[Question] Freeze a subtype model when it needs fields in a supertype

[AlexV525]

Context
We have a base class for models:

abstract class DataModel {
  const DataModel();

  Json toJson();

  @override
  String toString() => GlobalJsonEncoder.convert(toJson());
}

And we have an ORM model for most of subtype models:

abstract class ORMModel extends DataModel {
  const ORMModel({
    required this.id,
    required this.createTime,
    required this.updateTime,
  });

  final Object id;
  @JsonKey(fromJson: datetimeFromJson, toJson: datetimeToString)
  final DateTime createTime;
  @JsonKey(fromJson: datetimeFromJson, toJson: datetimeToString)
  final DateTime updateTime;

  ValueKey<String> valueKey([String tag = 'default']) {
    return ValueKey<String>(
      '$runtimeType-$id-${updateTime.millisecondsSinceEpoch}-$tag',
    );
  }
}

Consider we have a model like:

@immutable
@JsonSerializable()
class Item extends ORMModel {
  const Item({
    required this.type,
    required Object id,
    required DateTime createTime,
    required DateTime updateTime,
  }) : super(id: id, createTime: createTime, updateTime: updateTime);

  factory Item.fromJson(Json json) => _$ItemFromJson(json);

  final int type;

  @override
  Json toJson() => _$ItemToJson(this);
}

How do we manage to make Item freezed?

Describe the solution you'd like
Support to freeze model like above.

Describe alternatives you've considered
I know that getters are only supported with the _ constructor, but with that constructor, we still can't use fields in supertypes.

[rrousselGit]

There is no support for super constructors. Consider using implements/with instead of extends

[AlexV525]

Consider using implements/with instead of extends

This seems unimplementable at present, Item must extend DataModel/ORMModel to get through the constructor, which is required by the fromJson method.

[rrousselGit]

the DataModel you've described could be a mixin. The ORMModel too

mixin DataModel {
  Json toJson();

  @override
  String toString() => GlobalJsonEncoder.convert(toJson())
}

mixin ORMModel on DataModel {
  Object get id;
  DateTime get createTime;
  DateTime get updateTime;

  ValueKey<String> valueKey([String tag = 'default']) {
    return ValueKey<String>(
      '$runtimeType-$id-${updateTime.millisecondsSinceEpoch}-$tag',
    );
  }
}

@freezed
class Item with DataModel, ORMModel {
  const Item._();
  const factory Item({
    required this.type,
    required Object id,
    @JsonKey(fromJson: datetimeFromJson, toJson: datetimeToString)
     required DateTime createTime,
    @JsonKey(fromJson: datetimeFromJson, toJson: datetimeToString)
    required DateTime updateTime,
  }) = _Item;

  factory Item.fromJson(Json json) => _$ItemFromJson(json);
}

[CrossBread]

Thanks @rrousselGit , I've been scratching my head trying to sort out exactly how to do this and wondered if mixin was the solution, but it wasn't clear from the documentation whether Freezed would play well with fields coming from the mixin.

One further question for clarity, does the _$Item mixin go before the others so they also inherit from it, or after the others so that the generated mixin inherits from both DataModel and ORMModel?

@freezed
class Item with _$Item, DataModel, ORMModel {/*...*/}

Or

@freezed
class Item with DataModel, ORMModel, _$Item {/*...*/}

Thanks!

[jetaggart]

@CrossBread any chance you figured this out? Stuck on this same problem.