toJson and fromJson work differently with nested objects

[CarmeloBeeapp]

The two methods are working in different ways

for example using these classes:

@JsonSerializable()
class Parent {
  String name;
  String surname;
  Child child1;
  Child child2;

  factory Parent.fromJson(Map<String, dynamic> json) => _$ParentFromJson(json);

  Parent({required this.name, required this.surname, required this.child1, required this.child2});

  Map<String, dynamic> toJson() => _$ParentToJson(this);
}

@JsonSerializable()
class Child {
  String name;
  String surname;

  factory Child.fromJson(Map<String, dynamic> json) => _$ChildFromJson(json);

  Child({required this.name, required this.surname});

  Map<String, dynamic> toJson() => _$ChildToJson(this);
}

the fromJson methods are correctly:

Parent _$ParentFromJson(Map<String, dynamic> json) => Parent(
  name: json['name'] as String,
  surname: json['surname'] as String,
  child1: Child.fromJson(json['child1'] as Map<String, dynamic>),
  child2: Child.fromJson(json['child2'] as Map<String, dynamic>),
);

Child _$ChildFromJson(Map<String, dynamic> json) =>
    Child(name: json['name'] as String, surname: json['surname'] as String);

instead the toJson methods are the following

Map<String, dynamic> _$ParentToJson(Parent instance) => <String, dynamic>{
  'name': instance.name,
  'surname': instance.surname,
  'child1': instance.child1,
  'child2': instance.child2,
};

Map<String, dynamic> _$ChildToJson(Child instance) => <String, dynamic>{
  'name': instance.name,
  'surname': instance.surname,
};

with nested objects the toJson method doesn't convert the object in json.

As workaround at the moment is required to define a custom method to parse the nested object and pass it in the annotation

@JsonSerializable()
class Parent {
  String name;
  String surname;
  @JsonKey(toJson: childToJson)
  Child child1;
  @JsonKey(toJson: childToJson)
  Child child2;

  factory Parent.fromJson(Map<String, dynamic> json) => _$ParentFromJson(json);

  Parent({required this.name, required this.surname, required this.child1, required this.child2});

  Map<String, dynamic> toJson() => _$ParentToJson(this);
}

Map<String, dynamic> _$ParentToJson(Parent instance) => <String, dynamic>{
  'name': instance.name,
  'surname': instance.surname,
  'child1': childToJson(instance.child1),
  'child2': childToJson(instance.child2),
};