Question

I use ASP.NET MVC4 in my solution. I have the ViewModel below where I would like to validate that the field EmergencyReason is filled only if the field Date is today. I try this:

public class LoadingViewModel
{
    public DateTime Date { get; set; }

    [RequiredIf("Date", Comparison.IsEqualTo, DateTime.Today)]
    public string EmergencyReason { get; set; }
    ...
}

It doesn’t work. The third argument of RequiredIf must be a constant expression, …

Any idea how can I force the user to enter an EmergencyReason only if Date field is today?

Thanks.

Answer 1

You seem to be using some non-standard RequiredIf attribute which is not part of the standard ASP.NET MVC 4 package.

As you know C# allows you to only pass constant values to attributes. So one possibility is to write a custom attribute:

public class RequiredIfEqualToTodayAttribute: RequiredIfAttribute
{
    public RequiredIfEqualToTodayAttribute(string field)
        : base(field, Comparison.IsEqualTo, DateTime.Today)
    {
    }
}

and then:

public class LoadingViewModel
{
    public DateTime Date { get; set; }

    [RequiredIfEqualToToday("Date")]
    public string EmergencyReason { get; set; }

    ...
}