Deserialization fails when using generic types

[caneva20]

Hello @k-paxian! I'm here once again 😃

So, given the following models:

@jsonSerializable
class Foo {}

@jsonSerializable
abstract class BarBase<T> {
  T foo;
}

@jsonSerializable
class Bar extends BarBase<Foo> {}

I get the following error when trying to deserialize it:

Unhandled exception:
type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'Foo' of 'value'
#0      BarBase.foo= (file:///C:/dev/flutter/json_tests/bin/task.dart)
#1      _data.<anonymous closure> (file:///C:/dev/flutter/json_tests/bin/main.mapper.g.dart:25:3302)
#2      _InstanceMirrorImpl.invokeSetter (package:reflectable/src/reflectable_builder_based.dart:355:20)
#3      JsonMapper._deserializeObject.<anonymous closure> (package:dart_json_mapper/src/mapper.dart:881:12)
#4      JsonMapper._enumeratePublicProperties (package:dart_json_mapper/src/mapper.dart:457:14)
#5      JsonMapper._deserializeObject (package:dart_json_mapper/src/mapper.dart:836:5)
#6      JsonMapper.deserialize (package:dart_json_mapper/src/mapper.dart:62:21)
#7      main (file:///C:/dev/flutter/json_tests/bin/main.dart:12:25)

my main():

void main() {
  initializeJsonMapper();

  var bar = Bar()..foo = Foo();

  var json = JsonMapper.serialize(bar);
  var bar2 = JsonMapper.deserialize<Bar>(json);
}

• If I use var bar = Bar(); it works fine.
• I've tried using a template, but the same thing happens.
• I've tried putting @Json(typeNameProperty: 'typeName') on Foo and BarBase, but it doesn't seem to help.

I understand that what I'm trying to do is kinda weird (why would someone want to do it like that?), and if that is not possible to do (not a bug) that's fine, I'll find an alternative.

[k-paxian]

Generics are tough in terms of deserialization 🤷

Anyway, I've got some examples for you

• This commit elaborates on your example use case

• Tuples use case: https://github.com/k-paxian/dart-json-mapper/blob/master/mapper/test/test.tuple.dart

• General generics https://github.com/k-paxian/dart-json-mapper/blob/master/mapper/test/test.generics.dart

Hope this helps somehow 😄

[masoodmrx]

Hello @k-paxian

I have the same problem, but the error is different

my main()

void main() {
  initializeJsonMapper();
  String json = '{"Success":true,"Result":{"Id":1,"Name":"aa"}}';
  ApiResult<UserModel>? result = JsonMapper.deserialize<ApiResult<UserModel>>(json);

...
}

my models

@jsonSerializable
class ApiResult<T> {
  bool? Success;
  T? Result;

  ApiResult({
    this.Success,
    this.Result,
  });

  ApiResult<T>? fromJson(dynamic json) =>
      JsonMapper.deserialize<ApiResult<T>>(json);

  dynamic toJson() =>
      JsonMapper.serialize(this, SerializationOptions(indent: ''));
}

@jsonSerializable
class UserModel {
  int? Id;
  String? Name;

  UserModel({
    this.Id,
    this.Name,
  });
}

@jsonSerializable
@Json(valueDecorators: ApiResultUserModel.valueDecorators)
class ApiResultUserModel extends ApiResult<UserModel> {
  static Map<Type, ValueDecoratorFunction> valueDecorators() =>
      {typeOf<ApiResult<UserModel>>(): (value) => ApiResultUserModel.of(value)};

  ApiResultUserModel({
    bool? Success,
    UserModel? Result,
  }) : super(
          Success: Success,
          Result: Result,
        );

  factory ApiResultUserModel.of(ApiResult other) => ApiResultUserModel(
        Success: other.Success,
        Result: other.Result,
      );
}

Serialization is done without errors

The package you produced is very simple and practical compared to other packages 👍

[k-paxian]

@masoodmrx Thank you for reporting that, I've got your use case working at this commit.

Anyway, the ApiResultUserModel class is an obvious overhead to simulate generics support, which makes generics not generics anymore 😞

I've got a future plan to handle generics in a more clean way, just like this copy cat package does, due to lack of time this might be not soon enough 🤷

[masoodmrx]

Hello @k-paxian

The error I sent above has not been resolved yet and only gives this error in the web browser
Please solve the problem, I need it
Thank you very much ❤️

[k-paxian]

With version2.2.1 and those models below, seems OK now, please confirm on your side.

@jsonSerializable
class ApiResult<T> {
  bool? Success;
  T? Result;

  ApiResult({
    this.Success,
    this.Result,
  });

  ApiResult<T>? fromJson(dynamic json) =>
      JsonMapper.deserialize<ApiResult<T>>(json);

  dynamic toJson() =>
      JsonMapper.serialize(this, SerializationOptions(indent: ''));
}

@jsonSerializable
class UserModel {
  int? Id;
  String? Name;

  UserModel({
    this.Id,
    this.Name,
  });
}

@jsonSerializable
@Json(valueDecorators: ApiResultUserModel.valueDecorators)
class ApiResultUserModel extends ApiResult<UserModel> {
  static Map<Type, ValueDecoratorFunction> valueDecorators() =>
      {typeOf<ApiResult<UserModel>>(): (value) => ApiResultUserModel.of(value)};

  ApiResultUserModel({
    bool? Success,
    UserModel? Result,
  }) : super(
          Success: Success,
          Result: Result,
        );

  factory ApiResultUserModel.of(ApiResult other) => ApiResultUserModel(
        Success: other.Success,
        Result: JsonMapper.deserialize<UserModel>(other.Result), /// <= Attention: here is the change
      );
}

[masoodmrx]

Error fixed
Thank you very much ❤️