Mappers

Mappers are domain classes that convert objects from one type to another. They are useful when we want to convert data from one layer to another.

abstract interface class ObjectMapper {
  T mapObject<S, T>(S? object);

  Iterable<T> mapObjects<S, T>(Iterable<S> objects);
}

• mapObject converts a single object from one type to another.
• mapObjects converts a list of objects from one type to another.

We use auto_mappr to generate mappers. This package uses build_runner to generate mappers.

Below is an example of a mapper class:

abstract interface class PostMapper implements ObjectMapper {}

@AutoMappr(<MapType<Object, Object>>[
  MapType<PostDataContract, PostEntity>(),
  MapType<PostDataContract, PostDataObject>(fields: <Field>[
    Field.from('postId', from: 'id'),
  ]),
  MapType<PostDataObject, PostEntity>(fields: <Field>[
    Field.from('id', from: 'postId'),
  ]),
])
@LazySingleton(as: PostMapper)
class PostMapperImpl extends $PostMapperImpl implements PostMapper {
  @override
  T mapObject<S, T>(S? object) => convert(object);

  @override
  Iterable<T> mapObjects<S, T>(Iterable<S> objects) => convertIterable(objects);
}

• @AutoMappr is used to annotate the class as a mapper. The MapType parameter is used to specify the mapping between two types. The fields parameter is used to specify the mapping between two fields. The from parameter is used to specify the name of the field to map from. The to parameter is used to specify the name of the field to map to. If the to parameter is not specified, the name of the field to map to will be the same as the name of the field to map from.
• We implicitly added a field mapping from PostDataContract.id to PostDataObject.postId and vice versa. This is because the id field of PostDataContract is mapped to the postId field of PostDataObject by default.
• After implementing ObjectMapper, we point the implemented methods to the generated methods from $PostMapperImpl.

💡 TIP

• Use the code snippet shortcut mapper to create a mapper class.