ReferenceError：事件未定义firebase函数

Question

我当前正在开发约会应用程序，并且通知是该应用程序之一。结果，我一直在使用firebase函数来通知用户是否有新的约会被预定或取消。我收到未定义ReferenceError：事件的错误 Node.js代码

    'use strict'

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


exports.sendNotification = functions.database.ref('/Notifications/{PostKey}/{notification_id}').onWrite((data, context) => {

  const user_id = context.params.PostKey;
  const notification_id = context.params.notification_id;


  console.log('We have a notification from : ', user_id,'this also notification_id',notification_id);

    if(!event.data.val())
    {

    return console.log('A Notification has been deleted from the database : ', notification_id);

  }

  const deviceToken = admin.database().ref(`/User_Data/${user_id}/Device_Token`).once('value');
   console.log('A Notification has been deleted from the database : ', deviceToken);

  return deviceToken.then(result => {
      const token_id = result.val();

       const payload =
   {
       notification:
       {
           title:"Appointment has been booked",
           body: "one of your Appointmtnt has been booked",
           icon:"default"

       }
   };
    return admin.messaging().sendToDevice(token_id,payload).then(response =>
    {
         return console.log('This was the notification Feature');

    });


  });


});

错误日志 ReferenceError：事件未定义     在export.sendNotification.functions.database.ref.onWrite（/user_code/index.js:16:9）     在cloudFunctionNewSignature（/user_code/node_modules/firebase-functions/lib/cloud-functions.js:105:23）     在cloudFunction（/user_code/node_modules/firebase-functions/lib/cloud-functions.js:135:20）     在/var/tmp/worker/worker.js:733:24     在process._tickDomainCallback（内部/进程/next_tick.js:135:7） **数据库结构**

Answer 1

错误消息非常准确。告诉您在第16行使用了一个名为event的变量，但从未定义它：

if(!event.data.val())