public void CreateAuto(AutoHinzufügenViewModel viewModel)
 {
     if (viewModel.IsNew)
     {
         client.addCar(new AutoDto
         {
             Marke      = viewModel.Marke,
             Basistarif = viewModel.Basistarif,
             Tagestarif = viewModel.Tagestarif,
         });
     }
     else
     {
         AutoDto selectedCar = client.getCarById(viewModel.Id);
         selectedCar.Marke      = viewModel.Marke;
         selectedCar.Basistarif = viewModel.Basistarif;
         selectedCar.Tagestarif = viewModel.Tagestarif;
         client.modifyCar(selectedCar);
     }
 }