无法读取未定义的属性“user_id”

Question

我想通过 Firebase 云功能发送设备到设备的推送通知。我正在编写 node.js 脚本

exports.sendNotification = functions.database.ref('/messages/{user_id}/{rec_user_id}').onWrite((event) => {

const sender_user_id = event.params.user_id;
const receiver_user_id = event.params.rec_user_id;

console.log('We have a notification from : '+ sender_user_id+  " | Receiced by " + receiver_user_id);

return;

});

在 Firebase 云上部署功能后出现错误

TypeError: Cannot read property 'user_id' of undefined

完整的错误日志是：

TypeError: Cannot read property 'user_id' of undefined
at exports.sendNotification.functions.database.ref.onWrite.event (/user_code/index.js:28:40)
at Object.<anonymous> (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:112:27)
at next (native)
at /user_code/node_modules/firebase-functions/lib/cloud-functions.js:28:71
at __awaiter (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:24:12)
at cloudFunction (/user_code/node_modules/firebase-functions/lib/cloud-functions.js:82:36)
at /var/tmp/worker/worker.js:700:26
at process._tickDomainCallback (internal/process/next_tick.js:135:7)

我得到了here的答复

它工作正常，但是当我使用时

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

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

}

Firebase 日志再次开始给我一条错误消息说

Cannot read property 'val' of undefined

如何摆脱这些错误？ 提前致谢

Answer 1

关于val()你需要做以下事情：

exports.sendNotification = functions.database.ref('/messages/{user_id}/{rec_user_id}').onWrite((change,context) => {

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

由于您使用的是onWrite()，那么数据参数应该是change，它具有before 和after 属性，每个属性都是DataSnapshot，具有以下方法：

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

也供参考：

https://firebase.google.com/docs/reference/functions/functions.Change