What is a model class?

Store data type-safely with a model class.

What is a model class?

A model class is a Dart class that stores data in named, typed fields. Using a model instead of Map<String, dynamic> lets you access fields safely; if you mistype a key, the compiler warns you. Fields are usually final, so the object cannot change after it is created.

class Kullanici {
  final String ad;
  final int yas;

  Kullanici(this.ad, this.yas);
}

void main() {
  final k = Kullanici('Ayşe', 28);
  print(k.ad);  // Ayşe
}

final fields and the constructor

In a model class, fields are declared final and given their initial values by the constructor. final fields cannot be changed later, which keeps the data consistent throughout the program. The shorthand constructor Urun(this.ad, this.fiyat) assigns parameters directly to fields.

class Urun {
  final String ad;
  final int fiyat;

  Urun(this.ad, this.fiyat);
}

final u = Urun('Kalem', 15);
// u.fiyat = 20;  // Error: final cannot be assigned

Exercise Define a Kullanici model

Define a class named Kullanici with final String ad and final int yas fields. Assign values via the constructor. In main, create an instance and print its ad field with print.

Show example solution

class Kullanici {
  final String ad;
  final int yas;

  Kullanici(this.ad, this.yas);
}

void main() {
  final k = Kullanici('Mert', 30);
  print(k.ad);
}

Test yourself

What does a model class provide?
- Type-safe access to fields
- Automatic UI rendering
- Database connection
- Faster compilation
Show answer

Type-safe access to fields — A model class explicitly specifies field types, so the compiler warns on wrong access. UI rendering, database, and compilation speed are not the model's responsibility.

Declare a final field

class Kullanici {
  ____;
  final int yas;

  Kullanici(this.ad, this.yas);
}

Show answer

class Kullanici {
  final String ad;
  final int yas;

  Kullanici(this.ad, this.yas);
}

Model class parts

class Kullanici

Class declaration
final String ad

Immutable field
Kullanici(this.ad)

Constructor
k.ad

Field access

Next lesson: fromJson

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