javascript - 类型错误 : Cannot Read Property child of undefined

Question

我正在尝试创建一个 node.js firebase 函数，以便在我的实时数据库中每次在“通知”父节点内添加或更新节点时向用户发送通知。

这是我的 index.js-

let functions = require('firebase-functions');

let admin = require('firebase-admin');

admin.initializeApp();

exports.sendNotification = functions.database.ref('/Notifications/{postId}').onWrite((change, context) => {

//get the userId of the person receiving the notification because we need to get their token
 const receiverId = change.after.data.child('receiver_token').val();
 console.log("receiverId: ", receiverId);



 //get the message
 const message = change.after.data.child('content').val();
 console.log("message: ", message);



  const token = receiver_token;

  console.log("Construction the notification message.");
  const payload = {
    data: {
      data_type: "direct_message",
      title: "Open Up",
      message: message,

    }
  };

  return admin.messaging().sendToDevice(token, payload);
});

但每次都会出现错误，因为它说 change.after.data 的结果是未定义的。问题是什么。我该如何解决？

我的实时数据库结构:

Answer 1

改变这个:

const receiverId = change.after.data.child('receiver_token').val();
console.log("receiverId: ", receiverId);
//get the message
const message = change.after.data.child('content').val();
console.log("message: ", message); 

进入这个:

const receiverId = change.after.child('receiver_token').val();
console.log("receiverId: ", receiverId);
//get the message
const message = change.after.child('content').val();
console.log("message: ", message);

Both onWrite and onUpdate have the change parameter which has before and after fields. Each of these is a DataSnapshot with the same methods available in admin.database.DataSnapshot

admin.database.DataSnapshot 不包含名为 data 的字段，这就是您收到未定义错误的原因。