Realtime Database Triggers and Push Notification Firebase and iOS - ios

Question

I am following GitHub code on how to implement push notification based on realtime database triggers.
Here is the code and the link:
https://github.com/firebase/functions-samples/blob/master/fcm-notifications/functions/index.js
/**
* Copyright 2016 Google Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
'use strict';
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
/**
* Triggers when a user gets a new follower and sends a notification.
*
* Followers add a flag to `/followers/{followedUid}/{followerUid}`.
* Users save their device notification tokens to `/users/{followedUid}/notificationTokens/{notificationToken}`.
*/
exports.sendFollowerNotification = functions.database.ref('/followers/{followedUid}/{followerUid}').onWrite(event => {
const followerUid = event.params.followerUid;
const followedUid = event.params.followedUid;
// If un-follow we exit the function.
if (!event.data.val()) {
return console.log('User ', followerUid, 'un-followed user', followedUid);
}
console.log('We have a new follower UID:', followerUid, 'for user:', followerUid);
// Get the list of device notification tokens.
const getDeviceTokensPromise = admin.database().ref(`/users/${followedUid}/notificationTokens`).once('value');
// Get the follower profile.
const getFollowerProfilePromise = admin.auth().getUser(followerUid);
return Promise.all([getDeviceTokensPromise, getFollowerProfilePromise]).then(results => {
const tokensSnapshot = results[0];
const follower = results[1];
// Check if there are any device tokens.
if (!tokensSnapshot.hasChildren()) {
return console.log('There are no notification tokens to send to.');
}
console.log('There are', tokensSnapshot.numChildren(), 'tokens to send notifications to.');
console.log('Fetched follower profile', follower);
// Notification details.
const payload = {
notification: {
title: 'You have a new follower!',
body: `${follower.displayName} is now following you.`,
icon: follower.photoURL
}
};
// Listing all tokens.
const tokens = Object.keys(tokensSnapshot.val());
// Send notifications to all tokens.
return admin.messaging().sendToDevice(tokens, payload).then(response => {
// For each message check if there was an error.
const tokensToRemove = [];
response.results.forEach((result, index) => {
const error = result.error;
if (error) {
console.error('Failure sending notification to', tokens[index], error);
// Cleanup the tokens who are not registered anymore.
if (error.code === 'messaging/invalid-registration-token' ||
error.code === 'messaging/registration-token-not-registered') {
tokensToRemove.push(tokensSnapshot.ref.child(tokens[index]).remove());
}
}
});
return Promise.all(tokensToRemove);
});
});
});
My silly question, new to Functions and Node, is in this code notifications are sent to all users who tokens are saved, is that correct? and if it is how can I let's say send just to one particular person instead all?
I was thinking of saving token of each user in different nodes (children) so I can pick the one I want to send notification to. Does it work?
Thanks All

Answer 1

This code will send notification to just one user (follower in this example). This user can have multiple tokens, representing multiple devices, and hence the variable name: tokensSnapshot.
What you intend to do is very doable with Cloud Functions. You just have to be careful with paths of your nodes where you save users, or tokens, for instance. Also as Frank van Puffelen suggested, having some acquaintance with Admin SDK (Realtime Database and FCM) will really help you out.