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  • Support Optimizer Hints.

    In most databases, there is 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 Postgres (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 a 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.activerecord.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 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, /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.

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