public ActionResult Create(PrescriptionCreateVM model)
        {
            //The problem is that ViewModels is returning the entire object. You must create view models with Fields and Not Objects.
            Prescription _pres = new Prescription()
            {
                PrescriptionDate = model.PrescriptionDate,
                R_SPH = model.R_SPH,
                R_CYL = model.R_CYL,
                R_AXIS = model.R_AXIS,
                L_SPH = model.L_SPH,
                L_CYL = model.L_CYL,
                L_AXIS = model.L_AXIS,
                CustomerID = model.CustomerID

            };

            if (ModelState.IsValid)
            {
                db.Prescriptions.Add(_pres);
                db.SaveChanges();
                return RedirectToAction("Index");
            }

            return View();
        }
        // GET: /Prescription/Create
        public ActionResult Create(int CustomerID)
        {
            //we need this for the PartialView inside the view.
            var _customer = db.Customers.Find(CustomerID);

            PrescriptionCreateVM _viewmodel = new PrescriptionCreateVM
            {
                CustomerID = _customer.CustomerID,
                FullName = _customer.FullName,
                MobileNumber = _customer.MobileNumber,
                BirthDate = _customer.BirthDate,
                RegisterationDate = _customer.RegisterationDate
            };

            //we need to pass a ViewModel becuase it expects in the view.
            return View(_viewmodel);
        }