Document ID strategies in Firebase - Mini Project: Build & Apply

Document ID strategies

📖 Scenario: You are building a simple app that stores user profiles in a Firebase Firestore database. Each user profile needs a unique document ID. You want to learn different ways to assign these document IDs when adding data to Firestore.

🎯 Goal: Learn how to create Firestore documents with different document ID strategies: auto-generated IDs, custom string IDs, and using user emails as IDs.

📋 What You'll Learn

Create a Firestore collection called users.

Add a user document with an auto-generated ID.

Add a user document with a custom string ID.

Add a user document using the user's email as the document ID.

💡 Why This Matters

🌍 Real World

In real apps, choosing the right document ID strategy helps organize data and makes it easier to find and update records.

💼 Career

Understanding Firestore document IDs is essential for backend and full-stack developers working with Firebase to build scalable cloud applications.

1

Create Firestore collection and add a user with auto-generated ID

Write code to add a user document to the users collection with fields name set to "Alice" and age set to 30. Use Firestore's auto-generated document ID feature by calling add() on the collection reference.

Firebase

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

const db = getFirestore();
const usersCollection = collection(db, 'users');

// Add a user with auto-generated ID
// Your code here

Hint

Use addDoc() with the collection reference and an object for the user data.

2

Add a user document with a custom string ID

Write code to add a user document to the users collection with document ID "user_bob". The user data should have name set to "Bob" and age set to 25. Use the setDoc() function with a document reference created by doc().

Firebase

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

const db = getFirestore();
const usersCollection = collection(db, 'users');

addDoc(usersCollection, { name: 'Alice', age: 30 });

// Add a user with custom ID 'user_bob'
// Your code here

Hint

Create a document reference with doc() using the collection name and custom ID, then use setDoc() to add data.

3

Add a user document using the user's email as the document ID

Write code to add a user document to the users collection with document ID set to the user's email "[e-mail]". The user data should have name set to "Carol" and age set to 28. Use doc() and setDoc() functions.

Firebase

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

const db = getFirestore();
const usersCollection = collection(db, 'users');

addDoc(usersCollection, { name: 'Alice', age: 30 });

const bobDoc = doc(db, 'users', 'user_bob');
setDoc(bobDoc, { name: 'Bob', age: 25 });

// Add a user with email as document ID '[e-mail]'
// Your code here

Hint

Use the email string as the document ID by passing it to doc(), then add data with setDoc().

4

Complete Firestore document ID strategies example

Ensure the code includes all three user additions: one with auto-generated ID for Alice, one with custom ID "user_bob" for Bob, and one with email ID "[e-mail]" for Carol. The code should import all necessary Firestore functions and initialize the Firestore database.

Firebase

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

const db = getFirestore();
const usersCollection = collection(db, 'users');

addDoc(usersCollection, { name: 'Alice', age: 30 });

const bobDoc = doc(db, 'users', 'user_bob');
setDoc(bobDoc, { name: 'Bob', age: 25 });

const carolDoc = doc(db, 'users', '[e-mail]');
setDoc(carolDoc, { name: 'Carol', age: 28 });

// Finalize the Firestore document ID strategies example
// Your code here

Hint

Make sure all previous steps are combined and all imports and variables are included.

Practice

1. What is the main purpose of a document ID in Firebase?

easy

A. To uniquely identify each record in a collection

B. To store user passwords securely

C. To define the database location

D. To control access permissions

Solution

1. Step 1: Understand what a document ID represents

   A document ID is a unique identifier for each record in a Firebase collection, ensuring each document can be accessed individually.

2. Step 2: Differentiate from other database concepts

   Document IDs are not used for storing passwords, defining database location, or controlling access permissions.

3. Final Answer:

   To uniquely identify each record in a collection -> Option A

4. Quick Check:

   Document ID = Unique record identifier [OK]

Hint: Document ID uniquely names each record [OK]

Common Mistakes:

• Confusing document ID with security rules
• Thinking document ID stores data
• Mixing document ID with database path

2. Which of the following is the correct way to let Firebase generate a document ID automatically?

easy

A. Use collectionRef.doc() without arguments

B. Use collectionRef.doc('customID')

C. Use collectionRef.add(data)

D. Use collectionRef.set(data)

Solution

1. Step 1: Identify Firebase methods for adding documents

   The add() method adds a document with an auto-generated ID to a collection.

2. Step 2: Understand difference from doc() and set()

   doc() with no argument creates a reference but does not add data; set() requires a document reference.

3. Final Answer:

   Use collectionRef.add(data) -> Option C

4. Quick Check:

   Auto ID creation = add() method [OK]

Hint: Use add() to auto-generate document ID [OK]

Common Mistakes:

• Using doc() without set() does not create document
• Assuming set() auto-generates ID
• Passing custom ID when auto ID is needed

3. Given this code snippet, what will be the document ID of the new document?

const docRef = collectionRef.doc('user123');
docRef.set({name: 'Alice'});

medium

A. 'user123'

B. Auto-generated random ID

C. 'Alice'

D. Undefined

Solution

1. Step 1: Analyze the doc() method argument

   The doc('user123') call creates a document reference with ID 'user123'.

2. Step 2: Understand set() usage

   The set() method writes data to the document with the specified ID.

3. Final Answer:

   'user123' -> Option A

4. Quick Check:

   doc('user123') sets document ID = 'user123' [OK]

Hint: doc('ID') sets document ID explicitly [OK]

Common Mistakes:

• Thinking set() changes the ID
• Assuming ID is auto-generated here
• Confusing document data with ID

4. What is wrong with this code if the goal is to create a document with an auto-generated ID?

const docRef = collectionRef.doc();

medium

A. doc() requires a string argument

B. doc() without arguments does not create a document automatically

C. set() cannot be used with doc()

D. The data object is missing an ID field

Solution

1. Step 1: Understand doc() without arguments

   Calling doc() without arguments creates a reference with a random ID but does not create the document automatically.

2. Step 2: Confirm the issue

   The code only creates a DocumentReference; to create the document, set(data) or add(data) is needed.

3. Final Answer:

   doc() without arguments does not create a document automatically -> Option B

4. Quick Check:

   doc() alone ≠ document creation [OK]

Hint: doc() alone doesn't create document, set() must follow [OK]

Common Mistakes:

• Assuming doc() creates document immediately
• Thinking set() is invalid here
• Expecting doc() to require argument always

5. You want to create user profiles with document IDs matching their usernames for easy lookup. Which strategy is best?

hard

A. Create documents without IDs and rely on collection order

B. Let Firebase auto-generate IDs and store username inside document

C. Use random UUIDs as document IDs and index usernames separately

D. Use usernames as document IDs by calling doc(username)

Solution

1. Step 1: Understand the goal

   The goal is to have document IDs that match usernames for easy direct lookup.

2. Step 2: Evaluate strategies

   Using doc(username) sets the document ID to the username, enabling direct access by username.

3. Step 3: Compare with other options

   Auto-generated IDs or random UUIDs require extra queries to find username; no IDs or relying on order is unreliable.

4. Final Answer:

   Use usernames as document IDs by calling doc(username) -> Option D

5. Quick Check:

   Username as ID = direct lookup [OK]

Hint: Use username as doc ID for direct access [OK]

Common Mistakes:

• Relying on auto IDs for username lookup
• Ignoring need for unique IDs
• Assuming collection order is stable