get a single model instance by handle

        :param model: model
        :param handle: instance handle
        :return:

def get(self, model, **spec):
        """get a single model instance by handle

        :param model: model
        :param handle: instance handle
        :return:
        """

        handles = self.__find_handles(model, **spec)
        if len(handles) > 1:
            raise MultipleObjectsReturned()
        if not handles:
            raise ObjectDoesNotExist()
        return self.get_instance(model, handles[0])