Pseudo example

```
public HttpResponseMessage GetAll() {

    List<MyEntity> before = MyEntityRepository.GetAll();
    return Request.CreateResponse(HttpStatusCode.OK,
        new IEnumerable<MyExtendedEntity>({
            before.ForEach(x =>
                yield return new ExtendedEntity {
                    Property1    = x.Property1,
                    Property2    = x.Property2,
                    ExtendedProp = ExtendedPropProvider.getExtended(x)
                })
         );

```