public ActionResult Edit(Customer customer)
        {
            if (ModelState.IsValid)
            {
                customerRepository.InsertOrUpdate(customer);
                customerRepository.Save();
                return RedirectToAction("Index");
            }

            return View();
        }
 public void InsertOrUpdate(Customer customer)
 {
     if (customer.ID == default(int))
     {
         context.Customers.Add(customer);
     }
     else
     {
         context.Entry(customer).State = EntityState.Modified;
     }
 }