Unable to generate classname.g.dart class using freezed package

Question

I have a freezed class that looks like this:

@freezed
abstract class GiftGiver with _$GiftGiver {
  const factory GiftGiver({
    String? id,
    String? uid,
    String? imageUrl,
    String? giftDetails,
    String? listingDate,
    @Default(5) int listingFor,
    Timestamp? pickUpTime,
    @Default(false) canLeaveOutside,
  }) = _GiftGiver;

  factory GiftGiver.fromJson(Map<String, dynamic> json) =>
      _$GiftGiverFromJson(json);
}

The freezed class is generated fine but .g.dart class is not generated as I have Timestamp type. I saw some solution at https://github.com/rrousselGit/freezed#fromjson---classes-with-multiple-constructors but I am not understanding how to apply it to solve my problem.

Answer 1

After some research I found out the solution. For types that are not supported by JsonSerializable I needed to use JsonKey to create my own toJson and fromJson method. I am attaching one such class that has Timestamp and Also another nested class (MyPosition) inside it.

@freezed
class GiftGiver with _$GiftGiver {
  const factory GiftGiver({
    String? id,
    required String uid,
    required String imageUrl,
    required String giftDetails,
    required String listingDate,
    required int listingFor,
    @JsonKey(fromJson: _pickedTimeFromJson, toJson: _pickedTimeToJson)
        required Timestamp pickUpTime,
    required bool canLeaveOutside,
    @JsonKey(fromJson: _fromJson, toJson: _toJson) required MyPosition position,
  }) = _GiftGiver;

  factory GiftGiver.fromJson(Map<String, dynamic> json) =>
      _$GiftGiverFromJson(json);
}

Map<String, dynamic> _toJson(MyPosition myPosition) => myPosition.toJson();
MyPosition _fromJson(Map<String, dynamic> json) => MyPosition.fromJson(json);

Timestamp _pickedTimeToJson(Timestamp pickUpTime) => pickUpTime;
Timestamp _pickedTimeFromJson(Timestamp json) => json;

GiftGiver class uses MyPosition (another Freezed class) which looks like this =>

@freezed
class MyPosition with _$MyPosition {
  const factory MyPosition({
    required String geohash,
    @JsonKey(fromJson: _geoPointFromJson, toJson: _geoPointToJson)
        required GeoPoint geopoint,
  }) = _MyPosition;

  factory MyPosition.fromJson(Map<String, dynamic> json) =>
      _$MyPositionFromJson(json);
}

GeoPoint _geoPointToJson(GeoPoint geoPoint) => geoPoint;
GeoPoint _geoPointFromJson(GeoPoint json) => json;

To use MyPosition in GiftGiver properly I needed to create _toJson and _fromJson and tell GIftGiver how to decode and encode MyPosition field.

Answer 2

Maybe you need to add the json_serializable package in the dev_dependencies section in the pubspec.yaml file.

If this is your case, delete the pubspeck.lock file, and then run the command flutter pub get to generate the file pubspeck.lock again.

Then, run the command flutter packages pub run build_runner build --delete-conflicting-outputs and fix to generate the .g file

Answer 3

For this to work, you need this:

dependencies:
  # ...
  json_annotation: ^4.8.1

and

dev_dependencies:
  # ...
  freezed: ^2.3.4
  json_serializable: ^6.7.0

If not mistaken you need json_serializable for the .g.dart file to be generated. When I added that it generated the needed file.

I think that is used for the fromJson factory method.