ASP.Net MvC framework, Html.ValidationMessage tag

Question

In this code in an Edit view, the correct vendor name text appears but it is not validated when I blank its textbox and push Save. The Vendor is a property of the Order model, and VendorName is a property in the Vendor model. They relate referentially. My form does not all input into a single table, but on satellite tables as well.

<%= Html.TextBox("Vendor.VendorName")%>
<%= Html.ValidationMessage("Vendor.VendorName")%>

Why is validation not occuring?

This seems to work, but it seems like a hack to me:

using M = HelloUranus.Models
//...
    namespace HelloUranus.Controllers
    {

     public class OrderDetailController : Controller
     {
      //...

      private M.DBProxy db = new M.DBProxy();

      [AcceptVerbs(HttpVerbs.Post)]
      public ActionResult Edit(int id, FormCollection collection)
      {

        //...
        var orderDetail = db.GetOrderDetail(id);
        //...

        try
        {

          if (string.IsNullOrEmpty(Request.Form["Vendor.VendorName"]))
          {
             throw new Exception();
          }

          UpdateModel(orderDetail);

          db.Save();

          return RedirectToAction("Details", new {id = orderDetail.odID } );
        }

        catch
        {
          ModelState.AddRuleViolations(orderDetail.GetRuleViolations());

          return View(orderDetail);
        }
        //...
      }
      //...
    }

Answer 1

Did you write any validation code? You have to manually validate it in your controller. If you:

ModelState.IsValid = false;

in the controller, for example, you will see some validation. That will trigger the ValidationSummary on the View to be shown. To actually add a validation to a single form element, use:

ModelState.AddModelError("Vendor.VendorName", string.Format("Vendor name must be at least {0} characters.",10));

Note that this will also set the ModelState to an invalid state and thus trigger the ValidationSummary as well.