module

ActiveRecord

Ruby on Rails latest stable (v7.1.3.2) - 1 note

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).

ActiveRecord::Base

Associations between objects defined by simple class methods.

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

ActiveRecord::Associations::ClassMethods

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

ActiveRecord::Aggregations::ClassMethods

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

ActiveRecord::Validations

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

ActiveRecord::Callbacks

Inheritance hierarchies.

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

ActiveRecord::Base

Transactions.

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

ActiveRecord::Transactions::ClassMethods

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

ActiveRecord::Reflection::ClassMethods

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' )

ActiveRecord::Base and read about the built-in support for ActiveRecord::ConnectionAdapters::Mysql2Adapter ActiveRecord::ConnectionAdapters::PostgreSQLAdapter and ActiveRecord::ConnectionAdapters::SQLite3Adapter.

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[7.1] 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

ActiveRecord::Migration

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:

github.com/rails/rails/tree/main/activerecord

License

Active Record is released under the MIT license:

opensource.org/licenses/MIT

Support

API documentation is at:

api.rubyonrails.org

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

github.com/rails/rails/issues

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

discuss.rubyonrails.org/c/rubyonrails-core

frozen_string_literal: true

Constants

ORIGINAL_ATTRIBUTE_PREFIX = "original_"

UnknownAttributeError = ActiveModel::UnknownAttributeError

DeprecatedActiveJobRequiredError = Class.new(ActiveRecordError)

MigrationProxy = 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

Point = Struct.new(:x, :y)

Attributes

[RW]	reading_role
[RW]	writing_role
[RW]	db_warnings_ignore
[R]	db_warnings_action
[R]	default_timezone
[RW]	schema_cache_ignored_tables
[RW]	lazily_load_schema_cache
[RW]	disable_prepared_statements

Show files where this module is defined (297 files)

activerecord/examples/performance.rb activerecord/lib/active_record/serialization.rb activerecord/lib/active_record/disable_joins_association_relation.rb activerecord/lib/active_record/inheritance.rb activerecord/lib/active_record/associations/preloader.rb activerecord/lib/active_record/associations/association_scope.rb activerecord/lib/active_record/associations/preloader/branch.rb activerecord/lib/active_record/associations/preloader/batch.rb activerecord/lib/active_record/associations/preloader/through_association.rb activerecord/lib/active_record/associations/disable_joins_association_scope.rb activerecord/lib/active_record/associations/collection_proxy.rb activerecord/lib/active_record/associations/belongs_to_polymorphic_association.rb activerecord/lib/active_record/associations/alias_tracker.rb activerecord/lib/active_record/associations/has_one_through_association.rb activerecord/lib/active_record/associations/join_dependency/join_base.rb activerecord/lib/active_record/associations/join_dependency/join_association.rb activerecord/lib/active_record/associations/join_dependency/join_part.rb activerecord/lib/active_record/timestamp.rb activerecord/lib/active_record/encryption/cipher/aes256_gcm.rb activerecord/lib/active_record/encryption/key_provider.rb activerecord/lib/active_record/encryption/scheme.rb activerecord/lib/active_record/encryption/key_generator.rb activerecord/lib/active_record/encryption/config.rb activerecord/lib/active_record/encryption/derived_secret_key_provider.rb activerecord/lib/active_record/encryption/key.rb activerecord/lib/active_record/encryption/auto_filtered_parameters.rb activerecord/lib/active_record/encryption/encryptor.rb activerecord/lib/active_record/encryption/contexts.rb activerecord/lib/active_record/encryption/errors.rb activerecord/lib/active_record/encryption/envelope_encryption_key_provider.rb activerecord/lib/active_record/encryption/null_encryptor.rb activerecord/lib/active_record/encryption/encrypted_attribute_type.rb activerecord/lib/active_record/encryption/context.rb activerecord/lib/active_record/encryption/cipher.rb activerecord/lib/active_record/encryption/read_only_null_encryptor.rb activerecord/lib/active_record/encryption/encrypted_fixtures.rb activerecord/lib/active_record/encryption/properties.rb activerecord/lib/active_record/encryption/message_serializer.rb activerecord/lib/active_record/encryption/deterministic_key_provider.rb activerecord/lib/active_record/encryption/extended_deterministic_queries.rb activerecord/lib/active_record/encryption/encrypting_only_encryptor.rb activerecord/lib/active_record/encryption/configurable.rb activerecord/lib/active_record/encryption/extended_deterministic_uniqueness_validator.rb activerecord/lib/active_record/encryption/encryptable_record.rb activerecord/lib/active_record/encryption/message.rb activerecord/lib/active_record/runtime_registry.rb activerecord/lib/active_record/delegated_type.rb activerecord/lib/active_record/fixture_set/table_row.rb activerecord/lib/active_record/fixture_set/model_metadata.rb activerecord/lib/active_record/fixture_set/table_rows.rb activerecord/lib/active_record/fixture_set/file.rb activerecord/lib/active_record/railtie.rb activerecord/lib/active_record/explain.rb activerecord/lib/active_record/test_databases.rb activerecord/lib/active_record/statement_cache.rb activerecord/lib/active_record/sanitization.rb activerecord/lib/active_record/explain_registry.rb activerecord/lib/active_record/scoping/default.rb activerecord/lib/active_record/scoping/named.rb activerecord/lib/active_record/query_logs_formatter.rb activerecord/lib/active_record/coders/json.rb activerecord/lib/active_record/coders/yaml_column.rb activerecord/lib/active_record/coders/column_serializer.rb activerecord/lib/active_record/association_relation.rb activerecord/lib/active_record/attribute_assignment.rb activerecord/lib/active_record/secure_password.rb activerecord/lib/active_record/associations.rb activerecord/lib/active_record/scoping.rb activerecord/lib/active_record/type/time.rb activerecord/lib/active_record/type/internal/timezone.rb activerecord/lib/active_record/type/text.rb activerecord/lib/active_record/type/date_time.rb activerecord/lib/active_record/type/serialized.rb activerecord/lib/active_record/type/json.rb activerecord/lib/active_record/type/decimal_without_scale.rb activerecord/lib/active_record/type/unsigned_integer.rb activerecord/lib/active_record/type/hash_lookup_type_map.rb activerecord/lib/active_record/type/adapter_specific_registry.rb activerecord/lib/active_record/type/date.rb activerecord/lib/active_record/type/type_map.rb activerecord/lib/active_record/transactions.rb activerecord/lib/active_record/destroy_association_async_job.rb activerecord/lib/active_record/tasks/sqlite_database_tasks.rb activerecord/lib/active_record/tasks/mysql_database_tasks.rb activerecord/lib/active_record/tasks/postgresql_database_tasks.rb activerecord/lib/active_record/tasks/database_tasks.rb activerecord/lib/active_record/attribute_methods/serialization.rb activerecord/lib/active_record/attribute_methods/before_type_cast.rb activerecord/lib/active_record/attribute_methods/primary_key.rb activerecord/lib/active_record/attribute_methods/write.rb activerecord/lib/active_record/attribute_methods/time_zone_conversion.rb activerecord/lib/active_record/attribute_methods/dirty.rb activerecord/lib/active_record/attribute_methods/query.rb activerecord/lib/active_record/attribute_methods/read.rb activerecord/lib/active_record/explain_subscriber.rb activerecord/lib/active_record/deprecator.rb activerecord/lib/active_record/legacy_yaml_adapter.rb activerecord/lib/active_record/integration.rb activerecord/lib/active_record/normalization.rb activerecord/lib/active_record/signed_id.rb activerecord/lib/active_record/gem_version.rb activerecord/lib/active_record/persistence.rb activerecord/lib/active_record/railties/job_runtime.rb activerecord/lib/active_record/railties/controller_runtime.rb activerecord/lib/active_record/asynchronous_queries_tracker.rb activerecord/lib/active_record/schema_migration.rb activerecord/lib/active_record/table_metadata.rb activerecord/lib/active_record/enum.rb activerecord/lib/active_record/counter_cache.rb activerecord/lib/active_record/type.rb activerecord/lib/active_record/promise.rb activerecord/lib/active_record/relation/delegation.rb activerecord/lib/active_record/relation/predicate_builder.rb activerecord/lib/active_record/relation/merger.rb activerecord/lib/active_record/relation/calculations.rb activerecord/lib/active_record/relation/predicate_builder/relation_handler.rb activerecord/lib/active_record/relation/predicate_builder/association_query_value.rb activerecord/lib/active_record/relation/predicate_builder/basic_object_handler.rb activerecord/lib/active_record/relation/predicate_builder/range_handler.rb activerecord/lib/active_record/relation/predicate_builder/array_handler.rb activerecord/lib/active_record/relation/predicate_builder/polymorphic_array_value.rb activerecord/lib/active_record/relation/batches/batch_enumerator.rb activerecord/lib/active_record/relation/where_clause.rb activerecord/lib/active_record/relation/finder_methods.rb activerecord/lib/active_record/relation/query_methods.rb activerecord/lib/active_record/relation/spawn_methods.rb activerecord/lib/active_record/relation/batches.rb activerecord/lib/active_record/relation/from_clause.rb activerecord/lib/active_record/relation/query_attribute.rb activerecord/lib/active_record/relation/record_fetch_warning.rb activerecord/lib/active_record/errors.rb activerecord/lib/active_record/validations/presence.rb activerecord/lib/active_record/validations/absence.rb activerecord/lib/active_record/validations/associated.rb activerecord/lib/active_record/validations/numericality.rb activerecord/lib/active_record/validations/uniqueness.rb activerecord/lib/active_record/validations/length.rb activerecord/lib/active_record/reflection.rb activerecord/lib/active_record/touch_later.rb activerecord/lib/active_record/database_configurations/hash_config.rb activerecord/lib/active_record/database_configurations/database_config.rb activerecord/lib/active_record/database_configurations/url_config.rb activerecord/lib/active_record/database_configurations/connection_url_resolver.rb activerecord/lib/active_record/model_schema.rb activerecord/lib/active_record/querying.rb activerecord/lib/active_record/translation.rb activerecord/lib/active_record/base.rb activerecord/lib/active_record/store.rb activerecord/lib/active_record/version.rb activerecord/lib/active_record/encryption.rb activerecord/lib/active_record/type_caster.rb activerecord/lib/active_record/attributes.rb activerecord/lib/active_record/connection_adapters.rb activerecord/lib/active_record/token_for.rb activerecord/lib/active_record/callbacks.rb activerecord/lib/active_record/attribute_methods.rb activerecord/lib/active_record/nested_attributes.rb activerecord/lib/active_record/relation.rb activerecord/lib/active_record/schema.rb activerecord/lib/active_record/marshalling.rb activerecord/lib/active_record/validations.rb activerecord/lib/active_record/message_pack.rb activerecord/lib/active_record/migration/compatibility.rb activerecord/lib/active_record/migration/execution_strategy.rb activerecord/lib/active_record/migration/pending_migration_connection.rb activerecord/lib/active_record/migration/command_recorder.rb activerecord/lib/active_record/migration/join_table.rb activerecord/lib/active_record/migration/default_strategy.rb activerecord/lib/active_record/suppressor.rb activerecord/lib/active_record/insert_all.rb activerecord/lib/active_record/test_fixtures.rb activerecord/lib/active_record/dynamic_matchers.rb activerecord/lib/active_record/result.rb activerecord/lib/active_record/schema_dumper.rb activerecord/lib/active_record/connection_handling.rb activerecord/lib/active_record/query_logs.rb activerecord/lib/active_record/internal_metadata.rb activerecord/lib/active_record/fixtures.rb activerecord/lib/active_record/migration.rb activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb activerecord/lib/active_record/connection_adapters/schema_cache.rb activerecord/lib/active_record/connection_adapters/statement_pool.rb activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb activerecord/lib/active_record/connection_adapters/postgresql/schema_definitions.rb activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb activerecord/lib/active_record/connection_adapters/postgresql/database_statements.rb activerecord/lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb activerecord/lib/active_record/connection_adapters/postgresql/column.rb activerecord/lib/active_record/connection_adapters/postgresql/oid.rb activerecord/lib/active_record/connection_adapters/postgresql/type_metadata.rb activerecord/lib/active_record/connection_adapters/postgresql/schema_dumper.rb activerecord/lib/active_record/connection_adapters/postgresql/utils.rb activerecord/lib/active_record/connection_adapters/postgresql/schema_creation.rb activerecord/lib/active_record/connection_adapters/postgresql/quoting.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/bit_varying.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/timestamp.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/cidr.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/date_time.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/interval.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/inet.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/uuid.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/range.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/hstore.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/money.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/vector.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/legacy_point.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/enum.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/bytea.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/xml.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/timestamp_with_time_zone.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/point.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/oid.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/decimal.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/type_map_initializer.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/array.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/jsonb.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/bit.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/date.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/macaddr.rb activerecord/lib/active_record/connection_adapters/postgresql/oid/specialized_string.rb activerecord/lib/active_record/connection_adapters/postgresql/referential_integrity.rb activerecord/lib/active_record/connection_adapters/mysql2/database_statements.rb activerecord/lib/active_record/connection_adapters/pool_manager.rb activerecord/lib/active_record/connection_adapters/deduplicable.rb activerecord/lib/active_record/connection_adapters/trilogy_adapter.rb activerecord/lib/active_record/connection_adapters/column.rb activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb activerecord/lib/active_record/connection_adapters/trilogy/database_statements.rb activerecord/lib/active_record/connection_adapters/sql_type_metadata.rb activerecord/lib/active_record/connection_adapters/sqlite3/schema_definitions.rb activerecord/lib/active_record/connection_adapters/sqlite3/schema_statements.rb activerecord/lib/active_record/connection_adapters/sqlite3/database_statements.rb activerecord/lib/active_record/connection_adapters/sqlite3/explain_pretty_printer.rb activerecord/lib/active_record/connection_adapters/sqlite3/column.rb activerecord/lib/active_record/connection_adapters/sqlite3/schema_dumper.rb activerecord/lib/active_record/connection_adapters/sqlite3/schema_creation.rb activerecord/lib/active_record/connection_adapters/sqlite3/quoting.rb activerecord/lib/active_record/connection_adapters/abstract/connection_pool/reaper.rb activerecord/lib/active_record/connection_adapters/abstract/connection_pool/queue.rb activerecord/lib/active_record/connection_adapters/abstract/schema_definitions.rb activerecord/lib/active_record/connection_adapters/abstract/connection_pool.rb activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb activerecord/lib/active_record/connection_adapters/abstract/database_limits.rb activerecord/lib/active_record/connection_adapters/abstract/database_statements.rb activerecord/lib/active_record/connection_adapters/abstract/transaction.rb activerecord/lib/active_record/connection_adapters/abstract/schema_dumper.rb activerecord/lib/active_record/connection_adapters/abstract/connection_handler.rb activerecord/lib/active_record/connection_adapters/abstract/query_cache.rb activerecord/lib/active_record/connection_adapters/abstract/schema_creation.rb activerecord/lib/active_record/connection_adapters/abstract/savepoints.rb activerecord/lib/active_record/connection_adapters/abstract/quoting.rb activerecord/lib/active_record/connection_adapters/abstract_adapter.rb activerecord/lib/active_record/connection_adapters/pool_config.rb activerecord/lib/active_record/connection_adapters/mysql/schema_definitions.rb activerecord/lib/active_record/connection_adapters/mysql/schema_statements.rb activerecord/lib/active_record/connection_adapters/mysql/database_statements.rb activerecord/lib/active_record/connection_adapters/mysql/explain_pretty_printer.rb activerecord/lib/active_record/associations/join_dependency.rb activerecord/lib/active_record/associations/through_association.rb activerecord/lib/active_record/associations/association.rb activerecord/lib/active_record/associations/belongs_to_association.rb activerecord/lib/active_record/associations/has_many_association.rb activerecord/lib/active_record/associations/singular_association.rb activerecord/lib/active_record/associations/has_one_association.rb activerecord/lib/active_record/associations/collection_association.rb activerecord/lib/active_record/associations/has_many_through_association.rb activerecord/lib/active_record/connection_adapters/mysql/column.rb activerecord/lib/active_record/connection_adapters/mysql/type_metadata.rb activerecord/lib/active_record/connection_adapters/mysql/schema_dumper.rb activerecord/lib/active_record/connection_adapters/mysql/schema_creation.rb activerecord/lib/active_record/connection_adapters/mysql/quoting.rb activerecord/lib/active_record/query_cache.rb activerecord/lib/active_record/readonly_attributes.rb activerecord/lib/active_record/aggregations.rb activerecord/lib/active_record/autosave_association.rb activerecord/lib/active_record/secure_token.rb activerecord/lib/active_record/type_caster/map.rb activerecord/lib/active_record/type_caster/connection.rb activerecord/lib/active_record/no_touching.rb activerecord/lib/active_record/log_subscriber.rb activerecord/lib/active_record/future_result.rb activerecord/lib/active_record/database_configurations.rb activerecord/lib/active_record/core.rb activerecord/lib/active_record/middleware/database_selector/resolver/session.rb activerecord/lib/active_record/middleware/database_selector/resolver.rb activerecord/lib/active_record/middleware/database_selector.rb activerecord/lib/active_record/middleware/shard_selector.rb activerecord/lib/active_record/locking/optimistic.rb activerecord/lib/active_record/locking/pessimistic.rb activerecord/lib/rails/generators/active_record/multi_db/multi_db_generator.rb activerecord/lib/rails/generators/active_record/model/model_generator.rb activerecord/lib/rails/generators/active_record/migration/migration_generator.rb activerecord/lib/rails/generators/active_record/migration.rb activerecord/lib/rails/generators/active_record/application_record/application_record_generator.rb activerecord/lib/rails/generators/active_record.rb activerecord/lib/active_record.rb

April 3, 2009

13 thanks

The docs are in AR::Base

The docs you’re looking for are in ActiveRecord::Base