code: def retrieve(self, session, lookup_keys, *args, **kwargs):
          
          model = self._get_model(lookup_keys, session)
          return self.serialize_model(model)
docs: Retrieves a model using the lookup keys provided.
          Only one model should be returned by the lookup_keys
          or else the manager will fail.
  
          :param Session session: The SQLAlchemy session to use
          :param dict lookup_keys: A dictionary mapping the fields
              and their expected values
          :return: The dictionary of keys and values for the retrieved
              model.  The only values returned will be those specified by
              fields attrbute on the class
          :rtype: dict
          :raises: NotFoundException