app/helpers/groupable.rb
module Groupable
def self.included(base)
base.validates_presence_of :group
base.validates_existence_of :group
base.validates_existence_of :creator, :allow_nil => true
base.belongs_to :group
base.belongs_to :creator, :class_name => "User"
base.attr_protected :group_id, :creator_id
end
end