MyLittleSuite/dart_mapperdart_mapper

Generic Mapping

Map generic classes like Pagination<T> by declaring concrete type arguments in the mapper method.

Generic Mapping

dart_mapper supports mapping generic classes. Declare the mapper method with concrete type arguments and the generator resolves each field accordingly — including collection fields like List<T>.

Pagination Example

Define your generic DTO and domain classes:

class TodoDto {
  final String title;
  final bool completed;
  TodoDto({required this.title, required this.completed});
}

class Todo {
  final String title;
  final bool completed;
  Todo({required this.title, required this.completed});
}

class PaginationDto<T> {
  final List<T> items;
  final int page;
  final int totalPages;
  PaginationDto({required this.items, required this.page, required this.totalPages});
}

class Pagination<T> {
  final List<T> items;
  final int page;
  final int totalPages;
  Pagination({required this.items, required this.page, required this.totalPages});
}

Declare the mapper with concrete type arguments. The generator picks up the element-level converter automatically:

@Mapper()
abstract class PaginationMapper {
  Pagination<Todo> toPagination(PaginationDto<TodoDto> source);
  Todo toTodo(TodoDto source);
}

Generated:

@override
Pagination<Todo> toPagination(PaginationDto<TodoDto> source) {
  return Pagination(
    items: source.items.map(toTodo).toList(),
    page: source.page,
    totalPages: source.totalPages,
  );
}

Generic Wrapper Types

Single-field generic wrappers work the same way. Use concrete type arguments in the method signature:

class BoxDto<T> {
  final T content;
  final String tag;
  BoxDto(this.content, this.tag);
}

class Box {
  final Todo content;
  final String tag;
  Box(this.content, this.tag);
}

@Mapper()
abstract class BoxMapper {
  Box convert(BoxDto<TodoDto> source);
  Todo toTodo(TodoDto source);
}

Generated:

@override
Box convert(BoxDto<TodoDto> source) {
  return Box(
    toTodo(source.content),
    source.tag,
  );
}

Limitations

  • Concrete type arguments required: The mapper method must use fully resolved types (e.g. PaginationDto<TodoDto>). A signature like Pagination<T> convert(PaginationDto<T> source) where T is still an open type parameter is not supported.
  • Element converter required: When T maps to a custom class, a converter method for that type must be present in the same mapper (or via uses).

See Also

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