def association(name)
      if reflection = _scope.reflect_on_association(name)
        Association.new(self, reflection)
      else
        raise AssociationNotFoundError.new(_scope.model_name, name)
      end
    end
def association(name)
      if reflection = _scope.reflect_on_association(name)
        Association.new(self, reflection)
      else
        raise AssociationNotFoundError.new(_scope.model_name, name)
      end
    end
Constructs a new BabySqueel::Association. Raises
 an exception if the association is not found.