Flutter + Firebase in Production: 4 Apps, 18 Months, Key Lessons

// BAD: Reads ALL documents
final snapshot = await FirebaseFirestore.instance
    .collection('devices')
    .get();

// GOOD: Paginated + filtered
final snapshot = await FirebaseFirestore.instance
    .collection('devices')
    .where('userId', isEqualTo: currentUser.uid)
    .where('isActive', isEqualTo: true)
    .orderBy('lastSeen', descending: true)
    .limit(20)
    .get();

@riverpod
class DeviceController extends _$DeviceController {
  @override
  Future<List<Device>> build() async {
    final userId = ref.watch(currentUserProvider).value?.uid;
    if (userId == null) return [];
    
    return ref.watch(deviceRepositoryProvider).getDevices(userId);
  }
  
  Future<void> toggleDevice(String deviceId) async {
    final repo = ref.read(deviceRepositoryProvider);
    await repo.toggleDevice(deviceId);
    ref.invalidateSelf();
  }
}

class OfflineFirstRepository {
  final FirebaseFirestore _firestore;
  final SharedPreferences _prefs;
  
  Future<List<Device>> getDevices(String userId) async {
    try {
      // Try network first
      final snapshot = await _firestore
          .collection('devices')
          .where('userId', isEqualTo: userId)
          .get(const GetOptions(source: Source.server));
      
      // Cache locally
      await _cacheDevices(snapshot.docs);
      return _parseDevices(snapshot);
    } catch (e) {
      // Fallback to cache
      return _getCachedDevices();
    }
  }
}