Flutter null safety with fromJson - flutter

Question

Recently migrating to Flutter null safety feature, I have a lot of Classes that I need to update.
For my models, I use fromJson to deserialize the data from a json object. This forces me to put the late keyword for each field that is non optional.
Is that the right approach?
class ServerSession {
late String sessionId;
late String refreshToken;
late String accessToken;
ServerSession({required this.sessionId, required this.refreshToken, required this.accessToken});
ServerSession.fromJson(Map<String, dynamic> json) {
sessionId = json['session_id'] ?? json['sessionId'];
refreshToken = json['refresh_token'] ?? json['refreshToken'];
accessToken = json['access_token'] ?? json['accessToken'];
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = new Map<String, dynamic>();
data['sessionId'] = this.sessionId;
data['refreshToken'] = this.refreshToken;
data['accessToken'] = this.accessToken;
return data;
}
}

Answer 1

No, it is not. You should be using the initializer list for initializing fields of your class. You can read more about the initializer list in the language tour.
class ServerSession {
String sessionId;
String refreshToken;
String accessToken;
ServerSession({required this.sessionId, required this.refreshToken, required this.accessToken});
ServerSession.fromJson(Map<String, dynamic> json) :
sessionId = json['session_id'] ?? json['sessionId'],
refreshToken = json['refresh_token'] ?? json['refreshToken'],
accessToken = json['access_token'] ?? json['accessToken'];
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = new Map<String, dynamic>();
data['sessionId'] = this.sessionId;
data['refreshToken'] = this.refreshToken;
data['accessToken'] = this.accessToken;
return data;
}
}
I personally would use the "normal" constructor for the object and make fromJson a factory constructor, though either method works.
class ServerSession {
String sessionId;
String refreshToken;
String accessToken;
ServerSession({required this.sessionId, required this.refreshToken, required this.accessToken});
factory ServerSession.fromJson(Map<String, dynamic> json) {
return ServerSession(
sessionId: json['session_id'] ?? json['sessionId'],
refreshToken: json['refresh_token'] ?? json['refreshToken'],
accessToken: json['access_token'] ?? json['accessToken']
);
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = new Map<String, dynamic>();
data['sessionId'] = this.sessionId;
data['refreshToken'] = this.refreshToken;
data['accessToken'] = this.accessToken;
return data;
}
}