Firebase TypeError：无法读取未定义的属性“val” [英] Firebase TypeError: Cannot read property 'val' of undefined

问题描述

我已尝试使用Firebase云功能发送通知。我的项目结构

I have tried Firebase cloud function for sending a notification.My project structure

这是索引.js，

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.pushNotification = functions.database.ref('/messages').onWrite( event => {
console.log('Push notification event triggered');

    const message = event.data.val();
    const user = event.data.val();
    console.log(message);
    console.log(user);

    const topic = "myTopic";
    const payload = {
        "data": {
            "title": "New Message from " + user,
            "detail":message,
        }
    };

    return admin.messaging().sendToTopic(topic, payload);
   });

以上代码配置错误，当我在Node.js中部署时，LOG中的函数显示：

The above code is misconfigured, when I deploy in Node.js, LOG in Function shows:

TypeError：无法读取未定义的属性'val'。

"TypeError: Cannot read property 'val' of undefined".

实际上我正在尝试做什么：
我试图将快照加载中的信息提取到index.js中，这样当一个新的子项被添加到实时数据库时，它应该触发一个带有标题和正文的通知有效负载。

What Actually I am trying to do : I am trying to extract info from snapshot load into that index.js so that when a new child gets added to Real-time database, it should trigger a notification payload with a title and body.

在Android中，我使用子监听器，在添加新记录时进行监听

In Android, I use a child listener, for listening when a new record is added

FirebaseDatabase.getInstance().getReference().child("messages")

 OnChildAdded(.....){
 if (dataSnapshot != null) {
                    MessageModel messageModel = dataSnapshot.getValue(MessageModel.class);
                    if (messageModel != null) {
                            // do whatever
                           }
                   }

但是在index.js中，我无法解析它。
根据我的数据库结构如何固定index.js的一点指导将非常感激。
PS-我从来没有在JS
中编码如果你想要更多的上下文，我很乐意提供它。

But in index.js, I could not able to parse that. A bit guidance how to fixate index.js according to my database structure would be immensely appreciated. PS- I have never done coding in JS If you want more context, I'd be happy to provide it.

推荐答案

更改此内容：

exports.pushNotification = functions.database.ref('/messages').onWrite( event => {

const message = event.data.val();
const user = event.data.val();
});

到此：

exports.pushNotification = functions.database.ref('/messages').onWrite(( change,context) => {

const message = change.after.val();
});

请检查：

https://firebase.google.com/docs/functions/beta-v1 -diff＃realtime-database

云功能已更改，现在 onWrite 有两个参数更改和上下文

The cloud functions were changed and now onWrite has two parameters change and context

更改在之前有两个属性，在之后有，并且每个属性都是 DataSnapshot 使用此处列出的方法：

The change has two properties before and after and each of these is a DataSnapshot with the methods listed here:

https://firebase.google.com/docs/reference/admin/node/admin.database.DataSnapshot

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