code: def update(self, session, lookup_keys, updates, *args, **kwargs):
          
          model = self._get_model(lookup_keys, session)
          model = self._set_values_on_model(model, updates, fields=self.update_fields)
          session.commit()
          return self.serialize_model(model)
docs: Updates the model with the specified lookup_keys and returns
          the dictified object.
  
          :param Session session: The SQLAlchemy session to use
          :param dict lookup_keys: A dictionary mapping the fields
              and their expected values
          :param dict updates: The columns and the values to update
              them to.
          :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