Question

I am creating a custom property validation which should use the error string in the specified resource file when throwing a ValidationException. Am I right in assuming that if I throw an exception and don’t specify the error string in the parameters, it should use the ErrorMessageResourceName and ErrorMessageResourceType I specified in the constructor?

using System;
using System.ComponentModel.DataAnnotations;
using System.Text.RegularExpressions;

namespace OurProduct.Util
{
    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
    public class UniquenessAttribute : ValidationAttribute
    {
        public UniquenessAttribute()
        {
            ErrorMessageResourceName = "EmailUniqueError";
            ErrorMessageResourceType = typeof (Resources.OurThing);
        }

        protected override ValidationResult IsValid(object value)
        {
            throw new ValidationException();
        }
    }
}

Answer 1

The following should work, provided OurThing points to the generated strongly-typed resource class, for looking up localized strings, etc, and "EmailUniqueError" is one of the static properties of this class:

    public class UniquenessAttribute : ValidationAttribute
    {
        public UniquenessAttribute()
        {
            ErrorMessageResourceName = "EmailUniqueError";
            ErrorMessageResourceType = typeof (Resources.OurThing);
        }

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            if (failure) // to implement
                return new ValidationResult(FormatErrorMessage(validationContext.DisplayName));
            ...
        }
    }

Also make sure you’re validating all properties (if you use TryValidateObject for example, make sure the last parameter is set to true) when doing your tests.