MVC 3 validation not working for complex model - asp.net-mvc

Question

I have a UserFormModel which contains a UserModel which has a set of properties with the [Required] attribute set. I have read that MVC 3 out of the box will validate models within models by default. However when I submit an empty form in my view passing back a UserFormModel containing an empty UserModel the ModelState.IsValid is always true.
I have tried sending just the UserModel back to my controller and that validates ok. It just seem to be when I am working with complex models that it does not validate.
I have also tried it with the [Required] attribute on the User property within the UserFormModel (which I believe is not required for default behaviour to work) but still no validation takes place.
Any ideas on this one would be much appreciated.
public class UserFormModel
{
public UserModel User;
public IEnumerable<SelectListItem> Roles { get; set; }
}
public class UserModel : ModelBase
{
[Required]
public string UserName { get; set; }
public string Title { get; set; }
[Required]
public string FirstName { get; set; }
[Required]
public string LastName { get; set; }
}
[HttpPost]
public ActionResult Create(UserFormModel userFormModel)
{
if (ModelState.IsValid)
{
// Do Something
}
}

Answer 1

You should use properties not fields. So instead of:
public UserModel User;
you should have:
public UserModel User { get; set; }
The reason for this is that the default model binder works only with properties.

Answer 2

I believe that validation only goes one model property deep in the model. For example if you have the following model
public class Product
{
public int ProductId { get; set; }
[Required]
public int ProductName { get; set; }
[Required]
public decimal Price { get; set; }
}
public class ProductViewModel
{
[Required]
public Product Product { get; set; }
}
The validation against the product object in the view model will work, the validation against the product class will not with one caveat. If the Product class is a POCO class used in the entity framework code first method, the validation will work against the database. Validation against a view model will only work one deep in my experience.