Realtime Database vs Firestore decision in Firebase - Hands-On Comparison

Realtime Database vs Firestore Decision

📖 Scenario: You are building a simple chat app that stores messages and user info. You want to choose between Firebase Realtime Database and Firestore for your backend database.Both databases store data in real time but have different structures and features.

🎯 Goal: Create a small Firebase configuration that sets up a database reference and writes a message. Then add a config variable to choose between Realtime Database and Firestore. Finally, write the code to save a message to the selected database.

📋 What You'll Learn

Create a Firebase config object with apiKey and projectId

Add a variable useFirestore to select the database type

Write a function saveMessage that saves a message to the chosen database

Complete the Firebase initialization with the correct database reference

💡 Why This Matters

🌍 Real World

Choosing between Firebase Realtime Database and Firestore is common when building apps that need real-time data syncing, like chat apps or collaborative tools.

💼 Career

Understanding how to configure and use Firebase databases helps in roles like frontend developer, mobile app developer, and cloud engineer working with real-time applications.

1

Setup Firebase config object

Create a constant called firebaseConfig with these exact properties: apiKey set to "ABC123" and projectId set to "chat-app".

Firebase

# Create the firebaseConfig object with apiKey and projectId
# Your code here

Hint

Use const to create an object with two properties.

2

Add database selection variable

Add a constant called useFirestore and set it to true to select Firestore as the database.

Firebase

const firebaseConfig = {
  apiKey: "ABC123",
  projectId: "chat-app"
};

// Add useFirestore variable below
# Your code here

Hint

Use const useFirestore = true; to choose Firestore.

3

Write saveMessage function

Write a function called saveMessage that takes a message string parameter. Inside, use if (useFirestore) to check the database type. If true, call firestore.collection('messages').add({ text: message }). Otherwise, call realtimeDb.ref('messages').push({ text: message }).

Firebase

const firebaseConfig = {
  apiKey: "ABC123",
  projectId: "chat-app"
};

const useFirestore = true;

// Write saveMessage function below
# Your code here

Hint

Use an if statement to choose the database and call the correct method to save the message.

4

Initialize Firebase and database references

Add code to initialize Firebase with firebase.initializeApp(firebaseConfig). Then create constants firestore as firebase.firestore() and realtimeDb as firebase.database().

Firebase

const firebaseConfig = {
  apiKey: "ABC123",
  projectId: "chat-app"
};

const useFirestore = true;

function saveMessage(message) {
  if (useFirestore) {
    firestore.collection('messages').add({ text: message });
  } else {
    realtimeDb.ref('messages').push({ text: message });
  }
}

// Initialize Firebase and create firestore and realtimeDb constants
# Your code here

Hint

Call firebase.initializeApp with the config, then create the database references.

Practice

1. Which Firebase database is best suited for simple real-time syncing of data as a JSON tree?

easy

A. Realtime Database

B. Firestore

C. Cloud Storage

D. Firebase Hosting

Solution

1. Step 1: Understand data structure of Realtime Database

   Realtime Database stores data as a JSON tree, which is simple and fast for syncing.

2. Step 2: Compare with Firestore

   Firestore uses collections and documents, better for complex queries but not just simple JSON tree syncing.

3. Final Answer:

   Realtime Database -> Option A

4. Quick Check:

   Simple JSON tree sync = Realtime Database [OK]

Hint: Simple JSON tree and fast sync? Choose Realtime Database [OK]

Common Mistakes:

• Confusing Firestore with Realtime Database
• Choosing Cloud Storage for database needs
• Thinking Firebase Hosting stores data

2. Which syntax correctly references a document in Firestore?

easy

A. db.store('users').document('user1')

B. db.collection('users').doc('user1')

C. db.get('users/user1')

D. db.ref('users/user1')

Solution

1. Step 1: Recall Firestore document reference syntax

   Firestore uses collection().doc() to reference documents.

2. Step 2: Identify incorrect options

   db.ref() is Realtime Database syntax; db.get() and db.store() are invalid here.

3. Final Answer:

   db.collection('users').doc('user1') -> Option B

4. Quick Check:

   Firestore document ref = collection().doc() [OK]

Hint: Firestore uses collection().doc() syntax [OK]

Common Mistakes:

• Using Realtime Database syntax for Firestore
• Mixing method names like get() or store()
• Confusing document and collection references

3. Given this Firestore query code, what will be the output if the 'users' collection has documents with ages 20, 25, and 30?

db.collection('users').where('age', '>', 22).get().then(snapshot => {
  let result = [];
  snapshot.forEach(doc => result.push(doc.data().age));
  console.log(result);
});

medium

A. [25, 30]

B. [20, 25, 30]

C. [22, 25]

D. []

Solution

1. Step 1: Understand the query condition

   The query filters users where age is greater than 22, so ages 25 and 30 qualify.

2. Step 2: Determine the output array

   The code collects ages from matching documents, so output is [25, 30].

3. Final Answer:

   [25, 30] -> Option A

4. Quick Check:

   age > 22 = [25, 30] [OK]

Hint: Filter > 22 excludes 20, includes 25 and 30 [OK]

Common Mistakes:

• Including 20 which is not > 22
• Confusing >= with > operator
• Assuming empty result without checking data

4. You wrote this Realtime Database code but it throws an error:

firebase.database().collection('users').doc('user1').get()

What is the main issue?

medium

A. Missing authentication before accessing database

B. The get() method is asynchronous and needs await

C. Realtime Database does not have collection() or doc() methods

D. The database URL is not specified

Solution

1. Step 1: Identify API mismatch

   Realtime Database uses ref() instead of collection() and doc(), which are Firestore methods.

2. Step 2: Confirm correct method usage

   Using collection() and doc() on Realtime Database causes error because those methods don't exist there.

3. Final Answer:

   Realtime Database does not have collection() or doc() methods -> Option C

4. Quick Check:

   Realtime DB uses ref(), not collection()/doc() [OK]

Hint: Realtime DB uses ref(), not collection() or doc() [OK]

Common Mistakes:

• Assuming get() needs await causes confusion
• Blaming authentication without checking API
• Thinking database URL causes this syntax error

5. You need to build a chat app that requires fast real-time updates and simple data structure. Which Firebase database should you choose and why?

hard

A. Firestore, because it supports complex queries and offline caching

B. Firestore, because it scales better for large datasets

C. Realtime Database, because it stores data in collections and documents

D. Realtime Database, because it syncs data instantly as a JSON tree

Solution

1. Step 1: Analyze app requirements

   The chat app needs fast real-time updates and a simple data structure.

2. Step 2: Match requirements to database features

   Realtime Database syncs data instantly as a JSON tree, ideal for simple real-time apps.

3. Step 3: Eliminate incorrect options

   Firestore supports complex queries and scales well but is more complex; Realtime Database does not use collections/documents.

4. Final Answer:

   Realtime Database, because it syncs data instantly as a JSON tree -> Option D

5. Quick Check:

   Simple real-time chat = Realtime Database [OK]

Hint: Fast real-time + simple data? Pick Realtime Database [OK]

Common Mistakes:

• Choosing Firestore for simple real-time needs
• Confusing data structure of Realtime Database
• Assuming Realtime Database uses collections/documents