app/models/user_has_role.rb
class UserHasRole < ActiveRecord::Base
attr_accessible :user_id, :role_id
attr_accessible :user_id, :role_id, :as => :admin
belongs_to :user
belongs_to :role
validates_uniqueness_of :role_id, :scope => :user_id
validates_presence_of :role_id, :user_id
end
# == Schema Information
#
# Table name: user_has_roles
#
# id :integer not null, primary key
# user_id :integer
# role_id :integer
# created_at :datetime
# updated_at :datetime
#