How to map dynamic json api responses in dart

Question

I have an API response payload with dynamic data in the body. The API returns a list of objects in the data tag. I am trying to map the response to the appropriate model at runtime, however, I get an error message when doing so. How do I map the dynamic response objects at runtime without explicitly creating an API response model for each? Ideally the solution should be able to determine the target model the response object should be mapped to at runtime.

I get the following error with my code: The argument type 'List<Map<String, dynamic>>' can't be assigned to the parameter type 'Map<String, dynamic>'.

Following my attempt:

return ApiResponse<Team>.fromJson(json.decode(response.body), (data) => Team.fromJson(data) as List<Map<String, dynamic>>);

// Maps the API response to object
class ApiResponse<T> {
  int status;
  String? message;
  T data;

  ApiResponse({
    required this.status,
    this.message,
    required this.data,
  });

  factory ApiResponse.fromJson(Map<String, dynamic> json, Function(List<Map<String, dynamic>>) create) {
    return ApiResponse<T>(
      status: json['status'],
      message: json['message'],
      data: create(json['data']),
    );
  }
}

My models


class User{
  int? id;
  String? name;
  String? description;
  DateTime? createdAt;
  DateTime? updatedAt;

  User({
    this.id,
    this.name,
    this.description,
    this.createdAt,
    this.updatedAt
  });

  factory User.fromJson(Map<String, dynamic> json){
    return User(
      id: json['id'],
      name: json['name'],
      description: json['description'],
      createdAt: DateTime.parse(json['created_at']),
      updatedAt: DateTime.parse(json['updated_at']),
    );
  }
}


class Team {
  int id;
  String? name;
  String? region;
  DateTime? createdAt;
  DateTime? updatedAt;

  Team({
    required this.id,
    this.name,
    this.region,
    this.createdAt,
    this.updatedAt,
  });

  factory Team.fromJson(Map<String, dynamic> json){
    return Team(
      id: json['id'],
      name: json['name'],
      region: json['region'],
      createdAt: DateTime.parse(json['created_at']),
      updatedAt: DateTime.parse(json['updated_at']),
    );
  }
}

API response


{
  "status": 200,
  "message": "Returned",
  "data": [
    {
      "id": 1,
      "name": "Trevo Mgino",
      "description": "A Description",
      "created_at": "2021-09-29T06:47:03.000000Z",
      "updated_at": "2021-09-29T06:47:03.000000Z"
    }
  ],
}

{
  "status": 200,
  "message": "Activated",
  "data": [
    {
      "id": 1,
      "name": "Team A",
      "region": "Region 1",
      "created_at": "2021-09-29T06:47:03.000000Z",
      "updated_at": "2021-09-29T06:47:03.000000Z"
    },
    {
      "id": 2,
      "name": "Team B",
      "region": "Region 1",
      "created_at": "2021-09-29T06:47:03.000000Z",
      "updated_at": "2021-09-29T06:47:03.000000Z"
    }
  ],
}

just decode your json and pass this json team.formjson(json) — Muhammad Arbaz Zafar
– Muhammad Arbaz Zafar, Commented Oct 4, 2021 at 11:47

Lulupointu · Accepted Answer · 2021-10-04 11:49:19Z

Team.fromJson takes a Map<String, dynamic> as a parameters but you give it a List<Map<String, dynamic>>.

I think what you want is to change the first expression you gave to:

ApiResponse<Team>.fromJson(
  json.decode(response.body),
  (data) => data.map((teamJson) => Team.fromJson(teamJson)),
)

Also you could type safe your factory be using:

class ApiResponse<T> {
  int status;
  String? message;
  T data;

  ApiResponse({
    required this.status,
    this.message,
    required this.data,
  });

  factory ApiResponse.fromJson(
    Map<String, dynamic> json,
    T Function(List<Map<String, dynamic>>) create,
  ) {
    return ApiResponse<T>(
      status: json['status'],
      message: json['message'],
      data: create(json['data']),
    );
  }
}

If you do so you will also have to change your first expression again to write the right type (I think you made a mistake but maybe I'm wrong):

ApiResponse<List<Team>>.fromJson(
  json.decode(response.body),
  (data) => data.map((teamJson) => Team.fromJson(teamJson)).toList(),
);

theEUG · Accepted Answer · 2021-10-06 15:09:35Z

0

So I managed to resolve the issues with the following code:

// Maps the API response to object
class ApiResponse<T> {
  int status;
  String? message;
  T data;

  ApiResponse({
    required this.status,
    this.message,
    required this.data,
  });

  factory ApiResponse.fromJson(Map<String, dynamic> json, List<T> Function(List<dynamic>) create) {
    return ApiResponse<T>(
      status: json['status'],
      message: json['message'],
      data: create(json['data']),
    );
  }
}

Calling the mapper

return ApiResponse<Team>.fromJson(json.decode(response.body),
      (data) => data.map((tData) => Team.fromJson(tData)).toList());

answered Oct 6, 2021 at 15:09

theEUG

4097 silver badges18 bronze badges

Collectives™ on Stack Overflow

How to map dynamic json api responses in dart

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related