Postgres UUID primary keys for your Rails 3 apps.

uuid_primary_key.rb

class UuidPrimaryKey < ActiveRecord::Migration
  def up
    execute 'CREATE EXTENSION IF NOT EXISTS "uuid-ossp";'

    create_table :your_table, :id => false do |t|
      # etc...    
      t.timestamps
    end

    execute 'ALTER TABLE your_table ADD COLUMN id uuid DEFAULT uuid_generate_v4() PRIMARY KEY;'
  end

  def down
    drop_table :your_table
  end
end