How to create singleton database object and utilise in different files?

I want to create the database for my app and I'm using floor database. I have created entity, dao and database class like below.

@entity
class User{
  @primaryKey
  final int id;

  final String name;
  final String email;
  User(this.id, this.name, this.email);
}

@dao
abstract class UserDao {
  @Query('SELECT * FROM User')
  Future<List<User>> findAllUsers();

  @Query('DELETE FROM User WHERE id = :id')
  Future<void> deleteUserById(int id);

  @insert
  Future<void> insertUser(User user);
}

@Database(version: 1, entities: [User])
abstract class Appdatabase extends FloorDatabase{
  UserDao get userDao;
}

and I have created a database with name in my main.dart file like below.

 final database = await $FloorAppdatabase.databaseBuilder("MY_DATABASE").build();

I can store the data like this database.userDao().insertUser(user); But If i want to use database object in other file then I have to create it as a common one. Can someone help me how to create it as a common file and I can use it anywhere I want?

Solution

You can create a singleton class like the one below.

class DatabaseHelper {
  static final DatabaseHelper instance = DatabaseHelper._internal();

  DatabaseHelper._internal();

  late final AppDatabase database;

  Future<void> initializeDatabase() async {
    database = await $FloorAppDatabase.databaseBuilder("MY_DATABASE").build();
  }
}

you initialize the database it in the main

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await DatabaseHelper.instance.initializeDatabase();

  runApp(const MyApp());
}

And later, you can call it from anywhere using:

final database = DatabaseHelper.instance.database;
final user = User(1, 'Test', 'test@example.com');
database.userDao.insertUser(user);

or you can use the get_it package, you initialize the database with get_it like:

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  GetIt.I.registerSingletonAsync<AppDatabase>(() async {
    return $FloorAppDatabase.databaseBuilder("MY_DATABASE").build();
  });
  await GetIt.I.allReady();

  runApp(const MyApp());
}

And later, you can call it from anywhere using:

final database = GetIt.instance<AppDatabase>();
final user = User(4, 'John Doe', 'john.doe@example.com');
database.userDao.insertUser(user);