我在收到来自火力基地的通知时收到此错误

Question

'use strict'
const functions = require('firebase-functions');
const admin=require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotification=functions.database.ref('/notifications/{user_id}/{notification_id }').onWrite((change,context) =>{
const user_id=context.params.user_id;
const notification_id=context.params.notification_id;
console.log('The user ID is :',user_id);
if(!change.after.val()){
return console.log('A notification has been deleted from database:',notification_id);
}
const fromUser=admin.database().ref(`/notifications/${user_id}/${notification_id}`).once('value');
return fromUser.then(fromUserResult=>{
const from_user_id=fromUserResult.val().from; 
console.log('You have new notification from:   : ', from_user_id); 

const userQuery=admin.database().ref(`users/${from_user_id}/name`).once('value');
return userQuery.then(userResult=>{
const userName=userResult.val();
const deviceToken=admin.database().ref(`/users/${user_id}/device_token`).once('value');
return deviceToken.then(result =>{
const token_id=result.val();
const payload={
notification:{
title:"Friend Request",
body:`${userName} has sent you request`,
icon:"default"
}
};    
return admin.messaging().sendToDevice(token_id, payload);
}); 
});
});
});

类型错误： 无法读取 null 的属性"from" at fromUser.then.fromUserResult (/user_code/index.js：22：47( 在process._tickDomainCallback(内部/进程/next_tick.js：135：7(

Answer 1

您访问名为from的属性的唯一代码行是：

const from_user_id=fromUserResult.val().from; 

因此，fromUserResult.val()必须返回 null。

fromUserResult是一个 DataSnapshot 类型的对象。 根据 val(( 方法的 API 文档，如果查询位置没有数据，它可以返回 null。 因此，您必须在代码中检查这种情况。

Answer 2

我已经使用以下代码发送带有发件人姓名的通知：

'use strict'
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotification = functions.database.ref('/Notifications/{receiver_user_id}/{notification_id}')
.onWrite((data, context) => 
{
const receiver_user_id = context.params.receiver_user_id;
const notification_id = context.params.notification_id;
if(!data.after.val())
{
console.log('A notification has been deleted :' , notification_id);
return null;
}

const sender_user_id = admin.database().ref(`/Notifications/${receiver_user_id}/${notification_id}`).once('value');
return sender_user_id.then(fromUserResult => 
{
const from_sender_user_id = fromUserResult.val().from;
const userQuery = admin.database().ref(`/Users/${from_sender_user_id}/name`).once('value');
return userQuery.then(userResult => 
{
const senderUserName = userResult.val();
console.log('You have notification from :' , senderUserName);
const DeviceToken = admin.database().ref(`/Users/${receiver_user_id}/device_token`).once('value');
console.log('Checkpoint2');
return DeviceToken.then(result => 
{
const token_id = result.val();
const payload = 
{
notification:
{
//from_sender_user_id : from_sender_user_id,
title: "New Chat Request",
body: `${senderUserName} wants to connect with you`,
icon: "default"
}
};
return admin.messaging().sendToDevice(token_id, payload).then(response => 
{
console.log('This was the notification Feature');
return null;
}).catch(error => {
console.error(error);
res.error(500);
});
});
});
});
});