using UUID as primary key in rails and polymorph relationships

I'm creating a rails 3 application that will be decentralized and I need to use UUID as primary key for my tables, what would be the best gem, plugin for the Job. I also would like to know if it is possible to make in ActiveRecord polymorphic relationships without using the polymorphicable_type column for it, given the case that I'm using UUID.

I have created a demo开发者_如何学Go http://github.com/boriscy/uuidrails3 that uses UUID as keys, you should check the module UUIDHelper inside lib/ and also all the migrations. There is no need to add a primary key in the database, just an index, because primary keys verify uniqueness of the field, but we don't need that with UUID.

Put this file in the lib directory, and add this as an initializer:

class ActiveRecord::Base
  set_primary_key :uuid

  before_create :set_uuid

  def set_uuid
    self.uuid = UUID.generate(:compact)
  end
end

As for the relationships, vlad is right that ActiveRecord needs to know which table a record is in to find it. If you want this kind of functionality, try something else like MongoMapper.