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how to make factory construct of modal class when it contains a list of other modelclass in flutter?

I am learnign firebase , here i have just added some data to firebase collection but now i am failing to make factory constructor for getting data from fire base as document snapshot as i dont know how to deal for converting documentSnapshot to model class

thanks if you can implement and code for factory constructor


class Movie {
  String id;
  String name;

  Movie({required this.id, required this.name});

  toJson() {
    return {
      'Id': id,
      'Name': name,
    };
  }

  
}


class MovieCategory {
  String id;
  String name;
  List<Movie> movies;

  MovieCategory({required this.id, required this.name, required this.movies});

  toJson() {
    return {
      'Id': id,
      'Name': name,
      'Movies': movies.map((e) => e.toJson()).toList(),// check also this..is it ok?
    };
  }

  factory MovieCategory.fromSnapshot(
      DocumentSnapshot<Map<String, dynamic>> document) {
//dont know how to code for this..and it should return empty object if data is null..


}
}

List<MovieCategory> movieCategoryList = [
  MovieCategory(
    id: '1',
    name: 'BollyWood',
    movies: [
      Movie(id: '1', name: 'Hindi 1'),
      Movie(id: '2', name: 'Hindi 2'),
    ],
  ),
  MovieCategory(
    id: '2',
    name: 'HollyWood',
    movies: [
      Movie(id: '1', name: 'English 1'),
      Movie(id: '2', name: 'English 2'),
    ],
  )
];
Tags:

4

Answers


  1. 0

    add this to your MovieCategory class

    factory MovieCategory.fromSnapshot(
      DocumentSnapshot<Map<String, dynamic>> document) {

    final data=document.data()!;
    return MovieCategory(
        id: data['Id'],
        name: data['Name'],
      movies: (data['Movies'] as List<dynamic>).map((e) => Movie.fromMap(e)).toList()
        );

  }

    and aslo fromMap method to your Movie class

     factory Movie.fromMap(Map<String,dynamic> map){
    return Movie(
      id: map['Id'],
      name: map['Name'],
    );
  }
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  2. 0

    Extract the map from document and use it same, like you do with regular fromMap/fromJson method:

    factory MovieCategory.fromSnapshot(
      DocumentSnapshot<Map<String, dynamic>> document) {
    Map<String, dynamic>? map = document.data();

    return MovieCategory(
      id: map['id'] ?? '',
      name: map['name'] ?? '',
      movies: map['movies'] != null
          ? (map['movies'] as List<dynamic>)
              .map((e) => Movie.fromJson(e))
              .toList()
          : [],
    );   }
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  3. 0

    Data obtained from Firebase in the snapshots is in the form of a JSON Map<String, dynamic>, which could have as many nested fields, i.e. those "dynamic" values could be of any type including other Map<String, dynamic>.

    The easiest way for dealing with this is letting the library json_serializable just generate the code for you by annotating you class. This way you avoid forgetting adding fields or errors and typos.

    
import 'package:json_annotation/json_annotation.dart';

part 'movie.g.dart';

@JsonSerializable()
class Movie {
  String id;
  String name;

  const Movie({required this.id, required this.name});

  static Movie fromJson(Map<String, dynamic> json) => _$MovieFromJson(json);
  
  Map<String, dynamic> toJson() => _$MovieToJson(this);
}

@JsonSerializable()
class MovieCategory {
  String id;
  String name;
  List<Movie> movies;

  MovieCategory({required this.id, required this.name, required this.movies});

  static MovieCategory fromJson(Map<String, dynamic> json) => _$MovieCategoryFromJson(json);

  Map<String, dynamic> toJson() => _$MovieCategoryToJson(this);
}

    Then wherever you are getting your document snapshot:

    try {
  final MovieCategory movieCategory = MovieCategory.fromJson(docSnapshot.data()!);
} catch (e, s) {
  // TODO: Log your parsing error
}
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  4. 0 
    factory MovieCategory.fromSnapshot(DocumentSnapshot<Map<String, dynamic>> document) {
  Map<String, dynamic>? data = document.data();

  if (data == null) {
    return MovieCategory(id: '', name: '', movies: []);
  }

  List<dynamic>? movieDataList = data['Movies'];
  List<Movie> movies = [];

  if (movieDataList != null) {
    movies = movieDataList
        .map((movieData) => Movie(id: movieData['Id'], name: movieData['Name']))
        .toList();
  }

  return MovieCategory(
    id: data['Id'],
    name: data['Name'],
    movies: movies,
  );
}

    The MovieCategory class now includes the fromSnapshot factory constructor, which enables the conversion of a DocumentSnapshot from Firestore into a MovieCategory object.

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