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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)


Add the following to your Gemfile: ruby gem 'foreigner'

API Examples

Foreigner adds two methods to migrations.

  • add_foreign_key(from_table, to_table, options)
  • remove_foreign_key(from_table, to_table, options)

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

For example, given the following model: ```ruby 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: ruby add_foreign_key(:comments, :posts) The `:dependent` option can be moved from the `has_many` definition to the foreign key: ruby add_foreign_key(:comments, :posts, dependent: :delete) If the column is named `article_id` instead of `post_id`, use the `:column` option: ruby add_foreign_key(:comments, :posts, column: 'article_id') A name can be specified for the foreign key constraint: ruby add_foreign_key(:comments, :posts, name: 'comment_article_foreign_key') The `:column` and `:name` options create a foreign key with a custom name. In order to remove it you need to specify `:name`: ruby remove_foreign_key(:comments, name: 'comment_article_foreign_key') ```

Change Table Methods

Foreigner adds extra methods to create_table and change_table.

Create a new table with a foreign key: ruby create_table :products do |t| t.string :name t.integer :factory_id t.foreign_key :factories end Add a missing foreign key to comments: ruby change_table :comments do |t| t.foreign_key :posts, dependent: :delete end Remove an unwanted foreign key: ruby change_table :comments do |t| t.remove_foreign_key :users end

Database-specific options

Database-specific options will never be supported by foreigner. You can add them using :options: ruby add_foreign_key(:comments, :posts, options: 'ON UPDATE DEFERRED')

Foreigner Add-ons


Copyright (c) 2012 Matthew Higgins, released under the MIT license