method

add_foreign_key

Ruby on Rails latest stable (v7.1.3.2) - 1 note - Class: ActiveRecord::ConnectionAdapters::SchemaStatements

1.0.0
1.1.6
1.2.6
2.0.3
2.1.0
2.2.1
2.3.8
3.0.0
3.0.9
3.1.0
3.2.1
3.2.8
3.2.13
4.0.2
4.1.8
4.2.1 (0)
4.2.7 (5)
4.2.9 (0)
5.0.0.1 (0)
5.1.7 (0)
5.2.3 (9)
6.0.0 (0)
6.1.3.1 (0)
6.1.7.7 (0)
7.0.0 (38)
7.1.3.2 (34)
7.1.3.4 (0)
What's this?

add_foreign_key(from_table, to_table, **options) public

Adds a new foreign key. from_table is the table with the key column, to_table contains the referenced primary key.

The foreign key will be named after the following pattern: fk_rails_<identifier>. identifier is a 10 character long string which is deterministically generated from the from_table and column. A custom name can be specified with the :name option.

Creating a simple foreign key

add_foreign_key :articles, :authors

generates:

ALTER TABLE "articles" ADD CONSTRAINT fk_rails_e74ce85cbc FOREIGN KEY ("author_id") REFERENCES "authors" ("id")

Creating a foreign key, ignoring method call if the foreign key exists

add_foreign_key(:articles, :authors, if_not_exists: true)

Creating a foreign key on a specific column

add_foreign_key :articles, :users, column: :author_id, primary_key: "lng_id"

generates:

ALTER TABLE "articles" ADD CONSTRAINT fk_rails_58ca3d3a82 FOREIGN KEY ("author_id") REFERENCES "users" ("lng_id")

Creating a composite foreign key

Assuming "carts" table has "(shop_id, user_id)" as a primary key.

add_foreign_key :orders, :carts, primary_key: [:shop_id, :user_id]

generates:

ALTER TABLE "orders" ADD CONSTRAINT fk_rails_6f5e4cb3a4 FOREIGN KEY ("cart_shop_id", "cart_user_id") REFERENCES "carts" ("shop_id", "user_id")

Creating a cascading foreign key

add_foreign_key :articles, :authors, on_delete: :cascade

generates:

ALTER TABLE "articles" ADD CONSTRAINT fk_rails_e74ce85cbc FOREIGN KEY ("author_id") REFERENCES "authors" ("id") ON DELETE CASCADE

The options hash can include the following keys:

:column: The foreign key column name on from_table. Defaults to to_table.singularize + "_id". Pass an array to create a composite foreign key.
:primary_key: The primary key column name on to_table. Defaults to id. Pass an array to create a composite foreign key.
:name: The constraint name. Defaults to fk_rails_<identifier>.
:on_delete: Action that happens ON DELETE. Valid values are :nullify, :cascade, and :restrict
:on_update: Action that happens ON UPDATE. Valid values are :nullify, :cascade, and :restrict
:if_not_exists: Specifies if the foreign key already exists to not try to re-add it. This will avoid duplicate column errors.
:validate: (PostgreSQL only) Specify whether or not the constraint should be validated. Defaults to true.
:deferrable: (PostgreSQL only) Specify whether or not the foreign key should be deferrable. Valid values are booleans or :deferred or :immediate to specify the default behavior. Defaults to false.

Show source

# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 1140
      def add_foreign_key(from_table, to_table, **options)
        return unless use_foreign_keys?
        return if options[:if_not_exists] == true && foreign_key_exists?(from_table, to_table, **options.slice(:column))

        options = foreign_key_options(from_table, to_table, options)
        at = create_alter_table from_table
        at.add_foreign_key to_table, options

        execute schema_creation.accept(at)
      end

March 17, 2016 - (>= v4.2.1)

0 thanks

Default values

By default :on_update and :on_delete have :restrict value.

add_foreign_key

Related methods

Creating a simple foreign key

Creating a foreign key, ignoring method call if the foreign key exists

Creating a foreign key on a specific column

Creating a composite foreign key

Creating a cascading foreign key

Default values