Need help for an MVC order page which related to northwind db

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C#

SQL

MVC5

Dear All,

This is my order page. I have problem on "Add Product" that when i click it, Products don't appear in below grid. I give my OrderController code which related to "Add Product" :

public ActionResult AddProduct()
     {
         List<OrderDetailViewModel> orderDetails =
             (List<OrderDetailViewModel>)Session["OrderDetails"];

         OrderDetailViewModel vm = new OrderDetailViewModel();

         vm.ProductId = Convert.ToInt32(Request["AddProductId"]);
         vm.ProductName = Convert.ToString(Request["AddProductName"]);
         vm.Quantity = Convert.ToInt32(Request["AddQuantity"]);
         vm.UnitPrice = Convert.ToDecimal(Request["AddUnitPrice"]);

         orderDetails.Add(vm);

         return RedirectToAction("Create");
     }

and please also you can find view code:

<div id="pnlProductAdd">
    <form action="@Url.Action("AddProduct","Order")" id="frmProductAdd" method="post">
        <div class="row">
            <div class="col-md-3">
                Product: <select id="txtAddProductId" name="AddProductId">
                    <option value="">-- Select --</option>
                    @foreach (var product in Model.Products)
        {
                        <option value="@product.ProductID">@product.ProductName</option>
                    }
                </select>
            </div>
            <div class="col-md-3">
                Quantity: <input type="text" name="AddQuantity" id="txtAddQuantity" />
            </div>
            <div class="col-md-3">
                Price: <input type="text" name="AddUnitPrice" id="txtAddUnitPrice" />
            </div>
            <div class="col-md-3">
                <input type="button" id="btnAddProduct" value="Add Product" />
            </div>
        </div>
    </form>
</div>

What I have tried:

I have tried "selectlist" code on ordercontroller to solve this issue but i could not succeed. I think this code - vm.ProductName = Convert.ToString(Request["AddProductName"]); - that are mentioned in ordercontroller need to be modified.