Cloud Function Update Problem in Firestore Database - firebase

Question

I'm trying to build an Android application. In my Firestore database I have Users collection and Counters collection. In Counters collection I have userCounter. What I want to do is whenerever a new user logs in and I push it to firestore, userCounter to increase.
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
exports.addNewUser =
functions.firestore.document('Users/{userID}').onCreate((event) => {
var db = admin.firestore();
var counterRef = db.collection("Counters");
var temp = counterRef.doc("0").data().userCounter++;
counterRef.doc("0").update(
{
userCounter: temp
});
});
In this state, this function doesn't work, and I'm a newbie so I'd appreciate any help.
Thx beforehand
EDIT
After implementing Firebaser and Pablo Almécija Rodríguez's answers, my code looks like this.
const Firestore = require('#google-cloud/firestore');
const firestore = new Firestore({
projectId: process.env.GCP_PROJECT,
});
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
const db = admin.firestore();
exports.addNewUser =
functions.firestore.document('Users/{userId}').onCreate((snapShot) => {
const userCounterRef = db.collection('Counters').doc('Users');
return db.runTransaction(transaction => {
const doc = transaction.get(userCounterRef);
console.log("1");
const count = doc.data();
console.log(`5`);
const updatedCount = count + 1;
console.log(`6`);
return transaction.update(userCounterRef, {counter: updatedCount })
})
});
And this is the firebase console log. The problem is
const count = doc.data();
TypeError: doc.data is not a function
Firebase Console Log

Answer 1

I suggest you to create a collection named counters and inside it a document named users to handle counter for users. Here is the structure:
- counters (collection)
- users (document)
count: 0 (field)
Then, you should use a transaction to perform an update on this counter document to make sure you are working with up-to-date data to deal with concurrency (multiple accounts created at the same time)
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();
const db = admin.firestore();
exports.addNewUser =
functions.firestore.document('users/{userId}').onCreate((snapShot) => {
const userCounterRef = db.doc('counters/users');
return db.runTransaction(async transaction => {
const doc = await transaction.get(userCounterRef)
const { count } = doc.data()
const updatedCount = count + 1
return transaction.update(userCounterRef, {count: updatedCount })
})
});
https://firebase.google.com/docs/firestore/manage-data/transactions
EDIT: If you don't want to deal with async/await syntax, update your transaction like that :
return db.runTransaction(transaction => {
return transaction.get(userCounterRef)
.then(doc => {
const count = doc.data().count
const updatedCount = count + 1
transaction.update(userCounterRef, {count: updatedCount })
})
})

Answer 2

I have reproduced it in Cloud Functions, and this simple solution worked. Edited answer to fit Firebase, and it also uses the Firestore dependency for nodejs.
const Firestore = require('#google-cloud/firestore');
const firestore = new Firestore({
projectId: process.env.GCP_PROJECT,
});
const functions = require('firebase-functions');
//I am not using next two lines right now though
const admin = require('firebase-admin');
admin.initializeApp();
exports.helloFirestore =
functions.firestore.document('users/{userID}').onCreate((event) => {
const doc = firestore.doc('Counters/UserCounter/');
doc.get().then(docSnap => {
//Get the specific field you want to modify
return docSnap.get('userCount');
}).then(field => {
field++;
//Log entry to see the change happened
console.log(`Retrieved field value after +1: ${field}`);
//Update field of doc with the new value
doc.update({
userCount: field,
});
});
});
The wildcard you used should be fine, just be careful with the full path for the collection, mind the upper/lower case. For this case, this is how my package.json looks like:
{
"name": "sample-firestore",
"version": "0.0.1",
"dependencies": {
"#google-cloud/firestore": "^1.1.0",
"firebase-functions": "2.2.0",
"firebase-admin": "7.0.0"
}
}