Howdy, I have what should be a simple question. I have a set of validations that use System.CompontentModel.DataAnnotations . I have some validations that are specific to certain view models, so I'm comfortable with having the validation code in the same file as my models (as in the default AccountModels.cs file that ships with MVC2). But I have some common validations that apply to several models as well (valid email address format for example). When I cut/paste that validation to the second model that needs it, of course I get a duplicate definition error because they're in the same namespace (projectName.Models). So I thought of removing the common validations to a separate class within the namespace, expecting that all of my view models would be able to access the validations from there. Unexpectedly, the validations are no longer accessible. I've verified that they are still in the same namespace, and they are all public. I wouldn't expect that I would have to have any specific reference to them (tried adding using statement for the same namespace, but that didn't resolve it, and via the add references dialog, a project can't reference itself (makes sense).

So any idea why public validations that have simply been moved to another file in the same namespace aren't visible to my models?

CommonValidations.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Text.RegularExpressions;

namespace ProjectName.Models
{
    public class CommonValidations
    {
        [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = true, Inherited = true)]
        public sealed class EmailFormatValidAttribute : ValidationAttribute
        {
            public override bool IsValid(object value)
            {
                if (value != null)
                {
                    var expression = @"^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$";
                    return Regex.IsMatch(value.ToString(), expression);
                }
                else
                {
                    return false;
                }
            }
        }
    }
}

And here's the code that I want to use the validation from:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using Growums.Models;

namespace ProjectName.Models
{
    public class PrivacyModel
    {
        [Required(ErrorMessage="Required")]
        [EmailFormatValid(ErrorMessage="Invalid Email")]
        public string Email { get; set; }
    }
}