Flutter model for nested json object

Issue

I am new in Flutter. I have tried to developed Model class in dart. but always show the error message

Exception:type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'String', tt:#0      new User.fromJson

I don't understand, where my code will error. I want to solutions.

I want to convert model class in dart.

[
    {
        "route": {
            "routeID": "aaaaaaaa",
            "routeTitle": "bbbbbbbb"
        },
        "distributor": {
            "distributorID": "cccccccccccc",
            "distributorName": "ddddddddddd"
        },
        "visitDate": null
    }
]

I have been tried to my source code. like below code

import 'dart:convert';

List<User> userFromJson(String str) =>
    List<User>.from(json.decode(str).map((x) => User.fromJson(x)));

String userToJson(List<User> data) =>
    json.encode(List<dynamic>.from(data.map((x) => x.toJson())));

class User {
  User({
    this.visitDate,
    this.route,
    this.distributor,
  });

  String visitDate;
  String route;
  String distributor;

  factory User.fromJson(Map<String, dynamic> json) => User(
    visitDate: json["visitDate"],
    route: json["route"],
    distributor: json["distributor"],
  );

  Map<String, dynamic> toJson() => {
    "visitDate": visitDate,
    "route": route,
    "distributor": distributor,
  };
}

Route RouteFromJson(String str) => Route.fromJson(json.decode(str));

String RouteToJson(Route data) => json.encode(data.toJson());

class Route {
  Route({
    this.routeID,
    this.routeTitle,
  });

  String routeID;
  String routeTitle;

  factory Route.fromJson(Map<String, dynamic> json) => Route(
    routeID: json["routeID"],
    routeTitle: json["routeTitle"],
  );

  Map<String, dynamic> toJson() => {
    "routeID": routeID,
    "routeTitle": routeTitle,
  };
}
Distributor DistributorFromJson(String str) => Distributor.fromJson(json.decode(str));

String DistributorToJson(Distributor data) => json.encode(data.toJson());
class Distributor {
  Distributor({
    this.distributorID,
    this.distributorName,
  });

  String distributorID;
  String distributorName;

  factory Distributor.fromJson(Map<String, dynamic> json) => Distributor(
    distributorID: json["distributorID"],
    distributorName: json["distributorName"],
  );

  Map<String, dynamic> toJson() => {
    "distributorID": distributorID,
    "distributorName": distributorName,
  };
}

how to correct my model class. please help me. thanks

Solution

Change your User class like this :

 class User {
      User({
        this.visitDate,
        this.route,
        this.distributor,
      });
    
      String visitDate;
      Route route;
      Distributor distributor;
    
      factory User.fromJson(Map<String, dynamic> json) => User(
        visitDate: json["visitDate"],
        route = json['route'] != null ? Route.fromJson(json['route']) : null;
        distributor = json['distributor'] != null
            ? Distributor.fromJson(json['distributor'])
            : null;
      );
    
      Map<String, dynamic> toJson() => {
        "visitDate": visitDate,
        if (route != null) {
          data['route'] = this.route.toJson();
        }
        if (distributor != null) {
          data['distributor'] = this.distributor.toJson();
        }
      };
    }

Answered By - Mojtaba Ghiasi