Firebase cloud function / notification - firebase

Question

I am trying to make a notification function to deploy using cloud functions of firebase
I did the first part of the code and it was successfully done which is:
'use-strict'
const functions = require('firebase-functions');
//const paypal=require('paypal-rest-sdk');
const admin=require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotification=functions.firestore
.document("Users/{user_id}/Notifications/{notification_id}")
onWrite((change, context)=>{
const user_id=context.params.user_id;
const notification_id=context.params.notification_id;
});
without returning promise and it was ok but when i tried to complete like this:
'use-strict'
const functions = require('firebase-functions');
//const paypal=require('paypal-rest-sdk');
const admin=require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.sendNotification=functions.firestore
.document("Users/{user_id}/Notifications/{notification_id}")
.onWrite((change, context)=>{
const user_id=context.params.user_id;
const notification_id=context.params.notification_id;
return admin.firestore().collection("Users").doc(user_id)
.collection("Notifications")
.doc(notification_id)
.get()
.then(queryResult=>{
const from_user_id=queryResult.data().from;
const from_data=admin.firestore()
.collection("Users").doc(from_user_id).get();
const to_data=admin.firestore().collection("Users")
.doc(user_id).get();
return Promise.all([from_data,to_data]).then(result=>{
const from_name=result[0].data().name;
const to_name=result[1].data().name;
console.log("from :"+from_name+"TO"+to_name);
});
});
// console.log("user_id"+ user_id+ "notification_id"+notification_id);
});
I have these 2 errors in node.cm:
1-Avoid nesting promises
2-each then()should return a value
how can i fix this problem???

Answer 1

Send push notification through FCM and cloud function when a change in Firestore database
You can try like this
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
exports.sendNotification = functions.firestore
.document('/users/{documentId}')
.onWrite((change, context) => {
console.log("CHANGE in DOCUMENT ID : " + context.params.documentId);
// Fetch data using standard accessors
const userId = change.after.data().userId;
const ownerId = change.after.data().ownerId;
console.log('We have a new request UID:', userId, 'for owner:', ownerId);
const owner_data = admin.firestore().collection('users').doc(ownerId).get();
const user_data = admin.firestore().collection('users').doc(userId).get();
return Promise.all([owner_data, user_data]).then(result => {
const ownerFCMToken = result[0].data().fcmToken;
const userName = result[1].data().displayName;
console.log("OWNER Token : " + ownerFCMToken + " USER: " + userName);
const payload = {
notification: {
title: 'Test title!',
body: `${userName} sent you a following request.`
// icon: follower.photoURL
}
};
admin.messaging().sendToDevice(followedFCMToken, payload)
.then(function (response) {
console.log("Push response : " + response);
return response
})
.catch(function (error) {
console.error("Error in sending push");
});
});