UUID primary keys in Rails 3

Gemfile

# Gemfile
…
gem 'uuidtools' 
…

migrations.rb

# db/migrate/20110422210841_create_sites.rb
# 1.  :id => false
# 2.  :uuid 
#
class CreateSites < ActiveRecord::Migration
  def self.up
    create_table(:sites, :id => false) do |t|
      t.string :uuid, :limit => 36, :primary => true
      t.timestamps
    end
  end

  def self.down
    drop_table :sites
  end
end

site.rb

# app/models/site.rb
class Site < ActiveRecord::Base
  include Extensions::UUID
end

uuid.rb

# app/models/extensions/uuid.rb
#
module Extensions
  module UUID
    extend ActiveSupport::Concern

    included do
      # old rails versions 
      set_primary_key 'uuid'
      # later rails versions, untested:
      # self.primary_key = 'the_name'

      before_create :generate_uuid
      
      def generate_uuid
        self.id = UUIDTools::UUID.random_create.to_s
      end
    end
  end
end

For Rails 3.1+ check ActiveUUID