Flutter FetchData from API and save local with sqflite

Question

I have problem , went i'm fetch data from API and save to database local . So being a newbie in Flutter, I would like to find a way to save the data in a database for offline support.

This the problem error

Unhandled Exception: type 'String' is not a subtype of type 'List<dynamic>' in type cast

My Model Data like this

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

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

class Employee {
  int id;
  String id_surat;
  String nama;
  String nomor;
  String arti;

  Employee({
    this.id,
    this.id_surat,
    this.nama,
    this.nomor,
    this.arti,
  });

  factory Employee.fromJson(Map<String, dynamic> json) => Employee(
        id_surat: json["id_surat"],
        nama: json["nama"],
        nomor: json["nomor"],
        arti: json["arti"],
      );

  Map<String, dynamic> toJson() => {

        "id_surat": id_surat,
        "nama": nama,
        "nomor": nomor,
        "arti": arti,
      };
}

Here is the JSON parsing method that queries from the network:

class EmployeeApiProvider {
  Future<List<Employee>> getAllEmployees() async {
    var url = "EXAMPLE";
    Response response = await Dio().get(url);
    print(response.data);

    return (response.data as List).map((employee) {
      print('Inserting $employee');
      DBProvider.db.createEmployee(Employee.fromJson(employee));
    }).toList();
  }
}

And Response from API Server , like this .

[
{
id_surat: "1",
nama: "Al Fatihah",
nomor: "1",
arti: "Pembukaan"
},
{
id_surat: "2",
nama: "Al Baqarah",
nomor: "2",
arti: "Sapi Betina"
},
{
id_surat: "3",
nama: "Ali Imran",
nomor: "3",
arti: "Keluarga Imran"
},
{
id_surat: "4",
nama: "An Nisaa",
nomor: "4",
arti: "Wanita"
},
]

Solution

I think you should replace:

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

with:

String employeeToJson(List<Employee> data) => json.encode(data); 

You already pass in List<Employee> that you want to encode.

You shouldn't need List<dynamic>.from and that inner function which creates List<dynamic>. According to documentation, List<dynamic> is not directly encodable.

https://api.flutter.dev/flutter/dart-convert/jsonEncode.html