ModelState always valid - asp.net

Question

I've got something seemingly very simple not working.
I have got a model
public class Name: Entity
{
[StringLength(10), Required]
public virtual string Title { get; set; }
}
public class Customer: Entity
{
public virtual Name Name { get; set; }
}
a view model
public class CustomerViweModel
{
public Customer Customer { get; set; }
}
a view
<% using(Html.BeginForm()) { %>
<%= Html.LabelFor(m => m.Customer.Name.Title)%>
<%= Html.TextBoxFor(m => m.Customer.Name.Title)%>
<button type="submit">Submit</button>
<% } %>
and a controller
[HttpPost]
public ActionResult Index([Bind(Prefix = "Customer")] Customer customer)
{
if(ModelState.IsValid)
Save
else
return View();
}
No matter what I enter as the title (null, or a string > 10 chars), ModelState.IsValid is always true. The Title field in the Customer object has a value, so the data is being passed around, but not being validated?
Any clues?

Answer 1

In your View I don't see any text box or a field allowing to send data to the controller, only a label. Properties will not be validated if they are not posted. Add a textbox, leave it blank and your model won't be valid any more:
<%= Html.TextBoxFor(m => m.Customer.Name.Title)%>
UPDATE:
Here's the code I've used:
Model:
public class Name
{
[StringLength(10), Required]
public virtual string Title { get; set; }
}
public class Customer
{
public virtual Name Name { get; set; }
}
public class CustomerViewModel
{
public Customer Customer { get; set; }
}
Controller:
public class HomeController : Controller
{
public ActionResult Index()
{
return View();
}
[HttpPost]
public ActionResult Index([Bind(Prefix = "Customer")]Customer cs)
{
return View(new CustomerViewModel
{
Customer = cs
});
}
}
View:
<%# Page Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<MyApp.Models.CustomerViewModel>" %>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
<% using(Html.BeginForm()) { %>
<%= Html.LabelFor(m => m.Customer.Name.Title)%>
<%= Html.TextBoxFor(m => m.Customer.Name.Title)%>
<button type="submit">Submit</button>
<% } %>
</asp:Content>
When you submit this form a validation error is shown.
Remark1: I've omitted the Entity base class in the models as I don't how does it look.
Remark2: I've renamed the variable in the Index action to cs. I remember that there was some problems with this in ASP.NET MVC 1.0 when you had the prefix and the variable named the same but I am not sure whether this applies here and I think it was fixed.

Answer 2

Figured it out, it was becuase I'm referencing System.ComponentModel.DataAnnotations 3.6 instead of 3.5. From what I gather, 3.6 is for WCF RIA services only.