MyLittleSuite/dart_mapperdart_mapper

@SubclassMapping

Routes subclass source values to subclass target types in a sealed-class hierarchy.

@SubclassMapping

Instructs dart_mapper to dispatch the mapping to a different target subtype depending on the runtime type of the source. Apply one @SubclassMapping per source subclass.

Signature

const SubclassMapping({
  required Type source,
  required Type target,
})

Parameters

ParameterTypeDescription
sourceTypeThe source subclass type to match at runtime.
targetTypeThe target subclass type to produce for the matched source.

Usage

Define the source and target sealed class hierarchies, then annotate the mapping method:

// Source hierarchy
sealed class Shape {}
class Circle extends Shape { final double radius; Circle(this.radius); }
class Rectangle extends Shape { final double width, height; Rectangle(this.width, this.height); }

// Target hierarchy
sealed class ShapeDto {}
class CircleDto extends ShapeDto { final double radius; CircleDto(this.radius); }
class RectangleDto extends ShapeDto { final double width, height; RectangleDto(this.width, this.height); }

@Mapper()
abstract class ShapeMapper {
  @SubclassMapping(source: Circle, target: CircleDto)
  @SubclassMapping(source: Rectangle, target: RectangleDto)
  ShapeDto toDto(Shape shape);
}

The generated code uses a Dart 3 switch expression to dispatch:

// Generated
@override
ShapeDto toDto(Shape shape) {
  return switch (shape) {
    Circle c => _circleToCircleDto(c),
    Rectangle r => _rectangleToRectangleDto(r),
  };
}

Requirements

  • Each source type listed must be a concrete subtype of the method's source parameter type.
  • Each target type listed must be a concrete subtype of the method's return type.
  • Additional mapping methods for the subclass pairs are generated automatically by the mapper. You do not have to declare them.
  • The parent mapping method (toDto(Shape shape)) must be abstract — the generator overwrites it completely.

Field-Level Customization

To customize field mappings for a specific subclass pair, declare an explicit mapping method for it:

@Mapper()
abstract class ShapeMapper {
  @SubclassMapping(source: Circle, target: CircleDto)
  @SubclassMapping(source: Rectangle, target: RectangleDto)
  ShapeDto toDto(Shape shape);

  @Mapping(target: 'r', source: 'radius')
  CircleDto circleToDto(Circle circle);
}

When an explicit method for a subclass pair exists the generator uses it; otherwise it auto-generates one.

See Also

Edit this page on GitHub
@ValueMapping
@InheritConfiguration