rails--rails/activerecord/CHANGELOG.md

• Allow users to silence the "Rails couldn't infer whether you are using multiple databases..." message using config.active_record.suppress_multiple_database_warning.

  Omri Gabay

• Connections can be granularly switched for abstract classes when connected_to is called.

  This change allows connected_to to switch a role and/or shard for a single abstract class instead of all classes globally. Applications that want to use the new feature need to set config.active_record.legacy_connection_handling to false in their application configuration.

  Example usage:

  Given an application we have a User model that inherits from ApplicationRecord and a Dog model that inherits from AnimalsRecord. AnimalsRecord and ApplicationRecord have writing and reading connections as well as shard default, one, and two.

  ActiveRecord::Base.connected_to(role: :reading) do
    User.first # reads from default replica
    Dog.first # reads from default replica
  
    AnimalsRecord.connected_to(role: :writing, shard: :one) do
      User.first # reads from default replica
      Dog.first # reads from shard one primary
    end
  
    User.first # reads from default replica
    Dog.first # reads from default replica
  
    ApplicationRecord.connected_to(role: :writing, shard: :two) do
      User.first # reads from shard two primary
      Dog.first # reads from default replica
    end
  end
  

  Eileen M. Uchitelle, John Crepezzi

• Allow double-dash comment syntax when querying read-only databases

  James Adam

• Add values_at method.

  Returns an array containing the values associated with the given methods.

  topic = Topic.first
  topic.values_at(:title, :author_name)
  # => ["Budget", "Jason"]
  

  Similar to Hash#values_at but on an Active Record instance.

  Guillaume Briday

• Fix read_attribute_before_type_cast to consider attribute aliases.

  Marcelo Lauxen

• Support passing record to uniqueness validator :conditions callable:

  class Article < ApplicationRecord
    validates_uniqueness_of :title, conditions: ->(article) {
      published_at = article.published_at
      where(published_at: published_at.beginning_of_year..published_at.end_of_year)
    }
  end
  

  Eliot Sykes

• BatchEnumerator#update_all and BatchEnumerator#delete_all now return the total number of rows affected, just like their non-batched counterparts.

  Person.in_batches.update_all("first_name = 'Eugene'") # => 42
  Person.in_batches.delete_all # => 42
  

  Fixes #40287.

  Eugene Kenny

• Add support for PostgreSQL interval data type with conversion to ActiveSupport::Duration when loading records from database and serialization to ISO 8601 formatted duration string on save. Add support to define a column in migrations and get it in a schema dump. Optional column precision is supported.

  To use this in 6.1, you need to place the next string to your model file:

  attribute :duration, :interval
  

  To keep old behavior until 6.2 is released:

  attribute :duration, :string
  

  Example:

  create_table :events do |t|
    t.string   :name
    t.interval :duration
  end
  
  class Event < ApplicationRecord
    attribute :duration, :interval
  end
  
  Event.create!(name: 'Rock Fest', duration: 2.days)
  Event.last.duration # => 2 days
  Event.last.duration.iso8601 # => "P2D"
  Event.new(duration: 'P1DT12H3S').duration # => 1 day, 12 hours, and 3 seconds
  Event.new(duration: '1 day') # Unknown value will be ignored and NULL will be written to database
  

  Andrey Novikov

• Allow associations supporting the dependent: key to take dependent: :destroy_async.

  class Account < ActiveRecord::Base
      belongs_to :supplier, dependent: :destroy_async
  end
  

  :destroy_async will enqueue a job to destroy associated records in the background.

  DHH, George Claghorn, Cory Gwin, Rafael Mendonça França, Adrianna Chang

• Add SKIP_TEST_DATABASE environment variable to disable modifying the test database when rails db:create and rails db:drop are called.

  Jason Schweier

• connects_to can only be called on ActiveRecord::Base or abstract classes.

  Ensure that connects_to can only be called from ActiveRecord::Base or abstract classes. This protects the application from opening duplicate or too many connections.

  Eileen M. Uchitelle, John Crepezzi

• All connection adapters execute now raises ActiveRecord::ConnectionNotEstablished rather than ActiveRecord::StatementInvalid when they encounter a connection error.

  Jean Boussier

• Mysql2Adapter#quote_string now raises ActiveRecord::ConnectionNotEstablished rather than ActiveRecord::StatementInvalid when it can't connect to the MySQL server.

  Jean Boussier

• Add support for check constraints that are NOT VALID via validate: false (PostgreSQL-only).

  Alex Robbin

• Ensure the default configuration is considered primary or first for an environment

  If a multiple database application provides a configuration named primary, that will be treated as default. In applications that do not have a primary entry, the default database configuration will be the first configuration for an environment.

  Eileen M. Uchitelle

• Allow where references association names as joined table name aliases.

  class Comment < ActiveRecord::Base
    enum label: [:default, :child]
    has_many :children, class_name: "Comment", foreign_key: :parent_id
  end
  
  # ... FROM comments LEFT OUTER JOIN comments children ON ... WHERE children.label = 1
  Comment.includes(:children).where("children.label": "child")
  

  Ryuta Kamizono

• Support storing demodulized class name for polymorphic type.

  Before Rails 6.1, storing demodulized class name is supported only for STI type by store_full_sti_class class attribute.

  Now store_full_class_name class attribute can handle both STI and polymorphic types.

  Ryuta Kamizono

• Deprecate rails db:structure:{load, dump} tasks and extend rails db:schema:{load, dump} tasks to work with either :ruby or :sql format, depending on config.active_record.schema_format configuration value.

  fatkodima

• Respect the select values for eager loading.

  post = Post.select("UPPER(title) AS title").first
  post.title # => "WELCOME TO THE WEBLOG"
  post.body  # => ActiveModel::MissingAttributeError
  
  # Rails 6.0 (ignore the `select` values)
  post = Post.select("UPPER(title) AS title").eager_load(:comments).first
  post.title # => "Welcome to the weblog"
  post.body  # => "Such a lovely day"
  
  # Rails 6.1 (respect the `select` values)
  post = Post.select("UPPER(title) AS title").eager_load(:comments).first
  post.title # => "WELCOME TO THE WEBLOG"
  post.body  # => ActiveModel::MissingAttributeError
  

  Ryuta Kamizono

• Allow attribute's default to be configured but keeping its own type.

  class Post < ActiveRecord::Base
    attribute :written_at, default: -> { Time.now.utc }
  end
  
  # Rails 6.0
  Post.type_for_attribute(:written_at) # => #<Type::Value ... precision: nil, ...>
  
  # Rails 6.1
  Post.type_for_attribute(:written_at) # => #<Type::DateTime ... precision: 6, ...>
  

  Ryuta Kamizono

• Allow default to be configured for Enum.

  class Book < ActiveRecord::Base
    enum status: [:proposed, :written, :published], _default: :published
  end
  
  Book.new.status # => "published"
  

  Ryuta Kamizono

• Deprecate YAML loading from legacy format older than Rails 5.0.

  Ryuta Kamizono

• Added the setting ActiveRecord::Base.immutable_strings_by_default, which allows you to specify that all string columns should be frozen unless otherwise specified. This will reduce memory pressure for applications which do not generally mutate string properties of Active Record objects.

  Sean Griffin

• Deprecate map! and collect! on ActiveRecord::Result.

  Ryuta Kamizono

• Support relation.and for intersection as Set theory.

  david_and_mary = Author.where(id: [david, mary])
  mary_and_bob   = Author.where(id: [mary, bob])
  
  david_and_mary.merge(mary_and_bob) # => [mary, bob]
  
  david_and_mary.and(mary_and_bob) # => [mary]
  david_and_mary.or(mary_and_bob)  # => [david, mary, bob]
  

  Ryuta Kamizono

• Merging conditions on the same column no longer maintain both conditions, and will be consistently replaced by the latter condition in Rails 6.2. To migrate to Rails 6.2's behavior, use relation.merge(other, rewhere: true).

  # Rails 6.1 (IN clause is replaced by merger side equality condition)
  Author.where(id: [david.id, mary.id]).merge(Author.where(id: bob)) # => [bob]
  
  # Rails 6.1 (both conflict conditions exists, deprecated)
  Author.where(id: david.id..mary.id).merge(Author.where(id: bob)) # => []
  
  # Rails 6.1 with rewhere to migrate to Rails 6.2's behavior
  Author.where(id: david.id..mary.id).merge(Author.where(id: bob), rewhere: true) # => [bob]
  
  # Rails 6.2 (same behavior with IN clause, mergee side condition is consistently replaced)
  Author.where(id: [david.id, mary.id]).merge(Author.where(id: bob)) # => [bob]
  Author.where(id: david.id..mary.id).merge(Author.where(id: bob)) # => [bob]
  

  Ryuta Kamizono

• Do not mark Postgresql MAC address and UUID attributes as changed when the assigned value only varies by case.

  Peter Fry

• 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.

  Usage:

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

  Fixes #39516.

  Austen Madden

• Add basic support for CHECK constraints to database migrations.

  Usage:

  add_check_constraint :products, "price > 0", name: "price_check"
  remove_check_constraint :products, name: "price_check"
  

  fatkodima

• Add ActiveRecord::Base.strict_loading_by_default and ActiveRecord::Base.strict_loading_by_default= to enable/disable strict_loading mode by default for a model. The configuration's value is inheritable by subclasses, but they can override that value and it will not impact parent class.

  Usage:

  class Developer < ApplicationRecord
    self.strict_loading_by_default = true
  
    has_many :projects
  end
  
  dev = Developer.first
  dev.projects.first
  # => ActiveRecord::StrictLoadingViolationError Exception: Developer is marked as strict_loading and Project cannot be lazily loaded.
  

  bogdanvlviv

• Deprecate passing an Active Record object to quote/type_cast directly.

  Ryuta Kamizono

• Default engine ENGINE=InnoDB is no longer dumped to make schema more agnostic.

  Before:

  create_table "accounts", options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci", force: :cascade do |t|
  end
  

  After:

  create_table "accounts", charset: "utf8mb4", collation: "utf8mb4_0900_ai_ci", force: :cascade do |t|
  end
  

  Ryuta Kamizono

• Added delegated type as an alternative to single-table inheritance for representing class hierarchies. See ActiveRecord::DelegatedType for the full description.

  DHH

• Deprecate aggregations with group by duplicated fields.

  To migrate to Rails 6.2's behavior, use uniq!(:group) to deduplicate group fields.

  accounts = Account.group(:firm_id)
  
  # duplicated group fields, deprecated.
  accounts.merge(accounts.where.not(credit_limit: nil)).sum(:credit_limit)
  # => {
  #   [1, 1] => 50,
  #   [2, 2] => 60
  # }
  
  # use `uniq!(:group)` to deduplicate group fields.
  accounts.merge(accounts.where.not(credit_limit: nil)).uniq!(:group).sum(:credit_limit)
  # => {
  #   1 => 50,
  #   2 => 60
  # }
  

  Ryuta Kamizono

• Deprecate duplicated query annotations.

  To migrate to Rails 6.2's behavior, use uniq!(:annotate) to deduplicate query annotations.

  accounts = Account.where(id: [1, 2]).annotate("david and mary")
  
  # duplicated annotations, deprecated.
  accounts.merge(accounts.rewhere(id: 3))
  # SELECT accounts.* FROM accounts WHERE accounts.id = 3 /* david and mary */ /* david and mary */
  
  # use `uniq!(:annotate)` to deduplicate annotations.
  accounts.merge(accounts.rewhere(id: 3)).uniq!(:annotate)
  # SELECT accounts.* FROM accounts WHERE accounts.id = 3 /* david and mary */
  

  Ryuta Kamizono

• 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

• Support merging option :rewhere to allow mergee side condition to be replaced exactly.

  david_and_mary = Author.where(id: david.id..mary.id)
  
  # both conflict conditions exists
  david_and_mary.merge(Author.where(id: bob)) # => []
  
  # mergee side condition is replaced by rewhere
  david_and_mary.merge(Author.rewhere(id: bob)) # => [bob]
  
  # mergee side condition is replaced by rewhere option
  david_and_mary.merge(Author.where(id: bob), rewhere: true) # => [bob]
  

  Ryuta Kamizono

• Add support for finding records based on signed ids, which are tamper-proof, verified ids that can be set to expire and scoped with a purpose. This is particularly useful for things like password reset or email verification, where you want the bearer of the signed id to be able to interact with the underlying record, but usually only within a certain time period.

  signed_id = User.first.signed_id expires_in: 15.minutes, purpose: :password_reset
  
  User.find_signed signed_id # => nil, since the purpose does not match
  
  travel 16.minutes
  User.find_signed signed_id, purpose: :password_reset # => nil, since the signed id has expired
  
  travel_back
  User.find_signed signed_id, purpose: :password_reset # => User.first
  
  User.find_signed! "bad data" # => ActiveSupport::MessageVerifier::InvalidSignature
  

  DHH

• Support ALGORITHM = INSTANT DDL option for index operations on MySQL.

  Ryuta Kamizono

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

  Ryuta Kamizono

• Allow unscope to be aware of table name qualified values.

  It is possible to unscope only the column in the specified table.

  posts = Post.joins(:comments).group(:"posts.hidden")
  posts = posts.where("posts.hidden": false, "comments.hidden": false)
  
  posts.count
  # => { false => 10 }
  
  # unscope both hidden columns
  posts.unscope(where: :hidden).count
  # => { false => 11, true => 1 }
  
  # unscope only comments.hidden column
  posts.unscope(where: :"comments.hidden").count
  # => { false => 11 }
  

  Ryuta Kamizono, Slava Korolev

• Fix rewhere to truly overwrite collided where clause by new where clause.

  steve = Person.find_by(name: "Steve")
  david = Author.find_by(name: "David")
  
  relation = Essay.where(writer: steve)
  
  # Before
  relation.rewhere(writer: david).to_a # => []
  
  # After
  relation.rewhere(writer: david).to_a # => [david]
  

  Ryuta Kamizono

• Inspect time attributes with subsec.

  p Knot.create
  => #<Knot id: 1, created_at: "2016-05-05 01:29:47.116928000">
  

  akinomaeni

• Deprecate passing a column to type_cast.

  Ryuta Kamizono

• Deprecate in_clause_length and allowed_index_name_length in DatabaseLimits.

  Ryuta Kamizono

• Support bulk insert/upsert on relation to preserve scope values.

  Josef Šimánek, Ryuta Kamizono

• Preserve column comment value on changing column name on MySQL.

  Islam Taha

• Add support for if_exists option for removing an index.

  The remove_index method can take an if_exists option. If this is set to true an error won't be raised if the index doesn't exist.

  Eileen M. Uchitelle

• Remove ibm_db, informix, mssql, oracle, and oracle12 Arel visitors which are not used in the code base.

  Ryuta Kamizono

• Prevent build_association from touching a parent record if the record isn't persisted for has_one associations.

  Fixes #38219.

  Josh Brody

• Add support for if_not_exists option for adding index.

  The add_index method respects if_not_exists option. If it is set to true index won't be added.

  Usage:

    add_index :users, :account_id, if_not_exists: true
  

  The if_not_exists option passed to create_table also gets propagated to indexes created within that migration so that if table and its indexes exist then there is no attempt to create them again.

  Prathamesh Sonpatki

• Add ActiveRecord::Base#previously_new_record? to show if a record was new before the last save.

  Tom Ward

• Support descending order for find_each, find_in_batches, and in_batches.

  Batch processing methods allow you to work with the records in batches, greatly reducing memory consumption, but records are always batched from oldest id to newest.

  This change allows reversing the order, batching from newest to oldest. This is useful when you need to process newer batches of records first.

  Pass order: :desc to yield batches in descending order. The default remains order: :asc.

  Person.find_each(order: :desc) do |person|
    person.party_all_night!
  end
  

  Alexey Vasiliev

• Fix insert_all with enum values.

  Fixes #38716.

  Joel Blum

• Add support for db:rollback:name for multiple database applications.

  Multiple database applications will now raise if db:rollback is call and recommend using the db:rollback:[NAME] to rollback migrations.

  Eileen M. Uchitelle

• Relation#pick now uses already loaded results instead of making another query.

  Eugene Kenny

• Deprecate using return, break or throw to exit a transaction block after writes.

  Dylan Thacker-Smith

• Dump the schema or structure of a database when calling db:migrate:name.

  In previous versions of Rails, rails db:migrate would dump the schema of the database. In Rails 6, that holds true (rails db:migrate dumps all databases' schemas), but rails db:migrate:name does not share that behavior.

  Going forward, calls to rails db:migrate:name will dump the schema (or structure) of the database being migrated.

  Kyle Thompson

• Reset the ActiveRecord::Base connection after rails db:migrate:name.

  When rails db:migrate has finished, it ensures the ActiveRecord::Base connection is reset to its original configuration. Going forward, rails db:migrate:name will have the same behavior.

  Kyle Thompson

• Disallow calling connected_to on subclasses of ActiveRecord::Base.

  Behavior has not changed here but the previous API could be misleading to people who thought it would switch connections for only that class. connected_to switches the context from which we are getting connections, not the connections themselves.

  Eileen M. Uchitelle, John Crepezzi

• Add support for horizontal sharding to connects_to and connected_to.

  Applications can now connect to multiple shards and switch between their shards in an application. Note that the shard swapping is still a manual process as this change does not include an API for automatic shard swapping.

  Usage:

  Given the following configuration:

  # config/database.yml
  production:
    primary:
      database: my_database
    primary_shard_one:
      database: my_database_shard_one
  

  Connect to multiple shards:

  class ApplicationRecord < ActiveRecord::Base
    self.abstract_class = true
  
    connects_to shards: {
      default: { writing: :primary },
      shard_one: { writing: :primary_shard_one }
    }
  

  Swap between shards in your controller / model code:

  ActiveRecord::Base.connected_to(shard: :shard_one) do
    # Read from shard one
  end
  

  The horizontal sharding API also supports read replicas. See guides for more details.

  Eileen M. Uchitelle, John Crepezzi

• Deprecate spec_name in favor of name on database configurations.

  The accessors for spec_name on configs_for and DatabaseConfig are deprecated. Please use name instead.

  Deprecated behavior:

  db_config = ActiveRecord::Base.configs_for(env_name: "development", spec_name: "primary")
  db_config.spec_name
  

  New behavior:

  db_config = ActiveRecord::Base.configs_for(env_name: "development", name: "primary")
  db_config.name
  

  Eileen M. Uchitelle

• Add additional database-specific rake tasks for multi-database users.

  Previously, rails db:create, rails db:drop, and rails db:migrate were the only rails tasks that could operate on a single database. For example:

  rails db:create
  rails db:create:primary
  rails db:create:animals
  rails db:drop
  rails db:drop:primary
  rails db:drop:animals
  rails db:migrate
  rails db:migrate:primary
  rails db:migrate:animals
  

  With these changes, rails db:schema:dump, rails db:schema:load, rails db:structure:dump, rails db:structure:load and rails db:test:prepare can additionally operate on a single database. For example:

  rails db:schema:dump
  rails db:schema:dump:primary
  rails db:schema:dump:animals
  rails db:schema:load
  rails db:schema:load:primary
  rails db:schema:load:animals
  rails db:structure:dump
  rails db:structure:dump:primary
  rails db:structure:dump:animals
  rails db:structure:load
  rails db:structure:load:primary
  rails db:structure:load:animals
  rails db:test:prepare
  rails db:test:prepare:primary
  rails db:test:prepare:animals
  

  Kyle Thompson

• Add support for strict_loading mode on association declarations.

  Raise an error if attempting to load a record from an association that has been marked as strict_loading unless it was explicitly eager loaded.

  Usage:

  class Developer < ApplicationRecord
    has_many :projects, strict_loading: true
  end
  
  dev = Developer.first
  dev.projects.first
  # => ActiveRecord::StrictLoadingViolationError: The projects association is marked as strict_loading and cannot be lazily loaded.
  

  Kevin Deisz

• Add support for strict_loading mode to prevent lazy loading of records.

  Raise an error if a parent record is marked as strict_loading and attempts to lazily load its associations. This is useful for finding places you may want to preload an association and avoid additional queries.

  Usage:

  dev = Developer.strict_loading.first
  dev.audit_logs.to_a
  # => ActiveRecord::StrictLoadingViolationError: Developer is marked as strict_loading and AuditLog cannot be lazily loaded.
  

  Eileen M. Uchitelle, Aaron Patterson

• Add support for PostgreSQL 11+ partitioned indexes when using upsert_all.

  Sebastián Palma

• Adds support for if_not_exists to add_column and if_exists to remove_column.

  Applications can set their migrations to ignore exceptions raised when adding a column that already exists or when removing a column that does not exist.

  Example Usage:

  class AddColumnTitle < ActiveRecord::Migration[6.1]
    def change
      add_column :posts, :title, :string, if_not_exists: true
    end
  end
  

  class RemoveColumnTitle < ActiveRecord::Migration[6.1]
    def change
      remove_column :posts, :title, if_exists: true
    end
  end
  

  Eileen M. Uchitelle

• Regexp-escape table name for MS SQL Server.

  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 AdvisoryLockBase. 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

• Allow schema cache path to be defined in the database configuration file.

  For example:

  development:
    adapter: postgresql
    database: blog_development
    pool: 5
    schema_cache_path: tmp/schema/main.yml
  

  Katrina Owen

• Deprecate #remove_connection in favor of #remove_connection_pool when called on the handler.

  #remove_connection is deprecated in order to support returning a DatabaseConfig object instead of a Hash. Use #remove_connection_pool, #remove_connection will be removed in 6.2.

  Eileen M. Uchitelle, John Crepezzi

• Deprecate #default_hash and it's alias #[] on database configurations.

  Applications should use configs_for. #default_hash and #[] will be removed in 6.2.

  Eileen M. Uchitelle, John Crepezzi

• Add scale support to ActiveRecord::Validations::NumericalityValidator.

  Gannon McGibbon

• Find orphans by looking for missing relations through chaining where.missing:

  Before:

  Post.left_joins(:author).where(authors: { id: nil })
  

  After:

  Post.where.missing(:author)
  

  Tom Rossi

• 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

• Deprecate "primary" as the connection_specification_name for ActiveRecord::Base.

  "primary" has been deprecated as the connection_specification_name for ActiveRecord::Base in favor of using "ActiveRecord::Base". This change affects calls to ActiveRecord::Base.connection_handler.retrieve_connection and ActiveRecord::Base.connection_handler.remove_connection. If you're calling these methods with "primary", please switch to "ActiveRecord::Base".

  Eileen M. Uchitelle, John Crepezzi

• Add ActiveRecord::Validations::NumericalityValidator with support for casting floats using a database columns' precision value.

  Gannon McGibbon

• 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

• Skip test database when running db:create or db:drop in development with DATABASE_URL set.

  Brian Buchalter

• Don't allow mutations on the database configurations hash.

  Freeze the configurations hash to disallow directly changing it. If applications need to change the hash, for example to create databases for parallelization, they should use the DatabaseConfig object directly.

  Before:

  @db_config = ActiveRecord::Base.configurations.configs_for(env_name: "test", spec_name: "primary")
  @db_config.configuration_hash.merge!(idle_timeout: "0.02")
  

  After:

  @db_config = ActiveRecord::Base.configurations.configs_for(env_name: "test", spec_name: "primary")
  config = @db_config.configuration_hash.merge(idle_timeout: "0.02")
  db_config = ActiveRecord::DatabaseConfigurations::HashConfig.new(@db_config.env_name, @db_config.spec_name, config)
  

  Eileen M. Uchitelle, John Crepezzi

• Remove :connection_id from the sql.active_record notification.

  Aaron Patterson, Rafael Mendonça França

• The :name key will no longer be returned as part of DatabaseConfig#configuration_hash. Please use DatabaseConfig#owner_name instead.

  Eileen M. Uchitelle, John Crepezzi

• ActiveRecord's belongs_to_required_by_default flag can now be set per model.

  You can now opt-out/opt-in specific models from having their associations required by default.

  This change is meant to ease the process of migrating all your models to have their association required.

  Edouard Chin

• The connection_config method has been deprecated, please use connection_db_config instead which will return a DatabaseConfigurations::DatabaseConfig instead of a Hash.

  Eileen M. Uchitelle, John Crepezzi

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

  Resolves #34889.

  Patrick Rebsch

• The database kwarg is deprecated without replacement because it can't be used for sharding and creates an issue if it's used during a request. Applications that need to create new connections should use connects_to instead.

  Eileen M. Uchitelle, John Crepezzi

• Allow attributes to be fetched from Arel node groupings.

  Jeff Emminger, Gannon McGibbon

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

  Joshua Flanagan

• Calling methods like establish_connection with a Hash which is invalid (eg: no adapter) will now raise an error the same way as connections defined in config/database.yml.

  John Crepezzi

• Specifying implicit_order_column now subsorts the records by primary key if available to ensure deterministic results.

  Paweł Urbanek

• where(attr => []) now loads an empty result without making a query.

  John Hawthorn

• Fixed the performance regression for primary_keys introduced MySQL 8.0.

  Hiroyuki Ishii

• Add support for belongs_to to has_many inversing.

  Gannon McGibbon

• Allow length configuration for has_secure_token method. The minimum length is set at 24 characters.

  Before:

  has_secure_token :auth_token
  

  After:

  has_secure_token :default_token             # 24 characters
  has_secure_token :auth_token, length: 36    # 36 characters
  has_secure_token :invalid_token, length: 12 # => ActiveRecord::SecureToken::MinimumLengthError
  

  Bernardo de Araujo

• Deprecate DatabaseConfigurations#to_h. These connection hashes are still available via ActiveRecord::Base.configurations.configs_for.

  Eileen Uchitelle, John Crepezzi

• Add DatabaseConfig#configuration_hash to return database configuration hashes with symbol keys, and use all symbol-key configuration hashes internally. Deprecate DatabaseConfig#config which returns a String-keyed Hash with the same values.

  John Crepezzi, Eileen Uchitelle

• Allow column names to be passed to remove_index positionally along with other options.

  Passing other options can be necessary to make remove_index correctly reversible.

  Before:

  add_index    :reports, :report_id               # => works
  add_index    :reports, :report_id, unique: true # => works
  remove_index :reports, :report_id               # => works
  remove_index :reports, :report_id, unique: true # => ArgumentError
  

  After:

  remove_index :reports, :report_id, unique: true # => works
  

  Eugene Kenny

• Allow bulk ALTER statements to drop and recreate indexes with the same name.

  Eugene Kenny

• 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

• Stop trying to read yaml file fixtures when loading Active Record fixtures.

  Gannon McGibbon

• Deprecate .reorder(nil) with .first / .first! taking non-deterministic result.

  To continue taking non-deterministic result, use .take / .take! instead.

  Ryuta Kamizono

• Preserve user supplied joins order as much as possible.

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

  Ryuta Kamizono

• Allow matches_regex and does_not_match_regexp on the MySQL Arel visitor.

  James Pearson

• Allow specifying fixtures to be ignored by setting ignore in YAML file's '_fixture' section.

  Tongfei Gao

• 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]
  end
  

  Edu Depetris

• Make currency symbols optional for money column type in PostgreSQL.

  Joel Schneider

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

  Josh Goodall

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

  Guilherme Mansur

• Loading the schema for a model that has no table_name raises a TableNotSpecified error.

  Guilherme Mansur, Eugene Kenny

• 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

• Add support for multiple databases to rails db:abort_if_pending_migrations.

  Mark Lee

• 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

• Allow generated create_table migrations to include or skip timestamps.

  Michael Duchemin

Please check 6-0-stable for previous changes.