Firestore trigger functions in Firebase - Mini Project: Build & Apply

Firestore Trigger Functions

📖 Scenario: You are building a simple Firebase backend that reacts to changes in a Firestore database. You want to create functions that automatically run when documents are created or updated in a specific collection.

🎯 Goal: Build Firestore trigger functions that run when a document is created and when a document is updated in the users collection.

📋 What You'll Learn

Create a Firestore trigger function for document creation in the users collection.

Create a Firestore trigger function for document updates in the users collection.

Log a message inside each trigger function indicating the event type and document ID.

💡 Why This Matters

🌍 Real World

Automatically respond to database changes, such as sending notifications or updating related data.

💼 Career

Understanding Firestore triggers is essential for backend development with Firebase and building reactive cloud applications.

1

Set up Firebase Functions and import Firestore

Write the code to import functions from firebase-functions and initialize Firestore by importing admin from firebase-admin and calling admin.initializeApp().

Firebase

# Your code here

Need a hint?

Use require to import modules and call admin.initializeApp() to start Firebase Admin SDK.

2

Create a Firestore trigger for document creation

Create a Firestore trigger function called onUserCreate that runs when a document is created in the users collection. Use functions.firestore.document('users/{userId}').onCreate and log the message 'User created:' followed by the userId parameter.

Firebase

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

// Your code here

Need a hint?

Use context.params.userId to get the document ID from the path.

3

Create a Firestore trigger for document updates

Create a Firestore trigger function called onUserUpdate that runs when a document is updated in the users collection. Use functions.firestore.document('users/{userId}').onUpdate and log the message 'User updated:' followed by the userId parameter.

Firebase

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.onUserCreate = functions.firestore.document('users/{userId}').onCreate((snap, context) => {
  const userId = context.params.userId;
  console.log('User created:', userId);
});

// Your code here

Need a hint?

Use onUpdate and context.params.userId to get the document ID.

4

Export both trigger functions

Ensure both onUserCreate and onUserUpdate functions are exported from the module so Firebase can deploy them.

Firebase

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

exports.onUserCreate = functions.firestore.document('users/{userId}').onCreate((snap, context) => {
  const userId = context.params.userId;
  console.log('User created:', userId);
});

exports.onUserUpdate = functions.firestore.document('users/{userId}').onUpdate((change, context) => {
  const userId = context.params.userId;
  console.log('User updated:', userId);
});

// Your code here

Need a hint?

Make sure both functions are assigned to exports so Firebase can find them.