Creating collections and documents in Firebase - Try It Yourself

Creating collections and documents

📖 Scenario: You are building a simple app to store user profiles in a cloud database. Each user has a name and an email address. You will create a collection called users and add documents for each user.

🎯 Goal: Create a Firestore collection named users and add user documents with name and email fields.

📋 What You'll Learn

Create a Firestore collection called users

Add a document for a user with name and email fields

Add a second user document with the same fields

Use Firestore's setDoc method to add documents

💡 Why This Matters

🌍 Real World

Storing user profiles or any structured data in a cloud database for web or mobile apps.

💼 Career

Understanding how to create collections and documents in Firestore is essential for backend and full-stack developers working with Firebase.

1

Initialize Firestore and create the users collection reference

Write code to initialize Firestore and create a collection reference called usersRef for the users collection.

Firebase

// Initialize Firestore and create usersRef collection reference
// Your code here

Hint

Use collection(db, 'users') to create the collection reference.

2

Create a user object to add

Create a constant object called user1 with name set to 'Alice' and email set to '[e-mail]'.

Firebase

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

const firebaseConfig = {
  apiKey: 'your-api-key',
  authDomain: 'your-auth-domain',
  projectId: 'your-project-id',
  storageBucket: 'your-storage-bucket',
  messagingSenderId: 'your-messaging-sender-id',
  appId: 'your-app-id'
};

const app = initializeApp(firebaseConfig);
const db = getFirestore(app);
const usersRef = collection(db, 'users');

// Create user1 object with name and email
// Your code here

Hint

Use const user1 = { name: 'Alice', email: '[e-mail]' }.

3

Add the first user document to the users collection

Write code to add user1 as a document to the usersRef collection using the setDoc method with a document reference named user1Doc created by doc(usersRef, 'user1').

Firebase

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

const firebaseConfig = {
  apiKey: 'your-api-key',
  authDomain: 'your-auth-domain',
  projectId: 'your-project-id',
  storageBucket: 'your-storage-bucket',
  messagingSenderId: 'your-messaging-sender-id',
  appId: 'your-app-id'
};

const app = initializeApp(firebaseConfig);
const db = getFirestore(app);
const usersRef = collection(db, 'users');

const user1 = { name: 'Alice', email: '[e-mail]' };

// Create user1Doc and use setDoc to add user1
// Your code here

Hint

Use doc(usersRef, 'user1') to create the document reference and setDoc to add the data.

4

Add a second user document to the users collection

Create a constant object called user2 with name set to 'Bob' and email set to '[e-mail]'. Then create a document reference called user2Doc using doc(usersRef, 'user2') and add user2 to the collection using setDoc.

Firebase

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

const firebaseConfig = {
  apiKey: 'your-api-key',
  authDomain: 'your-auth-domain',
  projectId: 'your-project-id',
  storageBucket: 'your-storage-bucket',
  messagingSenderId: 'your-messaging-sender-id',
  appId: 'your-app-id'
};

const app = initializeApp(firebaseConfig);
const db = getFirestore(app);
const usersRef = collection(db, 'users');

const user1 = { name: 'Alice', email: '[e-mail]' };

const user1Doc = doc(usersRef, 'user1');
setDoc(user1Doc, user1);

// Create user2 object, user2Doc reference, and add user2 with setDoc
// Your code here

Hint

Repeat the steps for user1 but with user2 and user2Doc.

Practice

1. What is a collection in Firebase Firestore?

easy

A. A function to add data.

B. A single document storing data.

C. A group that holds multiple documents.

D. A method to delete documents.

Solution

1. Step 1: Understand Firestore structure

   Firestore organizes data in collections and documents.

2. Step 2: Define collection role

   A collection groups multiple documents together.

3. Final Answer:

   A group that holds multiple documents. -> Option C

4. Quick Check:

   Collection = group of documents [OK]

Hint: Collections hold documents, not single data items. [OK]

Common Mistakes:

• Confusing collection with a single document
• Thinking collection is a method
• Mixing collection with data fields

2. Which Firebase Firestore method creates a document with an auto-generated ID?

easy

A. set()

B. add()

C. update()

D. get()

Solution

1. Step 1: Recall document creation methods

   Firestore uses set() to create or overwrite documents with specific IDs.

2. Step 2: Identify method for auto-generated IDs

   The add() method creates a document with an auto-generated ID inside a collection.

3. Final Answer:

   add() -> Option B

4. Quick Check:

   Auto-ID document creation = add() [OK]

Hint: Use add() for auto-generated document IDs. [OK]

Common Mistakes:

• Using set() and expecting auto-ID
• Confusing update() with creation
• Using get() which only reads data

3. What will happen when this code runs?

db.collection('users').doc('user1').set({name: 'Anna', age: 25});

medium

A. Creates or overwrites 'user1' document with name and age.

B. Adds a new document with auto-generated ID.

C. Updates only the age field in 'user1' document.

D. Throws an error because set() needs add() instead.

Solution

1. Step 1: Analyze method usage

   set() on a doc reference creates or overwrites that document.

2. Step 2: Check document ID and data

   The doc ID is 'user1', so this document will be created or replaced with given data.

3. Final Answer:

   Creates or overwrites 'user1' document with name and age. -> Option A

4. Quick Check:

   set() on doc('user1') = overwrite/create [OK]

Hint: set() replaces document at given ID, add() creates new ID. [OK]

Common Mistakes:

• Thinking add() is needed for specific IDs
• Assuming update() is called by set()
• Confusing set() with partial update

4. Identify the error in this Firestore code:

db.collection('products').add({name: 'Book', price: 10}).doc('p1').set({price: 12});

medium

A. No error, code works fine.

B. set() cannot update price field.

C. Collection name 'products' is invalid.

D. add() returns a promise, chaining doc() is invalid.

Solution

1. Step 1: Understand add() return value

   add() returns a promise resolving to a document reference, not a direct reference.

2. Step 2: Check chaining doc() after add()

   Calling doc() on the promise or document reference from add() is invalid syntax.

3. Final Answer:

   add() returns a promise, chaining doc() is invalid. -> Option D

4. Quick Check:

   add() returns promise, cannot chain doc() directly [OK]

Hint: add() returns promise; await before doc() calls. [OK]

Common Mistakes:

• Chaining doc() immediately after add()
• Ignoring promise returned by add()
• Assuming set() cannot update fields

5. You want to create a collection 'orders' and add a document with a specific ID 'order123' containing {item: 'Pen', quantity: 3}. Which code snippet is correct?

hard

A. db.collection('orders').doc('order123').set({item: 'Pen', quantity: 3});

B. db.collection('orders').add({item: 'Pen', quantity: 3, id: 'order123'});

C. db.collection('orders').doc().set({item: 'Pen', quantity: 3, id: 'order123'});

D. db.collection('orders').set('order123', {item: 'Pen', quantity: 3});

Solution

1. Step 1: Identify method to create document with specific ID

   Use doc('order123') to specify the document ID explicitly.

2. Step 2: Use set() to create or overwrite document data

   set() writes the data to the specified document ID.

3. Final Answer:

   db.collection('orders').doc('order123').set({item: 'Pen', quantity: 3}); -> Option A

4. Quick Check:

   Specific ID document creation = doc(id).set() [OK]

Hint: Use doc('id').set() for specific document IDs. [OK]

Common Mistakes:

• Using add() with id field (does not set document ID)
• Calling doc() without ID for specific ID
• Using set() directly on collection