code: def first(self):
          
          params = self.dump()
          params['limit'] = 1
          content = self._do_request(params)
          results = content['results']
          if not results:
              raise LeanCloudError(101, 'Object not found')
          obj = self._new_object()
          obj._update_data(self._process_result(results[0]))
          return obj
docs: 根据查询获取最多一个对象。
  
          :return: 查询结果
          :rtype: Object
          :raise: LeanCloudError