Is this factory a bad practice? - dart

Question

I'm working for a generic CRUD Repository but I have some problems with the serialization of my classes. For solving this issue I have create a factory on my base Entity:
const factories = {
Product: Product.fromJson,
};
abstract class Entity {
[...]
factory Entity.fromJson({
required Type type,
required Map json,
}) {
final factory = factories[type];
if (factory == null) {
throw Exception('Type Error: ($type) not found on factories');
}
return factory(json: json);
}
Map get json => {'id': id};
}
And in my repository abraction I just use this factory:
abstract class IDioCrudRepository<E extends Entity> extends DioRepository {
IDioCrudRepository({required super.baseUrl});
FutureOr<E> get(String id) async {
final res = await dio.get('$baseUrl/$id');
return Entity.fromJson(
type: E,
json: res.data as Map,
) as E;
}
[...]
}
Dou you know guys if this is a bad practice?

Answer 1

I would suggest you , at least, to make a Builder class and to move all that code far from Entity. In this manner entity class would not have any responsibility on how to build itself from a key and a json map.
const factories = {
Product: Product.fromJson,
};
class EntityBuilder {
static Entity fromJson({
required Type type,
required Map json,
}) {
final factory = factories[type];
if (factory == null) {
throw Exception('Type Error: ($type) not found on factories');
}
return factory(json: json);
}
}
abstract class Entity {
[...]
Map get json => {'id': id};
}
abstract class IDioCrudRepository<E extends Entity> extends DioRepository {
IDioCrudRepository({required super.baseUrl});
FutureOr<E> get(String id) async {
final res = await dio.get('$baseUrl/$id');
return EntityBuilder.fromJson(
type: E,
json: res.data as Map,
) as E;
}
[...]
}