Subcollections in Firebase - Mini Project: Build & Apply

Firebase Subcollections Setup

📖 Scenario: You are building a simple app to store information about books and their reviews. Each book can have multiple reviews stored inside it as a subcollection.

🎯 Goal: Create a Firestore database structure with a books collection. Inside each book document, create a reviews subcollection to hold review documents.

📋 What You'll Learn

Create a books collection with one book document having ID book1 and a field title with value 'Learn Firebase'.

Create a variable reviewCount set to 0 to track the number of reviews.

Add a review document inside the reviews subcollection of book1 with ID review1 and fields user: 'Alice' and comment: 'Great book!'.

Update the reviewCount field in the book1 document to 1.

💡 Why This Matters

🌍 Real World

Storing related data in subcollections is common in apps like book reviews, social media comments, or orders with items.

💼 Career

Understanding Firestore subcollections is essential for building scalable and organized NoSQL databases in many cloud applications.

1

Create the books collection with one book document

Create a Firestore collection called books. Add a document with ID book1 and a field title set to 'Learn Firebase'.

Firebase

// Initialize Firestore and create the books collection with book1 document
// Your code here

Need a hint?

Use setDoc with doc(db, 'books', 'book1') to create the document.

2

Create a review count variable

Create a variable called reviewCount and set it to 0 to track the number of reviews.

Firebase

import { getFirestore, doc, setDoc } from 'firebase/firestore';

const db = getFirestore();

await setDoc(doc(db, 'books', 'book1'), { title: 'Learn Firebase' });

// Create reviewCount variable
// Your code here

Need a hint?

Use let reviewCount = 0; to create the variable.

3

Add a review document inside the reviews subcollection

Add a document with ID review1 inside the reviews subcollection of the book1 document. The review document should have fields user set to 'Alice' and comment set to 'Great book!'.

Firebase

import { getFirestore, doc, setDoc } from 'firebase/firestore';

const db = getFirestore();

await setDoc(doc(db, 'books', 'book1'), { title: 'Learn Firebase' });

let reviewCount = 0;

// Add review1 document inside reviews subcollection
// Your code here

Need a hint?

Use setDoc with doc(db, 'books', 'book1', 'reviews', 'review1') to add the review document.

4

Update the reviewCount field in the book1 document

Update the reviewCount field in the book1 document to 1.

Firebase

import { getFirestore, doc, setDoc } from 'firebase/firestore';

const db = getFirestore();

await setDoc(doc(db, 'books', 'book1'), { title: 'Learn Firebase' });

let reviewCount = 0;

await setDoc(doc(db, 'books', 'book1', 'reviews', 'review1'), { user: 'Alice', comment: 'Great book!' });

// Update reviewCount field in book1 document
// Your code here

Need a hint?

Use setDoc with { merge: true } to update only the reviewCount field.