README.rdoc

Path: README.rdoc
Last Update: Sun Feb 19 03:00:18 +0000 2012

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 (c) 2011 Matthew Higgins, released under the MIT license

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