Unknown type on deserialization. Need either specifiedType or discriminator field

Question

I have following json

{
    "status": 1,
    "msg": "Success",
    "data": {
        "getFeeCount": [
            {
                "yearId": "1",
                "yearName": "FY 2017-18"
            },
            {
                "yearId": "2",
                "yearName": "FY 2018-19"
            }
        ],
        "getFeeCat": [
            {
                "fee_cat_id": "1",
                "fee_cat_name": "1st Semester Tuition Fee"
            },
            {
                "fee_cat_id": "2",
                "fee_cat_name": "2nd Semester Tuition Fee"
            },
            {
                "fee_cat_id": "3",
                "fee_cat_name": "3rd Semester Tuition Fee"
            },
            {
                "fee_cat_id": "4",
                "fee_cat_name": "4th Semester Tuition Fee"
            },
            {
                "fee_cat_id": "5",
                "fee_cat_name": "5th Semester Tuition Fee"
            },
            {
                "fee_cat_id": "6",
                "fee_cat_name": "6th Semester Tuition Fee"
            },
            {
                "fee_cat_id": "7",
                "fee_cat_name": "7th Semester Tuition Fee"
            },
            {
                "fee_cat_id": "8",
                "fee_cat_name": "8th Semester Tuition Fee"
            },
            {
                "fee_cat_id": "9",
                "fee_cat_name": "Certification Fee Year 1"
            },
            {
                "fee_cat_id": "10",
                "fee_cat_name": "Certification Fee Year 2"
            },
            {
                "fee_cat_id": "11",
                "fee_cat_name": "Certification Fee Year 3"
            },
            {
                "fee_cat_id": "12",
                "fee_cat_name": "Certification Fee Year 4"
            }
        ]
    }
}

I am using built value in my project

library dashboard_fiscal_year_model;

import 'package:built_collection/built_collection.dart';
import 'package:built_value/built_value.dart';
import 'package:built_value/serializer.dart';

part 'dashboard_fiscal_year_model.g.dart';

abstract class DashboardFiscalYearModel
    implements
        Built<DashboardFiscalYearModel, DashboardFiscalYearModelBuilder> {
  DashboardFiscalYearModel._();

  factory DashboardFiscalYearModel(
          [updates(DashboardFiscalYearModelBuilder b)]) =
      _$DashboardFiscalYearModel;

  @BuiltValueField(wireName: 'status')
  int get status;
  @BuiltValueField(wireName: 'msg')
  String get msg;
  @BuiltValueField(wireName: 'data')
  DashboardFiscalYearData get data;

  static Serializer<DashboardFiscalYearModel> get serializer =>
      _$dashboardFiscalYearModelSerializer;
}

abstract class DashboardFiscalYearData
    implements Built<DashboardFiscalYearData, DashboardFiscalYearDataBuilder> {
  DashboardFiscalYearData._();

  factory DashboardFiscalYearData([updates(DashboardFiscalYearDataBuilder b)]) =
      _$DashboardFiscalYearData;

  @BuiltValueField(wireName: 'getFeeCount')
  BuiltList<GetFeeCount> get getFeeCount;
  @BuiltValueField(wireName: 'getFeeCat')
  BuiltList<GetFeeCat> get getFeeCat;

  static Serializer<DashboardFiscalYearData> get serializer =>
      _$dashboardFiscalYearDataSerializer;
}

abstract class GetFeeCount implements Built<GetFeeCount, GetFeeCountBuilder> {
  GetFeeCount._();

  factory GetFeeCount([updates(GetFeeCountBuilder b)]) = _$GetFeeCount;

  @nullable
  @BuiltValueField(wireName: 'yearId')
  String get yearId;
  @nullable
  @BuiltValueField(wireName: 'yearName')
  String get yearName;

  static Serializer<GetFeeCount> get serializer => _$getFeeCountSerializer;
}

abstract class GetFeeCat implements Built<GetFeeCat, GetFeeCatBuilder> {
  GetFeeCat._();

  factory GetFeeCat([updates(GetFeeCatBuilder b)]) = _$GetFeeCat;

  @nullable
  @BuiltValueField(wireName: 'fee_cat_id')
  String get feeCatId;
  @nullable
  @BuiltValueField(wireName: 'fee_cat_name')
  String get feeCatName;
}

but whenever I run my app I get the following error

[VERBOSE-2:ui_dart_state.cc(148)] Unhandled Exception: Deserializing '[status, 1, msg, Success, data, {getFeeCount: [{yearId: 1, yearName: FY 2017-...' to 'DashboardFiscalYearModel' failed due to: Deserializing '[getFeeCount, [{yearId: 1, yearName: FY 2017-18}, {yearId: 2, yearName: FY 20...' to 'DashboardFiscalYearData' failed due to: Deserializing '[{fee_cat_id: 1, fee_cat_name: 1st Semester Tuition Fee}, {fee_cat_id: 2, fee...' to 'BuiltList<GetFeeCat>' failed due to: Invalid argument(s): Unknown type on deserialization. Need either specifiedType or discriminator field.
#0      BuiltJsonSerializers._deserialize (package:built_value/src/built_json_serializers.dart:154:11)
#1      BuiltJsonSerializers.deserialize (package:built_value/src/built_json_serializers.dart:105:18)
#2      BuiltJsonSerializers.deserializeWith (package:built_value/src/built_json_serializers.dart:35:12)
#3      DashboardDropDownApiProvider.getFiscalYear (package:dice_admin/resources/dashboard/dashboard_fiscal_year/dashboard_fi<…>
[VERBOSE-2:shell.cc(178)] Dart Error: Unhandled exception:
'dart:isolate/runtime/libtimer_impl.dart': Failed assertion: line 433: '<optimized out>': is not true.
#0      _AssertionError._doThrowNew (dart:core/runtime/liberrors_patch.dart:40:39)
#1      _AssertionError._throwNew (dart:core/runtime/liberrors_patch.dart:36:5)
#2      _Timer._cancelWakeup (dart:isolate/runtime/libtimer_impl.dart:433:12)
#3      _Timer._notifyEventHandler (dart:isolate/runtime/libtimer_impl.dart:299:7)
#4      _Timer._handleMessage (dart:isolate/runtime/libtimer_impl.dart:419:5)
#5      _RawReceivePortImpl._handleMessage (dart:isolate/runtime/libisolate_patch.dart:171:12)

I have regenerated the code many times and the serialiser is also mapped properly I think.

I went through this post https://github.com/google/built_value.dart/issues/368 It uses a custom plugin, has built value resolved this issue or do I need to use the custom built value

Answer 1

import 'package:built_collection/built_collection.dart';
import 'package:built_value/serializer.dart';
import 'package:built_value/standard_json_plugin.dart';

part 'serializers.g.dart';

// ignore: always_specify_types
@SerializersFor([
 NameModel,             // Add model to here
])
final Serializers serializers =
    (_$serializers.toBuilder()..addPlugin(StandardJsonPlugin())).build();

List<T> deserializeListOf<T>(
  T Function(Map<String, dynamic>) fromMap,
  Iterable<dynamic> values,
) =>
    values
        .map((dynamic v) => fromMap(v as Map<String, dynamic>))
        .toList(growable: false);

Answer 2

I forgot to add Serailizer for GetFeeCat class