public ActionResult Index()
 {
     ViewBag.Products = Session[_productKey] as List<Product>;
     Order _order = new Order { CustomerID = 1, OrderDate = DateTime.Now, OrderID = 1 };
     _order.OrderLines = new List<OrderLine> { new OrderLine { ProductID = 1, Quantity = 3 }, new OrderLine { ProductID = 2, Quantity = 56 } };
     _order.Customers = Session[_customerKey] as List<Customer>; 
     return View(_order);
 }
 public ActionResult Index(Order order) 
 {
     ViewBag.Products = Session[_productKey] as List<Product>;
     order.Customers = Session[_customerKey] as List<Customer>;
     if (ModelState.IsValid) 
     {
         return View("DisplayOrder", order);
     }
     return View(order);
 }