Setting with merge option in Firebase - Mini Project: Build & Apply

Firebase Firestore: Setting Document Data with Merge Option

📖 Scenario: You are building a simple app that stores user profiles in Firebase Firestore. Sometimes you want to update only part of a user's profile without overwriting the entire document.

🎯 Goal: Learn how to use the set method with the merge: true option to update parts of a Firestore document safely.

📋 What You'll Learn

Create a Firestore document reference for a user with ID 'user123'.

Create an initial user profile object with name and age.

Use set to save the initial profile to Firestore.

Create an update object with a new age and city.

Use set with { merge: true } to update the user profile without deleting existing fields.

💡 Why This Matters

🌍 Real World

Updating user profiles or settings in Firestore without deleting existing data is common in apps.

💼 Career

Understanding how to safely update Firestore documents is essential for backend and full-stack developers working with Firebase.

1

Create Firestore document reference and initial user profile

Create a variable called userRef that references the Firestore document at users/user123. Then create a variable called initialProfile with the exact object { name: 'Alice', age: 30 }.

Firebase

// Your code here

Need a hint?

Use firestore.collection('users').doc('user123') to get the document reference.

2

Save the initial profile to Firestore

Use userRef.set(initialProfile) to save the initial profile object to Firestore.

Firebase

const userRef = firestore.collection('users').doc('user123');
const initialProfile = { name: 'Alice', age: 30 };
// Your code here

Need a hint?

Call set on userRef with initialProfile as argument.

3

Create an update object with new age and city

Create a variable called updateProfile with the exact object { age: 31, city: 'New York' }.

Firebase

const userRef = firestore.collection('users').doc('user123');
const initialProfile = { name: 'Alice', age: 30 };
userRef.set(initialProfile);
// Your code here

Need a hint?

Define updateProfile with the new age and city fields.

4

Update the user profile using set with merge option

Use userRef.set(updateProfile, { merge: true }) to update the Firestore document without overwriting the entire profile.

Firebase

const userRef = firestore.collection('users').doc('user123');
const initialProfile = { name: 'Alice', age: 30 };
userRef.set(initialProfile);
const updateProfile = { age: 31, city: 'New York' };
// Your code here

Need a hint?

Call set on userRef with updateProfile and the option { merge: true }.