Merge branch 'master' into unlock-minitest

152 files changed, 1789 insertions, 1011 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 1f8163db12..786bef7359 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,94 @@
+*   Skip query caching when working with batches of records (`find_each`, `find_in_batches`,
+    `in_batches`).
+
+    Previously, records would be fetched in batches, but all records would be retained in memory
+    until the end of the request or job.
+
+    *Eugene Kenny*
+
+*   Prevent errors raised by `sql.active_record` notification subscribers from being converted into
+    `ActiveRecord::StatementInvalid` exceptions.
+
+    *Dennis Taylor*
+
+*   Fix eager loading/preloading association with scope including joins.
+
+    Fixes #28324.
+
+    *Ryuta Kamizono*
+
+*   Fix transactions to apply state to child transactions
+
+    Previously if you had a nested transaction and the outer transaction was rolledback the record from the
+    inner transaction would still be marked as persisted.
+
+    This change fixes that by applying the state of the parent transaction to the child transaction when the
+    parent transaction is rolledback. This will correctly mark records from the inner transaction as not persisted.
+
+    *Eileen M. Uchitelle*, *Aaron Patterson*
+
+*   Deprecate `set_state` method in `TransactionState`
+
+    Deprecated the `set_state` method in favor of setting the state via specific methods. If you need to mark the
+    state of the transaction you can now use `rollback!`, `commit!` or `nullify!` instead of
+    `set_state(:rolledback)`, `set_state(:committed)`, or `set_state(nil)`.
+
+    *Eileen M. Uchitelle*, *Aaron Patterson*
+
+*   Deprecate delegating to `arel` in `Relation`.
+
+    *Ryuta Kamizono*
+
+*   Fix eager loading to respect `store_full_sti_class` setting.
+
+    *Ryuta Kamizono*
+
+*   Query cache was unavailable when entering the `ActiveRecord::Base.cache` block
+    without being connected.
+
+    *Tsukasa Oishi*
+
+*   Previously, when building records using a `has_many :through` association,
+    if the child records were deleted before the parent was saved, they would
+    still be persisted. Now, if child records are deleted before the parent is saved
+    on a `has_many :through` association, the child records will not be persisted.
+
+    *Tobias Kraze*
+
+*   Merging two relations representing nested joins no longer transforms the joins of
+    the merged relation into LEFT OUTER JOIN. Example to clarify:
+
+    ```
+    Author.joins(:posts).merge(Post.joins(:comments))
+    # Before the change:
+    #=> SELECT ... FROM authors INNER JOIN posts ON ... LEFT OUTER JOIN comments ON...
+
+    # After the change:
+    #=> SELECT ... FROM authors INNER JOIN posts ON ... INNER JOIN comments ON...
+    ```
+
+    TODO: Add to the Rails 5.2 upgrade guide
+
+    *Maxime Handfield Lapointe*
+
+*   `ActiveRecord::Persistence#touch` does not work well when optimistic locking enabled and
+    `locking_column`, without default value, is null in the database.
+
+    *bogdanvlviv*
+
+*   Fix destroying existing object does not work well when optimistic locking enabled and
+    `locking_column` is null in the database.
+
+    *bogdanvlviv*
+
+*   Use bulk INSERT to insert fixtures for better performance.
+
+    *Kir Shatrov*
+
+*   Prevent making bind param if casted value is nil.
+
+    *Ryuta Kamizono*
+
 *   Deprecate passing arguments and block at the same time to `count` and `sum` in `ActiveRecord::Calculations`.
 
     *Ryuta Kamizono*
diff --git a/activerecord/Rakefile b/activerecord/Rakefile
index 2d0d5bd657..fe5f9d1071 100644
--- a/activerecord/Rakefile
+++ b/activerecord/Rakefile
@@ -1,7 +1,7 @@
 require "rake/testtask"
 
-require File.expand_path("test/config", __dir__)
-require File.expand_path("test/support/config", __dir__)
+require_relative "test/config"
+require_relative "test/support/config"
 
 def run_without_aborting(*tasks)
   errors = []
diff --git a/activerecord/activerecord.gemspec b/activerecord/activerecord.gemspec
index 450ec0bba9..a626a1f21b 100644
--- a/activerecord/activerecord.gemspec
+++ b/activerecord/activerecord.gemspec
@@ -21,6 +21,11 @@ Gem::Specification.new do |s|
   s.extra_rdoc_files = %w(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
 
diff --git a/activerecord/bin/test b/activerecord/bin/test
index 3a9547e5c1..ab69f4f603 100755
--- a/activerecord/bin/test
+++ b/activerecord/bin/test
@@ -1,7 +1,7 @@
 #!/usr/bin/env ruby
 
 COMPONENT_ROOT = File.expand_path("..", __dir__)
-require File.expand_path("../tools/test", COMPONENT_ROOT)
+require_relative "../../tools/test"
 
 module Minitest
   def self.plugin_active_record_options(opts, options)
diff --git a/activerecord/lib/active_record.rb b/activerecord/lib/active_record.rb
index 29f49c6195..25d5e87317 100644
--- a/activerecord/lib/active_record.rb
+++ b/activerecord/lib/active_record.rb
@@ -26,8 +26,8 @@ require "active_support/rails"
 require "active_model"
 require "arel"
 
-require "active_record/version"
-require "active_record/attribute_set"
+require_relative "active_record/version"
+require_relative "active_record/attribute_set"
 
 module ActiveRecord
   extend ActiveSupport::Autoload
diff --git a/activerecord/lib/active_record/associations.rb b/activerecord/lib/active_record/associations.rb
index 7c37132d3a..e782196ce6 100644
--- a/activerecord/lib/active_record/associations.rb
+++ b/activerecord/lib/active_record/associations.rb
@@ -1,7 +1,7 @@
 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"
+require_relative "errors"
 
 module ActiveRecord
   class AssociationNotFoundError < ConfigurationError #:nodoc:
@@ -342,7 +342,7 @@ module ActiveRecord
       #                                     |            |  belongs_to  |
       #   generated methods                 | belongs_to | :polymorphic | has_one
       #   ----------------------------------+------------+--------------+---------
-      #   other(force_reload=false)         |     X      |      X       |    X
+      #   other                             |     X      |      X       |    X
       #   other=(other)                     |     X      |      X       |    X
       #   build_other(attributes={})        |     X      |              |    X
       #   create_other(attributes={})       |     X      |              |    X
@@ -352,7 +352,7 @@ module ActiveRecord
       #                                     |       |          | has_many
       #   generated methods                 | habtm | has_many | :through
       #   ----------------------------------+-------+----------+----------
-      #   others(force_reload=false)        |   X   |    X     |    X
+      #   others                            |   X   |    X     |    X
       #   others=(other,other,...)          |   X   |    X     |    X
       #   other_ids                         |   X   |    X     |    X
       #   other_ids=(id,id,...)             |   X   |    X     |    X
@@ -1187,7 +1187,7 @@ module ActiveRecord
         # +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)]
+        # [collection]
         #   Returns an array of all the associated objects.
         #   An empty array is returned if none are found.
         # [collection<<(object, ...)]
@@ -1407,7 +1407,7 @@ module ActiveRecord
         # +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)]
+        # [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,
@@ -1539,7 +1539,7 @@ module ActiveRecord
         # +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)]
+        # [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.
@@ -1701,7 +1701,7 @@ module ActiveRecord
         # +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)]
+        # [collection]
         #   Returns an array of all the associated objects.
         #   An empty array is returned if none are found.
         # [collection<<(object, ...)]
diff --git a/activerecord/lib/active_record/associations/alias_tracker.rb b/activerecord/lib/active_record/associations/alias_tracker.rb
index 4a5c821607..104de4f69d 100644
--- a/activerecord/lib/active_record/associations/alias_tracker.rb
+++ b/activerecord/lib/active_record/associations/alias_tracker.rb
@@ -4,21 +4,21 @@ module ActiveRecord
   module Associations
     # Keeps track of table aliases for ActiveRecord::Associations::JoinDependency
     class AliasTracker # :nodoc:
-      def self.create(connection, initial_table, type_caster)
+      def self.create(connection, initial_table)
         aliases = Hash.new(0)
         aliases[initial_table] = 1
-        new connection, aliases, type_caster
+        new(connection, aliases)
       end
 
-      def self.create_with_joins(connection, initial_table, joins, type_caster)
+      def self.create_with_joins(connection, initial_table, joins)
         if joins.empty?
-          create(connection, initial_table, type_caster)
+          create(connection, initial_table)
         else
           aliases = Hash.new { |h, k|
             h[k] = initial_count_for(connection, k, joins)
           }
           aliases[initial_table] = 1
-          new connection, aliases, type_caster
+          new(connection, aliases)
         end
       end
 
@@ -51,17 +51,16 @@ 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)
@@ -74,7 +73,7 @@ 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
 
diff --git a/activerecord/lib/active_record/associations/association.rb b/activerecord/lib/active_record/associations/association.rb
index ee2e79889f..1138ae3462 100644
--- a/activerecord/lib/active_record/associations/association.rb
+++ b/activerecord/lib/active_record/associations/association.rb
@@ -30,14 +30,6 @@ 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
@@ -94,7 +86,7 @@ module ActiveRecord
       # actually gets built.
       def association_scope
         if klass
-          @association_scope ||= AssociationScope.scope(self, klass.connection)
+          @association_scope ||= AssociationScope.scope(self)
         end
       end
 
@@ -276,7 +268,7 @@ module ActiveRecord
         end
 
         # Returns true if statement cache should be skipped on the association reader.
-        def skip_statement_cache?
+        def skip_statement_cache?(scope)
           reflection.has_scope? ||
             scope.eager_loading? ||
             klass.scope_attributes? ||
diff --git a/activerecord/lib/active_record/associations/association_scope.rb b/activerecord/lib/active_record/associations/association_scope.rb
index 1593b94f0c..6ef225b725 100644
--- a/activerecord/lib/active_record/associations/association_scope.rb
+++ b/activerecord/lib/active_record/associations/association_scope.rb
@@ -1,8 +1,8 @@
 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)
@@ -16,12 +16,12 @@ 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
+        alias_tracker = AliasTracker.create(klass.connection, klass.table_name)
         chain_head, chain_tail = get_chain(reflection, association, alias_tracker)
 
         scope.extending! reflection.extensions
@@ -112,7 +112,11 @@ module ActiveRecord
           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))
+            alias_name = tracker.aliased_table_for(
+              refl.table_name,
+              refl.alias_candidate(name),
+              refl.klass.type_caster
+            )
             proxy = ReflectionProxy.new(refl, alias_name)
             previous_reflection.next = proxy
             previous_reflection = proxy
@@ -138,7 +142,7 @@ module ActiveRecord
             # 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, table, scope_chain_item, owner)
+              item = eval_scope(reflection, table, scope_chain_item, owner)
 
               if scope_chain_item == refl.scope
                 scope.merge! item.except(:where, :includes)
@@ -159,9 +163,8 @@ module ActiveRecord
           scope
         end
 
-        def eval_scope(klass, table, scope, owner)
-          predicate_builder = PredicateBuilder.new(TableMetadata.new(klass, table))
-          ActiveRecord::Relation.create(klass, table, predicate_builder).instance_exec(owner, &scope)
+        def eval_scope(reflection, table, scope, owner)
+          reflection.build_scope(table).instance_exec(owner, &scope)
         end
     end
   end
diff --git a/activerecord/lib/active_record/associations/builder/collection_association.rb b/activerecord/lib/active_record/associations/builder/collection_association.rb
index edeb6491bd..c58b7d8160 100644
--- a/activerecord/lib/active_record/associations/builder/collection_association.rb
+++ b/activerecord/lib/active_record/associations/builder/collection_association.rb
@@ -1,6 +1,4 @@
-# This class is inherited by the has_many and has_many_and_belongs_to_many association classes
-
-require "active_record/associations"
+require_relative "../../associations"
 
 module ActiveRecord::Associations::Builder # :nodoc:
   class CollectionAssociation < Association #:nodoc:
diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index edc53e2517..a49fb155ee 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -44,10 +44,7 @@ module ActiveRecord
         if loaded?
           target.pluck(reflection.association_primary_key)
         else
-          @association_ids ||= (
-            column = "#{reflection.quoted_table_name}.#{reflection.association_primary_key}"
-            scope.pluck(column)
-          )
+          @association_ids ||= scope.pluck(reflection.association_primary_key)
         end
       end
 
@@ -69,6 +66,7 @@ module ActiveRecord
       def reset
         super
         @target = []
+        @association_ids = nil
       end
 
       def find(*args)
@@ -300,13 +298,14 @@ module ActiveRecord
       private
 
         def find_target
-          return scope.to_a if skip_statement_cache?
+          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|
               as = AssociationScope.create { params.bind }
-              target_scope.merge as.scope(self, conn)
+              target_scope.merge!(as.scope(self))
             }
           end
 
@@ -357,7 +356,10 @@ module ActiveRecord
             transaction do
               add_to_target(build_record(attributes)) do |record|
                 yield(record) if block_given?
-                insert_record(record, true, raise) { @_was_loaded = loaded? }
+                insert_record(record, true, raise) {
+                  @_was_loaded = loaded?
+                  @association_ids = nil
+                }
               end
             end
           end
@@ -430,7 +432,12 @@ module ActiveRecord
           records.each do |record|
             raise_on_type_mismatch!(record)
             add_to_target(record) do
-              result &&= insert_record(record, true, raise) { @_was_loaded = loaded? } unless owner.new_record?
+              unless owner.new_record?
+                result &&= insert_record(record, true, raise) {
+                  @_was_loaded = loaded?
+                  @association_ids = nil
+                }
+              end
             end
           end
 
diff --git a/activerecord/lib/active_record/associations/collection_proxy.rb b/activerecord/lib/active_record/associations/collection_proxy.rb
index 8cdb508c43..d77fcaf668 100644
--- a/activerecord/lib/active_record/associations/collection_proxy.rb
+++ b/activerecord/lib/active_record/associations/collection_proxy.rb
@@ -1114,6 +1114,7 @@ module ActiveRecord
       end
 
       def reset_scope # :nodoc:
+        @offsets = {}
         @scope = nil
         self
       end
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 53ffb3b68d..2fd20b4368 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -109,6 +109,11 @@ 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
diff --git a/activerecord/lib/active_record/associations/join_dependency.rb b/activerecord/lib/active_record/associations/join_dependency.rb
index 643226267c..04cdcb6a7f 100644
--- a/activerecord/lib/active_record/associations/join_dependency.rb
+++ b/activerecord/lib/active_record/associations/join_dependency.rb
@@ -93,7 +93,7 @@ module ActiveRecord
       #    joins # =>  []
       #
       def initialize(base, associations, joins, eager_loading: true)
-        @alias_tracker = AliasTracker.create_with_joins(base.connection, base.table_name, joins, base.type_caster)
+        @alias_tracker = AliasTracker.create_with_joins(base.connection, base.table_name, joins)
         @eager_loading = eager_loading
         tree = self.class.make_tree associations
         @join_root = JoinBase.new base, build(tree, base)
@@ -104,17 +104,17 @@ module ActiveRecord
         join_root.drop(1).map!(&:reflection)
       end
 
-      def join_constraints(outer_joins, join_type)
+      def join_constraints(joins_to_add, join_type)
         joins = join_root.children.flat_map { |child|
           make_join_constraints(join_root, child, join_type)
         }
 
-        joins.concat outer_joins.flat_map { |oj|
+        joins.concat joins_to_add.flat_map { |oj|
           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, child, join_type)
             }
           end
         }
@@ -185,7 +185,8 @@ module ActiveRecord
           node.reflection.chain.map { |reflection|
             alias_tracker.aliased_table_for(
               reflection.table_name,
-              table_alias_for(reflection, parent, reflection != node.reflection)
+              table_alias_for(reflection, parent, reflection != node.reflection),
+              reflection.klass.type_caster
             )
           }
         end
@@ -197,8 +198,7 @@ module ActiveRecord
 
         def table_alias_for(reflection, parent, join)
           name = "#{reflection.plural_name}_#{parent.table_name}"
-          name << "_join" if join
-          name
+          join ? "#{name}_join" : name
         end
 
         def walk(left, right)
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 97cfec0302..b14ddfeeeb 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_association.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_association.rb
@@ -1,4 +1,4 @@
-require "active_record/associations/join_dependency/join_part"
+require_relative "join_part"
 
 module ActiveRecord
   module Associations
@@ -34,37 +34,19 @@ module ActiveRecord
             table = tables.shift
             klass = reflection.klass
 
-            join_keys   = reflection.join_keys
-            key         = join_keys.key
-            foreign_key = join_keys.foreign_key
+            constraint = reflection.build_join_constraint(table, foreign_table)
 
-            constraint = build_constraint(klass, table, key, foreign_table, foreign_key)
-
-            predicate_builder = PredicateBuilder.new(TableMetadata.new(klass, table))
-            scope_chain_items = reflection.join_scopes(table, predicate_builder)
-            klass_scope       = reflection.klass_join_scope(table, predicate_builder)
-
-            scope_chain_items.concat [klass_scope].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)
 
-              binds << Relation::QueryAttribute.new(column.name, value, klass.type_for_attribute(column.name))
-              constraint = constraint.and klass.arel_attribute(reflection.type, table).eq(Arel::Nodes::BindParam.new)
+            if join_scope.arel.constraints.any?
+              binds.concat join_scope.bound_attributes
+              joins.concat join_scope.arel.join_sources
+              right = joins.last.right
+              right.expr = right.expr.and(join_scope.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
@@ -72,34 +54,6 @@ module ActiveRecord
           JoinInformation.new joins, binds
         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
-        end
-
         def table
           tables.first
         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 fca20514d1..6e0963425d 100644
--- a/activerecord/lib/active_record/associations/join_dependency/join_base.rb
+++ b/activerecord/lib/active_record/associations/join_dependency/join_base.rb
@@ -1,4 +1,4 @@
-require "active_record/associations/join_dependency/join_part"
+require_relative "join_part"
 
 module ActiveRecord
   module Associations
diff --git a/activerecord/lib/active_record/associations/preloader.rb b/activerecord/lib/active_record/associations/preloader.rb
index 9f77f38b35..a18994cec4 100644
--- a/activerecord/lib/active_record/associations/preloader.rb
+++ b/activerecord/lib/active_record/associations/preloader.rb
@@ -54,8 +54,6 @@ module ActiveRecord
         autoload :BelongsTo,           "active_record/associations/preloader/belongs_to"
       end
 
-      NULL_RELATION = Struct.new(:values, :where_clause, :joins_values).new({}, Relation::WhereClause.empty, [])
-
       # Eager loads the named associations for the given Active Record record(s).
       #
       # In this description, 'association name' shall refer to the name passed
@@ -93,7 +91,6 @@ module ActiveRecord
       def preload(records, associations, preload_scope = nil)
         records       = Array.wrap(records).compact.uniq
         associations  = Array.wrap(associations)
-        preload_scope = preload_scope || NULL_RELATION
 
         if records.empty?
           []
@@ -147,7 +144,7 @@ module ActiveRecord
         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)
+              loader = preloader_for(reflection, rs).new(rhs_klass, rs, reflection, scope)
               loader.run self
               loader
             end
@@ -159,6 +156,7 @@ module ActiveRecord
           records.each do |record|
             next unless record
             assoc = record.association(association)
+            next unless assoc.klass
             klasses = h[assoc.reflection] ||= {}
             (klasses[assoc.klass] ||= []) << record
           end
@@ -180,20 +178,11 @@ module ActiveRecord
           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
-          def self.owners; []; end
-        end
-
         # Returns a class containing the logic needed to load preload the data
         # and attach it to a relation. For example +Preloader::Association+ or
         # +Preloader::HasManyThrough+. The class returned implements a `run` method
         # that accepts a preloader.
-        def preloader_for(reflection, owners, rhs_klass)
-          return NullPreloader unless rhs_klass
-
+        def preloader_for(reflection, owners)
           if owners.first.association(reflection.name).loaded?
             return AlreadyLoaded
           end
diff --git a/activerecord/lib/active_record/associations/preloader/association.rb b/activerecord/lib/active_record/associations/preloader/association.rb
index 63ef3f2d8c..85343040db 100644
--- a/activerecord/lib/active_record/associations/preloader/association.rb
+++ b/activerecord/lib/active_record/associations/preloader/association.rb
@@ -11,7 +11,6 @@ module ActiveRecord
           @reflection    = reflection
           @preload_scope = preload_scope
           @model         = owners.first && owners.first.class
-          @scope         = nil
           @preloaded_records = []
         end
 
@@ -23,29 +22,11 @@ module ActiveRecord
           raise NotImplementedError
         end
 
-        def scope
-          @scope ||= build_scope
-        end
-
-        def records_for(ids)
-          scope.where(association_key_name => ids)
-        end
-
-        def table
-          klass.arel_table
-        end
-
         # The name of the key on the associated records
         def association_key_name
           raise NotImplementedError
         end
 
-        # This is overridden by HABTM as the condition should be on the foreign_key column in
-        # the join table
-        def association_key
-          klass.arel_attribute(association_key_name, table)
-        end
-
         # The name of the key on the model which declares the association
         def owner_key_name
           raise NotImplementedError
@@ -114,54 +95,35 @@ module ActiveRecord
             # Make several smaller queries if necessary or make one query if the adapter supports it
             slices = owner_keys.each_slice(klass.connection.in_clause_length || owner_keys.size)
             @preloaded_records = slices.flat_map do |slice|
-              records_for(slice).load(&block)
+              records_for(slice, &block)
             end
             @preloaded_records.group_by do |record|
               convert_key(record[association_key_name])
             end
           end
 
+          def records_for(ids, &block)
+            scope.where(association_key_name => ids).load(&block)
+          end
+
+          def scope
+            @scope ||= build_scope
+          end
+
           def reflection_scope
             @reflection_scope ||= reflection.scope_for(klass)
           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])
-
-            if preload_values[:select] || values[:select]
-              scope._select!(preload_values[:select] || values[:select])
-            end
-            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)
-            end
-
-            if order_values = preload_values[:order] || values[:order]
-              scope.order!(order_values)
-            end
-
-            if preload_values[:reordering] || values[:reordering]
-              scope.reordering_value = true
-            end
-
-            if preload_values[:readonly] || values[:readonly]
-              scope.readonly!
-            end
+            scope = klass.default_scoped
 
-            if options[:as]
-              scope.where!(klass.table_name => { reflection.type => model.base_class.sti_name })
+            if reflection.type
+              scope.where!(reflection.type => model.base_class.sti_name)
             end
 
-            scope.unscope_values = Array(values[:unscope]) + Array(preload_values[:unscope])
-            klass.default_scoped.merge(scope)
+            scope.merge!(reflection_scope)
+            scope.merge!(preload_scope) if preload_scope
+            scope
           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 8b954138cd..0999746cd5 100644
--- a/activerecord/lib/active_record/associations/preloader/through_association.rb
+++ b/activerecord/lib/active_record/associations/preloader/through_association.rb
@@ -11,6 +11,8 @@ module ActiveRecord
         end
 
         def associated_records_by_owner(preloader)
+          through_scope = through_scope()
+
           preloader.preload(owners,
                             through_reflection.name,
                             through_scope)
@@ -20,7 +22,7 @@ module ActiveRecord
             [owner, Array(center)]
           end
 
-          reset_association owners, through_reflection.name
+          reset_association(owners, through_reflection.name, through_scope)
 
           middle_records = through_records.flat_map(&:last)
 
@@ -63,7 +65,7 @@ module ActiveRecord
             id_map
           end
 
-          def reset_association(owners, association_name)
+          def reset_association(owners, association_name, through_scope)
             should_reset = (through_scope != through_reflection.klass.unscoped) ||
                (options[:source_type] && through_reflection.collection?)
 
@@ -77,17 +79,24 @@ module ActiveRecord
 
           def through_scope
             scope = through_reflection.klass.unscoped
+            values = reflection_scope.values
 
             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])
+                scope.includes_values = Array(values[:includes] || options[:source])
                 scope.where_clause = reflection_scope.where_clause
+                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
               end
 
-              scope.references! reflection_scope.values[:references]
-              if scope.eager_loading? && order_values = reflection_scope.values[:order]
+              scope.references! values[:references]
+              if scope.eager_loading? && order_values = values[:order]
                 scope = scope.order(order_values)
               end
             end
diff --git a/activerecord/lib/active_record/associations/singular_association.rb b/activerecord/lib/active_record/associations/singular_association.rb
index 91580a28d0..f8bbe4c2ed 100644
--- a/activerecord/lib/active_record/associations/singular_association.rb
+++ b/activerecord/lib/active_record/associations/singular_association.rb
@@ -36,13 +36,14 @@ module ActiveRecord
         end
 
         def find_target
-          return scope.take if skip_statement_cache?
+          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)
+              target_scope.merge!(as.scope(self)).limit(1)
             }
           end
 
@@ -63,6 +64,10 @@ module ActiveRecord
         end
 
         def _create_record(attributes, raise_error = false)
+          unless owner.persisted?
+            raise ActiveRecord::RecordNotSaved, "You cannot call create unless the parent is saved"
+          end
+
           record = build_record(attributes)
           yield(record) if block_given?
           saved = record.save
diff --git a/activerecord/lib/active_record/attribute.rb b/activerecord/lib/active_record/attribute.rb
index 38281158d8..78662433eb 100644
--- a/activerecord/lib/active_record/attribute.rb
+++ b/activerecord/lib/active_record/attribute.rb
@@ -122,7 +122,7 @@ module ActiveRecord
 
     def encode_with(coder)
       coder["name"] = name
-      coder["value_before_type_cast"] = value_before_type_cast if value_before_type_cast
+      coder["value_before_type_cast"] = value_before_type_cast unless value_before_type_cast.nil?
       coder["type"] = type if type
       coder["original_attribute"] = original_attribute if original_attribute
       coder["value"] = value if defined?(@value)
diff --git a/activerecord/lib/active_record/attribute/user_provided_default.rb b/activerecord/lib/active_record/attribute/user_provided_default.rb
index 57f8bbed76..c4e731fb28 100644
--- a/activerecord/lib/active_record/attribute/user_provided_default.rb
+++ b/activerecord/lib/active_record/attribute/user_provided_default.rb
@@ -1,4 +1,4 @@
-require "active_record/attribute"
+require_relative "../attribute"
 
 module ActiveRecord
   class Attribute # :nodoc:
diff --git a/activerecord/lib/active_record/attribute_methods/dirty.rb b/activerecord/lib/active_record/attribute_methods/dirty.rb
index 76987fb8f4..8c58e63931 100644
--- a/activerecord/lib/active_record/attribute_methods/dirty.rb
+++ b/activerecord/lib/active_record/attribute_methods/dirty.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 require "active_support/core_ext/module/attribute_accessors"
-require "active_record/attribute_mutation_tracker"
+require_relative "../attribute_mutation_tracker"
 
 module ActiveRecord
   module AttributeMethods
@@ -80,7 +80,7 @@ module ActiveRecord
         clear_mutation_trackers
       end
 
-      def raw_write_attribute(attr_name, *)
+      def write_attribute_without_type_cast(attr_name, *)
         result = super
         clear_attribute_change(attr_name)
         result
diff --git a/activerecord/lib/active_record/attribute_methods/primary_key.rb b/activerecord/lib/active_record/attribute_methods/primary_key.rb
index 2f32caa257..081aad434d 100644
--- a/activerecord/lib/active_record/attribute_methods/primary_key.rb
+++ b/activerecord/lib/active_record/attribute_methods/primary_key.rb
@@ -8,23 +8,20 @@ module ActiveRecord
       # Returns this record's primary key value wrapped in an array if one is
       # available.
       def to_key
-        sync_with_transaction_state
         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
+        _read_attribute(self.class.primary_key) if self.class.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
+        _write_attribute(self.class.primary_key, value) if self.class.primary_key
       end
 
       # Queries the primary key value.
@@ -57,16 +54,12 @@ module ActiveRecord
         end
 
         module ClassMethods
-          def define_method_attribute(attr_name)
-            super
+          ID_ATTRIBUTE_METHODS = %w(id id= id? id_before_type_cast id_was id_in_database).to_set
 
-            if attr_name == primary_key && attr_name != "id"
-              generated_attribute_methods.send(:alias_method, :id, primary_key)
-            end
+          def instance_method_already_implemented?(method_name)
+            super || primary_key && ID_ATTRIBUTE_METHODS.include?(method_name)
           end
 
-          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
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 4a8d231503..1f1efe8812 100644
--- a/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
+++ b/activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb
@@ -54,8 +54,7 @@ module ActiveRecord
       extend ActiveSupport::Concern
 
       included do
-        mattr_accessor :time_zone_aware_attributes, instance_writer: false
-        self.time_zone_aware_attributes = false
+        mattr_accessor :time_zone_aware_attributes, instance_writer: false, default: false
 
         class_attribute :skip_time_zone_conversion_for_attributes, instance_writer: false, default: []
         class_attribute :time_zone_aware_types, instance_writer: false, default: [ :datetime, :time ]
diff --git a/activerecord/lib/active_record/attribute_methods/write.rb b/activerecord/lib/active_record/attribute_methods/write.rb
index fe0e01db28..54b673c72e 100644
--- a/activerecord/lib/active_record/attribute_methods/write.rb
+++ b/activerecord/lib/active_record/attribute_methods/write.rb
@@ -17,7 +17,7 @@ module ActiveRecord
             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)
+                _write_attribute(name, value)
               end
               alias_method #{(name + '=').inspect}, :__temp__#{safe_name}=
               undef_method :__temp__#{safe_name}=
@@ -35,30 +35,27 @@ module ActiveRecord
           attr_name.to_s
         end
 
-        write_attribute_with_type_cast(name, value, true)
+        name = self.class.primary_key if name == "id".freeze && self.class.primary_key
+        _write_attribute(name, value)
       end
 
-      def raw_write_attribute(attr_name, value) # :nodoc:
-        write_attribute_with_type_cast(attr_name, value, false)
+      # 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
 
       private
-        # Handle *= for method_missing.
-        def attribute=(attribute_name, value)
-          write_attribute(attribute_name, value)
+        def write_attribute_without_type_cast(attr_name, value)
+          name = attr_name.to_s
+          @attributes.write_cast_value(name, 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)
-          end
-
-          value
+        # Handle *= for method_missing.
+        def attribute=(attribute_name, value)
+          _write_attribute(attribute_name, value)
         end
     end
   end
diff --git a/activerecord/lib/active_record/attribute_mutation_tracker.rb b/activerecord/lib/active_record/attribute_mutation_tracker.rb
index 4de993e169..a01a58f8a5 100644
--- a/activerecord/lib/active_record/attribute_mutation_tracker.rb
+++ b/activerecord/lib/active_record/attribute_mutation_tracker.rb
@@ -26,6 +26,7 @@ module ActiveRecord
     end
 
     def change_to_attribute(attr_name)
+      attr_name = attr_name.to_s
       if changed?(attr_name)
         [attributes[attr_name].original_value, attributes.fetch_value(attr_name)]
       end
@@ -44,7 +45,7 @@ module ActiveRecord
     end
 
     def changed_in_place?(attr_name)
-      attributes[attr_name].changed_in_place?
+      attributes[attr_name.to_s].changed_in_place?
     end
 
     def forget_change(attr_name)
@@ -54,7 +55,7 @@ module ActiveRecord
     end
 
     def original_value(attr_name)
-      attributes[attr_name].original_value
+      attributes[attr_name.to_s].original_value
     end
 
     def force_change(attr_name)
diff --git a/activerecord/lib/active_record/attribute_set.rb b/activerecord/lib/active_record/attribute_set.rb
index 01f9d815d5..6399e3de70 100644
--- a/activerecord/lib/active_record/attribute_set.rb
+++ b/activerecord/lib/active_record/attribute_set.rb
@@ -1,5 +1,5 @@
-require "active_record/attribute_set/builder"
-require "active_record/attribute_set/yaml_encoder"
+require_relative "attribute_set/builder"
+require_relative "attribute_set/yaml_encoder"
 
 module ActiveRecord
   class AttributeSet # :nodoc:
diff --git a/activerecord/lib/active_record/attribute_set/builder.rb b/activerecord/lib/active_record/attribute_set/builder.rb
index 2f624d32af..abe22b9ae4 100644
--- a/activerecord/lib/active_record/attribute_set/builder.rb
+++ b/activerecord/lib/active_record/attribute_set/builder.rb
@@ -1,4 +1,4 @@
-require "active_record/attribute"
+require_relative "../attribute"
 
 module ActiveRecord
   class AttributeSet # :nodoc:
diff --git a/activerecord/lib/active_record/attributes.rb b/activerecord/lib/active_record/attributes.rb
index 475b9beec4..dde22bcdaa 100644
--- a/activerecord/lib/active_record/attributes.rb
+++ b/activerecord/lib/active_record/attributes.rb
@@ -1,4 +1,4 @@
-require "active_record/attribute/user_provided_default"
+require_relative "attribute/user_provided_default"
 
 module ActiveRecord
   # See ActiveRecord::Attributes::ClassMethods for documentation
diff --git a/activerecord/lib/active_record/autosave_association.rb b/activerecord/lib/active_record/autosave_association.rb
index 829a4f6e86..70f0e2af8e 100644
--- a/activerecord/lib/active_record/autosave_association.rb
+++ b/activerecord/lib/active_record/autosave_association.rb
@@ -140,8 +140,7 @@ module ActiveRecord
 
     included do
       Associations::Builder::Association.extensions << AssociationBuilderExtension
-      mattr_accessor :index_nested_attribute_errors, instance_writer: false
-      self.index_nested_attribute_errors = false
+      mattr_accessor :index_nested_attribute_errors, instance_writer: false, default: false
     end
 
     module ClassMethods # :nodoc:
diff --git a/activerecord/lib/active_record/base.rb b/activerecord/lib/active_record/base.rb
index ac1aa2df45..f0e455478a 100644
--- a/activerecord/lib/active_record/base.rb
+++ b/activerecord/lib/active_record/base.rb
@@ -13,14 +13,14 @@ 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_relative "attribute_decorators"
+require_relative "define_callbacks"
+require_relative "errors"
+require_relative "log_subscriber"
+require_relative "explain_subscriber"
+require_relative "relation/delegation"
+require_relative "attributes"
+require_relative "type_caster"
 
 module ActiveRecord #:nodoc:
   # = Active Record
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 61bf5477aa..627b753f01 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb
@@ -679,7 +679,7 @@ module ActiveRecord
           # 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"
+          msg = "could not obtain ownership of all database connections in #{checkout_timeout} seconds".dup
 
           thread_report = []
           @connections.each do |conn|
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 c6811a4802..879626b72a 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb
@@ -51,9 +51,7 @@ module ActiveRecord
 
       # Returns a single value from a record
       def select_value(arel, name = nil, binds = [])
-        if result = select_rows(arel, 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:
@@ -68,6 +66,18 @@ module ActiveRecord
         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
+
+      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
@@ -296,6 +306,9 @@ 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)
         fixture = fixture.stringify_keys
 
@@ -308,16 +321,52 @@ module ActiveRecord
             raise Fixture::FixtureError, %(table "#{table_name}" has no column named #{name.inspect}.)
           end
         end
-        key_list = fixture.keys.map { |name| quote_column_name(name) }
-        value_list = binds.map(&:value_for_database).map do |value|
-          begin
-            quote(value)
-          rescue TypeError
-            quote(YAML.dump(value))
+
+        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
+
+      # 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)
+        return if fixtures.empty?
+
+        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
+              Arel.sql("DEFAULT")
+            end
           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)
+        manager = Arel::InsertManager.new
+        manager.into(table)
+        columns.each_key { |column| manager.columns << table[column] }
+        manager.values = manager.create_values_list(values)
+        execute manager.to_sql, "Fixtures Insert"
       end
 
       def empty_insert_statement_value
@@ -371,7 +420,11 @@ 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
 
@@ -381,6 +434,17 @@ module ActiveRecord
           end
           [relation, binds]
         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
+        end
     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 e53ba4e666..c352ddfc11 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb
@@ -108,6 +108,7 @@ module ActiveRecord
                   "sql.active_record",
                   sql: sql,
                   binds: binds,
+                  type_casted_binds: -> { type_casted_binds(binds) },
                   name: name,
                   connection_id: object_id,
                   cached: true,
@@ -123,6 +124,7 @@ module ActiveRecord
         # 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
 
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 a4fecc4a8e..8865e7c703 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb
@@ -22,7 +22,7 @@ module ActiveRecord
         private
 
           def visit_AlterTable(o)
-            sql = "ALTER TABLE #{quote_table_name(o.name)} "
+            sql = "ALTER TABLE #{quote_table_name(o.name)} ".dup
             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(" ")
@@ -30,17 +30,17 @@ module ActiveRecord
 
           def visit_ColumnDefinition(o)
             o.sql_type = type_to_sql(o.type, o.options)
-            column_sql = "#{quote_column_name(o.name)} #{o.sql_type}"
+            column_sql = "#{quote_column_name(o.name)} #{o.sql_type}".dup
             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)}".dup
           end
 
           def visit_TableDefinition(o)
-            create_sql = "CREATE#{' TEMPORARY' if o.temporary} TABLE #{quote_table_name(o.name)} "
+            create_sql = "CREATE#{' TEMPORARY' if o.temporary} TABLE #{quote_table_name(o.name)} ".dup
 
             statements = o.columns.map { |c| accept c }
             statements << accept(o.primary_keys) if o.primary_keys
@@ -55,7 +55,7 @@ module ActiveRecord
 
             create_sql << "(#{statements.join(', ')})" if statements.present?
             add_table_options!(create_sql, table_options(o))
-            create_sql << " AS #{@conn.to_sql(o.as)}" if o.as
+            create_sql << " AS #{to_sql(o.as)}" if o.as
             create_sql
           end
 
@@ -114,6 +114,11 @@ module ActiveRecord
             sql
           end
 
+          def to_sql(sql)
+            sql = sql.to_sql if sql.respond_to?(:to_sql)
+            sql
+          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)
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 16a398f631..475463c4fd 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -1,4 +1,4 @@
-require "active_record/migration/join_table"
+require_relative "../../migration/join_table"
 require "active_support/core_ext/string/access"
 require "digest"
 
@@ -31,7 +31,7 @@ module ActiveRecord
       # Returns the relation names useable to back Active Record models.
       # For most adapters this means all #tables and #views.
       def data_sources
-        select_values(data_source_sql, "SCHEMA")
+        query_values(data_source_sql, "SCHEMA")
       rescue NotImplementedError
         tables | views
       end
@@ -41,14 +41,14 @@ module ActiveRecord
       #   data_source_exists?(:ebooks)
       #
       def data_source_exists?(name)
-        select_values(data_source_sql(name), "SCHEMA").any? if name.present?
+        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
-        select_values(data_source_sql(type: "BASE TABLE"), "SCHEMA")
+        query_values(data_source_sql(type: "BASE TABLE"), "SCHEMA")
       end
 
       # Checks to see if the table +table_name+ exists on the database.
@@ -56,14 +56,14 @@ module ActiveRecord
       #   table_exists?(:developers)
       #
       def table_exists?(table_name)
-        select_values(data_source_sql(table_name, type: "BASE TABLE"), "SCHEMA").any? if table_name.present?
+        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
-        select_values(data_source_sql(type: "VIEW"), "SCHEMA")
+        query_values(data_source_sql(type: "VIEW"), "SCHEMA")
       end
 
       # Checks to see if the view +view_name+ exists on the database.
@@ -71,7 +71,7 @@ module ActiveRecord
       #   view_exists?(:ebooks)
       #
       def view_exists?(view_name)
-        select_values(data_source_sql(view_name, type: "VIEW"), "SCHEMA").any? if view_name.present?
+        query_values(data_source_sql(view_name, type: "VIEW"), "SCHEMA").any? if view_name.present?
       rescue NotImplementedError
         views.include?(view_name.to_s)
       end
@@ -188,6 +188,8 @@ module ActiveRecord
       #   The name of the primary key, if one is to be added automatically.
       #   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=}[rdoc-ref:AttributeMethods::PrimaryKey::ClassMethods#primary_key=] on the model
@@ -241,6 +243,23 @@ 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 integer NOT NULL,
+      #       client_id integer 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|
@@ -493,8 +512,7 @@ module ActiveRecord
       # * <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>.
+      #   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> -
@@ -992,7 +1010,7 @@ module ActiveRecord
 
       def dump_schema_information #:nodoc:
         versions = ActiveRecord::SchemaMigration.all_versions
-        insert_versions_sql(versions)
+        insert_versions_sql(versions) if versions.any?
       end
 
       def initialize_schema_migrations_table # :nodoc:
@@ -1330,7 +1348,7 @@ module ActiveRecord
           sm_table = quote_table_name(ActiveRecord::SchemaMigration.table_name)
 
           if versions.is_a?(Array)
-            sql = "INSERT INTO #{sm_table} (version) VALUES\n"
+            sql = "INSERT INTO #{sm_table} (version) VALUES\n".dup
             sql << versions.map { |v| "(#{quote(v)})" }.join(",\n")
             sql << ";\n\n"
             sql
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
index 19b7821494..f63d09039f 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/transaction.rb
@@ -1,10 +1,13 @@
 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?
@@ -19,15 +22,43 @@ module ActiveRecord
         @state == :rolledback
       end
 
+      def fully_completed?
+        completed?
+      end
+
       def completed?
         committed? || rolledback?
       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 commit!
+        @state = :committed
+      end
+
+      def nullify!
+        @state = nil
       end
     end
 
@@ -57,7 +88,7 @@ module ActiveRecord
       end
 
       def rollback
-        @state.set_state(:rolledback)
+        @state.rollback!
       end
 
       def rollback_records
@@ -72,7 +103,7 @@ module ActiveRecord
       end
 
       def commit
-        @state.set_state(:committed)
+        @state.commit!
       end
 
       def before_commit_records
@@ -100,8 +131,11 @@ module ActiveRecord
     end
 
     class SavepointTransaction < Transaction
-      def initialize(connection, savepoint_name, options, *args)
+      def initialize(connection, savepoint_name, parent_transaction, options, *args)
         super(connection, options, *args)
+
+        parent_transaction.state.add_child(@state)
+
         if options[:isolation]
           raise ActiveRecord::TransactionIsolationError, "cannot set transaction isolation in a nested transaction"
         end
@@ -155,7 +189,7 @@ module ActiveRecord
             if @stack.empty?
               RealTransaction.new(@connection, options, run_commit_callbacks: run_commit_callbacks)
             else
-              SavepointTransaction.new(@connection, "active_record_#{@stack.size}", options,
+              SavepointTransaction.new(@connection, "active_record_#{@stack.size}", @stack.last, options,
                                        run_commit_callbacks: run_commit_callbacks)
             end
 
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index 85d6fbe8b3..30b29e7007 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -1,9 +1,9 @@
-require "active_record/type"
-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_relative "../type"
+require_relative "determine_if_preparable_visitor"
+require_relative "schema_cache"
+require_relative "sql_type_metadata"
+require_relative "abstract/schema_dumper"
+require_relative "abstract/schema_creation"
 require "arel/collectors/bind"
 require "arel/collectors/sql_string"
 
@@ -147,7 +147,7 @@ module ActiveRecord
       # 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, ".dup
           if @owner == Thread.current
             msg << "it is already leased by the current thread."
           else
@@ -576,12 +576,14 @@ module ActiveRecord
             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
-        rescue => e
-          raise translate_exception_class(e, sql)
+          end
         end
 
         def translate_exception(exception, message)
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 648c869915..06976aa769 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -1,13 +1,13 @@
-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"
+require_relative "abstract_adapter"
+require_relative "statement_pool"
+require_relative "mysql/column"
+require_relative "mysql/explain_pretty_printer"
+require_relative "mysql/quoting"
+require_relative "mysql/schema_creation"
+require_relative "mysql/schema_definitions"
+require_relative "mysql/schema_dumper"
+require_relative "mysql/schema_statements"
+require_relative "mysql/type_metadata"
 
 require "active_support/core_ext/string/strip"
 
@@ -59,12 +59,12 @@ module ActiveRecord
         @statements = StatementPool.new(self.class.type_cast_config_to_integer(config[:statement_limit]))
 
         if version < "5.1.10"
-          raise "Your version of MySQL (#{full_version.match(/^\d+\.\d+\.\d+/)[0]}) is too old. Active Record supports MySQL >= 5.1.10."
+          raise "Your version of MySQL (#{version_string}) is too old. Active Record supports MySQL >= 5.1.10."
         end
       end
 
       def version #:nodoc:
-        @version ||= Version.new(full_version.match(/^\d+\.\d+\.\d+/)[0])
+        @version ||= Version.new(version_string)
       end
 
       def mariadb? # :nodoc:
@@ -120,11 +120,11 @@ module ActiveRecord
       end
 
       def get_advisory_lock(lock_name, timeout = 0) # :nodoc:
-        select_value("SELECT GET_LOCK(#{quote(lock_name)}, #{timeout})") == 1
+        query_value("SELECT GET_LOCK(#{quote(lock_name)}, #{timeout})") == 1
       end
 
       def release_advisory_lock(lock_name) # :nodoc:
-        select_value("SELECT RELEASE_LOCK(#{quote(lock_name)})") == 1
+        query_value("SELECT RELEASE_LOCK(#{quote(lock_name)})") == 1
       end
 
       def native_database_types
@@ -132,7 +132,7 @@ module ActiveRecord
       end
 
       def index_algorithms
-        { default: "ALGORITHM = DEFAULT", copy: "ALGORITHM = COPY", inplace: "ALGORITHM = INPLACE" }
+        { default: "ALGORITHM = DEFAULT".dup, copy: "ALGORITHM = COPY".dup, inplace: "ALGORITHM = INPLACE".dup }
       end
 
       # HELPER METHODS ===========================================
@@ -152,7 +152,7 @@ module ActiveRecord
       # 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")
@@ -267,7 +267,7 @@ module ActiveRecord
       end
 
       def current_database
-        select_value "SELECT DATABASE() as db"
+        query_value("SELECT database()", "SCHEMA")
       end
 
       # Returns the database character set.
@@ -287,7 +287,7 @@ module ActiveRecord
       def table_comment(table_name) # :nodoc:
         scope = quoted_scope(table_name)
 
-        select_value(<<-SQL.strip_heredoc, "SCHEMA")
+        query_value(<<-SQL.strip_heredoc, "SCHEMA")
           SELECT table_comment
           FROM information_schema.tables
           WHERE table_schema = #{scope[:schema]}
@@ -379,7 +379,7 @@ module ActiveRecord
 
       def add_index(table_name, column_name, options = {}) #:nodoc:
         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}"
+        sql = "CREATE #{index_type} INDEX #{quote_column_name(index_name)} #{index_using} ON #{quote_table_name(table_name)} (#{index_columns}) #{index_algorithm}".dup
         execute add_sql_comment!(sql, comment)
       end
 
@@ -393,7 +393,7 @@ module ActiveRecord
 
         scope = quoted_scope(table_name)
 
-        fk_info = select_all(<<-SQL.strip_heredoc, "SCHEMA")
+        fk_info = exec_query(<<-SQL.strip_heredoc, "SCHEMA")
           SELECT fk.referenced_table_name AS 'to_table',
                  fk.referenced_column_name AS 'primary_key',
                  fk.column_name AS 'column',
@@ -464,13 +464,13 @@ module ActiveRecord
             super
           end
 
-        sql << " unsigned" if unsigned && type != :primary_key
+        sql = "#{sql} unsigned" if unsigned && type != :primary_key
         sql
       end
 
       # SHOW VARIABLES LIKE 'name'
       def show_variable(name)
-        select_value("SELECT @@#{name}", "SCHEMA")
+        query_value("SELECT @@#{name}", "SCHEMA")
       rescue ActiveRecord::StatementInvalid
         nil
       end
@@ -480,7 +480,7 @@ module ActiveRecord
 
         scope = quoted_scope(table_name)
 
-        select_values(<<-SQL.strip_heredoc, "SCHEMA")
+        query_values(<<-SQL.strip_heredoc, "SCHEMA")
           SELECT column_name
           FROM information_schema.key_column_usage
           WHERE constraint_name = 'PRIMARY'
@@ -526,8 +526,25 @@ module ActiveRecord
         index.using == :btree || super
       end
 
+      def insert_fixtures(*)
+        without_sql_mode("NO_AUTO_VALUE_ON_ZERO") { super }
+      end
+
       private
 
+        def without_sql_mode(mode)
+          result = execute("SELECT @@SESSION.sql_mode")
+          current_mode = result.first[0]
+          return yield unless current_mode.include?(mode)
+
+          sql_mode = "REPLACE(@@sql_mode, '#{mode}', '')"
+          execute("SET @@SESSION.sql_mode = #{sql_mode}")
+          yield
+        ensure
+          sql_mode = "CONCAT(@@sql_mode, ',#{mode}')"
+          execute("SET @@SESSION.sql_mode = #{sql_mode}")
+        end
+
         def initialize_type_map(m)
           super
 
@@ -677,7 +694,7 @@ module ActiveRecord
             auto_increment: column.auto_increment?
           }
 
-          current_type = select_one("SHOW COLUMNS FROM #{quote_table_name(table_name)} LIKE '#{column_name}'", "SCHEMA")["Type"]
+          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))
@@ -761,7 +778,7 @@ module ActiveRecord
           # http://dev.mysql.com/doc/refman/5.7/en/set-statement.html#id944430
           # (trailing comma because variable_assignments will always have content)
           if @config[:encoding]
-            encoding = "NAMES #{@config[:encoding]}"
+            encoding = "NAMES #{@config[:encoding]}".dup
             encoding << " COLLATE #{@config[:collation]}" if @config[:collation]
             encoding << ", "
           end
@@ -787,7 +804,7 @@ module ActiveRecord
         end
 
         def create_table_info(table_name) # :nodoc:
-          select_one("SHOW CREATE TABLE #{quote_table_name(table_name)}")["Create Table"]
+          exec_query("SHOW CREATE TABLE #{quote_table_name(table_name)}", "SCHEMA").first["Create Table"]
         end
 
         def arel_visitor
@@ -837,7 +854,8 @@ module ActiveRecord
           end
         end
 
-        class MysqlJson < Type::Json # :nodoc:
+        def version_string
+          full_version.match(/^(?:5\.5\.5-)?(\d+\.\d+\.\d+)/)[1]
         end
 
         class MysqlString < Type::String # :nodoc:
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
index 8c67a7a80b..bda482a00f 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb
@@ -13,13 +13,8 @@ module ActiveRecord
           result
         end
 
-        # Returns an array of arrays containing the field values.
-        # Order is the same as that returned by +columns+.
-        def select_rows(arel, name = nil, binds = []) # :nodoc:
-          select_result(arel, name, binds) do |result|
-            @connection.next_result while @connection.more_results?
-            result.to_a
-          end
+        def query(sql, name = nil) # :nodoc:
+          execute(sql, name).to_a
         end
 
         # Executes the SQL statement in the context of this connection.
@@ -58,16 +53,6 @@ module ActiveRecord
             @connection.last_id
           end
 
-          def select_result(arel, name, binds)
-            arel, binds = binds_from_relation(arel, binds)
-            sql = to_sql(arel, binds)
-            if without_prepared_statement?(binds)
-              execute_and_free(sql, name) { |result| yield result }
-            else
-              exec_stmt_and_free(sql, name, binds, cache_stmt: true) { |_, result| yield result }
-            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
diff --git a/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb b/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb
index 083cd6340f..eea4984680 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb
@@ -16,7 +16,7 @@ module ActiveRecord
           end
 
           def visit_ChangeColumnDefinition(o)
-            change_column_sql = "CHANGE #{quote_column_name(o.name)} #{accept(o.column)}"
+            change_column_sql = "CHANGE #{quote_column_name(o.name)} #{accept(o.column)}".dup
             add_column_position!(change_column_sql, column_options(o.column))
           end
 
@@ -63,7 +63,7 @@ module ActiveRecord
 
           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)
+            add_sql_comment!("#{index_type} INDEX #{quote_column_name(index_name)} #{index_using} (#{index_columns})".dup, comment)
           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
index e2ba0ba1a0..a46d9f8cbb 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb
@@ -47,13 +47,13 @@ module ActiveRecord
           def schema_collation(column)
             if column.collation && table_name = column.table_name
               @table_collation_cache ||= {}
-              @table_collation_cache[table_name] ||= select_one("SHOW TABLE STATUS LIKE '#{table_name}'")["Collation"]
+              @table_collation_cache[table_name] ||= exec_query("SHOW TABLE STATUS LIKE #{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 mariadb?
+            if mariadb? && version < "10.2.5"
               create_table_info = create_table_info(column.table_name)
               if %r/#{quote_column_name(column.name)} #{Regexp.quote(column.sql_type)}(?: COLLATE \w+)? AS \((?<expression>.+?)\) #{column.extra}/ =~ create_table_info
                 $~[:expression].inspect
@@ -64,7 +64,7 @@ module ActiveRecord
                     " WHERE table_schema = #{scope[:schema]}" \
                     "   AND table_name = #{scope[:name]}" \
                     "   AND column_name = #{quote(column.name)}"
-              select_value(sql, "SCHEMA").inspect
+              query_value(sql, "SCHEMA").inspect
             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
index f9e1e046ea..24f8ff6367 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb
@@ -45,6 +45,13 @@ module ActiveRecord
           indexes
         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")
@@ -66,8 +73,8 @@ module ActiveRecord
 
           def new_column_from_field(table_name, field)
             type_metadata = fetch_type_metadata(field[:Type], field[:Extra])
-            if type_metadata.type == :datetime && field[:Default] == "CURRENT_TIMESTAMP"
-              default, default_function = nil, field[:Default]
+            if type_metadata.type == :datetime && /\ACURRENT_TIMESTAMP(?:\(\))?\z/i.match?(field[:Default])
+              default, default_function = nil, "CURRENT_TIMESTAMP"
             else
               default, default_function = field[:Default], nil
             end
@@ -95,7 +102,7 @@ module ActiveRecord
           def data_source_sql(name = nil, type: nil)
             scope = quoted_scope(name, type: type)
 
-            sql = "SELECT table_name FROM information_schema.tables"
+            sql = "SELECT table_name FROM information_schema.tables".dup
             sql << " WHERE table_schema = #{scope[:schema]}"
             sql << " AND table_name = #{scope[:name]}" if scope[:name]
             sql << " AND table_type = #{scope[:type]}" if scope[:type]
diff --git a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
index af55cfe2f6..c5c0a071e7 100644
--- a/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb
@@ -1,5 +1,5 @@
-require "active_record/connection_adapters/abstract_mysql_adapter"
-require "active_record/connection_adapters/mysql/database_statements"
+require_relative "abstract_mysql_adapter"
+require_relative "mysql/database_statements"
 
 gem "mysql2", ">= 0.3.18", "< 0.5"
 require "mysql2"
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 705e6063dc..ebf1715ed0 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb
@@ -7,30 +7,6 @@ module ActiveRecord
           PostgreSQL::ExplainPrettyPrinter.new.pp(exec_query(sql, "EXPLAIN", binds))
         end
 
-        def select_value(arel, name = nil, binds = []) # :nodoc:
-          select_result(arel, name, binds) do |result|
-            result.getvalue(0, 0) if result.ntuples > 0 && result.nfields > 0
-          end
-        end
-
-        def select_values(arel, name = nil, binds = []) # :nodoc:
-          select_result(arel, 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(arel, name = nil, binds = []) # :nodoc:
-          select_result(arel, name, binds) do |result|
-            result.values
-          end
-        end
-
         # The internal PostgreSQL identifier of the money data type.
         MONEY_COLUMN_TYPE_OID = 790 #:nodoc:
         # The internal PostgreSQL identifier of the BYTEA data type.
@@ -171,18 +147,14 @@ module ActiveRecord
         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
-
-          def select_result(arel, name, binds)
-            arel, binds = binds_from_relation(arel, binds)
-            sql = to_sql(arel, binds)
-            execute_and_clear(sql, name, binds) do |result|
-              yield result
-            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 4098250f3e..6666622c08 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid.rb
@@ -1,26 +1,25 @@
-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/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_relative "oid/array"
+require_relative "oid/bit"
+require_relative "oid/bit_varying"
+require_relative "oid/bytea"
+require_relative "oid/cidr"
+require_relative "oid/date_time"
+require_relative "oid/decimal"
+require_relative "oid/enum"
+require_relative "oid/hstore"
+require_relative "oid/inet"
+require_relative "oid/jsonb"
+require_relative "oid/money"
+require_relative "oid/oid"
+require_relative "oid/point"
+require_relative "oid/legacy_point"
+require_relative "oid/range"
+require_relative "oid/specialized_string"
+require_relative "oid/uuid"
+require_relative "oid/vector"
+require_relative "oid/xml"
 
-require "active_record/connection_adapters/postgresql/oid/type_map_initializer"
+require_relative "oid/type_map_initializer"
 
 module ActiveRecord
   module ConnectionAdapters
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 3c706c27c4..0000000000
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/json.rb
+++ /dev/null
@@ -1,10 +0,0 @@
-module ActiveRecord
-  module ConnectionAdapters
-    module PostgreSQL
-      module OID # :nodoc:
-        class Json < Type::Json # :nodoc:
-        end
-      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 7a91272d1c..cd7442e751 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 module ActiveRecord
   module ConnectionAdapters
     module PostgreSQL
@@ -22,7 +23,7 @@ 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.]/, "")
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..db92333ef7 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb
@@ -3,7 +3,7 @@ module ActiveRecord
     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/quoting.rb b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
index 44eb666965..ee4230c6f2 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb
@@ -78,7 +78,7 @@ module ActiveRecord
 
         private
           def lookup_cast_type(sql_type)
-            super(select_value("SELECT #{quote(sql_type)}::regtype::oid", "SCHEMA").to_i)
+            super(query_value("SELECT #{quote(sql_type)}::regtype::oid", "SCHEMA").to_i)
           end
 
           def _quote(value)
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 cb45d7ba6b..a710ea6cc9 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -60,7 +60,7 @@ module ActiveRecord
 
         # Returns true if schema exists.
         def schema_exists?(name)
-          select_value("SELECT COUNT(*) FROM pg_namespace WHERE nspname = #{quote(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.
@@ -73,7 +73,7 @@ module ActiveRecord
           table = quoted_scope(table_name)
           index = quoted_scope(index_name)
 
-          select_value(<<-SQL, "SCHEMA").to_i > 0
+          query_value(<<-SQL, "SCHEMA").to_i > 0
             SELECT COUNT(*)
             FROM pg_class t
             INNER JOIN pg_index d ON t.oid = d.indrelid
@@ -163,7 +163,7 @@ module ActiveRecord
         def table_comment(table_name) # :nodoc:
           scope = quoted_scope(table_name, type: "BASE TABLE")
           if scope[:name]
-            select_value(<<-SQL.strip_heredoc, "SCHEMA")
+            query_value(<<-SQL.strip_heredoc, "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
@@ -176,32 +176,32 @@ module ActiveRecord
 
         # 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 = 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 = 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 = 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_.*'
@@ -234,12 +234,12 @@ module ActiveRecord
 
         # 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.
@@ -257,7 +257,7 @@ module ActiveRecord
         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.
@@ -268,7 +268,7 @@ 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
             end
@@ -290,18 +290,16 @@ module ActiveRecord
 
           if pk && sequence
             quoted_sequence = quote_table_name(sequence)
-            max_pk = select_value("select MAX(#{quote_column_name pk}) from #{quote_table_name(table)}")
+            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 = select_value("SELECT seqmin from pg_sequence where seqrelid = '#{quoted_sequence}'::regclass")
+                minvalue = query_value("SELECT seqmin FROM pg_sequence WHERE seqrelid = #{quote(quoted_sequence)}::regclass", "SCHEMA")
               else
-                minvalue = select_value("SELECT min_value FROM #{quoted_sequence}")
+                minvalue = query_value("SELECT min_value FROM #{quoted_sequence}", "SCHEMA")
               end
             end
 
-            select_value(<<-end_sql, "SCHEMA")
-              SELECT setval('#{quoted_sequence}', #{max_pk ? max_pk : minvalue}, #{max_pk ? true : false})
-            end_sql
+            query_value("SELECT setval(#{quote(quoted_sequence)}, #{max_pk ? max_pk : minvalue}, #{max_pk ? true : false})", "SCHEMA")
           end
         end
 
@@ -325,7 +323,7 @@ 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? || result.empty?
@@ -343,7 +341,7 @@ 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
@@ -360,7 +358,7 @@ module ActiveRecord
         end
 
         def primary_keys(table_name) # :nodoc:
-          select_values(<<-SQL.strip_heredoc, "SCHEMA")
+          query_values(<<-SQL.strip_heredoc, "SCHEMA")
             SELECT a.attname
               FROM (
                      SELECT indrelid, indkey, generate_subscripts(indkey, 1) idx
@@ -408,7 +406,7 @@ module ActiveRecord
           quoted_table_name = quote_table_name(table_name)
           quoted_column_name = quote_column_name(column_name)
           sql_type = type_to_sql(type, options)
-          sql = "ALTER TABLE #{quoted_table_name} ALTER COLUMN #{quoted_column_name} TYPE #{sql_type}"
+          sql = "ALTER TABLE #{quoted_table_name} ALTER COLUMN #{quoted_column_name} TYPE #{sql_type}".dup
           if options[:collation]
             sql << " COLLATE \"#{options[:collation]}\""
           end
@@ -511,7 +509,7 @@ module ActiveRecord
 
         def foreign_keys(table_name)
           scope = quoted_scope(table_name)
-          fk_info = select_all(<<-SQL.strip_heredoc, "SCHEMA")
+          fk_info = exec_query(<<-SQL.strip_heredoc, "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
             FROM pg_constraint c
             JOIN pg_class t1 ON c.conrelid = t1.oid
@@ -568,7 +566,7 @@ module ActiveRecord
               super
             end
 
-          sql << "[]" if array && type != :primary_key
+          sql = "#{sql}[]" if array && type != :primary_key
           sql
         end
 
@@ -637,7 +635,7 @@ module ActiveRecord
             scope = quoted_scope(name, type: type)
             scope[:type] ||= "'r','v','m'" # (r)elation/table, (v)iew, (m)aterialized view
 
-            sql = "SELECT c.relname FROM pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace"
+            sql = "SELECT c.relname FROM pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace".dup
             sql << " WHERE n.nspname = #{scope[:schema]}"
             sql << " AND c.relname = #{scope[:name]}" if scope[:name]
             sql << " AND c.relkind IN (#{scope[:type]})"
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 5287dd6a51..8baef19030 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -2,20 +2,20 @@
 gem "pg", "~> 0.18"
 require "pg"
 
-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_relative "abstract_adapter"
+require_relative "statement_pool"
+require_relative "postgresql/column"
+require_relative "postgresql/database_statements"
+require_relative "postgresql/explain_pretty_printer"
+require_relative "postgresql/oid"
+require_relative "postgresql/quoting"
+require_relative "postgresql/referential_integrity"
+require_relative "postgresql/schema_creation"
+require_relative "postgresql/schema_definitions"
+require_relative "postgresql/schema_dumper"
+require_relative "postgresql/schema_statements"
+require_relative "postgresql/type_metadata"
+require_relative "postgresql/utils"
 
 module ActiveRecord
   module ConnectionHandling # :nodoc:
@@ -312,14 +312,14 @@ module ActiveRecord
         unless lock_id.is_a?(Integer) && lock_id.bit_length <= 63
           raise(ArgumentError, "Postgres requires advisory lock ids to be a signed 64 bit integer")
         end
-        select_value("SELECT pg_try_advisory_lock(#{lock_id});")
+        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, "Postgres requires advisory lock ids to be a signed 64 bit integer")
         end
-        select_value("SELECT pg_advisory_unlock(#{lock_id})")
+        query_value("SELECT pg_advisory_unlock(#{lock_id})")
       end
 
       def enable_extension(name)
@@ -336,15 +336,14 @@ module ActiveRecord
 
       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 = 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
       end
 
       def extensions
         if supports_extensions?
-          exec_query("SELECT extname from pg_extension", "SCHEMA").cast_values
+          exec_query("SELECT extname FROM pg_extension", "SCHEMA").cast_values
         else
           super
         end
@@ -352,14 +351,14 @@ module ActiveRecord
 
       # Returns the configured supported identifier length supported by PostgreSQL
       def table_alias_length
-        @max_identifier_length ||= select_value("SHOW max_identifier_length", "SCHEMA").to_i
+        @max_identifier_length ||= query_value("SHOW max_identifier_length", "SCHEMA").to_i
       end
       alias index_name_length table_alias_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?
@@ -723,11 +722,6 @@ module ActiveRecord
           end
         end
 
-        # Returns the current ID of a table's sequence.
-        def last_insert_id_result(sequence_name)
-          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:
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb
index e02491edb6..31e83f9260 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb
@@ -11,7 +11,7 @@ module ActiveRecord
           end
 
           exec_query("PRAGMA index_list(#{quote_table_name(table_name)})", "SCHEMA").map do |row|
-            index_sql = select_value(<<-SQL, "SCHEMA")
+            index_sql = query_value(<<-SQL, "SCHEMA")
               SELECT sql
               FROM sqlite_master
               WHERE name = #{quote(row['name'])} AND type = 'index'
@@ -67,7 +67,7 @@ module ActiveRecord
             scope = quoted_scope(name, type: type)
             scope[:type] ||= "'table','view'"
 
-            sql = "SELECT name FROM sqlite_master WHERE name <> 'sqlite_sequence'"
+            sql = "SELECT name FROM sqlite_master WHERE name <> 'sqlite_sequence'".dup
             sql << " AND name = #{scope[:name]}" if scope[:name]
             sql << " AND type IN (#{scope[:type]})"
             sql
diff --git a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
index 7233325d5a..04129841e4 100644
--- a/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb
@@ -1,11 +1,11 @@
-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"
+require_relative "abstract_adapter"
+require_relative "statement_pool"
+require_relative "sqlite3/explain_pretty_printer"
+require_relative "sqlite3/quoting"
+require_relative "sqlite3/schema_creation"
+require_relative "sqlite3/schema_definitions"
+require_relative "sqlite3/schema_dumper"
+require_relative "sqlite3/schema_statements"
 
 gem "sqlite3", "~> 1.3.6"
 require "sqlite3"
@@ -169,7 +169,7 @@ module ActiveRecord
       # REFERENTIAL INTEGRITY ====================================
 
       def disable_referential_integrity # :nodoc:
-        old = select_value("PRAGMA foreign_keys")
+        old = query_value("PRAGMA foreign_keys")
 
         begin
           execute("PRAGMA foreign_keys = OFF")
@@ -337,7 +337,7 @@ module ActiveRecord
       alias :add_belongs_to :add_reference
 
       def foreign_keys(table_name)
-        fk_info = select_all("PRAGMA foreign_key_list(#{quote(table_name)})", "SCHEMA")
+        fk_info = exec_query("PRAGMA foreign_key_list(#{quote(table_name)})", "SCHEMA")
         fk_info.map do |row|
           options = {
             column: row["from"],
@@ -349,6 +349,12 @@ module ActiveRecord
         end
       end
 
+      def insert_fixtures(rows, table_name)
+        rows.each do |row|
+          insert_fixture(row, table_name)
+        end
+      end
+
       private
 
         def table_structure(table_name)
@@ -437,7 +443,7 @@ module ActiveRecord
         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)
diff --git a/activerecord/lib/active_record/core.rb b/activerecord/lib/active_record/core.rb
index 8f78330d4a..198c712abc 100644
--- a/activerecord/lib/active_record/core.rb
+++ b/activerecord/lib/active_record/core.rb
@@ -56,8 +56,7 @@ 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:
@@ -67,16 +66,14 @@ 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
-      self.error_on_ignored_order = false
+      mattr_accessor :error_on_ignored_order, instance_writer: false, default: false
 
       def self.error_on_ignored_order_or_limit
         ActiveSupport::Deprecation.warn(<<-MSG.squish)
@@ -101,8 +98,7 @@ module ActiveRecord
       ##
       # :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:
@@ -110,8 +106,7 @@ module ActiveRecord
       # db:migrate rake task. 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:
@@ -120,8 +115,7 @@ 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:
@@ -130,7 +124,6 @@ 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
 
diff --git a/activerecord/lib/active_record/errors.rb b/activerecord/lib/active_record/errors.rb
index 18fac5af1b..60d4fb70e0 100644
--- a/activerecord/lib/active_record/errors.rb
+++ b/activerecord/lib/active_record/errors.rb
@@ -105,7 +105,7 @@ module ActiveRecord
   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
 
diff --git a/activerecord/lib/active_record/explain.rb b/activerecord/lib/active_record/explain.rb
index 8f7ae2c33c..eff5990f3a 100644
--- a/activerecord/lib/active_record/explain.rb
+++ b/activerecord/lib/active_record/explain.rb
@@ -1,4 +1,4 @@
-require "active_record/explain_registry"
+require_relative "explain_registry"
 
 module ActiveRecord
   module Explain
@@ -16,7 +16,7 @@ module ActiveRecord
     # Returns a formatted string ready to be logged.
     def exec_explain(queries) # :nodoc:
       str = queries.map do |sql, binds|
-        msg = "EXPLAIN for: #{sql}"
+        msg = "EXPLAIN for: #{sql}".dup
         unless binds.empty?
           msg << " "
           msg << binds.map { |attr| render_bind(attr) }.inspect
diff --git a/activerecord/lib/active_record/explain_subscriber.rb b/activerecord/lib/active_record/explain_subscriber.rb
index abd8cfc8f2..928720d011 100644
--- a/activerecord/lib/active_record/explain_subscriber.rb
+++ b/activerecord/lib/active_record/explain_subscriber.rb
@@ -1,5 +1,5 @@
 require "active_support/notifications"
-require "active_record/explain_registry"
+require_relative "explain_registry"
 
 module ActiveRecord
   class ExplainSubscriber # :nodoc:
diff --git a/activerecord/lib/active_record/fixtures.rb b/activerecord/lib/active_record/fixtures.rb
index bad6542be2..c9e97d9d2b 100644
--- a/activerecord/lib/active_record/fixtures.rb
+++ b/activerecord/lib/active_record/fixtures.rb
@@ -4,8 +4,8 @@ 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"
+require_relative "fixture_set/file"
+require_relative "errors"
 
 module ActiveRecord
   class FixtureClassNotFound < ActiveRecord::ActiveRecordError #:nodoc:
@@ -492,8 +492,7 @@ module ActiveRecord
       end
     end
 
-    cattr_accessor :all_loaded_fixtures
-    self.all_loaded_fixtures = {}
+    cattr_accessor :all_loaded_fixtures, default: {}
 
     class ClassCache
       def initialize(class_names, config)
@@ -568,9 +567,7 @@ module ActiveRecord
               end
 
               table_rows.each do |fixture_set_name, rows|
-                rows.each do |row|
-                  conn.insert_fixture(row, fixture_set_name)
-                end
+                conn.insert_fixtures(rows, fixture_set_name)
               end
 
               # Cap primary key sequences to max(pk).
diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index 5776807507..1753322274 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -245,7 +245,7 @@ module ActiveRecord
       def ensure_proper_type
         klass = self.class
         if klass.finder_needs_type_condition?
-          write_attribute(klass.inheritance_column, klass.sti_name)
+          _write_attribute(klass.inheritance_column, klass.sti_name)
         end
       end
   end
diff --git a/activerecord/lib/active_record/internal_metadata.rb b/activerecord/lib/active_record/internal_metadata.rb
index 25ee9d6bfe..89e5d153b8 100644
--- a/activerecord/lib/active_record/internal_metadata.rb
+++ b/activerecord/lib/active_record/internal_metadata.rb
@@ -1,5 +1,5 @@
-require "active_record/scoping/default"
-require "active_record/scoping/named"
+require_relative "scoping/default"
+require_relative "scoping/named"
 
 module ActiveRecord
   # This class is used to create a table that keeps track of values and keys such
diff --git a/activerecord/lib/active_record/locking/optimistic.rb b/activerecord/lib/active_record/locking/optimistic.rb
index 3c7110369b..522da6a571 100644
--- a/activerecord/lib/active_record/locking/optimistic.rb
+++ b/activerecord/lib/active_record/locking/optimistic.rb
@@ -62,8 +62,8 @@ module ActiveRecord
 
         def increment_lock
           lock_col = self.class.locking_column
-          previous_lock_value = send(lock_col).to_i
-          send(lock_col + "=", previous_lock_value + 1)
+          previous_lock_value = send(lock_col)
+          send("#{lock_col}=", previous_lock_value + 1)
         end
 
         def _create_record(attribute_names = self.attribute_names, *)
@@ -107,7 +107,8 @@ module ActiveRecord
 
           # If something went wrong, revert the locking_column value.
           rescue Exception
-            send(lock_col + "=", previous_lock_value.to_i)
+            send("#{lock_col}=", previous_lock_value.to_i)
+
             raise
           end
         end
@@ -127,7 +128,7 @@ module ActiveRecord
 
           if locking_enabled?
             locking_column = self.class.locking_column
-            relation = relation.where(locking_column => _read_attribute(locking_column))
+            relation = relation.where(locking_column => read_attribute_before_type_cast(locking_column))
           end
 
           relation
diff --git a/activerecord/lib/active_record/log_subscriber.rb b/activerecord/lib/active_record/log_subscriber.rb
index 2297c77835..e39ca5f6dc 100644
--- a/activerecord/lib/active_record/log_subscriber.rb
+++ b/activerecord/lib/active_record/log_subscriber.rb
@@ -29,7 +29,7 @@ module ActiveRecord
       binds = nil
 
       unless (payload[:binds] || []).empty?
-        casted_params = type_casted_binds(payload[:binds], payload[:type_casted_binds])
+        casted_params = type_casted_binds(payload[:type_casted_binds])
         binds = "  " + payload[:binds].zip(casted_params).map { |attr, value|
           render_bind(attr, value)
         }.inspect
@@ -42,9 +42,8 @@ module ActiveRecord
     end
 
     private
-
-      def type_casted_binds(binds, casted_binds)
-        casted_binds || ActiveRecord::Base.connection.type_casted_binds(binds)
+      def type_casted_binds(casted_binds)
+        casted_binds.respond_to?(:call) ? casted_binds.call : casted_binds
       end
 
       def render_bind(attr, value)
diff --git a/activerecord/lib/active_record/migration.rb b/activerecord/lib/active_record/migration.rb
index 51c82f4ced..42220b9a5e 100644
--- a/activerecord/lib/active_record/migration.rb
+++ b/activerecord/lib/active_record/migration.rb
@@ -157,7 +157,7 @@ module ActiveRecord
 
   class ProtectedEnvironmentError < ActiveRecordError #:nodoc:
     def initialize(env = "production")
-      msg = "You are attempting to run a destructive action against your '#{env}' database.\n"
+      msg = "You are attempting to run a destructive action against your '#{env}' database.\n".dup
       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)
@@ -166,7 +166,7 @@ module ActiveRecord
 
   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 attempting to modify a database that was last run in `#{ stored }` environment.\n".dup
       msg << "You are running in `#{ current }` environment. "
       msg << "If you are sure you want to continue, first set the environment using:\n\n"
       msg << "        bin/rails db:environment:set"
@@ -863,15 +863,17 @@ module ActiveRecord
         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 = "".dup
+          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
@@ -1239,7 +1241,7 @@ module ActiveRecord
           record_version_state_after_migrating(migration.version)
         end
       rescue => e
-        msg = "An error has occurred, "
+        msg = "An error has occurred, ".dup
         msg << "this and " if use_transaction?(migration)
         msg << "all later migrations canceled:\n\n#{e}"
         raise StandardError, msg, e.backtrace
diff --git a/activerecord/lib/active_record/model_schema.rb b/activerecord/lib/active_record/model_schema.rb
index 1179a60e9b..14e0f5bff7 100644
--- a/activerecord/lib/active_record/model_schema.rb
+++ b/activerecord/lib/active_record/model_schema.rb
@@ -446,7 +446,11 @@ module ActiveRecord
         def load_schema
           return if schema_loaded?
           @load_schema_monitor.synchronize do
-            load_schema! unless defined?(@columns_hash) && @columns_hash
+            return if defined?(@columns_hash) && @columns_hash
+
+            load_schema!
+
+            @schema_loaded = true
           end
         end
 
@@ -460,8 +464,6 @@ module ActiveRecord
               user_provided_default: false
             )
           end
-
-          @schema_loaded = true
         end
 
         def reload_schema_from_cache
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index f652c7c3a1..a9509e562a 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -333,7 +333,7 @@ module ActiveRecord
       updated_count = self.class.unscoped.where(self.class.primary_key => id).update_all(attributes)
 
       attributes.each do |k, v|
-        raw_write_attribute(k, v)
+        write_attribute_without_type_cast(k, v)
       end
 
       updated_count == 1
@@ -526,7 +526,7 @@ module ActiveRecord
 
         if locking_enabled?
           locking_column = self.class.locking_column
-          scope = scope.where(locking_column => _read_attribute(locking_column))
+          scope = scope.where(locking_column => read_attribute_before_type_cast(locking_column))
           changes[locking_column] = increment_lock
         end
 
diff --git a/activerecord/lib/active_record/query_cache.rb b/activerecord/lib/active_record/query_cache.rb
index ec246e97bc..e4c2e1f86f 100644
--- a/activerecord/lib/active_record/query_cache.rb
+++ b/activerecord/lib/active_record/query_cache.rb
@@ -5,20 +5,20 @@ 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 connected?
-          connection.cache(&block)
-        else
+        if configurations.empty?
           yield
+        else
+          connection.cache(&block)
         end
       end
 
       # 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 connected?
-          connection.uncached(&block)
-        else
+        if configurations.empty?
           yield
+        else
+          connection.uncached(&block)
         end
       end
     end
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 73518ca144..9cca103a18 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -48,8 +48,8 @@ module ActiveRecord
     # to avoid cross references when loading a constant for the
     # first time. Also, make it output to STDERR.
     console do |app|
-      require "active_record/railties/console_sandbox" if app.sandbox?
-      require "active_record/base"
+      require_relative "railties/console_sandbox" if app.sandbox?
+      require_relative "base"
       unless ActiveSupport::Logger.logger_outputs_to?(Rails.logger, STDERR, STDOUT)
         console = ActiveSupport::Logger.new(STDERR)
         Rails.logger.extend ActiveSupport::Logger.broadcast console
@@ -57,7 +57,7 @@ module ActiveRecord
     end
 
     runner do
-      require "active_record/base"
+      require_relative "base"
     end
 
     initializer "active_record.initialize_timezone" do
@@ -101,7 +101,7 @@ module ActiveRecord
     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_relative "relation/record_fetch_warning"
         end
       end
     end
@@ -139,7 +139,7 @@ end_warning
 
     # Expose database runtime to controller for logging.
     initializer "active_record.log_runtime" do
-      require "active_record/railties/controller_runtime"
+      require_relative "railties/controller_runtime"
       ActiveSupport.on_load(:action_controller) do
         include ActiveRecord::Railties::ControllerRuntime
       end
diff --git a/activerecord/lib/active_record/railties/controller_runtime.rb b/activerecord/lib/active_record/railties/controller_runtime.rb
index 8658188623..4030cdc158 100644
--- a/activerecord/lib/active_record/railties/controller_runtime.rb
+++ b/activerecord/lib/active_record/railties/controller_runtime.rb
@@ -1,5 +1,5 @@
 require "active_support/core_ext/module/attr_internal"
-require "active_record/log_subscriber"
+require_relative "../log_subscriber"
 
 module ActiveRecord
   module Railties # :nodoc:
diff --git a/activerecord/lib/active_record/railties/databases.rake b/activerecord/lib/active_record/railties/databases.rake
index 711099e9e1..abc7323341 100644
--- a/activerecord/lib/active_record/railties/databases.rake
+++ b/activerecord/lib/active_record/railties/databases.rake
@@ -187,7 +187,7 @@ db_namespace = namespace :db do
   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"
+      require_relative "../fixtures"
 
       base_dir = ActiveRecord::Tasks::DatabaseTasks.fixtures_path
 
@@ -209,7 +209,7 @@ db_namespace = namespace :db do
 
     # 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"
+      require_relative "../fixtures"
 
       label, id = ENV["LABEL"], ENV["ID"]
       raise "LABEL or ID required" if label.blank? && id.blank?
@@ -235,7 +235,7 @@ db_namespace = namespace :db do
   namespace :schema do
     desc "Creates a db/schema.rb file that is portable against any DB supported by Active Record"
     task dump: [:environment, :load_config] do
-      require "active_record/schema_dumper"
+      require_relative "../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)
diff --git a/activerecord/lib/active_record/reflection.rb b/activerecord/lib/active_record/reflection.rb
index e8ee8279fd..a453ca55c7 100644
--- a/activerecord/lib/active_record/reflection.rb
+++ b/activerecord/lib/active_record/reflection.rb
@@ -171,7 +171,7 @@ module ActiveRecord
       JoinKeys = Struct.new(:key, :foreign_key) # :nodoc:
 
       def join_keys
-        get_join_keys klass
+        @join_keys ||= get_join_keys(klass)
       end
 
       # Returns a list of scopes that should be applied for this Reflection
@@ -185,10 +185,34 @@ module ActiveRecord
       end
       deprecate :scope_chain
 
+      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.base_class.sti_name)
+        end
+
+        scope_chain_items.inject(klass_scope, &:merge!)
+      end
+
       def join_scopes(table, predicate_builder) # :nodoc:
         if scope
-          [ActiveRecord::Relation.create(klass, table, predicate_builder)
-            .instance_exec(&scope)]
+          [build_scope(table, predicate_builder).instance_exec(&scope)]
         else
           []
         end
@@ -200,12 +224,7 @@ module ActiveRecord
             scope.joins_values = scope.left_outer_joins_values = [].freeze
           }
         else
-          relation = ActiveRecord::Relation.create(
-            klass,
-            table,
-            predicate_builder,
-          )
-          klass.send(:build_default_scope, relation)
+          klass.default_scoped(build_scope(table, predicate_builder))
         end
       end
 
@@ -287,12 +306,19 @@ module ActiveRecord
         JoinKeys.new(join_pk(association_klass), join_fk)
       end
 
+      def build_scope(table, predicate_builder = predicate_builder(table))
+        Relation.create(klass, table, predicate_builder)
+      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 join_pk(_)
           foreign_key
@@ -570,7 +596,7 @@ module ActiveRecord
       end
 
       VALID_AUTOMATIC_INVERSE_MACROS = [:has_many, :has_one, :belongs_to]
-      INVALID_AUTOMATIC_INVERSE_OPTIONS = [:conditions, :through, :polymorphic, :foreign_key]
+      INVALID_AUTOMATIC_INVERSE_OPTIONS = [:conditions, :through, :foreign_key]
 
       def add_as_source(seed)
         seed
@@ -641,9 +667,8 @@ 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.
@@ -746,10 +771,6 @@ module ActiveRecord
     end
 
     class HasAndBelongsToManyReflection < AssociationReflection # :nodoc:
-      def initialize(name, scope, options, active_record)
-        super
-      end
-
       def macro; :has_and_belongs_to_many; end
 
       def collection?
diff --git a/activerecord/lib/active_record/relation.rb b/activerecord/lib/active_record/relation.rb
index 7a8f9abb36..76cf47a3ed 100644
--- a/activerecord/lib/active_record/relation.rb
+++ b/activerecord/lib/active_record/relation.rb
@@ -6,7 +6,7 @@ module ActiveRecord
                             :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]
 
@@ -18,7 +18,7 @@ module ActiveRecord
     attr_reader :table, :klass, :loaded, :predicate_builder
     alias :model :klass
     alias :loaded? :loaded
-    alias :locked? :locked
+    alias :locked? :lock_value
 
     def initialize(klass, table, predicate_builder, values = {})
       @klass  = klass
@@ -333,7 +333,7 @@ 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
+      previous, klass.current_scope = klass.current_scope(true), self
       yield
     ensure
       klass.current_scope = previous
@@ -657,20 +657,32 @@ module ActiveRecord
       end
 
       def exec_queries(&block)
-        @records = eager_loading? ? find_with_associations.freeze : @klass.find_by_sql(arel, bound_attributes, &block).freeze
-
-        preload = preload_values
-        preload += includes_values unless eager_loading?
-        preloader = nil
-        preload.each do |associations|
-          preloader ||= build_preloader
-          preloader.preload @records, associations
-        end
+        skip_query_cache_if_necessary do
+          @records = eager_loading? ? find_with_associations.freeze : @klass.find_by_sql(arel, bound_attributes, &block).freeze
+
+          preload = preload_values
+          preload += includes_values unless eager_loading?
+          preloader = nil
+          preload.each do |associations|
+            preloader ||= build_preloader
+            preloader.preload @records, associations
+          end
 
-        @records.each(&:readonly!) if readonly_value
+          @records.each(&:readonly!) if readonly_value
 
-        @loaded = true
-        @records
+          @loaded = true
+          @records
+        end
+      end
+
+      def skip_query_cache_if_necessary
+        if skip_query_cache_value
+          uncached do
+            yield
+          end
+        else
+          yield
+        end
       end
 
       def build_preloader
diff --git a/activerecord/lib/active_record/relation/batches.rb b/activerecord/lib/active_record/relation/batches.rb
index 13a2c3f511..c7e4f8a88a 100644
--- a/activerecord/lib/active_record/relation/batches.rb
+++ b/activerecord/lib/active_record/relation/batches.rb
@@ -1,4 +1,4 @@
-require "active_record/relation/batches/batch_enumerator"
+require_relative "batches/batch_enumerator"
 
 module ActiveRecord
   module Batches
@@ -209,6 +209,7 @@ module ActiveRecord
 
       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
diff --git a/activerecord/lib/active_record/relation/calculations.rb b/activerecord/lib/active_record/relation/calculations.rb
index c562f214c9..aaba6c71f2 100644
--- a/activerecord/lib/active_record/relation/calculations.rb
+++ b/activerecord/lib/active_record/relation/calculations.rb
@@ -41,7 +41,7 @@ module ActiveRecord
         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 5.3."
+            "This behavior is now deprecated and will result in an ArgumentError in Rails 6.0."
         end
 
         return super()
@@ -86,7 +86,7 @@ module ActiveRecord
         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 5.3."
+            "This behavior is now deprecated and will result in an ArgumentError in Rails 6.0."
         end
 
         return super()
@@ -184,7 +184,7 @@ module ActiveRecord
         relation.select_values = column_names.map { |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, bound_attributes) }
         result.cast_values(klass.attribute_types)
       end
     end
@@ -260,7 +260,7 @@ module ActiveRecord
           query_builder = relation.arel
         end
 
-        result = @klass.connection.select_all(query_builder, nil, bound_attributes)
+        result = skip_query_cache_if_necessary { @klass.connection.select_all(query_builder, nil, bound_attributes) }
         row    = result.first
         value  = row && row.values.first
         type   = result.column_types.fetch(column_alias) do
@@ -311,7 +311,7 @@ module ActiveRecord
         relation.group_values  = group_fields
         relation.select_values = select_values
 
-        calculated_data = @klass.connection.select_all(relation, nil, relation.bound_attributes)
+        calculated_data = skip_query_cache_if_necessary { @klass.connection.select_all(relation.arel, nil, relation.bound_attributes) }
 
         if association
           key_ids     = calculated_data.collect { |row| row[group_aliases.first] }
diff --git a/activerecord/lib/active_record/relation/delegation.rb b/activerecord/lib/active_record/relation/delegation.rb
index dada0fddf8..48c4dcdef4 100644
--- a/activerecord/lib/active_record/relation/delegation.rb
+++ b/activerecord/lib/active_record/relation/delegation.rb
@@ -44,8 +44,6 @@ module ActiveRecord
     delegate :table_name, :quoted_table_name, :primary_key, :quoted_primary_key,
              :connection, :columns_hash, to: :klass
 
-    delegate :ast, :locked, to: :arel
-
     module ClassSpecificRelation # :nodoc:
       extend ActiveSupport::Concern
 
@@ -91,6 +89,8 @@ module ActiveRecord
             self.class.delegate_to_scoped_klass(method)
             scoping { @klass.public_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."
             self.class.delegate method, to: :arel
             arel.public_send(method, *args, &block)
           else
@@ -115,15 +115,5 @@ module ActiveRecord
       def respond_to_missing?(method, _)
         super || @klass.respond_to?(method) || arel.respond_to?(method)
       end
-
-      def method_missing(method, *args, &block)
-        if @klass.respond_to?(method)
-          scoping { @klass.public_send(method, *args, &block) }
-        elsif arel.respond_to?(method)
-          arel.public_send(method, *args, &block)
-        else
-          super
-        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 1d661fa8ed..ac0b4f597e 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -147,8 +147,7 @@ module ActiveRecord
     def last(limit = nil)
       return find_last(limit) if loaded? || limit_value
 
-      result = limit(limit)
-      result.order!(arel_attribute(primary_key)) if order_values.empty? && primary_key
+      result = ordered_relation.limit(limit)
       result = result.reverse_order!
 
       limit ? result.reverse : result.first
@@ -316,7 +315,7 @@ module ActiveRecord
 
       relation = construct_relation_for_exists(relation, conditions)
 
-      connection.select_value(relation, "#{name} Exists", relation.bound_attributes) ? true : false
+      skip_query_cache_if_necessary { connection.select_value(relation.arel, "#{name} Exists", relation.bound_attributes) } ? true : false
     rescue ::RangeError
       false
     end
@@ -335,14 +334,14 @@ module ActiveRecord
       name = @klass.name
 
       if ids.nil?
-        error = "Couldn't find #{name}"
+        error = "Couldn't find #{name}".dup
         error << " with#{conditions}" if conditions
         raise RecordNotFound.new(error, name)
       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 #{name.pluralize} with '#{key}': "
+        error = "Couldn't find all #{name.pluralize} with '#{key}': ".dup
         error << "(#{ids.join(", ")})#{conditions} (found #{result_size} results, but was looking for #{expected_size})"
 
         raise RecordNotFound.new(error, name, primary_key, ids)
@@ -377,8 +376,7 @@ module ActiveRecord
           if ActiveRecord::NullRelation === relation
             []
           else
-            arel = relation.arel
-            rows = connection.select_all(arel, "SQL", relation.bound_attributes)
+            rows = skip_query_cache_if_necessary { connection.select_all(relation.arel, "SQL", relation.bound_attributes) }
             join_dependency.instantiate(rows, aliases)
           end
         end
@@ -425,9 +423,8 @@ module ActiveRecord
           "#{quoted_table_name}.#{quoted_primary_key}", relation.order_values)
 
         relation = relation.except(:select).select(values).distinct!
-        arel = relation.arel
 
-        id_rows = @klass.connection.select_all(arel, "SQL", relation.bound_attributes)
+        id_rows = skip_query_cache_if_necessary { @klass.connection.select_all(relation.arel, "SQL", relation.bound_attributes) }
         id_rows.map { |row| row[primary_key] }
       end
 
@@ -535,11 +532,7 @@ module ActiveRecord
         if loaded?
           records[index, limit] || []
         else
-          relation = if order_values.empty? && primary_key
-            order(arel_attribute(primary_key).asc)
-          else
-            self
-          end
+          relation = ordered_relation
 
           if limit_value.nil? || index < limit_value
             relation = relation.offset(offset_index + index) unless index.zero?
@@ -554,11 +547,7 @@ module ActiveRecord
         if loaded?
           records[-index]
         else
-          relation = if order_values.empty? && primary_key
-            order(arel_attribute(primary_key).asc)
-          else
-            self
-          end
+          relation = ordered_relation
 
           relation.to_a[-index]
           # TODO: can be made more performant on large result sets by
@@ -572,5 +561,13 @@ module ActiveRecord
       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
diff --git a/activerecord/lib/active_record/relation/predicate_builder.rb b/activerecord/lib/active_record/relation/predicate_builder.rb
index a6309e0b5c..eb80c9a00d 100644
--- a/activerecord/lib/active_record/relation/predicate_builder.rb
+++ b/activerecord/lib/active_record/relation/predicate_builder.rb
@@ -107,21 +107,26 @@ module ActiveRecord
             first = value.begin
             last = value.end
             unless first.respond_to?(:infinite?) && first.infinite?
-              binds << build_bind_param(column_name, first)
+              binds << build_bind_attribute(column_name, first)
               first = Arel::Nodes::BindParam.new
             end
             unless last.respond_to?(:infinite?) && last.infinite?
-              binds << build_bind_param(column_name, last)
+              binds << build_bind_attribute(column_name, last)
               last = Arel::Nodes::BindParam.new
             end
 
             result[column_name] = RangeHandler::RangeWithBinds.new(first, last, value.exclude_end?)
+          when value.is_a?(Relation)
+            binds.concat(value.bound_attributes)
           else
             if can_be_bound?(column_name, value)
-              result[column_name] = Arel::Nodes::BindParam.new
-              binds << build_bind_param(column_name, value)
-            elsif value.is_a?(Relation)
-              binds.concat(value.bound_attributes)
+              bind_attribute = build_bind_attribute(column_name, value)
+              if value.is_a?(StatementCache::Substitute) || !bind_attribute.value_for_database.nil?
+                result[column_name] = Arel::Nodes::BindParam.new
+                binds << bind_attribute
+              else
+                result[column_name] = nil
+              end
             end
           end
         end
@@ -164,17 +169,17 @@ module ActiveRecord
         end
       end
 
-      def build_bind_param(column_name, value)
+      def build_bind_attribute(column_name, value)
         Relation::QueryAttribute.new(column_name.to_s, value, table.type(column_name))
       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_relative "predicate_builder/array_handler"
+require_relative "predicate_builder/base_handler"
+require_relative "predicate_builder/basic_object_handler"
+require_relative "predicate_builder/range_handler"
+require_relative "predicate_builder/relation_handler"
 
-require "active_record/relation/predicate_builder/association_query_value"
-require "active_record/relation/predicate_builder/polymorphic_array_value"
+require_relative "predicate_builder/association_query_value"
+require_relative "predicate_builder/polymorphic_array_value"
diff --git a/activerecord/lib/active_record/relation/query_attribute.rb b/activerecord/lib/active_record/relation/query_attribute.rb
index a68e508fcc..0e1f64775d 100644
--- a/activerecord/lib/active_record/relation/query_attribute.rb
+++ b/activerecord/lib/active_record/relation/query_attribute.rb
@@ -1,4 +1,4 @@
-require "active_record/attribute"
+require_relative "../attribute"
 
 module ActiveRecord
   class Relation
diff --git a/activerecord/lib/active_record/relation/query_methods.rb b/activerecord/lib/active_record/relation/query_methods.rb
index 79e65baae5..79495ead91 100644
--- a/activerecord/lib/active_record/relation/query_methods.rb
+++ b/activerecord/lib/active_record/relation/query_methods.rb
@@ -1,7 +1,7 @@
-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_relative "from_clause"
+require_relative "query_attribute"
+require_relative "where_clause"
+require_relative "where_clause_factory"
 require "active_model/forbidden_attributes_protection"
 
 module ActiveRecord
@@ -913,6 +913,11 @@ module ActiveRecord
       self
     end
 
+    def skip_query_cache! # :nodoc:
+      self.skip_query_cache_value = true
+      self
+    end
+
     # Returns the Arel object associated with the relation.
     def arel # :nodoc:
       @arel ||= build_arel
@@ -1122,7 +1127,7 @@ module ActiveRecord
         validate_order_args(order_args)
 
         references = order_args.grep(String)
-        references.map! { |arg| arg =~ /^([a-zA-Z]\w*)\.(\w+)/ && $1 }.compact!
+        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
@@ -1167,7 +1172,7 @@ module ActiveRecord
         end
       end
 
-      STRUCTURAL_OR_METHODS = Relation::VALUE_METHODS - [:extending, :where, :having]
+      STRUCTURAL_OR_METHODS = Relation::VALUE_METHODS - [:extending, :where, :having, :unscope]
       def structurally_incompatible_values_for_or(other)
         STRUCTURAL_OR_METHODS.reject do |method|
           get_value(method) == other.get_value(method)
diff --git a/activerecord/lib/active_record/relation/spawn_methods.rb b/activerecord/lib/active_record/relation/spawn_methods.rb
index ada89b5ec3..ddf7f825c1 100644
--- a/activerecord/lib/active_record/relation/spawn_methods.rb
+++ b/activerecord/lib/active_record/relation/spawn_methods.rb
@@ -1,6 +1,6 @@
 require "active_support/core_ext/hash/except"
 require "active_support/core_ext/hash/slice"
-require "active_record/relation/merger"
+require_relative "merger"
 
 module ActiveRecord
   module SpawnMethods
diff --git a/activerecord/lib/active_record/relation/where_clause_factory.rb b/activerecord/lib/active_record/relation/where_clause_factory.rb
index 04bee73e8f..b862dd56a5 100644
--- a/activerecord/lib/active_record/relation/where_clause_factory.rb
+++ b/activerecord/lib/active_record/relation/where_clause_factory.rb
@@ -57,7 +57,7 @@ module ActiveRecord
             else
               column = klass.column_for_attribute(attribute)
 
-              binds << predicate_builder.send(:build_bind_param, attribute, value)
+              binds << predicate_builder.send(:build_bind_attribute, attribute, value)
               value = Arel::Nodes::BindParam.new
 
               predicate = if options[:case_sensitive]
diff --git a/activerecord/lib/active_record/schema_dumper.rb b/activerecord/lib/active_record/schema_dumper.rb
index 24b81aabc8..66a2846f3a 100644
--- a/activerecord/lib/active_record/schema_dumper.rb
+++ b/activerecord/lib/active_record/schema_dumper.rb
@@ -13,8 +13,7 @@ module ActiveRecord
     # A list of tables which should not be dumped to the schema.
     # 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
-    @@ignore_tables = []
+    cattr_accessor :ignore_tables, default: []
 
     class << self
       def dump(connection = ActiveRecord::Base.connection, stream = STDOUT, config = ActiveRecord::Base)
diff --git a/activerecord/lib/active_record/schema_migration.rb b/activerecord/lib/active_record/schema_migration.rb
index f59737afb0..6dbabd69a1 100644
--- a/activerecord/lib/active_record/schema_migration.rb
+++ b/activerecord/lib/active_record/schema_migration.rb
@@ -1,5 +1,5 @@
-require "active_record/scoping/default"
-require "active_record/scoping/named"
+require_relative "scoping/default"
+require_relative "scoping/named"
 
 module ActiveRecord
   # This class is used to create a table that keeps track of which migrations
diff --git a/activerecord/lib/active_record/scoping.rb b/activerecord/lib/active_record/scoping.rb
index 7c00e7e4ed..94e0ef6724 100644
--- a/activerecord/lib/active_record/scoping.rb
+++ b/activerecord/lib/active_record/scoping.rb
@@ -10,8 +10,8 @@ module ActiveRecord
     end
 
     module ClassMethods
-      def current_scope #:nodoc:
-        ScopeRegistry.value_for(:current_scope, self)
+      def current_scope(skip_inherited_scope = false) # :nodoc:
+        ScopeRegistry.value_for(:current_scope, self, skip_inherited_scope)
       end
 
       def current_scope=(scope) #:nodoc:
@@ -75,8 +75,9 @@ module ActiveRecord
       end
 
       # Obtains the value for a given +scope_type+ and +model+.
-      def value_for(scope_type, model)
+      def value_for(scope_type, model, skip_inherited_scope = false)
         raise_invalid_scope_type!(scope_type)
+        return @registry[scope_type][model.name] if skip_inherited_scope
         klass = model
         base = model.base_class
         while klass <= base
diff --git a/activerecord/lib/active_record/scoping/named.rb b/activerecord/lib/active_record/scoping/named.rb
index a61fdd6454..b4026fabb2 100644
--- a/activerecord/lib/active_record/scoping/named.rb
+++ b/activerecord/lib/active_record/scoping/named.rb
@@ -29,8 +29,7 @@ module ActiveRecord
           end
         end
 
-        def default_scoped # :nodoc:
-          scope = relation
+        def default_scoped(scope = relation) # :nodoc:
           build_default_scope(scope) || scope
         end
 
@@ -160,7 +159,7 @@ module ActiveRecord
           if body.respond_to?(:to_proc)
             singleton_class.send(:define_method, name) do |*args|
               scope = all
-              scope = scope.scoping { instance_exec(*args, &body) || scope }
+              scope = scope.instance_exec(*args, &body) || scope
               scope = scope.extending(extension) if extension
               scope
             end
diff --git a/activerecord/lib/active_record/tasks/mysql_database_tasks.rb b/activerecord/lib/active_record/tasks/mysql_database_tasks.rb
index 541165b3d1..ff6745f7b5 100644
--- a/activerecord/lib/active_record/tasks/mysql_database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/mysql_database_tasks.rb
@@ -59,7 +59,6 @@ module ActiveRecord
         args.concat(["--no-data"])
         args.concat(["--routines"])
         args.concat(["--skip-comments"])
-        args.concat(Array(extra_flags)) if extra_flags
 
         ignore_tables = ActiveRecord::SchemaDumper.ignore_tables
         if ignore_tables.any?
@@ -67,6 +66,7 @@ module ActiveRecord
         end
 
         args.concat(["#{configuration['database']}"])
+        args.unshift(*extra_flags) if extra_flags
 
         run_cmd("mysqldump", args, "dumping")
       end
@@ -75,7 +75,7 @@ module ActiveRecord
         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.concat(Array(extra_flags)) if extra_flags
+        args.unshift(*extra_flags) if extra_flags
 
         run_cmd("mysql", args, "loading")
       end
@@ -99,7 +99,7 @@ module ActiveRecord
 
         def error_class
           if configuration["adapter"].include?("jdbc")
-            require "active_record/railties/jdbcmysql_error"
+            require_relative "../railties/jdbcmysql_error"
             ArJdbcMySQL::Error
           elsif defined?(Mysql2)
             Mysql2::Error
@@ -151,7 +151,7 @@ IDENTIFIED BY '#{configuration['password']}' WITH GRANT OPTION;
         end
 
         def run_cmd_error(cmd, args, action)
-          msg = "failed to execute: `#{cmd}`\n"
+          msg = "failed to execute: `#{cmd}`\n".dup
           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
diff --git a/activerecord/lib/active_record/timestamp.rb b/activerecord/lib/active_record/timestamp.rb
index 55f3a194a9..26eea0bc24 100644
--- a/activerecord/lib/active_record/timestamp.rb
+++ b/activerecord/lib/active_record/timestamp.rb
@@ -86,7 +86,7 @@ module ActiveRecord
 
         all_timestamp_attributes_in_model.each do |column|
           if !attribute_present?(column)
-            write_attribute(column, current_time)
+            _write_attribute(column, current_time)
           end
         end
       end
@@ -100,7 +100,7 @@ module ActiveRecord
 
         timestamp_attributes_for_update_in_model.each do |column|
           next if will_save_change_to_attribute?(column)
-          write_attribute(column, current_time)
+          _write_attribute(column, current_time)
         end
       end
       super(*args)
@@ -126,7 +126,7 @@ module ActiveRecord
       self.class.send(:current_time_from_proper_timezone)
     end
 
-    def max_updated_column_timestamp(timestamp_names = self.class.send(:timestamp_attributes_for_update))
+    def max_updated_column_timestamp(timestamp_names = timestamp_attributes_for_update_in_model)
       timestamp_names
         .map { |attr| self[attr] }
         .compact
diff --git a/activerecord/lib/active_record/transactions.rb b/activerecord/lib/active_record/transactions.rb
index 45795fa287..463bb1f314 100644
--- a/activerecord/lib/active_record/transactions.rb
+++ b/activerecord/lib/active_record/transactions.rb
@@ -490,7 +490,7 @@ module ActiveRecord
       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
+          clear_transaction_record_state if transaction_state.fully_completed?
         end
       end
   end
diff --git a/activerecord/lib/active_record/type.rb b/activerecord/lib/active_record/type.rb
index 9ed6c95bf9..6f4e35b159 100644
--- a/activerecord/lib/active_record/type.rb
+++ b/activerecord/lib/active_record/type.rb
@@ -1,20 +1,20 @@
 require "active_model/type"
 
-require "active_record/type/internal/timezone"
+require_relative "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_relative "type/date"
+require_relative "type/date_time"
+require_relative "type/decimal_without_scale"
+require_relative "type/json"
+require_relative "type/time"
+require_relative "type/text"
+require_relative "type/unsigned_integer"
 
-require "active_record/type/serialized"
-require "active_record/type/adapter_specific_registry"
+require_relative "type/serialized"
+require_relative "type/adapter_specific_registry"
 
-require "active_record/type/type_map"
-require "active_record/type/hash_lookup_type_map"
+require_relative "type/type_map"
+require_relative "type/hash_lookup_type_map"
 
 module ActiveRecord
   module Type
diff --git a/activerecord/lib/active_record/type_caster.rb b/activerecord/lib/active_record/type_caster.rb
index f1686e4913..8b12a30c6a 100644
--- a/activerecord/lib/active_record/type_caster.rb
+++ b/activerecord/lib/active_record/type_caster.rb
@@ -1,5 +1,5 @@
-require "active_record/type_caster/map"
-require "active_record/type_caster/connection"
+require_relative "type_caster/map"
+require_relative "type_caster/connection"
 
 module ActiveRecord
   module TypeCaster # :nodoc:
diff --git a/activerecord/lib/active_record/validations.rb b/activerecord/lib/active_record/validations.rb
index 9633f226f0..046b69bee2 100644
--- a/activerecord/lib/active_record/validations.rb
+++ b/activerecord/lib/active_record/validations.rb
@@ -84,8 +84,8 @@ module ActiveRecord
   end
 end
 
-require "active_record/validations/associated"
-require "active_record/validations/uniqueness"
-require "active_record/validations/presence"
-require "active_record/validations/absence"
-require "active_record/validations/length"
+require_relative "validations/associated"
+require_relative "validations/uniqueness"
+require_relative "validations/presence"
+require_relative "validations/absence"
+require_relative "validations/length"
diff --git a/activerecord/test/cases/adapter_test.rb b/activerecord/test/cases/adapter_test.rb
index a1fb6427f9..827bcba121 100644
--- a/activerecord/test/cases/adapter_test.rb
+++ b/activerecord/test/cases/adapter_test.rb
@@ -211,6 +211,28 @@ module ActiveRecord
       end
     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
       result = @connection.select_all "SELECT * FROM posts"
       assert result.is_a?(ActiveRecord::Result)
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 2c778b1150..0000000000
--- a/activerecord/test/cases/adapters/mysql2/reserved_word_test.rb
+++ /dev/null
@@ -1,151 +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/virtual_column_test.rb b/activerecord/test/cases/adapters/mysql2/virtual_column_test.rb
index 442a4fb7b5..1c5ef2aa41 100644
--- a/activerecord/test/cases/adapters/mysql2/virtual_column_test.rb
+++ b/activerecord/test/cases/adapters/mysql2/virtual_column_test.rb
@@ -52,7 +52,7 @@ if ActiveRecord::Base.connection.supports_virtual_columns?
 
     def test_schema_dumping
       output = dump_table_schema("virtual_columns")
-      assert_match(/t\.virtual\s+"upper_name",\s+type: :string,\s+as: "UPPER\(`name`\)"$/i, output)
+      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: "LENGTH\(`name`\)",\s+stored: true$/i, output)
     end
   end
diff --git a/activerecord/test/cases/adapters/postgresql/array_test.rb b/activerecord/test/cases/adapters/postgresql/array_test.rb
index c78c6178ff..121c62dadf 100644
--- a/activerecord/test/cases/adapters/postgresql/array_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/array_test.rb
@@ -191,6 +191,12 @@ class PostgresqlArrayTest < ActiveRecord::PostgreSQLTestCase
     assert_equal(PgArray.last.tags, tag_values)
   end
 
+  def test_insert_fixtures
+    tag_values = ["val1", "val2", "val3_with_'_multiple_quote_'_chars"]
+    @connection.insert_fixtures([{ "tags" => tag_values }], "pg_arrays")
+    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))
diff --git a/activerecord/test/cases/adapters/postgresql/bytea_test.rb b/activerecord/test/cases/adapters/postgresql/bytea_test.rb
index 539c90f0bc..65baed34e9 100644
--- a/activerecord/test/cases/adapters/postgresql/bytea_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/bytea_test.rb
@@ -47,7 +47,7 @@ class PostgresqlByteaTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_type_cast_binary_value
-    data = "\u001F\x8B".force_encoding("BINARY")
+    data = "\u001F\x8B".dup.force_encoding("BINARY")
     assert_equal(data, @type.deserialize(data))
   end
 
diff --git a/activerecord/test/cases/adapters/postgresql/geometric_test.rb b/activerecord/test/cases/adapters/postgresql/geometric_test.rb
index c1f3a4ae2c..3b6840a1c9 100644
--- a/activerecord/test/cases/adapters/postgresql/geometric_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/geometric_test.rb
@@ -93,8 +93,6 @@ class PostgresqlPointTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_empty_string_assignment
-    assert_nothing_raised { PostgresqlPoint.new(x: "") }
-
     p = PostgresqlPoint.new(x: "")
     assert_nil p.x
   end
diff --git a/activerecord/test/cases/adapters/postgresql/money_test.rb b/activerecord/test/cases/adapters/postgresql/money_test.rb
index 1b5d8362af..ea060345a7 100644
--- a/activerecord/test/cases/adapters/postgresql/money_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/money_test.rb
@@ -47,10 +47,10 @@ class PostgresqlMoneyTest < ActiveRecord::PostgreSQLTestCase
 
   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)"))
+    assert_equal(12345678.12, type.cast("$12,345,678.12".dup))
+    assert_equal(12345678.12, type.cast("$12.345.678,12".dup))
+    assert_equal(-1.15, type.cast("-$1.15".dup))
+    assert_equal(-2.25, type.cast("($2.25)".dup))
   end
 
   def test_schema_dumping
@@ -60,7 +60,7 @@ class PostgresqlMoneyTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_create_and_update_money
-    money = PostgresqlMoney.create(wealth: "987.65")
+    money = PostgresqlMoney.create(wealth: "987.65".dup)
     assert_equal 987.65, money.wealth
 
     new_value = BigDecimal.new("123.45")
diff --git a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
index b55b766d20..26bf4d2090 100644
--- a/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/postgresql_adapter_test.rb
@@ -324,16 +324,16 @@ 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"
@@ -343,16 +343,16 @@ module ActiveRecord
         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
diff --git a/activerecord/test/cases/adapters/postgresql/uuid_test.rb b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
index 6ebe9d82a7..00de92cdfd 100644
--- a/activerecord/test/cases/adapters/postgresql/uuid_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
@@ -40,7 +40,8 @@ class PostgresqlUUIDTest < ActiveRecord::PostgreSQLTestCase
     drop_table "uuid_data_type"
   end
 
-  if ActiveRecord::Base.connection.supports_pgcrypto_uuid?
+  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
@@ -64,11 +65,11 @@ class PostgresqlUUIDTest < ActiveRecord::PostgreSQLTestCase
   end
 
   def test_add_column_with_null_true_and_default_nil
-    assert_nothing_raised do
-      connection.add_column :uuid_data_type, :thingy, :uuid, null: true, default: nil
-    end
+    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
@@ -123,7 +124,9 @@ class PostgresqlUUIDTest < ActiveRecord::PostgreSQLTestCase
      "Z0000C99-9C0B-4EF8-BB6D-6BB9BD380A11",
      "a0eebc999r0b4ef8ab6d6bb9bd380a11",
      "a0ee-bc99------4ef8-bb6d-6bb9-bd38-0a11",
-     "{a0eebc99-bb6d6bb9-bd380a11}"].each do |invalid_uuid|
+     "{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
diff --git a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
index 9a812e325e..cf0c37f70c 100644
--- a/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
+++ b/activerecord/test/cases/adapters/sqlite3/sqlite3_adapter_test.rb
@@ -165,7 +165,7 @@ module ActiveRecord
             data binary
           )
         eosql
-        str = "\x80".force_encoding("ASCII-8BIT")
+        str = "\x80".dup.force_encoding("ASCII-8BIT")
         binary = DualEncoding.new name: "いただきます！", data: str
         binary.save!
         assert_equal str, binary.data
@@ -174,7 +174,7 @@ module ActiveRecord
       end
 
       def test_type_cast_should_not_mutate_encoding
-        name = "hello".force_encoding(Encoding::ASCII_8BIT)
+        name = "hello".dup.force_encoding(Encoding::ASCII_8BIT)
         Owner.create(name: name)
         assert_equal Encoding::ASCII_8BIT, name.encoding
       ensure
diff --git a/activerecord/test/cases/associations/association_scope_test.rb b/activerecord/test/cases/associations/association_scope_test.rb
index c322333f6d..c54542ff7b 100644
--- a/activerecord/test/cases/associations/association_scope_test.rb
+++ b/activerecord/test/cases/associations/association_scope_test.rb
@@ -6,8 +6,7 @@ module ActiveRecord
   module Associations
     class AssociationScopeTest < ActiveRecord::TestCase
       test "does not duplicate conditions" do
-        scope = AssociationScope.scope(Author.new.association(:welcome_posts),
-                                        Author.connection)
+        scope = AssociationScope.scope(Author.new.association(:welcome_posts))
         binds = scope.where_clause.binds.map(&:value)
         assert_equal binds.uniq, binds
       end
diff --git a/activerecord/test/cases/associations/belongs_to_associations_test.rb b/activerecord/test/cases/associations/belongs_to_associations_test.rb
index c8b26232b6..a727cc6e60 100644
--- a/activerecord/test/cases/associations/belongs_to_associations_test.rb
+++ b/activerecord/test/cases/associations/belongs_to_associations_test.rb
@@ -380,7 +380,6 @@ class BelongsToAssociationsTest < ActiveRecord::TestCase
 
     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
diff --git a/activerecord/test/cases/associations/cascaded_eager_loading_test.rb b/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
index 3638c87968..7b0445025c 100644
--- a/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
+++ b/activerecord/test/cases/associations/cascaded_eager_loading_test.rb
@@ -34,18 +34,12 @@ class CascadedEagerLoadingTest < ActiveRecord::TestCase
   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 }
     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
   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 4f0fe3236e..61f39b4136 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
@@ -11,25 +11,32 @@ end
 
 class EagerLoadIncludeFullStiClassNamesTest < ActiveRecord::TestCase
   def setup
-    generate_test_objects
-  end
-
-  def generate_test_objects
     post = Namespaced::Post.create(title: "Great stuff", body: "This is not", author_id: 1)
-    Tagging.create(taggable: post)
+    @tagging = Tagging.create(taggable: post)
+    @old = ActiveRecord::Base.store_full_sti_class
   end
 
-  def test_class_names
-    old = ActiveRecord::Base.store_full_sti_class
+  def teardown
+    ActiveRecord::Base.store_full_sti_class = @old
+  end
 
+  def test_class_names_with_includes
     ActiveRecord::Base.store_full_sti_class = false
     post = Namespaced::Post.includes(: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
+    assert_equal @tagging, post.tagging
+  end
+
+  def test_class_names_with_eager_load
+    ActiveRecord::Base.store_full_sti_class = false
+    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.eager_load(:tagging).find_by_title("Great stuff")
+    assert_equal @tagging, post.tagging
   end
 end
diff --git a/activerecord/test/cases/associations/eager_test.rb b/activerecord/test/cases/associations/eager_test.rb
index 4271a09c9b..c0bab19e82 100644
--- a/activerecord/test/cases/associations/eager_test.rb
+++ b/activerecord/test/cases/associations/eager_test.rb
@@ -68,6 +68,11 @@ class EagerAssociationTest < ActiveRecord::TestCase
       "expected to find only david's posts"
   end
 
+  def test_loading_with_scope_including_joins
+    assert_equal clubs(:boring_club), Member.preload(:general_club).find(1).general_club
+    assert_equal clubs(:boring_club), Member.eager_load(:general_club).find(1).general_club
+  end
+
   def test_with_ordering
     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,
@@ -271,9 +276,6 @@ class EagerAssociationTest < ActiveRecord::TestCase
   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?
   end
 
diff --git a/activerecord/test/cases/associations/has_many_associations_test.rb b/activerecord/test/cases/associations/has_many_associations_test.rb
index 6102f98682..eeba8fa74f 100644
--- a/activerecord/test/cases/associations/has_many_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_associations_test.rb
@@ -241,6 +241,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     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.funky_bulbs.create!
@@ -744,6 +751,41 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     assert_equal client2, firm.clients.merge!(where: ["#{QUOTED_TYPE} = :type", { type: "Client" }], order: "id").first
   end
 
+  def test_find_first_after_reset_scope
+    firm = Firm.all.merge!(order: "id").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.all.merge!(order: "id").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.all.merge!(order: "id").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_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
@@ -2143,6 +2185,13 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     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
     firm = companies(:first_firm)
     contract = firm.contracts.create!
@@ -2322,8 +2371,9 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
     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
@@ -2511,6 +2561,11 @@ class HasManyAssociationsTest < ActiveRecord::TestCase
 
     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
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 9156f6d57a..1c2138a3d0 100644
--- a/activerecord/test/cases/associations/has_many_through_associations_test.rb
+++ b/activerecord/test/cases/associations/has_many_through_associations_test.rb
@@ -319,6 +319,17 @@ class HasManyThroughAssociationsTest < ActiveRecord::TestCase
     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")
diff --git a/activerecord/test/cases/associations/has_one_associations_test.rb b/activerecord/test/cases/associations/has_one_associations_test.rb
index 7c11d2e7fc..bf3b8dcd63 100644
--- a/activerecord/test/cases/associations/has_one_associations_test.rb
+++ b/activerecord/test/cases/associations/has_one_associations_test.rb
@@ -307,6 +307,15 @@ class HasOneAssociationsTest < ActiveRecord::TestCase
     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)
 
diff --git a/activerecord/test/cases/associations/inverse_associations_test.rb b/activerecord/test/cases/associations/inverse_associations_test.rb
index 467cc73ecd..9fbaa43274 100644
--- a/activerecord/test/cases/associations/inverse_associations_test.rb
+++ b/activerecord/test/cases/associations/inverse_associations_test.rb
@@ -24,11 +24,9 @@ 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
@@ -37,7 +35,6 @@ 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
@@ -46,11 +43,9 @@ 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
@@ -59,7 +54,6 @@ 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
@@ -107,24 +101,17 @@ class AutomaticInverseFindingTests < ActiveRecord::TestCase
   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"
 
     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"
   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 man_reflection.has_inverse?
   end
 end
 
@@ -145,41 +132,24 @@ class InverseAssociationTests < ActiveRecord::TestCase
 
   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?
 
     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?
 
     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?
 
     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?
 
     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?
 
     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
-  end
-
   def test_inverse_of_method_should_supply_the_actual_reflection_instance_it_is_the_inverse_of
     has_one_ref = Man.reflect_on_association(:face)
     assert_equal Face.reflect_on_association(:man), has_one_ref.inverse_of
diff --git a/activerecord/test/cases/attribute_test.rb b/activerecord/test/cases/attribute_test.rb
index 7cf6b498c9..e856d551c0 100644
--- a/activerecord/test/cases/attribute_test.rb
+++ b/activerecord/test/cases/attribute_test.rb
@@ -76,7 +76,7 @@ module ActiveRecord
     end
 
     test "duping dups the value" do
-      @type.expect(:deserialize, "type cast", ["a value"])
+      @type.expect(:deserialize, "type cast".dup, ["a value"])
       attribute = Attribute.from_database(nil, "a value", @type)
 
       value_from_orig = attribute.value
@@ -244,7 +244,7 @@ module ActiveRecord
     end
 
     test "with_type preserves mutations" do
-      attribute = Attribute.from_database(:foo, "", Type::Value.new)
+      attribute = Attribute.from_database(:foo, "".dup, Type::Value.new)
       attribute.value << "1"
 
       assert_equal 1, attribute.with_type(Type::Integer.new).value
diff --git a/activerecord/test/cases/batches_test.rb b/activerecord/test/cases/batches_test.rb
index fbc3fbb44f..dcd3af487b 100644
--- a/activerecord/test/cases/batches_test.rb
+++ b/activerecord/test/cases/batches_test.rb
@@ -1,4 +1,5 @@
 require "cases/helper"
+require "models/comment"
 require "models/post"
 require "models/subscriber"
 
@@ -152,7 +153,7 @@ 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 = "not a post".dup
     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
@@ -417,7 +418,7 @@ class EachTest < ActiveRecord::TestCase
   end
 
   def test_in_batches_should_not_use_records_after_yielding_them_in_case_original_array_is_modified
-    not_a_post = "not a post"
+    not_a_post = "not a post".dup
     def not_a_post.id
       raise StandardError.new("not_a_post had #id called on it")
     end
@@ -610,4 +611,64 @@ class EachTest < ActiveRecord::TestCase
     end
     assert_equal expected, actual
   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
+
+  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
+
+  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 1fc30e24d2..f6ac7990d1 100644
--- a/activerecord/test/cases/binary_test.rb
+++ b/activerecord/test/cases/binary_test.rb
@@ -10,7 +10,7 @@ unless current_adapter?(:DB2Adapter)
     FIXTURES = %w(flowers.jpg example.log test.txt)
 
     def test_mixed_encoding
-      str = "\x80"
+      str = "\x80".dup
       str.force_encoding("ASCII-8BIT")
 
       binary = Binary.new name: "いただきます！", data: str
diff --git a/activerecord/test/cases/calculations_test.rb b/activerecord/test/cases/calculations_test.rb
index adfca08289..9f44b583f6 100644
--- a/activerecord/test/cases/calculations_test.rb
+++ b/activerecord/test/cases/calculations_test.rb
@@ -580,8 +580,11 @@ class CalculationsTest < ActiveRecord::TestCase
   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
@@ -820,4 +823,46 @@ class CalculationsTest < ActiveRecord::TestCase
       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/connection_pool_test.rb b/activerecord/test/cases/connection_pool_test.rb
index 7e88c9cf7a..00a0187b57 100644
--- a/activerecord/test/cases/connection_pool_test.rb
+++ b/activerecord/test/cases/connection_pool_test.rb
@@ -499,21 +499,8 @@ module ActiveRecord
               if failed
                 second_thread_done.set
 
-                puts
-                puts ">>> test_disconnect_and_clear_reloadable_connections_are_able_to_preempt_other_waiting_threads / #{group_action_method}"
-                p [first_thread, second_thread]
-                p pool.stat
-                p pool.connections.map(&:owner)
-
                 first_thread.join(2)
                 second_thread.join(2)
-
-                puts "---"
-                p [first_thread, second_thread]
-                p pool.stat
-                p pool.connections.map(&:owner)
-                puts "<<<"
-                puts
               end
 
               first_thread.join(10) || raise("first_thread got stuck")
diff --git a/activerecord/test/cases/core_test.rb b/activerecord/test/cases/core_test.rb
index 3735572898..936f26ce04 100644
--- a/activerecord/test/cases/core_test.rb
+++ b/activerecord/test/cases/core_test.rb
@@ -35,7 +35,7 @@ class CoreTest < ActiveRecord::TestCase
 
   def test_pretty_print_new
     topic = Topic.new
-    actual = ""
+    actual = "".dup
     PP.pp(topic, StringIO.new(actual))
     expected = <<-PRETTY.strip_heredoc
     #<Topic:0xXXXXXX
@@ -64,7 +64,7 @@ class CoreTest < ActiveRecord::TestCase
 
   def test_pretty_print_persisted
     topic = topics(:first)
-    actual = ""
+    actual = "".dup
     PP.pp(topic, StringIO.new(actual))
     expected = <<-PRETTY.strip_heredoc
     #<Topic:0x\\w+
@@ -92,7 +92,7 @@ class CoreTest < ActiveRecord::TestCase
 
   def test_pretty_print_uninitialized
     topic = Topic.allocate
-    actual = ""
+    actual = "".dup
     PP.pp(topic, StringIO.new(actual))
     expected = "#<Topic:XXXXXX not initialized>\n"
     assert actual.start_with?(expected.split("XXXXXX").first)
@@ -105,7 +105,7 @@ class CoreTest < ActiveRecord::TestCase
         "inspecting topic"
       end
     end
-    actual = ""
+    actual = "".dup
     PP.pp(subtopic.new, StringIO.new(actual))
     assert_equal "inspecting topic\n", actual
   end
diff --git a/activerecord/test/cases/date_time_test.rb b/activerecord/test/cases/date_time_test.rb
index ad7da9de70..6cd98fe254 100644
--- a/activerecord/test/cases/date_time_test.rb
+++ b/activerecord/test/cases/date_time_test.rb
@@ -58,4 +58,17 @@ class DateTimeTest < ActiveRecord::TestCase
       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/enum_test.rb b/activerecord/test/cases/enum_test.rb
index db3da53487..4ef9a125e6 100644
--- a/activerecord/test/cases/enum_test.rb
+++ b/activerecord/test/cases/enum_test.rb
@@ -60,6 +60,7 @@ class EnumTest < ActiveRecord::TestCase
     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
@@ -69,6 +70,7 @@ class EnumTest < ActiveRecord::TestCase
     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
diff --git a/activerecord/test/cases/errors_test.rb b/activerecord/test/cases/errors_test.rb
index 73feb831d0..e90669e0c7 100644
--- a/activerecord/test/cases/errors_test.rb
+++ b/activerecord/test/cases/errors_test.rb
@@ -1,4 +1,4 @@
-require_relative "../cases/helper"
+require "cases/helper"
 
 class ErrorsTest < ActiveRecord::TestCase
   def test_can_be_instantiated_with_no_args
diff --git a/activerecord/test/cases/finder_test.rb b/activerecord/test/cases/finder_test.rb
index 4837a169fa..af21cd529f 100644
--- a/activerecord/test/cases/finder_test.rb
+++ b/activerecord/test/cases/finder_test.rb
@@ -1023,16 +1023,6 @@ 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_includes developer_names, "David"
-    assert_includes developer_names, "Jamis"
-  end
-
   def test_joins_dont_clobber_id
     first = Firm.
       joins("INNER JOIN companies clients ON clients.firm_id = companies.id").
@@ -1242,6 +1232,34 @@ class FinderTest < ActiveRecord::TestCase
     assert_equal tyre2, zyke.tyres.custom_find_by(id: tyre2.id)
   end
 
+  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(2) do
+        Topic.eager_load(:replies).limit(1).exists?
+        Topic.eager_load(:replies).limit(1).exists?
+      end
+
+      assert_queries(4) 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
diff --git a/activerecord/test/cases/fixtures_test.rb b/activerecord/test/cases/fixtures_test.rb
index e651f63c7e..f2fe724095 100644
--- a/activerecord/test/cases/fixtures_test.rb
+++ b/activerecord/test/cases/fixtures_test.rb
@@ -54,6 +54,31 @@ 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
+  end
+
   def test_broken_yaml_exception
     badyaml = Tempfile.new ["foo", ".yml"]
     badyaml.write "a: : "
@@ -248,7 +273,12 @@ class FixturesTest < ActiveRecord::TestCase
     e = assert_raise(ActiveRecord::Fixture::FixtureError) do
       ActiveRecord::FixtureSet.create_fixtures(FIXTURES_ROOT + "/naked/yml", "parrots")
     end
-    assert_equal(%(table "parrots" has no column named "arrr".), e.message)
+
+    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
diff --git a/activerecord/test/cases/json_shared_test_cases.rb b/activerecord/test/cases/json_shared_test_cases.rb
index 5aa41b9d6d..9a1c1c3f3f 100644
--- a/activerecord/test/cases/json_shared_test_cases.rb
+++ b/activerecord/test/cases/json_shared_test_cases.rb
@@ -169,6 +169,25 @@ module JSONSharedTestCases
     assert_not json.changed?
   end
 
+  def test_changes_in_place_ignores_key_order
+    json = klass.new
+    assert_not json.changed?
+
+    json.payload = { "three" => "four", "one" => "two" }
+    json.save!
+    json.reload
+
+    json.payload = { "three" => "four", "one" => "two" }
+    assert_not 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 json.changed?
+  end
+
   def test_changes_in_place_with_ruby_object
     time = Time.now.utc
     json = klass.create!(payload: time)
diff --git a/activerecord/test/cases/locking_test.rb b/activerecord/test/cases/locking_test.rb
index 3a3b8e51f9..2fc52393f2 100644
--- a/activerecord/test/cases/locking_test.rb
+++ b/activerecord/test/cases/locking_test.rb
@@ -167,6 +167,12 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     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 42, p1.lock_version
+  end
+
   def test_touch_existing_lock
     p1 = Person.find(1)
     assert_equal 0, p1.lock_version
@@ -186,6 +192,19 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     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 person.lock_version_changed?
+
+      person.save
+    end
+  end
+
   def test_lock_column_name_existing
     t1 = LegacyThing.find(1)
     t2 = LegacyThing.find(1)
@@ -225,10 +244,33 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     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.last
+    t2 = LockWithoutDefault.find(t1.id)
 
     assert_equal 0, t1.lock_version
     assert_nil t1.lock_version_before_type_cast
@@ -285,7 +327,7 @@ class OptimisticLockingTest < ActiveRecord::TestCase
     ActiveRecord::Base.connection.execute("INSERT INTO lock_without_defaults_cust(title) VALUES('title1')")
 
     t1 = LockWithCustomColumnWithoutDefault.last
-    t2 = LockWithCustomColumnWithoutDefault.last
+    t2 = LockWithCustomColumnWithoutDefault.find(t1.id)
 
     assert_equal 0, t1.custom_lock_version
     assert_nil t1.custom_lock_version_before_type_cast
@@ -434,6 +476,31 @@ class OptimisticLockingWithSchemaChangeTest < ActiveRecord::TestCase
     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 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
+
+    refute stale_object.destroyed?
+  end
+
   private
 
     def add_counter_column_to(model, col = "test_count")
diff --git a/activerecord/test/cases/migration/compatibility_test.rb b/activerecord/test/cases/migration/compatibility_test.rb
index 7a80bfb899..596a21dcbc 100644
--- a/activerecord/test/cases/migration/compatibility_test.rb
+++ b/activerecord/test/cases/migration/compatibility_test.rb
@@ -90,6 +90,21 @@ module ActiveRecord
         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)
diff --git a/activerecord/test/cases/migration/references_foreign_key_test.rb b/activerecord/test/cases/migration/references_foreign_key_test.rb
index f1ddac1ee2..718b9a0613 100644
--- a/activerecord/test/cases/migration/references_foreign_key_test.rb
+++ b/activerecord/test/cases/migration/references_foreign_key_test.rb
@@ -139,6 +139,16 @@ if ActiveRecord::Base.connection.supports_foreign_keys?
           end
         end
 
+        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
+
         test "foreign key methods respect pluralize_table_names" do
           begin
             original_pluralize_table_names = ActiveRecord::Base.pluralize_table_names
diff --git a/activerecord/test/cases/migration_test.rb b/activerecord/test/cases/migration_test.rb
index 57f94950f9..eff6e09eb7 100644
--- a/activerecord/test/cases/migration_test.rb
+++ b/activerecord/test/cases/migration_test.rb
@@ -502,11 +502,10 @@ class MigrationTest < ActiveRecord::TestCase
 
   unless mysql_enforcing_gtid_consistency?
     def test_create_table_with_query
-      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
@@ -514,11 +513,10 @@ class MigrationTest < ActiveRecord::TestCase
     end
 
     def test_create_table_with_query_from_relation
-      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
@@ -1017,8 +1015,8 @@ class CopyMigrationsTest < ActiveRecord::TestCase
     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")
diff --git a/activerecord/test/cases/nested_attributes_test.rb b/activerecord/test/cases/nested_attributes_test.rb
index 5a62cbd3a6..154faa56aa 100644
--- a/activerecord/test/cases/nested_attributes_test.rb
+++ b/activerecord/test/cases/nested_attributes_test.rb
@@ -117,7 +117,7 @@ class TestNestedAttributesInGeneral < ActiveRecord::TestCase
 
   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")
+    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
diff --git a/activerecord/test/cases/primary_keys_test.rb b/activerecord/test/cases/primary_keys_test.rb
index 80cbfdba06..31892cfff0 100644
--- a/activerecord/test/cases/primary_keys_test.rb
+++ b/activerecord/test/cases/primary_keys_test.rb
@@ -46,7 +46,7 @@ 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)
@@ -56,23 +56,36 @@ 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! }
+    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" }
+    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
     subscriber = Subscriber.find(subscribers(:first).nick)
     assert_equal(subscribers(:first).name, subscriber.name)
@@ -83,7 +96,7 @@ 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")
diff --git a/activerecord/test/cases/query_cache_test.rb b/activerecord/test/cases/query_cache_test.rb
index 17b5304cc4..54b65d1a86 100644
--- a/activerecord/test/cases/query_cache_test.rb
+++ b/activerecord/test/cases/query_cache_test.rb
@@ -42,7 +42,8 @@ class QueryCacheTest < ActiveRecord::TestCase
     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
       raise "lol borked"
     }
     assert_raises(RuntimeError) { mw.call({}) }
@@ -149,7 +150,8 @@ class QueryCacheTest < ActiveRecord::TestCase
     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({})
@@ -204,6 +206,52 @@ 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
@@ -274,18 +322,8 @@ class QueryCacheTest < ActiveRecord::TestCase
     end
   end
 
-  def test_cache_is_available_when_connection_is_connected
-    conf = ActiveRecord::Base.configurations
-
-    ActiveRecord::Base.configurations = {}
-    Task.cache do
-      assert_queries(1) { Task.find(1); Task.find(1) }
-    end
-  ensure
-    ActiveRecord::Base.configurations = conf
-  end
-
-  def test_cache_is_not_available_when_using_a_not_connected_connection
+  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")
@@ -295,15 +333,7 @@ class QueryCacheTest < ActiveRecord::TestCase
 
       Task.cache do
         begin
-          if in_memory_db?
-            Task.connection.create_table :tasks do |t|
-              t.datetime :starting
-              t.datetime :ending
-            end
-            ActiveRecord::FixtureSet.create_fixtures(self.class.fixture_path, ["tasks"], {}, ActiveRecord::Base)
-          end
-          Task.connection # warmup postgresql connection setup queries
-          assert_queries(2) { Task.find(1); Task.find(1) }
+          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
diff --git a/activerecord/test/cases/relation/delegation_test.rb b/activerecord/test/cases/relation/delegation_test.rb
index cb6e4d76d3..3b15f051b2 100644
--- a/activerecord/test/cases/relation/delegation_test.rb
+++ b/activerecord/test/cases/relation/delegation_test.rb
@@ -21,8 +21,22 @@ module ActiveRecord
     end
   end
 
+  module DeprecatedArelDelegationTests
+    AREL_METHODS = [
+      :with, :orders, :froms, :project, :projections, :taken, :constraints, :exists, :locked, :where_sql,
+      :ast, :source, :join_sources, :to_dot, :bind_values, :create_insert, :create_true, :create_false
+    ]
+
+    def test_deprecate_arel_delegation
+      AREL_METHODS.each do |method|
+        assert_deprecated { target.public_send(method) }
+      end
+    end
+  end
+
   class DelegationAssociationTest < ActiveRecord::TestCase
     include DelegationWhitelistTests
+    include DeprecatedArelDelegationTests
 
     fixtures :posts
 
@@ -33,6 +47,7 @@ module ActiveRecord
 
   class DelegationRelationTest < ActiveRecord::TestCase
     include DelegationWhitelistTests
+    include DeprecatedArelDelegationTests
 
     fixtures :comments
 
diff --git a/activerecord/test/cases/relation/merging_test.rb b/activerecord/test/cases/relation/merging_test.rb
index c3b39a9295..3901824aac 100644
--- a/activerecord/test/cases/relation/merging_test.rb
+++ b/activerecord/test/cases/relation/merging_test.rb
@@ -143,7 +143,7 @@ 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 dea787c07f..8e73baa70a 100644
--- a/activerecord/test/cases/relation/mutation_test.rb
+++ b/activerecord/test/cases/relation/mutation_test.rb
@@ -90,7 +90,7 @@ module ActiveRecord
       assert_equal [], relation.extending_values
     end
 
-    (Relation::SINGLE_VALUE_METHODS - [:lock, :reordering, :reverse_order, :create_with]).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")
@@ -162,5 +162,10 @@ module ActiveRecord
       relation.distinct! :foo
       assert_equal :foo, relation.distinct_value
     end
+
+    test "skip_query_cache!" do
+      relation.skip_query_cache!
+      assert relation.skip_query_cache_value
+    end
   end
 end
diff --git a/activerecord/test/cases/relation/or_test.rb b/activerecord/test/cases/relation/or_test.rb
index abb7ca72dd..61b6601580 100644
--- a/activerecord/test/cases/relation/or_test.rb
+++ b/activerecord/test/cases/relation/or_test.rb
@@ -59,6 +59,31 @@ module ActiveRecord
       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] }
diff --git a/activerecord/test/cases/relation/where_test.rb b/activerecord/test/cases/relation/where_test.rb
index cbc466d6b8..42dae4d569 100644
--- a/activerecord/test/cases/relation/where_test.rb
+++ b/activerecord/test/cases/relation/where_test.rb
@@ -15,7 +15,7 @@ require "models/vertex"
 
 module ActiveRecord
   class WhereTest < ActiveRecord::TestCase
-    fixtures :posts, :edges, :authors, :author_addresses, :binaries, :essays, :cars, :treasures, :price_estimates
+    fixtures :posts, :edges, :authors, :author_addresses, :binaries, :essays, :cars, :treasures, :price_estimates, :topics
 
     def test_where_copies_bind_params
       author = authors(:david)
@@ -48,6 +48,10 @@ 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
     end
diff --git a/activerecord/test/cases/relation_test.rb b/activerecord/test/cases/relation_test.rb
index e31e21e765..e4f68eef1b 100644
--- a/activerecord/test/cases/relation_test.rb
+++ b/activerecord/test/cases/relation_test.rb
@@ -7,7 +7,7 @@ require "models/rating"
 module ActiveRecord
   class RelationTest < ActiveRecord::TestCase
 
-    fixtures :posts, :comments, :authors, :author_addresses
+    fixtures :posts, :comments, :authors, :author_addresses, :ratings
 
     FakeKlass = Struct.new(:table_name, :name) do
       extend ActiveRecord::Delegation::DelegateCache
@@ -225,7 +225,26 @@ 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({ 2 => 1, 4 => 3, 5 => 1 }, authors(:david).posts.merge(posts_with_special_comments_with_ratings).count)
+      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_joins_as_join_dependency_pick_proper_parent
diff --git a/activerecord/test/cases/relations_test.rb b/activerecord/test/cases/relations_test.rb
index 81173945a3..eb3449b331 100644
--- a/activerecord/test/cases/relations_test.rb
+++ b/activerecord/test/cases/relations_test.rb
@@ -695,16 +695,6 @@ class RelationTest < ActiveRecord::TestCase
     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
@@ -1727,6 +1717,9 @@ class RelationTest < ActiveRecord::TestCase
     scope = Post.order("comments.body")
     assert_equal ["comments"], scope.references_values
 
+    scope = Post.order("#{Comment.quoted_table_name}.#{Comment.quoted_primary_key}")
+    assert_equal ["comments"], scope.references_values
+
     scope = Post.order("comments.body", "yaks.body")
     assert_equal ["comments", "yaks"], scope.references_values
 
@@ -1745,6 +1738,9 @@ class RelationTest < ActiveRecord::TestCase
     scope = Post.reorder("comments.body")
     assert_equal %w(comments), scope.references_values
 
+    scope = Post.reorder("#{Comment.quoted_table_name}.#{Comment.quoted_primary_key}")
+    assert_equal ["comments"], scope.references_values
+
     scope = Post.reorder("comments.body", "yaks.body")
     assert_equal %w(comments yaks), scope.references_values
 
@@ -2011,6 +2007,12 @@ class RelationTest < ActiveRecord::TestCase
     assert_equal binds, merged.bound_attributes
   end
 
+  def test_locked_should_not_build_arel
+    posts = Post.locked
+    assert posts.locked?
+    assert_nothing_raised { posts.lock!(false) }
+  end
+
   def test_relation_join_method
     assert_equal "Thank you for the welcome,Thank you again for the welcome", Post.first.comments.join(",")
   end
@@ -2032,4 +2034,46 @@ class RelationTest < ActiveRecord::TestCase
 
     assert_equal 2, posts.to_a.length
   end
+
+  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
+
+  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
+
+      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
+
+      assert_queries(4) do
+        Post.preload(:comments).skip_query_cache!.load
+        Post.preload(:comments).skip_query_cache!.load
+      end
+    end
+  end
 end
diff --git a/activerecord/test/cases/reserved_word_test.rb b/activerecord/test/cases/reserved_word_test.rb
new file mode 100644
index 0000000000..f3019a5326
--- /dev/null
+++ b/activerecord/test/cases/reserved_word_test.rb
@@ -0,0 +1,132 @@
+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, 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_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 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/schema_dumper_test.rb b/activerecord/test/cases/schema_dumper_test.rb
index 417c6f4832..4c81e825fa 100644
--- a/activerecord/test/cases/schema_dumper_test.rb
+++ b/activerecord/test/cases/schema_dumper_test.rb
@@ -17,6 +17,12 @@ 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|
@@ -320,7 +326,7 @@ 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?
diff --git a/activerecord/test/cases/scoping/relation_scoping_test.rb b/activerecord/test/cases/scoping/relation_scoping_test.rb
index 8535be8402..10553bf057 100644
--- a/activerecord/test/cases/scoping/relation_scoping_test.rb
+++ b/activerecord/test/cases/scoping/relation_scoping_test.rb
@@ -229,6 +229,15 @@ class RelationScopingTest < ActiveRecord::TestCase
     end
   end
 
+  def test_scoping_is_correctly_restored
+    Comment.unscoped do
+      SpecialComment.unscoped.created
+    end
+
+    assert_nil Comment.current_scope
+    assert_nil SpecialComment.current_scope
+  end
+
   def test_circular_joins_with_scoping_does_not_crash
     posts = Post.joins(comments: :post).scoping do
       Post.first(10)
diff --git a/activerecord/test/cases/tasks/mysql_rake_test.rb b/activerecord/test/cases/tasks/mysql_rake_test.rb
index c22d974536..9c6fb14376 100644
--- a/activerecord/test/cases/tasks/mysql_rake_test.rb
+++ b/activerecord/test/cases/tasks/mysql_rake_test.rb
@@ -296,7 +296,7 @@ if current_adapter?(:Mysql2Adapter)
 
       def test_structure_dump_with_extra_flags
         filename = "awesome-file.sql"
-        expected_command = ["mysqldump", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "--noop", "test-db"]
+        expected_command = ["mysqldump", "--noop", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "test-db"]
 
         assert_called_with(Kernel, :system, expected_command, returns: true) do
           with_structure_dump_flags(["--noop"]) do
@@ -364,7 +364,7 @@ if current_adapter?(:Mysql2Adapter)
 
       def test_structure_load
         filename = "awesome-file.sql"
-        expected_command = ["mysql", "--execute", %{SET FOREIGN_KEY_CHECKS = 0; SOURCE #{filename}; SET FOREIGN_KEY_CHECKS = 1}, "--database", "test-db", "--noop"]
+        expected_command = ["mysql", "--noop", "--execute", %{SET FOREIGN_KEY_CHECKS = 0; SOURCE #{filename}; SET FOREIGN_KEY_CHECKS = 1}, "--database", "test-db"]
 
         assert_called_with(Kernel, :system, expected_command, returns: true) do
           with_structure_load_flags(["--noop"]) do
diff --git a/activerecord/test/cases/transactions_test.rb b/activerecord/test/cases/transactions_test.rb
index 5c6d78b574..76a997ba8b 100644
--- a/activerecord/test/cases/transactions_test.rb
+++ b/activerecord/test/cases/transactions_test.rb
@@ -304,6 +304,76 @@ class TransactionTest < ActiveRecord::TestCase
     assert !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
+
+    refute_predicate topic_one, :persisted?
+    refute_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
+
+    refute_predicate topic_one, :persisted?
+    refute_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
+
+    refute_predicate topic_one, :persisted?
+    refute_predicate topic_two, :persisted?
+    refute_predicate topic_three, :persisted?
+  end
+
   def test_manually_rolling_back_a_transaction
     Topic.transaction do
       @first.approved  = true
@@ -595,6 +665,52 @@ class TransactionTest < ActiveRecord::TestCase
     assert_not topic.frozen?
   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.id
+  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.id = nil
+    assert_nil movie.id
+  end
+
   def test_rollback_of_frozen_records
     topic = Topic.create.freeze
     Topic.transaction do
@@ -679,6 +795,44 @@ class TransactionTest < ActiveRecord::TestCase
     assert 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_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|
diff --git a/activerecord/test/cases/yaml_serialization_test.rb b/activerecord/test/cases/yaml_serialization_test.rb
index bfc13d683d..dd8d2c1178 100644
--- a/activerecord/test/cases/yaml_serialization_test.rb
+++ b/activerecord/test/cases/yaml_serialization_test.rb
@@ -119,6 +119,14 @@ class YamlSerializationTest < ActiveRecord::TestCase
     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)
diff --git a/activerecord/test/fixtures/naked/yml/parrots.yml b/activerecord/test/fixtures/naked/yml/parrots.yml
index 3e10331105..76f66e01ae 100644
--- a/activerecord/test/fixtures/naked/yml/parrots.yml
+++ b/activerecord/test/fixtures/naked/yml/parrots.yml
@@ -1,2 +1,3 @@
 george:
   arrr: "Curious George"
+  foobar: Foobar
diff --git a/activerecord/test/migrations/magic/1_currencies_have_symbols.rb b/activerecord/test/migrations/magic/1_currencies_have_symbols.rb
index d4b0e6cd95..2ba2875751 100644
--- a/activerecord/test/migrations/magic/1_currencies_have_symbols.rb
+++ b/activerecord/test/migrations/magic/1_currencies_have_symbols.rb
@@ -1,3 +1,4 @@
+# frozen_string_literal: true
 # coding: ISO-8859-15
 
 class CurrenciesHaveSymbols < ActiveRecord::Migration::Current
diff --git a/activerecord/test/models/club.rb b/activerecord/test/models/club.rb
index 49d7b24a3b..3d441b1d48 100644
--- a/activerecord/test/models/club.rb
+++ b/activerecord/test/models/club.rb
@@ -8,6 +8,8 @@ class Club < ActiveRecord::Base
 
   has_many :favourites, -> { where(memberships: { favourite: true }) }, through: :memberships, source: :member
 
+  scope :general, -> { left_joins(:category).where(categories: { name: "General" }) }
+
   private
 
     def private_method
diff --git a/activerecord/test/models/comment.rb b/activerecord/test/models/comment.rb
index d227f6fe86..eecf923046 100644
--- a/activerecord/test/models/comment.rb
+++ b/activerecord/test/models/comment.rb
@@ -9,7 +9,6 @@ class Comment < ActiveRecord::Base
   belongs_to :post, counter_cache: true
   belongs_to :author,   polymorphic: true
   belongs_to :resource, polymorphic: true
-  belongs_to :developer
 
   has_many :ratings
 
diff --git a/activerecord/test/models/member.rb b/activerecord/test/models/member.rb
index 36f2461b84..b9597c6b9a 100644
--- a/activerecord/test/models/member.rb
+++ b/activerecord/test/models/member.rb
@@ -22,6 +22,7 @@ class Member < ActiveRecord::Base
   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_many :current_memberships, -> { where favourite: true }
   has_many :clubs, through: :current_memberships
diff --git a/activerecord/test/models/membership.rb b/activerecord/test/models/membership.rb
index 2c3ad230a7..0f8be0ad85 100644
--- a/activerecord/test/models/membership.rb
+++ b/activerecord/test/models/membership.rb
@@ -1,4 +1,5 @@
 class Membership < ActiveRecord::Base
+  enum type: %i(Membership CurrentMembership SuperMembership SelectedMembership TenantMembership)
   belongs_to :member
   belongs_to :club
 end
diff --git a/activerecord/test/models/post.rb b/activerecord/test/models/post.rb
index 4c913b3b72..ed64e0ee52 100644
--- a/activerecord/test/models/post.rb
+++ b/activerecord/test/models/post.rb
@@ -22,6 +22,7 @@ class Post < ActiveRecord::Base
   scope :ranked_by_comments,      -> { order("comments_count DESC") }
 
   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
diff --git a/activerecord/test/models/subject.rb b/activerecord/test/models/subject.rb
deleted file mode 100644
index 504f68a296..0000000000
--- a/activerecord/test/models/subject.rb
+++ /dev/null
@@ -1,14 +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
-
-  private
-    def set_email_address
-      unless persisted?
-        self.author_email_address = "test@test.com"
-      end
-    end
-end
diff --git a/activerecord/test/schema/schema.rb b/activerecord/test/schema/schema.rb
index 50f1d9bfe7..f534e9c00e 100644
--- a/activerecord/test/schema/schema.rb
+++ b/activerecord/test/schema/schema.rb
@@ -107,7 +107,7 @@ 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, default: false
@@ -453,11 +453,13 @@ ActiveRecord::Schema.define do
   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|
@@ -489,7 +491,7 @@ 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|
@@ -807,16 +809,19 @@ ActiveRecord::Schema.define do
     t.string :sponsorable_type
   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
+  create_table :string_key_objects, id: false, force: true do |t|
+    t.string :id, null: false
+    t.string :name
+    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