One possible issue is that jQuery Validate does [run any rules if the value of an element is empty][1]. 

You can get around this by [retriggering the validation][2] when the user loses focus:



    // select statements not firing null validation automatically
    $("select").blur(function () { $(this).valid() });

[1]: https://stackoverflow.com/a/14759805/1366033
[2]: https://stackoverflow.com/a/12195091/1366033

My view model defines property which has to be displayed as combo box. Property definition is:

    [Required]
    public int Processor { get; set; }

I'm using `DropDownListFor` to render combo box:

    <%=Html.DropDownListFor(r => r.Processor, Model.Processors, Model.Processor)%>

`Model.Processors` contains `IEnumerable<SelectListItem>` with one special item defined as:

    var noSelection = new SelectListItem
      {
        Text = String.Empty,
        Value = "0"
      };

Now I need to add validation to my combo box so that user must select different value then 'noSelection'. I hoped for some configuration of `RequiredAttribute` but it doesn't have default value setting.

Validating required selection in DropDownList

Answer