如何在 dart 中映射动态 json api 响应

Question

我有一个 API 响应负载，正文中有动态数据。 API 返回data 标记中的对象列表。我试图在运行时将响应映射到适当的模型，但是，这样做时会收到一条错误消息。如何在运行时映射动态响应对象而不为每个对象显式创建 API 响应模型？理想情况下，解决方案应该能够确定响应对象在运行时应该映射到的目标模型。

我的代码出现以下错误：The argument type 'List<Map<String, dynamic>>' can't be assigned to the parameter type 'Map<String, dynamic>'.

按照我的尝试：

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']),
    );
  }
}

我的模型

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 响应

{
  "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"
    }
  ],
}

Answer 1

Team.fromJson 将Map<String, dynamic> 作为参数，但你给它一个List<Map<String, dynamic>>。

我认为你想要的是改变你给的第一个表达式：

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

您还可以键入工厂正在使用的安全类型：

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']),
    );
  }
}

如果这样做，您还必须再次更改第一个表达式以编写正确的类型（我认为您犯了错误，但也许我错了）：

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

Answer 2

所以我设法用以下代码解决了问题：

// 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']),
    );
  }
}

调用映射器

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