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

License

Copyright © 2011 Matthew Higgins, released under the MIT license