*   Fix `bin/rails db:migrate` with specified `VERSION`.
    `bin/rails db:migrate` with empty VERSION behaves as without `VERSION`.
    Check a format of `VERSION`: Allow a migration version number
    or name of a migration file. Raise error if format of `VERSION` is invalid.
    Raise error if target migration doesn't exist.

    *bogdanvlviv*

*   Fixed a bug where column orders for an index weren't written to
    db/schema.rb when using the sqlite adapter.

    Fixes #30902.

    *Paul Kuruvilla*

*   Remove deprecated method `#sanitize_conditions`.

    *Rafael Mendonça França*

*   Remove deprecated method `#scope_chain`.

    *Rafael Mendonça França*

*   Remove deprecated configuration `.error_on_ignored_order_or_limit`.

    *Rafael Mendonça França*

*   Remove deprecated arguments from `#verify!`.

    *Rafael Mendonça França*

*   Remove deprecated argument `name` from `#indexes`.

    *Rafael Mendonça França*

*   Remove deprecated method `ActiveRecord::Migrator.schema_migrations_table_name`.

    *Rafael Mendonça França*

*   Remove deprecated method `supports_primary_key?`.

    *Rafael Mendonça França*

*   Remove deprecated method `supports_migrations?`.

    *Rafael Mendonça França*

*   Remove deprecated methods `initialize_schema_migrations_table` and `initialize_internal_metadata_table`.

    *Rafael Mendonça França*

*   Raises when calling `lock!` in a dirty record.

    *Rafael Mendonça França*

*   Remove deprecated support to passing a class to `:class_name` on associations.

    *Rafael Mendonça França*

*   Remove deprecated argument `default` from `index_name_exists?`.

    *Rafael Mendonça França*

*   Remove deprecated support to `quoted_id` when typecasting an Active Record object.

    *Rafael Mendonça França*

*   Fix `bin/rails db:setup` and `bin/rails db:test:prepare` create  wrong
    ar_internal_metadata's data for a test database.

    Before:
    ```
    $ RAILS_ENV=test rails dbconsole
    > SELECT * FROM ar_internal_metadata;
    key|value|created_at|updated_at
    environment|development|2017-09-11 23:14:10.815679|2017-09-11 23:14:10.815679
    ```

    After:
    ```
    $ RAILS_ENV=test rails dbconsole
    > SELECT * FROM ar_internal_metadata;
    key|value|created_at|updated_at
    environment|test|2017-09-11 23:14:10.815679|2017-09-11 23:14:10.815679
    ```

    Fixes #26731.

    *bogdanvlviv*

*   Fix longer sequence name detection for serial columns.

    Fixes #28332.

    *Ryuta Kamizono*

*   MySQL: Don't lose `auto_increment: true` in the `db/schema.rb`.

    Fixes #30894.

    *Ryuta Kamizono*

*   Fix `COUNT(DISTINCT ...)` for `GROUP BY` with `ORDER BY` and `LIMIT`.

    Fixes #30886.

    *Ryuta Kamizono*

*   PostgreSQL `tsrange` now preserves subsecond precision.

    PostgreSQL 9.1+ introduced range types, and Rails added support for using
    this datatype in Active Record. However, the serialization of
    `PostgreSQL::OID::Range` was incomplete, because it did not properly
    cast the bounds that make up the range. This led to subseconds being
    dropped in SQL commands:

    Before:

        connection.type_cast(tsrange.serialize(range_value))
        # => "[2010-01-01 13:30:00 UTC,2011-02-02 19:30:00 UTC)"

    Now:

        connection.type_cast(tsrange.serialize(range_value))
        # => "[2010-01-01 13:30:00.670277,2011-02-02 19:30:00.745125)"

    *Thomas Cannon*

*   Passing a `Set` to `Relation#where` now behaves the same as passing an
    array.

    *Sean Griffin*

*   Use given algorithm while removing index from database.

    Fixes #24190.

    *Mehmet Emin İNAÇ*

*   Update payload names for `sql.active_record` instrumentation to be
    more descriptive.

    Fixes #30586.

    *Jeremy Green*

*   Add new error class `TransactionTimeout` which will be raised
    when lock wait timeout exceeded.

    *Gabriel Courtemanche*

*   Remove deprecated `#migration_keys`.

    *Ryuta Kamizono*

*   Automatically guess the inverse associations for STI.

    *Yuichiro Kaneko*

*   Ensure `sum` honors `distinct` on `has_many :through` associations

    Fixes #16791.

    *Aaron Wortham*

*   Add `binary` fixture helper method.

    *Atsushi Yoshida*

*   When using `Relation#or`, extract the common conditions and put them before the OR condition.

    *Maxime Handfield Lapointe*

*   `Relation#or` now accepts two relations who have different values for
    `references` only, as `references` can be implicitly called by `where`.

    Fixes #29411.

    *Sean Griffin*

*   `ApplicationRecord` is no longer generated when generating models. If you
    need to generate it, it can be created with `rails g application_record`.

    *Lisa Ugray*

*   Fix `COUNT(DISTINCT ...)` with `ORDER BY` and `LIMIT` to keep the existing select list.

    *Ryuta Kamizono*

*   When a `has_one` association is destroyed by `dependent: destroy`,
    `destroyed_by_association` will now be set to the reflection, matching the
    behaviour of `has_many` associations.

    *Lisa Ugray*

*   Fix `unscoped(where: [columns])` removing the wrong bind values

    When the `where` is called on a relation after a `or`, unscoping the column of that later `where` removed
    bind values used by the `or` instead. (possibly other cases too)

    ```
    Post.where(id: 1).or(Post.where(id: 2)).where(foo: 3).unscope(where: :foo).to_sql
    # Currently:
    #     SELECT "posts".* FROM "posts" WHERE ("posts"."id" = 2 OR "posts"."id" = 3)
    # With fix:
    #     SELECT "posts".* FROM "posts" WHERE ("posts"."id" = 1 OR "posts"."id" = 2)
    ```

    *Maxime Handfield Lapointe*

*   Values constructed using multi-parameter assignment will now use the
    post-type-cast value for rendering in single-field form inputs.

    *Sean Griffin*

*   `Relation#joins` is no longer affected by the target model's
    `current_scope`, with the exception of `unscoped`.

    Fixes #29338.

    *Sean Griffin*

*   Change sqlite3 boolean serialization to use 1 and 0

    SQLite natively recognizes 1 and 0 as true and false, but does not natively
    recognize 't' and 'f' as was previously serialized.

    This change in serialization requires a migration of stored boolean data
    for SQLite databases, so it's implemented behind a configuration flag
    whose default false value is deprecated.

    *Lisa Ugray*

*   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 creation of 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*

*   Loading model schema from database is now thread-safe.

    Fixes #28589.

    *Vikrant Chaudhary*, *David Abdemoulaie*

*   Add `ActiveRecord::Base#cache_version` to support recyclable cache keys via the new versioned entries
    in `ActiveSupport::Cache`. This also means that `ActiveRecord::Base#cache_key` will now return a stable key
    that does not include a timestamp any more.

    NOTE: This feature is turned off by default, and `#cache_key` will still return cache keys with timestamps
    until you set `ActiveRecord::Base.cache_versioning = true`. That's the setting for all new apps on Rails 5.2+

    *DHH*

*   Respect `SchemaDumper.ignore_tables` in rake tasks for databases structure dump

    *Rusty Geldmacher*, *Guillermo Iguaran*

*   Add type caster to `RuntimeReflection#alias_name`

    Fixes #28959.

    *Jon Moss*

*   Deprecate `supports_statement_cache?`.

    *Ryuta Kamizono*

*   Raise error `UnknownMigrationVersionError` on the movement of migrations
    when the current migration does not exist.

    *bogdanvlviv*

*   Fix `bin/rails db:forward` first migration.

    *bogdanvlviv*

*   Support Descending Indexes for MySQL.

    MySQL 8.0.1 and higher supports descending indexes: `DESC` in an index definition is no longer ignored.
    See https://dev.mysql.com/doc/refman/8.0/en/descending-indexes.html.

    *Ryuta Kamizono*

*   Fix inconsistency with changed attributes when overriding AR attribute reader.

    *bogdanvlviv*

*   When calling the dynamic fixture accessor method with no arguments, it now returns all fixtures of this type.
    Previously this method always returned an empty array.

    *Kevin McPhillips*


Please check [5-1-stable](https://github.com/rails/rails/blob/5-1-stable/activerecord/CHANGELOG.md) for previous changes.
