Adding Validation to Entity Models

The generated class ItemRequest will always be a partial class. This allows you to write a second partial class which is marked with the necessary data annotations. In your case the partial class ItemRequest would look like this:

using System.ComponentModel;
using System.ComponentModel.DataAnnotations;

//make sure the namespace is equal to the other partial class ItemRequest
namespace MvcApplication1.Models 
{
    [MetadataType(typeof(ItemRequestMetaData))]
    public partial class ItemRequest
    {
    }

    public class ItemRequestMetaData
    {
        [Required]
        public int RequestId {get;set;}

        //...
    }
}