Flowdock
method

add_foreign_key

Importance_3
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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 articles_author_id_fk FOREIGN KEY ("author_id") REFERENCES "authors" ("id")
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 articles_author_id_fk 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"

:primary_key

The primary key column name on to_table. Defaults to id.

: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

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

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