instance method
add_foreign_key
Ruby on Rails 7.0.10
Since v4.2.9Signature
add_foreign_key(from_table, to_table, **options)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 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 toto_table.singularize + "_id" :primary_key-
The primary key column name on
to_table. Defaults toid. :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
:deferredor:immediateto specify the default behavior. Defaults tofalse.
Parameters
-
from_tablereq -
to_tablereq -
optionskeyrest
Source
# File activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb, line 1084
def add_foreign_key(from_table, to_table, **options)
return unless supports_foreign_keys?
return if options[:if_not_exists] == true && foreign_key_exists?(from_table, to_table)
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
Defined in activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb line 1084
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Defined in ActiveRecord::ConnectionAdapters::SchemaStatements