activerecord/test/cases/arel/visitors/ibm_db_test.rb
new file mode 100644
index 0000000000..2ddbec3266
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/ibm_db_test.rb
@@ -0,0 +1,73 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class IbmDbTest < Arel::Spec
+      before do
+        @visitor = IBM_DB.new Table.engine.connection
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it "uses FETCH FIRST n ROWS to limit results" do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(1)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT FETCH FIRST 1 ROWS ONLY"
+      end
+
+      it "uses FETCH FIRST n ROWS in updates with a limit" do
+        table = Table.new(:users)
+        stmt = Nodes::UpdateStatement.new
+        stmt.relation = table
+        stmt.limit = Nodes::Limit.new(Nodes.build_quoted(1))
+        stmt.key = table[:id]
+        sql = compile(stmt)
+        sql.must_be_like "UPDATE \"users\" WHERE \"users\".\"id\" IN (SELECT \"users\".\"id\" FROM \"users\" FETCH FIRST 1 ROWS ONLY)"
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            DECODE("users"."name", 'Aaron Patterson', 0, 1) = 0
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            DECODE("users"."first_name", "users"."last_name", 0, 1) = 0
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            DECODE("users"."first_name", "users"."last_name", 0, 1) = 1
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/informix_test.rb b/activerecord/test/cases/arel/visitors/informix_test.rb
new file mode 100644
index 0000000000..b6c2dd6ae7
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/informix_test.rb
@@ -0,0 +1,98 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class InformixTest < Arel::Spec
+      before do
+        @visitor = Informix.new Table.engine.connection
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it "uses FIRST n to limit results" do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(1)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT FIRST 1"
+      end
+
+      it "uses FIRST n in updates with a limit" do
+        table = Table.new(:users)
+        stmt = Nodes::UpdateStatement.new
+        stmt.relation = table
+        stmt.limit = Nodes::Limit.new(Nodes.build_quoted(1))
+        stmt.key = table[:id]
+        sql = compile(stmt)
+        sql.must_be_like "UPDATE \"users\" WHERE \"users\".\"id\" IN (SELECT FIRST 1 \"users\".\"id\" FROM \"users\")"
+      end
+
+      it "uses SKIP n to jump results" do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(10)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT SKIP 10"
+      end
+
+      it "uses SKIP before FIRST" do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(1)
+        stmt.offset = Nodes::Offset.new(1)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT SKIP 1 FIRST 1"
+      end
+
+      it "uses INNER JOIN to perform joins" do
+        core = Nodes::SelectCore.new
+        table = Table.new(:posts)
+        core.source = Nodes::JoinSource.new(table, [table.create_join(Table.new(:comments))])
+
+        stmt = Nodes::SelectStatement.new([core])
+        sql = compile(stmt)
+        sql.must_be_like 'SELECT FROM "posts" INNER JOIN "comments"'
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            CASE WHEN "users"."name" = 'Aaron Patterson' OR ("users"."name" IS NULL AND 'Aaron Patterson' IS NULL) THEN 0 ELSE 1 END = 0
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            CASE WHEN "users"."first_name" = "users"."last_name" OR ("users"."first_name" IS NULL AND "users"."last_name" IS NULL) THEN 0 ELSE 1 END = 0
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            CASE WHEN "users"."first_name" = "users"."last_name" OR ("users"."first_name" IS NULL AND "users"."last_name" IS NULL) THEN 0 ELSE 1 END = 1
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/mssql_test.rb b/activerecord/test/cases/arel/visitors/mssql_test.rb
new file mode 100644
index 0000000000..74f34b4dad
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/mssql_test.rb
@@ -0,0 +1,138 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class MssqlTest < Arel::Spec
+      before do
+        @visitor = MSSQL.new Table.engine.connection
+        @table = Arel::Table.new "users"
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it "should not modify query if no offset or limit" do
+        stmt = Nodes::SelectStatement.new
+        sql = compile(stmt)
+        sql.must_be_like "SELECT"
+      end
+
+      it "should go over table PK if no .order() or .group()" do
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.from = @table
+        stmt.limit = Nodes::Limit.new(10)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY \"users\".\"id\") as _row_num FROM \"users\") as _t WHERE _row_num BETWEEN 1 AND 10"
+      end
+
+      it "caches the PK lookup for order" do
+        connection = Minitest::Mock.new
+        connection.expect(:primary_key, ["id"], ["users"])
+
+        # We don't care how many times these methods are called
+        def connection.quote_table_name(*); ""; end
+        def connection.quote_column_name(*); ""; end
+
+        @visitor = MSSQL.new(connection)
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.from = @table
+        stmt.limit = Nodes::Limit.new(10)
+
+        compile(stmt)
+        compile(stmt)
+
+        connection.verify
+      end
+
+      it "should use TOP for limited deletes" do
+        stmt = Nodes::DeleteStatement.new
+        stmt.relation = @table
+        stmt.limit = Nodes::Limit.new(10)
+        sql = compile(stmt)
+
+        sql.must_be_like "DELETE TOP (10) FROM \"users\""
+      end
+
+      it "should go over query ORDER BY if .order()" do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(10)
+        stmt.orders << Nodes::SqlLiteral.new("order_by")
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY order_by) as _row_num) as _t WHERE _row_num BETWEEN 1 AND 10"
+      end
+
+      it "should go over query GROUP BY if no .order() and there is .group()" do
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.groups << Nodes::SqlLiteral.new("group_by")
+        stmt.limit = Nodes::Limit.new(10)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY group_by) as _row_num GROUP BY group_by) as _t WHERE _row_num BETWEEN 1 AND 10"
+      end
+
+      it "should use BETWEEN if both .limit() and .offset" do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(10)
+        stmt.offset = Nodes::Offset.new(20)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY ) as _row_num) as _t WHERE _row_num BETWEEN 21 AND 30"
+      end
+
+      it "should use >= if only .offset" do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(20)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY ) as _row_num) as _t WHERE _row_num >= 21"
+      end
+
+      it "should generate subquery for .count" do
+        stmt = Nodes::SelectStatement.new
+        stmt.limit = Nodes::Limit.new(10)
+        stmt.cores.first.projections << Nodes::Count.new("*")
+        sql = compile(stmt)
+        sql.must_be_like "SELECT COUNT(1) as count_id FROM (SELECT _t.* FROM (SELECT ROW_NUMBER() OVER (ORDER BY ) as _row_num) as _t WHERE _row_num BETWEEN 1 AND 10) AS subquery"
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            EXISTS (VALUES ("users"."name") INTERSECT VALUES ('Aaron Patterson'))
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            EXISTS (VALUES ("users"."first_name") INTERSECT VALUES ("users"."last_name"))
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            NOT EXISTS (VALUES ("users"."first_name") INTERSECT VALUES ("users"."last_name"))
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/mysql_test.rb b/activerecord/test/cases/arel/visitors/mysql_test.rb
new file mode 100644
index 0000000000..5f37587957
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/mysql_test.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class MysqlTest < Arel::Spec
+      before do
+        @visitor = MySQL.new Table.engine.connection
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      ###
+      # :'(
+      # http://dev.mysql.com/doc/refman/5.0/en/select.html#id3482214
+      it "defaults limit to 18446744073709551615" do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(1)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT FROM DUAL LIMIT 18446744073709551615 OFFSET 1"
+      end
+
+      it "should escape LIMIT" do
+        sc = Arel::Nodes::UpdateStatement.new
+        sc.relation = Table.new(:users)
+        sc.limit = Nodes::Limit.new(Nodes.build_quoted("omg"))
+        assert_equal("UPDATE \"users\" LIMIT 'omg'", compile(sc))
+      end
+
+      it "uses DUAL for empty from" do
+        stmt = Nodes::SelectStatement.new
+        sql = compile(stmt)
+        sql.must_be_like "SELECT FROM DUAL"
+      end
+
+      describe "locking" do
+        it "defaults to FOR UPDATE when locking" do
+          node = Nodes::Lock.new(Arel.sql("FOR UPDATE"))
+          compile(node).must_be_like "FOR UPDATE"
+        end
+
+        it "allows a custom string to be used as a lock" do
+          node = Nodes::Lock.new(Arel.sql("LOCK IN SHARE MODE"))
+          compile(node).must_be_like "LOCK IN SHARE MODE"
+        end
+      end
+
+      describe "concat" do
+        it "concats columns" do
+          @table = Table.new(:users)
+          query = @table[:name].concat(@table[:name])
+          compile(query).must_be_like %{
+            CONCAT("users"."name", "users"."name")
+          }
+        end
+
+        it "concats a string" do
+          @table = Table.new(:users)
+          query = @table[:name].concat(Nodes.build_quoted("abc"))
+          compile(query).must_be_like %{
+            CONCAT("users"."name", 'abc')
+          }
+        end
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            "users"."name" <=> 'Aaron Patterson'
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            "users"."first_name" <=> "users"."last_name"
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" <=> NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            NOT "users"."first_name" <=> "users"."last_name"
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ NOT "users"."name" <=> NULL }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/oracle12_test.rb b/activerecord/test/cases/arel/visitors/oracle12_test.rb
new file mode 100644
index 0000000000..4ce5cab4db
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/oracle12_test.rb
@@ -0,0 +1,100 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class Oracle12Test < Arel::Spec
+      before do
+        @visitor = Oracle12.new Table.engine.connection
+        @table = Table.new(:users)
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it "modified except to be minus" do
+        left = Nodes::SqlLiteral.new("SELECT * FROM users WHERE age > 10")
+        right = Nodes::SqlLiteral.new("SELECT * FROM users WHERE age > 20")
+        sql = compile Nodes::Except.new(left, right)
+        sql.must_be_like %{
+          ( SELECT * FROM users WHERE age > 10 MINUS SELECT * FROM users WHERE age > 20 )
+        }
+      end
+
+      it "generates select options offset then limit" do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(1)
+        stmt.limit = Nodes::Limit.new(10)
+        sql = compile(stmt)
+        sql.must_be_like "SELECT OFFSET 1 ROWS FETCH FIRST 10 ROWS ONLY"
+      end
+
+      describe "locking" do
+        it "generates ArgumentError if limit and lock are used" do
+          stmt = Nodes::SelectStatement.new
+          stmt.limit = Nodes::Limit.new(10)
+          stmt.lock = Nodes::Lock.new(Arel.sql("FOR UPDATE"))
+          assert_raises ArgumentError do
+            compile(stmt)
+          end
+        end
+
+        it "defaults to FOR UPDATE when locking" do
+          node = Nodes::Lock.new(Arel.sql("FOR UPDATE"))
+          compile(node).must_be_like "FOR UPDATE"
+        end
+      end
+
+      describe "Nodes::BindParam" do
+        it "increments each bind param" do
+          query = @table[:name].eq(Arel::Nodes::BindParam.new(1))
+            .and(@table[:id].eq(Arel::Nodes::BindParam.new(1)))
+          compile(query).must_be_like %{
+            "users"."name" = :a1 AND "users"."id" = :a2
+          }
+        end
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            DECODE("users"."name", 'Aaron Patterson', 0, 1) = 0
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            DECODE("users"."first_name", "users"."last_name", 0, 1) = 0
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            DECODE("users"."first_name", "users"."last_name", 0, 1) = 1
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/oracle_test.rb b/activerecord/test/cases/arel/visitors/oracle_test.rb
new file mode 100644
index 0000000000..893edc7f74
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/oracle_test.rb
@@ -0,0 +1,236 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class OracleTest < Arel::Spec
+      before do
+        @visitor = Oracle.new Table.engine.connection
+        @table = Table.new(:users)
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it "modifies order when there is distinct and first value" do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new("foo")
+        sql = compile(stmt)
+        sql.must_be_like %{
+          SELECT #{select} ORDER BY alias_0__
+        }
+      end
+
+      it "is idempotent with crazy query" do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new("foo")
+
+        sql = compile(stmt)
+        sql2 = compile(stmt)
+        sql.must_equal sql2
+      end
+
+      it "splits orders with commas" do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new("foo, bar")
+        sql = compile(stmt)
+        sql.must_be_like %{
+          SELECT #{select} ORDER BY alias_0__, alias_1__
+        }
+      end
+
+      it "splits orders with commas and function calls" do
+        # *sigh*
+        select = "DISTINCT foo.id, FIRST_VALUE(projects.name) OVER (foo) AS alias_0__"
+        stmt = Nodes::SelectStatement.new
+        stmt.cores.first.projections << Nodes::SqlLiteral.new(select)
+        stmt.orders << Nodes::SqlLiteral.new("NVL(LOWER(bar, foo), foo) DESC, UPPER(baz)")
+        sql = compile(stmt)
+        sql.must_be_like %{
+          SELECT #{select} ORDER BY alias_0__ DESC, alias_1__
+        }
+      end
+
+      describe "Nodes::SelectStatement" do
+        describe "limit" do
+          it "adds a rownum clause" do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = Nodes::Limit.new(10)
+            sql = compile stmt
+            sql.must_be_like %{ SELECT WHERE ROWNUM <= 10 }
+          end
+
+          it "is idempotent" do
+            stmt = Nodes::SelectStatement.new
+            stmt.orders << Nodes::SqlLiteral.new("foo")
+            stmt.limit = Nodes::Limit.new(10)
+            sql = compile stmt
+            sql2 = compile stmt
+            sql.must_equal sql2
+          end
+
+          it "creates a subquery when there is order_by" do
+            stmt = Nodes::SelectStatement.new
+            stmt.orders << Nodes::SqlLiteral.new("foo")
+            stmt.limit = Nodes::Limit.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (SELECT ORDER BY foo ) WHERE ROWNUM <= 10
+            }
+          end
+
+          it "creates a subquery when there is group by" do
+            stmt = Nodes::SelectStatement.new
+            stmt.cores.first.groups << Nodes::SqlLiteral.new("foo")
+            stmt.limit = Nodes::Limit.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (SELECT GROUP BY foo ) WHERE ROWNUM <= 10
+            }
+          end
+
+          it "creates a subquery when there is DISTINCT" do
+            stmt = Nodes::SelectStatement.new
+            stmt.cores.first.set_quantifier = Arel::Nodes::Distinct.new
+            stmt.cores.first.projections << Nodes::SqlLiteral.new("id")
+            stmt.limit = Arel::Nodes::Limit.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (SELECT DISTINCT id ) WHERE ROWNUM <= 10
+            }
+          end
+
+          it "creates a different subquery when there is an offset" do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = Nodes::Limit.new(10)
+            stmt.offset = Nodes::Offset.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (
+                SELECT raw_sql_.*, rownum raw_rnum_
+                FROM (SELECT ) raw_sql_
+                 WHERE rownum <= 20
+              )
+              WHERE raw_rnum_ > 10
+            }
+          end
+
+          it "creates a subquery when there is limit and offset with BindParams" do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = Nodes::Limit.new(Nodes::BindParam.new(1))
+            stmt.offset = Nodes::Offset.new(Nodes::BindParam.new(1))
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (
+                SELECT raw_sql_.*, rownum raw_rnum_
+                FROM (SELECT ) raw_sql_
+                 WHERE rownum <= (:a1 + :a2)
+              )
+              WHERE raw_rnum_ > :a3
+            }
+          end
+
+          it "is idempotent with different subquery" do
+            stmt = Nodes::SelectStatement.new
+            stmt.limit = Nodes::Limit.new(10)
+            stmt.offset = Nodes::Offset.new(10)
+            sql = compile stmt
+            sql2 = compile stmt
+            sql.must_equal sql2
+          end
+        end
+
+        describe "only offset" do
+          it "creates a select from subquery with rownum condition" do
+            stmt = Nodes::SelectStatement.new
+            stmt.offset = Nodes::Offset.new(10)
+            sql = compile stmt
+            sql.must_be_like %{
+              SELECT * FROM (
+                SELECT raw_sql_.*, rownum raw_rnum_
+                FROM (SELECT) raw_sql_
+              )
+              WHERE raw_rnum_ > 10
+            }
+          end
+        end
+      end
+
+      it "modified except to be minus" do
+        left = Nodes::SqlLiteral.new("SELECT * FROM users WHERE age > 10")
+        right = Nodes::SqlLiteral.new("SELECT * FROM users WHERE age > 20")
+        sql = compile Nodes::Except.new(left, right)
+        sql.must_be_like %{
+          ( SELECT * FROM users WHERE age > 10 MINUS SELECT * FROM users WHERE age > 20 )
+        }
+      end
+
+      describe "locking" do
+        it "defaults to FOR UPDATE when locking" do
+          node = Nodes::Lock.new(Arel.sql("FOR UPDATE"))
+          compile(node).must_be_like "FOR UPDATE"
+        end
+      end
+
+      describe "Nodes::BindParam" do
+        it "increments each bind param" do
+          query = @table[:name].eq(Arel::Nodes::BindParam.new(1))
+            .and(@table[:id].eq(Arel::Nodes::BindParam.new(1)))
+          compile(query).must_be_like %{
+            "users"."name" = :a1 AND "users"."id" = :a2
+          }
+        end
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            DECODE("users"."name", 'Aaron Patterson', 0, 1) = 0
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            DECODE("users"."first_name", "users"."last_name", 0, 1) = 0
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            DECODE("users"."first_name", "users"."last_name", 0, 1) = 1
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/postgres_test.rb b/activerecord/test/cases/arel/visitors/postgres_test.rb
new file mode 100644
index 0000000000..0f9efb20b4
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/postgres_test.rb
@@ -0,0 +1,320 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class PostgresTest < Arel::Spec
+      before do
+        @visitor = PostgreSQL.new Table.engine.connection
+        @table = Table.new(:users)
+        @attr = @table[:id]
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      describe "locking" do
+        it "defaults to FOR UPDATE" do
+          compile(Nodes::Lock.new(Arel.sql("FOR UPDATE"))).must_be_like %{
+            FOR UPDATE
+          }
+        end
+
+        it "allows a custom string to be used as a lock" do
+          node = Nodes::Lock.new(Arel.sql("FOR SHARE"))
+          compile(node).must_be_like %{
+            FOR SHARE
+          }
+        end
+      end
+
+      it "should escape LIMIT" do
+        sc = Arel::Nodes::SelectStatement.new
+        sc.limit = Nodes::Limit.new(Nodes.build_quoted("omg"))
+        sc.cores.first.projections << Arel.sql("DISTINCT ON")
+        sc.orders << Arel.sql("xyz")
+        sql = compile(sc)
+        assert_match(/LIMIT 'omg'/, sql)
+        assert_equal 1, sql.scan(/LIMIT/).length, "should have one limit"
+      end
+
+      it "should support DISTINCT ON" do
+        core = Arel::Nodes::SelectCore.new
+        core.set_quantifier = Arel::Nodes::DistinctOn.new(Arel.sql("aaron"))
+        assert_match "DISTINCT ON ( aaron )", compile(core)
+      end
+
+      it "should support DISTINCT" do
+        core = Arel::Nodes::SelectCore.new
+        core.set_quantifier = Arel::Nodes::Distinct.new
+        assert_equal "SELECT DISTINCT", compile(core)
+      end
+
+      it "encloses LATERAL queries in parens" do
+        subquery = @table.project(:id).where(@table[:name].matches("foo%"))
+        compile(subquery.lateral).must_be_like %{
+          LATERAL (SELECT id FROM "users" WHERE "users"."name" ILIKE 'foo%')
+        }
+      end
+
+      it "produces LATERAL queries with alias" do
+        subquery = @table.project(:id).where(@table[:name].matches("foo%"))
+        compile(subquery.lateral("bar")).must_be_like %{
+          LATERAL (SELECT id FROM "users" WHERE "users"."name" ILIKE 'foo%') bar
+        }
+      end
+
+      describe "Nodes::Matches" do
+        it "should know how to visit" do
+          node = @table[:name].matches("foo%")
+          node.must_be_kind_of Nodes::Matches
+          node.case_sensitive.must_equal(false)
+          compile(node).must_be_like %{
+            "users"."name" ILIKE 'foo%'
+          }
+        end
+
+        it "should know how to visit case sensitive" do
+          node = @table[:name].matches("foo%", nil, true)
+          node.case_sensitive.must_equal(true)
+          compile(node).must_be_like %{
+            "users"."name" LIKE 'foo%'
+          }
+        end
+
+        it "can handle ESCAPE" do
+          node = @table[:name].matches("foo!%", "!")
+          compile(node).must_be_like %{
+            "users"."name" ILIKE 'foo!%' ESCAPE '!'
+          }
+        end
+
+        it "can handle subqueries" do
+          subquery = @table.project(:id).where(@table[:name].matches("foo%"))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" ILIKE 'foo%')
+          }
+        end
+      end
+
+      describe "Nodes::DoesNotMatch" do
+        it "should know how to visit" do
+          node = @table[:name].does_not_match("foo%")
+          node.must_be_kind_of Nodes::DoesNotMatch
+          node.case_sensitive.must_equal(false)
+          compile(node).must_be_like %{
+            "users"."name" NOT ILIKE 'foo%'
+          }
+        end
+
+        it "should know how to visit case sensitive" do
+          node = @table[:name].does_not_match("foo%", nil, true)
+          node.case_sensitive.must_equal(true)
+          compile(node).must_be_like %{
+            "users"."name" NOT LIKE 'foo%'
+          }
+        end
+
+        it "can handle ESCAPE" do
+          node = @table[:name].does_not_match("foo!%", "!")
+          compile(node).must_be_like %{
+            "users"."name" NOT ILIKE 'foo!%' ESCAPE '!'
+          }
+        end
+
+        it "can handle subqueries" do
+          subquery = @table.project(:id).where(@table[:name].does_not_match("foo%"))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" NOT ILIKE 'foo%')
+          }
+        end
+      end
+
+      describe "Nodes::Regexp" do
+        it "should know how to visit" do
+          node = @table[:name].matches_regexp("foo.*")
+          node.must_be_kind_of Nodes::Regexp
+          node.case_sensitive.must_equal(true)
+          compile(node).must_be_like %{
+            "users"."name" ~ 'foo.*'
+          }
+        end
+
+        it "can handle case insensitive" do
+          node = @table[:name].matches_regexp("foo.*", false)
+          node.must_be_kind_of Nodes::Regexp
+          node.case_sensitive.must_equal(false)
+          compile(node).must_be_like %{
+            "users"."name" ~* 'foo.*'
+          }
+        end
+
+        it "can handle subqueries" do
+          subquery = @table.project(:id).where(@table[:name].matches_regexp("foo.*"))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" ~ 'foo.*')
+          }
+        end
+      end
+
+      describe "Nodes::NotRegexp" do
+        it "should know how to visit" do
+          node = @table[:name].does_not_match_regexp("foo.*")
+          node.must_be_kind_of Nodes::NotRegexp
+          node.case_sensitive.must_equal(true)
+          compile(node).must_be_like %{
+            "users"."name" !~ 'foo.*'
+          }
+        end
+
+        it "can handle case insensitive" do
+          node = @table[:name].does_not_match_regexp("foo.*", false)
+          node.case_sensitive.must_equal(false)
+          compile(node).must_be_like %{
+            "users"."name" !~* 'foo.*'
+          }
+        end
+
+        it "can handle subqueries" do
+          subquery = @table.project(:id).where(@table[:name].does_not_match_regexp("foo.*"))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" !~ 'foo.*')
+          }
+        end
+      end
+
+      describe "Nodes::BindParam" do
+        it "increments each bind param" do
+          query = @table[:name].eq(Arel::Nodes::BindParam.new(1))
+            .and(@table[:id].eq(Arel::Nodes::BindParam.new(1)))
+          compile(query).must_be_like %{
+            "users"."name" = $1 AND "users"."id" = $2
+          }
+        end
+      end
+
+      describe "Nodes::Cube" do
+        it "should know how to visit with array arguments" do
+          node = Arel::Nodes::Cube.new([@table[:name], @table[:bool]])
+          compile(node).must_be_like %{
+            CUBE( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to visit with CubeDimension Argument" do
+          dimensions = Arel::Nodes::GroupingElement.new([@table[:name], @table[:bool]])
+          node = Arel::Nodes::Cube.new(dimensions)
+          compile(node).must_be_like %{
+            CUBE( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to generate parenthesis when supplied with many Dimensions" do
+          dim1 = Arel::Nodes::GroupingElement.new(@table[:name])
+          dim2 = Arel::Nodes::GroupingElement.new([@table[:bool], @table[:created_at]])
+          node = Arel::Nodes::Cube.new([dim1, dim2])
+          compile(node).must_be_like %{
+            CUBE( ( "users"."name" ), ( "users"."bool", "users"."created_at" ) )
+          }
+        end
+      end
+
+      describe "Nodes::GroupingSet" do
+        it "should know how to visit with array arguments" do
+          node = Arel::Nodes::GroupingSet.new([@table[:name], @table[:bool]])
+          compile(node).must_be_like %{
+            GROUPING SETS( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to visit with CubeDimension Argument" do
+          group = Arel::Nodes::GroupingElement.new([@table[:name], @table[:bool]])
+          node = Arel::Nodes::GroupingSet.new(group)
+          compile(node).must_be_like %{
+            GROUPING SETS( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to generate parenthesis when supplied with many Dimensions" do
+          group1 = Arel::Nodes::GroupingElement.new(@table[:name])
+          group2 = Arel::Nodes::GroupingElement.new([@table[:bool], @table[:created_at]])
+          node = Arel::Nodes::GroupingSet.new([group1, group2])
+          compile(node).must_be_like %{
+            GROUPING SETS( ( "users"."name" ), ( "users"."bool", "users"."created_at" ) )
+          }
+        end
+      end
+
+      describe "Nodes::RollUp" do
+        it "should know how to visit with array arguments" do
+          node = Arel::Nodes::RollUp.new([@table[:name], @table[:bool]])
+          compile(node).must_be_like %{
+            ROLLUP( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to visit with CubeDimension Argument" do
+          group = Arel::Nodes::GroupingElement.new([@table[:name], @table[:bool]])
+          node = Arel::Nodes::RollUp.new(group)
+          compile(node).must_be_like %{
+            ROLLUP( "users"."name", "users"."bool" )
+          }
+        end
+
+        it "should know how to generate parenthesis when supplied with many Dimensions" do
+          group1 = Arel::Nodes::GroupingElement.new(@table[:name])
+          group2 = Arel::Nodes::GroupingElement.new([@table[:bool], @table[:created_at]])
+          node = Arel::Nodes::RollUp.new([group1, group2])
+          compile(node).must_be_like %{
+            ROLLUP( ( "users"."name" ), ( "users"."bool", "users"."created_at" ) )
+          }
+        end
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            "users"."name" IS NOT DISTINCT FROM 'Aaron Patterson'
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            "users"."first_name" IS NOT DISTINCT FROM "users"."last_name"
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT DISTINCT FROM NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            "users"."first_name" IS DISTINCT FROM "users"."last_name"
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS DISTINCT FROM NULL }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/sqlite_test.rb b/activerecord/test/cases/arel/visitors/sqlite_test.rb
new file mode 100644
index 0000000000..ee4e07a675
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/sqlite_test.rb
@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+
+module Arel
+  module Visitors
+    class SqliteTest < Arel::Spec
+      before do
+        @visitor = SQLite.new Table.engine.connection
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it "defaults limit to -1" do
+        stmt = Nodes::SelectStatement.new
+        stmt.offset = Nodes::Offset.new(1)
+        sql = @visitor.accept(stmt, Collectors::SQLString.new).value
+        sql.must_be_like "SELECT LIMIT -1 OFFSET 1"
+      end
+
+      it "does not support locking" do
+        node = Nodes::Lock.new(Arel.sql("FOR UPDATE"))
+        assert_equal "", @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it "does not support boolean" do
+        node = Nodes::True.new()
+        assert_equal "1", @visitor.accept(node, Collectors::SQLString.new).value
+        node = Nodes::False.new()
+        assert_equal "0", @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            "users"."name" IS 'Aaron Patterson'
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            "users"."first_name" IS "users"."last_name"
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            "users"."first_name" IS NOT "users"."last_name"
+          }
+        end
+
+        it "should handle nil" do
+          @table = Table.new(:users)
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/arel/visitors/to_sql_test.rb b/activerecord/test/cases/arel/visitors/to_sql_test.rb
new file mode 100644
index 0000000000..4bfa799a96
--- /dev/null
+++ b/activerecord/test/cases/arel/visitors/to_sql_test.rb
@@ -0,0 +1,713 @@
+# frozen_string_literal: true
+
+require_relative "../helper"
+require "bigdecimal"
+
+module Arel
+  module Visitors
+    describe "the to_sql visitor" do
+      before do
+        @conn = FakeRecord::Base.new
+        @visitor = ToSql.new @conn.connection
+        @table = Table.new(:users)
+        @attr = @table[:id]
+      end
+
+      def compile(node)
+        @visitor.accept(node, Collectors::SQLString.new).value
+      end
+
+      it "works with BindParams" do
+        node = Nodes::BindParam.new(1)
+        sql = compile node
+        sql.must_be_like "?"
+      end
+
+      it "does not quote BindParams used as part of a Values" do
+        bp = Nodes::BindParam.new(1)
+        values = Nodes::Values.new([bp])
+        sql = compile values
+        sql.must_be_like "VALUES (?)"
+      end
+
+      it "can define a dispatch method" do
+        visited = false
+        viz = Class.new(Arel::Visitors::Visitor) {
+          define_method(:hello) do |node, c|
+            visited = true
+          end
+
+          def dispatch
+            { Arel::Table => "hello" }
+          end
+        }.new
+
+        viz.accept(@table, Collectors::SQLString.new)
+        assert visited, "hello method was called"
+      end
+
+      it "should not quote sql literals" do
+        node = @table[Arel.star]
+        sql = compile node
+        sql.must_be_like '"users".*'
+      end
+
+      it "should visit named functions" do
+        function = Nodes::NamedFunction.new("omg", [Arel.star])
+        assert_equal "omg(*)", compile(function)
+      end
+
+      it "should chain predications on named functions" do
+        function = Nodes::NamedFunction.new("omg", [Arel.star])
+        sql = compile(function.eq(2))
+        sql.must_be_like %{ omg(*) = 2 }
+      end
+
+      it "should handle nil with named functions" do
+        function = Nodes::NamedFunction.new("omg", [Arel.star])
+        sql = compile(function.eq(nil))
+        sql.must_be_like %{ omg(*) IS NULL }
+      end
+
+      it "should visit built-in functions" do
+        function = Nodes::Count.new([Arel.star])
+        assert_equal "COUNT(*)", compile(function)
+
+        function = Nodes::Sum.new([Arel.star])
+        assert_equal "SUM(*)", compile(function)
+
+        function = Nodes::Max.new([Arel.star])
+        assert_equal "MAX(*)", compile(function)
+
+        function = Nodes::Min.new([Arel.star])
+        assert_equal "MIN(*)", compile(function)
+
+        function = Nodes::Avg.new([Arel.star])
+        assert_equal "AVG(*)", compile(function)
+      end
+
+      it "should visit built-in functions operating on distinct values" do
+        function = Nodes::Count.new([Arel.star])
+        function.distinct = true
+        assert_equal "COUNT(DISTINCT *)", compile(function)
+
+        function = Nodes::Sum.new([Arel.star])
+        function.distinct = true
+        assert_equal "SUM(DISTINCT *)", compile(function)
+
+        function = Nodes::Max.new([Arel.star])
+        function.distinct = true
+        assert_equal "MAX(DISTINCT *)", compile(function)
+
+        function = Nodes::Min.new([Arel.star])
+        function.distinct = true
+        assert_equal "MIN(DISTINCT *)", compile(function)
+
+        function = Nodes::Avg.new([Arel.star])
+        function.distinct = true
+        assert_equal "AVG(DISTINCT *)", compile(function)
+      end
+
+      it "works with lists" do
+        function = Nodes::NamedFunction.new("omg", [Arel.star, Arel.star])
+        assert_equal "omg(*, *)", compile(function)
+      end
+
+      describe "Nodes::Equality" do
+        it "should escape strings" do
+          test = Table.new(:users)[:name].eq "Aaron Patterson"
+          compile(test).must_be_like %{
+            "users"."name" = 'Aaron Patterson'
+          }
+        end
+
+        it "should handle false" do
+          table = Table.new(:users)
+          val = Nodes.build_quoted(false, table[:active])
+          sql = compile Nodes::Equality.new(val, val)
+          sql.must_be_like %{ 'f' = 'f' }
+        end
+
+        it "should handle nil" do
+          sql = compile Nodes::Equality.new(@table[:name], nil)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe "Nodes::Grouping" do
+        it "wraps nested groupings in brackets only once" do
+          sql = compile Nodes::Grouping.new(Nodes::Grouping.new(Nodes.build_quoted("foo")))
+          sql.must_equal "('foo')"
+        end
+      end
+
+      describe "Nodes::NotEqual" do
+        it "should handle false" do
+          val = Nodes.build_quoted(false, @table[:active])
+          sql = compile Nodes::NotEqual.new(@table[:active], val)
+          sql.must_be_like %{ "users"."active" != 'f' }
+        end
+
+        it "should handle nil" do
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::NotEqual.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+
+      describe "Nodes::IsNotDistinctFrom" do
+        it "should construct a valid generic SQL statement" do
+          test = Table.new(:users)[:name].is_not_distinct_from "Aaron Patterson"
+          compile(test).must_be_like %{
+            CASE WHEN "users"."name" = 'Aaron Patterson' OR ("users"."name" IS NULL AND 'Aaron Patterson' IS NULL) THEN 0 ELSE 1 END = 0
+          }
+        end
+
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_not_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            CASE WHEN "users"."first_name" = "users"."last_name" OR ("users"."first_name" IS NULL AND "users"."last_name" IS NULL) THEN 0 ELSE 1 END = 0
+          }
+        end
+
+        it "should handle nil" do
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsNotDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NULL }
+        end
+      end
+
+      describe "Nodes::IsDistinctFrom" do
+        it "should handle column names on both sides" do
+          test = Table.new(:users)[:first_name].is_distinct_from Table.new(:users)[:last_name]
+          compile(test).must_be_like %{
+            CASE WHEN "users"."first_name" = "users"."last_name" OR ("users"."first_name" IS NULL AND "users"."last_name" IS NULL) THEN 0 ELSE 1 END = 1
+          }
+        end
+
+        it "should handle nil" do
+          val = Nodes.build_quoted(nil, @table[:active])
+          sql = compile Nodes::IsDistinctFrom.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" IS NOT NULL }
+        end
+      end
+
+      it "should visit string subclass" do
+        [
+          Class.new(String).new(":'("),
+          Class.new(Class.new(String)).new(":'("),
+        ].each do |obj|
+          val = Nodes.build_quoted(obj, @table[:active])
+          sql = compile Nodes::NotEqual.new(@table[:name], val)
+          sql.must_be_like %{ "users"."name" != ':\\'(' }
+        end
+      end
+
+      it "should visit_Class" do
+        compile(Nodes.build_quoted(DateTime)).must_equal "'DateTime'"
+      end
+
+      it "should escape LIMIT" do
+        sc = Arel::Nodes::SelectStatement.new
+        sc.limit = Arel::Nodes::Limit.new(Nodes.build_quoted("omg"))
+        assert_match(/LIMIT 'omg'/, compile(sc))
+      end
+
+      it "should contain a single space before ORDER BY" do
+        table = Table.new(:users)
+        test = table.order(table[:name])
+        sql = compile test
+        assert_match(/"users" ORDER BY/, sql)
+      end
+
+      it "should quote LIMIT without column type coercion" do
+        table = Table.new(:users)
+        sc = table.where(table[:name].eq(0)).take(1).ast
+        assert_match(/WHERE "users"."name" = 0 LIMIT 1/, compile(sc))
+      end
+
+      it "should visit_DateTime" do
+        dt = DateTime.now
+        table = Table.new(:users)
+        test = table[:created_at].eq dt
+        sql = compile test
+
+        sql.must_be_like %{"users"."created_at" = '#{dt.strftime("%Y-%m-%d %H:%M:%S")}'}
+      end
+
+      it "should visit_Float" do
+        test = Table.new(:products)[:price].eq 2.14
+        sql = compile test
+        sql.must_be_like %{"products"."price" = 2.14}
+      end
+
+      it "should visit_Not" do
+        sql = compile Nodes::Not.new(Arel.sql("foo"))
+        sql.must_be_like "NOT (foo)"
+      end
+
+      it "should apply Not to the whole expression" do
+        node = Nodes::And.new [@attr.eq(10), @attr.eq(11)]
+        sql = compile Nodes::Not.new(node)
+        sql.must_be_like %{NOT ("users"."id" = 10 AND "users"."id" = 11)}
+      end
+
+      it "should visit_As" do
+        as = Nodes::As.new(Arel.sql("foo"), Arel.sql("bar"))
+        sql = compile as
+        sql.must_be_like "foo AS bar"
+      end
+
+      it "should visit_Integer" do
+        compile 8787878092
+      end
+
+      it "should visit_Hash" do
+        compile(Nodes.build_quoted(a: 1))
+      end
+
+      it "should visit_Set" do
+        compile Nodes.build_quoted(Set.new([1, 2]))
+      end
+
+      it "should visit_BigDecimal" do
+        compile Nodes.build_quoted(BigDecimal("2.14"))
+      end
+
+      it "should visit_Date" do
+        dt = Date.today
+        table = Table.new(:users)
+        test = table[:created_at].eq dt
+        sql = compile test
+
+        sql.must_be_like %{"users"."created_at" = '#{dt.strftime("%Y-%m-%d")}'}
+      end
+
+      it "should visit_NilClass" do
+        compile(Nodes.build_quoted(nil)).must_be_like "NULL"
+      end
+
+      it "unsupported input should raise UnsupportedVisitError" do
+        error = assert_raises(UnsupportedVisitError) { compile(nil) }
+        assert_match(/\AUnsupported/, error.message)
+      end
+
+      it "should visit_Arel_SelectManager, which is a subquery" do
+        mgr = Table.new(:foo).project(:bar)
+        compile(mgr).must_be_like '(SELECT bar FROM "foo")'
+      end
+
+      it "should visit_Arel_Nodes_And" do
+        node = Nodes::And.new [@attr.eq(10), @attr.eq(11)]
+        compile(node).must_be_like %{
+          "users"."id" = 10 AND "users"."id" = 11
+        }
+      end
+
+      it "should visit_Arel_Nodes_Or" do
+        node = Nodes::Or.new @attr.eq(10), @attr.eq(11)
+        compile(node).must_be_like %{
+          "users"."id" = 10 OR "users"."id" = 11
+        }
+      end
+
+      it "should visit_Arel_Nodes_Assignment" do
+        column = @table["id"]
+        node = Nodes::Assignment.new(
+          Nodes::UnqualifiedColumn.new(column),
+          Nodes::UnqualifiedColumn.new(column)
+        )
+        compile(node).must_be_like %{
+          "id" = "id"
+        }
+      end
+
+      it "should visit visit_Arel_Attributes_Time" do
+        attr = Attributes::Time.new(@attr.relation, @attr.name)
+        compile attr
+      end
+
+      it "should visit_TrueClass" do
+        test = Table.new(:users)[:bool].eq(true)
+        compile(test).must_be_like %{ "users"."bool" = 't' }
+      end
+
+      describe "Nodes::Matches" do
+        it "should know how to visit" do
+          node = @table[:name].matches("foo%")
+          compile(node).must_be_like %{
+            "users"."name" LIKE 'foo%'
+          }
+        end
+
+        it "can handle ESCAPE" do
+          node = @table[:name].matches("foo!%", "!")
+          compile(node).must_be_like %{
+            "users"."name" LIKE 'foo!%' ESCAPE '!'
+          }
+        end
+
+        it "can handle subqueries" do
+          subquery = @table.project(:id).where(@table[:name].matches("foo%"))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" LIKE 'foo%')
+          }
+        end
+      end
+
+      describe "Nodes::DoesNotMatch" do
+        it "should know how to visit" do
+          node = @table[:name].does_not_match("foo%")
+          compile(node).must_be_like %{
+            "users"."name" NOT LIKE 'foo%'
+          }
+        end
+
+        it "can handle ESCAPE" do
+          node = @table[:name].does_not_match("foo!%", "!")
+          compile(node).must_be_like %{
+            "users"."name" NOT LIKE 'foo!%' ESCAPE '!'
+          }
+        end
+
+        it "can handle subqueries" do
+          subquery = @table.project(:id).where(@table[:name].does_not_match("foo%"))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" NOT LIKE 'foo%')
+          }
+        end
+      end
+
+      describe "Nodes::Ordering" do
+        it "should know how to visit" do
+          node = @attr.desc
+          compile(node).must_be_like %{
+            "users"."id" DESC
+          }
+        end
+      end
+
+      describe "Nodes::In" do
+        it "should know how to visit" do
+          node = @attr.in [1, 2, 3]
+          compile(node).must_be_like %{
+            "users"."id" IN (1, 2, 3)
+          }
+        end
+
+        it "should return 1=0 when empty right which is always false" do
+          node = @attr.in []
+          compile(node).must_equal "1=0"
+        end
+
+        it "can handle two dot ranges" do
+          node = @attr.between 1..3
+          compile(node).must_be_like %{
+            "users"."id" BETWEEN 1 AND 3
+          }
+        end
+
+        it "can handle three dot ranges" do
+          node = @attr.between 1...3
+          compile(node).must_be_like %{
+            "users"."id" >= 1 AND "users"."id" < 3
+          }
+        end
+
+        it "can handle ranges bounded by infinity" do
+          node = @attr.between 1..Float::INFINITY
+          compile(node).must_be_like %{
+            "users"."id" >= 1
+          }
+          node = @attr.between(-Float::INFINITY..3)
+          compile(node).must_be_like %{
+            "users"."id" <= 3
+          }
+          node = @attr.between(-Float::INFINITY...3)
+          compile(node).must_be_like %{
+            "users"."id" < 3
+          }
+          node = @attr.between(-Float::INFINITY..Float::INFINITY)
+          compile(node).must_be_like %{1=1}
+        end
+
+        it "can handle subqueries" do
+          table = Table.new(:users)
+          subquery = table.project(:id).where(table[:name].eq("Aaron"))
+          node = @attr.in subquery
+          compile(node).must_be_like %{
+            "users"."id" IN (SELECT id FROM "users" WHERE "users"."name" = 'Aaron')
+          }
+        end
+      end
+
+      describe "Nodes::InfixOperation" do
+        it "should handle Multiplication" do
+          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) * Arel::Attributes::Decimal.new(Table.new(:currency_rates), :rate)
+          compile(node).must_equal %("products"."price" * "currency_rates"."rate")
+        end
+
+        it "should handle Division" do
+          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) / 5
+          compile(node).must_equal %("products"."price" / 5)
+        end
+
+        it "should handle Addition" do
+          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) + 6
+          compile(node).must_equal %(("products"."price" + 6))
+        end
+
+        it "should handle Subtraction" do
+          node = Arel::Attributes::Decimal.new(Table.new(:products), :price) - 7
+          compile(node).must_equal %(("products"."price" - 7))
+        end
+
+        it "should handle Concatenation" do
+          table = Table.new(:users)
+          node = table[:name].concat(table[:name])
+          compile(node).must_equal %("users"."name" || "users"."name")
+        end
+
+        it "should handle BitwiseAnd" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) & 16
+          compile(node).must_equal %(("products"."bitmap" & 16))
+        end
+
+        it "should handle BitwiseOr" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) | 16
+          compile(node).must_equal %(("products"."bitmap" | 16))
+        end
+
+        it "should handle BitwiseXor" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) ^ 16
+          compile(node).must_equal %(("products"."bitmap" ^ 16))
+        end
+
+        it "should handle BitwiseShiftLeft" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) << 4
+          compile(node).must_equal %(("products"."bitmap" << 4))
+        end
+
+        it "should handle BitwiseShiftRight" do
+          node = Arel::Attributes::Integer.new(Table.new(:products), :bitmap) >> 4
+          compile(node).must_equal %(("products"."bitmap" >> 4))
+        end
+
+        it "should handle arbitrary operators" do
+          node = Arel::Nodes::InfixOperation.new(
+            "&&",
+            Arel::Attributes::String.new(Table.new(:products), :name),
+            Arel::Attributes::String.new(Table.new(:products), :name)
+          )
+          compile(node).must_equal %("products"."name" && "products"."name")
+        end
+      end
+
+      describe "Nodes::UnaryOperation" do
+        it "should handle BitwiseNot" do
+          node = ~ Arel::Attributes::Integer.new(Table.new(:products), :bitmap)
+          compile(node).must_equal %( ~ "products"."bitmap")
+        end
+
+        it "should handle arbitrary operators" do
+          node = Arel::Nodes::UnaryOperation.new("!", Arel::Attributes::String.new(Table.new(:products), :active))
+          compile(node).must_equal %( ! "products"."active")
+        end
+      end
+
+      describe "Nodes::Union" do
+        it "squashes parenthesis on multiple unions" do
+          subnode = Nodes::Union.new Arel.sql("left"), Arel.sql("right")
+          node = Nodes::Union.new subnode, Arel.sql("topright")
+          assert_equal("( left UNION right UNION topright )", compile(node))
+          subnode = Nodes::Union.new Arel.sql("left"), Arel.sql("right")
+          node = Nodes::Union.new Arel.sql("topleft"), subnode
+          assert_equal("( topleft UNION left UNION right )", compile(node))
+        end
+      end
+
+      describe "Nodes::UnionAll" do
+        it "squashes parenthesis on multiple union alls" do
+          subnode = Nodes::UnionAll.new Arel.sql("left"), Arel.sql("right")
+          node = Nodes::UnionAll.new subnode, Arel.sql("topright")
+          assert_equal("( left UNION ALL right UNION ALL topright )", compile(node))
+          subnode = Nodes::UnionAll.new Arel.sql("left"), Arel.sql("right")
+          node = Nodes::UnionAll.new Arel.sql("topleft"), subnode
+          assert_equal("( topleft UNION ALL left UNION ALL right )", compile(node))
+        end
+      end
+
+      describe "Nodes::NotIn" do
+        it "should know how to visit" do
+          node = @attr.not_in [1, 2, 3]
+          compile(node).must_be_like %{
+            "users"."id" NOT IN (1, 2, 3)
+          }
+        end
+
+        it "should return 1=1 when empty right which is always true" do
+          node = @attr.not_in []
+          compile(node).must_equal "1=1"
+        end
+
+        it "can handle two dot ranges" do
+          node = @attr.not_between 1..3
+          compile(node).must_equal(
+            %{("users"."id" < 1 OR "users"."id" > 3)}
+          )
+        end
+
+        it "can handle three dot ranges" do
+          node = @attr.not_between 1...3
+          compile(node).must_equal(
+            %{("users"."id" < 1 OR "users"."id" >= 3)}
+          )
+        end
+
+        it "can handle ranges bounded by infinity" do
+          node = @attr.not_between 1..Float::INFINITY
+          compile(node).must_be_like %{
+            "users"."id" < 1
+          }
+          node = @attr.not_between(-Float::INFINITY..3)
+          compile(node).must_be_like %{
+            "users"."id" > 3
+          }
+          node = @attr.not_between(-Float::INFINITY...3)
+          compile(node).must_be_like %{
+            "users"."id" >= 3
+          }
+          node = @attr.not_between(-Float::INFINITY..Float::INFINITY)
+          compile(node).must_be_like %{1=0}
+        end
+
+        it "can handle subqueries" do
+          table = Table.new(:users)
+          subquery = table.project(:id).where(table[:name].eq("Aaron"))
+          node = @attr.not_in subquery
+          compile(node).must_be_like %{
+            "users"."id" NOT IN (SELECT id FROM "users" WHERE "users"."name" = 'Aaron')
+          }
+        end
+      end
+
+      describe "Constants" do
+        it "should handle true" do
+          test = Table.new(:users).create_true
+          compile(test).must_be_like %{
+            TRUE
+          }
+        end
+
+        it "should handle false" do
+          test = Table.new(:users).create_false
+          compile(test).must_be_like %{
+            FALSE
+          }
+        end
+      end
+
+      describe "TableAlias" do
+        it "should use the underlying table for checking columns" do
+          test = Table.new(:users).alias("zomgusers")[:id].eq "3"
+          compile(test).must_be_like %{
+            "zomgusers"."id" = '3'
+          }
+        end
+      end
+
+      describe "distinct on" do
+        it "raises not implemented error" do
+          core = Arel::Nodes::SelectCore.new
+          core.set_quantifier = Arel::Nodes::DistinctOn.new(Arel.sql("aaron"))
+
+          assert_raises(NotImplementedError) do
+            compile(core)
+          end
+        end
+      end
+
+      describe "Nodes::Regexp" do
+        it "raises not implemented error" do
+          node = Arel::Nodes::Regexp.new(@table[:name], Nodes.build_quoted("foo%"))
+
+          assert_raises(NotImplementedError) do
+            compile(node)
+          end
+        end
+      end
+
+      describe "Nodes::NotRegexp" do
+        it "raises not implemented error" do
+          node = Arel::Nodes::NotRegexp.new(@table[:name], Nodes.build_quoted("foo%"))
+
+          assert_raises(NotImplementedError) do
+            compile(node)
+          end
+        end
+      end
+
+      describe "Nodes::Case" do
+        it "supports simple case expressions" do
+          node = Arel::Nodes::Case.new(@table[:name])
+            .when("foo").then(1)
+            .else(0)
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 1 ELSE 0 END
+          }
+        end
+
+        it "supports extended case expressions" do
+          node = Arel::Nodes::Case.new
+            .when(@table[:name].in(%w(foo bar))).then(1)
+            .else(0)
+
+          compile(node).must_be_like %{
+            CASE WHEN "users"."name" IN ('foo', 'bar') THEN 1 ELSE 0 END
+          }
+        end
+
+        it "works without default branch" do
+          node = Arel::Nodes::Case.new(@table[:name])
+            .when("foo").then(1)
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 1 END
+          }
+        end
+
+        it "allows chaining multiple conditions" do
+          node = Arel::Nodes::Case.new(@table[:name])
+            .when("foo").then(1)
+            .when("bar").then(2)
+            .else(0)
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 1 WHEN 'bar' THEN 2 ELSE 0 END
+          }
+        end
+
+        it "supports #when with two arguments and no #then" do
+          node = Arel::Nodes::Case.new @table[:name]
+
+          { foo: 1, bar: 0 }.reduce(node) { |_node, pair| _node.when(*pair) }
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 1 WHEN 'bar' THEN 0 END
+          }
+        end
+
+        it "can be chained as a predicate" do
+          node = @table[:name].when("foo").then("bar").else("baz")
+
+          compile(node).must_be_like %{
+            CASE "users"."name" WHEN 'foo' THEN 'bar' ELSE 'baz' END
+          }
+        end
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/associations/association_scope_test.rb b/activerecord/test/cases/associations/association_scope_test.rb
deleted file mode 100644
index 472e270f8c..0000000000
--- a/activerecord/test/cases/associations/association_scope_test.rb
+++ /dev/null
@@ -1,16 +0,0 @@
-require 'cases/helper'
-require 'models/post'
-require 'models/author'
-
-module ActiveRecord
-  module Associations
-    class AssociationScopeTest < ActiveRecord::TestCase
-      test 'does not duplicate conditions' do
-        scope = AssociationScope.scope(Author.new.association(:welcome_posts),
-                                        Author.connection)
-        binds = scope.where_clause.binds.map(&:value)
-        assert_equal binds.uniq, binds
-      end
-    end
-  end
-end
diff --git a/activerecord/test/cases/associations/belongs_to_associations_test.rb b/activerecord/test/cases/associations/belongs_to_associations_test.rb
index ebe08c618f..93dd427951 100644
--- a/activerecord/test/cases/associations/belongs_to_associations_test.rb
+++ b/activerecord/test/cases/associations/belongs_to_associations_test.rb
@@ -1,26 +1,30 @@
-require 'cases/helper'
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/company'
-require 'models/topic'
-require 'models/reply'
-require 'models/computer'
-require 'models/post'
-require 'models/author'
-require 'models/tag'
-require 'models/tagging'
-require 'models/comment'
-require 'models/sponsor'
-require 'models/member'
-require 'models/essay'
-require 'models/toy'
-require 'models/invoice'
-require 'models/line_item'
-require 'models/column'
-require 'models/record'
-require 'models/admin'
-require 'models/admin/user'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/developer"
+require "models/project"
+require "models/company"
+require "models/topic"
+require "models/reply"
+require "models/computer"
+require "models/post"
+require "models/author"
+require "models/tag"
+require "models/tagging"
+require "models/comment"
+require "models/sponsor"
+require "models/member"
+require "models/essay"
+require "models/toy"
+require "models/invoice"
+require "models/line_item"
+require "models/column"
+require "models/record"
+require "models/admin"
+require "models/admin/user"
+require "models/ship"
+require "models/treasure"
+require "models/parrot"
 
 class BelongsToAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :developers, :projects, :topics,
@@ -33,6 +37,21 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal companies(:first_firm).name, firm.name
   end
 
+  def test_assigning_belongs_to_on_destroyed_object
+    client = Client.create!(name: "Client")
+    client.destroy!
+    assert_raise(frozen_error_class) { client.firm = nil }
+    assert_raise(frozen_error_class) { client.firm = Firm.new(name: "Firm") }
+  end
+
+  def test_eager_loading_wont_mutate_owner_record
+    client = Client.eager_load(:firm_with_basic_id).first
+    assert_not_predicate client, :firm_id_came_from_user?
+
+    client = Client.preload(:firm_with_basic_id).first
+    assert_not_predicate client, :firm_id_came_from_user?
+  end
+
   def test_missing_attribute_error_is_raised_when_no_foreign_key_attribute
     assert_raises(ActiveModel::MissingAttributeError) { Client.select(:id).first.firm }
   end
@@ -41,17 +60,17 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     ActiveRecord::SQLCounter.clear_log
     Client.find(3).firm
   ensure
-    assert ActiveRecord::SQLCounter.log_all.all? { |sql| /order by/i !~ sql }, 'ORDER BY was used in the query'
+    assert ActiveRecord::SQLCounter.log_all.all? { |sql| /order by/i !~ sql }, "ORDER BY was used in the query"
   end
 
   def test_belongs_to_with_primary_key
-    client = Client.create(:name => "Primary key client", :firm_name => companies(:first_firm).name)
+    client = Client.create(name: "Primary key client", firm_name: companies(:first_firm).name)
     assert_equal companies(:first_firm).name, client.firm_with_primary_key.name
   end
 
   def test_belongs_to_with_primary_key_joins_on_correct_column
     sql = Client.joins(:firm_with_primary_key).to_sql
-    if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+    if current_adapter?(:Mysql2Adapter)
       assert_no_match(/`firm_with_primary_keys_companies`\.`id`/, sql)
       assert_match(/`firm_with_primary_keys_companies`\.`name`/, sql)
     elsif current_adapter?(:OracleAdapter)
@@ -75,7 +94,7 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     end
 
     account = model.new
-    assert account.valid?
+    assert_predicate account, :valid?
   ensure
     ActiveRecord::Base.belongs_to_required_by_default = original_value
   end
@@ -91,8 +110,8 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     end
 
     account = model.new
-    refute account.valid?
-    assert_equal [{error: :blank}], account.errors.details[:company]
+    assert_not_predicate account, :valid?
+    assert_equal [{ error: :blank }], account.errors.details[:company]
   ensure
     ActiveRecord::Base.belongs_to_required_by_default = original_value
   end
@@ -108,31 +127,69 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     end
 
     account = model.new
-    refute account.valid?
-    assert_equal [{error: :blank}], account.errors.details[:company]
+    assert_not_predicate account, :valid?
+    assert_equal [{ error: :blank }], account.errors.details[:company]
   ensure
     ActiveRecord::Base.belongs_to_required_by_default = original_value
   end
 
+  def test_default
+    david = developers(:david)
+    jamis = developers(:jamis)
+
+    model = Class.new(ActiveRecord::Base) do
+      self.table_name = "ships"
+      def self.name; "Temp"; end
+      belongs_to :developer, default: -> { david }
+    end
+
+    ship = model.create!
+    assert_equal david, ship.developer
+
+    ship = model.create!(developer: jamis)
+    assert_equal jamis, ship.developer
+
+    ship.update!(developer: nil)
+    assert_equal david, ship.developer
+  end
+
+  def test_default_with_lambda
+    model = Class.new(ActiveRecord::Base) do
+      self.table_name = "ships"
+      def self.name; "Temp"; end
+      belongs_to :developer, default: -> { default_developer }
+
+      def default_developer
+        Developer.first
+      end
+    end
+
+    ship = model.create!
+    assert_equal developers(:david), ship.developer
+
+    ship = model.create!(developer: developers(:jamis))
+    assert_equal developers(:jamis), ship.developer
+  end
+
   def test_default_scope_on_relations_is_not_cached
     counter = 0
 
     comments = Class.new(ActiveRecord::Base) {
-      self.table_name = 'comments'
-      self.inheritance_column = 'not_there'
+      self.table_name = "comments"
+      self.inheritance_column = "not_there"
 
       posts = Class.new(ActiveRecord::Base) {
-        self.table_name = 'posts'
-        self.inheritance_column = 'not_there'
+        self.table_name = "posts"
+        self.inheritance_column = "not_there"
 
         default_scope -> {
           counter += 1
-          where("id = :inc", :inc => counter)
+          where("id = :inc", inc: counter)
         }
 
-        has_many :comments, :anonymous_class => comments
+        has_many :comments, anonymous_class: comments
       }
-      belongs_to :post, :anonymous_class => posts, :inverse_of => false
+      belongs_to :post, anonymous_class: posts, inverse_of: false
     }
 
     assert_equal 0, counter
@@ -164,9 +221,9 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     Admin.const_set "Region", Class.new(ActiveRecord::Base)
 
     e = assert_raise(ActiveRecord::AssociationTypeMismatch) {
-      Admin::RegionalUser.new(region: 'wrong value')
+      Admin::RegionalUser.new(region: "wrong value")
     }
-    assert_match(/^Region\([^)]+\) expected, got String\([^)]+\)$/, e.message)
+    assert_match(/^Region\([^)]+\) expected, got "wrong value" which is an instance of String\([^)]+\)$/, e.message)
   ensure
     Admin.send :remove_const, "Region" if Admin.const_defined?("Region")
     Admin.send :remove_const, "RegionalUser" if Admin.const_defined?("RegionalUser")
@@ -175,6 +232,8 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
       remove_column :admin_users, :region_id if column_exists?(:admin_users, :region_id)
       drop_table :admin_regions, if_exists: true
     end
+
+    Admin::User.reset_column_information
   end
 
   def test_natural_assignment
@@ -201,15 +260,15 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   def test_eager_loading_with_primary_key
     Firm.create("name" => "Apple")
     Client.create("name" => "Citibank", :firm_name => "Apple")
-    citibank_result = Client.all.merge!(:where => {:name => "Citibank"}, :includes => :firm_with_primary_key).first
-    assert citibank_result.association(:firm_with_primary_key).loaded?
+    citibank_result = Client.all.merge!(where: { name: "Citibank" }, includes: :firm_with_primary_key).first
+    assert_predicate citibank_result.association(:firm_with_primary_key), :loaded?
   end
 
   def test_eager_loading_with_primary_key_as_symbol
     Firm.create("name" => "Apple")
     Client.create("name" => "Citibank", :firm_name => "Apple")
-    citibank_result = Client.all.merge!(:where => {:name => "Citibank"}, :includes => :firm_with_primary_key_symbols).first
-    assert citibank_result.association(:firm_with_primary_key_symbols).loaded?
+    citibank_result = Client.all.merge!(where: { name: "Citibank" }, includes: :firm_with_primary_key_symbols).first
+    assert_predicate citibank_result.association(:firm_with_primary_key_symbols), :loaded?
   end
 
   def test_creating_the_belonging_object
@@ -221,8 +280,17 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal apple, citibank.firm
   end
 
+  def test_creating_the_belonging_object_from_new_record
+    citibank = Account.new("credit_limit" => 10)
+    apple    = citibank.create_firm("name" => "Apple")
+    assert_equal apple, citibank.firm
+    citibank.save
+    citibank.reload
+    assert_equal apple, citibank.firm
+  end
+
   def test_creating_the_belonging_object_with_primary_key
-    client = Client.create(:name => "Primary key client")
+    client = Client.create(name: "Primary key client")
     apple  = client.create_firm_with_primary_key("name" => "Apple")
     assert_equal apple, client.firm_with_primary_key
     client.save
@@ -245,63 +313,99 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
   def test_building_the_belonging_object_with_explicit_sti_base_class
     account = Account.new
-    company = account.build_firm(:type => "Company")
+    company = account.build_firm(type: "Company")
     assert_kind_of Company, company, "Expected #{company.class} to be a Company"
   end
 
   def test_building_the_belonging_object_with_sti_subclass
     account = Account.new
-    company = account.build_firm(:type => "Firm")
+    company = account.build_firm(type: "Firm")
     assert_kind_of Firm, company, "Expected #{company.class} to be a Firm"
   end
 
   def test_building_the_belonging_object_with_an_invalid_type
     account = Account.new
-    assert_raise(ActiveRecord::SubclassNotFound) { account.build_firm(:type => "InvalidType") }
+    assert_raise(ActiveRecord::SubclassNotFound) { account.build_firm(type: "InvalidType") }
   end
 
   def test_building_the_belonging_object_with_an_unrelated_type
     account = Account.new
-    assert_raise(ActiveRecord::SubclassNotFound) { account.build_firm(:type => "Account") }
+    assert_raise(ActiveRecord::SubclassNotFound) { account.build_firm(type: "Account") }
   end
 
   def test_building_the_belonging_object_with_primary_key
-    client = Client.create(:name => "Primary key client")
+    client = Client.create(name: "Primary key client")
     apple  = client.build_firm_with_primary_key("name" => "Apple")
     client.save
     assert_equal apple.name, client.firm_name
   end
 
   def test_create!
-    client  = Client.create!(:name => "Jimmy")
-    account = client.create_account!(:credit_limit => 10)
+    client  = Client.create!(name: "Jimmy")
+    account = client.create_account!(credit_limit: 10)
     assert_equal account, client.account
-    assert account.persisted?
+    assert_predicate account, :persisted?
     client.save
     client.reload
     assert_equal account, client.account
   end
 
   def test_failing_create!
-    client  = Client.create!(:name => "Jimmy")
+    client = Client.create!(name: "Jimmy")
     assert_raise(ActiveRecord::RecordInvalid) { client.create_account! }
     assert_not_nil client.account
-    assert client.account.new_record?
+    assert_predicate client.account, :new_record?
+  end
+
+  def test_reloading_the_belonging_object
+    odegy_account = accounts(:odegy_account)
+
+    assert_equal "Odegy", odegy_account.firm.name
+    Company.where(id: odegy_account.firm_id).update_all(name: "ODEGY")
+    assert_equal "Odegy", odegy_account.firm.name
+
+    assert_equal "ODEGY", odegy_account.reload_firm.name
+  end
+
+  def test_reload_the_belonging_object_with_query_cache
+    odegy_account_id = accounts(:odegy_account).id
+
+    connection = ActiveRecord::Base.connection
+    connection.enable_query_cache!
+    connection.clear_query_cache
+
+    # Populate the cache with a query
+    odegy_account = Account.find(odegy_account_id)
+
+    # Populate the cache with a second query
+    odegy_account.firm
+
+    assert_equal 2, connection.query_cache.size
+
+    # Clear the cache and fetch the firm again, populating the cache with a query
+    assert_queries(1) { odegy_account.reload_firm }
+
+    # This query is not cached anymore, so it should make a real SQL query
+    assert_queries(1) { Account.find(odegy_account_id) }
+  ensure
+    ActiveRecord::Base.connection.disable_query_cache!
   end
 
   def test_natural_assignment_to_nil
     client = Client.find(3)
     client.firm = nil
     client.save
-    assert_nil client.firm(true)
+    client.association(:firm).reload
+    assert_nil client.firm
     assert_nil client.client_of
   end
 
   def test_natural_assignment_to_nil_with_primary_key
-    client = Client.create(:name => "Primary key client", :firm_name => companies(:first_firm).name)
+    client = Client.create(name: "Primary key client", firm_name: companies(:first_firm).name)
     client.firm_with_primary_key = nil
     client.save
-    assert_nil client.firm_with_primary_key(true)
+    client.association(:firm_with_primary_key).reload
+    assert_nil client.firm_with_primary_key
     assert_nil client.client_of
   end
 
@@ -318,20 +422,21 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   def test_polymorphic_association_class
     sponsor = Sponsor.new
     assert_nil sponsor.association(:sponsorable).send(:klass)
-    assert_nil sponsor.sponsorable(force_reload: true)
+    sponsor.association(:sponsorable).reload
+    assert_nil sponsor.sponsorable
 
-    sponsor.sponsorable_type = '' # the column doesn't have to be declared NOT NULL
+    sponsor.sponsorable_type = "" # the column doesn't have to be declared NOT NULL
     assert_nil sponsor.association(:sponsorable).send(:klass)
-    assert_nil sponsor.sponsorable(force_reload: true)
+    sponsor.association(:sponsorable).reload
+    assert_nil sponsor.sponsorable
 
-    sponsor.sponsorable = Member.new :name => "Bert"
+    sponsor.sponsorable = Member.new name: "Bert"
     assert_equal Member, sponsor.association(:sponsorable).send(:klass)
-    assert_equal "members", sponsor.association(:sponsorable).aliased_table_name
   end
 
   def test_with_polymorphic_and_condition
     sponsor = Sponsor.create
-    member = Member.create :name => "Bert"
+    member = Member.create name: "Bert"
     sponsor.sponsorable = member
 
     assert_equal member, sponsor.sponsorable
@@ -340,7 +445,23 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
   def test_with_select
     assert_equal 1, Company.find(2).firm_with_select.attributes.size
-    assert_equal 1, Company.all.merge!(:includes => :firm_with_select ).find(2).firm_with_select.attributes.size
+    assert_equal 1, Company.all.merge!(includes: :firm_with_select).find(2).firm_with_select.attributes.size
+  end
+
+  def test_belongs_to_without_counter_cache_option
+    # Ship has a conventionally named `treasures_count` column, but the counter_cache
+    # option is not given on the association.
+    ship = Ship.create(name: "Countless")
+
+    assert_no_difference lambda { ship.reload.treasures_count }, "treasures_count should not be changed unless counter_cache is given on the relation" do
+      treasure = Treasure.new(name: "Gold", ship: ship)
+      treasure.save
+    end
+
+    assert_no_difference lambda { ship.reload.treasures_count }, "treasures_count should not be changed unless counter_cache is given on the relation" do
+      treasure = ship.treasures.first
+      treasure.destroy
+    end
   end
 
   def test_belongs_to_counter
@@ -355,31 +476,70 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_belongs_to_counter_with_assigning_nil
-    post = Post.find(1)
-    comment = Comment.find(1)
+    topic = Topic.create!(title: "debate")
+    reply = Reply.create!(title: "blah!", content: "world around!", topic: topic)
+
+    assert_equal topic.id, reply.parent_id
+    assert_equal 1, topic.reload.replies.size
+
+    reply.topic = nil
+    reply.reload
+
+    assert_equal topic.id, reply.parent_id
+    assert_equal 1, topic.reload.replies.size
+
+    reply.topic = nil
+    reply.save!
+
+    assert_equal 0, topic.reload.replies.size
+  end
+
+  def test_belongs_to_counter_with_assigning_new_object
+    topic = Topic.create!(title: "debate")
+    reply = Reply.create!(title: "blah!", content: "world around!", topic: topic)
 
-    assert_equal post.id, comment.post_id
-    assert_equal 2, Post.find(post.id).comments.size
+    assert_equal topic.id, reply.parent_id
+    assert_equal 1, topic.reload.replies_count
 
-    comment.post = nil
+    topic2 = reply.build_topic(title: "debate2")
+    reply.save!
 
-    assert_equal 1, Post.find(post.id).comments.size
+    assert_not_equal topic.id, reply.parent_id
+    assert_equal topic2.id, reply.parent_id
+
+    assert_equal 0, topic.reload.replies_count
+    assert_equal 1, topic2.reload.replies_count
   end
 
   def test_belongs_to_with_primary_key_counter
     debate  = Topic.create("title" => "debate")
     debate2 = Topic.create("title" => "debate2")
-    reply   = Reply.create("title" => "blah!", "content" => "world around!", "parent_title" => "debate")
+    reply   = Reply.create("title" => "blah!", "content" => "world around!", "parent_title" => "debate2")
+
+    assert_equal 0, debate.reload.replies_count
+    assert_equal 1, debate2.reload.replies_count
+
+    reply.parent_title = "debate"
+    reply.save!
+
+    assert_equal 1, debate.reload.replies_count
+    assert_equal 0, debate2.reload.replies_count
+
+    assert_no_queries do
+      reply.topic_with_primary_key = debate
+    end
 
     assert_equal 1, debate.reload.replies_count
     assert_equal 0, debate2.reload.replies_count
 
     reply.topic_with_primary_key = debate2
+    reply.save!
 
     assert_equal 0, debate.reload.replies_count
     assert_equal 1, debate2.reload.replies_count
 
     reply.topic_with_primary_key = nil
+    reply.save!
 
     assert_equal 0, debate.reload.replies_count
     assert_equal 0, debate2.reload.replies_count
@@ -406,11 +566,13 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal 1, Topic.find(topic2.id).replies.size
 
     reply1.topic = nil
+    reply1.save!
 
     assert_equal 0, Topic.find(topic1.id).replies.size
     assert_equal 0, Topic.find(topic2.id).replies.size
 
     reply1.topic = topic1
+    reply1.save!
 
     assert_equal 1, Topic.find(topic1.id).replies.size
     assert_equal 0, Topic.find(topic2.id).replies.size
@@ -439,14 +601,65 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_belongs_to_counter_after_save
-    topic = Topic.create!(:title => "monday night")
-    topic.replies.create!(:title => "re: monday night", :content => "football")
+    topic = Topic.create!(title: "monday night")
+
+    assert_queries(2) do
+      topic.replies.create!(title: "re: monday night", content: "football")
+    end
+
     assert_equal 1, Topic.find(topic.id)[:replies_count]
 
     topic.save!
     assert_equal 1, Topic.find(topic.id)[:replies_count]
   end
 
+  def test_belongs_to_counter_after_touch
+    topic = Topic.create!(title: "topic")
+
+    assert_equal 0, topic.replies_count
+    assert_equal 0, topic.after_touch_called
+
+    reply = Reply.create!(title: "blah!", content: "world around!", topic_with_primary_key: topic)
+
+    assert_equal 1, topic.replies_count
+    assert_equal 1, topic.after_touch_called
+
+    reply.destroy!
+
+    assert_equal 0, topic.replies_count
+    assert_equal 2, topic.after_touch_called
+  end
+
+  def test_belongs_to_touch_with_reassigning
+    debate  = Topic.create!(title: "debate")
+    debate2 = Topic.create!(title: "debate2")
+    reply   = Reply.create!(title: "blah!", content: "world around!", parent_title: "debate2")
+
+    time = 1.day.ago
+
+    debate.touch(time: time)
+    debate2.touch(time: time)
+
+    assert_queries(3) do
+      reply.parent_title = "debate"
+      reply.save!
+    end
+
+    assert_operator debate.reload.updated_at, :>, time
+    assert_operator debate2.reload.updated_at, :>, time
+
+    debate.touch(time: time)
+    debate2.touch(time: time)
+
+    assert_queries(3) do
+      reply.topic_with_primary_key = debate2
+      reply.save!
+    end
+
+    assert_operator debate.reload.updated_at, :>, time
+    assert_operator debate2.reload.updated_at, :>, time
+  end
+
   def test_belongs_to_with_touch_option_on_touch
     line_item = LineItem.create!
     Invoice.create!(line_items: [line_item])
@@ -478,7 +691,9 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     line_item = LineItem.create!
     invoice = Invoice.create!(line_items: [line_item])
     initial = invoice.updated_at
-    line_item.touch
+    travel(1.second) do
+      line_item.touch
+    end
 
     assert_not_equal initial, invoice.reload.updated_at
   end
@@ -503,7 +718,7 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     line_item = LineItem.create!
     Invoice.create!(line_items: [line_item])
 
-    assert_queries(0) { line_item.save }
+    assert_no_queries { line_item.save }
   end
 
   def test_belongs_to_with_touch_option_on_destroy
@@ -540,8 +755,8 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_belongs_to_counter_when_update_columns
-    topic = Topic.create!(:title => "37s")
-    topic.replies.create!(:title => "re: 37s", :content => "rails")
+    topic = Topic.create!(title: "37s")
+    topic.replies.create!(title: "re: 37s", content: "rails")
     assert_equal 1, Topic.find(topic.id)[:replies_count]
 
     topic.update_columns(content: "rails is wonderful")
@@ -552,30 +767,31 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     final_cut = Client.new("name" => "Final Cut")
     firm = Firm.find(1)
     final_cut.firm = firm
-    assert !final_cut.persisted?
+    assert_not_predicate final_cut, :persisted?
     assert final_cut.save
-    assert final_cut.persisted?
-    assert firm.persisted?
+    assert_predicate final_cut, :persisted?
+    assert_predicate firm, :persisted?
+    assert_equal firm, final_cut.firm
+    final_cut.association(:firm).reload
     assert_equal firm, final_cut.firm
-    assert_equal firm, final_cut.firm(true)
   end
 
   def test_assignment_before_child_saved_with_primary_key
     final_cut = Client.new("name" => "Final Cut")
     firm = Firm.find(1)
     final_cut.firm_with_primary_key = firm
-    assert !final_cut.persisted?
+    assert_not_predicate final_cut, :persisted?
     assert final_cut.save
-    assert final_cut.persisted?
-    assert firm.persisted?
+    assert_predicate final_cut, :persisted?
+    assert_predicate firm, :persisted?
+    assert_equal firm, final_cut.firm_with_primary_key
+    final_cut.association(:firm_with_primary_key).reload
     assert_equal firm, final_cut.firm_with_primary_key
-    assert_equal firm, final_cut.firm_with_primary_key(true)
   end
 
   def test_new_record_with_foreign_key_but_no_object
     client = Client.new("firm_id" => 1)
-    # sometimes tests on Oracle fail if ORDER BY is not provided therefore add always :order with :first
-    assert_equal Firm.all.merge!(:order => "id").first, client.firm_with_basic_id
+    assert_equal Firm.first, client.firm_with_basic_id
   end
 
   def test_setting_foreign_key_after_nil_target_loaded
@@ -597,7 +813,13 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
   def test_dont_find_target_when_foreign_key_is_null
     tagging = taggings(:thinking_general)
-    assert_queries(0) { tagging.super_tag }
+    assert_no_queries { tagging.super_tag }
+  end
+
+  def test_dont_find_target_when_saving_foreign_key_after_stale_association_loaded
+    client = Client.create!(name: "Test client", firm_with_basic_id: Firm.find(1))
+    client.firm_id = Firm.create!(name: "Test firm").id
+    assert_queries(1) { client.save! }
   end
 
   def test_field_name_same_as_foreign_key
@@ -606,11 +828,12 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_counter_cache
-    topic = Topic.create :title => "Zoom-zoom-zoom"
+    topic = Topic.create title: "Zoom-zoom-zoom"
     assert_equal 0, topic[:replies_count]
 
-    reply = Reply.create(:title => "re: zoom", :content => "speedy quick!")
+    reply = Reply.create(title: "re: zoom", content: "speedy quick!")
     reply.topic = topic
+    reply.save!
 
     assert_equal 1, topic.reload[:replies_count]
     assert_equal 1, topic.replies.size
@@ -620,10 +843,10 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_counter_cache_double_destroy
-    topic = Topic.create :title => "Zoom-zoom-zoom"
+    topic = Topic.create title: "Zoom-zoom-zoom"
 
     5.times do
-      topic.replies.create(:title => "re: zoom", :content => "speedy quick!")
+      topic.replies.create(title: "re: zoom", content: "speedy quick!")
     end
 
     assert_equal 5, topic.reload[:replies_count]
@@ -640,10 +863,10 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_concurrent_counter_cache_double_destroy
-    topic = Topic.create :title => "Zoom-zoom-zoom"
+    topic = Topic.create title: "Zoom-zoom-zoom"
 
     5.times do
-      topic.replies.create(:title => "re: zoom", :content => "speedy quick!")
+      topic.replies.create(title: "re: zoom", content: "speedy quick!")
     end
 
     assert_equal 5, topic.reload[:replies_count]
@@ -661,11 +884,12 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_custom_counter_cache
-    reply = Reply.create(:title => "re: zoom", :content => "speedy quick!")
+    reply = Reply.create(title: "re: zoom", content: "speedy quick!")
     assert_equal 0, reply[:replies_count]
 
-    silly = SillyReply.create(:title => "gaga", :content => "boo-boo")
+    silly = SillyReply.create(title: "gaga", content: "boo-boo")
     silly.reply = reply
+    silly.save!
 
     assert_equal 1, reply.reload[:replies_count]
     assert_equal 1, reply.replies.size
@@ -674,10 +898,21 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal 17, reply.replies.size
   end
 
+  def test_replace_counter_cache
+    topic = Topic.create(title: "Zoom-zoom-zoom")
+    reply = Reply.create(title: "re: zoom", content: "speedy quick!")
+
+    reply.topic = topic
+    reply.save
+    topic.reload
+
+    assert_equal 1, topic.replies_count
+  end
+
   def test_association_assignment_sticks
     post = Post.first
 
-    author1, author2 = Author.all.merge!(:limit => 2).to_a
+    author1, author2 = Author.all.merge!(limit: 2).to_a
     assert_not_nil author1
     assert_not_nil author2
 
@@ -697,10 +932,10 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
   def test_cant_save_readonly_association
     assert_raise(ActiveRecord::ReadOnlyRecord) { companies(:first_client).readonly_firm.save! }
-    assert companies(:first_client).readonly_firm.readonly?
+    assert_predicate companies(:first_client).readonly_firm, :readonly?
   end
 
-  def test_test_polymorphic_assignment_foreign_key_type_string
+  def test_polymorphic_assignment_foreign_key_type_string
     comment = Comment.first
     comment.author   = Author.first
     comment.resource = Member.first
@@ -730,7 +965,7 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   def test_polymorphic_assignment_with_primary_key_foreign_type_field_updating
     # should update when assigning a saved record
     essay = Essay.new
-    writer = Author.create(:name => "David")
+    writer = Author.create(name: "David")
     essay.writer = writer
     assert_equal "Author", essay.writer_type
 
@@ -755,7 +990,7 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
   def test_assignment_updates_foreign_id_field_for_new_and_saved_records
     client = Client.new
-    saved_firm = Firm.create :name => "Saved"
+    saved_firm = Firm.create name: "Saved"
     new_firm = Firm.new
 
     client.firm = saved_firm
@@ -767,7 +1002,7 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
   def test_polymorphic_assignment_with_primary_key_updates_foreign_id_field_for_new_and_saved_records
     essay = Essay.new
-    saved_writer = Author.create(:name => "David")
+    saved_writer = Author.create(name: "David")
     new_writer = Author.new
 
     essay.writer = saved_writer
@@ -783,7 +1018,7 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_nil essay.writer_type
 
     essay.writer_id = 1
-    essay.writer_type = 'Author'
+    essay.writer_type = "Author"
 
     essay.writer = nil
     assert_nil essay.writer_id
@@ -805,14 +1040,14 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
     assert_nothing_raised do
       Account.find(@account.id).save!
-      Account.all.merge!(:includes => :firm).find(@account.id).save!
+      Account.all.merge!(includes: :firm).find(@account.id).save!
     end
 
     @account.firm.delete
 
     assert_nothing_raised do
       Account.find(@account.id).save!
-      Account.all.merge!(:includes => :firm).find(@account.id).save!
+      Account.all.merge!(includes: :firm).find(@account.id).save!
     end
   end
 
@@ -833,18 +1068,42 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
   def test_belongs_to_invalid_dependent_option_raises_exception
     error = assert_raise ArgumentError do
-      Class.new(Author).belongs_to :special_author_address, :dependent => :nullify
+      Class.new(Author).belongs_to :special_author_address, dependent: :nullify
+    end
+    assert_equal error.message, "The :dependent option must be one of [:destroy, :delete], but is :nullify"
+  end
+
+  class DestroyableBook < ActiveRecord::Base
+    self.table_name = "books"
+    belongs_to :author, class_name: "UndestroyableAuthor", dependent: :destroy
+  end
+
+  class UndestroyableAuthor < ActiveRecord::Base
+    self.table_name = "authors"
+    has_one :book, class_name: "DestroyableBook", foreign_key: "author_id"
+    before_destroy :dont
+
+    def dont
+      throw(:abort)
+    end
+  end
+
+  def test_dependency_should_halt_parent_destruction
+    author = UndestroyableAuthor.create!(name: "Test")
+    book = DestroyableBook.create!(author: author)
+
+    assert_no_difference ["UndestroyableAuthor.count", "DestroyableBook.count"] do
+      assert_not book.destroy
     end
-    assert_equal error.message, 'The :dependent option must be one of [:destroy, :delete], but is :nullify'
   end
 
   def test_attributes_are_being_set_when_initialized_from_belongs_to_association_with_where_clause
-    new_firm = accounts(:signals37).build_firm(:name => 'Apple')
+    new_firm = accounts(:signals37).build_firm(name: "Apple")
     assert_equal new_firm.name, "Apple"
   end
 
   def test_attributes_are_set_without_error_when_initialized_from_belongs_to_association_with_array_in_where_clause
-    new_account = Account.where(:credit_limit => [ 50, 60 ]).new
+    new_account = Account.where(credit_limit: [ 50, 60 ]).new
     assert_nil new_account.credit_limit
   end
 
@@ -856,15 +1115,15 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     firm_proxy                = client.send(:association_instance_get, :firm)
     firm_with_condition_proxy = client.send(:association_instance_get, :firm_with_condition)
 
-    assert !firm_proxy.stale_target?
-    assert !firm_with_condition_proxy.stale_target?
+    assert_not_predicate firm_proxy, :stale_target?
+    assert_not_predicate firm_with_condition_proxy, :stale_target?
     assert_equal companies(:first_firm), client.firm
     assert_equal companies(:first_firm), client.firm_with_condition
 
     client.client_of = companies(:another_firm).id
 
-    assert firm_proxy.stale_target?
-    assert firm_with_condition_proxy.stale_target?
+    assert_predicate firm_proxy, :stale_target?
+    assert_predicate firm_with_condition_proxy, :stale_target?
     assert_equal companies(:another_firm), client.firm
     assert_equal companies(:another_firm), client.firm_with_condition
   end
@@ -875,12 +1134,12 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     sponsor.sponsorable
     proxy = sponsor.send(:association_instance_get, :sponsorable)
 
-    assert !proxy.stale_target?
+    assert_not_predicate proxy, :stale_target?
     assert_equal members(:groucho), sponsor.sponsorable
 
     sponsor.sponsorable_id = members(:some_other_guy).id
 
-    assert proxy.stale_target?
+    assert_predicate proxy, :stale_target?
     assert_equal members(:some_other_guy), sponsor.sponsorable
   end
 
@@ -890,12 +1149,12 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     sponsor.sponsorable
     proxy = sponsor.send(:association_instance_get, :sponsorable)
 
-    assert !proxy.stale_target?
+    assert_not_predicate proxy, :stale_target?
     assert_equal members(:groucho), sponsor.sponsorable
 
-    sponsor.sponsorable_type = 'Firm'
+    sponsor.sponsorable_type = "Firm"
 
-    assert proxy.stale_target?
+    assert_predicate proxy, :stale_target?
     assert_equal companies(:first_firm), sponsor.sponsorable
   end
 
@@ -917,9 +1176,20 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     post    = posts(:welcome)
     comment = comments(:greetings)
 
-    assert_difference lambda { post.reload.tags_count }, -1 do
-      assert_difference 'comment.reload.tags_count', +1 do
+    assert_equal post.id, comment.id
+
+    assert_difference "post.reload.tags_count", -1 do
+      assert_difference "comment.reload.tags_count", +1 do
         tagging.taggable = comment
+        tagging.save!
+      end
+    end
+
+    assert_difference "comment.reload.tags_count", -1 do
+      assert_difference "post.reload.tags_count", +1 do
+        tagging.taggable_type = post.class.polymorphic_name
+        tagging.taggable_id = post.id
+        tagging.save!
       end
     end
   end
@@ -965,46 +1235,46 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_build_with_block
-    client = Client.create(:name => 'Client Company')
+    client = Client.create(name: "Client Company")
 
-    firm = client.build_firm{ |f| f.name = 'Agency Company' }
-    assert_equal 'Agency Company', firm.name
+    firm = client.build_firm { |f| f.name = "Agency Company" }
+    assert_equal "Agency Company", firm.name
   end
 
   def test_create_with_block
-    client = Client.create(:name => 'Client Company')
+    client = Client.create(name: "Client Company")
 
-    firm = client.create_firm{ |f| f.name = 'Agency Company' }
-    assert_equal 'Agency Company', firm.name
+    firm = client.create_firm { |f| f.name = "Agency Company" }
+    assert_equal "Agency Company", firm.name
   end
 
   def test_create_bang_with_block
-    client = Client.create(:name => 'Client Company')
+    client = Client.create(name: "Client Company")
 
-    firm = client.create_firm!{ |f| f.name = 'Agency Company' }
-    assert_equal 'Agency Company', firm.name
+    firm = client.create_firm! { |f| f.name = "Agency Company" }
+    assert_equal "Agency Company", firm.name
   end
 
   def test_should_set_foreign_key_on_create_association
-    client = Client.create! :name => "fuu"
+    client = Client.create! name: "fuu"
 
-    firm = client.create_firm :name => "baa"
+    firm = client.create_firm name: "baa"
     assert_equal firm.id, client.client_of
   end
 
   def test_should_set_foreign_key_on_create_association!
-    client = Client.create! :name => "fuu"
+    client = Client.create! name: "fuu"
 
-    firm = client.create_firm! :name => "baa"
+    firm = client.create_firm! name: "baa"
     assert_equal firm.id, client.client_of
   end
 
   def test_self_referential_belongs_to_with_counter_cache_assigning_nil
-    comment = Comment.create! :post => posts(:thinking), :body => "fuu"
+    comment = Comment.create! post: posts(:thinking), body: "fuu"
     comment.parent = nil
     comment.save!
 
-    assert_equal nil, comment.reload.parent
+    assert_nil comment.reload.parent
     assert_equal 0, comments(:greetings).reload.children_count
   end
 
@@ -1019,9 +1289,23 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal 1, parent.reload.children_count
   end
 
+  def test_belongs_to_with_out_of_range_value_assigning
+    model = Class.new(Comment) do
+      def self.name; "Temp"; end
+      validates :post, presence: true
+    end
+
+    comment = model.new
+    comment.post_id = 9223372036854775808 # out of range in the bigint
+
+    assert_nil comment.post
+    assert_not_predicate comment, :valid?
+    assert_equal [{ error: :blank }], comment.errors.details[:post]
+  end
+
   def test_polymorphic_with_custom_primary_key
     toy = Toy.create!
-    sponsor = Sponsor.create!(:sponsorable => toy)
+    sponsor = Sponsor.create!(sponsorable: toy)
 
     assert_equal toy, sponsor.reload.sponsorable
   end
@@ -1035,12 +1319,12 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
     citibank.firm_id = apple.id.to_s
 
-    assert !citibank.association(:firm).stale_target?
+    assert_not_predicate citibank.association(:firm), :stale_target?
   end
 
   def test_reflect_the_most_recent_change
     author1, author2 = Author.limit(2)
-    post = Post.new(:title => "foo", :body=> "bar")
+    post = Post.new(title: "foo", body: "bar")
 
     post.author    = author1
     post.author_id = author2.id
@@ -1049,8 +1333,8 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     assert_equal post.author_id, author2.id
   end
 
-  test 'dangerous association name raises ArgumentError' do
-    [:errors, 'errors', :save, 'save'].each do |name|
+  test "dangerous association name raises ArgumentError" do
+    [:errors, "errors", :save, "save"].each do |name|
       assert_raises(ArgumentError, "Association #{name} should not be allowed") do
         Class.new(ActiveRecord::Base) do
           belongs_to name
@@ -1059,11 +1343,22 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
     end
   end
 
-  test 'belongs_to works with model called Record' do
+  test "belongs_to works with model called Record" do
     record = Record.create!
     Column.create! record: record
     assert_equal 1, Column.count
   end
+
+  def test_multiple_counter_cache_with_after_create_update
+    post = posts(:welcome)
+    parent = comments(:greetings)
+
+    assert_difference "parent.reload.children_count", +1 do
+      assert_difference "post.reload.comments_count", +1 do
+        CommentWithAfterCreateUpdate.create(body: "foo", post: post, parent: parent)
+      end
+    end
+  end
 end
 
 class BelongsToWithForeignKeyTest < ActiveRecord::TestCase
diff --git a/activerecord/test/cases/associations/bidirectional_destroy_dependencies_test.rb b/activerecord/test/cases/associations/bidirectional_destroy_dependencies_test.rb
new file mode 100644
index 0000000000..88221b012e
--- /dev/null
+++ b/activerecord/test/cases/associations/bidirectional_destroy_dependencies_test.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/content"
+
+class BidirectionalDestroyDependenciesTest < ActiveRecord::TestCase
+  fixtures :content, :content_positions
+
+  def setup
+    Content.destroyed_ids.clear
+    ContentPosition.destroyed_ids.clear
+  end
+
+  def test_bidirectional_dependence_when_destroying_item_with_belongs_to_association
+    content_position = ContentPosition.find(1)
+    content = content_position.content
+    assert_not_nil content
+
+    content_position.destroy
+
+    assert_equal [content_position.id], ContentPosition.destroyed_ids
+    assert_equal [content.id], Content.destroyed_ids
+  end
+
+  def test_bidirectional_dependence_when_destroying_item_with_has_one_association
+    content = Content.find(1)
+    content_position = content.content_position
+    assert_not_nil content_position
+
+    content.destroy
+
+    assert_equal [content.id], Content.destroyed_ids
+    assert_equal [content_position.id], ContentPosition.destroyed_ids
+  end
+
+  def test_bidirectional_dependence_when_destroying_item_with_has_one_association_fails_first_time
+    content = ContentWhichRequiresTwoDestroyCalls.find(1)
+
+    2.times { content.destroy }
+
+    assert_equal content.destroyed?, true
+  end
+end
diff --git a/activerecord/test/cases/associations/callbacks_test.rb b/activerecord/test/cases/associations/callbacks_test.rb
index a531e0e02c..25d55dc4c9 100644
--- a/activerecord/test/cases/associations/callbacks_test.rb
+++ b/activerecord/test/cases/associations/callbacks_test.rb
@@ -1,19 +1,21 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/author'
-require 'models/project'
-require 'models/developer'
-require 'models/computer'
-require 'models/company'
+require "models/post"
+require "models/author"
+require "models/project"
+require "models/developer"
+require "models/computer"
+require "models/company"
 
 class AssociationCallbacksTest < ActiveRecord::TestCase
-  fixtures :posts, :authors, :projects, :developers
+  fixtures :posts, :authors, :author_addresses, :projects, :developers
 
   def setup
     @david = authors(:david)
     @thinking = posts(:thinking)
     @authorless = posts(:authorless)
-    assert @david.post_log.empty?
+    assert_empty @david.post_log
   end
 
   def test_adding_macro_callbacks
@@ -61,20 +63,20 @@ class AssociationCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_has_many_callbacks_with_create
-    morten = Author.create :name => "Morten"
-    post = morten.posts_with_proc_callbacks.create! :title => "Hello", :body => "How are you doing?"
+    morten = Author.create name: "Morten"
+    post = morten.posts_with_proc_callbacks.create! title: "Hello", body: "How are you doing?"
     assert_equal ["before_adding<new>", "after_adding#{post.id}"], morten.post_log
   end
 
   def test_has_many_callbacks_with_create!
-    morten = Author.create! :name => "Morten"
-    post = morten.posts_with_proc_callbacks.create :title => "Hello", :body => "How are you doing?"
+    morten = Author.create! name: "Morten"
+    post = morten.posts_with_proc_callbacks.create title: "Hello", body: "How are you doing?"
     assert_equal ["before_adding<new>", "after_adding#{post.id}"], morten.post_log
   end
 
   def test_has_many_callbacks_for_save_on_parent
-    jack = Author.new :name => "Jack"
-    jack.posts_with_callbacks.build :title => "Call me back!", :body => "Before you wake up and after you sleep"
+    jack = Author.new name: "Jack"
+    jack.posts_with_callbacks.build title: "Call me back!", body: "Before you wake up and after you sleep"
 
     callback_log = ["before_adding<new>", "after_adding#{jack.posts_with_callbacks.first.id}"]
     assert_equal callback_log, jack.post_log
@@ -84,8 +86,8 @@ class AssociationCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_has_many_callbacks_for_destroy_on_parent
-    firm = Firm.create! :name => "Firm"
-    client = firm.clients.create! :name => "Client"
+    firm = Firm.create! name: "Firm"
+    client = firm.clients.create! name: "Client"
     firm.destroy
 
     assert_equal ["before_remove#{client.id}", "after_remove#{client.id}"], firm.log
@@ -94,7 +96,7 @@ class AssociationCallbacksTest < ActiveRecord::TestCase
   def test_has_and_belongs_to_many_add_callback
     david = developers(:david)
     ar = projects(:active_record)
-    assert ar.developers_log.empty?
+    assert_empty ar.developers_log
     ar.developers_with_callbacks << david
     assert_equal ["before_adding#{david.id}", "after_adding#{david.id}"], ar.developers_log
     ar.developers_with_callbacks << david
@@ -108,41 +110,40 @@ class AssociationCallbacksTest < ActiveRecord::TestCase
     klass = Class.new(Project) do
       def self.name; Project.name; end
       has_and_belongs_to_many :developers_with_callbacks,
-                                :class_name => "Developer",
-                                :before_add => lambda { |o,r|
+                                class_name: "Developer",
+                                before_add: lambda { |o, r|
         dev     = r
         new_dev = r.new_record?
       }
     end
     rec = klass.create!
-    alice = Developer.new(:name => 'alice')
+    alice = Developer.new(name: "alice")
     rec.developers_with_callbacks << alice
     assert_equal alice, dev
     assert_not_nil new_dev
     assert new_dev, "record should not have been saved"
-    assert_not alice.new_record?
+    assert_not_predicate alice, :new_record?
   end
 
   def test_has_and_belongs_to_many_after_add_called_after_save
     ar = projects(:active_record)
-    assert ar.developers_log.empty?
-    alice = Developer.new(:name => 'alice')
+    assert_empty ar.developers_log
+    alice = Developer.new(name: "alice")
     ar.developers_with_callbacks << alice
-    assert_equal"after_adding#{alice.id}", ar.developers_log.last
+    assert_equal "after_adding#{alice.id}", ar.developers_log.last
 
-    bob = ar.developers_with_callbacks.create(:name => 'bob')
+    bob = ar.developers_with_callbacks.create(name: "bob")
     assert_equal "after_adding#{bob.id}", ar.developers_log.last
 
-    ar.developers_with_callbacks.build(:name => 'charlie')
+    ar.developers_with_callbacks.build(name: "charlie")
     assert_equal "after_adding<new>", ar.developers_log.last
   end
 
-
   def test_has_and_belongs_to_many_remove_callback
     david = developers(:david)
     jamis = developers(:jamis)
     activerecord = projects(:active_record)
-    assert activerecord.developers_log.empty?
+    assert_empty activerecord.developers_log
     activerecord.developers_with_callbacks.delete(david)
     assert_equal ["before_removing#{david.id}", "after_removing#{david.id}"], activerecord.developers_log
 
@@ -153,21 +154,21 @@ class AssociationCallbacksTest < ActiveRecord::TestCase
 
   def test_has_and_belongs_to_many_does_not_fire_callbacks_on_clear
     activerecord = projects(:active_record)
-    assert activerecord.developers_log.empty?
+    assert_empty activerecord.developers_log
     if activerecord.developers_with_callbacks.size == 0
       activerecord.developers << developers(:david)
       activerecord.developers << developers(:jamis)
       activerecord.reload
       assert activerecord.developers_with_callbacks.size == 2
     end
-    activerecord.developers_with_callbacks.flat_map {|d| ["before_removing#{d.id}","after_removing#{d.id}"]}.sort
+    activerecord.developers_with_callbacks.flat_map { |d| ["before_removing#{d.id}", "after_removing#{d.id}"] }.sort
     assert activerecord.developers_with_callbacks.clear
-    assert_predicate activerecord.developers_log, :empty?
+    assert_empty activerecord.developers_log
   end
 
   def test_has_many_and_belongs_to_many_callbacks_for_save_on_parent
-    project = Project.new :name => "Callbacks"
-    project.developers_with_callbacks.build :name => "Jack", :salary => 95000
+    project = Project.new name: "Callbacks"
+    project.developers_with_callbacks.build name: "Jack", salary: 95000
 
     callback_log = ["before_adding<new>", "after_adding<new>"]
     assert_equal callback_log, project.developers_log
@@ -177,14 +178,14 @@ class AssociationCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_dont_add_if_before_callback_raises_exception
-    assert !@david.unchangable_posts.include?(@authorless)
+    assert_not_includes @david.unchangeable_posts, @authorless
     begin
-      @david.unchangable_posts << @authorless
+      @david.unchangeable_posts << @authorless
     rescue Exception
     end
-    assert @david.post_log.empty?
-    assert !@david.unchangable_posts.include?(@authorless)
+    assert_empty @david.post_log
+    assert_not_includes @david.unchangeable_posts, @authorless
     @david.reload
-    assert !@david.unchangable_posts.include?(@authorless)
+    assert_not_includes @david.unchangeable_posts, @authorless
   end
 end
diff --git a/activerecord/test/cases/associations/cascaded_eager_loading_test.rb b/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
index 51d8e0523e..a9e22c7643 100644
--- a/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
+++ b/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
@@ -1,56 +1,52 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/comment'
-require 'models/author'
-require 'models/categorization'
-require 'models/category'
-require 'models/company'
-require 'models/topic'
-require 'models/reply'
-require 'models/person'
-require 'models/vertex'
-require 'models/edge'
+require "models/post"
+require "models/comment"
+require "models/author"
+require "models/categorization"
+require "models/category"
+require "models/company"
+require "models/topic"
+require "models/reply"
+require "models/person"
+require "models/vertex"
+require "models/edge"
 
 class CascadedEagerLoadingTest < ActiveRecord::TestCase
-  fixtures :authors, :mixins, :companies, :posts, :topics, :accounts, :comments,
+  fixtures :authors, :author_addresses, :mixins, :companies, :posts, :topics, :accounts, :comments,
            :categorizations, :people, :categories, :edges, :vertices
 
   def test_eager_association_loading_with_cascaded_two_levels
-    authors = Author.all.merge!(:includes=>{:posts=>:comments}, :order=>"authors.id").to_a
+    authors = Author.all.merge!(includes: { posts: :comments }, order: "authors.id").to_a
     assert_equal 3, authors.size
     assert_equal 5, authors[0].posts.size
     assert_equal 3, authors[1].posts.size
-    assert_equal 10, authors[0].posts.collect{|post| post.comments.size }.inject(0){|sum,i| sum+i}
+    assert_equal 10, authors[0].posts.collect { |post| post.comments.size }.inject(0) { |sum, i| sum + i }
   end
 
   def test_eager_association_loading_with_cascaded_two_levels_and_one_level
-    authors = Author.all.merge!(:includes=>[{:posts=>:comments}, :categorizations], :order=>"authors.id").to_a
+    authors = Author.all.merge!(includes: [{ posts: :comments }, :categorizations], order: "authors.id").to_a
     assert_equal 3, authors.size
     assert_equal 5, authors[0].posts.size
     assert_equal 3, authors[1].posts.size
-    assert_equal 10, authors[0].posts.collect{|post| post.comments.size }.inject(0){|sum,i| sum+i}
+    assert_equal 10, authors[0].posts.collect { |post| post.comments.size }.inject(0) { |sum, i| sum + i }
     assert_equal 1, authors[0].categorizations.size
     assert_equal 2, authors[1].categorizations.size
   end
 
   def test_eager_association_loading_with_hmt_does_not_table_name_collide_when_joining_associations
-    assert_nothing_raised do
-      Author.joins(:posts).eager_load(:comments).where(:posts => {:tags_count => 1}).to_a
-    end
-    authors = Author.joins(:posts).eager_load(:comments).where(:posts => {:tags_count => 1}).to_a
-    assert_equal 1, assert_no_queries { authors.size }
+    authors = Author.joins(:posts).eager_load(:comments).where(posts: { tags_count: 1 }).to_a
+    assert_equal 3, assert_no_queries { authors.size }
     assert_equal 10, assert_no_queries { authors[0].comments.size }
   end
 
   def test_eager_association_loading_grafts_stashed_associations_to_correct_parent
-    assert_nothing_raised do
-      Person.eager_load(:primary_contact => :primary_contact).where('primary_contacts_people_2.first_name = ?', 'Susan').order('people.id').to_a
-    end
-    assert_equal people(:michael), Person.eager_load(:primary_contact => :primary_contact).where('primary_contacts_people_2.first_name = ?', 'Susan').order('people.id').first
+    assert_equal people(:michael), Person.eager_load(primary_contact: :primary_contact).where("primary_contacts_people_2.first_name = ?", "Susan").order("people.id").first
   end
 
   def test_cascaded_eager_association_loading_with_join_for_count
-    categories = Category.joins(:categorizations).includes([{:posts=>:comments}, :authors])
+    categories = Category.joins(:categorizations).includes([{ posts: :comments }, :authors])
 
     assert_equal 4, categories.count
     assert_equal 4, categories.to_a.count
@@ -59,7 +55,7 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   end
 
   def test_cascaded_eager_association_loading_with_duplicated_includes
-    categories = Category.includes(:categorizations).includes(:categorizations => :author).where("categorizations.id is not null").references(:categorizations)
+    categories = Category.includes(:categorizations).includes(categorizations: :author).where("categorizations.id is not null").references(:categorizations)
     assert_nothing_raised do
       assert_equal 3, categories.count
       assert_equal 3, categories.to_a.size
@@ -67,7 +63,7 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   end
 
   def test_cascaded_eager_association_loading_with_twice_includes_edge_cases
-    categories = Category.includes(:categorizations => :author).includes(:categorizations => :post).where("posts.id is not null").references(:posts)
+    categories = Category.includes(categorizations: :author).includes(categorizations: :post).where("posts.id is not null").references(:posts)
     assert_nothing_raised do
       assert_equal 3, categories.count
       assert_equal 3, categories.to_a.size
@@ -82,29 +78,29 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   end
 
   def test_eager_association_loading_with_cascaded_two_levels_with_two_has_many_associations
-    authors = Author.all.merge!(:includes=>{:posts=>[:comments, :categorizations]}, :order=>"authors.id").to_a
+    authors = Author.all.merge!(includes: { posts: [:comments, :categorizations] }, order: "authors.id").to_a
     assert_equal 3, authors.size
     assert_equal 5, authors[0].posts.size
     assert_equal 3, authors[1].posts.size
-    assert_equal 10, authors[0].posts.collect{|post| post.comments.size }.inject(0){|sum,i| sum+i}
+    assert_equal 10, authors[0].posts.collect { |post| post.comments.size }.inject(0) { |sum, i| sum + i }
   end
 
   def test_eager_association_loading_with_cascaded_two_levels_and_self_table_reference
-    authors = Author.all.merge!(:includes=>{:posts=>[:comments, :author]}, :order=>"authors.id").to_a
+    authors = Author.all.merge!(includes: { posts: [:comments, :author] }, order: "authors.id").to_a
     assert_equal 3, authors.size
     assert_equal 5, authors[0].posts.size
     assert_equal authors(:david).name, authors[0].name
-    assert_equal [authors(:david).name], authors[0].posts.collect{|post| post.author.name}.uniq
+    assert_equal [authors(:david).name], authors[0].posts.collect { |post| post.author.name }.uniq
   end
 
   def test_eager_association_loading_with_cascaded_two_levels_with_condition
-    authors = Author.all.merge!(:includes=>{:posts=>:comments}, :where=>"authors.id=1", :order=>"authors.id").to_a
+    authors = Author.all.merge!(includes: { posts: :comments }, where: "authors.id=1", order: "authors.id").to_a
     assert_equal 1, authors.size
     assert_equal 5, authors[0].posts.size
   end
 
   def test_eager_association_loading_with_cascaded_three_levels_by_ping_pong
-    firms = Firm.all.merge!(:includes=>{:account=>{:firm=>:account}}, :order=>"companies.id").to_a
+    firms = Firm.all.merge!(includes: { account: { firm: :account } }, order: "companies.id").to_a
     assert_equal 2, firms.size
     assert_equal firms.first.account, firms.first.account.firm.account
     assert_equal companies(:first_firm).account, assert_no_queries { firms.first.account.firm.account }
@@ -112,7 +108,7 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   end
 
   def test_eager_association_loading_with_has_many_sti
-    topics = Topic.all.merge!(:includes => :replies, :order => 'topics.id').to_a
+    topics = Topic.all.merge!(includes: :replies, order: "topics.id").to_a
     first, second, = topics(:first).replies.size, topics(:second).replies.size
     assert_no_queries do
       assert_equal first, topics[0].replies.size
@@ -121,11 +117,10 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   end
 
   def test_eager_association_loading_with_has_many_sti_and_subclasses
-    silly = SillyReply.new(:title => "gaga", :content => "boo-boo", :parent_id => 1)
-    silly.parent_id = 1
-    assert silly.save
+    reply = Reply.new(title: "gaga", content: "boo-boo", parent_id: 1)
+    assert reply.save
 
-    topics = Topic.all.merge!(:includes => :replies, :order => ['topics.id', 'replies_topics.id']).to_a
+    topics = Topic.all.merge!(includes: :replies, order: ["topics.id", "replies_topics.id"]).to_a
     assert_no_queries do
       assert_equal 2, topics[0].replies.size
       assert_equal 0, topics[1].replies.size
@@ -133,14 +128,14 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   end
 
   def test_eager_association_loading_with_belongs_to_sti
-    replies = Reply.all.merge!(:includes => :topic, :order => 'topics.id').to_a
-    assert replies.include?(topics(:second))
-    assert !replies.include?(topics(:first))
+    replies = Reply.all.merge!(includes: :topic, order: "topics.id").to_a
+    assert_includes replies, topics(:second)
+    assert_not_includes replies, topics(:first)
     assert_equal topics(:first), assert_no_queries { replies.first.topic }
   end
 
   def test_eager_association_loading_with_multiple_stis_and_order
-    author = Author.all.merge!(:includes => { :posts => [ :special_comments , :very_special_comment ] }, :order => ['authors.name', 'comments.body', 'very_special_comments_posts.body'], :where => 'posts.id = 4').first
+    author = Author.all.merge!(includes: { posts: [ :special_comments, :very_special_comment ] }, order: ["authors.name", "comments.body", "very_special_comments_posts.body"], where: "posts.id = 4").first
     assert_equal authors(:david), author
     assert_no_queries do
       author.posts.first.special_comments
@@ -149,7 +144,7 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   end
 
   def test_eager_association_loading_of_stis_with_multiple_references
-    authors = Author.all.merge!(:includes => { :posts => { :special_comments => { :post => [ :special_comments, :very_special_comment ] } } }, :order => 'comments.body, very_special_comments_posts.body', :where => 'posts.id = 4').to_a
+    authors = Author.all.merge!(includes: { posts: { special_comments: { post: [ :special_comments, :very_special_comment ] } } }, order: "comments.body, very_special_comments_posts.body", where: "posts.id = 4").to_a
     assert_equal [authors(:david)], authors
     assert_no_queries do
       authors.first.posts.first.special_comments.first.post.special_comments
@@ -158,20 +153,30 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   end
 
   def test_eager_association_loading_where_first_level_returns_nil
-    authors = Author.all.merge!(:includes => {:post_about_thinking => :comments}, :order => 'authors.id DESC').to_a
+    authors = Author.all.merge!(includes: { post_about_thinking: :comments }, order: "authors.id DESC").to_a
     assert_equal [authors(:bob), authors(:mary), authors(:david)], authors
     assert_no_queries do
       authors[2].post_about_thinking.comments.first
     end
   end
 
+  def test_preload_through_missing_records
+    post = Post.where.not(author_id: Author.select(:id)).preload(author: { comments: :post }).first!
+    assert_no_queries { assert_nil post.author }
+  end
+
+  def test_eager_association_loading_with_missing_first_record
+    posts = Post.where(id: 3).preload(author: { comments: :post }).to_a
+    assert_equal posts.size, 1
+  end
+
   def test_eager_association_loading_with_recursive_cascading_four_levels_has_many_through
-    source = Vertex.all.merge!(:includes=>{:sinks=>{:sinks=>{:sinks=>:sinks}}}, :order => 'vertices.id').first
+    source = Vertex.all.merge!(includes: { sinks: { sinks: { sinks: :sinks } } }, order: "vertices.id").first
     assert_equal vertices(:vertex_4), assert_no_queries { source.sinks.first.sinks.first.sinks.first }
   end
 
   def test_eager_association_loading_with_recursive_cascading_four_levels_has_and_belongs_to_many
-    sink = Vertex.all.merge!(:includes=>{:sources=>{:sources=>{:sources=>:sources}}}, :order => 'vertices.id DESC').first
+    sink = Vertex.all.merge!(includes: { sources: { sources: { sources: :sources } } }, order: "vertices.id DESC").first
     assert_equal vertices(:vertex_1), assert_no_queries { sink.sources.first.sources.first.sources.first.sources.first }
   end
 
@@ -183,6 +188,6 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
     assert_equal 1, authors[1].comments.size
     assert_equal 5, authors[0].posts.size
     assert_equal 3, authors[1].posts.size
-    assert_equal 3, authors[0].posts.collect { |post| post.categorizations.size }.inject(0) { |sum, i| sum+i }
+    assert_equal 3, authors[0].posts.collect { |post| post.categorizations.size }.inject(0) { |sum, i| sum + i }
   end
 end
diff --git a/activerecord/test/cases/associations/eager_load_includes_full_sti_class_test.rb b/activerecord/test/cases/associations/eager_load_includes_full_sti_class_test.rb
index 75a6295350..5fca972aee 100644
--- a/activerecord/test/cases/associations/eager_load_includes_full_sti_class_test.rb
+++ b/activerecord/test/cases/associations/eager_load_includes_full_sti_class_test.rb
@@ -1,36 +1,88 @@
-require 'cases/helper'
-require 'models/post'
-require 'models/tagging'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/post"
+require "models/tagging"
 
 module Namespaced
   class Post < ActiveRecord::Base
-    self.table_name = 'posts'
-    has_one :tagging, :as => :taggable, :class_name => 'Tagging'
+    self.table_name = "posts"
+    has_one :tagging, as: :taggable, class_name: "Tagging"
+
+    def self.polymorphic_name
+      sti_name
+    end
   end
 end
 
-class EagerLoadIncludeFullStiClassNamesTest < ActiveRecord::TestCase
-
+module PolymorphicFullStiClassNamesSharedTest
   def setup
-    generate_test_objects
+    @old_store_full_sti_class = ActiveRecord::Base.store_full_sti_class
+    ActiveRecord::Base.store_full_sti_class = store_full_sti_class
+
+    post = Namespaced::Post.create(title: "Great stuff", body: "This is not", author_id: 1)
+    @tagging = Tagging.create(taggable: post)
   end
 
-  def generate_test_objects
-    post = Namespaced::Post.create( :title => 'Great stuff', :body => 'This is not', :author_id => 1 )
-    Tagging.create( :taggable => post )
+  def teardown
+    ActiveRecord::Base.store_full_sti_class = @old_store_full_sti_class
   end
 
   def test_class_names
-    old = ActiveRecord::Base.store_full_sti_class
+    ActiveRecord::Base.store_full_sti_class = !store_full_sti_class
+    post = Namespaced::Post.find_by_title("Great stuff")
+    assert_nil post.tagging
+
+    ActiveRecord::Base.store_full_sti_class = store_full_sti_class
+    post = Namespaced::Post.find_by_title("Great stuff")
+    assert_equal @tagging, post.tagging
+  end
+
+  def test_class_names_with_includes
+    ActiveRecord::Base.store_full_sti_class = !store_full_sti_class
+    post = Namespaced::Post.includes(:tagging).find_by_title("Great stuff")
+    assert_nil post.tagging
+
+    ActiveRecord::Base.store_full_sti_class = store_full_sti_class
+    post = Namespaced::Post.includes(:tagging).find_by_title("Great stuff")
+    assert_equal @tagging, post.tagging
+  end
 
-    ActiveRecord::Base.store_full_sti_class = false
-    post = Namespaced::Post.includes(:tagging).find_by_title('Great stuff')
+  def test_class_names_with_eager_load
+    ActiveRecord::Base.store_full_sti_class = !store_full_sti_class
+    post = Namespaced::Post.eager_load(:tagging).find_by_title("Great stuff")
     assert_nil post.tagging
 
-    ActiveRecord::Base.store_full_sti_class = true
-    post = Namespaced::Post.includes(:tagging).find_by_title('Great stuff')
-    assert_instance_of Tagging, post.tagging
-  ensure
-    ActiveRecord::Base.store_full_sti_class = old
+    ActiveRecord::Base.store_full_sti_class = store_full_sti_class
+    post = Namespaced::Post.eager_load(:tagging).find_by_title("Great stuff")
+    assert_equal @tagging, post.tagging
   end
+
+  def test_class_names_with_find_by
+    post = Namespaced::Post.find_by_title("Great stuff")
+
+    ActiveRecord::Base.store_full_sti_class = !store_full_sti_class
+    assert_nil Tagging.find_by(taggable: post)
+
+    ActiveRecord::Base.store_full_sti_class = store_full_sti_class
+    assert_equal @tagging, Tagging.find_by(taggable: post)
+  end
+end
+
+class PolymorphicFullStiClassNamesTest < ActiveRecord::TestCase
+  include PolymorphicFullStiClassNamesSharedTest
+
+  private
+    def store_full_sti_class
+      true
+    end
+end
+
+class PolymorphicNonFullStiClassNamesTest < ActiveRecord::TestCase
+  include PolymorphicFullStiClassNamesSharedTest
+
+  private
+    def store_full_sti_class
+      false
+    end
 end
diff --git a/activerecord/test/cases/associations/eager_load_nested_include_test.rb b/activerecord/test/cases/associations/eager_load_nested_include_test.rb
index f571198079..525ad3197a 100644
--- a/activerecord/test/cases/associations/eager_load_nested_include_test.rb
+++ b/activerecord/test/cases/associations/eager_load_nested_include_test.rb
@@ -1,18 +1,20 @@
-require 'cases/helper'
-require 'models/post'
-require 'models/tag'
-require 'models/author'
-require 'models/comment'
-require 'models/category'
-require 'models/categorization'
-require 'models/tagging'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/post"
+require "models/tag"
+require "models/author"
+require "models/comment"
+require "models/category"
+require "models/categorization"
+require "models/tagging"
 
 module Remembered
   extend ActiveSupport::Concern
 
   included do
     after_create :remember
-  protected
+  private
     def remember; self.class.remembered << self; end
   end
 
@@ -23,30 +25,30 @@ module Remembered
 end
 
 class ShapeExpression < ActiveRecord::Base
-  belongs_to :shape, :polymorphic => true
-  belongs_to :paint, :polymorphic => true
+  belongs_to :shape, polymorphic: true
+  belongs_to :paint, polymorphic: true
 end
 
 class Circle < ActiveRecord::Base
-  has_many :shape_expressions, :as => :shape
+  has_many :shape_expressions, as: :shape
   include Remembered
 end
 class Square < ActiveRecord::Base
-  has_many :shape_expressions, :as => :shape
+  has_many :shape_expressions, as: :shape
   include Remembered
 end
 class Triangle < ActiveRecord::Base
-  has_many :shape_expressions, :as => :shape
+  has_many :shape_expressions, as: :shape
   include Remembered
 end
-class PaintColor  < ActiveRecord::Base
-  has_many   :shape_expressions, :as => :paint
-  belongs_to :non_poly, :foreign_key => "non_poly_one_id", :class_name => "NonPolyOne"
+class PaintColor < ActiveRecord::Base
+  has_many   :shape_expressions, as: :paint
+  belongs_to :non_poly, foreign_key: "non_poly_one_id", class_name: "NonPolyOne"
   include Remembered
 end
 class PaintTexture < ActiveRecord::Base
-  has_many   :shape_expressions, :as => :paint
-  belongs_to :non_poly, :foreign_key => "non_poly_two_id", :class_name => "NonPolyTwo"
+  has_many   :shape_expressions, as: :paint
+  belongs_to :non_poly, foreign_key: "non_poly_two_id", class_name: "NonPolyTwo"
   include Remembered
 end
 class NonPolyOne < ActiveRecord::Base
@@ -58,8 +60,6 @@ class NonPolyTwo < ActiveRecord::Base
   include Remembered
 end
 
-
-
 class EagerLoadPolyAssocsTest < ActiveRecord::TestCase
   NUM_SIMPLE_OBJS = 50
   NUM_SHAPE_EXPRESSIONS = 100
@@ -78,21 +78,21 @@ class EagerLoadPolyAssocsTest < ActiveRecord::TestCase
       [Circle, Square, Triangle, NonPolyOne, NonPolyTwo].map(&:create!)
     end
     1.upto(NUM_SIMPLE_OBJS) do
-      PaintColor.create!(:non_poly_one_id => NonPolyOne.sample.id)
-      PaintTexture.create!(:non_poly_two_id => NonPolyTwo.sample.id)
+      PaintColor.create!(non_poly_one_id: NonPolyOne.sample.id)
+      PaintTexture.create!(non_poly_two_id: NonPolyTwo.sample.id)
     end
     1.upto(NUM_SHAPE_EXPRESSIONS) do
       shape_type = [Circle, Square, Triangle].sample
       paint_type = [PaintColor, PaintTexture].sample
-      ShapeExpression.create!(:shape_type => shape_type.to_s, :shape_id => shape_type.sample.id,
-                              :paint_type => paint_type.to_s, :paint_id => paint_type.sample.id)
+      ShapeExpression.create!(shape_type: shape_type.to_s, shape_id: shape_type.sample.id,
+                              paint_type: paint_type.to_s, paint_id: paint_type.sample.id)
     end
   end
 
   def test_include_query
-    res = ShapeExpression.all.merge!(:includes => [ :shape, { :paint => :non_poly } ]).to_a
+    res = ShapeExpression.all.merge!(includes: [ :shape, { paint: :non_poly } ]).to_a
     assert_equal NUM_SHAPE_EXPRESSIONS, res.size
-    assert_queries(0) do
+    assert_no_queries do
       res.each do |se|
         assert_not_nil se.paint.non_poly, "this is the association that was loading incorrectly before the change"
         assert_not_nil se.shape, "just making sure other associations still work"
@@ -103,10 +103,10 @@ end
 
 class EagerLoadNestedIncludeWithMissingDataTest < ActiveRecord::TestCase
   def setup
-    @davey_mcdave = Author.create(:name => 'Davey McDave')
-    @first_post = @davey_mcdave.posts.create(:title => 'Davey Speaks', :body => 'Expressive wordage')
-    @first_comment = @first_post.comments.create(:body => 'Inflamatory doublespeak')
-    @first_categorization = @davey_mcdave.categorizations.create(:category => Category.first, :post => @first_post)
+    @davey_mcdave = Author.create(name: "Davey McDave")
+    @first_post = @davey_mcdave.posts.create(title: "Davey Speaks", body: "Expressive wordage")
+    @first_comment = @first_post.comments.create(body: "Inflamatory doublespeak")
+    @first_categorization = @davey_mcdave.categorizations.create(category: Category.first, post: @first_post)
   end
 
   teardown do
@@ -119,8 +119,8 @@ class EagerLoadNestedIncludeWithMissingDataTest < ActiveRecord::TestCase
   def test_missing_data_in_a_nested_include_should_not_cause_errors_when_constructing_objects
     assert_nothing_raised do
       # @davey_mcdave doesn't have any author_favorites
-      includes = {:posts => :comments, :categorizations => :category, :author_favorites => :favorite_author }
-      Author.all.merge!(:includes => includes, :where => {:authors => {:name => @davey_mcdave.name}}, :order => 'categories.name').to_a
+      includes = { posts: :comments, categorizations: :category, author_favorites: :favorite_author }
+      Author.all.merge!(includes: includes, where: { authors: { name: @davey_mcdave.name } }, order: "categories.name").to_a
     end
   end
 end
diff --git a/activerecord/test/cases/associations/eager_singularization_test.rb b/activerecord/test/cases/associations/eager_singularization_test.rb
index a61a070331..420a5a805b 100644
--- a/activerecord/test/cases/associations/eager_singularization_test.rb
+++ b/activerecord/test/cases/associations/eager_singularization_test.rb
@@ -1,7 +1,7 @@
-require "cases/helper"
+# frozen_string_literal: true
 
+require "cases/helper"
 
-if ActiveRecord::Base.connection.supports_migrations?
 class EagerSingularizationTest < ActiveRecord::TestCase
   class Virus < ActiveRecord::Base
     belongs_to :octopus
@@ -25,10 +25,10 @@ class EagerSingularizationTest < ActiveRecord::TestCase
 
   class Crisis < ActiveRecord::Base
     has_and_belongs_to_many :messes
-    has_many :analyses, :dependent => :destroy
-    has_many :successes, :through => :analyses
-    has_many :dresses, :dependent => :destroy
-    has_many :compresses, :through => :dresses
+    has_many :analyses, dependent: :destroy
+    has_many :successes, through: :analyses
+    has_many :dresses, dependent: :destroy
+    has_many :compresses, through: :dresses
   end
 
   class Analysis < ActiveRecord::Base
@@ -37,8 +37,8 @@ class EagerSingularizationTest < ActiveRecord::TestCase
   end
 
   class Success < ActiveRecord::Base
-    has_many :analyses, :dependent => :destroy
-    has_many :crises, :through => :analyses
+    has_many :analyses, dependent: :destroy
+    has_many :crises, through: :analyses
   end
 
   class Dress < ActiveRecord::Base
@@ -65,7 +65,7 @@ class EagerSingularizationTest < ActiveRecord::TestCase
     connection.create_table :buses do |t|
       t.column :name, :string
     end
-    connection.create_table :crises_messes, :id => false do |t|
+    connection.create_table :crises_messes, id: false do |t|
       t.column :crisis_id, :integer
       t.column :mess_id, :integer
     end
@@ -104,45 +104,45 @@ class EagerSingularizationTest < ActiveRecord::TestCase
     connection.drop_table :compresses
   end
 
-  def connection
-    ActiveRecord::Base.connection
-  end
-
   def test_eager_no_extra_singularization_belongs_to
     assert_nothing_raised do
-      Virus.all.merge!(:includes => :octopus).to_a
+      Virus.all.merge!(includes: :octopus).to_a
     end
   end
 
   def test_eager_no_extra_singularization_has_one
     assert_nothing_raised do
-      Octopus.all.merge!(:includes => :virus).to_a
+      Octopus.all.merge!(includes: :virus).to_a
     end
   end
 
   def test_eager_no_extra_singularization_has_many
     assert_nothing_raised do
-      Bus.all.merge!(:includes => :passes).to_a
+      Bus.all.merge!(includes: :passes).to_a
     end
   end
 
   def test_eager_no_extra_singularization_has_and_belongs_to_many
     assert_nothing_raised do
-      Crisis.all.merge!(:includes => :messes).to_a
-      Mess.all.merge!(:includes => :crises).to_a
+      Crisis.all.merge!(includes: :messes).to_a
+      Mess.all.merge!(includes: :crises).to_a
     end
   end
 
   def test_eager_no_extra_singularization_has_many_through_belongs_to
     assert_nothing_raised do
-      Crisis.all.merge!(:includes => :successes).to_a
+      Crisis.all.merge!(includes: :successes).to_a
     end
   end
 
   def test_eager_no_extra_singularization_has_many_through_has_many
     assert_nothing_raised do
-      Crisis.all.merge!(:includes => :compresses).to_a
+      Crisis.all.merge!(includes: :compresses).to_a
     end
   end
-end
+
+  private
+    def connection
+      ActiveRecord::Base.connection
+    end
 end
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index ffbf60e390..b37e59038e 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -1,29 +1,46 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/tagging'
-require 'models/tag'
-require 'models/comment'
-require 'models/author'
-require 'models/essay'
-require 'models/category'
-require 'models/company'
-require 'models/person'
-require 'models/reader'
-require 'models/owner'
-require 'models/pet'
-require 'models/reference'
-require 'models/job'
-require 'models/subscriber'
-require 'models/subscription'
-require 'models/book'
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/member'
-require 'models/membership'
-require 'models/club'
-require 'models/categorization'
-require 'models/sponsor'
+require "models/post"
+require "models/tagging"
+require "models/tag"
+require "models/comment"
+require "models/author"
+require "models/essay"
+require "models/category"
+require "models/company"
+require "models/person"
+require "models/reader"
+require "models/owner"
+require "models/pet"
+require "models/reference"
+require "models/job"
+require "models/subscriber"
+require "models/subscription"
+require "models/book"
+require "models/citation"
+require "models/developer"
+require "models/computer"
+require "models/project"
+require "models/member"
+require "models/membership"
+require "models/club"
+require "models/categorization"
+require "models/sponsor"
+require "models/mentor"
+require "models/contract"
+
+class EagerLoadingTooManyIdsTest < ActiveRecord::TestCase
+  fixtures :citations
+
+  def test_preloading_too_many_ids
+    assert_equal Citation.count, Citation.preload(:reference_of).to_a.size
+  end
+
+  def test_eager_loading_too_may_ids
+    assert_equal Citation.count, Citation.eager_load(:citations).offset(0).size
+  end
+end
 
 class EagerAssociationTest < ActiveRecord::TestCase
   fixtures :posts, :comments, :authors, :essays, :author_addresses, :categories, :categories_posts,
@@ -32,42 +49,113 @@ class EagerAssociationTest < ActiveRecord::TestCase
             :developers, :projects, :developers_projects, :members, :memberships, :clubs, :sponsors
 
   def test_eager_with_has_one_through_join_model_with_conditions_on_the_through
-    member = Member.all.merge!(:includes => :favourite_club).find(members(:some_other_guy).id)
+    member = Member.all.merge!(includes: :favourite_club).find(members(:some_other_guy).id)
     assert_nil member.favourite_club
   end
 
+  def test_should_work_inverse_of_with_eager_load
+    author = authors(:david)
+    assert_same author, author.posts.first.author
+    assert_same author, author.posts.eager_load(:comments).first.author
+  end
+
   def test_loading_with_one_association
-    posts = Post.all.merge!(:includes => :comments).to_a
+    posts = Post.all.merge!(includes: :comments).to_a
     post = posts.find { |p| p.id == 1 }
     assert_equal 2, post.comments.size
-    assert post.comments.include?(comments(:greetings))
+    assert_includes post.comments, comments(:greetings)
 
-    post = Post.all.merge!(:includes => :comments, :where => "posts.title = 'Welcome to the weblog'").first
+    post = Post.all.merge!(includes: :comments, where: "posts.title = 'Welcome to the weblog'").first
     assert_equal 2, post.comments.size
-    assert post.comments.include?(comments(:greetings))
+    assert_includes post.comments, comments(:greetings)
 
-    posts = Post.all.merge!(:includes => :last_comment).to_a
+    posts = Post.all.merge!(includes: :last_comment).to_a
     post = posts.find { |p| p.id == 1 }
     assert_equal Post.find(1).last_comment, post.last_comment
   end
 
   def test_loading_with_one_association_with_non_preload
-    posts = Post.all.merge!(:includes => :last_comment, :order => 'comments.id DESC').to_a
+    posts = Post.all.merge!(includes: :last_comment, order: "comments.id DESC").to_a
     post = posts.find { |p| p.id == 1 }
     assert_equal Post.find(1).last_comment, post.last_comment
   end
 
   def test_loading_conditions_with_or
     posts = authors(:david).posts.references(:comments).merge(
-      :includes => :comments,
-      :where => "comments.body like 'Normal%' OR comments.#{QUOTED_TYPE} = 'SpecialComment'"
+      includes: :comments,
+      where: "comments.body like 'Normal%' OR comments.#{QUOTED_TYPE} = 'SpecialComment'"
     ).to_a
     assert_nil posts.detect { |p| p.author_id != authors(:david).id },
       "expected to find only david's posts"
   end
 
+  def test_loading_with_scope_including_joins
+    member = Member.first
+    assert_equal members(:groucho), member
+    assert_equal clubs(:boring_club), member.general_club
+
+    member = Member.preload(:general_club).first
+    assert_equal members(:groucho), member
+    assert_equal clubs(:boring_club), member.general_club
+
+    member = Member.eager_load(:general_club).first
+    assert_equal members(:groucho), member
+    assert_equal clubs(:boring_club), member.general_club
+  end
+
+  def test_loading_association_with_same_table_joins
+    super_memberships = [memberships(:super_membership_of_boring_club)]
+
+    member = Member.joins(:favourite_memberships).first
+    assert_equal members(:groucho), member
+    assert_equal super_memberships, member.super_memberships
+
+    member = Member.joins(:favourite_memberships).preload(:super_memberships).first
+    assert_equal members(:groucho), member
+    assert_equal super_memberships, member.super_memberships
+
+    member = Member.joins(:favourite_memberships).eager_load(:super_memberships).first
+    assert_equal members(:groucho), member
+    assert_equal super_memberships, member.super_memberships
+  end
+
+  def test_loading_association_with_intersection_joins
+    member = Member.joins(:current_membership).first
+    assert_equal members(:groucho), member
+    assert_equal clubs(:boring_club), member.club
+    assert_equal memberships(:membership_of_boring_club), member.current_membership
+
+    member = Member.joins(:current_membership).preload(:club, :current_membership).first
+    assert_equal members(:groucho), member
+    assert_equal clubs(:boring_club), member.club
+    assert_equal memberships(:membership_of_boring_club), member.current_membership
+
+    member = Member.joins(:current_membership).eager_load(:club, :current_membership).first
+    assert_equal members(:groucho), member
+    assert_equal clubs(:boring_club), member.club
+    assert_equal memberships(:membership_of_boring_club), member.current_membership
+  end
+
+  def test_loading_associations_dont_leak_instance_state
+    assertions = ->(firm) {
+      assert_equal companies(:first_firm), firm
+
+      assert_predicate firm.association(:readonly_account), :loaded?
+      assert_predicate firm.association(:accounts), :loaded?
+
+      assert_equal accounts(:signals37), firm.readonly_account
+      assert_equal [accounts(:signals37)], firm.accounts
+
+      assert_predicate firm.readonly_account, :readonly?
+      assert firm.accounts.none?(&:readonly?)
+    }
+
+    assertions.call(Firm.preload(:readonly_account, :accounts).first)
+    assertions.call(Firm.eager_load(:readonly_account, :accounts).first)
+  end
+
   def test_with_ordering
-    list = Post.all.merge!(:includes => :comments, :order => "posts.id DESC").to_a
+    list = Post.all.merge!(includes: :comments, order: "posts.id DESC").to_a
     [:other_by_mary, :other_by_bob, :misc_by_mary, :misc_by_bob, :eager_other,
      :sti_habtm, :sti_post_and_comments, :sti_comments, :authorless, :thinking, :welcome
     ].each_with_index do |post, index|
@@ -88,115 +176,123 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_no_queries { authors.map(&:post) }
   end
 
+  def test_calculate_with_string_in_from_and_eager_loading
+    assert_equal 10, Post.from("authors, posts").eager_load(:comments).where("posts.author_id = authors.id").count
+  end
+
   def test_with_two_tables_in_from_without_getting_double_quoted
     posts = Post.select("posts.*").from("authors, posts").eager_load(:comments).where("posts.author_id = authors.id").order("posts.id").to_a
     assert_equal 2, posts.first.comments.size
   end
 
   def test_loading_with_multiple_associations
-    posts = Post.all.merge!(:includes => [ :comments, :author, :categories ], :order => "posts.id").to_a
+    posts = Post.all.merge!(includes: [ :comments, :author, :categories ], order: "posts.id").to_a
     assert_equal 2, posts.first.comments.size
     assert_equal 2, posts.first.categories.size
-    assert posts.first.comments.include?(comments(:greetings))
+    assert_includes posts.first.comments, comments(:greetings)
   end
 
   def test_duplicate_middle_objects
-    comments = Comment.all.merge!(:where => 'post_id = 1', :includes => [:post => :author]).to_a
+    comments = Comment.all.merge!(where: "post_id = 1", includes: [post: :author]).to_a
     assert_no_queries do
-      comments.each {|comment| comment.post.author.name}
+      comments.each { |comment| comment.post.author.name }
     end
   end
 
   def test_preloading_has_many_in_multiple_queries_with_more_ids_than_database_can_handle
-    Comment.connection.expects(:in_clause_length).at_least_once.returns(5)
-    posts = Post.all.merge!(:includes=>:comments).to_a
-    assert_equal 11, posts.size
+    assert_called(Comment.connection, :in_clause_length, returns: 5) do
+      posts = Post.all.merge!(includes: :comments).to_a
+      assert_equal 11, posts.size
+    end
   end
 
   def test_preloading_has_many_in_one_queries_when_database_has_no_limit_on_ids_it_can_handle
-    Comment.connection.expects(:in_clause_length).at_least_once.returns(nil)
-    posts = Post.all.merge!(:includes=>:comments).to_a
-    assert_equal 11, posts.size
+    assert_called(Comment.connection, :in_clause_length, returns: nil) do
+      posts = Post.all.merge!(includes: :comments).to_a
+      assert_equal 11, posts.size
+    end
   end
 
   def test_preloading_habtm_in_multiple_queries_with_more_ids_than_database_can_handle
-    Comment.connection.expects(:in_clause_length).at_least_once.returns(5)
-    posts = Post.all.merge!(:includes=>:categories).to_a
-    assert_equal 11, posts.size
+    assert_called(Comment.connection, :in_clause_length, times: 2, returns: 5) do
+      posts = Post.all.merge!(includes: :categories).to_a
+      assert_equal 11, posts.size
+    end
   end
 
   def test_preloading_habtm_in_one_queries_when_database_has_no_limit_on_ids_it_can_handle
-    Comment.connection.expects(:in_clause_length).at_least_once.returns(nil)
-    posts = Post.all.merge!(:includes=>:categories).to_a
-    assert_equal 11, posts.size
+    assert_called(Comment.connection, :in_clause_length, times: 2, returns: nil) do
+      posts = Post.all.merge!(includes: :categories).to_a
+      assert_equal 11, posts.size
+    end
   end
 
   def test_load_associated_records_in_one_query_when_adapter_has_no_limit
-    Comment.connection.expects(:in_clause_length).at_least_once.returns(nil)
-
-    post = posts(:welcome)
-    assert_queries(2) do
-      Post.includes(:comments).where(:id => post.id).to_a
+    assert_called(Comment.connection, :in_clause_length, returns: nil) do
+      post = posts(:welcome)
+      assert_queries(2) do
+        Post.includes(:comments).where(id: post.id).to_a
+      end
     end
   end
 
   def test_load_associated_records_in_several_queries_when_many_ids_passed
-    Comment.connection.expects(:in_clause_length).at_least_once.returns(1)
-
-    post1, post2 = posts(:welcome), posts(:thinking)
-    assert_queries(3) do
-      Post.includes(:comments).where(:id => [post1.id, post2.id]).to_a
+    assert_called(Comment.connection, :in_clause_length, returns: 1) do
+      post1, post2 = posts(:welcome), posts(:thinking)
+      assert_queries(3) do
+        Post.includes(:comments).where(id: [post1.id, post2.id]).to_a
+      end
     end
   end
 
   def test_load_associated_records_in_one_query_when_a_few_ids_passed
-    Comment.connection.expects(:in_clause_length).at_least_once.returns(3)
-
-    post = posts(:welcome)
-    assert_queries(2) do
-      Post.includes(:comments).where(:id => post.id).to_a
+    assert_called(Comment.connection, :in_clause_length, returns: 3) do
+      post = posts(:welcome)
+      assert_queries(2) do
+        Post.includes(:comments).where(id: post.id).to_a
+      end
     end
   end
 
   def test_including_duplicate_objects_from_belongs_to
-    popular_post = Post.create!(:title => 'foo', :body => "I like cars!")
-    comment = popular_post.comments.create!(:body => "lol")
-    popular_post.readers.create!(:person => people(:michael))
-    popular_post.readers.create!(:person => people(:david))
+    popular_post = Post.create!(title: "foo", body: "I like cars!")
+    comment = popular_post.comments.create!(body: "lol")
+    popular_post.readers.create!(person: people(:michael))
+    popular_post.readers.create!(person: people(:david))
 
-    readers = Reader.all.merge!(:where => ["post_id = ?", popular_post.id],
-                                :includes => {:post => :comments}).to_a
+    readers = Reader.all.merge!(where: ["post_id = ?", popular_post.id],
+                                includes: { post: :comments }).to_a
     readers.each do |reader|
       assert_equal [comment], reader.post.comments
     end
   end
 
   def test_including_duplicate_objects_from_has_many
-    car_post = Post.create!(:title => 'foo', :body => "I like cars!")
+    car_post = Post.create!(title: "foo", body: "I like cars!")
     car_post.categories << categories(:general)
     car_post.categories << categories(:technology)
 
-    comment = car_post.comments.create!(:body => "hmm")
-    categories = Category.all.merge!(:where => { 'posts.id' => car_post.id },
-                                 :includes => {:posts => :comments}).to_a
+    comment = car_post.comments.create!(body: "hmm")
+    categories = Category.all.merge!(where: { "posts.id" => car_post.id },
+                                 includes: { posts: :comments }).to_a
     categories.each do |category|
       assert_equal [comment], category.posts[0].comments
     end
   end
 
   def test_associations_loaded_for_all_records
-    post = Post.create!(:title => 'foo', :body => "I like cars!")
-    SpecialComment.create!(:body => 'Come on!', :post => post)
-    first_category = Category.create! :name => 'First!', :posts => [post]
-    second_category = Category.create! :name => 'Second!', :posts => [post]
+    post = Post.create!(title: "foo", body: "I like cars!")
+    SpecialComment.create!(body: "Come on!", post: post)
+    first_category = Category.create! name: "First!", posts: [post]
+    second_category = Category.create! name: "Second!", posts: [post]
 
-    categories = Category.where(:id => [first_category.id, second_category.id]).includes(:posts => :special_comments)
+    categories = Category.where(id: [first_category.id, second_category.id]).includes(posts: :special_comments)
     assert_equal categories.map { |category| category.posts.first.special_comments.loaded? }, [true, true]
   end
 
   def test_finding_with_includes_on_has_many_association_with_same_include_includes_only_once
     author_id = authors(:david).id
-    author = assert_queries(3) { Author.all.merge!(:includes => {:posts_with_comments => :comments}).find(author_id) } # find the author, then find the posts, then find the comments
+    author = assert_queries(3) { Author.all.merge!(includes: { posts_with_comments: :comments }).find(author_id) } # find the author, then find the posts, then find the comments
     author.posts_with_comments.each do |post_with_comments|
       assert_equal post_with_comments.comments.length, post_with_comments.comments.count
       assert_nil post_with_comments.comments.to_a.uniq!
@@ -207,7 +303,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
     author = authors(:david)
     post = author.post_about_thinking_with_last_comment
     last_comment = post.last_comment
-    author = assert_queries(3) { Author.all.merge!(:includes => {:post_about_thinking_with_last_comment => :last_comment}).find(author.id)} # find the author, then find the posts, then find the comments
+    author = assert_queries(3) { Author.all.merge!(includes: { post_about_thinking_with_last_comment: :last_comment }).find(author.id) } # find the author, then find the posts, then find the comments
     assert_no_queries do
       assert_equal post, author.post_about_thinking_with_last_comment
       assert_equal last_comment, author.post_about_thinking_with_last_comment.last_comment
@@ -218,7 +314,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
     post = posts(:welcome)
     author = post.author
     author_address = author.author_address
-    post = assert_queries(3) { Post.all.merge!(:includes => {:author_with_address => :author_address}).find(post.id) } # find the post, then find the author, then find the address
+    post = assert_queries(3) { Post.all.merge!(includes: { author_with_address: :author_address }).find(post.id) } # find the post, then find the author, then find the address
     assert_no_queries do
       assert_equal author, post.author_with_address
       assert_equal author_address, post.author_with_address.author_address
@@ -228,53 +324,50 @@ class EagerAssociationTest < ActiveRecord::TestCase
   def test_finding_with_includes_on_null_belongs_to_association_with_same_include_includes_only_once
     post = posts(:welcome)
     post.update!(author: nil)
-    post = assert_queries(1) { Post.all.merge!(includes: {author_with_address: :author_address}).find(post.id) }
+    post = assert_queries(1) { Post.all.merge!(includes: { author_with_address: :author_address }).find(post.id) }
     # find the post, then find the author which is null so no query for the author or address
     assert_no_queries do
-      assert_equal nil, post.author_with_address
+      assert_nil post.author_with_address
     end
   end
 
   def test_finding_with_includes_on_null_belongs_to_polymorphic_association
     sponsor = sponsors(:moustache_club_sponsor_for_groucho)
     sponsor.update!(sponsorable: nil)
-    sponsor = assert_queries(1) { Sponsor.all.merge!(:includes => :sponsorable).find(sponsor.id) }
+    sponsor = assert_queries(1) { Sponsor.all.merge!(includes: :sponsorable).find(sponsor.id) }
     assert_no_queries do
-      assert_equal nil, sponsor.sponsorable
+      assert_nil sponsor.sponsorable
     end
   end
 
   def test_finding_with_includes_on_empty_polymorphic_type_column
     sponsor = sponsors(:moustache_club_sponsor_for_groucho)
-    sponsor.update!(sponsorable_type: '', sponsorable_id: nil) # sponsorable_type column might be declared NOT NULL
+    sponsor.update!(sponsorable_type: "", sponsorable_id: nil) # sponsorable_type column might be declared NOT NULL
     sponsor = assert_queries(1) do
-      assert_nothing_raised { Sponsor.all.merge!(:includes => :sponsorable).find(sponsor.id) }
+      assert_nothing_raised { Sponsor.all.merge!(includes: :sponsorable).find(sponsor.id) }
     end
     assert_no_queries do
-      assert_equal nil, sponsor.sponsorable
+      assert_nil sponsor.sponsorable
     end
   end
 
   def test_loading_from_an_association
-    posts = authors(:david).posts.merge(:includes => :comments, :order => "posts.id").to_a
+    posts = authors(:david).posts.merge(includes: :comments, order: "posts.id").to_a
     assert_equal 2, posts.first.comments.size
   end
 
   def test_loading_from_an_association_that_has_a_hash_of_conditions
-    assert_nothing_raised do
-      Author.all.merge!(:includes => :hello_posts_with_hash_conditions).to_a
-    end
-    assert !Author.all.merge!(:includes => :hello_posts_with_hash_conditions).find(authors(:david).id).hello_posts.empty?
+    assert_not_empty Author.all.merge!(includes: :hello_posts_with_hash_conditions).find(authors(:david).id).hello_posts
   end
 
   def test_loading_with_no_associations
-    assert_nil Post.all.merge!(:includes => :author).find(posts(:authorless).id).author
+    assert_nil Post.all.merge!(includes: :author).find(posts(:authorless).id).author
   end
 
   # Regression test for 21c75e5
   def test_nested_loading_does_not_raise_exception_when_association_does_not_exist
     assert_nothing_raised do
-      Post.all.merge!(:includes => {:author => :author_addresss}).find(posts(:authorless).id)
+      Post.all.merge!(includes: { author: :author_addresss }).find(posts(:authorless).id)
     end
   end
 
@@ -282,117 +375,117 @@ class EagerAssociationTest < ActiveRecord::TestCase
     post_id = Comment.where(author_id: nil).where.not(post_id: nil).first.post_id
 
     assert_nothing_raised do
-      Post.preload(:comments => [{:author => :essays}]).find(post_id)
+      Post.preload(comments: [{ author: :essays }]).find(post_id)
     end
   end
 
   def test_nested_loading_through_has_one_association
-    aa = AuthorAddress.all.merge!(:includes => {:author => :posts}).find(author_addresses(:david_address).id)
+    aa = AuthorAddress.all.merge!(includes: { author: :posts }).find(author_addresses(:david_address).id)
     assert_equal aa.author.posts.count, aa.author.posts.length
   end
 
   def test_nested_loading_through_has_one_association_with_order
-    aa = AuthorAddress.all.merge!(:includes => {:author => :posts}, :order => 'author_addresses.id').find(author_addresses(:david_address).id)
+    aa = AuthorAddress.all.merge!(includes: { author: :posts }, order: "author_addresses.id").find(author_addresses(:david_address).id)
     assert_equal aa.author.posts.count, aa.author.posts.length
   end
 
   def test_nested_loading_through_has_one_association_with_order_on_association
-    aa = AuthorAddress.all.merge!(:includes => {:author => :posts}, :order => 'authors.id').find(author_addresses(:david_address).id)
+    aa = AuthorAddress.all.merge!(includes: { author: :posts }, order: "authors.id").find(author_addresses(:david_address).id)
     assert_equal aa.author.posts.count, aa.author.posts.length
   end
 
   def test_nested_loading_through_has_one_association_with_order_on_nested_association
-    aa = AuthorAddress.all.merge!(:includes => {:author => :posts}, :order => 'posts.id').find(author_addresses(:david_address).id)
+    aa = AuthorAddress.all.merge!(includes: { author: :posts }, order: "posts.id").find(author_addresses(:david_address).id)
     assert_equal aa.author.posts.count, aa.author.posts.length
   end
 
   def test_nested_loading_through_has_one_association_with_conditions
     aa = AuthorAddress.references(:author_addresses).merge(
-      :includes => {:author => :posts},
-      :where => "author_addresses.id > 0"
+      includes: { author: :posts },
+      where: "author_addresses.id > 0"
     ).find author_addresses(:david_address).id
     assert_equal aa.author.posts.count, aa.author.posts.length
   end
 
   def test_nested_loading_through_has_one_association_with_conditions_on_association
     aa = AuthorAddress.references(:authors).merge(
-      :includes => {:author => :posts},
-      :where => "authors.id > 0"
+      includes: { author: :posts },
+      where: "authors.id > 0"
     ).find author_addresses(:david_address).id
     assert_equal aa.author.posts.count, aa.author.posts.length
   end
 
   def test_nested_loading_through_has_one_association_with_conditions_on_nested_association
     aa = AuthorAddress.references(:posts).merge(
-      :includes => {:author => :posts},
-      :where => "posts.id > 0"
+      includes: { author: :posts },
+      where: "posts.id > 0"
     ).find author_addresses(:david_address).id
     assert_equal aa.author.posts.count, aa.author.posts.length
   end
 
   def test_eager_association_loading_with_belongs_to_and_foreign_keys
-    pets = Pet.all.merge!(:includes => :owner).to_a
+    pets = Pet.all.merge!(includes: :owner).to_a
     assert_equal 4, pets.length
   end
 
   def test_eager_association_loading_with_belongs_to
-    comments = Comment.all.merge!(:includes => :post).to_a
+    comments = Comment.all.merge!(includes: :post).to_a
     assert_equal 11, comments.length
     titles = comments.map { |c| c.post.title }
-    assert titles.include?(posts(:welcome).title)
-    assert titles.include?(posts(:sti_post_and_comments).title)
+    assert_includes titles, posts(:welcome).title
+    assert_includes titles, posts(:sti_post_and_comments).title
   end
 
   def test_eager_association_loading_with_belongs_to_and_limit
-    comments = Comment.all.merge!(:includes => :post, :limit => 5, :order => 'comments.id').to_a
+    comments = Comment.all.merge!(includes: :post, limit: 5, order: "comments.id").to_a
     assert_equal 5, comments.length
-    assert_equal [1,2,3,5,6], comments.collect(&:id)
+    assert_equal [1, 2, 3, 5, 6], comments.collect(&:id)
   end
 
   def test_eager_association_loading_with_belongs_to_and_limit_and_conditions
-    comments = Comment.all.merge!(:includes => :post, :where => 'post_id = 4', :limit => 3, :order => 'comments.id').to_a
+    comments = Comment.all.merge!(includes: :post, where: "post_id = 4", limit: 3, order: "comments.id").to_a
     assert_equal 3, comments.length
-    assert_equal [5,6,7], comments.collect(&:id)
+    assert_equal [5, 6, 7], comments.collect(&:id)
   end
 
   def test_eager_association_loading_with_belongs_to_and_limit_and_offset
-    comments = Comment.all.merge!(:includes => :post, :limit => 3, :offset => 2, :order => 'comments.id').to_a
+    comments = Comment.all.merge!(includes: :post, limit: 3, offset: 2, order: "comments.id").to_a
     assert_equal 3, comments.length
-    assert_equal [3,5,6], comments.collect(&:id)
+    assert_equal [3, 5, 6], comments.collect(&:id)
   end
 
   def test_eager_association_loading_with_belongs_to_and_limit_and_offset_and_conditions
-    comments = Comment.all.merge!(:includes => :post, :where => 'post_id = 4', :limit => 3, :offset => 1, :order => 'comments.id').to_a
+    comments = Comment.all.merge!(includes: :post, where: "post_id = 4", limit: 3, offset: 1, order: "comments.id").to_a
     assert_equal 3, comments.length
-    assert_equal [6,7,8], comments.collect(&:id)
+    assert_equal [6, 7, 8], comments.collect(&:id)
   end
 
   def test_eager_association_loading_with_belongs_to_and_limit_and_offset_and_conditions_array
-    comments = Comment.all.merge!(:includes => :post, :where => ['post_id = ?',4], :limit => 3, :offset => 1, :order => 'comments.id').to_a
+    comments = Comment.all.merge!(includes: :post, where: ["post_id = ?", 4], limit: 3, offset: 1, order: "comments.id").to_a
     assert_equal 3, comments.length
-    assert_equal [6,7,8], comments.collect(&:id)
+    assert_equal [6, 7, 8], comments.collect(&:id)
   end
 
   def test_eager_association_loading_with_belongs_to_and_conditions_string_with_unquoted_table_name
     assert_nothing_raised do
-      Comment.includes(:post).references(:posts).where('posts.id = ?', 4)
+      Comment.includes(:post).references(:posts).where("posts.id = ?", 4)
     end
   end
 
   def test_eager_association_loading_with_belongs_to_and_conditions_hash
     comments = []
     assert_nothing_raised do
-      comments = Comment.all.merge!(:includes => :post, :where => {:posts => {:id => 4}}, :limit => 3, :order => 'comments.id').to_a
+      comments = Comment.all.merge!(includes: :post, where: { posts: { id: 4 } }, limit: 3, order: "comments.id").to_a
     end
     assert_equal 3, comments.length
-    assert_equal [5,6,7], comments.collect(&:id)
+    assert_equal [5, 6, 7], comments.collect(&:id)
     assert_no_queries do
       comments.first.post
     end
   end
 
   def test_eager_association_loading_with_belongs_to_and_conditions_string_with_quoted_table_name
-    quoted_posts_id= Comment.connection.quote_table_name('posts') + '.' + Comment.connection.quote_column_name('id')
+    quoted_posts_id = Comment.connection.quote_table_name("posts") + "." + Comment.connection.quote_column_name("id")
     assert_nothing_raised do
       Comment.includes(:post).references(:posts).where("#{quoted_posts_id} = ?", 4)
     end
@@ -400,61 +493,61 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   def test_eager_association_loading_with_belongs_to_and_order_string_with_unquoted_table_name
     assert_nothing_raised do
-      Comment.all.merge!(:includes => :post, :order => 'posts.id').to_a
+      Comment.all.merge!(includes: :post, order: "posts.id").to_a
     end
   end
 
   def test_eager_association_loading_with_belongs_to_and_order_string_with_quoted_table_name
-    quoted_posts_id= Comment.connection.quote_table_name('posts') + '.' + Comment.connection.quote_column_name('id')
+    quoted_posts_id = Comment.connection.quote_table_name("posts") + "." + Comment.connection.quote_column_name("id")
     assert_nothing_raised do
-      Comment.includes(:post).references(:posts).order(quoted_posts_id)
+      Comment.includes(:post).references(:posts).order(Arel.sql(quoted_posts_id))
     end
   end
 
   def test_eager_association_loading_with_belongs_to_and_limit_and_multiple_associations
-    posts = Post.all.merge!(:includes => [:author, :very_special_comment], :limit => 1, :order => 'posts.id').to_a
+    posts = Post.all.merge!(includes: [:author, :very_special_comment], limit: 1, order: "posts.id").to_a
     assert_equal 1, posts.length
     assert_equal [1], posts.collect(&:id)
   end
 
   def test_eager_association_loading_with_belongs_to_and_limit_and_offset_and_multiple_associations
-    posts = Post.all.merge!(:includes => [:author, :very_special_comment], :limit => 1, :offset => 1, :order => 'posts.id').to_a
+    posts = Post.all.merge!(includes: [:author, :very_special_comment], limit: 1, offset: 1, order: "posts.id").to_a
     assert_equal 1, posts.length
     assert_equal [2], posts.collect(&:id)
   end
 
   def test_eager_association_loading_with_belongs_to_inferred_foreign_key_from_association_name
-    author_favorite = AuthorFavorite.all.merge!(:includes => :favorite_author).first
+    author_favorite = AuthorFavorite.all.merge!(includes: :favorite_author).first
     assert_equal authors(:mary), assert_no_queries { author_favorite.favorite_author }
   end
 
   def test_eager_load_belongs_to_quotes_table_and_column_names
     job = Job.includes(:ideal_reference).find jobs(:unicyclist).id
     references(:michael_unicyclist)
-    assert_no_queries{ assert_equal references(:michael_unicyclist), job.ideal_reference}
+    assert_no_queries { assert_equal references(:michael_unicyclist), job.ideal_reference }
   end
 
   def test_eager_load_has_one_quotes_table_and_column_names
-    michael = Person.all.merge!(:includes => :favourite_reference).find(people(:michael).id)
+    michael = Person.all.merge!(includes: :favourite_reference).find(people(:michael).id)
     references(:michael_unicyclist)
-    assert_no_queries{ assert_equal references(:michael_unicyclist), michael.favourite_reference}
+    assert_no_queries { assert_equal references(:michael_unicyclist), michael.favourite_reference }
   end
 
   def test_eager_load_has_many_quotes_table_and_column_names
-    michael = Person.all.merge!(:includes => :references).find(people(:michael).id)
-    references(:michael_magician,:michael_unicyclist)
-    assert_no_queries{ assert_equal references(:michael_magician,:michael_unicyclist), michael.references.sort_by(&:id) }
+    michael = Person.all.merge!(includes: :references).find(people(:michael).id)
+    references(:michael_magician, :michael_unicyclist)
+    assert_no_queries { assert_equal references(:michael_magician, :michael_unicyclist), michael.references.sort_by(&:id) }
   end
 
   def test_eager_load_has_many_through_quotes_table_and_column_names
-    michael = Person.all.merge!(:includes => :jobs).find(people(:michael).id)
+    michael = Person.all.merge!(includes: :jobs).find(people(:michael).id)
     jobs(:magician, :unicyclist)
-    assert_no_queries{ assert_equal jobs(:unicyclist, :magician), michael.jobs.sort_by(&:id) }
+    assert_no_queries { assert_equal jobs(:unicyclist, :magician), michael.jobs.sort_by(&:id) }
   end
 
   def test_eager_load_has_many_with_string_keys
     subscriptions = subscriptions(:webster_awdr, :webster_rfr)
-    subscriber =Subscriber.all.merge!(:includes => :subscriptions).find(subscribers(:second).id)
+    subscriber = Subscriber.all.merge!(includes: :subscriptions).find(subscribers(:second).id)
     assert_equal subscriptions, subscriber.subscriptions.sort_by(&:id)
   end
 
@@ -465,32 +558,32 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
     b = Book.create!
 
-    Subscription.create!(:subscriber_id => "PL", :book_id => b.id)
+    Subscription.create!(subscriber_id: "PL", book_id: b.id)
     s.reload
     s.book_ids = s.book_ids
   end
 
   def test_eager_load_has_many_through_with_string_keys
     books = books(:awdr, :rfr)
-    subscriber = Subscriber.all.merge!(:includes => :books).find(subscribers(:second).id)
+    subscriber = Subscriber.all.merge!(includes: :books).find(subscribers(:second).id)
     assert_equal books, subscriber.books.sort_by(&:id)
   end
 
   def test_eager_load_belongs_to_with_string_keys
     subscriber = subscribers(:second)
-    subscription = Subscription.all.merge!(:includes => :subscriber).find(subscriptions(:webster_awdr).id)
+    subscription = Subscription.all.merge!(includes: :subscriber).find(subscriptions(:webster_awdr).id)
     assert_equal subscriber, subscription.subscriber
   end
 
   def test_eager_association_loading_with_explicit_join
-    posts = Post.all.merge!(:includes => :comments, :joins => "INNER JOIN authors ON posts.author_id = authors.id AND authors.name = 'Mary'", :limit => 1, :order => 'author_id').to_a
+    posts = Post.all.merge!(includes: :comments, joins: "INNER JOIN authors ON posts.author_id = authors.id AND authors.name = 'Mary'", limit: 1, order: "author_id").to_a
     assert_equal 1, posts.length
   end
 
   def test_eager_with_has_many_through
-    posts_with_comments = people(:michael).posts.merge(:includes => :comments, :order => 'posts.id').to_a
-    posts_with_author = people(:michael).posts.merge(:includes => :author, :order => 'posts.id').to_a
-    posts_with_comments_and_author = people(:michael).posts.merge(:includes => [ :comments, :author ], :order => 'posts.id').to_a
+    posts_with_comments = people(:michael).posts.merge(includes: :comments, order: "posts.id").to_a
+    posts_with_author = people(:michael).posts.merge(includes: :author, order: "posts.id").to_a
+    posts_with_comments_and_author = people(:michael).posts.merge(includes: [ :comments, :author ], order: "posts.id").to_a
     assert_equal 2, posts_with_comments.inject(0) { |sum, post| sum + post.comments.size }
     assert_equal authors(:david), assert_no_queries { posts_with_author.first.author }
     assert_equal authors(:david), assert_no_queries { posts_with_comments_and_author.first.author }
@@ -498,35 +591,43 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   def test_eager_with_has_many_through_a_belongs_to_association
     author = authors(:mary)
-    Post.create!(:author => author, :title => "TITLE", :body => "BODY")
-    author.author_favorites.create(:favorite_author_id => 1)
-    author.author_favorites.create(:favorite_author_id => 2)
-    posts_with_author_favorites = author.posts.merge(:includes => :author_favorites).to_a
+    Post.create!(author: author, title: "TITLE", body: "BODY")
+    author.author_favorites.create(favorite_author_id: 1)
+    author.author_favorites.create(favorite_author_id: 2)
+    posts_with_author_favorites = author.posts.merge(includes: :author_favorites).to_a
     assert_no_queries { posts_with_author_favorites.first.author_favorites.first.author_id }
   end
 
   def test_eager_with_has_many_through_an_sti_join_model
-    author = Author.all.merge!(:includes => :special_post_comments, :order => 'authors.id').first
+    author = Author.all.merge!(includes: :special_post_comments, order: "authors.id").first
     assert_equal [comments(:does_it_hurt)], assert_no_queries { author.special_post_comments }
   end
 
+  def test_preloading_has_many_through_with_implicit_source
+    authors = Author.includes(:very_special_comments).to_a
+    assert_no_queries do
+      special_comment_authors = authors.map { |author| [author.name, author.very_special_comments.size] }
+      assert_equal [["David", 1], ["Mary", 0], ["Bob", 0]], special_comment_authors
+    end
+  end
+
   def test_eager_with_has_many_through_an_sti_join_model_with_conditions_on_both
-    author = Author.all.merge!(:includes => :special_nonexistent_post_comments, :order => 'authors.id').first
+    author = Author.all.merge!(includes: :special_nonexistent_post_comments, order: "authors.id").first
     assert_equal [], author.special_nonexistent_post_comments
   end
 
   def test_eager_with_has_many_through_join_model_with_conditions
-    assert_equal Author.all.merge!(:includes => :hello_post_comments,
-                             :order => 'authors.id').first.hello_post_comments.sort_by(&:id),
-                 Author.all.merge!(:order => 'authors.id').first.hello_post_comments.sort_by(&:id)
+    assert_equal Author.all.merge!(includes: :hello_post_comments,
+                             order: "authors.id").first.hello_post_comments.sort_by(&:id),
+                 Author.all.merge!(order: "authors.id").first.hello_post_comments.sort_by(&:id)
   end
 
   def test_eager_with_has_many_through_join_model_with_conditions_on_top_level
-    assert_equal comments(:more_greetings), Author.all.merge!(:includes => :comments_with_order_and_conditions).find(authors(:david).id).comments_with_order_and_conditions.first
+    assert_equal comments(:more_greetings), Author.all.merge!(includes: :comments_with_order_and_conditions).find(authors(:david).id).comments_with_order_and_conditions.first
   end
 
   def test_eager_with_has_many_through_join_model_with_include
-    author_comments = Author.all.merge!(:includes => :comments_with_include).find(authors(:david).id).comments_with_include.to_a
+    author_comments = Author.all.merge!(includes: :comments_with_include).find(authors(:david).id).comments_with_include.to_a
     assert_no_queries do
       author_comments.first.post.title
     end
@@ -534,7 +635,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   def test_eager_with_has_many_through_with_conditions_join_model_with_include
     post_tags = Post.find(posts(:welcome).id).misc_tags
-    eager_post_tags = Post.all.merge!(:includes => :misc_tags).find(1).misc_tags
+    eager_post_tags = Post.all.merge!(includes: :misc_tags).find(1).misc_tags
     assert_equal post_tags, eager_post_tags
   end
 
@@ -545,67 +646,67 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_with_has_many_and_limit
-    posts = Post.all.merge!(:order => 'posts.id asc', :includes => [ :author, :comments ], :limit => 2).to_a
+    posts = Post.all.merge!(order: "posts.id asc", includes: [ :author, :comments ], limit: 2).to_a
     assert_equal 2, posts.size
     assert_equal 3, posts.inject(0) { |sum, post| sum + post.comments.size }
   end
 
   def test_eager_with_has_many_and_limit_and_conditions
-    posts = Post.all.merge!(:includes => [ :author, :comments ], :limit => 2, :where => "posts.body = 'hello'", :order => "posts.id").to_a
+    posts = Post.all.merge!(includes: [ :author, :comments ], limit: 2, where: "posts.body = 'hello'", order: "posts.id").to_a
     assert_equal 2, posts.size
-    assert_equal [4,5], posts.collect(&:id)
+    assert_equal [4, 5], posts.collect(&:id)
   end
 
   def test_eager_with_has_many_and_limit_and_conditions_array
-    posts = Post.all.merge!(:includes => [ :author, :comments ], :limit => 2, :where => [ "posts.body = ?", 'hello' ], :order => "posts.id").to_a
+    posts = Post.all.merge!(includes: [ :author, :comments ], limit: 2, where: [ "posts.body = ?", "hello" ], order: "posts.id").to_a
     assert_equal 2, posts.size
-    assert_equal [4,5], posts.collect(&:id)
+    assert_equal [4, 5], posts.collect(&:id)
   end
 
   def test_eager_with_has_many_and_limit_and_conditions_array_on_the_eagers
-    posts = Post.includes(:author, :comments).limit(2).references(:author).where("authors.name = ?", 'David')
+    posts = Post.includes(:author, :comments).limit(2).references(:author).where("authors.name = ?", "David")
     assert_equal 2, posts.size
 
-    count = Post.includes(:author, :comments).limit(2).references(:author).where("authors.name = ?", 'David').count
+    count = Post.includes(:author, :comments).limit(2).references(:author).where("authors.name = ?", "David").count
     assert_equal posts.size, count
   end
 
   def test_eager_with_has_many_and_limit_and_high_offset
-    posts = Post.all.merge!(:includes => [ :author, :comments ], :limit => 2, :offset => 10, :where => { 'authors.name' => 'David' }).to_a
+    posts = Post.all.merge!(includes: [ :author, :comments ], limit: 2, offset: 10, where: { "authors.name" => "David" }).to_a
     assert_equal 0, posts.size
   end
 
   def test_eager_with_has_many_and_limit_and_high_offset_and_multiple_array_conditions
     assert_queries(1) do
       posts = Post.references(:authors, :comments).
-        merge(:includes => [ :author, :comments ], :limit => 2, :offset => 10,
-          :where => [ "authors.name = ? and comments.body = ?", 'David', 'go crazy' ]).to_a
+        merge(includes: [ :author, :comments ], limit: 2, offset: 10,
+          where: [ "authors.name = ? and comments.body = ?", "David", "go crazy" ]).to_a
       assert_equal 0, posts.size
     end
   end
 
   def test_eager_with_has_many_and_limit_and_high_offset_and_multiple_hash_conditions
     assert_queries(1) do
-      posts = Post.all.merge!(:includes => [ :author, :comments ], :limit => 2, :offset => 10,
-        :where => { 'authors.name' => 'David', 'comments.body' => 'go crazy' }).to_a
+      posts = Post.all.merge!(includes: [ :author, :comments ], limit: 2, offset: 10,
+        where: { "authors.name" => "David", "comments.body" => "go crazy" }).to_a
       assert_equal 0, posts.size
     end
   end
 
   def test_count_eager_with_has_many_and_limit_and_high_offset
-    posts = Post.all.merge!(:includes => [ :author, :comments ], :limit => 2, :offset => 10, :where => { 'authors.name' => 'David' }).count(:all)
+    posts = Post.all.merge!(includes: [ :author, :comments ], limit: 2, offset: 10, where: { "authors.name" => "David" }).count(:all)
     assert_equal 0, posts
   end
 
   def test_eager_with_has_many_and_limit_with_no_results
-    posts = Post.all.merge!(:includes => [ :author, :comments ], :limit => 2, :where => "posts.title = 'magic forest'").to_a
+    posts = Post.all.merge!(includes: [ :author, :comments ], limit: 2, where: "posts.title = 'magic forest'").to_a
     assert_equal 0, posts.size
   end
 
   def test_eager_count_performed_on_a_has_many_association_with_multi_table_conditional
     author = authors(:david)
     author_posts_without_comments = author.posts.select { |post| post.comments.blank? }
-    assert_equal author_posts_without_comments.size, author.posts.includes(:comments).where('comments.id is null').references(:comments).count
+    assert_equal author_posts_without_comments.size, author.posts.includes(:comments).where("comments.id is null").references(:comments).count
   end
 
   def test_eager_count_performed_on_a_has_many_through_association_with_multi_table_conditional
@@ -615,13 +716,13 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_with_has_and_belongs_to_many_and_limit
-    posts = Post.all.merge!(:includes => :categories, :order => "posts.id", :limit => 3).to_a
+    posts = Post.all.merge!(includes: :categories, order: "posts.id", limit: 3).to_a
     assert_equal 3, posts.size
     assert_equal 2, posts[0].categories.size
     assert_equal 1, posts[1].categories.size
     assert_equal 0, posts[2].categories.size
-    assert posts[0].categories.include?(categories(:technology))
-    assert posts[1].categories.include?(categories(:general))
+    assert_includes posts[0].categories, categories(:technology)
+    assert_includes posts[1].categories, categories(:general)
   end
 
   # Since the preloader for habtm gets raw row hashes from the database and then
@@ -681,32 +782,32 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_association_loading_with_habtm
-    posts = Post.all.merge!(:includes => :categories, :order => "posts.id").to_a
+    posts = Post.all.merge!(includes: :categories, order: "posts.id").to_a
     assert_equal 2, posts[0].categories.size
     assert_equal 1, posts[1].categories.size
     assert_equal 0, posts[2].categories.size
-    assert posts[0].categories.include?(categories(:technology))
-    assert posts[1].categories.include?(categories(:general))
+    assert_includes posts[0].categories, categories(:technology)
+    assert_includes posts[1].categories, categories(:general)
   end
 
   def test_eager_with_inheritance
-    SpecialPost.all.merge!(:includes => [ :comments ]).to_a
+    SpecialPost.all.merge!(includes: [ :comments ]).to_a
   end
 
   def test_eager_has_one_with_association_inheritance
-    post = Post.all.merge!(:includes => [ :very_special_comment ]).find(4)
+    post = Post.all.merge!(includes: [ :very_special_comment ]).find(4)
     assert_equal "VerySpecialComment", post.very_special_comment.class.to_s
   end
 
   def test_eager_has_many_with_association_inheritance
-    post = Post.all.merge!(:includes => [ :special_comments ]).find(4)
+    post = Post.all.merge!(includes: [ :special_comments ]).find(4)
     post.special_comments.each do |special_comment|
       assert special_comment.is_a?(SpecialComment)
     end
   end
 
   def test_eager_habtm_with_association_inheritance
-    post = Post.all.merge!(:includes => [ :special_categories ]).find(6)
+    post = Post.all.merge!(includes: [ :special_categories ]).find(6)
     assert_equal 1, post.special_categories.size
     post.special_categories.each do |special_category|
       assert_equal "SpecialCategory", special_category.class.to_s
@@ -715,8 +816,8 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   def test_eager_with_has_one_dependent_does_not_destroy_dependent
     assert_not_nil companies(:first_firm).account
-    f = Firm.all.merge!(:includes => :account,
-            :where => ["companies.name = ?", "37signals"]).first
+    f = Firm.all.merge!(includes: :account,
+            where: ["companies.name = ?", "37signals"]).first
     assert_not_nil f.account
     assert_equal companies(:first_firm, :reload).account, f.account
   end
@@ -729,22 +830,61 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_with_invalid_association_reference
-    assert_raise(ActiveRecord::AssociationNotFoundError, "Association was not found; perhaps you misspelled it?  You specified :include => :monkeys") {
-      Post.all.merge!(:includes=> :monkeys ).find(6)
+    e = assert_raise(ActiveRecord::AssociationNotFoundError) {
+      Post.all.merge!(includes: :monkeys).find(6)
     }
-    assert_raise(ActiveRecord::AssociationNotFoundError, "Association was not found; perhaps you misspelled it?  You specified :include => :monkeys") {
-      Post.all.merge!(:includes=>[ :monkeys ]).find(6)
+    assert_equal("Association named 'monkeys' was not found on Post; perhaps you misspelled it?", e.message)
+
+    e = assert_raise(ActiveRecord::AssociationNotFoundError) {
+      Post.all.merge!(includes: [ :monkeys ]).find(6)
     }
-    assert_raise(ActiveRecord::AssociationNotFoundError, "Association was not found; perhaps you misspelled it?  You specified :include => :monkeys") {
-      Post.all.merge!(:includes=>[ 'monkeys' ]).find(6)
+    assert_equal("Association named 'monkeys' was not found on Post; perhaps you misspelled it?", e.message)
+
+    e = assert_raise(ActiveRecord::AssociationNotFoundError) {
+      Post.all.merge!(includes: [ "monkeys" ]).find(6)
     }
-    assert_raise(ActiveRecord::AssociationNotFoundError, "Association was not found; perhaps you misspelled it?  You specified :include => :monkeys, :elephants") {
-      Post.all.merge!(:includes=>[ :monkeys, :elephants ]).find(6)
+    assert_equal("Association named 'monkeys' was not found on Post; perhaps you misspelled it?", e.message)
+
+    e = assert_raise(ActiveRecord::AssociationNotFoundError) {
+      Post.all.merge!(includes: [ :monkeys, :elephants ]).find(6)
     }
+    assert_equal("Association named 'monkeys' was not found on Post; perhaps you misspelled it?", e.message)
+  end
+
+  def test_eager_has_many_through_with_order
+    tag = OrderedTag.create(name: "Foo")
+    post1 = Post.create!(title: "Beaches", body: "I like beaches!")
+    post2 = Post.create!(title: "Pools", body: "I like pools!")
+
+    Tagging.create!(taggable_type: "Post", taggable_id: post1.id, tag: tag)
+    Tagging.create!(taggable_type: "Post", taggable_id: post2.id, tag: tag)
+
+    tag_with_includes = OrderedTag.includes(:tagged_posts).find(tag.id)
+    assert_equal tag_with_includes.ordered_taggings.map(&:taggable).map(&:title), tag_with_includes.tagged_posts.map(&:title)
+  end
+
+  def test_eager_has_many_through_multiple_with_order
+    tag1 = OrderedTag.create!(name: "Bar")
+    tag2 = OrderedTag.create!(name: "Foo")
+
+    post1 = Post.create!(title: "Beaches", body: "I like beaches!")
+    post2 = Post.create!(title: "Pools", body: "I like pools!")
+
+    Tagging.create!(taggable: post1, tag: tag1)
+    Tagging.create!(taggable: post2, tag: tag1)
+    Tagging.create!(taggable: post2, tag: tag2)
+    Tagging.create!(taggable: post1, tag: tag2)
+
+    tags_with_includes = OrderedTag.where(id: [tag1, tag2].map(&:id)).includes(:tagged_posts).order(:id).to_a
+    tag1_with_includes = tags_with_includes.first
+    tag2_with_includes = tags_with_includes.last
+
+    assert_equal([post2, post1].map(&:title), tag1_with_includes.tagged_posts.map(&:title))
+    assert_equal([post1, post2].map(&:title), tag2_with_includes.tagged_posts.map(&:title))
   end
 
   def test_eager_with_default_scope
-    developer = EagerDeveloperWithDefaultScope.where(:name => 'David').first
+    developer = EagerDeveloperWithDefaultScope.where(name: "David").first
     projects = Project.order(:id).to_a
     assert_no_queries do
       assert_equal(projects, developer.projects)
@@ -752,7 +892,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_with_default_scope_as_class_method
-    developer = EagerDeveloperWithClassMethodDefaultScope.where(:name => 'David').first
+    developer = EagerDeveloperWithClassMethodDefaultScope.where(name: "David").first
     projects = Project.order(:id).to_a
     assert_no_queries do
       assert_equal(projects, developer.projects)
@@ -769,7 +909,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_with_default_scope_as_class_method_using_find_by_method
-    developer = EagerDeveloperWithClassMethodDefaultScope.find_by(name: 'David')
+    developer = EagerDeveloperWithClassMethodDefaultScope.find_by(name: "David")
     projects = Project.order(:id).to_a
     assert_no_queries do
       assert_equal(projects, developer.projects)
@@ -777,7 +917,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_with_default_scope_as_lambda
-    developer = EagerDeveloperWithLambdaDefaultScope.where(:name => 'David').first
+    developer = EagerDeveloperWithLambdaDefaultScope.where(name: "David").first
     projects = Project.order(:id).to_a
     assert_no_queries do
       assert_equal(projects, developer.projects)
@@ -786,8 +926,8 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   def test_eager_with_default_scope_as_block
     # warm up the habtm cache
-    EagerDeveloperWithBlockDefaultScope.where(:name => 'David').first.projects
-    developer = EagerDeveloperWithBlockDefaultScope.where(:name => 'David').first
+    EagerDeveloperWithBlockDefaultScope.where(name: "David").first.projects
+    developer = EagerDeveloperWithBlockDefaultScope.where(name: "David").first
     projects = Project.order(:id).to_a
     assert_no_queries do
       assert_equal(projects, developer.projects)
@@ -795,30 +935,26 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_eager_with_default_scope_as_callable
-    developer = EagerDeveloperWithCallableDefaultScope.where(:name => 'David').first
+    developer = EagerDeveloperWithCallableDefaultScope.where(name: "David").first
     projects = Project.order(:id).to_a
     assert_no_queries do
       assert_equal(projects, developer.projects)
     end
   end
 
-  def find_all_ordered(className, include=nil)
-    className.all.merge!(:order=>"#{className.table_name}.#{className.primary_key}", :includes=>include).to_a
-  end
-
   def test_limited_eager_with_order
     assert_equal(
       posts(:thinking, :sti_comments),
       Post.all.merge!(
-        :includes => [:author, :comments], :where => { 'authors.name' => 'David' },
-        :order => 'UPPER(posts.title)', :limit => 2, :offset => 1
+        includes: [:author, :comments], where: { "authors.name" => "David" },
+        order: Arel.sql("UPPER(posts.title)"), limit: 2, offset: 1
       ).to_a
     )
     assert_equal(
       posts(:sti_post_and_comments, :sti_comments),
       Post.all.merge!(
-        :includes => [:author, :comments], :where => { 'authors.name' => 'David' },
-        :order => 'UPPER(posts.title) DESC', :limit => 2, :offset => 1
+        includes: [:author, :comments], where: { "authors.name" => "David" },
+        order: Arel.sql("UPPER(posts.title) DESC"), limit: 2, offset: 1
       ).to_a
     )
   end
@@ -827,15 +963,15 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_equal(
       posts(:thinking, :sti_comments),
       Post.all.merge!(
-        :includes => [:author, :comments], :where => { 'authors.name' => 'David' },
-        :order => ['UPPER(posts.title)', 'posts.id'], :limit => 2, :offset => 1
+        includes: [:author, :comments], where: { "authors.name" => "David" },
+        order: [Arel.sql("UPPER(posts.title)"), "posts.id"], limit: 2, offset: 1
       ).to_a
     )
     assert_equal(
       posts(:sti_post_and_comments, :sti_comments),
       Post.all.merge!(
-        :includes => [:author, :comments], :where => { 'authors.name' => 'David' },
-        :order => ['UPPER(posts.title) DESC', 'posts.id'], :limit => 2, :offset => 1
+        includes: [:author, :comments], where: { "authors.name" => "David" },
+        order: [Arel.sql("UPPER(posts.title) DESC"), "posts.id"], limit: 2, offset: 1
       ).to_a
     )
   end
@@ -844,25 +980,25 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_equal(
       people(:david, :susan),
       Person.references(:number1_fans_people).merge(
-        :includes => [:readers, :primary_contact, :number1_fan],
-        :where => "number1_fans_people.first_name like 'M%'",
-        :order => 'people.id', :limit => 2, :offset => 0
+        includes: [:readers, :primary_contact, :number1_fan],
+        where: "number1_fans_people.first_name like 'M%'",
+        order: "people.id", limit: 2, offset: 0
       ).to_a
     )
   end
 
   def test_polymorphic_type_condition
-    post = Post.all.merge!(:includes => :taggings).find(posts(:thinking).id)
-    assert post.taggings.include?(taggings(:thinking_general))
-    post = SpecialPost.all.merge!(:includes => :taggings).find(posts(:thinking).id)
-    assert post.taggings.include?(taggings(:thinking_general))
+    post = Post.all.merge!(includes: :taggings).find(posts(:thinking).id)
+    assert_includes post.taggings, taggings(:thinking_general)
+    post = SpecialPost.all.merge!(includes: :taggings).find(posts(:thinking).id)
+    assert_includes post.taggings, taggings(:thinking_general)
   end
 
   def test_eager_with_multiple_associations_with_same_table_has_many_and_habtm
     # Eager includes of has many and habtm associations aren't necessarily sorted in the same way
     def assert_equal_after_sort(item1, item2, item3 = nil)
-      assert_equal(item1.sort{|a,b| a.id <=> b.id}, item2.sort{|a,b| a.id <=> b.id})
-      assert_equal(item3.sort{|a,b| a.id <=> b.id}, item2.sort{|a,b| a.id <=> b.id}) if item3
+      assert_equal(item1.sort { |a, b| a.id <=> b.id }, item2.sort { |a, b| a.id <=> b.id })
+      assert_equal(item3.sort { |a, b| a.id <=> b.id }, item2.sort { |a, b| a.id <=> b.id }) if item3
     end
     # Test regular association, association with conditions, association with
     # STI, and association with conditions assured not to be true
@@ -891,7 +1027,11 @@ class EagerAssociationTest < ActiveRecord::TestCase
     d2 = find_all_ordered(Firm, :account)
     d1.each_index do |i|
       assert_equal(d1[i], d2[i])
-      assert_equal(d1[i].account, d2[i].account)
+      if d1[i].account.nil?
+        assert_nil(d2[i].account)
+      else
+        assert_equal(d1[i].account, d2[i].account)
+      end
     end
   end
 
@@ -901,28 +1041,34 @@ class EagerAssociationTest < ActiveRecord::TestCase
     d2 = find_all_ordered(Client, firm_types)
     d1.each_index do |i|
       assert_equal(d1[i], d2[i])
-      firm_types.each { |type| assert_equal(d1[i].send(type), d2[i].send(type)) }
+      firm_types.each do |type|
+        if (expected = d1[i].send(type)).nil?
+          assert_nil(d2[i].send(type))
+        else
+          assert_equal(expected, d2[i].send(type))
+        end
+      end
     end
   end
   def test_eager_with_valid_association_as_string_not_symbol
-    assert_nothing_raised { Post.all.merge!(:includes => 'comments').to_a }
+    assert_nothing_raised { Post.all.merge!(includes: "comments").to_a }
   end
 
   def test_eager_with_floating_point_numbers
     assert_queries(2) do
       # Before changes, the floating point numbers will be interpreted as table names and will cause this to run in one query
-      Comment.all.merge!(:where => "123.456 = 123.456", :includes => :post).to_a
+      Comment.all.merge!(where: "123.456 = 123.456", includes: :post).to_a
     end
   end
 
   def test_preconfigured_includes_with_belongs_to
     author = posts(:welcome).author_with_posts
-    assert_no_queries {assert_equal 5, author.posts.size}
+    assert_no_queries { assert_equal 5, author.posts.size }
   end
 
   def test_preconfigured_includes_with_has_one
     comment = posts(:sti_comments).very_special_comment_with_post
-    assert_no_queries {assert_equal posts(:sti_comments), comment.post}
+    assert_no_queries { assert_equal posts(:sti_comments), comment.post }
   end
 
   def test_eager_association_with_scope_with_joins
@@ -964,13 +1110,13 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_association_loading_notification
-    notifications = messages_for('instantiation.active_record') do
-      Developer.all.merge!(:includes => 'projects', :where => { 'developers_projects.access_level' => 1 }, :limit => 5).to_a.size
+    notifications = messages_for("instantiation.active_record") do
+      Developer.all.merge!(includes: "projects", where: { "developers_projects.access_level" => 1 }, limit: 5).to_a.size
     end
 
     message = notifications.first
     payload = message.last
-    count = Developer.all.merge!(:includes => 'projects', :where => { 'developers_projects.access_level' => 1 }, :limit => 5).to_a.size
+    count = Developer.all.merge!(includes: "projects", where: { "developers_projects.access_level" => 1 }, limit: 5).to_a.size
 
     # eagerloaded row count should be greater than just developer count
     assert_operator payload[:record_count], :>, count
@@ -978,7 +1124,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_base_messages
-    notifications = messages_for('instantiation.active_record') do
+    notifications = messages_for("instantiation.active_record") do
       Developer.all.to_a
     end
     message = notifications.first
@@ -1000,61 +1146,55 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   def test_load_with_sti_sharing_association
-    assert_queries(2) do #should not do 1 query per subclass
+    assert_queries(2) do # should not do 1 query per subclass
       Comment.includes(:post).to_a
     end
   end
 
   def test_conditions_on_join_table_with_include_and_limit
-    assert_equal 3, Developer.all.merge!(:includes => 'projects', :where => { 'developers_projects.access_level' => 1 }, :limit => 5).to_a.size
+    assert_equal 3, Developer.all.merge!(includes: "projects", where: { "developers_projects.access_level" => 1 }, limit: 5).to_a.size
   end
 
   def test_dont_create_temporary_active_record_instances
     Developer.instance_count = 0
-    developers = Developer.all.merge!(:includes => 'projects', :where => { 'developers_projects.access_level' => 1 }, :limit => 5).to_a
+    developers = Developer.all.merge!(includes: "projects", where: { "developers_projects.access_level" => 1 }, limit: 5).to_a
     assert_equal developers.count, Developer.instance_count
   end
 
   def test_order_on_join_table_with_include_and_limit
-    assert_equal 5, Developer.all.merge!(:includes => 'projects', :order => 'developers_projects.joined_on DESC', :limit => 5).to_a.size
+    assert_equal 5, Developer.all.merge!(includes: "projects", order: "developers_projects.joined_on DESC", limit: 5).to_a.size
   end
 
   def test_eager_loading_with_order_on_joined_table_preloads
     posts = assert_queries(2) do
-      Post.all.merge!(:joins => :comments, :includes => :author, :order => 'comments.id DESC').to_a
+      Post.all.merge!(joins: :comments, includes: :author, order: "comments.id DESC").to_a
     end
     assert_equal posts(:eager_other), posts[1]
-    assert_equal authors(:mary), assert_no_queries { posts[1].author}
+    assert_equal authors(:mary), assert_no_queries { posts[1].author }
   end
 
   def test_eager_loading_with_conditions_on_joined_table_preloads
     posts = assert_queries(2) do
-      Post.all.merge!(:select => 'distinct posts.*', :includes => :author, :joins => [:comments], :where => "comments.body like 'Thank you%'", :order => 'posts.id').to_a
-    end
-    assert_equal [posts(:welcome)], posts
-    assert_equal authors(:david), assert_no_queries { posts[0].author}
-
-    posts = assert_queries(2) do
-      Post.all.merge!(:select => 'distinct posts.*', :includes => :author, :joins => [:comments], :where => "comments.body like 'Thank you%'", :order => 'posts.id').to_a
+      Post.all.merge!(select: "distinct posts.*", includes: :author, joins: [:comments], where: "comments.body like 'Thank you%'", order: "posts.id").to_a
     end
     assert_equal [posts(:welcome)], posts
-    assert_equal authors(:david), assert_no_queries { posts[0].author}
+    assert_equal authors(:david), assert_no_queries { posts[0].author }
 
     posts = assert_queries(2) do
-      Post.all.merge!(:includes => :author, :joins => {:taggings => :tag}, :where => "tags.name = 'General'", :order => 'posts.id').to_a
+      Post.all.merge!(includes: :author, joins: { taggings: :tag }, where: "tags.name = 'General'", order: "posts.id").to_a
     end
     assert_equal posts(:welcome, :thinking), posts
 
     posts = assert_queries(2) do
-      Post.all.merge!(:includes => :author, :joins => {:taggings => {:tag => :taggings}}, :where => "taggings_tags.super_tag_id=2", :order => 'posts.id').to_a
+      Post.all.merge!(includes: :author, joins: { taggings: { tag: :taggings } }, where: "taggings_tags.super_tag_id=2", order: "posts.id").to_a
     end
     assert_equal posts(:welcome, :thinking), posts
   end
 
   def test_preload_has_many_with_association_condition_and_default_scope
-    post = Post.create!(:title => 'Beaches', :body => "I like beaches!")
-    Reader.create! :person => people(:david), :post => post
-    LazyReader.create! :person => people(:susan), :post => post
+    post = Post.create!(title: "Beaches", body: "I like beaches!")
+    Reader.create! person: people(:david), post: post
+    LazyReader.create! person: people(:susan), post: post
 
     assert_equal 1, post.lazy_readers.to_a.size
     assert_equal 2, post.lazy_readers_skimmers_or_not.to_a.size
@@ -1065,39 +1205,39 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   def test_eager_loading_with_conditions_on_string_joined_table_preloads
     posts = assert_queries(2) do
-      Post.all.merge!(:select => 'distinct posts.*', :includes => :author, :joins => "INNER JOIN comments on comments.post_id = posts.id", :where => "comments.body like 'Thank you%'", :order => 'posts.id').to_a
+      Post.all.merge!(select: "distinct posts.*", includes: :author, joins: "INNER JOIN comments on comments.post_id = posts.id", where: "comments.body like 'Thank you%'", order: "posts.id").to_a
     end
     assert_equal [posts(:welcome)], posts
-    assert_equal authors(:david), assert_no_queries { posts[0].author}
+    assert_equal authors(:david), assert_no_queries { posts[0].author }
 
     posts = assert_queries(2) do
-      Post.all.merge!(:select => 'distinct posts.*', :includes => :author, :joins => ["INNER JOIN comments on comments.post_id = posts.id"], :where => "comments.body like 'Thank you%'", :order => 'posts.id').to_a
+      Post.all.merge!(select: "distinct posts.*", includes: :author, joins: ["INNER JOIN comments on comments.post_id = posts.id"], where: "comments.body like 'Thank you%'", order: "posts.id").to_a
     end
     assert_equal [posts(:welcome)], posts
-    assert_equal authors(:david), assert_no_queries { posts[0].author}
+    assert_equal authors(:david), assert_no_queries { posts[0].author }
   end
 
   def test_eager_loading_with_select_on_joined_table_preloads
     posts = assert_queries(2) do
-      Post.all.merge!(:select => 'posts.*, authors.name as author_name', :includes => :comments, :joins => :author, :order => 'posts.id').to_a
+      Post.all.merge!(select: "posts.*, authors.name as author_name", includes: :comments, joins: :author, order: "posts.id").to_a
     end
-    assert_equal 'David', posts[0].author_name
-    assert_equal posts(:welcome).comments, assert_no_queries { posts[0].comments}
+    assert_equal "David", posts[0].author_name
+    assert_equal posts(:welcome).comments, assert_no_queries { posts[0].comments }
   end
 
   def test_eager_loading_with_conditions_on_join_model_preloads
     authors = assert_queries(2) do
-      Author.all.merge!(:includes => :author_address, :joins => :comments, :where => "posts.title like 'Welcome%'").to_a
+      Author.all.merge!(includes: :author_address, joins: :comments, where: "posts.title like 'Welcome%'").to_a
     end
     assert_equal authors(:david), authors[0]
     assert_equal author_addresses(:david_address), authors[0].author_address
   end
 
   def test_preload_belongs_to_uses_exclusive_scope
-    people = Person.males.merge(:includes => :primary_contact).to_a
+    people = Person.males.merge(includes: :primary_contact).to_a
     assert_not_equal people.length, 0
     people.each do |person|
-      assert_no_queries {assert_not_nil person.primary_contact}
+      assert_no_queries { assert_not_nil person.primary_contact }
       assert_equal Person.find(person.id).primary_contact, person.primary_contact
     end
   end
@@ -1121,9 +1261,9 @@ class EagerAssociationTest < ActiveRecord::TestCase
     expected = Firm.find(1).clients_using_primary_key.sort_by(&:name)
     # Oracle adapter truncates alias to 30 characters
     if current_adapter?(:OracleAdapter)
-      firm = Firm.all.merge!(:includes => :clients_using_primary_key, :order => 'clients_using_primary_keys_companies'[0,30]+'.name').find(1)
+      firm = Firm.all.merge!(includes: :clients_using_primary_key, order: "clients_using_primary_keys_companies"[0, 30] + ".name").find(1)
     else
-      firm = Firm.all.merge!(:includes => :clients_using_primary_key, :order => 'clients_using_primary_keys_companies.name').find(1)
+      firm = Firm.all.merge!(includes: :clients_using_primary_key, order: "clients_using_primary_keys_companies.name").find(1)
     end
     assert_no_queries do
       assert_equal expected, firm.clients_using_primary_key
@@ -1132,7 +1272,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   def test_preload_has_one_using_primary_key
     expected = accounts(:signals37)
-    firm = Firm.all.merge!(:includes => :account_using_primary_key, :order => 'companies.id').first
+    firm = Firm.all.merge!(includes: :account_using_primary_key, order: "companies.id").first
     assert_no_queries do
       assert_equal expected, firm.account_using_primary_key
     end
@@ -1140,94 +1280,123 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   def test_include_has_one_using_primary_key
     expected = accounts(:signals37)
-    firm = Firm.all.merge!(:includes => :account_using_primary_key, :order => 'accounts.id').to_a.detect {|f| f.id == 1}
+    firm = Firm.all.merge!(includes: :account_using_primary_key, order: "accounts.id").to_a.detect { |f| f.id == 1 }
     assert_no_queries do
       assert_equal expected, firm.account_using_primary_key
     end
   end
 
   def test_preloading_empty_belongs_to
-    c = Client.create!(:name => 'Foo', :client_of => Company.maximum(:id) + 1)
+    c = Client.create!(name: "Foo", client_of: Company.maximum(:id) + 1)
 
     client = assert_queries(2) { Client.preload(:firm).find(c.id) }
     assert_no_queries { assert_nil client.firm }
+    assert_equal c.client_of, client.client_of
   end
 
   def test_preloading_empty_belongs_to_polymorphic
-    t = Tagging.create!(:taggable_type => 'Post', :taggable_id => Post.maximum(:id) + 1, :tag => tags(:general))
+    t = Tagging.create!(taggable_type: "Post", taggable_id: Post.maximum(:id) + 1, tag: tags(:general))
 
     tagging = assert_queries(2) { Tagging.preload(:taggable).find(t.id) }
     assert_no_queries { assert_nil tagging.taggable }
+    assert_equal t.taggable_id, tagging.taggable_id
   end
 
   def test_preloading_through_empty_belongs_to
-    c = Client.create!(:name => 'Foo', :client_of => Company.maximum(:id) + 1)
+    c = Client.create!(name: "Foo", client_of: Company.maximum(:id) + 1)
 
     client = assert_queries(2) { Client.preload(:accounts).find(c.id) }
     assert_no_queries { assert client.accounts.empty? }
   end
 
   def test_preloading_has_many_through_with_distinct
-    mary = Author.includes(:unique_categorized_posts).where(:id => authors(:mary).id).first
+    mary = Author.includes(:unique_categorized_posts).where(id: authors(:mary).id).first
     assert_equal 1, mary.unique_categorized_posts.length
     assert_equal 1, mary.unique_categorized_post_ids.length
   end
 
+  def test_preloading_has_one_using_reorder
+    klass = Class.new(ActiveRecord::Base) do
+      def self.name; "TempAuthor"; end
+      self.table_name = "authors"
+      has_one :post, class_name: "PostWithDefaultScope", foreign_key: :author_id
+      has_one :reorderd_post, -> { reorder(title: :desc) }, class_name: "PostWithDefaultScope", foreign_key: :author_id
+    end
+
+    author = klass.first
+    # PRECONDITION: make sure ordering results in different results
+    assert_not_equal author.post, author.reorderd_post
+
+    preloaded_reorderd_post = klass.preload(:reorderd_post).first.reorderd_post
+
+    assert_equal author.reorderd_post, preloaded_reorderd_post
+    assert_equal Post.order(title: :desc).first.title, preloaded_reorderd_post.title
+  end
+
   def test_preloading_polymorphic_with_custom_foreign_type
     sponsor = sponsors(:moustache_club_sponsor_for_groucho)
     groucho = members(:groucho)
 
     sponsor = assert_queries(2) {
-      Sponsor.includes(:thing).where(:id => sponsor.id).first
+      Sponsor.includes(:thing).where(id: sponsor.id).first
     }
     assert_no_queries { assert_equal groucho, sponsor.thing }
   end
 
   def test_joins_with_includes_should_preload_via_joins
-    post = assert_queries(1) { Post.includes(:comments).joins(:comments).order('posts.id desc').to_a.first }
+    post = assert_queries(1) { Post.includes(:comments).joins(:comments).order("posts.id desc").to_a.first }
 
-    assert_queries(0) do
+    assert_no_queries do
       assert_not_equal 0, post.comments.to_a.count
     end
   end
 
   def test_join_eager_with_empty_order_should_generate_valid_sql
-    assert_nothing_raised(ActiveRecord::StatementInvalid) do
-      Post.includes(:comments).order("").where(:comments => {:body => "Thank you for the welcome"}).first
-    end
-  end
-
-  def test_join_eager_with_nil_order_should_generate_valid_sql
-    assert_nothing_raised(ActiveRecord::StatementInvalid) do
-      Post.includes(:comments).order(nil).where(:comments => {:body => "Thank you for the welcome"}).first
+    assert_nothing_raised do
+      Post.includes(:comments).order("").where(comments: { body: "Thank you for the welcome" }).first
     end
   end
 
   def test_deep_including_through_habtm
     # warm up habtm cache
-    posts = Post.all.merge!(:includes => {:categories => :categorizations}, :order => "posts.id").to_a
+    posts = Post.all.merge!(includes: { categories: :categorizations }, order: "posts.id").to_a
     posts[0].categories[0].categorizations.length
 
-    posts = Post.all.merge!(:includes => {:categories => :categorizations}, :order => "posts.id").to_a
+    posts = Post.all.merge!(includes: { categories: :categorizations }, order: "posts.id").to_a
     assert_no_queries { assert_equal 2, posts[0].categories[0].categorizations.length }
     assert_no_queries { assert_equal 1, posts[0].categories[1].categorizations.length }
     assert_no_queries { assert_equal 2, posts[1].categories[0].categorizations.length }
   end
 
+  def test_eager_load_multiple_associations_with_references
+    mentor = Mentor.create!(name: "Barış Can DAYLIK")
+    developer = Developer.create!(name: "Mehmet Emin İNAÇ", mentor: mentor)
+    Contract.create!(developer: developer)
+    project = Project.create!(name: "VNGRS", mentor: mentor)
+    project.developers << developer
+    projects = Project.references(:mentors).includes(mentor: { developers: :contracts }, developers: :contracts)
+    assert_equal projects.last.mentor.developers.first.contracts, projects.last.developers.last.contracts
+  end
+
+  def test_preloading_has_many_through_with_custom_scope
+    project = Project.includes(:developers_named_david_with_hash_conditions).find(projects(:active_record).id)
+    assert_equal [developers(:david)], project.developers_named_david_with_hash_conditions
+  end
+
   test "scoping with a circular preload" do
-    assert_equal Comment.find(1), Comment.preload(:post => :comments).scoping { Comment.find(1) }
+    assert_equal Comment.find(1), Comment.preload(post: :comments).scoping { Comment.find(1) }
   end
 
   test "circular preload does not modify unscoped" do
     expected = FirstPost.unscoped.find(2)
-    FirstPost.preload(:comments => :first_post).find(1)
+    FirstPost.preload(comments: :first_post).find(1)
     assert_equal expected, FirstPost.unscoped.find(2)
   end
 
   test "preload ignores the scoping" do
     assert_equal(
       Comment.find(1).post,
-      Post.where('1 = 0').scoping { Comment.preload(:post).find(1).post }
+      Post.where("1 = 0").scoping { Comment.preload(:post).find(1).post }
     )
   end
 
@@ -1252,10 +1421,10 @@ class EagerAssociationTest < ActiveRecord::TestCase
   end
 
   test "works in combination with order(:symbol) and reorder(:symbol)" do
-    author = Author.includes(:posts).references(:posts).order(:name).find_by('posts.title IS NOT NULL')
+    author = Author.includes(:posts).references(:posts).order(:name).find_by("posts.title IS NOT NULL")
     assert_equal authors(:bob), author
 
-    author = Author.includes(:posts).references(:posts).reorder(:name).find_by('posts.title IS NOT NULL')
+    author = Author.includes(:posts).references(:posts).reorder(:name).find_by("posts.title IS NOT NULL")
     assert_equal authors(:bob), author
   end
 
@@ -1281,6 +1450,8 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
     assert_nothing_raised do
       authors(:david).essays.includes(:writer).any?
+      authors(:david).essays.includes(:writer).exists?
+      authors(:david).essays.includes(:owner).where("name IS NOT NULL").exists?
     end
   end
 
@@ -1295,7 +1466,7 @@ class EagerAssociationTest < ActiveRecord::TestCase
 
   test "including associations with where.not adds implicit references" do
     author = assert_queries(2) {
-      Author.includes(:posts).where.not(posts: { title: 'Welcome to the weblog'} ).last
+      Author.includes(:posts).where.not(posts: { title: "Welcome to the weblog" }).last
     }
 
     assert_no_queries {
@@ -1325,45 +1496,130 @@ class EagerAssociationTest < ActiveRecord::TestCase
     assert_match message, error.message
   end
 
+  test "preload with invalid argument" do
+    exception = assert_raises(ArgumentError) do
+      Author.preload(10).to_a
+    end
+    assert_equal("10 was not recognized for preload", exception.message)
+  end
+
+  test "associations with extensions are not instance dependent" do
+    assert_nothing_raised do
+      Author.includes(:posts_with_extension).to_a
+    end
+  end
+
+  test "including associations with extensions and an instance dependent scope is not supported" do
+    e = assert_raises(ArgumentError) do
+      Author.includes(:posts_with_extension_and_instance).to_a
+    end
+    assert_match(/Preloading instance dependent scopes is not supported/, e.message)
+  end
+
   test "preloading readonly association" do
     # has-one
     firm = Firm.where(id: "1").preload(:readonly_account).first!
-    assert firm.readonly_account.readonly?
+    assert_predicate firm.readonly_account, :readonly?
 
     # has_and_belongs_to_many
     project = Project.where(id: "2").preload(:readonly_developers).first!
-    assert project.readonly_developers.first.readonly?
+    assert_predicate project.readonly_developers.first, :readonly?
 
     # has-many :through
     david = Author.where(id: "1").preload(:readonly_comments).first!
-    assert david.readonly_comments.first.readonly?
+    assert_predicate david.readonly_comments.first, :readonly?
+  end
+
+  test "eager-loading non-readonly association" do
+    # has_one
+    firm = Firm.where(id: "1").eager_load(:account).first!
+    assert_not_predicate firm.account, :readonly?
+
+    # has_and_belongs_to_many
+    project = Project.where(id: "2").eager_load(:developers).first!
+    assert_not_predicate project.developers.first, :readonly?
+
+    # has_many :through
+    david = Author.where(id: "1").eager_load(:comments).first!
+    assert_not_predicate david.comments.first, :readonly?
+
+    # belongs_to
+    post = Post.where(id: "1").eager_load(:author).first!
+    assert_not_predicate post.author, :readonly?
   end
 
   test "eager-loading readonly association" do
     # has-one
     firm = Firm.where(id: "1").eager_load(:readonly_account).first!
-    assert firm.readonly_account.readonly?
+    assert_predicate firm.readonly_account, :readonly?
 
     # has_and_belongs_to_many
     project = Project.where(id: "2").eager_load(:readonly_developers).first!
-    assert project.readonly_developers.first.readonly?
+    assert_predicate project.readonly_developers.first, :readonly?
 
     # has-many :through
     david = Author.where(id: "1").eager_load(:readonly_comments).first!
-    assert david.readonly_comments.first.readonly?
+    assert_predicate david.readonly_comments.first, :readonly?
 
     # belongs_to
-    post = Post.where(id: "1").eager_load(:author).first!
-    assert post.author.readonly?
+    post = Post.where(id: "1").eager_load(:readonly_author).first!
+    assert_predicate post.readonly_author, :readonly?
   end
 
   test "preloading a polymorphic association with references to the associated table" do
-    post = Post.includes(:tags).references(:tags).where('tags.name = ?', 'General').first
+    post = Post.includes(:tags).references(:tags).where("tags.name = ?", "General").first
     assert_equal posts(:welcome), post
   end
 
   test "eager-loading a polymorphic association with references to the associated table" do
-    post = Post.eager_load(:tags).where('tags.name = ?', 'General').first
+    post = Post.eager_load(:tags).where("tags.name = ?", "General").first
     assert_equal posts(:welcome), post
   end
+
+  test "eager-loading with a polymorphic association won't work consistently" do
+    assert_raise(ActiveRecord::EagerLoadPolymorphicError) { authors(:david).essays.eager_load(:writer).to_a }
+    assert_raise(ActiveRecord::EagerLoadPolymorphicError) { authors(:david).essays.eager_load(:writer).count }
+    assert_raise(ActiveRecord::EagerLoadPolymorphicError) { authors(:david).essays.eager_load(:writer).exists? }
+  end
+
+  # CollectionProxy#reader is expensive, so the preloader avoids calling it.
+  test "preloading has_many_through association avoids calling association.reader" do
+    assert_not_called_on_instance_of(ActiveRecord::Associations::HasManyAssociation, :reader) do
+      Author.preload(:readonly_comments).first!
+    end
+  end
+
+  test "preloading through a polymorphic association doesn't require the association to exist" do
+    sponsors = []
+    assert_queries 5 do
+      sponsors = Sponsor.where(sponsorable_id: 1).preload(sponsorable: [:post, :membership]).to_a
+    end
+    # check the preload worked
+    assert_queries 0 do
+      sponsors.map(&:sponsorable).map { |s| s.respond_to?(:posts) ? s.post.author : s.membership }
+    end
+  end
+
+  test "preloading a regular association through a polymorphic association doesn't require the association to exist on all types" do
+    sponsors = []
+    assert_queries 6 do
+      sponsors = Sponsor.where(sponsorable_id: 1).preload(sponsorable: [{ post: :first_comment }, :membership]).to_a
+    end
+    # check the preload worked
+    assert_queries 0 do
+      sponsors.map(&:sponsorable).map { |s| s.respond_to?(:posts) ? s.post.author : s.membership }
+    end
+  end
+
+  test "preloading a regular association with a typo through a polymorphic association still raises" do
+    # this test contains an intentional typo of first -> fist
+    assert_raises(ActiveRecord::AssociationNotFoundError) do
+      Sponsor.where(sponsorable_id: 1).preload(sponsorable: [{ post: :fist_comment }, :membership]).to_a
+    end
+  end
+
+  private
+    def find_all_ordered(klass, include = nil)
+      klass.order("#{klass.table_name}.#{klass.primary_key}").includes(include).to_a
+    end
 end
diff --git a/activerecord/test/cases/associations/extension_test.rb b/activerecord/test/cases/associations/extension_test.rb
index b161cde335..aef8f31112 100644
--- a/activerecord/test/cases/associations/extension_test.rb
+++ b/activerecord/test/cases/associations/extension_test.rb
@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/comment'
-require 'models/project'
-require 'models/developer'
-require 'models/computer'
-require 'models/company_in_module'
+require "models/post"
+require "models/comment"
+require "models/project"
+require "models/developer"
+require "models/computer"
+require "models/company_in_module"
 
 class AssociationsExtensionsTest < ActiveRecord::TestCase
   fixtures :projects, :developers, :developers_projects, :comments, :posts
@@ -36,6 +38,11 @@ class AssociationsExtensionsTest < ActiveRecord::TestCase
     assert_equal comments(:greetings), posts(:welcome).comments.not_again.find_most_recent
   end
 
+  def test_extension_with_dirty_target
+    comment = posts(:welcome).comments.build(body: "New comment")
+    assert_equal comment, posts(:welcome).comments.with_content("New comment")
+  end
+
   def test_marshalling_extensions
     david = developers(:david)
     assert_equal projects(:action_controller), david.projects.find_most_recent
@@ -45,7 +52,7 @@ class AssociationsExtensionsTest < ActiveRecord::TestCase
     # Marshaling an association shouldn't make it unusable by wiping its reflection.
     assert_not_nil david.association(:projects).reflection
 
-    david_too  = Marshal.load(marshalled)
+    david_too = Marshal.load(marshalled)
     assert_equal projects(:action_controller), david_too.projects.find_most_recent
   end
 
@@ -63,14 +70,20 @@ class AssociationsExtensionsTest < ActiveRecord::TestCase
     extend!(Developer)
     extend!(MyApplication::Business::Developer)
 
-    assert Object.const_get 'DeveloperAssociationNameAssociationExtension'
-    assert MyApplication::Business.const_get 'DeveloperAssociationNameAssociationExtension'
+    assert Object.const_get "DeveloperAssociationNameAssociationExtension"
+    assert MyApplication::Business.const_get "DeveloperAssociationNameAssociationExtension"
   end
 
   def test_proxy_association_after_scoped
     post = posts(:welcome)
     assert_equal post.association(:comments), post.comments.the_association
-    assert_equal post.association(:comments), post.comments.where('1=1').the_association
+    assert_equal post.association(:comments), post.comments.where("1=1").the_association
+  end
+
+  def test_association_with_default_scope
+    assert_raises OopsError do
+      posts(:welcome).comments.destroy_all
+    end
   end
 
   private
diff --git a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
index e584c94ad8..515eb65d37 100644
--- a/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_and_belongs_to_many_associations_test.rb
@@ -1,82 +1,89 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/company'
-require 'models/customer'
-require 'models/order'
-require 'models/categorization'
-require 'models/category'
-require 'models/post'
-require 'models/author'
-require 'models/tag'
-require 'models/tagging'
-require 'models/parrot'
-require 'models/person'
-require 'models/pirate'
-require 'models/treasure'
-require 'models/price_estimate'
-require 'models/club'
-require 'models/member'
-require 'models/membership'
-require 'models/sponsor'
-require 'models/country'
-require 'models/treaty'
-require 'models/vertex'
-require 'models/publisher'
-require 'models/publisher/article'
-require 'models/publisher/magazine'
-require 'active_support/core_ext/string/conversions'
+require "models/developer"
+require "models/computer"
+require "models/project"
+require "models/company"
+require "models/course"
+require "models/customer"
+require "models/order"
+require "models/categorization"
+require "models/category"
+require "models/post"
+require "models/author"
+require "models/tag"
+require "models/tagging"
+require "models/parrot"
+require "models/person"
+require "models/pirate"
+require "models/professor"
+require "models/treasure"
+require "models/price_estimate"
+require "models/club"
+require "models/user"
+require "models/member"
+require "models/membership"
+require "models/sponsor"
+require "models/lesson"
+require "models/student"
+require "models/country"
+require "models/treaty"
+require "models/vertex"
+require "models/publisher"
+require "models/publisher/article"
+require "models/publisher/magazine"
+require "active_support/core_ext/string/conversions"
 
 class ProjectWithAfterCreateHook < ActiveRecord::Base
-  self.table_name = 'projects'
+  self.table_name = "projects"
   has_and_belongs_to_many :developers,
-    :class_name => "DeveloperForProjectWithAfterCreateHook",
-    :join_table => "developers_projects",
-    :foreign_key => "project_id",
-    :association_foreign_key => "developer_id"
+    class_name: "DeveloperForProjectWithAfterCreateHook",
+    join_table: "developers_projects",
+    foreign_key: "project_id",
+    association_foreign_key: "developer_id"
 
   after_create :add_david
 
   def add_david
-    david = DeveloperForProjectWithAfterCreateHook.find_by_name('David')
+    david = DeveloperForProjectWithAfterCreateHook.find_by_name("David")
     david.projects << self
   end
 end
 
 class DeveloperForProjectWithAfterCreateHook < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
   has_and_belongs_to_many :projects,
-    :class_name => "ProjectWithAfterCreateHook",
-    :join_table => "developers_projects",
-    :association_foreign_key => "project_id",
-    :foreign_key => "developer_id"
+    class_name: "ProjectWithAfterCreateHook",
+    join_table: "developers_projects",
+    association_foreign_key: "project_id",
+    foreign_key: "developer_id"
 end
 
 class ProjectWithSymbolsForKeys < ActiveRecord::Base
-  self.table_name = 'projects'
+  self.table_name = "projects"
   has_and_belongs_to_many :developers,
-    :class_name => "DeveloperWithSymbolsForKeys",
-    :join_table => :developers_projects,
-    :foreign_key => :project_id,
-    :association_foreign_key => "developer_id"
+    class_name: "DeveloperWithSymbolsForKeys",
+    join_table: :developers_projects,
+    foreign_key: :project_id,
+    association_foreign_key: "developer_id"
 end
 
 class DeveloperWithSymbolsForKeys < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
   has_and_belongs_to_many :projects,
-    :class_name => "ProjectWithSymbolsForKeys",
-    :join_table => :developers_projects,
-    :association_foreign_key => :project_id,
-    :foreign_key => "developer_id"
+    class_name: "ProjectWithSymbolsForKeys",
+    join_table: :developers_projects,
+    association_foreign_key: :project_id,
+    foreign_key: "developer_id"
 end
 
 class SubDeveloper < Developer
-  self.table_name = 'developers'
+  self.table_name = "developers"
   has_and_belongs_to_many :special_projects,
-    :join_table => 'developers_projects',
-    :foreign_key => "project_id",
-    :association_foreign_key => "developer_id"
+    join_table: "developers_projects",
+    foreign_key: "project_id",
+    association_foreign_key: "developer_id"
 end
 
 class DeveloperWithSymbolClassName < Developer
@@ -86,26 +93,50 @@ end
 class DeveloperWithExtendOption < Developer
   module NamedExtension
     def category
-      'sns'
+      "sns"
     end
   end
 
   has_and_belongs_to_many :projects, extend: NamedExtension
 end
 
+class ProjectUnscopingDavidDefaultScope < ActiveRecord::Base
+  self.table_name = "projects"
+  has_and_belongs_to_many :developers, -> { unscope(where: "name") },
+    class_name: "LazyBlockDeveloperCalledDavid",
+    join_table: "developers_projects",
+    foreign_key: "project_id",
+    association_foreign_key: "developer_id"
+end
+
+class Kitchen < ActiveRecord::Base
+  has_one :sink
+end
+
+class Sink < ActiveRecord::Base
+  has_and_belongs_to_many :sources, join_table: :edges
+  belongs_to :kitchen
+  accepts_nested_attributes_for :kitchen
+end
+
+class Source < ActiveRecord::Base
+  self.table_name = "men"
+  has_and_belongs_to_many :sinks, join_table: :edges
+end
+
 class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :categories, :posts, :categories_posts, :developers, :projects, :developers_projects,
            :parrots, :pirates, :parrots_pirates, :treasures, :price_estimates, :tags, :taggings, :computers
 
   def setup_data_for_habtm_case
-    ActiveRecord::Base.connection.execute('delete from countries_treaties')
+    ActiveRecord::Base.connection.execute("delete from countries_treaties")
 
-    country = Country.new(:name => 'India')
-    country.country_id = 'c1'
+    country = Country.new(name: "India")
+    country.country_id = "c1"
     country.save!
 
-    treaty = Treaty.new(:name => 'peace')
-    treaty.treaty_id = 't1'
+    treaty = Treaty.new(name: "peace")
+    treaty.treaty_id = "t1"
     country.treaties << treaty
   end
 
@@ -119,32 +150,45 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     setup_data_for_habtm_case
 
     con = ActiveRecord::Base.connection
-    sql = 'select * from countries_treaties'
+    sql = "select * from countries_treaties"
     record = con.select_rows(sql).last
-    assert_equal 'c1', record[0]
-    assert_equal 't1', record[1]
+    assert_equal "c1", record[0]
+    assert_equal "t1", record[1]
   end
 
   def test_proper_usage_of_primary_keys_and_join_table
     setup_data_for_habtm_case
 
-    assert_equal 'country_id', Country.primary_key
-    assert_equal 'treaty_id', Treaty.primary_key
+    assert_equal "country_id", Country.primary_key
+    assert_equal "treaty_id", Treaty.primary_key
 
     country = Country.first
     assert_equal 1, country.treaties.count
   end
 
+  def test_join_table_composite_primary_key_should_not_warn
+    country = Country.new(name: "India")
+    country.country_id = "c1"
+    country.save!
+
+    treaty = Treaty.new(name: "peace")
+    treaty.treaty_id = "t1"
+    warning = capture(:stderr) do
+      country.treaties << treaty
+    end
+    assert_no_match(/WARNING: Active Record does not support composite primary key\./, warning)
+  end
+
   def test_has_and_belongs_to_many
     david = Developer.find(1)
 
-    assert !david.projects.empty?
+    assert_not_empty david.projects
     assert_equal 2, david.projects.size
 
     active_record = Project.find(1)
-    assert !active_record.developers.empty?
+    assert_not_empty active_record.developers
     assert_equal 3, active_record.developers.size
-    assert active_record.developers.include?(david)
+    assert_includes active_record.developers, david
   end
 
   def test_adding_single
@@ -157,8 +201,8 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     jamis.projects << action_controller
 
     assert_equal 2, jamis.projects.size
-    assert_equal 2, jamis.projects(true).size
-    assert_equal 2, action_controller.developers(true).size
+    assert_equal 2, jamis.projects.reload.size
+    assert_equal 2, action_controller.developers.reload.size
   end
 
   def test_adding_type_mismatch
@@ -176,9 +220,9 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
 
     action_controller.developers << jamis
 
-    assert_equal 2, jamis.projects(true).size
+    assert_equal 2, jamis.projects.reload.size
     assert_equal 2, action_controller.developers.size
-    assert_equal 2, action_controller.developers(true).size
+    assert_equal 2, action_controller.developers.reload.size
   end
 
   def test_adding_from_the_project_fixed_timestamp
@@ -192,9 +236,9 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     action_controller.developers << jamis
 
     assert_equal updated_at, jamis.updated_at
-    assert_equal 2, jamis.projects(true).size
+    assert_equal 2, jamis.projects.reload.size
     assert_equal 2, action_controller.developers.size
-    assert_equal 2, action_controller.developers(true).size
+    assert_equal 2, action_controller.developers.reload.size
   end
 
   def test_adding_multiple
@@ -203,7 +247,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     aredridel.projects.reload
     aredridel.projects.push(Project.find(1), Project.find(2))
     assert_equal 2, aredridel.projects.size
-    assert_equal 2, aredridel.projects(true).size
+    assert_equal 2, aredridel.projects.reload.size
   end
 
   def test_adding_a_collection
@@ -212,7 +256,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     aredridel.projects.reload
     aredridel.projects.concat([Project.find(1), Project.find(2)])
     assert_equal 2, aredridel.projects.size
-    assert_equal 2, aredridel.projects(true).size
+    assert_equal 2, aredridel.projects.reload.size
   end
 
   def test_habtm_adding_before_save
@@ -220,20 +264,20 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     no_of_projects = Project.count
     aredridel = Developer.new("name" => "Aredridel")
     aredridel.projects.concat([Project.find(1), p = Project.new("name" => "Projekt")])
-    assert !aredridel.persisted?
-    assert !p.persisted?
+    assert_not_predicate aredridel, :persisted?
+    assert_not_predicate p, :persisted?
     assert aredridel.save
-    assert aredridel.persisted?
-    assert_equal no_of_devels+1, Developer.count
-    assert_equal no_of_projects+1, Project.count
+    assert_predicate aredridel, :persisted?
+    assert_equal no_of_devels + 1, Developer.count
+    assert_equal no_of_projects + 1, Project.count
     assert_equal 2, aredridel.projects.size
-    assert_equal 2, aredridel.projects(true).size
+    assert_equal 2, aredridel.projects.reload.size
   end
 
   def test_habtm_saving_multiple_relationships
     new_project = Project.new("name" => "Grimetime")
     amount_of_developers = 4
-    developers = (0...amount_of_developers).collect {|i| Developer.create(:name => "JME #{i}") }.reverse
+    developers = (0...amount_of_developers).reverse_each.map { |i| Developer.create(name: "JME #{i}") }
 
     new_project.developer_ids = [developers[0].id, developers[1].id]
     new_project.developers_with_callback_ids = [developers[2].id, developers[3].id]
@@ -258,54 +302,61 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_habtm_collection_size_from_params
-    devel = Developer.new({
+    devel = Developer.new(
       projects_attributes: {
-        '0' => {}
-      }
-    })
+        "0" => {}
+      })
 
     assert_equal 1, devel.projects.size
   end
 
   def test_build
     devel = Developer.find(1)
-    proj = assert_no_queries(ignore_none: false) { devel.projects.build("name" => "Projekt") }
-    assert !devel.projects.loaded?
+
+    # Load schema information so we don't query below if running just this test.
+    Project.define_attribute_methods
+
+    proj = assert_no_queries { devel.projects.build("name" => "Projekt") }
+    assert_not_predicate devel.projects, :loaded?
 
     assert_equal devel.projects.last, proj
-    assert devel.projects.loaded?
+    assert_predicate devel.projects, :loaded?
 
-    assert !proj.persisted?
+    assert_not_predicate proj, :persisted?
     devel.save
-    assert proj.persisted?
+    assert_predicate proj, :persisted?
     assert_equal devel.projects.last, proj
     assert_equal Developer.find(1).projects.sort_by(&:id).last, proj  # prove join table is updated
   end
 
   def test_new_aliased_to_build
     devel = Developer.find(1)
-    proj = assert_no_queries(ignore_none: false) { devel.projects.new("name" => "Projekt") }
-    assert !devel.projects.loaded?
+
+    # Load schema information so we don't query below if running just this test.
+    Project.define_attribute_methods
+
+    proj = assert_no_queries { devel.projects.new("name" => "Projekt") }
+    assert_not_predicate devel.projects, :loaded?
 
     assert_equal devel.projects.last, proj
-    assert devel.projects.loaded?
+    assert_predicate devel.projects, :loaded?
 
-    assert !proj.persisted?
+    assert_not_predicate proj, :persisted?
     devel.save
-    assert proj.persisted?
+    assert_predicate proj, :persisted?
     assert_equal devel.projects.last, proj
     assert_equal Developer.find(1).projects.sort_by(&:id).last, proj  # prove join table is updated
   end
 
   def test_build_by_new_record
-    devel = Developer.new(:name => "Marcel", :salary => 75000)
-    devel.projects.build(:name => "Make bed")
-    proj2 = devel.projects.build(:name => "Lie in it")
+    devel = Developer.new(name: "Marcel", salary: 75000)
+    devel.projects.build(name: "Make bed")
+    proj2 = devel.projects.build(name: "Lie in it")
     assert_equal devel.projects.last, proj2
-    assert !proj2.persisted?
+    assert_not_predicate proj2, :persisted?
     devel.save
-    assert devel.persisted?
-    assert proj2.persisted?
+    assert_predicate devel, :persisted?
+    assert_predicate proj2, :persisted?
     assert_equal devel.projects.last, proj2
     assert_equal Developer.find_by_name("Marcel").projects.last, proj2  # prove join table is updated
   end
@@ -313,40 +364,27 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   def test_create
     devel = Developer.find(1)
     proj = devel.projects.create("name" => "Projekt")
-    assert !devel.projects.loaded?
+    assert_not_predicate devel.projects, :loaded?
 
     assert_equal devel.projects.last, proj
-    assert !devel.projects.loaded?
+    assert_not_predicate devel.projects, :loaded?
 
-    assert proj.persisted?
+    assert_predicate proj, :persisted?
     assert_equal Developer.find(1).projects.sort_by(&:id).last, proj  # prove join table is updated
   end
 
-  def test_create_by_new_record
-    devel = Developer.new(:name => "Marcel", :salary => 75000)
-    devel.projects.build(:name => "Make bed")
-    proj2 = devel.projects.build(:name => "Lie in it")
-    assert_equal devel.projects.last, proj2
-    assert !proj2.persisted?
-    devel.save
-    assert devel.persisted?
-    assert proj2.persisted?
-    assert_equal devel.projects.last, proj2
-    assert_equal Developer.find_by_name("Marcel").projects.last, proj2  # prove join table is updated
-  end
-
   def test_creation_respects_hash_condition
     # in Oracle '' is saved as null therefore need to save ' ' in not null column
-    post = categories(:general).post_with_conditions.build(:body => ' ')
+    post = categories(:general).post_with_conditions.build(body: " ")
 
-    assert        post.save
-    assert_equal  'Yet Another Testing Title', post.title
+    assert post.save
+    assert_equal "Yet Another Testing Title", post.title
 
     # in Oracle '' is saved as null therefore need to save ' ' in not null column
-    another_post = categories(:general).post_with_conditions.create(:body => ' ')
+    another_post = categories(:general).post_with_conditions.create(body: " ")
 
-    assert        another_post.persisted?
-    assert_equal  'Yet Another Testing Title', another_post.title
+    assert_predicate another_post, :persisted?
+    assert_equal "Yet Another Testing Title", another_post.title
   end
 
   def test_distinct_after_the_fact
@@ -355,7 +393,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     dev.projects << projects(:active_record)
 
     assert_equal 3, dev.projects.size
-    assert_equal 1, dev.projects.distinct.size
+    assert_equal 1, dev.projects.uniq.size
   end
 
   def test_distinct_before_the_fact
@@ -391,8 +429,8 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     david.projects.delete(active_record)
 
     assert_equal 1, david.projects.size
-    assert_equal 1, david.projects(true).size
-    assert_equal 2, active_record.developers(true).size
+    assert_equal 1, david.projects.reload.size
+    assert_equal 2, active_record.developers.reload.size
   end
 
   def test_deleting_array
@@ -400,7 +438,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     david.projects.reload
     david.projects.delete(Project.all.to_a)
     assert_equal 0, david.projects.size
-    assert_equal 0, david.projects(true).size
+    assert_equal 0, david.projects.reload.size
   end
 
   def test_deleting_all
@@ -408,15 +446,15 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     david.projects.reload
     david.projects.clear
     assert_equal 0, david.projects.size
-    assert_equal 0, david.projects(true).size
+    assert_equal 0, david.projects.reload.size
   end
 
   def test_removing_associations_on_destroy
     david = DeveloperWithBeforeDestroyRaise.find(1)
-    assert !david.projects.empty?
+    assert_not_empty david.projects
     david.destroy
-    assert david.projects.empty?
-    assert DeveloperWithBeforeDestroyRaise.connection.select_all("SELECT * FROM developers_projects WHERE developer_id = 1").empty?
+    assert_empty david.projects
+    assert_empty DeveloperWithBeforeDestroyRaise.connection.select_all("SELECT * FROM developers_projects WHERE developer_id = 1")
   end
 
   def test_destroying
@@ -431,10 +469,10 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     end
 
     join_records = Developer.connection.select_all("SELECT * FROM developers_projects WHERE developer_id = #{david.id} AND project_id = #{project.id}")
-    assert join_records.empty?
+    assert_empty join_records
 
     assert_equal 1, david.reload.projects.size
-    assert_equal 1, david.projects(true).size
+    assert_equal 1, david.projects.reload.size
   end
 
   def test_destroying_many
@@ -447,32 +485,32 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     end
 
     join_records = Developer.connection.select_all("SELECT * FROM developers_projects WHERE developer_id = #{david.id}")
-    assert join_records.empty?
+    assert_empty join_records
 
     assert_equal 0, david.reload.projects.size
-    assert_equal 0, david.projects(true).size
+    assert_equal 0, david.projects.reload.size
   end
 
   def test_destroy_all
     david = Developer.find(1)
     david.projects.reload
-    assert !david.projects.empty?
+    assert_not_empty david.projects
 
     assert_no_difference "Project.count" do
       david.projects.destroy_all
     end
 
     join_records = Developer.connection.select_all("SELECT * FROM developers_projects WHERE developer_id = #{david.id}")
-    assert join_records.empty?
+    assert_empty join_records
 
-    assert david.projects.empty?
-    assert david.projects(true).empty?
+    assert_empty david.projects
+    assert_empty david.projects.reload
   end
 
   def test_destroy_associations_destroys_multiple_associations
     george = parrots(:george)
-    assert !george.pirates.empty?
-    assert !george.treasures.empty?
+    assert_not_empty george.pirates
+    assert_not_empty george.treasures
 
     assert_no_difference "Pirate.count" do
       assert_no_difference "Treasure.count" do
@@ -481,12 +519,12 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     end
 
     join_records = Parrot.connection.select_all("SELECT * FROM parrots_pirates WHERE parrot_id = #{george.id}")
-    assert join_records.empty?
-    assert george.pirates(true).empty?
+    assert_empty join_records
+    assert_empty george.pirates.reload
 
     join_records = Parrot.connection.select_all("SELECT * FROM parrots_treasures WHERE parrot_id = #{george.id}")
-    assert join_records.empty?
-    assert george.treasures(true).empty?
+    assert_empty join_records
+    assert_empty george.treasures.reload
   end
 
   def test_associations_with_conditions
@@ -518,9 +556,9 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
 
     developer = project.developers.first
 
-    assert_no_queries(ignore_none: false) do
-      assert project.developers.loaded?
-      assert project.developers.include?(developer)
+    assert_no_queries do
+      assert_predicate project.developers, :loaded?
+      assert_includes project.developers, developer
     end
   end
 
@@ -529,19 +567,19 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     developer = project.developers.first
 
     project.reload
-    assert ! project.developers.loaded?
+    assert_not_predicate project.developers, :loaded?
     assert_queries(1) do
-      assert project.developers.include?(developer)
+      assert_includes project.developers, developer
     end
-    assert ! project.developers.loaded?
+    assert_not_predicate project.developers, :loaded?
   end
 
   def test_include_returns_false_for_non_matching_record_to_verify_scoping
     project = projects(:active_record)
-    developer = Developer.create :name => "Bryan", :salary => 50_000
+    developer = Developer.create name: "Bryan", salary: 50_000
 
-    assert ! project.developers.loaded?
-    assert ! project.developers.include?(developer)
+    assert_not_predicate project.developers, :loaded?
+    assert_not project.developers.include?(developer)
   end
 
   def test_find_with_merged_options
@@ -552,32 +590,32 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
 
   def test_dynamic_find_should_respect_association_order
     # Developers are ordered 'name DESC, id DESC'
-    high_id_jamis = projects(:active_record).developers.create(:name => 'Jamis')
+    high_id_jamis = projects(:active_record).developers.create(name: "Jamis")
 
-    assert_equal high_id_jamis, projects(:active_record).developers.merge(:where => "name = 'Jamis'").first
-    assert_equal high_id_jamis, projects(:active_record).developers.find_by_name('Jamis')
+    assert_equal high_id_jamis, projects(:active_record).developers.merge(where: "name = 'Jamis'").first
+    assert_equal high_id_jamis, projects(:active_record).developers.find_by_name("Jamis")
   end
 
   def test_find_should_append_to_association_order
-    ordered_developers = projects(:active_record).developers.order('projects.id')
-    assert_equal ['developers.name desc, developers.id desc', 'projects.id'], ordered_developers.order_values
+    ordered_developers = projects(:active_record).developers.order("projects.id")
+    assert_equal ["developers.name desc, developers.id desc", "projects.id"], ordered_developers.order_values
   end
 
   def test_dynamic_find_all_should_respect_readonly_access
-    projects(:active_record).readonly_developers.each { |d| assert_raise(ActiveRecord::ReadOnlyRecord) { d.save!  } if d.valid?}
+    projects(:active_record).readonly_developers.each { |d| assert_raise(ActiveRecord::ReadOnlyRecord) { d.save!  } if d.valid? }
     projects(:active_record).readonly_developers.each(&:readonly?)
   end
 
   def test_new_with_values_in_collection
-    jamis = DeveloperForProjectWithAfterCreateHook.find_by_name('Jamis')
-    david = DeveloperForProjectWithAfterCreateHook.find_by_name('David')
-    project = ProjectWithAfterCreateHook.new(:name => "Cooking with Bertie")
+    jamis = DeveloperForProjectWithAfterCreateHook.find_by_name("Jamis")
+    david = DeveloperForProjectWithAfterCreateHook.find_by_name("David")
+    project = ProjectWithAfterCreateHook.new(name: "Cooking with Bertie")
     project.developers << jamis
     project.save!
     project.reload
 
-    assert project.developers.include?(jamis)
-    assert project.developers.include?(david)
+    assert_includes project.developers, jamis
+    assert_includes project.developers, david
   end
 
   def test_find_in_association_with_options
@@ -588,8 +626,8 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_association_with_extend_option
-    eponine = DeveloperWithExtendOption.create(name: 'Eponine')
-    assert_equal 'sns', eponine.projects.category
+    eponine = DeveloperWithExtendOption.create(name: "Eponine")
+    assert_equal "sns", eponine.projects.category
   end
 
   def test_replace_with_less
@@ -604,7 +642,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     david.projects = [projects(:action_controller), Project.new("name" => "ActionWebSearch")]
     david.save
     assert_equal 2, david.projects.length
-    assert !david.projects.include?(projects(:active_record))
+    assert_not_includes david.projects, projects(:active_record)
   end
 
   def test_replace_on_new_object
@@ -622,9 +660,9 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     developer.special_projects << special_project
     developer.reload
 
-    assert developer.projects.include?(special_project)
-    assert developer.special_projects.include?(special_project)
-    assert !developer.special_projects.include?(other_project)
+    assert_includes developer.projects, special_project
+    assert_includes developer.special_projects, special_project
+    assert_not_includes developer.special_projects, other_project
   end
 
   def test_symbol_join_table
@@ -634,7 +672,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     assert_includes developer.sym_special_projects, sp
   end
 
-  def test_update_attributes_after_push_without_duplicate_join_table_rows
+  def test_update_columns_after_push_without_duplicate_join_table_rows
     developer = Developer.new("name" => "Kano")
     project = SpecialProject.create("name" => "Special Project")
     assert developer.save
@@ -654,7 +692,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_habtm_respects_select
-    categories(:technology).select_testing_posts(true).each do |o|
+    categories(:technology).select_testing_posts.reload.each do |o|
       assert_respond_to o, :correctness_marker
     end
     assert_respond_to categories(:technology).select_testing_posts.first, :correctness_marker
@@ -665,28 +703,17 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_habtm_respects_select_query_method
-    assert_equal ['id'], developers(:david).projects.select(:id).first.attributes.keys
+    assert_equal ["id"], developers(:david).projects.select(:id).first.attributes.keys
   end
 
   def test_join_table_alias
-    # FIXME: `references` has no impact on the aliases generated for the join
-    # query.  The fact that we pass `:developers_projects_join` to `references`
-    # and that the SQL string contains `developers_projects_join` is merely a
-    # coincidence.
     assert_equal(
       3,
-      Developer.references(:developers_projects_join).merge(
-        :includes => {:projects => :developers},
-        :where => 'projects_developers_projects_join.joined_on IS NOT NULL'
-      ).to_a.size
+      Developer.includes(projects: :developers).where.not("projects_developers_projects_join.joined_on": nil).to_a.size
     )
   end
 
   def test_join_with_group
-    # FIXME: `references` has no impact on the aliases generated for the join
-    # query.  The fact that we pass `:developers_projects_join` to `references`
-    # and that the SQL string contains `developers_projects_join` is merely a
-    # coincidence.
     group = Developer.columns.inject([]) do |g, c|
       g << "developers.#{c.name}"
       g << "developers_projects_2.#{c.name}"
@@ -695,16 +722,13 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
 
     assert_equal(
       3,
-      Developer.references(:developers_projects_join).merge(
-        :includes => {:projects => :developers}, :where => 'projects_developers_projects_join.joined_on IS NOT NULL',
-        :group => group.join(",")
-      ).to_a.size
+      Developer.includes(projects: :developers).where.not("projects_developers_projects_join.joined_on": nil).group(group.join(",")).to_a.size
     )
   end
 
   def test_find_grouped
-    all_posts_from_category1 = Post.all.merge!(:where => "category_id = 1", :joins => :categories).to_a
-    grouped_posts_of_category1 = Post.all.merge!(:where => "category_id = 1", :group => "author_id", :select => 'count(posts.id) as posts_count', :joins => :categories).to_a
+    all_posts_from_category1 = Post.all.merge!(where: "category_id = 1", joins: :categories).to_a
+    grouped_posts_of_category1 = Post.all.merge!(where: "category_id = 1", group: "author_id", select: "count(posts.id) as posts_count", joins: :categories).to_a
     assert_equal 5, all_posts_from_category1.size
     assert_equal 2, grouped_posts_of_category1.size
   end
@@ -715,8 +739,8 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_find_scoped_grouped_having
-    assert_equal 2, projects(:active_record).well_payed_salary_groups.to_a.size
-    assert projects(:active_record).well_payed_salary_groups.all? { |g| g.salary > 10000 }
+    assert_equal 2, projects(:active_record).well_paid_salary_groups.to_a.size
+    assert projects(:active_record).well_paid_salary_groups.all? { |g| g.salary > 10000 }
   end
 
   def test_get_ids
@@ -726,8 +750,8 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
 
   def test_get_ids_for_loaded_associations
     developer = developers(:david)
-    developer.projects(true)
-    assert_queries(0) do
+    developer.projects.reload
+    assert_no_queries do
       developer.project_ids
       developer.project_ids
     end
@@ -735,9 +759,9 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
 
   def test_get_ids_for_unloaded_associations_does_not_load_them
     developer = developers(:david)
-    assert !developer.projects.loaded?
+    assert_not_predicate developer.projects, :loaded?
     assert_equal projects(:active_record, :action_controller).map(&:id).sort, developer.project_ids.sort
-    assert !developer.projects.loaded?
+    assert_not_predicate developer.projects, :loaded?
   end
 
   def test_assign_ids
@@ -751,13 +775,23 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
 
   def test_assign_ids_ignoring_blanks
     developer = Developer.new("name" => "Joe")
-    developer.project_ids = [projects(:active_record).id, nil, projects(:action_controller).id, '']
+    developer.project_ids = [projects(:active_record).id, nil, projects(:action_controller).id, ""]
     developer.save
     developer.reload
     assert_equal 2, developer.projects.length
     assert_equal [projects(:active_record), projects(:action_controller)].map(&:id).sort, developer.project_ids.sort
   end
 
+  def test_singular_ids_are_reloaded_after_collection_concat
+    student = Student.create(name: "Alberto Almagro")
+    student.lesson_ids
+
+    lesson = Lesson.create(name: "DSI")
+    student.lessons << lesson
+
+    assert_includes student.lesson_ids, lesson.id
+  end
+
   def test_scoped_find_on_through_association_doesnt_return_read_only_records
     tag = Post.find(1).tags.find_by_name("General")
 
@@ -767,12 +801,12 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_has_many_through_polymorphic_has_manys_works
-    assert_equal [10, 20].to_set, pirates(:redbeard).treasure_estimates.map(&:price).to_set
+    assert_equal ["$10.00", "$20.00"].to_set, pirates(:redbeard).treasure_estimates.map(&:price).to_set
   end
 
   def test_symbols_as_keys
-    developer = DeveloperWithSymbolsForKeys.new(:name => 'David')
-    project = ProjectWithSymbolsForKeys.new(:name => 'Rails Testing')
+    developer = DeveloperWithSymbolsForKeys.new(name: "David")
+    project = ProjectWithSymbolsForKeys.new(name: "Rails Testing")
     project.developers << developer
     project.save!
 
@@ -785,7 +819,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   def test_dynamic_find_should_respect_association_include
     # SQL error in sort clause if :include is not included
     # due to Unknown column 'authors.id'
-    assert Category.find(1).posts_with_authors_sorted_by_author_id.find_by_title('Welcome to the weblog')
+    assert Category.find(1).posts_with_authors_sorted_by_author_id.find_by_title("Welcome to the weblog")
   end
 
   def test_count
@@ -794,9 +828,10 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_association_proxy_transaction_method_starts_transaction_in_association_class
-    Post.expects(:transaction)
-    Category.first.posts.transaction do
-      # nothing
+    assert_called(Post, :transaction) do
+      Category.first.posts.transaction do
+        # nothing
+      end
     end
   end
 
@@ -815,13 +850,13 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     assert_no_queries { david.projects.columns }
   end
 
-  def test_attributes_are_being_set_when_initialized_from_habm_association_with_where_clause
-    new_developer = projects(:action_controller).developers.where(:name => "Marcelo").build
+  def test_attributes_are_being_set_when_initialized_from_habtm_association_with_where_clause
+    new_developer = projects(:action_controller).developers.where(name: "Marcelo").build
     assert_equal new_developer.name, "Marcelo"
   end
 
-  def test_attributes_are_being_set_when_initialized_from_habm_association_with_multiple_where_clauses
-    new_developer = projects(:action_controller).developers.where(:name => "Marcelo").where(:salary => 90_000).build
+  def test_attributes_are_being_set_when_initialized_from_habtm_association_with_multiple_where_clauses
+    new_developer = projects(:action_controller).developers.where(name: "Marcelo").where(salary: 90_000).build
     assert_equal new_developer.name, "Marcelo"
     assert_equal new_developer.salary, 90_000
   end
@@ -829,7 +864,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   def test_include_method_in_has_and_belongs_to_many_association_should_return_true_for_instance_added_with_build
     project = Project.new
     developer = project.developers.build
-    assert project.developers.include?(developer)
+    assert_includes project.developers, developer
   end
 
   def test_destruction_does_not_error_without_primary_key
@@ -844,9 +879,9 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
 
   def test_has_and_belongs_to_many_associations_on_new_records_use_null_relations
     projects = Developer.new.projects
-    assert_no_queries(ignore_none: false) do
+    assert_no_queries do
       assert_equal [], projects
-      assert_equal [], projects.where(title: 'omg')
+      assert_equal [], projects.where(title: "omg")
       assert_equal [], projects.pluck(:title)
       assert_equal 0, projects.count
     end
@@ -860,7 +895,7 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     treasure.valid?
 
     assert_equal 1, treasure.rich_people.size
-    assert_nil rich_person.first_name, 'should not run associated person validation on create when validate: false'
+    assert_nil rich_person.first_name, "should not run associated person validation on create when validate: false"
   end
 
   def test_association_with_validate_false_does_not_run_associated_validation_callbacks_on_update
@@ -873,11 +908,11 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
     treasure.valid?
 
     assert_equal 1, treasure.rich_people.size
-    assert_equal person_first_name, rich_person.first_name, 'should not run associated person validation on update when validate: false'
+    assert_equal person_first_name, rich_person.first_name, "should not run associated person validation on update when validate: false"
   end
 
   def test_custom_join_table
-    assert_equal 'edges', Vertex.reflect_on_association(:sources).join_table
+    assert_equal "edges", Vertex.reflect_on_association(:sources).join_table
   end
 
   def test_has_and_belongs_to_many_in_a_namespaced_model_pointing_to_a_namespaced_model
@@ -901,20 +936,91 @@ class HasAndBelongsToManyAssociationsTest < ActiveRecord::TestCase
   def test_redefine_habtm
     child = SubDeveloper.new("name" => "Aredridel")
     child.special_projects << SpecialProject.new("name" => "Special Project")
-    assert child.save, 'child object should be saved'
+    assert child.save, "child object should be saved"
   end
 
   def test_habtm_with_reflection_using_class_name_and_fixtures
-    assert_not_nil Developer._reflections['shared_computers']
+    assert_not_nil Developer._reflections["shared_computers"]
     # Checking the fixture for named association is important here, because it's the only way
     # we've been able to reproduce this bug
-    assert_not_nil File.read(File.expand_path("../../../fixtures/developers.yml", __FILE__)).index("shared_computers")
+    assert_not_nil File.read(File.expand_path("../../fixtures/developers.yml", __dir__)).index("shared_computers")
     assert_equal developers(:david).shared_computers.first, computers(:laptop)
   end
 
   def test_with_symbol_class_name
-    assert_nothing_raised NoMethodError do
-      DeveloperWithSymbolClassName.new
+    assert_nothing_raised do
+      developer = DeveloperWithSymbolClassName.new
+      developer.projects
+    end
+  end
+
+  def test_alternate_database
+    professor = Professor.create(name: "Plum")
+    course = Course.create(name: "Forensics")
+    assert_equal 0, professor.courses.count
+    assert_nothing_raised do
+      professor.courses << course
+    end
+    assert_equal 1, professor.courses.count
+  end
+
+  def test_habtm_scope_can_unscope
+    project = ProjectUnscopingDavidDefaultScope.new
+    project.save!
+
+    developer = LazyBlockDeveloperCalledDavid.new(name: "Not David")
+    developer.save!
+    project.developers << developer
+
+    projects = ProjectUnscopingDavidDefaultScope.includes(:developers).where(id: project.id)
+    assert_equal 1, projects.first.developers.size
+  end
+
+  def test_preloaded_associations_size
+    assert_equal Project.first.salaried_developers.size,
+      Project.preload(:salaried_developers).first.salaried_developers.size
+
+    assert_equal Project.includes(:salaried_developers).references(:salaried_developers).first.salaried_developers.size,
+      Project.preload(:salaried_developers).first.salaried_developers.size
+
+    # Nested HATBM
+    first_project = Developer.first.projects.first
+    preloaded_first_project =
+      Developer.preload(projects: :salaried_developers).
+        first.
+        projects.
+        detect { |p| p.id == first_project.id }
+
+    assert preloaded_first_project.salaried_developers.loaded?, true
+    assert_equal first_project.salaried_developers.size, preloaded_first_project.salaried_developers.size
+  end
+
+  def test_has_and_belongs_to_many_is_useable_with_belongs_to_required_by_default
+    assert_difference "Project.first.developers_required_by_default.size", 1 do
+      Project.first.developers_required_by_default.create!(name: "Sean", salary: 50000)
+    end
+  end
+
+  def test_association_name_is_the_same_as_join_table_name
+    user = User.create!
+    assert_nothing_raised { user.jobs_pool.clear }
+  end
+
+  def test_has_and_belongs_to_many_while_partial_writes_false
+    begin
+      original_partial_writes = ActiveRecord::Base.partial_writes
+      ActiveRecord::Base.partial_writes = false
+      developer = Developer.new(name: "Mehmet Emin İNAÇ")
+      developer.projects << Project.new(name: "Bounty")
+
+      assert developer.save
+    ensure
+      ActiveRecord::Base.partial_writes = original_partial_writes
     end
   end
+
+  def test_has_and_belongs_to_many_with_belongs_to
+    sink = Sink.create! kitchen: Kitchen.new, sources: [Source.new]
+    assert_equal 1, sink.sources.count
+  end
 end
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 2c4e2a875c..d13e1a86e9 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -1,94 +1,108 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/company'
-require 'models/contract'
-require 'models/topic'
-require 'models/reply'
-require 'models/category'
-require 'models/image'
-require 'models/post'
-require 'models/author'
-require 'models/essay'
-require 'models/comment'
-require 'models/person'
-require 'models/reader'
-require 'models/tagging'
-require 'models/tag'
-require 'models/invoice'
-require 'models/line_item'
-require 'models/car'
-require 'models/bulb'
-require 'models/engine'
-require 'models/categorization'
-require 'models/minivan'
-require 'models/speedometer'
-require 'models/reference'
-require 'models/job'
-require 'models/college'
-require 'models/student'
-require 'models/pirate'
-require 'models/ship'
-require 'models/ship_part'
-require 'models/tyre'
-require 'models/subscriber'
-require 'models/subscription'
-require 'models/zine'
-require 'models/interest'
+require "models/developer"
+require "models/computer"
+require "models/project"
+require "models/company"
+require "models/contract"
+require "models/topic"
+require "models/reply"
+require "models/category"
+require "models/image"
+require "models/post"
+require "models/author"
+require "models/essay"
+require "models/comment"
+require "models/person"
+require "models/reader"
+require "models/tagging"
+require "models/tag"
+require "models/invoice"
+require "models/line_item"
+require "models/car"
+require "models/bulb"
+require "models/engine"
+require "models/categorization"
+require "models/minivan"
+require "models/speedometer"
+require "models/reference"
+require "models/college"
+require "models/student"
+require "models/pirate"
+require "models/ship"
+require "models/ship_part"
+require "models/treasure"
+require "models/parrot"
+require "models/tyre"
+require "models/subscriber"
+require "models/subscription"
+require "models/zine"
+require "models/interest"
 
 class HasManyAssociationsTestForReorderWithJoinDependency < ActiveRecord::TestCase
-  fixtures :authors, :posts, :comments
+  fixtures :authors, :author_addresses, :posts, :comments
 
   def test_should_generate_valid_sql
     author = authors(:david)
     # this can fail on adapters which require ORDER BY expressions to be included in the SELECT expression
     # if the reorder clauses are not correctly handled
-    assert author.posts_with_comments_sorted_by_comment_id.where('comments.id > 0').reorder('posts.comments_count DESC', 'posts.tags_count DESC').last
+    assert author.posts_with_comments_sorted_by_comment_id.where("comments.id > 0").reorder("posts.comments_count DESC", "posts.tags_count DESC").last
   end
 end
 
 class HasManyAssociationsTestPrimaryKeys < ActiveRecord::TestCase
-  fixtures :authors, :essays, :subscribers, :subscriptions, :people
+  fixtures :authors, :author_addresses, :essays, :subscribers, :subscriptions, :people
 
   def test_custom_primary_key_on_new_record_should_fetch_with_query
-    subscriber = Subscriber.new(nick: 'webster132')
-    assert !subscriber.subscriptions.loaded?
+    subscriber = Subscriber.new(nick: "webster132")
+    assert_not_predicate subscriber.subscriptions, :loaded?
 
     assert_queries 1 do
       assert_equal 2, subscriber.subscriptions.size
     end
 
-    assert_equal subscriber.subscriptions, Subscription.where(subscriber_id: 'webster132')
+    assert_equal Subscription.where(subscriber_id: "webster132"), subscriber.subscriptions
   end
 
   def test_association_primary_key_on_new_record_should_fetch_with_query
-    author = Author.new(:name => "David")
-    assert !author.essays.loaded?
+    author = Author.new(name: "David")
+    assert_not_predicate author.essays, :loaded?
 
     assert_queries 1 do
       assert_equal 1, author.essays.size
     end
 
-    assert_equal author.essays, Essay.where(writer_id: "David")
+    assert_equal Essay.where(writer_id: "David"), author.essays
   end
 
   def test_has_many_custom_primary_key
     david = authors(:david)
-    assert_equal david.essays, Essay.where(writer_id: "David")
+    assert_equal Essay.where(writer_id: "David"), david.essays
+  end
+
+  def test_ids_on_unloaded_association_with_custom_primary_key
+    david = people(:david)
+    assert_equal Essay.where(writer_id: "David").pluck(:id), david.essay_ids
+  end
+
+  def test_ids_on_loaded_association_with_custom_primary_key
+    david = people(:david)
+    david.essays.load
+    assert_equal Essay.where(writer_id: "David").pluck(:id), david.essay_ids
   end
 
   def test_has_many_assignment_with_custom_primary_key
     david = people(:david)
 
     assert_equal ["A Modest Proposal"], david.essays.map(&:name)
-    david.essays = [Essay.create!(name: "Remote Work" )]
+    david.essays = [Essay.create!(name: "Remote Work")]
     assert_equal ["Remote Work"], david.essays.map(&:name)
   end
 
   def test_blank_custom_primary_key_on_new_record_should_not_run_queries
     author = Author.new
-    assert !author.essays.loaded?
+    assert_not_predicate author.essays, :loaded?
 
     assert_queries 0 do
       assert_equal 0, author.essays.size
@@ -98,8 +112,8 @@ end
 
 class HasManyAssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :categories, :companies, :developers, :projects,
-           :developers_projects, :topics, :authors, :comments,
-           :posts, :readers, :taggings, :cars, :jobs, :tags,
+           :developers_projects, :topics, :authors, :author_addresses, :comments,
+           :posts, :readers, :taggings, :cars, :tags,
            :categorizations, :zines, :interests
 
   def setup
@@ -114,14 +128,14 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_anonymous_has_many
     developer = Class.new(ActiveRecord::Base) {
-      self.table_name = 'developers'
+      self.table_name = "developers"
       dev = self
 
       developer_project = Class.new(ActiveRecord::Base) {
-        self.table_name = 'developers_projects'
-        belongs_to :developer, :anonymous_class => dev
+        self.table_name = "developers_projects"
+        belongs_to :developer, anonymous_class: dev
       }
-      has_many :developer_projects, :anonymous_class => developer_project, :foreign_key => 'developer_id'
+      has_many :developer_projects, anonymous_class: developer_project, foreign_key: "developer_id"
     }
     dev = developer.first
     named = Developer.find(dev.id)
@@ -133,20 +147,20 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_default_scope_on_relations_is_not_cached
     counter = 0
     posts = Class.new(ActiveRecord::Base) {
-      self.table_name = 'posts'
-      self.inheritance_column = 'not_there'
+      self.table_name = "posts"
+      self.inheritance_column = "not_there"
       post = self
 
       comments = Class.new(ActiveRecord::Base) {
-        self.table_name = 'comments'
-        self.inheritance_column = 'not_there'
-        belongs_to :post, :anonymous_class => post
+        self.table_name = "comments"
+        self.inheritance_column = "not_there"
+        belongs_to :post, anonymous_class: post
         default_scope -> {
           counter += 1
-          where("id = :inc", :inc => counter)
+          where("id = :inc", inc: counter)
         }
       }
-      has_many :comments, :anonymous_class => comments, :foreign_key => 'post_id'
+      has_many :comments, anonymous_class: comments, foreign_key: "post_id"
     }
     assert_equal 0, counter
     post = posts.first
@@ -157,18 +171,20 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_has_many_build_with_options
-    college = College.create(name: 'UFMT')
-    Student.create(active: true, college_id: college.id, name: 'Sarah')
+    college = College.create(name: "UFMT")
+    Student.create(active: true, college_id: college.id, name: "Sarah")
 
     assert_equal college.students, Student.where(active: true, college_id: college.id)
   end
 
   def test_add_record_to_collection_should_change_its_updated_at
-    ship = Ship.create(name: 'dauntless')
-    part = ShipPart.create(name: 'cockpit')
+    ship = Ship.create(name: "dauntless")
+    part = ShipPart.create(name: "cockpit")
     updated_at = part.updated_at
 
-    ship.parts << part
+    travel(1.second) do
+      ship.parts << part
+    end
 
     assert_equal part.ship, ship
     assert_not_equal part.updated_at, updated_at
@@ -177,67 +193,88 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_clear_collection_should_not_change_updated_at
     # GH#17161: .clear calls delete_all (and returns the association),
     # which is intended to not touch associated objects's updated_at field
-    ship = Ship.create(name: 'dauntless')
-    part = ShipPart.create(name: 'cockpit', ship_id: ship.id)
+    ship = Ship.create(name: "dauntless")
+    part = ShipPart.create(name: "cockpit", ship_id: ship.id)
 
     ship.parts.clear
     part.reload
 
-    assert_equal nil, part.ship
-    assert !part.updated_at_changed?
+    assert_nil part.ship
+    assert_not_predicate part, :updated_at_changed?
   end
 
   def test_create_from_association_should_respect_default_scope
-    car = Car.create(:name => 'honda')
-    assert_equal 'honda', car.name
+    car = Car.create(name: "honda")
+    assert_equal "honda", car.name
 
     bulb = Bulb.create
-    assert_equal 'defaulty', bulb.name
+    assert_equal "defaulty", bulb.name
 
     bulb = car.bulbs.build
-    assert_equal 'defaulty', bulb.name
+    assert_equal "defaulty", bulb.name
 
     bulb = car.bulbs.create
-    assert_equal 'defaulty', bulb.name
+    assert_equal "defaulty", bulb.name
+  end
+
+  def test_build_and_create_from_association_should_respect_passed_attributes_over_default_scope
+    car = Car.create(name: "honda")
+
+    bulb = car.bulbs.build(name: "exotic")
+    assert_equal "exotic", bulb.name
 
-    bulb = car.bulbs.create(:name => 'exotic')
-    assert_equal 'exotic', bulb.name
+    bulb = car.bulbs.create(name: "exotic")
+    assert_equal "exotic", bulb.name
+
+    bulb = car.awesome_bulbs.build(frickinawesome: false)
+    assert_equal false, bulb.frickinawesome
+
+    bulb = car.awesome_bulbs.create(frickinawesome: false)
+    assert_equal false, bulb.frickinawesome
   end
 
   def test_build_from_association_should_respect_scope
     author = Author.new
 
     post = author.thinking_posts.build
-    assert_equal 'So I was thinking', post.title
+    assert_equal "So I was thinking", post.title
   end
 
   def test_create_from_association_with_nil_values_should_work
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
 
     bulb = car.bulbs.new(nil)
-    assert_equal 'defaulty', bulb.name
+    assert_equal "defaulty", bulb.name
 
     bulb = car.bulbs.build(nil)
-    assert_equal 'defaulty', bulb.name
+    assert_equal "defaulty", bulb.name
 
     bulb = car.bulbs.create(nil)
-    assert_equal 'defaulty', bulb.name
+    assert_equal "defaulty", bulb.name
+  end
+
+  def test_build_from_association_sets_inverse_instance
+    car = Car.new(name: "honda")
+
+    bulb = car.bulbs.build
+    assert_equal car, bulb.car
   end
 
   def test_do_not_call_callbacks_for_delete_all
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
     car.funky_bulbs.create!
+    assert_equal 1, car.funky_bulbs.count
     assert_nothing_raised { car.reload.funky_bulbs.delete_all }
-    assert_equal 0, Bulb.count, "bulbs should have been deleted using :delete_all strategy"
+    assert_equal 0, car.funky_bulbs.count, "bulbs should have been deleted using :delete_all strategy"
   end
 
   def test_delete_all_on_association_is_the_same_as_not_loaded
     author = authors :david
-    author.thinking_posts.create!(:body => "test")
+    author.thinking_posts.create!(body: "test")
     author.reload
     expected_sql = capture_sql { author.thinking_posts.delete_all }
 
-    author.thinking_posts.create!(:body => "test")
+    author.thinking_posts.create!(body: "test")
     author.reload
     author.thinking_posts.inspect
     loaded_sql = capture_sql { author.thinking_posts.delete_all }
@@ -246,11 +283,11 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_delete_all_on_association_with_nil_dependency_is_the_same_as_not_loaded
     author = authors :david
-    author.posts.create!(:title => "test", :body => "body")
+    author.posts.create!(title: "test", body: "body")
     author.reload
     expected_sql = capture_sql { author.posts.delete_all }
 
-    author.posts.create!(:title => "test", :body => "body")
+    author.posts.create!(title: "test", body: "body")
     author.reload
     author.posts.to_a
     loaded_sql = capture_sql { author.posts.delete_all }
@@ -265,29 +302,29 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_building_the_associated_object_with_explicit_sti_base_class
     firm = DependentFirm.new
-    company = firm.companies.build(:type => "Company")
+    company = firm.companies.build(type: "Company")
     assert_kind_of Company, company, "Expected #{company.class} to be a Company"
   end
 
   def test_building_the_associated_object_with_sti_subclass
     firm = DependentFirm.new
-    company = firm.companies.build(:type => "Client")
+    company = firm.companies.build(type: "Client")
     assert_kind_of Client, company, "Expected #{company.class} to be a Client"
   end
 
   def test_building_the_associated_object_with_an_invalid_type
     firm = DependentFirm.new
-    assert_raise(ActiveRecord::SubclassNotFound) { firm.companies.build(:type => "Invalid") }
+    assert_raise(ActiveRecord::SubclassNotFound) { firm.companies.build(type: "Invalid") }
   end
 
   def test_building_the_associated_object_with_an_unrelated_type
     firm = DependentFirm.new
-    assert_raise(ActiveRecord::SubclassNotFound) { firm.companies.build(:type => "Account") }
+    assert_raise(ActiveRecord::SubclassNotFound) { firm.companies.build(type: "Account") }
   end
 
   test "building the association with an array" do
     speedometer = Speedometer.new(speedometer_id: "a")
-    data = [{name: "first"}, {name: "second"}]
+    data = [{ name: "first" }, { name: "second" }]
     speedometer.minivans.build(data)
 
     assert_equal 2, speedometer.minivans.size
@@ -296,24 +333,24 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_association_keys_bypass_attribute_protection
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
 
     bulb = car.bulbs.new
     assert_equal car.id, bulb.car_id
 
-    bulb = car.bulbs.new :car_id => car.id + 1
+    bulb = car.bulbs.new car_id: car.id + 1
     assert_equal car.id, bulb.car_id
 
     bulb = car.bulbs.build
     assert_equal car.id, bulb.car_id
 
-    bulb = car.bulbs.build :car_id => car.id + 1
+    bulb = car.bulbs.build car_id: car.id + 1
     assert_equal car.id, bulb.car_id
 
     bulb = car.bulbs.create
     assert_equal car.id, bulb.car_id
 
-    bulb = car.bulbs.create :car_id => car.id + 1
+    bulb = car.bulbs.create car_id: car.id + 1
     assert_equal car.id, bulb.car_id
   end
 
@@ -323,22 +360,43 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     line_item = invoice.line_items.new
     assert_equal invoice.id, line_item.invoice_id
 
-    line_item = invoice.line_items.new :invoice_id => invoice.id + 1
+    line_item = invoice.line_items.new invoice_id: invoice.id + 1
     assert_equal invoice.id, line_item.invoice_id
 
     line_item = invoice.line_items.build
     assert_equal invoice.id, line_item.invoice_id
 
-    line_item = invoice.line_items.build :invoice_id => invoice.id + 1
+    line_item = invoice.line_items.build invoice_id: invoice.id + 1
     assert_equal invoice.id, line_item.invoice_id
 
     line_item = invoice.line_items.create
     assert_equal invoice.id, line_item.invoice_id
 
-    line_item = invoice.line_items.create :invoice_id => invoice.id + 1
+    line_item = invoice.line_items.create invoice_id: invoice.id + 1
     assert_equal invoice.id, line_item.invoice_id
   end
 
+  class SpecialAuthor < ActiveRecord::Base
+    self.table_name = "authors"
+    has_many :books, class_name: "SpecialBook", foreign_key: :author_id
+  end
+
+  class SpecialBook < ActiveRecord::Base
+    self.table_name = "books"
+
+    belongs_to :author
+    enum read_status: { unread: 0, reading: 2, read: 3, forgotten: nil }
+  end
+
+  def test_association_enum_works_properly
+    author = SpecialAuthor.create!(name: "Test")
+    book = SpecialBook.create!(read_status: "reading")
+    author.books << book
+
+    assert_equal "reading", book.read_status
+    assert_not_equal 0, SpecialAuthor.joins(:books).where(books: { read_status: "reading" }).count
+  end
+
   # When creating objects on the association, we must not do it within a scope (even though it
   # would be convenient), because this would cause that scope to be applied to any callbacks etc.
   def test_build_and_create_should_not_happen_within_scope
@@ -356,54 +414,106 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_no_sql_should_be_fired_if_association_already_loaded
-    Car.create(:name => 'honda')
+    Car.create(name: "honda")
     bulbs = Car.first.bulbs
     bulbs.to_a # to load all instances of bulbs
 
     assert_no_queries do
       bulbs.first()
-      bulbs.first({})
     end
 
     assert_no_queries do
       bulbs.second()
-      bulbs.second({})
     end
 
     assert_no_queries do
       bulbs.third()
-      bulbs.third({})
     end
 
     assert_no_queries do
       bulbs.fourth()
-      bulbs.fourth({})
     end
 
     assert_no_queries do
       bulbs.fifth()
-      bulbs.fifth({})
     end
 
     assert_no_queries do
       bulbs.forty_two()
-      bulbs.forty_two({})
+    end
+
+    assert_no_queries do
+      bulbs.third_to_last()
+    end
+
+    assert_no_queries do
+      bulbs.second_to_last()
     end
 
     assert_no_queries do
       bulbs.last()
-      bulbs.last({})
+    end
+  end
+
+  def test_finder_method_with_dirty_target
+    company = companies(:first_firm)
+    new_clients = []
+
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    assert_no_queries do
+      new_clients << company.clients_of_firm.build(name: "Another Client")
+      new_clients << company.clients_of_firm.build(name: "Another Client II")
+      new_clients << company.clients_of_firm.build(name: "Another Client III")
+    end
+
+    assert_not_predicate company.clients_of_firm, :loaded?
+    assert_queries(1) do
+      assert_same new_clients[0], company.clients_of_firm.third
+      assert_same new_clients[1], company.clients_of_firm.fourth
+      assert_same new_clients[2], company.clients_of_firm.fifth
+      assert_same new_clients[0], company.clients_of_firm.third_to_last
+      assert_same new_clients[1], company.clients_of_firm.second_to_last
+      assert_same new_clients[2], company.clients_of_firm.last
+    end
+  end
+
+  def test_finder_bang_method_with_dirty_target
+    company = companies(:first_firm)
+    new_clients = []
+
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    assert_no_queries do
+      new_clients << company.clients_of_firm.build(name: "Another Client")
+      new_clients << company.clients_of_firm.build(name: "Another Client II")
+      new_clients << company.clients_of_firm.build(name: "Another Client III")
+    end
+
+    assert_not_predicate company.clients_of_firm, :loaded?
+    assert_queries(1) do
+      assert_same new_clients[0], company.clients_of_firm.third!
+      assert_same new_clients[1], company.clients_of_firm.fourth!
+      assert_same new_clients[2], company.clients_of_firm.fifth!
+      assert_same new_clients[0], company.clients_of_firm.third_to_last!
+      assert_same new_clients[1], company.clients_of_firm.second_to_last!
+      assert_same new_clients[2], company.clients_of_firm.last!
     end
   end
 
   def test_create_resets_cached_counters
-    person = Person.create!(:first_name => 'tenderlove')
+    Reader.delete_all
+
+    person = Person.create!(first_name: "tenderlove")
+
     post   = Post.first
 
     assert_equal [], person.readers
     assert_nil person.readers.find_by_post_id(post.id)
 
-    person.readers.create(:post_id => post.id)
+    person.readers.create(post_id: post.id)
 
     assert_equal 1, person.readers.count
     assert_equal 1, person.readers.length
@@ -411,25 +521,36 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal person, person.readers.first.person
   end
 
-  def force_signal37_to_load_all_clients_of_firm
-    companies(:first_firm).clients_of_firm.each {|f| }
+  def test_update_all_respects_association_scope
+    person = Person.new
+    person.first_name = "Naruto"
+    person.references << Reference.new
+    person.save!
+    assert_equal 1, person.references.update_all(favourite: true)
+  end
+
+  def test_exists_respects_association_scope
+    person = Person.new
+    person.first_name = "Sasuke"
+    person.references << Reference.new
+    person.save!
+    assert_predicate person.references, :exists?
   end
 
-  # sometimes tests on Oracle fail if ORDER BY is not provided therefore add always :order with :first
   def test_counting_with_counter_sql
-    assert_equal 3, Firm.all.merge!(:order => "id").first.clients.count
+    assert_equal 3, Firm.first.clients.count
   end
 
   def test_counting
-    assert_equal 3, Firm.all.merge!(:order => "id").first.plain_clients.count
+    assert_equal 3, Firm.first.plain_clients.count
   end
 
   def test_counting_with_single_hash
-    assert_equal 1, Firm.all.merge!(:order => "id").first.plain_clients.where(:name => "Microsoft").count
+    assert_equal 1, Firm.first.plain_clients.where(name: "Microsoft").count
   end
 
   def test_counting_with_column_name_and_hash
-    assert_equal 3, Firm.all.merge!(:order => "id").first.plain_clients.count(:name)
+    assert_equal 3, Firm.first.plain_clients.count(:name)
   end
 
   def test_counting_with_association_limit
@@ -439,11 +560,11 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_finding
-    assert_equal 3, Firm.all.merge!(:order => "id").first.clients.length
+    assert_equal 3, Firm.first.clients.length
   end
 
   def test_finding_array_compatibility
-    assert_equal 3, Firm.order(:id).find{|f| f.id > 0}.clients.length
+    assert_equal 3, Firm.order(:id).find { |f| f.id > 0 }.clients.length
   end
 
   def test_find_many_with_merged_options
@@ -453,13 +574,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_find_should_append_to_association_order
-    ordered_clients =  companies(:first_firm).clients_sorted_desc.order('companies.id')
-    assert_equal ['id DESC', 'companies.id'], ordered_clients.order_values
+    ordered_clients = companies(:first_firm).clients_sorted_desc.order("companies.id")
+    assert_equal ["id DESC", "companies.id"], ordered_clients.order_values
   end
 
   def test_dynamic_find_should_respect_association_order
     assert_equal companies(:another_first_firm_client), companies(:first_firm).clients_sorted_desc.where("type = 'Client'").first
-    assert_equal companies(:another_first_firm_client), companies(:first_firm).clients_sorted_desc.find_by_type('Client')
+    assert_equal companies(:another_first_firm_client), companies(:first_firm).clients_sorted_desc.find_by_type("Client")
   end
 
   def test_taking
@@ -479,16 +600,28 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_taking_with_a_number
+    klass = Class.new(Author) do
+      has_many :posts, -> { order(:id) }
+
+      def self.name
+        "Author"
+      end
+    end
+
     # taking from unloaded Relation
-    bob = Author.find(authors(:bob).id)
+    bob = klass.find(authors(:bob).id)
+    new_post = bob.posts.build
+    assert_not_predicate bob.posts, :loaded?
     assert_equal [posts(:misc_by_bob)], bob.posts.take(1)
-    bob = Author.find(authors(:bob).id)
     assert_equal [posts(:misc_by_bob), posts(:other_by_bob)], bob.posts.take(2)
+    assert_equal [posts(:misc_by_bob), posts(:other_by_bob), new_post], bob.posts.take(3)
 
     # taking from loaded Relation
-    bob.posts.to_a
-    assert_equal [posts(:misc_by_bob)], authors(:bob).posts.take(1)
-    assert_equal [posts(:misc_by_bob), posts(:other_by_bob)], authors(:bob).posts.take(2)
+    bob.posts.load
+    assert_predicate bob.posts, :loaded?
+    assert_equal [posts(:misc_by_bob)], bob.posts.take(1)
+    assert_equal [posts(:misc_by_bob), posts(:other_by_bob)], bob.posts.take(2)
+    assert_equal [posts(:misc_by_bob), posts(:other_by_bob), new_post], bob.posts.take(3)
   end
 
   def test_taking_with_inverse_of
@@ -507,46 +640,41 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_finding_default_orders
-    assert_equal "Summit", Firm.all.merge!(:order => "id").first.clients.first.name
+    assert_equal "Summit", Firm.first.clients.first.name
   end
 
   def test_finding_with_different_class_name_and_order
-    assert_equal "Apex", Firm.all.merge!(:order => "id").first.clients_sorted_desc.first.name
+    assert_equal "Apex", Firm.first.clients_sorted_desc.first.name
   end
 
   def test_finding_with_foreign_key
-    assert_equal "Microsoft", Firm.all.merge!(:order => "id").first.clients_of_firm.first.name
+    assert_equal "Microsoft", Firm.first.clients_of_firm.first.name
   end
 
   def test_finding_with_condition
-    assert_equal "Microsoft", Firm.all.merge!(:order => "id").first.clients_like_ms.first.name
+    assert_equal "Microsoft", Firm.first.clients_like_ms.first.name
   end
 
   def test_finding_with_condition_hash
-    assert_equal "Microsoft", Firm.all.merge!(:order => "id").first.clients_like_ms_with_hash_conditions.first.name
+    assert_equal "Microsoft", Firm.first.clients_like_ms_with_hash_conditions.first.name
   end
 
   def test_finding_using_primary_key
-    assert_equal "Summit", Firm.all.merge!(:order => "id").first.clients_using_primary_key.first.name
+    assert_equal "Summit", Firm.first.clients_using_primary_key.first.name
   end
 
   def test_update_all_on_association_accessed_before_save
-    firm = Firm.new(name: 'Firm')
-    clients_proxy_id = firm.clients.object_id
+    firm = Firm.new(name: "Firm")
     firm.clients << Client.first
     firm.save!
-    assert_equal firm.clients.count, firm.clients.update_all(description: 'Great!')
-    assert_not_equal clients_proxy_id, firm.clients.object_id
+    assert_equal firm.clients.count, firm.clients.update_all(description: "Great!")
   end
 
   def test_update_all_on_association_accessed_before_save_with_explicit_foreign_key
-    # We can use the same cached proxy object because the id is available for the scope
-    firm = Firm.new(name: 'Firm', id: 100)
-    clients_proxy_id = firm.clients.object_id
+    firm = Firm.new(name: "Firm", id: 100)
     firm.clients << Client.first
     firm.save!
-    assert_equal firm.clients.count, firm.clients.update_all(description: 'Great!')
-    assert_equal clients_proxy_id, firm.clients.object_id
+    assert_equal firm.clients.count, firm.clients.update_all(description: "Great!")
   end
 
   def test_belongs_to_sanity
@@ -555,7 +683,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_find_ids
-    firm = Firm.all.merge!(:order => "id").first
+    firm = Firm.first
 
     assert_raise(ActiveRecord::RecordNotFound) { firm.clients.find }
 
@@ -574,9 +702,23 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::RecordNotFound) { firm.clients.find(2, 99) }
   end
 
+  def test_find_one_message_on_primary_key
+    firm = Firm.first
+
+    e = assert_raises(ActiveRecord::RecordNotFound) do
+      firm.clients.find(0)
+    end
+    assert_equal 0, e.id
+    assert_equal "id", e.primary_key
+    assert_equal "Client", e.model
+    assert_match (/\ACouldn't find Client with 'id'=0/), e.message
+  end
+
   def test_find_ids_and_inverse_of
     force_signal37_to_load_all_clients_of_firm
 
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     firm = companies(:first_firm)
     client = firm.clients_of_firm.find(3)
     assert_kind_of Client, client
@@ -587,7 +729,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_find_all
-    firm = Firm.all.merge!(:order => "id").first
+    firm = Firm.first
     assert_equal 3, firm.clients.where("#{QUOTED_TYPE} = 'Client'").to_a.length
     assert_equal 1, firm.clients.where("name = 'Summit'").to_a.length
   end
@@ -595,67 +737,143 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_find_each
     firm = companies(:first_firm)
 
-    assert ! firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
 
     assert_queries(4) do
-      firm.clients.find_each(:batch_size => 1) {|c| assert_equal firm.id, c.firm_id }
+      firm.clients.find_each(batch_size: 1) { |c| assert_equal firm.id, c.firm_id }
     end
 
-    assert ! firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_find_each_with_conditions
     firm = companies(:first_firm)
 
     assert_queries(2) do
-      firm.clients.where(name: 'Microsoft').find_each(batch_size: 1) do |c|
+      firm.clients.where(name: "Microsoft").find_each(batch_size: 1) do |c|
         assert_equal firm.id, c.firm_id
         assert_equal "Microsoft", c.name
       end
     end
 
-    assert ! firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_find_in_batches
     firm = companies(:first_firm)
 
-    assert ! firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
 
     assert_queries(2) do
-      firm.clients.find_in_batches(:batch_size => 2) do |clients|
-        clients.each {|c| assert_equal firm.id, c.firm_id }
+      firm.clients.find_in_batches(batch_size: 2) do |clients|
+        clients.each { |c| assert_equal firm.id, c.firm_id }
       end
     end
 
-    assert ! firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_find_all_sanitized
-    # sometimes tests on Oracle fail if ORDER BY is not provided therefore add always :order with :first
-    firm = Firm.all.merge!(:order => "id").first
+    firm = Firm.first
     summit = firm.clients.where("name = 'Summit'").to_a
     assert_equal summit, firm.clients.where("name = ?", "Summit").to_a
-    assert_equal summit, firm.clients.where("name = :name", { :name => "Summit" }).to_a
+    assert_equal summit, firm.clients.where("name = :name", name: "Summit").to_a
   end
 
   def test_find_first
-    firm = Firm.all.merge!(:order => "id").first
+    firm = Firm.first
     client2 = Client.find(2)
     assert_equal firm.clients.first, firm.clients.order("id").first
     assert_equal client2, firm.clients.where("#{QUOTED_TYPE} = 'Client'").order("id").first
   end
 
   def test_find_first_sanitized
-    firm = Firm.all.merge!(:order => "id").first
+    firm = Firm.first
     client2 = Client.find(2)
-    assert_equal client2, firm.clients.merge!(:where => ["#{QUOTED_TYPE} = ?", 'Client'], :order => "id").first
-    assert_equal client2, firm.clients.merge!(:where => ["#{QUOTED_TYPE} = :type", { :type => 'Client' }], :order => "id").first
+    assert_equal client2, firm.clients.where("#{QUOTED_TYPE} = ?", "Client").first
+    assert_equal client2, firm.clients.where("#{QUOTED_TYPE} = :type", type: "Client").first
+  end
+
+  def test_find_first_after_reset_scope
+    firm = Firm.first
+    collection = firm.clients
+
+    original_object = collection.first
+    assert_same original_object, collection.first, "Expected second call to #first to cache the same object"
+
+    # It should return a different object, since the association has been reloaded
+    assert_not_same original_object, firm.clients.first, "Expected #first to return a new object"
+  end
+
+  def test_find_first_after_reset
+    firm = Firm.first
+    collection = firm.clients
+
+    original_object = collection.first
+    assert_same original_object, collection.first, "Expected second call to #first to cache the same object"
+    collection.reset
+
+    # It should return a different object, since the association has been reloaded
+    assert_not_same original_object, collection.first, "Expected #first after #reset to return a new object"
+  end
+
+  def test_find_first_after_reload
+    firm = Firm.first
+    collection = firm.clients
+
+    original_object = collection.first
+    assert_same original_object, collection.first, "Expected second call to #first to cache the same object"
+    collection.reload
+
+    # It should return a different object, since the association has been reloaded
+    assert_not_same original_object, collection.first, "Expected #first after #reload to return a new object"
+  end
+
+  def test_reload_with_query_cache
+    connection = ActiveRecord::Base.connection
+    connection.enable_query_cache!
+    connection.clear_query_cache
+
+    # Populate the cache with a query
+    firm = Firm.first
+    # Populate the cache with a second query
+    firm.clients.load
+
+    assert_equal 2, connection.query_cache.size
+
+    # Clear the cache and fetch the clients again, populating the cache with a query
+    assert_queries(1) { firm.clients.reload }
+    # This query is cached, so it shouldn't make a real SQL query
+    assert_queries(0) { firm.clients.load }
+
+    assert_equal 1, connection.query_cache.size
+  ensure
+    ActiveRecord::Base.connection.disable_query_cache!
+  end
+
+  def test_reloading_unloaded_associations_with_query_cache
+    connection = ActiveRecord::Base.connection
+    connection.enable_query_cache!
+    connection.clear_query_cache
+
+    firm = Firm.create!(name: "firm name")
+    client = firm.clients.create!(name: "client name")
+    firm.clients.to_a # add request to cache
+
+    connection.uncached do
+      client.update!(name: "new client name")
+    end
+
+    firm = Firm.find(firm.id)
+
+    assert_equal [client.name], firm.clients.reload.map(&:name)
+  ensure
+    ActiveRecord::Base.connection.disable_query_cache!
   end
 
   def test_find_all_with_include_and_conditions
     assert_nothing_raised do
-      Developer.all.merge!(:joins => :audit_logs, :where => {'audit_logs.message' => nil, :name => 'Smith'}).to_a
+      Developer.all.merge!(joins: :audit_logs, where: { "audit_logs.message" => nil, :name => "Smith" }).to_a
     end
   end
 
@@ -665,8 +883,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_find_grouped
-    all_clients_of_firm1 = Client.all.merge!(:where => "firm_id = 1").to_a
-    grouped_clients_of_firm1 = Client.all.merge!(:where => "firm_id = 1", :group => "firm_id", :select => 'firm_id, count(id) as clients_count').to_a
+    all_clients_of_firm1 = Client.all.merge!(where: "firm_id = 1").to_a
+    grouped_clients_of_firm1 = Client.all.merge!(where: "firm_id = 1", group: "firm_id", select: "firm_id, count(id) as clients_count").to_a
     assert_equal 3, all_clients_of_firm1.size
     assert_equal 1, grouped_clients_of_firm1.size
   end
@@ -679,7 +897,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_find_scoped_grouped_having
-    assert_equal 1, authors(:david).popular_grouped_posts.length
+    assert_equal 2, authors(:david).popular_grouped_posts.length
     assert_equal 0, authors(:mary).popular_grouped_posts.length
   end
 
@@ -688,30 +906,39 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_select_query_method
-    assert_equal ['id', 'body'], posts(:welcome).comments.select(:id, :body).first.attributes.keys
+    assert_equal ["id", "body"], posts(:welcome).comments.select(:id, :body).first.attributes.keys
   end
 
   def test_select_with_block
     assert_equal [1], posts(:welcome).comments.select { |c| c.id == 1 }.map(&:id)
   end
 
+  def test_select_with_block_and_dirty_target
+    assert_equal 2, posts(:welcome).comments.select { true }.size
+    posts(:welcome).comments.build
+    assert_equal 3, posts(:welcome).comments.select { true }.size
+  end
+
   def test_select_without_foreign_key
     assert_equal companies(:first_firm).accounts.first.credit_limit, companies(:first_firm).accounts.select(:credit_limit).first.credit_limit
   end
 
   def test_adding
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     natural = Client.new("name" => "Natural Company")
     companies(:first_firm).clients_of_firm << natural
     assert_equal 3, companies(:first_firm).clients_of_firm.size # checking via the collection
-    assert_equal 3, companies(:first_firm).clients_of_firm(true).size # checking using the db
+    assert_equal 3, companies(:first_firm).clients_of_firm.reload.size # checking using the db
     assert_equal natural, companies(:first_firm).clients_of_firm.last
   end
 
   def test_adding_using_create
     first_firm = companies(:first_firm)
     assert_equal 3, first_firm.plain_clients.size
-    first_firm.plain_clients.create(:name => "Natural Company")
+    first_firm.plain_clients.create(name: "Natural Company")
     assert_equal 4, first_firm.plain_clients.length
     assert_equal 4, first_firm.plain_clients.size
   end
@@ -719,7 +946,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_create_with_bang_on_has_many_when_parent_is_new_raises
     error = assert_raise(ActiveRecord::RecordNotSaved) do
       firm = Firm.new
-      firm.plain_clients.create! :name=>"Whoever"
+      firm.plain_clients.create! name: "Whoever"
     end
 
     assert_equal "You cannot call create unless the parent is saved", error.message
@@ -728,7 +955,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_regular_create_on_has_many_when_parent_is_new_raises
     error = assert_raise(ActiveRecord::RecordNotSaved) do
       firm = Firm.new
-      firm.plain_clients.create :name=>"Whoever"
+      firm.plain_clients.create name: "Whoever"
     end
 
     assert_equal "You cannot call create unless the parent is saved", error.message
@@ -736,7 +963,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_create_with_bang_on_has_many_raises_when_record_not_saved
     assert_raise(ActiveRecord::RecordInvalid) do
-      firm = Firm.all.merge!(:order => "id").first
+      firm = Firm.first
       firm.plain_clients.create!
     end
   end
@@ -757,26 +984,32 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_adding_a_collection
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     companies(:first_firm).clients_of_firm.concat([Client.new("name" => "Natural Company"), Client.new("name" => "Apple")])
     assert_equal 4, companies(:first_firm).clients_of_firm.size
-    assert_equal 4, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 4, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_transactions_when_adding_to_persisted
-    good = Client.new(:name => "Good")
-    bad  = Client.new(:name => "Bad", :raise_on_save => true)
+    good = Client.new(name: "Good")
+    bad  = Client.new(name: "Bad", raise_on_save: true)
 
     begin
       companies(:first_firm).clients_of_firm.concat(good, bad)
     rescue Client::RaisedOnSave
     end
 
-    assert !companies(:first_firm).clients_of_firm(true).include?(good)
+    assert_not_includes companies(:first_firm).clients_of_firm.reload, good
   end
 
   def test_transactions_when_adding_to_new_record
-    assert_no_queries(ignore_none: false) do
-      firm = Firm.new
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    firm = Firm.new
+    assert_no_queries do
       firm.clients_of_firm.concat(Client.new("name" => "Natural Company"))
     end
   end
@@ -790,21 +1023,29 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_new_aliased_to_build
     company = companies(:first_firm)
-    new_client = assert_no_queries(ignore_none: false) { company.clients_of_firm.new("name" => "Another Client") }
-    assert !company.clients_of_firm.loaded?
+
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    new_client = assert_no_queries { company.clients_of_firm.new("name" => "Another Client") }
+    assert_not_predicate company.clients_of_firm, :loaded?
 
     assert_equal "Another Client", new_client.name
-    assert !new_client.persisted?
+    assert_not_predicate new_client, :persisted?
     assert_equal new_client, company.clients_of_firm.last
   end
 
   def test_build
     company = companies(:first_firm)
-    new_client = assert_no_queries(ignore_none: false) { company.clients_of_firm.build("name" => "Another Client") }
-    assert !company.clients_of_firm.loaded?
+
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    new_client = assert_no_queries { company.clients_of_firm.build("name" => "Another Client") }
+    assert_not_predicate company.clients_of_firm, :loaded?
 
     assert_equal "Another Client", new_client.name
-    assert !new_client.persisted?
+    assert_not_predicate new_client, :persisted?
     assert_equal new_client, company.clients_of_firm.last
   end
 
@@ -813,13 +1054,34 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     company.clients_of_firm.build("name" => "Another Client")
     company.clients_of_firm.build("name" => "Yet Another Client")
     assert_equal 4, company.clients_of_firm.size
+    assert_equal 4, company.clients_of_firm.uniq.size
   end
 
   def test_collection_not_empty_after_building
     company = companies(:first_firm)
-    assert_predicate company.contracts, :empty?
+    assert_empty company.contracts
     company.contracts.build
-    assert_not_predicate company.contracts, :empty?
+    assert_not_empty company.contracts
+  end
+
+  def test_collection_size_with_dirty_target
+    post = posts(:thinking)
+    assert_equal [], post.reader_ids
+    assert_equal 0, post.readers.size
+    post.readers.reset
+    post.readers.build
+    assert_equal [nil], post.reader_ids
+    assert_equal 1, post.readers.size
+  end
+
+  def test_collection_empty_with_dirty_target
+    post = posts(:thinking)
+    assert_equal [], post.reader_ids
+    assert_empty post.readers
+    post.readers.reset
+    post.readers.build
+    assert_equal [nil], post.reader_ids
+    assert_not_empty post.readers
   end
 
   def test_collection_size_twice_for_regressions
@@ -836,24 +1098,30 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_build_many
     company = companies(:first_firm)
-    new_clients = assert_no_queries(ignore_none: false) { company.clients_of_firm.build([{"name" => "Another Client"}, {"name" => "Another Client II"}]) }
+
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    new_clients = assert_no_queries { company.clients_of_firm.build([{ "name" => "Another Client" }, { "name" => "Another Client II" }]) }
     assert_equal 2, new_clients.size
   end
 
   def test_build_followed_by_save_does_not_load_target
     companies(:first_firm).clients_of_firm.build("name" => "Another Client")
     assert companies(:first_firm).save
-    assert !companies(:first_firm).clients_of_firm.loaded?
+    assert_not_predicate companies(:first_firm).clients_of_firm, :loaded?
   end
 
   def test_build_without_loading_association
     first_topic = topics(:first)
-    Reply.column_names
 
     assert_equal 1, first_topic.replies.length
 
+    # Load schema information so we don't query below if running just this test.
+    Reply.define_attribute_methods
+
     assert_no_queries do
-      first_topic.replies.build(:title => "Not saved", :content => "Superstars")
+      first_topic.replies.build(title: "Not saved", content: "Superstars")
       assert_equal 2, first_topic.replies.size
     end
 
@@ -862,18 +1130,26 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_build_via_block
     company = companies(:first_firm)
-    new_client = assert_no_queries(ignore_none: false) { company.clients_of_firm.build {|client| client.name = "Another Client" } }
-    assert !company.clients_of_firm.loaded?
+
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    new_client = assert_no_queries { company.clients_of_firm.build { |client| client.name = "Another Client" } }
+    assert_not_predicate company.clients_of_firm, :loaded?
 
     assert_equal "Another Client", new_client.name
-    assert !new_client.persisted?
+    assert_not_predicate new_client, :persisted?
     assert_equal new_client, company.clients_of_firm.last
   end
 
   def test_build_many_via_block
     company = companies(:first_firm)
-    new_clients = assert_no_queries(ignore_none: false) do
-      company.clients_of_firm.build([{"name" => "Another Client"}, {"name" => "Another Client II"}]) do |client|
+
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    new_clients = assert_no_queries do
+      company.clients_of_firm.build([{ "name" => "Another Client" }, { "name" => "Another Client II" }]) do |client|
         client.name = "changed"
       end
     end
@@ -884,15 +1160,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_create_without_loading_association
-    first_firm  = companies(:first_firm)
-    Firm.column_names
-    Client.column_names
+    first_firm = companies(:first_firm)
 
     assert_equal 2, first_firm.clients_of_firm.size
     first_firm.clients_of_firm.reset
 
     assert_queries(1) do
-      first_firm.clients_of_firm.create(:name => "Superstars")
+      first_firm.clients_of_firm.create(name: "Superstars")
     end
 
     assert_equal 3, first_firm.clients_of_firm.size
@@ -900,28 +1174,34 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_create
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     new_client = companies(:first_firm).clients_of_firm.create("name" => "Another Client")
-    assert new_client.persisted?
+    assert_predicate new_client, :persisted?
     assert_equal new_client, companies(:first_firm).clients_of_firm.last
-    assert_equal new_client, companies(:first_firm).clients_of_firm(true).last
+    assert_equal new_client, companies(:first_firm).clients_of_firm.reload.last
   end
 
   def test_create_many
-    companies(:first_firm).clients_of_firm.create([{"name" => "Another Client"}, {"name" => "Another Client II"}])
-    assert_equal 4, companies(:first_firm).clients_of_firm(true).size
+    companies(:first_firm).clients_of_firm.create([{ "name" => "Another Client" }, { "name" => "Another Client II" }])
+    assert_equal 4, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_create_followed_by_save_does_not_load_target
     companies(:first_firm).clients_of_firm.create("name" => "Another Client")
     assert companies(:first_firm).save
-    assert !companies(:first_firm).clients_of_firm.loaded?
+    assert_not_predicate companies(:first_firm).clients_of_firm, :loaded?
   end
 
   def test_deleting
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     companies(:first_firm).clients_of_firm.delete(companies(:first_firm).clients_of_firm.first)
     assert_equal 1, companies(:first_firm).clients_of_firm.size
-    assert_equal 1, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 1, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_deleting_before_save
@@ -932,6 +1212,25 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal 0, new_firm.clients_of_firm.size
   end
 
+  def test_has_many_without_counter_cache_option
+    # Ship has a conventionally named `treasures_count` column, but the counter_cache
+    # option is not given on the association.
+    ship = Ship.create(name: "Countless", treasures_count: 10)
+
+    assert_not_predicate Ship.reflect_on_association(:treasures), :has_cached_counter?
+
+    # Count should come from sql count() of treasures rather than treasures_count attribute
+    assert_equal ship.treasures.size, 0
+
+    assert_no_difference lambda { ship.reload.treasures_count }, "treasures_count should not be changed" do
+      ship.treasures.create(name: "Gold")
+    end
+
+    assert_no_difference lambda { ship.reload.treasures_count }, "treasures_count should not be changed" do
+      ship.treasures.destroy_all
+    end
+  end
+
   def test_deleting_updates_counter_cache
     topic = Topic.order("id ASC").first
     assert_equal topic.replies.to_a.size, topic.replies_count
@@ -971,6 +1270,38 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal 2, topic.reload.replies.size
   end
 
+  def test_counter_cache_updates_in_memory_after_update_with_inverse_of_disabled
+    topic = Topic.create!(title: "Zoom-zoom-zoom")
+
+    assert_equal 0, topic.replies_count
+
+    reply1 = Reply.create!(title: "re: zoom", content: "speedy quick!")
+    reply2 = Reply.create!(title: "re: zoom 2", content: "OMG lol!")
+
+    assert_queries(4) do
+      topic.replies << [reply1, reply2]
+    end
+
+    assert_equal 2, topic.replies_count
+    assert_equal 2, topic.reload.replies_count
+  end
+
+  def test_counter_cache_updates_in_memory_after_update_with_inverse_of_enabled
+    category = Category.create!(name: "Counter Cache")
+
+    assert_nil category.categorizations_count
+
+    categorization1 = Categorization.create!
+    categorization2 = Categorization.create!
+
+    assert_queries(4) do
+      category.categorizations << [categorization1, categorization2]
+    end
+
+    assert_equal 2, category.categorizations_count
+    assert_equal 2, category.reload.categorizations_count
+  end
+
   def test_pushing_association_updates_counter_cache
     topic = Topic.order("id ASC").first
     reply = Reply.create!
@@ -1008,8 +1339,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_calling_empty_with_counter_cache
     post = posts(:welcome)
-    assert_queries(0) do
-      assert_not post.comments.empty?
+    assert_no_queries do
+      assert_not_empty post.comments
     end
   end
 
@@ -1021,20 +1352,20 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_calling_update_attributes_on_id_changes_the_counter_cache
+  def test_calling_update_on_id_changes_the_counter_cache
     topic = Topic.order("id ASC").first
     original_count = topic.replies.to_a.size
     assert_equal original_count, topic.replies_count
 
     first_reply = topic.replies.first
-    first_reply.update_attributes(:parent_id => nil)
+    first_reply.update(parent_id: nil)
     assert_equal original_count - 1, topic.reload.replies_count
 
-    first_reply.update_attributes(:parent_id => topic.id)
+    first_reply.update(parent_id: topic.id)
     assert_equal original_count, topic.reload.replies_count
   end
 
-  def test_calling_update_attributes_changing_ids_doesnt_change_counter_cache
+  def test_calling_update_changing_ids_doesnt_change_counter_cache
     topic1 = Topic.find(1)
     topic2 = Topic.find(3)
     original_count1 = topic1.replies.to_a.size
@@ -1043,26 +1374,32 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     reply1 = topic1.replies.first
     reply2 = topic2.replies.first
 
-    reply1.update_attributes(:parent_id => topic2.id)
+    reply1.update(parent_id: topic2.id)
     assert_equal original_count1 - 1, topic1.reload.replies_count
     assert_equal original_count2 + 1, topic2.reload.replies_count
 
-    reply2.update_attributes(:parent_id => topic1.id)
+    reply2.update(parent_id: topic1.id)
     assert_equal original_count1, topic1.reload.replies_count
     assert_equal original_count2, topic2.reload.replies_count
   end
 
   def test_deleting_a_collection
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     companies(:first_firm).clients_of_firm.create("name" => "Another Client")
     assert_equal 3, companies(:first_firm).clients_of_firm.size
     companies(:first_firm).clients_of_firm.delete([companies(:first_firm).clients_of_firm[0], companies(:first_firm).clients_of_firm[1], companies(:first_firm).clients_of_firm[2]])
     assert_equal 0, companies(:first_firm).clients_of_firm.size
-    assert_equal 0, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 0, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_delete_all
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     companies(:first_firm).dependent_clients_of_firm.create("name" => "Another Client")
     clients = companies(:first_firm).dependent_clients_of_firm.to_a
     assert_equal 3, clients.count
@@ -1074,17 +1411,20 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_delete_all_with_not_yet_loaded_association_collection
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     companies(:first_firm).clients_of_firm.create("name" => "Another Client")
     assert_equal 3, companies(:first_firm).clients_of_firm.size
     companies(:first_firm).clients_of_firm.reset
     companies(:first_firm).clients_of_firm.delete_all
     assert_equal 0, companies(:first_firm).clients_of_firm.size
-    assert_equal 0, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 0, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_transaction_when_deleting_persisted
-    good = Client.new(:name => "Good")
-    bad  = Client.new(:name => "Bad", :raise_on_destroy => true)
+    good = Client.new(name: "Good")
+    bad  = Client.new(name: "Bad", raise_on_destroy: true)
 
     companies(:first_firm).clients_of_firm = [good, bad]
 
@@ -1093,12 +1433,15 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     rescue Client::RaisedOnDestroy
     end
 
-    assert_equal [good, bad], companies(:first_firm).clients_of_firm(true)
+    assert_equal [good, bad], companies(:first_firm).clients_of_firm.reload
   end
 
   def test_transaction_when_deleting_new_record
-    assert_no_queries(ignore_none: false) do
-      firm = Firm.new
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    firm = Firm.new
+    assert_no_queries do
       client = Client.new("name" => "New Client")
       firm.clients_of_firm << client
       firm.clients_of_firm.destroy(client)
@@ -1113,7 +1456,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     firm.clients_of_firm.clear
 
     assert_equal 0, firm.clients_of_firm.size
-    assert_equal 0, firm.clients_of_firm(true).size
+    assert_equal 0, firm.clients_of_firm.reload.size
     assert_equal [], Client.destroyed_client_ids[firm.id]
 
     # Should not be destroyed since the association is not dependent.
@@ -1125,7 +1468,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_clearing_updates_counter_cache
     topic = Topic.first
 
-    assert_difference 'topic.reload.replies_count', -1 do
+    assert_difference "topic.reload.replies_count", -1 do
       topic.replies.clear
     end
   end
@@ -1134,7 +1477,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     car = Car.first
     car.engines.create!
 
-    assert_difference 'car.reload.engines_count', -1 do
+    assert_difference "car.reload.engines_count", -1 do
       car.engines.clear
     end
   end
@@ -1149,7 +1492,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     firm.dependent_clients_of_firm.clear
 
     assert_equal 0, firm.dependent_clients_of_firm.size
-    assert_equal 0, firm.dependent_clients_of_firm(true).size
+    assert_equal 0, firm.dependent_clients_of_firm.reload.size
     assert_equal [], Client.destroyed_client_ids[firm.id]
 
     # Should be destroyed since the association is dependent.
@@ -1182,7 +1525,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     firm.exclusively_dependent_clients_of_firm.clear
 
     assert_equal 0, firm.exclusively_dependent_clients_of_firm.size
-    assert_equal 0, firm.exclusively_dependent_clients_of_firm(true).size
+    assert_equal 0, firm.exclusively_dependent_clients_of_firm.reload.size
     # no destroy-filters should have been called
     assert_equal [], Client.destroyed_client_ids[firm.id]
 
@@ -1192,8 +1535,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_dependent_association_respects_optional_conditions_on_delete
     firm = companies(:odegy)
-    Client.create(:client_of => firm.id, :name => "BigShot Inc.")
-    Client.create(:client_of => firm.id, :name => "SmallTime Inc.")
+    Client.create(client_of: firm.id, name: "BigShot Inc.")
+    Client.create(client_of: firm.id, name: "SmallTime Inc.")
     # only one of two clients is included in the association due to the :conditions key
     assert_equal 2, Client.where(client_of: firm.id).size
     assert_equal 1, firm.dependent_conditional_clients_of_firm.size
@@ -1204,8 +1547,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_dependent_association_respects_optional_sanitized_conditions_on_delete
     firm = companies(:odegy)
-    Client.create(:client_of => firm.id, :name => "BigShot Inc.")
-    Client.create(:client_of => firm.id, :name => "SmallTime Inc.")
+    Client.create(client_of: firm.id, name: "BigShot Inc.")
+    Client.create(client_of: firm.id, name: "SmallTime Inc.")
     # only one of two clients is included in the association due to the :conditions key
     assert_equal 2, Client.where(client_of: firm.id).size
     assert_equal 1, firm.dependent_sanitized_conditional_clients_of_firm.size
@@ -1216,11 +1559,11 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_dependent_association_respects_optional_hash_conditions_on_delete
     firm = companies(:odegy)
-    Client.create(:client_of => firm.id, :name => "BigShot Inc.")
-    Client.create(:client_of => firm.id, :name => "SmallTime Inc.")
+    Client.create(client_of: firm.id, name: "BigShot Inc.")
+    Client.create(client_of: firm.id, name: "SmallTime Inc.")
     # only one of two clients is included in the association due to the :conditions key
     assert_equal 2, Client.where(client_of: firm.id).size
-    assert_equal 1, firm.dependent_sanitized_conditional_clients_of_firm.size
+    assert_equal 1, firm.dependent_hash_conditional_clients_of_firm.size
     firm.destroy
     # only the correctly associated client should have been deleted
     assert_equal 1, Client.where(client_of: firm.id).size
@@ -1231,7 +1574,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     # break the vanilla firm_id foreign key
     assert_equal 3, firm.clients.count
     firm.clients.first.update_columns(firm_id: nil)
-    assert_equal 2, firm.clients(true).count
+    assert_equal 2, firm.clients.reload.count
     assert_equal 2, firm.clients_using_primary_key_with_delete_all.count
     old_record = firm.clients_using_primary_key_with_delete_all.first
     firm = Firm.first
@@ -1242,13 +1585,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_creation_respects_hash_condition
     ms_client = companies(:first_firm).clients_like_ms_with_hash_conditions.build
 
-    assert        ms_client.save
-    assert_equal  'Microsoft', ms_client.name
+    assert ms_client.save
+    assert_equal "Microsoft", ms_client.name
 
     another_ms_client = companies(:first_firm).clients_like_ms_with_hash_conditions.create
 
-    assert        another_ms_client.persisted?
-    assert_equal  'Microsoft', another_ms_client.name
+    assert_predicate another_ms_client, :persisted?
+    assert_equal "Microsoft", another_ms_client.name
   end
 
   def test_clearing_without_initial_access
@@ -1257,22 +1600,25 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     firm.clients_of_firm.clear
 
     assert_equal 0, firm.clients_of_firm.size
-    assert_equal 0, firm.clients_of_firm(true).size
+    assert_equal 0, firm.clients_of_firm.reload.size
   end
 
   def test_deleting_a_item_which_is_not_in_the_collection
     force_signal37_to_load_all_clients_of_firm
-    summit = Client.find_by_name('Summit')
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
+    summit = Client.find_by_name("Summit")
     companies(:first_firm).clients_of_firm.delete(summit)
     assert_equal 2, companies(:first_firm).clients_of_firm.size
-    assert_equal 2, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 2, companies(:first_firm).clients_of_firm.reload.size
     assert_equal 2, summit.client_of
   end
 
-  def test_deleting_by_fixnum_id
+  def test_deleting_by_integer_id
     david = Developer.find(1)
 
-    assert_difference 'david.projects.count', -1 do
+    assert_difference "david.projects.count", -1 do
       assert_equal 1, david.projects.delete(1).size
     end
 
@@ -1282,8 +1628,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_deleting_by_string_id
     david = Developer.find(1)
 
-    assert_difference 'david.projects.count', -1 do
-      assert_equal 1, david.projects.delete('1').size
+    assert_difference "david.projects.count", -1 do
+      assert_equal 1, david.projects.delete("1").size
     end
 
     assert_equal 1, david.projects.size
@@ -1298,38 +1644,47 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_destroying
     force_signal37_to_load_all_clients_of_firm
 
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     assert_difference "Client.count", -1 do
       companies(:first_firm).clients_of_firm.destroy(companies(:first_firm).clients_of_firm.first)
     end
 
     assert_equal 1, companies(:first_firm).reload.clients_of_firm.size
-    assert_equal 1, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 1, companies(:first_firm).clients_of_firm.reload.size
   end
 
-  def test_destroying_by_fixnum_id
+  def test_destroying_by_integer_id
     force_signal37_to_load_all_clients_of_firm
 
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     assert_difference "Client.count", -1 do
       companies(:first_firm).clients_of_firm.destroy(companies(:first_firm).clients_of_firm.first.id)
     end
 
     assert_equal 1, companies(:first_firm).reload.clients_of_firm.size
-    assert_equal 1, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 1, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_destroying_by_string_id
     force_signal37_to_load_all_clients_of_firm
 
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     assert_difference "Client.count", -1 do
       companies(:first_firm).clients_of_firm.destroy(companies(:first_firm).clients_of_firm.first.id.to_s)
     end
 
     assert_equal 1, companies(:first_firm).reload.clients_of_firm.size
-    assert_equal 1, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 1, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_destroying_a_collection
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     companies(:first_firm).clients_of_firm.create("name" => "Another Client")
     assert_equal 3, companies(:first_firm).clients_of_firm.size
 
@@ -1338,35 +1693,37 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     end
 
     assert_equal 1, companies(:first_firm).reload.clients_of_firm.size
-    assert_equal 1, companies(:first_firm).clients_of_firm(true).size
+    assert_equal 1, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_destroy_all
     force_signal37_to_load_all_clients_of_firm
+
+    assert_predicate companies(:first_firm).clients_of_firm, :loaded?
+
     clients = companies(:first_firm).clients_of_firm.to_a
-    assert !clients.empty?, "37signals has clients after load"
+    assert_not clients.empty?, "37signals has clients after load"
     destroyed = companies(:first_firm).clients_of_firm.destroy_all
     assert_equal clients.sort_by(&:id), destroyed.sort_by(&:id)
     assert destroyed.all?(&:frozen?), "destroyed clients should be frozen"
     assert companies(:first_firm).clients_of_firm.empty?, "37signals has no clients after destroy all"
-    assert companies(:first_firm).clients_of_firm(true).empty?, "37signals has no clients after destroy all and refresh"
+    assert companies(:first_firm).clients_of_firm.reload.empty?, "37signals has no clients after destroy all and refresh"
   end
 
   def test_dependence
     firm = companies(:first_firm)
     assert_equal 3, firm.clients.size
     firm.destroy
-    assert Client.all.merge!(:where => "firm_id=#{firm.id}").to_a.empty?
+    assert_empty Client.all.merge!(where: "firm_id=#{firm.id}").to_a
   end
 
   def test_dependence_for_associations_with_hash_condition
     david = authors(:david)
-    assert_difference('Post.count', -1) { assert david.destroy }
+    assert_difference("Post.count", -1) { assert david.destroy }
   end
 
   def test_destroy_dependent_when_deleted_from_association
-    # sometimes tests on Oracle fail if ORDER BY is not provided therefore add always :order with :first
-    firm = Firm.all.merge!(:order => "id").first
+    firm = Firm.first
     assert_equal 3, firm.clients.size
 
     client = firm.clients.first
@@ -1393,7 +1750,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
     firm.destroy rescue "do nothing"
 
-    assert_equal 3, Client.all.merge!(:where => "firm_id=#{firm.id}").to_a.size
+    assert_equal 3, Client.all.merge!(where: "firm_id=#{firm.id}").to_a.size
   end
 
   def test_dependence_on_account
@@ -1417,28 +1774,47 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_restrict_with_exception
-    firm = RestrictedWithExceptionFirm.create!(:name => 'restrict')
-    firm.companies.create(:name => 'child')
+    firm = RestrictedWithExceptionFirm.create!(name: "restrict")
+    firm.companies.create(name: "child")
 
-    assert !firm.companies.empty?
+    assert_not_empty firm.companies
     assert_raise(ActiveRecord::DeleteRestrictionError) { firm.destroy }
-    assert RestrictedWithExceptionFirm.exists?(:name => 'restrict')
-    assert firm.companies.exists?(:name => 'child')
+    assert RestrictedWithExceptionFirm.exists?(name: "restrict")
+    assert firm.companies.exists?(name: "child")
   end
 
   def test_restrict_with_error
-    firm = RestrictedWithErrorFirm.create!(:name => 'restrict')
-    firm.companies.create(:name => 'child')
+    firm = RestrictedWithErrorFirm.create!(name: "restrict")
+    firm.companies.create(name: "child")
 
-    assert !firm.companies.empty?
+    assert_not_empty firm.companies
 
     firm.destroy
 
-    assert !firm.errors.empty?
+    assert_not_empty firm.errors
 
     assert_equal "Cannot delete record because dependent companies exist", firm.errors[:base].first
-    assert RestrictedWithErrorFirm.exists?(:name => 'restrict')
-    assert firm.companies.exists?(:name => 'child')
+    assert RestrictedWithErrorFirm.exists?(name: "restrict")
+    assert firm.companies.exists?(name: "child")
+  end
+
+  def test_restrict_with_error_with_locale
+    I18n.backend = I18n::Backend::Simple.new
+    I18n.backend.store_translations "en", activerecord: { attributes: { restricted_with_error_firm: { companies: "client companies" } } }
+    firm = RestrictedWithErrorFirm.create!(name: "restrict")
+    firm.companies.create(name: "child")
+
+    assert_not_empty firm.companies
+
+    firm.destroy
+
+    assert_not_empty firm.errors
+
+    assert_equal "Cannot delete record because dependent client companies exist", firm.errors[:base].first
+    assert RestrictedWithErrorFirm.exists?(name: "restrict")
+    assert firm.companies.exists?(name: "child")
+  ensure
+    I18n.backend.reload!
   end
 
   def test_included_in_collection
@@ -1446,10 +1822,10 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_included_in_collection_for_new_records
-    client = Client.create(:name => 'Persisted')
+    client = Client.create(name: "Persisted")
     assert_nil client.client_of
     assert_equal false, Firm.new.clients_of_firm.include?(client),
-     'includes a client that does not belong to any firm'
+     "includes a client that does not belong to any firm"
   end
 
   def test_adding_array_and_collection
@@ -1457,7 +1833,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_replace_with_less
-    firm = Firm.all.merge!(:order => "id").first
+    firm = Firm.first
     firm.clients = [companies(:first_client)]
     assert firm.save, "Could not save firm"
     firm.reload
@@ -1471,7 +1847,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_replace_with_new
-    firm = Firm.all.merge!(:order => "id").first
+    firm = Firm.first
     firm.clients = [companies(:second_client), Client.new("name" => "New Client")]
     firm.save
     firm.reload
@@ -1484,8 +1860,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     account = Account.new
     orig_accounts = firm.accounts.to_a
 
-    assert !account.valid?
-    assert !orig_accounts.empty?
+    assert_not_predicate account, :valid?
+    assert_not_empty orig_accounts
     error = assert_raise ActiveRecord::RecordNotSaved do
       firm.accounts = [account]
     end
@@ -1500,16 +1876,16 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     firm.clients = []
     firm.save
 
-    assert_queries(0, ignore_none: true) do
+    assert_no_queries do
       firm.clients = []
     end
 
-    assert_equal [], firm.send('clients=', [])
+    assert_equal [], firm.send("clients=", [])
   end
 
   def test_transactions_when_replacing_on_persisted
-    good = Client.new(:name => "Good")
-    bad  = Client.new(:name => "Bad", :raise_on_save => true)
+    good = Client.new(name: "Good")
+    bad  = Client.new(name: "Bad", raise_on_save: true)
 
     companies(:first_firm).clients_of_firm = [good]
 
@@ -1518,12 +1894,15 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     rescue Client::RaisedOnSave
     end
 
-    assert_equal [good], companies(:first_firm).clients_of_firm(true)
+    assert_equal [good], companies(:first_firm).clients_of_firm.reload
   end
 
   def test_transactions_when_replacing_on_new_record
-    assert_no_queries(ignore_none: false) do
-      firm = Firm.new
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    firm = Firm.new
+    assert_no_queries do
       firm.clients_of_firm = [Client.new("name" => "New Client")]
     end
   end
@@ -1534,8 +1913,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_get_ids_for_loaded_associations
     company = companies(:first_firm)
-    company.clients(true)
-    assert_queries(0) do
+    company.clients.reload
+    assert_no_queries do
       company.client_ids
       company.client_ids
     end
@@ -1543,9 +1922,14 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_get_ids_for_unloaded_associations_does_not_load_them
     company = companies(:first_firm)
-    assert !company.clients.loaded?
+    assert_not_predicate company.clients, :loaded?
     assert_equal [companies(:first_client).id, companies(:second_client).id, companies(:another_first_firm_client).id], company.client_ids
-    assert !company.clients.loaded?
+    assert_not_predicate company.clients, :loaded?
+  end
+
+  def test_counter_cache_on_unloaded_association
+    car = Car.create(name: "My AppliCar")
+    assert_equal car.engines.size, 0
   end
 
   def test_get_ids_ignores_include_option
@@ -1557,11 +1941,11 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_get_ids_for_association_on_new_record_does_not_try_to_find_records
-    Company.columns  # Load schema information so we don't query below
-    Contract.columns # if running just this test.
+    # Load schema information so we don't query below if running just this test.
+    companies(:first_client).contract_ids
 
     company = Company.new
-    assert_queries(0) do
+    assert_no_queries do
       company.contract_ids
     end
 
@@ -1572,7 +1956,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     contract_a = Contract.create!
     contract_b = Contract.create!
     Contract.create! # another contract
-    company = Company.new(:name => "Some Company")
+    company = Company.new(name: "Some Company")
 
     company.contract_ids = [contract_a.id, contract_b.id]
     assert_equal [contract_a.id, contract_b.id], company.contract_ids
@@ -1584,11 +1968,11 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_assign_ids_ignoring_blanks
-    firm = Firm.create!(:name => 'Apple')
-    firm.client_ids = [companies(:first_client).id, nil, companies(:second_client).id, '']
+    firm = Firm.create!(name: "Apple")
+    firm.client_ids = [companies(:first_client).id, nil, companies(:second_client).id, ""]
     firm.save!
 
-    assert_equal 2, firm.clients(true).size
+    assert_equal 2, firm.clients.reload.size
     assert_equal true, firm.clients.include?(companies(:second_client))
   end
 
@@ -1600,14 +1984,21 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     [
       lambda { authors(:mary).comment_ids = [comments(:greetings).id, comments(:more_greetings).id] },
       lambda { authors(:mary).comments = [comments(:greetings), comments(:more_greetings)] },
-      lambda { authors(:mary).comments << Comment.create!(:body => "Yay", :post_id => 424242) },
+      lambda { authors(:mary).comments << Comment.create!(body: "Yay", post_id: 424242) },
       lambda { authors(:mary).comments.delete(authors(:mary).comments.first) },
-    ].each {|block| assert_raise(ActiveRecord::HasManyThroughCantAssociateThroughHasOneOrManyReflection, &block) }
+    ].each { |block| assert_raise(ActiveRecord::HasManyThroughCantAssociateThroughHasOneOrManyReflection, &block) }
+  end
+
+  def test_associations_order_should_be_priority_over_throughs_order
+    david = authors(:david)
+    expected = [12, 10, 9, 8, 7, 6, 5, 3, 2, 1]
+    assert_equal expected, david.comments_desc.map(&:id)
+    assert_equal expected, Author.includes(:comments_desc).find(david.id).comments_desc.map(&:id)
   end
 
   def test_dynamic_find_should_respect_association_order_for_through
     assert_equal Comment.find(10), authors(:david).comments_desc.where("comments.type = 'SpecialComment'").first
-    assert_equal Comment.find(10), authors(:david).comments_desc.find_by_type('SpecialComment')
+    assert_equal Comment.find(10), authors(:david).comments_desc.find_by_type("SpecialComment")
   end
 
   def test_has_many_through_respects_hash_conditions
@@ -1622,7 +2013,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     client = firm.clients.first
 
     assert_no_queries do
-      assert firm.clients.loaded?
+      assert_predicate firm.clients, :loaded?
       assert_equal true, firm.clients.include?(client)
     end
   end
@@ -1632,18 +2023,18 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     client = firm.clients.first
 
     firm.reload
-    assert ! firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
     assert_queries(1) do
       assert_equal true, firm.clients.include?(client)
     end
-    assert ! firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_include_returns_false_for_non_matching_record_to_verify_scoping
     firm = companies(:first_firm)
-    client = Client.create!(:name => 'Not Associated')
+    client = Client.create!(name: "Not Associated")
 
-    assert ! firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
     assert_equal false, firm.clients.include?(client)
   end
 
@@ -1652,15 +2043,15 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     firm.clients.first
     firm.clients.second
     firm.clients.last
-    assert !firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_calling_first_or_last_on_loaded_association_should_not_fetch_with_query
     firm = companies(:first_firm)
     firm.clients.load_target
-    assert firm.clients.loaded?
+    assert_predicate firm.clients, :loaded?
 
-    assert_no_queries(ignore_none: false) do
+    assert_no_queries do
       firm.clients.first
       assert_equal 2, firm.clients.first(2).size
       firm.clients.last
@@ -1670,8 +2061,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_calling_first_or_last_on_existing_record_with_build_should_load_association
     firm = companies(:first_firm)
-    firm.clients.build(:name => 'Foo')
-    assert !firm.clients.loaded?
+    firm.clients.build(name: "Foo")
+    assert_not_predicate firm.clients, :loaded?
 
     assert_queries 1 do
       firm.clients.first
@@ -1679,13 +2070,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
       firm.clients.last
     end
 
-    assert firm.clients.loaded?
+    assert_predicate firm.clients, :loaded?
   end
 
   def test_calling_first_nth_or_last_on_existing_record_with_create_should_not_load_association
     firm = companies(:first_firm)
-    firm.clients.create(:name => 'Foo')
-    assert !firm.clients.loaded?
+    firm.clients.create(name: "Foo")
+    assert_not_predicate firm.clients, :loaded?
 
     assert_queries 3 do
       firm.clients.first
@@ -1693,7 +2084,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
       firm.clients.last
     end
 
-    assert !firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_calling_first_nth_or_last_on_new_record_should_not_run_queries
@@ -1708,15 +2099,15 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_calling_first_or_last_with_integer_on_association_should_not_load_association
     firm = companies(:first_firm)
-    firm.clients.create(:name => 'Foo')
-    assert !firm.clients.loaded?
+    firm.clients.create(name: "Foo")
+    assert_not_predicate firm.clients, :loaded?
 
     assert_queries 2 do
       firm.clients.first(2)
       firm.clients.last(2)
     end
 
-    assert !firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_calling_many_should_count_instead_of_loading_association
@@ -1724,37 +2115,38 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_queries(1) do
       firm.clients.many?  # use count query
     end
-    assert !firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_calling_many_on_loaded_association_should_not_use_query
     firm = companies(:first_firm)
-    firm.clients.collect  # force load
+    firm.clients.load  # force load
     assert_no_queries { assert firm.clients.many? }
   end
 
   def test_calling_many_should_defer_to_collection_if_using_a_block
     firm = companies(:first_firm)
     assert_queries(1) do
-      firm.clients.expects(:size).never
-      firm.clients.many? { true }
+      assert_not_called(firm.clients, :size) do
+        firm.clients.many? { true }
+      end
     end
-    assert firm.clients.loaded?
+    assert_predicate firm.clients, :loaded?
   end
 
   def test_calling_many_should_return_false_if_none_or_one
     firm = companies(:another_firm)
-    assert !firm.clients_like_ms.many?
+    assert_not_predicate firm.clients_like_ms, :many?
     assert_equal 0, firm.clients_like_ms.size
 
     firm = companies(:first_firm)
-    assert !firm.limited_clients.many?
+    assert_not_predicate firm.limited_clients, :many?
     assert_equal 1, firm.limited_clients.size
   end
 
   def test_calling_many_should_return_true_if_more_than_one
     firm = companies(:first_firm)
-    assert firm.clients.many?
+    assert_predicate firm.clients, :many?
     assert_equal 3, firm.clients.size
   end
 
@@ -1763,33 +2155,34 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_queries(1) do
       firm.clients.none?  # use count query
     end
-    assert !firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_calling_none_on_loaded_association_should_not_use_query
     firm = companies(:first_firm)
-    firm.clients.collect  # force load
-    assert_no_queries { assert ! firm.clients.none? }
+    firm.clients.load  # force load
+    assert_no_queries { assert_not firm.clients.none? }
   end
 
   def test_calling_none_should_defer_to_collection_if_using_a_block
     firm = companies(:first_firm)
     assert_queries(1) do
-      firm.clients.expects(:size).never
-      firm.clients.none? { true }
+      assert_not_called(firm.clients, :size) do
+        firm.clients.none? { true }
+      end
     end
-    assert firm.clients.loaded?
+    assert_predicate firm.clients, :loaded?
   end
 
   def test_calling_none_should_return_true_if_none
     firm = companies(:another_firm)
-    assert firm.clients_like_ms.none?
+    assert_predicate firm.clients_like_ms, :none?
     assert_equal 0, firm.clients_like_ms.size
   end
 
   def test_calling_none_should_return_false_if_any
     firm = companies(:first_firm)
-    assert !firm.limited_clients.none?
+    assert_not_predicate firm.limited_clients, :none?
     assert_equal 1, firm.limited_clients.size
   end
 
@@ -1798,39 +2191,40 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_queries(1) do
       firm.clients.one?  # use count query
     end
-    assert !firm.clients.loaded?
+    assert_not_predicate firm.clients, :loaded?
   end
 
   def test_calling_one_on_loaded_association_should_not_use_query
     firm = companies(:first_firm)
-    firm.clients.collect  # force load
-    assert_no_queries { assert ! firm.clients.one? }
+    firm.clients.load  # force load
+    assert_no_queries { assert_not firm.clients.one? }
   end
 
   def test_calling_one_should_defer_to_collection_if_using_a_block
     firm = companies(:first_firm)
     assert_queries(1) do
-      firm.clients.expects(:size).never
-      firm.clients.one? { true }
+      assert_not_called(firm.clients, :size) do
+        firm.clients.one? { true }
+      end
     end
-    assert firm.clients.loaded?
+    assert_predicate firm.clients, :loaded?
   end
 
   def test_calling_one_should_return_false_if_zero
     firm = companies(:another_firm)
-    assert ! firm.clients_like_ms.one?
+    assert_not_predicate firm.clients_like_ms, :one?
     assert_equal 0, firm.clients_like_ms.size
   end
 
   def test_calling_one_should_return_true_if_one
     firm = companies(:first_firm)
-    assert firm.limited_clients.one?
+    assert_predicate firm.limited_clients, :one?
     assert_equal 1, firm.limited_clients.size
   end
 
   def test_calling_one_should_return_false_if_more_than_one
     firm = companies(:first_firm)
-    assert ! firm.clients.one?
+    assert_not_predicate firm.clients, :one?
     assert_equal 3, firm.clients.size
   end
 
@@ -1838,13 +2232,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     old = ActiveRecord::Base.store_full_sti_class
     ActiveRecord::Base.store_full_sti_class = true
 
-    firm = Namespaced::Firm.create({ :name => 'Some Company' })
-    firm.clients.create({ :name => 'Some Client' })
+    firm = Namespaced::Firm.create(name: "Some Company")
+    firm.clients.create(name: "Some Client")
 
     stats = Namespaced::Firm.all.merge!(
-      :select => "#{Namespaced::Firm.table_name}.id, COUNT(#{Namespaced::Client.table_name}.id) AS num_clients",
-      :joins  => :clients,
-      :group  => "#{Namespaced::Firm.table_name}.id"
+      select: "#{Namespaced::Firm.table_name}.id, COUNT(#{Namespaced::Client.table_name}.id) AS num_clients",
+      joins: :clients,
+      group: "#{Namespaced::Firm.table_name}.id"
     ).find firm.id
     assert_equal 1, stats.num_clients.to_i
   ensure
@@ -1852,9 +2246,10 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_association_proxy_transaction_method_starts_transaction_in_association_class
-    Comment.expects(:transaction)
-    Post.first.comments.transaction do
-      # nothing
+    assert_called(Comment, :transaction) do
+      Post.first.comments.transaction do
+        # nothing
+      end
     end
   end
 
@@ -1863,43 +2258,45 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal client_association.new.attributes, client_association.send(:new).attributes
   end
 
-  def test_respond_to_private_class_methods
-    client_association = companies(:first_firm).clients
-    assert !client_association.respond_to?(:private_method)
-    assert client_association.respond_to?(:private_method, true)
-  end
-
   def test_creating_using_primary_key
-    firm = Firm.all.merge!(:order => "id").first
-    client = firm.clients_using_primary_key.create!(:name => 'test')
+    firm = Firm.first
+    client = firm.clients_using_primary_key.create!(name: "test")
     assert_equal firm.name, client.firm_name
   end
 
   def test_defining_has_many_association_with_delete_all_dependency_lazily_evaluates_target_class
-    ActiveRecord::Reflection::AssociationReflection.any_instance.expects(:class_name).never
-    class_eval(<<-EOF, __FILE__, __LINE__ + 1)
-      class DeleteAllModel < ActiveRecord::Base
-        has_many :nonentities, :dependent => :delete_all
-      end
-    EOF
+    assert_not_called_on_instance_of(
+      ActiveRecord::Reflection::AssociationReflection,
+      :class_name,
+    ) do
+      class_eval(<<-EOF, __FILE__, __LINE__ + 1)
+        class DeleteAllModel < ActiveRecord::Base
+          has_many :nonentities, :dependent => :delete_all
+        end
+      EOF
+    end
   end
 
   def test_defining_has_many_association_with_nullify_dependency_lazily_evaluates_target_class
-    ActiveRecord::Reflection::AssociationReflection.any_instance.expects(:class_name).never
-    class_eval(<<-EOF, __FILE__, __LINE__ + 1)
-      class NullifyModel < ActiveRecord::Base
-        has_many :nonentities, :dependent => :nullify
-      end
-    EOF
+    assert_not_called_on_instance_of(
+      ActiveRecord::Reflection::AssociationReflection,
+      :class_name,
+    ) do
+      class_eval(<<-EOF, __FILE__, __LINE__ + 1)
+        class NullifyModel < ActiveRecord::Base
+          has_many :nonentities, :dependent => :nullify
+        end
+      EOF
+    end
   end
 
   def test_attributes_are_being_set_when_initialized_from_has_many_association_with_where_clause
-    new_comment = posts(:welcome).comments.where(:body => "Some content").build
+    new_comment = posts(:welcome).comments.where(body: "Some content").build
     assert_equal new_comment.body, "Some content"
   end
 
   def test_attributes_are_being_set_when_initialized_from_has_many_association_with_multiple_where_clauses
-    new_comment = posts(:welcome).comments.where(:body => "Some content").where(:type => 'SpecialComment').build
+    new_comment = posts(:welcome).comments.where(body: "Some content").where(type: "SpecialComment").build
     assert_equal new_comment.body, "Some content"
     assert_equal new_comment.type, "SpecialComment"
     assert_equal new_comment.post_id, posts(:welcome).id
@@ -1913,7 +2310,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_load_target_respects_protected_attributes
     topic = Topic.create!
-    reply = topic.replies.create(:title => "reply 1")
+    reply = topic.replies.create(title: "reply 1")
     reply.approved = false
     reply.save!
 
@@ -1940,7 +2337,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_merging_with_custom_attribute_writer
-    bulb = Bulb.new(:color => "red")
+    bulb = Bulb.new(color: "red")
     assert_equal "RED!", bulb.color
 
     car = Car.create!
@@ -1950,13 +2347,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_abstract_class_with_polymorphic_has_many
-    post = SubStiPost.create! :title => "fooo", :body => "baa"
-    tagging = Tagging.create! :taggable => post
+    post = SubStiPost.create! title: "fooo", body: "baa"
+    tagging = Tagging.create! taggable: post
     assert_equal [tagging], post.taggings
   end
 
   def test_with_polymorphic_has_many_with_custom_columns_name
-    post = Post.create! :title => 'foo', :body => 'bar'
+    post = Post.create! title: "foo", body: "bar"
     image = Image.create!
 
     post.images << image
@@ -1966,10 +2363,17 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   def test_build_with_polymorphic_has_many_does_not_allow_to_override_type_and_id
     welcome = posts(:welcome)
-    tagging = welcome.taggings.build(:taggable_id => 99, :taggable_type => 'ShouldNotChange')
+    tagging = welcome.taggings.build(taggable_id: 99, taggable_type: "ShouldNotChange")
 
     assert_equal welcome.id, tagging.taggable_id
-    assert_equal 'Post', tagging.taggable_type
+    assert_equal "Post", tagging.taggable_type
+  end
+
+  def test_build_from_polymorphic_association_sets_inverse_instance
+    post = Post.new
+    tagging = post.taggings.build
+
+    assert_equal post, tagging.taggable
   end
 
   def test_dont_call_save_callbacks_twice_on_has_many
@@ -1981,30 +2385,30 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_association_attributes_are_available_to_after_initialize
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
     bulb = car.bulbs.build
 
-    assert_equal car.id, bulb.attributes_after_initialize['car_id']
+    assert_equal car.id, bulb.attributes_after_initialize["car_id"]
   end
 
   def test_attributes_are_set_when_initialized_from_has_many_null_relationship
-    car  = Car.new name: 'honda'
-    bulb = car.bulbs.where(name: 'headlight').first_or_initialize
-    assert_equal 'headlight', bulb.name
+    car  = Car.new name: "honda"
+    bulb = car.bulbs.where(name: "headlight").first_or_initialize
+    assert_equal "headlight", bulb.name
   end
 
   def test_attributes_are_set_when_initialized_from_polymorphic_has_many_null_relationship
-    post    = Post.new title: 'title', body: 'bar'
-    tag     = Tag.create!(name: 'foo')
+    post    = Post.new title: "title", body: "bar"
+    tag     = Tag.create!(name: "foo")
 
     tagging = post.taggings.where(tag: tag).first_or_initialize
 
     assert_equal tag.id, tagging.tag_id
-    assert_equal 'Post', tagging.taggable_type
+    assert_equal "Post", tagging.taggable_type
   end
 
   def test_replace
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
     bulb1 = car.bulbs.create
     bulb2 = Bulb.create
 
@@ -2015,7 +2419,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_replace_returns_target
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
     bulb1 = car.bulbs.create
     bulb2 = car.bulbs.create
     bulb3 = Bulb.create
@@ -2029,18 +2433,31 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   def test_collection_association_with_private_kernel_method
     firm = companies(:first_firm)
     assert_equal [accounts(:signals37)], firm.accounts.open
+    assert_equal [accounts(:signals37)], firm.accounts.available
+  end
+
+  def test_association_with_or_doesnt_set_inverse_instance_key
+    firm = companies(:first_firm)
+    accounts = firm.accounts.or(Account.where(firm_id: nil)).order(:id)
+    assert_equal [firm.id, nil], accounts.map(&:firm_id)
+  end
+
+  def test_association_with_rewhere_doesnt_set_inverse_instance_key
+    firm = companies(:first_firm)
+    accounts = firm.accounts.rewhere(firm_id: [firm.id, nil]).order(:id)
+    assert_equal [firm.id, nil], accounts.map(&:firm_id)
   end
 
   test "first_or_initialize adds the record to the association" do
-    firm = Firm.create! name: 'omg'
+    firm = Firm.create! name: "omg"
     client = firm.clients_of_firm.first_or_initialize
     assert_equal [client], firm.clients_of_firm
   end
 
   test "first_or_create adds the record to the association" do
-    firm = Firm.create! name: 'omg'
+    firm = Firm.create! name: "omg"
     firm.clients_of_firm.load_target
-    client = firm.clients_of_firm.first_or_create name: 'lol'
+    client = firm.clients_of_firm.first_or_create name: "lol"
     assert_equal [client], firm.clients_of_firm
     assert_equal [client], firm.reload.clients_of_firm
   end
@@ -2049,7 +2466,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     post = posts(:welcome)
 
     assert post.taggings_with_delete_all.count > 0
-    assert !post.taggings_with_delete_all.loaded?
+    assert_not_predicate post.taggings_with_delete_all, :loaded?
 
     # 2 queries: one DELETE and another to update the counter cache
     assert_queries(2) do
@@ -2060,9 +2477,9 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   test "has many associations on new records use null relations" do
     post = Post.new
 
-    assert_no_queries(ignore_none: false) do
+    assert_no_queries do
       assert_equal [], post.comments
-      assert_equal [], post.comments.where(body: 'omg')
+      assert_equal [], post.comments.where(body: "omg")
       assert_equal [], post.comments.pluck(:body)
       assert_equal 0,  post.comments.sum(:id)
       assert_equal 0,  post.comments.count
@@ -2071,7 +2488,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
   test "collection proxy respects default scope" do
     author = authors(:mary)
-    assert !author.first_posts.exists?
+    assert_not_predicate author.first_posts, :exists?
   end
 
   test "association with extend option" do
@@ -2083,14 +2500,22 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   test "association with extend option with multiple extensions" do
     post = posts(:welcome)
     assert_equal "lifo",  post.comments_with_extend_2.author
-    assert_equal "hello", post.comments_with_extend_2.greeting
+    assert_equal "hullo", post.comments_with_extend_2.greeting
+  end
+
+  test "extend option affects per association" do
+    post = posts(:welcome)
+    assert_equal "lifo",  post.comments_with_extend.author
+    assert_equal "lifo",  post.comments_with_extend_2.author
+    assert_equal "hello", post.comments_with_extend.greeting
+    assert_equal "hullo", post.comments_with_extend_2.greeting
   end
 
   test "delete record with complex joins" do
     david = authors(:david)
 
     post = david.posts.first
-    post.type = 'PostWithSpecialCategorization'
+    post.type = "PostWithSpecialCategorization"
     post.save
 
     categorization = post.categorizations.first
@@ -2103,8 +2528,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
   end
 
   test "does not duplicate associations when used with natural primary keys" do
-    speedometer = Speedometer.create!(id: '4')
-    speedometer.minivans.create!(minivan_id: 'a-van-red' ,name: 'a van', color: 'red')
+    speedometer = Speedometer.create!(id: "4")
+    speedometer.minivans.create!(minivan_id: "a-van-red", name: "a van", color: "red")
 
     assert_equal 1, speedometer.minivans.to_a.size, "Only one association should be present:\n#{speedometer.minivans.to_a}"
     assert_equal 1, speedometer.reload.minivans.to_a.size
@@ -2119,12 +2544,33 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal [bulb1, bulb2], car.all_bulbs.sort_by(&:id)
   end
 
-  test 'unscopes the default scope of associated model when used with include' do
+  test "can unscope and where the default scope of the associated model" do
+    Car.has_many :other_bulbs, -> { unscope(where: [:name]).where(name: "other") }, class_name: "Bulb"
+    car = Car.create!
+    bulb1 = Bulb.create! name: "defaulty", car: car
+    bulb2 = Bulb.create! name: "other",    car: car
+
+    assert_equal [bulb1], car.bulbs
+    assert_equal [bulb2], car.other_bulbs
+  end
+
+  test "can rewhere the default scope of the associated model" do
+    Car.has_many :old_bulbs, -> { rewhere(name: "old") }, class_name: "Bulb"
+    car = Car.create!
+    bulb1 = Bulb.create! name: "defaulty", car: car
+    bulb2 = Bulb.create! name: "old",      car: car
+
+    assert_equal [bulb1], car.bulbs
+    assert_equal [bulb2], car.old_bulbs
+  end
+
+  test "unscopes the default scope of associated model when used with include" do
     car = Car.create!
     bulb = Bulb.create! name: "other", car: car
 
-    assert_equal bulb, Car.find(car.id).all_bulbs.first
-    assert_equal bulb, Car.includes(:all_bulbs).find(car.id).all_bulbs.first
+    assert_equal [bulb], Car.find(car.id).all_bulbs
+    assert_equal [bulb], Car.includes(:all_bulbs).find(car.id).all_bulbs
+    assert_equal [bulb], Car.eager_load(:all_bulbs).find(car.id).all_bulbs
   end
 
   test "raises RecordNotDestroyed when replaced child can't be destroyed" do
@@ -2139,7 +2585,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal "Failed to destroy the record", error.message
   end
 
-  test 'updates counter cache when default scope is given' do
+  test "updates counter cache when default scope is given" do
     topic = DefaultRejectedTopic.create approved: true
 
     assert_difference "topic.reload.replies_count", 1 do
@@ -2147,8 +2593,8 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     end
   end
 
-  test 'dangerous association name raises ArgumentError' do
-    [:errors, 'errors', :save, 'save'].each do |name|
+  test "dangerous association name raises ArgumentError" do
+    [:errors, "errors", :save, "save"].each do |name|
       assert_raises(ArgumentError, "Association #{name} should not be allowed") do
         Class.new(ActiveRecord::Base) do
           has_many name
@@ -2157,16 +2603,16 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     end
   end
 
-  test 'passes custom context validation to validate children' do
+  test "passes custom context validation to validate children" do
     pirate = FamousPirate.new
     pirate.famous_ships << ship = FamousShip.new
 
-    assert pirate.valid?
+    assert_predicate pirate, :valid?
     assert_not pirate.valid?(:conference)
     assert_equal "can't be blank", ship.errors[:name].first
   end
 
-  test 'association with instance dependent scope' do
+  test "association with instance dependent scope" do
     bob = authors(:bob)
     Post.create!(title: "signed post by bob", body: "stuff", author: authors(:bob))
     Post.create!(title: "anonymous post", body: "more stuff", author: authors(:bob))
@@ -2176,7 +2622,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal [], authors(:david).posts_with_signature.map(&:title)
   end
 
-  test 'associations autosaves when object is already persited' do
+  test "associations autosaves when object is already persisted" do
     bulb = Bulb.create!
     tyre = Tyre.create!
 
@@ -2189,7 +2635,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal 1, car.tyres.count
   end
 
-  test 'associations replace in memory when records have the same id' do
+  test "associations replace in memory when records have the same id" do
     bulb = Bulb.create!
     car = Car.create!(bulbs: [bulb])
 
@@ -2200,7 +2646,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal "foo", car.bulbs.first.name
   end
 
-  test 'in memory replacement executes no queries' do
+  test "in memory replacement executes no queries" do
     bulb = Bulb.create!
     car = Car.create!(bulbs: [bulb])
 
@@ -2211,7 +2657,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     end
   end
 
-  test 'in memory replacements do not execute callbacks' do
+  test "in memory replacements do not execute callbacks" do
     raise_after_add = false
     klass = Class.new(ActiveRecord::Base) do
       self.table_name = :cars
@@ -2232,7 +2678,7 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     end
   end
 
-  test 'in memory replacements sets inverse instance' do
+  test "in memory replacements sets inverse instance" do
     bulb = Bulb.create!
     car = Car.create!(bulbs: [bulb])
 
@@ -2242,7 +2688,16 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_same car, new_bulb.car
   end
 
-  test 'in memory replacement maintains order' do
+  test "reattach to new objects replaces inverse association and foreign key" do
+    bulb = Bulb.create!(car: Car.create!)
+    assert bulb.car_id
+    car = Car.new
+    car.bulbs << bulb
+    assert_equal car, bulb.car
+    assert_nil bulb.car_id
+  end
+
+  test "in memory replacement maintains order" do
     first_bulb = Bulb.create!
     second_bulb = Bulb.create!
     car = Car.create!(bulbs: [first_bulb, second_bulb])
@@ -2252,4 +2707,184 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
     assert_equal [first_bulb, second_bulb], car.bulbs
   end
+
+  test "association size calculation works with default scoped selects when not previously fetched" do
+    firm = Firm.create!(name: "Firm")
+    5.times { firm.developers_with_select << Developer.create!(name: "Developer") }
+
+    same_firm = Firm.find(firm.id)
+    assert_equal 5, same_firm.developers_with_select.size
+  end
+
+  test "prevent double insertion of new object when the parent association loaded in the after save callback" do
+    reset_callbacks(:save, Bulb) do
+      Bulb.after_save { |record| record.car.bulbs.load }
+
+      car = Car.create!
+      car.bulbs << Bulb.new
+
+      assert_equal 1, car.bulbs.size
+    end
+  end
+
+  test "prevent double firing the before save callback of new object when the parent association saved in the callback" do
+    reset_callbacks(:save, Bulb) do
+      count = 0
+      Bulb.before_save { |record| record.car.save && count += 1 }
+
+      car = Car.create!
+      car.bulbs.create!
+
+      assert_equal 1, count
+    end
+  end
+
+  test "calling size on an association that has not been loaded performs a query" do
+    car = Car.create!
+    Bulb.create(car_id: car.id)
+
+    car_two = Car.create!
+
+    assert_queries(1) do
+      assert_equal 1, car.bulbs.size
+    end
+
+    assert_queries(1) do
+      assert_equal 0, car_two.bulbs.size
+    end
+  end
+
+  test "calling size on an association that has been loaded does not perform query" do
+    car = Car.create!
+    Bulb.create(car_id: car.id)
+    car.bulb_ids
+
+    car_two = Car.create!
+    car_two.bulb_ids
+
+    assert_no_queries do
+      assert_equal 1, car.bulbs.size
+    end
+
+    assert_no_queries do
+      assert_equal 0, car_two.bulbs.size
+    end
+  end
+
+  test "calling empty on an association that has not been loaded performs a query" do
+    car = Car.create!
+    Bulb.create(car_id: car.id)
+
+    car_two = Car.create!
+
+    assert_queries(1) do
+      assert_not_empty car.bulbs
+    end
+
+    assert_queries(1) do
+      assert_empty car_two.bulbs
+    end
+  end
+
+  test "calling empty on an association that has been loaded does not performs query" do
+    car = Car.create!
+    Bulb.create(car_id: car.id)
+    car.bulb_ids
+
+    car_two = Car.create!
+    car_two.bulb_ids
+
+    assert_no_queries do
+      assert_not_empty car.bulbs
+    end
+
+    assert_no_queries do
+      assert_empty car_two.bulbs
+    end
+  end
+
+  class AuthorWithErrorDestroyingAssociation < ActiveRecord::Base
+    self.table_name = "authors"
+    has_many :posts_with_error_destroying,
+      class_name: "PostWithErrorDestroying",
+      foreign_key: :author_id,
+      dependent: :destroy
+  end
+
+  class PostWithErrorDestroying < ActiveRecord::Base
+    self.table_name = "posts"
+    self.inheritance_column = nil
+    before_destroy -> { throw :abort }
+  end
+
+  def test_destroy_does_not_raise_when_association_errors_on_destroy
+    assert_no_difference "AuthorWithErrorDestroyingAssociation.count" do
+      author = AuthorWithErrorDestroyingAssociation.first
+
+      assert_not author.destroy
+    end
+  end
+
+  def test_destroy_with_bang_bubbles_errors_from_associations
+    error = assert_raises ActiveRecord::RecordNotDestroyed do
+      AuthorWithErrorDestroyingAssociation.first.destroy!
+    end
+
+    assert_instance_of PostWithErrorDestroying, error.record
+  end
+
+  def test_ids_reader_memoization
+    car = Car.create!(name: "Tofaş")
+    bulb = Bulb.create!(car: car)
+
+    assert_equal [bulb.id], car.bulb_ids
+    assert_no_queries { car.bulb_ids }
+
+    bulb2 = car.bulbs.create!
+
+    assert_equal [bulb.id, bulb2.id], car.bulb_ids
+    assert_no_queries { car.bulb_ids }
+  end
+
+  def test_loading_association_in_validate_callback_doesnt_affect_persistence
+    reset_callbacks(:validation, Bulb) do
+      Bulb.after_validation { |record| record.car.bulbs.load }
+
+      car = Car.create!(name: "Car")
+      bulb = car.bulbs.create!
+
+      assert_equal [bulb], car.bulbs
+    end
+  end
+
+  def test_create_children_could_be_rolled_back_by_after_save
+    firm = Firm.create!(name: "A New Firm, Inc")
+    assert_no_difference "Client.count" do
+      client = firm.clients.create(name: "New Client") do |cli|
+        cli.rollback_on_save = true
+        assert_not cli.rollback_on_create_called
+      end
+      assert client.rollback_on_create_called
+    end
+  end
+
+  private
+
+    def force_signal37_to_load_all_clients_of_firm
+      companies(:first_firm).clients_of_firm.load_target
+    end
+
+    def reset_callbacks(kind, klass)
+      old_callbacks = {}
+      old_callbacks[klass] = klass.send("_#{kind}_callbacks").dup
+      klass.subclasses.each do |subclass|
+        old_callbacks[subclass] = subclass.send("_#{kind}_callbacks").dup
+      end
+      yield
+    ensure
+      klass.send("_#{kind}_callbacks=", old_callbacks[klass])
+      klass.subclasses.each do |subclass|
+        subclass.send("_#{kind}_callbacks=", old_callbacks[subclass])
+      end
+    end
 end
diff --git a/activerecord/test/cases/associations/has_many_through_associations_test.rb b/activerecord/test/cases/associations/has_many_through_associations_test.rb
index c34387f06d..7b405c74c4 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -1,31 +1,38 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/person'
-require 'models/reference'
-require 'models/job'
-require 'models/reader'
-require 'models/comment'
-require 'models/rating'
-require 'models/tag'
-require 'models/tagging'
-require 'models/author'
-require 'models/owner'
-require 'models/pet'
-require 'models/toy'
-require 'models/contract'
-require 'models/company'
-require 'models/developer'
-require 'models/computer'
-require 'models/subscriber'
-require 'models/book'
-require 'models/subscription'
-require 'models/essay'
-require 'models/category'
-require 'models/categorization'
-require 'models/member'
-require 'models/membership'
-require 'models/club'
-require 'models/organization'
+require "models/post"
+require "models/person"
+require "models/reference"
+require "models/job"
+require "models/reader"
+require "models/comment"
+require "models/rating"
+require "models/tag"
+require "models/tagging"
+require "models/author"
+require "models/owner"
+require "models/pet"
+require "models/pet_treasure"
+require "models/toy"
+require "models/treasure"
+require "models/contract"
+require "models/company"
+require "models/developer"
+require "models/computer"
+require "models/subscriber"
+require "models/book"
+require "models/subscription"
+require "models/essay"
+require "models/category"
+require "models/categorization"
+require "models/member"
+require "models/membership"
+require "models/club"
+require "models/organization"
+require "models/user"
+require "models/family"
+require "models/family_tree"
 
 class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   fixtures :posts, :readers, :people, :comments, :authors, :categories, :taggings, :tags,
@@ -35,8 +42,13 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   # Dummies to force column loads so query counts are clean.
   def setup
-    Person.create :first_name => 'gummy'
-    Reader.create :person_id => 0, :post_id => 0
+    Person.create first_name: "gummy"
+    Reader.create person_id: 0, post_id: 0
+  end
+
+  def test_marshal_dump
+    preloaded = Post.includes(:first_blue_tags).first
+    assert_equal preloaded, Marshal.load(Marshal.dump(preloaded))
   end
 
   def test_preload_sti_rhs_class
@@ -47,9 +59,9 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_preload_sti_middle_relation
-    club = Club.create!(name: 'Aaron cool banana club')
-    member1 = Member.create!(name: 'Aaron')
-    member2 = Member.create!(name: 'Cat')
+    club = Club.create!(name: "Aaron cool banana club")
+    member1 = Member.create!(name: "Aaron")
+    member2 = Member.create!(name: "Cat")
 
     SuperMembership.create! club: club, member: member1
     CurrentMembership.create! club: club, member: member2
@@ -59,21 +71,26 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
                  club1.members.sort_by(&:id)
   end
 
-  def make_model(name)
-    Class.new(ActiveRecord::Base) { define_singleton_method(:name) { name } }
+  def test_preload_multiple_instances_of_the_same_record
+    club = Club.create!(name: "Aaron cool banana club")
+    Membership.create! club: club, member: Member.create!(name: "Aaron")
+    Membership.create! club: club, member: Member.create!(name: "Bob")
+
+    preloaded_clubs = Club.joins(:memberships).preload(:membership).to_a
+    assert_no_queries { preloaded_clubs.each(&:membership) }
   end
 
-  def test_ordered_habtm
+  def test_ordered_has_many_through
     person_prime = Class.new(ActiveRecord::Base) do
-      def self.name; 'Person'; end
+      def self.name; "Person"; end
 
       has_many :readers
-      has_many :posts, -> { order('posts.id DESC') }, :through => :readers
+      has_many :posts, -> { order("posts.id DESC") }, through: :readers
     end
     posts = person_prime.includes(:posts).first.posts
 
     assert_operator posts.length, :>, 1
-    posts.each_cons(2) do |left,right|
+    posts.each_cons(2) do |left, right|
       assert_operator left.id, :>, right.id
     end
   end
@@ -83,7 +100,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     subscription = make_model "Subscription"
     subscriber   = make_model "Subscriber"
 
-    subscriber.primary_key = 'nick'
+    subscriber.primary_key = "nick"
     subscription.belongs_to :book,       anonymous_class: book
     subscription.belongs_to :subscriber, anonymous_class: subscriber
 
@@ -104,8 +121,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   def test_no_pk_join_table_append
     lesson, _, student = make_no_pk_hm_t
 
-    sicp = lesson.new(:name => "SICP")
-    ben = student.new(:name => "Ben Bitdiddle")
+    sicp = lesson.new(name: "SICP")
+    ben = student.new(name: "Ben Bitdiddle")
     sicp.students << ben
     assert sicp.save!
   end
@@ -113,17 +130,17 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   def test_no_pk_join_table_delete
     lesson, lesson_student, student = make_no_pk_hm_t
 
-    sicp = lesson.new(:name => "SICP")
-    ben = student.new(:name => "Ben Bitdiddle")
-    louis = student.new(:name => "Louis Reasoner")
+    sicp = lesson.new(name: "SICP")
+    ben = student.new(name: "Ben Bitdiddle")
+    louis = student.new(name: "Louis Reasoner")
     sicp.students << ben
     sicp.students << louis
     assert sicp.save!
 
     sicp.students.reload
     assert_operator lesson_student.count, :>=, 2
-    assert_no_difference('student.count') do
-      assert_difference('lesson_student.count', -2) do
+    assert_no_difference("student.count") do
+      assert_difference("lesson_student.count", -2) do
         sicp.students.destroy(*student.all.to_a)
       end
     end
@@ -137,8 +154,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       after_destroy_called = true
     end
 
-    sicp = lesson.new(:name => "SICP")
-    ben = student.new(:name => "Ben Bitdiddle")
+    sicp = lesson.new(name: "SICP")
+    ben = student.new(name: "Ben Bitdiddle")
     sicp.students << ben
     assert sicp.save!
 
@@ -147,20 +164,6 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     assert after_destroy_called, "after destroy should be called"
   end
 
-  def make_no_pk_hm_t
-    lesson = make_model 'Lesson'
-    student = make_model 'Student'
-
-    lesson_student = make_model 'LessonStudent'
-    lesson_student.table_name = 'lessons_students'
-
-    lesson_student.belongs_to :lesson, :anonymous_class => lesson
-    lesson_student.belongs_to :student, :anonymous_class => student
-    lesson.has_many :lesson_students, :anonymous_class => lesson_student
-    lesson.has_many :students, :through => :lesson_students, :anonymous_class => student
-    [lesson, lesson_student, student]
-  end
-
   def test_pk_is_not_required_for_join
     post  = Post.includes(:scategories).first
     post2 = Post.includes(:categories).first
@@ -173,7 +176,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     person = Person.new
     post = Post.new
     person.posts << post
-    assert person.posts.include?(post)
+    assert_includes person.posts, post
   end
 
   def test_associate_existing
@@ -185,18 +188,18 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     end
 
     assert_queries(1) do
-      assert post.people.include?(person)
+      assert_includes post.people, person
     end
 
-    assert post.reload.people(true).include?(person)
+    assert_includes post.reload.people.reload, person
   end
 
   def test_delete_all_for_with_dependent_option_destroy
     person = people(:david)
     assert_equal 1, person.jobs_with_dependent_destroy.count
 
-    assert_no_difference 'Job.count' do
-      assert_difference 'Reference.count', -1 do
+    assert_no_difference "Job.count" do
+      assert_difference "Reference.count", -1 do
         person.reload.jobs_with_dependent_destroy.delete_all
       end
     end
@@ -206,8 +209,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     person = people(:david)
     assert_equal 1, person.jobs_with_dependent_nullify.count
 
-    assert_no_difference 'Job.count' do
-      assert_no_difference 'Reference.count' do
+    assert_no_difference "Job.count" do
+      assert_no_difference "Reference.count" do
         person.reload.jobs_with_dependent_nullify.delete_all
       end
     end
@@ -217,8 +220,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     person = people(:david)
     assert_equal 1, person.jobs_with_dependent_delete_all.count
 
-    assert_no_difference 'Job.count' do
-      assert_difference 'Reference.count', -1 do
+    assert_no_difference "Job.count" do
+      assert_difference "Reference.count", -1 do
         person.reload.jobs_with_dependent_delete_all.delete_all
       end
     end
@@ -229,14 +232,14 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     post   = posts(:thinking)
     post.people.concat [person]
     assert_equal 1, post.people.size
-    assert_equal 1, post.people(true).size
+    assert_equal 1, post.people.reload.size
   end
 
   def test_associate_existing_record_twice_should_add_to_target_twice
     post   = posts(:thinking)
     person = people(:david)
 
-    assert_difference 'post.people.to_a.count', 2 do
+    assert_difference "post.people.to_a.count", 2 do
       post.people << person
       post.people << person
     end
@@ -246,7 +249,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     post   = posts(:thinking)
     person = people(:david)
 
-    assert_difference 'post.people.count', 2 do
+    assert_difference "post.people.count", 2 do
       post.people << person
       post.people << person
     end
@@ -259,20 +262,23 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     post.people << person
     post.people << person
 
-    counts = ['post.people.count', 'post.people.to_a.count', 'post.readers.count', 'post.readers.to_a.count']
+    counts = ["post.people.count", "post.people.to_a.count", "post.readers.count", "post.readers.to_a.count"]
     assert_difference counts, -2 do
       post.people.delete(person)
     end
 
-    assert !post.people.reload.include?(person)
+    assert_not_includes post.people.reload, person
   end
 
   def test_associating_new
     assert_queries(1) { posts(:thinking) }
     new_person = nil # so block binding catches it
 
-    assert_queries(0) do
-      new_person = Person.new :first_name => 'bob'
+    # Load schema information so we don't query below if running just this test.
+    Person.define_attribute_methods
+
+    assert_no_queries do
+      new_person = Person.new first_name: "bob"
     end
 
     # Associating new records always saves them
@@ -282,59 +288,73 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     end
 
     assert_queries(1) do
-      assert posts(:thinking).people.include?(new_person)
+      assert_includes posts(:thinking).people, new_person
     end
 
-    assert posts(:thinking).reload.people(true).include?(new_person)
+    assert_includes posts(:thinking).reload.people.reload, new_person
   end
 
   def test_associate_new_by_building
     assert_queries(1) { posts(:thinking) }
 
-    assert_queries(0) do
-      posts(:thinking).people.build(:first_name => "Bob")
-      posts(:thinking).people.new(:first_name => "Ted")
+    # Load schema information so we don't query below if running just this test.
+    Person.define_attribute_methods
+
+    assert_no_queries do
+      posts(:thinking).people.build(first_name: "Bob")
+      posts(:thinking).people.new(first_name: "Ted")
     end
 
     # Should only need to load the association once
     assert_queries(1) do
-      assert posts(:thinking).people.collect(&:first_name).include?("Bob")
-      assert posts(:thinking).people.collect(&:first_name).include?("Ted")
+      assert_includes posts(:thinking).people.collect(&:first_name), "Bob"
+      assert_includes posts(:thinking).people.collect(&:first_name), "Ted"
     end
 
     # 2 queries for each new record (1 to save the record itself, 1 for the join model)
     #    * 2 new records = 4
     # + 1 query to save the actual post = 5
     assert_queries(5) do
-      posts(:thinking).body += '-changed'
+      posts(:thinking).body += "-changed"
       posts(:thinking).save
     end
 
-    assert posts(:thinking).reload.people(true).collect(&:first_name).include?("Bob")
-    assert posts(:thinking).reload.people(true).collect(&:first_name).include?("Ted")
+    assert_includes posts(:thinking).reload.people.reload.collect(&:first_name), "Bob"
+    assert_includes posts(:thinking).reload.people.reload.collect(&:first_name), "Ted"
   end
 
   def test_build_then_save_with_has_many_inverse
     post   = posts(:thinking)
-    person = post.people.build(:first_name => "Bob")
+    person = post.people.build(first_name: "Bob")
     person.save
     post.reload
 
-    assert post.people.include?(person)
+    assert_includes post.people, person
   end
 
   def test_build_then_save_with_has_one_inverse
     post   = posts(:thinking)
-    person = post.single_people.build(:first_name => "Bob")
+    person = post.single_people.build(first_name: "Bob")
     person.save
     post.reload
 
-    assert post.single_people.include?(person)
+    assert_includes post.single_people, person
+  end
+
+  def test_build_then_remove_then_save
+    post = posts(:thinking)
+    post.people.build(first_name: "Bob")
+    ted = post.people.build(first_name: "Ted")
+    post.people.delete(ted)
+    post.save!
+    post.reload
+
+    assert_equal ["Bob"], post.people.collect(&:first_name)
   end
 
   def test_both_parent_ids_set_when_saving_new
-    post = Post.new(title: 'Hello', body: 'world')
-    person = Person.new(first_name: 'Sean')
+    post = Post.new(title: "Hello", body: "world")
+    person = Person.new(first_name: "Sean")
 
     post.people = [person]
     post.save
@@ -346,17 +366,17 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_delete_association
-    assert_queries(2){posts(:welcome);people(:michael); }
+    assert_queries(2) { posts(:welcome);people(:michael); }
 
     assert_queries(1) do
       posts(:welcome).people.delete(people(:michael))
     end
 
     assert_queries(1) do
-      assert posts(:welcome).people.empty?
+      assert_empty posts(:welcome).people
     end
 
-    assert posts(:welcome).reload.people(true).empty?
+    assert_empty posts(:welcome).reload.people.reload
   end
 
   def test_destroy_association
@@ -366,8 +386,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       end
     end
 
-    assert posts(:welcome).reload.people.empty?
-    assert posts(:welcome).people(true).empty?
+    assert_empty posts(:welcome).reload.people
+    assert_empty posts(:welcome).people.reload
   end
 
   def test_destroy_all
@@ -377,8 +397,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       end
     end
 
-    assert posts(:welcome).reload.people.empty?
-    assert posts(:welcome).people(true).empty?
+    assert_empty posts(:welcome).reload.people
+    assert_empty posts(:welcome).people.reload
   end
 
   def test_should_raise_exception_for_destroying_mismatching_records
@@ -392,15 +412,15 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
     person    = people(:michael)
     job       = jobs(:magician)
-    reference = Reference.where(:job_id => job.id, :person_id => person.id).first
+    reference = Reference.where(job_id: job.id, person_id: person.id).first
 
-    assert_no_difference ['Job.count', 'Reference.count'] do
-      assert_difference 'person.jobs.count', -1 do
+    assert_no_difference ["Job.count", "Reference.count"] do
+      assert_difference "person.jobs.count", -1 do
         person.jobs_with_dependent_nullify.delete(job)
       end
     end
 
-    assert_equal nil, reference.reload.job_id
+    assert_nil reference.reload.job_id
   ensure
     Reference.make_comments = false
   end
@@ -414,14 +434,14 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     # Make sure we're not deleting everything
     assert person.jobs.count >= 2
 
-    assert_no_difference 'Job.count' do
-      assert_difference ['person.jobs.count', 'Reference.count'], -1 do
+    assert_no_difference "Job.count" do
+      assert_difference ["person.jobs.count", "Reference.count"], -1 do
         person.jobs_with_dependent_delete_all.delete(job)
       end
     end
 
     # Check that the destroy callback on Reference did not run
-    assert_equal nil, person.reload.comments
+    assert_nil person.reload.comments
   ensure
     Reference.make_comments = false
   end
@@ -435,8 +455,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     # Make sure we're not deleting everything
     assert person.jobs.count >= 2
 
-    assert_no_difference 'Job.count' do
-      assert_difference ['person.jobs.count', 'Reference.count'], -1 do
+    assert_no_difference "Job.count" do
+      assert_difference ["person.jobs.count", "Reference.count"], -1 do
         person.jobs_with_dependent_destroy.delete(job)
       end
     end
@@ -453,8 +473,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     # Create a reference which is not linked to a job. This should not be destroyed.
     person.references.create!
 
-    assert_no_difference 'Job.count' do
-      assert_difference 'Reference.count', -person.jobs.count do
+    assert_no_difference "Job.count" do
+      assert_difference "Reference.count", -person.jobs.count do
         person.destroy
       end
     end
@@ -466,8 +486,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     # Create a reference which is not linked to a job. This should not be destroyed.
     person.references.create!
 
-    assert_no_difference 'Job.count' do
-      assert_difference 'Reference.count', -person.jobs.count do
+    assert_no_difference "Job.count" do
+      assert_difference "Reference.count", -person.jobs.count do
         person.destroy
       end
     end
@@ -478,41 +498,41 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
     references = person.references.to_a
 
-    assert_no_difference ['Reference.count', 'Job.count'] do
+    assert_no_difference ["Reference.count", "Job.count"] do
       person.destroy
     end
 
     references.each do |reference|
-      assert_equal nil, reference.reload.job_id
+      assert_nil reference.reload.job_id
     end
   end
 
   def test_update_counter_caches_on_delete
     post = posts(:welcome)
-    tag  = post.tags.create!(:name => 'doomed')
+    tag  = post.tags.create!(name: "doomed")
 
-    assert_difference ['post.reload.tags_count'], -1 do
+    assert_difference ["post.reload.tags_count"], -1 do
       posts(:welcome).tags.delete(tag)
     end
   end
 
   def test_update_counter_caches_on_delete_with_dependent_destroy
     post = posts(:welcome)
-    tag  = post.tags.create!(:name => 'doomed')
+    tag  = post.tags.create!(name: "doomed")
     post.update_columns(tags_with_destroy_count: post.tags.count)
 
-    assert_difference ['post.reload.tags_with_destroy_count'], -1 do
+    assert_difference ["post.reload.tags_with_destroy_count"], -1 do
       posts(:welcome).tags_with_destroy.delete(tag)
     end
   end
 
   def test_update_counter_caches_on_delete_with_dependent_nullify
     post = posts(:welcome)
-    tag  = post.tags.create!(:name => 'doomed')
+    tag  = post.tags.create!(name: "doomed")
     post.update_columns(tags_with_nullify_count: post.tags.count)
 
-    assert_no_difference 'post.reload.tags_count' do
-      assert_difference 'post.reload.tags_with_nullify_count', -1 do
+    assert_no_difference "post.reload.tags_count" do
+      assert_difference "post.reload.tags_with_nullify_count", -1 do
         posts(:welcome).tags_with_nullify.delete(tag)
       end
     end
@@ -520,7 +540,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_update_counter_caches_on_replace_association
     post = posts(:welcome)
-    tag  = post.tags.create!(:name => 'doomed')
+    tag  = post.tags.create!(name: "doomed")
     tag.tagged_posts << posts(:thinking)
 
     tag.tagged_posts = []
@@ -531,15 +551,25 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_update_counter_caches_on_destroy
     post = posts(:welcome)
-    tag  = post.tags.create!(name: 'doomed')
+    tag  = post.tags.create!(name: "doomed")
 
-    assert_difference 'post.reload.tags_count', -1 do
+    assert_difference "post.reload.tags_count", -1 do
       tag.tagged_posts.destroy(post)
     end
   end
 
+  def test_update_counter_caches_on_destroy_with_indestructible_through_record
+    post = posts(:welcome)
+    tag  = post.indestructible_tags.create!(name: "doomed")
+    post.update_columns(indestructible_tags_count: post.indestructible_tags.count)
+
+    assert_no_difference "post.reload.indestructible_tags_count" do
+      posts(:welcome).indestructible_tags.destroy(tag)
+    end
+  end
+
   def test_replace_association
-    assert_queries(4){posts(:welcome);people(:david);people(:michael); posts(:welcome).people(true)}
+    assert_queries(4) { posts(:welcome);people(:david);people(:michael); posts(:welcome).people.reload }
 
     # 1 query to delete the existing reader (michael)
     # 1 query to associate the new reader (david)
@@ -547,35 +577,35 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       posts(:welcome).people = [people(:david)]
     end
 
-    assert_queries(0){
-      assert posts(:welcome).people.include?(people(:david))
-      assert !posts(:welcome).people.include?(people(:michael))
-    }
+    assert_no_queries do
+      assert_includes posts(:welcome).people, people(:david)
+      assert_not_includes posts(:welcome).people, people(:michael)
+    end
 
-    assert posts(:welcome).reload.people(true).include?(people(:david))
-    assert !posts(:welcome).reload.people(true).include?(people(:michael))
+    assert_includes posts(:welcome).reload.people.reload, people(:david)
+    assert_not_includes posts(:welcome).reload.people.reload, people(:michael)
   end
 
   def test_replace_order_is_preserved
     posts(:welcome).people.clear
     posts(:welcome).people = [people(:david), people(:michael)]
-    assert_equal [people(:david).id, people(:michael).id], posts(:welcome).readers.order('id').map(&:person_id)
+    assert_equal [people(:david).id, people(:michael).id], posts(:welcome).readers.order("id").map(&:person_id)
 
     # Test the inverse order in case the first success was a coincidence
     posts(:welcome).people.clear
     posts(:welcome).people = [people(:michael), people(:david)]
-    assert_equal [people(:michael).id, people(:david).id], posts(:welcome).readers.order('id').map(&:person_id)
+    assert_equal [people(:michael).id, people(:david).id], posts(:welcome).readers.order("id").map(&:person_id)
   end
 
   def test_replace_by_id_order_is_preserved
     posts(:welcome).people.clear
     posts(:welcome).person_ids = [people(:david).id, people(:michael).id]
-    assert_equal [people(:david).id, people(:michael).id], posts(:welcome).readers.order('id').map(&:person_id)
+    assert_equal [people(:david).id, people(:michael).id], posts(:welcome).readers.order("id").map(&:person_id)
 
     # Test the inverse order in case the first success was a coincidence
     posts(:welcome).people.clear
     posts(:welcome).person_ids = [people(:michael).id, people(:david).id]
-    assert_equal [people(:michael).id, people(:david).id], posts(:welcome).readers.order('id').map(&:person_id)
+    assert_equal [people(:michael).id, people(:david).id], posts(:welcome).readers.order("id").map(&:person_id)
   end
 
   def test_associate_with_create
@@ -584,15 +614,15 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     # 1 query for the new record, 1 for the join table record
     # No need to update the actual collection yet!
     assert_queries(2) do
-      posts(:thinking).people.create(:first_name=>"Jeb")
+      posts(:thinking).people.create(first_name: "Jeb")
     end
 
     # *Now* we actually need the collection so it's loaded
     assert_queries(1) do
-      assert posts(:thinking).people.collect(&:first_name).include?("Jeb")
+      assert_includes posts(:thinking).people.collect(&:first_name), "Jeb"
     end
 
-    assert posts(:thinking).reload.people(true).collect(&:first_name).include?("Jeb")
+    assert_includes posts(:thinking).reload.people.reload.collect(&:first_name), "Jeb"
   end
 
   def test_through_record_is_built_when_created_with_where
@@ -603,82 +633,82 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_associate_with_create_and_no_options
     peeps = posts(:thinking).people.count
-    posts(:thinking).people.create(:first_name => 'foo')
+    posts(:thinking).people.create(first_name: "foo")
     assert_equal peeps + 1, posts(:thinking).people.count
   end
 
   def test_associate_with_create_with_through_having_conditions
     impatient_people = posts(:thinking).impatient_people.count
-    posts(:thinking).impatient_people.create!(:first_name => 'foo')
+    posts(:thinking).impatient_people.create!(first_name: "foo")
     assert_equal impatient_people + 1, posts(:thinking).impatient_people.count
   end
 
   def test_associate_with_create_exclamation_and_no_options
     peeps = posts(:thinking).people.count
-    posts(:thinking).people.create!(:first_name => 'foo')
+    posts(:thinking).people.create!(first_name: "foo")
     assert_equal peeps + 1, posts(:thinking).people.count
   end
 
   def test_create_on_new_record
     p = Post.new
 
-    error = assert_raises(ActiveRecord::RecordNotSaved) { p.people.create(:first_name => "mew") }
+    error = assert_raises(ActiveRecord::RecordNotSaved) { p.people.create(first_name: "mew") }
     assert_equal "You cannot call create unless the parent is saved", error.message
 
-    error = assert_raises(ActiveRecord::RecordNotSaved) { p.people.create!(:first_name => "snow") }
+    error = assert_raises(ActiveRecord::RecordNotSaved) { p.people.create!(first_name: "snow") }
     assert_equal "You cannot call create unless the parent is saved", error.message
   end
 
   def test_associate_with_create_and_invalid_options
     firm = companies(:first_firm)
-    assert_no_difference('firm.developers.count') { assert_nothing_raised { firm.developers.create(:name => '0') } }
+    assert_no_difference("firm.developers.count") { assert_nothing_raised { firm.developers.create(name: "0") } }
   end
 
   def test_associate_with_create_and_valid_options
     firm = companies(:first_firm)
-    assert_difference('firm.developers.count', 1) { firm.developers.create(:name => 'developer') }
+    assert_difference("firm.developers.count", 1) { firm.developers.create(name: "developer") }
   end
 
   def test_associate_with_create_bang_and_invalid_options
     firm = companies(:first_firm)
-    assert_no_difference('firm.developers.count') { assert_raises(ActiveRecord::RecordInvalid) { firm.developers.create!(:name => '0') } }
+    assert_no_difference("firm.developers.count") { assert_raises(ActiveRecord::RecordInvalid) { firm.developers.create!(name: "0") } }
   end
 
   def test_associate_with_create_bang_and_valid_options
     firm = companies(:first_firm)
-    assert_difference('firm.developers.count', 1) { firm.developers.create!(:name => 'developer') }
+    assert_difference("firm.developers.count", 1) { firm.developers.create!(name: "developer") }
   end
 
   def test_push_with_invalid_record
     firm = companies(:first_firm)
-    assert_raises(ActiveRecord::RecordInvalid) { firm.developers << Developer.new(:name => '0') }
+    assert_raises(ActiveRecord::RecordInvalid) { firm.developers << Developer.new(name: "0") }
   end
 
   def test_push_with_invalid_join_record
     repair_validations(Contract) do
-      Contract.validate {|r| r.errors[:base] << 'Invalid Contract' }
+      Contract.validate { |r| r.errors[:base] << "Invalid Contract" }
 
       firm = companies(:first_firm)
-      lifo = Developer.new(:name => 'lifo')
+      lifo = Developer.new(name: "lifo")
       assert_raises(ActiveRecord::RecordInvalid) { firm.developers << lifo }
 
-      lifo = Developer.create!(:name => 'lifo')
+      lifo = Developer.create!(name: "lifo")
       assert_raises(ActiveRecord::RecordInvalid) { firm.developers << lifo }
     end
   end
 
   def test_clear_associations
-    assert_queries(2) { posts(:welcome);posts(:welcome).people(true) }
+    assert_queries(2) { posts(:welcome);posts(:welcome).people.reload }
 
     assert_queries(1) do
       posts(:welcome).people.clear
     end
 
-    assert_queries(0) do
-      assert posts(:welcome).people.empty?
+    assert_no_queries do
+      assert_empty posts(:welcome).people
     end
 
-    assert posts(:welcome).reload.people(true).empty?
+    assert_empty posts(:welcome).reload.people.reload
   end
 
   def test_association_callback_ordering
@@ -692,7 +722,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       [:added, :after, "Michael"]
     ], log.last(2)
 
-    post.people_with_callbacks.push(people(:david), Person.create!(:first_name => "Bob"), Person.new(:first_name => "Lary"))
+    post.people_with_callbacks.push(people(:david), Person.create!(first_name: "Bob"), Person.new(first_name: "Lary"))
     assert_equal [
       [:added, :before, "David"],
       [:added, :after, "David"],
@@ -700,21 +730,21 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       [:added, :after, "Bob"],
       [:added, :before, "Lary"],
       [:added, :after, "Lary"]
-    ],log.last(6)
+    ], log.last(6)
 
-    post.people_with_callbacks.build(:first_name => "Ted")
+    post.people_with_callbacks.build(first_name: "Ted")
     assert_equal [
       [:added, :before, "Ted"],
       [:added, :after, "Ted"]
     ], log.last(2)
 
-    post.people_with_callbacks.create(:first_name => "Sam")
+    post.people_with_callbacks.create(first_name: "Sam")
     assert_equal [
       [:added, :before, "Sam"],
       [:added, :after, "Sam"]
     ], log.last(2)
 
-    post.people_with_callbacks = [people(:michael),people(:david), Person.new(:first_name => "Julian"), Person.create!(:first_name => "Roger")]
+    post.people_with_callbacks = [people(:michael), people(:david), Person.new(first_name: "Julian"), Person.create!(first_name: "Roger")]
     assert_equal((%w(Ted Bob Sam Lary) * 2).sort, log[-12..-5].collect(&:last).sort)
     assert_equal [
       [:added, :before, "Julian"],
@@ -722,12 +752,24 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
       [:added, :before, "Roger"],
       [:added, :after, "Roger"]
     ], log.last(4)
+
+    post.people_with_callbacks.build { |person| person.first_name = "Ted" }
+    assert_equal [
+      [:added, :before, "Ted"],
+      [:added, :after, "Ted"]
+    ], log.last(2)
+
+    post.people_with_callbacks.create { |person| person.first_name = "Sam" }
+    assert_equal [
+      [:added, :before, "Sam"],
+      [:added, :after, "Sam"]
+    ], log.last(2)
   end
 
   def test_dynamic_find_should_respect_association_include
     # SQL error in sort clause if :include is not included
     # due to Unknown column 'comments.id'
-    assert Person.find(1).posts_with_comments_sorted_by_comment_id.find_by_title('Welcome to the weblog')
+    assert Person.find(1).posts_with_comments_sorted_by_comment_id.find_by_title("Welcome to the weblog")
   end
 
   def test_count_with_include_should_alias_join_table
@@ -743,15 +785,16 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_get_ids_for_has_many_through_with_conditions_should_not_preload
-    Tagging.create!(:taggable_type => 'Post', :taggable_id => posts(:welcome).id, :tag => tags(:misc))
-    ActiveRecord::Associations::Preloader.expects(:new).never
-    posts(:welcome).misc_tag_ids
+    Tagging.create!(taggable_type: "Post", taggable_id: posts(:welcome).id, tag: tags(:misc))
+    assert_not_called(ActiveRecord::Associations::Preloader, :new) do
+      posts(:welcome).misc_tag_ids
+    end
   end
 
   def test_get_ids_for_loaded_associations
     person = people(:michael)
-    person.posts(true)
-    assert_queries(0) do
+    person.posts.reload
+    assert_no_queries do
       person.post_ids
       person.post_ids
     end
@@ -759,29 +802,30 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_get_ids_for_unloaded_associations_does_not_load_them
     person = people(:michael)
-    assert !person.posts.loaded?
+    assert_not_predicate person.posts, :loaded?
     assert_equal [posts(:welcome).id, posts(:authorless).id].sort, person.post_ids.sort
-    assert !person.posts.loaded?
+    assert_not_predicate person.posts, :loaded?
   end
 
   def test_association_proxy_transaction_method_starts_transaction_in_association_class
-    Tag.expects(:transaction)
-    Post.first.tags.transaction do
-      # nothing
+    assert_called(Tag, :transaction) do
+      Post.first.tags.transaction do
+        # nothing
+      end
     end
   end
 
   def test_has_many_association_through_a_belongs_to_association_where_the_association_doesnt_exist
-    post = Post.create!(:title => "TITLE", :body => "BODY")
+    post = Post.create!(title: "TITLE", body: "BODY")
     assert_equal [], post.author_favorites
   end
 
   def test_has_many_association_through_a_belongs_to_association
     author = authors(:mary)
-    post = Post.create!(:author => author, :title => "TITLE", :body => "BODY")
-    author.author_favorites.create(:favorite_author_id => 1)
-    author.author_favorites.create(:favorite_author_id => 2)
-    author.author_favorites.create(:favorite_author_id => 3)
+    post = Post.create!(author: author, title: "TITLE", body: "BODY")
+    author.author_favorites.create(favorite_author_id: 1)
+    author.author_favorites.create(favorite_author_id: 2)
+    author.author_favorites.create(favorite_author_id: 3)
     assert_equal post.author.author_favorites, post.author_favorites
   end
 
@@ -805,37 +849,37 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_modifying_has_many_through_has_one_reflection_should_raise
     [
-      lambda { authors(:david).very_special_comments = [VerySpecialComment.create!(:body => "Gorp!", :post_id => 1011), VerySpecialComment.create!(:body => "Eep!", :post_id => 1012)] },
-      lambda { authors(:david).very_special_comments << VerySpecialComment.create!(:body => "Hoohah!", :post_id => 1013) },
+      lambda { authors(:david).very_special_comments = [VerySpecialComment.create!(body: "Gorp!", post_id: 1011), VerySpecialComment.create!(body: "Eep!", post_id: 1012)] },
+      lambda { authors(:david).very_special_comments << VerySpecialComment.create!(body: "Hoohah!", post_id: 1013) },
       lambda { authors(:david).very_special_comments.delete(authors(:david).very_special_comments.first) },
-    ].each {|block| assert_raise(ActiveRecord::HasManyThroughCantAssociateThroughHasOneOrManyReflection, &block) }
+    ].each { |block| assert_raise(ActiveRecord::HasManyThroughCantAssociateThroughHasOneOrManyReflection, &block) }
   end
 
   def test_has_many_association_through_a_has_many_association_to_self
-    sarah = Person.create!(:first_name => 'Sarah', :primary_contact_id => people(:susan).id, :gender => 'F', :number1_fan_id => 1)
-    john = Person.create!(:first_name => 'John', :primary_contact_id => sarah.id, :gender => 'M', :number1_fan_id => 1)
+    sarah = Person.create!(first_name: "Sarah", primary_contact_id: people(:susan).id, gender: "F", number1_fan_id: 1)
+    john = Person.create!(first_name: "John", primary_contact_id: sarah.id, gender: "M", number1_fan_id: 1)
     assert_equal sarah.agents, [john]
-    assert_equal people(:susan).agents.flat_map(&:agents), people(:susan).agents_of_agents
+    assert_equal people(:susan).agents.flat_map(&:agents).sort, people(:susan).agents_of_agents.sort
   end
 
   def test_associate_existing_with_nonstandard_primary_key_on_belongs_to
-    Categorization.create(:author => authors(:mary), :named_category_name => categories(:general).name)
+    Categorization.create(author: authors(:mary), named_category_name: categories(:general).name)
     assert_equal categories(:general), authors(:mary).named_categories.first
   end
 
   def test_collection_build_with_nonstandard_primary_key_on_belongs_to
     author   = authors(:mary)
-    category = author.named_categories.build(:name => "Primary")
+    category = author.named_categories.build(name: "Primary")
     author.save
-    assert Categorization.exists?(:author_id => author.id, :named_category_name => category.name)
-    assert author.named_categories(true).include?(category)
+    assert Categorization.exists?(author_id: author.id, named_category_name: category.name)
+    assert_includes author.named_categories.reload, category
   end
 
   def test_collection_create_with_nonstandard_primary_key_on_belongs_to
     author   = authors(:mary)
-    category = author.named_categories.create(:name => "Primary")
-    assert Categorization.exists?(:author_id => author.id, :named_category_name => category.name)
-    assert author.named_categories(true).include?(category)
+    category = author.named_categories.create(name: "Primary")
+    assert Categorization.exists?(author_id: author.id, named_category_name: category.name)
+    assert_includes author.named_categories.reload, category
   end
 
   def test_collection_exists
@@ -847,10 +891,10 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_collection_delete_with_nonstandard_primary_key_on_belongs_to
     author   = authors(:mary)
-    category = author.named_categories.create(:name => "Primary")
+    category = author.named_categories.create(name: "Primary")
     author.named_categories.delete(category)
-    assert !Categorization.exists?(:author_id => author.id, :named_category_name => category.name)
-    assert author.named_categories(true).empty?
+    assert_not Categorization.exists?(author_id: author.id, named_category_name: category.name)
+    assert_empty author.named_categories.reload
   end
 
   def test_collection_singular_ids_getter_with_string_primary_keys
@@ -867,35 +911,52 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal [dev], company.developers
   end
 
+  def test_collection_singular_ids_setter_with_required_type_cast
+    company = companies(:rails_core)
+    dev = Developer.first
+
+    company.developer_ids = [dev.id.to_s]
+    assert_equal [dev], company.developers
+  end
+
   def test_collection_singular_ids_setter_with_string_primary_keys
     assert_nothing_raised do
       book = books(:awdr)
       book.subscriber_ids = [subscribers(:second).nick]
-      assert_equal [subscribers(:second)], book.subscribers(true)
+      assert_equal [subscribers(:second)], book.subscribers.reload
 
       book.subscriber_ids = []
-      assert_equal [], book.subscribers(true)
+      assert_equal [], book.subscribers.reload
     end
-
   end
 
   def test_collection_singular_ids_setter_raises_exception_when_invalid_ids_set
     company = companies(:rails_core)
-    ids =  [Developer.first.id, -9999]
-    assert_raises(ActiveRecord::RecordNotFound) {company.developer_ids= ids}
+    ids = [Developer.first.id, -9999]
+    e = assert_raises(ActiveRecord::RecordNotFound) { company.developer_ids = ids }
+    msg = "Couldn't find all Developers with 'id': (1, -9999) (found 1 results, but was looking for 2). Couldn't find Developer with id -9999."
+    assert_equal(msg, e.message)
+  end
+
+  def test_collection_singular_ids_through_setter_raises_exception_when_invalid_ids_set
+    author = authors(:david)
+    ids = [categories(:general).name, "Unknown"]
+    e = assert_raises(ActiveRecord::RecordNotFound) { author.essay_category_ids = ids }
+    msg = "Couldn't find all Categories with 'name': (General, Unknown) (found 1 results, but was looking for 2). Couldn't find Category with name Unknown."
+    assert_equal msg, e.message
   end
 
   def test_build_a_model_from_hm_through_association_with_where_clause
-    assert_nothing_raised { books(:awdr).subscribers.where(:nick => "marklazz").build }
+    assert_nothing_raised { books(:awdr).subscribers.where(nick: "marklazz").build }
   end
 
   def test_attributes_are_being_set_when_initialized_from_hm_through_association_with_where_clause
-    new_subscriber = books(:awdr).subscribers.where(:nick => "marklazz").build
+    new_subscriber = books(:awdr).subscribers.where(nick: "marklazz").build
     assert_equal new_subscriber.nick, "marklazz"
   end
 
   def test_attributes_are_being_set_when_initialized_from_hm_through_association_with_multiple_where_clauses
-    new_subscriber = books(:awdr).subscribers.where(:nick => "marklazz").where(:name => 'Marcelo Giorgi').build
+    new_subscriber = books(:awdr).subscribers.where(nick: "marklazz").where(name: "Marcelo Giorgi").build
     assert_equal new_subscriber.nick, "marklazz"
     assert_equal new_subscriber.name, "Marcelo Giorgi"
   end
@@ -904,19 +965,19 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     person = Person.new
     reference = person.references.build
     job = reference.build_job
-    assert person.jobs.include?(job)
+    assert_includes person.jobs, job
   end
 
   def test_include_method_in_association_through_should_return_true_for_instance_added_with_nested_builds
     author = Author.new
     post = author.posts.build
     comment = post.comments.build
-    assert author.comments.include?(comment)
+    assert_includes author.comments, comment
   end
 
   def test_through_association_readonly_should_be_false
-    assert !people(:michael).posts.first.readonly?
-    assert !people(:michael).posts.to_a.first.readonly?
+    assert_not_predicate people(:michael).posts.first, :readonly?
+    assert_not_predicate people(:michael).posts.to_a.first, :readonly?
   end
 
   def test_can_update_through_association
@@ -925,10 +986,17 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     end
   end
 
+  def test_has_many_through_polymorphic_with_rewhere
+    post = TaggedPost.create!(title: "Tagged", body: "Post")
+    tag = post.tags.create!(name: "Tag")
+    assert_equal [tag], TaggedPost.preload(:tags).last.tags
+    assert_equal [tag], TaggedPost.eager_load(:tags).last.tags
+  end
+
   def test_has_many_through_polymorphic_with_primary_key_option
     assert_equal [categories(:general)], authors(:david).essay_categories
 
-    authors = Author.joins(:essay_categories).where('categories.id' => categories(:general).id)
+    authors = Author.joins(:essay_categories).where("categories.id" => categories(:general).id)
     assert_equal authors(:david), authors.first
 
     assert_equal [owners(:blackbeard)], authors(:david).essay_owners
@@ -940,7 +1008,7 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   def test_has_many_through_with_primary_key_option
     assert_equal [categories(:general)], authors(:david).essay_categories_2
 
-    authors = Author.joins(:essay_categories_2).where('categories.id' => categories(:general).id)
+    authors = Author.joins(:essay_categories_2).where("categories.id" => categories(:general).id)
     assert_equal authors(:david), authors.first
   end
 
@@ -952,30 +1020,30 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_has_many_through_with_default_scope_on_join_model
-    assert_equal posts(:welcome).comments.order('id').to_a, authors(:david).comments_on_first_posts
+    assert_equal posts(:welcome).comments.order("id").to_a, authors(:david).comments_on_first_posts
   end
 
   def test_create_has_many_through_with_default_scope_on_join_model
-    category = authors(:david).special_categories.create(:name => "Foo")
-    assert_equal 1, category.categorizations.where(:special => true).count
+    category = authors(:david).special_categories.create(name: "Foo")
+    assert_equal 1, category.categorizations.where(special: true).count
   end
 
   def test_joining_has_many_through_with_distinct
-    mary = Author.joins(:unique_categorized_posts).where(:id => authors(:mary).id).first
+    mary = Author.joins(:unique_categorized_posts).where(id: authors(:mary).id).first
     assert_equal 1, mary.unique_categorized_posts.length
     assert_equal 1, mary.unique_categorized_post_ids.length
   end
 
   def test_joining_has_many_through_belongs_to
-    posts = Post.joins(:author_categorizations).order('posts.id').
-                 where('categorizations.id' => categorizations(:mary_thinking_sti).id)
+    posts = Post.joins(:author_categorizations).order("posts.id").
+                 where("categorizations.id" => categorizations(:mary_thinking_sti).id)
 
     assert_equal [posts(:eager_other), posts(:misc_by_mary), posts(:other_by_mary)], posts
   end
 
   def test_select_chosen_fields_only
     author = authors(:david)
-    assert_equal ['body', 'id'].sort, author.comments.select('comments.body').first.attributes.keys.sort
+    assert_equal ["body", "id"].sort, author.comments.select("comments.body").first.attributes.keys.sort
   end
 
   def test_get_has_many_through_belongs_to_ids_with_conditions
@@ -998,12 +1066,12 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     post.author_categorizations
     proxy = post.send(:association_instance_get, :author_categorizations)
 
-    assert !proxy.stale_target?
+    assert_not_predicate proxy, :stale_target?
     assert_equal authors(:mary).categorizations.sort_by(&:id), post.author_categorizations.sort_by(&:id)
 
     post.author_id = authors(:david).id
 
-    assert proxy.stale_target?
+    assert_predicate proxy, :stale_target?
     assert_equal authors(:david).categorizations.sort_by(&:id), post.author_categorizations.sort_by(&:id)
   end
 
@@ -1018,15 +1086,15 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     post    = posts(:welcome)
     address = author_addresses(:david_address)
 
-    assert post.author_addresses.include?(address)
+    assert_includes post.author_addresses, address
     post.author_addresses.delete(address)
-    assert post[:author_count].nil?
+    assert_predicate post[:author_count], :nil?
   end
 
   def test_primary_key_option_on_source
     post     = posts(:welcome)
     category = categories(:general)
-    Categorization.create!(:post_id => post.id, :named_category_name => category.name)
+    Categorization.create!(post_id: post.id, named_category_name: category.name)
 
     assert_equal [category], post.named_categories
     assert_equal [category.name], post.named_category_ids # checks when target loaded
@@ -1035,29 +1103,29 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_create_should_not_raise_exception_when_join_record_has_errors
     repair_validations(Categorization) do
-      Categorization.validate { |r| r.errors[:base] << 'Invalid Categorization' }
-      Category.create(:name => 'Fishing', :authors => [Author.first])
+      Categorization.validate { |r| r.errors[:base] << "Invalid Categorization" }
+      Category.create(name: "Fishing", authors: [Author.first])
     end
   end
 
   def test_assign_array_to_new_record_builds_join_records
-    c = Category.new(:name => 'Fishing', :authors => [Author.first])
+    c = Category.new(name: "Fishing", authors: [Author.first])
     assert_equal 1, c.categorizations.size
   end
 
   def test_create_bang_should_raise_exception_when_join_record_has_errors
     repair_validations(Categorization) do
-      Categorization.validate { |r| r.errors[:base] << 'Invalid Categorization' }
+      Categorization.validate { |r| r.errors[:base] << "Invalid Categorization" }
       assert_raises(ActiveRecord::RecordInvalid) do
-        Category.create!(:name => 'Fishing', :authors => [Author.first])
+        Category.create!(name: "Fishing", authors: [Author.first])
       end
     end
   end
 
   def test_save_bang_should_raise_exception_when_join_record_has_errors
     repair_validations(Categorization) do
-      Categorization.validate { |r| r.errors[:base] << 'Invalid Categorization' }
-      c = Category.new(:name => 'Fishing', :authors => [Author.first])
+      Categorization.validate { |r| r.errors[:base] << "Invalid Categorization" }
+      c = Category.new(name: "Fishing", authors: [Author.first])
       assert_raises(ActiveRecord::RecordInvalid) do
         c.save!
       end
@@ -1066,41 +1134,79 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_save_returns_falsy_when_join_record_has_errors
     repair_validations(Categorization) do
-      Categorization.validate { |r| r.errors[:base] << 'Invalid Categorization' }
-      c = Category.new(:name => 'Fishing', :authors => [Author.first])
+      Categorization.validate { |r| r.errors[:base] << "Invalid Categorization" }
+      c = Category.new(name: "Fishing", authors: [Author.first])
       assert_not c.save
     end
   end
 
   def test_preloading_empty_through_association_via_joins
-    person = Person.create!(:first_name => "Gaga")
-    person = Person.where(:id => person.id).where('readers.id = 1 or 1=1').references(:readers).includes(:posts).to_a.first
+    person = Person.create!(first_name: "Gaga")
+    person = Person.where(id: person.id).where("readers.id = 1 or 1=1").references(:readers).includes(:posts).to_a.first
 
-    assert person.posts.loaded?, 'person.posts should be loaded'
+    assert person.posts.loaded?, "person.posts should be loaded"
     assert_equal [], person.posts
   end
 
+  def test_preloading_empty_through_with_polymorphic_source_association
+    owner = Owner.create!(name: "Rainbow Unicat")
+    pet = Pet.create!(owner: owner)
+    person = Person.create!(first_name: "Gaga")
+    treasure = Treasure.create!(looter: person)
+    non_looted_treasure = Treasure.create!()
+    PetTreasure.create!(pet: pet, treasure: treasure, rainbow_color: "Ultra violet indigo")
+    PetTreasure.create!(pet: pet, treasure: non_looted_treasure, rainbow_color: "Ultra violet indigo")
+
+    assert_equal [person], Owner.where(name: "Rainbow Unicat").includes(pets: :persons).first.persons.to_a
+  end
+
   def test_explicitly_joining_join_table
     assert_equal owners(:blackbeard).toys, owners(:blackbeard).toys.with_pet
   end
 
   def test_has_many_through_with_polymorphic_source
-    post = tags(:general).tagged_posts.create! :title => "foo", :body => "bar"
+    post = tags(:general).tagged_posts.create! title: "foo", body: "bar"
     assert_equal [tags(:general)], post.reload.tags
   end
 
   def test_has_many_through_obeys_order_on_through_association
     owner = owners(:blackbeard)
-    assert owner.toys.to_sql.include?("pets.name desc")
+    assert_includes owner.toys.to_sql, "pets.name desc"
     assert_equal ["parrot", "bulbul"], owner.toys.map { |r| r.pet.name }
   end
 
+  def test_has_many_through_associations_sum_on_columns
+    post1 = Post.create(title: "active", body: "sample")
+    post2 = Post.create(title: "inactive", body: "sample")
+
+    person1 = Person.create(first_name: "aaron", followers_count: 1)
+    person2 = Person.create(first_name: "schmit", followers_count: 2)
+    person3 = Person.create(first_name: "bill", followers_count: 3)
+    person4 = Person.create(first_name: "cal", followers_count: 4)
+
+    Reader.create(post_id: post1.id, person_id: person1.id)
+    Reader.create(post_id: post1.id, person_id: person2.id)
+    Reader.create(post_id: post1.id, person_id: person3.id)
+    Reader.create(post_id: post1.id, person_id: person4.id)
+
+    Reader.create(post_id: post2.id, person_id: person1.id)
+    Reader.create(post_id: post2.id, person_id: person2.id)
+    Reader.create(post_id: post2.id, person_id: person3.id)
+    Reader.create(post_id: post2.id, person_id: person4.id)
+
+    active_persons = Person.joins(:readers).joins(:posts).distinct(true).where("posts.title" => "active")
+
+    assert_equal active_persons.map(&:followers_count).reduce(:+), 10
+    assert_equal active_persons.sum(:followers_count), 10
+    assert_equal active_persons.sum(:followers_count), active_persons.map(&:followers_count).reduce(:+)
+  end
+
   def test_has_many_through_associations_on_new_records_use_null_relations
     person = Person.new
 
-    assert_no_queries(ignore_none: false) do
+    assert_no_queries do
       assert_equal [], person.posts
-      assert_equal [], person.posts.where(body: 'omg')
+      assert_equal [], person.posts.where(body: "omg")
       assert_equal [], person.posts.pluck(:body)
       assert_equal 0,  person.posts.sum(:tags_count)
       assert_equal 0,  person.posts.count
@@ -1109,10 +1215,10 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_many_through_with_default_scope_on_the_target
     person = people(:michael)
-    assert_equal [posts(:thinking)], person.first_posts
+    assert_equal [posts(:thinking).id], person.first_posts.map(&:id)
 
     readers(:michael_authorless).update(first_post_id: 1)
-    assert_equal [posts(:thinking)], person.reload.first_posts
+    assert_equal [posts(:thinking).id], person.reload.first_posts.map(&:id)
   end
 
   def test_has_many_through_with_includes_in_through_association_scope
@@ -1132,9 +1238,9 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_has_many_through_unscope_default_scope
-    post = Post.create!(:title => 'Beaches', :body => "I like beaches!")
-    Reader.create! :person => people(:david), :post => post
-    LazyReader.create! :person => people(:susan), :post => post
+    post = Post.create!(title: "Beaches", body: "I like beaches!")
+    Reader.create! person: people(:david), post: post
+    LazyReader.create! person: people(:susan), post: post
 
     assert_equal 2, post.people.to_a.size
     assert_equal 1, post.lazy_people.to_a.size
@@ -1144,8 +1250,8 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_has_many_through_add_with_sti_middle_relation
-    club = SuperClub.create!(name: 'Fight Club')
-    member = Member.create!(name: 'Tyler Durden')
+    club = SuperClub.create!(name: "Fight Club")
+    member = Member.create!(name: "Tyler Durden")
 
     club.members << member
     assert_equal 1, SuperMembership.where(member_id: member.id, club_id: club.id).count
@@ -1165,4 +1271,169 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
 
     assert_nil Club.new.special_favourites.distinct_value
   end
+
+  def test_has_many_through_do_not_cache_association_reader_if_the_though_method_has_default_scopes
+    member = Member.create!
+    club = Club.create!
+    TenantMembership.create!(
+      member: member,
+      club: club
+    )
+
+    TenantMembership.current_member = member
+
+    tenant_clubs = member.tenant_clubs
+    assert_equal [club], tenant_clubs
+
+    TenantMembership.current_member = nil
+
+    other_member = Member.create!
+    other_club = Club.create!
+    TenantMembership.create!(
+      member: other_member,
+      club: other_club
+    )
+
+    tenant_clubs = other_member.tenant_clubs
+    assert_equal [other_club], tenant_clubs
+  ensure
+    TenantMembership.current_member = nil
+  end
+
+  def test_has_many_through_with_scope_that_has_joined_same_table_with_parent_relation
+    assert_equal authors(:david), Author.joins(:comments_for_first_author).take
+  end
+
+  def test_has_many_through_with_left_joined_same_table_with_through_table
+    assert_equal [comments(:eager_other_comment1)], authors(:mary).comments.left_joins(:post)
+  end
+
+  def test_has_many_through_with_unscope_should_affect_to_through_scope
+    assert_equal [comments(:eager_other_comment1)], authors(:mary).unordered_comments
+  end
+
+  def test_has_many_through_with_scope_should_accept_string_and_hash_join
+    assert_equal authors(:david), Author.joins({ comments_for_first_author: :post }, "inner join posts posts_alias on authors.id = posts_alias.author_id").eager_load(:categories).take
+  end
+
+  def test_has_many_through_with_scope_should_respect_table_alias
+    family = Family.create!
+    users = 3.times.map { User.create! }
+    FamilyTree.create!(member: users[0], family: family)
+    FamilyTree.create!(member: users[1], family: family)
+    FamilyTree.create!(member: users[2], family: family, token: "wat")
+
+    assert_equal 2, users[0].family_members.to_a.size
+    assert_equal 0, users[2].family_members.to_a.size
+  end
+
+  def test_through_scope_is_affected_by_unscoping
+    author = authors(:david)
+
+    expected = author.comments.to_a
+    FirstPost.unscoped do
+      assert_equal expected.sort_by(&:id), author.comments_on_first_posts.sort_by(&:id)
+    end
+  end
+
+  def test_through_scope_isnt_affected_by_scoping
+    author = authors(:david)
+
+    expected = author.comments_on_first_posts.to_a
+    FirstPost.where(id: 2).scoping do
+      author.comments_on_first_posts.reset
+      assert_equal expected.sort_by(&:id), author.comments_on_first_posts.sort_by(&:id)
+    end
+  end
+
+  def test_incorrectly_ordered_through_associations
+    assert_raises(ActiveRecord::HasManyThroughOrderError) do
+      DeveloperWithIncorrectlyOrderedHasManyThrough.create(
+        companies: [Company.create]
+      )
+    end
+  end
+
+  def test_has_many_through_update_ids_with_conditions
+    author = Author.create!(name: "Bill")
+    category = categories(:general)
+
+    author.update(
+      special_categories_with_condition_ids: [category.id],
+      nonspecial_categories_with_condition_ids: [category.id]
+    )
+
+    assert_equal [category.id], author.special_categories_with_condition_ids
+    assert_equal [category.id], author.nonspecial_categories_with_condition_ids
+
+    author.update(nonspecial_categories_with_condition_ids: [])
+    author.reload
+
+    assert_equal [category.id], author.special_categories_with_condition_ids
+    assert_equal [], author.nonspecial_categories_with_condition_ids
+  end
+
+  def test_single_has_many_through_association_with_unpersisted_parent_instance
+    post_with_single_has_many_through = Class.new(Post) do
+      def self.name; "PostWithSingleHasManyThrough"; end
+      has_many :subscriptions, through: :author
+    end
+    post = post_with_single_has_many_through.new
+
+    post.author = authors(:mary)
+    book1 = Book.create!(name: "essays on single has many through associations 1")
+    post.author.books << book1
+    subscription1 = Subscription.first
+    book1.subscriptions << subscription1
+    assert_equal [subscription1], post.subscriptions.to_a
+
+    post.author = authors(:bob)
+    book2 = Book.create!(name: "essays on single has many through associations 2")
+    post.author.books << book2
+    subscription2 = Subscription.second
+    book2.subscriptions << subscription2
+    assert_equal [subscription2], post.subscriptions.to_a
+  end
+
+  def test_nested_has_many_through_association_with_unpersisted_parent_instance
+    post_with_nested_has_many_through = Class.new(Post) do
+      def self.name; "PostWithNestedHasManyThrough"; end
+      has_many :books, through: :author
+      has_many :subscriptions, through: :books
+    end
+    post = post_with_nested_has_many_through.new
+
+    post.author = authors(:mary)
+    book1 = Book.create!(name: "essays on nested has many through associations 1")
+    post.author.books << book1
+    subscription1 = Subscription.first
+    book1.subscriptions << subscription1
+    assert_equal [subscription1], post.subscriptions.to_a
+
+    post.author = authors(:bob)
+    book2 = Book.create!(name: "essays on nested has many through associations 2")
+    post.author.books << book2
+    subscription2 = Subscription.second
+    book2.subscriptions << subscription2
+    assert_equal [subscription2], post.subscriptions.to_a
+  end
+
+  private
+    def make_model(name)
+      Class.new(ActiveRecord::Base) { define_singleton_method(:name) { name } }
+    end
+
+    def make_no_pk_hm_t
+      lesson = make_model "Lesson"
+      student = make_model "Student"
+
+      lesson_student = make_model "LessonStudent"
+      lesson_student.table_name = "lessons_students"
+
+      lesson_student.belongs_to :lesson, anonymous_class: lesson
+      lesson_student.belongs_to :student, anonymous_class: student
+      lesson.has_many :lesson_students, anonymous_class: lesson_student
+      lesson.has_many :students, through: :lesson_students, anonymous_class: student
+      [lesson, lesson_student, student]
+    end
 end
diff --git a/activerecord/test/cases/associations/has_one_associations_test.rb b/activerecord/test/cases/associations/has_one_associations_test.rb
index 5c2e5e7b43..adfb3ce072 100644
--- a/activerecord/test/cases/associations/has_one_associations_test.rb
+++ b/activerecord/test/cases/associations/has_one_associations_test.rb
@@ -1,19 +1,21 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/company'
-require 'models/ship'
-require 'models/pirate'
-require 'models/car'
-require 'models/bulb'
-require 'models/author'
-require 'models/image'
-require 'models/post'
+require "models/developer"
+require "models/computer"
+require "models/project"
+require "models/company"
+require "models/ship"
+require "models/pirate"
+require "models/car"
+require "models/bulb"
+require "models/author"
+require "models/image"
+require "models/post"
 
 class HasOneAssociationsTest < ActiveRecord::TestCase
   self.use_transactional_tests = false unless supports_savepoints?
-  fixtures :accounts, :companies, :developers, :projects, :developers_projects, :ships, :pirates
+  fixtures :accounts, :companies, :developers, :projects, :developers_projects, :ships, :pirates, :authors, :author_addresses
 
   def setup
     Account.destroyed_account_ids.clear
@@ -28,21 +30,22 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     ActiveRecord::SQLCounter.clear_log
     companies(:first_firm).account
   ensure
-    assert ActiveRecord::SQLCounter.log_all.all? { |sql| /order by/i !~ sql }, 'ORDER BY was used in the query'
+    log_all = ActiveRecord::SQLCounter.log_all
+    assert log_all.all? { |sql| /order by/i !~ sql }, "ORDER BY was used in the query: #{log_all}"
   end
 
   def test_has_one_cache_nils
     firm = companies(:another_firm)
     assert_queries(1) { assert_nil firm.account }
-    assert_queries(0) { assert_nil firm.account }
+    assert_no_queries { assert_nil firm.account }
 
-    firms = Firm.all.merge!(:includes => :account).to_a
-    assert_queries(0) { firms.each(&:account) }
+    firms = Firm.includes(:account).to_a
+    assert_no_queries { firms.each(&:account) }
   end
 
   def test_with_select
     assert_equal Firm.find(1).account_with_select.attributes.size, 2
-    assert_equal Firm.all.merge!(:includes => :account_with_select).find(1).account_with_select.attributes.size, 2
+    assert_equal Firm.all.merge!(includes: :account_with_select).find(1).account_with_select.attributes.size, 2
   end
 
   def test_finding_using_primary_key
@@ -102,11 +105,19 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   def test_nullification_on_association_change
     firm = companies(:rails_core)
     old_account_id = firm.account.id
-    firm.account = Account.new(:credit_limit => 5)
+    firm.account = Account.new(credit_limit: 5)
     # account is dependent with nullify, therefore its firm_id should be nil
     assert_nil Account.find(old_account_id).firm_id
   end
 
+  def test_nullification_on_destroyed_association
+    developer = Developer.create!(name: "Someone")
+    ship = Ship.create!(name: "Planet Caravan", developer: developer)
+    ship.destroy
+    assert_not_predicate ship, :persisted?
+    assert_not_predicate developer, :persisted?
+  end
+
   def test_natural_assignment_to_nil_after_destroy
     firm = companies(:rails_core)
     old_account_id = firm.account.id
@@ -117,12 +128,12 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_association_change_calls_delete
-    companies(:first_firm).deletable_account = Account.new(:credit_limit => 5)
+    companies(:first_firm).deletable_account = Account.new(credit_limit: 5)
     assert_equal [], Account.destroyed_account_ids[companies(:first_firm).id]
   end
 
   def test_association_change_calls_destroy
-    companies(:first_firm).account = Account.new(:credit_limit => 5)
+    companies(:first_firm).account = Account.new(credit_limit: 5)
     assert_equal [companies(:first_firm).id], Account.destroyed_account_ids[companies(:first_firm).id]
   end
 
@@ -162,34 +173,52 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_dependence_with_nil_associate
-    firm = DependentFirm.new(:name => 'nullify')
+    firm = DependentFirm.new(name: "nullify")
     firm.save!
     assert_nothing_raised { firm.destroy }
   end
 
   def test_restrict_with_exception
-    firm = RestrictedWithExceptionFirm.create!(:name => 'restrict')
-    firm.create_account(:credit_limit => 10)
+    firm = RestrictedWithExceptionFirm.create!(name: "restrict")
+    firm.create_account(credit_limit: 10)
 
     assert_not_nil firm.account
 
     assert_raise(ActiveRecord::DeleteRestrictionError) { firm.destroy }
-    assert RestrictedWithExceptionFirm.exists?(:name => 'restrict')
-    assert firm.account.present?
+    assert RestrictedWithExceptionFirm.exists?(name: "restrict")
+    assert_predicate firm.account, :present?
   end
 
   def test_restrict_with_error
-    firm = RestrictedWithErrorFirm.create!(:name => 'restrict')
-    firm.create_account(:credit_limit => 10)
+    firm = RestrictedWithErrorFirm.create!(name: "restrict")
+    firm.create_account(credit_limit: 10)
 
     assert_not_nil firm.account
 
     firm.destroy
 
-    assert !firm.errors.empty?
+    assert_not_empty firm.errors
     assert_equal "Cannot delete record because a dependent account exists", firm.errors[:base].first
-    assert RestrictedWithErrorFirm.exists?(:name => 'restrict')
-    assert firm.account.present?
+    assert RestrictedWithErrorFirm.exists?(name: "restrict")
+    assert_predicate firm.account, :present?
+  end
+
+  def test_restrict_with_error_with_locale
+    I18n.backend = I18n::Backend::Simple.new
+    I18n.backend.store_translations "en", activerecord: { attributes: { restricted_with_error_firm: { account: "firm account" } } }
+    firm = RestrictedWithErrorFirm.create!(name: "restrict")
+    firm.create_account(credit_limit: 10)
+
+    assert_not_nil firm.account
+
+    firm.destroy
+
+    assert_not_empty firm.errors
+    assert_equal "Cannot delete record because a dependent firm account exists", firm.errors[:base].first
+    assert RestrictedWithErrorFirm.exists?(name: "restrict")
+    assert_predicate firm.account, :present?
+  ensure
+    I18n.backend.reload!
   end
 
   def test_successful_build_association
@@ -202,9 +231,13 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_build_association_dont_create_transaction
-    assert_no_queries(ignore_none: false) {
-      Firm.new.build_account
-    }
+    # Load schema information so we don't query below if running just this test.
+    Account.define_attribute_methods
+
+    firm = Firm.new
+    assert_no_queries do
+      firm.build_account
+    end
   end
 
   def test_building_the_associated_object_with_implicit_sti_base_class
@@ -215,24 +248,24 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
 
   def test_building_the_associated_object_with_explicit_sti_base_class
     firm = DependentFirm.new
-    company = firm.build_company(:type => "Company")
+    company = firm.build_company(type: "Company")
     assert_kind_of Company, company, "Expected #{company.class} to be a Company"
   end
 
   def test_building_the_associated_object_with_sti_subclass
     firm = DependentFirm.new
-    company = firm.build_company(:type => "Client")
+    company = firm.build_company(type: "Client")
     assert_kind_of Client, company, "Expected #{company.class} to be a Client"
   end
 
   def test_building_the_associated_object_with_an_invalid_type
     firm = DependentFirm.new
-    assert_raise(ActiveRecord::SubclassNotFound) { firm.build_company(:type => "Invalid") }
+    assert_raise(ActiveRecord::SubclassNotFound) { firm.build_company(type: "Invalid") }
   end
 
   def test_building_the_associated_object_with_an_unrelated_type
     firm = DependentFirm.new
-    assert_raise(ActiveRecord::SubclassNotFound) { firm.build_company(:type => "Account") }
+    assert_raise(ActiveRecord::SubclassNotFound) { firm.build_company(type: "Account") }
   end
 
   def test_build_and_create_should_not_happen_within_scope
@@ -250,19 +283,19 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_create_association
-    firm = Firm.create(:name => "GlobalMegaCorp")
-    account = firm.create_account(:credit_limit => 1000)
+    firm = Firm.create(name: "GlobalMegaCorp")
+    account = firm.create_account(credit_limit: 1000)
     assert_equal account, firm.reload.account
   end
 
   def test_create_association_with_bang
-    firm = Firm.create(:name => "GlobalMegaCorp")
-    account = firm.create_account!(:credit_limit => 1000)
+    firm = Firm.create(name: "GlobalMegaCorp")
+    account = firm.create_account!(credit_limit: 1000)
     assert_equal account, firm.reload.account
   end
 
   def test_create_association_with_bang_failing
-    firm = Firm.create(:name => "GlobalMegaCorp")
+    firm = Firm.create(name: "GlobalMegaCorp")
     assert_raise ActiveRecord::RecordInvalid do
       firm.create_account!
     end
@@ -274,13 +307,55 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_create_with_inexistent_foreign_key_failing
-    firm = Firm.create(name: 'GlobalMegaCorp')
+    firm = Firm.create(name: "GlobalMegaCorp")
 
     assert_raises(ActiveRecord::UnknownAttributeError) do
       firm.create_account_with_inexistent_foreign_key
     end
   end
 
+  def test_create_when_parent_is_new_raises
+    firm = Firm.new
+    error = assert_raise(ActiveRecord::RecordNotSaved) do
+      firm.create_account
+    end
+
+    assert_equal "You cannot call create unless the parent is saved", error.message
+  end
+
+  def test_reload_association
+    odegy = companies(:odegy)
+
+    assert_equal 53, odegy.account.credit_limit
+    Account.where(id: odegy.account.id).update_all(credit_limit: 80)
+    assert_equal 53, odegy.account.credit_limit
+
+    assert_equal 80, odegy.reload_account.credit_limit
+  end
+
+  def test_reload_association_with_query_cache
+    odegy_id = companies(:odegy).id
+
+    connection = ActiveRecord::Base.connection
+    connection.enable_query_cache!
+    connection.clear_query_cache
+
+    # Populate the cache with a query
+    odegy = Company.find(odegy_id)
+    # Populate the cache with a second query
+    odegy.account
+
+    assert_equal 2, connection.query_cache.size
+
+    # Clear the cache and fetch the account again, populating the cache with a query
+    assert_queries(1) { odegy.reload_account }
+
+    # This query is not cached anymore, so it should make a real SQL query
+    assert_queries(1) { Company.find(odegy_id) }
+  ensure
+    ActiveRecord::Base.connection.disable_query_cache!
+  end
+
   def test_build
     firm = Firm.new("name" => "GlobalMegaCorp")
     firm.save
@@ -320,7 +395,7 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
 
   def test_finding_with_interpolated_condition
     firm = Firm.first
-    superior = firm.clients.create(:name => 'SuperiorCo')
+    superior = firm.clients.create(name: "SuperiorCo")
     superior.rating = 10
     superior.save
     assert_equal 10, firm.clients_with_interpolated_conditions.first.rating
@@ -329,14 +404,15 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   def test_assignment_before_child_saved
     firm = Firm.find(1)
     firm.account = a = Account.new("credit_limit" => 1000)
-    assert a.persisted?
+    assert_predicate a, :persisted?
+    assert_equal a, firm.account
     assert_equal a, firm.account
+    firm.association(:account).reload
     assert_equal a, firm.account
-    assert_equal a, firm.account(true)
   end
 
   def test_save_still_works_after_accessing_nil_has_one
-    jp = Company.new :name => 'Jaded Pixel'
+    jp = Company.new name: "Jaded Pixel"
     jp.dummy_account.nil?
 
     assert_nothing_raised do
@@ -346,7 +422,7 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
 
   def test_cant_save_readonly_association
     assert_raise(ActiveRecord::ReadOnlyRecord) { companies(:first_firm).readonly_account.save!  }
-    assert companies(:first_firm).readonly_account.readonly?
+    assert_predicate companies(:first_firm).readonly_account, :readonly?
   end
 
   def test_has_one_proxy_should_not_respond_to_private_methods
@@ -365,14 +441,14 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
 
     assert_nothing_raised do
       Firm.find(@firm.id).save!
-      Firm.all.merge!(:includes => :account).find(@firm.id).save!
+      Firm.all.merge!(includes: :account).find(@firm.id).save!
     end
 
     @firm.account.destroy
 
     assert_nothing_raised do
       Firm.find(@firm.id).save!
-      Firm.all.merge!(:includes => :account).find(@firm.id).save!
+      Firm.all.merge!(includes: :account).find(@firm.id).save!
     end
   end
 
@@ -384,12 +460,12 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
 
   def test_create_respects_hash_condition
     account = companies(:first_firm).create_account_limit_500_with_hash_conditions
-    assert       account.persisted?
+    assert_predicate account, :persisted?
     assert_equal 500, account.credit_limit
   end
 
   def test_attributes_are_being_set_when_initialized_from_has_one_association_with_where_clause
-    new_account = companies(:first_firm).build_account(:firm_name => 'Account')
+    new_account = companies(:first_firm).build_account(firm_name: "Account")
     assert_equal new_account.firm_name, "Account"
   end
 
@@ -401,9 +477,9 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     new_ship = pirate.create_ship
     assert_not_equal ships(:black_pearl), new_ship
     assert_equal new_ship, pirate.ship
-    assert new_ship.new_record?
+    assert_predicate new_ship, :new_record?
     assert_nil orig_ship.pirate_id
-    assert !orig_ship.changed? # check it was saved
+    assert_not orig_ship.changed? # check it was saved
   end
 
   def test_creation_failure_with_dependent_option
@@ -411,8 +487,8 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     orig_ship = pirate.dependent_ship
 
     new_ship = pirate.create_dependent_ship
-    assert new_ship.new_record?
-    assert orig_ship.destroyed?
+    assert_predicate new_ship, :new_record?
+    assert_predicate orig_ship, :destroyed?
   end
 
   def test_creation_failure_due_to_new_record_should_raise_error
@@ -432,14 +508,14 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     pirate = pirates(:blackbeard)
     pirate.ship.name = nil
 
-    assert !pirate.ship.valid?
+    assert_not_predicate pirate.ship, :valid?
     error = assert_raise(ActiveRecord::RecordNotSaved) do
       pirate.ship = ships(:interceptor)
     end
 
     assert_equal ships(:black_pearl), pirate.ship
     assert_equal pirate.id, pirate.ship.pirate_id
-    assert_equal "Failed to remove the existing associated ship. " +
+    assert_equal "Failed to remove the existing associated ship. " \
                  "The record failed to save after its foreign key was set to nil.", error.message
   end
 
@@ -459,63 +535,63 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_association_keys_bypass_attribute_protection
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
 
     bulb = car.build_bulb
     assert_equal car.id, bulb.car_id
 
-    bulb = car.build_bulb :car_id => car.id + 1
+    bulb = car.build_bulb car_id: car.id + 1
     assert_equal car.id, bulb.car_id
 
     bulb = car.create_bulb
     assert_equal car.id, bulb.car_id
 
-    bulb = car.create_bulb :car_id => car.id + 1
+    bulb = car.create_bulb car_id: car.id + 1
     assert_equal car.id, bulb.car_id
   end
 
   def test_association_protect_foreign_key
-    pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
+    pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
 
     ship = pirate.build_ship
     assert_equal pirate.id, ship.pirate_id
 
-    ship = pirate.build_ship :pirate_id => pirate.id + 1
+    ship = pirate.build_ship pirate_id: pirate.id + 1
     assert_equal pirate.id, ship.pirate_id
 
     ship = pirate.create_ship
     assert_equal pirate.id, ship.pirate_id
 
-    ship = pirate.create_ship :pirate_id => pirate.id + 1
+    ship = pirate.create_ship pirate_id: pirate.id + 1
     assert_equal pirate.id, ship.pirate_id
   end
 
   def test_build_with_block
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
 
-    bulb = car.build_bulb{ |b| b.color = 'Red' }
-    assert_equal 'RED!', bulb.color
+    bulb = car.build_bulb { |b| b.color = "Red" }
+    assert_equal "RED!", bulb.color
   end
 
   def test_create_with_block
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
 
-    bulb = car.create_bulb{ |b| b.color = 'Red' }
-    assert_equal 'RED!', bulb.color
+    bulb = car.create_bulb { |b| b.color = "Red" }
+    assert_equal "RED!", bulb.color
   end
 
   def test_create_bang_with_block
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
 
-    bulb = car.create_bulb!{ |b| b.color = 'Red' }
-    assert_equal 'RED!', bulb.color
+    bulb = car.create_bulb! { |b| b.color = "Red" }
+    assert_equal "RED!", bulb.color
   end
 
   def test_association_attributes_are_available_to_after_initialize
-    car = Car.create(:name => 'honda')
+    car = Car.create(name: "honda")
     bulb = car.create_bulb
 
-    assert_equal car.id, bulb.attributes_after_initialize['car_id']
+    assert_equal car.id, bulb.attributes_after_initialize["car_id"]
   end
 
   def test_has_one_transaction
@@ -535,36 +611,36 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
 
   def test_has_one_assignment_dont_trigger_save_on_change_of_same_object
     pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
-    ship = pirate.build_ship(name: 'old name')
+    ship = pirate.build_ship(name: "old name")
     ship.save!
 
-    ship.name = 'new name'
-    assert ship.changed?
+    ship.name = "new name"
+    assert_predicate ship, :changed?
     assert_queries(1) do
       # One query for updating name, not triggering query for updating pirate_id
       pirate.ship = ship
     end
 
-    assert_equal 'new name', pirate.ship.reload.name
+    assert_equal "new name", pirate.ship.reload.name
   end
 
   def test_has_one_assignment_triggers_save_on_change_on_replacing_object
     pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
-    ship = pirate.build_ship(name: 'old name')
+    ship = pirate.build_ship(name: "old name")
     ship.save!
 
-    new_ship = Ship.create(name: 'new name')
+    new_ship = Ship.create(name: "new name")
     assert_queries(2) do
-      # One query for updating name and second query for updating pirate_id
+      # One query to nullify the old ship, one query to update the new ship
       pirate.ship = new_ship
     end
 
-    assert_equal 'new name', pirate.ship.reload.name
+    assert_equal "new name", pirate.ship.reload.name
   end
 
   def test_has_one_autosave_with_primary_key_manually_set
-    post = Post.create(id: 1234, title: "Some title", body: 'Some content')
-    author = Author.new(id: 33, name: 'Hank Moody')
+    post = Post.create(id: 1234, title: "Some title", body: "Some content")
+    author = Author.new(id: 33, name: "Hank Moody")
 
     author.post = post
     author.save
@@ -575,7 +651,7 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_has_one_loading_for_new_record
-    post = Post.create!(author_id: 42, title: 'foo', body: 'bar')
+    post = Post.create!(author_id: 42, title: "foo", body: "bar")
     author = Author.new(id: 42)
     assert_equal post, author.post
   end
@@ -589,7 +665,7 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_with_polymorphic_has_one_with_custom_columns_name
-    post = Post.create! :title => 'foo', :body => 'bar'
+    post = Post.create! title: "foo", body: "bar"
     image = Image.create!
 
     post.main_image = image
@@ -598,8 +674,8 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     assert_equal image, post.main_image
   end
 
-  test 'dangerous association name raises ArgumentError' do
-    [:errors, 'errors', :save, 'save'].each do |name|
+  test "dangerous association name raises ArgumentError" do
+    [:errors, "errors", :save, "save"].each do |name|
       assert_raises(ArgumentError, "Association #{name} should not be allowed") do
         Class.new(ActiveRecord::Base) do
           has_one name
@@ -607,4 +683,100 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
       end
     end
   end
+
+  class SpecialBook < ActiveRecord::Base
+    self.table_name = "books"
+    belongs_to :author, class_name: "SpecialAuthor"
+    has_one :subscription, class_name: "SpecialSupscription", foreign_key: "subscriber_id"
+
+    enum status: [:proposed, :written, :published]
+  end
+
+  class SpecialAuthor < ActiveRecord::Base
+    self.table_name = "authors"
+    has_one :book, class_name: "SpecialBook", foreign_key: "author_id"
+  end
+
+  class SpecialSupscription < ActiveRecord::Base
+    self.table_name = "subscriptions"
+    belongs_to :book, class_name: "SpecialBook"
+  end
+
+  def test_association_enum_works_properly
+    author = SpecialAuthor.create!(name: "Test")
+    book = SpecialBook.create!(status: "published")
+    author.book = book
+
+    assert_equal "published", book.status
+    assert_not_equal 0, SpecialAuthor.joins(:book).where(books: { status: "published" }).count
+  end
+
+  def test_association_enum_works_properly_with_nested_join
+    author = SpecialAuthor.create!(name: "Test")
+    book = SpecialBook.create!(status: "published")
+    author.book = book
+
+    where_clause = { books: { subscriptions: { subscriber_id: nil } } }
+    assert_nothing_raised do
+      SpecialAuthor.joins(book: :subscription).where.not(where_clause)
+    end
+  end
+
+  class DestroyByParentBook < ActiveRecord::Base
+    self.table_name = "books"
+    belongs_to :author, class_name: "DestroyByParentAuthor"
+    before_destroy :dont, unless: :destroyed_by_association
+
+    def dont
+      throw(:abort)
+    end
+  end
+
+  class DestroyByParentAuthor < ActiveRecord::Base
+    self.table_name = "authors"
+    has_one :book, class_name: "DestroyByParentBook", foreign_key: "author_id", dependent: :destroy
+  end
+
+  test "destroyed_by_association set in child destroy callback on parent destroy" do
+    author = DestroyByParentAuthor.create!(name: "Test")
+    book = DestroyByParentBook.create!(author: author)
+
+    author.destroy
+
+    assert_not DestroyByParentBook.exists?(book.id)
+  end
+
+  test "destroyed_by_association set in child destroy callback on replace" do
+    author = DestroyByParentAuthor.create!(name: "Test")
+    book = DestroyByParentBook.create!(author: author)
+
+    author.book = DestroyByParentBook.create!
+    author.save!
+
+    assert_not DestroyByParentBook.exists?(book.id)
+  end
+
+  class UndestroyableBook < ActiveRecord::Base
+    self.table_name = "books"
+    belongs_to :author, class_name: "DestroyableAuthor"
+    before_destroy :dont
+
+    def dont
+      throw(:abort)
+    end
+  end
+
+  class DestroyableAuthor < ActiveRecord::Base
+    self.table_name = "authors"
+    has_one :book, class_name: "UndestroyableBook", foreign_key: "author_id", dependent: :destroy
+  end
+
+  def test_dependency_should_halt_parent_destruction
+    author = DestroyableAuthor.create!(name: "Test")
+    UndestroyableBook.create!(author: author)
+
+    assert_no_difference ["DestroyableAuthor.count", "UndestroyableBook.count"] do
+      assert_not author.destroy
+    end
+  end
 end
diff --git a/activerecord/test/cases/associations/has_one_through_associations_test.rb b/activerecord/test/cases/associations/has_one_through_associations_test.rb
index f8772547a2..0309663943 100644
--- a/activerecord/test/cases/associations/has_one_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_one_through_associations_test.rb
@@ -1,25 +1,31 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/club'
-require 'models/member_type'
-require 'models/member'
-require 'models/membership'
-require 'models/sponsor'
-require 'models/organization'
-require 'models/member_detail'
-require 'models/minivan'
-require 'models/dashboard'
-require 'models/speedometer'
-require 'models/category'
-require 'models/author'
-require 'models/essay'
-require 'models/owner'
-require 'models/post'
-require 'models/comment'
-require 'models/categorization'
+require "models/club"
+require "models/member_type"
+require "models/member"
+require "models/membership"
+require "models/sponsor"
+require "models/organization"
+require "models/member_detail"
+require "models/minivan"
+require "models/dashboard"
+require "models/speedometer"
+require "models/category"
+require "models/author"
+require "models/essay"
+require "models/owner"
+require "models/post"
+require "models/comment"
+require "models/categorization"
+require "models/customer"
+require "models/carrier"
+require "models/shop_account"
+require "models/customer_carrier"
 
 class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   fixtures :member_types, :members, :clubs, :memberships, :sponsors, :organizations, :minivans,
-           :dashboards, :speedometers, :authors, :posts, :comments, :categories, :essays, :owners
+           :dashboards, :speedometers, :authors, :author_addresses, :posts, :comments, :categories, :essays, :owners
 
   def setup
     @member = members(:groucho)
@@ -30,14 +36,26 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_creating_association_creates_through_record
-    new_member = Member.create(:name => "Chris")
-    new_member.club = Club.create(:name => "LRUG")
+    new_member = Member.create(name: "Chris")
+    new_member.club = Club.create(name: "LRUG")
     assert_not_nil new_member.current_membership
     assert_not_nil new_member.club
   end
 
+  def test_creating_association_builds_through_record
+    new_member = Member.create(name: "Chris")
+    new_club = new_member.association(:club).build
+    assert new_member.current_membership
+    assert_equal new_club, new_member.club
+    assert_predicate new_club, :new_record?
+    assert_predicate new_member.current_membership, :new_record?
+    assert new_member.save
+    assert_predicate new_club, :persisted?
+    assert_predicate new_member.current_membership, :persisted?
+  end
+
   def test_creating_association_builds_through_record_for_new
-    new_member = Member.new(:name => "Jane")
+    new_member = Member.new(name: "Jane")
     new_member.club = clubs(:moustache_club)
     assert new_member.current_membership
     assert_equal clubs(:moustache_club), new_member.current_membership.club
@@ -46,9 +64,27 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal clubs(:moustache_club), new_member.club
   end
 
+  def test_building_multiple_associations_builds_through_record
+    member_type = MemberType.create!
+    member = Member.create!
+    member_detail_with_one_association = MemberDetail.new(member_type: member_type)
+    assert_predicate member_detail_with_one_association.member, :new_record?
+    member_detail_with_two_associations = MemberDetail.new(member_type: member_type, admittable: member)
+    assert_predicate member_detail_with_two_associations.member, :new_record?
+  end
+
+  def test_creating_multiple_associations_creates_through_record
+    member_type = MemberType.create!
+    member = Member.create!
+    member_detail_with_one_association = MemberDetail.create!(member_type: member_type)
+    assert_not_predicate member_detail_with_one_association.member, :new_record?
+    member_detail_with_two_associations = MemberDetail.create!(member_type: member_type, admittable: member)
+    assert_not_predicate member_detail_with_two_associations.member, :new_record?
+  end
+
   def test_creating_association_sets_both_parent_ids_for_new
-    member = Member.new(name: 'Sean Griffin')
-    club = Club.new(name: 'Da Club')
+    member = Member.new(name: "Sean Griffin")
+    club = Club.new(name: "Da Club")
 
     member.club = club
 
@@ -61,7 +97,7 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_replace_target_record
-    new_club = Club.create(:name => "Marx Bros")
+    new_club = Club.create(name: "Marx Bros")
     @member.club = new_club
     @member.reload
     assert_equal new_club, @member.club
@@ -69,7 +105,7 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_replacing_target_record_deletes_old_association
     assert_no_difference "Membership.count" do
-      new_club = Club.create(:name => "Bananarama")
+      new_club = Club.create(name: "Bananarama")
       @member.club = new_club
       @member.reload
     end
@@ -78,40 +114,47 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   def test_set_record_to_nil_should_delete_association
     @member.club = nil
     @member.reload
-    assert_equal nil, @member.current_membership
+    assert_nil @member.current_membership
     assert_nil @member.club
   end
 
+  def test_set_record_after_delete_association
+    @member.club = nil
+    @member.club = clubs(:moustache_club)
+    @member.reload
+    assert_equal clubs(:moustache_club), @member.club
+  end
+
   def test_has_one_through_polymorphic
     assert_equal clubs(:moustache_club), @member.sponsor_club
   end
 
   def test_has_one_through_eager_loading
-    members = assert_queries(3) do #base table, through table, clubs table
-      Member.all.merge!(:includes => :club, :where => ["name = ?", "Groucho Marx"]).to_a
+    members = assert_queries(3) do # base table, through table, clubs table
+      Member.all.merge!(includes: :club, where: ["name = ?", "Groucho Marx"]).to_a
     end
     assert_equal 1, members.size
-    assert_not_nil assert_no_queries {members[0].club}
+    assert_not_nil assert_no_queries { members[0].club }
   end
 
   def test_has_one_through_eager_loading_through_polymorphic
-    members = assert_queries(3) do #base table, through table, clubs table
-      Member.all.merge!(:includes => :sponsor_club, :where => ["name = ?", "Groucho Marx"]).to_a
+    members = assert_queries(3) do # base table, through table, clubs table
+      Member.all.merge!(includes: :sponsor_club, where: ["name = ?", "Groucho Marx"]).to_a
     end
     assert_equal 1, members.size
-    assert_not_nil assert_no_queries {members[0].sponsor_club}
+    assert_not_nil assert_no_queries { members[0].sponsor_club }
   end
 
   def test_has_one_through_with_conditions_eager_loading
     # conditions on the through table
-    assert_equal clubs(:moustache_club), Member.all.merge!(:includes => :favourite_club).find(@member.id).favourite_club
+    assert_equal clubs(:moustache_club), Member.all.merge!(includes: :favourite_club).find(@member.id).favourite_club
     memberships(:membership_of_favourite_club).update_columns(favourite: false)
-    assert_equal nil,                    Member.all.merge!(:includes => :favourite_club).find(@member.id).reload.favourite_club
+    assert_nil Member.all.merge!(includes: :favourite_club).find(@member.id).reload.favourite_club
 
     # conditions on the source table
-    assert_equal clubs(:moustache_club), Member.all.merge!(:includes => :hairy_club).find(@member.id).hairy_club
+    assert_equal clubs(:moustache_club), Member.all.merge!(includes: :hairy_club).find(@member.id).hairy_club
     clubs(:moustache_club).update_columns(name: "Association of Clean-Shaven Persons")
-    assert_equal nil,                    Member.all.merge!(:includes => :hairy_club).find(@member.id).reload.hairy_club
+    assert_nil Member.all.merge!(includes: :hairy_club).find(@member.id).reload.hairy_club
   end
 
   def test_has_one_through_polymorphic_with_source_type
@@ -119,31 +162,31 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_eager_has_one_through_polymorphic_with_source_type
-    clubs = Club.all.merge!(:includes => :sponsored_member, :where => ["name = ?","Moustache and Eyebrow Fancier Club"]).to_a
+    clubs = Club.all.merge!(includes: :sponsored_member, where: ["name = ?", "Moustache and Eyebrow Fancier Club"]).to_a
     # Only the eyebrow fanciers club has a sponsored_member
-    assert_not_nil assert_no_queries {clubs[0].sponsored_member}
+    assert_not_nil assert_no_queries { clubs[0].sponsored_member }
   end
 
   def test_has_one_through_nonpreload_eagerloading
     members = assert_queries(1) do
-      Member.all.merge!(:includes => :club, :where => ["members.name = ?", "Groucho Marx"], :order => 'clubs.name').to_a #force fallback
+      Member.all.merge!(includes: :club, where: ["members.name = ?", "Groucho Marx"], order: "clubs.name").to_a # force fallback
     end
     assert_equal 1, members.size
-    assert_not_nil assert_no_queries {members[0].club}
+    assert_not_nil assert_no_queries { members[0].club }
   end
 
   def test_has_one_through_nonpreload_eager_loading_through_polymorphic
     members = assert_queries(1) do
-      Member.all.merge!(:includes => :sponsor_club, :where => ["members.name = ?", "Groucho Marx"], :order => 'clubs.name').to_a #force fallback
+      Member.all.merge!(includes: :sponsor_club, where: ["members.name = ?", "Groucho Marx"], order: "clubs.name").to_a # force fallback
     end
     assert_equal 1, members.size
-    assert_not_nil assert_no_queries {members[0].sponsor_club}
+    assert_not_nil assert_no_queries { members[0].sponsor_club }
   end
 
   def test_has_one_through_nonpreload_eager_loading_through_polymorphic_with_more_than_one_through_record
-    Sponsor.new(:sponsor_club => clubs(:crazy_club), :sponsorable => members(:groucho)).save!
+    Sponsor.new(sponsor_club: clubs(:crazy_club), sponsorable: members(:groucho)).save!
     members = assert_queries(1) do
-      Member.all.merge!(:includes => :sponsor_club, :where => ["members.name = ?", "Groucho Marx"], :order => 'clubs.name DESC').to_a #force fallback
+      Member.all.merge!(includes: :sponsor_club, where: ["members.name = ?", "Groucho Marx"], order: "clubs.name DESC").to_a # force fallback
     end
     assert_equal 1, members.size
     assert_not_nil assert_no_queries { members[0].sponsor_club }
@@ -155,8 +198,8 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_assigning_association_correctly_assigns_target
-    new_member = Member.create(:name => "Chris")
-    new_member.club = new_club = Club.create(:name => "LRUG")
+    new_member = Member.create(name: "Chris")
+    new_member.club = new_club = Club.create(name: "LRUG")
     assert_equal new_club, new_member.association(:club).target
   end
 
@@ -172,37 +215,37 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_assigning_to_has_one_through_preserves_decorated_join_record
     @organization = organizations(:nsa)
-    assert_difference 'MemberDetail.count', 1 do
-      @member_detail = MemberDetail.new(:extra_data => 'Extra')
+    assert_difference "MemberDetail.count", 1 do
+      @member_detail = MemberDetail.new(extra_data: "Extra")
       @member.member_detail = @member_detail
       @member.organization = @organization
     end
     assert_equal @organization, @member.organization
-    assert @organization.members.include?(@member)
-    assert_equal 'Extra', @member.member_detail.extra_data
+    assert_includes @organization.members, @member
+    assert_equal "Extra", @member.member_detail.extra_data
   end
 
   def test_reassigning_has_one_through
     @organization = organizations(:nsa)
     @new_organization = organizations(:discordians)
 
-    assert_difference 'MemberDetail.count', 1 do
-      @member_detail = MemberDetail.new(:extra_data => 'Extra')
+    assert_difference "MemberDetail.count", 1 do
+      @member_detail = MemberDetail.new(extra_data: "Extra")
       @member.member_detail = @member_detail
       @member.organization = @organization
     end
     assert_equal @organization, @member.organization
-    assert_equal 'Extra', @member.member_detail.extra_data
-    assert @organization.members.include?(@member)
-    assert !@new_organization.members.include?(@member)
+    assert_equal "Extra", @member.member_detail.extra_data
+    assert_includes @organization.members, @member
+    assert_not_includes @new_organization.members, @member
 
-    assert_no_difference 'MemberDetail.count' do
+    assert_no_difference "MemberDetail.count" do
       @member.organization = @new_organization
     end
     assert_equal @new_organization, @member.organization
-    assert_equal 'Extra', @member.member_detail.extra_data
-    assert !@organization.members.include?(@member)
-    assert @new_organization.members.include?(@member)
+    assert_equal "Extra", @member.member_detail.extra_data
+    assert_not_includes @organization.members, @member
+    assert_includes @new_organization.members, @member
   end
 
   def test_preloading_has_one_through_on_belongs_to
@@ -213,10 +256,10 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
     @member.member_detail = @member_detail
     @member.organization = @organization
     @member_details = assert_queries(3) do
-      MemberDetail.all.merge!(:includes => :member_type).to_a
+      MemberDetail.all.merge!(includes: :member_type).to_a
     end
     @new_detail = @member_details[0]
-    assert @new_detail.send(:association, :member_type).loaded?
+    assert_predicate @new_detail.send(:association, :member_type), :loaded?
     assert_no_queries { @new_detail.member_type }
   end
 
@@ -226,36 +269,38 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
 
     assert_nothing_raised do
       Club.find(@club.id).save!
-      Club.all.merge!(:includes => :sponsored_member).find(@club.id).save!
+      Club.all.merge!(includes: :sponsored_member).find(@club.id).save!
     end
 
     @club.sponsor.destroy
 
     assert_nothing_raised do
       Club.find(@club.id).save!
-      Club.all.merge!(:includes => :sponsored_member).find(@club.id).save!
+      Club.all.merge!(includes: :sponsored_member).find(@club.id).save!
     end
   end
 
   def test_through_belongs_to_after_destroy
-    @member_detail = MemberDetail.new(:extra_data => 'Extra')
+    @member_detail = MemberDetail.new(extra_data: "Extra")
     @member.member_detail = @member_detail
     @member.save!
 
     assert_not_nil @member_detail.member_type
     @member_detail.destroy
     assert_queries(1) do
-      assert_not_nil @member_detail.member_type(true)
+      @member_detail.association(:member_type).reload
+      assert_not_nil @member_detail.member_type
     end
 
     @member_detail.member.destroy
     assert_queries(1) do
-      assert_nil @member_detail.member_type(true)
+      @member_detail.association(:member_type).reload
+      assert_nil @member_detail.member_type
     end
   end
 
   def test_value_is_properly_quoted
-    minivan = Minivan.find('m1')
+    minivan = Minivan.find("m1")
     assert_nothing_raised do
       minivan.dashboard
     end
@@ -264,7 +309,7 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   def test_has_one_through_polymorphic_with_primary_key_option
     assert_equal categories(:general), authors(:david).essay_category
 
-    authors = Author.joins(:essay_category).where('categories.id' => categories(:general).id)
+    authors = Author.joins(:essay_category).where("categories.id" => categories(:general).id)
     assert_equal authors(:david), authors.first
 
     assert_equal owners(:blackbeard), authors(:david).essay_owner
@@ -276,12 +321,12 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
   def test_has_one_through_with_primary_key_option
     assert_equal categories(:general), authors(:david).essay_category_2
 
-    authors = Author.joins(:essay_category_2).where('categories.id' => categories(:general).id)
+    authors = Author.joins(:essay_category_2).where("categories.id" => categories(:general).id)
     assert_equal authors(:david), authors.first
   end
 
   def test_has_one_through_with_default_scope_on_join_model
-    assert_equal posts(:welcome).comments.order('id').first, authors(:david).comment_on_first_post
+    assert_equal posts(:welcome).comments.order("id").first, authors(:david).comment_on_first_post
   end
 
   def test_has_one_through_many_raises_exception
@@ -302,12 +347,12 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
     minivan.dashboard
     proxy = minivan.send(:association_instance_get, :dashboard)
 
-    assert !proxy.stale_target?
+    assert_not_predicate proxy, :stale_target?
     assert_equal dashboards(:cool_first), minivan.dashboard
 
     minivan.speedometer_id = speedometers(:second).id
 
-    assert proxy.stale_target?
+    assert_predicate proxy, :stale_target?
     assert_equal dashboards(:second), minivan.dashboard
   end
 
@@ -319,7 +364,7 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
 
     minivan.speedometer_id = speedometers(:second).id
 
-    assert proxy.stale_target?
+    assert_predicate proxy, :stale_target?
     assert_equal dashboards(:second), minivan.dashboard
   end
 
@@ -344,4 +389,34 @@ class HasOneThroughAssociationsTest < ActiveRecord::TestCase
       end
     end
   end
+
+  def test_has_one_through_do_not_cache_association_reader_if_the_though_method_has_default_scopes
+    customer = Customer.create!
+    carrier = Carrier.create!
+    customer_carrier = CustomerCarrier.create!(
+      customer: customer,
+      carrier: carrier,
+    )
+    account = ShopAccount.create!(customer_carrier: customer_carrier)
+
+    CustomerCarrier.current_customer = customer
+
+    account_carrier = account.carrier
+    assert_equal carrier, account_carrier
+
+    CustomerCarrier.current_customer = nil
+
+    other_carrier = Carrier.create!
+    other_customer = Customer.create!
+    other_customer_carrier = CustomerCarrier.create!(
+      customer: other_customer,
+      carrier: other_carrier,
+    )
+    other_account = ShopAccount.create!(customer_carrier: other_customer_carrier)
+
+    account_carrier = other_account.carrier
+    assert_equal other_carrier, account_carrier
+  ensure
+    CustomerCarrier.current_customer = nil
+  end
 end
diff --git a/activerecord/test/cases/associations/inner_join_association_test.rb b/activerecord/test/cases/associations/inner_join_association_test.rb
index b3fe759ad9..c33dcdee61 100644
--- a/activerecord/test/cases/associations/inner_join_association_test.rb
+++ b/activerecord/test/cases/associations/inner_join_association_test.rb
@@ -1,16 +1,18 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/comment'
-require 'models/author'
-require 'models/essay'
-require 'models/category'
-require 'models/categorization'
-require 'models/person'
-require 'models/tagging'
-require 'models/tag'
+require "models/post"
+require "models/comment"
+require "models/author"
+require "models/essay"
+require "models/category"
+require "models/categorization"
+require "models/person"
+require "models/tagging"
+require "models/tag"
 
 class InnerJoinAssociationTest < ActiveRecord::TestCase
-  fixtures :authors, :essays, :posts, :comments, :categories, :categories_posts, :categorizations,
+  fixtures :authors, :author_addresses, :essays, :posts, :comments, :categories, :categories_posts, :categorizations,
            :taggings, :tags
 
   def test_construct_finder_sql_applies_aliases_tables_on_association_conditions
@@ -20,11 +22,29 @@ class InnerJoinAssociationTest < ActiveRecord::TestCase
 
   def test_construct_finder_sql_does_not_table_name_collide_on_duplicate_associations
     assert_nothing_raised do
-      sql = Person.joins(:agents => {:agents => :agents}).joins(:agents => {:agents => {:primary_contact => :agents}}).to_sql
+      sql = Person.joins(agents: { agents: :agents }).joins(agents: { agents: { primary_contact: :agents } }).to_sql
       assert_match(/agents_people_4/i, sql)
     end
   end
 
+  def test_construct_finder_sql_does_not_table_name_collide_on_duplicate_associations_with_left_outer_joins
+    sql = Person.joins(agents: :agents).left_outer_joins(agents: :agents).to_sql
+    assert_match(/agents_people_4/i, sql)
+  end
+
+  def test_construct_finder_sql_does_not_table_name_collide_with_string_joins
+    sql = Person.joins(:agents).joins("JOIN people agents_people ON agents_people.primary_contact_id = people.id").to_sql
+    assert_match(/agents_people_2/i, sql)
+  end
+
+  def test_construct_finder_sql_does_not_table_name_collide_with_aliased_joins
+    people = Person.arel_table
+    agents = people.alias("agents_people")
+    constraint = agents[:primary_contact_id].eq(people[:id])
+    sql = Person.joins(:agents).joins(agents.create_join(agents, agents.create_on(constraint))).to_sql
+    assert_match(/agents_people_2/i, sql)
+  end
+
   def test_construct_finder_sql_ignores_empty_joins_hash
     sql = Author.joins({}).to_sql
     assert_no_match(/JOIN/i, sql)
@@ -47,7 +67,7 @@ class InnerJoinAssociationTest < ActiveRecord::TestCase
   end
 
   def test_join_conditions_allow_nil_associations
-    authors = Author.includes(:essays).where(:essays => {:id => nil})
+    authors = Author.includes(:essays).where(essays: { id: nil })
     assert_equal 2, authors.count
   end
 
@@ -58,56 +78,56 @@ class InnerJoinAssociationTest < ActiveRecord::TestCase
   end
 
   def test_find_with_implicit_inner_joins_honors_readonly_with_select
-    authors = Author.joins(:posts).select('authors.*').to_a
-    assert !authors.empty?, "expected authors to be non-empty"
-    assert authors.all? {|a| !a.readonly? }, "expected no authors to be readonly"
+    authors = Author.joins(:posts).select("authors.*").to_a
+    assert_not authors.empty?, "expected authors to be non-empty"
+    assert authors.all? { |a| !a.readonly? }, "expected no authors to be readonly"
   end
 
   def test_find_with_implicit_inner_joins_honors_readonly_false
     authors = Author.joins(:posts).readonly(false).to_a
-    assert !authors.empty?, "expected authors to be non-empty"
-    assert authors.all? {|a| !a.readonly? }, "expected no authors to be readonly"
+    assert_not authors.empty?, "expected authors to be non-empty"
+    assert authors.all? { |a| !a.readonly? }, "expected no authors to be readonly"
   end
 
   def test_find_with_implicit_inner_joins_does_not_set_associations
-    authors = Author.joins(:posts).select('authors.*').to_a
-    assert !authors.empty?, "expected authors to be non-empty"
+    authors = Author.joins(:posts).select("authors.*").to_a
+    assert_not authors.empty?, "expected authors to be non-empty"
     assert authors.all? { |a| !a.instance_variable_defined?(:@posts) }, "expected no authors to have the @posts association loaded"
   end
 
   def test_count_honors_implicit_inner_joins
-    real_count = Author.all.to_a.sum{|a| a.posts.count }
+    real_count = Author.all.to_a.sum { |a| a.posts.count }
     assert_equal real_count, Author.joins(:posts).count, "plain inner join count should match the number of referenced posts records"
   end
 
   def test_calculate_honors_implicit_inner_joins
-    real_count = Author.all.to_a.sum{|a| a.posts.count }
-    assert_equal real_count, Author.joins(:posts).calculate(:count, 'authors.id'), "plain inner join count should match the number of referenced posts records"
+    real_count = Author.all.to_a.sum { |a| a.posts.count }
+    assert_equal real_count, Author.joins(:posts).calculate(:count, "authors.id"), "plain inner join count should match the number of referenced posts records"
   end
 
   def test_calculate_honors_implicit_inner_joins_and_distinct_and_conditions
-    real_count = Author.all.to_a.select {|a| a.posts.any? {|p| p.title =~ /^Welcome/} }.length
-    authors_with_welcoming_post_titles = Author.all.merge!(joins: :posts, where: "posts.title like 'Welcome%'").distinct.calculate(:count, 'authors.id')
+    real_count = Author.all.to_a.select { |a| a.posts.any? { |p| p.title.start_with?("Welcome") } }.length
+    authors_with_welcoming_post_titles = Author.all.merge!(joins: :posts, where: "posts.title like 'Welcome%'").distinct.calculate(:count, "authors.id")
     assert_equal real_count, authors_with_welcoming_post_titles, "inner join and conditions should have only returned authors posting titles starting with 'Welcome'"
   end
 
   def test_find_with_sti_join
-    scope = Post.joins(:special_comments).where(:id => posts(:sti_comments).id)
+    scope = Post.joins(:special_comments).where(id: posts(:sti_comments).id)
 
     # The join should match SpecialComment and its subclasses only
-    assert scope.where("comments.type" => "Comment").empty?
-    assert !scope.where("comments.type" => "SpecialComment").empty?
-    assert !scope.where("comments.type" => "SubSpecialComment").empty?
+    assert_empty scope.where("comments.type" => "Comment")
+    assert_not_empty scope.where("comments.type" => "SpecialComment")
+    assert_not_empty scope.where("comments.type" => "SubSpecialComment")
   end
 
   def test_find_with_conditions_on_reflection
-    assert !posts(:welcome).comments.empty?
-    assert Post.joins(:nonexistent_comments).where(:id => posts(:welcome).id).empty? # [sic!]
+    assert_not_empty posts(:welcome).comments
+    assert Post.joins(:nonexistent_comments).where(id: posts(:welcome).id).empty? # [sic!]
   end
 
   def test_find_with_conditions_on_through_reflection
-    assert !posts(:welcome).tags.empty?
-    assert Post.joins(:misc_tags).where(:id => posts(:welcome).id).empty?
+    assert_not_empty posts(:welcome).tags
+    assert_empty Post.joins(:misc_tags).where(id: posts(:welcome).id)
   end
 
   test "the default scope of the target is applied when joining associations" do
@@ -120,8 +140,8 @@ class InnerJoinAssociationTest < ActiveRecord::TestCase
 
   test "the default scope of the target is correctly aliased when joining associations" do
     author = Author.create! name: "Jon"
-    author.categories.create! name: 'Not Special'
-    author.special_categories.create! name: 'Special'
+    author.categories.create! name: "Not Special"
+    author.special_categories.create! name: "Special"
 
     categories = author.categories.includes(:special_categorizations).references(:special_categorizations).to_a
     assert_equal 2, categories.size
@@ -129,8 +149,8 @@ class InnerJoinAssociationTest < ActiveRecord::TestCase
 
   test "the correct records are loaded when including an aliased association" do
     author = Author.create! name: "Jon"
-    author.categories.create! name: 'Not Special'
-    author.special_categories.create! name: 'Special'
+    author.categories.create! name: "Not Special"
+    author.special_categories.create! name: "Special"
 
     categories = author.categories.eager_load(:special_categorizations).order(:name).to_a
     assert_equal 0, categories.first.special_categorizations.size
diff --git a/activerecord/test/cases/associations/inverse_associations_test.rb b/activerecord/test/cases/associations/inverse_associations_test.rb
index 423b8238b1..eb4dc73423 100644
--- a/activerecord/test/cases/associations/inverse_associations_test.rb
+++ b/activerecord/test/cases/associations/inverse_associations_test.rb
@@ -1,18 +1,27 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/man'
-require 'models/face'
-require 'models/interest'
-require 'models/zine'
-require 'models/club'
-require 'models/sponsor'
-require 'models/rating'
-require 'models/comment'
-require 'models/car'
-require 'models/bulb'
-require 'models/mixed_case_monkey'
-require 'models/admin'
-require 'models/admin/account'
-require 'models/admin/user'
+require "models/man"
+require "models/face"
+require "models/interest"
+require "models/zine"
+require "models/club"
+require "models/sponsor"
+require "models/rating"
+require "models/comment"
+require "models/car"
+require "models/bulb"
+require "models/mixed_case_monkey"
+require "models/admin"
+require "models/admin/account"
+require "models/admin/user"
+require "models/developer"
+require "models/company"
+require "models/project"
+require "models/author"
+require "models/post"
+require "models/department"
+require "models/hotel"
 
 class AutomaticInverseFindingTests < ActiveRecord::TestCase
   fixtures :ratings, :comments, :cars
@@ -21,11 +30,9 @@ class AutomaticInverseFindingTests < ActiveRecord::TestCase
     monkey_reflection = MixedCaseMonkey.reflect_on_association(:man)
     man_reflection = Man.reflect_on_association(:mixed_case_monkey)
 
-    assert_respond_to monkey_reflection, :has_inverse?
     assert monkey_reflection.has_inverse?, "The monkey reflection should have an inverse"
     assert_equal man_reflection, monkey_reflection.inverse_of, "The monkey reflection's inverse should be the man reflection"
 
-    assert_respond_to man_reflection, :has_inverse?
     assert man_reflection.has_inverse?, "The man reflection should have an inverse"
     assert_equal monkey_reflection, man_reflection.inverse_of, "The man reflection's inverse should be the monkey reflection"
   end
@@ -34,7 +41,6 @@ class AutomaticInverseFindingTests < ActiveRecord::TestCase
     account_reflection = Admin::Account.reflect_on_association(:users)
     user_reflection = Admin::User.reflect_on_association(:account)
 
-    assert_respond_to account_reflection, :has_inverse?
     assert account_reflection.has_inverse?, "The Admin::Account reflection should have an inverse"
     assert_equal user_reflection, account_reflection.inverse_of, "The Admin::Account reflection's inverse should be the Admin::User reflection"
   end
@@ -43,11 +49,9 @@ class AutomaticInverseFindingTests < ActiveRecord::TestCase
     car_reflection = Car.reflect_on_association(:bulb)
     bulb_reflection = Bulb.reflect_on_association(:car)
 
-    assert_respond_to car_reflection, :has_inverse?
     assert car_reflection.has_inverse?, "The Car reflection should have an inverse"
     assert_equal bulb_reflection, car_reflection.inverse_of, "The Car reflection's inverse should be the Bulb reflection"
 
-    assert_respond_to bulb_reflection, :has_inverse?
     assert bulb_reflection.has_inverse?, "The Bulb reflection should have an inverse"
     assert_equal car_reflection, bulb_reflection.inverse_of, "The Bulb reflection's inverse should be the Car reflection"
   end
@@ -56,11 +60,24 @@ class AutomaticInverseFindingTests < ActiveRecord::TestCase
     comment_reflection = Comment.reflect_on_association(:ratings)
     rating_reflection = Rating.reflect_on_association(:comment)
 
-    assert_respond_to comment_reflection, :has_inverse?
     assert comment_reflection.has_inverse?, "The Comment reflection should have an inverse"
     assert_equal rating_reflection, comment_reflection.inverse_of, "The Comment reflection's inverse should be the Rating reflection"
   end
 
+  def test_has_many_and_belongs_to_should_find_inverse_automatically_for_sti
+    author_reflection = Author.reflect_on_association(:posts)
+    author_child_reflection = Author.reflect_on_association(:special_posts)
+    post_reflection = Post.reflect_on_association(:author)
+
+    assert_respond_to author_reflection, :has_inverse?
+    assert author_reflection.has_inverse?, "The Author reflection should have an inverse"
+    assert_equal post_reflection, author_reflection.inverse_of, "The Author reflection's inverse should be the Post reflection"
+
+    assert_respond_to author_child_reflection, :has_inverse?
+    assert author_child_reflection.has_inverse?, "The Author reflection should have an inverse"
+    assert_equal post_reflection, author_child_reflection.inverse_of, "The Author reflection's inverse should be the Post reflection"
+  end
+
   def test_has_one_and_belongs_to_automatic_inverse_shares_objects
     car = Car.first
     bulb = Bulb.create!(car: car)
@@ -80,10 +97,10 @@ class AutomaticInverseFindingTests < ActiveRecord::TestCase
 
     assert_equal rating.comment, comment, "The Rating's comment should be the original Comment"
 
-    rating.comment.body = "Brogramming is the act of programming, like a bro."
+    rating.comment.body = "Fennec foxes are the smallest of the foxes."
     assert_equal rating.comment.body, comment.body, "Changing the Comment's body on the association should change the original Comment's body"
 
-    comment.body = "Broseiden is the king of the sea of bros."
+    comment.body = "Kittens are adorable."
     assert_equal comment.body, rating.comment.body, "Changing the original Comment's body should change the Comment's body on the association"
   end
 
@@ -94,87 +111,63 @@ class AutomaticInverseFindingTests < ActiveRecord::TestCase
 
     assert_equal rating.comment, comment, "The Rating's comment should be the original Comment"
 
-    rating.comment.body = "Brogramming is the act of programming, like a bro."
+    rating.comment.body = "Fennec foxes are the smallest of the foxes."
     assert_equal rating.comment.body, comment.body, "Changing the Comment's body on the association should change the original Comment's body"
 
-    comment.body = "Broseiden is the king of the sea of bros."
+    comment.body = "Kittens are adorable."
     assert_equal comment.body, rating.comment.body, "Changing the original Comment's body should change the Comment's body on the association"
   end
 
   def test_polymorphic_and_has_many_through_relationships_should_not_have_inverses
     sponsor_reflection = Sponsor.reflect_on_association(:sponsorable)
 
-    assert_respond_to sponsor_reflection, :has_inverse?
-    assert !sponsor_reflection.has_inverse?, "A polymorphic association should not find an inverse automatically"
+    assert_not sponsor_reflection.has_inverse?, "A polymorphic association should not find an inverse automatically"
 
     club_reflection = Club.reflect_on_association(:members)
 
-    assert_respond_to club_reflection, :has_inverse?
-    assert !club_reflection.has_inverse?, "A has_many_through association should not find an inverse automatically"
+    assert_not club_reflection.has_inverse?, "A has_many_through association should not find an inverse automatically"
   end
 
-  def test_polymorphic_relationships_should_still_not_have_inverses_when_non_polymorphic_relationship_has_the_same_name
+  def test_polymorphic_has_one_should_find_inverse_automatically
     man_reflection = Man.reflect_on_association(:polymorphic_face_without_inverse)
-    face_reflection = Face.reflect_on_association(:man)
-
-    assert_respond_to face_reflection, :has_inverse?
-    assert face_reflection.has_inverse?, "For this test, the non-polymorphic association must have an inverse"
 
-    assert_respond_to man_reflection, :has_inverse?
-    assert !man_reflection.has_inverse?, "The target of a polymorphic association should not find an inverse automatically"
+    assert_predicate man_reflection, :has_inverse?
   end
 end
 
 class InverseAssociationTests < ActiveRecord::TestCase
   def test_should_allow_for_inverse_of_options_in_associations
-    assert_nothing_raised(ArgumentError, 'ActiveRecord should allow the inverse_of options on has_many') do
-      Class.new(ActiveRecord::Base).has_many(:wheels, :inverse_of => :car)
+    assert_nothing_raised do
+      Class.new(ActiveRecord::Base).has_many(:wheels, inverse_of: :car)
     end
 
-    assert_nothing_raised(ArgumentError, 'ActiveRecord should allow the inverse_of options on has_one') do
-      Class.new(ActiveRecord::Base).has_one(:engine, :inverse_of => :car)
+    assert_nothing_raised do
+      Class.new(ActiveRecord::Base).has_one(:engine, inverse_of: :car)
     end
 
-    assert_nothing_raised(ArgumentError, 'ActiveRecord should allow the inverse_of options on belongs_to') do
-      Class.new(ActiveRecord::Base).belongs_to(:car, :inverse_of => :driver)
+    assert_nothing_raised do
+      Class.new(ActiveRecord::Base).belongs_to(:car, inverse_of: :driver)
     end
   end
 
   def test_should_be_able_to_ask_a_reflection_if_it_has_an_inverse
     has_one_with_inverse_ref = Man.reflect_on_association(:face)
-    assert_respond_to has_one_with_inverse_ref, :has_inverse?
-    assert has_one_with_inverse_ref.has_inverse?
+    assert_predicate has_one_with_inverse_ref, :has_inverse?
 
     has_many_with_inverse_ref = Man.reflect_on_association(:interests)
-    assert_respond_to has_many_with_inverse_ref, :has_inverse?
-    assert has_many_with_inverse_ref.has_inverse?
+    assert_predicate has_many_with_inverse_ref, :has_inverse?
 
     belongs_to_with_inverse_ref = Face.reflect_on_association(:man)
-    assert_respond_to belongs_to_with_inverse_ref, :has_inverse?
-    assert belongs_to_with_inverse_ref.has_inverse?
+    assert_predicate belongs_to_with_inverse_ref, :has_inverse?
 
     has_one_without_inverse_ref = Club.reflect_on_association(:sponsor)
-    assert_respond_to has_one_without_inverse_ref, :has_inverse?
-    assert !has_one_without_inverse_ref.has_inverse?
+    assert_not_predicate has_one_without_inverse_ref, :has_inverse?
 
     has_many_without_inverse_ref = Club.reflect_on_association(:memberships)
-    assert_respond_to has_many_without_inverse_ref, :has_inverse?
-    assert !has_many_without_inverse_ref.has_inverse?
+    assert_not_predicate has_many_without_inverse_ref, :has_inverse?
 
     belongs_to_without_inverse_ref = Sponsor.reflect_on_association(:sponsor_club)
-    assert_respond_to belongs_to_without_inverse_ref, :has_inverse?
-    assert !belongs_to_without_inverse_ref.has_inverse?
-  end
-
-  def test_should_be_able_to_ask_a_reflection_what_it_is_the_inverse_of
-    has_one_ref = Man.reflect_on_association(:face)
-    assert_respond_to has_one_ref, :inverse_of
-
-    has_many_ref = Man.reflect_on_association(:interests)
-    assert_respond_to has_many_ref, :inverse_of
-
-    belongs_to_ref = Face.reflect_on_association(:man)
-    assert_respond_to belongs_to_ref, :inverse_of
+    assert_not_predicate belongs_to_without_inverse_ref, :has_inverse?
   end
 
   def test_inverse_of_method_should_supply_the_actual_reflection_instance_it_is_the_inverse_of
@@ -198,6 +191,26 @@ class InverseAssociationTests < ActiveRecord::TestCase
     belongs_to_ref = Sponsor.reflect_on_association(:sponsor_club)
     assert_nil belongs_to_ref.inverse_of
   end
+
+  def test_polymorphic_associations_dont_attempt_to_find_inverse_of
+    belongs_to_ref = Sponsor.reflect_on_association(:sponsor)
+    assert_raise(ArgumentError) { belongs_to_ref.klass }
+    assert_nil belongs_to_ref.inverse_of
+
+    belongs_to_ref = Face.reflect_on_association(:human)
+    assert_raise(ArgumentError) { belongs_to_ref.klass }
+    assert_nil belongs_to_ref.inverse_of
+  end
+
+  def test_this_inverse_stuff
+    firm = Firm.create!(name: "Adequate Holdings")
+    Project.create!(name: "Project 1", firm: firm)
+    Developer.create!(name: "Gorbypuff", firm: firm)
+
+    new_project = Project.last
+    assert Project.reflect_on_association(:lead_developer).inverse_of.present?, "Expected inverse of to be present"
+    assert new_project.lead_developer.present?, "Expected lead developer to be present on the project"
+  end
 end
 
 class InverseHasOneTests < ActiveRecord::TestCase
@@ -207,73 +220,72 @@ class InverseHasOneTests < ActiveRecord::TestCase
     m = men(:gordon)
     f = m.face
     assert_equal m.name, f.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to parent instance"
-    f.man.name = 'Mungo'
+    f.man.name = "Mungo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to child-owned instance"
   end
 
-
   def test_parent_instance_should_be_shared_with_eager_loaded_child_on_find
-    m = Man.all.merge!(:where => {:name => 'Gordon'}, :includes => :face).first
+    m = Man.all.merge!(where: { name: "Gordon" }, includes: :face).first
     f = m.face
     assert_equal m.name, f.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to parent instance"
-    f.man.name = 'Mungo'
+    f.man.name = "Mungo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to child-owned instance"
 
-    m = Man.all.merge!(:where => {:name => 'Gordon'}, :includes => :face, :order => 'faces.id').first
+    m = Man.all.merge!(where: { name: "Gordon" }, includes: :face, order: "faces.id").first
     f = m.face
     assert_equal m.name, f.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to parent instance"
-    f.man.name = 'Mungo'
+    f.man.name = "Mungo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to child-owned instance"
   end
 
   def test_parent_instance_should_be_shared_with_newly_built_child
     m = Man.first
-    f = m.build_face(:description => 'haunted')
+    f = m.build_face(description: "haunted")
     assert_not_nil f.man
     assert_equal m.name, f.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to parent instance"
-    f.man.name = 'Mungo'
+    f.man.name = "Mungo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to just-built-child-owned instance"
   end
 
   def test_parent_instance_should_be_shared_with_newly_created_child
     m = Man.first
-    f = m.create_face(:description => 'haunted')
+    f = m.create_face(description: "haunted")
     assert_not_nil f.man
     assert_equal m.name, f.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to parent instance"
-    f.man.name = 'Mungo'
+    f.man.name = "Mungo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to newly-created-child-owned instance"
   end
 
   def test_parent_instance_should_be_shared_with_newly_created_child_via_bang_method
     m = Man.first
-    f = m.create_face!(:description => 'haunted')
+    f = m.create_face!(description: "haunted")
     assert_not_nil f.man
     assert_equal m.name, f.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to parent instance"
-    f.man.name = 'Mungo'
+    f.man.name = "Mungo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to newly-created-child-owned instance"
   end
 
   def test_parent_instance_should_be_shared_with_replaced_via_accessor_child
     m = Man.first
-    f = Face.new(:description => 'haunted')
+    f = Face.new(description: "haunted")
     m.face = f
     assert_not_nil f.man
     assert_equal m.name, f.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to parent instance"
-    f.man.name = 'Mungo'
+    f.man.name = "Mungo"
     assert_equal m.name, f.man.name, "Name of man should be the same after changes to replaced-child-owned instance"
   end
 
@@ -283,74 +295,95 @@ class InverseHasOneTests < ActiveRecord::TestCase
 end
 
 class InverseHasManyTests < ActiveRecord::TestCase
-  fixtures :men, :interests
+  fixtures :men, :interests, :posts, :authors, :author_addresses
 
   def test_parent_instance_should_be_shared_with_every_child_on_find
     m = men(:gordon)
     is = m.interests
     is.each do |i|
       assert_equal m.name, i.man.name, "Name of man should be the same before changes to parent instance"
-      m.name = 'Bongo'
+      m.name = "Bongo"
       assert_equal m.name, i.man.name, "Name of man should be the same after changes to parent instance"
-      i.man.name = 'Mungo'
+      i.man.name = "Mungo"
       assert_equal m.name, i.man.name, "Name of man should be the same after changes to child-owned instance"
     end
   end
 
+  def test_parent_instance_should_be_shared_with_every_child_on_find_for_sti
+    a = authors(:david)
+    ps = a.posts
+    ps.each do |p|
+      assert_equal a.name, p.author.name, "Name of man should be the same before changes to parent instance"
+      a.name = "Bongo"
+      assert_equal a.name, p.author.name, "Name of man should be the same after changes to parent instance"
+      p.author.name = "Mungo"
+      assert_equal a.name, p.author.name, "Name of man should be the same after changes to child-owned instance"
+    end
+
+    sps = a.special_posts
+    sps.each do |sp|
+      assert_equal a.name, sp.author.name, "Name of man should be the same before changes to parent instance"
+      a.name = "Bongo"
+      assert_equal a.name, sp.author.name, "Name of man should be the same after changes to parent instance"
+      sp.author.name = "Mungo"
+      assert_equal a.name, sp.author.name, "Name of man should be the same after changes to child-owned instance"
+    end
+  end
+
   def test_parent_instance_should_be_shared_with_eager_loaded_children
-    m = Man.all.merge!(:where => {:name => 'Gordon'}, :includes => :interests).first
+    m = Man.all.merge!(where: { name: "Gordon" }, includes: :interests).first
     is = m.interests
     is.each do |i|
       assert_equal m.name, i.man.name, "Name of man should be the same before changes to parent instance"
-      m.name = 'Bongo'
+      m.name = "Bongo"
       assert_equal m.name, i.man.name, "Name of man should be the same after changes to parent instance"
-      i.man.name = 'Mungo'
+      i.man.name = "Mungo"
       assert_equal m.name, i.man.name, "Name of man should be the same after changes to child-owned instance"
     end
 
-    m = Man.all.merge!(:where => {:name => 'Gordon'}, :includes => :interests, :order => 'interests.id').first
+    m = Man.all.merge!(where: { name: "Gordon" }, includes: :interests, order: "interests.id").first
     is = m.interests
     is.each do |i|
       assert_equal m.name, i.man.name, "Name of man should be the same before changes to parent instance"
-      m.name = 'Bongo'
+      m.name = "Bongo"
       assert_equal m.name, i.man.name, "Name of man should be the same after changes to parent instance"
-      i.man.name = 'Mungo'
+      i.man.name = "Mungo"
       assert_equal m.name, i.man.name, "Name of man should be the same after changes to child-owned instance"
     end
   end
 
   def test_parent_instance_should_be_shared_with_newly_block_style_built_child
     m = Man.first
-    i = m.interests.build {|ii| ii.topic = 'Industrial Revolution Re-enactment'}
+    i = m.interests.build { |ii| ii.topic = "Industrial Revolution Re-enactment" }
     assert_not_nil i.topic, "Child attributes supplied to build via blocks should be populated"
     assert_not_nil i.man
     assert_equal m.name, i.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to parent instance"
-    i.man.name = 'Mungo'
+    i.man.name = "Mungo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to just-built-child-owned instance"
   end
 
   def test_parent_instance_should_be_shared_with_newly_created_via_bang_method_child
     m = Man.first
-    i = m.interests.create!(:topic => 'Industrial Revolution Re-enactment')
+    i = m.interests.create!(topic: "Industrial Revolution Re-enactment")
     assert_not_nil i.man
     assert_equal m.name, i.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to parent instance"
-    i.man.name = 'Mungo'
+    i.man.name = "Mungo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to newly-created-child-owned instance"
   end
 
   def test_parent_instance_should_be_shared_with_newly_block_style_created_child
     m = Man.first
-    i = m.interests.create {|ii| ii.topic = 'Industrial Revolution Re-enactment'}
+    i = m.interests.create { |ii| ii.topic = "Industrial Revolution Re-enactment" }
     assert_not_nil i.topic, "Child attributes supplied to create via blocks should be populated"
     assert_not_nil i.man
     assert_equal m.name, i.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to parent instance"
-    i.man.name = 'Mungo'
+    i.man.name = "Mungo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to newly-created-child-owned instance"
   end
 
@@ -372,25 +405,25 @@ class InverseHasManyTests < ActiveRecord::TestCase
 
   def test_parent_instance_should_be_shared_with_poked_in_child
     m = men(:gordon)
-    i = Interest.create(:topic => 'Industrial Revolution Re-enactment')
+    i = Interest.create(topic: "Industrial Revolution Re-enactment")
     m.interests << i
     assert_not_nil i.man
     assert_equal m.name, i.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to parent instance"
-    i.man.name = 'Mungo'
+    i.man.name = "Mungo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to newly-created-child-owned instance"
   end
 
   def test_parent_instance_should_be_shared_with_replaced_via_accessor_children
     m = Man.first
-    i = Interest.new(:topic => 'Industrial Revolution Re-enactment')
+    i = Interest.new(topic: "Industrial Revolution Re-enactment")
     m.interests = [i]
     assert_not_nil i.man
     assert_equal m.name, i.man.name, "Name of man should be the same before changes to parent instance"
-    m.name = 'Bongo'
+    m.name = "Bongo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to parent instance"
-    i.man.name = 'Mungo'
+    i.man.name = "Mungo"
     assert_equal m.name, i.man.name, "Name of man should be the same after changes to replaced-child-owned instance"
   end
 
@@ -431,7 +464,7 @@ class InverseHasManyTests < ActiveRecord::TestCase
     assert man.equal?(man.interests.first.man), "Two inverses should lead back to the same object that was originally held"
     assert man.equal?(man.interests.find(interest.id).man), "Two inversions should lead back to the same object that was originally held"
 
-    assert_equal man.name, man.interests.find(interest.id).man.name, "The name of the man should match before the name is changed"
+    assert_nil man.interests.find(interest.id).man.name, "The name of the man should match before the name is changed"
     man.name = "Ben Bitdiddle"
     assert_equal man.name, man.interests.find(interest.id).man.name, "The name of the man should match after the parent name is changed"
     man.interests.find(interest.id).man.name = "Alyssa P. Hacker"
@@ -443,7 +476,7 @@ class InverseHasManyTests < ActiveRecord::TestCase
     interest = Interest.create!(man: man)
 
     man.interests.find(interest.id)
-    assert_not man.interests.loaded?
+    assert_not_predicate man.interests, :loaded?
   end
 
   def test_raise_record_not_found_error_when_invalid_ids_are_passed
@@ -463,7 +496,10 @@ class InverseHasManyTests < ActiveRecord::TestCase
   def test_raise_record_not_found_error_when_no_ids_are_passed
     man = Man.create!
 
-    assert_raise(ActiveRecord::RecordNotFound) { man.interests.find() }
+    exception = assert_raise(ActiveRecord::RecordNotFound) { man.interests.load.find() }
+
+    assert_equal exception.model, "Interest"
+    assert_equal exception.primary_key, "id"
   end
 
   def test_trying_to_use_inverses_that_dont_exist_should_raise_an_error
@@ -472,7 +508,7 @@ class InverseHasManyTests < ActiveRecord::TestCase
 
   def test_child_instance_should_point_to_parent_without_saving
     man = Man.new
-    i = Interest.create(:topic => 'Industrial Revolution Re-enactment')
+    i = Interest.create(topic: "Industrial Revolution Re-enactment")
 
     man.interests << i
     assert_not_nil i.man
@@ -480,7 +516,34 @@ class InverseHasManyTests < ActiveRecord::TestCase
     i.man.name = "Charles"
     assert_equal i.man.name, man.name
 
-    assert !man.persisted?
+    assert_not_predicate man, :persisted?
+  end
+
+  def test_inverse_instance_should_be_set_before_find_callbacks_are_run
+    reset_callbacks(Interest, :find) do
+      Interest.after_find { raise unless association(:man).loaded? && man.present? }
+
+      assert_predicate Man.first.interests.reload, :any?
+      assert_predicate Man.includes(:interests).first.interests, :any?
+      assert_predicate Man.joins(:interests).includes(:interests).first.interests, :any?
+    end
+  end
+
+  def test_inverse_instance_should_be_set_before_initialize_callbacks_are_run
+    reset_callbacks(Interest, :initialize) do
+      Interest.after_initialize { raise unless association(:man).loaded? && man.present? }
+
+      assert_predicate Man.first.interests.reload, :any?
+      assert_predicate Man.includes(:interests).first.interests, :any?
+      assert_predicate Man.joins(:interests).includes(:interests).first.interests, :any?
+    end
+  end
+
+  def reset_callbacks(target, type)
+    old_callbacks = target.send(:get_callbacks, type).deep_dup
+    yield
+  ensure
+    target.send(:set_callbacks, type, old_callbacks) if old_callbacks
   end
 end
 
@@ -491,49 +554,49 @@ class InverseBelongsToTests < ActiveRecord::TestCase
     f = faces(:trusting)
     m = f.man
     assert_equal f.description, m.face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to child instance"
-    m.face.description = 'pleasing'
+    m.face.description = "pleasing"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to parent-owned instance"
   end
 
   def test_eager_loaded_child_instance_should_be_shared_with_parent_on_find
-    f = Face.all.merge!(:includes => :man, :where => {:description => 'trusting'}).first
+    f = Face.all.merge!(includes: :man, where: { description: "trusting" }).first
     m = f.man
     assert_equal f.description, m.face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to child instance"
-    m.face.description = 'pleasing'
+    m.face.description = "pleasing"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to parent-owned instance"
 
-    f = Face.all.merge!(:includes => :man, :order => 'men.id', :where => {:description => 'trusting'}).first
+    f = Face.all.merge!(includes: :man, order: "men.id", where: { description: "trusting" }).first
     m = f.man
     assert_equal f.description, m.face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to child instance"
-    m.face.description = 'pleasing'
+    m.face.description = "pleasing"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to parent-owned instance"
   end
 
   def test_child_instance_should_be_shared_with_newly_built_parent
     f = faces(:trusting)
-    m = f.build_man(:name => 'Charles')
+    m = f.build_man(name: "Charles")
     assert_not_nil m.face
     assert_equal f.description, m.face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to child instance"
-    m.face.description = 'pleasing'
+    m.face.description = "pleasing"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to just-built-parent-owned instance"
   end
 
   def test_child_instance_should_be_shared_with_newly_created_parent
     f = faces(:trusting)
-    m = f.create_man(:name => 'Charles')
+    m = f.create_man(name: "Charles")
     assert_not_nil m.face
     assert_equal f.description, m.face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to child instance"
-    m.face.description = 'pleasing'
+    m.face.description = "pleasing"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to newly-created-parent-owned instance"
   end
 
@@ -541,24 +604,24 @@ class InverseBelongsToTests < ActiveRecord::TestCase
     i = interests(:trainspotting)
     m = i.man
     assert_not_nil m.interests
-    iz = m.interests.detect { |_iz| _iz.id == i.id}
+    iz = m.interests.detect { |_iz| _iz.id == i.id }
     assert_not_nil iz
     assert_equal i.topic, iz.topic, "Interest topics should be the same before changes to child"
-    i.topic = 'Eating cheese with a spoon'
+    i.topic = "Eating cheese with a spoon"
     assert_not_equal i.topic, iz.topic, "Interest topics should not be the same after changes to child"
-    iz.topic = 'Cow tipping'
+    iz.topic = "Cow tipping"
     assert_not_equal i.topic, iz.topic, "Interest topics should not be the same after changes to parent-owned instance"
   end
 
   def test_child_instance_should_be_shared_with_replaced_via_accessor_parent
     f = Face.first
-    m = Man.new(:name => 'Charles')
+    m = Man.new(name: "Charles")
     f.man = m
     assert_not_nil m.face
     assert_equal f.description, m.face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to child instance"
-    m.face.description = 'pleasing'
+    m.face.description = "pleasing"
     assert_equal f.description, m.face.description, "Description of face should be the same after changes to replaced-parent-owned instance"
   end
 
@@ -571,30 +634,30 @@ class InversePolymorphicBelongsToTests < ActiveRecord::TestCase
   fixtures :men, :faces, :interests
 
   def test_child_instance_should_be_shared_with_parent_on_find
-    f = Face.all.merge!(:where => {:description => 'confused'}).first
+    f = Face.all.merge!(where: { description: "confused" }).first
     m = f.polymorphic_man
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same after changes to child instance"
-    m.polymorphic_face.description = 'pleasing'
+    m.polymorphic_face.description = "pleasing"
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same after changes to parent-owned instance"
   end
 
   def test_eager_loaded_child_instance_should_be_shared_with_parent_on_find
-    f = Face.all.merge!(:where => {:description => 'confused'}, :includes => :man).first
+    f = Face.all.merge!(where: { description: "confused" }, includes: :man).first
     m = f.polymorphic_man
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same after changes to child instance"
-    m.polymorphic_face.description = 'pleasing'
+    m.polymorphic_face.description = "pleasing"
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same after changes to parent-owned instance"
 
-    f = Face.all.merge!(:where => {:description => 'confused'}, :includes => :man, :order => 'men.id').first
+    f = Face.all.merge!(where: { description: "confused" }, includes: :man, order: "men.id").first
     m = f.polymorphic_man
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same before changes to child instance"
-    f.description = 'gormless'
+    f.description = "gormless"
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same after changes to child instance"
-    m.polymorphic_face.description = 'pleasing'
+    m.polymorphic_face.description = "pleasing"
     assert_equal f.description, m.polymorphic_face.description, "Description of face should be the same after changes to parent-owned instance"
   end
 
@@ -606,23 +669,9 @@ class InversePolymorphicBelongsToTests < ActiveRecord::TestCase
     face.polymorphic_man = new_man
 
     assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same before changes to parent instance"
-    face.description = 'Bongo'
-    assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same after changes to parent instance"
-    new_man.polymorphic_face.description = 'Mungo'
-    assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same after changes to replaced-parent-owned instance"
-  end
-
-  def test_child_instance_should_be_shared_with_replaced_via_method_parent
-    face = faces(:confused)
-    new_man = Man.new
-
-    assert_not_nil face.polymorphic_man
-    face.polymorphic_man = new_man
-
-    assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same before changes to parent instance"
-    face.description = 'Bongo'
+    face.description = "Bongo"
     assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same after changes to parent instance"
-    new_man.polymorphic_face.description = 'Mungo'
+    new_man.polymorphic_face.description = "Mungo"
     assert_equal face.description, new_man.polymorphic_face.description, "Description of face should be the same after changes to replaced-parent-owned instance"
   end
 
@@ -638,22 +687,32 @@ class InversePolymorphicBelongsToTests < ActiveRecord::TestCase
     assert_equal old_inversed_man.object_id, new_inversed_man.object_id
   end
 
+  def test_inversed_instance_should_not_be_reloaded_after_stale_state_changed_with_validation
+    face = Face.new man: Man.new
+
+    old_inversed_man = face.man
+    face.save!
+    new_inversed_man = face.man
+
+    assert_equal old_inversed_man.object_id, new_inversed_man.object_id
+  end
+
   def test_should_not_try_to_set_inverse_instances_when_the_inverse_is_a_has_many
     i = interests(:llama_wrangling)
     m = i.polymorphic_man
     assert_not_nil m.polymorphic_interests
-    iz = m.polymorphic_interests.detect { |_iz| _iz.id == i.id}
+    iz = m.polymorphic_interests.detect { |_iz| _iz.id == i.id }
     assert_not_nil iz
     assert_equal i.topic, iz.topic, "Interest topics should be the same before changes to child"
-    i.topic = 'Eating cheese with a spoon'
+    i.topic = "Eating cheese with a spoon"
     assert_not_equal i.topic, iz.topic, "Interest topics should not be the same after changes to child"
-    iz.topic = 'Cow tipping'
+    iz.topic = "Cow tipping"
     assert_not_equal i.topic, iz.topic, "Interest topics should not be the same after changes to parent-owned instance"
   end
 
   def test_trying_to_access_inverses_that_dont_exist_shouldnt_raise_an_error
     # Ideally this would, if only for symmetry's sake with other association types
-    assert_nothing_raised(ActiveRecord::InverseOfAssociationNotFoundError) { Face.first.horrible_polymorphic_man }
+    assert_nothing_raised { Face.first.horrible_polymorphic_man }
   end
 
   def test_trying_to_set_polymorphic_inverses_that_dont_exist_at_all_should_raise_an_error
@@ -663,10 +722,20 @@ class InversePolymorphicBelongsToTests < ActiveRecord::TestCase
 
   def test_trying_to_set_polymorphic_inverses_that_dont_exist_on_the_instance_being_set_should_raise_an_error
     # passes because Man does have the correct inverse_of
-    assert_nothing_raised(ActiveRecord::InverseOfAssociationNotFoundError) { Face.first.polymorphic_man = Man.first }
+    assert_nothing_raised { Face.first.polymorphic_man = Man.first }
     # fails because Interest does have the correct inverse_of
     assert_raise(ActiveRecord::InverseOfAssociationNotFoundError) { Face.first.polymorphic_man = Interest.first }
   end
+
+  def test_favors_has_one_associations_for_inverse_of
+    inverse_name = Post.reflect_on_association(:author).inverse_of.name
+    assert_equal :post, inverse_name
+  end
+
+  def test_finds_inverse_of_for_plural_associations
+    inverse_name = Department.reflect_on_association(:hotel).inverse_of.name
+    assert_equal :departments, inverse_name
+  end
 end
 
 # NOTE - these tests might not be meaningful, ripped as they were from the parental_control plugin
@@ -675,7 +744,7 @@ class InverseMultipleHasManyInversesForSameModel < ActiveRecord::TestCase
   fixtures :men, :interests, :zines
 
   def test_that_we_can_load_associations_that_have_the_same_reciprocal_name_from_different_models
-    assert_nothing_raised(ActiveRecord::AssociationTypeMismatch) do
+    assert_nothing_raised do
       i = Interest.first
       i.zine
       i.man
@@ -683,10 +752,10 @@ class InverseMultipleHasManyInversesForSameModel < ActiveRecord::TestCase
   end
 
   def test_that_we_can_create_associations_that_have_the_same_reciprocal_name_from_different_models
-    assert_nothing_raised(ActiveRecord::AssociationTypeMismatch) do
+    assert_nothing_raised do
       i = Interest.first
-      i.build_zine(:title => 'Get Some in Winter! 2008')
-      i.build_man(:name => 'Gordon')
+      i.build_zine(title: "Get Some in Winter! 2008")
+      i.build_man(name: "Gordon")
       i.save!
     end
   end
diff --git a/activerecord/test/cases/associations/join_model_test.rb b/activerecord/test/cases/associations/join_model_test.rb
index 5575419c35..9d1c73c33b 100644
--- a/activerecord/test/cases/associations/join_model_test.rb
+++ b/activerecord/test/cases/associations/join_model_test.rb
@@ -1,38 +1,40 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/tag'
-require 'models/tagging'
-require 'models/post'
-require 'models/rating'
-require 'models/item'
-require 'models/comment'
-require 'models/author'
-require 'models/category'
-require 'models/categorization'
-require 'models/vertex'
-require 'models/edge'
-require 'models/book'
-require 'models/citation'
-require 'models/aircraft'
-require 'models/engine'
-require 'models/car'
+require "models/tag"
+require "models/tagging"
+require "models/post"
+require "models/rating"
+require "models/item"
+require "models/comment"
+require "models/author"
+require "models/category"
+require "models/categorization"
+require "models/vertex"
+require "models/edge"
+require "models/book"
+require "models/citation"
+require "models/aircraft"
+require "models/engine"
+require "models/car"
 
 class AssociationsJoinModelTest < ActiveRecord::TestCase
   self.use_transactional_tests = false unless supports_savepoints?
 
-  fixtures :posts, :authors, :categories, :categorizations, :comments, :tags, :taggings, :author_favorites, :vertices, :items, :books,
+  fixtures :posts, :authors, :author_addresses, :categories, :categorizations, :comments, :tags, :taggings, :author_favorites, :vertices, :items, :books,
     # Reload edges table from fixtures as otherwise repeated test was failing
     :edges
 
   def test_has_many
-    assert authors(:david).categories.include?(categories(:general))
+    assert_includes authors(:david).categories, categories(:general)
   end
 
   def test_has_many_inherited
-    assert authors(:mary).categories.include?(categories(:sti_test))
+    assert_includes authors(:mary).categories, categories(:sti_test)
   end
 
   def test_inherited_has_many
-    assert categories(:sti_test).authors.include?(authors(:mary))
+    assert_includes categories(:sti_test).authors, authors(:mary)
   end
 
   def test_has_many_distinct_through_join_model
@@ -42,11 +44,11 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_has_many_distinct_through_count
     author = authors(:mary)
-    assert !authors(:mary).unique_categorized_posts.loaded?
+    assert_not_predicate authors(:mary).unique_categorized_posts, :loaded?
     assert_queries(1) { assert_equal 1, author.unique_categorized_posts.count }
     assert_queries(1) { assert_equal 1, author.unique_categorized_posts.count(:title) }
     assert_queries(1) { assert_equal 0, author.unique_categorized_posts.where(title: nil).count(:title) }
-    assert !authors(:mary).unique_categorized_posts.loaded?
+    assert_not_predicate authors(:mary).unique_categorized_posts, :loaded?
   end
 
   def test_has_many_distinct_through_find
@@ -88,7 +90,7 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_polymorphic_has_many_going_through_join_model_with_custom_select_and_joins
     assert_equal tags(:general), tag = posts(:welcome).tags.add_joins_and_select.first
-    assert_nothing_raised(NoMethodError) { tag.author_id }
+    assert_nothing_raised { tag.author_id }
   end
 
   def test_polymorphic_has_many_going_through_join_model_with_custom_foreign_key
@@ -97,11 +99,11 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_polymorphic_has_many_create_model_with_inheritance_and_custom_base_class
-    post = SubStiPost.create :title => 'SubStiPost', :body => 'SubStiPost body'
-    assert_instance_of SubStiPost, post
+    post = SubAbstractStiPost.create title: "SubAbstractStiPost", body: "SubAbstractStiPost body"
+    assert_instance_of SubAbstractStiPost, post
 
-    tagging = tags(:misc).taggings.create(:taggable => post)
-    assert_equal "SubStiPost", tagging.taggable_type
+    tagging = tags(:misc).taggings.create(taggable: post)
+    assert_equal "SubAbstractStiPost", tagging.taggable_type
   end
 
   def test_polymorphic_has_many_going_through_join_model_with_inheritance
@@ -116,12 +118,12 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     post = posts(:thinking)
     assert_instance_of SpecialPost, post
 
-    tagging = tags(:misc).taggings.create(:taggable => post)
+    tagging = tags(:misc).taggings.create(taggable: post)
     assert_equal "Post", tagging.taggable_type
   end
 
   def test_polymorphic_has_one_create_model_with_inheritance
-    tagging = tags(:misc).create_tagging(:taggable => posts(:thinking))
+    tagging = tags(:misc).create_tagging(taggable: posts(:thinking))
     assert_equal "Post", tagging.taggable_type
   end
 
@@ -142,7 +144,7 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_set_polymorphic_has_one_on_new_record
     tagging = tags(:misc).taggings.create
-    post = Post.new :title => "foo", :body => "bar"
+    post = Post.new title: "foo", body: "bar"
     post.tagging = tagging
     post.save!
 
@@ -153,50 +155,50 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_create_polymorphic_has_many_with_scope
     old_count = posts(:welcome).taggings.count
-    tagging = posts(:welcome).taggings.create(:tag => tags(:misc))
+    tagging = posts(:welcome).taggings.create(tag: tags(:misc))
     assert_equal "Post", tagging.taggable_type
-    assert_equal old_count+1, posts(:welcome).taggings.count
+    assert_equal old_count + 1, posts(:welcome).taggings.count
   end
 
   def test_create_bang_polymorphic_with_has_many_scope
     old_count = posts(:welcome).taggings.count
-    tagging = posts(:welcome).taggings.create!(:tag => tags(:misc))
+    tagging = posts(:welcome).taggings.create!(tag: tags(:misc))
     assert_equal "Post", tagging.taggable_type
-    assert_equal old_count+1, posts(:welcome).taggings.count
+    assert_equal old_count + 1, posts(:welcome).taggings.count
   end
 
   def test_create_polymorphic_has_one_with_scope
     old_count = Tagging.count
-    tagging = posts(:welcome).create_tagging(:tag => tags(:misc))
+    tagging = posts(:welcome).create_tagging(tag: tags(:misc))
     assert_equal "Post", tagging.taggable_type
-    assert_equal old_count+1, Tagging.count
+    assert_equal old_count + 1, Tagging.count
   end
 
   def test_delete_polymorphic_has_many_with_delete_all
     assert_equal 1, posts(:welcome).taggings.count
-    posts(:welcome).taggings.first.update_columns taggable_type: 'PostWithHasManyDeleteAll'
+    posts(:welcome).taggings.first.update_columns taggable_type: "PostWithHasManyDeleteAll"
     post = find_post_with_dependency(1, :has_many, :taggings, :delete_all)
 
     old_count = Tagging.count
     post.destroy
-    assert_equal old_count-1, Tagging.count
+    assert_equal old_count - 1, Tagging.count
     assert_equal 0, posts(:welcome).taggings.count
   end
 
   def test_delete_polymorphic_has_many_with_destroy
     assert_equal 1, posts(:welcome).taggings.count
-    posts(:welcome).taggings.first.update_columns taggable_type: 'PostWithHasManyDestroy'
+    posts(:welcome).taggings.first.update_columns taggable_type: "PostWithHasManyDestroy"
     post = find_post_with_dependency(1, :has_many, :taggings, :destroy)
 
     old_count = Tagging.count
     post.destroy
-    assert_equal old_count-1, Tagging.count
+    assert_equal old_count - 1, Tagging.count
     assert_equal 0, posts(:welcome).taggings.count
   end
 
   def test_delete_polymorphic_has_many_with_nullify
     assert_equal 1, posts(:welcome).taggings.count
-    posts(:welcome).taggings.first.update_columns taggable_type: 'PostWithHasManyNullify'
+    posts(:welcome).taggings.first.update_columns taggable_type: "PostWithHasManyNullify"
     post = find_post_with_dependency(1, :has_many, :taggings, :nullify)
 
     old_count = Tagging.count
@@ -207,24 +209,26 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_delete_polymorphic_has_one_with_destroy
     assert posts(:welcome).tagging
-    posts(:welcome).tagging.update_columns taggable_type: 'PostWithHasOneDestroy'
+    posts(:welcome).tagging.update_columns taggable_type: "PostWithHasOneDestroy"
     post = find_post_with_dependency(1, :has_one, :tagging, :destroy)
 
     old_count = Tagging.count
     post.destroy
-    assert_equal old_count-1, Tagging.count
-    assert_nil posts(:welcome).tagging(true)
+    assert_equal old_count - 1, Tagging.count
+    posts(:welcome).association(:tagging).reload
+    assert_nil posts(:welcome).tagging
   end
 
   def test_delete_polymorphic_has_one_with_nullify
     assert posts(:welcome).tagging
-    posts(:welcome).tagging.update_columns taggable_type: 'PostWithHasOneNullify'
+    posts(:welcome).tagging.update_columns taggable_type: "PostWithHasOneNullify"
     post = find_post_with_dependency(1, :has_one, :tagging, :nullify)
 
     old_count = Tagging.count
     post.destroy
     assert_equal old_count, Tagging.count
-    assert_nil posts(:welcome).tagging(true)
+    posts(:welcome).association(:tagging).reload
+    assert_nil posts(:welcome).tagging
   end
 
   def test_has_many_with_piggyback
@@ -233,15 +237,15 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_create_through_has_many_with_piggyback
     category = categories(:sti_test)
-    ernie = category.authors_with_select.create(:name => 'Ernie')
+    ernie = category.authors_with_select.create(name: "Ernie")
     assert_nothing_raised do
-      assert_equal ernie, category.authors_with_select.detect {|a| a.name == 'Ernie'}
+      assert_equal ernie, category.authors_with_select.detect { |a| a.name == "Ernie" }
     end
   end
 
   def test_include_has_many_through
-    posts              = Post.all.merge!(:order => 'posts.id').to_a
-    posts_with_authors = Post.all.merge!(:includes => :authors, :order => 'posts.id').to_a
+    posts              = Post.all.merge!(order: "posts.id").to_a
+    posts_with_authors = Post.all.merge!(includes: :authors, order: "posts.id").to_a
     assert_equal posts.length, posts_with_authors.length
     posts.length.times do |i|
       assert_equal posts[i].authors.length, assert_no_queries { posts_with_authors[i].authors.length }
@@ -265,8 +269,8 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_include_polymorphic_has_many_through
-    posts           = Post.all.merge!(:order => 'posts.id').to_a
-    posts_with_tags = Post.all.merge!(:includes => :tags, :order => 'posts.id').to_a
+    posts           = Post.all.merge!(order: "posts.id").to_a
+    posts_with_tags = Post.all.merge!(includes: :tags, order: "posts.id").to_a
     assert_equal posts.length, posts_with_tags.length
     posts.length.times do |i|
       assert_equal posts[i].tags.length, assert_no_queries { posts_with_tags[i].tags.length }
@@ -274,8 +278,8 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_include_polymorphic_has_many
-    posts               = Post.all.merge!(:order => 'posts.id').to_a
-    posts_with_taggings = Post.all.merge!(:includes => :taggings, :order => 'posts.id').to_a
+    posts               = Post.all.merge!(order: "posts.id").to_a
+    posts_with_taggings = Post.all.merge!(includes: :taggings, order: "posts.id").to_a
     assert_equal posts.length, posts_with_taggings.length
     posts.length.times do |i|
       assert_equal posts[i].taggings.length, assert_no_queries { posts_with_taggings[i].taggings.length }
@@ -300,7 +304,7 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_has_many_array_methods_called_by_method_missing
-    assert authors(:david).categories.any? { |category| category.name == 'General' }
+    assert authors(:david).categories.any? { |category| category.name == "General" }
     assert_nothing_raised { authors(:david).categories.sort }
   end
 
@@ -322,12 +326,12 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_has_many_through_with_custom_primary_key_on_has_many_source
-    assert_equal [authors(:david), authors(:bob)], posts(:thinking).authors_using_custom_pk.order('authors.id')
+    assert_equal [authors(:david), authors(:bob)], posts(:thinking).authors_using_custom_pk.order("authors.id")
   end
 
   def test_belongs_to_polymorphic_with_counter_cache
     assert_equal 1, posts(:welcome)[:tags_count]
-    tagging = posts(:welcome).taggings.create(:tag => tags(:general))
+    tagging = posts(:welcome).taggings.create(tag: tags(:general))
     assert_equal 2, posts(:welcome, :reload)[:tags_count]
     tagging.destroy
     assert_equal 1, posts(:welcome, :reload)[:tags_count]
@@ -352,7 +356,7 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     end
 
     assert_raise ActiveRecord::EagerLoadPolymorphicError do
-      tags(:general).taggings.includes(:taggable).where('bogus_table.column = 1').references(:bogus_table).to_a
+      tags(:general).taggings.includes(:taggable).where("bogus_table.column = 1").references(:bogus_table).to_a
     end
   end
 
@@ -361,8 +365,15 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     assert_equal posts(:welcome, :thinking).sort_by(&:id), tags(:general).tagged_posts.sort_by(&:id)
   end
 
+  def test_has_many_polymorphic_associations_merges_through_scope
+    Tag.has_many :null_taggings, -> { none }, class_name: :Tagging
+    Tag.has_many :null_tagged_posts, through: :null_taggings, source: "taggable", source_type: "Post"
+    assert_equal [], tags(:general).null_tagged_posts
+    assert_not_equal [], tags(:general).tagged_posts
+  end
+
   def test_eager_has_many_polymorphic_with_source_type
-    tag_with_include = Tag.all.merge!(:includes => :tagged_posts).find(tags(:general).id)
+    tag_with_include = Tag.all.merge!(includes: :tagged_posts).find(tags(:general).id)
     desired = posts(:welcome, :thinking)
     assert_no_queries do
       # added sort by ID as otherwise test using JRuby was failing as array elements were in different order
@@ -372,19 +383,19 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_has_many_through_has_many_find_all
-    assert_equal comments(:greetings), authors(:david).comments.order('comments.id').to_a.first
+    assert_equal comments(:greetings), authors(:david).comments.order("comments.id").to_a.first
   end
 
   def test_has_many_through_has_many_find_all_with_custom_class
-    assert_equal comments(:greetings), authors(:david).funky_comments.order('comments.id').to_a.first
+    assert_equal comments(:greetings), authors(:david).funky_comments.order("comments.id").to_a.first
   end
 
   def test_has_many_through_has_many_find_first
-    assert_equal comments(:greetings), authors(:david).comments.order('comments.id').first
+    assert_equal comments(:greetings), authors(:david).comments.order("comments.id").first
   end
 
   def test_has_many_through_has_many_find_conditions
-    options = { :where => "comments.#{QUOTED_TYPE}='SpecialComment'", :order => 'comments.id' }
+    options = { where: "comments.#{QUOTED_TYPE}='SpecialComment'", order: "comments.id" }
     assert_equal comments(:does_it_hurt), authors(:david).comments.merge(options).first
   end
 
@@ -393,7 +404,7 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_has_many_through_polymorphic_has_one
-    assert_equal Tagging.find(1,2).sort_by(&:id), authors(:david).taggings_2
+    assert_equal Tagging.find(1, 2).sort_by(&:id), authors(:david).taggings_2.sort_by(&:id)
   end
 
   def test_has_many_through_polymorphic_has_many
@@ -404,20 +415,20 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     author            = Author.includes(:taggings).find authors(:david).id
     expected_taggings = taggings(:welcome_general, :thinking_general)
     assert_no_queries do
-      assert_equal expected_taggings, author.taggings.distinct.sort_by(&:id)
+      assert_equal expected_taggings, author.taggings.uniq.sort_by(&:id)
     end
   end
 
   def test_eager_load_has_many_through_has_many
-    author = Author.all.merge!(:where => ['name = ?', 'David'], :includes => :comments, :order => 'comments.id').first
+    author = Author.all.merge!(where: ["name = ?", "David"], includes: :comments, order: "comments.id").first
     SpecialComment.new; VerySpecialComment.new
     assert_no_queries do
-      assert_equal [1,2,3,5,6,7,8,9,10,12], author.comments.collect(&:id)
+      assert_equal [1, 2, 3, 5, 6, 7, 8, 9, 10, 12], author.comments.collect(&:id)
     end
   end
 
   def test_eager_load_has_many_through_has_many_with_conditions
-    post = Post.all.merge!(:includes => :invalid_tags).first
+    post = Post.all.merge!(includes: :invalid_tags).first
     assert_no_queries do
       post.invalid_tags
     end
@@ -425,8 +436,8 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_eager_belongs_to_and_has_one_not_singularized
     assert_nothing_raised do
-      Author.all.merge!(:includes => :author_address).first
-      AuthorAddress.all.merge!(:includes => :author).first
+      Author.all.merge!(includes: :author_address).first
+      AuthorAddress.all.merge!(includes: :author).first
     end
   end
 
@@ -436,15 +447,15 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_add_to_self_referential_has_many_through
-    new_author = Author.create(:name => "Bob")
-    authors(:david).author_favorites.create :favorite_author => new_author
+    new_author = Author.create(name: "Bob")
+    authors(:david).author_favorites.create favorite_author: new_author
     assert_equal new_author, authors(:david).reload.favorite_authors.first
   end
 
   def test_has_many_through_uses_conditions_specified_on_the_has_many_association
     author = Author.first
-    assert author.comments.present?
-    assert author.nonexistent_comments.blank?
+    assert_predicate author.comments, :present?
+    assert_predicate author.nonexistent_comments, :blank?
   end
 
   def test_has_many_through_uses_correct_attributes
@@ -453,60 +464,59 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_associating_unsaved_records_with_has_many_through
     saved_post = posts(:thinking)
-    new_tag = Tag.new(:name => "new")
+    new_tag = Tag.new(name: "new")
 
     saved_post.tags << new_tag
-    assert new_tag.persisted? #consistent with habtm!
-    assert saved_post.persisted?
-    assert saved_post.tags.include?(new_tag)
-
-    assert new_tag.persisted?
-    assert saved_post.reload.tags(true).include?(new_tag)
+    assert new_tag.persisted? # consistent with habtm!
+    assert_predicate saved_post, :persisted?
+    assert_includes saved_post.tags, new_tag
 
+    assert_predicate new_tag, :persisted?
+    assert_includes saved_post.reload.tags.reload, new_tag
 
-    new_post = Post.new(:title => "Association replacement works!", :body => "You best believe it.")
+    new_post = Post.new(title: "Association replacement works!", body: "You best believe it.")
     saved_tag = tags(:general)
 
     new_post.tags << saved_tag
-    assert !new_post.persisted?
-    assert saved_tag.persisted?
-    assert new_post.tags.include?(saved_tag)
+    assert_not_predicate new_post, :persisted?
+    assert_predicate saved_tag, :persisted?
+    assert_includes new_post.tags, saved_tag
 
     new_post.save!
-    assert new_post.persisted?
-    assert new_post.reload.tags(true).include?(saved_tag)
+    assert_predicate new_post, :persisted?
+    assert_includes new_post.reload.tags.reload, saved_tag
 
-    assert !posts(:thinking).tags.build.persisted?
-    assert !posts(:thinking).tags.new.persisted?
+    assert_not_predicate posts(:thinking).tags.build, :persisted?
+    assert_not_predicate posts(:thinking).tags.new, :persisted?
   end
 
   def test_create_associate_when_adding_to_has_many_through
     count = posts(:thinking).tags.count
-    push = Tag.create!(:name => 'pushme')
+    push = Tag.create!(name: "pushme")
     post_thinking = posts(:thinking)
     assert_nothing_raised { post_thinking.tags << push }
-    assert_nil( wrong = post_thinking.tags.detect { |t| t.class != Tag },
-                message = "Expected a Tag in tags collection, got #{wrong.class}.")
-    assert_nil( wrong = post_thinking.taggings.detect { |t| t.class != Tagging },
-                message = "Expected a Tagging in taggings collection, got #{wrong.class}.")
+    assert_nil(wrong = post_thinking.tags.detect { |t| t.class != Tag },
+               "Expected a Tag in tags collection, got #{wrong.class}.")
+    assert_nil(wrong = post_thinking.taggings.detect { |t| t.class != Tagging },
+               "Expected a Tagging in taggings collection, got #{wrong.class}.")
     assert_equal(count + 1, post_thinking.reload.tags.size)
-    assert_equal(count + 1, post_thinking.tags(true).size)
+    assert_equal(count + 1, post_thinking.tags.reload.size)
 
-    assert_kind_of Tag, post_thinking.tags.create!(:name => 'foo')
-    assert_nil( wrong = post_thinking.tags.detect { |t| t.class != Tag },
-                message = "Expected a Tag in tags collection, got #{wrong.class}.")
-    assert_nil( wrong = post_thinking.taggings.detect { |t| t.class != Tagging },
-                message = "Expected a Tagging in taggings collection, got #{wrong.class}.")
+    assert_kind_of Tag, post_thinking.tags.create!(name: "foo")
+    assert_nil(wrong = post_thinking.tags.detect { |t| t.class != Tag },
+               "Expected a Tag in tags collection, got #{wrong.class}.")
+    assert_nil(wrong = post_thinking.taggings.detect { |t| t.class != Tagging },
+               "Expected a Tagging in taggings collection, got #{wrong.class}.")
     assert_equal(count + 2, post_thinking.reload.tags.size)
-    assert_equal(count + 2, post_thinking.tags(true).size)
+    assert_equal(count + 2, post_thinking.tags.reload.size)
 
-    assert_nothing_raised { post_thinking.tags.concat(Tag.create!(:name => 'abc'), Tag.create!(:name => 'def')) }
-    assert_nil( wrong = post_thinking.tags.detect { |t| t.class != Tag },
-                message = "Expected a Tag in tags collection, got #{wrong.class}.")
-    assert_nil( wrong = post_thinking.taggings.detect { |t| t.class != Tagging },
-                message = "Expected a Tagging in taggings collection, got #{wrong.class}.")
+    assert_nothing_raised { post_thinking.tags.concat(Tag.create!(name: "abc"), Tag.create!(name: "def")) }
+    assert_nil(wrong = post_thinking.tags.detect { |t| t.class != Tag },
+               "Expected a Tag in tags collection, got #{wrong.class}.")
+    assert_nil(wrong = post_thinking.taggings.detect { |t| t.class != Tagging },
+               "Expected a Tagging in taggings collection, got #{wrong.class}.")
     assert_equal(count + 4, post_thinking.reload.tags.size)
-    assert_equal(count + 4, post_thinking.tags(true).size)
+    assert_equal(count + 4, post_thinking.tags.reload.size)
 
     # Raises if the wrong reflection name is used to set the Edge belongs_to
     assert_nothing_raised { vertices(:vertex_1).sinks << vertices(:vertex_5) }
@@ -519,14 +529,14 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   def test_has_many_through_collection_size_doesnt_load_target_if_not_loaded
     author = authors(:david)
     assert_equal 10, author.comments.size
-    assert !author.comments.loaded?
+    assert_not_predicate author.comments, :loaded?
   end
 
   def test_has_many_through_collection_size_uses_counter_cache_if_it_exists
     c = categories(:general)
     c.categorizations_count = 100
     assert_equal 100, c.categorizations.size
-    assert !c.categorizations.loaded?
+    assert_not_predicate c.categorizations, :loaded?
   end
 
   def test_adding_junk_to_has_many_through_should_raise_type_mismatch
@@ -541,47 +551,47 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   def test_delete_associate_when_deleting_from_has_many_through_with_nonstandard_id
     count = books(:awdr).references.count
     references_before = books(:awdr).references
-    book = Book.create!(:name => 'Getting Real')
+    book = Book.create!(name: "Getting Real")
     book_awdr = books(:awdr)
     book_awdr.references << book
-    assert_equal(count + 1, book_awdr.references(true).size)
+    assert_equal(count + 1, book_awdr.references.reload.size)
 
     assert_nothing_raised { book_awdr.references.delete(book) }
     assert_equal(count, book_awdr.references.size)
-    assert_equal(count, book_awdr.references(true).size)
+    assert_equal(count, book_awdr.references.reload.size)
     assert_equal(references_before.sort, book_awdr.references.sort)
   end
 
   def test_delete_associate_when_deleting_from_has_many_through
     count = posts(:thinking).tags.count
     tags_before = posts(:thinking).tags.sort
-    tag = Tag.create!(:name => 'doomed')
+    tag = Tag.create!(name: "doomed")
     post_thinking = posts(:thinking)
     post_thinking.tags << tag
-    assert_equal(count + 1, post_thinking.taggings(true).size)
-    assert_equal(count + 1, post_thinking.reload.tags(true).size)
+    assert_equal(count + 1, post_thinking.taggings.reload.size)
+    assert_equal(count + 1, post_thinking.reload.tags.reload.size)
     assert_not_equal(tags_before, post_thinking.tags.sort)
 
     assert_nothing_raised { post_thinking.tags.delete(tag) }
     assert_equal(count, post_thinking.tags.size)
-    assert_equal(count, post_thinking.tags(true).size)
-    assert_equal(count, post_thinking.taggings(true).size)
+    assert_equal(count, post_thinking.tags.reload.size)
+    assert_equal(count, post_thinking.taggings.reload.size)
     assert_equal(tags_before, post_thinking.tags.sort)
   end
 
   def test_delete_associate_when_deleting_from_has_many_through_with_multiple_tags
     count = posts(:thinking).tags.count
     tags_before = posts(:thinking).tags.sort
-    doomed = Tag.create!(:name => 'doomed')
-    doomed2 = Tag.create!(:name => 'doomed2')
-    quaked = Tag.create!(:name => 'quaked')
+    doomed = Tag.create!(name: "doomed")
+    doomed2 = Tag.create!(name: "doomed2")
+    quaked = Tag.create!(name: "quaked")
     post_thinking = posts(:thinking)
     post_thinking.tags << doomed << doomed2
-    assert_equal(count + 2, post_thinking.reload.tags(true).size)
+    assert_equal(count + 2, post_thinking.reload.tags.reload.size)
 
     assert_nothing_raised { post_thinking.tags.delete(doomed, doomed2, quaked) }
     assert_equal(count, post_thinking.tags.size)
-    assert_equal(count, post_thinking.tags(true).size)
+    assert_equal(count, post_thinking.tags.reload.size)
     assert_equal(tags_before, post_thinking.tags.sort)
   end
 
@@ -589,10 +599,10 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::AssociationTypeMismatch) { posts(:thinking).tags.delete(Object.new) }
   end
 
-  def test_deleting_by_fixnum_id_from_has_many_through
+  def test_deleting_by_integer_id_from_has_many_through
     post = posts(:thinking)
 
-    assert_difference 'post.tags.count', -1 do
+    assert_difference "post.tags.count", -1 do
       assert_equal 1, post.tags.delete(1).size
     end
 
@@ -602,8 +612,8 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   def test_deleting_by_string_id_from_has_many_through
     post = posts(:thinking)
 
-    assert_difference 'post.tags.count', -1 do
-      assert_equal 1, post.tags.delete('1').size
+    assert_difference "post.tags.count", -1 do
+      assert_equal 1, post.tags.delete("1").size
     end
 
     assert_equal 0, post.tags.size
@@ -633,26 +643,26 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
 
   def test_polymorphic_has_many
     expected = taggings(:welcome_general)
-    p = Post.all.merge!(:includes => :taggings).find(posts(:welcome).id)
-    assert_no_queries {assert p.taggings.include?(expected)}
-    assert posts(:welcome).taggings.include?(taggings(:welcome_general))
+    p = Post.all.merge!(includes: :taggings).find(posts(:welcome).id)
+    assert_no_queries { assert_includes p.taggings, expected }
+    assert_includes posts(:welcome).taggings, taggings(:welcome_general)
   end
 
   def test_polymorphic_has_one
     expected = posts(:welcome)
 
-    tagging  = Tagging.all.merge!(:includes => :taggable).find(taggings(:welcome_general).id)
-    assert_no_queries { assert_equal expected, tagging.taggable}
+    tagging  = Tagging.all.merge!(includes: :taggable).find(taggings(:welcome_general).id)
+    assert_no_queries { assert_equal expected, tagging.taggable }
   end
 
   def test_polymorphic_belongs_to
-    p = Post.all.merge!(:includes => {:taggings => :taggable}).find(posts(:welcome).id)
-    assert_no_queries {assert_equal posts(:welcome), p.taggings.first.taggable}
+    p = Post.all.merge!(includes: { taggings: :taggable }).find(posts(:welcome).id)
+    assert_no_queries { assert_equal posts(:welcome), p.taggings.first.taggable }
   end
 
   def test_preload_polymorphic_has_many_through
-    posts           = Post.all.merge!(:order => 'posts.id').to_a
-    posts_with_tags = Post.all.merge!(:includes => :tags, :order => 'posts.id').to_a
+    posts           = Post.all.merge!(order: "posts.id").to_a
+    posts_with_tags = Post.all.merge!(includes: :tags, order: "posts.id").to_a
     assert_equal posts.length, posts_with_tags.length
     posts.length.times do |i|
       assert_equal posts[i].tags.length, assert_no_queries { posts_with_tags[i].tags.length }
@@ -660,26 +670,26 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_preload_polymorph_many_types
-    taggings = Tagging.all.merge!(:includes => :taggable, :where => ['taggable_type != ?', 'FakeModel']).to_a
+    taggings = Tagging.all.merge!(includes: :taggable, where: ["taggable_type != ?", "FakeModel"]).to_a
     assert_no_queries do
       taggings.first.taggable.id
       taggings[1].taggable.id
     end
 
     taggables = taggings.map(&:taggable)
-    assert taggables.include?(items(:dvd))
-    assert taggables.include?(posts(:welcome))
+    assert_includes taggables, items(:dvd)
+    assert_includes taggables, posts(:welcome)
   end
 
   def test_preload_nil_polymorphic_belongs_to
     assert_nothing_raised do
-      Tagging.all.merge!(:includes => :taggable, :where => ['taggable_type IS NULL']).to_a
+      Tagging.all.merge!(includes: :taggable, where: ["taggable_type IS NULL"]).to_a
     end
   end
 
   def test_preload_polymorphic_has_many
-    posts               = Post.all.merge!(:order => 'posts.id').to_a
-    posts_with_taggings = Post.all.merge!(:includes => :taggings, :order => 'posts.id').to_a
+    posts               = Post.all.merge!(order: "posts.id").to_a
+    posts_with_taggings = Post.all.merge!(includes: :taggings, order: "posts.id").to_a
     assert_equal posts.length, posts_with_taggings.length
     posts.length.times do |i|
       assert_equal posts[i].taggings.length, assert_no_queries { posts_with_taggings[i].taggings.length }
@@ -687,7 +697,7 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
   end
 
   def test_belongs_to_shared_parent
-    comments = Comment.all.merge!(:includes => :post, :where => 'post_id = 1').to_a
+    comments = Comment.all.merge!(includes: :post, where: "post_id = 1").to_a
     assert_no_queries do
       assert_equal comments.first.post, comments[1].post
     end
@@ -700,8 +710,8 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     category = david.categories.first
 
     assert_no_queries do
-      assert david.categories.loaded?
-      assert david.categories.include?(category)
+      assert_predicate david.categories, :loaded?
+      assert_includes david.categories, category
     end
   end
 
@@ -710,42 +720,59 @@ class AssociationsJoinModelTest < ActiveRecord::TestCase
     category = david.categories.first
 
     david.reload
-    assert ! david.categories.loaded?
+    assert_not_predicate david.categories, :loaded?
     assert_queries(1) do
-      assert david.categories.include?(category)
+      assert_includes david.categories, category
     end
-    assert ! david.categories.loaded?
+    assert_not_predicate david.categories, :loaded?
   end
 
   def test_has_many_through_include_returns_false_for_non_matching_record_to_verify_scoping
     david = authors(:david)
-    category = Category.create!(:name => 'Not Associated')
+    category = Category.create!(name: "Not Associated")
 
-    assert ! david.categories.loaded?
-    assert ! david.categories.include?(category)
+    assert_not_predicate david.categories, :loaded?
+    assert_not david.categories.include?(category)
   end
 
   def test_has_many_through_goes_through_all_sti_classes
-    sub_sti_post = SubStiPost.create!(:title => 'test', :body => 'test', :author_id => 1)
-    new_comment = sub_sti_post.comments.create(:body => 'test')
+    sub_sti_post = SubStiPost.create!(title: "test", body: "test", author_id: 1)
+    new_comment = sub_sti_post.comments.create(body: "test")
 
     assert_equal [9, 10, new_comment.id], authors(:david).sti_post_comments.map(&:id).sort
   end
 
   def test_has_many_with_pluralize_table_names_false
-    aircraft = Aircraft.create!(:name => "Airbus 380")
-    engine = Engine.create!(:car_id => aircraft.id)
+    aircraft = Aircraft.create!(name: "Airbus 380")
+    engine = Engine.create!(car_id: aircraft.id)
     assert_equal aircraft.engines, [engine]
   end
 
+  def test_proper_error_message_for_eager_load_and_includes_association_errors
+    includes_error = assert_raises(ActiveRecord::ConfigurationError) {
+      Post.includes(:nonexistent_relation).where(nonexistent_relation: { name: "Rochester" }).find(1)
+    }
+    assert_equal("Can't join 'Post' to association named 'nonexistent_relation'; perhaps you misspelled it?", includes_error.message)
+
+    eager_load_error = assert_raises(ActiveRecord::ConfigurationError) {
+      Post.eager_load(:nonexistent_relation).where(nonexistent_relation: { name: "Rochester" }).find(1)
+    }
+    assert_equal("Can't join 'Post' to association named 'nonexistent_relation'; perhaps you misspelled it?", eager_load_error.message)
+
+    includes_and_eager_load_error = assert_raises(ActiveRecord::ConfigurationError) {
+      Post.eager_load(:nonexistent_relation).includes(:nonexistent_relation).where(nonexistent_relation: { name: "Rochester" }).find(1)
+    }
+    assert_equal("Can't join 'Post' to association named 'nonexistent_relation'; perhaps you misspelled it?", includes_and_eager_load_error.message)
+  end
+
   private
     # create dynamic Post models to allow different dependency options
     def find_post_with_dependency(post_id, association, association_name, dependency)
       class_name = "PostWith#{association.to_s.classify}#{dependency.to_s.classify}"
       Post.find(post_id).update_columns type: class_name
       klass = Object.const_set(class_name, Class.new(ActiveRecord::Base))
-      klass.table_name = 'posts'
-      klass.send(association, association_name, :as => :taggable, :dependent => dependency)
+      klass.table_name = "posts"
+      klass.send(association, association_name, as: :taggable, dependent: dependency)
       klass.find(post_id)
     end
 end
diff --git a/activerecord/test/cases/associations/left_outer_join_association_test.rb b/activerecord/test/cases/associations/left_outer_join_association_test.rb
new file mode 100644
index 0000000000..0e54e8c1b0
--- /dev/null
+++ b/activerecord/test/cases/associations/left_outer_join_association_test.rb
@@ -0,0 +1,91 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/post"
+require "models/comment"
+require "models/author"
+require "models/essay"
+require "models/category"
+require "models/categorization"
+require "models/person"
+
+class LeftOuterJoinAssociationTest < ActiveRecord::TestCase
+  fixtures :authors, :author_addresses, :essays, :posts, :comments, :categorizations, :people
+
+  def test_construct_finder_sql_applies_aliases_tables_on_association_conditions
+    result = Author.left_outer_joins(:thinking_posts, :welcome_posts).to_a
+    assert_equal authors(:david), result.first
+  end
+
+  def test_construct_finder_sql_does_not_table_name_collide_on_duplicate_associations
+    assert_nothing_raised do
+      queries = capture_sql do
+        Person.left_outer_joins(agents: { agents: :agents })
+              .left_outer_joins(agents: { agents: { primary_contact: :agents } }).to_a
+      end
+      assert queries.any? { |sql| /agents_people_4/i.match?(sql) }
+    end
+  end
+
+  def test_left_outer_joins_count_is_same_as_size_of_loaded_results
+    assert_equal 17, Post.left_outer_joins(:comments).to_a.size
+    assert_equal 17, Post.left_outer_joins(:comments).count
+  end
+
+  def test_left_joins_aliases_left_outer_joins
+    assert_equal Post.left_outer_joins(:comments).to_sql, Post.left_joins(:comments).to_sql
+  end
+
+  def test_left_outer_joins_return_has_value_for_every_comment
+    all_post_ids = Post.pluck(:id)
+    assert_equal all_post_ids, all_post_ids & Post.left_outer_joins(:comments).pluck(:id)
+  end
+
+  def test_left_outer_joins_actually_does_a_left_outer_join
+    queries = capture_sql { Author.left_outer_joins(:posts).to_a }
+    assert queries.any? { |sql| /LEFT OUTER JOIN/i.match?(sql) }
+  end
+
+  def test_construct_finder_sql_ignores_empty_left_outer_joins_hash
+    queries = capture_sql { Author.left_outer_joins({}).to_a }
+    assert queries.none? { |sql| /LEFT OUTER JOIN/i.match?(sql) }
+  end
+
+  def test_construct_finder_sql_ignores_empty_left_outer_joins_array
+    queries = capture_sql { Author.left_outer_joins([]).to_a }
+    assert queries.none? { |sql| /LEFT OUTER JOIN/i.match?(sql) }
+  end
+
+  def test_left_outer_joins_forbids_to_use_string_as_argument
+    assert_raise(ArgumentError) { Author.left_outer_joins('LEFT OUTER JOIN "posts" ON "posts"."user_id" = "users"."id"').to_a }
+  end
+
+  def test_join_conditions_added_to_join_clause
+    queries = capture_sql { Author.left_outer_joins(:essays).to_a }
+    assert queries.any? { |sql| /writer_type.*?=.*?(Author|\?|\$1|\:a1)/i.match?(sql) }
+    assert queries.none? { |sql| /WHERE/i.match?(sql) }
+  end
+
+  def test_find_with_sti_join
+    scope = Post.left_outer_joins(:special_comments).where(id: posts(:sti_comments).id)
+
+    # The join should match SpecialComment and its subclasses only
+    assert_empty scope.where("comments.type" => "Comment")
+    assert_not_empty scope.where("comments.type" => "SpecialComment")
+    assert_not_empty scope.where("comments.type" => "SubSpecialComment")
+  end
+
+  def test_does_not_override_select
+    authors = Author.select("authors.name, #{%{(authors.author_address_id || ' ' || authors.author_address_extra_id) as addr_id}}").left_outer_joins(:posts)
+    assert_predicate authors, :any?
+    assert_respond_to authors.first, :addr_id
+  end
+
+  test "the default scope of the target is applied when joining associations" do
+    author = Author.create! name: "Jon"
+    author.categorizations.create!
+    author.categorizations.create! special: true
+
+    assert_equal [author], Author.where(id: author).left_outer_joins(:special_categorizations)
+  end
+end
diff --git a/activerecord/test/cases/associations/nested_through_associations_test.rb b/activerecord/test/cases/associations/nested_through_associations_test.rb
index 31b68c940e..5821744530 100644
--- a/activerecord/test/cases/associations/nested_through_associations_test.rb
+++ b/activerecord/test/cases/associations/nested_through_associations_test.rb
@@ -1,30 +1,37 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/author'
-require 'models/post'
-require 'models/person'
-require 'models/reference'
-require 'models/job'
-require 'models/reader'
-require 'models/comment'
-require 'models/tag'
-require 'models/tagging'
-require 'models/subscriber'
-require 'models/book'
-require 'models/subscription'
-require 'models/rating'
-require 'models/member'
-require 'models/member_detail'
-require 'models/member_type'
-require 'models/sponsor'
-require 'models/club'
-require 'models/organization'
-require 'models/category'
-require 'models/categorization'
-require 'models/membership'
-require 'models/essay'
+require "models/author"
+require "models/post"
+require "models/person"
+require "models/reference"
+require "models/job"
+require "models/reader"
+require "models/comment"
+require "models/tag"
+require "models/tagging"
+require "models/subscriber"
+require "models/book"
+require "models/subscription"
+require "models/rating"
+require "models/member"
+require "models/member_detail"
+require "models/member_type"
+require "models/sponsor"
+require "models/club"
+require "models/organization"
+require "models/category"
+require "models/categorization"
+require "models/membership"
+require "models/essay"
+require "models/hotel"
+require "models/department"
+require "models/chef"
+require "models/cake_designer"
+require "models/drink_designer"
 
 class NestedThroughAssociationsTest < ActiveRecord::TestCase
-  fixtures :authors, :books, :posts, :subscriptions, :subscribers, :tags, :taggings,
+  fixtures :authors, :author_addresses, :books, :posts, :subscriptions, :subscribers, :tags, :taggings,
            :people, :readers, :references, :jobs, :ratings, :comments, :members, :member_details,
            :member_types, :sponsors, :clubs, :organizations, :categories, :categories_posts,
            :categorizations, :memberships, :essays
@@ -65,13 +72,13 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_many_through_has_many_with_has_many_through_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Author.where('tags.id' => tags(:general).id),
+      Author.where("tags.id" => tags(:general).id),
       [authors(:david)], :tags
     )
 
     # This ensures that the polymorphism of taggings is being observed correctly
-    authors = Author.joins(:tags).where('taggings.taggable_type' => 'FakeModel')
-    assert authors.empty?
+    authors = Author.joins(:tags).where("taggings.taggable_type" => "FakeModel")
+    assert_empty authors
   end
 
   # has_many through
@@ -79,7 +86,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   # Through: has_many through
   def test_has_many_through_has_many_through_with_has_many_source_reflection
     luke, david = subscribers(:first), subscribers(:second)
-    assert_equal [luke, david, david], authors(:david).subscribers.order('subscribers.nick')
+    assert_equal [luke, david, david], authors(:david).subscribers.order("subscribers.nick")
   end
 
   def test_has_many_through_has_many_through_with_has_many_source_reflection_preload
@@ -93,7 +100,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   def test_has_many_through_has_many_through_with_has_many_source_reflection_preload_via_joins
     # All authors with subscribers where one of the subscribers' nick is 'alterself'
     assert_includes_and_joins_equal(
-      Author.where('subscribers.nick' => 'alterself'),
+      Author.where("subscribers.nick" => "alterself"),
       [authors(:david)], :subscribers
     )
   end
@@ -115,7 +122,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_many_through_has_one_with_has_one_through_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Member.where('member_types.id' => member_types(:founding).id),
+      Member.where("member_types.id" => member_types(:founding).id),
       [members(:groucho)], :nested_member_types
     )
   end
@@ -130,14 +137,14 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   def test_has_many_through_has_one_through_with_has_one_source_reflection_preload
     members = assert_queries(4) { Member.includes(:nested_sponsors).to_a }
     mustache = sponsors(:moustache_club_sponsor_for_groucho)
-    assert_no_queries(ignore_none: false) do
+    assert_no_queries do
       assert_equal [mustache], members.first.nested_sponsors
     end
   end
 
   def test_has_many_through_has_one_through_with_has_one_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Member.where('sponsors.id' => sponsors(:moustache_club_sponsor_for_groucho).id),
+      Member.where("sponsors.id" => sponsors(:moustache_club_sponsor_for_groucho).id),
       [members(:groucho)], :nested_sponsors
     )
   end
@@ -149,7 +156,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     groucho_details, other_details = member_details(:groucho), member_details(:some_other_guy)
 
     assert_equal [groucho_details, other_details],
-                 members(:groucho).organization_member_details.order('member_details.id')
+                 members(:groucho).organization_member_details.order("member_details.id")
   end
 
   def test_has_many_through_has_one_with_has_many_through_source_reflection_preload
@@ -164,13 +171,13 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_many_through_has_one_with_has_many_through_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Member.where('member_details.id' => member_details(:groucho).id).order('member_details.id'),
+      Member.where("member_details.id" => member_details(:groucho).id).order("member_details.id"),
       [members(:groucho), members(:some_other_guy)], :organization_member_details
     )
 
     members = Member.joins(:organization_member_details).
-                     where('member_details.id' => 9)
-    assert members.empty?
+                     where("member_details.id" => 9)
+    assert_empty members
   end
 
   # has_many through
@@ -180,7 +187,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     groucho_details, other_details = member_details(:groucho), member_details(:some_other_guy)
 
     assert_equal [groucho_details, other_details],
-                 members(:groucho).organization_member_details_2.order('member_details.id')
+                 members(:groucho).organization_member_details_2.order("member_details.id")
   end
 
   def test_has_many_through_has_one_through_with_has_many_source_reflection_preload
@@ -189,20 +196,20 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
 
     # postgresql test if randomly executed then executes "SHOW max_identifier_length". Hence
     # the need to ignore certain predefined sqls that deal with system calls.
-    assert_no_queries(ignore_none: false) do
+    assert_no_queries do
       assert_equal [groucho_details, other_details], members.first.organization_member_details_2.sort_by(&:id)
     end
   end
 
   def test_has_many_through_has_one_through_with_has_many_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Member.where('member_details.id' => member_details(:groucho).id).order('member_details.id'),
+      Member.where("member_details.id" => member_details(:groucho).id).order("member_details.id"),
       [members(:groucho), members(:some_other_guy)], :organization_member_details_2
     )
 
     members = Member.joins(:organization_member_details_2).
-                     where('member_details.id' => 9)
-    assert members.empty?
+                     where("member_details.id" => 9)
+    assert_empty members
   end
 
   # has_many through
@@ -211,7 +218,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   def test_has_many_through_has_many_with_has_and_belongs_to_many_source_reflection
     general, cooking = categories(:general), categories(:cooking)
 
-    assert_equal [general, cooking], authors(:bob).post_categories.order('categories.id')
+    assert_equal [general, cooking], authors(:bob).post_categories.order("categories.id")
   end
 
   def test_has_many_through_has_many_with_has_and_belongs_to_many_source_reflection_preload
@@ -228,7 +235,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     Author.joins(:post_categories).first
 
     assert_includes_and_joins_equal(
-      Author.where('categories.id' => categories(:cooking).id),
+      Author.where("categories.id" => categories(:cooking).id),
       [authors(:bob)], :post_categories
     )
   end
@@ -239,7 +246,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   def test_has_many_through_has_and_belongs_to_many_with_has_many_source_reflection
     greetings, more = comments(:greetings), comments(:more_greetings)
 
-    assert_equal [greetings, more], categories(:technology).post_comments.order('comments.id')
+    assert_equal [greetings, more], categories(:technology).post_comments.order("comments.id")
   end
 
   def test_has_many_through_has_and_belongs_to_many_with_has_many_source_reflection_preload
@@ -257,7 +264,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     Category.joins(:post_comments).first
 
     assert_includes_and_joins_equal(
-      Category.where('comments.id' => comments(:more_greetings).id).order('categories.id'),
+      Category.where("comments.id" => comments(:more_greetings).id).order("categories.id"),
       [categories(:general), categories(:technology)], :post_comments
     )
   end
@@ -268,7 +275,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   def test_has_many_through_has_many_with_has_many_through_habtm_source_reflection
     greetings, more = comments(:greetings), comments(:more_greetings)
 
-    assert_equal [greetings, more], authors(:bob).category_post_comments.order('comments.id')
+    assert_equal [greetings, more], authors(:bob).category_post_comments.order("comments.id")
   end
 
   def test_has_many_through_has_many_with_has_many_through_habtm_source_reflection_preload
@@ -285,7 +292,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     Author.joins(:category_post_comments).first
 
     assert_includes_and_joins_equal(
-      Author.where('comments.id' => comments(:does_it_hurt).id).order('authors.id'),
+      Author.where("comments.id" => comments(:does_it_hurt).id).order("authors.id"),
       [authors(:david), authors(:mary)], :category_post_comments
     )
   end
@@ -308,7 +315,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_many_through_has_many_through_with_belongs_to_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Author.where('tags.id' => tags(:general).id),
+      Author.where("tags.id" => tags(:general).id),
       [authors(:david)], :tagging_tags
     )
   end
@@ -320,7 +327,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     welcome_general, thinking_general = taggings(:welcome_general), taggings(:thinking_general)
 
     assert_equal [welcome_general, thinking_general],
-                 categorizations(:david_welcome_general).post_taggings.order('taggings.id')
+                 categorizations(:david_welcome_general).post_taggings.order("taggings.id")
   end
 
   def test_has_many_through_belongs_to_with_has_many_through_source_reflection_preload
@@ -334,7 +341,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_many_through_belongs_to_with_has_many_through_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Categorization.where('taggings.id' => taggings(:welcome_general).id).order('taggings.id'),
+      Categorization.where("taggings.id" => taggings(:welcome_general).id).order("taggings.id"),
       [categorizations(:david_welcome_general)], :post_taggings
     )
   end
@@ -357,7 +364,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_one_through_has_one_with_has_one_through_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Member.where('member_types.id' => member_types(:founding).id),
+      Member.where("member_types.id" => member_types(:founding).id),
       [members(:groucho)], :nested_member_type
     )
   end
@@ -391,7 +398,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
 
   def test_has_one_through_has_one_through_with_belongs_to_source_reflection_preload_via_joins
     assert_includes_and_joins_equal(
-      Member.where('categories.id' => categories(:technology).id),
+      Member.where("categories.id" => categories(:technology).id),
       [members(:blarpy_winkup)], :club_category
     )
   end
@@ -404,7 +411,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   def test_distinct_has_many_through_a_has_many_through_association_on_through_reflection
     author = authors(:david)
     assert_equal [subscribers(:first), subscribers(:second)],
-                 author.distinct_subscribers.order('subscribers.nick')
+                 author.distinct_subscribers.order("subscribers.nick")
   end
 
   def test_nested_has_many_through_with_a_table_referenced_multiple_times
@@ -413,26 +420,31 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
                  author.similar_posts.sort_by(&:id)
 
     # Mary and Bob both have posts in misc, but they are the only ones.
-    authors = Author.joins(:similar_posts).where('posts.id' => posts(:misc_by_bob).id)
+    authors = Author.joins(:similar_posts).where("posts.id" => posts(:misc_by_bob).id)
     assert_equal [authors(:mary), authors(:bob)], authors.distinct.sort_by(&:id)
 
     # Check the polymorphism of taggings is being observed correctly (in both joins)
-    authors = Author.joins(:similar_posts).where('taggings.taggable_type' => 'FakeModel')
-    assert authors.empty?
-    authors = Author.joins(:similar_posts).where('taggings_authors_join.taggable_type' => 'FakeModel')
-    assert authors.empty?
+    authors = Author.joins(:similar_posts).where("taggings.taggable_type" => "FakeModel")
+    assert_empty authors
+    authors = Author.joins(:similar_posts).where("taggings_authors_join.taggable_type" => "FakeModel")
+    assert_empty authors
+  end
+
+  def test_nested_has_many_through_with_scope_on_polymorphic_reflection
+    authors = Author.joins(:ordered_posts).where("posts.id" => posts(:misc_by_bob).id)
+    assert_equal [authors(:mary), authors(:bob)], authors.distinct.sort_by(&:id)
   end
 
   def test_has_many_through_with_foreign_key_option_on_through_reflection
-    assert_equal [posts(:welcome), posts(:authorless)], people(:david).agents_posts.order('posts.id')
+    assert_equal [posts(:welcome), posts(:authorless)], people(:david).agents_posts.order("posts.id")
     assert_equal [authors(:david)], references(:david_unicyclist).agents_posts_authors
 
-    references = Reference.joins(:agents_posts_authors).where('authors.id' => authors(:david).id)
+    references = Reference.joins(:agents_posts_authors).where("authors.id" => authors(:david).id)
     assert_equal [references(:david_unicyclist)], references
   end
 
   def test_has_many_through_with_foreign_key_option_on_source_reflection
-    assert_equal [people(:michael), people(:susan)], jobs(:unicyclist).agents.order('people.id')
+    assert_equal [people(:michael), people(:susan)], jobs(:unicyclist).agents.order("people.id")
 
     jobs = Job.joins(:agents)
     assert_equal [jobs(:unicyclist), jobs(:unicyclist)], jobs
@@ -443,19 +455,19 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal [ratings(:special_comment_rating), ratings(:sub_special_comment_rating)], ratings
 
     # Ensure STI is respected in the join
-    scope = Post.joins(:special_comments_ratings).where(:id => posts(:sti_comments).id)
-    assert scope.where("comments.type" => "Comment").empty?
-    assert !scope.where("comments.type" => "SpecialComment").empty?
-    assert !scope.where("comments.type" => "SubSpecialComment").empty?
+    scope = Post.joins(:special_comments_ratings).where(id: posts(:sti_comments).id)
+    assert_empty scope.where("comments.type" => "Comment")
+    assert_not_empty scope.where("comments.type" => "SpecialComment")
+    assert_not_empty scope.where("comments.type" => "SubSpecialComment")
   end
 
   def test_has_many_through_with_sti_on_nested_through_reflection
     taggings = posts(:sti_comments).special_comments_ratings_taggings
     assert_equal [taggings(:special_comment_rating)], taggings
 
-    scope = Post.joins(:special_comments_ratings_taggings).where(:id => posts(:sti_comments).id)
-    assert scope.where("comments.type" => "Comment").empty?
-    assert !scope.where("comments.type" => "SpecialComment").empty?
+    scope = Post.joins(:special_comments_ratings_taggings).where(id: posts(:sti_comments).id)
+    assert_empty scope.where("comments.type" => "Comment")
+    assert_not_empty scope.where("comments.type" => "SpecialComment")
   end
 
   def test_nested_has_many_through_writers_should_raise_error
@@ -495,7 +507,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     groucho = members(:groucho)
     founding = member_types(:founding)
 
-    assert_raises(ActiveRecord::HasManyThroughNestedAssociationsAreReadonly) do
+    assert_raises(ActiveRecord::HasOneThroughNestedAssociationsAreReadonly) do
       groucho.nested_member_type = founding
     end
   end
@@ -505,7 +517,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   end
 
   def test_nested_has_many_through_with_conditions_on_through_associations_preload
-    assert Author.where('tags.id' => 100).joins(:misc_post_first_blue_tags).empty?
+    assert_empty Author.where("tags.id" => 100).joins(:misc_post_first_blue_tags)
 
     authors = assert_queries(3) { Author.includes(:misc_post_first_blue_tags).to_a.sort_by(&:id) }
     blue = tags(:blue)
@@ -518,7 +530,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   def test_nested_has_many_through_with_conditions_on_through_associations_preload_via_joins
     # Pointless condition to force single-query loading
     assert_includes_and_joins_equal(
-      Author.where('tags.id = tags.id').references(:tags),
+      Author.where("tags.id = tags.id").references(:tags),
       [authors(:bob)], :misc_post_first_blue_tags
     )
   end
@@ -539,7 +551,7 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
   def test_nested_has_many_through_with_conditions_on_source_associations_preload_via_joins
     # Pointless condition to force single-query loading
     assert_includes_and_joins_equal(
-      Author.where('tags.id = tags.id').references(:tags),
+      Author.where("tags.id = tags.id").references(:tags),
       [authors(:bob)], :misc_post_first_blue_tags_2
     )
   end
@@ -548,13 +560,13 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     assert_equal [categories(:general)], organizations(:nsa).author_essay_categories
 
     organizations = Organization.joins(:author_essay_categories).
-                                 where('categories.id' => categories(:general).id)
+                                 where("categories.id" => categories(:general).id)
     assert_equal [organizations(:nsa)], organizations
 
     assert_equal categories(:general), organizations(:nsa).author_owned_essay_category
 
     organizations = Organization.joins(:author_owned_essay_category).
-                                 where('categories.id' => categories(:general).id)
+                                 where("categories.id" => categories(:general).id)
     assert_equal [organizations(:nsa)], organizations
   end
 
@@ -562,9 +574,40 @@ class NestedThroughAssociationsTest < ActiveRecord::TestCase
     c = Categorization.new
     c.author = authors(:david)
     c.post_taggings.to_a
-    assert !c.post_taggings.empty?
+    assert_not_empty c.post_taggings
     c.save
-    assert !c.post_taggings.empty?
+    assert_not_empty c.post_taggings
+  end
+
+  def test_polymorphic_has_many_through_when_through_association_has_not_loaded
+    cake_designer = CakeDesigner.create!(chef: Chef.new)
+    drink_designer = DrinkDesigner.create!(chef: Chef.new)
+    department = Department.create!(chefs: [cake_designer.chef, drink_designer.chef])
+    Hotel.create!(departments: [department])
+    hotel = Hotel.includes(:cake_designers, :drink_designers).take
+
+    assert_equal [cake_designer], hotel.cake_designers
+    assert_equal [drink_designer], hotel.drink_designers
+  end
+
+  def test_polymorphic_has_many_through_when_through_association_has_already_loaded
+    cake_designer = CakeDesigner.create!(chef: Chef.new)
+    drink_designer = DrinkDesigner.create!(chef: Chef.new)
+    department = Department.create!(chefs: [cake_designer.chef, drink_designer.chef])
+    Hotel.create!(departments: [department])
+    hotel = Hotel.includes(:chefs, :cake_designers, :drink_designers).take
+
+    assert_equal [cake_designer], hotel.cake_designers
+    assert_equal [drink_designer], hotel.drink_designers
+  end
+
+  def test_polymorphic_has_many_through_joined_different_table_twice
+    cake_designer = CakeDesigner.create!(chef: Chef.new)
+    drink_designer = DrinkDesigner.create!(chef: Chef.new)
+    department = Department.create!(chefs: [cake_designer.chef, drink_designer.chef])
+    hotel = Hotel.create!(departments: [department])
+
+    assert_equal hotel, Hotel.joins(:cake_designers, :drink_designers).take
   end
 
   private
diff --git a/activerecord/test/cases/associations/required_test.rb b/activerecord/test/cases/associations/required_test.rb
index 3e5494e897..65a3bb5efe 100644
--- a/activerecord/test/cases/associations/required_test.rb
+++ b/activerecord/test/cases/associations/required_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class RequiredAssociationsTest < ActiveRecord::TestCase
@@ -18,18 +20,25 @@ class RequiredAssociationsTest < ActiveRecord::TestCase
   end
 
   teardown do
-    @connection.drop_table 'parents', if_exists: true
-    @connection.drop_table 'children', if_exists: true
+    @connection.drop_table "parents", if_exists: true
+    @connection.drop_table "children", if_exists: true
   end
 
-  test "belongs_to associations are not required by default" do
-    model = subclass_of(Child) do
-      belongs_to :parent, inverse_of: false,
-        class_name: "RequiredAssociationsTest::Parent"
-    end
+  test "belongs_to associations can be optional by default" do
+    begin
+      original_value = ActiveRecord::Base.belongs_to_required_by_default
+      ActiveRecord::Base.belongs_to_required_by_default = false
 
-    assert model.new.save
-    assert model.new(parent: Parent.new).save
+      model = subclass_of(Child) do
+        belongs_to :parent, inverse_of: false,
+          class_name: "RequiredAssociationsTest::Parent"
+      end
+
+      assert model.new.save
+      assert model.new(parent: Parent.new).save
+    ensure
+      ActiveRecord::Base.belongs_to_required_by_default = original_value
+    end
   end
 
   test "required belongs_to associations have presence validated" do
@@ -46,6 +55,27 @@ class RequiredAssociationsTest < ActiveRecord::TestCase
     assert record.save
   end
 
+  test "belongs_to associations can be required by default" do
+    begin
+      original_value = ActiveRecord::Base.belongs_to_required_by_default
+      ActiveRecord::Base.belongs_to_required_by_default = true
+
+      model = subclass_of(Child) do
+        belongs_to :parent, inverse_of: false,
+          class_name: "RequiredAssociationsTest::Parent"
+      end
+
+      record = model.new
+      assert_not record.save
+      assert_equal ["Parent must exist"], record.errors.full_messages
+
+      record.parent = Parent.new
+      assert record.save
+    ensure
+      ActiveRecord::Base.belongs_to_required_by_default = original_value
+    end
+  end
+
   test "has_one associations are not required by default" do
     model = subclass_of(Parent) do
       has_one :child, inverse_of: false,
@@ -92,11 +122,11 @@ class RequiredAssociationsTest < ActiveRecord::TestCase
 
   private
 
-  def subclass_of(klass, &block)
-    subclass = Class.new(klass, &block)
-    def subclass.name
-      superclass.name
+    def subclass_of(klass, &block)
+      subclass = Class.new(klass, &block)
+      def subclass.name
+        superclass.name
+      end
+      subclass
     end
-    subclass
-  end
 end
diff --git a/activerecord/test/cases/associations_test.rb b/activerecord/test/cases/associations_test.rb
index 3d202a5527..081da95df7 100644
--- a/activerecord/test/cases/associations_test.rb
+++ b/activerecord/test/cases/associations_test.rb
@@ -1,89 +1,86 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/computer'
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/company'
-require 'models/categorization'
-require 'models/category'
-require 'models/post'
-require 'models/author'
-require 'models/comment'
-require 'models/tag'
-require 'models/tagging'
-require 'models/person'
-require 'models/reader'
-require 'models/parrot'
-require 'models/ship_part'
-require 'models/ship'
-require 'models/liquid'
-require 'models/molecule'
-require 'models/electron'
-require 'models/man'
-require 'models/interest'
+require "models/computer"
+require "models/developer"
+require "models/project"
+require "models/company"
+require "models/categorization"
+require "models/category"
+require "models/post"
+require "models/author"
+require "models/comment"
+require "models/tag"
+require "models/tagging"
+require "models/person"
+require "models/reader"
+require "models/ship_part"
+require "models/ship"
+require "models/liquid"
+require "models/molecule"
+require "models/electron"
+require "models/man"
+require "models/interest"
 
 class AssociationsTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :developers, :projects, :developers_projects,
-           :computers, :people, :readers, :authors, :author_favorites
+           :computers, :people, :readers, :authors, :author_addresses, :author_favorites
 
   def test_eager_loading_should_not_change_count_of_children
-    liquid = Liquid.create(:name => 'salty')
-    molecule = liquid.molecules.create(:name => 'molecule_1')
-    molecule.electrons.create(:name => 'electron_1')
-    molecule.electrons.create(:name => 'electron_2')
+    liquid = Liquid.create(name: "salty")
+    molecule = liquid.molecules.create(name: "molecule_1")
+    molecule.electrons.create(name: "electron_1")
+    molecule.electrons.create(name: "electron_2")
 
-    liquids = Liquid.includes(:molecules => :electrons).references(:molecules).where('molecules.id is not null')
+    liquids = Liquid.includes(molecules: :electrons).references(:molecules).where("molecules.id is not null")
     assert_equal 1, liquids[0].molecules.length
   end
 
   def test_subselect
     author = authors :david
     favs = author.author_favorites
-    fav2 = author.author_favorites.where(:author => Author.where(id: author.id)).to_a
+    fav2 = author.author_favorites.where(author: Author.where(id: author.id)).to_a
     assert_equal favs, fav2
   end
 
   def test_loading_the_association_target_should_keep_child_records_marked_for_destruction
-    ship = Ship.create!(:name => "The good ship Dollypop")
-    part = ship.parts.create!(:name => "Mast")
+    ship = Ship.create!(name: "The good ship Dollypop")
+    part = ship.parts.create!(name: "Mast")
     part.mark_for_destruction
-    ship.parts.send(:load_target)
-    assert ship.parts[0].marked_for_destruction?
+    assert_predicate ship.parts[0], :marked_for_destruction?
   end
 
   def test_loading_the_association_target_should_load_most_recent_attributes_for_child_records_marked_for_destruction
-    ship = Ship.create!(:name => "The good ship Dollypop")
-    part = ship.parts.create!(:name => "Mast")
+    ship = Ship.create!(name: "The good ship Dollypop")
+    part = ship.parts.create!(name: "Mast")
     part.mark_for_destruction
-    ShipPart.find(part.id).update_columns(name: 'Deck')
-    ship.parts.send(:load_target)
-    assert_equal 'Deck', ship.parts[0].name
+    ShipPart.find(part.id).update_columns(name: "Deck")
+    assert_equal "Deck", ship.parts[0].name
   end
 
-
   def test_include_with_order_works
-    assert_nothing_raised {Account.all.merge!(:order => 'id', :includes => :firm).first}
-    assert_nothing_raised {Account.all.merge!(:order => :id, :includes => :firm).first}
+    assert_nothing_raised { Account.all.merge!(order: "id", includes: :firm).first }
+    assert_nothing_raised { Account.all.merge!(order: :id, includes: :firm).first }
   end
 
   def test_bad_collection_keys
-    assert_raise(ArgumentError, 'ActiveRecord should have barked on bad collection keys') do
-      Class.new(ActiveRecord::Base).has_many(:wheels, :name => 'wheels')
+    assert_raise(ArgumentError, "ActiveRecord should have barked on bad collection keys") do
+      Class.new(ActiveRecord::Base).has_many(:wheels, name: "wheels")
     end
   end
 
   def test_should_construct_new_finder_sql_after_create
-    person = Person.new :first_name => 'clark'
+    person = Person.new first_name: "clark"
     assert_equal [], person.readers.to_a
     person.save!
-    reader = Reader.create! :person => person, :post => Post.new(:title => "foo", :body => "bar")
+    reader = Reader.create! person: person, post: Post.new(title: "foo", body: "bar")
     assert person.readers.find(reader.id)
   end
 
   def test_force_reload
     firm = Firm.new("name" => "A New Firm, Inc")
     firm.save
-    firm.clients.each {} # forcing to load all clients
+    firm.clients.each { } # forcing to load all clients
     assert firm.clients.empty?, "New firm shouldn't have client objects"
     assert_equal 0, firm.clients.size, "New firm should have 0 clients"
 
@@ -93,8 +90,10 @@ class AssociationsTest < ActiveRecord::TestCase
     assert firm.clients.empty?, "New firm should have cached no client objects"
     assert_equal 0, firm.clients.size, "New firm should have cached 0 clients count"
 
-    assert !firm.clients(true).empty?, "New firm should have reloaded client objects"
-    assert_equal 1, firm.clients(true).size, "New firm should have reloaded clients count"
+    firm.clients.reload
+
+    assert_not firm.clients.empty?, "New firm should have reloaded client objects"
+    assert_equal 1, firm.clients.size, "New firm should have reloaded clients count"
   end
 
   def test_using_limitable_reflections_helper
@@ -103,102 +102,99 @@ class AssociationsTest < ActiveRecord::TestCase
     has_many_reflections = [Tag.reflect_on_association(:taggings), Developer.reflect_on_association(:projects)]
     mixed_reflections = (belongs_to_reflections + has_many_reflections).uniq
     assert using_limitable_reflections.call(belongs_to_reflections), "Belong to associations are limitable"
-    assert !using_limitable_reflections.call(has_many_reflections), "All has many style associations are not limitable"
-    assert !using_limitable_reflections.call(mixed_reflections), "No collection associations (has many style) should pass"
-  end
-
-  def test_force_reload_is_uncached
-    firm = Firm.create!("name" => "A New Firm, Inc")
-    Client.create!("name" => "TheClient.com", :firm => firm)
-    ActiveRecord::Base.cache do
-      firm.clients.each {}
-      assert_queries(0) { assert_not_nil firm.clients.each {} }
-      assert_queries(1) { assert_not_nil firm.clients(true).each {} }
-    end
+    assert_not using_limitable_reflections.call(has_many_reflections), "All has many style associations are not limitable"
+    assert_not using_limitable_reflections.call(mixed_reflections), "No collection associations (has many style) should pass"
   end
 
   def test_association_with_references
     firm = companies(:first_firm)
-    assert_includes firm.association_with_references.references_values, 'foo'
+    assert_includes firm.association_with_references.references_values, "foo"
   end
-
 end
 
 class AssociationProxyTest < ActiveRecord::TestCase
-  fixtures :authors, :posts, :categorizations, :categories, :developers, :projects, :developers_projects
+  fixtures :authors, :author_addresses, :posts, :categorizations, :categories, :developers, :projects, :developers_projects
 
   def test_push_does_not_load_target
     david = authors(:david)
 
-    david.posts << (post = Post.new(:title => "New on Edge", :body => "More cool stuff!"))
-    assert !david.posts.loaded?
-    assert david.posts.include?(post)
+    david.posts << (post = Post.new(title: "New on Edge", body: "More cool stuff!"))
+    assert_not_predicate david.posts, :loaded?
+    assert_includes david.posts, post
   end
 
   def test_push_has_many_through_does_not_load_target
     david = authors(:david)
 
     david.categories << categories(:technology)
-    assert !david.categories.loaded?
-    assert david.categories.include?(categories(:technology))
+    assert_not_predicate david.categories, :loaded?
+    assert_includes david.categories, categories(:technology)
   end
 
   def test_push_followed_by_save_does_not_load_target
     david = authors(:david)
 
-    david.posts << (post = Post.new(:title => "New on Edge", :body => "More cool stuff!"))
-    assert !david.posts.loaded?
+    david.posts << (post = Post.new(title: "New on Edge", body: "More cool stuff!"))
+    assert_not_predicate david.posts, :loaded?
     david.save
-    assert !david.posts.loaded?
-    assert david.posts.include?(post)
+    assert_not_predicate david.posts, :loaded?
+    assert_includes david.posts, post
   end
 
   def test_push_does_not_lose_additions_to_new_record
-    josh = Author.new(:name => "Josh")
-    josh.posts << Post.new(:title => "New on Edge", :body => "More cool stuff!")
-    assert josh.posts.loaded?
+    josh = Author.new(name: "Josh")
+    josh.posts << Post.new(title: "New on Edge", body: "More cool stuff!")
+    assert_predicate josh.posts, :loaded?
     assert_equal 1, josh.posts.size
   end
 
   def test_append_behaves_like_push
-    josh = Author.new(:name => "Josh")
-    josh.posts.append Post.new(:title => "New on Edge", :body => "More cool stuff!")
-    assert josh.posts.loaded?
+    josh = Author.new(name: "Josh")
+    josh.posts.append Post.new(title: "New on Edge", body: "More cool stuff!")
+    assert_predicate josh.posts, :loaded?
     assert_equal 1, josh.posts.size
   end
 
   def test_prepend_is_not_defined
-    josh = Author.new(:name => "Josh")
+    josh = Author.new(name: "Josh")
     assert_raises(NoMethodError) { josh.posts.prepend Post.new }
   end
 
   def test_save_on_parent_does_not_load_target
     david = developers(:david)
 
-    assert !david.projects.loaded?
+    assert_not_predicate david.projects, :loaded?
     david.update_columns(created_at: Time.now)
-    assert !david.projects.loaded?
+    assert_not_predicate david.projects, :loaded?
+  end
+
+  def test_load_does_load_target
+    david = developers(:david)
+
+    assert_not_predicate david.projects, :loaded?
+    david.projects.load
+    assert_predicate david.projects, :loaded?
   end
 
   def test_inspect_does_not_reload_a_not_yet_loaded_target
-    andreas = Developer.new :name => 'Andreas', :log => 'new developer added'
-    assert !andreas.audit_logs.loaded?
+    andreas = Developer.new name: "Andreas", log: "new developer added"
+    assert_not_predicate andreas.audit_logs, :loaded?
     assert_match(/message: "new developer added"/, andreas.audit_logs.inspect)
   end
 
   def test_save_on_parent_saves_children
-    developer = Developer.create :name => "Bryan", :salary => 50_000
+    developer = Developer.create name: "Bryan", salary: 50_000
     assert_equal 1, developer.reload.audit_logs.size
   end
 
   def test_create_via_association_with_block
-    post = authors(:david).posts.create(:title => "New on Edge") {|p| p.body = "More cool stuff!"}
+    post = authors(:david).posts.create(title: "New on Edge") { |p| p.body = "More cool stuff!" }
     assert_equal post.title, "New on Edge"
     assert_equal post.body, "More cool stuff!"
   end
 
   def test_create_with_bang_via_association_with_block
-    post = authors(:david).posts.create!(:title => "New on Edge") {|p| p.body = "More cool stuff!"}
+    post = authors(:david).posts.create!(title: "New on Edge") { |p| p.body = "More cool stuff!" }
     assert_equal post.title, "New on Edge"
     assert_equal post.body, "More cool stuff!"
   end
@@ -216,7 +212,7 @@ class AssociationProxyTest < ActiveRecord::TestCase
   end
 
   def test_scoped_allows_conditions
-    assert developers(:david).projects.merge(where: 'foo').to_sql.include?('foo')
+    assert developers(:david).projects.merge(where: "foo").to_sql.include?("foo")
   end
 
   test "getting a scope from an association" do
@@ -228,7 +224,14 @@ class AssociationProxyTest < ActiveRecord::TestCase
 
   test "proxy object is cached" do
     david = developers(:david)
-    assert david.projects.equal?(david.projects)
+    assert_same david.projects, david.projects
+  end
+
+  test "proxy object can be stubbed" do
+    david = developers(:david)
+    david.projects.define_singleton_method(:extra_method) { 42 }
+
+    assert_equal 42, david.projects.extra_method
   end
 
   test "inverses get set of subsets of the association" do
@@ -244,16 +247,25 @@ class AssociationProxyTest < ActiveRecord::TestCase
 
   test "first! works on loaded associations" do
     david = authors(:david)
-    assert_equal david.posts.first, david.posts.reload.first!
+    assert_equal david.first_posts.first, david.first_posts.reload.first!
+    assert_predicate david.first_posts, :loaded?
+    assert_no_queries { david.first_posts.first! }
+  end
+
+  def test_pluck_uses_loaded_target
+    david = authors(:david)
+    assert_equal david.first_posts.pluck(:title), david.first_posts.load.pluck(:title)
+    assert_predicate david.first_posts, :loaded?
+    assert_no_queries { david.first_posts.pluck(:title) }
   end
 
   def test_reset_unloads_target
     david = authors(:david)
     david.posts.reload
 
-    assert david.posts.loaded?
+    assert_predicate david.posts, :loaded?
     david.posts.reset
-    assert !david.posts.loaded?
+    assert_not_predicate david.posts, :loaded?
   end
 end
 
@@ -261,18 +273,18 @@ class OverridingAssociationsTest < ActiveRecord::TestCase
   class DifferentPerson < ActiveRecord::Base; end
 
   class PeopleList < ActiveRecord::Base
-    has_and_belongs_to_many :has_and_belongs_to_many, :before_add => :enlist
-    has_many :has_many, :before_add => :enlist
+    has_and_belongs_to_many :has_and_belongs_to_many, before_add: :enlist
+    has_many :has_many, before_add: :enlist
     belongs_to :belongs_to
     has_one :has_one
   end
 
   class DifferentPeopleList < PeopleList
     # Different association with the same name, callbacks should be omitted here.
-    has_and_belongs_to_many :has_and_belongs_to_many, :class_name => 'DifferentPerson'
-    has_many :has_many, :class_name => 'DifferentPerson'
-    belongs_to :belongs_to, :class_name => 'DifferentPerson'
-    has_one :has_one, :class_name => 'DifferentPerson'
+    has_and_belongs_to_many :has_and_belongs_to_many, class_name: "DifferentPerson"
+    has_many :has_many, class_name: "DifferentPerson"
+    belongs_to :belongs_to, class_name: "DifferentPerson"
+    has_one :has_one, class_name: "DifferentPerson"
   end
 
   def test_habtm_association_redefinition_callbacks_should_differ_and_not_inherited
diff --git a/activerecord/test/cases/attribute_decorators_test.rb b/activerecord/test/cases/attribute_decorators_test.rb
index 2aeb2601c2..42eca233ce 100644
--- a/activerecord/test/cases/attribute_decorators_test.rb
+++ b/activerecord/test/cases/attribute_decorators_test.rb
@@ -1,9 +1,11 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class AttributeDecoratorsTest < ActiveRecord::TestCase
     class Model < ActiveRecord::Base
-      self.table_name = 'attribute_decorators_model'
+      self.table_name = "attribute_decorators_model"
     end
 
     class StringDecorator < SimpleDelegator
@@ -28,19 +30,19 @@ module ActiveRecord
 
     teardown do
       return unless @connection
-      @connection.drop_table 'attribute_decorators_model', if_exists: true
+      @connection.drop_table "attribute_decorators_model", if_exists: true
       Model.attribute_type_decorations.clear
       Model.reset_column_information
     end
 
     test "attributes can be decorated" do
-      model = Model.new(a_string: 'Hello')
-      assert_equal 'Hello', model.a_string
+      model = Model.new(a_string: "Hello")
+      assert_equal "Hello", model.a_string
 
       Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
 
-      model = Model.new(a_string: 'Hello')
-      assert_equal 'Hello decorated!', model.a_string
+      model = Model.new(a_string: "Hello")
+      assert_equal "Hello decorated!", model.a_string
     end
 
     test "decoration does not eagerly load existing columns" do
@@ -51,54 +53,54 @@ module ActiveRecord
     end
 
     test "undecorated columns are not touched" do
-      Model.attribute :another_string, :string, default: 'something or other'
+      Model.attribute :another_string, :string, default: "something or other"
       Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
 
-      assert_equal 'something or other', Model.new.another_string
+      assert_equal "something or other", Model.new.another_string
     end
 
     test "decorators can be chained" do
       Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
       Model.decorate_attribute_type(:a_string, :other) { |t| StringDecorator.new(t) }
 
-      model = Model.new(a_string: 'Hello!')
+      model = Model.new(a_string: "Hello!")
 
-      assert_equal 'Hello! decorated! decorated!', model.a_string
+      assert_equal "Hello! decorated! decorated!", model.a_string
     end
 
     test "decoration of the same type multiple times is idempotent" do
       Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
       Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
 
-      model = Model.new(a_string: 'Hello')
-      assert_equal 'Hello decorated!', model.a_string
+      model = Model.new(a_string: "Hello")
+      assert_equal "Hello decorated!", model.a_string
     end
 
     test "decorations occur in order of declaration" do
       Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
       Model.decorate_attribute_type(:a_string, :other) do |type|
-        StringDecorator.new(type, 'decorated again!')
+        StringDecorator.new(type, "decorated again!")
       end
 
-      model = Model.new(a_string: 'Hello!')
+      model = Model.new(a_string: "Hello!")
 
-      assert_equal 'Hello! decorated! decorated again!', model.a_string
+      assert_equal "Hello! decorated! decorated again!", model.a_string
     end
 
     test "decorating attributes does not modify parent classes" do
-      Model.attribute :another_string, :string, default: 'whatever'
+      Model.attribute :another_string, :string, default: "whatever"
       Model.decorate_attribute_type(:a_string, :test) { |t| StringDecorator.new(t) }
       child_class = Class.new(Model)
       child_class.decorate_attribute_type(:another_string, :test) { |t| StringDecorator.new(t) }
       child_class.decorate_attribute_type(:a_string, :other) { |t| StringDecorator.new(t) }
 
-      model = Model.new(a_string: 'Hello!')
-      child = child_class.new(a_string: 'Hello!')
+      model = Model.new(a_string: "Hello!")
+      child = child_class.new(a_string: "Hello!")
 
-      assert_equal 'Hello! decorated!', model.a_string
-      assert_equal 'whatever', model.another_string
-      assert_equal 'Hello! decorated! decorated!', child.a_string
-      assert_equal 'whatever decorated!', child.another_string
+      assert_equal "Hello! decorated!", model.a_string
+      assert_equal "whatever", model.another_string
+      assert_equal "Hello! decorated! decorated!", child.a_string
+      assert_equal "whatever decorated!", child.another_string
     end
 
     class Multiplier < SimpleDelegator
@@ -116,9 +118,9 @@ module ActiveRecord
         Multiplier.new(type)
       end
 
-      model = Model.new(a_string: 'whatever', an_int: 1)
+      model = Model.new(a_string: "whatever", an_int: 1)
 
-      assert_equal 'whatever', model.a_string
+      assert_equal "whatever", model.a_string
       assert_equal 2, model.an_int
     end
   end
diff --git a/activerecord/test/cases/attribute_methods/read_test.rb b/activerecord/test/cases/attribute_methods/read_test.rb
index 74e556211b..54512068ee 100644
--- a/activerecord/test/cases/attribute_methods/read_test.rb
+++ b/activerecord/test/cases/attribute_methods/read_test.rb
@@ -1,20 +1,21 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'thread'
 
 module ActiveRecord
   module AttributeMethods
     class ReadTest < ActiveRecord::TestCase
-      class FakeColumn < Struct.new(:name)
+      FakeColumn = Struct.new(:name) do
         def type; :integer; end
       end
 
       def setup
-        @klass = Class.new do
+        @klass = Class.new(Class.new { def self.initialize_generated_modules; end }) do
           def self.superclass; Base; end
-          def self.base_class; self; end
+          def self.base_class?; true; end
           def self.decorate_matching_attribute_types(*); end
-          def self.initialize_generated_modules; end
 
+          include ActiveRecord::DefineCallbacks
           include ActiveRecord::AttributeMethods
 
           def self.attribute_names
@@ -40,13 +41,13 @@ module ActiveRecord
         instance = @klass.new
 
         @klass.attribute_names.each do |name|
-          assert !instance.methods.map(&:to_s).include?(name)
+          assert_not_includes instance.methods.map(&:to_s), name
         end
 
         @klass.define_attribute_methods
 
         @klass.attribute_names.each do |name|
-          assert instance.methods.map(&:to_s).include?(name), "#{name} is not defined"
+          assert_includes instance.methods.map(&:to_s), name, "#{name} is not defined"
         end
       end
 
diff --git a/activerecord/test/cases/attribute_methods_test.rb b/activerecord/test/cases/attribute_methods_test.rb
index ea2b94cbf4..0dbdd56ae6 100644
--- a/activerecord/test/cases/attribute_methods_test.rb
+++ b/activerecord/test/cases/attribute_methods_test.rb
@@ -1,16 +1,17 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/minimalistic'
-require 'models/developer'
-require 'models/computer'
-require 'models/auto_id'
-require 'models/boolean'
-require 'models/computer'
-require 'models/topic'
-require 'models/company'
-require 'models/category'
-require 'models/reply'
-require 'models/contact'
-require 'models/keyboard'
+require "models/minimalistic"
+require "models/developer"
+require "models/auto_id"
+require "models/boolean"
+require "models/computer"
+require "models/topic"
+require "models/company"
+require "models/category"
+require "models/reply"
+require "models/contact"
+require "models/keyboard"
 
 class AttributeMethodsTest < ActiveRecord::TestCase
   include InTimeZone
@@ -20,7 +21,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
   def setup
     @old_matchers = ActiveRecord::Base.send(:attribute_method_matchers).dup
     @target = Class.new(ActiveRecord::Base)
-    @target.table_name = 'topics'
+    @target.table_name = "topics"
   end
 
   teardown do
@@ -28,26 +29,52 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     ActiveRecord::Base.send(:attribute_method_matchers).concat(@old_matchers)
   end
 
-  def test_attribute_for_inspect
+  test "attribute_for_inspect with a string" do
     t = topics(:first)
     t.title = "The First Topic Now Has A Title With\nNewlines And More Than 50 Characters"
 
-    assert_equal %("#{t.written_on.to_s(:db)}"), t.attribute_for_inspect(:written_on)
     assert_equal '"The First Topic Now Has A Title With\nNewlines And ..."', t.attribute_for_inspect(:title)
   end
 
-  def test_attribute_present
+  test "attribute_for_inspect with a date" do
+    t = topics(:first)
+
+    assert_equal %("#{t.written_on.to_s(:db)}"), t.attribute_for_inspect(:written_on)
+  end
+
+  test "attribute_for_inspect with an array" do
+    t = topics(:first)
+    t.content = [Object.new]
+
+    assert_match %r(\[#<Object:0x[0-9a-f]+>\]), t.attribute_for_inspect(:content)
+  end
+
+  test "attribute_for_inspect with a long array" do
+    t = topics(:first)
+    t.content = (1..11).to_a
+
+    assert_equal "[1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]", t.attribute_for_inspect(:content)
+  end
+
+  test "attribute_for_inspect with a non-primary key id attribute" do
+    t = topics(:first).becomes(TitlePrimaryKeyTopic)
+    t.title = "The First Topic Now Has A Title With\nNewlines And More Than 50 Characters"
+
+    assert_equal "1", t.attribute_for_inspect(:id)
+  end
+
+  test "attribute_present" do
     t = Topic.new
     t.title = "hello there!"
     t.written_on = Time.now
     t.author_name = ""
     assert t.attribute_present?("title")
     assert t.attribute_present?("written_on")
-    assert !t.attribute_present?("content")
-    assert !t.attribute_present?("author_name")
+    assert_not t.attribute_present?("content")
+    assert_not t.attribute_present?("author_name")
   end
 
-  def test_attribute_present_with_booleans
+  test "attribute_present with booleans" do
     b1 = Boolean.new
     b1.value = false
     assert b1.attribute_present?(:value)
@@ -57,7 +84,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert b2.attribute_present?(:value)
 
     b3 = Boolean.new
-    assert !b3.attribute_present?(:value)
+    assert_not b3.attribute_present?(:value)
 
     b4 = Boolean.new
     b4.value = false
@@ -65,43 +92,44 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert Boolean.find(b4.id).attribute_present?(:value)
   end
 
-  def test_caching_nil_primary_key
+  test "caching a nil primary key" do
     klass = Class.new(Minimalistic)
-    klass.expects(:reset_primary_key).returns(nil).once
-    2.times { klass.primary_key }
+    assert_called(klass, :reset_primary_key, returns: nil) do
+      2.times { klass.primary_key }
+    end
   end
 
-  def test_attribute_keys_on_new_instance
+  test "attribute keys on a new instance" do
     t = Topic.new
-    assert_equal nil, t.title, "The topics table has a title column, so it should be nil"
+    assert_nil t.title, "The topics table has a title column, so it should be nil"
     assert_raise(NoMethodError) { t.title2 }
   end
 
-  def test_boolean_attributes
-    assert !Topic.find(1).approved?
-    assert Topic.find(2).approved?
+  test "boolean attributes" do
+    assert_not_predicate Topic.find(1), :approved?
+    assert_predicate Topic.find(2), :approved?
   end
 
-  def test_set_attributes
+  test "set attributes" do
     topic = Topic.find(1)
-    topic.attributes = { "title" => "Budget", "author_name" => "Jason" }
+    topic.attributes = { title: "Budget", author_name: "Jason" }
     topic.save
     assert_equal("Budget", topic.title)
     assert_equal("Jason", topic.author_name)
     assert_equal(topics(:first).author_email_address, Topic.find(1).author_email_address)
   end
 
-  def test_set_attributes_without_hash
+  test "set attributes without a hash" do
     topic = Topic.new
-    assert_raise(ArgumentError) { topic.attributes = '' }
+    assert_raise(ArgumentError) { topic.attributes = "" }
   end
 
-  def test_integers_as_nil
-    test = AutoId.create('value' => '')
+  test "integers as nil" do
+    test = AutoId.create(value: "")
     assert_nil AutoId.find(test.id).value
   end
 
-  def test_set_attributes_with_block
+  test "set attributes with a block" do
     topic = Topic.new do |t|
       t.title       = "Budget"
       t.author_name = "Jason"
@@ -111,7 +139,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal("Jason", topic.author_name)
   end
 
-  def test_respond_to?
+  test "respond_to?" do
     topic = Topic.find(1)
     assert_respond_to topic, "title"
     assert_respond_to topic, "title?"
@@ -121,79 +149,62 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_respond_to topic, :title=
     assert_respond_to topic, "author_name"
     assert_respond_to topic, "attribute_names"
-    assert !topic.respond_to?("nothingness")
-    assert !topic.respond_to?(:nothingness)
+    assert_not_respond_to topic, "nothingness"
+    assert_not_respond_to topic, :nothingness
   end
 
-  def test_respond_to_with_custom_primary_key
+  test "respond_to? with a custom primary key" do
     keyboard = Keyboard.create
     assert_not_nil keyboard.key_number
     assert_equal keyboard.key_number, keyboard.id
-    assert keyboard.respond_to?('key_number')
-    assert keyboard.respond_to?('id')
+    assert_respond_to keyboard, "key_number"
+    assert_respond_to keyboard, "id"
   end
 
-  def test_id_before_type_cast_with_custom_primary_key
+  test "id_before_type_cast with a custom primary key" do
     keyboard = Keyboard.create
-    keyboard.key_number = '10'
-    assert_equal '10', keyboard.id_before_type_cast
-    assert_equal nil, keyboard.read_attribute_before_type_cast('id')
-    assert_equal '10', keyboard.read_attribute_before_type_cast('key_number')
-    assert_equal '10', keyboard.read_attribute_before_type_cast(:key_number)
-  end
-
-  # Syck calls respond_to? before actually calling initialize
-  def test_respond_to_with_allocated_object
-    klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'topics'
-    end
-
-    topic = klass.allocate
-    assert !topic.respond_to?("nothingness")
-    assert !topic.respond_to?(:nothingness)
-    assert_respond_to topic, "title"
-    assert_respond_to topic, :title
+    keyboard.key_number = "10"
+    assert_equal "10", keyboard.id_before_type_cast
+    assert_nil keyboard.read_attribute_before_type_cast("id")
+    assert_equal "10", keyboard.read_attribute_before_type_cast("key_number")
+    assert_equal "10", keyboard.read_attribute_before_type_cast(:key_number)
   end
 
-  # IRB inspects the return value of "MyModel.allocate".
-  def test_allocated_object_can_be_inspected
+  # IRB inspects the return value of MyModel.allocate.
+  test "allocated objects can be inspected" do
     topic = Topic.allocate
     assert_equal "#<Topic not initialized>", topic.inspect
   end
 
-  def test_array_content
+  test "array content" do
+    content = %w( one two three )
     topic = Topic.new
-    topic.content = %w( one two three )
+    topic.content = content
     topic.save
 
-    assert_equal(%w( one two three ), Topic.find(topic.id).content)
+    assert_equal content, Topic.find(topic.id).content
   end
 
-  def test_read_attributes_before_type_cast
-    category = Category.new({:name=>"Test category", :type => nil})
-    category_attrs = {"name"=>"Test category", "id" => nil, "type" => nil, "categorizations_count" => nil}
-    assert_equal category_attrs , category.attributes_before_type_cast
+  test "read attributes_before_type_cast" do
+    category = Category.new(name: "Test category", type: nil)
+    category_attrs = { "name" => "Test category", "id" => nil, "type" => nil, "categorizations_count" => nil }
+    assert_equal category_attrs, category.attributes_before_type_cast
   end
 
-  if current_adapter?(:MysqlAdapter)
-    def test_read_attributes_before_type_cast_on_boolean
-      bool = Boolean.create({ "value" => false })
-      if RUBY_PLATFORM =~ /java/
-        # JRuby will return the value before typecast as string
-        assert_equal "0", bool.reload.attributes_before_type_cast["value"]
-      else
-        assert_equal 0, bool.reload.attributes_before_type_cast["value"]
-      end
+  if current_adapter?(:Mysql2Adapter)
+    test "read attributes_before_type_cast on a boolean" do
+      bool = Boolean.create!("value" => false)
+      assert_equal 0, bool.reload.attributes_before_type_cast["value"]
     end
   end
 
-  def test_read_attributes_before_type_cast_on_datetime
+  test "read attributes_before_type_cast on a datetime" do
     in_time_zone "Pacific Time (US & Canada)" do
       record = @target.new
 
       record.written_on = "345643456"
       assert_equal "345643456", record.written_on_before_type_cast
-      assert_equal nil, record.written_on
+      assert_nil record.written_on
 
       record.written_on = "2009-10-11 12:13:14"
       assert_equal "2009-10-11 12:13:14", record.written_on_before_type_cast
@@ -202,7 +213,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_read_attributes_after_type_cast_on_datetime
+  test "read attributes_after_type_cast on a date" do
     tz = "Pacific Time (US & Canada)"
 
     in_time_zone tz do
@@ -223,7 +234,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_hash_content
+  test "hash content" do
     topic = Topic.new
     topic.content = { "one" => 1, "two" => 2 }
     topic.save
@@ -237,7 +248,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal 3, Topic.find(topic.id).content["three"]
   end
 
-  def test_update_array_content
+  test "update array content" do
     topic = Topic.new
     topic.content = %w( one two three )
 
@@ -251,40 +262,40 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal(%w( one two three four five ), topic.content)
   end
 
-  def test_case_sensitive_attributes_hash
-    # DB2 is not case-sensitive
+  test "case-sensitive attributes hash" do
+    # DB2 is not case-sensitive.
     return true if current_adapter?(:DB2Adapter)
 
-    assert_equal @loaded_fixtures['computers']['workstation'].to_hash, Computer.first.attributes
+    assert_equal @loaded_fixtures["computers"]["workstation"].to_hash, Computer.first.attributes
   end
 
-  def test_attributes_without_primary_key
+  test "attributes without primary key" do
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'developers_projects'
+      self.table_name = "developers_projects"
     end
 
     assert_equal klass.column_names, klass.new.attributes.keys
-    assert_not klass.new.has_attribute?('id')
+    assert_not klass.new.has_attribute?("id")
   end
 
-  def test_hashes_not_mangled
-    new_topic = { :title => "New Topic" }
-    new_topic_values = { :title => "AnotherTopic" }
+  test "hashes are not mangled" do
+    new_topic = { title: "New Topic" }
+    new_topic_values = { title: "AnotherTopic" }
 
     topic = Topic.new(new_topic)
     assert_equal new_topic[:title], topic.title
 
-    topic.attributes= new_topic_values
+    topic.attributes = new_topic_values
     assert_equal new_topic_values[:title], topic.title
   end
 
-  def test_create_through_factory
-    topic = Topic.create("title" => "New Topic")
+  test "create through factory" do
+    topic = Topic.create(title: "New Topic")
     topicReloaded = Topic.find(topic.id)
     assert_equal(topic, topicReloaded)
   end
 
-  def test_write_attribute
+  test "write_attribute" do
     topic = Topic.new
     topic.send(:write_attribute, :title, "Still another topic")
     assert_equal "Still another topic", topic.title
@@ -299,7 +310,20 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "Still another topic: part 4", topic.title
   end
 
-  def test_read_attribute
+  test "write_attribute can write aliased attributes as well" do
+    topic = Topic.new(title: "Don't change the topic")
+    topic.write_attribute :heading, "New topic"
+
+    assert_equal "New topic", topic.title
+  end
+
+  test "write_attribute raises ActiveModel::MissingAttributeError when the attribute does not exist" do
+    topic = Topic.first
+    assert_raises(ActiveModel::MissingAttributeError) { topic.update_columns(no_column_exists: "Hello!") }
+    assert_raises(ActiveModel::UnknownAttributeError) { topic.update(no_column_exists: "Hello!") }
+  end
+
+  test "read_attribute" do
     topic = Topic.new
     topic.title = "Don't change the topic"
     assert_equal "Don't change the topic", topic.read_attribute("title")
@@ -309,23 +333,33 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "Don't change the topic", topic[:title]
   end
 
-  def test_read_attribute_raises_missing_attribute_error_when_not_exists
-    computer = Computer.select('id').first
+  test "read_attribute can read aliased attributes as well" do
+    topic = Topic.new(title: "Don't change the topic")
+
+    assert_equal "Don't change the topic", topic.read_attribute("heading")
+    assert_equal "Don't change the topic", topic["heading"]
+
+    assert_equal "Don't change the topic", topic.read_attribute(:heading)
+    assert_equal "Don't change the topic", topic[:heading]
+  end
+
+  test "read_attribute raises ActiveModel::MissingAttributeError when the attribute does not exist" do
+    computer = Computer.select("id").first
     assert_raises(ActiveModel::MissingAttributeError) { computer[:developer] }
     assert_raises(ActiveModel::MissingAttributeError) { computer[:extendedWarranty] }
-    assert_raises(ActiveModel::MissingAttributeError) { computer[:no_column_exists] = 'Hello!' }
-    assert_nothing_raised { computer[:developer] = 'Hello!' }
+    assert_raises(ActiveModel::MissingAttributeError) { computer[:no_column_exists] = "Hello!" }
+    assert_nothing_raised { computer[:developer] = "Hello!" }
   end
 
-  def test_read_attribute_when_false
+  test "read_attribute when false" do
     topic = topics(:first)
     topic.approved = false
-    assert !topic.approved?, "approved should be false"
+    assert_not topic.approved?, "approved should be false"
     topic.approved = "false"
-    assert !topic.approved?, "approved should be false"
+    assert_not topic.approved?, "approved should be false"
   end
 
-  def test_read_attribute_when_true
+  test "read_attribute when true" do
     topic = topics(:first)
     topic.approved = true
     assert topic.approved?, "approved should be true"
@@ -333,13 +367,13 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert topic.approved?, "approved should be true"
   end
 
-  def test_read_write_boolean_attribute
+  test "boolean attributes writing and reading" do
     topic = Topic.new
     topic.approved = "false"
-    assert !topic.approved?, "approved should be false"
+    assert_not topic.approved?, "approved should be false"
 
     topic.approved = "false"
-    assert !topic.approved?, "approved should be false"
+    assert_not topic.approved?, "approved should be false"
 
     topic.approved = "true"
     assert topic.approved?, "approved should be true"
@@ -348,7 +382,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert topic.approved?, "approved should be true"
   end
 
-  def test_overridden_write_attribute
+  test "overridden write_attribute" do
     topic = Topic.new
     def topic.write_attribute(attr_name, value)
       super(attr_name, value.downcase)
@@ -367,7 +401,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "yet another topic: part 4", topic.title
   end
 
-  def test_overridden_read_attribute
+  test "overridden read_attribute" do
     topic = Topic.new
     topic.title = "Stop changing the topic"
     def topic.read_attribute(attr_name)
@@ -381,40 +415,40 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "STOP CHANGING THE TOPIC", topic[:title]
   end
 
-  def test_read_overridden_attribute
-    topic = Topic.new(:title => 'a')
-    def topic.title() 'b' end
-    assert_equal 'a', topic[:title]
+  test "read overridden attribute" do
+    topic = Topic.new(title: "a")
+    def topic.title() "b" end
+    assert_equal "a", topic[:title]
   end
 
-  def test_query_attribute_string
+  test "string attribute predicate" do
     [nil, "", " "].each do |value|
-      assert_equal false, Topic.new(:author_name => value).author_name?
+      assert_equal false, Topic.new(author_name: value).author_name?
     end
 
-    assert_equal true, Topic.new(:author_name => "Name").author_name?
+    assert_equal true, Topic.new(author_name: "Name").author_name?
   end
 
-  def test_query_attribute_number
+  test "number attribute predicate" do
     [nil, 0, "0"].each do |value|
-      assert_equal false, Developer.new(:salary => value).salary?
+      assert_equal false, Developer.new(salary: value).salary?
     end
 
-    assert_equal true, Developer.new(:salary => 1).salary?
-    assert_equal true, Developer.new(:salary => "1").salary?
+    assert_equal true, Developer.new(salary: 1).salary?
+    assert_equal true, Developer.new(salary: "1").salary?
   end
 
-  def test_query_attribute_boolean
+  test "boolean attribute predicate" do
     [nil, "", false, "false", "f", 0].each do |value|
-      assert_equal false, Topic.new(:approved => value).approved?
+      assert_equal false, Topic.new(approved: value).approved?
     end
 
     [true, "true", "1", 1].each do |value|
-      assert_equal true, Topic.new(:approved => value).approved?
+      assert_equal true, Topic.new(approved: value).approved?
     end
   end
 
-  def test_query_attribute_with_custom_fields
+  test "custom field attribute predicate" do
     object = Company.find_by_sql(<<-SQL).first
       SELECT c1.*, c2.type as string_value, c2.rating as int_value
         FROM companies c1, companies c2
@@ -423,107 +457,107 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     SQL
 
     assert_equal "Firm", object.string_value
-    assert object.string_value?
+    assert_predicate object, :string_value?
 
     object.string_value = "  "
-    assert !object.string_value?
+    assert_not_predicate object, :string_value?
 
     assert_equal 1, object.int_value.to_i
-    assert object.int_value?
+    assert_predicate object, :int_value?
 
     object.int_value = "0"
-    assert !object.int_value?
+    assert_not_predicate object, :int_value?
   end
 
-  def test_non_attribute_access_and_assignment
+  test "non-attribute read and write" do
     topic = Topic.new
-    assert !topic.respond_to?("mumbo")
+    assert_not_respond_to topic, "mumbo"
     assert_raise(NoMethodError) { topic.mumbo }
     assert_raise(NoMethodError) { topic.mumbo = 5 }
   end
 
-  def test_undeclared_attribute_method_does_not_affect_respond_to_and_method_missing
-    topic = @target.new(:title => 'Budget')
-    assert topic.respond_to?('title')
-    assert_equal 'Budget', topic.title
-    assert !topic.respond_to?('title_hello_world')
+  test "undeclared attribute method does not affect respond_to? and method_missing" do
+    topic = @target.new(title: "Budget")
+    assert_respond_to topic, "title"
+    assert_equal "Budget", topic.title
+    assert_not_respond_to topic, "title_hello_world"
     assert_raise(NoMethodError) { topic.title_hello_world }
   end
 
-  def test_declared_prefixed_attribute_method_affects_respond_to_and_method_missing
-    topic = @target.new(:title => 'Budget')
+  test "declared prefixed attribute method affects respond_to? and method_missing" do
+    topic = @target.new(title: "Budget")
     %w(default_ title_).each do |prefix|
       @target.class_eval "def #{prefix}attribute(*args) args end"
       @target.attribute_method_prefix prefix
 
       meth = "#{prefix}title"
-      assert topic.respond_to?(meth)
-      assert_equal ['title'], topic.send(meth)
-      assert_equal ['title', 'a'], topic.send(meth, 'a')
-      assert_equal ['title', 1, 2, 3], topic.send(meth, 1, 2, 3)
+      assert_respond_to topic, meth
+      assert_equal ["title"], topic.send(meth)
+      assert_equal ["title", "a"], topic.send(meth, "a")
+      assert_equal ["title", 1, 2, 3], topic.send(meth, 1, 2, 3)
     end
   end
 
-  def test_declared_suffixed_attribute_method_affects_respond_to_and_method_missing
+  test "declared suffixed attribute method affects respond_to? and method_missing" do
     %w(_default _title_default _it! _candidate= able?).each do |suffix|
       @target.class_eval "def attribute#{suffix}(*args) args end"
       @target.attribute_method_suffix suffix
-      topic = @target.new(:title => 'Budget')
+      topic = @target.new(title: "Budget")
 
       meth = "title#{suffix}"
-      assert topic.respond_to?(meth)
-      assert_equal ['title'], topic.send(meth)
-      assert_equal ['title', 'a'], topic.send(meth, 'a')
-      assert_equal ['title', 1, 2, 3], topic.send(meth, 1, 2, 3)
+      assert_respond_to topic, meth
+      assert_equal ["title"], topic.send(meth)
+      assert_equal ["title", "a"], topic.send(meth, "a")
+      assert_equal ["title", 1, 2, 3], topic.send(meth, 1, 2, 3)
     end
   end
 
-  def test_declared_affixed_attribute_method_affects_respond_to_and_method_missing
-    [['mark_', '_for_update'], ['reset_', '!'], ['default_', '_value?']].each do |prefix, suffix|
+  test "declared affixed attribute method affects respond_to? and method_missing" do
+    [["mark_", "_for_update"], ["reset_", "!"], ["default_", "_value?"]].each do |prefix, suffix|
       @target.class_eval "def #{prefix}attribute#{suffix}(*args) args end"
-      @target.attribute_method_affix({ :prefix => prefix, :suffix => suffix })
-      topic = @target.new(:title => 'Budget')
+      @target.attribute_method_affix(prefix: prefix, suffix: suffix)
+      topic = @target.new(title: "Budget")
 
       meth = "#{prefix}title#{suffix}"
-      assert topic.respond_to?(meth)
-      assert_equal ['title'], topic.send(meth)
-      assert_equal ['title', 'a'], topic.send(meth, 'a')
-      assert_equal ['title', 1, 2, 3], topic.send(meth, 1, 2, 3)
+      assert_respond_to topic, meth
+      assert_equal ["title"], topic.send(meth)
+      assert_equal ["title", "a"], topic.send(meth, "a")
+      assert_equal ["title", 1, 2, 3], topic.send(meth, 1, 2, 3)
     end
   end
 
-  def test_should_unserialize_attributes_for_frozen_records
-    myobj = {:value1 => :value2}
-    topic = Topic.create("content" => myobj)
+  test "should unserialize attributes for frozen records" do
+    myobj = { value1: :value2 }
+    topic = Topic.create(content: myobj)
     topic.freeze
     assert_equal myobj, topic.content
   end
 
-  def test_typecast_attribute_from_select_to_false
-    Topic.create(:title => 'Budget')
-    # Oracle does not support boolean expressions in SELECT
+  test "typecast attribute from select to false" do
+    Topic.create(title: "Budget")
+    # Oracle does not support boolean expressions in SELECT.
     if current_adapter?(:OracleAdapter, :FbAdapter)
-      topic = Topic.all.merge!(:select => "topics.*, 0 as is_test").first
+      topic = Topic.all.merge!(select: "topics.*, 0 as is_test").first
     else
-      topic = Topic.all.merge!(:select => "topics.*, 1=2 as is_test").first
+      topic = Topic.all.merge!(select: "topics.*, 1=2 as is_test").first
     end
-    assert !topic.is_test?
+    assert_not_predicate topic, :is_test?
   end
 
-  def test_typecast_attribute_from_select_to_true
-    Topic.create(:title => 'Budget')
-    # Oracle does not support boolean expressions in SELECT
+  test "typecast attribute from select to true" do
+    Topic.create(title: "Budget")
+    # Oracle does not support boolean expressions in SELECT.
     if current_adapter?(:OracleAdapter, :FbAdapter)
-      topic = Topic.all.merge!(:select => "topics.*, 1 as is_test").first
+      topic = Topic.all.merge!(select: "topics.*, 1 as is_test").first
     else
-      topic = Topic.all.merge!(:select => "topics.*, 2=2 as is_test").first
+      topic = Topic.all.merge!(select: "topics.*, 2=2 as is_test").first
     end
-    assert topic.is_test?
+    assert_predicate topic, :is_test?
   end
 
-  def test_raises_dangerous_attribute_error_when_defining_activerecord_method_in_model
+  test "raises ActiveRecord::DangerousAttributeError when defining an AR method in a model" do
     %w(save create_or_update).each do |method|
-      klass = Class.new ActiveRecord::Base
+      klass = Class.new(ActiveRecord::Base)
       klass.class_eval "def #{method}() 'defined #{method}' end"
       assert_raise ActiveRecord::DangerousAttributeError do
         klass.instance_method_already_implemented?(method)
@@ -531,7 +565,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_converted_values_are_returned_after_assignment
+  test "converted values are returned after assignment" do
     developer = Developer.new(name: 1337, salary: "50000")
 
     assert_equal "50000", developer.salary_before_type_cast
@@ -542,14 +576,11 @@ class AttributeMethodsTest < ActiveRecord::TestCase
 
     developer.save!
 
-    assert_equal "50000", developer.salary_before_type_cast
-    assert_equal 1337, developer.name_before_type_cast
-
     assert_equal 50000, developer.salary
     assert_equal "1337", developer.name
   end
 
-  def test_write_nil_to_time_attributes
+  test "write nil to time attribute" do
     in_time_zone "Pacific Time (US & Canada)" do
       record = @target.new
       record.written_on = nil
@@ -557,7 +588,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_write_time_to_date_attributes
+  test "write time to date attribute" do
     in_time_zone "Pacific Time (US & Canada)" do
       record = @target.new
       record.last_read = Time.utc(2010, 1, 1, 10)
@@ -565,7 +596,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_time_attributes_are_retrieved_in_current_time_zone
+  test "time attributes are retrieved in the current time zone" do
     in_time_zone "Pacific Time (US & Canada)" do
       utc_time = Time.utc(2008, 1, 1)
       record   = @target.new
@@ -577,7 +608,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_setting_time_zone_aware_attribute_to_utc
+  test "setting a time zone-aware attribute to UTC" do
     in_time_zone "Pacific Time (US & Canada)" do
       utc_time = Time.utc(2008, 1, 1)
       record   = @target.new
@@ -588,11 +619,11 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_setting_time_zone_aware_attribute_in_other_time_zone
+  test "setting time zone-aware attribute in other time zone" do
     utc_time = Time.utc(2008, 1, 1)
     cst_time = utc_time.in_time_zone("Central Time (US & Canada)")
     in_time_zone "Pacific Time (US & Canada)" do
-      record   = @target.new
+      record = @target.new
       record.written_on = cst_time
       assert_equal utc_time, record.written_on
       assert_equal ActiveSupport::TimeZone["Pacific Time (US & Canada)"], record.written_on.time_zone
@@ -600,23 +631,23 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_setting_time_zone_aware_read_attribute
+  test "setting time zone-aware read attribute" do
     utc_time = Time.utc(2008, 1, 1)
     cst_time = utc_time.in_time_zone("Central Time (US & Canada)")
     in_time_zone "Pacific Time (US & Canada)" do
-      record = @target.create(:written_on => cst_time).reload
+      record = @target.create(written_on: cst_time).reload
       assert_equal utc_time, record[:written_on]
       assert_equal ActiveSupport::TimeZone["Pacific Time (US & Canada)"], record[:written_on].time_zone
       assert_equal Time.utc(2007, 12, 31, 16), record[:written_on].time
     end
   end
 
-  def test_setting_time_zone_aware_attribute_with_string
+  test "setting time zone-aware attribute with a string" do
     utc_time = Time.utc(2008, 1, 1)
     (-11..13).each do |timezone_offset|
       time_string = utc_time.in_time_zone(timezone_offset).to_s
       in_time_zone "Pacific Time (US & Canada)" do
-        record   = @target.new
+        record = @target.new
         record.written_on = time_string
         assert_equal Time.zone.parse(time_string), record.written_on
         assert_equal ActiveSupport::TimeZone["Pacific Time (US & Canada)"], record.written_on.time_zone
@@ -625,30 +656,30 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_time_zone_aware_attribute_saved
+  test "time zone-aware attribute saved" do
     in_time_zone 1 do
-      record = @target.create(:written_on => '2012-02-20 10:00')
+      record = @target.create(written_on: "2012-02-20 10:00")
 
-      record.written_on = '2012-02-20 09:00'
+      record.written_on = "2012-02-20 09:00"
       record.save
       assert_equal Time.zone.local(2012, 02, 20, 9), record.reload.written_on
     end
   end
 
-  def test_setting_time_zone_aware_attribute_to_blank_string_returns_nil
+  test "setting a time zone-aware attribute to a blank string returns nil" do
     in_time_zone "Pacific Time (US & Canada)" do
-      record   = @target.new
-      record.written_on = ' '
+      record = @target.new
+      record.written_on = " "
       assert_nil record.written_on
       assert_nil record[:written_on]
     end
   end
 
-  def test_setting_time_zone_aware_attribute_interprets_time_zone_unaware_string_in_time_zone
-    time_string = 'Tue Jan 01 00:00:00 2008'
+  test "setting a time zone-aware attribute interprets time zone-unaware string in time zone" do
+    time_string = "Tue Jan 01 00:00:00 2008"
     (-11..13).each do |timezone_offset|
       in_time_zone timezone_offset do
-        record   = @target.new
+        record = @target.new
         record.written_on = time_string
         assert_equal Time.zone.parse(time_string), record.written_on
         assert_equal ActiveSupport::TimeZone[timezone_offset], record.written_on.time_zone
@@ -657,10 +688,10 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_setting_time_zone_aware_datetime_in_current_time_zone
+  test "setting a time zone-aware datetime in the current time zone" do
     utc_time = Time.utc(2008, 1, 1)
     in_time_zone "Pacific Time (US & Canada)" do
-      record   = @target.new
+      record = @target.new
       record.written_on = utc_time.in_time_zone
       assert_equal utc_time, record.written_on
       assert_equal ActiveSupport::TimeZone["Pacific Time (US & Canada)"], record.written_on.time_zone
@@ -668,7 +699,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_yaml_dumping_record_with_time_zone_aware_attribute
+  test "YAML dumping a record with time zone-aware attribute" do
     in_time_zone "Pacific Time (US & Canada)" do
       record = Topic.new(id: 1)
       record.written_on = "Jan 01 00:00:00 2014"
@@ -676,7 +707,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_setting_time_zone_aware_time_in_current_time_zone
+  test "setting a time zone-aware time in the current time zone" do
     in_time_zone "Pacific Time (US & Canada)" do
       record = @target.new
       time_string = "10:00:00"
@@ -686,12 +717,12 @@ class AttributeMethodsTest < ActiveRecord::TestCase
       assert_equal expected_time, record.bonus_time
       assert_equal ActiveSupport::TimeZone["Pacific Time (US & Canada)"], record.bonus_time.time_zone
 
-      record.bonus_time = ''
+      record.bonus_time = ""
       assert_nil record.bonus_time
     end
   end
 
-  def test_setting_time_zone_aware_time_with_dst
+  test "setting a time zone-aware time with DST" do
     in_time_zone "Pacific Time (US & Canada)" do
       current_time = Time.zone.local(2014, 06, 15, 10)
       record = @target.new(bonus_time: current_time)
@@ -705,19 +736,36 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_removing_time_zone_aware_types
+  test "setting invalid string to a zone-aware time attribute" do
+    in_time_zone "Pacific Time (US & Canada)" do
+      record = @target.new
+      time_string = "ABC"
+
+      record.bonus_time = time_string
+      assert_nil record.bonus_time
+    end
+  end
+
+  test "removing time zone-aware types" do
     with_time_zone_aware_types(:datetime) do
       in_time_zone "Pacific Time (US & Canada)" do
         record = @target.new(bonus_time: "10:00:00")
         expected_time = Time.utc(2000, 01, 01, 10)
 
         assert_equal expected_time, record.bonus_time
-        assert record.bonus_time.utc?
+        assert_predicate record.bonus_time, :utc?
       end
     end
   end
 
-  def test_setting_time_zone_conversion_for_attributes_should_write_value_on_class_variable
+  test "time zone-aware attributes do not recurse infinitely on invalid values" do
+    in_time_zone "Pacific Time (US & Canada)" do
+      record = @target.new(bonus_time: [])
+      assert_nil record.bonus_time
+    end
+  end
+
+  test "setting a time_zone_conversion_for_attributes should write the value on a class variable" do
     Topic.skip_time_zone_conversion_for_attributes = [:field_a]
     Minimalistic.skip_time_zone_conversion_for_attributes = [:field_b]
 
@@ -725,44 +773,44 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal [:field_b], Minimalistic.skip_time_zone_conversion_for_attributes
   end
 
-  def test_read_attributes_respect_access_control
+  test "attribute readers respect access control" do
     privatize("title")
 
-    topic = @target.new(:title => "The pros and cons of programming naked.")
-    assert !topic.respond_to?(:title)
+    topic = @target.new(title: "The pros and cons of programming naked.")
+    assert_not_respond_to topic, :title
     exception = assert_raise(NoMethodError) { topic.title }
-    assert exception.message.include?("private method")
+    assert_includes exception.message, "private method"
     assert_equal "I'm private", topic.send(:title)
   end
 
-  def test_write_attributes_respect_access_control
+  test "attribute writers respect access control" do
     privatize("title=(value)")
 
     topic = @target.new
-    assert !topic.respond_to?(:title=)
-    exception = assert_raise(NoMethodError) { topic.title = "Pants"}
-    assert exception.message.include?("private method")
+    assert_not_respond_to topic, :title=
+    exception = assert_raise(NoMethodError) { topic.title = "Pants" }
+    assert_includes exception.message, "private method"
     topic.send(:title=, "Very large pants")
   end
 
-  def test_question_attributes_respect_access_control
+  test "attribute predicates respect access control" do
     privatize("title?")
 
-    topic = @target.new(:title => "Isaac Newton's pants")
-    assert !topic.respond_to?(:title?)
+    topic = @target.new(title: "Isaac Newton's pants")
+    assert_not_respond_to topic, :title?
     exception = assert_raise(NoMethodError) { topic.title? }
-    assert exception.message.include?("private method")
+    assert_includes exception.message, "private method"
     assert topic.send(:title?)
   end
 
-  def test_bulk_update_respects_access_control
+  test "bulk updates respect access control" do
     privatize("title=(value)")
 
-    assert_raise(ActiveRecord::UnknownAttributeError) { @target.new(:title => "Rants about pants") }
-    assert_raise(ActiveRecord::UnknownAttributeError) { @target.new.attributes = { :title => "Ants in pants" } }
+    assert_raise(ActiveRecord::UnknownAttributeError) { @target.new(title: "Rants about pants") }
+    assert_raise(ActiveRecord::UnknownAttributeError) { @target.new.attributes = { title: "Ants in pants" } }
   end
 
-  def test_bulk_update_raise_unknown_attribute_error
+  test "bulk update raises ActiveRecord::UnknownAttributeError" do
     error = assert_raises(ActiveRecord::UnknownAttributeError) {
       Topic.new(hello: "world")
     }
@@ -771,43 +819,45 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "unknown attribute 'hello' for Topic.", error.message
   end
 
-  def test_methods_override_in_multi_level_subclass
+  test "method overrides in multi-level subclasses" do
     klass = Class.new(Developer) do
       def name
         "dev:#{read_attribute(:name)}"
       end
     end
 
-    2.times { klass = Class.new klass }
-    dev = klass.new(name: 'arthurnn')
+    2.times { klass = Class.new(klass) }
+    dev = klass.new(name: "arthurnn")
     dev.save!
-    assert_equal 'dev:arthurnn', dev.reload.name
+    assert_equal "dev:arthurnn", dev.reload.name
   end
 
-  def test_global_methods_are_overwritten
+  test "global methods are overwritten" do
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'computers'
+      self.table_name = "computers"
     end
 
-    assert !klass.instance_method_already_implemented?(:system)
+    assert_not klass.instance_method_already_implemented?(:system)
     computer = klass.new
     assert_nil computer.system
   end
 
-  def test_global_methods_are_overwritte_when_subclassing
-    klass = Class.new(ActiveRecord::Base) { self.abstract_class = true }
+  test "global methods are overwritten when subclassing" do
+    klass = Class.new(ActiveRecord::Base) do
+      self.abstract_class = true
+    end
 
     subklass = Class.new(klass) do
-      self.table_name = 'computers'
+      self.table_name = "computers"
     end
 
-    assert !klass.instance_method_already_implemented?(:system)
-    assert !subklass.instance_method_already_implemented?(:system)
+    assert_not klass.instance_method_already_implemented?(:system)
+    assert_not subklass.instance_method_already_implemented?(:system)
     computer = subklass.new
     assert_nil computer.system
   end
 
-  def test_instance_method_should_be_defined_on_the_base_class
+  test "instance methods should be defined on the base class" do
     subklass = Class.new(Topic)
 
     Topic.define_attribute_methods
@@ -823,14 +873,21 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert subklass.method_defined?(:id), "subklass is missing id method"
   end
 
-  def test_read_attribute_with_nil_should_not_asplode
-    assert_equal nil, Topic.new.read_attribute(nil)
+  test "define_attribute_method works with both symbol and string" do
+    klass = Class.new(ActiveRecord::Base)
+
+    assert_nothing_raised { klass.define_attribute_method(:foo) }
+    assert_nothing_raised { klass.define_attribute_method("bar") }
+  end
+
+  test "read_attribute with nil should not asplode" do
+    assert_nil Topic.new.read_attribute(nil)
   end
 
   # If B < A, and A defines an accessor for 'foo', we don't want to override
   # that by defining a 'foo' method in the generated methods module for B.
   # (That module will be inserted between the two, e.g. [B, <GeneratedAttributes>, A].)
-  def test_inherited_custom_accessors
+  test "inherited custom accessors" do
     klass = new_topic_like_ar_class do
       self.abstract_class = true
       def title; "omg"; end
@@ -846,9 +903,9 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal "lol", topic.author_name
   end
 
-  def test_inherited_custom_accessors_with_reserved_names
+  test "inherited custom accessors with reserved names" do
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'computers'
+      self.table_name = "computers"
       self.abstract_class = true
       def system; "omg"; end
       def system=(val); self.developer = val; end
@@ -864,18 +921,18 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal 99, computer.developer
   end
 
-  def test_on_the_fly_super_invokable_generated_attribute_methods_via_method_missing
+  test "on_the_fly_super_invokable_generated_attribute_methods_via_method_missing" do
     klass = new_topic_like_ar_class do
       def title
-        super + '!'
+        super + "!"
       end
     end
 
     real_topic = topics(:first)
-    assert_equal real_topic.title + '!', klass.find(real_topic.id).title
+    assert_equal real_topic.title + "!", klass.find(real_topic.id).title
   end
 
-  def test_on_the_fly_super_invokable_generated_predicate_attribute_methods_via_method_missing
+  test "on-the-fly super-invokable generated attribute predicates via method_missing" do
     klass = new_topic_like_ar_class do
       def title?
         !super
@@ -886,7 +943,7 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal !real_topic.title?, klass.find(real_topic.id).title?
   end
 
-  def test_calling_super_when_parent_does_not_define_method_raises_error
+  test "calling super when the parent does not define method raises NoMethodError" do
     klass = new_topic_like_ar_class do
       def some_method_that_is_not_on_super
         super
@@ -898,46 +955,46 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_attribute_method?
+  test "attribute_method?" do
     assert @target.attribute_method?(:title)
     assert @target.attribute_method?(:title=)
     assert_not @target.attribute_method?(:wibble)
   end
 
-  def test_attribute_method_returns_false_if_table_does_not_exist
-    @target.table_name = 'wibble'
+  test "attribute_method? returns false if the table does not exist" do
+    @target.table_name = "wibble"
     assert_not @target.attribute_method?(:title)
   end
 
-  def test_attribute_names_on_new_record
+  test "attribute_names on a new record" do
     model = @target.new
 
     assert_equal @target.column_names, model.attribute_names
   end
 
-  def test_attribute_names_on_queried_record
+  test "attribute_names on a queried record" do
     model = @target.last!
 
     assert_equal @target.column_names, model.attribute_names
   end
 
-  def test_attribute_names_with_custom_select
-    model = @target.select('id').last!
+  test "attribute_names with a custom select" do
+    model = @target.select("id").last!
 
-    assert_equal ['id'], model.attribute_names
-    # Sanity check, make sure other columns exist
-    assert_not_equal ['id'], @target.column_names
+    assert_equal ["id"], model.attribute_names
+    # Sanity check, make sure other columns exist.
+    assert_not_equal ["id"], @target.column_names
   end
 
-  def test_came_from_user
+  test "came_from_user?" do
     model = @target.first
 
-    assert_not model.id_came_from_user?
+    assert_not_predicate model, :id_came_from_user?
     model.id = "omg"
-    assert model.id_came_from_user?
+    assert_predicate model, :id_came_from_user?
   end
 
-  def test_accessed_fields
+  test "accessed_fields" do
     model = @target.first
 
     assert_equal [], model.accessed_fields
@@ -947,40 +1004,37 @@ class AttributeMethodsTest < ActiveRecord::TestCase
     assert_equal ["title"], model.accessed_fields
   end
 
-  private
-
-  def new_topic_like_ar_class(&block)
-    klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'topics'
-      class_eval(&block)
-    end
-
-    assert_empty klass.generated_attribute_methods.instance_methods(false)
-    klass
+  test "generated attribute methods ancestors have correct class" do
+    mod = Topic.send(:generated_attribute_methods)
+    assert_match %r(GeneratedAttributeMethods), mod.inspect
   end
 
-  def with_time_zone_aware_types(*types)
-    old_types = ActiveRecord::Base.time_zone_aware_types
-    ActiveRecord::Base.time_zone_aware_types = types
-    yield
-  ensure
-    ActiveRecord::Base.time_zone_aware_types = old_types
-  end
+  private
 
-  def cached_columns
-    Topic.columns.map(&:name)
-  end
+    def new_topic_like_ar_class(&block)
+      klass = Class.new(ActiveRecord::Base) do
+        self.table_name = "topics"
+        class_eval(&block)
+      end
 
-  def time_related_columns_on_topic
-    Topic.columns.select { |c| [:time, :date, :datetime, :timestamp].include?(c.type) }
-  end
+      assert_empty klass.send(:generated_attribute_methods).instance_methods(false)
+      klass
+    end
 
-  def privatize(method_signature)
-    @target.class_eval(<<-private_method, __FILE__, __LINE__ + 1)
-      private
-      def #{method_signature}
-        "I'm private"
-      end
-    private_method
-  end
+    def with_time_zone_aware_types(*types)
+      old_types = ActiveRecord::Base.time_zone_aware_types
+      ActiveRecord::Base.time_zone_aware_types = types
+      yield
+    ensure
+      ActiveRecord::Base.time_zone_aware_types = old_types
+    end
+
+    def privatize(method_signature)
+      @target.class_eval(<<-private_method, __FILE__, __LINE__ + 1)
+        private
+        def #{method_signature}
+          "I'm private"
+        end
+      private_method
+    end
 end
diff --git a/activerecord/test/cases/attribute_set_test.rb b/activerecord/test/cases/attribute_set_test.rb
deleted file mode 100644
index 9d927481ec..0000000000
--- a/activerecord/test/cases/attribute_set_test.rb
+++ /dev/null
@@ -1,211 +0,0 @@
-require 'cases/helper'
-
-module ActiveRecord
-  class AttributeSetTest < ActiveRecord::TestCase
-    test "building a new set from raw attributes" do
-      builder = AttributeSet::Builder.new(foo: Type::Integer.new, bar: Type::Float.new)
-      attributes = builder.build_from_database(foo: '1.1', bar: '2.2')
-
-      assert_equal 1, attributes[:foo].value
-      assert_equal 2.2, attributes[:bar].value
-      assert_equal :foo, attributes[:foo].name
-      assert_equal :bar, attributes[:bar].name
-    end
-
-    test "building with custom types" do
-      builder = AttributeSet::Builder.new(foo: Type::Float.new)
-      attributes = builder.build_from_database({ foo: '3.3', bar: '4.4' }, { bar: Type::Integer.new })
-
-      assert_equal 3.3, attributes[:foo].value
-      assert_equal 4, attributes[:bar].value
-    end
-
-    test "[] returns a null object" do
-      builder = AttributeSet::Builder.new(foo: Type::Float.new)
-      attributes = builder.build_from_database(foo: '3.3')
-
-      assert_equal '3.3', attributes[:foo].value_before_type_cast
-      assert_equal nil, attributes[:bar].value_before_type_cast
-      assert_equal :bar, attributes[:bar].name
-    end
-
-    test "duping creates a new hash and dups each attribute" do
-      builder = AttributeSet::Builder.new(foo: Type::Integer.new, bar: Type::String.new)
-      attributes = builder.build_from_database(foo: 1, bar: 'foo')
-
-      # Ensure the type cast value is cached
-      attributes[:foo].value
-      attributes[:bar].value
-
-      duped = attributes.dup
-      duped.write_from_database(:foo, 2)
-      duped[:bar].value << 'bar'
-
-      assert_equal 1, attributes[:foo].value
-      assert_equal 2, duped[:foo].value
-      assert_equal 'foo', attributes[:bar].value
-      assert_equal 'foobar', duped[:bar].value
-    end
-
-    test "freezing cloned set does not freeze original" do
-      attributes = AttributeSet.new({})
-      clone = attributes.clone
-
-      clone.freeze
-
-      assert clone.frozen?
-      assert_not attributes.frozen?
-    end
-
-    test "to_hash returns a hash of the type cast values" do
-      builder = AttributeSet::Builder.new(foo: Type::Integer.new, bar: Type::Float.new)
-      attributes = builder.build_from_database(foo: '1.1', bar: '2.2')
-
-      assert_equal({ foo: 1, bar: 2.2 }, attributes.to_hash)
-      assert_equal({ foo: 1, bar: 2.2 }, attributes.to_h)
-    end
-
-    test "to_hash maintains order" do
-      builder = AttributeSet::Builder.new(foo: Type::Integer.new, bar: Type::Float.new)
-      attributes = builder.build_from_database(foo: '2.2', bar: '3.3')
-
-      attributes[:bar]
-      hash = attributes.to_h
-
-      assert_equal [[:foo, 2], [:bar, 3.3]], hash.to_a
-    end
-
-    test "values_before_type_cast" do
-      builder = AttributeSet::Builder.new(foo: Type::Integer.new, bar: Type::Integer.new)
-      attributes = builder.build_from_database(foo: '1.1', bar: '2.2')
-
-      assert_equal({ foo: '1.1', bar: '2.2' }, attributes.values_before_type_cast)
-    end
-
-    test "known columns are built with uninitialized attributes" do
-      attributes = attributes_with_uninitialized_key
-      assert attributes[:foo].initialized?
-      assert_not attributes[:bar].initialized?
-    end
-
-    test "uninitialized attributes are not included in the attributes hash" do
-      attributes = attributes_with_uninitialized_key
-      assert_equal({ foo: 1 }, attributes.to_hash)
-    end
-
-    test "uninitialized attributes are not included in keys" do
-      attributes = attributes_with_uninitialized_key
-      assert_equal [:foo], attributes.keys
-    end
-
-    test "uninitialized attributes return false for key?" do
-      attributes = attributes_with_uninitialized_key
-      assert attributes.key?(:foo)
-      assert_not attributes.key?(:bar)
-    end
-
-    test "unknown attributes return false for key?" do
-      attributes = attributes_with_uninitialized_key
-      assert_not attributes.key?(:wibble)
-    end
-
-    test "fetch_value returns the value for the given initialized attribute" do
-      builder = AttributeSet::Builder.new(foo: Type::Integer.new, bar: Type::Float.new)
-      attributes = builder.build_from_database(foo: '1.1', bar: '2.2')
-
-      assert_equal 1, attributes.fetch_value(:foo)
-      assert_equal 2.2, attributes.fetch_value(:bar)
-    end
-
-    test "fetch_value returns nil for unknown attributes" do
-      attributes = attributes_with_uninitialized_key
-      assert_nil attributes.fetch_value(:wibble) { "hello" }
-    end
-
-    test "fetch_value returns nil for unknown attributes when types has a default" do
-      types = Hash.new(Type::Value.new)
-      builder = AttributeSet::Builder.new(types)
-      attributes = builder.build_from_database
-
-      assert_nil attributes.fetch_value(:wibble) { "hello" }
-    end
-
-    test "fetch_value uses the given block for uninitialized attributes" do
-      attributes = attributes_with_uninitialized_key
-      value = attributes.fetch_value(:bar) { |n| n.to_s + '!' }
-      assert_equal 'bar!', value
-    end
-
-    test "fetch_value returns nil for uninitialized attributes if no block is given" do
-      attributes = attributes_with_uninitialized_key
-      assert_nil attributes.fetch_value(:bar)
-    end
-
-    test "the primary_key is always initialized" do
-      builder = AttributeSet::Builder.new({ foo: Type::Integer.new }, :foo)
-      attributes = builder.build_from_database
-
-      assert attributes.key?(:foo)
-      assert_equal [:foo], attributes.keys
-      assert attributes[:foo].initialized?
-    end
-
-    class MyType
-      def cast(value)
-        return if value.nil?
-        value + " from user"
-      end
-
-      def deserialize(value)
-        return if value.nil?
-        value + " from database"
-      end
-    end
-
-    test "write_from_database sets the attribute with database typecasting" do
-      builder = AttributeSet::Builder.new(foo: MyType.new)
-      attributes = builder.build_from_database
-
-      assert_nil attributes.fetch_value(:foo)
-
-      attributes.write_from_database(:foo, "value")
-
-      assert_equal "value from database", attributes.fetch_value(:foo)
-    end
-
-    test "write_from_user sets the attribute with user typecasting" do
-      builder = AttributeSet::Builder.new(foo: MyType.new)
-      attributes = builder.build_from_database
-
-      assert_nil attributes.fetch_value(:foo)
-
-      attributes.write_from_user(:foo, "value")
-
-      assert_equal "value from user", attributes.fetch_value(:foo)
-    end
-
-    def attributes_with_uninitialized_key
-      builder = AttributeSet::Builder.new(foo: Type::Integer.new, bar: Type::Float.new)
-      builder.build_from_database(foo: '1.1')
-    end
-
-    test "freezing doesn't prevent the set from materializing" do
-      builder = AttributeSet::Builder.new(foo: Type::String.new)
-      attributes = builder.build_from_database(foo: "1")
-
-      attributes.freeze
-      assert_equal({ foo: "1" }, attributes.to_hash)
-    end
-
-    test "#accessed_attributes returns only attributes which have been read" do
-      builder = AttributeSet::Builder.new(foo: Type::Value.new, bar: Type::Value.new)
-      attributes = builder.build_from_database(foo: "1", bar: "2")
-
-      assert_equal [], attributes.accessed
-
-      attributes.fetch_value(:foo)
-
-      assert_equal [:foo], attributes.accessed
-    end
-  end
-end
diff --git a/activerecord/test/cases/attribute_test.rb b/activerecord/test/cases/attribute_test.rb
deleted file mode 100644
index aa419c7a67..0000000000
--- a/activerecord/test/cases/attribute_test.rb
+++ /dev/null
@@ -1,192 +0,0 @@
-require 'cases/helper'
-require 'minitest/mock'
-
-module ActiveRecord
-  class AttributeTest < ActiveRecord::TestCase
-    setup do
-      @type = Minitest::Mock.new
-      @type.expect(:==, false, [false])
-    end
-
-    teardown do
-      assert @type.verify
-    end
-
-    test "from_database + read type casts from database" do
-      @type.expect(:deserialize, 'type cast from database', ['a value'])
-      attribute = Attribute.from_database(nil, 'a value', @type)
-
-      type_cast_value = attribute.value
-
-      assert_equal 'type cast from database', type_cast_value
-    end
-
-    test "from_user + read type casts from user" do
-      @type.expect(:cast, 'type cast from user', ['a value'])
-      attribute = Attribute.from_user(nil, 'a value', @type)
-
-      type_cast_value = attribute.value
-
-      assert_equal 'type cast from user', type_cast_value
-    end
-
-    test "reading memoizes the value" do
-      @type.expect(:deserialize, 'from the database', ['whatever'])
-      attribute = Attribute.from_database(nil, 'whatever', @type)
-
-      type_cast_value = attribute.value
-      second_read = attribute.value
-
-      assert_equal 'from the database', type_cast_value
-      assert_same type_cast_value, second_read
-    end
-
-    test "reading memoizes falsy values" do
-      @type.expect(:deserialize, false, ['whatever'])
-      attribute = Attribute.from_database(nil, 'whatever', @type)
-
-      attribute.value
-      attribute.value
-    end
-
-    test "read_before_typecast returns the given value" do
-      attribute = Attribute.from_database(nil, 'raw value', @type)
-
-      raw_value = attribute.value_before_type_cast
-
-      assert_equal 'raw value', raw_value
-    end
-
-    test "from_database + read_for_database type casts to and from database" do
-      @type.expect(:deserialize, 'read from database', ['whatever'])
-      @type.expect(:serialize, 'ready for database', ['read from database'])
-      attribute = Attribute.from_database(nil, 'whatever', @type)
-
-      serialize = attribute.value_for_database
-
-      assert_equal 'ready for database', serialize
-    end
-
-    test "from_user + read_for_database type casts from the user to the database" do
-      @type.expect(:cast, 'read from user', ['whatever'])
-      @type.expect(:serialize, 'ready for database', ['read from user'])
-      attribute = Attribute.from_user(nil, 'whatever', @type)
-
-      serialize = attribute.value_for_database
-
-      assert_equal 'ready for database', serialize
-    end
-
-    test "duping dups the value" do
-      @type.expect(:deserialize, 'type cast', ['a value'])
-      attribute = Attribute.from_database(nil, 'a value', @type)
-
-      value_from_orig = attribute.value
-      value_from_clone = attribute.dup.value
-      value_from_orig << ' foo'
-
-      assert_equal 'type cast foo', value_from_orig
-      assert_equal 'type cast', value_from_clone
-    end
-
-    test "duping does not dup the value if it is not dupable" do
-      @type.expect(:deserialize, false, ['a value'])
-      attribute = Attribute.from_database(nil, 'a value', @type)
-
-      assert_same attribute.value, attribute.dup.value
-    end
-
-    test "duping does not eagerly type cast if we have not yet type cast" do
-      attribute = Attribute.from_database(nil, 'a value', @type)
-      attribute.dup
-    end
-
-    class MyType
-      def cast(value)
-        value + " from user"
-      end
-
-      def deserialize(value)
-        value + " from database"
-      end
-    end
-
-    test "with_value_from_user returns a new attribute with the value from the user" do
-      old = Attribute.from_database(nil, "old", MyType.new)
-      new = old.with_value_from_user("new")
-
-      assert_equal "old from database", old.value
-      assert_equal "new from user", new.value
-    end
-
-    test "with_value_from_database returns a new attribute with the value from the database" do
-      old = Attribute.from_user(nil, "old", MyType.new)
-      new = old.with_value_from_database("new")
-
-      assert_equal "old from user", old.value
-      assert_equal "new from database", new.value
-    end
-
-    test "uninitialized attributes yield their name if a block is given to value" do
-      block = proc { |name| name.to_s + "!" }
-      foo = Attribute.uninitialized(:foo, nil)
-      bar = Attribute.uninitialized(:bar, nil)
-
-      assert_equal "foo!", foo.value(&block)
-      assert_equal "bar!", bar.value(&block)
-    end
-
-    test "uninitialized attributes have no value" do
-      assert_nil Attribute.uninitialized(:foo, nil).value
-    end
-
-    test "attributes equal other attributes with the same constructor arguments" do
-      first = Attribute.from_database(:foo, 1, Type::Integer.new)
-      second = Attribute.from_database(:foo, 1, Type::Integer.new)
-      assert_equal first, second
-    end
-
-    test "attributes do not equal attributes with different names" do
-      first = Attribute.from_database(:foo, 1, Type::Integer.new)
-      second = Attribute.from_database(:bar, 1, Type::Integer.new)
-      assert_not_equal first, second
-    end
-
-    test "attributes do not equal attributes with different types" do
-      first = Attribute.from_database(:foo, 1, Type::Integer.new)
-      second = Attribute.from_database(:foo, 1, Type::Float.new)
-      assert_not_equal first, second
-    end
-
-    test "attributes do not equal attributes with different values" do
-      first = Attribute.from_database(:foo, 1, Type::Integer.new)
-      second = Attribute.from_database(:foo, 2, Type::Integer.new)
-      assert_not_equal first, second
-    end
-
-    test "attributes do not equal attributes of other classes" do
-      first = Attribute.from_database(:foo, 1, Type::Integer.new)
-      second = Attribute.from_user(:foo, 1, Type::Integer.new)
-      assert_not_equal first, second
-    end
-
-    test "an attribute has not been read by default" do
-      attribute = Attribute.from_database(:foo, 1, Type::Value.new)
-      assert_not attribute.has_been_read?
-    end
-
-    test "an attribute has been read when its value is calculated" do
-      attribute = Attribute.from_database(:foo, 1, Type::Value.new)
-      attribute.value
-      assert attribute.has_been_read?
-    end
-
-    test "an attribute can not be mutated if it has not been read,
-      and skips expensive calculations" do
-      type_which_raises_from_all_methods = Object.new
-      attribute = Attribute.from_database(:foo, "bar", type_which_raises_from_all_methods)
-
-      assert_not attribute.changed_in_place_from?("bar")
-    end
-  end
-end
diff --git a/activerecord/test/cases/attributes_test.rb b/activerecord/test/cases/attributes_test.rb
index eeda9335ad..2632aec7ab 100644
--- a/activerecord/test/cases/attributes_test.rb
+++ b/activerecord/test/cases/attributes_test.rb
@@ -1,10 +1,12 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 class OverloadedType < ActiveRecord::Base
   attribute :overloaded_float, :integer
   attribute :overloaded_string_with_limit, :string, limit: 50
   attribute :non_existent_decimal, :decimal
-  attribute :string_with_default, :string, default: 'the overloaded default'
+  attribute :string_with_default, :string, default: "the overloaded default"
 end
 
 class ChildOfOverloadedType < OverloadedType
@@ -15,7 +17,7 @@ class GrandchildOfOverloadedType < ChildOfOverloadedType
 end
 
 class UnoverloadedType < ActiveRecord::Base
-  self.table_name = 'overloaded_types'
+  self.table_name = "overloaded_types"
 end
 
 module ActiveRecord
@@ -38,51 +40,60 @@ module ActiveRecord
       data.reload
 
       assert_equal 2, data.overloaded_float
-      assert_kind_of Fixnum, OverloadedType.last.overloaded_float
+      assert_kind_of Integer, OverloadedType.last.overloaded_float
       assert_equal 2.0, UnoverloadedType.last.overloaded_float
       assert_kind_of Float, UnoverloadedType.last.overloaded_float
     end
 
     test "properties assigned in constructor" do
-      data = OverloadedType.new(overloaded_float: '3.3')
+      data = OverloadedType.new(overloaded_float: "3.3")
 
       assert_equal 3, data.overloaded_float
     end
 
     test "overloaded properties with limit" do
-      assert_equal 50, OverloadedType.type_for_attribute('overloaded_string_with_limit').limit
-      assert_equal 255, UnoverloadedType.type_for_attribute('overloaded_string_with_limit').limit
+      assert_equal 50, OverloadedType.type_for_attribute("overloaded_string_with_limit").limit
+      assert_equal 255, UnoverloadedType.type_for_attribute("overloaded_string_with_limit").limit
     end
 
     test "nonexistent attribute" do
       data = OverloadedType.new(non_existent_decimal: 1)
 
-      assert_equal BigDecimal.new(1), data.non_existent_decimal
+      assert_equal BigDecimal(1), data.non_existent_decimal
       assert_raise ActiveRecord::UnknownAttributeError do
         UnoverloadedType.new(non_existent_decimal: 1)
       end
     end
 
+    test "model with nonexistent attribute with default value can be saved" do
+      klass = Class.new(OverloadedType) do
+        attribute :non_existent_string_with_default, :string, default: "nonexistent"
+      end
+
+      model = klass.new
+      assert model.save
+    end
+
     test "changing defaults" do
       data = OverloadedType.new
       unoverloaded_data = UnoverloadedType.new
 
-      assert_equal 'the overloaded default', data.string_with_default
-      assert_equal 'the original default', unoverloaded_data.string_with_default
+      assert_equal "the overloaded default", data.string_with_default
+      assert_equal "the original default", unoverloaded_data.string_with_default
     end
 
     test "defaults are not touched on the columns" do
-      assert_equal 'the original default', OverloadedType.columns_hash['string_with_default'].default
+      assert_equal "the original default", OverloadedType.columns_hash["string_with_default"].default
     end
 
     test "children inherit custom properties" do
-      data = ChildOfOverloadedType.new(overloaded_float: '4.4')
+      data = ChildOfOverloadedType.new(overloaded_float: "4.4")
 
       assert_equal 4, data.overloaded_float
     end
 
     test "children can override parents" do
-      data = GrandchildOfOverloadedType.new(overloaded_float: '4.4')
+      data = GrandchildOfOverloadedType.new(overloaded_float: "4.4")
 
       assert_equal 4.4, data.overloaded_float
     end
@@ -97,13 +108,15 @@ module ActiveRecord
 
       assert_equal 6, klass.attribute_types.length
       assert_equal 6, klass.column_defaults.length
-      assert_not klass.attribute_types.include?('wibble')
+      assert_equal 6, klass.attribute_names.length
+      assert_not klass.attribute_types.include?("wibble")
 
       klass.attribute :wibble, Type::Value.new
 
       assert_equal 7, klass.attribute_types.length
       assert_equal 7, klass.column_defaults.length
-      assert klass.attribute_types.include?('wibble')
+      assert_equal 7, klass.attribute_names.length
+      assert_includes klass.attribute_types, "wibble"
     end
 
     test "the given default value is cast from user" do
@@ -135,6 +148,31 @@ module ActiveRecord
       assert_equal 2, klass.new.counter
     end
 
+    test "procs for default values are evaluated even after column_defaults is called" do
+      klass = Class.new(OverloadedType) do
+        @@counter = 0
+        attribute :counter, :integer, default: -> { @@counter += 1 }
+      end
+
+      assert_equal 1, klass.new.counter
+
+      # column_defaults will increment the counter since the proc is called
+      klass.column_defaults
+
+      assert_equal 3, klass.new.counter
+    end
+
+    test "procs are memoized before type casting" do
+      klass = Class.new(OverloadedType) do
+        @@counter = 0
+        attribute :counter, :integer, default: -> { @@counter += 1 }
+      end
+
+      model = klass.new
+      assert_equal 1, model.counter_before_type_cast
+      assert_equal 1, model.counter_before_type_cast
+    end
+
     test "user provided defaults are persisted even if unchanged" do
       model = OverloadedType.create!
 
@@ -142,7 +180,7 @@ module ActiveRecord
     end
 
     if current_adapter?(:PostgreSQLAdapter)
-      test "arrays types can be specified" do
+      test "array types can be specified" do
         klass = Class.new(OverloadedType) do
           attribute :my_array, :string, limit: 50, array: true
           attribute :my_int_array, :integer, array: true
@@ -152,7 +190,7 @@ module ActiveRecord
           Type::String.new(limit: 50))
         int_array = ConnectionAdapters::PostgreSQL::OID::Array.new(
           Type::Integer.new)
-        refute_equal string_array, int_array
+        assert_not_equal string_array, int_array
         assert_equal string_array, klass.type_for_attribute("my_array")
         assert_equal int_array, klass.type_for_attribute("my_int_array")
       end
@@ -167,10 +205,81 @@ module ActiveRecord
           Type::String.new(limit: 50))
         int_range = ConnectionAdapters::PostgreSQL::OID::Range.new(
           Type::Integer.new)
-        refute_equal string_range, int_range
+        assert_not_equal string_range, int_range
         assert_equal string_range, klass.type_for_attribute("my_range")
         assert_equal int_range, klass.type_for_attribute("my_int_range")
       end
     end
+
+    test "attributes added after subclasses load are inherited" do
+      parent = Class.new(ActiveRecord::Base) do
+        self.table_name = "topics"
+      end
+
+      child = Class.new(parent)
+      child.new # => force a schema load
+
+      parent.attribute(:foo, Type::Value.new)
+
+      assert_equal(:bar, child.new(foo: :bar).foo)
+    end
+
+    test "attributes not backed by database columns are not dirty when unchanged" do
+      assert_not_predicate OverloadedType.new, :non_existent_decimal_changed?
+    end
+
+    test "attributes not backed by database columns are always initialized" do
+      OverloadedType.create!
+      model = OverloadedType.first
+
+      assert_nil model.non_existent_decimal
+      model.non_existent_decimal = "123"
+      assert_equal 123, model.non_existent_decimal
+    end
+
+    test "attributes not backed by database columns return the default on models loaded from database" do
+      child = Class.new(OverloadedType) do
+        attribute :non_existent_decimal, :decimal, default: 123
+      end
+      child.create!
+      model = child.first
+
+      assert_equal 123, model.non_existent_decimal
+    end
+
+    test "attributes not backed by database columns properly interact with mutation and dirty" do
+      child = Class.new(ActiveRecord::Base) do
+        self.table_name = "topics"
+        attribute :foo, :string, default: "lol"
+      end
+      child.create!
+      model = child.first
+
+      assert_equal "lol", model.foo
+
+      model.foo << "asdf"
+      assert_equal "lolasdf", model.foo
+      assert_predicate model, :foo_changed?
+
+      model.reload
+      assert_equal "lol", model.foo
+
+      model.foo = "lol"
+      assert_not_predicate model, :changed?
+    end
+
+    test "attributes not backed by database columns appear in inspect" do
+      inspection = OverloadedType.new.inspect
+
+      assert_includes inspection, "non_existent_decimal"
+    end
+
+    test "attributes do not require a type" do
+      klass = Class.new(OverloadedType) do
+        attribute :no_type
+      end
+      assert_equal 1, klass.new(no_type: 1).no_type
+      assert_equal "foo", klass.new(no_type: "foo").no_type
+    end
   end
 end
diff --git a/activerecord/test/cases/autosave_association_test.rb b/activerecord/test/cases/autosave_association_test.rb
index 80b5a0004d..88df0eed55 100644
--- a/activerecord/test/cases/autosave_association_test.rb
+++ b/activerecord/test/cases/autosave_association_test.rb
@@ -1,54 +1,59 @@
-require 'cases/helper'
-require 'models/bird'
-require 'models/comment'
-require 'models/company'
-require 'models/customer'
-require 'models/developer'
-require 'models/computer'
-require 'models/invoice'
-require 'models/line_item'
-require 'models/order'
-require 'models/parrot'
-require 'models/person'
-require 'models/pirate'
-require 'models/post'
-require 'models/reader'
-require 'models/ship'
-require 'models/ship_part'
-require 'models/tag'
-require 'models/tagging'
-require 'models/treasure'
-require 'models/eye'
-require 'models/electron'
-require 'models/molecule'
-require 'models/member'
-require 'models/member_detail'
-require 'models/organization'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/bird"
+require "models/post"
+require "models/comment"
+require "models/company"
+require "models/contract"
+require "models/customer"
+require "models/developer"
+require "models/computer"
+require "models/invoice"
+require "models/line_item"
+require "models/order"
+require "models/parrot"
+require "models/pirate"
+require "models/project"
+require "models/ship"
+require "models/ship_part"
+require "models/tag"
+require "models/tagging"
+require "models/treasure"
+require "models/eye"
+require "models/electron"
+require "models/molecule"
+require "models/member"
+require "models/member_detail"
+require "models/organization"
+require "models/guitar"
+require "models/tuning_peg"
+require "models/reply"
 
 class TestAutosaveAssociationsInGeneral < ActiveRecord::TestCase
   def test_autosave_validation
     person = Class.new(ActiveRecord::Base) {
-      self.table_name = 'people'
-      validate :should_be_cool, :on => :create
-      def self.name; 'Person'; end
+      self.table_name = "people"
+      validate :should_be_cool, on: :create
+      def self.name; "Person"; end
 
       private
 
-      def should_be_cool
-        unless self.first_name == 'cool'
-          errors.add :first_name, "not cool"
+        def should_be_cool
+          unless first_name == "cool"
+            errors.add :first_name, "not cool"
+          end
         end
-      end
     }
     reference = Class.new(ActiveRecord::Base) {
       self.table_name = "references"
-      def self.name; 'Reference'; end
+      def self.name; "Reference"; end
       belongs_to :person, autosave: true, anonymous_class: person
     }
 
-    u = person.create!(first_name: 'cool')
-    u.update_attributes!(first_name: 'nah') # still valid because validation only applies on 'create'
-    assert reference.create!(person: u).persisted?
+    u = person.create!(first_name: "cool")
+    u.update!(first_name: "nah") # still valid because validation only applies on 'create'
+    assert_predicate reference.create!(person: u), :persisted?
   end
 
   def test_should_not_add_the_same_callbacks_multiple_times_for_has_one
@@ -67,56 +72,64 @@ class TestAutosaveAssociationsInGeneral < ActiveRecord::TestCase
     assert_no_difference_when_adding_callbacks_twice_for Pirate, :parrots
   end
 
+  def test_cyclic_autosaves_do_not_add_multiple_validations
+    ship = ShipWithoutNestedAttributes.new
+    ship.prisoners.build
+
+    assert_not_predicate ship, :valid?
+    assert_equal 1, ship.errors[:name].length
+  end
+
   private
 
-  def assert_no_difference_when_adding_callbacks_twice_for(model, association_name)
-    reflection = model.reflect_on_association(association_name)
-    assert_no_difference "callbacks_for_model(#{model.name}).length" do
-      model.send(:add_autosave_association_callbacks, reflection)
+    def assert_no_difference_when_adding_callbacks_twice_for(model, association_name)
+      reflection = model.reflect_on_association(association_name)
+      assert_no_difference "callbacks_for_model(#{model.name}).length" do
+        model.send(:add_autosave_association_callbacks, reflection)
+      end
     end
-  end
 
-  def callbacks_for_model(model)
-    model.instance_variables.grep(/_callbacks$/).flat_map do |ivar|
-      model.instance_variable_get(ivar)
+    def callbacks_for_model(model)
+      model.instance_variables.grep(/_callbacks$/).flat_map do |ivar|
+        model.instance_variable_get(ivar)
+      end
     end
-  end
 end
 
 class TestDefaultAutosaveAssociationOnAHasOneAssociation < ActiveRecord::TestCase
   fixtures :companies, :accounts
 
   def test_should_save_parent_but_not_invalid_child
-    firm = Firm.new(:name => 'GlobalMegaCorp')
-    assert firm.valid?
+    firm = Firm.new(name: "GlobalMegaCorp")
+    assert_predicate firm, :valid?
 
     firm.build_account_using_primary_key
-    assert !firm.build_account_using_primary_key.valid?
+    assert_not_predicate firm.build_account_using_primary_key, :valid?
 
     assert firm.save
-    assert !firm.account_using_primary_key.persisted?
+    assert_not_predicate firm.account_using_primary_key, :persisted?
   end
 
   def test_save_fails_for_invalid_has_one
     firm = Firm.first
-    assert firm.valid?
+    assert_predicate firm, :valid?
 
     firm.build_account
 
-    assert !firm.account.valid?
-    assert !firm.valid?
-    assert !firm.save
+    assert_not_predicate firm.account, :valid?
+    assert_not_predicate firm, :valid?
+    assert_not firm.save
     assert_equal ["is invalid"], firm.errors["account"]
   end
 
   def test_save_succeeds_for_invalid_has_one_with_validate_false
     firm = Firm.first
-    assert firm.valid?
+    assert_predicate firm, :valid?
 
     firm.build_unvalidated_account
 
-    assert !firm.unvalidated_account.valid?
-    assert firm.valid?
+    assert_not_predicate firm.unvalidated_account, :valid?
+    assert_predicate firm, :valid?
     assert firm.save
   end
 
@@ -125,10 +138,10 @@ class TestDefaultAutosaveAssociationOnAHasOneAssociation < ActiveRecord::TestCas
 
     account = firm.build_account("credit_limit" => 1000)
     assert_equal account, firm.account
-    assert !account.persisted?
+    assert_not_predicate account, :persisted?
     assert firm.save
     assert_equal account, firm.account
-    assert account.persisted?
+    assert_predicate account, :persisted?
   end
 
   def test_build_before_either_saved
@@ -136,38 +149,40 @@ class TestDefaultAutosaveAssociationOnAHasOneAssociation < ActiveRecord::TestCas
 
     firm.account = account = Account.new("credit_limit" => 1000)
     assert_equal account, firm.account
-    assert !account.persisted?
+    assert_not_predicate account, :persisted?
     assert firm.save
     assert_equal account, firm.account
-    assert account.persisted?
+    assert_predicate account, :persisted?
   end
 
   def test_assignment_before_parent_saved
     firm = Firm.new("name" => "GlobalMegaCorp")
     firm.account = a = Account.find(1)
-    assert !firm.persisted?
+    assert_not_predicate firm, :persisted?
     assert_equal a, firm.account
     assert firm.save
     assert_equal a, firm.account
-    assert_equal a, firm.account(true)
+    firm.association(:account).reload
+    assert_equal a, firm.account
   end
 
   def test_assignment_before_either_saved
     firm = Firm.new("name" => "GlobalMegaCorp")
     firm.account = a = Account.new("credit_limit" => 1000)
-    assert !firm.persisted?
-    assert !a.persisted?
+    assert_not_predicate firm, :persisted?
+    assert_not_predicate a, :persisted?
     assert_equal a, firm.account
     assert firm.save
-    assert firm.persisted?
-    assert a.persisted?
+    assert_predicate firm, :persisted?
+    assert_predicate a, :persisted?
+    assert_equal a, firm.account
+    firm.association(:account).reload
     assert_equal a, firm.account
-    assert_equal a, firm.account(true)
   end
 
   def test_not_resaved_when_unchanged
-    firm = Firm.all.merge!(:includes => :account).first
-    firm.name += '-changed'
+    firm = Firm.all.merge!(includes: :account).first
+    firm.name += "-changed"
     assert_queries(1) { firm.save! }
 
     firm = Firm.first
@@ -184,21 +199,21 @@ class TestDefaultAutosaveAssociationOnAHasOneAssociation < ActiveRecord::TestCas
   end
 
   def test_callbacks_firing_order_on_create
-    eye = Eye.create(:iris_attributes => {:color => 'honey'})
+    eye = Eye.create(iris_attributes: { color: "honey" })
     assert_equal [true, false], eye.after_create_callbacks_stack
   end
 
   def test_callbacks_firing_order_on_update
-    eye = Eye.create(iris_attributes: {color: 'honey'})
-    eye.update(iris_attributes: {color: 'green'})
+    eye = Eye.create(iris_attributes: { color: "honey" })
+    eye.update(iris_attributes: { color: "green" })
     assert_equal [true, false], eye.after_update_callbacks_stack
   end
 
   def test_callbacks_firing_order_on_save
-    eye = Eye.create(iris_attributes: {color: 'honey'})
+    eye = Eye.create(iris_attributes: { color: "honey" })
     assert_equal [false, false], eye.after_save_callbacks_stack
 
-    eye.update(iris_attributes: {color: 'blue'})
+    eye.update(iris_attributes: { color: "blue" })
     assert_equal [false, false, false, false], eye.after_save_callbacks_stack
   end
 end
@@ -207,34 +222,34 @@ class TestDefaultAutosaveAssociationOnABelongsToAssociation < ActiveRecord::Test
   fixtures :companies, :posts, :tags, :taggings
 
   def test_should_save_parent_but_not_invalid_child
-    client = Client.new(:name => 'Joe (the Plumber)')
-    assert client.valid?
+    client = Client.new(name: "Joe (the Plumber)")
+    assert_predicate client, :valid?
 
     client.build_firm
-    assert !client.firm.valid?
+    assert_not_predicate client.firm, :valid?
 
     assert client.save
-    assert !client.firm.persisted?
+    assert_not_predicate client.firm, :persisted?
   end
 
   def test_save_fails_for_invalid_belongs_to
     # Oracle saves empty string as NULL therefore :message changed to one space
-    assert log = AuditLog.create(:developer_id => 0, :message => " ")
+    assert log = AuditLog.create(developer_id: 0, message: " ")
 
     log.developer = Developer.new
-    assert !log.developer.valid?
-    assert !log.valid?
-    assert !log.save
+    assert_not_predicate log.developer, :valid?
+    assert_not_predicate log, :valid?
+    assert_not log.save
     assert_equal ["is invalid"], log.errors["developer"]
   end
 
   def test_save_succeeds_for_invalid_belongs_to_with_validate_false
     # Oracle saves empty string as NULL therefore :message changed to one space
-    assert log = AuditLog.create(:developer_id => 0, :message=> " ")
+    assert log = AuditLog.create(developer_id: 0, message: " ")
 
     log.unvalidated_developer = Developer.new
-    assert !log.unvalidated_developer.valid?
-    assert log.valid?
+    assert_not_predicate log.unvalidated_developer, :valid?
+    assert_predicate log, :valid?
     assert log.save
   end
 
@@ -243,25 +258,27 @@ class TestDefaultAutosaveAssociationOnABelongsToAssociation < ActiveRecord::Test
     apple = Firm.new("name" => "Apple")
     client.firm = apple
     assert_equal apple, client.firm
-    assert !apple.persisted?
+    assert_not_predicate apple, :persisted?
     assert client.save
     assert apple.save
-    assert apple.persisted?
+    assert_predicate apple, :persisted?
+    assert_equal apple, client.firm
+    client.association(:firm).reload
     assert_equal apple, client.firm
-    assert_equal apple, client.firm(true)
   end
 
   def test_assignment_before_either_saved
     final_cut = Client.new("name" => "Final Cut")
     apple = Firm.new("name" => "Apple")
     final_cut.firm = apple
-    assert !final_cut.persisted?
-    assert !apple.persisted?
+    assert_not_predicate final_cut, :persisted?
+    assert_not_predicate apple, :persisted?
     assert final_cut.save
-    assert final_cut.persisted?
-    assert apple.persisted?
+    assert_predicate final_cut, :persisted?
+    assert_predicate apple, :persisted?
+    assert_equal apple, final_cut.firm
+    final_cut.association(:firm).reload
     assert_equal apple, final_cut.firm
-    assert_equal apple, final_cut.firm(true)
   end
 
   def test_store_two_association_with_one_save
@@ -348,77 +365,170 @@ class TestDefaultAutosaveAssociationOnABelongsToAssociation < ActiveRecord::Test
 
   def test_store_association_with_a_polymorphic_relationship
     num_tagging = Tagging.count
-    tags(:misc).create_tagging(:taggable => posts(:thinking))
+    tags(:misc).create_tagging(taggable: posts(:thinking))
     assert_equal num_tagging + 1, Tagging.count
   end
 
   def test_build_and_then_save_parent_should_not_reload_target
     client = Client.first
-    apple = client.build_firm(:name => "Apple")
+    apple = client.build_firm(name: "Apple")
     client.save!
     assert_no_queries { assert_equal apple, client.firm }
   end
 
   def test_validation_does_not_validate_stale_association_target
-    valid_developer   = Developer.create!(:name => "Dude", :salary => 50_000)
+    valid_developer   = Developer.create!(name: "Dude", salary: 50_000)
     invalid_developer = Developer.new()
 
-    auditlog = AuditLog.new(:message => "foo")
+    auditlog = AuditLog.new(message: "foo")
     auditlog.developer    = invalid_developer
     auditlog.developer_id = valid_developer.id
 
-    assert auditlog.valid?
+    assert_predicate auditlog, :valid?
   end
 end
 
 class TestDefaultAutosaveAssociationOnAHasManyAssociationWithAcceptsNestedAttributes < ActiveRecord::TestCase
   def test_invalid_adding_with_nested_attributes
     molecule = Molecule.new
-    valid_electron = Electron.new(name: 'electron')
+    valid_electron = Electron.new(name: "electron")
     invalid_electron = Electron.new
 
     molecule.electrons = [valid_electron, invalid_electron]
     molecule.save
 
-    assert_not invalid_electron.valid?
-    assert valid_electron.valid?
-    assert_not molecule.persisted?, 'Molecule should not be persisted when its electrons are invalid'
+    assert_not_predicate invalid_electron, :valid?
+    assert_predicate valid_electron, :valid?
+    assert_not molecule.persisted?, "Molecule should not be persisted when its electrons are invalid"
+  end
+
+  def test_errors_should_be_indexed_when_passed_as_array
+    guitar = Guitar.new
+    tuning_peg_valid = TuningPeg.new
+    tuning_peg_valid.pitch = 440.0
+    tuning_peg_invalid = TuningPeg.new
+
+    guitar.tuning_pegs = [tuning_peg_valid, tuning_peg_invalid]
+
+    assert_not_predicate tuning_peg_invalid, :valid?
+    assert_predicate tuning_peg_valid, :valid?
+    assert_not_predicate guitar, :valid?
+    assert_equal ["is not a number"], guitar.errors["tuning_pegs[1].pitch"]
+    assert_not_equal ["is not a number"], guitar.errors["tuning_pegs.pitch"]
+  end
+
+  def test_errors_should_be_indexed_when_global_flag_is_set
+    old_attribute_config = ActiveRecord::Base.index_nested_attribute_errors
+    ActiveRecord::Base.index_nested_attribute_errors = true
+
+    molecule = Molecule.new
+    valid_electron = Electron.new(name: "electron")
+    invalid_electron = Electron.new
+
+    molecule.electrons = [valid_electron, invalid_electron]
+
+    assert_not_predicate invalid_electron, :valid?
+    assert_predicate valid_electron, :valid?
+    assert_not_predicate molecule, :valid?
+    assert_equal ["can't be blank"], molecule.errors["electrons[1].name"]
+    assert_not_equal ["can't be blank"], molecule.errors["electrons.name"]
+  ensure
+    ActiveRecord::Base.index_nested_attribute_errors = old_attribute_config
+  end
+
+  def test_errors_details_should_be_set
+    molecule = Molecule.new
+    valid_electron = Electron.new(name: "electron")
+    invalid_electron = Electron.new
+
+    molecule.electrons = [valid_electron, invalid_electron]
+
+    assert_not_predicate invalid_electron, :valid?
+    assert_predicate valid_electron, :valid?
+    assert_not_predicate molecule, :valid?
+    assert_equal [{ error: :blank }], molecule.errors.details[:"electrons.name"]
+  end
+
+  def test_errors_details_should_be_indexed_when_passed_as_array
+    guitar = Guitar.new
+    tuning_peg_valid = TuningPeg.new
+    tuning_peg_valid.pitch = 440.0
+    tuning_peg_invalid = TuningPeg.new
+
+    guitar.tuning_pegs = [tuning_peg_valid, tuning_peg_invalid]
+
+    assert_not_predicate tuning_peg_invalid, :valid?
+    assert_predicate tuning_peg_valid, :valid?
+    assert_not_predicate guitar, :valid?
+    assert_equal [{ error: :not_a_number, value: nil }], guitar.errors.details[:"tuning_pegs[1].pitch"]
+    assert_equal [], guitar.errors.details[:"tuning_pegs.pitch"]
+  end
+
+  def test_errors_details_should_be_indexed_when_global_flag_is_set
+    old_attribute_config = ActiveRecord::Base.index_nested_attribute_errors
+    ActiveRecord::Base.index_nested_attribute_errors = true
+
+    molecule = Molecule.new
+    valid_electron = Electron.new(name: "electron")
+    invalid_electron = Electron.new
+
+    molecule.electrons = [valid_electron, invalid_electron]
+
+    assert_not_predicate invalid_electron, :valid?
+    assert_predicate valid_electron, :valid?
+    assert_not_predicate molecule, :valid?
+    assert_equal [{ error: :blank }], molecule.errors.details[:"electrons[1].name"]
+    assert_equal [], molecule.errors.details[:"electrons.name"]
+  ensure
+    ActiveRecord::Base.index_nested_attribute_errors = old_attribute_config
   end
 
   def test_valid_adding_with_nested_attributes
     molecule = Molecule.new
-    valid_electron = Electron.new(name: 'electron')
+    valid_electron = Electron.new(name: "electron")
 
     molecule.electrons = [valid_electron]
     molecule.save
 
-    assert valid_electron.valid?
-    assert molecule.persisted?
+    assert_predicate valid_electron, :valid?
+    assert_predicate molecule, :persisted?
     assert_equal 1, molecule.electrons.count
   end
 end
 
 class TestDefaultAutosaveAssociationOnAHasManyAssociation < ActiveRecord::TestCase
-  fixtures :companies, :people
+  fixtures :companies, :developers
 
   def test_invalid_adding
     firm = Firm.find(1)
-    assert !(firm.clients_of_firm << c = Client.new)
-    assert !c.persisted?
-    assert !firm.valid?
-    assert !firm.save
-    assert !c.persisted?
+    assert_not (firm.clients_of_firm << c = Client.new)
+    assert_not_predicate c, :persisted?
+    assert_not_predicate firm, :valid?
+    assert_not firm.save
+    assert_not_predicate c, :persisted?
   end
 
   def test_invalid_adding_before_save
     new_firm = Firm.new("name" => "A New Firm, Inc")
     new_firm.clients_of_firm.concat([c = Client.new, Client.new("name" => "Apple")])
-    assert !c.persisted?
-    assert !c.valid?
-    assert !new_firm.valid?
-    assert !new_firm.save
-    assert !c.persisted?
-    assert !new_firm.persisted?
+    assert_not_predicate c, :persisted?
+    assert_not_predicate c, :valid?
+    assert_not_predicate new_firm, :valid?
+    assert_not new_firm.save
+    assert_not_predicate c, :persisted?
+    assert_not_predicate new_firm, :persisted?
+  end
+
+  def test_adding_unsavable_association
+    new_firm = Firm.new("name" => "A New Firm, Inc")
+    client = new_firm.clients.new("name" => "Apple")
+    client.throw_on_save = true
+
+    assert_predicate client, :valid?
+    assert_predicate new_firm, :valid?
+    assert_not new_firm.save
+    assert_not_predicate new_firm, :persisted?
+    assert_not_predicate client, :persisted?
   end
 
   def test_invalid_adding_with_validate_false
@@ -426,10 +536,10 @@ class TestDefaultAutosaveAssociationOnAHasManyAssociation < ActiveRecord::TestCa
     client = Client.new
     firm.unvalidated_clients_of_firm << client
 
-    assert firm.valid?
-    assert !client.valid?
+    assert_predicate firm, :valid?
+    assert_not_predicate client, :valid?
     assert firm.save
-    assert !client.persisted?
+    assert_not_predicate client, :persisted?
   end
 
   def test_valid_adding_with_validate_false
@@ -438,25 +548,53 @@ class TestDefaultAutosaveAssociationOnAHasManyAssociation < ActiveRecord::TestCa
     firm = Firm.first
     client = Client.new("name" => "Apple")
 
-    assert firm.valid?
-    assert client.valid?
-    assert !client.persisted?
+    assert_predicate firm, :valid?
+    assert_predicate client, :valid?
+    assert_not_predicate client, :persisted?
 
     firm.unvalidated_clients_of_firm << client
 
     assert firm.save
-    assert client.persisted?
+    assert_predicate client, :persisted?
     assert_equal no_of_clients + 1, Client.count
   end
 
+  def test_parent_should_save_children_record_with_foreign_key_validation_set_in_before_save_callback
+    company = NewlyContractedCompany.new(name: "test")
+
+    assert company.save
+    assert_not_empty company.reload.new_contracts
+  end
+
+  def test_parent_should_not_get_saved_with_duplicate_children_records
+    assert_no_difference "Reply.count" do
+      assert_no_difference "SillyUniqueReply.count" do
+        reply = Reply.new
+        reply.silly_unique_replies.build([
+          { content: "Best content" },
+          { content: "Best content" }
+        ])
+
+        assert_not reply.save
+        assert_equal ["is invalid"], reply.errors[:silly_unique_replies]
+        assert_empty reply.silly_unique_replies.first.errors
+
+        assert_equal(
+          ["has already been taken"],
+          reply.silly_unique_replies.last.errors[:content]
+        )
+      end
+    end
+  end
+
   def test_invalid_build
     new_client = companies(:first_firm).clients_of_firm.build
-    assert !new_client.persisted?
-    assert !new_client.valid?
+    assert_not_predicate new_client, :persisted?
+    assert_not_predicate new_client, :valid?
     assert_equal new_client, companies(:first_firm).clients_of_firm.last
-    assert !companies(:first_firm).save
-    assert !new_client.persisted?
-    assert_equal 2, companies(:first_firm).clients_of_firm(true).size
+    assert_not companies(:first_firm).save
+    assert_not_predicate new_client, :persisted?
+    assert_equal 2, companies(:first_firm).clients_of_firm.reload.size
   end
 
   def test_adding_before_save
@@ -474,14 +612,14 @@ class TestDefaultAutosaveAssociationOnAHasManyAssociation < ActiveRecord::TestCa
     assert_equal no_of_firms, Firm.count      # Firm was not saved to database.
     assert_equal no_of_clients, Client.count  # Clients were not saved to database.
     assert new_firm.save
-    assert new_firm.persisted?
-    assert c.persisted?
+    assert_predicate new_firm, :persisted?
+    assert_predicate c, :persisted?
     assert_equal new_firm, c.firm
     assert_equal no_of_firms + 1, Firm.count      # Firm was saved to database.
     assert_equal no_of_clients + 2, Client.count  # Clients were saved to database.
 
     assert_equal 2, new_firm.clients_of_firm.size
-    assert_equal 2, new_firm.clients_of_firm(true).size
+    assert_equal 2, new_firm.clients_of_firm.reload.size
   end
 
   def test_assign_ids
@@ -490,60 +628,76 @@ class TestDefaultAutosaveAssociationOnAHasManyAssociation < ActiveRecord::TestCa
     firm.save
     firm.reload
     assert_equal 2, firm.clients.length
-    assert firm.clients.include?(companies(:second_client))
+    assert_includes firm.clients, companies(:second_client)
   end
 
   def test_assign_ids_for_through_a_belongs_to
-    post = Post.new(:title => "Assigning IDs works!", :body => "You heard it here first, folks!")
-    post.person_ids = [people(:david).id, people(:michael).id]
-    post.save
-    post.reload
-    assert_equal 2, post.people.length
-    assert post.people.include?(people(:david))
+    firm = Firm.new("name" => "Apple")
+    firm.developer_ids = [developers(:david).id, developers(:jamis).id]
+    firm.save
+    firm.reload
+    assert_equal 2, firm.developers.length
+    assert_includes firm.developers, developers(:david)
   end
 
   def test_build_before_save
     company = companies(:first_firm)
-    new_client = assert_no_queries(ignore_none: false) { company.clients_of_firm.build("name" => "Another Client") }
-    assert !company.clients_of_firm.loaded?
 
-    company.name += '-changed'
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    new_client = assert_no_queries { company.clients_of_firm.build("name" => "Another Client") }
+    assert_not_predicate company.clients_of_firm, :loaded?
+
+    company.name += "-changed"
     assert_queries(2) { assert company.save }
-    assert new_client.persisted?
-    assert_equal 3, company.clients_of_firm(true).size
+    assert_predicate new_client, :persisted?
+    assert_equal 3, company.clients_of_firm.reload.size
   end
 
   def test_build_many_before_save
     company = companies(:first_firm)
-    assert_no_queries(ignore_none: false) { company.clients_of_firm.build([{"name" => "Another Client"}, {"name" => "Another Client II"}]) }
 
-    company.name += '-changed'
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    assert_no_queries { company.clients_of_firm.build([{ "name" => "Another Client" }, { "name" => "Another Client II" }]) }
+
+    company.name += "-changed"
     assert_queries(3) { assert company.save }
-    assert_equal 4, company.clients_of_firm(true).size
+    assert_equal 4, company.clients_of_firm.reload.size
   end
 
   def test_build_via_block_before_save
     company = companies(:first_firm)
-    new_client = assert_no_queries(ignore_none: false) { company.clients_of_firm.build {|client| client.name = "Another Client" } }
-    assert !company.clients_of_firm.loaded?
 
-    company.name += '-changed'
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    new_client = assert_no_queries { company.clients_of_firm.build { |client| client.name = "Another Client" } }
+    assert_not_predicate company.clients_of_firm, :loaded?
+
+    company.name += "-changed"
     assert_queries(2) { assert company.save }
-    assert new_client.persisted?
-    assert_equal 3, company.clients_of_firm(true).size
+    assert_predicate new_client, :persisted?
+    assert_equal 3, company.clients_of_firm.reload.size
   end
 
   def test_build_many_via_block_before_save
     company = companies(:first_firm)
-    assert_no_queries(ignore_none: false) do
-      company.clients_of_firm.build([{"name" => "Another Client"}, {"name" => "Another Client II"}]) do |client|
+
+    # Load schema information so we don't query below if running just this test.
+    Client.define_attribute_methods
+
+    assert_no_queries do
+      company.clients_of_firm.build([{ "name" => "Another Client" }, { "name" => "Another Client II" }]) do |client|
         client.name = "changed"
       end
     end
 
-    company.name += '-changed'
+    company.name += "-changed"
     assert_queries(3) { assert company.save }
-    assert_equal 4, company.clients_of_firm(true).size
+    assert_equal 4, company.clients_of_firm.reload.size
   end
 
   def test_replace_on_new_object
@@ -552,7 +706,7 @@ class TestDefaultAutosaveAssociationOnAHasManyAssociation < ActiveRecord::TestCa
     assert firm.save
     firm.reload
     assert_equal 2, firm.clients.length
-    assert firm.clients.include?(Client.find_by_name("New Client"))
+    assert_includes firm.clients, Client.find_by_name("New Client")
   end
 end
 
@@ -561,67 +715,67 @@ class TestDefaultAutosaveAssociationOnNewRecord < ActiveRecord::TestCase
     new_account = Account.new("credit_limit" => 1000)
     new_firm = Firm.new("name" => "some firm")
 
-    assert !new_firm.persisted?
+    assert_not_predicate new_firm, :persisted?
     new_account.firm = new_firm
     new_account.save!
 
-    assert new_firm.persisted?
+    assert_predicate new_firm, :persisted?
 
     new_account = Account.new("credit_limit" => 1000)
     new_autosaved_firm = Firm.new("name" => "some firm")
 
-    assert !new_autosaved_firm.persisted?
+    assert_not_predicate new_autosaved_firm, :persisted?
     new_account.unautosaved_firm = new_autosaved_firm
     new_account.save!
 
-    assert !new_autosaved_firm.persisted?
+    assert_not_predicate new_autosaved_firm, :persisted?
   end
 
   def test_autosave_new_record_on_has_one_can_be_disabled_per_relationship
     firm = Firm.new("name" => "some firm")
     account = Account.new("credit_limit" => 1000)
 
-    assert !account.persisted?
+    assert_not_predicate account, :persisted?
     firm.account = account
     firm.save!
 
-    assert account.persisted?
+    assert_predicate account, :persisted?
 
     firm = Firm.new("name" => "some firm")
     account = Account.new("credit_limit" => 1000)
 
     firm.unautosaved_account = account
 
-    assert !account.persisted?
+    assert_not_predicate account, :persisted?
     firm.unautosaved_account = account
     firm.save!
 
-    assert !account.persisted?
+    assert_not_predicate account, :persisted?
   end
 
   def test_autosave_new_record_on_has_many_can_be_disabled_per_relationship
     firm = Firm.new("name" => "some firm")
     account = Account.new("credit_limit" => 1000)
 
-    assert !account.persisted?
+    assert_not_predicate account, :persisted?
     firm.accounts << account
 
     firm.save!
-    assert account.persisted?
+    assert_predicate account, :persisted?
 
     firm = Firm.new("name" => "some firm")
     account = Account.new("credit_limit" => 1000)
 
-    assert !account.persisted?
+    assert_not_predicate account, :persisted?
     firm.unautosaved_accounts << account
 
     firm.save!
-    assert !account.persisted?
+    assert_not_predicate account, :persisted?
   end
 
   def test_autosave_new_record_with_after_create_callback
-    post = PostWithAfterCreateCallback.new(title: 'Captain Murphy', body: 'is back')
-    post.comments.build(body: 'foo')
+    post = PostWithAfterCreateCallback.new(title: "Captain Murphy", body: "is back")
+    post.comments.build(body: "foo")
     post.save!
 
     assert_not_nil post.author_id
@@ -632,8 +786,8 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
   self.use_transactional_tests = false
 
   setup do
-    @pirate = Pirate.create(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @ship = @pirate.create_ship(:name => 'Nights Dirty Lightning')
+    @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @ship = @pirate.create_ship(name: "Nights Dirty Lightning")
   end
 
   teardown do
@@ -649,18 +803,18 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
     @pirate.mark_for_destruction
     @pirate.ship.mark_for_destruction
 
-    assert !@pirate.reload.marked_for_destruction?
-    assert !@pirate.ship.reload.marked_for_destruction?
+    assert_not_predicate @pirate.reload, :marked_for_destruction?
+    assert_not_predicate @pirate.ship.reload, :marked_for_destruction?
   end
 
   # has_one
-  def test_should_destroy_a_child_association_as_part_of_the_save_transaction_if_it_was_marked_for_destroyal
-    assert !@pirate.ship.marked_for_destruction?
+  def test_should_destroy_a_child_association_as_part_of_the_save_transaction_if_it_was_marked_for_destruction
+    assert_not_predicate @pirate.ship, :marked_for_destruction?
 
     @pirate.ship.mark_for_destruction
     id = @pirate.ship.id
 
-    assert @pirate.ship.marked_for_destruction?
+    assert_predicate @pirate.ship, :marked_for_destruction?
     assert Ship.find_by_id(id)
 
     @pirate.save
@@ -669,12 +823,13 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
   end
 
   def test_should_skip_validation_on_a_child_association_if_marked_for_destruction
-    @pirate.ship.name = ''
-    assert !@pirate.valid?
+    @pirate.ship.name = ""
+    assert_not_predicate @pirate, :valid?
 
     @pirate.ship.mark_for_destruction
-    @pirate.ship.expects(:valid?).never
-    assert_difference('Ship.count', -1) { @pirate.save! }
+    assert_not_called(@pirate.ship, :valid?) do
+      assert_difference("Ship.count", -1) { @pirate.save! }
+    end
   end
 
   def test_a_child_marked_for_destruction_should_not_be_destroyed_twice
@@ -692,13 +847,14 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
       def save(*args)
         super
         destroy
-        raise 'Oh noes!'
+        raise "Oh noes!"
       end
     end
 
     @ship.pirate.catchphrase = "Changed Catchphrase"
+    @ship.name_will_change!
 
-    assert_raise(RuntimeError) { assert !@pirate.save }
+    assert_raise(RuntimeError) { assert_not @pirate.save }
     assert_not_nil @pirate.reload.ship
   end
 
@@ -709,18 +865,19 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
   end
 
   def test_should_not_save_changed_has_one_unchanged_object_if_child_is_saved
-    @pirate.ship.expects(:save).never
-    assert @pirate.save
+    assert_not_called(@pirate.ship, :save) do
+      assert @pirate.save
+    end
   end
 
   # belongs_to
-  def test_should_destroy_a_parent_association_as_part_of_the_save_transaction_if_it_was_marked_for_destroyal
-    assert !@ship.pirate.marked_for_destruction?
+  def test_should_destroy_a_parent_association_as_part_of_the_save_transaction_if_it_was_marked_for_destruction
+    assert_not_predicate @ship.pirate, :marked_for_destruction?
 
     @ship.pirate.mark_for_destruction
     id = @ship.pirate.id
 
-    assert @ship.pirate.marked_for_destruction?
+    assert_predicate @ship.pirate, :marked_for_destruction?
     assert Pirate.find_by_id(id)
 
     @ship.save
@@ -729,12 +886,13 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
   end
 
   def test_should_skip_validation_on_a_parent_association_if_marked_for_destruction
-    @ship.pirate.catchphrase = ''
-    assert !@ship.valid?
+    @ship.pirate.catchphrase = ""
+    assert_not_predicate @ship, :valid?
 
     @ship.pirate.mark_for_destruction
-    @ship.pirate.expects(:valid?).never
-    assert_difference('Pirate.count', -1) { @ship.save! }
+    assert_not_called(@ship.pirate, :valid?) do
+      assert_difference("Pirate.count", -1) { @ship.save! }
+    end
   end
 
   def test_a_parent_marked_for_destruction_should_not_be_destroyed_twice
@@ -752,29 +910,29 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
       def save(*args)
         super
         destroy
-        raise 'Oh noes!'
+        raise "Oh noes!"
       end
     end
 
     @ship.pirate.catchphrase = "Changed Catchphrase"
 
-    assert_raise(RuntimeError) { assert !@ship.save }
+    assert_raise(RuntimeError) { assert_not @ship.save }
     assert_not_nil @ship.reload.pirate
   end
 
   def test_should_save_changed_child_objects_if_parent_is_saved
-    @pirate = @ship.create_pirate(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @parrot = @pirate.parrots.create!(:name => 'Posideons Killer')
+    @pirate = @ship.create_pirate(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @parrot = @pirate.parrots.create!(name: "Posideons Killer")
     @parrot.name = "NewName"
     @ship.save
 
-    assert_equal 'NewName', @parrot.reload.name
+    assert_equal "NewName", @parrot.reload.name
   end
 
   def test_should_destroy_has_many_as_part_of_the_save_transaction_if_they_were_marked_for_destruction
-    2.times { |i| @pirate.birds.create!(:name => "birds_#{i}") }
+    2.times { |i| @pirate.birds.create!(name: "birds_#{i}") }
 
-    assert !@pirate.birds.any?(&:marked_for_destruction?)
+    assert_not @pirate.birds.any?(&:marked_for_destruction?)
 
     @pirate.birds.each(&:mark_for_destruction)
     klass = @pirate.birds.first.class
@@ -784,7 +942,7 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
     ids.each { |id| assert klass.find_by_id(id) }
 
     @pirate.save
-    assert @pirate.reload.birds.empty?
+    assert_empty @pirate.reload.birds
     ids.each { |id| assert_nil klass.find_by_id(id) }
   end
 
@@ -792,62 +950,67 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
     @pirate.birds.create!(name: :parrot)
     @pirate.birds.first.destroy
     @pirate.save!
-    assert @pirate.reload.birds.empty?
+    assert_empty @pirate.reload.birds
   end
 
   def test_should_skip_validation_on_has_many_if_marked_for_destruction
-    2.times { |i| @pirate.birds.create!(:name => "birds_#{i}") }
+    2.times { |i| @pirate.birds.create!(name: "birds_#{i}") }
 
-    @pirate.birds.each { |bird| bird.name = '' }
-    assert !@pirate.valid?
+    @pirate.birds.each { |bird| bird.name = "" }
+    assert_not_predicate @pirate, :valid?
 
-    @pirate.birds.each do |bird|
-      bird.mark_for_destruction
-      bird.expects(:valid?).never
+    @pirate.birds.each(&:mark_for_destruction)
+
+    assert_not_called(@pirate.birds.first, :valid?) do
+      assert_not_called(@pirate.birds.last, :valid?) do
+        assert_difference("Bird.count", -2) { @pirate.save! }
+      end
     end
-    assert_difference("Bird.count", -2) { @pirate.save! }
   end
 
   def test_should_skip_validation_on_has_many_if_destroyed
-    @pirate.birds.create!(:name => "birds_1")
+    @pirate.birds.create!(name: "birds_1")
 
-    @pirate.birds.each { |bird| bird.name = '' }
-    assert !@pirate.valid?
+    @pirate.birds.each { |bird| bird.name = "" }
+    assert_not_predicate @pirate, :valid?
 
     @pirate.birds.each(&:destroy)
-    assert @pirate.valid?
+    assert_predicate @pirate, :valid?
   end
 
   def test_a_child_marked_for_destruction_should_not_be_destroyed_twice_while_saving_has_many
-    @pirate.birds.create!(:name => "birds_1")
+    @pirate.birds.create!(name: "birds_1")
 
     @pirate.birds.each(&:mark_for_destruction)
     assert @pirate.save
 
-    @pirate.birds.each { |bird| bird.expects(:destroy).never }
-    assert @pirate.save
+    @pirate.birds.each do |bird|
+      assert_not_called(bird, :destroy) do
+        assert @pirate.save
+      end
+    end
   end
 
   def test_should_rollback_destructions_if_an_exception_occurred_while_saving_has_many
-    2.times { |i| @pirate.birds.create!(:name => "birds_#{i}") }
+    2.times { |i| @pirate.birds.create!(name: "birds_#{i}") }
     before = @pirate.birds.map { |c| c.mark_for_destruction ; c }
 
     # Stub the destroy method of the second child to raise an exception
     class << before.last
       def destroy(*args)
         super
-        raise 'Oh noes!'
+        raise "Oh noes!"
       end
     end
 
-    assert_raise(RuntimeError) { assert !@pirate.save }
+    assert_raise(RuntimeError) { assert_not @pirate.save }
     assert_equal before, @pirate.reload.birds
   end
 
   def test_when_new_record_a_child_marked_for_destruction_should_not_affect_other_records_from_saving
-    @pirate = @ship.build_pirate(:catchphrase => "Arr' now I shall keep me eye on you matey!") # new record
+    @pirate = @ship.build_pirate(catchphrase: "Arr' now I shall keep me eye on you matey!") # new record
 
-    3.times { |i| @pirate.birds.build(:name => "birds_#{i}") }
+    3.times { |i| @pirate.birds.build(name: "birds_#{i}") }
     @pirate.birds[1].mark_for_destruction
     @pirate.save!
 
@@ -873,8 +1036,8 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
     define_method("test_should_run_add_callback_#{callback_type}s_for_has_many") do
       association_name_with_callbacks = "birds_with_#{callback_type}_callbacks"
 
-      pirate = Pirate.new(:catchphrase => "Arr")
-      pirate.send(association_name_with_callbacks).build(:name => "Crowe the One-Eyed")
+      pirate = Pirate.new(catchphrase: "Arr")
+      pirate.send(association_name_with_callbacks).build(name: "Crowe the One-Eyed")
 
       expected = [
         "before_adding_#{callback_type}_bird_<new>",
@@ -887,7 +1050,7 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
     define_method("test_should_run_remove_callback_#{callback_type}s_for_has_many") do
       association_name_with_callbacks = "birds_with_#{callback_type}_callbacks"
 
-      @pirate.send(association_name_with_callbacks).create!(:name => "Crowe the One-Eyed")
+      @pirate.send(association_name_with_callbacks).create!(name: "Crowe the One-Eyed")
       @pirate.send(association_name_with_callbacks).each(&:mark_for_destruction)
       child_id = @pirate.send(association_name_with_callbacks).first.id
 
@@ -904,71 +1067,73 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
   end
 
   def test_should_destroy_habtm_as_part_of_the_save_transaction_if_they_were_marked_for_destruction
-    2.times { |i| @pirate.parrots.create!(:name => "parrots_#{i}") }
+    2.times { |i| @pirate.parrots.create!(name: "parrots_#{i}") }
 
-    assert !@pirate.parrots.any?(&:marked_for_destruction?)
+    assert_not @pirate.parrots.any?(&:marked_for_destruction?)
     @pirate.parrots.each(&:mark_for_destruction)
 
     assert_no_difference "Parrot.count" do
       @pirate.save
     end
 
-    assert @pirate.reload.parrots.empty?
+    assert_empty @pirate.reload.parrots
 
     join_records = Pirate.connection.select_all("SELECT * FROM parrots_pirates WHERE pirate_id = #{@pirate.id}")
-    assert join_records.empty?
+    assert_empty join_records
   end
 
   def test_should_skip_validation_on_habtm_if_marked_for_destruction
-    2.times { |i| @pirate.parrots.create!(:name => "parrots_#{i}") }
+    2.times { |i| @pirate.parrots.create!(name: "parrots_#{i}") }
+
+    @pirate.parrots.each { |parrot| parrot.name = "" }
+    assert_not_predicate @pirate, :valid?
 
-    @pirate.parrots.each { |parrot| parrot.name = '' }
-    assert !@pirate.valid?
+    @pirate.parrots.each { |parrot| parrot.mark_for_destruction }
 
-    @pirate.parrots.each do |parrot|
-      parrot.mark_for_destruction
-      parrot.expects(:valid?).never
+    assert_not_called(@pirate.parrots.first, :valid?) do
+      assert_not_called(@pirate.parrots.last, :valid?) do
+        @pirate.save!
+      end
     end
 
-    @pirate.save!
-    assert @pirate.reload.parrots.empty?
+    assert_empty @pirate.reload.parrots
   end
 
   def test_should_skip_validation_on_habtm_if_destroyed
-    @pirate.parrots.create!(:name => "parrots_1")
+    @pirate.parrots.create!(name: "parrots_1")
 
-    @pirate.parrots.each { |parrot| parrot.name = '' }
-    assert !@pirate.valid?
+    @pirate.parrots.each { |parrot| parrot.name = "" }
+    assert_not_predicate @pirate, :valid?
 
     @pirate.parrots.each(&:destroy)
-    assert @pirate.valid?
+    assert_predicate @pirate, :valid?
   end
 
   def test_a_child_marked_for_destruction_should_not_be_destroyed_twice_while_saving_habtm
-    @pirate.parrots.create!(:name => "parrots_1")
+    @pirate.parrots.create!(name: "parrots_1")
 
     @pirate.parrots.each(&:mark_for_destruction)
     assert @pirate.save
 
     Pirate.transaction do
-      assert_queries(0) do
+      assert_no_queries do
         assert @pirate.save
       end
     end
   end
 
   def test_should_rollback_destructions_if_an_exception_occurred_while_saving_habtm
-    2.times { |i| @pirate.parrots.create!(:name => "parrots_#{i}") }
+    2.times { |i| @pirate.parrots.create!(name: "parrots_#{i}") }
     before = @pirate.parrots.map { |c| c.mark_for_destruction ; c }
 
     class << @pirate.association(:parrots)
       def destroy(*args)
         super
-        raise 'Oh noes!'
+        raise "Oh noes!"
       end
     end
 
-    assert_raise(RuntimeError) { assert !@pirate.save }
+    assert_raise(RuntimeError) { assert_not @pirate.save }
     assert_equal before, @pirate.reload.parrots
   end
 
@@ -977,8 +1142,8 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
     define_method("test_should_run_add_callback_#{callback_type}s_for_habtm") do
       association_name_with_callbacks = "parrots_with_#{callback_type}_callbacks"
 
-      pirate = Pirate.new(:catchphrase => "Arr")
-      pirate.send(association_name_with_callbacks).build(:name => "Crowe the One-Eyed")
+      pirate = Pirate.new(catchphrase: "Arr")
+      pirate.send(association_name_with_callbacks).build(name: "Crowe the One-Eyed")
 
       expected = [
         "before_adding_#{callback_type}_parrot_<new>",
@@ -991,7 +1156,7 @@ class TestDestroyAsPartOfAutosaveAssociation < ActiveRecord::TestCase
     define_method("test_should_run_remove_callback_#{callback_type}s_for_habtm") do
       association_name_with_callbacks = "parrots_with_#{callback_type}_callbacks"
 
-      @pirate.send(association_name_with_callbacks).create!(:name => "Crowe the One-Eyed")
+      @pirate.send(association_name_with_callbacks).create!(name: "Crowe the One-Eyed")
       @pirate.send(association_name_with_callbacks).each(&:mark_for_destruction)
       child_id = @pirate.send(association_name_with_callbacks).first.id
 
@@ -1013,60 +1178,60 @@ class TestAutosaveAssociationOnAHasOneAssociation < ActiveRecord::TestCase
 
   def setup
     super
-    @pirate = Pirate.create(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @ship = @pirate.create_ship(:name => 'Nights Dirty Lightning')
+    @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @ship = @pirate.create_ship(name: "Nights Dirty Lightning")
   end
 
   def test_should_still_work_without_an_associated_model
     @ship.destroy
     @pirate.reload.catchphrase = "Arr"
     @pirate.save
-    assert_equal 'Arr', @pirate.reload.catchphrase
+    assert_equal "Arr", @pirate.reload.catchphrase
   end
 
   def test_should_automatically_save_the_associated_model
-    @pirate.ship.name = 'The Vile Insanity'
+    @pirate.ship.name = "The Vile Insanity"
     @pirate.save
-    assert_equal 'The Vile Insanity', @pirate.reload.ship.name
+    assert_equal "The Vile Insanity", @pirate.reload.ship.name
   end
 
   def test_changed_for_autosave_should_handle_cycles
     @ship.pirate = @pirate
-    assert_queries(0) { @ship.save! }
+    assert_no_queries { @ship.save! }
 
     @parrot = @pirate.parrots.create(name: "some_name")
-    @parrot.name="changed_name"
+    @parrot.name = "changed_name"
     assert_queries(1) { @ship.save! }
-    assert_queries(0) { @ship.save! }
+    assert_no_queries { @ship.save! }
   end
 
   def test_should_automatically_save_bang_the_associated_model
-    @pirate.ship.name = 'The Vile Insanity'
+    @pirate.ship.name = "The Vile Insanity"
     @pirate.save!
-    assert_equal 'The Vile Insanity', @pirate.reload.ship.name
+    assert_equal "The Vile Insanity", @pirate.reload.ship.name
   end
 
   def test_should_automatically_validate_the_associated_model
-    @pirate.ship.name = ''
-    assert @pirate.invalid?
-    assert @pirate.errors[:"ship.name"].any?
+    @pirate.ship.name = ""
+    assert_predicate @pirate, :invalid?
+    assert_predicate @pirate.errors[:"ship.name"], :any?
   end
 
   def test_should_merge_errors_on_the_associated_models_onto_the_parent_even_if_it_is_not_valid
     @pirate.ship.name   = nil
     @pirate.catchphrase = nil
-    assert @pirate.invalid?
-    assert @pirate.errors[:"ship.name"].any?
-    assert @pirate.errors[:catchphrase].any?
+    assert_predicate @pirate, :invalid?
+    assert_predicate @pirate.errors[:"ship.name"], :any?
+    assert_predicate @pirate.errors[:catchphrase], :any?
   end
 
   def test_should_not_ignore_different_error_messages_on_the_same_attribute
     old_validators = Ship._validators.deep_dup
     old_callbacks = Ship._validate_callbacks.deep_dup
-    Ship.validates_format_of :name, :with => /\w/
+    Ship.validates_format_of :name, with: /\w/
     @pirate.ship.name   = ""
     @pirate.catchphrase = nil
-    assert @pirate.invalid?
+    assert_predicate @pirate, :invalid?
     assert_equal ["can't be blank", "is invalid"], @pirate.errors[:"ship.name"]
   ensure
     Ship._validators = old_validators if old_validators
@@ -1074,49 +1239,49 @@ class TestAutosaveAssociationOnAHasOneAssociation < ActiveRecord::TestCase
   end
 
   def test_should_still_allow_to_bypass_validations_on_the_associated_model
-    @pirate.catchphrase = ''
-    @pirate.ship.name = ''
-    @pirate.save(:validate => false)
+    @pirate.catchphrase = ""
+    @pirate.ship.name = ""
+    @pirate.save(validate: false)
     # Oracle saves empty string as NULL
     if current_adapter?(:OracleAdapter)
       assert_equal [nil, nil], [@pirate.reload.catchphrase, @pirate.ship.name]
     else
-      assert_equal ['', ''], [@pirate.reload.catchphrase, @pirate.ship.name]
+      assert_equal ["", ""], [@pirate.reload.catchphrase, @pirate.ship.name]
     end
   end
 
   def test_should_allow_to_bypass_validations_on_associated_models_at_any_depth
-    2.times { |i| @pirate.ship.parts.create!(:name => "part #{i}") }
+    2.times { |i| @pirate.ship.parts.create!(name: "part #{i}") }
 
-    @pirate.catchphrase = ''
-    @pirate.ship.name = ''
-    @pirate.ship.parts.each { |part| part.name = '' }
-    @pirate.save(:validate => false)
+    @pirate.catchphrase = ""
+    @pirate.ship.name = ""
+    @pirate.ship.parts.each { |part| part.name = "" }
+    @pirate.save(validate: false)
 
     values = [@pirate.reload.catchphrase, @pirate.ship.name, *@pirate.ship.parts.map(&:name)]
     # Oracle saves empty string as NULL
     if current_adapter?(:OracleAdapter)
       assert_equal [nil, nil, nil, nil], values
     else
-      assert_equal ['', '', '', ''], values
+      assert_equal ["", "", "", ""], values
     end
   end
 
   def test_should_still_raise_an_ActiveRecordRecord_Invalid_exception_if_we_want_that
-    @pirate.ship.name = ''
+    @pirate.ship.name = ""
     assert_raise(ActiveRecord::RecordInvalid) do
       @pirate.save!
     end
   end
 
   def test_should_not_save_and_return_false_if_a_callback_cancelled_saving
-    pirate = Pirate.new(:catchphrase => 'Arr')
-    ship = pirate.build_ship(:name => 'The Vile Insanity')
+    pirate = Pirate.new(catchphrase: "Arr")
+    ship = pirate.build_ship(name: "The Vile Insanity")
     ship.cancel_save_from_callback = true
 
-    assert_no_difference 'Pirate.count' do
-      assert_no_difference 'Ship.count' do
-        assert !pirate.save
+    assert_no_difference "Pirate.count" do
+      assert_no_difference "Ship.count" do
+        assert_not pirate.save
       end
     end
   end
@@ -1124,23 +1289,30 @@ class TestAutosaveAssociationOnAHasOneAssociation < ActiveRecord::TestCase
   def test_should_rollback_any_changes_if_an_exception_occurred_while_saving
     before = [@pirate.catchphrase, @pirate.ship.name]
 
-    @pirate.catchphrase = 'Arr'
-    @pirate.ship.name = 'The Vile Insanity'
+    @pirate.catchphrase = "Arr"
+    @pirate.ship.name = "The Vile Insanity"
 
     # Stub the save method of the @pirate.ship instance to raise an exception
     class << @pirate.ship
       def save(*args)
         super
-        raise 'Oh noes!'
+        raise "Oh noes!"
       end
     end
 
-    assert_raise(RuntimeError) { assert !@pirate.save }
+    assert_raise(RuntimeError) { assert_not @pirate.save }
     assert_equal before, [@pirate.reload.catchphrase, @pirate.ship.name]
   end
 
   def test_should_not_load_the_associated_model
-    assert_queries(1) { @pirate.catchphrase = 'Arr'; @pirate.save! }
+    assert_queries(1) { @pirate.catchphrase = "Arr"; @pirate.save! }
+  end
+
+  def test_mark_for_destruction_is_ignored_without_autosave_true
+    ship = ShipWithoutNestedAttributes.new(name: "The Black Flag")
+    ship.parts.build.mark_for_destruction
+
+    assert_not_predicate ship, :valid?
   end
 end
 
@@ -1158,7 +1330,7 @@ class TestAutosaveAssociationOnAHasOneThroughAssociation < ActiveRecord::TestCas
     class << @member.organization
       def save(*args)
         super
-        raise 'Oh noes!'
+        raise "Oh noes!"
       end
     end
     assert_nothing_raised { @member.save }
@@ -1170,70 +1342,70 @@ class TestAutosaveAssociationOnABelongsToAssociation < ActiveRecord::TestCase
 
   def setup
     super
-    @ship = Ship.create(:name => 'Nights Dirty Lightning')
-    @pirate = @ship.create_pirate(:catchphrase => "Don' botharrr talkin' like one, savvy?")
+    @ship = Ship.create(name: "Nights Dirty Lightning")
+    @pirate = @ship.create_pirate(catchphrase: "Don' botharrr talkin' like one, savvy?")
   end
 
   def test_should_still_work_without_an_associated_model
     @pirate.destroy
     @ship.reload.name = "The Vile Insanity"
     @ship.save
-    assert_equal 'The Vile Insanity', @ship.reload.name
+    assert_equal "The Vile Insanity", @ship.reload.name
   end
 
   def test_should_automatically_save_the_associated_model
-    @ship.pirate.catchphrase = 'Arr'
+    @ship.pirate.catchphrase = "Arr"
     @ship.save
-    assert_equal 'Arr', @ship.reload.pirate.catchphrase
+    assert_equal "Arr", @ship.reload.pirate.catchphrase
   end
 
   def test_should_automatically_save_bang_the_associated_model
-    @ship.pirate.catchphrase = 'Arr'
+    @ship.pirate.catchphrase = "Arr"
     @ship.save!
-    assert_equal 'Arr', @ship.reload.pirate.catchphrase
+    assert_equal "Arr", @ship.reload.pirate.catchphrase
   end
 
   def test_should_automatically_validate_the_associated_model
-    @ship.pirate.catchphrase = ''
-    assert @ship.invalid?
-    assert @ship.errors[:"pirate.catchphrase"].any?
+    @ship.pirate.catchphrase = ""
+    assert_predicate @ship, :invalid?
+    assert_predicate @ship.errors[:"pirate.catchphrase"], :any?
   end
 
   def test_should_merge_errors_on_the_associated_model_onto_the_parent_even_if_it_is_not_valid
     @ship.name = nil
     @ship.pirate.catchphrase = nil
-    assert @ship.invalid?
-    assert @ship.errors[:name].any?
-    assert @ship.errors[:"pirate.catchphrase"].any?
+    assert_predicate @ship, :invalid?
+    assert_predicate @ship.errors[:name], :any?
+    assert_predicate @ship.errors[:"pirate.catchphrase"], :any?
   end
 
   def test_should_still_allow_to_bypass_validations_on_the_associated_model
-    @ship.pirate.catchphrase = ''
-    @ship.name = ''
-    @ship.save(:validate => false)
+    @ship.pirate.catchphrase = ""
+    @ship.name = ""
+    @ship.save(validate: false)
     # Oracle saves empty string as NULL
     if current_adapter?(:OracleAdapter)
       assert_equal [nil, nil], [@ship.reload.name, @ship.pirate.catchphrase]
     else
-      assert_equal ['', ''], [@ship.reload.name, @ship.pirate.catchphrase]
+      assert_equal ["", ""], [@ship.reload.name, @ship.pirate.catchphrase]
     end
   end
 
   def test_should_still_raise_an_ActiveRecordRecord_Invalid_exception_if_we_want_that
-    @ship.pirate.catchphrase = ''
+    @ship.pirate.catchphrase = ""
     assert_raise(ActiveRecord::RecordInvalid) do
       @ship.save!
     end
   end
 
   def test_should_not_save_and_return_false_if_a_callback_cancelled_saving
-    ship = Ship.new(:name => 'The Vile Insanity')
-    pirate = ship.build_pirate(:catchphrase => 'Arr')
+    ship = Ship.new(name: "The Vile Insanity")
+    pirate = ship.build_pirate(catchphrase: "Arr")
     pirate.cancel_save_from_callback = true
 
-    assert_no_difference 'Ship.count' do
-      assert_no_difference 'Pirate.count' do
-        assert !ship.save
+    assert_no_difference "Ship.count" do
+      assert_no_difference "Pirate.count" do
+        assert_not ship.save
       end
     end
   end
@@ -1241,41 +1413,41 @@ class TestAutosaveAssociationOnABelongsToAssociation < ActiveRecord::TestCase
   def test_should_rollback_any_changes_if_an_exception_occurred_while_saving
     before = [@ship.pirate.catchphrase, @ship.name]
 
-    @ship.pirate.catchphrase = 'Arr'
-    @ship.name = 'The Vile Insanity'
+    @ship.pirate.catchphrase = "Arr"
+    @ship.name = "The Vile Insanity"
 
     # Stub the save method of the @ship.pirate instance to raise an exception
     class << @ship.pirate
       def save(*args)
         super
-        raise 'Oh noes!'
+        raise "Oh noes!"
       end
     end
 
-    assert_raise(RuntimeError) { assert !@ship.save }
+    assert_raise(RuntimeError) { assert_not @ship.save }
     assert_equal before, [@ship.pirate.reload.catchphrase, @ship.reload.name]
   end
 
   def test_should_not_load_the_associated_model
-    assert_queries(1) { @ship.name = 'The Vile Insanity'; @ship.save! }
+    assert_queries(1) { @ship.name = "The Vile Insanity"; @ship.save! }
   end
 end
 
 module AutosaveAssociationOnACollectionAssociationTests
   def test_should_automatically_save_the_associated_models
-    new_names = ['Grace OMalley', 'Privateers Greed']
+    new_names = ["Grace OMalley", "Privateers Greed"]
     @pirate.send(@association_name).each_with_index { |child, i| child.name = new_names[i] }
 
     @pirate.save
-    assert_equal new_names, @pirate.reload.send(@association_name).map(&:name)
+    assert_equal new_names.sort, @pirate.reload.send(@association_name).map(&:name).sort
   end
 
   def test_should_automatically_save_bang_the_associated_models
-    new_names = ['Grace OMalley', 'Privateers Greed']
+    new_names = ["Grace OMalley", "Privateers Greed"]
     @pirate.send(@association_name).each_with_index { |child, i| child.name = new_names[i] }
 
     @pirate.save!
-    assert_equal new_names, @pirate.reload.send(@association_name).map(&:name)
+    assert_equal new_names.sort, @pirate.reload.send(@association_name).map(&:name).sort
   end
 
   def test_should_update_children_when_autosave_is_true_and_parent_is_new_but_child_is_not
@@ -1288,51 +1460,59 @@ module AutosaveAssociationOnACollectionAssociationTests
     assert_equal "Squawky", parrot.reload.name
   end
 
+  def test_should_not_update_children_when_parent_creation_with_no_reason
+    parrot = Parrot.create!(name: "Polly")
+    assert_equal 0, parrot.updated_count
+
+    Pirate.create!(parrot_ids: [parrot.id], catchphrase: "Arrrr")
+    assert_equal 0, parrot.reload.updated_count
+  end
+
   def test_should_automatically_validate_the_associated_models
-    @pirate.send(@association_name).each { |child| child.name = '' }
+    @pirate.send(@association_name).each { |child| child.name = "" }
 
-    assert !@pirate.valid?
+    assert_not_predicate @pirate, :valid?
     assert_equal ["can't be blank"], @pirate.errors["#{@association_name}.name"]
-    assert @pirate.errors[@association_name].empty?
+    assert_empty @pirate.errors[@association_name]
   end
 
   def test_should_not_use_default_invalid_error_on_associated_models
-    @pirate.send(@association_name).build(:name => '')
+    @pirate.send(@association_name).build(name: "")
 
-    assert !@pirate.valid?
+    assert_not_predicate @pirate, :valid?
     assert_equal ["can't be blank"], @pirate.errors["#{@association_name}.name"]
-    assert @pirate.errors[@association_name].empty?
+    assert_empty @pirate.errors[@association_name]
   end
 
   def test_should_default_invalid_error_from_i18n
-    I18n.backend.store_translations(:en, activerecord: {errors: { models:
+    I18n.backend.store_translations(:en, activerecord: { errors: { models:
       { @associated_model_name.to_s.to_sym => { blank: "cannot be blank" } }
-    }})
+    } })
 
-    @pirate.send(@association_name).build(name: '')
+    @pirate.send(@association_name).build(name: "")
 
-    assert !@pirate.valid?
+    assert_not_predicate @pirate, :valid?
     assert_equal ["cannot be blank"], @pirate.errors["#{@association_name}.name"]
     assert_equal ["#{@association_name.to_s.humanize} name cannot be blank"], @pirate.errors.full_messages
-    assert @pirate.errors[@association_name].empty?
+    assert_empty @pirate.errors[@association_name]
   ensure
     I18n.backend = I18n::Backend::Simple.new
   end
 
   def test_should_merge_errors_on_the_associated_models_onto_the_parent_even_if_it_is_not_valid
-    @pirate.send(@association_name).each { |child| child.name = '' }
+    @pirate.send(@association_name).each { |child| child.name = "" }
     @pirate.catchphrase = nil
 
-    assert !@pirate.valid?
+    assert_not_predicate @pirate, :valid?
     assert_equal ["can't be blank"], @pirate.errors["#{@association_name}.name"]
-    assert @pirate.errors[:catchphrase].any?
+    assert_predicate @pirate.errors[:catchphrase], :any?
   end
 
   def test_should_allow_to_bypass_validations_on_the_associated_models_on_update
-    @pirate.catchphrase = ''
-    @pirate.send(@association_name).each { |child| child.name = '' }
+    @pirate.catchphrase = ""
+    @pirate.send(@association_name).each { |child| child.name = "" }
 
-    assert @pirate.save(:validate => false)
+    assert @pirate.save(validate: false)
     # Oracle saves empty string as NULL
     if current_adapter?(:OracleAdapter)
       assert_equal [nil, nil, nil], [
@@ -1341,7 +1521,7 @@ module AutosaveAssociationOnACollectionAssociationTests
         @pirate.send(@association_name).last.name
       ]
     else
-      assert_equal ['', '', ''], [
+      assert_equal ["", "", ""], [
         @pirate.reload.catchphrase,
         @pirate.send(@association_name).first.name,
         @pirate.send(@association_name).last.name
@@ -1359,64 +1539,64 @@ module AutosaveAssociationOnACollectionAssociationTests
   def test_should_allow_to_bypass_validations_on_the_associated_models_on_create
     assert_difference("#{ @association_name == :birds ? 'Bird' : 'Parrot' }.count", 2) do
       2.times { @pirate.send(@association_name).build }
-      @pirate.save(:validate => false)
+      @pirate.save(validate: false)
     end
   end
 
   def test_should_not_save_and_return_false_if_a_callback_cancelled_saving_in_either_create_or_update
-    @pirate.catchphrase = 'Changed'
-    @child_1.name = 'Changed'
+    @pirate.catchphrase = "Changed"
+    @child_1.name = "Changed"
     @child_1.cancel_save_from_callback = true
 
-    assert !@pirate.save
+    assert_not @pirate.save
     assert_equal "Don' botharrr talkin' like one, savvy?", @pirate.reload.catchphrase
     assert_equal "Posideons Killer", @child_1.reload.name
 
-    new_pirate = Pirate.new(:catchphrase => 'Arr')
-    new_child = new_pirate.send(@association_name).build(:name => 'Grace OMalley')
+    new_pirate = Pirate.new(catchphrase: "Arr")
+    new_child = new_pirate.send(@association_name).build(name: "Grace OMalley")
     new_child.cancel_save_from_callback = true
 
-    assert_no_difference 'Pirate.count' do
+    assert_no_difference "Pirate.count" do
       assert_no_difference "#{new_child.class.name}.count" do
-        assert !new_pirate.save
+        assert_not new_pirate.save
       end
     end
   end
 
   def test_should_rollback_any_changes_if_an_exception_occurred_while_saving
     before = [@pirate.catchphrase, *@pirate.send(@association_name).map(&:name)]
-    new_names = ['Grace OMalley', 'Privateers Greed']
+    new_names = ["Grace OMalley", "Privateers Greed"]
 
-    @pirate.catchphrase = 'Arr'
+    @pirate.catchphrase = "Arr"
     @pirate.send(@association_name).each_with_index { |child, i| child.name = new_names[i] }
 
     # Stub the save method of the first child instance to raise an exception
     class << @pirate.send(@association_name).first
       def save(*args)
         super
-        raise 'Oh noes!'
+        raise "Oh noes!"
       end
     end
 
-    assert_raise(RuntimeError) { assert !@pirate.save }
+    assert_raise(RuntimeError) { assert_not @pirate.save }
     assert_equal before, [@pirate.reload.catchphrase, *@pirate.send(@association_name).map(&:name)]
   end
 
   def test_should_still_raise_an_ActiveRecordRecord_Invalid_exception_if_we_want_that
-    @pirate.send(@association_name).each { |child| child.name = '' }
+    @pirate.send(@association_name).each { |child| child.name = "" }
     assert_raise(ActiveRecord::RecordInvalid) do
       @pirate.save!
     end
   end
 
   def test_should_not_load_the_associated_models_if_they_were_not_loaded_yet
-    assert_queries(1) { @pirate.catchphrase = 'Arr'; @pirate.save! }
+    assert_queries(1) { @pirate.catchphrase = "Arr"; @pirate.save! }
 
     @pirate.send(@association_name).load_target
 
     assert_queries(3) do
-      @pirate.catchphrase = 'Yarr'
-      new_names = ['Grace OMalley', 'Privateers Greed']
+      @pirate.catchphrase = "Yarr"
+      new_names = ["Grace OMalley", "Privateers Greed"]
       @pirate.send(@association_name).each_with_index { |child, i| child.name = new_names[i] }
       @pirate.save!
     end
@@ -1431,9 +1611,9 @@ class TestAutosaveAssociationOnAHasManyAssociation < ActiveRecord::TestCase
     @association_name = :birds
     @associated_model_name = :bird
 
-    @pirate = Pirate.create(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @child_1 = @pirate.birds.create(:name => 'Posideons Killer')
-    @child_2 = @pirate.birds.create(:name => 'Killer bandita Dionne')
+    @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @child_1 = @pirate.birds.create(name: "Posideons Killer")
+    @child_2 = @pirate.birds.create(name: "Killer bandita Dionne")
   end
 
   include AutosaveAssociationOnACollectionAssociationTests
@@ -1449,8 +1629,8 @@ class TestAutosaveAssociationOnAHasAndBelongsToManyAssociation < ActiveRecord::T
     @habtm = true
 
     @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
-    @child_1 = @pirate.parrots.create(name: 'Posideons Killer')
-    @child_2 = @pirate.parrots.create(name: 'Killer bandita Dionne')
+    @child_1 = @pirate.parrots.create(name: "Posideons Killer")
+    @child_2 = @pirate.parrots.create(name: "Killer bandita Dionne")
   end
 
   include AutosaveAssociationOnACollectionAssociationTests
@@ -1466,8 +1646,8 @@ class TestAutosaveAssociationOnAHasAndBelongsToManyAssociationWithAcceptsNestedA
     @habtm = true
 
     @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
-    @child_1 = @pirate.parrots.create(name: 'Posideons Killer')
-    @child_2 = @pirate.parrots.create(name: 'Killer bandita Dionne')
+    @child_1 = @pirate.parrots.create(name: "Posideons Killer")
+    @child_2 = @pirate.parrots.create(name: "Killer bandita Dionne")
   end
 
   include AutosaveAssociationOnACollectionAssociationTests
@@ -1478,15 +1658,15 @@ class TestAutosaveAssociationValidationsOnAHasManyAssociation < ActiveRecord::Te
 
   def setup
     super
-    @pirate = Pirate.create(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @pirate.birds.create(:name => 'cookoo')
+    @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @pirate.birds.create(name: "cookoo")
   end
 
   test "should automatically validate associations" do
-    assert @pirate.valid?
-    @pirate.birds.each { |bird| bird.name = '' }
+    assert_predicate @pirate, :valid?
+    @pirate.birds.each { |bird| bird.name = "" }
 
-    assert !@pirate.valid?
+    assert_not_predicate @pirate, :valid?
   end
 end
 
@@ -1495,21 +1675,21 @@ class TestAutosaveAssociationValidationsOnAHasOneAssociation < ActiveRecord::Tes
 
   def setup
     super
-    @pirate = Pirate.create(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @pirate.create_ship(:name => 'titanic')
+    @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @pirate.create_ship(name: "titanic")
     super
   end
 
   test "should automatically validate associations with :validate => true" do
-    assert @pirate.valid?
-    @pirate.ship.name = ''
-    assert !@pirate.valid?
+    assert_predicate @pirate, :valid?
+    @pirate.ship.name = ""
+    assert_not_predicate @pirate, :valid?
   end
 
   test "should not automatically add validate associations without :validate => true" do
-    assert @pirate.valid?
-    @pirate.non_validated_ship.name = ''
-    assert @pirate.valid?
+    assert_predicate @pirate, :valid?
+    @pirate.non_validated_ship.name = ""
+    assert_predicate @pirate, :valid?
   end
 end
 
@@ -1518,19 +1698,19 @@ class TestAutosaveAssociationValidationsOnABelongsToAssociation < ActiveRecord::
 
   def setup
     super
-    @pirate = Pirate.create(:catchphrase => "Don' botharrr talkin' like one, savvy?")
+    @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
   end
 
   test "should automatically validate associations with :validate => true" do
-    assert @pirate.valid?
-    @pirate.parrot = Parrot.new(:name => '')
-    assert !@pirate.valid?
+    assert_predicate @pirate, :valid?
+    @pirate.parrot = Parrot.new(name: "")
+    assert_not_predicate @pirate, :valid?
   end
 
   test "should not automatically validate associations without :validate => true" do
-    assert @pirate.valid?
-    @pirate.non_validated_parrot = Parrot.new(:name => '')
-    assert @pirate.valid?
+    assert_predicate @pirate, :valid?
+    @pirate.non_validated_parrot = Parrot.new(name: "")
+    assert_predicate @pirate, :valid?
   end
 end
 
@@ -1539,21 +1719,21 @@ class TestAutosaveAssociationValidationsOnAHABTMAssociation < ActiveRecord::Test
 
   def setup
     super
-    @pirate = Pirate.create(:catchphrase => "Don' botharrr talkin' like one, savvy?")
+    @pirate = Pirate.create(catchphrase: "Don' botharrr talkin' like one, savvy?")
   end
 
   test "should automatically validate associations with :validate => true" do
-    assert @pirate.valid?
-    @pirate.parrots = [ Parrot.new(:name => 'popuga') ]
-    @pirate.parrots.each { |parrot| parrot.name = '' }
-    assert !@pirate.valid?
+    assert_predicate @pirate, :valid?
+    @pirate.parrots = [ Parrot.new(name: "popuga") ]
+    @pirate.parrots.each { |parrot| parrot.name = "" }
+    assert_not_predicate @pirate, :valid?
   end
 
   test "should not automatically validate associations without :validate => true" do
-    assert @pirate.valid?
-    @pirate.non_validated_parrots = [ Parrot.new(:name => 'popuga') ]
-    @pirate.non_validated_parrots.each { |parrot| parrot.name = '' }
-    assert @pirate.valid?
+    assert_predicate @pirate, :valid?
+    @pirate.non_validated_parrots = [ Parrot.new(name: "popuga") ]
+    @pirate.non_validated_parrots.each { |parrot| parrot.name = "" }
+    assert_predicate @pirate, :valid?
   end
 end
 
@@ -1574,7 +1754,7 @@ class TestAutosaveAssociationValidationMethodsGeneration < ActiveRecord::TestCas
   end
 
   test "should not generate validation methods for has_one associations without :validate => true" do
-    assert !@pirate.respond_to?(:validate_associated_records_for_non_validated_ship)
+    assert_not_respond_to @pirate, :validate_associated_records_for_non_validated_ship
   end
 
   test "should generate validation methods for belongs_to associations with :validate => true" do
@@ -1582,7 +1762,7 @@ class TestAutosaveAssociationValidationMethodsGeneration < ActiveRecord::TestCas
   end
 
   test "should not generate validation methods for belongs_to associations without :validate => true" do
-    assert !@pirate.respond_to?(:validate_associated_records_for_non_validated_parrot)
+    assert_not_respond_to @pirate, :validate_associated_records_for_non_validated_parrot
   end
 
   test "should generate validation methods for HABTM associations with :validate => true" do
@@ -1593,6 +1773,52 @@ end
 class TestAutosaveAssociationWithTouch < ActiveRecord::TestCase
   def test_autosave_with_touch_should_not_raise_system_stack_error
     invoice = Invoice.create
-    assert_nothing_raised { invoice.line_items.create(:amount => 10) }
+    assert_nothing_raised { invoice.line_items.create(amount: 10) }
+  end
+end
+
+class TestAutosaveAssociationOnAHasManyAssociationWithInverse < ActiveRecord::TestCase
+  class Post < ActiveRecord::Base
+    has_many :comments, inverse_of: :post
+  end
+
+  class Comment < ActiveRecord::Base
+    belongs_to :post, inverse_of: :comments
+
+    attr_accessor :post_comments_count
+    after_save do
+      self.post_comments_count = post.comments.count
+    end
+  end
+
+  def setup
+    Comment.delete_all
+  end
+
+  def test_after_save_callback_with_autosave
+    post = Post.new(title: "Test", body: "...")
+    comment = post.comments.build(body: "...")
+    post.save!
+
+    assert_equal 1, post.comments.count
+    assert_equal 1, comment.post_comments_count
+  end
+end
+
+class TestAutosaveAssociationOnAHasManyAssociationDefinedInSubclassWithAcceptsNestedAttributes < ActiveRecord::TestCase
+  def test_should_update_children_when_asssociation_redefined_in_subclass
+    agency = Agency.create!(name: "Agency")
+    valid_project = Project.create!(firm: agency, name: "Initial")
+    agency.update!(
+      "projects_attributes" => {
+        "0" => {
+          "name" => "Updated",
+          "id" => valid_project.id
+        }
+      }
+    )
+    valid_project.reload
+
+    assert_equal "Updated", valid_project.name
   end
 end
diff --git a/activerecord/test/cases/base_test.rb b/activerecord/test/cases/base_test.rb
index 31c31e4329..09e5517449 100644
--- a/activerecord/test/cases/base_test.rb
+++ b/activerecord/test/cases/base_test.rb
@@ -1,34 +1,32 @@
-# -*- coding: utf-8 -*-
+# frozen_string_literal: true
 
 require "cases/helper"
-require 'active_support/concurrency/latch'
-require 'models/post'
-require 'models/author'
-require 'models/topic'
-require 'models/reply'
-require 'models/category'
-require 'models/company'
-require 'models/customer'
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/default'
-require 'models/auto_id'
-require 'models/boolean'
-require 'models/column_name'
-require 'models/subscriber'
-require 'models/keyboard'
-require 'models/comment'
-require 'models/minimalistic'
-require 'models/warehouse_thing'
-require 'models/parrot'
-require 'models/person'
-require 'models/edge'
-require 'models/joke'
-require 'models/bird'
-require 'models/car'
-require 'models/bulb'
-require 'rexml/document'
+require "models/post"
+require "models/author"
+require "models/topic"
+require "models/reply"
+require "models/category"
+require "models/categorization"
+require "models/company"
+require "models/customer"
+require "models/developer"
+require "models/computer"
+require "models/project"
+require "models/default"
+require "models/auto_id"
+require "models/column_name"
+require "models/subscriber"
+require "models/comment"
+require "models/minimalistic"
+require "models/warehouse_thing"
+require "models/parrot"
+require "models/person"
+require "models/edge"
+require "models/joke"
+require "models/bird"
+require "models/car"
+require "models/bulb"
+require "concurrent/atomic/count_down_latch"
 
 class FirstAbstractClass < ActiveRecord::Base
   self.abstract_class = true
@@ -37,8 +35,6 @@ class SecondAbstractClass < FirstAbstractClass
   self.abstract_class = true
 end
 class Photo < SecondAbstractClass; end
-class Category < ActiveRecord::Base; end
-class Categorization < ActiveRecord::Base; end
 class Smarts < ActiveRecord::Base; end
 class CreditCard < ActiveRecord::Base
   class PinNumber < ActiveRecord::Base
@@ -49,8 +45,6 @@ class CreditCard < ActiveRecord::Base
   class Brand < Category; end
 end
 class MasterCreditCard < ActiveRecord::Base; end
-class Post < ActiveRecord::Base; end
-class Computer < ActiveRecord::Base; end
 class NonExistentTable < ActiveRecord::Base; end
 class TestOracleDefault < ActiveRecord::Base; end
 
@@ -60,12 +54,6 @@ end
 
 class Weird < ActiveRecord::Base; end
 
-class Boolean < ActiveRecord::Base
-  def has_fun
-    super
-  end
-end
-
 class LintTest < ActiveRecord::TestCase
   include ActiveModel::Lint::Tests
 
@@ -77,18 +65,17 @@ class LintTest < ActiveRecord::TestCase
 end
 
 class BasicsTest < ActiveRecord::TestCase
-  fixtures :topics, :companies, :developers, :projects, :computers, :accounts, :minimalistics, 'warehouse-things', :authors, :categorizations, :categories, :posts
+  fixtures :topics, :companies, :developers, :projects, :computers, :accounts, :minimalistics, "warehouse-things", :authors, :author_addresses, :categorizations, :categories, :posts
 
   def test_column_names_are_escaped
     conn      = ActiveRecord::Base.connection
     classname = conn.class.name[/[^:]*$/]
     badchar   = {
-      'SQLite3Adapter'    => '"',
-      'MysqlAdapter'      => '`',
-      'Mysql2Adapter'     => '`',
-      'PostgreSQLAdapter' => '"',
-      'OracleAdapter'     => '"',
-      'FbAdapter'         => '"'
+      "SQLite3Adapter"    => '"',
+      "Mysql2Adapter"     => "`",
+      "PostgreSQLAdapter" => '"',
+      "OracleAdapter"     => '"',
+      "FbAdapter"         => '"'
     }.fetch(classname) {
       raise "need a bad char for #{classname}"
     }
@@ -105,17 +92,25 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_columns_should_obey_set_primary_key
     pk = Subscriber.columns_hash[Subscriber.primary_key]
-    assert_equal 'nick', pk.name, 'nick should be primary key'
+    assert_equal "nick", pk.name, "nick should be primary key"
   end
 
   def test_primary_key_with_no_id
     assert_nil Edge.primary_key
   end
 
-  unless current_adapter?(:PostgreSQLAdapter, :OracleAdapter, :SQLServerAdapter, :FbAdapter)
-    def test_limit_with_comma
-      assert Topic.limit("1,2").to_a
-    end
+  def test_primary_key_and_references_columns_should_be_identical_type
+    pk = Author.columns_hash["id"]
+    ref = Post.columns_hash["author_id"]
+
+    assert_equal pk.sql_type, ref.sql_type
+  end
+
+  def test_many_mutations
+    car = Car.new name: "<3<3<3"
+    car.engines_count = 0
+    20_000.times { car.engines_count += 1 }
+    assert car.save
   end
 
   def test_limit_without_comma
@@ -145,20 +140,14 @@ class BasicsTest < ActiveRecord::TestCase
     end
   end
 
-  unless current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-    def test_limit_should_allow_sql_literal
-      assert_equal 1, Topic.limit(Arel.sql('2-1')).to_a.length
-    end
-  end
-
   def test_select_symbol
     topic_ids = Topic.select(:id).map(&:id).sort
     assert_equal Topic.pluck(:id).sort, topic_ids
   end
 
   def test_table_exists
-    assert !NonExistentTable.table_exists?
-    assert Topic.table_exists?
+    assert_not_predicate NonExistentTable, :table_exists?
+    assert_predicate Topic, :table_exists?
   end
 
   def test_preserving_date_objects
@@ -171,17 +160,17 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_previously_changed
     topic = Topic.first
-    topic.title = '<3<3<3'
+    topic.title = "<3<3<3"
     assert_equal({}, topic.previous_changes)
 
     topic.save!
     expected = ["The First Topic", "<3<3<3"]
-    assert_equal(expected, topic.previous_changes['title'])
+    assert_equal(expected, topic.previous_changes["title"])
   end
 
   def test_previously_changed_dup
     topic = Topic.first
-    topic.title = '<3<3<3'
+    topic.title = "<3<3<3"
     topic.save!
 
     t2 = topic.dup
@@ -206,7 +195,7 @@ class BasicsTest < ActiveRecord::TestCase
     )
 
     # For adapters which support microsecond resolution.
-    if current_adapter?(:PostgreSQLAdapter, :SQLite3Adapter) || mysql_56?
+    if subsecond_precision_supported?
       assert_equal 11, Topic.find(1).written_on.sec
       assert_equal 223300, Topic.find(1).written_on.usec
       assert_equal 9900, Topic.find(2).written_on.usec
@@ -215,10 +204,10 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_preserving_time_objects_with_local_time_conversion_to_default_timezone_utc
-    with_env_tz 'America/New_York' do
+    with_env_tz eastern_time_zone do
       with_timezone_config default: :utc do
         time = Time.local(2000)
-        topic = Topic.create('written_on' => time)
+        topic = Topic.create("written_on" => time)
         saved_time = Topic.find(topic.id).reload.written_on
         assert_equal time, saved_time
         assert_equal [0, 0, 0, 1, 1, 2000, 6, 1, false, "EST"], time.to_a
@@ -228,11 +217,11 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_preserving_time_objects_with_time_with_zone_conversion_to_default_timezone_utc
-    with_env_tz 'America/New_York' do
+    with_env_tz eastern_time_zone do
       with_timezone_config default: :utc do
-        Time.use_zone 'Central Time (US & Canada)' do
+        Time.use_zone "Central Time (US & Canada)" do
           time = Time.zone.local(2000)
-          topic = Topic.create('written_on' => time)
+          topic = Topic.create("written_on" => time)
           saved_time = Topic.find(topic.id).reload.written_on
           assert_equal time, saved_time
           assert_equal [0, 0, 0, 1, 1, 2000, 6, 1, false, "CST"], time.to_a
@@ -243,10 +232,10 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_preserving_time_objects_with_utc_time_conversion_to_default_timezone_local
-    with_env_tz 'America/New_York' do
+    with_env_tz eastern_time_zone do
       with_timezone_config default: :local do
         time = Time.utc(2000)
-        topic = Topic.create('written_on' => time)
+        topic = Topic.create("written_on" => time)
         saved_time = Topic.find(topic.id).reload.written_on
         assert_equal time, saved_time
         assert_equal [0, 0, 0, 1, 1, 2000, 6, 1, false, "UTC"], time.to_a
@@ -256,11 +245,11 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_preserving_time_objects_with_time_with_zone_conversion_to_default_timezone_local
-    with_env_tz 'America/New_York' do
+    with_env_tz eastern_time_zone do
       with_timezone_config default: :local do
-        Time.use_zone 'Central Time (US & Canada)' do
+        Time.use_zone "Central Time (US & Canada)" do
           time = Time.zone.local(2000)
-          topic = Topic.create('written_on' => time)
+          topic = Topic.create("written_on" => time)
           saved_time = Topic.find(topic.id).reload.written_on
           assert_equal time, saved_time
           assert_equal [0, 0, 0, 1, 1, 2000, 6, 1, false, "CST"], time.to_a
@@ -270,6 +259,14 @@ class BasicsTest < ActiveRecord::TestCase
     end
   end
 
+  def eastern_time_zone
+    if Gem.win_platform?
+      "EST5EDT"
+    else
+      "America/New_York"
+    end
+  end
+
   def test_custom_mutator
     topic = Topic.find(1)
     # This mutator is protected in the class definition
@@ -278,49 +275,50 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_initialize_with_attributes
-    topic = Topic.new({
-      "title" => "initialized from attributes", "written_on" => "2003-12-12 23:23"
-    })
+    topic = Topic.new(
+      "title" => "initialized from attributes", "written_on" => "2003-12-12 23:23")
 
     assert_equal("initialized from attributes", topic.title)
   end
 
   def test_initialize_with_invalid_attribute
-    Topic.new({ "title" => "test",
-      "last_read(1i)" => "2005", "last_read(2i)" => "2", "last_read(3i)" => "31"})
-  rescue ActiveRecord::MultiparameterAssignmentErrors => ex
+    ex = assert_raise(ActiveRecord::MultiparameterAssignmentErrors) do
+      Topic.new("title" => "test",
+        "written_on(4i)" => "16", "written_on(5i)" => "24", "written_on(6i)" => "00")
+    end
+
     assert_equal(1, ex.errors.size)
-    assert_equal("last_read", ex.errors[0].attribute)
+    assert_equal("written_on", ex.errors[0].attribute)
   end
 
   def test_create_after_initialize_without_block
-    cb = CustomBulb.create(:name => 'Dude')
-    assert_equal('Dude', cb.name)
+    cb = CustomBulb.create(name: "Dude")
+    assert_equal("Dude", cb.name)
     assert_equal(true, cb.frickinawesome)
   end
 
   def test_create_after_initialize_with_block
-    cb = CustomBulb.create {|c| c.name = 'Dude' }
-    assert_equal('Dude', cb.name)
+    cb = CustomBulb.create { |c| c.name = "Dude" }
+    assert_equal("Dude", cb.name)
     assert_equal(true, cb.frickinawesome)
   end
 
   def test_create_after_initialize_with_array_param
-    cbs = CustomBulb.create([{ name: 'Dude' }, { name: 'Bob' }])
-    assert_equal 'Dude', cbs[0].name
-    assert_equal 'Bob', cbs[1].name
+    cbs = CustomBulb.create([{ name: "Dude" }, { name: "Bob" }])
+    assert_equal "Dude", cbs[0].name
+    assert_equal "Bob", cbs[1].name
     assert cbs[0].frickinawesome
-    assert !cbs[1].frickinawesome
+    assert_not cbs[1].frickinawesome
   end
 
   def test_load
-    topics = Topic.all.merge!(:order => 'id').to_a
+    topics = Topic.all.merge!(order: "id").to_a
     assert_equal(5, topics.size)
     assert_equal(topics(:first).title, topics.first.title)
   end
 
   def test_load_with_condition
-    topics = Topic.all.merge!(:where => "author_name = 'Mary'").to_a
+    topics = Topic.all.merge!(where: "author_name = 'Mary'").to_a
 
     assert_equal(1, topics.size)
     assert_equal(topics(:second).title, topics.first.title)
@@ -440,9 +438,9 @@ class BasicsTest < ActiveRecord::TestCase
     Post.reset_table_name
   end
 
-  if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+  if current_adapter?(:Mysql2Adapter)
     def test_update_all_with_order_and_limit
-      assert_equal 1, Topic.limit(1).order('id DESC').update_all(:content => 'bulk updated!')
+      assert_equal 1, Topic.limit(1).order("id DESC").update_all(content: "bulk updated!")
     end
   end
 
@@ -453,7 +451,7 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_default_values
     topic = Topic.new
-    assert topic.approved?
+    assert_predicate topic, :approved?
     assert_nil topic.written_on
     assert_nil topic.bonus_time
     assert_nil topic.last_read
@@ -461,7 +459,7 @@ class BasicsTest < ActiveRecord::TestCase
     topic.save
 
     topic = Topic.find(topic.id)
-    assert topic.approved?
+    assert_predicate topic, :approved?
     assert_nil topic.last_read
 
     # Oracle has some funky default handling, so it requires a bit of
@@ -487,12 +485,12 @@ class BasicsTest < ActiveRecord::TestCase
 
     def test_utc_as_time_zone_and_new
       with_timezone_config default: :utc do
-        attributes = { "bonus_time(1i)"=>"2000",
-          "bonus_time(2i)"=>"1",
-          "bonus_time(3i)"=>"1",
-          "bonus_time(4i)"=>"10",
-          "bonus_time(5i)"=>"35",
-          "bonus_time(6i)"=>"50" }
+        attributes = { "bonus_time(1i)" => "2000",
+          "bonus_time(2i)" => "1",
+          "bonus_time(3i)" => "1",
+          "bonus_time(4i)" => "10",
+          "bonus_time(5i)" => "35",
+          "bonus_time(6i)" => "50" }
         topic = Topic.new(attributes)
         assert_equal Time.utc(2000, 1, 1, 10, 35, 50), topic.bonus_time
       end
@@ -517,15 +515,16 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_find_by_slug
-    assert_equal Topic.find('1-meowmeow'), Topic.find(1)
+    assert_equal Topic.find("1-meowmeow"), Topic.find(1)
   end
 
   def test_find_by_slug_with_array
-    assert_equal Topic.find(['1-meowmeow', '2-hello']), Topic.find([1, 2])
+    assert_equal Topic.find([1, 2]), Topic.find(["1-meowmeow", "2-hello"])
+    assert_equal "The Second Topic of the day", Topic.find(["2-hello", "1-meowmeow"]).first.title
   end
 
   def test_find_by_slug_with_range
-    assert_equal Topic.where(id: '1-meowmeow'..'2-hello'), Topic.where(id: 1..2)
+    assert_equal Topic.where(id: "1-meowmeow".."2-hello"), Topic.where(id: 1..2)
   end
 
   def test_equality_of_new_records
@@ -534,7 +533,7 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_equality_of_destroyed_records
-    topic_1 = Topic.new(:title => 'test_1')
+    topic_1 = Topic.new(title: "test_1")
     topic_1.save
     topic_2 = Topic.find(topic_1.id)
     topic_1.destroy
@@ -543,8 +542,8 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_equality_with_blank_ids
-    one = Subscriber.new(:id => '')
-    two = Subscriber.new(:id => '')
+    one = Subscriber.new(id: "")
+    two = Subscriber.new(id: "")
     assert_equal one, two
   end
 
@@ -553,8 +552,8 @@ class BasicsTest < ActiveRecord::TestCase
     car.bulbs.build
     car.save
 
-    assert car.bulbs == Bulb.where(car_id: car.id), 'CollectionProxy should be comparable with Relation'
-    assert Bulb.where(car_id: car.id) == car.bulbs, 'Relation should be comparable with CollectionProxy'
+    assert car.bulbs == Bulb.where(car_id: car.id), "CollectionProxy should be comparable with Relation"
+    assert Bulb.where(car_id: car.id) == car.bulbs, "Relation should be comparable with CollectionProxy"
   end
 
   def test_equality_of_relation_and_array
@@ -562,7 +561,7 @@ class BasicsTest < ActiveRecord::TestCase
     car.bulbs.build
     car.save
 
-    assert Bulb.where(car_id: car.id) == car.bulbs.to_a, 'Relation should be comparable with Array'
+    assert Bulb.where(car_id: car.id) == car.bulbs.to_a, "Relation should be comparable with Array"
   end
 
   def test_equality_of_relation_and_association_relation
@@ -570,8 +569,8 @@ class BasicsTest < ActiveRecord::TestCase
     car.bulbs.build
     car.save
 
-    assert_equal Bulb.where(car_id: car.id), car.bulbs.includes(:car), 'Relation should be comparable with AssociationRelation'
-    assert_equal car.bulbs.includes(:car), Bulb.where(car_id: car.id), 'AssociationRelation should be comparable with Relation'
+    assert_equal Bulb.where(car_id: car.id), car.bulbs.includes(:car), "Relation should be comparable with AssociationRelation"
+    assert_equal car.bulbs.includes(:car), Bulb.where(car_id: car.id), "AssociationRelation should be comparable with Relation"
   end
 
   def test_equality_of_collection_proxy_and_association_relation
@@ -579,8 +578,8 @@ class BasicsTest < ActiveRecord::TestCase
     car.bulbs.build
     car.save
 
-    assert_equal car.bulbs, car.bulbs.includes(:car), 'CollectionProxy should be comparable with AssociationRelation'
-    assert_equal car.bulbs.includes(:car), car.bulbs, 'AssociationRelation should be comparable with CollectionProxy'
+    assert_equal car.bulbs, car.bulbs.includes(:car), "CollectionProxy should be comparable with AssociationRelation"
+    assert_equal car.bulbs.includes(:car), car.bulbs, "AssociationRelation should be comparable with CollectionProxy"
   end
 
   def test_hashing
@@ -602,24 +601,24 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_create_without_prepared_statement
     topic = Topic.connection.unprepared_statement do
-      Topic.create(:title => 'foo')
+      Topic.create(title: "foo")
     end
 
     assert_equal topic, Topic.find(topic.id)
   end
 
   def test_destroy_without_prepared_statement
-    topic = Topic.create(title: 'foo')
+    topic = Topic.create(title: "foo")
     Topic.connection.unprepared_statement do
       Topic.find(topic.id).destroy
     end
 
-    assert_equal nil, Topic.find_by_id(topic.id)
+    assert_nil Topic.find_by_id(topic.id)
   end
 
   def test_comparison_with_different_objects
     topic = Topic.create
-    category = Category.create(:name => "comparison")
+    category = Category.create(name: "comparison")
     assert_nil topic <=> category
   end
 
@@ -631,9 +630,9 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_readonly_attributes
-    assert_equal Set.new([ 'title' , 'comments_count' ]), ReadonlyTitlePost.readonly_attributes
+    assert_equal Set.new([ "title", "comments_count" ]), ReadonlyTitlePost.readonly_attributes
 
-    post = ReadonlyTitlePost.create(:title => "cannot change this", :body => "changeable")
+    post = ReadonlyTitlePost.create(title: "cannot change this", body: "changeable")
     post.reload
     assert_equal "cannot change this", post.title
 
@@ -645,8 +644,8 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_unicode_column_name
     Weird.reset_column_information
-    weird = Weird.create(:なまえ => 'たこ焼き仮面')
-    assert_equal 'たこ焼き仮面', weird.なまえ
+    weird = Weird.create(なまえ: "たこ焼き仮面")
+    assert_equal "たこ焼き仮面", weird.なまえ
   end
 
   unless current_adapter?(:PostgreSQLAdapter)
@@ -656,7 +655,7 @@ class BasicsTest < ActiveRecord::TestCase
 
       Weird.reset_column_information
 
-      assert_equal ["EUC-JP"], Weird.columns.map {|c| c.name.encoding.name }.uniq
+      assert_equal ["EUC-JP"], Weird.columns.map { |c| c.name.encoding.name }.uniq
     ensure
       silence_warnings { Encoding.default_internal = old_default_internal }
       Weird.reset_column_information
@@ -664,21 +663,21 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_non_valid_identifier_column_name
-    weird = Weird.create('a$b' => 'value')
+    weird = Weird.create("a$b" => "value")
     weird.reload
-    assert_equal 'value', weird.send('a$b')
-    assert_equal 'value', weird.read_attribute('a$b')
+    assert_equal "value", weird.send("a$b")
+    assert_equal "value", weird.read_attribute("a$b")
 
-    weird.update_columns('a$b' => 'value2')
+    weird.update_columns("a$b" => "value2")
     weird.reload
-    assert_equal 'value2', weird.send('a$b')
-    assert_equal 'value2', weird.read_attribute('a$b')
+    assert_equal "value2", weird.send("a$b")
+    assert_equal "value2", weird.read_attribute("a$b")
   end
 
   def test_group_weirds_by_from
-    Weird.create('a$b' => 'value', :from => 'aaron')
+    Weird.create("a$b" => "value", :from => "aaron")
     count = Weird.group(Weird.arel_table[:from]).count
-    assert_equal 1, count['aaron']
+    assert_equal 1, count["aaron"]
   end
 
   def test_attributes_on_dummy_time
@@ -707,46 +706,15 @@ class BasicsTest < ActiveRecord::TestCase
     assert_nil topic.bonus_time
   end
 
-  def test_boolean
-    b_nil = Boolean.create({ "value" => nil })
-    nil_id = b_nil.id
-    b_false = Boolean.create({ "value" => false })
-    false_id = b_false.id
-    b_true = Boolean.create({ "value" => true })
-    true_id = b_true.id
-
-    b_nil = Boolean.find(nil_id)
-    assert_nil b_nil.value
-    b_false = Boolean.find(false_id)
-    assert !b_false.value?
-    b_true = Boolean.find(true_id)
-    assert b_true.value?
-  end
-
-  def test_boolean_without_questionmark
-    b_true = Boolean.create({ "value" => true })
-    true_id = b_true.id
+  def test_attributes
+    category = Category.new(name: "Ruby")
 
-    subclass   = Class.new(Boolean).find true_id
-    superclass = Boolean.find true_id
+    expected_attributes = category.attribute_names.map do |attribute_name|
+      [attribute_name, category.public_send(attribute_name)]
+    end.to_h
 
-    assert_equal superclass.read_attribute(:has_fun), subclass.read_attribute(:has_fun)
-  end
-
-  def test_boolean_cast_from_string
-    b_blank = Boolean.create({ "value" => "" })
-    blank_id = b_blank.id
-    b_false = Boolean.create({ "value" => "0" })
-    false_id = b_false.id
-    b_true = Boolean.create({ "value" => "1" })
-    true_id = b_true.id
-
-    b_blank = Boolean.find(blank_id)
-    assert_nil b_blank.value
-    b_false = Boolean.find(false_id)
-    assert !b_false.value?
-    b_true = Boolean.find(true_id)
-    assert b_true.value?
+    assert_instance_of Hash, category.attributes
+    assert_equal expected_attributes, category.attributes
   end
 
   def test_new_record_returns_boolean
@@ -759,7 +727,7 @@ class BasicsTest < ActiveRecord::TestCase
     duped_topic = nil
     assert_nothing_raised { duped_topic = topic.dup }
     assert_equal topic.title, duped_topic.title
-    assert !duped_topic.persisted?
+    assert_not_predicate duped_topic, :persisted?
 
     # test if the attributes have been duped
     topic.title = "a"
@@ -777,7 +745,7 @@ class BasicsTest < ActiveRecord::TestCase
 
     # test if saved clone object differs from original
     duped_topic.save
-    assert duped_topic.persisted?
+    assert_predicate duped_topic, :persisted?
     assert_not_equal duped_topic.id, topic.id
 
     duped_topic.reload
@@ -787,8 +755,8 @@ class BasicsTest < ActiveRecord::TestCase
   DeveloperSalary = Struct.new(:amount)
   def test_dup_with_aggregate_of_same_name_as_attribute
     developer_with_aggregate = Class.new(ActiveRecord::Base) do
-      self.table_name = 'developers'
-      composed_of :salary, :class_name => 'BasicsTest::DeveloperSalary', :mapping => [%w(salary amount)]
+      self.table_name = "developers"
+      composed_of :salary, class_name: "BasicsTest::DeveloperSalary", mapping: [%w(salary amount)]
     end
 
     dev = developer_with_aggregate.find(1)
@@ -798,15 +766,15 @@ class BasicsTest < ActiveRecord::TestCase
     assert_nothing_raised { dup = dev.dup }
     assert_kind_of DeveloperSalary, dup.salary
     assert_equal dev.salary.amount, dup.salary.amount
-    assert !dup.persisted?
+    assert_not_predicate dup, :persisted?
 
-    # test if the attributes have been dupd
+    # test if the attributes have been duped
     original_amount = dup.salary.amount
     dev.salary.amount = 1
     assert_equal original_amount, dup.salary.amount
 
     assert dup.save
-    assert dup.persisted?
+    assert_predicate dup, :persisted?
     assert_not_equal dup.id, dev.id
   end
 
@@ -826,126 +794,87 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_clone_of_new_object_with_defaults
     developer = Developer.new
-    assert !developer.name_changed?
-    assert !developer.salary_changed?
+    assert_not_predicate developer, :name_changed?
+    assert_not_predicate developer, :salary_changed?
 
     cloned_developer = developer.clone
-    assert !cloned_developer.name_changed?
-    assert !cloned_developer.salary_changed?
+    assert_not_predicate cloned_developer, :name_changed?
+    assert_not_predicate cloned_developer, :salary_changed?
   end
 
   def test_clone_of_new_object_marks_attributes_as_dirty
-    developer = Developer.new :name => 'Bjorn', :salary => 100000
-    assert developer.name_changed?
-    assert developer.salary_changed?
+    developer = Developer.new name: "Bjorn", salary: 100000
+    assert_predicate developer, :name_changed?
+    assert_predicate developer, :salary_changed?
 
     cloned_developer = developer.clone
-    assert cloned_developer.name_changed?
-    assert cloned_developer.salary_changed?
+    assert_predicate cloned_developer, :name_changed?
+    assert_predicate cloned_developer, :salary_changed?
   end
 
   def test_clone_of_new_object_marks_as_dirty_only_changed_attributes
-    developer = Developer.new :name => 'Bjorn'
+    developer = Developer.new name: "Bjorn"
     assert developer.name_changed?            # obviously
-    assert !developer.salary_changed?         # attribute has non-nil default value, so treated as not changed
+    assert_not developer.salary_changed?         # attribute has non-nil default value, so treated as not changed
 
     cloned_developer = developer.clone
-    assert cloned_developer.name_changed?
-    assert !cloned_developer.salary_changed?  # ... and cloned instance should behave same
+    assert_predicate cloned_developer, :name_changed?
+    assert_not cloned_developer.salary_changed?  # ... and cloned instance should behave same
   end
 
   def test_dup_of_saved_object_marks_attributes_as_dirty
-    developer = Developer.create! :name => 'Bjorn', :salary => 100000
-    assert !developer.name_changed?
-    assert !developer.salary_changed?
+    developer = Developer.create! name: "Bjorn", salary: 100000
+    assert_not_predicate developer, :name_changed?
+    assert_not_predicate developer, :salary_changed?
 
     cloned_developer = developer.dup
     assert cloned_developer.name_changed?     # both attributes differ from defaults
-    assert cloned_developer.salary_changed?
+    assert_predicate cloned_developer, :salary_changed?
   end
 
   def test_dup_of_saved_object_marks_as_dirty_only_changed_attributes
-    developer = Developer.create! :name => 'Bjorn'
-    assert !developer.name_changed?           # both attributes of saved object should be treated as not changed
-    assert !developer.salary_changed?
+    developer = Developer.create! name: "Bjorn"
+    assert_not developer.name_changed?           # both attributes of saved object should be treated as not changed
+    assert_not_predicate developer, :salary_changed?
 
     cloned_developer = developer.dup
     assert cloned_developer.name_changed?     # ... but on cloned object should be
-    assert !cloned_developer.salary_changed?  # ... BUT salary has non-nil default which should be treated as not changed on cloned instance
+    assert_not cloned_developer.salary_changed?  # ... BUT salary has non-nil default which should be treated as not changed on cloned instance
   end
 
   def test_bignum
     company = Company.find(1)
-    company.rating = 2147483647
+    company.rating = 2147483648
     company.save
     company = Company.find(1)
-    assert_equal 2147483647, company.rating
+    assert_equal 2147483648, company.rating
   end
 
-  # TODO: extend defaults tests to other databases!
-  if current_adapter?(:PostgreSQLAdapter)
+  def test_bignum_pk
+    company = Company.create!(id: 2147483648, name: "foo")
+    assert_equal company, Company.find(company.id)
+  end
+
+  if current_adapter?(:PostgreSQLAdapter, :Mysql2Adapter, :SQLite3Adapter)
     def test_default
       with_timezone_config default: :local do
         default = Default.new
 
         # fixed dates / times
         assert_equal Date.new(2004, 1, 1), default.fixed_date
-        assert_equal Time.local(2004, 1,1,0,0,0,0), default.fixed_time
+        assert_equal Time.local(2004, 1, 1, 0, 0, 0, 0), default.fixed_time
 
         # char types
-        assert_equal 'Y', default.char1
-        assert_equal 'a varchar field', default.char2
-        assert_equal 'a text field', default.char3
+        assert_equal "Y", default.char1
+        assert_equal "a varchar field", default.char2
+        # Mysql text type can't have default value
+        unless current_adapter?(:Mysql2Adapter)
+          assert_equal "a text field", default.char3
+        end
       end
     end
   end
 
-  class NumericData < ActiveRecord::Base
-    self.table_name = 'numeric_data'
-
-    attribute :my_house_population, :integer
-    attribute :atoms_in_universe, :integer
-  end
-
-  def test_big_decimal_conditions
-    m = NumericData.new(
-      :bank_balance => 1586.43,
-      :big_bank_balance => BigDecimal("1000234000567.95"),
-      :world_population => 6000000000,
-      :my_house_population => 3
-    )
-    assert m.save
-    assert_equal 0, NumericData.where("bank_balance > ?", 2000.0).count
-  end
-
-  def test_numeric_fields
-    m = NumericData.new(
-      :bank_balance => 1586.43,
-      :big_bank_balance => BigDecimal("1000234000567.95"),
-      :world_population => 6000000000,
-      :my_house_population => 3
-    )
-    assert m.save
-
-    m1 = NumericData.find(m.id)
-    assert_not_nil m1
-
-    # As with migration_test.rb, we should make world_population >= 2**62
-    # to cover 64-bit platforms and test it is a Bignum, but the main thing
-    # is that it's an Integer.
-    assert_kind_of Integer, m1.world_population
-    assert_equal 6000000000, m1.world_population
-
-    assert_kind_of Fixnum, m1.my_house_population
-    assert_equal 3, m1.my_house_population
-
-    assert_kind_of BigDecimal, m1.bank_balance
-    assert_equal BigDecimal("1586.43"), m1.bank_balance
-
-    assert_kind_of BigDecimal, m1.big_bank_balance
-    assert_equal BigDecimal("1000234000567.95"), m1.big_bank_balance
-  end
-
   def test_auto_id
     auto = AutoId.new
     auto.save
@@ -969,28 +898,28 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_quoting_arrays
-    replies = Reply.all.merge!(:where => [ "id IN (?)", topics(:first).replies.collect(&:id) ]).to_a
+    replies = Reply.all.merge!(where: [ "id IN (?)", topics(:first).replies.collect(&:id) ]).to_a
     assert_equal topics(:first).replies.size, replies.size
 
-    replies = Reply.all.merge!(:where => [ "id IN (?)", [] ]).to_a
+    replies = Reply.all.merge!(where: [ "id IN (?)", [] ]).to_a
     assert_equal 0, replies.size
   end
 
   def test_quote
     author_name = "\\ \001 ' \n \\n \""
-    topic = Topic.create('author_name' => author_name)
+    topic = Topic.create("author_name" => author_name)
     assert_equal author_name, Topic.find(topic.id).author_name
   end
 
   def test_toggle_attribute
-    assert !topics(:first).approved?
+    assert_not_predicate topics(:first), :approved?
     topics(:first).toggle!(:approved)
-    assert topics(:first).approved?
+    assert_predicate topics(:first), :approved?
     topic = topics(:first)
     topic.toggle(:approved)
-    assert !topic.approved?
+    assert_not_predicate topic, :approved?
     topic.reload
-    assert topic.approved?
+    assert_predicate topic, :approved?
   end
 
   def test_reload
@@ -1002,12 +931,6 @@ class BasicsTest < ActiveRecord::TestCase
     assert_equal t1.title, t2.title
   end
 
-  def test_reload_with_exclusive_scope
-    dev = DeveloperCalledDavid.first
-    dev.update!(name: "NotDavid" )
-    assert_equal dev, dev.reload
-  end
-
   def test_switching_between_table_name
     k = Class.new(Joke)
 
@@ -1020,7 +943,7 @@ class BasicsTest < ActiveRecord::TestCase
     end
   end
 
-  def test_clear_cash_when_setting_table_name
+  def test_clear_cache_when_setting_table_name
     original_table_name = Joke.table_name
 
     Joke.table_name = "funny_jokes"
@@ -1063,7 +986,7 @@ class BasicsTest < ActiveRecord::TestCase
   def test_set_table_name_symbol_converted_to_string
     k = Class.new(Joke)
     k.table_name = :cold_jokes
-    assert_equal 'cold_jokes', k.table_name
+    assert_equal "cold_jokes", k.table_name
   end
 
   def test_quoted_table_name_after_set_table_name
@@ -1079,7 +1002,7 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_set_table_name_with_inheritance
-    k = Class.new( ActiveRecord::Base )
+    k = Class.new(ActiveRecord::Base)
     def k.name; "Foo"; end
     def k.table_name; super + "ks"; end
     assert_equal "foosks", k.table_name
@@ -1097,45 +1020,31 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_count_with_join
     res = Post.count_by_sql "SELECT COUNT(*) FROM posts LEFT JOIN comments ON posts.id=comments.post_id WHERE posts.#{QUOTED_TYPE} = 'Post'"
-
     res2 = Post.where("posts.#{QUOTED_TYPE} = 'Post'").joins("LEFT JOIN comments ON posts.id=comments.post_id").count
     assert_equal res, res2
 
-    res3 = nil
-    assert_nothing_raised do
-      res3 = Post.where("posts.#{QUOTED_TYPE} = 'Post'").joins("LEFT JOIN comments ON posts.id=comments.post_id").count
-    end
-    assert_equal res, res3
-
     res4 = Post.count_by_sql "SELECT COUNT(p.id) FROM posts p, comments co WHERE p.#{QUOTED_TYPE} = 'Post' AND p.id=co.post_id"
-    res5 = nil
-    assert_nothing_raised do
-      res5 = Post.where("p.#{QUOTED_TYPE} = 'Post' AND p.id=co.post_id").joins("p, comments co").select("p.id").count
-    end
-
+    res5 = Post.where("p.#{QUOTED_TYPE} = 'Post' AND p.id=co.post_id").joins("p, comments co").select("p.id").count
     assert_equal res4, res5
 
     res6 = Post.count_by_sql "SELECT COUNT(DISTINCT p.id) FROM posts p, comments co WHERE p.#{QUOTED_TYPE} = 'Post' AND p.id=co.post_id"
-    res7 = nil
-    assert_nothing_raised do
-      res7 = Post.where("p.#{QUOTED_TYPE} = 'Post' AND p.id=co.post_id").joins("p, comments co").select("p.id").distinct.count
-    end
+    res7 = Post.where("p.#{QUOTED_TYPE} = 'Post' AND p.id=co.post_id").joins("p, comments co").select("p.id").distinct.count
     assert_equal res6, res7
   end
 
   def test_no_limit_offset
     assert_nothing_raised do
-      Developer.all.merge!(:offset => 2).to_a
+      Developer.all.merge!(offset: 2).to_a
     end
   end
 
   def test_find_last
-    last  = Developer.last
-    assert_equal last, Developer.all.merge!(:order => 'id desc').first
+    last = Developer.last
+    assert_equal last, Developer.all.merge!(order: "id desc").first
   end
 
   def test_last
-    assert_equal Developer.all.merge!(:order => 'id desc').first, Developer.last
+    assert_equal Developer.all.merge!(order: "id desc").first, Developer.last
   end
 
   def test_all
@@ -1145,80 +1054,48 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_all_with_conditions
-    assert_equal Developer.all.merge!(:order => 'id desc').to_a, Developer.order('id desc').to_a
+    assert_equal Developer.all.merge!(order: "id desc").to_a, Developer.order("id desc").to_a
   end
 
   def test_find_ordered_last
-    last  = Developer.all.merge!(:order => 'developers.salary ASC').last
-    assert_equal last, Developer.all.merge!(:order => 'developers.salary ASC').to_a.last
+    last = Developer.all.merge!(order: "developers.salary ASC").last
+    assert_equal last, Developer.all.merge!(order: "developers.salary ASC").to_a.last
   end
 
   def test_find_reverse_ordered_last
-    last  = Developer.all.merge!(:order => 'developers.salary DESC').last
-    assert_equal last, Developer.all.merge!(:order => 'developers.salary DESC').to_a.last
+    last = Developer.all.merge!(order: "developers.salary DESC").last
+    assert_equal last, Developer.all.merge!(order: "developers.salary DESC").to_a.last
   end
 
   def test_find_multiple_ordered_last
-    last  = Developer.all.merge!(:order => 'developers.name, developers.salary DESC').last
-    assert_equal last, Developer.all.merge!(:order => 'developers.name, developers.salary DESC').to_a.last
+    last = Developer.all.merge!(order: "developers.name, developers.salary DESC").last
+    assert_equal last, Developer.all.merge!(order: "developers.name, developers.salary DESC").to_a.last
   end
 
   def test_find_keeps_multiple_order_values
-    combined = Developer.all.merge!(:order => 'developers.name, developers.salary').to_a
-    assert_equal combined, Developer.all.merge!(:order => ['developers.name', 'developers.salary']).to_a
+    combined = Developer.all.merge!(order: "developers.name, developers.salary").to_a
+    assert_equal combined, Developer.all.merge!(order: ["developers.name", "developers.salary"]).to_a
   end
 
   def test_find_keeps_multiple_group_values
-    combined = Developer.all.merge!(:group => 'developers.name, developers.salary, developers.id, developers.created_at, developers.updated_at, developers.created_on, developers.updated_on').to_a
-    assert_equal combined, Developer.all.merge!(:group => ['developers.name', 'developers.salary', 'developers.id', 'developers.created_at', 'developers.updated_at', 'developers.created_on', 'developers.updated_on']).to_a
+    combined = Developer.all.merge!(group: "developers.name, developers.salary, developers.id, developers.created_at, developers.updated_at, developers.created_on, developers.updated_on").to_a
+    assert_equal combined, Developer.all.merge!(group: ["developers.name", "developers.salary", "developers.id", "developers.created_at", "developers.updated_at", "developers.created_on", "developers.updated_on"]).to_a
   end
 
   def test_find_symbol_ordered_last
-    last  = Developer.all.merge!(:order => :salary).last
-    assert_equal last, Developer.all.merge!(:order => :salary).to_a.last
-  end
-
-  def test_abstract_class
-    assert !ActiveRecord::Base.abstract_class?
-    assert LoosePerson.abstract_class?
-    assert !LooseDescendant.abstract_class?
+    last = Developer.all.merge!(order: :salary).last
+    assert_equal last, Developer.all.merge!(order: :salary).to_a.last
   end
 
   def test_abstract_class_table_name
     assert_nil AbstractCompany.table_name
   end
 
-  def test_descends_from_active_record
-    assert !ActiveRecord::Base.descends_from_active_record?
-
-    # Abstract subclass of AR::Base.
-    assert LoosePerson.descends_from_active_record?
-
-    # Concrete subclass of an abstract class.
-    assert LooseDescendant.descends_from_active_record?
-
-    # Concrete subclass of AR::Base.
-    assert TightPerson.descends_from_active_record?
-
-    # Concrete subclass of a concrete class but has no type column.
-    assert TightDescendant.descends_from_active_record?
-
-    # Concrete subclass of AR::Base.
-    assert Post.descends_from_active_record?
-
-    # Abstract subclass of a concrete class which has a type column.
-    # This is pathological, as you'll never have Sub < Abstract < Concrete.
-    assert !StiPost.descends_from_active_record?
-
-    # Concrete subclasses an abstract class which has a type column.
-    assert !SubStiPost.descends_from_active_record?
-  end
-
   def test_find_on_abstract_base_class_doesnt_use_type_condition
     old_class = LooseDescendant
     Object.send :remove_const, :LooseDescendant
 
-    descendant = old_class.create! :first_name => 'bob'
+    descendant = old_class.create! first_name: "bob"
     assert_not_nil LoosePerson.find(descendant.id), "Should have found instance of LooseDescendant when finding abstract LoosePerson: #{descendant.inspect}"
   ensure
     unless Object.const_defined?(:LooseDescendant)
@@ -1227,7 +1104,7 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_assert_queries
-    query = lambda { ActiveRecord::Base.connection.execute 'select count(*) from developers' }
+    query = lambda { ActiveRecord::Base.connection.execute "select count(*) from developers" }
     assert_queries(2) { 2.times { query.call } }
     assert_queries 1, &query
     assert_no_queries { assert true }
@@ -1238,9 +1115,9 @@ class BasicsTest < ActiveRecord::TestCase
     log = StringIO.new
     ActiveRecord::Base.logger = ActiveSupport::Logger.new(log)
     ActiveRecord::Base.logger.level = Logger::WARN
-    ActiveRecord::Base.benchmark("Debug Topic Count", :level => :debug) { Topic.count }
-    ActiveRecord::Base.benchmark("Warn Topic Count",  :level => :warn)  { Topic.count }
-    ActiveRecord::Base.benchmark("Error Topic Count", :level => :error) { Topic.count }
+    ActiveRecord::Base.benchmark("Debug Topic Count", level: :debug) { Topic.count }
+    ActiveRecord::Base.benchmark("Warn Topic Count",  level: :warn)  { Topic.count }
+    ActiveRecord::Base.benchmark("Error Topic Count", level: :error) { Topic.count }
     assert_no_match(/Debug Topic Count/, log.string)
     assert_match(/Warn Topic Count/, log.string)
     assert_match(/Error Topic Count/, log.string)
@@ -1252,61 +1129,18 @@ class BasicsTest < ActiveRecord::TestCase
     original_logger = ActiveRecord::Base.logger
     log = StringIO.new
     ActiveRecord::Base.logger = ActiveSupport::Logger.new(log)
-    ActiveRecord::Base.benchmark("Logging", :level => :debug, :silence => false)  { ActiveRecord::Base.logger.debug "Quiet" }
+    ActiveRecord::Base.logger.level = Logger::DEBUG
+    ActiveRecord::Base.benchmark("Logging", level: :debug, silence: false)  { ActiveRecord::Base.logger.debug "Quiet" }
     assert_match(/Quiet/, log.string)
   ensure
     ActiveRecord::Base.logger = original_logger
   end
 
-  def test_compute_type_success
-    assert_equal Author, ActiveRecord::Base.send(:compute_type, 'Author')
-  end
-
-  def test_compute_type_nonexistent_constant
-    e = assert_raises NameError do
-      ActiveRecord::Base.send :compute_type, 'NonexistentModel'
-    end
-    assert_equal 'uninitialized constant ActiveRecord::Base::NonexistentModel', e.message
-    assert_equal 'ActiveRecord::Base::NonexistentModel', e.name
-  end
-
-  def test_compute_type_no_method_error
-    ActiveSupport::Dependencies.stubs(:safe_constantize).raises(NoMethodError)
-    assert_raises NoMethodError do
-      ActiveRecord::Base.send :compute_type, 'InvalidModel'
-    end
-  end
-
-  def test_compute_type_on_undefined_method
-    error = nil
-    begin
-      Class.new(Author) do
-        alias_method :foo, :bar
-      end
-    rescue => e
-      error = e
-    end
-
-    ActiveSupport::Dependencies.stubs(:safe_constantize).raises(e)
-
-    exception = assert_raises NameError do
-      ActiveRecord::Base.send :compute_type, 'InvalidModel'
-    end
-    assert_equal error.message, exception.message
-  end
-
-  def test_compute_type_argument_error
-    ActiveSupport::Dependencies.stubs(:safe_constantize).raises(ArgumentError)
-    assert_raises ArgumentError do
-      ActiveRecord::Base.send :compute_type, 'InvalidModel'
-    end
-  end
-
   def test_clear_cache!
     # preheat cache
-    c1 = Post.connection.schema_cache.columns('posts')
+    c1 = Post.connection.schema_cache.columns("posts")
     ActiveRecord::Base.clear_cache!
-    c2 = Post.connection.schema_cache.columns('posts')
+    c2 = Post.connection.schema_cache.columns("posts")
     c1.each_with_index do |v, i|
       assert_not_same v, c2[i]
     end
@@ -1318,17 +1152,18 @@ class BasicsTest < ActiveRecord::TestCase
     UnloadablePost.send(:current_scope=, UnloadablePost.all)
 
     UnloadablePost.unloadable
-    assert_not_nil ActiveRecord::Scoping::ScopeRegistry.value_for(:current_scope, "UnloadablePost")
+    klass = UnloadablePost
+    assert_not_nil ActiveRecord::Scoping::ScopeRegistry.value_for(:current_scope, klass)
     ActiveSupport::Dependencies.remove_unloadable_constants!
-    assert_nil ActiveRecord::Scoping::ScopeRegistry.value_for(:current_scope, "UnloadablePost")
+    assert_nil ActiveRecord::Scoping::ScopeRegistry.value_for(:current_scope, klass)
   ensure
-    Object.class_eval{ remove_const :UnloadablePost } if defined?(UnloadablePost)
+    Object.class_eval { remove_const :UnloadablePost } if defined?(UnloadablePost)
   end
 
   def test_marshal_round_trip
     expected = posts(:welcome)
     marshalled = Marshal.dump(expected)
-    actual   = Marshal.load(marshalled)
+    actual = Marshal.load(marshalled)
 
     assert_equal expected.attributes, actual.attributes
   end
@@ -1395,6 +1230,19 @@ class BasicsTest < ActiveRecord::TestCase
                  Company.attribute_names
   end
 
+  def test_has_attribute
+    assert Company.has_attribute?("id")
+    assert Company.has_attribute?("type")
+    assert Company.has_attribute?("name")
+    assert_not Company.has_attribute?("lastname")
+    assert_not Company.has_attribute?("age")
+  end
+
+  def test_has_attribute_with_symbol
+    assert Company.has_attribute?(:id)
+    assert_not Company.has_attribute?(:age)
+  end
+
   def test_attribute_names_on_table_not_exists
     assert_equal [], NonExistentTable.attribute_names
   end
@@ -1404,18 +1252,12 @@ class BasicsTest < ActiveRecord::TestCase
   end
 
   def test_touch_should_raise_error_on_a_new_object
-    company = Company.new(:rating => 1, :name => "37signals", :firm_name => "37signals")
+    company = Company.new(rating: 1, name: "37signals", firm_name: "37signals")
     assert_raises(ActiveRecord::ActiveRecordError) do
       company.touch :updated_at
     end
   end
 
-  def test_uniq_delegates_to_scoped
-    assert_deprecated do
-      assert_equal Bird.all.distinct, Bird.uniq
-    end
-  end
-
   def test_distinct_delegates_to_scoped
     assert_equal Bird.all.distinct, Bird.distinct
   end
@@ -1426,37 +1268,47 @@ class BasicsTest < ActiveRecord::TestCase
 
   def test_column_types_typecast
     topic = Topic.first
-    assert_not_equal 't.lo', topic.author_name
+    assert_not_equal "t.lo", topic.author_name
 
     attrs = topic.attributes.dup
-    attrs.delete 'id'
+    attrs.delete "id"
 
     typecast = Class.new(ActiveRecord::Type::Value) {
-      def cast value
+      def cast(value)
         "t.lo"
       end
     }
 
-    types = { 'author_name' => typecast.new }
+    types = { "author_name" => typecast.new }
     topic = Topic.instantiate(attrs, types)
 
-    assert_equal 't.lo', topic.author_name
+    assert_equal "t.lo", topic.author_name
   end
 
   def test_typecasting_aliases
-    assert_equal 10, Topic.select('10 as tenderlove').first.tenderlove
+    assert_equal 10, Topic.select("10 as tenderlove").first.tenderlove
   end
 
   def test_slice
-    company = Company.new(:rating => 1, :name => "37signals", :firm_name => "37signals")
+    company = Company.new(rating: 1, name: "37signals", firm_name: "37signals")
     hash = company.slice(:name, :rating, "arbitrary_method")
     assert_equal hash[:name], company.name
-    assert_equal hash['name'], company.name
+    assert_equal hash["name"], company.name
     assert_equal hash[:rating], company.rating
-    assert_equal hash['arbitrary_method'], company.arbitrary_method
+    assert_equal hash["arbitrary_method"], company.arbitrary_method
     assert_equal hash[:arbitrary_method], company.arbitrary_method
     assert_nil hash[:firm_name]
-    assert_nil hash['firm_name']
+    assert_nil hash["firm_name"]
+  end
+
+  def test_slice_accepts_array_argument
+    attrs = {
+      title: "slice",
+      author_name: "@Cohen-Carlisle",
+      content: "accept arrays so I don't have to splat"
+    }.with_indifferent_access
+    topic = Topic.new(attrs)
+    assert_equal attrs, topic.slice(attrs.keys)
   end
 
   def test_default_values_are_deeply_dupped
@@ -1467,7 +1319,7 @@ class BasicsTest < ActiveRecord::TestCase
 
   test "scoped can take a values hash" do
     klass = Class.new(ActiveRecord::Base)
-    assert_equal ['foo'], klass.all.merge!(select: 'foo').select_values
+    assert_equal ["foo"], klass.all.merge!(select: "foo").select_values
   end
 
   test "connection_handler can be overridden" do
@@ -1506,20 +1358,20 @@ class BasicsTest < ActiveRecord::TestCase
     orig_handler = klass.connection_handler
     new_handler = ActiveRecord::ConnectionAdapters::ConnectionHandler.new
     after_handler = nil
-    latch1 = ActiveSupport::Concurrency::Latch.new
-    latch2 = ActiveSupport::Concurrency::Latch.new
+    latch1 = Concurrent::CountDownLatch.new
+    latch2 = Concurrent::CountDownLatch.new
 
     t = Thread.new do
       klass.connection_handler = new_handler
-      latch1.release
-      latch2.await
+      latch1.count_down
+      latch2.wait
       after_handler = klass.connection_handler
     end
 
-    latch1.await
+    latch1.wait
 
     klass.connection_handler = orig_handler
-    latch2.release
+    latch2.count_down
     t.join
 
     assert_equal after_handler, new_handler
@@ -1533,13 +1385,99 @@ class BasicsTest < ActiveRecord::TestCase
     assert_not_equal Post.new.hash, Post.new.hash
   end
 
+  test "records of different classes have different hashes" do
+    assert_not_equal Post.new(id: 1).hash, Developer.new(id: 1).hash
+  end
+
   test "resetting column information doesn't remove attribute methods" do
     topic = topics(:first)
 
-    assert_not topic.id_changed?
+    assert_not_predicate topic, :id_changed?
 
     Topic.reset_column_information
 
-    assert_not topic.id_changed?
+    assert_not_predicate topic, :id_changed?
+  end
+
+  test "ignored columns are not present in columns_hash" do
+    cache_columns = Developer.connection.schema_cache.columns_hash(Developer.table_name)
+    assert_includes cache_columns.keys, "first_name"
+    assert_not_includes Developer.columns_hash.keys, "first_name"
+    assert_not_includes SubDeveloper.columns_hash.keys, "first_name"
+    assert_not_includes SymbolIgnoredDeveloper.columns_hash.keys, "first_name"
+  end
+
+  test "ignored columns have no attribute methods" do
+    assert_not_respond_to Developer.new, :first_name
+    assert_not_respond_to Developer.new, :first_name=
+    assert_not_respond_to Developer.new, :first_name?
+    assert_not_respond_to SubDeveloper.new, :first_name
+    assert_not_respond_to SubDeveloper.new, :first_name=
+    assert_not_respond_to SubDeveloper.new, :first_name?
+    assert_not_respond_to SymbolIgnoredDeveloper.new, :first_name
+    assert_not_respond_to SymbolIgnoredDeveloper.new, :first_name=
+    assert_not_respond_to SymbolIgnoredDeveloper.new, :first_name?
+  end
+
+  test "ignored columns don't prevent explicit declaration of attribute methods" do
+    assert_respond_to Developer.new, :last_name
+    assert_respond_to Developer.new, :last_name=
+    assert_respond_to Developer.new, :last_name?
+    assert_respond_to SubDeveloper.new, :last_name
+    assert_respond_to SubDeveloper.new, :last_name=
+    assert_respond_to SubDeveloper.new, :last_name?
+    assert_respond_to SymbolIgnoredDeveloper.new, :last_name
+    assert_respond_to SymbolIgnoredDeveloper.new, :last_name=
+    assert_respond_to SymbolIgnoredDeveloper.new, :last_name?
+  end
+
+  test "ignored columns are stored as an array of string" do
+    assert_equal(%w(first_name last_name), Developer.ignored_columns)
+    assert_equal(%w(first_name last_name), SymbolIgnoredDeveloper.ignored_columns)
+  end
+
+  test "when #reload called, ignored columns' attribute methods are not defined" do
+    developer = Developer.create!(name: "Developer")
+    assert_not_respond_to developer, :first_name
+    assert_not_respond_to developer, :first_name=
+
+    developer.reload
+
+    assert_not_respond_to developer, :first_name
+    assert_not_respond_to developer, :first_name=
+  end
+
+  test "ignored columns not included in SELECT" do
+    query = Developer.all.to_sql.downcase
+
+    # ignored column
+    assert_not query.include?("first_name")
+
+    # regular column
+    assert query.include?("name")
+  end
+
+  test "column names are quoted when using #from clause and model has ignored columns" do
+    assert_not_empty Developer.ignored_columns
+    query = Developer.from("developers").to_sql
+    quoted_id = "#{Developer.quoted_table_name}.#{Developer.quoted_primary_key}"
+
+    assert_match(/SELECT #{Regexp.escape(quoted_id)}.* FROM developers/, query)
+  end
+
+  test "using table name qualified column names unless having SELECT list explicitly" do
+    assert_equal developers(:david), Developer.from("developers").joins(:shared_computers).take
+  end
+
+  test "protected environments by default is an array with production" do
+    assert_equal ["production"], ActiveRecord::Base.protected_environments
+  end
+
+  def test_protected_environments_are_stored_as_an_array_of_string
+    previous_protected_environments = ActiveRecord::Base.protected_environments
+    ActiveRecord::Base.protected_environments = [:staging, "production"]
+    assert_equal ["staging", "production"], ActiveRecord::Base.protected_environments
+  ensure
+    ActiveRecord::Base.protected_environments = previous_protected_environments
   end
 end
diff --git a/activerecord/test/cases/batches_test.rb b/activerecord/test/cases/batches_test.rb
index 0791dde1f2..d21218a997 100644
--- a/activerecord/test/cases/batches_test.rb
+++ b/activerecord/test/cases/batches_test.rb
@@ -1,6 +1,9 @@
-require 'cases/helper'
-require 'models/post'
-require 'models/subscriber'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/comment"
+require "models/post"
+require "models/subscriber"
 
 class EachTest < ActiveRecord::TestCase
   fixtures :posts, :subscribers
@@ -8,12 +11,12 @@ class EachTest < ActiveRecord::TestCase
   def setup
     @posts = Post.order("id asc")
     @total = Post.count
-    Post.count('id') # preheat arel's table cache
+    Post.count("id") # preheat arel's table cache
   end
 
   def test_each_should_execute_one_query_per_batch
     assert_queries(@total + 1) do
-      Post.find_each(:batch_size => 1) do |post|
+      Post.find_each(batch_size: 1) do |post|
         assert_kind_of Post, post
       end
     end
@@ -21,31 +24,29 @@ class EachTest < ActiveRecord::TestCase
 
   def test_each_should_not_return_query_chain_and_execute_only_one_query
     assert_queries(1) do
-      result = Post.find_each(:batch_size => 100000){ }
+      result = Post.find_each(batch_size: 100000) { }
       assert_nil result
     end
   end
 
   def test_each_should_return_an_enumerator_if_no_block_is_present
     assert_queries(1) do
-      Post.find_each(:batch_size => 100000).with_index do |post, index|
+      Post.find_each(batch_size: 100000).with_index do |post, index|
         assert_kind_of Post, post
         assert_kind_of Integer, index
       end
     end
   end
 
-  if Enumerator.method_defined? :size
-    def test_each_should_return_a_sized_enumerator
-      assert_equal 11, Post.find_each(batch_size: 1).size
-      assert_equal 5, Post.find_each(batch_size:  2, begin_at: 7).size
-      assert_equal 11, Post.find_each(batch_size: 10_000).size
-    end
+  def test_each_should_return_a_sized_enumerator
+    assert_equal 11, Post.find_each(batch_size: 1).size
+    assert_equal 5, Post.find_each(batch_size:  2, start: 7).size
+    assert_equal 11, Post.find_each(batch_size: 10_000).size
   end
 
   def test_each_enumerator_should_execute_one_query_per_batch
     assert_queries(@total + 1) do
-      Post.find_each(:batch_size => 1).with_index do |post, index|
+      Post.find_each(batch_size: 1).with_index do |post, index|
         assert_kind_of Post, post
         assert_kind_of Integer, index
       end
@@ -53,7 +54,7 @@ class EachTest < ActiveRecord::TestCase
   end
 
   def test_each_should_raise_if_select_is_set_without_id
-    assert_raise(RuntimeError) do
+    assert_raise(ArgumentError) do
       Post.select(:title).find_each(batch_size: 1) { |post|
         flunk "should not call this block"
       }
@@ -62,27 +63,45 @@ class EachTest < ActiveRecord::TestCase
 
   def test_each_should_execute_if_id_is_in_select
     assert_queries(6) do
-      Post.select("id, title, type").find_each(:batch_size => 2) do |post|
+      Post.select("id, title, type").find_each(batch_size: 2) do |post|
         assert_kind_of Post, post
       end
     end
   end
 
-  def test_warn_if_limit_scope_is_set
-    ActiveRecord::Base.logger.expects(:warn)
-    Post.limit(1).find_each { |post| post }
+  test "find_each should honor limit if passed a block" do
+    limit = @total - 1
+    total = 0
+
+    Post.limit(limit).find_each do |post|
+      total += 1
+    end
+
+    assert_equal limit, total
+  end
+
+  test "find_each should honor limit if no block is passed" do
+    limit = @total - 1
+    total = 0
+
+    Post.limit(limit).find_each.each do |post|
+      total += 1
+    end
+
+    assert_equal limit, total
   end
 
   def test_warn_if_order_scope_is_set
-    ActiveRecord::Base.logger.expects(:warn)
-    Post.order("title").find_each { |post| post }
+    assert_called(ActiveRecord::Base.logger, :warn) do
+      Post.order("title").find_each { |post| post }
+    end
   end
 
   def test_logger_not_required
     previous_logger = ActiveRecord::Base.logger
     ActiveRecord::Base.logger = nil
     assert_nothing_raised do
-      Post.limit(1).find_each { |post| post }
+      Post.order("comments_count DESC").find_each { |post| post }
     end
   ensure
     ActiveRecord::Base.logger = previous_logger
@@ -90,7 +109,7 @@ class EachTest < ActiveRecord::TestCase
 
   def test_find_in_batches_should_return_batches
     assert_queries(@total + 1) do
-      Post.find_in_batches(:batch_size => 1) do |batch|
+      Post.find_in_batches(batch_size: 1) do |batch|
         assert_kind_of Array, batch
         assert_kind_of Post, batch.first
       end
@@ -99,16 +118,16 @@ class EachTest < ActiveRecord::TestCase
 
   def test_find_in_batches_should_start_from_the_start_option
     assert_queries(@total) do
-      Post.find_in_batches(batch_size: 1, begin_at: 2) do |batch|
+      Post.find_in_batches(batch_size: 1, start: 2) do |batch|
         assert_kind_of Array, batch
         assert_kind_of Post, batch.first
       end
     end
   end
 
-  def test_find_in_batches_should_end_at_the_end_option
+  def test_find_in_batches_should_end_at_the_finish_option
     assert_queries(6) do
-      Post.find_in_batches(batch_size: 1, end_at: 5) do |batch|
+      Post.find_in_batches(batch_size: 1, finish: 5) do |batch|
         assert_kind_of Array, batch
         assert_kind_of Post, batch.first
       end
@@ -117,18 +136,18 @@ class EachTest < ActiveRecord::TestCase
 
   def test_find_in_batches_shouldnt_execute_query_unless_needed
     assert_queries(2) do
-      Post.find_in_batches(:batch_size => @total) {|batch| assert_kind_of Array, batch }
+      Post.find_in_batches(batch_size: @total) { |batch| assert_kind_of Array, batch }
     end
 
     assert_queries(1) do
-      Post.find_in_batches(:batch_size => @total + 1) {|batch| assert_kind_of Array, batch }
+      Post.find_in_batches(batch_size: @total + 1) { |batch| assert_kind_of Array, batch }
     end
   end
 
   def test_find_in_batches_should_quote_batch_order
     c = Post.connection
-    assert_sql(/ORDER BY #{c.quote_table_name('posts')}.#{c.quote_column_name('id')}/) do
-      Post.find_in_batches(:batch_size => 1) do |batch|
+    assert_sql(/ORDER BY #{c.quote_table_name('posts')}\.#{c.quote_column_name('id')}/) do
+      Post.find_in_batches(batch_size: 1) do |batch|
         assert_kind_of Array, batch
         assert_kind_of Post, batch.first
       end
@@ -136,15 +155,16 @@ class EachTest < ActiveRecord::TestCase
   end
 
   def test_find_in_batches_should_not_use_records_after_yielding_them_in_case_original_array_is_modified
-    not_a_post = "not a post"
-    not_a_post.stubs(:id).raises(StandardError, "not_a_post had #id called on it")
-
-    assert_nothing_raised do
-      Post.find_in_batches(:batch_size => 1) do |batch|
-        assert_kind_of Array, batch
-        assert_kind_of Post, batch.first
+    not_a_post = +"not a post"
+    def not_a_post.id; end
+    not_a_post.stub(:id, -> { raise StandardError.new("not_a_post had #id called on it") }) do
+      assert_nothing_raised do
+        Post.find_in_batches(batch_size: 1) do |batch|
+          assert_kind_of Array, batch
+          assert_kind_of Post, batch.first
 
-        batch.map! { not_a_post }
+          batch.map! { not_a_post }
+        end
       end
     end
   end
@@ -158,7 +178,43 @@ class EachTest < ActiveRecord::TestCase
     end
     # posts.first will be ordered using id only. Title order scope should not apply here
     assert_not_equal first_post, posts.first
-    assert_equal posts(:welcome), posts.first
+    assert_equal posts(:welcome).id, posts.first.id
+  end
+
+  def test_find_in_batches_should_error_on_ignore_the_order
+    assert_raise(ArgumentError) do
+      PostWithDefaultScope.find_in_batches(error_on_ignore: true) { }
+    end
+  end
+
+  def test_find_in_batches_should_not_error_if_config_overridden
+    # Set the config option which will be overridden
+    prev = ActiveRecord::Base.error_on_ignored_order
+    ActiveRecord::Base.error_on_ignored_order = true
+    assert_nothing_raised do
+      PostWithDefaultScope.find_in_batches(error_on_ignore: false) { }
+    end
+  ensure
+    # Set back to default
+    ActiveRecord::Base.error_on_ignored_order = prev
+  end
+
+  def test_find_in_batches_should_error_on_config_specified_to_error
+    # Set the config option
+    prev = ActiveRecord::Base.error_on_ignored_order
+    ActiveRecord::Base.error_on_ignored_order = true
+    assert_raise(ArgumentError) do
+      PostWithDefaultScope.find_in_batches() { }
+    end
+  ensure
+    # Set back to default
+    ActiveRecord::Base.error_on_ignored_order = prev
+  end
+
+  def test_find_in_batches_should_not_error_by_default
+    assert_nothing_raised do
+      PostWithDefaultScope.find_in_batches() { }
+    end
   end
 
   def test_find_in_batches_should_not_ignore_the_default_scope_if_it_is_other_then_order
@@ -172,16 +228,16 @@ class EachTest < ActiveRecord::TestCase
 
   def test_find_in_batches_should_not_modify_passed_options
     assert_nothing_raised do
-      Post.find_in_batches({ batch_size: 42, begin_at: 1 }.freeze){}
+      Post.find_in_batches({ batch_size: 42, start: 1 }.freeze) { }
     end
   end
 
   def test_find_in_batches_should_use_any_column_as_primary_key
-    nick_order_subscribers = Subscriber.order('nick asc')
+    nick_order_subscribers = Subscriber.order("nick asc")
     start_nick = nick_order_subscribers.second.nick
 
     subscribers = []
-    Subscriber.find_in_batches(batch_size: 1, begin_at: start_nick) do |batch|
+    Subscriber.find_in_batches(batch_size: 1, start: start_nick) do |batch|
       subscribers.concat(batch)
     end
 
@@ -199,8 +255,8 @@ class EachTest < ActiveRecord::TestCase
 
   def test_find_in_batches_should_return_an_enumerator
     enum = nil
-    assert_queries(0) do
-      enum = Post.find_in_batches(:batch_size => 1)
+    assert_no_queries do
+      enum = Post.find_in_batches(batch_size: 1)
     end
     assert_queries(4) do
       enum.first(4) do |batch|
@@ -210,34 +266,398 @@ class EachTest < ActiveRecord::TestCase
     end
   end
 
-  def test_find_in_batches_start_deprecated
-    assert_deprecated do
-      assert_queries(@total) do
-        Post.find_in_batches(batch_size: 1, start: 2) do |batch|
-          assert_kind_of Array, batch
-          assert_kind_of Post, batch.first
+  test "find_in_batches should honor limit if passed a block" do
+    limit = @total - 1
+    total = 0
+
+    Post.limit(limit).find_in_batches do |batch|
+      total += batch.size
+    end
+
+    assert_equal limit, total
+  end
+
+  test "find_in_batches should honor limit if no block is passed" do
+    limit = @total - 1
+    total = 0
+
+    Post.limit(limit).find_in_batches.each do |batch|
+      total += batch.size
+    end
+
+    assert_equal limit, total
+  end
+
+  def test_in_batches_should_not_execute_any_query
+    assert_no_queries do
+      assert_kind_of ActiveRecord::Batches::BatchEnumerator, Post.in_batches(of: 2)
+    end
+  end
+
+  def test_in_batches_should_yield_relation_if_block_given
+    assert_queries(6) do
+      Post.in_batches(of: 2) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+      end
+    end
+  end
+
+  def test_in_batches_should_be_enumerable_if_no_block_given
+    assert_queries(6) do
+      Post.in_batches(of: 2).each do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+      end
+    end
+  end
+
+  def test_in_batches_each_record_should_yield_record_if_block_is_given
+    assert_queries(6) do
+      Post.in_batches(of: 2).each_record do |post|
+        assert_predicate post.title, :present?
+        assert_kind_of Post, post
+      end
+    end
+  end
+
+  def test_in_batches_each_record_should_return_enumerator_if_no_block_given
+    assert_queries(6) do
+      Post.in_batches(of: 2).each_record.with_index do |post, i|
+        assert_predicate post.title, :present?
+        assert_kind_of Post, post
+      end
+    end
+  end
+
+  def test_in_batches_each_record_should_be_ordered_by_id
+    ids = Post.order("id ASC").pluck(:id)
+    assert_queries(6) do
+      Post.in_batches(of: 2).each_record.with_index do |post, i|
+        assert_equal ids[i], post.id
+      end
+    end
+  end
+
+  def test_in_batches_update_all_affect_all_records
+    assert_queries(6 + 6) do # 6 selects, 6 updates
+      Post.in_batches(of: 2).update_all(title: "updated-title")
+    end
+    assert_equal Post.all.pluck(:title), ["updated-title"] * Post.count
+  end
+
+  def test_in_batches_delete_all_should_not_delete_records_in_other_batches
+    not_deleted_count = Post.where("id <= 2").count
+    Post.where("id > 2").in_batches(of: 2).delete_all
+    assert_equal 0, Post.where("id > 2").count
+    assert_equal not_deleted_count, Post.count
+  end
+
+  def test_in_batches_should_not_be_loaded
+    Post.in_batches(of: 1) do |relation|
+      assert_not_predicate relation, :loaded?
+    end
+
+    Post.in_batches(of: 1, load: false) do |relation|
+      assert_not_predicate relation, :loaded?
+    end
+  end
+
+  def test_in_batches_should_be_loaded
+    Post.in_batches(of: 1, load: true) do |relation|
+      assert_predicate relation, :loaded?
+    end
+  end
+
+  def test_in_batches_if_not_loaded_executes_more_queries
+    assert_queries(@total + 1) do
+      Post.in_batches(of: 1, load: false) do |relation|
+        assert_not_predicate relation, :loaded?
+      end
+    end
+  end
+
+  def test_in_batches_should_return_relations
+    assert_queries(@total + 1) do
+      Post.in_batches(of: 1) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+      end
+    end
+  end
+
+  def test_in_batches_should_start_from_the_start_option
+    post = Post.order("id ASC").where("id >= ?", 2).first
+    assert_queries(2) do
+      relation = Post.in_batches(of: 1, start: 2).first
+      assert_equal post, relation.first
+    end
+  end
+
+  def test_in_batches_should_end_at_the_finish_option
+    post = Post.order("id DESC").where("id <= ?", 5).first
+    assert_queries(7) do
+      relation = Post.in_batches(of: 1, finish: 5, load: true).reverse_each.first
+      assert_equal post, relation.last
+    end
+  end
+
+  def test_in_batches_shouldnt_execute_query_unless_needed
+    assert_queries(2) do
+      Post.in_batches(of: @total) { |relation| assert_kind_of ActiveRecord::Relation, relation }
+    end
+
+    assert_queries(1) do
+      Post.in_batches(of: @total + 1) { |relation| assert_kind_of ActiveRecord::Relation, relation }
+    end
+  end
+
+  def test_in_batches_should_quote_batch_order
+    c = Post.connection
+    assert_sql(/ORDER BY #{c.quote_table_name('posts')}\.#{c.quote_column_name('id')}/) do
+      Post.in_batches(of: 1) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+        assert_kind_of Post, relation.first
+      end
+    end
+  end
+
+  def test_in_batches_should_not_use_records_after_yielding_them_in_case_original_array_is_modified
+    not_a_post = +"not a post"
+    def not_a_post.id
+      raise StandardError.new("not_a_post had #id called on it")
+    end
+
+    assert_nothing_raised do
+      Post.in_batches(of: 1) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+        assert_kind_of Post, relation.first
+
+        relation = [not_a_post] * relation.count
+      end
+    end
+  end
+
+  def test_in_batches_should_not_ignore_default_scope_without_order_statements
+    special_posts_ids = SpecialPostWithDefaultScope.all.map(&:id).sort
+    posts = []
+    SpecialPostWithDefaultScope.in_batches do |relation|
+      posts.concat(relation)
+    end
+    assert_equal special_posts_ids, posts.map(&:id)
+  end
+
+  def test_in_batches_should_not_modify_passed_options
+    assert_nothing_raised do
+      Post.in_batches({ of: 42, start: 1 }.freeze) { }
+    end
+  end
+
+  def test_in_batches_should_use_any_column_as_primary_key
+    nick_order_subscribers = Subscriber.order("nick asc")
+    start_nick = nick_order_subscribers.second.nick
+
+    subscribers = []
+    Subscriber.in_batches(of: 1, start: start_nick) do |relation|
+      subscribers.concat(relation)
+    end
+
+    assert_equal nick_order_subscribers[1..-1].map(&:id), subscribers.map(&:id)
+  end
+
+  def test_in_batches_should_use_any_column_as_primary_key_when_start_is_not_specified
+    assert_queries(Subscriber.count + 1) do
+      Subscriber.in_batches(of: 1, load: true) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+        assert_kind_of Subscriber, relation.first
+      end
+    end
+  end
+
+  def test_in_batches_should_return_an_enumerator
+    enum = nil
+    assert_no_queries do
+      enum = Post.in_batches(of: 1)
+    end
+    assert_queries(4) do
+      enum.first(4) do |relation|
+        assert_kind_of ActiveRecord::Relation, relation
+        assert_kind_of Post, relation.first
+      end
+    end
+  end
+
+  def test_in_batches_relations_should_not_overlap_with_each_other
+    seen_posts = []
+    Post.in_batches(of: 2, load: true) do |relation|
+      relation.to_a.each do |post|
+        assert_not seen_posts.include?(post)
+        seen_posts << post
+      end
+    end
+  end
+
+  def test_in_batches_relations_with_condition_should_not_overlap_with_each_other
+    seen_posts = []
+    author_id = Post.first.author_id
+    posts_by_author = Post.where(author_id: author_id)
+    Post.in_batches(of: 2) do |batch|
+      seen_posts += batch.where(author_id: author_id)
+    end
+
+    assert_equal posts_by_author.pluck(:id).sort, seen_posts.map(&:id).sort
+  end
+
+  def test_in_batches_relations_update_all_should_not_affect_matching_records_in_other_batches
+    Post.update_all(author_id: 0)
+    person = Post.last
+    person.update(author_id: 1)
+
+    Post.in_batches(of: 2) do |batch|
+      batch.where("author_id >= 1").update_all("author_id = author_id + 1")
+    end
+    assert_equal 2, person.reload.author_id # incremented only once
+  end
+
+  def test_find_in_batches_should_return_a_sized_enumerator
+    assert_equal 11, Post.find_in_batches(batch_size: 1).size
+    assert_equal 6, Post.find_in_batches(batch_size: 2).size
+    assert_equal 4, Post.find_in_batches(batch_size: 2, start: 4).size
+    assert_equal 4, Post.find_in_batches(batch_size: 3).size
+    assert_equal 1, Post.find_in_batches(batch_size: 10_000).size
+  end
+
+  [true, false].each do |load|
+    test "in_batches should return limit records when limit is less than batch size and load is #{load}" do
+      limit      = 3
+      batch_size = 5
+      total      = 0
+
+      Post.limit(limit).in_batches(of: batch_size, load: load) do |batch|
+        total += batch.count
+      end
+
+      assert_equal limit, total
+    end
+
+    test "in_batches should return limit records when limit is greater than batch size and load is #{load}" do
+      limit      = 5
+      batch_size = 3
+      total      = 0
+
+      Post.limit(limit).in_batches(of: batch_size, load: load) do |batch|
+        total += batch.count
+      end
+
+      assert_equal limit, total
+    end
+
+    test "in_batches should return limit records when limit is a multiple of the batch size and load is #{load}" do
+      limit      = 6
+      batch_size = 3
+      total      = 0
+
+      Post.limit(limit).in_batches(of: batch_size, load: load) do |batch|
+        total += batch.count
+      end
+
+      assert_equal limit, total
+    end
+
+    test "in_batches should return no records if the limit is 0 and load is #{load}" do
+      limit      = 0
+      batch_size = 1
+      total      = 0
+
+      Post.limit(limit).in_batches(of: batch_size, load: load) do |batch|
+        total += batch.count
+      end
+
+      assert_equal limit, total
+    end
+
+    test "in_batches should return all if the limit is greater than the number of records when load is #{load}" do
+      limit      = @total + 1
+      batch_size = 1
+      total      = 0
+
+      Post.limit(limit).in_batches(of: batch_size, load: load) do |batch|
+        total += batch.count
+      end
+
+      assert_equal @total, total
+    end
+  end
+
+  test ".find_each respects table alias" do
+    assert_queries(1) do
+      table_alias = Post.arel_table.alias("omg_posts")
+      table_metadata = ActiveRecord::TableMetadata.new(Post, table_alias)
+      predicate_builder = ActiveRecord::PredicateBuilder.new(table_metadata)
+
+      posts = ActiveRecord::Relation.create(
+        Post,
+        table: table_alias,
+        predicate_builder: predicate_builder
+      )
+      posts.find_each { }
+    end
+  end
+
+  test ".find_each bypasses the query cache for its own queries" do
+    Post.cache do
+      assert_queries(2) do
+        Post.find_each { }
+        Post.find_each { }
+      end
+    end
+  end
+
+  test ".find_each does not disable the query cache inside the given block" do
+    Post.cache do
+      Post.find_each(start: 1, finish: 1) do |post|
+        assert_queries(1) do
+          post.comments.count
+          post.comments.count
         end
       end
     end
   end
 
-  def test_find_each_start_deprecated
-    assert_deprecated do
-      assert_queries(@total) do
-        Post.find_each(batch_size: 1, start: 2) do |post|
-          assert_kind_of Post, post
+  test ".find_in_batches bypasses the query cache for its own queries" do
+    Post.cache do
+      assert_queries(2) do
+        Post.find_in_batches { }
+        Post.find_in_batches { }
+      end
+    end
+  end
+
+  test ".find_in_batches does not disable the query cache inside the given block" do
+    Post.cache do
+      Post.find_in_batches(start: 1, finish: 1) do |batch|
+        assert_queries(1) do
+          batch.first.comments.count
+          batch.first.comments.count
         end
       end
     end
   end
 
-  if Enumerator.method_defined? :size
-    def test_find_in_batches_should_return_a_sized_enumerator
-      assert_equal 11, Post.find_in_batches(:batch_size => 1).size
-      assert_equal 6, Post.find_in_batches(:batch_size => 2).size
-      assert_equal 4, Post.find_in_batches(batch_size: 2, begin_at: 4).size
-      assert_equal 4, Post.find_in_batches(:batch_size => 3).size
-      assert_equal 1, Post.find_in_batches(:batch_size => 10_000).size
+  test ".in_batches bypasses the query cache for its own queries" do
+    Post.cache do
+      assert_queries(2) do
+        Post.in_batches { }
+        Post.in_batches { }
+      end
+    end
+  end
+
+  test ".in_batches does not disable the query cache inside the given block" do
+    Post.cache do
+      Post.in_batches(start: 1, finish: 1) do |relation|
+        assert_queries(1) do
+          relation.count
+          relation.count
+        end
+      end
     end
   end
 end
diff --git a/activerecord/test/cases/binary_test.rb b/activerecord/test/cases/binary_test.rb
index 86dee929bf..58abdb47f7 100644
--- a/activerecord/test/cases/binary_test.rb
+++ b/activerecord/test/cases/binary_test.rb
@@ -1,30 +1,28 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 # Without using prepared statements, it makes no sense to test
 # BLOB data with DB2, because the length of a statement
 # is limited to 32KB.
 unless current_adapter?(:DB2Adapter)
-  require 'models/binary'
+  require "models/binary"
 
   class BinaryTest < ActiveRecord::TestCase
     FIXTURES = %w(flowers.jpg example.log test.txt)
 
     def test_mixed_encoding
-      str = "\x80"
-      str.force_encoding('ASCII-8BIT')
+      str = +"\x80"
+      str.force_encoding("ASCII-8BIT")
 
-      binary = Binary.new :name => 'いただきます！', :data => str
+      binary = Binary.new name: "いただきます！", data: str
       binary.save!
       binary.reload
       assert_equal str, binary.data
 
       name = binary.name
 
-      # MySQL adapter doesn't properly encode things, so we have to do it
-      if current_adapter?(:MysqlAdapter)
-        name.force_encoding(Encoding::UTF_8)
-      end
-      assert_equal 'いただきます！', name
+      assert_equal "いただきます！", name
     end
 
     def test_load_save
@@ -32,16 +30,16 @@ unless current_adapter?(:DB2Adapter)
 
       FIXTURES.each do |filename|
         data = File.read(ASSETS_ROOT + "/#{filename}")
-        data.force_encoding('ASCII-8BIT')
+        data.force_encoding("ASCII-8BIT")
         data.freeze
 
-        bin = Binary.new(:data => data)
-        assert_equal data, bin.data, 'Newly assigned data differs from original'
+        bin = Binary.new(data: data)
+        assert_equal data, bin.data, "Newly assigned data differs from original"
 
         bin.save!
-        assert_equal data, bin.data, 'Data differs from original after save'
+        assert_equal data, bin.data, "Data differs from original after save"
 
-        assert_equal data, bin.reload.data, 'Reloaded data differs from original'
+        assert_equal data, bin.reload.data, "Reloaded data differs from original"
       end
     end
   end
diff --git a/activerecord/test/cases/bind_parameter_test.rb b/activerecord/test/cases/bind_parameter_test.rb
index 1e38b97c4a..bd5f157ca1 100644
--- a/activerecord/test/cases/bind_parameter_test.rb
+++ b/activerecord/test/cases/bind_parameter_test.rb
@@ -1,49 +1,61 @@
-require 'cases/helper'
-require 'models/topic'
-require 'models/author'
-require 'models/post'
+# frozen_string_literal: true
 
-module ActiveRecord
-  class BindParameterTest < ActiveRecord::TestCase
-    fixtures :topics, :authors, :posts
+require "cases/helper"
+require "models/topic"
+require "models/author"
+require "models/post"
 
-    class LogListener
-      attr_accessor :calls
+if ActiveRecord::Base.connection.prepared_statements
+  module ActiveRecord
+    class BindParameterTest < ActiveRecord::TestCase
+      fixtures :topics, :authors, :author_addresses, :posts
 
-      def initialize
-        @calls = []
+      class LogListener
+        attr_accessor :calls
+
+        def initialize
+          @calls = []
+        end
+
+        def call(*args)
+          calls << args
+        end
       end
 
-      def call(*args)
-        calls << args
+      def setup
+        super
+        @connection = ActiveRecord::Base.connection
+        @subscriber = LogListener.new
+        @pk = Topic.columns_hash[Topic.primary_key]
+        @subscription = ActiveSupport::Notifications.subscribe("sql.active_record", @subscriber)
       end
-    end
 
-    def setup
-      super
-      @connection = ActiveRecord::Base.connection
-      @subscriber = LogListener.new
-      @pk = Topic.columns_hash[Topic.primary_key]
-      @subscription = ActiveSupport::Notifications.subscribe('sql.active_record', @subscriber)
-    end
+      def teardown
+        ActiveSupport::Notifications.unsubscribe(@subscription)
+      end
 
-    teardown do
-      ActiveSupport::Notifications.unsubscribe(@subscription)
-    end
+      def test_too_many_binds
+        bind_params_length = @connection.send(:bind_params_length)
+
+        topics = Topic.where(id: (1 .. bind_params_length).to_a << 2**63)
+        assert_equal Topic.count, topics.count
+
+        topics = Topic.where.not(id: (1 .. bind_params_length).to_a << 2**63)
+        assert_equal 0, topics.count
+      end
 
-    if ActiveRecord::Base.connection.supports_statement_cache?
       def test_bind_from_join_in_subquery
-        subquery = Author.joins(:thinking_posts).where(name: 'David')
-        scope = Author.from(subquery, 'authors').where(id: 1)
+        subquery = Author.joins(:thinking_posts).where(name: "David")
+        scope = Author.from(subquery, "authors").where(id: 1)
         assert_equal 1, scope.count
       end
 
       def test_binds_are_logged
-        sub   = @connection.substitute_at(@pk)
+        sub   = Arel::Nodes::BindParam.new(1)
         binds = [Relation::QueryAttribute.new("id", 1, Type::Value.new)]
         sql   = "select * from topics where id = #{sub.to_sql}"
 
-        @connection.exec_query(sql, 'SQL', binds)
+        @connection.exec_query(sql, "SQL", binds)
 
         message = @subscriber.calls.find { |args| args[4][:sql] == sql }
         assert_equal binds, message[4][:binds]
@@ -52,37 +64,55 @@ module ActiveRecord
       def test_find_one_uses_binds
         Topic.find(1)
         message = @subscriber.calls.find { |args| args[4][:binds].any? { |attr| attr.value == 1 } }
-        assert message, 'expected a message with binds'
+        assert message, "expected a message with binds"
       end
 
-      def test_logs_bind_vars_after_type_cast
-        payload = {
-          :name  => 'SQL',
-          :sql   => 'select * from topics where id = ?',
-          :binds => [Relation::QueryAttribute.new("id", "10", Type::Integer.new)]
-        }
-        event  = ActiveSupport::Notifications::Event.new(
-          'foo',
-          Time.now,
-          Time.now,
-          123,
-          payload)
-
-        logger = Class.new(ActiveRecord::LogSubscriber) {
-          attr_reader :debugs
-          def initialize
-            super
-            @debugs = []
-          end
-
-          def debug str
-            @debugs << str
-          end
-        }.new
-
-        logger.sql event
-        assert_match([[@pk.name, 10]].inspect, logger.debugs.first)
+      def test_logs_binds_after_type_cast
+        binds = [Relation::QueryAttribute.new("id", "10", Type::Integer.new)]
+        assert_logs_binds(binds)
       end
+
+      def test_logs_legacy_binds_after_type_cast
+        binds = [[@pk, "10"]]
+        assert_logs_binds(binds)
+      end
+
+      def test_deprecate_supports_statement_cache
+        assert_deprecated { ActiveRecord::Base.connection.supports_statement_cache? }
+      end
+
+      private
+        def assert_logs_binds(binds)
+          payload = {
+            name: "SQL",
+            sql: "select * from topics where id = ?",
+            binds: binds,
+            type_casted_binds: @connection.type_casted_binds(binds)
+          }
+
+          event = ActiveSupport::Notifications::Event.new(
+            "foo",
+            Time.now,
+            Time.now,
+            123,
+            payload)
+
+          logger = Class.new(ActiveRecord::LogSubscriber) {
+            attr_reader :debugs
+
+            def initialize
+              super
+              @debugs = []
+            end
+
+            def debug(str)
+              @debugs << str
+            end
+          }.new
+
+          logger.sql(event)
+          assert_match([[@pk.name, 10]].inspect, logger.debugs.first)
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/boolean_test.rb b/activerecord/test/cases/boolean_test.rb
new file mode 100644
index 0000000000..ab9f974e2c
--- /dev/null
+++ b/activerecord/test/cases/boolean_test.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/boolean"
+
+class BooleanTest < ActiveRecord::TestCase
+  def test_boolean
+    b_nil   = Boolean.create!(value: nil)
+    b_false = Boolean.create!(value: false)
+    b_true  = Boolean.create!(value: true)
+
+    assert_nil Boolean.find(b_nil.id).value
+    assert_not_predicate Boolean.find(b_false.id), :value?
+    assert_predicate Boolean.find(b_true.id), :value?
+  end
+
+  def test_boolean_without_questionmark
+    b_true = Boolean.create!(value: true)
+
+    subclass   = Class.new(Boolean).find(b_true.id)
+    superclass = Boolean.find(b_true.id)
+
+    assert_equal superclass.read_attribute(:has_fun), subclass.read_attribute(:has_fun)
+  end
+
+  def test_boolean_cast_from_string
+    b_blank = Boolean.create!(value: "")
+    b_false = Boolean.create!(value: "0")
+    b_true  = Boolean.create!(value: "1")
+
+    assert_nil Boolean.find(b_blank.id).value
+    assert_not_predicate Boolean.find(b_false.id), :value?
+    assert_predicate Boolean.find(b_true.id), :value?
+  end
+
+  def test_find_by_boolean_string
+    b_false = Boolean.create!(value: "false")
+    b_true  = Boolean.create!(value: "true")
+
+    assert_equal b_false, Boolean.find_by(value: "false")
+    assert_equal b_true, Boolean.find_by(value: "true")
+  end
+end
diff --git a/activerecord/test/cases/cache_key_test.rb b/activerecord/test/cases/cache_key_test.rb
new file mode 100644
index 0000000000..3a569f226e
--- /dev/null
+++ b/activerecord/test/cases/cache_key_test.rb
@@ -0,0 +1,53 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+module ActiveRecord
+  class CacheKeyTest < ActiveRecord::TestCase
+    self.use_transactional_tests = false
+
+    class CacheMe < ActiveRecord::Base
+      self.cache_versioning = false
+    end
+
+    class CacheMeWithVersion < ActiveRecord::Base
+      self.cache_versioning = true
+    end
+
+    setup do
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table(:cache_mes, force: true) { |t| t.timestamps }
+      @connection.create_table(:cache_me_with_versions, force: true) { |t| t.timestamps }
+    end
+
+    teardown do
+      @connection.drop_table :cache_mes, if_exists: true
+      @connection.drop_table :cache_me_with_versions, if_exists: true
+    end
+
+    test "cache_key format is not too precise" do
+      record = CacheMe.create
+      key = record.cache_key
+
+      assert_equal key, record.reload.cache_key
+    end
+
+    test "cache_key has no version when versioning is on" do
+      record = CacheMeWithVersion.create
+      assert_equal "active_record/cache_key_test/cache_me_with_versions/#{record.id}", record.cache_key
+    end
+
+    test "cache_version is only there when versioning is on" do
+      assert_predicate CacheMeWithVersion.create.cache_version, :present?
+      assert_not_predicate CacheMe.create.cache_version, :present?
+    end
+
+    test "cache_key_with_version always has both key and version" do
+      r1 = CacheMeWithVersion.create
+      assert_equal "active_record/cache_key_test/cache_me_with_versions/#{r1.id}-#{r1.updated_at.to_s(:usec)}", r1.cache_key_with_version
+
+      r2 = CacheMe.create
+      assert_equal "active_record/cache_key_test/cache_mes/#{r2.id}-#{r2.updated_at.to_s(:usec)}", r2.cache_key_with_version
+    end
+  end
+end
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index aa10817527..5c9ed42173 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -1,41 +1,46 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/club'
-require 'models/company'
+require "models/book"
+require "models/club"
+require "models/company"
 require "models/contract"
-require 'models/edge'
-require 'models/organization'
-require 'models/possession'
-require 'models/topic'
-require 'models/reply'
-require 'models/minivan'
-require 'models/speedometer'
-require 'models/ship_part'
-require 'models/treasure'
-require 'models/developer'
-require 'models/comment'
-require 'models/rating'
-require 'models/post'
-
-class NumericData < ActiveRecord::Base
-  self.table_name = 'numeric_data'
-
-  attribute :world_population, :integer
-  attribute :my_house_population, :integer
-  attribute :atoms_in_universe, :integer
-end
+require "models/edge"
+require "models/organization"
+require "models/possession"
+require "models/topic"
+require "models/reply"
+require "models/numeric_data"
+require "models/minivan"
+require "models/speedometer"
+require "models/ship_part"
+require "models/treasure"
+require "models/developer"
+require "models/post"
+require "models/comment"
+require "models/rating"
 
 class CalculationsTest < ActiveRecord::TestCase
-  fixtures :companies, :accounts, :topics, :speedometers, :minivans
+  fixtures :companies, :accounts, :topics, :speedometers, :minivans, :books, :posts, :comments
 
   def test_should_sum_field
     assert_equal 318, Account.sum(:credit_limit)
   end
 
+  def test_should_sum_arel_attribute
+    assert_equal 318, Account.sum(Account.arel_table[:credit_limit])
+  end
+
   def test_should_average_field
     value = Account.average(:credit_limit)
     assert_equal 53.0, value
   end
 
+  def test_should_average_arel_attribute
+    value = Account.average(Account.arel_table[:credit_limit])
+    assert_equal 53.0, value
+  end
+
   def test_should_resolve_aliased_attributes
     assert_equal 318, Account.sum(:available_credit)
   end
@@ -47,7 +52,7 @@ class CalculationsTest < ActiveRecord::TestCase
 
   def test_should_return_integer_average_if_db_returns_such
     ShipPart.delete_all
-    ShipPart.create!(:id => 3, :name => 'foo')
+    ShipPart.create!(id: 3, name: "foo")
     value = ShipPart.average(:id)
     assert_equal 3, value
   end
@@ -60,35 +65,47 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 60, Account.maximum(:credit_limit)
   end
 
+  def test_should_get_maximum_of_arel_attribute
+    assert_equal 60, Account.maximum(Account.arel_table[:credit_limit])
+  end
+
   def test_should_get_maximum_of_field_with_include
     assert_equal 55, Account.where("companies.name != 'Summit'").references(:companies).includes(:firm).maximum(:credit_limit)
   end
 
+  def test_should_get_maximum_of_arel_attribute_with_include
+    assert_equal 55, Account.where("companies.name != 'Summit'").references(:companies).includes(:firm).maximum(Account.arel_table[:credit_limit])
+  end
+
   def test_should_get_minimum_of_field
     assert_equal 50, Account.minimum(:credit_limit)
   end
 
+  def test_should_get_minimum_of_arel_attribute
+    assert_equal 50, Account.minimum(Account.arel_table[:credit_limit])
+  end
+
   def test_should_group_by_field
     c = Account.group(:firm_id).sum(:credit_limit)
-    [1,6,2].each do |firm_id|
-      assert c.keys.include?(firm_id), "Group #{c.inspect} does not contain firm_id #{firm_id}"
+    [1, 6, 2].each do |firm_id|
+      assert_includes c.keys, firm_id, "Group #{c.inspect} does not contain firm_id #{firm_id}"
     end
   end
 
   def test_should_group_by_arel_attribute
     c = Account.group(Account.arel_table[:firm_id]).sum(:credit_limit)
-    [1,6,2].each do |firm_id|
-      assert c.keys.include?(firm_id), "Group #{c.inspect} does not contain firm_id #{firm_id}"
+    [1, 6, 2].each do |firm_id|
+      assert_includes c.keys, firm_id, "Group #{c.inspect} does not contain firm_id #{firm_id}"
     end
   end
 
   def test_should_group_by_multiple_fields
-    c = Account.group('firm_id', :credit_limit).count(:all)
-    [ [nil, 50], [1, 50], [6, 50], [6, 55], [9, 53], [2, 60] ].each { |firm_and_limit| assert c.keys.include?(firm_and_limit) }
+    c = Account.group("firm_id", :credit_limit).count(:all)
+    [ [nil, 50], [1, 50], [6, 50], [6, 55], [9, 53], [2, 60] ].each { |firm_and_limit| assert_includes c.keys, firm_and_limit }
   end
 
   def test_should_group_by_multiple_fields_having_functions
-    c = Topic.group(:author_name, 'COALESCE(type, title)').count(:all)
+    c = Topic.group(:author_name, "COALESCE(type, title)").count(:all)
     assert_equal 1, c[["Carl", "The Third Topic of the day"]]
     assert_equal 1, c[["Mary", "Reply"]]
     assert_equal 1, c[["David", "The First Topic"]]
@@ -102,6 +119,25 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_equal 60,   c[2]
   end
 
+  def test_should_generate_valid_sql_with_joins_and_group
+    assert_nothing_raised do
+      AuditLog.joins(:developer).group(:id).count
+    end
+  end
+
+  def test_should_calculate_against_given_relation
+    developer = Developer.create!(name: "developer")
+    developer.audit_logs.create!(message: "first log")
+    developer.audit_logs.create!(message: "second log")
+
+    c = developer.audit_logs.joins(:developer).group(:id).count
+
+    assert_equal developer.audit_logs.count, c.size
+    developer.audit_logs.each do |log|
+      assert_equal 1, c[log.id]
+    end
+  end
+
   def test_should_order_by_grouped_field
     c = Account.group(:firm_id).order("firm_id").sum(:credit_limit)
     assert_equal [1, 2, 6, 9], c.keys.compact
@@ -125,12 +161,20 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_limit_should_apply_before_count
-    accounts = Account.limit(3).where('firm_id IS NOT NULL')
+    accounts = Account.limit(4)
 
     assert_equal 3, accounts.count(:firm_id)
     assert_equal 3, accounts.select(:firm_id).count
   end
 
+  def test_limit_should_apply_before_count_arel_attribute
+    accounts = Account.limit(4)
+
+    firm_id_attribute = Account.arel_table[:firm_id]
+    assert_equal 3, accounts.count(firm_id_attribute)
+    assert_equal 3, accounts.select(firm_id_attribute).count
+  end
+
   def test_count_should_shortcut_with_limit_zero
     accounts = Account.limit(0)
 
@@ -178,15 +222,76 @@ class CalculationsTest < ActiveRecord::TestCase
     assert_match "credit_limit, firm_name", e.message
   end
 
+  def test_apply_distinct_in_count
+    queries = assert_sql do
+      Account.distinct.count
+      Account.group(:firm_id).distinct.count
+    end
+
+    queries.each do |query|
+      # `table_alias_length` in `column_alias_for` would execute
+      # "SHOW max_identifier_length" statement in PostgreSQL adapter.
+      next if query == "SHOW max_identifier_length"
+      assert_match %r{\ASELECT(?! DISTINCT) COUNT\(DISTINCT\b}, query
+    end
+  end
+
+  def test_count_with_eager_loading_and_custom_order
+    posts = Post.includes(:comments).order("comments.id")
+    assert_queries(1) { assert_equal 11, posts.count }
+    assert_queries(1) { assert_equal 11, posts.count(:all) }
+  end
+
+  def test_count_with_eager_loading_and_custom_order_and_distinct
+    posts = Post.includes(:comments).order("comments.id").distinct
+    assert_queries(1) { assert_equal 11, posts.count }
+    assert_queries(1) { assert_equal 11, posts.count(:all) }
+  end
+
+  def test_distinct_count_all_with_custom_select_and_order
+    accounts = Account.distinct.select("credit_limit % 10").order(Arel.sql("credit_limit % 10"))
+    assert_queries(1) { assert_equal 3, accounts.count(:all) }
+    assert_queries(1) { assert_equal 3, accounts.load.size }
+  end
+
+  def test_distinct_count_with_order_and_limit
+    assert_equal 4, Account.distinct.order(:firm_id).limit(4).count
+  end
+
+  def test_distinct_count_with_order_and_offset
+    assert_equal 4, Account.distinct.order(:firm_id).offset(2).count
+  end
+
+  def test_distinct_count_with_order_and_limit_and_offset
+    assert_equal 4, Account.distinct.order(:firm_id).limit(4).offset(2).count
+  end
+
+  def test_distinct_joins_count_with_order_and_limit
+    assert_equal 3, Account.joins(:firm).distinct.order(:firm_id).limit(3).count
+  end
+
+  def test_distinct_joins_count_with_order_and_offset
+    assert_equal 3, Account.joins(:firm).distinct.order(:firm_id).offset(2).count
+  end
+
+  def test_distinct_joins_count_with_order_and_limit_and_offset
+    assert_equal 3, Account.joins(:firm).distinct.order(:firm_id).limit(3).offset(2).count
+  end
+
+  def test_distinct_count_with_group_by_and_order_and_limit
+    assert_equal({ 6 => 2 }, Account.group(:firm_id).distinct.order("1 DESC").limit(1).count)
+  end
+
   def test_should_group_by_summed_field_having_condition
-    c = Account.group(:firm_id).having('sum(credit_limit) > 50').sum(:credit_limit)
+    c = Account.group(:firm_id).having("sum(credit_limit) > 50").sum(:credit_limit)
     assert_nil        c[1]
     assert_equal 105, c[6]
     assert_equal 60,  c[2]
   end
 
   def test_should_group_by_summed_field_having_condition_from_select
-    c = Account.select("MIN(credit_limit) AS min_credit_limit").group(:firm_id).having("MIN(credit_limit) > 50").sum(:credit_limit)
+    skip unless current_adapter?(:Mysql2Adapter, :SQLite3Adapter)
+    c = Account.select("MIN(credit_limit) AS min_credit_limit").group(:firm_id).having("min_credit_limit > 50").sum(:credit_limit)
     assert_nil       c[1]
     assert_equal 60, c[2]
     assert_equal 53, c[9]
@@ -200,52 +305,52 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_should_sum_field_with_conditions
-    assert_equal 105, Account.where('firm_id = 6').sum(:credit_limit)
+    assert_equal 105, Account.where("firm_id = 6").sum(:credit_limit)
   end
 
   def test_should_return_zero_if_sum_conditions_return_nothing
-    assert_equal 0, Account.where('1 = 2').sum(:credit_limit)
-    assert_equal 0, companies(:rails_core).companies.where('1 = 2').sum(:id)
+    assert_equal 0, Account.where("1 = 2").sum(:credit_limit)
+    assert_equal 0, companies(:rails_core).companies.where("1 = 2").sum(:id)
   end
 
   def test_sum_should_return_valid_values_for_decimals
-    NumericData.create(:bank_balance => 19.83)
+    NumericData.create(bank_balance: 19.83)
     assert_equal 19.83, NumericData.sum(:bank_balance)
   end
 
   def test_should_return_type_casted_values_with_group_and_expression
-    assert_equal 0.5, Account.group(:firm_name).sum('0.01 * credit_limit')['37signals']
+    assert_equal 0.5, Account.group(:firm_name).sum("0.01 * credit_limit")["37signals"]
   end
 
   def test_should_group_by_summed_field_with_conditions
-    c = Account.where('firm_id > 1').group(:firm_id).sum(:credit_limit)
+    c = Account.where("firm_id > 1").group(:firm_id).sum(:credit_limit)
     assert_nil        c[1]
     assert_equal 105, c[6]
     assert_equal 60,  c[2]
   end
 
   def test_should_group_by_summed_field_with_conditions_and_having
-    c = Account.where('firm_id > 1').group(:firm_id).
-     having('sum(credit_limit) > 60').sum(:credit_limit)
+    c = Account.where("firm_id > 1").group(:firm_id).
+     having("sum(credit_limit) > 60").sum(:credit_limit)
     assert_nil        c[1]
     assert_equal 105, c[6]
     assert_nil        c[2]
   end
 
   def test_should_group_by_fields_with_table_alias
-    c = Account.group('accounts.firm_id').sum(:credit_limit)
+    c = Account.group("accounts.firm_id").sum(:credit_limit)
     assert_equal 50,  c[1]
     assert_equal 105, c[6]
     assert_equal 60,  c[2]
   end
 
   def test_should_calculate_with_invalid_field
-    assert_equal 6, Account.calculate(:count, '*')
+    assert_equal 6, Account.calculate(:count, "*")
     assert_equal 6, Account.calculate(:count, :all)
   end
 
   def test_should_calculate_grouped_with_invalid_field
-    c = Account.group('accounts.firm_id').count(:all)
+    c = Account.group("accounts.firm_id").count(:all)
     assert_equal 1, c[1]
     assert_equal 2, c[6]
     assert_equal 1, c[2]
@@ -259,8 +364,8 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_should_group_by_association_with_non_numeric_foreign_key
-    Speedometer.create! id: 'ABC'
-    Minivan.create! id: 'OMG', speedometer_id: 'ABC'
+    Speedometer.create! id: "ABC"
+    Minivan.create! id: "OMG", speedometer_id: "ABC"
 
     c = Minivan.group(:speedometer).count(:all)
     first_key = c.keys.first
@@ -269,7 +374,7 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_should_calculate_grouped_association_with_foreign_key_option
-    Account.belongs_to :another_firm, :class_name => 'Firm', :foreign_key => 'firm_id'
+    Account.belongs_to :another_firm, class_name: "Firm", foreign_key: "firm_id"
     c = Account.group(:another_firm).count(:all)
     assert_equal 1, c[companies(:first_firm)]
     assert_equal 2, c[companies(:rails_core)]
@@ -279,17 +384,17 @@ class CalculationsTest < ActiveRecord::TestCase
   def test_should_calculate_grouped_by_function
     c = Company.group("UPPER(#{QUOTED_TYPE})").count(:all)
     assert_equal 2, c[nil]
-    assert_equal 1, c['DEPENDENTFIRM']
-    assert_equal 5, c['CLIENT']
-    assert_equal 2, c['FIRM']
+    assert_equal 1, c["DEPENDENTFIRM"]
+    assert_equal 5, c["CLIENT"]
+    assert_equal 2, c["FIRM"]
   end
 
   def test_should_calculate_grouped_by_function_with_table_alias
     c = Company.group("UPPER(companies.#{QUOTED_TYPE})").count(:all)
     assert_equal 2, c[nil]
-    assert_equal 1, c['DEPENDENTFIRM']
-    assert_equal 5, c['CLIENT']
-    assert_equal 2, c['FIRM']
+    assert_equal 1, c["DEPENDENTFIRM"]
+    assert_equal 5, c["CLIENT"]
+    assert_equal 2, c["FIRM"]
   end
 
   def test_should_not_overshadow_enumerable_sum
@@ -305,19 +410,19 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_should_sum_scoped_field_with_conditions
-    assert_equal 8,  companies(:rails_core).companies.where('id > 7').sum(:id)
+    assert_equal 8,  companies(:rails_core).companies.where("id > 7").sum(:id)
   end
 
   def test_should_group_by_scoped_field
     c = companies(:rails_core).companies.group(:name).sum(:id)
-    assert_equal 7, c['Leetsoft']
-    assert_equal 8, c['Jadedpixel']
+    assert_equal 7, c["Leetsoft"]
+    assert_equal 8, c["Jadedpixel"]
   end
 
   def test_should_group_by_summed_field_through_association_and_having
-    c = companies(:rails_core).companies.group(:name).having('sum(id) > 7').sum(:id)
-    assert_nil      c['Leetsoft']
-    assert_equal 8, c['Jadedpixel']
+    c = companies(:rails_core).companies.group(:name).having("sum(id) > 7").sum(:id)
+    assert_nil      c["Leetsoft"]
+    assert_equal 8, c["Jadedpixel"]
   end
 
   def test_should_count_selected_field_with_include
@@ -332,7 +437,7 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_should_perform_joined_include_when_referencing_included_tables
-    joined_count = Account.includes(:firm).where(:companies => {:name => '37signals'}).count
+    joined_count = Account.includes(:firm).where(companies: { name: "37signals" }).count
     assert_equal 1, joined_count
   end
 
@@ -343,26 +448,35 @@ class CalculationsTest < ActiveRecord::TestCase
 
   def test_should_count_scoped_select_with_options
     Account.update_all("credit_limit = NULL")
-    Account.last.update_columns('credit_limit' => 49)
-    Account.first.update_columns('credit_limit' => 51)
+    Account.last.update_columns("credit_limit" => 49)
+    Account.first.update_columns("credit_limit" => 51)
 
-    assert_equal 1, Account.select("credit_limit").where('credit_limit >= 50').count
+    assert_equal 1, Account.select("credit_limit").where("credit_limit >= 50").count
   end
 
   def test_should_count_manual_select_with_include
     assert_equal 6, Account.select("DISTINCT accounts.id").includes(:firm).count
   end
 
+  def test_count_selected_arel_attribute
+    assert_equal 5, Account.select(Account.arel_table[:firm_id]).count
+    assert_equal 4, Account.distinct.select(Account.arel_table[:firm_id]).count
+  end
+
   def test_count_with_column_parameter
     assert_equal 5, Account.count(:firm_id)
   end
 
+  def test_count_with_arel_attribute
+    assert_equal 5, Account.count(Account.arel_table[:firm_id])
+  end
+
+  def test_count_with_arel_star
+    assert_equal 6, Account.count(Arel.star)
+  end
+
   def test_count_with_distinct
     assert_equal 4, Account.select(:credit_limit).distinct.count
-
-    assert_deprecated do
-      assert_equal 4, Account.select(:credit_limit).uniq.count
-    end
   end
 
   def test_count_with_aliased_attribute
@@ -374,14 +488,29 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_should_count_field_in_joined_table
-    assert_equal 5, Account.joins(:firm).count('companies.id')
-    assert_equal 4, Account.joins(:firm).distinct.count('companies.id')
+    assert_equal 5, Account.joins(:firm).count("companies.id")
+    assert_equal 4, Account.joins(:firm).distinct.count("companies.id")
+  end
+
+  def test_count_arel_attribute_in_joined_table_with
+    assert_equal 5, Account.joins(:firm).count(Company.arel_table[:id])
+    assert_equal 4, Account.joins(:firm).distinct.count(Company.arel_table[:id])
+  end
+
+  def test_count_selected_arel_attribute_in_joined_table
+    assert_equal 5, Account.joins(:firm).select(Company.arel_table[:id]).count
+    assert_equal 4, Account.joins(:firm).distinct.select(Company.arel_table[:id]).count
   end
 
   def test_should_count_field_in_joined_table_with_group_by
-    c = Account.group('accounts.firm_id').joins(:firm).count('companies.id')
+    c = Account.group("accounts.firm_id").joins(:firm).count("companies.id")
+
+    [1, 6, 2, 9].each { |firm_id| assert_includes c.keys, firm_id }
+  end
 
-    [1,6,2,9].each { |firm_id| assert c.keys.include?(firm_id) }
+  def test_should_count_field_of_root_table_with_conflicting_group_by_column
+    assert_equal({ 1 => 1 }, Firm.joins(:accounts).group(:firm_id).count)
+    assert_equal({ 1 => 1 }, Firm.joins(:accounts).group("accounts.firm_id").count)
   end
 
   def test_count_with_no_parameters_isnt_deprecated
@@ -401,14 +530,17 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_count_with_where_and_order
-    assert_equal 1, Account.where(firm_name: '37signals').count
-    assert_equal 1, Account.where(firm_name: '37signals').order(:firm_name).count
-    assert_equal 1, Account.where(firm_name: '37signals').order(:firm_name).reverse_order.count
+    assert_equal 1, Account.where(firm_name: "37signals").count
+    assert_equal 1, Account.where(firm_name: "37signals").order(:firm_name).count
+    assert_equal 1, Account.where(firm_name: "37signals").order(:firm_name).reverse_order.count
+  end
+
+  def test_count_with_block
+    assert_equal 4, Account.count { |account| account.credit_limit.modulo(10).zero? }
   end
 
   def test_should_sum_expression
-    # Oracle adapter returns floating point value 636.0 after SUM
-    if current_adapter?(:OracleAdapter)
+    if current_adapter?(:SQLite3Adapter, :Mysql2Adapter, :PostgreSQLAdapter, :OracleAdapter)
       assert_equal 636, Account.sum("2 * credit_limit")
     else
       assert_equal 636, Account.sum("2 * credit_limit").to_i
@@ -416,69 +548,69 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_sum_expression_returns_zero_when_no_records_to_sum
-    assert_equal 0, Account.where('1 = 2').sum("2 * credit_limit")
+    assert_equal 0, Account.where("1 = 2").sum("2 * credit_limit")
   end
 
   def test_count_with_from_option
-    assert_equal Company.count(:all), Company.from('companies').count(:all)
+    assert_equal Company.count(:all), Company.from("companies").count(:all)
     assert_equal Account.where("credit_limit = 50").count(:all),
-        Account.from('accounts').where("credit_limit = 50").count(:all)
-    assert_equal Company.where(:type => "Firm").count(:type),
-        Company.where(:type => "Firm").from('companies').count(:type)
+        Account.from("accounts").where("credit_limit = 50").count(:all)
+    assert_equal Company.where(type: "Firm").count(:type),
+        Company.where(type: "Firm").from("companies").count(:type)
   end
 
   def test_sum_with_from_option
-    assert_equal Account.sum(:credit_limit), Account.from('accounts').sum(:credit_limit)
+    assert_equal Account.sum(:credit_limit), Account.from("accounts").sum(:credit_limit)
     assert_equal Account.where("credit_limit > 50").sum(:credit_limit),
-        Account.where("credit_limit > 50").from('accounts').sum(:credit_limit)
+        Account.where("credit_limit > 50").from("accounts").sum(:credit_limit)
   end
 
   def test_average_with_from_option
-    assert_equal Account.average(:credit_limit), Account.from('accounts').average(:credit_limit)
+    assert_equal Account.average(:credit_limit), Account.from("accounts").average(:credit_limit)
     assert_equal Account.where("credit_limit > 50").average(:credit_limit),
-        Account.where("credit_limit > 50").from('accounts').average(:credit_limit)
+        Account.where("credit_limit > 50").from("accounts").average(:credit_limit)
   end
 
   def test_minimum_with_from_option
-    assert_equal Account.minimum(:credit_limit), Account.from('accounts').minimum(:credit_limit)
+    assert_equal Account.minimum(:credit_limit), Account.from("accounts").minimum(:credit_limit)
     assert_equal Account.where("credit_limit > 50").minimum(:credit_limit),
-        Account.where("credit_limit > 50").from('accounts').minimum(:credit_limit)
+        Account.where("credit_limit > 50").from("accounts").minimum(:credit_limit)
   end
 
   def test_maximum_with_from_option
-    assert_equal Account.maximum(:credit_limit), Account.from('accounts').maximum(:credit_limit)
+    assert_equal Account.maximum(:credit_limit), Account.from("accounts").maximum(:credit_limit)
     assert_equal Account.where("credit_limit > 50").maximum(:credit_limit),
-        Account.where("credit_limit > 50").from('accounts').maximum(:credit_limit)
+        Account.where("credit_limit > 50").from("accounts").maximum(:credit_limit)
   end
 
   def test_maximum_with_not_auto_table_name_prefix_if_column_included
-    Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
+    Company.create!(name: "test", contracts: [Contract.new(developer_id: 7)])
 
     assert_equal 7, Company.includes(:contracts).maximum(:developer_id)
   end
 
   def test_minimum_with_not_auto_table_name_prefix_if_column_included
-    Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
+    Company.create!(name: "test", contracts: [Contract.new(developer_id: 7)])
 
     assert_equal 7, Company.includes(:contracts).minimum(:developer_id)
   end
 
   def test_sum_with_not_auto_table_name_prefix_if_column_included
-    Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
+    Company.create!(name: "test", contracts: [Contract.new(developer_id: 7)])
 
     assert_equal 7, Company.includes(:contracts).sum(:developer_id)
   end
 
-  def test_from_option_with_specified_index
-    if Edge.connection.adapter_name == 'MySQL' or Edge.connection.adapter_name == 'Mysql2'
-      assert_equal Edge.count(:all), Edge.from('edges USE INDEX(unique_edge_index)').count(:all)
-      assert_equal Edge.where('sink_id < 5').count(:all),
-          Edge.from('edges USE INDEX(unique_edge_index)').where('sink_id < 5').count(:all)
+  if current_adapter?(:Mysql2Adapter)
+    def test_from_option_with_specified_index
+      assert_equal Edge.count(:all), Edge.from("edges USE INDEX(unique_edge_index)").count(:all)
+      assert_equal Edge.where("sink_id < 5").count(:all),
+          Edge.from("edges USE INDEX(unique_edge_index)").where("sink_id < 5").count(:all)
     end
   end
 
   def test_from_option_with_table_different_than_class
-    assert_equal Account.count(:all), Company.from('accounts').count(:all)
+    assert_equal Account.count(:all), Company.from("accounts").count(:all)
   end
 
   def test_distinct_is_honored_when_used_with_count_operation_after_group
@@ -491,22 +623,37 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_pluck
-    assert_equal [1,2,3,4,5], Topic.order(:id).pluck(:id)
+    assert_equal [1, 2, 3, 4, 5], Topic.order(:id).pluck(:id)
   end
 
   def test_pluck_without_column_names
-    assert_equal [[1, "Firm", 1, nil, "37signals", nil, 1, nil, ""]],
-      Company.order(:id).limit(1).pluck
+    if current_adapter?(:OracleAdapter)
+      assert_equal [[1, "Firm", 1, nil, "37signals", nil, 1, nil, nil]], Company.order(:id).limit(1).pluck
+    else
+      assert_equal [[1, "Firm", 1, nil, "37signals", nil, 1, nil, ""]], Company.order(:id).limit(1).pluck
+    end
   end
 
   def test_pluck_type_cast
     topic = topics(:first)
-    relation = Topic.where(:id => topic.id)
+    relation = Topic.where(id: topic.id)
     assert_equal [ topic.approved ], relation.pluck(:approved)
     assert_equal [ topic.last_read ], relation.pluck(:last_read)
     assert_equal [ topic.written_on ], relation.pluck(:written_on)
   end
 
+  def test_pluck_with_type_cast_does_not_corrupt_the_query_cache
+    topic = topics(:first)
+    relation = Topic.where(id: topic.id)
+    assert_queries 1 do
+      Topic.cache do
+        kind = relation.select(:written_on).load.first.read_attribute_before_type_cast(:written_on).class
+        relation.pluck(:written_on)
+        assert_kind_of kind, relation.select(:written_on).load.first.read_attribute_before_type_cast(:written_on)
+      end
+    end
+  end
+
   def test_pluck_and_distinct
     assert_equal [50, 53, 55, 60], Account.order(:credit_limit).distinct.pluck(:credit_limit)
   end
@@ -518,42 +665,42 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_pluck_on_aliased_attribute
-    assert_equal 'The First Topic', Topic.order(:id).pluck(:heading).first
+    assert_equal "The First Topic", Topic.order(:id).pluck(:heading).first
   end
 
   def test_pluck_with_serialization
-    t = Topic.create!(:content => { :foo => :bar })
-    assert_equal [{:foo => :bar}], Topic.where(:id => t.id).pluck(:content)
+    t = Topic.create!(content: { foo: :bar })
+    assert_equal [{ foo: :bar }], Topic.where(id: t.id).pluck(:content)
   end
 
   def test_pluck_with_qualified_column_name
-    assert_equal [1,2,3,4,5], Topic.order(:id).pluck("topics.id")
+    assert_equal [1, 2, 3, 4, 5], Topic.order(:id).pluck("topics.id")
   end
 
   def test_pluck_auto_table_name_prefix
-    c = Company.create!(:name => "test", :contracts => [Contract.new])
+    c = Company.create!(name: "test", contracts: [Contract.new])
     assert_equal [c.id], Company.joins(:contracts).pluck(:id)
   end
 
   def test_pluck_if_table_included
-    c = Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
+    c = Company.create!(name: "test", contracts: [Contract.new(developer_id: 7)])
     assert_equal [c.id], Company.includes(:contracts).where("contracts.id" => c.contracts.first).pluck(:id)
   end
 
   def test_pluck_not_auto_table_name_prefix_if_column_joined
-    Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
+    Company.create!(name: "test", contracts: [Contract.new(developer_id: 7)])
     assert_equal [7], Company.joins(:contracts).pluck(:developer_id)
   end
 
   def test_pluck_with_selection_clause
-    assert_equal [50, 53, 55, 60], Account.pluck('DISTINCT credit_limit').sort
-    assert_equal [50, 53, 55, 60], Account.pluck('DISTINCT accounts.credit_limit').sort
-    assert_equal [50, 53, 55, 60], Account.pluck('DISTINCT(credit_limit)').sort
+    assert_equal [50, 53, 55, 60], Account.pluck(Arel.sql("DISTINCT credit_limit")).sort
+    assert_equal [50, 53, 55, 60], Account.pluck(Arel.sql("DISTINCT accounts.credit_limit")).sort
+    assert_equal [50, 53, 55, 60], Account.pluck(Arel.sql("DISTINCT(credit_limit)")).sort
 
     # MySQL returns "SUM(DISTINCT(credit_limit))" as the column name unless
     # an alias is provided.  Without the alias, the column cannot be found
     # and properly typecast.
-    assert_equal [50 + 53 + 55 + 60], Account.pluck('SUM(DISTINCT(credit_limit)) as credit_limit')
+    assert_equal [50 + 53 + 55 + 60], Account.pluck(Arel.sql("SUM(DISTINCT(credit_limit)) as credit_limit"))
   end
 
   def test_plucks_with_ids
@@ -562,11 +709,34 @@ class CalculationsTest < ActiveRecord::TestCase
 
   def test_pluck_with_includes_limit_and_empty_result
     assert_equal [], Topic.includes(:replies).limit(0).pluck(:id)
-    assert_equal [], Topic.includes(:replies).limit(1).where('0 = 1').pluck(:id)
+    assert_equal [], Topic.includes(:replies).limit(1).where("0 = 1").pluck(:id)
+  end
+
+  def test_pluck_with_includes_offset
+    assert_equal [5], Topic.includes(:replies).order(:id).offset(4).pluck(:id)
+    assert_equal [], Topic.includes(:replies).order(:id).offset(5).pluck(:id)
+  end
+
+  def test_group_by_with_limit
+    expected = { "Post" => 8, "SpecialPost" => 1 }
+    actual = Post.includes(:comments).group(:type).order(:type).limit(2).count("comments.id")
+    assert_equal expected, actual
+  end
+
+  def test_group_by_with_offset
+    expected = { "SpecialPost" => 1, "StiPost" => 2 }
+    actual = Post.includes(:comments).group(:type).order(:type).offset(1).count("comments.id")
+    assert_equal expected, actual
+  end
+
+  def test_group_by_with_limit_and_offset
+    expected = { "SpecialPost" => 1 }
+    actual = Post.includes(:comments).group(:type).order(:type).offset(1).limit(1).count("comments.id")
+    assert_equal expected, actual
   end
 
   def test_pluck_not_auto_table_name_prefix_if_column_included
-    Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
+    Company.create!(name: "test", contracts: [Contract.new(developer_id: 7)])
     ids = Company.includes(:contracts).pluck(:developer_id)
     assert_equal Company.count, ids.length
     assert_equal [7], ids.compact
@@ -587,12 +757,12 @@ class CalculationsTest < ActiveRecord::TestCase
 
   def test_pluck_with_multiple_columns_and_selection_clause
     assert_equal [[1, 50], [2, 50], [3, 50], [4, 60], [5, 55], [6, 53]],
-      Account.pluck('id, credit_limit')
+      Account.pluck("id, credit_limit")
   end
 
   def test_pluck_with_multiple_columns_and_includes
-    Company.create!(:name => "test", :contracts => [Contract.new(:developer_id => 7)])
-    companies_and_developers = Company.order('companies.id').includes(:contracts).pluck(:name, :developer_id)
+    Company.create!(name: "test", contracts: [Contract.new(developer_id: 7)])
+    companies_and_developers = Company.order("companies.id").includes(:contracts).pluck(:name, :developer_id)
 
     assert_equal Company.count, companies_and_developers.length
     assert_equal ["37signals", nil], companies_and_developers.first
@@ -600,21 +770,21 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_pluck_with_reserved_words
-    Possession.create!(:where => "Over There")
+    Possession.create!(where: "Over There")
 
     assert_equal ["Over There"], Possession.pluck(:where)
   end
 
   def test_pluck_replaces_select_clause
     taks_relation = Topic.select(:approved, :id).order(:id)
-    assert_equal [1,2,3,4,5], taks_relation.pluck(:id)
+    assert_equal [1, 2, 3, 4, 5], taks_relation.pluck(:id)
     assert_equal [false, true, true, true, true], taks_relation.pluck(:approved)
   end
 
   def test_pluck_columns_with_same_name
     expected = [["The First Topic", "The Second Topic of the day"], ["The Third Topic of the day", "The Fourth Topic of the day"]]
     actual = Topic.joins(:replies)
-      .pluck('topics.title', 'replies_topics.title')
+      .pluck("topics.title", "replies_topics.title")
     assert_equal expected, actual
   end
 
@@ -633,26 +803,49 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_pluck_loaded_relation
+    Company.attribute_names # Load schema information so we don't query below
     companies = Company.order(:id).limit(3).load
+
     assert_no_queries do
-      assert_equal ['37signals', 'Summit', 'Microsoft'], companies.pluck(:name)
+      assert_equal ["37signals", "Summit", "Microsoft"], companies.pluck(:name)
     end
   end
 
   def test_pluck_loaded_relation_multiple_columns
+    Company.attribute_names # Load schema information so we don't query below
     companies = Company.order(:id).limit(3).load
+
     assert_no_queries do
-      assert_equal [[1, '37signals'], [2, 'Summit'], [3, 'Microsoft']], companies.pluck(:id, :name)
+      assert_equal [[1, "37signals"], [2, "Summit"], [3, "Microsoft"]], companies.pluck(:id, :name)
     end
   end
 
   def test_pluck_loaded_relation_sql_fragment
+    Company.attribute_names # Load schema information so we don't query below
     companies = Company.order(:name).limit(3).load
+
     assert_queries 1 do
-      assert_equal ['37signals', 'Apex', 'Ex Nihilo'], companies.pluck('DISTINCT name')
+      assert_equal ["37signals", "Apex", "Ex Nihilo"], companies.pluck(Arel.sql("DISTINCT name"))
     end
   end
 
+  def test_pick_one
+    assert_equal "The First Topic", Topic.order(:id).pick(:heading)
+    assert_nil Topic.none.pick(:heading)
+    assert_nil Topic.where("1=0").pick(:heading)
+  end
+
+  def test_pick_two
+    assert_equal ["David", "david@loudthinking.com"], Topic.order(:id).pick(:author_name, :author_email_address)
+    assert_nil Topic.none.pick(:author_name, :author_email_address)
+    assert_nil Topic.where("1=0").pick(:author_name, :author_email_address)
+  end
+
+  def test_pick_delegate_to_all
+    cool_first = minivans(:cool_first)
+    assert_equal cool_first.color, Minivan.pick(:color)
+  end
+
   def test_grouped_calculation_with_polymorphic_relation
     part = ShipPart.create!(name: "has trinket")
     part.trinkets.create!
@@ -666,8 +859,8 @@ class CalculationsTest < ActiveRecord::TestCase
   end
 
   def test_should_reference_correct_aliases_while_joining_tables_of_has_many_through_association
-    assert_nothing_raised ActiveRecord::StatementInvalid do
-      developer = Developer.create!(name: 'developer')
+    assert_nothing_raised do
+      developer = Developer.create!(name: "developer")
       developer.ratings.includes(comment: :post).where(posts: { id: 1 }).count
     end
   end
@@ -681,4 +874,94 @@ class CalculationsTest < ActiveRecord::TestCase
     end
     assert block_called
   end
+
+  def test_having_with_strong_parameters
+    protected_params = Class.new do
+      attr_reader :permitted
+      alias :permitted? :permitted
+
+      def initialize(parameters)
+        @parameters = parameters
+        @permitted = false
+      end
+
+      def to_h
+        @parameters
+      end
+
+      def permit!
+        @permitted = true
+        self
+      end
+    end
+
+    params = protected_params.new(credit_limit: "50")
+
+    assert_raises(ActiveModel::ForbiddenAttributesError) do
+      Account.group(:id).having(params)
+    end
+
+    result = Account.group(:id).having(params.permit!)
+    assert_equal 50, result[0].credit_limit
+    assert_equal 50, result[1].credit_limit
+    assert_equal 50, result[2].credit_limit
+  end
+
+  def test_group_by_attribute_with_custom_type
+    assert_equal({ "proposed" => 2, "published" => 2 }, Book.group(:status).count)
+  end
+
+  def test_deprecate_count_with_block_and_column_name
+    assert_deprecated do
+      assert_equal 6, Account.count(:firm_id) { true }
+    end
+  end
+
+  def test_deprecate_sum_with_block_and_column_name
+    assert_deprecated do
+      assert_equal 6, Account.sum(:firm_id) { 1 }
+    end
+  end
+
+  test "#skip_query_cache! for #pluck" do
+    Account.cache do
+      assert_queries(1) do
+        Account.pluck(:credit_limit)
+        Account.pluck(:credit_limit)
+      end
+
+      assert_queries(2) do
+        Account.all.skip_query_cache!.pluck(:credit_limit)
+        Account.all.skip_query_cache!.pluck(:credit_limit)
+      end
+    end
+  end
+
+  test "#skip_query_cache! for a simple calculation" do
+    Account.cache do
+      assert_queries(1) do
+        Account.calculate(:sum, :credit_limit)
+        Account.calculate(:sum, :credit_limit)
+      end
+
+      assert_queries(2) do
+        Account.all.skip_query_cache!.calculate(:sum, :credit_limit)
+        Account.all.skip_query_cache!.calculate(:sum, :credit_limit)
+      end
+    end
+  end
+
+  test "#skip_query_cache! for a grouped calculation" do
+    Account.cache do
+      assert_queries(1) do
+        Account.group(:firm_id).calculate(:sum, :credit_limit)
+        Account.group(:firm_id).calculate(:sum, :credit_limit)
+      end
+
+      assert_queries(2) do
+        Account.all.skip_query_cache!.group(:firm_id).calculate(:sum, :credit_limit)
+        Account.all.skip_query_cache!.group(:firm_id).calculate(:sum, :credit_limit)
+      end
+    end
+  end
 end
diff --git a/activerecord/test/cases/callbacks_test.rb b/activerecord/test/cases/callbacks_test.rb
index 73ac30e547..0ea3fb86a6 100644
--- a/activerecord/test/cases/callbacks_test.rb
+++ b/activerecord/test/cases/callbacks_test.rb
@@ -1,22 +1,20 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/developer'
-require 'models/computer'
+require "models/developer"
+require "models/computer"
 
 class CallbackDeveloper < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
   class << self
-    def callback_string(callback_method)
-      "history << [#{callback_method.to_sym.inspect}, :string]"
-    end
-
     def callback_proc(callback_method)
       Proc.new { |model| model.history << [callback_method, :proc] }
     end
 
     def define_callback_method(callback_method)
       define_method(callback_method) do
-        self.history << [callback_method, :method]
+        history << [callback_method, :method]
       end
       send(callback_method, :"#{callback_method}")
     end
@@ -31,9 +29,8 @@ class CallbackDeveloper < ActiveRecord::Base
   end
 
   ActiveRecord::Callbacks::CALLBACKS.each do |callback_method|
-    next if callback_method.to_s =~ /^around_/
+    next if callback_method.to_s.start_with?("around_")
     define_callback_method(callback_method)
-    send(callback_method, callback_string(callback_method))
     send(callback_method, callback_proc(callback_method))
     send(callback_method, callback_object(callback_method))
     send(callback_method) { |model| model.history << [callback_method, :block] }
@@ -44,30 +41,24 @@ class CallbackDeveloper < ActiveRecord::Base
   end
 end
 
-class CallbackDeveloperWithFalseValidation < CallbackDeveloper
-  before_validation proc { |model| model.history << [:before_validation, :returning_false]; false }
-  before_validation proc { |model| model.history << [:before_validation, :should_never_get_here] }
-end
-
 class CallbackDeveloperWithHaltedValidation < CallbackDeveloper
   before_validation proc { |model| model.history << [:before_validation, :throwing_abort]; throw(:abort) }
   before_validation proc { |model| model.history << [:before_validation, :should_never_get_here] }
 end
 
 class ParentDeveloper < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
   attr_accessor :after_save_called
-  before_validation {|record| record.after_save_called = true}
+  before_validation { |record| record.after_save_called = true }
 end
 
 class ChildDeveloper < ParentDeveloper
-
 end
 
 class ImmutableDeveloper < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
-  validates_inclusion_of :salary, :in => 50000..200000
+  validates_inclusion_of :salary, in: 50000..200000
 
   before_save :cancel
   before_destroy :cancel
@@ -79,7 +70,7 @@ class ImmutableDeveloper < ActiveRecord::Base
 end
 
 class DeveloperWithCanceledCallbacks < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
   validates_inclusion_of :salary, in: 50000..200000
 
@@ -93,19 +84,19 @@ class DeveloperWithCanceledCallbacks < ActiveRecord::Base
 end
 
 class OnCallbacksDeveloper < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
   before_validation { history << :before_validation }
-  before_validation(:on => :create){ history << :before_validation_on_create }
-  before_validation(:on => :update){ history << :before_validation_on_update }
+  before_validation(on: :create) { history << :before_validation_on_create }
+  before_validation(on: :update) { history << :before_validation_on_update }
 
   validate do
     history << :validate
   end
 
   after_validation { history << :after_validation }
-  after_validation(:on => :create){ history << :after_validation_on_create }
-  after_validation(:on => :update){ history << :after_validation_on_update }
+  after_validation(on: :create) { history << :after_validation_on_create }
+  after_validation(on: :update) { history << :after_validation_on_update }
 
   def history
     @history ||= []
@@ -113,24 +104,24 @@ class OnCallbacksDeveloper < ActiveRecord::Base
 end
 
 class ContextualCallbacksDeveloper < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
   before_validation { history << :before_validation }
-  before_validation :before_validation_on_create_and_update, :on => [ :create, :update ]
+  before_validation :before_validation_on_create_and_update, on: [ :create, :update ]
 
   validate do
     history << :validate
   end
 
   after_validation { history << :after_validation }
-  after_validation :after_validation_on_create_and_update, :on => [ :create, :update ]
+  after_validation :after_validation_on_create_and_update, on: [ :create, :update ]
 
   def before_validation_on_create_and_update
-    history << "before_validation_on_#{self.validation_context}".to_sym
+    history << "before_validation_on_#{validation_context}".to_sym
   end
 
   def after_validation_on_create_and_update
-    history << "after_validation_on_#{self.validation_context}".to_sym
+    history << "after_validation_on_#{validation_context}".to_sym
   end
 
   def history
@@ -138,25 +129,8 @@ class ContextualCallbacksDeveloper < ActiveRecord::Base
   end
 end
 
-class CallbackCancellationDeveloper < ActiveRecord::Base
-  self.table_name = 'developers'
-
-  attr_reader   :after_save_called, :after_create_called, :after_update_called, :after_destroy_called
-  attr_accessor :cancel_before_save, :cancel_before_create, :cancel_before_update, :cancel_before_destroy
-
-  before_save    {defined?(@cancel_before_save) ? !@cancel_before_save : false}
-  before_create  { !@cancel_before_create  }
-  before_update  { !@cancel_before_update  }
-  before_destroy { !@cancel_before_destroy }
-
-  after_save    { @after_save_called    = true }
-  after_update  { @after_update_called  = true }
-  after_create  { @after_create_called  = true }
-  after_destroy { @after_destroy_called = true }
-end
-
 class CallbackHaltedDeveloper < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
   attr_reader   :after_save_called, :after_create_called, :after_update_called, :after_destroy_called
   attr_accessor :cancel_before_save, :cancel_before_create, :cancel_before_update, :cancel_before_destroy
@@ -179,7 +153,6 @@ class CallbacksTest < ActiveRecord::TestCase
     david = CallbackDeveloper.new
     assert_equal [
       [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
       [ :after_initialize,            :proc   ],
       [ :after_initialize,            :object ],
       [ :after_initialize,            :block  ],
@@ -190,12 +163,10 @@ class CallbacksTest < ActiveRecord::TestCase
     david = CallbackDeveloper.find(1)
     assert_equal [
       [ :after_find,            :method ],
-      [ :after_find,            :string ],
       [ :after_find,            :proc   ],
       [ :after_find,            :object ],
       [ :after_find,            :block  ],
       [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
       [ :after_initialize,            :proc   ],
       [ :after_initialize,            :object ],
       [ :after_initialize,            :block  ],
@@ -207,17 +178,14 @@ class CallbacksTest < ActiveRecord::TestCase
     david.valid?
     assert_equal [
       [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
       [ :after_initialize,            :proc   ],
       [ :after_initialize,            :object ],
       [ :after_initialize,            :block  ],
       [ :before_validation,           :method ],
-      [ :before_validation,           :string ],
       [ :before_validation,           :proc   ],
       [ :before_validation,           :object ],
       [ :before_validation,           :block  ],
       [ :after_validation,            :method ],
-      [ :after_validation,            :string ],
       [ :after_validation,            :proc   ],
       [ :after_validation,            :object ],
       [ :after_validation,            :block  ],
@@ -229,22 +197,18 @@ class CallbacksTest < ActiveRecord::TestCase
     david.valid?
     assert_equal [
       [ :after_find,            :method ],
-      [ :after_find,            :string ],
       [ :after_find,            :proc   ],
       [ :after_find,            :object ],
       [ :after_find,            :block  ],
       [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
       [ :after_initialize,            :proc   ],
       [ :after_initialize,            :object ],
       [ :after_initialize,            :block  ],
       [ :before_validation,           :method ],
-      [ :before_validation,           :string ],
       [ :before_validation,           :proc   ],
       [ :before_validation,           :object ],
       [ :before_validation,           :block  ],
       [ :after_validation,            :method ],
-      [ :after_validation,            :string ],
       [ :after_validation,            :proc   ],
       [ :after_validation,            :object ],
       [ :after_validation,            :block  ],
@@ -252,53 +216,45 @@ class CallbacksTest < ActiveRecord::TestCase
   end
 
   def test_create
-    david = CallbackDeveloper.create('name' => 'David', 'salary' => 1000000)
+    david = CallbackDeveloper.create("name" => "David", "salary" => 1000000)
     assert_equal [
       [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
       [ :after_initialize,            :proc   ],
       [ :after_initialize,            :object ],
       [ :after_initialize,            :block  ],
       [ :before_validation,           :method ],
-      [ :before_validation,           :string ],
       [ :before_validation,           :proc   ],
       [ :before_validation,           :object ],
       [ :before_validation,           :block  ],
       [ :after_validation,            :method ],
-      [ :after_validation,            :string ],
       [ :after_validation,            :proc   ],
       [ :after_validation,            :object ],
       [ :after_validation,            :block  ],
       [ :before_save,                 :method ],
-      [ :before_save,                 :string ],
       [ :before_save,                 :proc   ],
       [ :before_save,                 :object ],
       [ :before_save,                 :block  ],
       [ :before_create,               :method ],
-      [ :before_create,               :string ],
       [ :before_create,               :proc   ],
       [ :before_create,               :object ],
       [ :before_create,               :block  ],
       [ :after_create,                :method ],
-      [ :after_create,                :string ],
       [ :after_create,                :proc   ],
       [ :after_create,                :object ],
       [ :after_create,                :block  ],
       [ :after_save,                  :method ],
-      [ :after_save,                  :string ],
       [ :after_save,                  :proc   ],
       [ :after_save,                  :object ],
       [ :after_save,                  :block  ],
       [ :after_commit,                :block  ],
       [ :after_commit,                :object ],
       [ :after_commit,                :proc   ],
-      [ :after_commit,                :string ],
       [ :after_commit,                :method ]
     ], david.history
   end
 
   def test_validate_on_create
-    david = OnCallbacksDeveloper.create('name' => 'David', 'salary' => 1000000)
+    david = OnCallbacksDeveloper.create("name" => "David", "salary" => 1000000)
     assert_equal [
       :before_validation,
       :before_validation_on_create,
@@ -309,7 +265,7 @@ class CallbacksTest < ActiveRecord::TestCase
   end
 
   def test_validate_on_contextual_create
-    david = ContextualCallbacksDeveloper.create('name' => 'David', 'salary' => 1000000)
+    david = ContextualCallbacksDeveloper.create("name" => "David", "salary" => 1000000)
     assert_equal [
       :before_validation,
       :before_validation_on_create,
@@ -324,49 +280,40 @@ class CallbacksTest < ActiveRecord::TestCase
     david.save
     assert_equal [
       [ :after_find,            :method ],
-      [ :after_find,            :string ],
       [ :after_find,            :proc   ],
       [ :after_find,            :object ],
       [ :after_find,            :block  ],
       [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
       [ :after_initialize,            :proc   ],
       [ :after_initialize,            :object ],
       [ :after_initialize,            :block  ],
       [ :before_validation,           :method ],
-      [ :before_validation,           :string ],
       [ :before_validation,           :proc   ],
       [ :before_validation,           :object ],
       [ :before_validation,           :block  ],
       [ :after_validation,            :method ],
-      [ :after_validation,            :string ],
       [ :after_validation,            :proc   ],
       [ :after_validation,            :object ],
       [ :after_validation,            :block  ],
       [ :before_save,                 :method ],
-      [ :before_save,                 :string ],
       [ :before_save,                 :proc   ],
       [ :before_save,                 :object ],
       [ :before_save,                 :block  ],
       [ :before_update,               :method ],
-      [ :before_update,               :string ],
       [ :before_update,               :proc   ],
       [ :before_update,               :object ],
       [ :before_update,               :block  ],
       [ :after_update,                :method ],
-      [ :after_update,                :string ],
       [ :after_update,                :proc   ],
       [ :after_update,                :object ],
       [ :after_update,                :block  ],
       [ :after_save,                  :method ],
-      [ :after_save,                  :string ],
       [ :after_save,                  :proc   ],
       [ :after_save,                  :object ],
       [ :after_save,                  :block  ],
       [ :after_commit,                :block  ],
       [ :after_commit,                :object ],
       [ :after_commit,                :proc   ],
-      [ :after_commit,                :string ],
       [ :after_commit,                :method ]
     ], david.history
   end
@@ -400,29 +347,24 @@ class CallbacksTest < ActiveRecord::TestCase
     david.destroy
     assert_equal [
       [ :after_find,            :method ],
-      [ :after_find,            :string ],
       [ :after_find,            :proc   ],
       [ :after_find,            :object ],
       [ :after_find,            :block  ],
       [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
       [ :after_initialize,            :proc   ],
       [ :after_initialize,            :object ],
       [ :after_initialize,            :block  ],
       [ :before_destroy,              :method ],
-      [ :before_destroy,              :string ],
       [ :before_destroy,              :proc   ],
       [ :before_destroy,              :object ],
       [ :before_destroy,              :block  ],
       [ :after_destroy,               :method ],
-      [ :after_destroy,               :string ],
       [ :after_destroy,               :proc   ],
       [ :after_destroy,               :object ],
       [ :after_destroy,               :block  ],
       [ :after_commit,                :block  ],
       [ :after_commit,                :object ],
       [ :after_commit,                :proc   ],
-      [ :after_commit,                :string ],
       [ :after_commit,                :method ]
     ], david.history
   end
@@ -432,165 +374,71 @@ class CallbacksTest < ActiveRecord::TestCase
     CallbackDeveloper.delete(david.id)
     assert_equal [
       [ :after_find,            :method ],
-      [ :after_find,            :string ],
       [ :after_find,            :proc   ],
       [ :after_find,            :object ],
       [ :after_find,            :block  ],
       [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
       [ :after_initialize,            :proc   ],
       [ :after_initialize,            :object ],
       [ :after_initialize,            :block  ],
     ], david.history
   end
 
-  def test_deprecated_before_save_returning_false
-    david = ImmutableDeveloper.find(1)
-    assert_deprecated do
-      assert david.valid?
-      assert !david.save
-      exc = assert_raise(ActiveRecord::RecordNotSaved) { david.save! }
-      assert_equal exc.record, david
-      assert_equal "Failed to save the record", exc.message
-    end
-
-    david = ImmutableDeveloper.find(1)
-    david.salary = 10_000_000
-    assert !david.valid?
-    assert !david.save
-    assert_raise(ActiveRecord::RecordInvalid) { david.save! }
-
-    someone = CallbackCancellationDeveloper.find(1)
-    someone.cancel_before_save = true
-    assert_deprecated do
-      assert someone.valid?
-      assert !someone.save
-    end
-    assert_save_callbacks_not_called(someone)
-  end
-
-  def test_deprecated_before_create_returning_false
-    someone = CallbackCancellationDeveloper.new
-    someone.cancel_before_create = true
-    assert_deprecated do
-      assert someone.valid?
-      assert !someone.save
-    end
-    assert_save_callbacks_not_called(someone)
-  end
-
-  def test_deprecated_before_update_returning_false
-    someone = CallbackCancellationDeveloper.find(1)
-    someone.cancel_before_update = true
-    assert_deprecated do
-      assert someone.valid?
-      assert !someone.save
-    end
-    assert_save_callbacks_not_called(someone)
-  end
-
-  def test_deprecated_before_destroy_returning_false
-    david = ImmutableDeveloper.find(1)
-    assert_deprecated do
-      assert !david.destroy
-      exc = assert_raise(ActiveRecord::RecordNotDestroyed) { david.destroy! }
-      assert_equal exc.record, david
-      assert_equal "Failed to destroy the record", exc.message
-    end
-    assert_not_nil ImmutableDeveloper.find_by_id(1)
-
-    someone = CallbackCancellationDeveloper.find(1)
-    someone.cancel_before_destroy = true
-    assert_deprecated do
-      assert !someone.destroy
-      assert_raise(ActiveRecord::RecordNotDestroyed) { someone.destroy! }
-    end
-    assert !someone.after_destroy_called
-  end
-
   def assert_save_callbacks_not_called(someone)
-    assert !someone.after_save_called
-    assert !someone.after_create_called
-    assert !someone.after_update_called
+    assert_not someone.after_save_called
+    assert_not someone.after_create_called
+    assert_not someone.after_update_called
   end
   private :assert_save_callbacks_not_called
 
   def test_before_create_throwing_abort
     someone = CallbackHaltedDeveloper.new
     someone.cancel_before_create = true
-    assert someone.valid?
-    assert !someone.save
+    assert_predicate someone, :valid?
+    assert_not someone.save
     assert_save_callbacks_not_called(someone)
   end
 
   def test_before_save_throwing_abort
     david = DeveloperWithCanceledCallbacks.find(1)
-    assert david.valid?
-    assert !david.save
+    assert_predicate david, :valid?
+    assert_not david.save
     exc = assert_raise(ActiveRecord::RecordNotSaved) { david.save! }
-    assert_equal exc.record, david
+    assert_equal david, exc.record
 
     david = DeveloperWithCanceledCallbacks.find(1)
     david.salary = 10_000_000
-    assert !david.valid?
-    assert !david.save
+    assert_not_predicate david, :valid?
+    assert_not david.save
     assert_raise(ActiveRecord::RecordInvalid) { david.save! }
 
     someone = CallbackHaltedDeveloper.find(1)
     someone.cancel_before_save = true
-    assert someone.valid?
-    assert !someone.save
+    assert_predicate someone, :valid?
+    assert_not someone.save
     assert_save_callbacks_not_called(someone)
   end
 
   def test_before_update_throwing_abort
     someone = CallbackHaltedDeveloper.find(1)
     someone.cancel_before_update = true
-    assert someone.valid?
-    assert !someone.save
+    assert_predicate someone, :valid?
+    assert_not someone.save
     assert_save_callbacks_not_called(someone)
   end
 
   def test_before_destroy_throwing_abort
     david = DeveloperWithCanceledCallbacks.find(1)
-    assert !david.destroy
+    assert_not david.destroy
     exc = assert_raise(ActiveRecord::RecordNotDestroyed) { david.destroy! }
-    assert_equal exc.record, david
+    assert_equal david, exc.record
     assert_not_nil ImmutableDeveloper.find_by_id(1)
 
     someone = CallbackHaltedDeveloper.find(1)
     someone.cancel_before_destroy = true
-    assert !someone.destroy
+    assert_not someone.destroy
     assert_raise(ActiveRecord::RecordNotDestroyed) { someone.destroy! }
-    assert !someone.after_destroy_called
-  end
-
-  def test_callback_returning_false
-    david = CallbackDeveloperWithFalseValidation.find(1)
-    assert_deprecated { david.save }
-    assert_equal [
-      [ :after_find,            :method ],
-      [ :after_find,            :string ],
-      [ :after_find,            :proc   ],
-      [ :after_find,            :object ],
-      [ :after_find,            :block  ],
-      [ :after_initialize,            :method ],
-      [ :after_initialize,            :string ],
-      [ :after_initialize,            :proc   ],
-      [ :after_initialize,            :object ],
-      [ :after_initialize,            :block  ],
-      [ :before_validation,           :method ],
-      [ :before_validation,           :string ],
-      [ :before_validation,           :proc   ],
-      [ :before_validation,           :object ],
-      [ :before_validation,           :block  ],
-      [ :before_validation, :returning_false  ],
-      [ :after_rollback, :block  ],
-      [ :after_rollback, :object ],
-      [ :after_rollback, :proc   ],
-      [ :after_rollback, :string ],
-      [ :after_rollback, :method ],
-    ], david.history
+    assert_not someone.after_destroy_called
   end
 
   def test_callback_throwing_abort
@@ -598,17 +446,14 @@ class CallbacksTest < ActiveRecord::TestCase
     david.save
     assert_equal [
       [ :after_find,        :method ],
-      [ :after_find,        :string ],
       [ :after_find,        :proc   ],
       [ :after_find,        :object ],
       [ :after_find,        :block  ],
       [ :after_initialize,  :method ],
-      [ :after_initialize,  :string ],
       [ :after_initialize,  :proc   ],
       [ :after_initialize,  :object ],
       [ :after_initialize,  :block  ],
       [ :before_validation, :method ],
-      [ :before_validation, :string ],
       [ :before_validation, :proc   ],
       [ :before_validation, :object ],
       [ :before_validation, :block  ],
@@ -616,21 +461,46 @@ class CallbacksTest < ActiveRecord::TestCase
       [ :after_rollback,    :block  ],
       [ :after_rollback,    :object ],
       [ :after_rollback,    :proc   ],
-      [ :after_rollback,    :string ],
       [ :after_rollback,    :method ],
     ], david.history
   end
 
   def test_inheritance_of_callbacks
     parent = ParentDeveloper.new
-    assert !parent.after_save_called
+    assert_not parent.after_save_called
     parent.save
     assert parent.after_save_called
 
     child = ChildDeveloper.new
-    assert !child.after_save_called
+    assert_not child.after_save_called
     child.save
     assert child.after_save_called
   end
 
+  def test_before_save_doesnt_allow_on_option
+    exception = assert_raises ArgumentError do
+      Class.new(ActiveRecord::Base) do
+        before_save(on: :create) { }
+      end
+    end
+    assert_equal "Unknown key: :on. Valid keys are: :if, :unless, :prepend", exception.message
+  end
+
+  def test_around_save_doesnt_allow_on_option
+    exception = assert_raises ArgumentError do
+      Class.new(ActiveRecord::Base) do
+        around_save(on: :create) { }
+      end
+    end
+    assert_equal "Unknown key: :on. Valid keys are: :if, :unless, :prepend", exception.message
+  end
+
+  def test_after_save_doesnt_allow_on_option
+    exception = assert_raises ArgumentError do
+      Class.new(ActiveRecord::Base) do
+        after_save(on: :create) { }
+      end
+    end
+    assert_equal "Unknown key: :on. Valid keys are: :if, :unless, :prepend", exception.message
+  end
 end
diff --git a/activerecord/test/cases/clone_test.rb b/activerecord/test/cases/clone_test.rb
index 5e43082c33..eea36ee736 100644
--- a/activerecord/test/cases/clone_test.rb
+++ b/activerecord/test/cases/clone_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
+require "models/topic"
 
 module ActiveRecord
   class CloneTest < ActiveRecord::TestCase
@@ -8,9 +10,9 @@ module ActiveRecord
     def test_persisted
       topic = Topic.first
       cloned = topic.clone
-      assert topic.persisted?, 'topic persisted'
-      assert cloned.persisted?, 'topic persisted'
-      assert !cloned.new_record?, 'topic is not new'
+      assert topic.persisted?, "topic persisted"
+      assert cloned.persisted?, "topic persisted"
+      assert_not cloned.new_record?, "topic is not new"
     end
 
     def test_stays_frozen
@@ -18,23 +20,23 @@ module ActiveRecord
       topic.freeze
 
       cloned = topic.clone
-      assert cloned.persisted?, 'topic persisted'
-      assert !cloned.new_record?, 'topic is not new'
-      assert cloned.frozen?, 'topic should be frozen'
+      assert cloned.persisted?, "topic persisted"
+      assert_not cloned.new_record?, "topic is not new"
+      assert cloned.frozen?, "topic should be frozen"
     end
 
     def test_shallow
       topic = Topic.first
       cloned = topic.clone
-      topic.author_name = 'Aaron'
-      assert_equal 'Aaron', cloned.author_name
+      topic.author_name = "Aaron"
+      assert_equal "Aaron", cloned.author_name
     end
 
     def test_freezing_a_cloned_model_does_not_freeze_clone
       cloned = Topic.new
       clone = cloned.clone
       cloned.freeze
-      assert_not clone.frozen?
+      assert_not_predicate clone, :frozen?
     end
   end
 end
diff --git a/activerecord/test/cases/coders/json_test.rb b/activerecord/test/cases/coders/json_test.rb
new file mode 100644
index 0000000000..e40d576b39
--- /dev/null
+++ b/activerecord/test/cases/coders/json_test.rb
@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+module ActiveRecord
+  module Coders
+    class JSONTest < ActiveRecord::TestCase
+      def test_returns_nil_if_empty_string_given
+        assert_nil JSON.load("")
+      end
+
+      def test_returns_nil_if_nil_given
+        assert_nil JSON.load(nil)
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/coders/yaml_column_test.rb b/activerecord/test/cases/coders/yaml_column_test.rb
index b72c54f97b..4a5559c62f 100644
--- a/activerecord/test/cases/coders/yaml_column_test.rb
+++ b/activerecord/test/cases/coders/yaml_column_test.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 
 require "cases/helper"
 
@@ -5,54 +6,56 @@ module ActiveRecord
   module Coders
     class YAMLColumnTest < ActiveRecord::TestCase
       def test_initialize_takes_class
-        coder = YAMLColumn.new(Object)
+        coder = YAMLColumn.new("attr_name", Object)
         assert_equal Object, coder.object_class
       end
 
       def test_type_mismatch_on_different_classes_on_dump
-        coder = YAMLColumn.new(Array)
-        assert_raises(SerializationTypeMismatch) do
+        coder = YAMLColumn.new("tags", Array)
+        error = assert_raises(SerializationTypeMismatch) do
           coder.dump("a")
         end
+        assert_equal %{can't dump `tags`: was supposed to be a Array, but was a String. -- "a"}, error.to_s
       end
 
       def test_type_mismatch_on_different_classes
-        coder = YAMLColumn.new(Array)
-        assert_raises(SerializationTypeMismatch) do
+        coder = YAMLColumn.new("tags", Array)
+        error = assert_raises(SerializationTypeMismatch) do
           coder.load "--- foo"
         end
+        assert_equal %{can't load `tags`: was supposed to be a Array, but was a String. -- "foo"}, error.to_s
       end
 
       def test_nil_is_ok
-        coder = YAMLColumn.new
+        coder = YAMLColumn.new("attr_name")
         assert_nil coder.load "--- "
       end
 
       def test_returns_new_with_different_class
-        coder = YAMLColumn.new SerializationTypeMismatch
+        coder = YAMLColumn.new("attr_name", SerializationTypeMismatch)
         assert_equal SerializationTypeMismatch, coder.load("--- ").class
       end
 
       def test_returns_string_unless_starts_with_dash
-        coder = YAMLColumn.new
-        assert_equal 'foo', coder.load("foo")
+        coder = YAMLColumn.new("attr_name")
+        assert_equal "foo", coder.load("foo")
       end
 
       def test_load_handles_other_classes
-        coder = YAMLColumn.new
+        coder = YAMLColumn.new("attr_name")
         assert_equal [], coder.load([])
       end
 
       def test_load_doesnt_swallow_yaml_exceptions
-        coder = YAMLColumn.new
-        bad_yaml = '--- {'
+        coder = YAMLColumn.new("attr_name")
+        bad_yaml = "--- {"
         assert_raises(Psych::SyntaxError) do
           coder.load(bad_yaml)
         end
       end
 
       def test_load_doesnt_handle_undefined_class_or_module
-        coder = YAMLColumn.new
+        coder = YAMLColumn.new("attr_name")
         missing_class_yaml = '--- !ruby/object:DoesNotExistAndShouldntEver {}\n'
         assert_raises(ArgumentError) do
           coder.load(missing_class_yaml)
diff --git a/activerecord/test/cases/collection_cache_key_test.rb b/activerecord/test/cases/collection_cache_key_test.rb
new file mode 100644
index 0000000000..483383257b
--- /dev/null
+++ b/activerecord/test/cases/collection_cache_key_test.rb
@@ -0,0 +1,175 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/computer"
+require "models/developer"
+require "models/project"
+require "models/topic"
+require "models/post"
+require "models/comment"
+
+module ActiveRecord
+  class CollectionCacheKeyTest < ActiveRecord::TestCase
+    fixtures :developers, :projects, :developers_projects, :topics, :comments, :posts
+
+    test "collection_cache_key on model" do
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, Developer.collection_cache_key)
+    end
+
+    test "cache_key for relation" do
+      developers = Developer.where(salary: 100000).order(updated_at: :desc)
+      last_developer_timestamp = developers.first.updated_at
+
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
+
+      /\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/ =~ developers.cache_key
+
+      assert_equal ActiveSupport::Digest.hexdigest(developers.to_sql), $1
+      assert_equal developers.count.to_s, $2
+      assert_equal last_developer_timestamp.to_s(ActiveRecord::Base.cache_timestamp_format), $3
+    end
+
+    test "cache_key for relation with limit" do
+      developers = Developer.where(salary: 100000).order(updated_at: :desc).limit(5)
+      last_developer_timestamp = developers.first.updated_at
+
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
+
+      /\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/ =~ developers.cache_key
+
+      assert_equal ActiveSupport::Digest.hexdigest(developers.to_sql), $1
+      assert_equal developers.count.to_s, $2
+      assert_equal last_developer_timestamp.to_s(ActiveRecord::Base.cache_timestamp_format), $3
+    end
+
+    test "cache_key for relation with custom select and limit" do
+      developers = Developer.where(salary: 100000).order(updated_at: :desc).limit(5)
+      developers_with_select = developers.select("developers.*")
+      last_developer_timestamp = developers.first.updated_at
+
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers_with_select.cache_key)
+
+      /\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/ =~ developers_with_select.cache_key
+
+      assert_equal ActiveSupport::Digest.hexdigest(developers_with_select.to_sql), $1
+      assert_equal developers.count.to_s, $2
+      assert_equal last_developer_timestamp.to_s(ActiveRecord::Base.cache_timestamp_format), $3
+    end
+
+    test "cache_key for loaded relation" do
+      developers = Developer.where(salary: 100000).order(updated_at: :desc).limit(5).load
+      last_developer_timestamp = developers.first.updated_at
+
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
+
+      /\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/ =~ developers.cache_key
+
+      assert_equal ActiveSupport::Digest.hexdigest(developers.to_sql), $1
+      assert_equal developers.count.to_s, $2
+      assert_equal last_developer_timestamp.to_s(ActiveRecord::Base.cache_timestamp_format), $3
+    end
+
+    test "cache_key for relation with table alias" do
+      table_alias = Developer.arel_table.alias("omg_developers")
+      table_metadata = ActiveRecord::TableMetadata.new(Developer, table_alias)
+      predicate_builder = ActiveRecord::PredicateBuilder.new(table_metadata)
+
+      developers = ActiveRecord::Relation.create(
+        Developer,
+        table: table_alias,
+        predicate_builder: predicate_builder
+      )
+      developers = developers.where(salary: 100000).order(updated_at: :desc)
+      last_developer_timestamp = developers.first.updated_at
+
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
+
+      /\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/ =~ developers.cache_key
+
+      assert_equal ActiveSupport::Digest.hexdigest(developers.to_sql), $1
+      assert_equal developers.count.to_s, $2
+      assert_equal last_developer_timestamp.to_s(ActiveRecord::Base.cache_timestamp_format), $3
+    end
+
+    test "cache_key for relation with includes" do
+      comments = Comment.includes(:post).where("posts.type": "Post")
+      assert_match(/\Acomments\/query-(\h+)-(\d+)-(\d+)\z/, comments.cache_key)
+    end
+
+    test "cache_key for loaded relation with includes" do
+      comments = Comment.includes(:post).where("posts.type": "Post").load
+      assert_match(/\Acomments\/query-(\h+)-(\d+)-(\d+)\z/, comments.cache_key)
+    end
+
+    test "it triggers at most one query" do
+      developers = Developer.where(name: "David")
+
+      assert_queries(1) { developers.cache_key }
+      assert_no_queries { developers.cache_key }
+    end
+
+    test "it doesn't trigger any query if the relation is already loaded" do
+      developers = Developer.where(name: "David").load
+      assert_no_queries { developers.cache_key }
+    end
+
+    test "relation cache_key changes when the sql query changes" do
+      developers = Developer.where(name: "David")
+      other_relation = Developer.where(name: "David").where("1 = 1")
+
+      assert_not_equal developers.cache_key, other_relation.cache_key
+    end
+
+    test "cache_key for empty relation" do
+      developers = Developer.where(name: "Non Existent Developer")
+      assert_match(/\Adevelopers\/query-(\h+)-0\z/, developers.cache_key)
+    end
+
+    test "cache_key with custom timestamp column" do
+      topics = Topic.where("title like ?", "%Topic%")
+      last_topic_timestamp = topics(:fifth).written_on.utc.to_s(:usec)
+      assert_match(last_topic_timestamp, topics.cache_key(:written_on))
+    end
+
+    test "cache_key with unknown timestamp column" do
+      topics = Topic.where("title like ?", "%Topic%")
+      assert_raises(ActiveRecord::StatementInvalid) { topics.cache_key(:published_at) }
+    end
+
+    test "collection proxy provides a cache_key" do
+      developers = projects(:active_record).developers
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
+    end
+
+    test "cache_key for loaded collection with zero size" do
+      Comment.delete_all
+      posts = Post.includes(:comments)
+      empty_loaded_collection = posts.first.comments
+
+      assert_match(/\Acomments\/query-(\h+)-0\z/, empty_loaded_collection.cache_key)
+    end
+
+    test "cache_key for queries with offset which return 0 rows" do
+      developers = Developer.offset(20)
+      assert_match(/\Adevelopers\/query-(\h+)-0\z/, developers.cache_key)
+    end
+
+    test "cache_key with a relation having selected columns" do
+      developers = Developer.select(:salary)
+
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
+    end
+
+    test "cache_key with a relation having distinct and order" do
+      developers = Developer.distinct.order(:salary).limit(5)
+
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
+    end
+
+    test "cache_key with a relation having custom select and order" do
+      developers = Developer.select("name AS dev_name").order("dev_name DESC").limit(5)
+
+      assert_match(/\Adevelopers\/query-(\h+)-(\d+)-(\d+)\z/, developers.cache_key)
+    end
+  end
+end
diff --git a/activerecord/test/cases/column_alias_test.rb b/activerecord/test/cases/column_alias_test.rb
index 40707d9cb2..a883d21fb8 100644
--- a/activerecord/test/cases/column_alias_test.rb
+++ b/activerecord/test/cases/column_alias_test.rb
@@ -1,17 +1,19 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
+require "models/topic"
 
 class TestColumnAlias < ActiveRecord::TestCase
   fixtures :topics
 
-  QUERY = if 'Oracle' == ActiveRecord::Base.connection.adapter_name
-            'SELECT id AS pk FROM topics WHERE ROWNUM < 2'
-          else
-            'SELECT id AS pk FROM topics'
-          end
+  QUERY = if "Oracle" == ActiveRecord::Base.connection.adapter_name
+    "SELECT id AS pk FROM topics WHERE ROWNUM < 2"
+  else
+    "SELECT id AS pk FROM topics"
+  end
 
   def test_column_alias
     records = Topic.connection.select_all(QUERY)
-    assert_equal 'pk', records[0].keys[0]
+    assert_equal "pk", records[0].keys[0]
   end
 end
diff --git a/activerecord/test/cases/column_definition_test.rb b/activerecord/test/cases/column_definition_test.rb
index 14b95ecab1..cbd2b44589 100644
--- a/activerecord/test/cases/column_definition_test.rb
+++ b/activerecord/test/cases/column_definition_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -6,76 +8,26 @@ module ActiveRecord
       def setup
         @adapter = AbstractAdapter.new(nil)
         def @adapter.native_database_types
-          {:string => "varchar"}
+          { string: "varchar" }
         end
-        @viz = @adapter.schema_creation
+        @viz = @adapter.send(:schema_creation)
       end
 
       # Avoid column definitions in create table statements like:
       # `title` varchar(255) DEFAULT NULL
       def test_should_not_include_default_clause_when_default_is_null
-        column = Column.new("title", nil, SqlTypeMetadata.new(limit: 20))
-        column_def = ColumnDefinition.new(
-          column.name, "string",
-          column.limit, column.precision, column.scale, column.default, column.null)
-          assert_equal "title varchar(20)", @viz.accept(column_def)
+        column_def = ColumnDefinition.new("title", "string", limit: 20)
+        assert_equal "title varchar(20)", @viz.accept(column_def)
       end
 
       def test_should_include_default_clause_when_default_is_present
-        column = Column.new("title", "Hello", SqlTypeMetadata.new(limit: 20))
-        column_def = ColumnDefinition.new(
-          column.name, "string",
-          column.limit, column.precision, column.scale, column.default, column.null)
-          assert_equal %Q{title varchar(20) DEFAULT 'Hello'}, @viz.accept(column_def)
+        column_def = ColumnDefinition.new("title", "string", limit: 20, default: "Hello")
+        assert_equal "title varchar(20) DEFAULT 'Hello'", @viz.accept(column_def)
       end
 
       def test_should_specify_not_null_if_null_option_is_false
-        type_metadata = SqlTypeMetadata.new(limit: 20)
-        column = Column.new("title", "Hello", type_metadata, false)
-        column_def = ColumnDefinition.new(
-          column.name, "string",
-          column.limit, column.precision, column.scale, column.default, column.null)
-          assert_equal %Q{title varchar(20) DEFAULT 'Hello' NOT NULL}, @viz.accept(column_def)
-      end
-
-      if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-        def test_should_set_default_for_mysql_binary_data_types
-          type = SqlTypeMetadata.new(type: :binary, sql_type: "binary(1)")
-          binary_column = AbstractMysqlAdapter::Column.new("title", "a", type)
-          assert_equal "a", binary_column.default
-
-          type = SqlTypeMetadata.new(type: :binary, sql_type: "varbinary")
-          varbinary_column = AbstractMysqlAdapter::Column.new("title", "a", type)
-          assert_equal "a", varbinary_column.default
-        end
-
-        def test_should_not_set_default_for_blob_and_text_data_types
-          assert_raise ArgumentError do
-            AbstractMysqlAdapter::Column.new("title", "a", SqlTypeMetadata.new(sql_type: "blob"))
-          end
-
-          text_type = AbstractMysqlAdapter::MysqlTypeMetadata.new(
-            SqlTypeMetadata.new(type: :text))
-          assert_raise ArgumentError do
-            AbstractMysqlAdapter::Column.new("title", "Hello", text_type)
-          end
-
-          text_column = AbstractMysqlAdapter::Column.new("title", nil, text_type)
-          assert_equal nil, text_column.default
-
-          not_null_text_column = AbstractMysqlAdapter::Column.new("title", nil, text_type, false)
-          assert_equal "", not_null_text_column.default
-        end
-
-        def test_has_default_should_return_false_for_blob_and_text_data_types
-          binary_type = SqlTypeMetadata.new(sql_type: "blob")
-          blob_column = AbstractMysqlAdapter::Column.new("title", nil, binary_type)
-          assert !blob_column.has_default?
-
-          text_type = SqlTypeMetadata.new(type: :text)
-          text_column = AbstractMysqlAdapter::Column.new("title", nil, text_type)
-          assert !text_column.has_default?
-        end
+        column_def = ColumnDefinition.new("title", "string", limit: 20, default: "Hello", null: false)
+        assert_equal "title varchar(20) DEFAULT 'Hello' NOT NULL", @viz.accept(column_def)
       end
     end
   end
diff --git a/activerecord/test/cases/comment_test.rb b/activerecord/test/cases/comment_test.rb
new file mode 100644
index 0000000000..584e03d196
--- /dev/null
+++ b/activerecord/test/cases/comment_test.rb
@@ -0,0 +1,168 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/schema_dumping_helper"
+
+if ActiveRecord::Base.connection.supports_comments?
+  class CommentTest < ActiveRecord::TestCase
+    include SchemaDumpingHelper
+
+    class Commented < ActiveRecord::Base
+      self.table_name = "commenteds"
+    end
+
+    class BlankComment < ActiveRecord::Base
+    end
+
+    setup do
+      @connection = ActiveRecord::Base.connection
+
+      @connection.create_table("commenteds", comment: "A table with comment", force: true) do |t|
+        t.string  "name",    comment: "Comment should help clarify the column purpose"
+        t.boolean "obvious", comment: "Question is: should you comment obviously named objects?"
+        t.string  "content"
+        t.index   "name",    comment: %Q["Very important" index that powers all the performance.\nAnd it's fun!]
+      end
+
+      @connection.create_table("blank_comments", comment: " ", force: true) do |t|
+        t.string :space_comment, comment: " "
+        t.string :empty_comment, comment: ""
+        t.string :nil_comment, comment: nil
+        t.string :absent_comment
+        t.index :space_comment, comment: " "
+        t.index :empty_comment, comment: ""
+        t.index :nil_comment, comment: nil
+        t.index :absent_comment
+      end
+
+      Commented.reset_column_information
+      BlankComment.reset_column_information
+    end
+
+    teardown do
+      @connection.drop_table "commenteds", if_exists: true
+      @connection.drop_table "blank_comments", if_exists: true
+    end
+
+    def test_column_created_in_block
+      column = Commented.columns_hash["name"]
+      assert_equal :string, column.type
+      assert_equal "Comment should help clarify the column purpose", column.comment
+    end
+
+    def test_blank_columns_created_in_block
+      %w[ space_comment empty_comment nil_comment absent_comment ].each do |field|
+        column = BlankComment.columns_hash[field]
+        assert_equal :string, column.type
+        assert_nil column.comment
+      end
+    end
+
+    def test_blank_indexes_created_in_block
+      @connection.indexes("blank_comments").each do |index|
+        assert_nil index.comment
+      end
+    end
+
+    def test_add_column_with_comment_later
+      @connection.add_column :commenteds, :rating, :integer, comment: "I am running out of imagination"
+      Commented.reset_column_information
+      column = Commented.columns_hash["rating"]
+
+      assert_equal :integer, column.type
+      assert_equal "I am running out of imagination", column.comment
+    end
+
+    def test_add_index_with_comment_later
+      unless current_adapter?(:OracleAdapter)
+        @connection.add_index :commenteds, :obvious, name: "idx_obvious", comment: "We need to see obvious comments"
+        index = @connection.indexes("commenteds").find { |idef| idef.name == "idx_obvious" }
+        assert_equal "We need to see obvious comments", index.comment
+      end
+    end
+
+    def test_add_comment_to_column
+      @connection.change_column :commenteds, :content, :string, comment: "Whoa, content describes itself!"
+
+      Commented.reset_column_information
+      column = Commented.columns_hash["content"]
+
+      assert_equal :string, column.type
+      assert_equal "Whoa, content describes itself!", column.comment
+    end
+
+    def test_remove_comment_from_column
+      @connection.change_column :commenteds, :obvious, :string, comment: nil
+
+      Commented.reset_column_information
+      column = Commented.columns_hash["obvious"]
+
+      assert_equal :string, column.type
+      assert_nil column.comment
+    end
+
+    def test_schema_dump_with_comments
+      # Do all the stuff from other tests
+      @connection.add_column    :commenteds, :rating, :integer, comment: "I am running out of imagination"
+      @connection.change_column :commenteds, :content, :string, comment: "Whoa, content describes itself!"
+      @connection.change_column :commenteds, :content, :string
+      @connection.change_column :commenteds, :obvious, :string, comment: nil
+      @connection.add_index     :commenteds, :obvious, name: "idx_obvious", comment: "We need to see obvious comments"
+
+      # And check that these changes are reflected in dump
+      output = dump_table_schema "commenteds"
+      assert_match %r[create_table "commenteds",.*\s+comment: "A table with comment"], output
+      assert_match %r[t\.string\s+"name",\s+comment: "Comment should help clarify the column purpose"], output
+      assert_match %r[t\.string\s+"obvious"\n], output
+      assert_match %r[t\.string\s+"content",\s+comment: "Whoa, content describes itself!"], output
+      if current_adapter?(:OracleAdapter)
+        assert_match %r[t\.integer\s+"rating",\s+precision: 38,\s+comment: "I am running out of imagination"], output
+      else
+        assert_match %r[t\.integer\s+"rating",\s+comment: "I am running out of imagination"], output
+        assert_match %r[t\.index\s+.+\s+comment: "\\\"Very important\\\" index that powers all the performance.\\nAnd it's fun!"], output
+        assert_match %r[t\.index\s+.+\s+name: "idx_obvious",\s+comment: "We need to see obvious comments"], output
+      end
+    end
+
+    def test_schema_dump_omits_blank_comments
+      output = dump_table_schema "blank_comments"
+
+      assert_match %r[create_table "blank_comments"], output
+      assert_no_match %r[create_table "blank_comments",.+comment:], output
+
+      assert_match %r[t\.string\s+"space_comment"\n], output
+      assert_no_match %r[t\.string\s+"space_comment", comment:\n], output
+
+      assert_match %r[t\.string\s+"empty_comment"\n], output
+      assert_no_match %r[t\.string\s+"empty_comment", comment:\n], output
+
+      assert_match %r[t\.string\s+"nil_comment"\n], output
+      assert_no_match %r[t\.string\s+"nil_comment", comment:\n], output
+
+      assert_match %r[t\.string\s+"absent_comment"\n], output
+      assert_no_match %r[t\.string\s+"absent_comment", comment:\n], output
+    end
+
+    def test_change_table_comment
+      @connection.change_table_comment :commenteds, "Edited table comment"
+      assert_equal "Edited table comment", @connection.table_comment("commenteds")
+    end
+
+    def test_change_table_comment_to_nil
+      @connection.change_table_comment :commenteds, nil
+      assert_nil @connection.table_comment("commenteds")
+    end
+
+    def test_change_column_comment
+      @connection.change_column_comment :commenteds, :name, "Edited column comment"
+      column = Commented.columns_hash["name"]
+      assert_equal "Edited column comment", column.comment
+    end
+
+    def test_change_column_comment_to_nil
+      @connection.change_column_comment :commenteds, :name, nil
+      column = Commented.columns_hash["name"]
+      assert_nil column.comment
+    end
+  end
+end
diff --git a/activerecord/test/cases/connection_adapters/adapter_leasing_test.rb b/activerecord/test/cases/connection_adapters/adapter_leasing_test.rb
index 580568c8ac..72838ff56b 100644
--- a/activerecord/test/cases/connection_adapters/adapter_leasing_test.rb
+++ b/activerecord/test/cases/connection_adapters/adapter_leasing_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -17,37 +19,37 @@ module ActiveRecord
       end
 
       def test_in_use?
-        assert_not @adapter.in_use?, 'adapter is not in use'
-        assert @adapter.lease, 'lease adapter'
-        assert @adapter.in_use?, 'adapter is in use'
+        assert_not @adapter.in_use?, "adapter is not in use"
+        assert @adapter.lease, "lease adapter"
+        assert @adapter.in_use?, "adapter is in use"
       end
 
       def test_lease_twice
-        assert @adapter.lease, 'should lease adapter'
+        assert @adapter.lease, "should lease adapter"
         assert_raises(ActiveRecordError) do
           @adapter.lease
         end
       end
 
       def test_expire_mutates_in_use
-        assert @adapter.lease, 'lease adapter'
-        assert @adapter.in_use?, 'adapter is in use'
+        assert @adapter.lease, "lease adapter"
+        assert @adapter.in_use?, "adapter is in use"
         @adapter.expire
-        assert_not @adapter.in_use?, 'adapter is in use'
+        assert_not @adapter.in_use?, "adapter is in use"
       end
 
       def test_close
-        pool = Pool.new(ConnectionSpecification.new({}, nil))
+        pool = Pool.new(ConnectionSpecification.new("primary", {}, nil))
         pool.insert_connection_for_test! @adapter
         @adapter.pool = pool
 
         # Make sure the pool marks the connection in use
         assert_equal @adapter, pool.connection
-        assert @adapter.in_use?
+        assert_predicate @adapter, :in_use?
 
         # Close should put the adapter back in the pool
         @adapter.close
-        assert_not @adapter.in_use?
+        assert_not_predicate @adapter, :in_use?
 
         assert_equal @adapter, pool.connection
       end
diff --git a/activerecord/test/cases/connection_adapters/connection_handler_test.rb b/activerecord/test/cases/connection_adapters/connection_handler_test.rb
index 9b1865e8bb..51d0cc3d12 100644
--- a/activerecord/test/cases/connection_adapters/connection_handler_test.rb
+++ b/activerecord/test/cases/connection_adapters/connection_handler_test.rb
@@ -1,46 +1,203 @@
+# frozen_string_literal: true
+
 require "cases/helper"
+require "models/person"
 
 module ActiveRecord
   module ConnectionAdapters
     class ConnectionHandlerTest < ActiveRecord::TestCase
-      def setup
-        @klass    = Class.new(Base)   { def self.name; 'klass';    end }
-        @subklass = Class.new(@klass) { def self.name; 'subklass'; end }
+      self.use_transactional_tests = false
 
+      fixtures :people
+
+      def setup
         @handler = ConnectionHandler.new
-        @pool    = @handler.establish_connection(@klass, Base.connection_pool.spec)
+        @spec_name = "primary"
+        @pool = @handler.establish_connection(ActiveRecord::Base.configurations["arunit"])
       end
 
-      def test_retrieve_connection
-        assert @handler.retrieve_connection(@klass)
+      def test_default_env_fall_back_to_default_env_when_rails_env_or_rack_env_is_empty_string
+        original_rails_env = ENV["RAILS_ENV"]
+        original_rack_env  = ENV["RACK_ENV"]
+        ENV["RAILS_ENV"]   = ENV["RACK_ENV"] = ""
+
+        assert_equal "default_env", ActiveRecord::ConnectionHandling::DEFAULT_ENV.call
+      ensure
+        ENV["RAILS_ENV"] = original_rails_env
+        ENV["RACK_ENV"]  = original_rack_env
       end
 
-      def test_active_connections?
-        assert !@handler.active_connections?
-        assert @handler.retrieve_connection(@klass)
-        assert @handler.active_connections?
-        @handler.clear_active_connections!
-        assert !@handler.active_connections?
+      def test_establish_connection_uses_spec_name
+        old_config = ActiveRecord::Base.configurations
+        config = { "readonly" => { "adapter" => "sqlite3" } }
+        ActiveRecord::Base.configurations = config
+        resolver = ConnectionAdapters::ConnectionSpecification::Resolver.new(ActiveRecord::Base.configurations)
+        spec =   resolver.spec(:readonly)
+        @handler.establish_connection(spec.to_hash)
+
+        assert_not_nil @handler.retrieve_connection_pool("readonly")
+      ensure
+        ActiveRecord::Base.configurations = old_config
+        @handler.remove_connection("readonly")
       end
 
-      def test_retrieve_connection_pool_with_ar_base
-        assert_nil @handler.retrieve_connection_pool(ActiveRecord::Base)
+      def test_establish_connection_using_3_levels_config
+        previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+
+        config = {
+          "default_env" => {
+            "readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" },
+            "primary"  => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" }
+          },
+          "another_env" => {
+            "readonly" => { "adapter" => "sqlite3", "database" => "db/bad-readonly.sqlite3" },
+            "primary"  => { "adapter" => "sqlite3", "database" => "db/bad-primary.sqlite3" }
+          },
+          "common" => { "adapter" => "sqlite3", "database" => "db/common.sqlite3" }
+        }
+        @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+        @handler.establish_connection(:common)
+        @handler.establish_connection(:primary)
+        @handler.establish_connection(:readonly)
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("readonly")
+        assert_equal "db/readonly.sqlite3", pool.spec.config[:database]
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("primary")
+        assert_equal "db/primary.sqlite3", pool.spec.config[:database]
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("common")
+        assert_equal "db/common.sqlite3", pool.spec.config[:database]
+      ensure
+        ActiveRecord::Base.configurations = @prev_configs
+        ENV["RAILS_ENV"] = previous_env
       end
 
-      def test_retrieve_connection_pool
-        assert_not_nil @handler.retrieve_connection_pool(@klass)
+      unless in_memory_db?
+        def test_establish_connection_using_3_level_config_defaults_to_default_env_primary_db
+          previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+
+          config = {
+            "default_env" => {
+              "primary"  => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" },
+              "readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" }
+            },
+            "another_env" => {
+              "primary"  => { "adapter" => "sqlite3", "database" => "db/another-primary.sqlite3" },
+              "readonly" => { "adapter" => "sqlite3", "database" => "db/another-readonly.sqlite3" }
+            }
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          ActiveRecord::Base.establish_connection
+
+          assert_match "db/primary.sqlite3", ActiveRecord::Base.connection.pool.spec.config[:database]
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ENV["RAILS_ENV"] = previous_env
+          ActiveRecord::Base.establish_connection(:arunit)
+          FileUtils.rm_rf "db"
+        end
+
+        def test_establish_connection_using_2_level_config_defaults_to_default_env_primary_db
+          previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+
+          config = {
+            "default_env" => {
+              "adapter" => "sqlite3", "database" => "db/primary.sqlite3"
+            },
+            "another_env" => {
+              "adapter" => "sqlite3", "database" => "db/bad-primary.sqlite3"
+            }
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          ActiveRecord::Base.establish_connection
+
+          assert_match "db/primary.sqlite3", ActiveRecord::Base.connection.pool.spec.config[:database]
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ENV["RAILS_ENV"] = previous_env
+          ActiveRecord::Base.establish_connection(:arunit)
+          FileUtils.rm_rf "db"
+        end
       end
 
-      def test_retrieve_connection_pool_uses_superclass_when_no_subclass_connection
-        assert_not_nil @handler.retrieve_connection_pool(@subklass)
+      def test_establish_connection_using_two_level_configurations
+        config = { "development" => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" } }
+        @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+        @handler.establish_connection(:development)
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("development")
+        assert_equal "db/primary.sqlite3", pool.spec.config[:database]
+      ensure
+        ActiveRecord::Base.configurations = @prev_configs
+      end
+
+      def test_establish_connection_using_top_level_key_in_two_level_config
+        config = {
+          "development" => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" },
+          "development_readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" }
+        }
+        @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+        @handler.establish_connection(:development_readonly)
+
+        assert_not_nil pool = @handler.retrieve_connection_pool("development_readonly")
+        assert_equal "db/readonly.sqlite3", pool.spec.config[:database]
+      ensure
+        ActiveRecord::Base.configurations = @prev_configs
+      end
+
+      def test_symbolized_configurations_assignment
+        @prev_configs = ActiveRecord::Base.configurations
+        config = {
+          development: {
+            primary: {
+              adapter: "sqlite3",
+              database: "db/development.sqlite3",
+            },
+          },
+          test: {
+            primary: {
+              adapter: "sqlite3",
+              database: "db/test.sqlite3",
+            },
+          },
+        }
+        ActiveRecord::Base.configurations = config
+        ActiveRecord::Base.configurations.configs_for.each do |db_config|
+          assert_instance_of ActiveRecord::DatabaseConfigurations::HashConfig, db_config
+          assert_instance_of String, db_config.env_name
+          assert_instance_of String, db_config.spec_name
+          db_config.config.keys.each do |key|
+            assert_instance_of String, key
+          end
+        end
+      ensure
+        ActiveRecord::Base.configurations = @prev_configs
+      end
+
+      def test_retrieve_connection
+        assert @handler.retrieve_connection(@spec_name)
+      end
+
+      def test_active_connections?
+        assert_not_predicate @handler, :active_connections?
+        assert @handler.retrieve_connection(@spec_name)
+        assert_predicate @handler, :active_connections?
+        @handler.clear_active_connections!
+        assert_not_predicate @handler, :active_connections?
       end
 
-      def test_retrieve_connection_pool_uses_superclass_pool_after_subclass_establish_and_remove
-        sub_pool = @handler.establish_connection(@subklass, Base.connection_pool.spec)
-        assert_same sub_pool, @handler.retrieve_connection_pool(@subklass)
+      def test_retrieve_connection_pool
+        assert_not_nil @handler.retrieve_connection_pool(@spec_name)
+      end
 
-        @handler.remove_connection @subklass
-        assert_same @pool, @handler.retrieve_connection_pool(@subklass)
+      def test_retrieve_connection_pool_with_invalid_id
+        assert_nil @handler.retrieve_connection_pool("foo")
       end
 
       def test_connection_pools
@@ -69,9 +226,78 @@ module ActiveRecord
           rd.close
         end
 
+        def test_forked_child_doesnt_mangle_parent_connection
+          object_id = ActiveRecord::Base.connection.object_id
+          assert_predicate ActiveRecord::Base.connection, :active?
+
+          rd, wr = IO.pipe
+          rd.binmode
+          wr.binmode
+
+          pid = fork {
+            rd.close
+            if ActiveRecord::Base.connection.active?
+              wr.write Marshal.dump ActiveRecord::Base.connection.object_id
+            end
+            wr.close
+
+            exit # allow finalizers to run
+          }
+
+          wr.close
+
+          Process.waitpid pid
+          assert_not_equal object_id, Marshal.load(rd.read)
+          rd.close
+
+          assert_equal 3, ActiveRecord::Base.connection.select_value("SELECT COUNT(*) FROM people")
+        end
+
+        unless in_memory_db?
+          def test_forked_child_recovers_from_disconnected_parent
+            object_id = ActiveRecord::Base.connection.object_id
+            assert_predicate ActiveRecord::Base.connection, :active?
+
+            rd, wr = IO.pipe
+            rd.binmode
+            wr.binmode
+
+            outer_pid = fork {
+              ActiveRecord::Base.connection.disconnect!
+
+              pid = fork {
+                rd.close
+                if ActiveRecord::Base.connection.active?
+                  pair = [ActiveRecord::Base.connection.object_id,
+                          ActiveRecord::Base.connection.select_value("SELECT COUNT(*) FROM people")]
+                  wr.write Marshal.dump pair
+                end
+                wr.close
+
+                exit # allow finalizers to run
+              }
+
+              Process.waitpid pid
+            }
+
+            wr.close
+
+            Process.waitpid outer_pid
+            child_id, child_count = Marshal.load(rd.read)
+
+            assert_not_equal object_id, child_id
+            rd.close
+
+            assert_equal 3, child_count
+
+            # Outer connection is unaffected
+            assert_equal 6, ActiveRecord::Base.connection.select_value("SELECT 2 * COUNT(*) FROM people")
+          end
+        end
+
         def test_retrieve_connection_pool_copies_schema_cache_from_ancestor_pool
           @pool.schema_cache = @pool.connection.schema_cache
-          @pool.schema_cache.add('posts')
+          @pool.schema_cache.add("posts")
 
           rd, wr = IO.pipe
           rd.binmode
@@ -79,7 +305,7 @@ module ActiveRecord
 
           pid = fork {
             rd.close
-            pool = @handler.retrieve_connection_pool(@klass)
+            pool = @handler.retrieve_connection_pool(@spec_name)
             wr.write Marshal.dump pool.schema_cache.size
             wr.close
             exit!
@@ -91,6 +317,71 @@ module ActiveRecord
           assert_equal @pool.schema_cache.size, Marshal.load(rd.read)
           rd.close
         end
+
+        def test_pool_from_any_process_for_uses_most_recent_spec
+          skip unless current_adapter?(:SQLite3Adapter)
+
+          file = Tempfile.new "lol.sqlite3"
+
+          rd, wr = IO.pipe
+          rd.binmode
+          wr.binmode
+
+          pid = fork do
+            ActiveRecord::Base.configurations["arunit"]["database"] = file.path
+            ActiveRecord::Base.establish_connection(:arunit)
+
+            pid2 = fork do
+              wr.write ActiveRecord::Base.connection_config[:database]
+              wr.close
+            end
+
+            Process.waitpid pid2
+          end
+
+          Process.waitpid pid
+
+          wr.close
+
+          assert_equal file.path, rd.read
+
+          rd.close
+        ensure
+          if file
+            file.close
+            file.unlink
+          end
+        end
+
+        def test_a_class_using_custom_pool_and_switching_back_to_primary
+          klass2 = Class.new(Base) { def self.name; "klass2"; end }
+
+          assert_same klass2.connection, ActiveRecord::Base.connection
+
+          pool = klass2.establish_connection(ActiveRecord::Base.connection_pool.spec.config)
+          assert_same klass2.connection, pool.connection
+          assert_not_same klass2.connection, ActiveRecord::Base.connection
+
+          klass2.remove_connection
+
+          assert_same klass2.connection, ActiveRecord::Base.connection
+        end
+
+        def test_connection_specification_name_should_fallback_to_parent
+          klassA = Class.new(Base)
+          klassB = Class.new(klassA)
+
+          assert_equal klassB.connection_specification_name, klassA.connection_specification_name
+          klassA.connection_specification_name = "readonly"
+          assert_equal "readonly", klassB.connection_specification_name
+        end
+
+        def test_remove_connection_should_not_remove_parent
+          klass2 = Class.new(Base) { def self.name; "klass2"; end }
+          klass2.remove_connection
+          assert_not_nil ActiveRecord::Base.connection
+          assert_same klass2.connection, ActiveRecord::Base.connection
+        end
       end
     end
   end
diff --git a/activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb b/activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb
new file mode 100644
index 0000000000..a394430dfe
--- /dev/null
+++ b/activerecord/test/cases/connection_adapters/connection_handlers_multi_db_test.rb
@@ -0,0 +1,285 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/person"
+
+module ActiveRecord
+  module ConnectionAdapters
+    class ConnectionHandlersMultiDbTest < ActiveRecord::TestCase
+      self.use_transactional_tests = false
+
+      fixtures :people
+
+      def setup
+        @handlers = { writing: ConnectionHandler.new, reading: ConnectionHandler.new }
+        @rw_handler = @handlers[:writing]
+        @ro_handler = @handlers[:reading]
+        @spec_name = "primary"
+        @rw_pool = @handlers[:writing].establish_connection(ActiveRecord::Base.configurations["arunit"])
+        @ro_pool = @handlers[:reading].establish_connection(ActiveRecord::Base.configurations["arunit"])
+      end
+
+      def teardown
+        ActiveRecord::Base.connection_handlers = { writing: ActiveRecord::Base.default_connection_handler }
+      end
+
+      class MultiConnectionTestModel < ActiveRecord::Base
+      end
+
+      def test_multiple_connection_handlers_works_in_a_threaded_environment
+        tf_writing = Tempfile.open "test_writing"
+        tf_reading = Tempfile.open "test_reading"
+
+        MultiConnectionTestModel.connects_to database: { writing: { database: tf_writing.path, adapter: "sqlite3" }, reading: { database: tf_reading.path, adapter: "sqlite3" } }
+
+        MultiConnectionTestModel.connection.execute("CREATE TABLE `test_1` (connection_role VARCHAR (255))")
+        MultiConnectionTestModel.connection.execute("INSERT INTO test_1 VALUES ('writing')")
+
+        ActiveRecord::Base.connected_to(role: :reading) do
+          MultiConnectionTestModel.connection.execute("CREATE TABLE `test_1` (connection_role VARCHAR (255))")
+          MultiConnectionTestModel.connection.execute("INSERT INTO test_1 VALUES ('reading')")
+        end
+
+        read_latch = Concurrent::CountDownLatch.new
+        write_latch = Concurrent::CountDownLatch.new
+
+        MultiConnectionTestModel.connection
+
+        thread = Thread.new do
+          MultiConnectionTestModel.connection
+
+          write_latch.wait
+          assert_equal "writing", MultiConnectionTestModel.connection.select_value("SELECT connection_role from test_1")
+          read_latch.count_down
+        end
+
+        ActiveRecord::Base.connected_to(role: :reading) do
+          write_latch.count_down
+          assert_equal "reading", MultiConnectionTestModel.connection.select_value("SELECT connection_role from test_1")
+          read_latch.wait
+        end
+
+        thread.join
+      ensure
+        tf_reading.close
+        tf_reading.unlink
+        tf_writing.close
+        tf_writing.unlink
+      end
+
+      unless in_memory_db?
+        def test_establish_connection_using_3_levels_config
+          previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+
+          config = {
+            "default_env" => {
+              "readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" },
+              "primary"  => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" }
+            }
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          ActiveRecord::Base.connects_to(database: { writing: :primary, reading: :readonly })
+
+          assert_not_nil pool = ActiveRecord::Base.connection_handlers[:writing].retrieve_connection_pool("primary")
+          assert_equal "db/primary.sqlite3", pool.spec.config[:database]
+
+          assert_not_nil pool = ActiveRecord::Base.connection_handlers[:reading].retrieve_connection_pool("primary")
+          assert_equal "db/readonly.sqlite3", pool.spec.config[:database]
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ActiveRecord::Base.establish_connection(:arunit)
+          ENV["RAILS_ENV"] = previous_env
+        end
+
+        def test_switching_connections_via_handler
+          previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+
+          config = {
+            "default_env" => {
+              "readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" },
+              "primary"  => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" }
+            }
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          ActiveRecord::Base.connects_to(database: { writing: :primary, reading: :readonly })
+
+          ActiveRecord::Base.connected_to(role: :reading) do
+            @ro_handler = ActiveRecord::Base.connection_handler
+            assert_equal ActiveRecord::Base.connection_handler, ActiveRecord::Base.connection_handlers[:reading]
+          end
+
+          ActiveRecord::Base.connected_to(role: :writing) do
+            assert_equal ActiveRecord::Base.connection_handler, ActiveRecord::Base.connection_handlers[:writing]
+            assert_not_equal @ro_handler, ActiveRecord::Base.connection_handler
+          end
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ActiveRecord::Base.establish_connection(:arunit)
+          ENV["RAILS_ENV"] = previous_env
+        end
+
+        def test_switching_connections_with_database_url
+          previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+          previous_url, ENV["DATABASE_URL"] = ENV["DATABASE_URL"], "postgres://localhost/foo"
+
+          ActiveRecord::Base.connected_to(database: { writing: "postgres://localhost/bar" }) do
+            handler = ActiveRecord::Base.connection_handler
+            assert_equal handler, ActiveRecord::Base.connection_handlers[:writing]
+
+            assert_not_nil pool = handler.retrieve_connection_pool("primary")
+            assert_equal({ adapter: "postgresql", database: "bar", host: "localhost" }, pool.spec.config)
+          end
+        ensure
+          ActiveRecord::Base.establish_connection(:arunit)
+          ENV["RAILS_ENV"] = previous_env
+          ENV["DATABASE_URL"] = previous_url
+        end
+
+        def test_switching_connections_with_database_config_hash
+          previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+          config = { adapter: "sqlite3", database: "db/readonly.sqlite3" }
+
+          ActiveRecord::Base.connected_to(database: { writing: config }) do
+            handler = ActiveRecord::Base.connection_handler
+            assert_equal handler, ActiveRecord::Base.connection_handlers[:writing]
+
+            assert_not_nil pool = handler.retrieve_connection_pool("primary")
+            assert_equal(config, pool.spec.config)
+          end
+        ensure
+          ActiveRecord::Base.establish_connection(:arunit)
+          ENV["RAILS_ENV"] = previous_env
+        end
+
+        def test_switching_connections_with_database_and_role_raises
+          error = assert_raises(ArgumentError) do
+            ActiveRecord::Base.connected_to(database: :readonly, role: :writing) { }
+          end
+          assert_equal "connected_to can only accept a `database` or a `role` argument, but not both arguments.", error.message
+        end
+
+        def test_switching_connections_without_database_and_role_raises
+          error = assert_raises(ArgumentError) do
+            ActiveRecord::Base.connected_to { }
+          end
+          assert_equal "must provide a `database` or a `role`.", error.message
+        end
+
+        def test_switching_connections_with_database_symbol
+          previous_env, ENV["RAILS_ENV"] = ENV["RAILS_ENV"], "default_env"
+
+          config = {
+            "default_env" => {
+              "readonly" => { adapter: "sqlite3", database: "db/readonly.sqlite3" },
+              "primary"  => { adapter: "sqlite3", database: "db/primary.sqlite3" }
+            }
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          ActiveRecord::Base.connected_to(database: :readonly) do
+            handler = ActiveRecord::Base.connection_handler
+            assert_equal handler, ActiveRecord::Base.connection_handlers[:readonly]
+
+            assert_not_nil pool = handler.retrieve_connection_pool("primary")
+            assert_equal(config["default_env"]["readonly"], pool.spec.config)
+          end
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ActiveRecord::Base.establish_connection(:arunit)
+          ENV["RAILS_ENV"] = previous_env
+        end
+
+        def test_connects_to_with_single_configuration
+          config = {
+            "development" => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" },
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          ActiveRecord::Base.connects_to database: { writing: :development }
+
+          assert_equal 1, ActiveRecord::Base.connection_handlers.size
+          assert_equal ActiveRecord::Base.connection_handler, ActiveRecord::Base.connection_handlers[:writing]
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ActiveRecord::Base.establish_connection(:arunit)
+        end
+
+        def test_connects_to_using_top_level_key_in_two_level_config
+          config = {
+            "development" => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" },
+            "development_readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" }
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          ActiveRecord::Base.connects_to database: { writing: :development, reading: :development_readonly }
+
+          assert_not_nil pool = ActiveRecord::Base.connection_handlers[:reading].retrieve_connection_pool("primary")
+          assert_equal "db/readonly.sqlite3", pool.spec.config[:database]
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ActiveRecord::Base.establish_connection(:arunit)
+        end
+
+        def test_connects_to_returns_array_of_established_connections
+          config = {
+            "development" => { "adapter" => "sqlite3", "database" => "db/primary.sqlite3" },
+            "development_readonly" => { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" }
+          }
+          @prev_configs, ActiveRecord::Base.configurations = ActiveRecord::Base.configurations, config
+
+          result = ActiveRecord::Base.connects_to database: { writing: :development, reading: :development_readonly }
+
+          assert_equal(
+            [
+              ActiveRecord::Base.connection_handlers[:writing].retrieve_connection_pool("primary"),
+              ActiveRecord::Base.connection_handlers[:reading].retrieve_connection_pool("primary")
+            ],
+            result
+          )
+        ensure
+          ActiveRecord::Base.configurations = @prev_configs
+          ActiveRecord::Base.establish_connection(:arunit)
+        end
+      end
+
+      def test_connection_pools
+        assert_equal([@rw_pool], @handlers[:writing].connection_pools)
+        assert_equal([@ro_pool], @handlers[:reading].connection_pools)
+      end
+
+      def test_retrieve_connection
+        assert @rw_handler.retrieve_connection(@spec_name)
+        assert @ro_handler.retrieve_connection(@spec_name)
+      end
+
+      def test_active_connections?
+        assert_not_predicate @rw_handler, :active_connections?
+        assert_not_predicate @ro_handler, :active_connections?
+
+        assert @rw_handler.retrieve_connection(@spec_name)
+        assert @ro_handler.retrieve_connection(@spec_name)
+
+        assert_predicate @rw_handler, :active_connections?
+        assert_predicate @ro_handler, :active_connections?
+
+        @rw_handler.clear_active_connections!
+        assert_not_predicate @rw_handler, :active_connections?
+
+        @ro_handler.clear_active_connections!
+        assert_not_predicate @ro_handler, :active_connections?
+      end
+
+      def test_retrieve_connection_pool
+        assert_not_nil @rw_handler.retrieve_connection_pool(@spec_name)
+        assert_not_nil @ro_handler.retrieve_connection_pool(@spec_name)
+      end
+
+      def test_retrieve_connection_pool_with_invalid_id
+        assert_nil @rw_handler.retrieve_connection_pool("foo")
+        assert_nil @ro_handler.retrieve_connection_pool("foo")
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/connection_adapters/connection_specification_test.rb b/activerecord/test/cases/connection_adapters/connection_specification_test.rb
index ea2196cda2..f81b73c344 100644
--- a/activerecord/test/cases/connection_adapters/connection_specification_test.rb
+++ b/activerecord/test/cases/connection_adapters/connection_specification_test.rb
@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
   module ConnectionAdapters
     class ConnectionSpecificationTest < ActiveRecord::TestCase
       def test_dup_deep_copy_config
-        spec = ConnectionSpecification.new({ :a => :b }, "bar")
+        spec = ConnectionSpecification.new("primary", { a: :b }, "bar")
         assert_not_equal(spec.config.object_id, spec.dup.config.object_id)
       end
     end
diff --git a/activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb b/activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb
index 9ee92a3cd2..06c1c51724 100644
--- a/activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb
+++ b/activerecord/test/cases/connection_adapters/merge_and_resolve_default_url_config_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -16,62 +18,65 @@ module ActiveRecord
       end
 
       def resolve_config(config)
-        ActiveRecord::ConnectionHandling::MergeAndResolveDefaultUrlConfig.new(config).resolve
+        configs = ActiveRecord::DatabaseConfigurations.new(config)
+        configs.to_h
       end
 
       def resolve_spec(spec, config)
-        ConnectionSpecification::Resolver.new(resolve_config(config)).resolve(spec)
+        configs = ActiveRecord::DatabaseConfigurations.new(config)
+        resolver = ConnectionAdapters::ConnectionSpecification::Resolver.new(configs)
+        resolver.resolve(spec, spec)
       end
 
       def test_resolver_with_database_uri_and_current_env_symbol_key
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
         config   = { "not_production" => {  "adapter" => "not_postgres", "database" => "not_foo" } }
         actual   = resolve_spec(:default_env, config)
-        expected = { "adapter"=>"postgresql", "database"=>"foo", "host"=>"localhost" }
+        expected = { "adapter" => "postgresql", "database" => "foo", "host" => "localhost", "name" => "default_env" }
         assert_equal expected, actual
       end
 
       def test_resolver_with_database_uri_and_current_env_symbol_key_and_rails_env
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
-        ENV['RAILS_ENV']    = "foo"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
+        ENV["RAILS_ENV"]    = "foo"
 
         config   = { "not_production" => { "adapter" => "not_postgres", "database" => "not_foo" } }
         actual   = resolve_spec(:foo, config)
-        expected = { "adapter" => "postgresql", "database" => "foo", "host" => "localhost" }
+        expected = { "adapter" => "postgresql", "database" => "foo", "host" => "localhost", "name" => "foo" }
         assert_equal expected, actual
       end
 
       def test_resolver_with_database_uri_and_current_env_symbol_key_and_rack_env
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
-        ENV['RACK_ENV']     = "foo"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
+        ENV["RACK_ENV"]     = "foo"
 
         config   = { "not_production" => { "adapter" => "not_postgres", "database" => "not_foo" } }
         actual   = resolve_spec(:foo, config)
-        expected = { "adapter" => "postgresql", "database" => "foo", "host" => "localhost" }
+        expected = { "adapter" => "postgresql", "database" => "foo", "host" => "localhost", "name" => "foo" }
         assert_equal expected, actual
       end
 
       def test_resolver_with_database_uri_and_known_key
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
         config   = { "production" => { "adapter" => "not_postgres", "database" => "not_foo", "host" => "localhost" } }
         actual   = resolve_spec(:production, config)
-        expected = { "adapter"=>"not_postgres", "database"=>"not_foo", "host"=>"localhost" }
+        expected = { "adapter" => "not_postgres", "database" => "not_foo", "host" => "localhost", "name" => "production" }
         assert_equal expected, actual
       end
 
       def test_resolver_with_database_uri_and_unknown_symbol_key
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
-        config   = { "not_production" => {  "adapter" => "not_postgres", "database" => "not_foo" } }
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
+        config = { "not_production" => {  "adapter" => "not_postgres", "database" => "not_foo" } }
         assert_raises AdapterNotSpecified do
           resolve_spec(:production, config)
         end
       end
 
       def test_resolver_with_database_uri_and_supplied_url
-        ENV['DATABASE_URL'] = "not-postgres://not-localhost/not_foo"
+        ENV["DATABASE_URL"] = "not-postgres://not-localhost/not_foo"
         config   = { "production" => {  "adapter" => "also_not_postgres", "database" => "also_not_foo" } }
         actual   = resolve_spec("postgres://localhost/foo", config)
-        expected = { "adapter"=>"postgresql", "database"=>"foo", "host"=>"localhost" }
+        expected = { "adapter" => "postgresql", "database" => "foo", "host" => "localhost" }
         assert_equal expected, actual
       end
 
@@ -82,18 +87,18 @@ module ActiveRecord
       end
 
       def test_environment_does_not_exist_in_config_url_does_exist
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
         config      = { "not_default_env" => {  "adapter" => "not_postgres", "database" => "not_foo" } }
         actual      = resolve_config(config)
-        expect_prod = { "adapter"=>"postgresql", "database"=>"foo", "host"=>"localhost" }
+        expect_prod = { "adapter" => "postgresql", "database" => "foo", "host" => "localhost" }
         assert_equal expect_prod, actual["default_env"]
       end
 
       def test_url_with_hyphenated_scheme
-        ENV['DATABASE_URL'] = "ibm-db://localhost/foo"
+        ENV["DATABASE_URL"] = "ibm-db://localhost/foo"
         config   = { "default_env" => { "adapter" => "not_postgres", "database" => "not_foo", "host" => "localhost" } }
         actual   = resolve_spec(:default_env, config)
-        expected = { "adapter"=>"ibm_db", "database"=>"foo", "host"=>"localhost" }
+        expected = { "adapter" => "ibm_db", "database" => "foo", "host" => "localhost", "name" => "default_env" }
         assert_equal expected, actual
       end
 
@@ -134,7 +139,7 @@ module ActiveRecord
       end
 
       def test_blank_with_database_url
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
 
         config   = {}
         actual   = resolve_config(config)
@@ -142,18 +147,18 @@ module ActiveRecord
                      "database" => "foo",
                      "host"     => "localhost" }
         assert_equal expected, actual["default_env"]
-        assert_equal nil,      actual["production"]
-        assert_equal nil,      actual["development"]
-        assert_equal nil,      actual["test"]
-        assert_equal nil,      actual[:default_env]
-        assert_equal nil,      actual[:production]
-        assert_equal nil,      actual[:development]
-        assert_equal nil,      actual[:test]
+        assert_nil actual["production"]
+        assert_nil actual["development"]
+        assert_nil actual["test"]
+        assert_nil actual[:default_env]
+        assert_nil actual[:production]
+        assert_nil actual[:development]
+        assert_nil actual[:test]
       end
 
       def test_blank_with_database_url_with_rails_env
-        ENV['RAILS_ENV'] = "not_production"
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
+        ENV["RAILS_ENV"] = "not_production"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
 
         config   = {}
         actual   = resolve_config(config)
@@ -162,20 +167,20 @@ module ActiveRecord
                      "host"     => "localhost" }
 
         assert_equal expected, actual["not_production"]
-        assert_equal nil,      actual["production"]
-        assert_equal nil,      actual["default_env"]
-        assert_equal nil,      actual["development"]
-        assert_equal nil,      actual["test"]
-        assert_equal nil,      actual[:default_env]
-        assert_equal nil,      actual[:not_production]
-        assert_equal nil,      actual[:production]
-        assert_equal nil,      actual[:development]
-        assert_equal nil,      actual[:test]
+        assert_nil actual["production"]
+        assert_nil actual["default_env"]
+        assert_nil actual["development"]
+        assert_nil actual["test"]
+        assert_nil actual[:default_env]
+        assert_nil actual[:not_production]
+        assert_nil actual[:production]
+        assert_nil actual[:development]
+        assert_nil actual[:test]
       end
 
       def test_blank_with_database_url_with_rack_env
-        ENV['RACK_ENV'] = "not_production"
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
+        ENV["RACK_ENV"] = "not_production"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
 
         config   = {}
         actual   = resolve_config(config)
@@ -184,19 +189,19 @@ module ActiveRecord
                      "host"     => "localhost" }
 
         assert_equal expected, actual["not_production"]
-        assert_equal nil,      actual["production"]
-        assert_equal nil,      actual["default_env"]
-        assert_equal nil,      actual["development"]
-        assert_equal nil,      actual["test"]
-        assert_equal nil,      actual[:default_env]
-        assert_equal nil,      actual[:not_production]
-        assert_equal nil,      actual[:production]
-        assert_equal nil,      actual[:development]
-        assert_equal nil,      actual[:test]
+        assert_nil actual["production"]
+        assert_nil actual["default_env"]
+        assert_nil actual["development"]
+        assert_nil actual["test"]
+        assert_nil actual[:default_env]
+        assert_nil actual[:not_production]
+        assert_nil actual[:production]
+        assert_nil actual[:development]
+        assert_nil actual[:test]
       end
 
       def test_database_url_with_ipv6_host_and_port
-        ENV['DATABASE_URL'] = "postgres://[::1]:5454/foo"
+        ENV["DATABASE_URL"] = "postgres://[::1]:5454/foo"
 
         config   = {}
         actual   = resolve_config(config)
@@ -208,12 +213,12 @@ module ActiveRecord
       end
 
       def test_url_sub_key_with_database_url
-        ENV['DATABASE_URL'] = "NOT-POSTGRES://localhost/NOT_FOO"
+        ENV["DATABASE_URL"] = "NOT-POSTGRES://localhost/NOT_FOO"
 
         config   = { "default_env" => { "url" => "postgres://localhost/foo" } }
         actual   = resolve_config(config)
         expected = { "default_env" =>
-                    { "adapter"  => "postgresql",
+                    { "adapter" => "postgresql",
                        "database" => "foo",
                        "host"     => "localhost"
                       }
@@ -222,9 +227,9 @@ module ActiveRecord
       end
 
       def test_merge_no_conflicts_with_database_url
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
 
-        config   = {"default_env" => { "pool" => "5" } }
+        config   = { "default_env" => { "pool" => "5" } }
         actual   = resolve_config(config)
         expected = { "default_env" =>
                      { "adapter"  => "postgresql",
@@ -237,9 +242,9 @@ module ActiveRecord
       end
 
       def test_merge_conflicts_with_database_url
-        ENV['DATABASE_URL'] = "postgres://localhost/foo"
+        ENV["DATABASE_URL"] = "postgres://localhost/foo"
 
-        config   = {"default_env" => { "adapter" => "NOT-POSTGRES", "database" => "NOT-FOO", "pool" => "5" } }
+        config   = { "default_env" => { "adapter" => "NOT-POSTGRES", "database" => "NOT-FOO", "pool" => "5" } }
         actual   = resolve_config(config)
         expected = { "default_env" =>
                      { "adapter"  => "postgresql",
diff --git a/activerecord/test/cases/connection_adapters/mysql_type_lookup_test.rb b/activerecord/test/cases/connection_adapters/mysql_type_lookup_test.rb
index 80244d1439..02e76ce146 100644
--- a/activerecord/test/cases/connection_adapters/mysql_type_lookup_test.rb
+++ b/activerecord/test/cases/connection_adapters/mysql_type_lookup_test.rb
@@ -1,65 +1,78 @@
+# frozen_string_literal: true
+
 require "cases/helper"
+require "support/connection_helper"
 
-if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-module ActiveRecord
-  module ConnectionAdapters
-    class MysqlTypeLookupTest < ActiveRecord::TestCase
-      setup do
-        @connection = ActiveRecord::Base.connection
-      end
+if current_adapter?(:Mysql2Adapter)
+  module ActiveRecord
+    module ConnectionAdapters
+      class MysqlTypeLookupTest < ActiveRecord::TestCase
+        include ConnectionHelper
 
-      def test_boolean_types
-        emulate_booleans(true) do
-          assert_lookup_type :boolean, 'tinyint(1)'
-          assert_lookup_type :boolean, 'TINYINT(1)'
+        setup do
+          @connection = ActiveRecord::Base.connection
         end
-      end
 
-      def test_string_types
-        assert_lookup_type :string, "enum('one', 'two', 'three')"
-        assert_lookup_type :string, "ENUM('one', 'two', 'three')"
-        assert_lookup_type :string, "set('one', 'two', 'three')"
-        assert_lookup_type :string, "SET('one', 'two', 'three')"
-      end
+        def teardown
+          reset_connection
+        end
 
-      def test_enum_type_with_value_matching_other_type
-        assert_lookup_type :string, "ENUM('unicode', '8bit', 'none')"
-      end
+        def test_boolean_types
+          emulate_booleans(true) do
+            assert_lookup_type :boolean, "tinyint(1)"
+            assert_lookup_type :boolean, "TINYINT(1)"
+          end
+        end
 
-      def test_binary_types
-        assert_lookup_type :binary, 'bit'
-        assert_lookup_type :binary, 'BIT'
-      end
+        def test_string_types
+          assert_lookup_type :string, "enum('one', 'two', 'three')"
+          assert_lookup_type :string, "ENUM('one', 'two', 'three')"
+          assert_lookup_type :string, "set('one', 'two', 'three')"
+          assert_lookup_type :string, "SET('one', 'two', 'three')"
+        end
 
-      def test_integer_types
-        emulate_booleans(false) do
-          assert_lookup_type :integer, 'tinyint(1)'
-          assert_lookup_type :integer, 'TINYINT(1)'
-          assert_lookup_type :integer, 'year'
-          assert_lookup_type :integer, 'YEAR'
+        def test_set_type_with_value_matching_other_type
+          assert_lookup_type :string, "SET('unicode', '8bit', 'none', 'time')"
         end
-      end
 
-      private
+        def test_enum_type_with_value_matching_other_type
+          assert_lookup_type :string, "ENUM('unicode', '8bit', 'none')"
+        end
 
-      def assert_lookup_type(type, lookup)
-        cast_type = @connection.type_map.lookup(lookup)
-        assert_equal type, cast_type.type
-      end
+        def test_binary_types
+          assert_lookup_type :binary, "bit"
+          assert_lookup_type :binary, "BIT"
+        end
 
-      def emulate_booleans(value)
-        old_emulate_booleans = @connection.emulate_booleans
-        change_emulate_booleans(value)
-        yield
-      ensure
-        change_emulate_booleans(old_emulate_booleans)
-      end
+        def test_integer_types
+          emulate_booleans(false) do
+            assert_lookup_type :integer, "tinyint(1)"
+            assert_lookup_type :integer, "TINYINT(1)"
+            assert_lookup_type :integer, "year"
+            assert_lookup_type :integer, "YEAR"
+          end
+        end
 
-      def change_emulate_booleans(value)
-        @connection.emulate_booleans = value
-        @connection.clear_cache!
+        private
+
+          def assert_lookup_type(type, lookup)
+            cast_type = @connection.send(:type_map).lookup(lookup)
+            assert_equal type, cast_type.type
+          end
+
+          def emulate_booleans(value)
+            old_emulate_booleans = @connection.emulate_booleans
+            change_emulate_booleans(value)
+            yield
+          ensure
+            change_emulate_booleans(old_emulate_booleans)
+          end
+
+          def change_emulate_booleans(value)
+            @connection.emulate_booleans = value
+            @connection.clear_cache!
+          end
       end
     end
   end
 end
-end
diff --git a/activerecord/test/cases/connection_adapters/quoting_test.rb b/activerecord/test/cases/connection_adapters/quoting_test.rb
deleted file mode 100644
index 59dcb96ebc..0000000000
--- a/activerecord/test/cases/connection_adapters/quoting_test.rb
+++ /dev/null
@@ -1,13 +0,0 @@
-require "cases/helper"
-
-module ActiveRecord
-  module ConnectionAdapters
-    module Quoting
-      class QuotingTest < ActiveRecord::TestCase
-        def test_quoting_classes
-          assert_equal "'Object'", AbstractAdapter.new(nil).quote(Object)
-        end
-      end
-    end
-  end
-end
diff --git a/activerecord/test/cases/connection_adapters/schema_cache_test.rb b/activerecord/test/cases/connection_adapters/schema_cache_test.rb
index c7531f5418..67496381d1 100644
--- a/activerecord/test/cases/connection_adapters/schema_cache_test.rb
+++ b/activerecord/test/cases/connection_adapters/schema_cache_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -9,28 +11,55 @@ module ActiveRecord
       end
 
       def test_primary_key
-        assert_equal 'id', @cache.primary_keys('posts')
+        assert_equal "id", @cache.primary_keys("posts")
+      end
+
+      def test_yaml_dump_and_load
+        @cache.columns("posts")
+        @cache.columns_hash("posts")
+        @cache.data_sources("posts")
+        @cache.primary_keys("posts")
+
+        new_cache = YAML.load(YAML.dump(@cache))
+        assert_no_queries do
+          assert_equal 12, new_cache.columns("posts").size
+          assert_equal 12, new_cache.columns_hash("posts").size
+          assert new_cache.data_sources("posts")
+          assert_equal "id", new_cache.primary_keys("posts")
+        end
+      end
+
+      def test_yaml_loads_5_1_dump
+        body = File.open(schema_dump_path).read
+        cache = YAML.load(body)
+
+        assert_no_queries do
+          assert_equal 11, cache.columns("posts").size
+          assert_equal 11, cache.columns_hash("posts").size
+          assert cache.data_sources("posts")
+          assert_equal "id", cache.primary_keys("posts")
+        end
       end
 
       def test_primary_key_for_non_existent_table
-        assert_nil @cache.primary_keys('omgponies')
+        assert_nil @cache.primary_keys("omgponies")
       end
 
       def test_caches_columns
-        columns = @cache.columns('posts')
-        assert_equal columns, @cache.columns('posts')
+        columns = @cache.columns("posts")
+        assert_equal columns, @cache.columns("posts")
       end
 
       def test_caches_columns_hash
-        columns_hash = @cache.columns_hash('posts')
-        assert_equal columns_hash, @cache.columns_hash('posts')
+        columns_hash = @cache.columns_hash("posts")
+        assert_equal columns_hash, @cache.columns_hash("posts")
       end
 
       def test_clearing
-        @cache.columns('posts')
-        @cache.columns_hash('posts')
-        @cache.tables('posts')
-        @cache.primary_keys('posts')
+        @cache.columns("posts")
+        @cache.columns_hash("posts")
+        @cache.data_sources("posts")
+        @cache.primary_keys("posts")
 
         @cache.clear!
 
@@ -38,19 +67,35 @@ module ActiveRecord
       end
 
       def test_dump_and_load
-        @cache.columns('posts')
-        @cache.columns_hash('posts')
-        @cache.tables('posts')
-        @cache.primary_keys('posts')
+        @cache.columns("posts")
+        @cache.columns_hash("posts")
+        @cache.data_sources("posts")
+        @cache.primary_keys("posts")
 
         @cache = Marshal.load(Marshal.dump(@cache))
 
-        assert_equal 11, @cache.columns('posts').size
-        assert_equal 11, @cache.columns_hash('posts').size
-        assert @cache.tables('posts')
-        assert_equal 'id', @cache.primary_keys('posts')
+        assert_no_queries do
+          assert_equal 12, @cache.columns("posts").size
+          assert_equal 12, @cache.columns_hash("posts").size
+          assert @cache.data_sources("posts")
+          assert_equal "id", @cache.primary_keys("posts")
+        end
+      end
+
+      def test_data_source_exist
+        assert @cache.data_source_exists?("posts")
+        assert_not @cache.data_source_exists?("foo")
       end
 
+      def test_clear_data_source_cache
+        @cache.clear_data_source_cache!("posts")
+      end
+
+      private
+
+        def schema_dump_path
+          "test/assets/schema_dump_5_1.yml"
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/connection_adapters/type_lookup_test.rb b/activerecord/test/cases/connection_adapters/type_lookup_test.rb
index 7566863653..1c79d776f0 100644
--- a/activerecord/test/cases/connection_adapters/type_lookup_test.rb
+++ b/activerecord/test/cases/connection_adapters/type_lookup_test.rb
@@ -1,110 +1,120 @@
-require "cases/helper"
+# frozen_string_literal: true
 
-unless current_adapter?(:PostgreSQLAdapter) # PostgreSQL does not use type strigns for lookup
-module ActiveRecord
-  module ConnectionAdapters
-    class TypeLookupTest < ActiveRecord::TestCase
-      setup do
-        @connection = ActiveRecord::Base.connection
-      end
+require "cases/helper"
 
-      def test_boolean_types
-        assert_lookup_type :boolean, 'boolean'
-        assert_lookup_type :boolean, 'BOOLEAN'
-      end
+unless current_adapter?(:PostgreSQLAdapter) # PostgreSQL does not use type strings for lookup
+  module ActiveRecord
+    module ConnectionAdapters
+      class TypeLookupTest < ActiveRecord::TestCase
+        setup do
+          @connection = ActiveRecord::Base.connection
+        end
 
-      def test_string_types
-        assert_lookup_type :string, 'char'
-        assert_lookup_type :string, 'varchar'
-        assert_lookup_type :string, 'VARCHAR'
-        assert_lookup_type :string, 'varchar(255)'
-        assert_lookup_type :string, 'character varying'
-      end
+        def test_boolean_types
+          assert_lookup_type :boolean, "boolean"
+          assert_lookup_type :boolean, "BOOLEAN"
+        end
 
-      def test_binary_types
-        assert_lookup_type :binary, 'binary'
-        assert_lookup_type :binary, 'BINARY'
-        assert_lookup_type :binary, 'blob'
-        assert_lookup_type :binary, 'BLOB'
-      end
+        def test_string_types
+          assert_lookup_type :string, "char"
+          assert_lookup_type :string, "varchar"
+          assert_lookup_type :string, "VARCHAR"
+          assert_lookup_type :string, "varchar(255)"
+          assert_lookup_type :string, "character varying"
+        end
 
-      def test_text_types
-        assert_lookup_type :text, 'text'
-        assert_lookup_type :text, 'TEXT'
-        assert_lookup_type :text, 'clob'
-        assert_lookup_type :text, 'CLOB'
-      end
+        def test_binary_types
+          assert_lookup_type :binary, "binary"
+          assert_lookup_type :binary, "BINARY"
+          assert_lookup_type :binary, "blob"
+          assert_lookup_type :binary, "BLOB"
+        end
 
-      def test_date_types
-        assert_lookup_type :date, 'date'
-        assert_lookup_type :date, 'DATE'
-      end
+        def test_text_types
+          assert_lookup_type :text, "text"
+          assert_lookup_type :text, "TEXT"
+          assert_lookup_type :text, "clob"
+          assert_lookup_type :text, "CLOB"
+        end
 
-      def test_time_types
-        assert_lookup_type :time, 'time'
-        assert_lookup_type :time, 'TIME'
-      end
+        def test_date_types
+          assert_lookup_type :date, "date"
+          assert_lookup_type :date, "DATE"
+        end
 
-      def test_datetime_types
-        assert_lookup_type :datetime, 'datetime'
-        assert_lookup_type :datetime, 'DATETIME'
-        assert_lookup_type :datetime, 'timestamp'
-        assert_lookup_type :datetime, 'TIMESTAMP'
-      end
+        def test_time_types
+          assert_lookup_type :time, "time"
+          assert_lookup_type :time, "TIME"
+        end
 
-      def test_decimal_types
-        assert_lookup_type :decimal, 'decimal'
-        assert_lookup_type :decimal, 'decimal(2,8)'
-        assert_lookup_type :decimal, 'DECIMAL'
-        assert_lookup_type :decimal, 'numeric'
-        assert_lookup_type :decimal, 'numeric(2,8)'
-        assert_lookup_type :decimal, 'NUMERIC'
-        assert_lookup_type :decimal, 'number'
-        assert_lookup_type :decimal, 'number(2,8)'
-        assert_lookup_type :decimal, 'NUMBER'
-      end
+        def test_datetime_types
+          assert_lookup_type :datetime, "datetime"
+          assert_lookup_type :datetime, "DATETIME"
+          assert_lookup_type :datetime, "timestamp"
+          assert_lookup_type :datetime, "TIMESTAMP"
+        end
 
-      def test_float_types
-        assert_lookup_type :float, 'float'
-        assert_lookup_type :float, 'FLOAT'
-        assert_lookup_type :float, 'double'
-        assert_lookup_type :float, 'DOUBLE'
-      end
+        def test_decimal_types
+          assert_lookup_type :decimal, "decimal"
+          assert_lookup_type :decimal, "decimal(2,8)"
+          assert_lookup_type :decimal, "DECIMAL"
+          assert_lookup_type :decimal, "numeric"
+          assert_lookup_type :decimal, "numeric(2,8)"
+          assert_lookup_type :decimal, "NUMERIC"
+          assert_lookup_type :decimal, "number"
+          assert_lookup_type :decimal, "number(2,8)"
+          assert_lookup_type :decimal, "NUMBER"
+        end
 
-      def test_integer_types
-        assert_lookup_type :integer, 'integer'
-        assert_lookup_type :integer, 'INTEGER'
-        assert_lookup_type :integer, 'tinyint'
-        assert_lookup_type :integer, 'smallint'
-        assert_lookup_type :integer, 'bigint'
-      end
+        def test_float_types
+          assert_lookup_type :float, "float"
+          assert_lookup_type :float, "FLOAT"
+          assert_lookup_type :float, "double"
+          assert_lookup_type :float, "DOUBLE"
+        end
 
-      def test_bigint_limit
-        cast_type = @connection.type_map.lookup("bigint")
-        if current_adapter?(:OracleAdapter)
-          assert_equal 19, cast_type.limit
-        else
-          assert_equal 8, cast_type.limit
+        def test_integer_types
+          assert_lookup_type :integer, "integer"
+          assert_lookup_type :integer, "INTEGER"
+          assert_lookup_type :integer, "tinyint"
+          assert_lookup_type :integer, "smallint"
+          assert_lookup_type :integer, "bigint"
         end
-      end
 
-      def test_decimal_without_scale
-        types = %w{decimal(2) decimal(2,0) numeric(2) numeric(2,0) number(2) number(2,0)}
-        types.each do |type|
-          cast_type = @connection.type_map.lookup(type)
+        def test_bigint_limit
+          limit = @connection.send(:type_map).lookup("bigint").send(:_limit)
+          if current_adapter?(:OracleAdapter)
+            assert_equal 19, limit
+          else
+            assert_equal 8, limit
+          end
+        end
 
-          assert_equal :decimal, cast_type.type
-          assert_equal 2, cast_type.cast(2.1)
+        def test_decimal_without_scale
+          if current_adapter?(:OracleAdapter)
+            {
+              decimal: %w{decimal(2) decimal(2,0) numeric(2) numeric(2,0)},
+              integer: %w{number(2) number(2,0)}
+            }
+          else
+            { decimal: %w{decimal(2) decimal(2,0) numeric(2) numeric(2,0) number(2) number(2,0)} }
+          end.each do |expected_type, types|
+            types.each do |type|
+              cast_type = @connection.send(:type_map).lookup(type)
+
+              assert_equal expected_type, cast_type.type
+              assert_equal 2, cast_type.cast(2.1)
+            end
+          end
         end
-      end
 
-      private
+        private
 
-      def assert_lookup_type(type, lookup)
-        cast_type = @connection.type_map.lookup(lookup)
-        assert_equal type, cast_type.type
+          def assert_lookup_type(type, lookup)
+            cast_type = @connection.send(:type_map).lookup(lookup)
+            assert_equal type, cast_type.type
+          end
       end
     end
   end
 end
-end
diff --git a/activerecord/test/cases/connection_management_test.rb b/activerecord/test/cases/connection_management_test.rb
index dff6ea0fb0..b9b5cc0e28 100644
--- a/activerecord/test/cases/connection_management_test.rb
+++ b/activerecord/test/cases/connection_management_test.rb
@@ -1,9 +1,13 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "rack"
 
 module ActiveRecord
   module ConnectionAdapters
     class ConnectionManagementTest < ActiveRecord::TestCase
+      self.use_transactional_tests = false
+
       class App
         attr_reader :calls
         def initialize
@@ -12,88 +16,99 @@ module ActiveRecord
 
         def call(env)
           @calls << env
-          [200, {}, ['hi mom']]
+          [200, {}, ["hi mom"]]
         end
       end
 
       def setup
         @env = {}
         @app = App.new
-        @management = ConnectionManagement.new(@app)
+        @management = middleware(@app)
 
         # make sure we have an active connection
         assert ActiveRecord::Base.connection
-        assert ActiveRecord::Base.connection_handler.active_connections?
+        assert_predicate ActiveRecord::Base.connection_handler, :active_connections?
       end
 
       def test_app_delegation
-        manager = ConnectionManagement.new(@app)
+        manager = middleware(@app)
 
         manager.call @env
         assert_equal [@env], @app.calls
       end
 
-      def test_connections_are_active_after_call
-        @management.call(@env)
-        assert ActiveRecord::Base.connection_handler.active_connections?
-      end
-
       def test_body_responds_to_each
         _, _, body = @management.call(@env)
         bits = []
         body.each { |bit| bits << bit }
-        assert_equal ['hi mom'], bits
+        assert_equal ["hi mom"], bits
       end
 
       def test_connections_are_cleared_after_body_close
         _, _, body = @management.call(@env)
         body.close
-        assert !ActiveRecord::Base.connection_handler.active_connections?
+        assert_not_predicate ActiveRecord::Base.connection_handler, :active_connections?
       end
 
-      def test_active_connections_are_not_cleared_on_body_close_during_test
-        @env['rack.test'] = true
-        _, _, body = @management.call(@env)
-        body.close
-        assert ActiveRecord::Base.connection_handler.active_connections?
+      def test_active_connections_are_not_cleared_on_body_close_during_transaction
+        ActiveRecord::Base.transaction do
+          _, _, body = @management.call(@env)
+          body.close
+          assert_predicate ActiveRecord::Base.connection_handler, :active_connections?
+        end
       end
 
       def test_connections_closed_if_exception
         app       = Class.new(App) { def call(env); raise NotImplementedError; end }.new
-        explosive = ConnectionManagement.new(app)
+        explosive = middleware(app)
         assert_raises(NotImplementedError) { explosive.call(@env) }
-        assert !ActiveRecord::Base.connection_handler.active_connections?
+        assert_not_predicate ActiveRecord::Base.connection_handler, :active_connections?
       end
 
-      def test_connections_not_closed_if_exception_and_test
-        @env['rack.test'] = true
-        app               = Class.new(App) { def call(env); raise; end }.new
-        explosive         = ConnectionManagement.new(app)
-        assert_raises(RuntimeError) { explosive.call(@env) }
-        assert ActiveRecord::Base.connection_handler.active_connections?
-      end
-
-      def test_connections_closed_if_exception_and_explicitly_not_test
-        @env['rack.test'] = false
-        app       = Class.new(App) { def call(env); raise NotImplementedError; end }.new
-        explosive = ConnectionManagement.new(app)
-        assert_raises(NotImplementedError) { explosive.call(@env) }
-        assert !ActiveRecord::Base.connection_handler.active_connections?
+      def test_connections_not_closed_if_exception_inside_transaction
+        ActiveRecord::Base.transaction do
+          app               = Class.new(App) { def call(env); raise RuntimeError; end }.new
+          explosive         = middleware(app)
+          assert_raises(RuntimeError) { explosive.call(@env) }
+          assert_predicate ActiveRecord::Base.connection_handler, :active_connections?
+        end
       end
 
       test "doesn't clear active connections when running in a test case" do
-        @env['rack.test'] = true
-        @management.call(@env)
-        assert ActiveRecord::Base.connection_handler.active_connections?
+        executor.wrap do
+          @management.call(@env)
+          assert_predicate ActiveRecord::Base.connection_handler, :active_connections?
+        end
       end
 
       test "proxy is polite to its body and responds to it" do
         body = Class.new(String) { def to_path; "/path"; end }.new
         app = lambda { |_| [200, {}, body] }
-        response_body = ConnectionManagement.new(app).call(@env)[2]
-        assert response_body.respond_to?(:to_path)
-        assert_equal response_body.to_path, "/path"
+        response_body = middleware(app).call(@env)[2]
+        assert_respond_to response_body, :to_path
+        assert_equal "/path", response_body.to_path
+      end
+
+      test "doesn't mutate the original response" do
+        original_response = [200, {}, "hi"]
+        app = lambda { |_| original_response }
+        middleware(app).call(@env)[2]
+        assert_equal "hi", original_response.last
       end
+
+      private
+        def executor
+          @executor ||= Class.new(ActiveSupport::Executor).tap do |exe|
+            ActiveRecord::QueryCache.install_executor_hooks(exe)
+          end
+        end
+
+        def middleware(app)
+          lambda do |env|
+            a, b, c = executor.wrap { app.call(env) }
+            [a, b, Rack::BodyProxy.new(c) { }]
+          end
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/connection_pool_test.rb b/activerecord/test/cases/connection_pool_test.rb
index c905772193..633d56e479 100644
--- a/activerecord/test/cases/connection_pool_test.rb
+++ b/activerecord/test/cases/connection_pool_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'active_support/concurrency/latch'
+require "concurrent/atomic/count_down_latch"
 
 module ActiveRecord
   module ConnectionAdapters
@@ -33,12 +35,12 @@ module ActiveRecord
 
       def test_checkout_after_close
         connection = pool.connection
-        assert connection.in_use?
+        assert_predicate connection, :in_use?
 
         connection.close
-        assert !connection.in_use?
+        assert_not_predicate connection, :in_use?
 
-        assert pool.connection.in_use?
+        assert_predicate pool.connection, :in_use?
       end
 
       def test_released_connection_moves_between_threads
@@ -78,18 +80,20 @@ module ActiveRecord
       end
 
       def test_active_connection_in_use
-        assert !pool.active_connection?
+        assert_not_predicate pool, :active_connection?
         main_thread = pool.connection
 
-        assert pool.active_connection?
+        assert_predicate pool, :active_connection?
 
         main_thread.close
 
-        assert !pool.active_connection?
+        assert_not_predicate pool, :active_connection?
       end
 
       def test_full_pool_exception
-        @pool.size.times { @pool.checkout }
+        @pool.checkout_timeout = 0.001 # no need to delay test suite by waiting the whole full default timeout
+        @pool.size.times { assert @pool.checkout }
+
         assert_raises(ConnectionTimeoutError) do
           @pool.checkout
         end
@@ -107,6 +111,44 @@ module ActiveRecord
         assert_equal connection, t.join.value
       end
 
+      def test_full_pool_blocking_shares_load_interlock
+        @pool.instance_variable_set(:@size, 1)
+
+        load_interlock_latch = Concurrent::CountDownLatch.new
+        connection_latch = Concurrent::CountDownLatch.new
+
+        able_to_get_connection = false
+        able_to_load = false
+
+        thread_with_load_interlock = Thread.new do
+          ActiveSupport::Dependencies.interlock.running do
+            load_interlock_latch.count_down
+            connection_latch.wait
+
+            @pool.with_connection do
+              able_to_get_connection = true
+            end
+          end
+        end
+
+        thread_with_last_connection = Thread.new do
+          @pool.with_connection do
+            connection_latch.count_down
+            load_interlock_latch.wait
+
+            ActiveSupport::Dependencies.interlock.loading do
+              able_to_load = true
+            end
+          end
+        end
+
+        thread_with_load_interlock.join
+        thread_with_last_connection.join
+
+        assert able_to_get_connection
+        assert able_to_load
+      end
+
       def test_removing_releases_latch
         cs = @pool.size.times.map { @pool.checkout }
         t = Thread.new { @pool.checkout }
@@ -133,15 +175,15 @@ module ActiveRecord
       end
 
       def test_reap_inactive
-        ready = ActiveSupport::Concurrency::Latch.new
+        ready = Concurrent::CountDownLatch.new
         @pool.checkout
         child = Thread.new do
           @pool.checkout
           @pool.checkout
-          ready.release
+          ready.count_down
           Thread.stop
         end
-        ready.await
+        ready.wait
 
         assert_equal 3, active_connections(@pool).size
 
@@ -151,16 +193,106 @@ module ActiveRecord
 
         assert_equal 1, active_connections(@pool).size
       ensure
-        @pool.connections.each(&:close)
+        @pool.connections.each { |conn| conn.close if conn.in_use? }
+      end
+
+      def test_idle_timeout_configuration
+        @pool.disconnect!
+        spec = ActiveRecord::Base.connection_pool.spec
+        spec.config.merge!(idle_timeout: "0.02")
+        @pool = ConnectionPool.new(spec)
+        idle_conn = @pool.checkout
+        @pool.checkin(idle_conn)
+
+        idle_conn.instance_variable_set(
+          :@idle_since,
+          Concurrent.monotonic_time - 0.01
+        )
+
+        @pool.flush
+        assert_equal 1, @pool.connections.length
+
+        idle_conn.instance_variable_set(
+          :@idle_since,
+          Concurrent.monotonic_time - 0.02
+        )
+
+        @pool.flush
+        assert_equal 0, @pool.connections.length
+      end
+
+      def test_disable_flush
+        @pool.disconnect!
+        spec = ActiveRecord::Base.connection_pool.spec
+        spec.config.merge!(idle_timeout: -5)
+        @pool = ConnectionPool.new(spec)
+        idle_conn = @pool.checkout
+        @pool.checkin(idle_conn)
+
+        idle_conn.instance_variable_set(
+          :@idle_since,
+          Concurrent.monotonic_time - 1
+        )
+
+        @pool.flush
+        assert_equal 1, @pool.connections.length
+      end
+
+      def test_flush
+        idle_conn = @pool.checkout
+        recent_conn = @pool.checkout
+        active_conn = @pool.checkout
+
+        @pool.checkin idle_conn
+        @pool.checkin recent_conn
+
+        assert_equal 3, @pool.connections.length
+
+        idle_conn.instance_variable_set(
+          :@idle_since,
+          Concurrent.monotonic_time - 1000
+        )
+
+        @pool.flush(30)
+
+        assert_equal 2, @pool.connections.length
+
+        assert_equal [recent_conn, active_conn].sort_by(&:__id__), @pool.connections.sort_by(&:__id__)
+      ensure
+        @pool.checkin active_conn
+      end
+
+      def test_flush_bang
+        idle_conn = @pool.checkout
+        recent_conn = @pool.checkout
+        active_conn = @pool.checkout
+        _dead_conn = Thread.new { @pool.checkout }.join
+
+        @pool.checkin idle_conn
+        @pool.checkin recent_conn
+
+        assert_equal 4, @pool.connections.length
+
+        def idle_conn.seconds_idle
+          1000
+        end
+
+        @pool.flush!
+
+        assert_equal 1, @pool.connections.length
+
+        assert_equal [active_conn].sort_by(&:__id__), @pool.connections.sort_by(&:__id__)
+      ensure
+        @pool.checkin active_conn
       end
 
       def test_remove_connection
         conn = @pool.checkout
-        assert conn.in_use?
+        assert_predicate conn, :in_use?
 
         length = @pool.connections.length
         @pool.remove conn
-        assert conn.in_use?
+        assert_predicate conn, :in_use?
         assert_equal(length - 1, @pool.connections.length)
       ensure
         conn.close
@@ -175,23 +307,23 @@ module ActiveRecord
       end
 
       def test_active_connection?
-        assert !@pool.active_connection?
+        assert_not_predicate @pool, :active_connection?
         assert @pool.connection
-        assert @pool.active_connection?
+        assert_predicate @pool, :active_connection?
         @pool.release_connection
-        assert !@pool.active_connection?
+        assert_not_predicate @pool, :active_connection?
       end
 
       def test_checkout_behaviour
         pool = ConnectionPool.new ActiveRecord::Base.connection_pool.spec
-        connection = pool.connection
-        assert_not_nil connection
+        main_connection = pool.connection
+        assert_not_nil main_connection
         threads = []
         4.times do |i|
           threads << Thread.new(i) do
-            connection = pool.connection
-            assert_not_nil connection
-            connection.close
+            thread_connection = pool.connection
+            assert_not_nil thread_connection
+            thread_connection.close
           end
         end
 
@@ -203,6 +335,14 @@ module ActiveRecord
         end.join
       end
 
+      def test_checkout_order_is_lifo
+        conn1 = @pool.checkout
+        conn2 = @pool.checkout
+        @pool.checkin conn1
+        @pool.checkin conn2
+        assert_equal [conn2, conn1], 2.times.map { @pool.checkout }
+      end
+
       # The connection pool is "fair" if threads waiting for
       # connections receive them in the order in which they began
       # waiting.  This ensures that we don't timeout one HTTP request
@@ -307,14 +447,17 @@ module ActiveRecord
         end
       end
 
-      def test_automatic_reconnect=
+      def test_automatic_reconnect_restores_after_disconnect
         pool = ConnectionPool.new ActiveRecord::Base.connection_pool.spec
         assert pool.automatic_reconnect
         assert pool.connection
 
         pool.disconnect!
         assert pool.connection
+      end
 
+      def test_automatic_reconnect_can_be_disabled
+        pool = ConnectionPool.new ActiveRecord::Base.connection_pool.spec
         pool.disconnect!
         pool.automatic_reconnect = false
 
@@ -335,11 +478,26 @@ module ActiveRecord
       # is called with an anonymous class
       def test_anonymous_class_exception
         anonymous = Class.new(ActiveRecord::Base)
-        handler = ActiveRecord::Base.connection_handler
 
-        assert_raises(RuntimeError) {
-          handler.establish_connection anonymous, nil
-        }
+        assert_raises(RuntimeError) do
+          anonymous.establish_connection
+        end
+      end
+
+      class ConnectionTestModel < ActiveRecord::Base
+      end
+
+      def test_connection_notification_is_called
+        payloads = []
+        subscription = ActiveSupport::Notifications.subscribe("!connection.active_record") do |name, started, finished, unique_id, payload|
+          payloads << payload
+        end
+        ConnectionTestModel.establish_connection :arunit
+
+        assert_equal [:config, :connection_id, :spec_name], payloads[0].keys.sort
+        assert_equal "ActiveRecord::ConnectionAdapters::ConnectionPoolTest::ConnectionTestModel", payloads[0][:spec_name]
+      ensure
+        ActiveSupport::Notifications.unsubscribe(subscription) if subscription
       end
 
       def test_pool_sets_connection_schema_cache
@@ -360,13 +518,13 @@ module ActiveRecord
       def test_concurrent_connection_establishment
         assert_operator @pool.connections.size, :<=, 1
 
-        all_threads_in_new_connection = ActiveSupport::Concurrency::Latch.new(@pool.size - @pool.connections.size)
-        all_go                        = ActiveSupport::Concurrency::Latch.new
+        all_threads_in_new_connection = Concurrent::CountDownLatch.new(@pool.size - @pool.connections.size)
+        all_go                        = Concurrent::CountDownLatch.new
 
         @pool.singleton_class.class_eval do
           define_method(:new_connection) do
-            all_threads_in_new_connection.release
-            all_go.await
+            all_threads_in_new_connection.count_down
+            all_go.wait
             super()
           end
         end
@@ -381,19 +539,20 @@ module ActiveRecord
             # the kernel of the whole test is here, everything else is just scaffolding,
             # this latch will not be released unless conn. pool allows for concurrent
             # connection creation
-            all_threads_in_new_connection.await
+            all_threads_in_new_connection.wait
           end
         rescue Timeout::Error
-          flunk 'pool unable to establish connections concurrently or implementation has ' <<
-                'changed, this test then needs to patch a different :new_connection method'
+          flunk "pool unable to establish connections concurrently or implementation has " \
+                "changed, this test then needs to patch a different :new_connection method"
         ensure
           # clean up the threads
-          all_go.release
+          all_go.count_down
           connecting_threads.map(&:join)
         end
       end
 
       def test_non_bang_disconnect_and_clear_reloadable_connections_throw_exception_if_threads_dont_return_their_conns
+        Thread.report_on_exception, original_report_on_exception = false, Thread.report_on_exception
         @pool.checkout_timeout = 0.001 # no need to delay test suite by waiting the whole full default timeout
         [:disconnect, :clear_reloadable_connections].each do |group_action_method|
           @pool.with_connection do |connection|
@@ -402,6 +561,8 @@ module ActiveRecord
             end
           end
         end
+      ensure
+        Thread.report_on_exception = original_report_on_exception
       end
 
       def test_disconnect_and_clear_reloadable_connections_attempt_to_wait_for_threads_to_return_their_conns
@@ -418,7 +579,7 @@ module ActiveRecord
               assert_nil timed_join_result
 
               # assert that since this is within default timeout our connection hasn't been forcefully taken away from us
-              assert @pool.active_connection?
+              assert_predicate @pool, :active_connection?
             end
           ensure
             thread.join if thread && !timed_join_result # clean up the other thread
@@ -426,13 +587,16 @@ module ActiveRecord
         end
       end
 
-      def test_bang_versions_of_disconnect_and_clear_reloadable_connections_if_unable_to_aquire_all_connections_proceed_anyway
+      def test_bang_versions_of_disconnect_and_clear_reloadable_connections_if_unable_to_acquire_all_connections_proceed_anyway
         @pool.checkout_timeout = 0.001 # no need to delay test suite by waiting the whole full default timeout
         [:disconnect!, :clear_reloadable_connections!].each do |group_action_method|
           @pool.with_connection do |connection|
             Thread.new { @pool.send(group_action_method) }.join
             # assert connection has been forcefully taken away from us
-            assert_not @pool.active_connection?
+            assert_not_predicate @pool, :active_connection?
+
+            # make a new connection for with_connection to clean up
+            @pool.connection
           end
         end
       end
@@ -441,49 +605,50 @@ module ActiveRecord
         with_single_connection_pool do |pool|
           [:disconnect, :disconnect!, :clear_reloadable_connections, :clear_reloadable_connections!].each do |group_action_method|
             conn               = pool.connection # drain the only available connection
-            second_thread_done = ActiveSupport::Concurrency::Latch.new
-
-            # create a first_thread and let it get into the FIFO queue first
-            first_thread = Thread.new do
-              pool.with_connection { second_thread_done.await }
-            end
+            second_thread_done = Concurrent::Event.new
 
-            # wait for first_thread to get in queue
-            Thread.pass until pool.num_waiting_in_queue == 1
-
-            # create a different, later thread, that will attempt to do a "group action",
-            # but because of the group action semantics it should be able to preempt the
-            # first_thread when a connection is made available
-            second_thread = Thread.new do
-              pool.send(group_action_method)
-              second_thread_done.release
-            end
-
-            # wait for second_thread to get in queue
-            Thread.pass until pool.num_waiting_in_queue == 2
-
-            # return the only available connection
-            pool.checkin(conn)
-
-            # if the second_thread is not able to preempt the first_thread,
-            # they will temporarily (until either of them timeouts with ConnectionTimeoutError)
-            # deadlock and a join(2) timeout will be reached
-            failed = true unless second_thread.join(2)
-
-            #--- post test clean up start
-            second_thread_done.release if failed
-
-            # after `pool.disconnect()` the first thread will be left stuck in queue, no need to wait for
-            # it to timeout with ConnectionTimeoutError
-            if (group_action_method == :disconnect || group_action_method == :disconnect!) && pool.num_waiting_in_queue > 0
-              pool.with_connection {} # create a new connection in case there are threads still stuck in a queue
+            begin
+              # create a first_thread and let it get into the FIFO queue first
+              first_thread = Thread.new do
+                pool.with_connection { second_thread_done.wait }
+              end
+
+              # wait for first_thread to get in queue
+              Thread.pass until pool.num_waiting_in_queue == 1
+
+              # create a different, later thread, that will attempt to do a "group action",
+              # but because of the group action semantics it should be able to preempt the
+              # first_thread when a connection is made available
+              second_thread = Thread.new do
+                pool.send(group_action_method)
+                second_thread_done.set
+              end
+
+              # wait for second_thread to get in queue
+              Thread.pass until pool.num_waiting_in_queue == 2
+
+              # return the only available connection
+              pool.checkin(conn)
+
+              # if the second_thread is not able to preempt the first_thread,
+              # they will temporarily (until either of them timeouts with ConnectionTimeoutError)
+              # deadlock and a join(2) timeout will be reached
+              assert second_thread.join(2), "#{group_action_method} is not able to preempt other waiting threads"
+
+            ensure
+              # post test clean up
+              failed = !second_thread_done.set?
+
+              if failed
+                second_thread_done.set
+
+                first_thread.join(2)
+                second_thread.join(2)
+              end
+
+              first_thread.join(10) || raise("first_thread got stuck")
+              second_thread.join(10) || raise("second_thread got stuck")
             end
-
-            first_thread.join
-            second_thread.join
-            #--- post test clean up end
-
-            flunk "#{group_action_method} is not able to preempt other waiting threads" if failed
           end
         end
       end
@@ -496,7 +661,7 @@ module ActiveRecord
           end
 
           stuck_thread = Thread.new do
-            pool.with_connection {}
+            pool.with_connection { }
           end
 
           # wait for stuck_thread to get in queue
@@ -505,21 +670,41 @@ module ActiveRecord
           pool.clear_reloadable_connections
 
           unless stuck_thread.join(2)
-            flunk 'clear_reloadable_connections must not let other connection waiting threads get stuck in queue'
+            flunk "clear_reloadable_connections must not let other connection waiting threads get stuck in queue"
           end
 
           assert_equal 0, pool.num_waiting_in_queue
         end
       end
 
-      private
-      def with_single_connection_pool
-        one_conn_spec = ActiveRecord::Base.connection_pool.spec.dup
-        one_conn_spec.config[:pool] = 1 # this is safe to do, because .dupped ConnectionSpecification also auto-dups its config
-        yield(pool = ConnectionPool.new(one_conn_spec))
-      ensure
-        pool.disconnect! if pool
+      def test_connection_pool_stat
+        with_single_connection_pool do |pool|
+          pool.with_connection do |connection|
+            stats = pool.stat
+            assert_equal({ size: 1, connections: 1, busy: 1, dead: 0, idle: 0, waiting: 0, checkout_timeout: 5 }, stats)
+          end
+
+          stats = pool.stat
+          assert_equal({ size: 1, connections: 1, busy: 0, dead: 0, idle: 1, waiting: 0, checkout_timeout: 5 }, stats)
+
+          Thread.new do
+            pool.checkout
+            Thread.current.kill
+          end.join
+
+          stats = pool.stat
+          assert_equal({ size: 1, connections: 1, busy: 0, dead: 1, idle: 0, waiting: 0, checkout_timeout: 5 }, stats)
+        end
       end
+
+      private
+        def with_single_connection_pool
+          one_conn_spec = ActiveRecord::Base.connection_pool.spec.dup
+          one_conn_spec.config[:pool] = 1 # this is safe to do, because .dupped ConnectionSpecification also auto-dups its config
+          yield(pool = ConnectionPool.new(one_conn_spec))
+        ensure
+          pool.disconnect! if pool
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/connection_specification/resolver_test.rb b/activerecord/test/cases/connection_specification/resolver_test.rb
index 3c2f5d4219..72be14f507 100644
--- a/activerecord/test/cases/connection_specification/resolver_test.rb
+++ b/activerecord/test/cases/connection_specification/resolver_test.rb
@@ -1,64 +1,79 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
   module ConnectionAdapters
     class ConnectionSpecification
       class ResolverTest < ActiveRecord::TestCase
-        def resolve(spec, config={})
-          Resolver.new(config).resolve(spec)
+        def resolve(spec, config = {})
+          configs = ActiveRecord::DatabaseConfigurations.new(config)
+          resolver = ConnectionAdapters::ConnectionSpecification::Resolver.new(configs)
+          resolver.resolve(spec, spec)
         end
 
-        def spec(spec, config={})
-          Resolver.new(config).spec(spec)
+        def spec(spec, config = {})
+          configs = ActiveRecord::DatabaseConfigurations.new(config)
+          resolver = ConnectionAdapters::ConnectionSpecification::Resolver.new(configs)
+          resolver.spec(spec)
         end
 
         def test_url_invalid_adapter
           error = assert_raises(LoadError) do
-            spec 'ridiculous://foo?encoding=utf8'
+            spec "ridiculous://foo?encoding=utf8"
           end
 
-          assert_match "Could not load 'active_record/connection_adapters/ridiculous_adapter'", error.message
+          assert_match "Could not load the 'ridiculous' Active Record adapter. Ensure that the adapter is spelled correctly in config/database.yml and that you've added the necessary adapter gem to your Gemfile.", error.message
         end
 
         # The abstract adapter is used simply to bypass the bit of code that
         # checks that the adapter file can be required in.
 
         def test_url_from_environment
-          spec = resolve :production, 'production' => 'abstract://foo?encoding=utf8'
+          spec = resolve :production, "production" => "abstract://foo?encoding=utf8"
           assert_equal({
             "adapter"  =>  "abstract",
             "host"     =>  "foo",
-            "encoding" => "utf8" }, spec)
+            "encoding" => "utf8",
+            "name"     => "production" }, spec)
         end
 
         def test_url_sub_key
-          spec = resolve :production, 'production' => {"url" => 'abstract://foo?encoding=utf8'}
+          spec = resolve :production, "production" => { "url" => "abstract://foo?encoding=utf8" }
           assert_equal({
             "adapter"  => "abstract",
             "host"     => "foo",
-            "encoding" => "utf8" }, spec)
+            "encoding" => "utf8",
+            "name"     => "production" }, spec)
         end
 
         def test_url_sub_key_merges_correctly
-          hash = {"url" => 'abstract://foo?encoding=utf8&', "adapter" => "sqlite3", "host" => "bar", "pool" => "3"}
-          spec = resolve :production, 'production' => hash
+          hash = { "url" => "abstract://foo?encoding=utf8&", "adapter" => "sqlite3", "host" => "bar", "pool" => "3" }
+          spec = resolve :production, "production" => hash
           assert_equal({
             "adapter"  => "abstract",
             "host"     => "foo",
             "encoding" => "utf8",
-            "pool"     => "3" }, spec)
+            "pool"     => "3",
+            "name"     => "production" }, spec)
         end
 
         def test_url_host_no_db
-          spec = resolve 'abstract://foo?encoding=utf8'
+          spec = resolve "abstract://foo?encoding=utf8"
           assert_equal({
             "adapter"  => "abstract",
             "host"     => "foo",
             "encoding" => "utf8" }, spec)
         end
 
+        def test_url_missing_scheme
+          spec = resolve "foo"
+          assert_equal({
+            "database" => "foo" }, spec)
+        end
+
         def test_url_host_db
-          spec = resolve 'abstract://foo/bar?encoding=utf8'
+          spec = resolve "abstract://foo/bar?encoding=utf8"
           assert_equal({
             "adapter"  => "abstract",
             "database" => "bar",
@@ -67,7 +82,7 @@ module ActiveRecord
         end
 
         def test_url_port
-          spec = resolve 'abstract://foo:123?encoding=utf8'
+          spec = resolve "abstract://foo:123?encoding=utf8"
           assert_equal({
             "adapter"  => "abstract",
             "port"     => 123,
@@ -76,40 +91,50 @@ module ActiveRecord
         end
 
         def test_encoded_password
-          password = 'am@z1ng_p@ssw0rd#!'
+          password = "am@z1ng_p@ssw0rd#!"
           encoded_password = URI.encode_www_form_component(password)
           spec = resolve "abstract://foo:#{encoded_password}@localhost/bar"
           assert_equal password, spec["password"]
         end
 
         def test_url_with_authority_for_sqlite3
-          spec = resolve 'sqlite3:///foo_test'
-          assert_equal('/foo_test', spec["database"])
+          spec = resolve "sqlite3:///foo_test"
+          assert_equal("/foo_test", spec["database"])
         end
 
         def test_url_absolute_path_for_sqlite3
-          spec = resolve 'sqlite3:/foo_test'
-          assert_equal('/foo_test', spec["database"])
+          spec = resolve "sqlite3:/foo_test"
+          assert_equal("/foo_test", spec["database"])
         end
 
         def test_url_relative_path_for_sqlite3
-          spec = resolve 'sqlite3:foo_test'
-          assert_equal('foo_test', spec["database"])
+          spec = resolve "sqlite3:foo_test"
+          assert_equal("foo_test", spec["database"])
         end
 
         def test_url_memory_db_for_sqlite3
-          spec = resolve 'sqlite3::memory:'
-          assert_equal(':memory:', spec["database"])
+          spec = resolve "sqlite3::memory:"
+          assert_equal(":memory:", spec["database"])
         end
 
         def test_url_sub_key_for_sqlite3
-          spec = resolve :production, 'production' => {"url" => 'sqlite3:foo?encoding=utf8'}
+          spec = resolve :production, "production" => { "url" => "sqlite3:foo?encoding=utf8" }
           assert_equal({
             "adapter"  => "sqlite3",
             "database" => "foo",
-            "encoding" => "utf8" }, spec)
+            "encoding" => "utf8",
+            "name"     => "production" }, spec)
         end
 
+        def test_spec_name_on_key_lookup
+          spec = spec(:readonly, "readonly" => { "adapter" => "sqlite3" })
+          assert_equal "readonly", spec.name
+        end
+
+        def test_spec_name_with_inline_config
+          spec = spec("adapter" => "sqlite3")
+          assert_equal "primary", spec.name, "should default to primary id"
+        end
       end
     end
   end
diff --git a/activerecord/test/cases/core_test.rb b/activerecord/test/cases/core_test.rb
index 3cb98832c5..36e3d543cd 100644
--- a/activerecord/test/cases/core_test.rb
+++ b/activerecord/test/cases/core_test.rb
@@ -1,8 +1,9 @@
-require 'cases/helper'
-require 'models/person'
-require 'models/topic'
-require 'pp'
-require 'active_support/core_ext/string/strip'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/person"
+require "models/topic"
+require "pp"
 
 class NonExistentTable < ActiveRecord::Base; end
 
@@ -10,8 +11,8 @@ class CoreTest < ActiveRecord::TestCase
   fixtures :topics
 
   def test_inspect_class
-    assert_equal 'ActiveRecord::Base', ActiveRecord::Base.inspect
-    assert_equal 'LoosePerson(abstract)', LoosePerson.inspect
+    assert_equal "ActiveRecord::Base", ActiveRecord::Base.inspect
+    assert_equal "LoosePerson(abstract)", LoosePerson.inspect
     assert_match(/^Topic\(id: integer, title: string/, Topic.inspect)
   end
 
@@ -25,8 +26,13 @@ class CoreTest < ActiveRecord::TestCase
   end
 
   def test_inspect_limited_select_instance
-    assert_equal %(#<Topic id: 1>), Topic.all.merge!(:select => 'id', :where => 'id = 1').first.inspect
-    assert_equal %(#<Topic id: 1, title: "The First Topic">), Topic.all.merge!(:select => 'id, title', :where => 'id = 1').first.inspect
+    assert_equal %(#<Topic id: 1>), Topic.all.merge!(select: "id", where: "id = 1").first.inspect
+    assert_equal %(#<Topic id: 1, title: "The First Topic">), Topic.all.merge!(select: "id, title", where: "id = 1").first.inspect
+  end
+
+  def test_inspect_instance_with_non_primary_key_id_attribute
+    topic = topics(:first).becomes(TitlePrimaryKeyTopic)
+    assert_match(/id: 1/, topic.inspect)
   end
 
   def test_inspect_class_without_table
@@ -35,68 +41,68 @@ class CoreTest < ActiveRecord::TestCase
 
   def test_pretty_print_new
     topic = Topic.new
-    actual = ''
+    actual = +""
     PP.pp(topic, StringIO.new(actual))
-    expected = <<-PRETTY.strip_heredoc
-    #<Topic:0xXXXXXX
-     id: nil,
-     title: nil,
-     author_name: nil,
-     author_email_address: "test@test.com",
-     written_on: nil,
-     bonus_time: nil,
-     last_read: nil,
-     content: nil,
-     important: nil,
-     approved: true,
-     replies_count: 0,
-     unique_replies_count: 0,
-     parent_id: nil,
-     parent_title: nil,
-     type: nil,
-     group: nil,
-     created_at: nil,
-     updated_at: nil>
+    expected = <<~PRETTY
+      #<Topic:0xXXXXXX
+       id: nil,
+       title: nil,
+       author_name: nil,
+       author_email_address: "test@test.com",
+       written_on: nil,
+       bonus_time: nil,
+       last_read: nil,
+       content: nil,
+       important: nil,
+       approved: true,
+       replies_count: 0,
+       unique_replies_count: 0,
+       parent_id: nil,
+       parent_title: nil,
+       type: nil,
+       group: nil,
+       created_at: nil,
+       updated_at: nil>
     PRETTY
-    assert actual.start_with?(expected.split('XXXXXX').first)
-    assert actual.end_with?(expected.split('XXXXXX').last)
+    assert actual.start_with?(expected.split("XXXXXX").first)
+    assert actual.end_with?(expected.split("XXXXXX").last)
   end
 
   def test_pretty_print_persisted
     topic = topics(:first)
-    actual = ''
+    actual = +""
     PP.pp(topic, StringIO.new(actual))
-    expected = <<-PRETTY.strip_heredoc
-    #<Topic:0x\\w+
-     id: 1,
-     title: "The First Topic",
-     author_name: "David",
-     author_email_address: "david@loudthinking.com",
-     written_on: 2003-07-16 14:28:11 UTC,
-     bonus_time: 2000-01-01 14:28:00 UTC,
-     last_read: Thu, 15 Apr 2004,
-     content: "Have a nice day",
-     important: nil,
-     approved: false,
-     replies_count: 1,
-     unique_replies_count: 0,
-     parent_id: nil,
-     parent_title: nil,
-     type: nil,
-     group: nil,
-     created_at: [^,]+,
-     updated_at: [^,>]+>
+    expected = <<~PRETTY
+      #<Topic:0x\\w+
+       id: 1,
+       title: "The First Topic",
+       author_name: "David",
+       author_email_address: "david@loudthinking.com",
+       written_on: 2003-07-16 14:28:11 UTC,
+       bonus_time: 2000-01-01 14:28:00 UTC,
+       last_read: Thu, 15 Apr 2004,
+       content: "Have a nice day",
+       important: nil,
+       approved: false,
+       replies_count: 1,
+       unique_replies_count: 0,
+       parent_id: nil,
+       parent_title: nil,
+       type: nil,
+       group: nil,
+       created_at: [^,]+,
+       updated_at: [^,>]+>
     PRETTY
     assert_match(/\A#{expected}\z/, actual)
   end
 
   def test_pretty_print_uninitialized
     topic = Topic.allocate
-    actual = ''
+    actual = +""
     PP.pp(topic, StringIO.new(actual))
     expected = "#<Topic:XXXXXX not initialized>\n"
-    assert actual.start_with?(expected.split('XXXXXX').first)
-    assert actual.end_with?(expected.split('XXXXXX').last)
+    assert actual.start_with?(expected.split("XXXXXX").first)
+    assert actual.end_with?(expected.split("XXXXXX").last)
   end
 
   def test_pretty_print_overridden_by_inspect
@@ -105,8 +111,15 @@ class CoreTest < ActiveRecord::TestCase
         "inspecting topic"
       end
     end
-    actual = ''
+    actual = +""
     PP.pp(subtopic.new, StringIO.new(actual))
     assert_equal "inspecting topic\n", actual
   end
+
+  def test_pretty_print_with_non_primary_key_id_attribute
+    topic = topics(:first).becomes(TitlePrimaryKeyTopic)
+    actual = +""
+    PP.pp(topic, StringIO.new(actual))
+    assert_match(/id: 1/, actual)
+  end
 end
diff --git a/activerecord/test/cases/counter_cache_test.rb b/activerecord/test/cases/counter_cache_test.rb
index 1f5055b2a2..99d286dc52 100644
--- a/activerecord/test/cases/counter_cache_test.rb
+++ b/activerecord/test/cases/counter_cache_test.rb
@@ -1,29 +1,32 @@
-require 'cases/helper'
-require 'models/topic'
-require 'models/car'
-require 'models/wheel'
-require 'models/engine'
-require 'models/reply'
-require 'models/category'
-require 'models/categorization'
-require 'models/dog'
-require 'models/dog_lover'
-require 'models/person'
-require 'models/friendship'
-require 'models/subscriber'
-require 'models/subscription'
-require 'models/book'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/topic"
+require "models/car"
+require "models/aircraft"
+require "models/wheel"
+require "models/engine"
+require "models/reply"
+require "models/category"
+require "models/categorization"
+require "models/dog"
+require "models/dog_lover"
+require "models/person"
+require "models/friendship"
+require "models/subscriber"
+require "models/subscription"
+require "models/book"
 
 class CounterCacheTest < ActiveRecord::TestCase
   fixtures :topics, :categories, :categorizations, :cars, :dogs, :dog_lovers, :people, :friendships, :subscribers, :subscriptions, :books
 
   class ::SpecialTopic < ::Topic
-    has_many :special_replies, :foreign_key => 'parent_id'
-    has_many :lightweight_special_replies, -> { select('topics.id, topics.title') }, :foreign_key => 'parent_id', :class_name => 'SpecialReply'
+    has_many :special_replies, foreign_key: "parent_id"
+    has_many :lightweight_special_replies, -> { select("topics.id, topics.title") }, foreign_key: "parent_id", class_name: "SpecialReply"
   end
 
   class ::SpecialReply < ::Reply
-    belongs_to :special_topic, :foreign_key => 'parent_id', :counter_cache => 'replies_count'
+    belongs_to :special_topic, foreign_key: "parent_id", counter_cache: "replies_count"
   end
 
   setup do
@@ -31,13 +34,13 @@ class CounterCacheTest < ActiveRecord::TestCase
   end
 
   test "increment counter" do
-    assert_difference '@topic.reload.replies_count' do
+    assert_difference "@topic.reload.replies_count" do
       Topic.increment_counter(:replies_count, @topic.id)
     end
   end
 
   test "decrement counter" do
-    assert_difference '@topic.reload.replies_count', -1 do
+    assert_difference "@topic.reload.replies_count", -1 do
       Topic.decrement_counter(:replies_count, @topic.id)
     end
   end
@@ -47,7 +50,7 @@ class CounterCacheTest < ActiveRecord::TestCase
     Topic.increment_counter(:replies_count, @topic.id)
 
     # check that it gets reset
-    assert_difference '@topic.reload.replies_count', -1 do
+    assert_difference "@topic.reload.replies_count", -1 do
       Topic.reset_counters(@topic.id, :replies)
     end
   end
@@ -57,31 +60,31 @@ class CounterCacheTest < ActiveRecord::TestCase
     Topic.increment_counter(:replies_count, @topic.id)
 
     # check that it gets reset
-    assert_difference '@topic.reload.replies_count', -1 do
+    assert_difference "@topic.reload.replies_count", -1 do
       Topic.reset_counters(@topic.id, :replies_count)
     end
   end
 
-  test 'reset multiple counters' do
+  test "reset multiple counters" do
     Topic.update_counters @topic.id, replies_count: 1, unique_replies_count: 1
-    assert_difference ['@topic.reload.replies_count', '@topic.reload.unique_replies_count'], -1 do
+    assert_difference ["@topic.reload.replies_count", "@topic.reload.unique_replies_count"], -1 do
       Topic.reset_counters(@topic.id, :replies, :unique_replies)
     end
   end
 
   test "reset counters with string argument" do
-    Topic.increment_counter('replies_count', @topic.id)
+    Topic.increment_counter("replies_count", @topic.id)
 
-    assert_difference '@topic.reload.replies_count', -1 do
-      Topic.reset_counters(@topic.id, 'replies')
+    assert_difference "@topic.reload.replies_count", -1 do
+      Topic.reset_counters(@topic.id, "replies")
     end
   end
 
   test "reset counters with modularized and camelized classnames" do
-    special = SpecialTopic.create!(:title => 'Special')
+    special = SpecialTopic.create!(title: "Special")
     SpecialTopic.increment_counter(:replies_count, special.id)
 
-    assert_difference 'special.reload.replies_count', -1 do
+    assert_difference "special.reload.replies_count", -1 do
       SpecialTopic.reset_counters(special.id, :special_replies)
     end
   end
@@ -102,10 +105,10 @@ class CounterCacheTest < ActiveRecord::TestCase
     DogLover.increment_counter(:bred_dogs_count, david.id)
     DogLover.increment_counter(:trained_dogs_count, david.id)
 
-    assert_difference 'david.reload.bred_dogs_count', -1 do
+    assert_difference "david.reload.bred_dogs_count", -1 do
       DogLover.reset_counters(david.id, :bred_dogs)
     end
-    assert_difference 'david.reload.trained_dogs_count', -1 do
+    assert_difference "david.reload.trained_dogs_count", -1 do
       DogLover.reset_counters(david.id, :trained_dogs)
     end
   end
@@ -115,26 +118,26 @@ class CounterCacheTest < ActiveRecord::TestCase
     assert_equal 2, category.categorizations.count
     assert_nil category.categorizations_count
 
-    Category.update_counters(category.id, :categorizations_count => category.categorizations.count)
+    Category.update_counters(category.id, categorizations_count: category.categorizations.count)
     assert_equal 2, category.reload.categorizations_count
   end
 
   test "update counter for decrement" do
-    assert_difference '@topic.reload.replies_count', -3 do
-      Topic.update_counters(@topic.id, :replies_count => -3)
+    assert_difference "@topic.reload.replies_count", -3 do
+      Topic.update_counters(@topic.id, replies_count: -3)
     end
   end
 
   test "update counters of multiple records" do
     t1, t2 = topics(:first, :second)
 
-    assert_difference ['t1.reload.replies_count', 't2.reload.replies_count'], 2 do
-      Topic.update_counters([t1.id, t2.id], :replies_count => 2)
+    assert_difference ["t1.reload.replies_count", "t2.reload.replies_count"], 2 do
+      Topic.update_counters([t1.id, t2.id], replies_count: 2)
     end
   end
 
-  test 'update multiple counters' do
-    assert_difference ['@topic.reload.replies_count', '@topic.reload.unique_replies_count'], 2 do
+  test "update multiple counters" do
+    assert_difference ["@topic.reload.replies_count", "@topic.reload.unique_replies_count"], 2 do
       Topic.update_counters @topic.id, replies_count: 2, unique_replies_count: 2
     end
   end
@@ -143,25 +146,25 @@ class CounterCacheTest < ActiveRecord::TestCase
     david, joanna = dog_lovers(:david, :joanna)
     joanna = joanna # squelch a warning
 
-    assert_difference 'joanna.reload.dogs_count', -1 do
+    assert_difference "joanna.reload.dogs_count", -1 do
       david.destroy
     end
   end
 
   test "reset the right counter if two have the same foreign key" do
     michael = people(:michael)
-    assert_nothing_raised(ActiveRecord::StatementInvalid) do
+    assert_nothing_raised do
       Person.reset_counters(michael.id, :friends_too)
     end
   end
 
   test "reset counter of has_many :through association" do
-    subscriber = subscribers('second')
-    Subscriber.reset_counters(subscriber.id, 'books')
-    Subscriber.increment_counter('books_count', subscriber.id)
+    subscriber = subscribers("second")
+    Subscriber.reset_counters(subscriber.id, "books")
+    Subscriber.increment_counter("books_count", subscriber.id)
 
-    assert_difference 'subscriber.reload.books_count', -1 do
-      Subscriber.reset_counters(subscriber.id, 'books')
+    assert_difference "subscriber.reload.books_count", -1 do
+      Subscriber.reset_counters(subscriber.id, "books")
     end
   end
 
@@ -173,10 +176,10 @@ class CounterCacheTest < ActiveRecord::TestCase
   end
 
   test "reset counter works with select declared on association" do
-    special = SpecialTopic.create!(:title => 'Special')
+    special = SpecialTopic.create!(title: "Special")
     SpecialTopic.increment_counter(:replies_count, special.id)
 
-    assert_difference 'special.reload.replies_count', -1 do
+    assert_difference "special.reload.replies_count", -1 do
       SpecialTopic.reset_counters(special.id, :lightweight_special_replies)
     end
   end
@@ -198,4 +201,167 @@ class CounterCacheTest < ActiveRecord::TestCase
     assert_equal 2, car.engines_count
     assert_equal 2, car.reload.engines_count
   end
+
+  test "update counters in a polymorphic relationship" do
+    aircraft = Aircraft.create!
+
+    assert_difference "aircraft.reload.wheels_count" do
+      aircraft.wheels << Wheel.create!
+    end
+
+    assert_difference "aircraft.reload.wheels_count", -1 do
+      aircraft.wheels.first.destroy
+    end
+  end
+
+  test "update counters doesn't touch timestamps by default" do
+    @topic.update_column :updated_at, 5.minutes.ago
+    previously_updated_at = @topic.updated_at
+
+    Topic.update_counters(@topic.id, replies_count: -1)
+
+    assert_equal previously_updated_at, @topic.updated_at
+  end
+
+  test "update counters doesn't touch timestamps with touch: []" do
+    @topic.update_column :updated_at, 5.minutes.ago
+    previously_updated_at = @topic.updated_at
+
+    Topic.update_counters(@topic.id, replies_count: -1, touch: [])
+
+    assert_equal previously_updated_at, @topic.updated_at
+  end
+
+  test "update counters with touch: true" do
+    assert_touching @topic, :updated_at do
+      Topic.update_counters(@topic.id, replies_count: -1, touch: true)
+    end
+  end
+
+  test "update counters of multiple records with touch: true" do
+    t1, t2 = topics(:first, :second)
+
+    assert_touching t1, :updated_at do
+      assert_difference ["t1.reload.replies_count", "t2.reload.replies_count"], 2 do
+        Topic.update_counters([t1.id, t2.id], replies_count: 2, touch: true)
+      end
+    end
+  end
+
+  test "update multiple counters with touch: true" do
+    assert_touching @topic, :updated_at do
+      Topic.update_counters(@topic.id, replies_count: 2, unique_replies_count: 2, touch: true)
+    end
+  end
+
+  test "reset counters with touch: true" do
+    assert_touching @topic, :updated_at do
+      Topic.reset_counters(@topic.id, :replies, touch: true)
+    end
+  end
+
+  test "reset multiple counters with touch: true" do
+    assert_touching @topic, :updated_at do
+      Topic.update_counters(@topic.id, replies_count: 1, unique_replies_count: 1)
+      Topic.reset_counters(@topic.id, :replies, :unique_replies, touch: true)
+    end
+  end
+
+  test "increment counters with touch: true" do
+    assert_touching @topic, :updated_at do
+      Topic.increment_counter(:replies_count, @topic.id, touch: true)
+    end
+  end
+
+  test "decrement counters with touch: true" do
+    assert_touching @topic, :updated_at do
+      Topic.decrement_counter(:replies_count, @topic.id, touch: true)
+    end
+  end
+
+  test "update counters with touch: :written_on" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.update_counters(@topic.id, replies_count: -1, touch: :written_on)
+    end
+  end
+
+  test "update multiple counters with touch: :written_on" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.update_counters(@topic.id, replies_count: 2, unique_replies_count: 2, touch: :written_on)
+    end
+  end
+
+  test "reset counters with touch: :written_on" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.reset_counters(@topic.id, :replies, touch: :written_on)
+    end
+  end
+
+  test "reset multiple counters with touch: :written_on" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.update_counters(@topic.id, replies_count: 1, unique_replies_count: 1)
+      Topic.reset_counters(@topic.id, :replies, :unique_replies, touch: :written_on)
+    end
+  end
+
+  test "increment counters with touch: :written_on" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.increment_counter(:replies_count, @topic.id, touch: :written_on)
+    end
+  end
+
+  test "decrement counters with touch: :written_on" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.decrement_counter(:replies_count, @topic.id, touch: :written_on)
+    end
+  end
+
+  test "update counters with touch: %i( updated_at written_on )" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.update_counters(@topic.id, replies_count: -1, touch: %i( updated_at written_on ))
+    end
+  end
+
+  test "update multiple counters with touch: %i( updated_at written_on )" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.update_counters(@topic.id, replies_count: 2, unique_replies_count: 2, touch: %i( updated_at written_on ))
+    end
+  end
+
+  test "reset counters with touch: %i( updated_at written_on )" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.reset_counters(@topic.id, :replies, touch: %i( updated_at written_on ))
+    end
+  end
+
+  test "reset multiple counters with touch: %i( updated_at written_on )" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.update_counters(@topic.id, replies_count: 1, unique_replies_count: 1)
+      Topic.reset_counters(@topic.id, :replies, :unique_replies, touch: %i( updated_at written_on ))
+    end
+  end
+
+  test "increment counters with touch: %i( updated_at written_on )" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.increment_counter(:replies_count, @topic.id, touch: %i( updated_at written_on ))
+    end
+  end
+
+  test "decrement counters with touch: %i( updated_at written_on )" do
+    assert_touching @topic, :updated_at, :written_on do
+      Topic.decrement_counter(:replies_count, @topic.id, touch: %i( updated_at written_on ))
+    end
+  end
+
+  private
+    def assert_touching(record, *attributes)
+      record.update_columns attributes.map { |attr| [ attr, 5.minutes.ago ] }.to_h
+      touch_times = attributes.map { |attr| [ attr, record.public_send(attr) ] }.to_h
+
+      yield
+
+      touch_times.each do |attr, previous_touch_time|
+        assert_operator previous_touch_time, :<, record.reload.public_send(attr)
+      end
+    end
 end
diff --git a/activerecord/test/cases/custom_locking_test.rb b/activerecord/test/cases/custom_locking_test.rb
index e8290297e3..f52b26e9ec 100644
--- a/activerecord/test/cases/custom_locking_test.rb
+++ b/activerecord/test/cases/custom_locking_test.rb
@@ -1,15 +1,17 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/person'
+require "models/person"
 
 module ActiveRecord
   class CustomLockingTest < ActiveRecord::TestCase
     fixtures :people
 
     def test_custom_lock
-      if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-        assert_match 'SHARE MODE', Person.lock('LOCK IN SHARE MODE').to_sql
+      if current_adapter?(:Mysql2Adapter)
+        assert_match "SHARE MODE", Person.lock("LOCK IN SHARE MODE").to_sql
         assert_sql(/LOCK IN SHARE MODE/) do
-          Person.all.merge!(:lock => 'LOCK IN SHARE MODE').find(1)
+          Person.all.merge!(lock: "LOCK IN SHARE MODE").find(1)
         end
       end
     end
diff --git a/activerecord/test/cases/database_statements_test.rb b/activerecord/test/cases/database_statements_test.rb
index c689e97d83..1c934602ec 100644
--- a/activerecord/test/cases/database_statements_test.rb
+++ b/activerecord/test/cases/database_statements_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class DatabaseStatementsTest < ActiveRecord::TestCase
@@ -5,15 +7,31 @@ class DatabaseStatementsTest < ActiveRecord::TestCase
     @connection = ActiveRecord::Base.connection
   end
 
-  def test_insert_should_return_the_inserted_id
-    # Oracle adapter uses prefetched primary key values from sequence and passes them to connection adapter insert method
-    if current_adapter?(:OracleAdapter)
-      sequence_name = "accounts_seq"
-      id_value = @connection.next_sequence_value(sequence_name)
-      id = @connection.insert("INSERT INTO accounts (id, firm_id,credit_limit) VALUES (accounts_seq.nextval,42,5000)", nil, :id, id_value, sequence_name)
-    else
-      id = @connection.insert("INSERT INTO accounts (firm_id,credit_limit) VALUES (42,5000)")
+  unless current_adapter?(:OracleAdapter)
+    def test_exec_insert
+      result = @connection.exec_insert("INSERT INTO accounts (firm_id,credit_limit) VALUES (42,5000)", nil, [])
+      assert_not_nil @connection.send(:last_inserted_id, result)
     end
-    assert_not_nil id
   end
+
+  def test_insert_should_return_the_inserted_id
+    assert_not_nil return_the_inserted_id(method: :insert)
+  end
+
+  def test_create_should_return_the_inserted_id
+    assert_not_nil return_the_inserted_id(method: :create)
+  end
+
+  private
+
+    def return_the_inserted_id(method:)
+      # Oracle adapter uses prefetched primary key values from sequence and passes them to connection adapter insert method
+      if current_adapter?(:OracleAdapter)
+        sequence_name = "accounts_seq"
+        id_value = @connection.next_sequence_value(sequence_name)
+        @connection.send(method, "INSERT INTO accounts (id, firm_id,credit_limit) VALUES (accounts_seq.nextval,42,5000)", nil, :id, id_value, sequence_name)
+      else
+        @connection.send(method, "INSERT INTO accounts (firm_id,credit_limit) VALUES (42,5000)")
+      end
+    end
 end
diff --git a/activerecord/test/cases/invalid_date_test.rb b/activerecord/test/cases/date_test.rb
index 426a350379..9f412cdb63 100644
--- a/activerecord/test/cases/invalid_date_test.rb
+++ b/activerecord/test/cases/date_test.rb
@@ -1,7 +1,21 @@
-require 'cases/helper'
-require 'models/topic'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/topic"
+
+class DateTest < ActiveRecord::TestCase
+  def test_date_with_time_value
+    time_value = Time.new(2016, 05, 11, 19, 0, 0)
+    topic = Topic.create(last_read: time_value)
+    assert_equal topic, Topic.find_by(last_read: time_value)
+  end
+
+  def test_date_with_string_value
+    string_value = "2016-05-11 19:00:00"
+    topic = Topic.create(last_read: string_value)
+    assert_equal topic, Topic.find_by(last_read: string_value)
+  end
 
-class InvalidDateTest < ActiveRecord::TestCase
   def test_assign_valid_dates
     valid_dates = [[2007, 11, 30], [1993, 2, 28], [2008, 2, 29]]
 
@@ -19,7 +33,7 @@ class InvalidDateTest < ActiveRecord::TestCase
 
     invalid_dates.each do |date_src|
       assert_nothing_raised do
-        topic = Topic.new({"last_read(1i)" => date_src[0].to_s, "last_read(2i)" => date_src[1].to_s, "last_read(3i)" => date_src[2].to_s})
+        topic = Topic.new("last_read(1i)" => date_src[0].to_s, "last_read(2i)" => date_src[1].to_s, "last_read(3i)" => date_src[2].to_s)
         # Oracle DATE columns are datetime columns and Oracle adapter returns Time value
         if current_adapter?(:OracleAdapter)
           assert_equal(topic.last_read.to_date, Time.local(*date_src).to_date, "The date should be modified according to the behavior of the Time object")
diff --git a/activerecord/test/cases/date_time_precision_test.rb b/activerecord/test/cases/date_time_precision_test.rb
index 698f1b852e..e64a8372d0 100644
--- a/activerecord/test/cases/date_time_precision_test.rb
+++ b/activerecord/test/cases/date_time_precision_test.rb
@@ -1,111 +1,107 @@
-require 'cases/helper'
-require 'support/schema_dumping_helper'
+# frozen_string_literal: true
 
-if ActiveRecord::Base.connection.supports_datetime_with_precision?
-class DateTimePrecisionTest < ActiveRecord::TestCase
-  include SchemaDumpingHelper
-  self.use_transactional_tests = false
+require "cases/helper"
+require "support/schema_dumping_helper"
 
-  class Foo < ActiveRecord::Base; end
+if subsecond_precision_supported?
+  class DateTimePrecisionTest < ActiveRecord::TestCase
+    include SchemaDumpingHelper
+    self.use_transactional_tests = false
 
-  setup do
-    @connection = ActiveRecord::Base.connection
-  end
+    class Foo < ActiveRecord::Base; end
 
-  teardown do
-    @connection.drop_table :foos, if_exists: true
-  end
+    setup do
+      @connection = ActiveRecord::Base.connection
+      Foo.reset_column_information
+    end
 
-  def test_datetime_data_type_with_precision
-    @connection.create_table(:foos, force: true)
-    @connection.add_column :foos, :created_at, :datetime, precision: 0
-    @connection.add_column :foos, :updated_at, :datetime, precision: 5
-    assert_equal 0, activerecord_column_option('foos', 'created_at', 'precision')
-    assert_equal 5, activerecord_column_option('foos', 'updated_at', 'precision')
-  end
+    teardown do
+      @connection.drop_table :foos, if_exists: true
+    end
 
-  def test_timestamps_helper_with_custom_precision
-    @connection.create_table(:foos, force: true) do |t|
-      t.timestamps precision: 4
+    def test_datetime_data_type_with_precision
+      @connection.create_table(:foos, force: true)
+      @connection.add_column :foos, :created_at, :datetime, precision: 0
+      @connection.add_column :foos, :updated_at, :datetime, precision: 5
+      assert_equal 0, Foo.columns_hash["created_at"].precision
+      assert_equal 5, Foo.columns_hash["updated_at"].precision
     end
-    assert_equal 4, activerecord_column_option('foos', 'created_at', 'precision')
-    assert_equal 4, activerecord_column_option('foos', 'updated_at', 'precision')
-  end
 
-  def test_passing_precision_to_datetime_does_not_set_limit
-    @connection.create_table(:foos, force: true) do |t|
-      t.timestamps precision: 4
+    def test_datetime_precision_is_truncated_on_assignment
+      @connection.create_table(:foos, force: true)
+      @connection.add_column :foos, :created_at,  :datetime, precision: 0
+      @connection.add_column :foos, :updated_at, :datetime, precision: 6
+
+      time = ::Time.now.change(nsec: 123456789)
+      foo = Foo.new(created_at: time, updated_at: time)
+
+      assert_equal 0, foo.created_at.nsec
+      assert_equal 123456000, foo.updated_at.nsec
+
+      foo.save!
+      foo.reload
+
+      assert_equal 0, foo.created_at.nsec
+      assert_equal 123456000, foo.updated_at.nsec
     end
-    assert_nil activerecord_column_option('foos', 'created_at', 'limit')
-    assert_nil activerecord_column_option('foos', 'updated_at', 'limit')
-  end
 
-  def test_invalid_datetime_precision_raises_error
-    assert_raises ActiveRecord::ActiveRecordError do
+    def test_timestamps_helper_with_custom_precision
       @connection.create_table(:foos, force: true) do |t|
-        t.timestamps precision: 7
+        t.timestamps precision: 4
       end
+      assert_equal 4, Foo.columns_hash["created_at"].precision
+      assert_equal 4, Foo.columns_hash["updated_at"].precision
     end
-  end
 
-  def test_database_agrees_with_activerecord_about_precision
-    @connection.create_table(:foos, force: true) do |t|
-      t.timestamps precision: 4
+    def test_passing_precision_to_datetime_does_not_set_limit
+      @connection.create_table(:foos, force: true) do |t|
+        t.timestamps precision: 4
+      end
+      assert_nil Foo.columns_hash["created_at"].limit
+      assert_nil Foo.columns_hash["updated_at"].limit
     end
-    assert_equal 4, database_datetime_precision('foos', 'created_at')
-    assert_equal 4, database_datetime_precision('foos', 'updated_at')
-  end
 
-  def test_formatting_datetime_according_to_precision
-    @connection.create_table(:foos, force: true) do |t|
-      t.datetime :created_at, precision: 0
-      t.datetime :updated_at, precision: 4
+    def test_invalid_datetime_precision_raises_error
+      assert_raises ActiveRecord::ActiveRecordError do
+        @connection.create_table(:foos, force: true) do |t|
+          t.timestamps precision: 7
+        end
+      end
     end
-    date = ::Time.utc(2014, 8, 17, 12, 30, 0, 999999)
-    Foo.create!(created_at: date, updated_at: date)
-    assert foo = Foo.find_by(created_at: date)
-    assert_equal 1, Foo.where(updated_at: date).count
-    assert_equal date.to_s, foo.created_at.to_s
-    assert_equal date.to_s, foo.updated_at.to_s
-    assert_equal 000000, foo.created_at.usec
-    assert_equal 999900, foo.updated_at.usec
-  end
 
-  def test_schema_dump_includes_datetime_precision
-    @connection.create_table(:foos, force: true) do |t|
-      t.timestamps precision: 6
+    def test_formatting_datetime_according_to_precision
+      @connection.create_table(:foos, force: true) do |t|
+        t.datetime :created_at, precision: 0
+        t.datetime :updated_at, precision: 4
+      end
+      date = ::Time.utc(2014, 8, 17, 12, 30, 0, 999999)
+      Foo.create!(created_at: date, updated_at: date)
+      assert foo = Foo.find_by(created_at: date)
+      assert_equal 1, Foo.where(updated_at: date).count
+      assert_equal date.to_s, foo.created_at.to_s
+      assert_equal date.to_s, foo.updated_at.to_s
+      assert_equal 000000, foo.created_at.usec
+      assert_equal 999900, foo.updated_at.usec
     end
-    output = dump_table_schema("foos")
-    assert_match %r{t\.datetime\s+"created_at",\s+precision: 6,\s+null: false$}, output
-    assert_match %r{t\.datetime\s+"updated_at",\s+precision: 6,\s+null: false$}, output
-  end
 
-  if current_adapter?(:PostgreSQLAdapter)
-    def test_datetime_precision_with_zero_should_be_dumped
+    def test_schema_dump_includes_datetime_precision
       @connection.create_table(:foos, force: true) do |t|
-        t.timestamps precision: 0
+        t.timestamps precision: 6
       end
       output = dump_table_schema("foos")
-      assert_match %r{t\.datetime\s+"created_at",\s+precision: 0,\s+null: false$}, output
-      assert_match %r{t\.datetime\s+"updated_at",\s+precision: 0,\s+null: false$}, output
+      assert_match %r{t\.datetime\s+"created_at",\s+precision: 6,\s+null: false$}, output
+      assert_match %r{t\.datetime\s+"updated_at",\s+precision: 6,\s+null: false$}, output
     end
-  end
 
-  private
-
-  def database_datetime_precision(table_name, column_name)
-    results = @connection.exec_query("SELECT column_name, datetime_precision FROM information_schema.columns WHERE table_name = '#{table_name}'")
-    result = results.find do |result_hash|
-      result_hash["column_name"] == column_name
-    end
-    result && result["datetime_precision"].to_i
-  end
-
-  def activerecord_column_option(tablename, column_name, option)
-    result = @connection.columns(tablename).find do |column|
-      column.name == column_name
+    if current_adapter?(:PostgreSQLAdapter, :SQLServerAdapter)
+      def test_datetime_precision_with_zero_should_be_dumped
+        @connection.create_table(:foos, force: true) do |t|
+          t.timestamps precision: 0
+        end
+        output = dump_table_schema("foos")
+        assert_match %r{t\.datetime\s+"created_at",\s+precision: 0,\s+null: false$}, output
+        assert_match %r{t\.datetime\s+"updated_at",\s+precision: 0,\s+null: false$}, output
+      end
     end
-    result && result.send(option)
   end
 end
-end
diff --git a/activerecord/test/cases/date_time_test.rb b/activerecord/test/cases/date_time_test.rb
index 4cbff564aa..b5f35aff0e 100644
--- a/activerecord/test/cases/date_time_test.rb
+++ b/activerecord/test/cases/date_time_test.rb
@@ -1,12 +1,14 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/task'
+require "models/topic"
+require "models/task"
 
 class DateTimeTest < ActiveRecord::TestCase
   include InTimeZone
 
   def test_saves_both_date_and_time
-    with_env_tz 'America/New_York' do
+    with_env_tz "America/New_York" do
       with_timezone_config default: :utc do
         time_values = [1807, 2, 10, 15, 30, 45]
         # create DateTime value with local time zone offset
@@ -25,7 +27,7 @@ class DateTimeTest < ActiveRecord::TestCase
 
   def test_assign_empty_date_time
     task = Task.new
-    task.starting = ''
+    task.starting = ""
     task.ending = nil
     assert_nil task.starting
     assert_nil task.ending
@@ -34,28 +36,41 @@ class DateTimeTest < ActiveRecord::TestCase
   def test_assign_bad_date_time_with_timezone
     in_time_zone "Pacific Time (US & Canada)" do
       task = Task.new
-      task.starting = '2014-07-01T24:59:59GMT'
+      task.starting = "2014-07-01T24:59:59GMT"
       assert_nil task.starting
     end
   end
 
   def test_assign_empty_date
     topic = Topic.new
-    topic.last_read = ''
+    topic.last_read = ""
     assert_nil topic.last_read
   end
 
   def test_assign_empty_time
     topic = Topic.new
-    topic.bonus_time = ''
+    topic.bonus_time = ""
     assert_nil topic.bonus_time
   end
 
   def test_assign_in_local_timezone
-    now = DateTime.now
+    now = DateTime.civil(2017, 3, 1, 12, 0, 0)
     with_timezone_config default: :local do
       task = Task.new starting: now
       assert_equal now, task.starting
     end
   end
+
+  def test_date_time_with_string_value_with_subsecond_precision
+    skip unless subsecond_precision_supported?
+    string_value = "2017-07-04 14:19:00.5"
+    topic = Topic.create(written_on: string_value)
+    assert_equal topic, Topic.find_by(written_on: string_value)
+  end
+
+  def test_date_time_with_string_value_with_non_iso_format
+    string_value = "04/07/2017 2:19pm"
+    topic = Topic.create(written_on: string_value)
+    assert_equal topic, Topic.find_by(written_on: string_value)
+  end
 end
diff --git a/activerecord/test/cases/defaults_test.rb b/activerecord/test/cases/defaults_test.rb
index 67fddebf45..5d02e59ef6 100644
--- a/activerecord/test/cases/defaults_test.rb
+++ b/activerecord/test/cases/defaults_test.rb
@@ -1,20 +1,16 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/default'
-require 'models/entrant'
+require "support/schema_dumping_helper"
+require "models/default"
+require "models/entrant"
 
 class DefaultTest < ActiveRecord::TestCase
   def test_nil_defaults_for_not_null_columns
-    column_defaults =
-      if current_adapter?(:MysqlAdapter) && (Mysql.client_version < 50051 || (50100..50122).include?(Mysql.client_version))
-        { 'id' => nil, 'name' => '',  'course_id' => nil }
-      else
-        { 'id' => nil, 'name' => nil, 'course_id' => nil }
-      end
-
-    column_defaults.each do |name, default|
+    %w(id name course_id).each do |name|
       column = Entrant.columns_hash[name]
-      assert !column.null, "#{name} column should be NOT NULL"
-      assert_equal default, column.default, "#{name} column should be DEFAULT #{default.inspect}"
+      assert_not column.null, "#{name} column should be NOT NULL"
+      assert_not column.default, "#{name} column should be DEFAULT 'nil'"
     end
   end
 
@@ -57,7 +53,7 @@ class DefaultNumbersTest < ActiveRecord::TestCase
 
   def test_default_decimal_number
     record = DefaultNumber.new
-    assert_equal BigDecimal.new("2.78"), record.decimal_number
+    assert_equal BigDecimal("2.78"), record.decimal_number
     assert_equal "2.78", record.decimal_number_before_type_cast
   end
 end
@@ -87,7 +83,64 @@ class DefaultStringsTest < ActiveRecord::TestCase
   end
 end
 
-if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+if current_adapter?(:PostgreSQLAdapter)
+  class PostgresqlDefaultExpressionTest < ActiveRecord::TestCase
+    include SchemaDumpingHelper
+
+    test "schema dump includes default expression" do
+      output = dump_table_schema("defaults")
+      if ActiveRecord::Base.connection.postgresql_version >= 100000
+        assert_match %r/t\.date\s+"modified_date",\s+default: -> { "CURRENT_DATE" }/, output
+        assert_match %r/t\.datetime\s+"modified_time",\s+default: -> { "CURRENT_TIMESTAMP" }/, output
+      else
+        assert_match %r/t\.date\s+"modified_date",\s+default: -> { "\('now'::text\)::date" }/, output
+        assert_match %r/t\.datetime\s+"modified_time",\s+default: -> { "now\(\)" }/, output
+      end
+      assert_match %r/t\.date\s+"modified_date_function",\s+default: -> { "now\(\)" }/, output
+      assert_match %r/t\.datetime\s+"modified_time_function",\s+default: -> { "now\(\)" }/, output
+    end
+  end
+end
+
+if current_adapter?(:Mysql2Adapter)
+  class MysqlDefaultExpressionTest < ActiveRecord::TestCase
+    include SchemaDumpingHelper
+
+    if supports_default_expression?
+      test "schema dump includes default expression" do
+        output = dump_table_schema("defaults")
+        assert_match %r/t\.binary\s+"uuid",\s+limit: 36,\s+default: -> { "\(uuid\(\)\)" }/i, output
+      end
+    end
+
+    if subsecond_precision_supported?
+      test "schema dump datetime includes default expression" do
+        output = dump_table_schema("datetime_defaults")
+        assert_match %r/t\.datetime\s+"modified_datetime",\s+default: -> { "CURRENT_TIMESTAMP(?:\(\))?" }/i, output
+      end
+
+      test "schema dump datetime includes precise default expression" do
+        output = dump_table_schema("datetime_defaults")
+        assert_match %r/t\.datetime\s+"precise_datetime",.+default: -> { "CURRENT_TIMESTAMP\(6\)" }/i, output
+      end
+
+      test "schema dump timestamp includes default expression" do
+        output = dump_table_schema("timestamp_defaults")
+        assert_match %r/t\.timestamp\s+"modified_timestamp",\s+default: -> { "CURRENT_TIMESTAMP(?:\(\))?" }/i, output
+      end
+
+      test "schema dump timestamp includes precise default expression" do
+        output = dump_table_schema("timestamp_defaults")
+        assert_match %r/t\.timestamp\s+"precise_timestamp",.+default: -> { "CURRENT_TIMESTAMP\(6\)" }/i, output
+      end
+
+      test "schema dump timestamp without default expression" do
+        output = dump_table_schema("timestamp_defaults")
+        assert_match %r/t\.timestamp\s+"nullable_timestamp"$/, output
+      end
+    end
+  end
+
   class DefaultsTestWithoutTransactionalFixtures < ActiveRecord::TestCase
     # ActiveRecord::Base#create! (and #save and other related methods) will
     # open a new transaction. When in transactional tests mode, this will
@@ -108,93 +161,66 @@ if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
       ActiveRecord::Base.establish_connection connection
     end
 
-    # MySQL cannot have defaults on text/blob columns. It reports the
-    # default value as null.
-    #
-    # Despite this, in non-strict mode, MySQL will use an empty string
-    # as the default value of the field, if no other value is
-    # specified.
+    # Strict mode controls how MySQL handles invalid or missing values
+    # in data-change statements such as INSERT or UPDATE. A value can be
+    # invalid for several reasons. For example, it might have the wrong
+    # data type for the column, or it might be out of range. A value is
+    # missing when a new row to be inserted does not contain a value for
+    # a non-NULL column that has no explicit DEFAULT clause in its definition.
+    # (For a NULL column, NULL is inserted if the value is missing.)
     #
-    # Therefore, in non-strict mode, we want column.default to report
-    # an empty string as its default, to be consistent with that.
+    # If strict mode is not in effect, MySQL inserts adjusted values for
+    # invalid or missing values and produces warnings. In strict mode,
+    # you can produce this behavior by using INSERT IGNORE or UPDATE IGNORE.
     #
-    # In strict mode, column.default should be nil.
-    def test_mysql_text_not_null_defaults_non_strict
+    # https://dev.mysql.com/doc/refman/5.7/en/sql-mode.html#sql-mode-strict
+    def test_mysql_not_null_defaults_non_strict
       using_strict(false) do
-        with_text_blob_not_null_table do |klass|
+        with_mysql_not_null_table do |klass|
           record = klass.new
-          assert_equal '', record.non_null_blob
-          assert_equal '', record.non_null_text
-
-          assert_nil record.null_blob
-          assert_nil record.null_text
+          assert_nil record.non_null_integer
+          assert_nil record.non_null_string
+          assert_nil record.non_null_text
+          assert_nil record.non_null_blob
 
           record.save!
           record.reload
 
-          assert_equal '', record.non_null_text
-          assert_equal '', record.non_null_blob
-
-          assert_nil record.null_text
-          assert_nil record.null_blob
+          assert_equal 0,  record.non_null_integer
+          assert_equal "", record.non_null_string
+          assert_equal "", record.non_null_text
+          assert_equal "", record.non_null_blob
         end
       end
     end
 
-    def test_mysql_text_not_null_defaults_strict
+    def test_mysql_not_null_defaults_strict
       using_strict(true) do
-        with_text_blob_not_null_table do |klass|
+        with_mysql_not_null_table do |klass|
           record = klass.new
-          assert_nil record.non_null_blob
+          assert_nil record.non_null_integer
+          assert_nil record.non_null_string
           assert_nil record.non_null_text
-          assert_nil record.null_blob
-          assert_nil record.null_text
+          assert_nil record.non_null_blob
 
-          assert_raises(ActiveRecord::StatementInvalid) { klass.create }
+          assert_raises(ActiveRecord::NotNullViolation) { klass.create }
         end
       end
     end
 
-    def with_text_blob_not_null_table
+    def with_mysql_not_null_table
       klass = Class.new(ActiveRecord::Base)
-      klass.table_name = 'test_mysql_text_not_null_defaults'
+      klass.table_name = "test_mysql_not_null_defaults"
       klass.connection.create_table klass.table_name do |t|
-        t.column :non_null_text, :text, :null => false
-        t.column :non_null_blob, :blob, :null => false
-        t.column :null_text, :text, :null => true
-        t.column :null_blob, :blob, :null => true
+        t.integer :non_null_integer, null: false
+        t.string  :non_null_string,  null: false
+        t.text    :non_null_text,    null: false
+        t.blob    :non_null_blob,    null: false
       end
 
       yield klass
     ensure
       klass.connection.drop_table(klass.table_name) rescue nil
     end
-
-    # MySQL uses an implicit default 0 rather than NULL unless in strict mode.
-    # We use an implicit NULL so schema.rb is compatible with other databases.
-    def test_mysql_integer_not_null_defaults
-      klass = Class.new(ActiveRecord::Base)
-      klass.table_name = 'test_integer_not_null_default_zero'
-      klass.connection.create_table klass.table_name do |t|
-        t.column :zero, :integer, :null => false, :default => 0
-        t.column :omit, :integer, :null => false
-      end
-
-      assert_equal '0', klass.columns_hash['zero'].default
-      assert !klass.columns_hash['zero'].null
-      # 0 in MySQL 4, nil in 5.
-      assert [0, nil].include?(klass.columns_hash['omit'].default)
-      assert !klass.columns_hash['omit'].null
-
-      assert_raise(ActiveRecord::StatementInvalid) { klass.create! }
-
-      assert_nothing_raised do
-        instance = klass.create!(:omit => 1)
-        assert_equal 0, instance.zero
-        assert_equal 1, instance.omit
-      end
-    ensure
-      klass.connection.drop_table(klass.table_name) rescue nil
-    end
   end
 end
diff --git a/activerecord/test/cases/dirty_test.rb b/activerecord/test/cases/dirty_test.rb
index f5aaf22e13..dfd74bfcb4 100644
--- a/activerecord/test/cases/dirty_test.rb
+++ b/activerecord/test/cases/dirty_test.rb
@@ -1,122 +1,104 @@
-require 'cases/helper'
-require 'models/topic'    # For booleans
-require 'models/pirate'   # For timestamps
-require 'models/parrot'
-require 'models/person'   # For optimistic locking
-require 'models/aircraft'
+# frozen_string_literal: true
 
-class Pirate # Just reopening it, not defining it
-  attr_accessor :detected_changes_in_after_update # Boolean for if changes are detected
-  attr_accessor :changes_detected_in_after_update # Actual changes
-
-  after_update :check_changes
-
-private
-  # after_save/update and the model itself
-  # can end up checking dirty status and acting on the results
-  def check_changes
-    if self.changed?
-      self.detected_changes_in_after_update = true
-      self.changes_detected_in_after_update = self.changes
-    end
-  end
-end
-
-class NumericData < ActiveRecord::Base
-  self.table_name = 'numeric_data'
-end
+require "cases/helper"
+require "models/topic"    # For booleans
+require "models/pirate"   # For timestamps
+require "models/parrot"
+require "models/person"   # For optimistic locking
+require "models/aircraft"
+require "models/numeric_data"
 
 class DirtyTest < ActiveRecord::TestCase
   include InTimeZone
 
   # Dummy to force column loads so query counts are clean.
   def setup
-    Person.create :first_name => 'foo'
+    Person.create first_name: "foo"
   end
 
   def test_attribute_changes
     # New record - no changes.
     pirate = Pirate.new
-    assert !pirate.catchphrase_changed?
-    assert_nil pirate.catchphrase_change
+    assert_equal false, pirate.catchphrase_changed?
+    assert_equal false, pirate.non_validated_parrot_id_changed?
 
     # Change catchphrase.
-    pirate.catchphrase = 'arrr'
-    assert pirate.catchphrase_changed?
+    pirate.catchphrase = "arrr"
+    assert_predicate pirate, :catchphrase_changed?
     assert_nil pirate.catchphrase_was
-    assert_equal [nil, 'arrr'], pirate.catchphrase_change
+    assert_equal [nil, "arrr"], pirate.catchphrase_change
 
     # Saved - no changes.
     pirate.save!
-    assert !pirate.catchphrase_changed?
+    assert_not_predicate pirate, :catchphrase_changed?
     assert_nil pirate.catchphrase_change
 
     # Same value - no changes.
-    pirate.catchphrase = 'arrr'
-    assert !pirate.catchphrase_changed?
+    pirate.catchphrase = "arrr"
+    assert_not_predicate pirate, :catchphrase_changed?
     assert_nil pirate.catchphrase_change
   end
 
   def test_time_attributes_changes_with_time_zone
-    in_time_zone 'Paris' do
+    in_time_zone "Paris" do
       target = Class.new(ActiveRecord::Base)
-      target.table_name = 'pirates'
+      target.table_name = "pirates"
 
       # New record - no changes.
       pirate = target.new
-      assert !pirate.created_on_changed?
+      assert_not_predicate pirate, :created_on_changed?
       assert_nil pirate.created_on_change
 
       # Saved - no changes.
-      pirate.catchphrase = 'arrrr, time zone!!'
+      pirate.catchphrase = "arrrr, time zone!!"
       pirate.save!
-      assert !pirate.created_on_changed?
+      assert_not_predicate pirate, :created_on_changed?
       assert_nil pirate.created_on_change
 
       # Change created_on.
       old_created_on = pirate.created_on
       pirate.created_on = Time.now - 1.day
-      assert pirate.created_on_changed?
+      assert_predicate pirate, :created_on_changed?
       assert_kind_of ActiveSupport::TimeWithZone, pirate.created_on_was
       assert_equal old_created_on, pirate.created_on_was
       pirate.created_on = old_created_on
-      assert !pirate.created_on_changed?
+      assert_not_predicate pirate, :created_on_changed?
     end
   end
 
   def test_setting_time_attributes_with_time_zone_field_to_itself_should_not_be_marked_as_a_change
-    in_time_zone 'Paris' do
+    in_time_zone "Paris" do
       target = Class.new(ActiveRecord::Base)
-      target.table_name = 'pirates'
+      target.table_name = "pirates"
 
-      pirate = target.create
+      pirate = target.create!
       pirate.created_on = pirate.created_on
-      assert !pirate.created_on_changed?
+      assert_not_predicate pirate, :created_on_changed?
     end
   end
 
   def test_time_attributes_changes_without_time_zone_by_skip
-    in_time_zone 'Paris' do
+    in_time_zone "Paris" do
       target = Class.new(ActiveRecord::Base)
-      target.table_name = 'pirates'
+      target.table_name = "pirates"
 
       target.skip_time_zone_conversion_for_attributes = [:created_on]
 
       # New record - no changes.
       pirate = target.new
-      assert !pirate.created_on_changed?
+      assert_not_predicate pirate, :created_on_changed?
       assert_nil pirate.created_on_change
 
       # Saved - no changes.
-      pirate.catchphrase = 'arrrr, time zone!!'
+      pirate.catchphrase = "arrrr, time zone!!"
       pirate.save!
-      assert !pirate.created_on_changed?
+      assert_not_predicate pirate, :created_on_changed?
       assert_nil pirate.created_on_change
 
       # Change created_on.
       old_created_on = pirate.created_on
       pirate.created_on = Time.now + 1.day
-      assert pirate.created_on_changed?
+      assert_predicate pirate, :created_on_changed?
       # kind_of does not work because
       # ActiveSupport::TimeWithZone.name == 'Time'
       assert_instance_of Time, pirate.created_on_was
@@ -127,23 +109,23 @@ class DirtyTest < ActiveRecord::TestCase
   def test_time_attributes_changes_without_time_zone
     with_timezone_config aware_attributes: false do
       target = Class.new(ActiveRecord::Base)
-      target.table_name = 'pirates'
+      target.table_name = "pirates"
 
       # New record - no changes.
       pirate = target.new
-      assert !pirate.created_on_changed?
+      assert_not_predicate pirate, :created_on_changed?
       assert_nil pirate.created_on_change
 
       # Saved - no changes.
-      pirate.catchphrase = 'arrrr, time zone!!'
+      pirate.catchphrase = "arrrr, time zone!!"
       pirate.save!
-      assert !pirate.created_on_changed?
+      assert_not_predicate pirate, :created_on_changed?
       assert_nil pirate.created_on_change
 
       # Change created_on.
       old_created_on = pirate.created_on
       pirate.created_on = Time.now + 1.day
-      assert pirate.created_on_changed?
+      assert_predicate pirate, :created_on_changed?
       # kind_of does not work because
       # ActiveSupport::TimeWithZone.name == 'Time'
       assert_instance_of Time, pirate.created_on_was
@@ -151,28 +133,27 @@ class DirtyTest < ActiveRecord::TestCase
     end
   end
 
-
   def test_aliased_attribute_changes
     # the actual attribute here is name, title is an
     # alias setup via alias_attribute
     parrot = Parrot.new
-    assert !parrot.title_changed?
+    assert_not_predicate parrot, :title_changed?
     assert_nil parrot.title_change
 
-    parrot.name = 'Sam'
-    assert parrot.title_changed?
+    parrot.name = "Sam"
+    assert_predicate parrot, :title_changed?
     assert_nil parrot.title_was
     assert_equal parrot.name_change, parrot.title_change
   end
 
   def test_restore_attribute!
-    pirate = Pirate.create!(:catchphrase => 'Yar!')
-    pirate.catchphrase = 'Ahoy!'
+    pirate = Pirate.create!(catchphrase: "Yar!")
+    pirate.catchphrase = "Ahoy!"
 
     pirate.restore_catchphrase!
     assert_equal "Yar!", pirate.catchphrase
     assert_equal Hash.new, pirate.changes
-    assert !pirate.catchphrase_changed?
+    assert_not_predicate pirate, :catchphrase_changed?
   end
 
   def test_nullable_number_not_marked_as_changed_if_new_value_is_blank
@@ -180,7 +161,7 @@ class DirtyTest < ActiveRecord::TestCase
 
     ["", nil].each do |value|
       pirate.parrot_id = value
-      assert !pirate.parrot_id_changed?
+      assert_not_predicate pirate, :parrot_id_changed?
       assert_nil pirate.parrot_id_change
     end
   end
@@ -190,7 +171,7 @@ class DirtyTest < ActiveRecord::TestCase
 
     ["", nil].each do |value|
       numeric_data.bank_balance = value
-      assert !numeric_data.bank_balance_changed?
+      assert_not_predicate numeric_data, :bank_balance_changed?
       assert_nil numeric_data.bank_balance_change
     end
   end
@@ -200,15 +181,15 @@ class DirtyTest < ActiveRecord::TestCase
 
     ["", nil].each do |value|
       numeric_data.temperature = value
-      assert !numeric_data.temperature_changed?
+      assert_not_predicate numeric_data, :temperature_changed?
       assert_nil numeric_data.temperature_change
     end
   end
 
   def test_nullable_datetime_not_marked_as_changed_if_new_value_is_blank
-    in_time_zone 'Edinburgh' do
+    in_time_zone "Edinburgh" do
       target = Class.new(ActiveRecord::Base)
-      target.table_name = 'topics'
+      target.table_name = "topics"
 
       topic = target.create
       assert_nil topic.written_on
@@ -216,7 +197,7 @@ class DirtyTest < ActiveRecord::TestCase
       ["", nil].each do |value|
         topic.written_on = value
         assert_nil topic.written_on
-        assert !topic.written_on_changed?
+        assert_not_predicate topic, :written_on_changed?
       end
     end
   end
@@ -224,40 +205,40 @@ class DirtyTest < ActiveRecord::TestCase
   def test_integer_zero_to_string_zero_not_marked_as_changed
     pirate = Pirate.new
     pirate.parrot_id = 0
-    pirate.catchphrase = 'arrr'
+    pirate.catchphrase = "arrr"
     assert pirate.save!
 
-    assert !pirate.changed?
+    assert_not_predicate pirate, :changed?
 
-    pirate.parrot_id = '0'
-    assert !pirate.changed?
+    pirate.parrot_id = "0"
+    assert_not_predicate pirate, :changed?
   end
 
   def test_integer_zero_to_integer_zero_not_marked_as_changed
     pirate = Pirate.new
     pirate.parrot_id = 0
-    pirate.catchphrase = 'arrr'
+    pirate.catchphrase = "arrr"
     assert pirate.save!
 
-    assert !pirate.changed?
+    assert_not_predicate pirate, :changed?
 
     pirate.parrot_id = 0
-    assert !pirate.changed?
+    assert_not_predicate pirate, :changed?
   end
 
   def test_float_zero_to_string_zero_not_marked_as_changed
-    data = NumericData.new :temperature => 0.0
+    data = NumericData.new temperature: 0.0
     data.save!
 
-    assert_not data.changed?
+    assert_not_predicate data, :changed?
 
-    data.temperature = '0'
+    data.temperature = "0"
     assert_empty data.changes
 
-    data.temperature = '0.0'
+    data.temperature = "0.0"
     assert_empty data.changes
 
-    data.temperature = '0.00'
+    data.temperature = "0.00"
     assert_empty data.changes
   end
 
@@ -269,108 +250,115 @@ class DirtyTest < ActiveRecord::TestCase
 
     # check the change from 1 to ''
     pirate = Pirate.find_by_catchphrase("Yarrrr, me hearties")
-    pirate.parrot_id = ''
-    assert pirate.parrot_id_changed?
+    pirate.parrot_id = ""
+    assert_predicate pirate, :parrot_id_changed?
     assert_equal([1, nil], pirate.parrot_id_change)
     pirate.save
 
     # check the change from nil to 0
     pirate = Pirate.find_by_catchphrase("Yarrrr, me hearties")
     pirate.parrot_id = 0
-    assert pirate.parrot_id_changed?
+    assert_predicate pirate, :parrot_id_changed?
     assert_equal([nil, 0], pirate.parrot_id_change)
     pirate.save
 
     # check the change from 0 to ''
     pirate = Pirate.find_by_catchphrase("Yarrrr, me hearties")
-    pirate.parrot_id = ''
-    assert pirate.parrot_id_changed?
+    pirate.parrot_id = ""
+    assert_predicate pirate, :parrot_id_changed?
     assert_equal([0, nil], pirate.parrot_id_change)
   end
 
   def test_object_should_be_changed_if_any_attribute_is_changed
     pirate = Pirate.new
-    assert !pirate.changed?
+    assert_not_predicate pirate, :changed?
     assert_equal [], pirate.changed
     assert_equal Hash.new, pirate.changes
 
-    pirate.catchphrase = 'arrr'
-    assert pirate.changed?
+    pirate.catchphrase = "arrr"
+    assert_predicate pirate, :changed?
     assert_nil pirate.catchphrase_was
     assert_equal %w(catchphrase), pirate.changed
-    assert_equal({'catchphrase' => [nil, 'arrr']}, pirate.changes)
+    assert_equal({ "catchphrase" => [nil, "arrr"] }, pirate.changes)
 
     pirate.save
-    assert !pirate.changed?
+    assert_not_predicate pirate, :changed?
     assert_equal [], pirate.changed
     assert_equal Hash.new, pirate.changes
   end
 
   def test_attribute_will_change!
-    pirate = Pirate.create!(:catchphrase => 'arr')
+    pirate = Pirate.create!(catchphrase: "arr")
 
-    assert !pirate.catchphrase_changed?
+    assert_not_predicate pirate, :catchphrase_changed?
     assert pirate.catchphrase_will_change!
-    assert pirate.catchphrase_changed?
-    assert_equal ['arr', 'arr'], pirate.catchphrase_change
+    assert_predicate pirate, :catchphrase_changed?
+    assert_equal ["arr", "arr"], pirate.catchphrase_change
 
-    pirate.catchphrase << ' matey!'
-    assert pirate.catchphrase_changed?
-    assert_equal ['arr', 'arr matey!'], pirate.catchphrase_change
+    pirate.catchphrase << " matey!"
+    assert_predicate pirate, :catchphrase_changed?
+    assert_equal ["arr", "arr matey!"], pirate.catchphrase_change
+  end
+
+  def test_virtual_attribute_will_change
+    parrot = Parrot.create!(name: "Ruby")
+    parrot.send(:attribute_will_change!, :cancel_save_from_callback)
+    assert_predicate parrot, :has_changes_to_save?
   end
 
   def test_association_assignment_changes_foreign_key
-    pirate = Pirate.create!(:catchphrase => 'jarl')
-    pirate.parrot = Parrot.create!(:name => 'Lorre')
-    assert pirate.changed?
+    pirate = Pirate.create!(catchphrase: "jarl")
+    pirate.parrot = Parrot.create!(name: "Lorre")
+    assert_predicate pirate, :changed?
     assert_equal %w(parrot_id), pirate.changed
   end
 
   def test_attribute_should_be_compared_with_type_cast
     topic = Topic.new
-    assert topic.approved?
-    assert !topic.approved_changed?
+    assert_predicate topic, :approved?
+    assert_not_predicate topic, :approved_changed?
 
     # Coming from web form.
-    params = {:topic => {:approved => 1}}
+    params = { topic: { approved: 1 } }
     # In the controller.
     topic.attributes = params[:topic]
-    assert topic.approved?
-    assert !topic.approved_changed?
+    assert_predicate topic, :approved?
+    assert_not_predicate topic, :approved_changed?
   end
 
   def test_partial_update
-    pirate = Pirate.new(:catchphrase => 'foo')
+    pirate = Pirate.new(catchphrase: "foo")
     old_updated_on = 1.hour.ago.beginning_of_day
 
     with_partial_writes Pirate, false do
       assert_queries(2) { 2.times { pirate.save! } }
-      Pirate.where(id: pirate.id).update_all(:updated_on => old_updated_on)
+      Pirate.where(id: pirate.id).update_all(updated_on: old_updated_on)
     end
 
     with_partial_writes Pirate, true do
-      assert_queries(0) { 2.times { pirate.save! } }
+      assert_no_queries { 2.times { pirate.save! } }
       assert_equal old_updated_on, pirate.reload.updated_on
 
-      assert_queries(1) { pirate.catchphrase = 'bar'; pirate.save! }
+      assert_queries(1) { pirate.catchphrase = "bar"; pirate.save! }
       assert_not_equal old_updated_on, pirate.reload.updated_on
     end
   end
 
   def test_partial_update_with_optimistic_locking
-    person = Person.new(:first_name => 'foo')
-    old_lock_version = 1
+    person = Person.new(first_name: "foo")
 
     with_partial_writes Person, false do
       assert_queries(2) { 2.times { person.save! } }
-      Person.where(id: person.id).update_all(:first_name => 'baz')
+      Person.where(id: person.id).update_all(first_name: "baz")
     end
 
+    old_lock_version = person.lock_version
+
     with_partial_writes Person, true do
-      assert_queries(0) { 2.times { person.save! } }
+      assert_no_queries { 2.times { person.save! } }
       assert_equal old_lock_version, person.reload.lock_version
 
-      assert_queries(1) { person.first_name = 'bar'; person.save! }
+      assert_queries(1) { person.first_name = "bar"; person.save! }
       assert_not_equal old_lock_version, person.reload.lock_version
     end
   end
@@ -378,7 +366,7 @@ class DirtyTest < ActiveRecord::TestCase
   def test_changed_attributes_should_be_preserved_if_save_failure
     pirate = Pirate.new
     pirate.parrot_id = 1
-    assert !pirate.save
+    assert_not pirate.save
     check_pirate_after_save_failure(pirate)
 
     pirate = Pirate.new
@@ -388,71 +376,70 @@ class DirtyTest < ActiveRecord::TestCase
   end
 
   def test_reload_should_clear_changed_attributes
-    pirate = Pirate.create!(:catchphrase => "shiver me timbers")
+    pirate = Pirate.create!(catchphrase: "shiver me timbers")
     pirate.catchphrase = "*hic*"
-    assert pirate.changed?
+    assert_predicate pirate, :changed?
     pirate.reload
-    assert !pirate.changed?
+    assert_not_predicate pirate, :changed?
   end
 
   def test_dup_objects_should_not_copy_dirty_flag_from_creator
-    pirate = Pirate.create!(:catchphrase => "shiver me timbers")
+    pirate = Pirate.create!(catchphrase: "shiver me timbers")
     pirate_dup = pirate.dup
     pirate_dup.restore_catchphrase!
     pirate.catchphrase = "I love Rum"
-    assert pirate.catchphrase_changed?
-    assert !pirate_dup.catchphrase_changed?
+    assert_predicate pirate, :catchphrase_changed?
+    assert_not_predicate pirate_dup, :catchphrase_changed?
   end
 
   def test_reverted_changes_are_not_dirty
     phrase = "shiver me timbers"
-    pirate = Pirate.create!(:catchphrase => phrase)
+    pirate = Pirate.create!(catchphrase: phrase)
     pirate.catchphrase = "*hic*"
-    assert pirate.changed?
+    assert_predicate pirate, :changed?
     pirate.catchphrase = phrase
-    assert !pirate.changed?
+    assert_not_predicate pirate, :changed?
   end
 
   def test_reverted_changes_are_not_dirty_after_multiple_changes
     phrase = "shiver me timbers"
-    pirate = Pirate.create!(:catchphrase => phrase)
+    pirate = Pirate.create!(catchphrase: phrase)
     10.times do |i|
       pirate.catchphrase = "*hic*" * i
-      assert pirate.changed?
+      assert_predicate pirate, :changed?
     end
-    assert pirate.changed?
+    assert_predicate pirate, :changed?
     pirate.catchphrase = phrase
-    assert !pirate.changed?
+    assert_not_predicate pirate, :changed?
   end
 
-
   def test_reverted_changes_are_not_dirty_going_from_nil_to_value_and_back
-    pirate = Pirate.create!(:catchphrase => "Yar!")
+    pirate = Pirate.create!(catchphrase: "Yar!")
 
     pirate.parrot_id = 1
-    assert pirate.changed?
-    assert pirate.parrot_id_changed?
-    assert !pirate.catchphrase_changed?
+    assert_predicate pirate, :changed?
+    assert_predicate pirate, :parrot_id_changed?
+    assert_not_predicate pirate, :catchphrase_changed?
 
     pirate.parrot_id = nil
-    assert !pirate.changed?
-    assert !pirate.parrot_id_changed?
-    assert !pirate.catchphrase_changed?
+    assert_not_predicate pirate, :changed?
+    assert_not_predicate pirate, :parrot_id_changed?
+    assert_not_predicate pirate, :catchphrase_changed?
   end
 
   def test_save_should_store_serialized_attributes_even_with_partial_writes
     with_partial_writes(Topic) do
-      topic = Topic.create!(:content => {:a => "a"})
+      topic = Topic.create!(content: { a: "a" })
 
-      assert_not topic.changed?
+      assert_not_predicate topic, :changed?
 
       topic.content[:b] = "b"
 
-      assert topic.changed?
+      assert_predicate topic, :changed?
 
       topic.save!
 
-      assert_not topic.changed?
+      assert_not_predicate topic, :changed?
       assert_equal "b", topic.content[:b]
 
       topic.reload
@@ -463,28 +450,37 @@ class DirtyTest < ActiveRecord::TestCase
 
   def test_save_always_should_update_timestamps_when_serialized_attributes_are_present
     with_partial_writes(Topic) do
-      topic = Topic.create!(:content => {:a => "a"})
+      topic = Topic.create!(content: { a: "a" })
       topic.save!
 
       updated_at = topic.updated_at
-      topic.content[:hello] = 'world'
-      topic.save!
+      travel(1.second) do
+        topic.content[:hello] = "world"
+        topic.save!
+      end
 
       assert_not_equal updated_at, topic.updated_at
-      assert_equal 'world', topic.content[:hello]
+      assert_equal "world", topic.content[:hello]
     end
   end
 
   def test_save_should_not_save_serialized_attribute_with_partial_writes_if_not_present
     with_partial_writes(Topic) do
-      Topic.create!(:author_name => 'Bill', :content => {:a => "a"})
-      topic = Topic.select('id, author_name').first
-      topic.update_columns author_name: 'John'
-      topic = Topic.first
-      assert_not_nil topic.content
+      topic = Topic.create!(author_name: "Bill", content: { a: "a" })
+      topic = Topic.select("id, author_name").find(topic.id)
+      topic.update_columns author_name: "John"
+      assert_not_nil topic.reload.content
     end
   end
 
+  def test_changes_to_save_should_not_mutate_array_of_hashes
+    topic = Topic.new(author_name: "Bill", content: [{ a: "a" }])
+
+    topic.changes_to_save
+
+    assert_equal [{ a: "a" }], topic.content
+  end
+
   def test_previous_changes
     # original values should be in previous_changes
     pirate = Pirate.new
@@ -494,13 +490,13 @@ class DirtyTest < ActiveRecord::TestCase
     pirate.save!
 
     assert_equal 4, pirate.previous_changes.size
-    assert_equal [nil, "arrr"], pirate.previous_changes['catchphrase']
-    assert_equal [nil, pirate.id], pirate.previous_changes['id']
-    assert_nil pirate.previous_changes['updated_on'][0]
-    assert_not_nil pirate.previous_changes['updated_on'][1]
-    assert_nil pirate.previous_changes['created_on'][0]
-    assert_not_nil pirate.previous_changes['created_on'][1]
-    assert !pirate.previous_changes.key?('parrot_id')
+    assert_equal [nil, "arrr"], pirate.previous_changes["catchphrase"]
+    assert_equal [nil, pirate.id], pirate.previous_changes["id"]
+    assert_nil pirate.previous_changes["updated_on"][0]
+    assert_not_nil pirate.previous_changes["updated_on"][1]
+    assert_nil pirate.previous_changes["created_on"][0]
+    assert_not_nil pirate.previous_changes["created_on"][1]
+    assert_not pirate.previous_changes.key?("parrot_id")
 
     # original values should be in previous_changes
     pirate = Pirate.new
@@ -510,106 +506,116 @@ class DirtyTest < ActiveRecord::TestCase
     pirate.save
 
     assert_equal 4, pirate.previous_changes.size
-    assert_equal [nil, "arrr"], pirate.previous_changes['catchphrase']
-    assert_equal [nil, pirate.id], pirate.previous_changes['id']
-    assert pirate.previous_changes.include?('updated_on')
-    assert pirate.previous_changes.include?('created_on')
-    assert !pirate.previous_changes.key?('parrot_id')
+    assert_equal [nil, "arrr"], pirate.previous_changes["catchphrase"]
+    assert_equal [nil, pirate.id], pirate.previous_changes["id"]
+    assert_includes pirate.previous_changes, "updated_on"
+    assert_includes pirate.previous_changes, "created_on"
+    assert_not pirate.previous_changes.key?("parrot_id")
 
     pirate.catchphrase = "Yar!!"
     pirate.reload
     assert_equal Hash.new, pirate.previous_changes
 
     pirate = Pirate.find_by_catchphrase("arrr")
+
+    travel(1.second)
+
     pirate.catchphrase = "Me Maties!"
     pirate.save!
 
     assert_equal 2, pirate.previous_changes.size
-    assert_equal ["arrr", "Me Maties!"], pirate.previous_changes['catchphrase']
-    assert_not_nil pirate.previous_changes['updated_on'][0]
-    assert_not_nil pirate.previous_changes['updated_on'][1]
-    assert !pirate.previous_changes.key?('parrot_id')
-    assert !pirate.previous_changes.key?('created_on')
+    assert_equal ["arrr", "Me Maties!"], pirate.previous_changes["catchphrase"]
+    assert_not_nil pirate.previous_changes["updated_on"][0]
+    assert_not_nil pirate.previous_changes["updated_on"][1]
+    assert_not pirate.previous_changes.key?("parrot_id")
+    assert_not pirate.previous_changes.key?("created_on")
 
     pirate = Pirate.find_by_catchphrase("Me Maties!")
+
+    travel(1.second)
+
     pirate.catchphrase = "Thar She Blows!"
     pirate.save
 
     assert_equal 2, pirate.previous_changes.size
-    assert_equal ["Me Maties!", "Thar She Blows!"], pirate.previous_changes['catchphrase']
-    assert_not_nil pirate.previous_changes['updated_on'][0]
-    assert_not_nil pirate.previous_changes['updated_on'][1]
-    assert !pirate.previous_changes.key?('parrot_id')
-    assert !pirate.previous_changes.key?('created_on')
+    assert_equal ["Me Maties!", "Thar She Blows!"], pirate.previous_changes["catchphrase"]
+    assert_not_nil pirate.previous_changes["updated_on"][0]
+    assert_not_nil pirate.previous_changes["updated_on"][1]
+    assert_not pirate.previous_changes.key?("parrot_id")
+    assert_not pirate.previous_changes.key?("created_on")
+
+    travel(1.second)
 
     pirate = Pirate.find_by_catchphrase("Thar She Blows!")
     pirate.update(catchphrase: "Ahoy!")
 
     assert_equal 2, pirate.previous_changes.size
-    assert_equal ["Thar She Blows!", "Ahoy!"], pirate.previous_changes['catchphrase']
-    assert_not_nil pirate.previous_changes['updated_on'][0]
-    assert_not_nil pirate.previous_changes['updated_on'][1]
-    assert !pirate.previous_changes.key?('parrot_id')
-    assert !pirate.previous_changes.key?('created_on')
+    assert_equal ["Thar She Blows!", "Ahoy!"], pirate.previous_changes["catchphrase"]
+    assert_not_nil pirate.previous_changes["updated_on"][0]
+    assert_not_nil pirate.previous_changes["updated_on"][1]
+    assert_not pirate.previous_changes.key?("parrot_id")
+    assert_not pirate.previous_changes.key?("created_on")
+
+    travel(1.second)
 
     pirate = Pirate.find_by_catchphrase("Ahoy!")
     pirate.update_attribute(:catchphrase, "Ninjas suck!")
 
     assert_equal 2, pirate.previous_changes.size
-    assert_equal ["Ahoy!", "Ninjas suck!"], pirate.previous_changes['catchphrase']
-    assert_not_nil pirate.previous_changes['updated_on'][0]
-    assert_not_nil pirate.previous_changes['updated_on'][1]
-    assert !pirate.previous_changes.key?('parrot_id')
-    assert !pirate.previous_changes.key?('created_on')
-  end
-
-  if ActiveRecord::Base.connection.supports_migrations?
-    class Testings < ActiveRecord::Base; end
-    def test_field_named_field
-      ActiveRecord::Base.connection.create_table :testings do |t|
-        t.string :field
-      end
-      assert_nothing_raised do
-        Testings.new.attributes
-      end
-    ensure
-      ActiveRecord::Base.connection.drop_table :testings rescue nil
+    assert_equal ["Ahoy!", "Ninjas suck!"], pirate.previous_changes["catchphrase"]
+    assert_not_nil pirate.previous_changes["updated_on"][0]
+    assert_not_nil pirate.previous_changes["updated_on"][1]
+    assert_not pirate.previous_changes.key?("parrot_id")
+    assert_not pirate.previous_changes.key?("created_on")
+  end
+
+  class Testings < ActiveRecord::Base; end
+  def test_field_named_field
+    ActiveRecord::Base.connection.create_table :testings do |t|
+      t.string :field
     end
+    assert_nothing_raised do
+      Testings.new.attributes
+    end
+  ensure
+    ActiveRecord::Base.connection.drop_table :testings rescue nil
+    ActiveRecord::Base.clear_cache!
   end
 
   def test_datetime_attribute_can_be_updated_with_fractional_seconds
-    in_time_zone 'Paris' do
+    skip "Fractional seconds are not supported" unless subsecond_precision_supported?
+    in_time_zone "Paris" do
       target = Class.new(ActiveRecord::Base)
-      target.table_name = 'topics'
+      target.table_name = "topics"
 
-      written_on = Time.utc(2012, 12, 1, 12, 0, 0).in_time_zone('Paris')
+      written_on = Time.utc(2012, 12, 1, 12, 0, 0).in_time_zone("Paris")
 
-      topic = target.create(:written_on => written_on)
+      topic = target.create(written_on: written_on)
       topic.written_on += 0.3
 
-      assert topic.written_on_changed?, 'Fractional second update not detected'
+      assert topic.written_on_changed?, "Fractional second update not detected"
     end
   end
 
   def test_datetime_attribute_doesnt_change_if_zone_is_modified_in_string
-    time_in_paris = Time.utc(2014, 1, 1, 12, 0, 0).in_time_zone('Paris')
-    pirate = Pirate.create!(:catchphrase => 'rrrr', :created_on => time_in_paris)
+    time_in_paris = Time.utc(2014, 1, 1, 12, 0, 0).in_time_zone("Paris")
+    pirate = Pirate.create!(catchphrase: "rrrr", created_on: time_in_paris)
 
-    pirate.created_on = pirate.created_on.in_time_zone('Tokyo').to_s
-    assert !pirate.created_on_changed?
+    pirate.created_on = pirate.created_on.in_time_zone("Tokyo").to_s
+    assert_not_predicate pirate, :created_on_changed?
   end
 
   test "partial insert" do
     with_partial_writes Person do
       jon = nil
       assert_sql(/first_name/i) do
-        jon = Person.create! first_name: 'Jon'
+        jon = Person.create! first_name: "Jon"
       end
 
-      assert ActiveRecord::SQLCounter.log_all.none? { |sql| sql =~ /followers_count/ }
+      assert ActiveRecord::SQLCounter.log_all.none? { |sql| sql.include?("followers_count") }
 
       jon.reload
-      assert_equal 'Jon', jon.first_name
+      assert_equal "Jon", jon.first_name
       assert_equal 0, jon.followers_count
       assert_not_nil jon.id
     end
@@ -627,7 +633,7 @@ class DirtyTest < ActiveRecord::TestCase
     pirate = Pirate.create!(catchphrase: "arrrr")
     pirate.catchphrase << " matey!"
 
-    assert pirate.catchphrase_changed?
+    assert_predicate pirate, :catchphrase_changed?
     expected_changes = {
       "catchphrase" => ["arrrr", "arrrr matey!"]
     }
@@ -635,13 +641,13 @@ class DirtyTest < ActiveRecord::TestCase
     assert_equal("arrrr", pirate.catchphrase_was)
     assert pirate.catchphrase_changed?(from: "arrrr")
     assert_not pirate.catchphrase_changed?(from: "anything else")
-    assert pirate.changed_attributes.include?(:catchphrase)
+    assert_includes pirate.changed_attributes, :catchphrase
 
     pirate.save!
     pirate.reload
 
     assert_equal "arrrr matey!", pirate.catchphrase
-    assert_not pirate.changed?
+    assert_not_predicate pirate, :changed?
   end
 
   test "in place mutation for binary" do
@@ -652,19 +658,60 @@ class DirtyTest < ActiveRecord::TestCase
 
     binary = klass.create!(data: "\\\\foo")
 
-    assert_not binary.changed?
+    assert_not_predicate binary, :changed?
 
     binary.data = binary.data.dup
 
-    assert_not binary.changed?
+    assert_not_predicate binary, :changed?
 
     binary = klass.last
 
-    assert_not binary.changed?
+    assert_not_predicate binary, :changed?
 
     binary.data << "bar"
 
-    assert binary.changed?
+    assert_predicate binary, :changed?
+  end
+
+  test "changes is correct for subclass" do
+    foo = Class.new(Pirate) do
+      def catchphrase
+        super.upcase
+      end
+    end
+
+    pirate = foo.create!(catchphrase: "arrrr")
+
+    new_catchphrase = "arrrr matey!"
+
+    pirate.catchphrase = new_catchphrase
+    assert_predicate pirate, :catchphrase_changed?
+
+    expected_changes = {
+      "catchphrase" => ["arrrr", new_catchphrase]
+    }
+
+    assert_equal new_catchphrase.upcase, pirate.catchphrase
+    assert_equal expected_changes, pirate.changes
+  end
+
+  test "changes is correct if override attribute reader" do
+    pirate = Pirate.create!(catchphrase: "arrrr")
+    def pirate.catchphrase
+      super.upcase
+    end
+
+    new_catchphrase = "arrrr matey!"
+
+    pirate.catchphrase = new_catchphrase
+    assert_predicate pirate, :catchphrase_changed?
+
+    expected_changes = {
+      "catchphrase" => ["arrrr", new_catchphrase]
+    }
+
+    assert_equal new_catchphrase.upcase, pirate.catchphrase
+    assert_equal expected_changes, pirate.changes
   end
 
   test "attribute_changed? doesn't compute in-place changes for unrelated attributes" do
@@ -674,27 +721,45 @@ class DirtyTest < ActiveRecord::TestCase
       end
     end
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'people'
+      self.table_name = "people"
       attribute :foo, test_type_class.new
     end
 
     model = klass.new(first_name: "Jim")
-    assert model.first_name_changed?
+    assert_predicate model, :first_name_changed?
   end
 
   test "attribute_will_change! doesn't try to save non-persistable attributes" do
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'people'
+      self.table_name = "people"
       attribute :non_persisted_attribute, :string
     end
 
     record = klass.new(first_name: "Sean")
     record.non_persisted_attribute_will_change!
 
-    assert record.non_persisted_attribute_changed?
+    assert_predicate record, :non_persisted_attribute_changed?
     assert record.save
   end
 
+  test "virtual attributes are not written with partial_writes off" do
+    with_partial_writes(ActiveRecord::Base, false) do
+      klass = Class.new(ActiveRecord::Base) do
+        self.table_name = "people"
+        attribute :non_persisted_attribute, :string
+      end
+
+      record = klass.new(first_name: "Sean")
+      record.non_persisted_attribute_will_change!
+
+      assert record.save
+
+      record.non_persisted_attribute_will_change!
+
+      assert record.save
+    end
+  end
+
   test "mutating and then assigning doesn't remove the change" do
     pirate = Pirate.create!(catchphrase: "arrrr")
     pirate.catchphrase << " matey!"
@@ -719,6 +784,126 @@ class DirtyTest < ActiveRecord::TestCase
     assert_equal "arr", pirate.catchphrase
   end
 
+  test "attributes assigned but not selected are dirty" do
+    person = Person.select(:id).first
+    assert_not_predicate person, :changed?
+
+    person.first_name = "Sean"
+    assert_predicate person, :changed?
+
+    person.first_name = nil
+    assert_predicate person, :changed?
+  end
+
+  test "attributes not selected are still missing after save" do
+    person = Person.select(:id).first
+    assert_raises(ActiveModel::MissingAttributeError) { person.first_name }
+    assert person.save # calls forget_attribute_assignments
+    assert_raises(ActiveModel::MissingAttributeError) { person.first_name }
+  end
+
+  test "saved_change_to_attribute? returns whether a change occurred in the last save" do
+    person = Person.create!(first_name: "Sean")
+
+    assert_predicate person, :saved_change_to_first_name?
+    assert_not_predicate person, :saved_change_to_gender?
+    assert person.saved_change_to_first_name?(from: nil, to: "Sean")
+    assert person.saved_change_to_first_name?(from: nil)
+    assert person.saved_change_to_first_name?(to: "Sean")
+    assert_not person.saved_change_to_first_name?(from: "Jim", to: "Sean")
+    assert_not person.saved_change_to_first_name?(from: "Jim")
+    assert_not person.saved_change_to_first_name?(to: "Jim")
+  end
+
+  test "saved_change_to_attribute returns the change that occurred in the last save" do
+    person = Person.create!(first_name: "Sean", gender: "M")
+
+    assert_equal [nil, "Sean"], person.saved_change_to_first_name
+    assert_equal [nil, "M"], person.saved_change_to_gender
+
+    person.update(first_name: "Jim")
+
+    assert_equal ["Sean", "Jim"], person.saved_change_to_first_name
+    assert_nil person.saved_change_to_gender
+  end
+
+  test "attribute_before_last_save returns the original value before saving" do
+    person = Person.create!(first_name: "Sean", gender: "M")
+
+    assert_nil person.first_name_before_last_save
+    assert_nil person.gender_before_last_save
+
+    person.first_name = "Jim"
+
+    assert_nil person.first_name_before_last_save
+    assert_nil person.gender_before_last_save
+
+    person.save
+
+    assert_equal "Sean", person.first_name_before_last_save
+    assert_equal "M", person.gender_before_last_save
+  end
+
+  test "saved_changes? returns whether the last call to save changed anything" do
+    person = Person.create!(first_name: "Sean")
+
+    assert_predicate person, :saved_changes?
+
+    person.save
+
+    assert_not_predicate person, :saved_changes?
+  end
+
+  test "saved_changes returns a hash of all the changes that occurred" do
+    person = Person.create!(first_name: "Sean", gender: "M")
+
+    assert_equal [nil, "Sean"], person.saved_changes[:first_name]
+    assert_equal [nil, "M"], person.saved_changes[:gender]
+    assert_equal %w(id first_name gender created_at updated_at).sort, person.saved_changes.keys.sort
+
+    travel(1.second) do
+      person.update(first_name: "Jim")
+    end
+
+    assert_equal ["Sean", "Jim"], person.saved_changes[:first_name]
+    assert_equal %w(first_name lock_version updated_at).sort, person.saved_changes.keys.sort
+  end
+
+  test "changed? in after callbacks returns false" do
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = "people"
+
+      after_save do
+        raise "changed? should be false" if changed?
+        raise "has_changes_to_save? should be false" if has_changes_to_save?
+        raise "saved_changes? should be true" unless saved_changes?
+        raise "id_in_database should not be nil" if id_in_database.nil?
+      end
+    end
+
+    person = klass.create!(first_name: "Sean")
+    assert_not_predicate person, :changed?
+  end
+
+  test "changed? in around callbacks after yield returns false" do
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = "people"
+
+      around_create :check_around
+
+      def check_around
+        yield
+        raise "changed? should be false" if changed?
+        raise "has_changes_to_save? should be false" if has_changes_to_save?
+        raise "saved_changes? should be true" unless saved_changes?
+        raise "id_in_database should not be nil" if id_in_database.nil?
+      end
+    end
+
+    person = klass.create!(first_name: "Sean")
+    assert_not_predicate person, :changed?
+  end
+
   private
     def with_partial_writes(klass, on = true)
       old = klass.partial_writes?
@@ -729,8 +914,8 @@ class DirtyTest < ActiveRecord::TestCase
     end
 
     def check_pirate_after_save_failure(pirate)
-      assert pirate.changed?
-      assert pirate.parrot_id_changed?
+      assert_predicate pirate, :changed?
+      assert_predicate pirate, :parrot_id_changed?
       assert_equal %w(parrot_id), pirate.changed
       assert_nil pirate.parrot_id_was
     end
diff --git a/activerecord/test/cases/disconnected_test.rb b/activerecord/test/cases/disconnected_test.rb
index c25089a420..533665d0f4 100644
--- a/activerecord/test/cases/disconnected_test.rb
+++ b/activerecord/test/cases/disconnected_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class TestRecord < ActiveRecord::Base
diff --git a/activerecord/test/cases/dup_test.rb b/activerecord/test/cases/dup_test.rb
index 638cffe0e6..a2efbf89f9 100644
--- a/activerecord/test/cases/dup_test.rb
+++ b/activerecord/test/cases/dup_test.rb
@@ -1,20 +1,23 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/reply'
-require 'models/topic'
+require "models/reply"
+require "models/topic"
+require "models/movie"
 
 module ActiveRecord
   class DupTest < ActiveRecord::TestCase
     fixtures :topics
 
     def test_dup
-      assert !Topic.new.freeze.dup.frozen?
+      assert_not_predicate Topic.new.freeze.dup, :frozen?
     end
 
     def test_not_readonly
       topic = Topic.first
 
       duped = topic.dup
-      assert !duped.readonly?, 'should not be readonly'
+      assert_not duped.readonly?, "should not be readonly"
     end
 
     def test_is_readonly
@@ -22,15 +25,15 @@ module ActiveRecord
       topic.readonly!
 
       duped = topic.dup
-      assert duped.readonly?, 'should be readonly'
+      assert duped.readonly?, "should be readonly"
     end
 
     def test_dup_not_persisted
       topic = Topic.first
       duped = topic.dup
 
-      assert !duped.persisted?, 'topic not persisted'
-      assert duped.new_record?, 'topic is new'
+      assert_not duped.persisted?, "topic not persisted"
+      assert duped.new_record?, "topic is new"
     end
 
     def test_dup_not_destroyed
@@ -38,7 +41,7 @@ module ActiveRecord
       topic.destroy
 
       duped = topic.dup
-      assert_not duped.destroyed?
+      assert_not_predicate duped, :destroyed?
     end
 
     def test_dup_has_no_id
@@ -49,9 +52,9 @@ module ActiveRecord
 
     def test_dup_with_modified_attributes
       topic = Topic.first
-      topic.author_name = 'Aaron'
+      topic.author_name = "Aaron"
       duped = topic.dup
-      assert_equal 'Aaron', duped.author_name
+      assert_equal "Aaron", duped.author_name
     end
 
     def test_dup_with_changes
@@ -60,10 +63,10 @@ module ActiveRecord
 
       topic.attributes = dbtopic.attributes.except("id")
 
-      #duped has no timestamp values
+      # duped has no timestamp values
       duped = dbtopic.dup
 
-      #clear topic timestamp values
+      # clear topic timestamp values
       topic.send(:clear_timestamp_attributes)
 
       assert_equal topic.changes, duped.changes
@@ -71,10 +74,10 @@ module ActiveRecord
 
     def test_dup_topics_are_independent
       topic = Topic.first
-      topic.author_name = 'Aaron'
+      topic.author_name = "Aaron"
       duped = topic.dup
 
-      duped.author_name = 'meow'
+      duped.author_name = "meow"
 
       assert_not_equal topic.changes, duped.changes
     end
@@ -83,11 +86,11 @@ module ActiveRecord
       topic = Topic.first
       duped = topic.dup
 
-      duped.author_name = 'meow'
-      topic.author_name = 'Aaron'
+      duped.author_name = "meow"
+      topic.author_name = "Aaron"
 
-      assert_equal 'Aaron', topic.author_name
-      assert_equal 'meow', duped.author_name
+      assert_equal "Aaron", topic.author_name
+      assert_equal "meow", duped.author_name
     end
 
     def test_dup_timestamps_are_cleared
@@ -98,7 +101,7 @@ module ActiveRecord
       # temporary change to the topic object
       topic.updated_at -= 3.days
 
-      #dup should not preserve the timestamps if present
+      # dup should not preserve the timestamps if present
       new_topic = topic.dup
       assert_nil new_topic.updated_at
       assert_nil new_topic.created_at
@@ -124,27 +127,29 @@ module ActiveRecord
 
         duped = topic.dup
         duped.title = nil
-        assert duped.invalid?
+        assert_predicate duped, :invalid?
 
         topic.title = nil
-        duped.title = 'Mathematics'
-        assert topic.invalid?
-        assert duped.valid?
+        duped.title = "Mathematics"
+        assert_predicate topic, :invalid?
+        assert_predicate duped, :valid?
       end
     end
 
     def test_dup_with_default_scope
       prev_default_scopes = Topic.default_scopes
-      Topic.default_scopes = [proc { Topic.where(:approved => true) }]
-      topic = Topic.new(:approved => false)
-      assert !topic.dup.approved?, "should not be overridden by default scopes"
+      Topic.default_scopes = [proc { Topic.where(approved: true) }]
+      topic = Topic.new(approved: false)
+      assert_not topic.dup.approved?, "should not be overridden by default scopes"
     ensure
       Topic.default_scopes = prev_default_scopes
     end
 
     def test_dup_without_primary_key
+      skip if current_adapter?(:OracleAdapter)
+
       klass = Class.new(ActiveRecord::Base) do
-        self.table_name = 'parrots_pirates'
+        self.table_name = "parrots_pirates"
       end
 
       record = klass.create!
@@ -153,5 +158,20 @@ module ActiveRecord
         record.dup
       end
     end
+
+    def test_dup_record_not_persisted_after_rollback_transaction
+      movie = Movie.new(name: "test")
+
+      assert_raises(ActiveRecord::RecordInvalid) do
+        Movie.transaction do
+          movie.save!
+          duped = movie.dup
+          duped.name = nil
+          duped.save!
+        end
+      end
+
+      assert_not movie.persisted?
+    end
   end
 end
diff --git a/activerecord/test/cases/enum_test.rb b/activerecord/test/cases/enum_test.rb
index ba23049a92..867ce7082b 100644
--- a/activerecord/test/cases/enum_test.rb
+++ b/activerecord/test/cases/enum_test.rb
@@ -1,23 +1,27 @@
-require 'cases/helper'
-require 'models/book'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/author"
+require "models/book"
 
 class EnumTest < ActiveRecord::TestCase
-  fixtures :books
+  fixtures :books, :authors, :author_addresses
 
   setup do
     @book = books(:awdr)
   end
 
   test "query state by predicate" do
-    assert @book.published?
-    assert_not @book.written?
-    assert_not @book.proposed?
+    assert_predicate @book, :published?
+    assert_not_predicate @book, :written?
+    assert_not_predicate @book, :proposed?
 
-    assert @book.read?
-    assert @book.in_english?
-    assert @book.author_visibility_visible?
-    assert @book.illustrator_visibility_visible?
-    assert @book.with_medium_font_size?
+    assert_predicate @book, :read?
+    assert_predicate @book, :in_english?
+    assert_predicate @book, :author_visibility_visible?
+    assert_predicate @book, :illustrator_visibility_visible?
+    assert_predicate @book, :with_medium_font_size?
+    assert_predicate @book, :medium_to_read?
   end
 
   test "query state with strings" do
@@ -26,6 +30,7 @@ class EnumTest < ActiveRecord::TestCase
     assert_equal "english", @book.language
     assert_equal "visible", @book.author_visibility
     assert_equal "visible", @book.illustrator_visibility
+    assert_equal "medium", @book.difficulty
   end
 
   test "find via scope" do
@@ -34,78 +39,83 @@ class EnumTest < ActiveRecord::TestCase
     assert_equal @book, Book.in_english.first
     assert_equal @book, Book.author_visibility_visible.first
     assert_equal @book, Book.illustrator_visibility_visible.first
+    assert_equal @book, Book.medium_to_read.first
+    assert_equal books(:ddd), Book.forgotten.first
+    assert_equal books(:rfr), authors(:david).unpublished_books.first
   end
 
   test "find via where with values" do
     published, written = Book.statuses[:published], Book.statuses[:written]
 
     assert_equal @book, Book.where(status: published).first
-    refute_equal @book, Book.where(status: written).first
+    assert_not_equal @book, Book.where(status: written).first
     assert_equal @book, Book.where(status: [published]).first
-    refute_equal @book, Book.where(status: [written]).first
-    refute_equal @book, Book.where("status <> ?", published).first
+    assert_not_equal @book, Book.where(status: [written]).first
+    assert_not_equal @book, Book.where("status <> ?", published).first
     assert_equal @book, Book.where("status <> ?", written).first
   end
 
   test "find via where with symbols" do
     assert_equal @book, Book.where(status: :published).first
-    refute_equal @book, Book.where(status: :written).first
+    assert_not_equal @book, Book.where(status: :written).first
     assert_equal @book, Book.where(status: [:published]).first
-    refute_equal @book, Book.where(status: [:written]).first
-    refute_equal @book, Book.where.not(status: :published).first
+    assert_not_equal @book, Book.where(status: [:written]).first
+    assert_not_equal @book, Book.where.not(status: :published).first
     assert_equal @book, Book.where.not(status: :written).first
+    assert_equal books(:ddd), Book.where(read_status: :forgotten).first
   end
 
   test "find via where with strings" do
     assert_equal @book, Book.where(status: "published").first
-    refute_equal @book, Book.where(status: "written").first
+    assert_not_equal @book, Book.where(status: "written").first
     assert_equal @book, Book.where(status: ["published"]).first
-    refute_equal @book, Book.where(status: ["written"]).first
-    refute_equal @book, Book.where.not(status: "published").first
+    assert_not_equal @book, Book.where(status: ["written"]).first
+    assert_not_equal @book, Book.where.not(status: "published").first
     assert_equal @book, Book.where.not(status: "written").first
+    assert_equal books(:ddd), Book.where(read_status: "forgotten").first
   end
 
   test "build from scope" do
-    assert Book.written.build.written?
-    refute Book.written.build.proposed?
+    assert_predicate Book.written.build, :written?
+    assert_not_predicate Book.written.build, :proposed?
   end
 
   test "build from where" do
-    assert Book.where(status: Book.statuses[:written]).build.written?
-    refute Book.where(status: Book.statuses[:written]).build.proposed?
-    assert Book.where(status: :written).build.written?
-    refute Book.where(status: :written).build.proposed?
-    assert Book.where(status: "written").build.written?
-    refute Book.where(status: "written").build.proposed?
+    assert_predicate Book.where(status: Book.statuses[:written]).build, :written?
+    assert_not_predicate Book.where(status: Book.statuses[:written]).build, :proposed?
+    assert_predicate Book.where(status: :written).build, :written?
+    assert_not_predicate Book.where(status: :written).build, :proposed?
+    assert_predicate Book.where(status: "written").build, :written?
+    assert_not_predicate Book.where(status: "written").build, :proposed?
   end
 
   test "update by declaration" do
     @book.written!
-    assert @book.written?
+    assert_predicate @book, :written?
     @book.in_english!
-    assert @book.in_english?
+    assert_predicate @book, :in_english?
     @book.author_visibility_visible!
-    assert @book.author_visibility_visible?
+    assert_predicate @book, :author_visibility_visible?
   end
 
   test "update by setter" do
     @book.update! status: :written
-    assert @book.written?
+    assert_predicate @book, :written?
   end
 
   test "enum methods are overwritable" do
     assert_equal "do publish work...", @book.published!
-    assert @book.published?
+    assert_predicate @book, :published?
   end
 
   test "direct assignment" do
     @book.status = :written
-    assert @book.written?
+    assert_predicate @book, :written?
   end
 
   test "assign string value" do
     @book.status = "written"
-    assert @book.written?
+    assert_predicate @book, :written?
   end
 
   test "enum changed attributes" do
@@ -122,8 +132,8 @@ class EnumTest < ActiveRecord::TestCase
     old_language = @book.language
     @book.status = :proposed
     @book.language = :spanish
-    assert_equal [old_status, 'proposed'], @book.changes[:status]
-    assert_equal [old_language, 'spanish'], @book.changes[:language]
+    assert_equal [old_status, "proposed"], @book.changes[:status]
+    assert_equal [old_language, "spanish"], @book.changes[:language]
   end
 
   test "enum attribute was" do
@@ -145,8 +155,8 @@ class EnumTest < ActiveRecord::TestCase
   test "enum attribute changed to" do
     @book.status = :proposed
     @book.language = :french
-    assert @book.attribute_changed?(:status, to: 'proposed')
-    assert @book.attribute_changed?(:language, to: 'french')
+    assert @book.attribute_changed?(:status, to: "proposed")
+    assert @book.attribute_changed?(:language, to: "french")
   end
 
   test "enum attribute changed from" do
@@ -163,8 +173,8 @@ class EnumTest < ActiveRecord::TestCase
     old_language = @book.language
     @book.status = :proposed
     @book.language = :french
-    assert @book.attribute_changed?(:status, from: old_status, to: 'proposed')
-    assert @book.attribute_changed?(:language, from: old_language, to: 'french')
+    assert @book.attribute_changed?(:status, from: old_status, to: "proposed")
+    assert @book.attribute_changed?(:language, from: old_language, to: "french")
   end
 
   test "enum didn't change" do
@@ -216,12 +226,12 @@ class EnumTest < ActiveRecord::TestCase
   end
 
   test "assign empty string value" do
-    @book.status = ''
+    @book.status = ""
     assert_nil @book.status
   end
 
   test "assign long empty string value" do
-    @book.status = '   '
+    @book.status = "   "
     assert_nil @book.status
   end
 
@@ -232,25 +242,56 @@ class EnumTest < ActiveRecord::TestCase
   end
 
   test "building new objects with enum scopes" do
-    assert Book.written.build.written?
-    assert Book.read.build.read?
-    assert Book.in_spanish.build.in_spanish?
-    assert Book.illustrator_visibility_invisible.build.illustrator_visibility_invisible?
+    assert_predicate Book.written.build, :written?
+    assert_predicate Book.read.build, :read?
+    assert_predicate Book.in_spanish.build, :in_spanish?
+    assert_predicate Book.illustrator_visibility_invisible.build, :illustrator_visibility_invisible?
   end
 
   test "creating new objects with enum scopes" do
-    assert Book.written.create.written?
-    assert Book.read.create.read?
-    assert Book.in_spanish.create.in_spanish?
-    assert Book.illustrator_visibility_invisible.create.illustrator_visibility_invisible?
+    assert_predicate Book.written.create, :written?
+    assert_predicate Book.read.create, :read?
+    assert_predicate Book.in_spanish.create, :in_spanish?
+    assert_predicate Book.illustrator_visibility_invisible.create, :illustrator_visibility_invisible?
+  end
+
+  test "_before_type_cast" do
+    assert_equal 2, @book.status_before_type_cast
+    assert_equal "published", @book.status
+
+    @book.status = "published"
+
+    assert_equal "published", @book.status_before_type_cast
+    assert_equal "published", @book.status
   end
 
-  test "_before_type_cast returns the enum label (required for form fields)" do
-    if @book.status_came_from_user?
-      assert_equal "published", @book.status_before_type_cast
-    else
-      assert_equal "published", @book.status
+  test "invalid definition values raise an ArgumentError" do
+    e = assert_raises(ArgumentError) do
+      Class.new(ActiveRecord::Base) do
+        self.table_name = "books"
+        enum status: [proposed: 1, written: 2, published: 3]
+      end
     end
+
+    assert_match(/must be either a hash, an array of symbols, or an array of strings./, e.message)
+
+    e = assert_raises(ArgumentError) do
+      Class.new(ActiveRecord::Base) do
+        self.table_name = "books"
+        enum status: { "" => 1, "active" => 2 }
+      end
+    end
+
+    assert_match(/Enum label name must not be blank/, e.message)
+
+    e = assert_raises(ArgumentError) do
+      Class.new(ActiveRecord::Base) do
+        self.table_name = "books"
+        enum status: ["active", ""]
+      end
+    end
+
+    assert_match(/Enum label name must not be blank/, e.message)
   end
 
   test "reserved enum names" do
@@ -296,6 +337,24 @@ class EnumTest < ActiveRecord::TestCase
     end
   end
 
+  test "reserved enum values for relation" do
+    relation_method_samples = [
+      :records,
+      :to_ary,
+      :scope_for_create
+    ]
+
+    relation_method_samples.each do |value|
+      e = assert_raises(ArgumentError, "enum value `#{value}` should not be allowed") do
+        Class.new(ActiveRecord::Base) do
+          self.table_name = "books"
+          enum category: [:other, value]
+        end
+      end
+      assert_match(/You tried to define an enum named .* on the model/, e.message)
+    end
+  end
+
   test "overriding enum method should not raise" do
     assert_nothing_raised do
       Class.new(ActiveRecord::Base) do
@@ -318,29 +377,29 @@ class EnumTest < ActiveRecord::TestCase
 
   test "validate uniqueness" do
     klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Book'; end
+      def self.name; "Book"; end
       enum status: [:proposed, :written]
       validates_uniqueness_of :status
     end
     klass.delete_all
     klass.create!(status: "proposed")
     book = klass.new(status: "written")
-    assert book.valid?
+    assert_predicate book, :valid?
     book.status = "proposed"
-    assert_not book.valid?
+    assert_not_predicate book, :valid?
   end
 
   test "validate inclusion of value in array" do
     klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Book'; end
+      def self.name; "Book"; end
       enum status: [:proposed, :written]
       validates_inclusion_of :status, in: ["written"]
     end
     klass.delete_all
     invalid_book = klass.new(status: "proposed")
-    assert_not invalid_book.valid?
+    assert_not_predicate invalid_book, :valid?
     valid_book = klass.new(status: "written")
-    assert valid_book.valid?
+    assert_predicate valid_book, :valid?
   end
 
   test "enums are distinct per class" do
@@ -356,11 +415,11 @@ class EnumTest < ActiveRecord::TestCase
 
     book1 = klass1.proposed.create!
     book1.status = :written
-    assert_equal ['proposed', 'written'], book1.status_change
+    assert_equal ["proposed", "written"], book1.status_change
 
     book2 = klass2.drafted.create!
     book2.status = :uploaded
-    assert_equal ['drafted', 'uploaded'], book2.status_change
+    assert_equal ["drafted", "uploaded"], book2.status_change
   end
 
   test "enums are inheritable" do
@@ -372,11 +431,11 @@ class EnumTest < ActiveRecord::TestCase
 
     book1 = subklass1.proposed.create!
     book1.status = :written
-    assert_equal ['proposed', 'written'], book1.status_change
+    assert_equal ["proposed", "written"], book1.status_change
 
     book2 = subklass2.drafted.create!
     book2.status = :uploaded
-    assert_equal ['drafted', 'uploaded'], book2.status_change
+    assert_equal ["drafted", "uploaded"], book2.status_change
   end
 
   test "declare multiple enums at a time" do
@@ -387,23 +446,76 @@ class EnumTest < ActiveRecord::TestCase
     end
 
     book1 = klass.proposed.create!
-    assert book1.proposed?
+    assert_predicate book1, :proposed?
 
     book2 = klass.single.create!
-    assert book2.single?
+    assert_predicate book2, :single?
+  end
+
+  test "enum with alias_attribute" do
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = "books"
+      alias_attribute :aliased_status, :status
+      enum aliased_status: [:proposed, :written, :published]
+    end
+
+    book = klass.proposed.create!
+    assert_predicate book, :proposed?
+    assert_equal "proposed", book.aliased_status
+
+    book = klass.find(book.id)
+    assert_predicate book, :proposed?
+    assert_equal "proposed", book.aliased_status
   end
 
   test "query state by predicate with prefix" do
-    assert @book.author_visibility_visible?
-    assert_not @book.author_visibility_invisible?
-    assert @book.illustrator_visibility_visible?
-    assert_not @book.illustrator_visibility_invisible?
+    assert_predicate @book, :author_visibility_visible?
+    assert_not_predicate @book, :author_visibility_invisible?
+    assert_predicate @book, :illustrator_visibility_visible?
+    assert_not_predicate @book, :illustrator_visibility_invisible?
   end
 
   test "query state by predicate with custom prefix" do
-    assert @book.in_english?
-    assert_not @book.in_spanish?
-    assert_not @book.in_french?
+    assert_predicate @book, :in_english?
+    assert_not_predicate @book, :in_spanish?
+    assert_not_predicate @book, :in_french?
+  end
+
+  test "query state by predicate with custom suffix" do
+    assert_predicate @book, :medium_to_read?
+    assert_not_predicate @book, :easy_to_read?
+    assert_not_predicate @book, :hard_to_read?
+  end
+
+  test "enum methods with custom suffix defined" do
+    assert_respond_to @book.class, :easy_to_read
+    assert_respond_to @book.class, :medium_to_read
+    assert_respond_to @book.class, :hard_to_read
+
+    assert_respond_to @book, :easy_to_read?
+    assert_respond_to @book, :medium_to_read?
+    assert_respond_to @book, :hard_to_read?
+
+    assert_respond_to @book, :easy_to_read!
+    assert_respond_to @book, :medium_to_read!
+    assert_respond_to @book, :hard_to_read!
+  end
+
+  test "update enum attributes with custom suffix" do
+    @book.medium_to_read!
+    assert_not_predicate @book, :easy_to_read?
+    assert_predicate @book, :medium_to_read?
+    assert_not_predicate @book, :hard_to_read?
+
+    @book.easy_to_read!
+    assert_predicate @book, :easy_to_read?
+    assert_not_predicate @book, :medium_to_read?
+    assert_not_predicate @book, :hard_to_read?
+
+    @book.hard_to_read!
+    assert_not_predicate @book, :easy_to_read?
+    assert_not_predicate @book, :medium_to_read?
+    assert_predicate @book, :hard_to_read?
   end
 
   test "uses default status when no status is provided in fixtures" do
@@ -411,4 +523,18 @@ class EnumTest < ActiveRecord::TestCase
     assert book.proposed?, "expected fixture to default to proposed status"
     assert book.in_english?, "expected fixture to default to english language"
   end
+
+  test "uses default value from database on initialization" do
+    book = Book.new
+    assert_predicate book, :proposed?
+  end
+
+  test "uses default value from database on initialization when using custom mapping" do
+    book = Book.new
+    assert_predicate book, :hard?
+  end
+
+  test "data type of Enum type" do
+    assert_equal :integer, Book.type_for_attribute("status").type
+  end
 end
diff --git a/activerecord/test/cases/errors_test.rb b/activerecord/test/cases/errors_test.rb
new file mode 100644
index 0000000000..b90e6a66c5
--- /dev/null
+++ b/activerecord/test/cases/errors_test.rb
@@ -0,0 +1,18 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+class ErrorsTest < ActiveRecord::TestCase
+  def test_can_be_instantiated_with_no_args
+    base = ActiveRecord::ActiveRecordError
+    error_klasses = ObjectSpace.each_object(Class).select { |klass| klass < base }
+
+    (error_klasses - [ActiveRecord::AmbiguousSourceReflectionForThroughAssociation]).each do |error_klass|
+      begin
+        error_klass.new.inspect
+      rescue ArgumentError
+        raise "Instance of #{error_klass} can't be initialized with no arguments"
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/explain_subscriber_test.rb b/activerecord/test/cases/explain_subscriber_test.rb
index 2dee8a26a5..79a0630193 100644
--- a/activerecord/test/cases/explain_subscriber_test.rb
+++ b/activerecord/test/cases/explain_subscriber_test.rb
@@ -1,6 +1,8 @@
-require 'cases/helper'
-require 'active_record/explain_subscriber'
-require 'active_record/explain_registry'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "active_record/explain_subscriber"
+require "active_record/explain_registry"
 
 if ActiveRecord::Base.connection.supports_explain?
   class ExplainSubscriberTest < ActiveRecord::TestCase
@@ -13,43 +15,43 @@ if ActiveRecord::Base.connection.supports_explain?
 
     def test_collects_nothing_if_the_payload_has_an_exception
       SUBSCRIBER.finish(nil, nil, exception: Exception.new)
-      assert queries.empty?
+      assert_empty queries
     end
 
     def test_collects_nothing_for_ignored_payloads
       ActiveRecord::ExplainSubscriber::IGNORED_PAYLOADS.each do |ip|
         SUBSCRIBER.finish(nil, nil, name: ip)
       end
-      assert queries.empty?
+      assert_empty queries
     end
 
     def test_collects_nothing_if_collect_is_false
       ActiveRecord::ExplainRegistry.collect = false
-      SUBSCRIBER.finish(nil, nil, name: 'SQL', sql: 'select 1 from users', binds: [1, 2])
-      assert queries.empty?
+      SUBSCRIBER.finish(nil, nil, name: "SQL", sql: "select 1 from users", binds: [1, 2])
+      assert_empty queries
     end
 
     def test_collects_pairs_of_queries_and_binds
-      sql   = 'select 1 from users'
+      sql   = "select 1 from users"
       binds = [1, 2]
-      SUBSCRIBER.finish(nil, nil, name: 'SQL', sql: sql, binds: binds)
+      SUBSCRIBER.finish(nil, nil, name: "SQL", sql: sql, binds: binds)
       assert_equal 1, queries.size
       assert_equal sql, queries[0][0]
       assert_equal binds, queries[0][1]
     end
 
-    def test_collects_nothing_if_the_statement_is_not_whitelisted
-      SUBSCRIBER.finish(nil, nil, name: 'SQL', sql: 'SHOW max_identifier_length')
-      assert queries.empty?
+    def test_collects_nothing_if_the_statement_is_not_explainable
+      SUBSCRIBER.finish(nil, nil, name: "SQL", sql: "SHOW max_identifier_length")
+      assert_empty queries
     end
 
     def test_collects_nothing_if_the_statement_is_only_partially_matched
-      SUBSCRIBER.finish(nil, nil, name: 'SQL', sql: 'select_db yo_mama')
-      assert queries.empty?
+      SUBSCRIBER.finish(nil, nil, name: "SQL", sql: "select_db yo_mama")
+      assert_empty queries
     end
 
     def test_collects_cte_queries
-      SUBSCRIBER.finish(nil, nil, name: 'SQL', sql: 'with s as (values(3)) select 1 from s')
+      SUBSCRIBER.finish(nil, nil, name: "SQL", sql: "with s as (values(3)) select 1 from s")
       assert_equal 1, queries.size
     end
 
diff --git a/activerecord/test/cases/explain_test.rb b/activerecord/test/cases/explain_test.rb
index f1d5511bb8..a0e75f4e89 100644
--- a/activerecord/test/cases/explain_test.rb
+++ b/activerecord/test/cases/explain_test.rb
@@ -1,6 +1,7 @@
-require 'cases/helper'
-require 'models/car'
-require 'active_support/core_ext/string/strip'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/car"
 
 if ActiveRecord::Base.connection.supports_explain?
   class ExplainTest < ActiveRecord::TestCase
@@ -15,13 +16,13 @@ if ActiveRecord::Base.connection.supports_explain?
     end
 
     def test_relation_explain
-      message = Car.where(:name => 'honda').explain
+      message = Car.where(name: "honda").explain
       assert_match(/^EXPLAIN for:/, message)
     end
 
     def test_collecting_queries_for_explain
       queries = ActiveRecord::Base.collecting_queries_for_explain do
-        Car.where(:name => 'honda').to_a
+        Car.where(name: "honda").to_a
       end
 
       sql, binds = queries[0]
@@ -30,7 +31,7 @@ if ActiveRecord::Base.connection.supports_explain?
         assert_equal 1, binds.length
         assert_equal "honda", binds.last.value
       else
-        assert_match 'honda', sql
+        assert_match "honda", sql
       end
     end
 
@@ -39,38 +40,49 @@ if ActiveRecord::Base.connection.supports_explain?
       binds   = [[], []]
       queries = sqls.zip(binds)
 
-      connection.stubs(:explain).returns('query plan foo', 'query plan bar')
-      expected = sqls.map {|sql| "EXPLAIN for: #{sql}\nquery plan #{sql}"}.join("\n")
-      assert_equal expected, base.exec_explain(queries)
+      stub_explain_for_query_plans do
+        expected = sqls.map { |sql| "EXPLAIN for: #{sql}\nquery plan #{sql}" }.join("\n")
+        assert_equal expected, base.exec_explain(queries)
+      end
     end
 
     def test_exec_explain_with_binds
-      cols = [Object.new, Object.new]
-      cols[0].expects(:name).returns('wadus')
-      cols[1].expects(:name).returns('chaflan')
-
       sqls    = %w(foo bar)
-      binds   = [[[cols[0], 1]], [[cols[1], 2]]]
+      binds   = [[bind_param("wadus", 1)], [bind_param("chaflan", 2)]]
       queries = sqls.zip(binds)
 
-      connection.stubs(:explain).returns("query plan foo\n", "query plan bar\n")
-      expected = <<-SQL.strip_heredoc
-        EXPLAIN for: #{sqls[0]} [["wadus", 1]]
-        query plan foo
+      stub_explain_for_query_plans(["query plan foo\n", "query plan bar\n"]) do
+        expected = <<~SQL
+          EXPLAIN for: #{sqls[0]} [["wadus", 1]]
+          query plan foo
 
-        EXPLAIN for: #{sqls[1]} [["chaflan", 2]]
-        query plan bar
-      SQL
-      assert_equal expected, base.exec_explain(queries)
+          EXPLAIN for: #{sqls[1]} [["chaflan", 2]]
+          query plan bar
+        SQL
+        assert_equal expected, base.exec_explain(queries)
+      end
     end
 
     def test_unsupported_connection_adapter
-      connection.stubs(:supports_explain?).returns(false)
+      connection.stub(:supports_explain?, false) do
+        assert_not_called(base.logger, :warn) do
+          Car.where(name: "honda").to_a
+        end
+      end
+    end
 
-      base.logger.expects(:warn).never
+    private
 
-      Car.where(:name => 'honda').to_a
-    end
+      def stub_explain_for_query_plans(query_plans = ["query plan foo", "query plan bar"])
+        explain_called = 0
 
+        connection.stub(:explain, proc { explain_called += 1; query_plans[explain_called - 1] }) do
+          yield
+        end
+      end
+
+      def bind_param(name, value)
+        ActiveRecord::Relation::QueryAttribute.new(name, value, ActiveRecord::Type::Value.new)
+      end
   end
 end
diff --git a/activerecord/test/cases/filter_attributes_test.rb b/activerecord/test/cases/filter_attributes_test.rb
new file mode 100644
index 0000000000..47161a547a
--- /dev/null
+++ b/activerecord/test/cases/filter_attributes_test.rb
@@ -0,0 +1,136 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/admin"
+require "models/admin/user"
+require "models/admin/account"
+require "models/user"
+require "pp"
+
+class FilterAttributesTest < ActiveRecord::TestCase
+  fixtures :"admin/users", :"admin/accounts"
+
+  setup do
+    @previous_filter_attributes = ActiveRecord::Base.filter_attributes
+    ActiveRecord::Base.filter_attributes = [:name]
+  end
+
+  teardown do
+    ActiveRecord::Base.filter_attributes = @previous_filter_attributes
+  end
+
+  test "filter_attributes" do
+    Admin::User.all.each do |user|
+      assert_includes user.inspect, "name: [FILTERED]"
+      assert_equal 1, user.inspect.scan("[FILTERED]").length
+    end
+
+    Admin::Account.all.each do |account|
+      assert_includes account.inspect, "name: [FILTERED]"
+      assert_equal 1, account.inspect.scan("[FILTERED]").length
+    end
+  end
+
+  test "string filter_attributes perform pertial match" do
+    ActiveRecord::Base.filter_attributes = ["n"]
+    Admin::Account.all.each do |account|
+      assert_includes account.inspect, "name: [FILTERED]"
+      assert_equal 1, account.inspect.scan("[FILTERED]").length
+    end
+  end
+
+  test "regex filter_attributes are accepted" do
+    ActiveRecord::Base.filter_attributes = [/\An\z/]
+    account = Admin::Account.find_by(name: "37signals")
+    assert_includes account.inspect, 'name: "37signals"'
+    assert_equal 0, account.inspect.scan("[FILTERED]").length
+
+    ActiveRecord::Base.filter_attributes = [/\An/]
+    account = Admin::Account.find_by(name: "37signals")
+    assert_includes account.reload.inspect, "name: [FILTERED]"
+    assert_equal 1, account.inspect.scan("[FILTERED]").length
+  end
+
+  test "proc filter_attributes are accepted" do
+    ActiveRecord::Base.filter_attributes = [ lambda { |key, value| value.reverse! if key == "name" } ]
+    account = Admin::Account.find_by(name: "37signals")
+    assert_includes account.inspect, 'name: "slangis73"'
+  end
+
+  test "filter_attributes could be overwritten by models" do
+    Admin::Account.all.each do |account|
+      assert_includes account.inspect, "name: [FILTERED]"
+      assert_equal 1, account.inspect.scan("[FILTERED]").length
+    end
+
+    begin
+      Admin::Account.filter_attributes = []
+
+      # Above changes should not impact other models
+      Admin::User.all.each do |user|
+        assert_includes user.inspect, "name: [FILTERED]"
+        assert_equal 1, user.inspect.scan("[FILTERED]").length
+      end
+
+      Admin::Account.all.each do |account|
+        assert_not_includes account.inspect, "name: [FILTERED]"
+        assert_equal 0, account.inspect.scan("[FILTERED]").length
+      end
+    ensure
+      Admin::Account.remove_instance_variable(:@filter_attributes)
+    end
+  end
+
+  test "filter_attributes should not filter nil value" do
+    account = Admin::Account.new
+
+    assert_includes account.inspect, "name: nil"
+    assert_not_includes account.inspect, "name: [FILTERED]"
+    assert_equal 0, account.inspect.scan("[FILTERED]").length
+  end
+
+  test "filter_attributes should handle [FILTERED] value properly" do
+    begin
+      User.filter_attributes = ["auth"]
+      user = User.new(token: "[FILTERED]", auth_token: "[FILTERED]")
+
+      assert_includes user.inspect, "auth_token: [FILTERED]"
+      assert_includes user.inspect, 'token: "[FILTERED]"'
+    ensure
+      User.remove_instance_variable(:@filter_attributes)
+    end
+  end
+
+  test "filter_attributes on pretty_print" do
+    user = admin_users(:david)
+    actual = "".dup
+    PP.pp(user, StringIO.new(actual))
+
+    assert_includes actual, "name: [FILTERED]"
+    assert_equal 1, actual.scan("[FILTERED]").length
+  end
+
+  test "filter_attributes on pretty_print should not filter nil value" do
+    user = Admin::User.new
+    actual = "".dup
+    PP.pp(user, StringIO.new(actual))
+
+    assert_includes actual, "name: nil"
+    assert_not_includes actual, "name: [FILTERED]"
+    assert_equal 0, actual.scan("[FILTERED]").length
+  end
+
+  test "filter_attributes on pretty_print should handle [FILTERED] value properly" do
+    begin
+      User.filter_attributes = ["auth"]
+      user = User.new(token: "[FILTERED]", auth_token: "[FILTERED]")
+      actual = "".dup
+      PP.pp(user, StringIO.new(actual))
+
+      assert_includes actual, "auth_token: [FILTERED]"
+      assert_includes actual, 'token: "[FILTERED]"'
+    ensure
+      User.remove_instance_variable(:@filter_attributes)
+    end
+  end
+end
diff --git a/activerecord/test/cases/finder_respond_to_test.rb b/activerecord/test/cases/finder_respond_to_test.rb
index 6ab2657c44..e0acd30c22 100644
--- a/activerecord/test/cases/finder_respond_to_test.rb
+++ b/activerecord/test/cases/finder_respond_to_test.rb
@@ -1,13 +1,14 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
+require "models/topic"
 
 class FinderRespondToTest < ActiveRecord::TestCase
-
   fixtures :topics
 
   def test_should_preserve_normal_respond_to_behaviour_on_base
     assert_respond_to ActiveRecord::Base, :new
-    assert !ActiveRecord::Base.respond_to?(:find_by_something)
+    assert_not_respond_to ActiveRecord::Base, :find_by_something
   end
 
   def test_should_preserve_normal_respond_to_behaviour_and_respond_to_newly_added_method
@@ -42,19 +43,19 @@ class FinderRespondToTest < ActiveRecord::TestCase
   end
 
   def test_should_not_respond_to_find_by_one_missing_attribute
-    assert !Topic.respond_to?(:find_by_undertitle)
+    assert_not_respond_to Topic, :find_by_undertitle
   end
 
   def test_should_not_respond_to_find_by_invalid_method_syntax
-    assert !Topic.respond_to?(:fail_to_find_by_title)
-    assert !Topic.respond_to?(:find_by_title?)
-    assert !Topic.respond_to?(:fail_to_find_or_create_by_title)
-    assert !Topic.respond_to?(:find_or_create_by_title?)
+    assert_not_respond_to Topic, :fail_to_find_by_title
+    assert_not_respond_to Topic, :find_by_title?
+    assert_not_respond_to Topic, :fail_to_find_or_create_by_title
+    assert_not_respond_to Topic, :find_or_create_by_title?
   end
 
   private
 
-  def ensure_topic_method_is_not_cached(method_id)
-    class << Topic; self; end.send(:remove_method, method_id) if Topic.public_methods.include? method_id
-  end
+    def ensure_topic_method_is_not_cached(method_id)
+      class << Topic; self; end.send(:remove_method, method_id) if Topic.public_methods.include? method_id
+    end
 end
diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index 4b819a82e8..52fd9291b2 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -1,35 +1,39 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/author'
-require 'models/categorization'
-require 'models/comment'
-require 'models/company'
-require 'models/tagging'
-require 'models/topic'
-require 'models/reply'
-require 'models/entrant'
-require 'models/project'
-require 'models/developer'
-require 'models/computer'
-require 'models/customer'
-require 'models/toy'
-require 'models/matey'
-require 'models/dog'
-require 'models/car'
-require 'models/tyre'
+require "models/post"
+require "models/author"
+require "models/categorization"
+require "models/comment"
+require "models/company"
+require "models/tagging"
+require "models/topic"
+require "models/reply"
+require "models/rating"
+require "models/entrant"
+require "models/project"
+require "models/developer"
+require "models/computer"
+require "models/customer"
+require "models/toy"
+require "models/matey"
+require "models/dog"
+require "models/car"
+require "models/tyre"
+require "models/subscriber"
 
 class FinderTest < ActiveRecord::TestCase
-  fixtures :companies, :topics, :entrants, :developers, :developers_projects, :posts, :comments, :accounts, :authors, :customers, :categories, :categorizations, :cars
+  fixtures :companies, :topics, :entrants, :developers, :developers_projects, :posts, :comments, :accounts, :authors, :author_addresses, :customers, :categories, :categorizations, :cars
 
   def test_find_by_id_with_hash
-    assert_raises(ActiveRecord::StatementInvalid) do
-      Post.find_by_id(:limit => 1)
+    assert_nothing_raised do
+      Post.find_by_id(limit: 1)
     end
   end
 
   def test_find_by_title_and_id_with_hash
-    assert_raises(ActiveRecord::StatementInvalid) do
-      Post.find_by_title_and_id('foo', :limit => 1)
+    assert_nothing_raised do
+      Post.find_by_title_and_id("foo", limit: 1)
     end
   end
 
@@ -43,13 +47,97 @@ class FinderTest < ActiveRecord::TestCase
     end
     assert_equal "should happen", exception.message
 
-    assert_nothing_raised(RuntimeError) do
+    assert_nothing_raised do
       Topic.all.find(-> { raise "should not happen" }) { |e| e.title == topics(:first).title }
     end
   end
 
-  def test_find_passing_active_record_object_is_deprecated
-    assert_deprecated do
+  def test_find_with_ids_returning_ordered
+    records = Topic.find([4, 2, 5])
+    assert_equal "The Fourth Topic of the day", records[0].title
+    assert_equal "The Second Topic of the day", records[1].title
+    assert_equal "The Fifth Topic of the day", records[2].title
+
+    records = Topic.find(4, 2, 5)
+    assert_equal "The Fourth Topic of the day", records[0].title
+    assert_equal "The Second Topic of the day", records[1].title
+    assert_equal "The Fifth Topic of the day", records[2].title
+
+    records = Topic.find(["4", "2", "5"])
+    assert_equal "The Fourth Topic of the day", records[0].title
+    assert_equal "The Second Topic of the day", records[1].title
+    assert_equal "The Fifth Topic of the day", records[2].title
+
+    records = Topic.find("4", "2", "5")
+    assert_equal "The Fourth Topic of the day", records[0].title
+    assert_equal "The Second Topic of the day", records[1].title
+    assert_equal "The Fifth Topic of the day", records[2].title
+  end
+
+  def test_find_with_ids_and_order_clause
+    # The order clause takes precedence over the informed ids
+    records = Topic.order(:author_name).find([5, 3, 1])
+    assert_equal "The Third Topic of the day", records[0].title
+    assert_equal "The First Topic",            records[1].title
+    assert_equal "The Fifth Topic of the day", records[2].title
+
+    records = Topic.order(:id).find([5, 3, 1])
+    assert_equal "The First Topic",            records[0].title
+    assert_equal "The Third Topic of the day", records[1].title
+    assert_equal "The Fifth Topic of the day", records[2].title
+  end
+
+  def test_find_with_ids_with_limit_and_order_clause
+    # The order clause takes precedence over the informed ids
+    records = Topic.limit(2).order(:id).find([5, 3, 1])
+    assert_equal 2, records.size
+    assert_equal "The First Topic",            records[0].title
+    assert_equal "The Third Topic of the day", records[1].title
+  end
+
+  def test_find_with_ids_and_limit
+    records = Topic.limit(3).find([3, 2, 5, 1, 4])
+    assert_equal 3, records.size
+    assert_equal "The Third Topic of the day",  records[0].title
+    assert_equal "The Second Topic of the day", records[1].title
+    assert_equal "The Fifth Topic of the day",  records[2].title
+  end
+
+  def test_find_with_ids_where_and_limit
+    # Please note that Topic 1 is the only not approved so
+    # if it were among the first 3 it would raise an ActiveRecord::RecordNotFound
+    records = Topic.where(approved: true).limit(3).find([3, 2, 5, 1, 4])
+    assert_equal 3, records.size
+    assert_equal "The Third Topic of the day",  records[0].title
+    assert_equal "The Second Topic of the day", records[1].title
+    assert_equal "The Fifth Topic of the day",  records[2].title
+  end
+
+  def test_find_with_ids_and_offset
+    records = Topic.offset(2).find([3, 2, 5, 1, 4])
+    assert_equal 3, records.size
+    assert_equal "The Fifth Topic of the day",  records[0].title
+    assert_equal "The First Topic",             records[1].title
+    assert_equal "The Fourth Topic of the day", records[2].title
+  end
+
+  def test_find_with_ids_with_no_id_passed
+    exception = assert_raises(ActiveRecord::RecordNotFound) { Topic.find }
+    assert_equal exception.model, "Topic"
+    assert_equal exception.primary_key, "id"
+  end
+
+  def test_find_with_ids_with_id_out_of_range
+    exception = assert_raises(ActiveRecord::RecordNotFound) do
+      Topic.find("9999999999999999999999999999999")
+    end
+
+    assert_equal exception.model, "Topic"
+    assert_equal exception.primary_key, "id"
+  end
+
+  def test_find_passing_active_record_object_is_not_permitted
+    assert_raises(ArgumentError) do
       Topic.find(Topic.last)
     end
   end
@@ -58,7 +146,7 @@ class FinderTest < ActiveRecord::TestCase
     gc_disabled = GC.disable
     Post.where("author_id" => nil)  # warm up
     x = Symbol.all_symbols.count
-    Post.where("title" => {"xxxqqqq" => "bar"})
+    Post.where("title" => { "xxxqqqq" => "bar" })
     assert_equal x, Symbol.all_symbols.count
   ensure
     GC.enable if gc_disabled == false
@@ -67,7 +155,7 @@ class FinderTest < ActiveRecord::TestCase
   # find should handle strings that come from URLs
   # (example: Category.find(params[:id]))
   def test_find_with_string
-    assert_equal(Topic.find(1).title,Topic.find("1").title)
+    assert_equal(Topic.find(1).title, Topic.find("1").title)
   end
 
   def test_exists
@@ -75,22 +163,49 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal true, Topic.exists?("1")
     assert_equal true, Topic.exists?(title: "The First Topic")
     assert_equal true, Topic.exists?(heading: "The First Topic")
-    assert_equal true, Topic.exists?(:author_name => "Mary", :approved => true)
+    assert_equal true, Topic.exists?(author_name: "Mary", approved: true)
     assert_equal true, Topic.exists?(["parent_id = ?", 1])
     assert_equal true, Topic.exists?(id: [1, 9999])
 
     assert_equal false, Topic.exists?(45)
+    assert_equal false, Topic.exists?(9999999999999999999999999999999)
     assert_equal false, Topic.exists?(Topic.new.id)
 
-    assert_raise(NoMethodError) { Topic.exists?([1,2]) }
+    assert_raise(NoMethodError) { Topic.exists?([1, 2]) }
+  end
+
+  def test_exists_with_scope
+    davids = Author.where(name: "David")
+    assert_equal true, davids.exists?
+    assert_equal true, davids.exists?(authors(:david).id)
+    assert_equal false, davids.exists?(authors(:mary).id)
+    assert_equal false, davids.exists?("42")
+    assert_equal false, davids.exists?(42)
+    assert_equal false, davids.exists?(davids.new.id)
+
+    fake = Author.where(name: "fake author")
+    assert_equal false, fake.exists?
+    assert_equal false, fake.exists?(authors(:david).id)
+  end
+
+  def test_exists_uses_existing_scope
+    post = authors(:david).posts.first
+    authors = Author.includes(:posts).where(name: "David", posts: { id: post.id })
+    assert_equal true, authors.exists?(authors(:david).id)
+  end
+
+  def test_any_with_scope_on_hash_includes
+    post = authors(:david).posts.first
+    categories = Categorization.includes(author: :posts).where(posts: { id: post.id })
+    assert_equal true, categories.exists?
   end
 
   def test_exists_with_polymorphic_relation
-    post = Post.create!(title: 'Post', body: 'default', taggings: [Tagging.new(comment: 'tagging comment')])
-    relation = Post.tagged_with_comment('tagging comment')
+    post = Post.create!(title: "Post", body: "default", taggings: [Tagging.new(comment: "tagging comment")])
+    relation = Post.tagged_with_comment("tagging comment")
 
-    assert_equal true, relation.exists?(title: ['Post'])
-    assert_equal true, relation.exists?(['title LIKE ?', 'Post%'])
+    assert_equal true, relation.exists?(title: ["Post"])
+    assert_equal true, relation.exists?(["title LIKE ?", "Post%"])
     assert_equal true, relation.exists?
     assert_equal true, relation.exists?(post.id)
     assert_equal true, relation.exists?(post.id.to_s)
@@ -98,17 +213,21 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal false, relation.exists?(false)
   end
 
-  def test_exists_passing_active_record_object_is_deprecated
-    assert_deprecated do
-      Topic.exists?(Topic.new)
-    end
+  def test_exists_with_string
+    assert_equal false, Subscriber.exists?("foo")
+    assert_equal false, Subscriber.exists?("   ")
+
+    Subscriber.create!(id: "foo")
+    Subscriber.create!(id: "   ")
+
+    assert_equal true, Subscriber.exists?("foo")
+    assert_equal true, Subscriber.exists?("   ")
   end
 
-  def test_exists_fails_when_parameter_has_invalid_type
-    assert_raises(RangeError) do
-      assert_equal false, Topic.exists?(("9"*53).to_i) # number that's bigger than int
+  def test_exists_passing_active_record_object_is_not_permitted
+    assert_raises(ArgumentError) do
+      Topic.exists?(Topic.new)
     end
-    assert_equal false, Topic.exists?("foo")
   end
 
   def test_exists_does_not_select_columns_without_alias
@@ -135,26 +254,55 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal true, Topic.first.replies.exists?
   end
 
-  # ensures +exists?+ runs valid SQL by excluding order value
-  def test_exists_with_order
+  def test_exists_with_empty_hash_arg
+    assert_equal true, Topic.exists?({})
+  end
+
+  # Ensure +exists?+ runs without an error by excluding distinct value.
+  # See https://github.com/rails/rails/pull/26981.
+  def test_exists_with_order_and_distinct
     assert_equal true, Topic.order(:id).distinct.exists?
   end
 
+  # Ensure +exists?+ runs without an error by excluding order value.
+  def test_exists_with_order
+    assert_equal true, Topic.order(Arel.sql("invalid sql here")).exists?
+  end
+
+  def test_exists_with_joins
+    assert_equal true, Topic.joins(:replies).where(replies_topics: { approved: true }).order("replies_topics.created_at DESC").exists?
+  end
+
+  def test_exists_with_left_joins
+    assert_equal true, Topic.left_joins(:replies).where(replies_topics: { approved: true }).order("replies_topics.created_at DESC").exists?
+  end
+
+  def test_exists_with_eager_load
+    assert_equal true, Topic.eager_load(:replies).where(replies_topics: { approved: true }).order("replies_topics.created_at DESC").exists?
+  end
+
   def test_exists_with_includes_limit_and_empty_result
-    assert_equal false, Topic.includes(:replies).limit(0).exists?
-    assert_equal false, Topic.includes(:replies).limit(1).where('0 = 1').exists?
+    assert_no_queries { assert_equal false, Topic.includes(:replies).limit(0).exists? }
+    assert_queries(1) { assert_equal false, Topic.includes(:replies).limit(1).where("0 = 1").exists? }
   end
 
   def test_exists_with_distinct_association_includes_and_limit
     author = Author.first
-    assert_equal false, author.unique_categorized_posts.includes(:special_comments).limit(0).exists?
-    assert_equal true, author.unique_categorized_posts.includes(:special_comments).limit(1).exists?
+    unique_categorized_posts = author.unique_categorized_posts.includes(:special_comments)
+    assert_no_queries { assert_equal false, unique_categorized_posts.limit(0).exists? }
+    assert_queries(1) { assert_equal true, unique_categorized_posts.limit(1).exists? }
   end
 
   def test_exists_with_distinct_association_includes_limit_and_order
     author = Author.first
-    assert_equal false, author.unique_categorized_posts.includes(:special_comments).order('comments.tags_count DESC').limit(0).exists?
-    assert_equal true, author.unique_categorized_posts.includes(:special_comments).order('comments.tags_count DESC').limit(1).exists?
+    unique_categorized_posts = author.unique_categorized_posts.includes(:special_comments).order("comments.tags_count DESC")
+    assert_no_queries { assert_equal false, unique_categorized_posts.limit(0).exists? }
+    assert_queries(1) { assert_equal true, unique_categorized_posts.limit(1).exists? }
+  end
+
+  def test_exists_should_reference_correct_aliases_while_joining_tables_of_has_many_through_association
+    ratings = developers(:david).ratings.includes(comment: :post).where(posts: { id: 1 })
+    assert_queries(1) { assert_not_predicate ratings.limit(1), :exists? }
   end
 
   def test_exists_with_empty_table_and_no_args_given
@@ -164,22 +312,20 @@ class FinderTest < ActiveRecord::TestCase
 
   def test_exists_with_aggregate_having_three_mappings
     existing_address = customers(:david).address
-    assert_equal true, Customer.exists?(:address => existing_address)
+    assert_equal true, Customer.exists?(address: existing_address)
   end
 
   def test_exists_with_aggregate_having_three_mappings_with_one_difference
     existing_address = customers(:david).address
-    assert_equal false, Customer.exists?(:address =>
-      Address.new(existing_address.street, existing_address.city, existing_address.country + "1"))
-    assert_equal false, Customer.exists?(:address =>
-      Address.new(existing_address.street, existing_address.city + "1", existing_address.country))
-    assert_equal false, Customer.exists?(:address =>
-      Address.new(existing_address.street + "1", existing_address.city, existing_address.country))
+    assert_equal false, Customer.exists?(address: Address.new(existing_address.street, existing_address.city, existing_address.country + "1"))
+    assert_equal false, Customer.exists?(address: Address.new(existing_address.street, existing_address.city + "1", existing_address.country))
+    assert_equal false, Customer.exists?(address: Address.new(existing_address.street + "1", existing_address.city, existing_address.country))
   end
 
   def test_exists_does_not_instantiate_records
-    Developer.expects(:instantiate).never
-    Developer.exists?
+    assert_not_called(Developer, :instantiate) do
+      Developer.exists?
+    end
   end
 
   def test_find_by_array_of_one_id
@@ -193,8 +339,10 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_find_by_ids_with_limit_and_offset
-    assert_equal 2, Entrant.limit(2).find([1,3,2]).size
-    assert_equal 1, Entrant.limit(3).offset(2).find([1,3,2]).size
+    assert_equal 2, Entrant.limit(2).find([1, 3, 2]).size
+    entrants = Entrant.limit(3).offset(2).find([1, 3, 2])
+    assert_equal 1, entrants.size
+    assert_equal "Ruby Guru", entrants.first.name
 
     # Also test an edge case: If you have 11 results, and you set a
     #   limit of 3 and offset of 9, then you should find that there
@@ -202,32 +350,43 @@ class FinderTest < ActiveRecord::TestCase
     devs = Developer.all
     last_devs = Developer.limit(3).offset(9).find devs.map(&:id)
     assert_equal 2, last_devs.size
+    assert_equal "fixture_10", last_devs[0].name
+    assert_equal "Jamis", last_devs[1].name
   end
 
   def test_find_with_large_number
-    assert_raises(ActiveRecord::RecordNotFound) { Topic.find('9999999999999999999999999999999') }
+    assert_raises(ActiveRecord::RecordNotFound) { Topic.find("9999999999999999999999999999999") }
   end
 
   def test_find_by_with_large_number
-    assert_nil Topic.find_by(id: '9999999999999999999999999999999')
+    assert_nil Topic.find_by(id: "9999999999999999999999999999999")
   end
 
   def test_find_by_id_with_large_number
-    assert_nil Topic.find_by_id('9999999999999999999999999999999')
+    assert_nil Topic.find_by_id("9999999999999999999999999999999")
   end
 
   def test_find_on_relation_with_large_number
-    assert_nil Topic.where('1=1').find_by(id: 9999999999999999999999999999999)
+    assert_raises(ActiveRecord::RecordNotFound) do
+      Topic.where("1=1").find(9999999999999999999999999999999)
+    end
+  end
+
+  def test_find_by_on_relation_with_large_number
+    assert_nil Topic.where("1=1").find_by(id: 9999999999999999999999999999999)
   end
 
   def test_find_by_bang_on_relation_with_large_number
     assert_raises(ActiveRecord::RecordNotFound) do
-      Topic.where('1=1').find_by!(id: 9999999999999999999999999999999)
+      Topic.where("1=1").find_by!(id: 9999999999999999999999999999999)
     end
   end
 
   def test_find_an_empty_array
-    assert_equal [], Topic.find([])
+    empty_array = []
+    result = Topic.find(empty_array)
+    assert_equal [], result
+    assert_not_same empty_array, result
   end
 
   def test_find_doesnt_have_implicit_ordering
@@ -239,7 +398,7 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_find_with_group_and_sanitized_having_method
-    developers = Developer.group(:salary).having("sum(salary) > ?", 10000).select('salary').to_a
+    developers = Developer.group(:salary).having("sum(salary) > ?", 10000).select("salary").to_a
     assert_equal 3, developers.size
     assert_equal 3, developers.map(&:salary).uniq.size
     assert developers.all? { |developer| developer.salary > 10000 }
@@ -264,8 +423,19 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal [Account], accounts.collect(&:class).uniq
   end
 
+  def test_find_by_association_subquery
+    author = authors(:david)
+    assert_equal author.post, Post.find_by(author: Author.where(id: author))
+    assert_equal author.post, Post.find_by(author_id: Author.where(id: author))
+  end
+
+  def test_find_by_and_where_consistency_with_active_record_instance
+    author = authors(:david)
+    assert_equal Post.where(author_id: author).take, Post.find_by(author_id: author)
+  end
+
   def test_take
-    assert_equal topics(:first), Topic.take
+    assert_equal topics(:first), Topic.where("title = 'The First Topic'").take
   end
 
   def test_take_failing
@@ -308,6 +478,7 @@ class FinderTest < ActiveRecord::TestCase
     expected = topics(:first)
     expected.touch # PostgreSQL changes the default order if no order clause is used
     assert_equal expected, Topic.first
+    assert_equal expected, Topic.limit(5).first
   end
 
   def test_model_class_responds_to_first_bang
@@ -330,6 +501,7 @@ class FinderTest < ActiveRecord::TestCase
     expected = topics(:second)
     expected.touch # PostgreSQL changes the default order if no order clause is used
     assert_equal expected, Topic.second
+    assert_equal expected, Topic.limit(5).second
   end
 
   def test_model_class_responds_to_second_bang
@@ -352,6 +524,7 @@ class FinderTest < ActiveRecord::TestCase
     expected = topics(:third)
     expected.touch # PostgreSQL changes the default order if no order clause is used
     assert_equal expected, Topic.third
+    assert_equal expected, Topic.limit(5).third
   end
 
   def test_model_class_responds_to_third_bang
@@ -374,6 +547,7 @@ class FinderTest < ActiveRecord::TestCase
     expected = topics(:fourth)
     expected.touch # PostgreSQL changes the default order if no order clause is used
     assert_equal expected, Topic.fourth
+    assert_equal expected, Topic.limit(5).fourth
   end
 
   def test_model_class_responds_to_fourth_bang
@@ -396,6 +570,7 @@ class FinderTest < ActiveRecord::TestCase
     expected = topics(:fifth)
     expected.touch # PostgreSQL changes the default order if no order clause is used
     assert_equal expected, Topic.fifth
+    assert_equal expected, Topic.limit(5).fifth
   end
 
   def test_model_class_responds_to_fifth_bang
@@ -406,6 +581,66 @@ class FinderTest < ActiveRecord::TestCase
     end
   end
 
+  def test_second_to_last
+    assert_equal topics(:fourth).title, Topic.second_to_last.title
+
+    # test with offset
+    assert_equal topics(:fourth), Topic.offset(1).second_to_last
+    assert_equal topics(:fourth), Topic.offset(2).second_to_last
+    assert_equal topics(:fourth), Topic.offset(3).second_to_last
+    assert_nil Topic.offset(4).second_to_last
+    assert_nil Topic.offset(5).second_to_last
+
+    # test with limit
+    assert_nil Topic.limit(1).second
+    assert_nil Topic.limit(1).second_to_last
+  end
+
+  def test_second_to_last_have_primary_key_order_by_default
+    expected = topics(:fourth)
+    expected.touch # PostgreSQL changes the default order if no order clause is used
+    assert_equal expected, Topic.second_to_last
+  end
+
+  def test_model_class_responds_to_second_to_last_bang
+    assert Topic.second_to_last!
+    Topic.delete_all
+    assert_raises_with_message ActiveRecord::RecordNotFound, "Couldn't find Topic" do
+      Topic.second_to_last!
+    end
+  end
+
+  def test_third_to_last
+    assert_equal topics(:third).title, Topic.third_to_last.title
+
+    # test with offset
+    assert_equal topics(:third), Topic.offset(1).third_to_last
+    assert_equal topics(:third), Topic.offset(2).third_to_last
+    assert_nil Topic.offset(3).third_to_last
+    assert_nil Topic.offset(4).third_to_last
+    assert_nil Topic.offset(5).third_to_last
+
+    # test with limit
+    assert_nil Topic.limit(1).third
+    assert_nil Topic.limit(1).third_to_last
+    assert_nil Topic.limit(2).third
+    assert_nil Topic.limit(2).third_to_last
+  end
+
+  def test_third_to_last_have_primary_key_order_by_default
+    expected = topics(:third)
+    expected.touch # PostgreSQL changes the default order if no order clause is used
+    assert_equal expected, Topic.third_to_last
+  end
+
+  def test_model_class_responds_to_third_to_last_bang
+    assert Topic.third_to_last!
+    Topic.delete_all
+    assert_raises_with_message ActiveRecord::RecordNotFound, "Couldn't find Topic" do
+      Topic.third_to_last!
+    end
+  end
+
   def test_last_bang_present
     assert_nothing_raised do
       assert_equal topics(:second), Topic.where("title = 'The Second Topic of the day'").last!
@@ -427,25 +662,83 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_take_and_first_and_last_with_integer_should_use_sql_limit
-    assert_sql(/LIMIT 3|ROWNUM <= 3/) { Topic.take(3).entries }
-    assert_sql(/LIMIT 2|ROWNUM <= 2/) { Topic.first(2).entries }
-    assert_sql(/LIMIT 5|ROWNUM <= 5/) { Topic.last(5).entries }
+    assert_sql(/LIMIT|ROWNUM <=|FETCH FIRST/) { Topic.take(3).entries }
+    assert_sql(/LIMIT|ROWNUM <=|FETCH FIRST/) { Topic.first(2).entries }
+    assert_sql(/LIMIT|ROWNUM <=|FETCH FIRST/) { Topic.last(5).entries }
   end
 
   def test_last_with_integer_and_order_should_keep_the_order
     assert_equal Topic.order("title").to_a.last(2), Topic.order("title").last(2)
   end
 
-  def test_last_with_integer_and_order_should_not_use_sql_limit
-    query = assert_sql { Topic.order("title").last(5).entries }
-    assert_equal 1, query.length
-    assert_no_match(/LIMIT/, query.first)
+  def test_last_with_integer_and_order_should_use_sql_limit
+    relation = Topic.order("title")
+    assert_queries(1) { relation.last(5) }
+    assert_not_predicate relation, :loaded?
+  end
+
+  def test_last_with_integer_and_reorder_should_use_sql_limit
+    relation = Topic.reorder("title")
+    assert_queries(1) { relation.last(5) }
+    assert_not_predicate relation, :loaded?
   end
 
-  def test_last_with_integer_and_reorder_should_not_use_sql_limit
-    query = assert_sql { Topic.reorder("title").last(5).entries }
-    assert_equal 1, query.length
-    assert_no_match(/LIMIT/, query.first)
+  def test_last_on_loaded_relation_should_not_use_sql
+    relation = Topic.limit(10).load
+    assert_no_queries do
+      relation.last
+      relation.last(2)
+    end
+  end
+
+  def test_last_with_irreversible_order
+    assert_raises(ActiveRecord::IrreversibleOrderError) do
+      Topic.order(Arel.sql("coalesce(author_name, title)")).last
+    end
+  end
+
+  def test_last_on_relation_with_limit_and_offset
+    post = posts("sti_comments")
+
+    comments = post.comments.order(id: :asc)
+    assert_equal comments.limit(2).to_a.last, comments.limit(2).last
+    assert_equal comments.limit(2).to_a.last(2), comments.limit(2).last(2)
+    assert_equal comments.limit(2).to_a.last(3), comments.limit(2).last(3)
+
+    assert_equal comments.offset(2).to_a.last, comments.offset(2).last
+    assert_equal comments.offset(2).to_a.last(2), comments.offset(2).last(2)
+    assert_equal comments.offset(2).to_a.last(3), comments.offset(2).last(3)
+
+    comments = comments.offset(1)
+    assert_equal comments.limit(2).to_a.last, comments.limit(2).last
+    assert_equal comments.limit(2).to_a.last(2), comments.limit(2).last(2)
+    assert_equal comments.limit(2).to_a.last(3), comments.limit(2).last(3)
+  end
+
+  def test_first_on_relation_with_limit_and_offset
+    post = posts("sti_comments")
+
+    comments = post.comments.order(id: :asc)
+    assert_equal comments.limit(2).to_a.first, comments.limit(2).first
+    assert_equal comments.limit(2).to_a.first(2), comments.limit(2).first(2)
+    assert_equal comments.limit(2).to_a.first(3), comments.limit(2).first(3)
+
+    assert_equal comments.offset(2).to_a.first, comments.offset(2).first
+    assert_equal comments.offset(2).to_a.first(2), comments.offset(2).first(2)
+    assert_equal comments.offset(2).to_a.first(3), comments.offset(2).first(3)
+
+    comments = comments.offset(1)
+    assert_equal comments.limit(2).to_a.first, comments.limit(2).first
+    assert_equal comments.limit(2).to_a.first(2), comments.limit(2).first(2)
+    assert_equal comments.limit(2).to_a.first(3), comments.limit(2).first(3)
+  end
+
+  def test_first_have_determined_order_by_default
+    expected = [companies(:second_client), companies(:another_client)]
+    clients = Client.where(name: expected.map(&:name))
+
+    assert_equal expected, clients.first(2)
+    assert_equal expected, clients.limit(5).first(2)
   end
 
   def test_take_and_first_and_last_with_integer_should_return_an_array
@@ -464,12 +757,12 @@ class FinderTest < ActiveRecord::TestCase
 
   def test_find_only_some_columns
     topic = Topic.select("author_name").find(1)
-    assert_raise(ActiveModel::MissingAttributeError) {topic.title}
-    assert_raise(ActiveModel::MissingAttributeError) {topic.title?}
+    assert_raise(ActiveModel::MissingAttributeError) { topic.title }
+    assert_raise(ActiveModel::MissingAttributeError) { topic.title? }
     assert_nil topic.read_attribute("title")
     assert_equal "David", topic.author_name
-    assert !topic.attribute_present?("title")
-    assert !topic.attribute_present?(:title)
+    assert_not topic.attribute_present?("title")
+    assert_not topic.attribute_present?(:title)
     assert topic.attribute_present?("author_name")
     assert_respond_to topic, "author_name"
   end
@@ -484,9 +777,14 @@ class FinderTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::RecordNotFound) { Topic.where(approved: true).find(1) }
   end
 
-  def test_find_on_hash_conditions_with_explicit_table_name
-    assert Topic.where('topics.approved' => false).find(1)
-    assert_raise(ActiveRecord::RecordNotFound) { Topic.where('topics.approved' => true).find(1) }
+  def test_find_on_hash_conditions_with_qualified_attribute_dot_notation_string
+    assert Topic.where("topics.approved" => false).find(1)
+    assert_raise(ActiveRecord::RecordNotFound) { Topic.where("topics.approved" => true).find(1) }
+  end
+
+  def test_find_on_hash_conditions_with_qualified_attribute_dot_notation_symbol
+    assert Topic.where('topics.approved': false).find(1)
+    assert_raise(ActiveRecord::RecordNotFound) { Topic.where('topics.approved': true).find(1) }
   end
 
   def test_find_on_hash_conditions_with_hashed_table_name
@@ -495,28 +793,28 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_find_on_combined_explicit_and_hashed_table_names
-    assert Topic.where('topics.approved' => false, topics: { author_name: "David" }).find(1)
-    assert_raise(ActiveRecord::RecordNotFound) { Topic.where('topics.approved' => true, topics: { author_name: "David" }).find(1) }
-    assert_raise(ActiveRecord::RecordNotFound) { Topic.where('topics.approved' => false, topics: { author_name: "Melanie" }).find(1) }
+    assert Topic.where("topics.approved" => false, topics: { author_name: "David" }).find(1)
+    assert_raise(ActiveRecord::RecordNotFound) { Topic.where("topics.approved" => true, topics: { author_name: "David" }).find(1) }
+    assert_raise(ActiveRecord::RecordNotFound) { Topic.where("topics.approved" => false, topics: { author_name: "Melanie" }).find(1) }
   end
 
   def test_find_with_hash_conditions_on_joined_table
-    firms = Firm.joins(:account).where(:accounts => { :credit_limit => 50 })
+    firms = Firm.joins(:account).where(accounts: { credit_limit: 50 })
     assert_equal 1, firms.size
     assert_equal companies(:first_firm), firms.first
   end
 
   def test_find_with_hash_conditions_on_joined_table_and_with_range
-    firms = DependentFirm.joins(:account).where(name: 'RailsCore', accounts: { credit_limit: 55..60 })
+    firms = DependentFirm.joins(:account).where(name: "RailsCore", accounts: { credit_limit: 55..60 })
     assert_equal 1, firms.size
     assert_equal companies(:rails_core), firms.first
   end
 
   def test_find_on_hash_conditions_with_explicit_table_name_and_aggregate
     david = customers(:david)
-    assert Customer.where('customers.name' => david.name, :address => david.address).find(david.id)
+    assert Customer.where("customers.name" => david.name, :address => david.address).find(david.id)
     assert_raise(ActiveRecord::RecordNotFound) {
-      Customer.where('customers.name' => david.name + "1", :address => david.address).find(david.id)
+      Customer.where("customers.name" => david.name + "1", :address => david.address).find(david.id)
     }
   end
 
@@ -525,34 +823,42 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_find_on_hash_conditions_with_range
-    assert_equal [1,2], Topic.where(id: 1..2).to_a.map(&:id).sort
+    assert_equal [1, 2], Topic.where(id: 1..2).to_a.map(&:id).sort
     assert_raise(ActiveRecord::RecordNotFound) { Topic.where(id: 2..3).find(1) }
   end
 
   def test_find_on_hash_conditions_with_end_exclusive_range
-    assert_equal [1,2,3], Topic.where(id: 1..3).to_a.map(&:id).sort
-    assert_equal [1,2], Topic.where(id: 1...3).to_a.map(&:id).sort
+    assert_equal [1, 2, 3], Topic.where(id: 1..3).to_a.map(&:id).sort
+    assert_equal [1, 2], Topic.where(id: 1...3).to_a.map(&:id).sort
     assert_raise(ActiveRecord::RecordNotFound) { Topic.where(id: 2...3).find(3) }
   end
 
   def test_find_on_hash_conditions_with_multiple_ranges
-    assert_equal [1,2,3], Comment.where(id: 1..3, post_id: 1..2).to_a.map(&:id).sort
+    assert_equal [1, 2, 3], Comment.where(id: 1..3, post_id: 1..2).to_a.map(&:id).sort
     assert_equal [1], Comment.where(id: 1..1, post_id: 1..10).to_a.map(&:id).sort
   end
 
   def test_find_on_hash_conditions_with_array_of_integers_and_ranges
-    assert_equal [1,2,3,5,6,7,8,9], Comment.where(id: [1..2, 3, 5, 6..8, 9]).to_a.map(&:id).sort
+    assert_equal [1, 2, 3, 5, 6, 7, 8, 9], Comment.where(id: [1..2, 3, 5, 6..8, 9]).to_a.map(&:id).sort
   end
 
   def test_find_on_hash_conditions_with_array_of_ranges
-    assert_equal [1,2,6,7,8], Comment.where(id: [1..2, 6..8]).to_a.map(&:id).sort
+    assert_equal [1, 2, 6, 7, 8], Comment.where(id: [1..2, 6..8]).to_a.map(&:id).sort
+  end
+
+  def test_find_on_hash_conditions_with_open_ended_range
+    assert_equal [1, 2, 3], Comment.where(id: Float::INFINITY..3).to_a.map(&:id).sort
+  end
+
+  def test_find_on_hash_conditions_with_numeric_range_for_string
+    topic = Topic.create!(title: "12 Factor App")
+    assert_equal [topic], Topic.where(title: 10..2).to_a
   end
 
   def test_find_on_multiple_hash_conditions
     assert Topic.where(author_name: "David", title: "The First Topic", replies_count: 1, approved: false).find(1)
     assert_raise(ActiveRecord::RecordNotFound) { Topic.where(author_name: "David", title: "The First Topic", replies_count: 1, approved: true).find(1) }
     assert_raise(ActiveRecord::RecordNotFound) { Topic.where(author_name: "David", title: "HHC", replies_count: 1, approved: false).find(1) }
-    assert_raise(ActiveRecord::RecordNotFound) { Topic.where(author_name: "David", title: "The First Topic", replies_count: 1, approved: true).find(1) }
   end
 
   def test_condition_interpolation
@@ -587,9 +893,9 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_hash_condition_find_with_array
-    p1, p2 = Post.limit(2).order('id asc').to_a
-    assert_equal [p1, p2], Post.where(id: [p1, p2]).order('id asc').to_a
-    assert_equal [p1, p2], Post.where(id: [p1, p2.id]).order('id asc').to_a
+    p1, p2 = Post.limit(2).order("id asc").to_a
+    assert_equal [p1, p2], Post.where(id: [p1, p2]).order("id asc").to_a
+    assert_equal [p1, p2], Post.where(id: [p1, p2.id]).order("id asc").to_a
   end
 
   def test_hash_condition_find_with_nil
@@ -601,56 +907,75 @@ class FinderTest < ActiveRecord::TestCase
   def test_hash_condition_find_with_aggregate_having_one_mapping
     balance = customers(:david).balance
     assert_kind_of Money, balance
-    found_customer = Customer.where(:balance => balance).first
+    found_customer = Customer.where(balance: balance).first
     assert_equal customers(:david), found_customer
   end
 
+  def test_hash_condition_find_with_aggregate_having_three_mappings_array
+    david_address = customers(:david).address
+    zaphod_address = customers(:zaphod).address
+    barney_address = customers(:barney).address
+    assert_kind_of Address, david_address
+    assert_kind_of Address, zaphod_address
+    found_customers = Customer.where(address: [david_address, zaphod_address, barney_address])
+    assert_equal [customers(:david), customers(:zaphod), customers(:barney)], found_customers.sort_by(&:id)
+  end
+
+  def test_hash_condition_find_with_aggregate_having_one_mapping_array
+    david_balance = customers(:david).balance
+    zaphod_balance = customers(:zaphod).balance
+    assert_kind_of Money, david_balance
+    assert_kind_of Money, zaphod_balance
+    found_customers = Customer.where(balance: [david_balance, zaphod_balance])
+    assert_equal [customers(:david), customers(:zaphod)], found_customers.sort_by(&:id)
+  end
+
   def test_hash_condition_find_with_aggregate_attribute_having_same_name_as_field_and_key_value_being_aggregate
     gps_location = customers(:david).gps_location
     assert_kind_of GpsLocation, gps_location
-    found_customer = Customer.where(:gps_location => gps_location).first
+    found_customer = Customer.where(gps_location: gps_location).first
     assert_equal customers(:david), found_customer
   end
 
   def test_hash_condition_find_with_aggregate_having_one_mapping_and_key_value_being_attribute_value
     balance = customers(:david).balance
     assert_kind_of Money, balance
-    found_customer = Customer.where(:balance => balance.amount).first
+    found_customer = Customer.where(balance: balance.amount).first
     assert_equal customers(:david), found_customer
   end
 
   def test_hash_condition_find_with_aggregate_attribute_having_same_name_as_field_and_key_value_being_attribute_value
     gps_location = customers(:david).gps_location
     assert_kind_of GpsLocation, gps_location
-    found_customer = Customer.where(:gps_location => gps_location.gps_location).first
+    found_customer = Customer.where(gps_location: gps_location.gps_location).first
     assert_equal customers(:david), found_customer
   end
 
   def test_hash_condition_find_with_aggregate_having_three_mappings
     address = customers(:david).address
     assert_kind_of Address, address
-    found_customer = Customer.where(:address => address).first
+    found_customer = Customer.where(address: address).first
     assert_equal customers(:david), found_customer
   end
 
   def test_hash_condition_find_with_one_condition_being_aggregate_and_another_not
     address = customers(:david).address
     assert_kind_of Address, address
-    found_customer = Customer.where(:address => address, :name => customers(:david).name).first
+    found_customer = Customer.where(address: address, name: customers(:david).name).first
     assert_equal customers(:david), found_customer
   end
 
   def test_condition_utc_time_interpolation_with_default_timezone_local
-    with_env_tz 'America/New_York' do
+    with_env_tz "America/New_York" do
       with_timezone_config default: :local do
         topic = Topic.first
-        assert_equal topic, Topic.where(['written_on = ?', topic.written_on.getutc]).first
+        assert_equal topic, Topic.where(["written_on = ?", topic.written_on.getutc]).first
       end
     end
   end
 
   def test_hash_condition_utc_time_interpolation_with_default_timezone_local
-    with_env_tz 'America/New_York' do
+    with_env_tz "America/New_York" do
       with_timezone_config default: :local do
         topic = Topic.first
         assert_equal topic, Topic.where(written_on: topic.written_on.getutc).first
@@ -659,16 +984,16 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_condition_local_time_interpolation_with_default_timezone_utc
-    with_env_tz 'America/New_York' do
+    with_env_tz "America/New_York" do
       with_timezone_config default: :utc do
         topic = Topic.first
-        assert_equal topic, Topic.where(['written_on = ?', topic.written_on.getlocal]).first
+        assert_equal topic, Topic.where(["written_on = ?", topic.written_on.getlocal]).first
       end
     end
   end
 
   def test_hash_condition_local_time_interpolation_with_default_timezone_utc
-    with_env_tz 'America/New_York' do
+    with_env_tz "America/New_York" do
       with_timezone_config default: :utc do
         topic = Topic.first
         assert_equal topic, Topic.where(written_on: topic.written_on.getlocal).first
@@ -685,109 +1010,27 @@ class FinderTest < ActiveRecord::TestCase
       Company.where(["id=? AND name = ?", 2]).first
     }
     assert_raise(ActiveRecord::PreparedStatementInvalid) {
-     Company.where(["id=?", 2, 3, 4]).first
+      Company.where(["id=?", 2, 3, 4]).first
     }
   end
 
   def test_bind_variables_with_quotes
-    Company.create("name" => "37signals' go'es agains")
-    assert Company.where(["name = ?", "37signals' go'es agains"]).first
+    Company.create("name" => "37signals' go'es against")
+    assert Company.where(["name = ?", "37signals' go'es against"]).first
   end
 
   def test_named_bind_variables_with_quotes
-    Company.create("name" => "37signals' go'es agains")
-    assert Company.where(["name = :name", {name: "37signals' go'es agains"}]).first
-  end
-
-  def test_bind_arity
-    assert_nothing_raised                                 { bind '' }
-    assert_raise(ActiveRecord::PreparedStatementInvalid) { bind '', 1 }
-
-    assert_raise(ActiveRecord::PreparedStatementInvalid) { bind '?' }
-    assert_nothing_raised                                 { bind '?', 1 }
-    assert_raise(ActiveRecord::PreparedStatementInvalid) { bind '?', 1, 1  }
+    Company.create("name" => "37signals' go'es against")
+    assert Company.where(["name = :name", { name: "37signals' go'es against" }]).first
   end
 
   def test_named_bind_variables
-    assert_equal '1', bind(':a', :a => 1) # ' ruby-mode
-    assert_equal '1 1', bind(':a :a', :a => 1)  # ' ruby-mode
-
-    assert_nothing_raised { bind("'+00:00'", :foo => "bar") }
-
     assert_kind_of Firm, Company.where(["name = :name", { name: "37signals" }]).first
     assert_nil Company.where(["name = :name", { name: "37signals!" }]).first
     assert_nil Company.where(["name = :name", { name: "37signals!' OR 1=1" }]).first
     assert_kind_of Time, Topic.where(["id = :id", { id: 1 }]).first.written_on
   end
 
-  class SimpleEnumerable
-    include Enumerable
-
-    def initialize(ary)
-      @ary = ary
-    end
-
-    def each(&b)
-      @ary.each(&b)
-    end
-  end
-
-  def test_bind_enumerable
-    quoted_abc = %(#{ActiveRecord::Base.connection.quote('a')},#{ActiveRecord::Base.connection.quote('b')},#{ActiveRecord::Base.connection.quote('c')})
-
-    assert_equal '1,2,3', bind('?', [1, 2, 3])
-    assert_equal quoted_abc, bind('?', %w(a b c))
-
-    assert_equal '1,2,3', bind(':a', :a => [1, 2, 3])
-    assert_equal quoted_abc, bind(':a', :a => %w(a b c)) # '
-
-    assert_equal '1,2,3', bind('?', SimpleEnumerable.new([1, 2, 3]))
-    assert_equal quoted_abc, bind('?', SimpleEnumerable.new(%w(a b c)))
-
-    assert_equal '1,2,3', bind(':a', :a => SimpleEnumerable.new([1, 2, 3]))
-    assert_equal quoted_abc, bind(':a', :a => SimpleEnumerable.new(%w(a b c))) # '
-  end
-
-  def test_bind_empty_enumerable
-    quoted_nil = ActiveRecord::Base.connection.quote(nil)
-    assert_equal quoted_nil, bind('?', [])
-    assert_equal " in (#{quoted_nil})", bind(' in (?)', [])
-    assert_equal "foo in (#{quoted_nil})", bind('foo in (?)', [])
-  end
-
-  def test_bind_empty_string
-    quoted_empty = ActiveRecord::Base.connection.quote('')
-    assert_equal quoted_empty, bind('?', '')
-  end
-
-  def test_bind_chars
-    quoted_bambi = ActiveRecord::Base.connection.quote("Bambi")
-    quoted_bambi_and_thumper = ActiveRecord::Base.connection.quote("Bambi\nand\nThumper")
-    assert_equal "name=#{quoted_bambi}", bind('name=?', "Bambi")
-    assert_equal "name=#{quoted_bambi_and_thumper}", bind('name=?', "Bambi\nand\nThumper")
-    assert_equal "name=#{quoted_bambi}", bind('name=?', "Bambi".mb_chars)
-    assert_equal "name=#{quoted_bambi_and_thumper}", bind('name=?', "Bambi\nand\nThumper".mb_chars)
-  end
-
-  def test_bind_record
-    o = Struct.new(:quoted_id).new(1)
-    assert_equal '1', bind('?', o)
-
-    os = [o] * 3
-    assert_equal '1,1,1', bind('?', os)
-  end
-
-  def test_named_bind_with_postgresql_type_casts
-    l = Proc.new { bind(":a::integer '2009-01-01'::date", :a => '10') }
-    assert_nothing_raised(&l)
-    assert_equal "#{ActiveRecord::Base.connection.quote('10')}::integer '2009-01-01'::date", l.call
-  end
-
-  def test_string_sanitation
-    assert_not_equal "'something ' 1=1'", ActiveRecord::Base.sanitize("something ' 1=1")
-    assert_equal "'something; select table'", ActiveRecord::Base.sanitize("something; select table")
-  end
-
   def test_count_by_sql
     assert_equal(0, Entrant.count_by_sql("SELECT COUNT(*) FROM entrants WHERE id > 3"))
     assert_equal(1, Entrant.count_by_sql(["SELECT COUNT(*) FROM entrants WHERE id > ?", 2]))
@@ -807,7 +1050,7 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_find_by_on_attribute_that_is_a_reserved_word
-    dog_alias = 'Dog'
+    dog_alias = "Dog"
     dog = Dog.create(alias: dog_alias)
 
     assert_equal dog, Dog.find_by_alias(dog_alias)
@@ -824,7 +1067,7 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_find_by_one_attribute_with_conditions
-    assert_equal accounts(:rails_core_account), Account.where('firm_id = ?', 6).find_by_credit_limit(50)
+    assert_equal accounts(:rails_core_account), Account.where("firm_id = ?", 6).find_by_credit_limit(50)
   end
 
   def test_find_by_one_attribute_that_is_an_aggregate
@@ -864,12 +1107,12 @@ class FinderTest < ActiveRecord::TestCase
   def test_dynamic_finder_on_one_attribute_with_conditions_returns_same_results_after_caching
     # ensure this test can run independently of order
     class << Account; self; end.send(:remove_method, :find_by_credit_limit) if Account.public_methods.include?(:find_by_credit_limit)
-    a = Account.where('firm_id = ?', 6).find_by_credit_limit(50)
-    assert_equal a, Account.where('firm_id = ?', 6).find_by_credit_limit(50) # find_by_credit_limit has been cached
+    a = Account.where("firm_id = ?", 6).find_by_credit_limit(50)
+    assert_equal a, Account.where("firm_id = ?", 6).find_by_credit_limit(50) # find_by_credit_limit has been cached
   end
 
   def test_find_by_one_attribute_with_several_options
-    assert_equal accounts(:unknown), Account.order('id DESC').where('id != ?', 3).find_by_credit_limit(50)
+    assert_equal accounts(:unknown), Account.order("id DESC").where("id != ?", 3).find_by_credit_limit(50)
   end
 
   def test_find_by_one_missing_attribute
@@ -892,15 +1135,6 @@ class FinderTest < ActiveRecord::TestCase
     assert_raise(ArgumentError) { Topic.find_by_title_and_author_name("The First Topic") }
   end
 
-  def test_find_last_with_offset
-    devs = Developer.order('id')
-
-    assert_equal devs[2], Developer.offset(2).first
-    assert_equal devs[-3], Developer.offset(2).last
-    assert_equal devs[-3], Developer.offset(2).last
-    assert_equal devs[-3], Developer.offset(2).order('id DESC').first
-  end
-
   def test_find_by_nil_attribute
     topic = Topic.find_by_last_read nil
     assert_not_nil topic
@@ -916,20 +1150,10 @@ class FinderTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::StatementInvalid) { Topic.find_by_sql "select 1 from badtable" }
   end
 
-  def test_find_all_with_join
-    developers_on_project_one = Developer.
-      joins('LEFT JOIN developers_projects ON developers.id = developers_projects.developer_id').
-      where('project_id=1').to_a
-    assert_equal 3, developers_on_project_one.length
-    developer_names = developers_on_project_one.map(&:name)
-    assert developer_names.include?('David')
-    assert developer_names.include?('Jamis')
-  end
-
   def test_joins_dont_clobber_id
     first = Firm.
-      joins('INNER JOIN companies clients ON clients.firm_id = companies.id').
-      where('companies.id = 1').first
+      joins("INNER JOIN companies clients ON clients.firm_id = companies.id").
+      where("companies.id = 1").first
     assert_equal 1, first.id
   end
 
@@ -943,12 +1167,12 @@ class FinderTest < ActiveRecord::TestCase
 
   def test_find_by_id_with_conditions_with_or
     assert_nothing_raised do
-      Post.where("posts.id <= 3 OR posts.#{QUOTED_TYPE} = 'Post'").find([1,2,3])
+      Post.where("posts.id <= 3 OR posts.#{QUOTED_TYPE} = 'Post'").find([1, 2, 3])
     end
   end
 
   def test_find_ignores_previously_inserted_record
-    Post.create!(:title => 'test', :body => 'it out')
+    Post.create!(title: "test", body: "it out")
     assert_equal [], Post.where(id: nil)
   end
 
@@ -957,13 +1181,13 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_find_by_empty_in_condition
-    assert_equal [], Post.where('id in (?)', [])
+    assert_equal [], Post.where("id in (?)", [])
   end
 
   def test_find_by_records
-    p1, p2 = Post.limit(2).order('id asc').to_a
-    assert_equal [p1, p2], Post.where(['id in (?)', [p1, p2]]).order('id asc')
-    assert_equal [p1, p2], Post.where(['id in (?)', [p1, p2.id]]).order('id asc')
+    p1, p2 = Post.limit(2).order("id asc").to_a
+    assert_equal [p1, p2], Post.where(["id in (?)", [p1, p2]]).order("id asc")
+    assert_equal [p1, p2], Post.where(["id in (?)", [p1, p2.id]]).order("id asc")
   end
 
   def test_select_value
@@ -975,8 +1199,8 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_select_values
-    assert_equal ["1","2","3","4","5","6","7","8","9", "10", "11"], Company.connection.select_values("SELECT id FROM companies ORDER BY id").map!(&:to_s)
-    assert_equal ["37signals","Summit","Microsoft", "Flamboyant Software", "Ex Nihilo", "RailsCore", "Leetsoft", "Jadedpixel", "Odegy", "Ex Nihilo Part Deux", "Apex"], Company.connection.select_values("SELECT name FROM companies ORDER BY id")
+    assert_equal ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10", "11"], Company.connection.select_values("SELECT id FROM companies ORDER BY id").map!(&:to_s)
+    assert_equal ["37signals", "Summit", "Microsoft", "Flamboyant Software", "Ex Nihilo", "RailsCore", "Leetsoft", "Jadedpixel", "Odegy", "Ex Nihilo Part Deux", "Apex"], Company.connection.select_values("SELECT name FROM companies ORDER BY id")
   end
 
   def test_select_rows
@@ -984,33 +1208,41 @@ class FinderTest < ActiveRecord::TestCase
       [["1", "1", nil, "37signals"],
        ["2", "1", "2", "Summit"],
        ["3", "1", "1", "Microsoft"]],
-      Company.connection.select_rows("SELECT id, firm_id, client_of, name FROM companies WHERE id IN (1,2,3) ORDER BY id").map! {|i| i.map! {|j| j.to_s unless j.nil?}})
+      Company.connection.select_rows("SELECT id, firm_id, client_of, name FROM companies WHERE id IN (1,2,3) ORDER BY id").map! { |i| i.map! { |j| j.to_s unless j.nil? } })
     assert_equal [["1", "37signals"], ["2", "Summit"], ["3", "Microsoft"]],
-      Company.connection.select_rows("SELECT id, name FROM companies WHERE id IN (1,2,3) ORDER BY id").map! {|i| i.map! {|j| j.to_s unless j.nil?}}
+      Company.connection.select_rows("SELECT id, name FROM companies WHERE id IN (1,2,3) ORDER BY id").map! { |i| i.map! { |j| j.to_s unless j.nil? } }
   end
 
   def test_find_with_order_on_included_associations_with_construct_finder_sql_for_association_limiting_and_is_distinct
-    assert_equal 2, Post.includes(authors: :author_address).order('author_addresses.id DESC ').limit(2).to_a.size
+    assert_equal 2, Post.includes(authors: :author_address).
+      where.not(author_addresses: { id: nil }).
+      order("author_addresses.id DESC").limit(2).to_a.size
 
     assert_equal 3, Post.includes(author: :author_address, authors: :author_address).
-                              order('author_addresses_authors.id DESC ').limit(3).to_a.size
+      where.not(author_addresses_authors: { id: nil }).
+      order("author_addresses_authors.id DESC").limit(3).to_a.size
+  end
+
+  def test_find_with_eager_loading_collection_and_ordering_by_collection_primary_key
+    assert_equal Post.first, Post.eager_load(comments: :ratings).
+      order("posts.id, ratings.id, comments.id").first
   end
 
   def test_find_with_nil_inside_set_passed_for_one_attribute
     client_of = Company.
       where(client_of: [2, 1, nil],
-            name: ['37signals', 'Summit', 'Microsoft']).
-      order('client_of DESC').
+            name: ["37signals", "Summit", "Microsoft"]).
+      order("client_of DESC").
       map(&:client_of)
 
-    assert client_of.include?(nil)
+    assert_includes client_of, nil
     assert_equal [2, 1].sort, client_of.compact.sort
   end
 
   def test_find_with_nil_inside_set_passed_for_attribute
     client_of = Company.
       where(client_of: [nil]).
-      order('client_of DESC').
+      order("client_of DESC").
       map(&:client_of)
 
     assert_equal [], client_of.compact
@@ -1018,20 +1250,30 @@ class FinderTest < ActiveRecord::TestCase
 
   def test_with_limiting_with_custom_select
     posts = Post.references(:authors).merge(
-      :includes => :author, :select => 'posts.*, authors.id as "author_id"',
-      :limit => 3, :order => 'posts.id'
+      includes: :author, select: 'posts.*, authors.id as "author_id"',
+      limit: 3, order: "posts.id"
     ).to_a
     assert_equal 3, posts.size
     assert_equal [0, 1, 1], posts.map(&:author_id).sort
   end
 
+  def test_find_one_message_on_primary_key
+    e = assert_raises(ActiveRecord::RecordNotFound) do
+      Car.find(0)
+    end
+    assert_equal 0, e.id
+    assert_equal "id", e.primary_key
+    assert_equal "Car", e.model
+    assert_equal "Couldn't find Car with 'id'=0", e.message
+  end
+
   def test_find_one_message_with_custom_primary_key
     table_with_custom_primary_key do |model|
       model.primary_key = :name
       e = assert_raises(ActiveRecord::RecordNotFound) do
-        model.find 'Hello World!'
+        model.find "Hello World!"
       end
-      assert_equal %Q{Couldn't find MercedesCar with 'name'=Hello World!}, e.message
+      assert_equal "Couldn't find MercedesCar with 'name'=Hello World!", e.message
     end
   end
 
@@ -1039,9 +1281,9 @@ class FinderTest < ActiveRecord::TestCase
     table_with_custom_primary_key do |model|
       model.primary_key = :name
       e = assert_raises(ActiveRecord::RecordNotFound) do
-        model.find 'Hello', 'World!'
+        model.find "Hello", "World!"
       end
-      assert_equal %Q{Couldn't find all MercedesCars with 'name': (Hello, World!) (found 0 results, but was looking for 2)}, e.message
+      assert_equal "Couldn't find all MercedesCars with 'name': (Hello, World!) (found 0 results, but was looking for 2).", e.message
     end
   end
 
@@ -1052,7 +1294,7 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   def test_finder_with_offset_string
-    assert_nothing_raised(ActiveRecord::StatementInvalid) { Topic.offset("3").to_a }
+    assert_nothing_raised { Topic.offset("3").to_a }
   end
 
   test "find_by with hash conditions returns the first matching record" do
@@ -1064,16 +1306,20 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   test "find_by with multi-arg conditions returns the first matching record" do
-    assert_equal posts(:eager_other), Post.find_by('id = ?', posts(:eager_other).id)
+    assert_equal posts(:eager_other), Post.find_by("id = ?", posts(:eager_other).id)
+  end
+
+  test "find_by with range conditions returns the first matching record" do
+    assert_equal posts(:eager_other), Post.find_by(id: posts(:eager_other).id...posts(:misc_by_bob).id)
   end
 
   test "find_by returns nil if the record is missing" do
-    assert_equal nil, Post.find_by("1 = 0")
+    assert_nil Post.find_by("1 = 0")
   end
 
   test "find_by with associations" do
     assert_equal authors(:david), Post.find_by(author: authors(:david)).author
-    assert_equal authors(:mary) , Post.find_by(author: authors(:mary) ).author
+    assert_equal authors(:mary), Post.find_by(author: authors(:mary)).author
   end
 
   test "find_by doesn't have implicit ordering" do
@@ -1089,7 +1335,7 @@ class FinderTest < ActiveRecord::TestCase
   end
 
   test "find_by! with multi-arg conditions returns the first matching record" do
-    assert_equal posts(:eager_other), Post.find_by!('id = ?', posts(:eager_other).id)
+    assert_equal posts(:eager_other), Post.find_by!("id = ?", posts(:eager_other).id)
   end
 
   test "find_by! doesn't have implicit ordering" do
@@ -1122,19 +1368,39 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal tyre2, zyke.tyres.custom_find_by(id: tyre2.id)
   end
 
-  protected
-    def bind(statement, *vars)
-      if vars.first.is_a?(Hash)
-        ActiveRecord::Base.send(:replace_named_bind_variables, statement, vars.first)
-      else
-        ActiveRecord::Base.send(:replace_bind_variables, statement, vars)
+  test "#skip_query_cache! for #exists?" do
+    Topic.cache do
+      assert_queries(1) do
+        Topic.exists?
+        Topic.exists?
+      end
+
+      assert_queries(2) do
+        Topic.all.skip_query_cache!.exists?
+        Topic.all.skip_query_cache!.exists?
+      end
+    end
+  end
+
+  test "#skip_query_cache! for #exists? with a limited eager load" do
+    Topic.cache do
+      assert_queries(1) do
+        Topic.eager_load(:replies).limit(1).exists?
+        Topic.eager_load(:replies).limit(1).exists?
+      end
+
+      assert_queries(2) do
+        Topic.eager_load(:replies).limit(1).skip_query_cache!.exists?
+        Topic.eager_load(:replies).limit(1).skip_query_cache!.exists?
       end
     end
+  end
 
+  private
     def table_with_custom_primary_key
       yield(Class.new(Toy) do
         def self.name
-          'MercedesCar'
+          "MercedesCar"
         end
       end)
     end
@@ -1143,5 +1409,4 @@ class FinderTest < ActiveRecord::TestCase
       err = assert_raises(exception_class) { block.call }
       assert_match message, err.message
     end
-
 end
diff --git a/activerecord/test/cases/fixture_set/file_test.rb b/activerecord/test/cases/fixture_set/file_test.rb
index 92efa8aca7..ff99988cb5 100644
--- a/activerecord/test/cases/fixture_set/file_test.rb
+++ b/activerecord/test/cases/fixture_set/file_test.rb
@@ -1,5 +1,7 @@
-require 'cases/helper'
-require 'tempfile'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "tempfile"
 
 module ActiveRecord
   class FixtureSet
@@ -15,7 +17,7 @@ module ActiveRecord
           called = true
           assert_equal 6, fh.to_a.length
         end
-        assert called, 'block called'
+        assert called, "block called"
       end
 
       def test_names
@@ -31,8 +33,8 @@ module ActiveRecord
 
       def test_values
         File.open(::File.join(FIXTURES_ROOT, "accounts.yml")) do |fh|
-          assert_equal [1,2,3,4,5,6].sort, fh.to_a.map(&:last).map { |x|
-            x['id']
+          assert_equal [1, 2, 3, 4, 5, 6].sort, fh.to_a.map(&:last).map { |x|
+            x["id"]
           }.sort
         end
       end
@@ -45,7 +47,7 @@ module ActiveRecord
       end
 
       def test_empty_file
-        tmp_yaml ['empty', 'yml'], '' do |t|
+        tmp_yaml ["empty", "yml"], "" do |t|
           assert_equal [], File.open(t.path) { |fh| fh.to_a }
         end
       end
@@ -53,7 +55,7 @@ module ActiveRecord
       # A valid YAML file is not necessarily a value Fixture file. Make sure
       # an exception is raised if the format is not valid Fixture format.
       def test_wrong_fixture_format_string
-        tmp_yaml ['empty', 'yml'], 'qwerty' do |t|
+        tmp_yaml ["empty", "yml"], "qwerty" do |t|
           assert_raises(ActiveRecord::Fixture::FormatError) do
             File.open(t.path) { |fh| fh.to_a }
           end
@@ -61,7 +63,7 @@ module ActiveRecord
       end
 
       def test_wrong_fixture_format_nested
-        tmp_yaml ['empty', 'yml'], 'one: two' do |t|
+        tmp_yaml ["empty", "yml"], "one: two" do |t|
           assert_raises(ActiveRecord::Fixture::FormatError) do
             File.open(t.path) { |fh| fh.to_a }
           end
@@ -75,9 +77,9 @@ module ActiveRecord
           end
         end
         yaml = "one:\n  name: <%= fixture_helper %>\n"
-        tmp_yaml ['curious', 'yml'], yaml do |t|
+        tmp_yaml ["curious", "yml"], yaml do |t|
           golden =
-              [["one", {"name" => "Fixture helper"}]]
+              [["one", { "name" => "Fixture helper" }]]
           assert_equal golden, File.open(t.path) { |fh| fh.to_a }
         end
         ActiveRecord::FixtureSet.context_class.class_eval do
@@ -95,15 +97,15 @@ one:
   File: <%= File.name %>
 END
 
-        golden = [['one', {
-          'ActiveRecord' => 'constant',
-          'ActiveRecord_FixtureSet' => 'constant',
-          'FixtureSet' => nil,
-          'ActiveRecord_FixtureSet_File' => 'constant',
-          'File' => 'File'
+        golden = [["one", {
+          "ActiveRecord" => "constant",
+          "ActiveRecord_FixtureSet" => "constant",
+          "FixtureSet" => nil,
+          "ActiveRecord_FixtureSet_File" => "constant",
+          "File" => "File"
         }]]
 
-        tmp_yaml ['curious', 'yml'], yaml do |t|
+        tmp_yaml ["curious", "yml"], yaml do |t|
           assert_equal golden, File.open(t.path) { |fh| fh.to_a }
         end
       end
@@ -113,8 +115,8 @@ END
       def test_independent_render_contexts
         yaml1 = "<% def leaked_method; 'leak'; end %>\n"
         yaml2 = "one:\n  name: <%= leaked_method %>\n"
-        tmp_yaml ['leaky', 'yml'], yaml1 do |t1|
-          tmp_yaml ['curious', 'yml'], yaml2 do |t2|
+        tmp_yaml ["leaky", "yml"], yaml1 do |t1|
+          tmp_yaml ["curious", "yml"], yaml2 do |t2|
             File.open(t1.path) { |fh| fh.to_a }
             assert_raises(NameError) do
               File.open(t2.path) { |fh| fh.to_a }
@@ -123,16 +125,34 @@ END
         end
       end
 
-      private
-      def tmp_yaml(name, contents)
-        t = Tempfile.new name
-        t.binmode
-        t.write contents
-        t.close
-        yield t
-      ensure
-        t.close true
+      def test_removes_fixture_config_row
+        File.open(::File.join(FIXTURES_ROOT, "other_posts.yml")) do |fh|
+          assert_equal(["second_welcome"], fh.each.map { |name, _| name })
+        end
+      end
+
+      def test_extracts_model_class_from_config_row
+        File.open(::File.join(FIXTURES_ROOT, "other_posts.yml")) do |fh|
+          assert_equal "Post", fh.model_class
+        end
       end
+
+      def test_erb_filename
+        filename = "filename.yaml"
+        erb = File.new(filename).send(:prepare_erb, "<% Rails.env %>\n")
+        assert_equal erb.filename, filename
+      end
+
+      private
+        def tmp_yaml(name, contents)
+          t = Tempfile.new name
+          t.binmode
+          t.write contents
+          t.close
+          yield t
+        ensure
+          t.close true
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/fixtures_test.rb b/activerecord/test/cases/fixtures_test.rb
index 03a187ae92..a5592fc86a 100644
--- a/activerecord/test/cases/fixtures_test.rb
+++ b/activerecord/test/cases/fixtures_test.rb
@@ -1,33 +1,40 @@
-require 'cases/helper'
-require 'models/admin'
-require 'models/admin/account'
-require 'models/admin/randomly_named_c1'
-require 'models/admin/user'
-require 'models/binary'
-require 'models/book'
-require 'models/bulb'
-require 'models/category'
-require 'models/company'
-require 'models/computer'
-require 'models/course'
-require 'models/developer'
-require 'models/computer'
-require 'models/joke'
-require 'models/matey'
-require 'models/parrot'
-require 'models/pirate'
-require 'models/doubloon'
-require 'models/post'
-require 'models/randomly_named_c1'
-require 'models/reply'
-require 'models/ship'
-require 'models/task'
-require 'models/topic'
-require 'models/traffic_light'
-require 'models/treasure'
-require 'tempfile'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/connection_helper"
+require "models/admin"
+require "models/admin/account"
+require "models/admin/randomly_named_c1"
+require "models/admin/user"
+require "models/binary"
+require "models/book"
+require "models/bulb"
+require "models/category"
+require "models/post"
+require "models/comment"
+require "models/company"
+require "models/computer"
+require "models/course"
+require "models/developer"
+require "models/dog"
+require "models/doubloon"
+require "models/joke"
+require "models/matey"
+require "models/other_dog"
+require "models/parrot"
+require "models/pirate"
+require "models/randomly_named_c1"
+require "models/reply"
+require "models/ship"
+require "models/task"
+require "models/topic"
+require "models/traffic_light"
+require "models/treasure"
+require "tempfile"
 
 class FixturesTest < ActiveRecord::TestCase
+  include ConnectionHelper
+
   self.use_instantiated_fixtures = true
   self.use_transactional_tests = false
 
@@ -52,13 +59,271 @@ class FixturesTest < ActiveRecord::TestCase
     end
   end
 
+  class InsertQuerySubscriber
+    attr_reader :events
+
+    def initialize
+      @events = []
+    end
+
+    def call(_, _, _, _, values)
+      @events << values[:sql] if values[:sql] =~ /INSERT/
+    end
+  end
+
+  if current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter)
+    def test_bulk_insert
+      begin
+        subscriber = InsertQuerySubscriber.new
+        subscription = ActiveSupport::Notifications.subscribe("sql.active_record", subscriber)
+        create_fixtures("bulbs")
+        assert_equal 1, subscriber.events.size, "It takes one INSERT query to insert two fixtures"
+      ensure
+        ActiveSupport::Notifications.unsubscribe(subscription)
+      end
+    end
+
+    def test_bulk_insert_multiple_table_with_a_multi_statement_query
+      subscriber = InsertQuerySubscriber.new
+      subscription = ActiveSupport::Notifications.subscribe("sql.active_record", subscriber)
+
+      create_fixtures("bulbs", "authors", "computers")
+
+      expected_sql = <<~EOS.chop
+        INSERT INTO #{ActiveRecord::Base.connection.quote_table_name("bulbs")} .*
+        INSERT INTO #{ActiveRecord::Base.connection.quote_table_name("authors")} .*
+        INSERT INTO #{ActiveRecord::Base.connection.quote_table_name("computers")} .*
+      EOS
+      assert_equal 1, subscriber.events.size
+      assert_match(/#{expected_sql}/, subscriber.events.first)
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscription)
+    end
+
+    def test_bulk_insert_with_a_multi_statement_query_raises_an_exception_when_any_insert_fails
+      require "models/aircraft"
+
+      assert_equal false, Aircraft.columns_hash["wheels_count"].null
+      fixtures = {
+        "aircraft" => [
+          { "name" => "working_aircrafts", "wheels_count" => 2 },
+          { "name" => "broken_aircrafts", "wheels_count" => nil },
+        ]
+      }
+
+      assert_no_difference "Aircraft.count" do
+        assert_raises(ActiveRecord::NotNullViolation) do
+          ActiveRecord::Base.connection.insert_fixtures_set(fixtures)
+        end
+      end
+    end
+
+    def test_bulk_insert_with_a_multi_statement_query_in_a_nested_transaction
+      fixtures = {
+        "traffic_lights" => [
+          { "location" => "US", "state" => ["NY"], "long_state" => ["a"] },
+        ]
+      }
+
+      assert_difference "TrafficLight.count" do
+        ActiveRecord::Base.transaction do
+          conn = ActiveRecord::Base.connection
+          assert_equal 1, conn.open_transactions
+          conn.insert_fixtures_set(fixtures)
+          assert_equal 1, conn.open_transactions
+        end
+      end
+    end
+  end
+
+  if current_adapter?(:Mysql2Adapter)
+    def test_bulk_insert_with_multi_statements_enabled
+      run_without_connection do |orig_connection|
+        ActiveRecord::Base.establish_connection(
+          orig_connection.merge(flags: %w[MULTI_STATEMENTS])
+        )
+
+        fixtures = {
+          "traffic_lights" => [
+            { "location" => "US", "state" => ["NY"], "long_state" => ["a"] },
+          ]
+        }
+
+        ActiveRecord::Base.connection.stub(:supports_set_server_option?, false) do
+          assert_nothing_raised do
+            conn = ActiveRecord::Base.connection
+            conn.execute("SELECT 1; SELECT 2;")
+            conn.raw_connection.abandon_results!
+          end
+
+          assert_difference "TrafficLight.count" do
+            ActiveRecord::Base.transaction do
+              conn = ActiveRecord::Base.connection
+              assert_equal 1, conn.open_transactions
+              conn.insert_fixtures_set(fixtures)
+              assert_equal 1, conn.open_transactions
+            end
+          end
+
+          assert_nothing_raised do
+            conn = ActiveRecord::Base.connection
+            conn.execute("SELECT 1; SELECT 2;")
+            conn.raw_connection.abandon_results!
+          end
+        end
+      end
+    end
+
+    def test_bulk_insert_with_multi_statements_disabled
+      run_without_connection do |orig_connection|
+        ActiveRecord::Base.establish_connection(
+          orig_connection.merge(flags: [])
+        )
+
+        fixtures = {
+          "traffic_lights" => [
+            { "location" => "US", "state" => ["NY"], "long_state" => ["a"] },
+          ]
+        }
+
+        ActiveRecord::Base.connection.stub(:supports_set_server_option?, false) do
+          assert_raises(ActiveRecord::StatementInvalid) do
+            conn = ActiveRecord::Base.connection
+            conn.execute("SELECT 1; SELECT 2;")
+            conn.raw_connection.abandon_results!
+          end
+
+          assert_difference "TrafficLight.count" do
+            conn = ActiveRecord::Base.connection
+            conn.insert_fixtures_set(fixtures)
+          end
+
+          assert_raises(ActiveRecord::StatementInvalid) do
+            conn = ActiveRecord::Base.connection
+            conn.execute("SELECT 1; SELECT 2;")
+            conn.raw_connection.abandon_results!
+          end
+        end
+      end
+    end
+
+    def test_insert_fixtures_set_raises_an_error_when_max_allowed_packet_is_smaller_than_fixtures_set_size
+      conn = ActiveRecord::Base.connection
+      mysql_margin = 2
+      packet_size = 1024
+      bytes_needed_to_have_a_1024_bytes_fixture = 858
+      fixtures = {
+        "traffic_lights" => [
+          { "location" => "US", "state" => ["NY"], "long_state" => ["a" * bytes_needed_to_have_a_1024_bytes_fixture] },
+        ]
+      }
+
+      conn.stub(:max_allowed_packet, packet_size - mysql_margin) do
+        error = assert_raises(ActiveRecord::ActiveRecordError) { conn.insert_fixtures_set(fixtures) }
+        assert_match(/Fixtures set is too large #{packet_size}\./, error.message)
+      end
+    end
+
+    def test_insert_fixture_set_when_max_allowed_packet_is_bigger_than_fixtures_set_size
+      conn = ActiveRecord::Base.connection
+      packet_size = 1024
+      fixtures = {
+        "traffic_lights" => [
+          { "location" => "US", "state" => ["NY"], "long_state" => ["a" * 51] },
+        ]
+      }
+
+      conn.stub(:max_allowed_packet, packet_size) do
+        assert_difference "TrafficLight.count" do
+          conn.insert_fixtures_set(fixtures)
+        end
+      end
+    end
+
+    def test_insert_fixtures_set_split_the_total_sql_into_two_chunks_smaller_than_max_allowed_packet
+      subscriber = InsertQuerySubscriber.new
+      subscription = ActiveSupport::Notifications.subscribe("sql.active_record", subscriber)
+      conn = ActiveRecord::Base.connection
+      packet_size = 1024
+      fixtures = {
+        "traffic_lights" => [
+          { "location" => "US", "state" => ["NY"], "long_state" => ["a" * 450] },
+        ],
+        "comments" => [
+          { "post_id" => 1, "body" => "a" * 450 },
+        ]
+      }
+
+      conn.stub(:max_allowed_packet, packet_size) do
+        conn.insert_fixtures_set(fixtures)
+
+        assert_equal 2, subscriber.events.size
+        assert_operator subscriber.events.first.bytesize, :<, packet_size
+        assert_operator subscriber.events.second.bytesize, :<, packet_size
+      end
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscription)
+    end
+
+    def test_insert_fixtures_set_concat_total_sql_into_a_single_packet_smaller_than_max_allowed_packet
+      subscriber = InsertQuerySubscriber.new
+      subscription = ActiveSupport::Notifications.subscribe("sql.active_record", subscriber)
+      conn = ActiveRecord::Base.connection
+      packet_size = 1024
+      fixtures = {
+        "traffic_lights" => [
+          { "location" => "US", "state" => ["NY"], "long_state" => ["a" * 200] },
+        ],
+        "comments" => [
+          { "post_id" => 1, "body" => "a" * 200 },
+        ]
+      }
+
+      conn.stub(:max_allowed_packet, packet_size) do
+        assert_difference ["TrafficLight.count", "Comment.count"], +1 do
+          conn.insert_fixtures_set(fixtures)
+        end
+      end
+      assert_equal 1, subscriber.events.size
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscription)
+    end
+  end
+
+  def test_auto_value_on_primary_key
+    fixtures = [
+      { "name" => "first", "wheels_count" => 2 },
+      { "name" => "second", "wheels_count" => 3 }
+    ]
+    conn = ActiveRecord::Base.connection
+    assert_nothing_raised do
+      conn.insert_fixtures_set({ "aircraft" => fixtures }, ["aircraft"])
+    end
+    result = conn.select_all("SELECT name, wheels_count FROM aircraft ORDER BY id")
+    assert_equal fixtures, result.to_a
+  end
+
+  def test_deprecated_insert_fixtures
+    fixtures = [
+      { "name" => "first", "wheels_count" => 2 },
+      { "name" => "second", "wheels_count" => 3 }
+    ]
+    conn = ActiveRecord::Base.connection
+    conn.delete("DELETE FROM aircraft")
+    assert_deprecated do
+      conn.insert_fixtures(fixtures, "aircraft")
+    end
+    result = conn.select_all("SELECT name, wheels_count FROM aircraft ORDER BY id")
+    assert_equal fixtures, result.to_a
+  end
+
   def test_broken_yaml_exception
-    badyaml = Tempfile.new ['foo', '.yml']
-    badyaml.write 'a: : '
+    badyaml = Tempfile.new ["foo", ".yml"]
+    badyaml.write "a: : "
     badyaml.flush
 
     dir  = File.dirname badyaml.path
-    name = File.basename badyaml.path, '.yml'
+    name = File.basename badyaml.path, ".yml"
     assert_raises(ActiveRecord::Fixture::FormatError) do
       ActiveRecord::FixtureSet.create_fixtures(dir, name)
     end
@@ -69,8 +334,8 @@ class FixturesTest < ActiveRecord::TestCase
 
   def test_create_fixtures
     fixtures = ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT, "parrots")
-    assert Parrot.find_by_name('Curious George'), 'George is not in the database'
-    assert fixtures.detect { |f| f.name == 'parrots' }, "no fixtures named 'parrots' in #{fixtures.map(&:name).inspect}"
+    assert Parrot.find_by_name("Curious George"), "George is not in the database"
+    assert fixtures.detect { |f| f.name == "parrots" }, "no fixtures named 'parrots' in #{fixtures.map(&:name).inspect}"
   end
 
   def test_multiple_clean_fixtures
@@ -81,10 +346,10 @@ class FixturesTest < ActiveRecord::TestCase
   end
 
   def test_create_symbol_fixtures
-    fixtures = ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT, :collections, :collections => Course) { Course.connection }
+    fixtures = ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT, :collections, collections: Course) { Course.connection }
 
-    assert Course.find_by_name('Collection'), 'course is not in the database'
-    assert fixtures.detect { |f| f.name == 'collections' }, "no fixtures named 'collections' in #{fixtures.map(&:name).inspect}"
+    assert Course.find_by_name("Collection"), "course is not in the database"
+    assert fixtures.detect { |f| f.name == "collections" }, "no fixtures named 'collections' in #{fixtures.map(&:name).inspect}"
   end
 
   def test_attributes
@@ -93,6 +358,24 @@ class FixturesTest < ActiveRecord::TestCase
     assert_nil(topics["second"]["author_email_address"])
   end
 
+  def test_no_args_returns_all
+    all_topics = topics
+    assert_equal 5, all_topics.length
+    assert_equal "The First Topic", all_topics.first["title"]
+    assert_equal 5, all_topics.last.id
+  end
+
+  def test_no_args_record_returns_all_without_array
+    all_binaries = binaries
+    assert_kind_of(Array, all_binaries)
+    assert_equal 2, binaries.length
+  end
+
+  def test_nil_raises
+    assert_raise(StandardError) { topics(nil) }
+    assert_raise(StandardError) { topics([nil]) }
+  end
+
   def test_inserts
     create_fixtures("topics")
     first_row = ActiveRecord::Base.connection.select_one("SELECT * FROM topics WHERE author_name = 'David'")
@@ -102,64 +385,62 @@ class FixturesTest < ActiveRecord::TestCase
     assert_nil(second_row["author_email_address"])
   end
 
-  if ActiveRecord::Base.connection.supports_migrations?
-    def test_inserts_with_pre_and_suffix
-      # Reset cache to make finds on the new table work
-      ActiveRecord::FixtureSet.reset_cache
-
-      ActiveRecord::Base.connection.create_table :prefix_other_topics_suffix do |t|
-        t.column :title, :string
-        t.column :author_name, :string
-        t.column :author_email_address, :string
-        t.column :written_on, :datetime
-        t.column :bonus_time, :time
-        t.column :last_read, :date
-        t.column :content, :string
-        t.column :approved, :boolean, :default => true
-        t.column :replies_count, :integer, :default => 0
-        t.column :parent_id, :integer
-        t.column :type, :string, :limit => 50
-      end
+  def test_inserts_with_pre_and_suffix
+    # Reset cache to make finds on the new table work
+    ActiveRecord::FixtureSet.reset_cache
 
-      # Store existing prefix/suffix
-      old_prefix = ActiveRecord::Base.table_name_prefix
-      old_suffix = ActiveRecord::Base.table_name_suffix
+    ActiveRecord::Base.connection.create_table :prefix_other_topics_suffix do |t|
+      t.column :title, :string
+      t.column :author_name, :string
+      t.column :author_email_address, :string
+      t.column :written_on, :datetime
+      t.column :bonus_time, :time
+      t.column :last_read, :date
+      t.column :content, :string
+      t.column :approved, :boolean, default: true
+      t.column :replies_count, :integer, default: 0
+      t.column :parent_id, :integer
+      t.column :type, :string, limit: 50
+    end
 
-      # Set a prefix/suffix we can test against
-      ActiveRecord::Base.table_name_prefix = 'prefix_'
-      ActiveRecord::Base.table_name_suffix = '_suffix'
+    # Store existing prefix/suffix
+    old_prefix = ActiveRecord::Base.table_name_prefix
+    old_suffix = ActiveRecord::Base.table_name_suffix
 
-      other_topic_klass = Class.new(ActiveRecord::Base) do
-        def self.name
-          "OtherTopic"
-        end
+    # Set a prefix/suffix we can test against
+    ActiveRecord::Base.table_name_prefix = "prefix_"
+    ActiveRecord::Base.table_name_suffix = "_suffix"
+
+    other_topic_klass = Class.new(ActiveRecord::Base) do
+      def self.name
+        "OtherTopic"
       end
+    end
 
-      topics = [create_fixtures("other_topics")].flatten.first
+    topics = [create_fixtures("other_topics")].flatten.first
 
-      # This checks for a caching problem which causes a bug in the fixtures
-      # class-level configuration helper.
-      assert_not_nil topics, "Fixture data inserted, but fixture objects not returned from create"
+    # This checks for a caching problem which causes a bug in the fixtures
+    # class-level configuration helper.
+    assert_not_nil topics, "Fixture data inserted, but fixture objects not returned from create"
 
-      first_row = ActiveRecord::Base.connection.select_one("SELECT * FROM prefix_other_topics_suffix WHERE author_name = 'David'")
-      assert_not_nil first_row, "The prefix_other_topics_suffix table appears to be empty despite create_fixtures: the row with author_name = 'David' was not found"
-      assert_equal("The First Topic", first_row["title"])
+    first_row = ActiveRecord::Base.connection.select_one("SELECT * FROM prefix_other_topics_suffix WHERE author_name = 'David'")
+    assert_not_nil first_row, "The prefix_other_topics_suffix table appears to be empty despite create_fixtures: the row with author_name = 'David' was not found"
+    assert_equal("The First Topic", first_row["title"])
 
-      second_row = ActiveRecord::Base.connection.select_one("SELECT * FROM prefix_other_topics_suffix WHERE author_name = 'Mary'")
-      assert_nil(second_row["author_email_address"])
+    second_row = ActiveRecord::Base.connection.select_one("SELECT * FROM prefix_other_topics_suffix WHERE author_name = 'Mary'")
+    assert_nil(second_row["author_email_address"])
 
-      assert_equal :prefix_other_topics_suffix, topics.table_name.to_sym
-      # This assertion should preferably be the last in the list, because calling
-      # other_topic_klass.table_name sets a class-level instance variable
-      assert_equal :prefix_other_topics_suffix, other_topic_klass.table_name.to_sym
+    assert_equal :prefix_other_topics_suffix, topics.table_name.to_sym
+    # This assertion should preferably be the last in the list, because calling
+    # other_topic_klass.table_name sets a class-level instance variable
+    assert_equal :prefix_other_topics_suffix, other_topic_klass.table_name.to_sym
 
-    ensure
-      # Restore prefix/suffix to its previous values
-      ActiveRecord::Base.table_name_prefix = old_prefix
-      ActiveRecord::Base.table_name_suffix = old_suffix
+  ensure
+    # Restore prefix/suffix to its previous values
+    ActiveRecord::Base.table_name_prefix = old_prefix
+    ActiveRecord::Base.table_name_suffix = old_suffix
 
-      ActiveRecord::Base.connection.drop_table :prefix_other_topics_suffix rescue nil
-    end
+    ActiveRecord::Base.connection.drop_table :prefix_other_topics_suffix rescue nil
   end
 
   def test_insert_with_datetime
@@ -170,7 +451,7 @@ class FixturesTest < ActiveRecord::TestCase
 
   def test_logger_level_invariant
     level = ActiveRecord::Base.logger.level
-    create_fixtures('topics')
+    create_fixtures("topics")
     assert_equal level, ActiveRecord::Base.logger.level
   end
 
@@ -184,7 +465,6 @@ class FixturesTest < ActiveRecord::TestCase
   end
 
   def test_fixtures_from_root_yml_with_instantiation
-    # assert_equal 2, @accounts.size
     assert_equal 50, @unknown.credit_limit
   end
 
@@ -193,37 +473,63 @@ class FixturesTest < ActiveRecord::TestCase
   end
 
   def test_empty_yaml_fixture
-    assert_not_nil ActiveRecord::FixtureSet.new( Account.connection, "accounts", Account, FIXTURES_ROOT + "/naked/yml/accounts")
+    assert_not_nil ActiveRecord::FixtureSet.new(nil, "accounts", Account, FIXTURES_ROOT + "/naked/yml/accounts")
   end
 
   def test_empty_yaml_fixture_with_a_comment_in_it
-    assert_not_nil ActiveRecord::FixtureSet.new( Account.connection, "companies", Company, FIXTURES_ROOT + "/naked/yml/companies")
+    assert_not_nil ActiveRecord::FixtureSet.new(nil, "companies", Company, FIXTURES_ROOT + "/naked/yml/companies")
   end
 
   def test_nonexistent_fixture_file
     nonexistent_fixture_path = FIXTURES_ROOT + "/imnothere"
 
-    #sanity check to make sure that this file never exists
-    assert Dir[nonexistent_fixture_path+"*"].empty?
+    # sanity check to make sure that this file never exists
+    assert_empty Dir[nonexistent_fixture_path + "*"]
 
     assert_raise(Errno::ENOENT) do
-      ActiveRecord::FixtureSet.new( Account.connection, "companies", Company, nonexistent_fixture_path)
+      ActiveRecord::FixtureSet.new(nil, "companies", Company, nonexistent_fixture_path)
     end
   end
 
   def test_dirty_dirty_yaml_file
-    assert_raise(ActiveRecord::Fixture::FormatError) do
-      ActiveRecord::FixtureSet.new( Account.connection, "courses", Course, FIXTURES_ROOT + "/naked/yml/courses")
+    fixture_path = FIXTURES_ROOT + "/naked/yml/courses"
+    error = assert_raise(ActiveRecord::Fixture::FormatError) do
+      ActiveRecord::FixtureSet.new(nil, "courses", Course, fixture_path)
+    end
+    assert_equal "fixture is not a hash: #{fixture_path}.yml", error.to_s
+  end
+
+  def test_yaml_file_with_one_invalid_fixture
+    fixture_path = FIXTURES_ROOT + "/naked/yml/courses_with_invalid_key"
+    error = assert_raise(ActiveRecord::Fixture::FormatError) do
+      ActiveRecord::FixtureSet.new(nil, "courses", Course, fixture_path)
+    end
+    assert_equal "fixture key is not a hash: #{fixture_path}.yml, keys: [\"two\"]", error.to_s
+  end
+
+  def test_yaml_file_with_invalid_column
+    e = assert_raise(ActiveRecord::Fixture::FixtureError) do
+      ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT + "/naked/yml", "parrots")
+    end
+
+    if current_adapter?(:SQLite3Adapter)
+      assert_equal(%(table "parrots" has no column named "arrr".), e.message)
+    else
+      assert_equal(%(table "parrots" has no columns named "arrr", "foobar".), e.message)
     end
   end
 
+  def test_yaml_file_with_symbol_columns
+    ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT + "/naked/yml", "trees")
+  end
+
   def test_omap_fixtures
     assert_nothing_raised do
-      fixtures = ActiveRecord::FixtureSet.new(Account.connection, 'categories', Category, FIXTURES_ROOT + "/categories_ordered")
+      fixtures = ActiveRecord::FixtureSet.new(nil, "categories", Category, FIXTURES_ROOT + "/categories_ordered")
 
       fixtures.each.with_index do |(name, fixture), i|
         assert_equal "fixture_no_#{i}", name
-        assert_equal "Category #{i}", fixture['name']
+        assert_equal "Category #{i}", fixture["name"]
       end
     end
   end
@@ -239,10 +545,11 @@ class FixturesTest < ActiveRecord::TestCase
   end
 
   def test_binary_in_fixtures
-    data = File.open(ASSETS_ROOT + "/flowers.jpg", 'rb') { |f| f.read }
-    data.force_encoding('ASCII-8BIT')
+    data = File.open(ASSETS_ROOT + "/flowers.jpg", "rb") { |f| f.read }
+    data.force_encoding("ASCII-8BIT")
     data.freeze
     assert_equal data, @flowers.data
+    assert_equal data, @binary_helper.data
   end
 
   def test_serialized_fixtures
@@ -250,26 +557,27 @@ class FixturesTest < ActiveRecord::TestCase
   end
 
   def test_fixtures_are_set_up_with_database_env_variable
-    db_url_tmp = ENV['DATABASE_URL']
-    ENV['DATABASE_URL'] = "sqlite3::memory:"
-    ActiveRecord::Base.stubs(:configurations).returns({})
-    test_case = Class.new(ActiveRecord::TestCase) do
-      fixtures :accounts
-
-      def test_fixtures
-        assert accounts(:signals37)
+    db_url_tmp = ENV["DATABASE_URL"]
+    ENV["DATABASE_URL"] = "sqlite3::memory:"
+    ActiveRecord::Base.stub(:configurations, {}) do
+      test_case = Class.new(ActiveRecord::TestCase) do
+        fixtures :accounts
+
+        def test_fixtures
+          assert accounts(:signals37)
+        end
       end
-    end
 
-    result = test_case.new(:test_fixtures).run
+      result = test_case.new(:test_fixtures).run
 
-    assert result.passed?, "Expected #{result.name} to pass:\n#{result}"
+      assert result.passed?, "Expected #{result.name} to pass:\n#{result}"
+    end
   ensure
-    ENV['DATABASE_URL'] = db_url_tmp
+    ENV["DATABASE_URL"] = db_url_tmp
   end
 end
 
-class HasManyThroughFixture < ActiveSupport::TestCase
+class HasManyThroughFixture < ActiveRecord::TestCase
   def make_model(name)
     Class.new(ActiveRecord::Base) { define_singleton_method(:name) { name } }
   end
@@ -280,17 +588,17 @@ class HasManyThroughFixture < ActiveSupport::TestCase
     treasure = make_model "Treasure"
 
     pt.table_name = "parrots_treasures"
-    pt.belongs_to :parrot, :anonymous_class => parrot
-    pt.belongs_to :treasure, :anonymous_class => treasure
+    pt.belongs_to :parrot, anonymous_class: parrot
+    pt.belongs_to :treasure, anonymous_class: treasure
 
-    parrot.has_many :parrot_treasures, :anonymous_class => pt
-    parrot.has_many :treasures, :through => :parrot_treasures
+    parrot.has_many :parrot_treasures, anonymous_class: pt
+    parrot.has_many :treasures, through: :parrot_treasures
 
-    parrots = File.join FIXTURES_ROOT, 'parrots'
+    parrots = File.join FIXTURES_ROOT, "parrots"
 
-    fs = ActiveRecord::FixtureSet.new parrot.connection, "parrots", parrot, parrots
+    fs = ActiveRecord::FixtureSet.new(nil, "parrots", parrot, parrots)
     rows = fs.table_rows
-    assert_equal load_has_and_belongs_to_many['parrots_treasures'], rows['parrots_treasures']
+    assert_equal load_has_and_belongs_to_many["parrots_treasures"], rows["parrots_treasures"]
   end
 
   def test_has_many_through_with_renamed_table
@@ -298,26 +606,30 @@ class HasManyThroughFixture < ActiveSupport::TestCase
     parrot = make_model "Parrot"
     treasure = make_model "Treasure"
 
-    pt.belongs_to :parrot, :anonymous_class => parrot
-    pt.belongs_to :treasure, :anonymous_class => treasure
+    pt.belongs_to :parrot, anonymous_class: parrot
+    pt.belongs_to :treasure, anonymous_class: treasure
 
-    parrot.has_many :parrot_treasures, :anonymous_class => pt
-    parrot.has_many :treasures, :through => :parrot_treasures
+    parrot.has_many :parrot_treasures, anonymous_class: pt
+    parrot.has_many :treasures, through: :parrot_treasures
 
-    parrots = File.join FIXTURES_ROOT, 'parrots'
+    parrots = File.join FIXTURES_ROOT, "parrots"
 
-    fs = ActiveRecord::FixtureSet.new parrot.connection, "parrots", parrot, parrots
+    fs = ActiveRecord::FixtureSet.new(nil, "parrots", parrot, parrots)
     rows = fs.table_rows
-    assert_equal load_has_and_belongs_to_many['parrots_treasures'], rows['parrot_treasures']
+    assert_equal load_has_and_belongs_to_many["parrots_treasures"], rows["parrot_treasures"]
+  end
+
+  def test_has_and_belongs_to_many_order
+    assert_equal ["parrots", "parrots_treasures"], load_has_and_belongs_to_many.keys
   end
 
   def load_has_and_belongs_to_many
     parrot = make_model "Parrot"
     parrot.has_and_belongs_to_many :treasures
 
-    parrots = File.join FIXTURES_ROOT, 'parrots'
+    parrots = File.join FIXTURES_ROOT, "parrots"
 
-    fs = ActiveRecord::FixtureSet.new parrot.connection, "parrots", parrot, parrots
+    fs = ActiveRecord::FixtureSet.new(nil, "parrots", parrot, parrots)
     fs.table_rows
   end
 end
@@ -326,9 +638,10 @@ if Account.connection.respond_to?(:reset_pk_sequence!)
   class FixturesResetPkSequenceTest < ActiveRecord::TestCase
     fixtures :accounts
     fixtures :companies
+    self.use_transactional_tests = false
 
     def setup
-      @instances = [Account.new(:credit_limit => 50), Company.new(:name => 'RoR Consulting'), Course.new(name: 'Test')]
+      @instances = [Account.new(credit_limit: 50), Company.new(name: "RoR Consulting"), Course.new(name: "Test")]
       ActiveRecord::FixtureSet.reset_cache # make sure tables get reinitialized
     end
 
@@ -357,7 +670,7 @@ if Account.connection.respond_to?(:reset_pk_sequence!)
     def test_create_fixtures_resets_sequences_when_not_cached
       @instances.each do |instance|
         max_id = create_fixtures(instance.class.table_name).first.fixtures.inject(0) do |_max_id, (_, fixture)|
-          fixture_id = fixture['id'].to_i
+          fixture_id = fixture["id"].to_i
           fixture_id > _max_id ? fixture_id : _max_id
         end
 
@@ -374,14 +687,14 @@ class FixturesWithoutInstantiationTest < ActiveRecord::TestCase
   fixtures :topics, :developers, :accounts
 
   def test_without_complete_instantiation
-    assert !defined?(@first)
-    assert !defined?(@topics)
-    assert !defined?(@developers)
-    assert !defined?(@accounts)
+    assert_not defined?(@first)
+    assert_not defined?(@topics)
+    assert_not defined?(@developers)
+    assert_not defined?(@accounts)
   end
 
   def test_fixtures_from_root_yml_without_instantiation
-    assert !defined?(@unknown), "@unknown is not defined"
+    assert_not defined?(@unknown), "@unknown is not defined"
   end
 
   def test_visibility_of_accessor_method
@@ -401,9 +714,11 @@ class FixturesWithoutInstantiationTest < ActiveRecord::TestCase
   end
 
   def test_reloading_fixtures_through_accessor_methods
+    topic = Struct.new(:title)
     assert_equal "The First Topic", topics(:first).title
-    @loaded_fixtures['topics']['first'].expects(:find).returns(stub(:title => "Fresh Topic!"))
-    assert_equal "Fresh Topic!", topics(:first, true).title
+    assert_called(@loaded_fixtures["topics"]["first"], :find, returns: topic.new("Fresh Topic!")) do
+      assert_equal "Fresh Topic!", topics(:first, true).title
+    end
   end
 end
 
@@ -414,7 +729,7 @@ class FixturesWithoutInstanceInstantiationTest < ActiveRecord::TestCase
   fixtures :topics, :developers, :accounts
 
   def test_without_instance_instantiation
-    assert !defined?(@first), "@first is not defined"
+    assert_not defined?(@first), "@first is not defined"
   end
 end
 
@@ -466,7 +781,6 @@ class SetupSubclassTest < SetupTest
   end
 end
 
-
 class OverlappingFixturesTest < ActiveRecord::TestCase
   fixtures :topics, :developers
   fixtures :developers, :accounts
@@ -497,18 +811,50 @@ class OverRideFixtureMethodTest < ActiveRecord::TestCase
 
   def topics(name)
     topic = super
-    topic.title = 'omg'
+    topic.title = "omg"
     topic
   end
 
   def test_fixture_methods_can_be_overridden
     x = topics :first
-    assert_equal 'omg', x.title
+    assert_equal "omg", x.title
+  end
+end
+
+class FixtureWithSetModelClassTest < ActiveRecord::TestCase
+  fixtures :other_posts, :other_comments
+
+  # Set to false to blow away fixtures cache and ensure our fixtures are loaded
+  # and thus takes into account the +set_model_class+.
+  self.use_transactional_tests = false
+
+  def test_uses_fixture_class_defined_in_yaml
+    assert_kind_of Post, other_posts(:second_welcome)
+  end
+
+  def test_loads_the_associations_to_fixtures_with_set_model_class
+    post = other_posts(:second_welcome)
+    comment = other_comments(:second_greetings)
+    assert_equal [comment], post.comments
+    assert_equal post, comment.post
+  end
+end
+
+class SetFixtureClassPrevailsTest < ActiveRecord::TestCase
+  set_fixture_class bad_posts: Post
+  fixtures :bad_posts
+
+  # Set to false to blow away fixtures cache and ensure our fixtures are loaded
+  # and thus takes into account the +set_model_class+.
+  self.use_transactional_tests = false
+
+  def test_uses_set_fixture_class
+    assert_kind_of Post, bad_posts(:bad_welcome)
   end
 end
 
 class CheckSetTableNameFixturesTest < ActiveRecord::TestCase
-  set_fixture_class :funny_jokes => Joke
+  set_fixture_class funny_jokes: Joke
   fixtures :funny_jokes
   # Set to false to blow away fixtures cache and ensure our fixtures are loaded
   # and thus takes into account our set_fixture_class
@@ -520,7 +866,7 @@ class CheckSetTableNameFixturesTest < ActiveRecord::TestCase
 end
 
 class FixtureNameIsNotTableNameFixturesTest < ActiveRecord::TestCase
-  set_fixture_class :items => Book
+  set_fixture_class items: Book
   fixtures :items
   # Set to false to blow away fixtures cache and ensure our fixtures are loaded
   # and thus takes into account our set_fixture_class
@@ -532,7 +878,7 @@ class FixtureNameIsNotTableNameFixturesTest < ActiveRecord::TestCase
 end
 
 class FixtureNameIsNotTableNameMultipleFixturesTest < ActiveRecord::TestCase
-  set_fixture_class :items => Book, :funny_jokes => Joke
+  set_fixture_class items: Book, funny_jokes: Joke
   fixtures :items, :funny_jokes
   # Set to false to blow away fixtures cache and ensure our fixtures are loaded
   # and thus takes into account our set_fixture_class
@@ -548,7 +894,7 @@ class FixtureNameIsNotTableNameMultipleFixturesTest < ActiveRecord::TestCase
 end
 
 class CustomConnectionFixturesTest < ActiveRecord::TestCase
-  set_fixture_class :courses => Course
+  set_fixture_class courses: Course
   fixtures :courses
   self.use_transactional_tests = false
 
@@ -563,7 +909,7 @@ class CustomConnectionFixturesTest < ActiveRecord::TestCase
 end
 
 class TransactionalFixturesOnCustomConnectionTest < ActiveRecord::TestCase
-  set_fixture_class :courses => Course
+  set_fixture_class courses: Course
   fixtures :courses
   self.use_transactional_tests = true
 
@@ -577,6 +923,66 @@ class TransactionalFixturesOnCustomConnectionTest < ActiveRecord::TestCase
   end
 end
 
+class TransactionalFixturesOnConnectionNotification < ActiveRecord::TestCase
+  self.use_transactional_tests = true
+  self.use_instantiated_fixtures = false
+
+  def test_transaction_created_on_connection_notification
+    connection = Class.new do
+      attr_accessor :pool
+
+      def transaction_open?; end
+      def begin_transaction(*args); end
+      def rollback_transaction(*args); end
+    end.new
+
+    connection.pool = Class.new do
+      def lock_thread=(lock_thread); end
+    end.new
+
+    assert_called_with(connection, :begin_transaction, [joinable: false]) do
+      fire_connection_notification(connection)
+    end
+  end
+
+  def test_notification_established_transactions_are_rolled_back
+    connection = Class.new do
+      attr_accessor :rollback_transaction_called
+      attr_accessor :pool
+
+      def transaction_open?; true; end
+      def begin_transaction(*args); end
+      def rollback_transaction(*args)
+        @rollback_transaction_called = true
+      end
+    end.new
+
+    connection.pool = Class.new do
+      def lock_thread=(lock_thread); end
+    end.new
+
+    fire_connection_notification(connection)
+    teardown_fixtures
+
+    assert(connection.rollback_transaction_called, "Expected <mock connection>#rollback_transaction to be called but was not")
+  end
+
+  private
+
+    def fire_connection_notification(connection)
+      assert_called_with(ActiveRecord::Base.connection_handler, :retrieve_connection, ["book"], returns: connection) do
+        message_bus = ActiveSupport::Notifications.instrumenter
+        payload = {
+          spec_name: "book",
+          config: nil,
+          connection_id: connection.object_id
+        }
+
+        message_bus.instrument("!connection.active_record", payload) { }
+      end
+    end
+end
+
 class InvalidTableNameFixturesTest < ActiveRecord::TestCase
   fixtures :funny_jokes
   # Set to false to blow away fixtures cache and ensure our fixtures are loaded
@@ -591,7 +997,7 @@ class InvalidTableNameFixturesTest < ActiveRecord::TestCase
 end
 
 class CheckEscapedYamlFixturesTest < ActiveRecord::TestCase
-  set_fixture_class :funny_jokes => Joke
+  set_fixture_class funny_jokes: Joke
   fixtures :funny_jokes
   # Set to false to blow away fixtures cache and ensure our fixtures are loaded
   # and thus takes into account our set_fixture_class
@@ -634,7 +1040,7 @@ class FixturesBrokenRollbackTest < ActiveRecord::TestCase
 
   private
     def load_fixtures(config)
-      raise 'argh'
+      raise "argh"
     end
 end
 
@@ -644,7 +1050,7 @@ class LoadAllFixturesTest < ActiveRecord::TestCase
     self.class.fixtures :all
 
     if File.symlink? FIXTURES_ROOT + "/all/admin"
-      assert_equal %w(admin/accounts admin/users developers people tasks), fixture_table_names.sort
+      assert_equal %w(admin/accounts admin/users developers namespaced/accounts people tasks), fixture_table_names.sort
     end
   ensure
     ActiveRecord::FixtureSet.reset_cache
@@ -653,11 +1059,11 @@ end
 
 class LoadAllFixturesWithPathnameTest < ActiveRecord::TestCase
   def test_all_there
-    self.class.fixture_path = Pathname.new(FIXTURES_ROOT).join('all')
+    self.class.fixture_path = Pathname.new(FIXTURES_ROOT).join("all")
     self.class.fixtures :all
 
     if File.symlink? FIXTURES_ROOT + "/all/admin"
-      assert_equal %w(admin/accounts admin/users developers people tasks), fixture_table_names.sort
+      assert_equal %w(admin/accounts admin/users developers namespaced/accounts people tasks), fixture_table_names.sort
     end
   ensure
     ActiveRecord::FixtureSet.reset_cache
@@ -666,7 +1072,7 @@ end
 
 class FasterFixturesTest < ActiveRecord::TestCase
   self.use_transactional_tests = false
-  fixtures :categories, :authors
+  fixtures :categories, :authors, :author_addresses
 
   def load_extra_fixture(name)
     fixture = create_fixtures(name).first
@@ -675,28 +1081,30 @@ class FasterFixturesTest < ActiveRecord::TestCase
   end
 
   def test_cache
-    assert ActiveRecord::FixtureSet.fixture_is_cached?(ActiveRecord::Base.connection, 'categories')
-    assert ActiveRecord::FixtureSet.fixture_is_cached?(ActiveRecord::Base.connection, 'authors')
+    assert ActiveRecord::FixtureSet.fixture_is_cached?(ActiveRecord::Base.connection, "categories")
+    assert ActiveRecord::FixtureSet.fixture_is_cached?(ActiveRecord::Base.connection, "authors")
 
     assert_no_queries do
-      create_fixtures('categories')
-      create_fixtures('authors')
+      create_fixtures("categories")
+      create_fixtures("authors")
     end
 
-    load_extra_fixture('posts')
-    assert ActiveRecord::FixtureSet.fixture_is_cached?(ActiveRecord::Base.connection, 'posts')
+    load_extra_fixture("posts")
+    assert ActiveRecord::FixtureSet.fixture_is_cached?(ActiveRecord::Base.connection, "posts")
     self.class.setup_fixture_accessors :posts
-    assert_equal 'Welcome to the weblog', posts(:welcome).title
+    assert_equal "Welcome to the weblog", posts(:welcome).title
   end
 end
 
 class FoxyFixturesTest < ActiveRecord::TestCase
+  # Set to false to blow away fixtures cache and ensure our fixtures are loaded
+  self.use_transactional_tests = false
   fixtures :parrots, :parrots_pirates, :pirates, :treasures, :mateys, :ships, :computers,
            :developers, :"admin/accounts", :"admin/users", :live_parrots, :dead_parrots, :books
 
-  if ActiveRecord::Base.connection.adapter_name == 'PostgreSQL'
-    require 'models/uuid_parent'
-    require 'models/uuid_child'
+  if ActiveRecord::Base.connection.adapter_name == "PostgreSQL"
+    require "models/uuid_parent"
+    require "models/uuid_child"
     fixtures :uuid_parents, :uuid_children
   end
 
@@ -713,8 +1121,8 @@ class FoxyFixturesTest < ActiveRecord::TestCase
     assert_equal 207281424, ActiveRecord::FixtureSet.identify(:ruby)
     assert_equal 1066363776, ActiveRecord::FixtureSet.identify(:sapphire_2)
 
-    assert_equal 'f92b6bda-0d0d-5fe1-9124-502b18badded', ActiveRecord::FixtureSet.identify(:daddy, :uuid)
-    assert_equal 'b4b10018-ad47-595d-b42f-d8bdaa6d01bf', ActiveRecord::FixtureSet.identify(:sonny, :uuid)
+    assert_equal "f92b6bda-0d0d-5fe1-9124-502b18badded", ActiveRecord::FixtureSet.identify(:daddy, :uuid)
+    assert_equal "b4b10018-ad47-595d-b42f-d8bdaa6d01bf", ActiveRecord::FixtureSet.identify(:sonny, :uuid)
   end
 
   TIMESTAMP_COLUMNS = %w(created_at created_on updated_at updated_on)
@@ -783,13 +1191,13 @@ class FoxyFixturesTest < ActiveRecord::TestCase
   def test_supports_inline_habtm
     assert(parrots(:george).treasures.include?(treasures(:diamond)))
     assert(parrots(:george).treasures.include?(treasures(:sapphire)))
-    assert(!parrots(:george).treasures.include?(treasures(:ruby)))
+    assert_not(parrots(:george).treasures.include?(treasures(:ruby)))
   end
 
   def test_supports_inline_habtm_with_specified_id
     assert(parrots(:polly).treasures.include?(treasures(:ruby)))
     assert(parrots(:polly).treasures.include?(treasures(:sapphire)))
-    assert(!parrots(:polly).treasures.include?(treasures(:diamond)))
+    assert_not(parrots(:polly).treasures.include?(treasures(:diamond)))
   end
 
   def test_supports_yaml_arrays
@@ -812,7 +1220,7 @@ class FoxyFixturesTest < ActiveRecord::TestCase
     assert_equal("X marks the spot!", pirates(:mark).catchphrase)
   end
 
-  def test_supports_label_interpolation_for_fixnum_label
+  def test_supports_label_interpolation_for_integer_label
     assert_equal("#1 pirate!", pirates(1).catchphrase)
   end
 
@@ -839,15 +1247,15 @@ class FoxyFixturesTest < ActiveRecord::TestCase
   end
 
   def test_namespaced_models
-    assert admin_accounts(:signals37).users.include?(admin_users(:david))
+    assert_includes admin_accounts(:signals37).users, admin_users(:david)
     assert_equal 2, admin_accounts(:signals37).users.size
   end
 
   def test_resolves_enums
-    assert books(:awdr).published?
-    assert books(:awdr).read?
-    assert books(:rfr).proposed?
-    assert books(:ddd).published?
+    assert_predicate books(:awdr), :published?
+    assert_predicate books(:awdr), :read?
+    assert_predicate books(:rfr), :proposed?
+    assert_predicate books(:ddd), :published?
   end
 end
 
@@ -864,14 +1272,14 @@ end
 class CustomNameForFixtureOrModelTest < ActiveRecord::TestCase
   ActiveRecord::FixtureSet.reset_cache
 
-  set_fixture_class :randomly_named_a9         =>
+  set_fixture_class :randomly_named_a9 =>
                         ClassNameThatDoesNotFollowCONVENTIONS,
                     :'admin/randomly_named_a9' =>
                         Admin::ClassNameThatDoesNotFollowCONVENTIONS1,
-                    'admin/randomly_named_b0'  =>
+                    "admin/randomly_named_b0"  =>
                         Admin::ClassNameThatDoesNotFollowCONVENTIONS2
 
-  fixtures :randomly_named_a9, 'admin/randomly_named_a9',
+  fixtures :randomly_named_a9, "admin/randomly_named_a9",
            :'admin/randomly_named_b0'
 
   def test_named_accessor_for_randomly_named_fixture_and_class
@@ -887,8 +1295,8 @@ class CustomNameForFixtureOrModelTest < ActiveRecord::TestCase
   end
 
   def test_table_name_is_defined_in_the_model
-    assert_equal 'randomly_named_table2', ActiveRecord::FixtureSet::all_loaded_fixtures["admin/randomly_named_a9"].table_name
-    assert_equal 'randomly_named_table2', Admin::ClassNameThatDoesNotFollowCONVENTIONS1.table_name
+    assert_equal "randomly_named_table2", ActiveRecord::FixtureSet.all_loaded_fixtures["admin/randomly_named_a9"].table_name
+    assert_equal "randomly_named_table2", Admin::ClassNameThatDoesNotFollowCONVENTIONS1.table_name
   end
 end
 
@@ -913,3 +1321,46 @@ class FixturesWithAbstractBelongsTo < ActiveRecord::TestCase
     assert_equal pirates(:blackbeard), doubloons(:blackbeards_doubloon).pirate
   end
 end
+
+class FixtureClassNamesTest < ActiveRecord::TestCase
+  def setup
+    @saved_cache = fixture_class_names.dup
+  end
+
+  def teardown
+    fixture_class_names.replace(@saved_cache)
+  end
+
+  test "fixture_class_names returns nil for unregistered identifier" do
+    assert_nil fixture_class_names["unregistered_identifier"]
+  end
+end
+
+class SameNameDifferentDatabaseFixturesTest < ActiveRecord::TestCase
+  fixtures :dogs, :other_dogs
+
+  test "fixtures are properly loaded" do
+    # Force loading the fixtures again to reproduce issue
+    ActiveRecord::FixtureSet.reset_cache
+    create_fixtures("dogs", "other_dogs")
+
+    assert_kind_of Dog, dogs(:sophie)
+    assert_kind_of OtherDog, other_dogs(:lassie)
+  end
+end
+
+class NilFixturePathTest < ActiveRecord::TestCase
+  test "raises an error when all fixtures loaded" do
+    error = assert_raises(StandardError) do
+      TestCase = Class.new(ActiveRecord::TestCase)
+      TestCase.class_eval do
+        self.fixture_path = nil
+        fixtures :all
+      end
+    end
+    assert_equal <<~MSG.squish, error.message
+      No fixture path found.
+      Please set `NilFixturePathTest::TestCase.fixture_path`.
+    MSG
+  end
+end
diff --git a/activerecord/test/cases/forbidden_attributes_protection_test.rb b/activerecord/test/cases/forbidden_attributes_protection_test.rb
index f4e7646f03..101fa118c8 100644
--- a/activerecord/test/cases/forbidden_attributes_protection_test.rb
+++ b/activerecord/test/cases/forbidden_attributes_protection_test.rb
@@ -1,14 +1,22 @@
-require 'cases/helper'
-require 'active_support/core_ext/hash/indifferent_access'
-require 'models/person'
-require 'models/company'
+# frozen_string_literal: true
 
-class ProtectedParams < ActiveSupport::HashWithIndifferentAccess
+require "cases/helper"
+require "active_support/core_ext/hash/indifferent_access"
+
+require "models/company"
+require "models/person"
+require "models/ship"
+require "models/ship_part"
+require "models/treasure"
+
+class ProtectedParams
   attr_accessor :permitted
   alias :permitted? :permitted
 
+  delegate :keys, :key?, :has_key?, :empty?, to: :@parameters
+
   def initialize(attributes)
-    super(attributes)
+    @parameters = attributes.with_indifferent_access
     @permitted = false
   end
 
@@ -17,6 +25,18 @@ class ProtectedParams < ActiveSupport::HashWithIndifferentAccess
     self
   end
 
+  def [](key)
+    @parameters[key]
+  end
+
+  def to_h
+    @parameters
+  end
+
+  def stringify_keys
+    dup
+  end
+
   def dup
     super.tap do |duplicate|
       duplicate.instance_variable_set :@permitted, @permitted
@@ -26,40 +46,40 @@ end
 
 class ForbiddenAttributesProtectionTest < ActiveRecord::TestCase
   def test_forbidden_attributes_cannot_be_used_for_mass_assignment
-    params = ProtectedParams.new(first_name: 'Guille', gender: 'm')
+    params = ProtectedParams.new(first_name: "Guille", gender: "m")
     assert_raises(ActiveModel::ForbiddenAttributesError) do
       Person.new(params)
     end
   end
 
   def test_permitted_attributes_can_be_used_for_mass_assignment
-    params = ProtectedParams.new(first_name: 'Guille', gender: 'm')
+    params = ProtectedParams.new(first_name: "Guille", gender: "m")
     params.permit!
     person = Person.new(params)
 
-    assert_equal 'Guille', person.first_name
-    assert_equal 'm', person.gender
+    assert_equal "Guille", person.first_name
+    assert_equal "m", person.gender
   end
 
   def test_forbidden_attributes_cannot_be_used_for_sti_inheritance_column
-    params = ProtectedParams.new(type: 'Client')
+    params = ProtectedParams.new(type: "Client")
     assert_raises(ActiveModel::ForbiddenAttributesError) do
       Company.new(params)
     end
   end
 
   def test_permitted_attributes_can_be_used_for_sti_inheritance_column
-    params = ProtectedParams.new(type: 'Client')
+    params = ProtectedParams.new(type: "Client")
     params.permit!
     person = Company.new(params)
     assert_equal person.class, Client
   end
 
   def test_regular_hash_should_still_be_used_for_mass_assignment
-    person = Person.new(first_name: 'Guille', gender: 'm')
+    person = Person.new(first_name: "Guille", gender: "m")
 
-    assert_equal 'Guille', person.first_name
-    assert_equal 'm', person.gender
+    assert_equal "Guille", person.first_name
+    assert_equal "m", person.gender
   end
 
   def test_blank_attributes_should_not_raise
@@ -68,32 +88,79 @@ class ForbiddenAttributesProtectionTest < ActiveRecord::TestCase
   end
 
   def test_create_with_checks_permitted
-    params = ProtectedParams.new(first_name: 'Guille', gender: 'm')
+    params = ProtectedParams.new(first_name: "Guille", gender: "m")
 
     assert_raises(ActiveModel::ForbiddenAttributesError) do
       Person.create_with(params).create!
     end
   end
 
+  def test_create_with_works_with_permitted_params
+    params = ProtectedParams.new(first_name: "Guille").permit!
+
+    person = Person.create_with(params).create!
+    assert_equal "Guille", person.first_name
+  end
+
   def test_create_with_works_with_params_values
-    params = ProtectedParams.new(first_name: 'Guille')
+    params = ProtectedParams.new(first_name: "Guille")
 
     person = Person.create_with(first_name: params[:first_name]).create!
-    assert_equal 'Guille', person.first_name
+    assert_equal "Guille", person.first_name
   end
 
   def test_where_checks_permitted
-    params = ProtectedParams.new(first_name: 'Guille', gender: 'm')
+    params = ProtectedParams.new(first_name: "Guille", gender: "m")
 
     assert_raises(ActiveModel::ForbiddenAttributesError) do
       Person.where(params).create!
     end
   end
 
+  def test_where_works_with_permitted_params
+    params = ProtectedParams.new(first_name: "Guille").permit!
+
+    person = Person.where(params).create!
+    assert_equal "Guille", person.first_name
+  end
+
   def test_where_works_with_params_values
-    params = ProtectedParams.new(first_name: 'Guille')
+    params = ProtectedParams.new(first_name: "Guille")
 
     person = Person.where(first_name: params[:first_name]).create!
-    assert_equal 'Guille', person.first_name
+    assert_equal "Guille", person.first_name
+  end
+
+  def test_where_not_checks_permitted
+    params = ProtectedParams.new(first_name: "Guille", gender: "m")
+
+    assert_raises(ActiveModel::ForbiddenAttributesError) do
+      Person.where().not(params)
+    end
+  end
+
+  def test_where_not_works_with_permitted_params
+    params = ProtectedParams.new(first_name: "Guille").permit!
+    Person.create!(params)
+    assert_empty Person.where.not(params).select { |p| p.first_name == "Guille" }
+  end
+
+  def test_strong_params_style_objects_work_with_singular_associations
+    params = ProtectedParams.new(name: "Stern", ship_attributes: ProtectedParams.new(name: "The Black Rock").permit!).permit!
+    part = ShipPart.new(params)
+
+    assert_equal "Stern", part.name
+    assert_equal "The Black Rock", part.ship.name
+  end
+
+  def test_strong_params_style_objects_work_with_collection_associations
+    params = ProtectedParams.new(
+      trinkets_attributes: ProtectedParams.new(
+        "0" => ProtectedParams.new(name: "Necklace").permit!,
+        "1" => ProtectedParams.new(name: "Spoon").permit!)).permit!
+    part = ShipPart.new(params)
+
+    assert_equal "Necklace", part.trinkets[0].name
+    assert_equal "Spoon", part.trinkets[1].name
   end
 end
diff --git a/activerecord/test/cases/habtm_destroy_order_test.rb b/activerecord/test/cases/habtm_destroy_order_test.rb
index 2ce0de360e..b15e1b48c4 100644
--- a/activerecord/test/cases/habtm_destroy_order_test.rb
+++ b/activerecord/test/cases/habtm_destroy_order_test.rb
@@ -1,24 +1,26 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "models/lesson"
 require "models/student"
 
 class HabtmDestroyOrderTest < ActiveRecord::TestCase
   test "may not delete a lesson with students" do
-    sicp = Lesson.new(:name => "SICP")
-    ben = Student.new(:name => "Ben Bitdiddle")
+    sicp = Lesson.new(name: "SICP")
+    ben = Student.new(name: "Ben Bitdiddle")
     sicp.students << ben
     sicp.save!
     assert_raises LessonError do
-      assert_no_difference('Lesson.count') do
+      assert_no_difference("Lesson.count") do
         sicp.destroy
       end
     end
-    assert !sicp.destroyed?
+    assert_not_predicate sicp, :destroyed?
   end
 
-  test 'should not raise error if have foreign key in the join table' do
-    student = Student.new(:name => "Ben Bitdiddle")
-    lesson = Lesson.new(:name => "SICP")
+  test "should not raise error if have foreign key in the join table" do
+    student = Student.new(name: "Ben Bitdiddle")
+    lesson = Lesson.new(name: "SICP")
     lesson.students << student
     lesson.save!
     assert_nothing_raised do
@@ -29,8 +31,8 @@ class HabtmDestroyOrderTest < ActiveRecord::TestCase
   test "not destroying a student with lessons leaves student<=>lesson association intact" do
     # test a normal before_destroy doesn't destroy the habtm joins
     begin
-      sicp = Lesson.new(:name => "SICP")
-      ben = Student.new(:name => "Ben Bitdiddle")
+      sicp = Lesson.new(name: "SICP")
+      ben = Student.new(name: "Ben Bitdiddle")
       # add a before destroy to student
       Student.class_eval do
         before_destroy do
@@ -40,7 +42,7 @@ class HabtmDestroyOrderTest < ActiveRecord::TestCase
       ben.lessons << sicp
       ben.save!
       ben.destroy
-      assert !ben.reload.lessons.empty?
+      assert_not_empty ben.reload.lessons
     ensure
       # get rid of it so Student is still like it was
       Student.reset_callbacks(:destroy)
@@ -49,13 +51,13 @@ class HabtmDestroyOrderTest < ActiveRecord::TestCase
 
   test "not destroying a lesson with students leaves student<=>lesson association intact" do
     # test a more aggressive before_destroy  doesn't destroy the habtm joins and still throws the exception
-    sicp = Lesson.new(:name => "SICP")
-    ben = Student.new(:name => "Ben Bitdiddle")
+    sicp = Lesson.new(name: "SICP")
+    ben = Student.new(name: "Ben Bitdiddle")
     sicp.students << ben
     sicp.save!
     assert_raises LessonError do
       sicp.destroy
     end
-    assert !sicp.reload.students.empty?
+    assert_not_empty sicp.reload.students
   end
 end
diff --git a/activerecord/test/cases/helper.rb b/activerecord/test/cases/helper.rb
index 12c793c408..730cd663a2 100644
--- a/activerecord/test/cases/helper.rb
+++ b/activerecord/test/cases/helper.rb
@@ -1,18 +1,16 @@
-require File.expand_path('../../../../load_paths', __FILE__)
+# frozen_string_literal: true
 
-require 'config'
+require "config"
 
-require 'active_support/testing/autorun'
-require 'stringio'
+require "stringio"
 
-require 'active_record'
-require 'cases/test_case'
-require 'active_support/dependencies'
-require 'active_support/logger'
-require 'active_support/core_ext/string/strip'
+require "active_record"
+require "cases/test_case"
+require "active_support/dependencies"
+require "active_support/logger"
 
-require 'support/config'
-require 'support/connection'
+require "support/config"
+require "support/connection"
 
 # TODO: Move all these random hacks into the ARTest namespace and into the support/ dir
 
@@ -28,10 +26,7 @@ I18n.enforce_available_locales = false
 ARTest.connect
 
 # Quote "type" if it's a reserved word for the current connection.
-QUOTED_TYPE = ActiveRecord::Base.connection.quote_column_name('type')
-
-# FIXME: Remove this when the deprecation cycle on TZ aware types by default ends.
-ActiveRecord::Base.time_zone_aware_types << :time
+QUOTED_TYPE = ActiveRecord::Base.connection.quote_column_name("type")
 
 def current_adapter?(*types)
   types.any? do |type|
@@ -45,24 +40,32 @@ def in_memory_db?
   ActiveRecord::Base.connection_pool.spec.config[:database] == ":memory:"
 end
 
-def mysql_56?
-  current_adapter?(:MysqlAdapter, :Mysql2Adapter) &&
-    ActiveRecord::Base.connection.send(:version).join(".") >= "5.6.0"
+def subsecond_precision_supported?
+  ActiveRecord::Base.connection.supports_datetime_with_precision?
 end
 
 def mysql_enforcing_gtid_consistency?
-  current_adapter?(:MysqlAdapter, :Mysql2Adapter) && 'ON' == ActiveRecord::Base.connection.show_variable('enforce_gtid_consistency')
+  current_adapter?(:Mysql2Adapter) && "ON" == ActiveRecord::Base.connection.show_variable("enforce_gtid_consistency")
+end
+
+def supports_default_expression?
+  if current_adapter?(:PostgreSQLAdapter)
+    true
+  elsif current_adapter?(:Mysql2Adapter)
+    conn = ActiveRecord::Base.connection
+    !conn.mariadb? && conn.version >= "8.0.13"
+  end
 end
 
 def supports_savepoints?
   ActiveRecord::Base.connection.supports_savepoints?
 end
 
-def with_env_tz(new_tz = 'US/Eastern')
-  old_tz, ENV['TZ'] = ENV['TZ'], new_tz
+def with_env_tz(new_tz = "US/Eastern")
+  old_tz, ENV["TZ"] = ENV["TZ"], new_tz
   yield
 ensure
-  old_tz ? ENV['TZ'] = old_tz : ENV.delete('TZ')
+  old_tz ? ENV["TZ"] = old_tz : ENV.delete("TZ")
 end
 
 def with_timezone_config(cfg)
@@ -136,20 +139,6 @@ def disable_extension!(extension, connection)
   connection.reconnect!
 end
 
-require "cases/validations_repair_helper"
-class ActiveSupport::TestCase
-  include ActiveRecord::TestFixtures
-  include ActiveRecord::ValidationsRepairHelper
-
-  self.fixture_path = FIXTURES_ROOT
-  self.use_instantiated_fixtures  = false
-  self.use_transactional_tests = true
-
-  def create_fixtures(*fixture_set_names, &block)
-    ActiveRecord::FixtureSet.create_fixtures(ActiveSupport::TestCase.fixture_path, fixture_set_names, fixture_class_names, &block)
-  end
-end
-
 def load_schema
   # silence verbose schema loading
   original_stdout = $stdout
@@ -163,6 +152,8 @@ def load_schema
   if File.exist?(adapter_specific_schema_file)
     load adapter_specific_schema_file
   end
+
+  ActiveRecord::FixtureSet.reset_cache
 ensure
   $stdout = original_stdout
 end
@@ -189,17 +180,15 @@ end
 module InTimeZone
   private
 
-  def in_time_zone(zone)
-    old_zone  = Time.zone
-    old_tz    = ActiveRecord::Base.time_zone_aware_attributes
-
-    Time.zone = zone ? ActiveSupport::TimeZone[zone] : nil
-    ActiveRecord::Base.time_zone_aware_attributes = !zone.nil?
-    yield
-  ensure
-    Time.zone = old_zone
-    ActiveRecord::Base.time_zone_aware_attributes = old_tz
-  end
+    def in_time_zone(zone)
+      old_zone  = Time.zone
+      old_tz    = ActiveRecord::Base.time_zone_aware_attributes
+
+      Time.zone = zone ? ActiveSupport::TimeZone[zone] : nil
+      ActiveRecord::Base.time_zone_aware_attributes = !zone.nil?
+      yield
+    ensure
+      Time.zone = old_zone
+      ActiveRecord::Base.time_zone_aware_attributes = old_tz
+    end
 end
-
-require 'mocha/setup' # FIXME: stop using mocha
diff --git a/activerecord/test/cases/hot_compatibility_test.rb b/activerecord/test/cases/hot_compatibility_test.rb
index 5ba9a1029a..7b388ebc5e 100644
--- a/activerecord/test/cases/hot_compatibility_test.rb
+++ b/activerecord/test/cases/hot_compatibility_test.rb
@@ -1,7 +1,11 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/connection_helper"
 
 class HotCompatibilityTest < ActiveRecord::TestCase
   self.use_transactional_tests = false
+  include ConnectionHelper
 
   setup do
     @klass = Class.new(ActiveRecord::Base) do
@@ -10,7 +14,7 @@ class HotCompatibilityTest < ActiveRecord::TestCase
         t.string :bar
       end
 
-      def self.name; 'HotCompatibility'; end
+      def self.name; "HotCompatibility"; end
     end
   end
 
@@ -33,22 +37,108 @@ class HotCompatibilityTest < ActiveRecord::TestCase
 
     # but we can successfully create a record so long as we don't
     # reference the removed column
-    record = @klass.create! foo: 'foo'
+    record = @klass.create! foo: "foo"
     record.reload
-    assert_equal 'foo', record.foo
+    assert_equal "foo", record.foo
   end
 
   test "update after remove_column" do
-    record = @klass.create! foo: 'foo'
+    record = @klass.create! foo: "foo"
     assert_equal 3, @klass.columns.length
     @klass.connection.remove_column :hot_compatibilities, :bar
     assert_equal 3, @klass.columns.length
 
     record.reload
-    assert_equal 'foo', record.foo
-    record.foo = 'bar'
+    assert_equal "foo", record.foo
+    record.foo = "bar"
     record.save!
     record.reload
-    assert_equal 'bar', record.foo
+    assert_equal "bar", record.foo
+  end
+
+  if current_adapter?(:PostgreSQLAdapter) && ActiveRecord::Base.connection.prepared_statements
+    test "cleans up after prepared statement failure in a transaction" do
+      with_two_connections do |original_connection, ddl_connection|
+        record = @klass.create! bar: "bar"
+
+        # prepare the reload statement in a transaction
+        @klass.transaction do
+          record.reload
+        end
+
+        assert get_prepared_statement_cache(@klass.connection).any?,
+          "expected prepared statement cache to have something in it"
+
+        # add a new column
+        ddl_connection.add_column :hot_compatibilities, :baz, :string
+
+        assert_raise(ActiveRecord::PreparedStatementCacheExpired) do
+          @klass.transaction do
+            record.reload
+          end
+        end
+
+        assert_empty get_prepared_statement_cache(@klass.connection),
+          "expected prepared statement cache to be empty but it wasn't"
+      end
+    end
+
+    test "cleans up after prepared statement failure in nested transactions" do
+      with_two_connections do |original_connection, ddl_connection|
+        record = @klass.create! bar: "bar"
+
+        # prepare the reload statement in a transaction
+        @klass.transaction do
+          record.reload
+        end
+
+        assert get_prepared_statement_cache(@klass.connection).any?,
+          "expected prepared statement cache to have something in it"
+
+        # add a new column
+        ddl_connection.add_column :hot_compatibilities, :baz, :string
+
+        assert_raise(ActiveRecord::PreparedStatementCacheExpired) do
+          @klass.transaction do
+            @klass.transaction do
+              @klass.transaction do
+                record.reload
+              end
+            end
+          end
+        end
+
+        assert_empty get_prepared_statement_cache(@klass.connection),
+          "expected prepared statement cache to be empty but it wasn't"
+      end
+    end
   end
+
+  private
+
+    def get_prepared_statement_cache(connection)
+      connection.instance_variable_get(:@statements)
+        .instance_variable_get(:@cache)[Process.pid]
+    end
+
+    # Rails will automatically clear the prepared statements on the connection
+    # that runs the migration, so we use two connections to simulate what would
+    # actually happen on a production system; we'd have one connection running the
+    # migration from the rake task ("ddl_connection" here), and we'd have another
+    # connection in a web worker.
+    def with_two_connections
+      run_without_connection do |original_connection|
+        ActiveRecord::Base.establish_connection(original_connection.merge(pool_size: 2))
+        begin
+          ddl_connection = ActiveRecord::Base.connection_pool.checkout
+          begin
+            yield original_connection, ddl_connection
+          ensure
+            ActiveRecord::Base.connection_pool.checkin ddl_connection
+          end
+        ensure
+          ActiveRecord::Base.clear_all_connections!
+        end
+      end
+    end
 end
diff --git a/activerecord/test/cases/i18n_test.rb b/activerecord/test/cases/i18n_test.rb
index a428f1d87b..22981c142a 100644
--- a/activerecord/test/cases/i18n_test.rb
+++ b/activerecord/test/cases/i18n_test.rb
@@ -1,45 +1,46 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/reply'
+require "models/topic"
+require "models/reply"
 
 class ActiveRecordI18nTests < ActiveRecord::TestCase
-
   def setup
     I18n.backend = I18n::Backend::Simple.new
   end
 
   def test_translated_model_attributes
-    I18n.backend.store_translations 'en', :activerecord => {:attributes => {:topic => {:title => 'topic title attribute'} } }
-    assert_equal 'topic title attribute', Topic.human_attribute_name('title')
+    I18n.backend.store_translations "en", activerecord: { attributes: { topic: { title: "topic title attribute" } } }
+    assert_equal "topic title attribute", Topic.human_attribute_name("title")
   end
 
   def test_translated_model_attributes_with_symbols
-    I18n.backend.store_translations 'en', :activerecord => {:attributes => {:topic => {:title => 'topic title attribute'} } }
-    assert_equal 'topic title attribute', Topic.human_attribute_name(:title)
+    I18n.backend.store_translations "en", activerecord: { attributes: { topic: { title: "topic title attribute" } } }
+    assert_equal "topic title attribute", Topic.human_attribute_name(:title)
   end
 
   def test_translated_model_attributes_with_sti
-    I18n.backend.store_translations 'en', :activerecord => {:attributes => {:reply => {:title => 'reply title attribute'} } }
-    assert_equal 'reply title attribute', Reply.human_attribute_name('title')
+    I18n.backend.store_translations "en", activerecord: { attributes: { reply: { title: "reply title attribute" } } }
+    assert_equal "reply title attribute", Reply.human_attribute_name("title")
   end
 
   def test_translated_model_attributes_with_sti_fallback
-    I18n.backend.store_translations 'en', :activerecord => {:attributes => {:topic => {:title => 'topic title attribute'} } }
-    assert_equal 'topic title attribute', Reply.human_attribute_name('title')
+    I18n.backend.store_translations "en", activerecord: { attributes: { topic: { title: "topic title attribute" } } }
+    assert_equal "topic title attribute", Reply.human_attribute_name("title")
   end
 
   def test_translated_model_names
-    I18n.backend.store_translations 'en', :activerecord => {:models => {:topic => 'topic model'} }
-    assert_equal 'topic model', Topic.model_name.human
+    I18n.backend.store_translations "en", activerecord: { models: { topic: "topic model" } }
+    assert_equal "topic model", Topic.model_name.human
   end
 
   def test_translated_model_names_with_sti
-    I18n.backend.store_translations 'en', :activerecord => {:models => {:reply => 'reply model'} }
-    assert_equal 'reply model', Reply.model_name.human
+    I18n.backend.store_translations "en", activerecord: { models: { reply: "reply model" } }
+    assert_equal "reply model", Reply.model_name.human
   end
 
   def test_translated_model_names_with_sti_fallback
-    I18n.backend.store_translations 'en', :activerecord => {:models => {:topic => 'topic model'} }
-    assert_equal 'topic model', Reply.model_name.human
+    I18n.backend.store_translations "en", activerecord: { models: { topic: "topic model" } }
+    assert_equal "topic model", Reply.model_name.human
   end
 end
diff --git a/activerecord/test/cases/inheritance_test.rb b/activerecord/test/cases/inheritance_test.rb
index f67d85603a..3d3189900f 100644
--- a/activerecord/test/cases/inheritance_test.rb
+++ b/activerecord/test/cases/inheritance_test.rb
@@ -1,11 +1,16 @@
-require 'cases/helper'
-require 'models/company'
-require 'models/person'
-require 'models/post'
-require 'models/project'
-require 'models/subscriber'
-require 'models/vegetables'
-require 'models/shop'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/author"
+require "models/company"
+require "models/membership"
+require "models/person"
+require "models/post"
+require "models/project"
+require "models/subscriber"
+require "models/vegetables"
+require "models/shop"
+require "models/sponsor"
 
 module InheritanceTestHelper
   def with_store_full_sti_class(&block)
@@ -27,11 +32,11 @@ end
 
 class InheritanceTest < ActiveRecord::TestCase
   include InheritanceTestHelper
-  fixtures :companies, :projects, :subscribers, :accounts, :vegetables
+  fixtures :companies, :projects, :subscribers, :accounts, :vegetables, :memberships
 
   def test_class_with_store_full_sti_class_returns_full_name
     with_store_full_sti_class do
-      assert_equal 'Namespaced::Company', Namespaced::Company.sti_name
+      assert_equal "Namespaced::Company", Namespaced::Company.sti_name
     end
   end
 
@@ -40,32 +45,78 @@ class InheritanceTest < ActiveRecord::TestCase
     company = company.dup
     company.extend(Module.new {
       def _read_attribute(name)
-        return '  ' if name == 'type'
+        return "  " if name == "type"
         super
       end
     })
     company.save!
     company = Company.all.to_a.find { |x| x.id == company.id }
-    assert_equal '  ', company.type
+    assert_equal "  ", company.type
   end
 
   def test_class_without_store_full_sti_class_returns_demodulized_name
     without_store_full_sti_class do
-      assert_equal 'Company', Namespaced::Company.sti_name
+      assert_equal "Company", Namespaced::Company.sti_name
+    end
+  end
+
+  def test_compute_type_success
+    assert_equal Author, Company.send(:compute_type, "Author")
+  end
+
+  def test_compute_type_nonexistent_constant
+    e = assert_raises NameError do
+      Company.send :compute_type, "NonexistentModel"
+    end
+    assert_equal "uninitialized constant Company::NonexistentModel", e.message
+    assert_equal "Company::NonexistentModel", e.name
+  end
+
+  def test_compute_type_no_method_error
+    ActiveSupport::Dependencies.stub(:safe_constantize, proc { raise NoMethodError }) do
+      assert_raises NoMethodError do
+        Company.send :compute_type, "InvalidModel"
+      end
+    end
+  end
+
+  def test_compute_type_on_undefined_method
+    error = nil
+    begin
+      Class.new(Author) do
+        alias_method :foo, :bar
+      end
+    rescue => e
+      error = e
+    end
+
+    ActiveSupport::Dependencies.stub(:safe_constantize, proc { raise e }) do
+      exception = assert_raises NameError do
+        Company.send :compute_type, "InvalidModel"
+      end
+      assert_equal error.message, exception.message
+    end
+  end
+
+  def test_compute_type_argument_error
+    ActiveSupport::Dependencies.stub(:safe_constantize, proc { raise ArgumentError }) do
+      assert_raises ArgumentError do
+        Company.send :compute_type, "InvalidModel"
+      end
     end
   end
 
   def test_should_store_demodulized_class_name_with_store_full_sti_class_option_disabled
     without_store_full_sti_class do
       item = Namespaced::Company.new
-      assert_equal 'Company', item[:type]
+      assert_equal "Company", item[:type]
     end
   end
 
   def test_should_store_full_class_name_with_store_full_sti_class_option_enabled
     with_store_full_sti_class do
       item = Namespaced::Company.new
-      assert_equal 'Namespaced::Company', item[:type]
+      assert_equal "Namespaced::Company", item[:type]
     end
   end
 
@@ -77,25 +128,71 @@ class InheritanceTest < ActiveRecord::TestCase
     end
   end
 
+  def test_descends_from_active_record
+    assert_not_predicate ActiveRecord::Base, :descends_from_active_record?
+
+    # Abstract subclass of AR::Base.
+    assert_predicate LoosePerson, :descends_from_active_record?
+
+    # Concrete subclass of an abstract class.
+    assert_predicate LooseDescendant, :descends_from_active_record?
+
+    # Concrete subclass of AR::Base.
+    assert_predicate TightPerson, :descends_from_active_record?
+
+    # Concrete subclass of a concrete class but has no type column.
+    assert_predicate TightDescendant, :descends_from_active_record?
+
+    # Concrete subclass of AR::Base.
+    assert_predicate Post, :descends_from_active_record?
+
+    # Concrete subclasses of a concrete class which has a type column.
+    assert_not_predicate StiPost, :descends_from_active_record?
+    assert_not_predicate SubStiPost, :descends_from_active_record?
+
+    # Abstract subclass of a concrete class which has a type column.
+    # This is pathological, as you'll never have Sub < Abstract < Concrete.
+    assert_not_predicate AbstractStiPost, :descends_from_active_record?
+
+    # Concrete subclass of an abstract class which has a type column.
+    assert_not_predicate SubAbstractStiPost, :descends_from_active_record?
+  end
+
   def test_company_descends_from_active_record
-    assert !ActiveRecord::Base.descends_from_active_record?
-    assert AbstractCompany.descends_from_active_record?, 'AbstractCompany should descend from ActiveRecord::Base'
-    assert Company.descends_from_active_record?, 'Company should descend from ActiveRecord::Base'
-    assert !Class.new(Company).descends_from_active_record?, 'Company subclass should not descend from ActiveRecord::Base'
+    assert_not_predicate ActiveRecord::Base, :descends_from_active_record?
+    assert AbstractCompany.descends_from_active_record?, "AbstractCompany should descend from ActiveRecord::Base"
+    assert Company.descends_from_active_record?, "Company should descend from ActiveRecord::Base"
+    assert_not Class.new(Company).descends_from_active_record?, "Company subclass should not descend from ActiveRecord::Base"
+  end
+
+  def test_abstract_class
+    assert_not_predicate ActiveRecord::Base, :abstract_class?
+    assert_predicate LoosePerson, :abstract_class?
+    assert_not_predicate LooseDescendant, :abstract_class?
   end
 
   def test_inheritance_base_class
     assert_equal Post, Post.base_class
+    assert_predicate Post, :base_class?
     assert_equal Post, SpecialPost.base_class
+    assert_not_predicate SpecialPost, :base_class?
     assert_equal Post, StiPost.base_class
-    assert_equal SubStiPost, SubStiPost.base_class
+    assert_not_predicate StiPost, :base_class?
+    assert_equal Post, SubStiPost.base_class
+    assert_not_predicate SubStiPost, :base_class?
+    assert_equal SubAbstractStiPost, SubAbstractStiPost.base_class
+    assert_predicate SubAbstractStiPost, :base_class?
   end
 
   def test_abstract_inheritance_base_class
     assert_equal LoosePerson, LoosePerson.base_class
+    assert_predicate LoosePerson, :base_class?
     assert_equal LooseDescendant, LooseDescendant.base_class
+    assert_predicate LooseDescendant, :base_class?
     assert_equal TightPerson, TightPerson.base_class
+    assert_predicate TightPerson, :base_class?
     assert_equal TightPerson, TightDescendant.base_class
+    assert_not_predicate TightDescendant, :base_class?
   end
 
   def test_base_class_activerecord_error
@@ -133,7 +230,7 @@ class InheritanceTest < ActiveRecord::TestCase
   def test_becomes_and_change_tracking_for_inheritance_columns
     cucumber = Vegetable.find(1)
     cabbage = cucumber.becomes!(Cabbage)
-    assert_equal ['Cucumber', 'Cabbage'], cabbage.custom_type_change
+    assert_equal ["Cucumber", "Cabbage"], cabbage.custom_type_change
   end
 
   def test_alt_becomes_bang_resets_inheritance_type_column
@@ -148,13 +245,13 @@ class InheritanceTest < ActiveRecord::TestCase
   end
 
   def test_inheritance_find_all
-    companies = Company.all.merge!(:order => 'id').to_a
+    companies = Company.all.merge!(order: "id").to_a
     assert_kind_of Firm, companies[0], "37signals should be a firm"
     assert_kind_of Client, companies[1], "Summit should be a client"
   end
 
   def test_alt_inheritance_find_all
-    companies = Vegetable.all.merge!(:order => 'id').to_a
+    companies = Vegetable.all.merge!(order: "id").to_a
     assert_kind_of Cucumber, companies[0]
     assert_kind_of Cabbage, companies[1]
   end
@@ -169,7 +266,7 @@ class InheritanceTest < ActiveRecord::TestCase
   end
 
   def test_alt_inheritance_save
-    cabbage = Cabbage.new(:name => 'Savoy')
+    cabbage = Cabbage.new(name: "Savoy")
     cabbage.save!
 
     savoy = Vegetable.find(cabbage.id)
@@ -182,12 +279,27 @@ class InheritanceTest < ActiveRecord::TestCase
   end
 
   def test_inheritance_new_with_base_class
-    company = Company.new(:type => 'Company')
+    company = Company.new(type: "Company")
     assert_equal Company, company.class
   end
 
   def test_inheritance_new_with_subclass
-    firm = Company.new(:type => 'Firm')
+    firm = Company.new(type: "Firm")
+    assert_equal Firm, firm.class
+  end
+
+  def test_where_new_with_subclass
+    firm = Company.where(type: "Firm").new
+    assert_equal Firm, firm.class
+  end
+
+  def test_where_create_with_subclass
+    firm = Company.where(type: "Firm").create(name: "Basecamp")
+    assert_equal Firm, firm.class
+  end
+
+  def test_where_create_bang_with_subclass
+    firm = Company.where(type: "Firm").create!(name: "Basecamp")
     assert_equal Firm, firm.class
   end
 
@@ -206,40 +318,63 @@ class InheritanceTest < ActiveRecord::TestCase
   end
 
   def test_new_with_invalid_type
-    assert_raise(ActiveRecord::SubclassNotFound) { Company.new(:type => 'InvalidType') }
+    assert_raise(ActiveRecord::SubclassNotFound) { Company.new(type: "InvalidType") }
   end
 
   def test_new_with_unrelated_type
-    assert_raise(ActiveRecord::SubclassNotFound) { Company.new(:type => 'Account') }
+    assert_raise(ActiveRecord::SubclassNotFound) { Company.new(type: "Account") }
+  end
+
+  def test_where_new_with_invalid_type
+    assert_raise(ActiveRecord::SubclassNotFound) { Company.where(type: "InvalidType").new }
+  end
+
+  def test_where_new_with_unrelated_type
+    assert_raise(ActiveRecord::SubclassNotFound) { Company.where(type: "Account").new }
+  end
+
+  def test_where_create_with_invalid_type
+    assert_raise(ActiveRecord::SubclassNotFound) { Company.where(type: "InvalidType").create }
+  end
+
+  def test_where_create_with_unrelated_type
+    assert_raise(ActiveRecord::SubclassNotFound) { Company.where(type: "Account").create }
+  end
+
+  def test_where_create_bang_with_invalid_type
+    assert_raise(ActiveRecord::SubclassNotFound) { Company.where(type: "InvalidType").create! }
+  end
+
+  def test_where_create_bang_with_unrelated_type
+    assert_raise(ActiveRecord::SubclassNotFound) { Company.where(type: "Account").create! }
   end
 
   def test_new_with_unrelated_namespaced_type
     without_store_full_sti_class do
       e = assert_raises ActiveRecord::SubclassNotFound do
-        Namespaced::Company.new(type: 'Firm')
+        Namespaced::Company.new(type: "Firm")
       end
 
       assert_equal "Invalid single-table inheritance type: Namespaced::Firm is not a subclass of Namespaced::Company", e.message
     end
   end
 
-
   def test_new_with_complex_inheritance
-    assert_nothing_raised { Client.new(type: 'VerySpecialClient') }
+    assert_nothing_raised { Client.new(type: "VerySpecialClient") }
   end
 
   def test_new_without_storing_full_sti_class
     without_store_full_sti_class do
-      item = Company.new(type: 'SpecialCo')
+      item = Company.new(type: "SpecialCo")
       assert_instance_of Company::SpecialCo, item
     end
   end
 
   def test_new_with_autoload_paths
-    path = File.expand_path('../../models/autoloadable', __FILE__)
+    path = File.expand_path("../models/autoloadable", __dir__)
     ActiveSupport::Dependencies.autoload_paths << path
 
-    firm = Company.new(:type => 'ExtraFirm')
+    firm = Company.new(type: "ExtraFirm")
     assert_equal ExtraFirm, firm.class
   ensure
     ActiveSupport::Dependencies.autoload_paths.reject! { |p| p == path }
@@ -272,7 +407,7 @@ class InheritanceTest < ActiveRecord::TestCase
     Client.update_all "name = 'I am a client'"
     assert_equal "I am a client", Client.first.name
     # Order by added as otherwise Oracle tests were failing because of different order of results
-    assert_equal "37signals", Firm.all.merge!(:order => "id").to_a.first.name
+    assert_equal "37signals", Firm.all.merge!(order: "id").to_a.first.name
   end
 
   def test_alt_update_all_within_inheritance
@@ -294,51 +429,52 @@ class InheritanceTest < ActiveRecord::TestCase
   end
 
   def test_find_first_within_inheritance
-    assert_kind_of Firm, Company.all.merge!(:where => "name = '37signals'").first
-    assert_kind_of Firm, Firm.all.merge!(:where => "name = '37signals'").first
-    assert_nil Client.all.merge!(:where => "name = '37signals'").first
+    assert_kind_of Firm, Company.all.merge!(where: "name = '37signals'").first
+    assert_kind_of Firm, Firm.all.merge!(where: "name = '37signals'").first
+    assert_nil Client.all.merge!(where: "name = '37signals'").first
   end
 
   def test_alt_find_first_within_inheritance
-    assert_kind_of Cabbage, Vegetable.all.merge!(:where => "name = 'his cabbage'").first
-    assert_kind_of Cabbage, Cabbage.all.merge!(:where => "name = 'his cabbage'").first
-    assert_nil Cucumber.all.merge!(:where => "name = 'his cabbage'").first
+    assert_kind_of Cabbage, Vegetable.all.merge!(where: "name = 'his cabbage'").first
+    assert_kind_of Cabbage, Cabbage.all.merge!(where: "name = 'his cabbage'").first
+    assert_nil Cucumber.all.merge!(where: "name = 'his cabbage'").first
   end
 
   def test_complex_inheritance
     very_special_client = VerySpecialClient.create("name" => "veryspecial")
     assert_equal very_special_client, VerySpecialClient.where("name = 'veryspecial'").first
-    assert_equal very_special_client, SpecialClient.all.merge!(:where => "name = 'veryspecial'").first
-    assert_equal very_special_client, Company.all.merge!(:where => "name = 'veryspecial'").first
-    assert_equal very_special_client, Client.all.merge!(:where => "name = 'veryspecial'").first
-    assert_equal 1, Client.all.merge!(:where => "name = 'Summit'").to_a.size
+    assert_equal very_special_client, SpecialClient.all.merge!(where: "name = 'veryspecial'").first
+    assert_equal very_special_client, Company.all.merge!(where: "name = 'veryspecial'").first
+    assert_equal very_special_client, Client.all.merge!(where: "name = 'veryspecial'").first
+    assert_equal 1, Client.all.merge!(where: "name = 'Summit'").to_a.size
     assert_equal very_special_client, Client.find(very_special_client.id)
   end
 
   def test_alt_complex_inheritance
     king_cole = KingCole.create("name" => "uniform heads")
     assert_equal king_cole, KingCole.where("name = 'uniform heads'").first
-    assert_equal king_cole, GreenCabbage.all.merge!(:where => "name = 'uniform heads'").first
-    assert_equal king_cole, Cabbage.all.merge!(:where => "name = 'uniform heads'").first
-    assert_equal king_cole, Vegetable.all.merge!(:where => "name = 'uniform heads'").first
-    assert_equal 1, Cabbage.all.merge!(:where => "name = 'his cabbage'").to_a.size
+    assert_equal king_cole, GreenCabbage.all.merge!(where: "name = 'uniform heads'").first
+    assert_equal king_cole, Cabbage.all.merge!(where: "name = 'uniform heads'").first
+    assert_equal king_cole, Vegetable.all.merge!(where: "name = 'uniform heads'").first
+    assert_equal 1, Cabbage.all.merge!(where: "name = 'his cabbage'").to_a.size
     assert_equal king_cole, Cabbage.find(king_cole.id)
   end
 
   def test_eager_load_belongs_to_something_inherited
-    account = Account.all.merge!(:includes => :firm).find(1)
+    account = Account.all.merge!(includes: :firm).find(1)
     assert account.association(:firm).loaded?, "association was not eager loaded"
   end
 
   def test_alt_eager_loading
-    cabbage = RedCabbage.all.merge!(:includes => :seller).find(4)
+    cabbage = RedCabbage.all.merge!(includes: :seller).find(4)
     assert cabbage.association(:seller).loaded?, "association was not eager loaded"
   end
 
   def test_eager_load_belongs_to_primary_key_quoting
     con = Account.connection
-    assert_sql(/#{con.quote_table_name('companies')}.#{con.quote_column_name('id')} = 1/) do
-      Account.all.merge!(:includes => :firm).find(1)
+    bind_param = Arel::Nodes::BindParam.new(nil)
+    assert_sql(/#{con.quote_table_name('companies')}\.#{con.quote_column_name('id')} = (?:#{Regexp.quote(bind_param.to_sql)}|1)/) do
+      Account.all.merge!(includes: :firm).find(1)
     end
   end
 
@@ -348,25 +484,24 @@ class InheritanceTest < ActiveRecord::TestCase
 
   def test_inheritance_without_mapping
     assert_kind_of SpecialSubscriber, SpecialSubscriber.find("webster132")
-    assert_nothing_raised { s = SpecialSubscriber.new("name" => "And breaaaaathe!"); s.id = 'roger'; s.save }
+    assert_nothing_raised { s = SpecialSubscriber.new("name" => "And breaaaaathe!"); s.id = "roger"; s.save }
   end
 
   def test_scope_inherited_properly
     assert_nothing_raised { Company.of_first_firm }
     assert_nothing_raised { Client.of_first_firm }
   end
+
+  def test_inheritance_with_default_scope
+    assert_equal 1, SelectedMembership.count(:all)
+  end
 end
 
 class InheritanceComputeTypeTest < ActiveRecord::TestCase
   include InheritanceTestHelper
   fixtures :companies
 
-  def setup
-    ActiveSupport::Dependencies.log_activity = true
-  end
-
   teardown do
-    ActiveSupport::Dependencies.log_activity = false
     self.class.const_remove :FirmOnTheFly rescue nil
     Firm.const_remove :FirmOnTheFly rescue nil
   end
@@ -374,7 +509,7 @@ class InheritanceComputeTypeTest < ActiveRecord::TestCase
   def test_instantiation_doesnt_try_to_require_corresponding_file
     without_store_full_sti_class do
       foo = Firm.first.clone
-      foo.type = 'FirmOnTheFly'
+      foo.type = "FirmOnTheFly"
       foo.save!
 
       # Should fail without FirmOnTheFly in the type condition.
@@ -395,8 +530,131 @@ class InheritanceComputeTypeTest < ActiveRecord::TestCase
   end
 
   def test_sti_type_from_attributes_disabled_in_non_sti_class
-    phone = Shop::Product::Type.new(name: 'Phone')
-    product = Shop::Product.new(:type => phone)
+    phone = Shop::Product::Type.new(name: "Phone")
+    product = Shop::Product.new(type: phone)
     assert product.save
   end
+
+  def test_inheritance_new_with_subclass_as_default
+    original_type = Company.columns_hash["type"].default
+    ActiveRecord::Base.connection.change_column_default :companies, :type, "Firm"
+    Company.reset_column_information
+
+    firm = Company.new # without arguments
+    assert_equal "Firm", firm.type
+    assert_instance_of Firm, firm
+
+    firm = Company.new(firm_name: "Shri Hans Plastic") # with arguments
+    assert_equal "Firm", firm.type
+    assert_instance_of Firm, firm
+
+    client = Client.new
+    assert_equal "Client", client.type
+    assert_instance_of Client, client
+
+    firm = Company.new(type: "Client") # overwrite the default type
+    assert_equal "Client", firm.type
+    assert_instance_of Client, firm
+  ensure
+    ActiveRecord::Base.connection.change_column_default :companies, :type, original_type
+    Company.reset_column_information
+  end
+end
+
+class InheritanceAttributeTest < ActiveRecord::TestCase
+  class Company < ActiveRecord::Base
+    self.table_name = "companies"
+    attribute :type, :string, default: "InheritanceAttributeTest::Startup"
+  end
+
+  class Startup < Company
+  end
+
+  class Empire < Company
+  end
+
+  def test_inheritance_new_with_subclass_as_default
+    startup = Company.new # without arguments
+    assert_equal "InheritanceAttributeTest::Startup", startup.type
+    assert_instance_of Startup, startup
+
+    empire = Company.new(type: "InheritanceAttributeTest::Empire") # without arguments
+    assert_equal "InheritanceAttributeTest::Empire", empire.type
+    assert_instance_of Empire, empire
+  end
+end
+
+class InheritanceAttributeMappingTest < ActiveRecord::TestCase
+  setup do
+    @old_registry = ActiveRecord::Type.registry
+    ActiveRecord::Type.registry = ActiveRecord::Type::AdapterSpecificRegistry.new
+    ActiveRecord::Type.register :omg_sti, InheritanceAttributeMappingTest::OmgStiType
+    Company.delete_all
+    Sponsor.delete_all
+  end
+
+  teardown do
+    ActiveRecord::Type.registry = @old_registry
+  end
+
+  class OmgStiType < ActiveRecord::Type::String
+    def cast_value(value)
+      if value =~ /\Aomg_(.+)\z/
+        $1.classify
+      else
+        value
+      end
+    end
+
+    def serialize(value)
+      if value
+        "omg_%s" % value.underscore
+      end
+    end
+  end
+
+  class Company < ActiveRecord::Base
+    self.table_name = "companies"
+    attribute :type, :omg_sti
+  end
+
+  class Startup < Company; end
+  class Empire < Company; end
+
+  class Sponsor < ActiveRecord::Base
+    self.table_name = "sponsors"
+    attribute :sponsorable_type, :omg_sti
+
+    belongs_to :sponsorable, polymorphic: true
+  end
+
+  def test_sti_with_custom_type
+    Startup.create! name: "a Startup"
+    Empire.create! name: "an Empire"
+
+    assert_equal [["a Startup", "omg_inheritance_attribute_mapping_test/startup"],
+                  ["an Empire", "omg_inheritance_attribute_mapping_test/empire"]], ActiveRecord::Base.connection.select_rows("SELECT name, type FROM companies").sort
+    assert_equal [["a Startup", "InheritanceAttributeMappingTest::Startup"],
+                  ["an Empire", "InheritanceAttributeMappingTest::Empire"]], Company.all.map { |a| [a.name, a.type] }.sort
+
+    startup = Startup.first
+    startup.becomes! Empire
+    startup.save!
+
+    assert_equal [["a Startup", "omg_inheritance_attribute_mapping_test/empire"],
+                  ["an Empire", "omg_inheritance_attribute_mapping_test/empire"]], ActiveRecord::Base.connection.select_rows("SELECT name, type FROM companies").sort
+
+    assert_equal [["a Startup", "InheritanceAttributeMappingTest::Empire"],
+                  ["an Empire", "InheritanceAttributeMappingTest::Empire"]], Company.all.map { |a| [a.name, a.type] }.sort
+  end
+
+  def test_polymorphic_associations_custom_type
+    startup = Startup.create! name: "a Startup"
+    sponsor = Sponsor.create! sponsorable: startup
+
+    assert_equal ["omg_inheritance_attribute_mapping_test/company"], ActiveRecord::Base.connection.select_values("SELECT sponsorable_type FROM sponsors")
+
+    sponsor = Sponsor.first
+    assert_equal startup, sponsor.sponsorable
+  end
 end
diff --git a/activerecord/test/cases/instrumentation_test.rb b/activerecord/test/cases/instrumentation_test.rb
new file mode 100644
index 0000000000..e6e8468757
--- /dev/null
+++ b/activerecord/test/cases/instrumentation_test.rb
@@ -0,0 +1,72 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/book"
+
+module ActiveRecord
+  class InstrumentationTest < ActiveRecord::TestCase
+    def test_payload_name_on_load
+      Book.create(name: "test book")
+      subscriber = ActiveSupport::Notifications.subscribe("sql.active_record") do |*args|
+        event = ActiveSupport::Notifications::Event.new(*args)
+        if event.payload[:sql].match "SELECT"
+          assert_equal "Book Load", event.payload[:name]
+        end
+      end
+      Book.first
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscriber) if subscriber
+    end
+
+    def test_payload_name_on_create
+      subscriber = ActiveSupport::Notifications.subscribe("sql.active_record") do |*args|
+        event = ActiveSupport::Notifications::Event.new(*args)
+        if event.payload[:sql].match "INSERT"
+          assert_equal "Book Create", event.payload[:name]
+        end
+      end
+      Book.create(name: "test book")
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscriber) if subscriber
+    end
+
+    def test_payload_name_on_update
+      subscriber = ActiveSupport::Notifications.subscribe("sql.active_record") do |*args|
+        event = ActiveSupport::Notifications::Event.new(*args)
+        if event.payload[:sql].match "UPDATE"
+          assert_equal "Book Update", event.payload[:name]
+        end
+      end
+      book = Book.create(name: "test book")
+      book.update_attribute(:name, "new name")
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscriber) if subscriber
+    end
+
+    def test_payload_name_on_update_all
+      subscriber = ActiveSupport::Notifications.subscribe("sql.active_record") do |*args|
+        event = ActiveSupport::Notifications::Event.new(*args)
+        if event.payload[:sql].match "UPDATE"
+          assert_equal "Book Update All", event.payload[:name]
+        end
+      end
+      Book.create(name: "test book")
+      Book.update_all(name: "new name")
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscriber) if subscriber
+    end
+
+    def test_payload_name_on_destroy
+      subscriber = ActiveSupport::Notifications.subscribe("sql.active_record") do |*args|
+        event = ActiveSupport::Notifications::Event.new(*args)
+        if event.payload[:sql].match "DELETE"
+          assert_equal "Book Destroy", event.payload[:name]
+        end
+      end
+      book = Book.create(name: "test book")
+      book.destroy
+    ensure
+      ActiveSupport::Notifications.unsubscribe(subscriber) if subscriber
+    end
+  end
+end
diff --git a/activerecord/test/cases/integration_test.rb b/activerecord/test/cases/integration_test.rb
index 018b7b0d8f..5687afbc71 100644
--- a/activerecord/test/cases/integration_test.rb
+++ b/activerecord/test/cases/integration_test.rb
@@ -1,10 +1,11 @@
+# frozen_string_literal: true
 
-require 'cases/helper'
-require 'models/company'
-require 'models/developer'
-require 'models/computer'
-require 'models/owner'
-require 'models/pet'
+require "cases/helper"
+require "models/company"
+require "models/developer"
+require "models/computer"
+require "models/owner"
+require "models/pet"
 
 class IntegrationTest < ActiveRecord::TestCase
   fixtures :companies, :developers, :owners, :pets
@@ -15,59 +16,85 @@ class IntegrationTest < ActiveRecord::TestCase
 
   def test_to_param_returns_nil_if_not_persisted
     client = Client.new
-    assert_equal nil, client.to_param
+    assert_nil client.to_param
   end
 
   def test_to_param_returns_id_if_not_persisted_but_id_is_set
     client = Client.new
     client.id = 1
-    assert_equal '1', client.to_param
+    assert_equal "1", client.to_param
   end
 
   def test_to_param_class_method
     firm = Firm.find(4)
-    assert_equal '4-flamboyant-software', firm.to_param
+    assert_equal "4-flamboyant-software", firm.to_param
+  end
+
+  def test_to_param_class_method_truncates_words_properly
+    firm = Firm.find(4)
+    firm.name << ", Inc."
+    assert_equal "4-flamboyant-software", firm.to_param
+  end
+
+  def test_to_param_class_method_truncates_after_parameterize
+    firm = Firm.find(4)
+    firm.name = "Huey, Dewey, & Louie LLC"
+    #               123456789T123456789v
+    assert_equal "4-huey-dewey-louie-llc", firm.to_param
+  end
+
+  def test_to_param_class_method_truncates_after_parameterize_with_hyphens
+    firm = Firm.find(4)
+    firm.name = "Door-to-Door Wash-n-Fold Service"
+    #               123456789T123456789v
+    assert_equal "4-door-to-door-wash-n", firm.to_param
   end
 
   def test_to_param_class_method_truncates
     firm = Firm.find(4)
-    firm.name = 'a ' * 100
-    assert_equal '4-a-a-a-a-a-a-a-a-a', firm.to_param
+    firm.name = "a " * 100
+    assert_equal "4-a-a-a-a-a-a-a-a-a-a", firm.to_param
   end
 
   def test_to_param_class_method_truncates_edge_case
     firm = Firm.find(4)
-    firm.name = 'David HeinemeierHansson'
-    assert_equal '4-david', firm.to_param
+    firm.name = "David HeinemeierHansson"
+    assert_equal "4-david", firm.to_param
+  end
+
+  def test_to_param_class_method_truncates_case_shown_in_doc
+    firm = Firm.find(4)
+    firm.name = "David Heinemeier Hansson"
+    assert_equal "4-david-heinemeier", firm.to_param
   end
 
   def test_to_param_class_method_squishes
     firm = Firm.find(4)
     firm.name = "ab \n" * 100
-    assert_equal '4-ab-ab-ab-ab-ab-ab', firm.to_param
+    assert_equal "4-ab-ab-ab-ab-ab-ab-ab", firm.to_param
   end
 
   def test_to_param_class_method_multibyte_character
     firm = Firm.find(4)
     firm.name = "戦場ヶ原 ひたぎ"
-    assert_equal '4', firm.to_param
+    assert_equal "4", firm.to_param
   end
 
   def test_to_param_class_method_uses_default_if_blank
     firm = Firm.find(4)
     firm.name = nil
-    assert_equal '4', firm.to_param
-    firm.name = ' '
-    assert_equal '4', firm.to_param
+    assert_equal "4", firm.to_param
+    firm.name = " "
+    assert_equal "4", firm.to_param
   end
 
   def test_to_param_class_method_uses_default_if_not_persisted
-    firm = Firm.new(name: 'Fancy Shirts')
-    assert_equal nil, firm.to_param
+    firm = Firm.new(name: "Fancy Shirts")
+    assert_nil firm.to_param
   end
 
   def test_to_param_with_no_arguments
-    assert_equal 'Firm', Firm.to_param
+    assert_equal "Firm", Firm.to_param
   end
 
   def test_cache_key_for_existing_record_is_not_timezone_dependent
@@ -81,7 +108,7 @@ class IntegrationTest < ActiveRecord::TestCase
 
   def test_cache_key_format_for_existing_record_with_updated_at
     dev = Developer.first
-    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:nsec)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:usec)}", dev.cache_key
   end
 
   def test_cache_key_format_for_existing_record_with_updated_at_and_custom_cache_timestamp_format
@@ -96,7 +123,9 @@ class IntegrationTest < ActiveRecord::TestCase
     owner.update_column :updated_at, Time.current
     key = owner.cache_key
 
-    assert pet.touch
+    travel(1.second) do
+      assert pet.touch
+    end
     assert_not_equal key, owner.reload.cache_key
   end
 
@@ -109,30 +138,121 @@ class IntegrationTest < ActiveRecord::TestCase
   def test_cache_key_for_updated_on
     dev = Developer.first
     dev.updated_at = nil
-    assert_equal "developers/#{dev.id}-#{dev.updated_on.utc.to_s(:nsec)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_on.utc.to_s(:usec)}", dev.cache_key
   end
 
   def test_cache_key_for_newer_updated_at
     dev = Developer.first
     dev.updated_at += 3600
-    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:nsec)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_at.utc.to_s(:usec)}", dev.cache_key
   end
 
   def test_cache_key_for_newer_updated_on
     dev = Developer.first
     dev.updated_on += 3600
-    assert_equal "developers/#{dev.id}-#{dev.updated_on.utc.to_s(:nsec)}", dev.cache_key
+    assert_equal "developers/#{dev.id}-#{dev.updated_on.utc.to_s(:usec)}", dev.cache_key
   end
 
   def test_cache_key_format_is_precise_enough
+    skip("Subsecond precision is not supported") unless subsecond_precision_supported?
     dev = Developer.first
     key = dev.cache_key
-    dev.touch
+    travel_to dev.updated_at + 0.000001 do
+      dev.touch
+    end
     assert_not_equal key, dev.cache_key
   end
 
+  def test_cache_key_format_is_not_too_precise
+    dev = Developer.first
+    dev.touch
+    key = dev.cache_key
+    assert_equal key, dev.reload.cache_key
+  end
+
+  def test_cache_version_format_is_precise_enough
+    skip("Subsecond precision is not supported") unless subsecond_precision_supported?
+    with_cache_versioning do
+      dev = Developer.first
+      version = dev.cache_version.to_param
+      travel_to Developer.first.updated_at + 0.000001 do
+        dev.touch
+      end
+      assert_not_equal version, dev.cache_version.to_param
+    end
+  end
+
+  def test_cache_version_format_is_not_too_precise
+    with_cache_versioning do
+      dev = Developer.first
+      dev.touch
+      key = dev.cache_version.to_param
+      assert_equal key, dev.reload.cache_version.to_param
+    end
+  end
+
   def test_named_timestamps_for_cache_key
-    owner = owners(:blackbeard)
-    assert_equal "owners/#{owner.id}-#{owner.happy_at.utc.to_s(:nsec)}", owner.cache_key(:updated_at, :happy_at)
+    assert_deprecated do
+      owner = owners(:blackbeard)
+      assert_equal "owners/#{owner.id}-#{owner.happy_at.utc.to_s(:usec)}", owner.cache_key(:updated_at, :happy_at)
+    end
+  end
+
+  def test_cache_key_when_named_timestamp_is_nil
+    assert_deprecated do
+      owner = owners(:blackbeard)
+      owner.happy_at = nil
+      assert_equal "owners/#{owner.id}", owner.cache_key(:happy_at)
+    end
+  end
+
+  def test_cache_key_is_stable_with_versioning_on
+    with_cache_versioning do
+      developer = Developer.first
+      first_key = developer.cache_key
+
+      developer.touch
+      second_key = developer.cache_key
+
+      assert_equal first_key, second_key
+    end
+  end
+
+  def test_cache_version_changes_with_versioning_on
+    with_cache_versioning do
+      developer     = Developer.first
+      first_version = developer.cache_version
+
+      travel 10.seconds do
+        developer.touch
+      end
+
+      second_version = developer.cache_version
+
+      assert_not_equal first_version, second_version
+    end
+  end
+
+  def test_cache_key_retains_version_when_custom_timestamp_is_used
+    with_cache_versioning do
+      developer = Developer.first
+      first_key = developer.cache_key_with_version
+
+      travel 10.seconds do
+        developer.touch
+      end
+
+      second_key = developer.cache_key_with_version
+
+      assert_not_equal first_key, second_key
+    end
+  end
+
+  def with_cache_versioning(value = true)
+    @old_cache_versioning = ActiveRecord::Base.cache_versioning
+    ActiveRecord::Base.cache_versioning = value
+    yield
+  ensure
+    ActiveRecord::Base.cache_versioning = @old_cache_versioning
   end
 end
diff --git a/activerecord/test/cases/invalid_connection_test.rb b/activerecord/test/cases/invalid_connection_test.rb
index 6523fc29fd..a1be9c2780 100644
--- a/activerecord/test/cases/invalid_connection_test.rb
+++ b/activerecord/test/cases/invalid_connection_test.rb
@@ -1,22 +1,26 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
-class TestAdapterWithInvalidConnection < ActiveRecord::TestCase
-  self.use_transactional_tests = false
+if current_adapter?(:Mysql2Adapter)
+  class TestAdapterWithInvalidConnection < ActiveRecord::TestCase
+    self.use_transactional_tests = false
 
-  class Bird < ActiveRecord::Base
-  end
+    class Bird < ActiveRecord::Base
+    end
 
-  def setup
-    # Can't just use current adapter; sqlite3 will create a database
-    # file on the fly.
-    Bird.establish_connection adapter: 'mysql', database: 'i_do_not_exist'
-  end
+    def setup
+      # Can't just use current adapter; sqlite3 will create a database
+      # file on the fly.
+      Bird.establish_connection adapter: "mysql2", database: "i_do_not_exist"
+    end
 
-  teardown do
-    Bird.remove_connection
-  end
+    teardown do
+      Bird.remove_connection
+    end
 
-  test "inspect on Model class does not raise" do
-    assert_equal "#{Bird.name} (call '#{Bird.name}.connection' to establish a connection)", Bird.inspect
+    test "inspect on Model class does not raise" do
+      assert_equal "#{Bird.name} (call '#{Bird.name}.connection' to establish a connection)", Bird.inspect
+    end
   end
 end
diff --git a/activerecord/test/cases/invertible_migration_test.rb b/activerecord/test/cases/invertible_migration_test.rb
index 99230aa3d5..6cf17ac15d 100644
--- a/activerecord/test/cases/invertible_migration_test.rb
+++ b/activerecord/test/cases/invertible_migration_test.rb
@@ -1,9 +1,14 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
+class Horse < ActiveRecord::Base
+end
+
 module ActiveRecord
   class InvertibleMigrationTest < ActiveRecord::TestCase
-    class SilentMigration < ActiveRecord::Migration
-      def write(text = '')
+    class SilentMigration < ActiveRecord::Migration::Current
+      def write(text = "")
         # sssshhhhh!!
       end
     end
@@ -17,6 +22,14 @@ module ActiveRecord
       end
     end
 
+    class InvertibleTransactionMigration < InvertibleMigration
+      def change
+        transaction do
+          super
+        end
+      end
+    end
+
     class InvertibleRevertMigration < SilentMigration
       def change
         revert do
@@ -76,7 +89,33 @@ module ActiveRecord
       end
     end
 
-    class LegacyMigration < ActiveRecord::Migration
+    class ChangeColumnDefault1 < SilentMigration
+      def change
+        create_table("horses") do |t|
+          t.column :name, :string, default: "Sekitoba"
+        end
+      end
+    end
+
+    class ChangeColumnDefault2 < SilentMigration
+      def change
+        change_column_default :horses, :name, from: "Sekitoba", to: "Diomed"
+      end
+    end
+
+    class DisableExtension1 < SilentMigration
+      def change
+        enable_extension "hstore"
+      end
+    end
+
+    class DisableExtension2 < SilentMigration
+      def change
+        disable_extension "hstore"
+      end
+    end
+
+    class LegacyMigration < ActiveRecord::Migration::Current
       def self.up
         create_table("horses") do |t|
           t.column :content, :text
@@ -122,6 +161,23 @@ module ActiveRecord
       end
     end
 
+    class RevertCustomForeignKeyTable < SilentMigration
+      def change
+        change_table(:horses) do |t|
+          t.references :owner, foreign_key: { to_table: :developers }
+        end
+      end
+    end
+
+    class UpOnlyMigration < SilentMigration
+      def change
+        add_column :horses, :oldie, :integer, default: 0
+        up_only { execute "update horses set oldie = 1" }
+      end
+    end
+
+    self.use_transactional_tests = false
+
     setup do
       @verbose_was, ActiveRecord::Migration.verbose = ActiveRecord::Migration.verbose, false
     end
@@ -167,7 +223,7 @@ module ActiveRecord
       migration = InvertibleMigration.new
       migration.migrate :up
       migration.migrate :down
-      assert !migration.connection.table_exists?("horses")
+      assert_not migration.connection.table_exists?("horses")
     end
 
     def test_migrate_revert
@@ -175,30 +231,30 @@ module ActiveRecord
       revert = InvertibleRevertMigration.new
       migration.migrate :up
       revert.migrate :up
-      assert !migration.connection.table_exists?("horses")
+      assert_not migration.connection.table_exists?("horses")
       revert.migrate :down
       assert migration.connection.table_exists?("horses")
       migration.migrate :down
-      assert !migration.connection.table_exists?("horses")
+      assert_not migration.connection.table_exists?("horses")
     end
 
     def test_migrate_revert_by_part
       InvertibleMigration.new.migrate :up
       received = []
       migration = InvertibleByPartsMigration.new
-      migration.test = ->(dir){
+      migration.test = ->(dir) {
         assert migration.connection.table_exists?("horses")
         assert migration.connection.table_exists?("new_horses")
         received << dir
       }
       migration.migrate :up
       assert_equal [:both, :up], received
-      assert !migration.connection.table_exists?("horses")
+      assert_not migration.connection.table_exists?("horses")
       assert migration.connection.table_exists?("new_horses")
       migration.migrate :down
       assert_equal [:both, :up, :both, :down], received
       assert migration.connection.table_exists?("horses")
-      assert !migration.connection.table_exists?("new_horses")
+      assert_not migration.connection.table_exists?("new_horses")
     end
 
     def test_migrate_revert_whole_migration
@@ -207,11 +263,11 @@ module ActiveRecord
         revert = RevertWholeMigration.new(klass)
         migration.migrate :up
         revert.migrate :up
-        assert !migration.connection.table_exists?("horses")
+        assert_not migration.connection.table_exists?("horses")
         revert.migrate :down
         assert migration.connection.table_exists?("horses")
         migration.migrate :down
-        assert !migration.connection.table_exists?("horses")
+        assert_not migration.connection.table_exists?("horses")
       end
     end
 
@@ -220,11 +276,57 @@ module ActiveRecord
       revert.migrate :down
       assert revert.connection.table_exists?("horses")
       revert.migrate :up
-      assert !revert.connection.table_exists?("horses")
+      assert_not revert.connection.table_exists?("horses")
+    end
+
+    def test_migrate_revert_transaction
+      migration = InvertibleTransactionMigration.new
+      migration.migrate :up
+      assert migration.connection.table_exists?("horses")
+      migration.migrate :down
+      assert_not migration.connection.table_exists?("horses")
+    end
+
+    def test_migrate_revert_change_column_default
+      migration1 = ChangeColumnDefault1.new
+      migration1.migrate(:up)
+      assert_equal "Sekitoba", Horse.new.name
+
+      migration2 = ChangeColumnDefault2.new
+      migration2.migrate(:up)
+      Horse.reset_column_information
+      assert_equal "Diomed", Horse.new.name
+
+      migration2.migrate(:down)
+      Horse.reset_column_information
+      assert_equal "Sekitoba", Horse.new.name
+    end
+
+    if current_adapter?(:PostgreSQLAdapter)
+      def test_migrate_enable_and_disable_extension
+        migration1 = InvertibleMigration.new
+        migration2 = DisableExtension1.new
+        migration3 = DisableExtension2.new
+
+        migration1.migrate(:up)
+        migration2.migrate(:up)
+        assert_equal true, Horse.connection.extension_enabled?("hstore")
+
+        migration3.migrate(:up)
+        assert_equal false, Horse.connection.extension_enabled?("hstore")
+
+        migration3.migrate(:down)
+        assert_equal true, Horse.connection.extension_enabled?("hstore")
+
+        migration2.migrate(:down)
+        assert_equal false, Horse.connection.extension_enabled?("hstore")
+      ensure
+        enable_extension!("hstore", ActiveRecord::Base.connection)
+      end
     end
 
     def test_revert_order
-      block = Proc.new{|t| t.string :name }
+      block = Proc.new { |t| t.string :name }
       recorder = ActiveRecord::Migration::CommandRecorder.new(ActiveRecord::Base.connection)
       recorder.instance_eval do
         create_table("apples", &block)
@@ -255,7 +357,7 @@ module ActiveRecord
     def test_legacy_down
       LegacyMigration.migrate :up
       LegacyMigration.migrate :down
-      assert !ActiveRecord::Base.connection.table_exists?("horses"), "horses should not exist"
+      assert_not ActiveRecord::Base.connection.table_exists?("horses"), "horses should not exist"
     end
 
     def test_up
@@ -266,22 +368,29 @@ module ActiveRecord
     def test_down
       LegacyMigration.up
       LegacyMigration.down
-      assert !ActiveRecord::Base.connection.table_exists?("horses"), "horses should not exist"
+      assert_not ActiveRecord::Base.connection.table_exists?("horses"), "horses should not exist"
     end
 
     def test_migrate_down_with_table_name_prefix
-      ActiveRecord::Base.table_name_prefix = 'p_'
-      ActiveRecord::Base.table_name_suffix = '_s'
+      ActiveRecord::Base.table_name_prefix = "p_"
+      ActiveRecord::Base.table_name_suffix = "_s"
       migration = InvertibleMigration.new
       migration.migrate(:up)
       assert_nothing_raised { migration.migrate(:down) }
-      assert !ActiveRecord::Base.connection.table_exists?("p_horses_s"), "p_horses_s should not exist"
+      assert_not ActiveRecord::Base.connection.table_exists?("p_horses_s"), "p_horses_s should not exist"
     ensure
-      ActiveRecord::Base.table_name_prefix = ActiveRecord::Base.table_name_suffix = ''
+      ActiveRecord::Base.table_name_prefix = ActiveRecord::Base.table_name_suffix = ""
+    end
+
+    def test_migrations_can_handle_foreign_keys_to_specific_tables
+      migration = RevertCustomForeignKeyTable.new
+      InvertibleMigration.migrate(:up)
+      migration.migrate(:up)
+      migration.migrate(:down)
     end
 
     # MySQL 5.7 and Oracle do not allow to create duplicate indexes on the same columns
-    unless current_adapter?(:MysqlAdapter, :Mysql2Adapter, :OracleAdapter)
+    unless current_adapter?(:Mysql2Adapter, :OracleAdapter)
       def test_migrate_revert_add_index_with_name
         RevertNamedIndexMigration1.new.migrate(:up)
         RevertNamedIndexMigration2.new.migrate(:up)
@@ -290,10 +399,27 @@ module ActiveRecord
         connection = ActiveRecord::Base.connection
         assert connection.index_exists?(:horses, :content),
                "index on content should exist"
-        assert !connection.index_exists?(:horses, :content, name: "horses_index_named"),
+        assert_not connection.index_exists?(:horses, :content, name: "horses_index_named"),
               "horses_index_named index should not exist"
       end
     end
 
+    def test_up_only
+      InvertibleMigration.new.migrate(:up)
+      horse1 = Horse.create
+      # populates existing horses with oldie = 1 but new ones have default 0
+      UpOnlyMigration.new.migrate(:up)
+      Horse.reset_column_information
+      horse1.reload
+      horse2 = Horse.create
+
+      assert 1, horse1.oldie # created before migration
+      assert 0, horse2.oldie # created after migration
+
+      UpOnlyMigration.new.migrate(:down) # should be no error
+      connection = ActiveRecord::Base.connection
+      assert_not connection.column_exists?(:horses, :oldie)
+      Horse.reset_column_information
+    end
   end
 end
diff --git a/activerecord/test/cases/json_attribute_test.rb b/activerecord/test/cases/json_attribute_test.rb
new file mode 100644
index 0000000000..afc39d0420
--- /dev/null
+++ b/activerecord/test/cases/json_attribute_test.rb
@@ -0,0 +1,35 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "cases/json_shared_test_cases"
+
+class JsonAttributeTest < ActiveRecord::TestCase
+  include JSONSharedTestCases
+  self.use_transactional_tests = false
+
+  class JsonDataTypeOnText < ActiveRecord::Base
+    self.table_name = "json_data_type"
+
+    attribute :payload,  :json
+    attribute :settings, :json
+
+    store_accessor :settings, :resolution
+  end
+
+  def setup
+    super
+    @connection.create_table("json_data_type") do |t|
+      t.string "payload"
+      t.string "settings"
+    end
+  end
+
+  private
+    def column_type
+      :string
+    end
+
+    def klass
+      JsonDataTypeOnText
+    end
+end
diff --git a/activerecord/test/cases/json_serialization_test.rb b/activerecord/test/cases/json_serialization_test.rb
index a222675918..82cf281cff 100644
--- a/activerecord/test/cases/json_serialization_test.rb
+++ b/activerecord/test/cases/json_serialization_test.rb
@@ -1,21 +1,23 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/contact'
-require 'models/post'
-require 'models/author'
-require 'models/tagging'
-require 'models/tag'
-require 'models/comment'
+require "models/contact"
+require "models/post"
+require "models/author"
+require "models/tagging"
+require "models/tag"
+require "models/comment"
 
 module JsonSerializationHelpers
   private
 
-  def set_include_root_in_json(value)
-    original_root_in_json = ActiveRecord::Base.include_root_in_json
-    ActiveRecord::Base.include_root_in_json = value
-    yield
-  ensure
-    ActiveRecord::Base.include_root_in_json = original_root_in_json
-  end
+    def set_include_root_in_json(value)
+      original_root_in_json = ActiveRecord::Base.include_root_in_json
+      ActiveRecord::Base.include_root_in_json = value
+      yield
+    ensure
+      ActiveRecord::Base.include_root_in_json = original_root_in_json
+    end
 end
 
 class JsonSerializationTest < ActiveRecord::TestCase
@@ -27,18 +29,18 @@ class JsonSerializationTest < ActiveRecord::TestCase
 
   def setup
     @contact = Contact.new(
-      :name        => 'Konata Izumi',
-      :age         => 16,
-      :avatar      => 'binarydata',
-      :created_at  => Time.utc(2006, 8, 1),
-      :awesome     => true,
-      :preferences => { :shows => 'anime' }
+      name: "Konata Izumi",
+      age: 16,
+      avatar: "binarydata",
+      created_at: Time.utc(2006, 8, 1),
+      awesome: true,
+      preferences: { shows: "anime" }
     )
   end
 
   def test_should_demodulize_root_in_json
     set_include_root_in_json(true) do
-      @contact = NamespacedContact.new name: 'whatever'
+      @contact = NamespacedContact.new name: "whatever"
       json = @contact.to_json
       assert_match %r{^\{"namespaced_contact":\{}, json
     end
@@ -51,7 +53,7 @@ class JsonSerializationTest < ActiveRecord::TestCase
       assert_match %r{^\{"contact":\{}, json
       assert_match %r{"name":"Konata Izumi"}, json
       assert_match %r{"age":16}, json
-      assert json.include?(%("created_at":#{ActiveSupport::JSON.encode(Time.utc(2006, 8, 1))}))
+      assert_includes json, %("created_at":#{ActiveSupport::JSON.encode(Time.utc(2006, 8, 1))})
       assert_match %r{"awesome":true}, json
       assert_match %r{"preferences":\{"shows":"anime"\}}, json
     end
@@ -62,28 +64,28 @@ class JsonSerializationTest < ActiveRecord::TestCase
 
     assert_match %r{"name":"Konata Izumi"}, json
     assert_match %r{"age":16}, json
-    assert json.include?(%("created_at":#{ActiveSupport::JSON.encode(Time.utc(2006, 8, 1))}))
+    assert_includes json, %("created_at":#{ActiveSupport::JSON.encode(Time.utc(2006, 8, 1))})
     assert_match %r{"awesome":true}, json
     assert_match %r{"preferences":\{"shows":"anime"\}}, json
   end
 
   def test_should_allow_attribute_filtering_with_only
-    json = @contact.to_json(:only => [:name, :age])
+    json = @contact.to_json(only: [:name, :age])
 
     assert_match %r{"name":"Konata Izumi"}, json
     assert_match %r{"age":16}, json
     assert_no_match %r{"awesome":true}, json
-    assert !json.include?(%("created_at":#{ActiveSupport::JSON.encode(Time.utc(2006, 8, 1))}))
+    assert_not_includes json, %("created_at":#{ActiveSupport::JSON.encode(Time.utc(2006, 8, 1))})
     assert_no_match %r{"preferences":\{"shows":"anime"\}}, json
   end
 
   def test_should_allow_attribute_filtering_with_except
-    json = @contact.to_json(:except => [:name, :age])
+    json = @contact.to_json(except: [:name, :age])
 
     assert_no_match %r{"name":"Konata Izumi"}, json
     assert_no_match %r{"age":16}, json
     assert_match %r{"awesome":true}, json
-    assert json.include?(%("created_at":#{ActiveSupport::JSON.encode(Time.utc(2006, 8, 1))}))
+    assert_includes json, %("created_at":#{ActiveSupport::JSON.encode(Time.utc(2006, 8, 1))})
     assert_match %r{"preferences":\{"shows":"anime"\}}, json
   end
 
@@ -93,16 +95,27 @@ class JsonSerializationTest < ActiveRecord::TestCase
     def @contact.favorite_quote; "Constraints are liberating"; end
 
     # Single method.
-    assert_match %r{"label":"Has cheezburger"}, @contact.to_json(:only => :name, :methods => :label)
+    assert_match %r{"label":"Has cheezburger"}, @contact.to_json(only: :name, methods: :label)
 
     # Both methods.
-    methods_json = @contact.to_json(:only => :name, :methods => [:label, :favorite_quote])
+    methods_json = @contact.to_json(only: :name, methods: [:label, :favorite_quote])
     assert_match %r{"label":"Has cheezburger"}, methods_json
     assert_match %r{"favorite_quote":"Constraints are liberating"}, methods_json
   end
 
+  def test_uses_serializable_hash_with_frozen_hash
+    def @contact.serializable_hash(options = nil)
+      super({ only: %w(name) }.freeze)
+    end
+
+    json = @contact.to_json
+    assert_match %r{"name":"Konata Izumi"}, json
+    assert_no_match %r{awesome}, json
+    assert_no_match %r{age}, json
+  end
+
   def test_uses_serializable_hash_with_only_option
-    def @contact.serializable_hash(options=nil)
+    def @contact.serializable_hash(options = nil)
       super(only: %w(name))
     end
 
@@ -113,7 +126,7 @@ class JsonSerializationTest < ActiveRecord::TestCase
   end
 
   def test_uses_serializable_hash_with_except_option
-    def @contact.serializable_hash(options=nil)
+    def @contact.serializable_hash(options = nil)
       super(except: %w(age))
     end
 
@@ -125,7 +138,7 @@ class JsonSerializationTest < ActiveRecord::TestCase
 
   def test_does_not_include_inheritance_column_from_sti
     @contact = ContactSti.new(@contact.attributes)
-    assert_equal 'ContactSti', @contact.type
+    assert_equal "ContactSti", @contact.type
 
     json = @contact.to_json
     assert_match %r{"name":"Konata Izumi"}, json
@@ -135,9 +148,9 @@ class JsonSerializationTest < ActiveRecord::TestCase
 
   def test_serializable_hash_with_default_except_option_and_excluding_inheritance_column_from_sti
     @contact = ContactSti.new(@contact.attributes)
-    assert_equal 'ContactSti', @contact.type
+    assert_equal "ContactSti", @contact.type
 
-    def @contact.serializable_hash(options={})
+    def @contact.serializable_hash(options = {})
       super({ except: %w(age) }.merge!(options))
     end
 
@@ -149,15 +162,13 @@ class JsonSerializationTest < ActiveRecord::TestCase
   end
 
   def test_serializable_hash_should_not_modify_options_in_argument
-    options = { :only => :name }
-    @contact.serializable_hash(options)
-
-    assert_nil options[:except]
+    options = { only: :name }.freeze
+    assert_nothing_raised { @contact.serializable_hash(options) }
   end
 end
 
 class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
-  fixtures :authors, :posts, :comments, :tags, :taggings
+  fixtures :authors, :author_addresses, :posts, :comments, :tags, :taggings
 
   include JsonSerializationHelpers
 
@@ -167,7 +178,7 @@ class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
   end
 
   def test_includes_uses_association_name
-    json = @david.to_json(:include => :posts)
+    json = @david.to_json(include: :posts)
 
     assert_match %r{"posts":\[}, json
 
@@ -183,7 +194,7 @@ class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
   end
 
   def test_includes_uses_association_name_and_applies_attribute_filters
-    json = @david.to_json(:include => { :posts => { :only => :title } })
+    json = @david.to_json(include: { posts: { only: :title } })
 
     assert_match %r{"name":"David"}, json
     assert_match %r{"posts":\[}, json
@@ -196,7 +207,7 @@ class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
   end
 
   def test_includes_fetches_second_level_associations
-    json = @david.to_json(:include => { :posts => { :include => { :comments => { :only => :body } } } })
+    json = @david.to_json(include: { posts: { include: { comments: { only: :body } } } })
 
     assert_match %r{"name":"David"}, json
     assert_match %r{"posts":\[}, json
@@ -209,12 +220,12 @@ class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
 
   def test_includes_fetches_nth_level_associations
     json = @david.to_json(
-      :include => {
-        :posts => {
-          :include => {
-            :taggings => {
-              :include => {
-                :tag => { :only => :name }
+      include: {
+        posts: {
+          include: {
+            taggings: {
+              include: {
+                tag: { only: :name }
               }
             }
           }
@@ -230,8 +241,8 @@ class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
 
   def test_includes_doesnt_merge_opts_from_base
     json = @david.to_json(
-      :only => :id,
-      :include => :posts
+      only: :id,
+      include: :posts
     )
 
     assert_match %{"title":"Welcome to the weblog"}, json
@@ -239,11 +250,11 @@ class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
 
   def test_should_not_call_methods_on_associations_that_dont_respond
     def @david.favorite_quote; "Constraints are liberating"; end
-    json = @david.to_json(:include => :posts, :methods => :favorite_quote)
+    json = @david.to_json(include: :posts, methods: :favorite_quote)
 
-    assert !@david.posts.first.respond_to?(:favorite_quote)
+    assert_not_respond_to @david.posts.first, :favorite_quote
     assert_match %r{"favorite_quote":"Constraints are liberating"}, json
-    assert_equal %r{"favorite_quote":}.match(json).size, 1
+    assert_equal 1, %r{"favorite_quote":}.match(json).size
   end
 
   def test_should_allow_only_option_for_list_of_authors
@@ -267,15 +278,15 @@ class DatabaseConnectedJsonEncodingTest < ActiveRecord::TestCase
   def test_should_allow_includes_for_list_of_authors
     authors = [@david, @mary]
     json = ActiveSupport::JSON.encode(authors,
-      :only => :name,
-      :include => {
-        :posts => { :only => :id }
+      only: :name,
+      include: {
+        posts: { only: :id }
       }
     )
 
     ['"name":"David"', '"posts":[', '{"id":1}', '{"id":2}', '{"id":4}',
      '{"id":5}', '{"id":6}', '"name":"Mary"', '"posts":[', '{"id":7}', '{"id":9}'].each do |fragment|
-      assert json.include?(fragment), json
+       assert_includes json, fragment, json
      end
   end
 
diff --git a/activerecord/test/cases/json_shared_test_cases.rb b/activerecord/test/cases/json_shared_test_cases.rb
new file mode 100644
index 0000000000..9b79803503
--- /dev/null
+++ b/activerecord/test/cases/json_shared_test_cases.rb
@@ -0,0 +1,269 @@
+# frozen_string_literal: true
+
+require "support/schema_dumping_helper"
+
+module JSONSharedTestCases
+  include SchemaDumpingHelper
+
+  class JsonDataType < ActiveRecord::Base
+    self.table_name = "json_data_type"
+
+    store_accessor :settings, :resolution
+  end
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+  end
+
+  def teardown
+    @connection.drop_table :json_data_type, if_exists: true
+    klass.reset_column_information
+  end
+
+  def test_column
+    column = klass.columns_hash["payload"]
+    assert_equal column_type, column.type
+    assert_type_match column_type, column.sql_type
+
+    type = klass.type_for_attribute("payload")
+    assert_not_predicate type, :binary?
+  end
+
+  def test_change_table_supports_json
+    @connection.change_table("json_data_type") do |t|
+      t.public_send column_type, "users"
+    end
+    klass.reset_column_information
+    column = klass.columns_hash["users"]
+    assert_equal column_type, column.type
+    assert_type_match column_type, column.sql_type
+  end
+
+  def test_schema_dumping
+    output = dump_table_schema("json_data_type")
+    assert_match(/t\.#{column_type}\s+"settings"/, output)
+  end
+
+  def test_cast_value_on_write
+    x = klass.new(payload: { "string" => "foo", :symbol => :bar })
+    assert_equal({ "string" => "foo", :symbol => :bar }, x.payload_before_type_cast)
+    assert_equal({ "string" => "foo", "symbol" => "bar" }, x.payload)
+    x.save!
+    assert_equal({ "string" => "foo", "symbol" => "bar" }, x.reload.payload)
+  end
+
+  def test_type_cast_json
+    type = klass.type_for_attribute("payload")
+
+    data = '{"a_key":"a_value"}'
+    hash = type.deserialize(data)
+    assert_equal({ "a_key" => "a_value" }, hash)
+    assert_equal({ "a_key" => "a_value" }, type.deserialize(data))
+
+    assert_equal({}, type.deserialize("{}"))
+    assert_equal({ "key" => nil }, type.deserialize('{"key": null}'))
+    assert_equal({ "c" => "}", '"a"' => 'b "a b' }, type.deserialize(%q({"c":"}", "\"a\"":"b \"a b"})))
+  end
+
+  def test_rewrite
+    @connection.execute(insert_statement_per_database('{"k":"v"}'))
+    x = klass.first
+    x.payload = { '"a\'' => "b" }
+    assert x.save!
+  end
+
+  def test_select
+    @connection.execute(insert_statement_per_database('{"k":"v"}'))
+    x = klass.first
+    assert_equal({ "k" => "v" }, x.payload)
+  end
+
+  def test_select_multikey
+    @connection.execute(insert_statement_per_database('{"k1":"v1", "k2":"v2", "k3":[1,2,3]}'))
+    x = klass.first
+    assert_equal({ "k1" => "v1", "k2" => "v2", "k3" => [1, 2, 3] }, x.payload)
+  end
+
+  def test_null_json
+    @connection.execute(insert_statement_per_database("null"))
+    x = klass.first
+    assert_nil(x.payload)
+  end
+
+  def test_select_nil_json_after_create
+    json = klass.create!(payload: nil)
+    x = klass.where(payload: nil).first
+    assert_equal(json, x)
+  end
+
+  def test_select_nil_json_after_update
+    json = klass.create!(payload: "foo")
+    x = klass.where(payload: nil).first
+    assert_nil(x)
+
+    json.update(payload: nil)
+    x = klass.where(payload: nil).first
+    assert_equal(json.reload, x)
+  end
+
+  def test_select_array_json_value
+    @connection.execute(insert_statement_per_database('["v0",{"k1":"v1"}]'))
+    x = klass.first
+    assert_equal(["v0", { "k1" => "v1" }], x.payload)
+  end
+
+  def test_rewrite_array_json_value
+    @connection.execute(insert_statement_per_database('["v0",{"k1":"v1"}]'))
+    x = klass.first
+    x.payload = ["v1", { "k2" => "v2" }, "v3"]
+    assert x.save!
+  end
+
+  def test_with_store_accessors
+    x = klass.new(resolution: "320×480")
+    assert_equal "320×480", x.resolution
+
+    x.save!
+    x = klass.first
+    assert_equal "320×480", x.resolution
+
+    x.resolution = "640×1136"
+    x.save!
+
+    x = klass.first
+    assert_equal "640×1136", x.resolution
+  end
+
+  def test_duplication_with_store_accessors
+    x = klass.new(resolution: "320×480")
+    assert_equal "320×480", x.resolution
+
+    y = x.dup
+    assert_equal "320×480", y.resolution
+  end
+
+  def test_yaml_round_trip_with_store_accessors
+    x = klass.new(resolution: "320×480")
+    assert_equal "320×480", x.resolution
+
+    y = YAML.load(YAML.dump(x))
+    assert_equal "320×480", y.resolution
+  end
+
+  def test_changes_in_place
+    json = klass.new
+    assert_not_predicate json, :changed?
+
+    json.payload = { "one" => "two" }
+    assert_predicate json, :changed?
+    assert_predicate json, :payload_changed?
+
+    json.save!
+    assert_not_predicate json, :changed?
+
+    json.payload["three"] = "four"
+    assert_predicate json, :payload_changed?
+
+    json.save!
+    json.reload
+
+    assert_equal({ "one" => "two", "three" => "four" }, json.payload)
+    assert_not_predicate json, :changed?
+  end
+
+  def test_changes_in_place_ignores_key_order
+    json = klass.new
+    assert_not_predicate json, :changed?
+
+    json.payload = { "three" => "four", "one" => "two" }
+    json.save!
+    json.reload
+
+    json.payload = { "three" => "four", "one" => "two" }
+    assert_not_predicate json, :changed?
+
+    json.payload = [{ "three" => "four", "one" => "two" }, { "seven" => "eight", "five" => "six" }]
+    json.save!
+    json.reload
+
+    json.payload = [{ "three" => "four", "one" => "two" }, { "seven" => "eight", "five" => "six" }]
+    assert_not_predicate json, :changed?
+  end
+
+  def test_changes_in_place_with_ruby_object
+    time = Time.now.utc
+    json = klass.create!(payload: time)
+
+    json.reload
+    assert_not_predicate json, :changed?
+
+    json.payload = time
+    assert_not_predicate json, :changed?
+  end
+
+  def test_assigning_string_literal
+    json = klass.create!(payload: "foo")
+    assert_equal "foo", json.payload
+  end
+
+  def test_assigning_number
+    json = klass.create!(payload: 1.234)
+    assert_equal 1.234, json.payload
+  end
+
+  def test_assigning_boolean
+    json = klass.create!(payload: true)
+    assert_equal true, json.payload
+  end
+
+  def test_not_compatible_with_serialize_json
+    new_klass = Class.new(klass) do
+      serialize :payload, JSON
+    end
+    assert_raises(ActiveRecord::AttributeMethods::Serialization::ColumnNotSerializableError) do
+      new_klass.new
+    end
+  end
+
+  class MySettings
+    def initialize(hash); @hash = hash end
+    def to_hash; @hash end
+    def self.load(hash); new(hash) end
+    def self.dump(object); object.to_hash end
+  end
+
+  def test_json_with_serialized_attributes
+    new_klass = Class.new(klass) do
+      serialize :settings, MySettings
+    end
+
+    new_klass.create!(settings: MySettings.new("one" => "two"))
+    record = new_klass.first
+
+    assert_instance_of MySettings, record.settings
+    assert_equal({ "one" => "two" }, record.settings.to_hash)
+
+    record.settings = MySettings.new("three" => "four")
+    record.save!
+
+    assert_equal({ "three" => "four" }, record.reload.settings.to_hash)
+  end
+
+  private
+    def klass
+      JsonDataType
+    end
+
+    def assert_type_match(type, sql_type)
+      native_type = ActiveRecord::Base.connection.native_database_types[type][:name]
+      assert_match %r(\A#{native_type}\b), sql_type
+    end
+
+    def insert_statement_per_database(values)
+      if current_adapter?(:OracleAdapter)
+        "insert into json_data_type (id, payload) VALUES (json_data_type_seq.nextval, '#{values}')"
+      else
+        "insert into json_data_type (payload) VALUES ('#{values}')"
+      end
+    end
+end
diff --git a/activerecord/test/cases/legacy_configurations_test.rb b/activerecord/test/cases/legacy_configurations_test.rb
new file mode 100644
index 0000000000..c36feb5116
--- /dev/null
+++ b/activerecord/test/cases/legacy_configurations_test.rb
@@ -0,0 +1,43 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+module ActiveRecord
+  class LegacyConfigurationsTest < ActiveRecord::TestCase
+    def test_can_turn_configurations_into_a_hash
+      assert ActiveRecord::Base.configurations.to_h.is_a?(Hash), "expected to be a hash but was not."
+      assert_equal ["arunit", "arunit2", "arunit_without_prepared_statements"].sort, ActiveRecord::Base.configurations.to_h.keys.sort
+    end
+
+    def test_each_is_deprecated
+      assert_deprecated do
+        ActiveRecord::Base.configurations.each do |db_config|
+          assert_equal "primary", db_config.spec_name
+        end
+      end
+    end
+
+    def test_first_is_deprecated
+      assert_deprecated do
+        db_config = ActiveRecord::Base.configurations.first
+        assert_equal "arunit", db_config.env_name
+        assert_equal "primary", db_config.spec_name
+      end
+    end
+
+    def test_fetch_is_deprecated
+      assert_deprecated do
+        db_config = ActiveRecord::Base.configurations.fetch("arunit").first
+        assert_equal "arunit", db_config.env_name
+        assert_equal "primary", db_config.spec_name
+      end
+    end
+
+    def test_values_are_deprecated
+      config_hashes = ActiveRecord::Base.configurations.configurations.map(&:config)
+      assert_deprecated do
+        assert_equal config_hashes, ActiveRecord::Base.configurations.values
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/locking_test.rb b/activerecord/test/cases/locking_test.rb
index dbdcc84b7d..33bd74e114 100644
--- a/activerecord/test/cases/locking_test.rb
+++ b/activerecord/test/cases/locking_test.rb
@@ -1,24 +1,27 @@
-require 'thread'
+# frozen_string_literal: true
+
+require "thread"
 require "cases/helper"
-require 'models/person'
-require 'models/job'
-require 'models/reader'
-require 'models/ship'
-require 'models/legacy_thing'
-require 'models/personal_legacy_thing'
-require 'models/reference'
-require 'models/string_key_object'
-require 'models/car'
-require 'models/bulb'
-require 'models/engine'
-require 'models/wheel'
-require 'models/treasure'
+require "models/person"
+require "models/job"
+require "models/reader"
+require "models/ship"
+require "models/legacy_thing"
+require "models/personal_legacy_thing"
+require "models/reference"
+require "models/string_key_object"
+require "models/car"
+require "models/bulb"
+require "models/engine"
+require "models/wheel"
+require "models/treasure"
+require "models/frog"
 
 class LockWithoutDefault < ActiveRecord::Base; end
 
 class LockWithCustomColumnWithoutDefault < ActiveRecord::Base
   self.table_name = :lock_without_defaults_cust
-  self.column_defaults # to test @column_defaults caching.
+  column_defaults # to test @column_defaults caching.
   self.locking_column = :custom_lock_version
 end
 
@@ -33,7 +36,7 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     p1 = Person.find(1)
     assert_equal 0, p1.lock_version
 
-    p1.first_name = 'anika2'
+    p1.first_name = "anika2"
     p1.save!
 
     assert_equal 1, p1.lock_version
@@ -45,12 +48,12 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     assert_equal 0, s1.lock_version
     assert_equal 0, s2.lock_version
 
-    s1.name = 'updated record'
+    s1.name = "updated record"
     s1.save!
     assert_equal 1, s1.lock_version
     assert_equal 0, s2.lock_version
 
-    s2.name = 'doubly updated record'
+    s2.name = "doubly updated record"
     assert_raise(ActiveRecord::StaleObjectError) { s2.save! }
   end
 
@@ -60,15 +63,15 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     assert_equal 0, s1.lock_version
     assert_equal 0, s2.lock_version
 
-    s1.name = 'updated record'
+    s1.name = "updated record"
     s1.save!
     assert_equal 1, s1.lock_version
     assert_equal 0, s2.lock_version
     assert_raise(ActiveRecord::StaleObjectError) { s2.destroy }
 
     assert s1.destroy
-    assert s1.frozen?
-    assert s1.destroyed?
+    assert_predicate s1, :frozen?
+    assert_predicate s1, :destroyed?
     assert_raises(ActiveRecord::RecordNotFound) { StringKeyObject.find("record1") }
   end
 
@@ -78,12 +81,12 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     assert_equal 0, p1.lock_version
     assert_equal 0, p2.lock_version
 
-    p1.first_name = 'stu'
+    p1.first_name = "stu"
     p1.save!
     assert_equal 1, p1.lock_version
     assert_equal 0, p2.lock_version
 
-    p2.first_name = 'sue'
+    p2.first_name = "sue"
     assert_raise(ActiveRecord::StaleObjectError) { p2.save! }
   end
 
@@ -94,7 +97,7 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     assert_equal 0, p1.lock_version
     assert_equal 0, p2.lock_version
 
-    p1.first_name = 'stu'
+    p1.first_name = "stu"
     p1.save!
     assert_equal 1, p1.lock_version
     assert_equal 0, p2.lock_version
@@ -102,8 +105,8 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     assert_raises(ActiveRecord::StaleObjectError) { p2.destroy }
 
     assert p1.destroy
-    assert p1.frozen?
-    assert p1.destroyed?
+    assert_predicate p1, :frozen?
+    assert_predicate p1, :destroyed?
     assert_raises(ActiveRecord::RecordNotFound) { Person.find(1) }
   end
 
@@ -113,60 +116,64 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     assert_equal 0, p1.lock_version
     assert_equal 0, p2.lock_version
 
-    p1.first_name = 'stu'
+    p1.first_name = "stu"
     p1.save!
     assert_equal 1, p1.lock_version
     assert_equal 0, p2.lock_version
 
-    p2.first_name = 'sue'
+    p2.first_name = "sue"
     assert_raise(ActiveRecord::StaleObjectError) { p2.save! }
-    p2.first_name = 'sue2'
+    p2.first_name = "sue2"
     assert_raise(ActiveRecord::StaleObjectError) { p2.save! }
   end
 
   def test_lock_new
-    p1 = Person.new(:first_name => 'anika')
+    p1 = Person.new(first_name: "anika")
     assert_equal 0, p1.lock_version
 
-    p1.first_name = 'anika2'
+    p1.first_name = "anika2"
     p1.save!
     p2 = Person.find(p1.id)
     assert_equal 0, p1.lock_version
     assert_equal 0, p2.lock_version
 
-    p1.first_name = 'anika3'
+    p1.first_name = "anika3"
     p1.save!
     assert_equal 1, p1.lock_version
     assert_equal 0, p2.lock_version
 
-    p2.first_name = 'sue'
+    p2.first_name = "sue"
     assert_raise(ActiveRecord::StaleObjectError) { p2.save! }
   end
 
   def test_lock_exception_record
-    p1 = Person.new(:first_name => 'mira')
+    p1 = Person.new(first_name: "mira")
     assert_equal 0, p1.lock_version
 
-    p1.first_name = 'mira2'
+    p1.first_name = "mira2"
     p1.save!
     p2 = Person.find(p1.id)
     assert_equal 0, p1.lock_version
     assert_equal 0, p2.lock_version
 
-    p1.first_name = 'mira3'
+    p1.first_name = "mira3"
     p1.save!
 
-    p2.first_name = 'sue'
+    p2.first_name = "sue"
     error = assert_raise(ActiveRecord::StaleObjectError) { p2.save! }
     assert_equal(error.record.object_id, p2.object_id)
   end
 
-  def test_lock_new_with_nil
-    p1 = Person.new(:first_name => 'anika')
+  def test_lock_new_when_explicitly_passing_nil
+    p1 = Person.new(first_name: "anika", lock_version: nil)
     p1.save!
-    p1.lock_version = nil # simulate bad fixture or column with no default
+    assert_equal 0, p1.lock_version
+  end
+
+  def test_lock_new_when_explicitly_passing_value
+    p1 = Person.new(first_name: "Douglas Adams", lock_version: 42)
     p1.save!
-    assert_equal 1, p1.lock_version
+    assert_equal 42, p1.lock_version
   end
 
   def test_touch_existing_lock
@@ -175,18 +182,71 @@ class OptimisticLockingTest < ActiveRecord::TestCase
 
     p1.touch
     assert_equal 1, p1.lock_version
+    assert_not p1.changed?, "Changes should have been cleared"
   end
 
   def test_touch_stale_object
-    person = Person.create!(first_name: 'Mehmet Emin')
+    person = Person.create!(first_name: "Mehmet Emin")
     stale_person = Person.find(person.id)
-    person.update_attribute(:gender, 'M')
+    person.update_attribute(:gender, "M")
 
     assert_raises(ActiveRecord::StaleObjectError) do
       stale_person.touch
     end
   end
 
+  def test_update_with_dirty_primary_key
+    assert_raises(ActiveRecord::RecordNotUnique) do
+      person = Person.find(1)
+      person.id = 2
+      person.save!
+    end
+
+    person = Person.find(1)
+    person.id = 42
+    person.save!
+
+    assert Person.find(42)
+    assert_raises(ActiveRecord::RecordNotFound) do
+      Person.find(1)
+    end
+  end
+
+  def test_delete_with_dirty_primary_key
+    person = Person.find(1)
+    person.id = 2
+    person.delete
+
+    assert Person.find(2)
+    assert_raises(ActiveRecord::RecordNotFound) do
+      Person.find(1)
+    end
+  end
+
+  def test_destroy_with_dirty_primary_key
+    person = Person.find(1)
+    person.id = 2
+    person.destroy
+
+    assert Person.find(2)
+    assert_raises(ActiveRecord::RecordNotFound) do
+      Person.find(1)
+    end
+  end
+
+  def test_explicit_update_lock_column_raise_error
+    person = Person.find(1)
+
+    assert_raises(ActiveRecord::StaleObjectError) do
+      person.first_name = "Douglas Adams"
+      person.lock_version = 42
+
+      assert_predicate person, :lock_version_changed?
+
+      person.save
+    end
+  end
+
   def test_lock_column_name_existing
     t1 = LegacyThing.find(1)
     t2 = LegacyThing.find(1)
@@ -203,11 +263,11 @@ class OptimisticLockingTest < ActiveRecord::TestCase
   end
 
   def test_lock_column_is_mass_assignable
-    p1 = Person.create(:first_name => 'bianca')
+    p1 = Person.create(first_name: "bianca")
     assert_equal 0, p1.lock_version
     assert_equal p1.lock_version, Person.new(p1.attributes).lock_version
 
-    p1.first_name = 'bianca2'
+    p1.first_name = "bianca2"
     p1.save!
     assert_equal 1, p1.lock_version
     assert_equal p1.lock_version, Person.new(p1.attributes).lock_version
@@ -215,28 +275,144 @@ class OptimisticLockingTest < ActiveRecord::TestCase
 
   def test_lock_without_default_sets_version_to_zero
     t1 = LockWithoutDefault.new
+
     assert_equal 0, t1.lock_version
+    assert_nil t1.lock_version_before_type_cast
+
+    t1.save!
+    t1.reload
 
-    t1.save
-    t1 = LockWithoutDefault.find(t1.id)
     assert_equal 0, t1.lock_version
+    assert_equal 0, t1.lock_version_before_type_cast
+  end
+
+  def test_touch_existing_lock_without_default_should_work_with_null_in_the_database
+    ActiveRecord::Base.connection.execute("INSERT INTO lock_without_defaults(title) VALUES('title1')")
+    t1 = LockWithoutDefault.last
+
+    assert_equal 0, t1.lock_version
+    assert_nil t1.lock_version_before_type_cast
+
+    t1.touch
+
+    assert_equal 1, t1.lock_version
+  end
+
+  def test_touch_stale_object_with_lock_without_default
+    t1 = LockWithoutDefault.create!(title: "title1")
+    stale_object = LockWithoutDefault.find(t1.id)
+
+    t1.update!(title: "title2")
+
+    assert_raises(ActiveRecord::StaleObjectError) do
+      stale_object.touch
+    end
+  end
+
+  def test_lock_without_default_should_work_with_null_in_the_database
+    ActiveRecord::Base.connection.execute("INSERT INTO lock_without_defaults(title) VALUES('title1')")
+    t1 = LockWithoutDefault.last
+    t2 = LockWithoutDefault.find(t1.id)
+
+    assert_equal 0, t1.lock_version
+    assert_nil t1.lock_version_before_type_cast
+    assert_equal 0, t2.lock_version
+    assert_nil t2.lock_version_before_type_cast
+
+    t1.title = "new title1"
+    t2.title = "new title2"
+
+    assert_nothing_raised { t1.save! }
+    assert_equal 1, t1.lock_version
+    assert_equal "new title1", t1.title
+
+    assert_raise(ActiveRecord::StaleObjectError) { t2.save! }
+    assert_equal 0, t2.lock_version
+    assert_equal "new title2", t2.title
+  end
+
+  def test_lock_without_default_queries_count
+    t1 = LockWithoutDefault.create(title: "title1")
+
+    assert_equal "title1", t1.title
+    assert_equal 0, t1.lock_version
+
+    assert_queries(1) { t1.update(title: "title2") }
+
+    t1.reload
+    assert_equal "title2", t1.title
+    assert_equal 1, t1.lock_version
+
+    t2 = LockWithoutDefault.new(title: "title1")
+
+    assert_queries(1) { t2.save! }
+
+    t2.reload
+    assert_equal "title1", t2.title
+    assert_equal 0, t2.lock_version
   end
 
   def test_lock_with_custom_column_without_default_sets_version_to_zero
     t1 = LockWithCustomColumnWithoutDefault.new
+
     assert_equal 0, t1.custom_lock_version
     assert_nil t1.custom_lock_version_before_type_cast
 
     t1.save!
     t1.reload
+
     assert_equal 0, t1.custom_lock_version
-    assert [0, "0"].include?(t1.custom_lock_version_before_type_cast)
+    assert_equal 0, t1.custom_lock_version_before_type_cast
+  end
+
+  def test_lock_with_custom_column_without_default_should_work_with_null_in_the_database
+    ActiveRecord::Base.connection.execute("INSERT INTO lock_without_defaults_cust(title) VALUES('title1')")
+
+    t1 = LockWithCustomColumnWithoutDefault.last
+    t2 = LockWithCustomColumnWithoutDefault.find(t1.id)
+
+    assert_equal 0, t1.custom_lock_version
+    assert_nil t1.custom_lock_version_before_type_cast
+    assert_equal 0, t2.custom_lock_version
+    assert_nil t2.custom_lock_version_before_type_cast
+
+    t1.title = "new title1"
+    t2.title = "new title2"
+
+    assert_nothing_raised { t1.save! }
+    assert_equal 1, t1.custom_lock_version
+    assert_equal "new title1", t1.title
+
+    assert_raise(ActiveRecord::StaleObjectError) { t2.save! }
+    assert_equal 0, t2.custom_lock_version
+    assert_equal "new title2", t2.title
+  end
+
+  def test_lock_with_custom_column_without_default_queries_count
+    t1 = LockWithCustomColumnWithoutDefault.create(title: "title1")
+
+    assert_equal "title1", t1.title
+    assert_equal 0, t1.custom_lock_version
+
+    assert_queries(1) { t1.update(title: "title2") }
+
+    t1.reload
+    assert_equal "title2", t1.title
+    assert_equal 1, t1.custom_lock_version
+
+    t2 = LockWithCustomColumnWithoutDefault.new(title: "title1")
+
+    assert_queries(1) { t2.save! }
+
+    t2.reload
+    assert_equal "title1", t2.title
+    assert_equal 0, t2.custom_lock_version
   end
 
   def test_readonly_attributes
-    assert_equal Set.new([ 'name' ]), ReadonlyNameShip.readonly_attributes
+    assert_equal Set.new([ "name" ]), ReadonlyNameShip.readonly_attributes
 
-    s = ReadonlyNameShip.create(:name => "unchangeable name")
+    s = ReadonlyNameShip.create(name: "unchangeable name")
     s.reload
     assert_equal "unchangeable name", s.name
 
@@ -255,7 +431,7 @@ class OptimisticLockingTest < ActiveRecord::TestCase
   # is nothing else being updated.
   def test_update_without_attributes_does_not_only_update_lock_version
     assert_nothing_raised do
-      p1 = Person.create!(:first_name => 'anika')
+      p1 = Person.create!(first_name: "anika")
       lock_version = p1.lock_version
       p1.save
       p1.reload
@@ -263,25 +439,65 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     end
   end
 
+  def test_counter_cache_with_touch_and_lock_version
+    car = Car.create!
+
+    assert_equal 0, car.wheels_count
+    assert_equal 0, car.lock_version
+
+    previously_updated_at = car.updated_at
+    previously_wheels_owned_at = car.wheels_owned_at
+    travel(1.second) do
+      Wheel.create!(wheelable: car)
+    end
+
+    assert_equal 1, car.reload.wheels_count
+    assert_equal 1, car.lock_version
+    assert_operator previously_updated_at, :<, car.updated_at
+    assert_operator previously_wheels_owned_at, :<, car.wheels_owned_at
+
+    previously_updated_at = car.updated_at
+    previously_wheels_owned_at = car.wheels_owned_at
+    travel(2.second) do
+      car.wheels.first.update(size: 42)
+    end
+
+    assert_equal 1, car.reload.wheels_count
+    assert_equal 2, car.lock_version
+    assert_operator previously_updated_at, :<, car.updated_at
+    assert_operator previously_wheels_owned_at, :<, car.wheels_owned_at
+
+    previously_updated_at = car.updated_at
+    previously_wheels_owned_at = car.wheels_owned_at
+    travel(3.second) do
+      car.wheels.first.destroy!
+    end
+
+    assert_equal 0, car.reload.wheels_count
+    assert_equal 3, car.lock_version
+    assert_operator previously_updated_at, :<, car.updated_at
+    assert_operator previously_wheels_owned_at, :<, car.wheels_owned_at
+  end
+
   def test_polymorphic_destroy_with_dependencies_and_lock_version
     car = Car.create!
 
-    assert_difference 'car.wheels.count'  do
-      car.wheels << Wheel.create!
+    assert_difference "car.wheels.count"  do
+      car.wheels.create
     end
-    assert_difference 'car.wheels.count', -1  do
-      car.destroy
+    assert_difference "car.wheels.count", -1  do
+      car.reload.destroy
     end
-    assert car.destroyed?
+    assert_predicate car, :destroyed?
   end
 
   def test_removing_has_and_belongs_to_many_associations_upon_destroy
-    p = RichPerson.create! first_name: 'Jon'
+    p = RichPerson.create! first_name: "Jon"
     p.treasures.create!
-    assert !p.treasures.empty?
+    assert_not_empty p.treasures
     p.destroy
-    assert p.treasures.empty?
-    assert RichPerson.connection.select_all("SELECT * FROM peoples_treasures WHERE rich_person_id = 1").empty?
+    assert_empty p.treasures
+    assert_empty RichPerson.connection.select_all("SELECT * FROM peoples_treasures WHERE rich_person_id = 1")
   end
 
   def test_yaml_dumping_with_lock_column
@@ -300,7 +516,7 @@ class OptimisticLockingWithSchemaChangeTest < ActiveRecord::TestCase
   # of a test (see test_increment_counter_*).
   self.use_transactional_tests = false
 
-  { :lock_version => Person, :custom_lock_version => LegacyThing }.each do |name, model|
+  { lock_version: Person, custom_lock_version: LegacyThing }.each do |name, model|
     define_method("test_increment_counter_updates_#{name}") do
       counter_test model, 1 do |id|
         model.increment_counter :test_count, id
@@ -315,7 +531,7 @@ class OptimisticLockingWithSchemaChangeTest < ActiveRecord::TestCase
 
     define_method("test_update_counters_updates_#{name}") do
       counter_test model, 1 do |id|
-        model.update_counters id, :test_count => 1
+        model.update_counters id, test_count: 1
       end
     end
   end
@@ -323,13 +539,13 @@ class OptimisticLockingWithSchemaChangeTest < ActiveRecord::TestCase
   # See Lighthouse ticket #1966
   def test_destroy_dependents
     # Establish dependent relationship between Person and PersonalLegacyThing
-    add_counter_column_to(Person, 'personal_legacy_things_count')
+    add_counter_column_to(Person, "personal_legacy_things_count")
     PersonalLegacyThing.reset_column_information
 
     # Make sure that counter incrementing doesn't cause problems
-    p1 = Person.new(:first_name => 'fjord')
+    p1 = Person.new(first_name: "fjord")
     p1.save!
-    t = PersonalLegacyThing.new(:person => p1)
+    t = PersonalLegacyThing.new(person: p1)
     t.save!
     p1.reload
     assert_equal 1, p1.personal_legacy_things_count
@@ -338,14 +554,39 @@ class OptimisticLockingWithSchemaChangeTest < ActiveRecord::TestCase
     assert_raises(ActiveRecord::RecordNotFound) { Person.find(p1.id) }
     assert_raises(ActiveRecord::RecordNotFound) { PersonalLegacyThing.find(t.id) }
   ensure
-    remove_counter_column_from(Person, 'personal_legacy_things_count')
+    remove_counter_column_from(Person, "personal_legacy_things_count")
     PersonalLegacyThing.reset_column_information
   end
 
+  def test_destroy_existing_object_with_locking_column_value_null_in_the_database
+    ActiveRecord::Base.connection.execute("INSERT INTO lock_without_defaults(title) VALUES('title1')")
+    t1 = LockWithoutDefault.last
+
+    assert_equal 0, t1.lock_version
+    assert_nil t1.lock_version_before_type_cast
+
+    t1.destroy
+
+    assert_predicate t1, :destroyed?
+  end
+
+  def test_destroy_stale_object
+    t1 = LockWithoutDefault.create!(title: "title1")
+    stale_object = LockWithoutDefault.find(t1.id)
+
+    t1.update!(title: "title2")
+
+    assert_raises(ActiveRecord::StaleObjectError) do
+      stale_object.destroy!
+    end
+
+    assert_not_predicate stale_object, :destroyed?
+  end
+
   private
 
-    def add_counter_column_to(model, col='test_count')
-      model.connection.add_column model.table_name, col, :integer, :null => false, :default => 0
+    def add_counter_column_to(model, col = "test_count")
+      model.connection.add_column model.table_name, col, :integer, null: false, default: 0
       model.reset_column_information
     end
 
@@ -368,7 +609,6 @@ class OptimisticLockingWithSchemaChangeTest < ActiveRecord::TestCase
     end
 end
 
-
 # TODO: test against the generated SQL since testing locking behavior itself
 # is so cumbersome. Will deadlock Ruby threads if the underlying db.execute
 # blocks, so separate script called by Kernel#system is needed.
@@ -405,14 +645,27 @@ unless in_memory_db?
       end
     end
 
-    # Locking a record reloads it.
-    def test_sane_lock_method
+    def test_lock_does_not_raise_when_the_object_is_not_dirty
+      person = Person.find 1
       assert_nothing_raised do
-        Person.transaction do
-          person = Person.find 1
-          old, person.first_name = person.first_name, 'fooman'
-          person.lock!
-          assert_equal old, person.first_name
+        person.lock!
+      end
+    end
+
+    def test_lock_raises_when_the_record_is_dirty
+      person = Person.find 1
+      person.first_name = "fooman"
+      assert_raises(RuntimeError) do
+        person.lock!
+      end
+    end
+
+    def test_locking_in_after_save_callback
+      assert_nothing_raised do
+        frog = ::Frog.create(name: "Old Frog")
+        frog.name = "New Frog"
+        assert_not_deprecated do
+          frog.save!
         end
       end
     end
@@ -420,19 +673,19 @@ unless in_memory_db?
     def test_with_lock_commits_transaction
       person = Person.find 1
       person.with_lock do
-        person.first_name = 'fooman'
+        person.first_name = "fooman"
         person.save!
       end
-      assert_equal 'fooman', person.reload.first_name
+      assert_equal "fooman", person.reload.first_name
     end
 
     def test_with_lock_rolls_back_transaction
       person = Person.find 1
       old = person.first_name
       person.with_lock do
-        person.first_name = 'fooman'
+        person.first_name = "fooman"
         person.save!
-        raise 'oops'
+        raise "oops"
       end rescue nil
       assert_equal old, person.reload.first_name
     end
@@ -441,47 +694,45 @@ unless in_memory_db?
       def test_lock_sending_custom_lock_statement
         Person.transaction do
           person = Person.find(1)
-          assert_sql(/LIMIT 1 FOR SHARE NOWAIT/) do
-            person.lock!('FOR SHARE NOWAIT')
+          assert_sql(/LIMIT \$?\d FOR SHARE NOWAIT/) do
+            person.lock!("FOR SHARE NOWAIT")
           end
         end
       end
     end
 
-    if current_adapter?(:PostgreSQLAdapter, :OracleAdapter)
-      def test_no_locks_no_wait
-        first, second = duel { Person.find 1 }
-        assert first.end > second.end
-      end
+    def test_no_locks_no_wait
+      first, second = duel { Person.find 1 }
+      assert first.end > second.end
+    end
 
-      protected
-        def duel(zzz = 5)
-          t0, t1, t2, t3 = nil, nil, nil, nil
-
-          a = Thread.new do
-            t0 = Time.now
-            Person.transaction do
-              yield
-              sleep zzz       # block thread 2 for zzz seconds
-            end
-            t1 = Time.now
-          end
+    private
+      def duel(zzz = 5)
+        t0, t1, t2, t3 = nil, nil, nil, nil
 
-          b = Thread.new do
-            sleep zzz / 2.0   # ensure thread 1 tx starts first
-            t2 = Time.now
-            Person.transaction { yield }
-            t3 = Time.now
+        a = Thread.new do
+          t0 = Time.now
+          Person.transaction do
+            yield
+            sleep zzz       # block thread 2 for zzz seconds
           end
+          t1 = Time.now
+        end
 
-          a.join
-          b.join
-
-          assert t1 > t0 + zzz
-          assert t2 > t0
-          assert t3 > t2
-          [t0.to_f..t1.to_f, t2.to_f..t3.to_f]
+        b = Thread.new do
+          sleep zzz / 2.0   # ensure thread 1 tx starts first
+          t2 = Time.now
+          Person.transaction { yield }
+          t3 = Time.now
         end
-    end
+
+        a.join
+        b.join
+
+        assert t1 > t0 + zzz
+        assert t2 > t0
+        assert t3 > t2
+        [t0.to_f..t1.to_f, t2.to_f..t3.to_f]
+      end
   end
 end
diff --git a/activerecord/test/cases/log_subscriber_test.rb b/activerecord/test/cases/log_subscriber_test.rb
index 4192d12ff4..ae2597adc8 100644
--- a/activerecord/test/cases/log_subscriber_test.rb
+++ b/activerecord/test/cases/log_subscriber_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "models/binary"
 require "models/developer"
@@ -7,6 +9,21 @@ require "active_support/log_subscriber/test_helper"
 class LogSubscriberTest < ActiveRecord::TestCase
   include ActiveSupport::LogSubscriber::TestHelper
   include ActiveSupport::Logger::Severity
+  REGEXP_CLEAR = Regexp.escape(ActiveRecord::LogSubscriber::CLEAR)
+  REGEXP_BOLD = Regexp.escape(ActiveRecord::LogSubscriber::BOLD)
+  REGEXP_MAGENTA = Regexp.escape(ActiveRecord::LogSubscriber::MAGENTA)
+  REGEXP_CYAN = Regexp.escape(ActiveRecord::LogSubscriber::CYAN)
+  SQL_COLORINGS = {
+      SELECT: Regexp.escape(ActiveRecord::LogSubscriber::BLUE),
+      INSERT: Regexp.escape(ActiveRecord::LogSubscriber::GREEN),
+      UPDATE: Regexp.escape(ActiveRecord::LogSubscriber::YELLOW),
+      DELETE: Regexp.escape(ActiveRecord::LogSubscriber::RED),
+      LOCK: Regexp.escape(ActiveRecord::LogSubscriber::WHITE),
+      ROLLBACK: Regexp.escape(ActiveRecord::LogSubscriber::RED),
+      TRANSACTION: REGEXP_CYAN,
+      OTHER: REGEXP_MAGENTA
+  }
+  Event = Struct.new(:duration, :payload)
 
   class TestDebugLogSubscriber < ActiveRecord::LogSubscriber
     attr_reader :debugs
@@ -16,8 +33,9 @@ class LogSubscriberTest < ActiveRecord::TestCase
       super
     end
 
-    def debug message
-      @debugs << message
+    def debug(progname = nil, &block)
+      @debugs << progname
+      super
     end
   end
 
@@ -26,6 +44,7 @@ class LogSubscriberTest < ActiveRecord::TestCase
   def setup
     @old_logger = ActiveRecord::Base.logger
     Developer.primary_key
+    ActiveRecord::Base.connection.materialize_transactions
     super
     ActiveRecord::LogSubscriber.attach_to(:active_record)
   end
@@ -41,25 +60,22 @@ class LogSubscriberTest < ActiveRecord::TestCase
   end
 
   def test_schema_statements_are_ignored
-    event = Struct.new(:duration, :payload)
-
     logger = TestDebugLogSubscriber.new
     assert_equal 0, logger.debugs.length
 
-    logger.sql(event.new(0, sql: 'hi mom!'))
+    logger.sql(Event.new(0.9, sql: "hi mom!"))
     assert_equal 1, logger.debugs.length
 
-    logger.sql(event.new(0, sql: 'hi mom!', name: 'foo'))
+    logger.sql(Event.new(0.9, sql: "hi mom!", name: "foo"))
     assert_equal 2, logger.debugs.length
 
-    logger.sql(event.new(0, sql: 'hi mom!', name: 'SCHEMA'))
+    logger.sql(Event.new(0.9, sql: "hi mom!", name: "SCHEMA"))
     assert_equal 2, logger.debugs.length
   end
 
   def test_sql_statements_are_not_squeezed
-    event = Struct.new(:duration, :payload)
     logger = TestDebugLogSubscriber.new
-    logger.sql(event.new(0, sql: 'ruby   rails'))
+    logger.sql(Event.new(0.9, sql: "ruby   rails"))
     assert_match(/ruby   rails/, logger.debugs.first)
   end
 
@@ -71,6 +87,84 @@ class LogSubscriberTest < ActiveRecord::TestCase
     assert_match(/SELECT .*?FROM .?developers.?/i, @logger.logged(:debug).last)
   end
 
+  def test_basic_query_logging_coloration
+    logger = TestDebugLogSubscriber.new
+    logger.colorize_logging = true
+    SQL_COLORINGS.each do |verb, color_regex|
+      logger.sql(Event.new(0.9, sql: verb.to_s))
+      assert_match(/#{REGEXP_BOLD}#{color_regex}#{verb}#{REGEXP_CLEAR}/i, logger.debugs.last)
+    end
+  end
+
+  def test_basic_payload_name_logging_coloration_generic_sql
+    logger = TestDebugLogSubscriber.new
+    logger.colorize_logging = true
+    SQL_COLORINGS.each do |verb, _|
+      logger.sql(Event.new(0.9, sql: verb.to_s))
+      assert_match(/#{REGEXP_BOLD}#{REGEXP_MAGENTA} \(0\.9ms\)#{REGEXP_CLEAR}/i, logger.debugs.last)
+
+      logger.sql(Event.new(0.9, sql: verb.to_s, name: "SQL"))
+      assert_match(/#{REGEXP_BOLD}#{REGEXP_MAGENTA}SQL \(0\.9ms\)#{REGEXP_CLEAR}/i, logger.debugs.last)
+    end
+  end
+
+  def test_basic_payload_name_logging_coloration_named_sql
+    logger = TestDebugLogSubscriber.new
+    logger.colorize_logging = true
+    SQL_COLORINGS.each do |verb, _|
+      logger.sql(Event.new(0.9, sql: verb.to_s, name: "Model Load"))
+      assert_match(/#{REGEXP_BOLD}#{REGEXP_CYAN}Model Load \(0\.9ms\)#{REGEXP_CLEAR}/i, logger.debugs.last)
+
+      logger.sql(Event.new(0.9, sql: verb.to_s, name: "Model Exists"))
+      assert_match(/#{REGEXP_BOLD}#{REGEXP_CYAN}Model Exists \(0\.9ms\)#{REGEXP_CLEAR}/i, logger.debugs.last)
+
+      logger.sql(Event.new(0.9, sql: verb.to_s, name: "ANY SPECIFIC NAME"))
+      assert_match(/#{REGEXP_BOLD}#{REGEXP_CYAN}ANY SPECIFIC NAME \(0\.9ms\)#{REGEXP_CLEAR}/i, logger.debugs.last)
+    end
+  end
+
+  def test_query_logging_coloration_with_nested_select
+    logger = TestDebugLogSubscriber.new
+    logger.colorize_logging = true
+    SQL_COLORINGS.slice(:SELECT, :INSERT, :UPDATE, :DELETE).each do |verb, color_regex|
+      logger.sql(Event.new(0.9, sql: "#{verb} WHERE ID IN SELECT"))
+      assert_match(/#{REGEXP_BOLD}#{REGEXP_MAGENTA} \(0\.9ms\)#{REGEXP_CLEAR}  #{REGEXP_BOLD}#{color_regex}#{verb} WHERE ID IN SELECT#{REGEXP_CLEAR}/i, logger.debugs.last)
+    end
+  end
+
+  def test_query_logging_coloration_with_multi_line_nested_select
+    logger = TestDebugLogSubscriber.new
+    logger.colorize_logging = true
+    SQL_COLORINGS.slice(:SELECT, :INSERT, :UPDATE, :DELETE).each do |verb, color_regex|
+      sql = <<-EOS
+        #{verb}
+        WHERE ID IN (
+          SELECT ID FROM THINGS
+        )
+      EOS
+      logger.sql(Event.new(0.9, sql: sql))
+      assert_match(/#{REGEXP_BOLD}#{REGEXP_MAGENTA} \(0\.9ms\)#{REGEXP_CLEAR}  #{REGEXP_BOLD}#{color_regex}.*#{verb}.*#{REGEXP_CLEAR}/mi, logger.debugs.last)
+    end
+  end
+
+  def test_query_logging_coloration_with_lock
+    logger = TestDebugLogSubscriber.new
+    logger.colorize_logging = true
+    sql = <<-EOS
+      SELECT * FROM
+        (SELECT * FROM mytable FOR UPDATE) ss
+      WHERE col1 = 5;
+    EOS
+    logger.sql(Event.new(0.9, sql: sql))
+    assert_match(/#{REGEXP_BOLD}#{REGEXP_MAGENTA} \(0\.9ms\)#{REGEXP_CLEAR}  #{REGEXP_BOLD}#{SQL_COLORINGS[:LOCK]}.*FOR UPDATE.*#{REGEXP_CLEAR}/mi, logger.debugs.last)
+
+    sql = <<-EOS
+      LOCK TABLE films IN SHARE MODE;
+    EOS
+    logger.sql(Event.new(0.9, sql: sql))
+    assert_match(/#{REGEXP_BOLD}#{REGEXP_MAGENTA} \(0\.9ms\)#{REGEXP_CLEAR}  #{REGEXP_BOLD}#{SQL_COLORINGS[:LOCK]}.*LOCK TABLE.*#{REGEXP_CLEAR}/mi, logger.debugs.last)
+  end
+
   def test_exists_query_logging
     Developer.exists? 1
     wait
@@ -79,6 +173,36 @@ class LogSubscriberTest < ActiveRecord::TestCase
     assert_match(/SELECT .*?FROM .?developers.?/i, @logger.logged(:debug).last)
   end
 
+  def test_vebose_query_logs
+    ActiveRecord::Base.verbose_query_logs = true
+
+    logger = TestDebugLogSubscriber.new
+    logger.sql(Event.new(0, sql: "hi mom!"))
+    assert_equal 2, @logger.logged(:debug).size
+    assert_match(/↳/, @logger.logged(:debug).last)
+  ensure
+    ActiveRecord::Base.verbose_query_logs = false
+  end
+
+  def test_verbose_query_with_ignored_callstack
+    ActiveRecord::Base.verbose_query_logs = true
+
+    logger = TestDebugLogSubscriber.new
+    def logger.extract_query_source_location(*); nil; end
+
+    logger.sql(Event.new(0, sql: "hi mom!"))
+    assert_equal 1, @logger.logged(:debug).size
+    assert_no_match(/↳/, @logger.logged(:debug).last)
+  ensure
+    ActiveRecord::Base.verbose_query_logs = false
+  end
+
+  def test_verbose_query_logs_disabled_by_default
+    logger = TestDebugLogSubscriber.new
+    logger.sql(Event.new(0, sql: "hi mom!"))
+    assert_no_match(/↳/, @logger.logged(:debug).last)
+  end
+
   def test_cached_queries
     ActiveRecord::Base.cache do
       Developer.all.load
@@ -111,11 +235,17 @@ class LogSubscriberTest < ActiveRecord::TestCase
     Thread.new { assert_equal 0, ActiveRecord::LogSubscriber.runtime }.join
   end
 
-  unless current_adapter?(:Mysql2Adapter)
+  if ActiveRecord::Base.connection.prepared_statements
     def test_binary_data_is_not_logged
-      Binary.create(data: 'some binary data')
+      Binary.create(data: "some binary data")
       wait
       assert_match(/<16 bytes of binary data>/, @logger.logged(:debug).join)
     end
+
+    def test_binary_data_hash
+      Binary.create(data: { a: 1 })
+      wait
+      assert_match(/<7 bytes of binary data>/, @logger.logged(:debug).join)
+    end
   end
 end
diff --git a/activerecord/test/cases/migration/change_schema_test.rb b/activerecord/test/cases/migration/change_schema_test.rb
index 83e50048ec..7777508349 100644
--- a/activerecord/test/cases/migration/change_schema_test.rb
+++ b/activerecord/test/cases/migration/change_schema_test.rb
@@ -1,4 +1,6 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class Migration
@@ -40,24 +42,24 @@ module ActiveRecord
 
       def test_create_table_with_not_null_column
         connection.create_table :testings do |t|
-          t.column :foo, :string, :null => false
+          t.column :foo, :string, null: false
         end
 
-        assert_raises(ActiveRecord::StatementInvalid) do
+        assert_raises(ActiveRecord::NotNullViolation) do
           connection.execute "insert into testings (foo) values (NULL)"
         end
       end
 
       def test_create_table_with_defaults
         # MySQL doesn't allow defaults on TEXT or BLOB columns.
-        mysql = current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+        mysql = current_adapter?(:Mysql2Adapter)
 
         connection.create_table :testings do |t|
-          t.column :one, :string, :default => "hello"
-          t.column :two, :boolean, :default => true
-          t.column :three, :boolean, :default => false
-          t.column :four, :integer, :default => 1
-          t.column :five, :text, :default => "hello" unless mysql
+          t.column :one, :string, default: "hello"
+          t.column :two, :boolean, default: true
+          t.column :three, :boolean, default: false
+          t.column :four, :integer, default: 1
+          t.column :five, :text, default: "hello" unless mysql
         end
 
         columns = connection.columns(:testings)
@@ -70,30 +72,30 @@ module ActiveRecord
         assert_equal "hello", one.default
         assert_equal true, connection.lookup_cast_type_from_column(two).deserialize(two.default)
         assert_equal false, connection.lookup_cast_type_from_column(three).deserialize(three.default)
-        assert_equal '1', four.default
+        assert_equal "1", four.default
         assert_equal "hello", five.default unless mysql
       end
 
       if current_adapter?(:PostgreSQLAdapter)
         def test_add_column_with_array
           connection.create_table :testings
-          connection.add_column :testings, :foo, :string, :array => true
+          connection.add_column :testings, :foo, :string, array: true
 
           columns = connection.columns(:testings)
           array_column = columns.detect { |c| c.name == "foo" }
 
-          assert array_column.array?
+          assert_predicate array_column, :array?
         end
 
         def test_create_table_with_array_column
           connection.create_table :testings do |t|
-            t.string :foo, :array => true
+            t.string :foo, array: true
           end
 
           columns = connection.columns(:testings)
           array_column = columns.detect { |c| c.name == "foo" }
 
-          assert array_column.array?
+          assert_predicate array_column, :array?
         end
       end
 
@@ -105,9 +107,9 @@ module ActiveRecord
         eight   = columns.detect { |c| c.name == "eight_int"   }
 
         if current_adapter?(:OracleAdapter)
-          assert_equal 'NUMBER(19)', eight.sql_type
+          assert_equal "NUMBER(19)", eight.sql_type
         elsif current_adapter?(:SQLite3Adapter)
-          assert_equal 'bigint', eight.sql_type
+          assert_equal "bigint", eight.sql_type
         else
           assert_equal :integer, eight.type
           assert_equal 8, eight.limit
@@ -118,13 +120,13 @@ module ActiveRecord
 
       def test_create_table_with_limits
         connection.create_table :testings do |t|
-          t.column :foo, :string, :limit => 255
+          t.column :foo, :string, limit: 255
 
           t.column :default_int, :integer
 
-          t.column :one_int,    :integer, :limit => 1
-          t.column :four_int,   :integer, :limit => 4
-          t.column :eight_int,  :integer, :limit => 8
+          t.column :one_int,    :integer, limit: 1
+          t.column :four_int,   :integer, limit: 4
+          t.column :eight_int,  :integer, limit: 8
         end
 
         columns = connection.columns(:testings)
@@ -137,20 +139,20 @@ module ActiveRecord
         eight   = columns.detect { |c| c.name == "eight_int"   }
 
         if current_adapter?(:PostgreSQLAdapter)
-          assert_equal 'integer', default.sql_type
-          assert_equal 'smallint', one.sql_type
-          assert_equal 'integer', four.sql_type
-          assert_equal 'bigint', eight.sql_type
-        elsif current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-          assert_match 'int(11)', default.sql_type
-          assert_match 'tinyint', one.sql_type
-          assert_match 'int', four.sql_type
-          assert_match 'bigint', eight.sql_type
+          assert_equal "integer", default.sql_type
+          assert_equal "smallint", one.sql_type
+          assert_equal "integer", four.sql_type
+          assert_equal "bigint", eight.sql_type
+        elsif current_adapter?(:Mysql2Adapter)
+          assert_match "int(11)", default.sql_type
+          assert_match "tinyint", one.sql_type
+          assert_match "int", four.sql_type
+          assert_match "bigint", eight.sql_type
         elsif current_adapter?(:OracleAdapter)
-          assert_equal 'NUMBER(38)', default.sql_type
-          assert_equal 'NUMBER(1)', one.sql_type
-          assert_equal 'NUMBER(4)', four.sql_type
-          assert_equal 'NUMBER(8)', eight.sql_type
+          assert_equal "NUMBER(38)", default.sql_type
+          assert_equal "NUMBER(1)", one.sql_type
+          assert_equal "NUMBER(4)", four.sql_type
+          assert_equal "NUMBER(8)", eight.sql_type
         end
       end
 
@@ -194,17 +196,28 @@ module ActiveRecord
         assert_equal "you can't redefine the primary key column 'testing_id'. To define a custom primary key, pass { id: false } to create_table.", error.message
       end
 
+      def test_create_table_raises_when_defining_existing_column
+        error = assert_raise(ArgumentError) do
+          connection.create_table :testings do |t|
+            t.column :testing_column, :string
+            t.column :testing_column, :integer
+          end
+        end
+
+        assert_equal "you can't define an already defined column 'testing_column'.", error.message
+      end
+
       def test_create_table_with_timestamps_should_create_datetime_columns
         connection.create_table table_name do |t|
           t.timestamps
         end
         created_columns = connection.columns(table_name)
 
-        created_at_column = created_columns.detect {|c| c.name == 'created_at' }
-        updated_at_column = created_columns.detect {|c| c.name == 'updated_at' }
+        created_at_column = created_columns.detect { |c| c.name == "created_at" }
+        updated_at_column = created_columns.detect { |c| c.name == "updated_at" }
 
-        assert !created_at_column.null
-        assert !updated_at_column.null
+        assert_not created_at_column.null
+        assert_not updated_at_column.null
       end
 
       def test_create_table_with_timestamps_should_create_datetime_columns_with_options
@@ -213,8 +226,8 @@ module ActiveRecord
         end
         created_columns = connection.columns(table_name)
 
-        created_at_column = created_columns.detect {|c| c.name == 'created_at' }
-        updated_at_column = created_columns.detect {|c| c.name == 'updated_at' }
+        created_at_column = created_columns.detect { |c| c.name == "created_at" }
+        updated_at_column = created_columns.detect { |c| c.name == "updated_at" }
 
         assert created_at_column.null
         assert updated_at_column.null
@@ -231,9 +244,9 @@ module ActiveRecord
           connection.create_table :testings do |t|
             t.column :foo, :string
           end
-          connection.add_column :testings, :bar, :string, :null => false
+          connection.add_column :testings, :bar, :string, null: false
 
-          assert_raise(ActiveRecord::StatementInvalid) do
+          assert_raise(ActiveRecord::NotNullViolation) do
             connection.execute "insert into testings (foo, bar) values ('hello', NULL)"
           end
         end
@@ -244,12 +257,16 @@ module ActiveRecord
           t.column :foo, :string
         end
 
-        con = connection
-        connection.execute "insert into testings (#{con.quote_column_name('id')}, #{con.quote_column_name('foo')}) values (1, 'hello')"
-        assert_nothing_raised {connection.add_column :testings, :bar, :string, :null => false, :default => "default" }
+        quoted_id  = connection.quote_column_name("id")
+        quoted_foo = connection.quote_column_name("foo")
+        quoted_bar = connection.quote_column_name("bar")
+        connection.execute("insert into testings (#{quoted_id}, #{quoted_foo}) values (1, 'hello')")
+        assert_nothing_raised do
+          connection.add_column :testings, :bar, :string, null: false, default: "default"
+        end
 
-        assert_raises(ActiveRecord::StatementInvalid) do
-          connection.execute "insert into testings (#{con.quote_column_name('id')}, #{con.quote_column_name('foo')}, #{con.quote_column_name('bar')}) values (2, 'hello', NULL)"
+        assert_raises(ActiveRecord::NotNullViolation) do
+          connection.execute("insert into testings (#{quoted_id}, #{quoted_foo}, #{quoted_bar}) values (2, 'hello', NULL)")
         end
       end
 
@@ -258,15 +275,18 @@ module ActiveRecord
           t.column :foo, :timestamp
         end
 
-        klass = Class.new(ActiveRecord::Base)
-        klass.table_name = 'testings'
+        column = connection.columns(:testings).find { |c| c.name == "foo" }
 
-        assert_equal :datetime, klass.columns_hash['foo'].type
+        assert_equal :datetime, column.type
 
         if current_adapter?(:PostgreSQLAdapter)
-          assert_equal 'timestamp without time zone', klass.columns_hash['foo'].sql_type
+          assert_equal "timestamp without time zone", column.sql_type
+        elsif current_adapter?(:Mysql2Adapter)
+          assert_equal "timestamp", column.sql_type
+        elsif current_adapter?(:OracleAdapter)
+          assert_equal "TIMESTAMP(6)", column.sql_type
         else
-          assert_equal klass.connection.type_to_sql('datetime'), klass.columns_hash['foo'].sql_type
+          assert_equal connection.type_to_sql("datetime"), column.sql_type
         end
       end
 
@@ -275,7 +295,7 @@ module ActiveRecord
           t.column :select, :string
         end
 
-        connection.change_column :testings, :select, :string, :limit => 10
+        connection.change_column :testings, :select, :string, limit: 10
 
         # Oracle needs primary key value from sequence
         if current_adapter?(:OracleAdapter)
@@ -290,17 +310,17 @@ module ActiveRecord
           t.column :title, :string
         end
         person_klass = Class.new(ActiveRecord::Base)
-        person_klass.table_name = 'testings'
+        person_klass.table_name = "testings"
 
-        person_klass.connection.add_column "testings", "wealth", :integer, :null => false, :default => 99
+        person_klass.connection.add_column "testings", "wealth", :integer, null: false, default: 99
         person_klass.reset_column_information
         assert_equal 99, person_klass.column_defaults["wealth"]
         assert_equal false, person_klass.columns_hash["wealth"].null
         # Oracle needs primary key value from sequence
         if current_adapter?(:OracleAdapter)
-          assert_nothing_raised {person_klass.connection.execute("insert into testings (id, title) values (testings_seq.nextval, 'tester')")}
+          assert_nothing_raised { person_klass.connection.execute("insert into testings (id, title) values (testings_seq.nextval, 'tester')") }
         else
-          assert_nothing_raised {person_klass.connection.execute("insert into testings (title) values ('tester')")}
+          assert_nothing_raised { person_klass.connection.execute("insert into testings (title) values ('tester')") }
         end
 
         # change column default to see that column doesn't lose its not null definition
@@ -317,19 +337,19 @@ module ActiveRecord
         assert_equal false, person_klass.columns_hash["money"].null
 
         # change column
-        person_klass.connection.change_column "testings", "money", :integer, :null => false, :default => 1000
+        person_klass.connection.change_column "testings", "money", :integer, null: false, default: 1000
         person_klass.reset_column_information
         assert_equal 1000, person_klass.column_defaults["money"]
         assert_equal false, person_klass.columns_hash["money"].null
 
         # change column, make it nullable and clear default
-        person_klass.connection.change_column "testings", "money", :integer, :null => true, :default => nil
+        person_klass.connection.change_column "testings", "money", :integer, null: true, default: nil
         person_klass.reset_column_information
         assert_nil person_klass.columns_hash["money"].default
         assert_equal true, person_klass.columns_hash["money"].null
 
         # change_column_null, make it not nullable and set null values to a default value
-        person_klass.connection.execute('UPDATE testings SET money = NULL')
+        person_klass.connection.execute("UPDATE testings SET money = NULL")
         person_klass.connection.change_column_null "testings", "money", false, 2000
         person_klass.reset_column_information
         assert_nil person_klass.columns_hash["money"].default
@@ -339,16 +359,16 @@ module ActiveRecord
 
       def test_change_column_null
         testing_table_with_only_foo_attribute do
-          notnull_migration = Class.new(ActiveRecord::Migration) do
+          notnull_migration = Class.new(ActiveRecord::Migration::Current) do
             def change
               change_column_null :testings, :foo, false
             end
           end
           notnull_migration.new.suppress_messages do
             notnull_migration.migrate(:up)
-            assert_equal false, connection.columns(:testings).find{ |c| c.name == "foo"}.null
+            assert_equal false, connection.columns(:testings).find { |c| c.name == "foo" }.null
             notnull_migration.migrate(:down)
-            assert connection.columns(:testings).find{ |c| c.name == "foo"}.null
+            assert connection.columns(:testings).find { |c| c.name == "foo" }.null
           end
         end
       end
@@ -365,7 +385,7 @@ module ActiveRecord
       def test_column_exists_with_type
         connection.create_table :testings do |t|
           t.column :foo, :string
-          t.column :bar, :decimal, :precision => 8, :scale => 2
+          t.column :bar, :decimal, precision: 8, scale: 2
         end
 
         assert connection.column_exists?(:testings, :foo, :string)
@@ -380,7 +400,7 @@ module ActiveRecord
           t.column :foo, :string, limit: 100
           t.column :bar, :decimal, precision: 8, scale: 2
           t.column :taggable_id, :integer, null: false
-          t.column :taggable_type, :string, default: 'Photo'
+          t.column :taggable_type, :string, default: "Photo"
         end
 
         assert connection.column_exists?(:testings, :foo, :string, limit: 100)
@@ -389,7 +409,7 @@ module ActiveRecord
         assert_not connection.column_exists?(:testings, :bar, :decimal, precision: nil, scale: nil)
         assert connection.column_exists?(:testings, :taggable_id, :integer, null: false)
         assert_not connection.column_exists?(:testings, :taggable_id, :integer, null: true)
-        assert connection.column_exists?(:testings, :taggable_type, :string, default: 'Photo')
+        assert connection.column_exists?(:testings, :taggable_type, :string, default: "Photo")
         assert_not connection.column_exists?(:testings, :taggable_type, :string, default: nil)
       end
 
@@ -399,7 +419,7 @@ module ActiveRecord
         end
         connection.change_table :testings do |t|
           assert t.column_exists?(:foo)
-          assert !(t.column_exists?(:bar))
+          assert_not (t.column_exists?(:bar))
         end
       end
 
@@ -415,13 +435,13 @@ module ActiveRecord
       end
 
       private
-      def testing_table_with_only_foo_attribute
-        connection.create_table :testings, :id => false do |t|
-          t.column :foo, :string
-        end
+        def testing_table_with_only_foo_attribute
+          connection.create_table :testings, id: false do |t|
+            t.column :foo, :string
+          end
 
-        yield
-      end
+          yield
+        end
     end
 
     if ActiveRecord::Base.connection.supports_foreign_keys?
@@ -442,7 +462,7 @@ module ActiveRecord
         end
 
         def test_create_table_with_force_cascade_drops_dependent_objects
-          skip "MySQL > 5.5 does not drop dependent objects with DROP TABLE CASCADE" if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+          skip "MySQL > 5.5 does not drop dependent objects with DROP TABLE CASCADE" if current_adapter?(:Mysql2Adapter)
           # can't re-create table referenced by foreign key
           assert_raises(ActiveRecord::StatementInvalid) do
             @connection.create_table :trains, force: true
diff --git a/activerecord/test/cases/migration/change_table_test.rb b/activerecord/test/cases/migration/change_table_test.rb
index 2ffe7a1b0d..c108d372d1 100644
--- a/activerecord/test/cases/migration/change_table_test.rb
+++ b/activerecord/test/cases/migration/change_table_test.rb
@@ -1,5 +1,6 @@
+# frozen_string_literal: true
+
 require "cases/migration/helper"
-require "minitest/mock"
 
 module ActiveRecord
   class Migration
@@ -96,7 +97,7 @@ module ActiveRecord
       def test_remove_timestamps_creates_updated_at_and_created_at
         with_change_table do |t|
           @connection.expect :remove_timestamps, nil, [:delete_me, { null: true }]
-          t.remove_timestamps({ null: true })
+          t.remove_timestamps(null: true)
         end
       end
 
@@ -158,8 +159,16 @@ module ActiveRecord
 
       def test_column_creates_column_with_options
         with_change_table do |t|
-          @connection.expect :add_column, nil, [:delete_me, :bar, :integer, {:null => false}]
-          t.column :bar, :integer, :null => false
+          @connection.expect :add_column, nil, [:delete_me, :bar, :integer, { null: false }]
+          t.column :bar, :integer, null: false
+        end
+      end
+
+      def test_column_creates_column_with_index
+        with_change_table do |t|
+          @connection.expect :add_column, nil, [:delete_me, :bar, :integer, {}]
+          @connection.expect :add_index, nil, [:delete_me, :bar, {}]
+          t.column :bar, :integer, index: true
         end
       end
 
@@ -172,8 +181,8 @@ module ActiveRecord
 
       def test_index_creates_index_with_options
         with_change_table do |t|
-          @connection.expect :add_index, nil, [:delete_me, :bar, {:unique => true}]
-          t.index :bar, :unique => true
+          @connection.expect :add_index, nil, [:delete_me, :bar, { unique: true }]
+          t.index :bar, unique: true
         end
       end
 
@@ -186,8 +195,8 @@ module ActiveRecord
 
       def test_index_exists_with_options
         with_change_table do |t|
-          @connection.expect :index_exists?, nil, [:delete_me, :bar, {:unique => true}]
-          t.index_exists?(:bar, :unique => true)
+          @connection.expect :index_exists?, nil, [:delete_me, :bar, { unique: true }]
+          t.index_exists?(:bar, unique: true)
         end
       end
 
@@ -207,8 +216,8 @@ module ActiveRecord
 
       def test_change_changes_column_with_options
         with_change_table do |t|
-          @connection.expect :change_column, nil, [:delete_me, :bar, :string, {:null => true}]
-          t.change :bar, :string, :null => true
+          @connection.expect :change_column, nil, [:delete_me, :bar, :string, { null: true }]
+          t.change :bar, :string, null: true
         end
       end
 
@@ -235,8 +244,8 @@ module ActiveRecord
 
       def test_remove_index_removes_index_with_options
         with_change_table do |t|
-          @connection.expect :remove_index, nil, [:delete_me, {:unique => true}]
-          t.remove_index :unique => true
+          @connection.expect :remove_index, nil, [:delete_me, { unique: true }]
+          t.remove_index unique: true
         end
       end
 
diff --git a/activerecord/test/cases/migration/column_attributes_test.rb b/activerecord/test/cases/migration/column_attributes_test.rb
index 8d8e661aa5..3022121f4c 100644
--- a/activerecord/test/cases/migration/column_attributes_test.rb
+++ b/activerecord/test/cases/migration/column_attributes_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/migration/helper"
 
 module ActiveRecord
@@ -9,7 +11,7 @@ module ActiveRecord
 
       def test_add_column_newline_default
         string = "foo\nbar"
-        add_column 'test_models', 'command', :string, :default => string
+        add_column "test_models", "command", :string, default: string
         TestModel.reset_column_information
 
         assert_equal string, TestModel.new.command
@@ -18,10 +20,10 @@ module ActiveRecord
       def test_add_remove_single_field_using_string_arguments
         assert_no_column TestModel, :last_name
 
-        add_column 'test_models', 'last_name', :string
+        add_column "test_models", "last_name", :string
         assert_column TestModel, :last_name
 
-        remove_column 'test_models', 'last_name'
+        remove_column "test_models", "last_name"
         assert_no_column TestModel, :last_name
       end
 
@@ -37,17 +39,17 @@ module ActiveRecord
 
       def test_add_column_without_limit
         # TODO: limit: nil should work with all adapters.
-        skip "MySQL wrongly enforces a limit of 255" if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+        skip "MySQL wrongly enforces a limit of 255" if current_adapter?(:Mysql2Adapter)
         add_column :test_models, :description, :string, limit: nil
         TestModel.reset_column_information
         assert_nil TestModel.columns_hash["description"].limit
       end
 
-      if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+      if current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter)
         def test_unabstracted_database_dependent_types
-          add_column :test_models, :intelligence_quotient, :tinyint
+          add_column :test_models, :intelligence_quotient, :smallint
           TestModel.reset_column_information
-          assert_match(/tinyint/, TestModel.columns_hash['intelligence_quotient'].sql_type)
+          assert_match(/smallint/, TestModel.columns_hash["intelligence_quotient"].sql_type)
         end
       end
 
@@ -56,17 +58,13 @@ module ActiveRecord
         # functionality. This allows us to more easily catch INSERT being broken,
         # but SELECT actually working fine.
         def test_native_decimal_insert_manual_vs_automatic
-          correct_value = '0012345678901234567890.0123456789'.to_d
+          correct_value = "0012345678901234567890.0123456789".to_d
 
-          connection.add_column "test_models", "wealth", :decimal, :precision => '30', :scale => '10'
+          connection.add_column "test_models", "wealth", :decimal, precision: "30", scale: "10"
 
           # Do a manual insertion
           if current_adapter?(:OracleAdapter)
             connection.execute "insert into test_models (id, wealth) values (people_seq.nextval, 12345678901234567890.0123456789)"
-          elsif current_adapter?(:MysqlAdapter) && Mysql.client_version < 50003 #before MySQL 5.0.3 decimals stored as strings
-            connection.execute "insert into test_models (wealth) values ('12345678901234567890.0123456789')"
-          elsif current_adapter?(:PostgreSQLAdapter)
-            connection.execute "insert into test_models (wealth) values (12345678901234567890.0123456789)"
           else
             connection.execute "insert into test_models (wealth) values (12345678901234567890.0123456789)"
           end
@@ -76,15 +74,13 @@ module ActiveRecord
           assert_kind_of BigDecimal, row.wealth
 
           # If this assert fails, that means the SELECT is broken!
-          unless current_adapter?(:SQLite3Adapter)
-            assert_equal correct_value, row.wealth
-          end
+          assert_equal correct_value, row.wealth
 
           # Reset to old state
           TestModel.delete_all
 
           # Now use the Rails insertion
-          TestModel.create :wealth => BigDecimal.new("12345678901234567890.0123456789")
+          TestModel.create wealth: BigDecimal("12345678901234567890.0123456789")
 
           # SELECT
           row = TestModel.first
@@ -96,26 +92,40 @@ module ActiveRecord
       end
 
       def test_add_column_with_precision_and_scale
-        connection.add_column 'test_models', 'wealth', :decimal, :precision => 9, :scale => 7
+        connection.add_column "test_models", "wealth", :decimal, precision: 9, scale: 7
 
-        wealth_column = TestModel.columns_hash['wealth']
+        wealth_column = TestModel.columns_hash["wealth"]
         assert_equal 9, wealth_column.precision
         assert_equal 7, wealth_column.scale
       end
 
+      # Test SQLite3 adapter specifically for decimal types with precision and scale
+      # attributes, since these need to be maintained in schema but aren't actually
+      # used in SQLite3 itself
       if current_adapter?(:SQLite3Adapter)
+        def test_change_column_with_new_precision_and_scale
+          connection.add_column "test_models", "wealth", :decimal, precision: 9, scale: 7
+
+          connection.change_column "test_models", "wealth", :decimal, precision: 12, scale: 8
+          TestModel.reset_column_information
+
+          wealth_column = TestModel.columns_hash["wealth"]
+          assert_equal 12, wealth_column.precision
+          assert_equal 8, wealth_column.scale
+        end
+
         def test_change_column_preserve_other_column_precision_and_scale
-          connection.add_column 'test_models', 'last_name', :string
-          connection.add_column 'test_models', 'wealth', :decimal, :precision => 9, :scale => 7
+          connection.add_column "test_models", "last_name", :string
+          connection.add_column "test_models", "wealth", :decimal, precision: 9, scale: 7
 
-          wealth_column = TestModel.columns_hash['wealth']
+          wealth_column = TestModel.columns_hash["wealth"]
           assert_equal 9, wealth_column.precision
           assert_equal 7, wealth_column.scale
 
-          connection.change_column 'test_models', 'last_name', :string, :null => false
+          connection.change_column "test_models", "last_name", :string, null: false
           TestModel.reset_column_information
 
-          wealth_column = TestModel.columns_hash['wealth']
+          wealth_column = TestModel.columns_hash["wealth"]
           assert_equal 9, wealth_column.precision
           assert_equal 7, wealth_column.scale
         end
@@ -128,55 +138,48 @@ module ActiveRecord
           add_column "test_models", "bio", :text
           add_column "test_models", "age", :integer
           add_column "test_models", "height", :float
-          add_column "test_models", "wealth", :decimal, :precision => '30', :scale => '10'
+          add_column "test_models", "wealth", :decimal, precision: "30", scale: "10"
           add_column "test_models", "birthday", :datetime
           add_column "test_models", "favorite_day", :date
           add_column "test_models", "moment_of_truth", :datetime
           add_column "test_models", "male", :boolean
 
-          TestModel.create :first_name => 'bob', :last_name => 'bobsen',
-            :bio => "I was born ....", :age => 18, :height => 1.78,
-            :wealth => BigDecimal.new("12345678901234567890.0123456789"),
-            :birthday => 18.years.ago, :favorite_day => 10.days.ago,
-            :moment_of_truth => "1782-10-10 21:40:18", :male => true
+          TestModel.create first_name: "bob", last_name: "bobsen",
+            bio: "I was born ....", age: 18, height: 1.78,
+            wealth: BigDecimal("12345678901234567890.0123456789"),
+            birthday: 18.years.ago, favorite_day: 10.days.ago,
+            moment_of_truth: "1782-10-10 21:40:18", male: true
 
           bob = TestModel.first
-          assert_equal 'bob', bob.first_name
-          assert_equal 'bobsen', bob.last_name
+          assert_equal "bob", bob.first_name
+          assert_equal "bobsen", bob.last_name
           assert_equal "I was born ....", bob.bio
           assert_equal 18, bob.age
 
           # Test for 30 significant digits (beyond the 16 of float), 10 of them
           # after the decimal place.
 
-          assert_equal BigDecimal.new("0012345678901234567890.0123456789"), bob.wealth
+          assert_equal BigDecimal("0012345678901234567890.0123456789"), bob.wealth
 
           assert_equal true, bob.male?
 
           assert_equal String, bob.first_name.class
           assert_equal String, bob.last_name.class
           assert_equal String, bob.bio.class
-          assert_equal Fixnum, bob.age.class
+          assert_kind_of Integer, bob.age
           assert_equal Time, bob.birthday.class
-
-          if current_adapter?(:OracleAdapter)
-            # Oracle doesn't differentiate between date/time
-            assert_equal Time, bob.favorite_day.class
-          else
-            assert_equal Date, bob.favorite_day.class
-          end
-
+          assert_equal Date, bob.favorite_day.class
           assert_instance_of TrueClass, bob.male?
           assert_kind_of BigDecimal, bob.wealth
         end
       end
 
-      if current_adapter?(:MysqlAdapter, :Mysql2Adapter, :PostgreSQLAdapter)
+      if current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter)
         def test_out_of_range_limit_should_raise
-          assert_raise(ActiveRecordError) { add_column :test_models, :integer_too_big, :integer, :limit => 10 }
+          assert_raise(ActiveRecordError) { add_column :test_models, :integer_too_big, :integer, limit: 10 }
 
           unless current_adapter?(:PostgreSQLAdapter)
-            assert_raise(ActiveRecordError) { add_column :test_models, :text_too_big, :integer, :limit => 0xfffffffff }
+            assert_raise(ActiveRecordError) { add_column :test_models, :text_too_big, :text, limit: 0xfffffffff }
           end
         end
       end
diff --git a/activerecord/test/cases/migration/column_positioning_test.rb b/activerecord/test/cases/migration/column_positioning_test.rb
index 4637970ce0..1c62a68cf9 100644
--- a/activerecord/test/cases/migration/column_positioning_test.rb
+++ b/activerecord/test/cases/migration/column_positioning_test.rb
@@ -1,4 +1,6 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class Migration
@@ -11,7 +13,7 @@ module ActiveRecord
 
         @connection = ActiveRecord::Base.connection
 
-        connection.create_table :testings, :id => false do |t|
+        connection.create_table :testings, id: false do |t|
           t.column :first, :integer
           t.column :second, :integer
           t.column :third, :integer
@@ -23,7 +25,7 @@ module ActiveRecord
         ActiveRecord::Base.primary_key_prefix_type = nil
       end
 
-      if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+      if current_adapter?(:Mysql2Adapter)
         def test_column_positioning
           assert_equal %w(first second third), conn.columns(:testings).map(&:name)
         end
@@ -34,22 +36,32 @@ module ActiveRecord
         end
 
         def test_add_column_with_positioning_first
-          conn.add_column :testings, :new_col, :integer, :first => true
+          conn.add_column :testings, :new_col, :integer, first: true
           assert_equal %w(new_col first second third), conn.columns(:testings).map(&:name)
         end
 
         def test_add_column_with_positioning_after
-          conn.add_column :testings, :new_col, :integer, :after => :first
+          conn.add_column :testings, :new_col, :integer, after: :first
           assert_equal %w(first new_col second third), conn.columns(:testings).map(&:name)
         end
 
         def test_change_column_with_positioning
-          conn.change_column :testings, :second, :integer, :first => true
+          conn.change_column :testings, :second, :integer, first: true
           assert_equal %w(second first third), conn.columns(:testings).map(&:name)
 
-          conn.change_column :testings, :second, :integer, :after => :third
+          conn.change_column :testings, :second, :integer, after: :third
           assert_equal %w(first third second), conn.columns(:testings).map(&:name)
         end
+
+        def test_add_reference_with_positioning_first
+          conn.add_reference :testings, :new, polymorphic: true, first: true
+          assert_equal %w(new_id new_type first second third), conn.columns(:testings).map(&:name)
+        end
+
+        def test_add_reference_with_positioning_after
+          conn.add_reference :testings, :new, polymorphic: true, after: :first
+          assert_equal %w(first new_id new_type second third), conn.columns(:testings).map(&:name)
+        end
       end
     end
   end
diff --git a/activerecord/test/cases/migration/columns_test.rb b/activerecord/test/cases/migration/columns_test.rb
index ab3f584350..cedd9c44e3 100644
--- a/activerecord/test/cases/migration/columns_test.rb
+++ b/activerecord/test/cases/migration/columns_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/migration/helper"
 
 module ActiveRecord
@@ -13,7 +15,7 @@ module ActiveRecord
         add_column "test_models", "girlfriend", :string
         TestModel.reset_column_information
 
-        TestModel.create :girlfriend => 'bobette'
+        TestModel.create girlfriend: "bobette"
 
         rename_column "test_models", "girlfriend", "exgirlfriend"
 
@@ -28,12 +30,12 @@ module ActiveRecord
       def test_rename_column_using_symbol_arguments
         add_column :test_models, :first_name, :string
 
-        TestModel.create :first_name => 'foo'
+        TestModel.create first_name: "foo"
 
         rename_column :test_models, :first_name, :nick_name
         TestModel.reset_column_information
-        assert TestModel.column_names.include?("nick_name")
-        assert_equal ['foo'], TestModel.all.map(&:nick_name)
+        assert_includes TestModel.column_names, "nick_name"
+        assert_equal ["foo"], TestModel.all.map(&:nick_name)
       end
 
       # FIXME: another integration test.  We should decouple this from the
@@ -41,31 +43,31 @@ module ActiveRecord
       def test_rename_column
         add_column "test_models", "first_name", "string"
 
-        TestModel.create :first_name => 'foo'
+        TestModel.create first_name: "foo"
 
         rename_column "test_models", "first_name", "nick_name"
         TestModel.reset_column_information
-        assert TestModel.column_names.include?("nick_name")
-        assert_equal ['foo'], TestModel.all.map(&:nick_name)
+        assert_includes TestModel.column_names, "nick_name"
+        assert_equal ["foo"], TestModel.all.map(&:nick_name)
       end
 
       def test_rename_column_preserves_default_value_not_null
-        add_column 'test_models', 'salary', :integer, :default => 70000
+        add_column "test_models", "salary", :integer, default: 70000
 
         default_before = connection.columns("test_models").find { |c| c.name == "salary" }.default
-        assert_equal '70000', default_before
+        assert_equal "70000", default_before
 
         rename_column "test_models", "salary", "annual_salary"
 
-        assert TestModel.column_names.include?("annual_salary")
+        assert_includes TestModel.column_names, "annual_salary"
         default_after = connection.columns("test_models").find { |c| c.name == "annual_salary" }.default
-        assert_equal '70000', default_after
+        assert_equal "70000", default_after
       end
 
-      if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+      if current_adapter?(:Mysql2Adapter)
         def test_mysql_rename_column_preserves_auto_increment
           rename_column "test_models", "id", "id_test"
-          assert connection.columns("test_models").find { |c| c.name == "id_test" }.auto_increment?
+          assert_predicate connection.columns("test_models").find { |c| c.name == "id_test" }, :auto_increment?
           TestModel.reset_column_information
         ensure
           rename_column "test_models", "id_test", "id"
@@ -74,30 +76,31 @@ module ActiveRecord
 
       def test_rename_nonexistent_column
         exception = if current_adapter?(:PostgreSQLAdapter, :OracleAdapter)
-                      ActiveRecord::StatementInvalid
-                    else
-                      ActiveRecord::ActiveRecordError
-                    end
+          ActiveRecord::StatementInvalid
+        else
+          ActiveRecord::ActiveRecordError
+        end
+
         assert_raise(exception) do
           rename_column "test_models", "nonexistent", "should_fail"
         end
       end
 
       def test_rename_column_with_sql_reserved_word
-        add_column 'test_models', 'first_name', :string
+        add_column "test_models", "first_name", :string
         rename_column "test_models", "first_name", "group"
 
-        assert TestModel.column_names.include?("group")
+        assert_includes TestModel.column_names, "group"
       end
 
       def test_rename_column_with_an_index
         add_column "test_models", :hat_name, :string
         add_index :test_models, :hat_name
 
-        assert_equal 1, connection.indexes('test_models').size
+        assert_equal 1, connection.indexes("test_models").size
         rename_column "test_models", "hat_name", "name"
 
-        assert_equal ['index_test_models_on_name'], connection.indexes('test_models').map(&:name)
+        assert_equal ["index_test_models_on_name"], connection.indexes("test_models").map(&:name)
       end
 
       def test_rename_column_with_multi_column_index
@@ -105,153 +108,167 @@ module ActiveRecord
         add_column "test_models", :hat_style, :string, limit: 100
         add_index "test_models", ["hat_style", "hat_size"], unique: true
 
-        rename_column "test_models", "hat_size", 'size'
+        rename_column "test_models", "hat_size", "size"
         if current_adapter? :OracleAdapter
-          assert_equal ['i_test_models_hat_style_size'], connection.indexes('test_models').map(&:name)
+          assert_equal ["i_test_models_hat_style_size"], connection.indexes("test_models").map(&:name)
         else
-          assert_equal ['index_test_models_on_hat_style_and_size'], connection.indexes('test_models').map(&:name)
+          assert_equal ["index_test_models_on_hat_style_and_size"], connection.indexes("test_models").map(&:name)
         end
 
-        rename_column "test_models", "hat_style", 'style'
+        rename_column "test_models", "hat_style", "style"
         if current_adapter? :OracleAdapter
-          assert_equal ['i_test_models_style_size'], connection.indexes('test_models').map(&:name)
+          assert_equal ["i_test_models_style_size"], connection.indexes("test_models").map(&:name)
         else
-          assert_equal ['index_test_models_on_style_and_size'], connection.indexes('test_models').map(&:name)
+          assert_equal ["index_test_models_on_style_and_size"], connection.indexes("test_models").map(&:name)
         end
       end
 
       def test_rename_column_does_not_rename_custom_named_index
         add_column "test_models", :hat_name, :string
-        add_index :test_models, :hat_name, :name => 'idx_hat_name'
+        add_index :test_models, :hat_name, name: "idx_hat_name"
 
-        assert_equal 1, connection.indexes('test_models').size
+        assert_equal 1, connection.indexes("test_models").size
         rename_column "test_models", "hat_name", "name"
-        assert_equal ['idx_hat_name'], connection.indexes('test_models').map(&:name)
+        assert_equal ["idx_hat_name"], connection.indexes("test_models").map(&:name)
       end
 
       def test_remove_column_with_index
         add_column "test_models", :hat_name, :string
         add_index :test_models, :hat_name
 
-        assert_equal 1, connection.indexes('test_models').size
+        assert_equal 1, connection.indexes("test_models").size
         remove_column("test_models", "hat_name")
-        assert_equal 0, connection.indexes('test_models').size
+        assert_equal 0, connection.indexes("test_models").size
       end
 
       def test_remove_column_with_multi_column_index
+        # MariaDB starting with 10.2.8
+        # Dropping a column that is part of a multi-column UNIQUE constraint is not permitted.
+        skip if current_adapter?(:Mysql2Adapter) && connection.mariadb? && connection.version >= "10.2.8"
+
         add_column "test_models", :hat_size, :integer
-        add_column "test_models", :hat_style, :string, :limit => 100
-        add_index "test_models", ["hat_style", "hat_size"], :unique => true
+        add_column "test_models", :hat_style, :string, limit: 100
+        add_index "test_models", ["hat_style", "hat_size"], unique: true
 
-        assert_equal 1, connection.indexes('test_models').size
+        assert_equal 1, connection.indexes("test_models").size
         remove_column("test_models", "hat_size")
 
         # Every database and/or database adapter has their own behavior
         # if it drops the multi-column index when any of the indexed columns dropped by remove_column.
         if current_adapter?(:PostgreSQLAdapter, :OracleAdapter)
-          assert_equal [], connection.indexes('test_models').map(&:name)
+          assert_equal [], connection.indexes("test_models").map(&:name)
         else
-          assert_equal ['index_test_models_on_hat_style_and_hat_size'], connection.indexes('test_models').map(&:name)
+          assert_equal ["index_test_models_on_hat_style_and_hat_size"], connection.indexes("test_models").map(&:name)
         end
       end
 
       def test_change_type_of_not_null_column
-        change_column "test_models", "updated_at", :datetime, :null => false
-        change_column "test_models", "updated_at", :datetime, :null => false
+        change_column "test_models", "updated_at", :datetime, null: false
+        change_column "test_models", "updated_at", :datetime, null: false
 
         TestModel.reset_column_information
-        assert_equal false, TestModel.columns_hash['updated_at'].null
+        assert_equal false, TestModel.columns_hash["updated_at"].null
       ensure
-        change_column "test_models", "updated_at", :datetime, :null => true
+        change_column "test_models", "updated_at", :datetime, null: true
       end
 
       def test_change_column_nullability
         add_column "test_models", "funny", :boolean
         assert TestModel.columns_hash["funny"].null, "Column 'funny' must initially allow nulls"
 
-        change_column "test_models", "funny", :boolean, :null => false, :default => true
+        change_column "test_models", "funny", :boolean, null: false, default: true
 
         TestModel.reset_column_information
         assert_not TestModel.columns_hash["funny"].null, "Column 'funny' must *not* allow nulls at this point"
 
-        change_column "test_models", "funny", :boolean, :null => true
+        change_column "test_models", "funny", :boolean, null: true
         TestModel.reset_column_information
         assert TestModel.columns_hash["funny"].null, "Column 'funny' must allow nulls again at this point"
       end
 
       def test_change_column
-        add_column 'test_models', 'age', :integer
-        add_column 'test_models', 'approved', :boolean, :default => true
+        add_column "test_models", "age", :integer
+        add_column "test_models", "approved", :boolean, default: true
 
         old_columns = connection.columns(TestModel.table_name)
 
-        assert old_columns.find { |c| c.name == 'age' && c.type == :integer }
+        assert old_columns.find { |c| c.name == "age" && c.type == :integer }
 
         change_column "test_models", "age", :string
 
         new_columns = connection.columns(TestModel.table_name)
 
-        assert_not new_columns.find { |c| c.name == 'age' and c.type == :integer }
-        assert new_columns.find { |c| c.name == 'age' and c.type == :string }
+        assert_not new_columns.find { |c| c.name == "age" && c.type == :integer }
+        assert new_columns.find { |c| c.name == "age" && c.type == :string }
 
         old_columns = connection.columns(TestModel.table_name)
         assert old_columns.find { |c|
           default = connection.lookup_cast_type_from_column(c).deserialize(c.default)
-          c.name == 'approved' && c.type == :boolean && default == true
+          c.name == "approved" && c.type == :boolean && default == true
         }
 
-        change_column :test_models, :approved, :boolean, :default => false
+        change_column :test_models, :approved, :boolean, default: false
         new_columns = connection.columns(TestModel.table_name)
 
         assert_not new_columns.find { |c|
           default = connection.lookup_cast_type_from_column(c).deserialize(c.default)
-          c.name == 'approved' and c.type == :boolean and default == true
+          c.name == "approved" && c.type == :boolean && default == true
         }
         assert new_columns.find { |c|
           default = connection.lookup_cast_type_from_column(c).deserialize(c.default)
-          c.name == 'approved' and c.type == :boolean and default == false
+          c.name == "approved" && c.type == :boolean && default == false
         }
-        change_column :test_models, :approved, :boolean, :default => true
+        change_column :test_models, :approved, :boolean, default: true
       end
 
       def test_change_column_with_nil_default
-        add_column "test_models", "contributor", :boolean, :default => true
-        assert TestModel.new.contributor?
+        add_column "test_models", "contributor", :boolean, default: true
+        assert_predicate TestModel.new, :contributor?
+
+        change_column "test_models", "contributor", :boolean, default: nil
+        TestModel.reset_column_information
+        assert_not_predicate TestModel.new, :contributor?
+        assert_nil TestModel.new.contributor
+      end
+
+      def test_change_column_to_drop_default_with_null_false
+        add_column "test_models", "contributor", :boolean, default: true, null: false
+        assert_predicate TestModel.new, :contributor?
 
-        change_column "test_models", "contributor", :boolean, :default => nil
+        change_column "test_models", "contributor", :boolean, default: nil, null: false
         TestModel.reset_column_information
-        assert_not TestModel.new.contributor?
+        assert_not_predicate TestModel.new, :contributor?
         assert_nil TestModel.new.contributor
       end
 
       def test_change_column_with_new_default
-        add_column "test_models", "administrator", :boolean, :default => true
-        assert TestModel.new.administrator?
+        add_column "test_models", "administrator", :boolean, default: true
+        assert_predicate TestModel.new, :administrator?
 
-        change_column "test_models", "administrator", :boolean, :default => false
+        change_column "test_models", "administrator", :boolean, default: false
         TestModel.reset_column_information
-        assert_not TestModel.new.administrator?
+        assert_not_predicate TestModel.new, :administrator?
       end
 
       def test_change_column_with_custom_index_name
         add_column "test_models", "category", :string
-        add_index :test_models, :category, name: 'test_models_categories_idx'
+        add_index :test_models, :category, name: "test_models_categories_idx"
 
-        assert_equal ['test_models_categories_idx'], connection.indexes('test_models').map(&:name)
-        change_column "test_models", "category", :string, null: false, default: 'article'
+        assert_equal ["test_models_categories_idx"], connection.indexes("test_models").map(&:name)
+        change_column "test_models", "category", :string, null: false, default: "article"
 
-        assert_equal ['test_models_categories_idx'], connection.indexes('test_models').map(&:name)
+        assert_equal ["test_models_categories_idx"], connection.indexes("test_models").map(&:name)
       end
 
       def test_change_column_with_long_index_name
-        table_name_prefix = 'test_models_'
-        long_index_name = table_name_prefix + ('x' * (connection.allowed_index_name_length - table_name_prefix.length))
+        table_name_prefix = "test_models_"
+        long_index_name = table_name_prefix + ("x" * (connection.allowed_index_name_length - table_name_prefix.length))
         add_column "test_models", "category", :string
         add_index :test_models, :category, name: long_index_name
 
-        change_column "test_models", "category", :string, null: false, default: 'article'
+        change_column "test_models", "category", :string, null: false, default: "article"
 
-        assert_equal [long_index_name], connection.indexes('test_models').map(&:name)
+        assert_equal [long_index_name], connection.indexes("test_models").map(&:name)
       end
 
       def test_change_column_default
@@ -287,7 +304,7 @@ module ActiveRecord
         remove_column("my_table", "col_two")
         rename_column("my_table", "col_one", "col_three")
 
-        assert_equal 'my_table_id', connection.primary_key('my_table')
+        assert_equal "my_table_id", connection.primary_key("my_table")
       ensure
         connection.drop_table(:my_table) rescue nil
       end
diff --git a/activerecord/test/cases/migration/command_recorder_test.rb b/activerecord/test/cases/migration/command_recorder_test.rb
index 99f1dc65b0..01f8628fc5 100644
--- a/activerecord/test/cases/migration/command_recorder_test.rb
+++ b/activerecord/test/cases/migration/command_recorder_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -12,7 +14,7 @@ module ActiveRecord
         recorder = CommandRecorder.new(Class.new {
           def america; end
         }.new)
-        assert recorder.respond_to?(:america)
+        assert_respond_to recorder, :america
       end
 
       def test_send_calls_super
@@ -25,25 +27,26 @@ module ActiveRecord
         recorder = CommandRecorder.new(Class.new {
           def create_table(name); end
         }.new)
-        assert recorder.respond_to?(:create_table), 'respond_to? create_table'
+        assert_respond_to recorder, :create_table
         recorder.send(:create_table, :horses)
         assert_equal [[:create_table, [:horses], nil]], recorder.commands
       end
 
       def test_unknown_commands_delegate
-        recorder = CommandRecorder.new(stub(:foo => 'bar'))
-        assert_equal 'bar', recorder.foo
+        recorder = Struct.new(:foo)
+        recorder = CommandRecorder.new(recorder.new("bar"))
+        assert_equal "bar", recorder.foo
       end
 
       def test_inverse_of_raise_exception_on_unknown_commands
         assert_raises(ActiveRecord::IrreversibleMigration) do
-          @recorder.inverse_of :execute, ['some sql']
+          @recorder.inverse_of :execute, ["some sql"]
         end
       end
 
       def test_irreversible_commands_raise_exception
         assert_raises(ActiveRecord::IrreversibleMigration) do
-          @recorder.revert{ @recorder.execute 'some sql' }
+          @recorder.revert { @recorder.execute "some sql" }
         end
       end
 
@@ -57,12 +60,12 @@ module ActiveRecord
           @recorder.record :create_table, [:hello]
           @recorder.record :create_table, [:world]
         end
-        tables = @recorder.commands.map{|_cmd, args, _block| args}
+        tables = @recorder.commands.map { |_cmd, args, _block| args }
         assert_equal [[:world], [:hello]], tables
       end
 
       def test_revert_order
-        block = Proc.new{|t| t.string :name }
+        block = Proc.new { |t| t.string :name }
         @recorder.instance_eval do
           create_table("apples", &block)
           revert do
@@ -114,13 +117,13 @@ module ActiveRecord
       end
 
       def test_invert_create_table_with_options_and_block
-        block = Proc.new{}
+        block = Proc.new { }
         drop_table = @recorder.inverse_of :create_table, [:people_reminders, id: false], &block
         assert_equal [:drop_table, [:people_reminders, id: false], block], drop_table
       end
 
       def test_invert_drop_table
-        block = Proc.new{}
+        block = Proc.new { }
         create_table = @recorder.inverse_of :drop_table, [:people_reminders, id: false], &block
         assert_equal [:create_table, [:people_reminders, id: false], block], create_table
       end
@@ -142,7 +145,7 @@ module ActiveRecord
       end
 
       def test_invert_drop_join_table
-        block = Proc.new{}
+        block = Proc.new { }
         create_join_table = @recorder.inverse_of :drop_join_table, [:musics, :artists, table_name: :catalog], &block
         assert_equal [:create_join_table, [:musics, :artists, table_name: :catalog], block], create_join_table
       end
@@ -165,7 +168,7 @@ module ActiveRecord
 
       def test_invert_change_column_default
         assert_raises(ActiveRecord::IrreversibleMigration) do
-          @recorder.inverse_of :change_column_default, [:table, :column, 'default_value']
+          @recorder.inverse_of :change_column_default, [:table, :column, "default_value"]
         end
       end
 
@@ -202,17 +205,17 @@ module ActiveRecord
 
       def test_invert_add_index
         remove = @recorder.inverse_of :add_index, [:table, [:one, :two]]
-        assert_equal [:remove_index, [:table, {column: [:one, :two]}]], remove
+        assert_equal [:remove_index, [:table, { column: [:one, :two] }]], remove
       end
 
       def test_invert_add_index_with_name
         remove = @recorder.inverse_of :add_index, [:table, [:one, :two], name: "new_index"]
-        assert_equal [:remove_index, [:table, {name: "new_index"}]], remove
+        assert_equal [:remove_index, [:table, { name: "new_index" }]], remove
       end
 
-      def test_invert_add_index_with_no_options
-        remove = @recorder.inverse_of :add_index, [:table, [:one, :two]]
-        assert_equal [:remove_index, [:table, {column: [:one, :two]}]], remove
+      def test_invert_add_index_with_algorithm_option
+        remove = @recorder.inverse_of :add_index, [:table, :one, algorithm: :concurrently]
+        assert_equal [:remove_index, [:table, { column: :one, algorithm: :concurrently }]], remove
       end
 
       def test_invert_remove_index
@@ -221,17 +224,17 @@ module ActiveRecord
       end
 
       def test_invert_remove_index_with_column
-        add = @recorder.inverse_of :remove_index, [:table, {column: [:one, :two], options: true}]
+        add = @recorder.inverse_of :remove_index, [:table, { column: [:one, :two], options: true }]
         assert_equal [:add_index, [:table, [:one, :two], options: true]], add
       end
 
       def test_invert_remove_index_with_name
-        add = @recorder.inverse_of :remove_index, [:table, {column: [:one, :two], name: "new_index"}]
+        add = @recorder.inverse_of :remove_index, [:table, { column: [:one, :two], name: "new_index" }]
         assert_equal [:add_index, [:table, [:one, :two], name: "new_index"]], add
       end
 
       def test_invert_remove_index_with_no_special_options
-        add = @recorder.inverse_of :remove_index, [:table, {column: [:one, :two]}]
+        add = @recorder.inverse_of :remove_index, [:table, { column: [:one, :two] }]
         assert_equal [:add_index, [:table, [:one, :two], {}]], add
       end
 
@@ -253,7 +256,7 @@ module ActiveRecord
 
       def test_invert_remove_timestamps
         add = @recorder.inverse_of :remove_timestamps, [:table, { null: true }]
-        assert_equal [:add_timestamps, [:table, {null: true }], nil], add
+        assert_equal [:add_timestamps, [:table, { null: true }], nil], add
       end
 
       def test_invert_add_reference
@@ -282,13 +285,13 @@ module ActiveRecord
       end
 
       def test_invert_enable_extension
-        disable = @recorder.inverse_of :enable_extension, ['uuid-ossp']
-        assert_equal [:disable_extension, ['uuid-ossp'], nil], disable
+        disable = @recorder.inverse_of :enable_extension, ["uuid-ossp"]
+        assert_equal [:disable_extension, ["uuid-ossp"], nil], disable
       end
 
       def test_invert_disable_extension
-        enable = @recorder.inverse_of :disable_extension, ['uuid-ossp']
-        assert_equal [:enable_extension, ['uuid-ossp'], nil], enable
+        enable = @recorder.inverse_of :disable_extension, ["uuid-ossp"]
+        assert_equal [:enable_extension, ["uuid-ossp"], nil], enable
       end
 
       def test_invert_add_foreign_key
@@ -326,11 +329,24 @@ module ActiveRecord
         assert_equal [:add_foreign_key, [:dogs, :people, primary_key: "person_id"]], enable
       end
 
+      def test_invert_remove_foreign_key_with_primary_key_and_to_table_in_options
+        enable = @recorder.inverse_of :remove_foreign_key, [:dogs, to_table: :people, primary_key: "uuid"]
+        assert_equal [:add_foreign_key, [:dogs, :people, primary_key: "uuid"]], enable
+      end
+
       def test_invert_remove_foreign_key_with_on_delete_on_update
         enable = @recorder.inverse_of :remove_foreign_key, [:dogs, :people, on_delete: :nullify, on_update: :cascade]
         assert_equal [:add_foreign_key, [:dogs, :people, on_delete: :nullify, on_update: :cascade]], enable
       end
 
+      def test_invert_remove_foreign_key_with_to_table_in_options
+        enable = @recorder.inverse_of :remove_foreign_key, [:dogs, to_table: :people]
+        assert_equal [:add_foreign_key, [:dogs, :people]], enable
+
+        enable = @recorder.inverse_of :remove_foreign_key, [:dogs, to_table: :people, column: :owner_id]
+        assert_equal [:add_foreign_key, [:dogs, :people, column: :owner_id]], enable
+      end
+
       def test_invert_remove_foreign_key_is_irreversible_without_to_table
         assert_raises ActiveRecord::IrreversibleMigration do
           @recorder.inverse_of :remove_foreign_key, [:dogs, column: "owner_id"]
@@ -344,6 +360,16 @@ module ActiveRecord
           @recorder.inverse_of :remove_foreign_key, [:dogs]
         end
       end
+
+      def test_invert_transaction_with_irreversible_inside_is_irreversible
+        assert_raises(ActiveRecord::IrreversibleMigration) do
+          @recorder.revert do
+            @recorder.transaction do
+              @recorder.execute "some sql"
+            end
+          end
+        end
+      end
     end
   end
 end
diff --git a/activerecord/test/cases/migration/compatibility_test.rb b/activerecord/test/cases/migration/compatibility_test.rb
new file mode 100644
index 0000000000..017ee7951e
--- /dev/null
+++ b/activerecord/test/cases/migration/compatibility_test.rb
@@ -0,0 +1,383 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/schema_dumping_helper"
+
+module ActiveRecord
+  class Migration
+    class CompatibilityTest < ActiveRecord::TestCase
+      attr_reader :connection
+      self.use_transactional_tests = false
+
+      def setup
+        super
+        @connection = ActiveRecord::Base.connection
+        @verbose_was = ActiveRecord::Migration.verbose
+        ActiveRecord::Migration.verbose = false
+
+        connection.create_table :testings do |t|
+          t.column :foo, :string, limit: 5
+          t.column :bar, :string, limit: 100
+        end
+      end
+
+      teardown do
+        connection.drop_table :testings rescue nil
+        ActiveRecord::Migration.verbose = @verbose_was
+        ActiveRecord::SchemaMigration.delete_all rescue nil
+      end
+
+      def test_migration_doesnt_remove_named_index
+        connection.add_index :testings, :foo, name: "custom_index_name"
+
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
+          def version; 101 end
+          def migrate(x)
+            remove_index :testings, :foo
+          end
+        }.new
+
+        assert connection.index_exists?(:testings, :foo, name: "custom_index_name")
+        assert_raise(StandardError) { ActiveRecord::Migrator.new(:up, [migration]).migrate }
+        assert connection.index_exists?(:testings, :foo, name: "custom_index_name")
+      end
+
+      def test_migration_does_remove_unnamed_index
+        connection.add_index :testings, :bar
+
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
+          def version; 101 end
+          def migrate(x)
+            remove_index :testings, :bar
+          end
+        }.new
+
+        assert connection.index_exists?(:testings, :bar)
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+        assert_not connection.index_exists?(:testings, :bar)
+      end
+
+      def test_references_does_not_add_index_by_default
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
+          def migrate(x)
+            create_table :more_testings do |t|
+              t.references :foo
+              t.belongs_to :bar, index: false
+            end
+          end
+        }.new
+
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+        assert_not connection.index_exists?(:more_testings, :foo_id)
+        assert_not connection.index_exists?(:more_testings, :bar_id)
+      ensure
+        connection.drop_table :more_testings rescue nil
+      end
+
+      def test_timestamps_have_null_constraints_if_not_present_in_migration_of_create_table
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
+          def migrate(x)
+            create_table :more_testings do |t|
+              t.timestamps
+            end
+          end
+        }.new
+
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+        assert connection.columns(:more_testings).find { |c| c.name == "created_at" }.null
+        assert connection.columns(:more_testings).find { |c| c.name == "updated_at" }.null
+      ensure
+        connection.drop_table :more_testings rescue nil
+      end
+
+      def test_timestamps_have_null_constraints_if_not_present_in_migration_of_change_table
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
+          def migrate(x)
+            change_table :testings do |t|
+              t.timestamps
+            end
+          end
+        }.new
+
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+        assert connection.columns(:testings).find { |c| c.name == "created_at" }.null
+        assert connection.columns(:testings).find { |c| c.name == "updated_at" }.null
+      end
+
+      def test_timestamps_have_null_constraints_if_not_present_in_migration_for_adding_timestamps_to_existing_table
+        migration = Class.new(ActiveRecord::Migration[4.2]) {
+          def migrate(x)
+            add_timestamps :testings
+          end
+        }.new
+
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+        assert connection.columns(:testings).find { |c| c.name == "created_at" }.null
+        assert connection.columns(:testings).find { |c| c.name == "updated_at" }.null
+      end
+
+      def test_legacy_migrations_raises_exception_when_inherited
+        e = assert_raises(StandardError) do
+          class_eval("class LegacyMigration < ActiveRecord::Migration; end")
+        end
+        assert_match(/LegacyMigration < ActiveRecord::Migration\[4\.2\]/, e.message)
+      end
+
+      def test_legacy_migrations_not_raise_exception_on_reverting_transaction
+        migration = Class.new(ActiveRecord::Migration[5.2]) {
+          def change
+            transaction do
+              execute "select 1"
+            end
+          end
+        }.new
+
+        assert_nothing_raised do
+          migration.migrate(:down)
+        end
+      end
+
+      if current_adapter?(:PostgreSQLAdapter)
+        class Testing < ActiveRecord::Base
+        end
+
+        def test_legacy_change_column_with_null_executes_update
+          migration = Class.new(ActiveRecord::Migration[5.1]) {
+            def migrate(x)
+              change_column :testings, :foo, :string, limit: 10, null: false, default: "foobar"
+            end
+          }.new
+
+          Testing.create!
+          ActiveRecord::Migrator.new(:up, [migration]).migrate
+          assert_equal ["foobar"], Testing.all.map(&:foo)
+        ensure
+          ActiveRecord::Base.clear_cache!
+        end
+      end
+    end
+  end
+end
+
+module LegacyPrimaryKeyTestCases
+  include SchemaDumpingHelper
+
+  class LegacyPrimaryKey < ActiveRecord::Base
+  end
+
+  def setup
+    @migration = nil
+    @verbose_was = ActiveRecord::Migration.verbose
+    ActiveRecord::Migration.verbose = false
+  end
+
+  def teardown
+    @migration.migrate(:down) if @migration
+    ActiveRecord::Migration.verbose = @verbose_was
+    ActiveRecord::SchemaMigration.delete_all rescue nil
+    LegacyPrimaryKey.reset_column_information
+  end
+
+  def test_legacy_primary_key_should_be_auto_incremented
+    @migration = Class.new(migration_class) {
+      def change
+        create_table :legacy_primary_keys do |t|
+          t.references :legacy_ref
+        end
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    assert_legacy_primary_key
+
+    legacy_ref = LegacyPrimaryKey.columns_hash["legacy_ref_id"]
+    assert_not_predicate legacy_ref, :bigint?
+
+    record1 = LegacyPrimaryKey.create!
+    assert_not_nil record1.id
+
+    record1.destroy
+
+    record2 = LegacyPrimaryKey.create!
+    assert_not_nil record2.id
+    assert_operator record2.id, :>, record1.id
+  end
+
+  def test_legacy_integer_primary_key_should_not_be_auto_incremented
+    skip if current_adapter?(:SQLite3Adapter)
+
+    @migration = Class.new(migration_class) {
+      def change
+        create_table :legacy_primary_keys, id: :integer do |t|
+        end
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    assert_raises(ActiveRecord::NotNullViolation) do
+      LegacyPrimaryKey.create!
+    end
+
+    schema = dump_table_schema "legacy_primary_keys"
+    assert_match %r{create_table "legacy_primary_keys", id: :integer, default: nil}, schema
+  end
+
+  def test_legacy_primary_key_in_create_table_should_be_integer
+    @migration = Class.new(migration_class) {
+      def change
+        create_table :legacy_primary_keys, id: false do |t|
+          t.primary_key :id
+        end
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    assert_legacy_primary_key
+  end
+
+  def test_legacy_primary_key_in_change_table_should_be_integer
+    @migration = Class.new(migration_class) {
+      def change
+        create_table :legacy_primary_keys, id: false do |t|
+          t.integer :dummy
+        end
+        change_table :legacy_primary_keys do |t|
+          t.primary_key :id
+        end
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    assert_legacy_primary_key
+  end
+
+  def test_add_column_with_legacy_primary_key_should_be_integer
+    @migration = Class.new(migration_class) {
+      def change
+        create_table :legacy_primary_keys, id: false do |t|
+          t.integer :dummy
+        end
+        add_column :legacy_primary_keys, :id, :primary_key
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    assert_legacy_primary_key
+  end
+
+  def test_legacy_join_table_foreign_keys_should_be_integer
+    @migration = Class.new(migration_class) {
+      def change
+        create_join_table :apples, :bananas do |t|
+        end
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    schema = dump_table_schema "apples_bananas"
+    assert_match %r{integer "apple_id", null: false}, schema
+    assert_match %r{integer "banana_id", null: false}, schema
+  end
+
+  def test_legacy_join_table_column_options_should_be_overwritten
+    @migration = Class.new(migration_class) {
+      def change
+        create_join_table :apples, :bananas, column_options: { type: :bigint } do |t|
+        end
+      end
+    }.new
+
+    @migration.migrate(:up)
+
+    schema = dump_table_schema "apples_bananas"
+    assert_match %r{bigint "apple_id", null: false}, schema
+    assert_match %r{bigint "banana_id", null: false}, schema
+  end
+
+  if current_adapter?(:Mysql2Adapter)
+    def test_legacy_bigint_primary_key_should_be_auto_incremented
+      @migration = Class.new(migration_class) {
+        def change
+          create_table :legacy_primary_keys, id: :bigint
+        end
+      }.new
+
+      @migration.migrate(:up)
+
+      legacy_pk = LegacyPrimaryKey.columns_hash["id"]
+      assert_predicate legacy_pk, :bigint?
+      assert_predicate legacy_pk, :auto_increment?
+
+      schema = dump_table_schema "legacy_primary_keys"
+      assert_match %r{create_table "legacy_primary_keys", (?!id: :bigint, default: nil)}, schema
+    end
+  else
+    def test_legacy_bigint_primary_key_should_not_be_auto_incremented
+      @migration = Class.new(migration_class) {
+        def change
+          create_table :legacy_primary_keys, id: :bigint do |t|
+          end
+        end
+      }.new
+
+      @migration.migrate(:up)
+
+      assert_raises(ActiveRecord::NotNullViolation) do
+        LegacyPrimaryKey.create!
+      end
+
+      schema = dump_table_schema "legacy_primary_keys"
+      assert_match %r{create_table "legacy_primary_keys", id: :bigint, default: nil}, schema
+    end
+  end
+
+  private
+    def assert_legacy_primary_key
+      assert_equal "id", LegacyPrimaryKey.primary_key
+
+      legacy_pk = LegacyPrimaryKey.columns_hash["id"]
+
+      assert_equal :integer, legacy_pk.type
+      assert_not_predicate legacy_pk, :bigint?
+      assert_not legacy_pk.null
+
+      if current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter)
+        schema = dump_table_schema "legacy_primary_keys"
+        assert_match %r{create_table "legacy_primary_keys", id: :(?:integer|serial), (?!default: nil)}, schema
+      end
+    end
+end
+
+module LegacyPrimaryKeyTest
+  class V5_0 < ActiveRecord::TestCase
+    include LegacyPrimaryKeyTestCases
+
+    self.use_transactional_tests = false
+
+    private
+      def migration_class
+        ActiveRecord::Migration[5.0]
+      end
+  end
+
+  class V4_2 < ActiveRecord::TestCase
+    include LegacyPrimaryKeyTestCases
+
+    self.use_transactional_tests = false
+
+    private
+      def migration_class
+        ActiveRecord::Migration[4.2]
+      end
+  end
+end
diff --git a/activerecord/test/cases/migration/create_join_table_test.rb b/activerecord/test/cases/migration/create_join_table_test.rb
index 8fd08fe4ce..e0cbb29dcf 100644
--- a/activerecord/test/cases/migration/create_join_table_test.rb
+++ b/activerecord/test/cases/migration/create_join_table_test.rb
@@ -1,4 +1,6 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class Migration
@@ -12,7 +14,7 @@ module ActiveRecord
 
       teardown do
         %w(artists_musics musics_videos catalog).each do |table_name|
-          connection.drop_table table_name if connection.tables.include?(table_name)
+          connection.drop_table table_name, if_exists: true
         end
       end
 
@@ -29,13 +31,13 @@ module ActiveRecord
       end
 
       def test_create_join_table_with_strings
-        connection.create_join_table 'artists', 'musics'
+        connection.create_join_table "artists", "musics"
 
         assert_equal %w(artist_id music_id), connection.columns(:artists_musics).map(&:name).sort
       end
 
       def test_create_join_table_with_symbol_and_string
-        connection.create_join_table :artists, 'musics'
+        connection.create_join_table :artists, "musics"
 
         assert_equal %w(artist_id music_id), connection.columns(:artists_musics).map(&:name).sort
       end
@@ -53,13 +55,13 @@ module ActiveRecord
       end
 
       def test_create_join_table_with_the_table_name_as_string
-        connection.create_join_table :artists, :musics, table_name: 'catalog'
+        connection.create_join_table :artists, :musics, table_name: "catalog"
 
         assert_equal %w(artist_id music_id), connection.columns(:catalog).map(&:name).sort
       end
 
       def test_create_join_table_with_column_options
-        connection.create_join_table :artists, :musics, column_options: {null: true}
+        connection.create_join_table :artists, :musics, column_options: { null: true }
 
         assert_equal [true, true], connection.columns(:artists_musics).map(&:null)
       end
@@ -67,7 +69,7 @@ module ActiveRecord
       def test_create_join_table_without_indexes
         connection.create_join_table :artists, :musics
 
-        assert connection.indexes(:artists_musics).blank?
+        assert_predicate connection.indexes(:artists_musics), :blank?
       end
 
       def test_create_join_table_with_index
@@ -78,66 +80,84 @@ module ActiveRecord
         assert_equal [%w(artist_id music_id)], connection.indexes(:artists_musics).map(&:columns)
       end
 
+      def test_create_join_table_respects_reference_key_type
+        connection.create_join_table :artists, :musics do |t|
+          t.references :video
+        end
+
+        artist_id, music_id, video_id = connection.columns(:artists_musics).sort_by(&:name)
+
+        assert_equal video_id.sql_type, artist_id.sql_type
+        assert_equal video_id.sql_type, music_id.sql_type
+      end
+
       def test_drop_join_table
         connection.create_join_table :artists, :musics
         connection.drop_join_table :artists, :musics
 
-        assert !connection.tables.include?('artists_musics')
+        assert_not connection.table_exists?("artists_musics")
       end
 
       def test_drop_join_table_with_strings
         connection.create_join_table :artists, :musics
-        connection.drop_join_table 'artists', 'musics'
+        connection.drop_join_table "artists", "musics"
 
-        assert !connection.tables.include?('artists_musics')
+        assert_not connection.table_exists?("artists_musics")
       end
 
       def test_drop_join_table_with_the_proper_order
         connection.create_join_table :videos, :musics
         connection.drop_join_table :videos, :musics
 
-        assert !connection.tables.include?('musics_videos')
+        assert_not connection.table_exists?("musics_videos")
       end
 
       def test_drop_join_table_with_the_table_name
         connection.create_join_table :artists, :musics, table_name: :catalog
         connection.drop_join_table :artists, :musics, table_name: :catalog
 
-        assert !connection.tables.include?('catalog')
+        assert_not connection.table_exists?("catalog")
       end
 
       def test_drop_join_table_with_the_table_name_as_string
-        connection.create_join_table :artists, :musics, table_name: 'catalog'
-        connection.drop_join_table :artists, :musics, table_name: 'catalog'
+        connection.create_join_table :artists, :musics, table_name: "catalog"
+        connection.drop_join_table :artists, :musics, table_name: "catalog"
 
-        assert !connection.tables.include?('catalog')
+        assert_not connection.table_exists?("catalog")
       end
 
       def test_drop_join_table_with_column_options
-        connection.create_join_table :artists, :musics, column_options: {null: true}
-        connection.drop_join_table :artists, :musics, column_options: {null: true}
+        connection.create_join_table :artists, :musics, column_options: { null: true }
+        connection.drop_join_table :artists, :musics, column_options: { null: true }
 
-        assert !connection.tables.include?('artists_musics')
+        assert_not connection.table_exists?("artists_musics")
       end
 
       def test_create_and_drop_join_table_with_common_prefix
         with_table_cleanup do
-          connection.create_join_table 'audio_artists', 'audio_musics'
-          assert_includes connection.tables, 'audio_artists_musics'
+          connection.create_join_table "audio_artists", "audio_musics"
+          assert connection.table_exists?("audio_artists_musics")
+
+          connection.drop_join_table "audio_artists", "audio_musics"
+          assert_not connection.table_exists?("audio_artists_musics"), "Should have dropped join table, but didn't"
+        end
+      end
 
-          connection.drop_join_table 'audio_artists', 'audio_musics'
-          assert !connection.tables.include?('audio_artists_musics'), "Should have dropped join table, but didn't"
+      if current_adapter?(:PostgreSQLAdapter)
+        def test_create_join_table_with_uuid
+          connection.create_join_table :artists, :musics, column_options: { type: :uuid }
+          assert_equal [:uuid, :uuid], connection.columns(:artists_musics).map(&:type)
         end
       end
 
       private
 
         def with_table_cleanup
-          tables_before = connection.tables
+          tables_before = connection.data_sources
 
           yield
         ensure
-          tables_after = connection.tables - tables_before
+          tables_after = connection.data_sources - tables_before
 
           tables_after.each do |table|
             connection.drop_table table
diff --git a/activerecord/test/cases/migration/foreign_key_test.rb b/activerecord/test/cases/migration/foreign_key_test.rb
index 72f2fa95f1..bb233fbf74 100644
--- a/activerecord/test/cases/migration/foreign_key_test.rb
+++ b/activerecord/test/cases/migration/foreign_key_test.rb
@@ -1,84 +1,184 @@
-require 'cases/helper'
-require 'support/ddl_helper'
-require 'support/schema_dumping_helper'
+# frozen_string_literal: true
 
-if ActiveRecord::Base.connection.supports_foreign_keys?
-module ActiveRecord
-  class Migration
-    class ForeignKeyTest < ActiveRecord::TestCase
-      include DdlHelper
-      include SchemaDumpingHelper
-      include ActiveSupport::Testing::Stream
-
-      class Rocket < ActiveRecord::Base
-      end
+require "cases/helper"
+require "support/schema_dumping_helper"
+
+if ActiveRecord::Base.connection.supports_foreign_keys_in_create?
+  module ActiveRecord
+    class Migration
+      class ForeignKeyInCreateTest < ActiveRecord::TestCase
+        def test_foreign_keys
+          foreign_keys = ActiveRecord::Base.connection.foreign_keys("fk_test_has_fk")
+          assert_equal 1, foreign_keys.size
 
-      class Astronaut < ActiveRecord::Base
+          fk = foreign_keys.first
+          assert_equal "fk_test_has_fk", fk.from_table
+          assert_equal "fk_test_has_pk", fk.to_table
+          assert_equal "fk_id", fk.column
+          assert_equal "pk_id", fk.primary_key
+          assert_equal "fk_name", fk.name unless current_adapter?(:SQLite3Adapter)
+        end
       end
 
-      setup do
-        @connection = ActiveRecord::Base.connection
-        @connection.create_table "rockets", force: true do |t|
-          t.string :name
+      class ForeignKeyChangeColumnTest < ActiveRecord::TestCase
+        self.use_transactional_tests = false
+
+        class Rocket < ActiveRecord::Base
+          has_many :astronauts
         end
 
-        @connection.create_table "astronauts", force: true do |t|
-          t.string :name
-          t.references :rocket
+        class Astronaut < ActiveRecord::Base
+          belongs_to :rocket
+        end
+
+        setup do
+          @connection = ActiveRecord::Base.connection
+          @connection.create_table "rockets", force: true do |t|
+            t.string :name
+          end
+
+          @connection.create_table "astronauts", force: true do |t|
+            t.string :name
+            t.references :rocket, foreign_key: true
+          end
+          Rocket.reset_column_information
+          Astronaut.reset_column_information
         end
-      end
 
-      teardown do
-        if defined?(@connection)
+        teardown do
           @connection.drop_table "astronauts", if_exists: true
           @connection.drop_table "rockets", if_exists: true
+          Rocket.reset_column_information
+          Astronaut.reset_column_information
         end
-      end
 
-      def test_foreign_keys
-        foreign_keys = @connection.foreign_keys("fk_test_has_fk")
-        assert_equal 1, foreign_keys.size
+        def test_change_column_of_parent_table
+          rocket = Rocket.create!(name: "myrocket")
+          rocket.astronauts << Astronaut.create!
 
-        fk = foreign_keys.first
-        assert_equal "fk_test_has_fk", fk.from_table
-        assert_equal "fk_test_has_pk", fk.to_table
-        assert_equal "fk_id", fk.column
-        assert_equal "pk_id", fk.primary_key
-        assert_equal "fk_name", fk.name
-      end
+          @connection.change_column_null :rockets, :name, false
 
-      def test_add_foreign_key_inferes_column
-        @connection.add_foreign_key :astronauts, :rockets
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
 
-        foreign_keys = @connection.foreign_keys("astronauts")
-        assert_equal 1, foreign_keys.size
+          fk = foreign_keys.first
+          assert_equal "myrocket", Rocket.first.name
+          assert_equal "astronauts", fk.from_table
+          assert_equal "rockets", fk.to_table
+        end
 
-        fk = foreign_keys.first
-        assert_equal "astronauts", fk.from_table
-        assert_equal "rockets", fk.to_table
-        assert_equal "rocket_id", fk.column
-        assert_equal "id", fk.primary_key
-        assert_equal("fk_rails_78146ddd2e", fk.name)
-      end
+        def test_rename_column_of_child_table
+          rocket = Rocket.create!(name: "myrocket")
+          rocket.astronauts << Astronaut.create!
+
+          @connection.rename_column :astronauts, :name, :astronaut_name
 
-      def test_add_foreign_key_with_column
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
+
+          fk = foreign_keys.first
+          assert_equal "myrocket", Rocket.first.name
+          assert_equal "astronauts", fk.from_table
+          assert_equal "rockets", fk.to_table
+        end
 
-        foreign_keys = @connection.foreign_keys("astronauts")
-        assert_equal 1, foreign_keys.size
+        def test_rename_reference_column_of_child_table
+          rocket = Rocket.create!(name: "myrocket")
+          rocket.astronauts << Astronaut.create!
 
-        fk = foreign_keys.first
-        assert_equal "astronauts", fk.from_table
-        assert_equal "rockets", fk.to_table
-        assert_equal "rocket_id", fk.column
-        assert_equal "id", fk.primary_key
-        assert_equal("fk_rails_78146ddd2e", fk.name)
+          @connection.rename_column :astronauts, :rocket_id, :new_rocket_id
+
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
+
+          fk = foreign_keys.first
+          assert_equal "myrocket", Rocket.first.name
+          assert_equal "astronauts", fk.from_table
+          assert_equal "rockets", fk.to_table
+          assert_equal "new_rocket_id", fk.options[:column]
+        end
       end
+    end
+  end
+end
+
+if ActiveRecord::Base.connection.supports_foreign_keys?
+  module ActiveRecord
+    class Migration
+      class ForeignKeyTest < ActiveRecord::TestCase
+        include SchemaDumpingHelper
+        include ActiveSupport::Testing::Stream
+
+        class Rocket < ActiveRecord::Base
+        end
+
+        class Astronaut < ActiveRecord::Base
+        end
+
+        setup do
+          @connection = ActiveRecord::Base.connection
+          @connection.create_table "rockets", force: true do |t|
+            t.string :name
+          end
+
+          @connection.create_table "astronauts", force: true do |t|
+            t.string :name
+            t.references :rocket
+          end
+        end
+
+        teardown do
+          @connection.drop_table "astronauts", if_exists: true
+          @connection.drop_table "rockets", if_exists: true
+        end
+
+        def test_foreign_keys
+          foreign_keys = @connection.foreign_keys("fk_test_has_fk")
+          assert_equal 1, foreign_keys.size
+
+          fk = foreign_keys.first
+          assert_equal "fk_test_has_fk", fk.from_table
+          assert_equal "fk_test_has_pk", fk.to_table
+          assert_equal "fk_id", fk.column
+          assert_equal "pk_id", fk.primary_key
+          assert_equal "fk_name", fk.name
+        end
+
+        def test_add_foreign_key_inferes_column
+          @connection.add_foreign_key :astronauts, :rockets
+
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
+
+          fk = foreign_keys.first
+          assert_equal "astronauts", fk.from_table
+          assert_equal "rockets", fk.to_table
+          assert_equal "rocket_id", fk.column
+          assert_equal "id", fk.primary_key
+          assert_equal("fk_rails_78146ddd2e", fk.name)
+        end
+
+        def test_add_foreign_key_with_column
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
+
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
+
+          fk = foreign_keys.first
+          assert_equal "astronauts", fk.from_table
+          assert_equal "rockets", fk.to_table
+          assert_equal "rocket_id", fk.column
+          assert_equal "id", fk.primary_key
+          assert_equal("fk_rails_78146ddd2e", fk.name)
+        end
+
+        def test_add_foreign_key_with_non_standard_primary_key
+          @connection.create_table :space_shuttles, id: false, force: true do |t|
+            t.bigint :pk, primary_key: true
+          end
 
-      def test_add_foreign_key_with_non_standard_primary_key
-        with_example_table @connection, "space_shuttles", "pk integer PRIMARY KEY" do
           @connection.add_foreign_key(:astronauts, :space_shuttles,
-                                      column: "rocket_id", primary_key: "pk", name: "custom_pk")
+            column: "rocket_id", primary_key: "pk", name: "custom_pk")
 
           foreign_keys = @connection.foreign_keys("astronauts")
           assert_equal 1, foreign_keys.size
@@ -87,218 +187,311 @@ module ActiveRecord
           assert_equal "astronauts", fk.from_table
           assert_equal "space_shuttles", fk.to_table
           assert_equal "pk", fk.primary_key
-
+        ensure
           @connection.remove_foreign_key :astronauts, name: "custom_pk"
+          @connection.drop_table :space_shuttles
         end
-      end
 
-      def test_add_on_delete_restrict_foreign_key
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :restrict
+        def test_add_on_delete_restrict_foreign_key
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :restrict
 
-        foreign_keys = @connection.foreign_keys("astronauts")
-        assert_equal 1, foreign_keys.size
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
 
-        fk = foreign_keys.first
-        if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-          # ON DELETE RESTRICT is the default on MySQL
-          assert_equal nil, fk.on_delete
-        else
-          assert_equal :restrict, fk.on_delete
+          fk = foreign_keys.first
+          if current_adapter?(:Mysql2Adapter)
+            # ON DELETE RESTRICT is the default on MySQL
+            assert_nil fk.on_delete
+          else
+            assert_equal :restrict, fk.on_delete
+          end
         end
-      end
 
-      def test_add_on_delete_cascade_foreign_key
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :cascade
+        def test_add_on_delete_cascade_foreign_key
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :cascade
 
-        foreign_keys = @connection.foreign_keys("astronauts")
-        assert_equal 1, foreign_keys.size
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
 
-        fk = foreign_keys.first
-        assert_equal :cascade, fk.on_delete
-      end
+          fk = foreign_keys.first
+          assert_equal :cascade, fk.on_delete
+        end
 
-      def test_add_on_delete_nullify_foreign_key
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :nullify
+        def test_add_on_delete_nullify_foreign_key
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :nullify
 
-        foreign_keys = @connection.foreign_keys("astronauts")
-        assert_equal 1, foreign_keys.size
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
 
-        fk = foreign_keys.first
-        assert_equal :nullify, fk.on_delete
-      end
+          fk = foreign_keys.first
+          assert_equal :nullify, fk.on_delete
+        end
 
-      def test_on_update_and_on_delete_raises_with_invalid_values
-        assert_raises ArgumentError do
-          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :invalid
+        def test_on_update_and_on_delete_raises_with_invalid_values
+          assert_raises ArgumentError do
+            @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :invalid
+          end
+
+          assert_raises ArgumentError do
+            @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_update: :invalid
+          end
         end
 
-        assert_raises ArgumentError do
-          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_update: :invalid
+        def test_add_foreign_key_with_on_update
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_update: :nullify
+
+          foreign_keys = @connection.foreign_keys("astronauts")
+          assert_equal 1, foreign_keys.size
+
+          fk = foreign_keys.first
+          assert_equal :nullify, fk.on_update
         end
-      end
 
-      def test_add_foreign_key_with_on_update
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_update: :nullify
+        def test_foreign_key_exists
+          @connection.add_foreign_key :astronauts, :rockets
 
-        foreign_keys = @connection.foreign_keys("astronauts")
-        assert_equal 1, foreign_keys.size
+          assert @connection.foreign_key_exists?(:astronauts, :rockets)
+          assert_not @connection.foreign_key_exists?(:astronauts, :stars)
+        end
 
-        fk = foreign_keys.first
-        assert_equal :nullify, fk.on_update
-      end
+        def test_foreign_key_exists_by_column
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
 
-      def test_foreign_key_exists
-        @connection.add_foreign_key :astronauts, :rockets
+          assert @connection.foreign_key_exists?(:astronauts, column: "rocket_id")
+          assert_not @connection.foreign_key_exists?(:astronauts, column: "star_id")
+        end
 
-        assert @connection.foreign_key_exists?(:astronauts, :rockets)
-        assert_not @connection.foreign_key_exists?(:astronauts, :stars)
-      end
+        def test_foreign_key_exists_by_name
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", name: "fancy_named_fk"
 
-      def test_foreign_key_exists_by_column
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
+          assert @connection.foreign_key_exists?(:astronauts, name: "fancy_named_fk")
+          assert_not @connection.foreign_key_exists?(:astronauts, name: "other_fancy_named_fk")
+        end
 
-        assert @connection.foreign_key_exists?(:astronauts, column: "rocket_id")
-        assert_not @connection.foreign_key_exists?(:astronauts, column: "star_id")
-      end
+        def test_remove_foreign_key_inferes_column
+          @connection.add_foreign_key :astronauts, :rockets
+
+          assert_equal 1, @connection.foreign_keys("astronauts").size
+          @connection.remove_foreign_key :astronauts, :rockets
+          assert_equal [], @connection.foreign_keys("astronauts")
+        end
 
-      def test_foreign_key_exists_by_name
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", name: "fancy_named_fk"
+        def test_remove_foreign_key_by_column
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
 
-        assert @connection.foreign_key_exists?(:astronauts, name: "fancy_named_fk")
-        assert_not @connection.foreign_key_exists?(:astronauts, name: "other_fancy_named_fk")
-      end
+          assert_equal 1, @connection.foreign_keys("astronauts").size
+          @connection.remove_foreign_key :astronauts, column: "rocket_id"
+          assert_equal [], @connection.foreign_keys("astronauts")
+        end
 
-      def test_remove_foreign_key_inferes_column
-        @connection.add_foreign_key :astronauts, :rockets
+        def test_remove_foreign_key_by_symbol_column
+          @connection.add_foreign_key :astronauts, :rockets, column: :rocket_id
 
-        assert_equal 1, @connection.foreign_keys("astronauts").size
-        @connection.remove_foreign_key :astronauts, :rockets
-        assert_equal [], @connection.foreign_keys("astronauts")
-      end
+          assert_equal 1, @connection.foreign_keys("astronauts").size
+          @connection.remove_foreign_key :astronauts, column: :rocket_id
+          assert_equal [], @connection.foreign_keys("astronauts")
+        end
 
-      def test_remove_foreign_key_by_column
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id"
+        def test_remove_foreign_key_by_name
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", name: "fancy_named_fk"
 
-        assert_equal 1, @connection.foreign_keys("astronauts").size
-        @connection.remove_foreign_key :astronauts, column: "rocket_id"
-        assert_equal [], @connection.foreign_keys("astronauts")
-      end
+          assert_equal 1, @connection.foreign_keys("astronauts").size
+          @connection.remove_foreign_key :astronauts, name: "fancy_named_fk"
+          assert_equal [], @connection.foreign_keys("astronauts")
+        end
 
-      def test_remove_foreign_key_by_symbol_column
-        @connection.add_foreign_key :astronauts, :rockets, column: :rocket_id
+        def test_remove_foreign_non_existing_foreign_key_raises
+          assert_raises ArgumentError do
+            @connection.remove_foreign_key :astronauts, :rockets
+          end
+        end
 
-        assert_equal 1, @connection.foreign_keys("astronauts").size
-        @connection.remove_foreign_key :astronauts, column: :rocket_id
-        assert_equal [], @connection.foreign_keys("astronauts")
-      end
+        if ActiveRecord::Base.connection.supports_validate_constraints?
+          def test_add_invalid_foreign_key
+            @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", validate: false
 
-      def test_remove_foreign_key_by_name
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", name: "fancy_named_fk"
+            foreign_keys = @connection.foreign_keys("astronauts")
+            assert_equal 1, foreign_keys.size
 
-        assert_equal 1, @connection.foreign_keys("astronauts").size
-        @connection.remove_foreign_key :astronauts, name: "fancy_named_fk"
-        assert_equal [], @connection.foreign_keys("astronauts")
-      end
+            fk = foreign_keys.first
+            assert_not_predicate fk, :validated?
+          end
 
-      def test_remove_foreign_non_existing_foreign_key_raises
-        assert_raises ArgumentError do
-          @connection.remove_foreign_key :astronauts, :rockets
+          def test_validate_foreign_key_infers_column
+            @connection.add_foreign_key :astronauts, :rockets, validate: false
+            assert_not_predicate @connection.foreign_keys("astronauts").first, :validated?
+
+            @connection.validate_foreign_key :astronauts, :rockets
+            assert_predicate @connection.foreign_keys("astronauts").first, :validated?
+          end
+
+          def test_validate_foreign_key_by_column
+            @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", validate: false
+            assert_not_predicate @connection.foreign_keys("astronauts").first, :validated?
+
+            @connection.validate_foreign_key :astronauts, column: "rocket_id"
+            assert_predicate @connection.foreign_keys("astronauts").first, :validated?
+          end
+
+          def test_validate_foreign_key_by_symbol_column
+            @connection.add_foreign_key :astronauts, :rockets, column: :rocket_id, validate: false
+            assert_not_predicate @connection.foreign_keys("astronauts").first, :validated?
+
+            @connection.validate_foreign_key :astronauts, column: :rocket_id
+            assert_predicate @connection.foreign_keys("astronauts").first, :validated?
+          end
+
+          def test_validate_foreign_key_by_name
+            @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", name: "fancy_named_fk", validate: false
+            assert_not_predicate @connection.foreign_keys("astronauts").first, :validated?
+
+            @connection.validate_foreign_key :astronauts, name: "fancy_named_fk"
+            assert_predicate @connection.foreign_keys("astronauts").first, :validated?
+          end
+
+          def test_validate_foreign_non_existing_foreign_key_raises
+            assert_raises ArgumentError do
+              @connection.validate_foreign_key :astronauts, :rockets
+            end
+          end
+
+          def test_validate_constraint_by_name
+            @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", name: "fancy_named_fk", validate: false
+
+            @connection.validate_constraint :astronauts, "fancy_named_fk"
+            assert_predicate @connection.foreign_keys("astronauts").first, :validated?
+          end
+        else
+          # Foreign key should still be created, but should not be invalid
+          def test_add_invalid_foreign_key
+            @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", validate: false
+
+            foreign_keys = @connection.foreign_keys("astronauts")
+            assert_equal 1, foreign_keys.size
+
+            fk = foreign_keys.first
+            assert_predicate fk, :validated?
+          end
         end
-      end
 
-      def test_schema_dumping
-        @connection.add_foreign_key :astronauts, :rockets
-        output = dump_table_schema "astronauts"
-        assert_match %r{\s+add_foreign_key "astronauts", "rockets"$}, output
-      end
+        def test_schema_dumping
+          @connection.add_foreign_key :astronauts, :rockets
+          output = dump_table_schema "astronauts"
+          assert_match %r{\s+add_foreign_key "astronauts", "rockets"$}, output
+        end
 
-      def test_schema_dumping_with_options
-        output = dump_table_schema "fk_test_has_fk"
-        assert_match %r{\s+add_foreign_key "fk_test_has_fk", "fk_test_has_pk", column: "fk_id", primary_key: "pk_id", name: "fk_name"$}, output
-      end
+        def test_schema_dumping_with_options
+          output = dump_table_schema "fk_test_has_fk"
+          assert_match %r{\s+add_foreign_key "fk_test_has_fk", "fk_test_has_pk", column: "fk_id", primary_key: "pk_id", name: "fk_name"$}, output
+        end
 
-      def test_schema_dumping_on_delete_and_on_update_options
-        @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :nullify, on_update: :cascade
+        def test_schema_dumping_with_custom_fk_ignore_pattern
+          original_pattern = ActiveRecord::SchemaDumper.fk_ignore_pattern
+          ActiveRecord::SchemaDumper.fk_ignore_pattern = /^ignored_/
+          @connection.add_foreign_key :astronauts, :rockets, name: :ignored_fk_astronauts_rockets
 
-        output = dump_table_schema "astronauts"
-        assert_match %r{\s+add_foreign_key "astronauts",.+on_update: :cascade,.+on_delete: :nullify$}, output
-      end
+          output = dump_table_schema "astronauts"
+          assert_match %r{\s+add_foreign_key "astronauts", "rockets"$}, output
+
+          ActiveRecord::SchemaDumper.fk_ignore_pattern = original_pattern
+        end
 
-      class CreateCitiesAndHousesMigration < ActiveRecord::Migration
-        def change
-          create_table("cities") { |t| }
+        def test_schema_dumping_on_delete_and_on_update_options
+          @connection.add_foreign_key :astronauts, :rockets, column: "rocket_id", on_delete: :nullify, on_update: :cascade
+
+          output = dump_table_schema "astronauts"
+          assert_match %r{\s+add_foreign_key "astronauts",.+on_update: :cascade,.+on_delete: :nullify$}, output
+        end
 
-          create_table("houses") do |t|
-            t.column :city_id, :integer
+        class CreateCitiesAndHousesMigration < ActiveRecord::Migration::Current
+          def change
+            create_table("cities") { |t| }
+
+            create_table("houses") do |t|
+              t.references :city
+            end
+            add_foreign_key :houses, :cities, column: "city_id"
+
+            # remove and re-add to test that schema is updated and not accidentally cached
+            remove_foreign_key :houses, :cities
+            add_foreign_key :houses, :cities, column: "city_id", on_delete: :cascade
           end
-          add_foreign_key :houses, :cities, column: "city_id"
         end
-      end
 
-      def test_add_foreign_key_is_reversible
-        migration = CreateCitiesAndHousesMigration.new
-        silence_stream($stdout) { migration.migrate(:up) }
-        assert_equal 1, @connection.foreign_keys("houses").size
-      ensure
-        silence_stream($stdout) { migration.migrate(:down) }
-      end
+        def test_add_foreign_key_is_reversible
+          migration = CreateCitiesAndHousesMigration.new
+          silence_stream($stdout) { migration.migrate(:up) }
+          assert_equal 1, @connection.foreign_keys("houses").size
+        ensure
+          silence_stream($stdout) { migration.migrate(:down) }
+        end
 
-      class CreateSchoolsAndClassesMigration < ActiveRecord::Migration
-        def change
-          create_table(:schools)
+        def test_foreign_key_constraint_is_not_cached_incorrectly
+          migration = CreateCitiesAndHousesMigration.new
+          silence_stream($stdout) { migration.migrate(:up) }
+          output = dump_table_schema "houses"
+          assert_match %r{\s+add_foreign_key "houses",.+on_delete: :cascade$}, output
+        ensure
+          silence_stream($stdout) { migration.migrate(:down) }
+        end
 
-          create_table(:classes) do |t|
-            t.column :school_id, :integer
+        class CreateSchoolsAndClassesMigration < ActiveRecord::Migration::Current
+          def change
+            create_table(:schools)
+
+            create_table(:classes) do |t|
+              t.references :school
+            end
+            add_foreign_key :classes, :schools
           end
-          add_foreign_key :classes, :schools
         end
-      end
 
-      def test_add_foreign_key_with_prefix
-        ActiveRecord::Base.table_name_prefix = 'p_'
-        migration = CreateSchoolsAndClassesMigration.new
-        silence_stream($stdout) { migration.migrate(:up) }
-        assert_equal 1, @connection.foreign_keys("p_classes").size
-      ensure
-        silence_stream($stdout) { migration.migrate(:down) }
-        ActiveRecord::Base.table_name_prefix = nil
-      end
+        def test_add_foreign_key_with_prefix
+          ActiveRecord::Base.table_name_prefix = "p_"
+          migration = CreateSchoolsAndClassesMigration.new
+          silence_stream($stdout) { migration.migrate(:up) }
+          assert_equal 1, @connection.foreign_keys("p_classes").size
+        ensure
+          silence_stream($stdout) { migration.migrate(:down) }
+          ActiveRecord::Base.table_name_prefix = nil
+        end
 
-      def test_add_foreign_key_with_suffix
-        ActiveRecord::Base.table_name_suffix = '_s'
-        migration = CreateSchoolsAndClassesMigration.new
-        silence_stream($stdout) { migration.migrate(:up) }
-        assert_equal 1, @connection.foreign_keys("classes_s").size
-      ensure
-        silence_stream($stdout) { migration.migrate(:down) }
-        ActiveRecord::Base.table_name_suffix = nil
+        def test_add_foreign_key_with_suffix
+          ActiveRecord::Base.table_name_suffix = "_s"
+          migration = CreateSchoolsAndClassesMigration.new
+          silence_stream($stdout) { migration.migrate(:up) }
+          assert_equal 1, @connection.foreign_keys("classes_s").size
+        ensure
+          silence_stream($stdout) { migration.migrate(:down) }
+          ActiveRecord::Base.table_name_suffix = nil
+        end
       end
-
     end
   end
-end
 else
-module ActiveRecord
-  class Migration
-    class NoForeignKeySupportTest < ActiveRecord::TestCase
-      setup do
-        @connection = ActiveRecord::Base.connection
-      end
+  module ActiveRecord
+    class Migration
+      class NoForeignKeySupportTest < ActiveRecord::TestCase
+        setup do
+          @connection = ActiveRecord::Base.connection
+        end
 
-      def test_add_foreign_key_should_be_noop
-        @connection.add_foreign_key :clubs, :categories
-      end
+        def test_add_foreign_key_should_be_noop
+          @connection.add_foreign_key :clubs, :categories
+        end
 
-      def test_remove_foreign_key_should_be_noop
-        @connection.remove_foreign_key :clubs, :categories
-      end
+        def test_remove_foreign_key_should_be_noop
+          @connection.remove_foreign_key :clubs, :categories
+        end
 
-      def test_foreign_keys_should_raise_not_implemented
-        assert_raises NotImplementedError do
-          @connection.foreign_keys("clubs")
+        unless current_adapter?(:SQLite3Adapter)
+          def test_foreign_keys_should_raise_not_implemented
+            assert_raises NotImplementedError do
+              @connection.foreign_keys("clubs")
+            end
+          end
         end
       end
     end
   end
 end
-end
diff --git a/activerecord/test/cases/migration/helper.rb b/activerecord/test/cases/migration/helper.rb
index 5bc0898f33..c056199140 100644
--- a/activerecord/test/cases/migration/helper.rb
+++ b/activerecord/test/cases/migration/helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -28,12 +30,12 @@ module ActiveRecord
         super
         TestModel.reset_table_name
         TestModel.reset_sequence_name
-        connection.drop_table :test_models rescue nil
+        connection.drop_table :test_models, if_exists: true
       end
 
       private
 
-      delegate(*CONNECTION_METHODS, to: :connection)
+        delegate(*CONNECTION_METHODS, to: :connection)
     end
   end
 end
diff --git a/activerecord/test/cases/migration/index_test.rb b/activerecord/test/cases/migration/index_test.rb
index b23b9a679f..f8fecc83cd 100644
--- a/activerecord/test/cases/migration/index_test.rb
+++ b/activerecord/test/cases/migration/index_test.rb
@@ -1,4 +1,6 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class Migration
@@ -11,12 +13,12 @@ module ActiveRecord
         @table_name = :testings
 
         connection.create_table table_name do |t|
-          t.column :foo, :string, :limit => 100
-          t.column :bar, :string, :limit => 100
+          t.column :foo, :string, limit: 100
+          t.column :bar, :string, limit: 100
 
           t.string :first_name
-          t.string :last_name, :limit => 100
-          t.string :key,       :limit => 100
+          t.string :last_name, limit: 100
+          t.string :key,       limit: 100
           t.boolean :administrator
         end
       end
@@ -28,32 +30,29 @@ module ActiveRecord
 
       def test_rename_index
         # keep the names short to make Oracle and similar behave
-        connection.add_index(table_name, [:foo], :name => 'old_idx')
-        connection.rename_index(table_name, 'old_idx', 'new_idx')
+        connection.add_index(table_name, [:foo], name: "old_idx")
+        connection.rename_index(table_name, "old_idx", "new_idx")
 
-        # if the adapter doesn't support the indexes call, pick defaults that let the test pass
-        assert_not connection.index_name_exists?(table_name, 'old_idx', false)
-        assert connection.index_name_exists?(table_name, 'new_idx', true)
+        assert_not connection.index_name_exists?(table_name, "old_idx")
+        assert connection.index_name_exists?(table_name, "new_idx")
       end
 
       def test_rename_index_too_long
-        too_long_index_name = good_index_name + 'x'
+        too_long_index_name = good_index_name + "x"
         # keep the names short to make Oracle and similar behave
-        connection.add_index(table_name, [:foo], :name => 'old_idx')
+        connection.add_index(table_name, [:foo], name: "old_idx")
         e = assert_raises(ArgumentError) {
-          connection.rename_index(table_name, 'old_idx', too_long_index_name)
+          connection.rename_index(table_name, "old_idx", too_long_index_name)
         }
         assert_match(/too long; the limit is #{connection.allowed_index_name_length} characters/, e.message)
 
-        # if the adapter doesn't support the indexes call, pick defaults that let the test pass
-        assert connection.index_name_exists?(table_name, 'old_idx', false)
+        assert connection.index_name_exists?(table_name, "old_idx")
       end
 
-
       def test_double_add_index
-        connection.add_index(table_name, [:foo], :name => 'some_idx')
+        connection.add_index(table_name, [:foo], name: "some_idx")
         assert_raises(ArgumentError) {
-          connection.add_index(table_name, [:foo], :name => 'some_idx')
+          connection.add_index(table_name, [:foo], name: "some_idx")
         }
       end
 
@@ -64,43 +63,43 @@ module ActiveRecord
       def test_add_index_works_with_long_index_names
         connection.add_index(table_name, "foo", name: good_index_name)
 
-        assert connection.index_name_exists?(table_name, good_index_name, false)
+        assert connection.index_name_exists?(table_name, good_index_name)
         connection.remove_index(table_name, name: good_index_name)
       end
 
       def test_add_index_does_not_accept_too_long_index_names
-        too_long_index_name = good_index_name + 'x'
+        too_long_index_name = good_index_name + "x"
 
         e = assert_raises(ArgumentError) {
           connection.add_index(table_name, "foo", name: too_long_index_name)
         }
         assert_match(/too long; the limit is #{connection.allowed_index_name_length} characters/, e.message)
 
-        assert_not connection.index_name_exists?(table_name, too_long_index_name, false)
-        connection.add_index(table_name, "foo", :name => good_index_name)
+        assert_not connection.index_name_exists?(table_name, too_long_index_name)
+        connection.add_index(table_name, "foo", name: good_index_name)
       end
 
       def test_internal_index_with_name_matching_database_limit
-        good_index_name = 'x' * connection.index_name_length
+        good_index_name = "x" * connection.index_name_length
         connection.add_index(table_name, "foo", name: good_index_name, internal: true)
 
-        assert connection.index_name_exists?(table_name, good_index_name, false)
+        assert connection.index_name_exists?(table_name, good_index_name)
         connection.remove_index(table_name, name: good_index_name)
       end
 
       def test_index_symbol_names
-        connection.add_index table_name, :foo, :name => :symbol_index_name
-        assert connection.index_exists?(table_name, :foo, :name => :symbol_index_name)
+        connection.add_index table_name, :foo, name: :symbol_index_name
+        assert connection.index_exists?(table_name, :foo, name: :symbol_index_name)
 
-        connection.remove_index table_name, :name => :symbol_index_name
-        assert_not connection.index_exists?(table_name, :foo, :name => :symbol_index_name)
+        connection.remove_index table_name, name: :symbol_index_name
+        assert_not connection.index_exists?(table_name, :foo, name: :symbol_index_name)
       end
 
       def test_index_exists
         connection.add_index :testings, :foo
 
         assert connection.index_exists?(:testings, :foo)
-        assert !connection.index_exists?(:testings, :bar)
+        assert_not connection.index_exists?(:testings, :bar)
       end
 
       def test_index_exists_on_multiple_columns
@@ -122,19 +121,32 @@ module ActiveRecord
       end
 
       def test_unique_index_exists
-        connection.add_index :testings, :foo, :unique => true
+        connection.add_index :testings, :foo, unique: true
 
-        assert connection.index_exists?(:testings, :foo, :unique => true)
+        assert connection.index_exists?(:testings, :foo, unique: true)
       end
 
       def test_named_index_exists
-        connection.add_index :testings, :foo, :name => "custom_index_name"
+        connection.add_index :testings, :foo, name: "custom_index_name"
 
-        assert connection.index_exists?(:testings, :foo, :name => "custom_index_name")
+        assert connection.index_exists?(:testings, :foo)
+        assert connection.index_exists?(:testings, :foo, name: "custom_index_name")
+        assert_not connection.index_exists?(:testings, :foo, name: "other_index_name")
+      end
+
+      def test_remove_named_index
+        connection.add_index :testings, :foo, name: "index_testings_on_custom_index_name"
+
+        assert connection.index_exists?(:testings, :foo)
+
+        assert_raise(ArgumentError) { connection.remove_index(:testings, "custom_index_name") }
+
+        connection.remove_index :testings, :foo
+        assert_not connection.index_exists?(:testings, :foo)
       end
 
       def test_add_index_attribute_length_limit
-        connection.add_index :testings, [:foo, :bar], :length => {:foo => 10, :bar => nil}
+        connection.add_index :testings, [:foo, :bar], length: { foo: 10, bar: nil }
 
         assert connection.index_exists?(:testings, [:foo, :bar])
       end
@@ -144,65 +156,64 @@ module ActiveRecord
         connection.remove_index("testings", "last_name")
 
         connection.add_index("testings", ["last_name", "first_name"])
-        connection.remove_index("testings", :column => ["last_name", "first_name"])
+        connection.remove_index("testings", column: ["last_name", "first_name"])
 
         # Oracle adapter cannot have specified index name larger than 30 characters
         # Oracle adapter is shortening index name when just column list is given
         unless current_adapter?(:OracleAdapter)
           connection.add_index("testings", ["last_name", "first_name"])
-          connection.remove_index("testings", :name => :index_testings_on_last_name_and_first_name)
+          connection.remove_index("testings", name: :index_testings_on_last_name_and_first_name)
           connection.add_index("testings", ["last_name", "first_name"])
           connection.remove_index("testings", "last_name_and_first_name")
         end
         connection.add_index("testings", ["last_name", "first_name"])
         connection.remove_index("testings", ["last_name", "first_name"])
 
-        connection.add_index("testings", ["last_name"], :length => 10)
+        connection.add_index("testings", ["last_name"], length: 10)
         connection.remove_index("testings", "last_name")
 
-        connection.add_index("testings", ["last_name"], :length => {:last_name => 10})
+        connection.add_index("testings", ["last_name"], length: { last_name: 10 })
         connection.remove_index("testings", ["last_name"])
 
-        connection.add_index("testings", ["last_name", "first_name"], :length => 10)
+        connection.add_index("testings", ["last_name", "first_name"], length: 10)
         connection.remove_index("testings", ["last_name", "first_name"])
 
-        connection.add_index("testings", ["last_name", "first_name"], :length => {:last_name => 10, :first_name => 20})
+        connection.add_index("testings", ["last_name", "first_name"], length: { last_name: 10, first_name: 20 })
         connection.remove_index("testings", ["last_name", "first_name"])
 
-        connection.add_index("testings", ["key"], :name => "key_idx", :unique => true)
-        connection.remove_index("testings", :name => "key_idx", :unique => true)
+        connection.add_index("testings", ["key"], name: "key_idx", unique: true)
+        connection.remove_index("testings", name: "key_idx", unique: true)
 
-        connection.add_index("testings", %w(last_name first_name administrator), :name => "named_admin")
-        connection.remove_index("testings", :name => "named_admin")
+        connection.add_index("testings", %w(last_name first_name administrator), name: "named_admin")
+        connection.remove_index("testings", name: "named_admin")
 
         # Selected adapters support index sort order
-        if current_adapter?(:SQLite3Adapter, :MysqlAdapter, :Mysql2Adapter, :PostgreSQLAdapter)
-          connection.add_index("testings", ["last_name"], :order => {:last_name => :desc})
+        if current_adapter?(:SQLite3Adapter, :Mysql2Adapter, :PostgreSQLAdapter)
+          connection.add_index("testings", ["last_name"], order: { last_name: :desc })
           connection.remove_index("testings", ["last_name"])
-          connection.add_index("testings", ["last_name", "first_name"], :order => {:last_name => :desc})
+          connection.add_index("testings", ["last_name", "first_name"], order: { last_name: :desc })
           connection.remove_index("testings", ["last_name", "first_name"])
-          connection.add_index("testings", ["last_name", "first_name"], :order => {:last_name => :desc, :first_name => :asc})
+          connection.add_index("testings", ["last_name", "first_name"], order: { last_name: :desc, first_name: :asc })
           connection.remove_index("testings", ["last_name", "first_name"])
-          connection.add_index("testings", ["last_name", "first_name"], :order => :desc)
+          connection.add_index("testings", ["last_name", "first_name"], order: :desc)
           connection.remove_index("testings", ["last_name", "first_name"])
         end
       end
 
       if current_adapter?(:PostgreSQLAdapter)
         def test_add_partial_index
-          connection.add_index("testings", "last_name", :where => "first_name = 'john doe'")
+          connection.add_index("testings", "last_name", where: "first_name = 'john doe'")
           assert connection.index_exists?("testings", "last_name")
 
           connection.remove_index("testings", "last_name")
-          assert !connection.index_exists?("testings", "last_name")
+          assert_not connection.index_exists?("testings", "last_name")
         end
       end
 
       private
         def good_index_name
-          'x' * connection.allowed_index_name_length
+          "x" * connection.allowed_index_name_length
         end
-
     end
   end
 end
diff --git a/activerecord/test/cases/migration/logger_test.rb b/activerecord/test/cases/migration/logger_test.rb
index bf6e684887..28f4cc124b 100644
--- a/activerecord/test/cases/migration/logger_test.rb
+++ b/activerecord/test/cases/migration/logger_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -8,7 +10,7 @@ module ActiveRecord
 
       Migration = Struct.new(:name, :version) do
         def disable_ddl_transaction; false end
-        def migrate direction
+        def migrate(direction)
           # do nothing
         end
       end
@@ -26,7 +28,7 @@ module ActiveRecord
       def test_migration_should_be_run_without_logger
         previous_logger = ActiveRecord::Base.logger
         ActiveRecord::Base.logger = nil
-        migrations = [Migration.new('a', 1), Migration.new('b', 2), Migration.new('c', 3)]
+        migrations = [Migration.new("a", 1), Migration.new("b", 2), Migration.new("c", 3)]
         ActiveRecord::Migrator.new(:up, migrations).migrate
       ensure
         ActiveRecord::Base.logger = previous_logger
diff --git a/activerecord/test/cases/migration/pending_migrations_test.rb b/activerecord/test/cases/migration/pending_migrations_test.rb
index 7afac83bd2..119bfd372a 100644
--- a/activerecord/test/cases/migration/pending_migrations_test.rb
+++ b/activerecord/test/cases/migration/pending_migrations_test.rb
@@ -1,51 +1,40 @@
-require 'cases/helper'
-require "minitest/mock"
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class Migration
-    class PendingMigrationsTest < ActiveRecord::TestCase
-      def setup
-        super
-        @connection = Minitest::Mock.new
-        @app = Minitest::Mock.new
-        conn = @connection
-        @pending = Class.new(CheckPending) {
-          define_method(:connection) { conn }
-        }.new(@app)
-        @pending.instance_variable_set :@last_check, -1 # Force checking
-      end
-
-      def teardown
-        assert @connection.verify
-        assert @app.verify
-        super
-      end
-
-      def test_errors_if_pending
-        @connection.expect :supports_migrations?, true
+    if current_adapter?(:SQLite3Adapter) && !in_memory_db?
+      class PendingMigrationsTest < ActiveRecord::TestCase
+        setup do
+          file = ActiveRecord::Base.connection.raw_connection.filename
+          @conn = ActiveRecord::Base.establish_connection adapter: "sqlite3", database: ":memory:", migrations_paths: MIGRATIONS_ROOT + "/valid"
+          source_db = SQLite3::Database.new file
+          dest_db = ActiveRecord::Base.connection.raw_connection
+          backup = SQLite3::Backup.new(dest_db, "main", source_db, "main")
+          backup.step(-1)
+          backup.finish
+        end
 
-        ActiveRecord::Migrator.stub :needs_migration?, true do
-          assert_raise ActiveRecord::PendingMigrationError do
-            @pending.call(nil)
-          end
+        teardown do
+          @conn.release_connection if @conn
+          ActiveRecord::Base.establish_connection :arunit
         end
-      end
 
-      def test_checks_if_supported
-        @connection.expect :supports_migrations?, true
-        @app.expect :call, nil, [:foo]
+        def test_errors_if_pending
+          ActiveRecord::Base.connection.drop_table "schema_migrations", if_exists: true
 
-        ActiveRecord::Migrator.stub :needs_migration?, false do
-          @pending.call(:foo)
+          assert_raises ActiveRecord::PendingMigrationError do
+            CheckPending.new(Proc.new { }).call({})
+          end
         end
-      end
 
-      def test_doesnt_check_if_unsupported
-        @connection.expect :supports_migrations?, false
-        @app.expect :call, nil, [:foo]
+        def test_checks_if_supported
+          ActiveRecord::SchemaMigration.create_table
+          migrator = Base.connection.migration_context
+          capture(:stdout) { migrator.migrate }
 
-        ActiveRecord::Migrator.stub :needs_migration?, true do
-          @pending.call(:foo)
+          assert_nil CheckPending.new(Proc.new { }).call({})
         end
       end
     end
diff --git a/activerecord/test/cases/migration/references_foreign_key_test.rb b/activerecord/test/cases/migration/references_foreign_key_test.rb
index 1594f99852..7a092103c7 100644
--- a/activerecord/test/cases/migration/references_foreign_key_test.rb
+++ b/activerecord/test/cases/migration/references_foreign_key_test.rb
@@ -1,153 +1,257 @@
-require 'cases/helper'
+# frozen_string_literal: true
 
-if ActiveRecord::Base.connection.supports_foreign_keys?
-module ActiveRecord
-  class Migration
-    class ReferencesForeignKeyTest < ActiveRecord::TestCase
-      setup do
-        @connection = ActiveRecord::Base.connection
-        @connection.create_table(:testing_parents, force: true)
-      end
+require "cases/helper"
 
-      teardown do
-        @connection.drop_table "testings", if_exists: true
-        @connection.drop_table "testing_parents", if_exists: true
-      end
+if ActiveRecord::Base.connection.supports_foreign_keys_in_create?
+  module ActiveRecord
+    class Migration
+      class ReferencesForeignKeyInCreateTest < ActiveRecord::TestCase
+        setup do
+          @connection = ActiveRecord::Base.connection
+          @connection.create_table(:testing_parents, force: true)
+        end
 
-      test "foreign keys can be created with the table" do
-        @connection.create_table :testings do |t|
-          t.references :testing_parent, foreign_key: true
+        teardown do
+          @connection.drop_table "testings", if_exists: true
+          @connection.drop_table "testing_parents", if_exists: true
         end
 
-        fk = @connection.foreign_keys("testings").first
-        assert_equal "testings", fk.from_table
-        assert_equal "testing_parents", fk.to_table
-      end
+        test "foreign keys can be created with the table" do
+          @connection.create_table :testings do |t|
+            t.references :testing_parent, foreign_key: true
+          end
 
-      test "no foreign key is created by default" do
-        @connection.create_table :testings do |t|
-          t.references :testing_parent
+          fk = @connection.foreign_keys("testings").first
+          assert_equal "testings", fk.from_table
+          assert_equal "testing_parents", fk.to_table
         end
 
-        assert_equal [], @connection.foreign_keys("testings")
-      end
+        test "no foreign key is created by default" do
+          @connection.create_table :testings do |t|
+            t.references :testing_parent
+          end
 
-      test "options hash can be passed" do
-        @connection.change_table :testing_parents do |t|
-          t.integer :other_id
-          t.index :other_id, unique: true
+          assert_equal [], @connection.foreign_keys("testings")
         end
-        @connection.create_table :testings do |t|
-          t.references :testing_parent, foreign_key: { primary_key: :other_id }
+
+        test "foreign keys can be created in one query when index is not added" do
+          assert_queries(1) do
+            @connection.create_table :testings do |t|
+              t.references :testing_parent, foreign_key: true, index: false
+            end
+          end
         end
 
-        fk = @connection.foreign_keys("testings").find { |k| k.to_table == "testing_parents" }
-        assert_equal "other_id", fk.primary_key
-      end
+        test "options hash can be passed" do
+          @connection.change_table :testing_parents do |t|
+            t.references :other, index: { unique: true }
+          end
+          @connection.create_table :testings do |t|
+            t.references :testing_parent, foreign_key: { primary_key: :other_id }
+          end
 
-      test "foreign keys cannot be added to polymorphic relations when creating the table" do
-        @connection.create_table :testings do |t|
-          assert_raises(ArgumentError) do
-            t.references :testing_parent, polymorphic: true, foreign_key: true
+          fk = @connection.foreign_keys("testings").find { |k| k.to_table == "testing_parents" }
+          assert_equal "other_id", fk.primary_key
+        end
+
+        test "to_table option can be passed" do
+          @connection.create_table :testings do |t|
+            t.references :parent, foreign_key: { to_table: :testing_parents }
           end
+          fks = @connection.foreign_keys("testings")
+          assert_equal([["testings", "testing_parents", "parent_id"]],
+                       fks.map { |fk| [fk.from_table, fk.to_table, fk.column] })
         end
       end
+    end
+  end
+end
 
-      test "foreign keys can be created while changing the table" do
-        @connection.create_table :testings
-        @connection.change_table :testings do |t|
-          t.references :testing_parent, foreign_key: true
+if ActiveRecord::Base.connection.supports_foreign_keys?
+  module ActiveRecord
+    class Migration
+      class ReferencesForeignKeyTest < ActiveRecord::TestCase
+        setup do
+          @connection = ActiveRecord::Base.connection
+          @connection.create_table(:testing_parents, force: true)
         end
 
-        fk = @connection.foreign_keys("testings").first
-        assert_equal "testings", fk.from_table
-        assert_equal "testing_parents", fk.to_table
-      end
+        teardown do
+          @connection.drop_table "testings", if_exists: true
+          @connection.drop_table "testing_parents", if_exists: true
+        end
 
-      test "foreign keys are not added by default when changing the table" do
-        @connection.create_table :testings
-        @connection.change_table :testings do |t|
-          t.references :testing_parent
+        test "foreign keys cannot be added to polymorphic relations when creating the table" do
+          @connection.create_table :testings do |t|
+            assert_raises(ArgumentError) do
+              t.references :testing_parent, polymorphic: true, foreign_key: true
+            end
+          end
         end
 
-        assert_equal [], @connection.foreign_keys("testings")
-      end
+        test "foreign keys can be created while changing the table" do
+          @connection.create_table :testings
+          @connection.change_table :testings do |t|
+            t.references :testing_parent, foreign_key: true
+          end
 
-      test "foreign keys accept options when changing the table" do
-        @connection.change_table :testing_parents do |t|
-          t.integer :other_id
-          t.index :other_id, unique: true
+          fk = @connection.foreign_keys("testings").first
+          assert_equal "testings", fk.from_table
+          assert_equal "testing_parents", fk.to_table
         end
-        @connection.create_table :testings
-        @connection.change_table :testings do |t|
-          t.references :testing_parent, foreign_key: { primary_key: :other_id }
+
+        test "foreign keys are not added by default when changing the table" do
+          @connection.create_table :testings
+          @connection.change_table :testings do |t|
+            t.references :testing_parent
+          end
+
+          assert_equal [], @connection.foreign_keys("testings")
         end
 
-        fk = @connection.foreign_keys("testings").find { |k| k.to_table == "testing_parents" }
-        assert_equal "other_id", fk.primary_key
-      end
+        test "foreign keys accept options when changing the table" do
+          @connection.change_table :testing_parents do |t|
+            t.references :other, index: { unique: true }
+          end
+          @connection.create_table :testings
+          @connection.change_table :testings do |t|
+            t.references :testing_parent, foreign_key: { primary_key: :other_id }
+          end
 
-      test "foreign keys cannot be added to polymorphic relations when changing the table" do
-        @connection.create_table :testings
-        @connection.change_table :testings do |t|
-          assert_raises(ArgumentError) do
-            t.references :testing_parent, polymorphic: true, foreign_key: true
+          fk = @connection.foreign_keys("testings").find { |k| k.to_table == "testing_parents" }
+          assert_equal "other_id", fk.primary_key
+        end
+
+        test "foreign keys cannot be added to polymorphic relations when changing the table" do
+          @connection.create_table :testings
+          @connection.change_table :testings do |t|
+            assert_raises(ArgumentError) do
+              t.references :testing_parent, polymorphic: true, foreign_key: true
+            end
           end
         end
-      end
 
-      test "foreign key column can be removed" do
-        @connection.create_table :testings do |t|
-          t.references :testing_parent, index: true, foreign_key: true
+        test "foreign key column can be removed" do
+          @connection.create_table :testings do |t|
+            t.references :testing_parent, index: true, foreign_key: true
+          end
+
+          assert_difference "@connection.foreign_keys('testings').size", -1 do
+            @connection.remove_reference :testings, :testing_parent, foreign_key: true
+          end
         end
 
-        assert_difference "@connection.foreign_keys('testings').size", -1 do
-          @connection.remove_reference :testings, :testing_parent, foreign_key: true
+        test "removing column removes foreign key" do
+          @connection.create_table :testings do |t|
+            t.references :testing_parent, index: true, foreign_key: true
+          end
+
+          assert_difference "@connection.foreign_keys('testings').size", -1 do
+            @connection.remove_column :testings, :testing_parent_id
+          end
         end
-      end
 
-      test "foreign key methods respect pluralize_table_names" do
-        begin
-          original_pluralize_table_names = ActiveRecord::Base.pluralize_table_names
-          ActiveRecord::Base.pluralize_table_names = false
-          @connection.create_table :testing
-          @connection.change_table :testing_parents do |t|
-            t.references :testing, foreign_key: true
+        test "foreign key methods respect pluralize_table_names" do
+          begin
+            original_pluralize_table_names = ActiveRecord::Base.pluralize_table_names
+            ActiveRecord::Base.pluralize_table_names = false
+            @connection.create_table :testing
+            @connection.change_table :testing_parents do |t|
+              t.references :testing, foreign_key: true
+            end
+
+            fk = @connection.foreign_keys("testing_parents").first
+            assert_equal "testing_parents", fk.from_table
+            assert_equal "testing", fk.to_table
+
+            assert_difference "@connection.foreign_keys('testing_parents').size", -1 do
+              @connection.remove_reference :testing_parents, :testing, foreign_key: true
+            end
+          ensure
+            ActiveRecord::Base.pluralize_table_names = original_pluralize_table_names
+            @connection.drop_table "testing", if_exists: true
           end
+        end
 
-          fk = @connection.foreign_keys("testing_parents").first
-          assert_equal "testing_parents", fk.from_table
-          assert_equal "testing", fk.to_table
+        class CreateDogsMigration < ActiveRecord::Migration::Current
+          def change
+            create_table :dog_owners
 
-          assert_difference "@connection.foreign_keys('testing_parents').size", -1 do
-            @connection.remove_reference :testing_parents, :testing, foreign_key: true
+            create_table :dogs do |t|
+              t.references :dog_owner, foreign_key: true
+            end
           end
+        end
+
+        def test_references_foreign_key_with_prefix
+          ActiveRecord::Base.table_name_prefix = "p_"
+          migration = CreateDogsMigration.new
+          silence_stream($stdout) { migration.migrate(:up) }
+          assert_equal 1, @connection.foreign_keys("p_dogs").size
         ensure
-          ActiveRecord::Base.pluralize_table_names = original_pluralize_table_names
-          @connection.drop_table "testing", if_exists: true
+          silence_stream($stdout) { migration.migrate(:down) }
+          ActiveRecord::Base.table_name_prefix = nil
+        end
+
+        def test_references_foreign_key_with_suffix
+          ActiveRecord::Base.table_name_suffix = "_s"
+          migration = CreateDogsMigration.new
+          silence_stream($stdout) { migration.migrate(:up) }
+          assert_equal 1, @connection.foreign_keys("dogs_s").size
+        ensure
+          silence_stream($stdout) { migration.migrate(:down) }
+          ActiveRecord::Base.table_name_suffix = nil
+        end
+
+        test "multiple foreign keys can be added to the same table" do
+          @connection.create_table :testings do |t|
+            t.references :parent1, foreign_key: { to_table: :testing_parents }
+            t.references :parent2, foreign_key: { to_table: :testing_parents }
+          end
+
+          fks = @connection.foreign_keys("testings").sort_by(&:column)
+
+          fk_definitions = fks.map { |fk| [fk.from_table, fk.to_table, fk.column] }
+          assert_equal([["testings", "testing_parents", "parent1_id"],
+                        ["testings", "testing_parents", "parent2_id"]], fk_definitions)
+        end
+
+        test "multiple foreign keys can be removed to the selected one" do
+          @connection.create_table :testings do |t|
+            t.references :parent1, foreign_key: { to_table: :testing_parents }
+            t.references :parent2, foreign_key: { to_table: :testing_parents }
+          end
+
+          assert_difference "@connection.foreign_keys('testings').size", -1 do
+            @connection.remove_reference :testings, :parent1, foreign_key: { to_table: :testing_parents }
+          end
+
+          fks = @connection.foreign_keys("testings").sort_by(&:column)
+
+          fk_definitions = fks.map { |fk| [fk.from_table, fk.to_table, fk.column] }
+          assert_equal([["testings", "testing_parents", "parent2_id"]], fk_definitions)
         end
       end
     end
   end
-end
 else
-class ReferencesWithoutForeignKeySupportTest < ActiveRecord::TestCase
-  setup do
-    @connection = ActiveRecord::Base.connection
-    @connection.create_table(:testing_parents, force: true)
-  end
-
-  teardown do
-    @connection.drop_table("testings", if_exists: true)
-    @connection.drop_table("testing_parents", if_exists: true)
-  end
+  class ReferencesWithoutForeignKeySupportTest < ActiveRecord::TestCase
+    setup do
+      @connection = ActiveRecord::Base.connection
+      @connection.create_table(:testing_parents, force: true)
+    end
 
-  test "ignores foreign keys defined with the table" do
-    @connection.create_table :testings do |t|
-      t.references :testing_parent, foreign_key: true
+    teardown do
+      @connection.drop_table("testings", if_exists: true)
+      @connection.drop_table("testing_parents", if_exists: true)
     end
 
-    assert_includes @connection.tables, "testings"
+    test "ignores foreign keys defined with the table" do
+      @connection.create_table :testings do |t|
+        t.references :testing_parent, foreign_key: true
+      end
+
+      assert_includes @connection.data_sources, "testings"
+    end
   end
 end
-end
diff --git a/activerecord/test/cases/migration/references_index_test.rb b/activerecord/test/cases/migration/references_index_test.rb
index ad6b828d0b..e41377d817 100644
--- a/activerecord/test/cases/migration/references_index_test.rb
+++ b/activerecord/test/cases/migration/references_index_test.rb
@@ -1,4 +1,6 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class Migration
@@ -17,42 +19,42 @@ module ActiveRecord
 
       def test_creates_index
         connection.create_table table_name do |t|
-          t.references :foo, :index => true
+          t.references :foo, index: true
         end
 
-        assert connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_foo_id)
+        assert connection.index_exists?(table_name, :foo_id, name: :index_testings_on_foo_id)
       end
 
-      def test_does_not_create_index
+      def test_creates_index_by_default_even_if_index_option_is_not_passed
         connection.create_table table_name do |t|
           t.references :foo
         end
 
-        assert_not connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_foo_id)
+        assert connection.index_exists?(table_name, :foo_id, name: :index_testings_on_foo_id)
       end
 
       def test_does_not_create_index_explicit
         connection.create_table table_name do |t|
-          t.references :foo, :index => false
+          t.references :foo, index: false
         end
 
-        assert_not connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_foo_id)
+        assert_not connection.index_exists?(table_name, :foo_id, name: :index_testings_on_foo_id)
       end
 
       def test_creates_index_with_options
         connection.create_table table_name do |t|
-          t.references :foo, :index => {:name => :index_testings_on_yo_momma}
-          t.references :bar, :index => {:unique => true}
+          t.references :foo, index: { name: :index_testings_on_yo_momma }
+          t.references :bar, index: { unique: true }
         end
 
-        assert connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_yo_momma)
-        assert connection.index_exists?(table_name, :bar_id, :name => :index_testings_on_bar_id, :unique => true)
+        assert connection.index_exists?(table_name, :foo_id, name: :index_testings_on_yo_momma)
+        assert connection.index_exists?(table_name, :bar_id, name: :index_testings_on_bar_id, unique: true)
       end
 
       unless current_adapter? :OracleAdapter
         def test_creates_polymorphic_index
           connection.create_table table_name do |t|
-            t.references :foo, :polymorphic => true, :index => true
+            t.references :foo, polymorphic: true, index: true
           end
 
           assert connection.index_exists?(table_name, [:foo_type, :foo_id], name: :index_testings_on_foo_type_and_foo_id)
@@ -62,35 +64,35 @@ module ActiveRecord
       def test_creates_index_for_existing_table
         connection.create_table table_name
         connection.change_table table_name do |t|
-          t.references :foo, :index => true
+          t.references :foo, index: true
         end
 
-        assert connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_foo_id)
+        assert connection.index_exists?(table_name, :foo_id, name: :index_testings_on_foo_id)
       end
 
-      def test_does_not_create_index_for_existing_table
+      def test_creates_index_for_existing_table_even_if_index_option_is_not_passed
         connection.create_table table_name
         connection.change_table table_name do |t|
           t.references :foo
         end
 
-        assert_not connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_foo_id)
+        assert connection.index_exists?(table_name, :foo_id, name: :index_testings_on_foo_id)
       end
 
       def test_does_not_create_index_for_existing_table_explicit
         connection.create_table table_name
         connection.change_table table_name do |t|
-          t.references :foo, :index => false
+          t.references :foo, index: false
         end
 
-        assert_not connection.index_exists?(table_name, :foo_id, :name => :index_testings_on_foo_id)
+        assert_not connection.index_exists?(table_name, :foo_id, name: :index_testings_on_foo_id)
       end
 
       unless current_adapter? :OracleAdapter
         def test_creates_polymorphic_index_for_existing_table
           connection.create_table table_name
           connection.change_table table_name do |t|
-            t.references :foo, :polymorphic => true, :index => true
+            t.references :foo, polymorphic: true, index: true
           end
 
           assert connection.index_exists?(table_name, [:foo_type, :foo_id], name: :index_testings_on_foo_type_and_foo_id)
diff --git a/activerecord/test/cases/migration/references_statements_test.rb b/activerecord/test/cases/migration/references_statements_test.rb
index f613fd66c3..769241ba12 100644
--- a/activerecord/test/cases/migration/references_statements_test.rb
+++ b/activerecord/test/cases/migration/references_statements_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/migration/helper"
 
 module ActiveRecord
@@ -30,14 +32,14 @@ module ActiveRecord
         assert column_exists?(table_name, :taggable_type, :string)
       end
 
-      def test_creates_reference_id_index
-        add_reference table_name, :user, index: true
-        assert index_exists?(table_name, :user_id)
+      def test_does_not_create_reference_id_index_if_index_is_false
+        add_reference table_name, :user, index: false
+        assert_not index_exists?(table_name, :user_id)
       end
 
-      def test_does_not_create_reference_id_index
+      def test_create_reference_id_index_even_if_index_option_is_not_passed
         add_reference table_name, :user
-        assert_not index_exists?(table_name, :user_id)
+        assert index_exists?(table_name, :user_id)
       end
 
       def test_creates_polymorphic_index
@@ -46,13 +48,33 @@ module ActiveRecord
       end
 
       def test_creates_reference_type_column_with_default
-        add_reference table_name, :taggable, polymorphic: { default: 'Photo' }, index: true
-        assert column_exists?(table_name, :taggable_type, :string, default: 'Photo')
+        add_reference table_name, :taggable, polymorphic: { default: "Photo" }, index: true
+        assert column_exists?(table_name, :taggable_type, :string, default: "Photo")
+      end
+
+      def test_creates_reference_type_column_with_not_null
+        connection.create_table table_name, force: true do |t|
+          t.references :taggable, null: false, polymorphic: true
+        end
+        assert column_exists?(table_name, :taggable_id, :integer, null: false)
+        assert column_exists?(table_name, :taggable_type, :string, null: false)
+      end
+
+      def test_does_not_share_options_with_reference_type_column
+        add_reference table_name, :taggable, type: :integer, limit: 2, polymorphic: true
+        assert column_exists?(table_name, :taggable_id, :integer, limit: 2)
+        assert column_exists?(table_name, :taggable_type, :string)
+        assert_not column_exists?(table_name, :taggable_type, :string, limit: 2)
       end
 
       def test_creates_named_index
-        add_reference table_name, :tag, index: { name: 'index_taggings_on_tag_id' }
-        assert index_exists?(table_name, :tag_id, name: 'index_taggings_on_tag_id')
+        add_reference table_name, :tag, index: { name: "index_taggings_on_tag_id" }
+        assert index_exists?(table_name, :tag_id, name: "index_taggings_on_tag_id")
+      end
+
+      def test_creates_named_unique_index
+        add_reference table_name, :tag, index: { name: "index_taggings_on_tag_id", unique: true }
+        assert index_exists?(table_name, :tag_id, name: "index_taggings_on_tag_id", unique: true)
       end
 
       def test_creates_reference_id_with_specified_type
@@ -105,12 +127,12 @@ module ActiveRecord
 
       private
 
-      def with_polymorphic_column
-        add_column table_name, :supplier_type, :string
-        add_index table_name, [:supplier_id, :supplier_type]
+        def with_polymorphic_column
+          add_column table_name, :supplier_type, :string
+          add_index table_name, [:supplier_id, :supplier_type]
 
-        yield
-      end
+          yield
+        end
     end
   end
 end
diff --git a/activerecord/test/cases/migration/rename_table_test.rb b/activerecord/test/cases/migration/rename_table_test.rb
index 6d742d3f2f..a9deb92585 100644
--- a/activerecord/test/cases/migration/rename_table_test.rb
+++ b/activerecord/test/cases/migration/rename_table_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/migration/helper"
 
 module ActiveRecord
@@ -9,9 +11,9 @@ module ActiveRecord
 
       def setup
         super
-        add_column 'test_models', :url, :string
-        remove_column 'test_models', :created_at
-        remove_column 'test_models', :updated_at
+        add_column "test_models", :url, :string
+        remove_column "test_models", :created_at
+        remove_column "test_models", :updated_at
       end
 
       def teardown
@@ -31,7 +33,7 @@ module ActiveRecord
 
           # Using explicit id in insert for compatibility across all databases
           connection.execute "INSERT INTO 'references' (url, created_at, updated_at) VALUES ('http://rubyonrails.com', 0, 0)"
-          assert_equal 'http://rubyonrails.com', connection.select_value("SELECT url FROM 'references' WHERE id=1")
+          assert_equal "http://rubyonrails.com", connection.select_value("SELECT url FROM 'references' WHERE id=1")
         ensure
           return unless renamed
           connection.rename_table :references, :test_models
@@ -45,7 +47,7 @@ module ActiveRecord
 
           connection.execute "INSERT INTO octopi (#{connection.quote_column_name('id')}, #{connection.quote_column_name('url')}) VALUES (1, 'http://www.foreverflying.com/octopus-black7.jpg')"
 
-          assert_equal 'http://www.foreverflying.com/octopus-black7.jpg', connection.select_value("SELECT url FROM octopi WHERE id=1")
+          assert_equal "http://www.foreverflying.com/octopus-black7.jpg", connection.select_value("SELECT url FROM octopi WHERE id=1")
         end
 
         def test_rename_table_with_an_index
@@ -55,18 +57,18 @@ module ActiveRecord
 
           connection.execute "INSERT INTO octopi (#{connection.quote_column_name('id')}, #{connection.quote_column_name('url')}) VALUES (1, 'http://www.foreverflying.com/octopus-black7.jpg')"
 
-          assert_equal 'http://www.foreverflying.com/octopus-black7.jpg', connection.select_value("SELECT url FROM octopi WHERE id=1")
+          assert_equal "http://www.foreverflying.com/octopus-black7.jpg", connection.select_value("SELECT url FROM octopi WHERE id=1")
           index = connection.indexes(:octopi).first
-          assert index.columns.include?("url")
-          assert_equal 'index_octopi_on_url', index.name
+          assert_includes index.columns, "url"
+          assert_equal "index_octopi_on_url", index.name
         end
 
         def test_rename_table_does_not_rename_custom_named_index
-          add_index :test_models, :url, name: 'special_url_idx'
+          add_index :test_models, :url, name: "special_url_idx"
 
           rename_table :test_models, :octopi
 
-          assert_equal ['special_url_idx'], connection.indexes(:octopi).map(&:name)
+          assert_equal ["special_url_idx"], connection.indexes(:octopi).map(&:name)
         end
       end
 
@@ -74,18 +76,39 @@ module ActiveRecord
         def test_rename_table_for_postgresql_should_also_rename_default_sequence
           rename_table :test_models, :octopi
 
-          pk, seq = connection.pk_and_sequence_for('octopi')
+          pk, seq = connection.pk_and_sequence_for("octopi")
 
           assert_equal ConnectionAdapters::PostgreSQL::Name.new("public", "octopi_#{pk}_seq"), seq
         end
 
+        def test_renaming_table_renames_primary_key
+          connection.create_table :cats, id: :uuid, default: "uuid_generate_v4()"
+          rename_table :cats, :felines
+
+          assert connection.table_exists? :felines
+          assert_not connection.table_exists? :cats
+
+          primary_key_name = connection.select_values(<<~SQL, "SCHEMA")[0]
+            SELECT c.relname
+              FROM pg_class c
+              JOIN pg_index i
+                ON c.oid = i.indexrelid
+             WHERE i.indisprimary
+               AND i.indrelid = 'felines'::regclass
+          SQL
+
+          assert_equal "felines_pkey", primary_key_name
+        ensure
+          connection.drop_table :cats, if_exists: true
+          connection.drop_table :felines, if_exists: true
+        end
+
         def test_renaming_table_doesnt_attempt_to_rename_non_existent_sequences
-          enable_extension!('uuid-ossp', connection)
-          connection.create_table :cats, id: :uuid
+          connection.create_table :cats, id: :uuid, default: "uuid_generate_v4()"
           assert_nothing_raised { rename_table :cats, :felines }
           assert connection.table_exists? :felines
+          assert_not connection.table_exists? :cats
         ensure
-          disable_extension!('uuid-ossp', connection)
           connection.drop_table :cats, if_exists: true
           connection.drop_table :felines, if_exists: true
         end
diff --git a/activerecord/test/cases/migration/table_and_index_test.rb b/activerecord/test/cases/migration/table_and_index_test.rb
deleted file mode 100644
index 24cba84a09..0000000000
--- a/activerecord/test/cases/migration/table_and_index_test.rb
+++ /dev/null
@@ -1,24 +0,0 @@
-require "cases/helper"
-
-module ActiveRecord
-  class Migration
-    class TableAndIndexTest < ActiveRecord::TestCase
-      def test_add_schema_info_respects_prefix_and_suffix
-        conn = ActiveRecord::Base.connection
-
-        conn.drop_table(ActiveRecord::Migrator.schema_migrations_table_name, if_exists: true)
-        # Use shorter prefix and suffix as in Oracle database identifier cannot be larger than 30 characters
-        ActiveRecord::Base.table_name_prefix = 'p_'
-        ActiveRecord::Base.table_name_suffix = '_s'
-        conn.drop_table(ActiveRecord::Migrator.schema_migrations_table_name, if_exists: true)
-
-        conn.initialize_schema_migrations_table
-
-        assert_equal "p_unique_schema_migrations_s", conn.indexes(ActiveRecord::Migrator.schema_migrations_table_name)[0][:name]
-      ensure
-        ActiveRecord::Base.table_name_prefix = ""
-        ActiveRecord::Base.table_name_suffix = ""
-      end
-    end
-  end
-end
diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index b2f209fe97..661163b4a1 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -1,11 +1,14 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "cases/migration/helper"
-require 'bigdecimal/util'
+require "bigdecimal/util"
+require "concurrent/atomic/count_down_latch"
 
-require 'models/person'
-require 'models/topic'
-require 'models/developer'
-require 'models/computer'
+require "models/person"
+require "models/topic"
+require "models/developer"
+require "models/computer"
 
 require MIGRATIONS_ROOT + "/valid/2_we_need_reminders"
 require MIGRATIONS_ROOT + "/rename/1_we_need_things"
@@ -42,10 +45,10 @@ class MigrationTest < ActiveRecord::TestCase
     ActiveRecord::Base.table_name_prefix = ""
     ActiveRecord::Base.table_name_suffix = ""
 
-    ActiveRecord::Base.connection.initialize_schema_migrations_table
-    ActiveRecord::Base.connection.execute "DELETE FROM #{ActiveRecord::Migrator.schema_migrations_table_name}"
+    ActiveRecord::SchemaMigration.create_table
+    ActiveRecord::SchemaMigration.delete_all
 
-    %w(things awesome_things prefix_things_suffix p_awesome_things_s ).each do |table|
+    %w(things awesome_things prefix_things_suffix p_awesome_things_s).each do |table|
       Thing.connection.drop_table(table) rescue nil
     end
     Thing.reset_column_information
@@ -58,7 +61,7 @@ class MigrationTest < ActiveRecord::TestCase
 
     %w(last_name key bio age height wealth birthday favorite_day
        moment_of_truth male administrator funny).each do |column|
-      Person.connection.remove_column('people', column) rescue nil
+      Person.connection.remove_column("people", column) rescue nil
     end
     Person.connection.remove_column("people", "first_name") rescue nil
     Person.connection.remove_column("people", "middle_name") rescue nil
@@ -68,54 +71,90 @@ class MigrationTest < ActiveRecord::TestCase
     ActiveRecord::Migration.verbose = @verbose_was
   end
 
+  def test_migrator_migrations_path_is_deprecated
+    assert_deprecated do
+      ActiveRecord::Migrator.migrations_path = "/whatever"
+    end
+  ensure
+    assert_deprecated do
+      ActiveRecord::Migrator.migrations_path = "db/migrate"
+    end
+  end
+
+  def test_migration_version_matches_component_version
+    assert_equal ActiveRecord::VERSION::STRING.to_f, ActiveRecord::Migration.current_version
+  end
+
   def test_migrator_versions
     migrations_path = MIGRATIONS_ROOT + "/valid"
-    old_path = ActiveRecord::Migrator.migrations_paths
-    ActiveRecord::Migrator.migrations_paths = migrations_path
+    migrator = ActiveRecord::MigrationContext.new(migrations_path)
 
-    ActiveRecord::Migrator.up(migrations_path)
-    assert_equal 3, ActiveRecord::Migrator.current_version
-    assert_equal 3, ActiveRecord::Migrator.last_version
-    assert_equal false, ActiveRecord::Migrator.needs_migration?
+    migrator.up
+    assert_equal 3, migrator.current_version
+    assert_equal false, migrator.needs_migration?
 
-    ActiveRecord::Migrator.down(MIGRATIONS_ROOT + "/valid")
-    assert_equal 0, ActiveRecord::Migrator.current_version
-    assert_equal 3, ActiveRecord::Migrator.last_version
-    assert_equal true, ActiveRecord::Migrator.needs_migration?
+    migrator.down
+    assert_equal 0, migrator.current_version
+    assert_equal true, migrator.needs_migration?
 
-    ActiveRecord::SchemaMigration.create!(:version => ActiveRecord::Migrator.last_version)
-    assert_equal true, ActiveRecord::Migrator.needs_migration?
-  ensure
-    ActiveRecord::Migrator.migrations_paths = old_path
+    ActiveRecord::SchemaMigration.create!(version: 3)
+    assert_equal true, migrator.needs_migration?
   end
 
   def test_migration_detection_without_schema_migration_table
-    ActiveRecord::Base.connection.drop_table 'schema_migrations', if_exists: true
+    ActiveRecord::Base.connection.drop_table "schema_migrations", if_exists: true
 
     migrations_path = MIGRATIONS_ROOT + "/valid"
-    old_path = ActiveRecord::Migrator.migrations_paths
-    ActiveRecord::Migrator.migrations_paths = migrations_path
+    migrator = ActiveRecord::MigrationContext.new(migrations_path)
 
-    assert_equal true, ActiveRecord::Migrator.needs_migration?
-  ensure
-    ActiveRecord::Migrator.migrations_paths = old_path
+    assert_equal true, migrator.needs_migration?
   end
 
   def test_any_migrations
-    old_path = ActiveRecord::Migrator.migrations_paths
-    ActiveRecord::Migrator.migrations_paths = MIGRATIONS_ROOT + "/valid"
+    migrator = ActiveRecord::MigrationContext.new(MIGRATIONS_ROOT + "/valid")
 
-    assert ActiveRecord::Migrator.any_migrations?
+    assert_predicate migrator, :any_migrations?
 
-    ActiveRecord::Migrator.migrations_paths = MIGRATIONS_ROOT + "/empty"
+    migrator_empty = ActiveRecord::MigrationContext.new(MIGRATIONS_ROOT + "/empty")
 
-    assert_not ActiveRecord::Migrator.any_migrations?
-  ensure
-    ActiveRecord::Migrator.migrations_paths = old_path
+    assert_not_predicate migrator_empty, :any_migrations?
   end
 
   def test_migration_version
-    ActiveRecord::Migrator.run(:up, MIGRATIONS_ROOT + "/version_check", 20131219224947)
+    migrator = ActiveRecord::MigrationContext.new(MIGRATIONS_ROOT + "/version_check")
+    assert_equal 0, migrator.current_version
+    migrator.up(20131219224947)
+    assert_equal 20131219224947, migrator.current_version
+  end
+
+  def test_create_table_raises_if_already_exists
+    connection = Person.connection
+    connection.create_table :testings, force: true do |t|
+      t.string :foo
+    end
+
+    assert_raise(ActiveRecord::StatementInvalid) do
+      connection.create_table :testings do |t|
+        t.string :foo
+      end
+    end
+  ensure
+    connection.drop_table :testings, if_exists: true
+  end
+
+  def test_create_table_with_if_not_exists_true
+    connection = Person.connection
+    connection.create_table :testings, force: true do |t|
+      t.string :foo
+    end
+
+    assert_nothing_raised do
+      connection.create_table :testings, if_not_exists: true do |t|
+        t.string :foo
+      end
+    end
+  ensure
+    connection.drop_table :testings, if_exists: true
   end
 
   def test_create_table_with_force_true_does_not_drop_nonexisting_table
@@ -125,24 +164,20 @@ class MigrationTest < ActiveRecord::TestCase
 
     assert_not_equal temp_conn, Person.connection
 
-    temp_conn.create_table :testings2, :force => true do |t|
+    temp_conn.create_table :testings2, force: true do |t|
       t.column :foo, :string
     end
   ensure
     Person.connection.drop_table :testings2, if_exists: true
   end
 
-  def connection
-    ActiveRecord::Base.connection
-  end
-
   def test_migration_instance_has_connection
-    migration = Class.new(ActiveRecord::Migration).new
-    assert_equal connection, migration.connection
+    migration = Class.new(ActiveRecord::Migration::Current).new
+    assert_equal ActiveRecord::Base.connection, migration.connection
   end
 
   def test_method_missing_delegates_to_connection
-    migration = Class.new(ActiveRecord::Migration) {
+    migration = Class.new(ActiveRecord::Migration::Current) {
       def connection
         Class.new {
           def create_table; "hi mom!"; end
@@ -156,16 +191,16 @@ class MigrationTest < ActiveRecord::TestCase
   def test_add_table_with_decimals
     Person.connection.drop_table :big_numbers rescue nil
 
-    assert !BigNumber.table_exists?
+    assert_not_predicate BigNumber, :table_exists?
     GiveMeBigNumbers.up
     BigNumber.reset_column_information
 
     assert BigNumber.create(
-      :bank_balance => 1586.43,
-      :big_bank_balance => BigDecimal("1000234000567.95"),
-      :world_population => 6000000000,
-      :my_house_population => 3,
-      :value_of_e => BigDecimal("2.7182818284590452353602875")
+      bank_balance: 1586.43,
+      big_bank_balance: BigDecimal("1000234000567.95"),
+      world_population: 2**62,
+      my_house_population: 3,
+      value_of_e: BigDecimal("2.7182818284590452353602875")
     )
 
     b = BigNumber.first
@@ -177,11 +212,9 @@ class MigrationTest < ActiveRecord::TestCase
     assert_not_nil b.my_house_population
     assert_not_nil b.value_of_e
 
-    # TODO: set world_population >= 2**62 to cover 64-bit platforms and test
-    # is_a?(Bignum)
     assert_kind_of Integer, b.world_population
-    assert_equal 6000000000, b.world_population
-    assert_kind_of Fixnum, b.my_house_population
+    assert_equal 2**62, b.world_population
+    assert_kind_of Integer, b.my_house_population
     assert_equal 3, b.my_house_population
     assert_kind_of BigDecimal, b.bank_balance
     assert_equal BigDecimal("1586.43"), b.bank_balance
@@ -197,8 +230,6 @@ class MigrationTest < ActiveRecord::TestCase
       # of 0, they take on the compile-time limit for precision and scale,
       # so the following should succeed unless you have used really wacky
       # compilation options
-      # - SQLite2 has the default behavior of preserving all data sent in,
-      # so this happens there too
       assert_kind_of BigDecimal, b.value_of_e
       assert_equal BigDecimal("2.7182818284590452353602875"), b.value_of_e
     elsif current_adapter?(:SQLite3Adapter)
@@ -207,7 +238,7 @@ class MigrationTest < ActiveRecord::TestCase
       assert_in_delta BigDecimal("2.71828182845905"), b.value_of_e, 0.00000000000001
     else
       # - SQL standard is an integer
-      assert_kind_of Fixnum, b.value_of_e
+      assert_kind_of Integer, b.value_of_e
       assert_equal 2, b.value_of_e
     end
 
@@ -217,21 +248,22 @@ class MigrationTest < ActiveRecord::TestCase
 
   def test_filtering_migrations
     assert_no_column Person, :last_name
-    assert !Reminder.table_exists?
+    assert_not_predicate Reminder, :table_exists?
 
     name_filter = lambda { |migration| migration.name == "ValidPeopleHaveLastNames" }
-    ActiveRecord::Migrator.up(MIGRATIONS_ROOT + "/valid", &name_filter)
+    migrator = ActiveRecord::MigrationContext.new(MIGRATIONS_ROOT + "/valid")
+    migrator.up(&name_filter)
 
     assert_column Person, :last_name
     assert_raise(ActiveRecord::StatementInvalid) { Reminder.first }
 
-    ActiveRecord::Migrator.down(MIGRATIONS_ROOT + "/valid", &name_filter)
+    migrator.down(&name_filter)
 
     assert_no_column Person, :last_name
     assert_raise(ActiveRecord::StatementInvalid) { Reminder.first }
   end
 
-  class MockMigration < ActiveRecord::Migration
+  class MockMigration < ActiveRecord::Migration::Current
     attr_reader :went_up, :went_down
     def initialize
       @went_up   = false
@@ -251,33 +283,33 @@ class MigrationTest < ActiveRecord::TestCase
 
   def test_instance_based_migration_up
     migration = MockMigration.new
-    assert !migration.went_up, 'have not gone up'
-    assert !migration.went_down, 'have not gone down'
+    assert_not migration.went_up, "have not gone up"
+    assert_not migration.went_down, "have not gone down"
 
     migration.migrate :up
-    assert migration.went_up, 'have gone up'
-    assert !migration.went_down, 'have not gone down'
+    assert migration.went_up, "have gone up"
+    assert_not migration.went_down, "have not gone down"
   end
 
   def test_instance_based_migration_down
     migration = MockMigration.new
-    assert !migration.went_up, 'have not gone up'
-    assert !migration.went_down, 'have not gone down'
+    assert_not migration.went_up, "have not gone up"
+    assert_not migration.went_down, "have not gone down"
 
     migration.migrate :down
-    assert !migration.went_up, 'have gone up'
-    assert migration.went_down, 'have not gone down'
+    assert_not migration.went_up, "have gone up"
+    assert migration.went_down, "have not gone down"
   end
 
   if ActiveRecord::Base.connection.supports_ddl_transactions?
     def test_migrator_one_up_with_exception_and_rollback
       assert_no_column Person, :last_name
 
-      migration = Class.new(ActiveRecord::Migration) {
+      migration = Class.new(ActiveRecord::Migration::Current) {
         def version; 100 end
         def migrate(x)
           add_column "people", "last_name", :string
-          raise 'Something broke'
+          raise "Something broke"
         end
       }.new
 
@@ -294,11 +326,11 @@ class MigrationTest < ActiveRecord::TestCase
     def test_migrator_one_up_with_exception_and_rollback_using_run
       assert_no_column Person, :last_name
 
-      migration = Class.new(ActiveRecord::Migration) {
+      migration = Class.new(ActiveRecord::Migration::Current) {
         def version; 100 end
         def migrate(x)
           add_column "people", "last_name", :string
-          raise 'Something broke'
+          raise "Something broke"
         end
       }.new
 
@@ -306,7 +338,7 @@ class MigrationTest < ActiveRecord::TestCase
 
       e = assert_raise(StandardError) { migrator.run }
 
-      assert_equal "An error has occurred, this migration was canceled:\n\nSomething broke", e.message
+      assert_equal "An error has occurred, this and all later migrations canceled:\n\nSomething broke", e.message
 
       assert_no_column Person, :last_name,
         "On error, the Migrator should revert schema changes but it did not."
@@ -315,13 +347,13 @@ class MigrationTest < ActiveRecord::TestCase
     def test_migration_without_transaction
       assert_no_column Person, :last_name
 
-      migration = Class.new(ActiveRecord::Migration) {
-        self.disable_ddl_transaction!
+      migration = Class.new(ActiveRecord::Migration::Current) {
+        disable_ddl_transaction!
 
         def version; 101 end
         def migrate(x)
           add_column "people", "last_name", :string
-          raise 'Something broke'
+          raise "Something broke"
         end
       }.new
 
@@ -333,36 +365,94 @@ class MigrationTest < ActiveRecord::TestCase
         "without ddl transactions, the Migrator should not rollback on error but it did."
     ensure
       Person.reset_column_information
-      if Person.column_names.include?('last_name')
-        Person.connection.remove_column('people', 'last_name')
+      if Person.column_names.include?("last_name")
+        Person.connection.remove_column("people", "last_name")
       end
     end
   end
 
   def test_schema_migrations_table_name
-    original_schema_migrations_table_name = ActiveRecord::Migrator.schema_migrations_table_name
+    original_schema_migrations_table_name = ActiveRecord::Base.schema_migrations_table_name
 
-    assert_equal "schema_migrations", ActiveRecord::Migrator.schema_migrations_table_name
+    assert_equal "schema_migrations", ActiveRecord::SchemaMigration.table_name
     ActiveRecord::Base.table_name_prefix = "prefix_"
     ActiveRecord::Base.table_name_suffix = "_suffix"
     Reminder.reset_table_name
-    assert_equal "prefix_schema_migrations_suffix", ActiveRecord::Migrator.schema_migrations_table_name
+    assert_equal "prefix_schema_migrations_suffix", ActiveRecord::SchemaMigration.table_name
     ActiveRecord::Base.schema_migrations_table_name = "changed"
     Reminder.reset_table_name
-    assert_equal "prefix_changed_suffix", ActiveRecord::Migrator.schema_migrations_table_name
+    assert_equal "prefix_changed_suffix", ActiveRecord::SchemaMigration.table_name
     ActiveRecord::Base.table_name_prefix = ""
     ActiveRecord::Base.table_name_suffix = ""
     Reminder.reset_table_name
-    assert_equal "changed", ActiveRecord::Migrator.schema_migrations_table_name
+    assert_equal "changed", ActiveRecord::SchemaMigration.table_name
   ensure
     ActiveRecord::Base.schema_migrations_table_name = original_schema_migrations_table_name
     Reminder.reset_table_name
   end
 
+  def test_internal_metadata_table_name
+    original_internal_metadata_table_name = ActiveRecord::Base.internal_metadata_table_name
+
+    assert_equal "ar_internal_metadata", ActiveRecord::InternalMetadata.table_name
+    ActiveRecord::Base.table_name_prefix = "p_"
+    ActiveRecord::Base.table_name_suffix = "_s"
+    Reminder.reset_table_name
+    assert_equal "p_ar_internal_metadata_s", ActiveRecord::InternalMetadata.table_name
+    ActiveRecord::Base.internal_metadata_table_name = "changed"
+    Reminder.reset_table_name
+    assert_equal "p_changed_s", ActiveRecord::InternalMetadata.table_name
+    ActiveRecord::Base.table_name_prefix = ""
+    ActiveRecord::Base.table_name_suffix = ""
+    Reminder.reset_table_name
+    assert_equal "changed", ActiveRecord::InternalMetadata.table_name
+  ensure
+    ActiveRecord::Base.internal_metadata_table_name = original_internal_metadata_table_name
+    Reminder.reset_table_name
+  end
+
+  def test_internal_metadata_stores_environment
+    current_env     = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call
+    migrations_path = MIGRATIONS_ROOT + "/valid"
+    migrator = ActiveRecord::MigrationContext.new(migrations_path)
+
+    migrator.up
+    assert_equal current_env, ActiveRecord::InternalMetadata[:environment]
+
+    original_rails_env  = ENV["RAILS_ENV"]
+    original_rack_env   = ENV["RACK_ENV"]
+    ENV["RAILS_ENV"]    = ENV["RACK_ENV"] = "foofoo"
+    new_env = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call
+
+    assert_not_equal current_env, new_env
+
+    sleep 1 # mysql by default does not store fractional seconds in the database
+    migrator.up
+    assert_equal new_env, ActiveRecord::InternalMetadata[:environment]
+  ensure
+    ENV["RAILS_ENV"] = original_rails_env
+    ENV["RACK_ENV"]  = original_rack_env
+    migrator.up
+  end
+
+  def test_internal_metadata_stores_environment_when_other_data_exists
+    ActiveRecord::InternalMetadata.delete_all
+    ActiveRecord::InternalMetadata[:foo] = "bar"
+
+    current_env     = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call
+    migrations_path = MIGRATIONS_ROOT + "/valid"
+
+    current_env = ActiveRecord::ConnectionHandling::DEFAULT_ENV.call
+    migrator = ActiveRecord::MigrationContext.new(migrations_path)
+    migrator.up
+    assert_equal current_env, ActiveRecord::InternalMetadata[:environment]
+    assert_equal "bar", ActiveRecord::InternalMetadata[:foo]
+  end
+
   def test_proper_table_name_on_migration
     reminder_class = new_isolated_reminder_class
     migration = ActiveRecord::Migration.new
-    assert_equal "table", migration.proper_table_name('table')
+    assert_equal "table", migration.proper_table_name("table")
     assert_equal "table", migration.proper_table_name(:table)
     assert_equal "reminders", migration.proper_table_name(reminder_class)
     reminder_class.reset_table_name
@@ -371,26 +461,26 @@ class MigrationTest < ActiveRecord::TestCase
     # Use the model's own prefix/suffix if a model is given
     ActiveRecord::Base.table_name_prefix = "ARprefix_"
     ActiveRecord::Base.table_name_suffix = "_ARsuffix"
-    reminder_class.table_name_prefix = 'prefix_'
-    reminder_class.table_name_suffix = '_suffix'
+    reminder_class.table_name_prefix = "prefix_"
+    reminder_class.table_name_suffix = "_suffix"
     reminder_class.reset_table_name
     assert_equal "prefix_reminders_suffix", migration.proper_table_name(reminder_class)
-    reminder_class.table_name_prefix = ''
-    reminder_class.table_name_suffix = ''
+    reminder_class.table_name_prefix = ""
+    reminder_class.table_name_suffix = ""
     reminder_class.reset_table_name
 
     # Use AR::Base's prefix/suffix if string or symbol is given
     ActiveRecord::Base.table_name_prefix = "prefix_"
     ActiveRecord::Base.table_name_suffix = "_suffix"
     reminder_class.reset_table_name
-    assert_equal "prefix_table_suffix", migration.proper_table_name('table', migration.table_name_options)
+    assert_equal "prefix_table_suffix", migration.proper_table_name("table", migration.table_name_options)
     assert_equal "prefix_table_suffix", migration.proper_table_name(:table, migration.table_name_options)
   end
 
   def test_rename_table_with_prefix_and_suffix
-    assert !Thing.table_exists?
-    ActiveRecord::Base.table_name_prefix = 'p_'
-    ActiveRecord::Base.table_name_suffix = '_s'
+    assert_not_predicate Thing, :table_exists?
+    ActiveRecord::Base.table_name_prefix = "p_"
+    ActiveRecord::Base.table_name_suffix = "_s"
     Thing.reset_table_name
     Thing.reset_sequence_name
     WeNeedThings.up
@@ -409,9 +499,9 @@ class MigrationTest < ActiveRecord::TestCase
   end
 
   def test_add_drop_table_with_prefix_and_suffix
-    assert !Reminder.table_exists?
-    ActiveRecord::Base.table_name_prefix = 'prefix_'
-    ActiveRecord::Base.table_name_suffix = '_suffix'
+    assert_not_predicate Reminder, :table_exists?
+    ActiveRecord::Base.table_name_prefix = "prefix_"
+    ActiveRecord::Base.table_name_suffix = "_suffix"
     Reminder.reset_table_name
     Reminder.reset_sequence_name
     Reminder.reset_column_information
@@ -428,7 +518,7 @@ class MigrationTest < ActiveRecord::TestCase
   def test_create_table_with_binary_column
     assert_nothing_raised {
       Person.connection.create_table :binary_testings do |t|
-        t.column "data", :binary, :null => false
+        t.column "data", :binary, null: false
       end
     }
 
@@ -436,38 +526,51 @@ class MigrationTest < ActiveRecord::TestCase
     data_column = columns.detect { |c| c.name == "data" }
 
     assert_nil data_column.default
-
+  ensure
     Person.connection.drop_table :binary_testings, if_exists: true
   end
 
   unless mysql_enforcing_gtid_consistency?
     def test_create_table_with_query
-      Person.connection.drop_table :table_from_query_testings rescue nil
-      Person.connection.create_table(:person, force: true)
-
-      Person.connection.create_table :table_from_query_testings, as: "SELECT id FROM person"
+      Person.connection.create_table :table_from_query_testings, as: "SELECT id FROM people WHERE id = 1"
 
       columns = Person.connection.columns(:table_from_query_testings)
+      assert_equal [1], Person.connection.select_values("SELECT * FROM table_from_query_testings")
       assert_equal 1, columns.length
       assert_equal "id", columns.first.name
-
+    ensure
       Person.connection.drop_table :table_from_query_testings rescue nil
     end
 
     def test_create_table_with_query_from_relation
-      Person.connection.drop_table :table_from_query_testings rescue nil
-      Person.connection.create_table(:person, force: true)
-
-      Person.connection.create_table :table_from_query_testings, as: Person.select(:id)
+      Person.connection.create_table :table_from_query_testings, as: Person.select(:id).where(id: 1)
 
       columns = Person.connection.columns(:table_from_query_testings)
+      assert_equal [1], Person.connection.select_values("SELECT * FROM table_from_query_testings")
       assert_equal 1, columns.length
       assert_equal "id", columns.first.name
-
+    ensure
       Person.connection.drop_table :table_from_query_testings rescue nil
     end
   end
 
+  if current_adapter?(:SQLite3Adapter)
+    def test_allows_sqlite3_rollback_on_invalid_column_type
+      Person.connection.create_table :something, force: true do |t|
+        t.column :number, :integer
+        t.column :name, :string
+        t.column :foo, :bar
+      end
+      assert Person.connection.column_exists?(:something, :foo)
+      assert_nothing_raised { Person.connection.remove_column :something, :foo, :bar }
+      assert_not Person.connection.column_exists?(:something, :foo)
+      assert Person.connection.column_exists?(:something, :name)
+      assert Person.connection.column_exists?(:something, :number)
+    ensure
+      Person.connection.drop_table :something, if_exists: true
+    end
+  end
+
   if current_adapter? :OracleAdapter
     def test_create_table_with_custom_sequence_name
       # table name is 29 chars, the standard sequence name will
@@ -475,7 +578,7 @@ class MigrationTest < ActiveRecord::TestCase
       assert_nothing_raised do
         begin
           Person.connection.create_table :table_with_name_thats_just_ok do |t|
-            t.column :foo, :string, :null => false
+            t.column :foo, :string, null: false
           end
         ensure
           Person.connection.drop_table :table_with_name_thats_just_ok rescue nil
@@ -486,15 +589,15 @@ class MigrationTest < ActiveRecord::TestCase
       assert_nothing_raised do
         begin
           Person.connection.create_table :table_with_name_thats_just_ok,
-            :sequence_name => 'suitably_short_seq' do |t|
-            t.column :foo, :string, :null => false
+            sequence_name: "suitably_short_seq" do |t|
+            t.column :foo, :string, null: false
           end
 
           Person.connection.execute("select suitably_short_seq.nextval from dual")
 
         ensure
           Person.connection.drop_table :table_with_name_thats_just_ok,
-            :sequence_name => 'suitably_short_seq' rescue nil
+            sequence_name: "suitably_short_seq" rescue nil
         end
       end
 
@@ -505,30 +608,126 @@ class MigrationTest < ActiveRecord::TestCase
     end
   end
 
-  if current_adapter?(:MysqlAdapter, :Mysql2Adapter, :PostgreSQLAdapter)
-    def test_out_of_range_limit_should_raise
-      Person.connection.drop_table :test_limits rescue nil
+  if current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter)
+    def test_out_of_range_integer_limit_should_raise
       e = assert_raise(ActiveRecord::ActiveRecordError, "integer limit didn't raise") do
-        Person.connection.create_table :test_integer_limits, :force => true do |t|
-          t.column :bigone, :integer, :limit => 10
+        Person.connection.create_table :test_integer_limits, force: true do |t|
+          t.column :bigone, :integer, limit: 10
         end
       end
 
       assert_match(/No integer type has byte size 10/, e.message)
+    ensure
+      Person.connection.drop_table :test_integer_limits, if_exists: true
+    end
+  end
+
+  if current_adapter?(:Mysql2Adapter)
+    def test_out_of_range_text_limit_should_raise
+      e = assert_raise(ActiveRecord::ActiveRecordError, "text limit didn't raise") do
+        Person.connection.create_table :test_text_limits, force: true do |t|
+          t.text :bigtext, limit: 0xfffffffff
+        end
+      end
+
+      assert_match(/No text type has byte length #{0xfffffffff}/, e.message)
+    ensure
+      Person.connection.drop_table :test_text_limits, if_exists: true
+    end
+  end
 
-      unless current_adapter?(:PostgreSQLAdapter)
-        assert_raise(ActiveRecord::ActiveRecordError, "text limit didn't raise") do
-          Person.connection.create_table :test_text_limits, :force => true do |t|
-            t.column :bigtext, :text, :limit => 0xfffffffff
+  if ActiveRecord::Base.connection.supports_advisory_locks?
+    def test_migrator_generates_valid_lock_id
+      migration = Class.new(ActiveRecord::Migration::Current).new
+      migrator = ActiveRecord::Migrator.new(:up, [migration], 100)
+
+      lock_id = migrator.send(:generate_migrator_advisory_lock_id)
+
+      assert ActiveRecord::Base.connection.get_advisory_lock(lock_id),
+        "the Migrator should have generated a valid lock id, but it didn't"
+      assert ActiveRecord::Base.connection.release_advisory_lock(lock_id),
+        "the Migrator should have generated a valid lock id, but it didn't"
+    end
+
+    def test_generate_migrator_advisory_lock_id
+      # It is important we are consistent with how we generate this so that
+      # exclusive locking works across migrator versions
+      migration = Class.new(ActiveRecord::Migration::Current).new
+      migrator = ActiveRecord::Migrator.new(:up, [migration], 100)
+
+      lock_id = migrator.send(:generate_migrator_advisory_lock_id)
+
+      current_database = ActiveRecord::Base.connection.current_database
+      salt = ActiveRecord::Migrator::MIGRATOR_SALT
+      expected_id = Zlib.crc32(current_database) * salt
+
+      assert lock_id == expected_id, "expected lock id generated by the migrator to be #{expected_id}, but it was #{lock_id} instead"
+      assert lock_id.bit_length <= 63, "lock id must be a signed integer of max 63 bits magnitude"
+    end
+
+    def test_migrator_one_up_with_unavailable_lock
+      assert_no_column Person, :last_name
+
+      migration = Class.new(ActiveRecord::Migration::Current) {
+        def version; 100 end
+        def migrate(x)
+          add_column "people", "last_name", :string
+        end
+      }.new
+
+      migrator = ActiveRecord::Migrator.new(:up, [migration], 100)
+      lock_id = migrator.send(:generate_migrator_advisory_lock_id)
+
+      with_another_process_holding_lock(lock_id) do
+        assert_raise(ActiveRecord::ConcurrentMigrationError) { migrator.migrate }
+      end
+
+      assert_no_column Person, :last_name,
+        "without an advisory lock, the Migrator should not make any changes, but it did."
+    end
+
+    def test_migrator_one_up_with_unavailable_lock_using_run
+      assert_no_column Person, :last_name
+
+      migration = Class.new(ActiveRecord::Migration::Current) {
+        def version; 100 end
+        def migrate(x)
+          add_column "people", "last_name", :string
+        end
+      }.new
+
+      migrator = ActiveRecord::Migrator.new(:up, [migration], 100)
+      lock_id = migrator.send(:generate_migrator_advisory_lock_id)
+
+      with_another_process_holding_lock(lock_id) do
+        assert_raise(ActiveRecord::ConcurrentMigrationError) { migrator.run }
+      end
+
+      assert_no_column Person, :last_name,
+        "without an advisory lock, the Migrator should not make any changes, but it did."
+    end
+
+    def test_with_advisory_lock_raises_the_right_error_when_it_fails_to_release_lock
+      migration = Class.new(ActiveRecord::Migration::Current).new
+      migrator = ActiveRecord::Migrator.new(:up, [migration], 100)
+      lock_id = migrator.send(:generate_migrator_advisory_lock_id)
+
+      e = assert_raises(ActiveRecord::ConcurrentMigrationError) do
+        silence_stream($stderr) do
+          migrator.send(:with_advisory_lock) do
+            ActiveRecord::Base.connection.release_advisory_lock(lock_id)
           end
         end
       end
 
-      Person.connection.drop_table :test_limits rescue nil
+      assert_match(
+        /#{ActiveRecord::ConcurrentMigrationError::RELEASE_LOCK_FAILED_MESSAGE}/,
+        e.message
+      )
     end
   end
 
-  protected
+  private
     # This is needed to isolate class_attribute assignments like `table_name_prefix`
     # for each test case.
     def new_isolated_reminder_class
@@ -537,20 +736,44 @@ class MigrationTest < ActiveRecord::TestCase
         def self.base_class; self; end
       }
     end
+
+    def with_another_process_holding_lock(lock_id)
+      thread_lock = Concurrent::CountDownLatch.new
+      test_terminated = Concurrent::CountDownLatch.new
+
+      other_process = Thread.new do
+        begin
+          conn = ActiveRecord::Base.connection_pool.checkout
+          conn.get_advisory_lock(lock_id)
+          thread_lock.count_down
+          test_terminated.wait # hold the lock open until we tested everything
+        ensure
+          conn.release_advisory_lock(lock_id)
+          ActiveRecord::Base.connection_pool.checkin(conn)
+        end
+      end
+
+      thread_lock.wait # wait until the 'other process' has the lock
+
+      yield
+
+      test_terminated.count_down
+      other_process.join
+    end
 end
 
 class ReservedWordsMigrationTest < ActiveRecord::TestCase
   def test_drop_index_from_table_named_values
     connection = Person.connection
-    connection.create_table :values, :force => true do |t|
+    connection.create_table :values, force: true do |t|
       t.integer :value
     end
 
     assert_nothing_raised do
       connection.add_index :values, :value
-      connection.remove_index :values, :column => :value
+      connection.remove_index :values, column: :value
     end
-
+  ensure
     connection.drop_table :values rescue nil
   end
 end
@@ -562,11 +785,11 @@ class ExplicitlyNamedIndexMigrationTest < ActiveRecord::TestCase
       t.integer :value
     end
 
-    assert_nothing_raised ArgumentError do
-      connection.add_index :values, :value, name: 'a_different_name'
-      connection.remove_index :values, column: :value, name: 'a_different_name'
+    assert_nothing_raised do
+      connection.add_index :values, :value, name: "a_different_name"
+      connection.remove_index :values, column: :value, name: "a_different_name"
     end
-
+  ensure
     connection.drop_table :values rescue nil
   end
 end
@@ -575,7 +798,7 @@ if ActiveRecord::Base.connection.supports_bulk_alter?
   class BulkAlterTableMigrationsTest < ActiveRecord::TestCase
     def setup
       @connection = Person.connection
-      @connection.create_table(:delete_me, :force => true) {|t| }
+      @connection.create_table(:delete_me, force: true) { |t| }
       Person.reset_column_information
       Person.reset_sequence_name
     end
@@ -585,19 +808,28 @@ if ActiveRecord::Base.connection.supports_bulk_alter?
     end
 
     def test_adding_multiple_columns
-      assert_queries(1) do
+      classname = ActiveRecord::Base.connection.class.name[/[^:]*$/]
+      expected_query_count = {
+        "Mysql2Adapter"     => 1,
+        "PostgreSQLAdapter" => 2, # one for bulk change, one for comment
+      }.fetch(classname) {
+        raise "need an expected query count for #{classname}"
+      }
+
+      assert_queries(expected_query_count) do
         with_bulk_change_table do |t|
           t.column :name, :string
           t.string :qualification, :experience
-          t.integer :age, :default => 0
-          t.date :birthdate
+          t.integer :age, default: 0
+          t.date :birthdate, comment: "This is a comment"
           t.timestamps null: true
         end
       end
 
       assert_equal 8, columns.size
-      [:name, :qualification, :experience].each {|s| assert_equal :string, column(s).type }
-      assert_equal '0', column(:age).default
+      [:name, :qualification, :experience].each { |s| assert_equal :string, column(s).type }
+      assert_equal "0", column(:age).default
+      assert_equal "This is a comment", column(:birthdate).comment
     end
 
     def test_removing_columns
@@ -605,7 +837,7 @@ if ActiveRecord::Base.connection.supports_bulk_alter?
         t.string :qualification, :experience
       end
 
-      [:qualification, :experience].each {|c| assert column(c) }
+      [:qualification, :experience].each { |c| assert column(c) }
 
       assert_queries(1) do
         with_bulk_change_table do |t|
@@ -614,7 +846,7 @@ if ActiveRecord::Base.connection.supports_bulk_alter?
         end
       end
 
-      [:qualification, :experience].each {|c| assert ! column(c) }
+      [:qualification, :experience].each { |c| assert_not column(c) }
       assert column(:qualification_experience)
     end
 
@@ -625,10 +857,17 @@ if ActiveRecord::Base.connection.supports_bulk_alter?
         t.integer :age
       end
 
-      # Adding an index fires a query every time to check if an index already exists or not
-      assert_queries(3) do
+      classname = ActiveRecord::Base.connection.class.name[/[^:]*$/]
+      expected_query_count = {
+        "Mysql2Adapter"     => 3, # Adding an index fires a query every time to check if an index already exists or not
+        "PostgreSQLAdapter" => 2,
+      }.fetch(classname) {
+        raise "need an expected query count for #{classname}"
+      }
+
+      assert_queries(expected_query_count) do
         with_bulk_change_table do |t|
-          t.index :username, :unique => true, :name => :awesome_username_index
+          t.index :username, unique: true, name: :awesome_username_index
           t.index [:name, :age]
         end
       end
@@ -636,8 +875,8 @@ if ActiveRecord::Base.connection.supports_bulk_alter?
       assert_equal 2, indexes.size
 
       name_age_index = index(:index_delete_me_on_name_and_age)
-      assert_equal ['name', 'age'].sort, name_age_index.columns.sort
-      assert ! name_age_index.unique
+      assert_equal ["name", "age"].sort, name_age_index.columns.sort
+      assert_not name_age_index.unique
 
       assert index(:awesome_username_index).unique
     end
@@ -650,14 +889,22 @@ if ActiveRecord::Base.connection.supports_bulk_alter?
 
       assert index(:index_delete_me_on_name)
 
-      assert_queries(3) do
+      classname = ActiveRecord::Base.connection.class.name[/[^:]*$/]
+      expected_query_count = {
+        "Mysql2Adapter"     => 3, # Adding an index fires a query every time to check if an index already exists or not
+        "PostgreSQLAdapter" => 2,
+      }.fetch(classname) {
+        raise "need an expected query count for #{classname}"
+      }
+
+      assert_queries(expected_query_count) do
         with_bulk_change_table do |t|
           t.remove_index :name
-          t.index :name, :name => :new_name_index, :unique => true
+          t.index :name, name: :new_name_index, unique: true
         end
       end
 
-      assert ! index(:index_delete_me_on_name)
+      assert_not index(:index_delete_me_on_name)
 
       new_name_index = index(:new_name_index)
       assert new_name_index.unique
@@ -669,51 +916,56 @@ if ActiveRecord::Base.connection.supports_bulk_alter?
         t.date :birthdate
       end
 
-      assert ! column(:name).default
+      assert_not column(:name).default
       assert_equal :date, column(:birthdate).type
 
-      # One query for columns (delete_me table)
-      # One query for primary key (delete_me table)
-      # One query to do the bulk change
-      assert_queries(3, :ignore_none => true) do
+      classname = ActiveRecord::Base.connection.class.name[/[^:]*$/]
+      expected_query_count = {
+        "Mysql2Adapter"     => 3, # one query for columns, one query for primary key, one query to do the bulk change
+        "PostgreSQLAdapter" => 3, # one query for columns, one for bulk change, one for comment
+      }.fetch(classname) {
+        raise "need an expected query count for #{classname}"
+      }
+
+      assert_queries(expected_query_count, ignore_none: true) do
         with_bulk_change_table do |t|
-          t.change :name, :string, :default => 'NONAME'
-          t.change :birthdate, :datetime
+          t.change :name, :string, default: "NONAME"
+          t.change :birthdate, :datetime, comment: "This is a comment"
         end
       end
 
-      assert_equal 'NONAME', column(:name).default
+      assert_equal "NONAME", column(:name).default
       assert_equal :datetime, column(:birthdate).type
+      assert_equal "This is a comment", column(:birthdate).comment
     end
 
-    protected
+    private
 
-    def with_bulk_change_table
-      # Reset columns/indexes cache as we're changing the table
-      @columns = @indexes = nil
+      def with_bulk_change_table
+        # Reset columns/indexes cache as we're changing the table
+        @columns = @indexes = nil
 
-      Person.connection.change_table(:delete_me, :bulk => true) do |t|
-        yield t
+        Person.connection.change_table(:delete_me, bulk: true) do |t|
+          yield t
+        end
       end
-    end
 
-    def column(name)
-      columns.detect {|c| c.name == name.to_s }
-    end
+      def column(name)
+        columns.detect { |c| c.name == name.to_s }
+      end
 
-    def columns
-      @columns ||= Person.connection.columns('delete_me')
-    end
+      def columns
+        @columns ||= Person.connection.columns("delete_me")
+      end
 
-    def index(name)
-      indexes.detect {|i| i.name == name.to_s }
-    end
+      def index(name)
+        indexes.detect { |i| i.name == name.to_s }
+      end
 
-    def indexes
-      @indexes ||= Person.connection.indexes('delete_me')
-    end
+      def indexes
+        @indexes ||= Person.connection.indexes("delete_me")
+      end
   end # AlterTableMigrationsTest
-
 end
 
 class CopyMigrationsTest < ActiveRecord::TestCase
@@ -733,18 +985,18 @@ class CopyMigrationsTest < ActiveRecord::TestCase
     @migrations_path = MIGRATIONS_ROOT + "/valid"
     @existing_migrations = Dir[@migrations_path + "/*.rb"]
 
-    copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy"})
+    copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/to_copy")
     assert File.exist?(@migrations_path + "/4_people_have_hobbies.bukkits.rb")
     assert File.exist?(@migrations_path + "/5_people_have_descriptions.bukkits.rb")
     assert_equal [@migrations_path + "/4_people_have_hobbies.bukkits.rb", @migrations_path + "/5_people_have_descriptions.bukkits.rb"], copied.map(&:filename)
 
     expected = "# This migration comes from bukkits (originally 1)"
-    assert_equal expected, IO.readlines(@migrations_path + "/4_people_have_hobbies.bukkits.rb")[0].chomp
+    assert_equal expected, IO.readlines(@migrations_path + "/4_people_have_hobbies.bukkits.rb")[1].chomp
 
     files_count = Dir[@migrations_path + "/*.rb"].length
-    copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy"})
+    copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/to_copy")
     assert_equal files_count, Dir[@migrations_path + "/*.rb"].length
-    assert copied.empty?
+    assert_empty copied
   ensure
     clear
   end
@@ -775,7 +1027,7 @@ class CopyMigrationsTest < ActiveRecord::TestCase
     @existing_migrations = Dir[@migrations_path + "/*.rb"]
 
     travel_to(Time.utc(2010, 7, 26, 10, 10, 10)) do
-      copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy_with_timestamps"})
+      copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/to_copy_with_timestamps")
       assert File.exist?(@migrations_path + "/20100726101010_people_have_hobbies.bukkits.rb")
       assert File.exist?(@migrations_path + "/20100726101011_people_have_descriptions.bukkits.rb")
       expected = [@migrations_path + "/20100726101010_people_have_hobbies.bukkits.rb",
@@ -783,9 +1035,9 @@ class CopyMigrationsTest < ActiveRecord::TestCase
       assert_equal expected, copied.map(&:filename)
 
       files_count = Dir[@migrations_path + "/*.rb"].length
-      copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy_with_timestamps"})
+      copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/to_copy_with_timestamps")
       assert_equal files_count, Dir[@migrations_path + "/*.rb"].length
-      assert copied.empty?
+      assert_empty copied
     end
   ensure
     clear
@@ -820,14 +1072,14 @@ class CopyMigrationsTest < ActiveRecord::TestCase
     @existing_migrations = Dir[@migrations_path + "/*.rb"]
 
     travel_to(Time.utc(2010, 2, 20, 10, 10, 10)) do
-      ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy_with_timestamps"})
+      ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/to_copy_with_timestamps")
       assert File.exist?(@migrations_path + "/20100301010102_people_have_hobbies.bukkits.rb")
       assert File.exist?(@migrations_path + "/20100301010103_people_have_descriptions.bukkits.rb")
 
       files_count = Dir[@migrations_path + "/*.rb"].length
-      copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy_with_timestamps"})
+      copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/to_copy_with_timestamps")
       assert_equal files_count, Dir[@migrations_path + "/*.rb"].length
-      assert copied.empty?
+      assert_empty copied
     end
   ensure
     clear
@@ -838,17 +1090,17 @@ class CopyMigrationsTest < ActiveRecord::TestCase
     @migrations_path = MIGRATIONS_ROOT + "/valid"
     @existing_migrations = Dir[@migrations_path + "/*.rb"]
 
-    copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/magic"})
+    copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/magic")
     assert File.exist?(@migrations_path + "/4_currencies_have_symbols.bukkits.rb")
     assert_equal [@migrations_path + "/4_currencies_have_symbols.bukkits.rb"], copied.map(&:filename)
 
-    expected = "# coding: ISO-8859-15\n# This migration comes from bukkits (originally 1)"
-    assert_equal expected, IO.readlines(@migrations_path + "/4_currencies_have_symbols.bukkits.rb")[0..1].join.chomp
+    expected = "# frozen_string_literal: true\n# coding: ISO-8859-15\n# This migration comes from bukkits (originally 1)"
+    assert_equal expected, IO.readlines(@migrations_path + "/4_currencies_have_symbols.bukkits.rb")[0..2].join.chomp
 
     files_count = Dir[@migrations_path + "/*.rb"].length
-    copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/magic"})
+    copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/magic")
     assert_equal files_count, Dir[@migrations_path + "/*.rb"].length
-    assert copied.empty?
+    assert_empty copied
   ensure
     clear
   end
@@ -863,7 +1115,7 @@ class CopyMigrationsTest < ActiveRecord::TestCase
 
     skipped = []
     on_skip = Proc.new { |name, migration| skipped << "#{name} #{migration.name}" }
-    copied = ActiveRecord::Migration.copy(@migrations_path, sources, :on_skip => on_skip)
+    copied = ActiveRecord::Migration.copy(@migrations_path, sources, on_skip: on_skip)
     assert_equal 2, copied.length
 
     assert_equal 1, skipped.length
@@ -881,8 +1133,8 @@ class CopyMigrationsTest < ActiveRecord::TestCase
 
     skipped = []
     on_skip = Proc.new { |name, migration| skipped << "#{name} #{migration.name}" }
-    copied = ActiveRecord::Migration.copy(@migrations_path, sources, :on_skip => on_skip)
-    ActiveRecord::Migration.copy(@migrations_path, sources, :on_skip => on_skip)
+    copied = ActiveRecord::Migration.copy(@migrations_path, sources, on_skip: on_skip)
+    ActiveRecord::Migration.copy(@migrations_path, sources, on_skip: on_skip)
 
     assert_equal 2, copied.length
     assert_equal 0, skipped.length
@@ -895,7 +1147,7 @@ class CopyMigrationsTest < ActiveRecord::TestCase
     @existing_migrations = []
 
     travel_to(Time.utc(2010, 7, 26, 10, 10, 10)) do
-      copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy_with_timestamps"})
+      copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/to_copy_with_timestamps")
       assert File.exist?(@migrations_path + "/20100726101010_people_have_hobbies.bukkits.rb")
       assert File.exist?(@migrations_path + "/20100726101011_people_have_descriptions.bukkits.rb")
       assert_equal 2, copied.length
@@ -910,7 +1162,7 @@ class CopyMigrationsTest < ActiveRecord::TestCase
     @existing_migrations = []
 
     travel_to(Time.utc(2010, 7, 26, 10, 10, 10)) do
-      copied = ActiveRecord::Migration.copy(@migrations_path, {:bukkits => MIGRATIONS_ROOT + "/to_copy_with_timestamps"})
+      copied = ActiveRecord::Migration.copy(@migrations_path, bukkits: MIGRATIONS_ROOT + "/to_copy_with_timestamps")
       assert File.exist?(@migrations_path + "/20100726101010_people_have_hobbies.bukkits.rb")
       assert File.exist?(@migrations_path + "/20100726101011_people_have_descriptions.bukkits.rb")
       assert_equal 2, copied.length
@@ -922,10 +1174,13 @@ class CopyMigrationsTest < ActiveRecord::TestCase
   def test_check_pending_with_stdlib_logger
     old, ActiveRecord::Base.logger = ActiveRecord::Base.logger, ::Logger.new($stdout)
     quietly do
-      assert_nothing_raised { ActiveRecord::Migration::CheckPending.new(Proc.new {}).call({}) }
+      assert_nothing_raised { ActiveRecord::Migration::CheckPending.new(Proc.new { }).call({}) }
     end
   ensure
     ActiveRecord::Base.logger = old
   end
 
+  def test_unknown_migration_version_should_raise_an_argument_error
+    assert_raise(ArgumentError) { ActiveRecord::Migration[1.0] }
+  end
 end
diff --git a/activerecord/test/cases/migrator_test.rb b/activerecord/test/cases/migrator_test.rb
index 2ff6938e7b..30e199f1c5 100644
--- a/activerecord/test/cases/migrator_test.rb
+++ b/activerecord/test/cases/migrator_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "cases/migration/helper"
 
@@ -6,12 +8,12 @@ class MigratorTest < ActiveRecord::TestCase
 
   # Use this class to sense if migrations have gone
   # up or down.
-  class Sensor < ActiveRecord::Migration
+  class Sensor < ActiveRecord::Migration::Current
     attr_reader :went_up, :went_down
 
-    def initialize name = self.class.name, version = nil
+    def initialize(name = self.class.name, version = nil)
       super
-      @went_up  = false
+      @went_up = false
       @went_down = false
     end
 
@@ -45,100 +47,182 @@ class MigratorTest < ActiveRecord::TestCase
   end
 
   def test_migrator_with_duplicate_names
-    assert_raises(ActiveRecord::DuplicateMigrationNameError, "Multiple migrations have the name Chunky") do
-      list = [ActiveRecord::Migration.new('Chunky'), ActiveRecord::Migration.new('Chunky')]
+    e = assert_raises(ActiveRecord::DuplicateMigrationNameError) do
+      list = [ActiveRecord::Migration.new("Chunky"), ActiveRecord::Migration.new("Chunky")]
       ActiveRecord::Migrator.new(:up, list)
     end
+    assert_match(/Multiple migrations have the name Chunky/, e.message)
   end
 
   def test_migrator_with_duplicate_versions
     assert_raises(ActiveRecord::DuplicateMigrationVersionError) do
-      list = [ActiveRecord::Migration.new('Foo', 1), ActiveRecord::Migration.new('Bar', 1)]
+      list = [ActiveRecord::Migration.new("Foo", 1), ActiveRecord::Migration.new("Bar", 1)]
       ActiveRecord::Migrator.new(:up, list)
     end
   end
 
   def test_migrator_with_missing_version_numbers
     assert_raises(ActiveRecord::UnknownMigrationVersionError) do
-      list = [ActiveRecord::Migration.new('Foo', 1), ActiveRecord::Migration.new('Bar', 2)]
+      list = [ActiveRecord::Migration.new("Foo", 1), ActiveRecord::Migration.new("Bar", 2)]
       ActiveRecord::Migrator.new(:up, list, 3).run
     end
+
+    assert_raises(ActiveRecord::UnknownMigrationVersionError) do
+      list = [ActiveRecord::Migration.new("Foo", 1), ActiveRecord::Migration.new("Bar", 2)]
+      ActiveRecord::Migrator.new(:up, list, -1).run
+    end
+
+    assert_raises(ActiveRecord::UnknownMigrationVersionError) do
+      list = [ActiveRecord::Migration.new("Foo", 1), ActiveRecord::Migration.new("Bar", 2)]
+      ActiveRecord::Migrator.new(:up, list, 0).run
+    end
+
+    assert_raises(ActiveRecord::UnknownMigrationVersionError) do
+      list = [ActiveRecord::Migration.new("Foo", 1), ActiveRecord::Migration.new("Bar", 2)]
+      ActiveRecord::Migrator.new(:up, list, 3).migrate
+    end
+
+    assert_raises(ActiveRecord::UnknownMigrationVersionError) do
+      list = [ActiveRecord::Migration.new("Foo", 1), ActiveRecord::Migration.new("Bar", 2)]
+      ActiveRecord::Migrator.new(:up, list, -1).migrate
+    end
   end
 
   def test_finds_migrations
-    migrations = ActiveRecord::Migrator.migrations(MIGRATIONS_ROOT + "/valid")
+    migrations = ActiveRecord::MigrationContext.new(MIGRATIONS_ROOT + "/valid").migrations
 
-    [[1, 'ValidPeopleHaveLastNames'], [2, 'WeNeedReminders'], [3, 'InnocentJointable']].each_with_index do |pair, i|
+    [[1, "ValidPeopleHaveLastNames"], [2, "WeNeedReminders"], [3, "InnocentJointable"]].each_with_index do |pair, i|
       assert_equal migrations[i].version, pair.first
       assert_equal migrations[i].name, pair.last
     end
   end
 
   def test_finds_migrations_in_subdirectories
-    migrations = ActiveRecord::Migrator.migrations(MIGRATIONS_ROOT + "/valid_with_subdirectories")
+    migrations = ActiveRecord::MigrationContext.new(MIGRATIONS_ROOT + "/valid_with_subdirectories").migrations
 
-    [[1, 'ValidPeopleHaveLastNames'], [2, 'WeNeedReminders'], [3, 'InnocentJointable']].each_with_index do |pair, i|
+    [[1, "ValidPeopleHaveLastNames"], [2, "WeNeedReminders"], [3, "InnocentJointable"]].each_with_index do |pair, i|
       assert_equal migrations[i].version, pair.first
       assert_equal migrations[i].name, pair.last
     end
   end
 
   def test_finds_migrations_from_two_directories
-    directories = [MIGRATIONS_ROOT + '/valid_with_timestamps', MIGRATIONS_ROOT + '/to_copy_with_timestamps']
-    migrations = ActiveRecord::Migrator.migrations directories
+    directories = [MIGRATIONS_ROOT + "/valid_with_timestamps", MIGRATIONS_ROOT + "/to_copy_with_timestamps"]
+    migrations = ActiveRecord::MigrationContext.new(directories).migrations
 
     [[20090101010101, "PeopleHaveHobbies"],
      [20090101010202, "PeopleHaveDescriptions"],
      [20100101010101, "ValidWithTimestampsPeopleHaveLastNames"],
      [20100201010101, "ValidWithTimestampsWeNeedReminders"],
      [20100301010101, "ValidWithTimestampsInnocentJointable"]].each_with_index do |pair, i|
-      assert_equal pair.first, migrations[i].version
-      assert_equal pair.last, migrations[i].name
+       assert_equal pair.first, migrations[i].version
+       assert_equal pair.last, migrations[i].name
      end
   end
 
   def test_finds_migrations_in_numbered_directory
-    migrations = ActiveRecord::Migrator.migrations [MIGRATIONS_ROOT + '/10_urban']
+    migrations = ActiveRecord::MigrationContext.new(MIGRATIONS_ROOT + "/10_urban").migrations
     assert_equal 9, migrations[0].version
-    assert_equal 'AddExpressions', migrations[0].name
+    assert_equal "AddExpressions", migrations[0].name
   end
 
   def test_relative_migrations
     list = Dir.chdir(MIGRATIONS_ROOT) do
-      ActiveRecord::Migrator.migrations("valid")
+      ActiveRecord::MigrationContext.new("valid").migrations
     end
 
     migration_proxy = list.find { |item|
-      item.name == 'ValidPeopleHaveLastNames'
+      item.name == "ValidPeopleHaveLastNames"
     }
-    assert migration_proxy, 'should find pending migration'
+    assert migration_proxy, "should find pending migration"
   end
 
   def test_finds_pending_migrations
-    ActiveRecord::SchemaMigration.create!(:version => '1')
-    migration_list = [ActiveRecord::Migration.new('foo', 1), ActiveRecord::Migration.new('bar', 3)]
+    ActiveRecord::SchemaMigration.create!(version: "1")
+    migration_list = [ActiveRecord::Migration.new("foo", 1), ActiveRecord::Migration.new("bar", 3)]
     migrations = ActiveRecord::Migrator.new(:up, migration_list).pending_migrations
 
     assert_equal 1, migrations.size
     assert_equal migration_list.last, migrations.first
   end
 
+  def test_migrations_status
+    path = MIGRATIONS_ROOT + "/valid"
+
+    ActiveRecord::SchemaMigration.create(version: 2)
+    ActiveRecord::SchemaMigration.create(version: 10)
+
+    assert_equal [
+      ["down", "001", "Valid people have last names"],
+      ["up",   "002", "We need reminders"],
+      ["down", "003", "Innocent jointable"],
+      ["up",   "010", "********** NO FILE **********"],
+    ], ActiveRecord::MigrationContext.new(path).migrations_status
+  end
+
+  def test_migrations_status_in_subdirectories
+    path = MIGRATIONS_ROOT + "/valid_with_subdirectories"
+
+    ActiveRecord::SchemaMigration.create(version: 2)
+    ActiveRecord::SchemaMigration.create(version: 10)
+
+    assert_equal [
+      ["down", "001", "Valid people have last names"],
+      ["up",   "002", "We need reminders"],
+      ["down", "003", "Innocent jointable"],
+      ["up",   "010", "********** NO FILE **********"],
+    ], ActiveRecord::MigrationContext.new(path).migrations_status
+  end
+
+  def test_migrations_status_with_schema_define_in_subdirectories
+    path = MIGRATIONS_ROOT + "/valid_with_subdirectories"
+    prev_paths = ActiveRecord::Migrator.migrations_paths
+    ActiveRecord::Migrator.migrations_paths = path
+
+    ActiveRecord::Schema.define(version: 3) do
+    end
+
+    assert_equal [
+      ["up", "001", "Valid people have last names"],
+      ["up", "002", "We need reminders"],
+      ["up", "003", "Innocent jointable"],
+    ], ActiveRecord::MigrationContext.new(path).migrations_status
+  ensure
+    ActiveRecord::Migrator.migrations_paths = prev_paths
+  end
+
+  def test_migrations_status_from_two_directories
+    paths = [MIGRATIONS_ROOT + "/valid_with_timestamps", MIGRATIONS_ROOT + "/to_copy_with_timestamps"]
+
+    ActiveRecord::SchemaMigration.create(version: "20100101010101")
+    ActiveRecord::SchemaMigration.create(version: "20160528010101")
+
+    assert_equal [
+      ["down", "20090101010101", "People have hobbies"],
+      ["down", "20090101010202", "People have descriptions"],
+      ["up",   "20100101010101", "Valid with timestamps people have last names"],
+      ["down", "20100201010101", "Valid with timestamps we need reminders"],
+      ["down", "20100301010101", "Valid with timestamps innocent jointable"],
+      ["up",   "20160528010101", "********** NO FILE **********"],
+    ], ActiveRecord::MigrationContext.new(paths).migrations_status
+  end
+
   def test_migrator_interleaved_migrations
-    pass_one = [Sensor.new('One', 1)]
+    pass_one = [Sensor.new("One", 1)]
 
     ActiveRecord::Migrator.new(:up, pass_one).migrate
     assert pass_one.first.went_up
     assert_not pass_one.first.went_down
 
-    pass_two = [Sensor.new('One', 1), Sensor.new('Three', 3)]
+    pass_two = [Sensor.new("One", 1), Sensor.new("Three", 3)]
     ActiveRecord::Migrator.new(:up, pass_two).migrate
     assert_not pass_two[0].went_up
     assert pass_two[1].went_up
     assert pass_two.all? { |x| !x.went_down }
 
-    pass_three = [Sensor.new('One', 1),
-                  Sensor.new('Two', 2),
-                  Sensor.new('Three', 3)]
+    pass_three = [Sensor.new("One", 1),
+                  Sensor.new("Two", 2),
+                  Sensor.new("Three", 3)]
 
     ActiveRecord::Migrator.new(:down, pass_three).migrate
     assert pass_three[0].went_down
@@ -148,25 +232,28 @@ class MigratorTest < ActiveRecord::TestCase
 
   def test_up_calls_up
     migrations = [Sensor.new(nil, 0), Sensor.new(nil, 1), Sensor.new(nil, 2)]
-    ActiveRecord::Migrator.new(:up, migrations).migrate
+    migrator = ActiveRecord::Migrator.new(:up, migrations)
+    migrator.migrate
     assert migrations.all?(&:went_up)
     assert migrations.all? { |m| !m.went_down }
-    assert_equal 2, ActiveRecord::Migrator.current_version
+    assert_equal 2, migrator.current_version
   end
 
   def test_down_calls_down
     test_up_calls_up
 
     migrations = [Sensor.new(nil, 0), Sensor.new(nil, 1), Sensor.new(nil, 2)]
-    ActiveRecord::Migrator.new(:down, migrations).migrate
+    migrator = ActiveRecord::Migrator.new(:down, migrations)
+    migrator.migrate
     assert migrations.all? { |m| !m.went_up }
     assert migrations.all?(&:went_down)
-    assert_equal 0, ActiveRecord::Migrator.current_version
+    assert_equal 0, migrator.current_version
   end
 
   def test_current_version
-    ActiveRecord::SchemaMigration.create!(:version => '1000')
-    assert_equal 1000, ActiveRecord::Migrator.current_version
+    ActiveRecord::SchemaMigration.create!(version: "1000")
+    migrator = ActiveRecord::MigrationContext.new("db/migrate")
+    assert_equal 1000, migrator.current_version
   end
 
   def test_migrator_one_up
@@ -205,38 +292,42 @@ class MigratorTest < ActiveRecord::TestCase
 
   def test_migrator_double_up
     calls, migrations = sensors(3)
-    assert_equal(0, ActiveRecord::Migrator.current_version)
+    migrator = ActiveRecord::Migrator.new(:up, migrations, 1)
+    assert_equal(0, migrator.current_version)
 
-    ActiveRecord::Migrator.new(:up, migrations, 1).migrate
+    migrator.migrate
     assert_equal [[:up, 1]], calls
     calls.clear
 
-    ActiveRecord::Migrator.new(:up, migrations, 1).migrate
+    migrator.migrate
     assert_equal [], calls
   end
 
   def test_migrator_double_down
     calls, migrations = sensors(3)
+    migrator = ActiveRecord::Migrator.new(:up, migrations, 1)
 
-    assert_equal(0, ActiveRecord::Migrator.current_version)
+    assert_equal 0, migrator.current_version
 
-    ActiveRecord::Migrator.new(:up, migrations, 1).run
+    migrator.run
     assert_equal [[:up, 1]], calls
     calls.clear
 
-    ActiveRecord::Migrator.new(:down, migrations, 1).run
+    migrator = ActiveRecord::Migrator.new(:down, migrations, 1)
+    migrator.run
     assert_equal [[:down, 1]], calls
     calls.clear
 
-    ActiveRecord::Migrator.new(:down, migrations, 1).run
+    migrator.run
     assert_equal [], calls
 
-    assert_equal(0, ActiveRecord::Migrator.current_version)
+    assert_equal 0, migrator.current_version
   end
 
   def test_migrator_verbosity
     _, migrations = sensors(3)
 
+    ActiveRecord::Migration.verbose = true
     ActiveRecord::Migrator.new(:up, migrations, 1).migrate
     assert_not_equal 0, ActiveRecord::Migration.message_count
 
@@ -249,7 +340,6 @@ class MigratorTest < ActiveRecord::TestCase
   def test_migrator_verbosity_off
     _, migrations = sensors(3)
 
-    ActiveRecord::Migration.message_count = 0
     ActiveRecord::Migration.verbose = false
     ActiveRecord::Migrator.new(:up, migrations, 1).migrate
     assert_equal 0, ActiveRecord::Migration.message_count
@@ -277,112 +367,142 @@ class MigratorTest < ActiveRecord::TestCase
 
   def test_migrator_going_down_due_to_version_target
     calls, migrator = migrator_class(3)
+    migrator = migrator.new("valid")
 
-    migrator.up("valid", 1)
+    migrator.up(1)
     assert_equal [[:up, 1]], calls
     calls.clear
 
-    migrator.migrate("valid", 0)
+    migrator.migrate(0)
     assert_equal [[:down, 1]], calls
     calls.clear
 
-    migrator.migrate("valid")
+    migrator.migrate
     assert_equal [[:up, 1], [:up, 2], [:up, 3]], calls
   end
 
+  def test_migrator_output_when_running_multiple_migrations
+    _, migrator = migrator_class(3)
+    migrator = migrator.new("valid")
+
+    result = migrator.migrate
+    assert_equal(3, result.count)
+
+    # Nothing migrated from duplicate run
+    result = migrator.migrate
+    assert_equal(0, result.count)
+
+    result = migrator.rollback
+    assert_equal(1, result.count)
+  end
+
+  def test_migrator_output_when_running_single_migration
+    _, migrator = migrator_class(1)
+    migrator = migrator.new("valid")
+
+    result = migrator.run(:up, 1)
+
+    assert_equal(1, result.version)
+  end
+
   def test_migrator_rollback
     _, migrator = migrator_class(3)
+    migrator = migrator.new("valid")
 
-    migrator.migrate("valid")
-    assert_equal(3, ActiveRecord::Migrator.current_version)
+    migrator.migrate
+    assert_equal(3, migrator.current_version)
 
-    migrator.rollback("valid")
-    assert_equal(2, ActiveRecord::Migrator.current_version)
+    migrator.rollback
+    assert_equal(2, migrator.current_version)
 
-    migrator.rollback("valid")
-    assert_equal(1, ActiveRecord::Migrator.current_version)
+    migrator.rollback
+    assert_equal(1, migrator.current_version)
 
-    migrator.rollback("valid")
-    assert_equal(0, ActiveRecord::Migrator.current_version)
+    migrator.rollback
+    assert_equal(0, migrator.current_version)
 
-    migrator.rollback("valid")
-    assert_equal(0, ActiveRecord::Migrator.current_version)
+    migrator.rollback
+    assert_equal(0, migrator.current_version)
   end
 
   def test_migrator_db_has_no_schema_migrations_table
     _, migrator = migrator_class(3)
+    migrator = migrator.new("valid")
 
     ActiveRecord::Base.connection.drop_table "schema_migrations", if_exists: true
-    assert_not ActiveRecord::Base.connection.table_exists?('schema_migrations')
-    migrator.migrate("valid", 1)
-    assert ActiveRecord::Base.connection.table_exists?('schema_migrations')
+    assert_not ActiveRecord::Base.connection.table_exists?("schema_migrations")
+    migrator.migrate(1)
+    assert ActiveRecord::Base.connection.table_exists?("schema_migrations")
   end
 
   def test_migrator_forward
     _, migrator = migrator_class(3)
-    migrator.migrate("/valid", 1)
-    assert_equal(1, ActiveRecord::Migrator.current_version)
+    migrator = migrator.new("/valid")
+    migrator.migrate(1)
+    assert_equal(1, migrator.current_version)
 
-    migrator.forward("/valid", 2)
-    assert_equal(3, ActiveRecord::Migrator.current_version)
+    migrator.forward(2)
+    assert_equal(3, migrator.current_version)
 
-    migrator.forward("/valid")
-    assert_equal(3, ActiveRecord::Migrator.current_version)
+    migrator.forward
+    assert_equal(3, migrator.current_version)
   end
 
   def test_only_loads_pending_migrations
     # migrate up to 1
-    ActiveRecord::SchemaMigration.create!(:version => '1')
+    ActiveRecord::SchemaMigration.create!(version: "1")
 
     calls, migrator = migrator_class(3)
-    migrator.migrate("valid", nil)
+    migrator = migrator.new("valid")
+    migrator.migrate
 
     assert_equal [[:up, 2], [:up, 3]], calls
   end
 
   def test_get_all_versions
     _, migrator = migrator_class(3)
+    migrator = migrator.new("valid")
 
-    migrator.migrate("valid")
-    assert_equal([1,2,3], ActiveRecord::Migrator.get_all_versions)
+    migrator.migrate
+    assert_equal([1, 2, 3], migrator.get_all_versions)
 
-    migrator.rollback("valid")
-    assert_equal([1,2], ActiveRecord::Migrator.get_all_versions)
+    migrator.rollback
+    assert_equal([1, 2], migrator.get_all_versions)
 
-    migrator.rollback("valid")
-    assert_equal([1], ActiveRecord::Migrator.get_all_versions)
+    migrator.rollback
+    assert_equal([1], migrator.get_all_versions)
 
-    migrator.rollback("valid")
-    assert_equal([], ActiveRecord::Migrator.get_all_versions)
+    migrator.rollback
+    assert_equal([], migrator.get_all_versions)
   end
 
   private
-  def m(name, version)
-    x = Sensor.new name, version
-    x.extend(Module.new {
-      define_method(:up) { yield(:up, x); super() }
-      define_method(:down) { yield(:down, x); super() }
-    }) if block_given?
-  end
-
-  def sensors(count)
-    calls = []
-    migrations = count.times.map { |i|
-      m(nil, i + 1) { |c,migration|
-        calls << [c, migration.version]
+    def m(name, version)
+      x = Sensor.new name, version
+      x.extend(Module.new {
+        define_method(:up) { yield(:up, x); super() }
+        define_method(:down) { yield(:down, x); super() }
+      }) if block_given?
+    end
+
+    def sensors(count)
+      calls = []
+      migrations = count.times.map { |i|
+        m(nil, i + 1) { |c, migration|
+          calls << [c, migration.version]
+        }
       }
-    }
-    [calls, migrations]
-  end
+      [calls, migrations]
+    end
 
-  def migrator_class(count)
-    calls, migrations = sensors(count)
+    def migrator_class(count)
+      calls, migrations = sensors(count)
 
-    migrator = Class.new(ActiveRecord::Migrator).extend(Module.new {
-      define_method(:migrations) { |paths|
-        migrations
+      migrator = Class.new(ActiveRecord::MigrationContext) {
+        define_method(:migrations) { |*|
+          migrations
+        }
       }
-    })
-    [calls, migrator]
-  end
+      [calls, migrator]
+    end
 end
diff --git a/activerecord/test/cases/mixin_test.rb b/activerecord/test/cases/mixin_test.rb
index 7ebdcac711..fdb8ac6ab3 100644
--- a/activerecord/test/cases/mixin_test.rb
+++ b/activerecord/test/cases/mixin_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class Mixin < ActiveRecord::Base
@@ -10,10 +12,6 @@ class TouchTest < ActiveRecord::TestCase
     travel_to Time.now
   end
 
-  teardown do
-    travel_back
-  end
-
   def test_update
     stamped = Mixin.new
 
@@ -41,13 +39,12 @@ class TouchTest < ActiveRecord::TestCase
 
     old_updated_at = stamped.updated_at
 
-    travel 5.minutes do
-      stamped.lft_will_change!
-      stamped.save
+    travel 5.minutes
+    stamped.lft_will_change!
+    stamped.save
 
-      assert_equal Time.now, stamped.updated_at
-      assert_equal old_updated_at, stamped.created_at
-    end
+    assert_equal Time.now, stamped.updated_at
+    assert_equal old_updated_at, stamped.created_at
   end
 
   def test_create_turned_off
@@ -64,5 +61,4 @@ class TouchTest < ActiveRecord::TestCase
   ensure
     Mixin.record_timestamps = true
   end
-
 end
diff --git a/activerecord/test/cases/modules_test.rb b/activerecord/test/cases/modules_test.rb
index 7f31325f47..87455e4fcb 100644
--- a/activerecord/test/cases/modules_test.rb
+++ b/activerecord/test/cases/modules_test.rb
@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/company_in_module'
-require 'models/shop'
-require 'models/developer'
-require 'models/computer'
+require "models/company_in_module"
+require "models/shop"
+require "models/developer"
+require "models/computer"
 
 class ModulesTest < ActiveRecord::TestCase
   fixtures :accounts, :companies, :projects, :developers, :collections, :products, :variants
@@ -30,8 +32,8 @@ class ModulesTest < ActiveRecord::TestCase
 
   def test_module_spanning_associations
     firm = MyApplication::Business::Firm.first
-    assert !firm.clients.empty?, "Firm should have clients"
-    assert_nil firm.class.table_name.match('::'), "Firm shouldn't have the module appear in its table name"
+    assert_not firm.clients.empty?, "Firm should have clients"
+    assert_nil firm.class.table_name.match("::"), "Firm shouldn't have the module appear in its table name"
   end
 
   def test_module_spanning_has_and_belongs_to_many_associations
@@ -41,7 +43,7 @@ class ModulesTest < ActiveRecord::TestCase
   end
 
   def test_associations_spanning_cross_modules
-    account = MyApplication::Billing::Account.all.merge!(:order => 'id').first
+    account = MyApplication::Billing::Account.all.merge!(order: "id").first
     assert_kind_of MyApplication::Business::Firm, account.firm
     assert_kind_of MyApplication::Billing::Firm, account.qualified_billing_firm
     assert_kind_of MyApplication::Billing::Firm, account.unqualified_billing_firm
@@ -50,20 +52,20 @@ class ModulesTest < ActiveRecord::TestCase
   end
 
   def test_find_account_and_include_company
-    account = MyApplication::Billing::Account.all.merge!(:includes => :firm).find(1)
+    account = MyApplication::Billing::Account.all.merge!(includes: :firm).find(1)
     assert_kind_of MyApplication::Business::Firm, account.firm
   end
 
   def test_table_name
-    assert_equal 'accounts', MyApplication::Billing::Account.table_name, 'table_name for ActiveRecord model in module'
-    assert_equal 'companies', MyApplication::Business::Client.table_name, 'table_name for ActiveRecord model subclass'
-    assert_equal 'company_contacts', MyApplication::Business::Client::Contact.table_name, 'table_name for ActiveRecord model enclosed by another ActiveRecord model'
+    assert_equal "accounts", MyApplication::Billing::Account.table_name, "table_name for ActiveRecord model in module"
+    assert_equal "companies", MyApplication::Business::Client.table_name, "table_name for ActiveRecord model subclass"
+    assert_equal "company_contacts", MyApplication::Business::Client::Contact.table_name, "table_name for ActiveRecord model enclosed by another ActiveRecord model"
   end
 
   def test_assign_ids
     firm = MyApplication::Business::Firm.first
 
-    assert_nothing_raised NameError, "Should be able to resolve all class constants via reflection" do
+    assert_nothing_raised do
       firm.client_ids = [MyApplication::Business::Client.first.id]
     end
   end
@@ -72,9 +74,9 @@ class ModulesTest < ActiveRecord::TestCase
   def test_eager_loading_in_modules
     clients = []
 
-    assert_nothing_raised NameError, "Should be able to resolve all class constants via reflection" do
-      clients << MyApplication::Business::Client.references(:accounts).merge!(:includes => {:firm => :account}, :where => 'accounts.id IS NOT NULL').find(3)
-      clients << MyApplication::Business::Client.includes(:firm => :account).find(3)
+    assert_nothing_raised do
+      clients << MyApplication::Business::Client.references(:accounts).merge!(includes: { firm: :account }, where: "accounts.id IS NOT NULL").find(3)
+      clients << MyApplication::Business::Client.includes(firm: :account).find(3)
     end
 
     clients.each do |client|
@@ -85,9 +87,9 @@ class ModulesTest < ActiveRecord::TestCase
   end
 
   def test_module_table_name_prefix
-    assert_equal 'prefixed_companies', MyApplication::Business::Prefixed::Company.table_name, 'inferred table_name for ActiveRecord model in module with table_name_prefix'
-    assert_equal 'prefixed_companies', MyApplication::Business::Prefixed::Nested::Company.table_name, 'table_name for ActiveRecord model in nested module with a parent table_name_prefix'
-    assert_equal 'companies', MyApplication::Business::Prefixed::Firm.table_name, 'explicit table_name for ActiveRecord model in module with table_name_prefix should not be prefixed'
+    assert_equal "prefixed_companies", MyApplication::Business::Prefixed::Company.table_name, "inferred table_name for ActiveRecord model in module with table_name_prefix"
+    assert_equal "prefixed_companies", MyApplication::Business::Prefixed::Nested::Company.table_name, "table_name for ActiveRecord model in nested module with a parent table_name_prefix"
+    assert_equal "companies", MyApplication::Business::Prefixed::Firm.table_name, "explicit table_name for ActiveRecord model in module with table_name_prefix should not be prefixed"
   end
 
   def test_module_table_name_prefix_with_global_prefix
@@ -101,21 +103,21 @@ class ModulesTest < ActiveRecord::TestCase
                 MyApplication::Business::Prefixed::Nested::Company,
                 MyApplication::Billing::Account ]
 
-    ActiveRecord::Base.table_name_prefix = 'global_'
+    ActiveRecord::Base.table_name_prefix = "global_"
     classes.each(&:reset_table_name)
-    assert_equal 'global_companies', MyApplication::Business::Company.table_name, 'inferred table_name for ActiveRecord model in module without table_name_prefix'
-    assert_equal 'prefixed_companies', MyApplication::Business::Prefixed::Company.table_name, 'inferred table_name for ActiveRecord model in module with table_name_prefix'
-    assert_equal 'prefixed_companies', MyApplication::Business::Prefixed::Nested::Company.table_name, 'table_name for ActiveRecord model in nested module with a parent table_name_prefix'
-    assert_equal 'companies', MyApplication::Business::Prefixed::Firm.table_name, 'explicit table_name for ActiveRecord model in module with table_name_prefix should not be prefixed'
+    assert_equal "global_companies", MyApplication::Business::Company.table_name, "inferred table_name for ActiveRecord model in module without table_name_prefix"
+    assert_equal "prefixed_companies", MyApplication::Business::Prefixed::Company.table_name, "inferred table_name for ActiveRecord model in module with table_name_prefix"
+    assert_equal "prefixed_companies", MyApplication::Business::Prefixed::Nested::Company.table_name, "table_name for ActiveRecord model in nested module with a parent table_name_prefix"
+    assert_equal "companies", MyApplication::Business::Prefixed::Firm.table_name, "explicit table_name for ActiveRecord model in module with table_name_prefix should not be prefixed"
   ensure
-    ActiveRecord::Base.table_name_prefix = ''
+    ActiveRecord::Base.table_name_prefix = ""
     classes.each(&:reset_table_name)
   end
 
   def test_module_table_name_suffix
-    assert_equal 'companies_suffixed', MyApplication::Business::Suffixed::Company.table_name, 'inferred table_name for ActiveRecord model in module with table_name_suffix'
-    assert_equal 'companies_suffixed', MyApplication::Business::Suffixed::Nested::Company.table_name, 'table_name for ActiveRecord model in nested module with a parent table_name_suffix'
-    assert_equal 'companies', MyApplication::Business::Suffixed::Firm.table_name, 'explicit table_name for ActiveRecord model in module with table_name_suffix should not be suffixed'
+    assert_equal "companies_suffixed", MyApplication::Business::Suffixed::Company.table_name, "inferred table_name for ActiveRecord model in module with table_name_suffix"
+    assert_equal "companies_suffixed", MyApplication::Business::Suffixed::Nested::Company.table_name, "table_name for ActiveRecord model in nested module with a parent table_name_suffix"
+    assert_equal "companies", MyApplication::Business::Suffixed::Firm.table_name, "explicit table_name for ActiveRecord model in module with table_name_suffix should not be suffixed"
   end
 
   def test_module_table_name_suffix_with_global_suffix
@@ -129,14 +131,14 @@ class ModulesTest < ActiveRecord::TestCase
                 MyApplication::Business::Suffixed::Nested::Company,
                 MyApplication::Billing::Account ]
 
-    ActiveRecord::Base.table_name_suffix = '_global'
+    ActiveRecord::Base.table_name_suffix = "_global"
     classes.each(&:reset_table_name)
-    assert_equal 'companies_global', MyApplication::Business::Company.table_name, 'inferred table_name for ActiveRecord model in module without table_name_suffix'
-    assert_equal 'companies_suffixed', MyApplication::Business::Suffixed::Company.table_name, 'inferred table_name for ActiveRecord model in module with table_name_suffix'
-    assert_equal 'companies_suffixed', MyApplication::Business::Suffixed::Nested::Company.table_name, 'table_name for ActiveRecord model in nested module with a parent table_name_suffix'
-    assert_equal 'companies', MyApplication::Business::Suffixed::Firm.table_name, 'explicit table_name for ActiveRecord model in module with table_name_suffix should not be suffixed'
+    assert_equal "companies_global", MyApplication::Business::Company.table_name, "inferred table_name for ActiveRecord model in module without table_name_suffix"
+    assert_equal "companies_suffixed", MyApplication::Business::Suffixed::Company.table_name, "inferred table_name for ActiveRecord model in module with table_name_suffix"
+    assert_equal "companies_suffixed", MyApplication::Business::Suffixed::Nested::Company.table_name, "table_name for ActiveRecord model in nested module with a parent table_name_suffix"
+    assert_equal "companies", MyApplication::Business::Suffixed::Firm.table_name, "explicit table_name for ActiveRecord model in module with table_name_suffix should not be suffixed"
   ensure
-    ActiveRecord::Base.table_name_suffix = ''
+    ActiveRecord::Base.table_name_suffix = ""
     classes.each(&:reset_table_name)
   end
 
@@ -153,7 +155,7 @@ class ModulesTest < ActiveRecord::TestCase
     ActiveRecord::Base.store_full_sti_class = true
 
     collection = Shop::Collection.first
-    assert !collection.products.empty?, "Collection should have products"
+    assert_not collection.products.empty?, "Collection should have products"
     assert_nothing_raised { collection.destroy }
   ensure
     ActiveRecord::Base.store_full_sti_class = old
@@ -164,7 +166,7 @@ class ModulesTest < ActiveRecord::TestCase
     ActiveRecord::Base.store_full_sti_class = true
 
     product = Shop::Product.first
-    assert !product.variants.empty?, "Product should have variants"
+    assert_not product.variants.empty?, "Product should have variants"
     assert_nothing_raised { product.destroy }
   ensure
     ActiveRecord::Base.store_full_sti_class = old
diff --git a/activerecord/test/cases/multiparameter_attributes_test.rb b/activerecord/test/cases/multiparameter_attributes_test.rb
index ae18573126..6f3903eed4 100644
--- a/activerecord/test/cases/multiparameter_attributes_test.rb
+++ b/activerecord/test/cases/multiparameter_attributes_test.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/customer'
+require "models/topic"
+require "models/customer"
 
 class MultiParameterAttributeTest < ActiveRecord::TestCase
   fixtures :topics
@@ -11,15 +13,13 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
     topic.attributes = attributes
     # note that extra #to_date call allows test to pass for Oracle, which
     # treats dates/times the same
-    assert_date_from_db Date.new(2004, 6, 24), topic.last_read.to_date
+    assert_equal Date.new(2004, 6, 24), topic.last_read.to_date
   end
 
   def test_multiparameter_attributes_on_date_with_empty_year
     attributes = { "last_read(1i)" => "", "last_read(2i)" => "6", "last_read(3i)" => "24" }
     topic = Topic.find(1)
     topic.attributes = attributes
-    # note that extra #to_date call allows test to pass for Oracle, which
-    # treats dates/times the same
     assert_nil topic.last_read
   end
 
@@ -27,8 +27,6 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
     attributes = { "last_read(1i)" => "2004", "last_read(2i)" => "", "last_read(3i)" => "24" }
     topic = Topic.find(1)
     topic.attributes = attributes
-    # note that extra #to_date call allows test to pass for Oracle, which
-    # treats dates/times the same
     assert_nil topic.last_read
   end
 
@@ -36,8 +34,6 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
     attributes = { "last_read(1i)" => "2004", "last_read(2i)" => "6", "last_read(3i)" => "" }
     topic = Topic.find(1)
     topic.attributes = attributes
-    # note that extra #to_date call allows test to pass for Oracle, which
-    # treats dates/times the same
     assert_nil topic.last_read
   end
 
@@ -45,8 +41,6 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
     attributes = { "last_read(1i)" => "", "last_read(2i)" => "6", "last_read(3i)" => "" }
     topic = Topic.find(1)
     topic.attributes = attributes
-    # note that extra #to_date call allows test to pass for Oracle, which
-    # treats dates/times the same
     assert_nil topic.last_read
   end
 
@@ -54,8 +48,6 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
     attributes = { "last_read(1i)" => "2004", "last_read(2i)" => "", "last_read(3i)" => "" }
     topic = Topic.find(1)
     topic.attributes = attributes
-    # note that extra #to_date call allows test to pass for Oracle, which
-    # treats dates/times the same
     assert_nil topic.last_read
   end
 
@@ -63,8 +55,6 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
     attributes = { "last_read(1i)" => "", "last_read(2i)" => "", "last_read(3i)" => "24" }
     topic = Topic.find(1)
     topic.attributes = attributes
-    # note that extra #to_date call allows test to pass for Oracle, which
-    # treats dates/times the same
     assert_nil topic.last_read
   end
 
@@ -214,6 +204,20 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
     Topic.reset_column_information
   end
 
+  def test_multiparameter_attributes_on_time_with_time_zone_aware_attributes_and_invalid_time_params
+    with_timezone_config aware_attributes: true do
+      Topic.reset_column_information
+      attributes = {
+        "written_on(1i)" => "2004", "written_on(2i)" => "", "written_on(3i)" => ""
+      }
+      topic = Topic.find(1)
+      topic.attributes = attributes
+      assert_nil topic.written_on
+    end
+  ensure
+    Topic.reset_column_information
+  end
+
   def test_multiparameter_attributes_on_time_with_time_zone_aware_attributes_false
     with_timezone_config default: :local, aware_attributes: false, zone: -28800 do
       attributes = {
@@ -223,7 +227,7 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
       topic = Topic.find(1)
       topic.attributes = attributes
       assert_equal Time.local(2004, 6, 24, 16, 24, 0), topic.written_on
-      assert_equal false, topic.written_on.respond_to?(:time_zone)
+      assert_not_respond_to topic.written_on, :time_zone
     end
   end
 
@@ -238,7 +242,7 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
       topic = Topic.find(1)
       topic.attributes = attributes
       assert_equal Time.utc(2004, 6, 24, 16, 24, 0), topic.written_on
-      assert_equal false, topic.written_on.respond_to?(:time_zone)
+      assert_not_respond_to topic.written_on, :time_zone
     end
   ensure
     Topic.skip_time_zone_conversion_for_attributes = []
@@ -257,11 +261,24 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
         topic = Topic.find(1)
         topic.attributes = attributes
         assert_equal Time.zone.local(2000, 1, 1, 16, 24, 0), topic.bonus_time
-        assert_not topic.bonus_time.utc?
+        assert_not_predicate topic.bonus_time, :utc?
+
+        attributes = {
+          "written_on(1i)" => "2000", "written_on(2i)" => "", "written_on(3i)" => "",
+          "written_on(4i)" => "", "written_on(5i)" => ""
+        }
+        topic.attributes = attributes
+        assert_nil topic.written_on
       end
     ensure
       Topic.reset_column_information
     end
+
+    def test_multiparameter_attributes_setting_time_attribute
+      topic = Topic.new("bonus_time(4i)" => "01", "bonus_time(5i)" => "05")
+      assert_equal 1, topic.bonus_time.hour
+      assert_equal 5, topic.bonus_time.min
+    end
   end
 
   def test_multiparameter_attributes_on_time_with_empty_seconds
@@ -276,16 +293,15 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
     end
   end
 
-  unless current_adapter? :OracleAdapter
-    def test_multiparameter_attributes_setting_time_attribute
-      topic = Topic.new( "bonus_time(4i)"=> "01", "bonus_time(5i)" => "05" )
-      assert_equal 1, topic.bonus_time.hour
-      assert_equal 5, topic.bonus_time.min
-    end
+  def test_multiparameter_attributes_setting_date_attribute
+    topic = Topic.new("written_on(1i)" => "1952", "written_on(2i)" => "3", "written_on(3i)" => "11")
+    assert_equal 1952, topic.written_on.year
+    assert_equal 3, topic.written_on.month
+    assert_equal 11, topic.written_on.day
   end
 
-  def test_multiparameter_attributes_setting_date_attribute
-    topic = Topic.new( "written_on(1i)" => "1952", "written_on(2i)" => "3", "written_on(3i)" => "11" )
+  def test_create_with_multiparameter_attributes_setting_date_attribute
+    topic = Topic.create_with("written_on(1i)" => "1952", "written_on(2i)" => "3", "written_on(3i)" => "11").new
     assert_equal 1952, topic.written_on.year
     assert_equal 3, topic.written_on.month
     assert_equal 11, topic.written_on.day
@@ -293,11 +309,25 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
 
   def test_multiparameter_attributes_setting_date_and_time_attribute
     topic = Topic.new(
-        "written_on(1i)" => "1952",
-        "written_on(2i)" => "3",
-        "written_on(3i)" => "11",
-        "written_on(4i)" => "13",
-        "written_on(5i)" => "55")
+      "written_on(1i)" => "1952",
+      "written_on(2i)" => "3",
+      "written_on(3i)" => "11",
+      "written_on(4i)" => "13",
+      "written_on(5i)" => "55")
+    assert_equal 1952, topic.written_on.year
+    assert_equal 3, topic.written_on.month
+    assert_equal 11, topic.written_on.day
+    assert_equal 13, topic.written_on.hour
+    assert_equal 55, topic.written_on.min
+  end
+
+  def test_create_with_multiparameter_attributes_setting_date_and_time_attribute
+    topic = Topic.create_with(
+      "written_on(1i)" => "1952",
+      "written_on(2i)" => "3",
+      "written_on(3i)" => "11",
+      "written_on(4i)" => "13",
+      "written_on(5i)" => "55").new
     assert_equal 1952, topic.written_on.year
     assert_equal 3, topic.written_on.month
     assert_equal 11, topic.written_on.day
@@ -306,8 +336,8 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
   end
 
   def test_multiparameter_attributes_setting_time_but_not_date_on_date_field
-    assert_raise( ActiveRecord::MultiparameterAssignmentErrors ) do
-      Topic.new( "written_on(4i)" => "13", "written_on(5i)" => "55" )
+    assert_raise(ActiveRecord::MultiparameterAssignmentErrors) do
+      Topic.new("written_on(4i)" => "13", "written_on(5i)" => "55")
     end
   end
 
@@ -355,4 +385,15 @@ class MultiParameterAttributeTest < ActiveRecord::TestCase
 
     assert_equal("address", ex.errors[0].attribute)
   end
+
+  def test_multiparameter_assigned_attributes_did_not_come_from_user
+    topic = Topic.new(
+      "written_on(1i)" => "1952",
+      "written_on(2i)" => "3",
+      "written_on(3i)" => "11",
+      "written_on(4i)" => "13",
+      "written_on(5i)" => "55",
+    )
+    assert_not_predicate topic, :written_on_came_from_user?
+  end
 end
diff --git a/activerecord/test/cases/multiple_db_test.rb b/activerecord/test/cases/multiple_db_test.rb
index 39cdcf5403..192d2f5251 100644
--- a/activerecord/test/cases/multiple_db_test.rb
+++ b/activerecord/test/cases/multiple_db_test.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/entrant'
-require 'models/bird'
-require 'models/course'
+require "models/entrant"
+require "models/bird"
+require "models/course"
 
 class MultipleDbTest < ActiveRecord::TestCase
   self.use_transactional_tests = false
@@ -24,6 +26,13 @@ class MultipleDbTest < ActiveRecord::TestCase
     assert_equal(ActiveRecord::Base.connection, Entrant.connection)
   end
 
+  def test_swapping_the_connection
+    old_spec_name, Course.connection_specification_name = Course.connection_specification_name, "primary"
+    assert_equal(Entrant.connection, Course.connection)
+  ensure
+    Course.connection_specification_name = old_spec_name
+  end
+
   def test_find
     c1 = Course.find(1)
     assert_equal "Ruby Development", c1.name
@@ -53,7 +62,7 @@ class MultipleDbTest < ActiveRecord::TestCase
 
     ActiveSupport::Dependencies.clear
     Object.send(:remove_const, :Course)
-    require_dependency 'models/course'
+    require_dependency "models/course"
 
     assert Course.connection
   end
@@ -83,14 +92,9 @@ class MultipleDbTest < ActiveRecord::TestCase
     assert_equal "Ruby Developer", Entrant.find(1).name
   end
 
-  def test_arel_table_engines
-    assert_not_equal Entrant.arel_engine, Bird.arel_engine
-    assert_not_equal Entrant.arel_engine, Course.arel_engine
-  end
-
   def test_connection
-    assert_equal Entrant.arel_engine.connection, Bird.arel_engine.connection
-    assert_not_equal Entrant.arel_engine.connection, Course.arel_engine.connection
+    assert_same Entrant.connection, Bird.connection
+    assert_not_same Entrant.connection, Course.connection
   end
 
   unless in_memory_db?
@@ -104,7 +108,7 @@ class MultipleDbTest < ActiveRecord::TestCase
     def test_associations_should_work_when_model_has_no_connection
       begin
         ActiveRecord::Base.remove_connection
-        assert_nothing_raised ActiveRecord::ConnectionNotEstablished do
+        assert_nothing_raised do
           College.first.courses.first
         end
       ensure
diff --git a/activerecord/test/cases/nested_attributes_test.rb b/activerecord/test/cases/nested_attributes_test.rb
index d72225f3d3..bb1c1ea17d 100644
--- a/activerecord/test/cases/nested_attributes_test.rb
+++ b/activerecord/test/cases/nested_attributes_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "models/pirate"
 require "models/ship"
@@ -9,11 +11,11 @@ require "models/man"
 require "models/interest"
 require "models/owner"
 require "models/pet"
-require 'active_support/hash_with_indifferent_access'
+require "active_support/hash_with_indifferent_access"
 
 class TestNestedAttributesInGeneral < ActiveRecord::TestCase
   teardown do
-    Pirate.accepts_nested_attributes_for :ship, :allow_destroy => true, :reject_if => proc(&:empty?)
+    Pirate.accepts_nested_attributes_for :ship, allow_destroy: true, reject_if: proc(&:empty?)
   end
 
   def test_base_should_have_an_empty_nested_attributes_options
@@ -30,28 +32,28 @@ class TestNestedAttributesInGeneral < ActiveRecord::TestCase
   end
 
   def test_should_not_build_a_new_record_using_reject_all_even_if_destroy_is_given
-    pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    pirate.birds_with_reject_all_blank_attributes = [{:name => '', :color => '', :_destroy => '0'}]
+    pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    pirate.birds_with_reject_all_blank_attributes = [{ name: "", color: "", _destroy: "0" }]
     pirate.save!
 
-    assert pirate.birds_with_reject_all_blank.empty?
+    assert_empty pirate.birds_with_reject_all_blank
   end
 
   def test_should_not_build_a_new_record_if_reject_all_blank_returns_false
-    pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    pirate.birds_with_reject_all_blank_attributes = [{:name => '', :color => ''}]
+    pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    pirate.birds_with_reject_all_blank_attributes = [{ name: "", color: "" }]
     pirate.save!
 
-    assert pirate.birds_with_reject_all_blank.empty?
+    assert_empty pirate.birds_with_reject_all_blank
   end
 
   def test_should_build_a_new_record_if_reject_all_blank_does_not_return_false
-    pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    pirate.birds_with_reject_all_blank_attributes = [{:name => 'Tweetie', :color => ''}]
+    pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    pirate.birds_with_reject_all_blank_attributes = [{ name: "Tweetie", color: "" }]
     pirate.save!
 
     assert_equal 1, pirate.birds_with_reject_all_blank.count
-    assert_equal 'Tweetie', pirate.birds_with_reject_all_blank.first.name
+    assert_equal "Tweetie", pirate.birds_with_reject_all_blank.first.name
   end
 
   def test_should_raise_an_ArgumentError_for_non_existing_associations
@@ -61,114 +63,134 @@ class TestNestedAttributesInGeneral < ActiveRecord::TestCase
     assert_equal "No association found for name `honesty'. Has it been defined yet?", exception.message
   end
 
+  def test_should_raise_an_UnknownAttributeError_for_non_existing_nested_attributes
+    exception = assert_raise ActiveModel::UnknownAttributeError do
+      Pirate.new(ship_attributes: { sail: true })
+    end
+    assert_equal "unknown attribute 'sail' for Ship.", exception.message
+  end
+
   def test_should_disable_allow_destroy_by_default
     Pirate.accepts_nested_attributes_for :ship
 
     pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
-    ship = pirate.create_ship(name: 'Nights Dirty Lightning')
+    ship = pirate.create_ship(name: "Nights Dirty Lightning")
 
-    pirate.update(ship_attributes: { '_destroy' => true, :id => ship.id })
+    pirate.update(ship_attributes: { "_destroy" => true, :id => ship.id })
 
-    assert_nothing_raised(ActiveRecord::RecordNotFound) { pirate.ship.reload }
+    assert_nothing_raised { pirate.ship.reload }
   end
 
   def test_a_model_should_respond_to_underscore_destroy_and_return_if_it_is_marked_for_destruction
-    ship = Ship.create!(:name => 'Nights Dirty Lightning')
-    assert !ship._destroy
+    ship = Ship.create!(name: "Nights Dirty Lightning")
+    assert_not ship._destroy
     ship.mark_for_destruction
     assert ship._destroy
   end
 
   def test_reject_if_method_without_arguments
-    Pirate.accepts_nested_attributes_for :ship, :reject_if => :new_record?
+    Pirate.accepts_nested_attributes_for :ship, reject_if: :new_record?
 
-    pirate = Pirate.new(:catchphrase => "Stop wastin' me time")
-    pirate.ship_attributes = { :name => 'Black Pearl' }
-    assert_no_difference('Ship.count') { pirate.save! }
+    pirate = Pirate.new(catchphrase: "Stop wastin' me time")
+    pirate.ship_attributes = { name: "Black Pearl" }
+    assert_no_difference("Ship.count") { pirate.save! }
   end
 
   def test_reject_if_method_with_arguments
-    Pirate.accepts_nested_attributes_for :ship, :reject_if => :reject_empty_ships_on_create
+    Pirate.accepts_nested_attributes_for :ship, reject_if: :reject_empty_ships_on_create
 
-    pirate = Pirate.new(:catchphrase => "Stop wastin' me time")
-    pirate.ship_attributes = { :name => 'Red Pearl', :_reject_me_if_new => true }
-    assert_no_difference('Ship.count') { pirate.save! }
+    pirate = Pirate.new(catchphrase: "Stop wastin' me time")
+    pirate.ship_attributes = { name: "Red Pearl", _reject_me_if_new: true }
+    assert_no_difference("Ship.count") { pirate.save! }
 
     # pirate.reject_empty_ships_on_create returns false for saved pirate records
     # in the previous step note that pirate gets saved but ship fails
-    pirate.ship_attributes = { :name => 'Red Pearl', :_reject_me_if_new => true }
-    assert_difference('Ship.count') { pirate.save! }
+    pirate.ship_attributes = { name: "Red Pearl", _reject_me_if_new: true }
+    assert_difference("Ship.count") { pirate.save! }
   end
 
   def test_reject_if_with_indifferent_keys
-    Pirate.accepts_nested_attributes_for :ship, :reject_if => proc {|attributes| attributes[:name].blank? }
+    Pirate.accepts_nested_attributes_for :ship, reject_if: proc { |attributes| attributes[:name].blank? }
 
-    pirate = Pirate.new(:catchphrase => "Stop wastin' me time")
-    pirate.ship_attributes = { :name => 'Hello Pearl' }
-    assert_difference('Ship.count') { pirate.save! }
+    pirate = Pirate.new(catchphrase: "Stop wastin' me time")
+    pirate.ship_attributes = { name: "Hello Pearl" }
+    assert_difference("Ship.count") { pirate.save! }
   end
 
   def test_reject_if_with_a_proc_which_returns_true_always_for_has_one
-    Pirate.accepts_nested_attributes_for :ship, :reject_if => proc {|attributes| true }
-    pirate = Pirate.new(catchphrase: "Stop wastin' me time")
-    ship = pirate.create_ship(name: 's1')
-    pirate.update({ship_attributes: { name: 's2', id: ship.id } })
-    assert_equal 's1', ship.reload.name
+    Pirate.accepts_nested_attributes_for :ship, reject_if: proc { |attributes| true }
+    pirate = Pirate.create(catchphrase: "Stop wastin' me time")
+    ship = pirate.create_ship(name: "s1")
+    pirate.update(ship_attributes: { name: "s2", id: ship.id })
+    assert_equal "s1", ship.reload.name
   end
 
   def test_reuse_already_built_new_record
     pirate = Pirate.new
     ship_built_first = pirate.build_ship
-    pirate.ship_attributes = { name: 'Ship 1' }
+    pirate.ship_attributes = { name: "Ship 1" }
     assert_equal ship_built_first.object_id, pirate.ship.object_id
   end
 
   def test_do_not_allow_assigning_foreign_key_when_reusing_existing_new_record
     pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
     pirate.build_ship
-    pirate.ship_attributes = { name: 'Ship 1', pirate_id: pirate.id + 1 }
+    pirate.ship_attributes = { name: "Ship 1", pirate_id: pirate.id + 1 }
     assert_equal pirate.id, pirate.ship.pirate_id
   end
 
   def test_reject_if_with_a_proc_which_returns_true_always_for_has_many
-    Man.accepts_nested_attributes_for :interests, :reject_if => proc {|attributes| true }
+    Man.accepts_nested_attributes_for :interests, reject_if: proc { |attributes| true }
     man = Man.create(name: "John")
-    interest = man.interests.create(topic: 'photography')
-    man.update({interests_attributes: { topic: 'gardening', id: interest.id } })
-    assert_equal 'photography', interest.reload.topic
+    interest = man.interests.create(topic: "photography")
+    man.update(interests_attributes: { topic: "gardening", id: interest.id })
+    assert_equal "photography", interest.reload.topic
   end
 
   def test_destroy_works_independent_of_reject_if
-    Man.accepts_nested_attributes_for :interests, :reject_if => proc {|attributes| true }, :allow_destroy => true
+    Man.accepts_nested_attributes_for :interests, reject_if: proc { |attributes| true }, allow_destroy: true
     man = Man.create(name: "Jon")
-    interest = man.interests.create(topic: 'the ladies')
-    man.update({interests_attributes: { _destroy: "1", id: interest.id } })
-    assert man.reload.interests.empty?
+    interest = man.interests.create(topic: "the ladies")
+    man.update(interests_attributes: { _destroy: "1", id: interest.id })
+    assert_empty man.reload.interests
+  end
+
+  def test_reject_if_is_not_short_circuited_if_allow_destroy_is_false
+    Pirate.accepts_nested_attributes_for :ship, reject_if: ->(a) { a[:name] == "The Golden Hind" }, allow_destroy: false
+
+    pirate = Pirate.create!(catchphrase: "Stop wastin' me time", ship_attributes: { name: "White Pearl", _destroy: "1" })
+    assert_equal "White Pearl", pirate.reload.ship.name
+
+    pirate.update!(ship_attributes: { id: pirate.ship.id, name: "The Golden Hind", _destroy: "1" })
+    assert_equal "White Pearl", pirate.reload.ship.name
+
+    pirate.update!(ship_attributes: { id: pirate.ship.id, name: "Black Pearl", _destroy: "1" })
+    assert_equal "Black Pearl", pirate.reload.ship.name
   end
 
   def test_has_many_association_updating_a_single_record
     Man.accepts_nested_attributes_for(:interests)
-    man = Man.create(name: 'John')
-    interest = man.interests.create(topic: 'photography')
-    man.update({interests_attributes: {topic: 'gardening', id: interest.id}})
-    assert_equal 'gardening', interest.reload.topic
+    man = Man.create(name: "John")
+    interest = man.interests.create(topic: "photography")
+    man.update(interests_attributes: { topic: "gardening", id: interest.id })
+    assert_equal "gardening", interest.reload.topic
   end
 
   def test_reject_if_with_blank_nested_attributes_id
     # When using a select list to choose an existing 'ship' id, with include_blank: true
-    Pirate.accepts_nested_attributes_for :ship, :reject_if => proc {|attributes| attributes[:id].blank? }
+    Pirate.accepts_nested_attributes_for :ship, reject_if: proc { |attributes| attributes[:id].blank? }
 
-    pirate = Pirate.new(:catchphrase => "Stop wastin' me time")
-    pirate.ship_attributes = { :id => "" }
-    assert_nothing_raised(ActiveRecord::RecordNotFound) { pirate.save! }
+    pirate = Pirate.new(catchphrase: "Stop wastin' me time")
+    pirate.ship_attributes = { id: "" }
+    assert_nothing_raised { pirate.save! }
   end
 
   def test_first_and_array_index_zero_methods_return_the_same_value_when_nested_attributes_are_set_to_update_existing_record
     Man.accepts_nested_attributes_for(:interests)
-    man = Man.create(:name => "John")
-    interest = man.interests.create :topic => 'gardening'
+    man = Man.create(name: "John")
+    interest = man.interests.create topic: "gardening"
     man = Man.find man.id
-    man.interests_attributes = [{:id => interest.id, :topic => 'gardening'}]
+    man.interests_attributes = [{ id: interest.id, topic: "gardening" }]
     assert_equal man.interests.first.topic, man.interests[0].topic
   end
 
@@ -176,11 +198,11 @@ class TestNestedAttributesInGeneral < ActiveRecord::TestCase
     mean_pirate_class = Class.new(Pirate) do
       accepts_nested_attributes_for :parrot
       def parrot_attributes=(attrs)
-        super(attrs.merge(:color => "blue"))
+        super(attrs.merge(color: "blue"))
       end
     end
     mean_pirate = mean_pirate_class.new
-    mean_pirate.parrot_attributes = { :name => "James" }
+    mean_pirate.parrot_attributes = { name: "James" }
     assert_equal "James", mean_pirate.parrot.name
     assert_equal "blue", mean_pirate.parrot.color
   end
@@ -192,20 +214,32 @@ class TestNestedAttributesInGeneral < ActiveRecord::TestCase
       accepts_nested_attributes_for :parrot
     end
     mean_pirate = mean_pirate_class.new
-    mean_pirate.parrot_attributes = { :name => "James" }
+    mean_pirate.parrot_attributes = { name: "James" }
     assert_equal "James", mean_pirate.parrot.name
   end
+
+  def test_should_not_create_duplicates_with_create_with
+    Man.accepts_nested_attributes_for(:interests)
+
+    assert_difference("Interest.count", 1) do
+      Man.create_with(
+        interests_attributes: [{ topic: "Pirate king" }]
+      ).find_or_create_by!(
+        name: "Monkey D. Luffy"
+      )
+    end
+  end
 end
 
 class TestNestedAttributesOnAHasOneAssociation < ActiveRecord::TestCase
   def setup
-    @pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @ship = @pirate.create_ship(:name => 'Nights Dirty Lightning')
+    @pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @ship = @pirate.create_ship(name: "Nights Dirty Lightning")
   end
 
   def test_should_raise_argument_error_if_trying_to_build_polymorphic_belongs_to
     exception = assert_raise ArgumentError do
-      Treasure.new(:name => 'pearl', :looter_attributes => {:catchphrase => "Arrr"})
+      Treasure.new(name: "pearl", looter_attributes: { catchphrase: "Arrr" })
     end
     assert_equal "Cannot build association `looter'. Are you trying to build a polymorphic one-to-one association?", exception.message
   end
@@ -216,15 +250,15 @@ class TestNestedAttributesOnAHasOneAssociation < ActiveRecord::TestCase
 
   def test_should_build_a_new_record_if_there_is_no_id
     @ship.destroy
-    @pirate.reload.ship_attributes = { :name => 'Davy Jones Gold Dagger' }
+    @pirate.reload.ship_attributes = { name: "Davy Jones Gold Dagger" }
 
-    assert !@pirate.ship.persisted?
-    assert_equal 'Davy Jones Gold Dagger', @pirate.ship.name
+    assert_not_predicate @pirate.ship, :persisted?
+    assert_equal "Davy Jones Gold Dagger", @pirate.ship.name
   end
 
   def test_should_not_build_a_new_record_if_there_is_no_id_and_destroy_is_truthy
     @ship.destroy
-    @pirate.reload.ship_attributes = { :name => 'Davy Jones Gold Dagger', :_destroy => '1' }
+    @pirate.reload.ship_attributes = { name: "Davy Jones Gold Dagger", _destroy: "1" }
 
     assert_nil @pirate.ship
   end
@@ -237,53 +271,54 @@ class TestNestedAttributesOnAHasOneAssociation < ActiveRecord::TestCase
   end
 
   def test_should_replace_an_existing_record_if_there_is_no_id
-    @pirate.reload.ship_attributes = { :name => 'Davy Jones Gold Dagger' }
+    @pirate.reload.ship_attributes = { name: "Davy Jones Gold Dagger" }
 
-    assert !@pirate.ship.persisted?
-    assert_equal 'Davy Jones Gold Dagger', @pirate.ship.name
-    assert_equal 'Nights Dirty Lightning', @ship.name
+    assert_not_predicate @pirate.ship, :persisted?
+    assert_equal "Davy Jones Gold Dagger", @pirate.ship.name
+    assert_equal "Nights Dirty Lightning", @ship.name
   end
 
   def test_should_not_replace_an_existing_record_if_there_is_no_id_and_destroy_is_truthy
-    @pirate.reload.ship_attributes = { :name => 'Davy Jones Gold Dagger', :_destroy => '1' }
+    @pirate.reload.ship_attributes = { name: "Davy Jones Gold Dagger", _destroy: "1" }
 
     assert_equal @ship, @pirate.ship
-    assert_equal 'Nights Dirty Lightning', @pirate.ship.name
+    assert_equal "Nights Dirty Lightning", @pirate.ship.name
   end
 
   def test_should_modify_an_existing_record_if_there_is_a_matching_id
-    @pirate.reload.ship_attributes = { :id => @ship.id, :name => 'Davy Jones Gold Dagger' }
+    @pirate.reload.ship_attributes = { id: @ship.id, name: "Davy Jones Gold Dagger" }
 
     assert_equal @ship, @pirate.ship
-    assert_equal 'Davy Jones Gold Dagger', @pirate.ship.name
+    assert_equal "Davy Jones Gold Dagger", @pirate.ship.name
   end
 
   def test_should_raise_RecordNotFound_if_an_id_is_given_but_doesnt_return_a_record
     exception = assert_raise ActiveRecord::RecordNotFound do
-      @pirate.ship_attributes = { :id => 1234567890 }
+      @pirate.ship_attributes = { id: 1234567890 }
     end
     assert_equal "Couldn't find Ship with ID=1234567890 for Pirate with ID=#{@pirate.id}", exception.message
   end
 
   def test_should_take_a_hash_with_string_keys_and_update_the_associated_model
-    @pirate.reload.ship_attributes = { 'id' => @ship.id, 'name' => 'Davy Jones Gold Dagger' }
+    @pirate.reload.ship_attributes = { "id" => @ship.id, "name" => "Davy Jones Gold Dagger" }
 
     assert_equal @ship, @pirate.ship
-    assert_equal 'Davy Jones Gold Dagger', @pirate.ship.name
+    assert_equal "Davy Jones Gold Dagger", @pirate.ship.name
   end
 
   def test_should_modify_an_existing_record_if_there_is_a_matching_composite_id
-    @ship.stubs(:id).returns('ABC1X')
-    @pirate.ship_attributes = { :id => @ship.id, :name => 'Davy Jones Gold Dagger' }
+    @ship.stub(:id, "ABC1X") do
+      @pirate.ship_attributes = { id: @ship.id, name: "Davy Jones Gold Dagger" }
 
-    assert_equal 'Davy Jones Gold Dagger', @pirate.ship.name
+      assert_equal "Davy Jones Gold Dagger", @pirate.ship.name
+    end
   end
 
   def test_should_destroy_an_existing_record_if_there_is_a_matching_id_and_destroy_is_truthy
     @pirate.ship.destroy
 
-    [1, '1', true, 'true'].each do |truth|
-      ship = @pirate.reload.create_ship(name: 'Mister Pablo')
+    [1, "1", true, "true"].each do |truth|
+      ship = @pirate.reload.create_ship(name: "Mister Pablo")
       @pirate.update(ship_attributes: { id: ship.id, _destroy: truth })
 
       assert_nil @pirate.reload.ship
@@ -292,7 +327,7 @@ class TestNestedAttributesOnAHasOneAssociation < ActiveRecord::TestCase
   end
 
   def test_should_not_destroy_an_existing_record_if_destroy_is_not_truthy
-    [nil, '0', 0, 'false', false].each do |not_truth|
+    [nil, "0", 0, "false", false].each do |not_truth|
       @pirate.update(ship_attributes: { id: @pirate.ship.id, _destroy: not_truth })
 
       assert_equal @ship, @pirate.reload.ship
@@ -300,39 +335,39 @@ class TestNestedAttributesOnAHasOneAssociation < ActiveRecord::TestCase
   end
 
   def test_should_not_destroy_an_existing_record_if_allow_destroy_is_false
-    Pirate.accepts_nested_attributes_for :ship, :allow_destroy => false, :reject_if => proc(&:empty?)
+    Pirate.accepts_nested_attributes_for :ship, allow_destroy: false, reject_if: proc(&:empty?)
 
-    @pirate.update(ship_attributes: { id: @pirate.ship.id, _destroy: '1' })
+    @pirate.update(ship_attributes: { id: @pirate.ship.id, _destroy: "1" })
 
     assert_equal @ship, @pirate.reload.ship
 
-    Pirate.accepts_nested_attributes_for :ship, :allow_destroy => true, :reject_if => proc(&:empty?)
+    Pirate.accepts_nested_attributes_for :ship, allow_destroy: true, reject_if: proc(&:empty?)
   end
 
   def test_should_also_work_with_a_HashWithIndifferentAccess
-    @pirate.ship_attributes = ActiveSupport::HashWithIndifferentAccess.new(:id => @ship.id, :name => 'Davy Jones Gold Dagger')
+    @pirate.ship_attributes = ActiveSupport::HashWithIndifferentAccess.new(id: @ship.id, name: "Davy Jones Gold Dagger")
 
-    assert @pirate.ship.persisted?
-    assert_equal 'Davy Jones Gold Dagger', @pirate.ship.name
+    assert_predicate @pirate.ship, :persisted?
+    assert_equal "Davy Jones Gold Dagger", @pirate.ship.name
   end
 
   def test_should_work_with_update_as_well
-    @pirate.update({ catchphrase: 'Arr', ship_attributes: { id: @ship.id, name: 'Mister Pablo' } })
+    @pirate.update(catchphrase: "Arr", ship_attributes: { id: @ship.id, name: "Mister Pablo" })
     @pirate.reload
 
-    assert_equal 'Arr', @pirate.catchphrase
-    assert_equal 'Mister Pablo', @pirate.ship.name
+    assert_equal "Arr", @pirate.catchphrase
+    assert_equal "Mister Pablo", @pirate.ship.name
   end
 
   def test_should_not_destroy_the_associated_model_until_the_parent_is_saved
-    @pirate.attributes = { :ship_attributes => { :id => @ship.id, :_destroy => '1' } }
+    @pirate.attributes = { ship_attributes: { id: @ship.id, _destroy: "1" } }
 
-    assert !@pirate.ship.destroyed?
-    assert @pirate.ship.marked_for_destruction?
+    assert_not_predicate @pirate.ship, :destroyed?
+    assert_predicate @pirate.ship, :marked_for_destruction?
 
     @pirate.save
 
-    assert @pirate.ship.destroyed?
+    assert_predicate @pirate.ship, :destroyed?
     assert_nil @pirate.reload.ship
   end
 
@@ -341,56 +376,55 @@ class TestNestedAttributesOnAHasOneAssociation < ActiveRecord::TestCase
   end
 
   def test_should_accept_update_only_option
-    @pirate.update(update_only_ship_attributes: { id: @pirate.ship.id, name: 'Mayflower' })
+    @pirate.update(update_only_ship_attributes: { id: @pirate.ship.id, name: "Mayflower" })
   end
 
   def test_should_create_new_model_when_nothing_is_there_and_update_only_is_true
     @ship.delete
 
-    @pirate.reload.update(update_only_ship_attributes: { name: 'Mayflower' })
+    @pirate.reload.update(update_only_ship_attributes: { name: "Mayflower" })
 
     assert_not_nil @pirate.ship
   end
 
   def test_should_update_existing_when_update_only_is_true_and_no_id_is_given
     @ship.delete
-    @ship = @pirate.create_update_only_ship(name: 'Nights Dirty Lightning')
+    @ship = @pirate.create_update_only_ship(name: "Nights Dirty Lightning")
 
-    @pirate.update(update_only_ship_attributes: { name: 'Mayflower' })
+    @pirate.update(update_only_ship_attributes: { name: "Mayflower" })
 
-    assert_equal 'Mayflower', @ship.reload.name
+    assert_equal "Mayflower", @ship.reload.name
     assert_equal @ship, @pirate.reload.ship
   end
 
   def test_should_update_existing_when_update_only_is_true_and_id_is_given
     @ship.delete
-    @ship = @pirate.create_update_only_ship(name: 'Nights Dirty Lightning')
+    @ship = @pirate.create_update_only_ship(name: "Nights Dirty Lightning")
 
-    @pirate.update(update_only_ship_attributes: { name: 'Mayflower', id: @ship.id })
+    @pirate.update(update_only_ship_attributes: { name: "Mayflower", id: @ship.id })
 
-    assert_equal 'Mayflower', @ship.reload.name
+    assert_equal "Mayflower", @ship.reload.name
     assert_equal @ship, @pirate.reload.ship
   end
 
   def test_should_destroy_existing_when_update_only_is_true_and_id_is_given_and_is_marked_for_destruction
-    Pirate.accepts_nested_attributes_for :update_only_ship, :update_only => true, :allow_destroy => true
+    Pirate.accepts_nested_attributes_for :update_only_ship, update_only: true, allow_destroy: true
     @ship.delete
-    @ship = @pirate.create_update_only_ship(name: 'Nights Dirty Lightning')
+    @ship = @pirate.create_update_only_ship(name: "Nights Dirty Lightning")
 
-    @pirate.update(update_only_ship_attributes: { name: 'Mayflower', id: @ship.id, _destroy: true })
+    @pirate.update(update_only_ship_attributes: { name: "Mayflower", id: @ship.id, _destroy: true })
 
     assert_nil @pirate.reload.ship
     assert_raise(ActiveRecord::RecordNotFound) { Ship.find(@ship.id) }
 
-    Pirate.accepts_nested_attributes_for :update_only_ship, :update_only => true, :allow_destroy => false
+    Pirate.accepts_nested_attributes_for :update_only_ship, update_only: true, allow_destroy: false
   end
-
 end
 
 class TestNestedAttributesOnABelongsToAssociation < ActiveRecord::TestCase
   def setup
-    @ship = Ship.new(:name => 'Nights Dirty Lightning')
-    @pirate = @ship.build_pirate(:catchphrase => 'Aye')
+    @ship = Ship.new(name: "Nights Dirty Lightning")
+    @pirate = @ship.build_pirate(catchphrase: "Aye")
     @ship.save!
   end
 
@@ -400,15 +434,15 @@ class TestNestedAttributesOnABelongsToAssociation < ActiveRecord::TestCase
 
   def test_should_build_a_new_record_if_there_is_no_id
     @pirate.destroy
-    @ship.reload.pirate_attributes = { :catchphrase => 'Arr' }
+    @ship.reload.pirate_attributes = { catchphrase: "Arr" }
 
-    assert !@ship.pirate.persisted?
-    assert_equal 'Arr', @ship.pirate.catchphrase
+    assert_not_predicate @ship.pirate, :persisted?
+    assert_equal "Arr", @ship.pirate.catchphrase
   end
 
   def test_should_not_build_a_new_record_if_there_is_no_id_and_destroy_is_truthy
     @pirate.destroy
-    @ship.reload.pirate_attributes = { :catchphrase => 'Arr', :_destroy => '1' }
+    @ship.reload.pirate_attributes = { catchphrase: "Arr", _destroy: "1" }
 
     assert_nil @ship.pirate
   end
@@ -421,52 +455,53 @@ class TestNestedAttributesOnABelongsToAssociation < ActiveRecord::TestCase
   end
 
   def test_should_replace_an_existing_record_if_there_is_no_id
-    @ship.reload.pirate_attributes = { :catchphrase => 'Arr' }
+    @ship.reload.pirate_attributes = { catchphrase: "Arr" }
 
-    assert !@ship.pirate.persisted?
-    assert_equal 'Arr', @ship.pirate.catchphrase
-    assert_equal 'Aye', @pirate.catchphrase
+    assert_not_predicate @ship.pirate, :persisted?
+    assert_equal "Arr", @ship.pirate.catchphrase
+    assert_equal "Aye", @pirate.catchphrase
   end
 
   def test_should_not_replace_an_existing_record_if_there_is_no_id_and_destroy_is_truthy
-    @ship.reload.pirate_attributes = { :catchphrase => 'Arr', :_destroy => '1' }
+    @ship.reload.pirate_attributes = { catchphrase: "Arr", _destroy: "1" }
 
     assert_equal @pirate, @ship.pirate
-    assert_equal 'Aye', @ship.pirate.catchphrase
+    assert_equal "Aye", @ship.pirate.catchphrase
   end
 
   def test_should_modify_an_existing_record_if_there_is_a_matching_id
-    @ship.reload.pirate_attributes = { :id => @pirate.id, :catchphrase => 'Arr' }
+    @ship.reload.pirate_attributes = { id: @pirate.id, catchphrase: "Arr" }
 
     assert_equal @pirate, @ship.pirate
-    assert_equal 'Arr', @ship.pirate.catchphrase
+    assert_equal "Arr", @ship.pirate.catchphrase
   end
 
   def test_should_raise_RecordNotFound_if_an_id_is_given_but_doesnt_return_a_record
     exception = assert_raise ActiveRecord::RecordNotFound do
-      @ship.pirate_attributes = { :id => 1234567890 }
+      @ship.pirate_attributes = { id: 1234567890 }
     end
     assert_equal "Couldn't find Pirate with ID=1234567890 for Ship with ID=#{@ship.id}", exception.message
   end
 
   def test_should_take_a_hash_with_string_keys_and_update_the_associated_model
-    @ship.reload.pirate_attributes = { 'id' => @pirate.id, 'catchphrase' => 'Arr' }
+    @ship.reload.pirate_attributes = { "id" => @pirate.id, "catchphrase" => "Arr" }
 
     assert_equal @pirate, @ship.pirate
-    assert_equal 'Arr', @ship.pirate.catchphrase
+    assert_equal "Arr", @ship.pirate.catchphrase
   end
 
   def test_should_modify_an_existing_record_if_there_is_a_matching_composite_id
-    @pirate.stubs(:id).returns('ABC1X')
-    @ship.pirate_attributes = { :id => @pirate.id, :catchphrase => 'Arr' }
+    @pirate.stub(:id, "ABC1X") do
+      @ship.pirate_attributes = { id: @pirate.id, catchphrase: "Arr" }
 
-    assert_equal 'Arr', @ship.pirate.catchphrase
+      assert_equal "Arr", @ship.pirate.catchphrase
+    end
   end
 
   def test_should_destroy_an_existing_record_if_there_is_a_matching_id_and_destroy_is_truthy
     @ship.pirate.destroy
-    [1, '1', true, 'true'].each do |truth|
-      pirate = @ship.reload.create_pirate(catchphrase: 'Arr')
+    [1, "1", true, "true"].each do |truth|
+      pirate = @ship.reload.create_pirate(catchphrase: "Arr")
       @ship.update(pirate_attributes: { id: pirate.id, _destroy: truth })
       assert_raise(ActiveRecord::RecordNotFound) { pirate.reload }
     end
@@ -487,34 +522,34 @@ class TestNestedAttributesOnABelongsToAssociation < ActiveRecord::TestCase
   end
 
   def test_should_not_destroy_an_existing_record_if_destroy_is_not_truthy
-    [nil, '0', 0, 'false', false].each do |not_truth|
+    [nil, "0", 0, "false", false].each do |not_truth|
       @ship.update(pirate_attributes: { id: @ship.pirate.id, _destroy: not_truth })
-      assert_nothing_raised(ActiveRecord::RecordNotFound) { @ship.pirate.reload }
+      assert_nothing_raised { @ship.pirate.reload }
     end
   end
 
   def test_should_not_destroy_an_existing_record_if_allow_destroy_is_false
-    Ship.accepts_nested_attributes_for :pirate, :allow_destroy => false, :reject_if => proc(&:empty?)
+    Ship.accepts_nested_attributes_for :pirate, allow_destroy: false, reject_if: proc(&:empty?)
 
-    @ship.update(pirate_attributes: { id: @ship.pirate.id, _destroy: '1' })
-    assert_nothing_raised(ActiveRecord::RecordNotFound) { @ship.pirate.reload }
+    @ship.update(pirate_attributes: { id: @ship.pirate.id, _destroy: "1" })
+    assert_nothing_raised { @ship.pirate.reload }
   ensure
-    Ship.accepts_nested_attributes_for :pirate, :allow_destroy => true, :reject_if => proc(&:empty?)
+    Ship.accepts_nested_attributes_for :pirate, allow_destroy: true, reject_if: proc(&:empty?)
   end
 
   def test_should_work_with_update_as_well
-    @ship.update({ name: 'Mister Pablo', pirate_attributes: { catchphrase: 'Arr' } })
+    @ship.update(name: "Mister Pablo", pirate_attributes: { catchphrase: "Arr" })
     @ship.reload
 
-    assert_equal 'Mister Pablo', @ship.name
-    assert_equal 'Arr', @ship.pirate.catchphrase
+    assert_equal "Mister Pablo", @ship.name
+    assert_equal "Arr", @ship.pirate.catchphrase
   end
 
   def test_should_not_destroy_the_associated_model_until_the_parent_is_saved
     pirate = @ship.pirate
 
-    @ship.attributes = { :pirate_attributes => { :id => pirate.id, '_destroy' => true } }
-    assert_nothing_raised(ActiveRecord::RecordNotFound) { Pirate.find(pirate.id) }
+    @ship.attributes = { pirate_attributes: { :id => pirate.id, "_destroy" => true } }
+    assert_nothing_raised { Pirate.find(pirate.id) }
     @ship.save
     assert_raise(ActiveRecord::RecordNotFound) { Pirate.find(pirate.id) }
   end
@@ -525,40 +560,40 @@ class TestNestedAttributesOnABelongsToAssociation < ActiveRecord::TestCase
 
   def test_should_create_new_model_when_nothing_is_there_and_update_only_is_true
     @pirate.delete
-    @ship.reload.attributes = { :update_only_pirate_attributes => { :catchphrase => 'Arr' } }
+    @ship.reload.attributes = { update_only_pirate_attributes: { catchphrase: "Arr" } }
 
-    assert !@ship.update_only_pirate.persisted?
+    assert_not_predicate @ship.update_only_pirate, :persisted?
   end
 
   def test_should_update_existing_when_update_only_is_true_and_no_id_is_given
     @pirate.delete
-    @pirate = @ship.create_update_only_pirate(catchphrase: 'Aye')
+    @pirate = @ship.create_update_only_pirate(catchphrase: "Aye")
 
-    @ship.update(update_only_pirate_attributes: { catchphrase: 'Arr' })
-    assert_equal 'Arr', @pirate.reload.catchphrase
+    @ship.update(update_only_pirate_attributes: { catchphrase: "Arr" })
+    assert_equal "Arr", @pirate.reload.catchphrase
     assert_equal @pirate, @ship.reload.update_only_pirate
   end
 
   def test_should_update_existing_when_update_only_is_true_and_id_is_given
     @pirate.delete
-    @pirate = @ship.create_update_only_pirate(catchphrase: 'Aye')
+    @pirate = @ship.create_update_only_pirate(catchphrase: "Aye")
 
-    @ship.update(update_only_pirate_attributes: { catchphrase: 'Arr', id: @pirate.id })
+    @ship.update(update_only_pirate_attributes: { catchphrase: "Arr", id: @pirate.id })
 
-    assert_equal 'Arr', @pirate.reload.catchphrase
+    assert_equal "Arr", @pirate.reload.catchphrase
     assert_equal @pirate, @ship.reload.update_only_pirate
   end
 
   def test_should_destroy_existing_when_update_only_is_true_and_id_is_given_and_is_marked_for_destruction
-    Ship.accepts_nested_attributes_for :update_only_pirate, :update_only => true, :allow_destroy => true
+    Ship.accepts_nested_attributes_for :update_only_pirate, update_only: true, allow_destroy: true
     @pirate.delete
-    @pirate = @ship.create_update_only_pirate(catchphrase: 'Aye')
+    @pirate = @ship.create_update_only_pirate(catchphrase: "Aye")
 
-    @ship.update(update_only_pirate_attributes: { catchphrase: 'Arr', id: @pirate.id, _destroy: true })
+    @ship.update(update_only_pirate_attributes: { catchphrase: "Arr", id: @pirate.id, _destroy: true })
 
     assert_raise(ActiveRecord::RecordNotFound) { @pirate.reload }
 
-    Ship.accepts_nested_attributes_for :update_only_pirate, :update_only => true, :allow_destroy => false
+    Ship.accepts_nested_attributes_for :update_only_pirate, update_only: true, allow_destroy: false
   end
 end
 
@@ -567,11 +602,17 @@ module NestedAttributesOnACollectionAssociationTests
     assert_respond_to @pirate, association_setter
   end
 
+  def test_should_raise_an_UnknownAttributeError_for_non_existing_nested_attributes_for_has_many
+    exception = assert_raise ActiveModel::UnknownAttributeError do
+      @pirate.parrots_attributes = [{ peg_leg: true }]
+    end
+    assert_equal "unknown attribute 'peg_leg' for Parrot.", exception.message
+  end
+
   def test_should_save_only_one_association_on_create
-    pirate = Pirate.create!({
-      :catchphrase => 'Arr',
-      association_getter => { 'foo' => { :name => 'Grace OMalley' } }
-    })
+    pirate = Pirate.create!(
+      :catchphrase => "Arr",
+      association_getter => { "foo" => { name: "Grace OMalley" } })
 
     assert_equal 1, pirate.reload.send(@association_name).count
   end
@@ -579,88 +620,89 @@ module NestedAttributesOnACollectionAssociationTests
   def test_should_take_a_hash_with_string_keys_and_assign_the_attributes_to_the_associated_models
     @alternate_params[association_getter].stringify_keys!
     @pirate.update @alternate_params
-    assert_equal ['Grace OMalley', 'Privateers Greed'], [@child_1.reload.name, @child_2.reload.name]
+    assert_equal ["Grace OMalley", "Privateers Greed"], [@child_1.reload.name, @child_2.reload.name]
   end
 
   def test_should_take_an_array_and_assign_the_attributes_to_the_associated_models
     @pirate.send(association_setter, @alternate_params[association_getter].values)
     @pirate.save
-    assert_equal ['Grace OMalley', 'Privateers Greed'], [@child_1.reload.name, @child_2.reload.name]
+    assert_equal ["Grace OMalley", "Privateers Greed"], [@child_1.reload.name, @child_2.reload.name]
   end
 
   def test_should_also_work_with_a_HashWithIndifferentAccess
-    @pirate.send(association_setter, ActiveSupport::HashWithIndifferentAccess.new('foo' => ActiveSupport::HashWithIndifferentAccess.new(:id => @child_1.id, :name => 'Grace OMalley')))
+    @pirate.send(association_setter, ActiveSupport::HashWithIndifferentAccess.new("foo" => ActiveSupport::HashWithIndifferentAccess.new(id: @child_1.id, name: "Grace OMalley")))
     @pirate.save
-    assert_equal 'Grace OMalley', @child_1.reload.name
+    assert_equal "Grace OMalley", @child_1.reload.name
   end
 
   def test_should_take_a_hash_and_assign_the_attributes_to_the_associated_models
     @pirate.attributes = @alternate_params
-    assert_equal 'Grace OMalley', @pirate.send(@association_name).first.name
-    assert_equal 'Privateers Greed', @pirate.send(@association_name).last.name
+    assert_equal "Grace OMalley", @pirate.send(@association_name).first.name
+    assert_equal "Privateers Greed", @pirate.send(@association_name).last.name
   end
 
   def test_should_not_load_association_when_updating_existing_records
     @pirate.reload
-    @pirate.send(association_setter, [{ :id => @child_1.id, :name => 'Grace OMalley' }])
-    assert ! @pirate.send(@association_name).loaded?
+    @pirate.send(association_setter, [{ id: @child_1.id, name: "Grace OMalley" }])
+    assert_not_predicate @pirate.send(@association_name), :loaded?
 
     @pirate.save
-    assert ! @pirate.send(@association_name).loaded?
-    assert_equal 'Grace OMalley', @child_1.reload.name
+    assert_not_predicate @pirate.send(@association_name), :loaded?
+    assert_equal "Grace OMalley", @child_1.reload.name
   end
 
   def test_should_not_overwrite_unsaved_updates_when_loading_association
     @pirate.reload
-    @pirate.send(association_setter, [{ :id => @child_1.id, :name => 'Grace OMalley' }])
-    assert_equal 'Grace OMalley', @pirate.send(@association_name).send(:load_target).find { |r| r.id == @child_1.id }.name
+    @pirate.send(association_setter, [{ id: @child_1.id, name: "Grace OMalley" }])
+    assert_equal "Grace OMalley", @pirate.send(@association_name).load_target.find { |r| r.id == @child_1.id }.name
   end
 
   def test_should_preserve_order_when_not_overwriting_unsaved_updates
     @pirate.reload
-    @pirate.send(association_setter, [{ :id => @child_1.id, :name => 'Grace OMalley' }])
-    assert_equal @child_1.id, @pirate.send(@association_name).send(:load_target).first.id
+    @pirate.send(association_setter, [{ id: @child_1.id, name: "Grace OMalley" }])
+    assert_equal @child_1.id, @pirate.send(@association_name).load_target.first.id
   end
 
   def test_should_refresh_saved_records_when_not_overwriting_unsaved_updates
     @pirate.reload
-    record = @pirate.class.reflect_on_association(@association_name).klass.new(name: 'Grace OMalley')
+    record = @pirate.class.reflect_on_association(@association_name).klass.new(name: "Grace OMalley")
     @pirate.send(@association_name) << record
     record.save!
-    @pirate.send(@association_name).last.update!(name: 'Polly')
-    assert_equal 'Polly', @pirate.send(@association_name).send(:load_target).last.name
+    @pirate.send(@association_name).last.update!(name: "Polly")
+    assert_equal "Polly", @pirate.send(@association_name).load_target.last.name
   end
 
   def test_should_not_remove_scheduled_destroys_when_loading_association
     @pirate.reload
-    @pirate.send(association_setter, [{ :id => @child_1.id, :_destroy => '1' }])
-    assert @pirate.send(@association_name).send(:load_target).find { |r| r.id == @child_1.id }.marked_for_destruction?
+    @pirate.send(association_setter, [{ id: @child_1.id, _destroy: "1" }])
+    assert_predicate @pirate.send(@association_name).load_target.find { |r| r.id == @child_1.id }, :marked_for_destruction?
   end
 
   def test_should_take_a_hash_with_composite_id_keys_and_assign_the_attributes_to_the_associated_models
-    @child_1.stubs(:id).returns('ABC1X')
-    @child_2.stubs(:id).returns('ABC2X')
-
-    @pirate.attributes = {
-      association_getter => [
-        { :id => @child_1.id, :name => 'Grace OMalley' },
-        { :id => @child_2.id, :name => 'Privateers Greed' }
-      ]
-    }
-
-    assert_equal ['Grace OMalley', 'Privateers Greed'], [@child_1.name, @child_2.name]
+    @child_1.stub(:id, "ABC1X") do
+      @child_2.stub(:id, "ABC2X") do
+        @pirate.attributes = {
+          association_getter => [
+            { id: @child_1.id, name: "Grace OMalley" },
+            { id: @child_2.id, name: "Privateers Greed" }
+          ]
+        }
+
+        assert_equal ["Grace OMalley", "Privateers Greed"], [@child_1.name, @child_2.name]
+      end
+    end
   end
 
   def test_should_raise_RecordNotFound_if_an_id_is_given_but_doesnt_return_a_record
     exception = assert_raise ActiveRecord::RecordNotFound do
-      @pirate.attributes = { association_getter => [{ :id => 1234567890 }] }
+      @pirate.attributes = { association_getter => [{ id: 1234567890 }] }
     end
     assert_equal "Couldn't find #{@child_1.class.name} with ID=1234567890 for Pirate with ID=#{@pirate.id}", exception.message
   end
 
   def test_should_raise_RecordNotFound_if_an_id_belonging_to_a_different_record_is_given
-    other_pirate = Pirate.create! catchphrase: 'Ahoy!'
-    other_child = other_pirate.send(@association_name).create! name: 'Buccaneers Servant'
+    other_pirate = Pirate.create! catchphrase: "Ahoy!"
+    other_child = other_pirate.send(@association_name).create! name: "Buccaneers Servant"
 
     exception = assert_raise ActiveRecord::RecordNotFound do
       @pirate.attributes = { association_getter => [{ id: other_child.id }] }
@@ -671,19 +713,19 @@ module NestedAttributesOnACollectionAssociationTests
   def test_should_automatically_build_new_associated_models_for_each_entry_in_a_hash_where_the_id_is_missing
     @pirate.send(@association_name).destroy_all
     @pirate.reload.attributes = {
-      association_getter => { 'foo' => { :name => 'Grace OMalley' }, 'bar' => { :name => 'Privateers Greed' }}
+      association_getter => { "foo" => { name: "Grace OMalley" }, "bar" => { name: "Privateers Greed" } }
     }
 
-    assert !@pirate.send(@association_name).first.persisted?
-    assert_equal 'Grace OMalley', @pirate.send(@association_name).first.name
+    assert_not_predicate @pirate.send(@association_name).first, :persisted?
+    assert_equal "Grace OMalley", @pirate.send(@association_name).first.name
 
-    assert !@pirate.send(@association_name).last.persisted?
-    assert_equal 'Privateers Greed', @pirate.send(@association_name).last.name
+    assert_not_predicate @pirate.send(@association_name).last, :persisted?
+    assert_equal "Privateers Greed", @pirate.send(@association_name).last.name
   end
 
   def test_should_not_assign_destroy_key_to_a_record
-    assert_nothing_raised ActiveRecord::UnknownAttributeError do
-      @pirate.send(association_setter, { 'foo' => { '_destroy' => '0' }})
+    assert_nothing_raised do
+      @pirate.send(association_setter, "foo" => { "_destroy" => "0" })
     end
   end
 
@@ -691,17 +733,17 @@ module NestedAttributesOnACollectionAssociationTests
     @pirate.send(@association_name).destroy_all
     @pirate.reload.attributes = {
       association_getter => {
-        'foo' => { :name => 'Grace OMalley' },
-        'bar' => { :name => 'Privateers Greed', '_destroy' => '1' }
+        "foo" => { name: "Grace OMalley" },
+        "bar" => { :name => "Privateers Greed", "_destroy" => "1" }
       }
     }
 
     assert_equal 1, @pirate.send(@association_name).length
-    assert_equal 'Grace OMalley', @pirate.send(@association_name).first.name
+    assert_equal "Grace OMalley", @pirate.send(@association_name).first.name
   end
 
   def test_should_ignore_new_associated_records_if_a_reject_if_proc_returns_false
-    @alternate_params[association_getter]['baz'] = {}
+    @alternate_params[association_getter]["baz"] = {}
     assert_no_difference("@pirate.send(@association_name).count") do
       @pirate.attributes = @alternate_params
     end
@@ -709,65 +751,65 @@ module NestedAttributesOnACollectionAssociationTests
 
   def test_should_sort_the_hash_by_the_keys_before_building_new_associated_models
     attributes = {}
-    attributes['123726353'] = { :name => 'Grace OMalley' }
-    attributes['2'] = { :name => 'Privateers Greed' } # 2 is lower then 123726353
+    attributes["123726353"] = { name: "Grace OMalley" }
+    attributes["2"] = { name: "Privateers Greed" } # 2 is lower then 123726353
     @pirate.send(association_setter, attributes)
 
-    assert_equal ['Posideons Killer', 'Killer bandita Dionne', 'Privateers Greed', 'Grace OMalley'].to_set, @pirate.send(@association_name).map(&:name).to_set
+    assert_equal ["Posideons Killer", "Killer bandita Dionne", "Privateers Greed", "Grace OMalley"].to_set, @pirate.send(@association_name).map(&:name).to_set
   end
 
   def test_should_raise_an_argument_error_if_something_else_than_a_hash_is_passed
-    assert_nothing_raised(ArgumentError) { @pirate.send(association_setter, {}) }
-    assert_nothing_raised(ArgumentError) { @pirate.send(association_setter, Hash.new) }
+    assert_nothing_raised { @pirate.send(association_setter, {}) }
+    assert_nothing_raised { @pirate.send(association_setter, Hash.new) }
 
     exception = assert_raise ArgumentError do
       @pirate.send(association_setter, "foo")
     end
-    assert_equal 'Hash or Array expected, got String ("foo")', exception.message
+    assert_equal %{Hash or Array expected for attribute `#{@association_name}`, got String ("foo")}, exception.message
   end
 
   def test_should_work_with_update_as_well
-    @pirate.update(catchphrase: 'Arr',
-      association_getter => { 'foo' => { :id => @child_1.id, :name => 'Grace OMalley' }})
+    @pirate.update(catchphrase: "Arr",
+      association_getter => { "foo" => { id: @child_1.id, name: "Grace OMalley" } })
 
-    assert_equal 'Grace OMalley', @child_1.reload.name
+    assert_equal "Grace OMalley", @child_1.reload.name
   end
 
   def test_should_update_existing_records_and_add_new_ones_that_have_no_id
-    @alternate_params[association_getter]['baz'] = { name: 'Buccaneers Servant' }
-    assert_difference('@pirate.send(@association_name).count', +1) do
+    @alternate_params[association_getter]["baz"] = { name: "Buccaneers Servant" }
+    assert_difference("@pirate.send(@association_name).count", +1) do
       @pirate.update @alternate_params
     end
-    assert_equal ['Grace OMalley', 'Privateers Greed', 'Buccaneers Servant'].to_set, @pirate.reload.send(@association_name).map(&:name).to_set
+    assert_equal ["Grace OMalley", "Privateers Greed", "Buccaneers Servant"].to_set, @pirate.reload.send(@association_name).map(&:name).to_set
   end
 
   def test_should_be_possible_to_destroy_a_record
-    ['1', 1, 'true', true].each do |true_variable|
-      record = @pirate.reload.send(@association_name).create!(:name => 'Grace OMalley')
+    ["1", 1, "true", true].each do |true_variable|
+      record = @pirate.reload.send(@association_name).create!(name: "Grace OMalley")
       @pirate.send(association_setter,
-        @alternate_params[association_getter].merge('baz' => { :id => record.id, '_destroy' => true_variable })
+        @alternate_params[association_getter].merge("baz" => { :id => record.id, "_destroy" => true_variable })
       )
 
-      assert_difference('@pirate.send(@association_name).count', -1) do
+      assert_difference("@pirate.send(@association_name).count", -1) do
         @pirate.save
       end
     end
   end
 
   def test_should_not_destroy_the_associated_model_with_a_non_truthy_argument
-    [nil, '', '0', 0, 'false', false].each do |false_variable|
-      @alternate_params[association_getter]['foo']['_destroy'] = false_variable
-      assert_no_difference('@pirate.send(@association_name).count') do
+    [nil, "", "0", 0, "false", false].each do |false_variable|
+      @alternate_params[association_getter]["foo"]["_destroy"] = false_variable
+      assert_no_difference("@pirate.send(@association_name).count") do
         @pirate.update(@alternate_params)
       end
     end
   end
 
   def test_should_not_destroy_the_associated_model_until_the_parent_is_saved
-    assert_no_difference('@pirate.send(@association_name).count') do
-      @pirate.send(association_setter, @alternate_params[association_getter].merge('baz' => { :id => @child_1.id, '_destroy' => true }))
+    assert_no_difference("@pirate.send(@association_name).count") do
+      @pirate.send(association_setter, @alternate_params[association_getter].merge("baz" => { :id => @child_1.id, "_destroy" => true }))
     end
-    assert_difference('@pirate.send(@association_name).count', -1) { @pirate.save }
+    assert_difference("@pirate.send(@association_name).count", -1) { @pirate.save }
   end
 
   def test_should_automatically_enable_autosave_on_the_association
@@ -781,10 +823,10 @@ module NestedAttributesOnACollectionAssociationTests
 
     repair_validations(Interest) do
       Interest.validates_presence_of(:man)
-      assert_difference 'Man.count' do
-        assert_difference 'Interest.count', 2 do
-          man = Man.create!(:name => 'John',
-                            :interests_attributes => [{:topic=>'Cars'}, {:topic=>'Sports'}])
+      assert_difference "Man.count" do
+        assert_difference "Interest.count", 2 do
+          man = Man.create!(name: "John",
+                            interests_attributes: [{ topic: "Cars" }, { topic: "Sports" }])
           assert_equal 2, man.interests.count
         end
       end
@@ -792,8 +834,8 @@ module NestedAttributesOnACollectionAssociationTests
   end
 
   def test_can_use_symbols_as_object_identifier
-    @pirate.attributes = { :parrots_attributes => { :foo => { :name => 'Lovely Day' }, :bar => { :name => 'Blown Away' } } }
-    assert_nothing_raised(NoMethodError) { @pirate.save! }
+    @pirate.attributes = { parrots_attributes: { foo: { name: "Lovely Day" }, bar: { name: "Blown Away" } } }
+    assert_nothing_raised { @pirate.save! }
   end
 
   def test_numeric_column_changes_from_zero_to_no_empty_string
@@ -801,22 +843,22 @@ module NestedAttributesOnACollectionAssociationTests
 
     repair_validations(Interest) do
       Interest.validates_numericality_of(:zine_id)
-      man = Man.create(name: 'John')
-      interest = man.interests.create(topic: 'bar', zine_id: 0)
+      man = Man.create(name: "John")
+      interest = man.interests.create(topic: "bar", zine_id: 0)
       assert interest.save
-      assert !man.update({interests_attributes: { id: interest.id, zine_id: 'foo' }})
+      assert_not man.update(interests_attributes: { id: interest.id, zine_id: "foo" })
     end
   end
 
   private
 
-  def association_setter
-    @association_setter ||= "#{@association_name}_attributes=".to_sym
-  end
+    def association_setter
+      @association_setter ||= "#{@association_name}_attributes=".to_sym
+    end
 
-  def association_getter
-    @association_getter ||= "#{@association_name}_attributes".to_sym
-  end
+    def association_getter
+      @association_getter ||= "#{@association_name}_attributes".to_sym
+    end
 end
 
 class TestNestedAttributesOnAHasManyAssociation < ActiveRecord::TestCase
@@ -824,16 +866,16 @@ class TestNestedAttributesOnAHasManyAssociation < ActiveRecord::TestCase
     @association_type = :has_many
     @association_name = :birds
 
-    @pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @pirate.birds.create!(:name => 'Posideons Killer')
-    @pirate.birds.create!(:name => 'Killer bandita Dionne')
+    @pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @pirate.birds.create!(name: "Posideons Killer")
+    @pirate.birds.create!(name: "Killer bandita Dionne")
 
     @child_1, @child_2 = @pirate.birds
 
     @alternate_params = {
-      :birds_attributes => {
-        'foo' => { :id => @child_1.id, :name => 'Grace OMalley' },
-        'bar' => { :id => @child_2.id, :name => 'Privateers Greed' }
+      birds_attributes: {
+        "foo" => { id: @child_1.id, name: "Grace OMalley" },
+        "bar" => { id: @child_2.id, name: "Privateers Greed" }
       }
     }
   end
@@ -846,16 +888,16 @@ class TestNestedAttributesOnAHasAndBelongsToManyAssociation < ActiveRecord::Test
     @association_type = :has_and_belongs_to_many
     @association_name = :parrots
 
-    @pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
-    @pirate.parrots.create!(:name => 'Posideons Killer')
-    @pirate.parrots.create!(:name => 'Killer bandita Dionne')
+    @pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    @pirate.parrots.create!(name: "Posideons Killer")
+    @pirate.parrots.create!(name: "Killer bandita Dionne")
 
     @child_1, @child_2 = @pirate.parrots
 
     @alternate_params = {
-      :parrots_attributes => {
-        'foo' => { :id => @child_1.id, :name => 'Grace OMalley' },
-        'bar' => { :id => @child_2.id, :name => 'Privateers Greed' }
+      parrots_attributes: {
+        "foo" => { id: @child_1.id, name: "Grace OMalley" },
+        "bar" => { id: @child_2.id, name: "Privateers Greed" }
       }
     }
   end
@@ -865,33 +907,33 @@ end
 
 module NestedAttributesLimitTests
   def teardown
-    Pirate.accepts_nested_attributes_for :parrots, :allow_destroy => true, :reject_if => proc(&:empty?)
+    Pirate.accepts_nested_attributes_for :parrots, allow_destroy: true, reject_if: proc(&:empty?)
   end
 
   def test_limit_with_less_records
-    @pirate.attributes = { :parrots_attributes => { 'foo' => { :name => 'Big Big Love' } } }
-    assert_difference('Parrot.count') { @pirate.save! }
+    @pirate.attributes = { parrots_attributes: { "foo" => { name: "Big Big Love" } } }
+    assert_difference("Parrot.count") { @pirate.save! }
   end
 
   def test_limit_with_number_exact_records
-    @pirate.attributes = { :parrots_attributes => { 'foo' => { :name => 'Lovely Day' }, 'bar' => { :name => 'Blown Away' } } }
-    assert_difference('Parrot.count', 2) { @pirate.save! }
+    @pirate.attributes = { parrots_attributes: { "foo" => { name: "Lovely Day" }, "bar" => { name: "Blown Away" } } }
+    assert_difference("Parrot.count", 2) { @pirate.save! }
   end
 
   def test_limit_with_exceeding_records
     assert_raises(ActiveRecord::NestedAttributes::TooManyRecords) do
-      @pirate.attributes = { :parrots_attributes => { 'foo' => { :name => 'Lovely Day' },
-                                                      'bar' => { :name => 'Blown Away' },
-                                                      'car' => { :name => 'The Happening' }} }
+      @pirate.attributes = { parrots_attributes: { "foo" => { name: "Lovely Day" },
+                                                      "bar" => { name: "Blown Away" },
+                                                      "car" => { name: "The Happening" } } }
     end
   end
 end
 
 class TestNestedAttributesLimitNumeric < ActiveRecord::TestCase
   def setup
-    Pirate.accepts_nested_attributes_for :parrots, :limit => 2
+    Pirate.accepts_nested_attributes_for :parrots, limit: 2
 
-    @pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
+    @pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
   end
 
   include NestedAttributesLimitTests
@@ -899,9 +941,9 @@ end
 
 class TestNestedAttributesLimitSymbol < ActiveRecord::TestCase
   def setup
-    Pirate.accepts_nested_attributes_for :parrots, :limit => :parrots_limit
+    Pirate.accepts_nested_attributes_for :parrots, limit: :parrots_limit
 
-    @pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?", :parrots_limit => 2)
+    @pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?", parrots_limit: 2)
   end
 
   include NestedAttributesLimitTests
@@ -909,9 +951,9 @@ end
 
 class TestNestedAttributesLimitProc < ActiveRecord::TestCase
   def setup
-    Pirate.accepts_nested_attributes_for :parrots, :limit => proc { 2 }
+    Pirate.accepts_nested_attributes_for :parrots, limit: proc { 2 }
 
-    @pirate = Pirate.create!(:catchphrase => "Don' botharrr talkin' like one, savvy?")
+    @pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
   end
 
   include NestedAttributesLimitTests
@@ -921,45 +963,44 @@ class TestNestedAttributesWithNonStandardPrimaryKeys < ActiveRecord::TestCase
   fixtures :owners, :pets
 
   def setup
-    Owner.accepts_nested_attributes_for :pets, :allow_destroy => true
+    Owner.accepts_nested_attributes_for :pets, allow_destroy: true
 
     @owner = owners(:ashley)
     @pet1, @pet2 = pets(:chew), pets(:mochi)
 
     @params = {
-      :pets_attributes => {
-        '0' => { :id => @pet1.id, :name => 'Foo' },
-        '1' => { :id => @pet2.id, :name => 'Bar' }
+      pets_attributes: {
+        "0" => { id: @pet1.id, name: "Foo" },
+        "1" => { id: @pet2.id, name: "Bar" }
       }
     }
   end
 
   def test_should_update_existing_records_with_non_standard_primary_key
     @owner.update(@params)
-    assert_equal ['Foo', 'Bar'], @owner.pets.map(&:name)
+    assert_equal ["Foo", "Bar"], @owner.pets.map(&:name)
   end
 
   def test_attr_accessor_of_child_should_be_value_provided_during_update
     @owner = owners(:ashley)
     @pet1 = pets(:chew)
-    attributes = {:pets_attributes => { "1"=> { :id => @pet1.id,
-                                                :name => "Foo2",
-                                                :current_user => "John",
-                                                :_destroy=>true }}}
+    attributes = { pets_attributes: { "1" => { id: @pet1.id,
+                                                name: "Foo2",
+                                                current_user: "John",
+                                                _destroy: true } } }
     @owner.update(attributes)
-    assert_equal 'John', Pet.after_destroy_output
+    assert_equal "John", Pet.after_destroy_output
   end
-
 end
 
 class TestHasOneAutosaveAssociationWhichItselfHasAutosaveAssociations < ActiveRecord::TestCase
   self.use_transactional_tests = false unless supports_savepoints?
 
   def setup
-    @pirate = Pirate.create!(:catchphrase => "My baby takes tha mornin' train!")
-    @ship = @pirate.create_ship(:name => "The good ship Dollypop")
-    @part = @ship.parts.create!(:name => "Mast")
-    @trinket = @part.trinkets.create!(:name => "Necklace")
+    @pirate = Pirate.create!(catchphrase: "My baby takes tha mornin' train!")
+    @ship = @pirate.create_ship(name: "The good ship Dollypop")
+    @part = @ship.parts.create!(name: "Mast")
+    @trinket = @part.trinkets.create!(name: "Necklace")
   end
 
   test "when great-grandchild changed in memory, saving parent should save great-grandchild" do
@@ -969,25 +1010,25 @@ class TestHasOneAutosaveAssociationWhichItselfHasAutosaveAssociations < ActiveRe
   end
 
   test "when great-grandchild changed via attributes, saving parent should save great-grandchild" do
-    @pirate.attributes = {:ship_attributes => {:id => @ship.id, :parts_attributes => [{:id => @part.id, :trinkets_attributes => [{:id => @trinket.id, :name => "changed"}]}]}}
+    @pirate.attributes = { ship_attributes: { id: @ship.id, parts_attributes: [{ id: @part.id, trinkets_attributes: [{ id: @trinket.id, name: "changed" }] }] } }
     @pirate.save
     assert_equal "changed", @trinket.reload.name
   end
 
   test "when great-grandchild marked_for_destruction via attributes, saving parent should destroy great-grandchild" do
-    @pirate.attributes = {:ship_attributes => {:id => @ship.id, :parts_attributes => [{:id => @part.id, :trinkets_attributes => [{:id => @trinket.id, :_destroy => true}]}]}}
-    assert_difference('@part.trinkets.count', -1) { @pirate.save }
+    @pirate.attributes = { ship_attributes: { id: @ship.id, parts_attributes: [{ id: @part.id, trinkets_attributes: [{ id: @trinket.id, _destroy: true }] }] } }
+    assert_difference("@part.trinkets.count", -1) { @pirate.save }
   end
 
   test "when great-grandchild added via attributes, saving parent should create great-grandchild" do
-    @pirate.attributes = {:ship_attributes => {:id => @ship.id, :parts_attributes => [{:id => @part.id, :trinkets_attributes => [{:name => "created"}]}]}}
-    assert_difference('@part.trinkets.count', 1) { @pirate.save }
+    @pirate.attributes = { ship_attributes: { id: @ship.id, parts_attributes: [{ id: @part.id, trinkets_attributes: [{ name: "created" }] }] } }
+    assert_difference("@part.trinkets.count", 1) { @pirate.save }
   end
 
   test "when extra records exist for associations, validate (which calls nested_records_changed_for_autosave?) should not load them up" do
     @trinket.name = "changed"
-    Ship.create!(:pirate => @pirate, :name => "The Black Rock")
-    ShipPart.create!(:ship => @ship, :name => "Stern")
+    Ship.create!(pirate: @pirate, name: "The Black Rock")
+    ShipPart.create!(ship: @ship, name: "Stern")
     assert_no_queries { @pirate.valid? }
   end
 end
@@ -996,27 +1037,27 @@ class TestHasManyAutosaveAssociationWhichItselfHasAutosaveAssociations < ActiveR
   self.use_transactional_tests = false unless supports_savepoints?
 
   def setup
-    @ship = Ship.create!(:name => "The good ship Dollypop")
-    @part = @ship.parts.create!(:name => "Mast")
-    @trinket = @part.trinkets.create!(:name => "Necklace")
+    @ship = Ship.create!(name: "The good ship Dollypop")
+    @part = @ship.parts.create!(name: "Mast")
+    @trinket = @part.trinkets.create!(name: "Necklace")
   end
 
   test "if association is not loaded and association record is saved and then in memory record attributes should be saved" do
-    @ship.parts_attributes=[{:id => @part.id,:name =>'Deck'}]
+    @ship.parts_attributes = [{ id: @part.id, name: "Deck" }]
     assert_equal 1, @ship.association(:parts).target.size
-    assert_equal 'Deck', @ship.parts[0].name
+    assert_equal "Deck", @ship.parts[0].name
   end
 
   test "if association is not loaded and child doesn't change and I am saving a grandchild then in memory record should be used" do
-    @ship.parts_attributes=[{:id => @part.id,:trinkets_attributes =>[{:id => @trinket.id, :name => 'Ruby'}]}]
+    @ship.parts_attributes = [{ id: @part.id, trinkets_attributes: [{ id: @trinket.id, name: "Ruby" }] }]
     assert_equal 1, @ship.association(:parts).target.size
-    assert_equal 'Mast', @ship.parts[0].name
+    assert_equal "Mast", @ship.parts[0].name
     assert_no_difference("@ship.parts[0].association(:trinkets).target.size") do
       @ship.parts[0].association(:trinkets).target.size
     end
-    assert_equal 'Ruby', @ship.parts[0].trinkets[0].name
+    assert_equal "Ruby", @ship.parts[0].trinkets[0].name
     @ship.save
-    assert_equal 'Ruby', @ship.parts[0].trinkets[0].name
+    assert_equal "Ruby", @ship.parts[0].trinkets[0].name
   end
 
   test "when grandchild changed in memory, saving parent should save grandchild" do
@@ -1026,25 +1067,25 @@ class TestHasManyAutosaveAssociationWhichItselfHasAutosaveAssociations < ActiveR
   end
 
   test "when grandchild changed via attributes, saving parent should save grandchild" do
-    @ship.attributes = {:parts_attributes => [{:id => @part.id, :trinkets_attributes => [{:id => @trinket.id, :name => "changed"}]}]}
+    @ship.attributes = { parts_attributes: [{ id: @part.id, trinkets_attributes: [{ id: @trinket.id, name: "changed" }] }] }
     @ship.save
     assert_equal "changed", @trinket.reload.name
   end
 
   test "when grandchild marked_for_destruction via attributes, saving parent should destroy grandchild" do
-    @ship.attributes = {:parts_attributes => [{:id => @part.id, :trinkets_attributes => [{:id => @trinket.id, :_destroy => true}]}]}
-    assert_difference('@part.trinkets.count', -1) { @ship.save }
+    @ship.attributes = { parts_attributes: [{ id: @part.id, trinkets_attributes: [{ id: @trinket.id, _destroy: true }] }] }
+    assert_difference("@part.trinkets.count", -1) { @ship.save }
   end
 
   test "when grandchild added via attributes, saving parent should create grandchild" do
-    @ship.attributes = {:parts_attributes => [{:id => @part.id, :trinkets_attributes => [{:name => "created"}]}]}
-    assert_difference('@part.trinkets.count', 1) { @ship.save }
+    @ship.attributes = { parts_attributes: [{ id: @part.id, trinkets_attributes: [{ name: "created" }] }] }
+    assert_difference("@part.trinkets.count", 1) { @ship.save }
   end
 
   test "when extra records exist for associations, validate (which calls nested_records_changed_for_autosave?) should not load them up" do
     @trinket.name = "changed"
-    Ship.create!(:name => "The Black Rock")
-    ShipPart.create!(:ship => @ship, :name => "Stern")
+    Ship.create!(name: "The Black Rock")
+    ShipPart.create!(ship: @ship, name: "Stern")
     assert_no_queries { @ship.valid? }
   end
 
@@ -1061,7 +1102,19 @@ class TestHasManyAutosaveAssociationWhichItselfHasAutosaveAssociations < ActiveR
   test "nested singular associations are validated" do
     part = ShipPart.new(name: "Stern", ship_attributes: { name: nil })
 
-    assert_not part.valid?
+    assert_not_predicate part, :valid?
     assert_equal ["Ship name can't be blank"], part.errors.full_messages
   end
 end
+
+class TestNestedAttributesWithExtend < ActiveRecord::TestCase
+  setup do
+    Pirate.accepts_nested_attributes_for :treasures
+  end
+
+  def test_extend_affects_nested_attributes
+    pirate = Pirate.create!(catchphrase: "Don' botharrr talkin' like one, savvy?")
+    pirate.treasures_attributes = [{ id: nil }]
+    assert_equal "from extension", pirate.treasures[0].name
+  end
+end
diff --git a/activerecord/test/cases/nested_attributes_with_callbacks_test.rb b/activerecord/test/cases/nested_attributes_with_callbacks_test.rb
index 43a69928b6..1d26057fdc 100644
--- a/activerecord/test/cases/nested_attributes_with_callbacks_test.rb
+++ b/activerecord/test/cases/nested_attributes_with_callbacks_test.rb
@@ -1,27 +1,29 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "models/pirate"
 require "models/bird"
 
 class NestedAttributesWithCallbacksTest < ActiveRecord::TestCase
   Pirate.has_many(:birds_with_add_load,
-                  :class_name => "Bird",
-                  :before_add => proc { |p,b|
+                  class_name: "Bird",
+                  before_add: proc { |p, b|
                     @@add_callback_called << b
                     p.birds_with_add_load.to_a
                   })
   Pirate.has_many(:birds_with_add,
-                  :class_name => "Bird",
-                  :before_add => proc { |p,b| @@add_callback_called << b })
+                  class_name: "Bird",
+                  before_add: proc { |p, b| @@add_callback_called << b })
 
   Pirate.accepts_nested_attributes_for(:birds_with_add_load,
                                        :birds_with_add,
-                                       :allow_destroy => true)
+                                       allow_destroy: true)
 
   def setup
     @@add_callback_called = []
     @pirate = Pirate.new.tap do |pirate|
       pirate.catchphrase = "Don't call me!"
-      pirate.birds_attributes = [{:name => 'Bird1'},{:name => 'Bird2'}]
+      pirate.birds_attributes = [{ name: "Bird1" }, { name: "Bird2" }]
       pirate.save!
     end
     @birds = @pirate.birds.to_a
@@ -37,7 +39,7 @@ class NestedAttributesWithCallbacksTest < ActiveRecord::TestCase
 
   def existing_birds_attributes
     @birds.map do |bird|
-      bird.attributes.slice("id","name")
+      bird.attributes.slice("id", "name")
     end
   end
 
@@ -46,22 +48,22 @@ class NestedAttributesWithCallbacksTest < ActiveRecord::TestCase
   end
 
   def new_bird_attributes
-     [{'name' => "New Bird"}]
+    [{ "name" => "New Bird" }]
   end
 
   def destroy_bird_attributes
-    [{'id' => bird_to_destroy.id.to_s, "_destroy" => true}]
+    [{ "id" => bird_to_destroy.id.to_s, "_destroy" => true }]
   end
 
   def update_new_and_destroy_bird_attributes
-    [{'id' => @birds[0].id.to_s, 'name' => 'New Name'},
-     {'name' => "New Bird"},
-     {'id' => bird_to_destroy.id.to_s, "_destroy" => true}]
+    [{ "id" => @birds[0].id.to_s, "name" => "New Name" },
+     { "name" => "New Bird" },
+     { "id" => bird_to_destroy.id.to_s, "_destroy" => true }]
   end
 
   # Characterizing when :before_add callback is called
   test ":before_add called for new bird when not loaded" do
-    assert_not @pirate.birds_with_add.loaded?
+    assert_not_predicate @pirate.birds_with_add, :loaded?
     @pirate.birds_with_add_attributes = new_bird_attributes
     assert_new_bird_with_callback_called
   end
@@ -78,7 +80,7 @@ class NestedAttributesWithCallbacksTest < ActiveRecord::TestCase
   end
 
   test ":before_add not called for identical assignment when not loaded" do
-    assert_not @pirate.birds_with_add.loaded?
+    assert_not_predicate @pirate.birds_with_add, :loaded?
     @pirate.birds_with_add_attributes = existing_birds_attributes
     assert_callbacks_not_called
   end
@@ -90,7 +92,7 @@ class NestedAttributesWithCallbacksTest < ActiveRecord::TestCase
   end
 
   test ":before_add not called for destroy assignment when not loaded" do
-    assert_not @pirate.birds_with_add.loaded?
+    assert_not_predicate @pirate.birds_with_add, :loaded?
     @pirate.birds_with_add_attributes = destroy_bird_attributes
     assert_callbacks_not_called
   end
@@ -109,7 +111,7 @@ class NestedAttributesWithCallbacksTest < ActiveRecord::TestCase
   # Ensuring that the records in the association target are updated,
   # whether the association is loaded before or not
   test "Assignment updates records in target when not loaded" do
-    assert_not @pirate.birds_with_add.loaded?
+    assert_not_predicate @pirate.birds_with_add, :loaded?
     @pirate.birds_with_add_attributes = update_new_and_destroy_bird_attributes
     assert_assignment_affects_records_in_target(:birds_with_add)
   end
@@ -120,14 +122,14 @@ class NestedAttributesWithCallbacksTest < ActiveRecord::TestCase
     assert_assignment_affects_records_in_target(:birds_with_add)
   end
 
-  test("Assignment updates records in target when not loaded" +
+  test("Assignment updates records in target when not loaded" \
        " and callback loads target") do
-    assert_not @pirate.birds_with_add_load.loaded?
+    assert_not_predicate @pirate.birds_with_add_load, :loaded?
     @pirate.birds_with_add_load_attributes = update_new_and_destroy_bird_attributes
     assert_assignment_affects_records_in_target(:birds_with_add_load)
   end
 
-  test("Assignment updates records in target when loaded" +
+  test("Assignment updates records in target when loaded" \
        " and callback loads target") do
     @pirate.birds_with_add_load.load_target
     @pirate.birds_with_add_load_attributes = update_new_and_destroy_bird_attributes
@@ -136,9 +138,9 @@ class NestedAttributesWithCallbacksTest < ActiveRecord::TestCase
 
   def assert_assignment_affects_records_in_target(association_name)
     association = @pirate.send(association_name)
-    assert association.detect {|b| b == bird_to_update }.name_changed?,
-      'Update record not updated'
-    assert association.detect {|b| b == bird_to_destroy }.marked_for_destruction?,
-      'Destroy record not marked for destruction'
+    assert association.detect { |b| b == bird_to_update }.name_changed?,
+      "Update record not updated"
+    assert association.detect { |b| b == bird_to_destroy }.marked_for_destruction?,
+      "Destroy record not marked for destruction"
   end
 end
diff --git a/activerecord/test/cases/null_relation_test.rb b/activerecord/test/cases/null_relation_test.rb
new file mode 100644
index 0000000000..ee96ea1af6
--- /dev/null
+++ b/activerecord/test/cases/null_relation_test.rb
@@ -0,0 +1,85 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/developer"
+require "models/comment"
+require "models/post"
+require "models/topic"
+
+class NullRelationTest < ActiveRecord::TestCase
+  fixtures :posts, :comments
+
+  def test_none
+    assert_no_queries do
+      assert_equal [], Developer.none
+      assert_equal [], Developer.all.none
+    end
+  end
+
+  def test_none_chainable
+    Developer.send(:load_schema)
+    assert_no_queries do
+      assert_equal [], Developer.none.where(name: "David")
+    end
+  end
+
+  def test_none_chainable_to_existing_scope_extension_method
+    assert_no_queries do
+      assert_equal 1, Topic.anonymous_extension.none.one
+    end
+  end
+
+  def test_none_chained_to_methods_firing_queries_straight_to_db
+    assert_no_queries do
+      assert_equal [],    Developer.none.pluck(:id, :name)
+      assert_equal 0,     Developer.none.delete_all
+      assert_equal 0,     Developer.none.update_all(name: "David")
+      assert_equal 0,     Developer.none.delete(1)
+      assert_equal false, Developer.none.exists?(1)
+    end
+  end
+
+  def test_null_relation_content_size_methods
+    assert_no_queries do
+      assert_equal 0,     Developer.none.size
+      assert_equal 0,     Developer.none.count
+      assert_equal true,  Developer.none.empty?
+      assert_equal true,  Developer.none.none?
+      assert_equal false, Developer.none.any?
+      assert_equal false, Developer.none.one?
+      assert_equal false, Developer.none.many?
+    end
+  end
+
+  def test_null_relation_metadata_methods
+    assert_equal "", Developer.none.to_sql
+    assert_equal({}, Developer.none.where_values_hash)
+  end
+
+  def test_null_relation_where_values_hash
+    assert_equal({ "salary" => 100_000 }, Developer.none.where(salary: 100_000).where_values_hash)
+  end
+
+  [:count, :sum].each do |method|
+    define_method "test_null_relation_#{method}" do
+      assert_no_queries do
+        assert_equal 0, Comment.none.public_send(method, :id)
+        assert_equal Hash.new, Comment.none.group(:post_id).public_send(method, :id)
+      end
+    end
+  end
+
+  [:average, :minimum, :maximum].each do |method|
+    define_method "test_null_relation_#{method}" do
+      assert_no_queries do
+        assert_nil Comment.none.public_send(method, :id)
+        assert_equal Hash.new, Comment.none.group(:post_id).public_send(method, :id)
+      end
+    end
+  end
+
+  def test_null_relation_in_where_condition
+    assert_operator Comment.count, :>, 0 # precondition, make sure there are comments.
+    assert_equal 0, Comment.where(post_id: Post.none).count
+  end
+end
diff --git a/activerecord/test/cases/numeric_data_test.rb b/activerecord/test/cases/numeric_data_test.rb
new file mode 100644
index 0000000000..079e664ee4
--- /dev/null
+++ b/activerecord/test/cases/numeric_data_test.rb
@@ -0,0 +1,93 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/numeric_data"
+
+class NumericDataTest < ActiveRecord::TestCase
+  def test_big_decimal_conditions
+    m = NumericData.new(
+      bank_balance: 1586.43,
+      big_bank_balance: BigDecimal("1000234000567.95"),
+      world_population: 6000000000,
+      my_house_population: 3
+    )
+    assert m.save
+    assert_equal 0, NumericData.where("bank_balance > ?", 2000.0).count
+  end
+
+  def test_numeric_fields
+    m = NumericData.new(
+      bank_balance: 1586.43,
+      big_bank_balance: BigDecimal("1000234000567.95"),
+      world_population: 2**62,
+      my_house_population: 3
+    )
+    assert m.save
+
+    m1 = NumericData.find_by(
+      bank_balance: 1586.43,
+      big_bank_balance: BigDecimal("1000234000567.95")
+    )
+
+    assert_kind_of Integer, m1.world_population
+    assert_equal 2**62, m1.world_population
+
+    assert_kind_of Integer, m1.my_house_population
+    assert_equal 3, m1.my_house_population
+
+    assert_kind_of BigDecimal, m1.bank_balance
+    assert_equal BigDecimal("1586.43"), m1.bank_balance
+
+    assert_kind_of BigDecimal, m1.big_bank_balance
+    assert_equal BigDecimal("1000234000567.95"), m1.big_bank_balance
+  end
+
+  def test_numeric_fields_with_scale
+    m = NumericData.new(
+      bank_balance: 1586.43122334,
+      big_bank_balance: BigDecimal("234000567.952344"),
+      world_population: 2**62,
+      my_house_population: 3
+    )
+    assert m.save
+
+    m1 = NumericData.find_by(
+      bank_balance: 1586.43122334,
+      big_bank_balance: BigDecimal("234000567.952344")
+    )
+
+    assert_kind_of Integer, m1.world_population
+    assert_equal 2**62, m1.world_population
+
+    assert_kind_of Integer, m1.my_house_population
+    assert_equal 3, m1.my_house_population
+
+    assert_kind_of BigDecimal, m1.bank_balance
+    assert_equal BigDecimal("1586.43"), m1.bank_balance
+
+    assert_kind_of BigDecimal, m1.big_bank_balance
+    assert_equal BigDecimal("234000567.95"), m1.big_bank_balance
+  end
+
+  if current_adapter?(:PostgreSQLAdapter)
+    def test_numeric_fields_with_nan
+      m = NumericData.new(
+        bank_balance: BigDecimal("NaN"),
+        big_bank_balance: BigDecimal("NaN"),
+        world_population: 2**62,
+        my_house_population: 3
+      )
+      assert_predicate m.bank_balance, :nan?
+      assert_predicate m.big_bank_balance, :nan?
+      assert m.save
+
+      m1 = NumericData.find_by(
+        bank_balance: BigDecimal("NaN"),
+        big_bank_balance: BigDecimal("NaN")
+      )
+
+      assert_predicate m1.bank_balance, :nan?
+      assert_predicate m1.big_bank_balance, :nan?
+    end
+  end
+end
diff --git a/activerecord/test/cases/persistence_test.rb b/activerecord/test/cases/persistence_test.rb
index 42e7507631..4830ff2b5f 100644
--- a/activerecord/test/cases/persistence_test.rb
+++ b/activerecord/test/cases/persistence_test.rb
@@ -1,98 +1,73 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/aircraft'
-require 'models/post'
-require 'models/comment'
-require 'models/author'
-require 'models/topic'
-require 'models/reply'
-require 'models/category'
-require 'models/company'
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/minimalistic'
-require 'models/warehouse_thing'
-require 'models/parrot'
-require 'models/minivan'
-require 'models/owner'
-require 'models/person'
-require 'models/pet'
-require 'models/toy'
-require 'rexml/document'
+require "models/aircraft"
+require "models/post"
+require "models/comment"
+require "models/author"
+require "models/topic"
+require "models/reply"
+require "models/category"
+require "models/company"
+require "models/developer"
+require "models/computer"
+require "models/project"
+require "models/minimalistic"
+require "models/parrot"
+require "models/minivan"
+require "models/person"
+require "models/ship"
+require "models/admin"
+require "models/admin/user"
 
 class PersistenceTest < ActiveRecord::TestCase
-  fixtures :topics, :companies, :developers, :projects, :computers, :accounts, :minimalistics, 'warehouse-things', :authors, :author_addresses, :categorizations, :categories, :posts, :minivans, :pets, :toys
-
-  # Oracle UPDATE does not support ORDER BY
-  unless current_adapter?(:OracleAdapter)
-    def test_update_all_ignores_order_without_limit_from_association
-      author = authors(:david)
-      assert_nothing_raised do
-        assert_equal author.posts_with_comments_and_categories.length, author.posts_with_comments_and_categories.update_all([ "body = ?", "bulk update!" ])
-      end
-    end
-
-    def test_update_all_doesnt_ignore_order
-      assert_equal authors(:david).id + 1, authors(:mary).id # make sure there is going to be a duplicate PK error
-      test_update_with_order_succeeds = lambda do |order|
-        begin
-          Author.order(order).update_all('id = id + 1')
-        rescue ActiveRecord::ActiveRecordError
-          false
-        end
-      end
-
-      if test_update_with_order_succeeds.call('id DESC')
-        assert !test_update_with_order_succeeds.call('id ASC') # test that this wasn't a fluke and using an incorrect order results in an exception
-      else
-        # test that we're failing because the current Arel's engine doesn't support UPDATE ORDER BY queries is using subselects instead
-        assert_sql(/\AUPDATE .+ \(SELECT .* ORDER BY id DESC\)\Z/i) do
-          test_update_with_order_succeeds.call('id DESC')
-        end
-      end
-    end
-
-    def test_update_all_with_order_and_limit_updates_subset_only
-      author = authors(:david)
-      assert_nothing_raised do
-        assert_equal 1, author.posts_sorted_by_id_limited.size
-        assert_equal 2, author.posts_sorted_by_id_limited.limit(2).to_a.size
-        assert_equal 1, author.posts_sorted_by_id_limited.update_all([ "body = ?", "bulk update!" ])
-        assert_equal "bulk update!", posts(:welcome).body
-        assert_not_equal "bulk update!", posts(:thinking).body
-      end
-    end
-  end
+  fixtures :topics, :companies, :developers, :accounts, :minimalistics, :authors, :author_addresses, :posts, :minivans
 
   def test_update_many
     topic_data = { 1 => { "content" => "1 updated" }, 2 => { "content" => "2 updated" } }
     updated = Topic.update(topic_data.keys, topic_data.values)
 
-    assert_equal 2, updated.size
+    assert_equal [1, 2], updated.map(&:id)
     assert_equal "1 updated", Topic.find(1).content
     assert_equal "2 updated", Topic.find(2).content
   end
 
-  def test_delete_all
-    assert Topic.count > 0
+  def test_update_many_with_duplicated_ids
+    updated = Topic.update([1, 1, 2], [
+      { "content" => "1 duplicated" }, { "content" => "1 updated" }, { "content" => "2 updated" }
+    ])
 
-    assert_equal Topic.count, Topic.delete_all
+    assert_equal [1, 1, 2], updated.map(&:id)
+    assert_equal "1 updated", Topic.find(1).content
+    assert_equal "2 updated", Topic.find(2).content
+  end
+
+  def test_update_many_with_invalid_id
+    topic_data = { 1 => { "content" => "1 updated" }, 2 => { "content" => "2 updated" }, 99999 => {} }
+
+    assert_raise(ActiveRecord::RecordNotFound) do
+      Topic.update(topic_data.keys, topic_data.values)
+    end
+
+    assert_not_equal "1 updated", Topic.find(1).content
+    assert_not_equal "2 updated", Topic.find(2).content
   end
 
-  def test_delete_all_with_joins_and_where_part_is_hash
-    where_args = {:toys => {:name => 'Bone'}}
-    count = Pet.joins(:toys).where(where_args).count
+  def test_class_level_update_is_affected_by_scoping
+    topic_data = { 1 => { "content" => "1 updated" }, 2 => { "content" => "2 updated" } }
 
-    assert_equal count, 1
-    assert_equal count, Pet.joins(:toys).where(where_args).delete_all
+    assert_raise(ActiveRecord::RecordNotFound) do
+      Topic.where("1=0").scoping { Topic.update(topic_data.keys, topic_data.values) }
+    end
+
+    assert_not_equal "1 updated", Topic.find(1).content
+    assert_not_equal "2 updated", Topic.find(2).content
   end
 
-  def test_delete_all_with_joins_and_where_part_is_not_hash
-    where_args = ['toys.name = ?', 'Bone']
-    count = Pet.joins(:toys).where(where_args).count
+  def test_delete_all
+    assert Topic.count > 0
 
-    assert_equal count, 1
-    assert_equal count, Pet.joins(:toys).where(where_args).delete_all
+    assert_equal Topic.count, Topic.delete_all
   end
 
   def test_increment_attribute
@@ -119,48 +94,119 @@ class PersistenceTest < ActiveRecord::TestCase
     assert_equal 59, accounts(:signals37, :reload).credit_limit
   end
 
-  def test_destroy_all
-    conditions = "author_name = 'Mary'"
-    topics_by_mary = Topic.all.merge!(:where => conditions, :order => 'id').to_a
-    assert ! topics_by_mary.empty?
+  def test_increment_updates_counter_in_db_using_offset
+    a1 = accounts(:signals37)
+    initial_credit = a1.credit_limit
+    a2 = Account.find(accounts(:signals37).id)
+    a1.increment!(:credit_limit)
+    a2.increment!(:credit_limit)
+    assert_equal initial_credit + 2, a1.reload.credit_limit
+  end
+
+  def test_increment_with_touch_updates_timestamps
+    topic = topics(:first)
+    assert_equal 1, topic.replies_count
+    previously_updated_at = topic.updated_at
+    travel(1.second) do
+      topic.increment!(:replies_count, touch: true)
+    end
+    assert_equal 2, topic.reload.replies_count
+    assert_operator previously_updated_at, :<, topic.updated_at
+  end
 
-    assert_difference('Topic.count', -topics_by_mary.size) do
-      destroyed = Topic.destroy_all(conditions).sort_by(&:id)
-      assert_equal topics_by_mary, destroyed
-      assert destroyed.all?(&:frozen?), "destroyed topics should be frozen"
+  def test_increment_with_touch_an_attribute_updates_timestamps
+    topic = topics(:first)
+    assert_equal 1, topic.replies_count
+    previously_updated_at = topic.updated_at
+    previously_written_on = topic.written_on
+    travel(1.second) do
+      topic.increment!(:replies_count, touch: :written_on)
     end
+    assert_equal 2, topic.reload.replies_count
+    assert_operator previously_updated_at, :<, topic.updated_at
+    assert_operator previously_written_on, :<, topic.written_on
+  end
+
+  def test_increment_with_no_arg
+    topic = topics(:first)
+    assert_raises(ArgumentError) { topic.increment! }
   end
 
   def test_destroy_many
-    clients = Client.all.merge!(:order => 'id').find([2, 3])
+    clients = Client.find([2, 3])
 
-    assert_difference('Client.count', -2) do
-      destroyed = Client.destroy([2, 3]).sort_by(&:id)
+    assert_difference("Client.count", -2) do
+      destroyed = Client.destroy([2, 3])
       assert_equal clients, destroyed
       assert destroyed.all?(&:frozen?), "destroyed clients should be frozen"
     end
   end
 
+  def test_destroy_many_with_invalid_id
+    clients = Client.find([2, 3])
+
+    assert_raise(ActiveRecord::RecordNotFound) do
+      Client.destroy([2, 3, 99999])
+    end
+
+    assert_equal clients, Client.find([2, 3])
+  end
+
   def test_becomes
     assert_kind_of Reply, topics(:first).becomes(Reply)
     assert_equal "The First Topic", topics(:first).becomes(Reply).title
   end
 
+  def test_becomes_after_reload_schema_from_cache
+    Reply.define_attribute_methods
+    Reply.serialize(:content) # invoke reload_schema_from_cache
+    assert_kind_of Reply, topics(:first).becomes(Reply)
+    assert_equal "The First Topic", topics(:first).becomes(Reply).title
+  end
+
   def test_becomes_includes_errors
-    company = Company.new(:name => nil)
-    assert !company.valid?
+    company = Company.new(name: nil)
+    assert_not_predicate company, :valid?
     original_errors = company.errors
     client = company.becomes(Client)
-    assert_equal original_errors, client.errors
+    assert_equal original_errors.keys, client.errors.keys
+  end
+
+  def test_becomes_errors_base
+    child_class = Class.new(Admin::User) do
+      store_accessor :settings, :foo
+
+      def self.name; "Admin::ChildUser"; end
+    end
+
+    admin = Admin::User.new
+    admin.errors.add :token, :invalid
+    child = admin.becomes(child_class)
+
+    assert_equal [:token], child.errors.keys
+    assert_nothing_raised do
+      child.errors.add :foo, :invalid
+    end
   end
 
-  def test_dupd_becomes_persists_changes_from_the_original
+  def test_duped_becomes_persists_changes_from_the_original
     original = topics(:first)
     copy = original.dup.becomes(Reply)
     copy.save!
     assert_equal "The First Topic", Topic.find(copy.id).title
   end
 
+  def test_becomes_wont_break_mutation_tracking
+    topic = topics(:first)
+    reply = topic.becomes(Reply)
+
+    assert_equal 1, topic.id_in_database
+    assert_empty topic.attributes_in_database
+
+    assert_equal 1, reply.id_in_database
+    assert_empty reply.attributes_in_database
+  end
+
   def test_becomes_includes_changed_attributes
     company = Company.new(name: "37signals")
     client = company.becomes(Client)
@@ -193,6 +239,30 @@ class PersistenceTest < ActiveRecord::TestCase
     assert_equal 41, accounts(:signals37, :reload).credit_limit
   end
 
+  def test_decrement_with_touch_updates_timestamps
+    topic = topics(:first)
+    assert_equal 1, topic.replies_count
+    previously_updated_at = topic.updated_at
+    travel(1.second) do
+      topic.decrement!(:replies_count, touch: true)
+    end
+    assert_equal 0, topic.reload.replies_count
+    assert_operator previously_updated_at, :<, topic.updated_at
+  end
+
+  def test_decrement_with_touch_an_attribute_updates_timestamps
+    topic = topics(:first)
+    assert_equal 1, topic.replies_count
+    previously_updated_at = topic.updated_at
+    previously_written_on = topic.written_on
+    travel(1.second) do
+      topic.decrement!(:replies_count, touch: :written_on)
+    end
+    assert_equal 0, topic.reload.replies_count
+    assert_operator previously_updated_at, :<, topic.updated_at
+    assert_operator previously_written_on, :<, topic.written_on
+  end
+
   def test_create
     topic = Topic.new
     topic.title = "New Topic"
@@ -202,7 +272,7 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_save!
-    topic = Topic.new(:title => "New Topic")
+    topic = Topic.new(title: "New Topic")
     assert topic.save!
 
     reply = WrongReply.new
@@ -232,7 +302,7 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_save_for_record_with_only_primary_key_that_is_provided
-    assert_nothing_raised { Minimalistic.create!(:id => 2) }
+    assert_nothing_raised { Minimalistic.create!(id: 2) }
   end
 
   def test_save_with_duping_of_destroyed_object
@@ -240,8 +310,8 @@ class PersistenceTest < ActiveRecord::TestCase
     developer.destroy
     new_developer = developer.dup
     new_developer.save
-    assert new_developer.persisted?
-    assert_not new_developer.destroyed?
+    assert_predicate new_developer, :persisted?
+    assert_not_predicate new_developer, :destroyed?
   end
 
   def test_create_many
@@ -252,12 +322,13 @@ class PersistenceTest < ActiveRecord::TestCase
 
   def test_create_columns_not_equal_attributes
     topic = Topic.instantiate(
-      'attributes' => {
-        'title'          => 'Another New Topic',
-        'does_not_exist' => 'test'
-      }
+      "title"          => "Another New Topic",
+      "does_not_exist" => "test"
     )
+    topic = topic.dup # reset @new_record
     assert_nothing_raised { topic.save }
+    assert_predicate topic, :persisted?
+    assert_equal "Another New Topic", topic.reload.title
   end
 
   def test_create_through_factory_with_block
@@ -301,9 +372,11 @@ class PersistenceTest < ActiveRecord::TestCase
     topic.title = "Still another topic"
     topic.save
 
-    topic_reloaded = Topic.instantiate(topic.attributes.merge('does_not_exist' => 'test'))
-    topic_reloaded.title = 'A New Topic'
+    topic_reloaded = Topic.instantiate(topic.attributes.merge("does_not_exist" => "test"))
+    topic_reloaded.title = "A New Topic"
     assert_nothing_raised { topic_reloaded.save }
+    assert_predicate topic_reloaded, :persisted?
+    assert_equal "A New Topic", topic_reloaded.reload.title
   end
 
   def test_update_for_record_with_only_primary_key
@@ -340,9 +413,25 @@ class PersistenceTest < ActiveRecord::TestCase
     assert_instance_of Reply, Reply.find(reply.id)
   end
 
+  def test_becomes_default_sti_subclass
+    original_type = Topic.columns_hash["type"].default
+    ActiveRecord::Base.connection.change_column_default :topics, :type, "Reply"
+    Topic.reset_column_information
+
+    reply = topics(:second)
+    assert_instance_of Reply, reply
+
+    topic = reply.becomes(Topic)
+    assert_instance_of Topic, topic
+
+  ensure
+    ActiveRecord::Base.connection.change_column_default :topics, :type, original_type
+    Topic.reset_column_information
+  end
+
   def test_update_after_create
     klass = Class.new(Topic) do
-      def self.name; 'Topic'; end
+      def self.name; "Topic"; end
       after_create do
         update_attribute("author_name", "David")
       end
@@ -357,25 +446,23 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_update_attribute_does_not_run_sql_if_attribute_is_not_changed
-    klass = Class.new(Topic) do
-      def self.name; 'Topic'; end
-    end
-    topic = klass.create(title: 'Another New Topic')
-    assert_queries(0) do
-      topic.update_attribute(:title, 'Another New Topic')
+    topic = Topic.create(title: "Another New Topic")
+    assert_no_queries do
+      assert topic.update_attribute(:title, "Another New Topic")
     end
   end
 
   def test_update_does_not_run_sql_if_record_has_not_changed
-    topic = Topic.create(title: 'Another New Topic')
-    assert_queries(0) { topic.update(title: 'Another New Topic') }
-    assert_queries(0) { topic.update_attributes(title: 'Another New Topic') }
+    topic = Topic.create(title: "Another New Topic")
+    assert_no_queries do
+      assert topic.update(title: "Another New Topic")
+    end
   end
 
   def test_delete
     topic = Topic.find(1)
-    assert_equal topic, topic.delete, 'topic.delete did not return self'
-    assert topic.frozen?, 'topic not frozen after delete'
+    assert_equal topic, topic.delete, "topic.delete did not return self"
+    assert topic.frozen?, "topic not frozen after delete"
     assert_raise(ActiveRecord::RecordNotFound) { Topic.find(topic.id) }
   end
 
@@ -384,103 +471,138 @@ class PersistenceTest < ActiveRecord::TestCase
     assert_not_nil Topic.find(2)
   end
 
+  def test_delete_isnt_affected_by_scoping
+    topic = Topic.find(1)
+    assert_difference("Topic.count", -1) do
+      Topic.where("1=0").scoping { topic.delete }
+    end
+  end
+
   def test_destroy
     topic = Topic.find(1)
-    assert_equal topic, topic.destroy, 'topic.destroy did not return self'
-    assert topic.frozen?, 'topic not frozen after destroy'
+    assert_equal topic, topic.destroy, "topic.destroy did not return self"
+    assert topic.frozen?, "topic not frozen after destroy"
     assert_raise(ActiveRecord::RecordNotFound) { Topic.find(topic.id) }
   end
 
   def test_destroy!
     topic = Topic.find(1)
-    assert_equal topic, topic.destroy!, 'topic.destroy! did not return self'
-    assert topic.frozen?, 'topic not frozen after destroy!'
+    assert_equal topic, topic.destroy!, "topic.destroy! did not return self"
+    assert topic.frozen?, "topic not frozen after destroy!"
     assert_raise(ActiveRecord::RecordNotFound) { Topic.find(topic.id) }
   end
 
-  def test_record_not_found_exception
+  def test_find_raises_record_not_found_exception
     assert_raise(ActiveRecord::RecordNotFound) { Topic.find(99999) }
   end
 
+  def test_update_raises_record_not_found_exception
+    assert_raise(ActiveRecord::RecordNotFound) { Topic.update(99999, approved: true) }
+  end
+
+  def test_destroy_raises_record_not_found_exception
+    assert_raise(ActiveRecord::RecordNotFound) { Topic.destroy(99999) }
+  end
+
   def test_update_all
     assert_equal Topic.count, Topic.update_all("content = 'bulk updated!'")
     assert_equal "bulk updated!", Topic.find(1).content
     assert_equal "bulk updated!", Topic.find(2).content
 
-    assert_equal Topic.count, Topic.update_all(['content = ?', 'bulk updated again!'])
+    assert_equal Topic.count, Topic.update_all(["content = ?", "bulk updated again!"])
     assert_equal "bulk updated again!", Topic.find(1).content
     assert_equal "bulk updated again!", Topic.find(2).content
 
-    assert_equal Topic.count, Topic.update_all(['content = ?', nil])
+    assert_equal Topic.count, Topic.update_all(["content = ?", nil])
     assert_nil Topic.find(1).content
   end
 
   def test_update_all_with_hash
     assert_not_nil Topic.find(1).last_read
-    assert_equal Topic.count, Topic.update_all(:content => 'bulk updated with hash!', :last_read => nil)
+    assert_equal Topic.count, Topic.update_all(content: "bulk updated with hash!", last_read: nil)
     assert_equal "bulk updated with hash!", Topic.find(1).content
     assert_equal "bulk updated with hash!", Topic.find(2).content
     assert_nil Topic.find(1).last_read
     assert_nil Topic.find(2).last_read
   end
 
-  def test_update_all_with_non_standard_table_name
-    assert_equal 1, WarehouseThing.where(id: 1).update_all(['value = ?', 0])
-    assert_equal 0, WarehouseThing.find(1).value
-  end
-
   def test_delete_new_record
-    client = Client.new
+    client = Client.new(name: "37signals")
     client.delete
-    assert client.frozen?
+    assert_predicate client, :frozen?
+
+    assert_not client.save
+    assert_raise(ActiveRecord::RecordNotSaved) { client.save! }
+
+    assert_predicate client, :frozen?
+    assert_raise(RuntimeError) { client.name = "something else" }
   end
 
   def test_delete_record_with_associations
     client = Client.find(3)
     client.delete
-    assert client.frozen?
+    assert_predicate client, :frozen?
     assert_kind_of Firm, client.firm
+
+    assert_not client.save
+    assert_raise(ActiveRecord::RecordNotSaved) { client.save! }
+
+    assert_predicate client, :frozen?
     assert_raise(RuntimeError) { client.name = "something else" }
   end
 
   def test_destroy_new_record
-    client = Client.new
+    client = Client.new(name: "37signals")
     client.destroy
-    assert client.frozen?
+    assert_predicate client, :frozen?
+
+    assert_not client.save
+    assert_raise(ActiveRecord::RecordNotSaved) { client.save! }
+
+    assert_predicate client, :frozen?
+    assert_raise(RuntimeError) { client.name = "something else" }
   end
 
   def test_destroy_record_with_associations
     client = Client.find(3)
     client.destroy
-    assert client.frozen?
+    assert_predicate client, :frozen?
     assert_kind_of Firm, client.firm
+
+    assert_not client.save
+    assert_raise(ActiveRecord::RecordNotSaved) { client.save! }
+
+    assert_predicate client, :frozen?
     assert_raise(RuntimeError) { client.name = "something else" }
   end
 
   def test_update_attribute
-    assert !Topic.find(1).approved?
+    assert_not_predicate Topic.find(1), :approved?
     Topic.find(1).update_attribute("approved", true)
-    assert Topic.find(1).approved?
+    assert_predicate Topic.find(1), :approved?
 
     Topic.find(1).update_attribute(:approved, false)
-    assert !Topic.find(1).approved?
+    assert_not_predicate Topic.find(1), :approved?
+
+    Topic.find(1).update_attribute(:change_approved_before_save, true)
+    assert_predicate Topic.find(1), :approved?
   end
 
   def test_update_attribute_for_readonly_attribute
-    minivan = Minivan.find('m1')
-    assert_raises(ActiveRecord::ActiveRecordError) { minivan.update_attribute(:color, 'black') }
+    minivan = Minivan.find("m1")
+    assert_raises(ActiveRecord::ActiveRecordError) { minivan.update_attribute(:color, "black") }
   end
 
   def test_update_attribute_with_one_updated
     t = Topic.first
-    t.update_attribute(:title, 'super_title')
-    assert_equal 'super_title', t.title
-    assert !t.changed?, "topic should not have changed"
-    assert !t.title_changed?, "title should not have changed"
-    assert_nil t.title_change, 'title change should be nil'
+    t.update_attribute(:title, "super_title")
+    assert_equal "super_title", t.title
+    assert_not t.changed?, "topic should not have changed"
+    assert_not t.title_changed?, "title should not have changed"
+    assert_nil t.title_change, "title change should be nil"
 
     t.reload
-    assert_equal 'super_title', t.title
+    assert_equal "super_title", t.title
   end
 
   def test_update_attribute_for_updated_at_on
@@ -500,14 +622,14 @@ class PersistenceTest < ActiveRecord::TestCase
   def test_update_column
     topic = Topic.find(1)
     topic.update_column("approved", true)
-    assert topic.approved?
+    assert_predicate topic, :approved?
     topic.reload
-    assert topic.approved?
+    assert_predicate topic, :approved?
 
     topic.update_column(:approved, false)
-    assert !topic.approved?
+    assert_not_predicate topic, :approved?
     topic.reload
-    assert !topic.approved?
+    assert_not_predicate topic, :approved?
   end
 
   def test_update_column_should_not_use_setter_method
@@ -540,17 +662,17 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_update_column_with_model_having_primary_key_other_than_id
-    minivan = Minivan.find('m1')
-    new_name = 'sebavan'
+    minivan = Minivan.find("m1")
+    new_name = "sebavan"
 
     minivan.update_column(:name, new_name)
     assert_equal new_name, minivan.name
   end
 
   def test_update_column_for_readonly_attribute
-    minivan = Minivan.find('m1')
+    minivan = Minivan.find("m1")
     prev_color = minivan.color
-    assert_raises(ActiveRecord::ActiveRecordError) { minivan.update_column(:color, 'black') }
+    assert_raises(ActiveRecord::ActiveRecordError) { minivan.update_column(:color, "black") }
     assert_equal prev_color, minivan.color
   end
 
@@ -569,35 +691,35 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_update_column_with_one_changed_and_one_updated
-    t = Topic.order('id').limit(1).first
+    t = Topic.order("id").limit(1).first
     author_name = t.author_name
-    t.author_name = 'John'
-    t.update_column(:title, 'super_title')
-    assert_equal 'John', t.author_name
-    assert_equal 'super_title', t.title
+    t.author_name = "John"
+    t.update_column(:title, "super_title")
+    assert_equal "John", t.author_name
+    assert_equal "super_title", t.title
     assert t.changed?, "topic should have changed"
     assert t.author_name_changed?, "author_name should have changed"
 
     t.reload
     assert_equal author_name, t.author_name
-    assert_equal 'super_title', t.title
+    assert_equal "super_title", t.title
   end
 
   def test_update_column_with_default_scope
     developer = DeveloperCalledDavid.first
-    developer.name = 'John'
+    developer.name = "John"
     developer.save!
 
-    assert developer.update_column(:name, 'Will'), 'did not update record due to default scope'
+    assert developer.update_column(:name, "Will"), "did not update record due to default scope"
   end
 
   def test_update_columns
     topic = Topic.find(1)
-    topic.update_columns({ "approved" => true, title: "Sebastian Topic" })
-    assert topic.approved?
+    topic.update_columns("approved" => true, title: "Sebastian Topic")
+    assert_predicate topic, :approved?
     assert_equal "Sebastian Topic", topic.title
     topic.reload
-    assert topic.approved?
+    assert_predicate topic, :approved?
     assert_equal "Sebastian Topic", topic.title
   end
 
@@ -614,35 +736,35 @@ class PersistenceTest < ActiveRecord::TestCase
 
   def test_update_columns_should_raise_exception_if_new_record
     topic = Topic.new
-    assert_raises(ActiveRecord::ActiveRecordError) { topic.update_columns({ approved: false }) }
+    assert_raises(ActiveRecord::ActiveRecordError) { topic.update_columns(approved: false) }
   end
 
   def test_update_columns_should_not_leave_the_object_dirty
     topic = Topic.find(1)
-    topic.update({ "content" => "--- Have a nice day\n...\n", :author_name => "Jose" })
+    topic.update("content" => "--- Have a nice day\n...\n", :author_name => "Jose")
 
     topic.reload
-    topic.update_columns({ content: "--- You too\n...\n", "author_name" => "Sebastian" })
+    topic.update_columns(content: "--- You too\n...\n", "author_name" => "Sebastian")
     assert_equal [], topic.changed
 
     topic.reload
-    topic.update_columns({ content: "--- Have a nice day\n...\n", author_name: "Jose" })
+    topic.update_columns(content: "--- Have a nice day\n...\n", author_name: "Jose")
     assert_equal [], topic.changed
   end
 
   def test_update_columns_with_model_having_primary_key_other_than_id
-    minivan = Minivan.find('m1')
-    new_name = 'sebavan'
+    minivan = Minivan.find("m1")
+    new_name = "sebavan"
 
     minivan.update_columns(name: new_name)
     assert_equal new_name, minivan.name
   end
 
   def test_update_columns_with_one_readonly_attribute
-    minivan = Minivan.find('m1')
+    minivan = Minivan.find("m1")
     prev_color = minivan.color
     prev_name = minivan.name
-    assert_raises(ActiveRecord::ActiveRecordError) { minivan.update_columns({ name: "My old minivan", color: 'black' }) }
+    assert_raises(ActiveRecord::ActiveRecordError) { minivan.update_columns(name: "My old minivan", color: "black") }
     assert_equal prev_color, minivan.color
     assert_equal prev_name, minivan.name
 
@@ -668,18 +790,18 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_update_columns_with_one_changed_and_one_updated
-    t = Topic.order('id').limit(1).first
+    t = Topic.order("id").limit(1).first
     author_name = t.author_name
-    t.author_name = 'John'
-    t.update_columns(title: 'super_title')
-    assert_equal 'John', t.author_name
-    assert_equal 'super_title', t.title
+    t.author_name = "John"
+    t.update_columns(title: "super_title")
+    assert_equal "John", t.author_name
+    assert_equal "super_title", t.title
     assert t.changed?, "topic should have changed"
     assert t.author_name_changed?, "author_name should have changed"
 
     t.reload
     assert_equal author_name, t.author_name
-    assert_equal 'super_title', t.title
+    assert_equal "super_title", t.title
   end
 
   def test_update_columns_changing_id
@@ -697,61 +819,53 @@ class PersistenceTest < ActiveRecord::TestCase
 
   def test_update_columns_with_default_scope
     developer = DeveloperCalledDavid.first
-    developer.name = 'John'
+    developer.name = "John"
     developer.save!
 
-    assert developer.update_columns(name: 'Will'), 'did not update record due to default scope'
+    assert developer.update_columns(name: "Will"), "did not update record due to default scope"
   end
 
   def test_update
     topic = Topic.find(1)
-    assert !topic.approved?
+    assert_not_predicate topic, :approved?
     assert_equal "The First Topic", topic.title
 
     topic.update("approved" => true, "title" => "The First Topic Updated")
     topic.reload
-    assert topic.approved?
+    assert_predicate topic, :approved?
     assert_equal "The First Topic Updated", topic.title
 
     topic.update(approved: false, title: "The First Topic")
     topic.reload
-    assert !topic.approved?
-    assert_equal "The First Topic", topic.title
-  end
-
-  def test_update_attributes
-    topic = Topic.find(1)
-    assert !topic.approved?
-    assert_equal "The First Topic", topic.title
-
-    topic.update_attributes("approved" => true, "title" => "The First Topic Updated")
-    topic.reload
-    assert topic.approved?
-    assert_equal "The First Topic Updated", topic.title
-
-    topic.update_attributes(approved: false, title: "The First Topic")
-    topic.reload
-    assert !topic.approved?
+    assert_not_predicate topic, :approved?
     assert_equal "The First Topic", topic.title
 
-    assert_raise(ActiveRecord::RecordNotUnique, ActiveRecord::StatementInvalid) do
-      topic.update_attributes(id: 3, title: "Hm is it possible?")
+    error = assert_raise(ActiveRecord::RecordNotUnique, ActiveRecord::StatementInvalid) do
+      topic.update(id: 3, title: "Hm is it possible?")
     end
+    assert_not_nil error.cause
     assert_not_equal "Hm is it possible?", Topic.find(3).title
 
-    topic.update_attributes(id: 1234)
+    topic.update(id: 1234)
     assert_nothing_raised { topic.reload }
     assert_equal topic.title, Topic.find(1234).title
   end
 
-  def test_update_attributes_parameters
+  def test_update_attributes
+    topic = Topic.find(1)
+    assert_deprecated do
+      topic.update_attributes("title" => "The First Topic Updated")
+    end
+  end
+
+  def test_update_parameters
     topic = Topic.find(1)
     assert_nothing_raised do
-      topic.update_attributes({})
+      topic.update({})
     end
 
     assert_raises(ArgumentError) do
-      topic.update_attributes(nil)
+      topic.update(nil)
     end
   end
 
@@ -777,24 +891,10 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_update_attributes!
-    Reply.validates_presence_of(:title)
     reply = Reply.find(2)
-    assert_equal "The Second Topic of the day", reply.title
-    assert_equal "Have a nice day", reply.content
-
-    reply.update_attributes!("title" => "The Second Topic of the day updated", "content" => "Have a nice evening")
-    reply.reload
-    assert_equal "The Second Topic of the day updated", reply.title
-    assert_equal "Have a nice evening", reply.content
-
-    reply.update_attributes!(title: "The Second Topic of the day", content: "Have a nice day")
-    reply.reload
-    assert_equal "The Second Topic of the day", reply.title
-    assert_equal "Have a nice day", reply.content
-
-    assert_raise(ActiveRecord::RecordInvalid) { reply.update_attributes!(title: nil, content: "Have a nice evening") }
-  ensure
-    Reply.clear_validators!
+    assert_deprecated do
+      reply.update_attributes!("title" => "The Second Topic of the day updated")
+    end
   end
 
   def test_destroyed_returns_boolean
@@ -810,7 +910,7 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_persisted_returns_boolean
-    developer = Developer.new(:name => "Jose")
+    developer = Developer.new(name: "Jose")
     assert_equal false, developer.persisted?
     developer.save!
     assert_equal true, developer.persisted?
@@ -830,18 +930,41 @@ class PersistenceTest < ActiveRecord::TestCase
     should_be_destroyed_reply = Reply.create("title" => "hello", "content" => "world")
     Topic.find(1).replies << should_be_destroyed_reply
 
-    Topic.destroy(1)
+    topic = Topic.destroy(1)
+    assert_predicate topic, :destroyed?
+
     assert_raise(ActiveRecord::RecordNotFound) { Topic.find(1) }
     assert_raise(ActiveRecord::RecordNotFound) { Reply.find(should_be_destroyed_reply.id) }
   end
 
+  def test_class_level_destroy_is_affected_by_scoping
+    should_not_be_destroyed_reply = Reply.create("title" => "hello", "content" => "world")
+    Topic.find(1).replies << should_not_be_destroyed_reply
+
+    assert_raise(ActiveRecord::RecordNotFound) do
+      Topic.where("1=0").scoping { Topic.destroy(1) }
+    end
+
+    assert_nothing_raised { Topic.find(1) }
+    assert_nothing_raised { Reply.find(should_not_be_destroyed_reply.id) }
+  end
+
   def test_class_level_delete
-    should_be_destroyed_reply = Reply.create("title" => "hello", "content" => "world")
-    Topic.find(1).replies << should_be_destroyed_reply
+    should_not_be_destroyed_reply = Reply.create("title" => "hello", "content" => "world")
+    Topic.find(1).replies << should_not_be_destroyed_reply
 
     Topic.delete(1)
     assert_raise(ActiveRecord::RecordNotFound) { Topic.find(1) }
-    assert_nothing_raised { Reply.find(should_be_destroyed_reply.id) }
+    assert_nothing_raised { Reply.find(should_not_be_destroyed_reply.id) }
+  end
+
+  def test_class_level_delete_is_affected_by_scoping
+    should_not_be_destroyed_reply = Reply.create("title" => "hello", "content" => "world")
+    Topic.find(1).replies << should_not_be_destroyed_reply
+
+    Topic.where("1=0").scoping { Topic.delete(1) }
+    assert_nothing_raised { Topic.find(1) }
+    assert_nothing_raised { Reply.find(should_not_be_destroyed_reply.id) }
   end
 
   def test_create_with_custom_timestamps
@@ -879,7 +1002,7 @@ class PersistenceTest < ActiveRecord::TestCase
   end
 
   def test_reload_removes_custom_selects
-    post = Post.select('posts.*, 1 as wibble').last!
+    post = Post.select("posts.*, 1 as wibble").last!
 
     assert_equal 1, post[:wibble]
     assert_nil post.reload[:wibble]
@@ -888,20 +1011,20 @@ class PersistenceTest < ActiveRecord::TestCase
   def test_find_via_reload
     post = Post.new
 
-    assert post.new_record?
+    assert_predicate post, :new_record?
 
     post.id = 1
     post.reload
 
     assert_equal "Welcome to the weblog", post.title
-    assert_not post.new_record?
+    assert_not_predicate post, :new_record?
   end
 
   def test_reload_via_querycache
     ActiveRecord::Base.connection.enable_query_cache!
     ActiveRecord::Base.connection.clear_query_cache
-    assert ActiveRecord::Base.connection.query_cache_enabled, 'cache should be on'
-    parrot = Parrot.create(:name => 'Shane')
+    assert ActiveRecord::Base.connection.query_cache_enabled, "cache should be on"
+    parrot = Parrot.create(name: "Shane")
 
     # populate the cache with the SELECT result
     found_parrot = Parrot.find(parrot.id)
@@ -910,49 +1033,50 @@ class PersistenceTest < ActiveRecord::TestCase
     # Manually update the 'name' attribute in the DB directly
     assert_equal 1, ActiveRecord::Base.connection.query_cache.length
     ActiveRecord::Base.uncached do
-      found_parrot.name = 'Mary'
+      found_parrot.name = "Mary"
       found_parrot.save
     end
 
     # Now reload, and verify that it gets the DB version, and not the querycache version
     found_parrot.reload
-    assert_equal 'Mary', found_parrot.name
+    assert_equal "Mary", found_parrot.name
 
     found_parrot = Parrot.find(parrot.id)
-    assert_equal 'Mary', found_parrot.name
+    assert_equal "Mary", found_parrot.name
   ensure
     ActiveRecord::Base.connection.disable_query_cache!
   end
 
-  class SaveTest < ActiveRecord::TestCase
-    self.use_transactional_tests = false
+  def test_save_touch_false
+    parrot = Parrot.create!(
+      name: "Bob",
+      created_at: 1.day.ago,
+      updated_at: 1.day.ago)
 
-    def test_save_touch_false
-      widget = Class.new(ActiveRecord::Base) do
-        connection.create_table :widgets, force: true do |t|
-          t.string :name
-          t.timestamps null: false
-        end
+    created_at = parrot.created_at
+    updated_at = parrot.updated_at
 
-        self.table_name = :widgets
-      end
+    parrot.name = "Barb"
+    parrot.save!(touch: false)
+    assert_equal parrot.created_at, created_at
+    assert_equal parrot.updated_at, updated_at
+  end
 
-      instance  = widget.create!({
-        name: 'Bob',
-        created_at: 1.day.ago,
-        updated_at: 1.day.ago
-      })
-
-      created_at = instance.created_at
-      updated_at = instance.updated_at
-
-      instance.name = 'Barb'
-      instance.save!(touch: false)
-      assert_equal instance.created_at, created_at
-      assert_equal instance.updated_at, updated_at
-    ensure
-      ActiveRecord::Base.connection.drop_table widget.table_name
-      widget.reset_column_information
-    end
+  def test_reset_column_information_resets_children
+    child_class = Class.new(Topic)
+    child_class.new # force schema to load
+
+    ActiveRecord::Base.connection.add_column(:topics, :foo, :string)
+    Topic.reset_column_information
+
+    # this should redefine attribute methods
+    child_class.new
+
+    assert child_class.instance_methods.include?(:foo)
+    assert child_class.instance_methods.include?(:foo_changed?)
+    assert_equal "bar", child_class.new(foo: :bar).foo
+  ensure
+    ActiveRecord::Base.connection.remove_column(:topics, :foo)
+    Topic.reset_column_information
   end
 end
diff --git a/activerecord/test/cases/pooled_connections_test.rb b/activerecord/test/cases/pooled_connections_test.rb
index daa3271777..fa7f759e51 100644
--- a/activerecord/test/cases/pooled_connections_test.rb
+++ b/activerecord/test/cases/pooled_connections_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "models/project"
 require "timeout"
@@ -18,7 +20,7 @@ class PooledConnectionsTest < ActiveRecord::TestCase
 
   # Will deadlock due to lack of Monitor timeouts in 1.9
   def checkout_checkin_connections(pool_size, threads)
-    ActiveRecord::Base.establish_connection(@connection.merge({:pool => pool_size, :checkout_timeout => 0.5}))
+    ActiveRecord::Base.establish_connection(@connection.merge(pool: pool_size, checkout_timeout: 0.5))
     @connection_count = 0
     @timed_out = 0
     threads.times do
@@ -36,7 +38,7 @@ class PooledConnectionsTest < ActiveRecord::TestCase
   end
 
   def checkout_checkin_connections_loop(pool_size, loops)
-    ActiveRecord::Base.establish_connection(@connection.merge({:pool => pool_size, :checkout_timeout => 0.5}))
+    ActiveRecord::Base.establish_connection(@connection.merge(pool: pool_size, checkout_timeout: 0.5))
     @connection_count = 0
     @timed_out = 0
     loops.times do
@@ -44,7 +46,7 @@ class PooledConnectionsTest < ActiveRecord::TestCase
         conn = ActiveRecord::Base.connection_pool.checkout
         ActiveRecord::Base.connection_pool.checkin conn
         @connection_count += 1
-        ActiveRecord::Base.connection.tables
+        ActiveRecord::Base.connection.data_sources
       rescue ActiveRecord::ConnectionTimeoutError
         @timed_out += 1
       end
@@ -66,7 +68,7 @@ class PooledConnectionsTest < ActiveRecord::TestCase
   end
 
   def test_pooled_connection_remove
-    ActiveRecord::Base.establish_connection(@connection.merge({:pool => 2, :checkout_timeout => 0.5}))
+    ActiveRecord::Base.establish_connection(@connection.merge(pool: 2, checkout_timeout: 0.5))
     old_connection = ActiveRecord::Base.connection
     extra_connection = ActiveRecord::Base.connection_pool.checkout
     ActiveRecord::Base.connection_pool.remove(extra_connection)
@@ -75,7 +77,7 @@ class PooledConnectionsTest < ActiveRecord::TestCase
 
   private
 
-  def add_record(name)
-    ActiveRecord::Base.connection_pool.with_connection { Project.create! :name => name }
-  end
+    def add_record(name)
+      ActiveRecord::Base.connection_pool.with_connection { Project.create! name: name }
+    end
 end unless in_memory_db?
diff --git a/activerecord/test/cases/primary_keys_test.rb b/activerecord/test/cases/primary_keys_test.rb
index 0745a37ee9..4ed7469039 100644
--- a/activerecord/test/cases/primary_keys_test.rb
+++ b/activerecord/test/cases/primary_keys_test.rb
@@ -1,12 +1,15 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
-require 'models/topic'
-require 'models/reply'
-require 'models/subscriber'
-require 'models/movie'
-require 'models/keyboard'
-require 'models/mixed_case_monkey'
-require 'models/dashboard'
+require "support/schema_dumping_helper"
+require "models/topic"
+require "models/reply"
+require "models/subscriber"
+require "models/movie"
+require "models/keyboard"
+require "models/mixed_case_monkey"
+require "models/dashboard"
+require "models/non_primary_key"
 
 class PrimaryKeysTest < ActiveRecord::TestCase
   fixtures :topics, :subscribers, :movies, :mixed_case_monkeys
@@ -45,7 +48,7 @@ class PrimaryKeysTest < ActiveRecord::TestCase
     topic = Topic.new
     topic.title = "New Topic"
     assert_nil topic.id
-    assert_nothing_raised { topic.save! }
+    topic.save!
     id = topic.id
 
     topicReloaded = Topic.find(id)
@@ -54,22 +57,35 @@ class PrimaryKeysTest < ActiveRecord::TestCase
 
   def test_customized_primary_key_auto_assigns_on_save
     Keyboard.delete_all
-    keyboard = Keyboard.new(:name => 'HHKB')
-    assert_nothing_raised { keyboard.save! }
-    assert_equal keyboard.id, Keyboard.find_by_name('HHKB').id
+    keyboard = Keyboard.new(name: "HHKB")
+    keyboard.save!
+    assert_equal keyboard.id, Keyboard.find_by_name("HHKB").id
   end
 
   def test_customized_primary_key_can_be_get_before_saving
     keyboard = Keyboard.new
     assert_nil keyboard.id
-    assert_nothing_raised { assert_nil keyboard.key_number }
+    assert_nil keyboard.key_number
   end
 
   def test_customized_string_primary_key_settable_before_save
     subscriber = Subscriber.new
-    assert_nothing_raised { subscriber.id = 'webster123' }
-    assert_equal 'webster123', subscriber.id
-    assert_equal 'webster123', subscriber.nick
+    subscriber.id = "webster123"
+    assert_equal "webster123", subscriber.id
+    assert_equal "webster123", subscriber.nick
+  end
+
+  def test_update_with_non_primary_key_id_column
+    subscriber = Subscriber.first
+    subscriber.update(update_count: 1)
+    subscriber.reload
+    assert_equal 1, subscriber.update_count
+  end
+
+  def test_update_columns_with_non_primary_key_id_column
+    subscriber = Subscriber.first
+    subscriber.update_columns(id: 1)
+    assert_not_equal 1, subscriber.nick
   end
 
   def test_string_key
@@ -82,13 +98,19 @@ class PrimaryKeysTest < ActiveRecord::TestCase
     subscriber.id = "jdoe"
     assert_equal("jdoe", subscriber.id)
     subscriber.name = "John Doe"
-    assert_nothing_raised { subscriber.save! }
+    subscriber.save!
     assert_equal("jdoe", subscriber.id)
 
     subscriberReloaded = Subscriber.find("jdoe")
     assert_equal("John Doe", subscriberReloaded.name)
   end
 
+  def test_id_column_that_is_not_primary_key
+    NonPrimaryKey.create!(id: 100)
+    actual = NonPrimaryKey.find_by(id: 100)
+    assert_match %r{<NonPrimaryKey id: 100}, actual.inspect
+  end
+
   def test_find_with_more_than_one_string_key
     assert_equal 2, Subscriber.find(subscribers(:first).nick, subscribers(:second).nick).length
   end
@@ -113,50 +135,45 @@ class PrimaryKeysTest < ActiveRecord::TestCase
   def test_delete_should_quote_pkey
     assert_nothing_raised { MixedCaseMonkey.delete(1) }
   end
+
   def test_update_counters_should_quote_pkey_and_quote_counter_columns
-    assert_nothing_raised { MixedCaseMonkey.update_counters(1, :fleaCount => 99) }
+    assert_nothing_raised { MixedCaseMonkey.update_counters(1, fleaCount: 99) }
   end
+
   def test_find_with_one_id_should_quote_pkey
     assert_nothing_raised { MixedCaseMonkey.find(1) }
   end
+
   def test_find_with_multiple_ids_should_quote_pkey
-    assert_nothing_raised { MixedCaseMonkey.find([1,2]) }
+    assert_nothing_raised { MixedCaseMonkey.find([1, 2]) }
   end
+
   def test_instance_update_should_quote_pkey
     assert_nothing_raised { MixedCaseMonkey.find(1).save }
   end
+
   def test_instance_destroy_should_quote_pkey
     assert_nothing_raised { MixedCaseMonkey.find(1).destroy }
   end
 
-  def test_supports_primary_key
-    assert_nothing_raised NoMethodError do
-      ActiveRecord::Base.connection.supports_primary_key?
-    end
-  end
-
   def test_primary_key_returns_value_if_it_exists
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'developers'
+      self.table_name = "developers"
     end
 
-    if ActiveRecord::Base.connection.supports_primary_key?
-      assert_equal 'id', klass.primary_key
-    end
+    assert_equal "id", klass.primary_key
   end
 
   def test_primary_key_returns_nil_if_it_does_not_exist
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'developers_projects'
+      self.table_name = "developers_projects"
     end
 
-    if ActiveRecord::Base.connection.supports_primary_key?
-      assert_nil klass.primary_key
-    end
+    assert_nil klass.primary_key
   end
 
   def test_quoted_primary_key_after_set_primary_key
-    k = Class.new( ActiveRecord::Base )
+    k = Class.new(ActiveRecord::Base)
     assert_equal k.connection.quote_column_name("id"), k.quoted_primary_key
     k.primary_key = "foo"
     assert_equal k.connection.quote_column_name("foo"), k.quoted_primary_key
@@ -168,25 +185,35 @@ class PrimaryKeysTest < ActiveRecord::TestCase
   end
 
   def test_primary_key_update_with_custom_key_name
-    dashboard = Dashboard.create!(dashboard_id: '1')
-    dashboard.id = '2'
+    dashboard = Dashboard.create!(dashboard_id: "1")
+    dashboard.id = "2"
     dashboard.save!
 
     dashboard = Dashboard.first
-    assert_equal '2', dashboard.id
+    assert_equal "2", dashboard.id
+  end
+
+  def test_create_without_primary_key_no_extra_query
+    skip if current_adapter?(:OracleAdapter)
+
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = "dashboards"
+    end
+    klass.create! # warmup schema cache
+    assert_queries(3, ignore_none: true) { klass.create! }
   end
 
   if current_adapter?(:PostgreSQLAdapter)
     def test_serial_with_quoted_sequence_name
       column = MixedCaseMonkey.columns_hash[MixedCaseMonkey.primary_key]
       assert_equal "nextval('\"mixed_case_monkeys_monkeyID_seq\"'::regclass)", column.default_function
-      assert column.serial?
+      assert_predicate column, :serial?
     end
 
     def test_serial_with_unquoted_sequence_name
       column = Topic.columns_hash[Topic.primary_key]
       assert_equal "nextval('topics_id_seq'::regclass)", column.default_function
-      assert column.serial?
+      assert_predicate column, :serial?
     end
   end
 end
@@ -199,17 +226,54 @@ class PrimaryKeyWithNoConnectionTest < ActiveRecord::TestCase
       connection = ActiveRecord::Base.remove_connection
 
       model = Class.new(ActiveRecord::Base)
-      model.primary_key = 'foo'
+      model.primary_key = "foo"
 
-      assert_equal 'foo', model.primary_key
+      assert_equal "foo", model.primary_key
 
       ActiveRecord::Base.establish_connection(connection)
 
-      assert_equal 'foo', model.primary_key
+      assert_equal "foo", model.primary_key
     end
   end
 end
 
+class PrimaryKeyWithAutoIncrementTest < ActiveRecord::TestCase
+  self.use_transactional_tests = false
+
+  class AutoIncrement < ActiveRecord::Base
+  end
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+  end
+
+  def teardown
+    @connection.drop_table(:auto_increments, if_exists: true)
+  end
+
+  def test_primary_key_with_integer
+    @connection.create_table(:auto_increments, id: :integer, force: true)
+    assert_auto_incremented
+  end
+
+  def test_primary_key_with_bigint
+    @connection.create_table(:auto_increments, id: :bigint, force: true)
+    assert_auto_incremented
+  end
+
+  private
+    def assert_auto_incremented
+      record1 = AutoIncrement.create!
+      assert_not_nil record1.id
+
+      record1.destroy
+
+      record2 = AutoIncrement.create!
+      assert_not_nil record2.id
+      assert_operator record2.id, :>, record1.id
+    end
+end
+
 class PrimaryKeyAnyTypeTest < ActiveRecord::TestCase
   include SchemaDumpingHelper
 
@@ -224,39 +288,129 @@ class PrimaryKeyAnyTypeTest < ActiveRecord::TestCase
   end
 
   teardown do
-    @connection.drop_table(:barcodes) if @connection.table_exists? :barcodes
+    @connection.drop_table(:barcodes, if_exists: true)
   end
 
   def test_any_type_primary_key
     assert_equal "code", Barcode.primary_key
 
-    column_type = Barcode.type_for_attribute(Barcode.primary_key)
-    assert_equal :string, column_type.type
-    assert_equal 42, column_type.limit
+    column = Barcode.column_for_attribute(Barcode.primary_key)
+    assert_not column.null
+    assert_equal :string, column.type
+    assert_equal 42, column.limit
+  ensure
+    Barcode.reset_column_information
   end
 
   test "schema dump primary key includes type and options" do
     schema = dump_table_schema "barcodes"
     assert_match %r{create_table "barcodes", primary_key: "code", id: :string, limit: 42}, schema
+    assert_no_match %r{t\.index \["code"\]}, schema
+  end
+
+  if current_adapter?(:Mysql2Adapter) && subsecond_precision_supported?
+    test "schema typed primary key column" do
+      @connection.create_table(:scheduled_logs, id: :timestamp, precision: 6, force: true)
+      schema = dump_table_schema("scheduled_logs")
+      assert_match %r/create_table "scheduled_logs", id: :timestamp, precision: 6/, schema
+    end
   end
 end
 
-if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-  class PrimaryKeyWithAnsiQuotesTest < ActiveRecord::TestCase
-    self.use_transactional_tests = false
+class CompositePrimaryKeyTest < ActiveRecord::TestCase
+  include SchemaDumpingHelper
+
+  self.use_transactional_tests = false
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+    @connection.schema_cache.clear!
+    @connection.create_table(:uber_barcodes, primary_key: ["region", "code"], force: true) do |t|
+      t.string :region
+      t.integer :code
+    end
+    @connection.create_table(:barcodes_reverse, primary_key: ["code", "region"], force: true) do |t|
+      t.string :region
+      t.integer :code
+    end
+    @connection.create_table(:travels, primary_key: ["from", "to"], force: true) do |t|
+      t.string :from
+      t.string :to
+    end
+  end
+
+  def teardown
+    @connection.drop_table :uber_barcodes, if_exists: true
+    @connection.drop_table :barcodes_reverse, if_exists: true
+    @connection.drop_table :travels, if_exists: true
+  end
 
-    def test_primary_key_method_with_ansi_quotes
-      con = ActiveRecord::Base.connection
-      con.execute("SET SESSION sql_mode='ANSI_QUOTES'")
-      assert_equal "id", con.primary_key("topics")
-    ensure
-      con.reconnect!
+  def test_composite_primary_key
+    assert_equal ["region", "code"], @connection.primary_keys("uber_barcodes")
+  end
+
+  def test_composite_primary_key_with_reserved_words
+    assert_equal ["from", "to"], @connection.primary_keys("travels")
+  end
+
+  def test_composite_primary_key_out_of_order
+    skip if current_adapter?(:SQLite3Adapter)
+    assert_equal ["code", "region"], @connection.primary_keys("barcodes_reverse")
+  end
+
+  def test_primary_key_issues_warning
+    model = Class.new(ActiveRecord::Base) do
+      def self.table_name
+        "uber_barcodes"
+      end
+    end
+    warning = capture(:stderr) do
+      assert_nil model.primary_key
     end
+    assert_match(/WARNING: Active Record does not support composite primary key\./, warning)
+  end
+
+  def test_collectly_dump_composite_primary_key
+    schema = dump_table_schema "uber_barcodes"
+    assert_match %r{create_table "uber_barcodes", primary_key: \["region", "code"\]}, schema
+  end
+
+  def test_dumping_composite_primary_key_out_of_order
+    skip if current_adapter?(:SQLite3Adapter)
+    schema = dump_table_schema "barcodes_reverse"
+    assert_match %r{create_table "barcodes_reverse", primary_key: \["code", "region"\]}, schema
+  end
+end
+
+class PrimaryKeyIntegerNilDefaultTest < ActiveRecord::TestCase
+  include SchemaDumpingHelper
+
+  self.use_transactional_tests = false
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+  end
+
+  def teardown
+    @connection.drop_table :int_defaults, if_exists: true
+  end
+
+  def test_schema_dump_primary_key_integer_with_default_nil
+    skip if current_adapter?(:SQLite3Adapter)
+    @connection.create_table(:int_defaults, id: :integer, default: nil, force: true)
+    schema = dump_table_schema "int_defaults"
+    assert_match %r{create_table "int_defaults", id: :integer, default: nil}, schema
+  end
+
+  def test_schema_dump_primary_key_bigint_with_default_nil
+    @connection.create_table(:int_defaults, id: :bigint, default: nil, force: true)
+    schema = dump_table_schema "int_defaults"
+    assert_match %r{create_table "int_defaults", id: :bigint, default: nil}, schema
   end
 end
 
-if current_adapter?(:PostgreSQLAdapter, :MysqlAdapter, :Mysql2Adapter)
-  class PrimaryKeyBigSerialTest < ActiveRecord::TestCase
+if current_adapter?(:PostgreSQLAdapter, :Mysql2Adapter)
+  class PrimaryKeyIntegerTest < ActiveRecord::TestCase
     include SchemaDumpingHelper
 
     self.use_transactional_tests = false
@@ -266,45 +420,55 @@ if current_adapter?(:PostgreSQLAdapter, :MysqlAdapter, :Mysql2Adapter)
 
     setup do
       @connection = ActiveRecord::Base.connection
-      if current_adapter?(:PostgreSQLAdapter)
-        @connection.create_table(:widgets, id: :bigserial, force: true)
-      else
-        @connection.create_table(:widgets, id: :bigint, force: true)
-      end
+      @pk_type = current_adapter?(:PostgreSQLAdapter) ? :serial : :integer
     end
 
     teardown do
       @connection.drop_table :widgets, if_exists: true
-      Widget.reset_column_information
     end
 
-    test "primary key column type with bigserial" do
-      column_type = Widget.type_for_attribute(Widget.primary_key)
-      assert_equal :integer, column_type.type
-      assert_equal 8, column_type.limit
+    test "primary key column type with serial/integer" do
+      @connection.create_table(:widgets, id: @pk_type, force: true)
+      column = @connection.columns(:widgets).find { |c| c.name == "id" }
+      assert_equal :integer, column.type
+      assert_not_predicate column, :bigint?
     end
 
-    test "primary key with bigserial are automatically numbered" do
+    test "primary key with serial/integer are automatically numbered" do
+      @connection.create_table(:widgets, id: @pk_type, force: true)
       widget = Widget.create!
       assert_not_nil widget.id
     end
 
-    test "schema dump primary key with bigserial" do
+    test "schema dump primary key with serial/integer" do
+      @connection.create_table(:widgets, id: @pk_type, force: true)
       schema = dump_table_schema "widgets"
-      if current_adapter?(:PostgreSQLAdapter)
-        assert_match %r{create_table "widgets", id: :bigserial}, schema
-      else
-        assert_match %r{create_table "widgets", id: :bigint}, schema
-      end
+      assert_match %r{create_table "widgets", id: :#{@pk_type}, }, schema
     end
 
-    if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
+    if current_adapter?(:Mysql2Adapter)
       test "primary key column type with options" do
-        @connection.create_table(:widgets, id: :primary_key, limit: 8, force: true)
-        column = @connection.columns(:widgets).find { |c| c.name == 'id' }
-        assert column.auto_increment?
+        @connection.create_table(:widgets, id: :primary_key, limit: 4, unsigned: true, force: true)
+        column = @connection.columns(:widgets).find { |c| c.name == "id" }
+        assert_predicate column, :auto_increment?
         assert_equal :integer, column.type
-        assert_equal 8, column.limit
+        assert_not_predicate column, :bigint?
+        assert_predicate column, :unsigned?
+
+        schema = dump_table_schema "widgets"
+        assert_match %r{create_table "widgets", id: :integer, unsigned: true, }, schema
+      end
+
+      test "bigint primary key with unsigned" do
+        @connection.create_table(:widgets, id: :bigint, unsigned: true, force: true)
+        column = @connection.columns(:widgets).find { |c| c.name == "id" }
+        assert_predicate column, :auto_increment?
+        assert_equal :integer, column.type
+        assert_predicate column, :bigint?
+        assert_predicate column, :unsigned?
+
+        schema = dump_table_schema "widgets"
+        assert_match %r{create_table "widgets", id: :bigint, unsigned: true, }, schema
       end
     end
   end
diff --git a/activerecord/test/cases/query_cache_test.rb b/activerecord/test/cases/query_cache_test.rb
index 2f0b5df286..565190c476 100644
--- a/activerecord/test/cases/query_cache_test.rb
+++ b/activerecord/test/cases/query_cache_test.rb
@@ -1,123 +1,166 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/task'
-require 'models/category'
-require 'models/post'
-require 'rack'
+require "models/topic"
+require "models/task"
+require "models/category"
+require "models/post"
+require "rack"
 
 class QueryCacheTest < ActiveRecord::TestCase
+  self.use_transactional_tests = false
+
   fixtures :tasks, :topics, :categories, :posts, :categories_posts
 
-  teardown do
+  class ShouldNotHaveExceptionsLogger < ActiveRecord::LogSubscriber
+    attr_reader :logger, :events
+
+    def initialize
+      super
+      @logger = ::Logger.new File::NULL
+      @exception = false
+      @events = []
+    end
+
+    def exception?
+      @exception
+    end
+
+    def sql(event)
+      @events << event
+      super
+    rescue
+      @exception = true
+    end
+  end
+
+  def teardown
     Task.connection.clear_query_cache
     ActiveRecord::Base.connection.disable_query_cache!
+    super
   end
 
   def test_exceptional_middleware_clears_and_disables_cache_on_error
-    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache off'
+    assert_cache :off
 
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       Task.find 1
       Task.find 1
-      assert_equal 1, ActiveRecord::Base.connection.query_cache.length
-      raise "lol borked"
-    }
-    assert_raises(RuntimeError) { mw.call({}) }
-
-    assert_equal 0, ActiveRecord::Base.connection.query_cache.length
-    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache off'
-  end
-
-  def test_exceptional_middleware_leaves_enabled_cache_alone
-    ActiveRecord::Base.connection.enable_query_cache!
-
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+      query_cache = ActiveRecord::Base.connection.query_cache
+      assert_equal 1, query_cache.length, query_cache.keys
       raise "lol borked"
     }
     assert_raises(RuntimeError) { mw.call({}) }
 
-    assert ActiveRecord::Base.connection.query_cache_enabled, 'cache on'
+    assert_cache :off
   end
 
-  def test_exceptional_middleware_assigns_original_connection_id_on_error
-    connection_id = ActiveRecord::Base.connection_id
-
-    mw = ActiveRecord::QueryCache.new lambda { |env|
-      ActiveRecord::Base.connection_id = self.object_id
-      raise "lol borked"
-    }
-    assert_raises(RuntimeError) { mw.call({}) }
-
-    assert_equal connection_id, ActiveRecord::Base.connection_id
+  def test_query_cache_across_threads
+    with_temporary_connection_pool do
+      begin
+        if in_memory_db?
+          # Separate connections to an in-memory database create an entirely new database,
+          # with an empty schema etc, so we just stub out this schema on the fly.
+          ActiveRecord::Base.connection_pool.with_connection do |connection|
+            connection.create_table :tasks do |t|
+              t.datetime :starting
+              t.datetime :ending
+            end
+          end
+          ActiveRecord::FixtureSet.create_fixtures(self.class.fixture_path, ["tasks"], {}, ActiveRecord::Base)
+        end
+
+        ActiveRecord::Base.connection_pool.connections.each do |conn|
+          assert_cache :off, conn
+        end
+
+        assert_not_predicate ActiveRecord::Base.connection, :nil?
+        assert_cache :off
+
+        middleware {
+          assert_cache :clean
+
+          Task.find 1
+          assert_cache :dirty
+
+          thread_1_connection = ActiveRecord::Base.connection
+          ActiveRecord::Base.clear_active_connections!
+          assert_cache :off, thread_1_connection
+
+          started = Concurrent::Event.new
+          checked = Concurrent::Event.new
+
+          thread_2_connection = nil
+          thread = Thread.new {
+            thread_2_connection = ActiveRecord::Base.connection
+
+            assert_equal thread_2_connection, thread_1_connection
+            assert_cache :off
+
+            middleware {
+              assert_cache :clean
+
+              Task.find 1
+              assert_cache :dirty
+
+              started.set
+              checked.wait
+
+              ActiveRecord::Base.clear_active_connections!
+            }.call({})
+          }
+
+          started.wait
+
+          thread_1_connection = ActiveRecord::Base.connection
+          assert_not_equal thread_1_connection, thread_2_connection
+          assert_cache :dirty, thread_2_connection
+          checked.set
+          thread.join
+
+          assert_cache :off, thread_2_connection
+        }.call({})
+
+        ActiveRecord::Base.connection_pool.connections.each do |conn|
+          assert_cache :off, conn
+        end
+      ensure
+        ActiveRecord::Base.connection_pool.disconnect!
+      end
+    end
   end
 
   def test_middleware_delegates
     called = false
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       called = true
       [200, {}, nil]
     }
     mw.call({})
-    assert called, 'middleware should delegate'
+    assert called, "middleware should delegate"
   end
 
   def test_middleware_caches
-    mw = ActiveRecord::QueryCache.new lambda { |env|
+    mw = middleware { |env|
       Task.find 1
       Task.find 1
-      assert_equal 1, ActiveRecord::Base.connection.query_cache.length
+      query_cache = ActiveRecord::Base.connection.query_cache
+      assert_equal 1, query_cache.length, query_cache.keys
       [200, {}, nil]
     }
     mw.call({})
   end
 
   def test_cache_enabled_during_call
-    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache off'
+    assert_cache :off
 
-    mw = ActiveRecord::QueryCache.new lambda { |env|
-      assert ActiveRecord::Base.connection.query_cache_enabled, 'cache on'
+    mw = middleware { |env|
+      assert_cache :clean
       [200, {}, nil]
     }
     mw.call({})
   end
 
-  def test_cache_on_during_body_write
-    streaming = Class.new do
-      def each
-        yield ActiveRecord::Base.connection.query_cache_enabled
-      end
-    end
-
-    mw = ActiveRecord::QueryCache.new lambda { |env|
-      [200, {}, streaming.new]
-    }
-    body = mw.call({}).last
-    body.each { |x| assert x, 'cache should be on' }
-    body.close
-    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache disabled'
-  end
-
-  def test_cache_off_after_close
-    mw = ActiveRecord::QueryCache.new lambda { |env| [200, {}, nil] }
-    body = mw.call({}).last
-
-    assert ActiveRecord::Base.connection.query_cache_enabled, 'cache enabled'
-    body.close
-    assert !ActiveRecord::Base.connection.query_cache_enabled, 'cache disabled'
-  end
-
-  def test_cache_clear_after_close
-    mw = ActiveRecord::QueryCache.new lambda { |env|
-      Post.first
-      [200, {}, nil]
-    }
-    body = mw.call({}).last
-
-    assert !ActiveRecord::Base.connection.query_cache.empty?, 'cache not empty'
-    body.close
-    assert ActiveRecord::Base.connection.query_cache.empty?, 'cache should be empty'
-  end
-
   def test_cache_passing_a_relation
     post = Post.first
     Post.cache do
@@ -147,7 +190,7 @@ class QueryCacheTest < ActiveRecord::TestCase
       Task.cache do
         assert_queries(2) { Task.find(1); Task.find(2) }
       end
-      assert_queries(0) { Task.find(1); Task.find(1); Task.find(2) }
+      assert_no_queries { Task.find(1); Task.find(1); Task.find(2) }
     end
   end
 
@@ -157,6 +200,52 @@ class QueryCacheTest < ActiveRecord::TestCase
     end
   end
 
+  def test_exists_queries_with_cache
+    Post.cache do
+      assert_queries(1) { Post.exists?; Post.exists? }
+    end
+  end
+
+  def test_select_all_with_cache
+    Post.cache do
+      assert_queries(1) do
+        2.times { Post.connection.select_all(Post.all) }
+      end
+    end
+  end
+
+  def test_select_one_with_cache
+    Post.cache do
+      assert_queries(1) do
+        2.times { Post.connection.select_one(Post.all) }
+      end
+    end
+  end
+
+  def test_select_value_with_cache
+    Post.cache do
+      assert_queries(1) do
+        2.times { Post.connection.select_value(Post.all) }
+      end
+    end
+  end
+
+  def test_select_values_with_cache
+    Post.cache do
+      assert_queries(1) do
+        2.times { Post.connection.select_values(Post.all) }
+      end
+    end
+  end
+
+  def test_select_rows_with_cache
+    Post.cache do
+      assert_queries(1) do
+        2.times { Post.connection.select_rows(Post.all) }
+      end
+    end
+  end
+
   def test_query_cache_dups_results_correctly
     Task.cache do
       now  = Time.now.utc
@@ -168,9 +257,55 @@ class QueryCacheTest < ActiveRecord::TestCase
     end
   end
 
+  def test_cache_notifications_can_be_overridden
+    logger = ShouldNotHaveExceptionsLogger.new
+    subscriber = ActiveSupport::Notifications.subscribe "sql.active_record", logger
+
+    connection = ActiveRecord::Base.connection.dup
+
+    def connection.cache_notification_info(sql, name, binds)
+      super.merge(neat: true)
+    end
+
+    connection.cache do
+      connection.select_all "select 1"
+      connection.select_all "select 1"
+    end
+
+    assert_equal true, logger.events.last.payload[:neat]
+  ensure
+    ActiveSupport::Notifications.unsubscribe subscriber
+  end
+
+  def test_cache_does_not_raise_exceptions
+    logger = ShouldNotHaveExceptionsLogger.new
+    subscriber = ActiveSupport::Notifications.subscribe "sql.active_record", logger
+
+    ActiveRecord::Base.cache do
+      assert_queries(1) { Task.find(1); Task.find(1) }
+    end
+
+    assert_not_predicate logger, :exception?
+  ensure
+    ActiveSupport::Notifications.unsubscribe subscriber
+  end
+
+  def test_query_cache_does_not_allow_sql_key_mutation
+    subscriber = ActiveSupport::Notifications.subscribe("sql.active_record") do |_, _, _, _, payload|
+      payload[:sql].downcase!
+    end
+
+    assert_raises frozen_error_class do
+      ActiveRecord::Base.cache do
+        assert_queries(1) { Task.find(1); Task.find(1) }
+      end
+    end
+  ensure
+    ActiveSupport::Notifications.unsubscribe subscriber
+  end
+
   def test_cache_is_flat
     Task.cache do
-      Topic.columns # don't count this query
       assert_queries(1) { Topic.find(1); Topic.find(1); }
     end
 
@@ -179,15 +314,10 @@ class QueryCacheTest < ActiveRecord::TestCase
     end
   end
 
-  def test_cache_does_not_wrap_string_results_in_arrays
+  def test_cache_does_not_wrap_results_in_arrays
     Task.cache do
-      # Oracle adapter returns count() as Fixnum or Float
-      if current_adapter?(:OracleAdapter)
-        assert_kind_of Numeric, Task.connection.select_value("SELECT count(*) AS count_all FROM tasks")
-      elsif current_adapter?(:SQLite3Adapter, :Mysql2Adapter, :PostgreSQLAdapter)
-        # Future versions of the sqlite3 adapter will return numeric
-        assert_instance_of Fixnum,
-         Task.connection.select_value("SELECT count(*) AS count_all FROM tasks")
+      if current_adapter?(:SQLite3Adapter, :Mysql2Adapter, :PostgreSQLAdapter, :OracleAdapter)
+        assert_equal 2, Task.connection.select_value("SELECT count(*) AS count_all FROM tasks")
       else
         assert_instance_of String, Task.connection.select_value("SELECT count(*) AS count_all FROM tasks")
       end
@@ -213,42 +343,190 @@ class QueryCacheTest < ActiveRecord::TestCase
     ActiveRecord::Base.configurations = conf
   end
 
+  def test_cache_is_available_when_using_a_not_connected_connection
+    skip "In-Memory DB can't test for using a not connected connection" if in_memory_db?
+    with_temporary_connection_pool do
+      spec_name = Task.connection_specification_name
+      conf = ActiveRecord::Base.configurations["arunit"].merge("name" => "test2")
+      ActiveRecord::Base.connection_handler.establish_connection(conf)
+      Task.connection_specification_name = "test2"
+      assert_not_predicate Task, :connected?
+
+      Task.cache do
+        begin
+          assert_queries(1) { Task.find(1); Task.find(1) }
+        ensure
+          ActiveRecord::Base.connection_handler.remove_connection(Task.connection_specification_name)
+          Task.connection_specification_name = spec_name
+        end
+      end
+    end
+  end
+
+  def test_query_cache_executes_new_queries_within_block
+    ActiveRecord::Base.connection.enable_query_cache!
+
+    # Warm up the cache by running the query
+    assert_queries(1) do
+      assert_equal 0, Post.where(title: "test").to_a.count
+    end
+
+    # Check that if the same query is run again, no queries are executed
+    assert_no_queries do
+      assert_equal 0, Post.where(title: "test").to_a.count
+    end
+
+    ActiveRecord::Base.connection.uncached do
+      # Check that new query is executed, avoiding the cache
+      assert_queries(1) do
+        assert_equal 0, Post.where(title: "test").to_a.count
+      end
+    end
+  end
+
   def test_query_cache_doesnt_leak_cached_results_of_rolled_back_queries
     ActiveRecord::Base.connection.enable_query_cache!
     post = Post.first
 
     Post.transaction do
-      post.update_attributes(title: 'rollback')
-      assert_equal 1, Post.where(title: 'rollback').to_a.count
+      post.update(title: "rollback")
+      assert_equal 1, Post.where(title: "rollback").to_a.count
       raise ActiveRecord::Rollback
     end
 
-    assert_equal 0, Post.where(title: 'rollback').to_a.count
+    assert_equal 0, Post.where(title: "rollback").to_a.count
 
     ActiveRecord::Base.connection.uncached do
-      assert_equal 0, Post.where(title: 'rollback').to_a.count
+      assert_equal 0, Post.where(title: "rollback").to_a.count
     end
 
     begin
       Post.transaction do
-        post.update_attributes(title: 'rollback')
-        assert_equal 1, Post.where(title: 'rollback').to_a.count
-        raise 'broken'
+        post.update(title: "rollback")
+        assert_equal 1, Post.where(title: "rollback").to_a.count
+        raise "broken"
       end
     rescue Exception
     end
 
-    assert_equal 0, Post.where(title: 'rollback').to_a.count
+    assert_equal 0, Post.where(title: "rollback").to_a.count
 
     ActiveRecord::Base.connection.uncached do
-      assert_equal 0, Post.where(title: 'rollback').to_a.count
+      assert_equal 0, Post.where(title: "rollback").to_a.count
     end
   end
+
+  def test_query_cached_even_when_types_are_reset
+    Task.cache do
+      # Warm the cache
+      Task.find(1)
+
+      # Preload the type cache again (so we don't have those queries issued during our assertions)
+      Task.connection.send(:reload_type_map)
+
+      # Clear places where type information is cached
+      Task.reset_column_information
+      Task.initialize_find_by_cache
+      Task.define_attribute_methods
+
+      assert_no_queries do
+        Task.find(1)
+      end
+    end
+  end
+
+  def test_query_cache_does_not_establish_connection_if_unconnected
+    with_temporary_connection_pool do
+      ActiveRecord::Base.clear_active_connections!
+      assert_not ActiveRecord::Base.connection_handler.active_connections? # sanity check
+
+      middleware {
+        assert_not ActiveRecord::Base.connection_handler.active_connections?, "QueryCache forced ActiveRecord::Base to establish a connection in setup"
+      }.call({})
+
+      assert_not ActiveRecord::Base.connection_handler.active_connections?, "QueryCache forced ActiveRecord::Base to establish a connection in cleanup"
+    end
+  end
+
+  def test_query_cache_is_enabled_on_connections_established_after_middleware_runs
+    with_temporary_connection_pool do
+      ActiveRecord::Base.clear_active_connections!
+      assert_not ActiveRecord::Base.connection_handler.active_connections? # sanity check
+
+      middleware {
+        assert_predicate ActiveRecord::Base.connection, :query_cache_enabled
+      }.call({})
+      assert_not_predicate ActiveRecord::Base.connection, :query_cache_enabled
+    end
+  end
+
+  def test_query_caching_is_local_to_the_current_thread
+    with_temporary_connection_pool do
+      ActiveRecord::Base.clear_active_connections!
+
+      middleware {
+        assert ActiveRecord::Base.connection_pool.query_cache_enabled
+        assert ActiveRecord::Base.connection.query_cache_enabled
+
+        Thread.new {
+          assert_not ActiveRecord::Base.connection_pool.query_cache_enabled
+          assert_not ActiveRecord::Base.connection.query_cache_enabled
+        }.join
+      }.call({})
+    end
+  end
+
+  def test_query_cache_is_enabled_on_all_connection_pools
+    middleware {
+      ActiveRecord::Base.connection_handler.connection_pool_list.each do |pool|
+        assert pool.query_cache_enabled
+        assert pool.connection.query_cache_enabled
+      end
+    }.call({})
+  end
+
+  private
+
+    def with_temporary_connection_pool
+      old_pool = ActiveRecord::Base.connection_handler.retrieve_connection_pool(ActiveRecord::Base.connection_specification_name)
+      new_pool = ActiveRecord::ConnectionAdapters::ConnectionPool.new ActiveRecord::Base.connection_pool.spec
+      ActiveRecord::Base.connection_handler.send(:owner_to_pool)["primary"] = new_pool
+
+      yield
+    ensure
+      ActiveRecord::Base.connection_handler.send(:owner_to_pool)["primary"] = old_pool
+    end
+
+    def middleware(&app)
+      executor = Class.new(ActiveSupport::Executor)
+      ActiveRecord::QueryCache.install_executor_hooks executor
+      lambda { |env| executor.wrap { app.call(env) } }
+    end
+
+    def assert_cache(state, connection = ActiveRecord::Base.connection)
+      case state
+      when :off
+        assert_not connection.query_cache_enabled, "cache should be off"
+        assert connection.query_cache.empty?, "cache should be empty"
+      when :clean
+        assert connection.query_cache_enabled, "cache should be on"
+        assert connection.query_cache.empty?, "cache should be empty"
+      when :dirty
+        assert connection.query_cache_enabled, "cache should be on"
+        assert_not connection.query_cache.empty?, "cache should be dirty"
+      else
+        raise "unknown state"
+      end
+    end
 end
 
 class QueryCacheExpiryTest < ActiveRecord::TestCase
   fixtures :tasks, :posts, :categories, :categories_posts
 
+  def teardown
+    Task.connection.clear_query_cache
+  end
+
   def test_cache_gets_cleared_after_migration
     # warm the cache
     Post.find(1)
@@ -262,61 +540,78 @@ class QueryCacheExpiryTest < ActiveRecord::TestCase
   end
 
   def test_find
-    Task.connection.expects(:clear_query_cache).times(1)
+    assert_called(Task.connection, :clear_query_cache) do
+      assert_not Task.connection.query_cache_enabled
+      Task.cache do
+        assert Task.connection.query_cache_enabled
+        Task.find(1)
 
-    assert !Task.connection.query_cache_enabled
-    Task.cache do
-      assert Task.connection.query_cache_enabled
-      Task.find(1)
+        Task.uncached do
+          assert_not Task.connection.query_cache_enabled
+          Task.find(1)
+        end
 
-      Task.uncached do
-        assert !Task.connection.query_cache_enabled
-        Task.find(1)
+        assert Task.connection.query_cache_enabled
       end
-
-      assert Task.connection.query_cache_enabled
+      assert_not Task.connection.query_cache_enabled
     end
-    assert !Task.connection.query_cache_enabled
   end
 
   def test_update
-    Task.connection.expects(:clear_query_cache).times(2)
-    Task.cache do
-      task = Task.find(1)
-      task.starting = Time.now.utc
-      task.save!
+    assert_called(Task.connection, :clear_query_cache, times: 2) do
+      Task.cache do
+        task = Task.find(1)
+        task.starting = Time.now.utc
+        task.save!
+      end
     end
   end
 
   def test_destroy
-    Task.connection.expects(:clear_query_cache).times(2)
-    Task.cache do
-      Task.find(1).destroy
+    assert_called(Task.connection, :clear_query_cache, times: 2) do
+      Task.cache do
+        Task.find(1).destroy
+      end
     end
   end
 
   def test_insert
-    ActiveRecord::Base.connection.expects(:clear_query_cache).times(2)
-    Task.cache do
-      Task.create!
+    assert_called(ActiveRecord::Base.connection, :clear_query_cache, times: 2) do
+      Task.cache do
+        Task.create!
+      end
     end
   end
 
   def test_cache_is_expired_by_habtm_update
-    ActiveRecord::Base.connection.expects(:clear_query_cache).times(2)
-    ActiveRecord::Base.cache do
-      c = Category.first
-      p = Post.first
-      p.categories << c
+    assert_called(ActiveRecord::Base.connection, :clear_query_cache, times: 2) do
+      ActiveRecord::Base.cache do
+        c = Category.first
+        p = Post.first
+        p.categories << c
+      end
     end
   end
 
   def test_cache_is_expired_by_habtm_delete
-    ActiveRecord::Base.connection.expects(:clear_query_cache).times(2)
-    ActiveRecord::Base.cache do
-      p = Post.find(1)
-      assert p.categories.any?
-      p.categories.delete_all
+    assert_called(ActiveRecord::Base.connection, :clear_query_cache, times: 2) do
+      ActiveRecord::Base.cache do
+        p = Post.find(1)
+        assert_predicate p.categories, :any?
+        p.categories.delete_all
+      end
+    end
+  end
+
+  test "threads use the same connection" do
+    @connection_1 = ActiveRecord::Base.connection.object_id
+
+    thread_a = Thread.new do
+      @connection_2 = ActiveRecord::Base.connection.object_id
     end
+
+    thread_a.join
+
+    assert_equal @connection_1, @connection_2
   end
 end
diff --git a/activerecord/test/cases/quoting_test.rb b/activerecord/test/cases/quoting_test.rb
index 6d91f96bf6..723fccc8d9 100644
--- a/activerecord/test/cases/quoting_test.rb
+++ b/activerecord/test/cases/quoting_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -8,28 +10,28 @@ module ActiveRecord
       end
 
       def test_quoted_true
-        assert_equal "'t'", @quoter.quoted_true
+        assert_equal "TRUE", @quoter.quoted_true
       end
 
       def test_quoted_false
-        assert_equal "'f'", @quoter.quoted_false
+        assert_equal "FALSE", @quoter.quoted_false
       end
 
       def test_quote_column_name
-        assert_equal "foo", @quoter.quote_column_name('foo')
+        assert_equal "foo", @quoter.quote_column_name("foo")
       end
 
       def test_quote_table_name
-        assert_equal "foo", @quoter.quote_table_name('foo')
+        assert_equal "foo", @quoter.quote_table_name("foo")
       end
 
       def test_quote_table_name_calls_quote_column_name
         @quoter.extend(Module.new {
           def quote_column_name(string)
-            'lol'
+            "lol"
           end
         })
-        assert_equal 'lol', @quoter.quote_table_name('foo')
+        assert_equal "lol", @quoter.quote_table_name("foo")
       end
 
       def test_quote_string
@@ -44,27 +46,86 @@ module ActiveRecord
         assert_equal t.to_s(:db), @quoter.quoted_date(t)
       end
 
-      def test_quoted_time_utc
+      def test_quoted_timestamp_utc
         with_timezone_config default: :utc do
           t = Time.now.change(usec: 0)
           assert_equal t.getutc.to_s(:db), @quoter.quoted_date(t)
         end
       end
 
-      def test_quoted_time_local
+      def test_quoted_timestamp_local
         with_timezone_config default: :local do
           t = Time.now.change(usec: 0)
           assert_equal t.getlocal.to_s(:db), @quoter.quoted_date(t)
         end
       end
 
-      def test_quoted_time_crazy
+      def test_quoted_timestamp_crazy
         with_timezone_config default: :asdfasdf do
           t = Time.now.change(usec: 0)
           assert_equal t.getlocal.to_s(:db), @quoter.quoted_date(t)
         end
       end
 
+      def test_quoted_time_utc
+        with_timezone_config default: :utc do
+          t = Time.now.change(usec: 0)
+
+          expected = t.change(year: 2000, month: 1, day: 1)
+          expected = expected.getutc.to_s(:db).slice(11..-1)
+
+          assert_equal expected, @quoter.quoted_time(t)
+        end
+      end
+
+      def test_quoted_time_local
+        with_timezone_config default: :local do
+          t = Time.now.change(usec: 0)
+
+          expected = t.change(year: 2000, month: 1, day: 1)
+          expected = expected.getlocal.to_s(:db).sub("2000-01-01 ", "")
+
+          assert_equal expected, @quoter.quoted_time(t)
+        end
+      end
+
+      def test_quoted_time_dst_utc
+        with_env_tz "America/New_York" do
+          with_timezone_config default: :utc do
+            t = Time.new(2000, 7, 1, 0, 0, 0, "+04:30")
+
+            expected = t.change(year: 2000, month: 1, day: 1)
+            expected = expected.getutc.to_s(:db).slice(11..-1)
+
+            assert_equal expected, @quoter.quoted_time(t)
+          end
+        end
+      end
+
+      def test_quoted_time_dst_local
+        with_env_tz "America/New_York" do
+          with_timezone_config default: :local do
+            t = Time.new(2000, 7, 1, 0, 0, 0, "+04:30")
+
+            expected = t.change(year: 2000, month: 1, day: 1)
+            expected = expected.getlocal.to_s(:db).slice(11..-1)
+
+            assert_equal expected, @quoter.quoted_time(t)
+          end
+        end
+      end
+
+      def test_quoted_time_crazy
+        with_timezone_config default: :asdfasdf do
+          t = Time.now.change(usec: 0)
+
+          expected = t.change(year: 2000, month: 1, day: 1)
+          expected = expected.getlocal.to_s(:db).sub("2000-01-01 ", "")
+
+          assert_equal expected, @quoter.quoted_time(t)
+        end
+      end
+
       def test_quoted_datetime_utc
         with_timezone_config default: :utc do
           t = Time.now.change(usec: 0).to_datetime
@@ -81,73 +142,156 @@ module ActiveRecord
         end
       end
 
-      def test_quote_with_quoted_id
-        assert_equal 1, @quoter.quote(Struct.new(:quoted_id).new(1), nil)
-      end
-
       def test_quote_nil
-        assert_equal 'NULL', @quoter.quote(nil, nil)
+        assert_equal "NULL", @quoter.quote(nil)
       end
 
       def test_quote_true
-        assert_equal @quoter.quoted_true, @quoter.quote(true, nil)
+        assert_equal @quoter.quoted_true, @quoter.quote(true)
       end
 
       def test_quote_false
-        assert_equal @quoter.quoted_false, @quoter.quote(false, nil)
+        assert_equal @quoter.quoted_false, @quoter.quote(false)
       end
 
       def test_quote_float
         float = 1.2
-        assert_equal float.to_s, @quoter.quote(float, nil)
+        assert_equal float.to_s, @quoter.quote(float)
       end
 
-      def test_quote_fixnum
-        fixnum = 1
-        assert_equal fixnum.to_s, @quoter.quote(fixnum, nil)
+      def test_quote_integer
+        integer = 1
+        assert_equal integer.to_s, @quoter.quote(integer)
       end
 
       def test_quote_bignum
         bignum = 1 << 100
-        assert_equal bignum.to_s, @quoter.quote(bignum, nil)
+        assert_equal bignum.to_s, @quoter.quote(bignum)
       end
 
       def test_quote_bigdecimal
-        bigdec = BigDecimal.new((1 << 100).to_s)
-        assert_equal bigdec.to_s('F'), @quoter.quote(bigdec, nil)
+        bigdec = BigDecimal((1 << 100).to_s)
+        assert_equal bigdec.to_s("F"), @quoter.quote(bigdec)
       end
 
       def test_dates_and_times
-        @quoter.extend(Module.new { def quoted_date(value) 'lol' end })
-        assert_equal "'lol'", @quoter.quote(Date.today, nil)
-        assert_equal "'lol'", @quoter.quote(Time.now, nil)
-        assert_equal "'lol'", @quoter.quote(DateTime.now, nil)
+        @quoter.extend(Module.new { def quoted_date(value) "lol" end })
+        assert_equal "'lol'", @quoter.quote(Date.today)
+        assert_equal "'lol'", @quoter.quote(Time.now)
+        assert_equal "'lol'", @quoter.quote(DateTime.now)
+      end
+
+      def test_quoting_classes
+        assert_equal "'Object'", @quoter.quote(Object)
       end
 
       def test_crazy_object
         crazy = Object.new
         e = assert_raises(TypeError) do
-          @quoter.quote(crazy, nil)
+          @quoter.quote(crazy)
         end
         assert_equal "can't quote Object", e.message
       end
 
       def test_quote_string_no_column
-        assert_equal "'lo\\\\l'", @quoter.quote('lo\l', nil)
+        assert_equal "'lo\\\\l'", @quoter.quote('lo\l')
       end
 
       def test_quote_as_mb_chars_no_column
         string = ActiveSupport::Multibyte::Chars.new('lo\l')
-        assert_equal "'lo\\\\l'", @quoter.quote(string, nil)
-      end
-
-      def test_string_with_crazy_column
-        assert_equal "'lo\\\\l'", @quoter.quote('lo\l')
+        assert_equal "'lo\\\\l'", @quoter.quote(string)
       end
 
       def test_quote_duration
         assert_equal "1800", @quoter.quote(30.minutes)
       end
     end
+
+    class TypeCastingTest < ActiveRecord::TestCase
+      def setup
+        @conn = ActiveRecord::Base.connection
+      end
+
+      def test_type_cast_symbol
+        assert_equal "foo", @conn.type_cast(:foo)
+      end
+
+      def test_type_cast_date
+        date = Date.today
+        if current_adapter?(:Mysql2Adapter)
+          expected = date
+        else
+          expected = @conn.quoted_date(date)
+        end
+        assert_equal expected, @conn.type_cast(date)
+      end
+
+      def test_type_cast_time
+        time = Time.now
+        if current_adapter?(:Mysql2Adapter)
+          expected = time
+        else
+          expected = @conn.quoted_date(time)
+        end
+        assert_equal expected, @conn.type_cast(time)
+      end
+
+      def test_type_cast_numeric
+        assert_equal 10, @conn.type_cast(10)
+        assert_equal 2.2, @conn.type_cast(2.2)
+      end
+
+      def test_type_cast_nil
+        assert_nil @conn.type_cast(nil)
+      end
+
+      def test_type_cast_unknown_should_raise_error
+        obj = Class.new.new
+        assert_raise(TypeError) { @conn.type_cast(obj) }
+      end
+    end
+
+    class QuoteBooleanTest < ActiveRecord::TestCase
+      def setup
+        @connection = ActiveRecord::Base.connection
+      end
+
+      def test_quote_returns_frozen_string
+        assert_predicate @connection.quote(true), :frozen?
+        assert_predicate @connection.quote(false), :frozen?
+      end
+
+      def test_type_cast_returns_frozen_value
+        assert_predicate @connection.type_cast(true), :frozen?
+        assert_predicate @connection.type_cast(false), :frozen?
+      end
+    end
+
+    if subsecond_precision_supported?
+      class QuoteARBaseTest < ActiveRecord::TestCase
+        class DatetimePrimaryKey < ActiveRecord::Base
+        end
+
+        def setup
+          @time = ::Time.utc(2017, 2, 14, 12, 34, 56, 789999)
+          @connection = ActiveRecord::Base.connection
+          @connection.create_table :datetime_primary_keys, id: :datetime, precision: 3, force: true
+        end
+
+        def teardown
+          @connection.drop_table :datetime_primary_keys, if_exists: true
+        end
+
+        def test_quote_ar_object
+          value = DatetimePrimaryKey.new(id: @time)
+          assert_equal "'2017-02-14 12:34:56.789000'",  @connection.quote(value)
+        end
+
+        def test_type_cast_ar_object
+          value = DatetimePrimaryKey.new(id: @time)
+          assert_equal @connection.type_cast(value.id),  @connection.type_cast(value)
+        end
+      end
+    end
   end
 end
diff --git a/activerecord/test/cases/readonly_test.rb b/activerecord/test/cases/readonly_test.rb
index 1c919f0b57..059fa76132 100644
--- a/activerecord/test/cases/readonly_test.rb
+++ b/activerecord/test/cases/readonly_test.rb
@@ -1,27 +1,30 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/author'
-require 'models/post'
-require 'models/comment'
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/reader'
-require 'models/person'
+require "models/author"
+require "models/post"
+require "models/comment"
+require "models/developer"
+require "models/computer"
+require "models/project"
+require "models/reader"
+require "models/person"
+require "models/ship"
 
 class ReadOnlyTest < ActiveRecord::TestCase
-  fixtures :authors, :posts, :comments, :developers, :projects, :developers_projects, :people, :readers
+  fixtures :authors, :author_addresses, :posts, :comments, :developers, :projects, :developers_projects, :people, :readers
 
   def test_cant_save_readonly_record
     dev = Developer.find(1)
-    assert !dev.readonly?
+    assert_not_predicate dev, :readonly?
 
     dev.readonly!
-    assert dev.readonly?
+    assert_predicate dev, :readonly?
 
     assert_nothing_raised do
-      dev.name = 'Luscious forbidden fruit.'
-      assert !dev.save
-      dev.name = 'Forbidden.'
+      dev.name = "Luscious forbidden fruit."
+      assert_not dev.save
+      dev.name = "Forbidden."
     end
 
     e = assert_raise(ActiveRecord::ReadOnlyRecord) { dev.save  }
@@ -34,74 +37,73 @@ class ReadOnlyTest < ActiveRecord::TestCase
     assert_equal "Developer is marked as readonly", e.message
   end
 
-
   def test_find_with_readonly_option
-    Developer.all.each { |d| assert !d.readonly? }
-    Developer.readonly(false).each { |d| assert !d.readonly? }
+    Developer.all.each { |d| assert_not d.readonly? }
+    Developer.readonly(false).each { |d| assert_not d.readonly? }
     Developer.readonly(true).each { |d| assert d.readonly? }
     Developer.readonly.each { |d| assert d.readonly? }
   end
 
   def test_find_with_joins_option_does_not_imply_readonly
-    Developer.joins('  ').each { |d| assert_not d.readonly? }
-    Developer.joins('  ').readonly(true).each { |d| assert d.readonly? }
+    Developer.joins("  ").each { |d| assert_not d.readonly? }
+    Developer.joins("  ").readonly(true).each { |d| assert d.readonly? }
 
-    Developer.joins(', projects').each { |d| assert_not d.readonly? }
-    Developer.joins(', projects').readonly(true).each { |d| assert d.readonly? }
+    Developer.joins(", projects").each { |d| assert_not d.readonly? }
+    Developer.joins(", projects").readonly(true).each { |d| assert d.readonly? }
   end
 
   def test_has_many_find_readonly
     post = Post.find(1)
-    assert !post.comments.empty?
-    assert !post.comments.any?(&:readonly?)
-    assert !post.comments.to_a.any?(&:readonly?)
+    assert_not_empty post.comments
+    assert_not post.comments.any?(&:readonly?)
+    assert_not post.comments.to_a.any?(&:readonly?)
     assert post.comments.readonly(true).all?(&:readonly?)
   end
 
   def test_has_many_with_through_is_not_implicitly_marked_readonly
     assert people = Post.find(1).people
-    assert !people.any?(&:readonly?)
+    assert_not people.any?(&:readonly?)
   end
 
   def test_has_many_with_through_is_not_implicitly_marked_readonly_while_finding_by_id
-    assert !posts(:welcome).people.find(1).readonly?
+    assert_not_predicate posts(:welcome).people.find(1), :readonly?
   end
 
   def test_has_many_with_through_is_not_implicitly_marked_readonly_while_finding_first
-    assert !posts(:welcome).people.first.readonly?
+    assert_not_predicate posts(:welcome).people.first, :readonly?
   end
 
   def test_has_many_with_through_is_not_implicitly_marked_readonly_while_finding_last
-    assert !posts(:welcome).people.last.readonly?
+    assert_not_predicate posts(:welcome).people.last, :readonly?
   end
 
   def test_readonly_scoping
-    Post.where('1=1').scoping do
-      assert !Post.find(1).readonly?
-      assert Post.readonly(true).find(1).readonly?
-      assert !Post.readonly(false).find(1).readonly?
+    Post.where("1=1").scoping do
+      assert_not_predicate Post.find(1), :readonly?
+      assert_predicate Post.readonly(true).find(1), :readonly?
+      assert_not_predicate Post.readonly(false).find(1), :readonly?
     end
 
-    Post.joins('   ').scoping do
-      assert !Post.find(1).readonly?
-      assert Post.readonly.find(1).readonly?
-      assert !Post.readonly(false).find(1).readonly?
+    Post.joins("   ").scoping do
+      assert_not_predicate Post.find(1), :readonly?
+      assert_predicate Post.readonly.find(1), :readonly?
+      assert_not_predicate Post.readonly(false).find(1), :readonly?
     end
 
     # Oracle barfs on this because the join includes unqualified and
     # conflicting column names
     unless current_adapter?(:OracleAdapter)
-      Post.joins(', developers').scoping do
-        assert_not Post.find(1).readonly?
-        assert Post.readonly.find(1).readonly?
-        assert !Post.readonly(false).find(1).readonly?
+      Post.joins(", developers").scoping do
+        assert_not_predicate Post.find(1), :readonly?
+        assert_predicate Post.readonly.find(1), :readonly?
+        assert_not_predicate Post.readonly(false).find(1), :readonly?
       end
     end
 
     Post.readonly(true).scoping do
-      assert Post.find(1).readonly?
-      assert Post.readonly.find(1).readonly?
-      assert !Post.readonly(false).find(1).readonly?
+      assert_predicate Post.find(1), :readonly?
+      assert_predicate Post.readonly.find(1), :readonly?
+      assert_not_predicate Post.readonly(false).find(1), :readonly?
     end
   end
 
@@ -109,10 +111,10 @@ class ReadOnlyTest < ActiveRecord::TestCase
     developer = Developer.find(1)
     project   = Post.find(1)
 
-    assert !developer.projects.all_as_method.first.readonly?
-    assert !developer.projects.all_as_scope.first.readonly?
+    assert_not_predicate developer.projects.all_as_method.first, :readonly?
+    assert_not_predicate developer.projects.all_as_scope.first, :readonly?
 
-    assert !project.comments.all_as_method.first.readonly?
-    assert !project.comments.all_as_scope.first.readonly?
+    assert_not_predicate project.comments.all_as_method.first, :readonly?
+    assert_not_predicate project.comments.all_as_scope.first, :readonly?
   end
 end
diff --git a/activerecord/test/cases/reaper_test.rb b/activerecord/test/cases/reaper_test.rb
index cccfc6774e..b630f782bc 100644
--- a/activerecord/test/cases/reaper_test.rb
+++ b/activerecord/test/cases/reaper_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -16,6 +18,7 @@ module ActiveRecord
 
       class FakePool
         attr_reader :reaped
+        attr_reader :flushed
 
         def initialize
           @reaped = false
@@ -24,20 +27,24 @@ module ActiveRecord
         def reap
           @reaped = true
         end
+
+        def flush
+          @flushed = true
+        end
       end
 
       # A reaper with nil time should never reap connections
       def test_nil_time
         fp = FakePool.new
-        assert !fp.reaped
+        assert_not fp.reaped
         reaper = ConnectionPool::Reaper.new(fp, nil)
         reaper.run
-        assert !fp.reaped
+        assert_not fp.reaped
       end
 
       def test_some_time
         fp = FakePool.new
-        assert !fp.reaped
+        assert_not fp.reaped
 
         reaper = ConnectionPool::Reaper.new(fp, 0.0001)
         reaper.run
@@ -45,6 +52,7 @@ module ActiveRecord
           Thread.pass
         end
         assert fp.reaped
+        assert fp.flushed
       end
 
       def test_pool_has_reaper
@@ -53,14 +61,14 @@ module ActiveRecord
 
       def test_reaping_frequency_configuration
         spec = ActiveRecord::Base.connection_pool.spec.dup
-        spec.config[:reaping_frequency] = 100
+        spec.config[:reaping_frequency] = "10.01"
         pool = ConnectionPool.new spec
-        assert_equal 100, pool.reaper.frequency
+        assert_equal 10.01, pool.reaper.frequency
       end
 
       def test_connection_pool_starts_reaper
         spec = ActiveRecord::Base.connection_pool.spec.dup
-        spec.config[:reaping_frequency] = '0.0001'
+        spec.config[:reaping_frequency] = "0.0001"
 
         pool = ConnectionPool.new spec
 
@@ -71,14 +79,14 @@ module ActiveRecord
         end
         Thread.pass while conn.nil?
 
-        assert conn.in_use?
+        assert_predicate conn, :in_use?
 
         child.terminate
 
         while conn.in_use?
           Thread.pass
         end
-        assert !conn.in_use?
+        assert_not_predicate conn, :in_use?
       end
     end
   end
diff --git a/activerecord/test/cases/reflection_test.rb b/activerecord/test/cases/reflection_test.rb
index 7b47c80331..abadafbad4 100644
--- a/activerecord/test/cases/reflection_test.rb
+++ b/activerecord/test/cases/reflection_test.rb
@@ -1,29 +1,31 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/customer'
-require 'models/company'
-require 'models/company_in_module'
-require 'models/ship'
-require 'models/pirate'
-require 'models/price_estimate'
-require 'models/essay'
-require 'models/author'
-require 'models/organization'
-require 'models/post'
-require 'models/tagging'
-require 'models/category'
-require 'models/book'
-require 'models/subscriber'
-require 'models/subscription'
-require 'models/tag'
-require 'models/sponsor'
-require 'models/edge'
-require 'models/hotel'
-require 'models/chef'
-require 'models/department'
-require 'models/cake_designer'
-require 'models/drink_designer'
-require 'models/recipe'
+require "models/topic"
+require "models/customer"
+require "models/company"
+require "models/company_in_module"
+require "models/ship"
+require "models/pirate"
+require "models/price_estimate"
+require "models/essay"
+require "models/author"
+require "models/organization"
+require "models/post"
+require "models/tagging"
+require "models/category"
+require "models/book"
+require "models/subscriber"
+require "models/subscription"
+require "models/tag"
+require "models/sponsor"
+require "models/edge"
+require "models/hotel"
+require "models/chef"
+require "models/department"
+require "models/cake_designer"
+require "models/drink_designer"
+require "models/recipe"
 
 class ReflectionTest < ActiveRecord::TestCase
   include ActiveRecord::Reflection
@@ -64,13 +66,16 @@ class ReflectionTest < ActiveRecord::TestCase
 
   def test_column_string_type_and_limit
     assert_equal :string, @first.column_for_attribute("title").type
+    assert_equal :string, @first.column_for_attribute(:title).type
+    assert_equal :string, @first.type_for_attribute("title").type
+    assert_equal :string, @first.type_for_attribute(:title).type
     assert_equal 250, @first.column_for_attribute("title").limit
   end
 
   def test_column_null_not_null
     subscriber = Subscriber.first
     assert subscriber.column_for_attribute("name").null
-    assert !subscriber.column_for_attribute("nick").null
+    assert_not subscriber.column_for_attribute("nick").null
   end
 
   def test_human_name_for_column
@@ -79,14 +84,20 @@ class ReflectionTest < ActiveRecord::TestCase
 
   def test_integer_columns
     assert_equal :integer, @first.column_for_attribute("id").type
+    assert_equal :integer, @first.column_for_attribute(:id).type
+    assert_equal :integer, @first.type_for_attribute("id").type
+    assert_equal :integer, @first.type_for_attribute(:id).type
   end
 
   def test_non_existent_columns_return_null_object
     column = @first.column_for_attribute("attribute_that_doesnt_exist")
     assert_instance_of ActiveRecord::ConnectionAdapters::NullColumn, column
     assert_equal "attribute_that_doesnt_exist", column.name
-    assert_equal nil, column.sql_type
-    assert_equal nil, column.type
+    assert_nil column.sql_type
+    assert_nil column.type
+
+    column = @first.column_for_attribute(:attribute_that_doesnt_exist)
+    assert_instance_of ActiveRecord::ConnectionAdapters::NullColumn, column
   end
 
   def test_non_existent_types_are_identity_types
@@ -96,10 +107,21 @@ class ReflectionTest < ActiveRecord::TestCase
     assert_equal object, type.deserialize(object)
     assert_equal object, type.cast(object)
     assert_equal object, type.serialize(object)
+
+    type = @first.type_for_attribute(:attribute_that_doesnt_exist)
+    assert_equal object, type.deserialize(object)
+    assert_equal object, type.cast(object)
+    assert_equal object, type.serialize(object)
   end
 
   def test_reflection_klass_for_nested_class_name
-    reflection = ActiveRecord::Reflection.create(:has_many, nil, nil, { :class_name => 'MyApplication::Business::Company' }, ActiveRecord::Base)
+    reflection = ActiveRecord::Reflection.create(
+      :has_many,
+      nil,
+      nil,
+      { class_name: "MyApplication::Business::Company" },
+      Customer
+    )
     assert_nothing_raised do
       assert_equal MyApplication::Business::Company, reflection.klass
     end
@@ -107,28 +129,28 @@ class ReflectionTest < ActiveRecord::TestCase
 
   def test_irregular_reflection_class_name
     ActiveSupport::Inflector.inflections do |inflect|
-      inflect.irregular 'plural_irregular', 'plurales_irregulares'
+      inflect.irregular "plural_irregular", "plurales_irregulares"
     end
-    reflection = ActiveRecord::Reflection.create(:has_many, 'plurales_irregulares', nil, {}, ActiveRecord::Base)
-    assert_equal 'PluralIrregular', reflection.class_name
+    reflection = ActiveRecord::Reflection.create(:has_many, "plurales_irregulares", nil, {}, ActiveRecord::Base)
+    assert_equal "PluralIrregular", reflection.class_name
   end
 
   def test_aggregation_reflection
     reflection_for_address = AggregateReflection.new(
-      :address, nil, { :mapping => [ %w(address_street street), %w(address_city city), %w(address_country country) ] }, Customer
+      :address, nil, { mapping: [ %w(address_street street), %w(address_city city), %w(address_country country) ] }, Customer
     )
 
     reflection_for_balance = AggregateReflection.new(
-      :balance, nil, { :class_name => "Money", :mapping => %w(balance amount) }, Customer
+      :balance, nil, { class_name: "Money", mapping: %w(balance amount) }, Customer
     )
 
     reflection_for_gps_location = AggregateReflection.new(
-      :gps_location, nil, { }, Customer
+      :gps_location, nil, {}, Customer
     )
 
-    assert Customer.reflect_on_all_aggregations.include?(reflection_for_gps_location)
-    assert Customer.reflect_on_all_aggregations.include?(reflection_for_balance)
-    assert Customer.reflect_on_all_aggregations.include?(reflection_for_address)
+    assert_includes Customer.reflect_on_all_aggregations, reflection_for_gps_location
+    assert_includes Customer.reflect_on_all_aggregations, reflection_for_balance
+    assert_includes Customer.reflect_on_all_aggregations, reflection_for_address
 
     assert_equal reflection_for_address, Customer.reflect_on_aggregation(:address)
 
@@ -141,37 +163,37 @@ class ReflectionTest < ActiveRecord::TestCase
     expected = Pirate.reflect_on_all_associations.select { |r| r.options[:autosave] }
     received = Pirate.reflect_on_all_autosave_associations
 
-    assert !received.empty?
+    assert_not_empty received
     assert_not_equal Pirate.reflect_on_all_associations.length, received.length
     assert_equal expected, received
   end
 
   def test_has_many_reflection
-    reflection_for_clients = ActiveRecord::Reflection.create(:has_many, :clients, nil, { :order => "id", :dependent => :destroy }, Firm)
+    reflection_for_clients = ActiveRecord::Reflection.create(:has_many, :clients, nil, { order: "id", dependent: :destroy }, Firm)
 
     assert_equal reflection_for_clients, Firm.reflect_on_association(:clients)
 
     assert_equal Client, Firm.reflect_on_association(:clients).klass
-    assert_equal 'companies', Firm.reflect_on_association(:clients).table_name
+    assert_equal "companies", Firm.reflect_on_association(:clients).table_name
 
     assert_equal Client, Firm.reflect_on_association(:clients_of_firm).klass
-    assert_equal 'companies', Firm.reflect_on_association(:clients_of_firm).table_name
+    assert_equal "companies", Firm.reflect_on_association(:clients_of_firm).table_name
   end
 
   def test_has_one_reflection
-    reflection_for_account = ActiveRecord::Reflection.create(:has_one, :account, nil, { :foreign_key => "firm_id", :dependent => :destroy }, Firm)
+    reflection_for_account = ActiveRecord::Reflection.create(:has_one, :account, nil, { foreign_key: "firm_id", dependent: :destroy }, Firm)
     assert_equal reflection_for_account, Firm.reflect_on_association(:account)
 
     assert_equal Account, Firm.reflect_on_association(:account).klass
-    assert_equal 'accounts', Firm.reflect_on_association(:account).table_name
+    assert_equal "accounts", Firm.reflect_on_association(:account).table_name
   end
 
   def test_belongs_to_inferred_foreign_key_from_assoc_name
     Company.belongs_to :foo
     assert_equal "foo_id", Company.reflect_on_association(:foo).foreign_key
-    Company.belongs_to :bar, :class_name => "Xyzzy"
+    Company.belongs_to :bar, class_name: "Xyzzy"
     assert_equal "bar_id", Company.reflect_on_association(:bar).foreign_key
-    Company.belongs_to :baz, :class_name => "Xyzzy", :foreign_key => "xyzzy_id"
+    Company.belongs_to :baz, class_name: "Xyzzy", foreign_key: "xyzzy_id"
     assert_equal "xyzzy_id", Company.reflect_on_association(:baz).foreign_key
   end
 
@@ -180,45 +202,45 @@ class ReflectionTest < ActiveRecord::TestCase
 
     assert_reflection MyApplication::Business::Firm,
       :clients_of_firm,
-      :klass      => MyApplication::Business::Client,
-      :class_name => 'Client',
-      :table_name => 'companies'
+      klass: MyApplication::Business::Client,
+      class_name: "Client",
+      table_name: "companies"
 
     assert_reflection MyApplication::Billing::Account,
       :firm,
-      :klass      => MyApplication::Business::Firm,
-      :class_name => 'MyApplication::Business::Firm',
-      :table_name => 'companies'
+      klass: MyApplication::Business::Firm,
+      class_name: "MyApplication::Business::Firm",
+      table_name: "companies"
 
     assert_reflection MyApplication::Billing::Account,
       :qualified_billing_firm,
-      :klass      => MyApplication::Billing::Firm,
-      :class_name => 'MyApplication::Billing::Firm',
-      :table_name => 'companies'
+      klass: MyApplication::Billing::Firm,
+      class_name: "MyApplication::Billing::Firm",
+      table_name: "companies"
 
     assert_reflection MyApplication::Billing::Account,
       :unqualified_billing_firm,
-      :klass      => MyApplication::Billing::Firm,
-      :class_name => 'Firm',
-      :table_name => 'companies'
+      klass: MyApplication::Billing::Firm,
+      class_name: "Firm",
+      table_name: "companies"
 
     assert_reflection MyApplication::Billing::Account,
       :nested_qualified_billing_firm,
-      :klass      => MyApplication::Billing::Nested::Firm,
-      :class_name => 'MyApplication::Billing::Nested::Firm',
-      :table_name => 'companies'
+      klass: MyApplication::Billing::Nested::Firm,
+      class_name: "MyApplication::Billing::Nested::Firm",
+      table_name: "companies"
 
     assert_reflection MyApplication::Billing::Account,
       :nested_unqualified_billing_firm,
-      :klass      => MyApplication::Billing::Nested::Firm,
-      :class_name => 'Nested::Firm',
-      :table_name => 'companies'
+      klass: MyApplication::Billing::Nested::Firm,
+      class_name: "Nested::Firm",
+      table_name: "companies"
   ensure
     ActiveRecord::Base.store_full_sti_class = true
   end
 
   def test_reflection_should_not_raise_error_when_compared_to_other_object
-    assert_not_equal Object.new, Firm._reflections['clients']
+    assert_not_equal Object.new, Firm._reflections["clients"]
   end
 
   def test_reflections_should_return_keys_as_strings
@@ -226,7 +248,7 @@ class ReflectionTest < ActiveRecord::TestCase
   end
 
   def test_has_and_belongs_to_many_reflection
-    assert_equal :has_and_belongs_to_many, Category.reflections['posts'].macro
+    assert_equal :has_and_belongs_to_many, Category.reflections["posts"].macro
     assert_equal :posts, Category.reflect_on_all_associations(:has_and_belongs_to_many).first.name
   end
 
@@ -245,37 +267,35 @@ class ReflectionTest < ActiveRecord::TestCase
     assert_equal expected, actual
   end
 
-  def test_scope_chain
-    expected = [
-      [Tagging.reflect_on_association(:tag).scope, Post.reflect_on_association(:first_blue_tags).scope],
-      [Post.reflect_on_association(:first_taggings).scope],
-      [Author.reflect_on_association(:misc_posts).scope]
-    ]
-    actual = Author.reflect_on_association(:misc_post_first_blue_tags).scope_chain
-    assert_equal expected, actual
+  def test_scope_chain_does_not_interfere_with_hmt_with_polymorphic_case
+    hotel = Hotel.create!
+    department = hotel.departments.create!
+    department.chefs.create!(employable: CakeDesigner.create!)
+    department.chefs.create!(employable: DrinkDesigner.create!)
 
-    expected = [
-      [
-        Tagging.reflect_on_association(:blue_tag).scope,
-        Post.reflect_on_association(:first_blue_tags_2).scope,
-        Author.reflect_on_association(:misc_post_first_blue_tags_2).scope
-      ],
-      [],
-      []
-    ]
-    actual = Author.reflect_on_association(:misc_post_first_blue_tags_2).scope_chain
-    assert_equal expected, actual
+    assert_equal 1, hotel.cake_designers.size
+    assert_equal 1, hotel.cake_designers.count
+    assert_equal 1, hotel.drink_designers.size
+    assert_equal 1, hotel.drink_designers.count
+    assert_equal 2, hotel.chefs.size
+    assert_equal 2, hotel.chefs.count
   end
 
-  def test_scope_chain_does_not_interfere_with_hmt_with_polymorphic_case
-    @hotel = Hotel.create!
-    @department = @hotel.departments.create!
-    @department.chefs.create!(employable: CakeDesigner.create!)
-    @department.chefs.create!(employable: DrinkDesigner.create!)
+  def test_scope_chain_does_not_interfere_with_hmt_with_polymorphic_case_and_sti
+    hotel = Hotel.create!
+    hotel.mocktail_designers << MocktailDesigner.create!
+
+    assert_equal 1, hotel.mocktail_designers.size
+    assert_equal 1, hotel.mocktail_designers.count
+    assert_equal 1, hotel.chef_lists.size
+    assert_equal 1, hotel.chef_lists.count
+
+    hotel.mocktail_designers = []
 
-    assert_equal 1, @hotel.cake_designers.size
-    assert_equal 1, @hotel.drink_designers.size
-    assert_equal 2, @hotel.chefs.size
+    assert_equal 0, hotel.mocktail_designers.size
+    assert_equal 0, hotel.mocktail_designers.count
+    assert_equal 0, hotel.chef_lists.size
+    assert_equal 0, hotel.chef_lists.count
   end
 
   def test_scope_chain_of_polymorphic_association_does_not_leak_into_other_hmt_associations
@@ -295,12 +315,12 @@ class ReflectionTest < ActiveRecord::TestCase
   end
 
   def test_nested?
-    assert !Author.reflect_on_association(:comments).nested?
-    assert Author.reflect_on_association(:tags).nested?
+    assert_not_predicate Author.reflect_on_association(:comments), :nested?
+    assert_predicate Author.reflect_on_association(:tags), :nested?
 
     # Only goes :through once, but the through_reflection is a has_and_belongs_to_many, so this is
     # a nested through association
-    assert Category.reflect_on_association(:post_comments).nested?
+    assert_predicate Category.reflect_on_association(:post_comments), :nested?
   end
 
   def test_association_primary_key
@@ -335,42 +355,49 @@ class ReflectionTest < ActiveRecord::TestCase
     assert_raises(ActiveRecord::UnknownPrimaryKey) { reflection.active_record_primary_key }
   end
 
+  def test_type
+    assert_equal "taggable_type", Post.reflect_on_association(:taggings).type.to_s
+    assert_equal "imageable_class", Post.reflect_on_association(:images).type.to_s
+    assert_nil Post.reflect_on_association(:readers).type
+  end
+
   def test_foreign_type
     assert_equal "sponsorable_type", Sponsor.reflect_on_association(:sponsorable).foreign_type.to_s
     assert_equal "sponsorable_type", Sponsor.reflect_on_association(:thing).foreign_type.to_s
+    assert_nil Sponsor.reflect_on_association(:sponsor_club).foreign_type
   end
 
   def test_collection_association
-    assert Pirate.reflect_on_association(:birds).collection?
-    assert Pirate.reflect_on_association(:parrots).collection?
+    assert_predicate Pirate.reflect_on_association(:birds), :collection?
+    assert_predicate Pirate.reflect_on_association(:parrots), :collection?
 
-    assert !Pirate.reflect_on_association(:ship).collection?
-    assert !Ship.reflect_on_association(:pirate).collection?
+    assert_not_predicate Pirate.reflect_on_association(:ship), :collection?
+    assert_not_predicate Ship.reflect_on_association(:pirate), :collection?
   end
 
   def test_default_association_validation
-    assert ActiveRecord::Reflection.create(:has_many, :clients, nil, {}, Firm).validate?
+    assert_predicate ActiveRecord::Reflection.create(:has_many, :clients, nil, {}, Firm), :validate?
 
-    assert !ActiveRecord::Reflection.create(:has_one, :client, nil, {}, Firm).validate?
-    assert !ActiveRecord::Reflection.create(:belongs_to, :client, nil, {}, Firm).validate?
+    assert_not_predicate ActiveRecord::Reflection.create(:has_one, :client, nil, {}, Firm), :validate?
+    assert_not_predicate ActiveRecord::Reflection.create(:belongs_to, :client, nil, {}, Firm), :validate?
   end
 
   def test_always_validate_association_if_explicit
-    assert ActiveRecord::Reflection.create(:has_one, :client, nil, { :validate => true }, Firm).validate?
-    assert ActiveRecord::Reflection.create(:belongs_to, :client, nil, { :validate => true }, Firm).validate?
-    assert ActiveRecord::Reflection.create(:has_many, :clients, nil, { :validate => true }, Firm).validate?
+    assert_predicate ActiveRecord::Reflection.create(:has_one, :client, nil, { validate: true }, Firm), :validate?
+    assert_predicate ActiveRecord::Reflection.create(:belongs_to, :client, nil, { validate: true }, Firm), :validate?
+    assert_predicate ActiveRecord::Reflection.create(:has_many, :clients, nil, { validate: true }, Firm), :validate?
   end
 
   def test_validate_association_if_autosave
-    assert ActiveRecord::Reflection.create(:has_one, :client, nil, { :autosave => true }, Firm).validate?
-    assert ActiveRecord::Reflection.create(:belongs_to, :client, nil, { :autosave => true }, Firm).validate?
-    assert ActiveRecord::Reflection.create(:has_many, :clients, nil, { :autosave => true }, Firm).validate?
+    assert_predicate ActiveRecord::Reflection.create(:has_one, :client, nil, { autosave: true }, Firm), :validate?
+    assert_predicate ActiveRecord::Reflection.create(:belongs_to, :client, nil, { autosave: true }, Firm), :validate?
+    assert_predicate ActiveRecord::Reflection.create(:has_many, :clients, nil, { autosave: true }, Firm), :validate?
   end
 
   def test_never_validate_association_if_explicit
-    assert !ActiveRecord::Reflection.create(:has_one, :client, nil, { :autosave => true, :validate => false }, Firm).validate?
-    assert !ActiveRecord::Reflection.create(:belongs_to, :client, nil, { :autosave => true, :validate => false }, Firm).validate?
-    assert !ActiveRecord::Reflection.create(:has_many, :clients, nil, { :autosave => true, :validate => false }, Firm).validate?
+    assert_not_predicate ActiveRecord::Reflection.create(:has_one, :client, nil, { autosave: true, validate: false }, Firm), :validate?
+    assert_not_predicate ActiveRecord::Reflection.create(:belongs_to, :client, nil, { autosave: true, validate: false }, Firm), :validate?
+    assert_not_predicate ActiveRecord::Reflection.create(:has_many, :clients, nil, { autosave: true, validate: false }, Firm), :validate?
   end
 
   def test_foreign_key
@@ -378,66 +405,75 @@ class ReflectionTest < ActiveRecord::TestCase
     assert_equal "category_id", Post.reflect_on_association(:categorizations).foreign_key.to_s
   end
 
-  def test_through_reflection_scope_chain_does_not_modify_other_reflections
-    orig_conds = Post.reflect_on_association(:first_blue_tags_2).scope_chain.inspect
-    Author.reflect_on_association(:misc_post_first_blue_tags_2).scope_chain
-    assert_equal orig_conds, Post.reflect_on_association(:first_blue_tags_2).scope_chain.inspect
-  end
-
   def test_symbol_for_class_name
     assert_equal Client, Firm.reflect_on_association(:unsorted_clients_with_symbol).klass
   end
 
+  def test_class_for_class_name
+    error = assert_raises(ArgumentError) do
+      ActiveRecord::Reflection.create(:has_many, :clients, nil, { class_name: Client }, Firm)
+    end
+    assert_equal "A class was passed to `:class_name` but we are expecting a string.", error.message
+  end
+
   def test_join_table
-    category = Struct.new(:table_name, :pluralize_table_names).new('categories', true)
-    product = Struct.new(:table_name, :pluralize_table_names).new('products', true)
+    category = Struct.new(:table_name, :pluralize_table_names).new("categories", true)
+    product = Struct.new(:table_name, :pluralize_table_names).new("products", true)
 
     reflection = ActiveRecord::Reflection.create(:has_many, :categories, nil, {}, product)
-    reflection.stubs(:klass).returns(category)
-    assert_equal 'categories_products', reflection.join_table
+    reflection.stub(:klass, category) do
+      assert_equal "categories_products", reflection.join_table
+    end
 
     reflection = ActiveRecord::Reflection.create(:has_many, :products, nil, {}, category)
-    reflection.stubs(:klass).returns(product)
-    assert_equal 'categories_products', reflection.join_table
+    reflection.stub(:klass, product) do
+      assert_equal "categories_products", reflection.join_table
+    end
   end
 
   def test_join_table_with_common_prefix
-    category = Struct.new(:table_name, :pluralize_table_names).new('catalog_categories', true)
-    product = Struct.new(:table_name, :pluralize_table_names).new('catalog_products', true)
+    category = Struct.new(:table_name, :pluralize_table_names).new("catalog_categories", true)
+    product = Struct.new(:table_name, :pluralize_table_names).new("catalog_products", true)
 
     reflection = ActiveRecord::Reflection.create(:has_many, :categories, nil, {}, product)
-    reflection.stubs(:klass).returns(category)
-    assert_equal 'catalog_categories_products', reflection.join_table
+    reflection.stub(:klass, category) do
+      assert_equal "catalog_categories_products", reflection.join_table
+    end
 
     reflection = ActiveRecord::Reflection.create(:has_many, :products, nil, {}, category)
-    reflection.stubs(:klass).returns(product)
-    assert_equal 'catalog_categories_products', reflection.join_table
+    reflection.stub(:klass, product) do
+      assert_equal "catalog_categories_products", reflection.join_table
+    end
   end
 
   def test_join_table_with_different_prefix
-    category = Struct.new(:table_name, :pluralize_table_names).new('catalog_categories', true)
-    page = Struct.new(:table_name, :pluralize_table_names).new('content_pages', true)
+    category = Struct.new(:table_name, :pluralize_table_names).new("catalog_categories", true)
+    page = Struct.new(:table_name, :pluralize_table_names).new("content_pages", true)
 
     reflection = ActiveRecord::Reflection.create(:has_many, :categories, nil, {}, page)
-    reflection.stubs(:klass).returns(category)
-    assert_equal 'catalog_categories_content_pages', reflection.join_table
+    reflection.stub(:klass, category) do
+      assert_equal "catalog_categories_content_pages", reflection.join_table
+    end
 
     reflection = ActiveRecord::Reflection.create(:has_many, :pages, nil, {}, category)
-    reflection.stubs(:klass).returns(page)
-    assert_equal 'catalog_categories_content_pages', reflection.join_table
+    reflection.stub(:klass, page) do
+      assert_equal "catalog_categories_content_pages", reflection.join_table
+    end
   end
 
   def test_join_table_can_be_overridden
-    category = Struct.new(:table_name, :pluralize_table_names).new('categories', true)
-    product = Struct.new(:table_name, :pluralize_table_names).new('products', true)
+    category = Struct.new(:table_name, :pluralize_table_names).new("categories", true)
+    product = Struct.new(:table_name, :pluralize_table_names).new("products", true)
 
-    reflection = ActiveRecord::Reflection.create(:has_many, :categories, nil, { :join_table => 'product_categories' }, product)
-    reflection.stubs(:klass).returns(category)
-    assert_equal 'product_categories', reflection.join_table
+    reflection = ActiveRecord::Reflection.create(:has_many, :categories, nil, { join_table: "product_categories" }, product)
+    reflection.stub(:klass, category) do
+      assert_equal "product_categories", reflection.join_table
+    end
 
-    reflection = ActiveRecord::Reflection.create(:has_many, :products, nil, { :join_table => 'product_categories' }, category)
-    reflection.stubs(:klass).returns(product)
-    assert_equal 'product_categories', reflection.join_table
+    reflection = ActiveRecord::Reflection.create(:has_many, :products, nil, { join_table: "product_categories" }, category)
+    reflection.stub(:klass, product) do
+      assert_equal "product_categories", reflection.join_table
+    end
   end
 
   def test_includes_accepts_symbols
@@ -456,7 +492,7 @@ class ReflectionTest < ActiveRecord::TestCase
     department.chefs.create!
 
     assert_nothing_raised do
-      assert_equal department.chefs, Hotel.includes(['departments' => 'chefs']).first.chefs
+      assert_equal department.chefs, Hotel.includes(["departments" => "chefs"]).first.chefs
     end
   end
 
diff --git a/activerecord/test/cases/relation/delegation_test.rb b/activerecord/test/cases/relation/delegation_test.rb
index 989f4e1e5d..a8030c2d64 100644
--- a/activerecord/test/cases/relation/delegation_test.rb
+++ b/activerecord/test/cases/relation/delegation_test.rb
@@ -1,38 +1,19 @@
-require 'cases/helper'
-require 'models/post'
-require 'models/comment'
+# frozen_string_literal: true
 
-module ActiveRecord
-  class DelegationTest < ActiveRecord::TestCase
-    fixtures :posts
-
-    def call_method(target, method)
-      method_arity = target.to_a.method(method).arity
-
-      if method_arity.zero?
-        target.public_send(method)
-      elsif method_arity < 0
-        if method == :shuffle!
-          target.public_send(method)
-        else
-          target.public_send(method, 1)
-        end
-       elsif method_arity == 1
-        target.public_send(method, 1)
-      else
-        raise NotImplementedError
-      end
-    end
-  end
+require "cases/helper"
+require "models/post"
+require "models/comment"
 
-  module DelegationWhitelistBlacklistTests
+module ActiveRecord
+  module ArrayDelegationTests
     ARRAY_DELEGATES = [
-      :+, :-, :|, :&, :[],
+      :+, :-, :|, :&, :[], :shuffle,
       :all?, :collect, :compact, :detect, :each, :each_cons, :each_with_index,
       :exclude?, :find_all, :flat_map, :group_by, :include?, :length,
-      :map, :none?, :one?, :partition, :reject, :reverse,
-      :sample, :second, :sort, :sort_by, :third,
-      :to_ary, :to_set, :to_xml, :to_yaml, :join
+      :map, :none?, :one?, :partition, :reject, :reverse, :rotate,
+      :sample, :second, :sort, :sort_by, :slice, :third, :index, :rindex,
+      :to_ary, :to_set, :to_xml, :to_yaml, :join,
+      :in_groups, :in_groups_of, :to_sentence, :to_formatted_s, :as_json
     ]
 
     ARRAY_DELEGATES.each do |method|
@@ -40,29 +21,65 @@ module ActiveRecord
         assert_respond_to target, method
       end
     end
+  end
+
+  module DeprecatedArelDelegationTests
+    AREL_METHODS = [
+      :with, :orders, :froms, :project, :projections, :taken, :constraints, :exists, :locked, :where_sql,
+      :ast, :source, :join_sources, :to_dot, :create_insert, :create_true, :create_false
+    ]
 
-    ActiveRecord::Delegation::BLACKLISTED_ARRAY_METHODS.each do |method|
-      define_method "test_#{method}_is_not_delegated_to_Array" do
-        assert_raises(NoMethodError) { call_method(target, method) }
+    def test_deprecate_arel_delegation
+      AREL_METHODS.each do |method|
+        assert_deprecated { target.public_send(method) }
+        assert_deprecated { target.public_send(method) }
       end
     end
   end
 
-  class DelegationAssociationTest < DelegationTest
-    include DelegationWhitelistBlacklistTests
+  class DelegationAssociationTest < ActiveRecord::TestCase
+    include ArrayDelegationTests
+    include DeprecatedArelDelegationTests
 
     def target
-      Post.first.comments
+      Post.new.comments
     end
   end
 
-  class DelegationRelationTest < DelegationTest
-    include DelegationWhitelistBlacklistTests
-
-    fixtures :comments
+  class DelegationRelationTest < ActiveRecord::TestCase
+    include ArrayDelegationTests
+    include DeprecatedArelDelegationTests
 
     def target
       Comment.all
     end
   end
+
+  class QueryingMethodsDelegationTest < ActiveRecord::TestCase
+    QUERYING_METHODS = [
+      :find, :take, :take!, :first, :first!, :last, :last!, :exists?, :any?, :many?, :none?, :one?,
+      :second, :second!, :third, :third!, :fourth, :fourth!, :fifth, :fifth!, :forty_two, :forty_two!, :third_to_last, :third_to_last!, :second_to_last, :second_to_last!,
+      :first_or_create, :first_or_create!, :first_or_initialize,
+      :find_or_create_by, :find_or_create_by!, :create_or_find_by, :create_or_find_by!, :find_or_initialize_by,
+      :find_by, :find_by!,
+      :destroy_all, :delete_all, :update_all,
+      :find_each, :find_in_batches, :in_batches,
+      :select, :group, :order, :except, :reorder, :limit, :offset, :joins, :left_joins, :left_outer_joins, :or,
+      :where, :rewhere, :preload, :eager_load, :includes, :from, :lock, :readonly, :extending,
+      :having, :create_with, :distinct, :references, :none, :unscope, :merge,
+      :count, :average, :minimum, :maximum, :sum, :calculate,
+      :pluck, :pick, :ids,
+    ]
+
+    def test_delegate_querying_methods
+      klass = Class.new(ActiveRecord::Base) do
+        self.table_name = "posts"
+      end
+
+      QUERYING_METHODS.each do |method|
+        assert_respond_to klass.all, method
+        assert_respond_to klass, method
+      end
+    end
+  end
 end
diff --git a/activerecord/test/cases/relation/delete_all_test.rb b/activerecord/test/cases/relation/delete_all_test.rb
new file mode 100644
index 0000000000..446d7621ea
--- /dev/null
+++ b/activerecord/test/cases/relation/delete_all_test.rb
@@ -0,0 +1,104 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/author"
+require "models/post"
+require "models/pet"
+require "models/toy"
+
+class DeleteAllTest < ActiveRecord::TestCase
+  fixtures :authors, :author_addresses, :posts, :pets, :toys
+
+  def test_destroy_all
+    davids = Author.where(name: "David")
+
+    # Force load
+    assert_equal [authors(:david)], davids.to_a
+    assert_predicate davids, :loaded?
+
+    assert_difference("Author.count", -1) do
+      destroyed = davids.destroy_all
+      assert_equal [authors(:david)], destroyed
+      assert_predicate destroyed.first, :frozen?
+    end
+
+    assert_equal [], davids.to_a
+    assert_predicate davids, :loaded?
+  end
+
+  def test_delete_all
+    davids = Author.where(name: "David")
+
+    assert_difference("Author.count", -1) { davids.delete_all }
+    assert_not_predicate davids, :loaded?
+  end
+
+  def test_delete_all_loaded
+    davids = Author.where(name: "David")
+
+    # Force load
+    assert_equal [authors(:david)], davids.to_a
+    assert_predicate davids, :loaded?
+
+    assert_difference("Author.count", -1) { davids.delete_all }
+
+    assert_equal [], davids.to_a
+    assert_predicate davids, :loaded?
+  end
+
+  def test_delete_all_with_unpermitted_relation_raises_error
+    assert_raises(ActiveRecord::ActiveRecordError) { Author.distinct.delete_all }
+    assert_raises(ActiveRecord::ActiveRecordError) { Author.group(:name).delete_all }
+    assert_raises(ActiveRecord::ActiveRecordError) { Author.having("SUM(id) < 3").delete_all }
+  end
+
+  def test_delete_all_with_joins_and_where_part_is_hash
+    pets = Pet.joins(:toys).where(toys: { name: "Bone" })
+
+    assert_equal true, pets.exists?
+    assert_equal pets.count, pets.delete_all
+  end
+
+  def test_delete_all_with_joins_and_where_part_is_not_hash
+    pets = Pet.joins(:toys).where("toys.name = ?", "Bone")
+
+    assert_equal true, pets.exists?
+    assert_equal pets.count, pets.delete_all
+  end
+
+  def test_delete_all_with_left_joins
+    pets = Pet.left_joins(:toys).where(toys: { name: "Bone" })
+
+    assert_equal true, pets.exists?
+    assert_equal pets.count, pets.delete_all
+  end
+
+  def test_delete_all_with_includes
+    pets = Pet.includes(:toys).where(toys: { name: "Bone" })
+
+    assert_equal true, pets.exists?
+    assert_equal pets.count, pets.delete_all
+  end
+
+  unless current_adapter?(:OracleAdapter)
+    def test_delete_all_with_order_and_limit_deletes_subset_only
+      author = authors(:david)
+      limited_posts = Post.where(author: author).order(:id).limit(1)
+      assert_equal 1, limited_posts.size
+      assert_equal 2, limited_posts.limit(2).size
+      assert_equal 1, limited_posts.delete_all
+      assert_raise(ActiveRecord::RecordNotFound) { posts(:welcome) }
+      assert posts(:thinking)
+    end
+
+    def test_delete_all_with_order_and_limit_and_offset_deletes_subset_only
+      author = authors(:david)
+      limited_posts = Post.where(author: author).order(:id).limit(1).offset(1)
+      assert_equal 1, limited_posts.size
+      assert_equal 2, limited_posts.limit(2).size
+      assert_equal 1, limited_posts.delete_all
+      assert_raise(ActiveRecord::RecordNotFound) { posts(:thinking) }
+      assert posts(:welcome)
+    end
+  end
+end
diff --git a/activerecord/test/cases/relation/merging_test.rb b/activerecord/test/cases/relation/merging_test.rb
index 0a2e874e4f..224e4f39a8 100644
--- a/activerecord/test/cases/relation/merging_test.rb
+++ b/activerecord/test/cases/relation/merging_test.rb
@@ -1,27 +1,29 @@
-require 'cases/helper'
-require 'models/author'
-require 'models/comment'
-require 'models/developer'
-require 'models/computer'
-require 'models/post'
-require 'models/project'
-require 'models/rating'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/author"
+require "models/comment"
+require "models/developer"
+require "models/computer"
+require "models/post"
+require "models/project"
+require "models/rating"
 
 class RelationMergingTest < ActiveRecord::TestCase
-  fixtures :developers, :comments, :authors, :posts
+  fixtures :developers, :comments, :authors, :author_addresses, :posts
 
   def test_relation_merging
-    devs = Developer.where("salary >= 80000").merge(Developer.limit(2)).merge(Developer.order('id ASC').where("id < 3"))
+    devs = Developer.where("salary >= 80000").merge(Developer.limit(2)).merge(Developer.order("id ASC").where("id < 3"))
     assert_equal [developers(:david), developers(:jamis)], devs.to_a
 
-    dev_with_count = Developer.limit(1).merge(Developer.order('id DESC')).merge(Developer.select('developers.*'))
+    dev_with_count = Developer.limit(1).merge(Developer.order("id DESC")).merge(Developer.select("developers.*"))
     assert_equal [developers(:poor_jamis)], dev_with_count.to_a
   end
 
   def test_relation_to_sql
     post = Post.first
     sql = post.comments.to_sql
-    assert_match(/.?post_id.? = #{post.id}\Z/i, sql)
+    assert_match(/.?post_id.? = #{post.id}\z/i, sql)
   end
 
   def test_relation_merging_with_arel_equalities_keeps_last_equality
@@ -34,10 +36,10 @@ class RelationMergingTest < ActiveRecord::TestCase
   def test_relation_merging_with_arel_equalities_keeps_last_equality_with_non_attribute_left_hand
     salary_attr = Developer.arel_table[:salary]
     devs = Developer.where(
-      Arel::Nodes::NamedFunction.new('abs', [salary_attr]).eq(80000)
+      Arel::Nodes::NamedFunction.new("abs", [salary_attr]).eq(80000)
     ).merge(
       Developer.where(
-        Arel::Nodes::NamedFunction.new('abs', [salary_attr]).eq(9000)
+        Arel::Nodes::NamedFunction.new("abs", [salary_attr]).eq(9000)
       )
     )
     assert_equal [developers(:poor_jamis)], devs.to_a
@@ -45,8 +47,8 @@ class RelationMergingTest < ActiveRecord::TestCase
 
   def test_relation_merging_with_eager_load
     relations = []
-    relations << Post.order('comments.id DESC').merge(Post.eager_load(:last_comment)).merge(Post.all)
-    relations << Post.eager_load(:last_comment).merge(Post.order('comments.id DESC')).merge(Post.all)
+    relations << Post.order("comments.id DESC").merge(Post.eager_load(:last_comment)).merge(Post.all)
+    relations << Post.eager_load(:last_comment).merge(Post.order("comments.id DESC")).merge(Post.all)
 
     relations.each do |posts|
       post = posts.find { |p| p.id == 1 }
@@ -56,7 +58,7 @@ class RelationMergingTest < ActiveRecord::TestCase
 
   def test_relation_merging_with_locks
     devs = Developer.lock.where("salary >= 80000").order("id DESC").merge(Developer.limit(2))
-    assert devs.locked.present?
+    assert_predicate devs, :locked?
   end
 
   def test_relation_merging_with_preload
@@ -66,29 +68,37 @@ class RelationMergingTest < ActiveRecord::TestCase
   end
 
   def test_relation_merging_with_joins
-    comments = Comment.joins(:post).where(:body => 'Thank you for the welcome').merge(Post.where(:body => 'Such a lovely day'))
+    comments = Comment.joins(:post).where(body: "Thank you for the welcome").merge(Post.where(body: "Such a lovely day"))
+    assert_equal 1, comments.count
+  end
+
+  def test_relation_merging_with_left_outer_joins
+    comments = Comment.joins(:post).where(body: "Thank you for the welcome").merge(Post.left_outer_joins(:author).where(body: "Such a lovely day"))
+
     assert_equal 1, comments.count
   end
 
+  def test_relation_merging_with_skip_query_cache
+    assert_equal Post.all.merge(Post.all.skip_query_cache!).skip_query_cache_value, true
+  end
+
   def test_relation_merging_with_association
     assert_queries(2) do  # one for loading post, and another one merged query
-      post = Post.where(:body => 'Such a lovely day').first
-      comments = Comment.where(:body => 'Thank you for the welcome').merge(post.comments)
+      post = Post.where(body: "Such a lovely day").first
+      comments = Comment.where(body: "Thank you for the welcome").merge(post.comments)
       assert_equal 1, comments.count
     end
   end
 
   test "merge collapses wheres from the LHS only" do
-    left  = Post.where(title: "omg").where(comments_count: 1)
+    left = Post.where(title: "omg").where(comments_count: 1)
     right = Post.where(title: "wtf").where(title: "bbq")
 
-    expected = [left.bound_attributes[1]] + right.bound_attributes
-    merged   = left.merge(right)
+    merged = left.merge(right)
 
-    assert_equal expected, merged.bound_attributes
-    assert !merged.to_sql.include?("omg")
-    assert merged.to_sql.include?("wtf")
-    assert merged.to_sql.include?("bbq")
+    assert_not_includes merged.to_sql, "omg"
+    assert_includes merged.to_sql, "wtf"
+    assert_includes merged.to_sql, "bbq"
   end
 
   def test_merging_reorders_bind_params
@@ -104,10 +114,31 @@ class RelationMergingTest < ActiveRecord::TestCase
     post = PostThatLoadsCommentsInAnAfterSaveHook.create!(title: "First Post", body: "Blah blah blah.")
     assert_equal "First comment!", post.comments.where(body: "First comment!").first_or_create.body
   end
+
+  def test_merging_with_from_clause
+    relation = Post.all
+    assert_empty relation.from_clause
+    relation = relation.merge(Post.from("posts"))
+    assert_not_empty relation.from_clause
+  end
+
+  def test_merging_with_from_clause_on_different_class
+    assert Comment.joins(:post).merge(Post.from("posts")).first
+  end
+
+  def test_merging_with_order_with_binds
+    relation = Post.all.merge(Post.order([Arel.sql("title LIKE ?"), "%suffix"]))
+    assert_equal ["title LIKE '%suffix'"], relation.order_values
+  end
+
+  def test_merging_with_order_without_binds
+    relation = Post.all.merge(Post.order(Arel.sql("title LIKE '%?'")))
+    assert_equal ["title LIKE '%?'"], relation.order_values
+  end
 end
 
 class MergingDifferentRelationsTest < ActiveRecord::TestCase
-  fixtures :posts, :authors, :developers
+  fixtures :posts, :authors, :author_addresses, :developers
 
   test "merging where relations" do
     hello_by_bob = Post.where(body: "hello").joins(:author).
@@ -136,7 +167,7 @@ class MergingDifferentRelationsTest < ActiveRecord::TestCase
     assert_equal ["Mary", "Mary", "Mary", "David"], posts_by_author_name
   end
 
-  test "relation merging (using a proc  argument)" do
+  test "relation merging (using a proc argument)" do
     dev = Developer.where(name: "Jamis").first
 
     comment_1 = dev.comments.create!(body: "I'm Jamis", post: Post.first)
diff --git a/activerecord/test/cases/relation/mutation_test.rb b/activerecord/test/cases/relation/mutation_test.rb
index ba4d9d2503..f82ecd4449 100644
--- a/activerecord/test/cases/relation/mutation_test.rb
+++ b/activerecord/test/cases/relation/mutation_test.rb
@@ -1,33 +1,10 @@
-require 'cases/helper'
-require 'models/post'
+# frozen_string_literal: true
 
-module ActiveRecord
-  class RelationMutationTest < ActiveSupport::TestCase
-    class FakeKlass < Struct.new(:table_name, :name)
-      extend ActiveRecord::Delegation::DelegateCache
-      inherited self
-
-      def connection
-        Post.connection
-      end
-
-      def relation_delegate_class(klass)
-        self.class.relation_delegate_class(klass)
-      end
-
-      def attribute_alias?(name)
-        false
-      end
-
-      def sanitize_sql(sql)
-        sql
-      end
-    end
-
-    def relation
-      @relation ||= Relation.new FakeKlass.new('posts'), Post.arel_table, Post.predicate_builder
-    end
+require "cases/helper"
+require "models/post"
 
+module ActiveRecord
+  class RelationMutationTest < ActiveRecord::TestCase
     (Relation::MULTI_VALUE_METHODS - [:references, :extending, :order, :unscope, :select]).each do |method|
       test "##{method}!" do
         assert relation.public_send("#{method}!", :foo).equal?(relation)
@@ -36,36 +13,37 @@ module ActiveRecord
     end
 
     test "#_select!" do
-      assert relation.public_send("_select!", :foo).equal?(relation)
-      assert_equal [:foo], relation.public_send("select_values")
+      assert relation._select!(:foo).equal?(relation)
+      assert_equal [:foo], relation.select_values
     end
 
-    test '#order!' do
-      assert relation.order!('name ASC').equal?(relation)
-      assert_equal ['name ASC'], relation.order_values
+    test "#order!" do
+      assert relation.order!("name ASC").equal?(relation)
+      assert_equal ["name ASC"], relation.order_values
     end
 
-    test '#order! with symbol prepends the table name' do
+    test "#order! with symbol prepends the table name" do
       assert relation.order!(:name).equal?(relation)
       node = relation.order_values.first
-      assert node.ascending?
+      assert_predicate node, :ascending?
       assert_equal :name, node.expr.name
       assert_equal "posts", node.expr.relation.name
     end
 
-    test '#order! on non-string does not attempt regexp match for references' do
+    test "#order! on non-string does not attempt regexp match for references" do
       obj = Object.new
-      obj.expects(:=~).never
-      assert relation.order!(obj)
-      assert_equal [obj], relation.order_values
+      assert_not_called(obj, :=~) do
+        assert relation.order!(obj)
+        assert_equal [obj], relation.order_values
+      end
     end
 
-    test '#references!' do
+    test "#references!" do
       assert relation.references!(:foo).equal?(relation)
-      assert relation.references_values.include?('foo')
+      assert_includes relation.references_values, "foo"
     end
 
-    test 'extending!' do
+    test "extending!" do
       mod, mod2 = Module.new, Module.new
 
       assert relation.extending!(mod).equal?(relation)
@@ -76,99 +54,97 @@ module ActiveRecord
       assert_equal [mod, mod2], relation.extending_values
     end
 
-    test 'extending! with empty args' do
+    test "extending! with empty args" do
       relation.extending!
       assert_equal [], relation.extending_values
     end
 
-    (Relation::SINGLE_VALUE_METHODS - [:lock, :reordering, :reverse_order, :create_with, :uniq]).each do |method|
+    (Relation::SINGLE_VALUE_METHODS - [:lock, :reordering, :reverse_order, :create_with, :skip_query_cache]).each do |method|
       test "##{method}!" do
         assert relation.public_send("#{method}!", :foo).equal?(relation)
         assert_equal :foo, relation.public_send("#{method}_value")
       end
     end
 
-    test '#from!' do
-      assert relation.from!('foo').equal?(relation)
-      assert_equal 'foo', relation.from_clause.value
+    test "#from!" do
+      assert relation.from!("foo").equal?(relation)
+      assert_equal "foo", relation.from_clause.value
     end
 
-    test '#lock!' do
-      assert relation.lock!('foo').equal?(relation)
-      assert_equal 'foo', relation.lock_value
+    test "#lock!" do
+      assert relation.lock!("foo").equal?(relation)
+      assert_equal "foo", relation.lock_value
     end
 
-    test '#reorder!' do
-      @relation = self.relation.order('foo')
+    test "#reorder!" do
+      @relation = relation.order("foo")
 
-      assert relation.reorder!('bar').equal?(relation)
-      assert_equal ['bar'], relation.order_values
+      assert relation.reorder!("bar").equal?(relation)
+      assert_equal ["bar"], relation.order_values
       assert relation.reordering_value
     end
 
-    test '#reorder! with symbol prepends the table name' do
+    test "#reorder! with symbol prepends the table name" do
       assert relation.reorder!(:name).equal?(relation)
       node = relation.order_values.first
 
-      assert node.ascending?
+      assert_predicate node, :ascending?
       assert_equal :name, node.expr.name
       assert_equal "posts", node.expr.relation.name
     end
 
-    test 'reverse_order!' do
-      @relation = Post.order('title ASC, comments_count DESC')
+    test "reverse_order!" do
+      @relation = Post.order("title ASC, comments_count DESC")
 
       relation.reverse_order!
 
-      assert_equal 'title DESC', relation.order_values.first
-      assert_equal 'comments_count ASC', relation.order_values.last
-
+      assert_equal "title DESC", relation.order_values.first
+      assert_equal "comments_count ASC", relation.order_values.last
 
       relation.reverse_order!
 
-      assert_equal 'title ASC', relation.order_values.first
-      assert_equal 'comments_count DESC', relation.order_values.last
+      assert_equal "title ASC", relation.order_values.first
+      assert_equal "comments_count DESC", relation.order_values.last
     end
 
-    test 'create_with!' do
-      assert relation.create_with!(foo: 'bar').equal?(relation)
-      assert_equal({foo: 'bar'}, relation.create_with_value)
+    test "create_with!" do
+      assert relation.create_with!(foo: "bar").equal?(relation)
+      assert_equal({ foo: "bar" }, relation.create_with_value)
     end
 
-    test 'test_merge!' do
+    test "merge!" do
       assert relation.merge!(select: :foo).equal?(relation)
       assert_equal [:foo], relation.select_values
     end
 
-    test 'merge with a proc' do
+    test "merge with a proc" do
       assert_equal [:foo], relation.merge(-> { select(:foo) }).select_values
     end
 
-    test 'none!' do
+    test "none!" do
       assert relation.none!.equal?(relation)
       assert_equal [NullRelation], relation.extending_values
       assert relation.is_a?(NullRelation)
     end
 
-    test 'distinct!' do
+    test "distinct!" do
       relation.distinct! :foo
       assert_equal :foo, relation.distinct_value
+    end
 
-      assert_deprecated do
-        assert_equal :foo, relation.uniq_value # deprecated access
-      end
+    test "skip_query_cache!" do
+      relation.skip_query_cache!
+      assert relation.skip_query_cache_value
     end
 
-    test 'uniq! was replaced by distinct!' do
-      assert_deprecated(/use distinct! instead/) do
-        relation.uniq! :foo
-      end
+    test "skip_preloading!" do
+      relation.skip_preloading!
+      assert relation.skip_preloading_value
+    end
 
-      assert_deprecated(/use distinct_value instead/) do
-        assert_equal :foo, relation.uniq_value # deprecated access
+    private
+      def relation
+        @relation ||= Relation.new(FakeKlass)
       end
-
-      assert_equal :foo, relation.distinct_value
-    end
   end
 end
diff --git a/activerecord/test/cases/relation/or_test.rb b/activerecord/test/cases/relation/or_test.rb
index 2006fc9611..065819e0f1 100644
--- a/activerecord/test/cases/relation/or_test.rb
+++ b/activerecord/test/cases/relation/or_test.rb
@@ -1,32 +1,37 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
+require "models/author"
+require "models/categorization"
+require "models/post"
 
 module ActiveRecord
   class OrTest < ActiveRecord::TestCase
     fixtures :posts
+    fixtures :authors, :author_addresses
 
     def test_or_with_relation
-      expected = Post.where('id = 1 or id = 2').to_a
-      assert_equal expected, Post.where('id = 1').or(Post.where('id = 2')).to_a
+      expected = Post.where("id = 1 or id = 2").to_a
+      assert_equal expected, Post.where("id = 1").or(Post.where("id = 2")).to_a
     end
 
     def test_or_identity
-      expected = Post.where('id = 1').to_a
-      assert_equal expected, Post.where('id = 1').or(Post.where('id = 1')).to_a
+      expected = Post.where("id = 1").to_a
+      assert_equal expected, Post.where("id = 1").or(Post.where("id = 1")).to_a
     end
 
     def test_or_with_null_left
-      expected = Post.where('id = 1').to_a
-      assert_equal expected, Post.none.or(Post.where('id = 1')).to_a
+      expected = Post.where("id = 1").to_a
+      assert_equal expected, Post.none.or(Post.where("id = 1")).to_a
     end
 
     def test_or_with_null_right
-      expected = Post.where('id = 1').to_a
-      assert_equal expected, Post.where('id = 1').or(Post.none).to_a
+      expected = Post.where("id = 1").to_a
+      assert_equal expected, Post.where("id = 1").or(Post.none).to_a
     end
 
     def test_or_with_bind_params
-      assert_equal Post.find([1, 2]), Post.where(id: 1).or(Post.where(id: 2)).to_a
+      assert_equal Post.find([1, 2]).sort_by(&:id), Post.where(id: 1).or(Post.where(id: 2)).sort_by(&:id)
     end
 
     def test_or_with_null_both
@@ -36,49 +41,97 @@ module ActiveRecord
 
     def test_or_without_left_where
       expected = Post.all
-      assert_equal expected, Post.or(Post.where('id = 1')).to_a
+      assert_equal expected, Post.or(Post.where("id = 1")).to_a
     end
 
     def test_or_without_right_where
       expected = Post.all
-      assert_equal expected, Post.where('id = 1').or(Post.all).to_a
+      assert_equal expected, Post.where("id = 1").or(Post.all).to_a
     end
 
     def test_or_preserves_other_querying_methods
-      expected = Post.where('id = 1 or id = 2 or id = 3').order('body asc').to_a
-      partial = Post.order('body asc')
-      assert_equal expected, partial.where('id = 1').or(partial.where(:id => [2, 3])).to_a
-      assert_equal expected, Post.order('body asc').where('id = 1').or(Post.order('body asc').where(:id => [2, 3])).to_a
+      expected = Post.where("id = 1 or id = 2 or id = 3").order("body asc").to_a
+      partial = Post.order("body asc")
+      assert_equal expected, partial.where("id = 1").or(partial.where(id: [2, 3])).to_a
+      assert_equal expected, Post.order("body asc").where("id = 1").or(Post.order("body asc").where(id: [2, 3])).to_a
     end
 
     def test_or_with_incompatible_relations
-      assert_raises ArgumentError do
-        Post.order('body asc').where('id = 1').or(Post.order('id desc').where(:id => [2, 3])).to_a
+      error = assert_raises ArgumentError do
+        Post.order("body asc").where("id = 1").or(Post.order("id desc").where(id: [2, 3])).to_a
+      end
+
+      assert_equal "Relation passed to #or must be structurally compatible. Incompatible values: [:order]", error.message
+    end
+
+    def test_or_with_unscope_where
+      expected = Post.where("id = 1 or id = 2")
+      partial = Post.where("id = 1 and id != 2")
+      assert_equal expected, partial.or(partial.unscope(:where).where("id = 2")).to_a
+    end
+
+    def test_or_with_unscope_where_column
+      expected = Post.where("id = 1 or id = 2")
+      partial = Post.where(id: 1).where.not(id: 2)
+      assert_equal expected, partial.or(partial.unscope(where: :id).where("id = 2")).to_a
+    end
+
+    def test_or_with_unscope_order
+      expected = Post.where("id = 1 or id = 2")
+      assert_equal expected, Post.order("body asc").where("id = 1").unscope(:order).or(Post.where("id = 2")).to_a
+    end
+
+    def test_or_with_incompatible_unscope
+      error = assert_raises ArgumentError do
+        Post.order("body asc").where("id = 1").or(Post.order("body asc").where("id = 2").unscope(:order)).to_a
       end
+
+      assert_equal "Relation passed to #or must be structurally compatible. Incompatible values: [:order]", error.message
     end
 
     def test_or_when_grouping
-      groups = Post.where('id < 10').group('body').select('body, COUNT(*) AS c')
-      expected = groups.having("COUNT(*) > 1 OR body like 'Such%'").to_a.map {|o| [o.body, o.c] }
-      assert_equal expected, groups.having('COUNT(*) > 1').or(groups.having("body like 'Such%'")).to_a.map {|o| [o.body, o.c] }
+      groups = Post.where("id < 10").group("body").select("body, COUNT(*) AS c")
+      expected = groups.having("COUNT(*) > 1 OR body like 'Such%'").to_a.map { |o| [o.body, o.c] }
+      assert_equal expected, groups.having("COUNT(*) > 1").or(groups.having("body like 'Such%'")).to_a.map { |o| [o.body, o.c] }
     end
 
     def test_or_with_named_scope
       expected = Post.where("id = 1 or body LIKE '\%a\%'").to_a
-      assert_equal expected, Post.where('id = 1').or(Post.containing_the_letter_a)
+      assert_equal expected, Post.where("id = 1").or(Post.containing_the_letter_a)
     end
 
     def test_or_inside_named_scope
-      expected = Post.where("body LIKE '\%a\%' OR title LIKE ?", "%'%").order('id DESC').to_a
+      expected = Post.where("body LIKE '\%a\%' OR title LIKE ?", "%'%").order("id DESC").to_a
       assert_equal expected, Post.order(id: :desc).typographically_interesting
     end
 
     def test_or_on_loaded_relation
-      expected = Post.where('id = 1 or id = 2').to_a
-      p = Post.where('id = 1')
+      expected = Post.where("id = 1 or id = 2").to_a
+      p = Post.where("id = 1")
       p.load
-      assert_equal p.loaded?, true
-      assert_equal expected, p.or(Post.where('id = 2')).to_a
+      assert_equal true, p.loaded?
+      assert_equal expected, p.or(Post.where("id = 2")).to_a
+    end
+
+    def test_or_with_non_relation_object_raises_error
+      assert_raises ArgumentError do
+        Post.where(id: [1, 2, 3]).or(title: "Rails")
+      end
+    end
+
+    def test_or_with_references_inequality
+      joined = Post.includes(:author)
+      actual = joined.where(authors: { id: 1 })
+        .or(joined.where(title: "I don't have any comments"))
+      expected = Author.find(1).posts + Post.where(title: "I don't have any comments")
+      assert_equal expected.sort_by(&:id), actual.sort_by(&:id)
+    end
+
+    def test_or_with_scope_on_association
+      author = Author.first
+      assert_nothing_raised do
+        author.top_posts.or(author.other_top_posts)
+      end
     end
   end
 end
diff --git a/activerecord/test/cases/relation/predicate_builder_test.rb b/activerecord/test/cases/relation/predicate_builder_test.rb
index 8f62014622..b432330deb 100644
--- a/activerecord/test/cases/relation/predicate_builder_test.rb
+++ b/activerecord/test/cases/relation/predicate_builder_test.rb
@@ -1,11 +1,13 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
+require "models/topic"
 
 module ActiveRecord
   class PredicateBuilderTest < ActiveRecord::TestCase
     def test_registering_new_handlers
       Topic.predicate_builder.register_handler(Regexp, proc do |column, value|
-        Arel::Nodes::InfixOperation.new('~', column, Arel.sql(value.source))
+        Arel::Nodes::InfixOperation.new("~", column, Arel.sql(value.source))
       end)
 
       assert_match %r{["`]topics["`]\.["`]title["`] ~ rails}i, Topic.where(title: /rails/).to_sql
diff --git a/activerecord/test/cases/relation/record_fetch_warning_test.rb b/activerecord/test/cases/relation/record_fetch_warning_test.rb
index 62f0a7cc49..22d32d75bc 100644
--- a/activerecord/test/cases/relation/record_fetch_warning_test.rb
+++ b/activerecord/test/cases/relation/record_fetch_warning_test.rb
@@ -1,28 +1,42 @@
-require 'cases/helper'
-require 'models/post'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/post"
+require "active_record/relation/record_fetch_warning"
 
 module ActiveRecord
   class RecordFetchWarningTest < ActiveRecord::TestCase
     fixtures :posts
 
-    def test_warn_on_records_fetched_greater_than
-      original_logger = ActiveRecord::Base.logger
-      orginal_warn_on_records_fetched_greater_than = ActiveRecord::Base.warn_on_records_fetched_greater_than
+    def setup
+      @original_logger = ActiveRecord::Base.logger
+      @original_warn_on_records_fetched_greater_than = ActiveRecord::Base.warn_on_records_fetched_greater_than
+      @log = StringIO.new
+    end
 
-      log = StringIO.new
-      ActiveRecord::Base.logger = ActiveSupport::Logger.new(log)
+    def teardown
+      ActiveRecord::Base.logger = @original_logger
+      ActiveRecord::Base.warn_on_records_fetched_greater_than = @original_warn_on_records_fetched_greater_than
+    end
+
+    def test_warn_on_records_fetched_greater_than_allowed_limit
+      ActiveRecord::Base.logger = ActiveSupport::Logger.new(@log)
       ActiveRecord::Base.logger.level = Logger::WARN
+      ActiveRecord::Base.warn_on_records_fetched_greater_than = 1
 
-      require 'active_record/relation/record_fetch_warning'
+      Post.all.to_a
 
-      ActiveRecord::Base.warn_on_records_fetched_greater_than = 1
+      assert_match(/Query fetched/, @log.string)
+    end
+
+    def test_does_not_warn_on_records_fetched_less_than_allowed_limit
+      ActiveRecord::Base.logger = ActiveSupport::Logger.new(@log)
+      ActiveRecord::Base.logger.level = Logger::WARN
+      ActiveRecord::Base.warn_on_records_fetched_greater_than = 100
 
       Post.all.to_a
 
-      assert_match(/Query fetched/, log.string)
-    ensure
-      ActiveRecord::Base.logger = original_logger
-      ActiveRecord::Base.warn_on_records_fetched_greater_than = orginal_warn_on_records_fetched_greater_than
+      assert_no_match(/Query fetched/, @log.string)
     end
   end
 end
diff --git a/activerecord/test/cases/relation/select_test.rb b/activerecord/test/cases/relation/select_test.rb
new file mode 100644
index 0000000000..dec8a6925d
--- /dev/null
+++ b/activerecord/test/cases/relation/select_test.rb
@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/post"
+
+module ActiveRecord
+  class SelectTest < ActiveRecord::TestCase
+    fixtures :posts
+
+    def test_select_with_nil_argument
+      expected = Post.select(:title).to_sql
+      assert_equal expected, Post.select(nil).select(:title).to_sql
+    end
+  end
+end
diff --git a/activerecord/test/cases/relation/update_all_test.rb b/activerecord/test/cases/relation/update_all_test.rb
new file mode 100644
index 0000000000..09c365f31b
--- /dev/null
+++ b/activerecord/test/cases/relation/update_all_test.rb
@@ -0,0 +1,239 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/author"
+require "models/category"
+require "models/comment"
+require "models/computer"
+require "models/developer"
+require "models/post"
+require "models/person"
+require "models/pet"
+require "models/toy"
+require "models/topic"
+require "models/tag"
+require "models/tagging"
+require "models/warehouse_thing"
+
+class UpdateAllTest < ActiveRecord::TestCase
+  fixtures :authors, :author_addresses, :comments, :developers, :posts, :people, :pets, :toys, :tags, :taggings, "warehouse-things"
+
+  class TopicWithCallbacks < ActiveRecord::Base
+    self.table_name = :topics
+    cattr_accessor :topic_count
+    before_update { |topic| topic.author_name = "David" if topic.author_name.blank? }
+    after_update { |topic| topic.class.topic_count = topic.class.count }
+  end
+
+  def test_update_all_with_scope
+    tag = Tag.first
+    Post.tagged_with(tag.id).update_all(title: "rofl")
+    posts = Post.tagged_with(tag.id).all.to_a
+    assert_operator posts.length, :>, 0
+    posts.each { |post| assert_equal "rofl", post.title }
+  end
+
+  def test_update_all_with_non_standard_table_name
+    assert_equal 1, WarehouseThing.where(id: 1).update_all(["value = ?", 0])
+    assert_equal 0, WarehouseThing.find(1).value
+  end
+
+  def test_update_all_with_blank_argument
+    assert_raises(ArgumentError) { Comment.update_all({}) }
+  end
+
+  def test_update_all_with_joins
+    pets = Pet.joins(:toys).where(toys: { name: "Bone" })
+
+    assert_equal true, pets.exists?
+    assert_equal pets.count, pets.update_all(name: "Bob")
+  end
+
+  def test_update_all_with_left_joins
+    pets = Pet.left_joins(:toys).where(toys: { name: "Bone" })
+
+    assert_equal true, pets.exists?
+    assert_equal pets.count, pets.update_all(name: "Bob")
+  end
+
+  def test_update_all_with_includes
+    pets = Pet.includes(:toys).where(toys: { name: "Bone" })
+
+    assert_equal true, pets.exists?
+    assert_equal pets.count, pets.update_all(name: "Bob")
+  end
+
+  def test_update_all_with_joins_and_limit
+    comments = Comment.joins(:post).where("posts.id" => posts(:welcome).id).limit(1)
+    assert_equal 1, comments.update_all(post_id: posts(:thinking).id)
+    assert_equal posts(:thinking), comments(:greetings).post
+  end
+
+  def test_update_all_with_joins_and_limit_and_order
+    comments = Comment.joins(:post).where("posts.id" => posts(:welcome).id).order("comments.id").limit(1)
+    assert_equal 1, comments.update_all(post_id: posts(:thinking).id)
+    assert_equal posts(:thinking), comments(:greetings).post
+    assert_equal posts(:welcome),  comments(:more_greetings).post
+  end
+
+  def test_update_all_with_joins_and_offset
+    all_comments = Comment.joins(:post).where("posts.id" => posts(:welcome).id)
+    count        = all_comments.count
+    comments     = all_comments.offset(1)
+
+    assert_equal count - 1, comments.update_all(post_id: posts(:thinking).id)
+  end
+
+  def test_update_all_with_joins_and_offset_and_order
+    all_comments = Comment.joins(:post).where("posts.id" => posts(:welcome).id).order("posts.id", "comments.id")
+    count        = all_comments.count
+    comments     = all_comments.offset(1)
+
+    assert_equal count - 1, comments.update_all(post_id: posts(:thinking).id)
+    assert_equal posts(:thinking), comments(:more_greetings).post
+    assert_equal posts(:welcome),  comments(:greetings).post
+  end
+
+  def test_update_counters_with_joins
+    assert_nil pets(:parrot).integer
+
+    Pet.joins(:toys).where(toys: { name: "Bone" }).update_counters(integer: 1)
+
+    assert_equal 1, pets(:parrot).reload.integer
+  end
+
+  def test_touch_all_updates_records_timestamps
+    david = developers(:david)
+    david_previously_updated_at = david.updated_at
+    jamis = developers(:jamis)
+    jamis_previously_updated_at = jamis.updated_at
+    Developer.where(name: "David").touch_all
+
+    assert_not_equal david_previously_updated_at, david.reload.updated_at
+    assert_equal jamis_previously_updated_at, jamis.reload.updated_at
+  end
+
+  def test_touch_all_with_custom_timestamp
+    developer = developers(:david)
+    previously_created_at = developer.created_at
+    previously_updated_at = developer.updated_at
+    Developer.where(name: "David").touch_all(:created_at)
+    developer.reload
+
+    assert_not_equal previously_created_at, developer.created_at
+    assert_not_equal previously_updated_at, developer.updated_at
+  end
+
+  def test_touch_all_with_given_time
+    developer = developers(:david)
+    previously_created_at = developer.created_at
+    previously_updated_at = developer.updated_at
+    new_time = Time.utc(2015, 2, 16, 4, 54, 0)
+    Developer.where(name: "David").touch_all(:created_at, time: new_time)
+    developer.reload
+
+    assert_not_equal previously_created_at, developer.created_at
+    assert_not_equal previously_updated_at, developer.updated_at
+    assert_equal new_time, developer.created_at
+    assert_equal new_time, developer.updated_at
+  end
+
+  def test_touch_all_updates_locking_column
+    person = people(:david)
+
+    assert_difference -> { person.reload.lock_version }, +1 do
+      Person.where(first_name: "David").touch_all
+    end
+  end
+
+  def test_update_on_relation
+    topic1 = TopicWithCallbacks.create! title: "arel", author_name: nil
+    topic2 = TopicWithCallbacks.create! title: "activerecord", author_name: nil
+    topics = TopicWithCallbacks.where(id: [topic1.id, topic2.id])
+    topics.update(title: "adequaterecord")
+
+    assert_equal TopicWithCallbacks.count, TopicWithCallbacks.topic_count
+
+    assert_equal "adequaterecord", topic1.reload.title
+    assert_equal "adequaterecord", topic2.reload.title
+    # Testing that the before_update callbacks have run
+    assert_equal "David", topic1.reload.author_name
+    assert_equal "David", topic2.reload.author_name
+  end
+
+  def test_update_with_ids_on_relation
+    topic1 = TopicWithCallbacks.create!(title: "arel", author_name: nil)
+    topic2 = TopicWithCallbacks.create!(title: "activerecord", author_name: nil)
+    topics = TopicWithCallbacks.none
+    topics.update(
+      [topic1.id, topic2.id],
+      [{ title: "adequaterecord" }, { title: "adequaterecord" }]
+    )
+
+    assert_equal TopicWithCallbacks.count, TopicWithCallbacks.topic_count
+
+    assert_equal "adequaterecord", topic1.reload.title
+    assert_equal "adequaterecord", topic2.reload.title
+    # Testing that the before_update callbacks have run
+    assert_equal "David", topic1.reload.author_name
+    assert_equal "David", topic2.reload.author_name
+  end
+
+  def test_update_on_relation_passing_active_record_object_is_not_permitted
+    topic = Topic.create!(title: "Foo", author_name: nil)
+    assert_raises(ArgumentError) do
+      Topic.where(id: topic.id).update(topic, title: "Bar")
+    end
+  end
+
+  # Oracle UPDATE does not support ORDER BY
+  unless current_adapter?(:OracleAdapter)
+    def test_update_all_ignores_order_without_limit_from_association
+      author = authors(:david)
+      assert_nothing_raised do
+        assert_equal author.posts_with_comments_and_categories.length, author.posts_with_comments_and_categories.update_all([ "body = ?", "bulk update!" ])
+      end
+    end
+
+    def test_update_all_doesnt_ignore_order
+      assert_equal authors(:david).id + 1, authors(:mary).id # make sure there is going to be a duplicate PK error
+      test_update_with_order_succeeds = lambda do |order|
+        begin
+          Author.order(order).update_all("id = id + 1")
+        rescue ActiveRecord::ActiveRecordError
+          false
+        end
+      end
+
+      if test_update_with_order_succeeds.call("id DESC")
+        # test that this wasn't a fluke and using an incorrect order results in an exception
+        assert_not test_update_with_order_succeeds.call("id ASC")
+      else
+        # test that we're failing because the current Arel's engine doesn't support UPDATE ORDER BY queries is using subselects instead
+        assert_sql(/\AUPDATE .+ \(SELECT .* ORDER BY id DESC\)\z/i) do
+          test_update_with_order_succeeds.call("id DESC")
+        end
+      end
+    end
+
+    def test_update_all_with_order_and_limit_updates_subset_only
+      author = authors(:david)
+      limited_posts = author.posts_sorted_by_id_limited
+      assert_equal 1, limited_posts.size
+      assert_equal 2, limited_posts.limit(2).size
+      assert_equal 1, limited_posts.update_all([ "body = ?", "bulk update!" ])
+      assert_equal "bulk update!", posts(:welcome).body
+      assert_not_equal "bulk update!", posts(:thinking).body
+    end
+
+    def test_update_all_with_order_and_limit_and_offset_updates_subset_only
+      author = authors(:david)
+      limited_posts = author.posts_sorted_by_id_limited.offset(1)
+      assert_equal 1, limited_posts.size
+      assert_equal 2, limited_posts.limit(2).size
+      assert_equal 1, limited_posts.update_all([ "body = ?", "bulk update!" ])
+      assert_equal "bulk update!", posts(:thinking).body
+      assert_not_equal "bulk update!", posts(:welcome).body
+    end
+  end
+end
diff --git a/activerecord/test/cases/relation/where_chain_test.rb b/activerecord/test/cases/relation/where_chain_test.rb
index 27bbd80f79..a68eb2b446 100644
--- a/activerecord/test/cases/relation/where_chain_test.rb
+++ b/activerecord/test/cases/relation/where_chain_test.rb
@@ -1,6 +1,8 @@
-require 'cases/helper'
-require 'models/post'
-require 'models/comment'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/post"
+require "models/comment"
 
 module ActiveRecord
   class WhereChainTest < ActiveRecord::TestCase
@@ -8,12 +10,12 @@ module ActiveRecord
 
     def setup
       super
-      @name = 'title'
+      @name = "title"
     end
 
     def test_not_inverts_where_clause
-      relation = Post.where.not(title: 'hello')
-      expected_where_clause = Post.where(title: 'hello').where_clause.invert
+      relation = Post.where.not(title: "hello")
+      expected_where_clause = Post.where(title: "hello").where_clause.invert
 
       assert_equal expected_where_clause, relation.where_clause
     end
@@ -25,55 +27,55 @@ module ActiveRecord
     end
 
     def test_association_not_eq
-      expected = Arel::Nodes::Grouping.new(Comment.arel_table[@name].not_eq(Arel::Nodes::BindParam.new))
-      relation = Post.joins(:comments).where.not(comments: {title: 'hello'})
+      expected = Comment.arel_table[@name].not_eq(Arel::Nodes::BindParam.new(1))
+      relation = Post.joins(:comments).where.not(comments: { title: "hello" })
       assert_equal(expected.to_sql, relation.where_clause.ast.to_sql)
     end
 
     def test_not_eq_with_preceding_where
-      relation = Post.where(title: 'hello').where.not(title: 'world')
+      relation = Post.where(title: "hello").where.not(title: "world")
       expected_where_clause =
-        Post.where(title: 'hello').where_clause +
-        Post.where(title: 'world').where_clause.invert
+        Post.where(title: "hello").where_clause +
+        Post.where(title: "world").where_clause.invert
 
       assert_equal expected_where_clause, relation.where_clause
     end
 
     def test_not_eq_with_succeeding_where
-      relation = Post.where.not(title: 'hello').where(title: 'world')
+      relation = Post.where.not(title: "hello").where(title: "world")
       expected_where_clause =
-        Post.where(title: 'hello').where_clause.invert +
-        Post.where(title: 'world').where_clause
+        Post.where(title: "hello").where_clause.invert +
+        Post.where(title: "world").where_clause
 
       assert_equal expected_where_clause, relation.where_clause
     end
 
     def test_chaining_multiple
-      relation = Post.where.not(author_id: [1, 2]).where.not(title: 'ruby on rails')
+      relation = Post.where.not(author_id: [1, 2]).where.not(title: "ruby on rails")
       expected_where_clause =
         Post.where(author_id: [1, 2]).where_clause.invert +
-        Post.where(title: 'ruby on rails').where_clause.invert
+        Post.where(title: "ruby on rails").where_clause.invert
 
       assert_equal expected_where_clause, relation.where_clause
     end
 
     def test_rewhere_with_one_condition
-      relation = Post.where(title: 'hello').where(title: 'world').rewhere(title: 'alone')
-      expected = Post.where(title: 'alone')
+      relation = Post.where(title: "hello").where(title: "world").rewhere(title: "alone")
+      expected = Post.where(title: "alone")
 
       assert_equal expected.where_clause, relation.where_clause
     end
 
     def test_rewhere_with_multiple_overwriting_conditions
-      relation = Post.where(title: 'hello').where(body: 'world').rewhere(title: 'alone', body: 'again')
-      expected = Post.where(title: 'alone', body: 'again')
+      relation = Post.where(title: "hello").where(body: "world").rewhere(title: "alone", body: "again")
+      expected = Post.where(title: "alone", body: "again")
 
       assert_equal expected.where_clause, relation.where_clause
     end
 
     def test_rewhere_with_one_overwriting_condition_and_one_unrelated
-      relation = Post.where(title: 'hello').where(body: 'world').rewhere(title: 'alone')
-      expected = Post.where(body: 'world', title: 'alone')
+      relation = Post.where(title: "hello").where(body: "world").rewhere(title: "alone")
+      expected = Post.where(body: "world", title: "alone")
 
       assert_equal expected.where_clause, relation.where_clause
     end
diff --git a/activerecord/test/cases/relation/where_clause_test.rb b/activerecord/test/cases/relation/where_clause_test.rb
index c20ed94d90..0b06cec40b 100644
--- a/activerecord/test/cases/relation/where_clause_test.rb
+++ b/activerecord/test/cases/relation/where_clause_test.rb
@@ -1,78 +1,86 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class ActiveRecord::Relation
   class WhereClauseTest < ActiveRecord::TestCase
     test "+ combines two where clauses" do
-      first_clause = WhereClause.new([table["id"].eq(bind_param)], [["id", 1]])
-      second_clause = WhereClause.new([table["name"].eq(bind_param)], [["name", "Sean"]])
+      first_clause = WhereClause.new([table["id"].eq(bind_param(1))])
+      second_clause = WhereClause.new([table["name"].eq(bind_param("Sean"))])
       combined = WhereClause.new(
-        [table["id"].eq(bind_param), table["name"].eq(bind_param)],
-        [["id", 1], ["name", "Sean"]],
+        [table["id"].eq(bind_param(1)), table["name"].eq(bind_param("Sean"))],
       )
 
       assert_equal combined, first_clause + second_clause
     end
 
     test "+ is associative, but not commutative" do
-      a = WhereClause.new(["a"], ["bind a"])
-      b = WhereClause.new(["b"], ["bind b"])
-      c = WhereClause.new(["c"], ["bind c"])
+      a = WhereClause.new(["a"])
+      b = WhereClause.new(["b"])
+      c = WhereClause.new(["c"])
 
       assert_equal a + (b + c), (a + b) + c
       assert_not_equal a + b, b + a
     end
 
     test "an empty where clause is the identity value for +" do
-      clause = WhereClause.new([table["id"].eq(bind_param)], [["id", 1]])
+      clause = WhereClause.new([table["id"].eq(bind_param(1))])
 
       assert_equal clause, clause + WhereClause.empty
     end
 
     test "merge combines two where clauses" do
-      a = WhereClause.new([table["id"].eq(1)], [])
-      b = WhereClause.new([table["name"].eq("Sean")], [])
-      expected = WhereClause.new([table["id"].eq(1), table["name"].eq("Sean")], [])
+      a = WhereClause.new([table["id"].eq(1)])
+      b = WhereClause.new([table["name"].eq("Sean")])
+      expected = WhereClause.new([table["id"].eq(1), table["name"].eq("Sean")])
 
       assert_equal expected, a.merge(b)
     end
 
     test "merge keeps the right side, when two equality clauses reference the same column" do
-      a = WhereClause.new([table["id"].eq(1), table["name"].eq("Sean")], [])
-      b = WhereClause.new([table["name"].eq("Jim")], [])
-      expected = WhereClause.new([table["id"].eq(1), table["name"].eq("Jim")], [])
+      a = WhereClause.new([table["id"].eq(1), table["name"].eq("Sean")])
+      b = WhereClause.new([table["name"].eq("Jim")])
+      expected = WhereClause.new([table["id"].eq(1), table["name"].eq("Jim")])
 
       assert_equal expected, a.merge(b)
     end
 
     test "merge removes bind parameters matching overlapping equality clauses" do
       a = WhereClause.new(
-        [table["id"].eq(bind_param), table["name"].eq(bind_param)],
-        [attribute("id", 1), attribute("name", "Sean")],
+        [table["id"].eq(bind_param(1)), table["name"].eq(bind_param("Sean"))],
       )
       b = WhereClause.new(
-        [table["name"].eq(bind_param)],
-        [attribute("name", "Jim")]
+        [table["name"].eq(bind_param("Jim"))],
       )
       expected = WhereClause.new(
-        [table["id"].eq(bind_param), table["name"].eq(bind_param)],
-        [attribute("id", 1), attribute("name", "Jim")],
+        [table["id"].eq(bind_param(1)), table["name"].eq(bind_param("Jim"))],
       )
 
       assert_equal expected, a.merge(b)
     end
 
     test "merge allows for columns with the same name from different tables" do
-      skip "This is not possible as of 4.2, and the binds do not yet contain sufficient information for this to happen"
-      # We might be able to change the implementation to remove conflicts by index, rather than column name
+      table2 = Arel::Table.new("table2")
+      a = WhereClause.new(
+        [table["id"].eq(bind_param(1)), table2["id"].eq(bind_param(2))],
+      )
+      b = WhereClause.new(
+        [table["id"].eq(bind_param(3))],
+      )
+      expected = WhereClause.new(
+        [table2["id"].eq(bind_param(2)), table["id"].eq(bind_param(3))],
+      )
+
+      assert_equal expected, a.merge(b)
     end
 
     test "a clause knows if it is empty" do
-      assert WhereClause.empty.empty?
-      assert_not WhereClause.new(["anything"], []).empty?
+      assert_empty WhereClause.empty
+      assert_not_empty WhereClause.new(["anything"])
     end
 
     test "invert cannot handle nil" do
-      where_clause = WhereClause.new([nil], [])
+      where_clause = WhereClause.new([nil])
 
       assert_raises ArgumentError do
         where_clause.invert
@@ -84,39 +92,53 @@ class ActiveRecord::Relation
       original = WhereClause.new([
         table["id"].in([1, 2, 3]),
         table["id"].eq(1),
+        table["id"].is_not_distinct_from(1),
+        table["id"].is_distinct_from(2),
         "sql literal",
         random_object
-      ], [])
+      ])
       expected = WhereClause.new([
         table["id"].not_in([1, 2, 3]),
         table["id"].not_eq(1),
+        table["id"].is_distinct_from(1),
+        table["id"].is_not_distinct_from(2),
         Arel::Nodes::Not.new(Arel::Nodes::SqlLiteral.new("sql literal")),
         Arel::Nodes::Not.new(random_object)
-      ], [])
+      ])
 
       assert_equal expected, original.invert
     end
 
-    test "accept removes binary predicates referencing a given column" do
+    test "except removes binary predicates referencing a given column" do
       where_clause = WhereClause.new([
         table["id"].in([1, 2, 3]),
-        table["name"].eq(bind_param),
-        table["age"].gteq(bind_param),
-      ], [
-        attribute("name", "Sean"),
-        attribute("age", 30),
+        table["name"].eq(bind_param("Sean")),
+        table["age"].gteq(bind_param(30)),
       ])
-      expected = WhereClause.new([table["age"].gteq(bind_param)], [attribute("age", 30)])
+      expected = WhereClause.new([table["age"].gteq(bind_param(30))])
 
       assert_equal expected, where_clause.except("id", "name")
     end
 
+    test "except jumps over unhandled binds (like with OR) correctly" do
+      wcs = (0..9).map do |i|
+        WhereClause.new([table["id#{i}"].eq(bind_param(i))])
+      end
+
+      wc = wcs[0] + wcs[1] + wcs[2].or(wcs[3]) + wcs[4] + wcs[5] + wcs[6].or(wcs[7]) + wcs[8] + wcs[9]
+
+      expected = wcs[0] + wcs[2].or(wcs[3]) + wcs[5] + wcs[6].or(wcs[7]) + wcs[9]
+      actual = wc.except("id1", "id2", "id4", "id7", "id8")
+
+      assert_equal expected, actual
+    end
+
     test "ast groups its predicates with AND" do
       predicates = [
         table["id"].in([1, 2, 3]),
-        table["name"].eq(bind_param),
+        table["name"].eq(bind_param(nil)),
       ]
-      where_clause = WhereClause.new(predicates, [])
+      where_clause = WhereClause.new(predicates)
       expected = Arel::Nodes::And.new(predicates)
 
       assert_equal expected, where_clause.ast
@@ -128,55 +150,96 @@ class ActiveRecord::Relation
         table["id"].in([1, 2, 3]),
         "foo = bar",
         random_object,
-      ], [])
+      ])
       expected = Arel::Nodes::And.new([
         table["id"].in([1, 2, 3]),
         Arel::Nodes::Grouping.new(Arel.sql("foo = bar")),
-        Arel::Nodes::Grouping.new(random_object),
+        random_object,
       ])
 
       assert_equal expected, where_clause.ast
     end
 
     test "ast removes any empty strings" do
-      where_clause = WhereClause.new([table["id"].in([1, 2, 3])], [])
-      where_clause_with_empty = WhereClause.new([table["id"].in([1, 2, 3]), ''], [])
+      where_clause = WhereClause.new([table["id"].in([1, 2, 3])])
+      where_clause_with_empty = WhereClause.new([table["id"].in([1, 2, 3]), ""])
 
       assert_equal where_clause.ast, where_clause_with_empty.ast
     end
 
     test "or joins the two clauses using OR" do
-      where_clause = WhereClause.new([table["id"].eq(bind_param)], [attribute("id", 1)])
-      other_clause = WhereClause.new([table["name"].eq(bind_param)], [attribute("name", "Sean")])
+      where_clause = WhereClause.new([table["id"].eq(bind_param(1))])
+      other_clause = WhereClause.new([table["name"].eq(bind_param("Sean"))])
       expected_ast =
         Arel::Nodes::Grouping.new(
-          Arel::Nodes::Or.new(table["id"].eq(bind_param), table["name"].eq(bind_param))
+          Arel::Nodes::Or.new(table["id"].eq(bind_param(1)), table["name"].eq(bind_param("Sean")))
         )
-      expected_binds = where_clause.binds + other_clause.binds
 
       assert_equal expected_ast.to_sql, where_clause.or(other_clause).ast.to_sql
-      assert_equal expected_binds, where_clause.or(other_clause).binds
     end
 
     test "or returns an empty where clause when either side is empty" do
-      where_clause = WhereClause.new([table["id"].eq(bind_param)], [attribute("id", 1)])
+      where_clause = WhereClause.new([table["id"].eq(bind_param(1))])
 
       assert_equal WhereClause.empty, where_clause.or(WhereClause.empty)
       assert_equal WhereClause.empty, WhereClause.empty.or(where_clause)
     end
 
-    private
+    test "or places common conditions before the OR" do
+      a = WhereClause.new(
+        [table["id"].eq(bind_param(1)), table["name"].eq(bind_param("Sean"))],
+      )
+      b = WhereClause.new(
+        [table["id"].eq(bind_param(1)), table["hair_color"].eq(bind_param("black"))],
+      )
+
+      common = WhereClause.new(
+        [table["id"].eq(bind_param(1))],
+      )
+
+      or_clause = WhereClause.new([table["name"].eq(bind_param("Sean"))])
+        .or(WhereClause.new([table["hair_color"].eq(bind_param("black"))]))
 
-    def table
-      Arel::Table.new("table")
+      assert_equal common + or_clause, a.or(b)
     end
 
-    def bind_param
-      Arel::Nodes::BindParam.new
+    test "or can detect identical or as being a common condition" do
+      common_or = WhereClause.new([table["name"].eq(bind_param("Sean"))])
+        .or(WhereClause.new([table["hair_color"].eq(bind_param("black"))]))
+
+      a = common_or + WhereClause.new([table["id"].eq(bind_param(1))])
+      b = common_or + WhereClause.new([table["foo"].eq(bind_param("bar"))])
+
+      new_or = WhereClause.new([table["id"].eq(bind_param(1))])
+        .or(WhereClause.new([table["foo"].eq(bind_param("bar"))]))
+
+      assert_equal common_or + new_or, a.or(b)
     end
 
-    def attribute(name, value)
-      ActiveRecord::Attribute.with_cast_value(name, value, ActiveRecord::Type::Value.new)
+    test "or will use only common conditions if one side only has common conditions" do
+      only_common = WhereClause.new([
+        table["id"].eq(bind_param(1)),
+        "foo = bar",
+      ])
+
+      common_with_extra = WhereClause.new([
+        table["id"].eq(bind_param(1)),
+        "foo = bar",
+        table["extra"].eq(bind_param("pluto")),
+      ])
+
+      assert_equal only_common, only_common.or(common_with_extra)
+      assert_equal only_common, common_with_extra.or(only_common)
     end
+
+    private
+
+      def table
+        Arel::Table.new("table")
+      end
+
+      def bind_param(value)
+        Arel::Nodes::BindParam.new(value)
+      end
   end
 end
diff --git a/activerecord/test/cases/relation/where_test.rb b/activerecord/test/cases/relation/where_test.rb
index 6af31017d6..99797528b2 100644
--- a/activerecord/test/cases/relation/where_test.rb
+++ b/activerecord/test/cases/relation/where_test.rb
@@ -1,12 +1,15 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "models/author"
 require "models/binary"
 require "models/cake_designer"
+require "models/car"
 require "models/chef"
+require "models/post"
 require "models/comment"
 require "models/edge"
 require "models/essay"
-require "models/post"
 require "models/price_estimate"
 require "models/topic"
 require "models/treasure"
@@ -14,11 +17,11 @@ require "models/vertex"
 
 module ActiveRecord
   class WhereTest < ActiveRecord::TestCase
-    fixtures :posts, :edges, :authors, :binaries, :essays
+    fixtures :posts, :edges, :authors, :author_addresses, :binaries, :essays, :cars, :treasures, :price_estimates, :topics
 
     def test_where_copies_bind_params
       author = authors(:david)
-      posts  = author.posts.where('posts.id != 1')
+      posts  = author.posts.where("posts.id != 1")
       joined = Post.where(id: posts)
 
       assert_operator joined.length, :>, 0
@@ -47,8 +50,12 @@ module ActiveRecord
       assert_equal [chef], chefs.to_a
     end
 
+    def test_where_with_casted_value_is_nil
+      assert_equal 4, Topic.where(last_read: "").count
+    end
+
     def test_rewhere_on_root
-      assert_equal posts(:welcome), Post.rewhere(title: 'Welcome to the weblog').first
+      assert_equal posts(:welcome), Post.rewhere(title: "Welcome to the weblog").first
     end
 
     def test_belongs_to_shallow_where
@@ -63,12 +70,12 @@ module ActiveRecord
     end
 
     def test_belongs_to_array_value_where
-      assert_equal Post.where(author_id: [1,2]).to_sql, Post.where(author: [1,2]).to_sql
+      assert_equal Post.where(author_id: [1, 2]).to_sql, Post.where(author: [1, 2]).to_sql
     end
 
     def test_belongs_to_nested_relation_where
-      expected = Post.where(author_id: Author.where(id: [1,2])).to_sql
-      actual   = Post.where(author:    Author.where(id: [1,2])).to_sql
+      expected = Post.where(author_id: Author.where(id: [1, 2])).to_sql
+      actual   = Post.where(author:    Author.where(id: [1, 2])).to_sql
 
       assert_equal expected, actual
     end
@@ -86,7 +93,7 @@ module ActiveRecord
     def test_belongs_to_nested_where_with_relation
       author = authors(:david)
 
-      expected = Author.where(id: author ).joins(:posts)
+      expected = Author.where(id: author).joins(:posts)
       actual   = Author.where(posts: { author_id: Author.where(id: author.id) }).joins(:posts)
 
       assert_equal expected.to_a, actual.to_a
@@ -96,27 +103,57 @@ module ActiveRecord
       treasure = Treasure.new
       treasure.id = 1
 
-      expected = PriceEstimate.where(estimate_of_type: 'Treasure', estimate_of_id: 1)
+      expected = PriceEstimate.where(estimate_of_type: "Treasure", estimate_of_id: 1)
       actual   = PriceEstimate.where(estimate_of: treasure)
 
       assert_equal expected.to_sql, actual.to_sql
     end
 
+    def test_polymorphic_shallow_where_not
+      treasure = treasures(:sapphire)
+
+      expected = [price_estimates(:diamond), price_estimates(:honda)]
+      actual   = PriceEstimate.where.not(estimate_of: treasure)
+
+      assert_equal expected.sort_by(&:id), actual.sort_by(&:id)
+    end
+
     def test_polymorphic_nested_array_where
       treasure = Treasure.new
       treasure.id = 1
       hidden = HiddenTreasure.new
       hidden.id = 2
 
-      expected = PriceEstimate.where(estimate_of_type: 'Treasure', estimate_of_id: [treasure, hidden])
+      expected = PriceEstimate.where(estimate_of_type: "Treasure", estimate_of_id: [treasure, hidden])
       actual   = PriceEstimate.where(estimate_of: [treasure, hidden])
 
       assert_equal expected.to_sql, actual.to_sql
     end
 
+    def test_polymorphic_nested_array_where_not
+      treasure = treasures(:diamond)
+      car = cars(:honda)
+
+      expected = [price_estimates(:sapphire_1), price_estimates(:sapphire_2)]
+      actual   = PriceEstimate.where.not(estimate_of: [treasure, car])
+
+      assert_equal expected.sort_by(&:id), actual.sort_by(&:id)
+    end
+
+    def test_polymorphic_array_where_multiple_types
+      treasure_1 = treasures(:diamond)
+      treasure_2 = treasures(:sapphire)
+      car = cars(:honda)
+
+      expected = [price_estimates(:diamond), price_estimates(:sapphire_1), price_estimates(:sapphire_2), price_estimates(:honda)].sort
+      actual = PriceEstimate.where(estimate_of: [treasure_1, treasure_2, car]).to_a.sort
+
+      assert_equal expected, actual
+    end
+
     def test_polymorphic_nested_relation_where
-      expected = PriceEstimate.where(estimate_of_type: 'Treasure', estimate_of_id: Treasure.where(id: [1,2]))
-      actual   = PriceEstimate.where(estimate_of: Treasure.where(id: [1,2]))
+      expected = PriceEstimate.where(estimate_of_type: "Treasure", estimate_of_id: Treasure.where(id: [1, 2]))
+      actual   = PriceEstimate.where(estimate_of: Treasure.where(id: [1, 2]))
 
       assert_equal expected.to_sql, actual.to_sql
     end
@@ -125,7 +162,7 @@ module ActiveRecord
       treasure = HiddenTreasure.new
       treasure.id = 1
 
-      expected = PriceEstimate.where(estimate_of_type: 'Treasure', estimate_of_id: 1)
+      expected = PriceEstimate.where(estimate_of_type: "Treasure", estimate_of_id: 1)
       actual   = PriceEstimate.where(estimate_of: treasure)
 
       assert_equal expected.to_sql, actual.to_sql
@@ -135,7 +172,7 @@ module ActiveRecord
       thing = Post.new
       thing.id = 1
 
-      expected = Treasure.where(price_estimates: { thing_type: 'Post', thing_id: 1 }).joins(:price_estimates)
+      expected = Treasure.where(price_estimates: { thing_type: "Post", thing_id: 1 }).joins(:price_estimates)
       actual   = Treasure.where(price_estimates: { thing: thing }).joins(:price_estimates)
 
       assert_equal expected.to_sql, actual.to_sql
@@ -145,7 +182,7 @@ module ActiveRecord
       treasure = HiddenTreasure.new
       treasure.id = 1
 
-      expected = Treasure.where(price_estimates: { estimate_of_type: 'Treasure', estimate_of_id: 1 }).joins(:price_estimates)
+      expected = Treasure.where(price_estimates: { estimate_of_type: "Treasure", estimate_of_id: 1 }).joins(:price_estimates)
       actual   = Treasure.where(price_estimates: { estimate_of: treasure }).joins(:price_estimates)
 
       assert_equal expected.to_sql, actual.to_sql
@@ -170,40 +207,40 @@ module ActiveRecord
       treasure.id = 1
       decorated_treasure = treasure_decorator.new(treasure)
 
-      expected = PriceEstimate.where(estimate_of_type: 'Treasure', estimate_of_id: 1)
+      expected = PriceEstimate.where(estimate_of_type: "Treasure", estimate_of_id: 1)
       actual   = PriceEstimate.where(estimate_of: decorated_treasure)
 
       assert_equal expected.to_sql, actual.to_sql
     end
 
     def test_aliased_attribute
-      expected = Topic.where(heading: 'The First Topic')
-      actual   = Topic.where(title: 'The First Topic')
+      expected = Topic.where(heading: "The First Topic")
+      actual   = Topic.where(title: "The First Topic")
 
       assert_equal expected.to_sql, actual.to_sql
     end
 
     def test_where_error
-      assert_raises(ActiveRecord::StatementInvalid) do
-        Post.where(:id => { 'posts.author_id' => 10 }).first
+      assert_nothing_raised do
+        Post.where(id: { "posts.author_id" => 10 }).first
       end
     end
 
     def test_where_with_table_name
       post = Post.first
-      assert_equal post, Post.where(:posts => { 'id' => post.id }).first
+      assert_equal post, Post.where(posts: { "id" => post.id }).first
     end
 
     def test_where_with_table_name_and_empty_hash
-      assert_equal 0, Post.where(:posts => {}).count
+      assert_equal 0, Post.where(posts: {}).count
     end
 
     def test_where_with_table_name_and_empty_array
-      assert_equal 0, Post.where(:id => []).count
+      assert_equal 0, Post.where(id: []).count
     end
 
     def test_where_with_empty_hash_and_no_foreign_key
-      assert_equal 0, Edge.where(:sink => {}).count
+      assert_equal 0, Edge.where(sink: {}).count
     end
 
     def test_where_with_blank_conditions
@@ -213,32 +250,32 @@ module ActiveRecord
     end
 
     def test_where_with_integer_for_string_column
-      count = Post.where(:title => 0).count
+      count = Post.where(title: 0).count
       assert_equal 0, count
     end
 
     def test_where_with_float_for_string_column
-      count = Post.where(:title => 0.0).count
+      count = Post.where(title: 0.0).count
       assert_equal 0, count
     end
 
     def test_where_with_boolean_for_string_column
-      count = Post.where(:title => false).count
+      count = Post.where(title: false).count
       assert_equal 0, count
     end
 
     def test_where_with_decimal_for_string_column
-      count = Post.where(:title => BigDecimal.new(0)).count
+      count = Post.where(title: BigDecimal(0)).count
       assert_equal 0, count
     end
 
     def test_where_with_duration_for_string_column
-      count = Post.where(:title => 0.seconds).count
+      count = Post.where(title: 0.seconds).count
       assert_equal 0, count
     end
 
     def test_where_with_integer_for_binary_column
-      count = Binary.where(:data => 0).count
+      count = Binary.where(data: 0).count
       assert_equal 0, count
     end
 
@@ -276,5 +313,54 @@ module ActiveRecord
 
       assert_equal essays(:david_modest_proposal), essay
     end
+
+    def test_where_with_relation_on_has_many_association
+      essay = essays(:david_modest_proposal)
+      author = Author.where(essays: Essay.where(id: essay.id)).first
+
+      assert_equal authors(:david), author
+    end
+
+    def test_where_with_relation_on_has_one_association
+      author = authors(:david)
+      author_address = AuthorAddress.where(author: Author.where(id: author.id)).first
+      assert_equal author_addresses(:david_address), author_address
+    end
+
+
+    def test_where_on_association_with_select_relation
+      essay = Essay.where(author: Author.where(name: "David").select(:name)).take
+      assert_equal essays(:david_modest_proposal), essay
+    end
+
+    def test_where_with_strong_parameters
+      protected_params = Class.new do
+        attr_reader :permitted
+        alias :permitted? :permitted
+
+        def initialize(parameters)
+          @parameters = parameters
+          @permitted = false
+        end
+
+        def to_h
+          @parameters
+        end
+
+        def permit!
+          @permitted = true
+          self
+        end
+      end
+
+      author = authors(:david)
+      params = protected_params.new(name: author.name)
+      assert_raises(ActiveModel::ForbiddenAttributesError) { Author.where(params) }
+      assert_equal author, Author.where(params.permit!).first
+    end
+
+    def test_where_with_unsupported_arguments
+      assert_raises(ArgumentError) { Author.where(42) }
+    end
   end
 end
diff --git a/activerecord/test/cases/relation_test.rb b/activerecord/test/cases/relation_test.rb
index 37d3965022..68161f6a84 100644
--- a/activerecord/test/cases/relation_test.rb
+++ b/activerecord/test/cases/relation_test.rb
@@ -1,125 +1,106 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/comment'
-require 'models/author'
-require 'models/rating'
+require "models/post"
+require "models/comment"
+require "models/author"
+require "models/rating"
+require "models/categorization"
 
 module ActiveRecord
   class RelationTest < ActiveRecord::TestCase
-    fixtures :posts, :comments, :authors
-
-    class FakeKlass < Struct.new(:table_name, :name)
-      extend ActiveRecord::Delegation::DelegateCache
-
-      inherited self
-
-      def self.connection
-        Post.connection
-      end
-
-      def self.table_name
-        'fake_table'
-      end
-    end
+    fixtures :posts, :comments, :authors, :author_addresses, :ratings, :categorizations
 
     def test_construction
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass, table: :b)
       assert_equal FakeKlass, relation.klass
       assert_equal :b, relation.table
-      assert !relation.loaded, 'relation is not loaded'
+      assert_not relation.loaded, "relation is not loaded"
     end
 
     def test_responds_to_model_and_returns_klass
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       assert_equal FakeKlass, relation.model
     end
 
     def test_initialize_single_values
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       (Relation::SINGLE_VALUE_METHODS - [:create_with]).each do |method|
         assert_nil relation.send("#{method}_value"), method.to_s
       end
-      assert_equal({}, relation.create_with_value)
+      value = relation.create_with_value
+      assert_equal({}, value)
+      assert_predicate value, :frozen?
     end
 
     def test_multi_value_initialize
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       Relation::MULTI_VALUE_METHODS.each do |method|
-        assert_equal [], relation.send("#{method}_values"), method.to_s
+        values = relation.send("#{method}_values")
+        assert_equal [], values, method.to_s
+        assert_predicate values, :frozen?, method.to_s
       end
     end
 
     def test_extensions
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       assert_equal [], relation.extensions
     end
 
     def test_empty_where_values_hash
-      relation = Relation.new(FakeKlass, :b, nil)
-      assert_equal({}, relation.where_values_hash)
-
-      relation.where! :hello
+      relation = Relation.new(FakeKlass)
       assert_equal({}, relation.where_values_hash)
     end
 
     def test_has_values
-      relation = Relation.new(Post, Post.arel_table, Post.predicate_builder)
-      relation.where! relation.table[:id].eq(10)
-      assert_equal({:id => 10}, relation.where_values_hash)
+      relation = Relation.new(Post)
+      relation.where!(id: 10)
+      assert_equal({ "id" => 10 }, relation.where_values_hash)
     end
 
     def test_values_wrong_table
-      relation = Relation.new(Post, Post.arel_table, Post.predicate_builder)
+      relation = Relation.new(Post)
       relation.where! Comment.arel_table[:id].eq(10)
       assert_equal({}, relation.where_values_hash)
     end
 
     def test_tree_is_not_traversed
-      relation = Relation.new(Post, Post.arel_table, Post.predicate_builder)
-      # FIXME: Remove the Arel::Nodes::Quoted in Rails 5.1
+      relation = Relation.new(Post)
       left     = relation.table[:id].eq(10)
       right    = relation.table[:id].eq(10)
-      combine  = left.and right
+      combine  = left.or(right)
       relation.where! combine
       assert_equal({}, relation.where_values_hash)
     end
 
-    def test_table_name_delegates_to_klass
-      relation = Relation.new(FakeKlass.new('posts'), :b, Post.predicate_builder)
-      assert_equal 'posts', relation.table_name
-    end
-
     def test_scope_for_create
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       assert_equal({}, relation.scope_for_create)
     end
 
     def test_create_with_value
-      relation = Relation.new(Post, Post.arel_table, Post.predicate_builder)
-      hash = { :hello => 'world' }
-      relation.create_with_value = hash
-      assert_equal hash, relation.scope_for_create
+      relation = Relation.new(Post)
+      relation.create_with_value = { hello: "world" }
+      assert_equal({ "hello" => "world" }, relation.scope_for_create)
     end
 
     def test_create_with_value_with_wheres
-      relation = Relation.new(Post, Post.arel_table, Post.predicate_builder)
-      # FIXME: Remove the Arel::Nodes::Quoted in Rails 5.1
-      relation.where! relation.table[:id].eq(10)
-      relation.create_with_value = {:hello => 'world'}
-      assert_equal({:hello => 'world', :id => 10}, relation.scope_for_create)
-    end
-
-    # FIXME: is this really wanted or expected behavior?
-    def test_scope_for_create_is_cached
-      relation = Relation.new(Post, Post.arel_table, Post.predicate_builder)
+      relation = Relation.new(Post)
       assert_equal({}, relation.scope_for_create)
 
-      # FIXME: Remove the Arel::Nodes::Quoted in Rails 5.1
-      relation.where! relation.table[:id].eq(10)
-      assert_equal({}, relation.scope_for_create)
+      relation.where!(id: 10)
+      assert_equal({ "id" => 10 }, relation.scope_for_create)
 
-      relation.create_with_value = {:hello => 'world'}
-      assert_equal({}, relation.scope_for_create)
+      relation.create_with_value = { hello: "world" }
+      assert_equal({ "hello" => "world", "id" => 10 }, relation.scope_for_create)
+    end
+
+    def test_empty_scope
+      relation = Relation.new(Post)
+      assert_predicate relation, :empty_scope?
+
+      relation.merge!(relation)
+      assert_predicate relation, :empty_scope?
     end
 
     def test_bad_constants_raise_errors
@@ -129,89 +110,89 @@ module ActiveRecord
     end
 
     def test_empty_eager_loading?
-      relation = Relation.new(FakeKlass, :b, nil)
-      assert !relation.eager_loading?
+      relation = Relation.new(FakeKlass)
+      assert_not_predicate relation, :eager_loading?
     end
 
     def test_eager_load_values
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       relation.eager_load! :b
-      assert relation.eager_loading?
+      assert_predicate relation, :eager_loading?
     end
 
     def test_references_values
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       assert_equal [], relation.references_values
       relation = relation.references(:foo).references(:omg, :lol)
-      assert_equal ['foo', 'omg', 'lol'], relation.references_values
+      assert_equal ["foo", "omg", "lol"], relation.references_values
     end
 
     def test_references_values_dont_duplicate
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       relation = relation.references(:foo).references(:foo)
-      assert_equal ['foo'], relation.references_values
+      assert_equal ["foo"], relation.references_values
     end
 
-    test 'merging a hash into a relation' do
-      relation = Relation.new(FakeKlass, :b, nil)
-      relation = relation.merge where: :lol, readonly: true
+    test "merging a hash into a relation" do
+      relation = Relation.new(Post)
+      relation = relation.merge where: { name: :lol }, readonly: true
 
-      assert_equal Relation::WhereClause.new([:lol], []), relation.where_clause
+      assert_equal({ "name" => :lol }, relation.where_clause.to_h)
       assert_equal true, relation.readonly_value
     end
 
-    test 'merging an empty hash into a relation' do
-      assert_equal Relation::WhereClause.empty, Relation.new(FakeKlass, :b, nil).merge({}).where_clause
+    test "merging an empty hash into a relation" do
+      assert_equal Relation::WhereClause.empty, Relation.new(FakeKlass).merge({}).where_clause
     end
 
-    test 'merging a hash with unknown keys raises' do
-      assert_raises(ArgumentError) { Relation::HashMerger.new(nil, omg: 'lol') }
+    test "merging a hash with unknown keys raises" do
+      assert_raises(ArgumentError) { Relation::HashMerger.new(nil, omg: "lol") }
     end
 
-    test 'merging nil or false raises' do
-      relation = Relation.new(FakeKlass, :b, nil)
+    test "merging nil or false raises" do
+      relation = Relation.new(FakeKlass)
 
       e = assert_raises(ArgumentError) do
         relation = relation.merge nil
       end
 
-      assert_equal 'invalid argument: nil.', e.message
+      assert_equal "invalid argument: nil.", e.message
 
       e = assert_raises(ArgumentError) do
         relation = relation.merge false
       end
 
-      assert_equal 'invalid argument: false.', e.message
+      assert_equal "invalid argument: false.", e.message
     end
 
-    test '#values returns a dup of the values' do
-      relation = Relation.new(FakeKlass, :b, nil).where! :foo
+    test "#values returns a dup of the values" do
+      relation = Relation.new(Post).where!(name: :foo)
       values   = relation.values
 
       values[:where] = nil
       assert_not_nil relation.where_clause
     end
 
-    test 'relations can be created with a values hash' do
-      relation = Relation.new(FakeKlass, :b, nil, select: [:foo])
+    test "relations can be created with a values hash" do
+      relation = Relation.new(FakeKlass, values: { select: [:foo] })
       assert_equal [:foo], relation.select_values
     end
 
-    test 'merging a hash interpolates conditions' do
+    test "merging a hash interpolates conditions" do
       klass = Class.new(FakeKlass) do
         def self.sanitize_sql(args)
-          raise unless args == ['foo = ?', 'bar']
-          'foo = bar'
+          raise unless args == ["foo = ?", "bar"]
+          "foo = bar"
         end
       end
 
-      relation = Relation.new(klass, :b, nil)
-      relation.merge!(where: ['foo = ?', 'bar'])
-      assert_equal Relation::WhereClause.new(['foo = bar'], []), relation.where_clause
+      relation = Relation.new(klass)
+      relation.merge!(where: ["foo = ?", "bar"])
+      assert_equal Relation::WhereClause.new(["foo = bar"]), relation.where_clause
     end
 
     def test_merging_readonly_false
-      relation = Relation.new(FakeKlass, :b, nil)
+      relation = Relation.new(FakeKlass)
       readonly_false_relation = relation.readonly(false)
       # test merging in both directions
       assert_equal false, relation.merge(readonly_false_relation).readonly_value
@@ -221,7 +202,50 @@ module ActiveRecord
     def test_relation_merging_with_merged_joins_as_symbols
       special_comments_with_ratings = SpecialComment.joins(:ratings)
       posts_with_special_comments_with_ratings = Post.group("posts.id").joins(:special_comments).merge(special_comments_with_ratings)
-      assert_equal 3, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count.length
+      assert_equal({ 4 => 2 }, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count)
+    end
+
+    def test_relation_merging_with_merged_symbol_joins_keeps_inner_joins
+      queries = capture_sql { Author.joins(:posts).merge(Post.joins(:comments)).to_a }
+
+      nb_inner_join = queries.sum { |sql| sql.scan(/INNER\s+JOIN/i).size }
+      assert_equal 2, nb_inner_join, "Wrong amount of INNER JOIN in query"
+      assert queries.none? { |sql| /LEFT\s+(OUTER)?\s+JOIN/i.match?(sql) }, "Shouldn't have any LEFT JOIN in query"
+    end
+
+    def test_relation_merging_with_merged_symbol_joins_has_correct_size_and_count
+      # Has one entry per comment
+      merged_authors_with_commented_posts_relation = Author.joins(:posts).merge(Post.joins(:comments))
+
+      post_ids_with_author = Post.joins(:author).pluck(:id)
+      manual_comments_on_post_that_have_author = Comment.where(post_id: post_ids_with_author).pluck(:id)
+
+      assert_equal manual_comments_on_post_that_have_author.size, merged_authors_with_commented_posts_relation.count
+      assert_equal manual_comments_on_post_that_have_author.size, merged_authors_with_commented_posts_relation.to_a.size
+    end
+
+    def test_relation_merging_with_merged_symbol_joins_is_aliased
+      categorizations_with_authors = Categorization.joins(:author)
+      queries = capture_sql { Post.joins(:author, :categorizations).merge(Author.select(:id)).merge(categorizations_with_authors).to_a }
+
+      nb_inner_join = queries.sum { |sql| sql.scan(/INNER\s+JOIN/i).size }
+      assert_equal 3, nb_inner_join, "Wrong amount of INNER JOIN in query"
+
+      # using `\W` as the column separator
+      assert queries.any? { |sql| %r[INNER\s+JOIN\s+#{Regexp.escape(Author.quoted_table_name)}\s+\Wauthors_categorizations\W]i.match?(sql) }, "Should be aliasing the child INNER JOINs in query"
+    end
+
+    def test_relation_with_merged_joins_aliased_works
+      categorizations_with_authors = Categorization.joins(:author)
+      posts_with_joins_and_merges = Post.joins(:author, :categorizations)
+                                        .merge(Author.select(:id)).merge(categorizations_with_authors)
+
+      author_with_posts = Author.joins(:posts).ids
+      categorizations_with_author = Categorization.joins(:author).ids
+      posts_with_author_and_categorizations = Post.joins(:categorizations).where(author_id: author_with_posts, categorizations: { id: categorizations_with_author }).ids
+
+      assert_equal posts_with_author_and_categorizations.size, posts_with_joins_and_merges.count
+      assert_equal posts_with_author_and_categorizations.size, posts_with_joins_and_merges.to_a.size
     end
 
     def test_relation_merging_with_joins_as_join_dependency_pick_proper_parent
@@ -234,32 +258,53 @@ module ActiveRecord
       assert_equal 3, relation.where(id: post.id).pluck(:id).size
     end
 
+    def test_merge_raises_with_invalid_argument
+      assert_raises ArgumentError do
+        relation = Relation.new(FakeKlass)
+        relation.merge(true)
+      end
+    end
+
     def test_respond_to_for_non_selected_element
       post = Post.select(:title).first
-      assert_equal false, post.respond_to?(:body), "post should not respond_to?(:body) since invoking it raises exception"
+      assert_not_respond_to post, :body, "post should not respond_to?(:body) since invoking it raises exception"
 
       silence_warnings { post = Post.select("'title' as post_title").first }
-      assert_equal false, post.respond_to?(:title), "post should not respond_to?(:body) since invoking it raises exception"
+      assert_not_respond_to post, :title, "post should not respond_to?(:body) since invoking it raises exception"
     end
 
     def test_select_quotes_when_using_from_clause
-      if sqlite3_version_includes_quoting_bug?
-        skip <<-ERROR.squish
-          You are using an outdated version of SQLite3 which has a bug in
-          quoted column names. Please update SQLite3 and rebuild the sqlite3
-          ruby gem
-        ERROR
-      end
+      skip_if_sqlite3_version_includes_quoting_bug
       quoted_join = ActiveRecord::Base.connection.quote_table_name("join")
       selected = Post.select(:join).from(Post.select("id as #{quoted_join}")).map(&:join)
       assert_equal Post.pluck(:id), selected
     end
 
+    def test_selecting_aliased_attribute_quotes_column_name_when_from_is_used
+      skip_if_sqlite3_version_includes_quoting_bug
+      klass = Class.new(ActiveRecord::Base) do
+        self.table_name = :test_with_keyword_column_name
+        alias_attribute :description, :desc
+      end
+      klass.create!(description: "foo")
+
+      assert_equal ["foo"], klass.select(:description).from(klass.all).map(&:desc)
+    end
+
     def test_relation_merging_with_merged_joins_as_strings
       join_string = "LEFT OUTER JOIN #{Rating.quoted_table_name} ON #{SpecialComment.quoted_table_name}.id = #{Rating.quoted_table_name}.comment_id"
       special_comments_with_ratings = SpecialComment.joins join_string
       posts_with_special_comments_with_ratings = Post.group("posts.id").joins(:special_comments).merge(special_comments_with_ratings)
-      assert_equal 3, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count.length
+      assert_equal({ 2 => 1, 4 => 3, 5 => 1 }, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count)
+    end
+
+    def test_relation_merging_keeps_joining_order
+      authors  = Author.where(id: 1)
+      posts    = Post.joins(:author).merge(authors)
+      comments = Comment.joins(:post).merge(posts)
+      ratings  = Rating.joins(:comment).merge(comments)
+
+      assert_equal 3, ratings.count
     end
 
     class EnsureRoundTripTypeCasting < ActiveRecord::Type::Value
@@ -267,19 +312,24 @@ module ActiveRecord
         :string
       end
 
+      def cast(value)
+        raise value unless value == "value from user"
+        "cast value"
+      end
+
       def deserialize(value)
         raise value unless value == "type cast for database"
         "type cast from database"
       end
 
       def serialize(value)
-        raise value unless value == "value from user"
+        raise value unless value == "cast value"
         "type cast for database"
       end
     end
 
     class UpdateAllTestModel < ActiveRecord::Base
-      self.table_name = 'posts'
+      self.table_name = "posts"
 
       attribute :body, EnsureRoundTripTypeCasting.new
     end
@@ -290,15 +340,33 @@ module ActiveRecord
       assert_equal "type cast from database", UpdateAllTestModel.first.body
     end
 
+    def test_skip_preloading_after_arel_has_been_generated
+      assert_nothing_raised do
+        relation = Comment.all
+        relation.arel
+        relation.skip_preloading!
+      end
+    end
+
     private
 
-    def sqlite3_version_includes_quoting_bug?
-      if current_adapter?(:SQLite3Adapter)
-        selected_quoted_column_names = ActiveRecord::Base.connection.exec_query(
-          'SELECT "join" FROM (SELECT id AS "join" FROM posts) subquery'
-        ).columns
-        ["join"] != selected_quoted_column_names
+      def skip_if_sqlite3_version_includes_quoting_bug
+        if sqlite3_version_includes_quoting_bug?
+          skip <<-ERROR.squish
+            You are using an outdated version of SQLite3 which has a bug in
+            quoted column names. Please update SQLite3 and rebuild the sqlite3
+            ruby gem
+          ERROR
+        end
+      end
+
+      def sqlite3_version_includes_quoting_bug?
+        if current_adapter?(:SQLite3Adapter)
+          selected_quoted_column_names = ActiveRecord::Base.connection.exec_query(
+            'SELECT "join" FROM (SELECT id AS "join" FROM posts) subquery'
+          ).columns
+          ["join"] != selected_quoted_column_names
+        end
       end
-    end
   end
 end
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 5f48c2b40f..e471ee8039 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -1,43 +1,44 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/tag'
-require 'models/tagging'
-require 'models/post'
-require 'models/topic'
-require 'models/comment'
-require 'models/author'
-require 'models/entrant'
-require 'models/developer'
-require 'models/computer'
-require 'models/reply'
-require 'models/company'
-require 'models/bird'
-require 'models/car'
-require 'models/engine'
-require 'models/tyre'
-require 'models/minivan'
-require 'models/aircraft'
+require "models/tag"
+require "models/tagging"
+require "models/post"
+require "models/topic"
+require "models/comment"
+require "models/author"
+require "models/entrant"
+require "models/developer"
+require "models/project"
+require "models/person"
+require "models/computer"
+require "models/reply"
+require "models/company"
+require "models/bird"
+require "models/car"
+require "models/engine"
+require "models/tyre"
+require "models/minivan"
 require "models/possession"
 require "models/reader"
+require "models/category"
+require "models/categorization"
+require "models/edge"
+require "models/subscriber"
 
 class RelationTest < ActiveRecord::TestCase
-  fixtures :authors, :topics, :entrants, :developers, :companies, :developers_projects, :accounts, :categories, :categorizations, :posts, :comments,
-    :tags, :taggings, :cars, :minivans
-
-  class TopicWithCallbacks < ActiveRecord::Base
-    self.table_name = :topics
-    before_update { |topic| topic.author_name = 'David' if topic.author_name.blank? }
-  end
+  fixtures :authors, :author_addresses, :topics, :entrants, :developers, :people, :companies, :developers_projects, :accounts, :categories, :categorizations, :categories_posts, :posts, :comments, :tags, :taggings, :cars, :minivans
 
   def test_do_not_double_quote_string_id
     van = Minivan.last
     assert van
-    assert_equal van.id, Minivan.where(:minivan_id => van).to_a.first.minivan_id
+    assert_equal van.id, Minivan.where(minivan_id: van).to_a.first.minivan_id
   end
 
   def test_do_not_double_quote_string_id_with_array
     van = Minivan.last
     assert van
-    assert_equal van, Minivan.where(:minivan_id => [van]).to_a.first
+    assert_equal van, Minivan.where(minivan_id: [van]).to_a.first
   end
 
   def test_two_scopes_with_includes_should_not_drop_any_include
@@ -52,12 +53,12 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_dynamic_finder
-    x = Post.where('author_id = ?', 1)
-    assert x.klass.respond_to?(:find_by_id), '@klass should handle dynamic finders'
+    x = Post.where("author_id = ?", 1)
+    assert_respond_to x.klass, :find_by_id
   end
 
   def test_multivalue_where
-    posts = Post.where('author_id = ? AND id = ?', 1, 1)
+    posts = Post.where("author_id = ? AND id = ?", 1, 1)
     assert_equal 1, posts.to_a.size
   end
 
@@ -95,28 +96,51 @@ class RelationTest < ActiveRecord::TestCase
       2.times { assert_equal 5, topics.to_a.size }
     end
 
-    assert topics.loaded?
+    assert_predicate topics, :loaded?
   end
 
   def test_scoped_first
-    topics = Topic.all.order('id ASC')
+    topics = Topic.all.order("id ASC")
 
     assert_queries(1) do
       2.times { assert_equal "The First Topic", topics.first.title }
     end
 
-    assert ! topics.loaded?
+    assert_not_predicate topics, :loaded?
   end
 
   def test_loaded_first
-    topics = Topic.all.order('id ASC')
+    topics = Topic.all.order("id ASC")
+    topics.load # force load
 
-    assert_queries(1) do
-      topics.to_a # force load
-      2.times { assert_equal "The First Topic", topics.first.title }
+    assert_no_queries do
+      assert_equal "The First Topic", topics.first.title
+    end
+
+    assert_predicate topics, :loaded?
+  end
+
+  def test_loaded_first_with_limit
+    topics = Topic.all.order("id ASC")
+    topics.load # force load
+
+    assert_no_queries do
+      assert_equal ["The First Topic",
+                    "The Second Topic of the day"], topics.first(2).map(&:title)
     end
 
-    assert topics.loaded?
+    assert_predicate topics, :loaded?
+  end
+
+  def test_first_get_more_than_available
+    topics = Topic.all.order("id ASC")
+    unloaded_first = topics.first(10)
+    topics.load # force load
+
+    assert_no_queries do
+      loaded_first = topics.first(10)
+      assert_equal unloaded_first, loaded_first
+    end
   end
 
   def test_reload
@@ -126,28 +150,28 @@ class RelationTest < ActiveRecord::TestCase
       2.times { topics.to_a }
     end
 
-    assert topics.loaded?
+    assert_predicate topics, :loaded?
 
     original_size = topics.to_a.size
-    Topic.create! :title => 'fake'
+    Topic.create! title: "fake"
 
     assert_queries(1) { topics.reload }
     assert_equal original_size + 1, topics.size
-    assert topics.loaded?
+    assert_predicate topics, :loaded?
   end
 
   def test_finding_with_subquery
-    relation = Topic.where(:approved => true)
-    assert_equal relation.to_a, Topic.select('*').from(relation).to_a
-    assert_equal relation.to_a, Topic.select('subquery.*').from(relation).to_a
-    assert_equal relation.to_a, Topic.select('a.*').from(relation, :a).to_a
+    relation = Topic.where(approved: true)
+    assert_equal relation.to_a, Topic.select("*").from(relation).to_a
+    assert_equal relation.to_a, Topic.select("subquery.*").from(relation).to_a
+    assert_equal relation.to_a, Topic.select("a.*").from(relation, :a).to_a
   end
 
   def test_finding_with_subquery_with_binds
     relation = Post.first.comments
-    assert_equal relation.to_a, Comment.select('*').from(relation).to_a
-    assert_equal relation.to_a, Comment.select('subquery.*').from(relation).to_a
-    assert_equal relation.to_a, Comment.select('a.*').from(relation, :a).to_a
+    assert_equal relation.to_a, Comment.select("*").from(relation).to_a
+    assert_equal relation.to_a, Comment.select("subquery.*").from(relation).to_a
+    assert_equal relation.to_a, Comment.select("a.*").from(relation, :a).to_a
   end
 
   def test_finding_with_subquery_without_select_does_not_change_the_select
@@ -158,25 +182,37 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_select_with_subquery_in_from_does_not_use_original_table_name
-    relation = Comment.group(:type).select('COUNT(post_id) AS post_count, type')
-    subquery = Comment.from(relation).select('type','post_count')
-    assert_equal(relation.map(&:post_count).sort,subquery.map(&:post_count).sort)
+    relation = Comment.group(:type).select("COUNT(post_id) AS post_count, type")
+    subquery = Comment.from(relation).select("type", "post_count")
+    assert_equal(relation.map(&:post_count).sort, subquery.map(&:post_count).sort)
   end
 
   def test_group_with_subquery_in_from_does_not_use_original_table_name
-    relation = Comment.group(:type).select('COUNT(post_id) AS post_count,type')
-    subquery = Comment.from(relation).group('type').average("post_count")
-    assert_equal(relation.map(&:post_count).sort,subquery.values.sort)
+    relation = Comment.group(:type).select("COUNT(post_id) AS post_count,type")
+    subquery = Comment.from(relation).group("type").average("post_count")
+    assert_equal(relation.map(&:post_count).sort, subquery.values.sort)
+  end
+
+  def test_finding_with_subquery_with_eager_loading_in_from
+    relation = Comment.includes(:post).where("posts.type": "Post")
+    assert_equal relation.to_a, Comment.select("*").from(relation).to_a
+    assert_equal relation.to_a, Comment.select("subquery.*").from(relation).to_a
+    assert_equal relation.to_a, Comment.select("a.*").from(relation, :a).to_a
+  end
+
+  def test_finding_with_subquery_with_eager_loading_in_where
+    relation = Comment.includes(:post).where("posts.type": "Post")
+    assert_equal relation.sort_by(&:id), Comment.where(id: relation).sort_by(&:id)
   end
 
   def test_finding_with_conditions
-    assert_equal ["David"], Author.where(:name => 'David').map(&:name)
-    assert_equal ['Mary'],  Author.where(["name = ?", 'Mary']).map(&:name)
-    assert_equal ['Mary'],  Author.where("name = ?", 'Mary').map(&:name)
+    assert_equal ["David"], Author.where(name: "David").map(&:name)
+    assert_equal ["Mary"],  Author.where(["name = ?", "Mary"]).map(&:name)
+    assert_equal ["Mary"],  Author.where("name = ?", "Mary").map(&:name)
   end
 
   def test_finding_with_order
-    topics = Topic.order('id')
+    topics = Topic.order("id")
     assert_equal 5, topics.to_a.size
     assert_equal topics(:first).title, topics.first.title
   end
@@ -188,19 +224,84 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_finding_with_assoc_order
-    topics = Topic.order(:id => :desc)
+    topics = Topic.order(id: :desc)
+    assert_equal 5, topics.to_a.size
+    assert_equal topics(:fifth).title, topics.first.title
+  end
+
+  def test_finding_with_arel_assoc_order
+    topics = Topic.order(Arel.sql("id") => :desc)
+    assert_equal 5, topics.to_a.size
+    assert_equal topics(:fifth).title, topics.first.title
+  end
+
+  def test_finding_with_reversed_assoc_order
+    topics = Topic.order(id: :asc).reverse_order
     assert_equal 5, topics.to_a.size
     assert_equal topics(:fifth).title, topics.first.title
   end
 
-  def test_finding_with_reverted_assoc_order
-    topics = Topic.order(:id => :asc).reverse_order
+  def test_finding_with_reversed_arel_assoc_order
+    topics = Topic.order(Arel.sql("id") => :asc).reverse_order
     assert_equal 5, topics.to_a.size
     assert_equal topics(:fifth).title, topics.first.title
   end
 
+  def test_reverse_order_with_function
+    topics = Topic.order(Arel.sql("length(title)")).reverse_order
+    assert_equal topics(:second).title, topics.first.title
+  end
+
+  def test_reverse_arel_assoc_order_with_function
+    topics = Topic.order(Arel.sql("length(title)") => :asc).reverse_order
+    assert_equal topics(:second).title, topics.first.title
+  end
+
+  def test_reverse_order_with_function_other_predicates
+    topics = Topic.order(Arel.sql("author_name, length(title), id")).reverse_order
+    assert_equal topics(:second).title, topics.first.title
+    topics = Topic.order(Arel.sql("length(author_name), id, length(title)")).reverse_order
+    assert_equal topics(:fifth).title, topics.first.title
+  end
+
+  def test_reverse_order_with_multiargument_function
+    assert_raises(ActiveRecord::IrreversibleOrderError) do
+      Topic.order(Arel.sql("concat(author_name, title)")).reverse_order
+    end
+    assert_raises(ActiveRecord::IrreversibleOrderError) do
+      Topic.order(Arel.sql("concat(lower(author_name), title)")).reverse_order
+    end
+    assert_raises(ActiveRecord::IrreversibleOrderError) do
+      Topic.order(Arel.sql("concat(author_name, lower(title))")).reverse_order
+    end
+    assert_raises(ActiveRecord::IrreversibleOrderError) do
+      Topic.order(Arel.sql("concat(lower(author_name), title, length(title)")).reverse_order
+    end
+  end
+
+  def test_reverse_arel_assoc_order_with_multiargument_function
+    assert_nothing_raised do
+      Topic.order(Arel.sql("REPLACE(title, '', '')") => :asc).reverse_order
+    end
+  end
+
+  def test_reverse_order_with_nulls_first_or_last
+    assert_raises(ActiveRecord::IrreversibleOrderError) do
+      Topic.order(Arel.sql("title NULLS FIRST")).reverse_order
+    end
+    assert_raises(ActiveRecord::IrreversibleOrderError) do
+      Topic.order(Arel.sql("title nulls last")).reverse_order
+    end
+  end
+
+  def test_default_reverse_order_on_table_without_primary_key
+    assert_raises(ActiveRecord::IrreversibleOrderError) do
+      Edge.all.reverse_order
+    end
+  end
+
   def test_order_with_hash_and_symbol_generates_the_same_sql
-    assert_equal Topic.order(:id).to_sql, Topic.order(:id => :asc).to_sql
+    assert_equal Topic.order(:id).to_sql, Topic.order(id: :asc).to_sql
   end
 
   def test_finding_with_desc_order_with_string
@@ -210,7 +311,7 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_finding_with_asc_order_with_string
-    topics = Topic.order(id: 'asc')
+    topics = Topic.order(id: "asc")
     assert_equal 5, topics.to_a.size
     assert_equal [topics(:first), topics(:second), topics(:third), topics(:fourth), topics(:fifth)], topics.to_a
   end
@@ -224,7 +325,7 @@ class RelationTest < ActiveRecord::TestCase
     assert_includes Topic.order(id: "DESC").to_sql, "DESC"
     assert_includes Topic.order(id: "desc").to_sql, "DESC"
     assert_includes Topic.order(id: :DESC).to_sql, "DESC"
-    assert_includes Topic.order(id: :desc).to_sql,"DESC"
+    assert_includes Topic.order(id: :desc).to_sql, "DESC"
   end
 
   def test_raising_exception_on_invalid_hash_params
@@ -238,7 +339,7 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_finding_with_order_concatenated
-    topics = Topic.order('author_name').order('title')
+    topics = Topic.order("author_name").order("title")
     assert_equal 5, topics.to_a.size
     assert_equal topics(:fourth).title, topics.first.title
   end
@@ -256,19 +357,19 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_finding_with_reorder
-    topics = Topic.order('author_name').order('title').reorder('id').to_a
+    topics = Topic.order("author_name").order("title").reorder("id").to_a
     topics_titles = topics.map(&:title)
-    assert_equal ['The First Topic', 'The Second Topic of the day', 'The Third Topic of the day', 'The Fourth Topic of the day', 'The Fifth Topic of the day'], topics_titles
+    assert_equal ["The First Topic", "The Second Topic of the day", "The Third Topic of the day", "The Fourth Topic of the day", "The Fifth Topic of the day"], topics_titles
   end
 
   def test_finding_with_reorder_by_aliased_attributes
-    topics = Topic.order('author_name').reorder(:heading)
+    topics = Topic.order("author_name").reorder(:heading)
     assert_equal 5, topics.to_a.size
     assert_equal topics(:fifth).title, topics.first.title
   end
 
   def test_finding_with_assoc_reorder_by_aliased_attributes
-    topics = Topic.order('author_name').reorder(heading: :desc)
+    topics = Topic.order("author_name").reorder(heading: :desc)
     assert_equal 5, topics.to_a.size
     assert_equal topics(:third).title, topics.first.title
   end
@@ -282,21 +383,32 @@ class RelationTest < ActiveRecord::TestCase
 
   def test_finding_with_cross_table_order_and_limit
     tags = Tag.includes(:taggings).
-              order("tags.name asc", "taggings.taggable_id asc", "REPLACE('abc', taggings.taggable_type, taggings.taggable_type)").
+              order("tags.name asc", "taggings.taggable_id asc", Arel.sql("REPLACE('abc', taggings.taggable_type, taggings.taggable_type)")).
               limit(1).to_a
     assert_equal 1, tags.length
   end
 
   def test_finding_with_complex_order_and_limit
-    tags = Tag.includes(:taggings).references(:taggings).order("REPLACE('abc', taggings.taggable_type, taggings.taggable_type)").limit(1).to_a
+    tags = Tag.includes(:taggings).references(:taggings).order(Arel.sql("REPLACE('abc', taggings.taggable_type, taggings.taggable_type)")).limit(1).to_a
     assert_equal 1, tags.length
   end
 
   def test_finding_with_complex_order
-    tags = Tag.includes(:taggings).references(:taggings).order("REPLACE('abc', taggings.taggable_type, taggings.taggable_type)").to_a
+    tags = Tag.includes(:taggings).references(:taggings).order(Arel.sql("REPLACE('abc', taggings.taggable_type, taggings.taggable_type)")).to_a
     assert_equal 3, tags.length
   end
 
+  def test_finding_with_sanitized_order
+    query = Tag.order([Arel.sql("field(id, ?)"), [1, 3, 2]]).to_sql
+    assert_match(/field\(id, 1,3,2\)/, query)
+
+    query = Tag.order([Arel.sql("field(id, ?)"), []]).to_sql
+    assert_match(/field\(id, NULL\)/, query)
+
+    query = Tag.order([Arel.sql("field(id, ?)"), nil]).to_sql
+    assert_match(/field\(id, NULL\)/, query)
+  end
+
   def test_finding_with_order_limit_and_offset
     entrants = Entrant.order("id ASC").limit(2).offset(1)
 
@@ -315,149 +427,32 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_select_with_block
-    even_ids = Developer.all.select {|d| d.id % 2 == 0 }.map(&:id)
+    even_ids = Developer.all.select { |d| d.id % 2 == 0 }.map(&:id)
     assert_equal [2, 4, 6, 8, 10], even_ids.sort
   end
 
-  def test_none
-    assert_no_queries(ignore_none: false) do
-      assert_equal [], Developer.none
-      assert_equal [], Developer.all.none
-    end
-  end
-
-  def test_none_chainable
-    assert_no_queries(ignore_none: false) do
-      assert_equal [], Developer.none.where(:name => 'David')
-    end
-  end
-
-  def test_none_chainable_to_existing_scope_extension_method
-    assert_no_queries(ignore_none: false) do
-      assert_equal 1, Topic.anonymous_extension.none.one
-    end
-  end
-
-  def test_none_chained_to_methods_firing_queries_straight_to_db
-    assert_no_queries(ignore_none: false) do
-      assert_equal [],    Developer.none.pluck(:id, :name)
-      assert_equal 0,     Developer.none.delete_all
-      assert_equal 0,     Developer.none.update_all(:name => 'David')
-      assert_equal 0,     Developer.none.delete(1)
-      assert_equal false, Developer.none.exists?(1)
-    end
-  end
-
-  def test_null_relation_content_size_methods
-    assert_no_queries(ignore_none: false) do
-      assert_equal 0,     Developer.none.size
-      assert_equal 0,     Developer.none.count
-      assert_equal true,  Developer.none.empty?
-      assert_equal true, Developer.none.none?
-      assert_equal false, Developer.none.any?
-      assert_equal false, Developer.none.one?
-      assert_equal false, Developer.none.many?
-    end
-  end
-
-  def test_null_relation_calculations_methods
-    assert_no_queries(ignore_none: false) do
-      assert_equal 0, Developer.none.count
-      assert_equal 0, Developer.none.calculate(:count, nil)
-      assert_equal nil, Developer.none.calculate(:average, 'salary')
-    end
-  end
-
-  def test_null_relation_metadata_methods
-    assert_equal "", Developer.none.to_sql
-    assert_equal({}, Developer.none.where_values_hash)
-  end
-
-  def test_null_relation_where_values_hash
-    assert_equal({ 'salary' => 100_000 }, Developer.none.where(salary: 100_000).where_values_hash)
-  end
-
-  def test_null_relation_sum
-    ac = Aircraft.new
-    assert_equal Hash.new, ac.engines.group(:id).sum(:id)
-    assert_equal        0, ac.engines.count
-    ac.save
-    assert_equal Hash.new, ac.engines.group(:id).sum(:id)
-    assert_equal        0, ac.engines.count
-  end
-
-  def test_null_relation_count
-    ac = Aircraft.new
-    assert_equal Hash.new, ac.engines.group(:id).count
-    assert_equal        0, ac.engines.count
-    ac.save
-    assert_equal Hash.new, ac.engines.group(:id).count
-    assert_equal        0, ac.engines.count
-  end
-
-  def test_null_relation_size
-    ac = Aircraft.new
-    assert_equal Hash.new, ac.engines.group(:id).size
-    assert_equal        0, ac.engines.size
-    ac.save
-    assert_equal Hash.new, ac.engines.group(:id).size
-    assert_equal        0, ac.engines.size
-  end
-
-  def test_null_relation_average
-    ac = Aircraft.new
-    assert_equal Hash.new, ac.engines.group(:car_id).average(:id)
-    assert_equal        nil, ac.engines.average(:id)
-    ac.save
-    assert_equal Hash.new, ac.engines.group(:car_id).average(:id)
-    assert_equal        nil, ac.engines.average(:id)
-  end
-
-  def test_null_relation_minimum
-    ac = Aircraft.new
-    assert_equal Hash.new, ac.engines.group(:car_id).minimum(:id)
-    assert_equal        nil, ac.engines.minimum(:id)
-    ac.save
-    assert_equal Hash.new, ac.engines.group(:car_id).minimum(:id)
-    assert_equal        nil, ac.engines.minimum(:id)
-  end
-
-  def test_null_relation_maximum
-    ac = Aircraft.new
-    assert_equal Hash.new, ac.engines.group(:car_id).maximum(:id)
-    assert_equal        nil, ac.engines.maximum(:id)
-    ac.save
-    assert_equal Hash.new, ac.engines.group(:car_id).maximum(:id)
-    assert_equal        nil, ac.engines.maximum(:id)
-  end
-
-  def test_null_relation_in_where_condition
-    assert_operator Comment.count, :>, 0 # precondition, make sure there are comments.
-    assert_equal 0, Comment.where(post_id: Post.none).to_a.size
-  end
-
   def test_joins_with_nil_argument
     assert_nothing_raised { DependentFirm.joins(nil).first }
   end
 
   def test_finding_with_hash_conditions_on_joined_table
-    firms = DependentFirm.joins(:account).where({:name => 'RailsCore', :accounts => { :credit_limit => 55..60 }}).to_a
+    firms = DependentFirm.joins(:account).where(name: "RailsCore", accounts: { credit_limit: 55..60 }).to_a
     assert_equal 1, firms.size
     assert_equal companies(:rails_core), firms.first
   end
 
   def test_find_all_with_join
-    developers_on_project_one = Developer.joins('LEFT JOIN developers_projects ON developers.id = developers_projects.developer_id').
-      where('project_id=1').to_a
+    developers_on_project_one = Developer.joins("LEFT JOIN developers_projects ON developers.id = developers_projects.developer_id").
+      where("project_id=1").to_a
 
     assert_equal 3, developers_on_project_one.length
     developer_names = developers_on_project_one.map(&:name)
-    assert developer_names.include?('David')
-    assert developer_names.include?('Jamis')
+    assert_includes developer_names, "David"
+    assert_includes developer_names, "Jamis"
   end
 
   def test_find_on_hash_conditions
-    assert_equal Topic.all.merge!(:where => {:approved => false}).to_a, Topic.where({ :approved => false }).to_a
+    assert_equal Topic.all.merge!(where: { approved: false }).to_a, Topic.where(approved: false).to_a
   end
 
   def test_joins_with_string_array
@@ -485,18 +480,10 @@ class RelationTest < ActiveRecord::TestCase
     assert_nothing_raised { Topic.reorder([]) }
   end
 
-  def test_scoped_responds_to_delegated_methods
-    relation = Topic.all
-
-    ["map", "uniq", "sort", "insert", "delete", "update"].each do |method|
-      assert_respond_to relation, method, "Topic.all should respond to #{method.inspect}"
-    end
-  end
-
-  def test_respond_to_delegates_to_relation
+  def test_respond_to_delegates_to_arel
     relation = Topic.all
     fake_arel = Struct.new(:responds) {
-      def respond_to? method, access = false
+      def respond_to?(method, access = false)
         responds << [method, access]
       end
     }.new []
@@ -506,32 +493,28 @@ class RelationTest < ActiveRecord::TestCase
 
     relation.respond_to?(:matching_attributes)
     assert_equal [:matching_attributes, false], fake_arel.responds.first
-
-    fake_arel.responds = []
-    relation.respond_to?(:matching_attributes, true)
-    assert_equal [:matching_attributes, true], fake_arel.responds.first
   end
 
   def test_respond_to_dynamic_finders
     relation = Topic.all
 
     ["find_by_title", "find_by_title_and_author_name"].each do |method|
-      assert_respond_to relation, method, "Topic.all should respond to #{method.inspect}"
+      assert_respond_to relation, method
     end
   end
 
   def test_respond_to_class_methods_and_scopes
-    assert Topic.all.respond_to?(:by_lifo)
+    assert_respond_to Topic.all, :by_lifo
   end
 
   def test_find_with_readonly_option
-    Developer.all.each { |d| assert !d.readonly? }
+    Developer.all.each { |d| assert_not d.readonly? }
     Developer.all.readonly.each { |d| assert d.readonly? }
   end
 
   def test_eager_association_loading_of_stis_with_multiple_references
-    authors = Author.eager_load(:posts => { :special_comments => { :post => [ :special_comments, :very_special_comment ] } }).
-      order('comments.body, very_special_comments_posts.body').where('posts.id = 4').to_a
+    authors = Author.eager_load(posts: { special_comments: { post: [ :special_comments, :very_special_comment ] } }).
+      order("comments.body, very_special_comments_posts.body").where("posts.id = 4").to_a
 
     assert_equal [authors(:david)], authors
     assert_no_queries do
@@ -542,27 +525,27 @@ class RelationTest < ActiveRecord::TestCase
 
   def test_find_with_preloaded_associations
     assert_queries(2) do
-      posts = Post.preload(:comments).order('posts.id')
+      posts = Post.preload(:comments).order("posts.id")
       assert posts.first.comments.first
     end
 
     assert_queries(2) do
-      posts = Post.preload(:comments).order('posts.id')
+      posts = Post.preload(:comments).order("posts.id")
       assert posts.first.comments.first
     end
 
     assert_queries(2) do
-      posts = Post.preload(:author).order('posts.id')
+      posts = Post.preload(:author).order("posts.id")
       assert posts.first.author
     end
 
     assert_queries(2) do
-      posts = Post.preload(:author).order('posts.id')
+      posts = Post.preload(:author).order("posts.id")
       assert posts.first.author
     end
 
     assert_queries(3) do
-      posts = Post.preload(:author, :comments).order('posts.id')
+      posts = Post.preload(:author, :comments).order("posts.id")
       assert posts.first.author
       assert posts.first.comments.first
     end
@@ -577,58 +560,48 @@ class RelationTest < ActiveRecord::TestCase
 
   def test_find_with_included_associations
     assert_queries(2) do
-      posts = Post.includes(:comments).order('posts.id')
+      posts = Post.includes(:comments).order("posts.id")
       assert posts.first.comments.first
     end
 
     assert_queries(2) do
-      posts = Post.all.includes(:comments).order('posts.id')
+      posts = Post.all.includes(:comments).order("posts.id")
       assert posts.first.comments.first
     end
 
     assert_queries(2) do
-      posts = Post.includes(:author).order('posts.id')
+      posts = Post.includes(:author).order("posts.id")
       assert posts.first.author
     end
 
     assert_queries(3) do
-      posts = Post.includes(:author, :comments).order('posts.id')
+      posts = Post.includes(:author, :comments).order("posts.id")
       assert posts.first.author
       assert posts.first.comments.first
     end
   end
 
-  def test_default_scope_with_conditions_string
-    assert_equal Developer.where(name: 'David').map(&:id).sort, DeveloperCalledDavid.all.map(&:id).sort
-    assert_nil DeveloperCalledDavid.create!.name
-  end
-
-  def test_default_scope_with_conditions_hash
-    assert_equal Developer.where(name: 'Jamis').map(&:id).sort, DeveloperCalledJamis.all.map(&:id).sort
-    assert_equal 'Jamis', DeveloperCalledJamis.create!.name
-  end
-
   def test_default_scoping_finder_methods
-    developers = DeveloperCalledDavid.order('id').map(&:id).sort
-    assert_equal Developer.where(name: 'David').map(&:id).sort, developers
+    developers = DeveloperCalledDavid.order("id").map(&:id).sort
+    assert_equal Developer.where(name: "David").map(&:id).sort, developers
   end
 
   def test_includes_with_select
-    query = Post.select('comments_count AS ranking').order('ranking').includes(:comments)
+    query = Post.select("comments_count AS ranking").order("ranking").includes(:comments)
       .where(comments: { id: 1 })
 
-    assert_equal ['comments_count AS ranking'], query.select_values
+    assert_equal ["comments_count AS ranking"], query.select_values
     assert_equal 1, query.to_a.size
   end
 
   def test_preloading_with_associations_and_merges
-    post = Post.create! title: 'Uhuu', body: 'body'
+    post = Post.create! title: "Uhuu", body: "body"
     reader = Reader.create! post_id: post.id, person_id: 1
-    comment = Comment.create! post_id: post.id, body: 'body'
+    comment = Comment.create! post_id: post.id, body: "body"
 
-    assert !comment.respond_to?(:readers)
+    assert_not_respond_to comment, :readers
 
-    post_rel = Post.preload(:readers).joins(:readers).where(title: 'Uhuu')
+    post_rel = Post.preload(:readers).joins(:readers).where(title: "Uhuu")
     result_comment = Comment.joins(:post).merge(post_rel).to_a.first
     assert_equal comment, result_comment
 
@@ -637,7 +610,7 @@ class RelationTest < ActiveRecord::TestCase
       assert_equal [reader], result_comment.post.readers.to_a
     end
 
-    post_rel = Post.includes(:readers).where(title: 'Uhuu')
+    post_rel = Post.includes(:readers).where(title: "Uhuu")
     result_comment = Comment.joins(:post).merge(post_rel).first
     assert_equal comment, result_comment
 
@@ -648,17 +621,17 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_preloading_with_associations_default_scopes_and_merges
-    post = Post.create! title: 'Uhuu', body: 'body'
+    post = Post.create! title: "Uhuu", body: "body"
     reader = Reader.create! post_id: post.id, person_id: 1
 
-    post_rel = PostWithPreloadDefaultScope.preload(:readers).joins(:readers).where(title: 'Uhuu')
+    post_rel = PostWithPreloadDefaultScope.preload(:readers).joins(:readers).where(title: "Uhuu")
     result_post = PostWithPreloadDefaultScope.all.merge(post_rel).to_a.first
 
     assert_no_queries do
       assert_equal [reader], result_post.readers.to_a
     end
 
-    post_rel = PostWithIncludesDefaultScope.includes(:readers).where(title: 'Uhuu')
+    post_rel = PostWithIncludesDefaultScope.includes(:readers).where(title: "Uhuu")
     result_post = PostWithIncludesDefaultScope.all.merge(post_rel).to_a.first
 
     assert_no_queries do
@@ -670,11 +643,11 @@ class RelationTest < ActiveRecord::TestCase
     posts = Post.preload(:comments)
     post = posts.find { |p| p.id == 1 }
     assert_equal 2, post.comments.size
-    assert post.comments.include?(comments(:greetings))
+    assert_includes post.comments, comments(:greetings)
 
     post = Post.where("posts.title = 'Welcome to the weblog'").preload(:comments).first
     assert_equal 2, post.comments.size
-    assert post.comments.include?(comments(:greetings))
+    assert_includes post.comments, comments(:greetings)
 
     posts = Post.preload(:last_comment)
     post = posts.find { |p| p.id == 1 }
@@ -683,9 +656,9 @@ class RelationTest < ActiveRecord::TestCase
 
   def test_to_sql_on_eager_join
     expected = assert_sql {
-      Post.eager_load(:last_comment).order('comments.id DESC').to_a
+      Post.eager_load(:last_comment).order("comments.id DESC").to_a
     }.first
-    actual = Post.eager_load(:last_comment).order('comments.id DESC').to_sql
+    actual = Post.eager_load(:last_comment).order("comments.id DESC").to_sql
     assert_equal expected, actual
   end
 
@@ -696,7 +669,7 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_loading_with_one_association_with_non_preload
-    posts = Post.eager_load(:last_comment).order('comments.id DESC')
+    posts = Post.eager_load(:last_comment).order("comments.id DESC")
     post = posts.find { |p| p.id == 1 }
     assert_equal Post.find(1).last_comment, post.last_comment
   end
@@ -707,7 +680,6 @@ class RelationTest < ActiveRecord::TestCase
     expected_taggings = taggings(:welcome_general, :thinking_general)
 
     assert_no_queries do
-      assert_equal expected_taggings, author.taggings.distinct.sort_by(&:id)
       assert_equal expected_taggings, author.taggings.uniq.sort_by(&:id)
     end
 
@@ -720,40 +692,40 @@ class RelationTest < ActiveRecord::TestCase
     author = Author.all.find_by_id!(authors(:david).id)
     assert_equal "David", author.name
 
-    assert_raises(ActiveRecord::RecordNotFound) { Author.all.find_by_id_and_name!(20, 'invalid') }
+    assert_raises(ActiveRecord::RecordNotFound) { Author.all.find_by_id_and_name!(20, "invalid") }
   end
 
   def test_find_id
     authors = Author.all
 
     david = authors.find(authors(:david).id)
-    assert_equal 'David', david.name
+    assert_equal "David", david.name
 
-    assert_raises(ActiveRecord::RecordNotFound) { authors.where(:name => 'lifo').find('42') }
+    assert_raises(ActiveRecord::RecordNotFound) { authors.where(name: "lifo").find("42") }
   end
 
   def test_find_ids
-    authors = Author.order('id ASC')
+    authors = Author.order("id ASC")
 
     results = authors.find(authors(:david).id, authors(:mary).id)
     assert_kind_of Array, results
     assert_equal 2, results.size
-    assert_equal 'David', results[0].name
-    assert_equal 'Mary', results[1].name
+    assert_equal "David", results[0].name
+    assert_equal "Mary", results[1].name
     assert_equal results, authors.find([authors(:david).id, authors(:mary).id])
 
-    assert_raises(ActiveRecord::RecordNotFound) { authors.where(:name => 'lifo').find(authors(:david).id, '42') }
-    assert_raises(ActiveRecord::RecordNotFound) { authors.find(['42', 43]) }
+    assert_raises(ActiveRecord::RecordNotFound) { authors.where(name: "lifo").find(authors(:david).id, "42") }
+    assert_raises(ActiveRecord::RecordNotFound) { authors.find(["42", 43]) }
   end
 
   def test_find_in_empty_array
-    authors = Author.all.where(:id => [])
-    assert authors.to_a.blank?
+    authors = Author.all.where(id: [])
+    assert_predicate authors.to_a, :blank?
   end
 
   def test_where_with_ar_object
     author = Author.first
-    authors = Author.all.where(:id => author)
+    authors = Author.all.where(id: author)
     assert_equal 1, authors.to_a.length
   end
 
@@ -763,15 +735,6 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal author, authors.first
   end
 
-  class Mary < Author; end
-
-  def test_find_by_classname
-    Author.create!(:name => Mary.name)
-    assert_deprecated do
-      assert_equal 1, Author.where(:name => Mary).size
-    end
-  end
-
   def test_find_by_id_with_list_of_ar
     author = Author.first
     authors = Author.find_by_id([author])
@@ -781,25 +744,25 @@ class RelationTest < ActiveRecord::TestCase
   def test_find_all_using_where_twice_should_or_the_relation
     david = authors(:david)
     relation = Author.unscoped
-    relation = relation.where(:name => david.name)
-    relation = relation.where(:name => 'Santiago')
-    relation = relation.where(:id => david.id)
+    relation = relation.where(name: david.name)
+    relation = relation.where(name: "Santiago")
+    relation = relation.where(id: david.id)
     assert_equal [], relation.to_a
   end
 
   def test_multi_where_ands_queries
     relation = Author.unscoped
     david = authors(:david)
-    sql = relation.where(:name => david.name).where(:name => 'Santiago').to_sql
-    assert_match('AND', sql)
+    sql = relation.where(name: david.name).where(name: "Santiago").to_sql
+    assert_match("AND", sql)
   end
 
   def test_find_all_with_multiple_should_use_and
     david = authors(:david)
     relation = [
-      { :name => david.name },
-      { :name => 'Santiago' },
-      { :name => 'tenderlove' },
+      { name: david.name },
+      { name: "Santiago" },
+      { name: "tenderlove" },
     ].inject(Author.unscoped) do |memo, param|
       memo.where(param)
     end
@@ -815,20 +778,18 @@ class RelationTest < ActiveRecord::TestCase
 
   def test_find_all_using_where_with_relation
     david = authors(:david)
-    # switching the lines below would succeed in current rails
-    # assert_queries(2) {
     assert_queries(1) {
-      relation = Author.where(:id => Author.where(:id => david.id))
+      relation = Author.where(id: Author.where(id: david.id))
       assert_equal [david], relation.to_a
     }
 
     assert_queries(1) {
-      relation = Author.where('id in (?)', Author.where(id: david).select(:id))
+      relation = Author.where("id in (?)", Author.where(id: david).select(:id))
       assert_equal [david], relation.to_a
     }
 
     assert_queries(1) do
-      relation = Author.where('id in (:author_ids)', author_ids: Author.where(id: david).select(:id))
+      relation = Author.where("id in (:author_ids)", author_ids: Author.where(id: david).select(:id))
       assert_equal [david], relation.to_a
     end
   end
@@ -843,22 +804,20 @@ class RelationTest < ActiveRecord::TestCase
     end
 
     assert_queries(1) do
-      relation = Post.where('id in (?)', david.posts.select(:id))
-      assert_equal davids_posts, relation.order(:id).to_a, 'should process Relation as bind variables'
+      relation = Post.where("id in (?)", david.posts.select(:id))
+      assert_equal davids_posts, relation.order(:id).to_a, "should process Relation as bind variables"
     end
 
     assert_queries(1) do
-      relation = Post.where('id in (:post_ids)', post_ids: david.posts.select(:id))
-      assert_equal davids_posts, relation.order(:id).to_a, 'should process Relation as named bind variables'
+      relation = Post.where("id in (:post_ids)", post_ids: david.posts.select(:id))
+      assert_equal davids_posts, relation.order(:id).to_a, "should process Relation as named bind variables"
     end
   end
 
   def test_find_all_using_where_with_relation_and_alternate_primary_key
     cool_first = minivans(:cool_first)
-    # switching the lines below would succeed in current rails
-    # assert_queries(2) {
     assert_queries(1) {
-      relation = Minivan.where(:minivan_id => Minivan.where(:name => cool_first.name))
+      relation = Minivan.where(minivan_id: Minivan.where(name: cool_first.name))
       assert_equal [cool_first], relation.to_a
     }
   end
@@ -866,10 +825,10 @@ class RelationTest < ActiveRecord::TestCase
   def test_find_all_using_where_with_relation_does_not_alter_select_values
     david = authors(:david)
 
-    subquery = Author.where(:id => david.id)
+    subquery = Author.where(id: david.id)
 
     assert_queries(1) {
-      relation = Author.where(:id => subquery)
+      relation = Author.where(id: subquery)
       assert_equal [david], relation.to_a
     }
 
@@ -879,94 +838,32 @@ class RelationTest < ActiveRecord::TestCase
   def test_find_all_using_where_with_relation_with_joins
     david = authors(:david)
     assert_queries(1) {
-      relation = Author.where(:id => Author.joins(:posts).where(:id => david.id))
+      relation = Author.where(id: Author.joins(:posts).where(id: david.id))
       assert_equal [david], relation.to_a
     }
   end
 
-
   def test_find_all_using_where_with_relation_with_select_to_build_subquery
     david = authors(:david)
     assert_queries(1) {
-      relation = Author.where(:name => Author.where(:id => david.id).select(:name))
+      relation = Author.where(name: Author.where(id: david.id).select(:name))
       assert_equal [david], relation.to_a
     }
   end
 
-  def test_exists
-    davids = Author.where(:name => 'David')
-    assert davids.exists?
-    assert davids.exists?(authors(:david).id)
-    assert ! davids.exists?(authors(:mary).id)
-    assert ! davids.exists?("42")
-    assert ! davids.exists?(42)
-    assert ! davids.exists?(davids.new.id)
-
-    fake  = Author.where(:name => 'fake author')
-    assert ! fake.exists?
-    assert ! fake.exists?(authors(:david).id)
-  end
-
-  def test_exists_uses_existing_scope
-    post = authors(:david).posts.first
-    authors = Author.includes(:posts).where(name: "David", posts: { id: post.id })
-    assert authors.exists?(authors(:david).id)
-  end
-
   def test_last
     authors = Author.all
     assert_equal authors(:bob), authors.last
   end
 
-  def test_destroy_all
-    davids = Author.where(:name => 'David')
-
-    # Force load
-    assert_equal [authors(:david)], davids.to_a
-    assert davids.loaded?
-
-    assert_difference('Author.count', -1) { davids.destroy_all }
-
-    assert_equal [], davids.to_a
-    assert davids.loaded?
-  end
-
-  def test_delete_all
-    davids = Author.where(:name => 'David')
-
-    assert_difference('Author.count', -1) { davids.delete_all }
-    assert ! davids.loaded?
-  end
-
-  def test_delete_all_loaded
-    davids = Author.where(:name => 'David')
-
-    # Force load
-    assert_equal [authors(:david)], davids.to_a
-    assert davids.loaded?
-
-    assert_difference('Author.count', -1) { davids.delete_all }
-
-    assert_equal [], davids.to_a
-    assert davids.loaded?
-  end
-
-  def test_delete_all_with_unpermitted_relation_raises_error
-    assert_raises(ActiveRecord::ActiveRecordError) { Author.limit(10).delete_all }
-    assert_raises(ActiveRecord::ActiveRecordError) { Author.distinct.delete_all }
-    assert_raises(ActiveRecord::ActiveRecordError) { Author.group(:name).delete_all }
-    assert_raises(ActiveRecord::ActiveRecordError) { Author.having('SUM(id) < 3').delete_all }
-    assert_raises(ActiveRecord::ActiveRecordError) { Author.offset(10).delete_all }
-  end
-
   def test_select_with_aggregates
     posts = Post.select(:title, :body)
 
     assert_equal 11, posts.count(:all)
     assert_equal 11, posts.size
-    assert posts.any?
-    assert posts.many?
-    assert_not posts.empty?
+    assert_predicate posts, :any?
+    assert_predicate posts, :many?
+    assert_not_empty posts
   end
 
   def test_select_takes_a_variable_list_of_args
@@ -995,8 +892,13 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal 11, posts.count(:all)
     assert_equal 11, posts.count(:id)
 
-    assert_equal 1, posts.where('comments_count > 1').count
-    assert_equal 9, posts.where(:comments_count => 0).count
+    assert_equal 3, posts.where("comments_count > 1").count
+    assert_equal 6, posts.where(comments_count: 0).count
+  end
+
+  def test_count_with_block
+    posts = Post.all
+    assert_equal 8, posts.count { |p| p.comments_count.even? }
   end
 
   def test_count_on_association_relation
@@ -1007,42 +909,52 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal author.posts.where(author_id: author.id).size, posts.count
 
     assert_equal 0, author.posts.where(author_id: another_author.id).size
-    assert author.posts.where(author_id: another_author.id).empty?
+    assert_empty author.posts.where(author_id: another_author.id)
   end
 
   def test_count_with_distinct
     posts = Post.all
 
-    assert_equal 3, posts.distinct(true).count(:comments_count)
+    assert_equal 4, posts.distinct(true).count(:comments_count)
     assert_equal 11, posts.distinct(false).count(:comments_count)
 
-    assert_equal 3, posts.distinct(true).select(:comments_count).count
+    assert_equal 4, posts.distinct(true).select(:comments_count).count
     assert_equal 11, posts.distinct(false).select(:comments_count).count
   end
 
-  def test_update_all_with_scope
-    tag = Tag.first
-    Post.tagged_with(tag.id).update_all title: "rofl"
-    list = Post.tagged_with(tag.id).all.to_a
-    assert_operator list.length, :>, 0
-    list.each { |post| assert_equal 'rofl', post.title }
+  def test_size_with_distinct
+    posts = Post.distinct.select(:author_id, :comments_count)
+    assert_queries(1) { assert_equal 8, posts.size }
+    assert_queries(1) { assert_equal 8, posts.load.size }
+  end
+
+  def test_size_with_eager_loading_and_custom_order
+    posts = Post.includes(:comments).order("comments.id")
+    assert_queries(1) { assert_equal 11, posts.size }
+    assert_queries(1) { assert_equal 11, posts.load.size }
+  end
+
+  def test_size_with_eager_loading_and_custom_order_and_distinct
+    posts = Post.includes(:comments).order("comments.id").distinct
+    assert_queries(1) { assert_equal 11, posts.size }
+    assert_queries(1) { assert_equal 11, posts.load.size }
   end
 
   def test_count_explicit_columns
-    Post.update_all(:comments_count => nil)
+    Post.update_all(comments_count: nil)
     posts = Post.all
 
-    assert_equal [0], posts.select('comments_count').where('id is not null').group('id').order('id').count.values.uniq
-    assert_equal 0, posts.where('id is not null').select('comments_count').count
+    assert_equal [0], posts.select("comments_count").where("id is not null").group("id").order("id").count.values.uniq
+    assert_equal 0, posts.where("id is not null").select("comments_count").count
 
-    assert_equal 11, posts.select('comments_count').count('id')
-    assert_equal 0, posts.select('comments_count').count
+    assert_equal 11, posts.select("comments_count").count("id")
+    assert_equal 0, posts.select("comments_count").count
     assert_equal 0, posts.count(:comments_count)
-    assert_equal 0, posts.count('comments_count')
+    assert_equal 0, posts.count("comments_count")
   end
 
   def test_multiple_selects
-    post = Post.all.select('comments_count').select('title').order("id ASC").first
+    post = Post.all.select("comments_count").select("title").order("id ASC").first
     assert_equal "Welcome to the weblog", post.title
     assert_equal 2, post.comments_count
   end
@@ -1051,31 +963,31 @@ class RelationTest < ActiveRecord::TestCase
     posts = Post.all
 
     assert_queries(1) { assert_equal 11, posts.size }
-    assert ! posts.loaded?
+    assert_not_predicate posts, :loaded?
 
-    best_posts = posts.where(:comments_count => 0)
-    best_posts.to_a # force load
-    assert_no_queries { assert_equal 9, best_posts.size }
+    best_posts = posts.where(comments_count: 0)
+    best_posts.load # force load
+    assert_no_queries { assert_equal 6, best_posts.size }
   end
 
   def test_size_with_limit
     posts = Post.limit(10)
 
     assert_queries(1) { assert_equal 10, posts.size }
-    assert ! posts.loaded?
+    assert_not_predicate posts, :loaded?
 
-    best_posts = posts.where(:comments_count => 0)
-    best_posts.to_a # force load
-    assert_no_queries { assert_equal 9, best_posts.size }
+    best_posts = posts.where(comments_count: 0)
+    best_posts.load # force load
+    assert_no_queries { assert_equal 6, best_posts.size }
   end
 
   def test_size_with_zero_limit
     posts = Post.limit(0)
 
     assert_no_queries { assert_equal 0, posts.size }
-    assert ! posts.loaded?
+    assert_not_predicate posts, :loaded?
 
-    posts.to_a # force load
+    posts.load # force load
     assert_no_queries { assert_equal 0, posts.size }
   end
 
@@ -1083,13 +995,13 @@ class RelationTest < ActiveRecord::TestCase
     posts = Post.limit(0)
 
     assert_no_queries { assert_equal true, posts.empty? }
-    assert ! posts.loaded?
+    assert_not_predicate posts, :loaded?
   end
 
   def test_count_complex_chained_relations
-    posts = Post.select('comments_count').where('id is not null').group("author_id").where("comments_count > 0")
+    posts = Post.select("comments_count").where("id is not null").group("author_id").where("comments_count > 0")
 
-    expected = { 1 => 2 }
+    expected = { 1 => 4, 2 => 1 }
     assert_equal expected, posts.count
   end
 
@@ -1097,14 +1009,14 @@ class RelationTest < ActiveRecord::TestCase
     posts = Post.all
 
     assert_queries(1) { assert_equal false, posts.empty? }
-    assert ! posts.loaded?
+    assert_not_predicate posts, :loaded?
 
-    no_posts = posts.where(:title => "")
+    no_posts = posts.where(title: "")
     assert_queries(1) { assert_equal true, no_posts.empty? }
-    assert ! no_posts.loaded?
+    assert_not_predicate no_posts, :loaded?
 
-    best_posts = posts.where(:comments_count => 0)
-    best_posts.to_a # force load
+    best_posts = posts.where(comments_count: 0)
+    best_posts.load # force load
     assert_no_queries { assert_equal false, best_posts.empty? }
   end
 
@@ -1112,11 +1024,11 @@ class RelationTest < ActiveRecord::TestCase
     posts = Post.select("comments_count").where("id is not null").group("author_id").where("comments_count > 0")
 
     assert_queries(1) { assert_equal false, posts.empty? }
-    assert ! posts.loaded?
+    assert_not_predicate posts, :loaded?
 
-    no_posts = posts.where(:title => "")
+    no_posts = posts.where(title: "")
     assert_queries(1) { assert_equal true, no_posts.empty? }
-    assert ! no_posts.loaded?
+    assert_not_predicate no_posts, :loaded?
   end
 
   def test_any
@@ -1128,17 +1040,17 @@ class RelationTest < ActiveRecord::TestCase
     # the SHOW TABLES result to be cached so we don't have to do it again in the block.
     #
     # This is obviously a rubbish fix but it's the best I can come up with for now...
-    posts.where(:id => nil).any?
+    posts.where(id: nil).any?
 
     assert_queries(3) do
       assert posts.any? # Uses COUNT()
-      assert ! posts.where(:id => nil).any?
+      assert_not_predicate posts.where(id: nil), :any?
 
-      assert posts.any? {|p| p.id > 0 }
-      assert ! posts.any? {|p| p.id <= 0 }
+      assert posts.any? { |p| p.id > 0 }
+      assert_not posts.any? { |p| p.id <= 0 }
     end
 
-    assert posts.loaded?
+    assert_predicate posts, :loaded?
   end
 
   def test_many
@@ -1146,50 +1058,60 @@ class RelationTest < ActiveRecord::TestCase
 
     assert_queries(2) do
       assert posts.many? # Uses COUNT()
-      assert posts.many? {|p| p.id > 0 }
-      assert ! posts.many? {|p| p.id < 2 }
+      assert posts.many? { |p| p.id > 0 }
+      assert_not posts.many? { |p| p.id < 2 }
     end
 
-    assert posts.loaded?
+    assert_predicate posts, :loaded?
   end
 
   def test_many_with_limits
     posts = Post.all
 
-    assert posts.many?
-    assert ! posts.limit(1).many?
+    assert_predicate posts, :many?
+    assert_not_predicate posts.limit(1), :many?
   end
 
   def test_none?
     posts = Post.all
     assert_queries(1) do
-      assert ! posts.none? # Uses COUNT()
+      assert_not posts.none? # Uses COUNT()
     end
 
-    assert ! posts.loaded?
+    assert_not_predicate posts, :loaded?
 
     assert_queries(1) do
-      assert posts.none? {|p| p.id < 0 }
-      assert ! posts.none? {|p| p.id == 1 }
+      assert posts.none? { |p| p.id < 0 }
+      assert_not posts.none? { |p| p.id == 1 }
     end
 
-    assert posts.loaded?
+    assert_predicate posts, :loaded?
   end
 
   def test_one
     posts = Post.all
     assert_queries(1) do
-      assert ! posts.one? # Uses COUNT()
+      assert_not posts.one? # Uses COUNT()
     end
 
-    assert ! posts.loaded?
+    assert_not_predicate posts, :loaded?
 
     assert_queries(1) do
-      assert ! posts.one? {|p| p.id < 3 }
-      assert posts.one? {|p| p.id == 1 }
+      assert_not posts.one? { |p| p.id < 3 }
+      assert posts.one? { |p| p.id == 1 }
     end
 
-    assert posts.loaded?
+    assert_predicate posts, :loaded?
+  end
+
+  def test_to_a_should_dup_target
+    posts = Post.all
+
+    original_size = posts.size
+    removed = posts.to_a.pop
+
+    assert_equal original_size, posts.size
+    assert_includes posts.to_a, removed
   end
 
   def test_build
@@ -1200,11 +1122,11 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_scoped_build
-    posts = Post.where(:title => 'You told a lie')
+    posts = Post.where(title: "You told a lie")
 
     post = posts.new
     assert_kind_of Post, post
-    assert_equal 'You told a lie', post.title
+    assert_equal "You told a lie", post.title
   end
 
   def test_create
@@ -1212,11 +1134,11 @@ class RelationTest < ActiveRecord::TestCase
 
     sparrow = birds.create
     assert_kind_of Bird, sparrow
-    assert !sparrow.persisted?
+    assert_not_predicate sparrow, :persisted?
 
-    hen = birds.where(:name => 'hen').create
-    assert hen.persisted?
-    assert_equal 'hen', hen.name
+    hen = birds.where(name: "hen").create
+    assert_predicate hen, :persisted?
+    assert_equal "hen", hen.name
   end
 
   def test_create_bang
@@ -1224,201 +1146,248 @@ class RelationTest < ActiveRecord::TestCase
 
     assert_raises(ActiveRecord::RecordInvalid) { birds.create! }
 
-    hen = birds.where(:name => 'hen').create!
+    hen = birds.where(name: "hen").create!
     assert_kind_of Bird, hen
-    assert hen.persisted?
-    assert_equal 'hen', hen.name
+    assert_predicate hen, :persisted?
+    assert_equal "hen", hen.name
+  end
+
+  def test_create_with_polymorphic_association
+    author = authors(:david)
+    post = posts(:welcome)
+    comment = Comment.where(post: post, author: author).create!(body: "hello")
+
+    assert_equal author, comment.author
+    assert_equal post, comment.post
   end
 
   def test_first_or_create
-    parrot = Bird.where(:color => 'green').first_or_create(:name => 'parrot')
+    parrot = Bird.where(color: "green").first_or_create(name: "parrot")
     assert_kind_of Bird, parrot
-    assert parrot.persisted?
-    assert_equal 'parrot', parrot.name
-    assert_equal 'green', parrot.color
+    assert_predicate parrot, :persisted?
+    assert_equal "parrot", parrot.name
+    assert_equal "green", parrot.color
 
-    same_parrot = Bird.where(:color => 'green').first_or_create(:name => 'parakeet')
+    same_parrot = Bird.where(color: "green").first_or_create(name: "parakeet")
     assert_kind_of Bird, same_parrot
-    assert same_parrot.persisted?
+    assert_predicate same_parrot, :persisted?
     assert_equal parrot, same_parrot
   end
 
   def test_first_or_create_with_no_parameters
-    parrot = Bird.where(:color => 'green').first_or_create
+    parrot = Bird.where(color: "green").first_or_create
     assert_kind_of Bird, parrot
-    assert !parrot.persisted?
-    assert_equal 'green', parrot.color
+    assert_not_predicate parrot, :persisted?
+    assert_equal "green", parrot.color
   end
 
   def test_first_or_create_with_block
-    parrot = Bird.where(:color => 'green').first_or_create { |bird| bird.name = 'parrot' }
+    parrot = Bird.where(color: "green").first_or_create { |bird| bird.name = "parrot" }
     assert_kind_of Bird, parrot
-    assert parrot.persisted?
-    assert_equal 'green', parrot.color
-    assert_equal 'parrot', parrot.name
+    assert_predicate parrot, :persisted?
+    assert_equal "green", parrot.color
+    assert_equal "parrot", parrot.name
 
-    same_parrot = Bird.where(:color => 'green').first_or_create { |bird| bird.name = 'parakeet' }
+    same_parrot = Bird.where(color: "green").first_or_create { |bird| bird.name = "parakeet" }
     assert_equal parrot, same_parrot
   end
 
   def test_first_or_create_with_array
-    several_green_birds = Bird.where(:color => 'green').first_or_create([{:name => 'parrot'}, {:name => 'parakeet'}])
+    several_green_birds = Bird.where(color: "green").first_or_create([{ name: "parrot" }, { name: "parakeet" }])
     assert_kind_of Array, several_green_birds
     several_green_birds.each { |bird| assert bird.persisted? }
 
-    same_parrot = Bird.where(:color => 'green').first_or_create([{:name => 'hummingbird'}, {:name => 'macaw'}])
+    same_parrot = Bird.where(color: "green").first_or_create([{ name: "hummingbird" }, { name: "macaw" }])
     assert_kind_of Bird, same_parrot
     assert_equal several_green_birds.first, same_parrot
   end
 
   def test_first_or_create_bang_with_valid_options
-    parrot = Bird.where(:color => 'green').first_or_create!(:name => 'parrot')
+    parrot = Bird.where(color: "green").first_or_create!(name: "parrot")
     assert_kind_of Bird, parrot
-    assert parrot.persisted?
-    assert_equal 'parrot', parrot.name
-    assert_equal 'green', parrot.color
+    assert_predicate parrot, :persisted?
+    assert_equal "parrot", parrot.name
+    assert_equal "green", parrot.color
 
-    same_parrot = Bird.where(:color => 'green').first_or_create!(:name => 'parakeet')
+    same_parrot = Bird.where(color: "green").first_or_create!(name: "parakeet")
     assert_kind_of Bird, same_parrot
-    assert same_parrot.persisted?
+    assert_predicate same_parrot, :persisted?
     assert_equal parrot, same_parrot
   end
 
   def test_first_or_create_bang_with_invalid_options
-    assert_raises(ActiveRecord::RecordInvalid) { Bird.where(:color => 'green').first_or_create!(:pirate_id => 1) }
+    assert_raises(ActiveRecord::RecordInvalid) { Bird.where(color: "green").first_or_create!(pirate_id: 1) }
   end
 
   def test_first_or_create_bang_with_no_parameters
-    assert_raises(ActiveRecord::RecordInvalid) { Bird.where(:color => 'green').first_or_create! }
+    assert_raises(ActiveRecord::RecordInvalid) { Bird.where(color: "green").first_or_create! }
   end
 
   def test_first_or_create_bang_with_valid_block
-    parrot = Bird.where(:color => 'green').first_or_create! { |bird| bird.name = 'parrot' }
+    parrot = Bird.where(color: "green").first_or_create! { |bird| bird.name = "parrot" }
     assert_kind_of Bird, parrot
-    assert parrot.persisted?
-    assert_equal 'green', parrot.color
-    assert_equal 'parrot', parrot.name
+    assert_predicate parrot, :persisted?
+    assert_equal "green", parrot.color
+    assert_equal "parrot", parrot.name
 
-    same_parrot = Bird.where(:color => 'green').first_or_create! { |bird| bird.name = 'parakeet' }
+    same_parrot = Bird.where(color: "green").first_or_create! { |bird| bird.name = "parakeet" }
     assert_equal parrot, same_parrot
   end
 
   def test_first_or_create_bang_with_invalid_block
     assert_raise(ActiveRecord::RecordInvalid) do
-      Bird.where(:color => 'green').first_or_create! { |bird| bird.pirate_id = 1 }
+      Bird.where(color: "green").first_or_create! { |bird| bird.pirate_id = 1 }
     end
   end
 
   def test_first_or_create_with_valid_array
-    several_green_birds = Bird.where(:color => 'green').first_or_create!([{:name => 'parrot'}, {:name => 'parakeet'}])
+    several_green_birds = Bird.where(color: "green").first_or_create!([{ name: "parrot" }, { name: "parakeet" }])
     assert_kind_of Array, several_green_birds
     several_green_birds.each { |bird| assert bird.persisted? }
 
-    same_parrot = Bird.where(:color => 'green').first_or_create!([{:name => 'hummingbird'}, {:name => 'macaw'}])
+    same_parrot = Bird.where(color: "green").first_or_create!([{ name: "hummingbird" }, { name: "macaw" }])
     assert_kind_of Bird, same_parrot
     assert_equal several_green_birds.first, same_parrot
   end
 
   def test_first_or_create_with_invalid_array
-    assert_raises(ActiveRecord::RecordInvalid) { Bird.where(:color => 'green').first_or_create!([ {:name => 'parrot'}, {:pirate_id => 1} ]) }
+    assert_raises(ActiveRecord::RecordInvalid) { Bird.where(color: "green").first_or_create!([ { name: "parrot" }, { pirate_id: 1 } ]) }
   end
 
   def test_first_or_initialize
-    parrot = Bird.where(:color => 'green').first_or_initialize(:name => 'parrot')
+    parrot = Bird.where(color: "green").first_or_initialize(name: "parrot")
     assert_kind_of Bird, parrot
-    assert !parrot.persisted?
-    assert parrot.valid?
-    assert parrot.new_record?
-    assert_equal 'parrot', parrot.name
-    assert_equal 'green', parrot.color
+    assert_not_predicate parrot, :persisted?
+    assert_predicate parrot, :valid?
+    assert_predicate parrot, :new_record?
+    assert_equal "parrot", parrot.name
+    assert_equal "green", parrot.color
   end
 
   def test_first_or_initialize_with_no_parameters
-    parrot = Bird.where(:color => 'green').first_or_initialize
+    parrot = Bird.where(color: "green").first_or_initialize
     assert_kind_of Bird, parrot
-    assert !parrot.persisted?
-    assert !parrot.valid?
-    assert parrot.new_record?
-    assert_equal 'green', parrot.color
+    assert_not_predicate parrot, :persisted?
+    assert_not_predicate parrot, :valid?
+    assert_predicate parrot, :new_record?
+    assert_equal "green", parrot.color
   end
 
   def test_first_or_initialize_with_block
-    parrot = Bird.where(:color => 'green').first_or_initialize { |bird| bird.name = 'parrot' }
+    parrot = Bird.where(color: "green").first_or_initialize { |bird| bird.name = "parrot" }
     assert_kind_of Bird, parrot
-    assert !parrot.persisted?
-    assert parrot.valid?
-    assert parrot.new_record?
-    assert_equal 'green', parrot.color
-    assert_equal 'parrot', parrot.name
+    assert_not_predicate parrot, :persisted?
+    assert_predicate parrot, :valid?
+    assert_predicate parrot, :new_record?
+    assert_equal "green", parrot.color
+    assert_equal "parrot", parrot.name
   end
 
   def test_find_or_create_by
-    assert_nil Bird.find_by(name: 'bob')
+    assert_nil Bird.find_by(name: "bob")
 
-    bird = Bird.find_or_create_by(name: 'bob')
-    assert bird.persisted?
+    bird = Bird.find_or_create_by(name: "bob")
+    assert_predicate bird, :persisted?
 
-    assert_equal bird, Bird.find_or_create_by(name: 'bob')
+    assert_equal bird, Bird.find_or_create_by(name: "bob")
   end
 
   def test_find_or_create_by_with_create_with
-    assert_nil Bird.find_by(name: 'bob')
+    assert_nil Bird.find_by(name: "bob")
 
-    bird = Bird.create_with(color: 'green').find_or_create_by(name: 'bob')
-    assert bird.persisted?
-    assert_equal 'green', bird.color
+    bird = Bird.create_with(color: "green").find_or_create_by(name: "bob")
+    assert_predicate bird, :persisted?
+    assert_equal "green", bird.color
 
-    assert_equal bird, Bird.create_with(color: 'blue').find_or_create_by(name: 'bob')
+    assert_equal bird, Bird.create_with(color: "blue").find_or_create_by(name: "bob")
   end
 
   def test_find_or_create_by!
-    assert_raises(ActiveRecord::RecordInvalid) { Bird.find_or_create_by!(color: 'green') }
+    assert_raises(ActiveRecord::RecordInvalid) { Bird.find_or_create_by!(color: "green") }
+  end
+
+  def test_create_or_find_by
+    assert_nil Subscriber.find_by(nick: "bob")
+
+    subscriber = Subscriber.create!(nick: "bob")
+
+    assert_equal subscriber, Subscriber.create_or_find_by(nick: "bob")
+    assert_not_equal subscriber, Subscriber.create_or_find_by(nick: "cat")
+  end
+
+  def test_create_or_find_by_with_non_unique_attributes
+    Subscriber.create!(nick: "bob", name: "the builder")
+
+    assert_raises(ActiveRecord::RecordNotFound) do
+      Subscriber.create_or_find_by(nick: "bob", name: "the cat")
+    end
+  end
+
+  def test_create_or_find_by_within_transaction
+    assert_nil Subscriber.find_by(nick: "bob")
+
+    subscriber = Subscriber.create!(nick: "bob")
+
+    Subscriber.transaction do
+      assert_equal subscriber, Subscriber.create_or_find_by(nick: "bob")
+      assert_not_equal subscriber, Subscriber.create_or_find_by(nick: "cat")
+    end
   end
 
   def test_find_or_initialize_by
-    assert_nil Bird.find_by(name: 'bob')
+    assert_nil Bird.find_by(name: "bob")
 
-    bird = Bird.find_or_initialize_by(name: 'bob')
-    assert bird.new_record?
+    bird = Bird.find_or_initialize_by(name: "bob")
+    assert_predicate bird, :new_record?
     bird.save!
 
-    assert_equal bird, Bird.find_or_initialize_by(name: 'bob')
+    assert_equal bird, Bird.find_or_initialize_by(name: "bob")
   end
 
-  def test_explicit_create_scope
-    hens = Bird.where(:name => 'hen')
-    assert_equal 'hen', hens.new.name
+  def test_explicit_create_with
+    hens = Bird.where(name: "hen")
+    assert_equal "hen", hens.new.name
+
+    hens = hens.create_with(name: "cock")
+    assert_equal "cock", hens.new.name
+  end
 
-    hens = hens.create_with(:name => 'cock')
-    assert_equal 'cock', hens.new.name
+  def test_create_with_nested_attributes
+    assert_difference("Project.count", 1) do
+      developers = Developer.where(name: "Aaron")
+      developers = developers.create_with(
+        projects_attributes: [{ name: "p1" }]
+      )
+      developers.create!
+    end
   end
 
   def test_except
-    relation = Post.where(:author_id => 1).order('id ASC').limit(1)
+    relation = Post.where(author_id: 1).order("id ASC").limit(1)
     assert_equal [posts(:welcome)], relation.to_a
 
     author_posts = relation.except(:order, :limit)
-    assert_equal Post.where(:author_id => 1).to_a, author_posts.to_a
+    assert_equal Post.where(author_id: 1).to_a, author_posts.to_a
 
     all_posts = relation.except(:where, :order, :limit)
     assert_equal Post.all, all_posts
   end
 
   def test_only
-    relation = Post.where(:author_id => 1).order('id ASC').limit(1)
+    relation = Post.where(author_id: 1).order("id ASC").limit(1)
     assert_equal [posts(:welcome)], relation.to_a
 
     author_posts = relation.only(:where)
-    assert_equal Post.where(:author_id => 1).to_a, author_posts.to_a
+    assert_equal Post.where(author_id: 1).to_a, author_posts.to_a
 
     all_posts = relation.only(:limit)
-    assert_equal Post.limit(1).to_a.first, all_posts.first
+    assert_equal Post.limit(1).to_a, all_posts.to_a
   end
 
   def test_anonymous_extension
-    relation = Post.where(:author_id => 1).order('id ASC').extending do
+    relation = Post.where(author_id: 1).order("id ASC").extending do
       def author
-        'lifo'
+        "lifo"
       end
     end
 
@@ -1427,7 +1396,7 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_named_extension
-    relation = Post.where(:author_id => 1).order('id ASC').extending(Post::NamedExtension)
+    relation = Post.where(author_id: 1).order("id ASC").extending(Post::NamedExtension)
     assert_equal "lifo", relation.author
     assert_equal "lifo", relation.limit(1).author
   end
@@ -1437,29 +1406,29 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_default_scope_order_with_scope_order
-    assert_equal 'zyke', CoolCar.order_using_new_style.limit(1).first.name
-    assert_equal 'zyke', FastCar.order_using_new_style.limit(1).first.name
+    assert_equal "zyke", CoolCar.order_using_new_style.limit(1).first.name
+    assert_equal "zyke", FastCar.order_using_new_style.limit(1).first.name
   end
 
   def test_order_using_scoping
-    car1 = CoolCar.order('id DESC').scoping do
-      CoolCar.all.merge!(order: 'id asc').first
+    car1 = CoolCar.order("id DESC").scoping do
+      CoolCar.all.merge!(order: "id asc").first
     end
-    assert_equal 'zyke', car1.name
+    assert_equal "zyke", car1.name
 
-    car2 = FastCar.order('id DESC').scoping do
-      FastCar.all.merge!(order: 'id asc').first
+    car2 = FastCar.order("id DESC").scoping do
+      FastCar.all.merge!(order: "id asc").first
     end
-    assert_equal 'zyke', car2.name
+    assert_equal "zyke", car2.name
   end
 
   def test_unscoped_block_style
-    assert_equal 'honda', CoolCar.unscoped { CoolCar.order_using_new_style.limit(1).first.name}
-    assert_equal 'honda', FastCar.unscoped { FastCar.order_using_new_style.limit(1).first.name}
+    assert_equal "honda", CoolCar.unscoped { CoolCar.order_using_new_style.limit(1).first.name }
+    assert_equal "honda", FastCar.unscoped { FastCar.order_using_new_style.limit(1).first.name }
   end
 
   def test_intersection_with_array
-    relation = Author.where(:name => "David")
+    relation = Author.where(name: "David")
     rails_author = relation.first
 
     assert_equal [rails_author], [rails_author] & relation
@@ -1471,92 +1440,31 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   def test_ordering_with_extra_spaces
-    assert_equal authors(:david), Author.order('id DESC , name DESC').last
-  end
-
-  def test_update_all_with_blank_argument
-    assert_raises(ArgumentError) { Comment.update_all({}) }
-  end
-
-  def test_update_all_with_joins
-    comments = Comment.joins(:post).where('posts.id' => posts(:welcome).id)
-    count    = comments.count
-
-    assert_equal count, comments.update_all(:post_id => posts(:thinking).id)
-    assert_equal posts(:thinking), comments(:greetings).post
-  end
-
-  def test_update_all_with_joins_and_limit
-    comments = Comment.joins(:post).where('posts.id' => posts(:welcome).id).limit(1)
-    assert_equal 1, comments.update_all(:post_id => posts(:thinking).id)
-  end
-
-  def test_update_all_with_joins_and_limit_and_order
-    comments = Comment.joins(:post).where('posts.id' => posts(:welcome).id).order('comments.id').limit(1)
-    assert_equal 1, comments.update_all(:post_id => posts(:thinking).id)
-    assert_equal posts(:thinking), comments(:greetings).post
-    assert_equal posts(:welcome),  comments(:more_greetings).post
-  end
-
-  def test_update_all_with_joins_and_offset
-    all_comments = Comment.joins(:post).where('posts.id' => posts(:welcome).id)
-    count        = all_comments.count
-    comments     = all_comments.offset(1)
-
-    assert_equal count - 1, comments.update_all(:post_id => posts(:thinking).id)
-  end
-
-  def test_update_all_with_joins_and_offset_and_order
-    all_comments = Comment.joins(:post).where('posts.id' => posts(:welcome).id).order('posts.id', 'comments.id')
-    count        = all_comments.count
-    comments     = all_comments.offset(1)
-
-    assert_equal count - 1, comments.update_all(:post_id => posts(:thinking).id)
-    assert_equal posts(:thinking), comments(:more_greetings).post
-    assert_equal posts(:welcome),  comments(:greetings).post
-  end
-
-  def test_update_on_relation
-    topic1 = TopicWithCallbacks.create! title: 'arel', author_name: nil
-    topic2 = TopicWithCallbacks.create! title: 'activerecord', author_name: nil
-    topics = TopicWithCallbacks.where(id: [topic1.id, topic2.id])
-    topics.update(title: 'adequaterecord')
-
-    assert_equal 'adequaterecord', topic1.reload.title
-    assert_equal 'adequaterecord', topic2.reload.title
-    # Testing that the before_update callbacks have run
-    assert_equal 'David', topic1.reload.author_name
-    assert_equal 'David', topic2.reload.author_name
+    assert_equal authors(:david), Author.order("id DESC , name DESC").last
   end
 
   def test_distinct
-    tag1 = Tag.create(:name => 'Foo')
-    tag2 = Tag.create(:name => 'Foo')
+    tag1 = Tag.create(name: "Foo")
+    tag2 = Tag.create(name: "Foo")
 
-    query = Tag.select(:name).where(:id => [tag1.id, tag2.id])
+    query = Tag.select(:name).where(id: [tag1.id, tag2.id])
 
-    assert_equal ['Foo', 'Foo'], query.map(&:name)
+    assert_equal ["Foo", "Foo"], query.map(&:name)
     assert_sql(/DISTINCT/) do
-      assert_equal ['Foo'], query.distinct.map(&:name)
-      assert_deprecated { assert_equal ['Foo'], query.uniq.map(&:name) }
+      assert_equal ["Foo"], query.distinct.map(&:name)
     end
     assert_sql(/DISTINCT/) do
-      assert_equal ['Foo'], query.distinct(true).map(&:name)
-      assert_deprecated { assert_equal ['Foo'], query.uniq(true).map(&:name) }
-    end
-    assert_equal ['Foo', 'Foo'], query.distinct(true).distinct(false).map(&:name)
-
-    assert_deprecated do
-      assert_equal ['Foo', 'Foo'], query.uniq(true).uniq(false).map(&:name)
+      assert_equal ["Foo"], query.distinct(true).map(&:name)
     end
+    assert_equal ["Foo", "Foo"], query.distinct(true).distinct(false).map(&:name)
   end
 
   def test_doesnt_add_having_values_if_options_are_blank
-    scope = Post.having('')
-    assert scope.having_clause.empty?
+    scope = Post.having("")
+    assert_empty scope.having_clause
 
     scope = Post.having([])
-    assert scope.having_clause.empty?
+    assert_empty scope.having_clause
   end
 
   def test_having_with_binds_for_both_where_and_having
@@ -1582,72 +1490,86 @@ class RelationTest < ActiveRecord::TestCase
 
   def test_references_triggers_eager_loading
     scope = Post.includes(:comments)
-    assert !scope.eager_loading?
-    assert scope.references(:comments).eager_loading?
+    assert_not_predicate scope, :eager_loading?
+    assert_predicate scope.references(:comments), :eager_loading?
   end
 
   def test_references_doesnt_trigger_eager_loading_if_reference_not_included
     scope = Post.references(:comments)
-    assert !scope.eager_loading?
+    assert_not_predicate scope, :eager_loading?
   end
 
   def test_automatically_added_where_references
-    scope = Post.where(:comments => { :body => "Bla" })
-    assert_equal ['comments'], scope.references_values
+    scope = Post.where(comments: { body: "Bla" })
+    assert_equal ["comments"], scope.references_values
 
-    scope = Post.where('comments.body' => 'Bla')
-    assert_equal ['comments'], scope.references_values
+    scope = Post.where("comments.body" => "Bla")
+    assert_equal ["comments"], scope.references_values
   end
 
   def test_automatically_added_where_not_references
     scope = Post.where.not(comments: { body: "Bla" })
-    assert_equal ['comments'], scope.references_values
+    assert_equal ["comments"], scope.references_values
 
-    scope = Post.where.not('comments.body' => 'Bla')
-    assert_equal ['comments'], scope.references_values
+    scope = Post.where.not("comments.body" => "Bla")
+    assert_equal ["comments"], scope.references_values
   end
 
   def test_automatically_added_having_references
-    scope = Post.having(:comments => { :body => "Bla" })
-    assert_equal ['comments'], scope.references_values
+    scope = Post.having(comments: { body: "Bla" })
+    assert_equal ["comments"], scope.references_values
 
-    scope = Post.having('comments.body' => 'Bla')
-    assert_equal ['comments'], scope.references_values
+    scope = Post.having("comments.body" => "Bla")
+    assert_equal ["comments"], scope.references_values
   end
 
   def test_automatically_added_order_references
-    scope = Post.order('comments.body')
-    assert_equal ['comments'], scope.references_values
+    scope = Post.order("comments.body")
+    assert_equal ["comments"], scope.references_values
+
+    scope = Post.order(Arel.sql("#{Comment.quoted_table_name}.#{Comment.quoted_primary_key}"))
+    if current_adapter?(:OracleAdapter)
+      assert_equal ["COMMENTS"], scope.references_values
+    else
+      assert_equal ["comments"], scope.references_values
+    end
 
-    scope = Post.order('comments.body', 'yaks.body')
-    assert_equal ['comments', 'yaks'], scope.references_values
+    scope = Post.order("comments.body", "yaks.body")
+    assert_equal ["comments", "yaks"], scope.references_values
 
     # Don't infer yaks, let's not go down that road again...
-    scope = Post.order('comments.body, yaks.body')
-    assert_equal ['comments'], scope.references_values
+    scope = Post.order("comments.body, yaks.body")
+    assert_equal ["comments"], scope.references_values
 
-    scope = Post.order('comments.body asc')
-    assert_equal ['comments'], scope.references_values
+    scope = Post.order("comments.body asc")
+    assert_equal ["comments"], scope.references_values
 
-    scope = Post.order('foo(comments.body)')
+    scope = Post.order(Arel.sql("foo(comments.body)"))
     assert_equal [], scope.references_values
   end
 
   def test_automatically_added_reorder_references
-    scope = Post.reorder('comments.body')
+    scope = Post.reorder("comments.body")
     assert_equal %w(comments), scope.references_values
 
-    scope = Post.reorder('comments.body', 'yaks.body')
+    scope = Post.reorder(Arel.sql("#{Comment.quoted_table_name}.#{Comment.quoted_primary_key}"))
+    if current_adapter?(:OracleAdapter)
+      assert_equal ["COMMENTS"], scope.references_values
+    else
+      assert_equal ["comments"], scope.references_values
+    end
+
+    scope = Post.reorder("comments.body", "yaks.body")
     assert_equal %w(comments yaks), scope.references_values
 
     # Don't infer yaks, let's not go down that road again...
-    scope = Post.reorder('comments.body, yaks.body')
+    scope = Post.reorder("comments.body, yaks.body")
     assert_equal %w(comments), scope.references_values
 
-    scope = Post.reorder('comments.body asc')
+    scope = Post.reorder("comments.body asc")
     assert_equal %w(comments), scope.references_values
 
-    scope = Post.reorder('foo(comments.body)')
+    scope = Post.reorder(Arel.sql("foo(comments.body)"))
     assert_equal [], scope.references_values
   end
 
@@ -1672,7 +1594,7 @@ class RelationTest < ActiveRecord::TestCase
     # checking if there are topics is used before you actually display them,
     # thus it shouldn't invoke an extra count query.
     assert_no_queries { assert topics.present? }
-    assert_no_queries { assert !topics.blank? }
+    assert_no_queries { assert_not topics.blank? }
 
     # shows count of topics and loops after loading the query should not trigger extra queries either.
     assert_no_queries { topics.size }
@@ -1682,7 +1604,7 @@ class RelationTest < ActiveRecord::TestCase
     # count always trigger the COUNT query.
     assert_queries(1) { topics.count }
 
-    assert topics.loaded?
+    assert_predicate topics, :loaded?
   end
 
   test "find_by with hash conditions returns the first matching record" do
@@ -1694,11 +1616,11 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   test "find_by with multi-arg conditions returns the first matching record" do
-    assert_equal posts(:eager_other), Post.order(:id).find_by('author_id = ?', 2)
+    assert_equal posts(:eager_other), Post.order(:id).find_by("author_id = ?", 2)
   end
 
   test "find_by returns nil if the record is missing" do
-    assert_equal nil, Post.all.find_by("1 = 0")
+    assert_nil Post.all.find_by("1 = 0")
   end
 
   test "find_by doesn't have implicit ordering" do
@@ -1718,7 +1640,7 @@ class RelationTest < ActiveRecord::TestCase
   end
 
   test "find_by! with multi-arg conditions returns the first matching record" do
-    assert_equal posts(:eager_other), Post.order(:id).find_by!('author_id = ?', 2)
+    assert_equal posts(:eager_other), Post.order(:id).find_by!("author_id = ?", 2)
   end
 
   test "find_by! doesn't have implicit ordering" do
@@ -1740,7 +1662,7 @@ class RelationTest < ActiveRecord::TestCase
     relation.to_a
 
     assert_raises(ActiveRecord::ImmutableRelation) do
-      relation.where! 'foo'
+      relation.where! "foo"
     end
   end
 
@@ -1758,7 +1680,7 @@ class RelationTest < ActiveRecord::TestCase
     relation.to_a
 
     assert_raises(ActiveRecord::ImmutableRelation) do
-      relation.merge! where: 'foo'
+      relation.merge! where: "foo"
     end
   end
 
@@ -1773,7 +1695,7 @@ class RelationTest < ActiveRecord::TestCase
 
   test "relations with cached arel can't be mutated [internal API]" do
     relation = Post.all
-    relation.count
+    relation.arel
 
     assert_raises(ActiveRecord::ImmutableRelation) { relation.limit!(5) }
     assert_raises(ActiveRecord::ImmutableRelation) { relation.where!("1 = 2") }
@@ -1789,6 +1711,12 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal "#<ActiveRecord::Relation [#{Post.limit(10).map(&:inspect).join(', ')}, ...]>", relation.inspect
   end
 
+  test "relations don't load all records in #inspect" do
+    assert_sql(/LIMIT|ROWNUM <=|FETCH FIRST/) do
+      Post.all.inspect
+    end
+  end
+
   test "already-loaded relations don't perform a new query in #inspect" do
     relation = Post.limit(2)
     relation.to_a
@@ -1800,19 +1728,27 @@ class RelationTest < ActiveRecord::TestCase
     end
   end
 
-  test 'using a custom table affects the wheres' do
-    table_alias = Post.arel_table.alias('omg_posts')
+  test "using a custom table affects the wheres" do
+    post = posts(:welcome)
 
-    table_metadata = ActiveRecord::TableMetadata.new(Post, table_alias)
-    predicate_builder = ActiveRecord::PredicateBuilder.new(table_metadata)
-    relation = ActiveRecord::Relation.new(Post, table_alias, predicate_builder)
-    relation.where!(:foo => "bar")
+    assert_equal post, custom_post_relation.where!(title: post.title).take
+  end
+
+  test "using a custom table with joins affects the joins" do
+    post = posts(:welcome)
+
+    assert_equal post, custom_post_relation.joins(:author).where!(title: post.title).take
+  end
 
-    node = relation.arel.constraints.first.grep(Arel::Attributes::Attribute).first
-    assert_equal table_alias, node.relation
+  test "arel_attribute respects a custom table" do
+    assert_equal [posts(:sti_comments)], custom_post_relation.ranked_by_comments.limit_by(1).to_a
   end
 
-  test '#load' do
+  test "alias_tracker respects a custom table" do
+    assert_equal posts(:welcome), custom_post_relation("categories_posts").joins(:categories).first
+  end
+
+  test "#load" do
     relation = Post.all
     assert_queries(1) do
       assert_equal relation, relation.load
@@ -1820,9 +1756,9 @@ class RelationTest < ActiveRecord::TestCase
     assert_no_queries { relation.to_a }
   end
 
-  test 'group with select and includes' do
-    authors_count = Post.select('author_id, COUNT(author_id) AS num_posts').
-      group('author_id').order('author_id').includes(:author).to_a
+  test "group with select and includes" do
+    authors_count = Post.select("author_id, COUNT(author_id) AS num_posts").
+      group("author_id").order("author_id").includes(:author).to_a
 
     assert_no_queries do
       result = authors_count.map do |post|
@@ -1843,46 +1779,114 @@ class RelationTest < ActiveRecord::TestCase
   test "delegations do not leak to other classes" do
     Topic.all.by_lifo
     assert Topic.all.class.method_defined?(:by_lifo)
-    assert !Post.all.respond_to?(:by_lifo)
+    assert_not_respond_to Post.all, :by_lifo
+  end
+
+  def test_unscope_with_subquery
+    p1 = Post.where(id: 1)
+    p2 = Post.where(id: 2)
+
+    assert_not_equal p1, p2
+
+    comments = Comment.where(post: p1).unscope(where: :post_id).where(post: p2)
+
+    assert_not_equal p1.first.comments, comments
+    assert_equal p2.first.comments, comments
+  end
+
+  def test_unscope_specific_where_value
+    posts = Post.where(title: "Welcome to the weblog", body: "Such a lovely day")
+
+    assert_equal 1, posts.count
+    assert_equal 1, posts.unscope(where: :title).count
+    assert_equal 1, posts.unscope(where: :body).count
   end
 
-  def test_unscope_removes_binds
-    left  = Post.where(id: Arel::Nodes::BindParam.new)
-    column = Post.columns_hash['id']
-    left.bind_values += [[column, 20]]
+  def test_locked_should_not_build_arel
+    posts = Post.locked
+    assert_predicate posts, :locked?
+    assert_nothing_raised { posts.lock!(false) }
+  end
 
-    relation = left.unscope(where: :id)
-    assert_equal [], relation.bind_values
+  def test_relation_join_method
+    assert_equal "Thank you for the welcome,Thank you again for the welcome", Post.first.comments.join(",")
   end
 
-  def test_merging_removes_rhs_bind_parameters
-    left  = Post.where(id: 20)
-    right   = Post.where(id: [1,2,3,4])
+  def test_relation_with_private_kernel_method
+    accounts = Account.all
+    assert_equal [accounts(:signals37)], accounts.open
+    assert_equal [accounts(:signals37)], accounts.available
+
+    sub_accounts = SubAccount.all
+    assert_equal [accounts(:signals37)], sub_accounts.open
+    assert_equal [accounts(:signals37)], sub_accounts.available
+  end
 
-    merged = left.merge(right)
-    assert_equal [], merged.bind_values
+  test "#skip_query_cache!" do
+    Post.cache do
+      assert_queries(1) do
+        Post.all.load
+        Post.all.load
+      end
+
+      assert_queries(2) do
+        Post.all.skip_query_cache!.load
+        Post.all.skip_query_cache!.load
+      end
+    end
   end
 
-  def test_merging_keeps_lhs_bind_parameters
-    binds = [ActiveRecord::Relation::QueryAttribute.new("id", 20, Post.type_for_attribute("id"))]
+  test "#skip_query_cache! with an eager load" do
+    Post.cache do
+      assert_queries(1) do
+        Post.eager_load(:comments).load
+        Post.eager_load(:comments).load
+      end
 
-    right  = Post.where(id: 20)
-    left   = Post.where(id: 10)
+      assert_queries(2) do
+        Post.eager_load(:comments).skip_query_cache!.load
+        Post.eager_load(:comments).skip_query_cache!.load
+      end
+    end
+  end
+
+  test "#skip_query_cache! with a preload" do
+    Post.cache do
+      assert_queries(2) do
+        Post.preload(:comments).load
+        Post.preload(:comments).load
+      end
 
-    merged = left.merge(right)
-    assert_equal binds, merged.bound_attributes
+      assert_queries(4) do
+        Post.preload(:comments).skip_query_cache!.load
+        Post.preload(:comments).skip_query_cache!.load
+      end
+    end
   end
 
-  def test_merging_reorders_bind_params
-    post  = Post.first
-    right = Post.where(id: post.id)
-    left  = Post.where(title: post.title)
+  test "#where with set" do
+    david = authors(:david)
+    mary = authors(:mary)
 
-    merged = left.merge(right)
-    assert_equal post, merged.first
+    authors = Author.where(name: ["David", "Mary"].to_set)
+    assert_equal [david, mary], authors
   end
 
-  def test_relation_join_method
-    assert_equal 'Thank you for the welcome,Thank you again for the welcome', Post.first.comments.join(",")
+  test "#where with empty set" do
+    authors = Author.where(name: Set.new)
+    assert_empty authors
   end
+
+  private
+    def custom_post_relation(alias_name = "omg_posts")
+      table_alias = Post.arel_table.alias(alias_name)
+      table_metadata = ActiveRecord::TableMetadata.new(Post, table_alias)
+      predicate_builder = ActiveRecord::PredicateBuilder.new(table_metadata)
+
+      ActiveRecord::Relation.create(
+        Post,
+        table: table_alias,
+        predicate_builder: predicate_builder
+      )
+    end
 end
diff --git a/activerecord/test/cases/reload_models_test.rb b/activerecord/test/cases/reload_models_test.rb
index 431fbf1297..72f4bfaf6d 100644
--- a/activerecord/test/cases/reload_models_test.rb
+++ b/activerecord/test/cases/reload_models_test.rb
@@ -1,22 +1,26 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/owner'
-require 'models/pet'
+require "models/owner"
+require "models/pet"
 
 class ReloadModelsTest < ActiveRecord::TestCase
+  include ActiveSupport::Testing::Isolation
+
   fixtures :pets, :owners
 
   def test_has_one_with_reload
-    pet = Pet.find_by_name('parrot')
-    pet.owner = Owner.find_by_name('ashley')
+    pet = Pet.find_by_name("parrot")
+    pet.owner = Owner.find_by_name("ashley")
 
     # Reload the class Owner, simulating auto-reloading of model classes in a
     # development environment. Note that meanwhile the class Pet is not
     # reloaded, simulating a class that is present in a plugin.
     Object.class_eval { remove_const :Owner }
-    Kernel.load(File.expand_path(File.join(File.dirname(__FILE__), "../models/owner.rb")))
+    Kernel.load(File.expand_path("../models/owner.rb", __dir__))
 
-    pet = Pet.find_by_name('parrot')
-    pet.owner = Owner.find_by_name('ashley')
-    assert_equal pet.owner, Owner.find_by_name('ashley')
+    pet = Pet.find_by_name("parrot")
+    pet.owner = Owner.find_by_name("ashley")
+    assert_equal pet.owner, Owner.find_by_name("ashley")
   end
-end
+end unless in_memory_db?
diff --git a/activerecord/test/cases/reserved_word_test.rb b/activerecord/test/cases/reserved_word_test.rb
new file mode 100644
index 0000000000..e32605fd11
--- /dev/null
+++ b/activerecord/test/cases/reserved_word_test.rb
@@ -0,0 +1,141 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+class ReservedWordTest < ActiveRecord::TestCase
+  self.use_instantiated_fixtures = true
+  self.use_transactional_tests = false
+
+  class Group < ActiveRecord::Base
+    Group.table_name = "group"
+    belongs_to :select
+    has_one :values
+  end
+
+  class Select < ActiveRecord::Base
+    Select.table_name = "select"
+    has_many :groups
+  end
+
+  class Values < ActiveRecord::Base
+    Values.table_name = "values"
+  end
+
+  class Distinct < ActiveRecord::Base
+    Distinct.table_name = "distinct"
+    has_and_belongs_to_many :selects
+    has_many :values, through: :groups
+  end
+
+  def setup
+    @connection = ActiveRecord::Base.connection
+    @connection.create_table :select, force: true
+    @connection.create_table :distinct, force: true
+    @connection.create_table :distinct_select, id: false, force: true do |t|
+      t.belongs_to :distinct
+      t.belongs_to :select
+    end
+    @connection.create_table :group, force: true do |t|
+      t.string :order
+      t.belongs_to :select
+    end
+    @connection.create_table :values, primary_key: :as, force: true do |t|
+      t.belongs_to :group
+    end
+  end
+
+  def teardown
+    @connection.drop_table :select, if_exists: true
+    @connection.drop_table :distinct, if_exists: true
+    @connection.drop_table :distinct_select, if_exists: true
+    @connection.drop_table :group, if_exists: true
+    @connection.drop_table :values, if_exists: true
+    @connection.drop_table :order, if_exists: true
+  end
+
+  def test_create_tables
+    assert_not @connection.table_exists?(:order)
+
+    @connection.create_table :order do |t|
+      t.string :group
+    end
+
+    assert @connection.table_exists?(:order)
+  end
+
+  def test_rename_tables
+    assert_nothing_raised { @connection.rename_table(:group, :order) }
+  end
+
+  def test_change_columns
+    assert_nothing_raised { @connection.change_column_default(:group, :order, "whatever") }
+    assert_nothing_raised { @connection.change_column("group", "order", :text, default: nil) }
+    assert_nothing_raised { @connection.rename_column(:group, :order, :values) }
+  end
+
+  def test_introspect
+    assert_equal ["id", "order", "select_id"], @connection.columns(:group).map(&:name).sort
+    assert_equal ["index_group_on_select_id"], @connection.indexes(:group).map(&:name).sort
+  end
+
+  def test_activerecord_model
+    x = Group.new
+    x.order = "x"
+    x.save!
+    x.order = "y"
+    x.save!
+    assert_equal x, Group.find_by_order("y")
+    assert_equal x, Group.find(x.id)
+  end
+
+  def test_delete_all_with_subselect
+    create_test_fixtures :values
+    assert_equal 1, Values.order(:as).limit(1).offset(1).delete_all
+    assert_raise(ActiveRecord::RecordNotFound) { Values.find(2) }
+    assert Values.find(1)
+  end
+
+  def test_has_one_associations
+    create_test_fixtures :group, :values
+    v = Group.find(1).values
+    assert_equal 2, v.id
+  end
+
+  def test_belongs_to_associations
+    create_test_fixtures :select, :group
+    gs = Select.find(2).groups
+    assert_equal 2, gs.length
+    assert_equal [2, 3], gs.collect(&:id).sort
+  end
+
+  def test_has_and_belongs_to_many
+    create_test_fixtures :select, :distinct, :distinct_select
+    s = Distinct.find(1).selects
+    assert_equal 2, s.length
+    assert_equal [1, 2], s.collect(&:id).sort
+  end
+
+  def test_activerecord_introspection
+    assert_predicate Group, :table_exists?
+    assert_equal ["id", "order", "select_id"], Group.columns.map(&:name).sort
+  end
+
+  def test_calculations_work_with_reserved_words
+    create_test_fixtures :group
+    assert_equal 3, Group.count
+  end
+
+  def test_associations_work_with_reserved_words
+    create_test_fixtures :select, :group
+    selects = Select.all.merge!(includes: [:groups]).to_a
+    assert_no_queries do
+      selects.each { |select| select.groups }
+    end
+  end
+
+  private
+    # custom fixture loader, uses FixtureSet#create_fixtures and appends base_path to the current file's path
+    def create_test_fixtures(*fixture_names)
+      ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT + "/reserved_words", fixture_names)
+    end
+end
diff --git a/activerecord/test/cases/result_test.rb b/activerecord/test/cases/result_test.rb
index dec01dfa76..825aee2423 100644
--- a/activerecord/test/cases/result_test.rb
+++ b/activerecord/test/cases/result_test.rb
@@ -1,44 +1,69 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
   class ResultTest < ActiveRecord::TestCase
     def result
-      Result.new(['col_1', 'col_2'], [
-        ['row 1 col 1', 'row 1 col 2'],
-        ['row 2 col 1', 'row 2 col 2'],
-        ['row 3 col 1', 'row 3 col 2'],
+      Result.new(["col_1", "col_2"], [
+        ["row 1 col 1", "row 1 col 2"],
+        ["row 2 col 1", "row 2 col 2"],
+        ["row 3 col 1", "row 3 col 2"],
       ])
     end
 
+    test "includes_column?" do
+      assert result.includes_column?("col_1")
+      assert_not result.includes_column?("foo")
+    end
+
     test "length" do
       assert_equal 3, result.length
     end
 
-    test "to_hash returns row_hashes" do
+    test "to_a returns row_hashes" do
       assert_equal [
-        {'col_1' => 'row 1 col 1', 'col_2' => 'row 1 col 2'},
-        {'col_1' => 'row 2 col 1', 'col_2' => 'row 2 col 2'},
-        {'col_1' => 'row 3 col 1', 'col_2' => 'row 3 col 2'},
-      ], result.to_hash
+        { "col_1" => "row 1 col 1", "col_2" => "row 1 col 2" },
+        { "col_1" => "row 2 col 1", "col_2" => "row 2 col 2" },
+        { "col_1" => "row 3 col 1", "col_2" => "row 3 col 2" },
+      ], result.to_a
+    end
+
+    test "to_hash (deprecated) returns row_hashes" do
+      assert_deprecated do
+        assert_equal [
+          { "col_1" => "row 1 col 1", "col_2" => "row 1 col 2" },
+          { "col_1" => "row 2 col 1", "col_2" => "row 2 col 2" },
+          { "col_1" => "row 3 col 1", "col_2" => "row 3 col 2" },
+        ], result.to_hash
+      end
+    end
+
+    test "first returns first row as a hash" do
+      assert_equal(
+        { "col_1" => "row 1 col 1", "col_2" => "row 1 col 2" }, result.first)
+    end
+
+    test "last returns last row as a hash" do
+      assert_equal(
+        { "col_1" => "row 3 col 1", "col_2" => "row 3 col 2" }, result.last)
     end
 
     test "each with block returns row hashes" do
       result.each do |row|
-        assert_equal ['col_1', 'col_2'], row.keys
+        assert_equal ["col_1", "col_2"], row.keys
       end
     end
 
     test "each without block returns an enumerator" do
       result.each.with_index do |row, index|
-        assert_equal ['col_1', 'col_2'], row.keys
+        assert_equal ["col_1", "col_2"], row.keys
         assert_kind_of Integer, index
       end
     end
 
-    if Enumerator.method_defined? :size
-      test "each without block returns a sized enumerator" do
-        assert_equal 3, result.each.size
-      end
+    test "each without block returns a sized enumerator" do
+      assert_equal 3, result.each.size
     end
 
     test "cast_values returns rows after type casting" do
diff --git a/activerecord/test/cases/sanitize_test.rb b/activerecord/test/cases/sanitize_test.rb
index 262e0abc22..778cf86ac3 100644
--- a/activerecord/test/cases/sanitize_test.rb
+++ b/activerecord/test/cases/sanitize_test.rb
@@ -1,7 +1,10 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/binary'
-require 'models/author'
-require 'models/post'
+require "models/binary"
+require "models/author"
+require "models/post"
+require "models/customer"
 
 class SanitizeTest < ActiveRecord::TestCase
   def setup
@@ -9,64 +12,174 @@ class SanitizeTest < ActiveRecord::TestCase
 
   def test_sanitize_sql_array_handles_string_interpolation
     quoted_bambi = ActiveRecord::Base.connection.quote_string("Bambi")
-    assert_equal "name=#{quoted_bambi}", Binary.send(:sanitize_sql_array, ["name=%s", "Bambi"])
-    assert_equal "name=#{quoted_bambi}", Binary.send(:sanitize_sql_array, ["name=%s", "Bambi".mb_chars])
+    assert_equal "name='#{quoted_bambi}'", Binary.sanitize_sql_array(["name='%s'", "Bambi"])
+    assert_equal "name='#{quoted_bambi}'", Binary.sanitize_sql_array(["name='%s'", "Bambi".mb_chars])
     quoted_bambi_and_thumper = ActiveRecord::Base.connection.quote_string("Bambi\nand\nThumper")
-    assert_equal "name=#{quoted_bambi_and_thumper}",Binary.send(:sanitize_sql_array, ["name=%s", "Bambi\nand\nThumper"])
-    assert_equal "name=#{quoted_bambi_and_thumper}",Binary.send(:sanitize_sql_array, ["name=%s", "Bambi\nand\nThumper".mb_chars])
+    assert_equal "name='#{quoted_bambi_and_thumper}'", Binary.sanitize_sql_array(["name='%s'", "Bambi\nand\nThumper"])
+    assert_equal "name='#{quoted_bambi_and_thumper}'", Binary.sanitize_sql_array(["name='%s'", "Bambi\nand\nThumper".mb_chars])
   end
 
   def test_sanitize_sql_array_handles_bind_variables
     quoted_bambi = ActiveRecord::Base.connection.quote("Bambi")
-    assert_equal "name=#{quoted_bambi}", Binary.send(:sanitize_sql_array, ["name=?", "Bambi"])
-    assert_equal "name=#{quoted_bambi}", Binary.send(:sanitize_sql_array, ["name=?", "Bambi".mb_chars])
+    assert_equal "name=#{quoted_bambi}", Binary.sanitize_sql_array(["name=?", "Bambi"])
+    assert_equal "name=#{quoted_bambi}", Binary.sanitize_sql_array(["name=?", "Bambi".mb_chars])
+    quoted_bambi_and_thumper = ActiveRecord::Base.connection.quote("Bambi\nand\nThumper")
+    assert_equal "name=#{quoted_bambi_and_thumper}", Binary.sanitize_sql_array(["name=?", "Bambi\nand\nThumper"])
+    assert_equal "name=#{quoted_bambi_and_thumper}", Binary.sanitize_sql_array(["name=?", "Bambi\nand\nThumper".mb_chars])
+  end
+
+  def test_sanitize_sql_array_handles_named_bind_variables
+    quoted_bambi = ActiveRecord::Base.connection.quote("Bambi")
+    assert_equal "name=#{quoted_bambi}", Binary.sanitize_sql_array(["name=:name", name: "Bambi"])
+    assert_equal "name=#{quoted_bambi} AND id=1", Binary.sanitize_sql_array(["name=:name AND id=:id", name: "Bambi", id: 1])
+
     quoted_bambi_and_thumper = ActiveRecord::Base.connection.quote("Bambi\nand\nThumper")
-    assert_equal "name=#{quoted_bambi_and_thumper}", Binary.send(:sanitize_sql_array, ["name=?", "Bambi\nand\nThumper"])
-    assert_equal "name=#{quoted_bambi_and_thumper}", Binary.send(:sanitize_sql_array, ["name=?", "Bambi\nand\nThumper".mb_chars])
+    assert_equal "name=#{quoted_bambi_and_thumper}", Binary.sanitize_sql_array(["name=:name", name: "Bambi\nand\nThumper"])
+    assert_equal "name=#{quoted_bambi_and_thumper} AND name2=#{quoted_bambi_and_thumper}", Binary.sanitize_sql_array(["name=:name AND name2=:name", name: "Bambi\nand\nThumper"])
   end
 
   def test_sanitize_sql_array_handles_relations
-    david = Author.create!(name: 'David')
+    david = Author.create!(name: "David")
     david_posts = david.posts.select(:id)
 
     sub_query_pattern = /\(\bselect\b.*?\bwhere\b.*?\)/i
 
-    select_author_sql = Post.send(:sanitize_sql_array, ['id in (?)', david_posts])
-    assert_match(sub_query_pattern, select_author_sql, 'should sanitize `Relation` as subquery for bind variables')
+    select_author_sql = Post.sanitize_sql_array(["id in (?)", david_posts])
+    assert_match(sub_query_pattern, select_author_sql, "should sanitize `Relation` as subquery for bind variables")
 
-    select_author_sql = Post.send(:sanitize_sql_array, ['id in (:post_ids)', post_ids: david_posts])
-    assert_match(sub_query_pattern, select_author_sql, 'should sanitize `Relation` as subquery for named bind variables')
+    select_author_sql = Post.sanitize_sql_array(["id in (:post_ids)", post_ids: david_posts])
+    assert_match(sub_query_pattern, select_author_sql, "should sanitize `Relation` as subquery for named bind variables")
   end
 
   def test_sanitize_sql_array_handles_empty_statement
-    select_author_sql = Post.send(:sanitize_sql_array, [''])
-    assert_equal('', select_author_sql)
+    select_author_sql = Post.sanitize_sql_array([""])
+    assert_equal("", select_author_sql)
   end
 
   def test_sanitize_sql_like
-    assert_equal '100\%', Binary.send(:sanitize_sql_like, '100%')
-    assert_equal 'snake\_cased\_string', Binary.send(:sanitize_sql_like, 'snake_cased_string')
-    assert_equal 'C:\\\\Programs\\\\MsPaint', Binary.send(:sanitize_sql_like, 'C:\\Programs\\MsPaint')
-    assert_equal 'normal string 42', Binary.send(:sanitize_sql_like, 'normal string 42')
+    assert_equal '100\%', Binary.sanitize_sql_like("100%")
+    assert_equal 'snake\_cased\_string', Binary.sanitize_sql_like("snake_cased_string")
+    assert_equal 'C:\\\\Programs\\\\MsPaint', Binary.sanitize_sql_like('C:\\Programs\\MsPaint')
+    assert_equal "normal string 42", Binary.sanitize_sql_like("normal string 42")
   end
 
   def test_sanitize_sql_like_with_custom_escape_character
-    assert_equal '100!%', Binary.send(:sanitize_sql_like, '100%', '!')
-    assert_equal 'snake!_cased!_string', Binary.send(:sanitize_sql_like, 'snake_cased_string', '!')
-    assert_equal 'great!!', Binary.send(:sanitize_sql_like, 'great!', '!')
-    assert_equal 'C:\\Programs\\MsPaint', Binary.send(:sanitize_sql_like, 'C:\\Programs\\MsPaint', '!')
-    assert_equal 'normal string 42', Binary.send(:sanitize_sql_like, 'normal string 42', '!')
+    assert_equal "100!%", Binary.sanitize_sql_like("100%", "!")
+    assert_equal "snake!_cased!_string", Binary.sanitize_sql_like("snake_cased_string", "!")
+    assert_equal "great!!", Binary.sanitize_sql_like("great!", "!")
+    assert_equal 'C:\\Programs\\MsPaint', Binary.sanitize_sql_like('C:\\Programs\\MsPaint', "!")
+    assert_equal "normal string 42", Binary.sanitize_sql_like("normal string 42", "!")
   end
 
   def test_sanitize_sql_like_example_use_case
     searchable_post = Class.new(Post) do
-      def self.search(term)
-        where("title LIKE ?", sanitize_sql_like(term, '!'))
+      def self.search_as_method(term)
+        where("title LIKE ?", sanitize_sql_like(term, "!"))
       end
+
+      scope :search_as_scope, -> (term) {
+        where("title LIKE ?", sanitize_sql_like(term, "!"))
+      }
+    end
+
+    assert_sql(/LIKE '20!% !_reduction!_!!'/) do
+      searchable_post.search_as_method("20% _reduction_!").to_a
     end
 
     assert_sql(/LIKE '20!% !_reduction!_!!'/) do
-      searchable_post.search("20% _reduction_!").to_a
+      searchable_post.search_as_scope("20% _reduction_!").to_a
+    end
+  end
+
+  def test_bind_arity
+    assert_nothing_raised                                { bind "" }
+    assert_raise(ActiveRecord::PreparedStatementInvalid) { bind "", 1 }
+
+    assert_raise(ActiveRecord::PreparedStatementInvalid) { bind "?" }
+    assert_nothing_raised                                { bind "?", 1 }
+    assert_raise(ActiveRecord::PreparedStatementInvalid) { bind "?", 1, 1 }
+  end
+
+  def test_named_bind_variables
+    assert_equal "1", bind(":a", a: 1) # ' ruby-mode
+    assert_equal "1 1", bind(":a :a", a: 1)  # ' ruby-mode
+
+    assert_nothing_raised { bind("'+00:00'", foo: "bar") }
+  end
+
+  def test_named_bind_arity
+    assert_nothing_raised                                { bind "name = :name", name: "37signals" }
+    assert_nothing_raised                                { bind "name = :name", name: "37signals", id: 1 }
+    assert_raise(ActiveRecord::PreparedStatementInvalid) { bind "name = :name", id: 1 }
+  end
+
+  class SimpleEnumerable
+    include Enumerable
+
+    def initialize(ary)
+      @ary = ary
+    end
+
+    def each(&b)
+      @ary.each(&b)
     end
   end
+
+  def test_bind_enumerable
+    quoted_abc = %(#{ActiveRecord::Base.connection.quote('a')},#{ActiveRecord::Base.connection.quote('b')},#{ActiveRecord::Base.connection.quote('c')})
+
+    assert_equal "1,2,3", bind("?", [1, 2, 3])
+    assert_equal quoted_abc, bind("?", %w(a b c))
+
+    assert_equal "1,2,3", bind(":a", a: [1, 2, 3])
+    assert_equal quoted_abc, bind(":a", a: %w(a b c)) # '
+
+    assert_equal "1,2,3", bind("?", SimpleEnumerable.new([1, 2, 3]))
+    assert_equal quoted_abc, bind("?", SimpleEnumerable.new(%w(a b c)))
+
+    assert_equal "1,2,3", bind(":a", a: SimpleEnumerable.new([1, 2, 3]))
+    assert_equal quoted_abc, bind(":a", a: SimpleEnumerable.new(%w(a b c))) # '
+  end
+
+  def test_bind_empty_enumerable
+    quoted_nil = ActiveRecord::Base.connection.quote(nil)
+    assert_equal quoted_nil, bind("?", [])
+    assert_equal " in (#{quoted_nil})", bind(" in (?)", [])
+    assert_equal "foo in (#{quoted_nil})", bind("foo in (?)", [])
+  end
+
+  def test_bind_empty_string
+    quoted_empty = ActiveRecord::Base.connection.quote("")
+    assert_equal quoted_empty, bind("?", "")
+  end
+
+  def test_bind_chars
+    quoted_bambi = ActiveRecord::Base.connection.quote("Bambi")
+    quoted_bambi_and_thumper = ActiveRecord::Base.connection.quote("Bambi\nand\nThumper")
+    assert_equal "name=#{quoted_bambi}", bind("name=?", "Bambi")
+    assert_equal "name=#{quoted_bambi_and_thumper}", bind("name=?", "Bambi\nand\nThumper")
+    assert_equal "name=#{quoted_bambi}", bind("name=?", "Bambi".mb_chars)
+    assert_equal "name=#{quoted_bambi_and_thumper}", bind("name=?", "Bambi\nand\nThumper".mb_chars)
+  end
+
+  def test_named_bind_with_postgresql_type_casts
+    l = Proc.new { bind(":a::integer '2009-01-01'::date", a: "10") }
+    assert_nothing_raised(&l)
+    assert_equal "#{ActiveRecord::Base.connection.quote('10')}::integer '2009-01-01'::date", l.call
+  end
+
+  def test_deprecated_expand_hash_conditions_for_aggregates
+    assert_deprecated do
+      assert_equal({ "balance" => 50 }, Customer.send(:expand_hash_conditions_for_aggregates, balance: Money.new(50)))
+    end
+  end
+
+  private
+    def bind(statement, *vars)
+      if vars.first.is_a?(Hash)
+        ActiveRecord::Base.send(:replace_named_bind_variables, statement, vars.first)
+      else
+        ActiveRecord::Base.send(:replace_bind_variables, statement, vars)
+      end
+    end
 end
diff --git a/activerecord/test/cases/schema_dumper_test.rb b/activerecord/test/cases/schema_dumper_test.rb
index feb1c29656..dda3efa47c 100644
--- a/activerecord/test/cases/schema_dumper_test.rb
+++ b/activerecord/test/cases/schema_dumper_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'support/schema_dumping_helper'
+require "support/schema_dumping_helper"
 
 class SchemaDumperTest < ActiveRecord::TestCase
   include SchemaDumpingHelper
@@ -17,10 +19,16 @@ class SchemaDumperTest < ActiveRecord::TestCase
     dump_all_table_schema []
   end
 
+  def test_dump_schema_information_with_empty_versions
+    ActiveRecord::SchemaMigration.delete_all
+    schema_info = ActiveRecord::Base.connection.dump_schema_information
+    assert_no_match(/INSERT INTO/, schema_info)
+  end
+
   def test_dump_schema_information_outputs_lexically_ordered_versions
     versions = %w{ 20100101010101 20100201010101 20100301010101 }
     versions.reverse_each do |v|
-      ActiveRecord::SchemaMigration.create!(:version => v)
+      ActiveRecord::SchemaMigration.create!(version: v)
     end
 
     schema_info = ActiveRecord::Base.connection.dump_schema_information
@@ -29,20 +37,18 @@ class SchemaDumperTest < ActiveRecord::TestCase
     ActiveRecord::SchemaMigration.delete_all
   end
 
-  def test_magic_comment
-    assert_match "# encoding: #{Encoding.default_external.name}", standard_dump
-  end
-
   def test_schema_dump
     output = standard_dump
     assert_match %r{create_table "accounts"}, output
     assert_match %r{create_table "authors"}, output
+    assert_no_match %r{(?<=, ) do \|t\|}, output
     assert_no_match %r{create_table "schema_migrations"}, output
+    assert_no_match %r{create_table "ar_internal_metadata"}, output
   end
 
   def test_schema_dump_uses_force_cascade_on_create_table
     output = dump_table_schema "authors"
-    assert_match %r{create_table "authors", force: :cascade}, output
+    assert_match %r{create_table "authors",.* force: :cascade}, output
   end
 
   def test_schema_dump_excludes_sqlite_sequence
@@ -55,38 +61,35 @@ class SchemaDumperTest < ActiveRecord::TestCase
     assert_match %r{create_table "CamelCase"}, output
   end
 
-  def assert_line_up(lines, pattern, required = false)
+  def assert_no_line_up(lines, pattern)
     return assert(true) if lines.empty?
     matches = lines.map { |line| line.match(pattern) }
-    assert matches.all? if required
     matches.compact!
     return assert(true) if matches.empty?
-    assert_equal 1, matches.map{ |match| match.offset(0).first }.uniq.length
+    line_matches = lines.map { |line| [line, line.match(pattern)] }.select { |line, match| match }
+    assert line_matches.all? { |line, match|
+      start = match.offset(0).first
+      line[start - 2..start - 1] == ", "
+    }
   end
 
   def column_definition_lines(output = standard_dump)
-    output.scan(/^( *)create_table.*?\n(.*?)^\1end/m).map{ |m| m.last.split(/\n/) }
+    output.scan(/^( *)create_table.*?\n(.*?)^\1end/m).map { |m| m.last.split(/\n/) }
   end
 
-  def test_types_line_up
+  def test_types_no_line_up
     column_definition_lines.each do |column_set|
       next if column_set.empty?
 
-      lengths = column_set.map do |column|
-        if match = column.match(/\bt\.\w+\s+"/)
-          match[0].length
-        end
-      end.compact
-
-      assert_equal 1, lengths.uniq.length
+      assert column_set.all? { |column| !column.match(/\bt\.\w+\s{2,}/) }
     end
   end
 
-  def test_arguments_line_up
+  def test_arguments_no_line_up
     column_definition_lines.each do |column_set|
-      assert_line_up(column_set, /default: /)
-      assert_line_up(column_set, /limit: /)
-      assert_line_up(column_set, /null: /)
+      assert_no_line_up(column_set, /default: /)
+      assert_no_line_up(column_set, /limit: /)
+      assert_no_line_up(column_set, /null: /)
     end
   end
 
@@ -103,61 +106,47 @@ class SchemaDumperTest < ActiveRecord::TestCase
   def test_schema_dump_includes_limit_constraint_for_integer_columns
     output = dump_all_table_schema([/^(?!integer_limits)/])
 
-    assert_match %r{c_int_without_limit}, output
+    assert_match %r{"c_int_without_limit"(?!.*limit)}, output
 
     if current_adapter?(:PostgreSQLAdapter)
-      assert_no_match %r{c_int_without_limit.*limit:}, output
-
       assert_match %r{c_int_1.*limit: 2}, output
       assert_match %r{c_int_2.*limit: 2}, output
 
       # int 3 is 4 bytes in postgresql
-      assert_match %r{c_int_3.*}, output
-      assert_no_match %r{c_int_3.*limit:}, output
-
-      assert_match %r{c_int_4.*}, output
-      assert_no_match %r{c_int_4.*limit:}, output
-    elsif current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-      assert_match %r{c_int_without_limit.*limit: 4}, output
-
+      assert_match %r{"c_int_3"(?!.*limit)}, output
+      assert_match %r{"c_int_4"(?!.*limit)}, output
+    elsif current_adapter?(:Mysql2Adapter)
       assert_match %r{c_int_1.*limit: 1}, output
       assert_match %r{c_int_2.*limit: 2}, output
       assert_match %r{c_int_3.*limit: 3}, output
 
-      assert_match %r{c_int_4.*}, output
-      assert_no_match %r{c_int_4.*:limit}, output
+      assert_match %r{"c_int_4"(?!.*limit)}, output
     elsif current_adapter?(:SQLite3Adapter)
-      assert_no_match %r{c_int_without_limit.*limit:}, output
-
       assert_match %r{c_int_1.*limit: 1}, output
       assert_match %r{c_int_2.*limit: 2}, output
       assert_match %r{c_int_3.*limit: 3}, output
       assert_match %r{c_int_4.*limit: 4}, output
     end
 
-    if current_adapter?(:SQLite3Adapter)
-      assert_match %r{c_int_5.*limit: 5}, output
-      assert_match %r{c_int_6.*limit: 6}, output
-      assert_match %r{c_int_7.*limit: 7}, output
-      assert_match %r{c_int_8.*limit: 8}, output
-    elsif current_adapter?(:OracleAdapter)
+    if current_adapter?(:SQLite3Adapter, :OracleAdapter)
       assert_match %r{c_int_5.*limit: 5}, output
       assert_match %r{c_int_6.*limit: 6}, output
       assert_match %r{c_int_7.*limit: 7}, output
       assert_match %r{c_int_8.*limit: 8}, output
     else
-      assert_match %r{c_int_5.*limit: 8}, output
-      assert_match %r{c_int_6.*limit: 8}, output
-      assert_match %r{c_int_7.*limit: 8}, output
-      assert_match %r{c_int_8.*limit: 8}, output
+      assert_match %r{t\.bigint\s+"c_int_5"$}, output
+      assert_match %r{t\.bigint\s+"c_int_6"$}, output
+      assert_match %r{t\.bigint\s+"c_int_7"$}, output
+      assert_match %r{t\.bigint\s+"c_int_8"$}, output
     end
   end
 
   def test_schema_dump_with_string_ignored_table
-    output = dump_all_table_schema(['accounts'])
+    output = dump_all_table_schema(["accounts"])
     assert_no_match %r{create_table "accounts"}, output
     assert_match %r{create_table "authors"}, output
     assert_no_match %r{create_table "schema_migrations"}, output
+    assert_no_match %r{create_table "ar_internal_metadata"}, output
   end
 
   def test_schema_dump_with_regexp_ignored_table
@@ -165,30 +154,51 @@ class SchemaDumperTest < ActiveRecord::TestCase
     assert_no_match %r{create_table "accounts"}, output
     assert_match %r{create_table "authors"}, output
     assert_no_match %r{create_table "schema_migrations"}, output
+    assert_no_match %r{create_table "ar_internal_metadata"}, output
   end
 
   def test_schema_dumps_index_columns_in_right_order
-    index_definition = standard_dump.split(/\n/).grep(/t\.index.*company_index/).first.strip
-    if current_adapter?(:MysqlAdapter, :Mysql2Adapter, :PostgreSQLAdapter)
-      assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index", using: :btree', index_definition
+    index_definition = dump_table_schema("companies").split(/\n/).grep(/t\.index.*company_index/).first.strip
+    if current_adapter?(:Mysql2Adapter)
+      if ActiveRecord::Base.connection.supports_index_sort_order?
+        assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index", length: { type: 10 }, order: { rating: :desc }', index_definition
+      else
+        assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index", length: { type: 10 }', index_definition
+      end
+    elsif ActiveRecord::Base.connection.supports_index_sort_order?
+      assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index", order: { rating: :desc }', index_definition
     else
       assert_equal 't.index ["firm_id", "type", "rating"], name: "company_index"', index_definition
     end
   end
 
   def test_schema_dumps_partial_indices
-    index_definition = standard_dump.split(/\n/).grep(/t\.index.*company_partial_index/).first.strip
-    if current_adapter?(:PostgreSQLAdapter)
-      assert_equal 't.index ["firm_id", "type"], name: "company_partial_index", where: "(rating > 10)", using: :btree', index_definition
-    elsif current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-      assert_equal 't.index ["firm_id", "type"], name: "company_partial_index", using: :btree', index_definition
-    elsif current_adapter?(:SQLite3Adapter) && ActiveRecord::Base.connection.supports_partial_index?
-      assert_equal 't.index ["firm_id", "type"], name: "company_partial_index", where: "rating > 10"', index_definition
+    index_definition = dump_table_schema("companies").split(/\n/).grep(/t\.index.*company_partial_index/).first.strip
+    if ActiveRecord::Base.connection.supports_partial_index?
+      assert_equal 't.index ["firm_id", "type"], name: "company_partial_index", where: "(rating > 10)"', index_definition
     else
       assert_equal 't.index ["firm_id", "type"], name: "company_partial_index"', index_definition
     end
   end
 
+  def test_schema_dumps_index_sort_order
+    index_definition = dump_table_schema("companies").split(/\n/).grep(/t\.index.*_name_and_rating/).first.strip
+    if ActiveRecord::Base.connection.supports_index_sort_order?
+      assert_equal 't.index ["name", "rating"], name: "index_companies_on_name_and_rating", order: :desc', index_definition
+    else
+      assert_equal 't.index ["name", "rating"], name: "index_companies_on_name_and_rating"', index_definition
+    end
+  end
+
+  def test_schema_dumps_index_length
+    index_definition = dump_table_schema("companies").split(/\n/).grep(/t\.index.*_name_and_description/).first.strip
+    if current_adapter?(:Mysql2Adapter)
+      assert_equal 't.index ["name", "description"], name: "index_companies_on_name_and_description", length: 10', index_definition
+    else
+      assert_equal 't.index ["name", "description"], name: "index_companies_on_name_and_description"', index_definition
+    end
+  end
+
   def test_schema_dump_should_honor_nonstandard_primary_keys
     output = standard_dump
     match = output.match(%r{create_table "movies"(.*)do})
@@ -197,16 +207,43 @@ class SchemaDumperTest < ActiveRecord::TestCase
   end
 
   def test_schema_dump_should_use_false_as_default
-    output = standard_dump
+    output = dump_table_schema "booleans"
     assert_match %r{t\.boolean\s+"has_fun",.+default: false}, output
   end
 
-  if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-    def test_schema_dump_should_add_default_value_for_mysql_text_field
-      output = standard_dump
-      assert_match %r{t\.text\s+"body",\s+limit: 65535,\s+null: false$}, output
+  def test_schema_dump_does_not_include_limit_for_text_field
+    output = dump_table_schema "admin_users"
+    assert_match %r{t\.text\s+"params"$}, output
+  end
+
+  def test_schema_dump_does_not_include_limit_for_binary_field
+    output = dump_table_schema "binaries"
+    assert_match %r{t\.binary\s+"data"$}, output
+  end
+
+  def test_schema_dump_does_not_include_limit_for_float_field
+    output = dump_table_schema "numeric_data"
+    assert_match %r{t\.float\s+"temperature"$}, output
+  end
+
+  if ActiveRecord::Base.connection.supports_expression_index?
+    def test_schema_dump_expression_indices
+      index_definition = dump_table_schema("companies").split(/\n/).grep(/t\.index.*company_expression_index/).first.strip
+      index_definition.sub!(/, name: "company_expression_index"\z/, "")
+
+      if current_adapter?(:PostgreSQLAdapter)
+        assert_match %r{CASE.+lower\(\(name\)::text\).+END\) DESC"\z}i, index_definition
+      elsif current_adapter?(:Mysql2Adapter)
+        assert_match %r{CASE.+lower\(`name`\).+END\) DESC"\z}i, index_definition
+      elsif current_adapter?(:SQLite3Adapter)
+        assert_match %r{CASE.+lower\(name\).+END\) DESC"\z}i, index_definition
+      else
+        assert false
+      end
     end
+  end
 
+  if current_adapter?(:Mysql2Adapter)
     def test_schema_dump_includes_length_for_mysql_binary_fields
       output = standard_dump
       assert_match %r{t\.binary\s+"var_binary",\s+limit: 255$}, output
@@ -215,12 +252,12 @@ class SchemaDumperTest < ActiveRecord::TestCase
 
     def test_schema_dump_includes_length_for_mysql_blob_and_text_fields
       output = standard_dump
-      assert_match %r{t\.binary\s+"tiny_blob",\s+limit: 255$}, output
-      assert_match %r{t\.binary\s+"normal_blob",\s+limit: 65535$}, output
+      assert_match %r{t\.blob\s+"tiny_blob",\s+limit: 255$}, output
+      assert_match %r{t\.binary\s+"normal_blob"$}, output
       assert_match %r{t\.binary\s+"medium_blob",\s+limit: 16777215$}, output
       assert_match %r{t\.binary\s+"long_blob",\s+limit: 4294967295$}, output
       assert_match %r{t\.text\s+"tiny_text",\s+limit: 255$}, output
-      assert_match %r{t\.text\s+"normal_text",\s+limit: 65535$}, output
+      assert_match %r{t\.text\s+"normal_text"$}, output
       assert_match %r{t\.text\s+"medium_text",\s+limit: 16777215$}, output
       assert_match %r{t\.text\s+"long_text",\s+limit: 4294967295$}, output
     end
@@ -231,9 +268,9 @@ class SchemaDumperTest < ActiveRecord::TestCase
     end
 
     def test_schema_dumps_index_type
-      output = standard_dump
-      assert_match %r{t\.index \["awesome"\], name: "index_key_tests_on_awesome", type: :fulltext}, output
-      assert_match %r{t\.index \["pizza"\], name: "index_key_tests_on_pizza", using: :btree}, output
+      output = dump_table_schema "key_tests"
+      assert_match %r{t\.index \["awesome"\], name: "index_key_tests_on_awesome", type: :fulltext$}, output
+      assert_match %r{t\.index \["pizza"\], name: "index_key_tests_on_pizza"$}, output
     end
   end
 
@@ -244,35 +281,62 @@ class SchemaDumperTest < ActiveRecord::TestCase
 
   if current_adapter?(:PostgreSQLAdapter)
     def test_schema_dump_includes_bigint_default
-      output = standard_dump
-      assert_match %r{t\.integer\s+"bigint_default",\s+limit: 8,\s+default: 0}, output
+      output = dump_table_schema "defaults"
+      assert_match %r{t\.bigint\s+"bigint_default",\s+default: 0}, output
     end
 
     def test_schema_dump_includes_limit_on_array_type
-      output = standard_dump
-      assert_match %r{t\.integer\s+"big_int_data_points\",\s+limit: 8,\s+array: true}, output
+      output = dump_table_schema "bigint_array"
+      assert_match %r{t\.bigint\s+"big_int_data_points\",\s+array: true}, output
     end
 
     def test_schema_dump_allows_array_of_decimal_defaults
-      output = standard_dump
+      output = dump_table_schema "bigint_array"
       assert_match %r{t\.decimal\s+"decimal_array_default",\s+default: \["1.23", "3.45"\],\s+array: true}, output
     end
 
-    if ActiveRecord::Base.connection.supports_extensions?
-      def test_schema_dump_includes_extensions
-        connection = ActiveRecord::Base.connection
+    def test_schema_dump_interval_type
+      output = dump_table_schema "postgresql_times"
+      assert_match %r{t\.interval\s+"time_interval"$}, output
+      assert_match %r{t\.interval\s+"scaled_time_interval",\s+precision: 6$}, output
+    end
+
+    def test_schema_dump_oid_type
+      output = dump_table_schema "postgresql_oids"
+      assert_match %r{t\.oid\s+"obj_id"$}, output
+    end
+
+    def test_schema_dump_includes_extensions
+      connection = ActiveRecord::Base.connection
 
-        connection.stubs(:extensions).returns(['hstore'])
+      connection.stub(:extensions, ["hstore"]) do
         output = perform_schema_dump
         assert_match "# These are extensions that must be enabled", output
         assert_match %r{enable_extension "hstore"}, output
+      end
 
-        connection.stubs(:extensions).returns([])
+      connection.stub(:extensions, []) do
         output = perform_schema_dump
         assert_no_match "# These are extensions that must be enabled", output
         assert_no_match %r{enable_extension}, output
       end
     end
+
+    def test_schema_dump_includes_extensions_in_alphabetic_order
+      connection = ActiveRecord::Base.connection
+
+      connection.stub(:extensions, ["hstore", "uuid-ossp", "xml2"]) do
+        output = perform_schema_dump
+        enabled_extensions = output.scan(%r{enable_extension "(.+)"}).flatten
+        assert_equal ["hstore", "uuid-ossp", "xml2"], enabled_extensions
+      end
+
+      connection.stub(:extensions, ["uuid-ossp", "xml2", "hstore"]) do
+        output = perform_schema_dump
+        enabled_extensions = output.scan(%r{enable_extension "(.+)"}).flatten
+        assert_equal ["hstore", "uuid-ossp", "xml2"], enabled_extensions
+      end
+    end
   end
 
   def test_schema_dump_keeps_large_precision_integer_columns_as_decimal
@@ -297,7 +361,7 @@ class SchemaDumperTest < ActiveRecord::TestCase
 
   def test_schema_dump_keeps_id_false_when_id_is_false_and_unique_not_null_column_added
     output = standard_dump
-    assert_match %r{create_table "subscribers", id: false}, output
+    assert_match %r{create_table "string_key_objects", id: false}, output
   end
 
   if ActiveRecord::Base.connection.supports_foreign_keys?
@@ -312,17 +376,17 @@ class SchemaDumperTest < ActiveRecord::TestCase
     end
   end
 
-  class CreateDogMigration < ActiveRecord::Migration
+  class CreateDogMigration < ActiveRecord::Migration::Current
     def up
       create_table("dog_owners") do |t|
       end
 
       create_table("dogs") do |t|
         t.column :name, :string
-        t.column :owner_id, :integer
+        t.references :owner
+        t.index [:name]
+        t.foreign_key :dog_owners, column: "owner_id"
       end
-      add_index "dogs", [:name]
-      add_foreign_key :dogs, :dog_owners, column: "owner_id" if supports_foreign_keys?
     end
     def down
       drop_table("dogs")
@@ -332,8 +396,8 @@ class SchemaDumperTest < ActiveRecord::TestCase
 
   def test_schema_dump_with_table_name_prefix_and_suffix
     original, $stdout = $stdout, StringIO.new
-    ActiveRecord::Base.table_name_prefix = 'foo_'
-    ActiveRecord::Base.table_name_suffix = '_bar'
+    ActiveRecord::Base.table_name_prefix = "foo_"
+    ActiveRecord::Base.table_name_suffix = "_bar"
 
     migration = CreateDogMigration.new
     migration.migrate(:up)
@@ -342,6 +406,7 @@ class SchemaDumperTest < ActiveRecord::TestCase
     assert_no_match %r{create_table "foo_.+_bar"}, output
     assert_no_match %r{add_index "foo_.+_bar"}, output
     assert_no_match %r{create_table "schema_migrations"}, output
+    assert_no_match %r{create_table "ar_internal_metadata"}, output
 
     if ActiveRecord::Base.connection.supports_foreign_keys?
       assert_no_match %r{add_foreign_key "foo_.+_bar"}, output
@@ -350,7 +415,64 @@ class SchemaDumperTest < ActiveRecord::TestCase
   ensure
     migration.migrate(:down)
 
-    ActiveRecord::Base.table_name_suffix = ActiveRecord::Base.table_name_prefix = ''
+    ActiveRecord::Base.table_name_suffix = ActiveRecord::Base.table_name_prefix = ""
+    $stdout = original
+  end
+
+  def test_schema_dump_with_table_name_prefix_and_suffix_regexp_escape
+    original, $stdout = $stdout, StringIO.new
+    ActiveRecord::Base.table_name_prefix = "foo$"
+    ActiveRecord::Base.table_name_suffix = "$bar"
+
+    migration = CreateDogMigration.new
+    migration.migrate(:up)
+
+    output = perform_schema_dump
+    assert_no_match %r{create_table "foo\$.+\$bar"}, output
+    assert_no_match %r{add_index "foo\$.+\$bar"}, output
+    assert_no_match %r{create_table "schema_migrations"}, output
+    assert_no_match %r{create_table "ar_internal_metadata"}, output
+
+    if ActiveRecord::Base.connection.supports_foreign_keys?
+      assert_no_match %r{add_foreign_key "foo\$.+\$bar"}, output
+      assert_no_match %r{add_foreign_key "[^"]+", "foo\$.+\$bar"}, output
+    end
+  ensure
+    migration.migrate(:down)
+
+    ActiveRecord::Base.table_name_suffix = ActiveRecord::Base.table_name_prefix = ""
+    $stdout = original
+  end
+
+  def test_schema_dump_with_table_name_prefix_and_ignoring_tables
+    original, $stdout = $stdout, StringIO.new
+
+    create_cat_migration = Class.new(ActiveRecord::Migration::Current) do
+      def change
+        create_table("cats") do |t|
+        end
+        create_table("omg_cats") do |t|
+        end
+      end
+    end
+
+    original_table_name_prefix = ActiveRecord::Base.table_name_prefix
+    original_schema_dumper_ignore_tables = ActiveRecord::SchemaDumper.ignore_tables
+    ActiveRecord::Base.table_name_prefix = "omg_"
+    ActiveRecord::SchemaDumper.ignore_tables = ["cats"]
+    migration = create_cat_migration.new
+    migration.migrate(:up)
+
+    stream = StringIO.new
+    output = ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, stream).string
+
+    assert_match %r{create_table "omg_cats"}, output
+    assert_no_match %r{create_table "cats"}, output
+  ensure
+    migration.migrate(:down)
+    ActiveRecord::Base.table_name_prefix = original_table_name_prefix
+    ActiveRecord::SchemaDumper.ignore_tables = original_schema_dumper_ignore_tables
+
     $stdout = original
   end
 end
@@ -360,25 +482,40 @@ class SchemaDumperDefaultsTest < ActiveRecord::TestCase
 
   setup do
     @connection = ActiveRecord::Base.connection
-    @connection.create_table :defaults, force: true do |t|
+    @connection.create_table :dump_defaults, force: true do |t|
       t.string   :string_with_default,   default: "Hello!"
-      t.date     :date_with_default,     default: '2014-06-05'
+      t.date     :date_with_default,     default: "2014-06-05"
       t.datetime :datetime_with_default, default: "2014-06-05 07:17:04"
       t.time     :time_with_default,     default: "07:17:04"
+      t.decimal  :decimal_with_default,  default: "1234567890.0123456789", precision: 20, scale: 10
+    end
+
+    if current_adapter?(:PostgreSQLAdapter)
+      @connection.create_table :infinity_defaults, force: true do |t|
+        t.float    :float_with_inf_default,    default: Float::INFINITY
+        t.float    :float_with_nan_default,    default: Float::NAN
+      end
     end
   end
 
   teardown do
-    return unless @connection
-    @connection.drop_table 'defaults', if_exists: true
+    @connection.drop_table "dump_defaults", if_exists: true
   end
 
   def test_schema_dump_defaults_with_universally_supported_types
-    output = dump_table_schema('defaults')
+    output = dump_table_schema("dump_defaults")
 
     assert_match %r{t\.string\s+"string_with_default",.*?default: "Hello!"}, output
-    assert_match %r{t\.date\s+"date_with_default",\s+default: '2014-06-05'}, output
-    assert_match %r{t\.datetime\s+"datetime_with_default",\s+default: '2014-06-05 07:17:04'}, output
-    assert_match %r{t\.time\s+"time_with_default",\s+default: '2000-01-01 07:17:04'}, output
+    assert_match %r{t\.date\s+"date_with_default",\s+default: "2014-06-05"}, output
+    assert_match %r{t\.datetime\s+"datetime_with_default",\s+default: "2014-06-05 07:17:04"}, output
+    assert_match %r{t\.time\s+"time_with_default",\s+default: "2000-01-01 07:17:04"}, output
+    assert_match %r{t\.decimal\s+"decimal_with_default",\s+precision: 20,\s+scale: 10,\s+default: "1234567890.0123456789"}, output
+  end
+
+  def test_schema_dump_with_float_column_infinity_default
+    skip unless current_adapter?(:PostgreSQLAdapter)
+    output = dump_table_schema("infinity_defaults")
+    assert_match %r{t\.float\s+"float_with_inf_default",\s+default: ::Float::INFINITY}, output
+    assert_match %r{t\.float\s+"float_with_nan_default",\s+default: ::Float::NAN}, output
   end
 end
diff --git a/activerecord/test/cases/schema_loading_test.rb b/activerecord/test/cases/schema_loading_test.rb
new file mode 100644
index 0000000000..f539156466
--- /dev/null
+++ b/activerecord/test/cases/schema_loading_test.rb
@@ -0,0 +1,54 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+
+module SchemaLoadCounter
+  extend ActiveSupport::Concern
+
+  module ClassMethods
+    attr_accessor :load_schema_calls
+
+    def load_schema!
+      self.load_schema_calls ||= 0
+      self.load_schema_calls += 1
+      super
+    end
+  end
+end
+
+class SchemaLoadingTest < ActiveRecord::TestCase
+  def test_basic_model_is_loaded_once
+    klass = define_model
+    klass.new
+    assert_equal 1, klass.load_schema_calls
+  end
+
+  def test_model_with_custom_lock_is_loaded_once
+    klass = define_model do |c|
+      c.table_name = :lock_without_defaults_cust
+      c.locking_column = :custom_lock_version
+    end
+    klass.new
+    assert_equal 1, klass.load_schema_calls
+  end
+
+  def test_model_with_changed_custom_lock_is_loaded_twice
+    klass = define_model do |c|
+      c.table_name = :lock_without_defaults_cust
+    end
+    klass.new
+    klass.locking_column = :custom_lock_version
+    klass.new
+    assert_equal 2, klass.load_schema_calls
+  end
+
+  private
+
+    def define_model
+      Class.new(ActiveRecord::Base) do
+        include SchemaLoadCounter
+        self.table_name = :lock_without_defaults
+        yield self if block_given?
+      end
+    end
+end
diff --git a/activerecord/test/cases/scoping/default_scoping_test.rb b/activerecord/test/cases/scoping/default_scoping_test.rb
index 0dbc60940e..6281712df6 100644
--- a/activerecord/test/cases/scoping/default_scoping_test.rb
+++ b/activerecord/test/cases/scoping/default_scoping_test.rb
@@ -1,14 +1,20 @@
-require 'cases/helper'
-require 'models/post'
-require 'models/comment'
-require 'models/developer'
-require 'models/computer'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/post"
+require "models/comment"
+require "models/developer"
+require "models/project"
+require "models/computer"
+require "models/vehicle"
+require "models/cat"
+require "concurrent/atomic/cyclic_barrier"
 
 class DefaultScopingTest < ActiveRecord::TestCase
   fixtures :developers, :posts, :comments
 
   def test_default_scope
-    expected = Developer.all.merge!(:order => 'salary DESC').to_a.collect(&:salary)
+    expected = Developer.all.merge!(order: "salary DESC").to_a.collect(&:salary)
     received = DeveloperOrderedBySalary.all.collect(&:salary)
     assert_equal expected, received
   end
@@ -47,59 +53,48 @@ class DefaultScopingTest < ActiveRecord::TestCase
   end
 
   def test_default_scope_with_conditions_string
-    assert_equal Developer.where(name: 'David').map(&:id).sort, DeveloperCalledDavid.all.map(&:id).sort
-    assert_equal nil, DeveloperCalledDavid.create!.name
+    assert_equal Developer.where(name: "David").map(&:id).sort, DeveloperCalledDavid.all.map(&:id).sort
+    assert_nil DeveloperCalledDavid.create!.name
   end
 
   def test_default_scope_with_conditions_hash
-    assert_equal Developer.where(name: 'Jamis').map(&:id).sort, DeveloperCalledJamis.all.map(&:id).sort
-    assert_equal 'Jamis', DeveloperCalledJamis.create!.name
-  end
-
-  unless in_memory_db?
-    def test_default_scoping_with_threads
-      2.times do
-        Thread.new {
-          assert DeveloperOrderedBySalary.all.to_sql.include?('salary DESC')
-          DeveloperOrderedBySalary.connection.close
-        }.join
-      end
-    end
+    assert_equal Developer.where(name: "Jamis").map(&:id).sort, DeveloperCalledJamis.all.map(&:id).sort
+    assert_equal "Jamis", DeveloperCalledJamis.create!.name
   end
 
   def test_default_scope_with_inheritance
     wheres = InheritedPoorDeveloperCalledJamis.all.where_values_hash
-    assert_equal "Jamis", wheres['name']
-    assert_equal 50000,   wheres['salary']
+    assert_equal "Jamis", wheres["name"]
+    assert_equal 50000,   wheres["salary"]
   end
 
   def test_default_scope_with_module_includes
     wheres = ModuleIncludedPoorDeveloperCalledJamis.all.where_values_hash
-    assert_equal "Jamis", wheres['name']
-    assert_equal 50000,   wheres['salary']
+    assert_equal "Jamis", wheres["name"]
+    assert_equal 50000,   wheres["salary"]
   end
 
   def test_default_scope_with_multiple_calls
     wheres = MultiplePoorDeveloperCalledJamis.all.where_values_hash
-    assert_equal "Jamis", wheres['name']
-    assert_equal 50000,   wheres['salary']
+    assert_equal "Jamis", wheres["name"]
+    assert_equal 50000,   wheres["salary"]
   end
 
   def test_scope_overwrites_default
-    expected = Developer.all.merge!(order: 'salary DESC, name DESC').to_a.collect(&:name)
+    expected = Developer.all.merge!(order: "salary DESC, name DESC").to_a.collect(&:name)
     received = DeveloperOrderedBySalary.by_name.to_a.collect(&:name)
     assert_equal expected, received
   end
 
   def test_reorder_overrides_default_scope_order
-    expected = Developer.order('name DESC').collect(&:name)
-    received = DeveloperOrderedBySalary.reorder('name DESC').collect(&:name)
+    expected = Developer.order("name DESC").collect(&:name)
+    received = DeveloperOrderedBySalary.reorder("name DESC").collect(&:name)
     assert_equal expected, received
   end
 
   def test_order_after_reorder_combines_orders
-    expected = Developer.order('name DESC, id DESC').collect { |dev| [dev.name, dev.id] }
-    received = Developer.order('name ASC').reorder('name DESC').order('id DESC').collect { |dev| [dev.name, dev.id] }
+    expected = Developer.order("name DESC, id DESC").collect { |dev| [dev.name, dev.id] }
+    received = Developer.order("name ASC").reorder("name DESC").order("id DESC").collect { |dev| [dev.name, dev.id] }
     assert_equal expected, received
   end
 
@@ -110,107 +105,107 @@ class DefaultScopingTest < ActiveRecord::TestCase
   end
 
   def test_unscope_after_reordering_and_combining
-    expected = Developer.order('id DESC, name DESC').collect { |dev| [dev.name, dev.id] }
-    received = DeveloperOrderedBySalary.reorder('name DESC').unscope(:order).order('id DESC, name DESC').collect { |dev| [dev.name, dev.id] }
+    expected = Developer.order("id DESC, name DESC").collect { |dev| [dev.name, dev.id] }
+    received = DeveloperOrderedBySalary.reorder("name DESC").unscope(:order).order("id DESC, name DESC").collect { |dev| [dev.name, dev.id] }
     assert_equal expected, received
 
     expected_2 = Developer.all.collect { |dev| [dev.name, dev.id] }
-    received_2 = Developer.order('id DESC, name DESC').unscope(:order).collect { |dev| [dev.name, dev.id] }
+    received_2 = Developer.order("id DESC, name DESC").unscope(:order).collect { |dev| [dev.name, dev.id] }
     assert_equal expected_2, received_2
 
     expected_3 = Developer.all.collect { |dev| [dev.name, dev.id] }
-    received_3 = Developer.reorder('name DESC').unscope(:order).collect { |dev| [dev.name, dev.id] }
+    received_3 = Developer.reorder("name DESC").unscope(:order).collect { |dev| [dev.name, dev.id] }
     assert_equal expected_3, received_3
   end
 
   def test_unscope_with_where_attributes
-    expected = Developer.order('salary DESC').collect(&:name)
-    received = DeveloperOrderedBySalary.where(name: 'David').unscope(where: :name).collect(&:name)
-    assert_equal expected, received
+    expected = Developer.order("salary DESC").collect(&:name)
+    received = DeveloperOrderedBySalary.where(name: "David").unscope(where: :name).collect(&:name)
+    assert_equal expected.sort, received.sort
 
-    expected_2 = Developer.order('salary DESC').collect(&:name)
-    received_2 = DeveloperOrderedBySalary.select("id").where("name" => "Jamis").unscope({:where => :name}, :select).collect(&:name)
-    assert_equal expected_2, received_2
+    expected_2 = Developer.order("salary DESC").collect(&:name)
+    received_2 = DeveloperOrderedBySalary.select("id").where("name" => "Jamis").unscope({ where: :name }, :select).collect(&:name)
+    assert_equal expected_2.sort, received_2.sort
 
-    expected_3 = Developer.order('salary DESC').collect(&:name)
+    expected_3 = Developer.order("salary DESC").collect(&:name)
     received_3 = DeveloperOrderedBySalary.select("id").where("name" => "Jamis").unscope(:select, :where).collect(&:name)
-    assert_equal expected_3, received_3
+    assert_equal expected_3.sort, received_3.sort
 
-    expected_4 = Developer.order('salary DESC').collect(&:name)
+    expected_4 = Developer.order("salary DESC").collect(&:name)
     received_4 = DeveloperOrderedBySalary.where.not("name" => "Jamis").unscope(where: :name).collect(&:name)
-    assert_equal expected_4, received_4
+    assert_equal expected_4.sort, received_4.sort
 
-    expected_5 = Developer.order('salary DESC').collect(&:name)
+    expected_5 = Developer.order("salary DESC").collect(&:name)
     received_5 = DeveloperOrderedBySalary.where.not("name" => ["Jamis", "David"]).unscope(where: :name).collect(&:name)
-    assert_equal expected_5, received_5
+    assert_equal expected_5.sort, received_5.sort
 
-    expected_6 = Developer.order('salary DESC').collect(&:name)
-    received_6 = DeveloperOrderedBySalary.where(Developer.arel_table['name'].eq('David')).unscope(where: :name).collect(&:name)
-    assert_equal expected_6, received_6
+    expected_6 = Developer.order("salary DESC").collect(&:name)
+    received_6 = DeveloperOrderedBySalary.where(Developer.arel_table["name"].eq("David")).unscope(where: :name).collect(&:name)
+    assert_equal expected_6.sort, received_6.sort
 
-    expected_7 = Developer.order('salary DESC').collect(&:name)
-    received_7 = DeveloperOrderedBySalary.where(Developer.arel_table[:name].eq('David')).unscope(where: :name).collect(&:name)
-    assert_equal expected_7, received_7
+    expected_7 = Developer.order("salary DESC").collect(&:name)
+    received_7 = DeveloperOrderedBySalary.where(Developer.arel_table[:name].eq("David")).unscope(where: :name).collect(&:name)
+    assert_equal expected_7.sort, received_7.sort
   end
 
   def test_unscope_comparison_where_clauses
     # unscoped for WHERE (`developers`.`id` <= 2)
-    expected = Developer.order('salary DESC').collect(&:name)
+    expected = Developer.order("salary DESC").collect(&:name)
     received = DeveloperOrderedBySalary.where(id: -Float::INFINITY..2).unscope(where: :id).collect { |dev| dev.name }
-    assert_equal expected, received
+    assert_equal expected.sort, received.sort
 
     # unscoped for WHERE (`developers`.`id` < 2)
-    expected = Developer.order('salary DESC').collect(&:name)
+    expected = Developer.order("salary DESC").collect(&:name)
     received = DeveloperOrderedBySalary.where(id: -Float::INFINITY...2).unscope(where: :id).collect { |dev| dev.name }
-    assert_equal expected, received
+    assert_equal expected.sort, received.sort
   end
 
   def test_unscope_multiple_where_clauses
-    expected = Developer.order('salary DESC').collect(&:name)
-    received = DeveloperOrderedBySalary.where(name: 'Jamis').where(id: 1).unscope(where: [:name, :id]).collect(&:name)
-    assert_equal expected, received
+    expected = Developer.order("salary DESC").collect(&:name)
+    received = DeveloperOrderedBySalary.where(name: "Jamis").where(id: 1).unscope(where: [:name, :id]).collect(&:name)
+    assert_equal expected.sort, received.sort
   end
 
   def test_unscope_string_where_clauses_involved
-    dev_relation = Developer.order('salary DESC').where("created_at > ?", 1.year.ago)
+    dev_relation = Developer.order("salary DESC").where("created_at > ?", 1.year.ago)
     expected = dev_relation.collect(&:name)
 
-    dev_ordered_relation = DeveloperOrderedBySalary.where(name: 'Jamis').where("created_at > ?", 1.year.ago)
+    dev_ordered_relation = DeveloperOrderedBySalary.where(name: "Jamis").where("created_at > ?", 1.year.ago)
     received = dev_ordered_relation.unscope(where: [:name]).collect(&:name)
 
-    assert_equal expected, received
+    assert_equal expected.sort, received.sort
   end
 
   def test_unscope_with_grouping_attributes
-    expected = Developer.order('salary DESC').collect(&:name)
+    expected = Developer.order("salary DESC").collect(&:name)
     received = DeveloperOrderedBySalary.group(:name).unscope(:group).collect(&:name)
-    assert_equal expected, received
+    assert_equal expected.sort, received.sort
 
-    expected_2 = Developer.order('salary DESC').collect(&:name)
+    expected_2 = Developer.order("salary DESC").collect(&:name)
     received_2 = DeveloperOrderedBySalary.group("name").unscope(:group).collect(&:name)
-    assert_equal expected_2, received_2
+    assert_equal expected_2.sort, received_2.sort
   end
 
   def test_unscope_with_limit_in_query
-    expected = Developer.order('salary DESC').collect(&:name)
+    expected = Developer.order("salary DESC").collect(&:name)
     received = DeveloperOrderedBySalary.limit(1).unscope(:limit).collect(&:name)
-    assert_equal expected, received
+    assert_equal expected.sort, received.sort
   end
 
   def test_order_to_unscope_reordering
-    scope = DeveloperOrderedBySalary.order('salary DESC, name ASC').reverse_order.unscope(:order)
-    assert !(scope.to_sql =~ /order/i)
+    scope = DeveloperOrderedBySalary.order("salary DESC, name ASC").reverse_order.unscope(:order)
+    assert_no_match(/order/i, scope.to_sql)
   end
 
   def test_unscope_reverse_order
     expected = Developer.all.collect(&:name)
-    received = Developer.order('salary DESC').reverse_order.unscope(:order).collect(&:name)
+    received = Developer.order("salary DESC").reverse_order.unscope(:order).collect(&:name)
     assert_equal expected, received
   end
 
   def test_unscope_select
-    expected = Developer.order('salary ASC').collect(&:name)
-    received = Developer.order('salary DESC').reverse_order.select(:name).unscope(:select).collect(&:name)
+    expected = Developer.order("salary ASC").collect(&:name)
+    received = Developer.order("salary DESC").reverse_order.select(:name).unscope(:select).collect(&:name)
     assert_equal expected, received
 
     expected_2 = Developer.all.collect(&:id)
@@ -226,7 +221,19 @@ class DefaultScopingTest < ActiveRecord::TestCase
 
   def test_unscope_joins_and_select_on_developers_projects
     expected = Developer.all.collect(&:name)
-    received = Developer.joins('JOIN developers_projects ON id = developer_id').select(:id).unscope(:joins, :select).collect(&:name)
+    received = Developer.joins("JOIN developers_projects ON id = developer_id").select(:id).unscope(:joins, :select).collect(&:name)
+    assert_equal expected, received
+  end
+
+  def test_unscope_left_outer_joins
+    expected = Developer.all.collect(&:name)
+    received = Developer.left_outer_joins(:projects).select(:id).unscope(:left_outer_joins, :select).collect(&:name)
+    assert_equal expected, received
+  end
+
+  def test_unscope_left_joins
+    expected = Developer.all.collect(&:name)
+    received = Developer.left_joins(:projects).select(:id).unscope(:left_joins, :select).collect(&:name)
     assert_equal expected, received
   end
 
@@ -247,8 +254,8 @@ class DefaultScopingTest < ActiveRecord::TestCase
       scope :by_name, -> name { unscope(where: :name).where(name: name) }
     end
 
-    expected = developer_klass.where(name: 'Jamis').collect { |dev| [dev.name, dev.id] }
-    received = developer_klass.where(name: 'David').by_name('Jamis').collect { |dev| [dev.name, dev.id] }
+    expected = developer_klass.where(name: "Jamis").collect { |dev| [dev.name, dev.id] }
+    received = developer_klass.where(name: "David").by_name("Jamis").collect { |dev| [dev.name, dev.id] }
     assert_equal expected, received
   end
 
@@ -262,11 +269,11 @@ class DefaultScopingTest < ActiveRecord::TestCase
     end
 
     assert_raises(ArgumentError) do
-      Developer.order('name DESC').reverse_order.unscope(:reverse_order)
+      Developer.order("name DESC").reverse_order.unscope(:reverse_order)
     end
 
     assert_raises(ArgumentError) do
-      Developer.order('name DESC').where(name: "Jamis").unscope()
+      Developer.order("name DESC").where(name: "Jamis").unscope()
     end
   end
 
@@ -296,40 +303,40 @@ class DefaultScopingTest < ActiveRecord::TestCase
 
   def test_unscope_merging
     merged = Developer.where(name: "Jamis").merge(Developer.unscope(:where))
-    assert merged.where_clause.empty?
-    assert !merged.where(name: "Jon").where_clause.empty?
+    assert_empty merged.where_clause
+    assert_not_empty merged.where(name: "Jon").where_clause
   end
 
   def test_order_in_default_scope_should_not_prevail
-    expected = Developer.all.merge!(order: 'salary desc').to_a.collect(&:salary)
-    received = DeveloperOrderedBySalary.all.merge!(order: 'salary').to_a.collect(&:salary)
+    expected = Developer.all.merge!(order: "salary desc").to_a.collect(&:salary)
+    received = DeveloperOrderedBySalary.all.merge!(order: "salary").to_a.collect(&:salary)
     assert_equal expected, received
   end
 
   def test_create_attribute_overwrites_default_scoping
-    assert_equal 'David', PoorDeveloperCalledJamis.create!(:name => 'David').name
-    assert_equal 200000, PoorDeveloperCalledJamis.create!(:name => 'David', :salary => 200000).salary
+    assert_equal "David", PoorDeveloperCalledJamis.create!(name: "David").name
+    assert_equal 200000, PoorDeveloperCalledJamis.create!(name: "David", salary: 200000).salary
   end
 
   def test_create_attribute_overwrites_default_values
-    assert_equal nil, PoorDeveloperCalledJamis.create!(:salary => nil).salary
-    assert_equal 50000, PoorDeveloperCalledJamis.create!(:name => 'David').salary
+    assert_nil PoorDeveloperCalledJamis.create!(salary: nil).salary
+    assert_equal 50000, PoorDeveloperCalledJamis.create!(name: "David").salary
   end
 
   def test_default_scope_attribute
-    jamis = PoorDeveloperCalledJamis.new(:name => 'David')
+    jamis = PoorDeveloperCalledJamis.new(name: "David")
     assert_equal 50000, jamis.salary
   end
 
   def test_where_attribute
-    aaron = PoorDeveloperCalledJamis.where(:salary => 20).new(:name => 'Aaron')
+    aaron = PoorDeveloperCalledJamis.where(salary: 20).new(name: "Aaron")
     assert_equal 20, aaron.salary
-    assert_equal 'Aaron', aaron.name
+    assert_equal "Aaron", aaron.name
   end
 
   def test_where_attribute_merge
-    aaron = PoorDeveloperCalledJamis.where(:name => 'foo').new(:name => 'Aaron')
-    assert_equal 'Aaron', aaron.name
+    aaron = PoorDeveloperCalledJamis.where(name: "foo").new(name: "Aaron")
+    assert_equal "Aaron", aaron.name
   end
 
   def test_scope_composed_by_limit_and_then_offset_is_equal_to_scope_composed_by_offset_and_then_limit
@@ -339,33 +346,53 @@ class DefaultScopingTest < ActiveRecord::TestCase
   end
 
   def test_create_with_merge
-    aaron = PoorDeveloperCalledJamis.create_with(:name => 'foo', :salary => 20).merge(
-              PoorDeveloperCalledJamis.create_with(:name => 'Aaron')).new
+    aaron = PoorDeveloperCalledJamis.create_with(name: "foo", salary: 20).merge(
+      PoorDeveloperCalledJamis.create_with(name: "Aaron")).new
     assert_equal 20, aaron.salary
-    assert_equal 'Aaron', aaron.name
+    assert_equal "Aaron", aaron.name
 
-    aaron = PoorDeveloperCalledJamis.create_with(:name => 'foo', :salary => 20).
-                                     create_with(:name => 'Aaron').new
+    aaron = PoorDeveloperCalledJamis.create_with(name: "foo", salary: 20).
+                                     create_with(name: "Aaron").new
     assert_equal 20, aaron.salary
-    assert_equal 'Aaron', aaron.name
+    assert_equal "Aaron", aaron.name
+  end
+
+  def test_create_with_using_both_string_and_symbol
+    jamis = PoorDeveloperCalledJamis.create_with(name: "foo").create_with("name" => "Aaron").new
+    assert_equal "Aaron", jamis.name
   end
 
   def test_create_with_reset
-    jamis = PoorDeveloperCalledJamis.create_with(:name => 'Aaron').create_with(nil).new
-    assert_equal 'Jamis', jamis.name
+    jamis = PoorDeveloperCalledJamis.create_with(name: "Aaron").create_with(nil).new
+    assert_equal "Jamis", jamis.name
+  end
+
+  def test_create_with_takes_precedence_over_where
+    developer = Developer.where(name: nil).create_with(name: "Aaron").new
+    assert_equal "Aaron", developer.name
+  end
+
+  def test_create_with_nested_attributes
+    assert_difference("Project.count", 1) do
+      Developer.create_with(
+        projects_attributes: [{ name: "p1" }]
+      ).scoping do
+        Developer.create!(name: "Aaron")
+      end
+    end
   end
 
   # FIXME: I don't know if this is *desired* behavior, but it is *today's*
   # behavior.
   def test_create_with_empty_hash_will_not_reset
-    jamis = PoorDeveloperCalledJamis.create_with(:name => 'Aaron').create_with({}).new
-    assert_equal 'Aaron', jamis.name
+    jamis = PoorDeveloperCalledJamis.create_with(name: "Aaron").create_with({}).new
+    assert_equal "Aaron", jamis.name
   end
 
   def test_unscoped_with_named_scope_should_not_have_default_scope
     assert_equal [DeveloperCalledJamis.find(developers(:poor_jamis).id)], DeveloperCalledJamis.poor
 
-    assert DeveloperCalledJamis.unscoped.poor.include?(developers(:david).becomes(DeveloperCalledJamis))
+    assert_includes DeveloperCalledJamis.unscoped.poor, developers(:david).becomes(DeveloperCalledJamis)
 
     assert_equal 11, DeveloperCalledJamis.unscoped.length
     assert_equal 1,  DeveloperCalledJamis.poor.length
@@ -373,6 +400,46 @@ class DefaultScopingTest < ActiveRecord::TestCase
     assert_equal 10, DeveloperCalledJamis.unscoped { DeveloperCalledJamis.poor }.length
   end
 
+  def test_default_scope_with_joins
+    assert_equal Comment.where(post_id: SpecialPostWithDefaultScope.pluck(:id)).count,
+                 Comment.joins(:special_post_with_default_scope).count
+    assert_equal Comment.where(post_id: Post.pluck(:id)).count,
+                 Comment.joins(:post).count
+  end
+
+  def test_joins_not_affected_by_scope_other_than_default_or_unscoped
+    without_scope_on_post = Comment.joins(:post).to_a
+    with_scope_on_post = nil
+    Post.where(id: [1, 5, 6]).scoping do
+      with_scope_on_post = Comment.joins(:post).to_a
+    end
+
+    assert_equal with_scope_on_post, without_scope_on_post
+  end
+
+  def test_unscoped_with_joins_should_not_have_default_scope
+    assert_equal SpecialPostWithDefaultScope.unscoped { Comment.joins(:special_post_with_default_scope).to_a },
+                 Comment.joins(:post).to_a
+  end
+
+  def test_sti_association_with_unscoped_not_affected_by_default_scope
+    post = posts(:thinking)
+    comments = [comments(:does_it_hurt)]
+
+    post.special_comments.update_all(deleted_at: Time.now)
+
+    assert_raises(ActiveRecord::RecordNotFound) { Post.joins(:special_comments).find(post.id) }
+    assert_equal [], post.special_comments
+
+    SpecialComment.unscoped do
+      assert_equal post, Post.joins(:special_comments).find(post.id)
+      assert_equal comments, Post.joins(:special_comments).find(post.id).special_comments
+      assert_equal comments, Post.eager_load(:special_comments).find(post.id).special_comments
+      assert_equal comments, Post.includes(:special_comments).find(post.id).special_comments
+      assert_equal comments, Post.preload(:special_comments).find(post.id).special_comments
+    end
+  end
+
   def test_default_scope_select_ignored_by_aggregations
     assert_equal DeveloperWithSelect.all.to_a.count, DeveloperWithSelect.count
   end
@@ -395,9 +462,9 @@ class DefaultScopingTest < ActiveRecord::TestCase
 
   def test_default_scope_include_with_count
     d = DeveloperWithIncludes.create!
-    d.audit_logs.create! :message => 'foo'
+    d.audit_logs.create! message: "foo"
 
-    assert_equal 1, DeveloperWithIncludes.where(:audit_logs => { :message => 'foo' }).count
+    assert_equal 1, DeveloperWithIncludes.where(audit_logs: { message: "foo" }).count
   end
 
   def test_default_scope_with_references_works_through_collection_association
@@ -418,24 +485,6 @@ class DefaultScopingTest < ActiveRecord::TestCase
     assert_equal comment, CommentWithDefaultScopeReferencesAssociation.find_by(id: comment.id)
   end
 
-  unless in_memory_db?
-    def test_default_scope_is_threadsafe
-      threads = []
-      assert_not_equal 1, ThreadsafeDeveloper.unscoped.count
-
-      threads << Thread.new do
-        Thread.current[:long_default_scope] = true
-        assert_equal 1, ThreadsafeDeveloper.all.to_a.count
-        ThreadsafeDeveloper.connection.close
-      end
-      threads << Thread.new do
-        assert_equal 1, ThreadsafeDeveloper.all.to_a.count
-        ThreadsafeDeveloper.connection.close
-      end
-      threads.each(&:join)
-    end
-  end
-
   test "additional conditions are ANDed with the default scope" do
     scope = DeveloperCalledJamis.where(name: "David")
     assert_equal 2, scope.where_clause.ast.children.length
@@ -451,6 +500,76 @@ class DefaultScopingTest < ActiveRecord::TestCase
   test "a scope can remove the condition from the default scope" do
     scope = DeveloperCalledJamis.david2
     assert_equal 1, scope.where_clause.ast.children.length
-    assert_equal Developer.where(name: "David"), scope
+    assert_equal Developer.where(name: "David").map(&:id), scope.map(&:id)
+  end
+
+  def test_with_abstract_class_where_clause_should_not_be_duplicated
+    scope = Bus.all
+    assert_equal scope.where_clause.ast.children.length, 1
+  end
+
+  def test_sti_conditions_are_not_carried_in_default_scope
+    ConditionalStiPost.create! body: ""
+    SubConditionalStiPost.create! body: ""
+    SubConditionalStiPost.create! title: "Hello world", body: ""
+
+    assert_equal 2, ConditionalStiPost.count
+    assert_equal 2, ConditionalStiPost.all.to_a.size
+    assert_equal 3, ConditionalStiPost.unscope(where: :title).to_a.size
+
+    assert_equal 1, SubConditionalStiPost.count
+    assert_equal 1, SubConditionalStiPost.all.to_a.size
+    assert_equal 2, SubConditionalStiPost.unscope(where: :title).to_a.size
+  end
+
+  def test_with_abstract_class_scope_should_be_executed_in_correct_context
+    vegetarian_pattern, gender_pattern = if current_adapter?(:Mysql2Adapter)
+      [/`lions`.`is_vegetarian`/, /`lions`.`gender`/]
+    elsif current_adapter?(:OracleAdapter)
+      [/"LIONS"."IS_VEGETARIAN"/, /"LIONS"."GENDER"/]
+    else
+      [/"lions"."is_vegetarian"/, /"lions"."gender"/]
+    end
+
+    assert_match vegetarian_pattern, Lion.all.to_sql
+    assert_match gender_pattern, Lion.female.to_sql
   end
 end
+
+class DefaultScopingWithThreadTest < ActiveRecord::TestCase
+  self.use_transactional_tests = false
+
+  def test_default_scoping_with_threads
+    2.times do
+      Thread.new {
+        assert_includes DeveloperOrderedBySalary.all.to_sql, "salary DESC"
+        DeveloperOrderedBySalary.connection.close
+      }.join
+    end
+  end
+
+  def test_default_scope_is_threadsafe
+    2.times { ThreadsafeDeveloper.unscoped.create! }
+
+    threads = []
+    assert_not_equal 1, ThreadsafeDeveloper.unscoped.count
+
+    barrier_1 = Concurrent::CyclicBarrier.new(2)
+    barrier_2 = Concurrent::CyclicBarrier.new(2)
+
+    threads << Thread.new do
+      Thread.current[:default_scope_delay] = -> { barrier_1.wait; barrier_2.wait }
+      assert_equal 1, ThreadsafeDeveloper.all.to_a.count
+      ThreadsafeDeveloper.connection.close
+    end
+    threads << Thread.new do
+      Thread.current[:default_scope_delay] = -> { barrier_2.wait }
+      barrier_1.wait
+      assert_equal 1, ThreadsafeDeveloper.all.to_a.count
+      ThreadsafeDeveloper.connection.close
+    end
+    threads.each(&:join)
+  ensure
+    ThreadsafeDeveloper.unscoped.destroy_all
+  end
+end unless in_memory_db?
diff --git a/activerecord/test/cases/scoping/named_scoping_test.rb b/activerecord/test/cases/scoping/named_scoping_test.rb
index e4cc533517..f707951a16 100644
--- a/activerecord/test/cases/scoping/named_scoping_test.rb
+++ b/activerecord/test/cases/scoping/named_scoping_test.rb
@@ -1,17 +1,19 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/topic'
-require 'models/comment'
-require 'models/reply'
-require 'models/author'
-require 'models/developer'
-require 'models/computer'
+require "models/post"
+require "models/topic"
+require "models/comment"
+require "models/reply"
+require "models/author"
+require "models/developer"
+require "models/computer"
 
 class NamedScopingTest < ActiveRecord::TestCase
   fixtures :posts, :authors, :topics, :comments, :author_addresses
 
   def test_implements_enumerable
-    assert !Topic.all.empty?
+    assert_not_empty Topic.all
 
     assert_equal Topic.all.to_a, Topic.base
     assert_equal Topic.all.to_a, Topic.base.to_a
@@ -23,8 +25,8 @@ class NamedScopingTest < ActiveRecord::TestCase
     all_posts = Topic.base
 
     assert_queries(1) do
-      all_posts.collect
-      all_posts.collect
+      all_posts.collect { true }
+      all_posts.collect { true }
     end
   end
 
@@ -33,12 +35,12 @@ class NamedScopingTest < ActiveRecord::TestCase
     all_posts.to_a
 
     new_post = Topic.create!
-    assert !all_posts.include?(new_post)
-    assert all_posts.reload.include?(new_post)
+    assert_not_includes all_posts, new_post
+    assert_includes all_posts.reload, new_post
   end
 
   def test_delegates_finds_and_calculations_to_the_base_class
-    assert !Topic.all.empty?
+    assert_not_empty Topic.all
 
     assert_equal Topic.all.to_a,                Topic.base.to_a
     assert_equal Topic.first,                   Topic.base.first
@@ -46,26 +48,33 @@ class NamedScopingTest < ActiveRecord::TestCase
     assert_equal Topic.average(:replies_count), Topic.base.average(:replies_count)
   end
 
+  def test_calling_merge_at_first_in_scope
+    Topic.class_eval do
+      scope :calling_merge_at_first_in_scope, Proc.new { merge(Topic.replied) }
+    end
+    assert_equal Topic.calling_merge_at_first_in_scope.to_a, Topic.replied.to_a
+  end
+
   def test_method_missing_priority_when_delegating
     klazz = Class.new(ActiveRecord::Base) do
       self.table_name = "topics"
-      scope :since, Proc.new { where('written_on >= ?', Time.now - 1.day) }
-      scope :to,    Proc.new { where('written_on <= ?', Time.now) }
+      scope :since, Proc.new { where("written_on >= ?", Time.now - 1.day) }
+      scope :to,    Proc.new { where("written_on <= ?", Time.now) }
     end
     assert_equal klazz.to.since.to_a, klazz.since.to.to_a
   end
 
   def test_scope_should_respond_to_own_methods_and_methods_of_the_proxy
-    assert Topic.approved.respond_to?(:limit)
-    assert Topic.approved.respond_to?(:count)
-    assert Topic.approved.respond_to?(:length)
+    assert_respond_to Topic.approved, :limit
+    assert_respond_to Topic.approved, :count
+    assert_respond_to Topic.approved, :length
   end
 
   def test_scopes_with_options_limit_finds_to_those_matching_the_criteria_specified
-    assert !Topic.all.merge!(:where => {:approved => true}).to_a.empty?
+    assert_not_empty Topic.all.merge!(where: { approved: true }).to_a
 
-    assert_equal Topic.all.merge!(:where => {:approved => true}).to_a, Topic.approved
-    assert_equal Topic.where(:approved => true).count, Topic.approved.count
+    assert_equal Topic.all.merge!(where: { approved: true }).to_a, Topic.approved
+    assert_equal Topic.where(approved: true).count, Topic.approved.count
   end
 
   def test_scopes_with_string_name_can_be_composed
@@ -75,17 +84,17 @@ class NamedScopingTest < ActiveRecord::TestCase
   end
 
   def test_scopes_are_composable
-    assert_equal((approved = Topic.all.merge!(:where => {:approved => true}).to_a), Topic.approved)
-    assert_equal((replied = Topic.all.merge!(:where => 'replies_count > 0').to_a), Topic.replied)
-    assert !(approved == replied)
-    assert !(approved & replied).empty?
+    assert_equal((approved = Topic.all.merge!(where: { approved: true }).to_a), Topic.approved)
+    assert_equal((replied = Topic.all.merge!(where: "replies_count > 0").to_a), Topic.replied)
+    assert_not (approved == replied)
+    assert_not_empty (approved & replied)
 
     assert_equal approved & replied, Topic.approved.replied
   end
 
   def test_procedural_scopes
-    topics_written_before_the_third = Topic.where('written_on < ?', topics(:third).written_on)
-    topics_written_before_the_second = Topic.where('written_on < ?', topics(:second).written_on)
+    topics_written_before_the_third = Topic.where("written_on < ?", topics(:third).written_on)
+    topics_written_before_the_second = Topic.where("written_on < ?", topics(:second).written_on)
     assert_not_equal topics_written_before_the_second, topics_written_before_the_third
 
     assert_equal topics_written_before_the_third, Topic.written_before(topics(:third).written_on)
@@ -101,31 +110,33 @@ class NamedScopingTest < ActiveRecord::TestCase
   def test_scope_with_object
     objects = Topic.with_object
     assert_operator objects.length, :>, 0
-    assert objects.all?(&:approved?), 'all objects should be approved'
+    assert objects.all?(&:approved?), "all objects should be approved"
   end
 
   def test_has_many_associations_have_access_to_scopes
     assert_not_equal Post.containing_the_letter_a, authors(:david).posts
-    assert !Post.containing_the_letter_a.empty?
+    assert_not_empty Post.containing_the_letter_a
 
-    assert_equal authors(:david).posts & Post.containing_the_letter_a, authors(:david).posts.containing_the_letter_a
+    expected = authors(:david).posts & Post.containing_the_letter_a
+    assert_equal expected.sort_by(&:id), authors(:david).posts.containing_the_letter_a.sort_by(&:id)
   end
 
   def test_scope_with_STI
-    assert_equal 3,Post.containing_the_letter_a.count
-    assert_equal 1,SpecialPost.containing_the_letter_a.count
+    assert_equal 3, Post.containing_the_letter_a.count
+    assert_equal 1, SpecialPost.containing_the_letter_a.count
   end
 
   def test_has_many_through_associations_have_access_to_scopes
     assert_not_equal Comment.containing_the_letter_e, authors(:david).comments
-    assert !Comment.containing_the_letter_e.empty?
+    assert_not_empty Comment.containing_the_letter_e
 
-    assert_equal authors(:david).comments & Comment.containing_the_letter_e, authors(:david).comments.containing_the_letter_e
+    expected = authors(:david).comments & Comment.containing_the_letter_e
+    assert_equal expected.sort_by(&:id), authors(:david).comments.containing_the_letter_e.sort_by(&:id)
   end
 
   def test_scopes_honor_current_scopes_from_when_defined
-    assert !Post.ranked_by_comments.limit_by(5).empty?
-    assert !authors(:david).posts.ranked_by_comments.limit_by(5).empty?
+    assert_not_empty Post.ranked_by_comments.limit_by(5)
+    assert_not_empty authors(:david).posts.ranked_by_comments.limit_by(5)
     assert_not_equal Post.ranked_by_comments.limit_by(5), authors(:david).posts.ranked_by_comments.limit_by(5)
     assert_not_equal Post.top(5), authors(:david).posts.top(5)
     # Oracle sometimes sorts differently if WHERE condition is changed
@@ -140,27 +151,43 @@ class NamedScopingTest < ActiveRecord::TestCase
     assert_equal "The scope body needs to be callable.", e.message
   end
 
+  def test_scopes_name_is_relation_method
+    conflicts = [
+      :records,
+      :to_ary,
+      :to_sql,
+      :explain
+    ]
+
+    conflicts.each do |name|
+      e = assert_raises ArgumentError do
+        Class.new(Post).class_eval { scope name, -> { where(approved: true) } }
+      end
+      assert_match(/You tried to define a scope named \"#{name}\" on the model/, e.message)
+    end
+  end
+
   def test_active_records_have_scope_named__all__
-    assert !Topic.all.empty?
+    assert_not_empty Topic.all
 
     assert_equal Topic.all.to_a, Topic.base
   end
 
   def test_active_records_have_scope_named__scoped__
     scope = Topic.where("content LIKE '%Have%'")
-    assert !scope.empty?
+    assert_not_empty scope
 
     assert_equal scope, Topic.all.merge!(where: "content LIKE '%Have%'")
   end
 
   def test_first_and_last_should_allow_integers_for_limit
-    assert_equal Topic.base.first(2), Topic.base.to_a.first(2)
+    assert_equal Topic.base.first(2), Topic.base.order("id").to_a.first(2)
     assert_equal Topic.base.last(2), Topic.base.order("id").to_a.last(2)
   end
 
   def test_first_and_last_should_not_use_query_when_results_are_loaded
     topics = Topic.base
-    topics.reload # force load
+    topics.load # force load
     assert_no_queries do
       topics.first
       topics.last
@@ -171,7 +198,7 @@ class NamedScopingTest < ActiveRecord::TestCase
     topics = Topic.base
     assert_queries(2) do
       topics.empty?  # use count query
-      topics.collect # force load
+      topics.load    # force load
       topics.empty?  # use loaded (no query)
     end
   end
@@ -180,7 +207,7 @@ class NamedScopingTest < ActiveRecord::TestCase
     topics = Topic.base
     assert_queries(2) do
       topics.any?    # use count query
-      topics.collect # force load
+      topics.load    # force load
       topics.any?    # use loaded (no query)
     end
   end
@@ -188,28 +215,29 @@ class NamedScopingTest < ActiveRecord::TestCase
   def test_any_should_call_proxy_found_if_using_a_block
     topics = Topic.base
     assert_queries(1) do
-      topics.expects(:empty?).never
-      topics.any? { true }
+      assert_not_called(topics, :empty?) do
+        topics.any? { true }
+      end
     end
   end
 
   def test_any_should_not_fire_query_if_scope_loaded
     topics = Topic.base
-    topics.collect # force load
+    topics.load # force load
     assert_no_queries { assert topics.any? }
   end
 
   def test_model_class_should_respond_to_any
-    assert Topic.any?
+    assert_predicate Topic, :any?
     Topic.delete_all
-    assert !Topic.any?
+    assert_not_predicate Topic, :any?
   end
 
   def test_many_should_not_load_results
     topics = Topic.base
     assert_queries(2) do
       topics.many?   # use count query
-      topics.collect # force load
+      topics.load    # force load
       topics.many?   # use loaded (no query)
     end
   end
@@ -217,35 +245,36 @@ class NamedScopingTest < ActiveRecord::TestCase
   def test_many_should_call_proxy_found_if_using_a_block
     topics = Topic.base
     assert_queries(1) do
-      topics.expects(:size).never
-      topics.many? { true }
+      assert_not_called(topics, :size) do
+        topics.many? { true }
+      end
     end
   end
 
   def test_many_should_not_fire_query_if_scope_loaded
     topics = Topic.base
-    topics.collect # force load
+    topics.load # force load
     assert_no_queries { assert topics.many? }
   end
 
   def test_many_should_return_false_if_none_or_one
-    topics = Topic.base.where(:id => 0)
-    assert !topics.many?
-    topics = Topic.base.where(:id => 1)
-    assert !topics.many?
+    topics = Topic.base.where(id: 0)
+    assert_not_predicate topics, :many?
+    topics = Topic.base.where(id: 1)
+    assert_not_predicate topics, :many?
   end
 
   def test_many_should_return_true_if_more_than_one
-    assert Topic.base.many?
+    assert_predicate Topic.base, :many?
   end
 
   def test_model_class_should_respond_to_many
     Topic.delete_all
-    assert !Topic.many?
+    assert_not_predicate Topic, :many?
     Topic.create!
-    assert !Topic.many?
+    assert_not_predicate Topic, :many?
     Topic.create!
-    assert Topic.many?
+    assert_predicate Topic, :many?
   end
 
   def test_should_build_on_top_of_scope
@@ -271,7 +300,14 @@ class NamedScopingTest < ActiveRecord::TestCase
   def test_should_build_on_top_of_chained_scopes
     topic = Topic.approved.by_lifo.build({})
     assert topic.approved
-    assert_equal 'lifo', topic.author_name
+    assert_equal "lifo", topic.author_name
+  end
+
+  def test_deprecated_delegating_private_method
+    assert_deprecated do
+      scope = Topic.all.by_private_lifo
+      assert_not scope.instance_variable_get(:@delegate_to_klass)
+    end
   end
 
   def test_reserved_scope_names
@@ -299,7 +335,7 @@ class NamedScopingTest < ActiveRecord::TestCase
       :relation,      # private class method on AR::Base
       :new,           # redefined class method on AR::Base
       :all,           # a default scope
-      :public,        # some imporant methods on Module and Class
+      :public,        # some important methods on Module and Class
       :protected,
       :private,
       :name,
@@ -318,12 +354,12 @@ class NamedScopingTest < ActiveRecord::TestCase
 
     conflicts.each do |name|
       e = assert_raises(ArgumentError, "scope `#{name}` should not be allowed") do
-        klass.class_eval { scope name, ->{ where(approved: true) } }
+        klass.class_eval { scope name, -> { where(approved: true) } }
       end
       assert_match(/You tried to define a scope named \"#{name}\" on the model/, e.message)
 
       e = assert_raises(ArgumentError, "scope `#{name}` should not be allowed") do
-        subklass.class_eval { scope name, ->{ where(approved: true) } }
+        subklass.class_eval { scope name, -> { where(approved: true) } }
       end
       assert_match(/You tried to define a scope named \"#{name}\" on the model/, e.message)
     end
@@ -331,12 +367,12 @@ class NamedScopingTest < ActiveRecord::TestCase
     non_conflicts.each do |name|
       assert_nothing_raised do
         silence_warnings do
-          klass.class_eval { scope name, ->{ where(approved: true) } }
+          klass.class_eval { scope name, -> { where(approved: true) } }
         end
       end
 
       assert_nothing_raised do
-        subklass.class_eval { scope name, ->{ where(approved: true) } }
+        subklass.class_eval { scope name, -> { where(approved: true) } }
       end
     end
   end
@@ -348,7 +384,7 @@ class NamedScopingTest < ActiveRecord::TestCase
     klass = Class.new(ActiveRecord::Base) do
       self.table_name = "topics"
       scope :"title containing space", -> { where("title LIKE '% %'") }
-      scope :approved, -> { where(:approved => true) }
+      scope :approved, -> { where(approved: true) }
     end
     assert_equal klass.send(:"title containing space"), klass.where("title LIKE '% %'")
     assert_equal klass.approved.send(:"title containing space"), klass.approved.where("title LIKE '% %'")
@@ -363,7 +399,7 @@ class NamedScopingTest < ActiveRecord::TestCase
   end
 
   def test_should_use_where_in_query_for_scope
-    assert_equal Developer.where(name: 'Jamis').to_set, Developer.where(id: Developer.jamises).to_set
+    assert_equal Developer.where(name: "Jamis").to_set, Developer.where(id: Developer.jamises).to_set
   end
 
   def test_size_should_use_count_when_results_are_not_loaded
@@ -375,7 +411,7 @@ class NamedScopingTest < ActiveRecord::TestCase
 
   def test_size_should_use_length_when_results_are_loaded
     topics = Topic.base
-    topics.reload # force load
+    topics.load # force load
     assert_no_queries do
       topics.size # use loaded (no query)
     end
@@ -394,16 +430,16 @@ class NamedScopingTest < ActiveRecord::TestCase
 
   def test_chaining_applies_last_conditions_when_creating
     post = Topic.rejected.new
-    assert !post.approved?
+    assert_not_predicate post, :approved?
 
     post = Topic.rejected.approved.new
-    assert post.approved?
+    assert_predicate post, :approved?
 
     post = Topic.approved.rejected.new
-    assert !post.approved?
+    assert_not_predicate post, :approved?
 
     post = Topic.approved.rejected.approved.new
-    assert post.approved?
+    assert_predicate post, :approved?
   end
 
   def test_chaining_combines_conditions_when_searching
@@ -422,12 +458,12 @@ class NamedScopingTest < ActiveRecord::TestCase
     assert_equal 4, Topic.approved.count
 
     assert_queries(5) do
-      Topic.approved.find_each(:batch_size => 1) {|t| assert t.approved? }
+      Topic.approved.find_each(batch_size: 1) { |t| assert t.approved? }
     end
 
     assert_queries(3) do
-      Topic.approved.find_in_batches(:batch_size => 2) do |group|
-        group.each {|t| assert t.approved? }
+      Topic.approved.find_in_batches(batch_size: 2) do |group|
+        group.each { |t| assert t.approved? }
       end
     end
   end
@@ -438,9 +474,29 @@ class NamedScopingTest < ActiveRecord::TestCase
     end
   end
 
+  def test_scopes_with_reserved_names
+    class << Topic
+      def public_method; end
+      public :public_method
+
+      def protected_method; end
+      protected :protected_method
+
+      def private_method; end
+      private :private_method
+    end
+
+    [:public_method, :protected_method, :private_method].each do |reserved_method|
+      assert Topic.respond_to?(reserved_method, true)
+      assert_called(ActiveRecord::Base.logger, :warn) do
+        silence_warnings { Topic.scope(reserved_method, -> { }) }
+      end
+    end
+  end
+
   def test_scopes_on_relations
     # Topic.replied
-    approved_topics = Topic.all.approved.order('id DESC')
+    approved_topics = Topic.all.approved.order("id DESC")
     assert_equal topics(:fifth), approved_topics.first
 
     replied_approved_topics = approved_topics.replied
@@ -448,9 +504,9 @@ class NamedScopingTest < ActiveRecord::TestCase
   end
 
   def test_index_on_scope
-    approved = Topic.approved.order('id ASC')
+    approved = Topic.approved.order("id ASC")
     assert_equal topics(:second), approved[0]
-    assert approved.loaded?
+    assert_predicate approved, :loaded?
   end
 
   def test_nested_scopes_queries_size
@@ -489,7 +545,7 @@ class NamedScopingTest < ActiveRecord::TestCase
   def test_scopes_to_get_newest
     post = posts(:welcome)
     old_last_comment = post.comments.newest
-    new_comment = post.comments.create(:body => "My new comment")
+    new_comment = post.comments.create(body: "My new comment")
     assert_equal new_comment, post.comments.newest
     assert_not_equal old_last_comment, post.comments.newest
   end
@@ -512,15 +568,34 @@ class NamedScopingTest < ActiveRecord::TestCase
 
   def test_eager_default_scope_relations_are_remove
     klass = Class.new(ActiveRecord::Base)
-    klass.table_name = 'posts'
+    klass.table_name = "posts"
 
     assert_raises(ArgumentError) do
-      klass.send(:default_scope, klass.where(:id => posts(:welcome).id))
+      klass.send(:default_scope, klass.where(id: posts(:welcome).id))
     end
   end
 
   def test_subclass_merges_scopes_properly
-    assert_equal 1, SpecialComment.where(body: 'go crazy').created.count
+    assert_equal 1, SpecialComment.where(body: "go crazy").created.count
   end
 
+  def test_model_class_should_respond_to_extending
+    assert_raises OopsError do
+      Comment.unscoped.oops_comments.destroy_all
+    end
+  end
+
+  def test_model_class_should_respond_to_none
+    assert_not_predicate Topic, :none?
+    Topic.delete_all
+    assert_predicate Topic, :none?
+  end
+
+  def test_model_class_should_respond_to_one
+    assert_not_predicate Topic, :one?
+    Topic.delete_all
+    assert_not_predicate Topic, :one?
+    Topic.create!
+    assert_predicate Topic, :one?
+  end
 end
diff --git a/activerecord/test/cases/scoping/relation_scoping_test.rb b/activerecord/test/cases/scoping/relation_scoping_test.rb
index 4bfffbe9c6..b4f4379e5e 100644
--- a/activerecord/test/cases/scoping/relation_scoping_test.rb
+++ b/activerecord/test/cases/scoping/relation_scoping_test.rb
@@ -1,16 +1,18 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/post'
-require 'models/author'
-require 'models/developer'
-require 'models/computer'
-require 'models/project'
-require 'models/comment'
-require 'models/category'
-require 'models/person'
-require 'models/reference'
+require "models/post"
+require "models/author"
+require "models/developer"
+require "models/computer"
+require "models/project"
+require "models/comment"
+require "models/category"
+require "models/person"
+require "models/reference"
 
 class RelationScopingTest < ActiveRecord::TestCase
-  fixtures :authors, :developers, :projects, :comments, :posts, :developers_projects
+  fixtures :authors, :author_addresses, :developers, :projects, :comments, :posts, :developers_projects
 
   setup do
     developers(:david)
@@ -28,7 +30,7 @@ class RelationScopingTest < ActiveRecord::TestCase
   def test_scope_breaks_caching_on_collections
     author = authors :david
     ids = author.reload.special_posts_with_default_scope.map(&:id)
-    assert_equal [1,5,6], ids.sort
+    assert_equal [1, 5, 6], ids.sort
     scoped_posts = SpecialPostWithDefaultScope.unscoped do
       author = authors :david
       author.reload.special_posts_with_default_scope.to_a
@@ -103,13 +105,13 @@ class RelationScopingTest < ActiveRecord::TestCase
     Developer.select("id, name").scoping do
       developer = Developer.where("name = 'David'").first
       assert_equal "David", developer.name
-      assert !developer.has_attribute?(:salary)
+      assert_not developer.has_attribute?(:salary)
     end
   end
 
   def test_scope_select_concatenates
     Developer.select("id, name").scoping do
-      developer = Developer.select('salary').where("name = 'David'").first
+      developer = Developer.select("salary").where("name = 'David'").first
       assert_equal 80000, developer.salary
       assert developer.has_attribute?(:id)
       assert developer.has_attribute?(:name)
@@ -122,7 +124,7 @@ class RelationScopingTest < ActiveRecord::TestCase
       assert_equal 1, Developer.count
     end
 
-    Developer.where('salary = 100000').scoping do
+    Developer.where("salary = 100000").scoping do
       assert_equal 8, Developer.count
       assert_equal 1, Developer.where("name LIKE 'fixture_1%'").count
     end
@@ -131,49 +133,49 @@ class RelationScopingTest < ActiveRecord::TestCase
   def test_scoped_find_include
     # with the include, will retrieve only developers for the given project
     scoped_developers = Developer.includes(:projects).scoping do
-      Developer.where('projects.id' => 2).to_a
+      Developer.where("projects.id" => 2).to_a
     end
-    assert scoped_developers.include?(developers(:david))
-    assert !scoped_developers.include?(developers(:jamis))
+    assert_includes scoped_developers, developers(:david)
+    assert_not_includes scoped_developers, developers(:jamis)
     assert_equal 1, scoped_developers.size
   end
 
   def test_scoped_find_joins
-    scoped_developers = Developer.joins('JOIN developers_projects ON id = developer_id').scoping do
-      Developer.where('developers_projects.project_id = 2').to_a
+    scoped_developers = Developer.joins("JOIN developers_projects ON id = developer_id").scoping do
+      Developer.where("developers_projects.project_id = 2").to_a
     end
 
-    assert scoped_developers.include?(developers(:david))
-    assert !scoped_developers.include?(developers(:jamis))
+    assert_includes scoped_developers, developers(:david)
+    assert_not_includes scoped_developers, developers(:jamis)
     assert_equal 1, scoped_developers.size
     assert_equal developers(:david).attributes, scoped_developers.first.attributes
   end
 
   def test_scoped_create_with_where
-    new_comment = VerySpecialComment.where(:post_id => 1).scoping do
-      VerySpecialComment.create :body => "Wonderful world"
+    new_comment = VerySpecialComment.where(post_id: 1).scoping do
+      VerySpecialComment.create body: "Wonderful world"
     end
 
     assert_equal 1, new_comment.post_id
-    assert Post.find(1).comments.include?(new_comment)
+    assert_includes Post.find(1).comments, new_comment
   end
 
   def test_scoped_create_with_create_with
-    new_comment = VerySpecialComment.create_with(:post_id => 1).scoping do
-      VerySpecialComment.create :body => "Wonderful world"
+    new_comment = VerySpecialComment.create_with(post_id: 1).scoping do
+      VerySpecialComment.create body: "Wonderful world"
     end
 
     assert_equal 1, new_comment.post_id
-    assert Post.find(1).comments.include?(new_comment)
+    assert_includes Post.find(1).comments, new_comment
   end
 
   def test_scoped_create_with_create_with_has_higher_priority
-    new_comment = VerySpecialComment.where(:post_id => 2).create_with(:post_id => 1).scoping do
-      VerySpecialComment.create :body => "Wonderful world"
+    new_comment = VerySpecialComment.where(post_id: 2).create_with(post_id: 1).scoping do
+      VerySpecialComment.create body: "Wonderful world"
     end
 
     assert_equal 1, new_comment.post_id
-    assert Post.find(1).comments.include?(new_comment)
+    assert_includes Post.find(1).comments, new_comment
   end
 
   def test_ensure_that_method_scoping_is_correctly_restored
@@ -193,7 +195,7 @@ class RelationScopingTest < ActiveRecord::TestCase
   end
 
   def test_update_all_default_scope_filters_on_joins
-    DeveloperFilteredOnJoins.update_all(:salary => 65000)
+    DeveloperFilteredOnJoins.update_all(salary: 65000)
     assert_equal 65000, Developer.find(developers(:david).id).salary
 
     # has not changed jamis
@@ -209,23 +211,79 @@ class RelationScopingTest < ActiveRecord::TestCase
     assert_not_equal [], Developer.all
   end
 
-  def test_current_scope_does_not_pollute_other_subclasses
-    Post.none.scoping do
-      assert StiPost.all.any?
+  def test_current_scope_does_not_pollute_sibling_subclasses
+    Comment.none.scoping do
+      assert_not_predicate SpecialComment.all, :any?
+      assert_not_predicate VerySpecialComment.all, :any?
+      assert_not_predicate SubSpecialComment.all, :any?
+    end
+
+    SpecialComment.none.scoping do
+      assert_predicate Comment.all, :any?
+      assert_predicate VerySpecialComment.all, :any?
+      assert_not_predicate SubSpecialComment.all, :any?
+    end
+
+    SubSpecialComment.none.scoping do
+      assert_predicate Comment.all, :any?
+      assert_predicate VerySpecialComment.all, :any?
+      assert_predicate SpecialComment.all, :any?
+    end
+  end
+
+  def test_scoping_is_correctly_restored
+    Comment.unscoped do
+      SpecialComment.unscoped.created
+    end
+
+    assert_nil Comment.send(:current_scope)
+    assert_nil SpecialComment.send(:current_scope)
+  end
+
+  def test_scoping_respects_current_class
+    Comment.unscoped do
+      assert_equal "a comment...", Comment.all.what_are_you
+      assert_equal "a special comment...", SpecialComment.all.what_are_you
+    end
+  end
+
+  def test_scoping_respects_sti_constraint
+    Comment.unscoped do
+      assert_equal comments(:greetings), Comment.find(1)
+      assert_raises(ActiveRecord::RecordNotFound) { SpecialComment.find(1) }
+    end
+  end
+
+  def test_scoping_works_in_the_scope_block
+    expected = SpecialPostWithDefaultScope.unscoped.to_a
+    assert_equal expected, SpecialPostWithDefaultScope.unscoped_all
+  end
+
+  def test_circular_joins_with_scoping_does_not_crash
+    posts = Post.joins(comments: :post).scoping do
+      Post.first(10)
+    end
+    assert_equal posts, Post.joins(comments: :post).first(10)
+  end
+
+  def test_circular_left_joins_with_scoping_does_not_crash
+    posts = Post.left_joins(comments: :post).scoping do
+      Post.first(10)
     end
+    assert_equal posts, Post.left_joins(comments: :post).first(10)
   end
 end
 
 class NestedRelationScopingTest < ActiveRecord::TestCase
-  fixtures :authors, :developers, :projects, :comments, :posts
+  fixtures :authors, :author_addresses, :developers, :projects, :comments, :posts
 
   def test_merge_options
-    Developer.where('salary = 80000').scoping do
+    Developer.where("salary = 80000").scoping do
       Developer.limit(10).scoping do
         devs = Developer.all
         sql = devs.to_sql
-        assert_match '(salary = 80000)', sql
-        assert_match 'LIMIT 10', sql
+        assert_match "(salary = 80000)", sql
+        assert_match(/LIMIT 10|ROWNUM <= 10|FETCH FIRST 10 ROWS ONLY/, sql)
       end
     end
   end
@@ -239,39 +297,39 @@ class NestedRelationScopingTest < ActiveRecord::TestCase
   end
 
   def test_replace_options
-    Developer.where(:name => 'David').scoping do
+    Developer.where(name: "David").scoping do
       Developer.unscoped do
-        assert_equal 'Jamis', Developer.where(:name => 'Jamis').first[:name]
+        assert_equal "Jamis", Developer.where(name: "Jamis").first[:name]
       end
 
-      assert_equal 'David', Developer.first[:name]
+      assert_equal "David", Developer.first[:name]
     end
   end
 
   def test_three_level_nested_exclusive_scoped_find
     Developer.where("name = 'Jamis'").scoping do
-      assert_equal 'Jamis', Developer.first.name
+      assert_equal "Jamis", Developer.first.name
 
       Developer.unscoped.where("name = 'David'") do
-        assert_equal 'David', Developer.first.name
+        assert_equal "David", Developer.first.name
 
         Developer.unscoped.where("name = 'Maiha'") do
-          assert_equal nil, Developer.first
+          assert_nil Developer.first
         end
 
         # ensure that scoping is restored
-        assert_equal 'David', Developer.first.name
+        assert_equal "David", Developer.first.name
       end
 
       # ensure that scoping is restored
-      assert_equal 'Jamis', Developer.first.name
+      assert_equal "Jamis", Developer.first.name
     end
   end
 
   def test_nested_scoped_create
-    comment = Comment.create_with(:post_id => 1).scoping do
-      Comment.create_with(:post_id => 2).scoping do
-        Comment.create :body => "Hey guys, nested scopes are broken. Please fix!"
+    comment = Comment.create_with(post_id: 1).scoping do
+      Comment.create_with(post_id: 2).scoping do
+        Comment.create body: "Hey guys, nested scopes are broken. Please fix!"
       end
     end
 
@@ -279,15 +337,15 @@ class NestedRelationScopingTest < ActiveRecord::TestCase
   end
 
   def test_nested_exclusive_scope_for_create
-    comment = Comment.create_with(:body => "Hey guys, nested scopes are broken. Please fix!").scoping do
-      Comment.unscoped.create_with(:post_id => 1).scoping do
-        assert Comment.new.body.blank?
-        Comment.create :body => "Hey guys"
+    comment = Comment.create_with(body: "Hey guys, nested scopes are broken. Please fix!").scoping do
+      Comment.unscoped.create_with(post_id: 1).scoping do
+        assert_predicate Comment.new.body, :blank?
+        Comment.create body: "Hey guys"
       end
     end
 
     assert_equal 1, comment.post_id
-    assert_equal 'Hey guys', comment.body
+    assert_equal "Hey guys", comment.body
   end
 end
 
@@ -299,24 +357,24 @@ class HasManyScopingTest < ActiveRecord::TestCase
   end
 
   def test_forwarding_of_static_methods
-    assert_equal 'a comment...', Comment.what_are_you
-    assert_equal 'a comment...', @welcome.comments.what_are_you
+    assert_equal "a comment...", Comment.what_are_you
+    assert_equal "a comment...", @welcome.comments.what_are_you
   end
 
   def test_forwarding_to_scoped
-    assert_equal 4, Comment.search_by_type('Comment').size
-    assert_equal 2, @welcome.comments.search_by_type('Comment').size
+    assert_equal 4, Comment.search_by_type("Comment").size
+    assert_equal 2, @welcome.comments.search_by_type("Comment").size
   end
 
   def test_nested_scope_finder
-    Comment.where('1=0').scoping do
+    Comment.where("1=0").scoping do
       assert_equal 0, @welcome.comments.count
-      assert_equal 'a comment...', @welcome.comments.what_are_you
+      assert_equal "a comment...", @welcome.comments.what_are_you
     end
 
-    Comment.where('1=1').scoping do
+    Comment.where("1=1").scoping do
       assert_equal 2, @welcome.comments.count
-      assert_equal 'a comment...', @welcome.comments.what_are_you
+      assert_equal "a comment...", @welcome.comments.what_are_you
     end
   end
 
@@ -331,7 +389,7 @@ class HasManyScopingTest < ActiveRecord::TestCase
   end
 
   def test_should_maintain_default_scope_on_eager_loaded_associations
-    michael = Person.where(:id => people(:michael).id).includes(:bad_references).first
+    michael = Person.where(id: people(:michael).id).includes(:bad_references).first
     magician = BadReference.find(1)
     assert_equal [magician], michael.bad_references
   end
@@ -345,19 +403,19 @@ class HasAndBelongsToManyScopingTest < ActiveRecord::TestCase
   end
 
   def test_forwarding_of_static_methods
-    assert_equal 'a category...', Category.what_are_you
-    assert_equal 'a category...', @welcome.categories.what_are_you
+    assert_equal "a category...", Category.what_are_you
+    assert_equal "a category...", @welcome.categories.what_are_you
   end
 
   def test_nested_scope_finder
-    Category.where('1=0').scoping do
+    Category.where("1=0").scoping do
       assert_equal 0, @welcome.categories.count
-      assert_equal 'a category...', @welcome.categories.what_are_you
+      assert_equal "a category...", @welcome.categories.what_are_you
     end
 
-    Category.where('1=1').scoping do
+    Category.where("1=1").scoping do
       assert_equal 2, @welcome.categories.count
-      assert_equal 'a category...', @welcome.categories.what_are_you
+      assert_equal "a category...", @welcome.categories.what_are_you
     end
   end
 end
diff --git a/activerecord/test/cases/secure_token_test.rb b/activerecord/test/cases/secure_token_test.rb
index e731443fc2..f5fa6aa302 100644
--- a/activerecord/test/cases/secure_token_test.rb
+++ b/activerecord/test/cases/secure_token_test.rb
@@ -1,5 +1,7 @@
-require 'cases/helper'
-require 'models/user'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/user"
 
 class SecureTokenTest < ActiveRecord::TestCase
   setup do
@@ -27,6 +29,6 @@ class SecureTokenTest < ActiveRecord::TestCase
     @user.token = "custom-secure-token"
     @user.save
 
-    assert_equal @user.token, "custom-secure-token"
+    assert_equal "custom-secure-token", @user.token
   end
 end
diff --git a/activerecord/test/cases/serialization_test.rb b/activerecord/test/cases/serialization_test.rb
index 35b13ea247..932780bfef 100644
--- a/activerecord/test/cases/serialization_test.rb
+++ b/activerecord/test/cases/serialization_test.rb
@@ -1,25 +1,27 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/contact'
-require 'models/topic'
-require 'models/book'
-require 'models/author'
-require 'models/post'
+require "models/contact"
+require "models/topic"
+require "models/book"
+require "models/author"
+require "models/post"
 
 class SerializationTest < ActiveRecord::TestCase
   fixtures :books
 
-  FORMATS = [ :xml, :json ]
+  FORMATS = [ :json ]
 
   def setup
     @contact_attributes = {
-      :name           => 'aaron stack',
-      :age            => 25,
-      :avatar         => 'binarydata',
-      :created_at     => Time.utc(2006, 8, 1),
-      :awesome        => false,
-      :preferences    => { :gem => '<strong>ruby</strong>' },
-      :alternative_id => nil,
-      :id             => nil
+      name: "aaron stack",
+      age: 25,
+      avatar: "binarydata",
+      created_at: Time.utc(2006, 8, 1),
+      awesome: false,
+      preferences: { gem: "<strong>ruby</strong>" },
+      alternative_id: nil,
+      id: nil
     }
   end
 
@@ -38,7 +40,7 @@ class SerializationTest < ActiveRecord::TestCase
 
   def test_serialize_should_allow_attribute_only_filtering
     FORMATS.each do |format|
-      @serialized = Contact.new(@contact_attributes).send("to_#{format}", :only => [ :age, :name ])
+      @serialized = Contact.new(@contact_attributes).send("to_#{format}", only: [ :age, :name ])
       contact = Contact.new.send("from_#{format}", @serialized)
       assert_equal @contact_attributes[:name], contact.name, "For #{format}"
       assert_nil contact.avatar, "For #{format}"
@@ -47,7 +49,7 @@ class SerializationTest < ActiveRecord::TestCase
 
   def test_serialize_should_allow_attribute_except_filtering
     FORMATS.each do |format|
-      @serialized = Contact.new(@contact_attributes).send("to_#{format}", :except => [ :age, :name ])
+      @serialized = Contact.new(@contact_attributes).send("to_#{format}", except: [ :age, :name ])
       contact = Contact.new.send("from_#{format}", @serialized)
       assert_nil contact.name, "For #{format}"
       assert_nil contact.age, "For #{format}"
@@ -60,20 +62,20 @@ class SerializationTest < ActiveRecord::TestCase
     ActiveRecord::Base.include_root_in_json = true
 
     klazz = Class.new(ActiveRecord::Base)
-    klazz.table_name = 'topics'
+    klazz.table_name = "topics"
     assert klazz.include_root_in_json
 
     klazz.include_root_in_json = false
     assert ActiveRecord::Base.include_root_in_json
-    assert !klazz.include_root_in_json
-    assert !klazz.new.include_root_in_json
+    assert_not klazz.include_root_in_json
+    assert_not klazz.new.include_root_in_json
   ensure
     ActiveRecord::Base.include_root_in_json = original_root_in_json
   end
 
   def test_read_attribute_for_serialization_with_format_without_method_missing
     klazz = Class.new(ActiveRecord::Base)
-    klazz.table_name = 'books'
+    klazz.table_name = "books"
 
     book = klazz.new
     assert_nil book.read_attribute_for_serialization(:format)
@@ -81,18 +83,18 @@ class SerializationTest < ActiveRecord::TestCase
 
   def test_read_attribute_for_serialization_with_format_after_init
     klazz = Class.new(ActiveRecord::Base)
-    klazz.table_name = 'books'
+    klazz.table_name = "books"
 
-    book = klazz.new(format: 'paperback')
-    assert_equal 'paperback', book.read_attribute_for_serialization(:format)
+    book = klazz.new(format: "paperback")
+    assert_equal "paperback", book.read_attribute_for_serialization(:format)
   end
 
   def test_read_attribute_for_serialization_with_format_after_find
     klazz = Class.new(ActiveRecord::Base)
-    klazz.table_name = 'books'
+    klazz.table_name = "books"
 
     book = klazz.find(books(:awdr).id)
-    assert_equal 'paperback', book.read_attribute_for_serialization(:format)
+    assert_equal "paperback", book.read_attribute_for_serialization(:format)
   end
 
   def test_find_records_by_serialized_attributes_through_join
diff --git a/activerecord/test/cases/serialized_attribute_test.rb b/activerecord/test/cases/serialized_attribute_test.rb
index 6056156698..1192b30b14 100644
--- a/activerecord/test/cases/serialized_attribute_test.rb
+++ b/activerecord/test/cases/serialized_attribute_test.rb
@@ -1,10 +1,12 @@
-require 'cases/helper'
-require 'models/topic'
-require 'models/reply'
-require 'models/person'
-require 'models/traffic_light'
-require 'models/post'
-require 'bcrypt'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/topic"
+require "models/reply"
+require "models/person"
+require "models/traffic_light"
+require "models/post"
+require "bcrypt"
 
 class SerializedAttributeTest < ActiveRecord::TestCase
   fixtures :topics, :posts
@@ -25,7 +27,7 @@ class SerializedAttributeTest < ActiveRecord::TestCase
   def test_serialized_attribute
     Topic.serialize("content", MyObject)
 
-    myobj = MyObject.new('value1', 'value2')
+    myobj = MyObject.new("value1", "value2")
     topic = Topic.create("content" => myobj)
     assert_equal(myobj, topic.content)
 
@@ -36,7 +38,7 @@ class SerializedAttributeTest < ActiveRecord::TestCase
   def test_serialized_attribute_in_base_class
     Topic.serialize("content", Hash)
 
-    hash = { 'content1' => 'value1', 'content2' => 'value2' }
+    hash = { "content1" => "value1", "content2" => "value2" }
     important_topic = ImportantTopic.create("content" => hash)
     assert_equal(hash, important_topic.content)
 
@@ -97,7 +99,7 @@ class SerializedAttributeTest < ActiveRecord::TestCase
   end
 
   def test_serialized_attribute_declared_in_subclass
-    hash = { 'important1' => 'value1', 'important2' => 'value2' }
+    hash = { "important1" => "value1", "important2" => "value2" }
     important_topic = ImportantTopic.create("important" => hash)
     assert_equal(hash, important_topic.important)
 
@@ -107,7 +109,7 @@ class SerializedAttributeTest < ActiveRecord::TestCase
   end
 
   def test_serialized_time_attribute
-    myobj = Time.local(2008,1,1,1,0)
+    myobj = Time.local(2008, 1, 1, 1, 0)
     topic = Topic.create("content" => myobj).reload
     assert_equal(myobj, topic.content)
   end
@@ -124,26 +126,26 @@ class SerializedAttributeTest < ActiveRecord::TestCase
   end
 
   def test_nil_not_serialized_without_class_constraint
-    assert Topic.new(:content => nil).save
-    assert_equal 1, Topic.where(:content => nil).count
+    assert Topic.new(content: nil).save
+    assert_equal 1, Topic.where(content: nil).count
   end
 
   def test_nil_not_serialized_with_class_constraint
     Topic.serialize :content, Hash
-    assert Topic.new(:content => nil).save
-    assert_equal 1, Topic.where(:content => nil).count
+    assert Topic.new(content: nil).save
+    assert_equal 1, Topic.where(content: nil).count
   end
 
   def test_serialized_attribute_should_raise_exception_on_assignment_with_wrong_type
     Topic.serialize(:content, Hash)
     assert_raise(ActiveRecord::SerializationTypeMismatch) do
-      Topic.new(content: 'string')
+      Topic.new(content: "string")
     end
   end
 
   def test_should_raise_exception_on_serialized_attribute_with_type_mismatch
-    myobj = MyObject.new('value1', 'value2')
-    topic = Topic.new(:content => myobj)
+    myobj = MyObject.new("value1", "value2")
+    topic = Topic.new(content: myobj)
     assert topic.save
     Topic.serialize(:content, Hash)
     assert_raise(ActiveRecord::SerializationTypeMismatch) { Topic.find(topic.id).content }
@@ -152,11 +154,32 @@ class SerializedAttributeTest < ActiveRecord::TestCase
   def test_serialized_attribute_with_class_constraint
     settings = { "color" => "blue" }
     Topic.serialize(:content, Hash)
-    topic = Topic.new(:content => settings)
+    topic = Topic.new(content: settings)
     assert topic.save
     assert_equal(settings, Topic.find(topic.id).content)
   end
 
+  def test_where_by_serialized_attribute_with_array
+    settings = [ "color" => "green" ]
+    Topic.serialize(:content, Array)
+    topic = Topic.create!(content: settings)
+    assert_equal topic, Topic.where(content: settings).take
+  end
+
+  def test_where_by_serialized_attribute_with_hash
+    settings = { "color" => "green" }
+    Topic.serialize(:content, Hash)
+    topic = Topic.create!(content: settings)
+    assert_equal topic, Topic.where(content: settings).take
+  end
+
+  def test_where_by_serialized_attribute_with_hash_in_array
+    settings = { "color" => "green" }
+    Topic.serialize(:content, Hash)
+    topic = Topic.create!(content: settings)
+    assert_equal topic, Topic.where(content: [settings]).take
+  end
+
   def test_serialized_default_class
     Topic.serialize(:content, Hash)
     topic = Topic.new
@@ -175,17 +198,17 @@ class SerializedAttributeTest < ActiveRecord::TestCase
   end
 
   def test_serialized_boolean_value_true
-    topic = Topic.new(:content => true)
+    topic = Topic.new(content: true)
     assert topic.save
     topic = topic.reload
-    assert_equal topic.content, true
+    assert_equal true, topic.content
   end
 
   def test_serialized_boolean_value_false
-    topic = Topic.new(:content => false)
+    topic = Topic.new(content: false)
     assert topic.save
     topic = topic.reload
-    assert_equal topic.content, false
+    assert_equal false, topic.content
   end
 
   def test_serialize_with_coder
@@ -200,18 +223,18 @@ class SerializedAttributeTest < ActiveRecord::TestCase
     end
 
     Topic.serialize(:content, some_class)
-    topic = Topic.new(:content => some_class.new('my value'))
+    topic = Topic.new(content: some_class.new("my value"))
     topic.save!
     topic.reload
     assert_kind_of some_class, topic.content
-    assert_equal topic.content, some_class.new('my value')
+    assert_equal some_class.new("my value"), topic.content
   end
 
   def test_serialize_attribute_via_select_method_when_time_zone_available
     with_timezone_config aware_attributes: true do
       Topic.serialize(:content, MyObject)
 
-      myobj = MyObject.new('value1', 'value2')
+      myobj = MyObject.new("value1", "value2")
       topic = Topic.create(content: myobj)
 
       assert_equal(myobj, Topic.select(:content).find(topic.id).content)
@@ -220,8 +243,8 @@ class SerializedAttributeTest < ActiveRecord::TestCase
   end
 
   def test_serialize_attribute_can_be_serialized_in_an_integer_column
-    insures = ['life']
-    person = SerializedPerson.new(first_name: 'David', insures: insures)
+    insures = ["life"]
+    person = SerializedPerson.new(first_name: "David", insures: insures)
     assert person.save
     person = person.reload
     assert_equal(insures, person.insures)
@@ -233,6 +256,20 @@ class SerializedAttributeTest < ActiveRecord::TestCase
     assert_equal [], light.long_state
   end
 
+  def test_unexpected_serialized_type
+    Topic.serialize :content, Hash
+    topic = Topic.create!(content: { zomg: true })
+
+    Topic.serialize :content, Array
+
+    topic.reload
+    error = assert_raise(ActiveRecord::SerializationTypeMismatch) do
+      topic.content
+    end
+    expected = "can't load `content`: was supposed to be a Array, but was a Hash. -- {:zomg=>true}"
+    assert_equal expected, error.to_s
+  end
+
   def test_serialized_column_should_unserialize_after_update_column
     t = Topic.create(content: "first")
     assert_equal("first", t.content)
@@ -256,7 +293,7 @@ class SerializedAttributeTest < ActiveRecord::TestCase
 
     topic = Topic.new(content: nil)
 
-    assert_not topic.content_changed?
+    assert_not_predicate topic, :content_changed?
   end
 
   def test_classes_without_no_arg_constructors_are_not_supported
@@ -285,7 +322,7 @@ class SerializedAttributeTest < ActiveRecord::TestCase
     topic = Topic.create!(content: {})
     topic2 = Topic.create!(content: nil)
 
-    assert_equal [topic, topic2], Topic.where(content: nil)
+    assert_equal [topic, topic2], Topic.where(content: nil).sort_by(&:id)
   end
 
   def test_nil_is_always_persisted_as_null
@@ -295,4 +332,65 @@ class SerializedAttributeTest < ActiveRecord::TestCase
     topic.update_attribute :content, nil
     assert_equal [topic], Topic.where(content: nil)
   end
+
+  def test_mutation_detection_does_not_double_serialize
+    coder = Object.new
+    def coder.dump(value)
+      return if value.nil?
+      value + " encoded"
+    end
+    def coder.load(value)
+      return if value.nil?
+      value.gsub(" encoded", "")
+    end
+    type = Class.new(ActiveModel::Type::Value) do
+      include ActiveModel::Type::Helpers::Mutable
+
+      def serialize(value)
+        return if value.nil?
+        value + " serialized"
+      end
+
+      def deserialize(value)
+        return if value.nil?
+        value.gsub(" serialized", "")
+      end
+    end.new
+    model = Class.new(Topic) do
+      attribute :foo, type
+      serialize :foo, coder
+    end
+
+    topic = model.create!(foo: "bar")
+    topic.foo
+    assert_not_predicate topic, :changed?
+  end
+
+  def test_serialized_attribute_works_under_concurrent_initial_access
+    model = Topic.dup
+
+    topic = model.last
+    topic.update group: "1"
+
+    model.serialize :group, JSON
+    model.reset_column_information
+
+    # This isn't strictly necessary for the test, but a little bit of
+    # knowledge of internals allows us to make failures far more likely.
+    model.define_singleton_method(:define_attribute) do |*args|
+      Thread.pass
+      super(*args)
+    end
+
+    threads = 4.times.map do
+      Thread.new do
+        topic.reload.group
+      end
+    end
+
+    # All the threads should retrieve the value knowing it is JSON, and
+    # thus decode it. If this fails, some threads will instead see the
+    # raw string ("1"), or raise an exception.
+    assert_equal [1] * threads.size, threads.map(&:value)
+  end
 end
diff --git a/activerecord/test/cases/statement_cache_test.rb b/activerecord/test/cases/statement_cache_test.rb
index a704b861cb..e3c12f68fd 100644
--- a/activerecord/test/cases/statement_cache_test.rb
+++ b/activerecord/test/cases/statement_cache_test.rb
@@ -1,8 +1,10 @@
-require 'cases/helper'
-require 'models/book'
-require 'models/liquid'
-require 'models/molecule'
-require 'models/electron'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/book"
+require "models/liquid"
+require "models/molecule"
+require "models/electron"
 
 module ActiveRecord
   class StatementCacheTest < ActiveRecord::TestCase
@@ -10,22 +12,20 @@ module ActiveRecord
       @connection = ActiveRecord::Base.connection
     end
 
-    #Cache v 1.1 tests
     def test_statement_cache
       Book.create(name: "my book")
       Book.create(name: "my other book")
 
       cache = StatementCache.create(Book.connection) do |params|
-        Book.where(:name => params.bind)
+        Book.where(name: params.bind)
       end
 
-      b = cache.execute([ "my book" ], Book, Book.connection)
+      b = cache.execute([ "my book" ], Book.connection)
       assert_equal "my book", b[0].name
-      b = cache.execute([ "my other book" ], Book, Book.connection)
+      b = cache.execute([ "my other book" ], Book.connection)
       assert_equal "my other book", b[0].name
     end
 
-
     def test_statement_cache_id
       b1 = Book.create(name: "my book")
       b2 = Book.create(name: "my other book")
@@ -34,9 +34,9 @@ module ActiveRecord
         Book.where(id: params.bind)
       end
 
-      b = cache.execute([ b1.id ], Book, Book.connection)
+      b = cache.execute([ b1.id ], Book.connection)
       assert_equal b1.name, b[0].name
-      b = cache.execute([ b2.id ], Book, Book.connection)
+      b = cache.execute([ b2.id ], Book.connection)
       assert_equal b2.name, b[0].name
     end
 
@@ -50,8 +50,6 @@ module ActiveRecord
       assert_equal("my other book", b.name)
     end
 
-    #End
-
     def test_statement_cache_with_simple_statement
       cache = ActiveRecord::StatementCache.create(Book.connection) do |params|
         Book.where(name: "my book").where("author_id > 3")
@@ -59,20 +57,20 @@ module ActiveRecord
 
       Book.create(name: "my book", author_id: 4)
 
-      books = cache.execute([], Book, Book.connection)
+      books = cache.execute([], Book.connection)
       assert_equal "my book", books[0].name
     end
 
     def test_statement_cache_with_complex_statement
       cache = ActiveRecord::StatementCache.create(Book.connection) do |params|
-        Liquid.joins(:molecules => :electrons).where('molecules.name' => 'dioxane', 'electrons.name' => 'lepton')
+        Liquid.joins(molecules: :electrons).where("molecules.name" => "dioxane", "electrons.name" => "lepton")
       end
 
-      salty = Liquid.create(name: 'salty')
-      molecule = salty.molecules.create(name: 'dioxane')
-      molecule.electrons.create(name: 'lepton')
+      salty = Liquid.create(name: "salty")
+      molecule = salty.molecules.create(name: "dioxane")
+      molecule.electrons.create(name: "lepton")
 
-      liquids = cache.execute([], Book, Book.connection)
+      liquids = cache.execute([], Book.connection)
       assert_equal "salty", liquids[0].name
     end
 
@@ -85,14 +83,52 @@ module ActiveRecord
         Book.create(name: "my book")
       end
 
-      first_books = cache.execute([], Book, Book.connection)
+      first_books = cache.execute([], Book.connection)
 
       3.times do
         Book.create(name: "my book")
       end
 
-      additional_books = cache.execute([], Book, Book.connection)
+      additional_books = cache.execute([], Book.connection)
       assert first_books != additional_books
     end
+
+    def test_unprepared_statements_dont_share_a_cache_with_prepared_statements
+      Book.create(name: "my book")
+      Book.create(name: "my other book")
+
+      book = Book.find_by(name: "my book")
+      other_book = Book.connection.unprepared_statement do
+        Book.find_by(name: "my other book")
+      end
+
+      assert_not_equal book, other_book
+    end
+
+    def test_find_by_does_not_use_statement_cache_if_table_name_is_changed
+      book = Book.create(name: "my book")
+
+      Book.find_by(name: book.name) # warming the statement cache.
+
+      # changing the table name should change the query that is not cached.
+      Book.table_name = :birds
+      assert_nil Book.find_by(name: book.name)
+    ensure
+      Book.table_name = :books
+    end
+
+    def test_find_does_not_use_statement_cache_if_table_name_is_changed
+      book = Book.create(name: "my book")
+
+      Book.find(book.id) # warming the statement cache.
+
+      # changing the table name should change the query that is not cached.
+      Book.table_name = :birds
+      assert_raise ActiveRecord::RecordNotFound do
+        Book.find(book.id)
+      end
+    ensure
+      Book.table_name = :books
+    end
   end
 end
diff --git a/activerecord/test/cases/store_test.rb b/activerecord/test/cases/store_test.rb
index e9cdf94c99..4457cfbd37 100644
--- a/activerecord/test/cases/store_test.rb
+++ b/activerecord/test/cases/store_test.rb
@@ -1,60 +1,82 @@
-require 'cases/helper'
-require 'models/admin'
-require 'models/admin/user'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/admin"
+require "models/admin/user"
 
 class StoreTest < ActiveRecord::TestCase
   fixtures :'admin/users'
 
   setup do
-    @john = Admin::User.create!(:name => 'John Doe', :color => 'black', :remember_login => true, :height => 'tall', :is_a_good_guy => true)
+    @john = Admin::User.create!(
+      name: "John Doe", color: "black", remember_login: true,
+      height: "tall", is_a_good_guy: true,
+      parent_name: "Quinn", partner_name: "Dallas",
+      partner_birthday: "1997-11-1"
+    )
   end
 
   test "reading store attributes through accessors" do
-    assert_equal 'black', @john.color
+    assert_equal "black", @john.color
     assert_nil @john.homepage
   end
 
   test "writing store attributes through accessors" do
-    @john.color = 'red'
-    @john.homepage = '37signals.com'
+    @john.color = "red"
+    @john.homepage = "37signals.com"
+
+    assert_equal "red", @john.color
+    assert_equal "37signals.com", @john.homepage
+  end
+
+  test "reading store attributes through accessors with prefix" do
+    assert_equal "Quinn", @john.parent_name
+    assert_nil @john.parent_birthday
+    assert_equal "Dallas", @john.partner_name
+    assert_equal "1997-11-1", @john.partner_birthday
+  end
+
+  test "writing store attributes through accessors with prefix" do
+    @john.partner_name = "River"
+    @john.partner_birthday = "1999-2-11"
 
-    assert_equal 'red', @john.color
-    assert_equal '37signals.com', @john.homepage
+    assert_equal "River", @john.partner_name
+    assert_equal "1999-2-11", @john.partner_birthday
   end
 
   test "accessing attributes not exposed by accessors" do
-    @john.settings[:icecream] = 'graeters'
+    @john.settings[:icecream] = "graeters"
     @john.save
 
-    assert_equal 'graeters', @john.reload.settings[:icecream]
+    assert_equal "graeters", @john.reload.settings[:icecream]
   end
 
   test "overriding a read accessor" do
-    @john.settings[:phone_number] = '1234567890'
+    @john.settings[:phone_number] = "1234567890"
 
-    assert_equal '(123) 456-7890', @john.phone_number
+    assert_equal "(123) 456-7890", @john.phone_number
   end
 
   test "overriding a read accessor using super" do
     @john.settings[:color] = nil
 
-    assert_equal 'red', @john.color
+    assert_equal "red", @john.color
   end
 
   test "updating the store will mark it as changed" do
-    @john.color = 'red'
-    assert @john.settings_changed?
+    @john.color = "red"
+    assert_predicate @john, :settings_changed?
   end
 
   test "updating the store populates the changed array correctly" do
-    @john.color = 'red'
-    assert_equal 'black', @john.settings_change[0]['color']
-    assert_equal 'red', @john.settings_change[1]['color']
+    @john.color = "red"
+    assert_equal "black", @john.settings_change[0]["color"]
+    assert_equal "red", @john.settings_change[1]["color"]
   end
 
   test "updating the store won't mark it as changed if an attribute isn't changed" do
     @john.color = @john.color
-    assert !@john.settings_changed?
+    assert_not_predicate @john, :settings_changed?
   end
 
   test "object initialization with not nullable column" do
@@ -67,75 +89,75 @@ class StoreTest < ActiveRecord::TestCase
   end
 
   test "overriding a write accessor" do
-    @john.phone_number = '(123) 456-7890'
+    @john.phone_number = "(123) 456-7890"
 
-    assert_equal '1234567890', @john.settings[:phone_number]
+    assert_equal "1234567890", @john.settings[:phone_number]
   end
 
   test "overriding a write accessor using super" do
-    @john.color = 'yellow'
+    @john.color = "yellow"
 
-    assert_equal 'blue', @john.color
+    assert_equal "blue", @john.color
   end
 
   test "preserve store attributes data in HashWithIndifferentAccess format without any conversion" do
-    @john.json_data = ActiveSupport::HashWithIndifferentAccess.new(:height => 'tall', 'weight' => 'heavy')
-    @john.height = 'low'
+    @john.json_data = ActiveSupport::HashWithIndifferentAccess.new(:height => "tall", "weight" => "heavy")
+    @john.height = "low"
     assert_equal true, @john.json_data.instance_of?(ActiveSupport::HashWithIndifferentAccess)
-    assert_equal 'low', @john.json_data[:height]
-    assert_equal 'low', @john.json_data['height']
-    assert_equal 'heavy', @john.json_data[:weight]
-    assert_equal 'heavy', @john.json_data['weight']
+    assert_equal "low", @john.json_data[:height]
+    assert_equal "low", @john.json_data["height"]
+    assert_equal "heavy", @john.json_data[:weight]
+    assert_equal "heavy", @john.json_data["weight"]
   end
 
   test "convert store attributes from Hash to HashWithIndifferentAccess saving the data and access attributes indifferently" do
-    user = Admin::User.find_by_name('Jamis')
-    assert_equal 'symbol',  user.settings[:symbol]
-    assert_equal 'symbol',  user.settings['symbol']
-    assert_equal 'string',  user.settings[:string]
-    assert_equal 'string',  user.settings['string']
+    user = Admin::User.find_by_name("Jamis")
+    assert_equal "symbol",  user.settings[:symbol]
+    assert_equal "symbol",  user.settings["symbol"]
+    assert_equal "string",  user.settings[:string]
+    assert_equal "string",  user.settings["string"]
     assert_equal true,      user.settings.instance_of?(ActiveSupport::HashWithIndifferentAccess)
 
-    user.height = 'low'
-    assert_equal 'symbol',  user.settings[:symbol]
-    assert_equal 'symbol',  user.settings['symbol']
-    assert_equal 'string',  user.settings[:string]
-    assert_equal 'string',  user.settings['string']
+    user.height = "low"
+    assert_equal "symbol",  user.settings[:symbol]
+    assert_equal "symbol",  user.settings["symbol"]
+    assert_equal "string",  user.settings[:string]
+    assert_equal "string",  user.settings["string"]
     assert_equal true,      user.settings.instance_of?(ActiveSupport::HashWithIndifferentAccess)
   end
 
-  test "convert store attributes from any format other than Hash or HashWithIndifferent access losing the data" do
+  test "convert store attributes from any format other than Hash or HashWithIndifferentAccess losing the data" do
     @john.json_data = "somedata"
-    @john.height = 'low'
+    @john.height = "low"
     assert_equal true, @john.json_data.instance_of?(ActiveSupport::HashWithIndifferentAccess)
-    assert_equal 'low', @john.json_data[:height]
-    assert_equal 'low', @john.json_data['height']
-    assert_equal false, @john.json_data.delete_if { |k, v| k == 'height' }.any?
+    assert_equal "low", @john.json_data[:height]
+    assert_equal "low", @john.json_data["height"]
+    assert_equal false, @john.json_data.delete_if { |k, v| k == "height" }.any?
   end
 
   test "reading store attributes through accessors encoded with JSON" do
-    assert_equal 'tall', @john.height
+    assert_equal "tall", @john.height
     assert_nil @john.weight
   end
 
   test "writing store attributes through accessors encoded with JSON" do
-    @john.height = 'short'
-    @john.weight = 'heavy'
+    @john.height = "short"
+    @john.weight = "heavy"
 
-    assert_equal 'short', @john.height
-    assert_equal 'heavy', @john.weight
+    assert_equal "short", @john.height
+    assert_equal "heavy", @john.weight
   end
 
   test "accessing attributes not exposed by accessors encoded with JSON" do
-    @john.json_data['somestuff'] = 'somecoolstuff'
+    @john.json_data["somestuff"] = "somecoolstuff"
     @john.save
 
-    assert_equal 'somecoolstuff', @john.reload.json_data['somestuff']
+    assert_equal "somecoolstuff", @john.reload.json_data["somestuff"]
   end
 
   test "updating the store will mark it as changed encoded with JSON" do
-    @john.height = 'short'
-    assert @john.json_data_changed?
+    @john.height = "short"
+    assert_predicate @john, :json_data_changed?
   end
 
   test "object initialization with not nullable column encoded with JSON" do
@@ -177,6 +199,7 @@ class StoreTest < ActiveRecord::TestCase
     assert_equal [:color], first_model.stored_attributes[:data]
     assert_equal [:color, :width, :height], second_model.stored_attributes[:data]
     assert_equal [:color, :area, :volume], third_model.stored_attributes[:data]
+    assert_equal [:color], first_model.stored_attributes[:data]
   end
 
   test "YAML coder initializes the store when a Nil value is given" do
@@ -191,4 +214,38 @@ class StoreTest < ActiveRecord::TestCase
     second_dump = YAML.dump(loaded)
     assert_equal @john, YAML.load(second_dump)
   end
+
+  test "read store attributes through accessors with default suffix" do
+    @john.configs[:two_factor_auth] = true
+    assert_equal true, @john.two_factor_auth_configs
+  end
+
+  test "write store attributes through accessors with default suffix" do
+    @john.two_factor_auth_configs = false
+    assert_equal false, @john.configs[:two_factor_auth]
+  end
+
+  test "read store attributes through accessors with custom suffix" do
+    @john.configs[:login_retry] = 3
+    assert_equal 3, @john.login_retry_config
+  end
+
+  test "write store attributes through accessors with custom suffix" do
+    @john.login_retry_config = 5
+    assert_equal 5, @john.configs[:login_retry]
+  end
+
+  test "read accessor without pre/suffix in the same store as other pre/suffixed accessors still works" do
+    @john.configs[:secret_question] = "What is your high school?"
+    assert_equal "What is your high school?", @john.secret_question
+  end
+
+  test "write accessor without pre/suffix in the same store as other pre/suffixed accessors still works" do
+    @john.secret_question = "What was the Rails version when you first worked on it?"
+    assert_equal "What was the Rails version when you first worked on it?", @john.configs[:secret_question]
+  end
+
+  test "prefix/suffix do not affect stored attributes" do
+    assert_equal [:secret_question, :two_factor_auth, :login_retry], Admin::User.stored_attributes[:configs]
+  end
 end
diff --git a/activerecord/test/cases/suppressor_test.rb b/activerecord/test/cases/suppressor_test.rb
index 72c5c16555..9be5356901 100644
--- a/activerecord/test/cases/suppressor_test.rb
+++ b/activerecord/test/cases/suppressor_test.rb
@@ -1,6 +1,8 @@
-require 'cases/helper'
-require 'models/notification'
-require 'models/user'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/notification"
+require "models/user"
 
 class SuppressorTest < ActiveRecord::TestCase
   def test_suppresses_create
@@ -15,22 +17,22 @@ class SuppressorTest < ActiveRecord::TestCase
   end
 
   def test_suppresses_update
-    user = User.create! token: 'asdf'
+    user = User.create! token: "asdf"
 
     User.suppress do
-      user.update token: 'ghjkl'
-      assert_equal 'asdf', user.reload.token
+      user.update token: "ghjkl"
+      assert_equal "asdf", user.reload.token
 
-      user.update! token: 'zxcvbnm'
-      assert_equal 'asdf', user.reload.token
+      user.update! token: "zxcvbnm"
+      assert_equal "asdf", user.reload.token
 
-      user.token = 'qwerty'
+      user.token = "qwerty"
       user.save
-      assert_equal 'asdf', user.reload.token
+      assert_equal "asdf", user.reload.token
 
-      user.token = 'uiop'
+      user.token = "uiop"
       user.save!
-      assert_equal 'asdf', user.reload.token
+      assert_equal "asdf", user.reload.token
     end
   end
 
@@ -46,7 +48,30 @@ class SuppressorTest < ActiveRecord::TestCase
     Notification.suppress { UserWithNotification.create! }
 
     assert_difference -> { Notification.count } do
-      Notification.create!
+      Notification.create!(message: "New Comment")
+    end
+  end
+
+  def test_suppresses_validations_on_create
+    assert_no_difference -> { Notification.count } do
+      Notification.suppress do
+        User.create
+        User.create!
+        User.new.save
+        User.new.save!
+      end
+    end
+  end
+
+  def test_suppresses_when_nested_multiple_times
+    assert_no_difference -> { Notification.count } do
+      Notification.suppress do
+        Notification.suppress { }
+        Notification.create
+        Notification.create!
+        Notification.new.save
+        Notification.new.save!
+      end
     end
   end
 end
diff --git a/activerecord/test/cases/tasks/database_tasks_test.rb b/activerecord/test/cases/tasks/database_tasks_test.rb
index 38164b2228..3fd1813d64 100644
--- a/activerecord/test/cases/tasks/database_tasks_test.rb
+++ b/activerecord/test/cases/tasks/database_tasks_test.rb
@@ -1,23 +1,111 @@
-require 'cases/helper'
-require 'active_record/tasks/database_tasks'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "active_record/tasks/database_tasks"
 
 module ActiveRecord
   module DatabaseTasksSetupper
     def setup
-      @mysql_tasks, @postgresql_tasks, @sqlite_tasks = stub, stub, stub
-      ActiveRecord::Tasks::MySQLDatabaseTasks.stubs(:new).returns @mysql_tasks
-      ActiveRecord::Tasks::PostgreSQLDatabaseTasks.stubs(:new).returns @postgresql_tasks
-      ActiveRecord::Tasks::SQLiteDatabaseTasks.stubs(:new).returns @sqlite_tasks
+      @mysql_tasks, @postgresql_tasks, @sqlite_tasks = Array.new(
+        3,
+        Class.new do
+          def create; end
+          def drop; end
+          def purge; end
+          def charset; end
+          def collation; end
+          def structure_dump(*); end
+          def structure_load(*); end
+        end.new
+      )
+
+      $stdout, @original_stdout = StringIO.new, $stdout
+      $stderr, @original_stderr = StringIO.new, $stderr
+    end
+
+    def teardown
+      $stdout, $stderr = @original_stdout, @original_stderr
+    end
+
+    def with_stubbed_new
+      ActiveRecord::Tasks::MySQLDatabaseTasks.stub(:new, @mysql_tasks) do
+        ActiveRecord::Tasks::PostgreSQLDatabaseTasks.stub(:new, @postgresql_tasks) do
+          ActiveRecord::Tasks::SQLiteDatabaseTasks.stub(:new, @sqlite_tasks) do
+            yield
+          end
+        end
+      end
     end
   end
 
   ADAPTERS_TASKS = {
-    mysql:      :mysql_tasks,
     mysql2:     :mysql_tasks,
     postgresql: :postgresql_tasks,
     sqlite3:    :sqlite_tasks
   }
 
+  class DatabaseTasksUtilsTask < ActiveRecord::TestCase
+    def test_raises_an_error_when_called_with_protected_environment
+      protected_environments = ActiveRecord::Base.protected_environments
+      current_env            = ActiveRecord::Base.connection.migration_context.current_environment
+
+      assert_called_on_instance_of(
+        ActiveRecord::MigrationContext,
+        :current_version,
+        times: 6,
+        returns: 1
+      ) do
+        assert_not_includes protected_environments, current_env
+        # Assert no error
+        ActiveRecord::Tasks::DatabaseTasks.check_protected_environments!
+
+        ActiveRecord::Base.protected_environments = [current_env]
+
+        assert_raise(ActiveRecord::ProtectedEnvironmentError) do
+          ActiveRecord::Tasks::DatabaseTasks.check_protected_environments!
+        end
+      end
+    ensure
+      ActiveRecord::Base.protected_environments = protected_environments
+    end
+
+    def test_raises_an_error_when_called_with_protected_environment_which_name_is_a_symbol
+      protected_environments = ActiveRecord::Base.protected_environments
+      current_env            = ActiveRecord::Base.connection.migration_context.current_environment
+      assert_called_on_instance_of(
+        ActiveRecord::MigrationContext,
+        :current_version,
+        times: 6,
+        returns: 1
+      ) do
+        assert_not_includes protected_environments, current_env
+        # Assert no error
+        ActiveRecord::Tasks::DatabaseTasks.check_protected_environments!
+
+        ActiveRecord::Base.protected_environments = [current_env.to_sym]
+        assert_raise(ActiveRecord::ProtectedEnvironmentError) do
+          ActiveRecord::Tasks::DatabaseTasks.check_protected_environments!
+        end
+      end
+    ensure
+      ActiveRecord::Base.protected_environments = protected_environments
+    end
+
+    def test_raises_an_error_if_no_migrations_have_been_made
+      ActiveRecord::InternalMetadata.stub(:table_exists?, false) do
+        assert_called_on_instance_of(
+          ActiveRecord::MigrationContext,
+          :current_version,
+          returns: 1
+        ) do
+          assert_raise(ActiveRecord::NoEnvironmentInSchemaError) do
+            ActiveRecord::Tasks::DatabaseTasks.check_protected_environments!
+          end
+        end
+      end
+    end
+  end
+
   class DatabaseTasksRegisterTask < ActiveRecord::TestCase
     def test_register_task
       klazz = Class.new do
@@ -26,16 +114,17 @@ module ActiveRecord
       end
       instance = klazz.new
 
-      klazz.stubs(:new).returns instance
-      instance.expects(:structure_dump).with("awesome-file.sql")
-
-      ActiveRecord::Tasks::DatabaseTasks.register_task(/foo/, klazz)
-      ActiveRecord::Tasks::DatabaseTasks.structure_dump({'adapter' => :foo}, "awesome-file.sql")
+      klazz.stub(:new, instance) do
+        assert_called_with(instance, :structure_dump, ["awesome-file.sql", nil]) do
+          ActiveRecord::Tasks::DatabaseTasks.register_task(/foo/, klazz)
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump({ "adapter" => :foo }, "awesome-file.sql")
+        end
+      end
     end
 
     def test_unregistered_task
       assert_raise(ActiveRecord::Tasks::DatabaseNotSupported) do
-        ActiveRecord::Tasks::DatabaseTasks.structure_dump({'adapter' => :bar}, "awesome-file.sql")
+        ActiveRecord::Tasks::DatabaseTasks.structure_dump({ "adapter" => :bar }, "awesome-file.sql")
       end
     end
   end
@@ -45,121 +134,324 @@ module ActiveRecord
 
     ADAPTERS_TASKS.each do |k, v|
       define_method("test_#{k}_create") do
-        eval("@#{v}").expects(:create)
-        ActiveRecord::Tasks::DatabaseTasks.create 'adapter' => k
+        with_stubbed_new do
+          assert_called(eval("@#{v}"), :create) do
+            ActiveRecord::Tasks::DatabaseTasks.create "adapter" => k
+          end
+        end
       end
     end
   end
 
+  class DatabaseTasksDumpSchemaCacheTest < ActiveRecord::TestCase
+    def test_dump_schema_cache
+      path = "/tmp/my_schema_cache.yml"
+      ActiveRecord::Tasks::DatabaseTasks.dump_schema_cache(ActiveRecord::Base.connection, path)
+      assert File.file?(path)
+    ensure
+      ActiveRecord::Base.clear_cache!
+      FileUtils.rm_rf(path)
+    end
+  end
+
   class DatabaseTasksCreateAllTest < ActiveRecord::TestCase
     def setup
-      @configurations = {'development' => {'database' => 'my-db'}}
+      @configurations = { "development" => { "database" => "my-db" } }
 
-      ActiveRecord::Base.stubs(:configurations).returns(@configurations)
+      $stdout, @original_stdout = StringIO.new, $stdout
+      $stderr, @original_stderr = StringIO.new, $stderr
     end
 
-    def test_ignores_configurations_without_databases
-      @configurations['development'].merge!('database' => nil)
+    def teardown
+      $stdout, $stderr = @original_stdout, @original_stderr
+    end
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create).never
+    def test_ignores_configurations_without_databases
+      @configurations["development"]["database"] = nil
 
-      ActiveRecord::Tasks::DatabaseTasks.create_all
+      with_stubbed_configurations_establish_connection do
+        assert_not_called(ActiveRecord::Tasks::DatabaseTasks, :create) do
+          ActiveRecord::Tasks::DatabaseTasks.create_all
+        end
+      end
     end
 
     def test_ignores_remote_databases
-      @configurations['development'].merge!('host' => 'my.server.tld')
-      $stderr.stubs(:puts).returns(nil)
+      @configurations["development"]["host"] = "my.server.tld"
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create).never
-
-      ActiveRecord::Tasks::DatabaseTasks.create_all
+      with_stubbed_configurations_establish_connection do
+        assert_not_called(ActiveRecord::Tasks::DatabaseTasks, :create) do
+          ActiveRecord::Tasks::DatabaseTasks.create_all
+        end
+      end
     end
 
     def test_warning_for_remote_databases
-      @configurations['development'].merge!('host' => 'my.server.tld')
+      @configurations["development"]["host"] = "my.server.tld"
 
-      $stderr.expects(:puts).with('This task only modifies local databases. my-db is on a remote host.')
+      with_stubbed_configurations_establish_connection do
+        ActiveRecord::Tasks::DatabaseTasks.create_all
 
-      ActiveRecord::Tasks::DatabaseTasks.create_all
+        assert_match "This task only modifies local databases. my-db is on a remote host.",
+          $stderr.string
+      end
     end
 
     def test_creates_configurations_with_local_ip
-      @configurations['development'].merge!('host' => '127.0.0.1')
-
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create)
+      @configurations["development"]["host"] = "127.0.0.1"
 
-      ActiveRecord::Tasks::DatabaseTasks.create_all
+      with_stubbed_configurations_establish_connection do
+        assert_called(ActiveRecord::Tasks::DatabaseTasks, :create) do
+          ActiveRecord::Tasks::DatabaseTasks.create_all
+        end
+      end
     end
 
     def test_creates_configurations_with_local_host
-      @configurations['development'].merge!('host' => 'localhost')
+      @configurations["development"]["host"] = "localhost"
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create)
-
-      ActiveRecord::Tasks::DatabaseTasks.create_all
+      with_stubbed_configurations_establish_connection do
+        assert_called(ActiveRecord::Tasks::DatabaseTasks, :create) do
+          ActiveRecord::Tasks::DatabaseTasks.create_all
+        end
+      end
     end
 
     def test_creates_configurations_with_blank_hosts
-      @configurations['development'].merge!('host' => nil)
+      @configurations["development"]["host"] = nil
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create)
-
-      ActiveRecord::Tasks::DatabaseTasks.create_all
+      with_stubbed_configurations_establish_connection do
+        assert_called(ActiveRecord::Tasks::DatabaseTasks, :create) do
+          ActiveRecord::Tasks::DatabaseTasks.create_all
+        end
+      end
     end
+
+    private
+      def with_stubbed_configurations_establish_connection
+        old_configurations = ActiveRecord::Base.configurations
+        ActiveRecord::Base.configurations = @configurations
+
+        # To refrain from connecting to a newly created empty DB in
+        # sqlite3_mem tests
+        ActiveRecord::Base.connection_handler.stub(:establish_connection, nil) do
+          yield
+        end
+      ensure
+        ActiveRecord::Base.configurations = old_configurations
+      end
   end
 
   class DatabaseTasksCreateCurrentTest < ActiveRecord::TestCase
     def setup
       @configurations = {
-        'development' => {'database' => 'dev-db'},
-        'test'        => {'database' => 'test-db'},
-        'production'  => {'database' => 'prod-db'}
+        "development" => { "database" => "dev-db" },
+        "test"        => { "database" => "test-db" },
+        "production"  => { "url" => "abstract://prod-db-host/prod-db" }
       }
-
-      ActiveRecord::Base.stubs(:configurations).returns(@configurations)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
     end
 
     def test_creates_current_environment_database
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create).
-        with('database' => 'prod-db')
+      with_stubbed_configurations_establish_connection do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :create,
+          ["database" => "test-db"],
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("test")
+          )
+        end
+      end
+    end
 
-      ActiveRecord::Tasks::DatabaseTasks.create_current(
-        ActiveSupport::StringInquirer.new('production')
-      )
+    def test_creates_current_environment_database_with_url
+      with_stubbed_configurations_establish_connection do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :create,
+          ["adapter" => "abstract", "database" => "prod-db", "host" => "prod-db-host"],
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("production")
+          )
+        end
+      end
     end
 
     def test_creates_test_and_development_databases_when_env_was_not_specified
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create).
-        with('database' => 'dev-db')
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create).
-        with('database' => 'test-db')
-      ENV.expects(:[]).with('RAILS_ENV').returns(nil)
-
-      ActiveRecord::Tasks::DatabaseTasks.create_current(
-        ActiveSupport::StringInquirer.new('development')
-      )
+      with_stubbed_configurations_establish_connection do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :create,
+          [
+            ["database" => "dev-db"],
+            ["database" => "test-db"]
+          ],
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
     end
 
-    def test_creates_only_development_database_when_rails_env_is_development
-      ActiveRecord::Tasks::DatabaseTasks.expects(:create).
-        with('database' => 'dev-db')
-      ENV.expects(:[]).with('RAILS_ENV').returns('development')
+    def test_creates_test_and_development_databases_when_rails_env_is_development
+      old_env = ENV["RAILS_ENV"]
+      ENV["RAILS_ENV"] = "development"
+
+      with_stubbed_configurations_establish_connection do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :create,
+          [
+            ["database" => "dev-db"],
+            ["database" => "test-db"]
+          ],
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
+    ensure
+      ENV["RAILS_ENV"] = old_env
+    end
 
-      ActiveRecord::Tasks::DatabaseTasks.create_current(
-        ActiveSupport::StringInquirer.new('development')
-      )
+    def test_establishes_connection_for_the_given_environments
+      ActiveRecord::Tasks::DatabaseTasks.stub(:create, nil) do
+        assert_called_with(ActiveRecord::Base, :establish_connection, [:development]) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
     end
 
-    def test_establishes_connection_for_the_given_environment
-      ActiveRecord::Tasks::DatabaseTasks.stubs(:create).returns true
+    private
+      def with_stubbed_configurations_establish_connection
+        old_configurations = ActiveRecord::Base.configurations
+        ActiveRecord::Base.configurations = @configurations
 
-      ActiveRecord::Base.expects(:establish_connection).with(:development)
+        ActiveRecord::Base.connection_handler.stub(:establish_connection, nil) do
+          yield
+        end
+      ensure
+        ActiveRecord::Base.configurations = old_configurations
+      end
+  end
 
-      ActiveRecord::Tasks::DatabaseTasks.create_current(
-        ActiveSupport::StringInquirer.new('development')
-      )
+  class DatabaseTasksCreateCurrentThreeTierTest < ActiveRecord::TestCase
+    def setup
+      @configurations = {
+        "development" => { "primary" => { "database" => "dev-db" }, "secondary" => { "database" => "secondary-dev-db" } },
+        "test" => { "primary" => { "database" => "test-db" }, "secondary" => { "database" => "secondary-test-db" } },
+        "production" => { "primary" => { "url" => "abstract://prod-db-host/prod-db" }, "secondary" => { "url" => "abstract://secondary-prod-db-host/secondary-prod-db" } }
+      }
+    end
+
+    def test_creates_current_environment_database
+      with_stubbed_configurations_establish_connection do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :create,
+          [
+            ["database" => "test-db"],
+            ["database" => "secondary-test-db"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("test")
+          )
+        end
+      end
+    end
+
+    def test_creates_current_environment_database_with_url
+      with_stubbed_configurations_establish_connection do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :create,
+          [
+            ["adapter" => "abstract", "database" => "prod-db", "host" => "prod-db-host"],
+            ["adapter" => "abstract", "database" => "secondary-prod-db", "host" => "secondary-prod-db-host"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("production")
+          )
+        end
+      end
     end
+
+    def test_creates_test_and_development_databases_when_env_was_not_specified
+      with_stubbed_configurations_establish_connection do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :create,
+          [
+            ["database" => "dev-db"],
+            ["database" => "secondary-dev-db"],
+            ["database" => "test-db"],
+            ["database" => "secondary-test-db"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
+    end
+
+    def test_creates_test_and_development_databases_when_rails_env_is_development
+      old_env = ENV["RAILS_ENV"]
+      ENV["RAILS_ENV"] = "development"
+
+      with_stubbed_configurations_establish_connection do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :create,
+          [
+            ["database" => "dev-db"],
+            ["database" => "secondary-dev-db"],
+            ["database" => "test-db"],
+            ["database" => "secondary-test-db"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
+    ensure
+      ENV["RAILS_ENV"] = old_env
+    end
+
+    def test_establishes_connection_for_the_given_environments_config
+      ActiveRecord::Tasks::DatabaseTasks.stub(:create, nil) do
+        assert_called_with(
+          ActiveRecord::Base,
+          :establish_connection,
+          [:development]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.create_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
+    end
+
+    private
+      def with_stubbed_configurations_establish_connection
+        old_configurations = ActiveRecord::Base.configurations
+        ActiveRecord::Base.configurations = @configurations
+
+        ActiveRecord::Base.connection_handler.stub(:establish_connection, nil) do
+          yield
+        end
+      ensure
+        ActiveRecord::Base.configurations = old_configurations
+      end
   end
 
   class DatabaseTasksDropTest < ActiveRecord::TestCase
@@ -167,123 +459,431 @@ module ActiveRecord
 
     ADAPTERS_TASKS.each do |k, v|
       define_method("test_#{k}_drop") do
-        eval("@#{v}").expects(:drop)
-        ActiveRecord::Tasks::DatabaseTasks.drop 'adapter' => k
+        with_stubbed_new do
+          assert_called(eval("@#{v}"), :drop) do
+            ActiveRecord::Tasks::DatabaseTasks.drop "adapter" => k
+          end
+        end
       end
     end
   end
 
   class DatabaseTasksDropAllTest < ActiveRecord::TestCase
     def setup
-      @configurations = {:development => {'database' => 'my-db'}}
+      @configurations = { development: { "database" => "my-db" } }
 
-      ActiveRecord::Base.stubs(:configurations).returns(@configurations)
+      $stdout, @original_stdout = StringIO.new, $stdout
+      $stderr, @original_stderr = StringIO.new, $stderr
     end
 
-    def test_ignores_configurations_without_databases
-      @configurations[:development].merge!('database' => nil)
+    def teardown
+      $stdout, $stderr = @original_stdout, @original_stderr
+    end
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop).never
+    def test_ignores_configurations_without_databases
+      @configurations[:development]["database"] = nil
 
-      ActiveRecord::Tasks::DatabaseTasks.drop_all
+      with_stubbed_configurations do
+        assert_not_called(ActiveRecord::Tasks::DatabaseTasks, :drop) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_all
+        end
+      end
     end
 
     def test_ignores_remote_databases
-      @configurations[:development].merge!('host' => 'my.server.tld')
-      $stderr.stubs(:puts).returns(nil)
+      @configurations[:development]["host"] = "my.server.tld"
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop).never
-
-      ActiveRecord::Tasks::DatabaseTasks.drop_all
+      with_stubbed_configurations do
+        assert_not_called(ActiveRecord::Tasks::DatabaseTasks, :drop) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_all
+        end
+      end
     end
 
     def test_warning_for_remote_databases
-      @configurations[:development].merge!('host' => 'my.server.tld')
+      @configurations[:development]["host"] = "my.server.tld"
 
-      $stderr.expects(:puts).with('This task only modifies local databases. my-db is on a remote host.')
+      with_stubbed_configurations do
+        ActiveRecord::Tasks::DatabaseTasks.drop_all
 
-      ActiveRecord::Tasks::DatabaseTasks.drop_all
+        assert_match "This task only modifies local databases. my-db is on a remote host.",
+          $stderr.string
+      end
     end
 
     def test_drops_configurations_with_local_ip
-      @configurations[:development].merge!('host' => '127.0.0.1')
-
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop)
+      @configurations[:development]["host"] = "127.0.0.1"
 
-      ActiveRecord::Tasks::DatabaseTasks.drop_all
+      with_stubbed_configurations do
+        assert_called(ActiveRecord::Tasks::DatabaseTasks, :drop) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_all
+        end
+      end
     end
 
     def test_drops_configurations_with_local_host
-      @configurations[:development].merge!('host' => 'localhost')
+      @configurations[:development]["host"] = "localhost"
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop)
-
-      ActiveRecord::Tasks::DatabaseTasks.drop_all
+      with_stubbed_configurations do
+        assert_called(ActiveRecord::Tasks::DatabaseTasks, :drop) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_all
+        end
+      end
     end
 
     def test_drops_configurations_with_blank_hosts
-      @configurations[:development].merge!('host' => nil)
+      @configurations[:development]["host"] = nil
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop)
-
-      ActiveRecord::Tasks::DatabaseTasks.drop_all
+      with_stubbed_configurations do
+        assert_called(ActiveRecord::Tasks::DatabaseTasks, :drop) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_all
+        end
+      end
     end
+
+    private
+      def with_stubbed_configurations
+        old_configurations = ActiveRecord::Base.configurations
+        ActiveRecord::Base.configurations = @configurations
+
+        yield
+      ensure
+        ActiveRecord::Base.configurations = old_configurations
+      end
   end
 
   class DatabaseTasksDropCurrentTest < ActiveRecord::TestCase
     def setup
       @configurations = {
-        'development' => {'database' => 'dev-db'},
-        'test'        => {'database' => 'test-db'},
-        'production'  => {'database' => 'prod-db'}
+        "development" => { "database" => "dev-db" },
+        "test"        => { "database" => "test-db" },
+        "production"  => { "url" => "abstract://prod-db-host/prod-db" }
       }
+    end
+
+    def test_drops_current_environment_database
+      with_stubbed_configurations do
+        assert_called_with(ActiveRecord::Tasks::DatabaseTasks, :drop,
+          ["database" => "test-db"]) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_current(
+            ActiveSupport::StringInquirer.new("test")
+          )
+        end
+      end
+    end
+
+    def test_drops_current_environment_database_with_url
+      with_stubbed_configurations do
+        assert_called_with(ActiveRecord::Tasks::DatabaseTasks, :drop,
+          ["adapter" => "abstract", "database" => "prod-db", "host" => "prod-db-host"]) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_current(
+            ActiveSupport::StringInquirer.new("production")
+          )
+        end
+      end
+    end
+
+    def test_drops_test_and_development_databases_when_env_was_not_specified
+      with_stubbed_configurations do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :drop,
+          [
+            ["database" => "dev-db"],
+            ["database" => "test-db"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
+    end
+
+    def test_drops_testand_development_databases_when_rails_env_is_development
+      old_env = ENV["RAILS_ENV"]
+      ENV["RAILS_ENV"] = "development"
+
+      with_stubbed_configurations do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :drop,
+          [
+            ["database" => "dev-db"],
+            ["database" => "test-db"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
+    ensure
+      ENV["RAILS_ENV"] = old_env
+    end
+
+    private
+      def with_stubbed_configurations
+        old_configurations = ActiveRecord::Base.configurations
+        ActiveRecord::Base.configurations = @configurations
+
+        yield
+      ensure
+        ActiveRecord::Base.configurations = old_configurations
+      end
+  end
 
-      ActiveRecord::Base.stubs(:configurations).returns(@configurations)
+  class DatabaseTasksDropCurrentThreeTierTest < ActiveRecord::TestCase
+    def setup
+      @configurations = {
+        "development" => { "primary" => { "database" => "dev-db" }, "secondary" => { "database" => "secondary-dev-db" } },
+        "test" => { "primary" => { "database" => "test-db" }, "secondary" => { "database" => "secondary-test-db" } },
+        "production" => { "primary" => { "url" => "abstract://prod-db-host/prod-db" }, "secondary" => { "url" => "abstract://secondary-prod-db-host/secondary-prod-db" } }
+      }
     end
 
     def test_drops_current_environment_database
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop).
-        with('database' => 'prod-db')
+      with_stubbed_configurations do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :drop,
+          [
+            ["database" => "test-db"],
+            ["database" => "secondary-test-db"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_current(
+            ActiveSupport::StringInquirer.new("test")
+          )
+        end
+      end
+    end
 
-      ActiveRecord::Tasks::DatabaseTasks.drop_current(
-        ActiveSupport::StringInquirer.new('production')
-      )
+    def test_drops_current_environment_database_with_url
+      with_stubbed_configurations do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :drop,
+          [
+            ["adapter" => "abstract", "database" => "prod-db", "host" => "prod-db-host"],
+            ["adapter" => "abstract", "database" => "secondary-prod-db", "host" => "secondary-prod-db-host"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_current(
+            ActiveSupport::StringInquirer.new("production")
+          )
+        end
+      end
     end
 
     def test_drops_test_and_development_databases_when_env_was_not_specified
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop).
-        with('database' => 'dev-db')
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop).
-        with('database' => 'test-db')
-      ENV.expects(:[]).with('RAILS_ENV').returns(nil)
-
-      ActiveRecord::Tasks::DatabaseTasks.drop_current(
-        ActiveSupport::StringInquirer.new('development')
-      )
+      with_stubbed_configurations do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :drop,
+          [
+            ["database" => "dev-db"],
+            ["database" => "secondary-dev-db"],
+            ["database" => "test-db"],
+            ["database" => "secondary-test-db"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
     end
 
-    def test_drops_only_development_database_when_rails_env_is_development
-      ActiveRecord::Tasks::DatabaseTasks.expects(:drop).
-        with('database' => 'dev-db')
-      ENV.expects(:[]).with('RAILS_ENV').returns('development')
+    def test_drops_testand_development_databases_when_rails_env_is_development
+      old_env = ENV["RAILS_ENV"]
+      ENV["RAILS_ENV"] = "development"
+
+      with_stubbed_configurations do
+        assert_called_with(
+          ActiveRecord::Tasks::DatabaseTasks,
+          :drop,
+          [
+            ["database" => "dev-db"],
+            ["database" => "secondary-dev-db"],
+            ["database" => "test-db"],
+            ["database" => "secondary-test-db"]
+          ]
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.drop_current(
+            ActiveSupport::StringInquirer.new("development")
+          )
+        end
+      end
+    ensure
+      ENV["RAILS_ENV"] = old_env
+    end
 
-      ActiveRecord::Tasks::DatabaseTasks.drop_current(
-        ActiveSupport::StringInquirer.new('development')
-      )
+    private
+      def with_stubbed_configurations
+        old_configurations = ActiveRecord::Base.configurations
+        ActiveRecord::Base.configurations = @configurations
+
+        yield
+      ensure
+        ActiveRecord::Base.configurations = old_configurations
+      end
+  end
+
+  if current_adapter?(:SQLite3Adapter) && !in_memory_db?
+    class DatabaseTasksMigrationTestCase < ActiveRecord::TestCase
+      self.use_transactional_tests = false
+
+      # Use a memory db here to avoid having to rollback at the end
+      setup do
+        migrations_path = MIGRATIONS_ROOT + "/valid"
+        file = ActiveRecord::Base.connection.raw_connection.filename
+        @conn = ActiveRecord::Base.establish_connection adapter: "sqlite3",
+          database: ":memory:", migrations_paths: migrations_path
+        source_db = SQLite3::Database.new file
+        dest_db = ActiveRecord::Base.connection.raw_connection
+        backup = SQLite3::Backup.new(dest_db, "main", source_db, "main")
+        backup.step(-1)
+        backup.finish
+      end
+
+      teardown do
+        @conn.release_connection if @conn
+        ActiveRecord::Base.establish_connection :arunit
+      end
+    end
+
+    class DatabaseTasksMigrateTest < DatabaseTasksMigrationTestCase
+      def test_migrate_set_and_unset_verbose_and_version_env_vars
+        verbose, version = ENV["VERBOSE"], ENV["VERSION"]
+        ENV["VERSION"] = "2"
+        ENV["VERBOSE"] = "false"
+
+        # run down migration because it was already run on copied db
+        assert_empty capture_migration_output
+
+        ENV.delete("VERSION")
+        ENV.delete("VERBOSE")
+
+        # re-run up migration
+        assert_includes capture_migration_output, "migrating"
+      ensure
+        ENV["VERBOSE"], ENV["VERSION"] = verbose, version
+      end
+
+      def test_migrate_set_and_unset_empty_values_for_verbose_and_version_env_vars
+        verbose, version = ENV["VERBOSE"], ENV["VERSION"]
+
+        ENV["VERSION"] = "2"
+        ENV["VERBOSE"] = "false"
+
+        # run down migration because it was already run on copied db
+        assert_empty capture_migration_output
+
+        ENV["VERBOSE"] = ""
+        ENV["VERSION"] = ""
+
+        # re-run up migration
+        assert_includes capture_migration_output, "migrating"
+      ensure
+        ENV["VERBOSE"], ENV["VERSION"] = verbose, version
+      end
+
+      def test_migrate_set_and_unset_nonsense_values_for_verbose_and_version_env_vars
+        verbose, version = ENV["VERBOSE"], ENV["VERSION"]
+
+        # run down migration because it was already run on copied db
+        ENV["VERSION"] = "2"
+        ENV["VERBOSE"] = "false"
+
+        assert_empty capture_migration_output
+
+        ENV["VERBOSE"] = "yes"
+        ENV["VERSION"] = "2"
+
+        # run no migration because 2 was already run
+        assert_empty capture_migration_output
+      ensure
+        ENV["VERBOSE"], ENV["VERSION"] = verbose, version
+      end
+
+      private
+        def capture_migration_output
+          capture(:stdout) do
+            ActiveRecord::Tasks::DatabaseTasks.migrate
+          end
+        end
+    end
+
+    class DatabaseTasksMigrateStatusTest < DatabaseTasksMigrationTestCase
+      def test_migrate_status_table
+        ActiveRecord::SchemaMigration.create_table
+        output = capture_migration_status
+        assert_match(/database: :memory:/, output)
+        assert_match(/down    001             Valid people have last names/, output)
+        assert_match(/down    002             We need reminders/, output)
+        assert_match(/down    003             Innocent jointable/, output)
+        ActiveRecord::SchemaMigration.drop_table
+      end
+
+      private
+
+        def capture_migration_status
+          capture(:stdout) do
+            ActiveRecord::Tasks::DatabaseTasks.migrate_status
+          end
+        end
     end
   end
 
-  class DatabaseTasksMigrateTest < ActiveRecord::TestCase
-    def test_migrate_receives_correct_env_vars
-      verbose, version = ENV['VERBOSE'], ENV['VERSION']
+  class DatabaseTasksMigrateErrorTest < ActiveRecord::TestCase
+    self.use_transactional_tests = false
+
+    def test_migrate_raise_error_on_invalid_version_format
+      version = ENV["VERSION"]
+
+      ENV["VERSION"] = "unknown"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.migrate }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "0.1.11"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.migrate }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "1.1.11"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.migrate }
+      assert_match(/Invalid format of target version/, e.message)
 
-      ENV['VERBOSE'] = 'false'
-      ENV['VERSION'] = '4'
+      ENV["VERSION"] = "0 "
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.migrate }
+      assert_match(/Invalid format of target version/, e.message)
 
-      ActiveRecord::Migrator.expects(:migrate).with(ActiveRecord::Migrator.migrations_paths, 4)
-      ActiveRecord::Tasks::DatabaseTasks.migrate
+      ENV["VERSION"] = "1."
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.migrate }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "1_"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.migrate }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "1_name"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.migrate }
+      assert_match(/Invalid format of target version/, e.message)
     ensure
-      ENV['VERBOSE'], ENV['VERSION'] = verbose, version
+      ENV["VERSION"] = version
+    end
+
+    def test_migrate_raise_error_on_failed_check_target_version
+      ActiveRecord::Tasks::DatabaseTasks.stub(:check_target_version, -> { raise "foo" }) do
+        e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.migrate }
+        assert_equal "foo", e.message
+      end
+    end
+
+    def test_migrate_clears_schema_cache_afterward
+      assert_called(ActiveRecord::Base, :clear_cache!) do
+        ActiveRecord::Tasks::DatabaseTasks.migrate
+      end
     end
   end
 
@@ -292,38 +892,55 @@ module ActiveRecord
 
     ADAPTERS_TASKS.each do |k, v|
       define_method("test_#{k}_purge") do
-        eval("@#{v}").expects(:purge)
-        ActiveRecord::Tasks::DatabaseTasks.purge 'adapter' => k
+        with_stubbed_new do
+          assert_called(eval("@#{v}"), :purge) do
+            ActiveRecord::Tasks::DatabaseTasks.purge "adapter" => k
+          end
+        end
       end
     end
   end
 
   class DatabaseTasksPurgeCurrentTest < ActiveRecord::TestCase
     def test_purges_current_environment_database
+      old_configurations = ActiveRecord::Base.configurations
       configurations = {
-        'development' => {'database' => 'dev-db'},
-        'test'        => {'database' => 'test-db'},
-        'production'  => {'database' => 'prod-db'}
+        "development" => { "database" => "dev-db" },
+        "test"        => { "database" => "test-db" },
+        "production"  => { "database" => "prod-db" }
       }
-      ActiveRecord::Base.stubs(:configurations).returns(configurations)
 
-      ActiveRecord::Tasks::DatabaseTasks.expects(:purge).
-        with('database' => 'prod-db')
-      ActiveRecord::Base.expects(:establish_connection).with(:production)
+      ActiveRecord::Base.configurations = configurations
 
-      ActiveRecord::Tasks::DatabaseTasks.purge_current('production')
+      assert_called_with(
+        ActiveRecord::Tasks::DatabaseTasks,
+        :purge,
+        ["database" => "prod-db"]
+      ) do
+        assert_called_with(ActiveRecord::Base, :establish_connection, [:production]) do
+          ActiveRecord::Tasks::DatabaseTasks.purge_current("production")
+        end
+      end
+    ensure
+      ActiveRecord::Base.configurations = old_configurations
     end
   end
 
   class DatabaseTasksPurgeAllTest < ActiveRecord::TestCase
     def test_purge_all_local_configurations
-      configurations = {:development => {'database' => 'my-db'}}
-      ActiveRecord::Base.stubs(:configurations).returns(configurations)
-
-      ActiveRecord::Tasks::DatabaseTasks.expects(:purge).
-        with('database' => 'my-db')
-
-      ActiveRecord::Tasks::DatabaseTasks.purge_all
+      old_configurations = ActiveRecord::Base.configurations
+      configurations = { development: { "database" => "my-db" } }
+      ActiveRecord::Base.configurations = configurations
+
+      assert_called_with(
+        ActiveRecord::Tasks::DatabaseTasks,
+        :purge,
+        ["database" => "my-db"]
+      ) do
+        ActiveRecord::Tasks::DatabaseTasks.purge_all
+      end
+    ensure
+      ActiveRecord::Base.configurations = old_configurations
     end
   end
 
@@ -332,8 +949,11 @@ module ActiveRecord
 
     ADAPTERS_TASKS.each do |k, v|
       define_method("test_#{k}_charset") do
-        eval("@#{v}").expects(:charset)
-        ActiveRecord::Tasks::DatabaseTasks.charset 'adapter' => k
+        with_stubbed_new do
+          assert_called(eval("@#{v}"), :charset) do
+            ActiveRecord::Tasks::DatabaseTasks.charset "adapter" => k
+          end
+        end
       end
     end
   end
@@ -343,19 +963,130 @@ module ActiveRecord
 
     ADAPTERS_TASKS.each do |k, v|
       define_method("test_#{k}_collation") do
-        eval("@#{v}").expects(:collation)
-        ActiveRecord::Tasks::DatabaseTasks.collation 'adapter' => k
+        with_stubbed_new do
+          assert_called(eval("@#{v}"), :collation) do
+            ActiveRecord::Tasks::DatabaseTasks.collation "adapter" => k
+          end
+        end
       end
     end
   end
 
+  class DatabaseTaskTargetVersionTest < ActiveRecord::TestCase
+    def test_target_version_returns_nil_if_version_does_not_exist
+      version = ENV.delete("VERSION")
+      assert_nil ActiveRecord::Tasks::DatabaseTasks.target_version
+    ensure
+      ENV["VERSION"] = version
+    end
+
+    def test_target_version_returns_nil_if_version_is_empty
+      version = ENV["VERSION"]
+
+      ENV["VERSION"] = ""
+      assert_nil ActiveRecord::Tasks::DatabaseTasks.target_version
+    ensure
+      ENV["VERSION"] = version
+    end
+
+    def test_target_version_returns_converted_to_integer_env_version_if_version_exists
+      version = ENV["VERSION"]
+
+      ENV["VERSION"] = "0"
+      assert_equal ENV["VERSION"].to_i, ActiveRecord::Tasks::DatabaseTasks.target_version
+
+      ENV["VERSION"] = "42"
+      assert_equal ENV["VERSION"].to_i, ActiveRecord::Tasks::DatabaseTasks.target_version
+
+      ENV["VERSION"] = "042"
+      assert_equal ENV["VERSION"].to_i, ActiveRecord::Tasks::DatabaseTasks.target_version
+    ensure
+      ENV["VERSION"] = version
+    end
+  end
+
+  class DatabaseTaskCheckTargetVersionTest < ActiveRecord::TestCase
+    def test_check_target_version_does_not_raise_error_on_empty_version
+      version = ENV["VERSION"]
+      ENV["VERSION"] = ""
+      assert_nothing_raised { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+    ensure
+      ENV["VERSION"] = version
+    end
+
+    def test_check_target_version_does_not_raise_error_if_version_is_not_setted
+      version = ENV.delete("VERSION")
+      assert_nothing_raised { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+    ensure
+      ENV["VERSION"] = version
+    end
+
+    def test_check_target_version_raises_error_on_invalid_version_format
+      version = ENV["VERSION"]
+
+      ENV["VERSION"] = "unknown"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "0.1.11"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "1.1.11"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "0 "
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "1."
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "1_"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+      assert_match(/Invalid format of target version/, e.message)
+
+      ENV["VERSION"] = "1_name"
+      e = assert_raise(RuntimeError) { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+      assert_match(/Invalid format of target version/, e.message)
+    ensure
+      ENV["VERSION"] = version
+    end
+
+    def test_check_target_version_does_not_raise_error_on_valid_version_format
+      version = ENV["VERSION"]
+
+      ENV["VERSION"] = "0"
+      assert_nothing_raised { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+
+      ENV["VERSION"] = "1"
+      assert_nothing_raised { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+
+      ENV["VERSION"] = "001"
+      assert_nothing_raised { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+
+      ENV["VERSION"] = "001_name.rb"
+      assert_nothing_raised { ActiveRecord::Tasks::DatabaseTasks.check_target_version }
+    ensure
+      ENV["VERSION"] = version
+    end
+  end
+
   class DatabaseTasksStructureDumpTest < ActiveRecord::TestCase
     include DatabaseTasksSetupper
 
     ADAPTERS_TASKS.each do |k, v|
       define_method("test_#{k}_structure_dump") do
-        eval("@#{v}").expects(:structure_dump).with("awesome-file.sql")
-        ActiveRecord::Tasks::DatabaseTasks.structure_dump({'adapter' => k}, "awesome-file.sql")
+        with_stubbed_new do
+          assert_called_with(
+            eval("@#{v}"), :structure_dump,
+            ["awesome-file.sql", nil]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump({ "adapter" => k }, "awesome-file.sql")
+          end
+        end
       end
     end
   end
@@ -365,31 +1096,41 @@ module ActiveRecord
 
     ADAPTERS_TASKS.each do |k, v|
       define_method("test_#{k}_structure_load") do
-        eval("@#{v}").expects(:structure_load).with("awesome-file.sql")
-        ActiveRecord::Tasks::DatabaseTasks.structure_load({'adapter' => k}, "awesome-file.sql")
+        with_stubbed_new do
+          assert_called_with(
+            eval("@#{v}"),
+            :structure_load,
+            ["awesome-file.sql", nil]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_load({ "adapter" => k }, "awesome-file.sql")
+          end
+        end
       end
     end
   end
 
   class DatabaseTasksCheckSchemaFileTest < ActiveRecord::TestCase
     def test_check_schema_file
-      Kernel.expects(:abort).with(regexp_matches(/awesome-file.sql/))
-      ActiveRecord::Tasks::DatabaseTasks.check_schema_file("awesome-file.sql")
+      assert_called_with(Kernel, :abort, [/awesome-file.sql/]) do
+        ActiveRecord::Tasks::DatabaseTasks.check_schema_file("awesome-file.sql")
+      end
     end
   end
 
   class DatabaseTasksCheckSchemaFileDefaultsTest < ActiveRecord::TestCase
     def test_check_schema_file_defaults
-      ActiveRecord::Tasks::DatabaseTasks.stubs(:db_dir).returns('/tmp')
-      assert_equal '/tmp/schema.rb', ActiveRecord::Tasks::DatabaseTasks.schema_file
+      ActiveRecord::Tasks::DatabaseTasks.stub(:db_dir, "/tmp") do
+        assert_equal "/tmp/schema.rb", ActiveRecord::Tasks::DatabaseTasks.schema_file
+      end
     end
   end
 
   class DatabaseTasksCheckSchemaFileSpecifiedFormatsTest < ActiveRecord::TestCase
-    {ruby: 'schema.rb', sql: 'structure.sql'}.each_pair do |fmt, filename|
+    { ruby: "schema.rb", sql: "structure.sql" }.each_pair do |fmt, filename|
       define_method("test_check_schema_file_for_#{fmt}_format") do
-        ActiveRecord::Tasks::DatabaseTasks.stubs(:db_dir).returns('/tmp')
-        assert_equal "/tmp/#{filename}", ActiveRecord::Tasks::DatabaseTasks.schema_file(fmt)
+        ActiveRecord::Tasks::DatabaseTasks.stub(:db_dir, "/tmp") do
+          assert_equal "/tmp/#{filename}", ActiveRecord::Tasks::DatabaseTasks.schema_file(fmt)
+        end
       end
     end
   end
diff --git a/activerecord/test/cases/tasks/mysql_rake_test.rb b/activerecord/test/cases/tasks/mysql_rake_test.rb
index d0deb4c273..552e623fd4 100644
--- a/activerecord/test/cases/tasks/mysql_rake_test.rb
+++ b/activerecord/test/cases/tasks/mysql_rake_test.rb
@@ -1,320 +1,409 @@
-require 'cases/helper'
-
-if current_adapter?(:MysqlAdapter, :Mysql2Adapter)
-module ActiveRecord
-  class MysqlDBCreateTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:create_database => true)
-      @configuration = {
-        'adapter'  => 'mysql',
-        'database' => 'my-app-db'
-      }
-
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
-
-    def test_establishes_connection_without_database
-      ActiveRecord::Base.expects(:establish_connection).
-        with('adapter' => 'mysql', 'database' => nil)
-
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
-    end
-
-    def test_creates_database_with_default_encoding_and_collation
-      @connection.expects(:create_database).
-        with('my-app-db', charset: 'utf8', collation: 'utf8_unicode_ci')
-
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
-    end
-
-    def test_creates_database_with_given_encoding_and_default_collation
-      @connection.expects(:create_database).
-        with('my-app-db', charset: 'utf8', collation: 'utf8_unicode_ci')
-
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration.merge('encoding' => 'utf8')
-    end
-
-    def test_creates_database_with_given_encoding_and_no_collation
-      @connection.expects(:create_database).
-        with('my-app-db', charset: 'latin1')
-
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration.merge('encoding' => 'latin1')
-    end
-
-    def test_creates_database_with_given_collation_and_no_encoding
-      @connection.expects(:create_database).
-        with('my-app-db', collation: 'latin1_swedish_ci')
-
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration.merge('collation' => 'latin1_swedish_ci')
-    end
+# frozen_string_literal: true
 
-    def test_establishes_connection_to_database
-      ActiveRecord::Base.expects(:establish_connection).with(@configuration)
+require "cases/helper"
+require "active_record/tasks/database_tasks"
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
-    end
-
-    def test_create_when_database_exists_outputs_info_to_stderr
-      $stderr.expects(:puts).with("my-app-db already exists").once
-
-      ActiveRecord::Base.connection.stubs(:create_database).raises(
-        ActiveRecord::StatementInvalid.new("Can't create database 'dev'; database exists:")
-      )
-
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
-    end
-  end
-
-  if current_adapter?(:MysqlAdapter)
-    class MysqlDBCreateAsRootTest < ActiveRecord::TestCase
+if current_adapter?(:Mysql2Adapter)
+  module ActiveRecord
+    class MysqlDBCreateTest < ActiveRecord::TestCase
       def setup
-        @connection    = stub("Connection", create_database: true)
-        @error         = Mysql::Error.new "Invalid permissions"
+        @connection    = Class.new { def create_database(*); end }.new
         @configuration = {
-          'adapter'  => 'mysql',
-          'database' => 'my-app-db',
-          'username' => 'pat',
-          'password' => 'wossname'
+          "adapter"  => "mysql2",
+          "database" => "my-app-db"
         }
-
-        $stdin.stubs(:gets).returns("secret\n")
-        $stdout.stubs(:print).returns(nil)
-        @error.stubs(:errno).returns(1045)
-        ActiveRecord::Base.stubs(:connection).returns(@connection)
-        ActiveRecord::Base.stubs(:establish_connection).
-          raises(@error).
-          then.returns(true)
+        $stdout, @original_stdout = StringIO.new, $stdout
+        $stderr, @original_stderr = StringIO.new, $stderr
       end
 
-      if defined?(::Mysql)
-        def test_root_password_is_requested
-          assert_permissions_granted_for "pat"
-          $stdin.expects(:gets).returns("secret\n")
+      def teardown
+        $stdout, $stderr = @original_stdout, @original_stderr
+      end
 
-          ActiveRecord::Tasks::DatabaseTasks.create @configuration
+      def test_establishes_connection_without_database
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [
+              [ "adapter" => "mysql2", "database" => nil ],
+              [ "adapter" => "mysql2", "database" => "my-app-db" ],
+            ]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
+          end
         end
       end
 
-      def test_connection_established_as_root
-        assert_permissions_granted_for "pat"
-        ActiveRecord::Base.expects(:establish_connection).with(
-          'adapter'  => 'mysql',
-          'database' => nil,
-          'username' => 'root',
-          'password' => 'secret'
-        )
-
-        ActiveRecord::Tasks::DatabaseTasks.create @configuration
+      def test_creates_database_with_no_default_options
+        with_stubbed_connection_establish_connection do
+          assert_called_with(@connection, :create_database, ["my-app-db", {}]) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
+          end
+        end
       end
 
-      def test_database_created_by_root
-        assert_permissions_granted_for "pat"
-        @connection.expects(:create_database).
-          with('my-app-db', :charset => 'utf8', :collation => 'utf8_unicode_ci')
-
-        ActiveRecord::Tasks::DatabaseTasks.create @configuration
+      def test_creates_database_with_given_encoding
+        with_stubbed_connection_establish_connection do
+          assert_called_with(@connection, :create_database, ["my-app-db", charset: "latin1"]) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration.merge("encoding" => "latin1")
+          end
+        end
       end
 
-      def test_grant_privileges_for_normal_user
-        assert_permissions_granted_for "pat"
-        ActiveRecord::Tasks::DatabaseTasks.create @configuration
+      def test_creates_database_with_given_collation
+        with_stubbed_connection_establish_connection do
+          assert_called_with(
+            @connection,
+            :create_database,
+            ["my-app-db", collation: "latin1_swedish_ci"]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration.merge("collation" => "latin1_swedish_ci")
+          end
+        end
       end
 
-      def test_do_not_grant_privileges_for_root_user
-        @configuration['username'] = 'root'
-        @configuration['password'] = ''
-        ActiveRecord::Tasks::DatabaseTasks.create @configuration
+      def test_establishes_connection_to_database
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [
+              ["adapter" => "mysql2", "database" => nil],
+              [@configuration]
+            ]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
+          end
+        end
       end
 
-      def test_connection_established_as_normal_user
-        assert_permissions_granted_for "pat"
-        ActiveRecord::Base.expects(:establish_connection).returns do
-          ActiveRecord::Base.expects(:establish_connection).with(
-            'adapter'  => 'mysql',
-            'database' => 'my-app-db',
-            'username' => 'pat',
-            'password' => 'secret'
-          )
+      def test_when_database_created_successfully_outputs_info_to_stdout
+        with_stubbed_connection_establish_connection do
+          ActiveRecord::Tasks::DatabaseTasks.create @configuration
 
-          raise @error
+          assert_equal "Created database 'my-app-db'\n", $stdout.string
         end
-
-        ActiveRecord::Tasks::DatabaseTasks.create @configuration
       end
 
-      def test_sends_output_to_stderr_when_other_errors
-        @error.stubs(:errno).returns(42)
+      def test_create_when_database_exists_outputs_info_to_stderr
+        with_stubbed_connection_establish_connection do
+          ActiveRecord::Base.connection.stub(
+            :create_database,
+            proc { raise ActiveRecord::Tasks::DatabaseAlreadyExists }
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
 
-        $stderr.expects(:puts).at_least_once.returns(nil)
-
-        ActiveRecord::Tasks::DatabaseTasks.create @configuration
+            assert_equal "Database 'my-app-db' already exists\n", $stderr.string
+          end
+        end
       end
 
       private
-        def assert_permissions_granted_for(db_user)
-          db_name = @configuration['database']
-          db_password = @configuration['password']
-          @connection.expects(:execute).with("GRANT ALL PRIVILEGES ON #{db_name}.* TO '#{db_user}'@'localhost' IDENTIFIED BY '#{db_password}' WITH GRANT OPTION;")
+
+        def with_stubbed_connection_establish_connection
+          ActiveRecord::Base.stub(:establish_connection, nil) do
+            ActiveRecord::Base.stub(:connection, @connection) do
+              yield
+            end
+          end
         end
     end
-  end
 
-  class MySQLDBDropTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:drop_database => true)
-      @configuration = {
-        'adapter'  => 'mysql',
-        'database' => 'my-app-db'
-      }
-
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+    class MysqlDBCreateWithInvalidPermissionsTest < ActiveRecord::TestCase
+      def setup
+        @error         = Mysql2::Error.new("Invalid permissions")
+        @configuration = {
+          "adapter"  => "mysql2",
+          "database" => "my-app-db",
+          "username" => "pat",
+          "password" => "wossname"
+        }
+        $stdout, @original_stdout = StringIO.new, $stdout
+        $stderr, @original_stderr = StringIO.new, $stderr
+      end
 
-    def test_establishes_connection_to_mysql_database
-      ActiveRecord::Base.expects(:establish_connection).with @configuration
+      def teardown
+        $stdout, $stderr = @original_stdout, @original_stderr
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.drop @configuration
+      def test_raises_error
+        ActiveRecord::Base.stub(:establish_connection, -> * { raise @error }) do
+          assert_raises(Mysql2::Error, "Invalid permissions") do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
+          end
+        end
+      end
     end
 
-    def test_drops_database
-      @connection.expects(:drop_database).with('my-app-db')
+    class MySQLDBDropTest < ActiveRecord::TestCase
+      def setup
+        @connection    = Class.new { def drop_database(name); end }.new
+        @configuration = {
+          "adapter"  => "mysql2",
+          "database" => "my-app-db"
+        }
+        $stdout, @original_stdout = StringIO.new, $stdout
+        $stderr, @original_stderr = StringIO.new, $stderr
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.drop @configuration
-    end
-  end
+      def teardown
+        $stdout, $stderr = @original_stdout, @original_stderr
+      end
 
-  class MySQLPurgeTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:recreate_database => true)
-      @configuration = {
-        'adapter'  => 'mysql',
-        'database' => 'test-db'
-      }
+      def test_establishes_connection_to_mysql_database
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [@configuration]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.drop @configuration
+          end
+        end
+      end
 
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+      def test_drops_database
+        with_stubbed_connection_establish_connection do
+          assert_called_with(@connection, :drop_database, ["my-app-db"]) do
+            ActiveRecord::Tasks::DatabaseTasks.drop @configuration
+          end
+        end
+      end
 
-    def test_establishes_connection_to_the_appropriate_database
-      ActiveRecord::Base.expects(:establish_connection).with(@configuration)
+      def test_when_database_dropped_successfully_outputs_info_to_stdout
+        with_stubbed_connection_establish_connection do
+          ActiveRecord::Tasks::DatabaseTasks.drop @configuration
 
-      ActiveRecord::Tasks::DatabaseTasks.purge @configuration
-    end
+          assert_equal "Dropped database 'my-app-db'\n", $stdout.string
+        end
+      end
 
-    def test_recreates_database_with_the_default_options
-      @connection.expects(:recreate_database).
-        with('test-db', charset: 'utf8', collation: 'utf8_unicode_ci')
+      private
 
-      ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+        def with_stubbed_connection_establish_connection
+          ActiveRecord::Base.stub(:establish_connection, nil) do
+            ActiveRecord::Base.stub(:connection, @connection) do
+              yield
+            end
+          end
+        end
     end
 
-    def test_recreates_database_with_the_given_options
-      @connection.expects(:recreate_database).
-        with('test-db', charset: 'latin', collation: 'latin1_swedish_ci')
+    class MySQLPurgeTest < ActiveRecord::TestCase
+      def setup
+        @connection    = Class.new { def recreate_database(*); end }.new
+        @configuration = {
+          "adapter"  => "mysql2",
+          "database" => "test-db"
+        }
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.purge @configuration.merge(
-        'encoding' => 'latin', 'collation' => 'latin1_swedish_ci')
-    end
-  end
+      def test_establishes_connection_to_the_appropriate_database
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [@configuration]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+          end
+        end
+      end
 
-  class MysqlDBCharsetTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:create_database => true)
-      @configuration = {
-        'adapter'  => 'mysql',
-        'database' => 'my-app-db'
-      }
+      def test_recreates_database_with_no_default_options
+        with_stubbed_connection_establish_connection do
+          assert_called_with(@connection, :recreate_database, ["test-db", {}]) do
+            ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+          end
+        end
+      end
 
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+      def test_recreates_database_with_the_given_options
+        with_stubbed_connection_establish_connection do
+          assert_called_with(
+            @connection,
+            :recreate_database,
+            ["test-db", charset: "latin", collation: "latin1_swedish_ci"]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.purge @configuration.merge(
+              "encoding" => "latin", "collation" => "latin1_swedish_ci")
+          end
+        end
+      end
+
+      private
 
-    def test_db_retrieves_charset
-      @connection.expects(:charset)
-      ActiveRecord::Tasks::DatabaseTasks.charset @configuration
+        def with_stubbed_connection_establish_connection
+          ActiveRecord::Base.stub(:establish_connection, nil) do
+            ActiveRecord::Base.stub(:connection, @connection) do
+              yield
+            end
+          end
+        end
     end
-  end
 
-  class MysqlDBCollationTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:create_database => true)
-      @configuration = {
-        'adapter'  => 'mysql',
-        'database' => 'my-app-db'
-      }
+    class MysqlDBCharsetTest < ActiveRecord::TestCase
+      def setup
+        @connection    = Class.new { def charset; end }.new
+        @configuration = {
+          "adapter"  => "mysql2",
+          "database" => "my-app-db"
+        }
+      end
 
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
+      def test_db_retrieves_charset
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called(@connection, :charset) do
+            ActiveRecord::Tasks::DatabaseTasks.charset @configuration
+          end
+        end
+      end
     end
 
-    def test_db_retrieves_collation
-      @connection.expects(:collation)
-      ActiveRecord::Tasks::DatabaseTasks.collation @configuration
-    end
-  end
+    class MysqlDBCollationTest < ActiveRecord::TestCase
+      def setup
+        @connection    = Class.new { def collation; end }.new
+        @configuration = {
+          "adapter"  => "mysql2",
+          "database" => "my-app-db"
+        }
+      end
 
-  class MySQLStructureDumpTest < ActiveRecord::TestCase
-    def setup
-      @configuration = {
-        'adapter'  => 'mysql',
-        'database' => 'test-db'
-      }
+      def test_db_retrieves_collation
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called(@connection, :collation) do
+            ActiveRecord::Tasks::DatabaseTasks.collation @configuration
+          end
+        end
+      end
     end
 
-    def test_structure_dump
-      filename = "awesome-file.sql"
-      Kernel.expects(:system).with("mysqldump", "--result-file", filename, "--no-data", "--routines", "test-db").returns(true)
+    class MySQLStructureDumpTest < ActiveRecord::TestCase
+      def setup
+        @configuration = {
+          "adapter"  => "mysql2",
+          "database" => "test-db"
+        }
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
-    end
+      def test_structure_dump
+        filename = "awesome-file.sql"
+        assert_called_with(
+          Kernel,
+          :system,
+          ["mysqldump", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "test-db"],
+          returns: true
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
+        end
+      end
 
-    def test_warn_when_external_structure_dump_fails
-      filename = "awesome-file.sql"
-      Kernel.expects(:system).with("mysqldump", "--result-file", filename, "--no-data", "--routines", "test-db").returns(false)
+      def test_structure_dump_with_extra_flags
+        filename = "awesome-file.sql"
+        expected_command = ["mysqldump", "--noop", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "test-db"]
 
-      warnings = capture(:stderr) do
-        ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
+        assert_called_with(Kernel, :system, expected_command, returns: true) do
+          with_structure_dump_flags(["--noop"]) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
+          end
+        end
       end
 
-      assert_match(/Could not dump the database structure/, warnings)
-    end
+      def test_structure_dump_with_ignore_tables
+        filename = "awesome-file.sql"
+        ActiveRecord::SchemaDumper.stub(:ignore_tables, ["foo", "bar"]) do
+          assert_called_with(
+            Kernel,
+            :system,
+            ["mysqldump", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "--ignore-table=test-db.foo", "--ignore-table=test-db.bar", "test-db"],
+            returns: true
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
+          end
+        end
+      end
 
-    def test_structure_dump_with_port_number
-      filename = "awesome-file.sql"
-      Kernel.expects(:system).with("mysqldump", "--port=10000", "--result-file", filename, "--no-data", "--routines", "test-db").returns(true)
+      def test_warn_when_external_structure_dump_command_execution_fails
+        filename = "awesome-file.sql"
+        assert_called_with(
+          Kernel,
+          :system,
+          ["mysqldump", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "test-db"],
+          returns: false
+        ) do
+          e = assert_raise(RuntimeError) {
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
+          }
+          assert_match(/^failed to execute: `mysqldump`$/, e.message)
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_dump(
-        @configuration.merge('port' => 10000),
-        filename)
-    end
+      def test_structure_dump_with_port_number
+        filename = "awesome-file.sql"
+        assert_called_with(
+          Kernel,
+          :system,
+          ["mysqldump", "--port=10000", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "test-db"],
+          returns: true
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump(
+            @configuration.merge("port" => 10000),
+            filename)
+        end
+      end
 
-    def test_structure_dump_with_ssl
-      filename = "awesome-file.sql"
-      Kernel.expects(:system).with("mysqldump", "--ssl-ca=ca.crt", "--result-file", filename, "--no-data", "--routines", "test-db").returns(true)
+      def test_structure_dump_with_ssl
+        filename = "awesome-file.sql"
+        assert_called_with(
+          Kernel,
+          :system,
+          ["mysqldump", "--ssl-ca=ca.crt", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "test-db"],
+          returns: true
+        ) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(
+              @configuration.merge("sslca" => "ca.crt"),
+              filename)
+          end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_dump(
-        @configuration.merge("sslca" => "ca.crt"),
-        filename)
+      private
+        def with_structure_dump_flags(flags)
+          old = ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags = flags
+          yield
+        ensure
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags = old
+        end
     end
-  end
 
-  class MySQLStructureLoadTest < ActiveRecord::TestCase
-    def setup
-      @configuration = {
-        'adapter'  => 'mysql',
-        'database' => 'test-db'
-      }
-    end
+    class MySQLStructureLoadTest < ActiveRecord::TestCase
+      def setup
+        @configuration = {
+          "adapter"  => "mysql2",
+          "database" => "test-db"
+        }
+      end
 
-    def test_structure_load
-      filename = "awesome-file.sql"
-      Kernel.expects(:system).with('mysql', '--execute', %{SET FOREIGN_KEY_CHECKS = 0; SOURCE #{filename}; SET FOREIGN_KEY_CHECKS = 1}, "--database", "test-db")
+      def test_structure_load
+        filename = "awesome-file.sql"
+        expected_command = ["mysql", "--noop", "--execute", %{SET FOREIGN_KEY_CHECKS = 0; SOURCE #{filename}; SET FOREIGN_KEY_CHECKS = 1}, "--database", "test-db"]
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_load(@configuration, filename)
+        assert_called_with(Kernel, :system, expected_command, returns: true) do
+          with_structure_load_flags(["--noop"]) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_load(@configuration, filename)
+          end
+        end
+      end
+
+      private
+        def with_structure_load_flags(flags)
+          old = ActiveRecord::Tasks::DatabaseTasks.structure_load_flags
+          ActiveRecord::Tasks::DatabaseTasks.structure_load_flags = flags
+          yield
+        ensure
+          ActiveRecord::Tasks::DatabaseTasks.structure_load_flags = old
+        end
     end
   end
-
-end
 end
diff --git a/activerecord/test/cases/tasks/postgresql_rake_test.rb b/activerecord/test/cases/tasks/postgresql_rake_test.rb
index 084302cde5..065ba7734c 100644
--- a/activerecord/test/cases/tasks/postgresql_rake_test.rb
+++ b/activerecord/test/cases/tasks/postgresql_rake_test.rb
@@ -1,278 +1,539 @@
-require 'cases/helper'
+# frozen_string_literal: true
 
-if current_adapter?(:PostgreSQLAdapter)
-module ActiveRecord
-  class PostgreSQLDBCreateTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:create_database => true)
-      @configuration = {
-        'adapter'  => 'postgresql',
-        'database' => 'my-app-db'
-      }
-
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
-
-    def test_establishes_connection_to_postgresql_database
-      ActiveRecord::Base.expects(:establish_connection).with(
-        'adapter'            => 'postgresql',
-        'database'           => 'postgres',
-        'schema_search_path' => 'public'
-      )
-
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
-    end
+require "cases/helper"
+require "active_record/tasks/database_tasks"
 
-    def test_creates_database_with_default_encoding
-      @connection.expects(:create_database).
-        with('my-app-db', @configuration.merge('encoding' => 'utf8'))
-
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
-    end
+if current_adapter?(:PostgreSQLAdapter)
+  module ActiveRecord
+    class PostgreSQLDBCreateTest < ActiveRecord::TestCase
+      def setup
+        @connection    = Class.new { def create_database(*); end }.new
+        @configuration = {
+          "adapter"  => "postgresql",
+          "database" => "my-app-db"
+        }
+        $stdout, @original_stdout = StringIO.new, $stdout
+        $stderr, @original_stderr = StringIO.new, $stderr
+      end
 
-    def test_creates_database_with_given_encoding
-      @connection.expects(:create_database).
-        with('my-app-db', @configuration.merge('encoding' => 'latin'))
+      def teardown
+        $stdout, $stderr = @original_stdout, @original_stderr
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration.
-        merge('encoding' => 'latin')
-    end
+      def test_establishes_connection_to_postgresql_database
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [
+              [
+                "adapter"            => "postgresql",
+                "database"           => "postgres",
+                "schema_search_path" => "public"
+              ],
+              [
+                "adapter"            => "postgresql",
+                "database"           => "my-app-db"
+              ]
+            ]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
+          end
+        end
+      end
 
-    def test_creates_database_with_given_collation_and_ctype
-      @connection.expects(:create_database).
-        with('my-app-db', @configuration.merge('encoding' => 'utf8', 'collation' => 'ja_JP.UTF8', 'ctype' => 'ja_JP.UTF8'))
+      def test_creates_database_with_default_encoding
+        with_stubbed_connection_establish_connection do
+          assert_called_with(
+            @connection,
+            :create_database,
+            ["my-app-db", @configuration.merge("encoding" => "utf8")]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
+          end
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration.
-        merge('collation' => 'ja_JP.UTF8', 'ctype' => 'ja_JP.UTF8')
-    end
+      def test_creates_database_with_given_encoding
+        with_stubbed_connection_establish_connection do
+          assert_called_with(
+            @connection,
+            :create_database,
+            ["my-app-db", @configuration.merge("encoding" => "latin")]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration.
+              merge("encoding" => "latin")
+          end
+        end
+      end
 
-    def test_establishes_connection_to_new_database
-      ActiveRecord::Base.expects(:establish_connection).with(@configuration)
+      def test_creates_database_with_given_collation_and_ctype
+        with_stubbed_connection_establish_connection do
+          assert_called_with(
+            @connection,
+            :create_database,
+            [
+              "my-app-db",
+              @configuration.merge(
+                "encoding" => "utf8",
+                "collation" => "ja_JP.UTF8",
+                "ctype" => "ja_JP.UTF8"
+              )
+            ]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration.
+              merge("collation" => "ja_JP.UTF8", "ctype" => "ja_JP.UTF8")
+          end
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
-    end
+      def test_establishes_connection_to_new_database
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [
+              [
+                "adapter"            => "postgresql",
+                "database"           => "postgres",
+                "schema_search_path" => "public"
+              ],
+              [
+                @configuration
+              ]
+            ]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
+          end
+        end
+      end
 
-    def test_db_create_with_error_prints_message
-      ActiveRecord::Base.stubs(:establish_connection).raises(Exception)
+      def test_db_create_with_error_prints_message
+        ActiveRecord::Base.stub(:connection, @connection) do
+          ActiveRecord::Base.stub(:establish_connection, -> * { raise Exception }) do
+            assert_raises(Exception) { ActiveRecord::Tasks::DatabaseTasks.create @configuration }
+            assert_match "Couldn't create '#{@configuration['database']}' database. Please check your configuration.", $stderr.string
+          end
+        end
+      end
 
-      $stderr.stubs(:puts).returns(true)
-      $stderr.expects(:puts).
-        with("Couldn't create database for #{@configuration.inspect}")
+      def test_when_database_created_successfully_outputs_info_to_stdout
+        with_stubbed_connection_establish_connection do
+          ActiveRecord::Tasks::DatabaseTasks.create @configuration
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
-    end
+          assert_equal "Created database 'my-app-db'\n", $stdout.string
+        end
+      end
 
-    def test_create_when_database_exists_outputs_info_to_stderr
-      $stderr.expects(:puts).with("my-app-db already exists").once
+      def test_create_when_database_exists_outputs_info_to_stderr
+        with_stubbed_connection_establish_connection do
+          ActiveRecord::Base.connection.stub(
+            :create_database,
+            proc { raise ActiveRecord::Tasks::DatabaseAlreadyExists }
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration
+
+            assert_equal "Database 'my-app-db' already exists\n", $stderr.string
+          end
+        end
+      end
 
-      ActiveRecord::Base.connection.stubs(:create_database).raises(
-        ActiveRecord::StatementInvalid.new('database "my-app-db" already exists')
-      )
+      private
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration
+        def with_stubbed_connection_establish_connection
+          ActiveRecord::Base.stub(:connection, @connection) do
+            ActiveRecord::Base.stub(:establish_connection, nil) do
+              yield
+            end
+          end
+        end
     end
-  end
 
-  class PostgreSQLDBDropTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:drop_database => true)
-      @configuration = {
-        'adapter'  => 'postgresql',
-        'database' => 'my-app-db'
-      }
+    class PostgreSQLDBDropTest < ActiveRecord::TestCase
+      def setup
+        @connection    = Class.new { def drop_database(*); end }.new
+        @configuration = {
+          "adapter"  => "postgresql",
+          "database" => "my-app-db"
+        }
+        $stdout, @original_stdout = StringIO.new, $stdout
+        $stderr, @original_stderr = StringIO.new, $stderr
+      end
 
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+      def teardown
+        $stdout, $stderr = @original_stdout, @original_stderr
+      end
 
-    def test_establishes_connection_to_postgresql_database
-      ActiveRecord::Base.expects(:establish_connection).with(
-        'adapter'            => 'postgresql',
-        'database'           => 'postgres',
-        'schema_search_path' => 'public'
-      )
+      def test_establishes_connection_to_postgresql_database
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [
+              "adapter"            => "postgresql",
+              "database"           => "postgres",
+              "schema_search_path" => "public"
+            ]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.drop @configuration
+          end
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.drop @configuration
-    end
+      def test_drops_database
+        with_stubbed_connection_establish_connection do
+          assert_called_with(
+            @connection,
+            :drop_database,
+            ["my-app-db"]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.drop @configuration
+          end
+        end
+      end
 
-    def test_drops_database
-      @connection.expects(:drop_database).with('my-app-db')
+      def test_when_database_dropped_successfully_outputs_info_to_stdout
+        with_stubbed_connection_establish_connection do
+          ActiveRecord::Tasks::DatabaseTasks.drop @configuration
 
-      ActiveRecord::Tasks::DatabaseTasks.drop @configuration
-    end
-  end
-
-  class PostgreSQLPurgeTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:create_database => true, :drop_database => true)
-      @configuration = {
-        'adapter'  => 'postgresql',
-        'database' => 'my-app-db'
-      }
-
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:clear_active_connections!).returns(true)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+          assert_equal "Dropped database 'my-app-db'\n", $stdout.string
+        end
+      end
 
-    def test_clears_active_connections
-      ActiveRecord::Base.expects(:clear_active_connections!)
+      private
 
-      ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+        def with_stubbed_connection_establish_connection
+          ActiveRecord::Base.stub(:connection, @connection) do
+            ActiveRecord::Base.stub(:establish_connection, nil) do
+              yield
+            end
+          end
+        end
     end
 
-    def test_establishes_connection_to_postgresql_database
-      ActiveRecord::Base.expects(:establish_connection).with(
-        'adapter'            => 'postgresql',
-        'database'           => 'postgres',
-        'schema_search_path' => 'public'
-      )
+    class PostgreSQLPurgeTest < ActiveRecord::TestCase
+      def setup
+        @connection = Class.new do
+          def create_database(*); end
+          def drop_database(*); end
+        end.new
+        @configuration = {
+          "adapter"  => "postgresql",
+          "database" => "my-app-db"
+        }
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.purge @configuration
-    end
+      def test_clears_active_connections
+        with_stubbed_connection do
+          ActiveRecord::Base.stub(:establish_connection, nil) do
+            assert_called(ActiveRecord::Base, :clear_active_connections!) do
+              ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+            end
+          end
+        end
+      end
 
-    def test_drops_database
-      @connection.expects(:drop_database).with('my-app-db')
+      def test_establishes_connection_to_postgresql_database
+        with_stubbed_connection do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [
+              [
+                "adapter"            => "postgresql",
+                "database"           => "postgres",
+                "schema_search_path" => "public"
+              ],
+              [
+                "adapter"            => "postgresql",
+                "database"           => "my-app-db"
+              ]
+            ]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+          end
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.purge @configuration
-    end
+      def test_drops_database
+        with_stubbed_connection do
+          ActiveRecord::Base.stub(:establish_connection, nil) do
+            assert_called_with(@connection, :drop_database, ["my-app-db"]) do
+              ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+            end
+          end
+        end
+      end
 
-    def test_creates_database
-      @connection.expects(:create_database).
-        with('my-app-db', @configuration.merge('encoding' => 'utf8'))
+      def test_creates_database
+        with_stubbed_connection do
+          ActiveRecord::Base.stub(:establish_connection, nil) do
+            assert_called_with(
+              @connection,
+              :create_database,
+              ["my-app-db", @configuration.merge("encoding" => "utf8")]
+            ) do
+              ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+            end
+          end
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.purge @configuration
-    end
+      def test_establishes_connection
+        with_stubbed_connection do
+          assert_called_with(
+            ActiveRecord::Base,
+            :establish_connection,
+            [
+              [
+                "adapter"            => "postgresql",
+                "database"           => "postgres",
+                "schema_search_path" => "public"
+              ],
+              [
+                @configuration
+              ]
+            ]
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+          end
+        end
+      end
 
-    def test_establishes_connection
-      ActiveRecord::Base.expects(:establish_connection).with(@configuration)
+      private
 
-      ActiveRecord::Tasks::DatabaseTasks.purge @configuration
+        def with_stubbed_connection
+          ActiveRecord::Base.stub(:connection, @connection) do
+            yield
+          end
+        end
     end
-  end
 
-  class PostgreSQLDBCharsetTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:create_database => true)
-      @configuration = {
-        'adapter'  => 'postgresql',
-        'database' => 'my-app-db'
-      }
-
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+    class PostgreSQLDBCharsetTest < ActiveRecord::TestCase
+      def setup
+        @connection = Class.new do
+          def create_database(*); end
+          def encoding; end
+        end.new
+        @configuration = {
+          "adapter"  => "postgresql",
+          "database" => "my-app-db"
+        }
+      end
 
-    def test_db_retrieves_charset
-      @connection.expects(:encoding)
-      ActiveRecord::Tasks::DatabaseTasks.charset @configuration
+      def test_db_retrieves_charset
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called(@connection, :encoding) do
+            ActiveRecord::Tasks::DatabaseTasks.charset @configuration
+          end
+        end
+      end
     end
-  end
 
-  class PostgreSQLDBCollationTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:create_database => true)
-      @configuration = {
-        'adapter'  => 'postgresql',
-        'database' => 'my-app-db'
-      }
-
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+    class PostgreSQLDBCollationTest < ActiveRecord::TestCase
+      def setup
+        @connection    = Class.new { def collation; end }.new
+        @configuration = {
+          "adapter"  => "postgresql",
+          "database" => "my-app-db"
+        }
+      end
 
-    def test_db_retrieves_collation
-      @connection.expects(:collation)
-      ActiveRecord::Tasks::DatabaseTasks.collation @configuration
+      def test_db_retrieves_collation
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called(@connection, :collation) do
+            ActiveRecord::Tasks::DatabaseTasks.collation @configuration
+          end
+        end
+      end
     end
-  end
 
-  class PostgreSQLStructureDumpTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub(:structure_dump => true)
-      @configuration = {
-        'adapter'  => 'postgresql',
-        'database' => 'my-app-db'
-      }
-      @filename = "awesome-file.sql"
-
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-      Kernel.stubs(:system)
-      File.stubs(:open)
-    end
+    class PostgreSQLStructureDumpTest < ActiveRecord::TestCase
+      def setup
+        @configuration = {
+          "adapter"  => "postgresql",
+          "database" => "my-app-db"
+        }
+        @filename = "/tmp/awesome-file.sql"
+        FileUtils.touch(@filename)
+      end
 
-    def test_structure_dump
-      Kernel.expects(:system).with("pg_dump -i -s -x -O -f #{@filename}  my-app-db").returns(true)
+      def teardown
+        FileUtils.rm_f(@filename)
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
-    end
+      def test_structure_dump
+        assert_called_with(
+          Kernel,
+          :system,
+          ["pg_dump", "-s", "-x", "-O", "-f", @filename, "my-app-db"],
+          returns: true
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
+        end
+      end
 
-    def test_structure_dump_with_schema_search_path
-      @configuration['schema_search_path'] = 'foo,bar'
+      def test_structure_dump_header_comments_removed
+        Kernel.stub(:system, true) do
+          File.write(@filename, "-- header comment\n\n-- more header comment\n statement \n-- lower comment\n")
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
 
-      Kernel.expects(:system).with("pg_dump -i -s -x -O -f #{@filename} --schema=foo --schema=bar my-app-db").returns(true)
+          assert_equal [" statement \n", "-- lower comment\n"], File.readlines(@filename).first(2)
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
-    end
+      def test_structure_dump_with_extra_flags
+        expected_command = ["pg_dump", "-s", "-x", "-O", "-f", @filename, "--noop", "my-app-db"]
 
-    def test_structure_dump_with_schema_search_path_and_dump_schemas_all
-      @configuration['schema_search_path'] = 'foo,bar'
+        assert_called_with(Kernel, :system, expected_command, returns: true) do
+          with_structure_dump_flags(["--noop"]) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
+          end
+        end
+      end
 
-      Kernel.expects(:system).with("pg_dump -i -s -x -O -f #{@filename}  my-app-db").returns(true)
+      def test_structure_dump_with_ignore_tables
+        assert_called(
+          ActiveRecord::SchemaDumper,
+          :ignore_tables,
+          returns: ["foo", "bar"]
+        ) do
+          assert_called_with(
+            Kernel,
+            :system,
+            ["pg_dump", "-s", "-x", "-O", "-f", @filename, "-T", "foo", "-T", "bar", "my-app-db"],
+            returns: true
+          ) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
+          end
+        end
+      end
 
-      with_dump_schemas(:all) do
-        ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
+      def test_structure_dump_with_schema_search_path
+        @configuration["schema_search_path"] = "foo,bar"
+
+        assert_called_with(
+          Kernel,
+          :system,
+          ["pg_dump", "-s", "-x", "-O", "-f", @filename, "--schema=foo", "--schema=bar", "my-app-db"],
+          returns: true
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
+        end
       end
-    end
 
-    def test_structure_dump_with_dump_schemas_string
-      Kernel.expects(:system).with("pg_dump -i -s -x -O -f #{@filename} --schema=foo --schema=bar my-app-db").returns(true)
+      def test_structure_dump_with_schema_search_path_and_dump_schemas_all
+        @configuration["schema_search_path"] = "foo,bar"
+
+        assert_called_with(
+          Kernel,
+          :system,
+          ["pg_dump", "-s", "-x", "-O", "-f", @filename,  "my-app-db"],
+          returns: true
+        ) do
+          with_dump_schemas(:all) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
+          end
+        end
+      end
 
-      with_dump_schemas('foo,bar') do
-        ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
+      def test_structure_dump_with_dump_schemas_string
+        assert_called_with(
+          Kernel,
+          :system,
+          ["pg_dump", "-s", "-x", "-O", "-f", @filename, "--schema=foo", "--schema=bar", "my-app-db"],
+          returns: true
+        ) do
+          with_dump_schemas("foo,bar") do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, @filename)
+          end
+        end
       end
-    end
 
-    private
+      def test_structure_dump_execution_fails
+        filename = "awesome-file.sql"
+        assert_called_with(
+          Kernel,
+          :system,
+          ["pg_dump", "-s", "-x", "-O", "-f", filename, "my-app-db"],
+          returns: nil
+        ) do
+          e = assert_raise(RuntimeError) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
+          end
+          assert_match("failed to execute:", e.message)
+        end
+      end
 
-    def with_dump_schemas(value, &block)
-      old_dump_schemas = ActiveRecord::Base.dump_schemas
-      ActiveRecord::Base.dump_schemas = value
-      yield
-    ensure
-      ActiveRecord::Base.dump_schemas = old_dump_schemas
+      private
+        def with_dump_schemas(value, &block)
+          old_dump_schemas = ActiveRecord::Base.dump_schemas
+          ActiveRecord::Base.dump_schemas = value
+          yield
+        ensure
+          ActiveRecord::Base.dump_schemas = old_dump_schemas
+        end
+
+        def with_structure_dump_flags(flags)
+          old = ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags = flags
+          yield
+        ensure
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags = old
+        end
     end
-  end
 
-  class PostgreSQLStructureLoadTest < ActiveRecord::TestCase
-    def setup
-      @connection    = stub
-      @configuration = {
-        'adapter'  => 'postgresql',
-        'database' => 'my-app-db'
-      }
-
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-      Kernel.stubs(:system)
-    end
+    class PostgreSQLStructureLoadTest < ActiveRecord::TestCase
+      def setup
+        @configuration = {
+          "adapter"  => "postgresql",
+          "database" => "my-app-db"
+        }
+      end
 
-    def test_structure_load
-      filename = "awesome-file.sql"
-      Kernel.expects(:system).with("psql -X -q -f #{filename} my-app-db")
+      def test_structure_load
+        filename = "awesome-file.sql"
+        assert_called_with(
+          Kernel,
+          :system,
+          ["psql", "-v", "ON_ERROR_STOP=1", "-q", "-X", "-f", filename, @configuration["database"]],
+          returns: true
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.structure_load(@configuration, filename)
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_load(@configuration, filename)
-    end
+      def test_structure_load_with_extra_flags
+        filename = "awesome-file.sql"
+        expected_command = ["psql", "-v", "ON_ERROR_STOP=1", "-q", "-X", "-f", filename, "--noop", @configuration["database"]]
 
-    def test_structure_load_accepts_path_with_spaces
-      filename = "awesome file.sql"
-      Kernel.expects(:system).with("psql -X -q -f awesome\\ file.sql my-app-db")
+        assert_called_with(Kernel, :system, expected_command, returns: true) do
+          with_structure_load_flags(["--noop"]) do
+            ActiveRecord::Tasks::DatabaseTasks.structure_load(@configuration, filename)
+          end
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_load(@configuration, filename)
+      def test_structure_load_accepts_path_with_spaces
+        filename = "awesome file.sql"
+        assert_called_with(
+          Kernel,
+          :system,
+          ["psql", "-v", "ON_ERROR_STOP=1", "-q", "-X", "-f", filename, @configuration["database"]],
+          returns: true
+        ) do
+          ActiveRecord::Tasks::DatabaseTasks.structure_load(@configuration, filename)
+        end
+      end
+
+      private
+        def with_structure_load_flags(flags)
+          old = ActiveRecord::Tasks::DatabaseTasks.structure_load_flags
+          ActiveRecord::Tasks::DatabaseTasks.structure_load_flags = flags
+          yield
+        ensure
+          ActiveRecord::Tasks::DatabaseTasks.structure_load_flags = old
+        end
     end
   end
-
-end
 end
diff --git a/activerecord/test/cases/tasks/sqlite_rake_test.rb b/activerecord/test/cases/tasks/sqlite_rake_test.rb
index 750d5e42dc..c1092b97c1 100644
--- a/activerecord/test/cases/tasks/sqlite_rake_test.rb
+++ b/activerecord/test/cases/tasks/sqlite_rake_test.rb
@@ -1,193 +1,264 @@
-require 'cases/helper'
-require 'pathname'
+# frozen_string_literal: true
 
-if current_adapter?(:SQLite3Adapter)
-module ActiveRecord
-  class SqliteDBCreateTest < ActiveRecord::TestCase
-    def setup
-      @database      = 'db_create.sqlite3'
-      @connection    = stub :connection
-      @configuration = {
-        'adapter'  => 'sqlite3',
-        'database' => @database
-      }
-
-      File.stubs(:exist?).returns(false)
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+require "cases/helper"
+require "active_record/tasks/database_tasks"
+require "pathname"
 
-    def test_db_checks_database_exists
-      File.expects(:exist?).with(@database).returns(false)
+if current_adapter?(:SQLite3Adapter)
+  module ActiveRecord
+    class SqliteDBCreateTest < ActiveRecord::TestCase
+      def setup
+        @database      = "db_create.sqlite3"
+        @configuration = {
+          "adapter"  => "sqlite3",
+          "database" => @database
+        }
+        $stdout, @original_stdout = StringIO.new, $stdout
+        $stderr, @original_stderr = StringIO.new, $stderr
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration, '/rails/root'
-    end
+      def teardown
+        $stdout, $stderr = @original_stdout, @original_stderr
+      end
 
-    def test_db_create_when_file_exists
-      File.stubs(:exist?).returns(true)
+      def test_db_checks_database_exists
+        ActiveRecord::Base.stub(:establish_connection, nil) do
+          assert_called_with(File, :exist?, [@database], returns: false) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root"
+          end
+        end
+      end
 
-      $stderr.expects(:puts).with("#{@database} already exists")
+      def test_when_db_created_successfully_outputs_info_to_stdout
+        ActiveRecord::Base.stub(:establish_connection, nil) do
+          ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root"
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration, '/rails/root'
-    end
+          assert_equal "Created database '#{@database}'\n", $stdout.string
+        end
+      end
 
-    def test_db_create_with_file_does_nothing
-      File.stubs(:exist?).returns(true)
-      $stderr.stubs(:puts).returns(nil)
+      def test_db_create_when_file_exists
+        File.stub(:exist?, true) do
+          ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root"
 
-      ActiveRecord::Base.expects(:establish_connection).never
+          assert_equal "Database '#{@database}' already exists\n", $stderr.string
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration, '/rails/root'
-    end
+      def test_db_create_with_file_does_nothing
+        File.stub(:exist?, true) do
+          assert_not_called(ActiveRecord::Base, :establish_connection) do
+            ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root"
+          end
+        end
+      end
 
-    def test_db_create_establishes_a_connection
-      ActiveRecord::Base.expects(:establish_connection).with(@configuration)
+      def test_db_create_establishes_a_connection
+        assert_called_with(ActiveRecord::Base, :establish_connection, [@configuration]) do
+          ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root"
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration, '/rails/root'
+      def test_db_create_with_error_prints_message
+        ActiveRecord::Base.stub(:establish_connection, proc { raise Exception }) do
+          assert_raises(Exception) { ActiveRecord::Tasks::DatabaseTasks.create @configuration, "/rails/root" }
+          assert_match "Couldn't create '#{@configuration['database']}' database. Please check your configuration.", $stderr.string
+        end
+      end
     end
 
-    def test_db_create_with_error_prints_message
-      ActiveRecord::Base.stubs(:establish_connection).raises(Exception)
-
-      $stderr.stubs(:puts).returns(true)
-      $stderr.expects(:puts).
-        with("Couldn't create database for #{@configuration.inspect}")
+    class SqliteDBDropTest < ActiveRecord::TestCase
+      def setup
+        @database      = "db_create.sqlite3"
+        @configuration = {
+          "adapter"  => "sqlite3",
+          "database" => @database
+        }
+        @path = Class.new do
+          def to_s; "/absolute/path" end
+          def absolute?; true end
+        end.new
+
+        $stdout, @original_stdout = StringIO.new, $stdout
+        $stderr, @original_stderr = StringIO.new, $stderr
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.create @configuration, '/rails/root'
-    end
-  end
+      def teardown
+        $stdout, $stderr = @original_stdout, @original_stderr
+      end
 
-  class SqliteDBDropTest < ActiveRecord::TestCase
-    def setup
-      @database      = "db_create.sqlite3"
-      @path          = stub(:to_s => '/absolute/path', :absolute? => true)
-      @configuration = {
-        'adapter'  => 'sqlite3',
-        'database' => @database
-      }
-
-      Pathname.stubs(:new).returns(@path)
-      File.stubs(:join).returns('/former/relative/path')
-      FileUtils.stubs(:rm).returns(true)
-    end
+      def test_creates_path_from_database
+        assert_called_with(Pathname, :new, [@database], returns: @path) do
+          ActiveRecord::Tasks::DatabaseTasks.drop @configuration, "/rails/root"
+        end
+      end
 
-    def test_creates_path_from_database
-      Pathname.expects(:new).with(@database).returns(@path)
+      def test_removes_file_with_absolute_path
+        Pathname.stub(:new, @path) do
+          assert_called_with(FileUtils, :rm, ["/absolute/path"]) do
+            ActiveRecord::Tasks::DatabaseTasks.drop @configuration, "/rails/root"
+          end
+        end
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.drop @configuration, '/rails/root'
-    end
+      def test_generates_absolute_path_with_given_root
+        Pathname.stub(:new, @path) do
+          @path.stub(:absolute?, false) do
+            assert_called_with(File, :join, ["/rails/root", @path],
+              returns: "/former/relative/path"
+            ) do
+              ActiveRecord::Tasks::DatabaseTasks.drop @configuration, "/rails/root"
+            end
+          end
+        end
+      end
 
-    def test_removes_file_with_absolute_path
-      File.stubs(:exist?).returns(true)
-      @path.stubs(:absolute?).returns(true)
+      def test_removes_file_with_relative_path
+        File.stub(:join, "/former/relative/path") do
+          @path.stub(:absolute?, false) do
+            assert_called_with(FileUtils, :rm, ["/former/relative/path"]) do
+              ActiveRecord::Tasks::DatabaseTasks.drop @configuration, "/rails/root"
+            end
+          end
+        end
+      end
 
-      FileUtils.expects(:rm).with('/absolute/path')
+      def test_when_db_dropped_successfully_outputs_info_to_stdout
+        FileUtils.stub(:rm, nil) do
+          ActiveRecord::Tasks::DatabaseTasks.drop @configuration, "/rails/root"
 
-      ActiveRecord::Tasks::DatabaseTasks.drop @configuration, '/rails/root'
+          assert_equal "Dropped database '#{@database}'\n", $stdout.string
+        end
+      end
     end
 
-    def test_generates_absolute_path_with_given_root
-      @path.stubs(:absolute?).returns(false)
-
-      File.expects(:join).with('/rails/root', @path).
-        returns('/former/relative/path')
+    class SqliteDBCharsetTest < ActiveRecord::TestCase
+      def setup
+        @database      = "db_create.sqlite3"
+        @connection    = Class.new { def encoding; end }.new
+        @configuration = {
+          "adapter"  => "sqlite3",
+          "database" => @database
+        }
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.drop @configuration, '/rails/root'
+      def test_db_retrieves_charset
+        ActiveRecord::Base.stub(:connection, @connection) do
+          assert_called(@connection, :encoding) do
+            ActiveRecord::Tasks::DatabaseTasks.charset @configuration, "/rails/root"
+          end
+        end
+      end
     end
 
-    def test_removes_file_with_relative_path
-      File.stubs(:exist?).returns(true)
-      @path.stubs(:absolute?).returns(false)
-
-      FileUtils.expects(:rm).with('/former/relative/path')
-
-      ActiveRecord::Tasks::DatabaseTasks.drop @configuration, '/rails/root'
-    end
-  end
+    class SqliteDBCollationTest < ActiveRecord::TestCase
+      def setup
+        @database      = "db_create.sqlite3"
+        @configuration = {
+          "adapter"  => "sqlite3",
+          "database" => @database
+        }
+      end
 
-  class SqliteDBCharsetTest < ActiveRecord::TestCase
-    def setup
-      @database      = 'db_create.sqlite3'
-      @connection    = stub :connection
-      @configuration = {
-        'adapter'  => 'sqlite3',
-        'database' => @database
-      }
-
-      File.stubs(:exist?).returns(false)
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
+      def test_db_retrieves_collation
+        assert_raise NoMethodError do
+          ActiveRecord::Tasks::DatabaseTasks.collation @configuration, "/rails/root"
+        end
+      end
     end
 
-    def test_db_retrieves_charset
-      @connection.expects(:encoding)
-      ActiveRecord::Tasks::DatabaseTasks.charset @configuration, '/rails/root'
-    end
-  end
+    class SqliteStructureDumpTest < ActiveRecord::TestCase
+      def setup
+        @database      = "db_create.sqlite3"
+        @configuration = {
+          "adapter"  => "sqlite3",
+          "database" => @database
+        }
 
-  class SqliteDBCollationTest < ActiveRecord::TestCase
-    def setup
-      @database      = 'db_create.sqlite3'
-      @connection    = stub :connection
-      @configuration = {
-        'adapter'  => 'sqlite3',
-        'database' => @database
-      }
-
-      File.stubs(:exist?).returns(false)
-      ActiveRecord::Base.stubs(:connection).returns(@connection)
-      ActiveRecord::Base.stubs(:establish_connection).returns(true)
-    end
+        `sqlite3 #{@database} 'CREATE TABLE bar(id INTEGER)'`
+        `sqlite3 #{@database} 'CREATE TABLE foo(id INTEGER)'`
+      end
 
-    def test_db_retrieves_collation
-      assert_raise NoMethodError do
-        ActiveRecord::Tasks::DatabaseTasks.collation @configuration, '/rails/root'
+      def test_structure_dump
+        dbfile   = @database
+        filename = "awesome-file.sql"
+
+        ActiveRecord::Tasks::DatabaseTasks.structure_dump @configuration, filename, "/rails/root"
+        assert File.exist?(dbfile)
+        assert File.exist?(filename)
+        assert_match(/CREATE TABLE foo/, File.read(filename))
+        assert_match(/CREATE TABLE bar/, File.read(filename))
+      ensure
+        FileUtils.rm_f(filename)
+        FileUtils.rm_f(dbfile)
       end
-    end
-  end
 
-  class SqliteStructureDumpTest < ActiveRecord::TestCase
-    def setup
-      @database      = "db_create.sqlite3"
-      @configuration = {
-        'adapter'  => 'sqlite3',
-        'database' => @database
-      }
-    end
+      def test_structure_dump_with_ignore_tables
+        dbfile   = @database
+        filename = "awesome-file.sql"
+        assert_called(ActiveRecord::SchemaDumper, :ignore_tables, returns: ["foo"]) do
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename, "/rails/root")
+        end
+        assert File.exist?(dbfile)
+        assert File.exist?(filename)
+        assert_match(/bar/, File.read(filename))
+        assert_no_match(/foo/, File.read(filename))
+      ensure
+        FileUtils.rm_f(filename)
+        FileUtils.rm_f(dbfile)
+      end
 
-    def test_structure_dump
-      dbfile   = @database
-      filename = "awesome-file.sql"
+      def test_structure_dump_execution_fails
+        dbfile   = @database
+        filename = "awesome-file.sql"
+        assert_called_with(
+          Kernel,
+          :system,
+          ["sqlite3", "--noop", "db_create.sqlite3", ".schema", out: "awesome-file.sql"],
+          returns: nil
+        ) do
+          e = assert_raise(RuntimeError) do
+            with_structure_dump_flags(["--noop"]) do
+              quietly { ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename, "/rails/root") }
+            end
+          end
+          assert_match("failed to execute:", e.message)
+        end
+      ensure
+        FileUtils.rm_f(filename)
+        FileUtils.rm_f(dbfile)
+      end
 
-      ActiveRecord::Tasks::DatabaseTasks.structure_dump @configuration, filename, '/rails/root'
-      assert File.exist?(dbfile)
-      assert File.exist?(filename)
-    ensure
-      FileUtils.rm_f(filename)
-      FileUtils.rm_f(dbfile)
+      private
+        def with_structure_dump_flags(flags)
+          old = ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags = flags
+          yield
+        ensure
+          ActiveRecord::Tasks::DatabaseTasks.structure_dump_flags = old
+        end
     end
-  end
 
-  class SqliteStructureLoadTest < ActiveRecord::TestCase
-    def setup
-      @database      = "db_create.sqlite3"
-      @configuration = {
-        'adapter'  => 'sqlite3',
-        'database' => @database
-      }
-    end
+    class SqliteStructureLoadTest < ActiveRecord::TestCase
+      def setup
+        @database      = "db_create.sqlite3"
+        @configuration = {
+          "adapter"  => "sqlite3",
+          "database" => @database
+        }
+      end
 
-    def test_structure_load
-      dbfile   = @database
-      filename = "awesome-file.sql"
+      def test_structure_load
+        dbfile   = @database
+        filename = "awesome-file.sql"
 
-      open(filename, 'w') { |f| f.puts("select datetime('now', 'localtime');") }
-      ActiveRecord::Tasks::DatabaseTasks.structure_load @configuration, filename, '/rails/root'
-      assert File.exist?(dbfile)
-    ensure
-      FileUtils.rm_f(filename)
-      FileUtils.rm_f(dbfile)
+        open(filename, "w") { |f| f.puts("select datetime('now', 'localtime');") }
+        ActiveRecord::Tasks::DatabaseTasks.structure_load @configuration, filename, "/rails/root"
+        assert File.exist?(dbfile)
+      ensure
+        FileUtils.rm_f(filename)
+        FileUtils.rm_f(dbfile)
+      end
     end
   end
 end
-end
diff --git a/activerecord/test/cases/test_case.rb b/activerecord/test/cases/test_case.rb
index 7761ea5612..40947767f3 100644
--- a/activerecord/test/cases/test_case.rb
+++ b/activerecord/test/cases/test_case.rb
@@ -1,22 +1,37 @@
-require 'active_support/test_case'
-require 'active_support/testing/stream'
+# frozen_string_literal: true
+
+require "active_support"
+require "active_support/testing/autorun"
+require "active_support/testing/method_call_assertions"
+require "active_support/testing/stream"
+require "active_record/fixtures"
+
+require "cases/validations_repair_helper"
 
 module ActiveRecord
   # = Active Record Test Case
   #
   # Defines some test assertions to test against SQL queries.
   class TestCase < ActiveSupport::TestCase #:nodoc:
+    include ActiveSupport::Testing::MethodCallAssertions
     include ActiveSupport::Testing::Stream
+    include ActiveRecord::TestFixtures
+    include ActiveRecord::ValidationsRepairHelper
 
-    def teardown
-      SQLCounter.clear_log
+    self.fixture_path = FIXTURES_ROOT
+    self.use_instantiated_fixtures = false
+    self.use_transactional_tests = true
+
+    def create_fixtures(*fixture_set_names, &block)
+      ActiveRecord::FixtureSet.create_fixtures(ActiveRecord::TestCase.fixture_path, fixture_set_names, fixture_class_names, &block)
     end
 
-    def assert_date_from_db(expected, actual, message = nil)
-      assert_equal expected.to_s, actual.to_s, message
+    def teardown
+      SQLCounter.clear_log
     end
 
     def capture_sql
+      ActiveRecord::Base.connection.materialize_transactions
       SQLCounter.clear_log
       yield
       SQLCounter.log_all.dup
@@ -27,13 +42,14 @@ module ActiveRecord
     ensure
       failed_patterns = []
       patterns_to_match.each do |pattern|
-        failed_patterns << pattern unless SQLCounter.log_all.any?{ |sql| pattern === sql }
+        failed_patterns << pattern unless SQLCounter.log_all.any? { |sql| pattern === sql }
       end
       assert failed_patterns.empty?, "Query pattern(s) #{failed_patterns.map(&:inspect).join(', ')} not found.#{SQLCounter.log.size == 0 ? '' : "\nQueries:\n#{SQLCounter.log.join("\n")}"}"
     end
 
     def assert_queries(num = 1, options = {})
       ignore_none = options.fetch(:ignore_none) { num == :any }
+      ActiveRecord::Base.connection.materialize_transactions
       SQLCounter.clear_log
       x = yield
       the_log = ignore_none ? SQLCounter.log_all : SQLCounter.log
@@ -51,11 +67,11 @@ module ActiveRecord
       assert_queries(0, options, &block)
     end
 
-    def assert_column(model, column_name, msg=nil)
+    def assert_column(model, column_name, msg = nil)
       assert has_column?(model, column_name), msg
     end
 
-    def assert_no_column(model, column_name, msg=nil)
+    def assert_no_column(model, column_name, msg = nil)
       assert_not has_column?(model, column_name), msg
     end
 
@@ -63,6 +79,10 @@ module ActiveRecord
       model.reset_column_information
       model.column_names.include?(column_name.to_s)
     end
+
+    def frozen_error_class
+      Object.const_defined?(:FrozenError) ? FrozenError : RuntimeError
+    end
   end
 
   class PostgreSQLTestCase < TestCase
@@ -77,12 +97,6 @@ module ActiveRecord
     end
   end
 
-  class MysqlTestCase < TestCase
-    def self.run(*args)
-      super if current_adapter?(:MysqlAdapter)
-    end
-  end
-
   class SQLite3TestCase < TestCase
     def self.run(*args)
       super if current_adapter?(:SQLite3Adapter)
@@ -95,16 +109,16 @@ module ActiveRecord
       def clear_log; self.log = []; self.log_all = []; end
     end
 
-    self.clear_log
+    clear_log
 
     self.ignored_sql = [/^PRAGMA/, /^SELECT currval/, /^SELECT CAST/, /^SELECT @@IDENTITY/, /^SELECT @@ROWCOUNT/, /^SAVEPOINT/, /^ROLLBACK TO SAVEPOINT/, /^RELEASE SAVEPOINT/, /^SHOW max_identifier_length/, /^BEGIN/, /^COMMIT/]
 
     # FIXME: this needs to be refactored so specific database can add their own
     # ignored SQL, or better yet, use a different notification for the queries
     # instead examining the SQL content.
-    oracle_ignored     = [/^select .*nextval/i, /^SAVEPOINT/, /^ROLLBACK TO/, /^\s*select .* from all_triggers/im, /^\s*select .* from all_constraints/im, /^\s*select .* from all_tab_cols/im]
-    mysql_ignored      = [/^SHOW TABLES/i, /^SHOW FULL FIELDS/, /^SHOW CREATE TABLE /i, /^SHOW VARIABLES /]
-    postgresql_ignored = [/^\s*select\b.*\bfrom\b.*pg_namespace\b/im, /^\s*select tablename\b.*from pg_tables\b/im, /^\s*select\b.*\battname\b.*\bfrom\b.*\bpg_attribute\b/im, /^SHOW search_path/i]
+    oracle_ignored     = [/^select .*nextval/i, /^SAVEPOINT/, /^ROLLBACK TO/, /^\s*select .* from all_triggers/im, /^\s*select .* from all_constraints/im, /^\s*select .* from all_tab_cols/im, /^\s*select .* from all_sequences/im]
+    mysql_ignored      = [/^SHOW FULL TABLES/i, /^SHOW FULL FIELDS/, /^SHOW CREATE TABLE /i, /^SHOW VARIABLES /, /^\s*SELECT (?:column_name|table_name)\b.*\bFROM information_schema\.(?:key_column_usage|tables)\b/im]
+    postgresql_ignored = [/^\s*select\b.*\bfrom\b.*pg_namespace\b/im, /^\s*select tablename\b.*from pg_tables\b/im, /^\s*select\b.*\battname\b.*\bfrom\b.*\bpg_attribute\b/im, /^SHOW search_path/i, /^\s*SELECT\b.*::regtype::oid\b/im]
     sqlite3_ignored =    [/^\s*SELECT name\b.*\bFROM sqlite_master/im, /^\s*SELECT sql\b.*\bFROM sqlite_master/im]
 
     [oracle_ignored, mysql_ignored, postgresql_ignored, sqlite3_ignored].each do |db_ignored_sql|
@@ -118,16 +132,13 @@ module ActiveRecord
     end
 
     def call(name, start, finish, message_id, values)
-      sql = values[:sql]
-
-      # FIXME: this seems bad. we should probably have a better way to indicate
-      # the query was cached
-      return if 'CACHE' == values[:name]
+      return if values[:cached]
 
+      sql = values[:sql]
       self.class.log_all << sql
-      self.class.log << sql unless ignore =~ sql
+      self.class.log << sql unless ignore.match?(sql)
     end
   end
 
-  ActiveSupport::Notifications.subscribe('sql.active_record', SQLCounter.new)
+  ActiveSupport::Notifications.subscribe("sql.active_record", SQLCounter.new)
 end
diff --git a/activerecord/test/cases/test_fixtures_test.rb b/activerecord/test/cases/test_fixtures_test.rb
index 3f4baf8378..4411410eda 100644
--- a/activerecord/test/cases/test_fixtures_test.rb
+++ b/activerecord/test/cases/test_fixtures_test.rb
@@ -1,34 +1,18 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 class TestFixturesTest < ActiveRecord::TestCase
   setup do
     @klass = Class.new
-    @klass.send(:include, ActiveRecord::TestFixtures)
-  end
-
-  def test_deprecated_use_transactional_fixtures=
-    assert_deprecated 'use use_transactional_tests= instead' do
-      @klass.use_transactional_fixtures = true
-    end
-  end
-
-  def test_use_transactional_tests_prefers_use_transactional_fixtures
-    ActiveSupport::Deprecation.silence do
-      @klass.use_transactional_fixtures = false
-    end
-
-    assert_equal false, @klass.use_transactional_tests
+    @klass.include(ActiveRecord::TestFixtures)
   end
 
   def test_use_transactional_tests_defaults_to_true
-    ActiveSupport::Deprecation.silence do
-      @klass.use_transactional_fixtures = nil
-    end
-
     assert_equal true, @klass.use_transactional_tests
   end
 
-  def test_use_transactional_tests_can_be_overriden
+  def test_use_transactional_tests_can_be_overridden
     @klass.use_transactional_tests = "foobar"
 
     assert_equal "foobar", @klass.use_transactional_tests
diff --git a/activerecord/test/cases/time_precision_test.rb b/activerecord/test/cases/time_precision_test.rb
index ff7a81fe60..086500de38 100644
--- a/activerecord/test/cases/time_precision_test.rb
+++ b/activerecord/test/cases/time_precision_test.rb
@@ -1,108 +1,103 @@
-require 'cases/helper'
-require 'support/schema_dumping_helper'
+# frozen_string_literal: true
 
-if ActiveRecord::Base.connection.supports_datetime_with_precision?
-class TimePrecisionTest < ActiveRecord::TestCase
-  include SchemaDumpingHelper
-  self.use_transactional_tests = false
+require "cases/helper"
+require "support/schema_dumping_helper"
 
-  class Foo < ActiveRecord::Base; end
+if subsecond_precision_supported?
+  class TimePrecisionTest < ActiveRecord::TestCase
+    include SchemaDumpingHelper
+    self.use_transactional_tests = false
 
-  setup do
-    @connection = ActiveRecord::Base.connection
-  end
-
-  teardown do
-    @connection.drop_table :foos, if_exists: true
-  end
+    class Foo < ActiveRecord::Base; end
 
-  def test_time_data_type_with_precision
-    @connection.create_table(:foos, force: true)
-    @connection.add_column :foos, :start,  :time, precision: 3
-    @connection.add_column :foos, :finish, :time, precision: 6
-    assert_equal 3, activerecord_column_option('foos', 'start',  'precision')
-    assert_equal 6, activerecord_column_option('foos', 'finish', 'precision')
-  end
+    setup do
+      @connection = ActiveRecord::Base.connection
+      Foo.reset_column_information
+    end
 
-  def test_passing_precision_to_time_does_not_set_limit
-    @connection.create_table(:foos, force: true) do |t|
-      t.time :start,  precision: 3
-      t.time :finish, precision: 6
+    teardown do
+      @connection.drop_table :foos, if_exists: true
     end
-    assert_nil activerecord_column_option('foos', 'start',  'limit')
-    assert_nil activerecord_column_option('foos', 'finish', 'limit')
-  end
 
-  def test_invalid_time_precision_raises_error
-    assert_raises ActiveRecord::ActiveRecordError do
-      @connection.create_table(:foos, force: true) do |t|
-        t.time :start,  precision: 7
-        t.time :finish, precision: 7
-      end
+    def test_time_data_type_with_precision
+      @connection.create_table(:foos, force: true)
+      @connection.add_column :foos, :start,  :time, precision: 3
+      @connection.add_column :foos, :finish, :time, precision: 6
+      assert_equal 3, Foo.columns_hash["start"].precision
+      assert_equal 6, Foo.columns_hash["finish"].precision
     end
-  end
 
-  def test_database_agrees_with_activerecord_about_precision
-    @connection.create_table(:foos, force: true) do |t|
-      t.time :start,  precision: 2
-      t.time :finish, precision: 4
+    def test_time_precision_is_truncated_on_assignment
+      @connection.create_table(:foos, force: true)
+      @connection.add_column :foos, :start,  :time, precision: 0
+      @connection.add_column :foos, :finish, :time, precision: 6
+
+      time = ::Time.now.change(nsec: 123456789)
+      foo = Foo.new(start: time, finish: time)
+
+      assert_equal 0, foo.start.nsec
+      assert_equal 123456000, foo.finish.nsec
+
+      foo.save!
+      foo.reload
+
+      assert_equal 0, foo.start.nsec
+      assert_equal 123456000, foo.finish.nsec
     end
-    assert_equal 2, database_datetime_precision('foos', 'start')
-    assert_equal 4, database_datetime_precision('foos', 'finish')
-  end
 
-  def test_formatting_time_according_to_precision
-    @connection.create_table(:foos, force: true) do |t|
-      t.time :start,  precision: 0
-      t.time :finish, precision: 4
+    def test_passing_precision_to_time_does_not_set_limit
+      @connection.create_table(:foos, force: true) do |t|
+        t.time :start,  precision: 3
+        t.time :finish, precision: 6
+      end
+      assert_nil Foo.columns_hash["start"].limit
+      assert_nil Foo.columns_hash["finish"].limit
     end
-    time = ::Time.utc(2000, 1, 1, 12, 30, 0, 999999)
-    Foo.create!(start: time, finish: time)
-    assert foo = Foo.find_by(start: time)
-    assert_equal 1, Foo.where(finish: time).count
-    assert_equal time.to_s, foo.start.to_s
-    assert_equal time.to_s, foo.finish.to_s
-    assert_equal 000000, foo.start.usec
-    assert_equal 999900, foo.finish.usec
-  end
 
-  def test_schema_dump_includes_time_precision
-    @connection.create_table(:foos, force: true) do |t|
-      t.time :start,  precision: 4
-      t.time :finish, precision: 6
+    def test_invalid_time_precision_raises_error
+      assert_raises ActiveRecord::ActiveRecordError do
+        @connection.create_table(:foos, force: true) do |t|
+          t.time :start,  precision: 7
+          t.time :finish, precision: 7
+        end
+      end
     end
-    output = dump_table_schema("foos")
-    assert_match %r{t\.time\s+"start",\s+precision: 4$}, output
-    assert_match %r{t\.time\s+"finish",\s+precision: 6$}, output
-  end
 
-  if current_adapter?(:PostgreSQLAdapter)
-    def test_time_precision_with_zero_should_be_dumped
+    def test_formatting_time_according_to_precision
       @connection.create_table(:foos, force: true) do |t|
         t.time :start,  precision: 0
-        t.time :finish, precision: 0
+        t.time :finish, precision: 4
       end
-      output = dump_table_schema("foos")
-      assert_match %r{t\.time\s+"start",\s+precision: 0$}, output
-      assert_match %r{t\.time\s+"finish",\s+precision: 0$}, output
+      time = ::Time.utc(2000, 1, 1, 12, 30, 0, 999999)
+      Foo.create!(start: time, finish: time)
+      assert foo = Foo.find_by(start: time)
+      assert_equal 1, Foo.where(finish: time).count
+      assert_equal time.to_s, foo.start.to_s
+      assert_equal time.to_s, foo.finish.to_s
+      assert_equal 000000, foo.start.usec
+      assert_equal 999900, foo.finish.usec
     end
-  end
 
-  private
-
-  def database_datetime_precision(table_name, column_name)
-    results = @connection.exec_query("SELECT column_name, datetime_precision FROM information_schema.columns WHERE table_name = '#{table_name}'")
-    result = results.find do |result_hash|
-      result_hash["column_name"] == column_name
+    def test_schema_dump_includes_time_precision
+      @connection.create_table(:foos, force: true) do |t|
+        t.time :start,  precision: 4
+        t.time :finish, precision: 6
+      end
+      output = dump_table_schema("foos")
+      assert_match %r{t\.time\s+"start",\s+precision: 4$}, output
+      assert_match %r{t\.time\s+"finish",\s+precision: 6$}, output
     end
-    result && result["datetime_precision"].to_i
-  end
 
-  def activerecord_column_option(tablename, column_name, option)
-    result = @connection.columns(tablename).find do |column|
-      column.name == column_name
+    if current_adapter?(:PostgreSQLAdapter, :SQLServerAdapter)
+      def test_time_precision_with_zero_should_be_dumped
+        @connection.create_table(:foos, force: true) do |t|
+          t.time :start,  precision: 0
+          t.time :finish, precision: 0
+        end
+        output = dump_table_schema("foos")
+        assert_match %r{t\.time\s+"start",\s+precision: 0$}, output
+        assert_match %r{t\.time\s+"finish",\s+precision: 0$}, output
+      end
     end
-    result && result.send(option)
   end
 end
-end
diff --git a/activerecord/test/cases/timestamp_test.rb b/activerecord/test/cases/timestamp_test.rb
index 5dab32995c..75ecd6fc40 100644
--- a/activerecord/test/cases/timestamp_test.rb
+++ b/activerecord/test/cases/timestamp_test.rb
@@ -1,12 +1,14 @@
-require 'cases/helper'
-require 'support/ddl_helper'
-require 'models/developer'
-require 'models/computer'
-require 'models/owner'
-require 'models/pet'
-require 'models/toy'
-require 'models/car'
-require 'models/task'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "support/ddl_helper"
+require "models/developer"
+require "models/computer"
+require "models/owner"
+require "models/pet"
+require "models/toy"
+require "models/car"
+require "models/task"
 
 class TimestampTest < ActiveRecord::TestCase
   fixtures :developers, :owners, :pets, :toys, :cars, :tasks
@@ -38,8 +40,8 @@ class TimestampTest < ActiveRecord::TestCase
 
     assert_not_equal @previously_updated_at, @developer.updated_at
     assert_equal previous_salary + 10000, @developer.salary
-    assert @developer.salary_changed?, 'developer salary should have changed'
-    assert @developer.changed?, 'developer should be marked as changed'
+    assert @developer.salary_changed?, "developer salary should have changed"
+    assert @developer.changed?, "developer should be marked as changed"
     @developer.reload
     assert_equal previous_salary, @developer.salary
   end
@@ -74,36 +76,51 @@ class TimestampTest < ActiveRecord::TestCase
   end
 
   def test_touching_updates_timestamp_with_given_time
-    previously_updated_at = @developer.updated_at 
-    new_time = Time.utc(2015, 2, 16, 0, 0, 0) 
-    @developer.touch(time: new_time) 
+    previously_updated_at = @developer.updated_at
+    new_time = Time.utc(2015, 2, 16, 0, 0, 0)
+    @developer.touch(time: new_time)
 
-    assert_not_equal previously_updated_at, @developer.updated_at 
-    assert_equal new_time, @developer.updated_at 
+    assert_not_equal previously_updated_at, @developer.updated_at
+    assert_equal new_time, @developer.updated_at
   end
 
   def test_touching_an_attribute_updates_timestamp
     previously_created_at = @developer.created_at
-    @developer.touch(:created_at)
+    travel(1.second) do
+      @developer.touch(:created_at)
+    end
 
-    assert !@developer.created_at_changed? , 'created_at should not be changed'
-    assert !@developer.changed?, 'record should not be changed'
+    assert_not @developer.created_at_changed?, "created_at should not be changed"
+    assert_not @developer.changed?, "record should not be changed"
     assert_not_equal previously_created_at, @developer.created_at
     assert_not_equal @previously_updated_at, @developer.updated_at
   end
 
+  def test_touching_update_at_attribute_as_symbol_updates_timestamp
+    travel(1.second) do
+      @developer.touch(:updated_at)
+    end
+
+    assert_not @developer.updated_at_changed?
+    assert_not @developer.changed?
+    assert_not_equal @previously_updated_at, @developer.updated_at
+  end
+
   def test_touching_an_attribute_updates_it
     task = Task.first
     previous_value = task.ending
     task.touch(:ending)
+
+    now = Time.now.change(usec: 0)
+
     assert_not_equal previous_value, task.ending
-    assert_in_delta Time.now, task.ending, 1
+    assert_in_delta now, task.ending, 1
   end
 
   def test_touching_an_attribute_updates_timestamp_with_given_time
-    previously_updated_at = @developer.updated_at 
+    previously_updated_at = @developer.updated_at
     previously_created_at = @developer.created_at
-    new_time = Time.utc(2015, 2, 16, 4, 54, 0) 
+    new_time = Time.utc(2015, 2, 16, 4, 54, 0)
     @developer.touch(:created_at, time: new_time)
 
     assert_not_equal previously_created_at, @developer.created_at
@@ -118,10 +135,12 @@ class TimestampTest < ActiveRecord::TestCase
     previous_ending = task.ending
     task.touch(:starting, :ending)
 
+    now = Time.now.change(usec: 0)
+
     assert_not_equal previous_starting, task.starting
     assert_not_equal previous_ending, task.ending
-    assert_in_delta Time.now, task.starting, 1
-    assert_in_delta Time.now, task.ending, 1
+    assert_in_delta now, task.starting, 1
+    assert_in_delta now, task.ending, 1
   end
 
   def test_touching_a_record_without_timestamps_is_unexceptional
@@ -130,13 +149,13 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_touching_a_no_touching_object
     Developer.no_touching do
-      assert @developer.no_touching?
-      assert !@owner.no_touching?
+      assert_predicate @developer, :no_touching?
+      assert_not_predicate @owner, :no_touching?
       @developer.touch
     end
 
-    assert !@developer.no_touching?
-    assert !@owner.no_touching?
+    assert_not_predicate @developer, :no_touching?
+    assert_not_predicate @owner, :no_touching?
     assert_equal @previously_updated_at, @developer.updated_at
   end
 
@@ -153,26 +172,26 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_global_no_touching
     ActiveRecord::Base.no_touching do
-      assert @developer.no_touching?
-      assert @owner.no_touching?
+      assert_predicate @developer, :no_touching?
+      assert_predicate @owner, :no_touching?
       @developer.touch
     end
 
-    assert !@developer.no_touching?
-    assert !@owner.no_touching?
+    assert_not_predicate @developer, :no_touching?
+    assert_not_predicate @owner, :no_touching?
     assert_equal @previously_updated_at, @developer.updated_at
   end
 
   def test_no_touching_threadsafe
     Thread.new do
       Developer.no_touching do
-        assert @developer.no_touching?
+        assert_predicate @developer, :no_touching?
 
         sleep(1)
       end
     end
 
-    assert !@developer.no_touching?
+    assert_not_predicate @developer, :no_touching?
   end
 
   def test_no_touching_with_callbacks
@@ -199,8 +218,10 @@ class TimestampTest < ActiveRecord::TestCase
     owner = pet.owner
     previously_owner_updated_at = owner.updated_at
 
-    pet.name = "Fluffy the Third"
-    pet.save
+    travel(1.second) do
+      pet.name = "Fluffy the Third"
+      pet.save
+    end
 
     assert_not_equal previously_owner_updated_at, pet.owner.updated_at
   end
@@ -210,27 +231,29 @@ class TimestampTest < ActiveRecord::TestCase
     owner = pet.owner
     previously_owner_updated_at = owner.updated_at
 
-    pet.destroy
+    travel(1.second) do
+      pet.destroy
+    end
 
     assert_not_equal previously_owner_updated_at, pet.owner.updated_at
   end
 
   def test_saving_a_new_record_belonging_to_invalid_parent_with_touch_should_not_raise_exception
     klass = Class.new(Owner) do
-      def self.name; 'Owner'; end
+      def self.name; "Owner"; end
       validate { errors.add(:base, :invalid) }
     end
 
     pet = Pet.new(owner: klass.new)
     pet.save!
 
-    assert pet.owner.new_record?
+    assert_predicate pet.owner, :new_record?
   end
 
   def test_saving_a_record_with_a_belongs_to_that_specifies_touching_a_specific_attribute_the_parent_should_update_that_attribute
     klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Pet'; end
-      belongs_to :owner, :touch => :happy_at
+      def self.name; "Pet"; end
+      belongs_to :owner, touch: :happy_at
     end
 
     pet   = klass.first
@@ -245,8 +268,8 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_touching_a_record_with_a_belongs_to_that_uses_a_counter_cache_should_update_the_parent
     klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Pet'; end
-      belongs_to :owner, :counter_cache => :use_count, :touch => true
+      def self.name; "Pet"; end
+      belongs_to :owner, counter_cache: :use_count, touch: true
     end
 
     pet = klass.first
@@ -254,16 +277,18 @@ class TimestampTest < ActiveRecord::TestCase
     owner.update_columns(happy_at: 3.days.ago)
     previously_owner_updated_at = owner.updated_at
 
-    pet.name = "I'm a parrot"
-    pet.save
+    travel(1.second) do
+      pet.name = "I'm a parrot"
+      pet.save
+    end
 
     assert_not_equal previously_owner_updated_at, pet.owner.updated_at
   end
 
   def test_touching_a_record_touches_parent_record_and_grandparent_record
     klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Toy'; end
-      belongs_to :pet, :touch => true
+      def self.name; "Toy"; end
+      belongs_to :pet, touch: true
     end
 
     toy = klass.first
@@ -280,12 +305,12 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_touching_a_record_touches_polymorphic_record
     klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Toy'; end
+      def self.name; "Toy"; end
     end
 
     wheel_klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Wheel'; end
-      belongs_to :wheelable, :polymorphic => true, :touch => true
+      def self.name; "Wheel"; end
+      belongs_to :wheelable, polymorphic: true, touch: true
     end
 
     toy = klass.first
@@ -302,7 +327,7 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_changing_parent_of_a_record_touches_both_new_and_old_parent_record
     klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Toy'; end
+      def self.name; "Toy"; end
       belongs_to :pet, touch: true
     end
 
@@ -328,12 +353,12 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_changing_parent_of_a_record_touches_both_new_and_old_polymorphic_parent_record_changes_within_same_class
     car_class = Class.new(ActiveRecord::Base) do
-      def self.name; 'Car'; end
+      def self.name; "Car"; end
     end
 
     wheel_class = Class.new(ActiveRecord::Base) do
-      def self.name; 'Wheel'; end
-      belongs_to :wheelable, :polymorphic => true, :touch => true
+      def self.name; "Wheel"; end
+      belongs_to :wheelable, polymorphic: true, touch: true
     end
 
     car1 = car_class.find(1)
@@ -355,16 +380,16 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_changing_parent_of_a_record_touches_both_new_and_old_polymorphic_parent_record_changes_with_other_class
     car_class = Class.new(ActiveRecord::Base) do
-      def self.name; 'Car'; end
+      def self.name; "Car"; end
     end
 
     toy_class = Class.new(ActiveRecord::Base) do
-      def self.name; 'Toy'; end
+      def self.name; "Toy"; end
     end
 
     wheel_class = Class.new(ActiveRecord::Base) do
-      def self.name; 'Wheel'; end
-      belongs_to :wheelable, :polymorphic => true, :touch => true
+      def self.name; "Wheel"; end
+      belongs_to :wheelable, polymorphic: true, touch: true
     end
 
     car = car_class.find(1)
@@ -386,7 +411,7 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_clearing_association_touches_the_old_record
     klass = Class.new(ActiveRecord::Base) do
-      def self.name; 'Toy'; end
+      def self.name; "Toy"; end
       belongs_to :pet, touch: true
     end
 
@@ -406,56 +431,30 @@ class TimestampTest < ActiveRecord::TestCase
 
   def test_timestamp_column_values_are_present_in_the_callbacks
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'people'
+      self.table_name = "people"
 
       before_create do
-        self.born_at = self.created_at
+        self.born_at = created_at
       end
     end
 
-    person = klass.create first_name: 'David'
+    person = klass.create first_name: "David"
     assert_not_equal person.born_at, nil
   end
 
-  def test_timestamp_attributes_for_create
-    toy = Toy.first
-    assert_equal [:created_at, :created_on], toy.send(:timestamp_attributes_for_create)
-  end
-
-  def test_timestamp_attributes_for_update
-    toy = Toy.first
-    assert_equal [:updated_at, :updated_on], toy.send(:timestamp_attributes_for_update)
-  end
-
-  def test_all_timestamp_attributes
-    toy = Toy.first
-    assert_equal [:created_at, :created_on, :updated_at, :updated_on], toy.send(:all_timestamp_attributes)
-  end
-
   def test_timestamp_attributes_for_create_in_model
     toy = Toy.first
-    assert_equal [:created_at], toy.send(:timestamp_attributes_for_create_in_model)
+    assert_equal ["created_at"], toy.send(:timestamp_attributes_for_create_in_model)
   end
 
   def test_timestamp_attributes_for_update_in_model
     toy = Toy.first
-    assert_equal [:updated_at], toy.send(:timestamp_attributes_for_update_in_model)
+    assert_equal ["updated_at"], toy.send(:timestamp_attributes_for_update_in_model)
   end
 
   def test_all_timestamp_attributes_in_model
     toy = Toy.first
-    assert_equal [:created_at, :updated_at], toy.send(:all_timestamp_attributes_in_model)
-  end
-
-  def test_index_is_created_for_both_timestamps
-    ActiveRecord::Base.connection.create_table(:foos, force: true) do |t|
-      t.timestamps(:foos, null: true, index: true)
-    end
-
-    indexes = ActiveRecord::Base.connection.indexes('foos')
-    assert_equal ['created_at', 'updated_at'], indexes.flat_map(&:columns).sort
-  ensure
-    ActiveRecord::Base.connection.drop_table(:foos)
+    assert_equal ["created_at", "updated_at"], toy.send(:all_timestamp_attributes_in_model)
   end
 end
 
@@ -475,4 +474,15 @@ class TimestampsWithoutTransactionTest < ActiveRecord::TestCase
       assert_nil post.updated_at
     end
   end
+
+  def test_index_is_created_for_both_timestamps
+    ActiveRecord::Base.connection.create_table(:foos, force: true) do |t|
+      t.timestamps null: true, index: true
+    end
+
+    indexes = ActiveRecord::Base.connection.indexes("foos")
+    assert_equal ["created_at", "updated_at"], indexes.flat_map(&:columns).sort
+  ensure
+    ActiveRecord::Base.connection.drop_table(:foos)
+  end
 end
diff --git a/activerecord/test/cases/touch_later_test.rb b/activerecord/test/cases/touch_later_test.rb
index 49ada22529..cd3d5ed7d1 100644
--- a/activerecord/test/cases/touch_later_test.rb
+++ b/activerecord/test/cases/touch_later_test.rb
@@ -1,9 +1,11 @@
-require 'cases/helper'
-require 'models/invoice'
-require 'models/line_item'
-require 'models/topic'
-require 'models/node'
-require 'models/tree'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/invoice"
+require "models/line_item"
+require "models/topic"
+require "models/node"
+require "models/tree"
 
 class TouchLaterTest < ActiveRecord::TestCase
   fixtures :nodes, :trees
@@ -11,7 +13,7 @@ class TouchLaterTest < ActiveRecord::TestCase
   def test_touch_laster_raise_if_non_persisted
     invoice = Invoice.new
     Invoice.transaction do
-      refute invoice.persisted?
+      assert_not_predicate invoice, :persisted?
       assert_raises(ActiveRecord::ActiveRecordError) do
         invoice.touch_later
       end
@@ -21,7 +23,16 @@ class TouchLaterTest < ActiveRecord::TestCase
   def test_touch_later_dont_set_dirty_attributes
     invoice = Invoice.create!
     invoice.touch_later
-    refute invoice.changed?
+    assert_not_predicate invoice, :changed?
+  end
+
+  def test_touch_later_respects_no_touching_policy
+    time = Time.now.utc - 25.days
+    topic = Topic.create!(updated_at: time, created_at: time)
+    Topic.no_touching do
+      topic.touch_later
+    end
+    assert_equal time.to_i, topic.updated_at.to_i
   end
 
   def test_touch_later_update_the_attributes
@@ -72,7 +83,7 @@ class TouchLaterTest < ActiveRecord::TestCase
   end
 
   def test_touch_touches_immediately_with_a_custom_time
-    time = Time.now.utc - 25.days
+    time = (Time.now.utc - 25.days).change(nsec: 0)
     topic = Topic.create!(updated_at: time, created_at: time)
     assert_equal time, topic.updated_at
     assert_equal time, topic.created_at
@@ -89,22 +100,20 @@ class TouchLaterTest < ActiveRecord::TestCase
 
   def test_touch_later_dont_hit_the_db
     invoice = Invoice.create!
-    assert_queries(0) do
+    assert_no_queries do
       invoice.touch_later
     end
   end
 
   def test_touching_three_deep
-    skip "Pending from #19324"
-
     previous_tree_updated_at        = trees(:root).updated_at
     previous_grandparent_updated_at = nodes(:grandparent).updated_at
     previous_parent_updated_at      = nodes(:parent_a).updated_at
     previous_child_updated_at       = nodes(:child_one_of_a).updated_at
 
-    travel 5.seconds
-
-    Node.create! parent: nodes(:child_one_of_a), tree: trees(:root)
+    travel 5.seconds do
+      Node.create! parent: nodes(:child_one_of_a), tree: trees(:root)
+    end
 
     assert_not_equal nodes(:child_one_of_a).reload.updated_at, previous_child_updated_at
     assert_not_equal nodes(:parent_a).reload.updated_at, previous_parent_updated_at
diff --git a/activerecord/test/cases/transaction_callbacks_test.rb b/activerecord/test/cases/transaction_callbacks_test.rb
index f2229939c8..aa6b7915a2 100644
--- a/activerecord/test/cases/transaction_callbacks_test.rb
+++ b/activerecord/test/cases/transaction_callbacks_test.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/owner'
-require 'models/pet'
-require 'models/topic'
+require "models/owner"
+require "models/pet"
+require "models/topic"
 
 class TransactionCallbacksTest < ActiveRecord::TestCase
   fixtures :topics, :owners, :pets
@@ -17,7 +19,7 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
 
     attr_accessor :save_on_after_create
     after_create do
-      self.save! if save_on_after_create
+      save! if save_on_after_create
     end
 
     def history
@@ -34,10 +36,11 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
 
     has_many :replies, class_name: "ReplyWithCallbacks", foreign_key: "parent_id"
 
+    before_commit { |record| record.do_before_commit(nil) }
     after_commit { |record| record.do_after_commit(nil) }
-    after_commit(on: :create) { |record| record.do_after_commit(:create) }
-    after_commit(on: :update) { |record| record.do_after_commit(:update) }
-    after_commit(on: :destroy) { |record| record.do_after_commit(:destroy) }
+    after_create_commit { |record| record.do_after_commit(:create) }
+    after_update_commit { |record| record.do_after_commit(:update) }
+    after_destroy_commit { |record| record.do_after_commit(:destroy) }
     after_rollback { |record| record.do_after_rollback(nil) }
     after_rollback(on: :create) { |record| record.do_after_rollback(:create) }
     after_rollback(on: :update) { |record| record.do_after_rollback(:update) }
@@ -47,6 +50,12 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
       @history ||= []
     end
 
+    def before_commit_block(on = nil, &block)
+      @before_commit ||= {}
+      @before_commit[on] ||= []
+      @before_commit[on] << block
+    end
+
     def after_commit_block(on = nil, &block)
       @after_commit ||= {}
       @after_commit[on] ||= []
@@ -59,14 +68,19 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
       @after_rollback[on] << block
     end
 
+    def do_before_commit(on)
+      blocks = @before_commit[on] if defined?(@before_commit)
+      blocks.each { |b| b.call(self) } if blocks
+    end
+
     def do_after_commit(on)
       blocks = @after_commit[on] if defined?(@after_commit)
-      blocks.each{|b| b.call(self)} if blocks
+      blocks.each { |b| b.call(self) } if blocks
     end
 
     def do_after_rollback(on)
       blocks = @after_rollback[on] if defined?(@after_rollback)
-      blocks.each{|b| b.call(self)} if blocks
+      blocks.each { |b| b.call(self) } if blocks
     end
   end
 
@@ -74,9 +88,23 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
     @first = TopicWithCallbacks.find(1)
   end
 
+  # FIXME: Test behavior, not implementation.
+  def test_before_commit_exception_should_pop_transaction_stack
+    @first.before_commit_block { raise "better pop this txn from the stack!" }
+
+    original_txn = @first.class.connection.current_transaction
+
+    begin
+      @first.save!
+      fail
+    rescue
+      assert_equal original_txn, @first.class.connection.current_transaction
+    end
+  end
+
   def test_call_after_commit_after_transaction_commits
-    @first.after_commit_block{|r| r.history << :after_commit}
-    @first.after_rollback_block{|r| r.history << :after_rollback}
+    @first.after_commit_block { |r| r.history << :after_commit }
+    @first.after_rollback_block { |r| r.history << :after_rollback }
 
     @first.save!
     assert_equal [:after_commit], @first.history
@@ -97,7 +125,7 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_only_call_after_commit_on_create_after_transaction_commits_for_new_record
-    new_record = TopicWithCallbacks.new(:title => "New topic", :written_on => Date.today)
+    new_record = TopicWithCallbacks.new(title: "New topic", written_on: Date.today)
     add_transaction_execution_blocks new_record
 
     new_record.save!
@@ -105,17 +133,34 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_only_call_after_commit_on_create_after_transaction_commits_for_new_record_if_create_succeeds_creating_through_association
-    topic = TopicWithCallbacks.create!(:title => "New topic", :written_on => Date.today)
+    topic = TopicWithCallbacks.create!(title: "New topic", written_on: Date.today)
     reply = topic.replies.create
 
     assert_equal [], reply.history
   end
 
+  def test_only_call_after_commit_on_destroy_after_transaction_commits_for_destroyed_new_record
+    new_record = TopicWithCallbacks.new(title: "New topic", written_on: Date.today)
+    add_transaction_execution_blocks new_record
+
+    new_record.destroy
+    assert_equal [:commit_on_destroy], new_record.history
+  end
+
+  def test_save_in_after_create_commit_wont_invoke_extra_after_create_commit
+    new_record = TopicWithCallbacks.new(title: "New topic", written_on: Date.today)
+    add_transaction_execution_blocks new_record
+    new_record.after_commit_block(:create) { |r| r.save! }
+
+    new_record.save!
+    assert_equal [:commit_on_create, :commit_on_update], new_record.history
+  end
+
   def test_only_call_after_commit_on_create_and_doesnt_leaky
-    r = ReplyWithCallbacks.new(content: 'foo')
+    r = ReplyWithCallbacks.new(content: "foo")
     r.save_on_after_create = true
     r.save!
-    r.content = 'bar'
+    r.content = "bar"
     r.save!
     r.save!
     assert_equal [:commit_on_create], r.history
@@ -129,21 +174,21 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_only_call_after_commit_on_top_level_transactions
-    @first.after_commit_block{|r| r.history << :after_commit}
-    assert @first.history.empty?
+    @first.after_commit_block { |r| r.history << :after_commit }
+    assert_empty @first.history
 
     @first.transaction do
       @first.transaction(requires_new: true) do
         @first.touch
       end
-      assert @first.history.empty?
+      assert_empty @first.history
     end
     assert_equal [:after_commit], @first.history
   end
 
   def test_call_after_rollback_after_transaction_rollsback
-    @first.after_commit_block{|r| r.history << :after_commit}
-    @first.after_rollback_block{|r| r.history << :after_rollback}
+    @first.after_commit_block { |r| r.history << :after_commit }
+    @first.after_rollback_block { |r| r.history << :after_rollback }
 
     Topic.transaction do
       @first.save!
@@ -187,7 +232,7 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_only_call_after_rollback_on_create_after_transaction_rollsback_for_new_record
-    new_record = TopicWithCallbacks.new(:title => "New topic", :written_on => Date.today)
+    new_record = TopicWithCallbacks.new(title: "New topic", written_on: Date.today)
     add_transaction_execution_blocks new_record
 
     Topic.transaction do
@@ -217,20 +262,20 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_only_call_after_rollback_on_records_rolled_back_to_a_savepoint
-    def @first.rollbacks(i=0); @rollbacks ||= 0; @rollbacks += i if i; end
-    def @first.commits(i=0); @commits ||= 0; @commits += i if i; end
-    @first.after_rollback_block{|r| r.rollbacks(1)}
-    @first.after_commit_block{|r| r.commits(1)}
+    def @first.rollbacks(i = 0); @rollbacks ||= 0; @rollbacks += i if i; end
+    def @first.commits(i = 0); @commits ||= 0; @commits += i if i; end
+    @first.after_rollback_block { |r| r.rollbacks(1) }
+    @first.after_commit_block { |r| r.commits(1) }
 
     second = TopicWithCallbacks.find(3)
-    def second.rollbacks(i=0); @rollbacks ||= 0; @rollbacks += i if i; end
-    def second.commits(i=0); @commits ||= 0; @commits += i if i; end
-    second.after_rollback_block{|r| r.rollbacks(1)}
-    second.after_commit_block{|r| r.commits(1)}
+    def second.rollbacks(i = 0); @rollbacks ||= 0; @rollbacks += i if i; end
+    def second.commits(i = 0); @commits ||= 0; @commits += i if i; end
+    second.after_rollback_block { |r| r.rollbacks(1) }
+    second.after_commit_block { |r| r.commits(1) }
 
     Topic.transaction do
       @first.save!
-      Topic.transaction(:requires_new => true) do
+      Topic.transaction(requires_new: true) do
         second.save!
         raise ActiveRecord::Rollback
       end
@@ -243,19 +288,19 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_only_call_after_rollback_on_records_rolled_back_to_a_savepoint_when_release_savepoint_fails
-    def @first.rollbacks(i=0); @rollbacks ||= 0; @rollbacks += i if i; end
-    def @first.commits(i=0); @commits ||= 0; @commits += i if i; end
+    def @first.rollbacks(i = 0); @rollbacks ||= 0; @rollbacks += i if i; end
+    def @first.commits(i = 0); @commits ||= 0; @commits += i if i; end
 
-    @first.after_rollback_block{|r| r.rollbacks(1)}
-    @first.after_commit_block{|r| r.commits(1)}
+    @first.after_rollback_block { |r| r.rollbacks(1) }
+    @first.after_commit_block { |r| r.commits(1) }
 
     Topic.transaction do
       @first.save
-      Topic.transaction(:requires_new => true) do
+      Topic.transaction(requires_new: true) do
         @first.save!
         raise ActiveRecord::Rollback
       end
-      Topic.transaction(:requires_new => true) do
+      Topic.transaction(requires_new: true) do
         @first.save!
         raise ActiveRecord::Rollback
       end
@@ -266,7 +311,7 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
   end
 
   def test_after_commit_callback_should_not_swallow_errors
-    @first.after_commit_block{ fail "boom" }
+    @first.after_commit_block { fail "boom" }
     assert_raises(RuntimeError) do
       Topic.transaction do
         @first.save!
@@ -277,8 +322,8 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
   def test_after_commit_callback_when_raise_should_not_restore_state
     first = TopicWithCallbacks.new
     second = TopicWithCallbacks.new
-    first.after_commit_block{ fail "boom" }
-    second.after_commit_block{ fail "boom" }
+    first.after_commit_block { fail "boom" }
+    second.after_commit_block { fail "boom" }
 
     begin
       Topic.transaction do
@@ -296,7 +341,7 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
 
   def test_after_rollback_callback_should_not_swallow_errors_when_set_to_raise
     error_class = Class.new(StandardError)
-    @first.after_rollback_block{ raise error_class }
+    @first.after_rollback_block { raise error_class }
     assert_raises(error_class) do
       Topic.transaction do
         @first.save!
@@ -310,8 +355,8 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
 
     first = TopicWithCallbacks.new
     second = TopicWithCallbacks.new
-    first.after_rollback_block{ raise error_class }
-    second.after_rollback_block{ raise error_class }
+    first.after_rollback_block { raise error_class }
+    second.after_rollback_block { raise error_class }
 
     begin
       Topic.transaction do
@@ -329,16 +374,36 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
 
   def test_after_rollback_callbacks_should_validate_on_condition
     assert_raise(ArgumentError) { Topic.after_rollback(on: :save) }
-    e = assert_raise(ArgumentError) { Topic.after_rollback(on: 'create') }
+    e = assert_raise(ArgumentError) { Topic.after_rollback(on: "create") }
     assert_match(/:on conditions for after_commit and after_rollback callbacks have to be one of \[:create, :destroy, :update\]/, e.message)
   end
 
   def test_after_commit_callbacks_should_validate_on_condition
     assert_raise(ArgumentError) { Topic.after_commit(on: :save) }
-    e = assert_raise(ArgumentError) { Topic.after_commit(on: 'create') }
+    e = assert_raise(ArgumentError) { Topic.after_commit(on: "create") }
     assert_match(/:on conditions for after_commit and after_rollback callbacks have to be one of \[:create, :destroy, :update\]/, e.message)
   end
 
+  def test_after_commit_chain_not_called_on_errors
+    record_1 = TopicWithCallbacks.create!
+    record_2 = TopicWithCallbacks.create!
+    record_3 = TopicWithCallbacks.create!
+    callbacks = []
+    record_1.after_commit_block { raise }
+    record_2.after_commit_block { callbacks << record_2.id }
+    record_3.after_commit_block { callbacks << record_3.id }
+    begin
+      TopicWithCallbacks.transaction do
+        record_1.save!
+        record_2.save!
+        record_3.save!
+      end
+    rescue
+      # From record_1.after_commit
+    end
+    assert_equal [], callbacks
+  end
+
   def test_saving_a_record_with_a_belongs_to_that_specifies_touching_the_parent_should_call_callbacks_on_the_parent_object
     pet   = Pet.first
     owner = pet.owner
@@ -366,6 +431,28 @@ class TransactionCallbacksTest < ActiveRecord::TestCase
     end
 end
 
+class TransactionAfterCommitCallbacksWithOptimisticLockingTest < ActiveRecord::TestCase
+  class PersonWithCallbacks < ActiveRecord::Base
+    self.table_name = :people
+
+    after_create_commit { |record| record.history << :commit_on_create }
+    after_update_commit { |record| record.history << :commit_on_update }
+    after_destroy_commit { |record| record.history << :commit_on_destroy }
+
+    def history
+      @history ||= []
+    end
+  end
+
+  def test_after_commit_callbacks_with_optimistic_locking
+    person = PersonWithCallbacks.create!(first_name: "first name")
+    person.update!(first_name: "another name")
+    person.destroy
+
+    assert_equal [:commit_on_create, :commit_on_update, :commit_on_destroy], person.history
+  end
+end
+
 class CallbacksOnMultipleActionsTest < ActiveRecord::TestCase
   self.use_transactional_tests = false
 
@@ -423,9 +510,52 @@ class CallbacksOnMultipleActionsTest < ActiveRecord::TestCase
   end
 end
 
+class CallbacksOnDestroyUpdateActionRaceTest < ActiveRecord::TestCase
+  class TopicWithHistory < ActiveRecord::Base
+    self.table_name = :topics
+
+    def self.clear_history
+      @@history = []
+    end
 
-class TransactionEnrollmentCallbacksTest < ActiveRecord::TestCase
+    def self.history
+      @@history ||= []
+    end
+  end
+
+  class TopicWithCallbacksOnDestroy < TopicWithHistory
+    after_commit(on: :destroy) { |record| record.class.history << :destroy }
+  end
+
+  class TopicWithCallbacksOnUpdate < TopicWithHistory
+    after_commit(on: :update) { |record| record.class.history << :update }
+  end
+
+  def test_trigger_once_on_multiple_deletions
+    TopicWithCallbacksOnDestroy.clear_history
+    topic = TopicWithCallbacksOnDestroy.new
+    topic.save
+    topic_clone = TopicWithCallbacksOnDestroy.find(topic.id)
+    topic.destroy
+    topic_clone.destroy
+
+    assert_equal [:destroy], TopicWithCallbacksOnDestroy.history
+  end
+
+  def test_trigger_on_update_where_row_was_deleted
+    TopicWithCallbacksOnUpdate.clear_history
+    topic = TopicWithCallbacksOnUpdate.new
+    topic.save
+    topic_clone = TopicWithCallbacksOnUpdate.find(topic.id)
+    topic.destroy
+    topic_clone.author_name = "Test Author"
+    topic_clone.save
+
+    assert_equal [], TopicWithCallbacksOnUpdate.history
+  end
+end
 
+class TransactionEnrollmentCallbacksTest < ActiveRecord::TestCase
   class TopicWithoutTransactionalEnrollmentCallbacks < ActiveRecord::Base
     self.table_name = :topics
 
@@ -444,16 +574,16 @@ class TransactionEnrollmentCallbacksTest < ActiveRecord::TestCase
 
   def test_commit_does_not_run_transactions_callbacks_without_enrollment
     @topic.transaction do
-      @topic.content = 'foo'
+      @topic.content = "foo"
       @topic.save!
     end
-    assert @topic.history.empty?
+    assert_empty @topic.history
   end
 
   def test_commit_run_transactions_callbacks_with_explicit_enrollment
     @topic.transaction do
       2.times do
-        @topic.content = 'foo'
+        @topic.content = "foo"
         @topic.save!
       end
       @topic.class.connection.add_transaction_record(@topic)
@@ -461,19 +591,30 @@ class TransactionEnrollmentCallbacksTest < ActiveRecord::TestCase
     assert_equal [:before_commit, :after_commit], @topic.history
   end
 
+  def test_commit_run_transactions_callbacks_with_nested_transactions
+    @topic.transaction do
+      @topic.transaction(requires_new: true) do
+        @topic.content = "foo"
+        @topic.save!
+        @topic.class.connection.add_transaction_record(@topic)
+      end
+    end
+    assert_equal [:before_commit, :after_commit], @topic.history
+  end
+
   def test_rollback_does_not_run_transactions_callbacks_without_enrollment
     @topic.transaction do
-      @topic.content = 'foo'
+      @topic.content = "foo"
       @topic.save!
       raise ActiveRecord::Rollback
     end
-    assert @topic.history.empty?
+    assert_empty @topic.history
   end
 
   def test_rollback_run_transactions_callbacks_with_explicit_enrollment
     @topic.transaction do
       2.times do
-        @topic.content = 'foo'
+        @topic.content = "foo"
         @topic.save!
       end
       @topic.class.connection.add_transaction_record(@topic)
@@ -482,3 +623,43 @@ class TransactionEnrollmentCallbacksTest < ActiveRecord::TestCase
     assert_equal [:rollback], @topic.history
   end
 end
+
+class CallbacksOnActionAndConditionTest < ActiveRecord::TestCase
+  self.use_transactional_tests = false
+
+  class TopicWithCallbacksOnActionAndCondition < ActiveRecord::Base
+    self.table_name = :topics
+
+    after_commit(on: [:create, :update], if: :run_callback?) { |record| record.history << :create_or_update }
+
+    def clear_history
+      @history = []
+    end
+
+    def history
+      @history ||= []
+    end
+
+    def run_callback?
+      self.history << :run_callback?
+      true
+    end
+
+    attr_accessor :save_before_commit_history, :update_title
+  end
+
+  def test_callback_on_action_with_condition
+    topic = TopicWithCallbacksOnActionAndCondition.new
+    topic.save
+    assert_equal [:run_callback?, :create_or_update], topic.history
+
+    topic.clear_history
+    topic.approved = true
+    topic.save
+    assert_equal [:run_callback?, :create_or_update], topic.history
+
+    topic.clear_history
+    topic.destroy
+    assert_equal [], topic.history
+  end
+end
diff --git a/activerecord/test/cases/transaction_isolation_test.rb b/activerecord/test/cases/transaction_isolation_test.rb
index 2f7d208ed2..2932969412 100644
--- a/activerecord/test/cases/transaction_isolation_test.rb
+++ b/activerecord/test/cases/transaction_isolation_test.rb
@@ -1,4 +1,6 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 unless ActiveRecord::Base.connection.supports_transaction_isolation?
   class TransactionIsolationUnsupportedTest < ActiveRecord::TestCase
@@ -9,22 +11,20 @@ unless ActiveRecord::Base.connection.supports_transaction_isolation?
 
     test "setting the isolation level raises an error" do
       assert_raises(ActiveRecord::TransactionIsolationError) do
-        Tag.transaction(isolation: :serializable) { }
+        Tag.transaction(isolation: :serializable) { Tag.connection.materialize_transactions }
       end
     end
   end
-end
-
-if ActiveRecord::Base.connection.supports_transaction_isolation?
+else
   class TransactionIsolationTest < ActiveRecord::TestCase
     self.use_transactional_tests = false
 
     class Tag < ActiveRecord::Base
-      self.table_name = 'tags'
+      self.table_name = "tags"
     end
 
     class Tag2 < ActiveRecord::Base
-      self.table_name = 'tags'
+      self.table_name = "tags"
     end
 
     setup do
@@ -63,18 +63,18 @@ if ActiveRecord::Base.connection.supports_transaction_isolation?
     # We are testing that a nonrepeatable read does not happen
     if ActiveRecord::Base.connection.transaction_isolation_levels.include?(:repeatable_read)
       test "repeatable read" do
-        tag = Tag.create(name: 'jon')
+        tag = Tag.create(name: "jon")
 
         Tag.transaction(isolation: :repeatable_read) do
           tag.reload
-          Tag2.find(tag.id).update(name: 'emily')
+          Tag2.find(tag.id).update(name: "emily")
 
           tag.reload
-          assert_equal 'jon', tag.name
+          assert_equal "jon", tag.name
         end
 
         tag.reload
-        assert_equal 'emily', tag.name
+        assert_equal "emily", tag.name
       end
     end
 
diff --git a/activerecord/test/cases/transactions_test.rb b/activerecord/test/cases/transactions_test.rb
index 2468a91969..50740054f7 100644
--- a/activerecord/test/cases/transactions_test.rb
+++ b/activerecord/test/cases/transactions_test.rb
@@ -1,16 +1,18 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/reply'
-require 'models/developer'
-require 'models/computer'
-require 'models/book'
-require 'models/author'
-require 'models/post'
-require 'models/movie'
+require "models/topic"
+require "models/reply"
+require "models/developer"
+require "models/computer"
+require "models/book"
+require "models/author"
+require "models/post"
+require "models/movie"
 
 class TransactionTest < ActiveRecord::TestCase
   self.use_transactional_tests = false
-  fixtures :topics, :developers, :authors, :posts
+  fixtures :topics, :developers, :authors, :author_addresses, :posts
 
   def setup
     @first, @second = Topic.find(1, 2).sort_by(&:id)
@@ -18,22 +20,22 @@ class TransactionTest < ActiveRecord::TestCase
 
   def test_persisted_in_a_model_with_custom_primary_key_after_failed_save
     movie = Movie.create
-    assert !movie.persisted?
+    assert_not_predicate movie, :persisted?
   end
 
   def test_raise_after_destroy
-    assert_not @first.frozen?
+    assert_not_predicate @first, :frozen?
 
     assert_raises(RuntimeError) {
       Topic.transaction do
         @first.destroy
-        assert @first.frozen?
+        assert_predicate @first, :frozen?
         raise
       end
     }
 
     assert @first.reload
-    assert_not @first.frozen?
+    assert_not_predicate @first, :frozen?
   end
 
   def test_successful
@@ -45,7 +47,7 @@ class TransactionTest < ActiveRecord::TestCase
     end
 
     assert Topic.find(1).approved?, "First should have been approved"
-    assert !Topic.find(2).approved?, "Second should have been unapproved"
+    assert_not Topic.find(2).approved?, "Second should have been unapproved"
   end
 
   def transaction_with_return
@@ -58,6 +60,11 @@ class TransactionTest < ActiveRecord::TestCase
     end
   end
 
+  def test_add_to_null_transaction
+    topic = Topic.new
+    topic.add_to_transaction
+  end
+
   def test_successful_with_return
     committed = false
 
@@ -73,7 +80,7 @@ class TransactionTest < ActiveRecord::TestCase
     assert committed
 
     assert Topic.find(1).approved?, "First should have been approved"
-    assert !Topic.find(2).approved?, "Second should have been unapproved"
+    assert_not Topic.find(2).approved?, "Second should have been unapproved"
   ensure
     Topic.connection.class_eval do
       remove_method :commit_db_transaction
@@ -93,7 +100,7 @@ class TransactionTest < ActiveRecord::TestCase
     end
 
     Topic.transaction do
-      @first.approved  = true
+      @first.approved = true
       @first.save!
     end
 
@@ -114,7 +121,7 @@ class TransactionTest < ActiveRecord::TestCase
     end
 
     assert Topic.find(1).approved?, "First should have been approved"
-    assert !Topic.find(2).approved?, "Second should have been unapproved"
+    assert_not Topic.find(2).approved?, "Second should have been unapproved"
   end
 
   def test_failing_on_exception
@@ -131,41 +138,41 @@ class TransactionTest < ActiveRecord::TestCase
     end
 
     assert @first.approved?, "First should still be changed in the objects"
-    assert !@second.approved?, "Second should still be changed in the objects"
+    assert_not @second.approved?, "Second should still be changed in the objects"
 
-    assert !Topic.find(1).approved?, "First shouldn't have been approved"
+    assert_not Topic.find(1).approved?, "First shouldn't have been approved"
     assert Topic.find(2).approved?, "Second should still be approved"
   end
 
   def test_raising_exception_in_callback_rollbacks_in_save
     def @first.after_save_for_transaction
-      raise 'Make the transaction rollback'
+      raise "Make the transaction rollback"
     end
 
     @first.approved = true
     e = assert_raises(RuntimeError) { @first.save }
     assert_equal "Make the transaction rollback", e.message
-    assert !Topic.find(1).approved?
+    assert_not_predicate Topic.find(1), :approved?
   end
 
   def test_rolling_back_in_a_callback_rollbacks_before_save
     def @first.before_save_for_transaction
       raise ActiveRecord::Rollback
     end
-    assert !@first.approved
+    assert_not @first.approved
 
     Topic.transaction do
-      @first.approved  = true
+      @first.approved = true
       @first.save!
     end
-    assert !Topic.find(@first.id).approved?, "Should not commit the approved flag"
+    assert_not Topic.find(@first.id).approved?, "Should not commit the approved flag"
   end
 
   def test_raising_exception_in_nested_transaction_restore_state_in_save
     topic = Topic.new
 
     def topic.after_save_for_transaction
-      raise 'Make the transaction rollback'
+      raise "Make the transaction rollback"
     end
 
     assert_raises(RuntimeError) do
@@ -175,13 +182,20 @@ class TransactionTest < ActiveRecord::TestCase
     assert topic.new_record?, "#{topic.inspect} should be new record"
   end
 
+  def test_transaction_state_is_cleared_when_record_is_persisted
+    author = Author.create! name: "foo"
+    author.name = nil
+    assert_not author.save
+    assert_not_predicate author, :new_record?
+  end
+
   def test_update_should_rollback_on_failure
     author = Author.find(1)
     posts_count = author.posts.size
     assert posts_count > 0
     status = author.update(name: nil, post_ids: [])
-    assert !status
-    assert_equal posts_count, author.posts(true).size
+    assert_not status
+    assert_equal posts_count, author.posts.reload.size
   end
 
   def test_update_should_rollback_on_failure!
@@ -191,24 +205,14 @@ class TransactionTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::RecordInvalid) do
       author.update!(name: nil, post_ids: [])
     end
-    assert_equal posts_count, author.posts(true).size
-  end
-
-  def test_cancellation_from_returning_false_in_before_filter
-    def @first.before_save_for_transaction
-      false
-    end
-
-    assert_deprecated do
-      @first.save
-    end
+    assert_equal posts_count, author.posts.reload.size
   end
 
   def test_cancellation_from_before_destroy_rollbacks_in_destroy
     add_cancelling_before_destroy_with_db_side_effect_to_topic @first
     nbooks_before_destroy = Book.count
     status = @first.destroy
-    assert !status
+    assert_not status
     @first.reload
     assert_equal nbooks_before_destroy, Book.count
   end
@@ -218,9 +222,9 @@ class TransactionTest < ActiveRecord::TestCase
       send("add_cancelling_before_#{filter}_with_db_side_effect_to_topic", @first)
       nbooks_before_save = Book.count
       original_author_name = @first.author_name
-      @first.author_name += '_this_should_not_end_up_in_the_db'
+      @first.author_name += "_this_should_not_end_up_in_the_db"
       status = @first.save
-      assert !status
+      assert_not status
       assert_equal original_author_name, @first.reload.author_name
       assert_equal nbooks_before_save, Book.count
     end
@@ -229,7 +233,7 @@ class TransactionTest < ActiveRecord::TestCase
       send("add_cancelling_before_#{filter}_with_db_side_effect_to_topic", @first)
       nbooks_before_save = Book.count
       original_author_name = @first.author_name
-      @first.author_name += '_this_should_not_end_up_in_the_db'
+      @first.author_name += "_this_should_not_end_up_in_the_db"
 
       begin
         @first.save!
@@ -244,18 +248,18 @@ class TransactionTest < ActiveRecord::TestCase
   def test_callback_rollback_in_create
     topic = Class.new(Topic) {
       def after_create_for_transaction
-        raise 'Make the transaction rollback'
+        raise "Make the transaction rollback"
       end
     }
 
-    new_topic = topic.new(:title                => "A new topic",
-                          :author_name          => "Ben",
-                          :author_email_address => "ben@example.com",
-                          :written_on           => "2003-07-16t15:28:11.2233+01:00",
-                          :last_read            => "2004-04-15",
-                          :bonus_time           => "2005-01-30t15:28:00.00+01:00",
-                          :content              => "Have a nice day",
-                          :approved             => false)
+    new_topic = topic.new(title: "A new topic",
+                          author_name: "Ben",
+                          author_email_address: "ben@example.com",
+                          written_on: "2003-07-16t15:28:11.2233+01:00",
+                          last_read: "2004-04-15",
+                          bonus_time: "2005-01-30t15:28:00.00+01:00",
+                          content: "Have a nice day",
+                          approved: false)
 
     new_record_snapshot = !new_topic.persisted?
     id_present = new_topic.has_attribute?(Topic.primary_key)
@@ -267,7 +271,11 @@ class TransactionTest < ActiveRecord::TestCase
       e = assert_raises(RuntimeError) { new_topic.save }
       assert_equal "Make the transaction rollback", e.message
       assert_equal new_record_snapshot, !new_topic.persisted?, "The topic should have its old persisted value"
-      assert_equal id_snapshot, new_topic.id, "The topic should have its old id"
+      if id_snapshot.nil?
+        assert_nil new_topic.id, "The topic should have its old id"
+      else
+        assert_equal id_snapshot, new_topic.id, "The topic should have its old id"
+      end
       assert_equal id_present, new_topic.has_attribute?(Topic.primary_key)
     end
   end
@@ -279,8 +287,20 @@ class TransactionTest < ActiveRecord::TestCase
       end
     }
 
-    new_topic = topic.create(:title => "A new topic")
-    assert !new_topic.persisted?, "The topic should not be persisted"
+    new_topic = topic.create(title: "A new topic")
+    assert_not new_topic.persisted?, "The topic should not be persisted"
+    assert_nil new_topic.id, "The topic should not have an ID"
+  end
+
+  def test_callback_rollback_in_create_with_rollback_exception
+    topic = Class.new(Topic) {
+      def after_create_for_transaction
+        raise ActiveRecord::Rollback
+      end
+    }
+
+    new_topic = topic.create(title: "A new topic")
+    assert_not new_topic.persisted?, "The topic should not be persisted"
     assert_nil new_topic.id, "The topic should not have an ID"
   end
 
@@ -295,7 +315,77 @@ class TransactionTest < ActiveRecord::TestCase
     end
 
     assert Topic.find(1).approved?, "First should have been approved"
-    assert !Topic.find(2).approved?, "Second should have been unapproved"
+    assert_not Topic.find(2).approved?, "Second should have been unapproved"
+  end
+
+  def test_nested_transaction_with_new_transaction_applies_parent_state_on_rollback
+    topic_one = Topic.new(title: "A new topic")
+    topic_two = Topic.new(title: "Another new topic")
+
+    Topic.transaction do
+      topic_one.save
+
+      Topic.transaction(requires_new: true) do
+        topic_two.save
+
+        assert_predicate topic_one, :persisted?
+        assert_predicate topic_two, :persisted?
+      end
+
+      raise ActiveRecord::Rollback
+    end
+
+    assert_not_predicate topic_one, :persisted?
+    assert_not_predicate topic_two, :persisted?
+  end
+
+  def test_nested_transaction_without_new_transaction_applies_parent_state_on_rollback
+    topic_one = Topic.new(title: "A new topic")
+    topic_two = Topic.new(title: "Another new topic")
+
+    Topic.transaction do
+      topic_one.save
+
+      Topic.transaction do
+        topic_two.save
+
+        assert_predicate topic_one, :persisted?
+        assert_predicate topic_two, :persisted?
+      end
+
+      raise ActiveRecord::Rollback
+    end
+
+    assert_not_predicate topic_one, :persisted?
+    assert_not_predicate topic_two, :persisted?
+  end
+
+  def test_double_nested_transaction_applies_parent_state_on_rollback
+    topic_one = Topic.new(title: "A new topic")
+    topic_two = Topic.new(title: "Another new topic")
+    topic_three = Topic.new(title: "Another new topic of course")
+
+    Topic.transaction do
+      topic_one.save
+
+      Topic.transaction do
+        topic_two.save
+
+        Topic.transaction do
+          topic_three.save
+        end
+      end
+
+      assert_predicate topic_one, :persisted?
+      assert_predicate topic_two, :persisted?
+      assert_predicate topic_three, :persisted?
+
+      raise ActiveRecord::Rollback
+    end
+
+    assert_not_predicate topic_one, :persisted?
+    assert_not_predicate topic_two, :persisted?
+    assert_not_predicate topic_three, :persisted?
   end
 
   def test_manually_rolling_back_a_transaction
@@ -309,15 +399,15 @@ class TransactionTest < ActiveRecord::TestCase
     end
 
     assert @first.approved?, "First should still be changed in the objects"
-    assert !@second.approved?, "Second should still be changed in the objects"
+    assert_not @second.approved?, "Second should still be changed in the objects"
 
-    assert !Topic.find(1).approved?, "First shouldn't have been approved"
+    assert_not Topic.find(1).approved?, "First shouldn't have been approved"
     assert Topic.find(2).approved?, "Second should still be approved"
   end
 
   def test_invalid_keys_for_transaction
     assert_raise ArgumentError do
-      Topic.transaction :nested => true do
+      Topic.transaction nested: true do
       end
     end
   end
@@ -330,7 +420,7 @@ class TransactionTest < ActiveRecord::TestCase
       @second.save!
 
       begin
-        Topic.transaction :requires_new => true do
+        Topic.transaction requires_new: true do
           @first.happy = false
           @first.save!
           raise
@@ -339,8 +429,8 @@ class TransactionTest < ActiveRecord::TestCase
       end
     end
 
-    assert @first.reload.approved?
-    assert !@second.reload.approved?
+    assert_predicate @first.reload, :approved?
+    assert_not_predicate @second.reload, :approved?
   end if Topic.connection.supports_savepoints?
 
   def test_force_savepoint_on_instance
@@ -351,7 +441,7 @@ class TransactionTest < ActiveRecord::TestCase
       @second.save!
 
       begin
-        @second.transaction :requires_new => true do
+        @second.transaction requires_new: true do
           @first.happy = false
           @first.save!
           raise
@@ -360,8 +450,8 @@ class TransactionTest < ActiveRecord::TestCase
       end
     end
 
-    assert @first.reload.approved?
-    assert !@second.reload.approved?
+    assert_predicate @first.reload, :approved?
+    assert_not_predicate @second.reload, :approved?
   end if Topic.connection.supports_savepoints?
 
   def test_no_savepoint_in_nested_transaction_without_force
@@ -381,8 +471,8 @@ class TransactionTest < ActiveRecord::TestCase
       end
     end
 
-    assert !@first.reload.approved?
-    assert !@second.reload.approved?
+    assert_not_predicate @first.reload, :approved?
+    assert_not_predicate @second.reload, :approved?
   end if Topic.connection.supports_savepoints?
 
   def test_many_savepoints
@@ -391,17 +481,17 @@ class TransactionTest < ActiveRecord::TestCase
       @first.save!
 
       begin
-        Topic.transaction :requires_new => true do
+        Topic.transaction requires_new: true do
           @first.content = "Two"
           @first.save!
 
           begin
-            Topic.transaction :requires_new => true do
+            Topic.transaction requires_new: true do
               @first.content = "Three"
               @first.save!
 
               begin
-                Topic.transaction :requires_new => true do
+                Topic.transaction requires_new: true do
                   @first.content = "Four"
                   @first.save!
                   raise
@@ -431,19 +521,19 @@ class TransactionTest < ActiveRecord::TestCase
 
   def test_using_named_savepoints
     Topic.transaction do
-      @first.approved  = true
+      @first.approved = true
       @first.save!
       Topic.connection.create_savepoint("first")
 
-      @first.approved  = false
+      @first.approved = false
       @first.save!
       Topic.connection.rollback_to_savepoint("first")
-      assert @first.reload.approved?
+      assert_predicate @first.reload, :approved?
 
-      @first.approved  = false
+      @first.approved = false
       @first.save!
       Topic.connection.release_savepoint("first")
-      assert_not @first.reload.approved?
+      assert_not_predicate @first.reload, :approved?
     end
   end if Topic.connection.supports_savepoints?
 
@@ -480,27 +570,31 @@ class TransactionTest < ActiveRecord::TestCase
   end
 
   def test_rollback_when_commit_raises
-    Topic.connection.expects(:begin_db_transaction)
-    Topic.connection.expects(:commit_db_transaction).raises('OH NOES')
-    Topic.connection.expects(:rollback_db_transaction)
-
-    assert_raise RuntimeError do
-      Topic.transaction do
-        # do nothing
+    assert_called(Topic.connection, :begin_db_transaction) do
+      Topic.connection.stub(:commit_db_transaction, -> { raise("OH NOES") }) do
+        assert_called(Topic.connection, :rollback_db_transaction) do
+          e = assert_raise RuntimeError do
+            Topic.transaction do
+              Topic.connection.materialize_transactions
+            end
+          end
+          assert_equal "OH NOES", e.message
+        end
       end
     end
   end
 
   def test_rollback_when_saving_a_frozen_record
-    topic = Topic.new(:title => 'test')
+    topic = Topic.new(title: "test")
     topic.freeze
-    e = assert_raise(RuntimeError) { topic.save }
-    assert_match(/frozen/i, e.message) # Not good enough, but we can't do much
-                                       # about it since there is no specific error
-                                       # for frozen objects.
-    assert !topic.persisted?, 'not persisted'
+    e = assert_raise(frozen_error_class) { topic.save }
+    # Not good enough, but we can't do much
+    # about it since there is no specific error
+    # for frozen objects.
+    assert_match(/frozen/i, e.message)
+    assert_not topic.persisted?, "not persisted"
     assert_nil topic.id
-    assert topic.frozen?, 'not frozen'
+    assert topic.frozen?, "not frozen"
   end
 
   def test_rollback_when_thread_killed
@@ -525,20 +619,20 @@ class TransactionTest < ActiveRecord::TestCase
     thread.join
 
     assert @first.approved?, "First should still be changed in the objects"
-    assert !@second.approved?, "Second should still be changed in the objects"
+    assert_not @second.approved?, "Second should still be changed in the objects"
 
-    assert !Topic.find(1).approved?, "First shouldn't have been approved"
+    assert_not Topic.find(1).approved?, "First shouldn't have been approved"
     assert Topic.find(2).approved?, "Second should still be approved"
   end
 
   def test_restore_active_record_state_for_all_records_in_a_transaction
     topic_without_callbacks = Class.new(ActiveRecord::Base) do
-      self.table_name = 'topics'
+      self.table_name = "topics"
     end
 
-    topic_1 = Topic.new(:title => 'test_1')
-    topic_2 = Topic.new(:title => 'test_2')
-    topic_3 = topic_without_callbacks.new(:title => 'test_3')
+    topic_1 = Topic.new(title: "test_1")
+    topic_2 = Topic.new(title: "test_2")
+    topic_3 = topic_without_callbacks.new(title: "test_3")
 
     Topic.transaction do
       assert topic_1.save
@@ -546,27 +640,27 @@ class TransactionTest < ActiveRecord::TestCase
       assert topic_3.save
       @first.save
       @second.destroy
-      assert topic_1.persisted?, 'persisted'
+      assert topic_1.persisted?, "persisted"
       assert_not_nil topic_1.id
-      assert topic_2.persisted?, 'persisted'
+      assert topic_2.persisted?, "persisted"
       assert_not_nil topic_2.id
-      assert topic_3.persisted?, 'persisted'
+      assert topic_3.persisted?, "persisted"
       assert_not_nil topic_3.id
-      assert @first.persisted?, 'persisted'
+      assert @first.persisted?, "persisted"
       assert_not_nil @first.id
-      assert @second.destroyed?, 'destroyed'
+      assert @second.destroyed?, "destroyed"
       raise ActiveRecord::Rollback
     end
 
-    assert !topic_1.persisted?, 'not persisted'
+    assert_not topic_1.persisted?, "not persisted"
     assert_nil topic_1.id
-    assert !topic_2.persisted?, 'not persisted'
+    assert_not topic_2.persisted?, "not persisted"
     assert_nil topic_2.id
-    assert !topic_3.persisted?, 'not persisted'
+    assert_not topic_3.persisted?, "not persisted"
     assert_nil topic_3.id
-    assert @first.persisted?, 'persisted'
+    assert @first.persisted?, "persisted"
     assert_not_nil @first.id
-    assert !@second.destroyed?, 'not destroyed'
+    assert_not @second.destroyed?, "not destroyed"
   end
 
   def test_restore_frozen_state_after_double_destroy
@@ -580,8 +674,130 @@ class TransactionTest < ActiveRecord::TestCase
       raise ActiveRecord::Rollback
     end
 
-    assert_not reply.frozen?
-    assert_not topic.frozen?
+    assert_not_predicate reply, :frozen?
+    assert_not_predicate topic, :frozen?
+  end
+
+  def test_restore_new_record_after_double_save
+    topic = Topic.new
+
+    Topic.transaction do
+      topic.save!
+      topic.save!
+      raise ActiveRecord::Rollback
+    end
+
+    assert_nil topic.id
+    assert_predicate topic, :new_record?
+  end
+
+  def test_dont_restore_new_record_in_subsequent_transaction
+    topic = Topic.new
+
+    Topic.transaction do
+      topic.save!
+      topic.save!
+    end
+
+    Topic.transaction do
+      topic.save!
+      raise ActiveRecord::Rollback
+    end
+
+    assert_predicate topic, :persisted?
+    assert_not_predicate topic, :new_record?
+  end
+
+  def test_restore_id_after_rollback
+    topic = Topic.new
+
+    Topic.transaction do
+      topic.save!
+      raise ActiveRecord::Rollback
+    end
+
+    assert_nil topic.id
+  end
+
+  def test_restore_custom_primary_key_after_rollback
+    movie = Movie.new(name: "foo")
+
+    Movie.transaction do
+      movie.save!
+      raise ActiveRecord::Rollback
+    end
+
+    assert_nil movie.movieid
+  end
+
+  def test_assign_id_after_rollback
+    topic = Topic.create!
+
+    Topic.transaction do
+      topic.save!
+      raise ActiveRecord::Rollback
+    end
+
+    topic.id = nil
+    assert_nil topic.id
+  end
+
+  def test_assign_custom_primary_key_after_rollback
+    movie = Movie.create!(name: "foo")
+
+    Movie.transaction do
+      movie.save!
+      raise ActiveRecord::Rollback
+    end
+
+    movie.movieid = nil
+    assert_nil movie.movieid
+  end
+
+  def test_read_attribute_after_rollback
+    topic = Topic.new
+
+    Topic.transaction do
+      topic.save!
+      raise ActiveRecord::Rollback
+    end
+
+    assert_nil topic.read_attribute(:id)
+  end
+
+  def test_read_attribute_with_custom_primary_key_after_rollback
+    movie = Movie.new(name: "foo")
+
+    Movie.transaction do
+      movie.save!
+      raise ActiveRecord::Rollback
+    end
+
+    assert_nil movie.read_attribute(:movieid)
+  end
+
+  def test_write_attribute_after_rollback
+    topic = Topic.create!
+
+    Topic.transaction do
+      topic.save!
+      raise ActiveRecord::Rollback
+    end
+
+    topic.write_attribute(:id, nil)
+    assert_nil topic.id
+  end
+
+  def test_write_attribute_with_custom_primary_key_after_rollback
+    movie = Movie.create!(name: "foo")
+
+    Movie.transaction do
+      movie.save!
+      raise ActiveRecord::Rollback
+    end
+
+    movie.write_attribute(:movieid, nil)
+    assert_nil movie.movieid
   end
 
   def test_rollback_of_frozen_records
@@ -590,7 +806,7 @@ class TransactionTest < ActiveRecord::TestCase
       topic.destroy
       raise ActiveRecord::Rollback
     end
-    assert topic.frozen?, 'frozen'
+    assert topic.frozen?, "frozen"
   end
 
   def test_rollback_for_freshly_persisted_records
@@ -599,7 +815,7 @@ class TransactionTest < ActiveRecord::TestCase
       topic.destroy
       raise ActiveRecord::Rollback
     end
-    assert topic.persisted?, 'persisted'
+    assert topic.persisted?, "persisted"
   end
 
   def test_sqlite_add_column_in_transaction
@@ -613,27 +829,27 @@ class TransactionTest < ActiveRecord::TestCase
 
     assert_nothing_raised do
       Topic.reset_column_information
-      Topic.connection.add_column('topics', 'stuff', :string)
-      assert Topic.column_names.include?('stuff')
+      Topic.connection.add_column("topics", "stuff", :string)
+      assert_includes Topic.column_names, "stuff"
 
       Topic.reset_column_information
-      Topic.connection.remove_column('topics', 'stuff')
-      assert !Topic.column_names.include?('stuff')
+      Topic.connection.remove_column("topics", "stuff")
+      assert_not_includes Topic.column_names, "stuff"
     end
 
     if Topic.connection.supports_ddl_transactions?
       assert_nothing_raised do
-        Topic.transaction { Topic.connection.add_column('topics', 'stuff', :string) }
+        Topic.transaction { Topic.connection.add_column("topics", "stuff", :string) }
       end
     else
       Topic.transaction do
-        assert_raise(ActiveRecord::StatementInvalid) { Topic.connection.add_column('topics', 'stuff', :string) }
+        assert_raise(ActiveRecord::StatementInvalid) { Topic.connection.add_column("topics", "stuff", :string) }
         raise ActiveRecord::Rollback
       end
     end
   ensure
     begin
-      Topic.connection.remove_column('topics', 'stuff')
+      Topic.connection.remove_column("topics", "stuff")
     rescue
     ensure
       Topic.reset_column_information
@@ -644,38 +860,76 @@ class TransactionTest < ActiveRecord::TestCase
     connection = Topic.connection
     transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction
 
-    assert transaction.open?
-    assert !transaction.state.rolledback?
-    assert !transaction.state.committed?
+    assert_predicate transaction, :open?
+    assert_not_predicate transaction.state, :rolledback?
+    assert_not_predicate transaction.state, :committed?
 
     transaction.rollback
 
-    assert transaction.state.rolledback?
-    assert !transaction.state.committed?
+    assert_predicate transaction.state, :rolledback?
+    assert_not_predicate transaction.state, :committed?
   end
 
   def test_transactions_state_from_commit
     connection = Topic.connection
     transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction
 
-    assert transaction.open?
-    assert !transaction.state.rolledback?
-    assert !transaction.state.committed?
+    assert_predicate transaction, :open?
+    assert_not_predicate transaction.state, :rolledback?
+    assert_not_predicate transaction.state, :committed?
+
+    transaction.commit
+
+    assert_not_predicate transaction.state, :rolledback?
+    assert_predicate transaction.state, :committed?
+  end
+
+  def test_set_state_method_is_deprecated
+    connection = Topic.connection
+    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction
 
     transaction.commit
 
-    assert !transaction.state.rolledback?
-    assert transaction.state.committed?
+    assert_deprecated do
+      transaction.state.set_state(:rolledback)
+    end
+  end
+
+  def test_mark_transaction_state_as_committed
+    connection = Topic.connection
+    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction
+
+    transaction.rollback
+
+    assert_equal :committed, transaction.state.commit!
+  end
+
+  def test_mark_transaction_state_as_rolledback
+    connection = Topic.connection
+    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction
+
+    transaction.commit
+
+    assert_equal :rolledback, transaction.state.rollback!
+  end
+
+  def test_mark_transaction_state_as_nil
+    connection = Topic.connection
+    transaction = ActiveRecord::ConnectionAdapters::TransactionManager.new(connection).begin_transaction
+
+    transaction.commit
+
+    assert_nil transaction.state.nullify!
   end
 
   def test_transaction_rollback_with_primarykeyless_tables
     connection = ActiveRecord::Base.connection
     connection.create_table(:transaction_without_primary_keys, force: true, id: false) do |t|
-       t.integer :thing_id
+      t.integer :thing_id
     end
 
     klass = Class.new(ActiveRecord::Base) do
-      self.table_name = 'transaction_without_primary_keys'
+      self.table_name = "transaction_without_primary_keys"
       after_commit { } # necessary to trigger the has_transactional_callbacks branch
     end
 
@@ -686,20 +940,90 @@ class TransactionTest < ActiveRecord::TestCase
       end
     end
   ensure
-    connection.drop_table 'transaction_without_primary_keys', if_exists: true
+    connection.drop_table "transaction_without_primary_keys", if_exists: true
   end
 
-  private
+  def test_empty_transaction_is_not_materialized
+    assert_no_queries do
+      Topic.transaction { }
+    end
+  end
+
+  def test_unprepared_statement_materializes_transaction
+    assert_sql(/BEGIN/i, /COMMIT/i) do
+      Topic.transaction { Topic.where("1=1").first }
+    end
+  end
+
+  if ActiveRecord::Base.connection.prepared_statements
+    def test_prepared_statement_materializes_transaction
+      Topic.first
+
+      assert_sql(/BEGIN/i, /COMMIT/i) do
+        Topic.transaction { Topic.first }
+      end
+    end
+  end
+
+  def test_savepoint_does_not_materialize_transaction
+    assert_no_queries do
+      Topic.transaction do
+        Topic.transaction(requires_new: true) { }
+      end
+    end
+  end
 
-  %w(validation save destroy).each do |filter|
-    define_method("add_cancelling_before_#{filter}_with_db_side_effect_to_topic") do |topic|
-      meta = class << topic; self; end
-      meta.send("define_method", "before_#{filter}_for_transaction") do
-        Book.create
-        throw(:abort)
+  def test_raising_does_not_materialize_transaction
+    assert_raise(RuntimeError) do
+      assert_no_queries do
+        Topic.transaction { raise }
       end
     end
   end
+
+  def test_accessing_raw_connection_materializes_transaction
+    assert_sql(/BEGIN/i, /COMMIT/i) do
+      Topic.transaction { Topic.connection.raw_connection }
+    end
+  end
+
+  def test_accessing_raw_connection_disables_lazy_transactions
+    Topic.connection.raw_connection
+
+    assert_sql(/BEGIN/i, /COMMIT/i) do
+      Topic.transaction { }
+    end
+  end
+
+  def test_checking_in_connection_reenables_lazy_transactions
+    connection = Topic.connection_pool.checkout
+    connection.raw_connection
+    Topic.connection_pool.checkin connection
+
+    assert_no_queries do
+      connection.transaction { }
+    end
+  end
+
+  def test_transactions_can_be_manually_materialized
+    assert_sql(/BEGIN/i, /COMMIT/i) do
+      Topic.transaction do
+        Topic.connection.materialize_transactions
+      end
+    end
+  end
+
+  private
+
+    %w(validation save destroy).each do |filter|
+      define_method("add_cancelling_before_#{filter}_with_db_side_effect_to_topic") do |topic|
+        meta = class << topic; self; end
+        meta.send("define_method", "before_#{filter}_for_transaction") do
+          Book.create
+          throw(:abort)
+        end
+      end
+    end
 end
 
 class TransactionsWithTransactionalFixturesTest < ActiveRecord::TestCase
@@ -716,7 +1040,7 @@ class TransactionsWithTransactionalFixturesTest < ActiveRecord::TestCase
         raise
       end
     rescue
-      assert !@first.reload.approved?
+      assert_not_predicate @first.reload, :approved?
     end
   end
 
@@ -737,31 +1061,29 @@ class TransactionsWithTransactionalFixturesTest < ActiveRecord::TestCase
       end
     end
 
-    assert !@first.reload.approved?
+    assert_not_predicate @first.reload, :approved?
   end
 end if Topic.connection.supports_savepoints?
 
-if current_adapter?(:PostgreSQLAdapter)
+if ActiveRecord::Base.connection.supports_transaction_isolation?
   class ConcurrentTransactionTest < TransactionTest
     # This will cause transactions to overlap and fail unless they are performed on
     # separate database connections.
-    unless in_memory_db?
-      def test_transaction_per_thread
-        threads = 3.times.map do
-          Thread.new do
-            Topic.transaction do
-              topic = Topic.find(1)
-              topic.approved = !topic.approved?
-              assert topic.save!
-              topic.approved = !topic.approved?
-              assert topic.save!
-            end
-            Topic.connection.close
+    def test_transaction_per_thread
+      threads = 3.times.map do
+        Thread.new do
+          Topic.transaction do
+            topic = Topic.find(1)
+            topic.approved = !topic.approved?
+            assert topic.save!
+            topic.approved = !topic.approved?
+            assert topic.save!
           end
+          Topic.connection.close
         end
-
-        threads.each(&:join)
       end
+
+      threads.each(&:join)
     end
 
     # Test for dirty reads among simultaneous transactions.
diff --git a/activerecord/test/cases/type/adapter_specific_registry_test.rb b/activerecord/test/cases/type/adapter_specific_registry_test.rb
index 8b836b4793..b58bdd5549 100644
--- a/activerecord/test/cases/type/adapter_specific_registry_test.rb
+++ b/activerecord/test/cases/type/adapter_specific_registry_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
diff --git a/activerecord/test/cases/type/date_time_test.rb b/activerecord/test/cases/type/date_time_test.rb
new file mode 100644
index 0000000000..c9558e25b5
--- /dev/null
+++ b/activerecord/test/cases/type/date_time_test.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/task"
+
+module ActiveRecord
+  module Type
+    class DateTimeTest < ActiveRecord::TestCase
+      def test_datetime_seconds_precision_applied_to_timestamp
+        skip "This test is invalid if subsecond precision isn't supported" unless subsecond_precision_supported?
+        p = Task.create!(starting: ::Time.now)
+        assert_equal p.starting.usec, p.reload.starting.usec
+      end
+    end
+  end
+end
diff --git a/activerecord/test/cases/type/decimal_test.rb b/activerecord/test/cases/type/decimal_test.rb
deleted file mode 100644
index fe49d0e79a..0000000000
--- a/activerecord/test/cases/type/decimal_test.rb
+++ /dev/null
@@ -1,51 +0,0 @@
-require "cases/helper"
-
-module ActiveRecord
-  module Type
-    class DecimalTest < ActiveRecord::TestCase
-      def test_type_cast_decimal
-        type = Decimal.new
-        assert_equal BigDecimal.new("0"), type.cast(BigDecimal.new("0"))
-        assert_equal BigDecimal.new("123"), type.cast(123.0)
-        assert_equal BigDecimal.new("1"), type.cast(:"1")
-      end
-
-      def test_type_cast_decimal_from_float_with_large_precision
-        type = Decimal.new(precision: ::Float::DIG + 2)
-        assert_equal BigDecimal.new("123.0"), type.cast(123.0)
-      end
-
-      def test_type_cast_from_float_with_unspecified_precision
-        type = Decimal.new
-        assert_equal 22.68.to_d, type.cast(22.68)
-      end
-
-      def test_type_cast_decimal_from_rational_with_precision
-        type = Decimal.new(precision: 2)
-        assert_equal BigDecimal("0.33"), type.cast(Rational(1, 3))
-      end
-
-      def test_type_cast_decimal_from_rational_without_precision_defaults_to_18_36
-        type = Decimal.new
-        assert_equal BigDecimal("0.333333333333333333E0"), type.cast(Rational(1, 3))
-      end
-
-      def test_type_cast_decimal_from_object_responding_to_d
-        value = Object.new
-        def value.to_d
-          BigDecimal.new("1")
-        end
-        type = Decimal.new
-        assert_equal BigDecimal("1"), type.cast(value)
-      end
-
-      def test_changed?
-        type = Decimal.new
-
-        assert type.changed?(5.0, 5.0, '5.0wibble')
-        assert_not type.changed?(5.0, 5.0, '5.0')
-        assert_not type.changed?(-5.0, -5.0, '-5.0')
-      end
-    end
-  end
-end
diff --git a/activerecord/test/cases/type/integer_test.rb b/activerecord/test/cases/type/integer_test.rb
index 0dcdbd0667..15d1a675a1 100644
--- a/activerecord/test/cases/type/integer_test.rb
+++ b/activerecord/test/cases/type/integer_test.rb
@@ -1,118 +1,20 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "models/company"
 
 module ActiveRecord
   module Type
     class IntegerTest < ActiveRecord::TestCase
-      test "simple values" do
-        type = Type::Integer.new
-        assert_equal 1, type.cast(1)
-        assert_equal 1, type.cast('1')
-        assert_equal 1, type.cast('1ignore')
-        assert_equal 0, type.cast('bad1')
-        assert_equal 0, type.cast('bad')
-        assert_equal 1, type.cast(1.7)
-        assert_equal 0, type.cast(false)
-        assert_equal 1, type.cast(true)
-        assert_nil type.cast(nil)
-      end
-
-      test "random objects cast to nil" do
-        type = Type::Integer.new
-        assert_nil type.cast([1,2])
-        assert_nil type.cast({1 => 2})
-        assert_nil type.cast(1..2)
-      end
-
       test "casting ActiveRecord models" do
         type = Type::Integer.new
-        firm = Firm.create(:name => 'Apple')
+        firm = Firm.create(name: "Apple")
         assert_nil type.cast(firm)
       end
 
-      test "casting objects without to_i" do
-        type = Type::Integer.new
-        assert_nil type.cast(::Object.new)
-      end
-
-      test "casting nan and infinity" do
-        type = Type::Integer.new
-        assert_nil type.cast(::Float::NAN)
-        assert_nil type.cast(1.0/0.0)
-      end
-
-      test "casting booleans for database" do
-        type = Type::Integer.new
-        assert_equal 1, type.serialize(true)
-        assert_equal 0, type.serialize(false)
-      end
-
-      test "changed?" do
-        type = Type::Integer.new
-
-        assert type.changed?(5, 5, '5wibble')
-        assert_not type.changed?(5, 5, '5')
-        assert_not type.changed?(5, 5, '5.0')
-        assert_not type.changed?(-5, -5, '-5')
-        assert_not type.changed?(-5, -5, '-5.0')
-        assert_not type.changed?(nil, nil, nil)
-      end
-
-      test "values below int min value are out of range" do
-        assert_raises(::RangeError) do
-          Integer.new.serialize(-2147483649)
-        end
-      end
-
-      test "values above int max value are out of range" do
-        assert_raises(::RangeError) do
-          Integer.new.serialize(2147483648)
-        end
-      end
-
-      test "very small numbers are out of range" do
-        assert_raises(::RangeError) do
-          Integer.new.serialize(-9999999999999999999999999999999)
-        end
-      end
-
-      test "very large numbers are out of range" do
-        assert_raises(::RangeError) do
-          Integer.new.serialize(9999999999999999999999999999999)
-        end
-      end
-
-      test "normal numbers are in range" do
-        type = Integer.new
-        assert_equal(0, type.serialize(0))
-        assert_equal(-1, type.serialize(-1))
-        assert_equal(1, type.serialize(1))
-      end
-
-      test "int max value is in range" do
-        assert_equal(2147483647, Integer.new.serialize(2147483647))
-      end
-
-      test "int min value is in range" do
-        assert_equal(-2147483648, Integer.new.serialize(-2147483648))
-      end
-
-      test "columns with a larger limit have larger ranges" do
-        type = Integer.new(limit: 8)
-
-        assert_equal(9223372036854775807, type.serialize(9223372036854775807))
-        assert_equal(-9223372036854775808, type.serialize(-9223372036854775808))
-        assert_raises(::RangeError) do
-          type.serialize(-9999999999999999999999999999999)
-        end
-        assert_raises(::RangeError) do
-          type.serialize(9999999999999999999999999999999)
-        end
-      end
-
       test "values which are out of range can be re-assigned" do
         klass = Class.new(ActiveRecord::Base) do
-          self.table_name = 'posts'
+          self.table_name = "posts"
           attribute :foo, :integer
         end
         model = klass.new
diff --git a/activerecord/test/cases/type/string_test.rb b/activerecord/test/cases/type/string_test.rb
index 56e9bf434d..9e7810a6a5 100644
--- a/activerecord/test/cases/type/string_test.rb
+++ b/activerecord/test/cases/type/string_test.rb
@@ -1,36 +1,24 @@
-require 'cases/helper'
+# frozen_string_literal: true
+
+require "cases/helper"
 
 module ActiveRecord
   class StringTypeTest < ActiveRecord::TestCase
-    test "type casting" do
-      type = Type::String.new
-      assert_equal "t", type.cast(true)
-      assert_equal "f", type.cast(false)
-      assert_equal "123", type.cast(123)
-    end
-
-    test "values are duped coming out" do
-      s = "foo"
-      type = Type::String.new
-      assert_not_same s, type.cast(s)
-      assert_not_same s, type.deserialize(s)
-    end
-
     test "string mutations are detected" do
       klass = Class.new(Base)
-      klass.table_name = 'authors'
+      klass.table_name = "authors"
 
-      author = klass.create!(name: 'Sean')
-      assert_not author.changed?
+      author = klass.create!(name: "Sean")
+      assert_not_predicate author, :changed?
 
-      author.name << ' Griffin'
-      assert author.name_changed?
+      author.name << " Griffin"
+      assert_predicate author, :name_changed?
 
       author.save!
       author.reload
 
-      assert_equal 'Sean Griffin', author.name
-      assert_not author.changed?
+      assert_equal "Sean Griffin", author.name
+      assert_not_predicate author, :changed?
     end
   end
 end
diff --git a/activerecord/test/cases/type/type_map_test.rb b/activerecord/test/cases/type/type_map_test.rb
index 172c6dfc4c..1ce515a90c 100644
--- a/activerecord/test/cases/type/type_map_test.rb
+++ b/activerecord/test/cases/type/type_map_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -15,7 +17,7 @@ module ActiveRecord
 
         mapping.register_type(/boolean/i, boolean)
 
-        assert_equal mapping.lookup('boolean'), boolean
+        assert_equal mapping.lookup("boolean"), boolean
       end
 
       def test_overriding_registered_types
@@ -26,26 +28,26 @@ module ActiveRecord
         mapping.register_type(/time/i, time)
         mapping.register_type(/time/i, timestamp)
 
-        assert_equal mapping.lookup('time'), timestamp
+        assert_equal mapping.lookup("time"), timestamp
       end
 
       def test_fuzzy_lookup
-        string = String.new
+        string = +""
         mapping = TypeMap.new
 
         mapping.register_type(/varchar/i, string)
 
-        assert_equal mapping.lookup('varchar(20)'), string
+        assert_equal mapping.lookup("varchar(20)"), string
       end
 
       def test_aliasing_types
-        string = String.new
+        string = +""
         mapping = TypeMap.new
 
         mapping.register_type(/string/i, string)
-        mapping.alias_type(/varchar/i, 'string')
+        mapping.alias_type(/varchar/i, "string")
 
-        assert_equal mapping.lookup('varchar'), string
+        assert_equal mapping.lookup("varchar"), string
       end
 
       def test_changing_type_changes_aliases
@@ -54,37 +56,37 @@ module ActiveRecord
         mapping = TypeMap.new
 
         mapping.register_type(/timestamp/i, time)
-        mapping.alias_type(/datetime/i, 'timestamp')
+        mapping.alias_type(/datetime/i, "timestamp")
         mapping.register_type(/timestamp/i, timestamp)
 
-        assert_equal mapping.lookup('datetime'), timestamp
+        assert_equal mapping.lookup("datetime"), timestamp
       end
 
       def test_aliases_keep_metadata
         mapping = TypeMap.new
 
         mapping.register_type(/decimal/i) { |sql_type| sql_type }
-        mapping.alias_type(/number/i, 'decimal')
+        mapping.alias_type(/number/i, "decimal")
 
-        assert_equal mapping.lookup('number(20)'), 'decimal(20)'
-        assert_equal mapping.lookup('number'), 'decimal'
+        assert_equal mapping.lookup("number(20)"), "decimal(20)"
+        assert_equal mapping.lookup("number"), "decimal"
       end
 
       def test_register_proc
-        string = String.new
+        string = +""
         binary = Binary.new
         mapping = TypeMap.new
 
         mapping.register_type(/varchar/i) do |type|
-          if type.include?('(')
+          if type.include?("(")
             string
           else
             binary
           end
         end
 
-        assert_equal mapping.lookup('varchar(20)'), string
-        assert_equal mapping.lookup('varchar'), binary
+        assert_equal mapping.lookup("varchar(20)"), string
+        assert_equal mapping.lookup("varchar"), binary
       end
 
       def test_additional_lookup_args
@@ -92,16 +94,16 @@ module ActiveRecord
 
         mapping.register_type(/varchar/i) do |type, limit|
           if limit > 255
-            'text'
+            "text"
           else
-            'string'
+            "string"
           end
         end
-        mapping.alias_type(/string/i, 'varchar')
+        mapping.alias_type(/string/i, "varchar")
 
-        assert_equal mapping.lookup('varchar', 200), 'string'
-        assert_equal mapping.lookup('varchar', 400), 'text'
-        assert_equal mapping.lookup('string', 400), 'text'
+        assert_equal mapping.lookup("varchar", 200), "string"
+        assert_equal mapping.lookup("varchar", 400), "text"
+        assert_equal mapping.lookup("string", 400), "text"
       end
 
       def test_requires_value_or_block
@@ -115,13 +117,13 @@ module ActiveRecord
       def test_lookup_non_strings
         mapping = HashLookupTypeMap.new
 
-        mapping.register_type(1, 'string')
-        mapping.register_type(2, 'int')
+        mapping.register_type(1, "string")
+        mapping.register_type(2, "int")
         mapping.alias_type(3, 1)
 
-        assert_equal mapping.lookup(1), 'string'
-        assert_equal mapping.lookup(2), 'int'
-        assert_equal mapping.lookup(3), 'string'
+        assert_equal mapping.lookup(1), "string"
+        assert_equal mapping.lookup(2), "int"
+        assert_equal mapping.lookup(3), "string"
         assert_kind_of Type::Value, mapping.lookup(4)
       end
 
@@ -174,4 +176,3 @@ module ActiveRecord
     end
   end
 end
-
diff --git a/activerecord/test/cases/type/unsigned_integer_test.rb b/activerecord/test/cases/type/unsigned_integer_test.rb
index f2c910eade..dd05cf3fff 100644
--- a/activerecord/test/cases/type/unsigned_integer_test.rb
+++ b/activerecord/test/cases/type/unsigned_integer_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
@@ -8,7 +10,7 @@ module ActiveRecord
       end
 
       test "minus value is out of range" do
-        assert_raises(::RangeError) do
+        assert_raises(ActiveModel::RangeError) do
           UnsignedInteger.new.serialize(-1)
         end
       end
diff --git a/activerecord/test/cases/type_test.rb b/activerecord/test/cases/type_test.rb
index d45a9b3141..93ae563c8b 100644
--- a/activerecord/test/cases/type_test.rb
+++ b/activerecord/test/cases/type_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class TypeTest < ActiveRecord::TestCase
diff --git a/activerecord/test/cases/types_test.rb b/activerecord/test/cases/types_test.rb
index 9b1859c2ce..3f7fb0a604 100644
--- a/activerecord/test/cases/types_test.rb
+++ b/activerecord/test/cases/types_test.rb
@@ -1,120 +1,17 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 module ActiveRecord
   module ConnectionAdapters
     class TypesTest < ActiveRecord::TestCase
-      def test_type_cast_boolean
-        type = Type::Boolean.new
-        assert type.cast('').nil?
-        assert type.cast(nil).nil?
-
-        assert type.cast(true)
-        assert type.cast(1)
-        assert type.cast('1')
-        assert type.cast('t')
-        assert type.cast('T')
-        assert type.cast('true')
-        assert type.cast('TRUE')
-        assert type.cast('on')
-        assert type.cast('ON')
-        assert type.cast(' ')
-        assert type.cast("\u3000\r\n")
-        assert type.cast("\u0000")
-        assert type.cast('SOMETHING RANDOM')
-
-        # explicitly check for false vs nil
-        assert_equal false, type.cast(false)
-        assert_equal false, type.cast(0)
-        assert_equal false, type.cast('0')
-        assert_equal false, type.cast('f')
-        assert_equal false, type.cast('F')
-        assert_equal false, type.cast('false')
-        assert_equal false, type.cast('FALSE')
-        assert_equal false, type.cast('off')
-        assert_equal false, type.cast('OFF')
-      end
-
-      def test_type_cast_float
-        type = Type::Float.new
-        assert_equal 1.0, type.cast("1")
-      end
-
-      def test_changing_float
-        type = Type::Float.new
-
-        assert type.changed?(5.0, 5.0, '5wibble')
-        assert_not type.changed?(5.0, 5.0, '5')
-        assert_not type.changed?(5.0, 5.0, '5.0')
-        assert_not type.changed?(nil, nil, nil)
-      end
-
-      def test_type_cast_binary
-        type = Type::Binary.new
-        assert_equal nil, type.cast(nil)
-        assert_equal "1", type.cast("1")
-        assert_equal 1, type.cast(1)
-      end
-
-      def test_type_cast_time
-        type = Type::Time.new
-        assert_equal nil, type.cast(nil)
-        assert_equal nil, type.cast('')
-        assert_equal nil, type.cast('ABC')
-
-        time_string = Time.now.utc.strftime("%T")
-        assert_equal time_string, type.cast(time_string).strftime("%T")
-      end
-
-      def test_type_cast_datetime_and_timestamp
-        type = Type::DateTime.new
-        assert_equal nil, type.cast(nil)
-        assert_equal nil, type.cast('')
-        assert_equal nil, type.cast('  ')
-        assert_equal nil, type.cast('ABC')
-
-        datetime_string = Time.now.utc.strftime("%FT%T")
-        assert_equal datetime_string, type.cast(datetime_string).strftime("%FT%T")
-      end
-
-      def test_type_cast_date
-        type = Type::Date.new
-        assert_equal nil, type.cast(nil)
-        assert_equal nil, type.cast('')
-        assert_equal nil, type.cast(' ')
-        assert_equal nil, type.cast('ABC')
-
-        date_string = Time.now.utc.strftime("%F")
-        assert_equal date_string, type.cast(date_string).strftime("%F")
-      end
-
-      def test_type_cast_duration_to_integer
-        type = Type::Integer.new
-        assert_equal 1800, type.cast(30.minutes)
-        assert_equal 7200, type.cast(2.hours)
-      end
-
-      def test_string_to_time_with_timezone
-        [:utc, :local].each do |zone|
-          with_timezone_config default: zone do
-            type = Type::DateTime.new
-            assert_equal Time.utc(2013, 9, 4, 0, 0, 0), type.cast("Wed, 04 Sep 2013 03:00:00 EAT")
-          end
-        end
-      end
-
-      def test_type_equality
-        assert_equal Type::Value.new, Type::Value.new
-        assert_not_equal Type::Value.new, Type::Integer.new
-        assert_not_equal Type::Value.new(precision: 1), Type::Value.new(precision: 2)
-      end
-
       def test_attributes_which_are_invalid_for_database_can_still_be_reassigned
         type_which_cannot_go_to_the_database = Type::Value.new
         def type_which_cannot_go_to_the_database.serialize(*)
           raise
         end
         klass = Class.new(ActiveRecord::Base) do
-          self.table_name = 'posts'
+          self.table_name = "posts"
           attribute :foo, type_which_cannot_go_to_the_database
         end
         model = klass.new
diff --git a/activerecord/test/cases/unconnected_test.rb b/activerecord/test/cases/unconnected_test.rb
index b210584644..9eefc32745 100644
--- a/activerecord/test/cases/unconnected_test.rb
+++ b/activerecord/test/cases/unconnected_test.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 
 class TestRecord < ActiveRecord::Base
@@ -28,6 +30,6 @@ class TestUnconnectedAdapter < ActiveRecord::TestCase
   end
 
   def test_underlying_adapter_no_longer_active
-    assert !@underlying.active?, "Removed adapter should no longer be active"
+    assert_not @underlying.active?, "Removed adapter should no longer be active"
   end
 end
diff --git a/activerecord/test/cases/unsafe_raw_sql_test.rb b/activerecord/test/cases/unsafe_raw_sql_test.rb
new file mode 100644
index 0000000000..d5d8f2a09a
--- /dev/null
+++ b/activerecord/test/cases/unsafe_raw_sql_test.rb
@@ -0,0 +1,319 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/post"
+require "models/comment"
+
+class UnsafeRawSqlTest < ActiveRecord::TestCase
+  fixtures :posts, :comments
+
+  test "order: allows string column name" do
+    ids_expected = Post.order(Arel.sql("title")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order("title").pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order("title").pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows symbol column name" do
+    ids_expected = Post.order(Arel.sql("title")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order(:title).pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order(:title).pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows downcase symbol direction" do
+    ids_expected = Post.order(Arel.sql("title") => Arel.sql("asc")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order(title: :asc).pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order(title: :asc).pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows upcase symbol direction" do
+    ids_expected = Post.order(Arel.sql("title") => Arel.sql("ASC")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order(title: :ASC).pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order(title: :ASC).pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows string direction" do
+    ids_expected = Post.order(Arel.sql("title") => Arel.sql("asc")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order(title: "asc").pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order(title: "asc").pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows multiple columns" do
+    ids_expected = Post.order(Arel.sql("author_id"), Arel.sql("title")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order(:author_id, :title).pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order(:author_id, :title).pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows mixed" do
+    ids_expected = Post.order(Arel.sql("author_id"), Arel.sql("title") => Arel.sql("asc")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order(:author_id, title: :asc).pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order(:author_id, title: :asc).pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows table and column name" do
+    ids_expected = Post.order(Arel.sql("title")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order("posts.title").pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order("posts.title").pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows column name and direction in string" do
+    ids_expected = Post.order(Arel.sql("title desc")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order("title desc").pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order("title desc").pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows table name, column name and direction in string" do
+    ids_expected = Post.order(Arel.sql("title desc")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order("posts.title desc").pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order("posts.title desc").pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: allows NULLS FIRST and NULLS LAST too" do
+    raise "precondition failed" if Post.count < 2
+
+    # Ensure there are NULL and non-NULL post types.
+    Post.first.update_column(:type, nil)
+    Post.last.update_column(:type, "Programming")
+
+    ["asc", "desc", ""].each do |direction|
+      %w(first last).each do |position|
+        ids_expected = Post.order(Arel.sql("type #{direction} nulls #{position}")).pluck(:id)
+
+        ids_depr     = with_unsafe_raw_sql_deprecated { Post.order("type #{direction} nulls #{position}").pluck(:id) }
+        ids_disabled = with_unsafe_raw_sql_disabled   { Post.order("type #{direction} nulls #{position}").pluck(:id) }
+
+        assert_equal ids_expected, ids_depr
+        assert_equal ids_expected, ids_disabled
+      end
+    end
+  end if current_adapter?(:PostgreSQLAdapter)
+
+  test "order: disallows invalid column name" do
+    with_unsafe_raw_sql_disabled do
+      assert_raises(ActiveRecord::UnknownAttributeReference) do
+        Post.order("len(title) asc").pluck(:id)
+      end
+    end
+  end
+
+  test "order: disallows invalid direction" do
+    with_unsafe_raw_sql_disabled do
+      assert_raises(ArgumentError) do
+        Post.order(title: :foo).pluck(:id)
+      end
+    end
+  end
+
+  test "order: disallows invalid column with direction" do
+    with_unsafe_raw_sql_disabled do
+      assert_raises(ActiveRecord::UnknownAttributeReference) do
+        Post.order("len(title)" => :asc).pluck(:id)
+      end
+    end
+  end
+
+  test "order: always allows Arel" do
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order(Arel.sql("length(title)")).pluck(:title) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order(Arel.sql("length(title)")).pluck(:title) }
+
+    assert_equal ids_depr, ids_disabled
+  end
+
+  test "order: allows Arel.sql with binds" do
+    ids_expected = Post.order(Arel.sql("REPLACE(title, 'misc', 'zzzz'), id")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order([Arel.sql("REPLACE(title, ?, ?), id"), "misc", "zzzz"]).pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order([Arel.sql("REPLACE(title, ?, ?), id"), "misc", "zzzz"]).pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: disallows invalid bind statement" do
+    with_unsafe_raw_sql_disabled do
+      assert_raises(ActiveRecord::UnknownAttributeReference) do
+        Post.order(["REPLACE(title, ?, ?), id", "misc", "zzzz"]).pluck(:id)
+      end
+    end
+  end
+
+  test "order: disallows invalid Array arguments" do
+    with_unsafe_raw_sql_disabled do
+      assert_raises(ActiveRecord::UnknownAttributeReference) do
+        Post.order(["author_id", "length(title)"]).pluck(:id)
+      end
+    end
+  end
+
+  test "order: allows valid Array arguments" do
+    ids_expected = Post.order(Arel.sql("author_id, length(title)")).pluck(:id)
+
+    ids_depr     = with_unsafe_raw_sql_deprecated { Post.order(["author_id", Arel.sql("length(title)")]).pluck(:id) }
+    ids_disabled = with_unsafe_raw_sql_disabled   { Post.order(["author_id", Arel.sql("length(title)")]).pluck(:id) }
+
+    assert_equal ids_expected, ids_depr
+    assert_equal ids_expected, ids_disabled
+  end
+
+  test "order: logs deprecation warning for unrecognized column" do
+    with_unsafe_raw_sql_deprecated do
+      assert_deprecated(/Dangerous query method/) do
+        Post.order("length(title)")
+      end
+    end
+  end
+
+  test "pluck: allows string column name" do
+    titles_expected = Post.pluck(Arel.sql("title"))
+
+    titles_depr     = with_unsafe_raw_sql_deprecated { Post.pluck("title") }
+    titles_disabled = with_unsafe_raw_sql_disabled   { Post.pluck("title") }
+
+    assert_equal titles_expected, titles_depr
+    assert_equal titles_expected, titles_disabled
+  end
+
+  test "pluck: allows symbol column name" do
+    titles_expected = Post.pluck(Arel.sql("title"))
+
+    titles_depr     = with_unsafe_raw_sql_deprecated { Post.pluck(:title) }
+    titles_disabled = with_unsafe_raw_sql_disabled   { Post.pluck(:title) }
+
+    assert_equal titles_expected, titles_depr
+    assert_equal titles_expected, titles_disabled
+  end
+
+  test "pluck: allows multiple column names" do
+    values_expected = Post.pluck(Arel.sql("title"), Arel.sql("id"))
+
+    values_depr     = with_unsafe_raw_sql_deprecated { Post.pluck(:title, :id) }
+    values_disabled = with_unsafe_raw_sql_disabled   { Post.pluck(:title, :id) }
+
+    assert_equal values_expected, values_depr
+    assert_equal values_expected, values_disabled
+  end
+
+  test "pluck: allows column names with includes" do
+    values_expected = Post.includes(:comments).pluck(Arel.sql("title"), Arel.sql("id"))
+
+    values_depr     = with_unsafe_raw_sql_deprecated { Post.includes(:comments).pluck(:title, :id) }
+    values_disabled = with_unsafe_raw_sql_disabled   { Post.includes(:comments).pluck(:title, :id) }
+
+    assert_equal values_expected, values_depr
+    assert_equal values_expected, values_disabled
+  end
+
+  test "pluck: allows auto-generated attributes" do
+    values_expected = Post.pluck(Arel.sql("tags_count"))
+
+    values_depr     = with_unsafe_raw_sql_deprecated { Post.pluck(:tags_count) }
+    values_disabled = with_unsafe_raw_sql_disabled   { Post.pluck(:tags_count) }
+
+    assert_equal values_expected, values_depr
+    assert_equal values_expected, values_disabled
+  end
+
+  test "pluck: allows table and column names" do
+    titles_expected = Post.pluck(Arel.sql("title"))
+
+    titles_depr     = with_unsafe_raw_sql_deprecated { Post.pluck("posts.title") }
+    titles_disabled = with_unsafe_raw_sql_disabled   { Post.pluck("posts.title") }
+
+    assert_equal titles_expected, titles_depr
+    assert_equal titles_expected, titles_disabled
+  end
+
+  test "pluck: disallows invalid column name" do
+    with_unsafe_raw_sql_disabled do
+      assert_raises(ActiveRecord::UnknownAttributeReference) do
+        Post.pluck("length(title)")
+      end
+    end
+  end
+
+  test "pluck: disallows invalid column name amongst valid names" do
+    with_unsafe_raw_sql_disabled do
+      assert_raises(ActiveRecord::UnknownAttributeReference) do
+        Post.pluck(:title, "length(title)")
+      end
+    end
+  end
+
+  test "pluck: disallows invalid column names with includes" do
+    with_unsafe_raw_sql_disabled do
+      assert_raises(ActiveRecord::UnknownAttributeReference) do
+        Post.includes(:comments).pluck(:title, "length(title)")
+      end
+    end
+  end
+
+  test "pluck: always allows Arel" do
+    values_depr     = with_unsafe_raw_sql_deprecated { Post.includes(:comments).pluck(:title, Arel.sql("length(title)")) }
+    values_disabled = with_unsafe_raw_sql_disabled   { Post.includes(:comments).pluck(:title, Arel.sql("length(title)")) }
+
+    assert_equal values_depr, values_disabled
+  end
+
+  test "pluck: logs deprecation warning" do
+    with_unsafe_raw_sql_deprecated do
+      assert_deprecated(/Dangerous query method/) do
+        Post.includes(:comments).pluck(:title, "length(title)")
+      end
+    end
+  end
+
+  def with_unsafe_raw_sql_disabled(&blk)
+    with_config(:disabled, &blk)
+  end
+
+  def with_unsafe_raw_sql_deprecated(&blk)
+    with_config(:deprecated, &blk)
+  end
+
+  def with_config(new_value, &blk)
+    old_value = ActiveRecord::Base.allow_unsafe_raw_sql
+    ActiveRecord::Base.allow_unsafe_raw_sql = new_value
+    blk.call
+  ensure
+    ActiveRecord::Base.allow_unsafe_raw_sql = old_value
+  end
+end
diff --git a/activerecord/test/cases/validations/absence_validation_test.rb b/activerecord/test/cases/validations/absence_validation_test.rb
index dd43ee358c..8235a54d8a 100644
--- a/activerecord/test/cases/validations/absence_validation_test.rb
+++ b/activerecord/test/cases/validations/absence_validation_test.rb
@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/face'
-require 'models/interest'
-require 'models/man'
-require 'models/topic'
+require "models/face"
+require "models/interest"
+require "models/man"
+require "models/topic"
 
 class AbsenceValidationTest < ActiveRecord::TestCase
   def test_non_association
@@ -11,8 +13,8 @@ class AbsenceValidationTest < ActiveRecord::TestCase
       validates_absence_of :name
     end
 
-    assert boy_klass.new.valid?
-    assert_not boy_klass.new(name: "Alex").valid?
+    assert_predicate boy_klass.new, :valid?
+    assert_not_predicate boy_klass.new(name: "Alex"), :valid?
   end
 
   def test_has_one_marked_for_destruction
@@ -42,7 +44,7 @@ class AbsenceValidationTest < ActiveRecord::TestCase
     assert_not boy.valid?, "should not be valid if has_many association is present"
 
     i2.mark_for_destruction
-    assert boy.valid?
+    assert_predicate boy, :valid?
   end
 
   def test_does_not_call_to_a_on_associations
@@ -52,24 +54,22 @@ class AbsenceValidationTest < ActiveRecord::TestCase
     end
 
     face_with_to_a = Face.new
-    def face_with_to_a.to_a; ['(/)', '(\)']; end
+    def face_with_to_a.to_a; ["(/)", '(\)']; end
 
     assert_nothing_raised { boy_klass.new(face: face_with_to_a).valid? }
   end
 
-  def test_does_not_validate_if_parent_record_is_validate_false
+  def test_validates_absence_of_virtual_attribute_on_model
     repair_validations(Interest) do
-      Interest.validates_absence_of(:topic)
-      interest = Interest.new(topic: Topic.new(title: "Math"))
-      interest.save!(validate: false)
-      assert interest.persisted?
+      Interest.send(:attr_accessor, :token)
+      Interest.validates_absence_of(:token)
+
+      interest = Interest.create!(topic: "Thought Leadering")
+      assert_predicate interest, :valid?
 
-      man = Man.new(interest_ids: [interest.id])
-      man.save!
+      interest.token = "tl"
 
-      assert_equal man.interests.size, 1
-      assert interest.valid?
-      assert man.valid?
+      assert_predicate interest, :invalid?
     end
   end
 end
diff --git a/activerecord/test/cases/validations/association_validation_test.rb b/activerecord/test/cases/validations/association_validation_test.rb
index bff5ffa65e..ce6d42b34b 100644
--- a/activerecord/test/cases/validations/association_validation_test.rb
+++ b/activerecord/test/cases/validations/association_validation_test.rb
@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/reply'
-require 'models/man'
-require 'models/interest'
+require "models/topic"
+require "models/reply"
+require "models/man"
+require "models/interest"
 
 class AssociationValidationTest < ActiveRecord::TestCase
   fixtures :topics
@@ -14,25 +16,25 @@ class AssociationValidationTest < ActiveRecord::TestCase
     Reply.validates_presence_of(:content)
     t = Topic.create("title" => "uhohuhoh", "content" => "whatever")
     t.replies << [r = Reply.new("title" => "A reply"), r2 = Reply.new("title" => "Another reply", "content" => "non-empty"), r3 = Reply.new("title" => "Yet another reply"), r4 = Reply.new("title" => "The last reply", "content" => "non-empty")]
-    assert !t.valid?
-    assert t.errors[:replies].any?
+    assert_not_predicate t, :valid?
+    assert_predicate t.errors[:replies], :any?
     assert_equal 1, r.errors.count  # make sure all associated objects have been validated
     assert_equal 0, r2.errors.count
     assert_equal 1, r3.errors.count
     assert_equal 0, r4.errors.count
     r.content = r3.content = "non-empty"
-    assert t.valid?
+    assert_predicate t, :valid?
   end
 
   def test_validates_associated_one
-    Reply.validates :topic, :associated => true
-    Topic.validates_presence_of( :content )
+    Reply.validates :topic, associated: true
+    Topic.validates_presence_of(:content)
     r = Reply.new("title" => "A reply", "content" => "with content!")
     r.topic = Topic.create("title" => "uhohuhoh")
-    assert !r.valid?
-    assert r.errors[:topic].any?
+    assert_not_predicate r, :valid?
+    assert_predicate r.errors[:topic], :any?
     r.topic.content = "non-empty"
-    assert r.valid?
+    assert_predicate r, :valid?
   end
 
   def test_validates_associated_marked_for_destruction
@@ -40,13 +42,25 @@ class AssociationValidationTest < ActiveRecord::TestCase
     Reply.validates_presence_of(:content)
     t = Topic.new
     t.replies << Reply.new
-    assert t.invalid?
+    assert_predicate t, :invalid?
     t.replies.first.mark_for_destruction
-    assert t.valid?
+    assert_predicate t, :valid?
+  end
+
+  def test_validates_associated_without_marked_for_destruction
+    reply = Class.new do
+      def valid?
+        true
+      end
+    end
+    Topic.validates_associated(:replies)
+    t = Topic.new
+    t.define_singleton_method(:replies) { [reply.new] }
+    assert_predicate t, :valid?
   end
 
   def test_validates_associated_with_custom_message_using_quotes
-    Reply.validates_associated :topic, :message=> "This string contains 'single' and \"double\" quotes"
+    Reply.validates_associated :topic, message: "This string contains 'single' and \"double\" quotes"
     Topic.validates_presence_of :content
     r = Reply.create("title" => "A reply", "content" => "with content!")
     r.topic = Topic.create("title" => "uhohuhoh")
@@ -57,19 +71,19 @@ class AssociationValidationTest < ActiveRecord::TestCase
   def test_validates_associated_missing
     Reply.validates_presence_of(:topic)
     r = Reply.create("title" => "A reply", "content" => "with content!")
-    assert !r.valid?
-    assert r.errors[:topic].any?
+    assert_not_predicate r, :valid?
+    assert_predicate r.errors[:topic], :any?
 
     r.topic = Topic.first
-    assert r.valid?
+    assert_predicate r, :valid?
   end
 
   def test_validates_presence_of_belongs_to_association__parent_is_new_record
     repair_validations(Interest) do
       # Note that Interest and Man have the :inverse_of option set
       Interest.validates_presence_of(:man)
-      man = Man.new(:name => 'John')
-      interest = man.interests.build(:topic => 'Airplanes')
+      man = Man.new(name: "John")
+      interest = man.interests.build(topic: "Airplanes")
       assert interest.valid?, "Expected interest to be valid, but was not. Interest should have a man object associated"
     end
   end
@@ -77,8 +91,8 @@ class AssociationValidationTest < ActiveRecord::TestCase
   def test_validates_presence_of_belongs_to_association__existing_parent
     repair_validations(Interest) do
       Interest.validates_presence_of(:man)
-      man = Man.create!(:name => 'John')
-      interest = man.interests.build(:topic => 'Airplanes')
+      man = Man.create!(name: "John")
+      interest = man.interests.build(topic: "Airplanes")
       assert interest.valid?, "Expected interest to be valid, but was not. Interest should have a man object associated"
     end
   end
diff --git a/activerecord/test/cases/validations/i18n_generate_message_validation_test.rb b/activerecord/test/cases/validations/i18n_generate_message_validation_test.rb
index 13d4d85afa..703c24b340 100644
--- a/activerecord/test/cases/validations/i18n_generate_message_validation_test.rb
+++ b/activerecord/test/cases/validations/i18n_generate_message_validation_test.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
+require "models/topic"
 
 class I18nGenerateMessageValidationTest < ActiveRecord::TestCase
   def setup
@@ -20,20 +22,20 @@ class I18nGenerateMessageValidationTest < ActiveRecord::TestCase
 
   # validates_associated: generate_message(attr_name, :invalid, :message => custom_message, :value => value)
   def test_generate_message_invalid_with_default_message
-    assert_equal 'is invalid', @topic.errors.generate_message(:title, :invalid, :value => 'title')
+    assert_equal "is invalid", @topic.errors.generate_message(:title, :invalid, value: "title")
   end
 
   def test_generate_message_invalid_with_custom_message
-    assert_equal 'custom message title', @topic.errors.generate_message(:title, :invalid, :message => 'custom message %{value}', :value => 'title')
+    assert_equal "custom message title", @topic.errors.generate_message(:title, :invalid, message: "custom message %{value}", value: "title")
   end
 
   # validates_uniqueness_of: generate_message(attr_name, :taken, :message => custom_message)
   def test_generate_message_taken_with_default_message
-    assert_equal "has already been taken", @topic.errors.generate_message(:title, :taken, :value => 'title')
+    assert_equal "has already been taken", @topic.errors.generate_message(:title, :taken, value: "title")
   end
 
   def test_generate_message_taken_with_custom_message
-    assert_equal 'custom message title', @topic.errors.generate_message(:title, :taken, :message => 'custom message %{value}', :value => 'title')
+    assert_equal "custom message title", @topic.errors.generate_message(:title, :taken, message: "custom message %{value}", value: "title")
   end
 
   # ActiveRecord#RecordInvalid exception
@@ -47,7 +49,7 @@ class I18nGenerateMessageValidationTest < ActiveRecord::TestCase
 
   test "RecordInvalid exception translation falls back to the :errors namespace" do
     reset_i18n_load_path do
-      I18n.backend.store_translations 'en', :errors => {:messages => {:record_invalid => 'fallback message'}}
+      I18n.backend.store_translations "en", errors: { messages: { record_invalid: "fallback message" } }
       topic = Topic.new
       topic.errors.add(:title, :blank)
       assert_equal "fallback message", ActiveRecord::RecordInvalid.new(topic).message
@@ -56,29 +58,29 @@ class I18nGenerateMessageValidationTest < ActiveRecord::TestCase
 
   test "translation for 'taken' can be overridden" do
     reset_i18n_load_path do
-      I18n.backend.store_translations "en", {errors: {attributes: {title: {taken: "Custom taken message" }}}}
-      assert_equal "Custom taken message", @topic.errors.generate_message(:title, :taken, :value => 'title')
+      I18n.backend.store_translations "en", errors: { attributes: { title: { taken: "Custom taken message" } } }
+      assert_equal "Custom taken message", @topic.errors.generate_message(:title, :taken, value: "title")
     end
   end
 
   test "translation for 'taken' can be overridden in activerecord scope" do
     reset_i18n_load_path do
-      I18n.backend.store_translations "en", {activerecord: {errors: {messages: {taken: "Custom taken message" }}}}
-      assert_equal "Custom taken message", @topic.errors.generate_message(:title, :taken, :value => 'title')
+      I18n.backend.store_translations "en", activerecord: { errors: { messages: { taken: "Custom taken message" } } }
+      assert_equal "Custom taken message", @topic.errors.generate_message(:title, :taken, value: "title")
     end
   end
 
   test "translation for 'taken' can be overridden in activerecord model scope" do
     reset_i18n_load_path do
-      I18n.backend.store_translations "en", {activerecord: {errors: {models: {topic: {taken: "Custom taken message" }}}}}
-      assert_equal "Custom taken message", @topic.errors.generate_message(:title, :taken, :value => 'title')
+      I18n.backend.store_translations "en", activerecord: { errors: { models: { topic: { taken: "Custom taken message" } } } }
+      assert_equal "Custom taken message", @topic.errors.generate_message(:title, :taken, value: "title")
     end
   end
 
   test "translation for 'taken' can be overridden in activerecord attributes scope" do
     reset_i18n_load_path do
-      I18n.backend.store_translations "en", {activerecord: {errors: {models: {topic: {attributes: {title: {taken: "Custom taken message" }}}}}}}
-      assert_equal "Custom taken message", @topic.errors.generate_message(:title, :taken, :value => 'title')
+      I18n.backend.store_translations "en", activerecord: { errors: { models: { topic: { attributes: { title: { taken: "Custom taken message" } } } } } }
+      assert_equal "Custom taken message", @topic.errors.generate_message(:title, :taken, value: "title")
     end
   end
 end
diff --git a/activerecord/test/cases/validations/i18n_validation_test.rb b/activerecord/test/cases/validations/i18n_validation_test.rb
index 268d7914b5..b7c52ea18c 100644
--- a/activerecord/test/cases/validations/i18n_validation_test.rb
+++ b/activerecord/test/cases/validations/i18n_validation_test.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/reply'
+require "models/topic"
+require "models/reply"
 
 class I18nValidationTest < ActiveRecord::TestCase
   repair_validations(Topic, Reply)
@@ -12,7 +14,7 @@ class I18nValidationTest < ActiveRecord::TestCase
     @old_load_path, @old_backend = I18n.load_path.dup, I18n.backend
     I18n.load_path.clear
     I18n.backend = I18n::Backend::Simple.new
-    I18n.backend.store_translations('en', :errors => {:messages => {:custom => nil}})
+    I18n.backend.store_translations("en", errors: { messages: { custom: nil } })
   end
 
   teardown do
@@ -21,12 +23,12 @@ class I18nValidationTest < ActiveRecord::TestCase
   end
 
   def unique_topic
-    @unique ||= Topic.create :title => 'unique!'
+    @unique ||= Topic.create title: "unique!"
   end
 
   def replied_topic
     @replied_topic ||= begin
-      topic = Topic.create(:title => "topic")
+      topic = Topic.create(title: "topic")
       topic.replies << Reply.new
       topic
     end
@@ -36,55 +38,48 @@ class I18nValidationTest < ActiveRecord::TestCase
   # are used to generate tests to keep things DRY
   #
   COMMON_CASES = [
-  # [ case,                                validation_options,            generate_message_options]
+    # [ case,                              validation_options,            generate_message_options]
     [ "given no options",                  {},                            {}],
-    [ "given custom message",              {:message => "custom"},        {:message => "custom"}],
-    [ "given if condition",                {:if     => lambda { true }},  {}],
-    [ "given unless condition",            {:unless => lambda { false }}, {}],
-    [ "given option that is not reserved", {:format => "jpg"},            {:format => "jpg" }]
-    # TODO Add :on case, but below doesn't work, because then the validation isn't run for some reason
-    #      even when using .save instead .valid?
-    # [ "given on condition",     {on: :save},                {}]
+    [ "given custom message",              { message: "custom" },        { message: "custom" }],
+    [ "given if condition",                { if: lambda { true } },  {}],
+    [ "given unless condition",            { unless: lambda { false } }, {}],
+    [ "given option that is not reserved", { format: "jpg" },            { format: "jpg" }],
+    [ "given on condition",                { on: [:create, :update] },     {}]
   ]
 
-  # validates_uniqueness_of w/ mocha
-
   COMMON_CASES.each do |name, validation_options, generate_message_options|
     test "validates_uniqueness_of on generated message #{name}" do
       Topic.validates_uniqueness_of :title, validation_options
       @topic.title = unique_topic.title
-      @topic.errors.expects(:generate_message).with(:title, :taken, generate_message_options.merge(:value => 'unique!'))
-      @topic.valid?
+      assert_called_with(@topic.errors, :generate_message, [:title, :taken, generate_message_options.merge(value: "unique!")]) do
+        @topic.valid?
+      end
     end
   end
 
-  # validates_associated w/ mocha
-
   COMMON_CASES.each do |name, validation_options, generate_message_options|
     test "validates_associated on generated message #{name}" do
       Topic.validates_associated :replies, validation_options
-      replied_topic.errors.expects(:generate_message).with(:replies, :invalid, generate_message_options.merge(:value => replied_topic.replies))
-      replied_topic.save
+      assert_called_with(replied_topic.errors, :generate_message, [:replies, :invalid, generate_message_options.merge(value: replied_topic.replies)]) do
+        replied_topic.save
+      end
     end
   end
 
-  # validates_associated w/o mocha
-
   def test_validates_associated_finds_custom_model_key_translation
-    I18n.backend.store_translations 'en', :activerecord => {:errors => {:models => {:topic => {:attributes => {:replies => {:invalid => 'custom message'}}}}}}
-    I18n.backend.store_translations 'en', :activerecord => {:errors => {:messages => {:invalid => 'global message'}}}
+    I18n.backend.store_translations "en", activerecord: { errors: { models: { topic: { attributes: { replies: { invalid: "custom message" } } } } } }
+    I18n.backend.store_translations "en", activerecord: { errors: { messages: { invalid: "global message" } } }
 
     Topic.validates_associated :replies
     replied_topic.valid?
-    assert_equal ['custom message'], replied_topic.errors[:replies].uniq
+    assert_equal ["custom message"], replied_topic.errors[:replies].uniq
   end
 
   def test_validates_associated_finds_global_default_translation
-    I18n.backend.store_translations 'en', :activerecord => {:errors => {:messages => {:invalid => 'global message'}}}
+    I18n.backend.store_translations "en", activerecord: { errors: { messages: { invalid: "global message" } } }
 
     Topic.validates_associated :replies
     replied_topic.valid?
-    assert_equal ['global message'], replied_topic.errors[:replies]
+    assert_equal ["global message"], replied_topic.errors[:replies]
   end
-
 end
diff --git a/activerecord/test/cases/validations/length_validation_test.rb b/activerecord/test/cases/validations/length_validation_test.rb
index f95f8f0b8f..1fbcdc271b 100644
--- a/activerecord/test/cases/validations/length_validation_test.rb
+++ b/activerecord/test/cases/validations/length_validation_test.rb
@@ -1,78 +1,80 @@
-# -*- coding: utf-8 -*-
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/owner'
-require 'models/pet'
-require 'models/person'
+require "models/owner"
+require "models/pet"
+require "models/person"
 
 class LengthValidationTest < ActiveRecord::TestCase
   fixtures :owners
 
   setup do
     @owner = Class.new(Owner) do
-      def self.name; 'Owner'; end
+      def self.name; "Owner"; end
     end
   end
 
-
   def test_validates_size_of_association
     assert_nothing_raised { @owner.validates_size_of :pets, minimum: 1 }
-    o = @owner.new('name' => 'nopets')
-    assert !o.save
-    assert o.errors[:pets].any?
-    o.pets.build('name' => 'apet')
-    assert o.valid?
+    o = @owner.new("name" => "nopets")
+    assert_not o.save
+    assert_predicate o.errors[:pets], :any?
+    o.pets.build("name" => "apet")
+    assert_predicate o, :valid?
   end
 
   def test_validates_size_of_association_using_within
     assert_nothing_raised { @owner.validates_size_of :pets, within: 1..2 }
-    o = @owner.new('name' => 'nopets')
-    assert !o.save
-    assert o.errors[:pets].any?
+    o = @owner.new("name" => "nopets")
+    assert_not o.save
+    assert_predicate o.errors[:pets], :any?
 
-    o.pets.build('name' => 'apet')
-    assert o.valid?
+    o.pets.build("name" => "apet")
+    assert_predicate o, :valid?
 
-    2.times { o.pets.build('name' => 'apet') }
-    assert !o.save
-    assert o.errors[:pets].any?
+    2.times { o.pets.build("name" => "apet") }
+    assert_not o.save
+    assert_predicate o.errors[:pets], :any?
   end
 
   def test_validates_size_of_association_utf8
     @owner.validates_size_of :pets, minimum: 1
-    o = @owner.new('name' => 'あいうえおかきくけこ')
-    assert !o.save
-    assert o.errors[:pets].any?
-    o.pets.build('name' => 'あいうえおかきくけこ')
-    assert o.valid?
+    o = @owner.new("name" => "あいうえおかきくけこ")
+    assert_not o.save
+    assert_predicate o.errors[:pets], :any?
+    o.pets.build("name" => "あいうえおかきくけこ")
+    assert_predicate o, :valid?
   end
 
   def test_validates_size_of_respects_records_marked_for_destruction
     @owner.validates_size_of :pets, minimum: 1
     owner = @owner.new
     assert_not owner.save
-    assert owner.errors[:pets].any?
+    assert_predicate owner.errors[:pets], :any?
     pet = owner.pets.build
-    assert owner.valid?
+    assert_predicate owner, :valid?
     assert owner.save
 
     pet_count = Pet.count
-    assert_not owner.update_attributes pets_attributes: [ {_destroy: 1, id: pet.id} ]
-    assert_not owner.valid?
-    assert owner.errors[:pets].any?
+    assert_not owner.update pets_attributes: [ { _destroy: 1, id: pet.id } ]
+    assert_not_predicate owner, :valid?
+    assert_predicate owner.errors[:pets], :any?
     assert_equal pet_count, Pet.count
   end
 
-  def test_does_not_validate_length_of_if_parent_record_is_validate_false
-    @owner.validates_length_of :name, minimum: 1
-    owner = @owner.new
-    owner.save!(validate: false)
-    assert owner.persisted?
+  def test_validates_length_of_virtual_attribute_on_model
+    repair_validations(Pet) do
+      Pet.send(:attr_accessor, :nickname)
+      Pet.validates_length_of(:name, minimum: 1)
+      Pet.validates_length_of(:nickname, minimum: 1)
 
-    pet = Pet.new(owner_id: owner.id)
-    pet.save!
+      pet = Pet.create!(name: "Fancy Pants", nickname: "Fancy")
 
-    assert_equal owner.pets.size, 1
-    assert owner.valid?
-    assert pet.valid?
+      assert_predicate pet, :valid?
+
+      pet.nickname = ""
+
+      assert_predicate pet, :invalid?
+    end
   end
 end
diff --git a/activerecord/test/cases/validations/presence_validation_test.rb b/activerecord/test/cases/validations/presence_validation_test.rb
index 6f8ad06ab6..63c3f67da2 100644
--- a/activerecord/test/cases/validations/presence_validation_test.rb
+++ b/activerecord/test/cases/validations/presence_validation_test.rb
@@ -1,9 +1,11 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/man'
-require 'models/face'
-require 'models/interest'
-require 'models/speedometer'
-require 'models/dashboard'
+require "models/man"
+require "models/face"
+require "models/interest"
+require "models/speedometer"
+require "models/dashboard"
 
 class PresenceValidationTest < ActiveRecord::TestCase
   class Boy < Man; end
@@ -13,10 +15,10 @@ class PresenceValidationTest < ActiveRecord::TestCase
   def test_validates_presence_of_non_association
     Boy.validates_presence_of(:name)
     b = Boy.new
-    assert b.invalid?
+    assert_predicate b, :invalid?
 
     b.name = "Alex"
-    assert b.valid?
+    assert_predicate b, :valid?
   end
 
   def test_validates_presence_of_has_one
@@ -31,23 +33,23 @@ class PresenceValidationTest < ActiveRecord::TestCase
     b = Boy.new
     f = Face.new
     b.face = f
-    assert b.valid?
+    assert_predicate b, :valid?
 
     f.mark_for_destruction
-    assert b.invalid?
+    assert_predicate b, :invalid?
   end
 
   def test_validates_presence_of_has_many_marked_for_destruction
     Boy.validates_presence_of(:interests)
     b = Boy.new
     b.interests << [i1 = Interest.new, i2 = Interest.new]
-    assert b.valid?
+    assert_predicate b, :valid?
 
     i1.mark_for_destruction
-    assert b.valid?
+    assert_predicate b, :valid?
 
     i2.mark_for_destruction
-    assert b.invalid?
+    assert_predicate b, :invalid?
   end
 
   def test_validates_presence_doesnt_convert_to_array
@@ -57,7 +59,7 @@ class PresenceValidationTest < ActiveRecord::TestCase
     dash = Dashboard.new
 
     # dashboard has to_a method
-    def dash.to_a; ['(/)', '(\)']; end
+    def dash.to_a; ["(/)", '(\)']; end
 
     s = speedometer.new
     s.dashboard = dash
@@ -65,19 +67,39 @@ class PresenceValidationTest < ActiveRecord::TestCase
     assert_nothing_raised { s.valid? }
   end
 
-  def test_does_not_validate_presence_of_if_parent_record_is_validate_false
+  def test_validates_presence_of_virtual_attribute_on_model
     repair_validations(Interest) do
+      Interest.send(:attr_accessor, :abbreviation)
       Interest.validates_presence_of(:topic)
+      Interest.validates_presence_of(:abbreviation)
+
+      interest = Interest.create!(topic: "Thought Leadering", abbreviation: "tl")
+      assert_predicate interest, :valid?
+
+      interest.abbreviation = ""
+
+      assert_predicate interest, :invalid?
+    end
+  end
+
+  def test_validations_run_on_persisted_record
+    repair_validations(Interest) do
       interest = Interest.new
-      interest.save!(validate: false)
-      assert interest.persisted?
+      interest.save!
+      assert_predicate interest, :valid?
 
-      man = Man.new(interest_ids: [interest.id])
-      man.save!
+      Interest.validates_presence_of(:topic)
 
-      assert_equal man.interests.size, 1
-      assert interest.valid?
-      assert man.valid?
+      assert_not_predicate interest, :valid?
+    end
+  end
+
+  def test_validates_presence_with_on_context
+    repair_validations(Interest) do
+      Interest.validates_presence_of(:topic, on: :required_name)
+      interest = Interest.new
+      interest.save!
+      assert_not interest.valid?(:required_name)
     end
   end
 end
diff --git a/activerecord/test/cases/validations/uniqueness_validation_test.rb b/activerecord/test/cases/validations/uniqueness_validation_test.rb
index 2608c84be2..8f6f47e5fb 100644
--- a/activerecord/test/cases/validations/uniqueness_validation_test.rb
+++ b/activerecord/test/cases/validations/uniqueness_validation_test.rb
@@ -1,9 +1,16 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/reply'
-require 'models/warehouse_thing'
-require 'models/guid'
-require 'models/event'
+require "models/topic"
+require "models/reply"
+require "models/warehouse_thing"
+require "models/guid"
+require "models/event"
+require "models/dashboard"
+require "models/uuid_item"
+require "models/author"
+require "models/person"
+require "models/essay"
 
 class Wizard < ActiveRecord::Base
   self.abstract_class = true
@@ -24,7 +31,7 @@ end
 class ReplyTitle; end
 
 class ReplyWithTitleObject < Reply
-  validates_uniqueness_of :content, :scope => :title
+  validates_uniqueness_of :content, scope: :title
 
   def title; ReplyTitle.new; end
 end
@@ -36,21 +43,33 @@ end
 
 class BigIntTest < ActiveRecord::Base
   INT_MAX_VALUE = 2147483647
-  self.table_name = 'cars'
+  self.table_name = "cars"
   validates :engines_count, uniqueness: true, inclusion: { in: 0..INT_MAX_VALUE }
 end
 
 class BigIntReverseTest < ActiveRecord::Base
   INT_MAX_VALUE = 2147483647
-  self.table_name = 'cars'
+  self.table_name = "cars"
   validates :engines_count, inclusion: { in: 0..INT_MAX_VALUE }
   validates :engines_count, uniqueness: true
 end
 
+class CoolTopic < Topic
+  validates_uniqueness_of :id
+end
+
+class TopicWithAfterCreate < Topic
+  after_create :set_author
+
+  def set_author
+    update!(author_name: "#{title} #{id}")
+  end
+end
+
 class UniquenessValidationTest < ActiveRecord::TestCase
   INT_MAX_VALUE = 2147483647
 
-  fixtures :topics, 'warehouse-things'
+  fixtures :topics, "warehouse-things"
 
   repair_validations(Topic, Reply)
 
@@ -64,8 +83,8 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert t.save, "Should still save t as unique"
 
     t2 = Topic.new("title" => "I'm uniqué!")
-    assert !t2.valid?, "Shouldn't be valid"
-    assert !t2.save, "Shouldn't save t2 as unique"
+    assert_not t2.valid?, "Shouldn't be valid"
+    assert_not t2.save, "Shouldn't save t2 as unique"
     assert_equal ["has already been taken"], t2.errors[:title]
 
     t2.title = "Now I am really also unique"
@@ -76,8 +95,8 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     Topic.alias_attribute :new_title, :title
     Topic.validates_uniqueness_of(:new_title)
 
-    topic = Topic.new(new_title: 'abc')
-    assert topic.valid?
+    topic = Topic.new(new_title: "abc")
+    assert_predicate topic, :valid?
   end
 
   def test_validates_uniqueness_with_nil_value
@@ -87,39 +106,39 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert t.save, "Should save t as unique"
 
     t2 = Topic.new("title" => nil)
-    assert !t2.valid?, "Shouldn't be valid"
-    assert !t2.save, "Shouldn't save t2 as unique"
+    assert_not t2.valid?, "Shouldn't be valid"
+    assert_not t2.save, "Shouldn't save t2 as unique"
     assert_equal ["has already been taken"], t2.errors[:title]
   end
 
   def test_validates_uniqueness_with_validates
-    Topic.validates :title, :uniqueness => true
-    Topic.create!('title' => 'abc')
+    Topic.validates :title, uniqueness: true
+    Topic.create!("title" => "abc")
 
-    t2 = Topic.new('title' => 'abc')
-    assert !t2.valid?
+    t2 = Topic.new("title" => "abc")
+    assert_not_predicate t2, :valid?
     assert t2.errors[:title]
   end
 
   def test_validate_uniqueness_when_integer_out_of_range
     entry = BigIntTest.create(engines_count: INT_MAX_VALUE + 1)
-    assert_equal entry.errors[:engines_count], ['is not included in the list']
+    assert_equal entry.errors[:engines_count], ["is not included in the list"]
   end
 
   def test_validate_uniqueness_when_integer_out_of_range_show_order_does_not_matter
     entry = BigIntReverseTest.create(engines_count: INT_MAX_VALUE + 1)
-    assert_equal entry.errors[:engines_count], ['is not included in the list']
+    assert_equal entry.errors[:engines_count], ["is not included in the list"]
   end
 
   def test_validates_uniqueness_with_newline_chars
-    Topic.validates_uniqueness_of(:title, :case_sensitive => false)
+    Topic.validates_uniqueness_of(:title, case_sensitive: false)
 
     t = Topic.new("title" => "new\nline")
     assert t.save, "Should save t as unique"
   end
 
   def test_validate_uniqueness_with_scope
-    Reply.validates_uniqueness_of(:content, :scope => "parent_id")
+    Reply.validates_uniqueness_of(:content, scope: "parent_id")
 
     t = Topic.create("title" => "I'm unique!")
 
@@ -127,7 +146,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert r1.valid?, "Saving r1"
 
     r2 = t.replies.create "title" => "r2", "content" => "hello world"
-    assert !r2.valid?, "Saving r2 first time"
+    assert_not r2.valid?, "Saving r2 first time"
 
     r2.content = "something else"
     assert r2.save, "Saving r2 second time"
@@ -137,8 +156,15 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert r3.valid?, "Saving r3"
   end
 
+  def test_validate_uniqueness_with_scope_invalid_syntax
+    error = assert_raises(ArgumentError) do
+      Reply.validates_uniqueness_of(:content, scope: { parent_id: false })
+    end
+    assert_match(/Pass a symbol or an array of symbols instead/, error.to_s)
+  end
+
   def test_validate_uniqueness_with_object_scope
-    Reply.validates_uniqueness_of(:content, :scope => :topic)
+    Reply.validates_uniqueness_of(:content, scope: :topic)
 
     t = Topic.create("title" => "I'm unique!")
 
@@ -146,7 +172,20 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert r1.valid?, "Saving r1"
 
     r2 = t.replies.create "title" => "r2", "content" => "hello world"
-    assert !r2.valid?, "Saving r2 first time"
+    assert_not r2.valid?, "Saving r2 first time"
+  end
+
+  def test_validate_uniqueness_with_polymorphic_object_scope
+    Essay.validates_uniqueness_of(:name, scope: :writer)
+
+    a = Author.create(name: "Sergey")
+    p = Person.create(first_name: "Sergey")
+
+    e1 = a.essays.create(name: "Essay")
+    assert e1.valid?, "Saving e1"
+
+    e2 = p.essays.create(name: "Essay")
+    assert e2.valid?, "Saving e2"
   end
 
   def test_validate_uniqueness_with_composed_attribute_scope
@@ -154,7 +193,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert r1.valid?, "Saving r1"
 
     r2 = ReplyWithTitleObject.create "title" => "r1", "content" => "hello world"
-    assert !r2.valid?, "Saving r2 first time"
+    assert_not r2.valid?, "Saving r2 first time"
   end
 
   def test_validate_uniqueness_with_object_arg
@@ -166,7 +205,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert r1.valid?, "Saving r1"
 
     r2 = t.replies.create "title" => "r2", "content" => "hello world"
-    assert !r2.valid?, "Saving r2 first time"
+    assert_not r2.valid?, "Saving r2 first time"
   end
 
   def test_validate_uniqueness_scoped_to_defining_class
@@ -176,7 +215,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert r1.valid?, "Saving r1"
 
     r2 = t.silly_unique_replies.create "title" => "r2", "content" => "a barrel of fun"
-    assert !r2.valid?, "Saving r2"
+    assert_not r2.valid?, "Saving r2"
 
     # Should succeed as validates_uniqueness_of only applies to
     # UniqueReply and its subclasses
@@ -185,7 +224,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
   end
 
   def test_validate_uniqueness_with_scope_array
-    Reply.validates_uniqueness_of(:author_name, :scope => [:author_email_address, :parent_id])
+    Reply.validates_uniqueness_of(:author_name, scope: [:author_email_address, :parent_id])
 
     t = Topic.create("title" => "The earth is actually flat!")
 
@@ -193,23 +232,23 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert r1.valid?, "Saving r1"
 
     r2 = t.replies.create "author_name" => "jeremy", "author_email_address" => "jeremy@rubyonrails.com", "title" => "You're crazy!", "content" => "Crazy reply again..."
-    assert !r2.valid?, "Saving r2. Double reply by same author."
+    assert_not r2.valid?, "Saving r2. Double reply by same author."
 
     r2.author_email_address = "jeremy_alt_email@rubyonrails.com"
     assert r2.save, "Saving r2 the second time."
 
     r3 = t.replies.create "author_name" => "jeremy", "author_email_address" => "jeremy_alt_email@rubyonrails.com", "title" => "You're wrong", "content" => "It's cubic"
-    assert !r3.valid?, "Saving r3"
+    assert_not r3.valid?, "Saving r3"
 
     r3.author_name = "jj"
     assert r3.save, "Saving r3 the second time."
 
     r3.author_name = "jeremy"
-    assert !r3.save, "Saving r3 the third time."
+    assert_not r3.save, "Saving r3 the third time."
   end
 
   def test_validate_case_insensitive_uniqueness
-    Topic.validates_uniqueness_of(:title, :parent_id, :case_sensitive => false, :allow_nil => true)
+    Topic.validates_uniqueness_of(:title, :parent_id, case_sensitive: false, allow_nil: true)
 
     t = Topic.new("title" => "I'm unique!", :parent_id => 2)
     assert t.save, "Should save t as unique"
@@ -218,17 +257,17 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert t.save, "Should still save t as unique"
 
     t2 = Topic.new("title" => "I'm UNIQUE!", :parent_id => 1)
-    assert !t2.valid?, "Shouldn't be valid"
-    assert !t2.save, "Shouldn't save t2 as unique"
-    assert t2.errors[:title].any?
-    assert t2.errors[:parent_id].any?
+    assert_not t2.valid?, "Shouldn't be valid"
+    assert_not t2.save, "Shouldn't save t2 as unique"
+    assert_predicate t2.errors[:title], :any?
+    assert_predicate t2.errors[:parent_id], :any?
     assert_equal ["has already been taken"], t2.errors[:title]
 
     t2.title = "I'm truly UNIQUE!"
-    assert !t2.valid?, "Shouldn't be valid"
-    assert !t2.save, "Shouldn't save t2 as unique"
-    assert t2.errors[:title].empty?
-    assert t2.errors[:parent_id].any?
+    assert_not t2.valid?, "Shouldn't be valid"
+    assert_not t2.save, "Shouldn't save t2 as unique"
+    assert_empty t2.errors[:title]
+    assert_predicate t2.errors[:parent_id], :any?
 
     t2.parent_id = 4
     assert t2.save, "Should now save t2 as unique"
@@ -242,15 +281,15 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     assert t_utf8.save, "Should save t_utf8 as unique"
 
     # If database hasn't UTF-8 character set, this test fails
-    if Topic.all.merge!(:select => 'LOWER(title) AS title').find(t_utf8.id).title == "я тоже уникальный!"
+    if Topic.all.merge!(select: "LOWER(title) AS title").find(t_utf8.id).title == "я тоже уникальный!"
       t2_utf8 = Topic.new("title" => "я тоже УНИКАЛЬНЫЙ!")
-      assert !t2_utf8.valid?, "Shouldn't be valid"
-      assert !t2_utf8.save, "Shouldn't save t2_utf8 as unique"
+      assert_not t2_utf8.valid?, "Shouldn't be valid"
+      assert_not t2_utf8.save, "Shouldn't save t2_utf8 as unique"
     end
   end
 
   def test_validate_case_sensitive_uniqueness_with_special_sql_like_chars
-    Topic.validates_uniqueness_of(:title, :case_sensitive => true)
+    Topic.validates_uniqueness_of(:title, case_sensitive: true)
 
     t = Topic.new("title" => "I'm unique!")
     assert t.save, "Should save t as unique"
@@ -263,7 +302,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
   end
 
   def test_validate_case_insensitive_uniqueness_with_special_sql_like_chars
-    Topic.validates_uniqueness_of(:title, :case_sensitive => false)
+    Topic.validates_uniqueness_of(:title, case_sensitive: false)
 
     t = Topic.new("title" => "I'm unique!")
     assert t.save, "Should save t as unique"
@@ -276,7 +315,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
   end
 
   def test_validate_case_sensitive_uniqueness
-    Topic.validates_uniqueness_of(:title, :case_sensitive => true, :allow_nil => true)
+    Topic.validates_uniqueness_of(:title, case_sensitive: true, allow_nil: true)
 
     t = Topic.new("title" => "I'm unique!")
     assert t.save, "Should save t as unique"
@@ -287,41 +326,41 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     t2 = Topic.new("title" => "I'M UNIQUE!")
     assert t2.valid?, "Should be valid"
     assert t2.save, "Should save t2 as unique"
-    assert t2.errors[:title].empty?
-    assert t2.errors[:parent_id].empty?
+    assert_empty t2.errors[:title]
+    assert_empty t2.errors[:parent_id]
     assert_not_equal ["has already been taken"], t2.errors[:title]
 
     t3 = Topic.new("title" => "I'M uNiQUe!")
     assert t3.valid?, "Should be valid"
     assert t3.save, "Should save t2 as unique"
-    assert t3.errors[:title].empty?
-    assert t3.errors[:parent_id].empty?
+    assert_empty t3.errors[:title]
+    assert_empty t3.errors[:parent_id]
     assert_not_equal ["has already been taken"], t3.errors[:title]
   end
 
   def test_validate_case_sensitive_uniqueness_with_attribute_passed_as_integer
-    Topic.validates_uniqueness_of(:title, :case_sensitive => true)
-    Topic.create!('title' => 101)
+    Topic.validates_uniqueness_of(:title, case_sensitive: true)
+    Topic.create!("title" => 101)
 
-    t2 = Topic.new('title' => 101)
-    assert !t2.valid?
+    t2 = Topic.new("title" => 101)
+    assert_not_predicate t2, :valid?
     assert t2.errors[:title]
   end
 
   def test_validate_uniqueness_with_non_standard_table_names
-    i1 = WarehouseThing.create(:value => 1000)
-    assert !i1.valid?, "i1 should not be valid"
+    i1 = WarehouseThing.create(value: 1000)
+    assert_not i1.valid?, "i1 should not be valid"
     assert i1.errors[:value].any?, "Should not be empty"
   end
 
   def test_validates_uniqueness_inside_scoping
     Topic.validates_uniqueness_of(:title)
 
-    Topic.where(:author_name => "David").scoping do
+    Topic.where(author_name: "David").scoping do
       t1 = Topic.new("title" => "I'm unique!", "author_name" => "Mary")
       assert t1.save
       t2 = Topic.new("title" => "I'm unique!", "author_name" => "David")
-      assert !t2.valid?
+      assert_not_predicate t2, :valid?
     end
   end
 
@@ -335,46 +374,68 @@ class UniquenessValidationTest < ActiveRecord::TestCase
   end
 
   def test_validate_uniqueness_with_limit
-    # Event.title is limited to 5 characters
-    e1 = Event.create(:title => "abcde")
-    assert e1.valid?, "Could not create an event with a unique, 5 character title"
-    e2 = Event.create(:title => "abcdefgh")
-    assert !e2.valid?, "Created an event whose title, with limit taken into account, is not unique"
+    if current_adapter?(:SQLite3Adapter)
+      # Event.title has limit 5, but SQLite doesn't truncate.
+      e1 = Event.create(title: "abcdefgh")
+      assert e1.valid?, "Could not create an event with a unique 8 characters title"
+
+      e2 = Event.create(title: "abcdefgh")
+      assert_not e2.valid?, "Created an event whose title is not unique"
+    elsif current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter, :OracleAdapter, :SQLServerAdapter)
+      assert_raise(ActiveRecord::ValueTooLong) do
+        Event.create(title: "abcdefgh")
+      end
+    else
+      assert_raise(ActiveRecord::StatementInvalid) do
+        Event.create(title: "abcdefgh")
+      end
+    end
   end
 
   def test_validate_uniqueness_with_limit_and_utf8
-    # Event.title is limited to 5 characters
-    e1 = Event.create(:title => "一二三四五")
-    assert e1.valid?, "Could not create an event with a unique, 5 character title"
-    e2 = Event.create(:title => "一二三四五六七八")
-    assert !e2.valid?, "Created an event whose title, with limit taken into account, is not unique"
+    if current_adapter?(:SQLite3Adapter)
+      # Event.title has limit 5, but SQLite doesn't truncate.
+      e1 = Event.create(title: "一二三四五六七八")
+      assert e1.valid?, "Could not create an event with a unique 8 characters title"
+
+      e2 = Event.create(title: "一二三四五六七八")
+      assert_not e2.valid?, "Created an event whose title is not unique"
+    elsif current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter, :OracleAdapter, :SQLServerAdapter)
+      assert_raise(ActiveRecord::ValueTooLong) do
+        Event.create(title: "一二三四五六七八")
+      end
+    else
+      assert_raise(ActiveRecord::StatementInvalid) do
+        Event.create(title: "一二三四五六七八")
+      end
+    end
   end
 
   def test_validate_straight_inheritance_uniqueness
-    w1 = IneptWizard.create(:name => "Rincewind", :city => "Ankh-Morpork")
+    w1 = IneptWizard.create(name: "Rincewind", city: "Ankh-Morpork")
     assert w1.valid?, "Saving w1"
 
     # Should use validation from base class (which is abstract)
-    w2 = IneptWizard.new(:name => "Rincewind", :city => "Quirm")
-    assert !w2.valid?, "w2 shouldn't be valid"
+    w2 = IneptWizard.new(name: "Rincewind", city: "Quirm")
+    assert_not w2.valid?, "w2 shouldn't be valid"
     assert w2.errors[:name].any?, "Should have errors for name"
     assert_equal ["has already been taken"], w2.errors[:name], "Should have uniqueness message for name"
 
-    w3 = Conjurer.new(:name => "Rincewind", :city => "Quirm")
-    assert !w3.valid?, "w3 shouldn't be valid"
+    w3 = Conjurer.new(name: "Rincewind", city: "Quirm")
+    assert_not w3.valid?, "w3 shouldn't be valid"
     assert w3.errors[:name].any?, "Should have errors for name"
     assert_equal ["has already been taken"], w3.errors[:name], "Should have uniqueness message for name"
 
-    w4 = Conjurer.create(:name => "The Amazing Bonko", :city => "Quirm")
+    w4 = Conjurer.create(name: "The Amazing Bonko", city: "Quirm")
     assert w4.valid?, "Saving w4"
 
-    w5 = Thaumaturgist.new(:name => "The Amazing Bonko", :city => "Lancre")
-    assert !w5.valid?, "w5 shouldn't be valid"
+    w5 = Thaumaturgist.new(name: "The Amazing Bonko", city: "Lancre")
+    assert_not w5.valid?, "w5 shouldn't be valid"
     assert w5.errors[:name].any?, "Should have errors for name"
     assert_equal ["has already been taken"], w5.errors[:name], "Should have uniqueness message for name"
 
-    w6 = Thaumaturgist.new(:name => "Mustrum Ridcully", :city => "Quirm")
-    assert !w6.valid?, "w6 shouldn't be valid"
+    w6 = Thaumaturgist.new(name: "Mustrum Ridcully", city: "Quirm")
+    assert_not w6.valid?, "w6 shouldn't be valid"
     assert w6.errors[:city].any?, "Should have errors for city"
     assert_equal ["has already been taken"], w6.errors[:city], "Should have uniqueness message for city"
   end
@@ -385,7 +446,7 @@ class UniquenessValidationTest < ActiveRecord::TestCase
     Topic.create("title" => "I'm an unapproved topic", "approved" => false)
 
     t3 = Topic.new("title" => "I'm a topic", "approved" => true)
-    assert !t3.valid?, "t3 shouldn't be valid"
+    assert_not t3.valid?, "t3 shouldn't be valid"
 
     t4 = Topic.new("title" => "I'm an unapproved topic", "approved" => false)
     assert t4.valid?, "t4 should be valid"
@@ -399,32 +460,98 @@ class UniquenessValidationTest < ActiveRecord::TestCase
 
   def test_validate_uniqueness_on_existing_relation
     event = Event.create
-    assert TopicWithUniqEvent.create(event: event).valid?
+    assert_predicate TopicWithUniqEvent.create(event: event), :valid?
 
     topic = TopicWithUniqEvent.new(event: event)
-    assert_not topic.valid?
-    assert_equal ['has already been taken'], topic.errors[:event]
+    assert_not_predicate topic, :valid?
+    assert_equal ["has already been taken"], topic.errors[:event]
   end
 
   def test_validate_uniqueness_on_empty_relation
     topic = TopicWithUniqEvent.new
-    assert topic.valid?
+    assert_predicate topic, :valid?
+  end
+
+  def test_validate_uniqueness_of_custom_primary_key
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = "keyboards"
+      self.primary_key = :key_number
+
+      validates_uniqueness_of :key_number
+
+      def self.name
+        "Keyboard"
+      end
+    end
+
+    klass.create!(key_number: 10)
+    key2 = klass.create!(key_number: 11)
+
+    key2.key_number = 10
+    assert_not_predicate key2, :valid?
+  end
+
+  def test_validate_uniqueness_without_primary_key
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = "dashboards"
+
+      validates_uniqueness_of :dashboard_id
+
+      def self.name; "Dashboard" end
+    end
+
+    abc = klass.create!(dashboard_id: "abc")
+    assert_predicate klass.new(dashboard_id: "xyz"), :valid?
+    assert_not_predicate klass.new(dashboard_id: "abc"), :valid?
+
+    abc.dashboard_id = "def"
+
+    e = assert_raises ActiveRecord::UnknownPrimaryKey do
+      abc.save!
+    end
+    assert_match(/\AUnknown primary key for table dashboards in model/, e.message)
+    assert_match(/Can not validate uniqueness for persisted record without primary key.\z/, e.message)
   end
 
-  def test_does_not_validate_uniqueness_of_if_parent_record_is_validate_false
-    Reply.validates_uniqueness_of(:content)
+  def test_validate_uniqueness_ignores_itself_when_primary_key_changed
+    Topic.validates_uniqueness_of(:title)
+
+    t = Topic.new("title" => "This is a unique title")
+    assert t.save, "Should save t as unique"
+
+    t.id += 1
+    assert t.valid?, "Should be valid"
+    assert t.save, "Should still save t as unique"
+  end
 
-    Reply.create!(content: "Topic Title")
+  def test_validate_uniqueness_with_after_create_performing_save
+    TopicWithAfterCreate.validates_uniqueness_of(:title)
+    topic = TopicWithAfterCreate.create!(title: "Title1")
+    assert topic.author_name.start_with?("Title1")
+
+    topic2 = TopicWithAfterCreate.new(title: "Title1")
+    assert_not_predicate topic2, :valid?
+    assert_equal(["has already been taken"], topic2.errors[:title])
+  end
+
+  def test_validate_uniqueness_uuid
+    skip unless current_adapter?(:PostgreSQLAdapter)
+    item = UuidItem.create!(uuid: SecureRandom.uuid, title: "item1")
+    item.update(title: "item1-title2")
+    assert_empty item.errors
+
+    item2 = UuidValidatingItem.create!(uuid: SecureRandom.uuid, title: "item2")
+    item2.update(title: "item2-title2")
+    assert_empty item2.errors
+  end
 
-    reply = Reply.new(content: "Topic Title")
-    reply.save!(validate: false)
-    assert reply.persisted?
+  def test_validate_uniqueness_regular_id
+    item = CoolTopic.create!(title: "MyItem")
+    assert_empty item.errors
 
-    topic = Topic.new(reply_ids: [reply.id])
-    topic.save!
+    item2 = CoolTopic.new(id: item.id, title: "MyItem2")
+    assert_not_predicate item2, :valid?
 
-    assert_equal topic.replies.size, 1
-    assert reply.valid?
-    assert topic.valid?
+    assert_equal(["has already been taken"], item2.errors[:id])
   end
 end
diff --git a/activerecord/test/cases/validations_repair_helper.rb b/activerecord/test/cases/validations_repair_helper.rb
index b30666d876..6dc3b64b2b 100644
--- a/activerecord/test/cases/validations_repair_helper.rb
+++ b/activerecord/test/cases/validations_repair_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ActiveRecord
   module ValidationsRepairHelper
     extend ActiveSupport::Concern
diff --git a/activerecord/test/cases/validations_test.rb b/activerecord/test/cases/validations_test.rb
index f4f316f393..66763c727f 100644
--- a/activerecord/test/cases/validations_test.rb
+++ b/activerecord/test/cases/validations_test.rb
@@ -1,11 +1,13 @@
+# frozen_string_literal: true
+
 require "cases/helper"
-require 'models/topic'
-require 'models/reply'
-require 'models/person'
-require 'models/developer'
-require 'models/computer'
-require 'models/parrot'
-require 'models/company'
+require "models/topic"
+require "models/reply"
+require "models/developer"
+require "models/computer"
+require "models/parrot"
+require "models/company"
+require "models/price_estimate"
 
 class ValidationsTest < ActiveRecord::TestCase
   fixtures :topics, :developers
@@ -17,7 +19,7 @@ class ValidationsTest < ActiveRecord::TestCase
   def test_valid_uses_create_context_when_new
     r = WrongReply.new
     r.title = "Wrong Create"
-    assert_not r.valid?
+    assert_not_predicate r, :valid?
     assert r.errors[:title].any?, "A reply with a bad title should mark that attribute as invalid"
     assert_equal ["is Wrong Create"], r.errors[:title], "A reply with a bad content should contain an error"
   end
@@ -36,8 +38,8 @@ class ValidationsTest < ActiveRecord::TestCase
   end
 
   def test_valid_using_special_context
-    r = WrongReply.new(:title => "Valid title")
-    assert !r.valid?(:special_case)
+    r = WrongReply.new(title: "Valid title")
+    assert_not r.valid?(:special_case)
     assert_equal "Invalid", r.errors[:author_name].join
 
     r.author_name = "secret"
@@ -52,6 +54,13 @@ class ValidationsTest < ActiveRecord::TestCase
     assert r.valid?(:special_case)
   end
 
+  def test_invalid_using_multiple_contexts
+    r = WrongReply.new(title: "Wrong Create")
+    assert r.invalid?([:special_case, :create])
+    assert_equal "Invalid", r.errors[:author_name].join
+    assert_equal "is Wrong Create", r.errors[:title].join
+  end
+
   def test_validate
     r = WrongReply.new
 
@@ -88,7 +97,7 @@ class ValidationsTest < ActiveRecord::TestCase
     assert_raise(ActiveRecord::RecordInvalid) do
       WrongReply.new.validate!(:special_case)
     end
-    r = WrongReply.new(:title => "Valid title", :author_name => "secret", :content => "Good")
+    r = WrongReply.new(title: "Valid title", author_name: "secret", content: "Good")
     assert r.validate!(:special_case)
   end
 
@@ -100,7 +109,7 @@ class ValidationsTest < ActiveRecord::TestCase
 
   def test_exception_on_create_bang_with_block
     assert_raise(ActiveRecord::RecordInvalid) do
-      WrongReply.create!({ "title" => "OK" }) do |r|
+      WrongReply.create!("title" => "OK") do |r|
         r.content = nil
       end
     end
@@ -116,21 +125,21 @@ class ValidationsTest < ActiveRecord::TestCase
 
   def test_save_without_validation
     reply = WrongReply.new
-    assert !reply.save
-    assert reply.save(:validate => false)
+    assert_not reply.save
+    assert reply.save(validate: false)
   end
 
   def test_validates_acceptance_of_with_non_existent_table
     Object.const_set :IncorporealModel, Class.new(ActiveRecord::Base)
 
-    assert_nothing_raised ActiveRecord::StatementInvalid do
+    assert_nothing_raised do
       IncorporealModel.validates_acceptance_of(:incorporeal_column)
     end
   end
 
   def test_throw_away_typing
     d = Developer.new("name" => "David", "salary" => "100,000")
-    assert !d.valid?
+    assert_not_predicate d, :valid?
     assert_equal 100, d.salary
     assert_equal "100,000", d.salary_before_type_cast
   end
@@ -149,16 +158,55 @@ class ValidationsTest < ActiveRecord::TestCase
   end
 
   def test_numericality_validation_with_mutation
-    Topic.class_eval do
+    klass = Class.new(Topic) do
       attribute :wibble, :string
       validates_numericality_of :wibble, only_integer: true
     end
 
-    topic = Topic.new(wibble: '123-4567')
-    topic.wibble.gsub!('-', '')
+    topic = klass.new(wibble: "123-4567")
+    topic.wibble.gsub!("-", "")
 
-    assert topic.valid?
-  ensure
-    Topic.reset_column_information
+    assert_predicate topic, :valid?
+  end
+
+  def test_numericality_validation_checks_against_raw_value
+    klass = Class.new(Topic) do
+      def self.model_name
+        ActiveModel::Name.new(self, nil, "Topic")
+      end
+      attribute :wibble, :decimal, scale: 2, precision: 9
+      validates_numericality_of :wibble, greater_than_or_equal_to: BigDecimal("97.18")
+    end
+
+    assert_not_predicate klass.new(wibble: "97.179"), :valid?
+    assert_not_predicate klass.new(wibble: 97.179), :valid?
+    assert_not_predicate klass.new(wibble: BigDecimal("97.179")), :valid?
+  end
+
+  def test_numericality_validator_wont_be_affected_by_custom_getter
+    price_estimate = PriceEstimate.new(price: 50)
+
+    assert_equal "$50.00", price_estimate.price
+    assert_equal 50, price_estimate.price_before_type_cast
+    assert_equal 50, price_estimate.read_attribute(:price)
+
+    assert_predicate price_estimate, :price_came_from_user?
+    assert_predicate price_estimate, :valid?
+
+    price_estimate.save!
+
+    assert_not_predicate price_estimate, :price_came_from_user?
+    assert_predicate price_estimate, :valid?
+  end
+
+  def test_acceptance_validator_doesnt_require_db_connection
+    klass = Class.new(ActiveRecord::Base) do
+      self.table_name = "posts"
+    end
+    klass.reset_column_information
+
+    assert_no_queries do
+      klass.validates_acceptance_of(:foo)
+    end
   end
 end
diff --git a/activerecord/test/cases/view_test.rb b/activerecord/test/cases/view_test.rb
index f9dca1e196..7e2d66c62a 100644
--- a/activerecord/test/cases/view_test.rb
+++ b/activerecord/test/cases/view_test.rb
@@ -1,7 +1,11 @@
+# frozen_string_literal: true
+
 require "cases/helper"
 require "models/book"
+require "support/schema_dumping_helper"
 
 module ViewBehavior
+  include SchemaDumpingHelper
   extend ActiveSupport::Concern
 
   included do
@@ -9,20 +13,21 @@ module ViewBehavior
   end
 
   class Ebook < ActiveRecord::Base
+    self.table_name = "ebooks'"
     self.primary_key = "id"
   end
 
   def setup
     super
     @connection = ActiveRecord::Base.connection
-    create_view "ebooks", <<-SQL
+    create_view "ebooks'", <<-SQL
       SELECT id, name, status FROM books WHERE format = 'ebook'
     SQL
   end
 
   def teardown
     super
-    drop_view "ebooks"
+    drop_view "ebooks'"
   end
 
   def test_reading
@@ -31,9 +36,23 @@ module ViewBehavior
     assert_equal ["Ruby for Rails"], books.map(&:name)
   end
 
+  def test_views
+    assert_equal [Ebook.table_name], @connection.views
+  end
+
+  def test_view_exists
+    view_name = Ebook.table_name
+    assert @connection.view_exists?(view_name), "'#{view_name}' view should exist"
+  end
+
   def test_table_exists
     view_name = Ebook.table_name
-    assert @connection.table_exists?(view_name), "'#{view_name}' table should exist"
+    assert_not @connection.table_exists?(view_name), "'#{view_name}' table should not exist"
+  end
+
+  def test_views_ara_valid_data_sources
+    view_name = Ebook.table_name
+    assert @connection.data_source_exists?(view_name), "'#{view_name}' should be a data source"
   end
 
   def test_column_definitions
@@ -43,71 +62,163 @@ module ViewBehavior
   end
 
   def test_attributes
-    assert_equal({"id" => 2, "name" => "Ruby for Rails", "status" => 0},
+    assert_equal({ "id" => 2, "name" => "Ruby for Rails", "status" => 0 },
                  Ebook.first.attributes)
   end
 
   def test_does_not_assume_id_column_as_primary_key
     model = Class.new(ActiveRecord::Base) do
-      self.table_name = "ebooks"
+      self.table_name = "ebooks'"
     end
     assert_nil model.primary_key
   end
+
+  def test_does_not_dump_view_as_table
+    schema = dump_table_schema "ebooks'"
+    assert_no_match %r{create_table "ebooks'"}, schema
+  end
+
+  private
+    def quote_table_name(name)
+      @connection.quote_table_name(name)
+    end
 end
 
 if ActiveRecord::Base.connection.supports_views?
-class ViewWithPrimaryKeyTest < ActiveRecord::TestCase
-  include ViewBehavior
+  class ViewWithPrimaryKeyTest < ActiveRecord::TestCase
+    include ViewBehavior
 
-  private
-  def create_view(name, query)
-    @connection.execute "CREATE VIEW #{name} AS #{query}"
-  end
+    private
+      def create_view(name, query)
+        @connection.execute "CREATE VIEW #{quote_table_name(name)} AS #{query}"
+      end
 
-  def drop_view(name)
-    @connection.execute "DROP VIEW #{name}" if @connection.table_exists? name
+      def drop_view(name)
+        @connection.execute "DROP VIEW #{quote_table_name(name)}" if @connection.view_exists? name
+      end
   end
-end
 
-class ViewWithoutPrimaryKeyTest < ActiveRecord::TestCase
-  fixtures :books
+  class ViewWithoutPrimaryKeyTest < ActiveRecord::TestCase
+    include SchemaDumpingHelper
+    fixtures :books
 
-  class Paperback < ActiveRecord::Base; end
+    class Paperback < ActiveRecord::Base; end
 
-  setup do
-    @connection = ActiveRecord::Base.connection
-    @connection.execute <<-SQL
-      CREATE VIEW paperbacks
-        AS SELECT name, status FROM books WHERE format = 'paperback'
-    SQL
-  end
+    setup do
+      @connection = ActiveRecord::Base.connection
+      @connection.execute <<-SQL
+        CREATE VIEW paperbacks
+          AS SELECT name, status FROM books WHERE format = 'paperback'
+      SQL
+    end
 
-  teardown do
-    @connection.execute "DROP VIEW paperbacks" if @connection.table_exists? "paperbacks"
-  end
+    teardown do
+      @connection.execute "DROP VIEW paperbacks" if @connection.view_exists? "paperbacks"
+    end
 
-  def test_reading
-    books = Paperback.all
-    assert_equal ["Agile Web Development with Rails"], books.map(&:name)
-  end
+    def test_reading
+      books = Paperback.all
+      assert_equal ["Agile Web Development with Rails"], books.map(&:name)
+    end
 
-  def test_table_exists
-    view_name = Paperback.table_name
-    assert @connection.table_exists?(view_name), "'#{view_name}' table should exist"
-  end
+    def test_views
+      assert_equal [Paperback.table_name], @connection.views
+    end
 
-  def test_column_definitions
-    assert_equal([["name", :string],
-                  ["status", :integer]], Paperback.columns.map { |c| [c.name, c.type] })
-  end
+    def test_view_exists
+      view_name = Paperback.table_name
+      assert @connection.view_exists?(view_name), "'#{view_name}' view should exist"
+    end
 
-  def test_attributes
-    assert_equal({"name" => "Agile Web Development with Rails", "status" => 2},
-                 Paperback.first.attributes)
+    def test_table_exists
+      view_name = Paperback.table_name
+      assert_not @connection.table_exists?(view_name), "'#{view_name}' table should not exist"
+    end
+
+    def test_column_definitions
+      assert_equal([["name", :string],
+                    ["status", :integer]], Paperback.columns.map { |c| [c.name, c.type] })
+    end
+
+    def test_attributes
+      assert_equal({ "name" => "Agile Web Development with Rails", "status" => 2 },
+                   Paperback.first.attributes)
+    end
+
+    def test_does_not_have_a_primary_key
+      assert_nil Paperback.primary_key
+    end
+
+    def test_does_not_dump_view_as_table
+      schema = dump_table_schema "paperbacks"
+      assert_no_match %r{create_table "paperbacks"}, schema
+    end
   end
 
-  def test_does_not_have_a_primary_key
-    assert_nil Paperback.primary_key
+  # sqlite dose not support CREATE, INSERT, and DELETE for VIEW
+  if current_adapter?(:Mysql2Adapter, :SQLServerAdapter) ||
+      current_adapter?(:PostgreSQLAdapter) && ActiveRecord::Base.connection.postgresql_version >= 90300
+
+    class UpdateableViewTest < ActiveRecord::TestCase
+      self.use_transactional_tests = false
+      fixtures :books
+
+      class PrintedBook < ActiveRecord::Base
+        self.primary_key = "id"
+      end
+
+      setup do
+        @connection = ActiveRecord::Base.connection
+        @connection.execute <<-SQL
+          CREATE VIEW printed_books
+            AS SELECT id, name, status, format FROM books WHERE format = 'paperback'
+        SQL
+      end
+
+      teardown do
+        @connection.execute "DROP VIEW printed_books" if @connection.view_exists? "printed_books"
+      end
+
+      def test_update_record
+        book = PrintedBook.first
+        book.name = "AWDwR"
+        book.save!
+        book.reload
+        assert_equal "AWDwR", book.name
+      end
+
+      def test_insert_record
+        PrintedBook.create! name: "Rails in Action", status: 0, format: "paperback"
+
+        new_book = PrintedBook.last
+        assert_equal "Rails in Action", new_book.name
+      end
+
+      def test_update_record_to_fail_view_conditions
+        book = PrintedBook.first
+        book.format = "ebook"
+        book.save!
+
+        assert_raises ActiveRecord::RecordNotFound do
+          book.reload
+        end
+      end
+    end
+  end # end of `if current_adapter?(:Mysql2Adapter, :PostgreSQLAdapter, :SQLServerAdapter)`
+end # end of `if ActiveRecord::Base.connection.supports_views?`
+
+if ActiveRecord::Base.connection.respond_to?(:supports_materialized_views?) &&
+    ActiveRecord::Base.connection.supports_materialized_views?
+  class MaterializedViewTest < ActiveRecord::PostgreSQLTestCase
+    include ViewBehavior
+
+    private
+      def create_view(name, query)
+        @connection.execute "CREATE MATERIALIZED VIEW #{quote_table_name(name)} AS #{query}"
+      end
+
+      def drop_view(name)
+        @connection.execute "DROP MATERIALIZED VIEW #{quote_table_name(name)}" if @connection.view_exists? name
+      end
   end
 end
-end
diff --git a/activerecord/test/cases/xml_serialization_test.rb b/activerecord/test/cases/xml_serialization_test.rb
deleted file mode 100644
index b30b50f597..0000000000
--- a/activerecord/test/cases/xml_serialization_test.rb
+++ /dev/null
@@ -1,447 +0,0 @@
-require "cases/helper"
-require "rexml/document"
-require 'models/contact'
-require 'models/post'
-require 'models/author'
-require 'models/comment'
-require 'models/company_in_module'
-require 'models/toy'
-require 'models/topic'
-require 'models/reply'
-require 'models/company'
-
-class XmlSerializationTest < ActiveRecord::TestCase
-  def test_should_serialize_default_root
-    @xml = Contact.new.to_xml
-    assert_match %r{^<contact>},  @xml
-    assert_match %r{</contact>$}, @xml
-  end
-
-  def test_should_serialize_default_root_with_namespace
-    @xml = Contact.new.to_xml :namespace=>"http://xml.rubyonrails.org/contact"
-    assert_match %r{^<contact xmlns="http://xml\.rubyonrails\.org/contact">},  @xml
-    assert_match %r{</contact>$}, @xml
-  end
-
-  def test_should_serialize_custom_root
-    @xml = Contact.new.to_xml :root => 'xml_contact'
-    assert_match %r{^<xml-contact>},  @xml
-    assert_match %r{</xml-contact>$}, @xml
-  end
-
-  def test_should_allow_undasherized_tags
-    @xml = Contact.new.to_xml :root => 'xml_contact', :dasherize => false
-    assert_match %r{^<xml_contact>},  @xml
-    assert_match %r{</xml_contact>$}, @xml
-    assert_match %r{<created_at},     @xml
-  end
-
-  def test_should_allow_camelized_tags
-    @xml = Contact.new.to_xml :root => 'xml_contact', :camelize => true
-    assert_match %r{^<XmlContact>},  @xml
-    assert_match %r{</XmlContact>$}, @xml
-    assert_match %r{<CreatedAt},    @xml
-  end
-
-  def test_should_allow_skipped_types
-    @xml = Contact.new(:age => 25).to_xml :skip_types => true
-    assert %r{<age>25</age>}.match(@xml)
-  end
-
-  def test_should_include_yielded_additions
-    @xml = Contact.new.to_xml do |xml|
-      xml.creator "David"
-    end
-    assert_match %r{<creator>David</creator>}, @xml
-  end
-
-  def test_to_xml_with_block
-    value = "Rockin' the block"
-    xml = Contact.new.to_xml(:skip_instruct => true) do |_xml|
-      _xml.tag! "arbitrary-element", value
-    end
-    assert_equal "<contact>", xml.first(9)
-    assert xml.include?(%(<arbitrary-element>#{value}</arbitrary-element>))
-  end
-
-  def test_should_skip_instruct_for_included_records
-    @contact = Contact.new
-    @contact.alternative = Contact.new(:name => 'Copa Cabana')
-    @xml = @contact.to_xml(:include => [ :alternative ])
-    assert_equal @xml.index('<?xml '), 0
-    assert_nil @xml.index('<?xml ', 1)
-  end
-end
-
-class DefaultXmlSerializationTest < ActiveRecord::TestCase
-  def setup
-    @contact = Contact.new(
-      :name        => 'aaron stack',
-      :age         => 25,
-      :avatar      => 'binarydata',
-      :created_at  => Time.utc(2006, 8, 1),
-      :awesome     => false,
-      :preferences => { :gem => 'ruby' }
-    )
-  end
-
-  def test_should_serialize_string
-    assert_match %r{<name>aaron stack</name>}, @contact.to_xml
-  end
-
-  def test_should_serialize_integer
-    assert_match %r{<age type="integer">25</age>}, @contact.to_xml
-  end
-
-  def test_should_serialize_binary
-    xml = @contact.to_xml
-    assert_match %r{YmluYXJ5ZGF0YQ==\n</avatar>},    xml
-    assert_match %r{<avatar(.*)(type="binary")},     xml
-    assert_match %r{<avatar(.*)(encoding="base64")}, xml
-  end
-
-  def test_should_serialize_datetime
-    assert_match %r{<created-at type=\"dateTime\">2006-08-01T00:00:00Z</created-at>}, @contact.to_xml
-  end
-
-  def test_should_serialize_boolean
-    assert_match %r{<awesome type=\"boolean\">false</awesome>}, @contact.to_xml
-  end
-
-  def test_should_serialize_hash
-    assert_match %r{<preferences>\s*<gem>ruby</gem>\s*</preferences>}m, @contact.to_xml
-  end
-
-  def test_uses_serializable_hash_with_only_option
-    def @contact.serializable_hash(options=nil)
-      super(only: %w(name))
-    end
-
-    xml = @contact.to_xml
-    assert_match %r{<name>aaron stack</name>}, xml
-    assert_no_match %r{age}, xml
-    assert_no_match %r{awesome}, xml
-  end
-
-  def test_uses_serializable_hash_with_except_option
-    def @contact.serializable_hash(options=nil)
-      super(except: %w(age))
-    end
-
-    xml = @contact.to_xml
-    assert_match %r{<name>aaron stack</name>}, xml
-    assert_match %r{<awesome type=\"boolean\">false</awesome>}, xml
-    assert_no_match %r{age}, xml
-  end
-
-  def test_does_not_include_inheritance_column_from_sti
-    @contact = ContactSti.new(@contact.attributes)
-    assert_equal 'ContactSti', @contact.type
-
-    xml = @contact.to_xml
-    assert_match %r{<name>aaron stack</name>}, xml
-    assert_no_match %r{<type}, xml
-    assert_no_match %r{ContactSti}, xml
-  end
-
-  def test_serializable_hash_with_default_except_option_and_excluding_inheritance_column_from_sti
-    @contact = ContactSti.new(@contact.attributes)
-    assert_equal 'ContactSti', @contact.type
-
-    def @contact.serializable_hash(options={})
-      super({ except: %w(age) }.merge!(options))
-    end
-
-    xml = @contact.to_xml
-    assert_match %r{<name>aaron stack</name>}, xml
-    assert_no_match %r{age}, xml
-    assert_no_match %r{<type}, xml
-    assert_no_match %r{ContactSti}, xml
-  end
-end
-
-class DefaultXmlSerializationTimezoneTest < ActiveRecord::TestCase
-  def test_should_serialize_datetime_with_timezone
-    with_timezone_config zone: "Pacific Time (US & Canada)" do
-      toy = Toy.create(:name => 'Mickey', :updated_at => Time.utc(2006, 8, 1))
-      assert_match %r{<updated-at type=\"dateTime\">2006-07-31T17:00:00-07:00</updated-at>}, toy.to_xml
-    end
-  end
-
-  def test_should_serialize_datetime_with_timezone_reloaded
-    with_timezone_config zone: "Pacific Time (US & Canada)" do
-      toy = Toy.create(:name => 'Minnie', :updated_at => Time.utc(2006, 8, 1)).reload
-      assert_match %r{<updated-at type=\"dateTime\">2006-07-31T17:00:00-07:00</updated-at>}, toy.to_xml
-    end
-  end
-end
-
-class NilXmlSerializationTest < ActiveRecord::TestCase
-  def setup
-    @xml = Contact.new.to_xml(:root => 'xml_contact')
-  end
-
-  def test_should_serialize_string
-    assert_match %r{<name nil="true"/>}, @xml
-  end
-
-  def test_should_serialize_integer
-    assert %r{<age (.*)/>}.match(@xml)
-    attributes = $1
-    assert_match %r{nil="true"}, attributes
-    assert_match %r{type="integer"}, attributes
-  end
-
-  def test_should_serialize_binary
-    assert %r{<avatar (.*)/>}.match(@xml)
-    attributes = $1
-    assert_match %r{type="binary"}, attributes
-    assert_match %r{encoding="base64"}, attributes
-    assert_match %r{nil="true"}, attributes
-  end
-
-  def test_should_serialize_datetime
-    assert %r{<created-at (.*)/>}.match(@xml)
-    attributes = $1
-    assert_match %r{nil="true"}, attributes
-    assert_match %r{type="dateTime"}, attributes
-  end
-
-  def test_should_serialize_boolean
-    assert %r{<awesome (.*)/>}.match(@xml)
-    attributes = $1
-    assert_match %r{type="boolean"}, attributes
-    assert_match %r{nil="true"}, attributes
-  end
-
-  def test_should_serialize_yaml
-    assert_match %r{<preferences nil=\"true\"/>}, @xml
-  end
-end
-
-class DatabaseConnectedXmlSerializationTest < ActiveRecord::TestCase
-  fixtures :topics, :companies, :accounts, :authors, :posts, :projects
-
-  def test_to_xml
-    xml = REXML::Document.new(topics(:first).to_xml(:indent => 0))
-    bonus_time_in_current_timezone = topics(:first).bonus_time.xmlschema
-    written_on_in_current_timezone = topics(:first).written_on.xmlschema
-
-    assert_equal "topic", xml.root.name
-    assert_equal "The First Topic" , xml.elements["//title"].text
-    assert_equal "David" , xml.elements["//author-name"].text
-    assert_match "Have a nice day", xml.elements["//content"].text
-
-    assert_equal "1", xml.elements["//id"].text
-    assert_equal "integer" , xml.elements["//id"].attributes['type']
-
-    assert_equal "1", xml.elements["//replies-count"].text
-    assert_equal "integer" , xml.elements["//replies-count"].attributes['type']
-
-    assert_equal written_on_in_current_timezone, xml.elements["//written-on"].text
-    assert_equal "dateTime" , xml.elements["//written-on"].attributes['type']
-
-    assert_equal "david@loudthinking.com", xml.elements["//author-email-address"].text
-
-    assert_equal nil, xml.elements["//parent-id"].text
-    assert_equal "integer", xml.elements["//parent-id"].attributes['type']
-    assert_equal "true", xml.elements["//parent-id"].attributes['nil']
-
-    # Oracle enhanced adapter allows to define Date attributes in model class (see topic.rb)
-    assert_equal "2004-04-15", xml.elements["//last-read"].text
-    assert_equal "date" , xml.elements["//last-read"].attributes['type']
-
-    # Oracle and DB2 don't have true boolean or time-only fields
-    unless current_adapter?(:OracleAdapter, :DB2Adapter)
-      assert_equal "false", xml.elements["//approved"].text
-      assert_equal "boolean" , xml.elements["//approved"].attributes['type']
-
-      assert_equal bonus_time_in_current_timezone, xml.elements["//bonus-time"].text
-      assert_equal "dateTime" , xml.elements["//bonus-time"].attributes['type']
-    end
-  end
-
-  def test_except_option
-    xml = topics(:first).to_xml(:indent => 0, :skip_instruct => true, :except => [:title, :replies_count])
-    assert_equal "<topic>", xml.first(7)
-    assert !xml.include?(%(<title>The First Topic</title>))
-    assert xml.include?(%(<author-name>David</author-name>))
-
-    xml = topics(:first).to_xml(:indent => 0, :skip_instruct => true, :except => [:title, :author_name, :replies_count])
-    assert !xml.include?(%(<title>The First Topic</title>))
-    assert !xml.include?(%(<author-name>David</author-name>))
-  end
-
-  # to_xml used to mess with the hash the user provided which
-  # caused the builder to be reused.  This meant the document kept
-  # getting appended to.
-
-  def test_modules
-    projects = MyApplication::Business::Project.all
-    xml = projects.to_xml
-    root = projects.first.class.to_s.underscore.pluralize.tr('/','_').dasherize
-    assert_match "<#{root} type=\"array\">", xml
-    assert_match "</#{root}>", xml
-  end
-
-  def test_passing_hash_shouldnt_reuse_builder
-    options = {:include=>:posts}
-    david = authors(:david)
-    first_xml_size = david.to_xml(options).size
-    second_xml_size = david.to_xml(options).size
-    assert_equal first_xml_size, second_xml_size
-  end
-
-  def test_include_uses_association_name
-    xml = authors(:david).to_xml :include=>:hello_posts, :indent => 0
-    assert_match %r{<hello-posts type="array">}, xml
-    assert_match %r{<hello-post type="Post">}, xml
-    assert_match %r{<hello-post type="StiPost">}, xml
-  end
-
-  def test_included_associations_should_skip_types
-    xml = authors(:david).to_xml :include=>:hello_posts, :indent => 0, :skip_types => true
-    assert_match %r{<hello-posts>}, xml
-    assert_match %r{<hello-post>}, xml
-    assert_match %r{<hello-post>}, xml
-  end
-
-  def test_including_has_many_association
-    xml = topics(:first).to_xml(:indent => 0, :skip_instruct => true, :include => :replies, :except => :replies_count)
-    assert_equal "<topic>", xml.first(7)
-    assert xml.include?(%(<replies type="array"><reply>))
-    assert xml.include?(%(<title>The Second Topic of the day</title>))
-  end
-
-  def test_including_belongs_to_association
-    xml = companies(:first_client).to_xml(:indent => 0, :skip_instruct => true, :include => :firm)
-    assert !xml.include?("<firm>")
-
-    xml = companies(:second_client).to_xml(:indent => 0, :skip_instruct => true, :include => :firm)
-    assert xml.include?("<firm>")
-  end
-
-  def test_including_multiple_associations
-    xml = companies(:first_firm).to_xml(:indent => 0, :skip_instruct => true, :include => [ :clients, :account ])
-    assert_equal "<firm>", xml.first(6)
-    assert xml.include?(%(<account>))
-    assert xml.include?(%(<clients type="array"><client>))
-  end
-
-  def test_including_association_with_options
-    xml = companies(:first_firm).to_xml(
-      :indent  => 0, :skip_instruct => true,
-      :include => { :clients => { :only => :name } }
-    )
-
-    assert_equal "<firm>", xml.first(6)
-    assert xml.include?(%(<client><name>Summit</name></client>))
-    assert xml.include?(%(<clients type="array"><client>))
-  end
-
-  def test_methods_are_called_on_object
-    xml = authors(:david).to_xml :methods => :label, :indent => 0
-    assert_match %r{<label>.*</label>}, xml
-  end
-
-  def test_should_not_call_methods_on_associations_that_dont_respond
-    xml = authors(:david).to_xml :include=>:hello_posts, :methods => :label, :indent => 2
-    assert !authors(:david).hello_posts.first.respond_to?(:label)
-    assert_match %r{^  <label>.*</label>}, xml
-    assert_no_match %r{^      <label>}, xml
-  end
-
-  def test_procs_are_called_on_object
-    proc = Proc.new { |options| options[:builder].tag!('nationality', 'Danish') }
-    xml = authors(:david).to_xml(:procs => [ proc ])
-    assert_match %r{<nationality>Danish</nationality>}, xml
-  end
-
-  def test_dual_arity_procs_are_called_on_object
-    proc = Proc.new { |options, record| options[:builder].tag!('name-reverse', record.name.reverse) }
-    xml = authors(:david).to_xml(:procs => [ proc ])
-    assert_match %r{<name-reverse>divaD</name-reverse>}, xml
-  end
-
-  def test_top_level_procs_arent_applied_to_associations
-    author_proc = Proc.new { |options| options[:builder].tag!('nationality', 'Danish') }
-    xml = authors(:david).to_xml(:procs => [ author_proc ], :include => :posts, :indent => 2)
-
-    assert_match %r{^  <nationality>Danish</nationality>}, xml
-    assert_no_match %r{^ {6}<nationality>Danish</nationality>}, xml
-  end
-
-  def test_procs_on_included_associations_are_called
-    posts_proc = Proc.new { |options| options[:builder].tag!('copyright', 'DHH') }
-    xml = authors(:david).to_xml(
-      :indent => 2,
-      :include => {
-        :posts => { :procs => [ posts_proc ] }
-      }
-    )
-
-    assert_no_match %r{^  <copyright>DHH</copyright>}, xml
-    assert_match %r{^ {6}<copyright>DHH</copyright>}, xml
-  end
-
-  def test_should_include_empty_has_many_as_empty_array
-    authors(:david).posts.delete_all
-    xml = authors(:david).to_xml :include=>:posts, :indent => 2
-
-    assert_equal [], Hash.from_xml(xml)['author']['posts']
-    assert_match %r{^  <posts type="array"/>}, xml
-  end
-
-  def test_should_has_many_array_elements_should_include_type_when_different_from_guessed_value
-    xml = authors(:david).to_xml :include=>:posts_with_comments, :indent => 2
-
-    assert Hash.from_xml(xml)
-    assert_match %r{^  <posts-with-comments type="array">}, xml
-    assert_match %r{^    <posts-with-comment type="Post">}, xml
-    assert_match %r{^    <posts-with-comment type="StiPost">}, xml
-
-    types = Hash.from_xml(xml)['author']['posts_with_comments'].collect {|t| t['type'] }
-    assert types.include?('SpecialPost')
-    assert types.include?('Post')
-    assert types.include?('StiPost')
-  end
-
-  def test_should_produce_xml_for_methods_returning_array
-    xml = authors(:david).to_xml(:methods => :social)
-    array = Hash.from_xml(xml)['author']['social']
-    assert_equal 2, array.size
-    assert array.include? 'twitter'
-    assert array.include? 'github'
-  end
-
-  def test_should_support_aliased_attributes
-    xml = Author.select("name as firstname").to_xml
-    Author.all.each do |author|
-      assert xml.include?(%(<firstname>#{author.name}</firstname>)), xml
-    end
-  end
-
-  def test_array_to_xml_including_has_many_association
-    xml = [ topics(:first), topics(:second) ].to_xml(:indent => 0, :skip_instruct => true, :include => :replies)
-    assert xml.include?(%(<replies type="array"><reply>))
-  end
-
-  def test_array_to_xml_including_methods
-    xml = [ topics(:first), topics(:second) ].to_xml(:indent => 0, :skip_instruct => true, :methods => [ :topic_id ])
-    assert xml.include?(%(<topic-id type="integer">#{topics(:first).topic_id}</topic-id>)), xml
-    assert xml.include?(%(<topic-id type="integer">#{topics(:second).topic_id}</topic-id>)), xml
-  end
-
-  def test_array_to_xml_including_has_one_association
-    xml = [ companies(:first_firm), companies(:rails_core) ].to_xml(:indent => 0, :skip_instruct => true, :include => :account)
-    assert xml.include?(companies(:first_firm).account.to_xml(:indent => 0, :skip_instruct => true))
-    assert xml.include?(companies(:rails_core).account.to_xml(:indent => 0, :skip_instruct => true))
-  end
-
-  def test_array_to_xml_including_belongs_to_association
-    xml = [ companies(:first_client), companies(:second_client), companies(:another_client) ].to_xml(:indent => 0, :skip_instruct => true, :include => :firm)
-    assert xml.include?(companies(:first_client).to_xml(:indent => 0, :skip_instruct => true))
-    assert xml.include?(companies(:second_client).firm.to_xml(:indent => 0, :skip_instruct => true))
-    assert xml.include?(companies(:another_client).firm.to_xml(:indent => 0, :skip_instruct => true))
-  end
-end
diff --git a/activerecord/test/cases/yaml_serialization_test.rb b/activerecord/test/cases/yaml_serialization_test.rb
index 56909a8630..60ebdce178 100644
--- a/activerecord/test/cases/yaml_serialization_test.rb
+++ b/activerecord/test/cases/yaml_serialization_test.rb
@@ -1,15 +1,17 @@
-require 'cases/helper'
-require 'models/topic'
-require 'models/reply'
-require 'models/post'
-require 'models/author'
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/topic"
+require "models/reply"
+require "models/post"
+require "models/author"
 
 class YamlSerializationTest < ActiveRecord::TestCase
-  fixtures :topics, :authors, :posts
+  fixtures :topics, :authors, :author_addresses, :posts
 
   def test_to_yaml_with_time_with_zone_should_not_raise_exception
     with_timezone_config aware_attributes: true, zone: "Pacific Time (US & Canada)" do
-      topic = Topic.new(:written_on => DateTime.now)
+      topic = Topic.new(written_on: DateTime.now)
       assert_nothing_raised { topic.to_yaml }
     end
   end
@@ -22,8 +24,8 @@ class YamlSerializationTest < ActiveRecord::TestCase
   end
 
   def test_roundtrip_serialized_column
-    topic = Topic.new(:content => {:omg=>:lol})
-    assert_equal({:omg=>:lol}, YAML.load(YAML.dump(topic)).content)
+    topic = Topic.new(content: { omg: :lol })
+    assert_equal({ omg: :lol }, YAML.load(YAML.dump(topic)).content)
   end
 
   def test_psych_roundtrip
@@ -67,16 +69,16 @@ class YamlSerializationTest < ActiveRecord::TestCase
     assert_not topic.new_record?, "Saved records are not new"
     assert_not YAML.load(YAML.dump(topic)).new_record?, "Saved record should not be new after deserialization"
 
-    topic = Topic.select('title').last
+    topic = Topic.select("title").last
 
     assert_not topic.new_record?, "Loaded records without ID are not new"
     assert_not YAML.load(YAML.dump(topic)).new_record?, "Record should not be new after deserialization"
   end
 
   def test_types_of_virtual_columns_are_not_changed_on_round_trip
-    author = Author.select('authors.*, count(posts.id) as posts_count')
+    author = Author.select("authors.*, count(posts.id) as posts_count")
       .joins(:posts)
-      .group('authors.id')
+      .group("authors.id")
       .first
     dumped = YAML.load(YAML.dump(author))
 
@@ -88,14 +90,14 @@ class YamlSerializationTest < ActiveRecord::TestCase
     coder = {}
     Topic.first.encode_with(coder)
 
-    assert coder['active_record_yaml_version']
+    assert coder["active_record_yaml_version"]
   end
 
   def test_deserializing_rails_41_yaml
     topic = YAML.load(yaml_fixture("rails_4_1"))
 
-    assert topic.new_record?
-    assert_equal nil, topic.id
+    assert_predicate topic, :new_record?
+    assert_nil topic.id
     assert_equal "The First Topic", topic.title
     assert_equal({ omg: :lol }, topic.content)
   end
@@ -103,19 +105,37 @@ class YamlSerializationTest < ActiveRecord::TestCase
   def test_deserializing_rails_4_2_0_yaml
     topic = YAML.load(yaml_fixture("rails_4_2_0"))
 
-    assert_not topic.new_record?
+    assert_not_predicate topic, :new_record?
     assert_equal 1, topic.id
     assert_equal "The First Topic", topic.title
     assert_equal("Have a nice day", topic.content)
   end
 
-  private
+  def test_yaml_encoding_keeps_mutations
+    author = Author.first
+    author.name = "Sean"
+    dumped = YAML.load(YAML.dump(author))
 
-  def yaml_fixture(file_name)
-    path = File.expand_path(
-      "../../support/yaml_compatibility_fixtures/#{file_name}.yml",
-      __FILE__
-    )
-    File.read(path)
+    assert_equal "Sean", dumped.name
+    assert_equal author.name_was, dumped.name_was
+    assert_equal author.changes, dumped.changes
   end
+
+  def test_yaml_encoding_keeps_false_values
+    topic = Topic.first
+    topic.approved = false
+    dumped = YAML.load(YAML.dump(topic))
+
+    assert_equal false, dumped.approved
+  end
+
+  private
+
+    def yaml_fixture(file_name)
+      path = File.expand_path(
+        "../support/yaml_compatibility_fixtures/#{file_name}.yml",
+        __dir__
+      )
+      File.read(path)
+    end
 end
diff --git a/activerecord/test/config.example.yml b/activerecord/test/config.example.yml
index e3b55d640e..18347cd07d 100644
--- a/activerecord/test/config.example.yml
+++ b/activerecord/test/config.example.yml
@@ -51,23 +51,15 @@ connections:
       password: arunit
       database: arunit2
 
-  mysql:
-    arunit:
-      username: rails
-      encoding: utf8
-      collation: utf8_unicode_ci
-    arunit2:
-      username: rails
-      encoding: utf8
-
   mysql2:
     arunit:
       username: rails
-      encoding: utf8
-      collation: utf8_unicode_ci
+      encoding: utf8mb4
+      collation: utf8mb4_unicode_ci
     arunit2:
       username: rails
-      encoding: utf8
+      encoding: utf8mb4
+      collation: utf8mb4_general_ci
 
   oracle:
      arunit:
@@ -86,6 +78,9 @@ connections:
   postgresql:
     arunit:
       min_messages: warning
+    arunit_without_prepared_statements:
+      min_messages: warning
+      prepared_statements: false
     arunit2:
       min_messages: warning
 
diff --git a/activerecord/test/config.rb b/activerecord/test/config.rb
index 6e2e8b2145..72cdfb16ef 100644
--- a/activerecord/test/config.rb
+++ b/activerecord/test/config.rb
@@ -1,4 +1,6 @@
-TEST_ROOT       = File.expand_path(File.dirname(__FILE__))
+# frozen_string_literal: true
+
+TEST_ROOT       = __dir__
 ASSETS_ROOT     = TEST_ROOT + "/assets"
 FIXTURES_ROOT   = TEST_ROOT + "/fixtures"
 MIGRATIONS_ROOT = TEST_ROOT + "/migrations"
diff --git a/activerecord/test/fixtures/.gitignore b/activerecord/test/fixtures/.gitignore
deleted file mode 100644
index 885029a512..0000000000
--- a/activerecord/test/fixtures/.gitignore
+++ /dev/null
@@ -1 +0,0 @@
-*.sqlite*
\ No newline at end of file
diff --git a/activerecord/test/fixtures/all/namespaced/accounts.yml b/activerecord/test/fixtures/all/namespaced/accounts.yml
new file mode 100644
index 0000000000..9e341a15af
--- /dev/null
+++ b/activerecord/test/fixtures/all/namespaced/accounts.yml
@@ -0,0 +1,2 @@
+signals37:
+  name: 37signals
diff --git a/activerecord/test/fixtures/author_addresses.yml b/activerecord/test/fixtures/author_addresses.yml
index 7b90572187..cf75e5998d 100644
--- a/activerecord/test/fixtures/author_addresses.yml
+++ b/activerecord/test/fixtures/author_addresses.yml
@@ -3,3 +3,9 @@ david_address:
 
 david_address_extra:
   id: 2
+
+mary_address:
+  id: 3
+
+bob_address:
+  id: 4
diff --git a/activerecord/test/fixtures/authors.yml b/activerecord/test/fixtures/authors.yml
index 832236a486..41c124179e 100644
--- a/activerecord/test/fixtures/authors.yml
+++ b/activerecord/test/fixtures/authors.yml
@@ -9,7 +9,9 @@ david:
 mary:
   id: 2
   name: Mary
+  author_address_id: 3
 
 bob:
   id: 3
   name: Bob
+  author_address_id: 4
diff --git a/activerecord/test/fixtures/bad_posts.yml b/activerecord/test/fixtures/bad_posts.yml
new file mode 100644
index 0000000000..addee8e3bf
--- /dev/null
+++ b/activerecord/test/fixtures/bad_posts.yml
@@ -0,0 +1,9 @@
+# Please do not use this fixture without `set_fixture_class` as Post
+
+_fixture:
+  model_class: BadPostModel
+
+bad_welcome:
+  author_id: 1
+  title: Welcome to the another weblog
+  body: It's really nice today
diff --git a/activerecord/test/fixtures/binaries.yml b/activerecord/test/fixtures/binaries.yml
index ec8f2facdc..53b7883369 100644
--- a/activerecord/test/fixtures/binaries.yml
+++ b/activerecord/test/fixtures/binaries.yml
@@ -131,3 +131,7 @@ flowers:
     SgCUASgCUASgCUASgAC74PbXOTvE5/En7jpSoLE8/wBn7uPJjKyj46T9D/NT
     pKsXyQzxNpdNP0/akB5484WkMKh4RfXG4UafNmH7b0UxWMrb7Nxg6rl9Z/Im
     w+vWq0iscQwxQroiUIvkKsRZQBKAJQBKAJQB/9k=
+
+binary_helper:
+  id: 2
+  data: <%= binary(ASSETS_ROOT + "/flowers.jpg") %>
diff --git a/activerecord/test/fixtures/books.yml b/activerecord/test/fixtures/books.yml
index a304fba399..699623a6f9 100644
--- a/activerecord/test/fixtures/books.yml
+++ b/activerecord/test/fixtures/books.yml
@@ -9,6 +9,7 @@ awdr:
   author_visibility: :visible
   illustrator_visibility: :visible
   font_size: :medium
+  difficulty: :medium
 
 rfr:
   author_id: 1
@@ -24,6 +25,7 @@ ddd:
   name: "Domain-Driven Design"
   format: "hardcover"
   status: 2
+  read_status: "forgotten"
 
 tlg:
   author_id: 1
diff --git a/activerecord/test/fixtures/citations.yml b/activerecord/test/fixtures/citations.yml
new file mode 100644
index 0000000000..396099621c
--- /dev/null
+++ b/activerecord/test/fixtures/citations.yml
@@ -0,0 +1,5 @@
+<% 65536.times do |i| %>
+fixture_no_<%= i %>:
+  id: <%= i %>
+  book2_id: <%= i*i %>
+<% end %>
diff --git a/activerecord/test/fixtures/content.yml b/activerecord/test/fixtures/content.yml
new file mode 100644
index 0000000000..0d12ee03dc
--- /dev/null
+++ b/activerecord/test/fixtures/content.yml
@@ -0,0 +1,3 @@
+content:
+  id: 1
+  title: How to use Rails
diff --git a/activerecord/test/fixtures/content_positions.yml b/activerecord/test/fixtures/content_positions.yml
new file mode 100644
index 0000000000..9e85773f8e
--- /dev/null
+++ b/activerecord/test/fixtures/content_positions.yml
@@ -0,0 +1,3 @@
+content_positions:
+  id: 1
+  content_id: 1
diff --git a/activerecord/test/fixtures/customers.yml b/activerecord/test/fixtures/customers.yml
index 0399ff83b9..7d6c1366d0 100644
--- a/activerecord/test/fixtures/customers.yml
+++ b/activerecord/test/fixtures/customers.yml
@@ -23,4 +23,13 @@ barney:
   address_street: Quiet Road
   address_city: Peaceful Town
   address_country: Tranquil Land
-  gps_location: NULL
\ No newline at end of file
+  gps_location: NULL
+
+mary:
+  id: 4
+  name: Mary
+  balance: 1
+  address_street: Funny Street
+  address_city: Peaceful Town
+  address_country: Nation Land
+  gps_location: NULL
diff --git a/activerecord/test/fixtures/memberships.yml b/activerecord/test/fixtures/memberships.yml
index a5d52bd438..f7ca227533 100644
--- a/activerecord/test/fixtures/memberships.yml
+++ b/activerecord/test/fixtures/memberships.yml
@@ -26,6 +26,13 @@ blarpy_winkup_crazy_club:
   favourite: false
   type: CurrentMembership
 
+super_membership_of_boring_club:
+  joined_on: <%= 3.weeks.ago.to_s(:db) %>
+  club: boring_club
+  member_id: 1
+  favourite: false
+  type: SuperMembership
+
 selected_membership_of_boring_club:
   joined_on: <%= 3.weeks.ago.to_s(:db) %>
   club: boring_club
diff --git a/activerecord/test/fixtures/minimalistics.yml b/activerecord/test/fixtures/minimalistics.yml
index c3ec546209..83df0551bc 100644
--- a/activerecord/test/fixtures/minimalistics.yml
+++ b/activerecord/test/fixtures/minimalistics.yml
@@ -1,2 +1,5 @@
+zero:
+  id: 0
+
 first:
   id: 1
diff --git a/activerecord/test/fixtures/naked/yml/courses_with_invalid_key.yml b/activerecord/test/fixtures/naked/yml/courses_with_invalid_key.yml
new file mode 100644
index 0000000000..6f9da79b45
--- /dev/null
+++ b/activerecord/test/fixtures/naked/yml/courses_with_invalid_key.yml
@@ -0,0 +1,3 @@
+one:
+  id: 1
+two: ['not a hash']
diff --git a/activerecord/test/fixtures/naked/yml/parrots.yml b/activerecord/test/fixtures/naked/yml/parrots.yml
new file mode 100644
index 0000000000..76f66e01ae
--- /dev/null
+++ b/activerecord/test/fixtures/naked/yml/parrots.yml
@@ -0,0 +1,3 @@
+george:
+  arrr: "Curious George"
+  foobar: Foobar
diff --git a/activerecord/test/fixtures/naked/yml/trees.yml b/activerecord/test/fixtures/naked/yml/trees.yml
new file mode 100644
index 0000000000..d163b98f21
--- /dev/null
+++ b/activerecord/test/fixtures/naked/yml/trees.yml
@@ -0,0 +1,3 @@
+root:
+  :id: 1
+  :name: The Root
diff --git a/activerecord/test/fixtures/other_comments.yml b/activerecord/test/fixtures/other_comments.yml
new file mode 100644
index 0000000000..55e8216ec7
--- /dev/null
+++ b/activerecord/test/fixtures/other_comments.yml
@@ -0,0 +1,6 @@
+_fixture:
+  model_class: Comment
+
+second_greetings:
+  post: second_welcome
+  body: Thank you for the second welcome
diff --git a/activerecord/test/fixtures/other_dogs.yml b/activerecord/test/fixtures/other_dogs.yml
new file mode 100644
index 0000000000..b576861929
--- /dev/null
+++ b/activerecord/test/fixtures/other_dogs.yml
@@ -0,0 +1,2 @@
+lassie:
+  id: 1
diff --git a/activerecord/test/fixtures/other_posts.yml b/activerecord/test/fixtures/other_posts.yml
new file mode 100644
index 0000000000..3e11a33802
--- /dev/null
+++ b/activerecord/test/fixtures/other_posts.yml
@@ -0,0 +1,8 @@
+_fixture:
+  model_class: Post
+
+second_welcome:
+  author_id: 1
+  title: Welcome to the another weblog
+  body: It's really nice today
+  comments_count: 1
diff --git a/activerecord/test/fixtures/posts.yml b/activerecord/test/fixtures/posts.yml
index 86d46f753a..8d7e1e0ae7 100644
--- a/activerecord/test/fixtures/posts.yml
+++ b/activerecord/test/fixtures/posts.yml
@@ -28,6 +28,7 @@ sti_comments:
   author_id: 1
   title: sti comments
   body: hello
+  comments_count: 5
   type: Post
 
 sti_post_and_comments:
@@ -35,6 +36,7 @@ sti_post_and_comments:
   author_id: 1
   title: sti me
   body: hello
+  comments_count: 2
   type: StiPost
 
 sti_habtm:
@@ -50,6 +52,8 @@ eager_other:
   title: eager loading with OR'd conditions
   body: hello
   type: Post
+  comments_count: 1
+  tags_count: 3
 
 misc_by_bob:
   id: 8
@@ -57,6 +61,7 @@ misc_by_bob:
   title: misc post by bob
   body: hello
   type: Post
+  tags_count: 1
 
 misc_by_mary:
   id: 9
@@ -64,6 +69,7 @@ misc_by_mary:
   title: misc post by mary
   body: hello
   type: Post
+  tags_count: 1
 
 other_by_bob:
   id: 10
@@ -71,6 +77,7 @@ other_by_bob:
   title: other post by bob
   body: hello
   type: Post
+  tags_count: 1
 
 other_by_mary:
   id: 11
@@ -78,3 +85,4 @@ other_by_mary:
   title: other post by mary
   body: hello
   type: Post
+  tags_count: 1
diff --git a/activerecord/test/fixtures/price_estimates.yml b/activerecord/test/fixtures/price_estimates.yml
index 1149ab17a2..406d65a142 100644
--- a/activerecord/test/fixtures/price_estimates.yml
+++ b/activerecord/test/fixtures/price_estimates.yml
@@ -1,7 +1,16 @@
-saphire_1:
+sapphire_1:
   price: 10
   estimate_of: sapphire (Treasure)
 
 sapphire_2:
   price: 20
   estimate_of: sapphire (Treasure)
+
+diamond:
+  price: 30
+  estimate_of: diamond (Treasure)
+
+honda:
+  price: 40
+  estimate_of_type: Car
+  estimate_of_id: 1
diff --git a/activerecord/test/fixtures/reserved_words/values.yml b/activerecord/test/fixtures/reserved_words/values.yml
index 7d109609ab..9ed9e5edc5 100644
--- a/activerecord/test/fixtures/reserved_words/values.yml
+++ b/activerecord/test/fixtures/reserved_words/values.yml
@@ -1,7 +1,7 @@
 values1:
-  id: 1
+  as: 1
   group_id: 2
 
 values2:
-  id: 2
+  as: 2
   group_id: 1
diff --git a/activerecord/test/fixtures/sponsors.yml b/activerecord/test/fixtures/sponsors.yml
index 2da541c539..02ddb8dd38 100644
--- a/activerecord/test/fixtures/sponsors.yml
+++ b/activerecord/test/fixtures/sponsors.yml
@@ -10,3 +10,6 @@ crazy_club_sponsor_for_groucho:
   sponsor_club: crazy_club
   sponsorable_id: 3
   sponsorable_type: Member
+sponsor_for_author_david:
+  sponsorable_id: 1
+  sponsorable_type: Author
diff --git a/activerecord/test/fixtures/subscribers.yml b/activerecord/test/fixtures/subscribers.yml
index c6a8c2fa24..0f6e0cd48e 100644
--- a/activerecord/test/fixtures/subscribers.yml
+++ b/activerecord/test/fixtures/subscribers.yml
@@ -6,6 +6,6 @@ second:
   nick: webster132
   name: David Heinemeier Hansson
 
-thrid:
+third:
   nick: swistak
   name: Marcin Raczkowski
\ No newline at end of file
diff --git a/activerecord/test/fixtures/teapots.yml b/activerecord/test/fixtures/teapots.yml
deleted file mode 100644
index ff515beb45..0000000000
--- a/activerecord/test/fixtures/teapots.yml
+++ /dev/null
@@ -1,3 +0,0 @@
-bob:
-  id: 1
-  name: Bob
diff --git a/activerecord/test/migrations/10_urban/9_add_expressions.rb b/activerecord/test/migrations/10_urban/9_add_expressions.rb
index 79a342e574..4b0d5fb6fa 100644
--- a/activerecord/test/migrations/10_urban/9_add_expressions.rb
+++ b/activerecord/test/migrations/10_urban/9_add_expressions.rb
@@ -1,4 +1,6 @@
-class AddExpressions < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class AddExpressions < ActiveRecord::Migration::Current
   def self.up
     create_table("expressions") do |t|
       t.column :expression, :string
diff --git a/activerecord/test/migrations/decimal/1_give_me_big_numbers.rb b/activerecord/test/migrations/decimal/1_give_me_big_numbers.rb
index 0aed7cbd84..7d4233fe31 100644
--- a/activerecord/test/migrations/decimal/1_give_me_big_numbers.rb
+++ b/activerecord/test/migrations/decimal/1_give_me_big_numbers.rb
@@ -1,10 +1,12 @@
-class GiveMeBigNumbers < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class GiveMeBigNumbers < ActiveRecord::Migration::Current
   def self.up
     create_table :big_numbers do |table|
-      table.column :bank_balance, :decimal, :precision => 10, :scale => 2
-      table.column :big_bank_balance, :decimal, :precision => 15, :scale => 2
-      table.column :world_population, :decimal, :precision => 10
-      table.column :my_house_population, :decimal, :precision => 2
+      table.column :bank_balance, :decimal, precision: 10, scale: 2
+      table.column :big_bank_balance, :decimal, precision: 15, scale: 2
+      table.column :world_population, :decimal, precision: 20
+      table.column :my_house_population, :decimal, precision: 2
       table.column :value_of_e, :decimal
     end
   end
diff --git a/activerecord/test/migrations/empty/.gitkeep b/activerecord/test/migrations/empty/.keep
index e69de29bb2..e69de29bb2 100644
--- a/activerecord/test/migrations/empty/.gitkeep
+++ b/activerecord/test/migrations/empty/.keep
diff --git a/activerecord/test/migrations/magic/1_currencies_have_symbols.rb b/activerecord/test/migrations/magic/1_currencies_have_symbols.rb
index c066c068c2..2ba2875751 100644
--- a/activerecord/test/migrations/magic/1_currencies_have_symbols.rb
+++ b/activerecord/test/migrations/magic/1_currencies_have_symbols.rb
@@ -1,9 +1,10 @@
+# frozen_string_literal: true
 # coding: ISO-8859-15
 
-class CurrenciesHaveSymbols < ActiveRecord::Migration
+class CurrenciesHaveSymbols < ActiveRecord::Migration::Current
   def self.up
-    # We use � for default currency symbol
-    add_column "currencies", "symbol", :string, :default => "�"
+    # We use € for default currency symbol
+    add_column "currencies", "symbol", :string, default: "€"
   end
 
   def self.down
diff --git a/activerecord/test/migrations/missing/1000_people_have_middle_names.rb b/activerecord/test/migrations/missing/1000_people_have_middle_names.rb
index 4b83d61beb..d3c9b127fb 100644
--- a/activerecord/test/migrations/missing/1000_people_have_middle_names.rb
+++ b/activerecord/test/migrations/missing/1000_people_have_middle_names.rb
@@ -1,4 +1,6 @@
-class PeopleHaveMiddleNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class PeopleHaveMiddleNames < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "middle_name", :string
   end
diff --git a/activerecord/test/migrations/missing/1_people_have_last_names.rb b/activerecord/test/migrations/missing/1_people_have_last_names.rb
index 68209f3ce9..bd5f5ea11e 100644
--- a/activerecord/test/migrations/missing/1_people_have_last_names.rb
+++ b/activerecord/test/migrations/missing/1_people_have_last_names.rb
@@ -1,4 +1,6 @@
-class PeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class PeopleHaveLastNames < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "last_name", :string
   end
diff --git a/activerecord/test/migrations/missing/3_we_need_reminders.rb b/activerecord/test/migrations/missing/3_we_need_reminders.rb
index 25bb49cb32..4647268c6e 100644
--- a/activerecord/test/migrations/missing/3_we_need_reminders.rb
+++ b/activerecord/test/migrations/missing/3_we_need_reminders.rb
@@ -1,4 +1,6 @@
-class WeNeedReminders < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class WeNeedReminders < ActiveRecord::Migration::Current
   def self.up
     create_table("reminders") do |t|
       t.column :content, :text
diff --git a/activerecord/test/migrations/missing/4_innocent_jointable.rb b/activerecord/test/migrations/missing/4_innocent_jointable.rb
index 002a1bf2a6..8063bc0558 100644
--- a/activerecord/test/migrations/missing/4_innocent_jointable.rb
+++ b/activerecord/test/migrations/missing/4_innocent_jointable.rb
@@ -1,6 +1,8 @@
-class InnocentJointable < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class InnocentJointable < ActiveRecord::Migration::Current
   def self.up
-    create_table("people_reminders", :id => false) do |t|
+    create_table("people_reminders", id: false) do |t|
       t.column :reminder_id, :integer
       t.column :person_id, :integer
     end
diff --git a/activerecord/test/migrations/rename/1_we_need_things.rb b/activerecord/test/migrations/rename/1_we_need_things.rb
index f5484ac54f..8e71a1d996 100644
--- a/activerecord/test/migrations/rename/1_we_need_things.rb
+++ b/activerecord/test/migrations/rename/1_we_need_things.rb
@@ -1,4 +1,6 @@
-class WeNeedThings < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class WeNeedThings < ActiveRecord::Migration::Current
   def self.up
     create_table("things") do |t|
       t.column :content, :text
diff --git a/activerecord/test/migrations/rename/2_rename_things.rb b/activerecord/test/migrations/rename/2_rename_things.rb
index 533a113ea8..110fe3f0fa 100644
--- a/activerecord/test/migrations/rename/2_rename_things.rb
+++ b/activerecord/test/migrations/rename/2_rename_things.rb
@@ -1,4 +1,6 @@
-class RenameThings < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class RenameThings < ActiveRecord::Migration::Current
   def self.up
     rename_table "things", "awesome_things"
   end
diff --git a/activerecord/test/migrations/to_copy/1_people_have_hobbies.rb b/activerecord/test/migrations/to_copy/1_people_have_hobbies.rb
index 639841f663..badccf65cc 100644
--- a/activerecord/test/migrations/to_copy/1_people_have_hobbies.rb
+++ b/activerecord/test/migrations/to_copy/1_people_have_hobbies.rb
@@ -1,4 +1,6 @@
-class PeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class PeopleHaveHobbies < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "hobbies", :text
   end
diff --git a/activerecord/test/migrations/to_copy/2_people_have_descriptions.rb b/activerecord/test/migrations/to_copy/2_people_have_descriptions.rb
index b3d0b30640..1d19d5d6f4 100644
--- a/activerecord/test/migrations/to_copy/2_people_have_descriptions.rb
+++ b/activerecord/test/migrations/to_copy/2_people_have_descriptions.rb
@@ -1,4 +1,6 @@
-class PeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class PeopleHaveDescriptions < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "description", :text
   end
diff --git a/activerecord/test/migrations/to_copy2/1_create_articles.rb b/activerecord/test/migrations/to_copy2/1_create_articles.rb
index 0f048d90f7..85c166b319 100644
--- a/activerecord/test/migrations/to_copy2/1_create_articles.rb
+++ b/activerecord/test/migrations/to_copy2/1_create_articles.rb
@@ -1,4 +1,6 @@
-class CreateArticles < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class CreateArticles < ActiveRecord::Migration::Current
   def self.up
   end
 
diff --git a/activerecord/test/migrations/to_copy2/2_create_comments.rb b/activerecord/test/migrations/to_copy2/2_create_comments.rb
index 0f048d90f7..1d213a1705 100644
--- a/activerecord/test/migrations/to_copy2/2_create_comments.rb
+++ b/activerecord/test/migrations/to_copy2/2_create_comments.rb
@@ -1,4 +1,6 @@
-class CreateArticles < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class CreateComments < ActiveRecord::Migration::Current
   def self.up
   end
 
diff --git a/activerecord/test/migrations/to_copy_with_name_collision/1_people_have_hobbies.rb b/activerecord/test/migrations/to_copy_with_name_collision/1_people_have_hobbies.rb
index e438cf5999..d9fef596f5 100644
--- a/activerecord/test/migrations/to_copy_with_name_collision/1_people_have_hobbies.rb
+++ b/activerecord/test/migrations/to_copy_with_name_collision/1_people_have_hobbies.rb
@@ -1,4 +1,6 @@
-class PeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class PeopleHaveHobbies < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "hobbies", :string
   end
diff --git a/activerecord/test/migrations/to_copy_with_timestamps/20090101010101_people_have_hobbies.rb b/activerecord/test/migrations/to_copy_with_timestamps/20090101010101_people_have_hobbies.rb
index 639841f663..badccf65cc 100644
--- a/activerecord/test/migrations/to_copy_with_timestamps/20090101010101_people_have_hobbies.rb
+++ b/activerecord/test/migrations/to_copy_with_timestamps/20090101010101_people_have_hobbies.rb
@@ -1,4 +1,6 @@
-class PeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class PeopleHaveHobbies < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "hobbies", :text
   end
diff --git a/activerecord/test/migrations/to_copy_with_timestamps/20090101010202_people_have_descriptions.rb b/activerecord/test/migrations/to_copy_with_timestamps/20090101010202_people_have_descriptions.rb
index b3d0b30640..1d19d5d6f4 100644
--- a/activerecord/test/migrations/to_copy_with_timestamps/20090101010202_people_have_descriptions.rb
+++ b/activerecord/test/migrations/to_copy_with_timestamps/20090101010202_people_have_descriptions.rb
@@ -1,4 +1,6 @@
-class PeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class PeopleHaveDescriptions < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "description", :text
   end
diff --git a/activerecord/test/migrations/to_copy_with_timestamps2/20090101010101_create_articles.rb b/activerecord/test/migrations/to_copy_with_timestamps2/20090101010101_create_articles.rb
index 0f048d90f7..85c166b319 100644
--- a/activerecord/test/migrations/to_copy_with_timestamps2/20090101010101_create_articles.rb
+++ b/activerecord/test/migrations/to_copy_with_timestamps2/20090101010101_create_articles.rb
@@ -1,4 +1,6 @@
-class CreateArticles < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class CreateArticles < ActiveRecord::Migration::Current
   def self.up
   end
 
diff --git a/activerecord/test/migrations/to_copy_with_timestamps2/20090101010202_create_comments.rb b/activerecord/test/migrations/to_copy_with_timestamps2/20090101010202_create_comments.rb
index 2b048edbb5..1d213a1705 100644
--- a/activerecord/test/migrations/to_copy_with_timestamps2/20090101010202_create_comments.rb
+++ b/activerecord/test/migrations/to_copy_with_timestamps2/20090101010202_create_comments.rb
@@ -1,4 +1,6 @@
-class CreateComments < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class CreateComments < ActiveRecord::Migration::Current
   def self.up
   end
 
diff --git a/activerecord/test/migrations/valid/1_valid_people_have_last_names.rb b/activerecord/test/migrations/valid/1_valid_people_have_last_names.rb
index 06cb911117..3bedcdcdf0 100644
--- a/activerecord/test/migrations/valid/1_valid_people_have_last_names.rb
+++ b/activerecord/test/migrations/valid/1_valid_people_have_last_names.rb
@@ -1,4 +1,6 @@
-class ValidPeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class ValidPeopleHaveLastNames < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "last_name", :string
   end
diff --git a/activerecord/test/migrations/valid/2_we_need_reminders.rb b/activerecord/test/migrations/valid/2_we_need_reminders.rb
index 25bb49cb32..4647268c6e 100644
--- a/activerecord/test/migrations/valid/2_we_need_reminders.rb
+++ b/activerecord/test/migrations/valid/2_we_need_reminders.rb
@@ -1,4 +1,6 @@
-class WeNeedReminders < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class WeNeedReminders < ActiveRecord::Migration::Current
   def self.up
     create_table("reminders") do |t|
       t.column :content, :text
diff --git a/activerecord/test/migrations/valid/3_innocent_jointable.rb b/activerecord/test/migrations/valid/3_innocent_jointable.rb
index 002a1bf2a6..8063bc0558 100644
--- a/activerecord/test/migrations/valid/3_innocent_jointable.rb
+++ b/activerecord/test/migrations/valid/3_innocent_jointable.rb
@@ -1,6 +1,8 @@
-class InnocentJointable < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class InnocentJointable < ActiveRecord::Migration::Current
   def self.up
-    create_table("people_reminders", :id => false) do |t|
+    create_table("people_reminders", id: false) do |t|
       t.column :reminder_id, :integer
       t.column :person_id, :integer
     end
diff --git a/activerecord/test/migrations/valid_with_subdirectories/1_valid_people_have_last_names.rb b/activerecord/test/migrations/valid_with_subdirectories/1_valid_people_have_last_names.rb
index 06cb911117..3bedcdcdf0 100644
--- a/activerecord/test/migrations/valid_with_subdirectories/1_valid_people_have_last_names.rb
+++ b/activerecord/test/migrations/valid_with_subdirectories/1_valid_people_have_last_names.rb
@@ -1,4 +1,6 @@
-class ValidPeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class ValidPeopleHaveLastNames < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "last_name", :string
   end
diff --git a/activerecord/test/migrations/valid_with_subdirectories/sub/2_we_need_reminders.rb b/activerecord/test/migrations/valid_with_subdirectories/sub/2_we_need_reminders.rb
index 25bb49cb32..4647268c6e 100644
--- a/activerecord/test/migrations/valid_with_subdirectories/sub/2_we_need_reminders.rb
+++ b/activerecord/test/migrations/valid_with_subdirectories/sub/2_we_need_reminders.rb
@@ -1,4 +1,6 @@
-class WeNeedReminders < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class WeNeedReminders < ActiveRecord::Migration::Current
   def self.up
     create_table("reminders") do |t|
       t.column :content, :text
diff --git a/activerecord/test/migrations/valid_with_subdirectories/sub1/3_innocent_jointable.rb b/activerecord/test/migrations/valid_with_subdirectories/sub1/3_innocent_jointable.rb
index 002a1bf2a6..8063bc0558 100644
--- a/activerecord/test/migrations/valid_with_subdirectories/sub1/3_innocent_jointable.rb
+++ b/activerecord/test/migrations/valid_with_subdirectories/sub1/3_innocent_jointable.rb
@@ -1,6 +1,8 @@
-class InnocentJointable < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class InnocentJointable < ActiveRecord::Migration::Current
   def self.up
-    create_table("people_reminders", :id => false) do |t|
+    create_table("people_reminders", id: false) do |t|
       t.column :reminder_id, :integer
       t.column :person_id, :integer
     end
diff --git a/activerecord/test/migrations/valid_with_timestamps/20100101010101_valid_with_timestamps_people_have_last_names.rb b/activerecord/test/migrations/valid_with_timestamps/20100101010101_valid_with_timestamps_people_have_last_names.rb
index 1da99ceaba..b938847170 100644
--- a/activerecord/test/migrations/valid_with_timestamps/20100101010101_valid_with_timestamps_people_have_last_names.rb
+++ b/activerecord/test/migrations/valid_with_timestamps/20100101010101_valid_with_timestamps_people_have_last_names.rb
@@ -1,4 +1,6 @@
-class ValidWithTimestampsPeopleHaveLastNames < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class ValidWithTimestampsPeopleHaveLastNames < ActiveRecord::Migration::Current
   def self.up
     add_column "people", "last_name", :string
   end
diff --git a/activerecord/test/migrations/valid_with_timestamps/20100201010101_valid_with_timestamps_we_need_reminders.rb b/activerecord/test/migrations/valid_with_timestamps/20100201010101_valid_with_timestamps_we_need_reminders.rb
index cb6d735c8b..94551e8208 100644
--- a/activerecord/test/migrations/valid_with_timestamps/20100201010101_valid_with_timestamps_we_need_reminders.rb
+++ b/activerecord/test/migrations/valid_with_timestamps/20100201010101_valid_with_timestamps_we_need_reminders.rb
@@ -1,4 +1,6 @@
-class ValidWithTimestampsWeNeedReminders < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class ValidWithTimestampsWeNeedReminders < ActiveRecord::Migration::Current
   def self.up
     create_table("reminders") do |t|
       t.column :content, :text
diff --git a/activerecord/test/migrations/valid_with_timestamps/20100301010101_valid_with_timestamps_innocent_jointable.rb b/activerecord/test/migrations/valid_with_timestamps/20100301010101_valid_with_timestamps_innocent_jointable.rb
index 4bd4b4714d..672edc5253 100644
--- a/activerecord/test/migrations/valid_with_timestamps/20100301010101_valid_with_timestamps_innocent_jointable.rb
+++ b/activerecord/test/migrations/valid_with_timestamps/20100301010101_valid_with_timestamps_innocent_jointable.rb
@@ -1,6 +1,8 @@
-class ValidWithTimestampsInnocentJointable < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class ValidWithTimestampsInnocentJointable < ActiveRecord::Migration::Current
   def self.up
-    create_table("people_reminders", :id => false) do |t|
+    create_table("people_reminders", id: false) do |t|
       t.column :reminder_id, :integer
       t.column :person_id, :integer
     end
diff --git a/activerecord/test/migrations/version_check/20131219224947_migration_version_check.rb b/activerecord/test/migrations/version_check/20131219224947_migration_version_check.rb
index 9d46485a31..91bfbbdfd1 100644
--- a/activerecord/test/migrations/version_check/20131219224947_migration_version_check.rb
+++ b/activerecord/test/migrations/version_check/20131219224947_migration_version_check.rb
@@ -1,4 +1,6 @@
-class MigrationVersionCheck < ActiveRecord::Migration
+# frozen_string_literal: true
+
+class MigrationVersionCheck < ActiveRecord::Migration::Current
   def self.up
     raise "incorrect migration version" unless version == 20131219224947
   end
diff --git a/activerecord/test/models/account.rb b/activerecord/test/models/account.rb
new file mode 100644
index 0000000000..639e395743
--- /dev/null
+++ b/activerecord/test/models/account.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+class Account < ActiveRecord::Base
+  belongs_to :firm, class_name: "Company"
+  belongs_to :unautosaved_firm, foreign_key: "firm_id", class_name: "Firm", autosave: false
+
+  alias_attribute :available_credit, :credit_limit
+
+  def self.destroyed_account_ids
+    @destroyed_account_ids ||= Hash.new { |h, k| h[k] = [] }
+  end
+
+  # Test private kernel method through collection proxy using has_many.
+  scope :open, -> { where("firm_name = ?", "37signals") }
+  scope :available, -> { open }
+
+  before_destroy do |account|
+    if account.firm
+      Account.destroyed_account_ids[account.firm.id] << account.id
+    end
+  end
+
+  validate :check_empty_credit_limit
+
+  private
+    def check_empty_credit_limit
+      errors.add("credit_limit", :blank) if credit_limit.blank?
+    end
+
+    def private_method
+      "Sir, yes sir!"
+    end
+end
+
+class SubAccount < Account
+  def self.instantiate_instance_of(klass, attributes, column_types = {}, &block)
+    klass = superclass
+    super
+  end
+  private_class_method :instantiate_instance_of
+end
diff --git a/activerecord/test/models/admin.rb b/activerecord/test/models/admin.rb
index a38e3f4846..a40b5a33b2 100644
--- a/activerecord/test/models/admin.rb
+++ b/activerecord/test/models/admin.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 module Admin
   def self.table_name_prefix
-    'admin_'
+    "admin_"
   end
 end
diff --git a/activerecord/test/models/admin/account.rb b/activerecord/test/models/admin/account.rb
index bd23192d20..41fe2d782b 100644
--- a/activerecord/test/models/admin/account.rb
+++ b/activerecord/test/models/admin/account.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::Account < ActiveRecord::Base
   has_many :users
 end
diff --git a/activerecord/test/models/admin/randomly_named_c1.rb b/activerecord/test/models/admin/randomly_named_c1.rb
index b64ae7fc41..d89b8dd293 100644
--- a/activerecord/test/models/admin/randomly_named_c1.rb
+++ b/activerecord/test/models/admin/randomly_named_c1.rb
@@ -1,7 +1,9 @@
-class Admin::ClassNameThatDoesNotFollowCONVENTIONS1 < ActiveRecord::Base

-  self.table_name = :randomly_named_table2

-end

-

-class Admin::ClassNameThatDoesNotFollowCONVENTIONS2 < ActiveRecord::Base

-  self.table_name = :randomly_named_table3

-end

+# frozen_string_literal: true
+
+class Admin::ClassNameThatDoesNotFollowCONVENTIONS1 < ActiveRecord::Base
+  self.table_name = :randomly_named_table2
+end
+
+class Admin::ClassNameThatDoesNotFollowCONVENTIONS2 < ActiveRecord::Base
+  self.table_name = :randomly_named_table3
+end
diff --git a/activerecord/test/models/admin/user.rb b/activerecord/test/models/admin/user.rb
index 48a110bd23..691f9f11be 100644
--- a/activerecord/test/models/admin/user.rb
+++ b/activerecord/test/models/admin/user.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Admin::User < ActiveRecord::Base
   class Coder
     def initialize(default = {})
@@ -15,26 +17,32 @@ class Admin::User < ActiveRecord::Base
 
   belongs_to :account
   store :params, accessors: [ :token ], coder: YAML
-  store :settings, :accessors => [ :color, :homepage ]
+  store :settings, accessors: [ :color, :homepage ]
   store_accessor :settings, :favorite_food
-  store :preferences, :accessors => [ :remember_login ]
-  store :json_data, :accessors => [ :height, :weight ], :coder => Coder.new
-  store :json_data_empty, :accessors => [ :is_a_good_guy ], :coder => Coder.new
+  store :parent, accessors: [:birthday, :name], prefix: true
+  store :spouse, accessors: [:birthday], prefix: :partner
+  store_accessor :spouse, :name, prefix: :partner
+  store :configs, accessors: [ :secret_question ]
+  store :configs, accessors: [ :two_factor_auth ], suffix: true
+  store_accessor :configs, :login_retry, suffix: :config
+  store :preferences, accessors: [ :remember_login ]
+  store :json_data, accessors: [ :height, :weight ], coder: Coder.new
+  store :json_data_empty, accessors: [ :is_a_good_guy ], coder: Coder.new
 
   def phone_number
-    read_store_attribute(:settings, :phone_number).gsub(/(\d{3})(\d{3})(\d{4})/,'(\1) \2-\3')
+    read_store_attribute(:settings, :phone_number).gsub(/(\d{3})(\d{3})(\d{4})/, '(\1) \2-\3')
   end
 
   def phone_number=(value)
-    write_store_attribute(:settings, :phone_number, value && value.gsub(/[^\d]/,''))
+    write_store_attribute(:settings, :phone_number, value && value.gsub(/[^\d]/, ""))
   end
 
   def color
-    super || 'red'
+    super || "red"
   end
 
   def color=(value)
-    value = 'blue' unless %w(black red green blue).include?(value)
+    value = "blue" unless %w(black red green blue).include?(value)
     super
   end
 end
diff --git a/activerecord/test/models/aircraft.rb b/activerecord/test/models/aircraft.rb
index 1f35ef45da..4fdea46cf7 100644
--- a/activerecord/test/models/aircraft.rb
+++ b/activerecord/test/models/aircraft.rb
@@ -1,4 +1,7 @@
+# frozen_string_literal: true
+
 class Aircraft < ActiveRecord::Base
   self.pluralize_table_names = false
-  has_many :engines, :foreign_key => "car_id"
+  has_many :engines, foreign_key: "car_id"
+  has_many :wheels, as: :wheelable
 end
diff --git a/activerecord/test/models/arunit2_model.rb b/activerecord/test/models/arunit2_model.rb
index 04b8b15d3d..5b0da8a249 100644
--- a/activerecord/test/models/arunit2_model.rb
+++ b/activerecord/test/models/arunit2_model.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ARUnit2Model < ActiveRecord::Base
   self.abstract_class = true
 end
diff --git a/activerecord/test/models/author.rb b/activerecord/test/models/author.rb
index 8c1f14bd36..8b5a2fa0c8 100644
--- a/activerecord/test/models/author.rb
+++ b/activerecord/test/models/author.rb
@@ -1,151 +1,169 @@
+# frozen_string_literal: true
+
 class Author < ActiveRecord::Base
   has_many :posts
   has_many :serialized_posts
   has_one :post
-  has_many :very_special_comments, :through => :posts
-  has_many :posts_with_comments, -> { includes(:comments) }, :class_name => "Post"
-  has_many :popular_grouped_posts, -> { includes(:comments).group("type").having("SUM(comments_count) > 1").select("type") }, :class_name => "Post"
-  has_many :posts_with_comments_sorted_by_comment_id, -> { includes(:comments).order('comments.id') }, :class_name => "Post"
-  has_many :posts_sorted_by_id_limited, -> { order('posts.id').limit(1) }, :class_name => "Post"
-  has_many :posts_with_categories, -> { includes(:categories) }, :class_name => "Post"
-  has_many :posts_with_comments_and_categories, -> { includes(:comments, :categories).order("posts.id") }, :class_name => "Post"
-  has_many :posts_with_special_categorizations, :class_name => 'PostWithSpecialCategorization'
-  has_one  :post_about_thinking, -> { where("posts.title like '%thinking%'") }, :class_name => 'Post'
-  has_one  :post_about_thinking_with_last_comment, -> { where("posts.title like '%thinking%'").includes(:last_comment) }, :class_name => 'Post'
+  has_many :very_special_comments, through: :posts
+  has_many :posts_with_comments, -> { includes(:comments) }, class_name: "Post"
+  has_many :popular_grouped_posts, -> { includes(:comments).group("type").having("SUM(comments_count) > 1").select("type") }, class_name: "Post"
+  has_many :posts_with_comments_sorted_by_comment_id, -> { includes(:comments).order("comments.id") }, class_name: "Post"
+  has_many :posts_sorted_by_id, -> { order(:id) }, class_name: "Post"
+  has_many :posts_sorted_by_id_limited, -> { order("posts.id").limit(1) }, class_name: "Post"
+  has_many :posts_with_categories, -> { includes(:categories) }, class_name: "Post"
+  has_many :posts_with_comments_and_categories, -> { includes(:comments, :categories).order("posts.id") }, class_name: "Post"
+  has_many :posts_with_special_categorizations, class_name: "PostWithSpecialCategorization"
+  has_one  :post_about_thinking, -> { where("posts.title like '%thinking%'") }, class_name: "Post"
+  has_one  :post_about_thinking_with_last_comment, -> { where("posts.title like '%thinking%'").includes(:last_comment) }, class_name: "Post"
   has_many :comments, through: :posts do
     def ratings
       Rating.joins(:comment).merge(self)
     end
   end
-  has_many :comments_containing_the_letter_e, :through => :posts, :source => :comments
-  has_many :comments_with_order_and_conditions, -> { order('comments.body').where("comments.body like 'Thank%'") }, :through => :posts, :source => :comments
-  has_many :comments_with_include, -> { includes(:post) }, :through => :posts, :source => :comments
+  has_many :comments_containing_the_letter_e, through: :posts, source: :comments
+  has_many :comments_with_order_and_conditions, -> { order("comments.body").where("comments.body like 'Thank%'") }, through: :posts, source: :comments
+  has_many :comments_with_include, -> { includes(:post).where(posts: { type: "Post" }) }, through: :posts, source: :comments
+  has_many :comments_for_first_author, -> { for_first_author }, through: :posts, source: :comments
 
   has_many :first_posts
-  has_many :comments_on_first_posts, -> { order('posts.id desc, comments.id asc') }, :through => :first_posts, :source => :comments
+  has_many :comments_on_first_posts, -> { order("posts.id desc, comments.id asc") }, through: :first_posts, source: :comments
 
   has_one :first_post
-  has_one :comment_on_first_post, -> { order('posts.id desc, comments.id asc') }, :through => :first_post, :source => :comments
+  has_one :comment_on_first_post, -> { order("posts.id desc, comments.id asc") }, through: :first_post, source: :comments
 
-  has_many :thinking_posts, -> { where(:title => 'So I was thinking') }, :dependent => :delete_all, :class_name => 'Post'
-  has_many :welcome_posts, -> { where(:title => 'Welcome to the weblog') }, :class_name => 'Post'
+  has_many :thinking_posts, -> { where(title: "So I was thinking") }, dependent: :delete_all, class_name: "Post"
+  has_many :welcome_posts, -> { where(title: "Welcome to the weblog") }, class_name: "Post"
 
   has_many :welcome_posts_with_one_comment,
-           -> { where(title: 'Welcome to the weblog').where('comments_count = ?', 1) },
-           class_name: 'Post'
+           -> { where(title: "Welcome to the weblog").where("comments_count = ?", 1) },
+           class_name: "Post"
   has_many :welcome_posts_with_comments,
-           -> { where(title: 'Welcome to the weblog').where(Post.arel_table[:comments_count].gt(0)) },
-           class_name: 'Post'
+           -> { where(title: "Welcome to the weblog").where(Post.arel_table[:comments_count].gt(0)) },
+           class_name: "Post"
 
-  has_many :comments_desc, -> { order('comments.id DESC') }, :through => :posts, :source => :comments
-  has_many :funky_comments, :through => :posts, :source => :comments
-  has_many :ordered_uniq_comments, -> { distinct.order('comments.id') }, :through => :posts, :source => :comments
-  has_many :ordered_uniq_comments_desc, -> { distinct.order('comments.id DESC') }, :through => :posts, :source => :comments
-  has_many :readonly_comments, -> { readonly }, :through => :posts, :source => :comments
+  has_many :comments_desc, -> { order("comments.id DESC") }, through: :posts_sorted_by_id, source: :comments
+  has_many :unordered_comments, -> { unscope(:order).distinct }, through: :posts_sorted_by_id_limited, source: :comments
+  has_many :funky_comments, through: :posts, source: :comments
+  has_many :ordered_uniq_comments, -> { distinct.order("comments.id") }, through: :posts, source: :comments
+  has_many :ordered_uniq_comments_desc, -> { distinct.order("comments.id DESC") }, through: :posts, source: :comments
+  has_many :readonly_comments, -> { readonly }, through: :posts, source: :comments
 
   has_many :special_posts
-  has_many :special_post_comments, :through => :special_posts, :source => :comments
-  has_many :special_posts_with_default_scope, :class_name => 'SpecialPostWithDefaultScope'
-
-  has_many :sti_posts, :class_name => 'StiPost'
-  has_many :sti_post_comments, :through => :sti_posts, :source => :comments
-
-  has_many :special_nonexistent_posts, -> { where("posts.body = 'nonexistent'") }, :class_name => "SpecialPost"
-  has_many :special_nonexistent_post_comments, -> { where('comments.post_id' => 0) }, :through => :special_nonexistent_posts, :source => :comments
-  has_many :nonexistent_comments, :through => :posts
-
-  has_many :hello_posts, -> { where "posts.body = 'hello'" }, :class_name => "Post"
-  has_many :hello_post_comments, :through => :hello_posts, :source => :comments
-  has_many :posts_with_no_comments, -> { where('comments.id' => nil).includes(:comments) }, :class_name => 'Post'
-
-  has_many :hello_posts_with_hash_conditions, -> { where(:body => 'hello') }, :class_name => "Post"
-  has_many :hello_post_comments_with_hash_conditions, :through =>
-:hello_posts_with_hash_conditions, :source => :comments
-
-  has_many :other_posts,          :class_name => "Post"
-  has_many :posts_with_callbacks, :class_name => "Post", :before_add => :log_before_adding,
-           :after_add     => :log_after_adding,
-           :before_remove => :log_before_removing,
-           :after_remove  => :log_after_removing
-  has_many :posts_with_proc_callbacks, :class_name => "Post",
-           :before_add    => Proc.new {|o, r| o.post_log << "before_adding#{r.id || '<new>'}"},
-           :after_add     => Proc.new {|o, r| o.post_log << "after_adding#{r.id || '<new>'}"},
-           :before_remove => Proc.new {|o, r| o.post_log << "before_removing#{r.id}"},
-           :after_remove  => Proc.new {|o, r| o.post_log << "after_removing#{r.id}"}
-  has_many :posts_with_multiple_callbacks, :class_name => "Post",
-           :before_add => [:log_before_adding, Proc.new {|o, r| o.post_log << "before_adding_proc#{r.id || '<new>'}"}],
-           :after_add  => [:log_after_adding,  Proc.new {|o, r| o.post_log << "after_adding_proc#{r.id || '<new>'}"}]
-  has_many :unchangable_posts, :class_name => "Post", :before_add => :raise_exception, :after_add => :log_after_adding
-
-  has_many :categorizations
-  has_many :categories, :through => :categorizations
-  has_many :named_categories, :through => :categorizations
+  has_many :special_post_comments, through: :special_posts, source: :comments
+  has_many :special_posts_with_default_scope, class_name: "SpecialPostWithDefaultScope"
+
+  has_many :sti_posts, class_name: "StiPost"
+  has_many :sti_post_comments, through: :sti_posts, source: :comments
+
+  has_many :special_nonexistent_posts, -> { where("posts.body = 'nonexistent'") }, class_name: "SpecialPost"
+  has_many :special_nonexistent_post_comments, -> { where("comments.post_id" => 0) }, through: :special_nonexistent_posts, source: :comments
+  has_many :nonexistent_comments, through: :posts
+
+  has_many :hello_posts, -> { where "posts.body = 'hello'" }, class_name: "Post"
+  has_many :hello_post_comments, through: :hello_posts, source: :comments
+  has_many :posts_with_no_comments, -> { where("comments.id" => nil).includes(:comments) }, class_name: "Post"
+
+  has_many :hello_posts_with_hash_conditions, -> { where(body: "hello") }, class_name: "Post"
+  has_many :hello_post_comments_with_hash_conditions, through: :hello_posts_with_hash_conditions, source: :comments
+
+  has_many :other_posts,          class_name: "Post"
+  has_many :posts_with_callbacks, class_name: "Post", before_add: :log_before_adding,
+           after_add: :log_after_adding,
+           before_remove: :log_before_removing,
+           after_remove: :log_after_removing
+  has_many :posts_with_proc_callbacks, class_name: "Post",
+           before_add: Proc.new { |o, r| o.post_log << "before_adding#{r.id || '<new>'}" },
+           after_add: Proc.new { |o, r| o.post_log << "after_adding#{r.id || '<new>'}" },
+           before_remove: Proc.new { |o, r| o.post_log << "before_removing#{r.id}" },
+           after_remove: Proc.new { |o, r| o.post_log << "after_removing#{r.id}" }
+  has_many :posts_with_multiple_callbacks, class_name: "Post",
+           before_add: [:log_before_adding, Proc.new { |o, r| o.post_log << "before_adding_proc#{r.id || '<new>'}" }],
+           after_add: [:log_after_adding,  Proc.new { |o, r| o.post_log << "after_adding_proc#{r.id || '<new>'}" }]
+  has_many :unchangeable_posts, class_name: "Post", before_add: :raise_exception, after_add: :log_after_adding
+
+  has_many :categorizations, -> { }
+  has_many :categories, through: :categorizations
+  has_many :named_categories, through: :categorizations
 
   has_many :special_categorizations
-  has_many :special_categories, :through => :special_categorizations, :source => :category
-  has_one  :special_category,   :through => :special_categorizations, :source => :category
+  has_many :special_categories, through: :special_categorizations, source: :category
+  has_one  :special_category,   through: :special_categorizations, source: :category
+
+  has_many :special_categories_with_conditions, -> { where(categorizations: { special: true }) }, through: :categorizations, source: :category
+  has_many :nonspecial_categories_with_conditions, -> { where(categorizations: { special: false }) }, through: :categorizations, source: :category
 
-  has_many :categories_like_general, -> { where(:name => 'General') }, :through => :categorizations, :source => :category, :class_name => 'Category'
+  has_many :categories_like_general, -> { where(name: "General") }, through: :categorizations, source: :category, class_name: "Category"
 
-  has_many :categorized_posts, :through => :categorizations, :source => :post
-  has_many :unique_categorized_posts, -> { distinct }, :through => :categorizations, :source => :post
+  has_many :categorized_posts, through: :categorizations, source: :post
+  has_many :unique_categorized_posts, -> { distinct }, through: :categorizations, source: :post
 
-  has_many :nothings, :through => :kateggorisatons, :class_name => 'Category'
+  has_many :nothings, through: :kateggorisatons, class_name: "Category"
 
   has_many :author_favorites
-  has_many :favorite_authors, -> { order('name') }, :through => :author_favorites
+  has_many :favorite_authors, -> { order("name") }, through: :author_favorites
 
-  has_many :taggings,        :through => :posts, :source => :taggings
-  has_many :taggings_2,      :through => :posts, :source => :tagging
-  has_many :tags,            :through => :posts
-  has_many :post_categories, :through => :posts, :source => :categories
-  has_many :tagging_tags,    :through => :taggings, :source => :tag
+  has_many :taggings,        through: :posts, source: :taggings
+  has_many :taggings_2,      through: :posts, source: :tagging
+  has_many :tags,            through: :posts
+  has_many :ordered_tags,    through: :posts
+  has_many :post_categories, through: :posts, source: :categories
+  has_many :tagging_tags,    through: :taggings, source: :tag
 
-  has_many :similar_posts, -> { distinct }, :through => :tags, :source => :tagged_posts
-  has_many :distinct_tags, -> { select("DISTINCT tags.*").order("tags.name") }, :through => :posts, :source => :tags
+  has_many :similar_posts, -> { distinct }, through: :tags, source: :tagged_posts
+  has_many :ordered_posts, -> { distinct }, through: :ordered_tags, source: :tagged_posts
+  has_many :distinct_tags, -> { select("DISTINCT tags.*").order("tags.name") }, through: :posts, source: :tags
 
-  has_many :tags_with_primary_key, :through => :posts
+  has_many :tags_with_primary_key, through: :posts
 
   has_many :books
-  has_many :subscriptions,        :through => :books
-  has_many :subscribers, -> { order("subscribers.nick") }, :through => :subscriptions
-  has_many :distinct_subscribers, -> { select("DISTINCT subscribers.*").order("subscribers.nick") }, :through => :subscriptions, :source => :subscriber
+  has_many :unpublished_books, -> { where(status: [:proposed, :written]) }, class_name: "Book"
+  has_many :subscriptions,        through: :books
+  has_many :subscribers, -> { order("subscribers.nick") }, through: :subscriptions
+  has_many :distinct_subscribers, -> { select("DISTINCT subscribers.*").order("subscribers.nick") }, through: :subscriptions, source: :subscriber
 
-  has_one :essay, :primary_key => :name, :as => :writer
-  has_one :essay_category, :through => :essay, :source => :category
-  has_one :essay_owner, :through => :essay, :source => :owner
+  has_one :essay, primary_key: :name, as: :writer
+  has_one :essay_category, through: :essay, source: :category
+  has_one :essay_owner, through: :essay, source: :owner
 
-  has_one :essay_2, :primary_key => :name, :class_name => 'Essay', :foreign_key => :author_id
-  has_one :essay_category_2, :through => :essay_2, :source => :category
+  has_one :essay_2, primary_key: :name, class_name: "Essay", foreign_key: :author_id
+  has_one :essay_category_2, through: :essay_2, source: :category
 
-  has_many :essays, :primary_key => :name, :as => :writer
-  has_many :essay_categories, :through => :essays, :source => :category
-  has_many :essay_owners, :through => :essays, :source => :owner
+  has_many :essays, primary_key: :name, as: :writer
+  has_many :essay_categories, through: :essays, source: :category
+  has_many :essay_owners, through: :essays, source: :owner
 
-  has_many :essays_2, :primary_key => :name, :class_name => 'Essay', :foreign_key => :author_id
-  has_many :essay_categories_2, :through => :essays_2, :source => :category
+  has_many :essays_2, primary_key: :name, class_name: "Essay", foreign_key: :author_id
+  has_many :essay_categories_2, through: :essays_2, source: :category
 
-  belongs_to :owned_essay, :primary_key => :name, :class_name => 'Essay'
-  has_one :owned_essay_category, :through => :owned_essay, :source => :category
+  belongs_to :owned_essay, primary_key: :name, class_name: "Essay"
+  has_one :owned_essay_category, through: :owned_essay, source: :category
 
-  belongs_to :author_address,       :dependent => :destroy
-  belongs_to :author_address_extra, :dependent => :delete, :class_name => "AuthorAddress"
+  belongs_to :author_address,       dependent: :destroy
+  belongs_to :author_address_extra, dependent: :delete, class_name: "AuthorAddress"
 
-  has_many :category_post_comments, :through => :categories, :source => :post_comments
+  has_many :category_post_comments, through: :categories, source: :post_comments
 
-  has_many :misc_posts, -> { where(:posts => { :title => ['misc post by bob', 'misc post by mary'] }) }, :class_name => 'Post'
-  has_many :misc_post_first_blue_tags, :through => :misc_posts, :source => :first_blue_tags
+  has_many :misc_posts, -> { where(posts: { title: ["misc post by bob", "misc post by mary"] }) }, class_name: "Post"
+  has_many :misc_post_first_blue_tags, through: :misc_posts, source: :first_blue_tags
 
-  has_many :misc_post_first_blue_tags_2, -> { where(:posts => { :title => ['misc post by bob', 'misc post by mary'] }) },
-           :through => :posts, :source => :first_blue_tags_2
+  has_many :misc_post_first_blue_tags_2, -> { where(posts: { title: ["misc post by bob", "misc post by mary"] }) },
+           through: :posts, source: :first_blue_tags_2
 
-  has_many :posts_with_default_include, :class_name => 'PostWithDefaultInclude'
-  has_many :comments_on_posts_with_default_include, :through => :posts_with_default_include, :source => :comments
+  has_many :posts_with_default_include, class_name: "PostWithDefaultInclude"
+  has_many :comments_on_posts_with_default_include, through: :posts_with_default_include, source: :comments
 
   has_many :posts_with_signature, ->(record) { where("posts.title LIKE ?", "%by #{record.name.downcase}%") }, class_name: "Post"
 
-  scope :relation_include_posts, -> { includes(:posts) }
-  scope :relation_include_tags,  -> { includes(:tags) }
+  has_many :posts_with_extension, -> { order(:title) }, class_name: "Post" do
+    def extension_method; end
+  end
+
+  has_many :posts_with_extension_and_instance, ->(record) { order(:title) }, class_name: "Post" do
+    def extension_method; end
+  end
+
+  has_many :top_posts, -> { order(id: :asc) }, class_name: "Post"
+  has_many :other_top_posts, -> { order(id: :asc) }, class_name: "Post"
 
   attr_accessor :post_log
   after_initialize :set_post_log
@@ -200,5 +218,5 @@ end
 
 class AuthorFavorite < ActiveRecord::Base
   belongs_to :author
-  belongs_to :favorite_author, :class_name => "Author"
+  belongs_to :favorite_author, class_name: "Author"
 end
diff --git a/activerecord/test/models/auto_id.rb b/activerecord/test/models/auto_id.rb
index 82c6544bd5..fd672603bb 100644
--- a/activerecord/test/models/auto_id.rb
+++ b/activerecord/test/models/auto_id.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AutoId < ActiveRecord::Base
   self.table_name = "auto_id_tests"
   self.primary_key = "auto_id"
diff --git a/activerecord/test/models/autoloadable/extra_firm.rb b/activerecord/test/models/autoloadable/extra_firm.rb
index 5578ba0d9b..c46e34c101 100644
--- a/activerecord/test/models/autoloadable/extra_firm.rb
+++ b/activerecord/test/models/autoloadable/extra_firm.rb
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 class ExtraFirm < Company
 end
diff --git a/activerecord/test/models/binary.rb b/activerecord/test/models/binary.rb
index 39b2f5090a..b93f87519f 100644
--- a/activerecord/test/models/binary.rb
+++ b/activerecord/test/models/binary.rb
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 class Binary < ActiveRecord::Base
 end
diff --git a/activerecord/test/models/bird.rb b/activerecord/test/models/bird.rb
index 2a51d903b8..be08636ac6 100644
--- a/activerecord/test/models/bird.rb
+++ b/activerecord/test/models/bird.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Bird < ActiveRecord::Base
   belongs_to :pirate
   validates_presence_of :name
@@ -5,7 +7,7 @@ class Bird < ActiveRecord::Base
   accepts_nested_attributes_for :pirate
 
   attr_accessor :cancel_save_from_callback
-  before_save :cancel_save_callback_method, :if => :cancel_save_from_callback
+  before_save :cancel_save_callback_method, if: :cancel_save_from_callback
   def cancel_save_callback_method
     throw(:abort)
   end
diff --git a/activerecord/test/models/book.rb b/activerecord/test/models/book.rb
index 24bfe47bbf..afdda1a81e 100644
--- a/activerecord/test/models/book.rb
+++ b/activerecord/test/models/book.rb
@@ -1,19 +1,23 @@
+# frozen_string_literal: true
+
 class Book < ActiveRecord::Base
-  has_many :authors
+  belongs_to :author
 
-  has_many :citations, :foreign_key => 'book1_id'
+  has_many :citations, foreign_key: "book1_id"
   has_many :references, -> { distinct }, through: :citations, source: :reference_of
 
   has_many :subscriptions
   has_many :subscribers, through: :subscriptions
 
   enum status: [:proposed, :written, :published]
-  enum read_status: {unread: 0, reading: 2, read: 3}
+  enum read_status: { unread: 0, reading: 2, read: 3, forgotten: nil }
   enum nullable_status: [:single, :married]
-  enum language: [:english, :spanish, :french], enum_prefix: :in
-  enum author_visibility: [:visible, :invisible], enum_prefix: true
-  enum illustrator_visibility: [:visible, :invisible], enum_prefix: true
-  enum font_size: [:small, :medium, :large], enum_prefix: :with, enum_suffix: true
+  enum language: [:english, :spanish, :french], _prefix: :in
+  enum author_visibility: [:visible, :invisible], _prefix: true
+  enum illustrator_visibility: [:visible, :invisible], _prefix: true
+  enum font_size: [:small, :medium, :large], _prefix: :with, _suffix: true
+  enum difficulty: [:easy, :medium, :hard], _suffix: :to_read
+  enum cover: { hard: "hard", soft: "soft" }
 
   def published!
     super
diff --git a/activerecord/test/models/boolean.rb b/activerecord/test/models/boolean.rb
index 7bae22e5f9..bee757fb9c 100644
--- a/activerecord/test/models/boolean.rb
+++ b/activerecord/test/models/boolean.rb
@@ -1,2 +1,7 @@
+# frozen_string_literal: true
+
 class Boolean < ActiveRecord::Base
+  def has_fun
+    super
+  end
 end
diff --git a/activerecord/test/models/bulb.rb b/activerecord/test/models/bulb.rb
index a6e83fe353..ab92f7025d 100644
--- a/activerecord/test/models/bulb.rb
+++ b/activerecord/test/models/bulb.rb
@@ -1,6 +1,9 @@
+# frozen_string_literal: true
+
 class Bulb < ActiveRecord::Base
-  default_scope { where(:name => 'defaulty') }
-  belongs_to :car, :touch => true
+  default_scope { where(name: "defaulty") }
+  belongs_to :car, touch: true
+  scope :awesome, -> { where(frickinawesome: true) }
 
   attr_reader :scope_after_initialize, :attributes_after_initialize
 
@@ -34,7 +37,7 @@ class CustomBulb < Bulb
   after_initialize :set_awesomeness
 
   def set_awesomeness
-    self.frickinawesome = true if name == 'Dude'
+    self.frickinawesome = true if name == "Dude"
   end
 end
 
diff --git a/activerecord/test/models/cake_designer.rb b/activerecord/test/models/cake_designer.rb
index 9c57ef573a..0b2a00edfd 100644
--- a/activerecord/test/models/cake_designer.rb
+++ b/activerecord/test/models/cake_designer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class CakeDesigner < ActiveRecord::Base
   has_one :chef, as: :employable
 end
diff --git a/activerecord/test/models/car.rb b/activerecord/test/models/car.rb
index 81263b79d1..8614926626 100644
--- a/activerecord/test/models/car.rb
+++ b/activerecord/test/models/car.rb
@@ -1,26 +1,33 @@
+# frozen_string_literal: true
+
 class Car < ActiveRecord::Base
   has_many :bulbs
   has_many :all_bulbs, -> { unscope where: :name }, class_name: "Bulb"
-  has_many :funky_bulbs, class_name: 'FunkyBulb', dependent: :destroy
-  has_many :failed_bulbs, class_name: 'FailedBulb', dependent: :destroy
-  has_many :foo_bulbs, -> { where(:name => 'foo') }, :class_name => "Bulb"
+  has_many :funky_bulbs, class_name: "FunkyBulb", dependent: :destroy
+  has_many :failed_bulbs, class_name: "FailedBulb", dependent: :destroy
+  has_many :foo_bulbs, -> { where(name: "foo") }, class_name: "Bulb"
+  has_many :awesome_bulbs, -> { awesome }, class_name: "Bulb"
 
   has_one :bulb
 
   has_many :tyres
-  has_many :engines, :dependent => :destroy, inverse_of: :my_car
-  has_many :wheels, :as => :wheelable, :dependent => :destroy
+  has_many :engines, dependent: :destroy, inverse_of: :my_car
+  has_many :wheels, as: :wheelable, dependent: :destroy
+
+  has_many :price_estimates, as: :estimate_of
 
   scope :incl_tyres, -> { includes(:tyres) }
   scope :incl_engines, -> { includes(:engines) }
 
-  scope :order_using_new_style,  -> { order('name asc') }
+  scope :order_using_new_style,  -> { order("name asc") }
+
+  attribute :wheels_owned_at, :datetime, default: -> { Time.now }
 end
 
 class CoolCar < Car
-  default_scope { order('name desc') }
+  default_scope { order("name desc") }
 end
 
 class FastCar < Car
-  default_scope { order('name desc') }
+  default_scope { order("name desc") }
 end
diff --git a/activerecord/test/models/carrier.rb b/activerecord/test/models/carrier.rb
new file mode 100644
index 0000000000..995a9d3bef
--- /dev/null
+++ b/activerecord/test/models/carrier.rb
@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class Carrier < ActiveRecord::Base
+end
diff --git a/activerecord/test/models/cat.rb b/activerecord/test/models/cat.rb
new file mode 100644
index 0000000000..43013964b6
--- /dev/null
+++ b/activerecord/test/models/cat.rb
@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class Cat < ActiveRecord::Base
+  self.abstract_class = true
+
+  enum gender: [:female, :male]
+
+  default_scope -> { where(is_vegetarian: false) }
+end
+
+class Lion < Cat
+end
diff --git a/activerecord/test/models/categorization.rb b/activerecord/test/models/categorization.rb
index 6588531de6..68b0ea90d3 100644
--- a/activerecord/test/models/categorization.rb
+++ b/activerecord/test/models/categorization.rb
@@ -1,18 +1,20 @@
+# frozen_string_literal: true
+
 class Categorization < ActiveRecord::Base
   belongs_to :post
-  belongs_to :category
-  belongs_to :named_category, :class_name => 'Category', :foreign_key => :named_category_name, :primary_key => :name
+  belongs_to :category, counter_cache: true
+  belongs_to :named_category, class_name: "Category", foreign_key: :named_category_name, primary_key: :name
   belongs_to :author
 
-  has_many :post_taggings, :through => :author, :source => :taggings
+  has_many :post_taggings, through: :author, source: :taggings
 
-  belongs_to :author_using_custom_pk,  :class_name => 'Author', :foreign_key => :author_id, :primary_key => :author_address_extra_id
-  has_many   :authors_using_custom_pk, :class_name => 'Author', :foreign_key => :id,        :primary_key => :category_id
+  belongs_to :author_using_custom_pk,  class_name: "Author", foreign_key: :author_id, primary_key: :author_address_extra_id
+  has_many   :authors_using_custom_pk, class_name: "Author", foreign_key: :id,        primary_key: :category_id
 end
 
 class SpecialCategorization < ActiveRecord::Base
-  self.table_name = 'categorizations'
-  default_scope { where(:special => true) }
+  self.table_name = "categorizations"
+  default_scope { where(special: true) }
 
   belongs_to :author
   belongs_to :category
diff --git a/activerecord/test/models/category.rb b/activerecord/test/models/category.rb
index 272223e1d8..2ccc00bed9 100644
--- a/activerecord/test/models/category.rb
+++ b/activerecord/test/models/category.rb
@@ -1,34 +1,45 @@
+# frozen_string_literal: true
+
 class Category < ActiveRecord::Base
   has_and_belongs_to_many :posts
-  has_and_belongs_to_many :special_posts, :class_name => "Post"
-  has_and_belongs_to_many :other_posts, :class_name => "Post"
-  has_and_belongs_to_many :posts_with_authors_sorted_by_author_id, -> { includes(:authors).order("authors.id") }, :class_name => "Post"
+  has_and_belongs_to_many :special_posts, class_name: "Post"
+  has_and_belongs_to_many :other_posts, class_name: "Post"
+  has_and_belongs_to_many :posts_with_authors_sorted_by_author_id, -> { includes(:authors).order("authors.id") }, class_name: "Post"
 
   has_and_belongs_to_many :select_testing_posts,
-                          -> { select 'posts.*, 1 as correctness_marker' },
-                          :class_name => 'Post',
-                          :foreign_key => 'category_id',
-                          :association_foreign_key => 'post_id'
+                          -> { select "posts.*, 1 as correctness_marker" },
+                          class_name: "Post",
+                          foreign_key: "category_id",
+                          association_foreign_key: "post_id"
 
   has_and_belongs_to_many :post_with_conditions,
-                          -> { where :title => 'Yet Another Testing Title' },
-                          :class_name => 'Post'
+                          -> { where title: "Yet Another Testing Title" },
+                          class_name: "Post"
 
-  has_and_belongs_to_many :popular_grouped_posts, -> { group("posts.type").having("sum(comments.post_id) > 2").includes(:comments) }, :class_name => "Post"
-  has_and_belongs_to_many :posts_grouped_by_title, -> { group("title").select("title") }, :class_name => "Post"
+  has_and_belongs_to_many :popular_grouped_posts, -> { group("posts.type").having("sum(comments.post_id) > 2").includes(:comments) }, class_name: "Post"
+  has_and_belongs_to_many :posts_grouped_by_title, -> { group("title").select("title") }, class_name: "Post"
 
   def self.what_are_you
-    'a category...'
+    "a category..."
   end
 
   has_many :categorizations
   has_many :special_categorizations
-  has_many :post_comments, :through => :posts, :source => :comments
+  has_many :post_comments, through: :posts, source: :comments
+
+  has_many :authors, through: :categorizations
+  has_many :authors_with_select, -> { select "authors.*, categorizations.post_id" }, through: :categorizations, source: :author
 
-  has_many :authors, :through => :categorizations
-  has_many :authors_with_select, -> { select 'authors.*, categorizations.post_id' }, :through => :categorizations, :source => :author
+  scope :general, -> { where(name: "General") }
 
-  scope :general, -> { where(:name => 'General') }
+  # Should be delegated `ast` and `locked` to `arel`.
+  def self.ast
+    raise
+  end
+
+  def self.locked
+    raise
+  end
 end
 
 class SpecialCategory < Category
diff --git a/activerecord/test/models/chef.rb b/activerecord/test/models/chef.rb
index 698a52e045..ff528644bc 100644
--- a/activerecord/test/models/chef.rb
+++ b/activerecord/test/models/chef.rb
@@ -1,4 +1,10 @@
+# frozen_string_literal: true
+
 class Chef < ActiveRecord::Base
   belongs_to :employable, polymorphic: true
   has_many :recipes
 end
+
+class ChefList < Chef
+  belongs_to :employable_list, polymorphic: true
+end
diff --git a/activerecord/test/models/citation.rb b/activerecord/test/models/citation.rb
index 3d87eb795c..cee3d18173 100644
--- a/activerecord/test/models/citation.rb
+++ b/activerecord/test/models/citation.rb
@@ -1,3 +1,6 @@
+# frozen_string_literal: true
+
 class Citation < ActiveRecord::Base
-  belongs_to :reference_of, :class_name => "Book", :foreign_key => :book2_id
+  belongs_to :reference_of, class_name: "Book", foreign_key: :book2_id
+  has_many :citations
 end
diff --git a/activerecord/test/models/club.rb b/activerecord/test/models/club.rb
index 6ceafe5858..2006e05fcf 100644
--- a/activerecord/test/models/club.rb
+++ b/activerecord/test/models/club.rb
@@ -1,23 +1,27 @@
+# frozen_string_literal: true
+
 class Club < ActiveRecord::Base
   has_one :membership
-  has_many :memberships, :inverse_of => false
-  has_many :members, :through => :memberships
+  has_many :memberships, inverse_of: false
+  has_many :members, through: :memberships
   has_one :sponsor
-  has_one :sponsored_member, :through => :sponsor, :source => :sponsorable, :source_type => "Member"
+  has_one :sponsored_member, through: :sponsor, source: :sponsorable, source_type: "Member"
   belongs_to :category
 
   has_many :favourites, -> { where(memberships: { favourite: true }) }, through: :memberships, source: :member
 
+  scope :general, -> { left_joins(:category).where(categories: { name: "General" }) }
+
   private
 
-  def private_method
-    "I'm sorry sir, this is a *private* club, not a *pirate* club"
-  end
+    def private_method
+      "I'm sorry sir, this is a *private* club, not a *pirate* club"
+    end
 end
 
 class SuperClub < ActiveRecord::Base
   self.table_name = "clubs"
 
-  has_many :memberships, class_name: 'SuperMembership', foreign_key: 'club_id'
+  has_many :memberships, class_name: "SuperMembership", foreign_key: "club_id"
   has_many :members, through: :memberships
 end
diff --git a/activerecord/test/models/college.rb b/activerecord/test/models/college.rb
index 501af4a8dd..52017dda42 100644
--- a/activerecord/test/models/college.rb
+++ b/activerecord/test/models/college.rb
@@ -1,5 +1,7 @@
-require_dependency 'models/arunit2_model'
-require 'active_support/core_ext/object/with_options'
+# frozen_string_literal: true
+
+require_dependency "models/arunit2_model"
+require "active_support/core_ext/object/with_options"
 
 class College < ARUnit2Model
   has_many :courses
diff --git a/activerecord/test/models/column.rb b/activerecord/test/models/column.rb
index 499358b4cf..d3cd419a00 100644
--- a/activerecord/test/models/column.rb
+++ b/activerecord/test/models/column.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Column < ActiveRecord::Base
   belongs_to :record
 end
diff --git a/activerecord/test/models/column_name.rb b/activerecord/test/models/column_name.rb
index 460eb4fe20..c6047c507b 100644
--- a/activerecord/test/models/column_name.rb
+++ b/activerecord/test/models/column_name.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class ColumnName < ActiveRecord::Base
   self.table_name = "colnametests"
 end
diff --git a/activerecord/test/models/comment.rb b/activerecord/test/models/comment.rb
index b38b17e90e..f0f0576709 100644
--- a/activerecord/test/models/comment.rb
+++ b/activerecord/test/models/comment.rb
@@ -1,25 +1,47 @@
+# frozen_string_literal: true
+
+# `counter_cache` requires association class before `attr_readonly`.
+class Post < ActiveRecord::Base; end
+
 class Comment < ActiveRecord::Base
-  scope :limit_by, lambda {|l| limit(l) }
+  scope :limit_by, lambda { |l| limit(l) }
   scope :containing_the_letter_e, -> { where("comments.body LIKE '%e%'") }
   scope :not_again, -> { where("comments.body NOT LIKE '%again%'") }
-  scope :for_first_post, -> { where(:post_id => 1) }
+  scope :for_first_post, -> { where(post_id: 1) }
   scope :for_first_author, -> { joins(:post).where("posts.author_id" => 1) }
   scope :created, -> { all }
 
-  belongs_to :post, :counter_cache => true
+  belongs_to :post, counter_cache: true
   belongs_to :author,   polymorphic: true
   belongs_to :resource, polymorphic: true
-  belongs_to :developer
 
   has_many :ratings
 
-  belongs_to :first_post, :foreign_key => :post_id
+  belongs_to :first_post, foreign_key: :post_id
+  belongs_to :special_post_with_default_scope, foreign_key: :post_id
+
+  has_many :children, class_name: "Comment", foreign_key: :parent_id
+  belongs_to :parent, class_name: "Comment", counter_cache: :children_count
+
+  class ::OopsError < RuntimeError; end
+
+  module OopsExtension
+    def destroy_all(*)
+      raise OopsError
+    end
+  end
+
+  default_scope { extending OopsExtension }
 
-  has_many :children, :class_name => 'Comment', :foreign_key => :parent_id
-  belongs_to :parent, :class_name => 'Comment', :counter_cache => :children_count
+  scope :oops_comments, -> { extending OopsExtension }
+
+  # Should not be called if extending modules that having the method exists on an association.
+  def self.greeting
+    raise
+  end
 
   def self.what_are_you
-    'a comment...'
+    "a comment..."
   end
 
   def self.search_by_type(q)
@@ -37,6 +59,11 @@ class Comment < ActiveRecord::Base
 end
 
 class SpecialComment < Comment
+  default_scope { where(deleted_at: nil) }
+
+  def self.what_are_you
+    "a special comment..."
+  end
 end
 
 class SubSpecialComment < SpecialComment
@@ -49,11 +76,17 @@ class CommentThatAutomaticallyAltersPostBody < Comment
   belongs_to :post, class_name: "PostThatLoadsCommentsInAnAfterSaveHook", foreign_key: :post_id
 
   after_save do |comment|
-    comment.post.update_attributes(body: "Automatically altered")
+    comment.post.update(body: "Automatically altered")
   end
 end
 
 class CommentWithDefaultScopeReferencesAssociation < Comment
-  default_scope ->{ includes(:developer).order('developers.name').references(:developer) }
+  default_scope -> { includes(:developer).order("developers.name").references(:developer) }
   belongs_to :developer
 end
+
+class CommentWithAfterCreateUpdate < Comment
+  after_create do
+    update(body: "bar")
+  end
+end
diff --git a/activerecord/test/models/company.rb b/activerecord/test/models/company.rb
index 67936e8e5d..838f515aad 100644
--- a/activerecord/test/models/company.rb
+++ b/activerecord/test/models/company.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AbstractCompany < ActiveRecord::Base
   self.abstract_class = true
 end
@@ -7,14 +9,13 @@ class Company < AbstractCompany
 
   validates_presence_of :name
 
-  has_one :dummy_account, :foreign_key => "firm_id", :class_name => "Account"
+  has_one :dummy_account, foreign_key: "firm_id", class_name: "Account"
   has_many :contracts
-  has_many :developers, :through => :contracts
-  has_many :accounts
+  has_many :developers, through: :contracts
 
   scope :of_first_firm, lambda {
-    joins(:account => :firm).
-    where('firms.id' => 1)
+    joins(account: :firm).
+    where("firms.id" => 1)
   }
 
   def arbitrary_method
@@ -23,12 +24,12 @@ class Company < AbstractCompany
 
   private
 
-  def private_method
-    "I am Jack's innermost fears and aspirations"
-  end
+    def private_method
+      "I am Jack's innermost fears and aspirations"
+    end
 
-  class SpecialCo < Company
-  end
+    class SpecialCo < Company
+    end
 end
 
 module Namespaced
@@ -36,7 +37,7 @@ module Namespaced
   end
 
   class Firm < ::Company
-    has_many :clients, :class_name => 'Namespaced::Client'
+    has_many :clients, class_name: "Namespaced::Client"
   end
 
   class Client < ::Company
@@ -46,45 +47,50 @@ end
 class Firm < Company
   to_param :name
 
-  has_many :clients, -> { order "id" }, :dependent => :destroy, :before_remove => :log_before_remove, :after_remove  => :log_after_remove
-  has_many :unsorted_clients, :class_name => "Client"
-  has_many :unsorted_clients_with_symbol, :class_name => :Client
-  has_many :clients_sorted_desc, -> { order "id DESC" }, :class_name => "Client"
-  has_many :clients_of_firm, -> { order "id" }, :foreign_key => "client_of", :class_name => "Client", :inverse_of => :firm
-  has_many :clients_ordered_by_name, -> { order "name" }, :class_name => "Client"
-  has_many :unvalidated_clients_of_firm, :foreign_key => "client_of", :class_name => "Client", :validate => false
-  has_many :dependent_clients_of_firm, -> { order "id" }, :foreign_key => "client_of", :class_name => "Client", :dependent => :destroy
-  has_many :exclusively_dependent_clients_of_firm, -> { order "id" }, :foreign_key => "client_of", :class_name => "Client", :dependent => :delete_all
-  has_many :limited_clients, -> { limit 1 }, :class_name => "Client"
-  has_many :clients_with_interpolated_conditions, ->(firm) { where "rating > #{firm.rating}" }, :class_name => "Client"
-  has_many :clients_like_ms, -> { where("name = 'Microsoft'").order("id") }, :class_name => "Client"
-  has_many :clients_like_ms_with_hash_conditions, -> { where(:name => 'Microsoft').order("id") }, :class_name => "Client"
-  has_many :plain_clients, :class_name => 'Client'
-  has_many :clients_using_primary_key, :class_name => 'Client',
-           :primary_key => 'name', :foreign_key => 'firm_name'
-  has_many :clients_using_primary_key_with_delete_all, :class_name => 'Client',
-           :primary_key => 'name', :foreign_key => 'firm_name', :dependent => :delete_all
-  has_many :clients_grouped_by_firm_id, -> { group("firm_id").select("firm_id") }, :class_name => "Client"
-  has_many :clients_grouped_by_name, -> { group("name").select("name") }, :class_name => "Client"
-
-  has_one :account, :foreign_key => "firm_id", :dependent => :destroy, :validate => true
-  has_one :unvalidated_account, :foreign_key => "firm_id", :class_name => 'Account', :validate => false
-  has_one :account_with_select, -> { select("id, firm_id") }, :foreign_key => "firm_id", :class_name=>'Account'
-  has_one :readonly_account, -> { readonly }, :foreign_key => "firm_id", :class_name => "Account"
+  has_many :clients, -> { order "id" }, dependent: :destroy, before_remove: :log_before_remove, after_remove: :log_after_remove
+  has_many :unsorted_clients, class_name: "Client"
+  has_many :unsorted_clients_with_symbol, class_name: :Client
+  has_many :clients_sorted_desc, -> { order "id DESC" }, class_name: "Client"
+  has_many :clients_of_firm, -> { order "id" }, foreign_key: "client_of", class_name: "Client", inverse_of: :firm
+  has_many :clients_ordered_by_name, -> { order "name" }, class_name: "Client"
+  has_many :unvalidated_clients_of_firm, foreign_key: "client_of", class_name: "Client", validate: false
+  has_many :dependent_clients_of_firm, -> { order "id" }, foreign_key: "client_of", class_name: "Client", dependent: :destroy
+  has_many :exclusively_dependent_clients_of_firm, -> { order "id" }, foreign_key: "client_of", class_name: "Client", dependent: :delete_all
+  has_many :limited_clients, -> { limit 1 }, class_name: "Client"
+  has_many :clients_with_interpolated_conditions, ->(firm) { where "rating > #{firm.rating}" }, class_name: "Client"
+  has_many :clients_like_ms, -> { where("name = 'Microsoft'").order("id") }, class_name: "Client"
+  has_many :clients_like_ms_with_hash_conditions, -> { where(name: "Microsoft").order("id") }, class_name: "Client"
+  has_many :plain_clients, class_name: "Client"
+  has_many :clients_using_primary_key, class_name: "Client",
+           primary_key: "name", foreign_key: "firm_name"
+  has_many :clients_using_primary_key_with_delete_all, class_name: "Client",
+           primary_key: "name", foreign_key: "firm_name", dependent: :delete_all
+  has_many :clients_grouped_by_firm_id, -> { group("firm_id").select("firm_id") }, class_name: "Client"
+  has_many :clients_grouped_by_name, -> { group("name").select("name") }, class_name: "Client"
+
+  has_one :account, foreign_key: "firm_id", dependent: :destroy, validate: true
+  has_one :unvalidated_account, foreign_key: "firm_id", class_name: "Account", validate: false
+  has_one :account_with_select, -> { select("id, firm_id") }, foreign_key: "firm_id", class_name: "Account"
+  has_one :readonly_account, -> { readonly }, foreign_key: "firm_id", class_name: "Account"
   # added order by id as in fixtures there are two accounts for Rails Core
   # Oracle tests were failing because of that as the second fixture was selected
-  has_one :account_using_primary_key, -> { order('id') }, :primary_key => "firm_id", :class_name => "Account"
-  has_one :account_using_foreign_and_primary_keys, :foreign_key => "firm_name", :primary_key => "name", :class_name => "Account"
-  has_one :account_with_inexistent_foreign_key, class_name: 'Account', foreign_key: "inexistent"
-  has_one :deletable_account, :foreign_key => "firm_id", :class_name => "Account", :dependent => :delete
+  has_one :account_using_primary_key, -> { order("id") }, primary_key: "firm_id", class_name: "Account"
+  has_one :account_using_foreign_and_primary_keys, foreign_key: "firm_name", primary_key: "name", class_name: "Account"
+  has_one :account_with_inexistent_foreign_key, class_name: "Account", foreign_key: "inexistent"
+  has_one :deletable_account, foreign_key: "firm_id", class_name: "Account", dependent: :delete
 
-  has_one :account_limit_500_with_hash_conditions, -> { where :credit_limit => 500 }, :foreign_key => "firm_id", :class_name => "Account"
+  has_one :account_limit_500_with_hash_conditions, -> { where credit_limit: 500 }, foreign_key: "firm_id", class_name: "Account"
 
-  has_one :unautosaved_account, :foreign_key => "firm_id", :class_name => 'Account', :autosave => false
+  has_one :unautosaved_account, foreign_key: "firm_id", class_name: "Account", autosave: false
   has_many :accounts
-  has_many :unautosaved_accounts, :foreign_key => "firm_id", :class_name => 'Account', :autosave => false
+  has_many :unautosaved_accounts, foreign_key: "firm_id", class_name: "Account", autosave: false
+
+  has_many :association_with_references, -> { references(:foo) }, class_name: "Client"
+
+  has_many :developers_with_select, -> { select("id, name, first_name") }, class_name: "Developer"
 
-  has_many :association_with_references, -> { references(:foo) }, :class_name => 'Client'
+  has_one :lead_developer, class_name: "Developer"
+  has_many :projects
 
   def log
     @log ||= []
@@ -101,32 +107,38 @@ class Firm < Company
 end
 
 class DependentFirm < Company
-  has_one :account, :foreign_key => "firm_id", :dependent => :nullify
-  has_many :companies, :foreign_key => 'client_of', :dependent => :nullify
-  has_one :company, :foreign_key => 'client_of', :dependent => :nullify
+  has_one :account, foreign_key: "firm_id", dependent: :nullify
+  has_many :companies, foreign_key: "client_of", dependent: :nullify
+  has_one :company, foreign_key: "client_of", dependent: :nullify
 end
 
 class RestrictedWithExceptionFirm < Company
-  has_one :account, -> { order("id") }, :foreign_key => "firm_id", :dependent => :restrict_with_exception
-  has_many :companies, -> { order("id") }, :foreign_key => 'client_of', :dependent => :restrict_with_exception
+  has_one :account, -> { order("id") }, foreign_key: "firm_id", dependent: :restrict_with_exception
+  has_many :companies, -> { order("id") }, foreign_key: "client_of", dependent: :restrict_with_exception
 end
 
 class RestrictedWithErrorFirm < Company
-  has_one :account, -> { order("id") }, :foreign_key => "firm_id", :dependent => :restrict_with_error
-  has_many :companies, -> { order("id") }, :foreign_key => 'client_of', :dependent => :restrict_with_error
+  has_one :account, -> { order("id") }, foreign_key: "firm_id", dependent: :restrict_with_error
+  has_many :companies, -> { order("id") }, foreign_key: "client_of", dependent: :restrict_with_error
+end
+
+class Agency < Firm
+  has_many :projects, foreign_key: :firm_id
+
+  accepts_nested_attributes_for :projects
 end
 
 class Client < Company
-  belongs_to :firm, :foreign_key => "client_of"
-  belongs_to :firm_with_basic_id, :class_name => "Firm", :foreign_key => "firm_id"
-  belongs_to :firm_with_select, -> { select("id") }, :class_name => "Firm", :foreign_key => "firm_id"
-  belongs_to :firm_with_other_name, :class_name => "Firm", :foreign_key => "client_of"
-  belongs_to :firm_with_condition, -> { where "1 = ?", 1 }, :class_name => "Firm", :foreign_key => "client_of"
-  belongs_to :firm_with_primary_key, :class_name => "Firm", :primary_key => "name", :foreign_key => "firm_name"
-  belongs_to :firm_with_primary_key_symbols, :class_name => "Firm", :primary_key => :name, :foreign_key => :firm_name
-  belongs_to :readonly_firm, -> { readonly }, :class_name => "Firm", :foreign_key => "firm_id"
-  belongs_to :bob_firm, -> { where :name => "Bob" }, :class_name => "Firm", :foreign_key => "client_of"
-  has_many :accounts, :through => :firm, :source => :accounts
+  belongs_to :firm, foreign_key: "client_of"
+  belongs_to :firm_with_basic_id, class_name: "Firm", foreign_key: "firm_id"
+  belongs_to :firm_with_select, -> { select("id") }, class_name: "Firm", foreign_key: "firm_id"
+  belongs_to :firm_with_other_name, class_name: "Firm", foreign_key: "client_of"
+  belongs_to :firm_with_condition, -> { where "1 = ?", 1 }, class_name: "Firm", foreign_key: "client_of"
+  belongs_to :firm_with_primary_key, class_name: "Firm", primary_key: "name", foreign_key: "firm_name"
+  belongs_to :firm_with_primary_key_symbols, class_name: "Firm", primary_key: :name, foreign_key: :firm_name
+  belongs_to :readonly_firm, -> { readonly }, class_name: "Firm", foreign_key: "firm_id"
+  belongs_to :bob_firm, -> { where name: "Bob" }, class_name: "Firm", foreign_key: "client_of"
+  has_many :accounts, through: :firm, source: :accounts
   belongs_to :account
 
   validate do
@@ -139,6 +151,21 @@ class Client < Company
     raise RaisedOnSave if raise_on_save
   end
 
+  attr_accessor :throw_on_save
+  before_save do
+    throw :abort if throw_on_save
+  end
+
+  attr_accessor :rollback_on_save
+  after_save do
+    raise ActiveRecord::Rollback if rollback_on_save
+  end
+
+  attr_accessor :rollback_on_create_called
+  after_rollback(on: :create) do |client|
+    client.rollback_on_create_called = true
+  end
+
   class RaisedOnDestroy < RuntimeError; end
   attr_accessor :raise_on_destroy
   before_destroy do
@@ -149,7 +176,7 @@ class Client < Company
   # is calling client.destroy, deleting from the database, or setting
   # foreign keys to NULL.
   def self.destroyed_client_ids
-    @destroyed_client_ids ||= Hash.new { |h,k| h[k] = [] }
+    @destroyed_client_ids ||= Hash.new { |h, k| h[k] = [] }
   end
 
   before_destroy do |client|
@@ -168,20 +195,13 @@ class Client < Company
 
   def overwrite_to_raise
   end
-
-  class << self
-    private
-
-    def private_method
-      "darkness"
-    end
-  end
 end
 
 class ExclusivelyDependentFirm < Company
-  has_one :account, :foreign_key => "firm_id", :dependent => :delete
-  has_many :dependent_sanitized_conditional_clients_of_firm, -> { order("id").where("name = 'BigShot Inc.'") }, :foreign_key => "client_of", :class_name => "Client", :dependent => :delete_all
-  has_many :dependent_conditional_clients_of_firm, -> { order("id").where("name = ?", 'BigShot Inc.') }, :foreign_key => "client_of", :class_name => "Client", :dependent => :delete_all
+  has_one :account, foreign_key: "firm_id", dependent: :delete
+  has_many :dependent_sanitized_conditional_clients_of_firm, -> { order("id").where("name = 'BigShot Inc.'") }, foreign_key: "client_of", class_name: "Client", dependent: :delete_all
+  has_many :dependent_hash_conditional_clients_of_firm, -> { order("id").where(name: "BigShot Inc.") }, foreign_key: "client_of", class_name: "Client", dependent: :delete_all
+  has_many :dependent_conditional_clients_of_firm, -> { order("id").where("name = ?", "BigShot Inc.") }, foreign_key: "client_of", class_name: "Client", dependent: :delete_all
 end
 
 class SpecialClient < Client
@@ -190,39 +210,12 @@ end
 class VerySpecialClient < SpecialClient
 end
 
-class Account < ActiveRecord::Base
-  belongs_to :firm, :class_name => 'Company'
-  belongs_to :unautosaved_firm, :foreign_key => "firm_id", :class_name => "Firm", :autosave => false
-
-  alias_attribute :available_credit, :credit_limit
-
-  def self.destroyed_account_ids
-    @destroyed_account_ids ||= Hash.new { |h,k| h[k] = [] }
-  end
-
-  # Test private kernel method through collection proxy using has_many.
-  def self.open
-    where('firm_name = ?', '37signals')
-  end
-
-  before_destroy do |account|
-    if account.firm
-      Account.destroyed_account_ids[account.firm.id] << account.id
-    end
-    true
-  end
-
-  validate :check_empty_credit_limit
-
-  protected
-
-  def check_empty_credit_limit
-    errors.add("credit_limit", :blank) if credit_limit.blank?
-  end
-
-  private
+class NewlyContractedCompany < Company
+  has_many :new_contracts, foreign_key: "company_id"
 
-  def private_method
-    "Sir, yes sir!"
+  before_save do
+    self.new_contracts << NewContract.new
   end
 end
+
+require "models/account"
diff --git a/activerecord/test/models/company_in_module.rb b/activerecord/test/models/company_in_module.rb
index bf0a0d1c3e..52b7e06a63 100644
--- a/activerecord/test/models/company_in_module.rb
+++ b/activerecord/test/models/company_in_module.rb
@@ -1,4 +1,6 @@
-require 'active_support/core_ext/object/with_options'
+# frozen_string_literal: true
+
+require "active_support/core_ext/object/with_options"
 
 module MyApplication
   module Business
@@ -6,23 +8,23 @@ module MyApplication
     end
 
     class Firm < Company
-      has_many :clients, -> { order("id") }, :dependent => :destroy
-      has_many :clients_sorted_desc, -> { order("id DESC") }, :class_name => "Client"
-      has_many :clients_of_firm, -> { order "id" }, :foreign_key => "client_of", :class_name => "Client"
-      has_many :clients_like_ms, -> { where("name = 'Microsoft'").order("id") }, :class_name => "Client"
-      has_one :account, :class_name => 'MyApplication::Billing::Account', :dependent => :destroy
+      has_many :clients, -> { order("id") }, dependent: :destroy
+      has_many :clients_sorted_desc, -> { order("id DESC") }, class_name: "Client"
+      has_many :clients_of_firm, -> { order "id" }, foreign_key: "client_of", class_name: "Client"
+      has_many :clients_like_ms, -> { where("name = 'Microsoft'").order("id") }, class_name: "Client"
+      has_one :account, class_name: "MyApplication::Billing::Account", dependent: :destroy
     end
 
     class Client < Company
-      belongs_to :firm, :foreign_key => "client_of"
-      belongs_to :firm_with_other_name, :class_name => "Firm", :foreign_key => "client_of"
+      belongs_to :firm, foreign_key: "client_of"
+      belongs_to :firm_with_other_name, class_name: "Firm", foreign_key: "client_of"
 
       class Contact < ActiveRecord::Base; end
     end
 
     class Developer < ActiveRecord::Base
       has_and_belongs_to_many :projects
-      validates_length_of :name, :within => (3..20)
+      validates_length_of :name, within: (3..20)
     end
 
     class Project < ActiveRecord::Base
@@ -31,14 +33,14 @@ module MyApplication
 
     module Prefixed
       def self.table_name_prefix
-        'prefixed_'
+        "prefixed_"
       end
 
       class Company < ActiveRecord::Base
       end
 
       class Firm < Company
-        self.table_name = 'companies'
+        self.table_name = "companies"
       end
 
       module Nested
@@ -49,14 +51,14 @@ module MyApplication
 
     module Suffixed
       def self.table_name_suffix
-        '_suffixed'
+        "_suffixed"
       end
 
       class Company < ActiveRecord::Base
       end
 
       class Firm < Company
-        self.table_name = 'companies'
+        self.table_name = "companies"
       end
 
       module Nested
@@ -68,31 +70,31 @@ module MyApplication
 
   module Billing
     class Firm < ActiveRecord::Base
-      self.table_name = 'companies'
+      self.table_name = "companies"
     end
 
     module Nested
       class Firm < ActiveRecord::Base
-        self.table_name = 'companies'
+        self.table_name = "companies"
       end
     end
 
     class Account < ActiveRecord::Base
-      with_options(:foreign_key => :firm_id) do |i|
-        i.belongs_to :firm, :class_name => 'MyApplication::Business::Firm'
-        i.belongs_to :qualified_billing_firm, :class_name => 'MyApplication::Billing::Firm'
-        i.belongs_to :unqualified_billing_firm, :class_name => 'Firm'
-        i.belongs_to :nested_qualified_billing_firm, :class_name => 'MyApplication::Billing::Nested::Firm'
-        i.belongs_to :nested_unqualified_billing_firm, :class_name => 'Nested::Firm'
+      with_options(foreign_key: :firm_id) do |i|
+        i.belongs_to :firm, class_name: "MyApplication::Business::Firm"
+        i.belongs_to :qualified_billing_firm, class_name: "MyApplication::Billing::Firm"
+        i.belongs_to :unqualified_billing_firm, class_name: "Firm"
+        i.belongs_to :nested_qualified_billing_firm, class_name: "MyApplication::Billing::Nested::Firm"
+        i.belongs_to :nested_unqualified_billing_firm, class_name: "Nested::Firm"
       end
 
       validate :check_empty_credit_limit
 
-      protected
+      private
 
-      def check_empty_credit_limit
-        errors.add("credit_card", :blank) if credit_card.blank?
-      end
+        def check_empty_credit_limit
+          errors.add("credit_card", :blank) if credit_card.blank?
+        end
     end
   end
 end
diff --git a/activerecord/test/models/computer.rb b/activerecord/test/models/computer.rb
index cc8deb1b2b..582b4a38b5 100644
--- a/activerecord/test/models/computer.rb
+++ b/activerecord/test/models/computer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Computer < ActiveRecord::Base
-  belongs_to :developer, :foreign_key=>'developer'
+  belongs_to :developer, foreign_key: "developer"
 end
diff --git a/activerecord/test/models/contact.rb b/activerecord/test/models/contact.rb
index 3ea17c3abf..6e02ff199b 100644
--- a/activerecord/test/models/contact.rb
+++ b/activerecord/test/models/contact.rb
@@ -1,11 +1,13 @@
+# frozen_string_literal: true
+
 module ContactFakeColumns
   def self.extended(base)
     base.class_eval do
-      establish_connection(:adapter => 'fake')
+      establish_connection(adapter: "fake")
 
-      connection.tables = [table_name]
+      connection.data_sources = [table_name]
       connection.primary_keys = {
-        table_name => 'id'
+        table_name => "id"
       }
 
       column :id,             :integer
@@ -19,7 +21,7 @@ module ContactFakeColumns
 
       serialize :preferences
 
-      belongs_to :alternative, :class_name => 'Contact'
+      belongs_to :alternative, class_name: "Contact"
     end
   end
 
@@ -37,5 +39,5 @@ class ContactSti < ActiveRecord::Base
   extend ContactFakeColumns
   column :type, :string
 
-  def type; 'ContactSti' end
+  def type; "ContactSti" end
 end
diff --git a/activerecord/test/models/content.rb b/activerecord/test/models/content.rb
new file mode 100644
index 0000000000..14bbee53d8
--- /dev/null
+++ b/activerecord/test/models/content.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+class Content < ActiveRecord::Base
+  self.table_name = "content"
+  has_one :content_position, dependent: :destroy
+
+  def self.destroyed_ids
+    @destroyed_ids ||= []
+  end
+
+  before_destroy do |object|
+    Content.destroyed_ids << object.id
+  end
+end
+
+class ContentWhichRequiresTwoDestroyCalls < ActiveRecord::Base
+  self.table_name = "content"
+  has_one :content_position, foreign_key: "content_id", dependent: :destroy
+
+  after_initialize do
+    @destroy_count = 0
+  end
+
+  before_destroy do
+    @destroy_count += 1
+    if @destroy_count == 1
+      throw :abort
+    end
+  end
+end
+
+class ContentPosition < ActiveRecord::Base
+  belongs_to :content, dependent: :destroy
+
+  def self.destroyed_ids
+    @destroyed_ids ||= []
+  end
+
+  before_destroy do |object|
+    ContentPosition.destroyed_ids << object.id
+  end
+end
diff --git a/activerecord/test/models/contract.rb b/activerecord/test/models/contract.rb
index cdf7b267b5..3f663375c4 100644
--- a/activerecord/test/models/contract.rb
+++ b/activerecord/test/models/contract.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 class Contract < ActiveRecord::Base
   belongs_to :company
-  belongs_to :developer
-  belongs_to :firm, :foreign_key => 'company_id'
+  belongs_to :developer, primary_key: :id
+  belongs_to :firm, foreign_key: "company_id"
 
   before_save :hi
   after_save :bye
@@ -18,3 +20,7 @@ class Contract < ActiveRecord::Base
     @bye_count += 1
   end
 end
+
+class NewContract < Contract
+  validates :company_id, presence: true
+end
diff --git a/activerecord/test/models/country.rb b/activerecord/test/models/country.rb
index 7db9a4e731..4b4a276a98 100644
--- a/activerecord/test/models/country.rb
+++ b/activerecord/test/models/country.rb
@@ -1,7 +1,5 @@
-class Country < ActiveRecord::Base
-
-  self.primary_key = :country_id
+# frozen_string_literal: true
 
+class Country < ActiveRecord::Base
   has_and_belongs_to_many :treaties
-
 end
diff --git a/activerecord/test/models/course.rb b/activerecord/test/models/course.rb
index f3d0e05ff7..4f346124ea 100644
--- a/activerecord/test/models/course.rb
+++ b/activerecord/test/models/course.rb
@@ -1,4 +1,6 @@
-require_dependency 'models/arunit2_model'
+# frozen_string_literal: true
+
+require_dependency "models/arunit2_model"
 
 class Course < ARUnit2Model
   belongs_to :college
diff --git a/activerecord/test/models/customer.rb b/activerecord/test/models/customer.rb
index afe4b3d707..bc501a5ce0 100644
--- a/activerecord/test/models/customer.rb
+++ b/activerecord/test/models/customer.rb
@@ -1,12 +1,15 @@
+# frozen_string_literal: true
+
 class Customer < ActiveRecord::Base
   cattr_accessor :gps_conversion_was_run
 
-  composed_of :address, :mapping => [ %w(address_street street), %w(address_city city), %w(address_country country) ], :allow_nil => true
-  composed_of :balance, :class_name => "Money", :mapping => %w(balance amount), :converter => Proc.new(&:to_money)
-  composed_of :gps_location, :allow_nil => true
-  composed_of :non_blank_gps_location, :class_name => "GpsLocation", :allow_nil => true, :mapping => %w(gps_location gps_location),
-              :converter => lambda { |gps| self.gps_conversion_was_run = true; gps.blank? ? nil : GpsLocation.new(gps)}
-  composed_of :fullname, :mapping => %w(name to_s), :constructor => Proc.new { |name| Fullname.parse(name) }, :converter => :parse
+  composed_of :address, mapping: [ %w(address_street street), %w(address_city city), %w(address_country country) ], allow_nil: true
+  composed_of :balance, class_name: "Money", mapping: %w(balance amount)
+  composed_of :gps_location, allow_nil: true
+  composed_of :non_blank_gps_location, class_name: "GpsLocation", allow_nil: true, mapping: %w(gps_location gps_location),
+              converter: lambda { |gps| self.gps_conversion_was_run = true; gps.blank? ? nil : GpsLocation.new(gps) }
+  composed_of :fullname, mapping: %w(name to_s), constructor: Proc.new { |name| Fullname.parse(name) }, converter: :parse
+  composed_of :fullname_no_converter, mapping: %w(name to_s), class_name: "Fullname"
 end
 
 class Address
@@ -55,7 +58,7 @@ class GpsLocation
   end
 
   def ==(other)
-    self.latitude == other.latitude && self.longitude == other.longitude
+    latitude == other.latitude && longitude == other.longitude
   end
 end
 
@@ -64,7 +67,12 @@ class Fullname
 
   def self.parse(str)
     return nil unless str
-    new(*str.to_s.split)
+
+    if str.is_a?(Hash)
+      new(str[:first], str[:last])
+    else
+      new(*str.to_s.split)
+    end
   end
 
   def initialize(first, last = nil)
diff --git a/activerecord/test/models/customer_carrier.rb b/activerecord/test/models/customer_carrier.rb
new file mode 100644
index 0000000000..6cb9d5239d
--- /dev/null
+++ b/activerecord/test/models/customer_carrier.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+class CustomerCarrier < ActiveRecord::Base
+  cattr_accessor :current_customer
+
+  belongs_to :customer
+  belongs_to :carrier
+
+  default_scope -> {
+    if current_customer
+      where(customer: current_customer)
+    else
+      all
+    end
+  }
+end
diff --git a/activerecord/test/models/dashboard.rb b/activerecord/test/models/dashboard.rb
index 1b3b54545f..d25ceeafb1 100644
--- a/activerecord/test/models/dashboard.rb
+++ b/activerecord/test/models/dashboard.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Dashboard < ActiveRecord::Base
   self.primary_key = :dashboard_id
 end
diff --git a/activerecord/test/models/default.rb b/activerecord/test/models/default.rb
index 887e9cc999..90f1046d87 100644
--- a/activerecord/test/models/default.rb
+++ b/activerecord/test/models/default.rb
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 class Default < ActiveRecord::Base
 end
diff --git a/activerecord/test/models/department.rb b/activerecord/test/models/department.rb
index 08004a0ed3..868b9bf4bf 100644
--- a/activerecord/test/models/department.rb
+++ b/activerecord/test/models/department.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Department < ActiveRecord::Base
   has_many :chefs
   belongs_to :hotel
diff --git a/activerecord/test/models/developer.rb b/activerecord/test/models/developer.rb
index d2a5a7fc49..8881c69368 100644
--- a/activerecord/test/models/developer.rb
+++ b/activerecord/test/models/developer.rb
@@ -1,4 +1,6 @@
-require 'ostruct'
+# frozen_string_literal: true
+
+require "ostruct"
 
 module DeveloperProjectsAssociationExtension2
   def find_least_recent
@@ -7,61 +9,72 @@ module DeveloperProjectsAssociationExtension2
 end
 
 class Developer < ActiveRecord::Base
+  self.ignored_columns = %w(first_name last_name)
+
   has_and_belongs_to_many :projects do
     def find_most_recent
       order("id DESC").first
     end
   end
 
+  belongs_to :mentor
+
   accepts_nested_attributes_for :projects
 
   has_and_belongs_to_many :shared_computers, class_name: "Computer"
 
   has_and_belongs_to_many :projects_extended_by_name,
       -> { extending(DeveloperProjectsAssociationExtension) },
-      :class_name => "Project",
-      :join_table => "developers_projects",
-      :association_foreign_key => "project_id"
+      class_name: "Project",
+      join_table: "developers_projects",
+      association_foreign_key: "project_id"
 
   has_and_belongs_to_many :projects_extended_by_name_twice,
       -> { extending(DeveloperProjectsAssociationExtension, DeveloperProjectsAssociationExtension2) },
-      :class_name => "Project",
-      :join_table => "developers_projects",
-      :association_foreign_key => "project_id"
+      class_name: "Project",
+      join_table: "developers_projects",
+      association_foreign_key: "project_id"
 
   has_and_belongs_to_many :projects_extended_by_name_and_block,
       -> { extending(DeveloperProjectsAssociationExtension) },
-      :class_name => "Project",
-      :join_table => "developers_projects",
-      :association_foreign_key => "project_id" do
+      class_name: "Project",
+      join_table: "developers_projects",
+      association_foreign_key: "project_id" do
         def find_least_recent
           order("id ASC").first
         end
       end
 
-  has_and_belongs_to_many :special_projects, :join_table => 'developers_projects', :association_foreign_key => 'project_id'
+  has_and_belongs_to_many :special_projects, join_table: "developers_projects", association_foreign_key: "project_id"
   has_and_belongs_to_many :sym_special_projects,
-                          :join_table => :developers_projects,
-                          :association_foreign_key => 'project_id',
-                          :class_name => 'SpecialProject'
+                          join_table: :developers_projects,
+                          association_foreign_key: "project_id",
+                          class_name: "SpecialProject"
 
   has_many :audit_logs
   has_many :contracts
-  has_many :firms, :through => :contracts, :source => :firm
+  has_many :firms, through: :contracts, source: :firm
   has_many :comments, ->(developer) { where(body: "I'm #{developer.name}") }
   has_many :ratings, through: :comments
+  has_one :ship, dependent: :nullify
 
-  scope :jamises, -> { where(:name => 'Jamis') }
+  belongs_to :firm
+  has_many :contracted_projects, class_name: "Project"
 
-  validates_inclusion_of :salary, :in => 50000..200000
-  validates_length_of    :name, :within => 3..20
+  scope :jamises, -> { where(name: "Jamis") }
+
+  validates_inclusion_of :salary, in: 50000..200000
+  validates_length_of    :name, within: 3..20
 
   before_create do |developer|
-    developer.audit_logs.build :message => "Computer created"
+    developer.audit_logs.build message: "Computer created"
   end
 
+  attr_accessor :last_name
+  define_attribute_method "last_name"
+
   def log=(message)
-    audit_logs.build :message => message
+    audit_logs.build message: message
   end
 
   after_find :track_instance_count
@@ -72,17 +85,27 @@ class Developer < ActiveRecord::Base
     self.class.instance_count += 1
   end
   private :track_instance_count
+end
+
+class SubDeveloper < Developer
+end
+
+class SymbolIgnoredDeveloper < ActiveRecord::Base
+  self.table_name = "developers"
+  self.ignored_columns = [:first_name, :last_name]
 
+  attr_accessor :last_name
+  define_attribute_method "last_name"
 end
 
 class AuditLog < ActiveRecord::Base
-  belongs_to :developer, :validate => true
-  belongs_to :unvalidated_developer, :class_name => 'Developer'
+  belongs_to :developer, validate: true
+  belongs_to :unvalidated_developer, class_name: "Developer"
 end
 
 class DeveloperWithBeforeDestroyRaise < ActiveRecord::Base
-  self.table_name = 'developers'
-  has_and_belongs_to_many :projects, :join_table => 'developers_projects', :foreign_key => 'developer_id'
+  self.table_name = "developers"
+  has_and_belongs_to_many :projects, join_table: "developers_projects", foreign_key: "developer_id"
   before_destroy :raise_if_projects_empty!
 
   def raise_if_projects_empty!
@@ -91,63 +114,63 @@ class DeveloperWithBeforeDestroyRaise < ActiveRecord::Base
 end
 
 class DeveloperWithSelect < ActiveRecord::Base
-  self.table_name = 'developers'
-  default_scope { select('name') }
+  self.table_name = "developers"
+  default_scope { select("name") }
 end
 
 class DeveloperWithIncludes < ActiveRecord::Base
-  self.table_name = 'developers'
-  has_many :audit_logs, :foreign_key => :developer_id
+  self.table_name = "developers"
+  has_many :audit_logs, foreign_key: :developer_id
   default_scope { includes(:audit_logs) }
 end
 
 class DeveloperFilteredOnJoins < ActiveRecord::Base
-  self.table_name = 'developers'
-  has_and_belongs_to_many :projects, -> { order('projects.id') }, :foreign_key => 'developer_id', :join_table => 'developers_projects'
+  self.table_name = "developers"
+  has_and_belongs_to_many :projects, -> { order("projects.id") }, foreign_key: "developer_id", join_table: "developers_projects"
 
   def self.default_scope
-    joins(:projects).where(:projects => { :name => 'Active Controller' })
+    joins(:projects).where(projects: { name: "Active Controller" })
   end
 end
 
 class DeveloperOrderedBySalary < ActiveRecord::Base
-  self.table_name = 'developers'
-  default_scope { order('salary DESC') }
+  self.table_name = "developers"
+  default_scope { order("salary DESC") }
 
-  scope :by_name, -> { order('name DESC') }
+  scope :by_name, -> { order("name DESC") }
 end
 
 class DeveloperCalledDavid < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
   default_scope { where("name = 'David'") }
 end
 
 class LazyLambdaDeveloperCalledDavid < ActiveRecord::Base
-  self.table_name = 'developers'
-  default_scope lambda { where(:name => 'David') }
+  self.table_name = "developers"
+  default_scope lambda { where(name: "David") }
 end
 
 class LazyBlockDeveloperCalledDavid < ActiveRecord::Base
-  self.table_name = 'developers'
-  default_scope { where(:name => 'David') }
+  self.table_name = "developers"
+  default_scope { where(name: "David") }
 end
 
 class CallableDeveloperCalledDavid < ActiveRecord::Base
-  self.table_name = 'developers'
-  default_scope OpenStruct.new(:call => where(:name => 'David'))
+  self.table_name = "developers"
+  default_scope OpenStruct.new(call: where(name: "David"))
 end
 
 class ClassMethodDeveloperCalledDavid < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
   def self.default_scope
-    where(:name => 'David')
+    where(name: "David")
   end
 end
 
 class ClassMethodReferencingScopeDeveloperCalledDavid < ActiveRecord::Base
-  self.table_name = 'developers'
-  scope :david, -> { where(:name => 'David') }
+  self.table_name = "developers"
+  scope :david, -> { where(name: "David") }
 
   def self.default_scope
     david
@@ -155,61 +178,61 @@ class ClassMethodReferencingScopeDeveloperCalledDavid < ActiveRecord::Base
 end
 
 class LazyBlockReferencingScopeDeveloperCalledDavid < ActiveRecord::Base
-  self.table_name = 'developers'
-  scope :david, -> { where(:name => 'David') }
+  self.table_name = "developers"
+  scope :david, -> { where(name: "David") }
   default_scope { david }
 end
 
 class DeveloperCalledJamis < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
-  default_scope { where(:name => 'Jamis') }
-  scope :poor, -> { where('salary < 150000') }
+  default_scope { where(name: "Jamis") }
+  scope :poor, -> { where("salary < 150000") }
   scope :david, -> { where name: "David" }
   scope :david2, -> { unscoped.where name: "David" }
 end
 
 class PoorDeveloperCalledJamis < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
-  default_scope -> { where(:name => 'Jamis', :salary => 50000) }
+  default_scope -> { where(name: "Jamis", salary: 50000) }
 end
 
 class InheritedPoorDeveloperCalledJamis < DeveloperCalledJamis
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
-  default_scope -> { where(:salary => 50000) }
+  default_scope -> { where(salary: 50000) }
 end
 
 class MultiplePoorDeveloperCalledJamis < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
-  default_scope -> { where(:name => 'Jamis') }
-  default_scope -> { where(:salary => 50000) }
+  default_scope -> { where(name: "Jamis") }
+  default_scope -> { where(salary: 50000) }
 end
 
 module SalaryDefaultScope
   extend ActiveSupport::Concern
 
-  included { default_scope { where(:salary => 50000) } }
+  included { default_scope { where(salary: 50000) } }
 end
 
 class ModuleIncludedPoorDeveloperCalledJamis < DeveloperCalledJamis
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
   include SalaryDefaultScope
 end
 
 class EagerDeveloperWithDefaultScope < ActiveRecord::Base
-  self.table_name = 'developers'
-  has_and_belongs_to_many :projects, -> { order('projects.id') }, :foreign_key => 'developer_id', :join_table => 'developers_projects'
+  self.table_name = "developers"
+  has_and_belongs_to_many :projects, -> { order("projects.id") }, foreign_key: "developer_id", join_table: "developers_projects"
 
   default_scope { includes(:projects) }
 end
 
 class EagerDeveloperWithClassMethodDefaultScope < ActiveRecord::Base
-  self.table_name = 'developers'
-  has_and_belongs_to_many :projects, -> { order('projects.id') }, :foreign_key => 'developer_id', :join_table => 'developers_projects'
+  self.table_name = "developers"
+  has_and_belongs_to_many :projects, -> { order("projects.id") }, foreign_key: "developer_id", join_table: "developers_projects"
 
   def self.default_scope
     includes(:projects)
@@ -217,31 +240,31 @@ class EagerDeveloperWithClassMethodDefaultScope < ActiveRecord::Base
 end
 
 class EagerDeveloperWithLambdaDefaultScope < ActiveRecord::Base
-  self.table_name = 'developers'
-  has_and_belongs_to_many :projects, -> { order('projects.id') }, :foreign_key => 'developer_id', :join_table => 'developers_projects'
+  self.table_name = "developers"
+  has_and_belongs_to_many :projects, -> { order("projects.id") }, foreign_key: "developer_id", join_table: "developers_projects"
 
   default_scope lambda { includes(:projects) }
 end
 
 class EagerDeveloperWithBlockDefaultScope < ActiveRecord::Base
-  self.table_name = 'developers'
-  has_and_belongs_to_many :projects, -> { order('projects.id') }, :foreign_key => 'developer_id', :join_table => 'developers_projects'
+  self.table_name = "developers"
+  has_and_belongs_to_many :projects, -> { order("projects.id") }, foreign_key: "developer_id", join_table: "developers_projects"
 
   default_scope { includes(:projects) }
 end
 
 class EagerDeveloperWithCallableDefaultScope < ActiveRecord::Base
-  self.table_name = 'developers'
-  has_and_belongs_to_many :projects, -> { order('projects.id') }, :foreign_key => 'developer_id', :join_table => 'developers_projects'
+  self.table_name = "developers"
+  has_and_belongs_to_many :projects, -> { order("projects.id") }, foreign_key: "developer_id", join_table: "developers_projects"
 
-  default_scope OpenStruct.new(:call => includes(:projects))
+  default_scope OpenStruct.new(call: includes(:projects))
 end
 
 class ThreadsafeDeveloper < ActiveRecord::Base
-  self.table_name = 'developers'
+  self.table_name = "developers"
 
   def self.default_scope
-    sleep 0.05 if Thread.current[:long_default_scope]
+    Thread.current[:default_scope_delay].call
     limit(1)
   end
 end
@@ -250,3 +273,9 @@ class CachedDeveloper < ActiveRecord::Base
   self.table_name = "developers"
   self.cache_timestamp_format = :number
 end
+
+class DeveloperWithIncorrectlyOrderedHasManyThrough < ActiveRecord::Base
+  self.table_name = "developers"
+  has_many :companies, through: :contracts
+  has_many :contracts, foreign_key: :developer_id
+end
diff --git a/activerecord/test/models/dog.rb b/activerecord/test/models/dog.rb
index b02b8447b8..75d284ac25 100644
--- a/activerecord/test/models/dog.rb
+++ b/activerecord/test/models/dog.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Dog < ActiveRecord::Base
   belongs_to :breeder, class_name: "DogLover", counter_cache: :bred_dogs_count
   belongs_to :trainer, class_name: "DogLover", counter_cache: :trained_dogs_count
diff --git a/activerecord/test/models/dog_lover.rb b/activerecord/test/models/dog_lover.rb
index 2c5be94aea..aabe914f77 100644
--- a/activerecord/test/models/dog_lover.rb
+++ b/activerecord/test/models/dog_lover.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class DogLover < ActiveRecord::Base
   has_many :trained_dogs, class_name: "Dog", foreign_key: :trainer_id, dependent: :destroy
   has_many :bred_dogs, class_name: "Dog", foreign_key: :breeder_id
diff --git a/activerecord/test/models/doubloon.rb b/activerecord/test/models/doubloon.rb
index 2b11d128e2..febadc3a5a 100644
--- a/activerecord/test/models/doubloon.rb
+++ b/activerecord/test/models/doubloon.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class AbstractDoubloon < ActiveRecord::Base
   # This has functionality that might be shared by multiple classes.
 
@@ -8,5 +10,5 @@ end
 class Doubloon < AbstractDoubloon
   # This uses an abstract class that defines attributes and associations.
 
-  self.table_name = 'doubloons'
+  self.table_name = "doubloons"
 end
diff --git a/activerecord/test/models/drink_designer.rb b/activerecord/test/models/drink_designer.rb
index 2db968ef11..eb6701b84e 100644
--- a/activerecord/test/models/drink_designer.rb
+++ b/activerecord/test/models/drink_designer.rb
@@ -1,3 +1,8 @@
+# frozen_string_literal: true
+
 class DrinkDesigner < ActiveRecord::Base
   has_one :chef, as: :employable
 end
+
+class MocktailDesigner < DrinkDesigner
+end
diff --git a/activerecord/test/models/edge.rb b/activerecord/test/models/edge.rb
index 55e0c31fcb..a04ab103de 100644
--- a/activerecord/test/models/edge.rb
+++ b/activerecord/test/models/edge.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 # This class models an edge in a directed graph.
 class Edge < ActiveRecord::Base
-  belongs_to :source, :class_name => 'Vertex', :foreign_key => 'source_id'
-  belongs_to :sink,   :class_name => 'Vertex', :foreign_key => 'sink_id'
+  belongs_to :source, class_name: "Vertex", foreign_key: "source_id"
+  belongs_to :sink,   class_name: "Vertex", foreign_key: "sink_id"
 end
diff --git a/activerecord/test/models/electron.rb b/activerecord/test/models/electron.rb
index 6fc270673f..902006b314 100644
--- a/activerecord/test/models/electron.rb
+++ b/activerecord/test/models/electron.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Electron < ActiveRecord::Base
   belongs_to :molecule
 
diff --git a/activerecord/test/models/engine.rb b/activerecord/test/models/engine.rb
index 851ff8c22b..396a52b3b9 100644
--- a/activerecord/test/models/engine.rb
+++ b/activerecord/test/models/engine.rb
@@ -1,4 +1,5 @@
+# frozen_string_literal: true
+
 class Engine < ActiveRecord::Base
-  belongs_to :my_car, :class_name => 'Car', :foreign_key => 'car_id',  :counter_cache => :engines_count
+  belongs_to :my_car, class_name: "Car", foreign_key: "car_id",  counter_cache: :engines_count
 end
-
diff --git a/activerecord/test/models/entrant.rb b/activerecord/test/models/entrant.rb
index 4682ce48c8..2c086e451f 100644
--- a/activerecord/test/models/entrant.rb
+++ b/activerecord/test/models/entrant.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Entrant < ActiveRecord::Base
   belongs_to :course
 end
diff --git a/activerecord/test/models/essay.rb b/activerecord/test/models/essay.rb
index ec4b982b5b..e59db4d877 100644
--- a/activerecord/test/models/essay.rb
+++ b/activerecord/test/models/essay.rb
@@ -1,5 +1,8 @@
+# frozen_string_literal: true
+
 class Essay < ActiveRecord::Base
-  belongs_to :writer, :primary_key => :name, :polymorphic => true
-  belongs_to :category, :primary_key => :name
-  has_one :owner, :primary_key => :name
+  belongs_to :author
+  belongs_to :writer, primary_key: :name, polymorphic: true
+  belongs_to :category, primary_key: :name
+  has_one :owner, primary_key: :name
 end
diff --git a/activerecord/test/models/event.rb b/activerecord/test/models/event.rb
index 365ab32b0b..a7cdc39e5c 100644
--- a/activerecord/test/models/event.rb
+++ b/activerecord/test/models/event.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Event < ActiveRecord::Base
   validates_uniqueness_of :title
 end
diff --git a/activerecord/test/models/eye.rb b/activerecord/test/models/eye.rb
index dc8ae2b3f6..f3608b62ef 100644
--- a/activerecord/test/models/eye.rb
+++ b/activerecord/test/models/eye.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Eye < ActiveRecord::Base
   attr_reader :after_create_callbacks_stack
   attr_reader :after_update_callbacks_stack
@@ -15,19 +17,19 @@ class Eye < ActiveRecord::Base
   after_create :trace_after_create2
   after_update :trace_after_update2
   after_save   :trace_after_save2
-  
+
   def trace_after_create
     (@after_create_callbacks_stack ||= []) << !iris.persisted?
   end
   alias trace_after_create2 trace_after_create
 
   def trace_after_update
-    (@after_update_callbacks_stack ||= []) << iris.changed?
+    (@after_update_callbacks_stack ||= []) << iris.has_changes_to_save?
   end
   alias trace_after_update2 trace_after_update
 
   def trace_after_save
-    (@after_save_callbacks_stack ||= []) << iris.changed?
+    (@after_save_callbacks_stack ||= []) << iris.has_changes_to_save?
   end
   alias trace_after_save2 trace_after_save
 end
diff --git a/activerecord/test/models/face.rb b/activerecord/test/models/face.rb
index 91e46f83e5..e900fd40fb 100644
--- a/activerecord/test/models/face.rb
+++ b/activerecord/test/models/face.rb
@@ -1,9 +1,16 @@
+# frozen_string_literal: true
+
 class Face < ActiveRecord::Base
-  belongs_to :man, :inverse_of => :face
-  belongs_to :polymorphic_man, :polymorphic => true, :inverse_of => :polymorphic_face
-  # Oracle identifier lengh is limited to 30 bytes or less, `polymorphic` renamed `poly`
-  belongs_to :poly_man_without_inverse, :polymorphic => true
+  belongs_to :man, inverse_of: :face
+  belongs_to :human, polymorphic: true
+  belongs_to :polymorphic_man, polymorphic: true, inverse_of: :polymorphic_face
+  # Oracle identifier length is limited to 30 bytes or less, `polymorphic` renamed `poly`
+  belongs_to :poly_man_without_inverse, polymorphic: true
   # These is a "broken" inverse_of for the purposes of testing
-  belongs_to :horrible_man, :class_name => 'Man', :inverse_of => :horrible_face
-  belongs_to :horrible_polymorphic_man, :polymorphic => true, :inverse_of => :horrible_polymorphic_face
+  belongs_to :horrible_man, class_name: "Man", inverse_of: :horrible_face
+  belongs_to :horrible_polymorphic_man, polymorphic: true, inverse_of: :horrible_polymorphic_face
+
+  validate do
+    man
+  end
 end
diff --git a/activerecord/test/models/family.rb b/activerecord/test/models/family.rb
new file mode 100644
index 0000000000..0713dba1a6
--- /dev/null
+++ b/activerecord/test/models/family.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class Family < ActiveRecord::Base
+  has_many :family_trees, -> { where(token: nil) }
+  has_many :members, through: :family_trees
+end
diff --git a/activerecord/test/models/family_tree.rb b/activerecord/test/models/family_tree.rb
new file mode 100644
index 0000000000..a8ea907c05
--- /dev/null
+++ b/activerecord/test/models/family_tree.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class FamilyTree < ActiveRecord::Base
+  belongs_to :member, class_name: "User", foreign_key: "member_id"
+  belongs_to :family
+end
diff --git a/activerecord/test/models/friendship.rb b/activerecord/test/models/friendship.rb
index 4b411ca8e0..9f1712a8ec 100644
--- a/activerecord/test/models/friendship.rb
+++ b/activerecord/test/models/friendship.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 class Friendship < ActiveRecord::Base
-  belongs_to :friend, class_name: 'Person'
+  belongs_to :friend, class_name: "Person"
   # friend_too exists to test a bug, and probably shouldn't be used elsewhere
-  belongs_to :friend_too, foreign_key: 'friend_id', class_name: 'Person', counter_cache: :friends_too_count
-  belongs_to :follower, class_name: 'Person'
+  belongs_to :friend_too, foreign_key: "friend_id", class_name: "Person", counter_cache: :friends_too_count
+  belongs_to :follower, class_name: "Person"
 end
diff --git a/activerecord/test/models/frog.rb b/activerecord/test/models/frog.rb
new file mode 100644
index 0000000000..73601aacdd
--- /dev/null
+++ b/activerecord/test/models/frog.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class Frog < ActiveRecord::Base
+  after_save do
+    with_lock do
+    end
+  end
+end
diff --git a/activerecord/test/models/guid.rb b/activerecord/test/models/guid.rb
index 05653ba498..ec71c37690 100644
--- a/activerecord/test/models/guid.rb
+++ b/activerecord/test/models/guid.rb
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 class Guid < ActiveRecord::Base
 end
diff --git a/activerecord/test/models/guitar.rb b/activerecord/test/models/guitar.rb
new file mode 100644
index 0000000000..649b998665
--- /dev/null
+++ b/activerecord/test/models/guitar.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class Guitar < ActiveRecord::Base
+  has_many :tuning_pegs, index_errors: true
+  accepts_nested_attributes_for :tuning_pegs
+end
diff --git a/activerecord/test/models/hotel.rb b/activerecord/test/models/hotel.rb
index 491f8dfde3..1a433c3cab 100644
--- a/activerecord/test/models/hotel.rb
+++ b/activerecord/test/models/hotel.rb
@@ -1,7 +1,13 @@
+# frozen_string_literal: true
+
 class Hotel < ActiveRecord::Base
   has_many :departments
   has_many :chefs, through: :departments
-  has_many :cake_designers, source_type: 'CakeDesigner', source: :employable, through: :chefs
-  has_many :drink_designers, source_type: 'DrinkDesigner', source: :employable, through: :chefs
+  has_many :cake_designers, source_type: "CakeDesigner", source: :employable, through: :chefs
+  has_many :drink_designers, source_type: "DrinkDesigner", source: :employable, through: :chefs
+
+  has_many :chef_lists, as: :employable_list
+  has_many :mocktail_designers, through: :chef_lists, source: :employable, source_type: "MocktailDesigner"
+
   has_many :recipes, through: :chefs
 end
diff --git a/activerecord/test/models/image.rb b/activerecord/test/models/image.rb
index 7ae8e4a7f6..b4808293cc 100644
--- a/activerecord/test/models/image.rb
+++ b/activerecord/test/models/image.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Image < ActiveRecord::Base
   belongs_to :imageable, foreign_key: :imageable_identifier, foreign_type: :imageable_class
 end
diff --git a/activerecord/test/models/interest.rb b/activerecord/test/models/interest.rb
index d5d9226204..899b8f9b9d 100644
--- a/activerecord/test/models/interest.rb
+++ b/activerecord/test/models/interest.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 class Interest < ActiveRecord::Base
-  belongs_to :man, :inverse_of => :interests
-  belongs_to :polymorphic_man, :polymorphic => true, :inverse_of => :polymorphic_interests
-  belongs_to :zine, :inverse_of => :interests
+  belongs_to :man, inverse_of: :interests
+  belongs_to :polymorphic_man, polymorphic: true, inverse_of: :polymorphic_interests
+  belongs_to :zine, inverse_of: :interests
 end
diff --git a/activerecord/test/models/invoice.rb b/activerecord/test/models/invoice.rb
index fc6ef0230e..1851792ed5 100644
--- a/activerecord/test/models/invoice.rb
+++ b/activerecord/test/models/invoice.rb
@@ -1,4 +1,6 @@
+# frozen_string_literal: true
+
 class Invoice < ActiveRecord::Base
-  has_many :line_items, :autosave => true
-  before_save {|record| record.balance = record.line_items.map(&:amount).sum }
+  has_many :line_items, autosave: true
+  before_save { |record| record.balance = record.line_items.map(&:amount).sum }
 end
diff --git a/activerecord/test/models/item.rb b/activerecord/test/models/item.rb
index c2571dd7fb..8d079d56e6 100644
--- a/activerecord/test/models/item.rb
+++ b/activerecord/test/models/item.rb
@@ -1,6 +1,8 @@
+# frozen_string_literal: true
+
 class AbstractItem < ActiveRecord::Base
   self.abstract_class = true
-  has_one :tagging, :as => :taggable
+  has_one :tagging, as: :taggable
 end
 
 class Item < AbstractItem
diff --git a/activerecord/test/models/job.rb b/activerecord/test/models/job.rb
index f7b0e787b1..52817a8435 100644
--- a/activerecord/test/models/job.rb
+++ b/activerecord/test/models/job.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 class Job < ActiveRecord::Base
   has_many :references
-  has_many :people, :through => :references
-  belongs_to :ideal_reference, :class_name => 'Reference'
+  has_many :people, through: :references
+  belongs_to :ideal_reference, class_name: "Reference"
 
-  has_many :agents, :through => :people
+  has_many :agents, through: :people
 end
diff --git a/activerecord/test/models/joke.rb b/activerecord/test/models/joke.rb
index edda4655dc..436ffb6471 100644
--- a/activerecord/test/models/joke.rb
+++ b/activerecord/test/models/joke.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 class Joke < ActiveRecord::Base
-  self.table_name = 'funny_jokes'
+  self.table_name = "funny_jokes"
 end
 
 class GoodJoke < ActiveRecord::Base
-  self.table_name = 'funny_jokes'
+  self.table_name = "funny_jokes"
 end
diff --git a/activerecord/test/models/keyboard.rb b/activerecord/test/models/keyboard.rb
index 39347e274e..d200e0fb56 100644
--- a/activerecord/test/models/keyboard.rb
+++ b/activerecord/test/models/keyboard.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Keyboard < ActiveRecord::Base
-  self.primary_key = 'key_number'
+  self.primary_key = "key_number"
 end
diff --git a/activerecord/test/models/legacy_thing.rb b/activerecord/test/models/legacy_thing.rb
index eead181a0e..e0210c8922 100644
--- a/activerecord/test/models/legacy_thing.rb
+++ b/activerecord/test/models/legacy_thing.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class LegacyThing < ActiveRecord::Base
   self.locking_column = :version
 end
diff --git a/activerecord/test/models/lesson.rb b/activerecord/test/models/lesson.rb
index 4c88153068..e546339689 100644
--- a/activerecord/test/models/lesson.rb
+++ b/activerecord/test/models/lesson.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class LessonError < Exception
 end
 
diff --git a/activerecord/test/models/line_item.rb b/activerecord/test/models/line_item.rb
index 0dd921a300..3a51cf03b2 100644
--- a/activerecord/test/models/line_item.rb
+++ b/activerecord/test/models/line_item.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class LineItem < ActiveRecord::Base
-  belongs_to :invoice, :touch => true
+  belongs_to :invoice, touch: true
 end
diff --git a/activerecord/test/models/liquid.rb b/activerecord/test/models/liquid.rb
index 69d4d7df1a..b2fd305d66 100644
--- a/activerecord/test/models/liquid.rb
+++ b/activerecord/test/models/liquid.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Liquid < ActiveRecord::Base
   self.table_name = :liquid
   has_many :molecules, -> { distinct }
diff --git a/activerecord/test/models/man.rb b/activerecord/test/models/man.rb
index 4fbb6b226b..e26920e951 100644
--- a/activerecord/test/models/man.rb
+++ b/activerecord/test/models/man.rb
@@ -1,11 +1,16 @@
+# frozen_string_literal: true
+
 class Man < ActiveRecord::Base
-  has_one :face, :inverse_of => :man
-  has_one :polymorphic_face, :class_name => 'Face', :as => :polymorphic_man, :inverse_of => :polymorphic_man
-  has_one :polymorphic_face_without_inverse, :class_name => 'Face', :as => :poly_man_without_inverse
-  has_many :interests, :inverse_of => :man
-  has_many :polymorphic_interests, :class_name => 'Interest', :as => :polymorphic_man, :inverse_of => :polymorphic_man
+  has_one :face, inverse_of: :man
+  has_one :polymorphic_face, class_name: "Face", as: :polymorphic_man, inverse_of: :polymorphic_man
+  has_one :polymorphic_face_without_inverse, class_name: "Face", as: :poly_man_without_inverse
+  has_many :interests, inverse_of: :man
+  has_many :polymorphic_interests, class_name: "Interest", as: :polymorphic_man, inverse_of: :polymorphic_man
   # These are "broken" inverse_of associations for the purposes of testing
-  has_one :dirty_face, :class_name => 'Face', :inverse_of => :dirty_man
-  has_many :secret_interests, :class_name => 'Interest', :inverse_of => :secret_man
+  has_one :dirty_face, class_name: "Face", inverse_of: :dirty_man
+  has_many :secret_interests, class_name: "Interest", inverse_of: :secret_man
   has_one :mixed_case_monkey
 end
+
+class Human < Man
+end
diff --git a/activerecord/test/models/matey.rb b/activerecord/test/models/matey.rb
index 47b0baa974..a77ac21e96 100644
--- a/activerecord/test/models/matey.rb
+++ b/activerecord/test/models/matey.rb
@@ -1,4 +1,6 @@
+# frozen_string_literal: true
+
 class Matey < ActiveRecord::Base
   belongs_to :pirate
-  belongs_to :target, :class_name => 'Pirate'
+  belongs_to :target, class_name: "Pirate"
 end
diff --git a/activerecord/test/models/member.rb b/activerecord/test/models/member.rb
index dc0566d8a7..6e33ac0a6d 100644
--- a/activerecord/test/models/member.rb
+++ b/activerecord/test/models/member.rb
@@ -1,32 +1,39 @@
+# frozen_string_literal: true
+
 class Member < ActiveRecord::Base
   has_one :current_membership
   has_one :selected_membership
   has_one :membership
-  has_one :club, :through => :current_membership
-  has_one :selected_club, :through => :selected_membership, :source => :club
-  has_one :favourite_club, -> { where "memberships.favourite = ?", true }, :through => :membership, :source => :club
-  has_one :hairy_club, -> { where :clubs => {:name => "Moustache and Eyebrow Fancier Club"} }, :through => :membership, :source => :club
-  has_one :sponsor, :as => :sponsorable
-  has_one :sponsor_club, :through => :sponsor
-  has_one :member_detail, :inverse_of => false
-  has_one :organization, :through => :member_detail
+  has_one :club, through: :current_membership
+  has_one :selected_club, through: :selected_membership, source: :club
+  has_one :favourite_club, -> { where "memberships.favourite = ?", true }, through: :membership, source: :club
+  has_one :hairy_club, -> { where clubs: { name: "Moustache and Eyebrow Fancier Club" } }, through: :membership, source: :club
+  has_one :sponsor, as: :sponsorable
+  has_one :sponsor_club, through: :sponsor
+  has_one :member_detail, inverse_of: false
+  has_one :organization, through: :member_detail
   belongs_to :member_type
 
-  has_many :nested_member_types, :through => :member_detail, :source => :member_type
-  has_one :nested_member_type, :through => :member_detail, :source => :member_type
+  has_many :nested_member_types, through: :member_detail, source: :member_type
+  has_one :nested_member_type, through: :member_detail, source: :member_type
+
+  has_many :nested_sponsors, through: :sponsor_club, source: :sponsor
+  has_one :nested_sponsor, through: :sponsor_club, source: :sponsor
 
-  has_many :nested_sponsors, :through => :sponsor_club, :source => :sponsor
-  has_one :nested_sponsor, :through => :sponsor_club, :source => :sponsor
+  has_many :organization_member_details, through: :member_detail
+  has_many :organization_member_details_2, through: :organization, source: :member_details
 
-  has_many :organization_member_details, :through => :member_detail
-  has_many :organization_member_details_2, :through => :organization, :source => :member_details
+  has_one :club_category, through: :club, source: :category
+  has_one :general_club, -> { general }, through: :current_membership, source: :club
 
-  has_one :club_category, :through => :club, :source => :category
+  has_many :super_memberships
+  has_many :favourite_memberships, -> { where(favourite: true) }, class_name: "Membership"
+  has_many :clubs, through: :favourite_memberships
 
-  has_many :current_memberships, -> { where :favourite => true }
-  has_many :clubs, :through => :current_memberships
+  has_many :tenant_memberships
+  has_many :tenant_clubs, through: :tenant_memberships, class_name: "Club", source: :club
 
-  has_one :club_through_many, :through => :current_memberships, :source => :club
+  has_one :club_through_many, through: :favourite_memberships, source: :club
 
   belongs_to :admittable, polymorphic: true
   has_one :premium_club, through: :admittable
@@ -34,5 +41,5 @@ end
 
 class SelfMember < ActiveRecord::Base
   self.table_name = "members"
-  has_and_belongs_to_many :friends, :class_name => "SelfMember", :join_table => "member_friends"
+  has_and_belongs_to_many :friends, class_name: "SelfMember", join_table: "member_friends"
 end
diff --git a/activerecord/test/models/member_detail.rb b/activerecord/test/models/member_detail.rb
index 9d253aa126..e121a849d0 100644
--- a/activerecord/test/models/member_detail.rb
+++ b/activerecord/test/models/member_detail.rb
@@ -1,7 +1,11 @@
+# frozen_string_literal: true
+
 class MemberDetail < ActiveRecord::Base
-  belongs_to :member, :inverse_of => false
+  belongs_to :member, inverse_of: false
   belongs_to :organization
-  has_one :member_type, :through => :member
+  has_one :member_type, through: :member
+  has_one :membership, through: :member
+  has_one :admittable, through: :member, source_type: "Member"
 
-  has_many :organization_member_details, :through => :organization, :source => :member_details
+  has_many :organization_member_details, through: :organization, source: :member_details
 end
diff --git a/activerecord/test/models/member_type.rb b/activerecord/test/models/member_type.rb
index a13561c72a..b49b168d03 100644
--- a/activerecord/test/models/member_type.rb
+++ b/activerecord/test/models/member_type.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class MemberType < ActiveRecord::Base
   has_many :members
 end
diff --git a/activerecord/test/models/membership.rb b/activerecord/test/models/membership.rb
index df7167ee93..09ee7544b3 100644
--- a/activerecord/test/models/membership.rb
+++ b/activerecord/test/models/membership.rb
@@ -1,4 +1,7 @@
+# frozen_string_literal: true
+
 class Membership < ActiveRecord::Base
+  enum type: %i(Membership CurrentMembership SuperMembership SelectedMembership TenantMembership)
   belongs_to :member
   belongs_to :club
 end
@@ -9,7 +12,7 @@ class CurrentMembership < Membership
 end
 
 class SuperMembership < Membership
-  belongs_to :member, -> { order('members.id DESC') }
+  belongs_to :member, -> { order("members.id DESC") }
   belongs_to :club
 end
 
@@ -18,3 +21,18 @@ class SelectedMembership < Membership
     select("'1' as foo")
   end
 end
+
+class TenantMembership < Membership
+  cattr_accessor :current_member
+
+  belongs_to :member
+  belongs_to :club
+
+  default_scope -> {
+    if current_member
+      where(member: current_member)
+    else
+      all
+    end
+  }
+end
diff --git a/activerecord/test/models/mentor.rb b/activerecord/test/models/mentor.rb
new file mode 100644
index 0000000000..2fbb62c435
--- /dev/null
+++ b/activerecord/test/models/mentor.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class Mentor < ActiveRecord::Base
+  has_many :developers
+end
diff --git a/activerecord/test/models/minimalistic.rb b/activerecord/test/models/minimalistic.rb
index 2e3f8e081a..c67b086853 100644
--- a/activerecord/test/models/minimalistic.rb
+++ b/activerecord/test/models/minimalistic.rb
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 class Minimalistic < ActiveRecord::Base
 end
diff --git a/activerecord/test/models/minivan.rb b/activerecord/test/models/minivan.rb
index 4fe79720ad..d9d331798a 100644
--- a/activerecord/test/models/minivan.rb
+++ b/activerecord/test/models/minivan.rb
@@ -1,9 +1,10 @@
+# frozen_string_literal: true
+
 class Minivan < ActiveRecord::Base
   self.primary_key = :minivan_id
 
   belongs_to :speedometer
-  has_one :dashboard, :through => :speedometer
+  has_one :dashboard, through: :speedometer
 
   attr_readonly :color
-
 end
diff --git a/activerecord/test/models/mixed_case_monkey.rb b/activerecord/test/models/mixed_case_monkey.rb
index 1c35006665..8e92f68817 100644
--- a/activerecord/test/models/mixed_case_monkey.rb
+++ b/activerecord/test/models/mixed_case_monkey.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class MixedCaseMonkey < ActiveRecord::Base
   belongs_to :man
 end
diff --git a/activerecord/test/models/molecule.rb b/activerecord/test/models/molecule.rb
index 26870c8f88..7da08a85c4 100644
--- a/activerecord/test/models/molecule.rb
+++ b/activerecord/test/models/molecule.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Molecule < ActiveRecord::Base
   belongs_to :liquid
   has_many :electrons
diff --git a/activerecord/test/models/movie.rb b/activerecord/test/models/movie.rb
index 0302abad1e..fa2ea900c7 100644
--- a/activerecord/test/models/movie.rb
+++ b/activerecord/test/models/movie.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Movie < ActiveRecord::Base
   self.primary_key = "movieid"
 
diff --git a/activerecord/test/models/node.rb b/activerecord/test/models/node.rb
index 07dd2dbccb..ae46c76b46 100644
--- a/activerecord/test/models/node.rb
+++ b/activerecord/test/models/node.rb
@@ -1,5 +1,7 @@
+# frozen_string_literal: true
+
 class Node < ActiveRecord::Base
   belongs_to :tree, touch: true
-  belongs_to :parent,   class_name: 'Node', touch: true, optional: true
-  has_many   :children, class_name: 'Node', foreign_key: :parent_id, dependent: :destroy
+  belongs_to :parent,   class_name: "Node", touch: true, optional: true
+  has_many   :children, class_name: "Node", foreign_key: :parent_id, dependent: :destroy
 end
diff --git a/activerecord/test/models/non_primary_key.rb b/activerecord/test/models/non_primary_key.rb
new file mode 100644
index 0000000000..e954375989
--- /dev/null
+++ b/activerecord/test/models/non_primary_key.rb
@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+class NonPrimaryKey < ActiveRecord::Base
+end
diff --git a/activerecord/test/models/notification.rb b/activerecord/test/models/notification.rb
index b4b4b8f1b6..3f8728af5e 100644
--- a/activerecord/test/models/notification.rb
+++ b/activerecord/test/models/notification.rb
@@ -1,2 +1,5 @@
+# frozen_string_literal: true
+
 class Notification < ActiveRecord::Base
+  validates_presence_of :message
 end
diff --git a/activerecord/test/models/numeric_data.rb b/activerecord/test/models/numeric_data.rb
new file mode 100644
index 0000000000..666e1a5778
--- /dev/null
+++ b/activerecord/test/models/numeric_data.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+class NumericData < ActiveRecord::Base
+  self.table_name = "numeric_data"
+  # Decimal columns with 0 scale being automatically treated as integers
+  # is deprecated, and will be removed in a future version of Rails.
+  attribute :world_population, :big_integer
+  attribute :my_house_population, :big_integer
+  attribute :atoms_in_universe, :big_integer
+end
diff --git a/activerecord/test/models/order.rb b/activerecord/test/models/order.rb
index e838c0b70d..36866b398f 100644
--- a/activerecord/test/models/order.rb
+++ b/activerecord/test/models/order.rb
@@ -1,4 +1,6 @@
+# frozen_string_literal: true
+
 class Order < ActiveRecord::Base
-  belongs_to :billing, :class_name => 'Customer', :foreign_key => 'billing_customer_id'
-  belongs_to :shipping, :class_name => 'Customer', :foreign_key => 'shipping_customer_id'
+  belongs_to :billing, class_name: "Customer", foreign_key: "billing_customer_id"
+  belongs_to :shipping, class_name: "Customer", foreign_key: "shipping_customer_id"
 end
diff --git a/activerecord/test/models/organization.rb b/activerecord/test/models/organization.rb
index f3e92f3067..099e7e38e0 100644
--- a/activerecord/test/models/organization.rb
+++ b/activerecord/test/models/organization.rb
@@ -1,14 +1,16 @@
+# frozen_string_literal: true
+
 class Organization < ActiveRecord::Base
   has_many :member_details
-  has_many :members, :through => :member_details
+  has_many :members, through: :member_details
 
-  has_many :authors, :primary_key => :name
-  has_many :author_essay_categories, :through => :authors, :source => :essay_categories
+  has_many :authors, primary_key: :name
+  has_many :author_essay_categories, through: :authors, source: :essay_categories
 
-  has_one :author, :primary_key => :name
-  has_one :author_owned_essay_category, :through => :author, :source => :owned_essay_category
+  has_one :author, primary_key: :name
+  has_one :author_owned_essay_category, through: :author, source: :owned_essay_category
 
-  has_many :posts, :through => :author, :source => :posts
+  has_many :posts, through: :author, source: :posts
 
-  scope :clubs, -> { from('clubs') }
+  scope :clubs, -> { from("clubs") }
 end
diff --git a/activerecord/test/models/other_dog.rb b/activerecord/test/models/other_dog.rb
new file mode 100644
index 0000000000..a0fda5ae1b
--- /dev/null
+++ b/activerecord/test/models/other_dog.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+require_dependency "models/arunit2_model"
+
+class OtherDog < ARUnit2Model
+  self.table_name = "dogs"
+end
diff --git a/activerecord/test/models/owner.rb b/activerecord/test/models/owner.rb
index cedb774b10..5fa50d9918 100644
--- a/activerecord/test/models/owner.rb
+++ b/activerecord/test/models/owner.rb
@@ -1,18 +1,21 @@
+# frozen_string_literal: true
+
 class Owner < ActiveRecord::Base
   self.primary_key = :owner_id
-  has_many :pets, -> { order 'pets.name desc' }
-  has_many :toys, :through => :pets
+  has_many :pets, -> { order "pets.name desc" }
+  has_many :toys, through: :pets
+  has_many :persons, through: :pets
 
-  belongs_to :last_pet, class_name: 'Pet'
+  belongs_to :last_pet, class_name: "Pet"
   scope :including_last_pet, -> {
-    select(%q[
+    select('
       owners.*, (
         select p.pet_id from pets p
         where p.owner_id = owners.owner_id
         order by p.name desc
         limit 1
       ) as last_pet_id
-    ]).includes(:last_pet)
+    ').includes(:last_pet)
   }
 
   after_commit :execute_blocks
diff --git a/activerecord/test/models/parrot.rb b/activerecord/test/models/parrot.rb
index b26035d944..3bb5316eca 100644
--- a/activerecord/test/models/parrot.rb
+++ b/activerecord/test/models/parrot.rb
@@ -1,29 +1,36 @@
+# frozen_string_literal: true
+
 class Parrot < ActiveRecord::Base
   self.inheritance_column = :parrot_sti_class
 
   has_and_belongs_to_many :pirates
   has_and_belongs_to_many :treasures
-  has_many :loots, :as => :looter
+  has_many :loots, as: :looter
   alias_attribute :title, :name
 
   validates_presence_of :name
 
-  attr_accessor :cancel_save_from_callback
-  before_save :cancel_save_callback_method, :if => :cancel_save_from_callback
+  attribute :cancel_save_from_callback
+  before_save :cancel_save_callback_method, if: :cancel_save_from_callback
   def cancel_save_callback_method
     throw(:abort)
   end
+
+  before_update :increment_updated_count
+  def increment_updated_count
+    self.updated_count += 1
+  end
+
+  def self.delete_all(*)
+    connection.delete("DELETE FROM parrots_pirates")
+    connection.delete("DELETE FROM parrots_treasures")
+    super
+  end
 end
 
 class LiveParrot < Parrot
 end
 
 class DeadParrot < Parrot
-  belongs_to :killer, :class_name => 'Pirate', foreign_key: :killer_id
-end
-
-class FunkyParrot < Parrot
-  before_destroy do
-    raise "before_destroy was called"
-  end
+  belongs_to :killer, class_name: "Pirate", foreign_key: :killer_id
 end
diff --git a/activerecord/test/models/person.rb b/activerecord/test/models/person.rb
index ad12f00d42..5cba1e440e 100644
--- a/activerecord/test/models/person.rb
+++ b/activerecord/test/models/person.rb
@@ -1,74 +1,74 @@
+# frozen_string_literal: true
+
 class Person < ActiveRecord::Base
   has_many :readers
   has_many :secure_readers
   has_one  :reader
 
-  has_many :posts, :through => :readers
-  has_many :secure_posts, :through => :secure_readers
-  has_many :posts_with_no_comments, -> { includes(:comments).where('comments.id is null').references(:comments) },
-                                    :through => :readers, :source => :post
+  has_many :posts, through: :readers
+  has_many :secure_posts, through: :secure_readers
+  has_many :posts_with_no_comments, -> { includes(:comments).where("comments.id is null").references(:comments) },
+                                    through: :readers, source: :post
 
-  has_many :friendships, foreign_key: 'friend_id'
+  has_many :friendships, foreign_key: "friend_id"
   # friends_too exists to test a bug, and probably shouldn't be used elsewhere
-  has_many :friends_too, foreign_key: 'friend_id', class_name: 'Friendship'
+  has_many :friends_too, foreign_key: "friend_id", class_name: "Friendship"
   has_many :followers, through: :friendships
 
   has_many :references
   has_many :bad_references
-  has_many :fixed_bad_references, -> { where :favourite => true }, :class_name => 'BadReference'
-  has_one  :favourite_reference, -> { where 'favourite=?', true }, :class_name => 'Reference'
-  has_many :posts_with_comments_sorted_by_comment_id, -> { includes(:comments).order('comments.id') }, :through => :readers, :source => :post
+  has_many :fixed_bad_references, -> { where favourite: true }, class_name: "BadReference"
+  has_one  :favourite_reference, -> { where "favourite=?", true }, class_name: "Reference"
+  has_many :posts_with_comments_sorted_by_comment_id, -> { includes(:comments).order("comments.id") }, through: :readers, source: :post
   has_many :first_posts, -> { where(id: [1, 2]) }, through: :readers
 
-  has_many :jobs, :through => :references
-  has_many :jobs_with_dependent_destroy,    :source => :job, :through => :references, :dependent => :destroy
-  has_many :jobs_with_dependent_delete_all, :source => :job, :through => :references, :dependent => :delete_all
-  has_many :jobs_with_dependent_nullify,    :source => :job, :through => :references, :dependent => :nullify
+  has_many :jobs, through: :references
+  has_many :jobs_with_dependent_destroy,    source: :job, through: :references, dependent: :destroy
+  has_many :jobs_with_dependent_delete_all, source: :job, through: :references, dependent: :delete_all
+  has_many :jobs_with_dependent_nullify,    source: :job, through: :references, dependent: :nullify
 
-  belongs_to :primary_contact, :class_name => 'Person'
-  has_many :agents, :class_name => 'Person', :foreign_key => 'primary_contact_id'
-  has_many :agents_of_agents, :through => :agents, :source => :agents
-  belongs_to :number1_fan, :class_name => 'Person'
+  belongs_to :primary_contact, class_name: "Person"
+  has_many :agents, class_name: "Person", foreign_key: "primary_contact_id"
+  has_many :agents_of_agents, through: :agents, source: :agents
+  belongs_to :number1_fan, class_name: "Person"
 
-  has_many :personal_legacy_things, :dependent => :destroy
+  has_many :personal_legacy_things, dependent: :destroy
 
-  has_many :agents_posts,         :through => :agents,       :source => :posts
-  has_many :agents_posts_authors, :through => :agents_posts, :source => :author
+  has_many :agents_posts,         through: :agents,       source: :posts
+  has_many :agents_posts_authors, through: :agents_posts, source: :author
   has_many :essays, primary_key: "first_name", foreign_key: "writer_id"
 
-  scope :males,   -> { where(:gender => 'M') }
-  scope :females, -> { where(:gender => 'F') }
+  scope :males,   -> { where(gender: "M") }
 end
 
 class PersonWithDependentDestroyJobs < ActiveRecord::Base
-  self.table_name = 'people'
+  self.table_name = "people"
 
-  has_many :references, :foreign_key => :person_id
-  has_many :jobs, :source => :job, :through => :references, :dependent => :destroy
+  has_many :references, foreign_key: :person_id
+  has_many :jobs, source: :job, through: :references, dependent: :destroy
 end
 
 class PersonWithDependentDeleteAllJobs < ActiveRecord::Base
-  self.table_name = 'people'
+  self.table_name = "people"
 
-  has_many :references, :foreign_key => :person_id
-  has_many :jobs, :source => :job, :through => :references, :dependent => :delete_all
+  has_many :references, foreign_key: :person_id
+  has_many :jobs, source: :job, through: :references, dependent: :delete_all
 end
 
 class PersonWithDependentNullifyJobs < ActiveRecord::Base
-  self.table_name = 'people'
+  self.table_name = "people"
 
-  has_many :references, :foreign_key => :person_id
-  has_many :jobs, :source => :job, :through => :references, :dependent => :nullify
+  has_many :references, foreign_key: :person_id
+  has_many :jobs, source: :job, through: :references, dependent: :nullify
 end
 
-
 class LoosePerson < ActiveRecord::Base
-  self.table_name = 'people'
+  self.table_name = "people"
   self.abstract_class = true
 
-  has_one    :best_friend,    :class_name => 'LoosePerson', :foreign_key => :best_friend_id
-  belongs_to :best_friend_of, :class_name => 'LoosePerson', :foreign_key => :best_friend_of_id
-  has_many   :best_friends,   :class_name => 'LoosePerson', :foreign_key => :best_friend_id
+  has_one    :best_friend,    class_name: "LoosePerson", foreign_key: :best_friend_id
+  belongs_to :best_friend_of, class_name: "LoosePerson", foreign_key: :best_friend_of_id
+  has_many   :best_friends,   class_name: "LoosePerson", foreign_key: :best_friend_id
 
   accepts_nested_attributes_for :best_friend, :best_friend_of, :best_friends
 end
@@ -76,11 +76,11 @@ end
 class LooseDescendant < LoosePerson; end
 
 class TightPerson < ActiveRecord::Base
-  self.table_name = 'people'
+  self.table_name = "people"
 
-  has_one    :best_friend,    :class_name => 'TightPerson', :foreign_key => :best_friend_id
-  belongs_to :best_friend_of, :class_name => 'TightPerson', :foreign_key => :best_friend_of_id
-  has_many   :best_friends,   :class_name => 'TightPerson', :foreign_key => :best_friend_id
+  has_one    :best_friend,    class_name: "TightPerson", foreign_key: :best_friend_id
+  belongs_to :best_friend_of, class_name: "TightPerson", foreign_key: :best_friend_of_id
+  has_many   :best_friends,   class_name: "TightPerson", foreign_key: :best_friend_id
 
   accepts_nested_attributes_for :best_friend, :best_friend_of, :best_friends
 end
@@ -88,56 +88,56 @@ end
 class TightDescendant < TightPerson; end
 
 class RichPerson < ActiveRecord::Base
-  self.table_name = 'people'
+  self.table_name = "people"
 
-  has_and_belongs_to_many :treasures, :join_table => 'peoples_treasures'
+  has_and_belongs_to_many :treasures, join_table: "peoples_treasures"
 
   before_validation :run_before_create, on: :create
   before_validation :run_before_validation
 
   private
 
-  def run_before_create
-    self.first_name = first_name.to_s + 'run_before_create'
-  end
+    def run_before_create
+      self.first_name = first_name.to_s + "run_before_create"
+    end
 
-  def run_before_validation
-    self.first_name = first_name.to_s + 'run_before_validation'
-  end
+    def run_before_validation
+      self.first_name = first_name.to_s + "run_before_validation"
+    end
 end
 
 class NestedPerson < ActiveRecord::Base
-  self.table_name = 'people'
+  self.table_name = "people"
 
-  has_one :best_friend, :class_name => 'NestedPerson', :foreign_key => :best_friend_id
-  accepts_nested_attributes_for :best_friend, :update_only => true
+  has_one :best_friend, class_name: "NestedPerson", foreign_key: :best_friend_id
+  accepts_nested_attributes_for :best_friend, update_only: true
 
   def comments=(new_comments)
     raise RuntimeError
   end
 
   def best_friend_first_name=(new_name)
-    assign_attributes({ :best_friend_attributes => { :first_name => new_name } })
+    assign_attributes(best_friend_attributes: { first_name: new_name })
   end
 end
 
 class Insure
   INSURES = %W{life annuality}
 
-  def self.load mask
+  def self.load(mask)
     INSURES.select do |insure|
       (1 << INSURES.index(insure)) & mask.to_i > 0
     end
   end
 
-  def self.dump insures
+  def self.dump(insures)
     numbers = insures.map { |insure| INSURES.index(insure) }
     numbers.inject(0) { |sum, n| sum + (1 << n) }
   end
 end
 
 class SerializedPerson < ActiveRecord::Base
-  self.table_name = 'people'
+  self.table_name = "people"
 
   serialize :insures, Insure
 end
diff --git a/activerecord/test/models/personal_legacy_thing.rb b/activerecord/test/models/personal_legacy_thing.rb
index a7ee3a0bca..ed8b70cfcc 100644
--- a/activerecord/test/models/personal_legacy_thing.rb
+++ b/activerecord/test/models/personal_legacy_thing.rb
@@ -1,4 +1,6 @@
+# frozen_string_literal: true
+
 class PersonalLegacyThing < ActiveRecord::Base
   self.locking_column = :version
-  belongs_to :person, :counter_cache => true
+  belongs_to :person, counter_cache: true
 end
diff --git a/activerecord/test/models/pet.rb b/activerecord/test/models/pet.rb
index f7970d7aab..9bda2109e6 100644
--- a/activerecord/test/models/pet.rb
+++ b/activerecord/test/models/pet.rb
@@ -1,9 +1,14 @@
+# frozen_string_literal: true
+
 class Pet < ActiveRecord::Base
   attr_accessor :current_user
 
   self.primary_key = :pet_id
-  belongs_to :owner, :touch => true
+  belongs_to :owner, touch: true
   has_many :toys
+  has_many :pet_treasures
+  has_many :treasures, through: :pet_treasures
+  has_many :persons, through: :treasures, source: :looter, source_type: "Person"
 
   class << self
     attr_accessor :after_destroy_output
diff --git a/activerecord/test/models/pet_treasure.rb b/activerecord/test/models/pet_treasure.rb
new file mode 100644
index 0000000000..47b9f57fad
--- /dev/null
+++ b/activerecord/test/models/pet_treasure.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class PetTreasure < ActiveRecord::Base
+  self.table_name = "pets_treasures"
+
+  belongs_to :pet
+  belongs_to :treasure
+end
diff --git a/activerecord/test/models/pirate.rb b/activerecord/test/models/pirate.rb
index 30545bdcd7..fd5083e597 100644
--- a/activerecord/test/models/pirate.rb
+++ b/activerecord/test/models/pirate.rb
@@ -1,47 +1,55 @@
+# frozen_string_literal: true
+
 class Pirate < ActiveRecord::Base
-  belongs_to :parrot, :validate => true
-  belongs_to :non_validated_parrot, :class_name => 'Parrot'
-  has_and_belongs_to_many :parrots, -> { order('parrots.id ASC') }, :validate => true
-  has_and_belongs_to_many :non_validated_parrots, :class_name => 'Parrot'
-  has_and_belongs_to_many :parrots_with_method_callbacks, :class_name => "Parrot",
-    :before_add    => :log_before_add,
-    :after_add     => :log_after_add,
-    :before_remove => :log_before_remove,
-    :after_remove  => :log_after_remove
-  has_and_belongs_to_many :parrots_with_proc_callbacks, :class_name => "Parrot",
-    :before_add    => proc {|p,pa| p.ship_log << "before_adding_proc_parrot_#{pa.id || '<new>'}"},
-    :after_add     => proc {|p,pa| p.ship_log << "after_adding_proc_parrot_#{pa.id || '<new>'}"},
-    :before_remove => proc {|p,pa| p.ship_log << "before_removing_proc_parrot_#{pa.id}"},
-    :after_remove  => proc {|p,pa| p.ship_log << "after_removing_proc_parrot_#{pa.id}"}
+  belongs_to :parrot, validate: true
+  belongs_to :non_validated_parrot, class_name: "Parrot"
+  has_and_belongs_to_many :parrots, -> { order("parrots.id ASC") }, validate: true
+  has_and_belongs_to_many :non_validated_parrots, class_name: "Parrot"
+  has_and_belongs_to_many :parrots_with_method_callbacks, class_name: "Parrot",
+    before_add: :log_before_add,
+    after_add: :log_after_add,
+    before_remove: :log_before_remove,
+    after_remove: :log_after_remove
+  has_and_belongs_to_many :parrots_with_proc_callbacks, class_name: "Parrot",
+    before_add: proc { |p, pa| p.ship_log << "before_adding_proc_parrot_#{pa.id || '<new>'}" },
+    after_add: proc { |p, pa| p.ship_log << "after_adding_proc_parrot_#{pa.id || '<new>'}" },
+    before_remove: proc { |p, pa| p.ship_log << "before_removing_proc_parrot_#{pa.id}" },
+    after_remove: proc { |p, pa| p.ship_log << "after_removing_proc_parrot_#{pa.id}" }
   has_and_belongs_to_many :autosaved_parrots, class_name: "Parrot", autosave: true
 
-  has_many :treasures, :as => :looter
-  has_many :treasure_estimates, :through => :treasures, :source => :price_estimates
+  module PostTreasuresExtension
+    def build(attributes = {})
+      super({ name: "from extension" }.merge(attributes))
+    end
+  end
+
+  has_many :treasures, as: :looter, extend: PostTreasuresExtension
+  has_many :treasure_estimates, through: :treasures, source: :price_estimates
 
   has_one :ship
-  has_one :update_only_ship, :class_name => 'Ship'
-  has_one :non_validated_ship, :class_name => 'Ship'
-  has_many :birds, -> { order('birds.id ASC') }
-  has_many :birds_with_method_callbacks, :class_name => "Bird",
-    :before_add    => :log_before_add,
-    :after_add     => :log_after_add,
-    :before_remove => :log_before_remove,
-    :after_remove  => :log_after_remove
-  has_many :birds_with_proc_callbacks, :class_name => "Bird",
-    :before_add     => proc {|p,b| p.ship_log << "before_adding_proc_bird_#{b.id || '<new>'}"},
-    :after_add      => proc {|p,b| p.ship_log << "after_adding_proc_bird_#{b.id || '<new>'}"},
-    :before_remove  => proc {|p,b| p.ship_log << "before_removing_proc_bird_#{b.id}"},
-    :after_remove   => proc {|p,b| p.ship_log << "after_removing_proc_bird_#{b.id}"}
-  has_many :birds_with_reject_all_blank, :class_name => "Bird"
-
-  has_one :foo_bulb, -> { where :name => 'foo' }, :foreign_key => :car_id, :class_name => "Bulb"
-
-  accepts_nested_attributes_for :parrots, :birds, :allow_destroy => true, :reject_if => proc(&:empty?)
-  accepts_nested_attributes_for :ship, :allow_destroy => true, :reject_if => proc(&:empty?)
-  accepts_nested_attributes_for :update_only_ship, :update_only => true
+  has_one :update_only_ship, class_name: "Ship"
+  has_one :non_validated_ship, class_name: "Ship"
+  has_many :birds, -> { order("birds.id ASC") }
+  has_many :birds_with_method_callbacks, class_name: "Bird",
+    before_add: :log_before_add,
+    after_add: :log_after_add,
+    before_remove: :log_before_remove,
+    after_remove: :log_after_remove
+  has_many :birds_with_proc_callbacks, class_name: "Bird",
+    before_add: proc { |p, b| p.ship_log << "before_adding_proc_bird_#{b.id || '<new>'}" },
+    after_add: proc { |p, b| p.ship_log << "after_adding_proc_bird_#{b.id || '<new>'}" },
+    before_remove: proc { |p, b| p.ship_log << "before_removing_proc_bird_#{b.id}" },
+    after_remove: proc { |p, b| p.ship_log << "after_removing_proc_bird_#{b.id}" }
+  has_many :birds_with_reject_all_blank, class_name: "Bird"
+
+  has_one :foo_bulb, -> { where name: "foo" }, foreign_key: :car_id, class_name: "Bulb"
+
+  accepts_nested_attributes_for :parrots, :birds, allow_destroy: true, reject_if: proc(&:empty?)
+  accepts_nested_attributes_for :ship, allow_destroy: true, reject_if: proc(&:empty?)
+  accepts_nested_attributes_for :update_only_ship, update_only: true
   accepts_nested_attributes_for :parrots_with_method_callbacks, :parrots_with_proc_callbacks,
-    :birds_with_method_callbacks, :birds_with_proc_callbacks, :allow_destroy => true
-  accepts_nested_attributes_for :birds_with_reject_all_blank, :reject_if => :all_blank
+    :birds_with_method_callbacks, :birds_with_proc_callbacks, allow_destroy: true
+  accepts_nested_attributes_for :birds_with_reject_all_blank, reject_if: :all_blank
 
   validates_presence_of :catchphrase
 
@@ -50,11 +58,11 @@ class Pirate < ActiveRecord::Base
   end
 
   def reject_empty_ships_on_create(attributes)
-    attributes.delete('_reject_me_if_new').present? && !persisted?
+    attributes.delete("_reject_me_if_new").present? && !persisted?
   end
 
   attr_accessor :cancel_save_from_callback, :parrots_limit
-  before_save :cancel_save_callback_method, :if => :cancel_save_from_callback
+  before_save :cancel_save_callback_method, if: :cancel_save_from_callback
   def cancel_save_callback_method
     throw(:abort)
   end
@@ -82,11 +90,11 @@ class Pirate < ActiveRecord::Base
 end
 
 class DestructivePirate < Pirate
-  has_one :dependent_ship, :class_name => 'Ship', :foreign_key => :pirate_id, :dependent => :destroy
+  has_one :dependent_ship, class_name: "Ship", foreign_key: :pirate_id, dependent: :destroy
 end
 
 class FamousPirate < ActiveRecord::Base
-  self.table_name = 'pirates'
+  self.table_name = "pirates"
   has_many :famous_ships
   validates_presence_of :catchphrase, on: :conference
 end
diff --git a/activerecord/test/models/possession.rb b/activerecord/test/models/possession.rb
index ddf759113b..9b843e1525 100644
--- a/activerecord/test/models/possession.rb
+++ b/activerecord/test/models/possession.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Possession < ActiveRecord::Base
-  self.table_name = 'having'
+  self.table_name = "having"
 end
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index 10f13b67da..710a75ad30 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Post < ActiveRecord::Base
   class CategoryPost < ActiveRecord::Base
     self.table_name = "categories_posts"
@@ -7,36 +9,38 @@ class Post < ActiveRecord::Base
 
   module NamedExtension
     def author
-      'lifo'
+      "lifo"
     end
   end
 
   module NamedExtension2
     def greeting
-      "hello"
+      "hullo"
     end
   end
 
   scope :containing_the_letter_a, -> { where("body LIKE '%a%'") }
   scope :titled_with_an_apostrophe, -> { where("title LIKE '%''%'") }
-  scope :ranked_by_comments,      -> { order("comments_count DESC") }
+  scope :ranked_by_comments, -> { order(arel_attribute(:comments_count).desc) }
 
-  scope :limit_by, lambda {|l| limit(l) }
+  scope :limit_by, lambda { |l| limit(l) }
+  scope :locked, -> { lock }
 
   belongs_to :author
+  belongs_to :readonly_author, -> { readonly }, class_name: "Author", foreign_key: :author_id
 
-  belongs_to :author_with_posts, -> { includes(:posts) }, :class_name => "Author", :foreign_key => :author_id
-  belongs_to :author_with_address, -> { includes(:author_address) }, :class_name => "Author", :foreign_key => :author_id
+  belongs_to :author_with_posts, -> { includes(:posts) }, class_name: "Author", foreign_key: :author_id
+  belongs_to :author_with_address, -> { includes(:author_address) }, class_name: "Author", foreign_key: :author_id
 
   def first_comment
     super.body
   end
-  has_one :first_comment, -> { order('id ASC') }, :class_name => 'Comment'
-  has_one :last_comment, -> { order('id desc') }, :class_name => 'Comment'
+  has_one :first_comment, -> { order("id ASC") }, class_name: "Comment"
+  has_one :last_comment, -> { order("id desc") }, class_name: "Comment"
 
-  scope :with_special_comments, -> { joins(:comments).where(:comments => {:type => 'SpecialComment'}) }
-  scope :with_very_special_comments, -> { joins(:comments).where(:comments => {:type => 'VerySpecialComment'}) }
-  scope :with_post, ->(post_id) { joins(:comments).where(:comments => { :post_id => post_id }) }
+  scope :with_special_comments, -> { joins(:comments).where(comments: { type: "SpecialComment" }) }
+  scope :with_very_special_comments, -> { joins(:comments).where(comments: { type: "VerySpecialComment" }) }
+  scope :with_post, ->(post_id) { joins(:comments).where(comments: { post_id: post_id }) }
 
   scope :with_comments, -> { preload(:comments) }
   scope :with_tags, -> { preload(:taggings) }
@@ -46,7 +50,7 @@ class Post < ActiveRecord::Base
 
   scope :typographically_interesting, -> { containing_the_letter_a.or(titled_with_an_apostrophe) }
 
-  has_many   :comments do
+  has_many :comments do
     def find_most_recent
       order("id DESC").first
     end
@@ -58,6 +62,10 @@ class Post < ActiveRecord::Base
     def the_association
       proxy_association
     end
+
+    def with_content(content)
+      self.detect { |comment| comment.body == content }
+    end
   end
 
   has_many :comments_with_extend, extend: NamedExtension, class_name: "Comment", foreign_key: "post_id" do
@@ -68,92 +76,96 @@ class Post < ActiveRecord::Base
 
   has_many :comments_with_extend_2, extend: [NamedExtension, NamedExtension2], class_name: "Comment", foreign_key: "post_id"
 
-  has_many :author_favorites, :through => :author
-  has_many :author_categorizations, :through => :author, :source => :categorizations
-  has_many :author_addresses, :through => :author
+  has_many :author_favorites, through: :author
+  has_many :author_categorizations, through: :author, source: :categorizations
+  has_many :author_addresses, through: :author
   has_many :author_address_extra_with_address,
     through: :author_with_address,
     source: :author_address_extra
 
   has_one  :very_special_comment
-  has_one  :very_special_comment_with_post, -> { includes(:post) }, :class_name => "VerySpecialComment"
-  has_one :very_special_comment_with_post_with_joins, -> { joins(:post).order('posts.id') }, class_name: "VerySpecialComment"
+  has_one  :very_special_comment_with_post, -> { includes(:post) }, class_name: "VerySpecialComment"
+  has_one :very_special_comment_with_post_with_joins, -> { joins(:post).order("posts.id") }, class_name: "VerySpecialComment"
   has_many :special_comments
-  has_many :nonexistent_comments, -> { where 'comments.id < 0' }, :class_name => 'Comment'
+  has_many :nonexistent_comments, -> { where "comments.id < 0" }, class_name: "Comment"
 
-  has_many :special_comments_ratings, :through => :special_comments, :source => :ratings
-  has_many :special_comments_ratings_taggings, :through => :special_comments_ratings, :source => :taggings
+  has_many :special_comments_ratings, through: :special_comments, source: :ratings
+  has_many :special_comments_ratings_taggings, through: :special_comments_ratings, source: :taggings
 
-  has_many :category_posts, :class_name => 'CategoryPost'
+  has_many :category_posts, class_name: "CategoryPost"
   has_many :scategories, through: :category_posts, source: :category
   has_and_belongs_to_many :categories
-  has_and_belongs_to_many :special_categories, :join_table => "categories_posts", :association_foreign_key => 'category_id'
+  has_and_belongs_to_many :special_categories, join_table: "categories_posts", association_foreign_key: "category_id"
 
-  has_many :taggings, :as => :taggable, :counter_cache => :tags_count
-  has_many :tags, :through => :taggings do
+  has_many :taggings, as: :taggable, counter_cache: :tags_count
+  has_many :tags, through: :taggings do
     def add_joins_and_select
-      select('tags.*, authors.id as author_id')
-        .joins('left outer join posts on taggings.taggable_id = posts.id left outer join authors on posts.author_id = authors.id')
+      select("tags.*, authors.id as author_id")
+        .joins("left outer join posts on taggings.taggable_id = posts.id left outer join authors on posts.author_id = authors.id")
         .to_a
     end
   end
 
-  has_many :taggings_with_delete_all, :class_name => 'Tagging', :as => :taggable, :dependent => :delete_all
-  has_many :taggings_with_destroy, :class_name => 'Tagging', :as => :taggable, :dependent => :destroy
+  has_many :indestructible_taggings, as: :taggable, counter_cache: :indestructible_tags_count
+  has_many :indestructible_tags, through: :indestructible_taggings, source: :tag
+
+  has_many :taggings_with_delete_all, class_name: "Tagging", as: :taggable, dependent: :delete_all, counter_cache: :taggings_with_delete_all_count
+  has_many :taggings_with_destroy, class_name: "Tagging", as: :taggable, dependent: :destroy, counter_cache: :taggings_with_destroy_count
 
-  has_many :tags_with_destroy, :through => :taggings, :source => :tag, :dependent => :destroy
-  has_many :tags_with_nullify, :through => :taggings, :source => :tag, :dependent => :nullify
+  has_many :tags_with_destroy, through: :taggings, source: :tag, dependent: :destroy, counter_cache: :tags_with_destroy_count
+  has_many :tags_with_nullify, through: :taggings, source: :tag, dependent: :nullify, counter_cache: :tags_with_nullify_count
 
-  has_many :misc_tags, -> { where :tags => { :name => 'Misc' } }, :through => :taggings, :source => :tag
-  has_many :funky_tags, :through => :taggings, :source => :tag
-  has_many :super_tags, :through => :taggings
-  has_many :tags_with_primary_key, :through => :taggings, :source => :tag_with_primary_key
-  has_one :tagging, :as => :taggable
+  has_many :misc_tags, -> { where tags: { name: "Misc" } }, through: :taggings, source: :tag
+  has_many :funky_tags, through: :taggings, source: :tag
+  has_many :super_tags, through: :taggings
+  has_many :ordered_tags, through: :taggings
+  has_many :tags_with_primary_key, through: :taggings, source: :tag_with_primary_key
+  has_one :tagging, as: :taggable
 
-  has_many :first_taggings, -> { where :taggings => { :comment => 'first' } }, :as => :taggable, :class_name => 'Tagging'
-  has_many :first_blue_tags, -> { where :tags => { :name => 'Blue' } }, :through => :first_taggings, :source => :tag
+  has_many :first_taggings, -> { where taggings: { comment: "first" } }, as: :taggable, class_name: "Tagging"
+  has_many :first_blue_tags, -> { where tags: { name: "Blue" } }, through: :first_taggings, source: :tag
 
-  has_many :first_blue_tags_2, -> { where :taggings => { :comment => 'first' } }, :through => :taggings, :source => :blue_tag
+  has_many :first_blue_tags_2, -> { where taggings: { comment: "first" } }, through: :taggings, source: :blue_tag
 
-  has_many :invalid_taggings, -> { where 'taggings.id < 0' }, :as => :taggable, :class_name => "Tagging"
-  has_many :invalid_tags, :through => :invalid_taggings, :source => :tag
+  has_many :invalid_taggings, -> { where "taggings.id < 0" }, as: :taggable, class_name: "Tagging"
+  has_many :invalid_tags, through: :invalid_taggings, source: :tag
 
-  has_many :categorizations, :foreign_key => :category_id
-  has_many :authors, :through => :categorizations
+  has_many :categorizations, foreign_key: :category_id
+  has_many :authors, through: :categorizations
 
-  has_many :categorizations_using_author_id, :primary_key => :author_id, :foreign_key => :post_id, :class_name => 'Categorization'
-  has_many :authors_using_author_id, :through => :categorizations_using_author_id, :source => :author
+  has_many :categorizations_using_author_id, primary_key: :author_id, foreign_key: :post_id, class_name: "Categorization"
+  has_many :authors_using_author_id, through: :categorizations_using_author_id, source: :author
 
-  has_many :taggings_using_author_id, :primary_key => :author_id, :as => :taggable, :class_name => 'Tagging'
-  has_many :tags_using_author_id, :through => :taggings_using_author_id, :source => :tag
+  has_many :taggings_using_author_id, primary_key: :author_id, as: :taggable, class_name: "Tagging"
+  has_many :tags_using_author_id, through: :taggings_using_author_id, source: :tag
 
-  has_many :images, :as => :imageable, :foreign_key => :imageable_identifier, :foreign_type => :imageable_class
-  has_one :main_image, :as => :imageable, :foreign_key => :imageable_identifier, :foreign_type => :imageable_class, :class_name => 'Image'
+  has_many :images, as: :imageable, foreign_key: :imageable_identifier, foreign_type: :imageable_class
+  has_one :main_image, as: :imageable, foreign_key: :imageable_identifier, foreign_type: :imageable_class, class_name: "Image"
 
-  has_many :standard_categorizations, :class_name => 'Categorization', :foreign_key => :post_id
-  has_many :author_using_custom_pk,  :through => :standard_categorizations
-  has_many :authors_using_custom_pk, :through => :standard_categorizations
-  has_many :named_categories, :through => :standard_categorizations
+  has_many :standard_categorizations, class_name: "Categorization", foreign_key: :post_id
+  has_many :author_using_custom_pk,  through: :standard_categorizations
+  has_many :authors_using_custom_pk, through: :standard_categorizations
+  has_many :named_categories, through: :standard_categorizations
 
   has_many :readers
   has_many :secure_readers
-  has_many :readers_with_person, -> { includes(:person) }, :class_name => "Reader"
-  has_many :people, :through => :readers
-  has_many :single_people, :through => :readers
-  has_many :people_with_callbacks, :source=>:person, :through => :readers,
-              :before_add    => lambda {|owner, reader| log(:added,   :before, reader.first_name) },
-              :after_add     => lambda {|owner, reader| log(:added,   :after,  reader.first_name) },
-              :before_remove => lambda {|owner, reader| log(:removed, :before, reader.first_name) },
-              :after_remove  => lambda {|owner, reader| log(:removed, :after,  reader.first_name) }
-  has_many :skimmers, -> { where :skimmer => true }, :class_name => 'Reader'
-  has_many :impatient_people, :through => :skimmers, :source => :person
+  has_many :readers_with_person, -> { includes(:person) }, class_name: "Reader"
+  has_many :people, through: :readers
+  has_many :single_people, through: :readers
+  has_many :people_with_callbacks, source: :person, through: :readers,
+              before_add: lambda { |owner, reader| log(:added,   :before, reader.first_name) },
+              after_add: lambda { |owner, reader| log(:added,   :after,  reader.first_name) },
+              before_remove: lambda { |owner, reader| log(:removed, :before, reader.first_name) },
+              after_remove: lambda { |owner, reader| log(:removed, :after,  reader.first_name) }
+  has_many :skimmers, -> { where skimmer: true }, class_name: "Reader"
+  has_many :impatient_people, through: :skimmers, source: :person
 
   has_many :lazy_readers
-  has_many :lazy_readers_skimmers_or_not, -> { where(skimmer: [ true, false ]) }, :class_name => 'LazyReader'
+  has_many :lazy_readers_skimmers_or_not, -> { where(skimmer: [ true, false ]) }, class_name: "LazyReader"
 
-  has_many :lazy_people, :through => :lazy_readers, :source => :person
-  has_many :lazy_readers_unscope_skimmers, -> { skimmers_or_not }, :class_name => 'LazyReader'
-  has_many :lazy_people_unscope_skimmers, :through => :lazy_readers_unscope_skimmers, :source => :person
+  has_many :lazy_people, through: :lazy_readers, source: :person
+  has_many :lazy_readers_unscope_skimmers, -> { skimmers_or_not }, class_name: "LazyReader"
+  has_many :lazy_people_unscope_skimmers, through: :lazy_readers_unscope_skimmers, source: :person
 
   def self.top(limit)
     ranked_by_comments.limit_by(limit)
@@ -167,7 +179,7 @@ class Post < ActiveRecord::Base
     @log = []
   end
 
-  def self.log(message=nil, side=nil, new_record=nil)
+  def self.log(message = nil, side = nil, new_record = nil)
     return @log if message.nil?
     @log << [message, side, new_record]
   end
@@ -176,61 +188,77 @@ end
 class SpecialPost < Post; end
 
 class StiPost < Post
+  has_one :special_comment, class_name: "SpecialComment"
+end
+
+class AbstractStiPost < Post
   self.abstract_class = true
-  has_one :special_comment, :class_name => "SpecialComment"
 end
 
 class SubStiPost < StiPost
   self.table_name = Post.table_name
 end
 
+class SubAbstractStiPost < AbstractStiPost; end
+
 class FirstPost < ActiveRecord::Base
-  self.table_name = 'posts'
-  default_scope { where(:id => 1) }
+  self.inheritance_column = :disabled
+  self.table_name = "posts"
+  default_scope { where(id: 1) }
+
+  has_many :comments, foreign_key: :post_id
+  has_one  :comment,  foreign_key: :post_id
+end
 
-  has_many :comments, :foreign_key => :post_id
-  has_one  :comment,  :foreign_key => :post_id
+class TaggedPost < Post
+  has_many :taggings, -> { rewhere(taggable_type: "TaggedPost") }, as: :taggable
+  has_many :tags, through: :taggings
 end
 
 class PostWithDefaultInclude < ActiveRecord::Base
-  self.table_name = 'posts'
+  self.inheritance_column = :disabled
+  self.table_name = "posts"
   default_scope { includes(:comments) }
-  has_many :comments, :foreign_key => :post_id
+  has_many :comments, foreign_key: :post_id
 end
 
 class PostWithSpecialCategorization < Post
-  has_many :categorizations, :foreign_key => :post_id
-  default_scope { where(:type => 'PostWithSpecialCategorization').joins(:categorizations).where(:categorizations => { :special => true }) }
+  has_many :categorizations, foreign_key: :post_id
+  default_scope { where(type: "PostWithSpecialCategorization").joins(:categorizations).where(categorizations: { special: true }) }
 end
 
 class PostWithDefaultScope < ActiveRecord::Base
-  self.table_name = 'posts'
+  self.inheritance_column = :disabled
+  self.table_name = "posts"
   default_scope { order(:title) }
 end
 
 class PostWithPreloadDefaultScope < ActiveRecord::Base
-  self.table_name = 'posts'
+  self.table_name = "posts"
 
-  has_many :readers, foreign_key: 'post_id'
+  has_many :readers, foreign_key: "post_id"
 
   default_scope { preload(:readers) }
 end
 
 class PostWithIncludesDefaultScope < ActiveRecord::Base
-  self.table_name = 'posts'
+  self.table_name = "posts"
 
-  has_many :readers, foreign_key: 'post_id'
+  has_many :readers, foreign_key: "post_id"
 
   default_scope { includes(:readers) }
 end
 
 class SpecialPostWithDefaultScope < ActiveRecord::Base
-  self.table_name = 'posts'
-  default_scope { where(:id => [1, 5,6]) }
+  self.inheritance_column = :disabled
+  self.table_name = "posts"
+  default_scope { where(id: [1, 5, 6]) }
+  scope :unscoped_all, -> { unscoped { all } }
 end
 
 class PostThatLoadsCommentsInAnAfterSaveHook < ActiveRecord::Base
-  self.table_name = 'posts'
+  self.inheritance_column = :disabled
+  self.table_name = "posts"
   has_many :comments, class_name: "CommentThatAutomaticallyAltersPostBody", foreign_key: :post_id
 
   after_save do |post|
@@ -239,7 +267,8 @@ class PostThatLoadsCommentsInAnAfterSaveHook < ActiveRecord::Base
 end
 
 class PostWithAfterCreateCallback < ActiveRecord::Base
-  self.table_name = 'posts'
+  self.inheritance_column = :disabled
+  self.table_name = "posts"
   has_many :comments, foreign_key: :post_id
 
   after_create do |post|
@@ -248,7 +277,8 @@ class PostWithAfterCreateCallback < ActiveRecord::Base
 end
 
 class PostWithCommentWithDefaultScopeReferencesAssociation < ActiveRecord::Base
-  self.table_name = 'posts'
+  self.inheritance_column = :disabled
+  self.table_name = "posts"
   has_many :comment_with_default_scope_references_associations, foreign_key: :post_id
   has_one :first_comment, class_name: "CommentWithDefaultScopeReferencesAssociation", foreign_key: :post_id
 end
@@ -256,3 +286,58 @@ end
 class SerializedPost < ActiveRecord::Base
   serialize :title
 end
+
+class ConditionalStiPost < Post
+  default_scope { where(title: "Untitled") }
+end
+
+class SubConditionalStiPost < ConditionalStiPost
+end
+
+class FakeKlass
+  extend ActiveRecord::Delegation::DelegateCache
+
+  class << self
+    def connection
+      Post.connection
+    end
+
+    def table_name
+      "posts"
+    end
+
+    def attribute_alias?(name)
+      false
+    end
+
+    def sanitize_sql(sql)
+      sql
+    end
+
+    def sanitize_sql_for_order(sql)
+      sql
+    end
+
+    def arel_attribute(name, table)
+      table[name]
+    end
+
+    def disallow_raw_sql!(*args)
+      # noop
+    end
+
+    def arel_table
+      Post.arel_table
+    end
+
+    def predicate_builder
+      Post.predicate_builder
+    end
+
+    def base_class?
+      true
+    end
+  end
+
+  inherited self
+end
diff --git a/activerecord/test/models/price_estimate.rb b/activerecord/test/models/price_estimate.rb
index d09e2a88a3..669d0991f7 100644
--- a/activerecord/test/models/price_estimate.rb
+++ b/activerecord/test/models/price_estimate.rb
@@ -1,4 +1,14 @@
+# frozen_string_literal: true
+
 class PriceEstimate < ActiveRecord::Base
-  belongs_to :estimate_of, :polymorphic => true
+  include ActiveSupport::NumberHelper
+
+  belongs_to :estimate_of, polymorphic: true
   belongs_to :thing, polymorphic: true
+
+  validates_numericality_of :price
+
+  def price
+    number_to_currency super
+  end
 end
diff --git a/activerecord/test/models/professor.rb b/activerecord/test/models/professor.rb
new file mode 100644
index 0000000000..abc23f40ff
--- /dev/null
+++ b/activerecord/test/models/professor.rb
@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+require_dependency "models/arunit2_model"
+
+class Professor < ARUnit2Model
+  has_and_belongs_to_many :courses
+end
diff --git a/activerecord/test/models/project.rb b/activerecord/test/models/project.rb
index 7f42a4b1f8..846cef625b 100644
--- a/activerecord/test/models/project.rb
+++ b/activerecord/test/models/project.rb
@@ -1,16 +1,29 @@
+# frozen_string_literal: true
+
 class Project < ActiveRecord::Base
-  has_and_belongs_to_many :developers, -> { distinct.order 'developers.name desc, developers.id desc' }
-  has_and_belongs_to_many :readonly_developers, -> { readonly }, :class_name => "Developer"
-  has_and_belongs_to_many :non_unique_developers, -> { order 'developers.name desc, developers.id desc' }, :class_name => 'Developer'
-  has_and_belongs_to_many :limited_developers, -> { limit 1 }, :class_name => "Developer"
-  has_and_belongs_to_many :developers_named_david, -> { where("name = 'David'").distinct }, :class_name => "Developer"
-  has_and_belongs_to_many :developers_named_david_with_hash_conditions, -> { where(:name => 'David').distinct }, :class_name => "Developer"
-  has_and_belongs_to_many :salaried_developers, -> { where "salary > 0" }, :class_name => "Developer"
-  has_and_belongs_to_many :developers_with_callbacks, :class_name => "Developer", :before_add => Proc.new {|o, r| o.developers_log << "before_adding#{r.id || '<new>'}"},
-                            :after_add => Proc.new {|o, r| o.developers_log << "after_adding#{r.id || '<new>'}"},
-                            :before_remove => Proc.new {|o, r| o.developers_log << "before_removing#{r.id}"},
-                            :after_remove => Proc.new {|o, r| o.developers_log << "after_removing#{r.id}"}
-  has_and_belongs_to_many :well_payed_salary_groups, -> { group("developers.salary").having("SUM(salary) > 10000").select("SUM(salary) as salary") }, :class_name => "Developer"
+  belongs_to :mentor
+  has_and_belongs_to_many :developers, -> { distinct.order "developers.name desc, developers.id desc" }
+  has_and_belongs_to_many :readonly_developers, -> { readonly }, class_name: "Developer"
+  has_and_belongs_to_many :non_unique_developers, -> { order "developers.name desc, developers.id desc" }, class_name: "Developer"
+  has_and_belongs_to_many :limited_developers, -> { limit 1 }, class_name: "Developer"
+  has_and_belongs_to_many :developers_named_david, -> { where("name = 'David'").distinct }, class_name: "Developer"
+  has_and_belongs_to_many :developers_named_david_with_hash_conditions, -> { where(name: "David").distinct }, class_name: "Developer"
+  has_and_belongs_to_many :salaried_developers, -> { where "salary > 0" }, class_name: "Developer"
+  has_and_belongs_to_many :developers_with_callbacks, class_name: "Developer", before_add: Proc.new { |o, r| o.developers_log << "before_adding#{r.id || '<new>'}" },
+                            after_add: Proc.new { |o, r| o.developers_log << "after_adding#{r.id || '<new>'}" },
+                            before_remove: Proc.new { |o, r| o.developers_log << "before_removing#{r.id}" },
+                            after_remove: Proc.new { |o, r| o.developers_log << "after_removing#{r.id}" }
+  has_and_belongs_to_many :well_paid_salary_groups, -> { group("developers.salary").having("SUM(salary) > 10000").select("SUM(salary) as salary") }, class_name: "Developer"
+  belongs_to :firm
+  has_one :lead_developer, through: :firm, inverse_of: :contracted_projects
+
+  begin
+    previous_value, ActiveRecord::Base.belongs_to_required_by_default =
+      ActiveRecord::Base.belongs_to_required_by_default, true
+    has_and_belongs_to_many :developers_required_by_default, class_name: "Developer"
+  ensure
+    ActiveRecord::Base.belongs_to_required_by_default = previous_value
+  end
 
   attr_accessor :developers_log
   after_initialize :set_developers_log
diff --git a/activerecord/test/models/publisher.rb b/activerecord/test/models/publisher.rb
index 0d4a7f9235..53677197c4 100644
--- a/activerecord/test/models/publisher.rb
+++ b/activerecord/test/models/publisher.rb
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 module Publisher
 end
diff --git a/activerecord/test/models/publisher/article.rb b/activerecord/test/models/publisher/article.rb
index d73a8eb936..355c22dcc5 100644
--- a/activerecord/test/models/publisher/article.rb
+++ b/activerecord/test/models/publisher/article.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Publisher::Article < ActiveRecord::Base
   has_and_belongs_to_many :magazines
   has_and_belongs_to_many :tags
diff --git a/activerecord/test/models/publisher/magazine.rb b/activerecord/test/models/publisher/magazine.rb
index 82e1a14008..425ede8df2 100644
--- a/activerecord/test/models/publisher/magazine.rb
+++ b/activerecord/test/models/publisher/magazine.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Publisher::Magazine < ActiveRecord::Base
   has_and_belongs_to_many :articles
 end
diff --git a/activerecord/test/models/randomly_named_c1.rb b/activerecord/test/models/randomly_named_c1.rb
index d4be1e13b4..f90a7b9336 100644
--- a/activerecord/test/models/randomly_named_c1.rb
+++ b/activerecord/test/models/randomly_named_c1.rb
@@ -1,3 +1,5 @@
-class ClassNameThatDoesNotFollowCONVENTIONS < ActiveRecord::Base

-  self.table_name = :randomly_named_table1

-end

+# frozen_string_literal: true
+
+class ClassNameThatDoesNotFollowCONVENTIONS < ActiveRecord::Base
+  self.table_name = :randomly_named_table1
+end
diff --git a/activerecord/test/models/rating.rb b/activerecord/test/models/rating.rb
index 25a52c4ad7..cf06bc6931 100644
--- a/activerecord/test/models/rating.rb
+++ b/activerecord/test/models/rating.rb
@@ -1,4 +1,6 @@
+# frozen_string_literal: true
+
 class Rating < ActiveRecord::Base
   belongs_to :comment
-  has_many :taggings, :as => :taggable
+  has_many :taggings, as: :taggable
 end
diff --git a/activerecord/test/models/reader.rb b/activerecord/test/models/reader.rb
index 91afc1898c..d25627e430 100644
--- a/activerecord/test/models/reader.rb
+++ b/activerecord/test/models/reader.rb
@@ -1,22 +1,24 @@
+# frozen_string_literal: true
+
 class Reader < ActiveRecord::Base
   belongs_to :post
-  belongs_to :person, :inverse_of => :readers
-  belongs_to :single_person, :class_name => 'Person', :foreign_key => :person_id, :inverse_of => :reader
+  belongs_to :person, inverse_of: :readers
+  belongs_to :single_person, class_name: "Person", foreign_key: :person_id, inverse_of: :reader
   belongs_to :first_post, -> { where(id: [2, 3]) }
 end
 
 class SecureReader < ActiveRecord::Base
   self.table_name = "readers"
 
-  belongs_to :secure_post, :class_name => "Post", :foreign_key => "post_id"
-  belongs_to :secure_person, :inverse_of => :secure_readers, :class_name => "Person", :foreign_key => "person_id"
+  belongs_to :secure_post, class_name: "Post", foreign_key: "post_id"
+  belongs_to :secure_person, inverse_of: :secure_readers, class_name: "Person", foreign_key: "person_id"
 end
 
 class LazyReader < ActiveRecord::Base
   self.table_name = "readers"
   default_scope -> { where(skimmer: true) }
 
-  scope :skimmers_or_not, -> { unscope(:where => :skimmer) }
+  scope :skimmers_or_not, -> { unscope(where: :skimmer) }
 
   belongs_to :post
   belongs_to :person
diff --git a/activerecord/test/models/recipe.rb b/activerecord/test/models/recipe.rb
index c387230603..e53f5c8fb1 100644
--- a/activerecord/test/models/recipe.rb
+++ b/activerecord/test/models/recipe.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Recipe < ActiveRecord::Base
   belongs_to :chef
 end
diff --git a/activerecord/test/models/record.rb b/activerecord/test/models/record.rb
index f77ac9fc03..63143e296a 100644
--- a/activerecord/test/models/record.rb
+++ b/activerecord/test/models/record.rb
@@ -1,2 +1,4 @@
+# frozen_string_literal: true
+
 class Record < ActiveRecord::Base
 end
diff --git a/activerecord/test/models/reference.rb b/activerecord/test/models/reference.rb
index c2f9068f57..2a7a1e3b77 100644
--- a/activerecord/test/models/reference.rb
+++ b/activerecord/test/models/reference.rb
@@ -1,8 +1,10 @@
+# frozen_string_literal: true
+
 class Reference < ActiveRecord::Base
   belongs_to :person
   belongs_to :job
 
-  has_many :agents_posts_authors, :through => :person
+  has_many :agents_posts_authors, through: :person
 
   class << self; attr_accessor :make_comments; end
   self.make_comments = false
@@ -17,6 +19,6 @@ class Reference < ActiveRecord::Base
 end
 
 class BadReference < ActiveRecord::Base
-  self.table_name = 'references'
-  default_scope { where(:favourite => false) }
+  self.table_name = "references"
+  default_scope { where(favourite: false) }
 end
diff --git a/activerecord/test/models/reply.rb b/activerecord/test/models/reply.rb
index 3e82e55d89..0807bcf875 100644
--- a/activerecord/test/models/reply.rb
+++ b/activerecord/test/models/reply.rb
@@ -1,27 +1,35 @@
-require 'models/topic'
+# frozen_string_literal: true
+
+require "models/topic"
 
 class Reply < Topic
-  belongs_to :topic, :foreign_key => "parent_id", :counter_cache => true
-  belongs_to :topic_with_primary_key, :class_name => "Topic", :primary_key => "title", :foreign_key => "parent_title", :counter_cache => "replies_count"
-  has_many :replies, :class_name => "SillyReply", :dependent => :destroy, :foreign_key => "parent_id"
+  belongs_to :topic, foreign_key: "parent_id", counter_cache: true
+  belongs_to :topic_with_primary_key, class_name: "Topic", primary_key: "title", foreign_key: "parent_title", counter_cache: "replies_count", touch: true
+  has_many :replies, class_name: "SillyReply", dependent: :destroy, foreign_key: "parent_id"
+  has_many :silly_unique_replies, dependent: :destroy, foreign_key: "parent_id"
+end
+
+class SillyReply < Topic
+  belongs_to :reply, foreign_key: "parent_id", counter_cache: :replies_count
 end
 
 class UniqueReply < Reply
-  belongs_to :topic, :foreign_key => 'parent_id', :counter_cache => true
-  validates_uniqueness_of :content, :scope => 'parent_id'
+  belongs_to :topic, foreign_key: "parent_id", counter_cache: true
+  validates_uniqueness_of :content, scope: "parent_id"
 end
 
 class SillyUniqueReply < UniqueReply
+  validates :content, uniqueness: true
 end
 
 class WrongReply < Reply
   validate :errors_on_empty_content
-  validate :title_is_wrong_create, :on => :create
+  validate :title_is_wrong_create, on: :create
 
   validate :check_empty_title
-  validate :check_content_mismatch, :on => :create
-  validate :check_wrong_update, :on => :update
-  validate :check_author_name_is_secret, :on => :special_case
+  validate :check_content_mismatch, on: :create
+  validate :check_wrong_update, on: :update
+  validate :check_author_name_is_secret, on: :special_case
 
   def check_empty_title
     errors[:title] << "Empty" unless attribute_present?("title")
@@ -50,12 +58,8 @@ class WrongReply < Reply
   end
 end
 
-class SillyReply < Reply
-  belongs_to :reply, :foreign_key => "parent_id", :counter_cache => :replies_count
-end
-
 module Web
   class Reply < Web::Topic
-    belongs_to :topic, :foreign_key => "parent_id", :counter_cache => true, :class_name => 'Web::Topic'
+    belongs_to :topic, foreign_key: "parent_id", counter_cache: true, class_name: "Web::Topic"
   end
 end
diff --git a/activerecord/test/models/ship.rb b/activerecord/test/models/ship.rb
index 312caef604..7973219a79 100644
--- a/activerecord/test/models/ship.rb
+++ b/activerecord/test/models/ship.rb
@@ -1,26 +1,41 @@
+# frozen_string_literal: true
+
 class Ship < ActiveRecord::Base
   self.record_timestamps = false
 
   belongs_to :pirate
-  belongs_to :update_only_pirate, :class_name => 'Pirate'
-  has_many :parts, :class_name => 'ShipPart'
+  belongs_to :update_only_pirate, class_name: "Pirate"
+  belongs_to :developer, dependent: :destroy
+  has_many :parts, class_name: "ShipPart"
   has_many :treasures
 
-  accepts_nested_attributes_for :parts, :allow_destroy => true
-  accepts_nested_attributes_for :pirate, :allow_destroy => true, :reject_if => proc(&:empty?)
-  accepts_nested_attributes_for :update_only_pirate, :update_only => true
+  accepts_nested_attributes_for :parts, allow_destroy: true
+  accepts_nested_attributes_for :pirate, allow_destroy: true, reject_if: proc(&:empty?)
+  accepts_nested_attributes_for :update_only_pirate, update_only: true
 
   validates_presence_of :name
 
   attr_accessor :cancel_save_from_callback
-  before_save :cancel_save_callback_method, :if => :cancel_save_from_callback
+  before_save :cancel_save_callback_method, if: :cancel_save_from_callback
   def cancel_save_callback_method
     throw(:abort)
   end
 end
 
+class ShipWithoutNestedAttributes < ActiveRecord::Base
+  self.table_name = "ships"
+  has_many :prisoners, inverse_of: :ship, foreign_key: :ship_id
+  has_many :parts, class_name: "ShipPart", foreign_key: :ship_id
+
+  validates :name, presence: true
+end
+
+class Prisoner < ActiveRecord::Base
+  belongs_to :ship, autosave: true, class_name: "ShipWithoutNestedAttributes", inverse_of: :prisoners
+end
+
 class FamousShip < ActiveRecord::Base
-  self.table_name = 'ships'
+  self.table_name = "ships"
   belongs_to :famous_pirate
   validates_presence_of :name, on: :conference
 end
diff --git a/activerecord/test/models/ship_part.rb b/activerecord/test/models/ship_part.rb
index 05c65f8a4a..f6d7a8ae5e 100644
--- a/activerecord/test/models/ship_part.rb
+++ b/activerecord/test/models/ship_part.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 class ShipPart < ActiveRecord::Base
   belongs_to :ship
-  has_many :trinkets, :class_name => "Treasure", :as => :looter
-  accepts_nested_attributes_for :trinkets, :allow_destroy => true
+  has_many :trinkets, class_name: "Treasure", as: :looter
+  accepts_nested_attributes_for :trinkets, allow_destroy: true
   accepts_nested_attributes_for :ship
 
   validates_presence_of :name
diff --git a/activerecord/test/models/shop.rb b/activerecord/test/models/shop.rb
index 607a0a5b41..92afe70b92 100644
--- a/activerecord/test/models/shop.rb
+++ b/activerecord/test/models/shop.rb
@@ -1,10 +1,12 @@
+# frozen_string_literal: true
+
 module Shop
   class Collection < ActiveRecord::Base
-    has_many :products, :dependent => :nullify
+    has_many :products, dependent: :nullify
   end
 
   class Product < ActiveRecord::Base
-    has_many :variants, :dependent => :delete_all
+    has_many :variants, dependent: :delete_all
     belongs_to :type
 
     class Type < ActiveRecord::Base
diff --git a/activerecord/test/models/shop_account.rb b/activerecord/test/models/shop_account.rb
new file mode 100644
index 0000000000..97fb058331
--- /dev/null
+++ b/activerecord/test/models/shop_account.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class ShopAccount < ActiveRecord::Base
+  belongs_to :customer
+  belongs_to :customer_carrier
+
+  has_one :carrier, through: :customer_carrier
+end
diff --git a/activerecord/test/models/speedometer.rb b/activerecord/test/models/speedometer.rb
index 497c3aba9a..e456907a22 100644
--- a/activerecord/test/models/speedometer.rb
+++ b/activerecord/test/models/speedometer.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Speedometer < ActiveRecord::Base
   self.primary_key = :speedometer_id
   belongs_to :dashboard
diff --git a/activerecord/test/models/sponsor.rb b/activerecord/test/models/sponsor.rb
index ec3dcf8a97..18ff103ffe 100644
--- a/activerecord/test/models/sponsor.rb
+++ b/activerecord/test/models/sponsor.rb
@@ -1,7 +1,10 @@
+# frozen_string_literal: true
+
 class Sponsor < ActiveRecord::Base
-  belongs_to :sponsor_club, :class_name => "Club", :foreign_key => "club_id"
-  belongs_to :sponsorable, :polymorphic => true
-  belongs_to :thing, :polymorphic => true, :foreign_type => :sponsorable_type, :foreign_key => :sponsorable_id
-  belongs_to :sponsorable_with_conditions, -> { where :name => 'Ernie'}, :polymorphic => true,
-             :foreign_type => 'sponsorable_type', :foreign_key => 'sponsorable_id'
+  belongs_to :sponsor_club, class_name: "Club", foreign_key: "club_id"
+  belongs_to :sponsorable, polymorphic: true
+  belongs_to :sponsor, polymorphic: true
+  belongs_to :thing, polymorphic: true, foreign_type: :sponsorable_type, foreign_key: :sponsorable_id
+  belongs_to :sponsorable_with_conditions, -> { where name: "Ernie" }, polymorphic: true,
+             foreign_type: "sponsorable_type", foreign_key: "sponsorable_id"
 end
diff --git a/activerecord/test/models/string_key_object.rb b/activerecord/test/models/string_key_object.rb
index f084ec1bdc..473c145f4c 100644
--- a/activerecord/test/models/string_key_object.rb
+++ b/activerecord/test/models/string_key_object.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class StringKeyObject < ActiveRecord::Base
   self.primary_key = :id
 end
diff --git a/activerecord/test/models/student.rb b/activerecord/test/models/student.rb
index 28a0b6c99b..e750798f74 100644
--- a/activerecord/test/models/student.rb
+++ b/activerecord/test/models/student.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Student < ActiveRecord::Base
   has_and_belongs_to_many :lessons
   belongs_to :college
diff --git a/activerecord/test/models/subject.rb b/activerecord/test/models/subject.rb
deleted file mode 100644
index 8e28f8b86b..0000000000
--- a/activerecord/test/models/subject.rb
+++ /dev/null
@@ -1,16 +0,0 @@
-# used for OracleSynonymTest, see test/synonym_test_oracle.rb
-#
-class Subject < ActiveRecord::Base
-
-  # added initialization of author_email_address in the same way as in Topic class
-  # as otherwise synonym test was failing
-  after_initialize :set_email_address
-
-  protected
-    def set_email_address
-      unless self.persisted?
-        self.author_email_address = 'test@test.com'
-      end
-    end
-
-end
diff --git a/activerecord/test/models/subscriber.rb b/activerecord/test/models/subscriber.rb
index 76e85a0cd3..b21969ca2d 100644
--- a/activerecord/test/models/subscriber.rb
+++ b/activerecord/test/models/subscriber.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 class Subscriber < ActiveRecord::Base
-  self.primary_key = 'nick'
+  self.primary_key = "nick"
   has_many :subscriptions
-  has_many :books, :through => :subscriptions
+  has_many :books, through: :subscriptions
 end
 
 class SpecialSubscriber < Subscriber
diff --git a/activerecord/test/models/subscription.rb b/activerecord/test/models/subscription.rb
index bcac4738a3..d1d5d21621 100644
--- a/activerecord/test/models/subscription.rb
+++ b/activerecord/test/models/subscription.rb
@@ -1,4 +1,6 @@
+# frozen_string_literal: true
+
 class Subscription < ActiveRecord::Base
-  belongs_to :subscriber, :counter_cache => :books_count
+  belongs_to :subscriber, counter_cache: :books_count
   belongs_to :book
 end
diff --git a/activerecord/test/models/tag.rb b/activerecord/test/models/tag.rb
index 80d4725f7e..c1a8890a8a 100644
--- a/activerecord/test/models/tag.rb
+++ b/activerecord/test/models/tag.rb
@@ -1,7 +1,16 @@
+# frozen_string_literal: true
+
 class Tag < ActiveRecord::Base
   has_many :taggings
-  has_many :taggables, :through => :taggings
+  has_many :taggables, through: :taggings
   has_one  :tagging
 
-  has_many :tagged_posts, :through => :taggings, :source => 'taggable', :source_type => 'Post'
+  has_many :tagged_posts, through: :taggings, source: "taggable", source_type: "Post"
+end
+
+class OrderedTag < Tag
+  self.table_name = "tags"
+
+  has_many :ordered_taggings, -> { order("taggings.id DESC") }, foreign_key: "tag_id", class_name: "Tagging"
+  has_many :tagged_posts, through: :ordered_taggings, source: "taggable", source_type: "Post"
 end
diff --git a/activerecord/test/models/tagging.rb b/activerecord/test/models/tagging.rb
index a6c05da26a..6d4230f6f4 100644
--- a/activerecord/test/models/tagging.rb
+++ b/activerecord/test/models/tagging.rb
@@ -1,13 +1,20 @@
+# frozen_string_literal: true
+
 # test that attr_readonly isn't called on the :taggable polymorphic association
 module Taggable
 end
 
 class Tagging < ActiveRecord::Base
   belongs_to :tag, -> { includes(:tagging) }
-  belongs_to :super_tag,   :class_name => 'Tag', :foreign_key => 'super_tag_id'
-  belongs_to :invalid_tag, :class_name => 'Tag', :foreign_key => 'tag_id'
-  belongs_to :blue_tag, -> { where :tags => { :name => 'Blue' } }, :class_name => 'Tag', :foreign_key => :tag_id
-  belongs_to :tag_with_primary_key, :class_name => 'Tag', :foreign_key => :tag_id, :primary_key => :custom_primary_key
-  belongs_to :taggable, :polymorphic => true, :counter_cache => :tags_count
-  has_many :things, :through => :taggable
+  belongs_to :super_tag,   class_name: "Tag", foreign_key: "super_tag_id"
+  belongs_to :invalid_tag, class_name: "Tag", foreign_key: "tag_id"
+  belongs_to :ordered_tag, class_name: "OrderedTag", foreign_key: "tag_id"
+  belongs_to :blue_tag, -> { where tags: { name: "Blue" } }, class_name: "Tag", foreign_key: :tag_id
+  belongs_to :tag_with_primary_key, class_name: "Tag", foreign_key: :tag_id, primary_key: :custom_primary_key
+  belongs_to :taggable, polymorphic: true, counter_cache: :tags_count
+  has_many :things, through: :taggable
+end
+
+class IndestructibleTagging < Tagging
+  before_destroy { throw :abort }
 end
diff --git a/activerecord/test/models/task.rb b/activerecord/test/models/task.rb
index e36989dd56..dabe3ce06b 100644
--- a/activerecord/test/models/task.rb
+++ b/activerecord/test/models/task.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Task < ActiveRecord::Base
   def updated_at
     ending
diff --git a/activerecord/test/models/topic.rb b/activerecord/test/models/topic.rb
index f81ffe1d90..03430154db 100644
--- a/activerecord/test/models/topic.rb
+++ b/activerecord/test/models/topic.rb
@@ -1,20 +1,30 @@
+# frozen_string_literal: true
+
 class Topic < ActiveRecord::Base
   scope :base, -> { all }
   scope :written_before, lambda { |time|
     if time
-      where 'written_on < ?', time
+      where "written_on < ?", time
     end
   }
-  scope :approved, -> { where(:approved => true) }
-  scope :rejected, -> { where(:approved => false) }
+  scope :approved, -> { where(approved: true) }
+  scope :rejected, -> { where(approved: false) }
 
   scope :scope_with_lambda, lambda { all }
 
-  scope :by_lifo, -> { where(:author_name => 'lifo') }
-  scope :replied, -> { where 'replies_count > 0' }
+  scope :by_private_lifo, -> { where(author_name: private_lifo) }
+  scope :by_lifo, -> { where(author_name: "lifo") }
+  scope :replied, -> { where "replies_count > 0" }
 
-  scope 'approved_as_string', -> { where(:approved => true) }
-  scope :anonymous_extension, -> { all } do
+  class << self
+    private
+      def private_lifo
+        "lifo"
+      end
+  end
+
+  scope "approved_as_string", -> { where(approved: true) }
+  scope :anonymous_extension, -> { } do
     def one
       1
     end
@@ -22,7 +32,7 @@ class Topic < ActiveRecord::Base
 
   scope :with_object, Class.new(Struct.new(:klass)) {
     def call
-      klass.where(:approved => true)
+      klass.where(approved: true)
     end
   }.new(self)
 
@@ -32,23 +42,17 @@ class Topic < ActiveRecord::Base
     end
   end
 
-  has_many :replies, :dependent => :destroy, :foreign_key => "parent_id"
-  has_many :approved_replies, -> { approved }, class_name: 'Reply', foreign_key: "parent_id", counter_cache: 'replies_count'
+  has_many :replies, dependent: :destroy, foreign_key: "parent_id", autosave: true
+  has_many :approved_replies, -> { approved }, class_name: "Reply", foreign_key: "parent_id", counter_cache: "replies_count"
 
-  has_many :unique_replies, :dependent => :destroy, :foreign_key => "parent_id"
-  has_many :silly_unique_replies, :dependent => :destroy, :foreign_key => "parent_id"
+  has_many :unique_replies, dependent: :destroy, foreign_key: "parent_id"
+  has_many :silly_unique_replies, dependent: :destroy, foreign_key: "parent_id"
 
   serialize :content
 
   before_create  :default_written_on
   before_destroy :destroy_children
 
-  # Explicitly define as :date column so that returned Oracle DATE values would be typecasted to Date and not Time.
-  # Some tests depend on assumption that this attribute will have Date values.
-  if current_adapter?(:OracleEnhancedAdapter)
-    set_date_columns :last_read
-  end
-
   def parent
     Topic.find(parent_id)
   end
@@ -69,29 +73,42 @@ class Topic < ActiveRecord::Base
 
   after_initialize :set_email_address
 
+  attr_accessor :change_approved_before_save
+  before_save :change_approved_callback
+
   class_attribute :after_initialize_called
   after_initialize do
     self.class.after_initialize_called = true
   end
 
+  attr_accessor :after_touch_called
+
+  after_initialize do
+    self.after_touch_called = 0
+  end
+
+  after_touch do
+    self.after_touch_called += 1
+  end
+
   def approved=(val)
     @custom_approved = val
     write_attribute(:approved, val)
   end
 
-  protected
+  private
 
     def default_written_on
       self.written_on = Time.now unless attribute_present?("written_on")
     end
 
     def destroy_children
-      self.class.delete_all "parent_id = #{id}"
+      self.class.where("parent_id = #{id}").delete_all
     end
 
     def set_email_address
-      unless self.persisted?
-        self.author_email_address = 'test@test.com'
+      unless persisted? || will_save_change_to_author_email_address?
+        self.author_email_address = "test@test.com"
       end
     end
 
@@ -100,6 +117,10 @@ class Topic < ActiveRecord::Base
     def before_destroy_for_transaction; end
     def after_save_for_transaction; end
     def after_create_for_transaction; end
+
+    def change_approved_callback
+      self.approved = change_approved_before_save unless change_approved_before_save.nil?
+    end
 end
 
 class ImportantTopic < Topic
@@ -117,8 +138,12 @@ class BlankTopic < Topic
   end
 end
 
+class TitlePrimaryKeyTopic < Topic
+  self.primary_key = :title
+end
+
 module Web
   class Topic < ActiveRecord::Base
-    has_many :replies, :dependent => :destroy, :foreign_key => "parent_id", :class_name => 'Web::Reply'
+    has_many :replies, dependent: :destroy, foreign_key: "parent_id", class_name: "Web::Reply"
   end
 end
diff --git a/activerecord/test/models/toy.rb b/activerecord/test/models/toy.rb
index ddc7048a56..4a5697eeb1 100644
--- a/activerecord/test/models/toy.rb
+++ b/activerecord/test/models/toy.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Toy < ActiveRecord::Base
   self.primary_key = :toy_id
   belongs_to :pet
diff --git a/activerecord/test/models/traffic_light.rb b/activerecord/test/models/traffic_light.rb
index a6b7edb882..0b88815cbd 100644
--- a/activerecord/test/models/traffic_light.rb
+++ b/activerecord/test/models/traffic_light.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class TrafficLight < ActiveRecord::Base
   serialize :state, Array
   serialize :long_state, Array
diff --git a/activerecord/test/models/treasure.rb b/activerecord/test/models/treasure.rb
index ffc65466d5..b51db56c37 100644
--- a/activerecord/test/models/treasure.rb
+++ b/activerecord/test/models/treasure.rb
@@ -1,10 +1,13 @@
+# frozen_string_literal: true
+
 class Treasure < ActiveRecord::Base
   has_and_belongs_to_many :parrots
-  belongs_to :looter, :polymorphic => true
+  belongs_to :looter, polymorphic: true
+  # No counter_cache option given
   belongs_to :ship
 
-  has_many :price_estimates, :as => :estimate_of
-  has_and_belongs_to_many :rich_people, join_table: 'peoples_treasures', validate: false
+  has_many :price_estimates, as: :estimate_of
+  has_and_belongs_to_many :rich_people, join_table: "peoples_treasures", validate: false
 
   accepts_nested_attributes_for :looter
 end
diff --git a/activerecord/test/models/treaty.rb b/activerecord/test/models/treaty.rb
index 41fd1350f3..b87a757d2a 100644
--- a/activerecord/test/models/treaty.rb
+++ b/activerecord/test/models/treaty.rb
@@ -1,7 +1,5 @@
-class Treaty < ActiveRecord::Base
-
-  self.primary_key = :treaty_id
+# frozen_string_literal: true
 
+class Treaty < ActiveRecord::Base
   has_and_belongs_to_many :countries
-
 end
diff --git a/activerecord/test/models/tree.rb b/activerecord/test/models/tree.rb
index dc29cccc9c..77050c5fff 100644
--- a/activerecord/test/models/tree.rb
+++ b/activerecord/test/models/tree.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Tree < ActiveRecord::Base
   has_many :nodes, dependent: :destroy
 end
diff --git a/activerecord/test/models/tuning_peg.rb b/activerecord/test/models/tuning_peg.rb
new file mode 100644
index 0000000000..6e052e1d0f
--- /dev/null
+++ b/activerecord/test/models/tuning_peg.rb
@@ -0,0 +1,6 @@
+# frozen_string_literal: true
+
+class TuningPeg < ActiveRecord::Base
+  belongs_to :guitar
+  validates_numericality_of :pitch
+end
diff --git a/activerecord/test/models/tyre.rb b/activerecord/test/models/tyre.rb
index e50a21ca68..d627026585 100644
--- a/activerecord/test/models/tyre.rb
+++ b/activerecord/test/models/tyre.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Tyre < ActiveRecord::Base
   belongs_to :car
 
diff --git a/activerecord/test/models/user.rb b/activerecord/test/models/user.rb
index f5dc93e994..3efbc45d2a 100644
--- a/activerecord/test/models/user.rb
+++ b/activerecord/test/models/user.rb
@@ -1,6 +1,18 @@
+# frozen_string_literal: true
+
+require "models/job"
+
 class User < ActiveRecord::Base
   has_secure_token
   has_secure_token :auth_token
+
+  has_and_belongs_to_many :jobs_pool,
+    class_name: "Job",
+    join_table: "jobs_pool"
+
+  has_one :family_tree, -> { where(token: nil) }, foreign_key: "member_id"
+  has_one :family, through: :family_tree
+  has_many :family_members, through: :family, source: :members
 end
 
 class UserWithNotification < User
diff --git a/activerecord/test/models/uuid_child.rb b/activerecord/test/models/uuid_child.rb
index a3d0962ad6..9fce361cc8 100644
--- a/activerecord/test/models/uuid_child.rb
+++ b/activerecord/test/models/uuid_child.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class UuidChild < ActiveRecord::Base
   belongs_to :uuid_parent
 end
diff --git a/activerecord/test/models/uuid_item.rb b/activerecord/test/models/uuid_item.rb
new file mode 100644
index 0000000000..41f68c4c18
--- /dev/null
+++ b/activerecord/test/models/uuid_item.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+class UuidItem < ActiveRecord::Base
+end
+
+class UuidValidatingItem < UuidItem
+  validates_uniqueness_of :uuid
+end
diff --git a/activerecord/test/models/uuid_parent.rb b/activerecord/test/models/uuid_parent.rb
index 5634f22d0c..05db61855e 100644
--- a/activerecord/test/models/uuid_parent.rb
+++ b/activerecord/test/models/uuid_parent.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class UuidParent < ActiveRecord::Base
   has_many :uuid_children
 end
diff --git a/activerecord/test/models/vegetables.rb b/activerecord/test/models/vegetables.rb
index 1f41cde3a5..cfaab08ed1 100644
--- a/activerecord/test/models/vegetables.rb
+++ b/activerecord/test/models/vegetables.rb
@@ -1,9 +1,10 @@
-class Vegetable < ActiveRecord::Base
+# frozen_string_literal: true
 
+class Vegetable < ActiveRecord::Base
   validates_presence_of :name
 
   def self.inheritance_column
-    'custom_type'
+    "custom_type"
   end
 end
 
@@ -20,5 +21,5 @@ class KingCole < GreenCabbage
 end
 
 class RedCabbage < Cabbage
-  belongs_to :seller, :class_name => 'Company'
+  belongs_to :seller, class_name: "Company"
 end
diff --git a/activerecord/test/models/vehicle.rb b/activerecord/test/models/vehicle.rb
new file mode 100644
index 0000000000..c9b3338522
--- /dev/null
+++ b/activerecord/test/models/vehicle.rb
@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+
+class Vehicle < ActiveRecord::Base
+  self.abstract_class = true
+  default_scope -> { where("tires_count IS NOT NULL") }
+end
+
+class Bus < Vehicle
+end
diff --git a/activerecord/test/models/vertex.rb b/activerecord/test/models/vertex.rb
index 48bb851e62..0ad8114898 100644
--- a/activerecord/test/models/vertex.rb
+++ b/activerecord/test/models/vertex.rb
@@ -1,9 +1,11 @@
+# frozen_string_literal: true
+
 # This class models a vertex in a directed graph.
 class Vertex < ActiveRecord::Base
-  has_many :sink_edges, :class_name => 'Edge', :foreign_key => 'source_id'
-  has_many :sinks, :through => :sink_edges
+  has_many :sink_edges, class_name: "Edge", foreign_key: "source_id"
+  has_many :sinks, through: :sink_edges
 
   has_and_belongs_to_many :sources,
-    :class_name => 'Vertex', :join_table => 'edges',
-    :foreign_key => 'sink_id', :association_foreign_key => 'source_id'
+    class_name: "Vertex", join_table: "edges",
+    foreign_key: "sink_id", association_foreign_key: "source_id"
 end
diff --git a/activerecord/test/models/warehouse_thing.rb b/activerecord/test/models/warehouse_thing.rb
index f20bd1a245..099633af55 100644
--- a/activerecord/test/models/warehouse_thing.rb
+++ b/activerecord/test/models/warehouse_thing.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class WarehouseThing < ActiveRecord::Base
   self.table_name = "warehouse-things"
 
diff --git a/activerecord/test/models/wheel.rb b/activerecord/test/models/wheel.rb
index 26868bce5e..22fc74995f 100644
--- a/activerecord/test/models/wheel.rb
+++ b/activerecord/test/models/wheel.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Wheel < ActiveRecord::Base
-  belongs_to :wheelable, :polymorphic => true, :counter_cache => true
+  belongs_to :wheelable, polymorphic: true, counter_cache: true, touch: :wheels_owned_at
 end
diff --git a/activerecord/test/models/without_table.rb b/activerecord/test/models/without_table.rb
index 50c824e4ac..fc0a52d6ad 100644
--- a/activerecord/test/models/without_table.rb
+++ b/activerecord/test/models/without_table.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class WithoutTable < ActiveRecord::Base
-  default_scope -> { where(:published => true) }
+  default_scope -> { where(published: true) }
 end
diff --git a/activerecord/test/models/zine.rb b/activerecord/test/models/zine.rb
index c2d0fdaf25..6f361665ef 100644
--- a/activerecord/test/models/zine.rb
+++ b/activerecord/test/models/zine.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 class Zine < ActiveRecord::Base
-  has_many :interests, :inverse_of => :zine
+  has_many :interests, inverse_of: :zine
 end
diff --git a/activerecord/test/schema/mysql2_specific_schema.rb b/activerecord/test/schema/mysql2_specific_schema.rb
index 52d3290c84..ccca9a2d9b 100644
--- a/activerecord/test/schema/mysql2_specific_schema.rb
+++ b/activerecord/test/schema/mysql2_specific_schema.rb
@@ -1,32 +1,57 @@
+# frozen_string_literal: true
+
 ActiveRecord::Schema.define do
+  if subsecond_precision_supported?
+    create_table :datetime_defaults, force: true do |t|
+      t.datetime :modified_datetime, default: -> { "CURRENT_TIMESTAMP" }
+      t.datetime :precise_datetime, precision: 6, default: -> { "CURRENT_TIMESTAMP(6)" }
+    end
+
+    create_table :timestamp_defaults, force: true do |t|
+      t.timestamp :nullable_timestamp
+      t.timestamp :modified_timestamp, default: -> { "CURRENT_TIMESTAMP" }
+      t.timestamp :precise_timestamp, precision: 6, default: -> { "CURRENT_TIMESTAMP(6)" }
+    end
+  end
+
+  create_table :defaults, force: true do |t|
+    t.date :fixed_date, default: "2004-01-01"
+    t.datetime :fixed_time, default: "2004-01-01 00:00:00"
+    t.column :char1, "char(1)", default: "Y"
+    t.string :char2, limit: 50, default: "a varchar field"
+    if supports_default_expression?
+      t.binary :uuid, limit: 36, default: -> { "(uuid())" }
+    end
+  end
+
   create_table :binary_fields, force: true do |t|
     t.binary :var_binary, limit: 255
     t.binary :var_binary_large, limit: 4095
-    t.column :tiny_blob, 'tinyblob', limit: 255
-    t.binary :normal_blob, limit: 65535
-    t.binary :medium_blob, limit: 16777215
-    t.binary :long_blob, limit: 2147483647
-    t.text   :tiny_text, limit: 255
-    t.text   :normal_text, limit: 65535
-    t.text   :medium_text, limit: 16777215
-    t.text   :long_text, limit: 2147483647
-  end
+    t.tinyblob   :tiny_blob
+    t.blob       :normal_blob
+    t.mediumblob :medium_blob
+    t.longblob   :long_blob
+    t.tinytext   :tiny_text
+    t.text       :normal_text
+    t.mediumtext :medium_text
+    t.longtext   :long_text
 
-  add_index :binary_fields, :var_binary
+    t.index :var_binary
+  end
 
-  create_table :key_tests, force: true, :options => 'ENGINE=MyISAM' do |t|
+  create_table :key_tests, force: true do |t|
     t.string :awesome
     t.string :pizza
     t.string :snacks
+    t.index :awesome, type: :fulltext, name: "index_key_tests_on_awesome"
+    t.index :pizza, using: :btree, name: "index_key_tests_on_pizza"
+    t.index :snacks, name: "index_key_tests_on_snack"
   end
 
-  add_index :key_tests, :awesome, :type => :fulltext, :name => 'index_key_tests_on_awesome'
-  add_index :key_tests, :pizza, :using => :btree, :name => 'index_key_tests_on_pizza'
-  add_index :key_tests, :snacks, :name => 'index_key_tests_on_snack'
-
   create_table :collation_tests, id: false, force: true do |t|
-    t.string :string_cs_column, limit: 1, collation: 'utf8_bin'
-    t.string :string_ci_column, limit: 1, collation: 'utf8_general_ci'
+    t.string :string_cs_column, limit: 1, collation: "utf8mb4_bin"
+    t.string :string_ci_column, limit: 1, collation: "utf8mb4_general_ci"
+    t.binary :binary_column,    limit: 1
   end
 
   ActiveRecord::Base.connection.execute <<-SQL
@@ -40,11 +65,22 @@ BEGIN
 END
 SQL
 
+  ActiveRecord::Base.connection.execute <<-SQL
+DROP PROCEDURE IF EXISTS topics;
+SQL
+
+  ActiveRecord::Base.connection.execute <<-SQL
+CREATE PROCEDURE topics(IN num INT) SQL SECURITY INVOKER
+BEGIN
+  select * from topics limit num;
+END
+SQL
+
   ActiveRecord::Base.connection.drop_table "enum_tests", if_exists: true
 
   ActiveRecord::Base.connection.execute <<-SQL
 CREATE TABLE enum_tests (
-  enum_column ENUM('text','blob','tiny','medium','long')
+  enum_column ENUM('text','blob','tiny','medium','long','unsigned','bigint')
 )
 SQL
 end
diff --git a/activerecord/test/schema/mysql_specific_schema.rb b/activerecord/test/schema/mysql_specific_schema.rb
deleted file mode 100644
index 90f5a60d7b..0000000000
--- a/activerecord/test/schema/mysql_specific_schema.rb
+++ /dev/null
@@ -1,62 +0,0 @@
-ActiveRecord::Schema.define do
-  create_table :binary_fields, force: true do |t|
-    t.binary :var_binary, limit: 255
-    t.binary :var_binary_large, limit: 4095
-    t.column :tiny_blob, 'tinyblob', limit: 255
-    t.binary :normal_blob, limit: 65535
-    t.binary :medium_blob, limit: 16777215
-    t.binary :long_blob, limit: 2147483647
-    t.text   :tiny_text, limit: 255
-    t.text   :normal_text, limit: 65535
-    t.text   :medium_text, limit: 16777215
-    t.text   :long_text, limit: 2147483647
-  end
-
-  add_index :binary_fields, :var_binary
-
-  create_table :key_tests, force: true, :options => 'ENGINE=MyISAM' do |t|
-    t.string :awesome
-    t.string :pizza
-    t.string :snacks
-  end
-
-  add_index :key_tests, :awesome, :type => :fulltext, :name => 'index_key_tests_on_awesome'
-  add_index :key_tests, :pizza, :using => :btree, :name => 'index_key_tests_on_pizza'
-  add_index :key_tests, :snacks, :name => 'index_key_tests_on_snack'
-
-  create_table :collation_tests, id: false, force: true do |t|
-    t.string :string_cs_column, limit: 1, collation: 'utf8_bin'
-    t.string :string_ci_column, limit: 1, collation: 'utf8_general_ci'
-  end
-
-  ActiveRecord::Base.connection.execute <<-SQL
-DROP PROCEDURE IF EXISTS ten;
-SQL
-
-  ActiveRecord::Base.connection.execute <<-SQL
-CREATE PROCEDURE ten() SQL SECURITY INVOKER
-BEGIN
-	select 10;
-END
-SQL
-
-  ActiveRecord::Base.connection.execute <<-SQL
-DROP PROCEDURE IF EXISTS topics;
-SQL
-
-  ActiveRecord::Base.connection.execute <<-SQL
-CREATE PROCEDURE topics() SQL SECURITY INVOKER
-BEGIN
-	select * from topics limit 1;
-END
-SQL
-
-  ActiveRecord::Base.connection.drop_table "enum_tests", if_exists: true
-
-  ActiveRecord::Base.connection.execute <<-SQL
-CREATE TABLE enum_tests (
-  enum_column ENUM('text','blob','tiny','medium','long')
-)
-SQL
-
-end
diff --git a/activerecord/test/schema/oracle_specific_schema.rb b/activerecord/test/schema/oracle_specific_schema.rb
index 264d9b8910..bc1e45ca80 100644
--- a/activerecord/test/schema/oracle_specific_schema.rb
+++ b/activerecord/test/schema/oracle_specific_schema.rb
@@ -1,5 +1,6 @@
-ActiveRecord::Schema.define do
+# frozen_string_literal: true
 
+ActiveRecord::Schema.define do
   execute "drop table test_oracle_defaults" rescue nil
   execute "drop sequence test_oracle_defaults_seq" rescue nil
   execute "drop sequence companies_nonstd_seq" rescue nil
@@ -36,5 +37,4 @@ create sequence test_oracle_defaults_seq minvalue 10000
   )
   SQL
   execute "create sequence defaults_seq minvalue 10000"
-
 end
diff --git a/activerecord/test/schema/postgresql_specific_schema.rb b/activerecord/test/schema/postgresql_specific_schema.rb
index df0362573b..975824ed51 100644
--- a/activerecord/test/schema/postgresql_specific_schema.rb
+++ b/activerecord/test/schema/postgresql_specific_schema.rb
@@ -1,67 +1,61 @@
+# frozen_string_literal: true
+
 ActiveRecord::Schema.define do
+  enable_extension!("uuid-ossp", ActiveRecord::Base.connection)
+  enable_extension!("pgcrypto",  ActiveRecord::Base.connection) if ActiveRecord::Base.connection.supports_pgcrypto_uuid?
 
-  enable_extension!('uuid-ossp', ActiveRecord::Base.connection)
+  uuid_default = connection.supports_pgcrypto_uuid? ? {} : { default: "uuid_generate_v4()" }
 
-  create_table :uuid_parents, id: :uuid, force: true do |t|
+  create_table :uuid_parents, id: :uuid, force: true, **uuid_default do |t|
     t.string :name
   end
 
-  create_table :uuid_children, id: :uuid, force: true do |t|
+  create_table :uuid_children, id: :uuid, force: true, **uuid_default do |t|
     t.string :name
     t.uuid :uuid_parent_id
   end
 
-  %w(postgresql_times postgresql_oids defaults postgresql_timestamp_with_zones
-      postgresql_partitioned_table postgresql_partitioned_table_parent).each do |table_name|
-    drop_table table_name, if_exists: true
+  create_table :defaults, force: true do |t|
+    t.date :modified_date, default: -> { "CURRENT_DATE" }
+    t.date :modified_date_function, default: -> { "now()" }
+    t.date :fixed_date, default: "2004-01-01"
+    t.datetime :modified_time, default: -> { "CURRENT_TIMESTAMP" }
+    t.datetime :modified_time_function, default: -> { "now()" }
+    t.datetime :fixed_time, default: "2004-01-01 00:00:00.000000-00"
+    t.column :char1, "char(1)", default: "Y"
+    t.string :char2, limit: 50, default: "a varchar field"
+    t.text :char3, default: "a text field"
+    t.bigint :bigint_default, default: -> { "0::bigint" }
+    t.text :multiline_default, default: "--- []
+
+"
+  end
+
+  create_table :postgresql_times, force: true do |t|
+    t.interval :time_interval
+    t.interval :scaled_time_interval, precision: 6
   end
 
-  execute 'DROP SEQUENCE IF EXISTS companies_nonstd_seq CASCADE'
-  execute 'CREATE SEQUENCE companies_nonstd_seq START 101 OWNED BY companies.id'
+  create_table :postgresql_oids, force: true do |t|
+    t.oid :obj_id
+  end
+
+  drop_table "postgresql_timestamp_with_zones", if_exists: true
+  drop_table "postgresql_partitioned_table", if_exists: true
+  drop_table "postgresql_partitioned_table_parent", if_exists: true
+
+  execute "DROP SEQUENCE IF EXISTS companies_nonstd_seq CASCADE"
+  execute "CREATE SEQUENCE companies_nonstd_seq START 101 OWNED BY companies.id"
   execute "ALTER TABLE companies ALTER COLUMN id SET DEFAULT nextval('companies_nonstd_seq')"
-  execute 'DROP SEQUENCE IF EXISTS companies_id_seq'
+  execute "DROP SEQUENCE IF EXISTS companies_id_seq"
 
-  execute 'DROP FUNCTION IF EXISTS partitioned_insert_trigger()'
+  execute "DROP FUNCTION IF EXISTS partitioned_insert_trigger()"
 
   %w(accounts_id_seq developers_id_seq projects_id_seq topics_id_seq customers_id_seq orders_id_seq).each do |seq_name|
     execute "SELECT setval('#{seq_name}', 100)"
   end
 
   execute <<_SQL
-    CREATE TABLE defaults (
-    id serial primary key,
-    modified_date date default CURRENT_DATE,
-    modified_date_function date default now(),
-    fixed_date date default '2004-01-01',
-    modified_time timestamp default CURRENT_TIMESTAMP,
-    modified_time_function timestamp default now(),
-    fixed_time timestamp default '2004-01-01 00:00:00.000000-00',
-    char1 char(1) default 'Y',
-    char2 character varying(50) default 'a varchar field',
-    char3 text default 'a text field',
-    bigint_default bigint default 0::bigint,
-    multiline_default text DEFAULT '--- []
-
-'::text
-);
-_SQL
-
-  execute <<_SQL
-  CREATE TABLE postgresql_times (
-    id SERIAL PRIMARY KEY,
-    time_interval INTERVAL,
-    scaled_time_interval INTERVAL(6)
-  );
-_SQL
-
-  execute <<_SQL
-  CREATE TABLE postgresql_oids (
-    id SERIAL PRIMARY KEY,
-    obj_id OID
-  );
-_SQL
-
-  execute <<_SQL
   CREATE TABLE postgresql_timestamp_with_zones (
     id SERIAL PRIMARY KEY,
     time TIMESTAMP WITH TIME ZONE
@@ -91,7 +85,7 @@ _SQL
       FOR EACH ROW EXECUTE PROCEDURE partitioned_insert_trigger();
 _SQL
   rescue ActiveRecord::StatementInvalid => e
-    if e.message =~ /language "plpgsql" does not exist/
+    if e.message.include?('language "plpgsql" does not exist')
       execute "CREATE LANGUAGE 'plpgsql';"
       retry
     else
@@ -109,4 +103,9 @@ _SQL
     t.integer :big_int_data_points, limit: 8, array: true
     t.decimal :decimal_array_default, array: true, default: [1.23, 3.45]
   end
+
+  create_table :uuid_items, force: true, id: false do |t|
+    t.uuid :uuid, primary_key: true, **uuid_default
+    t.string :title
+  end
 end
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 6872b49ad9..7034c773d2 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -1,11 +1,6 @@
+# frozen_string_literal: true
 
 ActiveRecord::Schema.define do
-  def except(adapter_names_to_exclude)
-    unless [adapter_names_to_exclude].flatten.include?(adapter_name)
-      yield
-    end
-  end
-
   # ------------------------------------------------------------------- #
   #                                                                     #
   #   Please keep these create table statements in alphabetical order   #
@@ -14,7 +9,7 @@ ActiveRecord::Schema.define do
   # ------------------------------------------------------------------- #
 
   create_table :accounts, force: true do |t|
-    t.integer :firm_id
+    t.references :firm, index: false
     t.string  :firm_name
     t.integer :credit_limit
   end
@@ -26,9 +21,12 @@ ActiveRecord::Schema.define do
   create_table :admin_users, force: true do |t|
     t.string :name
     t.string :settings, null: true, limit: 1024
+    t.string :parent, null: true, limit: 1024
+    t.string :spouse, null: true, limit: 1024
+    t.string :configs, null: true, limit: 1024
     # MySQL does not allow default values for blobs. Fake it out with a
     # big varchar below.
-    t.string :preferences, null: true, default: '', limit: 1024
+    t.string :preferences, null: true, default: "", limit: 1024
     t.string :json_data, null: true, limit: 1024
     t.string :json_data_empty, null: true, default: "", limit: 1024
     t.text :params
@@ -37,6 +35,8 @@ ActiveRecord::Schema.define do
 
   create_table :aircraft, force: true do |t|
     t.string :name
+    t.integer :wheels_count, default: 0, null: false
+    t.datetime :wheels_owned_at
   end
 
   create_table :articles, force: true do |t|
@@ -60,8 +60,8 @@ ActiveRecord::Schema.define do
 
   create_table :authors, force: true do |t|
     t.string :name, null: false
-    t.integer :author_address_id
-    t.integer :author_address_extra_id
+    t.references :author_address
+    t.references :author_address_extra
     t.string :organization_id
     t.string :owned_essay_id
   end
@@ -93,8 +93,8 @@ ActiveRecord::Schema.define do
     t.integer :pirate_id
   end
 
-  create_table :books, force: true do |t|
-    t.integer :author_id
+  create_table :books, id: :integer, force: true do |t|
+    t.references :author
     t.string :format
     t.column :name, :string
     t.column :status, :integer, default: 0
@@ -104,6 +104,8 @@ ActiveRecord::Schema.define do
     t.column :author_visibility, :integer, default: 0
     t.column :illustrator_visibility, :integer, default: 0
     t.column :font_size, :integer, default: 0
+    t.column :difficulty, :integer, default: 0
+    t.column :cover, :string, default: "hard"
   end
 
   create_table :booleans, force: true do |t|
@@ -111,10 +113,10 @@ ActiveRecord::Schema.define do
     t.boolean :has_fun, null: false, default: false
   end
 
-  create_table :bulbs, force: true do |t|
+  create_table :bulbs, primary_key: "ID", force: true do |t|
     t.integer :car_id
     t.string  :name
-    t.boolean :frickinawesome
+    t.boolean :frickinawesome, default: false
     t.string :color
   end
 
@@ -125,11 +127,17 @@ ActiveRecord::Schema.define do
   create_table :cars, force: true do |t|
     t.string  :name
     t.integer :engines_count
-    t.integer :wheels_count
+    t.integer :wheels_count, default: 0, null: false
+    t.datetime :wheels_owned_at
     t.column :lock_version, :integer, null: false, default: 0
     t.timestamps null: false
   end
 
+  create_table :old_cars, id: :integer, force: true do |t|
+  end
+
+  create_table :carriers, force: true
+
   create_table :categories, force: true do |t|
     t.string :name, null: false
     t.string :type
@@ -150,8 +158,9 @@ ActiveRecord::Schema.define do
   end
 
   create_table :citations, force: true do |t|
-    t.column :book1_id, :integer
-    t.column :book2_id, :integer
+    t.references :book1
+    t.references :book2
+    t.references :citation
   end
 
   create_table :clubs, force: true do |t|
@@ -188,22 +197,35 @@ ActiveRecord::Schema.define do
     t.string :resource_id
     t.string :resource_type
     t.integer :developer_id
+    t.datetime :updated_at
+    t.datetime :deleted_at
+    t.integer :comments
   end
 
   create_table :companies, force: true do |t|
     t.string  :type
-    t.integer :firm_id
+    t.references :firm, index: false
     t.string  :firm_name
     t.string  :name
-    t.integer :client_of
-    t.integer :rating, default: 1
+    t.bigint :client_of
+    t.bigint :rating, default: 1
     t.integer :account_id
     t.string :description, default: ""
+    t.index [:name, :rating], order: :desc
+    t.index [:name, :description], length: 10
+    t.index [:firm_id, :type, :rating], name: "company_index", length: { type: 10 }, order: { rating: :desc }
+    t.index [:firm_id, :type], name: "company_partial_index", where: "(rating > 10)"
+    t.index :name, name: "company_name_index", using: :btree
+    t.index "(CASE WHEN rating > 0 THEN lower(name) END) DESC", name: "company_expression_index" if supports_expression_index?
   end
 
-  add_index :companies, [:firm_id, :type, :rating], name: "company_index"
-  add_index :companies, [:firm_id, :type], name: "company_partial_index", where: "rating > 10"
-  add_index :companies, :name, name: 'company_name_index', using: :btree
+  create_table :content, force: true do |t|
+    t.string :title
+  end
+
+  create_table :content_positions, force: true do |t|
+    t.integer :content_id
+  end
 
   create_table :vegetables, force: true do |t|
     t.string :name
@@ -223,8 +245,8 @@ ActiveRecord::Schema.define do
   end
 
   create_table :contracts, force: true do |t|
-    t.integer :developer_id
-    t.integer :company_id
+    t.references :developer, index: false
+    t.references :company, index: false
   end
 
   create_table :customers, force: true do |t|
@@ -236,6 +258,11 @@ ActiveRecord::Schema.define do
     t.string  :gps_location
   end
 
+  create_table :customer_carriers, force: true do |t|
+    t.references :customer
+    t.references :carrier
+  end
+
   create_table :dashboards, force: true, id: false do |t|
     t.string :dashboard_id
     t.string :name
@@ -243,11 +270,21 @@ ActiveRecord::Schema.define do
 
   create_table :developers, force: true do |t|
     t.string   :name
+    t.string   :first_name
     t.integer  :salary, default: 70000
-    t.datetime :created_at
-    t.datetime :updated_at
-    t.datetime :created_on
-    t.datetime :updated_on
+    t.references :firm, index: false
+    t.integer :mentor_id
+    if subsecond_precision_supported?
+      t.datetime :created_at, precision: 6
+      t.datetime :updated_at, precision: 6
+      t.datetime :created_on, precision: 6
+      t.datetime :updated_on, precision: 6
+    else
+      t.datetime :created_at
+      t.datetime :updated_at
+      t.datetime :created_on
+      t.datetime :updated_on
+    end
   end
 
   create_table :developers_projects, force: true, id: false do |t|
@@ -278,11 +315,11 @@ ActiveRecord::Schema.define do
   create_table :edges, force: true, id: false do |t|
     t.column :source_id, :integer, null: false
     t.column :sink_id,   :integer, null: false
+    t.index [:source_id, :sink_id], unique: true, name: "unique_edge_index"
   end
-  add_index :edges, [:source_id, :sink_id], unique: true, name: 'unique_edge_index'
 
   create_table :engines, force: true do |t|
-    t.integer :car_id
+    t.references :car, index: false
   end
 
   create_table :entrants, force: true do |t|
@@ -305,6 +342,19 @@ ActiveRecord::Schema.define do
   create_table :eyes, force: true do |t|
   end
 
+  create_table :families, force: true do |t|
+  end
+
+  create_table :family_trees, force: true do |t|
+    t.references :family
+    t.references :member
+    t.string :token
+  end
+
+  create_table :frogs, force: true do |t|
+    t.string :name
+  end
+
   create_table :funny_jokes, force: true do |t|
     t.string :name
   end
@@ -331,6 +381,10 @@ ActiveRecord::Schema.define do
     t.column :key, :string
   end
 
+  create_table :guitars, force: true do |t|
+    t.string :color
+  end
+
   create_table :inept_wizards, force: true do |t|
     t.column :name, :string, null: false
     t.column :city, :string, null: false
@@ -346,7 +400,11 @@ ActiveRecord::Schema.define do
 
   create_table :invoices, force: true do |t|
     t.integer :balance
-    t.datetime :updated_at
+    if subsecond_precision_supported?
+      t.datetime :updated_at, precision: 6
+    else
+      t.datetime :updated_at
+    end
   end
 
   create_table :iris, force: true do |t|
@@ -362,11 +420,19 @@ ActiveRecord::Schema.define do
     t.integer :ideal_reference_id
   end
 
+  create_table :jobs_pool, force: true, id: false do |t|
+    t.references :job, null: false, index: true
+    t.references :user, null: false, index: true
+  end
+
   create_table :keyboards, force: true, id: false do |t|
     t.primary_key :key_number
     t.string      :name
   end
 
+  create_table :kitchens, force: true do |t|
+  end
+
   create_table :legacy_things, force: true do |t|
     t.integer :tps_report_number
     t.integer :version, null: false, default: 0
@@ -381,6 +447,14 @@ ActiveRecord::Schema.define do
     t.references :student
   end
 
+  create_table :students, force: true do |t|
+    t.string :name
+    t.boolean :active
+    t.integer :college_id
+  end
+
+  add_foreign_key :lessons_students, :students, on_delete: :cascade
+
   create_table :lint_models, force: true
 
   create_table :line_items, force: true do |t|
@@ -388,12 +462,21 @@ ActiveRecord::Schema.define do
     t.integer :amount
   end
 
+  create_table :lions, force: true do |t|
+    t.integer :gender
+    t.boolean :is_vegetarian, default: false
+  end
+
   create_table :lock_without_defaults, force: true do |t|
+    t.column :title, :string
     t.column :lock_version, :integer
+    t.timestamps null: true
   end
 
   create_table :lock_without_defaults_cust, force: true do |t|
+    t.column :title, :string
     t.column :custom_lock_version, :integer
+    t.timestamps null: true
   end
 
   create_table :magazines, force: true do |t|
@@ -407,7 +490,8 @@ ActiveRecord::Schema.define do
 
   create_table :members, force: true do |t|
     t.string :name
-    t.integer :member_type_id
+    t.references :member_type, index: false
+    t.references :admittable, polymorphic: true, index: false
   end
 
   create_table :member_details, force: true do |t|
@@ -425,13 +509,17 @@ ActiveRecord::Schema.define do
     t.datetime :joined_on
     t.integer :club_id, :member_id
     t.boolean :favourite, default: false
-    t.string :type
+    t.integer :type
   end
 
   create_table :member_types, force: true do |t|
     t.string :name
   end
 
+  create_table :mentors, force: true do |t|
+    t.string :name
+  end
+
   create_table :minivans, force: true, id: false do |t|
     t.string :minivan_id
     t.string :name
@@ -470,7 +558,7 @@ ActiveRecord::Schema.define do
   create_table :numeric_data, force: true do |t|
     t.decimal :bank_balance, precision: 10, scale: 2
     t.decimal :big_bank_balance, precision: 15, scale: 2
-    t.decimal :world_population, precision: 10, scale: 0
+    t.decimal :world_population, precision: 20, scale: 0
     t.decimal :my_house_population, precision: 2, scale: 0
     t.decimal :decimal_number_with_default, precision: 3, scale: 2, default: 2.78
     t.float   :temperature
@@ -496,7 +584,11 @@ ActiveRecord::Schema.define do
 
   create_table :owners, primary_key: :owner_id, force: true do |t|
     t.string :name
-    t.column :updated_at, :datetime
+    if subsecond_precision_supported?
+      t.column :updated_at, :datetime, precision: 6
+    else
+      t.column :updated_at, :datetime
+    end
     t.column :happy_at,   :datetime
     t.string :essay_id
   end
@@ -509,25 +601,55 @@ ActiveRecord::Schema.define do
     t.integer :non_poly_two_id
   end
 
-  create_table :parrots, force: true do |t|
-    t.column :name, :string
-    t.column :color, :string
-    t.column :parrot_sti_class, :string
-    t.column :killer_id, :integer
-    t.column :created_at, :datetime
-    t.column :created_on, :datetime
-    t.column :updated_at, :datetime
-    t.column :updated_on, :datetime
-  end
+  disable_referential_integrity do
+    create_table :parrots, force: :cascade do |t|
+      t.string :name
+      t.string :color
+      t.string :parrot_sti_class
+      t.integer :killer_id
+      t.integer :updated_count, :integer, default: 0
+      if subsecond_precision_supported?
+        t.datetime :created_at, precision: 0
+        t.datetime :created_on, precision: 0
+        t.datetime :updated_at, precision: 0
+        t.datetime :updated_on, precision: 0
+      else
+        t.datetime :created_at
+        t.datetime :created_on
+        t.datetime :updated_at
+        t.datetime :updated_on
+      end
+    end
 
-  create_table :parrots_pirates, id: false, force: true do |t|
-    t.column :parrot_id, :integer
-    t.column :pirate_id, :integer
-  end
+    create_table :pirates, force: :cascade do |t|
+      t.string :catchphrase
+      t.integer :parrot_id
+      t.integer :non_validated_parrot_id
+      if subsecond_precision_supported?
+        t.datetime :created_on, precision: 6
+        t.datetime :updated_on, precision: 6
+      else
+        t.datetime :created_on
+        t.datetime :updated_on
+      end
+    end
 
-  create_table :parrots_treasures, id: false, force: true do |t|
-    t.column :parrot_id, :integer
-    t.column :treasure_id, :integer
+    create_table :treasures, force: :cascade do |t|
+      t.string :name
+      t.string :type
+      t.references :looter, polymorphic: true
+      t.references :ship
+    end
+
+    create_table :parrots_pirates, id: false, force: true do |t|
+      t.references :parrot, foreign_key: true
+      t.references :pirate, foreign_key: true
+    end
+
+    create_table :parrots_treasures, id: false, force: true do |t|
+      t.references :parrot, foreign_key: true
+      t.references :treasure, foreign_key: true
+    end
   end
 
   create_table :people, force: true do |t|
@@ -560,20 +682,22 @@ ActiveRecord::Schema.define do
   create_table :pets, primary_key: :pet_id, force: true do |t|
     t.string :name
     t.integer :owner_id, :integer
-    t.timestamps null: false
+    if subsecond_precision_supported?
+      t.timestamps null: false, precision: 6
+    else
+      t.timestamps null: false
+    end
   end
 
-  create_table :pirates, force: true do |t|
-    t.column :catchphrase, :string
-    t.column :parrot_id, :integer
-    t.integer :non_validated_parrot_id
-    t.column :created_on, :datetime
-    t.column :updated_on, :datetime
+  create_table :pets_treasures, force: true do |t|
+    t.column :treasure_id, :integer
+    t.column :pet_id, :integer
+    t.column :rainbow_color, :string
   end
 
   create_table :posts, force: true do |t|
-    t.integer :author_id
-    t.string  :title, null: false
+    t.references :author
+    t.string :title, null: false
     # use VARCHAR2(4000) instead of CLOB datatype as CLOB data type has many limitations in
     # Oracle SELECT WHERE clause which causes many unit test failures
     if current_adapter?(:OracleAdapter)
@@ -586,6 +710,7 @@ ActiveRecord::Schema.define do
     t.integer :taggings_with_delete_all_count, default: 0
     t.integer :taggings_with_destroy_count, default: 0
     t.integer :tags_count, default: 0
+    t.integer :indestructible_tags_count, default: 0
     t.integer :tags_with_destroy_count, default: 0
     t.integer :tags_with_nullify_count, default: 0
   end
@@ -619,6 +744,8 @@ ActiveRecord::Schema.define do
   create_table :projects, force: true do |t|
     t.string :name
     t.string :type
+    t.references :firm, index: false
+    t.integer :mentor_id
   end
 
   create_table :randomly_named_table1, force: true do |t|
@@ -665,7 +792,10 @@ ActiveRecord::Schema.define do
   create_table :ships, force: true do |t|
     t.string :name
     t.integer :pirate_id
+    t.belongs_to :developer
     t.integer :update_only_pirate_id
+    # Conventionally named column for counter_cache
+    t.integer :treasures_count, default: 0
     t.datetime :created_at
     t.datetime :created_on
     t.datetime :updated_at
@@ -675,7 +805,24 @@ ActiveRecord::Schema.define do
   create_table :ship_parts, force: true do |t|
     t.string :name
     t.integer :ship_id
-    t.datetime :updated_at
+    if subsecond_precision_supported?
+      t.datetime :updated_at, precision: 6
+    else
+      t.datetime :updated_at
+    end
+  end
+
+  create_table :prisoners, force: true do |t|
+    t.belongs_to :ship
+  end
+
+  create_table :sinks, force: true do |t|
+    t.references :kitchen
+  end
+
+  create_table :shop_accounts, force: true do |t|
+    t.references :customer
+    t.references :customer_carrier
   end
 
   create_table :speedometers, force: true, id: false do |t|
@@ -686,28 +833,25 @@ ActiveRecord::Schema.define do
 
   create_table :sponsors, force: true do |t|
     t.integer :club_id
-    t.integer :sponsorable_id
-    t.string :sponsorable_type
+    t.references :sponsorable, polymorphic: true, index: false
+    t.references :sponsor, polymorphic: true, index: false
   end
 
-  create_table :string_key_objects, id: false, primary_key: :id, force: true do |t|
-    t.string     :id
-    t.string     :name
-    t.integer    :lock_version, null: false, default: 0
-  end
-
-  create_table :students, force: true do |t|
+  create_table :string_key_objects, id: false, force: true do |t|
+    t.string :id, null: false
     t.string :name
-    t.boolean :active
-    t.integer :college_id
+    t.integer :lock_version, null: false, default: 0
+    t.index :id, unique: true
   end
 
-  create_table :subscribers, force: true, id: false do |t|
+  create_table :subscribers, id: false, force: true do |t|
     t.string :nick, null: false
     t.string :name
-    t.column :books_count, :integer, null: false, default: 0
+    t.integer :id
+    t.integer :books_count, null: false, default: 0
+    t.integer :update_count, null: false, default: 0
+    t.index :nick, unique: true
   end
-  add_index :subscribers, :nick, unique: true
 
   create_table :subscriptions, force: true do |t|
     t.string :subscriber_id
@@ -725,6 +869,7 @@ ActiveRecord::Schema.define do
     t.column :taggable_type, :string
     t.column :taggable_id, :integer
     t.string :comment
+    t.string :type
   end
 
   create_table :tasks, force: true do |t|
@@ -736,7 +881,7 @@ ActiveRecord::Schema.define do
     t.string   :title, limit: 250
     t.string   :author_name
     t.string   :author_email_address
-    if mysql_56?
+    if subsecond_precision_supported?
       t.datetime :written_on, precision: 6
     else
       t.datetime :written_on
@@ -759,7 +904,11 @@ ActiveRecord::Schema.define do
     t.string   :parent_title
     t.string   :type
     t.string   :group
-    t.timestamps null: true
+    if subsecond_precision_supported?
+      t.timestamps null: true, precision: 6
+    else
+      t.timestamps null: true
+    end
   end
 
   create_table :toys, primary_key: :toy_id, force: true do |t|
@@ -776,12 +925,9 @@ ActiveRecord::Schema.define do
     t.datetime :updated_at
   end
 
-  create_table :treasures, force: true do |t|
-    t.column :name, :string
-    t.column :type, :string
-    t.column :looter_id, :integer
-    t.column :looter_type, :string
-    t.belongs_to :ship
+  create_table :tuning_pegs, force: true do |t|
+    t.integer :guitar_id
+    t.float :pitch
   end
 
   create_table :tyres, force: true do |t|
@@ -797,7 +943,7 @@ ActiveRecord::Schema.define do
     t.column :label, :string
   end
 
-  create_table 'warehouse-things', force: true do |t|
+  create_table "warehouse-things", force: true do |t|
     t.integer :value
   end
 
@@ -805,7 +951,6 @@ ActiveRecord::Schema.define do
     create_table(t, force: true) { }
   end
 
-  # NOTE - the following 4 tables are used by models that have :inverse_of options on the associations
   create_table :men, force: true do |t|
     t.string  :name
   end
@@ -819,6 +964,7 @@ ActiveRecord::Schema.define do
     t.string  :poly_man_without_inverse_type
     t.integer :horrible_polymorphic_man_id
     t.string  :horrible_polymorphic_man_type
+    t.references :human, polymorphic: true, index: false
   end
 
   create_table :interests, force: true do |t|
@@ -829,23 +975,26 @@ ActiveRecord::Schema.define do
     t.integer :zine_id
   end
 
-  create_table :wheels, force: true do |t|
-    t.references :wheelable, polymorphic: true
-  end
-
   create_table :zines, force: true do |t|
     t.string :title
   end
 
-  create_table :countries, force: true, id: false, primary_key: 'country_id' do |t|
-    t.string :country_id
+  create_table :wheels, force: true do |t|
+    t.integer :size
+    t.references :wheelable, polymorphic: true
+  end
+
+  create_table :countries, force: true, id: false do |t|
+    t.string :country_id, primary_key: true
     t.string :name
   end
-  create_table :treaties, force: true, id: false, primary_key: 'treaty_id' do |t|
-    t.string :treaty_id
+
+  create_table :treaties, force: true, id: false do |t|
+    t.string :treaty_id, primary_key: true
     t.string :name
   end
-  create_table :countries_treaties, force: true, id: false do |t|
+
+  create_table :countries_treaties, force: true, primary_key: [:country_id, :treaty_id] do |t|
     t.string :country_id, null: false
     t.string :treaty_id, null: false
   end
@@ -862,9 +1011,9 @@ ActiveRecord::Schema.define do
     t.string :name
   end
   create_table :weirds, force: true do |t|
-    t.string 'a$b'
-    t.string 'なまえ'
-    t.string 'from'
+    t.string "a$b"
+    t.string "なまえ"
+    t.string "from"
   end
 
   create_table :nodes, force: true do |t|
@@ -891,6 +1040,8 @@ ActiveRecord::Schema.define do
     t.integer :employable_id
     t.string :employable_type
     t.integer :department_id
+    t.string :employable_list_type
+    t.integer :employable_list_id
   end
   create_table :recipes, force: true do |t|
     t.integer :chef_id
@@ -900,30 +1051,35 @@ ActiveRecord::Schema.define do
   create_table :records, force: true do |t|
   end
 
-  except 'SQLite' do
-    # fk_test_has_fk should be before fk_test_has_pk
-    create_table :fk_test_has_fk, force: true do |t|
-      t.integer :fk_id, null: false
+  disable_referential_integrity do
+    create_table :fk_test_has_pk, primary_key: "pk_id", force: :cascade do |t|
     end
 
-    create_table :fk_test_has_pk, force: true, primary_key: "pk_id" do |t|
+    create_table :fk_test_has_fk, force: true do |t|
+      t.references :fk, null: false
+      t.foreign_key :fk_test_has_pk, column: "fk_id", name: "fk_name", primary_key: "pk_id"
     end
-
-    add_foreign_key :fk_test_has_fk, :fk_test_has_pk, column: "fk_id", name: "fk_name", primary_key: "pk_id"
-    add_foreign_key :lessons_students, :students
   end
 
   create_table :overloaded_types, force: true do |t|
     t.float :overloaded_float, default: 500
     t.float :unoverloaded_float
     t.string :overloaded_string_with_limit, limit: 255
-    t.string :string_with_default, default: 'the original default'
+    t.string :string_with_default, default: "the original default"
   end
 
   create_table :users, force: true do |t|
     t.string :token
     t.string :auth_token
   end
+
+  create_table :test_with_keyword_column_name, force: true do |t|
+    t.string :desc
+  end
+
+  create_table :non_primary_keys, force: true, id: false do |t|
+    t.integer :id
+  end
 end
 
 Course.connection.create_table :courses, force: true do |t|
@@ -934,3 +1090,14 @@ end
 College.connection.create_table :colleges, force: true do |t|
   t.column :name, :string, null: false
 end
+
+Professor.connection.create_table :professors, force: true do |t|
+  t.column :name, :string, null: false
+end
+
+Professor.connection.create_table :courses_professors, id: false, force: true do |t|
+  t.references :course
+  t.references :professor
+end
+
+OtherDog.connection.create_table :dogs, force: true
diff --git a/activerecord/test/schema/sqlite_specific_schema.rb b/activerecord/test/schema/sqlite_specific_schema.rb
index b5552c2755..18192292e4 100644
--- a/activerecord/test/schema/sqlite_specific_schema.rb
+++ b/activerecord/test/schema/sqlite_specific_schema.rb
@@ -1,22 +1,11 @@
+# frozen_string_literal: true
+
 ActiveRecord::Schema.define do
-  create_table :table_with_autoincrement, :force => true do |t|
-    t.column :name, :string
+  create_table :defaults, force: true do |t|
+    t.date :fixed_date, default: "2004-01-01"
+    t.datetime :fixed_time, default: "2004-01-01 00:00:00"
+    t.column :char1, "char(1)", default: "Y"
+    t.string :char2, limit: 50, default: "a varchar field"
+    t.text :char3, limit: 50, default: "a text field"
   end
-
-  execute "DROP TABLE fk_test_has_fk" rescue nil
-  execute "DROP TABLE fk_test_has_pk" rescue nil
-  execute <<_SQL
-  CREATE TABLE 'fk_test_has_pk' (
-    'pk_id' INTEGER NOT NULL PRIMARY KEY
-  );
-_SQL
-
-  execute <<_SQL
-  CREATE TABLE 'fk_test_has_fk' (
-    'id'    INTEGER NOT NULL PRIMARY KEY,
-    'fk_id' INTEGER NOT NULL,
-
-    FOREIGN KEY ('fk_id') REFERENCES 'fk_test_has_pk'('pk_id')
-  );
-_SQL
 end
diff --git a/activerecord/test/support/config.rb b/activerecord/test/support/config.rb
index 6d123688a3..bd6d5c339b 100644
--- a/activerecord/test/support/config.rb
+++ b/activerecord/test/support/config.rb
@@ -1,7 +1,9 @@
-require 'yaml'
-require 'erubis'
-require 'fileutils'
-require 'pathname'
+# frozen_string_literal: true
+
+require "yaml"
+require "erb"
+require "fileutils"
+require "pathname"
 
 module ARTest
   class << self
@@ -12,28 +14,29 @@ module ARTest
     private
 
     def config_file
-      Pathname.new(ENV['ARCONFIG'] || TEST_ROOT + '/config.yml')
+      Pathname.new(ENV["ARCONFIG"] || TEST_ROOT + "/config.yml")
     end
 
     def read_config
       unless config_file.exist?
-        FileUtils.cp TEST_ROOT + '/config.example.yml', config_file
+        FileUtils.cp TEST_ROOT + "/config.example.yml", config_file
       end
 
-      erb = Erubis::Eruby.new(config_file.read)
+      erb = ERB.new(config_file.read)
       expand_config(YAML.parse(erb.result(binding)).transform)
     end
 
     def expand_config(config)
-      config['connections'].each do |adapter, connection|
-        dbs = [['arunit', 'activerecord_unittest'], ['arunit2', 'activerecord_unittest2']]
+      config["connections"].each do |adapter, connection|
+        dbs = [["arunit", "activerecord_unittest"], ["arunit2", "activerecord_unittest2"],
+               ["arunit_without_prepared_statements", "activerecord_unittest"]]
         dbs.each do |name, dbname|
           unless connection[name].is_a?(Hash)
-            connection[name] = { 'database' => connection[name] }
+            connection[name] = { "database" => connection[name] }
           end
 
-          connection[name]['database'] ||= dbname
-          connection[name]['adapter']  ||= adapter
+          connection[name]["database"] ||= dbname
+          connection[name]["adapter"]  ||= adapter
         end
       end
 
diff --git a/activerecord/test/support/connection.rb b/activerecord/test/support/connection.rb
index d11fd9cfc1..2a4fa53460 100644
--- a/activerecord/test/support/connection.rb
+++ b/activerecord/test/support/connection.rb
@@ -1,14 +1,21 @@
-require 'active_support/logger'
-require 'models/college'
-require 'models/course'
+# frozen_string_literal: true
+
+require "active_support/logger"
+require "models/college"
+require "models/course"
+require "models/professor"
+require "models/other_dog"
 
 module ARTest
   def self.connection_name
-    ENV['ARCONN'] || config['default_connection']
+    ENV["ARCONN"] || config["default_connection"]
   end
 
   def self.connection_config
-    config['connections'][connection_name]
+    config.fetch("connections").fetch(connection_name) do
+      puts "Connection #{connection_name.inspect} not found. Available connections: #{config['connections'].keys.join(', ')}"
+      exit 1
+    end
   end
 
   def self.connect
diff --git a/activerecord/test/support/connection_helper.rb b/activerecord/test/support/connection_helper.rb
index 4a19e5df44..3bb1b370c1 100644
--- a/activerecord/test/support/connection_helper.rb
+++ b/activerecord/test/support/connection_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module ConnectionHelper
   def run_without_connection
     original_connection = ActiveRecord::Base.remove_connection
diff --git a/activerecord/test/support/ddl_helper.rb b/activerecord/test/support/ddl_helper.rb
index 43cb235e01..a18bf5ea0a 100644
--- a/activerecord/test/support/ddl_helper.rb
+++ b/activerecord/test/support/ddl_helper.rb
@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module DdlHelper
   def with_example_table(connection, table_name, definition = nil)
     connection.execute("CREATE TABLE #{table_name}(#{definition})")
diff --git a/activerecord/test/support/schema_dumping_helper.rb b/activerecord/test/support/schema_dumping_helper.rb
index 2d1651454d..777e6a7c1b 100644
--- a/activerecord/test/support/schema_dumping_helper.rb
+++ b/activerecord/test/support/schema_dumping_helper.rb
@@ -1,7 +1,9 @@
+# frozen_string_literal: true
+
 module SchemaDumpingHelper
   def dump_table_schema(table, connection = ActiveRecord::Base.connection)
     old_ignore_tables = ActiveRecord::SchemaDumper.ignore_tables
-    ActiveRecord::SchemaDumper.ignore_tables = connection.tables - [table]
+    ActiveRecord::SchemaDumper.ignore_tables = connection.data_sources - [table]
     stream = StringIO.new
     ActiveRecord::SchemaDumper.dump(ActiveRecord::Base.connection, stream)
     stream.string