nested model to entity conversion in flutter

I have 4 files

PostModel which extends Post(entity) &

PageModel which extends Page(entity)

A Post has List of pages in it and same I implemented for postModel which has list of pagemodels.

I'm getting an error '_$PostModel.pages' ('List Function()') isn't a valid override of 'Post.pages' ('List Function()').

import 'package:freezed_annotation/freezed_annotation.dart';
import 'package:flutter/foundation.dart';
import 'package:**/features/home/data/models/page_model.dart';
import 'package:**/features/home/domain/entities/post.dart';

part 'post_model.freezed.dart';
part 'post_model.g.dart';

@freezed
class PostModel extends Post with _$PostModel {
  const factory PostModel({
    required String id,
    required String title,
    required String body,
    required List<PageModel> pages,
  }) = _PostModel;

  factory PostModel.fromJson(Map<String, Object?> json) =>
      _$PostModelFromJson(json);
}

Post Class here :

class Post {
  final String id;
  final String title;
  final String body;
  final List<Page> pages;

  Post({
    required this.id,
    required this.title,
    required this.body,
    required this.pages,
  }  );
}

Solution

You won't be able to do that with freezed. You can look at the issues:

Inheritance is not supported

However, you could define an abstract class IPost and use it as an interface:

abstract class IPost {
  String get id;
  String get title;
  String get body;
  List<Page> get pages;

}

class Post implements IPost {

  Post({
    required this.id,
    required this.title,
    required this.body,
    required this.pages,
  }  );
  @override
  final String id;
  @override
  final String title;
  @override
  final String body;
  @override
  final List<Page> pages;
}

@freezed
class PostModel  with _$PostModel implements IPost {
  const factory PostModel({
    required String id,
    required String title,
    required String body,
    required List<Page> pages,
  }) = _PostModel;

  factory PostModel.fromJson(Map<String, Object?> json) =>
      _$PostModelFromJson(json);
}