Update method with flutter and sqlite generating error

Question

Good morning, I am updating to sqlite with Flutter and am having the following error:

NoSuchMethodError: The method 'update' was called on null.

I built the code according to the documentation where I receive a Model and make a map of the appropriate fields.

Future<void> updateCategoria(CategoriasModel categoriasModels) async {
  try {
   await db.update('categoria', categoriasModels.toMap(),
      where: "id = ?", whereArgs: [categoriasModels.id]);
   } catch (error) {
    print(error.toString());
  }
 }

and the model:

class CategoriasModel with ChangeNotifier {
  final int id;
  final String descricao;
  final int isReceita;

  CategoriasModel({
    this.id,
    this.descricao,
    this.isReceita,
  });

  Map<String, dynamic> toMap() {
    return {'id': id, 'descricao': descricao, 'isReceita': isReceita};
 }
}

other CRUD function are working normally.

Answer 1

The problem is occurring because the database was not initialized and has the value nulo. With that the method update cannot be used. The solution is to initialize the db before the method call update.

Example

Future<void> updateCategoria(CategoriasModel categoriasModels) async {
  try {
   // Inicialização do Database de exemplo (essa abordagem do exemplo
   // segue a implementação de utilizar um Helper Singleton, não é regra
   // e depende de como o projeto está trabalhando).
   final db = await DbHelper.getInstance().db;

   await db.update('categoria', categoriasModels.toMap(),
      where: "id = ?", whereArgs: [categoriasModels.id]);
   } catch (error) {
    print(error.toString());
  }
 }