public ActionResult billEdit(BillEditVM billEditVM, int?bill_id)
        {
            Bill bill = db.Bills.Find(bill_id);

            bill.bill_date       = billEditVM.bill_date;
            bill.bill_total      = billEditVM.bill_total;
            db.Entry(bill).State = EntityState.Modified;
            db.SaveChanges();
            return(RedirectToAction("billDetail"));
        }
        public ActionResult billEdit(int?id)
        {
            Bill       bill       = db.Bills.Find(id);
            BillEditVM billEditVM = new BillEditVM();

            billEditVM.bill_id          = bill.bill_id;
            billEditVM.customer_name    = bill.Customer.customer_name;
            billEditVM.customer_surname = bill.Customer.customer_surname;
            billEditVM.bill_total       = bill.bill_total;
            billEditVM.bill_date        = bill.bill_date;
            return(View(billEditVM));
        }