TypeError：无法读取未定义的属性“来自”答案

【问题标题】：TypeError: Cannot read property 'from' of undefinedTypeError：无法读取未定义的属性“来自”
【发布时间】：2019-01-01 19:48:08
【问题描述】：

我正在尝试编写一个函数，该函数在用户收到新评论并发送通知时触发。评论存储在 /Users/{user_id}/Notifications/{notification_id} 中。用户将他们的设备通知令牌保存到 /users/{userID}

    'use strict'

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

exports.sendNotif = functions.firestore.document('Users/{user_id}/Notifications/{notification_id}')
.onWrite((change,context) =>
{
    const user_id = context.params.user_id;
    const notification_id = context.params.notification_id;

    return admin.firestore().collection('Users').document(user_id).collection('Notifications').document(notification_id).get().then(queryResult=>{

      const from_user_id = queryResult.data().From;

      const from_data = admin.firestore().collection('Users').document(from_user_id).get();
      const to_data = admin.firestore().collection('Users').document(user_id).get();

      return Promise.all([from_data, to_data]).then(result => {

        const from_name = result[0].data().From;
        const to_name = result[1].data().From;

        console.log("FROM: " + from_name + "TO: " + to_name);

      });

    });

});

这是 package.json 文件。一切都是最新的

 {
  "name": "functions",
  "description": "Cloud Functions for Firebase",
  "scripts": {
    "serve": "firebase serve --only functions",
    "shell": "firebase functions:shell",
    "start": "npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "dependencies": {
    "firebase-admin": "^6.4.0",
    "firebase-functions": "^2.1.0"
  },
  "private": true
}


    {
  "name": "functions",
  "description": "Cloud Functions for Firebase",
  "scripts": {
    "serve": "firebase serve --only functions",
    "shell": "firebase functions:shell",
    "start": "npm run shell",
    "deploy": "firebase deploy --only functions",
    "logs": "firebase functions:log"
  },
  "dependencies": {
    "firebase-admin": "^6.4.0",
    "firebase-functions": "^2.1.0"
  },
  "private": true
}

Firebase 给出以下错误：

TypeError: Cannot read property 'from' of undefined
at Promise.all.then.result (/user_code/index.js:21:47)
at process._tickDomainCallback (internal/process/next_tick.js:135:7)

【问题讨论】：

您的代码始终使用From（大写F），而错误消息提到from（小写f）。您确定这是引发错误的代码吗？
我尝试了 F 的两种情况。如果使用大写 F，则错误对应于“From”，如果使用 f，则对应于“from”。
from_data = admin.firestore().collection('Users').document(from_user_id).get() 文档似乎不存在。在调用from_data.data() 之前，您需要检查if (from_data.exists) 。

标签： node.js firebase google-cloud-firestore firebase-admin

【解决方案1】：

请检查数组的长度（结果）。您应该记录结果。

 return Promise.all([from_data, to_data]).then(result => {
    console.log(result);

    const from_name = result[0].data().From;
    const to_name = result[1].data().From;

    console.log("FROM: " + from_name + "TO: " + to_name);

  });

【讨论】：