Firebase Realtime Database Skill

This skill defines how to correctly implement Firebase Realtime Database in Flutter applications, covering data modeling, queries, real-time sync, offline support, and security rules.

When to Use

Use this skill when working with Firebase Realtime Database for simple data models, low-latency sync, or presence functionality. For rich data models requiring complex queries and high scalability, use Cloud Firestore instead.

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1. Database Selection

Choose Realtime Database when the app needs:

• Simple data models with simple lookups.
• Extremely low-latency synchronization (typical response times under 10ms).
• Deep queries that return an entire subtree by default.
• Access to data at any granularity, down to individual leaf-node values.
• Frequent state-syncing with built-in presence functionality.

Choose Cloud Firestore instead for rich data models requiring queryability, scalability, and high availability.

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2. Setup and Configuration

flutter pub add firebase_database

import 'package:firebase_database/firebase_database.dart';

// After Firebase.initializeApp():
final DatabaseReference ref = FirebaseDatabase.instance.ref();

• Select the database location closest to users.
• Enable persistence for offline capabilities:

FirebaseDatabase.instance.setPersistenceEnabled(true);
FirebaseDatabase.instance.setPersistenceCacheSizeBytes(10000000); // 10MB

Setup Checklist

1. Confirm Firebase.initializeApp() completes before accessing FirebaseDatabase.instance.
2. Set persistence before any read/write operations.
3. Verify connectivity by writing a test value and reading it back.

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3. Data Structure

• Structure data as a flattened JSON tree, avoid deep nesting.
• Maximum nesting depth is 32 levels.
• Design the data structure to support the most common queries.
• Use push IDs for unique identifiers in list-type data: