how to convert date on my code...

  public OrderModel()
        {
            OrdersGrid = new JQGrid
            {
                Columns = new List<JQGridColumn>()
                                 {
                                     new JQGridColumn { DataField = "OrderID", 
                                                        // always set PrimaryKey for Add,Edit,Delete operations
                                                        // if not set, the first column will be assumed as primary key
                                                        PrimaryKey = true,
                                                        Editable = false,
                                                        Width = 50 },
                                     new JQGridColumn { DataField = "OrderDate", 
                                                        Editable = true,
                                                        Width = 100, 
                                                        DataType = typeof(DateTime),
                                                        DataFormatString = "{0:d}",
                                                        

                                                        
                                     },
                                     new JQGridColumn { DataField = "CustomerID", 
                                                        Editable = true,
                                                        Width = 100 },
                                     new JQGridColumn { DataField = "Freight", 
                                                        Editable = true,
                                                        Width = 75 },
                                     new JQGridColumn { DataField = "ShipName",
                                                        Editable =  true,
},
                                     new JQGridColumn { DataField = "ShipAddress",
                                                        Editable =  true,
                                                      }                                     
                                 },
                Width = Unit.Pixel(1000),
                Height = Unit.Pixel(400)
            };

            OrdersGrid.ToolBarSettings.ShowRefreshButton = true;
        }

        public JQGrid OrdersGrid { get; set; }
    }
}

public static string ToPersianDate(this DateTime date)
        {
            var dateTime = new DateTime(date.Year, date.Month, date.Day, new GregorianCalendar());
            var persianCalendar = new PersianCalendar();
            return persianCalendar.GetYear(dateTime) + "/" +
                   persianCalendar.GetMonth(dateTime).ToString("00") + "/" +
                   persianCalendar.GetDayOfMonth(dateTime).ToString("00");
        }

        public ActionResult GridDemo()
        {
   
            var gridModel = new OrderModel();
            var ordersGrid = gridModel.OrdersGrid;
        
            S/etUpGrid(ordersGrid);

          //my code for convert date...

            var list = new List<OrderModel>();
            
    NorthWindsDataContext ss = new NorthWindsDataContext();

            gridModel = (list.Select(t => new
            {

                OrderID = t.OrdersGrid.OrderID,
                OrderDate = t.OrderDate == null
                    ? ""
                    : new PersianDateTime(t.OrderDate.Value)
                        .ToString(PersianDateTimeFormat.DateShortTime)

            }))
            .ToList();



and so Other code for convert code ...

                   //OrdersGrid = new{product => new JQGrid
                   // {
                    
                   //     product.Id.ToString(CultureInfo.InvariantCulture),
                   //     product.Name,
                   //     product.DateTimeAdDateTime.ToPersianDate(),
                   //     product.Price.ToString(CultureInfo.InvariantCulture)
                    
                   // }

           // };

            // Pass the custmomized grid model to the View
            

            return View(gridModel);
        }