10 Powerful Reasons to Use Firebase as Your Mobile App Backend in 2025

📘 Chapter 3: Working with Firebase Realtime Database and Firestore

🔍 Overview

Every app needs a place to store and sync data, and Firebase offers two powerful NoSQL cloud database options—Realtime Database and Cloud Firestore. Both provide flexible, scalable data solutions with seamless integration into mobile and web apps. This chapter compares the two, demonstrates how to use them, and helps you decide which to choose for your project.

🧠 Key Concepts

• Firebase Realtime Database stores data as a single large JSON tree and provides low-latency synchronization.
• Cloud Firestore organizes data into collections and documents, offering more powerful querying and structure.

🔁 Realtime Database vs. Firestore: Comparison Table

🔧 Setting Up Firebase Database Services

🔹 Step 1: Enable the Database in Firebase Console

• Go to Firebase Console > Database
• Choose either Realtime Database or Firestore
• Set rules (test or production)

🔗 Firebase SDK Setup (Java for Android)

groovy

dependencies {

    implementation 'com.google.firebase:firebase-database:20.3.0' // Realtime DB

    implementation 'com.google.firebase:firebase-firestore:24.7.0' // Firestore

}

📘 Using Firebase Realtime Database

🔹 Saving Data

java

DatabaseReference dbRef = FirebaseDatabase.getInstance().getReference("users");

User user = new User("Alice", "alice@example.com");

dbRef.push().setValue(user);

🔹 Reading Data

java

dbRef.addValueEventListener(new ValueEventListener() {

    @Override

    public void onDataChange(DataSnapshot snapshot) {

        for (DataSnapshot userSnapshot : snapshot.getChildren()) {

            User user = userSnapshot.getValue(User.class);

        }

    }

    @Override

    public void onCancelled(DatabaseError error) {

        Log.w("FirebaseDB", "loadPost:onCancelled", error.toException());

    }

});

🔹 Updating Data

java

dbRef.child("userId123").child("email").setValue("newemail@example.com");

🔹 Realtime DB Use Case: Chat Application

JSON Tree Example:

json

"chats": {

  "room1": {

    "message1": {

      "sender": "John",

      "text": "Hello"

    },

    "message2": {

      "sender": "Jane",

      "text": "Hi!"

    }

  }

}

🔥 Using Cloud Firestore

🔹 Creating and Writing to a Document

java

FirebaseFirestore db = FirebaseFirestore.getInstance();

Map<String, Object> user = new HashMap<>();

user.put("name", "Bob");

user.put("email", "bob@example.com");

db.collection("users").add(user);

🔹 Reading Documents

java

db.collection("users").get()

  .addOnSuccessListener(querySnapshot -> {

      for (DocumentSnapshot doc : querySnapshot) {

          Log.d("Firestore", doc.getId() + " => " + doc.getData());

      }

  });

🔹 Updating a Document

java

db.collection("users").document("userId123")

  .update("email", "updated@example.com");

🔹 Firestore Use Case: E-Commerce Product Catalog

Firestore Structure Example:

bash

users/

  userId123/

    name: "Sara"

    email: "sara@example.com"

products/

  prod001/

    title: "Shoes"

    price: 49.99

orders/

  order789/

    userId: "userId123"

    items: ["prod001", "prod002"]

📊 Querying in Firestore

java

db.collection("products")

  .whereEqualTo("category", "shoes")

  .orderBy("price", Query.Direction.ASCENDING)

  .get()

  .addOnSuccessListener(querySnapshot -> {

      for (DocumentSnapshot doc : querySnapshot) {

          Log.d("Product", doc.getId() + " => " + doc.getData());

      }

  });

🔒 Securing Your Data: Firebase Rules

🔹 Realtime DB Rule

json

{

  "rules": {

    ".read": "auth != null",

    ".write": "auth != null"

  }

}

🔹 Firestore Rule

js

rules_version = '2';

service cloud.firestore {

  match /databases/{database}/documents {

    match /users/{userId} {

      allow read, write: if request.auth.uid == userId;

    }

  }

}

🌐 Offline Support

Both databases support offline capabilities:

• Realtime Database caches data and syncs when reconnected.
• Firestore provides better offline querying and local persistence.

java

FirebaseDatabase.getInstance().setPersistenceEnabled(true);

Firestore enables it automatically on mobile.

🧩 Choosing Between Realtime DB and Firestore

✅ Best Practices

• Use Firestore for most new apps due to scalability and querying
• Avoid nesting deeply in Realtime DB (limits query performance)
• Apply security rules early in development
• Normalize data in Firestore for easier querying
• Use pagination and batch writes to optimize performance
• Monitor reads/writes to control cost (Firestore charges per operation)

🧪 Testing and Debugging

• Use Firebase Emulator Suite to test database rules and operations locally.
• Use Firebase Console > Firestore / Realtime DB for real-time monitoring.
• Apply addOnFailureListener() for every operation to handle errors gracefully.

📌 Conclusion

Both Firebase Realtime Database and Firestore offer real-time, cloud-hosted NoSQL solutions that eliminate the need for traditional backend setup. Firestore is the newer, more structured option with powerful querying and scalability, while Realtime DB remains useful for ultra-fast syncing in simpler apps.

In the next chapter, we’ll explore Firebase Cloud Functions and how to automate server-side tasks and event-driven logic.