我们如何将变体消息(几种消息类型之一)放入 protobuf 消息中? [英] How can we put a variant message ( one of a few message types ) inside a protobuf message?

问题描述

我们如何将变体消息(几种消息类型之一)放入 protobuf 消息中?

How can we put a variant message ( one of a few message types ) inside a protobuf message?

message typeA {
    ....
}

message typeB {
    ....
}

message typeC {
    [typeB|typeA] payload;
}

推荐答案

你需要这样做:

message TypeC {
  optional TypeA a = 1;
  optional TypeB b = 2;
}

如果有很多变体，您可能还想添加一个标签字段，这样您就不必为每个变体都检查has_*().

If there are a lot of variants, you might also want to add a tag field so that you don't have to check has_*() for each one.

这在 Protobuf 文档中有介绍:https://developers.google.com/protocol-buffers/docs/techniques#union

This is covered in the Protobuf docs: https://developers.google.com/protocol-buffers/docs/techniques#union

附注.Protobufs 的这个缺失功能​​在 Cap'n Proto 中得到修复，这是同一作者(我)的一个新序列化系统:Cap'n Proto 为此目的实现了 "unions".在离开 Google 之前，我也在 Protobufs 中实现了联合，但是在我离开之前没有设法将我的更改合并到主线中.对不起.:(

PS. This missing feature of Protobufs is fixed in Cap'n Proto, a new serialization system by the same author (me): Cap'n Proto implements "unions" for this purpose. I had also implemented unions in Protobufs before leaving Google, but didn't manage to get my change merged into mainline before I left. Sorry. :(

看起来 Protobuf 团队最终合并了我的更改并发布了 2.6.0 版.:) 请参阅oneof 声明.

It looks like the Protobuf team eventually merged my change and released version 2.6.0 with it. :) See the oneof declaration.

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