Extend with fromJson in dart

Question

I have an Identity class in dart which looks (simplified) like this

class Identity {
  final String phoneNumber;

  Identity({@required this.phoneNumber});

  Identity.fromJson(Map<String, dynamic> json)
      : phoneNumber = json['phoneNumber'];

}

I will use this class to send an http POST to my identity service; this service will return a json which I want to map to ActiveIdentity, which looks like this (also simplified).

class ActiveIdentity extends Identity {
  final String id;

  ActiveIdentity.fromJson(Map<String, dynamic> json)
          : id = json['id'];
}

Now, is there a way to extend or call fromJson in Identity so that I can "extend" this method? Ideally when calling fromJson in ActiveIdentity I should receive a new ActiveIdentity instance with all properties inititalized (phoneNumber and id) but on ActiveIdentity I only want to deal with id.

I also tried to think about this in terms of mixins, but failed miserably... any idea on how would be the best way to achieve this?

Thanks!

Answer 1

I think the following should solve your problem:

class Identity {
  final String phoneNumber;

  Identity({@required this.phoneNumber});

  Identity.fromJson(Map<String, dynamic> json)
      : phoneNumber = json['phoneNumber'];
}

class ActiveIdentity extends Identity {
  final String id;

  ActiveIdentity.fromJson(Map<String, dynamic> json)
      : id = json['id'],
        super.fromJson(json) {
    print('$phoneNumber $id');
  }
}

Try having a look at the Dart documentation of constructors for clarification on this topic.