code: def dump(self):
          
          params = {
              'where': self._where,
          }
          if self._include:
              params['include'] = ','.join(self._include)
          if self._select:
              params['keys'] = ','.join(self._select)
          if self._include_acl is not None:
              params['returnACL'] = json.dumps(self._include_acl)
          if self._limit >= 0:
              params['limit'] = self._limit
          if self._skip > 0:
              params['skip'] = self._skip
          if self._order:
              params['order'] = ",".join(self._order)
          params.update(self._extra)
          return params
docs: :return: 当前对象的序列化结果
          :rtype: dict