ASP.NET MVC 2 client-side validation rules not being created

Question

MVC isn't generating the client-side validation rules for my viewmodel. The HTML just contains this:

<script type="text/javascript">
//<![CDATA[
if (!window.mvcClientValidationMetadata) { window.mvcClientValidationMetadata = []; }
window.mvcClientValidationMetadata.push({"Fields":[],"FormId":"form0","ReplaceValidationSummary":false});
//]]>
</script>

Note that Fields[] is empty!

My view is strongly-typed and uses the new strongly-typed HTML helpers (TextBoxFor(), etc).

View Model / Domain Model

public class ItemFormViewModel
{
    public Item Item { get; set; }
    [Required] [StringLength(100)] public string Whatever { get; set; } // for demo
}
[MetadataType(typeof(ItemMetadata))]
public class Item
{
    public string Name { get; set; }
    public string SKU { get; set; }
    public int QuantityRequired { get; set; }
    // etc.
}
public class ItemMetadata
{
    [Required] [StringLength(100)] public string Name { get; set; }
    [Required] [StringLength(50)] public string SKU { get; set; }
    [Range(0, Int32.MaxValue)] public int QuantityRequired { get; set; }
    // etc.
}

(I know I'm using a domain model as my / as part of my view model, which isn't a good practice, but disregard that for now.)

View

<%@ Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" 
Inherits="System.Web.Mvc.ViewPage<ItemFormViewModel>" %>

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <h2>Editing item: <%= Html.Encode(Model.Item.Name) %></h2>

    <% Html.EnableClientValidation(); %>
    <%= Html.ValidationSummary("Could not save the item.") %>

    <% using (Html.BeginForm()) { %>

        <%= Html.TextBoxFor(model => model.Item.Name) %>
        <%= Html.TextBoxFor(model => model.Item.SKU) %>
        <%= Html.TextBoxFor(model => model.Item.QuantityRequired) %>

        <%= Html.HiddenFor(model => model.Item.ItemID) %>

        <%= Html.TextBox("Whatever", Model.Whatever) %>
    <input type="submit" value="Save" />
    <% } %>
</asp:Content>

I included the Whatever property on the view model because I suspected that MVC wasn't recursively inspecting the sub-properties of ItemFormViewModel.Item, but even that isn't being validated? I've even tried delving into the MVC framework source code but have come up empty. What could be going on?

Answer 1

About five seconds after I posted the question, I realized something: My view didn't have ValidationMessage placeholders anywhere. I added <%= Html.ValidationMessageFor(model => model.Item.Name) %> and lo and behold, MVC added validation rules for Item.Name to the JS block at the bottom of the page.

It turns out that MVC does not emit client-side validation rules for a field unless you actually do one of the following:

1. Call Html.ValidationMessage() for the property.
2. Call Html.Validate() for the property. (This one won't output error messages)
3. Render the controls using Html.EditorForModel(). (source)

Doing any of these tells MVC, "This property of my viewmodel is editable by the user, so you should be validating it." Just using the HTML helper to stick a textbox on the page -- even if you're using the new strongly-typed helpers -- isn't enough.