public class CompoundViewModel
    {
        public IEnumerable<OrderDetail> AllOrderDetail { get; set; }
        public OrderDetail SelectedOrderDetail { get; set; }
    }

  public ActionResult Index()
        {
            var ordersdetails = db.OrdersDetails.Include(o => o.Good)
            ViewBag.GoodId = new SelectList(db.Goods, "Id", "Name");
             var model = new CompoundViewModel(){
                AllOrderDetail=ordersdetails.ToList()
            };
            return View(model);

        }

  [HttpPost]
        public ActionResult Index(CompoundViewModel compoundViewModel)
        {
                db.OrdersDetails.Add(compoundViewModel.SelectedOrderDetail);
                db.SaveChanges();
                ...
        }

  [HttpPost]
        public ActionResult Index(OrderController orderController)
        {
                db.OrdersDetails.Add(orderController);
                db.SaveChanges();
                ...
        }

@model TestSecure.Models.CompoundViewModel

@using (Html.BeginForm()) {
    @Html.ValidationSummary(true) 
  <fieldset>
        <div class="editor-field">
            @Html.DropDownList("GoodId", "<Выберите товар>")
            @Html.ValidationMessageFor(model => model.SelectedOrderDetail.GoodId)
        </div>
         <div class="editor-field">
            @Html.EditorFor(model => model.SelectedOrderDetail.GoodsCount)
            @Html.ValidationMessageFor(model =>model.SelectedOrderDetail.GoodsCount)
        </div>
        <p>
            <input type="submit" value="Send" />
        </p>
    </fieldset>
}
...

    public partial class OrderDetail
    {   
        [Key]
        public int Id { get; set; }
        public int OrderID { get; set; }
        public int? GoodId { get; set; }
        public Good Good { get; set; }
        public int GoodsCount { get; set; }
        
    }
    public partial class OrderDetail
    {
        public List<OrderDetail> orderDetailList { get; set; }

    }

   var ordersdetails = db.OrdersDetails.Include(o => o.Good)
                 .Where(p => p.OrderID == id);
return View(new OrderDetail { orderDetailList = ordersdetails.ToList() });