Summary - Model classes

Combine fromJson and toJson to write a typed class.

Bidirectional conversion in a model class

If a model class contains both fromJson and toJson, you can carry data in both directions: create an object from an API response, and convert user changes back to JSON to send to the server. Together these two methods cover both the read and write sides of the model.

class Urun {
  final String ad;
  final int fiyat;
  Urun(this.ad, this.fiyat);

  factory Urun.fromJson(Map<String, dynamic> json) {
    return Urun(json['ad'] as String, json['fiyat'] as int);
  }

  Map<String, dynamic> toJson() => {'ad': ad, 'fiyat': fiyat};
}

Exercise Complete the Urun model

Add a fromJson factory constructor and a toJson method to the Urun class. In main, create a Urun instance from the given Map and print its toJson output with jsonEncode.

Show example solution

import 'dart:convert';

class Urun {
  final String ad;
  final int fiyat;

  Urun(this.ad, this.fiyat);

  factory Urun.fromJson(Map<String, dynamic> json) {
    return Urun(json['ad'] as String, json['fiyat'] as int);
  }

  Map<String, dynamic> toJson() {
    return {'ad': ad, 'fiyat': fiyat};
  }
}

void main() {
  final u = Urun.fromJson({'ad': 'Kitap', 'fiyat': 50});
  print(jsonEncode(u.toJson()));
}

Test yourself

What does having both fromJson and toJson in a model enable?
- Automatic UI rendering
- Bidirectional JSON conversion
- Database connection
- Faster compilation
Show answer

Bidirectional JSON conversion — fromJson creates an object from JSON, toJson produces a Map from the object; together they enable bidirectional conversion. UI, database, and compilation speed are not the model's job.

Cast a JSON value

factory Urun.fromJson(Map<String, dynamic> json) {
  return Urun(
    json['ad'] ____,
    json['fiyat'] as int,
  );
}

Show answer

factory Urun.fromJson(Map<String, dynamic> json) {
  return Urun(
    json['ad'] as String,
    json['fiyat'] as int,
  );
}

Model summary

fromJson

Creates a model from JSON
toJson

Converts the model to a Map
final

Marks immutable fields
factory

Factory constructor

Next lesson: Project skeleton

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