JSON Serializable How to use JSON Serializable with Firestore

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JSON serializable provides a way to convert a dynamic Firestore Map to strongly typed Dart class instance.


Create a file named models.dart in the services folder. Each document or object in the database will be represented by a class.

I would recommend using null-safety for every property, then setting a default value if the property is in fact null in Firestore.

file_type_flutter services/models.dart
import 'package:json_annotation/json_annotation.dart';
part 'models.g.dart';

class Option {
  String value;
  String detail;
  bool correct;
  Option({this.value = '', this.detail = '', this.correct = false});
  factory Option.fromJson(Map<String, dynamic> json) => _$OptionFromJson(json);
  Map<String, dynamic> toJson() => _$OptionToJson(this);

class Question {
  String text;
  List<Option> options;
  Question({this.options = const [], this.text = ''});
  factory Question.fromJson(Map<String, dynamic> json) =>
  Map<String, dynamic> toJson() => _$QuestionToJson(this);

class Quiz {
  String id;
  String title;
  String description;
  String video;
  String topic;
  List<Question> questions;

      {this.title = '',
      this.video = '',
      this.description = '',
      this.id = '',
      this.topic = '',
      this.questions = const []});
  factory Quiz.fromJson(Map<String, dynamic> json) => _$QuizFromJson(json);
  Map<String, dynamic> toJson() => _$QuizToJson(this);

class Topic {
  late final String id;
  final String title;
  final String description;
  final String img;
  final List<Quiz> quizzes;

      {this.id = '',
      this.title = '',
      this.description = '',
      this.img = 'default.png',
      this.quizzes = const []});

  factory Topic.fromJson(Map<String, dynamic> json) => _$TopicFromJson(json);
  Map<String, dynamic> toJson() => _$TopicToJson(this);

class Report {
  String uid;
  int total;
  Map topics;

  Report({this.uid = '', this.topics = const {}, this.total = 0});
  factory Report.fromJson(Map<String, dynamic> json) => _$ReportFromJson(json);
  Map<String, dynamic> toJson() => _$ReportToJson(this);

Generating the Models Code

command line
flutter pub run build_runner build


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