Foreigner¶ ↑

Foreigner introduces a few methods to your migrations for adding and removing foreign key constraints. It also dumps foreign keys to schema.rb.

The following adapters are supported:

• mysql2

• postgres

• sqlite (foreign key methods are a no-op)

Installation¶ ↑

Add the following to your Gemfile:

gem 'foreigner'

API Examples¶ ↑

Foreigner adds two methods to migrations.

• add_foreign_key(from_table, to_table, options)

• remove_foreign_key(from_table, options)

(Options are documented in connection_adapters/abstract/schema_definitions.rb):

For example, given the following model:

class Comment < ActiveRecord::Base
  belongs_to :post
end

class Post < ActiveRecord::Base
  has_many :comments, :dependent => :delete_all
end

You should add a foreign key in your migration:

add_foreign_key(:comments, :posts)

The :dependent option can be moved from the has_many definition to the foreign key:

add_foreign_key(:comments, :posts, :dependent => :delete)

If the column is named article_id instead of post_id, use the :column option:

add_foreign_key(:comments, :posts, :column => 'article_id')

A name can be specified for the foreign key constraint:

add_foreign_key(:comments, :posts, :name => 'comment_article_foreign_key')

Change Table Methods¶ ↑

Foreigner adds extra methods to change_table.

Add a missing foreign key to comments:

change_table :comments do |t|
  t.foreign_key :posts, :dependent => :delete
end

Remove an unwanted foreign key:

change_table :comments do |t|
  t.remove_foreign_key :users
end

Additional t.references option for change_table¶ ↑

Foreigner extends table.references with the :foreign_key option. Pass true, and the default foreign key options are used:

change_table :comments do |t|
  t.references :post, :foreign_key => true
end

An options hash can also be passed. It accepts the same options as add_foreign_key:

change_table :comments do |t|
  t.references :author, :foreign_key => {:dependent => :restrict}
end

By default, t.references will not generate a foreign key.

License¶ ↑

Copyright © 2011 Matthew Higgins, released under the MIT license