Update field when document is added on Cloud Firestore [closed] - node.js

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I have a question regarding the use of Cloud Firestore Functions in my Android App (I'm writing on kotlin using Android Studio)
Having read some documentation I think it's possible to run a custom method in Firestore Functions when a new Document is created in my database. All I need to do is update a field.
The thing is that these functions on Cloud Firestore need to be written in JavaScript and I need to use Node.js, and I have 0 knowledge on this.
To any developer with Cloud Firestore knowledge, any guides or hints on this issue?

Answer 1

The thing is that these functions on Cloud Firestore need to be written in JavaScript and I need to use Node.js, and I have 0 knowledge on this.
Don't know if it helps, but the Cloud Functions can also be written in Python or Go. You can check out more complete information about the current runtimes and languages here.
But let's try to answer your question, shall we? I'll use the Node.js 8 Runtime in the examples below.
Introduction
Google Cloud Functions currently support 2 types of functions:
HTTP Functions, which are triggered by simple HTTP requests, and
Background Functions, which are triggered by events from Google Cloud's infrastructure, such as Cloud Firestore events. This is what you need, so let's focus on that.
Setup
Since you're using Cloud Firestore, I assume you already have a Firebase project set up. So the first step, if you don't have it yet, is to install the Firebase CLI and follow its instructions to setup your project locally. When asked, select the "Functions: Configure and deploy Cloud Functions" option to enable it and also "Use an existing project" to select your project.
$ firebase login
$ firebase init
Once you finish the setup, you'll essentially have the following structure in your directory:
firebase.json
.firebaserc
functions/
index.js
package.json
Now before you start coding, there's something you should know about Cloud Firestore events. There are 4 of them (the list is here):
onCreate: Triggered when a document is written to for the first time.
onUpdate: Triggered when a document already exists and has any value changed.
onDelete: Triggered when a document with data is deleted.
onWrite: Triggered when onCreate, onUpdate or onDelete is triggered.
Since you only need to capture a creation event, you'll write an onCreate event.
Coding
To do that, open the functions/index.js file and type the following piece of code:
const functions = require('firebase-functions');
// this function is triggered by "onCreate" Cloud Firestore events
// the "userId" is a wildcard that represents the id of the document created inside te "users" collection
// it will read the "email" field and insert the "lowercaseEmail" field
exports.onCreateUserInsertEmailLowercase = functions.firestore
.document('users/{userId}')
.onCreate((snapshot, context) => {
// "context" has info about the event
// reference: https://firebase.google.com/docs/reference/functions/cloud_functions_.eventcontext
const { userId } = context.params;
// "snapshot" is a representation of the document that was inserted
// reference: https://googleapis.dev/nodejs/firestore/latest/DocumentSnapshot.html
const email = snapshot.get('email');
console.log(`User ${userId} was inserted, with email ${email}`);
return null;
});
As you can probably guess, this is a really simple Cloud Function, that only logs the document's id and its "email" field. So now we go to the second part of your question: how can we edit this newly created document? Two options here: (1) update the document you just created and (2) update other document, so I'll separate it in 2 sections:
(1) Update the document you have just created
The answer lies in the "snapshot" parameter. Although it's just a representation of the document you inserted, it carries inside it a DocumentReference, which is a different type of object that has read, write and listening to changes capabilities. Let us use its set method to insert the new field. So let's change our current Function to do that:
const functions = require('firebase-functions');
// this function is triggered by "onCreate" Cloud Firestore events
// the "userId" is a wildcard that represents the id of the document created inside te "users" collection
// it will read the "email" field and insert the "lowercaseEmail" field
exports.onCreateUserInsertEmailLowercase = functions.firestore
.document('users/{userId}')
.onCreate((snapshot, context) => {
// "context" has info about the event
// reference: https://firebase.google.com/docs/reference/functions/cloud_functions_.eventcontext
const { userId } = context.params;
// "snapshot" is a representation of the document that was inserted
// reference: https://googleapis.dev/nodejs/firestore/latest/DocumentSnapshot.html
const email = snapshot.get('email');
console.log(`User ${userId} was inserted, with email ${email}`);
// converts the email to lowercase
const lowercaseEmail = email.toLowerCase();
// get the DocumentReference, with write powers
const documentReference = snapshot.ref;
// insert the new field
// the { merge: true } parameter is so that the whole document isn't overwritten
// that way, only the new field is added without changing its current content
return documentReference.set({ lowercaseEmail }, { merge: true });
});
(2) Update a document from another collection
For that, you're gonna need to add the firebase-admin to your project. It has all the admin privileges so you'll be able to write to any Cloud Firestore document inside your project.
Inside the functions directory, run:
$ npm install --save firebase-admin
And since you're already inside Google Cloud's infrastructure, initializing it is as simple as adding the following couple of lines to the index.js file:
const admin = require('firebase-admin');
admin.initializeApp();
Now all you have to do is use the Admin SDK to get a DocumentReference of the document you wish to update, and use it to update one of its fields.
For this example, I'll consider you have a collection called stats which contains a users document with a counter inside it that tracks the number of documents in the users collection:
// this updates the user count whenever a document is created inside the "users" collection
exports.onCreateUpdateUsersCounter = functions.firestore
.document('users/{userId}')
.onCreate(async (snapshot, context) => {
const statsDocumentReference = admin.firestore().doc('stats/users');
// a DocumentReference "get" returns a Promise containing a DocumentSnapshot
// that's why I'm using async/await
const statsDocumentSnapshot = await statsDocumentReference.get();
const currentCounter = statsDocumentSnapshot.get('counter');
// increased counter
const newCounter = currentCounter + 1;
// update the "counter" field with the increased value
return statsDocumentReference.update({ counter: newCounter });
});
And that's it!
Deploying
But now that you've got the coding part, how can you deploy it to make it run in your project, right? Let us use the Firebase CLI once more to deploy the new Cloud Functions.
Inside your project's root directory, run:
$ firebase deploy --only functions:onCreateUserInsertEmailLowercase
$ firebase deploy --only functions:onCreateUpdateUsersCounter
And that's pretty much the basics, but if you'd like, you can check its documentation for more info about deploying Cloud Functions.
Debugging
Ok, right, but how can we know it worked? Go to https://console.firebase.google.com and try it out! Insert a couple of documents and see the magic happens. And if you need a little debugging, click the "Functions" menu on the left-hand side and you'll be able to access your functions logs.
That's pretty much it for your use-case scenario, but if you'd like to go deeper into Cloud Functions, I really recommend its documentation. It's pretty complete, concise and organized. I left some links as a reference so you'll know where to look.
Cheers!