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Rails (August 19, 2021)

  • No changes.

Rails 6.0.4 (June 15, 2021)

  • Only warn about negative enums if a positive form that would cause conflicts exists.

    Fixes #39065.

    Alex Ghiculescu

  • Allow the inverse of a has_one association that was previously autosaved to be loaded.

    Fixes #34255.

    Steven Weber

  • Reset statement cache for association if table_name is changed.

    Fixes #36453.

    Ryuta Kamizono

  • Type cast extra select for eager loading.

    Ryuta Kamizono

  • Prevent collection associations from being autosaved multiple times.

    Fixes #39173.

    Eugene Kenny

  • Resolve issue with insert_all unique_by option when used with expression index.

    When the :unique_by option of ActiveRecord::Persistence.insert_all and ActiveRecord::Persistence.upsert_all was used with the name of an expression index, an error was raised. Adding a guard around the formatting behavior for the :unique_by corrects this.


    create_table :books, id: :integer, force: true do |t|
      t.column :name, :string
      t.index "lower(name)", unique: true
    Book.insert_all [{ name: "MyTest" }], unique_by: :index_books_on_lower_name

    Fixes #39516.

    Austen Madden

  • Fix preloading for polymorphic association with custom scope.

    Ryuta Kamizono

  • Allow relations with different SQL comments in the or method.

    Takumi Shotoku

  • Resolve conflict between counter cache and optimistic locking.

    Bump an Active Record instance's lock version after updating its counter cache. This avoids raising an unnecessary ActiveRecord::StaleObjectError upon subsequent transactions by maintaining parity with the corresponding database record's lock_version column.

    Fixes #16449.

    Aaron Lipman

  • Fix through association with source/through scope which has joins.

    Ryuta Kamizono

  • Fix through association to respect source scope for includes/preload.

    Ryuta Kamizono

  • Fix eager load with Arel joins to maintain the original joins order.

    Ryuta Kamizono

  • Fix group by count with eager loading + order + limit/offset.

    Ryuta Kamizono

  • Fix left joins order when merging multiple left joins from different associations.

    Ryuta Kamizono

  • Fix index creation to preserve index comment in bulk change table on MySQL.

    Ryuta Kamizono

  • Change remove_foreign_key to not check :validate option if database doesn't support the feature.

    Ryuta Kamizono

  • Fix the result of aggregations to maintain duplicated "group by" fields.

    Ryuta Kamizono

  • Do not return duplicated records when using preload.

    Bogdan Gusiev

Rails (May 05, 2021)

  • No changes.

Rails (March 26, 2021)

  • No changes.

Rails (February 10, 2021)

  • Fix possible DoS vector in PostgreSQL money type

    Carefully crafted input can cause a DoS via the regular expressions used for validating the money format in the PostgreSQL adapter. This patch fixes the regexp.

    Thanks to @dee-see from Hackerone for this patch!


    Aaron Patterson

Rails (October 07, 2020)

  • No changes.

Rails (September 09, 2020)

  • No changes.

Rails (June 17, 2020)

  • No changes.

Rails (May 18, 2020)

  • No changes.

Rails 6.0.3 (May 06, 2020)

  • Recommend applications don't use the database kwarg in connected_to

    The database kwarg in connected_to was meant to be used for one-off scripts but is often used in requests. This is really dangerous because it re-establishes a connection every time. It's deprecated in 6.1 and will be removed in 6.2 without replacement. This change soft deprecates it in 6.0 by removing documentation.

    Eileen M. Uchitelle

  • Fix support for PostgreSQL 11+ partitioned indexes.

    Sebastián Palma

  • Add support for beginless ranges, introduced in Ruby 2.7.

    Josh Goodall

  • Fix insert_all with enum values

    Fixes #38716.

    Joel Blum

  • Regexp-escape table name for MS SQL

    Add Regexp.escape to one method in ActiveRecord, so that table names with regular expression characters in them work as expected. Since MS SQL Server uses "[" and "]" to quote table and column names, and those characters are regular expression characters, methods like pluck and select fail in certain cases when used with the MS SQL Server adapter.

    Larry Reid

  • Store advisory locks on their own named connection.

    Previously advisory locks were taken out against a connection when a migration started. This works fine in single database applications but doesn't work well when migrations need to open new connections which results in the lock getting dropped.

    In order to fix this we are storing the advisory lock on a new connection with the connection specification name AdisoryLockBase. The caveat is that we need to maintain at least 2 connections to a database while migrations are running in order to do this.

    Eileen M. Uchitelle, John Crepezzi

  • Ensure :reading connections always raise if a write is attempted.

    Now Rails will raise an ActiveRecord::ReadOnlyError if any connection on the reading handler attempts to make a write. If your reading role needs to write you should name the role something other than :reading.

    Eileen M. Uchitelle

  • Enforce fresh ETag header after a collection's contents change by adding ActiveRecord::Relation#cache_key_with_version. This method will be used by ActionController::ConditionalGet to ensure that when collection cache versioning is enabled, requests using ConditionalGet don't return the same ETag header after a collection is modified. Fixes #38078.

    Aaron Lipman

  • A database URL can now contain a querystring value that contains an equal sign. This is needed to support passing PostgresSQL options.

    Joshua Flanagan

  • Retain explicit selections on the base model after applying includes and joins.

    Resolves #34889.

    Patrick Rebsch

Rails (March 19, 2020)

  • No changes.

Rails (December 18, 2019)

  • No changes.

Rails 6.0.2 (December 13, 2019)

  • Share the same connection pool for primary and replica databases in the transactional tests for the same database.

    Edouard Chin

  • Fix the preloader when one record is fetched using after_initialize but not the entire collection.

    Bradley Price

  • Fix collection callbacks not terminating when :abort is thrown.

    Edouard Chin, Ryuta Kamizono

  • Correctly deprecate where.not working as NOR for relations.

    12a9664 deprecated where.not working as NOR, however doing a relation query like where.not(relation: { ... }) wouldn't be properly deprecated and where.not would work as NAND instead.

    Edouard Chin

  • Fix db:migrate task with multiple databases to restore the connection to the previous database.

    The migrate task iterates and establish a connection over each db resulting in the last one to be used by subsequent rake tasks. We should reestablish a connection to the connection that was established before the migrate tasks was run

    Edouard Chin

  • Fix multi-threaded issue for AcceptanceValidator.

    Ryuta Kamizono

Rails 6.0.1 (November 5, 2019)

  • Common Table Expressions are allowed on read-only connections.

    Chris Morris

  • New record instantiation respects unscope.

    Ryuta Kamizono

  • Fixed a case where find_in_batches could halt too early.

    Takayuki Nakata

  • Autosaved associations always perform validations when a custom validation context is used.

    Tekin Suleyman

  • sql.active_record notifications now include the :connection in their payloads.

    Eugene Kenny

  • A rollback encountered in an after_commit callback does not reset previously-committed record state.

    Ryuta Kamizono

  • Fixed that join order was lost when eager-loading.

    Ryuta Kamizono

  • DESCRIBE queries are allowed on read-only connections.

    Dylan Thacker-Smith

  • Fixed that records that had been inspected could not be marshaled.

    Eugene Kenny

  • The connection pool reaper thread is respawned in forked processes. This fixes that idle connections in forked processes wouldn't be reaped.

    John Hawthorn

  • The memoized result of ActiveRecord::Relation#take is properly cleared when ActiveRecord::Relation#reset or ActiveRecord::Relation#reload is called.

    Anmol Arora

  • Fixed the performance regression for primary_keys introduced MySQL 8.0.

    Hiroyuki Ishii

  • insert, insert_all, upsert, and upsert_all now clear the query cache.

    Eugene Kenny

  • Call while_preventing_writes directly from connected_to.

    In some cases application authors want to use the database switching middleware and make explicit calls with connected_to. It's possible for an app to turn off writes and not turn them back on by the time we call connected_to(role: :writing).

    This change allows apps to fix this by assuming if a role is writing we want to allow writes, except in the case it's explicitly turned off.

    Eileen M. Uchitelle

  • Improve detection of ActiveRecord::StatementTimeout with mysql2 adapter in the edge case when the query is terminated during filesort.

    Kir Shatrov

Rails 6.0.0 (August 16, 2019)

  • Preserve user supplied joins order as much as possible.

    Fixes #36761, #34328, #24281, #12953.

    Ryuta Kamizono

  • Make the DATABASE_URL env variable only affect the primary connection. Add new env variables for multiple databases.

    John Crepezzi, Eileen Uchitelle

  • Add a warning for enum elements with 'not_' prefix.

    class Foo
      enum status: [:sent, :not_sent]

    Edu Depetris

  • Make currency symbols optional for money column type in PostgreSQL

    Joel Schneider

Rails 6.0.0.rc2 (July 22, 2019)

  • Add database_exists? method to connection adapters to check if a database exists.

    Guilherme Mansur

  • PostgreSQL: Fix GROUP BY with ORDER BY virtual count attribute.

    Fixes #36022.

    Ryuta Kamizono

  • Make ActiveRecord ConnectionPool.connections method thread-safe.

    Fixes #36465.

    Jeff Doering

  • Fix sqlite3 collation parsing when using decimal columns.

    Martin R. Schuster

  • Fix invalid schema when primary key column has a comment.

    Fixes #29966.

    Guilherme Goettems Schneider

  • Fix table comment also being applied to the primary key column.

    Guilherme Goettems Schneider

  • Fix merging left_joins to maintain its own join_type context.

    Fixes #36103.

    Ryuta Kamizono

Rails 6.0.0.rc1 (April 24, 2019)

  • Add touch option to has_one association.

    Abhay Nikam

  • Deprecate where.not working as NOR and will be changed to NAND in Rails 6.1.

    all = [treasures(:diamond), treasures(:sapphire), cars(:honda), treasures(:sapphire)]
    assert_equal all,

    In Rails 6.0:

    sapphire = treasures(:sapphire)
    nor = all.reject { |e|
      e.estimate_of_type == sapphire.class.polymorphic_name
    }.reject { |e|
      e.estimate_of_id ==
    assert_equal [cars(:honda)], nor
    without_sapphire = PriceEstimate.where.not(
      estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id:
    assert_equal nor,

    In Rails 6.1:

    sapphire = treasures(:sapphire)
    nand = all - [sapphire]
    assert_equal [treasures(:diamond), cars(:honda)], nand
    without_sapphire = PriceEstimate.where.not(
      estimate_of_type: sapphire.class.polymorphic_name, estimate_of_id:
    assert_equal nand,

    Ryuta Kamizono

  • Fix dirty tracking after rollback.

    Fixes #15018, #30167, #33868.

    Ryuta Kamizono

  • Add ActiveRecord::Relation#cache_version to support recyclable cache keys via the versioned entries in ActiveSupport::Cache. This also means that ActiveRecord::Relation#cache_key will now return a stable key that does not include the max timestamp or count 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.collection_cache_versioning = true. That's the setting for all new apps on Rails 6.0+

    Lachlan Sylvester

  • Fix dirty tracking for touch to track saved changes.

    Fixes #33429.

    Ryuta Kamzono

  • change_column_comment and change_table_comment are invertible only if to and from options are specified.

    Yoshiyuki Kinjo

  • Don't call commit/rollback callbacks when a record isn't saved.

    Fixes #29747.

    Ryuta Kamizono

  • Fix circular autosave: true causes invalid records to be saved.

    Prior to the fix, when there was a circular series of autosave: true associations, the callback for a has_many association was run while another instance of the same callback on the same association hadn't finished running. When control returned to the first instance of the callback, the instance variable had changed, and subsequent associated records weren't saved correctly. Specifically, the ID field for the belongs_to corresponding to the has_many was nil.

    Fixes #28080.

    Larry Reid

  • Raise ArgumentError for invalid :limit and :precision like as other options.


    add_column :items, :attr1, :binary,   size: 10      # => ArgumentError
    add_column :items, :attr2, :decimal,  scale: 10     # => ArgumentError
    add_column :items, :attr3, :integer,  limit: 10     # => ActiveRecordError
    add_column :items, :attr4, :datetime, precision: 10 # => ActiveRecordError


    add_column :items, :attr1, :binary,   size: 10      # => ArgumentError
    add_column :items, :attr2, :decimal,  scale: 10     # => ArgumentError
    add_column :items, :attr3, :integer,  limit: 10     # => ArgumentError
    add_column :items, :attr4, :datetime, precision: 10 # => ArgumentError

    Ryuta Kamizono

  • Association loading isn't to be affected by scoping consistently whether preloaded / eager loaded or not, with the exception of unscoped.


    Post.where("1=0").scoping do
      Comment.find(1).post                   # => nil
      Comment.preload(:post).find(1).post    # => #<Post id: 1, ...>
      Comment.eager_load(:post).find(1).post # => #<Post id: 1, ...>


    Post.where("1=0").scoping do
      Comment.find(1).post                   # => #<Post id: 1, ...>
      Comment.preload(:post).find(1).post    # => #<Post id: 1, ...>
      Comment.eager_load(:post).find(1).post # => #<Post id: 1, ...>

    Fixes #34638, #35398.

    Ryuta Kamizono

  • Add rails db:prepare to migrate or setup a database.

    Runs db:migrate if the database exists or db:setup if it doesn't.

    Roberto Miranda

  • Add after_save_commit callback as shortcut for after_commit :hook, on: [ :create, :update ].


  • Assign all attributes before calling build to ensure the child record is visible in before_add and after_add callbacks for has_many :through associations.

    Fixes #33249.

    Ryan H. Kerr

  • Add ActiveRecord::Relation#extract_associated for extracting associated records from a relation.

    # => Returns collection of User records


  • Add ActiveRecord::Relation#annotate for adding SQL comments to its queries.

    For example:

    Post.where(id: 123).annotate("this is a comment").to_sql
    # SELECT "posts".* FROM "posts" WHERE "posts"."id" = 123 /* this is a comment */

    This can be useful in instrumentation or other analysis of issued queries.

    Matt Yoho

  • Support Optimizer Hints.

    In most databases, a way to control the optimizer is by using optimizer hints, which can be specified within individual statements.

    Example (for MySQL):

    Topic.optimizer_hints("MAX_EXECUTION_TIME(50000)", "NO_INDEX_MERGE(topics)")
    # SELECT /*+ MAX_EXECUTION_TIME(50000) NO_INDEX_MERGE(topics) */ `topics`.* FROM `topics`

    Example (for PostgreSQL with pg_hint_plan):

    Topic.optimizer_hints("SeqScan(topics)", "Parallel(topics 8)")
    # SELECT /*+ SeqScan(topics) Parallel(topics 8) */ "topics".* FROM "topics"

    See also:

    Ryuta Kamizono

  • Fix query attribute method on user-defined attribute to be aware of typecasted value.

    For example, the following code no longer return false as casted non-empty string:

    class Post < ActiveRecord::Base
      attribute :user_defined_text, :text
    end "false").user_defined_text? # => true

    Yuji Kamijima

  • Quote empty ranges like other empty enumerables.

    Patrick Rebsch

  • Add insert_all/insert_all!/upsert_all methods to ActiveRecord::Persistence, allowing bulk inserts akin to the bulk updates provided by update_all and bulk deletes by delete_all.

    Supports skipping or upserting duplicates through the ON CONFLICT syntax for PostgreSQL (9.5+) and SQLite (3.24+) and ON DUPLICATE KEY UPDATE syntax for MySQL.

    Bob Lail

  • Add rails db:seed:replant that truncates tables of each database for current environment and loads the seeds.

    bogdanvlviv, DHH

  • Add ActiveRecord::Base.connection.truncate for SQLite3 adapter.


  • Deprecate mismatched collation comparison for uniqueness validator.

    Uniqueness validator will no longer enforce case sensitive comparison in Rails 6.1. To continue case sensitive comparison on the case insensitive column, pass case_sensitive: true option explicitly to the uniqueness validator.

    Ryuta Kamizono

  • Add reselect method. This is a short-hand for unscope(:select).select(fields).

    Fixes #27340.

    Willian Gustavo Veiga

  • Add negative scopes for all enum values.


    class Post < ActiveRecord::Base
      enum status: %i[ drafted active trashed ]
    Post.not_drafted # => where.not(status: :drafted)
    Post.not_active  # => where.not(status: :active)
    Post.not_trashed # => where.not(status: :trashed)


  • Fix different count calculation when using size with manual select with DISTINCT.

    Fixes #35214.

    Juani Villarejo

Rails 6.0.0.beta3 (March 11, 2019)

  • No changes.

Rails 6.0.0.beta2 (February 25, 2019)

  • Fix prepared statements caching to be enabled even when query caching is enabled.

    Ryuta Kamizono

  • Ensure update_all series cares about optimistic locking.

    Ryuta Kamizono

  • Don't allow where with non numeric string matches to 0 values.

    Ryuta Kamizono

  • Introduce ActiveRecord::Relation#destroy_by and ActiveRecord::Relation#delete_by.

    destroy_by allows relation to find all the records matching the condition and perform destroy_all on the matched records.


    Person.destroy_by(name: 'David')
    Person.destroy_by(name: 'David', rating: 4)
    david = Person.find_by(name: 'David')
    david.posts.destroy_by(id: [1, 2, 3])

    delete_by allows relation to find all the records matching the condition and perform delete_all on the matched records.


    Person.delete_by(name: 'David')
    Person.delete_by(name: 'David', rating: 4)
    david = Person.find_by(name: 'David')
    david.posts.delete_by(id: [1, 2, 3])

    Abhay Nikam

  • Don't allow where with invalid value matches to nil values.

    Fixes #33624.

    Ryuta Kamizono

  • SQLite3: Implement add_foreign_key and remove_foreign_key.

    Ryuta Kamizono

  • Deprecate using class level querying methods if the receiver scope regarded as leaked. Use klass.unscoped to avoid the leaking scope.

    Ryuta Kamizono

  • Allow applications to automatically switch connections.

    Adds a middleware and configuration options that can be used in your application to automatically switch between the writing and reading database connections.

    GET and HEAD requests will read from the replica unless there was a write in the last 2 seconds, otherwise they will read from the primary. Non-get requests will always write to the primary. The middleware accepts an argument for a Resolver class and an Operations class where you are able to change how the auto-switcher works to be most beneficial for your application.

    To use the middleware in your application you can use the following configuration options:

    config.active_record.database_selector = { delay: 2.seconds }
    config.active_record.database_resolver = ActiveRecord::Middleware::DatabaseSelector::Resolver
    config.active_record.database_resolver_context = ActiveRecord::Middleware::DatabaseSelector::Resolver::Session

    To change the database selection strategy, pass a custom class to the configuration options:

    config.active_record.database_selector = { delay: 10.seconds }
    config.active_record.database_resolver = MyResolver
    config.active_record.database_resolver_context = MyResolver::MyCookies

    Eileen M. Uchitelle

  • MySQL: Support :size option to change text and blob size.

    Ryuta Kamizono

  • Make t.timestamps with precision by default.

    Ryuta Kamizono

Rails 6.0.0.beta1 (January 18, 2019)

  • Remove deprecated #set_state from the transaction object.

    Rafael Mendonça França

  • Remove deprecated #supports_statement_cache? from the database adapters.

    Rafael Mendonça França

  • Remove deprecated #insert_fixtures from the database adapters.

    Rafael Mendonça França

  • Remove deprecated ActiveRecord::ConnectionAdapters::SQLite3Adapter#valid_alter_table_type?.

    Rafael Mendonça França

  • Do not allow passing the column name to sum when a block is passed.

    Rafael Mendonça França

  • Do not allow passing the column name to count when a block is passed.

    Rafael Mendonça França

  • Remove delegation of missing methods in a relation to arel.

    Rafael Mendonça França

  • Remove delegation of missing methods in a relation to private methods of the class.

    Rafael Mendonça França

  • Deprecate config.active_record.sqlite3.represent_boolean_as_integer.

    Rafael Mendonça França

  • Change SQLite3Adapter to always represent boolean values as integers.

    Rafael Mendonça França

  • Remove ability to specify a timestamp name for #cache_key.

    Rafael Mendonça França

  • Remove deprecated ActiveRecord::Migrator.migrations_path=.

    Rafael Mendonça França

  • Remove deprecated expand_hash_conditions_for_aggregates.

    Rafael Mendonça França

  • Set polymorphic type column to NULL on dependent: :nullify strategy.

    On polymorphic associations both the foreign key and the foreign type columns will be set to NULL.

    Laerti Papa

  • Allow permitted instance of ActionController::Parameters as argument of ActiveRecord::Relation#exists?.

    Gannon McGibbon

  • Add support for endless ranges introduces in Ruby 2.6.

    Greg Navis

  • Deprecate passing migrations_paths to connection.assume_migrated_upto_version.

    Ryuta Kamizono

  • MySQL: ROW_FORMAT=DYNAMIC create table option by default.

    Since MySQL 5.7.9, the innodb_default_row_format option defines the default row format for InnoDB tables. The default setting is DYNAMIC. The row format is required for indexing on varchar(255) with utf8mb4 columns.

    Ryuta Kamizono

  • Fix join table column quoting with SQLite.

    Gannon McGibbon

  • Allow disabling scopes generated by ActiveRecord.enum.

    Alfred Dominic

  • Ensure that delete_all on collection proxy returns affected count.

    Ryuta Kamizono

  • Reset scope after delete on collection association to clear stale offsets of removed records.

    Gannon McGibbon

  • Add the ability to prevent writes to a database for the duration of a block.

    Allows the application to prevent writes to a database. This can be useful when you're building out multiple databases and want to make sure you're not sending writes when you want a read.

    If while_preventing_writes is called and the query is considered a write query the database will raise an exception regardless of whether the database user is able to write.

    This is not meant to be a catch-all for write queries but rather a way to enforce read-only queries without opening a second connection. One purpose of this is to catch accidental writes, not all writes.

    Eileen M. Uchitelle

  • Allow aliased attributes to be used in #update_columns and #update.

    Gannon McGibbon

  • Allow spaces in postgres table names.

    Fixes issue where "user post" is misinterpreted as ""user"."post"" when quoting table names with the postgres adapter.

    Gannon McGibbon

  • Cached columns_hash fields should be excluded from ResultSet#column_types.

    PR #34528 addresses the inconsistent behaviour when attribute is defined for an ignored column. The following test was passing for SQLite and MySQL, but failed for PostgreSQL:

    class DeveloperName < ActiveRecord::Type::String
      def deserialize(value)
        "Developer: #{value}"
    class AttributedDeveloper < ActiveRecord::Base
      self.table_name = "developers"
      attribute :name,
      self.ignored_columns += ["name"]
    developer = AttributedDeveloper.create
    developer.update_column :name, "name"
    loaded_developer = AttributedDeveloper.where(id:"*").first
    puts # should be "Developer: name" but it's just "name"

    Dmitry Tsepelev

  • Make the implicit order column configurable.

    When calling ordered finder methods such as first or last without an explicit order clause, ActiveRecord sorts records by primary key. This can result in unpredictable and surprising behaviour when the primary key is not an auto-incrementing integer, for example when it's a UUID. This change makes it possible to override the column used for implicit ordering such that first and last will return more predictable results.


    class Project < ActiveRecord::Base
      self.implicit_order_column = "created_at"

    Tekin Suleyman

  • Bump minimum PostgreSQL version to 9.3.

    Yasuo Honda

  • Values of enum are frozen, raising an error when attempting to modify them.

    Emmanuel Byrd

  • Move ActiveRecord::StatementInvalid SQL to error property and include binds as separate error property.

    ActiveRecord::ConnectionAdapters::AbstractAdapter#translate_exception_class now requires binds to be passed as the last argument.

    ActiveRecord::ConnectionAdapters::AbstractAdapter#translate_exception now requires message, sql, and binds to be passed as keyword arguments.

    Subclasses of ActiveRecord::StatementInvalid must now provide sql: and binds: arguments to super.


    class MySubclassedError < ActiveRecord::StatementInvalid
      def initialize(message, sql:, binds:)
        super(message, sql: sql, binds: binds)

    Gannon McGibbon

  • Add an :if_not_exists option to create_table.


    create_table :posts, if_not_exists: true do |t|
      t.string :title

    That would execute:


    If the table already exists, if_not_exists: false (the default) raises an exception whereas if_not_exists: true does nothing.

    fatkodima, Stefan Kanev

  • Defining an Enum as a Hash with blank key, or as an Array with a blank value, now raises an ArgumentError.

    Christophe Maximin

  • Adds support for multiple databases to rails db:schema:cache:dump and rails db:schema:cache:clear.

    Gannon McGibbon

  • update_columns now correctly raises ActiveModel::MissingAttributeError if the attribute does not exist.

    Sean Griffin

  • Add support for hash and URL configs in database hash of ActiveRecord::Base.connected_to.

    User.connected_to(database: { writing: "postgres://foo" }) do
      User.create!(name: "Gannon")
    config = { "adapter" => "sqlite3", "database" => "db/readonly.sqlite3" }
    User.connected_to(database: { reading: config }) do

    Gannon McGibbon

  • Support default expression for MySQL.

    MySQL 8.0.13 and higher supports default value to be a function or expression.

    Ryuta Kamizono

  • Support expression indexes for MySQL.

    MySQL 8.0.13 and higher supports functional key parts that index expression values rather than column or column prefix values.

    Ryuta Kamizono

  • Fix collection cache key with limit and custom select to avoid ambiguous timestamp column error.

    Fixes #33056.

    Federico Martinez

  • Add basic API for connection switching to support multiple databases.

    1. Adds a connects_to method for models to connect to multiple databases. Example:
    class AnimalsModel < ApplicationRecord
      self.abstract_class = true
      connects_to database: { writing: :animals_primary, reading: :animals_replica }
    class Dog < AnimalsModel
      # connected to both the animals_primary db for writing and the animals_replica for reading
    1. Adds a connected_to block method for switching connection roles or connecting to a database that the model didn't connect to. Connecting to the database in this block is useful when you have another defined connection, for example slow_replica that you don't want to connect to by default but need in the console, or a specific code block.
    ActiveRecord::Base.connected_to(role: :reading) do
      Dog.first # finds dog from replica connected to AnimalsBase
      Book.first # doesn't have a reading connection, will raise an error
    ActiveRecord::Base.connected_to(database: :slow_replica) do
      SlowReplicaModel.first # if the db config has a slow_replica configuration this will be used to do the lookup, otherwise this will throw an exception

    Eileen M. Uchitelle

  • Enum raises on invalid definition values

    When defining a Hash enum it can be easy to use [] instead of {}. This commit checks that only valid definition values are provided, those can be a Hash, an array of Symbols or an array of Strings. Otherwise it raises an ArgumentError.

    Fixes #33961

    Alberto Almagro

  • Reloading associations now clears the Query Cache like Persistence#reload does.

    class Post < ActiveRecord::Base
      has_one :category
      belongs_to :author
      has_many :comments
    # Each of the following will now clear the query cache.

    Christophe Maximin

  • Added index option for change_table migration helpers. With this change you can create indexes while adding new columns into the existing tables.


    change_table(:languages) do |t|
      t.string :country_code, index: true

    Mehmet Emin İNAÇ

  • Fix transaction reverting for migrations.

    Before: Commands inside a transaction in a reverted migration ran uninverted. Now: This change fixes that by reverting commands inside transaction block.

    fatkodima, David Verhasselt

  • Raise an error instead of scanning the filesystem root when fixture_path is blank.

    Gannon McGibbon, Max Albrecht

  • Allow ActiveRecord::Base.configurations= to be set with a symbolized hash.

    Gannon McGibbon

  • Don't update counter cache unless the record is actually saved.

    Fixes #31493, #33113, #33117.

    Ryuta Kamizono

  • Deprecate ActiveRecord::Result#to_hash in favor of ActiveRecord::Result#to_a.

    Gannon McGibbon, Kevin Cheng

  • SQLite3 adapter supports expression indexes.

    create_table :users do |t|
      t.string :email
    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 calling #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, /phone/]
    Account.last.inspect # => #<Account id: 123, name: "DHH", credit_card_number: [FILTERED], telephone_number: [FILTERED] ...>
    SecureAccount.filter_attributes += [:name]
    SecureAccount.last.inspect # => #<SecureAccount id: 42, name: [FILTERED], credit_card_number: [FILTERED] ...>

    Zhang Kang, Yoshiyuki Kinjo

  • 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:

      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.

      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.


    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.


    Person.where(name: "David").touch_all(time:, 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 2.5.0 or newer.

    Jeremy Daer, Kasper Timm Hansen

  • 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.


  • Add Relation#pick as short-hand for single-value plucks.


Please check 5-2-stable for previous changes.