flutter freezed :Could not generate \`toJson\` code for \`data\` because of type

Issue

I am trying to create my model by freezed and json_serializable :

import 'package:freezed_annotation/freezed_annotation.dart';

part 'language_response_model.freezed.dart';
part 'language_response_model.g.dart';

@freezed
abstract class LanguageResourceResponseModel
    with _$LanguageResourceResponseModel {
  const factory LanguageResourceResponseModel({
    required String id,
    required List<ResourceDataModel> data,
  })  _LanguageResourceResponseModel;

  factory LanguageResourceResponseModel.fromJson(Map<String, dynamic> json) >
      _$LanguageResourceResponseModelFromJson(json);
}

@freezed
abstract class ResourceDataModel {
  const factory ResourceDataModel({
    required String key,
    required String value,
  })  _ResourceDataModel;

  factory ResourceDataModel.fromJson(Map<String, dynamic> json) >
      _$ResourceDataModelFromJson(json);
}

but I got this error :

Could not generate `toJson` code for `data` because of type `ResourceDataModel`.
package:test/splash/data/models/language_response_model.freezed.dart:144:33
    ╷
144 │   final List<ResourceDataModel> data;
    │                                 ^^^^
    ╵
[INFO] Running build completed, took 2.5s

[INFO] Caching finalized dependency graph...
[INFO] Caching finalized dependency graph completed, took 189ms

[SEVERE] Failed after 2.7s

What is the problem?

dependencies:
  json_annotation: ^4.3.0
  json_serializable: ^6.0.1
dev_dependencies:
  build_runner: ^2.1.5
  flutter_launcher_icons: ^0.9.1
  freezed: ^0.15.1+1
  freezed_annotation: ^0.15.0

Solution

ResourceDataModel is a @freezed-annotated class, so it needs to mix in _$ResourceDataModel.

@freezed
abstract class ResourceDataModel with _$ResourceDataModel {
  // ...
}

Without that mixin, ResourceDataModel does not contain a toJson() method, and thus LanguageResourceResponseModel.toJson() cannot serialize a List<ResourceDataModel>.

Answered By – Nitrodon

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