// GET: Rental/Cancel?rentalId=rentalId public ActionResult Cancel(Guid?rentalId) { if (!rentalId.HasValue) { return(new HttpStatusCodeResult(400)); } Ausleihe rental = m_rentalRepository.GetRentalById(rentalId.Value); if (rental != null) { // check if user is valid if (rental.Kunde.KundenKeyGUID == GetCurrentUserId()) { m_rentalRepository.CancelRental(rental.AusleiheKeyGUID); return(RedirectToAction("Index", "Rental")); } return(new HttpUnauthorizedResult()); } return(new HttpStatusCodeResult(400)); }