json.dart

import 'dart:convert';

void main() {
  final stringifiedJson = '{"id": "1", "name": "ford", "description": "fast car", "roof_material": "glass", "some_other_prop": "hello"}';

  final json = jsonDecode(stringifiedJson);
  final cabrio = Car.fromJson(json, 'cabrio') as Cabrio;
  print('Roof material: ${cabrio.roofMaterial}'); // null
  print('Some other prop: ${cabrio.someOtherProp}');
}


abstract class Car {
  int id;
  String name;
  String description;

  Car({
    required this.id,
    required this.name,
    required this.description,
  });

  factory Car.fromJson(Map<String, dynamic> json, String type) {
    Car car;
    if (type == 'cabrio') {
      car = Cabrio.fromJson(json);
      car.id = int.parse(json['id']);
      car.name = json['name'];
      car.description = json['description'];
      return car;
    }
    // other possible if-statements
    throw Exception('not our type');
  }
}


class Cabrio extends Car {
  String roofMaterial;
  String someOtherProp;

  Cabrio({
    required super.id,
    required super.name,
    required super.description,
    required this.roofMaterial,
    required this.someOtherProp
  });

  factory Cabrio.fromJson(Map<String, dynamic> json) =>
      Cabrio(
          id: int.parse(json['id']),
          name: json['name'],
          description: json['description'],
          roofMaterial: json['roof_material'],
          someOtherProp: json['some_other_prop']
      );
}