* SQLite3 adapter supports expression indexes
```
create_table :users do |t|
t.string :email
end
add_index :users, 'lower(email)', name: 'index_users_on_email', unique: true
```
*Gray Kemmey*
* Allow subclasses to redefine autosave callbacks for associated records.
Fixes #33305.
*Andrey Subbota*
* Bump minimum MySQL version to 5.5.8.
*Yasuo Honda*
* Use MySQL utf8mb4 character set by default.
`utf8mb4` character set with 4-Byte encoding supports supplementary characters including emoji.
The previous default 3-Byte encoding character set `utf8` is not enough to support them.
*Yasuo Honda*
* Fix duplicated record creation when using nested attributes with `create_with`.
*Darwin Wu*
* Configuration item `config.filter_parameters` could also filter out
sensitive values of database columns when call `#inspect`.
We also added `ActiveRecord::Base::filter_attributes`/`=` in order to
specify sensitive attributes to specific model.
```
Rails.application.config.filter_parameters += [:credit_card_number]
Account.last.inspect # => #<Account id: 123, name: "DHH", credit_card_number: [FILTERED] ...>
SecureAccount.filter_attributes += [:name]
SecureAccount.last.inspect # => #<SecureAccount id: 42, name: [FILTERED], credit_card_number: [FILTERED] ...>
```
*Zhang Kang*
* Deprecate `column_name_length`, `table_name_length`, `columns_per_table`,
`indexes_per_table`, `columns_per_multicolumn_index`, `sql_query_length`,
and `joins_per_query` methods in `DatabaseLimits`.
*Ryuta Kamizono*
* `ActiveRecord::Base.configurations` now returns an object.
`ActiveRecord::Base.configurations` used to return a hash, but this
is an inflexible data model. In order to improve multiple-database
handling in Rails, we've changed this to return an object. Some methods
are provided to make the object behave hash-like in order to ease the
transition process. Since most applications don't manipulate the hash
we've decided to add backwards-compatible functionality that will throw
a deprecation warning if used, however calling `ActiveRecord::Base.configurations`
will use the new version internally and externally.
For example, the following `database.yml`:
```
development:
adapter: sqlite3
database: db/development.sqlite3
```
Used to become a hash:
```
{ "development" => { "adapter" => "sqlite3", "database" => "db/development.sqlite3" } }
```
Is now converted into the following object:
```
#<ActiveRecord::DatabaseConfigurations:0x00007fd1acbdf800 @configurations=[
#<ActiveRecord::DatabaseConfigurations::HashConfig:0x00007fd1acbded10 @env_name="development",
@spec_name="primary", @config={"adapter"=>"sqlite3", "database"=>"db/development.sqlite3"}>
]
```
Iterating over the database configurations has also changed. Instead of
calling hash methods on the `configurations` hash directly, a new method `configs_for` has
been provided that allows you to select the correct configuration. `env_name`, and
`spec_name` arguments are optional. For example these return an array of
database config objects for the requested environment and a single database config object
will be returned for the requested environment and specification name respectively.
```
ActiveRecord::Base.configurations.configs_for(env_name: "development")
ActiveRecord::Base.configurations.configs_for(env_name: "development", spec_name: "primary")
```
*Eileen M. Uchitelle*, *Aaron Patterson*
* Add database configuration to disable advisory locks.
```
production:
adapter: postgresql
advisory_locks: false
```
*Guo Xiang*
* SQLite3 adapter `alter_table` method restores foreign keys.
*Yasuo Honda*
* Allow `:to_table` option to `invert_remove_foreign_key`.
Example:
remove_foreign_key :accounts, to_table: :owners
*Nikolay Epifanov*, *Rich Chen*
* Add environment & load_config dependency to `bin/rake db:seed` to enable
seed load in environments without Rails and custom DB configuration
*Tobias Bielohlawek*
* Fix default value for mysql time types with specified precision.
*Nikolay Kondratyev*
* Fix `touch` option to behave consistently with `Persistence#touch` method.
*Ryuta Kamizono*
* Migrations raise when duplicate column definition.
Fixes #33024.
*Federico Martinez*
* Bump minimum SQLite version to 3.8
*Yasuo Honda*
* Fix parent record should not get saved with duplicate children records.
Fixes #32940.
*Santosh Wadghule*
* Fix logic on disabling commit callbacks so they are not called unexpectedly when errors occur.
*Brian Durand*
* Ensure `Associations::CollectionAssociation#size` and `Associations::CollectionAssociation#empty?`
use loaded association ids if present.
*Graham Turner*
* Add support to preload associations of polymorphic associations when not all the records have the requested associations.
*Dana Sherson*
* Add `touch_all` method to `ActiveRecord::Relation`.
Example:
Person.where(name: "David").touch_all(time: Time.new(2020, 5, 16, 0, 0, 0))
*fatkodima*, *duggiefresh*
* Add `ActiveRecord::Base.base_class?` predicate.
*Bogdan Gusiev*
* Add custom prefix/suffix options to `ActiveRecord::Store.store_accessor`.
*Tan Huynh*, *Yukio Mizuta*
* Rails 6 requires Ruby 2.4.1 or newer.
*Jeremy Daer*
* Deprecate `update_attributes`/`!` in favor of `update`/`!`.
*Eddie Lebow*
* Add `ActiveRecord::Base.create_or_find_by`/`!` to deal with the SELECT/INSERT race condition in
`ActiveRecord::Base.find_or_create_by`/`!` by leaning on unique constraints in the database.
*DHH*
* Add `Relation#pick` as short-hand for single-value plucks.
*DHH*
Please check [5-2-stable](https://github.com/rails/rails/blob/5-2-stable/activerecord/CHANGELOG.md) for previous changes.
