code: def query(self):
          
  
          if self.target_class_name is None:
              target_class = leancloud.Object.extend(self.parent._class_name)
              query = leancloud.Query(target_class)
              query._extra['redirectClassNameForKey'] = self.key
          else:
              target_class = leancloud.Object.extend(self.target_class_name)
              query = leancloud.Query(target_class)
  
          query._add_condition('$relatedTo', 'object', self.parent._to_pointer())
          query._add_condition('$relatedTo', 'key', self.key)
  
          return query
docs: 获取指向 Relation 内容的 Query 对象。
  
          :rtype: leancloud.Query