How to Structure Data in Firestore

1// Root collection: users
2// Path: users/{userId}
3// Subcollection: users/{userId}/orders
4// Path: users/{userId}/orders/{orderId}
5
6import { collection, doc, setDoc, serverTimestamp } from 'firebase/firestore';
7import { db } from './firebase';
8
9// Root-level document
10await setDoc(doc(db, 'users', 'user-1'), {
11  displayName: 'Alice',
12  email: 'alice@example.com',
13  role: 'member',
14  createdAt: serverTimestamp()
15});
16
17// Subcollection document
18await setDoc(doc(db, 'users', 'user-1', 'orders', 'order-1'), {
19  total: 49.99,
20  status: 'shipped',
21  createdAt: serverTimestamp()
22});

1// Root collection for posts (queryable across all users)
2await setDoc(doc(db, 'posts', 'post-1'), {
3  title: 'My first post',
4  content: 'Hello world',
5  authorId: 'user-1',
6  authorName: 'Alice',  // Denormalized for display
7  tags: ['firebase', 'tutorial'],
8  likes: 42,
9  createdAt: serverTimestamp()
10});
11
12// Now you can query all posts, filter by tag, sort by likes, etc.
13// without knowing which user wrote them

1// Chat messages as a subcollection of chatRooms
2// Path: chatRooms/{roomId}/messages/{messageId}
3
4import { addDoc, collection, query, orderBy, limit, getDocs } from 'firebase/firestore';
5
6// Add a message to a room
7await addDoc(collection(db, 'chatRooms', 'room-1', 'messages'), {
8  text: 'Hello everyone!',
9  senderId: 'user-1',
10  senderName: 'Alice',
11  createdAt: serverTimestamp()
12});
13
14// Query messages for a specific room
15const q = query(
16  collection(db, 'chatRooms', 'room-1', 'messages'),
17  orderBy('createdAt', 'desc'),
18  limit(50)
19);
20const snapshot = await getDocs(q);

1// Denormalized post document — contains author info directly
2await setDoc(doc(db, 'posts', 'post-1'), {
3  title: 'Building with Firebase',
4  content: 'A comprehensive guide...',
5  authorId: 'user-1',
6  authorName: 'Alice Johnson',       // Denormalized from users collection
7  authorPhotoURL: 'https://...',     // Denormalized from users collection
8  categoryId: 'tutorials',
9  categoryName: 'Tutorials',          // Denormalized from categories
10  commentCount: 12,                   // Denormalized count
11  lastCommentAt: serverTimestamp(),   // Denormalized timestamp
12  createdAt: serverTimestamp()
13});
14
15// Now displaying a list of posts requires only ONE query
16// No need to fetch author data separately

1import { collectionGroup, query, where, getDocs } from 'firebase/firestore';
2
3// Find all pending orders across ALL users
4const pendingOrders = query(
5  collectionGroup(db, 'orders'),
6  where('status', '==', 'pending')
7);
8
9const snapshot = await getDocs(pendingOrders);
10snapshot.forEach((doc) => {
11  console.log(doc.ref.path); // users/user-1/orders/order-3
12  console.log(doc.data());
13});

1// Pattern: E-commerce product with reviews
2// Products = root collection (global catalog)
3// Reviews = subcollection under each product
4// User profile = root collection
5
6// Product document with denormalized review summary
7await setDoc(doc(db, 'products', 'prod-1'), {
8  name: 'Wireless Headphones',
9  price: 79.99,
10  category: 'electronics',
11  // Denormalized review summary (updated via Cloud Function)
12  reviewCount: 234,
13  averageRating: 4.6,
14  // Embedded map for small fixed data
15  dimensions: {
16    weight: '250g',
17    width: '18cm',
18    height: '20cm'
19  },
20  // Array for small list of primitives
21  tags: ['wireless', 'bluetooth', 'noise-canceling'],
22  createdAt: serverTimestamp()
23});
24
25// Individual reviews in subcollection
26await addDoc(collection(db, 'products', 'prod-1', 'reviews'), {
27  userId: 'user-1',
28  userName: 'Alice',
29  rating: 5,
30  text: 'Great sound quality!',
31  createdAt: serverTimestamp()
32});