Support for foreign key constraint in Rails

In Ruby on Rails, how to add foreign key constraint in migration?

From stackoverflow

• AFAIK, there isn't any built-in support for that, but there are several plugins that help you with that. You can also add them manually to your migration files, just use the execute method for that, e.g. (sample from Rails API):

    class MakeJoinUnique < ActiveRecord::Migration
      def self.up
        execute "ALTER TABLE `pages_linked_pages` ADD UNIQUE `page_id_linked_page_id` (`page_id`,`linked_page_id`)"
      end
  
      def self.down
        execute "ALTER TABLE `pages_linked_pages` DROP INDEX `page_id_linked_page_id`"
      end
    end
  

• http://blog.hasmanythrough.com/2007/1/15/basic-rails-association-cardinality

• Here's a gem-based solution that includes support for adding and removing foreign key constraints, doesn't fail with sqlite, and works correctly with schema.rb files:

  http://github.com/matthuhiggins/foreigner

• This is an update to the matthuhiggins-foreigner gem: http://github.com/sparkfly/foreigner

  Features:

  • rspec coverage, tested against PostgreSQL 8.3.9 and MySQL 5.0.90
  • Migration support
  • schema.rb support

  Future versions will include CHECK constraints for PostgreSQL, which is needed to implement multi-table inheritance.