ASP.NET MVC 2 validation using DTOs instead of domain entities

You shouldn't have more than one DTO per entity, so you should only have to apply the validation attributes once per DTO. If you need multiple entities for a View, include multiple DTO's as properties of your ViewModel.

You might find useful this.

And keep in mind that validation lives everywhere. There is nothing wrong if DTOs applies UI validation (like getting necessary fields filled, datetime in correct format etc.) and domain objects - domain validation (e.g. account has money before withdrawn operation).

You can't create validation universal. Best thing You can do - put it in appropriate places.

And weed that feeling about duplication out. Usage of DTOs usually means applying single responsibility principle. There is no duplication if you got 2 customer objects where one is responsible for carrying business logic and second that is responsible for displaying it.

Maybe you could use meta annotations, which puts the attributes on a separate class:

namespace MvcApplication1.Models
{
    [MetadataType(typeof(MovieMetaData))]
    public partial class Movie
    {
    }


    public class MovieMetaData
    {
        [Required]
        public object Title { get; set; }

        [Required]
        [StringLength(5)]
        public object Director { get; set; }


        [DisplayName("Date Released")]
        [Required]
        public object DateReleased { get; set; }
    }
}

Code sample was borrowed from this article.