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module ActiveRecord

Active Record – Object-relational mapping in Rails

Active Record connects classes to relational database tables to establish an almost zero-configuration persistence layer for applications. The library provides a base class that, when subclassed, sets up a mapping between the new class and an existing table in the database. In the context of an application, these classes are commonly referred to as models. Models can also be connected to other models; this is done by defining associations.

Active Record relies heavily on naming in that it uses class and association names to establish mappings between respective database tables and foreign key columns. Although these mappings can be defined explicitly, it’s recommended to follow naming conventions, especially when getting started with the library.

You can read more about Active Record in the Active Record Basics guide.

A short rundown of some of the major features:

  • Automated mapping between classes and tables, attributes and columns.

    class Product < ActiveRecord::Base
end

    The Product class is automatically mapped to the table named “products”, which might look like this:

    CREATE TABLE products (
  id bigint NOT NULL auto_increment,
  name varchar(255),
  PRIMARY KEY  (id)
);

    This would also define the following accessors: Product#name and Product#name=(new_name).

    Learn more

  • Associations between objects defined by simple class methods.

    class Firm < ActiveRecord::Base
  has_many   :clients
  has_one    :account
  belongs_to :conglomerate
end

    Learn more

  • Aggregations of value objects.

    class Account < ActiveRecord::Base
  composed_of :balance, class_name: 'Money',
              mapping: %w(balance amount)
  composed_of :address,
              mapping: [%w(address_street street), %w(address_city city)]
end

    Learn more

  • Validation rules that can differ for new or existing objects.

    class Account < ActiveRecord::Base
  validates :subdomain, :name, :email_address, :password, presence: true
  validates :subdomain, uniqueness: true
  validates :terms_of_service, acceptance: true, on: :create
  validates :password, :email_address, confirmation: true, on: :create
end

    Learn more

  • Callbacks available for the entire life cycle (instantiation, saving, destroying, validating, etc.).

    class Person < ActiveRecord::Base
  before_destroy :invalidate_payment_plan
  # the `invalidate_payment_plan` method gets called just before Person#destroy
end

    Learn more

  • Inheritance hierarchies.

    class Company < ActiveRecord::Base; end
class Firm < Company; end
class Client < Company; end
class PriorityClient < Client; end

    Learn more

  • Transactions.

    # Database transaction
Account.transaction do
  david.withdrawal(100)
  mary.deposit(100)
end

    Learn more

  • Reflections on columns, associations, and aggregations.

    reflection = Firm.reflect_on_association(:clients)
reflection.klass # => Client (class)
Firm.columns # Returns an array of column descriptors for the firms table

    Learn more

  • Database abstraction through simple adapters.

    # connect to SQLite3
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: 'dbfile.sqlite3')

# connect to MySQL with authentication
ActiveRecord::Base.establish_connection(
  adapter:  'mysql2',
  host:     'localhost',
  username: 'me',
  password: 'secret',
  database: 'activerecord'
)

    Learn more and read about the built-in support for MySQL, PostgreSQL, and SQLite3.

  • Logging support for Log4r and Logger.

    ActiveRecord::Base.logger = ActiveSupport::Logger.new(STDOUT)
ActiveRecord::Base.logger = Log4r::Logger.new('Application Log')

  • Database agnostic schema management with Migrations.

    class AddSystemSettings < ActiveRecord::Migration[7.2]
  def up
    create_table :system_settings do |t|
      t.string  :name
      t.string  :label
      t.text    :value
      t.string  :type
      t.integer :position
    end

    SystemSetting.create name: 'notice', label: 'Use notice?', value: 1
  end

  def down
    drop_table :system_settings
  end
end

    Learn more

Philosophy

Active Record is an implementation of the object-relational mapping (ORM) pattern by the same name described by Martin Fowler:

“An object that wraps a row in a database table or view, encapsulates the database access, and adds domain logic on that data.”

Active Record attempts to provide a coherent wrapper as a solution for the inconvenience that is object-relational mapping. The prime directive for this mapping has been to minimize the amount of code needed to build a real-world domain model. This is made possible by relying on a number of conventions that make it easy for Active Record to infer complex relations and structures from a minimal amount of explicit direction.

Convention over Configuration:

  • No XML files!

  • Lots of reflection and run-time extension

  • Magic is not inherently a bad word

Admit the Database:

  • Lets you drop down to SQL for odd cases and performance

  • Doesn’t attempt to duplicate or replace data definitions

Download and installation

The latest version of Active Record can be installed with RubyGems:

$ gem install activerecord

Source code can be downloaded as part of the Rails project on GitHub:

License

Active Record is released under the MIT license:

Support

API documentation is at:

Bug reports for the Ruby on Rails project can be filed here:

Feature requests should be discussed on the rails-core mailing list here:

Constants

MigrationProxy

MigrationProxy is used to defer loading of the actual migration classes until they are needed

Struct.new(:name, :version, :filename, :scope) do
def initialize(name, version, filename, scope)
super
@migration = nil
end

def basename
File.basename(filename)
end

delegate :migrate, :announce, :write, :disable_ddl_transaction, to: :migration

private
def migration
@migration ||= load_migration
end

def load_migration
Object.send(:remove_const, name) rescue nil

load(File.expand_path(filename))
name.constantize.new(name, version)
end
end

UnknownAttributeError

Active Model UnknownAttributeError

Raised when unknown attributes are supplied via mass assignment.

class Person
  include ActiveModel::AttributeAssignment
  include ActiveModel::Validations
end

person = Person.new
person.assign_attributes(name: 'Gorby')
# => ActiveModel::UnknownAttributeError: unknown attribute 'name' for Person.

ActiveModel::UnknownAttributeError

Attributes

[RW] application_record_class
[RW] before_committed_on_all_records
[RW] belongs_to_required_validates_foreign_key
[R] default_timezone
[RW] disable_prepared_statements
[RW] index_nested_attribute_errors
[RW] maintain_test_schema
[RW] query_transformers
[RW] raise_on_assign_to_attr_readonly
[RW] reading_role
[RW] run_after_transaction_callbacks_in_order_defined
[RW] writing_role

Public class methods

action_on_strict_loading_violation

Set the application to log or raise when an association violates strict loading. Defaults to :raise.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 366
singleton_class.attr_accessor :action_on_strict_loading_violation

allow_deprecated_singular_associations_name()

Source code GitHub 
# File activerecord/lib/active_record.rb, line 436
  def self.allow_deprecated_singular_associations_name
    ActiveRecord.deprecator.warn <<-WARNING.squish
      `Rails.application.config.active_record.allow_deprecated_singular_associations_name`
      is deprecated and will be removed in Rails 7.3.
    WARNING
  end

allow_deprecated_singular_associations_name=(value)

Source code GitHub 
# File activerecord/lib/active_record.rb, line 443
  def self.allow_deprecated_singular_associations_name=(value)
    ActiveRecord.deprecator.warn <<-WARNING.squish
      `Rails.application.config.active_record.allow_deprecated_singular_associations_name`
      is deprecated and will be removed in Rails 7.3.
    WARNING
  end

async_query_executor

Sets the async_query_executor for an application. By default the thread pool executor set to nil which will not run queries in the background. Applications must configure a thread pool executor to use this feature. Options are:

* nil - Does not initialize a thread pool executor. Any async calls will be
run in the foreground.
* :global_thread_pool - Initializes a single +Concurrent::ThreadPoolExecutor+
that uses the +async_query_concurrency+ for the +max_threads+ value.
* :multi_thread_pool - Initializes a +Concurrent::ThreadPoolExecutor+ for each
database connection. The initializer values are defined in the configuration hash.
Source code GitHub 
# File activerecord/lib/active_record.rb, line 276
singleton_class.attr_accessor :async_query_executor

commit_transaction_on_non_local_return()

Source code GitHub 
# File activerecord/lib/active_record.rb, line 336
  def self.commit_transaction_on_non_local_return
    ActiveRecord.deprecator.warn <<-WARNING.squish
      `Rails.application.config.active_record.commit_transaction_on_non_local_return`
      is deprecated and will be removed in Rails 7.3.
    WARNING
  end

commit_transaction_on_non_local_return=(value)

Source code GitHub 
# File activerecord/lib/active_record.rb, line 343
  def self.commit_transaction_on_non_local_return=(value)
    ActiveRecord.deprecator.warn <<-WARNING.squish
      `Rails.application.config.active_record.commit_transaction_on_non_local_return`
      is deprecated and will be removed in Rails 7.3.
    WARNING
  end

db_warnings_action

The action to take when database query produces warning. Must be one of :ignore, :log, :raise, :report, or a custom proc. The default is :ignore.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 218
singleton_class.attr_reader :db_warnings_action

db_warnings_action=(action)

Source code GitHub 
# File activerecord/lib/active_record.rb, line 220
def self.db_warnings_action=(action)
  @db_warnings_action =
    case action
    when :ignore
      nil
    when :log
      ->(warning) do
        warning_message = "[#{warning.class}] #{warning.message}"
        warning_message += " (#{warning.code})" if warning.code
        ActiveRecord::Base.logger.warn(warning_message)
      end
    when :raise
      ->(warning) { raise warning }
    when :report
      ->(warning) { Rails.error.report(warning, handled: true) }
    when Proc
      action
    else
      raise ArgumentError, "db_warnings_action must be one of :ignore, :log, :raise, :report, or a custom proc."
    end
end

db_warnings_ignore

Specify allowlist of database warnings.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 247
singleton_class.attr_accessor :db_warnings_ignore

default_timezone=(default_timezone)

Determines whether to use Time.utc (using :utc) or Time.local (using :local) when pulling dates and times from the database. This is set to :utc by default.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 203
def self.default_timezone=(default_timezone)
  unless %i(local utc).include?(default_timezone)
    raise ArgumentError, "default_timezone must be either :utc (default) or :local."
  end

  @default_timezone = default_timezone
end

disconnect_all!()

Explicitly closes all database connections in all pools.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 529
def self.disconnect_all!
  ConnectionAdapters::PoolConfig.disconnect_all!
end

dump_schema_after_migration

Specify whether schema dump should happen at the end of the bin/rails db:migrate command. This is true by default, which is useful for the development environment. This should ideally be false in the production environment where dumping schema is rarely needed.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 414
singleton_class.attr_accessor :dump_schema_after_migration

dump_schemas

Specifies which database schemas to dump when calling db:schema:dump. If the value is :schema_search_path (the default), any schemas listed in schema_search_path are dumped. Use :all to dump all schemas regardless of schema_search_path, or a string of comma separated schemas for a custom list.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 424
singleton_class.attr_accessor :dump_schemas

eager_load!()

Source code GitHub 
# File activerecord/lib/active_record.rb, line 518
def self.eager_load!
  super
  ActiveRecord::Locking.eager_load!
  ActiveRecord::Scoping.eager_load!
  ActiveRecord::Associations.eager_load!
  ActiveRecord::AttributeMethods.eager_load!
  ActiveRecord::ConnectionAdapters.eager_load!
  ActiveRecord::Encryption.eager_load!
end

error_on_ignored_order

Specifies if an error should be raised if the query has an order being ignored when doing batch queries. Useful in applications where the scope being ignored is error-worthy, rather than a warning.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 385
singleton_class.attr_accessor :error_on_ignored_order

gem_version()

Returns the currently loaded version of Active Record as a Gem::Version.

Source code GitHub 
# File activerecord/lib/active_record/gem_version.rb, line 5
def self.gem_version
  Gem::Version.new VERSION::STRING
end

generate_secure_token_on

Controls when to generate a value for has_secure_token declarations. Defaults to :create.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 479
singleton_class.attr_accessor :generate_secure_token_on

global_executor_concurrency=(global_executor_concurrency)

Set the global_executor_concurrency. This configuration value can only be used with the global thread pool async query executor.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 291
def self.global_executor_concurrency=(global_executor_concurrency)
  if self.async_query_executor.nil? || self.async_query_executor == :multi_thread_pool
    raise ArgumentError, "`global_executor_concurrency` cannot be set when using the executor is nil or set to multi_thead_pool. For multiple thread pools, please set the concurrency in your database configuration."
  end

  @global_executor_concurrency = global_executor_concurrency
end

lazily_load_schema_cache

Lazily load the schema cache. This option will load the schema cache when a connection is established rather than on boot. If set, config.active_record.use_schema_cache_dump will be set to false.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 188
singleton_class.attr_accessor :lazily_load_schema_cache

legacy_connection_handling=(_)

Source code GitHub 
# File activerecord/lib/active_record.rb, line 256
  def self.legacy_connection_handling=(_)
    raise ArgumentError, <<~MSG.squish
      The `legacy_connection_handling` setter was deprecated in 7.0 and removed in 7.1,
      but is still defined in your configuration. Please remove this call as it no longer
      has any effect."
    MSG
  end

marshalling_format_version()

Source code GitHub 
# File activerecord/lib/active_record.rb, line 482
def self.marshalling_format_version
  Marshalling.format_version
end

marshalling_format_version=(value)

Source code GitHub 
# File activerecord/lib/active_record.rb, line 486
def self.marshalling_format_version=(value)
  Marshalling.format_version = value
end

migration_strategy

Specify strategy to use for executing migrations.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 405
singleton_class.attr_accessor :migration_strategy

protocol_adapters

Provides a mapping between database protocols/DBMSs and the underlying database adapter to be used. This is used only by the DATABASE_URL environment variable.

Example

DATABASE_URL="mysql://myuser:mypass@localhost/somedatabase"

The above URL specifies that MySQL is the desired protocol/DBMS, and the application configuration can then decide which adapter to use. For this example the default mapping is from mysql to mysql2, but :trilogy is also supported.

ActiveRecord.protocol_adapters.mysql = "mysql2"

The protocols names are arbitrary, and external database adapters can be registered and set here.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 509
singleton_class.attr_accessor :protocol_adapters

queues

Specifies the names of the queues used by background jobs.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 318
singleton_class.attr_accessor :queues

raise_int_wider_than_64bit

Application configurable boolean that denotes whether or not to raise an exception when the PostgreSQLAdapter is provided with an integer that is wider than signed 64bit representation

Source code GitHub 
# File activerecord/lib/active_record.rb, line 465
singleton_class.attr_accessor :raise_int_wider_than_64bit

schema_cache_ignored_tables

A list of tables or regex’s to match tables to ignore when dumping the schema cache. For example if this is set to +[/^_/]+ the schema cache will not dump tables named with an underscore.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 196
singleton_class.attr_accessor :schema_cache_ignored_tables

schema_format

Specifies the format to use when dumping the database schema with Rails’ Rakefile. If :sql, the schema is dumped as (potentially database- specific) SQL statements. If :ruby, the schema is dumped as an ActiveRecord::Schema file which can be loaded into any database that supports migrations. Use :ruby if you want to have different database adapters for, e.g., your development and test environments.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 377
singleton_class.attr_accessor :schema_format

timestamped_migrations

Specify whether or not to use timestamps for migration versions

Source code GitHub 
# File activerecord/lib/active_record.rb, line 391
singleton_class.attr_accessor :timestamped_migrations

use_yaml_unsafe_load

Application configurable boolean that instructs the YAML Coder to use an unsafe load if set to true.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 457
singleton_class.attr_accessor :use_yaml_unsafe_load

validate_migration_timestamps

Specify whether or not to validate migration timestamps. When set, an error will be raised if a timestamp is more than a day ahead of the timestamp associated with the current time. timestamped_migrations must be set to true.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 399
singleton_class.attr_accessor :validate_migration_timestamps

verbose_query_logs

Specifies if the methods calling database queries should be logged below their relevant queries. Defaults to false.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 311
singleton_class.attr_accessor :verbose_query_logs

verify_foreign_keys_for_fixtures

If true, Rails will verify all foreign keys in the database after loading fixtures. An error will be raised if there are any foreign key violations, indicating incorrectly written fixtures. Supported by PostgreSQL and SQLite.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 433
singleton_class.attr_accessor :verify_foreign_keys_for_fixtures

version()

Returns the currently loaded version of Active Record as a Gem::Version.

Source code GitHub 
# File activerecord/lib/active_record/version.rb, line 7
def self.version
  gem_version
end

warn_on_records_fetched_greater_than

Specify a threshold for the size of query result sets. If the number of records in the set exceeds the threshold, a warning is logged. This can be used to identify queries which load thousands of records and potentially cause memory bloat.

Source code GitHub 
# File activerecord/lib/active_record.rb, line 356
singleton_class.attr_accessor :warn_on_records_fetched_greater_than

yaml_column_permitted_classes

Application configurable array that provides additional permitted classes to Psych safe_load in the YAML Coder

Source code GitHub 
# File activerecord/lib/active_record.rb, line 472
singleton_class.attr_accessor :yaml_column_permitted_classes

Namespace

Definition files

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