I'm a beginner so this question may sound trivial to you experts but i'm unable to understand the concept here. pls help In the Flutter Fire documentation, in CollectionReference and DocumentReference segment

  Movie({required this.title, required this.genre});

  Movie.fromJson(Map<String, Object?> json) // Here Movie.fromJson is created
    : this(
        title: json['title']! as String,
        genre: json['genre']! as String,
      );

  final String title;
  final String genre;

// What if i create fromJson like this. would it be valid?
// and upper function is just a simplified version of this
Object fromJson (Map<String, Object?> json) {
    return (
        title: json['title']! as String,
        genre: json['genre']! as String,);

  }

  Map<String, Object?> toJson() { // Here toJson is created differently
    return {
      'title': title,
      'genre': genre,
    };
  }

}

//Further they are used like this

final moviesRef = FirebaseFirestore.instance.collection('movies').withConverter<Movie>(
      fromFirestore: (snapshot, _) => Movie.fromJson(snapshot.data()!),
      toFirestore: (movie, _) => movie.toJson(),
    );

Why fromJson and toJson are created differently

CodePudding user response：

toJson converts Movie to a Map (to store in firestore), while fromJson converts the Map to the Movie (for easy use in flutter).

withConverter helps retain type safety, by automatically converting firebase's Map to Movie and back.