def changed?
      return false unless loaded?
      return true if added.length > 0
      return true if removed.length > 0
      false
    end
def changed?
      return false unless loaded?
      return true if added.length > 0
      return true if removed.length > 0
      false
    end
creates a new instance of an AssociationCollection
 Owner is the parent object, and association is the target