我想通过 firebase 云功能向设备发送推送通知。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 cloud 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)
我得到了答复here https://stackoverflow.com/questions/49647170/firebase-functions-cannot-read-property-user-id-of-undefined
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：
Cannot read property 'val' of undefined
如何消除这些错误？
提前致谢
关于val()您需要执行以下操作：
exports.sendNotification = functions.database.ref('/messages/{user_id}/{rec_user_id}').onWrite((change,context) => {
const afterData=change.after.val();
});
既然你正在使用onWrite()那么数据参数应该是change，其中有before and after属性，其中每一个都是一个DataSnapshot它有以下方法：
https://firebase.google.com/docs/reference/admin/node/admin.database.DataSnapshot https://firebase.google.com/docs/reference/admin/node/admin.database.DataSnapshot
也供参考：
https://firebase.google.com/docs/reference/functions/functions.Change https://firebase.google.com/docs/reference/functions/functions.Change
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