Firebase Functions extracting Token - node.js

Question

Trying to grab my FCM token from my Cloud Firestore using Firebase Function
my function code:
const functions = require("firebase-functions");
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotificationToFCMToken = functions.firestore.document('Posts/{likes}').onWrite(async (event) => {
const title = event.after.get('title');
const content = event.after.get('likes');
let userDoc = await admin.firestore().doc('Users').get();
let fcmToken = userDoc.get('{token}');
var message = {
notification: {
title: title,
body: "you have a new like",
},
token: fcmToken,
}
let response = await admin.messaging().send(message);
console.log(response);
});
My Firestore
Posts:
Users:
if I manually add the token everything works but just send every "like" to one device, my goal is to send a link to only the owner of the post

Answer 1

It's probably more alike this:
let userRef = event.after.get('ref'); // obviously the path is mandatory ...
let userDoc = await admin.firestore().doc(userRef).get(); // then this should match
let token = userDoc.get('token'); // and the token should be accessible
Add logging to see what you get: functions.logger.info('🞬🞬🞬 ' + JSON.stringify(event)); ...viewable at https://console.cloud.google.com/logs/query. When listening for Posts/{likes} you'd likely need an additional query - and when listening for Posts, you'd need to determine changes. Getting access to ref is required to make the subsequent query work.

Answer 2

Martin's answer is correct, but it seems that the ref field is of type Reference, see the slash at the beginning, plus the error you get.
So, if this assumption is correct, you should use the path property, as follows (adapting Martin's code):
let userRef = event.after.get('ref'); // obviously the path is mandatory ...
let userDoc = await admin.firestore().doc(userRef.path).get(); // then this should match
let token = userDoc.get('token'); // and the token should be accessible
In addition, in order to correctly manage the life cycle of your Cloud Function, you should do, at the end:
let response = await admin.messaging().send(message);
console.log(response);
return null;
or simply
return admin.messaging().send(message);