如果子消息没有字段,如何在protobuf消息上分配oneof字段?

我想创建一个大表 DeleteFromRow 突变。原版 Mutation 以及 删除FromRow 如下所示:

oneof mutation {
    // Set a cell's value.
    SetCell set_cell = 1;

    // Deletes cells from a column.
    DeleteFromColumn delete_from_column = 2;

    // Deletes cells from a column family.
    DeleteFromFamily delete_from_family = 3;

    // Deletes cells from the entire row.
    DeleteFromRow delete_from_row = 4;
  }
}

message DeleteFromRow {

}

在python中,不能直接实例化 删除FromRow 对象并设置 delete_from_row 的字段 突变 对那个物体。

所以这个 不起作用 :

request = bigtable_pb2.MutateRowRequest(table_name='tablename', row_key=row_key)
mutation = request.mutations.add()
mutation.delete_from_row = data_pb2.Mutation.DeleteFromRow()

由其他SO用户提出(请参见 this question ,结果是

AttributeError: Assignment not allowed to composite field "delete_from_row" in protocol message object.

根据 protobuf docs ,您应该通过设置其中一个子字段来设置一个one of字段。所以A DeleteFromFamily 突变的产生方式如下:

mutation.delete_from_family.family_name = 'some_family'

但是,我该怎么做呢 删除FromRow 没有字段的消息?