public ActionResult Index()
{
   var repo = new Repository();
   var dto = repo.GetDtoById(1); // Note, this doesn't know about the cache at all
}

public class Repository()
{
  [Cache(Duration = 10)]
  public DTO GetDtoById(int id)
  {
    // if it gets here, go get data from database, note this doesn't know about the cache at all
  }
}