Document-collection data model in Firebase - Mini Project: Build & Apply

Building a Simple Firestore Document-Collection Structure

📖 Scenario: You are creating a small app to store information about books in a library. Each book has a title, author, and year published. You will use Firestore's document-collection model to organize this data.

🎯 Goal: Build a Firestore structure with a collection called books. Each document in books will represent one book with fields for title, author, and year.

📋 What You'll Learn

Create a collection named books.

Add three book documents with exact fields and values.

Use a variable libraryRef to reference the books collection.

Write code to add a new book document to the books collection.

💡 Why This Matters

🌍 Real World

Firestore's document-collection model is used in many apps to store structured data like user profiles, product catalogs, or blog posts.

💼 Career

Understanding how to organize data in Firestore is essential for frontend and backend developers working with Firebase to build scalable, real-time applications.

1

Create the books collection with initial book documents

Create a Firestore collection reference called books and add three documents with these exact fields and values:
{ title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 },
{ title: '1984', author: 'George Orwell', year: 1949 },
{ title: 'To Kill a Mockingbird', author: 'Harper Lee', year: 1960 }.

Firebase

// Initialize Firestore and create the books collection reference
// Your code here

Hint

Use collection(db, 'books') to create the collection reference. Use addDoc to add each book document.

2

Create a variable libraryRef to reference the books collection

Create a new constant called libraryRef and assign it the value of the books collection reference.

Firebase

import { initializeApp } from 'firebase/app';
import { getFirestore, collection, addDoc } from 'firebase/firestore';

const firebaseConfig = {
  // Your Firebase config here
};

const app = initializeApp(firebaseConfig);
const db = getFirestore(app);

const books = collection(db, 'books');

const libraryRef = null; // Create libraryRef here

await addDoc(books, { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 });
await addDoc(books, { title: '1984', author: 'George Orwell', year: 1949 });
await addDoc(books, { title: 'To Kill a Mockingbird', author: 'Harper Lee', year: 1960 });

Hint

Assign libraryRef the value of books.

3

Add a new book document using libraryRef

Use await addDoc with libraryRef to add a new book document with these exact fields:
{ title: 'Brave New World', author: 'Aldous Huxley', year: 1932 }.

Firebase

import { initializeApp } from 'firebase/app';
import { getFirestore, collection, addDoc } from 'firebase/firestore';

const firebaseConfig = {
  // Your Firebase config here
};

const app = initializeApp(firebaseConfig);
const db = getFirestore(app);

const books = collection(db, 'books');
const libraryRef = books;

await addDoc(books, { title: 'The Great Gatsby', author: 'F. Scott Fitzgerald', year: 1925 });
await addDoc(books, { title: '1984', author: 'George Orwell', year: 1949 });
await addDoc(books, { title: 'To Kill a Mockingbird', author: 'Harper Lee', year: 1960 });

// Add new book document here

Hint

Use await addDoc(libraryRef, { ... }) to add the new book.

4

Complete the Firestore setup with proper async function wrapper

Wrap all Firestore calls inside an async function called setupLibrary and call it at the end of the code.

Firebase

import { initializeApp } from 'firebase/app';
import { getFirestore, collection, addDoc } from 'firebase/firestore';

const firebaseConfig = {
  // Your Firebase config here
};

const app = initializeApp(firebaseConfig);
const db = getFirestore(app);

// Wrap Firestore calls in async function
async function setupLibrary() {
  // Your code here
}

// Call the async function
setupLibrary();

Hint

Define an async function setupLibrary that contains all Firestore calls, then call it.

Practice

1. In Firebase's document-collection data model, what is the main container that holds documents?

easy

A. A collection

B. A table

C. A row

D. A field

Solution

1. Step 1: Understand Firebase data structure

   Firebase stores data in documents, and these documents are grouped inside collections.

2. Step 2: Identify the container for documents

   The container that holds multiple documents is called a collection, not a table, row, or field.

3. Final Answer:

   A collection -> Option A

4. Quick Check:

   Documents are inside collections [OK]

Hint: Remember: collections hold documents, like folders hold files [OK]

Common Mistakes:

• Confusing collections with tables from SQL
• Thinking documents are inside fields
• Mixing up rows with documents

2. Which of the following is the correct way to reference a document named user123 inside a collection users in Firebase?

easy

A. db.collection('users').doc('user123')

B. db.doc('users').doc('user123')

C. db.collection('user123').doc('users')

D. db.users('user123')

Solution

1. Step 1: Recall Firebase syntax for document reference

   To get a document inside a collection, use collection('name').doc('id').

2. Step 2: Match the correct syntax

   db.collection('users').doc('user123') uses db.collection('users').doc('user123'), which is the standard way.

3. Final Answer:

   db.collection('users').doc('user123') -> Option A

4. Quick Check:

   Use collection then doc to reference documents [OK]

Hint: Use collection('name').doc('id') to get a document [OK]

Common Mistakes:

• Swapping collection and doc order
• Using dot notation like db.users('user123')
• Using doc with full path incorrectly

3. Given this code snippet in Firebase:

const docRef = db.collection('books').doc('book1');
await docRef.set({ title: 'Learn Firebase', pages: 150 });
const snapshot = await db.collection('books').get();
const titles = snapshot.docs.map(doc => doc.data().title);
console.log(titles);

What will be printed in the console if the 'books' collection was empty before?

medium

A. []

B. ['book1']

C. ['Learn Firebase']

D. Error: Cannot read property 'title' of undefined

Solution

1. Step 1: Understand the code flow

   The code adds a document 'book1' with title and pages to 'books' collection, then fetches all documents in 'books'.

2. Step 2: Analyze the output of mapping titles

   Since 'books' was empty before, after adding 'book1', the collection has one document with title 'Learn Firebase'. Mapping titles returns ['Learn Firebase'].

3. Final Answer:

   ['Learn Firebase'] -> Option C

4. Quick Check:

   Added one doc, so titles list has one title [OK]

Hint: After set(), collection has that document; map titles returns it [OK]

Common Mistakes:

• Thinking snapshot is empty before set()
• Confusing document ID with title
• Expecting error due to async code

4. Consider this Firebase code snippet:

const userRef = db.collection('users').doc('user1');
userRef.get().then(doc => {
  if (doc.exists) {
    console.log(doc.data().name);
  } else {
    console.log('No such document!');
  }
});

If the document 'user1' does not exist, what will be printed?

medium

A. undefined

B. 'No such document!'

C. Error: doc.data() is undefined

D. null

Solution

1. Step 1: Check the existence condition

   The code checks if doc.exists is true before accessing data.

2. Step 2: Understand behavior when document missing

   If the document does not exist, doc.exists is false, so it prints 'No such document!'.

3. Final Answer:

   'No such document!' -> Option B

4. Quick Check:

   doc.exists false triggers else block [OK]

Hint: Check doc.exists before accessing data to avoid errors [OK]

Common Mistakes:

• Trying to access data without checking doc.exists
• Expecting undefined or null instead of message
• Confusing doc.exists with doc.data()

5. You want to store a list of users, each with multiple addresses, in Firebase. Which data model best fits this scenario?

hard

A. One document 'users' containing all users and their addresses as nested arrays

B. A single collection 'addresses' with documents containing user info and address combined

C. Multiple collections named after each user containing address documents

D. A collection 'users' with documents for each user, each containing a subcollection 'addresses' with address documents

Solution

1. Step 1: Understand hierarchical data in Firebase

   Firebase supports subcollections inside documents, which is ideal for related nested data.

2. Step 2: Choose the best structure for users and their multiple addresses

   Using a 'users' collection with each user document having an 'addresses' subcollection keeps data organized and scalable.

3. Final Answer:

   A collection 'users' with documents for each user, each containing a subcollection 'addresses' with address documents -> Option D

4. Quick Check:

   Use subcollections for nested related data [OK]

Hint: Use subcollections for nested lists like addresses per user [OK]

Common Mistakes:

• Storing all users and addresses in one big document
• Mixing user and address data in one collection without hierarchy
• Creating many collections named after users