实战构架 API 服务器-7.1 发布回复，是如何通过 topic_id 来定位文章的？

public function store(ReplyRequest $request, Topic $topic, Reply $reply) {
        $reply->content = $request->contents;
        $reply->topic_id = $topic->id;
        $reply->user_id = $this->user()->id;
        $reply->save();

        return $this->response->item($reply, new ReplyTransformer())
            ->setStatusCode(201);
    }

接口地址：

topics/{topic}/replies