Question

I have created a custom validation attribute by subclassing ValidationAttribute. The attribute is applied to my viewmodel at the class level as it needs to validate more than one property.

I am overriding

protected override ValidationResult IsValid(object value, ValidationContext validationContext)

and returning:

new ValidationResult("Always Fail", new List<string> { "DateOfBirth" }); 

in all cases where DateOfBirth is one of the properties on my view model.

When I run my application, I can see this getting hit. ModelState.IsValid is set to false correctly but when I inspect the ModelState contents, I see that the Property DateOfBirth does NOT contain any errors. Instead I have an empty string Key with a value of null and an exception containing the string I specified in my validation attribute.

This results in no error message being displayed in my UI when using ValidationMessageFor. If I use ValidationSummary, then I can see the error. This is because it is not associated with a property.

It looks as though it is ignoring the fact that I have specified the membername in the validation result.

Why is this and how do I fix it?

EXAMPLE CODE AS REQUESTED:

 [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
    public class ExampleValidationAttribute : ValidationAttribute
    {
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            // note that I will be doing complex validation of multiple properties when complete so this is why it is a class level attribute
            return new ValidationResult("Always Fail", new List<string> { "DateOfBirth" });
        }
    }

    [ExampleValidation]
    public class ExampleViewModel
    {
        public string DateOfBirth { get; set; }
    }

Answer 1

I am not aware of an easy way fix this behavior. That’s one of the reasons why I hate data annotations. Doing the same with FluentValidation would be a peace of cake:

public class ExampleViewModelValidator: AbstractValidator<ExampleViewModel>
{
    public ExampleViewModelValidator()
    {
        RuleFor(x => x.EndDate)
            .GreaterThan(x => x.StartDate)
            .WithMessage("end date must be after start date");
    }
}

FluentValidation has great support and integration with ASP.NET MVC.